U.S. patent application number 09/775664 was filed with the patent office on 2001-09-06 for inductively coupled plasma cvd.
Invention is credited to Ben-Dor, Monique, Berney, Butch, Demos, Alex, McMillin, Brian, Nguyen, Huong, Shufflebotham, Paul Kevin.
Application Number | 20010019903 09/775664 |
Document ID | / |
Family ID | 25094857 |
Filed Date | 2001-09-06 |
United States Patent
Application |
20010019903 |
Kind Code |
A1 |
Shufflebotham, Paul Kevin ;
et al. |
September 6, 2001 |
Inductively coupled plasma CVD
Abstract
A method of depositing a dielectric film on a substrate in a
process chamber of an inductively coupled plasma-enhanced chemical
vapor deposition reactor. Gap filling between electrically
conductive lines on a semiconductor substrate and depositing a cap
layer are achieved. Films having significantly improved physical
characteristics including reduced film stress are produced by
heating the substrate holder on which the substrate is positioned
in the process chamber.
Inventors: |
Shufflebotham, Paul Kevin;
(San jose, CA) ; McMillin, Brian; (Fremont,
CA) ; Demos, Alex; (San Francisco, CA) ;
Nguyen, Huong; (Danville, CA) ; Berney, Butch;
(Pleasanton, CA) ; Ben-Dor, Monique; (Palo Alto,
CA) |
Correspondence
Address: |
Peter K. Skiff
BURNS, DOANE, SWECKER & MATHIS, L. L. P.
P. O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
25094857 |
Appl. No.: |
09/775664 |
Filed: |
February 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09775664 |
Feb 5, 2001 |
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08772374 |
Dec 23, 1996 |
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6184158 |
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Current U.S.
Class: |
438/788 ;
118/723R; 257/E21.279; 257/E21.576; 427/255.28; 427/569 |
Current CPC
Class: |
H01L 21/02315 20130101;
H01L 21/02301 20130101; H01L 21/02362 20130101; Y10S 438/902
20130101; H01L 21/02164 20130101; H01L 21/76837 20130101; Y10S
438/906 20130101; H01L 21/02211 20130101; H01J 37/321 20130101;
H01L 21/31612 20130101; C23C 16/402 20130101; C23C 16/507 20130101;
H01L 21/02126 20130101; H01L 21/02274 20130101 |
Class at
Publication: |
438/788 ;
427/569; 427/255.28; 118/723.00R |
International
Class: |
C23C 016/00; H01L
021/31 |
Claims
What is claimed is:
1. A method of filling gaps between electrically conductive lines
on a semiconductor substrate comprising the steps of: providing a
substrate in a process chamber of an inductively coupled
plasma-enhanced chemical vapor deposition reactor; introducing a
process gas comprising a noble gas into the process chamber wherein
the amount of noble gas is sufficient to assist in gap filling; and
growing a dielectric film on the substrate, the dielectric film
being deposited in gaps between electrically conductive lines on
the substrate.
2. The method of claim 1, wherein the process gas further comprises
a silicon-containing reactant gas selected from the group
consisting of SiH.sub.4, SiF.sub.4, Si.sub.2H.sub.6, TEOS, TMCTS,
and mixtures thereof, said process further comprising decomposing
the silicon-containing reactant to form a silicon containing gas
and plasma phase reacting said silicon-containing gas on a surface
of the substrate.
3. The method of claim 2, wherein the process gas comprises a
reactant gas selected from the group consisting of H.sub.2,
O.sub.2, N.sub.2, NH.sub.3, NF.sub.3, N.sub.2O, and NO, and
mixtures thereof.
4. The method of claim 2, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
5. The method of claim 3, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
6. The method of claim 1, wherein the vacuum is maintained at about
1 mTorr to about 30 mTorr.
7. The method of claim 1, wherein the film is deposited on a
silicon wafer and the gaps are between conductor lines comprising
aluminum, copper, tungsten, and mixtures thereof.
8. The method of claim 1, further comprising applying a radio
frequency bias to the substrate.
9. The method of claim 8, wherein the step of applying a radio
frequency bias to the substrate comprises supporting the substrate
on a substrate holder having an electrode supplying a radio
frequency bias to the substrate, the radio frequency bias being
generated by supplying the electrode with at least 2 watts/cm.sup.2
of power.
10. The method of claim 8, wherein the radio frequency bias applied
to the a substrate is at a frequency of between about 100 kHz to 27
MHz.
11. The method of claim 1, wherein the substrate is positioned on a
substrate holder that is maintained at a temperature of about
80.degree. C. to 200.degree. C.
12. The method of claim 1, further comprising supplying a heat
transfer gas between a surface of the substrate and a surface of a
substrate support on which the substrate is supported during the
film growing step.
13. The method of claim 12, further comprising clamping the
substrate on an electrostatic or mechanical chuck during the film
growing step.
14. The method of claim 13, wherein heat transfer gas which
comprises helium and/or argon is supplied to a space between a
surface of the substrate and a surface of the chuck.
15. The method of claim 1, further comprising plasma phase reacting
an oxygen-containing gas in the gaps and removing polymer residues
in the gaps prior to the film growing step.
16. The method of claim 1, wherein the dielectric film comprises
silicon oxide.
17. The method of claim 1, wherein the dielectric film comprises
SiO.sub.2.
18. The method of claim 1, wherein the process gas includes a
silicon and fluorine-containing reactants and the dielectric film
comprises silicon oxyfluoride.
19. The method of claim 1, wherein the as mixture includes a
nitrogen-containing gas and the dielectric film comprises silicon
oxynitride
20. The method of claim 1, wherein the inductively coupled plasma
is generated by a substantially planar induction coil.
21. The method of claim 1, wherein the process gas is introduced
through a gas supply including orifices, at least some of the
orifices orienting the process gas along an axis of injection which
intersects an exposed surface of the substrate at an acute
angle.
22. The method of claim 21, wherein the step of introducing a
process gas comprises the step of supplying a gas or gas mixture
from a primary gas ring, wherein at least some of said gas or gas
mixture is directed toward said substrate.
23. The method of claim 22, wherein the step of introducing the gas
further comprises the step of supplying an additional gas or gas
mixture from a secondary gas ring.
24. The method of claim 22, wherein injectors are connected to said
primary gas ring, the injectors injecting at least some of said gas
or gas mixture into said chamber and directed toward the
substrate.
25. A method of filling gaps between electrically conductive lines
on a semiconductor substrate and depositing a capping layer over
the filled gaps comprising the steps of: providing a substrate in a
process chamber of an inductively coupled plasma-enhanced chemical
vapor deposition reactor; filling gaps between electrically
conductive lines on the substrate by introducing a first process
gas and growing a first dielectric film in the gaps at a first
deposition rate; and depositing a capping layer comprising a second
dielectric film onto the surface of said first dielectric film by
introducing a second process gas into the process chamber, said
layer being deposited at a second deposition rate that is higher
than the first deposition rate.
26. The method of claim 25, wherein the dielectric film comprises
silicon oxide, the first and second process gases including a
silicon reactant and an oxygen reactant, the second process gas
containing higher amounts of the silicon and oxygen reactants than
the first process gas.
27. The method of claim 25, wherein the dielectric film comprises
silicon oxide, the first and second process gasses including a
noble gas, the first process gas including a higher amount of the
noble gas than the second process gas.
