U.S. patent application number 11/544351 was filed with the patent office on 2007-05-03 for plasma for patterning advanced gate stacks.
Invention is credited to Werner Boullart, Marc Demand, Vasile Paraschiv, Denis Shamiryan.
Application Number | 20070099428 11/544351 |
Document ID | / |
Family ID | 37776895 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070099428 |
Kind Code |
A1 |
Shamiryan; Denis ; et
al. |
May 3, 2007 |
Plasma for patterning advanced gate stacks
Abstract
A plasma composition and its use in a method for the dry etching
of a stack of at least one material chemically too reactive towards
the use of a Cl-based plasma are provided. Small amounts of
nitrogen (5% up to 10%) can be added to a BCl.sub.3 comprising
plasma and used in an anisotropical dry etching method whereby a
passivation film is deposited onto the vertical sidewalls of stack
etched for protecting the vertical sidewalls from lateral attack
such that straight profiles can be obtained.
Inventors: |
Shamiryan; Denis; (Leuven,
BE) ; Paraschiv; Vasile; (Kessel-lo, BE) ;
Demand; Marc; (Jandrain-Jandrenouille, BE) ;
Boullart; Werner; (Binkom, BE) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
37776895 |
Appl. No.: |
11/544351 |
Filed: |
October 5, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60731608 |
Oct 28, 2005 |
|
|
|
60839897 |
Aug 23, 2006 |
|
|
|
Current U.S.
Class: |
438/712 ;
257/E21.201; 257/E21.204; 257/E21.311 |
Current CPC
Class: |
H01L 21/2807 20130101;
H01L 21/28088 20130101; H01L 21/32136 20130101; H01L 21/31122
20130101; H01L 29/517 20130101; H01L 29/78 20130101; H01L 29/513
20130101 |
Class at
Publication: |
438/712 |
International
Class: |
H01L 21/302 20060101
H01L021/302; H01L 21/461 20060101 H01L021/461 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2006 |
EP |
06121143.9 |
Claims
1. A dry-etch plasma composition for preserving a vertical profile
of a structure comprising a stack of layers, wherein a removable
water-soluble film is deposited onto the sidewalls of the stack
from the plasma composition during dry-etch patterning of the
stack, such that lateral attack of the patterned stack is
avoided.
2. The plasma composition of claim 1, wherein the plasma comprises
a boron-halogen compound and nitrogen.
3. The plasma composition of claim 2, further comprising an inert
compound.
4. The plasma composition of claim 2, wherein a ratio of the
boron-halogen compound to nitrogen is from 19:1 to 9:1.
5. The plasma composition of claim 2, wherein the boron-halogen
compound is BCl.sub.3.
6. The plasma composition of claim 1, wherein the stack of layers
is a metal gate-comprising stack.
7. The plasma composition of claim 6, wherein the metal
gate-comprising stack comprises TaN or TaN/TiN.
8. The plasma composition of claim 6, wherein at least one layer of
the stack of layers is a germanium-comprising layer.
9. The plasma composition of claim 8, wherein the germanium layer
is situated upon a layer to be patterned by the plasma
composition.
10. The plasma composition of claim 1, wherein the substrate bias
is different from zero.
11. The plasma composition of claim 1, wherein the plasma power is
from 100 W to 1200 W.
12. The plasma composition of claim 11, wherein the plasma power is
about 450 W.
13. The plasma composition of claim 1, wherein the pressure in the
plasma chamber is from 0.666 Pa to 10.665 Pa.
14. The plasma composition of claim 1, wherein the pressure in the
plasma chamber is 0.666 Pa.
15. The plasma composition of claim 1, wherein a temperature of the
plasma during patterning is below 100.degree. C.
16. The plasma composition of claim 1, wherein a temperature of the
plasma during patterning is about 60.degree. C.
17. The plasma composition of claim 1, wherein the plasma consists
of a boron-halogen compound and nitrogen, and wherein from 5% to
10% of the total plasma composition is nitrogen.
18. The plasma composition of claim 1, wherein the plasma consists
of a boron-halogen compound and nitrogen, and wherein less than 10%
of the total plasma composition is nitrogen.
19. The plasma composition of claim 1, wherein the plasma consists
of a boron-halogen compound and nitrogen, and wherein less than 8%
of the total plasma composition is nitrogen.
20. The plasma composition of claim 1, wherein the plasma is a
BCl.sub.3 plasma wherein 5% of the total plasma composition is
nitrogen.
21. An anisotropical dry etching method for patterning a stack of
layers to create a vertical structure, the method comprising the
steps of: patterning a stack of layers to create a vertical
structure by dry etching using a plasma composition comprising a
boron-halogen compound and nitrogen, wherein a protective and
water-soluble film is deposited from the plasma onto vertical
sidewalls of the structure during dry etching, such that a vertical
profile of the structure is preserved and lateral attack is avoided
during dry etching; and removing the film from the structure.
22. The method of claim 21, wherein the film is removed by a wet
removal process using water.
23. The method of claim 21, wherein a ratio of boron-halogen
compound to nitrogen is from 19:1 to 9:1.
24. The method of claim 21, wherein the boron-halogen compound is
BCl.sub.3.
25. The method of claim 21, wherein the plasma further comprises an
inert compound.
26. The method of claim 21, wherein the stack of layers is a metal
gate-comprising stack.
