U.S. patent application number 15/156421 was filed with the patent office on 2016-09-29 for tpir apparatus for monitoring tungsten hexafluoride processing to detect gas phase nucleation, and method and system utilizing same.
The applicant listed for this patent is Entegris, Inc.. Invention is credited to Jose I. Arno, Thomas H. Baum, Joseph R. Despres, Shkelqim Letaj, Steven M. Lurcott, Peng Zou.
Application Number | 20160281238 15/156421 |
Document ID | / |
Family ID | 43223393 |
Filed Date | 2016-09-29 |
United States Patent
Application |
20160281238 |
Kind Code |
A1 |
Arno; Jose I. ; et
al. |
September 29, 2016 |
TPIR APPARATUS FOR MONITORING TUNGSTEN HEXAFLUORIDE PROCESSING TO
DETECT GAS PHASE NUCLEATION, AND METHOD AND SYSTEM UTILIZING
SAME
Abstract
Apparatus and method for monitoring a vapor deposition
installation in which a gas mixture can undergo gas phase
nucleation (GPN) and/or chemically attack the product device, under
process conditions supportive of such behavior. The apparatus
includes a radiation source arranged to transmit source radiation
through a sample of the gas mixture, and a thermopile detector
assembly arranged to receive output radiation resulting from
interaction of the source radiation with the gas mixture sample,
and to responsively generate an output indicative of onset of the
gas phase nucleation and/or chemical attack when such onset occurs.
Such monitoring apparatus and methodology is useful in tungsten CVD
processing to achieve high rate tungsten film growth without GPN or
chemical attack.
Inventors: |
Arno; Jose I.; (Portland,
OR) ; Despres; Joseph R.; (Middletown, CT) ;
Letaj; Shkelqim; (Wolcott, CT) ; Lurcott; Steven
M.; (Deerfield Beach, FL) ; Baum; Thomas H.;
(New Fairfield, CT) ; Zou; Peng; (Santa Rosa,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Entegris, Inc. |
Billerica |
MA |
US |
|
|
Family ID: |
43223393 |
Appl. No.: |
15/156421 |
Filed: |
May 17, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13375053 |
Jan 21, 2012 |
9340878 |
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PCT/US10/36747 |
May 28, 2010 |
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15156421 |
|
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61182527 |
May 29, 2009 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 16/455 20130101;
G01N 21/3504 20130101; C23C 16/14 20130101; C23C 16/52
20130101 |
International
Class: |
C23C 16/52 20060101
C23C016/52; C23C 16/455 20060101 C23C016/455 |
Claims
1. A method of carrying out vapor deposition, comprising contacting
a substrate with a gas mixture containing gas species that can
cause gas phase nucleation and/or chemical attack under process
conditions supportive of such behavior, said process comprising:
impinging radiation on a sample of said gas mixture for interaction
of the radiation with one or more gas species in the gas mixture to
produce output radiation from said interaction having a
characteristic that is indicative of onset of said gas phase
nucleation and/or chemical attack when said onset occurs; and
processing said output radiation to responsively generate an output
indicative of onset of said gas phase nucleation and/or chemical
attack when said onset occurs.
2. The method of claim 1, wherein said processing includes
analyzing a spectral portion of said output radiation for a gas
species of interest to determine presence or absence of said
characteristic.
3. The method of claim 2, wherein said analyzing includes at least
one of the following: (i) determination of peak heights of one or
more gas species of the gas mixture; (ii) determination of
differences in peak heights between two or more of the gas species
of the gas mixture; (iii) determination of ratios of peak heights
of two or more of the gas species of the gas mixture; (iv)
determination of AUC of said spectral portion for one or more gas
species of the gas mixture; (v) determination of differences of AUC
for spectral portions for two or more gas species of the gas
mixture; (vi) determination of ratios of AUC for spectral portions
for two or more gas species of the gas mixture; (vii) determination
of slope of a spectral curve in a spectral portion of one or more
gas species of the gas mixture; (viii) determination of differences
of slopes of spectral curves in spectral portions of two or more
gas species of the gas mixture; (ix) determination of ratios of
slopes of spectral curves in spectral portions of two or more gas
species of the gas mixture; (x) determination of peak heights of
one or more gas species of the gas mixture at a predetermined point
in time; (xi) determination of differences in peak heights between
two or more of the gas species of the gas mixture at a
predetermined point in time; (xii) determination of ratios of peak
heights of two or more of the gas species of the gas mixture at a
predetermined point in time; and (xiii) monitoring of a gas species
reactant that is consumed during vapor deposition, as an indicator
of onset of gas phase nucleation and/or chemical attack.
4. The method of claim 1, wherein said processing includes
analyzing a spectral portion of said output radiation for a gas
species of interest to determine presence or absence of said
characteristic, wherein said vapor deposition comprises tungsten
chemical vapor deposition, and the gas mixture includes silane and
tungsten hexafluoride, wherein said analyzing includes querying a
database of spectra or spectral characteristics of the gas species
of interest, and correlating said spectral portion of the output
radiation with the database to generate said output indicative of
onset of said gas phase nucleation and/or chemical attack when said
onset occurs, and wherein said method further comprises controlling
the vapor deposition in response to said output, so as to avoid gas
phase nucleation and chemical attack.
