Method for manufacturing stacked capacitor

[0002] This application claims the priority benefit of Taiwan application serial no. 88106718, filed Apr. 27, 1999, the full disclosure of which is incorporated herein by reference.

[0003] 1. Field of Invention

[0004] The present invention relates to a method for manufacturing the capacitor of a semiconductor memory cell. More particularly, the present invention relates to a method for manufacturing a stacked capacitor of dynamic random access memory (DRAM).

[0005] 2. Description of Related Art

[0006] As semiconductor device manufacturing progresses into the deep sub-micron range, dimensions of each semiconductor are all reduced. One consequence of this is the reduction of space for accommodating a capacitor having a conventional DRAM structure. In contrast, the size of software needed to operate a computer is forever growing, and hence the needed memory capacity must be increased. In the presence of these conflicting requirements, some changes have to be made regarding the design of DRAM capacitors.

[0007] A stacked capacitor structure is the principle type of capacitor to be used in manufacturing semiconductor memory. The stacked type of capacitor has been used for quite some time and continues to be used, even in sub-micron device fabrication.

[0008] Stacked capacitors can be roughly classified into crown-shaped, fin-shaped, cylinder-shaped or spread-out type. Although any of these stacked capacitors is able to satisfy the high density requirement of DRAMs, simply using such conventional structures to fabricate the capacitor can hardly go beyond 256 megabit (Mb) memory capacity.

[0009] However, the memory capacity can be promoted by increasing the surface area of the lower electrode of a crown-shaped capacitor so that higher memory capacity becomes possible. For example, the surface area of a capacitor can be further increased by selectively growing hemispherical grains (HSGs) on the low electrode.

[0010] FIGS. 1A through 1E are cross-sectional views showing the progression of manufacturing steps in fabricating a conventional double-sided crown-shaped capacitor.

[0011] First, as shown in FIG. 1A, a substrate 100 having a number of devices (not shown) thereon is provided. Next, a silicon oxide layer 102 and a silicon nitride layer 104 are sequentially formed over the substrate 100. The silicon oxide layer 102 serves as an inter-layer dielectric (ILD) while the silicon nitride layer 104 serves as an etching stop layer during the fabrication of the double-sided crown-shaped capacitor. Both the silicon oxide layer 102 and the silicon nitride layer 104 can be formed using a chemical vapor deposition (CVD) method, for example.

[0012] Thereafter, photolithographic and etching operations are conducted to form a contact opening 106 that passes through the silicon oxide layer 102 and the silicon nitride layer 104. Next, a doped polysilicon plug is formed inside the contact opening 106. The doped silicon plug can be formed by first depositing a layer of doped polysilicon (not shown in the figure) over the silicon nitride layer 104 and filling the contact opening 106 using a chemical vapor deposition (CVD) process. Then, the doped polysilicon layer above the silicon nitride layer 104 is removed using, for example, a reactive ion etching (RIE) method.

[0013] Next, as shown in FIG. 1B, an insulation layer 108 is formed over the silicon nitride layer 104. The insulation layer 108 can be formed using, for example, a chemical vapor deposition (CVD) method. The insulation layer 108 is made, for example, from borophosphosilicate glass (BPSG). Thereafter, an opening 110 that exposes the contact opening 106 is formed using photolithographic and etching techniques.

[0014] Following, as shown in FIG. 1C, an amorphous silicon layer 112 conformal to the opening 110 and the surrounding insulation layer 108 is formed. The amorphous silicon layer 112 is formed using, for example, a low-pressure chemical vapor deposition (LPCVD) method.

[0015] Next, as shown in FIG. 1D, using the insulation layer 108 as a polishing stop layer, the amorphous silicon layer 112 above the insulation layer 108 are removed. Hence, only the amorphous silicon layer 112ainside the opening 110 remains. The method of removing portions of the amorphous silicon layer 112 includes a chemical-mechanical polishing (CMP) method.

[0016] Next, as shown in FIG. 1E, using the silicon nitride layer 104 as an etching stop layer, the insulation layer 108 above the silicon nitride layer 104 is removed using a wet etching method, for example. Hence, a crown-shaped capacitor structure is obtained.

