U.S. patent application number 10/904533 was filed with the patent office on 2006-05-18 for via reactive ion etching process.
This patent application is currently assigned to INTERNATIONAL BUSINESS MACHINES CORPORATION. Invention is credited to Peter Biolsi, Samuel S. Choi.
Application Number | 20060105572 10/904533 |
Document ID | / |
Family ID | 36318084 |
Filed Date | 2006-05-18 |
United States Patent
Application |
20060105572 |
Kind Code |
A1 |
Biolsi; Peter ; et
al. |
May 18, 2006 |
VIA REACTIVE ION ETCHING PROCESS
Abstract
Methods of etching a dielectric layer and a cap layer over a
conductor level to open a via to the conductor. The methods include
the provision of tetrafluoro methane (CF.sub.4) in a photoresist
strip. In addition, the methods may provide an increased amount of
tetrafluoro methane (CF.sub.4) in a dielectric layer etch, and
trifluoro methane (CHF.sub.3) in a cap layer etch. The invention
provides higher yield, more predictable etch rates, faster
processing, and removes the need for an ash step.
Inventors: |
Biolsi; Peter; (New Windsor,
NY) ; Choi; Samuel S.; (Beacon, NY) |
Correspondence
Address: |
HOFFMAN, WARNICK & D'ALESSANDRO LLC
75 STATE ST
14TH FL
ALBANY
NY
12207
US
|
Assignee: |
INTERNATIONAL BUSINESS MACHINES
CORPORATION
New Orchard Road
Armonk
NY
|
Family ID: |
36318084 |
Appl. No.: |
10/904533 |
Filed: |
November 15, 2004 |
Current U.S.
Class: |
438/706 ;
257/E21.252; 438/624 |
Current CPC
Class: |
H01L 21/02063 20130101;
H01L 21/31116 20130101 |
Class at
Publication: |
438/706 ;
438/624 |
International
Class: |
H01L 21/4763 20060101
H01L021/4763; H01L 21/461 20060101 H01L021/461; H01L 21/302
20060101 H01L021/302 |
Claims
1. (canceled)
2. A method of etching a dielectric layer and a cap layer over a
conductor level to open a via to a conductor, a pattern for the via
being provided by a photoresist, the method comprising the steps
of: etching the via through the dielectric layer; stripping the
photoresist using a plasma chemistry including tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to the
conductor; wherein the dielectric layer etching step includes using
approximately 80 mT of pressure, an RF energy of approximately 1200
W at 27 MHz and approximately 2700 W at 2 MHz, and a gas flow
including tetrafluoro methane (CF.sub.4) and carbon monoxide (CO)
in a gas flow ratio of no less than approximately 0.104 and no
greater than approximately 0.2.
3. The method of claim 2, wherein the gas flow during the
dielectric layer etching step includes no less than approximately
25 and no greater than approximately 40 standard cubic centimeters
per minute (sccm) of tetrafluoro methane (CF.sub.4), no less than
approximately 200 and no greater than approximately 240 sccm of
carbon monoxide (CO), and approximately 400 sccm of argon (Ar).
4. The method of claim 2, wherein the dielectric layer etching step
has an etch rate of approximately 95 .ANG.ngstroms/second
(.ANG./s).
5. The method of claim 2, wherein the photoresist stripping step
includes using a gas flow of no less than approximately 7 standard
cubic centimeters per minute (sccm) and no greater than
approximately 15 scam of the tetrafluoro methane (CF.sub.4).
6. A method of etching a dielectric layer and a cap layer over a
conductor level to open a via to a conductor, a pattern for the via
being provided by a photoresist, the method comprising the steps
of: etching the via through the dielectric layer; stripping the
photoresist using a plasma chemistry including tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to die
conductor; wherein the photoresist stripping step includes two
stages including: a first stage using approximately 120 mT of
pressure, an RF energy of approximately 1000 W at 27 MHz and
approximately 200 W at 2 MHz, and a gas flow including oxygen
(O.sub.2); and a second stage using approximately 400 mT of
pressure, an RF energy of approximately 1600 W at 2 MHz, and a gas
flow including the tetrafluoro methane (CF.sub.4) and oxygen
(O.sub.2) in a gas flow ratio no less than approximately 0.006 and
no greater than, approximately 0.016.
