Patent Publication Number: US-8535999-B2

Title: Stress memorization process improvement for improved technology performance

Description:
FIELD OF THE DISCLOSURE 
     The present disclosure relates to semiconductor substrates having a deformed gate region and a method of fabricating the same. More particularly, the present disclosure relates to n-type metal-oxide-semiconductor (NMOS) and p-type metal-oxide-semiconductor (PMOS) devices having improved device performance. 
     BACKGROUND 
     Ongoing efforts are being made to enhance carrier mobility in semiconductor devices to increase performance and/or reduce power consumption. The forming of stressed silicon channels by deforming the source/drain region is a known practice. Stress, sometimes referred to as strain, can enhance electron and hole mobility. The performance of a metal-oxide-semiconductor (MOS) device can be enhanced through a stressed-surface channel. 
     Typically, it is preferred for NMOS devices to have tensile stresses in their channel regions. It is also possible for NMOS devices to benefit from compressive stress in out of plane direction perpendicular to the channel region. PMOS devices benefit from either having compressive stresses in their channel regions and/or from tensile stress in out of plane direction perpendicular to the channel region. Stresses in channel regions can be applied by forming stressed source/drain regions, stressed gate electrodes, stressed contact etch stop layers, etc. One of the methods for applying a beneficial stress to a gate electrode of an NMOS device is to form a stress memorization layer, wherein a typical formation process includes blanket forming a stress memorization layer having an inherent stress, performing an annealing, and then removing the stress memorization layer. The beneficial stress, which is a tensile stress in the channel region and/or a compressive stress in an out-of-plane direction perpendicular to the channel region, is thus “memorized” by the source/drain regions and is imparted onto the channel region of the NMOS device or PMOS device. 
     SUMMARY OF THE DISCLOSURE 
     Described herein is a method of fabricating a semiconductor structure which comprises providing a semiconductor substrate; forming a gate structure on the semiconductor substrate; forming a source-drain implant region adjacent to the gate structure; forming a stress-transmitting dielectric layer on the source-drain implant region and the gate structure; removing the stress-transmitting dielectric layer; and performing an annealing step after the removing of the stress-transmitting dielectric layer. 
     Further described is a semiconductor structure, which comprises a semiconductor substrate; a gate structure on the semiconductor substrate; and a source-drain implant region adjacent to the gate structure; wherein the gate structure is deformed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other objects, aspects and advantages will be better understood from the following detailed description of the best and various embodiments with reference to the drawings, in which: 
         FIG. 1  shows a NMOS device including a substrate  100 , a doped source region  105 , a doped drain region  106 , a source/drain capping oxide layer  110 , a polycrystalline gate material  120 , a gate spacer  130 , an extension spacer  140 , and a source/drain spacer  150 . 
         FIG. 2  shows a stress memorization technique (SMT) layer  210  being applied onto the NMOS device. 
         FIG. 3  shows the NMOS device after the removal of the SMT layer and prior to the activation anneal of the source/drain region. 
     
    
    