5. The method of claim 1, wherein the one or more gas species
comprise WF.sub.6, SiF.sub.4 and SiH.sub.4.
6. The method of claim 1, comprising carrying out tungsten chemical
vapor deposition to avoid incidence of gas phase nucleation and
chemical attack in said deposition, wherein said chemical vapor
deposition comprises contacting a gas mixture comprising WF.sub.6
and SiH.sub.4, with a Ti:TiN layer on a microelectronic device
substrate, monitoring at least one of WF.sub.6, SiF.sub.4 and
SiH.sub.4 in an effluent from the chemical vapor deposition by TPIR
monitoring to detect said onset of gas phase nucleation and/or
chemical attack, and responsively controlling the chemical vapor
deposition to avoid incidence or continuation of gas phase
nucleation and/or chemical attack.
7. The method of claim 6, wherein said responsively controlling
comprises at least one of: (i) adjusting the relative
concentrations of WF.sub.6 and SiH.sub.4 in the gas mixture, and
(ii) change of a process condition of the chemical vapor
deposition.
8. The method of claim 6, wherein the monitoring comprises one or
more of: (i) determining peak heights, H.sub.WF6 and H.sub.SiF4, in
IR spectra of WF.sub.6, and SiF.sub.4; (ii) determining a peak
height difference (H.sub.WF6-H.sub.SiF4), in IR spectra of
WF.sub.6, and SiF.sub.4; (iii) determining a peak height ratio
(H.sub.WF6/H.sub.SiF4) of SiF.sub.4 and WF.sub.6, in IR spectra of
WF.sub.6, and SiF.sub.4; (iv) determining peak area under curve
(AUC) in IR spectra of WF.sub.6, and SiF.sub.4; (v) determining an
AUC difference (AUC.sub.SiF4-AUC.sub.WF6) in IR spectra of
WF.sub.6, and SiF.sub.4; (vi) determining an AUC ratio
(AUC.sub.SiF4/AUC.sub.WF6) in IR spectra of WF.sub.6, and
SiF.sub.4; (vii) determining slope, S, of spectral curves of IR
spectra of WF.sub.6, and SiF.sub.4; (viii) determining a difference
in slopes (S.sub.SiF4-S.sub.WF6) of spectral curves of IR spectra
of WF.sub.6, and SiF.sub.4; (ix) determining a slope ratio
(S.sub.SiF4/S.sub.WF6) of spectral curves of IR spectra of
WF.sub.6, and SiF.sub.4; (x) determining peak heights, H.sub.WF6
and H.sub.SiF4, in IR spectra of WF.sub.6, and SiF.sub.4 at a
predetermined time of operation; (xi) determining a peak height
difference (H.sub.WF6-H.sub.SiF4), in IR spectra of WF.sub.6, and
SiF.sub.4 at a predetermined time of operation; (xii) determining a
peak height ratio (H.sub.WF6/H.sub.SiF4) of SiF.sub.4 and WF.sub.6,
in IR spectra of WF.sub.6, and SiF.sub.4 at a predetermined time of
operation; and (xiii) monitoring silane concentration.
9. The method of claim 1, comprising determining occurrence of gas
phase nucleation in a chemical vapor deposition chamber having one
or more windows, comprising energizing an infrared radiation diode
laser to transmit IR radiation through a window into the chamber
for said impinging and interaction with vapor therein as said
sample during chemical vapor deposition in the chamber and
generating said output radiation from said interaction, detecting
with a photodiode detector the output radiation transmitted through
a same or different window of the chamber, and responsively
generating said output, indicative of occurrence or non-occurrence
of gas phase nucleation in the chemical vapor deposition
chamber.
10. The method of claim 9, wherein the chemical vapor deposition
chamber is arranged in an arrangement in which: (A) the chemical
vapor deposition chamber comprises a single window, and the
photodiode detector is arranged for detecting back-scatter IR
radiation indicative of occurrence of gas phase nucleation in the
chamber, or (B) the chemical vapor deposition chamber comprises two
windows in opposing registration with one another, with the
infrared radiation diode laser being arranged for transmitting IR
radiation through a first one of said windows, and the photodiode
detector being arranged for detecting output radiation transmitted
through a second one of said windows and indicative of occurrence
of gas phase nucleation in the chamber.
11. A process for controllably maintaining a process within a
predetermined operating regime, using a TPIR monitoring and control
system including a monitoring cell adapted to receive material from
the process, wherein the material in the monitoring cell interacts
with infrared radiation generated by the monitoring system and
infrared radiation resulting from such interaction is detected by a
TPIR detector of the TPIR monitoring and control system as a TPIR
monitoring output from the monitoring cell, said process
comprising: generating a TPIR monitoring output from the monitoring
cell; removing ambient radio frequency noise spikes from TPIR
monitoring output to produce a first refined data output; smoothing
the first refined data output using a binomial smoothing algorithm
to produce a second refined data output; calculating slope and
offset values for signals of material components monitored in the
monitoring cell; utilizing the slopes and offsets for the monitored
material components to temperature correct the second refined
output and produce a third refined output; conducting a peak search
algorithm of the third refined output and calculating peak heights
of the monitored material components, to generate peak heights of
such monitored material components, and determining from peak
height differences of such monitored material components whether
processing associated with the monitoring is within a predetermined
operating regime; and correspondingly modulating the process by
adjustment of one or more operating parameters thereof, to maintain
the process within the predetermined operating regime.
