Abstract:
A semiconductor device and a method for manufacturing the same are provided. In one embodiment, the method comprises: growing a first epitaxial layer on a substrate; forming a sacrificial gate stack on the first epitaxial layer; selectively etching the first epitaxial layer; growing and in-situ doping a second epitaxial layer on the substrate; forming a spacer on opposite sides of the sacrificial gate stack; and forming source/drain regions with the spacer as a mask.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims priority to Chinese Application No. 201210250438.6, entitled “SEMICONDUCTOR DEVICE AND METHOD FOR MANUFACTURING THE SAME,” filed on Jul. 19, 2012, which is incorporated herein by reference in their entirety. 
       TECHNICAL FIELD 
       [0002]    The present disclosure relates to the semiconductor field, and particularly, to a semiconductor device and a method for manufacturing the same. 
       BACKGROUND 
       [0003]    With continuous scaling down of semiconductor devices, short channel effects are becoming more significant. On solution to suppress the short channel effects is to reduce the junction depth of source/drain extension regions. To form such shallow extension regions, it is necessary to adopt low-energy ion implantation in extension implantation, followed by ultra-short annealing to activate implanted ions. This poses challenges on manufacture apparatus and manufacture processes. 
         [0004]    On the other hand, the ion implantation may cause substrate damages. Thus, an additional annealing process is needed to remove the damages. 
       SUMMARY 
       [0005]    The present disclosure provides, among others, a semiconductor device and a method for manufacturing the same. 
         [0006]    According to an aspect of the present disclosure, there is provided a method for manufacturing a semiconductor device, comprising: growing a first epitaxial layer on a substrate; forming a sacrificial gate stack on the first epitaxial layer; selectively etching the first epitaxial layer; growing and in-situ doping a second epitaxial layer on the substrate; forming a spacer on opposite sides of the sacrificial gate stack; and forming source/drain regions with the spacer as a mask. 
         [0007]    According to a further aspect of the present disclosure, there is provided a semiconductor device, comprising: a gate stack formed on a substrate; a first epitaxial layer, which is in-situ doped and grown on the substrate, and is configured as source/drain extension regions; and source/drain regions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The above and other objects, features, and advantages of the present disclosure will become apparent from following descriptions of embodiments with reference to the attached drawings, in which: 
           [0009]      FIGS. 1-6  are schematic views showing a flow of manufacturing a semiconductor device according to an embodiment of the present disclosure; and 
           [0010]      FIGS. 7-14  are schematic views showing a flow of manufacturing a semiconductor device according to a further embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0011]    Hereinafter, descriptions are given with reference to embodiments shown in the attached drawings. However, it is to be understood that these descriptions are illustrative and not intended to limit the present disclosure. Further, in the following, known structures and technologies are not described to avoid obscuring the present disclosure unnecessarily. 
         [0012]    In the drawings, various structures according to the embodiments are schematically shown. However, they are not drawn to scale, and some features may be enlarged while some features may be omitted for sake of clarity. Moreover, shapes and relative sizes and positions of regions and layers shown in the drawings are also illustrative, and deviations may occur due to manufacture tolerances and technique limitations in practice. Those skilled in the art can also devise regions/layers of other different shapes, and relative sizes and positions as desired. 
         [0013]    In the context of the present disclosure, when a layer/element is recited as being “on” a further layer/element, the layer/element can be disposed directly on the further layer/element, or otherwise there may be an intervening layer/element interposed therebetween. Further, if a layer/element is “on” a further layer/element in an orientation, then the layer/element can be “under” the further layer/element when the orientation is turned. 
         [0014]    Next, an embodiment of the present disclosure will be described in detail with reference to  FIGS. 1-6 . 
         [0015]    As shown in  FIG. 1 , a substrate  1000  is provided. The substrate  1000  may comprise any suitable substrate, including, but not limited to, a bulk semiconductor substrate such as a bulk Si substrate, a Semiconductor on Insulator (SOI) substrate, a SiGe substrate, and the like. For convenience, the following descriptions are given with respect to the bulk Si substrate by way of example. 