28. The method of claim 25, wherein an RF bias is applied to the
substrate during the gap filling and capping steps, the RF bias
being higher during the gap filling step than during the capping
step.
29. The method of claim 25, wherein the substrate is positioned on
a substrate holder that is maintained at a temperature of about
80.degree. C. to 200.degree. C.
30. The method of claim 25, wherein the process gas is introduced
through a gas supply including orifices, at least some of the
orifices orienting the process gas along an axis of injection which
intersects an exposed surface of the substrate at an acute
angle.
31. A method of depositing a dielectric film substrate comprising
the steps of: providing a substrate in a process chamber of an
inductively coupled plasma-enhanced chemical vapor deposition
reactor wherein the substrate is positioned on a substrate holder;
introducing a process gas comprising, a noble gas into the process
chamber wherein the amount of noble gas is sufficient to cause
sputter etching; controlling the temperature on a surface of the
substrate holder; and energizing the process gas into a plasma
state by inductively coupling RF energy into the process chamber
and growing a dielectric film on the substrate.
32. The method of claim 31, wherein the process gas further
comprises a silicon-containing reactant gas selected from the group
consisting of SiH.sub.4, Si.sub.2H.sub.6, SiF.sub.4, TEOS, TMCTS,
and mixtures thereof, said process further comprising decomposing
the silicon-containing reactant to form a silicon containing gas
and plasma phase reacting said silicon-containing gas on a surface
of the substrate.
33. The method of claim 32, wherein the process gas comprises a
reactant gas selected from the group consisting of H.sub.2,
O.sub.2, N.sub.2, NH.sub.3, NF.sub.3, N.sub.2O, and NO, and
mixtures thereof.
34. The method of claim 32, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
35. The method of claim 33, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
36. The method of claim 31, wherein the process chamber is a vacuum
maintained at about 1 mTorr to about 30 mTorr.
37. The method of claim 31, further comprising applying a radio
frequency bias to the substrate.
38. The method of claim 37, wherein the step of applying a radio
frequency bias to the substrate comprises supporting the substrate
on a substrate holder having an electrode supplying a radio
frequency bias to the substrate, the radio frequency bias being
generated by supplying the electrode with at least 2 watts/cm of
power.
39. The method of claim 37, wherein the radio frequency bias
applied to the substrate is at a frequency of between about 100 kHz
to 27 MHz.
40. The method of claim 31, wherein the substrate is positioned on
a substrate holder that is maintained at a temperature of about
80.degree. C. to 200.degree. C.
41. The method of claim 40, further comprising supplying a heat
transfer gas between a surface of the substrate and a surface of a
substrate holder.
42. The method of claim 41, further comprising clamping the
substrate on an electrostatic or mechanical chuck during the film
growing step.
43. The method of claim 42, wherein the heat transfer gas which
comprises helium and/or argon is supplied to a space between a
surface of the substrate and a surface of the chuck.
44. The method of claim 40, wherein the dielectric film comprises
silicon oxide.
45. The method of claim 40, wherein the dielectric film comprises
SiO.sub.2.
46. The method of claim 40, wherein the process gas includes a
silicon and fluorine-containing reactants and the dielectric film
comprises silicon oxyfluoride.
47. The method of claim 31, wherein the gas mixture includes a
nitrogen-containing gas and the dielectric film comprises silicon
oxynitride.
48. The method of claim 31, wherein the inductively coupled plasma
is generated by a substantially planar induction coil.
49. The method of claim 31, wherein the process gas is introduced
through a gas supply including orifices, at least some of the
orifices orienting the process gas along an axis of injection which
intersects an exposed surface of the substrate at an acute
angle.
50. An inductively coupled plasma processing system comprising: a
plasma processing chamber; a substrate holder supporting a
substrate within said processing chamber wherein the substrate
holder is at a temperature of about 80.degree. C. to 200.degree.
C.; an electrically-conductive coil disposed outside said
processing chamber; means for introducing a process gas into said
processing chamber; and an RF energy source which inductively
couples RF energy into the processing chamber to energize the
process gas into a plasma state.
51. The system of claim 50, wherein the process gas comprises a
silicon-containing reactant gas selected from the group consisting
of SiH.sub.4, SiF.sub.4, Si.sub.2H.sub.6, TEOS, TMCTS, and mixtures
thereof.
52. The system of claim 50, wherein the process gas comprises a
reactant gas selected from the group consisting of H.sub.2,
O.sub.2, N.sub.2, NH.sub.3, NF.sub.3, N.sub.2O, and NO, and
mixtures thereof.
53. The system of claim 50, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
54. The system of claim 50, wherein the process gas comprises a
reactant gas selected from the group consisting of boron-containing
gas, phosphorous-containing gas, and mixtures thereof.
55. The system of claim 50, wherein the process chamber is a vacuum
maintained at about 1 mTorr to about 30 mTorr.
56. The system of claim 50, wherein the substrate a further
comprising an RF generator that is connected to the substrate
produces an RF bias.
57. The system of claim 50, wherein the means for introducing the
process gas comprises a gas supply including orifices, at least
some of the orifices orienting the process gas along an axis of
injection which intersects an exposed surface of the substrate at
an acute angle.
58. The system of claim 50, wherein the coil is substantially
planar.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method and apparatus for
high-density plasma-enhanced chemical vapor deposition of
semiconducting and dielectric films and more particularly to
techniques for depositing such films into high aspect ratio gaps on
semiconductor substrates such as silicon wafers having metal
interconnection layers.
DESCRIPTION OF THE RELATED ART
[0002] Chemical vapor deposition (CVD) is conventionally used to
form various thin films in a semiconductor integrated circuit. CVD
can form thin films such as SiO.sub.2, Si.sub.3N.sub.4, Si or the
like with high purity and high quality. In the reaction process of
forming a thin film, a reaction vessel in which semiconductor
substrates are arranged can be heated to a high temperature
condition of 500 to 1000.degree. C. Raw material to be deposited
can be supplied through the vessel in the form of gaseous
constituents so that gaseous molecules are thermally dissociated
and combined in the gas and on a surface of the substrates so as to
form a thin film.
[0003] A plasma-enhanced CVD apparatus utilizes a plasma reaction
to create a reaction similar to that of the above-described CVD
apparatus, but at a relatively low temperature in order to form a
thin film. The plasma CVD apparatus includes a process chamber
consisting of a plasma generating chamber which may be separate
from or part of a reaction chamber, a gas introduction system, and
an exhaust system. Plasma is generated in such apparatus by various
plasma sources. A substrate support is provided in the reaction
chamber which may include a radio frequency (RF) biasing component
to apply an RF bias to the substrate and a cooling mechanism in
order to prevent a rise in temperature of the substrate due to the
plasma action.
[0004] Vacuum processing chambers are generally used for chemical
vapor depositing of materials on substrates by supplying deposition
gas to the vacuum chamber and applying of an RF field to the gas.
For example, parallel plate and electron-cyclotron resonance (ECR)
reactors have been commercially employed. See U.S. Pat. Nos.
4,340,462 and 5,200,232. The substrates are held in place within
the vacuum chamber during processing by substrate holders.
Conventional substrate holders include mechanical clamps and
electrostatic clamps (ESC). Examples of mechanical clamps and ESC
substrate holders are provided in U.S. Pat. No. 5,262,029 and U.S.
application Ser. No. 08/401,524 filed on Mar. 10, 1995.
