Abstract:
It is intended to enable simultaneous formation of concave capacitor storage electrodes and a convex bit contact plug electrode and thereby makes it possible to reduce spaces of margins for alignment errors by decreasing the number of lithography steps. Gate electrodes are formed on a p-well in such a manner that the gate electrode interval in storage electrode forming portions is longer than that in a bit contact plug forming portion, and sidewalls are then formed. An SiO 2  film is deposited, storage electrode forming holes and a bit contact plug forming holes are formed therein, and then a polysilicon film is deposited. Another SiO 2  film is deposited on the polysilicon film and etched back. Then, the polysilicon film is etched back. After etching of the SiO 2  films, capacitor insulating films and counter electrodes are formed and a bit line is also formed.

Description:
This application is a division of application Ser. No. 09/498,640, filed on Feb. 7, 2000, now abandoned, the entire contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor device having concave electrode and convex electrode and method of manufacturing thereof; and especially relates to semiconductor device having concave capacitor electrode and convex wiring electrode and method of manufacturing thereof in a DRAM (Dynamic Random Access Memory) etc. 
     2. Description of the Related Art 
     In typical DRAMs, each memory cell comprises one MOS (Metal Oxide Semiconductor) transistor and one capacitor for storing information. To secure larger capacitance, the technique in which the storage electrode portion of the capacitor is given a cylinder shape is widely employed. 
     FIG. 15 is a plan view showing the structure of a DRAM memory cell portion having a cylinder-shaped capacitor which is proposed in Symposium on VLSI Technology Digest of Technical Papers, pp. 22-23, 1996. 
     As shown in FIG. 15, gate electrodes  7  having sidewalls  9  on their side faces are formed so as to extend in the top-bottom direction in the figure. Source/drain diffusion layers  8  are formed between the gate electrodes  7  so as to be interposed between device isolation oxide films  2 . Cylinder-shaped storage electrodes  13  and a bit contact plug  14  are formed on and connected to the respective source/drain diffusion layers  8 . A counter electrode  17  is formed on each storage electrode  13  via a capacitor insulating film (not shown). 
     In the conventional example shown in FIG. 15, all the intervals between the gate electrodes  7  are substantially the same. That is, the conventional example is designed in such a manner that the interval between the gate electrodes  7  on both sides of the bit contact plug  14  is equal to the interval between the gate electrodes  7  on both sides of each storage electrode  13 . And the diameters of the storage electrodes  13  and the bit contact plug  14  are set approximately the same. 
     A manufacturing process of this conventional example will be described below with reference to FIGS. 16 to  18  which are sectional views taken along line XIV˜X VIII—X IV˜X VIII in FIG.  15  and arranged in order of steps. 
     As shown in FIG. 16A, device isolation oxide films (not shown) and gate oxide films  3  are formed on a p-well region  1  and gate electrodes  7  whose top surfaces are covered with SiN films  6  are formed thereon. All the intervals between the gate electrodes  7  are substantially the same. Then, source/drain diffusion layers  8  are formed by doping of an n-type impurity. Then, sidewalls  9  are formed on the side faces of the laminated films each having a gate electrode  7  and a SiN film  6 . 
     Then, as shown in FIG. 16B, an SiO 2  film  10  is deposited over the entire surface and subjected to anisotropic dry etching, whereby holes for exposing the surfaces of the respective source/drain diffusion layers  8  are formed. 
     Thereafter, as shown in FIG. 17A, a phosphorus-doped polysilicon film  11  and an SiO 2  film  12  are deposited over the entire surface. Then, as shown in FIG. 17B, the portion of the SiO 2  film  12  in a bit contact plug forming region is removed selectively and a phosphorus-doped polysilicon film  24  is deposited over the entire surface. 
