Patent Publication Number: US-9899517-B2

Title: Dislocation stress memorization technique (DSMT) on epitaxial channel devices

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of U.S. application Ser. No. 14/880,392 filed on Oct. 12, 2015 which is a Divisional of U.S. application Ser. No. 14/252,147 filed on Apr. 14, 2014 (now U.S. Pat. No. 9,419,136 issued on Aug. 16, 2016). The contents of the above-mentioned Applications are hereby incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     Modern day integrated circuits comprise millions or billions of transistors devices. Transistors devices operate as switches that allow charge carriers (e.g., electrons) to flow when turned on, and which prevent charge carriers from flowing when turned off. The performance of a transistor is influenced by a charge carrier mobility of a material from which the transistor is made. Charge carrier mobility is a measure of how quickly charge carriers move though a material in the presence of an electric field. Increased charge carrier mobility can provide for faster transistor switching speeds, at a fixed voltage, or lower voltage for the same switching speed. 
     In recent years, strain engineering has become a widely used method of improving the performance of transistor devices. Strain engineering induces a pressure onto either a channel region and/or onto source and drain regions of a transistor device. The pressure stretches the crystalline lattice of region(s) to increase the distance between atoms beyond their normal inter-atomic distance. By stretching the crystalline lattice, strain engineering increases charge carrier mobility and thereby improves device performance. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIG. 1  illustrates some embodiments of a transistor device having epitaxial source and drain regions comprising dislocation stress memorization (DSM) regions configured to provide stress to an epitaxial channel region. 
         FIG. 2  illustrates some additional embodiments of a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
         FIG. 3  illustrates a flow diagram of some embodiments of a method of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
         FIG. 4  illustrates a flow diagram of some additional embodiments of a method of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
         FIGS. 5-12  illustrate some embodiments of cross-sectional views of a semiconductor substrate showing a method of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     Over the past few decades the semiconductor industry has made continual advances in manufacturing technology, which have allowed for a steady reduction in transistor device size and constant improvement in transistor device performance. However, in recent years, as scaling has begun to reach the physical limitations of materials, scaling has begun to cause a number of problems with transistor devices. For example, as transistor gate lengths continue to decrease, local and global variations of transistor threshold voltages have become worse. For example, during fabrication of an integrated chip, a plurality of separate processing operations are used to form structural features of transistor devices. Such processing operations may introduce dopant impurities into a transistor channel that may cause variations in the threshold voltages of transistor devices and therefore performance degradation. Furthermore, increasing the dose used for pocket implantations, to improve short-channel control of transistor devices, aggravates such threshold voltage variations. 
     Accordingly, the present disclosure relates to a transistor device having epitaxial source and drain regions comprising dislocation stress memorization (DSM) regions configured to provide stress to an epitaxial channel region, to improve transistor device performance (including short channel control of transistor devices), and an associated method of formation. The transistor device comprises an epitaxial stack disposed over a semiconductor substrate, and a gate structure disposed over the epitaxial stack. An epitaxial source region and an epitaxial drain region are disposed within the epitaxial stack and the semiconductor substrate on opposing sides of the gate structure. A channel region extends below the gate structure between the epitaxial source and drain regions. First and second dislocation stress memorization (DSM) regions respectively extend from below the epitaxial source region to a first location within the epitaxial source region and from below the epitaxial drain region to a second location within the epitaxial drain region. The first and second DSM regions comprise material of the epitaxial source and drain regions and the semiconductor substrate and have a stressed lattice configured to generate stress within the channel region, to improve device performance. 
       FIG. 1  illustrates some embodiments of a transistor device  100  having epitaxial source and drain regions comprising dislocation stress memorization (DSM) regions configured to provide stress to an epitaxial channel region. 
     The transistor device  100  comprises a semiconductor substrate  102  (e.g., a silicon substrate). An epitaxial stack  103  having one or more epitaxial layers is disposed over the semiconductor substrate  102 . In some embodiments, the epitaxial stack  103  comprises a carbon doped epitaxial layer  104  disposed over the semiconductor substrate  102  and a lightly-doped epitaxial layer  106  (e.g., an epitaxial layer grown without doping, but having a low doping concentration due to back diffusion of dopants from the semiconductor substrate  102 ) disposed over the carbon doped epitaxial layer  104 . A gate structure  114  is disposed over the lightly-doped epitaxial layer  106 . 
