U.S. patent application number 10/911294 was filed with the patent office on 2005-03-17 for selective plasma etching process for aluminum oxide patterning.
Invention is credited to Moll, Peter, Tegen, Stefan.
Application Number | 20050056615 10/911294 |
Document ID | / |
Family ID | 34201786 |
Filed Date | 2005-03-17 |
United States Patent
Application |
20050056615 |
Kind Code |
A1 |
Moll, Peter ; et
al. |
March 17, 2005 |
Selective plasma etching process for aluminum oxide patterning
Abstract
This invention relates to a method for the selective and
directed plasma etching of aluminum oxide, in which a mixture
having the following constituents is used for etching: a. a
polymerizing gas comprising at least partially unsaturated,
perfluorinated hydrocarbon compounds; b. optionally a compound
having the formula CH.sub.xF.sub.y, where x=1-3 and y=4-x; c.
oxygen; and d. a suitable carrier gas; and this mixture as a
plasma, is brought into contact with the aluminum oxide to be
etched.
Inventors: |
Moll, Peter; (Dresden,
DE) ; Tegen, Stefan; (Dresden, DE) |
Correspondence
Address: |
JENKINS & WILSON, PA
3100 TOWER BLVD
SUITE 1400
DURHAM
NC
27707
US
|
Family ID: |
34201786 |
Appl. No.: |
10/911294 |
Filed: |
August 4, 2004 |
Current U.S.
Class: |
216/67 ;
257/E21.253 |
Current CPC
Class: |
H01L 21/31122
20130101 |
Class at
Publication: |
216/067 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 18, 2003 |
DE |
10338422.7 |
Claims
1. Method for the selective and directed plasma etching of aluminum
oxide, having the step of etching with a mixture having the
following constituents: a. a polymerizing gas comprising at least
partially unsaturated, perfluorinated hydrocarbon compounds; b.
optionally a compound having the formula CH.sub.xF.sub.y, where
x=1, 2 or 3 and y=4-x; c. oxygen; and d. a suitable carrier gas;
and this mixture as a plasma, is brought into contact with the
aluminum oxide to be etched.
2. Method according to claim 1, wherein C.sub.4F.sub.6 and/or
C.sub.5F.sub.8 are used as the at least partially unsaturated,
perfluorinated hydrocarbon compounds for gas a.
3. Method according to claim 1, wherein CH.sub.2F.sub.2 is used as
compound having the formula CH.sub.xF.sub.y.
4. Method according to claim 1, wherein argon is used as carrier
gas.
5. Method according to claim 1 wherein the volumetric ratio of the
constituents a:b:c:d is approximately 0.7-1.3:0-1:0.5-2:5-200,
preferably approximately 0.8-1.2:0.4-0.8:0.6-1.4:10-100.
6. Method according to claim 1 wherein the following combination of
constituents is used: a: C.sub.4F.sub.6; b: CH.sub.2F.sub.2; c:
O.sub.2; d: Ar.
7. Method according to claim 1, wherein the constituents a. to d.
are present in approximately the following ratios:
a:b:c:d=1:0.6:0.8:20.
8. Method according to claim 1, wherein the process pressure during
the etching of aluminum oxide is approximately 15 to approximately
100 mtorr, preferably approximately 40 to approximately 80
mtorr.
9. Method according to claim 1, wherein the method is effected as
part of the fabrication of a semiconductor structure in order to
produce an etched aluminum oxide layer.
10. Method according to claim 9, wherein the etching for producing
an etched aluminum oxide layer is followed by a patterning of an
underlying layer, preferably made of silicon, silicon nitride or
silicon oxide, the etched aluminum oxide layer being used as a
mask.
11. Use of the method according to claim 1, for controlled removal
of aluminum oxide on Si, silicon oxide, silicon oxynitride or
silicon nitride.
12. Use of the method according to claim 1, for etching barrier
layers or tunnel layers made of aluminum oxide that occur in
magnetic memories or in hard disk read heads.
13. Use of the method according to claim 1 in semiconductor
manufacturing, in particular in the course of contact hole
etching.