12. The process of claim 11, wherein the TPIR monitoring and
control system comprises a memory unit in which a data analysis
algorithm and associated monitoring and control operational
instructions for said process are stored, and from which said
instructions are able to be accessed and executed by a monitoring
and control system processor.
13. The process of claim 11, wherein: (A) the process comprises a
tungsten CVD process, and the predetermined operating regime
comprises a process operating regime that is free of GPN and/or Ti
attack; or (b) the process comprises a chemical process producing
an effluent, wherein said material from the process comprises
effluent material, and the predetermined operating regime comprises
effluent concentration below a predetermined value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional of U.S. patent application Ser. No.
13/375,053 filed Nov. 29, 2011 in the names of Jose I. Arno, et al.
for "TPIR APPARATUS FOR MONITORING TUNGSTEN HEXAFLUORIDE PROCESSING
TO DETECT GAS PHASE NUCLEATION, AND METHOD AND SYSTEM UTILIZING
SAME," now U.S. Pat. No. 9,340,878, which in turn is a U.S.
national phase under the provisions of 35 U.S.C. .sctn.371 of
International Patent Application No. PCT/US10/36747 filed May 28,
2010, which in turn claims the benefit of priority under 35 USC 119
of U.S. Provisional Patent Application 61/182,527 filed May 29,
2009 in the names of Jose I. Arno, et al. for "TPIR APPARATUS FOR
MONITORING TUNGSTEN HEXAFLUORIDE PROCESSING TO DETECT GAS PHASE
NUCLEATION, AND METHOD AND SYSTEM UTILIZING SAME." The disclosures
of U.S. patent application Ser. No. 13/375,053, International
Patent Application No. PCT/US10/36747, and U.S. Provisional Patent
Application 61/182,527 are hereby incorporated herein by reference
in their respective entireties, for all purposes.
FIELD OF THE INVENTION
[0002] The present invention relates to monitoring of processes by
thermopile infrared (TPIR) detectors, and more specifically to a
TPIR system arranged to monitor vapor deposition process
installations that are susceptible to undesirable behavior of vapor
deposition precursor species as a result of variable conditions in
process equipment in such installation, e.g., occurrence of gas
phase nucleation and chemical attack of surfaces or components. The
invention in one aspect relates to chemical vapor deposition (CVD)
of tungsten, and control of gas mixtures to suppress gas phase
nucleation (GPN) of particulates and attack of titanium and silicon
surfaces while effecting high rate tungsten deposition.
DESCRIPTION OF THE RELATED ART
[0003] In the manufacture of microelectronic devices, deposition of
tungsten films by chemical vapor deposition is commonly practiced,
using tungsten hexafluoride as a tungsten precursor and reducing
gases such as hydrogen or silane.
[0004] The use of hydrogen in such application produces films with
undesirable surface roughness, and induces occurrence of damaging
reactions at exposed silicon and titanium surfaces, resulting in
excessive leakage current and contact resistance, as well as
decreased film adhesion of the tungsten film. For such reasons,
silane is used to achieve high tungsten deposition rates and to
reduce the incidence of silicon and titanium attack by tungsten
hexafluoride or HF formed as a result of hydrogen reduction of
tungsten hexafluoride.
[0005] Silane reduction of WF.sub.6 to elemental tungsten, however,
can take place in the gas phase, by the reaction
WF.sub.6+SiH.sub.4.fwdarw.W (WSi)+SiF.sub.4+H.sub.2+HF. Such gas
phase nucleation of tungsten particles can result in significant
incorporation of tungsten particles in the deposited film, and is
desirably avoided.
[0006] Even when silane is used as a WF.sub.6 reducing agent,
however, chemical attack can be significant, depending on specific
process conditions. In general, chemical attack and gas phase
nucleation phenomena are interrelated, in that process conditions
that suppress one of such phenomena tend to enhance the other.
[0007] Adhesion issues of tungsten films can be ameliorated by use
of titanium/titanium nitride layers (referred to as a Ti:TiN
liner), but if hydrogen is used as a reducing agent, the rate of
tungsten film growth may be significantly reduced. Such reduced
growth rate in turn necessitates longer periods for achieving films
of the desired thickness, but such increased deposition periods
allows any weaknesses or discontinuities in the Ti:TiN liner to
facilitate chemical attack on the underlying material, and the
WF.sub.6 can attack the Ti:TiN liner to form TiF.sub.x species as
defects in the product tungsten film, e.g., by the reaction
WF6+TiN.fwdarw.TiF4+W+HF.
[0008] In consequence of the foregoing issues, the art continues to
seek improvements in tungsten deposition processes in
microelectronic device manufacturing applications.
SUMMARY
[0009] The present invention relates to apparatus and process for
monitoring vapor deposition installations wherein gas phase
mixtures containing deposition species can cause gas phase
nucleation and chemical attack depending on process conditions.
