# Patent

## Title
Method of making a CMOS semiconductor device using a stressed silicon-on-insulator (SOI) wafer

## Abstract

A method for forming a complementary metal oxide semiconductor (CMOS) semiconductor device includes providing a stressed silicon-on-insulator (sSOI) wafer comprising a stressed semiconductor layer having first and second laterally adjacent stressed semiconductor portions. The first stressed semiconductor portion defines a first active region. The second stressed semiconductor portion is replaced with an unstressed semiconductor portion. The unstressed semiconductor portion includes a first semiconductor material. The method further includes driving a second semiconductor material into the first semiconductor material of the unstressed semiconductor portion defining a second active region.

## Background
FIELD OF THE INVENTION
The present invention relates to the field of electronic devices, and more particularly, to a method of making semiconductor devices.
BACKGROUND OF THE INVENTION
Some semiconductor devices utilize semiconductor-on-insulator (SOI) technology, in which a thin layer of a semiconductor, such as silicon, is separated from a semiconductor substrate by a relatively thick electrically insulating layer. This thick electrically insulating layer is also referred to as a buried oxide (BOX) layer. The semiconductor layer typically has a thickness of a few nanometers, whereas the semiconductor substrate typically has a thickness of a few tens of nanometers.
SOI technology offer certain advantages compared to traditional bulk technology for Complementary Metal Oxide Semiconductor (CMOS) devices. CMOS devices include nMOSFET transistors and pMOSFET transistors both formed in the thin silicon layer which overlies the buried oxide (BOX) layer. SOI technology allows CMOS devices to operate at lower power consumption while providing the same performance level.
One particular type of SOI technology that is helping to allow for continued CMOS scaling is fully depleted SOI (FDSOI). As opposed to a partially depleted SOI (PDSOI) device, in an FDSOI device a relatively thin semiconductor channel layer is provided over the buried oxide (BOX) layer, such that the depletion region of the device covers the whole layer. FDSOI devices may provide advantages such as higher switching speeds and a reduction in threshold voltage roll off, as compared to PDSOI devices, for example.
To improve CMOS device performance, stress may be introduced into the channels of the field effect transistors (FETs). When applied in a longitudinal direction (i.e., in the direction of current flow), tensile stress is known to enhance electron mobility (i.e., n-channel MOSFET drive currents) while compressive stress is known to enhance hole mobility (i.e., p-channel MOSFET drive currents).
Consequently, tensile strained silicon-on-insulator (sSOI) is a main performance driver for nMOSFET transistors, and compressive strained silicon-germanium-on-insulator (SGOI) is a main performance driver for pMOSFET transistors.
To form an SGOI pMOSFET transistor on an sSOI substrate or wafer is difficult. Growing SiGe on an sSOI wafer often times leads to a rough surface resulting in mobility loss. In addition, a high germanium content in the silicon-germanium is needed to compensate for tensile strain. Otherwise, this leads to a high density of interface trap (DIT) value, where the DIT designates a density of traps at an interface between two layers.
One approach for forming a stressed Si/SiGe dual channel device is disclosed in U.S. published patent application no. 2013/0029478. An epitaxial SiGe layer is formed on an SOI substrate, and an Si cap layer is formed on the SiGe layer. A photoresist layer is formed on the Si cap layer, and part of the Si cap layer is removed. A Si layer is epitaxially grown on the exposed SiGe layer. An ion implantation is performed to distribute implanted ions within the silicon cap layer. Annealing is performed to relax the stress in part of the SiGe layer and transfer stress to the epitaxial Si material thereon to form strained silicon. The formed strained silicon is used to form an nMOSFET transistor channel and the region of the SiGe layer covered by photoresist is used to form a pMOSFET transistor channel.
Despite the existence of such configurations, further enhancements in SOI devices may be desirable in some applications, particularly when the SOI wafer is a stressed SOI wafer.
SUMMARY OF THE INVENTION
A method for forming a complementary metal oxide semiconductor (CMOS) semiconductor device comprises providing a stressed silicon-on-insulator (sSOI) wafer comprising a stressed semiconductor layer having first and second laterally adjacent stressed semiconductor portions, with the first stressed semiconductor portion defining a first active region. The method may further comprise replacing the second stressed semiconductor portion with an unstressed semiconductor portion, with the unstressed semiconductor portion comprising a first semiconductor material. A second semiconductor material may be driven into the first semiconductor material of the unstressed semiconductor portion to define a second active region.
The first semiconductor material may comprise silicon, and the second semiconductor material may comprise silicon and germanium. The second active region is advantageously formed in a relatively straightforward manner without the need for complex steps.