7. The method of claim 6, wherein the gas flow of the first stage
includes no less than approximately 900 standard cubic centimeters
per minute (sccm) and no greater than approximately 1100 sccm of
the oxygen O.sub.2.
8. The method of claim 6, wherein the gas flow of the second stage
includes no less than approximately 7 standard cubic centimeters
per minute (sccm) and no greater than approximately 15 sccm of the
tetrafluoro methane (CF.sub.4), and no less than approximately 900
sccm and no greater than approximately 1100 sccm of the oxygen
(O.sub.2).
9. The method of claim 6, wherein the cap layer etching step
includes using approximately 150 mT of pressure, an RF energy of
approximately 1000 W at 2 MHz and approximately 1500 W at 27 MHz,
and a gas flow including tetrafluoro methane (CF.sub.4) and
trifluoro methane (CHF.sub.3) in a gas flow ratio of no less than
approximately 2.33 and no greater than approximately 3.96.
10. The method of claim 9, wherein, in the case that the cap layer
has a thickness of no less than approximately 800 .ANG. and no
greater than 1200 .ANG., the cap layer etching step gas flow
includes no less than approximately 80 and no greater than
approximately 110 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 210 sccm of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
scam of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
11. The method of claim 9, wherein, in the case that the cap layer
has a thickness of no less than approximately 2500 .ANG. and no
greater than 3500 .ANG., the cap layer etching step gas flow
includes no less than approximately 7 and no greater than
approximately 13 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 210 sccm of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
sccm of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
12. (canceled)
13. A method of etching a dielectric layer and a cap layer over a
conductor level to open a via to a conductor, a pattern for the via
being provided by a photoresist, the method consisting of the steps
of: etching the via through the dielectric layer; stripping the
photoresist using a plasma chemistry including tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to the
conductor; wherein the dielectric layer etching step includes using
approximately 80 mT of pressure, an RF energy of approximately 1200
W at 27 MHz and approximately 2700 W at 2 MHz, and a gas flow
including tetrafluoro methane (CF.sub.4) and carbon monoxide (CO)
in a gas flow ratio of no less than approximately 0.104 and no
greater than approximately 0.2.
14. The method of claim 13, wherein the gas flow during the
dielectric layer etching step includes no less than approximately
25 and no greater than approximately 40 standard cubic centimeters
per minute (sccm) of tetrafluoro methane (CF.sub.4), no less than
approximately 200 and no greater than approximately 240 sccm of
carbon monoxide (CO), and approximately 400 sccm of argon (Ar).
15. The method of claim 13, wherein the photoresist stripping step
includes using a gas flow of no less than approximately 7 standard
cubic centimeters per minute (scam) and no greater than
approximately 15 sccm of the tetrafluoro methane (CF.sub.4).
16. The method of claim 13, wherein the photoresist stripping step
includes two stages including: a first stage using approximately
120 mT of pressure, an RE energy of approximately 1000 W at 27 MHz
and approximately 200 W at 2 MHz, and a gas flow including oxygen
(O.sub.2); and a second stage using approximately 400 mT of
pressure, an RF energy of approximately 1600 W at 2 MHz, and a gas
flow including the tetrafluoro methane (CF.sub.4) and oxygen
(O.sub.2) in a gas flow ratio no less than approximately 0.006 and
no greater than approximately 0.016.
17. The method of claim 16, wherein the gas flow of the first stage
includes no less than approximately 900 standard cubic centimeters
per minute (sccm) and no greater than approximately 1100 sccm of
the oxygen (O.sub.2).
18. The method of claim 16, wherein the gas flow of the second
stage includes no less than approximately 7 sccm and no greater
than approximately 15 sccm of the tetrafluoro methane (CF.sub.4),
and no less than approximately 900 sccm and no greater than
approximately 1100 scam of the oxygen (O.sub.2).
19. The method of claim 13, wherein the cap layer etching step
includes using approximately 150 mT of pressure, an RF energy of
approximately 1000 W at 2 MHz and approximately 1500 W at 27 MHz,
and a gas flow including tetrafluoro methane (CF.sub.4) and
trifluoro methane (CHF.sub.3) in a gas flow ratio of no less than
approximately 2.33 and no greater than approximately 3.96.
