Abstract:
The channels of first and second CMOS transistors can be selectively stressed. A gate structure of the first transistor includes a stressor that produces stress in the channel of the first transistor. A gate structure of the second transistor is disposed in contact with a layer of material that produces stress in the channel of the second transistor.

Description:
FIELD OF THE INVENTION 
   The invention relates generally to semiconductor integrated circuits and, more particularly, to strained channel transistors in semiconductor integrated circuits. 
   BACKGROUND OF THE INVENTION 
   It is well known in the semiconductor art that the performance of MOS transistors can be enhanced by creating a suitable strain (also referred to herein as stress) in the channel region, thereby producing a so-called strained channel transistor. For example, the performance of an n-channel transistor can be enhanced by creating a tensile strain in the channel region of the transistor, and the performance of a p-channel transistor can be enhanced by creating a compressive strain in the channel region of the transistor. 
   Some conventional strained channel transistors use a high-stress capping layer covering the transistors to create the desired stress. Other conventional strained channel transistors use silicide stressors on the gate structure to create the desired stress. The use of silicide stressors on the gate structure is described, for example, in U.S. Pat. No. 6,890,808, which is incorporated herein by reference. 
   In semiconductor integrated circuits that use complementary MOS (CMOS) transistor pairs, it is desirable to provide compressive strain in the channel region of the p-channel transistor, and tensile strain in the channel region of the n-channel transistor, thereby enhancing the performance of both types of transistors. However, with conventional approaches, it is relatively difficult to produce a CMOS transistor pair wherein the channel region of the p-channel transistor is subject to compressive strain, and the channel region of the n-channel transistor is subject to tensile strain. 
   It is therefore desirable to provide improved capabilities for producing semiconductor integrated circuits wherein the transistor channels are stressed in tension or compression as desired. 
   SUMMARY OF THE INVENTION 
   According to exemplary embodiments of the invention, the channels of first and second transistors can be selectively stressed. A gate structure of the first transistor includes a stressor that produces stress in the channel of the first transistor, and a gate structure of the second transistor is disposed in contact with a layer of material that produces stress in the channel of the second transistor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which: 
       FIG. 1  diagrammatically illustrates a semiconductor integrated circuit apparatus according to exemplary embodiments of the invention. 
       FIG. 2  diagrammatically illustrates a gate electrode deposition operation that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIGS. 3 and 4  diagrammatically illustrate gate implantation operations that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIG. 5  diagrammatically illustrates a gate etch operation that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIG. 6  diagrammatically illustrates hard mask deposition operation that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIG. 7  diagrammatically illustrates the structure produced by patterning and gate formation operations that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIG. 8  diagrammatically illustrates a spacer formation operation that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
       FIG. 9  diagrammatically illustrates the structure that remains after removing the spacers of  FIG. 8  according to exemplary embodiments of the invention. 
       FIG. 10  diagrammatically illustrates a silicide formation operation that can be used in the production of the apparatus of  FIG. 1  according to exemplary embodiments of the invention. 
   

   DETAILED DESCRIPTION 
   Exemplary embodiments of the invention can optimize the performance of n-channel and p-channel transistors by engineering the nature and magnitude of the strain in the channel regions of the transistors. As mentioned above, it is desirable to induce a longitudinal (i.e., in the source-to-drain direction) tensile strain in the channel of an n-channel transistor. It is also desirable to induce a longitudinal compressive strain in the channel of a p-channel transistor. According to some embodiments of the invention, poly-silicide on the gate electrode induces longitudinal compressive stress in the channel of a p-channel transistor, and a tensile capping layer induces longitudinal tensile stress in the channel of an n-channel transistor. An example of this is shown in  FIG. 1 . 
   In the structure of  FIG. 1 , an n-channel transistor  12  and a p-channel transistor  14  respectively include an p-type well  13  and a n-type well  15 . The wells  13  and  15  are formed in a semiconductor substrate  11 , and are isolated from one another by isolation structures STI (shallow trench isolation). The gate structure  18  of transistor  14  includes a silicide disposed on the gate electrode (P-gate) of transistor  14 . The gate structure  16  of transistor  12  has a construction similar to that of the gate structure  18 , but the gate electrode (N-gate) of gate structure  16  extends to a greater height above the substrate  11  than does the gate electrode (P-gate). 
   In particular, the gate electrode (N-gate) has a height of “a”, and the gate electrode P-gate has a height of “b”, where b&lt;a. In some embodiments, the height “a” of the N-gate electrode is at least approximately 200 angstroms greater than the height “b” of the P-gate electrode. This difference in height can be achieved by over-etching the P-gate electrode. As described, for example, in aforementioned U.S. Pat. No. 6,890,808, a silicide formed on an over-etched gate electrode (such as the electrode P-gate in  FIG. 1 ) acts as a stressor, and produces a longitudinal compressive stress in the channel (such as p-type channel  15  in  FIG. 1 ) of that transistor. 
   Also in  FIG. 1 , a capping layer  19  (a dielectric film in some embodiments) is disposed in generally overlying, surrounding and contacting relationship with respect to the gate structures  16  and  18 . It is known in the art that a capping layer such as layer  19  can be used to induce a desired stress (tensile or compressive) in an underlying transistor channel. In some embodiments, the capping layer  19  of  FIG. 1  induces a longitudinal tensile stress in the p-type well  13 . Accordingly, by virtue of the combination of the capping layer  19  and the stressor  17  (e.g., the illustrated silicide) on the over-etched gate electrode P-gate, exemplary embodiments of the invention can produce longitudinal compressive stress in the n-type well  15  and longitudinal tensile stress in the p-type well  13 . 
