Patent Document

INCORPORATION BY REFERENCE 
     This application claims the benefit of priority based on Japanese Patent Application No. 2008-076054, filed on Mar. 24, 2008, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for manufacturing a semiconductor device, more particularly, to a technique for forming memory cell contacts of a semiconductor memory device such as a DRAM (dynamic random access memory) and a pseudo SRAM (static random access memory). 
     2. Description of the Related Art 
     Recently, dimension reduction has been advanced in memory devices, such as DRAMs, which include one transistor and one capacitor in each memory cell, and pseudo SRAMs, which have the same cell structure as that of DRAMs. The dimension reduction provides an increased memory capacity while reducing the chip cost due to the yield increase. 
     The dimension reduction in the semiconductor memory cell is, however, undesirably accompanied by the difficulty in providing a clearance between the gate electrode and the cell contact within each memory cell. One known approach to address this problem is to use a self-align contact technique in which the cell contact is self-aligned with respect to the gate electrode with the cell contact size adjusted to be equal to the distance between adjacent gate electrodes. 
     The following is prior art documents found through the Applicant&#39;s search related to the present invention:
     Japanese Laid Open Patent Application No. JP-A 2000-269458,   Japanese Laid Open Patent Application No. JP-A 2007-067250,   Japanese Laid Open Patent Application No. 1993-343669, and   Japanese Laid Open Patent Application No. 1994-021089.   

     One issue in next generation semiconductor devices in which the gate length is reduced below the quarter micron order is production of minute particles during the gate electrode formation. Minute particles may work as etching masks and cause production of skirt-like etching residuals adjacent to the gate electrodes. The skirt-like etching residuals may be directly contacted to the cell contacts formed thereafter, causing short-circuiting between a bitline and a gate electrode or between a capacity electrode and the gate electrode. This may undesirably lower the production yield. It is also a problem that the defects resulting from the minute particles necessitate performing product screening for detecting initial defects with severe conditions. 
     The suppression of the above described phenomenon is of importance to achieve a high yield in a customer sub-constructor&#39;s production process and to maintain a high reliability in a market, especially in a case of the KGD (Known Good Die) business based on the SIP (System In Package) and the MCM (Multi Chip Module). One currently-used approach to address this problem is optimization of the etching conditions for reducing minute particles; however, further advance is desired to address the problem of minute particles, since the detection by an automatic defect detecting machine may face limitations with the further dimension reduction. 
     In the following, a detailed description is given of the problem of the minute particles, referring to  FIGS. 1A to 1H . At first, isolation oxide films  102  are formed within the surface portion of a P-type silicon substrate  101  by using a trench isolation technique. A gate oxide film  103  is then formed in active regions isolated by the isolation oxide films  102 . This is followed by sequentially depositing an N + -doped silicon film  104 , a tungsten silicide film  105 , and a CVD oxide film  106  to cover the P-type silicon substrate  101  as shown in  FIG. 1A . 
     The CVD oxide film  106  is then etched with a photoresist pattern used as a mask to form mask oxide films  107  as shown in  FIG. 1B . Furthermore, cell gate electrodes  108  are formed by subsequently etching the tungsten silicide film  105  and the N + -doped silicon film  104  with the mask oxide films  107  used as a mask. It should be noted that minute particles may be produced in the etching process of the N + -doped silicon film  104 , and the minute particles may work as a mask to locally produce residuals  109  from the N + -doped silicon film  104 . 
     This is followed by forming N-type diffusion layers  110  by an ion implantation technique with the cell gate electrodes  108  used as a mask as shown in  FIG. 1C . After a first nitride film  111  is then formed to cover the entire surface, an interlayer dielectric  112  is formed and then flattened by a CMP (chemical mechanical polishing) technique, as shown in  FIG. 1D . Subsequently, cell contact holes  113  are formed by etching the interlayer dielectric  112  with a photoresist pattern used as a mask and the first nitride film  111  used as a stopper, as shown in FIG.  1 E. Furthermore, the first nitride film  111  is etched back to expose the P-type silicon substrate  101  in the cell contact holes  113 . This process also results in the formation of sidewalls  114  from the first nitride film  111  on the side faces of the cell gate electrodes  108 . At this moment, portions of the residuals  109  are exposed because of the difference in the etching rate between the first nitride film  111  and the residuals  109 , which are formed of N + -doped silicon, as shown in  FIG. 1F . 
