Capacitor in semiconductor device having dual dielectric film structure and method for fabricating the same

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for fabricating a capacitor in a semiconductor device, and more particularly to a method for fabricating a capacitor in a semiconductor device having a dual dielectric film structure composed of Ta₂O₅/Si₃N₄, and a capacitor fabricated thereby.

[0003] 2. Description of the Prior Art

[0004] Recently, as high integration of memory products has become accelerated following the development of microscopic fabrication process technologies for semiconductors, unit cell area is largely decreased and driving voltage has been lowered considerably.

[0005] However, the necessary capacity of the capacitor for the driving of memory elements is required to increase above 25 fF per cell so as to suppress the contraction of the refresh time and to prevent the occurrence of soft errors, despite the reduction of the cell area.

[0006] Accordingly, recently a three dimensional type electrical charge storage electrode with hemispheric structure having a large surface area has been used for DRAM capacitor elements which utilize a nitride layer with a nitride layer/oxide layer (N/O) structure as a dielectric, and the height of the capacitor has been increased steadily.

[0007] Meanwhile, a depth of focus is not assured in the following exposure process due to the differences of height produced between a cell region and a peripheral circuit region when the height of the capacitor increases, which results in a bad effect upon the integration process which follows the wiring process.

[0008] As stated above, conventional N/O capacitor element comes to a limitation in assuring charging capacity of a capacitor requisite for future DRAM products such as those are over 256 M. As a result, as shown in FIGS. 1A to 1D, a capacitor made of Ta₂O₅ has been actively developed.

[0009] Referring to FIGS. 1A to 1D, a conventional fabricating method for a capacitor in a semiconductor device using a Ta₂O₅ dielectric film will be described as follows.

[0010] FIGS. 1A to 1D are sectional views illustrating steps of a fabricating method for a capacitor in a semiconductor device in accordance with the prior art.

[0011] According to the fabricating method of the prior art for a capacitor for a semiconductor device, as shown in FIG. 1A, an interlayer insulating film 3 is first deposited over a semiconductor substrate 1, photo-sensitive materials are distributed on the interlayer insulating film, and a first photo-mask (not shown) for making plug contacts is formed by carrying out an exposure process and a developing process using photolithography technology, and carrying out a selective patterning of the interlayer insulating film.

[0012] Then, a plug contact hole 5 exposing a portion of the semiconductor substrate 1 is formed by patterning the interlayer insulating film 3 with a first photo-mask (not shown), and then the first photo-mask is removed.

[0013] Subsequently, conductive materials are deposited on the plug contact hole 5 and the first interlayer insulating film 3, and a chemical-mechanical polishing (CMP) is carried out, resulting in the formation of a contact hole 7 in the plug contact hole 5.

[0014] Referring to FIG. 1B, a second interlayer insulating film 9 is deposited on an entire surface of the semiconductor substrate 1, and then photo-sensitive materials are distributed on the second interlayer insulating film 9, and a second photo-mask (not shown) for making plug contacts is formed by carrying out an exposure process and a developing process using photolithography technology and carrying out a selective patterning of the second interlayer insulating film.

[0015] Then, a contact hole 11 defining a lower electrode region is formed in the second interlayer insulating film 9 over the contact plug 7 by patterning of the second interlayer insulating film 9 with the second photo-mask (not shown), and then the second photo-mask (not shown) is removed.

[0016] Subsequently, a doped polysilicon layer (not shown) is deposited on the second interlayer insulating film 9 inclusive of the contact hole 11, and photo-sensitive materials are distributed thereon. In this instance, the production process of the polysilicon layer (not shown) is carried out by utilizing a LPCVD chamber so as to employ a capacitor module with a cylindrical structure or a concave structure as a lower electrode.

[0017] Then, a lower electrode 13 of cylindrical shape is formed by removing the photo-sensitive materials and the second interlayer insulating film 9 remaining after the CMP processing of the photo-sensitive materials and the doped polysilicon layer (not shown), the lower electrode being contacted with the contact plug 7. In this instance, a lower electrode having a concave structure can be formed in place of the cylindrical structure. In the above case, it is possible to remove just the photo-sensitive materials in order to form a lower electrode in the shape of concave structure after carrying out the CMP processing of the photo-sensitive materials and the doped polysilicon layer (not shown).

[0018] FIG. 1C shows the lower electrode 13 remaining after the removal of the photo-sensitive materials.