20. The method of claim 19, wherein, in the case that the cap layer
has a thickness of no less than approximately 800 .ANG. and no
greater than 1200 .ANG., the cap layer etching step gas flow
includes no less than approximately 80 and no greater than
approximately 110 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 210 sccm of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
sccm of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
21. The method of claim 19, wherein, in the case that the cap layer
has a thickness of no less than approximately 2500 .ANG. and no
greater than 3500 .ANG., the cap layer etching step gas flow
includes no less than approximately 7 and no greater than
approximately 13 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 210 scan of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
sccm of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
22. A method of etching a dielectric layer and a cap layer over a
conductor level to open a via to a conductor, a pattern for the via
being provided by a photoresist, the method comprising of the steps
of: etching the via through the dielectric layer using
approximately 80 mT of pressure, an RF energy of approximately 1200
W at 27 MHz and approximately 2700 W at 2 MHz, and a gas flow
including tetrafluoro methane (CF.sub.4) and carbon monoxide (CO)
in a gas flow ratio of no less than approximately 0.104 and no
greater than approximately 0.2; stripping the photoresist using a
plasma chemistry including tetrafluoro methane (CF.sub.4) using a
gas flow of no less than approximately 7 standard cubic centimeters
per minute (sccm) and no greater than approximately 15 sccm of the
tetrafluoro methane (CF.sub.4); and etching the cap layer to open
the via to the conductor using approximately 150 mT of pressure, an
RF energy of approximately 1000 W at 2 MHz and approximately 1500 W
at 27 MHz, and a gas flow including tetrafluoro methane (CF.sub.4)
and trifluoro methane (CHF.sub.3) in a gas flow ratio of no less
than approximately 2.33 and no greater than approximately 3.96.
23. The method of claim 22, wherein the gas flow the dielectric
layer etching step includes no less than approximately 25 and no
greater than approximately 40 standard cubic centimeters per minute
(sccm) of tetrafluoro methane (CF.sub.4), no less than
approximately 200 and no greater than approximately 240 sccm of
carbon monoxide (CO), and approximately 400 sccm of argon (Ar).
24. The method of claim 22, wherein die photoresist stripping step
includes two stages including: a first stage using approximately
120 mT of pressure, an RF energy of approximately 1000 W at 27 MHz
and approximately 200 W at 2 MHz, and a gas flow of no less than
approximately 900 standard cubic centimeters per minute (sccm) and
no greater than approximately 1100 sccm of oxygen (O.sub.2); and a
second stage using approximately 400 mT of pressure, an RF energy
of approximately 1600 W at 2 MHz, and a gas flow including the
tetrafluoro methane (CF.sub.4) and oxygen (O.sub.2) in a gas flow
ratio no less than approximately 0.006 and no greater than
approximately 0.016.
25. The method of claim 24, wherein the gas flow of the second
stage includes no less than approximately 900 sccm and no greater
than approximately 1100 sccm of the oxygen (O.sub.2).
26. The method of claim 22, wherein, in the case that the cap layer
has a thickness of no less than approximately 800 .ANG. and no
greater than 1200 .ANG., the cap layer etching step gas flow
includes no less than approximately 80 and no greater than
approximately 110 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 21.0 sccm of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
sccm of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
27. The method of claim 22, wherein, in the case that the cap layer
has a thickness of no less than approximately 2500 .ANG. and no
greater than 3500 .ANG., the cap layer etching step gas flow
includes no less than approximately 7 and no greater than
approximately 13 standard cubic centimeters per minute (sccm) of
oxygen (O.sub.2), no less than approximately 170 and no greater
than approximately 210 sccm of tetrafluoro methane (CF.sub.4), no
less than approximately 53 and no greater than approximately 73
sccm of trifluoro methane (CHF.sub.3), and approximately 400 sccm
of argon (Ar).
28-30. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates generally to semiconductor
fabrication, and more particularly, to a via reactive ion etching
process.
RELATED ART
[0002] In the semiconductor industry, reactive ion etching (RIE) is
used to open pathways for circuitry within a semiconductor chip.
One structure formed using RIE is a via, which electrically
connects conductors within different layers. RIE is a variation of
plasma (gas) etching in which a semiconductor wafer is placed on a
radio frequency (RF) powered electrode, and etching species are
extracted and accelerated from the plasma toward the surface to be
etched. A chemical etching reaction occurs which removes parts of
the surface. RIE is one of the most common etching techniques in
semiconductor manufacturing.
