# Patent

## Title
Structure of strained silicon on insulator and method of manufacturing the same

## Abstract

Provided is a strained SOI structure and a method of manufacturing the strained SOI structure. The strained SOI structure includes an insulating substrate, a SiO2 layer formed on the insulating substrate, and a strained silicon layer formed on the SiO2 layer.

## Background
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS
Priority is claimed to Korean Patent Application No. 10-2004-00103111, filed on Dec. 8, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a strained silicon on insulator (strained SOI) structure and a method of manufacturing the same, and more particularly, to a strained SOI structure having a small parasitic capacitance and high carrier mobility and a method of manufacturing the same.
2. Description of the Related Art
A strained silicon CMOS is a CMOS device that includes a thin, strained silicon layer on a relaxed SiGe layer. The mobility of electrons and holes within the strained silicon layer is known to be much higher than with a bulk silicon layer, and devices manufactured using a MOFET having a strained silicon channel have improved device performances compared to devices manufactured using a conventional (unstrained silicon) silicon substrate. The potential performance improvement of devices increases device driving current and mutual conductance and reduces power consumption.
The formation of the strained silicon layer is the result of tensile strain occurs on silicon grown on a substrate formed of a material having a greater lattice constant than the lattice constant of the silicon. The lattice constant of germanium Ge is approximately 4.2 which is greater than the lattice constant of silicon, and the lattice constant of silicon-germanium SiGe is linear to the concentration of germanium Ge. That is, the lattice constant of SiGe that contains 50% Ge is 1.02 times greater than the lattice constant of silicon. The epitaxial growth of silicon on a SiGe substrate generates the tensile strain of a silicon layer, and the SiGe substrate underneath the silicon layer is in a non-strained or relaxed state.
A method of forming a CMOS device having a strained silicon channel on a SiGe layer formed on an insulating substrate is disclosed in U.S. Pat. No. 6,059,895.
The difficulty in implementing the advantages of the strained silicon CMOS technique is the presence of a relaxed SiGe layer underneath the strained silicon layer. The SiGe layer interacts with the strained silicon layer in the processes of thermal oxidation, forming silicide, and annealing. Therefore, the improvement of device performance and a device yield that can be achieved may be limited during manufacturing a CMOS due to the difficulty of maintaining an integrity of material. Another disadvantage is that the thickness of the SiGe layer is added to the total thickness of a MOSFET main body. The addition of a thickness to the MOSFET is especially undesirable to the SOIFET structure since the additional thickness affects adversely to the super slim SOI device in which a MOSFET structure having a very thin channel is included.
SUMMARY OF THE INVENTION
The present invention provides a strained silicon on insulator (strained SOI) structure having a small parasitic capacitance and high carrier mobility and a method of manufacturing the same.
According to an aspect of the present invention, there is provided a strained SOI structure comprising: an insulating substrate; a SiO2 layer formed on the insulating substrate; and a strained silicon layer formed on the SiO2 layer.
The strained SOI structure can further comprise a bonding layer between the insulating substrate and the SiO2 layer, and the bonding layer can be formed one of SiO2 and polycrystalline silicon.
The insulating substrate can be a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed. The strained SOI structure can further comprise a protective layer that surrounds the insulating substrate and the protective layer can be formed of AIN.