         [0016]    On the substrate  1000 , an epitaxial layer  1004  may be grown by means of, for example, epitaxy. For example, the epitaxial layer  1004  may comprise SiGe (where an atomic percentage of Ge can be about 10%), with a thickness of about 5-10 nm. The thickness of the epitaxial layer  1004  substantially determines a thickness of source/drain extension regions to be formed later. 
         [0017]    Subsequently, as shown in  FIG. 2 , on the epitaxial layer  1004 , a sacrificial gate stack may be formed. For example, the sacrificial gate stack can be formed by sequentially depositing an oxide layer  1006  and a nitride layer  1008  and then patterning them. It is to be noted that there are various ways to form the sacrificial gate stack. The sacrificial gate stack comprising the oxide layer  1006  and the nitride layer  1008 , as shown in  FIG. 2 , is just an example. According to embodiments of the present disclosure, the sacrificial gate stack preferably comprises a dielectric material such as oxide, nitride or a combination thereof, instead of a crystal semiconductor material (e.g., polysilicon), for convenience of following processes. It is intended to prevent following selective epitaxy from occurring at the sacrificial gate stack. 
         [0018]    Next, as shown in  FIG. 3 , the epitaxial layer  1004  may be subjected to selective etching. Such selective etching may be accomplished by wet etching, dry etching, or a combination thereof. Due to the etching selectively between the epitaxial layer  1004  (e.g., SiGe) and the substrate (e.g., Si), the etching can be stopped on the substrate  1000 . A portion of the epitaxial layer  1004  underlying the sacrificial gate stack can be reserved due to the presence of the sacrificial gate stack. In the example shown in  FIG. 3 , lateral edges of the etched epitaxial layer  1004  are illustrated as being slightly recessed with respect to respective lateral edges of the sacrificial gate stack by an extent which can be controlled by conditions in the etching process. 
         [0019]    Then, as shown in  FIG. 4 , an epitaxial layer  1010  may be grown on portions of the substrate  1000  exposed by the above selective etching by means of, for example, epitaxy. The epitaxial layer  1010  may comprise Si. Because the sacrificial gate stack comprises dielectric materials such as oxide and nitride, the epitaxy will not occur at surfaces of the sacrificial gate stack. The epitaxial layer  1010  can be doped in-situ into an appropriate conductivity type while being grown. For example, for an n-type device, the epitaxial layer  1010  may be doped with n-type impurities, such as As or P, into the n-type; while for a p-type device, the epitaxial layer  1010  may be doped with p-type impurities, such as In, BF 2 , or B, into the p-type. The in-situ doped epitaxial layer  1010  can serve as extension regions of the device to be formed. 
         [0020]    Next, as shown in  FIG. 5 , a spacer  1012  may be formed on opposite sides of the sacrificial gate stack. For example, the spacer  1012  may comprise silicon nitride, silicon oxide, or a combination thereof. There are various ways to form the spacer, and thus detailed descriptions thereof are omitted here. 
         [0021]    Subsequently, as shown in  FIG. 6 , source/drain regions  1014  may be formed with the spacer as a mask. For example; the source/drain regions  1014  may be formed by means of ion implantation. Specifically, for an n-type device, n-type impurities such as As or P may be implanted; while for a p-type device, p-type impurities may be implanted. Following the ion implantation, annealing can be carried out to activate implanted ions. 
         [0022]    After that, a gate replacement process can be performed. Specifically, the sacrificial gate stack (comprising the nitride layer  1008  and the oxide layer  1006  in this example) can be removed by selective etching, resulting in a groove inside the spacer. Then, a gate dielectric layer and a gate conductor can be filled into the groove, to form a true gate stack. For example, the gate dielectric layer may comprise a high-K gate dielectric, and the gate conductor may comprise a metal gate conductor. 