     This is followed by filling the cell contact holes  113  with N + -doped silicon contacts  115  through depositing an N + -doped silicon film on the entire surface and performing an etch-back process. This may result in forming a short-circuiting portion  116  which undesirably short-circuits a cell gate electrode  108  and an N + -doped silicon contact  115 , because the residuals  109  are partially exposed and the exposed portions directly contacts to the N + -doped silicon contact  115  as shown in  FIG. 1G . Subsequently, capacitor contacts  117 , capacitor electrodes  118 , capacitor dielectrics  119 , and capacitor plates  120  are formed after forming an interlayer dielectric film. This is followed by forming bitline contacts  121  and bit lines  122  after forming another interlayer dielectric film so that the bit line contacts  121  are connected to the cell contacts  113 . As a result, DRAM memory cells, which each include one transistor and one capacitor, are completely manufactured as shown in  FIG. 1H . 
     The above-described manufacture process, however, suffers from a problem of short-circuiting between the bitlines  122  and the gate electrodes  108  and/or between the capacitor electrodes  118  and the cell gate electrodes  108 , because the cell gate electrodes  108  may be electrically connected to the contacts (each composed of a capacitor contact  117  and a bitline contact  121 ) through the residuals  109 , as described above. 
     SUMMARY 
     In an aspect of the present invention, a manufacture method of forming a semiconductor device includes: forming a plurality of gate electrodes through etching a conductive film deposited on a semiconductor substrate; forming a first nitride film to cover the gate electrodes; partially exposing the semiconductor substrate in a region between adjacent two of the gate electrodes through performing an etch-back process on the first nitride film; thermally oxidizing a residual of the gate electrode film remaining in the region between the adjacent two of the gate electrodes to change the residual into an thermal oxide film; and forming a contact in the region between the adjacent two of the gate electrodes. 
     In another aspect of the present invention, a semiconductor device includes: a gate electrode formed over a semiconductor substrate and covered with a sidewall; and a contact formed adjacent to the sidewall to provide a connection between a diffusion region of the semiconductor substrate and an interconnection provided above the gate electrode. The gate electrode and the contact are insulated by insulative material in at least a portion of the sidewall adjacent to a surface of the semiconductor substrate, and the insulative material is oxide of material of the gate electrode. 
     The present invention effectively avoids short-circuiting between a bitline and a cell gate electrode and/or short-circuiting between a capacitor electrode and a cell gate electrode. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain preferred embodiments taken in conjunction with the accompanying drawings, in which: 
         FIGS. 1A to 1H  are section views showing a typical manufacture method of a semiconductor device illustrated for explaining problems to be solved by the present invention; 
         FIGS. 2A to 2K  are section views showing a method for manufacturing a semiconductor device in a first embodiment of the present invention; and 
         FIGS. 3A to 3K  are section views showing a method for manufacturing a semiconductor device in a second embodiment of the present invention. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The invention will be now described herein with reference to illustrative embodiments. Those skilled in the art will recognize that many alternative embodiments can be accomplished using the teachings of the present invention and that the invention is not limited to the embodiments illustrated for explanatory purposes. 
     First Embodiment 
     Referring to  FIGS. 2A to 2K , a description is given below of an exemplary process of manufacturing a semiconductor device in a first embodiment of the present invention. The manufacture process of this embodiment begins with forming isolation oxide films  2  with a depth of 0.25 to 0.40 μm on the surface of a P-type silicon substrate  1  by using a trench isolation technique. Gate oxide films  3  are then formed with a thickness of 5 to 10 nm in respective active regions isolated by the isolation oxide films  2 . This is followed by sequentially forming an N + -doped silicon film  4  with a thickness of 0.1 to 0.15 μm, a tungsten silicide film  5  with a thickness of 0.1 to 0.15 μm, and a CVD oxide film  6  with a thickness of 0.2 to 0.3 μm to cover the P-type silicon substrate  1 , as shown in  FIG. 2A . 
