Method of forming silicon oxide layer in semiconductor manufacturing process using spin-on glass composition and isolation method using the same method

[0002] This application is a continuation-in-part of application Ser. No. 09/686,624, filed Oct. 12, 2000.

[0003] 1. Field of the Invention

[0004] The present invention relates to a method of forming a silicon oxide layer using a spin-on glass (SOG) composition useful in forming a silicon oxide layer in a semiconductor manufacturing process. More particularly, the present invention relates to a method of forming a silicon oxide layer applied as an insulating layer in a semiconductor manufacturing process using a spin-on glass composition including perhydro-polysilazane.

[0005] 2. Description of the Prior Art

[0006] The design of semiconductor devices has been progressing rapidly. In particular, this progress has required semiconductor devices to function with high operating speed, and to have a large storage capacitance. In order to satisfy such requirements, semiconductor devices with increased density, reliability, and response time are under development.

[0007] Integrated circuits are typically manufactured by forming a large number of active devices on a single substrate. After each device is formed and insulated, some of the devices are electrically interconnected during the manufacturing process to accomplish a desirable circuit function. Metal Oxide Semiconductor (MOS) and bipolar VLSI and ULSI devices, for example, have multilevel interconnection structures in which a large number of devices are interconnected. In such a multilevel interconnection structure, the topography of the top layer usually becomes increasingly irregular and uneven as the number of layers increases.

[0008] For example, a semiconductor wafer with two or more metal layers is typically formed as follows. A number of oxide layers, a polycrystalline silicon conductive layer, and a first metal wiring layer are formed on a semiconductor wafer. A first insulation layer is then formed on the resulting structure. Then, a via hole is formed for providing circuit paths to a second metal layer. At this time, the surface of the first insulation layer is uneven because the layers underlying the first insulation layer are uneven. When the second metal layer is directly formed on the first insulation layer, the second metal layer may fracture due to protrusions or cracks in the underlying insulation layer. In addition, there may be a decreased yield of the semiconductor device if the deposition state of the metal layer is poor. Accordingly, the insulation layer is typically planarized before formation of the via hole or the second metal layer that will be formed in a multilevel metal interconnection structure.

[0009] Various methods have been developed to planarize the insulation layer. These methods include utilizing a borophosphorous silicate glass (BPSG) layer, which has good reflow characteristic, or an SOG layer and a chemical mechanical polishing (CMP) method. In general, BPSG is widely utilized as an insulation layer material to fill gaps between metal wirings. However, depositing BPSG presents problems because it depends primarily on establishing special deposition parameters for the equipment utilized. In addition, the gases used in the process are expensive and severely toxic.

[0010] Furthermore, as the packing density increases and the design rule gradually decreases for manufacturing VLSI having 256 megabits or more, using BPSG as the insulation layer to fill gaps between wirings lowers the yield due to the occurrence of voids and bridges. In addition, an etch stop layer may be damaged during its subsequent formation. Thus, the prior art typically implements a reflowing process and an expensive CMP process to solve these problems.

[0011] An insulation layer formed by an SOG layer is known in the art as being manufactured by a simple coating process. This process produces a planar insulation layer. For example, U.S. Pat. No. 5,310,720 (issued to Shin et al.) discloses a method for making a silicon oxide layer. A polysilazane layer is formed, and then the polysilazane layer is heated in an oxygen atmosphere to convert it into a silicon oxide layer. U.S. Pat. No. 5,976,618 (issued to Shunichi Fukuyama et al.) discloses a method in which an inorganic SOG is deposited, and then two step heat treatment processes are implemented to convert the SOG layer into a silicon oxide layer.

[0012] The basic backbone structure of polysilazane-based SOG is composed of Si—N, Si—H and N—H bonds. The Si—N bonds are converted into (or substituted with) Si—O bonds by baking under an atmosphere including oxygen and water. A simple spin coating and a simple curing process are performed to convert the SOG layer into the silicon oxide layer. Accordingly, it is an economical method.

[0013] Not all of the Si—N bonds, however, are converted to Si—O bonds (see, for example, Japanese Patent Laid-Open No. Hei 11-145286). Accordingly, the silicon oxide layer has different insulating and electrical characteristics when compared to a pure silicon oxide layer such as one formed using a BPSG layer or a TEOS layer. For these reasons, using SOG to form a layer, and then convert it into a silicon oxide insulation layer has been avoided. In addition, because SOG is deposited by a spin coating method, the thickness of the thus formed silicon oxide layer is not sufficient to provide adequate coverage for conductive layers, such as gate electrodes and metal wirings.

[0014] The Applicants of the present invention have invented a spin-on glass composition including perhydropolysilazane providing the ability to bury a gap between metal wirings of VLSI degree having a high aspect ratio, bury a gap on a substrate without the need to apply a mechanical planarization, smooth surface discontinuities, and produce an oxide layer of a semiconductor device. The spin-on glass composition has substantially the same characteristics as an oxide layer of a semiconductor device formed by a chemical vapor deposition (CVD) method.

[0015] The Applicants of the present invention have accordingly filed a patent application, which is now pending, entitled: “SPIN-ON GLASS COMPOSITION AND METHOD OF FORMING SILICON OXIDE LAYER IN SEMICONDUCTOR MANUFACTURING PROCESS USING THE SAME,” with the USPTO as Ser. No. 09/686,624, on Oct. 12, 2000.

[0016] According to an embodiment of this method, a planar SOG layer is formed on a semiconductor substrate having a stepped portion or surface discontinuities by coating on the semiconductor substrate a spin-on glass composition including polysilazane having the chemical formula of —(SiH₂NH₂)_n— where n represents a positive integer, a weight average molecular weight within the range of about 4,000 to 8,000, and a molecular weight dispersion degree within the range of about 3.0 to 4.0. Finally, the SOG layer is cured to form a silicon oxide layer having a planar surface.

[0017] As for the silicon oxide layer, an isolation layer of an STI (shallow trench isolation) structure that may be formed on a semiconductor substrate having a stepped portion formed by grooves and protrusions may be illustrated to form an isolation structure.

[0018] The baking step is implemented by two steps of a pre-baking and a main-baking. The pre-baking of the SOG layer is implemented at a temperature within a range of about 100-500° C., more preferably within a range of about 100-400° C., for a period of about 1-5 minutes, and more preferably, for a period of about 2-3 minutes. The main-baking of the SOG layer is implemented at a temperature within a range of about 900-1,050° C.

[0019] At this time, the manufactured silicon oxide layer has a good gap filling characteristic for an STI structure including gaps having about 0.1-1 μm. However, according to a wet etching rate test, the etching rate decreases as the temperature of the main-baking increases, and a silicon oxide layer is formed at the surface portion of the silicon substrate and an active region.

[0020] FIG. 1 illustrates a cross-sectional view of an oxide formed on an inner surface of a trench. The device illustrated in FIG. 1 is manufactured by the following method. A pad oxide layer is formed on a silicon substrate 100 and then, a nitride layer and a high temperature oxide layer are sequentially formed on the pad oxide layer. The nitride layer is provided as an etch stopping layer for the subsequently implemented chemical mechanical polishing process and the high temperature oxide layer is provided as a hard mask layer.

