Abstract:
A method for forming a semiconductor structure. The method includes providing a semiconductor structure which includes (a) substrate, (b) a first semiconductor region on top of the substrate, wherein the first semiconductor region comprises a first semiconductor material and a second semiconductor material, which is different from the first semiconductor material, and wherein the first semiconductor region has a first crystallographic orientation, and (c) a third semiconductor region on top of the substrate which comprises the first and second semiconductor materials and has a second crystallographic orientation. The method further includes forming a second semiconductor region and a fourth semiconductor region on top of the first and the third semiconductor regions respectively. Both second and fourth semiconductor regions comprise the first and second semiconductor materials. The second semiconductor region has the first crystallographic orientation, whereas the fourth semiconductor region has the second crystallographic orientation.

Description:
[0001]    This application is a divisional application claiming priority to Ser. No. 11/419,308, filed May 19, 2006. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to semiconductor substrates and devices, and more specifically, to Hybrid Strained Orientated Substrates and Devices. 
         [0004]    2. Related Art 
         [0005]    In a typical semiconductor fabrication process, the P-channel transistors are preferably formed on ( 110 ) crystallographic oriented, compressively strained semiconductor region of a substrate, whereas the N-channel transistors are preferably formed on ( 100 ) crystallographic oriented, tensily strained semiconductor regions of the same substrate to optimize the operation of transistors. Therefore, there is a need for a method of forming a substrate that has both ( 110 ) crystallographic oriented, compressively strained and ( 100 ) crystallographic oriented, tensily strained semiconductor regions. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention provides a semiconductor structure fabrication method, comprising providing a semiconductor structure which includes (a) a substrate, (b) a first semiconductor region on top of the substrate, wherein the first semiconductor region comprises a first semiconductor material and a second semiconductor material, which is different from the first semiconductor material, and wherein the first semiconductor region has a first crystallographic orientation, and (c) a third semiconductor region on top of the substrate, wherein the third semiconductor region comprises the first and the second semiconductor materials, and wherein the third semiconductor region has a second crystallographic orientation; and forming a second semiconductor region and a fourth semiconductor region on top of the first and the third semiconductor regions respectively, wherein the second semiconductor region comprises the first and the second semiconductor materials, wherein the second semiconductor region has the first crystallographic orientation, wherein the fourth semiconductor region comprises the first and the second semiconductor materials, and wherein the fourth semiconductor region has the second crystallographic orientation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIGS. 1-15  show cross-section views of a semiconductor device structure going through a fabrication process, in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0008]      FIGS. 1-15  show cross-section views of a semiconductor device structure  100  going through a fabrication process, in accordance with embodiments of the present invention. More specifically, with reference to  FIG. 1 , in one embodiment, the fabrication process of the structure  100  starts with a semiconductor substrate  110 . Illustratively, the semiconductor substrate  110  comprises a mixture of silicon and germanium and has a crystallographic orientation of ( 100 ). It should be noted that the phrase “Si(1−x)Ge(x)” in  FIG. 1  indicates the ratio between the number of silicon atoms and the number of germanium atoms in the mixture is (1−x)/x, wherein the value of x is between 0 and 1. In an alternative embodiment, the semiconductor substrate  110  comprises only germanium. 
         [0009]    Next, in one embodiment, an insulating layer  120  such as a BOX (Buried oxide) layer is formed on top of the semiconductor substrate  110 . Illustratively, the BOX layer  120  comprises silicon dioxide (SiO2). In one embodiment, the BOX layer  120  can be formed by thermal oxidation. In an alternative embodiment, the insulating layer  120  is omitted. 
         [0010]    Next, with reference to  FIG. 2 , in one embodiment, an implanted hydrogen ion layer  210  is formed in the substrate  110 . Illustratively, the implanted hydrogen ion layer  210  is formed by ion implantation of hydrogen ions. It should be noted that, the implanted hydrogen ion layer  210  divides the semiconductor substrate  110  into two semiconductor layers  112  and  114 . In one embodiment, the thickness  112   a  of the semiconductor layer  112  is very thin and controlled. 
         [0011]    Next, in one embodiment, with reference to  FIG. 3 , a semiconductor layer  310  is bonded on top of the BOX layer  120  resulting in the structure  100  of  FIG. 3 . In an alternative embodiment, no insulating layer  120  is formed on top of the semiconductor substrate  110  and the semiconductor layer  310  is directly bonded on top of the semiconductor layer  110 . Illustratively, the layer  310  comprises silicon and has a crystallographic orientation of ( 110 ). 
