U.S. patent application number 11/429959 was filed with the patent office on 2006-09-14 for methods of etching photoresist on substrates.
This patent application is currently assigned to Lam Research Corporation. Invention is credited to Robert P. Chebi, Erik A. Edelberg, Gladys Sowan Lo.
Application Number | 20060201911 11/429959 |
Document ID | / |
Family ID | 33516986 |
Filed Date | 2006-09-14 |
United States Patent
Application |
20060201911 |
Kind Code |
A1 |
Edelberg; Erik A. ; et
al. |
September 14, 2006 |
Methods of etching photoresist on substrates
Abstract
Methods of etching a carbon-rich layer on organic photoresist
overlying an inorganic layer can utilize a process gas including
C.sub.xH.sub.yF.sub.z, where y.gtoreq.x and z.gtoreq.0, and one or
more optional components to generate a plasma effective to etch the
carbon-rich layer with low removal of the inorganic layer. The
carbon-rich layer can be removed in the same processing chamber, or
alternatively can be removed in a different processing chamber, as
used to remove the bulk photoresist.
Inventors: |
Edelberg; Erik A.; (Castro
Valley, CA) ; Chebi; Robert P.; (Foster City, CA)
; Lo; Gladys Sowan; (Fremont, CA) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Lam Research Corporation
|
Family ID: |
33516986 |
Appl. No.: |
11/429959 |
Filed: |
May 9, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10462830 |
Jun 17, 2003 |
7083903 |
|
|
11429959 |
May 9, 2006 |
|
|
|
Current U.S.
Class: |
216/67 ;
257/E21.256 |
Current CPC
Class: |
G03F 7/427 20130101;
H01L 21/31138 20130101 |
Class at
Publication: |
216/067 |
International
Class: |
C23F 1/00 20060101
C23F001/00 |
Claims
1. (canceled)
2. (canceled)
3. (canceled)
4. (canceled)
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. (canceled)
17. (canceled)
18. (canceled)
19. (canceled)
20. (canceled)
21. (canceled)
22. (canceled)
23. (canceled)
24. (canceled)
25. (canceled)
26. (canceled)
27. (canceled)
28. (canceled)
29. (canceled)
30. A method of etching an organic photoresist on a substrate,
comprising: positioning a substrate in a plasma processing chamber
of a plasma reactor, the substrate including an inorganic layer and
an organic photoresist overlying the inorganic layer, the
photoresist including a carbon-rich layer overlying bulk
photoresist; supplying a process gas to the plasma processing
chamber; generating a plasma from the process gas in the plasma
processing chamber; selectively etching the carbon-rich layer
relative to the inorganic layer while optionally applying an
external RF bias to the substrate; after etching the carbon-rich
layer, optionally removing the substrate from the plasma processing
chamber and placing the substrate in an ashing chamber; supplying
an ashing gas containing oxygen to (i) the plasma processing
chamber or (ii) the ashing chamber, in which the substrate is
positioned; generating a plasma from the ashing gas upstream from
the substrate; and etching the bulk photoresist.
31. The method of claim 30, wherein the plasma reactor is an
inductively coupled plasma reactor, and the substrate is
capacitively RF biased.
32. The method of claim 30, further comprising independently
controlling ion flux and ion energy.
33. The method of claim 30, wherein: the plasma reactor is an
inductively-coupled plasma reactor; a planar antenna inductively
couples RF energy into the plasma processing chamber through a
dielectric member; and the substrate is positioned in the plasma
processing chamber facing the dielectric member.
34. The method of claim 30, wherein the carbon-rich layer and the
bulk photoresist are etched in the plasma processing chamber.
35. The method of claim 30, wherein the carbon-rich layer is etched
in the plasma processing chamber, and the bulk photoresist is
etched in the ashing chamber.
36. The method of claim 30, wherein the process gas comprises
C.sub.xH.sub.yF.sub.z, where y.gtoreq.x and z.gtoreq.0, and at
least one of (i) an oxygen-containing gas, and (ii) a
hydrogen-containing gas different from the C.sub.xH.sub.yF.sub.z.
Description
BACKGROUND
[0001] Plasma processing apparatuses are used for processes
including plasma etching, physical vapor deposition, chemical vapor
deposition (CVD), ion implantation, and resist removal.
