Patent Document

BACKGROUND 
       [0001]    The present invention relates to semiconductor integrated circuits and, more particularly, relates to enhancing the performance of raised source/drains in MOSFET semiconductor devices. 
         [0002]    In-situ doped raised source/drain (RSD) has become a viable approach to enhance the performance of advanced MOSFETs (metal oxide semiconductor field effect transistors) by lowering the raised source/drain and simultaneously achieving ultra shallow junction. A side effect of RSD is the parasitic capacitance between the gate and the RSD. Faceted RSD has been demonstrated as an effective means to reduce the gate-to-source/drain parasitic capacitance. 
       BRIEF SUMMARY 
       [0003]    The various advantages and purposes of the exemplary embodiments as described above and hereafter are achieved by providing, according to a first aspect of the exemplary embodiments, a method of epitaxial replacement of a raised source/drain (RSD) including: forming a gate structure on a semiconductor substrate; forming a faceted dummy RSD adjacent to the gate structure such that a corner is formed between the gate structure and the faceted dummy RSD; forming a dielectric material over the corner; removing the faceted dummy RSD adjacent to the gate structure to leave a faceted corner in the dielectric material; epitaxially growing an RSD adjacent to the gate structure including epitaxially growing the RSD in the faceted corner in the dielectric material. 
         [0004]    According to a second aspect of the exemplary embodiments, there is provided a method of epitaxial replacement of a raised source/drain (RSD) including: forming first and second gate structures on a semiconductor substrate; forming a faceted dummy RSD adjacent to each of the first and second gate structures; depositing a dielectric material over the first and second gate structures and the faceted dummy RSD adjacent to each of the first and second gate structures; applying a first masking material to the dielectric material over the first gate structure and the faceted dummy RSD adjacent to the first gate structure; forming a spacer adjacent to the second gate structure from the dielectric material while removing the dielectric from the top of the second gate structure and the faceted dummy RSD adjacent to the second gate structure; removing the faceted dummy RSD adjacent to the second gate structure to leave a faceted corner in the spacer adjacent to the second gate structure; epitaxially growing an RSD adjacent to the second gate structure including epitaxially growing the RSD in the faceted corner in the spacer adjacent to the second gate structure; applying a second masking material to the second gate, spacer and the epitaxially grown RSD adjacent to the second gate structure; forming a spacer adjacent to the first gate structure from the dielectric material while removing the dielectric from the top of the first gate structure and the faceted dummy RSD adjacent to the first gate structure; removing the faceted dummy RSD adjacent to the first gate structure to leave a faceted corner in the spacer adjacent to the first gate structure; epitaxially growing an RSD adjacent to the first gate structure including epitaxially growing the RSD in the faceted corner in the spacer adjacent to the first gate structure; and annealing the semiconductor substrate. 
         [0005]    According to a third aspect of the exemplary embodiments, there is provided a semiconductor article including: a semiconductor substrate; a gate structure having a spacer adjacent to a conducting material of the gate structure wherein a corner of the spacer is faceted to create a faceted space between the faceted spacer and the semiconductor substrate; and a raised source/drain adjacent to the gate structure, the raised source/drain filling the faceted space and having a surface parallel to the semiconductor substrate. 
     
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         [0006]    The features of the exemplary embodiments believed to be novel and the elements characteristic of the exemplary embodiments are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The exemplary embodiments, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
           [0007]      FIGS. 1 to 10  are cross-sectional views illustrating the manufacturing of a semiconductor structure with epitaxial replacement of a raised source/drain according to the exemplary embodiments wherein: 
           [0008]      FIG. 1  illustrates the forming of gate structures on a semiconductor substrate having nFET and pFET regions; 
           [0009]      FIG. 2  illustrates the forming of dummy RSDS adjacent to the gate structures; 
           [0010]      FIG. 3  illustrates the deposition of a dielectric layer over the gate structures and dummy RSDS; 
           [0011]      FIG. 4  illustrates the masking of the nFET region while removing the dielectric layer in the pFET region; 
           [0012]      FIG. 5  illustrates the removal of the dummy RSD in the pFET region; 
           [0013]      FIG. 6  illustrates the forming of the real RSD in the pFET region; 
           [0014]      FIG. 7  illustrates the masking of the pFET region and removing of the dielectric layer in the nFET region; 
           [0015]      FIG. 8  illustrates the removal of the dummy RSD in the nFET region; 
           [0016]      FIG. 9  illustrates the forming of the real RSD in the nFET region; and 
           [0017]      FIG. 10  illustrates the annealing of the semiconductor structure to form extensions in the semiconductor substrate. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    To reduce any possible penalties in parasitic capacitance due to the RSD structure, a faceted epitaxy process is preferably employed. However, manufacturing MOSFETs with RSD by epitaxy with a faceted profile and high dopant concentration, particularly for the highly scaled devices with tight pitches, has been found extremely difficult to achieve. Therefore, there is a need for improving the manufacturing of MOSFETs with in-situ doped RSD. 