A mask layer may be formed over the first stressed semiconductor portion before replacing the second stressed semiconductor portion with the unstressed semiconductor portion.
Replacing the second stressed semiconductor portion with the unstressed semiconductor portion may comprises removing the second stressed semiconductor portion except for a second stressed semiconductor portion bottom layer, and forming the unstressed semiconductor portion on the second stressed semiconductor portion bottom layer. The second stressed semiconductor portion bottom layer may be annealed before forming the unstressed semiconductor portion. In addition, the unstressed semiconductor portion may also be annealed.
Driving the second semiconductor material into the first semiconductor material may comprise forming a second semiconductor layer comprising the second semiconductor material over the unstressed semiconductor portion, and oxidizing the second semiconductor layer to drive the second semiconductor material into the first semiconductor material.
The method may further comprise forming first and second gate stacks over the first and second active regions, respectively. First raised source and drain regions defining a first channel therebetween may be formed in the first active region under the first gate stack. Second raised source and drain regions defining a second channel therebetween may be formed in the second active region under the second gate stack.
The stressed SOI wafer may comprises a fully depleted SOI (FDSOI) wafer. The first active region may be for an n-channel metal-oxide semiconductor field-effect transistor, and the second active region may be for a p-channel metal-oxide semiconductor field-effect transistor.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top-level flowchart illustrating a method for forming a complementary metal oxide semiconductor (CMOS) semiconductor device in accordance with the present embodiment.
FIG. 2 is a more detailed flowchart illustrating the method of FIG. 1.
FIGS. 3-9 are a series of cross-sectional diagrams illustrating the method of FIG. 2.
FIG. 10 is a cross-sectional diagram of the CMOS semiconductor device formed by the method of FIG. 2.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. The embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout.
Referring initially to the flowchart 20 in FIG. 1, a method for forming a complementary metal oxide semiconductor (CMOS) semiconductor device includes, from the start (Block 21), providing a stressed silicon-on-insulator (sSOI) wafer at Block 22 comprising a stressed semiconductor layer having first and second laterally adjacent stressed semiconductor portions, with the first stressed semiconductor portion defining a first active region. The method further comprises replacing the second stressed semiconductor portion at Block 23 with an unstressed semiconductor portion, with the unstressed semiconductor portion comprising a first semiconductor material. A second semiconductor material may be driven into the first semiconductor material of the unstressed semiconductor portion at Block 24 to define a second active region. The method ends at Block 25.
The first semiconductor material may comprise silicon, and the second semiconductor material may comprise silicon and germanium. The second active region is advantageously formed in a relatively straightforward manner without the need for complex steps.
As will be discussed in greater detail below, a silicon-germanium-on-insulator (SGOI) p-channel metal-oxide semiconductor field-effect (pMOSFET) transistor is formed on a stressed silicon-on-insulator (sSOI) wafer. The stressed silicon on the sSOI corresponding to the pMOSFET is intentionally thinned, and a silicon-germanium layer is formed on the thinned stressed silicon. An re-channel metal-oxide semiconductor field-effect (nMOSFET) transistor is formed in the stressed silicon-on-insulator (sSOI) wafer.
A more detailed method for forming the CMOS semiconductor device 45 will now be discussed in reference to the flowchart 30 in FIG. 2 and to the process flow illustrated in FIGS. 3-8. From the start (Block 31), the method includes providing at Block 32 a stressed silicon-on-insulator (SOI) wafer 50 comprising a stressed semiconductor layer 56 having first and second laterally adjacent stressed semiconductor portions 70 and 80, as illustrated in FIG. 3. The first stressed semiconductor portion 70 defines a first active region 72.
The sSOI wafer 50 includes a semiconductor substrate or wafer 52, a buried oxide (BOX) layer 54 on the semiconductor substrate, and the stressed semiconductor layer 56 on the buried oxide layer. In one embodiment, the semiconductor substrate 52 comprises silicon, and the stressed semiconductor layer 56 also comprises silicon.
The sSOI wafer 50 may be a fully depleted SOI (FDSOI) wafer, as readily appreciated by those skilled in the art. In addition, the SOI wafer 50 may be an ultra-thin body and box (UTBB) wafer, as also readily appreciated by those skilled in the art. In one embodiment, a thickness of the semiconductor substrate 52 may be within a range of about 10 to 25 nm, and a thickness of the stressed semiconductor layer 56 may be within a range of about 7 to 10 nm, for example.
A mask layer 90 is formed over the first stressed semiconductor portion 70 at Block 34 and as illustrated in FIG. 4. The mask layer 90 protects the first stressed semiconductor portion 70 while a second active region is defined. The second active region is defined in the area corresponding to the second stressed semiconductor portion 80, which is laterally adjacent the first active region 72.