14. Method for fabricating an aluminum oxide hard mask, having the
steps of: a. providing an aluminum oxide layer on a substrate,
preferably a silicon, silicon nitride, silicon oxynitride and/or
silicon oxide substrate; b. providing a mask on the aluminum oxide
layer; and c. etching the aluminum oxide layer by the method
according to claim 1.
Description
[0001] The present invention relates to a method for the selective
and directed plasma etching of aluminum oxide, and to the use of
the method, in particular in semiconductor manufacturing.
[0002] Aluminum oxide has a high etching resistance toward etching
plasmas used for etching silicon, silicon oxide, silicon oxynitride
or silicon nitride. On account of this etching resistance, aluminum
oxide is proposed as a hard mask or stop layer. However, an
expedient use has failed hitherto primarily owing to the lack of a
selective and anisotropic dry etching process for aluminum
oxide.
[0003] There is likewise difficulty in classifying the dry etching
of aluminum oxide in use as high-k dielectric (gate material in
field-effect transistors or capacitory dielectric), as well as
tunnel barrier (such as e.g. hard disk read heads), or in
electroluminescent materials. In these cases, too, it would be
desirable to have a method for etching aluminum oxide
available.
[0004] On account of the poor selectivity of customary processes
for anisotropic etching, thicker hard or resist mask layers are
currently required for patterning the aluminum oxide and, moreover,
the etching attack on the underlying material is relatively large
due to the necessary overetch and the poor selectivity.
[0005] The sole selective etching process which is currently
established is only a wet-chemical and thus isotropic process for
removal of aluminum oxide. The disadvantages of this method
includes an isotropic, i.e. undirected etching behavior, for which
reason material removals and faults occur in particular at edge and
boundary layer regions, which contributes to the poor
controllability of the feature sizes. Wet-chemical processes are
therefore suitable only to a greater extent for structures
decreasing in size.
[0006] An anisotropic process for etching aluminum oxide with high
selectivity has not yet been described heretofore.
[0007] Instead, high mask layer thicknesses are currently used in
attempts to achieve as far as possible anisotropic patternings, and
the removal of aluminum oxide often takes place by means of
unadapted recipes, e.g. with Ar-based sputtering recipes.
[0008] Therefore, it is an object of the present invention to
provide a method for the controlled etching of aluminum oxide.
[0009] This object is achieved by means of a method in accordance
with Claim 1.
[0010] The present invention furthermore relates to the use of the
etching method according to the invention for the selective etching
of aluminum oxide with respect to silicon, photoresists and/or
metals.
[0011] Furthermore, the present invention encompasses the use of
the method according to the invention for etching barrier layers or
tunnel layers made of aluminum oxide that are used e.g. in magnetic
memories or in hard disk read heads.
[0012] The present invention also relates to the use of the method
according to the invention in semiconductor manufacturing, in
particular in the context of fabricating contact holes.
[0013] The present invention furthermore relates to a method for
fabricating an aluminum oxide hard mask.
[0014] Claim 1 relates to a method for the selective and directed
plasma etching of aluminum oxide, in which a mixture having the
following constituents is used for etching:
[0015] a. a polymerizing gas comprising at least partially
unsaturated, perfluorinated hydrocarbon compounds;
[0016] b. optionally a compound having the formula CH.sub.xF.sub.y,
where x=1, 2 or 3 and y=4-x;
[0017] c. oxygen; and
[0018] d. a suitable carrier gas;
[0019] and this mixture as a plasma, is brought into contact with
the aluminum oxide to be etched.
[0020] Although an optional constituent is specified under b., it
is preferred for the volumetric proportion of b. to be greater than
0.
[0021] For the first time, a selective and anisotropic etching
process for aluminum oxide has hereby been found, which at the same
time is compatible with customary plasma etching chambers and can
be used with utilization of customary gases, parameters and
temperatures. This has been made possible by means of the adapted
combination of the constituents, in particular by virtue of the
simultaneous presence of polymerizing components and components
effecting removal in sputtering/oxidizing fashion. It is assumed
that the polymerization provides an at least temporary protection
of surfaces against an excessively high degree of etching, while on
the other hand removing constituents effect the etching and prevent
an excessive formation of polymers. Constituent a. is a
polymerizing constituent. Constituent b. presumably likewise
contributes to polymerization, but due to the F component probably
also effects a degree of removal. Constituent c. acts in oxidizing
removing fashion and constituent d. acts principally as a dilution
gas. It could not be expected that such a combination of
constituents would enable a selective etching of aluminum
oxide.
