The present invention provides semiconductor structures and a method of fabricating such structures for application of MOSFET devices. The semiconductor structures are fabricated in such a way so that the layer structure in the regions of the wafer where n-MOSFETs are fabricated is different from the layer structure in regions of the wafers where p-MOSFETs are fabricated. The structures are fabricated by first forming a damaged region with a surface of a Si-containing substrate by ion implanting of a light atom such as He. A strained SiGe alloy is then formed on the Si-containing substrate containing the damaged region. An annealing step is then employed to cause substantial relaxation of the strained SiGe alloy via a defect initiated strain relaxation. Next, a strained semiconductor cap such as strained Si is formed on the relaxed SiGe alloy.

FIELD OF THE INVENTION

The present invention relates to semiconductor structures and to methods of fabricating such structures for application for n- and p-metal oxide semiconductor field effect transistor (MOSFET) devices. More particularly, these semiconductor structures are fabricated in such a way so that the layer structure in the regions of the wafer where n-MOSFETs are fabricated is different from the layer structure in regions of the wafers where p-MOSFETs are fabricated. The present invention is also directed to a method for producing structures for the n-MOSFET including a Si-containing layer under biaxial tensile strain, which is the active region of the n-MOSFET, thus enhancing the device performance compared to a similar n-MOSFET fabricated on a standard bulk Si or Si-on-insulator (SOI) substrate.

BACKGROUND OF THE INVENTION

It is now well established that the performance of n-MOSFETs fabricated in a Si-containing layer under biaxial tensile strain is enhanced compared to that of devices of comparable size fabricated in unstrained Si-containing, e.g., either in bulk Si or in SOI substrates. The magnitude of the n-MOSFET performance enhancement increases with increasing biaxial tensile strain in the Si. This finding is reported, for example, in K. Rim, et al., 2002 Symposium on VLSI Technology Digest of Technical Papers, 98 (2002).

It has also been demonstrated that the performance of p-MOSFETs is degraded compared to that of the same size device fabricated in bulk Si or SOI for values of the biaxial tensile strain less than about 1%. This is illustrated inFIGS. 1A and 1B;FIG. 1Aprovides data for electron mobility, whileFIG. 1Bprovides data for hole mobility.

However, for values of biaxial tensile strain greater than about 1%, the performance of the p-MOSFET is significantly enhanced compared to that of p-MOSFETS of similar size fabricated in an unstrained Si-containing material. Thus, a method to produce a Si-containing material under biaxial tensile strain of less than about 1% only in regions of the wafer where the n-MOSFETs will be fabricated and not in regions of the wafer where the p-MOSFETs will be fabricated is needed.

Several different methods to produce a Si-containing layer under biaxial tensile strain over the entire wafer surface have been implemented. These methods typically employ a strain-relaxed SiGe buffer layer that serves as a “virtual substrate” for the epitaxial growth of a pseudomorphic Si-containing layer under biaxial tensile strain. The degree of biaxial tensile strain in the Si-containing layer is determined by the alloy composition and degree of strain relaxation of the SiGe buffer layer. Because strain relaxation of the SiGe buffer layer typically occurs by the introduction of 60° misfit dislocations, great care must be taken when fabricating the SiGe buffer layer to minimize the threading arms associated with these misfit dislocations. The threading dislocations extend to the wafer surface where the devices are, and thus may degrade device performance.

The most commonly used SiGe virtual substrate consists of a very thick (several μm) SiGe layer in which the alloy composition is increased continuously, or in steps, up to the required value, followed by another very thick (several μm) layer of the desired uniform alloy composition. Such thick graded buffer layers have been shown to have a low density of threading dislocations and are thus potentially suitable for CMOS applications. See, for example, F. K. LeGoues, et al., J. Appl. Phys. 71, 4230 (1992); U.S. Pat. No. 5,659,187 to F. K. LeGoues, et al.; E. A. Fitzgerald, et al., Appl. Phys. Lett. 59, 811 (1991); and G. Kissinger, et al., Appl. Phys. Let. 66, 2083 (1995).