[0005] Plasma-enhanced chemical vapor deposition (PECVD) has been
used for depositing intermetal dielectric layers at low
temperatures in integrated circuit applications. A publication by
M. Gross et al. entitled "Silicon dioxide trench filling process in
a radio-frequency hollow cathode reactor", J. Vac. Sci. Technol. B
11(2), March/April 1993, describes a process for void-free silicon
dioxide filling of trenches using a hollow cathode reactor wherein
silane gas is fed through a top target which supports a low
frequency (1 MHz), low pressure (.about.0.2 Pa) oxygen and xenon
discharge. In this process, high ion bombardment and a low rate of
gas phase reaction produce an ion induced reaction with surface
adsorbates, leading to directional oxide film growth whereby
trenches with one micron openings and aspect ratios up to 2.5:1 are
filled at rates over 400 .ANG./min.
[0006] A publication by P. Shufflebotham et al. entitled "Biased
Electron Cyclotron Resonance Chemical-Vapor Deposition of Silicon
Dioxide Inter-Metal Dielectric Thin Films," Materials Science Forum
Vol. 140-142 (1993) describes a low-temperature single step
gap-filled process for use in inter-metal dielectric (IMD)
applications on wafers up to 200 mm in diameter wherein sub-0.5
micron high aspect ratio gaps are filled with SiO.sub.2 utilizing
an O.sub.2--Ar--SiH.sub.4 gas mixture in a biased electron
cyclotron resonance plasma-enhances chemical-vapor deposition
(ECR-CVD) system. That single step process replaced sequential
gap-filling and planarization steps wherein CVD SiO.sub.2 was
subjected to plasma etch-back steps, such technique being
unsuitable for gap widths below 0.5 microns and aspect ratios (gap
height:width) above 1.5:1.
[0007] Prior art apparatuses suffer from several serious
disadvantages with respect to IMD applications. ECR and helicon
sources which rely on magnetic fields are complex and expensive.
Moreover, magnetic fields have been implicated to cause damage to
semiconductor devices on the wafer. ECR, helicon and helical
resonator sources also generate plasmas remotely from the wafer,
making it very difficult to produce uniform and high quality films
at the same time and also difficult to perform in-situ plasma
cleans necessary to keep particulates under control without
additional equipment. Furthermore, ECR, helicon and helical
resonator, and domed inductively-coupled plasma systems require
large, complex dielectric vacuum vessels. As a corollary scale-up
is difficult and in-situ plasma cleaning is time consuming.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to processes that employ
an inductively coupled plasma-enhanced chemical vapor deposition
(IC PECVD) high density plasma system. The system is compact,
in-situ cleanable and produces high quality semiconductor and
dielectric films.
[0009] In one aspect, the invention is directed to a method for
filling gaps between electrically conductive lines on a
semiconductor substrate comprising the steps of: providing a
substrate in a process chamber of an inductively coupled
plasma-enhanced chemical vapor deposition reactor which can include
a substantially planar induction coil; introducing a process gas
which can include a noble gas into the process chamber wherein the
amount of noble gas is sufficient to assist in gap filling; and
growing a dielectric film on the substrate with dielectric film
being deposited in gaps between electrically conductive lines on
the substrate.
[0010] In another aspect, the invention is directed to a method for
filling gaps between electrically conductive lines on a
semiconductor substrate comprising the steps of: providing a
substrate in a process chamber of an inductively coupled
plasma-enhanced chemical vapor deposition reactor which can include
a substantially planar induction coil; filling gaps between
electrically conductive lines on the substrate by: (i) introducing
a first process gas which can include a noble gas into the process
chamber wherein the amount of noble gas is sufficient to assist in
gap filling; and (ii) growing a first dielectric film in the gaps
at a first deposition rate; and depositing a capping layer
comprising a second dielectric film onto the surface of said first
dielectric film by introducing a second process gas into the
process chamber, said capping layer being deposited at a second
deposition rate that is higher than the first deposition rate.
[0011] In a further aspect, the invention is directed to a method
of depositing a dielectric film on a substrate comprising the steps
of: providing a substrate in a process chamber of an inductively
coupled plasma-enhanced chemical vapor deposition reactor wherein
the substrate is positioned on a substrate holder; introducing a
process gas which can include a noble gas into the process chamber,
wherein the amount of noble gas is sufficient to assist in
depositing the dielectric film; controlling the temperature on a
surface of the substrate holder; and energizing the process gas
into a plasma state by inductively coupling RF energy into the
process chamber and growing a dielectric film on the substrate.
[0012] In yet another aspect, the invention is directed to an
inductively coupled plasma processing system comprising: a plasma
processing chamber, a substrate holder supporting a substrate
within said processing chamber wherein the substrate holder is at a
temperature of about 80.degree. C. to 200.degree. C., an
electrically-conductive coil that is disposed outside said
processing chamber; means for introducing a process gas into said
processing chamber; and an RF energy source which inductively
couples RF energy into the processing chamber to energize the
process gas into a plasma state. Planar and non-planar coils can be
employed however, a substantially planar coil is preferred.
[0013] Depending on the film to be deposited, the process gas may
comprise a silicon-containing reactant gas selected from the group
consisting of SiH.sub.4, SiF.sub.4, Si.sub.2H.sub.6, TEOS, TMCTS,
and mixtures thereof. The process gas may comprise a reactant gas
selected from the group consisting of H.sub.2, O.sub.2, N.sub.2,
NH.sub.3, NF.sub.3, N.sub.2O, and NO, and mixtures thereof.
Alternatively, the process gas may comprises a reactant gas
selected from the group consisting of boron-containing gas,
phosphorous-containing gas, and mixtures thereof. Most preferably,
the process gas may also include a noble gas such as argon.
[0014] According to one feature of the invention, the inductively
coupled plasma is generated by an RF antenna having a planar coil
design. Thus, the IC PECVD reactor can be easily scaled up to
accommodate, for example, 300 mm wafers and 600 mm.times.720 mm
flat panel displays. The inductively coupled plasma (ICP) source
generates uniform, high density plasmas over large areas
independently of the bias power used to control the ion sputter
energy. Unlike ECR or helicon sources, no magnets are required.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be described in greater detail with
reference to the accompanying drawings in which like elements bear
like reference numerals, and wherein:
[0016] FIG. 1 is a schematic of a high density inductively coupled
plasma reactor which can be used to carry out the process according
to the invention;
[0017] FIG. 2 comprises FTIR spectra of films deposited at various
oxygen to silane mass flow ratios (constant total flow).
[0018] FIGS. 3A, 3B, 3C, and 3D are scanning electron microscopy
(SEM) images of gap fills wherein all samples were decorated to
enhance imperfections in the film; the structures were polysilicon
on oxide and all depositions were for 3 minutes, except that of 3A,
which was for 1 minute;
[0019] FIG. 4 illustrates a plasma reactor with a gas injection
system; and
[0020] FIG. 5 illustrates an injector for the gas injection
system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Inductively Coupled Plasma-Enhanced CVD Reactor
[0022] FIG. 1 shows a ICP reactor 20 which can process substrates
with high density plasma. Suitable ICP reactors include TCP.TM.
systems from LAM Research Corp., Fremont, Calif. See also Ogle,
U.S. Pat. No. 4,948,458 which is incorporated herein. The reactor
includes a process chamber 21 in which plasma 22 is generated
adjacent substrate 23. The substrate is supported on water cooled
substrate support 24 and temperature control of the substrate is
achieved by supplying helium gas through conduit 25 to a space
between the substrate and the substrate support. The substrate
support can comprise an anodized aluminum electrode, which may be
heated, or a ceramic material having a buried electrode therein,
the electrode being powered by an RF source 26 and associated
circuitry 27 for providing RF matching, etc. The temperature of the
substrate during processing thereof is monitored by temperature
monitoring equipment 28 attached to temperature probe 29.