[0022] In a preferred embodiment of the present invention,
C.sub.4F.sub.6 (1,1,2,3,4,4-hexafluoro-1,3-butadiene) and/or
C.sub.5F.sub.8 is used as at least partially unsaturated,
perfluorinated hydrocarbon compound. Noncyclic compounds are
involved in this case. Particularly good selectivities with respect
to silicon and resist materials have been observed with these
compounds. C.sub.4F.sub.8 can likewise be used according to the
invention.
[0023] According to the invention, aluminum oxide is understood to
be Al.sub.2O.sub.3; however, the term also encompasses
nonstoichiometric aluminum oxide as may occur in aluminum layer
formations, if appropriate. Equally, the term silicon oxide is to
be understood as silicon dioxide; nonstoichiometric ratios may be
present in this case, too. The term silicon nitride encompasses
various silicon nitrides, in particular Si.sub.3N.sub.4.
[0024] The compounds CH.sub.xF.sub.y are likewise predominantly
contained in the gas mixture as a gas that supports the
polymerization. In a preferred embodiment, CH.sub.2F.sub.2 is used
as compound having the formula CH.sub.xF.sub.y.
[0025] According to the invention, the carrier gas or dilution gas
that is used may be any inert or largely inert gases, such as
argon, xenon, helium and/or neon. The use of argon as carrier gas
has turned out to be preferred, however. It is presumed that Ar is
ionized in small proportions in the plasma and thus contributes to
the removal of polymers forming on the surface.
[0026] The ratio of the constituents can be varied according to the
invention. Preferably, the volumetric ratio of the constituents
a:b:c:d is approximately 0.7-1.3:0-1:0.5-2:5-200, preferably
approximately 0.8-1.2:0.4-0.8:0.6-1.4:10-100.
[0027] Although b. may be 0 in the first volumetric ratio
specification, a value of approximately 0.1 is preferred as further
lower limit.
[0028] A particularly preferred combination of constituents is the
following composition:
[0029] a: C.sub.4F.sub.6; b:CH.sub.2F.sub.2; c:O.sub.2; d:Ar. It is
preferred, particularly in the case of this composition, for the
constituents a. to d. to be present approximately in the following
ratios: a:b:c:d=1:0.6:0.8:20.
[0030] According to the invention, the process pressure may be
varied by the person skilled in the art in accordance with the
requirements. By lowering the pressure it is possible to improve
the uniformity (at the same time with a reduced selectivity);
conversely, higher pressure permits a higher selectivity with
respect to resist with poorer uniformity of the etching. This may
be compensated for by the person skilled in the art through
adaptation of other process parameters (power, magnetic field
strength, etc.).
[0031] According to the invention, it is preferred for the process
pressure during the etching of aluminum oxide to be approximately 5
to 200 mtorr, more preferably approximately 15 to approximately 100
mtorr, even more preferably approximately 40 to approximately 80
mtorr.
[0032] The plasma power may be chosen and set by the person skilled
in the art in accordance with the apparatus used and the etching
requirements. When using an Applied Materials eMax 200 mm, (a
magnetically enhanced reactive ion etch chamber), a power of
approximately 1800 W at a process pressure of 40 mtorr and a
temperature of -15.degree. C. is a preferred value. The etching
process may be carried out using a magnetic field or without a
magnetic field. The magnetic field strength may be varied by the
person skilled in the art. If a magnetic field is used, a value of
approximately 100 gauss is a preferred guide value when using the
above apparatus and at 1800 W and 40 mtorr.
[0033] Generally, preferred ranges of parameters within which the
person skilled in the art may effect variation (relative to said
type of installation and 200 mm wafers) are:
[0034] Power 500-2500 watts, pressure 5-200 mT, temperature -25 to
15.degree. C., magnetic field 0-120G, gas flow (total) 50-1000
sccm.