In the ion implantation approach, a thin pseudomorphic or nearly pseudomorphic SiGe layer under biaxial compressive strain is first grown on a Si-containing substrate. He or other atoms are then implanted into this SiGe/Si-containing heterostructure. The implantation energy is chosen so that the projected range of the implanted He lies about 200 nm below the SiGe/Si interface. The wafer is then annealed in a furnace in a He or a N2atmosphere at temperatures above 700° C. for at least 10 minutes. He-induced bubbles or platelets are formed during annealing. These defects are nucleation sources for misfit dislocations that relieve about 70-80% of the compressive strain, depending on the thickness of the SiGe layer. The threading dislocation density in these SiGe buffer layers was found to correlate with the amount of He implanted into the SiGe layer; see J. Cai, et al., J. Appl. Phys. 95, 5347 (2004). For a given He dose, there is a minimum density for thinner SiGe layers and when the implanted atoms are relatively deep, but still close enough to the surface, that the SiGe layer relaxes (seeFIG. 2). The degree of strain relaxation increases with the thickness of the SiGe layer indicating that the SiGe layer should be as thick as possible for each alloy composition.

Little or no strain relaxation occurs in wafers that are not implanted and, which were annealed under the same conditions as the implanted wafers (seeFIGS. 3A and 3B). Finally, the device structure is completed by the epitaxial growth of an additional SiGe layer of the same alloy composition as the relaxed SiGe buffer layer or with the alloy composition chosen so that the in-plane lattice parameter is matched to that of the 70-80% strain-relaxed SiGe layer followed by a thin pseudomorphic Si-containing layer which is under biaxial tensile strain. The thickness of the resulting implanted and annealed SiGe buffer layer may be as little as 10% of the thickness of the graded SiGe buffer layer and has a comparable threading dislocation density and a smoother surface. This prior art method also offers the advantage of lowering the cost of device fabrication.

However, in view of the degraded performance of p-MOSFETs fabricated in Si-containing layers under biaxial tensile strain of <1%, further improvements are needed. Specifically, a new and improved method for fabricating structures including a strain-relaxed SiGe virtual substrate and a Si-containing layer under biaxial tensile strain only in areas of the wafer where the n-MOSFETS are to be fabricated and a different layer structure in areas of the wafers where the p-MOSFETs are to be fabricated is desirable.

SUMMARY OF THE INVENTION

The present invention relates to a method of obtaining a layered structure for application as a “virtual substrate” for strained layered devices such as field effect transistors (FETs) by employing ion implantation of He or other atoms to create defects that serve as dislocation nucleation sources. In order to avoid implanting He or other atoms into a SiGe layer, the inventive method provides a processing sequence in which He or another atom is first implanted into a Si-containing substrate with the implantation energy chosen so that the projected range of the He atoms is typically about 200 nm below the Si-containing substrate surface.

Subsequently, a strictly pseudomorphic or nearly pseudomorphic SiGe alloy layer is grown on the wafer at a temperature low enough that the He or other implanted atoms do not diffuse out from the substrate during the growth of this layer. A growth method known as rapid thermal chemical vapor deposition (RTCVD) in which the growth rate of the SiGe layer is relatively fast compared to other low temperature growth methods such as UHVCVD or MBE is ideal for the inventive process since out-diffusion of He or other implanted atoms is minimized. After the growth of the SiGe layer, the wafer is typically annealed in-situ in the growth chamber. Again the RTCVD method is ideally suited for the inventive process since in this epitaxial growth method the substrates are heated by arc lamps, thus allowing the substrate temperature to be changed very rapidly. After a suitable annealing procedure, which will depend on the implanted atoms, the substrate temperature is reduced to 600° C. and a pseudomorphic Si layer under biaxial tensile strain is grown.

