Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-09-09
2004-03-02
Nguyen, Thanh (Department: 2813)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S482000, C438S520000, C438S602000, C438S933000
Reexamination Certificate
active
06699764
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to devices for high speed CMOS integrated circuits, and specifically to commercial production of VLSI ICs having Si
1−x
Ge
x
layers by providing a layer of tensile strained silicon on a relaxed Si
1−x
Ge
x
layer to speed switching speeds for nMOS and pMOS transistors.
BACKGROUND OF THE INVENTION
There are many publications describing a thick layer of Si
1−x
Ge
x
with graded Ge composition (x) followed by a thick, relaxed Si
1−x
Ge
x
layer of constant x capped by a thin silicon film under tensile strain, which is used for fabricating high drain drive current MOS transistors. Due to the lattice parameter mismatch between the Si
1−x
Ge
x
layers and the silicon substrate, there is a high density of misfit dislocations at the SiGe/Si substrate interface, accompanied by numerous threading dislocations in the SiGe, some of which propagate all the way to the surface. The total SiGe thickness is on the order of several microns and the density of threading dislocations at the surface is still on the order of 1×10
5
cm
−2
. However, the very thick Si
1−x
Ge
x
layer and the high defect density of the conventional Si
1−x
Ge
x
process is not applicable for large-scale integrated circuit fabrication.
As demonstrated in S. Mantl et al.,
Strain relaxation of epitaxial SiGe layer on silicon
(100)
improved by hydrogen implantation,
Nuclear Instruments and Methods in Physics Research B vol. 147, 29 (1999), and expanded upon in the above-identified related Applications 1 and 2, strain relaxed high quality Si
1−x
Ge
x
layers on silicon can be obtained by hydrogen ion implantation and annealing. Hydrogen ion implantation forms a narrow defect band slightly below the SiGe/Si interface. During subsequent annealing hydrogen platelets and cavities form, nucleating misfit dislocations, and giving rise to strong enhanced strain relaxation in the Si
1−x
Ge
x
epilayer. Hydrogen ions may also terminate some threading dislocations, preventing them from propagating toward the Si
1−x
Ge
x
surface. The related Applications 1 and 2 provide methods to reduce defect density and fabricate high drive current MOS transistors on a relaxed Si
1−x
Ge
x
film having thickness on the order of about only 300 nm. However, the defect density of the Si
1−x
Ge
x
film by these processes is still not suitable to very large-scale integrated circuit fabrication.
Related Application 3 discloses a method to further reduce the defect density in Si
1−x
Ge
x
films. In this related method, a buried amorphous region in the film is fabricated, e.g., with Si
+
ion implantation, and then recrystallized through solid phase epitaxy (SPE) using as the seed the undamaged crystalline Si
1−x
Ge
x
region at the surface. However, the process window for making a buried amorphous region in SiGe may be rather narrow, because it has been consistently reported that SiGe is much more easily damaged by Si
+
ion implantation than silicon, A. N. Larsen et al.,
MeV ion implantation induced damage in relaxed Si
1−x
Ge
x
, J. Appl. Phys., vol. 81, 2208 (1997); T. E. Haynes, et al.,
Damage accumulation during ion implantation of unstrained Si
1−x
Ge
x
alloy layers,
Appl. Phys. Lett., vol. 61, 61 (1992); and D. Y. C. Lie, et al.,
Damage and strain in epitaxial Ge
x
Si
1−x
films irradiated with Si,
J. Appl. Phys. Vol. 74, 6039 (1993). The critical dose for amorphization, (&phgr;
c
), decreases with increasing Ge concentration. This holds true for both strained and relaxed SiGe. For 2 MeV Si
+
ions implanted at 27° C., &phgr;
c
=6.7e14 cm
−2
for 20% Ge but only 4.6e14 cm
−2
for 30% Ge, per Larsen et al. For 100 keV Si
+
ions implanted at room temperature, it has been reported that &phgr;
c
=7e14 cm
−2
and 2.5e14 cm
−2
for pure silicon and 10% Ge, respectively, Lie et al. For 80-90 keV Si
+
ions implanted at 77K, it has been reported that &phgr;
c
=1.5, 1.0, 0.8, and 0.5 e14 cm
−2
for 0%, 15%, 50%, and 100% Ge, respectively, Haynes et al. This effect is thought to be due to both an increase in the average energy density per ion deposited in the collision cascade and a stabilization of the damage through a reduction of defect mobility, Haynes et al. and Lie et al. There is also a strong dependence on the wafer temperature during implant, T
1
, with the damage decreasing at higher
T1
, so &phgr;
c
will depend on temperature, Haynes et al.