     DESCRIPTION OF THE BEST AND VARIOUS EMBODIMENTS 
     Turning to the drawings,  FIG. 1  shows an early processing step in the formation of a NMOS device of a substrate  100  having an oxide-containing capping layer  110 . The NMOS device is typically formed by a lithographic process. Also typically, the substrate of  FIG. 1   a  is silicon. The disclosure herein is exemplified for a NMOS device, but the method is also applicable to PMOS devices. 
     In another aspect of the disclosure, stress memorization technique is applied to field effect transistors (FET&#39;s), including n-channel FET (nFET) and p-channel FET (pFET). 
     Substrate  100  preferably comprises bulk silicon, although other commonly used structures and materials such as silicon on insulator (SOD can be used. Substrate  100  is preferably lightly doped. 
       FIG. 2  depicts the formation of the SMT layer  210  onto the NMOS device. The SMT layer causes beneficial stress to the gate material  120 . In particular, gate material  120  is plastically deformed and exerts a beneficial stress onto the underlying channel region located between source/drain regions  105  and  106 . The deformation of the channel region caused by the beneficial stress is illustrated by a change in shape of source/drain regions  105  and  106  to the shapes  105 ′ and  106 ′ depicted in  FIG. 2 . Gate material  120  retains its deformation, in whole or in part, after removal of the SMT layer and the subsequent annealing step. 
       FIG. 3  depicts the NMOS device after the removal of the SMT layer. The gate material maintains some of the deformation caused by the SMT layer, which acts upon the channel region. The NMOS device is then subjected to an annealing treatment to electrically activate the dopants in the source/drain regions. 
     With particularity, the stress-transmitting dielectric layer is a compressive stress-transmitting dielectric layer. Also with particularity, the stress-transmitting dielectric layer is a tensile stress-transmitting dielectric layer. 
     In a particular embodiment, stress is transferred by transferring a uniaxial compressive or tensile stress from the stress-transmitting dielectric layer to the gate structure. The uniaxial compressive or tensile stress in the gate structure is, with particularity, of from about 300 MPa to about 3 GPa. 
     In a particular embodiment, the annealing step is effected at a temperature of from about 950° C. to about 1,200° C. 
     With particularity, the stress-transmitting dielectric layer is a refractory metal nitride. Further, the refractory metal nitride is selected from the group consisting of TaN, TiN. WN, MoN, NbN, ReN, and a combination thereof. In a particular embodiment, the refractory metal nitride is TiN. 
     In a particular embodiment, a carrier concentration is substantially unchanged, before and after the annealing step. Further, the carrier is selected, with particularity, from the group consisting of a hole h +  and an electron e − . 
     In another particular embodiment, a capping layer is applied onto the source-drain implant region prior to the forming of the stress-transmitting dielectric layer. 
     With particularity, the stress-transmitting dielectric layer is a silicon oxide. 
     The stress-transmitting dielectric layer exerts, with particularity, a pressure of from about 300 MPa to about 3 GPa. 
     In another particular embodiment, the deformed gate structure is compressed in a direction perpendicular to the semiconductor substrate. In yet another particular embodiment, the deformed gate structure is elongated in a direction perpendicular to the semiconductor substrate. 
     With particularity, a shallow trench isolation is provided between the source-drain implant region and the gate structure. 
     In a particular embodiment, the gate structure is deformed by a compressive stress of from about 5 GPa to about 20 GPa. With particularity, the gate structure is deformed by a compressive stress of from about 300 MPa to about 3 GPa. 
     In a particular embodiment, a n-type metal-oxide semiconductor (NMOS) or a p-type metal-oxide semiconductor (PMOS) comprises a deformed gate structure. 
     It has been observed that device performance may be impaired by boron penetration into gate dielectrics, which may result in high leakage currents and degradation of the performance of the respective MOS devices. Boron penetration also affects the gate oxide integrity. The adverse effects are amplified in the related art by the presence of the SMT layer in the annealing step into which boron may diffuse. It is a particular advantage of the instant disclosure that boron diffusion is minimized because the SMT layer is removed prior to the annealing step. 
     The intermediate stages of manufacturing preferred embodiments of the present disclosure, which reduces the above-discussed adverse effects, are illustrated. Throughout the various views and illustrative embodiments of the present invention, like reference numbers are used to designate like elements. 
     As depicted in  FIG. 1 , a gate region  120  is provided on a device. Gate region  120  may include polysilicon, metals, metal silicides, metal nitrides, and other commonly used materials. With particularity, gate region  120  includes polysilicon. 
       FIG. 1  illustrates the doping with p-type impurities into drain region  106 . p-type impurities, such as boron, indium, and the like are introduced into region  106 . Typical dosage is between about 1E15/cm 2  and about 5E15/cm 2 . n-type pre-doping is performed to source region  105  in separate steps. One skilled in the art will realize the corresponding process steps. 
     Referring to  FIG. 1 , gate spacer  130  is formed by forming one or more spacer layers (not shown), and then etching the spacer layer(s). In the preferred embodiment, the spacer layer includes a nitride layer on a liner oxide layer. The preferred spacer deposition methods include PECVD, LPCVD, sub-atmospheric chemical vapor deposition (SACVD), and the like. 
     Referring to  FIG. 2 , a stress memorization layer  210  is blanket formed. In one embodiment, stress memorization layer  210  has a composite structure including, for example, an upper layer on a lower layer (not shown). In an exemplary embodiment, the upper layer comprises silicon nitride, while the lower layer comprises an oxide. In the embodiment shown in  FIG. 2 , stress memorization layer  210  includes a single layer, which may be formed of nitrides, oxynitrides, tetra ethyl ortho silicate (TEOS), and other materials with internal stresses. The single layered stress memorization layer  210  particularly has a tensile stress. With particularity, stress memorization layer  210  comprises a nitride. 
     Also with particularity, the method for forming stress memorization layer  210  includes low-pressure chemical vapor deposition (LPCVD). However, other methods such as plasma enhanced chemical vapor deposition may also be used. The formation temperature is preferably lower than about 800° C. 
     In  FIG. 3 , stress memorization layer  210  is removed. Subsequently, the device is annealed. For example, an RTA is performed with a temperature of between about 900° C. and about 1090° C. Other common annealing methods, such as flashing annealing, furnace annealing, laser annealing, and the like, can also be used. During and subsequent to the annealing, transferred stress is memorized by the gate region and continued to be applied to the channel regions. 
     According to the instant disclosure, the SMT layer is removed prior to the annealing step. Nonetheless, it is also possible to perform the annealing step with the stress memorization layer in place. In the latter case, the stress memorization layer is then removed after the annealing. However, removing the SMT layer prior to annealing helps retaining the dopant in the active region of the device, as illustrated in the Table below. 
     The following Table illustrates the improved retention of the dopant in the channel region. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 11B in Si 
                 11 B in SMT 
                 Total 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Example 1 
                 4.24E+13 
                 n/a 
                 4.24E+13 
               