[0021] Next, an anti-reflective layer (not shown) is formed on the high temperature oxide layer by depositing a silicone oxynitride compound (SiON) and a high temperature oxide layer pattern 116 is formed for defining an active pattern by utilizing a photolithography process.

[0022] The nitride layer and the pad oxide layer are etched by using the high temperature oxide layer pattern 116 as an etching mask to form a nitride layer pattern 114 and a pad oxide layer pattern 112. Then, an upper portion of the substrate 100 adjacent to the nitride layer pattern 114 is etched to form a trench 118.

[0023] Subsequently, an exposed portion of the trench 118 is heat treated under an oxidizing atmosphere to cure silicon damage induced by ion impaction of high energy during the process of etching the trench. Then, a trench inner wall oxide layer 120 is formed at the inner portion of the trench 118, including the bottom and side portions thereof, by an oxidation reaction of the exposed silicon with an oxidizing agent.

[0024] Next, the SOG composition suggested by the present Applicants is deposited on the semiconductor substrate 100 to fill the trench 118 and to form an SOG layer. Then, the SOG layer is baked. A pre-baking is implemented at a temperature range of about 100-500° C., preferably about 100-400° C. for about 1-5 minutes, more preferably for about 2-3 minutes. A main-baking is implemented at a temperature range of about 900-1050° C. to form silicon oxide. Then, an oxide layer 130 burying the trench is manufactured as illustrated in FIG. 1. The oxide layer 130 is formed from the SOG layer. At this time, it is known that the trench inner wall oxide layer 120 at the side wall portion designated by a circle A is thicker than the trench inner wall oxide layer 120 at the bottom portion. The oxide compound is thought to be formed by an oxidation reaction of silicon in the substrate 100 with oxygen contained in the oxidizing atmosphere when baked at 1000° C. or more under the oxidizing atmosphere.

[0025] The generation of the oxide may induce a shape defect at a dent portion after implementing a CMP process or may change the size of the active region.

[0026] Accordingly, it is a feature of an embodiment of the present invention to provide a method of forming a silicon oxide layer in a semiconductor manufacturing process by using a spin-on glass composition that restrains a formation of an oxide layer at the surface portion of a silicon substrate or an active region to give a good silicon oxide layer.

[0027] It is also a feature of an embodiment of the present invention to provide an isolation method of semiconductor devices by using the above-described method of forming the silicon oxide layer.

[0028] In accordance with these and other features of the invention, there is provided a method of manufacturing a silicon oxide layer in a semiconductor manufacturing process. A spin-on-glass (SOG) solution including polysilazane having the structure of —(SiH₂NH₂)_n— where n represents a positive integer, is coated on a semiconductor substrate having a stepped portion formed thereon to form a planar SOG layer. Then, a silicon oxide layer having a planar surface is formed by implementing a first heat treatment to convert the SOG layer into an oxide, and then implementing a second heat treatment to densify thus obtained oxide.

[0029] In accordance with another feature of an embodiment of the present invention, there is provided an isolation method of a device for defining an active region of a semiconductor device. A trench is formed by partially etching an upper portion of a semiconductor substrate. Then, a spin-on glass (SOG) solution including polysilazane having the structure of —(SiH₂NH₂)_n— where n represents a positive integer, a weight average molecular weight within the range of about 6,000 to about 8,000, and a molecular weight dispersion degree within the range of about 3.0 to about 4.0, is coated onto the semiconductor substrate having a stepped portion formed thereon, to form a planar SOG layer burying the trench. A first heat treatment of the SOG layer is implemented to convert polysilazane into silicon oxide. Then, a second heat treatment of thus converted silicon oxide is implemented to densify the converted silicon oxide to form a silicon oxide layer burying the trench. The active region of the semiconductor device is defined through forming a field oxide burying the trench by partially etching the silicon oxide layer.

[0030] According to various embodiments of the present invention, a uniform silicon oxide layer having substantially no voids can be formed by utilizing an SOG composition that completely covers a conductive layer having an aspect ratio of about 5:1 to 10:1 or other surface discontinuities. In addition, an oxidization of silicon in an active region can be restrained when implementing a first heat treatment to convert an SOG solution into silicon oxide and then a second heat treatment to densify thus converted silicon oxide, thereby securing the dimension stability.

[0031] These and other features and aspects of the present invention will be readily apparent to those of ordinary skill in the art upon review of the detailed description that follows.

[0032] FIG. 1 illustrates a cross-sectional view of an oxide formed at the inner wall of a trench when an SOG layer is baked by one heat treating process;

[0033] FIG. 2 illustrates a graph of the relationship between viscosity and shear rate of an SOG composition of the present invention;

[0034] FIGS. 3A-3K illustrate cross-sectional views of a method of forming a silicon oxide layer in a semiconductor manufacturing process according to an embodiment of the invention;

[0035] FIG. 4 illustrates a Fourier Transform infrared spectroscopy (FT-IR) diagram showing the light absorbance of a layer detected after pre-baking an SOG layer;

[0036] FIG. 5 illustrates a FT-IR diagram showing the light absorbance of a silicon oxide layer detected after main baking an SOG layer, according to the present invention;

[0037] FIGS. 6A-6G illustrate graphs of etching ratios of silicon oxide layers according to another embodiment of the present invention, and the etching ratios of silicon oxide layers formed by a conventional CVD method;

[0038] FIGS. 7A-7G illustrate cross-sectional views of an isolating method of a shallow trench device according to another embodiment of the present invention;

[0039] FIG. 8 illustrates a bar graph of normalized intensities of light absorbance obtained by an FT-IR for silicon oxide at an active region of a substrate, when a silicon oxide layer is formed according to the present invention;

[0040] FIG. 9 illustrates a graph of etching rates of a silicon oxide layer, according to the type of etching solution used, manufactured by a method of the present invention; and

[0041] FIG. 10 illustrates a graph of the uniformity of polishing obtained by examining the profile of an oxide layer after implementing a chemical mechanical polishing on a silicon oxide layer manufactured by Example 2 and a silicon oxide layer manufactured by a high density plasma method.

[0042] This application is a Continuation-in-part application of “SPIN-ON GLASS COMPOSITION AND METHOD OF FORMING SILICON OXIDE LAYER IN SEMICONDUCTOR MANUFACTURING PROCESS USING THE SAME,” by the present inventors, Ser. No. 09/686,624, filed on Oct. 12, 2000, which is incorporated by reference herein in it's entirety. This application also relies for priority upon Korean Patent Application No. 2001-31633, filed on Jun. 7, 2001, also entitled: “SPIN-ON GLASS COMPOSITION AND METHOD OF FORMING SILICON OXIDE LAYER IN SEMICONDUCTOR MANUFACTURING PROCESS USING THE SAME,” which is incorporated by reference herein in it's entirety.

[0043] The present invention now will be explained in more detail with reference to the attached drawings.