[0002] Photoresist materials are used in plasma processing
operations to pattern materials. Commercial photoresists are blends
of polymeric and other organic and inorganic materials. A
photoresist is applied onto a substrate, and radiation is passed
through a patterned mask to transfer the pattern into the resist
layer. The two broad classifications of photoresist are
negative-working resist and positive-working resist, which produce
negative and positive images, respectively. After being developed,
a pattern exists in the photoresist. The patterned photoresist can
be used to define features in substrates by etching, as well as to
deposit materials onto, or implant materials into, substrates.
SUMMARY OF THE INVENTION
[0003] Methods for etching organic photoresist on substrates are
provided. The methods can selectively etch photoresist relative to
the substrate.
[0004] A preferred embodiment of the methods of etching organic
photoresist on a substrate comprises positioning in a plasma
processing chamber a substrate including an inorganic layer and an
organic photoresist overlying the inorganic layer, the photoresist
including a carbon-rich layer overlying bulk photoresist; supplying
to the processing chamber a process gas comprising
C.sub.xH.sub.yF.sub.z (where y.gtoreq.x and z.gtoreq.0), and at
least one of (i) an oxygen-containing gas, and (ii) a
hydrogen-containing gas different from C.sub.xH.sub.yF.sub.z;
generating a plasma from the process gas; and selectively etching
the carbon-rich layer relative to the inorganic layer.
[0005] The bulk photoresist can be etched in the same plasma
processing chamber that is used to etch the carbon-rich layer.
Alternatively, the bulk photoresist can be etched in an ashing
chamber. The bulk photoresist preferably is etched using a
different chemistry than used to remove the carbon-rich layer.
[0006] Another preferred embodiment of the methods of etching
organic photoresist on a substrate comprises supplying to a plasma
processing chamber a process gas comprising CH.sub.3F and at least
one of (i) an oxygen-containing gas, and (ii) a hydrogen-containing
gas different from CH.sub.3F; generating a plasma from the process
gas; and selectively etching a carbon-rich layer on the substrate
relative to an inorganic layer on the substrate while applying an
external RF bias to the substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 schematically illustrates a process for removing an
ion-implanted, carbon-rich layer formed on photoresist overlying a
silicon substrate using a plasma generated from 100% O.sub.2 or
H.sub.2O vapor with RF bias applied to the substrate.
[0008] FIG. 2 is a scanning electron microscope (SEM) micrograph
showing typical residue present on the surface of a post-implant
substrate after etching an organic photoresist in an RF-biased
plasma source using 100% O.sub.2 or H.sub.2O vapor.
[0009] FIG. 3 depicts an exemplary inductively-coupled plasma
reactor which can be used to perform embodiments of the methods of
removing photoresist from substrates.
[0010] FIG. 4 depicts an exemplary parallel-plate plasma reactor
which can be used to perform embodiments of the methods of removing
photoresist from substrates.
[0011] FIG. 5 schematically illustrates a process for removing an
ion-implanted, carbon-rich layer formed on organic photoresist
overlying a silicon substrate using a plasma generated from a
process gas containing CH.sub.3F and O.sub.2 or H.sub.2O vapor with
RF bias applied to the substrate.
[0012] FIG. 6 is an SEM micrograph showing the surface of a
post-implant wafer after photoresist removal in an RF-biased plasma
source using a process gas containing CH.sub.3F and O.sub.2.
DETAILED DESCRIPTION
[0013] In integrated circuit (IC) manufacturing processes that
utilize ion implantation, shrinking device geometries, increased
ion implantation energies and doses, and new materials make it
increasingly difficult to produce residue-free devices. Residues
remaining from etching and ashing processes can produce undesirable
electrical effects and corrosion that reduce product yields. See E.
Pavel, "Combining Microwave Downstream and RF Plasma Technology for
Etch and Clean Applications," 196.sup.th Meeting of the
Electrochemical Society, (October, 1999).
[0014] In plasma processing techniques, such as plasma etching and
reactive ion etching (RIE), and in ion implantation, photoresist is
applied onto a substrate to protect selected regions of the
substrate from being exposed to ions and free radicals. Organic
polymer compositions have been formulated for such resist
applications.