[0035] In the case of the composition that turned out to be
particularly preferred above, where a:C.sub.4F.sub.6;
b:CH.sub.2F.sub.2; c:O.sub.2; d:Ar and where a:b:c:d=1:0.6:0.8:20,
a selectivity of 4.6:1 with respect to Si and 3:1 for resist
results at a process pressure of 40 mT (see examples).
[0036] The etching method according to the invention can thus be
integrated well in semiconductor manufacturing methods and may be
employed particularly where a selective etching with respect to
silicon and resist is required. One important possibility for
application of the method is in the formation of contact holes
(contact hole etching), where it is possible to use aluminum oxide
as a hard mask, an etching that is selective with respect to
silicon, silicon nitride, silicon oxynitride or silicon oxide being
carried out. Contact hole etching involves etching the aluminum
oxide layer according to resist lithography in accordance with the
method according to the invention, which is possible selectively
with respect to Si or resist. The subsequent patterning of the
underlying layer, such as e.g. silicon oxide or silicon nitride, is
effected according to conventional methods using the patterned
aluminum oxide layer as a hard mask. These etching methods attack
the aluminum oxide layer only insignificantly or not at all, with
the result that a good selectivity is ensured here as well.
[0037] After the etching, the etched aluminum oxide layer is
preferably used as a hard mask for patterning an underlying layer,
preferably made of silicon, silicon nitride or silicon oxide.
[0038] The method of the present invention is well suited to the
controlled removal of aluminum oxide on Si, silicon oxynitride,
silicon oxide and/or silicon nitride.
[0039] The method according to the invention may be used in
particular for the directed, selective dry etching of aluminum
oxide layers, preferably for the selective etching of aluminum
oxide layers with respect to silicon and photoresist.
[0040] Aluminum oxide layers occur for example as tunnel layers or
barrier layers in hard disk read heads or in magnetic memories. The
method of the present invention may preferably be used for etching
barrier layers or tunnel layers made of aluminum oxide that occur
in magnetic memories or in hard disk read heads.
[0041] Generally the method according to the invention may
preferably be used in semiconductor manufacturing in order to etch
and/or pattern aluminum oxide layers in that context. Such a
patterned layer may preferably be used as a hard mask for
patterning underlying layers made of silicon, silicon nitride
and/or silicon oxide, e.g. during contact hole etching.
[0042] Consequently, a further aspect of the present invention
relates to a method for fabricating an aluminum oxide hard mask,
having the steps of:
[0043] a. providing an aluminum oxide layer on a substrate,
preferably a silicon, silicon nitride, silicon oxynitride and/or
silicon oxide substrate;
[0044] b. providing a mask on the aluminum oxide layer;
[0045] c. etching the aluminum oxide layer by the method according
to one of Claims 1 to 8.
[0046] The use of highly polymerizing gases such as C.sub.4F.sub.6
or C.sub.5F.sub.8 in a mixture with Ar and CH.sub.xF.sub.y and
O.sub.2 enables, according to the invention, an aluminum oxide
etching which is highly selective with respect to Si and resist. A
factor that influences the etching is the selected ratio of the
polymerizing gases (C.sub.4F.sub.6, C.sub.5F.sub.8,
CH.sub.xF.sub.y) to oxygen and the corresponding dilution by Ar.
Preferred ratios are specified above.
[0047] Advantages of the present invention are e.g.:
[0048] 1. The etching process described facilitates the use of
aluminum oxide as a hard mask that has a good selectivity with
respect to Si, SiN and SiO.sub.2.
[0049] 2. Improved or controlled removal of aluminum oxide on Si,
SiO and SiN (high-K dielectrics e.g. as trench-dielectric or as
gate dielectric).
[0050] 3. Etching of the tunnel barrier in magnetic memories (MRAM)
is made possible or improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0051] FIG. 1 shows a diagram of the selectivity of Al.sub.2O.sub.3
with respect to Si.sub.3N.sub.4, SiO.sub.2, a resist and Si when
using the etching method according to the invention.
[0052] FIGS. 2 to 7 diagrammatically show various stages in the
production of contact holes using aluminum oxide as a hard mask, in
order to elucidate the present invention by way of example.