         [0012]    Next, in one embodiment, the structure  100  of  FIG. 3  can be annealed so that the structure  100  of  FIG. 3  splits along the hydrogen ion layer  210 . The upper portion of the structure  100  of  FIG. 3  after the split, illustratively, is turned upside down resulting in the structure  100  of  FIG. 4 . 
         [0013]    Next, with reference to  FIG. 5 , in one embodiment, a pad layer  510  is formed on top of the semiconductor layer  112 . Illustratively, the pad layer  510  comprises a silicon nitride layer and an optional underlying oxide layer. The silicon nitride layer can be formed by CVD (Chemical vapor deposition) and the underlying oxide layer may be formed by thermal oxidation or by CVD. Next, in one embodiment, the pad layer  510  is patterned resulting in the structure  100  of  FIG. 5A . Illustratively, the patterning of the pad layer  510  involves a lithographic process and one or multiple etching process. 
         [0014]    Next, with reference to  FIG. 5A , in one embodiment, the patterned pad layer  510  is used as a mask for selectively etching the semiconductor layer  112 , the BOX layer  120 , and the semiconductor layer  310  resulting in the structure  100  of  FIG. 6 . Illustratively, the etching of the semiconductor layer  112 , the BOX layer  120  and the semiconductor layer  310  involves a conventional etching process. Alternatively, the pad layer  510 , the semiconductor layer  112 , the BOX layer  120 , and the semiconductor layer  310  are patterned by using photoresist (not shown) as a mask, resulting in the same structure  100  shown in  FIG. 6 . 
         [0015]    Next, in one embodiment, with reference to  FIG. 7 , a spacer  710  is formed on the side wall  712  of structure  100 . Illustratively, the spacer  710  comprises silicon oxide or silicon nitride. In one embodiment, the spacer  710  is formed by (i) depositing a spacer layer (not shown) on top of the structure  100  of  FIG. 6  by CVD and then (ii) directionally etching the deposited spacer layer resulting in structure  100  of  FIG. 7 . 
         [0016]    Next, in one embodiment, with reference to  FIG. 8A , a semiconductor region  810  is formed on the surface  612  of the structure  100 . Illustratively, the semiconductor region  810  comprises a mixture of silicon and germanium and has a crystallographic orientation of ( 110 ). It should be noted that the phrase “Si(1−z)Ge(z)” in  FIG. 8A  indicates the ratio between the number of silicon atoms and the number of germanium atoms in the mixture is (1−z)/z, wherein the value of z is between 0 and 1. In one embodiment, z is smaller than x (i.e., z&lt;x), i.e., the concentration of germanium in the semiconductor region  810  is less than the germanium concentration in the semiconductor layer  112 . Illustratively, the semiconductor region  810  is formed by epitaxial growth. In one embodiment, the epitaxial growth is performed until the top surface  812  of the semiconductor region  810  is at a higher level than the top surface  512  of the nitride layer  510 . 
         [0017]    Next, in one embodiment, the semiconductor region  810  is recessed until the top surface  812  of the semiconductor region  810  is coplanar with top surface  112 ′ of the semiconductor layer  112  resulting in the structure  100  of  FIG. 8B . In one embodiment, the semiconductor region  810  is recessed by a reactive ion etching (RIE) process. In an alternative embodiment, the semiconductor region  810  is recessed by oxidizing the excessive semiconductor in region  810  and then selectively removing the formed oxide. Optionally, a planarization process such as CMP (chemical mechanical polishing) can be performed before the recess process. It should be noted that what remains of the semiconductor region  810  ( FIG. 8A ) after the recessing can be referred to as a semiconductor region  810   a  ( FIG. 8B ). 
         [0018]    Next, in one embodiment, the structure  100  of  FIG. 8B  is subjected to an etch process such as a wet etching process or a plasma etching process, which strips off the patterned pad layer  510  and a top portion of the spacer  710  to expose the top surface  112 ′ of the semiconductor layer  112  to the surrounding ambient resulting in the structure  100  of  FIG. 9 . It should be noted that what remains of the spacer  710  after the etching can be referred to as a spacer  710   a.    
         [0019]    Next, with reference to  FIG. 10 , in one embodiment, a hard mask layer  1010  is formed on top of the structure  100  of  FIG. 9 . Illustratively, the hard mask layer  1010  comprises a silicon nitride layer and an optional underlying silicon oxide layer. In one embodiment, the hard mask layer  1010  is formed on top of the structure  100  of  FIG. 9  by thermal oxidation followed by CVD of silicon nitride. 
         [0020]    Next, in one embodiment, with reference to  FIG. 11 , a trench  1110  is formed in the structure  100 . The trench  1110  is created at the location where the nitride spacer  710   a  of  FIG. 10  was. In one embodiment, the trench  1110  is formed by a conventional lithographic and etching process. 
