|Title of Invention||
A FINFET AND A METHOD FOR FORMING A GATE STRUCTURE AND ASSOCIATED SPACER FOR A FINFET
|Abstract||Methods for forming a spacer (44) for a first structure (24, 124), such as a gate structure of a FinFET, and at most a portion of a second structure (14), such as a fin, without detrimentally altering the second structure. The methods generate a first structure (24) having a top portion (30, 130) that overhangs an electrically conductive lower portion (32, 132) and a spacer (44) under the overhang (40, 140). The overhang (40, 140) may be removed after spacer processing. Relative to a FinFET, the overhang protects parts of the fin (14) such as regions adjacent and under the gate structure (24, 124) , and allows for exposing sidewalls of the fin (14) to other processing such as selective silicon growth and implantation. As a result, the methods allow sizing of the fin (14) and construction of the gate structure (24, 124) and spacer without detrimentally altering (e.g., eroding by forming a spacer thereon) the fin (14) during spacer processing. A FinFET (100) including a gate structure (24, 124) and spacer (44) is also disclosed|
METHODS OF FORMING STRUCTURE AND SPACER
AND RELATED FINFET
[ 0001] The present invention relates generally to CMOS processing.
[ 0002] Spacers are common structures in complementary metal-oxide semiconductor
( CMOS) processing provided to protect one structure from processing cone to an adjacent structure. Exemplary types of CMOS devices in which protective spacers must be used are Fin Field Effect Transistors (FinFETs) and MesaFETs. A FinFET. for example, structurally includes, among other things, a gate that extends over and along a ponion of each sidewall of a thin, vertical, silicon "fin." In FinFETS. a spacer is required for blocking implants at the gate edge and preventing silicide shorts to the gate. Conventional planar CMOS spacer processing presents a number.of problems relative to the fin. In particular, conventional processing to form the spacer for the gate results' in application to the fin. If conventional spacer processes are used, fin erosion during spacer etch is a potential problem. When the fin needs to be exceptionally thin, any additional etching can prevent attainment of the desired fin size. Another challenge is formation of a spacer along the gate without formation on the fin sidewalls and the top of the fin such that the part the part of the fin not adjacent to the gate can be exposed to implantation. In conventional spacer processing, a spacer formed on the sate also forms on the sidewalls of the fin due to the three-dimensional nature of the FinFET. In some cases, such as during sidewall implantation or source drain extension, this sidewall spacer is undesirable. Attempts to remove the fin sidewall spacer result in removing the spacer on the gate where a spacer is needed. Similar problems exist relative to other CMOS devices such as MesaFETs.
[ 0003] In view of the foregoing, there is a need in the art for an improved method for
forming a spacer on a first structure and at most a ponion of a second structure without detrimeatally altering the second structure during the spacer processing.
Disclosure of the Invention
[ 0004] The invention relates to methods for forming a spacer for a first structure, such
as a gate structure of a FinFET, and at most a portion of a second structure, such as a region of the fin adjacent to the gate, without detrimentally altering ('e.g.. eroding or forming a spacer thereon) the second structure. The methods generate a first structure (gate structure) having a top portion mat overhangs a lower portion and a spacer under the overhang. The overhang may be removed after spacer processing. The overhang protects the first structure and may protect parts of the second structure if the first structure overlaps the second structure. An example of this is a fin region adjacent and under the gate structure in a FinFET protected by a spacer, where the sidewalk of the fin are exposed to other processing such as selective silicon growth and implantation. As a result, the methods allow sizing of the second structure and construction of the first structure and spacer without detrimentally altering the second structure during spacer processing. The invention also relates to a FinFET including a gate structure and spacer formed by the methods.
[ 0005] The foregoing and other features of the invention will be apparent from the
following more particular description of best modes for carrying out the invention.
Brief Description of Drawings
[ 0006] The embodiments of this invention will be described in detail, with reference
to the following figures, wherein like designations denote like elements, and wherein:
[ 0007] Figure 1 shows a perspective view of a precursor structure of a FinFET
including a fin without a gate material.
[ 0008] Figures 2-A-B show cross-sectional views of a first and second step of the
[ 0009] Figures 3A-B show cross-sectional views of a third step of the methods.
 Figures 4A-B show cross-sectional views of a fourth'step according to a first
embodiment of the methods.
[ 0011] Figures 5A-B show cross-sectional views of a fourth step according to a
second embodiment of the methods.
[ 0012] Figures 6A-B show cross-sectionai views or a tilth step of the methods.
 Figures 7A-B show cross-sectional views of a sixth step of the methods and
spacer is not desired.