[0023] In order to provide a vacuum in chamber 21, a turbo pump is
connected to outlet port 30 and a pressure control valve can be
used to maintain the desired vacuum pressure. Process gases can be
supplied into the chamber by conduits 31, 32 which feed the
reactant gases to gas distribution rings extending around the
underside of dielectric window 33 or the process gases can be
supplied through a dielectric showerhead window. An external ICP
coil 34 located outside the chamber in the vicinity of the window
is supplied with RF power by RF source 35 and associated circuitry
36 for impedance matching, etc. As is apparent, the external
induction coil is substantially planar and generally comprises a
single conductive element formed into a planar spiral or a series
of concentric rings. The planar configuration allows the coil to be
readily scaled-up by employing a longer conductive element to
increase the coil diameter and therefore accommodate larger
substrates or multiple coil arrangements could be used to generate
a uniform plasma over a wide area. When a substrate is processed in
the chamber, the RF source 35 supplies the coil 34 with RF current
preferably at a range of about 100 kHz-27 MHz, and more preferably
at 13.56 MHz and the RF source 26 supplies the lower electrode with
RF current preferably at a range of about 100 kHz-27 MHz, and more
preferably at 400 kHz, 4 MHz or 13.56 MHz. A large DC sheath
voltage above the surface of a substrate can be provided by
supplying RF power to the electrode.
[0024] RF bias is applied to the substrate to generate ion
bombardment of the growing film during the gap filling step. The RF
frequency can be anything above the value necessary to sustain a
steady state sheath, which is a few hundred kHz. Substrate bias has
numerous beneficial effects on film properties, and can also be
used to simultaneously sputter the growing film in the gap-fill
step. This allows narrow, high aspect ratio gaps to be rapidly
filled with high quality dielectric. RF bias can be used during the
cap layer deposition step.
[0025] Reactor 20 can be used to carry out the gap filling process
of the invention wherein a heavy noble gas is used to increase the
etch-to-deposition rate ratio (EDR) for void-free filling of sub
0.5 .mu.m high aspect ratio gaps. Gap filling processes are further
described in copending application Ser. No. 08/623,825 filed on
Mar. 29, 1996 entitled "IMPROVED METHOD OF HIGH DENSITY PLASMA CVD
GAP-FILING," which application is incorporated herein. The heavy
noble gas is effective in sputtering comers of sidewalls of the
gaps such that the comers are facetted at an angle of about 45
degrees. The noble gas has a low ionization potential and forms
massive ions which enhance the sputtering rate at a given RF power
relative to the deposition rate, thus reducing the power required
to fill a given gap structure. Moreover, the low ionization
potential of the noble gas helps spread plasma generation and ion
bombardment more uniformly across the substrate. As xenon is the
heaviest of the non-reactive noble gasses, xenon is preferred as
the noble gas. Krypton can also be used even though it has a lower
mass and higher ionization potential than xenon. Argon is also
suitable as the noble gas. Preferably, the amount of noble gas
added is effective to provide a sputter etch component with a
magnitude on the order of the deposition rate such that the etch to
deposition rate ratio is preferably about 5% to 70%, and more
preferably about 10% to 40%.
[0026] In carrying out the deposition process in a ICP-CVD reactor,
the chamber can be maintained at a vacuum pressure of less than 100
mTorr and preferably 30 mTorr or less and more preferably from
about 1 mTorr to 5 mTorr. The flow rates of the individual
components of the process gas typically ranges from 10 to 200 sccm
for a 200 mm substrate and higher for larger substrates. A
turbomolecular pump throttled by a gate valve is used to control
the process pressure. The relative amount of each component will
depend, in part, on the stoichiometry of the compound(s) to be
deposited. The ICP power preferably ranges from 200 to 3000 watts,
and the RF bias power applied to the bottom electrode can range
from 0 to 3000 watts for a 200 mm substrate. Preferably the bottom
electrode has a surface area so that the RF bias power can supply
about 0-8 watts/cm.sup.2 and preferably at least 2 watts/cm.sup.2
of power. A heat transfer gas comprising, for example, helium
and/or argon can be supplied at a pressure of 1 to 10 Torr to
preferably maintain the substrate temperature at about -20.degree.
C. to 500.degree. C., and more preferably at about 100.degree. C.
to 400.degree. C. and most preferably about 150.degree. C. to
375.degree. C.
[0027] In order to prevent damage to metal lines or the
pre-existing films and structures on the substrate and to ensure
accurate and precise process control, a heated mechanical or
preferably an electrostatic chuck (ESC) is employed to hold the
substrate. The ESC is preferably bipolar or monopolar. Preferably,
the electrode is maintained at a temperature ranging from about
50.degree. C. to 350.degree. C., in order to maintain the
temperature of the wafer to about 325.degree. C. to 375.degree. C.
The preferred electrode temperature will depend on, among other
things, the RF bias level and the particular deposition step. For
example, during the gap-fill process, the electrode temperature is
preferably maintained between about 80.degree. C. (full bias) to
200.degree. C. (no bias). Similarly, during the capping process,
the electrode temperature is preferably maintained at between about
125.degree. C. (full bias) to 350.degree. C. (no bias). The
gap-fulling and capping processes are described herein. A suitable
chuck for temperature control is disclosed in copending application
Ser. No. ______, filed on Sep. 30, 1996, entitled "VARIABLE HIGH
TEMPERATURE CHUCK FOR HIGH DENSITY PLASMA CHEMICAL VAPOR
DEPOSITION", by Brian McMillin, which is incorporated herein.
[0028] During deposition the substrate (e.g., wafer ) is typically
maintained at a temperature that is higher than that of the ESC due
to the plasma heating. Consequently, even though the ESC may be
heated, its temperature is lower than that of the substrate. The
electrode preferably also provides for helium backside cooling for
substrate temperature control. The substrate temperature may be
controlled by regulating the level of the RF bias and the ESC
temperature and other parameters as described herein. As further
described in the experiments herein, the electrode temperature can
significantly influence the physical properties of the film
deposited.
[0029] ICP-CVD reactor is particularly suited for depositing
SiO.sub.2 for IMD applications as the films produced are of
excellent quality that are practically indistinguishable from
SiO.sub.2 grown by high temperature thermal oxidation of
crystalline Si (thermal oxide). In addition, the technique can fill
gaps as narrow as 0.25 .mu.m at aspect ratios of 3:1 and higher
with high quality material. Furthermore, deposition temperatures
can be below 450.degree. C. for compatibility with Al
metallizations and thickness uniformities are better than 2%
1-.sigma. on 8 in. (20.32 cm) wafers, with substantially no
variations in other film properties. Finally, in terms of process
manufacturability, ICP-CVD can achieve net deposition rates above
5,000 .ANG./min in the gap fill process. For the cap layer, ICP-CVD
can provide a deposition rate up to about 1.5 .mu.m/min with good
uniformity. It is understood that conductor lines can be made from
other suitable materials, including, for example, copper, tungsten,
and mixture thereof.