     Thereafter, as shown in FIG. 18A, the polysilicon film  24  is etched back so that its residual portion is buried in the portion of the polysilicon film  11  in the bit contact plug forming region. Then, as shown in FIG. 18B, after removing the top portions of the polysilicon films  11  and  24  by etching, the SiO 2  films  10  and  12  are removed by etching, whereby cylinder-shaped storage electrodes  13  and a bit contact plug  14  are formed. 
     Although not shown in figures, subsequently, capacitor insulating films and counter electrodes are formed on the surfaces of the respective storage electrodes  13  and the entire surface is covered with an interlayer insulating film. Then, a bit line that is connected to the bit contact plug  24  is formed. 
     With the recent miniaturization and increased integration densities of semiconductor devices, the intervals between constituent elements such as contacts and gate electrodes have become very small. Therefore, to increase margins for mask alignment errors in photolithography steps, processes using self-alignment have become very important. Further, to reduce the manufacturing cost of DRAMs etc. and shorten the TAT (Turn Around Time), how to decrease the number of times of use of photolithography is an important theme. 
     In the conventional manufacturing process described above, a cylinder shape is also formed in a bit contact plug forming portion in depositing a polysilicon film  11  to form cylinder-shaped storage electrodes  13  (see FIG.  17 A). Therefore, to form a plug, it is necessary to form holes in SiO 2  film  12 , deposit a phosphorus-doped polysilicon film again, and fill in the hole of the cylinder structure in the bit contact plug forming portion. That is, in the above described conventional manufacturing process, to fill in the hole in the bit contact plug forming portion, it is necessary to additionally execute (1) the photolithography step, (2) the step of selectively etching an SiO 2  film  12 , (3) the step of depositing a polysilicon film  24 , and (4) the step of etching back the polysilicon film  24 . 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to overcome the problems existing in the conventional technology to provide a novel semiconductor device and the novel manufacturing method of the semiconductor. 
     According to one aspect of the invention, there is provided a semiconductor device comprising: 
     a semiconductor substrate; 
     a convex electrode formed on said semiconductor substrate; 
     a first concave electrode formed on said semiconductor substrate, said first concave electrode made of the same layer to said convex electrode, and said first concave electrode having an external diameter greater than an external diameter of said convex electrode; and 
     a first transistor formed on said semiconductor substrate between said convex electrode and said first concave electrode, and connected said convex electrode and said first concave electrode. 
     According to another aspect of the invention, there is provided a method of manufacturing a semiconductor device comprising: 
     forming AMOS transistor on the semiconductor substrate; 
     forming a spacer layer on said transistor and said semiconductor substrate; 
     opening a first and a second windows from surface of said spacer layer to a source and a drain regions of said MOS transistor, the internal diameter of said first window being greater than the internal diameter of said second window; 
     forming a conductive layer on said spacer layer and the inside of said first and second windows so as to fill up the inside of said second window by said conductive layer and to remain concave hollow portion in said first window; and 
     removing said conductive layer on said spacer layer and said spacer layer to form a concave electrode by said conductive layer in said first window and a convex electrode by said conductive layer in said second window. 
     In the invention, in forming holes or windows for forming a concave storage electrode and a convex bit contact plug electrode in a spacer film (i.e., SiO 2  film  10 ), the diameter of a hole or window for forming the storage electrode is set larger than that of a hole or window for forming the bit contact plug. This makes it possible to form a polysilicon film in the holes for formation of concave storage electrodes and a convex bit contact plug electrode in such a manner that the hole or window for forming the convex bit contact plug electrode is completely filled with the polysilicon film but the hole or window for forming the concave storage electrode are not completely filled with the polysilicon film. That is, whereas cylinder-shaped concave polysilicon films are formed in the hole for forming the respective concave storage electrode forming holes, the hole for forming the convex bit contact plug is completely filled with polysilicon. 