The inventive process has clear advantages over previous methods, including those described in U.S. Pat. No. 6,709,903. For instance, by changing the order of the SiGe layer growth and the implantation of He or other atom species, the number of process steps is reduced from 4 to 2 steps, where a step is defined as the use of a single tool. Furthermore, by doing the growth of the SiGe layer, the annealing and the subsequent semiconductor cap growth sequentially in a single tool, the cleanliness of the substrate surface is maintained and substrate cleaning steps needed after ion implantation and after annealing in a furnace in the previous method can be eliminated.

Thus, the inventive method considerably reduces the cost of fabricating these strained semiconductor substrates. In a first embodiment of the present invention, the entire wafer has the same layered structure. Thus, it is desirable that the biaxial compressive strain in the semiconductor cap be about 1% or greater, in order that the p-MOSFET performance is not degraded.

A further advantage of the inventive process is that in the case of a SiGe layer with low mismatch strain, i.e., less than about 1%, the degradation in p-MOSFET performance can be avoided by implanting He or other atoms only in the regions where the n-MOSFETS will be fabricated. Provided the SiGe layer is thin enough, negligible strain relaxation of the SiGe layer occurs in areas of the wafer that are not implanted. Thus in those areas the in-plane lattice parameter of the semiconductor cap is the same as that of the underlying unstrained Si-containing substrate and p-MOSFETs fabricated in these areas will have the same performance as those fabricated in a bulk Si or SOI substrate. Thus in this second embodiment of the present invention, wherein only areas where n-MOSFET will be fabricated are implanted, the inventive process not only reduces fabrication costs but also produces n-MOSFETs with enhanced performance while avoiding degradation of the p-MOSFETs.

However, it is also known that the performance of p-MOSFETs fabricated in SiGe under biaxial compressive strain is enhanced compared to p-MOSFETs of comparable dimension fabricated in Si. Therefore, in a third embodiment of this invention, the semiconductor cap is removed from the areas of the substrates that were not implanted and the p-MOSFET is fabricated in the compressively strained SiGe layer. Thus, p-MOSFETs with enhanced performance compared to those fabricated in unstrained Si are obtained in addition to n-MOSFETs with enhanced performance fabricated in a semiconducting material under biaxial tensile strain.

In a fourth embodiment of this invention, implantation of He or other atoms is done only in areas of the Si-containing substrate where the n-MOSFETs are to be fabricated and the strictly pseudomorphic or nearly pseudomorphic SiGe layer is grown selectively only in those same areas and not in other areas where the p-MOSFETs or other circuit components are to be fabricated. The embodiments described previously are restricted to SiGe layers that are sufficiently thin that no strain relaxation occurs in areas of the wafer that were not implanted. The fourth embodiment of the present invention permits the use of a thicker SiGe layer to obtain increased strain relaxation of the SiGe and thus a higher degree of biaxial tensile strain in the semiconductor cap. Because the SiGe layer is relatively thin (<0.5 μm), this embodiment of the present invention is not expected to cause serious problems for later device fabrication steps.

It is also proposed that the areas of the substrate to be implanted with He or other atoms may be defined using a mask level that is used for device isolation. A blocking mask can be used to cover the areas of the wafer containing p-MOSFETs or other devices that are not to be implanted. In this way either all or only selected n-MOSFETs will be strained semiconductor devices. This same mask would also be used for the subsequent fabrication steps described above.

In broad terms, the method of the present invention includes the steps of:

forming at least one damaged region within a surface of a Si-containing substrate;

forming a strained SiGe alloy on at least a portion of said surface of said Si-containing substrate;

annealing at a temperature of about 700° C. or above to cause substantial relaxation of the strained SiGe alloy via defect initiated strain relaxation; and

forming a strained semiconductor cap on said strained SiGe alloy that has been substantially relaxed.