[0010] In one aspect, the invention relates to an apparatus for
monitoring a vapor deposition installation wherein a gas mixture
comprising gas species can cause gas phase nucleation and/or
chemical attack under process conditions supportive of such
behavior, the apparatus comprising: a radiation source arranged to
transmit source radiation through a sample of said gas mixture; and
a thermopile detector assembly arranged to receive output radiation
resulting from interaction of the source radiation with the gas
mixture sample, and to responsively generate an output indicative
of onset of said gas phase nucleation and/or chemical attack when
said onset occurs.
[0011] Another aspect of the invention relates to a method of
carrying out vapor deposition, comprising contacting a substrate
with a gas mixture containing gas species that can cause gas phase
nucleation and/or chemical attack under process conditions
supportive of such behavior, said process comprising:
impinging radiation on a sample of said gas mixture for interaction
of the radiation with one or more gas species in the gas mixture to
produce output radiation from said interaction having a
characteristic that is indicative of onset of said gas phase
nucleation and/or chemical attack when said onset occurs; and
processing said output radiation to responsively generate an output
indicative of onset of said gas phase nucleation and/or chemical
attack when said onset occurs.
[0012] In a further aspect, the invention relates to a method of
carrying out tungsten chemical vapor deposition to avoid incidence
of gas phase nucleation and chemical attack in said deposition,
wherein said chemical vapor deposition comprises contacting a gas
mixture comprising WF.sub.6 and SiH.sub.4, with a Ti:TiN layer on a
microelectronic device substrate, said method comprising monitoring
at least one of WF.sub.6, SiF.sub.4 and SiH.sub.4 in an effluent
from the chemical vapor deposition by TPIR monitoring to detect
onset of gas phase nucleation and/or chemical attack, and
responsively controlling the chemical vapor deposition to avoid
incidence or continuation of gas phase nucleation and/or chemical
attack.
[0013] In yet another aspect, the invention relates to an apparatus
for determining occurrence of gas phase nucleation in a chemical
vapor deposition chamber having one or more windows, comprising an
infrared radiation diode laser arranged to transmit IR radiation
through a window into the chamber for interaction with vapor
therein during chemical vapor deposition in the chamber to generate
output radiation from such interaction, and a photodiode detector
arranged to detect said output radiation transmitted through a same
or different window of the chamber and to responsively generate an
output indicative of occurrence or non-occurrence of gas phase
nucleation in the chemical vapor deposition chamber.
[0014] A still further aspect of the invention relates to a method
of determining occurrence of gas phase nucleation in a chemical
vapor deposition chamber having one or more windows, comprising
energizing an infrared radiation diode laser to transmit IR
radiation through a window into the chamber for interaction with
vapor therein during chemical vapor deposition in the chamber and
generate output radiation from such interaction, detecting with a
photodiode detector the output radiation transmitted through a same
or different window of the chamber, and responsively generating an
output indicative of occurrence or non-occurrence of gas phase
nucleation in the chemical vapor deposition chamber.
[0015] Yet another aspect of the invention relates to a process for
controllably maintaining a process within a predetermined operating
regime, using a TPIR monitoring and control system including a
monitoring cell adapted to receive material from the process,
wherein the material in the monitoring cell interacts with infrared
radiation generated by the monitoring system and infrared radiation
resulting from such interaction is detected by a TPIR detector of
the TPIR monitoring and control system as a TPIR monitoring output
from the monitoring cell, said process comprising:
generating a TPIR monitoring output from the monitoring cell;
removing ambient radio frequency noise spikes from TPIR monitoring
output to produce a first refined data output; smoothing the first
refined data output using a binomial smoothing algorithm to produce
a second refined data output; calculating slope and offset values
for signals of material components monitored in the monitoring
cell; utilizing the slopes and offsets for the monitored material
components to temperature correct the second refined output and
produce a third refined output; conducting a peak search algorithm
of the third refined output and calculating peak heights of the
monitored material components, to generate peak heights of such
monitored material components, and determining from peak height
differences of such monitored material components whether
processing associated with the monitoring is within a predetermined
operating regime; and correspondingly modulating the process by
adjustment of one or more operating parameters thereof, to maintain
the process within the predetermined operating regime.
[0016] Another aspect of the invention relates to a TPIR monitoring
and control system, comprising:
a monitoring cell adapted to receive material for monitoring; an
infrared source arranged to emit radiation that interacts with
material in the monitoring cell to produce output infrared
radiation resulting from such interaction; a TPIR detector arranged
to detect the output infrared radiation and responsively generate a
TPIR monitoring output for material monitored in the monitoring
cell; a computational module arranged for: [0017] generating a TPIR
monitoring output from the monitoring cell; [0018] removing ambient
radio frequency noise spikes from TPIR monitoring output to produce
a first refined data output; [0019] smoothing the first refined
data output using a binomial smoothing algorithm to produce a
second refined data output; [0020] calculating slope and offset
values for signals of material components monitored in the
monitoring cell; [0021] utilizing the slopes and offsets for the
monitored material components to temperature correct the second
refined output and produce a third refined output; [0022]
conducting a peak search algorithm of the third refined output and
calculating peak heights of the monitored material components, to
generate peak heights of such monitored material components, and
determining from peak height differences of such monitored material
components whether processing associated with the monitoring is
within a predetermined operating regime; and a controller coupled
with the computational module for correspondingly modulating the
process by adjustment of one or more operating parameters thereof,
to maintain the process within a predetermined operating
regime.