[0044] Whenever it is stated that a material, layer, or structure is formed or deposited on or over another material, layer, or structure, another material, layer, or structure may be intervening.

[0045] The spin-on glass composition used in the present invention is disclosed in the above U.S. patent application Ser. No. 09/686,624 and preferably includes polysilazane having the formula —(SiH₂NH₂)_n— where n represents a positive integer, a weight average molecular weight within the range of about 4,000 to 8,000, and a molecular weight dispersion degree within the range of about 3.0 to 4.0. Throughout this description, the expression “molecular weight dispersion degree” denotes the ratio of weight average molecular weight to number average molecular weight.

[0046] Methods of making polysilazane are widely known in the art. In one typical method, polysilazane is prepared by reacting halosilane with a Lewis base to obtain a complex compound and then reacting the complex compound with ammonia. Polysilazane also can be prepared by: (i) reacting a silicone halide such as SiCl₄or SiH₂Cl₂with amine; (ii) converting silazane into polysilazane utilizing an alkaline metal halide catalyst; (iii) dehydrogenating from a silane compound utilizing a transition complex metal compound and an amine compound; or the like.

[0047] U.S. Pat. No. 5,494,978 (issued to Yasuo Shinizu et al.) discloses a method of preparing a defoamed polysilazane utilizing inorganic polysilazane having a number average molecular weight of 100-100,000. U.S. Pat. No. 5,905,130 (issued to Hirohiko Nakahara et al.) discloses a method of preparing polysilazane by reacting a polyaminosilane compound with a polyhydrogenated nitrogen-containing compound in the presence of a base catalyst, or by reacting a polyhydrogenated silicone compound with a polyhydrogenated nitrogen-containing compound under a basic solid oxide catalyst. U.S. Pat. No. 5,436,398 (issued to Yasuo Shimizu et al.) discloses a method of preparing perhydropolysilazane having a number average molecular weight of about 1,120. U.S. Pat. No. 4,937,304 (issued to Ayama etal.) and U.S. Pat. No. 4,950,381 (issued to Takeuchi et al.) disclose methods for preparing polysilazanes having desired molecular weights. The disclosures of each of the aforementioned documents are incorporated by reference herein in their entirety.

[0048] The polysilazane utilized in the present invention may be prepared by any of the methods described above without limitation. In order to be used in various embodiments of the present invention, perhydropolysilazane prepared by the above methods is preferably fractionated according to its molecular weight. When the weight average molecular weight is below about 4,000, the outgassing amount may be increased, and the perhydropolysilazane may be converted into silicon oxide too rapidly which can generate cracks due to the low molecular weight. On the other hand, when the weight average molecular weight exceeds 8,000, the viscosity of the SOG solution may increase, which deteriorates the uniformity of the thus formed SOG layer. Accordingly, the weight average molecular weight of perhydropolysilazane used in the present invention is preferably in the range of about 4,000 to 8,000. More specifically, the weight average molecular weight of perhydropolysilazane is in the range of about 6,000 to 8.000 when an SOG layer is formed to bury a trench, and more preferably, it is in the range of about 6,500 to 7,000.

[0049] In addition, when the molecular weight dispersion degree of polysilazane, which is the ratio of weight average molecular weight to number average molecular weight, is below 3.0, the fractionation efficiency of polysilazane and the yield of fractionated polysilazane may be low. On the other hand, when the molecular weight dispersion degree exceeds 4.0, the converted silicon oxide layer may not be uniform. Accordingly, the molecular weight dispersion degree of polysilazane useful in the invention is preferably within the range of about 3.0 to 4.0, although conditions may exist for utility of the composition outside of this range. However, polysilazane having the molecular weight dispersion degree out of the range may also be used when occasion necessities.

[0050] An SOG composition is preferably a SOG solution prepared by dissolving the aforementioned polysilazane in a solvent, preferably an organic solvent. Any of a variety of organic or other solvents may be used in the present invention without limitation. Useful solvents preferably include an aromatic solvent, such as xylene, or an ether solvent, such as dibutyl ether. When the amount of polysilazane in the SOG solution exceeds 30% by weight, the polysilazane may, but not necessarily, have increased instability, the lifetime of the solution may decrease, and cracks may be formed. When the amount of polysilazane in the SOG solution is below 10% by weight, it may, but not necessarily, become difficult to control the thickness of the SOG layer. Accordingly, the amount of polysilazane in the SOG solution is preferably within the range of 10 to 30% by weight, based on the total weight of the composition, and more preferably, the amount is within the range of 18 to 25% by weight. It is also preferred that the solvent in the SOG solution be within the range of 70 to 90% by weight based on the total weight of the composition, and more preferably, within the range of 72 to 82% by weight.

[0051] The preferred contact angle of the SOG composition with an underlying layer, such as a silicon nitride layer, is preferably no more than 4°. The, adhesion of the SOG composition with the underlying layer may be insufficient when the contact angle exceeds 4°.

[0052] To achieve surface uniformity during the coating and curing process, the SOG solution preferably has a viscosity within the range of about 1 to 10 mPa·s, and more preferably, within the range of 1 to 8 mPa·s, at a predetermined shear rate. FIG. 2 illustrates a graph of the relationship between viscosity and shear rate of the SOG solution. The share rate is represented γ as a symbol and 1/s as a unit. In the graph of FIG. 2, the ordinate represents the viscosity (mPa·s), and the abscissa represents the shear rate (1/s). The viscosity of the SOG solution according to the present invention is preferably within the range of about 1 to 10 mPa·s, at a shear rate of 54-420 (1/s), as shown in FIG. 2. It can also be seen from FIG. 2 that the viscosity of the SOG composition may be within the range of about 1 to about 10 mPa·s, at a shear rate within the range of 10 to 1,000 (1/s).

[0053] The SOG solution may include at least one impurity compound including an element selected from boron, fluorine, phosphor, arsenic, carbon, oxygen, and mixtures thereof, as the occasion necessities. When at least an element selected from boron, fluorine, phosphor, and arsenic is included in the SOG solution among the impurity materials, a silicon oxide layer formed from the SOG solution will include the impurity material, and the layer may have characteristics similar to a conventional boron silicate glass (BSG) layer, BPSG layer, phosphorous silicate glass (PSG) layer, or the like. Conversion of SOG into a silicon oxide layer may be promoted when at least one of carbon and/or oxygen is included in the SOG solution as an impurity.

[0054] The SOG solution is preferably coated by a spin coating method onto a semiconductor substrate having surface discontinuities, such as conductive line patterns. This method is particularly useful in forming a planar SOG layer.

[0055] The surface discontinuity on the semiconductor substrate may result from conductive patterns. For example, conductive metal wiring patterns, such as gate electrode patterns or bit lines, result in stepped portions on the surface of the substrate. A distance between the two conductive patterns is not limited. In general, however, when the distance is greater than 1 μm, conventional methods of forming an oxide layer utilizing BPSG are adequate, but when the distance approaches 0.04 μm, for example, the method utilizing the SOG solution of the present invention offers greater possibilities of void filling. Accordingly, the method of the present invention is preferably applied to a semiconductor substrate having gaps of about 0.04-1 μm.