     An epitaxial source region  108   a  and an epitaxial drain region  108   b  are disposed within the epitaxial stack  103  and semiconductor substrate  102  on opposing sides of the gate structure  114 . The epitaxial source and drain regions,  108   a  and  108   b , may comprise a first doping type (e.g., n-type doping for an NMOS transistor) different than a second doping type of the epitaxial layers (p-type). A channel region  109  extends between the epitaxial source region  108   a  and the epitaxial drain region  108   b  within the epitaxial stack  103  of the transistor device  100 . In some embodiments, the epitaxial source and drain regions,  108   a  and  108   b , may comprise recesses, having a diamond-shape or V-shape, which have been filled with a stress-inducing material. In some embodiments, the stress inducing material may comprise silicon phosphate (SiP) (e.g., for n-channel MOSFET channel mobility enhancement). In other embodiments, the strain inducing material may comprise other materials such as silicon germanium (SiGe), silicon carbide (SiC), etc. 
     A first dislocation stress memorization (DSM) region  110   a  and a second DSM region  110   b  are disposed on opposing sides of the gate structure  114 . The first and second DSM regions,  110   a  and  110   b , comprise a re-crystallized amorphous material. The re-crystallized amorphous material of the first and second DSM regions,  110   a  and  110   b , comprises stacking defects,  111   a  and  111   b , along a (111) plane. The stacking defects,  111   a  and  111   b , which can be detected by electron microscopy (e.g., TEM), distort the bond length of the lattice within the first and second DSM regions,  110   a  and  110   b . For example, the stacking defects,  111   a  and  111   b , may cause the first and second DSM regions,  110   a  and  110   b , to have a stressed lattice with a smaller distance between atoms than normal. 
     The stressed lattices of the first and second DSM regions,  110   a  and  110   b , are configured to induce a stress on the channel region  109 , which increases charge carrier mobility and improves short channel effects of the transistor device  100 . The first and second DSM regions,  110   a  and  110   b , are also configured to stress a portion of the epitaxial source and drain regions,  108   a  and  108   b , and a portion of the underlying semiconductor substrate  102  (i.e., the first and second DSM regions,  110   a  and  110   b , comprise a semiconductor substrate material having a strained (i.e., re-crystallized) lattice and a source/drain epitaxial material having a strained lattice). In some embodiments, the stressed portion of the semiconductor substrate  102 , underlying the source and drain regions,  108  and  108   b , may comprise a stress inducing dopant, such as germanium, for example. In some embodiments, the first DSM region  110   a  may extend from a location below the epitaxial source region  108   a  to a recessed source contact  112   a  located along a top surface of the epitaxial source region  108   a . Similarly, the second DSM region  110   b  may extend from a location below the epitaxial drain region  108   b  to a recessed drain contact  112   b  located along a top surface of the epitaxial drain region  108   b.    
       FIG. 2  illustrates some additional embodiments of a transistor device  200  having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
     Transistor device  200  comprises a carbon doped epitaxial layer  104  disposed over a semiconductor substrate  102  and a lightly-doped epitaxial layer  106  disposed over the carbon doped epitaxial layer  104 . The carbon doped epitaxial layer  104  is configured to augment performance of the transistor device  200  (e.g., to improve local and global threshold voltage and drive current variations within the device) by mitigating dopant back diffusion from the semiconductor substrate  102  and to thereby generate a steep retrograde doping concentration profile of a channel region of transistor device  200 . In some embodiments, the carbon doped epitaxial layer  104  may have a carbon doping concentration of less than 1%. In some embodiments, the retrograde doping concentration profile may provide for a doping concentration that is less than 1e18 cm −3  at an interface between the lightly-doped epitaxial layer  106  and the gate structure  114 . 