[0017] Thereafter, hemispherical grains are formed on the exposed surface of amorphous silicon layer. Next, dielectric material is deposited to form a capacitor dielectric layer, and then an upper electrode is formed over the capacitor dielectric layer to form the double-sided crown-shaped capacitor. Since subsequent operations should be familiar to those skilled in the art of semiconductor manufacture, detailed descriptions are omitted here.

[0018] However, if the doping concentration in the amorphous silicon layer is insufficient in the manufacture of prior art, the hemispherical grains will have a undoped surface during its growth which results in a capacitance depletion effect. The capacitance depletion effect can contribute 25 percents degradation in capacity.

[0019] The capacitance depletion effect can be resolved due to an increment of the doping concentration in the amorphous silicon layer. Unfortunately, the high doping concentration in the amorphous silicon layer can inhibit the migration of silicon atoms resulting in the hemispherical grains being hard to form. The surface area-gain provided by hemispherical grains therefore decreases to affect the capacity of a capacitor.

[0020] The present invention provides a method of manufacturing a stacked capacitor that utilizes multi-amorphous silicon layer with different doping concentrations to resolve the capacitance depletion effect and the decrement of the area-gain of the hemispherical grains. Meanwhile, this invention utilizes a manufacture method of forming a trench line and a via applied in dual damascene process to get a double-sided double-crown-shaped capacitor with a more bottom electrode surface.

[0021] To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method of forming a stacked capacitor. The method includes providing a substrate and forming a first dielectric layer over the substrate. A contact opening is formed in the first dielectric layer and a conductive plug is formed inside the contact opening. A second dielectric layer is formed over the substrate and a trench line is formed in the second dielectric layer. A via is formed in the second dielectric layer beneath the trench line and the conductive plug is exposed. An undoped first amorphous silicon layer is formed conformally to the trench line and the via. A doped second amorphous silicon layer is formed over the undoped first amorphous silicon layer. An undoped third amorphous silicon layer is formed over the doped second amorphous silicon layer. A photoresist layer is formed over the substrate to fill the trench line and the via. The photoresist layer, the undoped third amorphous silicon layer, the doped second amorphous silicon layer and the undoped first amorphous silicon layer above the second dielectric layer are removed using the second dielectric layer as a polishing stop layer. The photoresist layer filling in the trench line, the via and the second dielectric layer is removed thereafter. A plurality of hemispherical grains are formed over an exposed surface of the undoped first amorphous silicon layer and the undoped third amorphous silicon layer. And, a doping process to the hemispherical grains, the undoped first amorphous silicon layer and the undoped third amorphous silicon layer is performed.

[0022] According to this invention, a manufacture method of a trench line and a via applied in dual damascene process is utilized to form a trench line and a via in a dielectric layer. Then, conformal multi-amorphous silicon layers with different doping concentration are formed on an exposed surface of the trench line and the via to serve as a bottom electrode of a double-sided double-crown-shaped capacitor. Furthermore, a phosphine (PH₃) treatment process is performed after hemispherical grains formed on the bottom electrode of the double-sided double-crown-shaped capacitor to increase the doping concentration of the bottom electrode surface of the capacitor.

[0023] Since this invention utilizes a manufacture method of a trench line and a via applied in dual damascene process to form a double-sided double-crown-shaped capacitor. It provides more bottom electrode surface of a capacitor to increase the capacitance of a memory device.

[0024] In this invention, a poly slurry having a good polish ability to amorphous silicon is used during a chemical mechanical polishing process. The poly slurry has a high polishing selectivity of amorphous silicon to silicon nitride, i.e. higher than 80, so that the polish end point is easily to be detected and good uniformity of a polished wafer can be promoted.

[0025] In this invention, an amorphous silicon layer formed as a double-sided double-crown-shaped structure has an undoped concentration surface which does not inhibit migration of silicon atoms during the formation of hemispherical grains. The hemispherical grains therefore are easily formed and possess a higher surface area-gain.

[0026] After the formation of the hemispherical grains, a phosphine (PH₃) treatment is performed to increase the doping concentration of the bottom electrode surface of a capacitor. Thus, the capacitance depletion effect can be resolved.

[0027] It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.