[0015] Photoresists are removed, or "stripped," from the underlying
substrate after the substrate has been processed by etching, ion
implantation, or the like. It is desirable that the photoresist
stripping process leave the substrate surface as clean as possible,
desirably without any residual polymer film or resist material. Wet
and dry stripping techniques can be used to remove photoresist. Wet
stripping techniques use solutions containing organic solvents or
acids. Dry stripping (or "ashing") techniques use an oxygen plasma
for photoresist removal.
[0016] Ion implantation fabrication techniques are used to dope
regions of a substrate with impurities to change the electrical
properties of the substrate. Ion implantation can be used as a
source of doping atoms, or to introduce regions of different
composition in a substrate. During ion implantation, ions are
accelerated at a sufficiently high voltage to penetrate the
substrate surface to a desired depth. Increasing the accelerating
voltage increases the depth of the concentration peak of the
impurities.
[0017] Regions of the substrate at which implantation is not
desired are protected with photoresist. However, the photoresist is
modified during implantation, and is rendered more difficult to
remove after implantation than a normal (non-implanted)
photoresist. Particularly, implanted ions damage regions of the
photoresist, thereby breaking near-surface C--H bonds and forming
carbon-carbon single and double bonds. The resulting tough,
carbon-rich or "carbonized" layer (or "skin" or "crust") of
cross-linked, implanted photoresist encapsulates the distinct
underlying bulk photoresist. The thickness of the carbon-rich layer
is a function of the implant species, voltage, dose and current.
The carbon-rich layer typically has a thickness of from about 200
.ANG. to about 2000 .ANG.. See, A. Kirkpatrick et al., "Eliminating
heavily implanted resist in sub-0.25-.mu.m devices," MICRO, 71
(July/August 1998). According to E. Pavel, as implant doses and
energies increase, implanted photoresist can become increasingly
more difficult to remove.
[0018] Carbon-rich layers can also be formed in organic photoresist
during plasma processing techniques, other than ion-implantation
techniques, in which ion bombardment of the photoresist also
occurs.
[0019] Oxygen plasma ashing techniques can remove the carbon-rich
layer, but only at a slow rate of about 500 .ANG./min or less. The
etching mechanism of these techniques is the radical reaction of
oxygen atoms with hydrocarbons in the photoresist to produce
H.sub.2O and CO.sub.2.
[0020] It has been determined that an external bias can be applied
to the substrate to enhance the removal rate of the cross-linked
layer. The applied bias provides energy to the carbon-rich layer,
which breaks carbon single bonds and thereby enhances reactions
with oxygen radicals.
[0021] However, it has also been determined that applying an
external bias to the substrate to enhance photoresist removal can
also produce undesired effects. FIG. 1 schematically depicts a
process of removing organic photoresist from an ion-implanted
substrate 10. The substrate 10 includes silicon 11 that is ion
implanted and a thin overlying inorganic layer 12 (e.g., a
silicon-containing layer, such as SiO.sub.x). A photoresist 16
applied over the inorganic layer 12 includes bulk photoresist 18,
and an overlying carbon-rich layer 20 formed by the
ion-implantation process. The photoresist 16 spacing is typically
about 0.25 .mu.m or less on the substrate 10. In a biased system,
energetic O.sub.2.sup.+ ions can cause sputtering of the inorganic
layer 12. Sputtering of the inorganic layer 12 is undesirable
because for typical process specifications the maximum amount of
inorganic material (e.g., oxide) loss during the removal of the
carbon-rich layer 20 and the bulk photoresist 18 is less than about
2 .ANG.. The carbon-rich layer 20 can typically have a thickness of
from about 200 to about 2000 .ANG., and the bulk photoresist 18 can
typically have a thickness of about several thousand angstroms. In
addition, sputtered inorganic material can re-deposit on the
substrate and on the photoresist, resulting in organic and
inorganic residue being present on the substrate after cleaning.
FIG. 2 is a scanning electron microscope (SEM) micrograph showing
residue present on the surface of a post-implant wafer at regions
at which photoresist is present on the substrate after photoresist
ashing in an RF-biased plasma source using 100% O.sub.2 or H.sub.2O
vapor.