27. The method of claim 26, wherein the metal gate-comprising stack
comprises TaN or TaN/TiN.
28. The method of claim 26, wherein at least one layer of the stack
of layers comprises germanium.
29. The method of claim 28 wherein the germanium-comprising layer
is situated upon a layer to be patterned by the plasma
composition.
30. The method of claim 21, wherein a substrate bias during
patterning is different from zero.
31. The method of claim 21, wherein a plasma power during
patterning is from 100 W to 1200 W.
32. The method of claim 21, wherein a plasma power during
patterning is about 450 W.
33. The method of claim 21, wherein a pressure in the plasma
chamber during patterning is from 0.666 Pa to 10.665 Pa.
34. The method of claim 21, wherein a pressure in the plasma
chamber during patterning is 0.666 Pa.
35. The method of claim 21, wherein the temperature of the plasma
during patterning is below 100.degree. C.
36. The method of claim 21, wherein the temperature of the plasma
during patterning is about 60.degree. C.
37. The method of claim 21, wherein the plasma consists of a
boron-halogen compound and nitrogen, and wherein from 5% to 10% of
the total plasma composition is nitrogen.
38. The method of claim 21, wherein the plasma consists of a
boron-halogen compound and nitrogen, and wherein less than 10% of
the total plasma composition is nitrogen.
39. The method of a claim 21, wherein the plasma consists of a
boron-halogen compound and nitrogen, and wherein less than 8% of
the total plasma composition is nitrogen.
40. The method of claim 21, wherein the plasma is a BCl.sub.3
plasma wherein 5% of the total plasma composition is nitrogen.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C. .sctn.
119(e) of U.S. provisional application Ser. No. 60/731,608, filed
Oct. 28, 2005, and U.S. provisional application Ser. No.
60/839,897, filed Aug. 23, 2006, the disclosures of which are
hereby expressly incorporated by reference in their entirety and
are hereby expressly made a portion of this application.
FIELD OF THE INVENTION
[0002] A method of dry etching of advanced gate stacks is provided
which can be used to etch metal gate comprising stacks and pure
germanium comprising stacks. An etch plasma composition is also
provided for dry etching of metal gate comprising stacks and pure
germanium comprising stacks, thereby preserving the vertical
profile of the gate stack after patterning.
BACKGROUND OF THE INVENTION
[0003] As the critical dimensions in CMOS manufacturing shrink for
the 90 nm technology node and beyond, conventional (poly) silicon
gates are being replaced by metal gates (meaning pure metals, metal
alloys or metal nitrides, etc) and SiO.sub.2 as a gate dielectric
is replaced by materials with higher dielectric constant (so called
"high-k dielectrics). The key challenge is to adapt the
conventional gate etch process flow to the metal gate stack.
Etching this metal gate stack now requires a process that defines
the metal gate profile without affecting the gate critical
dimension (CD) and stops on thin gate oxide without pitting or
punch through.
[0004] Etching of metal gates has been studied addressing metal
gate and gate oxide surface roughness, CD control, etch
selectivity, and low damage etching but none of them succeeded in
preserving the vertical profile of the gate stack after
patterning.
[0005] One of the promising chemistry for patterning of advanced
gate stacks (metal gate etch or high-k removal) is BCl.sub.3. The
main advantage of this plasma is that it can etch both metal gates
and high-k dielectric with reasonable selectivity to the Si
substrate. However, there are number of gate stack materials that
are incompatible with BCl.sub.3 plasma as they are too reactive. As
a result, BCl.sub.3 produces some undesirable lateral etch that
compromises the gate profiles. Two particular examples are Ge gates
and TaN metal gates. If a pure BCl.sub.3 plasma is applied during
the patterning of the gate stacks containing Ge or TaN a profile
distortion caused by lateral etch is observed.
SUMMARY OF THE INVENTION
[0006] A dry-etch plasma composition for preserving the vertical
profile of a structure comprising a stack of layers during
anisotropical dry-etch patterning is provided.
[0007] Said plasma composition is further characterized such that
during the dry-etch patterning of said stack a water-soluble film,
which is removable against the structure, is deposited onto the
sidewalls of said stack such that lateral attack of said patterned
stack is avoided.
[0008] Preferably, the plasma composition of preferred embodiments
is characterized as a plasma comprising a boron-halogen compound
and nitrogen and wherein the ratio of the boron-halogen compound to
nitrogen is from 19:1 up to 9:1. More preferred, the plasma
composition of the preferred embodiments is characterized as a
plasma composition wherein said plasma comprises a boron-halogen
compound, nitrogen and optionally an inert compound. Most preferred
said boron-halogen compound is BCl.sub.3.
[0009] Preferably, the plasma composition of the preferred
embodiments is characterized as a plasma comprising (or consisting
of) a boron-halogen compound and 5 up to 10% nitrogen (of the total
plasma composition).
[0010] More preferably, the plasma composition comprises (or
consists of) a boron-halogen compound and less than 10% nitrogen
(of the total plasma composition). More particularly, said
boron-halogen compound is BCl.sub.3.
[0011] Most preferred, said plasma is (i.e. consists of) a
BCl.sub.3 plasma further comprising (or to which is added) from 5%
to 10% nitrogen (based on the total plasma composition).
[0012] In a preferred embodiment, the stack of layers to be
patterned is a metal gate comprising stack.