[0056] A method of various embodiments of the present invention may also be applied to conductive pattern gaps of low aspect ratio (wherein the aspect ratio represents the ratio of a depth with respect to a distance of the gap). However, a conductive pattern having an aspect ratio of about 5:1 to about 10:1 is preferably applied in various embodiments of the invention.

[0057] Generally, closely spaced gaps in which conductive patterns are closely formed, such as a cell array region including gate electrodes, can be formed on a semiconductor substrate. In addition, a global stepped portion (or a sparsely separated gap portion) in which conductive patterns are sparsely formed, such as a peripheral circuit region, can also be formed on a semiconductor substrate. The present invention may be applied to a semiconductor substrate having closely spaced gaps with an aspect ratio within the range of from about 5:1 to about 10:1, and sparsely spaced stepped portions with an aspect ratio of about 1:1 or less.

[0058] Stepped portions also result from prominence/recess portions of the semiconductor substrate. In particular, an oxide layer may be formed by the method of the present invention, whereby the layer is preferably formed on stepped portions of the semiconductor substrate having grooves and protrusions. Forming the oxide layer in this manner is useful for manufacturing an isolation region having a shallow trench isolation (STI) structure. Stepped portions also result from metal wirings formed on an insulation layer. That is, a silicon oxide layer formed by the method of the present invention may be utilized as an insulation interlayer for insulating metal wirings formed on an insulation layer.

[0059] A curing method of the coated SOG layer will be described in detail below.

[0060] Advantageously, the SOG layer formed by the above method may be cured, thereby converting it into a silicon oxide layer with a planar surface. The curing step is performed by pre-baking and main-baking. Based on the teachings herein, those of ordinary skill in the art should be capable of curing the SOG layer, and converting it into a silicon oxide layer having a planar surface.

[0061] The pre-baking is preferably performed at a temperature within a range of about 100 to 500° C. for about 1-5 minutes. When the pre-baking temperature is below 100° C., organic solvent may possibly remain in the layer, and not be removed. On the other hand, when the pre-baking temperature is over 500° C., polysilazane at or below a certain depth may not be completely converted into silicon oxide at the subsequent main-baking procedure, and the surface portion may be rapidly converted into silicon oxide, which can generate cracks, thereby causing non-uniformity in a consequent silicon oxide layer.

[0062] When pre-baking is performed for less than one minute, organic solvents may remain in the layer, and not be fully removed. On the other hand, when pre-baking is performed for more than 5 minutes, a partial conversion into silicon oxide may occur at the surface of the SOG layer including perhydropolysilazane, thereby forming a partial crack even if the organic solvent was completely removed. Therefore, pre-baking is preferably performed at a temperature within a range of about 100 to 500° C., and for a period of time from about 1 to 5 minutes, and more preferably at a temperature within a range of 100 to 400° C., and for a period of time within a range of about 2 to 3 minutes.

[0063] The main baking is preferably conducted at a higher temperature and for a longer time, when compared to the pre-baking. The basic backbone structure of polysilazane-based SOG includes Si—N bonds. These Si—N bonds may be substituted with (or converted into) Si—O bonds by baking in an atmosphere including oxygen and water. According to conventional methods employing spin-on glass compositions described previously, not all of the Si—N bonds become substituted with Si—O bonds; and therefore, some Si—N bonds remain in the Si—O layer after coating the SOG solution and subsequent baking.

[0064] In accordance with a method of an embodiment of the present invention, however, no Si—N bonds remain after coating the SOG solution including polysilazane to form the SOG layer and implementing the curing process. Accordingly, the silicon oxide layer formed by various embodiments of the present invention has substantially the same characteristics as a pure silicon oxide layer formed by conventional CVD methods.

[0065] The main baking is preferably conducted at a temperature within a range of about 400 to 1,200° C. in order to convert polysilazane into silicon oxide. When the main baking temperature is below 400° C., curing may not be sufficient, and some Si—N bonds may remain, thereby deteriorating the characteristics of the oxide layer. On the other hand, when the main baking temperature is over 1,200° C., the planarity of the thus formed silicon oxide layer may be lowered, or cracks may occur. Therefore, main baking is preferably carried out at temperatures within a range of about 400 to 1,200° C., and more preferably, at temperatures within a range of about 400 to 1,000° C.

[0066] Furthermore, main baking is preferably conducted for a period of time ranging from about 10 to 180 minutes. When the main baking time is less than 10 minutes, the SOG layer may not be sufficiently converted into a silicon oxide layer. On the other hand, when the main-baking time exceeds 180 minutes, stress in a thus formed silicon oxide layer increases. Therefore, the main baking is preferably carried out for a period of time within a range of about 10 to 180 minutes, and more preferably within a range of 30 to 120 minutes.

[0067] The main baking is preferably carried out in an oxidizing atmosphere, or in an inert atmosphere that is appropriate for converting Si—N bonds into Si—O bonds. For example, useful environments for the main baking procedure include an atmosphere of oxygen, an atmosphere including water vapor, an atmosphere including a mixture of oxygen and water vapor, an atmosphere including nitrogen, and mixtures of these atmospheres. An atmosphere including water vapor is preferred, and it preferably contains from about 1.2 to about 86% by weight of water.

[0068] The temperature range of the main baking may be determined by considering its effect on an underlying structure. For example, when the underlying structure includes a trench formed by partially etching an upper portion of a semiconductor substrate and the SOG layer is formed to fill up the trench, the preferred temperature range of the main baking of the curing process is within a range of about 900 to 1,200° C. When the underlying structure includes a plurality of gate electrodes formed on the semiconductor substrate and the SOG layer is formed to completely cover the gate electrodes, the preferred temperature of the main baking is within a range of about 600 to 900° C. When the underlying structure includes a plurality of metal wiring patterns formed on an insulation layer disposed on the semiconductor substrate, and the SOG layer is formed to completely cover the metal wiring patterns, the preferred temperature of the main baking is within a range of about 400 to 450° C. Those of ordinary skill in the art should be capable of determining the appropriate temperature range for the main baking, using the guidelines provided herein. Thus the specific ranges of parameters set forth in this specification are not intended to limit the invention.

[0069] One coating of the SOG composition typically provides a silicon oxide layer having a thickness within a range of about 4,000 to 6,500 Å. Before coating the SOG composition, a silicon nitride layer having a thickness within a range of about 200 to 600 Å may be formed as an etch stop layer on an upper and side portion of the conductive patterns.

[0070] The SOG composition may be utilized for burying a trench or planarizing gate electrodes and/or metal patterns during the manufacture of a semiconductor device. Otherwise, the SOG composition may be utilized for burying the trench, while the conventional SOG composition or other method may be utilized for planarizing the gate electrodes and/or metal patterns. That is, the SOG composition may be applied for burying the trench or for planarizing the gate electrodes and/or metal patterns, and it should be understood that one of these two processes may be applied.