[0028] The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,

[0029] FIGS. 1A through 1E are cross-sectional views showing the progression of manufacturing steps in fabricating a conventional double-sided crown-shaped capacitor; and

[0030] FIGS. 2A through 2G are cross-sectional views showing the progression of manufacturing steps in fabricating a double-sided double-crown-shaped capacitor according to this invention.

[0031] Reference now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

[0032] FIGS. 2A through 2G are cross-sectional views showing the progression of manufacturing steps in fabricating a double-sided double-crown-shaped capacitor according to this invention.

[0033] As shown in FIG. 2A, a substrate 200 having a number of devices thereon is provided. A dielectric layer 202 is formed over the substrate 200. The dielectric layer 202 serves as an inter-layer dielectric layer formed using, for example, a chemical vapor deposition (CVD) process.

[0034] Photolithographic and etching techniques are used to form a contact opening 204 that passes through the dielectric layer 202. A conductive plug 206 is formed inside the contact opening 204. The conductive plug 206 is formed by first depositing a conductive layer (not shown in the figure) over the dielectric layer 202 and completely filling the contact opening 204 using, for example, a chemical vapor deposition (CVD) method. Then, the conductive layer above the dielectric layer 202 is removed using, for example, a reactive ion etching method. The conductive plug 206 can be made, for example, from doped polysilicon whose doping concentration is preferably around 5E19 ions/cm³.

[0035] A dielectric layer 208 is formed over the dielectric layer 202 and the conductive plug 206. For example, the dielectric layer 208 includes a silicon nitride layer 208a, a silicon oxide layer 208b, a silicon nitride layer 208c, a silicon oxide layer 208d, and a silicon nitride layer 208esequentially formed using a chemical vapor deposition (CVD) method.

[0036] As shown in FIG. 2B, photolithographic and etching techniques are used to form a trench line 210 and a via 212 passing through the dielectric layer 208. Preferably, the fabricating process for forming the trench line 210 and the via 212 includes a dual damascene process. For example, the trench line 210 is formed in the silicon nitride layer 208eand the silicon oxide layer 208dusing the silicon nitride layer 208cas an etching stop layer. The via 212 is formed in the silicon nitride layer 208a, the silicon oxide layer 208band the silicon nitride layer 208cunder the trench line 210 and exposes the conductive plug 206.

[0037] As shown in FIG. 2C, an amorphous silicon layer 214 conformal to the trench line 210, the via 212 and the surrounding dielectric layer 208 is formed. The amorphous silicon layer 214 can be formed, for example, using a low-pressure chemical vapor deposition (LPCVD) method at a temperature of between 510° C. to 520° C. Moreover, the amorphous silicon layer 214 of a tri-layer structure includes an undoped amorphous silicon layer 214a, a heavily doped amorphous silicon layer 214b, and an undoped amorphous silicon layer 214c.

[0038] The heavily doped amorphous silicon layer 214b, for example, has a doping concentration preferably around 6E20 ions/cm³. The heavily doped amorphous silicon layer 214bcan reduce the capacitance depletion effect.

[0039] In the subsequent step, a photoresist layer 216 is formed over the amorphous silicon layer 214 so that the trench line 210 and the via 212 is also filled.

[0040] As shown in FIG. 2D, the photoresist layer 216 and the amorphous silicon layer 214 above the dielectric layer 208 are removed using the silicon nitride layer 208eas an etching stop layer. Thus, only a portion of the photoresist layer 216aand a double-crown shaped amorphous silicon layer 218 remain inside the trench line 210 and the via 212. The double-crown shaped amorphous silicon layer 218 of a tri-layer structure includes an undoped amorphous silicon layer 218a, a heavily doped amorphous silicon layer 218b, and an undoped amorphous silicon layer 218c.

[0041] The photoresist layer 216 and the amorphous silicon layer 214 above the dielectric layer 208, for example, are removed using a chemical mechanical polishing (CMP) method.

[0042] Generally, a slurry with a good polish ability to oxide is used during the chemical mechanical polishing (CMP) process in prior art, and the slurry is referred as a oxide slurry. However, the oxide slurry usually has a low polishing selectivity of amorphous silicon to silicon nitride, i.e. 3˜5, so that the polish end point is hard to be detected and the polished wafer of worse uniformity is always performed.