According to another aspect of the present invention, there is provided a method of manufacturing a strained SOI structure, comprising: preparing a Si substrate and an insulating substrate; forming a porous silicon layer by anodizing a predetermined thickness of the Si substrate; forming a SiGe layer on the porous silicon layer; forming a strained silicon layer on the SiGe layer; forming a SiO2 layer on the strained silicon layer; activating a surface of the SiO2 layer by treating the surface of the SiO2 layer using oxygen O2 plasma; bonding the insulating substrate on the activated SiO2 layer; removing the SiGe layer by selectively etching after reversing the stacked structure so that the insulating substrate is placed on a lower position; and separating the porous silicon layer and the Si substrate from the strained silicon layer.
According to another aspect of the present invention, there is provided a method of manufacturing a strained SOI structure, comprising: preparing a Si substrate and an insulating substrate; forming a SiGe layer on the Si substrate; forming a porous SiGe layer by anodizing a predetermined thickness of the SiGe layer; forming a strained silicon layer on the porous SiGe layer; forming a SiO2 layer on the strained silicon layer; activating a surface of the SiO2 layer by treating the surface of the SiO2 layer using oxygen O2 plasma; bonding the insulating substrate on the activated SiO2 layer; removing the porous SiGe layer by selectively etching after reversing the stacked structure so that the insulating substrate is placed on a lower position; and separating the Si substrate from the strained silicon layer.
The insulating substrate can be a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed.
The preparing of the insulating substrate can include preparing an insulating substrate and forming a protective layer on a surface of the insulating substrate. Here, the protective layer is formed of AIN.
The preparing of the insulating substrate can include preparing an insulating substrate, forming a protective layer on a surface of the insulating substrate, and forming a bonding layer on the protective layer. Here, the bonding layer can be formed one of SiO2 and polycrystalline silicon.
According to another aspect of the present invention, there is provided a method of manufacturing a strained SOI structure, comprising: preparing a Si substrate and an insulating substrate; forming a SiO2 layer on the Si substrate; forming at least two SiO2 barrier ribs spaced a predetermined distance from each other by patterning the SiO2 layer; forming a SiGe layer on the Si substrate between the two barrier ribs; forming a strained silicon layer on the SiGe layer; removing the SiO2 barrier ribs; bonding the insulating substrate on the strained silicon layer; removing the SiGe layer by selectively etching after reversing the stacked structure so that the insulating substrate is placed on a lower position; and separating the Si substrate from the strained silicon layer.
The insulating substrate can be a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed.
The preparing of the insulating substrate can include preparing an insulating substrate and forming a protective layer on a surface of the insulating substrate. Here, the protective layer is formed of AIN.
The preparing of the insulating substrate can include preparing an insulating substrate, forming a protective layer on a surface of the insulating substrate, and forming a bonding layer on the protective layer.
Here, the bonding of the insulating substrate on the strained silicon layer can includes activating a surface of the bonding layer by treating using oxygen O2 plasma and bonding the insulating substrate on the strained silicon layer. The bonding layer can be formed one of SiO2 and polycrystalline silicon.