[0013] More preferred, said metal gate comprising stack comprises
at least one TaN layer or combinations of a TaN layer and a TiN
layer (referred to as TaN/TiN metal gates) wherein said TaN layer
is too sensitive to a (pure) BCl.sub.3 plasma. Or in other words
the stack of layers to be patterned is a stack wherein at least one
layer of said stack of layers is a TaN layer.
[0014] In another preferred embodiment, at least one layer of said
stack of layers to be patterned is a germanium comprising
layer.
[0015] Said germanium layer can be situated upon a layer to be
patterned by the plasma composition. Said germanium layer can be a
pure Ge layer.
[0016] Preferably, the plasma of the preferred embodiments (during
patterning) has a substrate bias which is different from zero.
[0017] Preferably, the plasma of the preferred embodiments (during
patterning) has a plasma power of from 100 W up to 1200 W. More
preferred said plasma power is about 450 W.
[0018] Preferably, the plasma of the preferred embodiments (during
patterning) has a pressure in the plasma chamber of minimum 0.666
Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred said
pressure is 0.666 Pa (5 mT).
[0019] Preferably, the plasma of the preferred embodiments (during
patterning) has a temperature below 100.degree. C. and most
preferred said plasma temperature during dry-etch patterning is
about 60.degree. C.
[0020] An anisotropical dry etching method is also provided using
the plasma composition of the preferred embodiments as described
above for patterning a stack of layers to create a vertical
structure wherein lateral attack during patterning of said stack is
avoided.
[0021] Preferably said method comprises the steps of first applying
a dry-etch step using the plasma composition of the preferred
embodiments wherein during the etching a protective and
water-soluble film is deposited onto the vertical sidewalls of said
structure such that the vertical profile of said structure is
preserved and lateral attack is avoided. In a next step said
water-soluble film is removed from said structure.
[0022] Said water-soluble film is preferably removed using a wet
removal process using water.
[0023] Use is provided of a plasma comprising (or consisting of)
BCl.sub.3, to which nitrogen is added to reach 5% to 10% of the
total volume of the resulting plasma composition, for etching a
(suitable) stack of layer (i.e. comprising at least one layer
etchable by said BCl.sub.3 component) and simultaneously
passivating (or protecting) the sidewalls of said stack of layers
from lateral etch.
[0024] A method is also provided for etching (or patterning) a
(suitable) stack of layers while/and simultaneously passivating (or
protecting) the sidewalls of said stack of layers comprising the
step of providing a plasma comprising (or consisting of) BCl.sub.3,
to which nitrogen is added to reach 5% to 10% of the total volume
of the resulting plasma composition.
[0025] Said use or said method is particularly useful for
(patterning) a stack of layers wherein at least one layer is
germanium, or at least one layer is TaN.
[0026] Said passivating (or protecting) effect results from the
formation and deposition of a film (or layer) which contains boron
and nitrogen (and further compounds such as oxygen) on the
sidewalls of said stack of layers. Said film obtainable by a method
of the preferred embodiments is also provided.
[0027] Said use or said method can be carried out in the framework
of CMOS manufacture.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] All drawings are intended to illustrate some aspects and
embodiments of the present invention. Not all alternatives and
options are shown and therefore the invention is not limited to the
content of the given drawings.
[0029] FIG. 1 shows FTIR (Fourier Transform Infrared Spectroscopy)
spectra of films deposited from BCl.sub.3/N.sub.2 plasma mixture
(70% BCl.sub.3) at 275.degree. C. and 60.degree. C.
[0030] FIG. 2 shows a Ge gate profile after the gate patterning and
before the high-k removal.
[0031] FIG. 3 shows a Ge gate profile after high-k removal by pure
BCl.sub.3 plasma for 10 seconds (FIG. 3A) and BCl.sub.3/N.sub.2
(10% N.sub.2) plasma for 20 seconds (FIG. 3B)
[0032] FIG. 4 shows a TaN gate profile after etching in pure
BCl.sub.3 plasma (FIG. 4A), an arrow indicates the lateral attack
of TaN. FIG. 4B shows a TaN gate profile after etching in
BCl.sub.3/N.sub.2 (5% N.sub.2) plasma.
[0033] FIG. 5 shows a TaN gate profile after etching in
BCl.sub.3/N.sub.2 plasma (FIG. 5A) and a TaN gate profile after
etching in BCl.sub.3/O.sub.2 plasma (FIG. 5B).
[0034] FIG. 6 illustrates the deposition rate of a BxNy film using
a BCl.sub.3/N.sub.2plasma (Pressure=1,333 Pa (10 mT)).
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0035] Exemplary embodiments are illustrated in referenced figures
of the drawings. It is intended that the embodiments and figures
herein are to be considered illustrative rather than
restrictive.
[0036] In the context of the preferred embodiments, the term
"critical dimension" (CD) as used herein is a broad term, and is to
be given its ordinary and customary meaning to a person of ordinary
skill in the art (and is not to be limited to a special or
customized meaning), and refers without limitation to the smallest
dimensions of geometrical features (e.g. width of gate electrode)
which can be formed during semiconductor device manufacturing. In
the context of the preferred embodiments the term "bias" as used
herein is a broad term, and is to be given its ordinary and
customary meaning to a person of ordinary skill in the art (and is
not to be limited to a special or customized meaning), and refers
without limitation to the voltage applied to the substrate during
patterning in a dry etch chamber.