         [0019]    There is proposed in the exemplary embodiments a replacement RSD scheme which decouples the faceted RSD profile requirement and the in-situ doping. According to the exemplary embodiments, a dummy RSD with a faceted profile is first formed after gate patterning and a spacer is then formed. The dummy RSD then may be removed and an in-situ doped epitaxy is performed to form the real RSD. 
         [0020]    Referring to the Figures in more detail, and particularly referring to  FIG. 1 , there is illustrated the results of initial processing steps that produce a semiconductor structure  10  that includes semiconductor substrate  12  having semiconductor gate structures  14 ,  16 . The semiconductor substrate may be any semiconductor substrate including bulk semiconductor substrates and semiconductor on insulator (SOI) substrates such as ETSOI (extra thin semiconductor on insulator) and PDSOI (partially-depleted semiconductor on insulator). The particular semiconductor substrate is unimportant to the present invention. 
         [0021]    The semiconductor material making up the bulk semiconductor substrate may be any semiconductor material, including but not limited to, silicon, silicon germanium, germanium, carbon doped silicon (carbon 0.2 atomic percent (a/o) to 6 a/o, with 0.5 a/o to 2.5 a/o typical), a III-V compound semiconductor, or a Il-VI compound semiconductor. Similarly, the semiconductor material making up the semiconductor on insulator (SOI) layer of an SOI substrate may be any semiconductor material, including but not limited to, silicon, silicon germanium, germanium, a III-V compound semiconductor, or a II-VI compound semiconductor. 
         [0022]    The semiconductor substrate  12  may also comprise a layered semiconductor such as, for example, silicon/silicon germanium, a silicon-on-insulator or a silicon germanium-on-insulator. A portion of the semiconductor substrate  12  or the entire semiconductor substrate  12  may be amorphous, polycrystalline, or monocrystalline. 
         [0023]    For purposes of illustration and not limitation, the semiconductor substrate  12  shown in  FIG. 1  may be an SOI substrate and may be an ETSOI substrate or a PDSOI substrate. The semiconductor substrate  12  includes a semiconductor base  18 , a buried insulating layer  20  and a top semiconductor layer  22 . The buried insulating layer  20  may be an oxide layer and, further, may be referred to as a BOX (buried oxide) layer. The semiconductor substrate  12  may be formed by conventional means. 
         [0024]    The semiconductor substrate  12  may further include a first device region  24  and a second device region  26  separated by an isolation region  28 . A first gate structure  14  may be positioned in the first device region  24  of the substrate  12  and a second gate structure  16  may be positioned in the second device region  26  of the substrate  12 . There may be other isolation regions  30 ,  32  to separate first device region  24  from a third device region (not shown) and second device region  26  from a fourth device region (not shown), respectively. 
         [0025]    First device region  24  may also be referred to as an N-type device region (where an nFET device may be formed) or a P-type device region (where a pFET device may be formed), while second region  26  may also be referred to as a P-type device region or an N-type device region, in which the first device region  24  has a different conductivity than the second device region  26 . For purposes of illustration and not limitation,  FIG. 1  illustrates a first device region  24  where an nFET device may be formed and second device region  26  where a pFET device may be formed. 