[0071] According to another embodiment of the present invention, the main baking process may be implemented in two-step heat treatment processes. When the heat treatment is implemented by one step, a measure at the active region might be changed by forming silicon oxide at a side wall of the trench through a reaction of a silicon source supplied from a semiconductor substrate with oxygen contained in an oxidizing atmosphere, as described above with reference to FIG. 1. Accordingly, when an SOG layer is formed by curing an SOG composition including polysilazane on a substrate from which a silicon source is provided, the heat treatment should be implemented in two steps in order to convert the SOG layer into silicon oxide.

[0072] First, the-first heat treatment of the SOG layer is implemented to convert polysilazane into oxide. At this time, the first heat treatment is implemented under an oxidizing atmosphere such as an oxygen atmosphere, a humidity atmosphere and a mixed atmosphere of oxygen and humidity, in a temperature range of about 500-1,000° C., more preferably about 600-900° C. Most preferably, the first heat treatment is implemented in a temperature range of about 800-900° C. for about 10-120 minutes.

[0073] Next, the second heat treatment onto thus obtained oxide from the first heat treatment is implemented under an oxidizing atmosphere, an inert gas atmosphere, a mixed atmosphere of the oxidizing atmosphere and the inert gas atmosphere, or a vacuum to densify the converted oxide. Particularly, the second heat treatment is preferably implemented under an inert gas atmosphere including nitrogen, and the second heat treatment is preferably implemented at a temperature range of about 600-1200° C., and more preferably about 900-1100° C. for about 10-120 minutes.

[0074] In particular, when the SOG layer is formed to bury a trench manufactured by partially etching an upper portion of the semiconductor substrate, the second heat treatment of the main baking is preferably implemented at a temperature range of about 900-1100° C.

[0075] Aspects of the present invention now will be explained with reference to the following non-limiting examples.

[0076] Preparation of an SOG Composition

[0077] Perhydropolysilazane having a weight average molecular weight of 4,500-7,000 and a molecular weight dispersion degree of 3.0-4.0 was obtained by fractionating commercially available perhydropolysilazane. The fractionated perhydropolysilazane was dissolved in xylene to obtain an SOG composition having a perhydropolysilazane concentration of 22-25% by weight, based on the total weight of the composition. The contact angle of the SOG composition was 4° or less with respect to an underlying silicon nitride layer.

[0078] The viscosity of the SOG composition was detected according to the variation of its shear rate. The viscosity characteristic is illustrated in FIG. 2. FIG. 2 illustrates a graph of the viscosity change with respect to the shear rate change of the SOG solution. The ordinate represents the viscosity (mPa·s) and the abscissa represents the shear rate (1/s). As can. be seen in FIG. 2, the SOG solution preferably has a uniform viscosity within the range of about 1 to 10 mPa·s, at a shear rate of about 10 to 1,000 (1/s), more preferably at a shear rate of about 54 to 420 (1/s).

[0079] Formation of an Oxide Layer

[0080] FIGS. 3A-3K illustrate cross-sectional views of a method of forming a silicon oxide layer in a semiconductor manufacturing process according to an embodiment of the present invention. Referring to FIG. 3A, there is provided a p-type substrate 10 formed of a semiconductor material, such as silicon (Si). Trenches 12 were formed on the substrate 10 by etching an isolation region. The depth of trench 12 was about 4,600 Å, and the width thereof was about 1,250 Å. On the substrate 10 on which the trenches 12 were formed, the SOG solution including perhydropolysilazane of which the weight average molecular weight is in the range of 6,000-8,000 and prepared as above was coated to a thickness of about 6,000 to 7,000 Å to form a first SOG layer 13.

[0081] Referring now to FIG. 3B, the first SOG layer 13 was pre-baked at about 100 to 500° C. for 1-5 minutes, and then main-baked at about 900 to 1,000° C. for about 30 minutes to convert the first SOG layer 13 into a first silicon oxide layer 13a.At this time, the baking was implemented under a water vapor atmosphere having a water content of about 86% by weight. Referring to FIG. 3C, the silicon oxide layer 13awas polished by a CMP method until the upper surface of the semiconductor substrate 10 was exposed to form device isolation regions where the inside portions of trenches 12 were filled with silicon oxide 14.

[0082] Referring to FIG. 3D, an n-type semiconductor region 20 was formed by doping an n-type impurity, such as phosphorous (P) ions, into a region for forming memory cells of the semiconductor substrate 10 (cell array region). In addition, a p-type well 30 was formed by doping a p-type impurity, such as boron (B) ions, into the cell array region and a portion of the peripheral circuit region. Finally, an n-type well 40 was formed by doping an n-type impurity, such as phosphorous (P) ions, into a remaining region of the peripheral circuit region.

[0083] Next, an impurity for controlling a threshold voltage, such as boron fluoride (BF₂) was doped into the p-type well 30 and the n-type well 40. Thereafter, each surface portion of the p-type well 30 and the n-type well 40 was cleaned utilizing a fluorine-based cleaning solution. The semiconductor substrate 10 was then wet oxidized to form a gate oxide layer 16 on each surface of the p-type well 30 and the n-type well 40. At this time, portions of the substrate within trenches 12 were also partially oxidized to form a continuous gate oxide layer 16. A thickness of the gate oxide layer 16 was about 40-200 Å.

[0084] Referring to FIG. 3E, a polysilicon layer was formed on the substrate 10, in which the silicon oxide 14 that filled the trenches 12 as a field oxide, and gate oxide layer 16 were formed. The polysilicon layer had a thickness of about 500 to 4,000 Å, and was formed by depositing polycrystalline silicon doped with an n-type impurity, such as phosphorous (P) ions, by a low pressure chemical vapor deposition (LPCVD) method. Then, tungsten silicide (SiW) and tungsten (W) were deposited by a sputtering method on the polysilicon layer to form a tungsten silicide layer and a tungsten layer which had respective thicknesses of about 1,000 to 2,000 Å. A silicon nitride layer was then deposited on the tungsten layer. The silicon nitride layer was formed to have a thickness of about 500 to 2,000 Å by a LPCVD, or a plasma enhanced chemical vapor deposition (PECVD) method. Those of ordinary skill in the art should be capable of forming the respective layers, using the guidelines provided herein.

[0085] A photoresist film was then formed on the silicon nitride layer, and the photoresist film was selectively exposed by utilizing a mask. Then, the photoresist film was developed to form a photoresist pattern 22 for forming gate electrodes. The silicon nitride layer, tungsten layer, tungsten nitride layer, and polysilicon layer were then etched one by one by utilizing the photoresist pattern 22 as an etching mask to form gate electrodes 24Ga, 24Gb, 24Gc and word lines 24WL composed of a polysilicon pattern 24a,a tungsten silicide pattern 24b,tungsten pattern 24c,and silicon nitride pattern 24d.Gate electrodes 24Ga and word lines 24WL were formed at the cell array region, and gate electrodes 24Gb and 24Gc were formed at the peripheral circuit region.