[0037] The term "selectivity" as used herein is a broad term, and
is to be given its ordinary and customary meaning to a person of
ordinary skill in the art (and is not to be limited to a special or
customized meaning), and refers without limitation to the etch rate
of a selected material towards another material. The material to be
etched away should have a much higher etch rate than the other
materials.
[0038] The term "ratio" as used herein is a broad term, and is to
be given its ordinary and customary meaning to a person of ordinary
skill in the art (and is not to be limited to a special or
customized meaning), and refers without limitation to an expression
of an amount of a first compound to a second compound, e.g. a ratio
of 9:1 means e.g. 9 sccm (standard centimeter cube per minute) of
the first compound and 1 sccm of the second compound.
[0039] Use of plasma composition according to the preferred
embodiments surprisingly results in the deposition of a BxNy film
during the etching of a structure wherein the deposition is
performed in a plasma etch chamber (e.g., Versys 2300 etch chamber
from LAM.RTM.) at low temperatures (e.g. 60.degree. C.), which was
never reported before (BN deposition is usually performed at
temperatures of 390.degree. C.-650.degree. C.). The BxNy film is
deposited at a rate as high as 10 nm/min to more than 100 nm/min
depending on the pressure, plasma power, gas flows, and plasma
composition (more specifically the BCl.sub.3 to N.sub.2 ratio).
Said deposited BxNy-like film, in contrast to a pure BN film, was
found to be easily decomposing by temperature (the film thickness
decreases at temperatures above 100.degree. C.) and soluble in
water at room temperatures.
[0040] The preferred embodiments are further related to the
patterning of a stack of layers, more specifically to the dry
etching of a stack of layers.
[0041] Said patterning is making use of a plasma etch compound
wherein at least one of the layers is too sensitive to said etch
compound. By adding an extra component to the plasma it is possible
to deposit a protective layer onto the stack of layers such that
said stack is protected for e.g. sidewall damage. Said protective
layer is deposited during the patterning (dry etching). Furthermore
said protective layer is sacrificial and hence easy removable.
[0042] The "sacrificial" layer, also referred to as "protective"
layer or "passivation" layer refers to the BxNy like film resulting
from the addition of nitrogen in the boron-halogen plasma, also
referred to as BxNy film or as to boron nitride like film, which is
deposited during etching. Said BxNy film is used as a "protective"
or "passivating" film during patterning/etching of a structure,
said BxNy film is also referred to as a sacrificial layer because
said layer is removed after patterning is completed. Due the
unstable character of the BxNy film and water soluble character
said BxNy film can be easily removed by e.g. a water rinse.
[0043] The term "BxNy" film refers to a film comprising mainly
boron and nitrogen which is further characterized as a
water-soluble film. The BxNy film of the preferred embodiments is
water soluble, in contrast to a pure BN which is insoluble in
water. The BxNy film contains hexagonal boron nitride, but is very
unlikely to be a stoichiometric BN. The BxNy film is therefore
referred to as BxNy wherein the integers x and y indicate that the
ratio of nitrogen and boron in the film is not fixed due to the
presence of other compounds (impurities) in the film such as water,
oxygen and/or ammonia which are possibly absorbed from the plasma
and/or atmosphere after dry-etching.
[0044] More specifically, the preferred embodiments relate to the
patterning of metal gate stacks or germanium gate stacks, more
specifically it relates to the dry etching of said gate stacks such
as TaN comprising metal gate stacks and to the dry etching of Ge
comprising stacks (or in other words a stack comprising e.g. a pure
Ge layer).
[0045] The methods and compositions of preferred embodiments can
solve or minimize the problem of lateral etch and profile attack
during the patterning of advanced gate stacks such as metal gate
stacks and germanium stacks by adding small amounts of nitrogen to
a boron-halogen plasma such as BCl.sub.3 plasma in order to improve
gate profile control. The mixture of BCl.sub.3/N.sub.2 plasma
results in a deposition of BxNy-like film that inhibits the lateral
etch but does not inhibit vertical etch as the formed BxNy-like
film is destroyed by ion bombardment.
[0046] A plasma composition is provided for patterning metal gate
stacks and/or germanium stacks wherein during the patterning of
said stack a protective and water-soluble film is deposited such
that the vertical profile of the stack is preserved and lateral
attack of said stack is avoided.
[0047] More specifically a plasma composition is provided for
patterning a stack of layers wherein at least one layer of said
stack is sensitive to one of the etch compounds.
[0048] The plasma composition is preferably a Boron-halogen
comprising plasma with small additions of nitrogen.
[0049] The Boron-halogen compound is preferably BCl.sub.3 and said
small additions of nitrogen are such that the ratio of the
boron-halogen compound to nitrogen is from 19:1 up to 9:1.
[0050] Optionally an inert compound can be added to the plasma
comprising boron-halogen and nitrogen. Said inert compound can be
e.g. argon or helium (He) and these compounds can be added to the
plasma in concentrations up to 50% of the total plasma composition.
It is further known that addition of inert compounds (meaning that
these compounds do not react with the substrate to be etched such
that volatile compounds are formed) can improve the dissociation
rate in the plasma and hence improve the etch rate and more
specifically in case of the invention improve the formation
(deposition) of a BxNy film. In that case the inert compound can be
seen as a catalyst.