         [0021]    Next, in one embodiment, with reference to  FIG. 12 , a shallow trench isolation (STI) region  1210  is formed in the trench  1110  of  FIG. 11 . Illustratively, the shallow trench isolation (STI) region  1210  comprises silicon dioxide. In one embodiment, the STI region  1210  is formed by filling the trench  1110  in  FIG. 11  with silicon dioxide followed by a planarization process such as CMP. 
         [0022]    Next, in one embodiment, the hard mask layer  1010  is removed resulting in the structure  100  of  FIG. 13 . Illustratively, the hard mask layer  1010  is removed by wet etching. 
         [0023]    Next, in one embodiment, with reference to  FIG. 14 , two semiconductor layers  1410  and  1420  are grown simultaneously on top of semiconductor layers  112  and  810   a , respectively. Illustratively, the semiconductor layers  1410  and  1420  comprise a mixture of silicon and germanium. It should be noted that the phrase “Si(1−y)Ge(y)” in  FIG. 14  indicates the ratio between the number of silicon atoms and the number of germanium atoms in the mixture is (1−y)/y, wherein the value of y is between 0 and 1. In one embodiment, the value of y is between the values of x and z (i.e., x&gt;y&gt;z). Illustratively, the semiconductor layers  1410  and  1420  are formed by epitaxial growth followed by CMP. Because the semiconductor layer  1410  is grown on the semiconductor layer  112 ; as a result, the crystallographic orientation of semiconductor layer  1410  is the same as the crystallographic orientation of the semiconductor layer  112  (i.e., ( 100 )). Similarly, the semiconductor layer  1420  is grown on the semiconductor layer  810   a ; as a result, the crystallographic orientation of semiconductor layer  1420  is the same as the crystallographic orientation of the semiconductor layer  810   a  (i.e., ( 110 )). It should be noted that the percentage of germanium atoms in the mixture in the semiconductor layer  1410  is less than that in the semiconductor layer  112  (i.e., y&lt;x); as a result, the semiconductor layer  1410  is tensily strained. On the other hand, the percentage of germanium atoms in the mixture in the semiconductor layer  1420  is more than that in the semiconductor layer  810   a  (i.e., y&gt;z); as a result, the semiconductor layer  1420  is compressively strained. 
         [0024]    Next, in one embodiment, with reference to  FIG. 15 , an N-channel transistor  1590   a  and a P-channel transistor  1590   b  are formed on the semiconductor layers  1410  and  1420  respectively. Illustratively, the N-channel transistor  1590   a  comprises a gate electrode  1510   a , a gate dielectric layer  1530   a , two source/drain regions  1410   a   1  and  1410   a   2 . In one embodiment, the N-channel transistor  1590   a  is formed by a conventional method. Similarly, the P-channel transistor  1590   b  comprises a gate electrode  1510   b , a gate dielectric layer  1530   b , two source/drain regions  1410   b   1  and  1410   b   2 . Illustratively, the P-channel transistor  1590   b  is formed by a conventional method. It should be noted that, the N-channel transistor  1590   a  is formed on ( 100 ), tensily strained semiconductor material; as a result, the operation of N-channel transistor  1590   a  is optimized. Similarly, the P-channel transistor  1590   b  is formed on ( 110 ), compressively strained semiconductor material; as a result, the operation of P-channel transistor  1590   b  is optimized. In one embodiment, the P-channel transistor  1590   b  and the N-channel transistor  1590   a  are electrically connected to form a CMOS device. 
         [0025]    In the embodiments described above, the regions  112 ,  810   a ,  1410 , and  1420  comprise a mixture of silicon and germanium. Alternatively, the regions  112 ,  810   a ,  1410 , and  1420  can comprise a mixture of silicon and carbon. In this case, the crystallographic orientation of the regions  310 ,  112 ,  810   a ,  1410 , and  1420  should be swapped. More specifically, with reference to  FIG. 14 , the crystallographic orientation of the semiconductor layers  310 ,  810   a  and  1420  is ( 100 ), whereas the crystallographic orientation of the semiconductor layers  112  and  1410  is ( 110 ). In this case, the ratio between the number of silicon atoms and the number of carbon atoms in the mixture of  112  is (1−x)/x; the ratio between the number of silicon atoms and the number of carbon atoms in the mixture of  810   a  is (1−z)/z; and the ratio between the number of silicon atoms and the number of carbon atoms in the mixture of  1410  and  1420  is (1−y)/y, wherein x&gt;y&gt;z. 
         [0026]    While particular embodiments of the present invention have been described herein for purposes of illustration, many modifications and changes will become apparent to those skilled in the art. Accordingly, the appended claims are intended to encompass all such modifications and changes as fall within the true spirit and scope of this invention.