         [0023]    Thus, a semiconductor device according to an embodiment of the present disclosure is achieved. As shown in  FIG. 6 , the semiconductor device comprises the in-situ doped epitaxial layer  1010  formed on the substrate. The epitaxial layer  1010  (especially, portions thereof close to a channel region) servers as the source/drain extension regions  1016  of the semiconductor device. The epitaxial layer  1010  has its thickness substantially determined by the thickness of the epitaxial layer  1004 , due to its formation process. In other words, the thickness of the epitaxial layer  1004  substantially determines the depth of the extension regions  1016 . Because the thickness of the epitaxial layer  1004  grown on the substrate can be controlled in a relatively accurate manner to be relatively thin, it is possible to from the extension regions  1016  which are relatively shallow. Further, the extension regions  1016  can be in-situ doped while being grown. As a result, it is possible to avoid ion implantation and thus avoid ultra-short annealing thereon. 
         [0024]    Hereinafter, a further embodiment of the present disclosure will be described in detail with reference to  FIGS. 7-14 . 
         [0025]    As shown in  FIG. 7 , a substrate  2000  is provided. The substrate  2000  may comprise any suitable substrate, including, but not limited to, a bulk semiconductor substrate such as a bulk Si substrate, a Semiconductor on Insulator (SOI) substrate, a SiGe substrate, and the like. For convenience, the following descriptions are given with respect to the bulk Si substrate by way of example. 
         [0026]    On the substrate  2000 , an epitaxial layer  2002  may be grown by means of, for example, epitaxy. For example, the epitaxial layer  2002  may comprise SiGe (where an atomic percentage of Ge can be about 10%), with a thickness of about 30-50 nm. The thickness of the epitaxial layer  2002  substantially determines a thickness of source/drain regions to be formed later. 
         [0027]    Further, on the epitaxial layer  2002 , a further epitaxial layer  2004  may be grown by means of, for example, epitaxy. For example, the epitaxial layer  2004  may comprise Si, with a thickness of about 5-10 nm. The thickness of the epitaxial layer  2004  substantially determines a thickness of source/drain extension regions to be formed later. 
         [0028]    Subsequently, as shown in  FIG. 8 , on the epitaxial layer  2004 , a sacrificial gate stack may be formed. For example, the sacrificial gate stack can be formed by sequentially depositing an oxide layer  2006  and a nitride layer  2008  and then patterning them. As for the sacrificial gate stack, reference may be made to the above descriptions in conjunction with  FIG. 2 . 
         [0029]    Next, as shown in  FIG. 9 , the epitaxial layer  2004  may be subjected to selective etching. Such selective etching may be accomplished by wet etching, dry etching, or a combination thereof. Due to the etching selectively between the epitaxial layer  2004  (e.g., Si) and the epitaxial layer  2002  (e.g., SiGe), the etching can be stopped on the epitaxial layer  2002 . A portion of the epitaxial layer  2004  underlying the sacrificial gate stack can be reserved due to the presence of the sacrificial gate stack. In the example shown in  FIG. 9 , lateral edges of the etched epitaxial layer  2004  are illustrated as being slightly recessed with respect to respective lateral edges of the sacrificial gate stack by an extent which can be controlled by conditions in the etching process. 
         [0030]    Then, as shown in  FIG. 10 , an epitaxial layer  2010  may be grown on portions of the epitaxial layer  2002  exposed by the above selective etching by means of, for example, epitaxy. The epitaxial layer  2010  may comprise Si. Because the sacrificial gate stack comprises dielectric materials such as oxide and nitride, the epitaxy will not occur at surfaces of the sacrificial gate stack. The epitaxial layer  2010  can be doped in-situ into an appropriate conductivity type while being grown. For example, for an n-type device, the epitaxial layer  2010  may be doped with n-type impurities, such as As or P, into the n-type; while for a p-type device, the epitaxial layer  2010  may be doped with p-type impurities, such as In, BF 2 , or B, into the p-type. The in-situ doped epitaxial layer  2010  can serve as extension regions of the device to be formed. 