[0086] The gate electrodes 24Ga and the word lines 24WL formed on the cell array region were manufactured so that the gaps between the gate electrodes were in a range of about 0.4 to 1 μm. An aspect ratio, which is the ratio of a depth with respect to a gap width of gate electrodes 24Ga and word lines 24WL, was within a range of about 5:1 to 10:1, thereby forming a closely stepped portion. On the other hand, the aspect ratio of the gate electrodes 24Gb and 24Gc formed on the peripheral circuit region, was less than 1:1 thereby forming a global stepped portion.

[0087] Referring to FIG. 3F, the photoresist pattern 22 was removed. In FIG. 3F, a p-type impurity doped region 25 (FIG. 3G) was formed in the n-type well 40 at both sides of the gate electrode 24Gc by doping a p-type impurity, such as boron ions, into the n-type well 20. Also, an n-type impurity doped region 27 (FIG. 3G) was formed in the p-type well 30 at both sides of the gate electrode 24Gb by doping an n-type impurity, such as phosphorous ions, into the p-type well 30. An n-type impurity doped region 26 (FIG. 3G) was formed in the p-type well 20 at both sides of gate electrodes 24Ga.

[0088] Referring to FIG. 3G, silicon nitride was deposited on the semiconductor substrate 10 by a chemical vapor deposition method to form a silicon nitride layer 32 having a thickness of about 200-600 Å. Next, the silicon nitride layer 32 on the cell array region was covered with a photoresist film, and the silicon nitride layer 32 on the peripheral circuit region was anisotropically etched to form a spacer 32aon side walls of the gate electrodes 24Gb and 24Gc (FIG. 3F) of the peripheral circuit region.

[0089] Next, a p+-type impurity doped region 42 (source, drain regions) was formed by doping a p-type impurity, such as boron ions, into the n-type well 40 of the peripheral circuit region. In addition, an n+-type impurity doped region 44 (source, drain regions) was formed by doping an n-type impurity, such as arsenic (As) ions, into the p-type well 30 of the peripheral circuit region.

[0090] Referring to FIG. 3H, an SOG solution was coated on the semiconductor substrate 10 to form a second SOG layer 50. The second SOG layer 50 was formed by a spin coating method, whereby the rotational velocity of the wafer was about 500-2,500 rpm. The weight average molecular weight of perhydropolysilazane contained in the SOG solution was about 4,000-6,000. A thickness of the second SOG layer 50 was in the range of about 7,500 to 8,200 Å. The second SOG layer 50 completely covered the gate electrodes 24Ga, 24Gb, 24Gc and word lines 24WL. Next, the second SOG layer 50 was pre-baked at a temperature within a range of about 100 to 500° C. for about 1 to 5 minutes, and then was main-baked at a temperature within a range of about 600 to 900° C. for about 10 to 180 minutes. The baking was conducted under at least one atmosphere selected from an oxygen atmosphere, a water vapor atmosphere, an atmosphere containing a mixture of oxygen and water vapor, a nitrogen atmosphere, or mixtures thereof. When the baking was implemented in a water vapor atmosphere, the water content in the atmosphere was controlled to be within a range of about 1.2-86% by weight.

[0091] During the curing process, Si—N bonds in the second SOG layer 50 were substituted with Si—O bonds to convert the second SOG layer 50 into a silicon oxide layer 50a(FIG. 31). A thickness of second silicon oxide layer 50adecreased by about 19-20% of the thickness of second SOG layer 50 during this process, as shown in FIG. 31.

[0092] Referring to FIG. 3J, a metal layer with a thickness of about 5,000 Å was formed by depositing a metal such as aluminum, tungsten, etc., on the second silicon oxide layer 50aby utilizing a common sputtering method. Metal patterns 52 having widths of about 6,600 Å, and gaps of about 8,400Å were formed by patterning the metal layer utilizing a photolithography process. Next, a third SOG layer 54 having a thickness range of about 3,800 to about 4,500 Å, and completely covering the metal patterns 52, was formed by spin coating the SOG solution. At this time, the weight average molecular weight of perhydropolysilazane in the third SOG layer 54 is in a range of about 4,500-7,500.

[0093] Referring to FIG. 3K, the third SOG layer 54 was pre-baked at a temperature within a range of about 100 to 500° C. for about 1-5 minutes, and then main-baked at a temperature within a range of about 400 to 450° C. for about 10-180 minutes. The main baking was conducted under a water vapor atmosphere. Then, Si—N bonds in the third SOG layer 54 were substituted with Si—O bonds through the curing process, and in accordance with an important feature of the present invention, the third SOG layer 54 was converted into a third silicon oxide layer 54ahaving a substantially planar surface.

[0094] A semiconductor device was manufactured by implementing a conventional semiconductor manufacturing process. Those of ordinary skill in the art should be capable of manufacturing a semiconductor device using the SOG composition and method of the various embodiments of the preset invention.

[0095] Light Absorbance of a Silicon Oxide Layer

[0096] An oxide layer was formed on a semiconductor substrate by the method described above with reference to FIGS. 3A-3K. The oxide layer was formed on a semiconductor substrate having a plurality of wiring layers having an aspect ratio within a range of about 5:1 to 10:1, and a gap between them within a range of about 0.04 to 1 μm. A silicon nitride layer having a thickness of about 400 Å was formed to cover the plurality of wiring layers and the semiconductor substrate.

[0097] A second SOG layer having a thickness of about 7,582 Å was formed by spin coating an SOG solution including polysilazane onto the semiconductor substrate. At this time, a rotational speed was controlled to be about 1,000 rpm.

[0098] The second SOG layer was pre-baked at 150° C. for about 3 minutes. After the pre-baking, a light absorbance of the SOG layer was detected by utilizing a FT-IR method. Those of ordinary skill in the art should be capable of using the FT-IR method to determine the light absorbance of the SOG layer. FIG. 4 illustrates a FT-IR diagram showing the light absorbance of a layer obtained after pre-baking the SOG layer. As shown in FIG. 4, light absorbing peaks are illustrated at some wavelength regions that represent bonds of N—H. Si—H, Si—N, Si—H, etc. after the pre-baking. At this time, a stress value was about 3.63×10⁸(dyne/cm²), and was detected with a stress gauge

[0099] After the pre-baking, the SOG layer was baked again (main baking) at 700° C. for 30 minutes to convert the SOG layer into a silicon oxide layer. FIG. 5 illustrates a FT-IR diagram of the light absorbance of the silicon oxide layer detected after the main baking. As shown in FIG. 5, the peaks of wavelength regions corresponding only to Si—O bonds remain after main baking. At this time, the stress value was −1.22×10⁸(dyne/cm²). From FIG. 5, it follows that all of the Si—N bonds in the SOG layer were converted into Si—O bonds. Accordingly, the SOG layer was completely converted into a silicon oxide layer.

[0100] In addition, no voids were observed in the silicon oxide layer formed on the semiconductor substrate having a plurality of wiring patterns. The plurality of wiring patterns had an aspect ratio within a range of about 5:1 to 10:1, and a gap within a range of about 0.04 to 1 μm.