The second stressed semiconductor portion 80 is replaced with an unstressed semiconductor portion 100, as illustrated in FIG. 6. The unstressed semiconductor portion 100 includes a first semiconductor material. More particularly, replacing the second stressed semiconductor portion 80 with the unstressed semiconductor portion 100 includes removing the second stressed semiconductor portion 80 at Block 36 except for a second stressed semiconductor portion bottom layer 81, as illustrated in FIG. 5.
The second stressed semiconductor portion 80 may be thinned based on an SC1 wet etch, for example. Alternatively, oxidation may be used to thin the second stressed semiconductor portion 80. With oxidation, a thin oxide layer is deposited and then oxidation occurs. Both the SC1 wet etch and the oxidation can be well controlled so that a thickness of the second stressed semiconductor portion bottom layer 81 may be within a range of about 2 to 3 nm, as readily appreciated by those skilled in the art.
To relax the second stressed semiconductor portion bottom layer 81, a high temperature anneal may be performed at Block 38. After the annealing, the unstressed semiconductor portion 100 is formed at Block 40 on the second stressed semiconductor portion bottom layer 81 and as illustrated in FIG. 6. The first semiconductor material making up the unstressed semiconductor portion 100 may be epitaxially grown, as readily appreciated by those skilled in the art. A thickness of the unstressed semiconductor portion 100 may be within a range of about 5 to 7 nm, for example. The first semiconductor material comprises silicon, for example, and is intrinsic, i.e., undoped. Intrinsic silicon helps to ensure that a top surface of the unstressed semiconductor portion 100 is unstressed.
Trench isolation regions 180 are formed at to bound the first active region 72 and the adjacent unstressed semiconductor portion 100, as illustrated in FIG. 7. Optionally, a chemical-mechanical polishing may be performed before the trench isolation regions 180.
To further relax the second stressed semiconductor portion bottom layer 81, another high temperature anneal may be performed at Block 42 after forming the unstressed semiconductor portion 100. Referring now to FIG. 8, a second semiconductor material is driven into the first semiconductor material of the unstressed semiconductor portion 100 defining the second active region 82.
More particularly, driving the second semiconductor material into the first semiconductor material includes forming a second semiconductor layer 110 and comprising the second semiconductor material over the unstressed semiconductor portion 100 at Block 43. In this example, the second semiconductor material comprises silicon and germanium. The silicon and germanium forming the second semiconductor layer 110 is epitaxially grown on the unstressed semiconductor portion 100. A thickness of the second semiconductor layer 110 may be within a range of about 5 to 7 nm, for example. Driving the second semiconductor material (i.e., silicon and germanium) into the first semiconductor material (i.e., silicon) is based on oxidizing the second semiconductor layer 110 at Block 44. This forms a new second stressed semiconductor portion 112.
Referring now to FIG. 9, the hard mask 90 is removed and the stressed silicon-on-insulator (SOI) wafer 50 includes the first stressed semiconductor portion 70 defining the first active region 72, and the new second stressed semiconductor portion 112 defining the second active region 82. The new second stressed semiconductor portion 112 defining the second active region 82 is advantageously formed in a relatively straightforward manner without the need for complex steps.
The method further comprises forming first and second gate stacks 120, 130 over the first and second active regions 72, 82, respectively, at Block 46. In the illustrated embodiment of the CMOS semiconductor device 45 shown in FIG. 10, the first gate stack 120 includes a gate dielectric layer 122, a gate electrode layer 124, and sidewall spacers 126. Similarly, the second gate stack 130 includes a gate dielectric layer 132, a gate electrode layer 134, and sidewall spacers 136.
First raised source and drain regions 140, 142 are formed at Block 47 to define a first channel 144 therebetween in the first active region 72 under the first gate stack 120. Similarly, second raised source and drain regions 150, 152 are formed at Block 48 to define a second channel 154 therebetween in the second active region 82 under the second gate stack 130.
The first channel region 144 is for an re-channel metal-oxide semiconductor field-effect transistor (nMOSFET) 160, and the second channel region 154 is for a p-channel metal-oxide semiconductor field-effect transistor (pMOSFET) 170. The nMOSFET 160 and the pMOSFET 170 are separated by a shallow trench isolation (STI) region 180. The method ends at Block 49.
In view of the above, a variety of different transistor structures may be implemented, including but not necessarily limited to: planar CMOS, high-k metal gate CMOS, PD-SOI, FD-SOI, UTBB, vertical double gate, buried gate, FinFET, tri-gate, multi-gate, 2D, 3D, raised source/drain, strained source/drain, strained channel, and combinations/hybrids thereof, for example.
Many modifications and other embodiments will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.

