Abstract:
The present invention is directed to a semiconductor device having a gate electrode includes of a plurality of sidewalls, each having a recess formed therein. The present invention is also directed to a method of forming a semiconductor device. In one illustrative embodiment, the method comprises forming a layer of dopant material in a layer of polysilicon and etching the layer of polysilicon to define a gate electrode having a plurality of sidewalls, each of which have a recess formed therein.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to semiconductor fabrication technology, and, more particularly, to a method of forming a gate electrode on a semiconductor device and a device incorporating same. 
     2. Description of the Related Art 
     There is a constant drive within the semiconductor industry to increase the operating speed of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for computers and electronic devices that operate at increasingly greater speeds. This demand for increased speed has resulted in a continual reduction in the size of semiconductor devices, e.g., transistors. That is, many components of a typical field effect transistor (FET), e.g., channel length, junction depths, gate dielectric thickness, and the like, are reduced. For example, all other things being equal, the smaller the channel length of the transistor, the faster the transistor will operate. Thus, there is a constant drive to reduce the size, or scale, of the components of a typical transistor to increase the overall speed of the transistor, as well as integrated circuit devices incorporating such transistors. Additionally, reducing the size, or scale, of the components of a typical transistor also increases the density, and number, of the transistors that can be produced on a given amount of wafer real estate, lowering the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors. 
     However, reducing the channel length of a transistor also increases “short-channel” effects, almost by definition, as well as “edge effects” that are relatively unimportant in long channel transistors. Short-channel effects include, among other things, an increased drain-source leakage current when the transistor is supposed to be switched “off.” This leakage is believed to be due to an enlarged depletion region relative to the shorter channel length. One of the edge effects that may influence transistor performance is known as Miller capacitance. The Miller capacitance is an overlap capacitance that arises because the conductive gate electrode almost invariably overlaps with a conductive portion of either the more heavily-doped source/drain regions or the less heavily-doped source/drain extension regions, if present, of a conventional transistor. 
     As shown in  FIG. 1 , for example, a conventional transistor  10  may be formed on a semiconducting substrate  12 , such as doped silicon. The transistor  10  is comprised of a gate electrode  16  formed above a gate oxide  14  that is formed above the surface  13  of the semiconducting substrate  12 . The gate electrode  16  and the gate oxide  14  may be separated from doped source/drain regions  18  of the transistor  10  by dielectric spacers  20 . The dielectric spacers  20  may be formed above doped source/drain extension regions  19 . As shown in  FIG. 1 , shallow trench isolation regions  25  may be provided to isolate the transistor  10  electrically from neighboring semiconductor devices, such as other transistors (not shown). 
     The extension regions  19  are typically provided to reduce the magnitude of the maximum channel electric field found close to the source/drain regions  18  of the transistor  10 , and, thereby, to reduce the associated hot-carrier effects. The lower (or lighter) doping of the extension regions  19 , relative to the doping of source/drain regions  18  of the transistor  10 , one typically lower or lighter by at least a factor of two or three, which reduces the magnitude of the maximum channel electric field found close to the doped source/drain regions  18  of the transistor  10 , but increases the source-to-drain resistances of the extension regions  19 . 
     As shown in  FIG. 1 , typically there are overlap regions where the edges  21  of the gate electrode  16  overlap with the edges  23  of the extension regions  19 . The typical amount of overlap may be about 200 Å, for example. These overlap regions of the drain region and the gate electrode give rise to the Miller capacitance. As the overall dimensions of the transistor  10  are reduced, the Miller capacitance becomes a more dominant factor, particularly affecting the switching speed of the transistor  10 . For example, when the transistor  10  is in an “off” state, there may be some residual charge stored in the overlap regions primarily due to the Miller capacitance. This “Miller charge” must be discharged before the transistor  10  may be switched from the “off” state to an “on” state, slowing down the switching speed. Similarly, the Miller capacitance in the overlap regions must be charged up again with the “Miller charge” after the transistor  10  is switched from the “on” state to the “off” state, further slowing down the switching speed. 
     The present invention is directed to a method and device that solves or at least reduces some or all of the aforementioned problems. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a semiconductor device having a novel gate electrode structure, and a method of making such a device. In one illustrative embodiment, the method comprises forming a gate dielectric layer above a semiconducting substrate and forming a gate electrode layer above the gate dielectric layer. The method further comprises implanting dopant atoms into the gate electrode layer to define a layer of dopant material in the gate electrode layer, and patterning at least the gate electrode layer to define a gate electrode comprised of a plurality of sidewalls that have a recess formed therein. 