[0022] Another undesirable effect of applying a bias voltage to the
substrate for carbon-rich layer removal is that oxygen ions of the
plasma may have sufficiently high energy to penetrate the thin
inorganic layer and oxidize the underlying silicon.
[0023] In light of the above-described findings, it has been
determined that process gases including C.sub.xH.sub.yF.sub.x
(where y.gtoreq.x and z.gtoreq.0) can be used in organic
photoresist etching processes to control, and preferably to
eliminate, sputtering and re-deposition, as well as growth, of
inorganic material. The inorganic material can be, for example, a
silicon-containing material (e.g., Si, SiO.sub.x [e.g. SiO.sub.2],
Si.sub.x N.sub.y [e.g., Si.sub.3 N.sub.4], Si.sub.x O.sub.y
N.sub.z, and the like), and HfO. The photoresist can be present on
various substrate materials including, e.g., silicon, SiO.sub.2,
Si.sub.3N.sub.4, and the like.
[0024] More particularly, preferred process gases for removing the
carbon-rich overlying bulk photoresist include
C.sub.xH.sub.yF.sub.z gases (where y.gtoreq.x and z.gtoreq.0),
e.g., CH.sub.2F.sub.2 and CH.sub.3F, preferably CH.sub.3F, and at
least one of an oxygen-containing gas and a hydrogen-containing gas
that is different from the C.sub.xH.sub.yF.sub.x. The process gas
can also include one or more other optional gases, such as N.sub.2.
Also, the process gas can include one or more inert carrier gases,
such as Ar, He, or the like.
[0025] The oxygen-containing gas is preferably O.sub.2, H.sub.2O
vapor, or a mixture thereof. The hydrogen-containing gas can be
H.sub.2, or the like. The gas mixture preferably comprises, by
volume, from about 5% to about 30% of C.sub.xH.sub.yF.sub.z (where
y.gtoreq.x and z.gtoreq.0), and from about 95% to about 70% of at
least one of the oxygen-containing gas and the hydrogen-containing
gas, and any optional gas. More preferably, the gas mixture
comprises at least about 10% C.sub.xH.sub.yF.sub.z (where
y.gtoreq.x and z.gtoreq.0), with the balance being an
oxygen-containing gas, a hydrogen-containing gas or a mixture
thereof, and optional gas.
[0026] It also has been determined that increasing the volume
percentage of C.sub.xH.sub.yF.sub.z in the gas mixture to above a
certain volume percentage can result in deposition of a
carbon-containing film onto the inorganic layer, rather than in net
removal of the inorganic layer (i.e., a decreased thickness of the
inorganic layer). However, the volume percentage of
C.sub.xH.sub.yF.sub.z in the gas mixture preferably is sufficiently
low to avoid incorporating fluorine into the underlying
substrate.
[0027] It also has been determined that when H.sub.2 is used as the
hydrogen-containing gas, the carbon-rich layer is softened, making
this layer easier to remove by etching.
[0028] It has also been determined that process gases including
CH.sub.3F can be used to remove the carbon-rich layer at a suitably
high etch rate and with a suitably high etch rate selectivity
relative to the inorganic layer. For example, process gas mixtures
containing CH.sub.3F and O.sub.2 can be used to remove a
carbon-rich layer having a thickness of 2000 .ANG. in about 30
seconds or less (i.e., at an etch rate of at least about 4000
.ANG./min), preferably in about 20 seconds or less (i.e., at an
etch rate of at least about 6000 .ANG./min). During the removal of
a carbon-rich layer having a thickness of about 200 to about 2000
.ANG., it is preferable that the plasma remove less than about 5
.ANG., more preferably less than about 2 .ANG., of the exposed
inorganic layer.
[0029] Other gases that can remove the carbon-rich layer include
CF.sub.4 and CHF.sub.3. However, these gases are not selective with
respect to the inorganic layer (e.g., to an SiO.sub.x layer).
Accordingly, these gases are not preferred for use in photoresist
removal processes for which selectivity to the inorganic layer is
desired, as these gases may remove more than an acceptable amount
of the inorganic layer during removal of the carbon-rich layer.
[0030] The photoresist can be any suitable organic polymer
composition. For example, the photoresist composition can include a
resin of the Novolak class, a polystyrene component, or the
like.