[0051] For the patterning of metal gates comprising TaN, such as
TaN metal gates and metal gates comprising layers of TaN and TiN
(TaN/TiN metal gates) the ratio of the boron-halogen compound to
nitrogen is below 9:1 (having more boron-halogen), more preferred
said ratio of the boron-halogen compound to nitrogen is below 11:1
and most preferred said ratio of the boron-halogen compound to
nitrogen is 19:1.
[0052] For the patterning of metal gates comprising TaN, such as
TaN metal gates and metal gates comprising combinations of TaN and
TiN layers (TaN/TiN metal gates) the ratio of BCl.sub.3 to nitrogen
is below 9:1, more preferred said ratio of BCl.sub.3 to nitrogen is
below 11:1 and most preferred said ratio of BCl.sub.3 to nitrogen
is 19:1.
[0053] For the patterning of germanium comprising stacks wherein
germanium is at least one of the layers of the stack and said
germanium layer needs to be protected to avoid lateral attack
during patterning of a layer situated under said germanium layer,
the ratio of the boron-halogen compound to nitrogen is higher than
19:1. More preferred said ratio of the boron-halogen compound to
nitrogen is higher than 11:1 and most preferred the ratio of the
boron-halogen compound to nitrogen is 9:1.
[0054] For the patterning of germanium comprising stacks wherein
germanium is at least one of the layers of the stack said germanium
layer needs to be protected to avoid lateral attack during
patterning of a layer situated under said germanium layer, the
ratio of BCl.sub.3 to nitrogen is higher than 19:1. More preferred
said ratio of BCl.sub.3 to nitrogen is higher than 11:1 and most
preferred the ratio of BCl.sub.3 to nitrogen is 9:1.
[0055] In a preferred embodiment, the plasma composition is
preferably a plasma comprising (or consisting of) a Boron-halogen
compound and nitrogen, or in other words small additions of
nitrogen in a boron-halogen plasma.
[0056] Preferably, the plasma comprises (or consists of) a
boron-halogen compound and 5% up to 10% nitrogen (of the total
plasma composition).
[0057] More preferred, the plasma composition comprises (or
consists of) a boron-halogen compound and less than 10% nitrogen
(of the total plasma composition) and most preferred said
boron-halogen is BCl.sub.3.
[0058] For the patterning of germanium comprising stacks wherein
said germanium layer needs to be protected to avoid lateral attack
during patterning of a layer situated under said germanium layer,
the amount of N.sub.2 to the total BCl.sub.3/N.sub.2 plasma
composition is higher than 5%, more preferred said amount of
N.sub.2 is higher than 8% N.sub.2 to the total BCl.sub.3/N.sub.2
plasma composition and most preferred said amount of N.sub.2 is 10%
to the total BCl.sub.3/N.sub.2 plasma composition.
[0059] For the patterning of metal gates such as TaN and/or
combinations of TaN and TiN (TaN/TiN metal gates) the amount of
N.sub.2 to the total BCl.sub.3/N.sub.2 plasma composition is lower
than 10%, more preferred said amount of N.sub.2 is lower than 8%
N.sub.2 to the total BCl.sub.3/N.sub.2 plasma composition and most
preferred said amount of N.sub.2 is 5% to the total
BCl.sub.3/N.sub.2 plasma composition.
[0060] Preferably the plasma of the preferred embodiments (during
patterning) has a substrate bias which is different from zero.
[0061] Preferably the plasma of the preferred embodiments (during
patterning) has a plasma power is from 100 W up to 1200 W. More
preferred said plasma power is about 450 W.
[0062] Preferably the plasma of the preferred embodiments (during
patterning) has a pressure in the plasma chamber of minimum 0.666
Pa (5 mT) and maximum 10.665 Pa (80 mT). More preferred said
pressure is 0.666 Pa (5 mT).
[0063] Preferably the plasma of the preferred embodiments (during
patterning) has a temperature below 100.degree. C. and most
preferred said plasma temperature during dry-etch patterning is
about 60.degree. C. A boron-nitrogen (B.sub.xN.sub.y or BN) film
deposited at higher temperatures is equal to a higher quality film
containing less (or no) impurities which is more difficult or even
not possible to remove.
[0064] A method is provided for the dry etching of non-Si
comprising gate stacks, said non-Si comprising gate stacks are
preferably metal gate comprising gate stacks such as TaN comprising
gate stacks and preferably metal gate stacks comprising a (pure)
germanium layer.
[0065] More specifically the dry-etching method of the preferred
embodiments uses a plasma composition wherein at least one layer of
said stack is too sensitive to one of the etch compounds.
[0066] Said dry etching method is characterized in that the
vertical profile of said gate stack is preserved after etching. The
method of the preferred embodiments solves or minimizes the problem
of negatively sloped gate profiles after dry etching by depositing
a sacrificial layer during the etching. Said sacrificial layer
serves as a passivating layer during dry etching such that the
vertical profile or CD of the gate stack is preserved.
[0067] The dry-etching method of the preferred embodiments solves
or minimizes the problem of lateral etch and profile attack during
the patterning of advanced gate stacks such as metal gate stacks
and germanium comprising stacks by adding small amounts of nitrogen
to a boron-halogen plasma such as BCl.sub.3 plasma in order to
improve gate profile control. The mixture of BCl.sub.3/N.sub.2
plasma results in a deposition of BxNy-like film that inhibits the
lateral etch but does not inhibit vertical etch as the formed
BxNy-like film is destroyed by ion bombardment.