     Therefore, the invention can prevent formation of a hole in the polysilicon film in the bit contact plug forming portion and hence can omit a photolithography step for filling in the hole, a selective etching step, a polysilicon deposition step, and a polysilicon etch back step, etc for filling up the hole to form the bit contact plug. This enables reduction of the manufacturing cost, increase of the production yield, and shortening of the TAT. Further, decreasing the number of photolithography steps, the invention dispenses with margins for errors of mask alignment that is necessary for photolithography. The invention can thus provide a structure and a manufacturing method that are advantageous in increasing the integration density. 
     These and other object of the present invention will be apparent to those of skill in the art from the appended claims when read in light of the following specification and accompanying figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a semiconductor device according to a first embodiment of the present invention. 
     FIGS. 2 to  7  are sectional views arranged in order of steps and showing a manufacturing process according to the first embodiment of the invention. 
     FIGS. 8 to  9  are sectional views arranged in order of steps and showing a manufacturing process according to a second embodiment of the invention. 
     FIGS. 10A and 10B are sectional views arranged in order of steps and showing a manufacturing process according to a third embodiment of the invention. 
     FIG. 11 is a plan view of a semiconductor device according to a fourth embodiment of the invention. 
     FIGS. 12 to  14  are sectional views arranged in order of steps and showing a manufacturing process according to the fourth embodiment of the invention. 
     FIG. 15 is a plan view of a conventional example. 
     FIGS. 16 to  18  are sectional views arranged in order of steps and showing a manufacturing process of the conventional example of FIG.  15 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be hereinafter described in detail with reference to the accompanying drawings. 
     First Embodiment 
     FIGS. 1 and 7 are a plan view and a sectional view of a semiconductor device according to a first embodiment of the present invention. As shown in FIG. 1 and 7, gate electrodes  7  having sidewalls  9  on their side faces are formed so as to extend in the top-bottom direction in the FIG.  1 . The two central gate electrodes  7  are formed on active regions and the gate electrodes  7  of the right end and the left end are formed on device isolation oxide films  2 . The interval between the two gate electrodes  7  on the active regions is set shorter than the interval between each gate electrode  7  on the active region and the corresponding gate electrode  7  on the device isolation oxide film  2 . Source/drain diffusion layers  8  are formed between the gate electrodes  7  so as to be interposed between the device isolation oxide films  2  in the top-bottom direction in FIG. 1. A convex bit contact plug electrode  14  and cylinder-shaped concave storage electrodes  13  are formed on and connected to the respective source/drain diffusion layers  8 . As shown in FIG. 1, the diameter of the storage electrodes  13  is set larger than that of the bit contact plug  14 . A counter electrode  17  is formed on each storage electrode  13  via a capacitor insulating film  15  in FIG.  7 . 
     A manufacturing process of the semiconductor device of FIG. 1 will be described below with reference to FIGS. 2A to  7  that are sectional views taken along line II˜X—II˜X in FIG.  1  and arranged in order of steps. 
     As shown in FIG. 2A, 500-nm-thick device isolation oxide films  2  are formed on a p-well region  1  provided on a semiconductor substrate (not shown) by an isolation technique such as an STI (Shallow Trench Isolation) method or a LOCOS (Local Oxidation of Silicon) method. Then, a 10-nm-thick gate oxide film  3  is formed by thermal oxidation, and a 100-nm-thick polysilicon film  4 , a 100-nm-thick tungsten silicide film (WSi film)  5 , and a 200-nm-thick SiN film  6  are deposited thereon sequentially by CVD (Chemical Vapor Deposition). Then, gate electrodes  7  are formed by simultaneously patterning these three deposition films by photolithography. At this time, as shown in FIG. 2A, the length of each gate electrode  7  (i.e., gate length) is set at 0.3 μm, the distance between each gate electrode  7  on the device isolation oxide film  2  and the corresponding gate electrode  7  on the active region is set at 0.5 μm, and the distance between the two gate electrodes  7  on the active region is set at 0.3 μm. After the formation of the gate electrodes  7 , source/drain diffusion layers  8  are formed by ion implantation of phosphorus or arsenic. 