[0030] The deposition of SiO.sub.2 into sub-0.5 micron high aspect
ratio gaps by the inventive process involves the simultaneous
deposition and sputtering of SiO.sub.2. The resultant anisotropic
deposition fills gaps from the bottom-up and the angular dependence
of the sputtering yield also prevents the tops of the gaps from
pinching off during deposition. An important feature of most high
density plasma systems is that the bias power determines the sheath
voltage above the wafer essentially independently of plasma
generation. High bias powers generate large sheath voltages, and
thus energetic ion bombardment of the wafer surface. In the absence
of an RF bias, the film quality and gap-filling performance tend to
be poor due to a jagged appearance of the sidewall film suggesting
that it is very porous and heavy deposits forming above metal lines
shadow the trench bottoms from deposition and eventually pinch-off
the gap, leaving a void.
[0031] ICP can generate a high density plasma (e.g., >about
1.times.10.sup.11 ions/cm.sup.3) and sustain it even at a very low
pressure (e.g., <about 10 mTorr). The advantages of high density
PECVD include increased throughput, uniform ion and radical
densities over large areas, and subsequent manufacturability of
scaled-up reactors. When complemented with a separate RF biasing of
the substrate electrode, ICP-CVD systems also allow independent
control of ion bombardment energy and provide an additional degree
of freedom to manipulate the plasma deposition process.
[0032] In ICP systems, SiO.sub.2 film growth occurs by an
ion-activated reaction between oxygen species impinging onto the
wafer from the plasma source and silane fragments adsorbed on the
wafer. Using ICP-CVD, sub-0.5 .mu.m, high aspect ratio gaps can be
filled with high quality SiO.sub.2 dielectric on 8 in. (20.32 cm)
diameter wafers. In essence, the ICP-CVD system provides a
manufacturable intermetal dielectric CVD process that utilizes high
density plasmas.
[0033] Process Gas Distribution System
[0034] It has been demonstrated that for high density PECVD,
improved deposition rate and uniformity can be achieved by
employing a gas distribution system which provides uniform, high
flow rate delivery of reactant gases onto the substrate surface, to
both increase the deposition rate and to minimize the chamber
cleaning requirements. A suitable gas distribution system is
disclosed in copending application Ser. No. 08/672,315, filed on
Jun. 28, 1996, entitled "FOCUSED AND THERMALLY CONTROLLED PLASMA
PROCESSING SYSTEM AND METHOD FOR HIGH DENSITY PLASMA CHEMICAL VAPOR
DEPOSITION OF DIELECTRIC FILMS," by Brian McMillin et al., which
application is incorporated herein.
[0035] FIG. 4 illustrates a plasma processing system comprising
such a gas distribution system. The system includes a substrate
support 130 and processing chamber 140. The support may comprise,
for example, an RF biased electrode. The support may be supported
from a lower endwall of the chamber or may be cantilevered,
extending from a sidewall of the chamber. The substrate 120 may be
clamped to the electrode either mechanically or
electrostatically.
[0036] The system further includes an antenna 150, such as the
planar multiturn coil shown in FIG. 4, a non-planar multiturn coil,
or an antenna having another shape, powered by a suitable RF source
and suitable RF impedance matching circuitry inductively couples RF
energy into the chamber to provide a high density plasma. The
chamber may include a suitable vacuum pumping apparatus for
maintaining the interior of the chamber at a desired pressure. A
dielectric window, such as the planar dielectric window 155 of
uniform thickness shown in FIG. 4, or a non-planar dielectric
window, is provided between the antenna 150 and the interior of the
processing chamber 140 and forms the vacuum wall at the top of the
processing chamber.
[0037] A primary gas ring 170 is provided below the dielectric
window 155. The gas ring 170 may be mechanically attached to the
chamber housing above the substrate. The gas ring 170 may be made
of, for example, aluminum or anodized aluminum.
[0038] A secondary gas ring 160 may also be provided below the
dielectric window 155. One or more gases such as Ar and O.sub.2 are
delivered into the chamber 140 through outlets in the secondary gas
ring 160. Any suitable gas ring may be used as the secondary gas
ring 160. The secondary gas ring 160 may be located above the gas
ring 170, separated by an optional spacer 165 formed of aluminum or
anodized aluminum, as shown in FIG. 4.
[0039] Alternatively, although not shown, the secondary gas ring
160 may be located below the gas ring 170, in between the gas ring
170 and the substrate 120, or the secondary gas ring 160 may be
located below the substrate 120 and oriented to inject gas
vertically from the chamber floor. Yet another alternative is that
the Ar and O.sub.2 may be supplied through outlets connected to the
chamber floor, with the spacer 165 separating the dielectric window
155 and the primary gas ring 170.
[0040] A plurality of detachable injectors 180 are connected to the
primary gas ring 170 to direct a process gas such as SiH.sub.4 or a
related silicon-containing gas such as SiF.sub.4, TEOS, and so on,
onto the substrate 120. These gases are delivered to the substrate
from the injectors 180 through injector exit orifices 187.
Additionally, reactant gases may be delivered through outlets in
the primary gas ring 170. The injectors may be made of any suitable
material such as aluminum, anodized aluminum, quartz or ceramics
such as Al.sub.2O.sub.3. Although two injectors are shown, any
number of injectors may be used. For example, an injector may be
connected to each of the outlets on the primary gas ring 170.
Preferably, eight to thirty-two injectors are employed on a 200 to
210 mm diameter ring 170 for a 200 mm substrate.
[0041] The injectors 180 are located above the plane of the
substrate 120, with their orifices at any suitable distance such
as, for example, 3 to 10 cm from the substrate. The injectors may,
according to a preferred embodiment, be spaced inside or outside of
the substrate periphery, for example, 0 to 5 cm from the substrate
periphery. This helps to ensure that any potential particle flakes
from the injectors will not fall onto the substrate and contaminate
it. The injectors may all be the same length or alternatively a
combination of different lengths can be used to enhance the
deposition rate and uniformity. The injectors are preferably
oriented such that at least some of the injectors direct the
process gas in a direction which intersects the exposed surface of
the substrate.
[0042] As opposed to previous gas injection systems designs which
rely predominantly on diffusion to distribute gas above the
substrate, the injectors according to one embodiment of the present
invention are oriented to inject gas in a direction which
intersects an exposed surface of the substrate at an acute angle.
The angle of injection may range from about 15 to <90 degrees,
preferably 15 to 45 degrees from the horizontal plane of the
substrate. The angle or axis of injection may be along the axis of
the injector or, alternatively, at an angle of up to 90 degrees or
more with respect to the axis of the injector. The exit orifice
diameter of the injectors may be between 0.010 and 0.060 inches,
preferably about 0.020 to 0.040 inches. The hollow core of the
injectors 180 may be drilled to about twice the diameter of the
exit orifices 187 to ensure that sonic flow occurs at the exit
orifice and not within the core of the injector. The flow rate of
SiH.sub.4 is preferably between 25-300 sccm for a 200 -mm substrate
but could be higher for larger substrates.
[0043] Another gas injection system that can be used employs a
plurality of injectors as illustrated in FIG. 5. In this
embodiment, the orifice 187A is oriented to introduce the gas along
an axis of injection (designated "A") in a direction pointing away
from the wafer 120A (and toward the dielectric window). The angle
or axis of injection may be along the axis of the injector
(designated "B") or, alternatively, at an angle of up to about 90
degrees or higher with respect to the axis of the injector. In this
configuration, the axis of injection may range from about 5 to
<90 degrees, preferably about 15 to 75 degrees, and most
preferably, about 15 to 45 degrees from the plane of the substrate.