     FIGS. 2-10  diagrammatically illustrate various operations that can be performed in the process of producing the structure of  FIG. 1  according to exemplary embodiments of the invention. Initially, n-type doped and p-type doped wells are formed (not explicitly shown) in semiconductor substrate  11  as active regions for the n-channel and p-channel transistors  12  and  14 , respectively. This is followed by gate dielectric formation, as illustrated generally in  FIG. 2 . In various embodiments, the gate dielectric may be formed by thermal oxidation, thermal oxidation followed by nitridation, chemical vapor deposition, sputtering, or other techniques known and used in the art for forming transistor gate dielectrics. In various embodiments, the gate dielectric includes a conventional material such as silicon dioxide or silicon oxynitride, with thicknesses ranging from approximately 8 angstroms (A) to approximately 100 angstroms. In some such embodiments, the gate oxide thickness is in a range from approximately 8 angstroms to approximately 10 angstroms. In various embodiments, the gate dielectric includes a high permittivity (high-k) material, with equivalent oxide thicknesses ranging from approximately 8 angstroms to approximately 100 angstroms. In various embodiments, the high-k material includes aluminum oxide Al 2 O 3 , hafnium oxide HfO 2 , zirconium oxide ZrO 2 , hafnium oxynitride HfON, hafnium silicate HfSiO 4 , zirconium silicate ZrSiO 4 , and lanthanum oxide La 2 O 3 . 
   After the gate dielectric has been formed, the gate electrode material  21  is deposited as shown in  FIG. 2 . The gate electrode material  21  is electrically isolated from the semiconductor substrate  11  by the gate dielectric. In various embodiments, the gate electrode material includes polycrystalline-silicon (poly-Si), poly-crystalline silicon-germanium (poly-SiGe), a refractory metal such as molybdenum and tungsten, compounds such as titanium nitride, and other conducting materials. In some embodiments, the gate electrode material is poly-Si and the gate dielectric is silicon oxynitride. In some embodiments, implants known as workfunction implants are introduced in the gate electrode material to alter the workfunction of the electrode. 
   As shown in  FIG. 3 , a gate mask  31  is deposited over the portion  21 A of the electrode material  21  associated with the p-channel transistor  14 . Thereafter, n-type gate electrode implantation is performed as shown generally at  33  in  FIG. 3 . Thereafter, as can be seen from  FIG. 4 , the gate mask  31  is removed, and a gate mask  41  is deposited over the portion  21 B of the gate electrode material  21  associated with the n-channel transistor  12 . Then, p-type gate electrode implantation (using e.g., B, Ga or In) is performed as shown generally at  43 . 
   After the p-type gate implant operation, the portion  21 A of gate electrode material  21  is etched back by using reactive ion etching (RIE), as shown in  FIG. 5 . The range of thickness of the p-type electrode is between 200 A and 1200 A and the range of the ratio between the thickness of the PMOS electrode and the NMOS electrode is from 1/5 to 4/5. The preferred thickness of p-type electrode is 50 nm, and the ratio between the thickness of the PMOS gate electrode and NMOS electrode is 1/2. After etching of the portion  21 A of the gate electrode material, a mask  51  is deposited on the etched portion  21 A, as shown in  FIG. 6 . Patterning and etching are then applied in generally conventional fashion to produce the gate electrodes P-gate and N-gate. The resulting structure is shown in  FIG. 7 . The patterning operation (e.g., photoresist patterning) defines the gate electrodes, and the etching operation forms the gate electrodes. In some embodiments, a plasma etch using chlorine and bromine chemistry is used to etch the gate electrode material with a high etch selectivity with respect to the gate dielectric. 
   After the formation of the gate electrodes, the source and drain extension regions and the pocket regions are formed (not explicitly shown). In various embodiments, this is achieved by ion implantation, plasma immersion ion implantation (PIII), and other techniques known and used in the art. Next, dielectric liners and spacer bodies are formed on the sidewalls of the gate electrode by deposition and selective etching of the spacer material to give a cross-section as shown in  FIG. 8 . In some embodiments, the spacer material includes a dielectric material such as silicon nitride or silicon dioxide. The spacer formation operation is followed by implantation of deep source and drain regions (not explicitly shown). 
   After source and drain implantation, the spacer body is removed, as shown in  FIG. 9 . Thereafter, in some embodiments, a silicide process is used to form silicide at various locations as shown in  FIG. 9 . In some embodiments, the conductive material for the silicide process is formed using a self-aligned silicide process, also known as a salicide process. In some embodiments, another metal deposition process is used to form the conductive material for the silicide. The silicide material forms on the source and drain regions  101 , and on the gate electrodes N-gate and P-gate, as shown in  FIG. 10 . The silicide formation on the gate electrodes N-gate and P-gate completes the respective gate structures  16  and  18  of the transistors  12  and  14  (see also  FIG. 1 ). 
   Next, the capping layer  19  of  FIG. 1  is formed over the transistors  12  and  14 . In some embodiments, the capping layer  19  is a high-stress film, for example, silicon nitride or any other suitable high-stress material. In various embodiments, the stress imparted by the capping layer  19  is either compressive or tensile in nature, and has a magnitude ranging from approximately 0.1 to approximately 4 giga-pascals (GPa). In some embodiments, the high-stress film is formed by a chemical vapor deposition (CVD) process, for example, a low-pressure CVD (LPCVD) process or a plasma-enhanced CVD (PECVD) process, as commonly known and used in the art. After formation of the capping layer  19 , contact etch, metallization and passivation (not explicitly shown) are performed to complete the device, as is conventional. 
   Although exemplary embodiments of the invention have been described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.