     Thereafter, as shown in FIG. 2B, an SiN film is deposited over the entire surface by LP-CVD (low-pressure CVD) and etch back is performed on the entire surface, whereby sidewalls  9  having a width of 0.1 μm are formed on the side faces of the gate electrodes  7 . Then, an SiO 2  film  10  is deposited by plasma CVD and its surface is planarized by CMP (Chemical Mechanical Polishing). The height of the planarized SiO 2  film  10  as measured from the diffusion layers  8  is set at about 750 nm. 
     Thereafter, as shown in FIG. 3A, the portions of the SiO 2  film  10  in the regions where storage electrodes  13  and a bit contact plug  14  (see FIG. 1) are to be formed are removed selectively by photolithography and dry etching. The diameter of holes or windows for forming concave storage electrodes are set at 0.5 μm. Meanwhile, the diameter of a hole or window for forming a convex bit contact plug electrode is set at and 0.3 μm. 
     Then, as shown in FIG. 3B, a phosphorus-doped polysilicon film  11  is deposited at a thickness of 200 nm by LP-CVD. As a result, the polysilicon film  11  is formed in cylinder form in the holes for forming storage electrodes while the hole for forming the bit contact plug is completely filled with the polysilicon film  11 . An SiO 2  film  12  is then deposited on the entire surface by plasma CVD. 
     Then, as shown in FIG. 4A, etch back is performed on the entire surface of the SiO 2  film  12  until the surfaces of the polysilicon film  11  are exposed. Then, as shown in FIG. 4B, etch back is performed on the entire surfaces of the polysilicon film  11 , whereby the surfaces of the SiO 2  films  10  are exposed. 
     Subsequently, as shown in FIG. 5A, the residual portions of the SiO 2  films  10  and  12  are completely removed by wet etching. As a result, cylinder-shaped concave storage electrodes  13  and a convex bit contact plug electrode  14  are formed at the same time. 
     Then, as shown in FIG. 5B, a dielectric film or a capacitor insulating film  15  of about 7 nm in thickness is deposited and a phosphorus-doped polysilicon film  16  of about 40 nm in thickness is deposited thereon by LP-CVD. Then, as shown in FIG. 6A, counter electrodes  17  are formed and the top surface of the convex bit contact plug electrode  14  is exposed by patterning the polysilicon film  16  and the capacitor insulating film  15  by photolithography and dry etching. At this time, the portions of the polysilicon film  16  and the capacitor insulating film  15  that are formed on the side faces of the bit contact plug  14  may be removed by etching. 
     Thereafter, an SiO 2  film  18  is deposited by CVD by using TEOS (tetraethoxysilane: Si(OC 2 H 5 ) 4 ) as a source gas and its surface is planarized by CMP. At this time, the thickness of the portion of the planarized SiO 2  film  18  above the top surface of the bit contact plug  14  is set at about 300 nm. Then, the SiO 2  film  18  is selectively removed by photolithography and dry etching, whereby a hole of 0.3 μm in diameter is formed that exposes the top surface of the bit contact plug  14  as shown in FIG.  6 B. 
     Finally, as shown in FIG. 7, a tungsten film  19  is deposited by CVD and a bit line is formed by patterning the tungsten film  19  by photolithography. Thereby, the top area of the convex bit contact plug electrode  14  is selectively connected to the tungsten wiring layer  19 . 