     Subsequently, mask oxide films  7  with a width of 0.11 to 0.2 μm are formed by etching the CVD oxide film  6  with a photoresist pattern used as a mask, as shown in  FIG. 2B . Furthermore, cell gate electrodes  8  of a polyside structure are formed by sequentially etching the tungsten silicide film  5  and the N+ doped silicon film  4  with the mask oxide films  7  used as a mask. It should be noted that this process suffers from a problem that minute particles of 0.05 to 0.15 μm produced in etching the N + -doped silicon film  4  may work as a mask and locally produce residuals  9  formed of N + -doped silicon. 
     N-type diffusion layers  10  are then formed by using the cell gate electrodes  8  as a mask through ion implantation of arsenic, for example, with a concentration of 1×10 13  to 5×10 13  cm −2 , as shown in  FIG. 2C . This is followed by forming a first nitride film  11  with a thickness of 0.05 to 0.1 μm to cover the entire structure, and then forming an interlayer dielectric  12  with the surface thereof flatten by a CMP technique as shown in  FIG. 2D . Subsequently, cell contact holes  13  with an opening of 0.1 to 0.18 μm are formed by etching the interlayer dielectric  12  with a photoresist pattern used as a mask and with the first nitride film  11  used as a stopper, as shown in  FIG. 2E . Furthermore, portions of the P-type silicon substrate  1  in the cell contacts holes  13  are exposed by etching back the first nitride film  11 . In this process, sidewalls  14  with a thickness of 0.03 to 0.08 μm of the first nitride film are concurrently formed on the side faces of the cell gate electrodes  8 . At this moment, portions of the residuals  9  are exposed because of the difference in the etching rate between the first nitride film  11  and the N + -doped silicon film  4  caused by the high selectivity of the etching, as shown in  FIG. 2F . 
     This is followed by forming a thermally-oxidized film  23  with a thickness of 10 to 25 nm through a thermal oxidization technique involving annealing in a dry air atmosphere in an electric furnace at a temperature of 85° C., for example. It should be noted that, in this process, the oxidization of the N + -doped silicon residuals  9  is enhanced due to the electron concentration higher than that of the N-type diffusion layers  10 , allowing transformation of almost the entire of the residuals  9  into oxidation-enhanced oxide films  24  as shown in  FIG. 2G . 
     A second nitride film  25  with a thickness of 30 to 80 nm is then formed to cover the entire structure as shown in  FIG. 2H . This is followed by partially exposing the P-type silicon substrate  1  by performing an etch-back process on the second nitride film  25 . The etch-back process results in removing the tip portion of the oxidation-enhanced oxide films  24 , forming cap oxide films  27  so as to cover the clearances between the sidewalls  26  formed from the second nitride film  25  and the P-type silicon substrate  1  as shown in  FIG. 2I . This is followed by filling the cell contact holes  13  with N + -doped silicon contacts  15  through depositing an N + -doped silicon film covering the entire surface and then performing an etch-back process on the entire surface, as shown in  FIG. 2J . Subsequently, capacitor contacts  17 , capacitor electrodes  18 , capacitor dielectric films  19 , and capacity plates  20  are formed above the cell gate electrodes  8  after forming another interlayer dielectric. This is followed by forming bitlines  22  and bitline contacts  21  providing connections between the bitlines  22  and the N + -doped silicon contacts  15  above the cell gate electrodes  8  after forming another interlayer dielectric. This completes the formation of DRAM memory cells, each including one transistor and one capacitor as shown in  FIG. 2K . 
     As described above, the manufacture process of the first embodiment of the present invention allows transforming almost the entire of the residuals  9  formed of N + -doped silicon into the oxidation-enhanced oxide films  24  by the thermal oxidization after the formation of the cell contact holes  13 , making use of the difference in the oxidization speed caused by the difference in the electron concentration between the N + -doped silicon film  4  and the P-type silicon substrate  1 . In addition, the formation of the sidewalls  26  from the second nitride film  25  which cover the oxidation-enhanced oxide films  24  allows electrically isolating the N + -doped silicon contacts  15  and the cell gate electrodes  8  from each other with the sidewalls  26  and the cap oxide films  27 . Specifically, the cell gate electrodes  8  and the N + -doped silicon contacts  15  are insulated by the cap oxide films  27 , which are formed of oxide of material used for the cell gate electrodes  8 , at the base region where the sidewalls  26  are in contact with the surface of the P-type silicon substrate  1 . This effectively avoids the short-circuiting between the bitlines  22  and the cell gate electrodes  8  and/or between the capacitor electrodes  18  and the cell gate electrodes  8 . 