This design retains the feature that the process gas is focused
above the wafer which leads to high deposition rates and good
uniformity, and further provides the advantage of reduced
susceptibility to orifice clogging. The reduced potential of the
orifice clogging thus allows more wafers to be processed before
injector cleaning is required, which ultimately improves the wafer
processing throughput.
[0044] Due to the small orifice size and number of injectors and
large flowrates of SiH.sub.4, a large pressure differential
develops between the gas ring 170 and the chamber interior. For
example, with the gas ring at a pressure of >1 Torr, and the
chamber interior at a pressure of about 10 mTorr, the pressure
differential is about 100:1. This results in choked, sonic flow at
the outlets of the injectors. The interior orifice of the injector
may also be contoured to provide supersonic flow at the outlet.
[0045] Injecting the SiH.sub.4 at sonic velocity inhibits the
plasma from penetrating the injectors. This design prevents
plasma-induced decomposition of the SiH.sub.4 and the subsequent
formation of amorphous silicon residues within the gas ring and
injector extension tubes.
Experimental
[0046] For gap filling and depositing a cap layer, the process
generally comprises an initial optional sputter clean/pre-heat step
in a plasma without any silicon-containing gas which is followed by
a high bias power gap-fill step. After the gap has been partially
filled, a final sacrificial or "cap" layer of film is deposited
preferably at low RF bias power. Preferably, the gap-fill step
fills substantially all or at least a major portion of the gap
before the cap layer is deposited. The cap layer deposition step
only requires enough bias power to keep the film quality adequate
as no sputtering during film growth is required. The cap layer is
deposited at a higher deposition rate than that of the gap-fill
step. Preferably, this cap film is partially removed in a
subsequent chemical-mechanical polishing (CMP) planarization
step.
[0047] The IC PECVD system generates a high density, low pressure
plasma in a process gas comprising components that form the
semiconducting or dielectric, and cap films. The inventive process
is applicable to depositing any suitable semiconducting, dielectric
and/or cap film including, for example, hydrogenated amorphous
silicon Si:H, silicon oxide SiO.sub.x, where x is 1.5 to 2.5,
silicon nitride, SiN, silicon oxyfluoride, SiO.sub.xF.sub.y where x
is 1.5 to 2.5 and y is 2 to 12, and mixtures thereof. It is
understood that both stoichiometric and non-stoichiometric
compounds can be deposited and the values of x and y can be
controlled by regulating the process parameters such as, for
example, the choice of reactant gases and their relative flow
rates. It is expected that inorganic and organic polymers can also
be deposited. A preferred dielectric and cap film comprises
SiO.sub.2. While the invention will be illustrated by describing
the deposition of SiO.sub.2, it is understood that the invention is
applicable to other films.
[0048] The components of the process gas will depend on the
semiconducting and/or dielectric film to be deposited. With respect
to silicon-containing films the process gas can comprise, for
example, silane (SiH.sub.4), tetraethylorthosilicate (TEOS),
1,3,5,7-tetramethylcyclotetrasiloxane (TMCTS), disilane
(Si.sub.2H.sub.6) or other silicon-containing organometallic gases.
The process gas may include a noble gas preferably Ar, Kr, Xe, and
mixtures thereof to control plasma properties or sputtering rates
particularly during the gap filling step prior to depositing the
cap layer. To incorporate non-silicon components into the film, the
process gas may include a reactant gas such as, for example,
H.sub.2, O.sub.2, N.sub.2, NH.sub.3, NF.sub.3, N.sub.2O , NO and
mixtures thereof. Reactant gases may also comprise boron and/or
phosphorous containing gases to produce boro-phospho-silicate glass
(BPSG), boro-silicate glass (BSG), and phospho-silicate gas (PSG)
films.
EXAMPLE I
[0049] (Gap-filling Process)
[0050] SiO.sub.2 IMD depositions were conducted in an ICP system
similar to that of FIG. 1. Mechanically-clamped 150 mm wafers were
employed. Two gas rings located at the bottom edge of window 33
were employed. One ring distributed the SiH.sub.4 and the other
distributed the Ar and O.sub.2. System parameters are set forth in
Table 1. The electrode temperature was maintained at 80.degree.
C.
1 TABLE 1 ICP RF power 1000 watts at 13.56 MHz Electrode bias RF
power 1000 watts at 400 kHz Ar mass flow rate 100 sccm O.sub.2 mass
flow rate 60 sccm SiH.sub.4 mass flow rate 40 sccm Wafer backside
He pressure 3 Torr Chamber pressure 3.75 milli-Torr (1000 l/s
pump)
[0051] Effect of Oxygen to Silane Mass Flow Ratio (at constant
total flow) on Film Properties
[0052] The film stoichiometry was determined by the chemical
composition of the plasma, established primarily by the ratio R of
the silane and oxygen mass flow rates:
R=Q.sub.siH4/(Q.sub.siH4+Q.sub.O2) where Q is the gas mass flow
rate. Note that the effective oxygen-silane ratio that the wafer
sees also depended on other process parameters. The effect of R on
the film properties is shown in Table 2.
2TABLE 2 Film O.sub.2 Flow SiH.sub.4 Flow Ratio Dep. Refractive OH
Rate Rate % Time Rate Stress Index* Content sccm sccm % sec
.ANG./min. MPa center mid-radius edge at. % 60 40 0.40 180 3460 -91
1.4630 1.4628 1.4633 2.72 70 30 0.30 280 2585 -74 1.4574 1.4579
1.4579 9.10 55 45 0.45 132 3969 -116 1.5414 1.5376 1.5628 0.43 80
20 0.20 9.43 50 50 0.50 120 5449 -66 0.31 50 50 0.50 104 5527 -66
1.6269 1.6203 0.28 65 35 0.35 101 3284 -90 8.79 70 30 0.30 280 2613
-65 1.4574 1.4572 1.4572 9.45 60 40 0.40 180 3591 -106 1.4638
1.4635 1.4647 2.20 80 20 0.20 480 1513 -63 1.4572 1.4571 1.4572
9.08 65 35 0.35 223 3317 -87 1.4584 1.4578 1.4586 8.85 100 0 0.00
300 0 *The refractive index was measured at the center, mid-radius
and edge of each wafer.
[0053] The plasma chemistry for the deposition can be broadly
classified into the following reactions:
R<0.5: SiH.sub.4-limited (2+n)O.sub.2+SiH.sub.4
.fwdarw.SiO.sub.2:(OH).- sub.4n+(2-2n)H.sub.2O (I)
R.gtoreq.0.5: O.sub.2-limited O.sub.2+SiH.sub.4
.fwdarw.SiO.sub.2:(H).sub.- 2n+(2-n)H.sub.2 (II)
[0054] Here, SiO.sub.2:(X).sub.n indicates an approximately
stoichiometric oxide containing some fraction n of X, where
0.ltoreq.n<1. Based on the OH contents measured, n was always
less than 0.025 (OH<10 at. %). Reaction (I) dominated as long as
film growth was silane-limited (R.ltoreq.0.5). This reaction
released increasing amounts of water into the plasma as R
decreased, which accounts for the observation that the OH
concentration in the films increased with decreasing R. Conversely,
operating in the oxygen-limited regime, reaction (II) (R>0.5)
resulted in increased H.sub.2 production, which accounts for the
increasing incorporation of H as Si--H (and the resulting
appearance of Si-rich, sub-oxide groups such as Si.sub.2O.sub.3) at
larger R. This also accounts for the higher chamber pressures
measured at high R, since turbomolecular pumps have low pumping
speeds in H.sub.2.
