Abstract:
Semiconductor devices and methods of fabrication. A device includes a semiconductor substrate, a gate electrode insulated from the semiconductor substrate by a gate insulation layer, LDD-type source/drain regions formed at both sides of the gate electrode, an interlayer insulation layer formed over the gate electrode and the substrate, and a shared contact piercing the interlayer insulation layer and contacting the gate electrode and one of the LDD-type source/drain regions including at least a part of a lightly doped drain region. Multiple-layer spacers are formed on both sides of the gate structure and used as a mask in forming the LDD-type regions. At least one layer of the spacer is removed in the contact opening to widen the opening to receive a contact plug.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
   This application is a Divisional of U.S. patent Ser. No. 10/112,413, filed on Mar. 29, 2002, now U.S. Pat. No. 6,927,461 which claims priority from Korean Patent Application No. 2001-35703, filed on Jun. 22, 2001, the contents of which are herein incorporated by reference in their entirety. 

   FIELD OF THE INVENTION 
   The present invention relates to a semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a semiconductor device having a shared contact that may decrease contact resistance and to a method of fabricating the same. 
   BACKGROUND OF THE INVENTION 
   As semiconductor devices become highly integrated, a MOS transistor begins to have a source/drain region of shallow junction. In order to increase reliability of the MOS transistor, a technique of forming LDD-type source/drain regions has been widely used. A gate spacer is formed at the sidewall of a gate electrode to form a LDD-type source/drain region. A silicon nitride layer having etch selectivity with a silicon oxide layer composing an interlayer insulation layer may be used to form a self-aligned contact suitable for a highly integrated semiconductor device as a conventional material layer to form a gate spacer. 
   To organize a circuit of a SRAM or non-memory semiconductor device, a gate electrode of one transistor may be directly connected with a source/drain region of another transistor. If the gate electrode and the source/drain region are closely arranged, a shared contact is formed for electrical connection instead of separate contacts. 
     FIG. 1  is an example of a layout of the SRAM cell using shared contacts. 
     FIGS. 2 through 4  illustrate cross-sectional views displaying a method of forming an LDD-type semiconductor device using a conventional shared contact. 
   Referring to  FIG. 2 , an isolation layer  2  is formed in a desired region of a semiconductor substrate  1  to isolate an active region. A gate insulation layer  3  is formed on the active region, and then a polysilicon layer  5  and a metal silicide layer  7  are sequentially stacked over the entire surface of the semiconductor substrate, including the gate insulation layer  3 , thereby forming a gate electrode layer. The gate electrode layer is then patterned to form a couple of gate patterns  8  crossing a top part of a desired region of the gate insulation layer  3 . Because the gate insulation layer  3  may be over-etched, the active region of both sides of the gate pattern  8  may be exposed. 
   Impurity ions are implanted in the active region in a dose amount of 1×10 12  to 1×10 13  atoms/cm 2  by using the gate pattern  8  as an ion-implantation mask. A low-concentration source/drain region  9  is formed in the active region located on both sides of each gate pattern  8 . Next, a gate spacer  11  of silicon nitride is formed on the sidewall of the gate pattern  8 . Impurity ions are implanted in the low-concentration source/drain region  9  in a dose amount of 1×10 15  to 5×10 15  atoms/cm 2  using the gate spacer  11  and the gate patterns  8  as ion-implantation masks. Thus, a high-concentration source/drain region  13  is formed, which has a higher impurity concentration than the low-concentration source/drain region  9 . The low-concentration source/drain region  9  and the high-concentration source/drain region  13  compose LDD-type source/drain regions  15 . 
   Referring to  FIG. 3 , oxide layer etching is performed with respect to the resultant structure, thereby exposing a silicon surface where the LDD-type source/drain regions  15  are formed. An etch-stopping layer  17  is formed over the entire surface. The etch-stopping layer  17  is made of a material layer having an etch selectivity with respect to silicon oxide. An interlayer insulation layer  19  is formed over the entire surface of the semiconductor substrate, including the etch-stopping layer  17 . 
   Referring to  FIG. 4 , the interlayer insulation layer  19  and the etch-stopping layer  17  are continuously patterned to form a contact hole  23  which exposes the metal silicide layer  7  in the gate pattern  8  and the neighboring source/drain region  13 . 
