METHODS OF FORMING STRAINED SEMICONDUCTOR CHANNELS
In various method embodiments, a device region in a semiconductor substrate and isolation regions adjacent to the device region are defined. The device region has a channel region and the isolation regions have strain-inducing regions laterally adjacent to the channel regions. The channel region is strained with a desired strain for carrier mobility enhancement, where at least one ion type is implanted with an energy resulting in a peak implant in the strain-inducing regions of the isolation regions. Other aspects and embodiments are provided herein.
This application is a divisional of U.S. application Ser. No. 11/506,986, filed Aug. 18, 2006, which is incorporated herein by reference in its entirety.
TECHNICAL FIELDThis disclosure relates generally to semiconductor devices, and more particularly, to strained semiconductor, devices and systems, and methods of forming the strained semiconductor, devices and systems.
BACKGROUNDThe semiconductor industry continues to strive for improvements in the speed and performance of semiconductor devices. Strained silicon technology has been shown to enhance carrier mobility in both n-channel and p-channel devices, and thus has been of interest to the semiconductor industry as a means to improve device speed and performance. Currently, strained silicon layers are used to increase electron mobility in n-channel CMOS transistors. There has been research and development activity to increase the hole mobility of p-channel CMOS transistors using strained silicon germanium layers on silicon.
One approach involves a silicon germanium layer on a silicon substrate, and a silicon capping layer on the silicon germanium layer. Both the silicon germanium and the silicon capping layers are strained if they are thin. The crystalline silicon layer is strained by a lattice mismatch between the silicon germanium layer and the crystalline silicon layer. The silicon germanium layer may be graded to a relaxed or unstrained layer to create more stress in the silicon cap layer. Strained silicon layers have been fabricated on thicker relaxed silicon germanium layers to improve the mobility of electrons in NMOS transistors. Structures with strained silicon on silicon germanium on insulators have been described as well as structures with strained silicon over a localized oxide insulator region. These structures yield high mobility and high performance transistors on a low capacitance insulating substrate.
Known techniques to strain channels and improve carrier mobilities in CMOS devices include improving electron mobility in NMOS transistors using a tensile strained silicon layer on silicon germanium, improving hole mobility using silicon germanium source/drain regions in trenches adjacent to the PMOS transistor to introduce uniaxial compressive stress in the channel of the PMOS transistor, improving electron mobility using silicon-carbide source/drain regions in trenches adjacent to an NMOS transistor to introduce tensile stress, and improving mobility for both NMOS and PMOS transistors using silicon nitride capping layers formed to introduce tensile stress for NMOS transistors and formed to introduce compressive stress for PMOS transistors.
Wafer bending has been used to investigate the effect of strain on mobility and distinguish between the effects of biaxial stress and uniaxial stress. Bonding a semiconductor onto bowed or bent substrates has been disclosed to introduce strain in the semiconductor. Stress can also be introduced by wafer bonding. Packaging can introduce mechanical stress by bending. Compressively-strained semiconductor layers have been bonded to a substrate.
The following detailed description refers to the accompanying drawings which show, by way of illustration, specific aspects and embodiments in which the present subject matter may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the present subject matter. The various embodiments of the present subject matter are not necessarily mutually exclusive as aspects of one embodiment can be combined with aspects of another embodiment. Other embodiments may be utilized and structural, logical, and electrical changes may be made without departing from the scope of the present subject matter. In the following description, the terms “wafer” and “substrate” are interchangeably used to refer generally to any structure on which integrated circuits are formed, and also to such structures during various stages of integrated circuit fabrication. Both terms include doped and undoped semiconductors, epitaxial layers of a semiconductor on a supporting semiconductor or insulating material, combinations of such layers, as well as other such structures that are known in the art. The term “horizontal” as used in this application is defined as a plane parallel to the conventional plane or surface of a wafer or substrate, regardless of the orientation of the wafer or substrate. The term “vertical” refers to a direction perpendicular to the horizontal as defined above. Prepositions, such as “on”, “side”, “higher”, “lower”, “over” and “under” are defined with respect to the conventional plane or surface being on the top surface of the wafer or substrate, regardless of the orientation of the wafer or substrate. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, along with the full scope of equivalents to which such claims are entitled.