[0003] Referring to FIG. 1, a semiconductor structure 10 including
large-via pad dielectric layers 12 prior to etching is shown.
Structure 10 includes a conductor level 14 including a dielectric
layer 16 (e.g., of silicon dioxide SiO.sub.2) surrounding conductor
18 (e.g., of copper Cu); a cap layer 20 (e.g., of silicon nitride
Si.sub.3N.sub.4) atop conductor level 14; a dielectric layer 22
(e.g., of silicon dioxide SiO.sub.2); another dielectric layer 24
(e.g., of silicon nitride Si.sub.3N.sub.4); and a patterned
photoresist 26. A typical large-via RIE process is conducted in a
single plasma chamber capable of two RF settings, e.g., 2 MHz and
27 MHz. One conventional RIE process includes the following steps:
etching of dielectric layer 24, etching dielectric layer 22 and
stopping on cap layer 20 so as to not expose conductor 18,
stripping photoresist 26, etching cap layer 20 to expose conductor
18, and finally, performing a nitrogen-hydrogen (N.sub.2H.sub.2)
plasma chemistry (ash) to remove residual RIE polymers from
conductor 18. More specifically, dielectric layer 22 etching may
occur, for example, using the following conditions: 80 mTorr (mT)
of pressure, an RF energy of 1800 watts (W) at 27 MHz and 600 W at
2 MHz, and a gas flow of 10 standard cubic centimeters per minute
(sccm) of tetrafluoro methane (CF.sub.4), 220 sccm of carbon
monoxide (CO) and 400 sccm of argon (Ar), resulting in an
approximately 45 .ANG.ngstrom/second (.ANG./s) etch rate. The
photoresist strip may use, for example, the following conditions in
two stages including: 800 mT of pressure, an RF energy of 800 W at
27 MHz, and a gas flow of 1000 sccm of oxygen (O.sub.2), followed
by 450 mT of pressure, 1200 W at 27 MHz and 200 W at 2 MHz, and a
gas flow including 1000 sccm of oxygen (O.sub.2). The dielectric
layer 20 etch may occur, for example, using the following
conditions: 150 mT of pressure, an RF energy of 1000 W at 2 MHz and
1500 W at 27 MHz, and a gas flow of 100 sccm of oxygen (O.sub.2),
190 sccm tetrafluoro methane (CF.sub.4) and 400 sccm argon (Ar).
The ash step may occur, for example, using the following
conditions: 200 mT of pressure, an RF energy of 1200 W at 27 MHz,
and a gas flow including 600 sccm nitrogen (N.sub.2) and 200 sccm
hydrogen (H.sub.2).
[0004] The conventional RIE process suffers from a number of
problems. First, conventional RIE techniques suffer from a low etch
rate because the gas flow for the process is typically centered at
the minimum operating range of a mass flow controller, which
reduces yields. Second, typical plasma processes are susceptible to
gas flow fluctuations, e.g., within a process chamber or between
different equipment, which results in widely varying etch rates.
Finally, with the movement of wafer fabrication facilities from the
conventional 200 mm wafer to the larger 300 mm wafer, process cycle
times of conventional RIE processes are considered too long. For
example, large via (LV) pads are the final level of 300 mm wafer
fabrication connecting the transistors to the wire bonds for the
final electrical test. The via RIE process for LV pads typically
takes approximately 5 minutes per wafer, which makes this step a
target for improvement.
[0005] In view of the foregoing, there is a need in the art for an
improved via RIE process that does not suffer from the problems of
the related art.
SUMMARY OF THE INVENTION
[0006] The invention includes methods of etching a dielectric layer
and a cap layer over a conductor level to open a via to the
conductor. The methods include the provision of tetrafluoro methane
(CF.sub.4) in a photoresist strip. In addition, the methods may
provide an increased amount of tetrafluoro methane (CF.sub.4) in a
dielectric layer etch, and trifluoro methane (CHF.sub.3) in a cap
layer etch. The invention provides higher yield, more predictable
etch rates, faster processing, and removes the need for an ash
step.
[0007] A first aspect of the invention is directed to a method of
etching a dielectric layer and a cap layer over a conductor level
to open a via to the conductor, a pattern for the via being
provided by a photoresist, the method comprising the steps of:
etching the via through the dielectric layer; stripping the
photoresist using a plasma chemistry including tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to the
conductor.