   Contact hole  23  will be filled with a metal to form a contact plug. It is therefore desired to maximize that portion of the surface area of the LDD-type source/drain regions  15  exposed by the contact hole. But the presence of gate spacer  11  limits the exposable area. A further problem arises from possible misalignment during a photo-lithography process. The contact hole  23  can be offset, which further reduces that portion of the surface area of the LDD-type source/drain regions  15  exposed by the contact hole  23 . In the worst case scenario, the source/drain region is not revealed at the bottom of the contact hole  23 . 
   When contact area is reduced, the contact resistance increases, interfering with normal operation of a device. This may result in degradation of the performance of the semiconductor device, or it may induce operation failure. 
   Additionally, as the width of the exposed surface of the source/drain region becomes smaller than the height of the gate pattern in the contact hole, the aspect ratio increases. This increases the difficulty of filling the contact hole with a barrier metal layer and a plug metal layer. This may result in formation of a void at the contact location on the source/drain region, thereby causing an operation failure and degrading reliability in a semiconductor device. 
   Conversely, using a conventional technique in which spacer thickness is reduced to increase contact exposure to the source/drain region, results in restricting the length of the lightly doped drain region which may result in degradation of transistor performance. 
   SUMMARY OF THE INVENTION 
   The present invention provides a semiconductor device which includes a semiconductor substrate, a gate electrode insulated from the semiconductor substrate by a gate insulation layer, LDD-type source/drain regions formed at both sides of the gate electrode, and an interlayer insulation layer formed over the gate electrode and the substrate. A shared contact pierces the interlayer insulation layer and contacts the gate electrode and one of the LDD-type source/drain regions. The contact between the shared contact and the LDD-type source/drain regions includes at least a portion of a lightly doped drain region. 
   The present invention additionally provides a method of forming a semiconductor device. A gate pattern is formed on a substrate. A low-concentration source/drain region is formed at a location in the substrate located at both sides of the gate pattern through ion-implantation. A spacer is formed, having an etch selectivity with respect to the gate pattern at the sidewall of the gate pattern. Ion-implantation is performed by using the gate pattern and the spacer as ion-implantation masks to form a high-concentration impurity ion-implantation region. An interlayer insulation layer is formed over the gate pattern at whose sidewall the spacer is formed. A shared contact hole is formed exposing parts of the top surface of the gate pattern and the LDD-type source/drain regions of the substrate adjacent to the gate pattern, and simultaneously etching and removing a certain width of the spacer together with the interlayer insulation layer at the shared contact region. 
   An advantage of the present invention is that it provides a semiconductor device that secures a sufficient contact region, and simultaneously forms a shared contact at a gate electrode. 
   Another advantage of present invention is that a bulky spacer is removed. This increases the process margin by having the spacer between the shared contact and the lightly doped drain region removed. 
   Another advantage of the present invention is that instances in which a source/drain region of a shared contact is not opened or narrowly opened by a spacer are restricted. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a layout of an SRAM cell in which a gate electrode is electrically connected with a source/drain region through a shared contact and in which the present invention may be implemented. 
       FIGS. 2 through 4  illustrate successive cross-sectional views explaining a method of forming an LDD-type semiconductor device using a conventional shared contact in the prior art. 
       FIGS. 5 through 8  are cross-sectional views showing successive steps of making a LDD-type semiconductor device using a shared contact according to a method of the present invention. 
       FIGS. 9 through 11  are cross-sectional views showing successive steps of making a LDD-type semiconductor device using a shared contact according to another method of the present invention. 
       FIG. 12  is a cross-sectional view displaying another embodiment of a LDD-type semiconductor device using a shared contact of the present invention. 
   

   DETAILED DESCRIPTION 
   As has been mentioned, the invention provides a semiconductor device with shared contacts, as seen in  FIG. 1 . The invention also provides methods of manufacturing the same. The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. 