[0068] Preferably the method of the preferred embodiments comprises
the steps of first applying a dry-etch step using the plasma
composition of the preferred embodiments whereby during the etching
a protective and water-soluble film is deposited onto the vertical
sidewalls of said structure such that the vertical profile of said
structure is preserved and lateral attack is avoided. In a next
step said water-soluble film is removed from said structure.
[0069] Said water-soluble film is preferably removed using a wet
removal process, most preferred said wet removal is using
water.
[0070] The dry-etching method of the preferred embodiments uses a
boron-halogen comprising plasma with small additions of
nitrogen.
[0071] The Boron-halogen compound is preferably BCl.sub.3 and said
small additions of nitrogen are such that the ratio of the
boron-halogen compound to nitrogen is from 19:1 up to 9:1.
[0072] Optionally an inert compound can be added to the plasma
comprising boron-halogen and nitrogen. Said inert compound can be
e.g. argon or helium (He) and these compounds can be added to the
plasma in concentrations up to 50% of the total plasma
composition.
[0073] In a method of the preferred embodiments for patterning
metal gates such as TaN metal gates and metal gates comprising
combinations of TaN and TiN (TaN/TiN metal gates), the ratio of the
boron-halogen compound to nitrogen is preferably below 9:1. More
preferably, said ratio of the boron-halogen compound to nitrogen is
below 11:1 and most preferred said ratio of the boron-halogen
compound to nitrogen is 19:1.
[0074] In particular, said boron-halogen compound is BCl.sub.3.
[0075] In a method of the preferred embodiments for patterning
germanium comprising stacks, wherein said germanium layer is a
layer of the stack which needs to be protected to avoid lateral
attack during patterning of a layer situated under said germanium
layer, the ratio of the boron-halogen compound to nitrogen is
preferably higher than 19:1. More preferred said ratio of the
boron-halogen compound to nitrogen is higher than 11:1 and most
preferred the ratio of the boron-halogen compound to nitrogen is
9:1.
[0076] In particular, said boron-halogen compound is BCl.sub.3.
[0077] In a preferred embodiment, the plasma composition used in a
method of the preferred embodiments is a plasma comprising (or
consisting of) a Boron-halogen compound and nitrogen, or in other
words small additions of nitrogen in a boron-halogen plasma.
[0078] Preferably, the plasma comprises (or consists of) a
boron-halogen compound and 5% up to 10% nitrogen (of the total
plasma composition).
[0079] More preferred, the plasma composition comprises (or
consists of) a boron-halogen compound and less than 10% nitrogen
(of the total plasma composition) and most preferred said
boron-halogen is BCl.sub.3.
[0080] In a method of the preferred embodiments for patterning
germanium comprising stacks wherein said germanium layer needs to
be protected to avoid lateral attack during patterning of a layer
situated under said germanium layer, the amount of N.sub.2 to the
total BCl.sub.3/N.sub.2 plasma composition is higher than 5%, more
preferred said amount of N.sub.2 is higher than 8% N.sub.2 to the
total BCl.sub.3/N.sub.2 plasma composition and most preferred said
amount of N.sub.2 is 10% to the total BCl.sub.3/N.sub.2 plasma
composition.
[0081] In a method of the preferred embodiments for patterning
metal gates such as TaN and/or combinations of TaN and TiN (TaN/TiN
metal gates), the amount of N.sub.2 to the total BCl.sub.3/N.sub.2
plasma composition is lower than 10%, more preferred said amount of
N.sub.2 is lower than 8% N.sub.2 to the total BCl.sub.3/N.sub.2
plasma composition and most preferred said amount of N.sub.2 is 5%
to the total BCl.sub.3/N.sub.2 plasma composition.
[0082] Preferably the plasma used in a method of the preferred
embodiments (during patterning) has a substrate bias which is
different from zero.
[0083] Preferably, said plasma has a plasma power of 100 W up to
1200 W. More preferred said plasma power is about 450 W.
[0084] Preferably, said plasma has a pressure in the plasma chamber
of minimum 0.666 Pa (5 mT) and maximum 10.665 Pa (80 mT). More
preferred said pressure is 0.666 Pa (5 mT).
[0085] Preferably, said plasma has a temperature below 100.degree.
C. and more preferred said plasma temperature during dry-etch
patterning is about 60.degree. C.
[0086] Indeed, a boron-nitrogen (B.sub.xN.sub.y or BN) film
deposited at higher temperatures is equal to a higher quality film
containing less (or no) impurities, which is more difficult or even
not possible to remove.
[0087] In relation to the drawings the preferred embodiments can
also be described as follows in the text below.
[0088] A method is provided for the dry etching of non-Si
comprising gate stacks, said non-Si comprising gate stacks are
preferably metal gate comprising gate stacks such as TaN comprising
gate stacks and preferably pure germanium comprising metal stacks.
Said dry etching method is characterized in that the vertical
profile of said gate stack is preserved after etching. The method
of the preferred embodiments solves the problem of negatively
sloped gate profiles after dry etching by depositing a sacrificial
layer during the etching. Said sacrificial layer serves as a
passivating layer during dry etching such that the vertical profile
or CD of the gate stack is preserved.