[0008] A second aspect of the invention includes a method of
etching a dielectric layer and a cap layer over a conductor level
to open a via to the conductor, a pattern for the via being
provided by a photoresist, the method consisting of the steps of:
etching the via through the dielectric layer; stripping the
photoresist using a plasma chemistry including tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to the
conductor.
[0009] A third aspect of the invention relates to a method of
etching a dielectric layer and a cap layer over a conductor level
to open a via to the conductor, a pattern for the via being
provided by a photoresist, the method comprising of the steps of:
etching the via through the dielectric layer using approximately 80
mT of pressure, an RF energy of approximately 1200 W at 27 MHz and
approximately 2700 W at 2 MHz, and a gas flow including tetrafluoro
methane (CF.sub.4) and carbon monoxide (CO) in a gas flow ratio of
no less than approximately 0.104 and no greater than approximately
0.2; stripping the photoresist using a plasma chemistry including
tetrafluoro methane (CF.sub.4) using a gas flow of no less than
approximately 7 standard cubic centimeters per minute (sccm) and no
greater than approximately 15 sccm of the tetrafluoro methane
(CF.sub.4); and etching the cap layer to open the via to the
conductor using approximately 150 mT of pressure, an RF energy of
approximately 1000 W at 2 MHz and approximately 1500 W at 27 MHz,
and a gas flow including tetrafluoro methane (CF.sub.4) and
trifluoro methane (CHF.sub.3) in a gas flow ratio of no less than
approximately 2.33 and no greater than approximately 3.96.
[0010] A fourth aspect of the invention relates to a method of
etching a first dielectric layer, a second dielectric layer and a
cap layer over a conductor level to open a via to the conductor, a
pattern for the via being provided by a photoresist, the method
comprising the steps of: etching the via through the first
dielectric layer; etching the via through the second dielectric
layer; stripping the photoresist using a plasma chemistry including
tetrafluoro methane (CF.sub.4); and etching the cap layer to open
the via to the conductor.
[0011] The foregoing and other features of the invention will be
apparent from the following more particular description of
embodiments of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] The embodiments of this invention will be described in
detail, with reference to the following figures, wherein like
designations denote like elements, and wherein:
[0013] FIG. 1 shows a conventional semiconductor structure
including large-via pad dielectric layers prior to etching.
[0014] FIGS. 2-5 show a method of etching a via according to the
invention.
[0015] FIG. 6 shows a semiconductor structure illustrating some of
the problems solved by the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] With reference to the accompanying drawings, FIG. 2-5 show a
method of etching a dielectric layer and a cap layer over a
conductor level to open a via to the conductor according to the
invention. The method modifies the conventional process such that
the process results in improved yields, more predictable etch rates
and greatly reduced processing time. The process begins with a
conventional semiconductor structure 10 including large-via pad
dielectric layers 12, similar to that shown in FIG. 1. Structure 10
includes a conductor level 14 including a dielectric layer 16
(e.g., of silicon dioxide SiO.sub.2 or any other appropriate
dielectric material) surrounding conductor 18 (e.g., of copper Cu);
a cap layer 20 atop conductor level 14; a dielectric layer 22;
another dielectric layer 24 (e.g., of silicon nitride
Si.sub.3N.sub.4 or any other dielectric material); and a patterned
photoresist 26. Patterned photoresist 26 includes a pattern
(opening) for the via to be formed. Dielectric layer 22 may include
any silicon dioxide (SiO.sub.2) type material such as hydrogenated
silicon oxycarbide (SiCOH), CORAL.TM. available from Novellus,
tetraethyl orthosilicate (Si(OC.sub.2H.sub.5).sub.4)(TEOS),
fluorine doped TEOS (FTEOS), fluorine doped silicate glass (FSG),
undoped silicate glass (USG), boro-phospho-silicate glass (BPSG),
etc. Cap layer 20 may include any typical cap material such as:
high density plasma (HDP) silicon nitride, ultraviolet light
transparent silicon nitride (UVN), silicon carbide (SiC), etc.
[0017] An initial step of the method includes, as shown in FIG. 2,
etching through dielectric (e.g., silicon nitride) layer 24. Since
the etch conditions 100 used may be any conventional method, this
step is not considered an integral part of the invention in all
cases.