## Claims

1. A method for forming a semiconductor device comprising:
providing a stressed silicon-on-insulator (SOI) wafer comprising a stressed semiconductor layer having first and second laterally adjacent stressed semiconductor portions, the first stressed semiconductor portion defining a first active region;
replacing the second stressed semiconductor portion with another semiconductor portion comprising a first semiconductor material; and
driving a second semiconductor material into the first semiconductor material of the other semiconductor portion defining a second active region.

2. The method according to claim 1 wherein the first semiconductor material comprises silicon, and the second semiconductor material comprises silicon and germanium.

3. The method according to claim 1 further comprising forming a mask layer over the first stressed semiconductor portion before replacing the second stressed semiconductor portion with the other semiconductor portion.

4. The method according to claim 1 wherein replacing the second stressed semiconductor portion with the other semiconductor portion comprises:
removing the second stressed semiconductor portion except for a second stressed semiconductor portion bottom layer; and
forming the other semiconductor portion on the second stressed semiconductor portion bottom layer.

5. The method according to claim 4 further comprising annealing the second stressed semiconductor portion bottom layer before forming the other semiconductor portion.

6. The method according to claim 4 further comprising annealing the other semiconductor portion.

7. The method according to claim 1 wherein driving the second semiconductor material into the first semiconductor material comprises:
forming a second semiconductor layer comprising the second semiconductor material over the other semiconductor portion; and
oxidizing the second semiconductor layer to drive the second semiconductor material into the first semiconductor material.

8. The method according to claim 1 further comprising:
forming first and second gate stacks over the first and second active regions, respectively;
forming first raised source and drain regions defining a first channel therebetween in the first active region under the first gate stack; and
forming second raised source and drain regions defining a second channel therebetween in the second active region under the second gate stack.

9. The method according to claim 8 wherein the first channel region is for an n-channel metal-oxide semiconductor field-effect transistor (nMOSFET) having a FinFET structure, and the second channel region is for a p-channel metal-oxide semiconductor field-effect transistor (pMOSFET) having a FinFET structure.

10. The method according to claim 1 wherein the stressed SOI wafer comprises a fully depleted SOI (FDSOI) wafer.

11. The method according to claim 1 wherein the first active region is for an n-channel metal-oxide semiconductor field-effect transistor, and the second active region is for a p-channel metal-oxide semiconductor field-effect transistor.

12. A method for forming semiconductor device comprising:
providing a stressed silicon-on-insulator (SOI) wafer comprising a stressed silicon layer having first and second laterally adjacent stressed silicon portions, the first stressed silicon portion defining a first active region; and
driving silicon-germanium into another silicon portion associated with the second stressed silicon portion defining a second active region.

13. The method according to claim 12 further comprising:
forming a mask layer over the first stressed silicon portion; and
replacing the second stressed silicon portion with the other silicon portion.

14. The method according to claim 13 wherein replacing the second stressed silicon portion with the other silicon portion comprises:
removing the second stressed silicon portion except for a second stressed silicon portion bottom layer; and
forming the other silicon portion on the second stressed silicon portion bottom layer.

15. The method according to claim 14 further comprising annealing the second stressed silicon portion bottom layer before forming the other silicon portion.

16. The method according to claim 14 further comprising annealing the other silicon portion.

17. The method according to claim 13 wherein driving the silicon-germanium into the other silicon portion comprises:
forming a silicon-germanium layer over the other silicon portion; and
oxidizing the silicon-germanium layer to drive the silicon-germanium into the other silicon portion.

18. The method according to claim 12 further comprising:
forming first and second gate stacks over the first and second active regions, respectively;
forming first raised source and drain regions defining a first channel therebetween in the first active region under the first gate stack; and
forming second raised source and drain regions defining a second channel therebetween in the second active region under the second gate stack.

19. The method according to claim 18 wherein the first channel region is for an n-channel metal-oxide semiconductor field-effect transistor (nMOSFET) having a FinFET structure, and the second channel region is for a p-channel metal-oxide semiconductor field-effect transistor (pMOSFET) having a FinFET structure.

20. The method according to claim 12 wherein the stressed SOI wafer comprises a fully depleted SOI (FDSOI) wafer.

21. The method according to claim 12 wherein the first active region is for an n-channel metal-oxide semiconductor field-effect transistor, and the second active region is for a p-channel metal-oxide semiconductor field-effect transistor.

22. A method for forming semiconductor device comprising:
providing a stressed silicon-on-insulator (SOI) wafer comprising a stressed silicon layer having first and second laterally adjacent stressed silicon portions, the first stressed silicon portion defining a first active region;
driving silicon-germanium into another silicon portion associated with the second stressed silicon portion defining a second active region;
forming first and second gate stacks over the first and second active regions, respectively;
forming first raised source and drain regions defining a first channel therebetween in the first active region under the first gate stack; and
forming second raised source and drain regions defining a second channel therebetween in the second active region under the second gate stack.

23. The method according to claim 22 wherein the first active region is for an n-channel metal-oxide semiconductor field-effect transistor, and the second active region is for a p-channel metal-oxide semiconductor field-effect transistor.