[0023] Other aspects, features and embodiments of the invention
will be more fully apparent from the ensuing disclosure and
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a schematic representation of a tungsten CVD
process system in which tungsten hexafluoride (WF.sub.6) and silane
(SiH.sub.4) are separately flowed to a deposition chamber including
a pedestal having a Ti liner (Ti:TiN layer structure) thereon,
wherein the process conditions are such as to favor a Ti attack
reaction.
[0025] FIG. 2 is a corresponding schematic representation of the
tungsten CVD process system of FIG. 1, wherein the process
conditions are conducive to occurrence of gas phase nucleation.
[0026] FIG. 3 is a schematic representation of a thermopile
infrared (TPIR) detector in which a broadband infrared (IR) source
is arranged to transmit IR radiation through a gas cell through
which a multicomponent gas mixture is flowed.
[0027] FIG. 4 is a perspective view of a TPIR monitoring apparatus
such as may be employed in a tungsten CVD process system in
accordance with the invention, in one embodiment thereof.
[0028] FIG. 5 is a perspective view of a TPIR monitoring apparatus
according to another embodiment.
[0029] FIG. 6 is a graph of the monitoring output of a TPIR
detector arranged for monitoring WF.sub.6, SiH.sub.4 and SiF.sub.4
in a tungsten CVD system, according to one embodiment of the
invention.
[0030] FIG. 7 is a graph of TPIR monitoring apparatus monitoring
data for a tungsten CVD system operating with a SiH.sub.4 flow rate
of 50 sccm and a WF.sub.6 flow rate of 300 sccm, and a monitoring
system delay of 0.7 seconds.
[0031] FIG. 8 is a graph of monitoring data from a tungsten CVD
system, in which ten different gas mixture recipes were evaluated,
with positive sign bars indicate that no GPN was occurring.
[0032] FIG. 9 shows a multi-pass arrangement of mirrors in which
the IR source at the left-hand side of the figure emits an IR
radiation beam that is reflected multiple times through the gas
cell before being passed to the TPIR detector.
[0033] FIG. 10 is a perspective view, and FIG. 11 is a front
elevation view, of an in-line multi-pass cell arrangement wherein
the monitoring apparatus optics are not exposed directly to the gas
flow.
[0034] FIG. 12 is a graph of wafer processing data for a TPIR
monitoring apparatus of the invention, for a 20 wafer lot,
including the top SiF.sub.4 spectrum, the intermediate WF.sub.6
spectrum and the bottom SiH.sub.4 spectrum, showing the
differentiated character of the three spectra.
[0035] FIG. 13 is a graph of TPIR monitoring data, for a TPIR
monitoring apparatus of the invention, with a silane flow rate of
40 sccm, and a tungsten hexafluoride flow rate of 250 sccm, and
with a monitoring apparatus delay of 0.7 second, showing the top
SiF.sub.4 spectrum, the intermediate WF.sub.6 spectrum and the
bottom SiH.sub.4 spectrum.
[0036] FIG. 14 is a graph of monitoring data from a tungsten CVD
system, in which nine different gas mixture recipes were evaluated,
with positive sign bars indicate that no GPN was occurring, and
negative sign bars indicate that GPN was occurring.
[0037] FIG. 15 is a schematic representation of a multi-pass cell
according to another aspect of the invention, in which 5 passes of
the IR radiation beam is achieved.
[0038] FIG. 16 is a schematic representation of another multi-pass
cell arrangement, in which mirrors are mounted inside a cylindrical
pipe interposed between an IR source and the TPIR detector
(sensor), to provide an extended radiation path length.
[0039] FIG. 17 is a graph of SiF.sub.4 signal to SiH.sub.4
flowrate, showing the correlation between the two, in a tungsten
CVD system including a TPIR monitoring apparatus of the
invention.
[0040] FIG. 18 is a graph of signal ratio of SiH.sub.4 signal to
WF.sub.6 signal, as a function of the ratio of the flowrate of
SiH.sub.4 to flowrate of WF.sub.6, showing the correlation between
the two, in a tungsten CVD system including a TPIR monitoring
apparatus of the invention.
[0041] FIG. 19 includes spectra of WF.sub.6, and SiF.sub.4,
illustrating detection of onset of GPN and/or Ti attack in a gas
stream containing silicon tetrafluoride (SiF.sub.4) and WF.sub.6,
with a TPIR monitoring apparatus programmably arranged to detect
peak heights of these components in the radiation output spectra of
the monitoring cell.
[0042] FIG. 20 includes spectra of WF.sub.6, and SiF.sub.4,
illustrating detection of onset of GPN and/or Ti attack in a gas
stream containing silicon tetrafluoride (SiF.sub.4) and WF.sub.6,
with a TPIR monitoring apparatus programmably arranged to detect
peak areas of the spectral curves of these components in the
radiation output of the monitoring cell.