[0018] Next, as shown in FIG. 3, the via is etched through
dielectric layer 22. In one embodiment, etching recipe 104 includes
using approximately 80 mTorr (mT) of pressure, and an RF energy of
approximately 1200 watts (W) at 27 MHz and approximately 2700 W at
2 MHz, which represents an increase in RF energy compared to the
conventional process. A gas flow for this embodiment includes
tetrafluoro methane (CF.sub.4) and carbon monoxide (CO) in a gas
flow ratio of approximately 0.104-0.200, and preferably about
0.136. Tetrafluoro methane (CF.sub.4) (also known as carbon
tetrafluoride) is an etchant that etches practically all
dielectrics, and is available, for example, under the brand name
Freon.RTM. 14 from Dupont. In one embodiment, the gas flow includes
approximately 25-40 sccm of tetrafluoro methane (CF.sub.4)
(preferably about 30 sccm), and approximately 200-240 sccm of
carbon monoxide (CO) (preferably about 220 sccm). In addition, the
gas flow includes approximately 400 sccm of argon (Ar). This etch
recipe 102 provides more than twice as fast an etch rate (i.e.,
approximately 95 .ANG.ngstroms/second (.ANG./s)) as the
conventional process due to an increased amount of tetrafluoro
methane (CF.sub.4). In addition, this etch recipe 102 is highly
selective to cap layer 20, and causes no changes in the etch
profile compared to the conventional process.
[0019] Referring to FIG. 4, a next step includes stripping the
photoresist using a plasma chemistry 102 including tetrafluoro
methane (CF.sub.4), which is not used in conventional stripping
processes. In one embodiment, the photoresist stripping step
includes two stages. A first stage uses approximately 120 mT of
pressure, and an RF energy of approximately 1000 W at 27 MHz and
approximately 200 W at 2 MHz. In one embodiment, a gas flow of
approximately 900-1100 sccm of oxygen (O.sub.2) (preferably about
1000 sccm) is used in the first stage. A second stage uses
approximately 400 mT of pressure, and an RF energy of approximately
1600 W at 2 MHz. A gas flow of the second stage includes
tetrafluoro methane (CF.sub.4) and oxygen (O.sub.2) in a gas flow
ratio of approximately 0.006-0.016, and preferably about 0.010.
During the second stage, the tetrafluoro methane (CF.sub.4) may be
provided at approximately 7-15 sccm (preferably about 10 sccm), and
the oxygen (O.sub.2) may be provided at approximately 900-1100 sccm
(preferably about 1000 sccm).
[0020] The photoresist strip step according to the invention adds
tetrafluoro methane (CF.sub.4) gas to remove photoresist polymer
134 (FIG. 6) left behind from the high RF energy used during the
dielectric etching 100 (FIG. 3). Contrary to expectations, however,
the addition of tetrafluoro methane (CF.sub.4) does not etch cap
layer 20 sufficiently to cause exposure of conductor 18, and does
not affect the etch profile. In particular, a low gas flow and
duration provides enough tetrafluoro methane (CF.sub.4) to obtain a
clean strip of the hardened photoresist polymer 134 (FIG. 6) while
minimizing the etching of cap layer 20. More significantly,
however, the addition of tetrafluoro methane (CF.sub.4) cuts the
etching time in approximately half compared to the conventional
process, which greatly increases the overall speed of the via RIE
process. In particular, this stage may last approximately 10-15
seconds, which is significantly shorter than the conventional
process, which typically lasts 20-30 seconds. Another advantage of
the tetrafluoro methane (CF.sub.4) usage is that it removes
residual polymer created by the oxygen (O.sub.2) etch (FIG. 3), and
leaves a clean cap layer 20 surface after photoresist strip. As
shown in FIG. 6, the oxygen (O.sub.2) etch with such a high RF
energy tends leave photoresist 26 (FIG. 3) harder than in
conventional RIE processes, which causes increased residual
photoresist polymer 134, e.g., carbon mixed with oxide. However,
the tetrafluoro methane (CF.sub.4) removes this residual
polymer.