[0055] The data also suggest that a significant change in the
process takes place near R=0.40. This transition was evident in all
film properties, as shown in Table 2, and appears to correspond to
the transition from a silane-limited chemistry, reaction (I), to an
oxygen-limited chemistry, reaction (II), discussed above. The
deposition rate depended linearly on silane flow, and the
silane-limited region (R<0.40) extrapolated to zero thickness at
zero flow, as would be expected.
[0056] Film stress is typically a function of the mechanical stress
due to differential thermal expansion between the film and
substrate, and the intrinsic film stress. The former is primarily
determined by the deposition temperature. In the latter case, the
film micro-structure and stoichiometry were the dominant factors.
In the SiH.sub.4-limited regime, the film stress appeared to depend
primarily on the deposition rate. It is believed that faster film
growth allowed less time for thermal relaxation and
sputtering/densification by ion bombardment. Films grown under
O.sub.2-limited conditions were less compressive, even though
deposited at higher deposition rates, than films grown under
O.sub.2-rich conditions.
[0057] The FTIR spectra, shown in FIG. 2, illustrate the relevance
of reactions I and II. At low R, Si--OH and Si--HOH absorbance
bands were observed, but not for Si--H. At high R, there was no
detectable Si-OH, but both Si--H and sub-oxide (Si.sub.2O.sub.3)
Si--O bands were present. At intermediate R, just on the
O.sub.2-rich side of the critical range, there appears to be
minimal Si--OH and Si--H incorporation. The intermediate R range is
optimum for achieving the desired dielectric constant. The
refractive index can also be used as a gauge for the preferred
operating conditions since refractive indices between 1.465 and
1.480 correspond to films having good dielectric constants.
[0058] Effect of ICP Power On Film Properties:
[0059] Table 3 shows how the film properties depend on the ICP
power with the basis power held constant at 1000 W.
3TABLE 3 SiO.sub.x ICP Refractive Power Dep. Rate Stress Index OH
Content W .ANG./min. MPa center mid-radius edge at. % 1200 3295
-196 1.4659 1.4664 1.4659 3.81 800 3103 -138 1.4731 1.4738 1.4743
0.65 600 3117 -128 1.4731 1.4879 1.4866 0.43 400 3008 -139 1.5178
1.5151 1.5139 0.53 200 2731 -123 1.5610 1.5606 1.5675 0.51 1200
3396 -208 1.4693 1.4691 1.4640 3.95 200 2674 -113 1.5510 1.5507
1.5515 0.60 600 3060 -142 1.4796 1.4772 1.4746 0.55
[0060] The effect that ICP power has on film properties is similar
in nature to that caused by the total flow. Both effects appear to
essentially be a deposition precursor supply phenomenon. Assuming
that the primary deposition precursor was generated through silane
dissociation, the supply of this species on the wafer surface will
depend on its rate of generation in the plasma and its rate of loss
to the pump and to deposition on the reactor walls. Both the total
flow and the ICP power could influence the effective R at the wafer
through either generation or loss based mechanisms.
[0061] In the case of precursor generation, calculations based on
bond strengths show that the energy required to dissociate
SiH.sub.4 should be less than that for O.sub.2. In this case,
increasing the silane supply (total flow) would preferentially
increase the supply of SiH.sub.x over any relevant oxygen species.
This drives the reaction chemistry to higher R, as observed. The
ICP power should also drive this process, although it is unclear
what the dependence should be.
[0062] Effect of Bias Power on Film Properties
[0063] The bias power was applied to the wafer in order to increase
the DC sheath potential, and thus the kinetic energy of the
bombarding ions, to the point where they sputter the film as it
grows. This improved the quality of the films in a variety of ways.
O.sub.2 plasma preceding deposition sputter cleans the wafer
surface, allowing a clean, adherent interface to form. Since ion
bombardment heats the wafer during deposition, temperature control
requires He backside cooling. Ion bombardment also tends to
preferentially sputter "etch" weak and nonequilibrium structures
from the film, and to produce densification through compaction.
This allows high quality films to be deposited at lower wafer
temperatures than otherwise possible. The dependence of the film
properties on bias power is shown in Table 4.
4TABLE 4 RF Bias Dep. Refractive OH Power Rate Stress Index Content
Watts .ANG./min. MPa center mid-radius edge at. % 1 3850 -295
1.4756 1.4751 1.4763 2.28 1 3853 -301 1.4750 1.4749 1.4758 2.30 1
3842 -315 1.4756 2.56 100 3858 -334 1.4759 2.64 100 3883 -368
1.4761 2.57 100 3893 -361 1.4767 4.05 200 3823 -348 1.4763 3.38 400
3835 -317 1.4744 4.73 500 3722 -117 1.4653 4.90 600 3652 -104
1.4644 3.77 800 3613 -93 1.4639 2.88 1000 3345 -96 1.4633 1.4627
1.4639 2.40 1000 3505 -108 1.4628 1.4622 1.4635 2.31 1000 3350 -96
1.4623 2.69 1000 3538 -105 1.4633 2.25 1200 3393 -107 1.4636 2.06
1400 3336 -123 1.4645 1.34 1600 3159 -101 1.4633 1.79
[0064] It was observed that general film properties underwent a
significant change between 400 and 500 watts. It is believed that
although the ion energy may have increased with bias power below
400 W, the ions did not have sufficient energy to sputter, so the
dominant effect of bias power in this regime was to enhance plasma
generation above the wafer. Above 400 W, the average ion energy was
presumably above the sputtering threshold for SiO.sub.2, and the
net deposition rate decreased as the sputtering component dominated
any effects due to secondary plasma generation.
[0065] Gap-Fill Deposition
[0066] Gap-fill performance can be predicted from the "etch to
deposition rate ratio", ER/DR, which is calculated from the
deposition rates with and without RF bias (the "zero-bias"
condition actually used 100 W to account for secondary plasma
generation): E/D=[DR(no bias)-DR(bias)] .div.DR(no bias), (where DR
denotes the deposition rate. Processes with higher E/D can fill
more aggressive gaps. Generally, the lowest possible E/D that will
fill the required gaps should be used in order to maximize the net
deposition rate. Of course, once the gaps are filled, the E/D
should be reduced to the minimum value needed to preserve film
quality, thus allowing the majority of the IMD layer to be
deposited at much higher rates.
[0067] The SEMs shown in FIGS. 3A, 3B, 3C, and 3D show examples of
good and bad gap-fill by ICP-CVD. FIG. 3A shows a partial fill
attempted with no bias power. The porous film morphology and the
"breadloaf" appearance of the film can be seen at the top of the
line. This eventually closes over to leave a void like that shown
in FIG. 3B. These are also the structures that are preferentially
sputtered away, since the sputtering yield is a maximum at
45.degree.. FIG. 3B gives an example of unsuccessful fill where
bias power was used, but the E/D was too low for the gap. Note that
the breadloaves closed early in the process, leaving a large, deep
gap. In FIG. 3C a tiny void formed just before the gap filled can
be seen next to an otherwise identical gap that filled
successfully. In this case E/D was marginal. The layering was done
deliberately by depositing a thin Si-rich layer periodically and
decorating the sample with the appropriate stain to bring out the
composition contrast. This clearly shows how the gap fills from the
bottom up, with little sidewall growth compared to that on
horizontal surfaces. The 45.degree. facets formed above the lines
by sputtering are also clearly visible. FIG. 3D shows how a
moderate E/D process (100 sccm Ar) completely filled an aggressive
gap. This shows that ICP-CVD can fill aggressive structures.