BRIEF DESCRIPTION OF THE DRAWINGS
The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:
FIG. 1 is a cross-sectional view of a strained SOI structure according to an embodiment of the present invention;
FIGS. 2A through 2L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a first embodiment of the present invention;
FIGS. 3A through 3L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a second embodiment of the present invention; and
FIGS. 4A through 4L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a third embodiment of the present invention.



DETAILED DESCRIPTION OF THE INVENTION
A strained SOI structure and a method of manufacturing the strained SOI structure will now be described more fully with reference to the accompanying drawings in which exemplary embodiments of the invention are shown.
FIG. 1 is a cross-sectional view of a strained SOI structure according to an embodiment of the present invention.
Referring to FIG. 1, a protective layer 12 that surround an insulating substrate 10, a bonding layer 14 formed on the protective layer 12, a SiO2 layer 28, and a strained silicon layer 26 are sequentially formed on the insulating substrate 10. The protective layer 12 and the bonding layer 14 are not requisite layers.
The insulating substrate 10 is a substrate selected from the group consisting of a glass substrate, a plastic substrate, and an oxide layer. Also, the protective layer 12 is formed of a material having characteristics of insulating, transparent, and resisting to an etchant, such as AIN. The bonding layer 14 is formed of SiO2 or polycrystalline silicon.
A strained SOI structure formed on the insulating substrate 10 has high performance, small parasitic capacitance, and high carrier mobility. Especially, the strained SOI structure can be applied to a front panel or a rear panel of a display panel by using a plastic substrate or a glass substrate as the insulating substrate 10.
FIGS. 2A through 2L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a first embodiment of the present invention. Here, like reference numerals refer to like elements throughout the drawings. The formation of material layers during the processes is formed using a well known thin film deposition apparatus such as ultra high vacuum chemical vapor deposition (UHV-CVD) or low pressure chemical vapor deposition (LPCVD).
Referring to FIGS. 2A through 2C, a protective layer 12 is formed on a surface of an insulating substrate 10. The protective layer 12 is formed of a material having characteristics of insulating, transparent, and resistance to an etchant, such as AIN. Next, a bonding layer 14 formed of a material, such as SiO2 or polycrystalline silicon, is formed on the protective layer 12. Here, the protective layer 12 and the bonding layer 14 are not requisite layers.
Referring to FIGS. 2D through 2H, after preparing a Si substrate 20, a porous silicon layer 22 is formed by anodizing a predetermined thickness of the Si substrate 20. To form the porous silicon layer 22, a predetermined thickness of the Si substrate 20 is anodized electrochemically in a mixed solution of fluoride hydrogen HF and ethanol.
Afterward, a SiGe layer 24, a strained silicon layer 26, and a SiO2 layer 28 are sequentially formed on the porous silicon layer 22. Here, the SiGe layer 24 has a relaxed structure. Accordingly, the strained silicon layer 26 can be formed on the SiGe layer 24.
Referring to FIGS. 2I through 2L, a surface of the SiO2 layer 28 is activated by treating the surface using oxygen O2 plasma. Next, the prepared insulating substrate 10 is bonded on the activated SiO2 layer 28. Here, a surface of the bonding layer 14 formed on the insulating substrate 10 can be activated by treating the surface using oxygen O2 plasma prior to bond the insulating substrate 10.
Next, the stacked structure is reversed so that the insulating substrate 10 can be placed in a lower position. Next, the SiGe layer 24 is removed by selective etching. Here, an etchant for selectively etching the SiGe layer 24 is a mixed solution of 50% HF:60% HNO3:H2O=1:90 ̃120:60. Other etchants that can selectively etch the SiGe layer 24 can also be used. Here, the echant readily reacts with the SiGe layer 24 not only on both side surfaces but also through the porous silicon layer 22 by being absorbed by the porous silicon layer 22.
The porous silicon layer 22 and the Si substrate 20 formed on the SiGe layer 24 can be separated from the strained silicon layer 26 by selectively removing the SiGe layer 24. As a result, as depicted in FIG. 2L, a strained SOI structure formed on the insulating substrate 10 can be obtained.
FIGS. 3A through 3L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a second embodiment of the present invention. Here, like reference numerals refer to like elements throughout the drawings. The formation of material layers during the processes is formed using a well known thin film deposition apparatus such as UHV-CVD or LPCVD.
Referring FIGS. 3A through 3C, after preparing an insulating substrate 10, a protective layer 12 is formed on the insulating substrate 10. The protective layer 12 is formed of a material having characteristics of insulating, transparent, and resistance to an etchant such as AIN. A bonding layer 14 formed of SiO2 or polycrystalline silicon is formed on the protective layer 12. The protective layer 12 and the bonding layer 14 are not requisite.