     Second Embodiment 
     FIGS. 8 to  9 B are sectional views that are arranged in order of steps and show a manufacturing process according to a second embodiment of the invention. A plan view of a semiconductor device according to the second embodiment is the same as the plan view (i.e., FIG. 1) of the semiconductor device according to the first embodiment, and the sectional views of FIGS. 8 to  9 B are taken along line II˜X—II˜X in FIG.  1 . In this embodiment, the steps to the one shown in FIG. 5A are the same as in the first embodiment except that the polysilicon film  11  is deposited at a thickness of about 180 nm rather than 200 nm in the first embodiment. After the processing has been made to reach the state of FIG. 5A, a 40-nm-thick phosphorus-doped amorphous silicon film  20  is deposited over the entire surface by LP-CVD as shown in FIG.  8 . Then, as shown in FIG. 9A, etch back is performed on the entire surface to leave the portions of the amorphous silicon film  20  only on the side faces of the vertical portion of the polysilicon films  11 . 
     Thereafter, HSG layers having fine asperity on their surfaces are formed on the side faces of the polysilicon films  11  by performing an HSG (Hemi-Spherical Grained Si) treatment. Specifically, after Si nuclei are formed on the surfaces of the amorphous silicon films  20  by inputting the wafer into a high-vacuum reaction furnace in which the temperature is increased to 550-570° C. and causing SiH 4  to flow for about 20 seconds, Si atoms in the amorphous silicon films  20  are accumulated on the Si nuclei by performing annealing in a high vacuum state. As a result, as shown in FIG. 9C, storage electrodes  13  and a bit contact plug  14  having HSG layers  21  on their side faces are formed. 
     Then, as in the first embodiment, capacitor insulating films, counter electrodes, an interlayer insulating film, and a bit line are formed as shown in FIG. 5B to FIG.  7 . 
     Third Embodiment 
     FIGS. 10A and 10B are sectional views that are arranged in order of steps and show a manufacturing process according to a third embodiment of the invention. A plan view of a semiconductor device according to the third embodiment is the same as the plan view (i.e., FIG. 1) of the semiconductor device according to the first embodiment, and the sectional views of FIGS. 10A and 10B are taken along line II˜X—II˜X in FIG.  1 . In this embodiment, phosphorus-doped amorphous silicon  22  is deposited instead of polysilicon.  11  that is deposited in the step of FIG. 3B in the first embodiment. As shown in FIG. 10A, the steps of processing a deposited amorphous silicon film  22  into storage electrodes and a bit contact plug are the same as the steps of FIGS. 2A to  5 A in the first embodiment. After the processing has been performed as shown in FIG. 10A, the same HSG treatment as in the second embodiment is performed, whereby.the amorphous silicon films  22  are converted into HSG layers  23  having fine asperity on their surfaces as shown in FIG.  10 B. 
     Then, capacitor insulating films, counter electrodes, an interlayer insulating film, and a bit line are formed by the same steps as shown in FIG. 5B to FIG. 7 of the first embodiment. 
     Fourth Embodiment 
     FIGS. 11 to  14 F show a fourth embodiment of the invention. That is, FIG. 11 is a plan view of a semiconductor device, and FIGS. 12A to  14 B are sectional views taken along line X II˜X I V—X II˜X I V in FIG.  11  and arranged in order of steps of a manufacturing process. In FIG. 11, the constituent elements having corresponding constituent elements in FIG. 1 are given the same reference numerals as the latter and redundant descriptions therefor will be omitted. In this embodiment, the interval between the gate electrodes  7  on both sides of each concave storage electrode  13  is set the same as the interval between the gate electrodes  7  on both sides of the convex bit contact plug electrode  14 . Further, in this embodiment, each concave storage electrode  13  overlaps, over a long length, with the gate electrode  7  on the device isolation oxide film  2  and the diameter of each concave storage electrode  13  is set larger than that of the convex bit contact plug electrode  14 . This enables simultaneous formation of the concave storage electrodes  13  and the convex bit contact plug electrode  14  as in the case of the first to third embodiments. 
     Next, the manufacturing process according to the fourth embodiment will be described with reference to FIGS. 12A to  14 B. 