         [0026]    The isolation region  28  separates the device regions  24 ,  26  of the SOI layer  22  and may be in direct physical contact with an upper surface of the BOX layer  20  or may extend into BOX layer  20 . Isolation region  28 , as well as isolation regions  30 ,  32  may be formed by conventional means. 
         [0027]    The first and second gate structures  14 ,  16  may be formed by conventional means. The first and second gate structures  14 ,  16  may each include a gate conductor  34  atop a gate dielectric  36 . Gate conductor  34  material may be polysilicon, but may also include elemental metals, metal alloys, metal silicides, and/or other conductive materials. Gate dielectric  36  may be a dielectric material, such as silicon oxide (SiO2), silicon nitride, oxynitride, or alternatively high-k dielectrics, such as oxides of Ta, Zr, Al, Hf or combinations thereof. The first and second gate structures  14 ,  16  may also include a gate cap  38  such as silicon nitride. 
         [0028]    A set of first spacers  40  may be conventionally formed in direct contact with the sidewalls of the first gate structure  14  and second gate structure  16 . The first spacers  40  may be composed of a dielectric, such as nitride, oxide, oxynitride, or a combination thereof. The thickness of the first spacers  40  determines the proximity of the subsequently formed raised source/drain (RSD) regions to the channel of the device. 
         [0029]    The first and second gate structures  14 ,  16  may be the real gate structures in the case of a gate-first process or may be dummy gate structures in the case of a gate-last process. 
         [0030]    Referring now to  FIG. 2 , dummy RSD structures  42  may be formed. In an exemplary embodiment, the dummy RSD structures  42  may comprise silicon germanium (SiGe). The dummy RSD structures  42  are faceted and may be grown from the 501 layer  22  in a selective epitaxial deposition process. Faceting may be tailored during the selective epitaxial deposition process by adjusting the alloy and dopant concentration, and reactor temperature, pressure, and etchant and precursor flows. As an example, high-germanium percentage silicon germanium (&gt;20%) favors the evolution of &lt;111&gt; facets at low temperatures (&lt;650 C), low pressures (&lt;50T, preferably UHV), and high partial pressures of HCI. Shallower facets (&lt;220&gt;, &lt;113&gt;, etc.) or flat morphologies evolve at moderate temperatures (near 650 C) but high precursor partial pressures and minimal etchant flows. 
         [0031]    Silicon germanium is preferably used since it may be removed selectively to silicon later, when the dummy epitaxy is removed. Any other epitaxial material that forms facets and may be removed selectively to the silicon underneath it may be used. Silicon germanium is preferred because of its selectivity to silicon and can be easily selectively removed. Phosphorous doped silicon (Si:P) can work too, since it may be removed selectively to silicon, but not as easily as silicon germanium. The dummy RSD structures  42  will be selectively removed in a later process step but are important now for forming a facet with respect to the first and second gate structures  14 ,  16 . 
         [0032]    Referring now to  FIG. 3 , a dielectric layer  44  is blanket deposited so as to cover the semiconductor structure  10  including the first and second gate structures  14 ,  16  and dummy RSD structures  42 . The dielectric layer  44  may comprise, for example, silicon nitride, silicon oxide, silicon oxynitride, boron nitride, high-k dielectric or any combination of these materials. Examples of high-k materials include but are not limited to metal oxides such as hafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. 
         [0033]    As illustrated in  FIG. 4 , the first device region  24  is masked off with a photoresist  46  while the second device region  26  is not masked off. The photoresist mask  46  may be conventionally formed by blanket deposition of a photoresist, exposing the photoresist to a suitable source of radiation and then developing to remove the unwanted photoresist. The semiconductor structure  10  then may undergo a reactive ion etching (RIE) process, indicated by arrows  48 , to remove the dielectric layer  44  from the dummy RSD structures  42  in the second device region  26  and form second spacer  50  adjacent to second gate structure  16 . 