[ 0015] With reference to the accompanying drawings. FIG. 1 is a perspective view of
a precursor structure 10 of a FinFET after gate etch. At this point in processing, structure 10 includes a substrate 12 upon which is formed a fin 14 of mono-crystalline silicon. The gate structure (not shown) will eventually be constructed over fin 14. A hardmask 16 is also provided to protect fin 14 during processing. Hardmask 16 may be? for example, silicon dioxide (oxide) or silicon nitride. Actual processing to establish this precursor structure 10 may include deposition of a hardmask 16. etching hardmask 16 and the underlying silicon to generate fin 14, conducting a sacrificial oxidation and gate oxidation of the silicon to generate structure oxide 18. It should be recognized that the above processing is simply exemplary izd that other processing may also be possible to achieve :h- illustrated structure. Fin 14. as
shown, is ready for generation of a gate structure and a spacer for the gate structure.
[ 0016] FIGS. 2-7 illustrate methods for forming a spacer for a gate and a spacer for at
most a portion of a fin during the spacer processing. In the drawings, those figures labeled
"A" show a cross-sectional view A-A across tin 14 as shown in FIG. I. and those labeled 'B"
show a cross-sectional view B-B as shown in FIG. I (through the gate structure once formed').
[ 0017] In a first step, shown in FIGS. ZA-B. a firs: material Z0 for generation of a gate
structure is deposited over fin 14. FIGS. ZA-B also show a second step in which a second material ZZ. 1ZZ is formed over first material Z0. (Second material ZZ. 122 includes the dual designation because the material may be provided in two different forms, as will be described in more detail below.) As also will be described in more detail below, second material 22. 1ZZ is different than first material Z0.
[ 0018] FIGS. 3A-3B show the next step in which a gate structure Z4 is formed in first
material Z0 and second material 22. 122. Forming may include applying and patterning (e.g.. with lithography) a hardmask 26, e.g., oxide (TEOS). over first material and second material 22. 122. and etching the materials to form gate structure 24. As shown in FIG. 3B. these steps are also applied to eventual source and drain regions 28 of fin 14. Subsequently. hardmask 26 is removed in a known fashion.
 FIGS. 4A-B and 5A-B illustrate two embodiments of the next step in which
second material 22, 122 is made to overhang first material 20. As noted above, second material 22, 122 is different than first material 20.
[ 0020] FIGS. 4A-B show a first embodiment in which second material 22 is formed
(in the step shown in FIGS. 2A-B) as a polycrystalline silicon (hereinafter 'polysilicon') such that it has an oxidation rate faster than first material 20. In order to provide these differential oxidation rates, in one embodiment, second material 22 may be a portion of first material 20 that is implanted with a dopant in a known fashion. The dopant may be any material that causes polysilicon second material 22 to oxidize at a faster rate than non-doped polysilicon. The dopant may be, for example, Arsenic (As) (preferred), Germanium (Ge), Cesium (Cs), Argon (Ar) or Flourine (F) or a combination thereof. In another embodiment, second material 22 that has a faster oxidation rate than first material 20 may be deposited on the first material, e.g., as polycrystalline silicon-germanium alloy. First material 20 may be, for example, non-doped polysilicon. According to this embodiment, second material 22 is made to overhang
electrically conductive lower portion 132 thereof.
[ 0022] With further regard to FIGS. 4A-B and 5A-B. it should be recognized that the
shapes of second materials 22. 122 as illustrated may van: depending on the embodiment
used and the specific processing provided. Accordingly, while the figures illustrate a bulbous
or umbrella-like shape for materials 20. 22. 122, other shapes that provide the overhang may
[ 0023] The next step includes forming a spacer under overhang 40. 140. The spacer
may be formed on the structure of either embodiment above. However, FIGS. 6A-B and 7 A-
B show onlv the embodiment of FIGS. 4A-B for brevity sake. In one embodiment for
forming a spacer, a spacer material 42 is conformally deposited, as shown in FIGS. 6A-B.
Spacer material may be, for example, silicon nitride, silicon oxide or a combination thereof.
Finally, as shown in FIGS. 7A-B. spacer materia! 42 is etched using a directional reactive ion etching process which removes material everywhere except under overhang 40. 140 to form a spacer 44.
[ 0024] Finishing processing (not shown) may follow. This processing may include.
for example, removal of oxide 34 from the sides of fin 14 (oxide remains as top portion 30 if dooed polvsilicon used) or removal of too ocrtion 130, i.e.. the siass. from sate structure 124 'if used). In the FinFETapplication, final processing may include, for example, implanting to set threshold voltage (Vt). doping the source/drain regions 28 of fin 14. selective silicon arowth to widen the source, drain regions 28 on fin 14. removing remaining oxide and forming cobalt-silicide (CoSi). conventional contact processing, finishing with appropriate metal levels, etc.