     First and second DSM regions,  110   a  and  110   b , extend along a vertical direction from a location below epitaxial source and drain regions,  108   a  and  108   b , to recessed source and drain contacts,  112   a  and  112   b , located along a top surface of the epitaxial source and drain regions,  108   a  and  108   b , respectively. In some embodiments, the recessed source and drain contacts,  112   a  and  112   b , may comprise nickel. In some embodiments, top surfaces of the DSM regions,  110   a  and  110   b , may have a divot or recess comprising the recessed source and drain contacts,  112   a  and  112   b . In some embodiments, the first and second DSM regions,  110   a  and  110   b , may have a bottom surface that is located at distance  202  below the epitaxial source and drain regions,  108   a  and  108   b , respectively. For example, the first and second DSM regions,  110   a  and  110   b , may extend to a distance  202  of greater than or equal to approximately 2 nm below the epitaxial source and drain regions,  108   a  and  108   b . In some embodiments, a height  204  of the epitaxial stack  103  is less than a height  206  of the first and second DSM regions,  110   a  and  110   b.    
     The first and second DSM regions,  110   a  and  110   b , extend along a lateral direction from a first position within the epitaxial source and drain regions,  108   a  and  108   b , to a second position within the epitaxial regions,  108   a  and  108   b . In some embodiments, the first and second positions are selected so that the DSM regions,  110   a  and  110   b , have a smaller width than the epitaxial source and drain regions,  108   a  and  108   b . In some embodiments, the first and second DSM regions,  110   a  and  110   b , may be laterally separated from the gate structure  112  by a relatively small distance  208  so as to enhance stress on the channel region. For example, the first or second DSM regions,  110   a  or  110   b , may be separated from the gate structure by a distance  208  that is less than approximately 10 nm. 
     In some embodiments, the gate structure  114  may comprise a stacked gate dielectric layer  210  and a gate electrode layer  212 . The gate dielectric layer  210  (e.g., a silicon dioxide layer, a high-k dielectric layer, etc.) is disposed onto the lightly-doped epitaxial layer  106 . The gate electrode layer  212  (e.g., a poly-silicon layer, a replacement metal gate layer, etc.) is disposed onto the gate dielectric layer  210 . In some embodiments, the gate dielectric layer  210  and a gate electrode layer  212  may be flanked by sidewall spacers  214 . In some embodiments, the sidewall spacers  214  may comprise nitride spacers. 
       FIG. 3  illustrates a flow diagram of some embodiments of a method  300  of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
     At  302 , a semiconductor substrate is provided. The semiconductor substrate may comprise an intrinsically doped semiconductor substrate having a first doping type (e.g., an n-type doping or a p-type doping). 
     At  304 , the semiconductor substrate is selectively etched to form a recess within the semiconductor substrate. 
     At  306 , an epitaxial growth process is performed to form an epitaxial stack within the recess. In some embodiments, the epitaxial stack may comprise a carbon doped epitaxial layer (e.g., SiC) and an un-doped epitaxial layer (e.g., silicon). The carbon doped epitaxial layer may be epitaxially grown onto a bottom surface of the recess, while the un-doped epitaxial layer may be epitaxially grown onto the carbon doped epitaxial layer. The carbon doped epitaxial layer is configured to mitigate back diffusion of dopants from the semiconductor substrate to form a steep retrograde doping profile within a channel region which results in a relatively low surface dopant concentration (e.g., less than 1e18 cm −3 ) that improves threshold voltage and drive current variations. 
     At  308 , a dislocation stress memorization technique (DSMT) is performed to form dislocation stress memorization (DSM) regions within the epitaxial stack and the semiconductor substrate at positions corresponding to source and drain regions of the transistor device. In some embodiments, the DSM regions may have a stressed lattice that has a smaller distance between atoms than normal (i.e., the lattice constant of the DSM region is smaller than the natural lattice constant not being stressed). In other embodiments, the DSM regions may have a stressed lattice that has a larger distance between atoms than normal. 
     At  310 , source and drain regions are formed within the semiconductor substrate at positions that abut a portion of the DSM regions. In some embodiments, the source and drain regions comprise epitaxial source and drain regions. In such embodiments, the epitaxial source and drain regions may be formed by selectively etching the semiconductor substrate to form source and drain cavities abutting a portion of the DSM regions, at  312 . In some embodiments, the cavities may comprise a portion of the DSM regions. Epitaxial material is then deposited within the source and drain cavities onto the portion of the DSM regions, at  314 . Since the epitaxial material is grown onto a portion of the DSM regions, the epitaxial material will have a stressed lattice due to the stressed lattice of the DSM regions, thereby causing the DSM regions to extend from the semiconductor substrate to the epitaxial source and drain regions. 