Disclosed herein, among other things, is a process to adjust volumes of strain-induced regions of isolation regions to provide device channels regions with a desired strain. Thus, the strain-induced region is expanded to provide a compressive strain for p-channel device, and the strain-induced region is reduced or contracted to provide a tensile strain for n-channel devices. According to various embodiments, a depth of the strain-induced region generally corresponds to a depth of a channel region. In various embodiments, the depth of the strain-induced region is about 200 Å. In various embodiments, the depth of the strain-induced region is about 100 Å.
For example, some embodiments implant helium ions in an amorphous silicon device isolation regions to create nanocavities. Oxygen is selectively implanted into the PMOS isolation regions, and forms a silicon oxide (SiOx) during a subsequent anneal. The formation of the silicon oxide expands the PMOS isolation regions, and thereby compressively strains the adjacent PMOS channel. Hydrogen and argon are selectively implanted into the NMOS isolation regions. An anneal after the implantation of hydrogen and argon recrystallizes the amorphous silicon in the NMOS isolation regions, compressing the NMOS isolation regions and thereby inducing tensile strain in the adjacent NMOS channel.
Various method embodiments strain the channel region with a desired strain for carrier mobility enhancement, including implanting at least one ion type with an energy resulting in a peak implant in the strain-inducing regions of the isolation regions. Various embodiments strain the channel region with a desired strain for carrier mobility enhancement, including forming nanocavities in the strain-inducing regions. Various embodiments strain the channel region with a desired tensile strain for electron mobility enhancement, including implanting helium in the strain-inducing regions, annealing to form nanocavities in the strain-inducing regions, implanting argon and hydrogen in the strain-inducing regions, and annealing to recrystallize the strain-inducing regions and tensilely strain the channel region. Various embodiments strain the channel region with a desired compressive strain for hole mobility enhancement, including implanting helium in the strain-inducing regions, annealing to form nanocavities in the strain-inducing regions, implanting oxygen in the strain-inducing regions, and annealing to form an oxide in the strain-inducing regions and compressively strain the channel region. In an embodiment, isolation regions are defined for both PMOS and NMOS, and silicon is etched to form isolation trenches. The outer-sidewalls of the trenches are selectively oxidized, where the inner sidewalls are protected by nitride. Amorphous silicon is deposited, and the surface is planarized. A shallow ion implant of helium (dose at least 3×1020 ions/cm3) only into the isolation regions to ensure implant distribution within 200 Å from the surface. The structure is annealed to create nanocavities. A thin oxide and nitride are deposited to seal the isolation surface. Prior to forming a gate oxide, oxygen is selectively implanted for the PMOS isolation region and hydrogen or hydrogen and Argon is selectively implanted for the NMOS region. The dose is at least 3×1020 ions/cm3 and the implant distribution is within 200 Å from the surface. Standard gate oxidation, post oxidation anneal, and gate and device processing can be performed. The thermal budget creates preferential oxidation of near-surface silicon at the helium-induced bubbles to induce compressive stress and strain for PMOS channels. Near-surface helium-hydrogen and argon bubble regions facilitate recrystallization of amorphous silicon at the near surface region for NMOS, shrinking the volume and inducing tensile stress and strain for the NMOS channel.
Various embodiments define isolation regions and amorphous silicon regions. A thin epitaxial silicon layer less than 1000 Å is formed on the surface of the silicon wafer. Helium is selectively implanted (with a dose greater than 3×1020 ions/cm3) for the PMOS region and Ar/H2 (each with a dose greater than 3×1020 ions/cm3) for the NMOS region. The implant peak is confined to a depth corresponding to the thickness of the epitaxial layer and 100 Å into the substrate, and a distribution of +/−100 Å from the peak. The surface is sealed until the gate oxidation steps. Standard gate oxidation, post oxidation anneal, and gate and device processing can be performed. The thermal budget creates stable helium bubbles in the PMOS isolation regions to induce compressive stress/strain for PMOS, and recrystallizes and forms epitaxial silicon top-down to the damaged Argon/H2 region, inducing tensile stress/strain in the NMOS channel region.