A substrate having a Si
1−x
Ge
x
layer with graded composition is often used for growing tensile-strained silicon films, wherein the highest Ge concentration is located at the surface, as described in related Application 1. In this case, it may be even more difficult to avoid damaging or amorphizing the surface layer, because the higher Ge content makes the surface more susceptible to damage. If so, there will be no crystalline seed at the surface to nucleate SPE, and SPE will proceed only from the bottom, usually resulting in a heavily defected film. The instant invention is a method for preserving the crystallinity of the surface layer, in order to use it as a seed for SPE of the underlying amorphized Si
1−x
Ge
x
film.
SUMMARY OF THE INVENTION
A method of fabricating a Si
1−X
Ge
X
film on a silicon substrate includes preparing a silicon substrate; epitaxially depositing a Si
1−X
Ge
X
layer on the silicon substrate forming a Si
1−X
Ge
X
/Si interface there between; epitaxially growing a silicon cap on the Si
1−X
Ge
X
layer; implanting hydrogen ions through the Si
1−X
Ge
X
layer to a depth of between about 3 nm to 100 nm below the Si
1−x
Ge
x
/Si interface; amorphizing the Si
1−X
Ge
X
layer to form an amorphous, graded SiGe layer; and annealing the structure at a temperature of between about 650° C. to 1100° C. for between about ten seconds and sixty minutes to recrystallize the SiGe layer.
It is an object of the invention to provide a method to produce low defect density, 200 nm to 500 nm thick relaxed Si
1−x
Ge
x
films with Ge content of up to 50% or more at the top surface for large-scale integrated circuit application.
Another object of the invention is to provide a method of commercial production of VLSI ICs having Si
1−x
Ge
x
layers.
A further object of the invention is to provide a strained silicon layer on a relaxed Si
1−x
Ge
x
layer.
Another object of the invention is to provide Si/Si
1−x
Ge
x
structure which will speed up the switching speed of nMOS and pMOS transistors.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.
REFERENCES:
patent: 6455871 (2002-09-01), Shim et al.
patent: 6464780 (2002-10-01), Mantl et al.
S. Mantl et al.,Strain relaxation of epitaxial SiGe layer on silicon(100)improved by hydrogen implantation, Nuclear Instruments and Methods in Physics Research B vol. 147, 29 (1999).
A.N. Larsen et al.,MeV ion implantation induced damage in relaxed in Si1-xGex, J. Appl. Phys., vol. 81, 2208 (1997).
T.E. Haynes, et al.,Damage accumulation during ion implantation of unstrained Si1-xGexalloy layers, Appl. Phys. Lett., vol. 61, 61 (1992).
D.Y.C. Lie, et al.,Damage and strain in epitaxial GexSi1-xfilms irradiated with Si,J. Appl. Phys. vol. 74, 6039 (1993).
D.C. Paine, et al.,The growth of strained Si1-xGexalloys on(001)sillicon using solid phase epitaxy, J. Mater. Res., vol. 5, 1023 (1990).
C. Lee, et al.,Kinetics of solid phase eptiaxial regrowth in amorphized Si0.88Ge0.12measured by time-resolved reflectivity, Appl. Phys. Lett., vol. 62, 501 (1993).
Q.Z. Hong, et al.,Solid phase epitaxy of stressed and stress-relaxed Ge-Si alloys, J. Appl. Phys. vol. 71, 1768 (1992).
Hsu Sheng Teng
Lee Jong-Jan
Maa Jer-shen
Tweet Douglas J.
Krieger Scott C.
Nguyen Thanh
Rabdau Matthew D.
Ripma David C.
Sharp Laboratories of America Inc.
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