[0043] FIG. 21 includes spectra of WF.sub.6, and SiF.sub.4,
illustrating detection of onset of GPN and/or Ti attack in a gas
stream containing silicon tetrafluoride (SiF.sub.4) and WF.sub.6,
with a TPIR monitoring apparatus programmably arranged to determine
the slope, S, of the spectral curves of these components
(S.sub.SiF4 and S.sub.WF6) in the radiation output of the
monitoring cell.
[0044] FIG. 22 includes spectra of WF.sub.6, and SiF.sub.4,
illustrating detection of onset of GPN and/or Ti attack in a gas
stream containing silicon tetrafluoride (SiF.sub.4) and WF.sub.6,
with a TPIR monitoring apparatus programmably arranged to monitor
peak heights at any specific point in time, rather than simply the
amplitude of the peaks.
[0045] FIG. 23 is a TPIR monitoring apparatus output, as employed
for detection of onset of GPN and/or Ti attack during tungsten
CVD.
[0046] FIG. 24 is a TPIR monitoring system output for a 4-channel
detector, including a reference channel and channels for silicon
tetrafluoride, tungsten hexafluoride and silane.
[0047] FIG. 25 is a graph of the output of the TPIR monitoring
system of FIG. 24, with the spikes removed.
[0048] FIG. 26 is a TPIR output for the 4-channel TPIR monitoring
system of FIGS. 24 and 25, prior to data smoothing.
[0049] FIG. 27 is a graph of TPIR monitoring system output, for the
data of FIG. 26, after data smoothing.
[0050] FIG. 28 is a graph of linear fitting of channel 3 to channel
4 in a 4-channel TPIR monitoring system, for calculation of slope
and offset.
[0051] FIG. 29 is an output of a TPIR monitoring system prior to
temperature correction.
[0052] FIG. 30 is a graph of output of the TPIR monitoring system
for which data appears in FIG. 29, after temperature correction of
such data.
[0053] FIG. 31 is a graph of output spectra for a tungsten CVD
system, showing peak search results obtained by searching a
tungsten hexafluoride signal.
[0054] FIG. 32 is a graph of TPIR monitoring system output, showing
peak heights of silicon tetrafluoride and tungsten
hexafluoride.
[0055] FIG. 33 is a graph of TPIR monitoring system output, showing
peak height difference between silicon tetrafluoride and tungsten
hexafluoride signals.
[0056] FIG. 34 shows spectra collected for WCVD process gases and
by-products involved in the WCVD nucleation stage, including IR
absorption bands for SiH.sub.4, WF.sub.6 and SiF.sub.4.
[0057] FIG. 35 is a schematic representation of the deposition
system, the TPIR system and the data acquisition system, in an
illustrative arrangement for carrying out TPIR monitoring.
[0058] FIG. 36 is a graph of spectral data collected with the TPIR
system during monitoring of the WCVD process without occurrence of
gas phase nucleation.
[0059] FIG. 37 shows IR spectral data obtained during the WCVD
process with the TPIR system, indicating the absence of GPN.
[0060] FIG. 38 shows the IR spectral data that were obtained during
the WCVD process using the multi-pass TPIR system and that were
processed to indicate conditions that specifically result in GPN,
based upon the analysis of measured WF.sub.6 and SiF.sub.4 signal
intensities and ratios.
DETAILED DESCRIPTION
[0061] The present invention relates to apparatus and process for
monitoring vapor deposition installations wherein gas phase
mixtures containing deposition species can cause gas phase
nucleation and chemical attack depending on process conditions.
[0062] The invention has particular utility for monitoring tungsten
deposition systems where tungsten hexafluoride and silane are used
as reagents for the deposition of tungsten on a substrate including
a Ti:TiN liner. Although the invention is described hereinafter
with particular reference to monitoring of tungsten CVD systems, it
will be appreciated that the utility of the invention is not thus
limited and that the invention may be usefully employed in a wide
variety of process systems susceptible to chemical attack of
substrates and gas phase nucleation as undesirable events in system
operation.
[0063] With reference to the thermopile infrared detectors utilized
in the apparatus of processes of the invention, TPIR assemblies of
widely variant type may be usefully employed in the broad practice
of the invention, including the TPIR assemblies and methodologies
described in U.S. Pat. No. 6,617,175 issued Sep. 9, 2003, U.S. Pat.
No. 7,011,614 issued Mar. 14, 2006, U.S. Pat. No. 6,821,795 issued
Nov. 23, 2004, U.S. Pat. No. 7,172,918 issued Feb. 6, 2007, U.S.
Pat. No. 7,011,614 issued Mar. 14, 2006, U.S. Pat. No. 7,129,519
issued Oct. 31, 2006 and U.S. Pat. No. 7,351,976 issued Apr. 1,
2008, all in the name of Jose Arno. The disclosures of all such
patents are hereby incorporated herein by reference in their
entireties, for all purposes.
[0064] As discussed in the Background section hereof, the incidence
of gas phase nucleation (GPN) and Ti:TiN attack are desirably
avoided in the deposition of tungsten on Ti:TiN layers. The present
invention resolves this issue by monitoring an effluent gas mixture
of the tungsten CVD process, to determine incipient occurrence
(onset) of GPN and Ti:TiN attack, and responsively modulate the
process conditions of the tungsten CVD process to achieve
reduction, and preferably elimination, of such GPN and Ti:TiN
attack, in relation to a corresponding tungsten CVD process lacking
such monitoring. The invention thereby permits active CVD
processing to be carried out with little or no occurrence of GPN
and Ti:TiN attack.