     In one illustrative embodiment, the present invention is directed to a device comprising a gate dielectric positioned above a semiconducting substrate, a gate electrode positioned above the gate dielectric, the gate electrode having a plurality of sidewalls having a recess formed therein, and a plurality of source/drain regions formed in the substrate. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which: 
         FIG. 1  is a cross-sectional view of an illustrative prior art transistor; 
         FIG. 2  is a cross-sectional view of a partially formed transistor; 
         FIG. 3  is the device of  FIG. 2  after an implantation process has been performed; 
         FIG. 4  is a cross-sectional view of the device depicted in  FIG. 3  after a patterning operation has been performed; 
         FIG. 5  is a cross-sectional view of the device shown in  FIG. 4  after additional processing operations have been performed; and 
         FIG. 6  is a cross-sectional view of an alternative embodiment to the device depicted in  FIG. 3  after a patterning operation has been performed. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
     The present invention will now be described with reference to  FIGS. 2-5 . Although the various regions and structures of a semiconductor device are depicted in the drawings as having very precise, sharp configurations and profiles, those skilled in the art recognize that, in reality, these regions and structures are not as precise as indicated in the drawings. Additionally, the relative sizes of the various features depicted in the drawings may be exaggerated or reduced as compared to the size of those feature sizes on fabricated devices. Nevertheless, the attached drawings are included to describe and explain illustrative examples of the present invention. 
     In general, the present invention is directed to a method of forming a gate electrode on a semiconductor device and to a device incorporating same. As will be readily apparent to those skilled in the art upon a complete reading of the present application, the present method is applicable to a variety of technologies, e.g., NMOS, PMOS, CMOS, etc., is readily applicable to a variety of devices, including, but not limited to, logic devices, memory devices, etc. 
     As shown in  FIG. 2 , a partially formed transistor  43  is comprised of a gate dielectric layer  40  formed above a surface  41  of a semiconducting substrate  42 , and a gate electrode layer  44  formed above the gate dielectric layer  40 . The various process layers depicted in  FIG. 2  may be formed by a variety of known techniques, e.g., thermal growth, chemical vapor deposition (“CVD”), plasma enhanced chemical vapor deposition (“PECVD”), physical vapor deposition (“PVD”), sputtering, etc. Moreover, the various process layers depicted in  FIG. 2  may be formed from a variety of materials. Thus, the particular materials of construction, as well as the techniques for forming the process layers depicted in  FIG. 2 , should not be considered a limitation of the present invention unless specifically recited in the appended claims. 
     For example, the semiconducting substrate  42  may be comprised of silicon or other semiconducting materials. The gate dielectric layer  40  may be comprised of a variety of materials, such as silicon dioxide, silicon oxynitride, a silicon dioxide/silicon nitride stack, etc. In one illustrative embodiment, the gate dielectric layer  40  is comprised of a thermally grown layer of silicon dioxide having a thickness ranging from approximately 15-30 Å. 
     The gate electrode layer  44  may also be comprised of a variety of materials, and it may be formed by a variety of techniques. For example, the gate electrode layer  44  may be comprised of polycrystalline silicon (polysilicon) or amorphous silicon. In one illustrative embodiment, the gate electrode layer  44  is comprised of a deposited layer of polysilicon having a thickness ranging from approximately 1800-5000 Å. 
     Next, as shown in  FIG. 3 , the partially formed transistor  43  is subjected to an ion implantation process, as indicated by arrows  46 , to form a layer of dopant material  48 . Dopants, such as boron, phosphorous, arsenic, nitrogen, antimony, indium, etc. may be used to form the layer of dopant material  48 . For example, for NMOS technology, the dopant used to form the layer of dopant material  48  may be arsenic or phosphorous. For PMOS devices, boron may be used. 
     The energy level and concentration of dopant atoms will vary depending upon the dopant selected to form the layer of dopant material  48  and the desired depth of the implant. In general, the concentration of dopant atoms will range from approximately 5×10 14 -5×10 15  atoms per square centimeter. In one illustrative embodiment where the dopant is arsenic, the concentration may vary between 9×10 14 -4×10 15  atoms/cm 2 . 