       FIG. 4  illustrates a flow diagram of some additional embodiments of a method  400  of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. 
     While disclosed methods (e.g., methods  300  and  400 ) are illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. 
     At  402 , a semiconductor substrate is provided. In various embodiments, the semiconductor substrate may comprise any type of semiconductor body (e.g., silicon, silicon-germanium, silicon-on-insulator, etc.) such as a semiconductor wafer and/or one or more die on a semiconductor wafer, as well as any other type of semiconductor and/or epitaxial layers associated therewith. 
     At  404 , a well/V t  implantation process is performed to introduce dopants into the semiconductor substrate. In some embodiments, a well anneal process may be performed on the semiconductor substrate after the well/Vt implantation process to activate dopants introduced by the well/V t  implantation process. 
     At  406 , the semiconductor substrate is selectively etched to form a recess within the well region along a top surface of the semiconductor substrate. 
     At  408 , an epitaxial growth process is performed to grow one or more epitaxial layers within the recess. In some embodiments, the one or more epitaxial layers may comprise a carbon doped epitaxial layer and an overlying un-doped epitaxial layer having no dopants (i.e., having an intrinsic doping concentration of approximately 1e15 cm −3 ). 
     At  410 , a dummy gate structure is formed over the one or more epitaxial layers. 
     At  412 , an LDD (lightly doped drain) and/or halo implantation process is performed. The LDD/halo implantation process introduces dopants into the semiconductor substrate. 
     At  414 , a dislocation stress memorization technique (DSMT) is performed to form DSM regions on opposing sides of the dummy gate structure. In some embodiments, the DSM regions may have a stressed lattice that has a smaller distance between atoms than normal (i.e., the lattice constant of the DSM region is smaller than the natural lattice constant not being stressed). In other embodiments, the DSM regions may have a stressed lattice that has a larger distance between atoms than normal. 
     In some embodiments, the DSMT may be performed by selectively implanting a stress inducing dopant into the one or more epitaxial layers and the underlying semiconductor substrate to form implantation regions at positions corresponding to source and drain regions of the transistor device, at  416 . A DSMT capping layer is formed over the implantation regions, at  418 . A high temperature anneal is performed, at  420 . The high temperature anneal causes the DSMT capping layer to form a re-crystallized amorphous material having stacking defects along (111) planes. The stacking defects induce a stress in the implantation regions, thereby forming the DSM regions. At  422 , the DSMT capping layer is removed. 
     At  424 , the one or more epitaxial layers and the underlying semiconductor substrate are selectively etched to form source and drain cavities. The selectively etch removes a portion of the DSM regions (formed at act  414 ), such that a bottom surface of the source and drain cavities abuts the DSM regions. 
     At  426 , epitaxial material (e.g., silicon phosphate) is formed within the source and drain cavities to form an epitaxial source region and an epitaxial drain region. Since the epitaxial material is grown onto a portion of the DSM regions, the epitaxial material will have a stressed lattice due to the stressed lattice of the DSM regions, thereby causing the stacking defects of the re-crystallized amorphous to extend along (111) planes to positions within the epitaxial source and drain regions. 
     At  428 , a replacement gate process is performed to replace the dummy gate structure with a gate dielectric layer and an overlying replacement metal gate electrode layer. In various embodiments, the dummy gate structure may be removed by a wet etching process and/or a dry etching process. In various embodiments, the gate dielectric layer may comprise an inter-layer gate dielectric layer or a high-k gate dielectric layer formed by a deposition technique. 
     At  430 , recessed source and drain contacts are formed within the epitaxial source and drain regions, respectively. The stacking defects may extend to a position abutting the recessed source and drain contacts. 
       FIGS. 5-12  illustrate some embodiments of cross-sectional views of a semiconductor substrate showing a method of forming a transistor device having epitaxial source and drain regions comprising DSM regions configured to provide stress to an epitaxial channel region. Although  FIGS. 5-12  are described in relation to method  400 , it will be appreciated that the structures disclosed in  FIGS. 5-12  are not limited to such a method. 