[0031] To remove the organic photoresist, the process gas including
C.sub.xH.sub.yF.sub.z (where y.gtoreq.x and z.gtoreq.0), and
preferably also at least one of an oxygen-containing gas and a
hydrogen-containing gas different from the C.sub.xH.sub.yF.sub.z,
is energized to generate a plasma.
[0032] The plasma is preferably generated from the process gas by
applying radio frequency (RF) to an electrically conductive coil
outside of the plasma processing chamber. The wafer is preferably
placed in the plasma generation region.
[0033] The plasma reactor is preferably an inductively coupled
plasma reactor. Embodiments of the methods of removing photoresist
from substrates can be performed in an inductively-coupled plasma
reactor, such as the reactor 100 shown in FIG. 3. The reactor 100
includes an interior 102 maintained at a desired vacuum pressure by
a vacuum pump connected to an outlet 104. Process gas can be
supplied to a showerhead arrangement by supplying gas from a gas
supply 106 to a plenum 108 extending around the underside of a
dielectric window 110. A high density plasma can be generated in
the interior 102 by supplying RF energy from an RF source 112 to an
external RF antenna 114, such as a planar spiral coil having one or
more turns disposed outside the dielectric window 110 on top of the
reactor 100.
[0034] A substrate 116, such as a semiconductor wafer, is supported
within the interior 102 of the reactor 100 on a substrate support
118. The substrate support 118 can include a chucking apparatus,
such as an electrostatic chuck 120, and the substrate 116 can be
surrounded by a dielectric focus ring 122. The chuck 120 can
include an RF biasing electrode for applying an RF bias to the
substrate during plasma processing of the substrate 116. The
process gas supplied by the gas supply 106 can flow through
channels between the dielectric window 110 and an underlying gas
distribution plate 124 and enter the interior 102 through gas
outlets in the plate 124. The reactor can also include a liner 126
extending from the plate 124.
[0035] An exemplary plasma reactor that can be used for generating
plasma is the 2300 TCP reactor from Lam Research Corporation.
Typical operation conditions for the plasma reactor are as follows:
from about 500 to about 1000 watts inductive power applied to upper
electrode (coil), reaction chamber pressure of from about 15 to
about 60 mTorr, and a total process gas flow rate of from about 200
to about 600 sccm.
[0036] Embodiments of the methods of removing photoresist from
substrates can also be performed in a parallel-plate plasma
reactor, such as reactor 200 shown in FIG. 4. The reactor 200
includes an interior 202 maintained at a desired vacuum pressure by
a vacuum pump 204 connected to an outlet 205 in a wall of the
reactor. Process gas can be supplied to a showerhead electrode 212
by supplying gas from a gas supply 206. A medium-density plasma can
be generated in the interior 202 by supplying RF energy from RF
source 208, 210 and RF source 214, 216 to the showerhead electrode
212, and to a bottom electrode of a chuck 220 of a substrate
support 218. Alternatively, the showerhead electrode 212 can be
electrically grounded, and RF energy at two different frequencies
can be supplied to the bottom electrode. Other capacitively-coupled
etch reactors can also be used, such as those having RF power
supplied only to a showerhead or upper electrode, or only to a
bottom electrode.
[0037] During removal of the carbon-rich layer, the substrate is
preferably maintained at a sufficiently low temperature on a
substrate support to prevent rupturing of the layer. For example, a
carbon-rich layer may rupture when solvents in the photoresist
composition are volatilized by heating, producing particles that
may deposit on the substrate. To avoid such rupturing of the
carbon-rich layer, the substrate is preferably maintained at a
temperature of less than about 150.degree. C., and more preferably
from about 20 to about 75.degree. C., and a chamber pressure of
less than about 500 mTorr during etching of the carbon-rich
layer.