Various structure embodiments include a device region and isolation regions adjacent to the device region. The device region includes a first source/drain region, a second source/drain region, and a channel region between the first source/drain region and the second source drain region. The isolation regions have strain-inducing regions laterally adjacent to the channel region and have a depth generally corresponding to a depth of the channel region. The channel region includes a strain induced by the strain-inducing regions in the isolation regions.
Various structure embodiments include a p-channel device and an n-channel device. The p-channel device includes a p-channel device region and p-channel isolation regions on opposing sides of the p-channel device region. The p-channel device region includes first and second source/drain regions and a p-channel region between the first and second source drain regions. The p-channel isolation regions have strain-inducing regions laterally adjacent to the p-channel region and have a depth generally corresponding to a depth of the p-channel region. The p-channel region includes a compressive strain induced by the strain-inducing regions in the p-channel isolation regions. The n-channel device includes an n-channel device region and n-channel isolation regions on opposing sides of the n-channel device region. The n-channel device region includes first and second source/drain regions and a n-channel region between the first and second source drain regions. The n-channel isolation regions have strain-inducing regions laterally adjacent to the n-channel region and having a depth generally corresponding to a depth of the n-channel region. The n-channel region includes a tensile strain induced by the strain-inducing regions in the n-channel isolation regions.
Various structure embodiments include a device region, a first isolation trench on a first side of the device region and a second isolation trench on a second side of the device region, and isolation regions adjacent to the device region. The device region includes a first source/drain region, a second source/drain region, and a channel region between the first source/drain region and the second source drain region. Each of the first and second isolation trenches have a strain-inducing region laterally adjacent to the channel region. The strain-inducing regions have a depth generally corresponding to a depth of the channel region. The isolation trenches have a stepped cross-sectional profile, where a step in the profile of the isolation trenches corresponds to a bottom of the strain-inducing region. The channel region includes a strain induced by the strain-inducing regions in the isolation regions.
The illustrated isolation trenches or regions include a strain-inducing region 110, as illustrated by the dotted line separating a top portion and bottom portion of the isolation region. The illustrated strain-inducing region has a depth that generally corresponds to a depth of the channel region. In the illustrated figures, ions are implanted into the strain-inducing region of the isolation region as part of a process to expand the strain-inducing region and compress the channel region. Various embodiments form nanocavities 111 in the strain-inducing region 110.
The illustrated isolation regions or trenches 202 include a strain-inducing region 210, as illustrated by the dotted line separating a top portion and bottom portion of the isolation region. The illustrated strain-inducing region has a depth that generally corresponds to a depth of the channel region. In the illustrated figures, ions are implanted into the strain-inducing region of the isolation region as part of a process to contract the strain-inducing region and tensile strain the channel region. Various embodiments form nanocavities 211 in the strain-inducing region.
The isolation trenches correspond to a first isolation region proximate to the first source/drain region and a second isolation region proximate to the second source drain region. These isolation regions or trenches can form part of an integrated isolation region (e.g. an isolation region surrounding an island device region).
It has been illustrated how the adjusted volume of the strain-inducing regions can provide the desired compressive or tensile strain in the channel direction, referred to herein as the x-direction. There are also stresses applied in the direction into the paper (referred to herein as the y-direction) and the vertical direction (referred to herein as the z-direction).
The tensile strain 1048 in the y-direction can be avoided by having the isolation regions constrained in the y-direction. In the z-direction, the edges of the implanted region are constrained by the un-implanted material. The implanted material wishes to move vertically and the un-implanted material does not. At the interface between the implanted and unimplanted material, the implanted material is under compression and the un-implanted material is in tension. With proper modeling, there can still be a large compressive strain in the direction of the transistor channel of a PMOS transistor.