     Second Embodiment 
     A description is then given of an exemplary process of manufacturing a semiconductor device in a second embodiment of the present invention, referring to  FIGS. 3A to 3K . The first embodiment is directed to provide a solution to the problem that the local residuals  9  formed of N + -doped silicon due to the formation of the minute particles of 0.05 to 0.15 μm working as a mask in the etching process of the N + -doped silicon film  4 . 
     On the other hand, the second embodiment is directed to avoid a problem caused by minute particles of 0.05 to 0.15 μm produced in etching the CVD oxide film  6  with a photoresist pattern used as a mask. 
     As shown in  FIG. 3A , the process of the second embodiment begins with forming the isolation oxide films  2 , the gate oxide films  3 , the N + -doped silicon film  4 , the tungsten silicide film  5 , and the CVD oxide film  6  in the same manner as that of the first embodiment. This is followed by forming the mask oxide films  7  by etching the CVD oxide film  6  with a photoresist pattern used as a mask. In this etching, some of the mask oxide films  7  (the third mask oxide film  7  from the right in  FIG. 3B ) are sometimes formed with dimensions larger than the design dimensions due to the minute particles  29  as shown in  FIG. 3B . 
     The cell gate electrodes  8  are then formed by sequentially etching the tungsten silicide film  5  and the N + -doped silicon film  4  with the mask oxide films  7  used as a mask. This may result in forming a length-enlarged cell gate electrode  30  having a length longer than a desired length at a portion where the dimension of a certain mask oxide film  7  is larger than the design dimension. This implies that there is a need for preventing short-circuiting between the length-enlarged cell gate electrode  30  and an adjacent N + -doped silicon contact  15  as shown in  FIG. 3C . 
     After forming the first nitride film  11  to cover the entire structure, the interlayer dielectric  12  is formed and the surface thereof is then flatten by a CMP technique as shown in  FIG. 3D . This is followed by forming the cell contact holes  13  by etching the interlayer dielectric  12  with a photoresist pattern used as a mask and with the first nitride film  11  used as a stopper as shown in  FIG. 3E . 
     One issue in forming the cell contact holes  13  so that the cell contact holes  13  are self-aligned to the cell gate electrodes  8  is that the sidewalls  14 , which are formed from the first nitride film  11 , sometimes have an insufficient thickness due to the increased length of the length-enlarged cell gate electrode  30  in the process for etching the interlayer dielectric  12  to expose the P type silicon substrate  1 . In this case, the side face  31  of the length-enlarged cell gate electrode  30  is exposed, as shown in  FIG. 3F . 
     A thermal oxidization is then performed, and this thermal oxidization allows changing the exposed portion of the length-enlarged cell gate electrode  30  into a side oxide film  32  while forming the thermal oxide film  23  on the P-type silicon substrate  11 , as shown in  FIG. 3G . A second nitride film  25  is then formed to cover the entire structure as shown in  FIG. 3H , and this is followed by performing an etch-back process to partially expose the P-type silicon substrate  1 . This results in forming the sidewalls  26 . The sidewalls  26 , which are formed to cover the side oxide film  32 , provides a double insulation structure as shown in  FIG. 3I . 
     Finally, the cell contact holes  13  are filled with the N + -doped silicon contacts  15  as shown in  FIG. 3J , and thus the semiconductor device similar to that of the first embodiment is manufactured as shown in  FIG. 3K . 
     The manufacture process of this embodiment provides secure insulation between the N + -doped silicon contacts  15  and the cell gate electrodes  8  with the sidewalls  26  formed from the second nitride film  25  and the side oxide film  32  formed from a portion of the length-enlarged cell gate electrode  30 , even when the length-enlarged cell gate electrode  30  is formed. This effectively avoids short-circuiting between the bitlines  22  and the cell gate electrodes  8  and/or between the capacitor electrodes  18  and the cell gate electrodes  8 . The manufacture process of the second embodiment, which involves the above described thermal oxidization process, provides advantages similar to those of the first embodiment. 
     It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope of the invention.

Technology Category: h