         [0034]    The photoresist mask  46  shown in  FIG. 4  may be conventionally stripped such as by an oxygen plasma to result in the structure illustrated in  FIG. 5 . The dummy RSD structures  42  in the second device region  26  are also removed such as by a gas-based HCI etch (or any other halide-based etch, i.e. chlorine, fluorine, etc.). The gas-based etch may be performed in the epitaxial reactor, The RSD structures  42  may also be removed by a wet etch such as TMAH (Tetramethylammonium hydroxide). The dummy RSD structures  42 , being made from SiGe, may be easily and selectively removed by the HCl etch in the second device region  26  without adversely affecting the underlying SOI layer  22 . It is noted that with the removal of the dummy RSD structures  42  from the second device region  26 , facets  52  remain in the second spacer  50 . The dummy RSD structures  42  in the first device region  24  are protected by dielectric layer  44  and so are not removed. 
         [0035]    Referring now to  FIG. 6 , an in-situ doped RSD  54  is epitaxially grown on SOI layer  22  in the second device region  26 . By in-situ doped, it is meant that the RSD  54  is doped while the RSD  54  is epitaxially grown, with the dopant gas flowing at the same time as the deposition gases. It should be understood that in-situ doping is optional and the RSD  54  may be doped by other means. The RSD  54  is grown by a non-faceted epitaxial growth process so that a planar surface  56  approximately parallel with SOI layer  22  is obtained. The non-faceted epitaxially grown RSD  54  may be formed by adjusting the epitaxial deposition parameters as described previously. While the RSD  54  is grown by a non-faceted epitaxial growth process, the RSD  54  fills the facet  52  in second spacer  50  so that the RSD  54  forms a faceted interface with second gate structure  16  at the corner of the second gate structure  16  and SOI layer  22 . In a preferred embodiment, the in-situ doped RSD  54  may be in-situ boron-doped silicon germanium (ISBD SiGe). The boron doping may be approximately 1×10 18  to 1×10 22  atoms/cm 3  with 1×10 20  to 4×10 20  atoms/cm 3  being more common. 
         [0036]    Referring now to  FIG. 7 , a thin hardmask  58 , such as 3 nanometers of silicon oxide, is selectively deposited in the second device region  26  so as to cover the second gate structure  16 , second spacer  50  and RSD  54 . The hardmask  58  may be removed from the first device region  24  by any etch selective to the dielectric layer  44 . For example, if the dielectric layer  44  is silicon nitride and the hardmask  58  is an oxide, oxide may be etched by an aqueous etchant containing hydrofluoric acid selective to nitride. As shown in  FIG. 7 , the hardmask  58  may be removed from the dielectric layer  44  in the first device region  24  as just described. Then, the second device region  26  is masked off with a photoresist  60  while the first device region  24  is not masked off. The photoresist mask  60  may be conventionally formed by blanket deposition of a photoresist, exposing the photoresist to a suitable source of radiation and then developing to remove the unwanted photoresist. The semiconductor structure  10  then may undergo a reactive ion etching (RIE) process, indicated by arrows  62 , to remove the dielectric layer  44  from the dummy RSD structures  42  in the first device region  24  and form second spacer  64  adjacent to first gate structure  14 . In an alternative process flow, the process step of removing the hardmask  58  from the dielectric layer  44  in the first device region  24  may be skipped and then after the RIE process described above, the hardmask  58  would become part of the spacer  64  in the first device region  24 . 
         [0037]    The photoresist  60  shown in  FIG. 7  may be conventionally stripped such as by an oxygen plasma to result in the structure illustrated in  FIG. 8 . The dummy RSD structures  42  in the first device region  24  are also removed such as by an HCl etch. The dummy RSD structures  42 , being made from SiGe, may be easily and selectively removed by the HCl etch without affecting the underlying SOI layer  22 . It is noted that with the removal of the dummy RSD structures  42  from the first device region  24 , facets  66  remain in the second spacer  64 . The second gate structure  16  and RSD  54  in the second device region  26  are protected by hardmask  58  and so are not affected by the etching of the dummy RSD structures  42  in the first device region  24 . 