       FIG. 5  illustrates a cross-sectional view  500  of some embodiments of a semiconductor substrate corresponding to acts  402 - 404 . 
     As shown in cross-sectional view  500 , a voltage threshold (V)/well implantation  502  is performed on the semiconductor substrate  504 . The V t /well implantation  502  is configured to introduce dopants  506  into the semiconductor substrate  504  to adjust the V t  (threshold voltage) applied to a transistor to allow current to flow in a channel region. In some embodiments, the V t /well implantation  502  may introduce a p-type dopant (e.g., boron) into the semiconductor substrate  504 , while in other embodiments the V t /well implantation  502  may introduce an n-type dopant (e.g., phosphorous, antimony, or arsenic) into the semiconductor substrate  504 . 
     In some embodiments, a well anneal process may be subsequently performed to activate the implanted dopants  506  introduce by the V t /well implantation  502 . The well anneal process is performed by exposing the semiconductor substrate  504  to an elevated temperature (e.g., greater than or equal to 400° C.). The well anneal process may also cure crystalline defects and/or cause diffusion and redistribution of dopant impurities to drive the implanted dopants  506  deeper into the semiconductor substrate  504  to from a well region. 
       FIG. 6  illustrates a cross-sectional view  600  of some embodiments of a semiconductor substrate corresponding to act  406 . 
     As shown in cross-sectional view  600 , the semiconductor substrate  504  is exposed to an etchant  602  that is configured to form a recess  604  within the semiconductor substrate  504  (i.e., to reduce the thickness of a portion of the semiconductor substrate  504 ). In some embodiments, the etchant  602  is configured to remove a thickness t eb  of a portion of the semiconductor substrate  504  that is between approximately 5 nm and approximately 30 nm, for example. In some embodiments, the etchant  602  may comprise a dry etchant (e.g., an ion bombardment) and/or a wet etchant (e.g., Tetramethylammonium hydroxide (TMAH), potassium hydroxide (KOH), etc.). 
       FIG. 7  illustrates a cross-sectional view  700  of some embodiments of a semiconductor substrate corresponding to act  408 . 
     As shown in cross-sectional view  700 , a carbon doped epitaxial layer  104  (e.g., silicon carbide (SiC) layer) is epitaxially grown within the recess  604  at a position overlying the semiconductor substrate  504 . An un-doped epitaxial layer  702  (e.g., an un-doped silicon layer) is epitaxially grown within the recess  604  at a position overlying the carbon doped epitaxial layer  104 . In some embodiments, the carbon doped epitaxial layer  104  may be grown to a thickness having a range of between approximately 2 nm and approximately 15 nm, and the un-doped epitaxial layer  702  may be grown to a thickness of between approximately 5 nm and approximately 30 nm. In some embodiments, the carbon doped epitaxial layer  104  may have a carbon concentration of approximately less than 1%. Such a carbon concentration allows for the carbon doped epitaxial layer  104  to be subsequently etched (e.g., in act  422 ). 
     In some embodiments, an oxidation process may subsequently be performed after formation of the carbon doped epitaxial layer  104  and the un-doped epitaxial layer  702  to form a thin oxide on a top surface of the un-doped epitaxial layer  702 . The oxidation process comprises a high temperature anneal, which may cause back diffusion of dopants from the well region to the carbon doped epitaxial layer  104  and the un-doped epitaxial layer  702 . Back diffusion of dopants into the un-doped epitaxial layer  702  causes the un-doped silicon layer to form a lightly doped epitaxial layer  106 . 
       FIG. 8  illustrates a cross-sectional view  800  of some embodiments of a semiconductor substrate corresponding to act  410 . 
     As shown in cross-sectional view  800 , a dummy gate structure  802  is formed over the lightly-doped epitaxial layer  106 . In some embodiments, the dummy gate structure  802  may comprise a polysilicon layer deposited onto the lightly-doped epitaxial layer  106  using a deposition technique (e.g., chemical vapor deposition, physical vapor deposition, etc.). Sidewall spacers  804  may be formed on the outer sidewalls of the dummy gate structure  802 . In some embodiments, the sidewall spacers  804  may be formed by depositing nitride onto the lightly-doped epitaxial layer  106  and selectively etching the nitride to form the sidewall spacers  804 . 