The isolation regions can be appropriately defined to provide a desired strain when the volume of the isolation regions are adjusted. Thus, for example, various embodiments adjust the volumes of isolation regions on a first side and on an opposing second side of the device region to provide a predominantly uniaxial strain. Various embodiments adjust volumes of isolation regions surrounding the device region to provide a predominantly biaxial strain.
According to various embodiments, the process to provide a desired compressive strain for a p-channel device includes engineering the process to induce a compressive strain within a range of approximately 0.2% and 1.0%. According to various embodiments, the process to provide a desired tensile strain for an n-channel device includes engineering the process to induce a tensile strain greater than approximately 0.5%. For example, various embodiments provide a tensile strain within a range of approximately 0.75% to approximately 1.5%. It is also desirable to reduce unnecessary strain and provide a margin for error without unduly affecting the mobility enhancement. Thus, it is desirable to provide a tensile strain in the range of approximately 1% to approximately 1.2%.
The top volume of isolation regions is expanded at 1665. According to various embodiments, expanding the top volume includes adding oxygen as illustrated at 1666, which can include implanting oxygen ions as illustrated at 1667. Expanding the top volume also includes annealing as illustrated at 1668. A p-channel transistor is formed at 1669.
The top volume of isolation regions are contracted at 1670. According to various embodiments, contracting the top volume includes creating damage in preparation to recrystallize the region, as illustrated at 1671. Various embodiments create damage using a noble gas implant 1672, a carbon, silicon or germanium implant 1673, or an argon and hydrogen implant 1674. Contracting the top volume also includes annealing as illustrated at 1675. Annealing 1675 can be the same process as 1668. N-channel transistors are formed at 1676.
The illustrated memory array 1990 includes a number of memory cells 1993 arranged in rows and columns, where word lines 1994 connect the memory cells in the rows and bit lines 1995 connect the memory cells in the columns. The read/write control circuitry 1991 includes word line select circuitry 1996, which functions to select a desired row. The read/write control circuitry 1991 further includes bit line select circuitry 1997, which functions to select a desired column. The read/write control circuitry 1991 further includes read circuitry 1998, which functions to detect a memory state for a selected memory cell in the memory array 1990.
The memory may be realized as a memory device containing p-channel transistors with compressively-strained channels formed according to various embodiments. It will be understood that embodiments are equally applicable to any size and type of memory circuit and are not intended to be limited to a particular type of memory device. Memory types include a DRAM, SRAM (Static Random Access Memory) or Flash memories. Additionally, the DRAM could be a synchronous DRAM commonly referred to as SGRAM (Synchronous Graphics Random Access Memory), SDRAM (Synchronous Dynamic Random Access Memory), SDRAM II, and DDR SDRAM (Double Data Rate SDRAM).
This disclosure includes several processes, circuit diagrams, and semiconductor structures. The present subject matter is not limited to a particular process order or logical arrangement. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown. This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments, and other embodiments, will be apparent to those of skill in the art upon reviewing the above description. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims
1. A semiconductor structure, comprising:
- a device region and isolation regions adjacent to the device region;
- the device region including a first source/drain region, a second source/drain region, and a channel region between the first source/drain region and the second source drain region;
- the isolation regions having strain-inducing regions laterally adjacent to the channel region and having a depth generally corresponding to a depth of the channel region; and
- the channel region including a strain induced by the strain-inducing regions in the isolation regions.
2. The structure of claim 1, wherein the strain-inducing regions include implanted helium ions.
3. The structure of claim 1, wherein the strain-inducing regions include nanocavities.
4. The structure of claim 3, wherein the strain-inducing regions include an oxide.
5. The structure of claim 4, wherein the oxide includes silicon dioxide.
6. The structure of claim 4, wherein the strain-inducing regions include an oxide formed using implanted oxygen ions.
7. The structure of claim 1, wherein the strain-inducing regions includes implanted argon ions.
8. The structure of claim 1, wherein the strain-inducing regions includes implanted hydrogen ions.
9. The structure of claim 1, wherein the strain-inducing regions includes implanted argon ions and implanted hydrogen ions.