   EMBODIMENT 1 
   Referring to  FIG. 5 , a starting point is shown for manufacturing a device according to the invention. A gate pattern  108  spaced from a semiconductor substrate  10  by a gate insulation layer  103  is formed. In forming the gate pattern  108 , the gate insulation layer  103  of the substrate  10  may be removed at the sides of the gate pattern. The gate pattern  108  is composed of a dual layer formed by stacking a polysilicon layer  105  and a metal silicide layer  107 . Through annealing to cure etch damage, a thin oxide layer (not illustrated) may be formed at the substrate  10  and the surface of the gate pattern  108 . Using the gate pattern as an etch mask, impurity ions are implanted yielding a low-concentration source/drain region  109 ′. A sample implantation might be performed, for example, in a dose amount of 1×10 12  to 1×10 14  atoms/cm 2  by applying low energy of 10 KeV. As the concentration of the implanted impurity ions decreases, the depth of the source/drain region in the substrate decreases. 
   Referring to  FIG. 6 , a first spacer layer  106  of silicon nitride is formed over the substrate  10 , covering the gate pattern  108  and the low-concentration source/drain region  109 ′. Next, a second spacer layer of silicon oxide is formed over the first spacer layer  106  and anisotropically etched to form a second spacer  111 . 
   Referring to  FIGS. 6 and 7 , areas of the first spacer layer  106 , exposed at the top surface of the gate pattern  108  and on the substrate  10  where the second spacer  111  is formed, are removed by an isotropic etching process using phosphoric acid, leaving a first spacer  106 ′ only between the second spacer  111  and the sidewall of the gate pattern  108 . Through the isotropic etching, the first spacer layer  106  between the second spacer  111  and the substrate is mostly removed. By using the gate pattern  108  and entire spacer  112 , composed of the first and second spacers  106  and  111 , as ion-implantation masks, impurity-ions are implanted. A sample implant might be performed, for example, in a high dose amount of 1×10 15  to 5×10 15  atoms/cm 2  and by applying energy of 40 KeV. This creates high-concentration source/drain regions  113  on the both sides of the gate pattern  108 , thereby forming LDD-type source/drain regions  115 . Regions  113  are spaced laterally from the gate pattern  108  a distance determined by the combined lateral thickness of spacers  112 ; i.e., a distance greater than the lateral thickness of spacer  106  alone. 
   Referring to  FIGS. 7 and 8 , an interlayer insulation layer  119  of silicon oxide, such as an undoped silicate glass (USG), is stacked over the gate pattern  108  where the entire spacers  112  are formed. Additionally, the interlayer insulation layer  119  is patterned to form a shared contact hole  139  exposing the top surface of the gate pattern  108  and a part of the LDD-type source/drain regions  115  in the substrate  10  adjacent the gate pattern. The interlayer insulation layer  119  and the second spacer  111  are formed of silicon oxide, so that the second spacer  111  is removed and the LDD-type source/drain regions  115  are exposed on the side of the first spacer  106  when the contact hole  139  of the shared contact is formed. Therefore, the contact surface at which the contact plug and the source/drain region are contacted with each other is widened in comparison to techniques in the prior art. A conductive layer (not shown) fills the contact hole to form a contact plug  150 . It will be observed that spacer  111  is not removed in the prior art.  FIG. 8  displays a partial cross-section of the semiconductor device of the present invention. The remaining spacer  106 ′ has a lateral thickness (width) less than the lateral spacing of adjoining highly doped drain region  113  and the width of lightly doped drain region  109 . 
   EMBODIMENT 2 
   Referring to  FIG. 9 , an etch-stopping layer  207  of silicon nitride is formed on the substrate  10  including over the gate pattern  108  and the low-concentration source/drain region  109 . A spacer layer of silicon oxide is deposited over layer  207  and anisotropically etched to form a spacer  211 . Impurity ions are implanted by using the spacer  211  and the gate pattern  108  as ion-implantation masks. A sample implant might be performed, for example, in a high dose amount of 1×10 15  to 5×10 15  atoms/cm2, by applying energy of approximately 60 KeV. This creates LDD-type source/drain regions  115  including a high-concentration source/drain region  113 , on both sides of the gate pattern  108 . Regions  113  are spaced laterally from the gate pattern  108  a distance determined by the combined lateral thickness of etch-stopping layer  207  and spacer  211 ; i.e., a distance greater than the lateral thickness of etch-stopping layer  207  alone. 