[0019] Referring now to FIG. 1D, a Ta₂O₅ thin film 15 is deposited on the lower electrode 13 and a TiN film for an upper electrode 17 is deposited on the thin film 15, thereby fabricating a capacitor in a semiconductor device. Furthermore, a doped poly-silicon layer, which functions as a buffer layer, can be deposited on the upper electrode 17 so as to secure structural stability and enhance the endurance property of the upper electrode against the thermal or electrical influences.

[0020] However, according to the above-noted prior art, vacancy atoms Ta arising from the differences of the composition ratio between Tantalum (Ta) and Oxygen (O) exist in the thin film, because the Ta₂O₅ thin film has an unstable stoichiometry.

[0021] Furthermore, carbon atoms and carbon compounds (C, CH₄, C₂H₂, etc), which are impurities, and water (H₂O) exist together in the thin film, due to reaction of the organic compound Ta(OC₂H₅)₅, which is a precursor of Ta₂O₅, with O₂ (or N₂O) gas at the time of the formation of the thin film.

[0022] As a result, leakage current increases due to carbon atoms, ions and radicals that exist as impurities in the Ta₂O₅ thin film, and the dielectric properties become deteriorated and damaged.

[0023] As regards an Si₃N₄ (7) dielectric film which is deposited by using DCS (Di-Chloro-Silane) gas, because the dielectric ratio is so low that it is limited in use as capacitor dielectric film of highly integrated semiconductor products, wherein a microscopic wiring process is employed for elements such as those below 0.16 m, therefore a Ta₂O₅ (25) dielectric film with a bigger dielectric ratio than previously has come to be employed.

[0024] However, as stated above, although the dielectric ratio of the Ta₂O₅ thin film is big itself, during the high temperature oxidation process which follows the deposition of Ta₂O₅ in the fabrication process of a capacitor, an interface oxide film (Si₂O, 3.85) having a low dielectric ratio is deposited on the surface of a polysilicon layer, which functions as a lower electrode, so as to solve the problems which originate from the Ta₂O₅ thin film itself. Therefore, the thickness of the oxidation film can not be lowered to below 30 , resulting in limitations in achieving a large charging capacity for a capacitor.

[0025] Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide a capacitor in a semiconductor device with a dual dielectric film structure, which is capable of providing larger charging capacity for a capacitor than a conventional dielectric material by employing a dual dielectric film composed of a Ta₂O₅/Si₃N₄ thin film structure, and can effectively suppress the occurrence of leakage current, thereby being suitable for a highly integrated semiconductor device, and a fabrication method therefor.

[0026] In order to accomplish this object in accordance with one aspect of the present invention, there is provided a method for fabricating a capacitor in a semiconductor device with a dual dielectric film, comprising the steps of: forming a lower electrode on a semiconductor substrate, forming a dielectric film of a dual dielectric film structure which is composed of an Si₃N₄ chloride-free thin film and a Ta₂O₅ thin film and is formed on the lower electrode, and forming an upper electrode on the dielectric film.

[0027] In accordance with another aspect of the present invention, there is provided a capacitor in a semiconductor device having a dual dielectric film, the capacitor comprising: a lower electrode formed on a semiconductor substrate, a dielectric film of a dual dielectric film structure composed of an Si₃N₄ thin film and a Ta₂O₅ thin film, which is formed on the lower electrode, and an upper electrode formed on the dielectric film.

[0028] The above and other objects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0029] FIGS. 1A to 1D are sectional views illustrating each step in a method for fabricating a capacitor in a semiconductor device in accordance with the conventional art;

[0030] FIGS. 2A to 2D are sectional views illustrating each step in a method for fabricating a capacitor in a semiconductor device having a dual dielectric film structure in accordance with the present invention.

[0031] Hereinafter, a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

[0032] FIGS. 2A to 2D are sectional views illustrating each step in a method for fabricating a capacitor in a semiconductor device having a dual dielectric film structure in accordance with the present invention.

[0033] In accordance with one embodiment of the present invention, as shown in FIG. 2A, a first interlayer insulating film 23 is first deposited on a semiconductor substrate 21, and then photo-sensitive materials are distributed thereon and a first photo-mask (not shown) for making a plug contact is formed by carrying out an exposure process and a developing process using photolithography technology and selective patterning of photo-sensitive materials.

[0034] Next, a plug contact hole 25, which exposes a portion of the semiconductor substrate 21, is formed by patterning of the first interlayer insulating film 23 using the first photo-mask (not shown) as a mask, and then the first photo-mask (not shown) is removed.