[0065] FIG. 1 is a schematic representation of a tungsten CVD
process system in which tungsten hexafluoride (WF.sub.6) and silane
(SiH.sub.4) are separately flowed to a deposition chamber including
a pedestal having a Ti liner (Ti:TiN layer structure) thereon,
wherein the process conditions are such as to favor the Ti attack
reaction
WF.sub.6+TiN=TiF.sub.4+W+HF
in which WF.sub.6 attacks the Ti liner, producing TiF.sub.4 and HF
as reaction by-products.
[0066] FIG. 2 is a corresponding schematic representation of the
tungsten CVD process system of FIG. 1, wherein the process
conditions have changed to favor the reaction
WF.sub.6+SiH.sub.4=W(WSi)+SiF.sub.4+H.sub.2+HF
in which gas phase nucleation is taking place, producing tungsten
silicide (WSi), SiF.sub.4, H.sub.2 and HF as reaction
by-products.
[0067] The operational problem illustrated by the FIG. 1 and FIG. 2
CVD process system conditions is establishing and maintaining the
process conditions regime that is free of GPN and Ti liner attack.
Such operating regime is difficult to stably maintain, since any
significant process condition fluctuations can result in GPN or Ti
liner attack occurring. There is thus a fine balance point between
GPN and Ti liner attack conditions.
[0068] FIG. 3 is a schematic representation of a thermopile
infrared (TPIR) detector in which a broadband infrared (IR) source
is arranged to transmit IR radiation through a gas cell through
which a multicomponent gas mixture is flowed. The radiation
transmitted through the cell thus interacts with the gas species in
the cell in a manner involving reflectance, absorption and
scattering of the radiation by the gas species in the gas mixture,
resulting in a radiation output from the cell that can then be
filtered by narrow bandgap infrared filters to spectral regions of
interest for the potential components of the gas mixture. The
resultingly filtered radiation then is impinged on TPIR detector
elements to produce an output DC signal for each of the spectral
regions of interest that is indicative of the presence and
concentration of the corresponding gas species producing a
radiation-interaction output in that spectral region.
[0069] The sensitivity of the TPIR system shown in FIG. 3 may be
enhanced by increasing the length of the IR radiation path, e.g.,
by use of mirrors and/or lenses in arrays providing such increased
effective length of the radiation path through the gas mixture in
the gas cell.
[0070] FIG. 4 is a perspective view of a TPIR monitoring apparatus
such as may be employed in a tungsten CVD process system in
accordance with the invention, in one embodiment thereof. The
monitoring apparatus includes a gas mixture inlet receiving gas
mixture from the tungsten CVD system, and a gas mixture outlet for
discharging monitored gas mixture for recycling or other
disposition in the process system. Intermediate the gas mixture
inlet and the gas mixture outlet is a gas cell through which the
gas mixture from the CVD system is flowed for interaction with the
IR radiation transmitted through the cell.
[0071] The IR radiation in the FIG. 4 apparatus is generated from
an IR source at an appropriate spectral region of the IR spectrum
for the gas mixture component(s) of interest Opposedly arranged to
the IR source is the TPIR detector. Although the TPIR detector in
the FIG. 4 apparatus is shown as being in line with the IR source,
it will be recognized that other arrangements may be employed in
which the TPIR detector is not in linear registration with the IR
source, but instead receives output radiation from the gas cell at
an other position, by means of an array of mirrors, lenses, etc.
situated to direct the output radiation from the gas cell to the
detector.
[0072] The detector in the TPIR monitoring apparatus of the
invention is employed to sense onset of gas phase nucleation or Ti
attack conditions and to produce a responsive output for modulating
the tungsten CVD process conditions so that occurrence or
continuation of GPN or Ti attack is avoided during the tungsten
deposition process. For sensing the onset of GPN, the TPIR detector
advantageously has a detection capability for particles as small as
0.2 micrometers (.mu.m) in size (diameter).
[0073] The detector of the TPIR apparatus is advantageously
arranged to monitor the effluent of the CVD process so that the
reaction product species resulting from GPN or Ti attack onset is
detected in the effluent stream passed through the gas cell, so
that a corresponding output is generated to establish, or
reestablish, non-GPN and non-Ti attack CVD operation.
[0074] The TPIR detector thus provides feedback control of the
tungsten CVD system so that CVD operation is maintained in a
non-GPN and non-Ti attack regime. The TPIR monitoring apparatus of
the invention may additionally be configured to provide end-point
monitoring capability for the CVD system, so that an effluent gas
composition indicating an endpoint of the CVD process is sensed,
and the TPIR apparatus responsively outputs a control signal to
terminate the monitoring operation and/or the CVD process.
[0075] The TPIR monitoring apparatus is advantageously arranged to
monitor the CVD effluent gas stream based on a correlation between
effluent characteristics such as concentration and temporal
profiles, and GPN or Ti attack events. The chemistry of normal
tungsten CVD processing and GPN events is sufficiently different
that the TPIR apparatus by monitoring concentration of gas effluent
species such as WF.sub.6, SiF.sub.4 and SiH.sub.4 can distinguish
such operating states, and generate an output correlative of the
specific one of such normal and GPN states that is currently taking
place in the CVD system.