       FIG. 9  illustrates a cross-sectional view  900  of some embodiments of a semiconductor substrate corresponding to act  412 . 
     As shown in cross-sectional view  900 , an LDD and/or halo implantation  902  is performed. The LDD and/or halo implantation  902  introduces dopants through an upper surface of the lightly-doped epitaxial layer  106 . The LDD implantation is configured to form LDD impurity regions,  904  and  906 , having a doping type that is different than that of well/V t  implantation. The halo implantation is configured to form halo implantation regions,  908  and  910 , having an opposite doping type as the LDD implantation into the periphery, but not the central portion, of a channel region. In some embodiments, the halo implantation  902  may be performed at a tilt angle Φ with respect to a top surface of the lightly-doped epitaxial layer  106 . In some embodiments, the tilt angle Φ may be 20° or less. Although cross-sectional view  900  illustrates the halo implantation as being performed prior to the formation of source and drain regions (e.g., regions  108   a  and  108   b ), it will be appreciated that in alternative embodiments the halo implantation may be performed after formation of the source and drain regions. 
       FIG. 10A-10C  illustrates cross-sectional views of some embodiments of a semiconductor substrate corresponding to act  414 . 
     As shown in cross-sectional view  1000  of  FIG. 10A , an implantation  1002  is performed to form amorphous regions  1004 . The amorphous regions  1004  extend from a top surface of the epitaxial stack  103  to a position within the semiconductor substrate  504  underlying the epitaxial stack  103 , so that a height of the amorphous regions  1004  is greater than a height of the epitaxial stack  103 . In some embodiments, the implantation  1002  may be configured to implant a dopant species comprising germanium. In some embodiments, the implantation  1002  may be configured to implant a low temperature germanium pre-amorphous implant at an implant dose less than approximately 2e15. In some embodiments, the temperature germanium pre-amorphous implant may cool the germanium dopant species to a temperature of between −50° C. and −200° C. prior to implantation  1002 . 
     As shown in cross-sectional view  1006  of  FIG. 10B , a DSMT cap layer  1008  (e.g., a nitride layer) is formed over the amorphous regions  1004 . A high temperature anneal  1010  is then performed. During the high temperature anneal  1010  the lattice of the amorphous regions  1004  are re-crystallized. The growth of the re-crystallized lattice will occur under stress conditions induced by the DSMT cap layer  1008  and result in re-crystallized amorphous regions  1012 . The re-crystallized amorphous regions  1012  comprise a stacking defect  1014  along a (111) plane. The stacking defect  1014  distorts the lattice of the amorphous regions  1004  thereby affecting bond length. For example, a compressive capping layer may induce a stacking defect that distorts the lattice of the amorphous regions to form a smaller bonding length leading to tensile stress. 
     As shown in cross-sectional view  1014  of  FIG. 10C , the DSMT cap layer  1008  is removed. Since the re-crystallized regions  1012  memorize the stress induced by the DSMT cap layer  1008 , when the DSMT cap layer  1008  is removed the re-crystallized regions  1012  maintain their stressed lattice configurations. 
       FIGS. 11A-11B  illustrates a cross-sectional view  1100  of some embodiments of a semiconductor substrate corresponding to acts  424 - 426 . 
     As shown in cross-sectional view  1100  of  FIG. 11A , an etchant  1102  is configured to selectively form a source cavity  1104   a  and a drain cavity  1104   b . The source and drain cavities,  1104   a  and  1104   b , extend from a top surface of the epitaxial stack  103  to a position above the bottom surface of the re-crystallized regions  1012 . For example, in some embodiments, the source and drain cavities,  1104   a  and  1104   b , may extend from a top surface of the epitaxial stack  103  to a position approximately greater than or equal to approximately 2 nm above the bottom surface of the re-crystallized regions  1012 . 