[0035] Subsequently, conductive materials are deposited over the plug contact hole 25 and the first interlayer insulating film 23, and then CMP process is carried out to result in forming of a contact plug 27 in the plug contact hole 25.

[0036] Referring now to FIG. 2B, a second interlayer insulating film 29 is deposited on the entire surface of the semiconductor structure and photo-sensitive materials are distributed thereon, then, a second photo-mask (not shown) is formed by carrying out an exposure process and a developing process using photolithography technology and selective patterning of photo-sensitive materials.

[0037] Next, a contact hole 31 defining a lower electrode region is formed in the second interlayer insulating film 29 over the contact plug 27 by patterning of the second interlayer insulating film 29 with the second photo-mask (not shown) as a mask, and then the second photo-mask (not shown) is removed.

[0038] Subsequently, a doped polysilicon layer (not shown) is deposited on the second interlayer insulating film 29, inclusive of the contact hole 31, and photo-sensitive materials are distributed thereon. In this instance, the production process of the polysilicon layer (not shown) is carried out by employing a LPCVD chamber so as to use a capacitor module in the shape of a cylindrical structure, a stacked structure or a concave structure as a lower electrode.

[0039] Then, a lower electrode 33 of the cylindrical shape is formed by removing the photo-sensitive materials and the second interlayer insulating film 29 remaining after the CMP process of removing the photo-sensitive materials and the doped polysilicon layer (not shown), the lower electrode being contacted with the contact plug 7. In this instance, a lower electrode with a concave structure can be formed in place of that having a cylindrical structure. In the above case, it is possible to remove just photo-sensitive materials to form a lower electrode in the shape of concave structure after carrying out the CMP process of removing the photo-sensitive materials and the doped polysilicon layer (not shown).

[0040] Referring now to FIG. 2C, a polysilicon layer 35 of hemi-spherical grain (HSG) shape is formed on a surface of the lower electrode 33 so as to increase the value of charging capacity for a capacitor, resulting in an increase of the area of the lower electrode 33.

[0041] Next, as shown in FIG. 2D, a first Si₃N₄ dielectric chloride-free thin film 37a is chemical vapor deposited on the lower electrode 33, by reacting a surface of the polysilicon layer on the lower electrode 33, at a temperature of 550 to 700 C. and under an atmosphere of NH₃ gas in an LP-CVD single chamber of an in-situ or ex-situ arrangement or in an electric furnace, with vaporized gas made of BTBAS bis (tertiary-butylamino-silane). The first Si₃N₄ dielectric thin film is formed so as to avoid formation of an oxide layer with a low dielectric ratio due to formation of natural oxide film (Si₂O) on the surface of the polysilicon layer in the shape of hemispherical grain, and to minimize formation of the oxide film with a low dielectric ratio, which is formed during successive depositing processes of Si₃N₄ chloride-free thin film.

[0042] The first Si₃N₄ dielectric thin film 37a is deposited as stated above to a thickness of 10 to 20 through a surface chemical reaction which occurs on the semiconductor substrate, and subsequently a second Ta₂O₅ dielectric thin film 37b is deposited to a thickness of 50 to 100 .

[0043] Alternatively, after a polysilicon layer is formed to act as a lower electrode 33, the first Si₃N₄ dielectric thin film 37a may be deposited on the lower electrode after removing the natural oxide film using a HF vapor or a HF solution in an in-situ or ex-situ chamber. Also, the first Si₃N₄ dielectric thin film 37a may be deposited on the lower electrode after cleaning an interface before and after carrying out surface treatment of the polysilicon layer using a HF compound, or after cleaning the interface using an NH₄OH or H₂SO₄ solution, etc., so as to enhance uniformity. In this instance, the source for silicon nitride is SiH₂NH (C₄H₉)₂;BTBASbis (tertiary-butylamino-silane) in liquid state, when the first Si₃N₄ dielectric chloride-free thin film has been deposited.

[0044] Furthermore, the source gas for the Si₃N₄ dielectric chloride-free thin film is obtained through the vaporization of proper amounts of BTBAS solution at a temperature range of 166 to 200 C., which is supplied to an evaporizer or an evaporation tube by means of a flow controller such as a LMFC (liquid mass flow controller).