EXAMPLES
[0053] 1. Etching and Selectivity Tests
[0054] Unpatterned wafer slices to which an Al.sub.2O.sub.3 layer
having a thickness of approximately 100 nm was applied by means of
ALD (Atomic Layer Deposition with organometallic precursor) were
provided with layers made of Si.sub.3N.sub.4, SiO.sub.2, a resist
(MUV (365 nm) resist from JSR; MUV=middle UV range) and Si at
selected regions in the conventional manner. It may be assumed that
other types of resist (e.g. for 248 nm/193 nm lithography) behave
similarly.
[0055] Afterward, with each of the wafer slices coated in this way,
a plasma etching was carried out with the following parameters:
1 Pressure: 15, 40 and 100 mT Time: 60 s Power: 1800 W Magnetic
field 100 G.
[0056] The apparatus used was the Applied Materials eMax 200 mm
described above.
[0057] After etching, the surface alterations, i.e. etching rate
and uniformity of the surface, were determined by ellipsometry. The
uniformity is specified in percent as (maximum etching rate minus
minimum etching rate)/(2.times.average etching rate).
[0058] The following results were obtained:
2 Etching rate Pressure nm/min Uniformity/% 15 mT 74.1 .+-.20.9 40
mT 50.8 .+-.37.9 100 mT 22.6 .+-.56.4
[0059] The selectivities S were furthermore determined. S=etching
rate Al.sub.2O.sub.3/etching rate reference material. The results
of the selectivities of aluminum oxide with respect to various
tested materials are illustrated graphically in FIG. 1. The
illustration in each case shows mean values from two tests. At 40
mT, selectivities of approximately 4.6 and 3 were obtained with
respect to Si and the resist. At 100 mT the values were
>10:1.
[0060] 2. Contact Hole Patterning
[0061] A following layer construction was produced according to
conventional methods known to the person skilled in the art (from
top to bottom):
[0062] Resist
[0063] Al.sub.2O.sub.3
[0064] Oxide
[0065] Si (or metal)
[0066] The following method steps were carried out:
[0067] Firstly, a contact hole lithography was effected in a
conventional manner. Afterward, the Al.sub.2O.sub.3 was patterned
by a process according to the invention, i.e. an etching method was
carried out with a mixture comprising
C.sub.4F.sub.6:CH.sub.2F.sub.2:O.sub.2:Ar in the ratio 1:0.6:0.8:20
at a process pressure of 40 mT. Further parameters:
3 Time: 60 s Power: 1800 W Magnetic field 100 G.
[0068] The apparatus used was the Applied Materials eMax 200
mm.
[0069] The resist was then removed (resist stripping) in a
conventional manner and the oxide was then patterned using the
Al.sub.2O.sub.3 as a hard mask. Stop on Si/metal. The
Al.sub.2O.sub.3 may subsequently be removed wet-chemically, if
required for process integration reasons.
[0070] In this way, the oxide lying below Al.sub.2O.sub.3 was able
to be patterned and etched simply and effectively using
Al.sub.2O.sub.3 as a hard mask. This example shows that the method
according to the invention can generally be used for contact hole
etching.
[0071] 3. Deep Trench with Al.sub.2O.sub.3 Hard Mask (Storage
Capacitor Patterning for DRAM)
[0072] A deep trench patterning is an etching with a very high
aspect ratio into the crystalline Si. This etching may be effected,
according to the invention, with very high selectivity with respect
to the Al.sub.2O.sub.3 hard mask.
[0073] A following layer construction was produced according to
conventional methods known to the person skilled in the art (from
top to bottom):
[0074] Resist (.about.150-350 nm)
[0075] Al.sub.2O.sub.3 (.about.50-200 nm)
[0076] Si.sub.3N.sub.4 (pad nitride .about.100-200 nm)
[0077] SiO.sub.2 (thin pad oxide)
[0078] The following method steps were carried out:
[0079] Firstly, a contact hole lithography was effected in a
conventional manner. The Al.sub.2O.sub.3 was subsequently patterned
by a process according to the invention, i.e. an etching method was
carried out with a mixture comprising
C.sub.4F.sub.6:CH.sub.2F.sub.2:O.sub.2: Ar in the ratio
1:0.6:0.8:20 at a process pressure of 40 mT. Further
parameters:
4 Time: 60 s Power: 1800 W Magnetic field 100 G.
[0080] The apparatus used was the Applied Materials eMax 200
mm.