[ 0025] The resulting FinFET 100. shown in FIGS. 7A-7B. includes, among other
things, a gate structure 24. 124 including an electrically conductive lower portion 32. 132 and an overhanging top portion 30. 130, a fin 14 extending through the lower portion, and a spacer 44 positioned under top portion 30, 130 of gate structure 24. 124 adjacent to conducting lower portion 32. 132. Top portion 30. 130 is made of a material (e.g.. oxide or glass) that is different than the material (e.g.. polvsilicon) of lower portion 32. 132 as described above.
[ 0026] In the previous description. "gate structure" 24, 124 has been described as
including a top portion 30, 130 and a lower portion 32, 132. It should be recognized, however, that top portion 30, 130 may not ultimately form an operative or active part of the actual gate used. For instance, at least a part of top portion 30, 130 and/or overhang 40, 140 may be removed to allow for contacts to be made to lower portion 32, 132 of gate structure 24,124.
[ 0027] While the invention has been described in conjunction with several preferred
embodiments, those skilled in the art will recognize that the invention can be practiced in various versions within the spirit and scope of the following claims.
[ 0028] ' The invention is userul for formating a spacer for a gate of a FinFET. and at
most a portion of a fin without detrimentally alrerina the fin.
A method for forming a spacer (44, for a first structure (24. 124) and a spacer for at most a portion of a second structure 1141. the method comprising the steps of:
depositing a first material 20):
forming a second material 22. 122) over the first material; forming the first structure from the first and second materials: making the second material overhang (40. 140) the first materiai: and forming a spacer (44) under the overhang.
The method of claim 1. wherein the second structure (14) is made of monocrystalline silicon, and the first material (20: is made of polycrystalline silicon.
The method of claim 1. wherein the second materiai (22) is formed such that the second material has a faster oxidation rate than the first material.
The method of claim 3. wherein the second material includes a dopant including at least one of the group comprising: Arsenic, Germanium. Cesium, Argon and Flourine.
The method of claim 3, wherein the second material is a deposited polycrystalline
The method of claim 3, wherein the step of making includes oxidation to form the overhang as a result of a differential oxidation rate of the second material (22) with respect to tke first material (20).
The method of claim 3, wherein the step of making includes forming oxide (34) on sides of the first structure (24) and the second structure (14).
The method of claim 1, whe.rein the second material (122) has'different thermal reflow properties than the first material.
The method of claim 8. wherein me second materral ■ 122} is one of8PSG and ?SG.
The method of claim 8. wherein the step of making includes heating the second material to cause the second material to reflow to form the overhang (40. 1-0 -.
The method :f :iai:n I. wherein the step of forming the spacer includer depositing a spacer material ■: 42 .■; ana
i i -
The method of claim ! i. wherein me spacer material -I '■ is at least one of silicon nitride and silicon oxide.
The method of claim 1. wherein the rirs; structure 2-. 12-; is a gate and the second structure (14 > is a fin of a FinFET • "100).
A method tor forming a gate structure 124. 124) and associated spacer t'4-; for a
FinFET. the method comprising the steps of:
depositing a first gate material forming a second material (22. 122) over the gate material, wherein :he second
material has a faster oxidation rate than the gate material:
forming the gate structure into the gate material and the second material: oxidizing to cause the second material to overhang (40; the gate material: and forming a spacer (44) under the overhang.
The method of claim 14. wherein the fin (14) is made of monocrystalline silicon and the gate material (20) is polycrystailine silicon.
The method of claim 14, -wherein the second material (22) is a polycrystailine silicon formed such that the second material has a faster oxidation rate than the first material.
The method of claim 14, wherein the step of oxidizing also forms oxide (54) on sides of the structure (14) and gate (24).
The method of claim 14, wherein the step of forming the spacer (44) includes: depositing a spacer material (42); and etching the spacer material away except under the overhang (40).
19. A FinFET comcrisins:
a gate structure (24. 124) inducing an electrically conductive lower portion (32. 132) and an overhanging top portion (30. 130:
a fin (\ -; extending through the lower ponion: and
a spacer ;44) positioned ur.de: the top portion of the gate structure adjacent to the lower portion.
20. The FinFET of claim 19. wherein the top ponion .'30, 130) is made of one of oxide
and glass, and the lower ponion (32. 132) is made of polycrystalline silicon.
21. The FinFET of claim 19. wherein the soacer (44) surrounds the lower nonion (32.
132) and portions of the fin (14) adjacent the gate (24. 124).
|Indian Patent Application Number||1279/CHENP/2005|
|PG Journal Number||47/2008|
|Date of Filing||16-Jun-2005|
|Name of Patentee||INTERNATIONAL BUSINESS MACHINES CORPORATION|
|Applicant Address||ARMONK, NEW YORK 10504|
|PCT International Classification Number||H01L 21/84|
|PCT International Application Number||PCT/US02/40869|
|PCT International Filing date||2002-12-19|