[0045] In this instance, the Si₃N₄ dielectric chloride-free thin film is chemical vapor deposited to a thickness of 10 to 30 , preferably 15 to 20 , while maintaining the temperature range of 550 to 700 C., the pressure range of 0.1 to 5 torr, preferably 0.2 to 0.5 torr, and the flow rate (NH₃/BTBAS) of NH₃ reaction gas to BTBAS at 1 to 10, preferably 50 to 200 cc of NH₃ against 20 to 100 cc for BTBAS.

[0046] Furthermore, the second amorphous Ta₂O₅ thin film 37b is deposited to a proper thickness of 50 to 100 by means of a CVD or an ALD method after the formation of the first Si₃N₄ thin film, and then these dielectric thin films are subjected to annealing using an electric furnace under an atmosphere of N₂O (N₂ or O₂) gas at 700 to 800 C. temperature for 5 to 120 minutes, thereby inducing crystallization. In this instance, crystallization can be induced by subjecting the dielectric films to annealing under an atmosphere of N₂O (or O₂) gas at 800 to 900 C. temperature for 30 to 120 minutes using an RTP (Rapid Thermal Process) in place of an electric furnace.

[0047] Also, the second Ta₂O₅ dielectric film 37b is deposited by means of a CVD or an ALD method under a temperature of 800 to 900 C. and a pressure of 0.1 to 5 torr using an organic metal compound such as tantalum ethylate Ta(OC₂H₅)₅ or penta-dimethyl-amino-tantalum Ta (N(CH₃)₂)₅ as a precursor.

[0048] In this instance, a Ta chemical vapor is obtained through the vaporization of proper amounts of a tantalum ethylate Ta(OC₂H₅)₅ solution or a penta-dimethyl-amino-tantalum Ta(N(CH₃)₂)₅ at a temperature range of 150 to 200 C., which is supplied to an vaporizer or an evaporation tube by way of a flow controller such as an MFC (mass flow controller).

[0049] Then, a TiN layer is deposited on the entire surface of the semiconductor device as an upper electrode 39 or formed simultaneously with a doped polysilicon layer as a buffer layer on the upper electrode so as to secure structural stability and to enhance the endurance properties of the upper electrode against thermal or electrical influences, thereby incorporating a capacitor for a semiconductor device. In this instance, the upper electrode 39 is made of metallic materials such as TiN, TaN, W, WN, Ru, RuO₂, Ir, IrO₂, Pt, etc., together with the doped polysilicon layer. Also, the upper electrode made of metallic material is formed through using a PE-CVD method, a RF magnetic sputtering method, a CVD method or an ALD method.

[0050] As explained above, according to the method for fabricating a capacitor in a semiconductor device having a dual dielectric film structure of the present invention, following advantages are achieved.

[0051] According to the method for fabricating a capacitor in a semiconductor device having a dual dielectric film structure of the present invention, the capacitor in the semiconductor device is fabricated by using Si₃N₄ chloride-free thin film as the first dielectric film and deposited by using BTBAS bis(tertiary-butylamino-silane). Accordingly, the oxide film having a low dielectric ratio and arising from the oxidation of the lower electrode at the time of fabricating a conventional capacitor, inclusive of the Ta₂O₅ thin film (25), can be substantially avoided. Also, the thickness (Tox) of the oxide film of the capacitor can be controlled to be below 30 .

[0052] Also, the Si₃N₄ chloride-free thin film deposited by using BTBAS is stronger in an oxidation persistent property than the Ta₂O₅ thin film at the time of being subjected to a high temperature oxidation treatment after the deposition of Ta₂O₅. Accordingly, the Si₃N₄ thin film can act as a diffusion barrier against activated oxygen. As a result, it is more preferable to deposit the Ta₂O₅ thin film to a thickness of at least 100 so as to fabricate the capacitor in the semiconductor device so that a large capacitance for a capacitor can be secured. Accordingly, the Si₃N₄ chloride-free thin film can be employed for a capacitor in highly integrated products.

[0053] Furthermore, the capacitor having a dual dielectric film structure composed of the Ta₂O₅/Si₃N₄ thin film is useful for the fabrication process of highly integrated device, which is specifically vulnerable to a high temperature thermal budget process, because a high temperature nitrification treatment process such as RTN (Rapid Thermal Nitrification), which is carried out under temperature of 800 to 900 C. and an atmosphere of NH₃ in order to avoid the oxidation of the lower electrode as has been in the conventional fabrication process of a capacitor made of Ta₂O₅ thin film, is not required.

[0054] Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.