In addition to the method described above, the present invention also is related to the semiconductor structure that is formed by the method. In broad terms, the semiconductor structure of the present invention comprises:

a Si-containing substrate having platelets and dislocation loops present therein;

at least one region of substantially relaxed SiGe located on a portion of said Si-containing substrate, said substantially relaxed SiGe is positioned atop said platelets and said dislocation loops; and

at least one region of a strained semiconductor located on said substantially relaxed SiGe.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides virtual substrates and a method of fabricating the same, will now be described in greater detail by referring to the following discussion, which makes reference toFIGS. 4-7. It is noted that the drawings of the present application are provided for illustrative purposes and thus they are not drawn to scale.

FIGS. 4A-4Dare cross sectional views depicting a virtual substrate through various processing steps of a first embodiment of the present invention. In broad terms, the first embodiment includes implanting ions of He or other atoms into a single crystal Si-containing substrate to form a damaged region within the substrate, forming a strained SiGe alloy layer on a surface of the Si-containing substrate, annealing to cause substantial relaxation of the strained SiGe alloy layer and formation of defects such as platelets and dislocation loops within the previous damaged region, and forming a strained semiconductor layer atop of the now substantially relaxed SiGe alloy layer. The first embodiment of the present invention is now described in greater detail.

FIG. 4Aillustrates a structure10that includes a single crystal Si-containing substrate12having a damaged region14located beneath the surface of the Si-containing substrate12. The term “Si-containing” as used throughout the present application denotes any semiconductor material that includes silicon. Illustratively, the Si-containing semiconductor material can comprise Si, SiGe, SiC, SiGeC, a silicon-on-insulator (SOI), a silicon germanium-on-insulator (SGOI) or other like material.

The damaged region14is formed by implanting light atoms, such as helium (He), hydrogen (H), deuterium (D), boron (B), nitrogen (N) or mixtures thereof, into the Si-containing substrate12. In one preferred embodiment, He is implanted into the single crystal Si-containing substrate12. The implanted ions may be implanted to any depth below the upper surface of the Si-containing substrate12. Typically, the ions are implanted from about 90 nm to about 300 nm below the upper surface of the Si-containing substrate12, with a projected range of 200 nm below the upper surface of the Si-containing substrate12being more typical.

Specifically, the damaged region14is formed by implanting at least one of the above mentioned atoms into the Si-containing substrate12at an ion dose from about 5×1015to about 2×1016cm−2. More typically, the ion dose used in creating the damaged region14within the Si-containing substrate12is from about 7×1015to about 1×1016cm−2.

The implanting step used in forming the damaged region14within the Si-containing substrate12may include a single implant step in which one of the above mentioned light atoms is used as the implanting species. It is also contemplated in the present invention to use multiple implant steps. For example, the present invention contemplates a first ion implant step in which a first light atom is implanted into the Si-containing substrate12, followed by a second ion implant step in which a second light atom (that can be the same or different, preferably different, from the first light atom) is implanted into the Si-containing substrate12. In such an embodiment, it is preferred that one of the implants includes at least a He ion implant step. When multiple ion implants are employed, the ions can be implanted to the same depth or at different depths (preferably within the ranges mentioned above) below the surface of the Si-containing substrate12.

In the first embodiment of the present invention, the light atoms are implanted across the entire area, i.e., surface, of the Si-containing substrate12. The ion implant can be performed utilizing standard ion implant tools that are well known to those skilled in the art.

Next, and as shown inFIG. 4B, a strained SiGe alloy layer16is formed atop the surface of the Si-containing substrate12that includes the damaged region14. By ‘strained’, it is meant that the SiGe alloy has a compressive or tensile stress associated therewith. The strained SiGe alloy layer is a nearly pseudomorphic or strictly pseudomorphic Si1−xGexmaterial in which x (the mole fraction of Ge) is uniform and is from about 0.01 to about less than 1, preferably x is from about 0.15 to about 0.40, or a graded composition in which x increases from 0 at the surface of the Si-containing substrate12to higher x values (typically ranging from about 0.01 to less than about 1) at the upper regions of the SiGe alloy layer16.