[0081] The resist was then removed (resist stripping) in a
conventional manner and the silicon nitride was then patterned.
[0082] As an alternative, after contact hole lithography, the
Al.sub.2O.sub.3 may be patterned by the above-described process
according to the invention together with the Si.sub.3N.sub.4
patterning in one etching step. The resist stripping is then
performed.
[0083] In accordance with this example, a relatively thick
Si.sub.3N.sub.4 layer could be etched effectively using
Al.sub.2O.sub.3 as a hard mask.
[0084] 4. Contact Hole Etching
[0085] An exemplary embodiment of the present invention is
illustrated diagrammatically in FIGS. 2 to 7 and explained in more
detail below. A method for fabricating self-aligned contacts is
involved in this case.
[0086] FIG. 2 shows an exemplary silicon semiconductor substrate 1
with a memory cell arrangement that is not illustrated in greater
detail. 60 designates an active region, for example a common
source/drain region of two memory cells. GS1, GS2 are two gate
stacks lying next to one another, which are constructed from a
polysilicon layer 10 with underlying (not illustrated) gate
dielectric layer (e.g. gate oxide), if appropriate a silicide layer
20 and a silicon nitride cap 30 and also a sidewall oxide layer 40.
CB designates the position at which a contact to the active region
60 is to be fabricated.
[0087] Between the two gate stacks GS1, GS2 it is necessary to
provide a contact type CB, which makes electrical contact with the
active region 60 between the two gate stacks GS1, GS2. Usually, the
contact hole for the contact CB is etched separately from other
contacts. In this case, the distance results, as is known, from the
increasing miniaturization that leads to an increase in the number
of chips per wafer and thus to a reduction of costs.
[0088] Afterward, as illustrated in FIG. 3, a silicon oxide layer,
e.g. a BPSG layer (borophosphosilicate glass), designated by
reference symbol 100, is deposited over the resulting structure.
Said BPSG layer 100 is made to flow in a subsequent heat treatment,
so that it does not leave any voids in particular between the
closely adjacent gate stacks GS1, GS2.
[0089] In a subsequent method step (not illustrated), a planarizing
ARC coating (anti-reflective coating) may be spun on, which
compensates for the remaining unevennesses of the surface of the
BPSG 100. If this does not suffice, a planarization, for example by
means of chemical mechanical polishing (CMP), may also be effected
after the heat treatment of the BPSG layer 100.
[0090] Afterward, as illustrated in FIG. 4, an Al.sub.2O.sub.3
layer, designated by reference symbol 110, is deposited on the
resulting structure. This Al.sub.2O.sub.3 layer later serves as a
hard mask for the selective etching of the underlying silicon
oxide. Furthermore, as is illustrated in FIG. 4, a resist layer 120
for the later patterning of the aluminum oxide layer 110 is
applied.
[0091] FIG. 5 shows the state after exposure of the resist in order
to form a mask for the patterning of the Al.sub.2O.sub.3 layer.
[0092] FIG. 6 shows the state after carrying out the etching method
according to the invention, e.g. with a mixture comprising
C.sub.4F.sub.6:CH.sub.2F.sub.2:O.sub.2:Ar in the ratio
1:0.6:0.8:20, at a process pressure of 40 mT. the method according
to the invention is thus utilized for producing a hard mask made of
aluminum oxide.
[0093] FIG. 7 then shows the state after selective etching of the
contact hole and removal of the resist layer. The contact hole is
subsequently filled. The aluminum oxide layer may be removed prior
to the contact hole being filled, e.g. with tungsten, but may also
remain and serve as a spacer from the substrate in order to keep
capacitive couplings low.
[0094] The selection of the substrate material and the geometry are
only by way of example and may be varied in many different ways. In
particular, the present invention can be employed not only for the
fabrication of contact holes but wherever aluminum oxide layers
have to be etched selectively with respect to silicon, photoresists
or metals or wherever silicon oxide, silicon nitride and/or silicon
oxynitride have to be etched selectively with respect to aluminum
oxide.
* * * * *