10. The structure of claim 1, wherein the channel region includes a tensile strain.
11. The structure of claim 10, wherein the tensile strain is within a range of approximately 0.75% to approximately 1.5%.
12. The structure of claim 1, wherein the channel region includes a compressive strain.
13. The structure of claim 12, wherein the compressive strain is within a range of approximately 0.2% to approximately 1.0%.
14. The structure of claim 1, wherein the strain is a predominantly uniaxial strain.
15. The structure of claim 1, wherein the strain is a predominantly biaxial strain.
16. The structure of claim 1, further comprising an epitaxial semiconductor layer on the device region and the isolation region.
17. A semiconductor structure, comprising:
- a p-channel device, including a p-channel device region and p-channel isolation regions on opposing sides of the p-channel device region, the p-channel device region including first and second source/drain regions and a p-channel region between the first and second source drain regions, the p-channel isolation regions having strain-inducing regions laterally adjacent to the p-channel region and having a depth generally corresponding to a depth of the p-channel region, and the p-channel region including a compressive strain induced by the strain-inducing regions in the p-channel isolation regions; and
- an n-channel device, including an n-channel device region and n-channel isolation regions on opposing sides of the n-channel device region, the n-channel device region including first and second source/drain regions and a n-channel region between the first and second source drain regions, the n-channel isolation regions having strain-inducing regions laterally adjacent to the n-channel region and having a depth generally corresponding to a depth of the n-channel region, and the n-channel region including a tensile strain induced by the strain-inducing regions in the n-channel isolation regions.
18. The structure of claim 17, wherein the strain-inducing regions of the n-channel isolation regions and the p-channel isolation regions include implanted helium ions.
19. The structure of claim 18, wherein the strain-inducing regions of the p-channel isolation regions include an oxide formed using implanted oxygen ions.
20. The structure of claim 18, wherein the strain-inducing regions of the n-channel isolation regions include implanted argon ions.
21. The structure of claim 20, wherein the strain-inducing regions of the n-channel isolation regions include implanted hydrogen ions.
22. The structure of claim 17, further comprising an epitaxial silicon layer on the p-channel isolation regions and the n-channel isolation regions.
23. The structure of claim 22, wherein the strain-inducing regions of the p-channel isolation regions include implanted helium ions.
24. The structure of claim 22, wherein the strain-inducing regions of the n-channel isolation regions include implanted argon ions.
25. The structure of claim 22, wherein the strain-inducing regions of the n-channel isolation regions include implanted hydrogen ions.
26. A semiconductor structure, comprising:
- a device region;
- a first isolation trench on a first side of the device region and a second isolation trench on a second side of the device region, and isolation regions adjacent to the device region;
- the device region including a first source/drain region, a second source/drain region, and a channel region between the first source/drain region and the second source drain region;
- each of the first and second isolation trenches having a strain-inducing region laterally adjacent to the channel region, the strain-inducing regions having a depth generally corresponding to a depth of the channel region, the isolation trenches having a stepped cross-sectional profile, wherein a step in the profile of the isolation trenches corresponds to a bottom of the strain-inducing region; and
- the channel region including a strain induced by the strain-inducing regions in the isolation regions.
27. The structure of claim 26, wherein the step in the profile reflects expanded strain-inducing regions that induce a compressive strain in the channel region.
28. The structure of claim 27, wherein the compressive strain includes a strain within a range of approximately 0.2% to approximately 1.0%.
29. The structure of claim 26, wherein the step in the profile reflects contracted strain-inducing regions that induce a tensile strain in the channel region.
30. The structure of claim 29, wherein the tensile strain includes a strain greater than approximately 0.5%.
31. The structure of claim 29, wherein the tensile strain includes a strain within a range of approximately 0.75% to approximately 1.5%.
Type: Application
Filed: Jun 17, 2011
Publication Date: Oct 13, 2011
Inventors: Arup Bhattacharyya (Essex Junction, VT), Leonard Forbes (Corvallis, OR), Paul A. Farrar (Bluffton, SC)
Application Number: 13/163,404
International Classification: H01L 27/092 (20060101);