Referring to FIGS. 3D through 3H, after preparing the Si substrate 20, a SiGe layer 24 having a predetermined thickness is formed on the Si substrate 20. Here, the SiGe layer 24 has a relaxed structure. Next, a porous SiGe layer 25 is formed by anodizing the SiGe layer 24. To form the porous SiGe layer 25, a predetermined thickness of the porous SiGe layer 25 is anodized electrochemically in a mixed solution of fluoride hydrogen HF and ethanol.
Next, the strained silicon layer 26 and the SiO2 layer 28 are sequentially formed on the porous SiGe layer 25.
Referring to FIGS. 3I through 3L, a surface of the SiO2 layer 28 is activated by treating the surface using oxygen O2 plasma. Next, the prepared insulating substrate 10 is bonded on the activated SiO2 layer 28. Here, a surface of the bonding layer 14 formed on the insulating substrate 10 can be activated by treating the surface using oxygen O2 plasma prior to bond the insulating substrate 10.
Next, the stacked structure is reversed so that the insulating substrate 10 can be placed in a lower position. Next, the porous SiGe layer 25 is removed by selective etching. Here, an etchant for selectively etching the porous SiGe layer 25 is a mixed solution of 50% HF:60% HNO3:H2O=1:90 ̃120:60. Other etchants that can selectively etch the porous SiGe layer 25 can also be used. Here, the etchant readily reacts with the porous SiGe layer 25 by being absorbed by the porous SiGe layer 25.
The Si substrate 20 formed on the porous SiGe layer 25 can be separated from the strained silicon layer 26 by selectively removing the porous SiGe layer 25. As a result, as depicted in FIG. 3L, a strained SOI structure formed on the insulating substrate 10 can be obtained.
FIGS. 4A through 4L are cross-sectional views illustrating a method of manufacturing a strained SOI structure according to a third embodiment of the present invention. Here, like reference numerals refer to like elements throughout the drawings. The formation of material layers during the processes is formed using a well known thin film deposition apparatus such as UHV-CVD or LPCVD.
Referring to FIGS. 4A through 4C, after preparing the insulating substrate 10, the protective layer 12 is formed on the insulating substrate 10. The protective layer 12 is formed of a material having characteristics of insulating, transparent, and resistance to an etchant, such as AIN. The bonding layer 14 formed of SiO2 or polycrystalline silicon is formed on the protective layer 12. The protective layer 12 and the bonding layer 14 are not requisite.
Referring to FIGS. 4D through 4H, after preparing the Si substrate 20, a SiO2 layer 21 having a predetermined thickness is formed on the Si substrate 20. At least two SiO2 barrier ribs 23 spaced a predetermined distance from each other are formed by patterning the SiO2 layer 21. A SiGe layer 24 and a strained silicon layer 26 are sequentially formed on the Si substrate 20 between the two SiO2 barrier ribs 23. Here, the SiGe layer 24 has a relaxed structure. Accordingly, the strained silicon layer 26 can be formed on the SiGe layer 24. Afterward, the SiO2 barrier ribs 23 are removed.
Referring to FIGS. 4I through 4L, a surface of the bonding layer 14 formed on the insulating substrate 10 is activated by treating the surface using oxygen O2 plasma. Next, the insulating substrate 10 is bonded on the strained silicon layer 26 formed on the Si substrate 20.
Next, the stacked structure is reversed so that the insulating substrate 10 can be placed in a lower position. Next, the SiGe layer 24 is removed by selective etching. Here, an etchant for selectively etching the SiGe layer 24 is a mixed solution of 50% HF:60% HNO3:H2O=1:90 ̃120:60. Other etchants that can selectively etch the SiGe layer 24 can also be used.
The Si substrate 20 formed on the SiGe layer 24 can be separated from the strained silicon layer 26 by selectively removing the SiGe layer 24. As a result, as depicted in FIG. 4L, a strained SOI structure formed on the insulating substrate 10 can be obtained.
The method of manufacturing a strained SOI structure according to embodiments of the present invention can readily form the strained SOI structure on an insulating substrate since the process for separating the substrate is as simple as that the SiGe layer can be removed by selective etching after a bonding process. Also, the method of manufacturing a strained SOI structure can use conventional manufacturing facilities without additional cost for equipment. Especially, the strained SOI structure can be formed on a substrate such as a plastic substrate or a glass substrate, which is weak to heat, since the method does not include an annealing process at a temperature higher than a conventional temperature of 1100° C. The strained SOI structure can be applied to a front substrate or a rear substrate of a display panel.
According to the present invention, a strained SOI structure formed on an insulating substrate such as a plastic substrate, a glass substrate, or a Si substrate on which an oxide layer is formed is provided. The strained SOI structure formed on the insulating substrate has high performance, a small parasite capacitance, and high carrier mobility. Also, the strained SOI structure can be applied to memory devices and semiconductor devices for next generation.
While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.