     In some embodiments, the etchant  1102  may comprise a multi-step etching process. For example, a first etching process may be used to form cavities comprising a U-shaped etch profile. In some embodiments, the first etching process may comprise a dry etch, wet etch, plasma etch, RIE etch, or a combination thereof. A second, anisotropic etch process may be subsequently performed on the cavities. In some embodiments, the anisotropic etch comprises a wet etch which utilizes TMAH as an etchant configured for preferred etch selectivity in the &lt;100&gt; direction of the Si or SOI substrate. The resultant etch profile of the source and drain cavities, other than the bottom surface, comprises a (100) crystal orientation after the anisotropic etch. 
     As shown in cross-sectional view  1106  of  FIG. 11B , a stress-inducing material is epitaxially deposited within the source and drain cavities,  1104   a  and  1104   b , to form epitaxial source and drain regions,  108   a  and  108   b . In some embodiments, the stress inducing material may comprise silicon phosphate (SiP). In other embodiments, the stress-inducing material may comprise other materials (e.g., SiGe or a carbon-containing material such as SiC). The stacking defects  1108  along the (111) planes extend into the epitaxial source and drain regions,  108   a  and  108   b , to form DSM regions,  110   a  and  110   b , since the stress-inducing material is epitaxial grown onto the underlying re-crystallized regions  1012 , which have strained lattice due to the DSMT process (act  414 ). 
       FIG. 12  illustrates a cross-sectional view  1200  of some embodiments of a semiconductor substrate corresponding to acts  428 - 430 . 
     As shown in cross-sectional view  1200 , a replacement gate process is performed. The replacement gate process removes the dummy gate structure  802  and forms an inter-layer gate dielectric layer or a high-k gate dielectric layer  1202  at a position replacing the dummy gate structure  802  (i.e., between sidewall spacers  804 ) using a deposition technique (e.g., chemical vapor deposition, physical vapor deposition, etc.). A replacement metal gate electrode layer  1204  is deposited over gate dielectric layer  1202  using a deposition technique. In some embodiments, the replacement metal gate electrode layer  1204  may comprise aluminum, for example. 
     Recessed source and drain contacts,  112   a  and  112   b , are respectively formed within the epitaxial source and drain regions,  108   a  and  108   b . The recessed source and drain contacts,  112   a  and  112   b , may be formed by selectively etching the epitaxial source and drain regions,  108   a  and  108   b , and then depositing a contact material using a deposition technique. In some embodiments, the recessed source and drain contacts,  112   a  and  112   b , may comprise nickel. In some embodiments, etching the epitaxial source and drain regions,  108   a  and  108   b , to form the recessed source and drain contacts,  112   a  and  112   b , will remove a section of the DSM regions,  110   a  and  110   b . For example, in some embodiments, top surfaces of the DSM regions,  110   a  and  110   b , may have a divot or recess comprising the recessed source and drain contacts,  112   a  and  112   b.    
     Therefore, the present disclosure relates to a transistor device having epitaxial source and drain regions comprising dislocation stress memorization (DSM) regions configured to provide stress to an epitaxial channel region, and an associated method of formation. 
     In some embodiments, the present disclosure relates to a transistor device. The transistor device comprises an epitaxial source region arranged within a substrate, and an epitaxial drain region arranged within the substrate and separated from the epitaxial source region by a channel region. The transistor device further comprises first and second dislocation stress memorization (DSM) regions having stressed lattices configured to generate stress within the channel region. The first DSM region extends from below the epitaxial source region to a first location within the epitaxial source region. The second DSM region extends from below the epitaxial drain region to a second location within the epitaxial drain region. 
     In other embodiments, the present disclosure relates to a transistor device. The transistor device comprises an epitaxial source region separated from an epitaxial drain region by a channel region underlying a gate structure. A first dislocation stress memorization (DSM) region comprising a first stressed lattice is arranged within and is laterally offset from opposing sidewalls of the epitaxial source region. A second DSM region comprising a second stressed lattice is arranged within and is laterally offset from opposing sidewalls of the epitaxial drain region. 
     In yet other embodiments, the present disclosure relates to a transistor device. The transistor device comprises an epitaxial source region separated from an epitaxial drain region by a channel region underlying a gate structure. A first stacking defect is arranged within and is laterally offset from opposing sidewalls of the epitaxial source region. A second stacking defect is arranged within and is laterally offset from opposing sidewalls of the epitaxial drain region. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.