   Referring to  FIGS. 9 and 10 , an interlayer insulation layer  119  of silicon oxide is deposited over the gate pattern  108  and the spacer  211 . The interlayer insulation layer  119  is patterned and etched to form a shared contact hole  239  exposing parts of the gate pattern  108  and the LDD-type source/drain regions  115  of the neighboring substrate. Because the spacer  211  is formed of silicon oxide like the interlayer insulation layer  119 , the spacer  211  is removed when the contact hole  239  is formed at the contact region. Even when a part of the contact region extends over the trench-type isolation layer  2  due to misalignment of the contact hole  239 , the isolation layer  2  is not damaged since the etch-stopping layer  207  covers on the trench-type isolation layer  2 . 
   Referring to  FIGS. 10 and 11 , after the contact hole  239  is formed at the interlayer insulation layer  119 , the etch-stopping layer  207  exposed in the contact region is removed by wet-etching. This exposes the top and side surfaces of the gate pattern  108  and containing the neighboring substrate the LDD-type source/drain regions  115 . A barrier layer  241  of titanium/titanium nitride is shallowly deposited over the surfaces of contact hole  239 , and the contact hole is filled with CVD tungsten. A planarization-etching process such as CMP is performed to leave a contact plug  243  in the contact hole. The contact plug  243  largely contacts the gate pattern  108  and the adjoining LDD-type source/drain region  115  of the substrate  10 , reducing the contact resistance in comparison to existing techniques wherein the spacer remains.  FIG. 11  illustrates a partial cross-section of the semiconductor device according to this embodiment of the present invention. 
   EMBODIMENT 3 
   Referring to  FIG. 12 , an etch-stopping layer  117  of silicon nitride or silicon oxinitride (SiON) is formed. An interlayer insulation layer  119  of silicon oxide is deposited over the etch-stopping layer  117 . The etch-stopping layer  117  is formed thinly at the top of the gate pattern  108  but thickly at the low part between the gate patterns  108  by employing a method such as HDP CVD. The interlayer insulation layer  119  and the etch-stopping layer  117  are patterned to form a shared contact hole  339  exposing part of the top surface of the gate pattern and the neighboring source/drain region. It is preferable to perform an anisotropic etching process which has a common etch selectivity with respect to the interlayer insulation layer  119  and the second spacer  111 , a low etch selectivity with respect to the etch-stopping layer  117 , and a tiny etch selectivity with respect to the metal silicide layer  107  of the top layer of the gate pattern  108 . This removes the etch-stopping layer  117 , the second spacer  111  and the interlayer insulation layer  119  at the contact region. The remnant etch-stopping layer  117  is then isotropically etched to expose the top surface of the gate pattern  108  and the LDD-type source/drain regions  115  at the contact region. During the anisotropic etching process, the first spacer  106  of silicon nitride may be removed according to the characteristic of an etchant. When a conductive layer fills the contact hole  339  to form a contact plug  350 , the contact surface at which the contact plug contacts the LDD-type source/drain regions  115  is widened in comparison to existing techniques wherein the second spacer  111  is not removed. 
   After forming LDD-type source/drain regions, when a shared contact is formed at a part of the gate electrode and a neighboring source/drain region, the spacer is removed for formation of the lightly doped drain region, thereby increasing a process margin. Thus, it is possible to avoid instances where a source/drain region of a shared contact is not opened or is narrowly constricted by a spacer. 
   A person skilled in the art will be able to practice the present invention in view of the description present in this document, which is to be taken as a whole. Numerous details have been set forth in order to provide a more thorough understanding of the invention. In other instances, well-known features have not been described in detail in order not to obscure unnecessarily the invention. In addition, in the attached figures, the thickness of layers and regions may be exaggerated for clarity. Moreover, when it is mentioned that a layer is on another layer or on a substrate, the layer in question may be formed directly on another layer or on the substrate, or a third layer may be interposed there between. 
   While the invention has been disclosed in its preferred form, the specific embodiments as disclosed and illustrated herein are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art in view of the present description that the invention may be modified in numerous ways. The inventor regards the subject matter of the invention to include all combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein. 
   The following claims define certain combinations and subcombinations, which are regarded as novel and non-obvious. Additional claims for other combinations and subcombinations of features, functions, elements and/or properties may be presented in this or a related document.