[0038] During etching of the carbon-rich layer, RF bias is
preferably applied to the substrate with a bias electrode provided
in the substrate support on which the substrate is supported. The
RF bias is preferably capacitive. The applied RF bias and the
generation of the plasma preferably are independently controllable
to independently control ion energy and ion flux, respectively. The
RF bias accelerates ions in the plasma and adds energy to the
substrate, which increases the removal rate of the carbon-rich
layer. The RF bias voltage applied to the substrate is preferably
less than about 100 volts (with respect to ground), more preferably
less than about 20 volts. It has been unexpectedly determined that
the combined use of fluorine in the process gas and an applied RF
bias to the substrate is effective to remove the carbon-rich layer
at a sufficiently high rate while also providing high selectivity
to inorganic material (e.g., oxide) present on the substrate. It
has further been determined that at a given volume percentage of
C.sub.xH.sub.yF.sub.z included in the process gas, the RF bias can
be maintained at a low level that reduces the inorganic material
removal rate from the substrate during etching of the carbon-rich
layer.
[0039] Referring to FIG. 5, it has been determined that the
addition of fluorine, preferably in a small amount, to a process
gas including an oxygen-containing gas, preferably O.sub.2,
H.sub.2O vapor or a mixture thereof, can reduce sputtering of the
inorganic layer 12 (e.g., an oxide layer) and the re-deposition of
sputtered inorganic material, if present, on the substrate.
Fluorine can also contribute to the removal of inorganic materials
that may be in or on the post-ion implant photoresist.
[0040] The addition of hydrogen to the process gas used to etch the
carbon-rich layer increases the etch rate by reacting with
cross-linked carbon. It is believed that fluorine may also enhance
the carbon-rich layer etch rate.
[0041] The addition of CH.sub.x species to the process gas used to
etch the carbon-rich layer causes a passivating layer 22 to form on
the oxide layer 12 and the photoresist 16 (see FIG. 5), which
reduces the amount of ion-induced oxide growth and oxide
sputtering.
[0042] The complete removal of the carbon-rich layer 20 can be
detected during the etching process by using an endpoint detection
technique, which can deternine the time at which the underlying
bulk photoresist is exposed. The endpoint for carbon-rich layer
removal is preferably determined by an optical emission technique.
For example, the optical emission technique can monitor the
emission from carbon monoxide (CO) at a wavelength of about 520 nm.
During the removal of the carbon-rich layer, a small CO signal is
produced due to the low etch rate. Once the carbon-rich layer is
opened, the exposed underlying bulk photoresist is etched at a
faster rate than the carbon-rich layer and, consequently, the CO
concentration and the corresponding CO signal increase.
[0043] After removal of the carbon-rich layer, the underlying bulk
photoresist is preferably removed using a different photoresist
etch process. For example, the bulk photoresist can be removed by
oxygen ashing at a higher temperature than the temperature
preferably used during the carbon-rich layer etching step. For
example, the substrate temperature can range from about 200.degree.
C. to about 280.degree. C. during the bulk photoresist etching
step. The chamber pressure is preferably greater than about 500
mTorr during bulk photoresist removal. Oxygen ashing also can
achieve a high removal rate of the bulk photoresist. For example,
an O.sub.2/N.sub.2 plasma can remove the bulk photoresist at a rate
of from about 4 to about 6 microns/min. An optional over-ash step
can also be used. Volatile solvents in the photoresist can be
exhausted from the plasma processing chamber as the photoresist is
ashed.
[0044] The bulk photoresist is preferably removed using a plasma
generated upstream from the substrate. The bulk photoresist removal
step can be performed in the same processing chamber that is used
to etch the carbon-rich layer. Alternatively, the bulk photoresist
can be removed by etching in a different processing chamber. That
is, the substrate can be removed from the processing chamber after
etching the carbon-rich layer, and placed in a different processing
chamber to etch the bulk photoresist. Using different processing
chambers can obviate changing gas chemistries and/or the substrate
temperature during removal of the carbon-rich layer and ashing.
[0045] Exemplary process conditions for removing the carbon-rich
layer are as follows: chamber pressure of about 90 mTorr, about
1000 Watts of power applied to upper electrode (coil), about 5
Watts of power applied to bias electrode, total process gas flow
rate of about 400 sccm, and substrate temperature of about
75.degree. C. Exemplary process conditions for removing bulk
photoresist are as follows: chamber pressure of about 1000 mTorr,
about 2500 Watts of power applied to the plasma source, total
process gas flow rate of about 4400 sccm, and substrate temperature
of about 220.degree. C.