[0043] Therefore, a poly slurry having a good polish ability to amorphous silicon is used during the chemical mechanical polishing (CMP) process in this invention. The poly slurry has a high polishing selectivity of amorphous silicon to silicon nitride, i.e. higher than 80, so that the polish end point is easy to be detected and the polished wafer of good uniformity is performed.

[0044] As shown in FIG. 2E, thereafter, the photoresist layer 216ainside the trench line 210 and the via 212 is also removed using, for example, a wet etching method. Ultimately, only the double-crown-shaped amorphous silicon layer 218 remains inside the trench line 210 and the via 212.

[0045] The dielectric layer 208 is removed using, for example, a wet etching method.

[0046] As shown in FIG. 2F, subsequently, a multitude of hemispherical grains 220 is formed on the exposed surface of the double-crown-shaped amorphous silicon layer 218. The hemispherical grains 220 are formed over the amorphous silicon layer 218 by first seeding nuclei for forming hemispherical grains 220 selectively over the double-crown-shaped amorphous silicon layer 218. The seeding can be done using silane (SiH₄) or disilane (Si₂H₆) in a high vacuum (about 10⁻³to 10⁻⁴Torr). A heat treatment is then carried out, in an ultra high vacuum (about 10⁻⁸to 10⁻⁹Torr) so that silicon atoms inside the double-crown-shaped amorphous silicon layer 218 are able to migrate towards the respective nuclei. The nuclei are grown into hemispherical grains 220.

[0047] Since the hemispherical grains 220 is formed on a surface of the two undoped amorphous silicon layer 218aand 218cso that the migration of the silicon atoms in the undoped amorphous silicon layer 218aand 218care not inhibited. The hemispherical grains 220 are therefore easily formed and possess a higher surface area-gain.

[0048] As shown in FIG. 2G, a doping process for the hemispherical grains 220, the undoped amorphous silicon layer 218aand 218cis performed to result in doped hemispherical grains 224, doped amorphous silicon layer 222aand 222c. Thus, the capacitance depletion effect can be resolved.

[0049] The doping process is performed by using, for example, a phosphine (PH₃) treatment of about 5 to 30 minutes with a phosphine (PH₃) gas pressure of around 1 to 10 torr and at a temperature of between about 700° C. to 750° C.

[0050] Subsequent operations of forming a capacitor dielectric layer and an upper electrode are formed over the doped hemispherical grains 224, doped amorphous silicon layer 222aand 222c, and a double-sided double-crown-shaped capacitor is completely manufactured. These process are familiar to those skilled in semiconductor manufacture, therefore, detailed description is omitted.

[0051] In short, this invention utilizes a manufacture method of a trench line and a via applied in dual damascene process to form a trench line and a via in a dielectric layer. Then, multi-amorphous silicon layers with different doping concentration are conformally formed on a exposed surface of the trench line and the via to serve as a bottom electrode of a double-sided double-crown-shaped capacitor. Furthermore, a phosphine (PH₃) treatment process is performed after hemispherical grains formed on the bottom electrode of the double-sided double-crown-shaped capacitor to increase the doping concentration of the bottom electrode surface of the capacitor.

[0052] Since this invention utilizes a manufacture method of a trench line and a via applied in dual damascene process to form a double-sided double-crown-shaped capacitor. It provides more bottom electrode surface of a capacitor to increase the capacitance of a memory device.

[0053] In this invention, a poly slurry having a good polish ability to amorphous silicon is used during a chemical mechanical polishing process. The poly slurry has a high polishing selectivity of amorphous silicon to silicon nitride, i.e. higher than 80, so that the polish end point is easily to be detected and good uniformity of a polished wafer can be promoted.

[0054] In this invention, an amorphous silicon layer formed as a double-sided double-crown-shaped structure has an undoped concentration surface which does not inhibit migration of silicon atoms during the formation of hemispherical grains. The hemispherical grains therefore are easily formed and possess a higher surface area-gain.

[0055] After the formation of the hemispherical grains, a phosphine (PH₃) treatment is performed to increase the doping concentration of the bottom electrode surface of a capacitor. Thus, the capacitance depletion effect can be resolved.

[0056] It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.