The strained SiGe alloy16has a thickness that may vary depending upon the composition of the SiGe alloy layer16and the technique that is used in forming the same. Typically, the strained SiGe alloy layer16has a thickness from about 5 to about 500 nm, with a thickness from about 75 to about 250 nm being more typical.

The strained SiGe alloy layer16is formed utilizing any epitaxial growth process which is capable of forming such a layer atop a single crystal Si-containing substrate. Examples of various growth processes that can be used to deposit the strained SiGe alloy layer16atop the single crystal Si-containing substrate12containing the damaged region14include ultra-high vacuum chemical vapor deposition (UHVCVD), rapid thermal chemical vapor deposition (RTCVD), CVD, molecular beam epitaxy, plasma enhanced chemical vapor deposition (PECVD), ion assisted deposition or chemical beam epitaxy. It is preferred, however, to employ RTCVD to grow the strained SiGe alloy layer16on the surface of the Si-containing substrate12that contains the damaged region14. In RTCVD, the growth rate is relatively fast compared to other low temperature (on the order of about 600° C. or less) growth methods thereby minimizing the out-diffusion of the ions from the damaged region14.

The structure shown inFIG. 4Bis then subjected to an annealing step which is capable of substantially relaxing the strained SiGe alloy layer16by way of the formation of platelets and dislocation loops. The resultant structure formed after this annealing step has been performed is shown, for example, inFIG. 4C. In the illustrated structure ofFIG. 4C, reference numeral18denotes the substantially relaxed SiGe alloy layer, reference numeral20denotes platelets or bubbles, and reference numeral22denotes dislocation loops or dislocation half loops. It is noted that the terms “platelets” and “bubbles can be interchangeably used in the present invention, while the terms “dislocation loops” and “dislocation half loops” can be interchangeable used. Specifically, the annealing is performed at a temperature above 700° C. in a non-oxidizing ambient. More typically, the annealing is performed at temperature within a range from about 750° to about 900° C. Various heating schemes including different ramp-up steps, soak cycles and cool down steps can be employed. A single ambient can be used throughout the entire process or different ambients, as desired, can be used during the annealing cycle.

The term “non-oxidizing” as used herein includes any ambient that does not include oxygen or a source of oxygen. Examples of such non-oxidizing ambients include, for instance, He, Ne, Ar, Xe, H2, N2or mixtures thereof.

The anneal can be performed using a furnace anneal, a rapid thermal anneal, a laser anneal, a spike anneal or other related annealing processes that are capable of at least substantially relaxing a strained SiGe alloy layer via platelet and dislocation loop formation (‘via defect initiated strain relaxation’). In one preferred embodiment, the annealing is performed using an arc lamp which allows the wafer temperature to be changed very rapidly. The anneal can be performed in the same reactor chamber that is used to grow layers16and24, or it can be performed in a different reactor chamber than used to form layer16or layer24. In a preferred embodiment, it is preferred that the annealing be preformed in-situ, i.e., in the same reactor chamber that was used to grow layer16and layer24.

As indicated above, the annealing step causes substantial relaxation of the strained SiGe alloy layer. By “substantial relaxation” is meant a measured relaxation value of at least 60% or greater. Preferably, the strained SiGe alloy layer16after annealing has a measured relaxation value of greater than 85%. The resultant substantially relaxed SiGe alloy layer18has a very low number of defects (such as threading defects) present therein. That is, the substantially relaxed SiGe alloy layer18has a defect density of about 5E7 (i.e., 5×107) cm−2or less.

The annealing step, as mentioned above, causes platelets or bubbles20and dislocation loops or dislocation half loops22to form in the previous damaged region14. Specifically, platelets or bubbles20are formed during annealing at a depth from about 100 to about 200 nm below the upper surface of the Si-containing substrate12. The high strain in the region of the platelets or bubbles20results in the nucleation of dislocation half loops (i.e., dislocation loops22) at the platelets or bubbles20. The dislocation loops or half loops22glide to the interface between the substrate12and the strained SiGe alloy layer16where long misfit dislocation segments that relieve the lattice mismatch strain in layer16are formed.