## Claims

1. A method of manufacturing a strained SOI structure, comprising:
preparing a Si substrate and an insulating substrate;
forming a porous silicon layer by anodizing a predetermined thickness of the Si substrate;
forming a SiGe layer on the porous silicon layer;
forming a strained silicon layer on the SiGe layer;
forming a SiO2 layer on the strained silicon layer;
activating a surface of the SiO2 layer by treating the surface of the SiO2 layer using oxygen O2 plasma;
bonding the insulating substrate on the activated SiO2 layer;
removing the SiGe layer by selectively etching; and
separating the porous silicon layer and the Si substrate from the strained silicon layer.

2. The method of claim 1, wherein the insulating substrate is a substrate selected from the group consisting of a glass substrate, a plastic substrate, and a Si substrate on which an oxide layer is formed.

3. The method of claim 1, wherein the preparing of the insulating substrate includes:
preparing an insulating substrate; and
forming a protective layer on a surface of the insulating substrate.

4. The method of claim 3, wherein the protective layer is formed of AIN.

5. The method of claim 1, wherein the preparing of the insulating substrate includes:
preparing an insulating substrate;
forming a protective layer on a surface of the insulating substrate; and
forming a bonding layer on the protective layer.

6. The method of claim 5, wherein the bonding layer is formed from at least one of SiO2 and polycrystalline silicon.

7. A method of manufacturing a strained SOI structure, comprising:
preparing a Si substrate and an insulating substrate;
forming a first layer on the Si substrate, wherein the first layer is one of (1) a porous silicon layer formed by anodizing a predetermined thickness of the Si substrate and (2) a SiGe layer on the Si substrate;
forming a second layer on the first layer, wherein the second layer is (1) a SiGe layer, when the first layer is a porous silicon layer and (2) a porous SiGe layer formed by anodizing a predetermined thickness of the SiGe layer, when the first layer is a SiGe layer;
forming a strained silicon layer on the second layer;
forming a SiO2 layer on the strained silicon layer;
activating a surface of the SiO2 layer by treating the surface of the SiO2 layer using oxygen O2 plasma;
bonding the insulating substrate on the activated SiO2 layer;
removing the second layer by selectively etching; and
separating the first layer and the Si substrate from the strained silicon layer.

8. A method of manufacturing a strained SOI structure, comprising:
preparing a Si substrate and an insulating substrate;
forming a first layer on the Si substrate, wherein the first layer is one of (1) a porous silicon layer formed by anodizing a predetermined thickness of the Si substrate and (2) an SiO2 layer, which is patterned to form at least two SiO2 barrier ribs spaced a predetermined distance from each other, on the Si substrate;
forming a SiGe layer on (1) the first layer when the first layer is a porous silicon layer and (2) on the Si substrate between the two barrier ribs when the first layer is an SiO2 layer;
forming a strained silicon layer on the SiGe layer;
(1) forming a SiO2 layer on the strained silicon layer and activating a surface of the SiO2 layer by treating the surface of the SiO2 layer using oxygen O2 plasma when the first layer is a porous silicon layer or (2) removing the SiO2 barrier ribs when the SiO2 barrier ribs are present;
bonding the insulating substrate on (1) on the activated SiO2 layer when present or (2) the strained silicon layer when SiO2 barrier ribs have been removed;
removing the SiGe layer by selectively etching; and
separating the Si substrate from the strained silicon layer.