[0021] Referring to FIG. 5, the next step includes etching cap
layer 20 to open the via to conductor 18. In one embodiment, the
cap layer etching step includes an etch recipe 106 using
approximately 150 mT of pressure, and an RF energy of approximately
1000 W at 2 MHz and approximately 1500 W at 27 MHz. A gas flow
includes tetrafluoro methane (CF.sub.4) and trifluoro methane
(CHF.sub.3) in a gas flow ratio of approximately 2.33-3.96.
Trifluoro methane (CHF.sub.3) (also known as fluoroform) is
available, for example, under trade name Freon.RTM. 23 from Dupont.
The addition of trifluoro methane (CHF.sub.3) is presented in this
step to improve sidewall profile striations, which would lead to
higher contact resistance. In one embodiment, the gas flow includes
approximately 80-110 sccm of oxygen (O.sub.2) (preferably about 100
sccm), approximately 170-210 sccm of the tetrafluoro methane
(CF.sub.4) (preferably about 190 sccm), and approximately 53-73
sccm of the trifluoro methane (CHF.sub.3) (preferably about 63
sccm). The gas flow also includes approximately 400 sccm of argon
(Ar).
[0022] With further regard to the cap layer etching step, for
certain types of vias, the thickness of cap layer 20 may be thicker
than in other via pad dielectric stacks. For instance, the above
values are optimal for a cap layer 20 having a thickness of
approximately 800-1200 .ANG., i.e., about 1000 .ANG., of, for
example, silicon nitride. However, thicker cap layers 120 of, for
example, silicon nitride, such as shown in FIG. 6, are subject to
undercutting 130 and metal oxidation 132 that lead to higher
contact resistance when the above-described amount of oxygen
(O.sub.2) is used. To address this situation, in an alternative
embodiment, the gas flow includes the same gases and rates as
described above, except the amount of oxygen (O.sub.2) is reduced
by a factor of approximately 10, which prevents the undercutting.
In one embodiment, the amount of oxygen is approximately 7-13 sccm,
and is preferably about 10 sccm. This amount of oxygen (O.sub.2)
has been found sufficient for cap layers 120 (FIG. 6) having a
thickness of approximately 2500-3500 .ANG., i.e., about 3000 .ANG.,
of, for example, silicon nitride. In particular, the given oxygen
gas flow results in no lateral undercut 130 (FIG. 6), minimal metal
oxidation 134 (FIG. 6), and does not compromise etching time.
Further decrease in oxygen gas, however, results in a dramatic drop
in etch rate.
[0023] The above-described method also reduces processing time by
eliminating the need for a nitrogen-hydrogen plasma chemistry (ash)
step as in conventional via RIE processing. This saves
approximately 45 seconds per wafer. The invention also attains
required wall profile angle, provides high selectivity of
dielectric layer 22 etching chemistry 104 to cap layer 20, and
minimal oxidation of a surface of metal 18. The invention can be
applied to any large via pads requiring high etching selectivity to
a cap layer 20, minimal cap layer 20 undercutting, and reduced
metal oxidation. The invention provides higher yield, more
predictable etch rates, and faster processing, and removes the need
for an ash step.
[0024] The following table summarizes the RIE etch parameters for a
preferred embodiment: TABLE-US-00001 Cap Layer Cap Layer Dielectric
Photoresist Photoresist 20 120 Layer 22 Stage 1 Stage 2
(.about.1000 .ANG.) (.about.3000 .ANG.) Pressure (mT) 80 120 400
150 150 RF energy (W) 27 MHz 1200 1000 0 1500 1500 2 MHz 2700 200
1600 1000 1000 Gas Flow (sccm) CH.sub.4 25-40 0 7-15 170-210
170-210 CHF.sub.3 0 0 0 53-73 53-73 CO 200-240 0 0 0 0 O.sub.2 0
900-1100 900-1100 80-110 7-13 Ar 400 0 0 400 400 Gas Flow Ratios:
CF.sub.4/CO 0.104-0.200 -- -- -- -- CF.sub.4/O.sub.2 -- --
0.006-0.0160 -- -- CF.sub.4/CHF.sub.3 -- -- -- 2.33-3.96
2.33-3.96
[0025] While this invention has been described in conjunction with
the specific embodiments outlined above, it is evident that many
alternatives, modifications and variations will be apparent to
those skilled in the art. Accordingly, the embodiments of the
invention as set forth above are intended to be illustrative, not
limiting. Various changes may be made without departing from the
spirit and scope of the invention as defined in the following
claims.
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