         [0038]    Referring now to  FIG. 9 , an in-situ doped RSD  68  is epitaxially grown in the first device region  24 . It should be understood that in-situ doping is optional and the RSD  68  may be doped by other means. The RSD  68  is grown by a non-faceted epitaxial growth process similar to that for RSD  54  so that a planar surface  70  approximately parallel with SOI layer  22  is obtained. While the RSD  68  is grown by a non-faceted epitaxial growth process, the RSD  68  fills the facet  66  in second spacer  64  so that the RSD  68  forms a faceted interface with first gate structure  14  at the corner of the first gate structure  14  and SOI layer  22 . In a preferred embodiment, the in-situ doped RSD  68  may be in-situ phosphorus-doped silicon (ISPD Si), in-situ phosphorus-doped and carbon-doped silicon (ISPD Si:C), in-situ arsenic-doped silicon (ISAD Si) or in-situ phosphorus-doped silicon germanium (ISPD SiGe). The approximate doping of the silicon or silicon germanium may be 1×10 18  to 1×10 22  atoms/cm 3  with 1×10 20  to 7×10 20  atoms/cm 3  being more common. 
         [0039]    The semiconductor structure  10  then may undergo a fast anneal to drive the dopants from the RSD  68  into the SOI layer  22  to form extensions  72  and the dopants from the RSD  54  into the SOI layer  22  to form extensions  74 . The resulting structure is illustrated in  FIG. 10 . In a preferred embodiment, the fast anneal may be a spike anneal in which the semiconductor structure is rapidly heated to a peak temperature of approximately 1000-1100° C. and then immediately cooled after reaching the peak temperature. In addition, the fast anneal may also include rapid thermal anneal (RTA), laser anneal, flash anneal, furnace anneal, or any suitable combination of these techniques. The anneal temperature, depending on the anneal technique, may range from 600 C to 1300 C. 
         [0040]    It should be understood that the fast anneal may be optional in those cases where it is not necessary to drive in the dopants. For example, if the extension is formed by an implant and laser anneal followed by forming of the RSD, a light anneal may just be necessary to link up the RSD with the extension. 
         [0041]    If the first and second gate structures  14 ,  16  cannot tolerate the high temperatures of the fast anneal, then a gate-last process may be needed to replace the first and second gate structures  14 ,  16  (which would be dummy gate structures) after the fast anneal with the real first and second gate structures  14 ,  16 . 
         [0042]    The hardmask  58  shown in  FIG. 9  may be conventionally removed either before or after the fast anneal. Conventional removal of the hardmask  58  may be by any suitable etch. For example, in the case that the hardmask  58  is silicon oxide, it may be removed by an aqueous solution containing hydrofluoric acid. However, the hardmask  58  should be in place during the formation of the in-situ doped RSD  68 . 
         [0043]    The first and second gate structures  14 ,  16  may be the real gate structures which would remain in place during further processing. These first and second gate structures  14 ,  16  may be formed by a gate first process. Alternatively, the first and second gate structures  14 ,  16  shown, for example, in  FIG. 1  may be dummy structures and it may be desirable to replace the dummy first and second gate structures  14 ,  16  with real first and second gate structures  14 ,  16  after formation of the epitaxially formed RSDS  54 ,  68  shown, for example, in  FIG. 10  in a gate last process. 
         [0044]    There are at least two significant advantages to the exemplary embodiments. A first significant advantage is that the RSD that replaces the dummy RSD is grown by a non-faceted epitaxial process and yet a faceted epitaxial RSD is obtained at the corner where the RSD meets the gate structure. Another significant advantage is the first spacer is the same for both the nFET and pFET gate structures so that the replacement RSD is spaced from the channel the same amount for both the nFET and pFET gate structures. 
         [0045]    While not shown, it should be understood that further processing may take place to form contacts in the first and second device regions  24 ,  26  as well as back end of the line processing to form the various layers of metallization so as to complete the formation of the nFET and pFET devices in the semiconductor structure  10 . 
         [0046]    It should be understood further that while the process flow illustrated in the Figures results in the first device region  24  being masked off while the second device region  26  is defined, the process flow may be reversed so that the second device region  26  is masked off while the first device region  24  is defined. 
         [0047]    It will be apparent to those skilled in the art having regard to this disclosure that other modifications of the exemplary embodiments beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.

Technology Category: 5