[0089] A composition is provided of a plasma used to etch materials
that are too sensitive to Cl-based plasmas. If those materials are
etched with pure Cl-based plasmas such as BCl.sub.3 plasmas, the
etch profiles are distorted because these materials are etched in
the lateral direction as well. Examples of said materials are metal
gate comprising gate stacks such as TaN comprising gate stacks and
pure germanium comprising metal stacks. The plasma of the preferred
embodiments solves or minimizes the problem of damage caused by
Cl-based plasmas, more specifically this is achieved by adding
small amounts of nitrogen to the Cl-based plasma. For the
patterning of metal gate comprising gate stacks such as TaN
comprising gate stacks and pure germanium comprising metal stacks
said Cl compound is preferably BCl.sub.3. The amount of nitrogen
added to the plasma is preferably from 5% up to 10%. The addition
of nitrogen to a Cl-based plasma such as BCl.sub.3 preserves the
vertical profile through the formation of a passivating
B.sub.xN.sub.y-like layer on the vertical surfaces.
[0090] A Cl-based plasma with small additions of nitrogen for the
patterning of non-Si based stacks is also provided. Said patterning
is further characterized as a patterning which avoids lateral
etching and preserves the vertical profile. Said stacks are
preferably metal gate comprising gate stacks such as TaN comprising
gate stacks and preferably pure germanium comprising metal stacks.
For patterning TaN comprising gate stacks and pure Germanium
comprising gate stacks, said Cl compound is BCl.sub.3.
EXAMPLES
[0091] The method of the preferred embodiments as well as the
plasma and its use can be applied to any material that can be
etched by Cl-based plasma but is too chemically reactive and has
significant lateral etch component. Said lateral etch can be
blocked by a BxNy-like passivation film deposited onto the vertical
sidewalls while at the meanwhile the vertical etch is not
significantly affected.
[0092] The BCl.sub.3/N.sub.2 plasma was applied for patterning of
two different stacks as described in Example 1 and 2: pure Ge gates
and TaN metal gates in the TiN/TaN gate stack. In both cases, the
lateral attack of the gate material was prevented by addition of
small amount of N.sub.2 (5%-10%) to the BCl.sub.3 plasma.
Furthermore the plasma settings were optimized and illustrated in
Example 3. The deposited (passivation) BxNy-like layer of the
preferred embodiments is characterized by FTIR and illustrated in
Example 4.
Example 1
Application of BCl.sub.3/N.sub.2 Plasma for TaN Gate Profile
Control
[0093] The BCl.sub.3/N.sub.2 plasma was used to etch TaN metal
gates, in the example presented here said TaN metal gate is present
in a TiN/TaN gate stack where 15 nm TaN is in the contact with the
gate dielectric and 70 nm TiN covers the TaN or in other words 70
nm TiN is situated on top of said 15 nm TaN.
[0094] The most critical step is TaN etching after TiN patterning.
BCl.sub.3 plasma is used here for the TaN patterning as it is
selective to the Si substrate and can be used as high-k removal as
well.
[0095] If TaN is etched with pure BCl.sub.3 plasma, then a notch
(lateral attack) is observed in the TaN layer.
[0096] FIG. 4A shows the gate profile after etching in pure
BCl.sub.3, an arrow indicates the lateral attack of TaN.
[0097] The addition of 5% of N.sub.2 to the BCl.sub.3 plasma
resulted in a straight TaN profile without the lateral attack of
the TaN layer.
[0098] The effect of N.sub.2 addition is illustrated in FIG. 4B. A
B.sub.xN.sub.y comprising passivation layer will be deposited onto
the vertical sidewalls of the stack during patterning, said
B.sub.xN.sub.y comprising passivation layer will protect the TaN
during patterning and avoid lateral attack.
[0099] The deposition of a B.sub.xN.sub.y comprising layer onto the
horizontal surfaces will be negligible due to a continuous ion
bombardment in the vertical direction (in other words the
B.sub.xN.sub.y comprising layer will be removed immediately after
deposition onto horizontal surfaces).
[0100] This means that the deposition of the BxNy like film
inhibits the lateral etch but does not inhibit vertical etch as the
formed BxNy-like film is destroyed by ion bombardment.
[0101] A straight TaN profile can also be obtained by using a
BCl.sub.3/O.sub.2 plasma mixture, as shown in FIG. 5B. However, the
presence of O.sub.2 in the etching plasma will have a detrimental
effect on the high-k dielectric and, therefore, is preferably
avoided.
[0102] After patterning of the TaN comprising gate stack, the
B.sub.xN.sub.y comprising passivation layer can be removed by a wet
treatment e.g. a removal in water.
Example 2
Application of BCl.sub.3/N.sub.2 Plasma for Pure Ge Gate Profile
Control
[0103] The BCl.sub.3/N.sub.2 plasma was used to pattern pure Ge
gates having a high-k dielectric underneath (in the presented case
the high-k dielectric is HfO.sub.2). The high-k dielectric must be
removed selectively to the underlying Si substrate.
[0104] The Ge gate profile just after patterning and before high-k
removal as shown in FIG. 2 is straight.
[0105] The conventional way of HfO.sub.2 removal is etching in
BCl.sub.3 plasma. If high-k is removed by such plasma, the Ge gate
suffers from profile distortion while addition of 10% N.sub.2 to
the BCl.sub.3 plasma preserves the profile even if the removal time
is doubled as shown in FIG. 3.