[0046] FIG. 6 shows an SEM micrograph taken of a substrate surface
after performing a photoresist removal process according to a
preferred embodiment. The substrate was ion implanted with arsenic
at a dose of about 2.times.10.sup.15 atoms/cm.sup.2, and at an
implantation energy of 40 keV. The etching process included
removing the carbon-rich layer formed on the bulk photoresist using
an O.sub.2/CH.sub.3F process gas with RF bias applied to the
substrate, and then removing the underlying bulk photoresist using
an O.sub.2/N.sub.2 process gas. As shown in FIG. 6, the photoresist
was completely removed and no post-etch residue is present on the
wafer. The carbon-rich layer removal endpoint time with the
addition of CH.sub.3F also was significantly reduced. While not
wishing to be bound to any particular theory, this result is
believed to be due to H (and also possibly F) included in the
process gas enhancing the etch rate of the carbon-rich layer.
EXAMPLES
[0047] Silicon wafers were ion implanted with arsenic at a dose of
about 2.times.10.sup.15 atorns/cm.sup.2 and at an implantation
energy of 40 keV to produce a carbon-rich layer on underlying bulk
photoresist. The Table below shows the etch rates that were
determined for silicon oxide, bulk photoresist, and the carbon-rich
layer at different additions of CH.sub.3F (on a volume percent
basis) to an O.sub.2-containing process gas, which was used to
generate plasma to remove the carbon-rich layer. During stripping
of the carbon-rich layer, an RF bias at a power level of 5 watts
was applied to the substrate.
[0048] The bulk photoresist etch rate was estimated by placing a
non-implanted organic photoresist having a known thickness in a
processing chamber and partially stripping the photoresist. As bulk
photoresist is also non-implanted material, the calculated bulk
photoresist etch rate approximates the etch rate of bulk
photoresist underlying an implanted carbon-rich layer. The
carbon-rich layer thickness was measured using an SEM prior to
stripping. The carbon-rich layer etch rate was calculated by
measuring the endpoint time of the etch, and determining the
thickness reduction of the carbon-rich layer. TABLE-US-00001 TABLE
% CH.sub.3F Oxide Etch Rate Bulk Photoresist Carbon-rich Layer
(vol. %) (.ANG./min) Etch Rate (.ANG./min) Etch Rate (.ANG./min)
0.0 1 4174 1300 2.5 5 4742 10.0 3 5642 2400 15.0 -1 5004 30 -8
>6000
[0049] The test results show that the oxide etch rate increases
with a small addition of CH.sub.3F, but decreases with increased
additions of CH.sub.3F. The oxide removal rate is reduced by adding
more than 2.5% by volume of CH.sub.3F to the process gas. The bulk
photoresist etch rate is increased by increasing the volume percent
of CH.sub.3F. The carbon-rich layer etch rate is also enhanced by
the addition of CH.sub.3F.
[0050] The test results demonstrate the existence of a process
regime within which CH.sub.3F passivates and protects the SiO.sub.x
surface from chemical and/or physical attack. The oxide etch rate
increases with the addition of CH.sub.3F up to a CH.sub.3F
percentage at which passivation of the inorganic layer is
sufficiently large to stop the etching of the inorganic layer.
While not wishing to be bound to any particular theory, the
enhanced photoresist etch rate is believed to be due to the
presence of both H and F radicals in the plasma.
[0051] For comparison, gas mixtures containing 10% CF.sub.4
(balance O.sub.2), and 10% CHF.sub.3 (balance O.sub.2), were used
to generate a plasma and remove the carbon-rich layer on bulk
photoresist from ion-implanted silicon wafers. The oxide etch rate
for the gas mixture containing CF.sub.4 was 27 .ANG./min, and the
oxide etch rate for the gas mixture containing CHF.sub.3 was 15
.ANG./min. These oxide etch rates are too high for photoresist
removal processes that have stringent maximum oxide removal
specifications, such as those having a maximum oxide etch rate of
about 5 .ANG./min, and especially those having a maximum oxide etch
rate of less than about 2 .ANG./min.
[0052] While the invention has been described in detail with
reference to specific embodiments thereof, it will be apparent to
those skilled in the art that various changes and modifications can
be made, and equivalents employed, without departing from the scope
of the appended claims.
* * * * *