               
                 Comparative example 
                 3.38E+13 
                 1.47E+13 
                 4.85E+13 
               
               
                   
               
            
           
         
       
     
     Example 1 was subjected to an annealing treatment after the removal of the SMT layer. The comparative example was subjected to an annealing treatment without removal of the SMT layer. The dopant concentration, here boron, was measured subsequent to the annealing treatment. The dopant concentration in the channel region ( 11 B in Si) of the comparative example is reduced by comparison to Example 1. Further, the instant disclosure provides for a method in which the dopant concentration of the entire active region, i.e., also in the source/drain region, is maintained. 
     The embodiments described hereinabove are further intended to explain best modes known of practicing it and to enable others skilled in the art to utilize the disclosure in such, or other, embodiments and with the various modifications required by the particular applications or uses. Accordingly, the description is not intended to limit it to the form disclosed herein. Also, it is intended that the appended claims be construed to include alternative embodiments. 
     The foregoing description of the disclosure illustrates and describes the present disclosure. Additionally, the disclosure shows and describes only the preferred embodiments but, as mentioned above, it is to be understood that the disclosure is capable of use in various other combinations, modifications, and environments and is capable of changes or modifications within the scope of the concept as expressed herein, commensurate with the above teachings and/or the skill or knowledge of the relevant art. 
     The term “comprising” (and its grammatical variations) as used herein is used in the inclusive sense of “having” or “including” and not in the exclusive sense of “consisting only of.” The terms “a” and “the” as used herein are understood to encompass the plural as well as the singular. 
     All publications, patents and patent applications cited in this specification are herein incorporated by reference, and for any and all purpose, as if each individual publication, patent or patent application were specifically and individually indicated to be incorporated by reference. In the case of inconsistencies, the present disclosure will prevail.