[0101] Detecting an Etching Rate of Silicon Oxide

[0102] A. Forming a silicon oxide layer utilizing SOG

[0103] An SOG solution was coated onto a bare wafer to form a SOG layer. The SOG solution was coated by a spin coating method whereby a rotational velocity of the wafer was about 1,000 rpm. The SOG layer was deposited to a thickness of about 7,500 to about 8,200 Å. Next, the SOG layer was pre-baked at about 150° C. for about 3 minutes, and then main-baked at about 700° C. for about 30 minutes. The main baking was conducted under a water vapor atmosphere whereby the content of water vapor in this atmosphere was in the range of about 1.2-86% by weight. Si—N bonds in the SOG layer were substituted with Si—O bonds during the curing process and the SOG layer was converted to a silicon oxide layer. The thickness of the thus formed silicon oxide layer was about 6,400 Å.

[0104] B. Forming an Oxide Layer by a CVD Method

[0105] A high density plasma (HDP) CVD-oxide layer was formed on a bare wafer by utilizing silane gas and oxygen as a source gas, and argon gas as a carrier gas. A thickness of thus formed CVD-oxide layer was about 6,000 Å.

[0106] C. Detecting the Wet Etching Rate

[0107] The silicon oxide layer formed by the method of the present invention and the CVD-oxide layer formed by the CVD method were respectively etched. The respective wet etching processes were conducted by using the same etching solution for a constant period of time, and etching rate was detected with a constant time interval. The results are illustrated in FIGS. 6A-6F.

[0108] FIG. 6A represents curves illustrating the etching rates detected at a time interval of 1 minute for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in a solution obtained by diluting a buffer etching solution including ammonium fluoride into distilled water (NH₄F and HF diluted in distilled water) at room temperature (25° C.).

[0109] FIG. 6B represents curves illustrating the etching rates detected at a time interval of 1 minute for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in an aqueous solution of diluted hydrofluoric acid (DI:HF=100:1) at room temperature (25° C.).

[0110] FIG. 6C represents curves illustrating the etching rates detected at a time interval of ten minutes for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in a mixed etching solution of NH₄OH:H₂O₂:H₂O in a ratio of 0.25:1:5 at 70° C.

[0111] FIG. 6D represents curves illustrating the etching rates detected at a time interval of ten minutes for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in phosphoric acid at 165° C.

[0112] FIG. 6E represents curves illustrating the etching rates detected at a time interval of ten minutes for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in a mixed etching solution of H₂SO₄:H₂O₂in a ratio of 6:1 at 130° C.

[0113] FIG. 6F represents curves illustrating the etching rates detected at a time interval of ten minutes for the oxide layer formed by a method of the present invention and the oxide layer formed by the CVD method. Wet etching was carried out in a mixed etching solution of NH₄OH:H₂O₂:H₂O in a ratio of 0.25:1:5 at 50° C.

[0114] D. Detecting the Dry Etching Rate

[0115] The oxide layer formed by the method of the present invention and the oxide layer formed by the CVD method were introduced into a same chamber and etching rates were repeatedly detected by utilizing a same etching gas. Pressure in the chamber was controlled to 30 mTorr and output power in the chamber was 1,700 W. The etching gas utilized was C₅F₈:C₄F₈:O₂:Ar in flowing rates of 8 sccm, 4 sccm, 6 sccm and 500 sccm, respectively. The detected etching rates are illustrated as graphs in FIG. 6G.

[0116] From FIGS. 6A-6G, it can be noted that the wet and dry etching rates of the silicon oxide layer formed by the present invention were quite similar to the wet and dry etching rates of the silicon oxide layer formed by the conventional CVD method. Accordingly, a planarized layer or an inter insulation layer formed by utilizing the SOG layer according to the present invention has properties similar to the conventional CVD-oxide layer.

[0117] Through repeated experiments by the present inventors, a silicon oxide layer free from voids may be formed on a semiconductor substrate having wiring layers that have an aspect ratio within the range of about 5:1 to 10:1, and a gap within the range of about 0.04 to 1 μm. Utilizing the SOG composition of the present invention may form such a silicon oxide layer. According to the present invention, utilizing SOG may form a silicon oxide layer free from voids with a planarity required for 256 MDRAM.

[0118] Preparation of an SOG Composition

[0119] Perhydropolysilazane having a weight average molecular weight in the range of about 6,000-8,000 and a molecular weight dispersion of 3.0-4.0, was prepared by implementing the same method described in Example 1. A spin-on-glass composition was prepared by dissolving perhydropolysilazane in xylene in a concentration of about 22-25% by weight.

[0120] Shallow Trench Isolation

[0121] When the field oxide 14 illustrated in FIG. 3 is formed to bury the trench of the highly integrated semiconductor device according to Example 1, a thick oxide layer is formed at an inner wall of the trench as illustrated in FIG. 1.

[0122] FIGS. 7A-7G illustrate cross-sectional views of an isolating method of a shallow trench device according to another embodiment of the present invention.

[0123] Referring to FIG. 7A, a pad oxide layer 201 having a thickness of about 100-200 Å was formed by a thermal oxidation process on a semiconductor substrate 200 made of silicon. Then, a nitride layer was deposited to a thickness of about 100-1000 Å by an LPCVD (low pressure chemical vapor deposition) method on the pad oxide layer 201 to form a polishing stopping layer 203. The polishing stopping layer 203 was provided for stopping polishing during a subsequent CMP process.

[0124] Next, a high temperature oxide (HTO) layer was deposited by an LPCVD method to a thickness of about 500-1000 Å on the polishing stopping layer 203 to form a hard mask layer 205. Silicon oxynitride (SiON) was deposited on the hard mask layer 205 to a thickness of about 200-800 Å by an LPCVD method to form an anti-reflective layer (not shown). The anti-reflective layer functioned to prevent a diffused reflection during implementing a photolithography process and was removed during a subsequent process of trench formation.

[0125] Referring to FIG. 7B, a hard mask pattern 206 for forming an active pattern was formed by dry etching the anti-reflective layer and the hard mask layer 205 by the photolithography process. Then, the polishing stopping layer 203 and the pad oxide layer 201 were etched by using the hard mask pattern 206 as an etching mask to form a polishing stopping layer pattern 204 and a pad oxide layer pattern 202.

[0126] Referring to FIG. 7C, a trench 210 was formed by etching an exposed substrate 200 to a depth of about 2000-5000 Å by using the hard mask pattern 206. Preferably, the depth of the trench 210 was 4600 Å and the width thereof was 1250 Å. At this time, the anti-reflective layer was removed and the hard mask pattern 206 was etched to a predetermined thickness.

[0127] Referring to FIG. 7D, the exposed portion of the trench 210 was heat treated under an oxidizing atmosphere in order to cure silicon damage induced on the semiconductor substrate 200 by ion impaction of high energy during the trench etching process. Then, a trench inner wall oxide layer 212 was formed at the inner wall of the trench 210 including bottom and side portions of the trench 210 to a thickness of about 20-300 Å by an oxidation reaction between the exposed silicon and an oxidizing agent.