[0106] FIG. 3A shows the Ge gate profile after high-k removal by a
pure BCl.sub.3 plasma for 10 seconds and FIG. 3B shows the Ge gate
profile after high-k removal by a BCl.sub.3/N.sub.2 (10% N.sub.2)
plasma for 20 seconds. No lateral attack of the Ge profile is seen
in FIG. 3B.
[0107] It can be concluded that addition of small amounts of
N.sub.2 (in the presented case 10% N.sub.2 was added) to the
BCl.sub.3 plasma during high-k removal preserves the shape of the
Ge gate. This is due to the deposition of a BxNy-like passivation
film on the gate (vertical) sidewalls. Said BxNy-like passivation
film is a sacrificial layer which can be removed afterwards by wet
treatment.
Example 3
Plasma Parameters Used to Deposit a BxNy Passivation Film
[0108] The plasma parameters used for the deposition of a BxNy
passivation film during TaN metal gate patterning as presented in
Example 1 using a plasma of a preferred embodiment are as follows:
pressure 0.666 Pa (5 mT), plasma power 450 W, flow BCl.sub.3 95
sccm (standard centimeter cube per minute), flow N.sub.2 5 sccm,
and substrate bias 55V.
[0109] The plasma parameters used for the deposition of a BxNy
passivation film during high-k removal in a Ge gate stacks as
presented in Example 2 are as follows: pressure 0.666 Pa (5 mT),
plasma power 450 W, substrate bias 30V, BCl.sub.3 90 sccm, N.sub.2
10 sccm.
Example 4
Characterization of the Deposited BxNy Layer
[0110] Using the plasma composition (BCl.sub.3/N.sub.2) and method
of the preferred embodiments resulted in the deposition of a BxNy
layer. Said BxNy film was characterized by Fourier Transmission
Infra-Red spectrometry (FTIR) and X-ray Photoelectron Spectroscopy
(XPS). It was found that a plasma mixture of BCl.sub.3 and N.sub.2
resulted in the deposition of a BxNy film onto a (flat) wafer
surface if no bias was applied to the substrate (to avoid ion
bombardment). Said BxNy film was deposited in an etch chamber (LAM
Versys 2300) at 60.degree. C. and 275.degree. C. at a rate as high
as 300 nm/min depending on the pressure, plasma power, gas flows
and BCl.sub.3 to N.sub.2 ratio.
[0111] The FTIR spectra of the BxNy films deposited at 60.degree.
C. and 275.degree. C. (for comparison) are shown in FIG. 1. A
strong peak at about 1400 cm.sup.-1 is attributed to a hexagonal
boron nitride (h-BN). This peak dominate the spectrum of the film
deposited at 275.degree. C. but the spectrum of the film deposited
at 60.degree. C. contains number of other peaks and, therefore,
that film is not pure BN.
[0112] The XPS analysis of the surface of the film deposited at
60.degree. C. showed primarily boron (about 36%), nitrogen (about
20%) and oxygen (about 36%). Some carbon (about 7%) is attributed
to the contamination from the atmosphere. The amount of chlorine
did not exceed 1%. As the deposition plasma contains no O.sub.2,
the significant amount of oxygen in the film is a sign of the film
oxidation during the atmosphere exposure.
[0113] The deposited BxNy-like film was found to be easily
decomposing by temperature (the film thickness decreases at
temperatures above 100.degree. C.) and soluble in water at room
temperatures. These properties make cleaning of any deposited
inhibitor layer easy: the water rinse is enough to clean any
BxNy-like film that is left after the gate patterning.
[0114] It can be concluded that by mixing BCl.sub.3 and N.sub.2 in
a plasma etch chamber it is possible to deposit a BxNy-like film
that contains almost no Cl.sub.2. The film is relatively unstable
and can be easily removed by a water rinse, as it is soluble in
water.
[0115] All references cited herein are incorporated herein by
reference in their entirety. To the extent publications and patents
or patent applications incorporated by reference contradict the
disclosure contained in the specification, the specification is
intended to supersede and/or take precedence over any such
contradictory material.
[0116] The term "comprising" as used herein is synonymous with
"including," "containing," or "characterized by," and is inclusive
or open-ended and does not exclude additional, unrecited elements
or method steps.
[0117] All numbers expressing quantities of ingredients, reaction
conditions, and so forth used in the specification and claims are
to be understood as being modified in all instances by the term
"about." Accordingly, unless indicated to the contrary, the
numerical parameters set forth in the specification and attached
claims are approximations that may vary depending upon the desired
properties sought to be obtained by the present invention. At the
very least, and not as an attempt to limit the application of the
doctrine of equivalents to the scope of the claims, each numerical
parameter should be construed in light of the number of significant
digits and ordinary rounding approaches.
[0118] The above description provides several methods and materials
of the present invention. This invention is susceptible to
modifications in the methods and materials, as well as alterations
in the fabrication methods and equipment. Such modifications will
become apparent to those skilled in the art from a consideration of
this disclosure or practice of the invention disclosed herein.
Consequently, it is not intended that this invention be limited to
the specific embodiments disclosed herein, but that it cover all
modifications and alternatives coming within the true scope and
spirit of the invention as embodied in the attached claims.
* * * * *