It should be noted that the steps of forming a strained SiGe alloy layer and annealing can be repeated any number of times to provide a multilayered structure.

After annealing, a strained semiconductor cap24is formed atop the structure shown inFIG. 4Cso as to provide the structure shown inFIG. 4D. The strained semiconductor cap24includes any type of semiconducting material such as, for example, Si, SiGe, Ge, SiC, SiGeC or multilayers thereof. Typically, the strained semiconductor cap24is Si.

The strained semiconductor cap24is formed utilizing any of the above mentioned epitaxial growth processes. It should be noted that the growth of layers16and24can occur in the same reactor chamber in which the vacuum is not broken between the deposition of the two layers. Alternatively, layers16and24can be formed in different reactor chambers.

The strained semiconductor cap24can be under either tensile or compressive strain. Typically, and in one embodiment a biaxial tensile strained semiconductor cap24having less than 1% strain is formed. In another embodiment, a biaxial tensile strained material having greater than 1% strain is formed. The thickness of the strained semiconductor cap24formed can vary depending on the type of semiconductor material and method used to deposit the same. Typically, the thickness of the as deposited strained semiconductor cap24is from about 10 to about 40 nm, with a thickness from about 15 to about 30 nm being even more typical.

The resultant structure shown inFIG. 4Dincludes blanket layers of relaxed SiGe alloy layer18and strained semiconductor cap24atop the Si-containing substrate12that includes platelets or bubbles20and dislocation loops or dislocation half loops22.

FIGS. 5A-5Dshow a second embodiment of the present invention in which strained and unstrained areas of a semiconductor cap are formed atop relaxed and strained areas of a SiGe alloy layer. This second embodiment of the present invention is similar to the first embodiment except that the implant of the light atoms into the Si-containing substrate are done selectively to form discrete and isolated damaged regions with the Si-containing substrate.

FIG. 5Aillustrates the structure50that is formed after the selective ion implant step. As shown, discrete and isolated damaged regions14are formed within the Si-containing substrate12. Although two discrete and isolated damaged regions are shown, the present invention works when as little as one, or more than two discrete and isolated damaged regions are formed within the Si-containing substrate12.

Unlike the first embodiment in which a blanket ion implant step was used, the second embodiment implants the light atoms into the Si-containing substrate12utilizing a masked ion implantation process. The mask can be formed atop the Si-containing substrate12prior to implantation by lithography or alternatively a mask above the surface of the Si-containing substrate12can be used during the implant step itself. The type of light atoms and conditions used in the masked ion implantation step are the same as those described above in the first embodiment wherein a maskless, i.e., blanket, ion implant was performed.

Next, and as shown inFIG. 5B, a strained SiGe alloy layer16is formed on the surface of the Si-containing substrate12that includes the discrete and isolated damaged regions14. The formation of the strained SiGe alloy layer16is performed as described above in the first embodiment of the present invention.

The annealing step described above is then performed, and the structure shown inFIG. 5Cis obtained. As shown, during annealing areas of the strained SiGe alloy layer16(above the damaged regions) are substantially relaxed during the annealing, while other areas of the strained SiGe alloy layer (above portions of the substrate not containing any damaged region) remain unchanged after annealing. InFIG. 5C, reference numeral18denotes the substantially relaxed SiGe areas, while reference numeral16denotes the areas of the strained SiGe layer that remain strained after annealing. It is noted that the substantial relaxation of the strained SiGe alloy layer16occurs in regions of the layer that overlay the damaged region14. As was the case in the first embodiment, platelets or bubbles20and dislocation loops or dislocation half loops22form during the anneal in the regions containing the damaged region which, in turn, cause strain relaxation of overlaying areas of the strained SiGe alloy layer16.