         [0031]    Next, as shown in  FIG. 11 , a spacer  2012  may be formed on opposite sides of the sacrificial gate stack. For example, the spacer  2012  may comprise silicon nitride, silicon oxide, or a combination thereof. There are various ways to form the spacer, and thus detailed descriptions thereof are omitted here. 
         [0032]    Subsequently, as shown in  FIG. 12 , the epitaxial layer  2020  and the epitaxial layer  2002  may be subjected to selective etching with the spacer as a mask. Such selective etching may be accomplished by wet etching, dry etching, or a combination thereof. Due to the presence of the sacrificial gate stack and the spacer, portions of the epitaxial layer  2020  and the epitaxial layer  2002  underlying them are reserved. 
         [0033]    Then, as shown in  FIG. 13 , an epitaxial layer  2014  may be grown on portions of the substrate  2000  exposed by the above selective etching by means of, for example, epitaxy. The epitaxial layer  2014  may comprise Si. Because the sacrificial gate stack comprises dielectric materials such as oxide and nitride, the epitaxy will not occur at surfaces of the sacrificial gate stack. The epitaxial layer  2014  can be doped in-situ into an appropriate conductivity type while being grown. For example, for an n-type device, the epitaxial layer  2014  may be doped with n-type impurities, such as As or P, into the n-type; while for a p-type device, the epitaxial layer  2014  may be doped with p-type impurities, such as In, BF 2 , or B, into the p-type. The in-situ doped epitaxial layer  2014  can serve as source/drain regions of the device to be formed. Further, the remaining portions of the in- situ doped epitaxial layer  2010  can serve as the source/drain extensions  2016  of the device. 
         [0034]    According to an example of the present disclosure, to improve performances of the device, the epitaxial layer  2014  may comprise SiGe (for a p-type device, where an atomic percentage of Ge can be greater than about 30%) or Si:C (for an n-type device). The epitaxial layer  2014  in such a configuration can apply stress to a channel region of the device, so as to enhance the mobility of carriers and thus improve the performances of the device. 
         [0035]    After that, a gate replacement process can be performed. Specifically, the sacrificial gate stack (comprising the nitride layer  2008  and the oxide layer  2006  in this example) can be removed by selective etching, resulting in a groove inside the spacer. Then, a gate dielectric layer  2018  and a gate conductor  2020  can be filled into the groove, to form a true gate stack. For example, the gate dielectric layer  2018  may comprise a high-K gate dielectric, and the gate conductor  2020  may comprise a metal gate conductor. There may be further a work-function adjustment layer (not shown) interposed between the gate dielectric layer  2018  and the gate conductor  2020 . Then, an inter-layer dielectric layer  2022  (e.g., oxide) may be formed by means of, for example, deposition, and then subjected to CMP, resulting in the semiconductor device shown in  FIG. 14 . 
         [0036]    As shown in  FIG. 14 , the semiconductor device comprises a gate stack (including the gate dielectric layer  2018  and the gate conductor  2020 ) formed on the substrate. The in-situ doped epitaxial layer  2010  serves as the source/drain extension regions  2016  of the semiconductor device. Like the above described embodiment, the extension regions  2016  formed in such a way can be controlled to be relatively shallow, and also it is possible to avoid ion implantation. 
         [0037]    Further, the semiconductor device comprises the source/drain regions formed of the epitaxial layer  2014 . Likewise, the source/drain regions can be in-situ doped while being grown. As a result, it is possible to avoid ion implantation and thus avoid ultra-short annealing thereon. 
         [0038]    From the foregoing, it will be appreciated that specific embodiments of the disclosure have been described herein for purposes of illustration, but that various modifications may be made without deviating from the disclosure. In addition, many of the elements of one embodiment may be combined with other embodiments in addition to or in lieu of the elements of the other embodiments. Accordingly, the technology is not limited except as by the appended claims.