     As shown in FIG. 12A, a 500-nm-thick device isolation oxide films  2  are formed on a p-well region  1  by a known isolation technique. Then, a 10-nm-thick gate oxide film  3  is formed by thermal oxidation, and a 100-nm-thick polysilicon film  4 , a 100-nm-thick tungsten silicide film  5 , and a 200-nm-thick SiN film  6  are deposited thereon sequentially by CVD. Then, gate electrodes  7  are formed by patterning these three deposition films by photolithography and dry etching. At this time, the length of each gate electrode  7  is set at 0.3 μm and the distance between the gate electrodes  7  is also set at 0.3 μm. After the formation of the gate electrodes  7 , source/drain diffusion layers  8  are formed by implantation of phosphorus or arsenic ions. 
     Thereafter, as shown in FIG. 12B, after SiN film sidewalls  9  having a width of 0.1 μm are formed, an SiO 2  film  10  is deposited by plasma CVD. Then, the surface of the SiO 2  film  10  is planarized by CMP so that the height of the planarized SiO 2  film  10  as measured from the diffusion layers  8  is set at about 800 nm. 
     Thereafter, as shown in FIG. 13A, the portions of the SiO 2  film  10  in the regions where concave storage electrodes  13  and a convex bit contact plug electrode  14  (see FIG. 11) are to be formed are removed selectively by photolithography and dry etching. The diameter of resulting concave.storage electrode forming holes and the diameter of a resulting convex bit contact plug electrode forming hole are set at 0.5 μm and 0.3 μm, respectively. 
     Then, as shown in FIG. 13B, a phosphorus-doped polysilicon film  11  is deposited at a thickness of 200 nm by LP-CVD. As a result, the polysilicon film  11  is formed in cylinder form in holes for forming the storage electrode while a hole for forming the bit contact plug is completely filled with the polysilicon film  11 . An SiO 2  film  12  is then deposited on the entire surface by plasma CVD. 
     Then, as shown in FIG. 14A, etch back is performed on the entire surface of the SiO 2  film  12  until the surfaces of the polysilicon film  11  are exposed. Then, etch back is performed on the entire surfaces of the polysilicon film  11  until the surfaces of the SiO 2  films  10  are exposed. 
     Subsequently, as shown in FIG. 14B, the residual portions of the SiO 2  films  10  and  12  are completely removed by wet etching. As a result, cylinder-shaped concave storage electrodes  13  and a convex bit contact plug electrode  14  are formed at the same time. 
     Then, capacitor insulating films, counter electrodes, an interlayer insulating film, and a bit line are formed by the same steps as in the first embodiment. 
     The fourth embodiment can make the interval between the gate electrodes on both sides of each cylinder-shaped storage electrode smaller than in the first embodiment, and has an advantage that the cell size can be reduced. 
     While preferred embodiments of the present invention have been described, it is to be understood that the invention is to be defined by appended claims when read in light of the specification and when accorded their full range of equivalent. For example, the storage electrodes and the bit contact plug may be formed by using a material other than polysilicon, such as W or TiN. It is possible to form HSG layers on the side faces of films of such a material other than polysilicon. The concave storage electrodes and the convex bit contact plug electrode need not always be shaped like a circular concave cylinder or a cylindrical convex pole, and may assume a rectangular concave cylinder or a rectangular convex pole. Further, the CVD film planarization technique may be etch back rather than CMP. 
     As described above, according to the invention, a convex bit contact plug electrode and cylinder-shaped concave storage electrodes can be formed simultaneously by a complete self-alignment process. That is, steps for forming only a bit contact plug that are necessary in the conventional manufacturing process can be eliminated; one photolithography step, one selective etching step, one polysilicon film growing step, and one polysilicon film etch back step can be eliminated. Therefore, according to the invention, since there is no photolithography step, it is no longer necessary to provide margins for mask alignment errors. As a result, the invention not only contributes to miniaturization and increase in integration density of semiconductor devices but also enables reduction of the manufacturing cost of DRAMS etc. and shortening of the TAT.