Next, a semiconductor cap52is formed atop the structure including the SiGe layer that has substantially relaxed areas18and strained areas16. The semiconductor cap52includes any of the semiconductor materials that where mentioned in connection with cap24of the first embodiment of the present invention. The semiconductor cap52is formed utilizing the same processing as that used to deposit the strained semiconductor layer24. In this embodiment, the areas of the semiconductor cap52that are located above relaxed areas18are strained (labeled as54inFIG. 5D), while the areas of the semiconductor cap52that are located above the strained areas16are unstrained (labeled as56inFIG. 5D).

The third embodiment of the present invention is identical to the second embodiment described above, except that the unstrained areas56are removed from the structure shown inFIG. 5Dutilizing a selective etching process. Specifically, the selective etching process is performed by forming a patterned resist (not shown) atop the strained areas54of semiconductor cap52by deposition and lithography. The patterned resist protects the strained areas54, while leaving the unstrained areas56exposed. The exposed unstrained areas56are then removed by a dry etching process such as reactive ion etching, ion beam etching, plasma etching or laser ablation.FIG. 6shows the structure that is formed after this selective removal process.

A fourth embodiment of the present invention is shown inFIGS. 7A-7D. This embodiment begins by providing the structure50shown inFIG. 7A. As shown, the structure50includes Si-containing substrate12having discrete and isolated damaged regions14located therein. The structure shown inFIG. 7Ais the same as that shown inFIG. 5A; therefore the processing described above in regarding toFIG. 5Ais applicable here for this embodiment of the present invention. Specifically, a masked ion implantation process is used to create the structure50shown inFIG. 7A.

Next, and as shown inFIG. 7B, areas of strained SiGe alloy16are selectively grown atop of the Si-containing substrate12in those regions that lay above the discrete and isolated damaged regions14. The selective growth of strained SiGe alloy16can be achieved by either utilizing the same or different patterned mask as that used in forming the discrete and isolated damaged regions14within Si-containing substrate12. The growth of the SiGe alloy layer is achieved utilizing one of the growth methods mentioned above in which a patterned mask is typically first formed on the surface of the Si-containing substrate12. The patterned mask can be formed prior to or after the ion implant step. Preferably, the patterned mask used to selectively form the areas of strained SiGe alloy16is formed prior to ion implantation.

The structure containing the areas of selectively grown strained SiGe alloy16is then annealed, as described above in the first embodiment of the present invention, providing the structure shown inFIG. 7C. The structure illustrated inFIG. 7C, includes areas of substantially relaxed SiGe18, platelets20and dislocation loops22.

Next, and as shown inFIG. 7D, a strained semiconductor cap, preferably strained Si,24is selectively grown atop the areas of substantially relaxed SiGe alloy18. The strained semiconductor cap24is formed utilizing one of the growth processes described above. A patterned mask can be used prior to the selective growth of the strained semiconductor cap24. The patterned mask can be the same or different patterned mask as used in forming regions14or areas of strained SiGe alloy.

In any of the four embodiments mentioned above, one or more metal oxide semiconductor field effect transistors (MOSFETs) can be formed on the structure after annealing and growth of the semiconductor layer atop the substantially relaxed SiGe alloy. The MOSFETSs are formed utilizing conventional complementary metal oxide semiconductor (CMOS) processing that is well known in the art.

In the first embodiment, the entire structure has the same layered structure. Thus, it is desirable that the biaxial compressive strain in layer24be about 1% or greater, in order that the p-MOSFET performance is not degraded.

In the second embodiment, p-MOSFETs are fabricated atop the unstrained regions56of semiconductor layer52, while n-MOSFETS are fabricating atop the strained regions54of semiconductor layer52.

In the third embodiment of the present invention, p-MOSFETs are fabricated atop the areas of strained SiGe16, while n-MOSFETs are fabricated atop the remaining areas of strained semiconductor54.

In the fourth embodiment, the p-MOSFETs are fabricated on the substrate12, while the n-MOSFETs are fabricated on the strained semiconductor layer24.