[0128] After that, an SOG layer 213 was formed to a thickness of about 6000-7000 Å by filling the SOG composition into the trench 210.

[0129] Referring to FIG. 7E, a pre-baking of the SOG layer 213 was implemented at a temperature range of about 100-500° C. for about 1-5 minutes.

[0130] Then, a heat treatment was implemented under an oxidizing atmosphere at a temperature range of about 800-900° C., preferably at about 850° C., for about 10-120 minutes, preferably for about 60 minutes to convert the SOG layer 213 into silicon oxide. At this time, the atmosphere was a humidity atmosphere of which humidity was about 86% by weight.

[0131] After that, a second heat treatment was implemented to densify the converted silicon oxide and convert it into a silicon oxide layer 214 (FIG. 7E). The second heat treatment was implemented under an oxidizing atmosphere, an inert gas atmosphere, or a mixed atmosphere thereof. Preferably, the second heat treatment was implemented under an inert gas atmosphere such as a nitrogen gas atmosphere. Preferably, the second heat treatment was implemented at a temperature range of about 900-1100° C. for about 10-120 minutes, and more preferably, at a temperature of about 1000° C. for about 30 minutes.

[0132] Referring to FIG. 7F, thus formed silicon oxide layer 216 was polished by a CMP method until the polishing stopping layer 204 on the semiconductor substrate 200 was exposed. Then, an inner portion of the trench 210 was buried with silicon oxide 216.

[0133] Referring to FIG. 7G, the polishing stopping layer pattern 204 was removed by a strip process using phosphoric acid to complete the isolation, as illustrated in FIG. 7G.

[0134] Detecting of a Formation of Substrate Oxide

[0135] EXPERIMENT 1

[0136] An SOG layer was formed on a blanket wafer and the pre-baking and the main-baking were implemented, in the same manner as in Example 1.

[0137] EXPERIMENT 2

[0138] An SOG layer was formed on a blanket wafer and the pre-baking, the first heat treatment at 850° C. for about 1 hour under a humidity atmosphere and the second heat treatment at 1000° C. for about 30 minutes under an oxygen gas atmosphere were implemented to obtain a silicon oxide layer, in the same manner as in Example 2.

[0139] EXPERIMENT 3

[0140] A silicon oxide layer was formed by implementing the same method as in Experiment 2, except that the second heat treatment was implemented under a nitrogen gas atmosphere

[0141] EXPERIMENT 4

[0142] A silicon oxide layer was formed by implementing the same method as in Experiment 2, except that the second heat treatment was implemented at 1050° C.

[0143] EXPERIMENT 5

[0144] A silicon oxide layer was formed by implementing the same method as in Experiment 2, except that the first heat treatment was implemented at 900° C.

[0145] Detecting an Oxidizing State at the Substrate Surface

[0146] FT-IR analyses were conducted with respect to a stretching peak of an Si—O bond on the surface of the substrate for the wafers onto which the baking processes were conducted according to Experiments 1-5. FIG. 8 illustrates a bar graph of normalized intensities of light absorbance obtained by a. FT-IR for silicon oxide at an active region of a substrate, when a silicon oxide layer is formed according to the present invention. As known from FIG. 8, the silicon oxide layers obtained by implementing two-step heat treatments as illustrated in Experiments 2-5 include somewhat larger amounts of oxides when comparing with the silicon oxide layer obtained by implementing one-step heat treatments as illustrated in Experiment 1. Among the oxides produced from the substrate by Experiments 2-5, the amount of the oxide from Experiment 3 was the smallest.

[0147] Detecting Wet Etching Rate and Etching Uniformity

[0148] Etching rates of silicon oxide layers formed by converting the SOG manufactured by Experiments 2-4 and a silicon oxide layer manufactured by a high density plasma method were detected according to the kind of etching solutions used. Wet etching was implemented for a constant time period using the same etching solution and the etching rate was detected with a constant time interval. As for the etching solution, SC-1 solution (a mixture of ammonia, hydrogen peroxide and deionized water), LAL solution (a mixture of ammonium fluoride and hydrogen fluoride) and phosphoric acid were applied. The result is illustrated in FIG. 9 as a graph. In FIG. 9, the axis of ordinate represents the etching rate, and the axis of abscissa represents the etching solutions and the kind of the etched oxides.

[0149] From FIG. 9, it is confirmed that the silicon oxide layers manufactured from Experiments 2-5 give similar etching rates with that manufactured from Experiment 1.

[0150] Polishing Test

[0151] A chemical mechanical polishing was implemented after burying a trench in the semiconductor substrate having the same patterns described in Example 2 by utilizing the silicon oxide layer manufactured by Example 2 (the baking process was implemented as described in Experiment 3) and the silicone oxide layer manufactured by using the high density plasma method. The polishing was implemented until the polishing stopping layer was exposed and a profile of the oxide layer was examined to inspect the polishing uniformity. The result is illustrated in FIG. 10. In FIG. 10, the graph designated by ▪ corresponds to the result obtained after polishing the silicon oxide layer manufactured by the high density plasma method, while the graph designated by □ corresponds to the result obtained after polishing the silicon oxide layer manufactured by Experiment 3. During the polishing, the same silica was used for the manufacture of a slurry. In FIG. 10, the axis of the ordinates represents a polishing degree after completing the polishing (unit: Å). The polishing time was about 180-200 seconds for the silicon oxide layer manufactured by the high density plasma method, while being about 100 seconds for the silicon oxide layer manufactured by Experiment 3. From FIG. 10, the polishing amount of the silicon oxide layer manufactured by the high density plasma method was about 300-500 Å, while that manufactured by Experiment 3 was about 100-200 Å.

[0152] It is known from FIG. 10 that the polishing uniformity of the silicon oxide layer manufactured by Example 2 is about two times better than that manufactured by the conventional high density plasma method, and the polishing time of the former is about half of that of the latter.

[0153] In addition, the silicon oxide layer manufactured by Example 2 has no voids and gives a good gap filling characteristic. However, the oxide layer manufactured by the high density plasma method has a lot of voids on the trench portion. Further, in the silicon oxide layer manufactured by Example 2, silicon of the active region was not oxidized and the oxide layer was densified to the bottom portion of the trench, thereby giving a good oxide layer characteristic.

[0154] According to the present invention, a silicon oxide layer free from voids with a planarity required for 256 megabit devices may be formed by utilizing the SOG solution. In addition, a dimension stability may be secured by converting the SOG composition into silicon oxide by a first heat treatment and then densifying the converted silicon oxide for restraining an oxidation of silicon at the active region.

[0155] Preferred embodiments of the present invention have been disclosed herein and, although specific terms are employed, they are used and are to be interpreted in a generic and a descriptive sense only and not for purpose of limitation. Accordingly, it will be understood by those of ordinary skill in the art that various changes in form and details may be made without departing from the spirit and scope of the invention as set forth in the following claims.