     The depth of the layer of dopant material  48  may be varied as a matter of design choice. In general, the layer of dopant material  48  should not be placed so deep that the implanted dopant material may adversely impact the integrity or ability of the gate dielectric layer  40  to perform its intended functions, or to otherwise negatively impact transistor performance. Depending on the particular dopants selected to form the layer of dopant material  48 , the distribution or spread of the dopant atoms will vary. For example, all other things being equal, arsenic will have a distribution that is greater than that of phosphorous. Thus, the particular energy used during the ion implantation process will vary depending upon the particular application under consideration. In one illustrative example where arsenic is implanted into a gate electrode comprised of polysilicon, the implant process may be performed at an energy level ranging from approximately 20-50 keV. 
     In general, the majority of the layer of dopant material  48  should be positioned slightly above the gate dielectric layer  40 . Note that in the illustrated situation depicted in  FIG. 3 , a region  47  of the gate electrode layer  44  is positioned between the layer of dopant material  48  and the gate dielectric layer  40 . In practice, the precise boundaries of the region  47 , if it exists, will be difficult to define, and it will vary from location to location across the area of the gate electrode layer  44 . This is due in part to the nature of the ion implantation process as well as subsequent heating operations that may be performed on the device, which may tend to cause the implanted dopant materials to move. 
     Nevertheless, the layer of dopant material  48  should be positioned relatively close to the gate dielectric layer  40 . Thus, in one illustrative embodiment of the present invention, the region  47  of the gate electrode layer  44  may have a thickness ranging from approximately 50-500 Å. Of course, as stated above, depending upon the particular application and the particular process flow under consideration, the region  47 , if it exists at all, may become vanishingly thin, and it may not be uniform across the surface of the gate dielectric layer  40 . 
     Next, as shown in  FIG. 4 , the gate electrode layer  44  and the gate dielectric layer  40  are patterned to define a gate stack  50  comprised of a gate electrode  44 A having sides  52  and a gate dielectric layer  40 A. This patterning may be accomplished using known photolithography and etching techniques. For example, the etch process may involve an anisotropic plasma etching process. Note that, although it is depicted in  FIG. 4  that both the gate electrode layer  44  and gate dielectric layer  40  are removed, that is not necessarily required. For example, portions of the gate dielectric layer  40  extending beyond the sides  52  of the gate electrode  44 A may be removed, if at all, in subsequent processing operations. 
     As seen in  FIG. 4 , using the present invention, a recessed region  54  is formed in the sides  52  of the gate electrode  44 A. This occurs because the etch rate of, for example, polysilicon, is a function of the dopant atoms present in the layer of polysilicon. Thus, by forming the layer of dopant material  48 , the portion of the gate electrode  44 A having the higher concentration of dopant atoms will etch at a faster rate than other portions of the gate electrode  44 . This results in the gate electrode  44 A having the recess  54  formed in the sides  52  of the gate electrode  44 A. These recesses  54  may extend for the entire width of the gate electrode  44 A, i.e., extend into the drawing page, that is in the active region of the device. 
     The precise size and configuration of the recess  54  will vary depending on a variety of factors, such as the type of dopant atoms implanted, the distribution of the dopant atoms, etc. In general, as an approximation, the recesses  54  may have a shape that roughly corresponds to the concentration profile of the dopant atoms in the layer of dopant material  48 , although it may not appear as smooth and precise as the recess  54  depicted in FIG.  5 . The wider the distribution profile of the dopant atoms, the wider (in the vertical direction) will be the recess  54 . Similarly, the narrower the distribution profile, the narrower (in the vertical direction) will be the recess  54 . Additionally, the peak depth of the recesses  54 , as indicated by region  55 , may vary between approximately 100-300 Å, and the width of the recesses  54 , as defined between points  57  and  59 , may vary between approximately 500-1000 Å. 
     Next, additional processing operations are performed to complete the formation of the transistor  43 . For example, as shown in  FIG. 5 , sidewall spacers  56  are formed adjacent the gate stack  50  and the source/drain regions  58  are formed in the substrate  42 . 
     The present invention may be used to produce a structure that will assist in reducing the Miller capacitance associated with the device and thereby improve device performance. That is, through use of the present invention, the amount and extent of the overlap between the gate electrode  44 A and the source/drain region  58  may be reduced, thereby reducing the Miller capacitance, which may improve device performance. 
     The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. Furthermore, no limitations are intended to the details of construction or design herein shown, other than as described in the claims below. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the claims below.