Example II
[0068] (Gap-fill and Capping Processes)
[0069] SiO.sub.2 IMD and capping depositions were conducted in an
ICP system similar to that of FIG. 4. In this example 200 mm wafers
were processed. The wafers were
[0070] In these depositions (0.5 .mu.m gaps), argon was included in
the process gas.
[0071] However, the addition of argon is not always necessary as
indicated in the preferred ranges. In the deposition of the cap
layer, the initial deposition can employ a high electrode RF bias
power to produce a good quality film. Thereafter, a lower bias
power can be applied (preferably while maintaining about the same
electrode temperature) to produce a sacrificial cap layer of lesser
quality. Typically this sacrificial cap layer is substantially
removed in a subsequent planarization process.
[0072] Generally a higher substrate temperature improves deposited
film properties.
[0073] Typically, there are two primary contributors to the
substrate temperature: (1) thermal heating from the substrate
support (ESC) and (2) plasma heating which comes primarily from the
electrode RF bias power and, to a lesser extent, from the source
(ICP, ECR, etc) power.
[0074] In the prior art, increasing the source and bias power have
been used to increase the substrate temperature in an attempt to
improve film quality. However, this often leads to a tradeoff
amoung the desired film properties as demonstrated by the results
below which examine the effect of helium backside pressure, power
and chamber height.
[0075] Effect of Helium Backside Pressure, Power and Chamber
Height
[0076] A series of depositions were conducted wherein spacer
height, helium cooling pressure and power level of the ICP-CVD
device were varied to modulate the substrate temperature with an
80.degree. C. electrode temperature. Table 6 presents the results.
Substrate temperatures near 400.degree. C. were found to produce
high quality oxides. Among other things, a high substrate
temperature drives off volatile species and improves film density.
For deposition 3 where no helium was used, it was estimated that
the wafer temperature was over 450.degree. C.
[0077] In the first three-wafer set, the helium pressure was
reduced from 2 Torr to 0 Torr (i.e. no cooling) and this caused an
increase in the substrate temperature range from 275.degree. C. to
over 400.degree. C. The film characteristics indicated that high
wafer temperatures produced high quality film. Low OH levels were
found in the films and all of the other film properties were
excellent. The advantage of using high wafer temperature is that it
does not cause adverse effects with respect to the film stress, OH
% and wet etch ratio.
[0078] The second set of wafers (deposition no. 4, 5 and 6)
demonstrate the effects of using helium and argon cooling gas for
substrate temperature control. The first 3-wafer set used helium,
and the second set of three wafers used argon for cooling. The
results show that helium and argon produced similar process
results. The first and third set of 3-wafers compare the effect of
plasma heating of the wafer. The wafer heating was accomplished by
decreasing the distance between the ICP coil to the substrate
surface (spacer height). The results indicated that film quality
changed going from high to lower gap spacing for the same power
level process. The OH% remained the same and the wet etch ratio
improved at lower pacing comparing the 2 or 1 Torr helium cooling
case. However, more compressive tress was observed when lower gap
spacing was used.
[0079] When comparing the third 3-wafer set to the last 2 wafers in
Table 6, the ICP power was decreased from 2500 to 2000 watts. The
data show that less compressive stress was observed by decreasing
the power. The wet etch ratio was degraded indicating that less
plasma heating changed the film structure possibly making the film
more porous. Therefore, the wet etch ratio is better at higher
power levels.
5 TABLE 6 Uniform- Film OH Wet Process Dep. rate ity (% 1- Ref.
Stress content etch conditions .ANG./min. Sigma) Index (MPa) (at %)
ratio 1 6/2/2500 9371 3.63% 1.477 -246 1.7% 7.38 2 6/1/2500 9317
3.60% 1.480 -195 1.3% 6.67 3 6/0/2500 8129 2.83% 1.482 -65 0.3%
1.83 4 6/2/2500 9419 3.68% 1.478 -242 0.46% 8.02 5 6/1/2500 9420
3.65% 1.475 -175 0.88% 7.64 6 6/1/2500 9452 3.53% 1.472 -219 1.37%
7.98 7 0/2/2500 9146 6.47% 1.479 -377 1.0% 3.67 8 0/1/2500 9111
6.35% 1.478 -349 2.5% 3.22 9 0/3/2500 9159 6.60% 1.477 -370 0.4%
3.40 10 0/2/2000 8884 4.53% 1.479 -227 1.1% 5.29 11 0/1/2000 8870
4.86% 1.478 -168 0.1% 4.97 * The process conditions were spacer
height (cm), helium cooling pressure (Torr), and (3) ICP power
(watts). The RF bias was zero for each case.
[0080] Effect of Heated Electrode on Film Properties
[0081] In contrast to the approach of using the source and bias
powers to increase the substrate temperature, it was demonstrated
that using a higher electrode temperature can lead to improved film
quality and a wider process window, without a tradeoff among the
desired values of film stress, OH % and/or wet etch ratio.
[0082] This is illustrated by the results shown in Table 7, where
cap layer deposition results with a 70 and 120.degree. C. electrode
are summarized for cases with and without an applied RF bias.
Preferably, in preparing a cap layer film the wet etch ratio is
<2:1, the OH % is .ltoreq.about 1%, and the magnitude of film
stress is less than 200 Mpa. Simply increasing the plasma heating
of the wafer by increasing the bias from 0 to 2000 W leads to a
decrease in the wet etch ratio, but this also leads to an
undesirable increase in film stress. In contrast, by using a higher
temperature electrode, both the film stress and wet etch ratio are
reduced for cases with and without RF bias power. Hence, a
preferred process uses a thermally controlled electrode with a
temperature that is selectable from the range of about 60 to
200.degree. C.
6TABLE 7 Comparison of film properties with 70 and 120.degree. C.
electrodes. Wafer Temp Wet Etch (.degree. C.) Stress (MPa) % OH
Rate Ratio 70.degree. 120.degree. 70.degree. 120.degree. 70.degree.
120.degree. 70.degree. 120.degree. ESC ESC ESC ESC ESC ESC ESC ESC
Cap Layer 340 375 -250 -190 1.8 0.7 1.5 1.3 with bias Cap Layer 140
170 -193 -128 1.9 1.4 3.8 2.7 w/out bias Process parameters used
are set forth is Table 5
[0083] Another benefit of employing a higher electrode temperature
is that the ranges for the other process conditions including, for
example, pressure, reactant gas flow rates, and TCP power are wider
so that a broader set of operating conditions can be employed.
[0084] The foregoing has described the principles, preferred
embodiments and modes of operation of the present invention.
However, the invention should not be construed as being limited to
the particular embodiments discussed. Thus, the above-described
embodiments should be regarded as illustrative rather than
restrictive, and it should be appreciated that variations may be
made in those embodiments by workers skilled in the art without
departing from the scope of the present invention as defined by the
following claims.
* * * * *