[0076] The TPIR monitoring apparatus for such purpose may be
programmatically arranged to perform a software algorithm in the
monitoring operation that will provide an output alarm signal
and/or other control signal under GPN conditions.
[0077] Corresponding monitoring considerations and arrangements are
likewise applicable to Ti attack conditions.
[0078] FIG. 5 is a perspective view of the TPIR monitoring
apparatus according to another embodiment, showing a central gas
cell having flanged ends for coupling with closure members, and
radially extending inlet and outlet passages with flanged ends for
coupling with the flow circuitry of the CVD system. The IR source
is at the upper end of the apparatus, opposite to the TPIR detector
assembly module at the lower end of the apparatus, with each of the
source and detector components being connected to tubular members
that in turn communicate with an interior volume of the gas
cell.
[0079] The TPIR apparatus in one implementation has a single pass
radiation transmission capability with a radiation pathlength of 13
inches on a standard spool piece, installed on a pump line of the
CVD system.
[0080] FIG. 6 is a graph of the monitoring output of a TPIR
detector arranged for monitoring WF.sub.6, SiH.sub.4 and SiF.sub.4
in a tungsten CVD system, according to one embodiment of the
invention, wherein the top spectral output is SiF.sub.4, the
intermediate spectral output closely matching the SiF.sub.4 output
at its peak, but having a deeper trough than the SiF.sub.4 output,
is WF.sub.6, and the bottom spectral output is SiF.sub.4.
[0081] FIG. 7 is a graph of TPIR monitoring apparatus monitoring
data for a tungsten CVD system operating with a SiH.sub.4 flow rate
of 50 sccm and a WF.sub.6 flow rate of 300 sccm, and a monitoring
system delay of 0.7 seconds. The spectrum having an output peak
above 100 units (arbitrary output scale) at approximately 11:11 AM
and shortly after 11:20 AM is the WF.sub.6 spectrum, and the
spectrum having three peaks above 100 units between 11:14 AM and
11:19 AM is the SiF.sub.4 spectrum. These peaks show that the
respective spectra are quantitatively sufficient to provide
capability for monitoring of GPN conditions.
[0082] In a specific test of a monitoring apparatus of the present
invention in a tungsten CVD system, ten different gas mixture
recipes were evaluated, with the results shown in FIG. 8. In the
FIG. 8 graph, positive sign bars indicate that no GPN was
occurring. Eye inspection (EI) determinations were correlated with
the data, showing that IR detection was clean in instances in which
GPN was clearly visible by EI determination.
[0083] These and other empirical results show that GPN is caused by
excessive SiH.sub.4 or SiH.sub.4 being dispensed much earlier than
WF.sub.6, and that variances in peak height of SiF.sub.4 and
WF.sub.6 can be correlated to GPN. Thus, the timing as well as the
concentration of WF.sub.6 and SiH.sub.4 are critical for GPN. The
monitoring operation entails no disturbance of the wafer processing
operation, and continuous monitoring is readily carried out.
[0084] In the TPIR monitoring apparatus of the invention, the gas
cell can be of a single-pass or a multi-pass character. FIG. 9
shows a multi-pass arrangement of mirrors in which the IR source at
the left-hand side of the figure emits an IR radiation beam that is
reflected multiple times through the gas cell before being passed
to the TPIR detector.
[0085] FIG. 10 is a perspective view, and FIG. 11 is a front
elevation view, of an in-line multi-pass cell arrangement wherein
the monitoring apparatus optics are not exposed directly to the gas
flow, and wherein an 8-fold increase in radiation path length is
obtained.
[0086] FIG. 12 is a graph of wafer processing data for a TPIR
monitoring apparatus of the invention, for a 20 wafer lot,
including the top SiF.sub.4 spectrum, the intermediate WF.sub.6
spectrum and the bottom SiH.sub.4 spectrum, showing the
differentiated character of the three spectra.
[0087] FIG. 13 is a graph of TPIR monitoring data, for a TPIR
monitoring apparatus of the invention, with a silane flow rate of
40 sccm, and a tungsten hexafluoride flow rate of 250 sccm, and
with a monitoring apparatus delay of 0.7 second, showing the top
SiF.sub.4 spectrum, the intermediate WF.sub.6 spectrum and the
bottom SiH.sub.4 spectrum. The data again show the differentiated
character of the three spectra.
[0088] In another test of a monitoring apparatus of the present
invention in a tungsten CVD system, nine different gas mixture
recipes were evaluated, with the results shown in FIG. 14. In the
FIG. 14 graph, positive sign bars indicate that no GPN was
occurring, and negative sign bars indicate that GPN was occurring.
The data in FIG. 14 show that it is possible to identify strong GPN
and non-GPN events.
[0089] Empirical testing of TPIR apparatus of the invention show
that the SiH.sub.4 flowrate and delay time between SiH.sub.4 and
WF.sub.6 delivery are two major factors that cause GPN. The TPIR
apparatus of the invention can readily provide accurate measurement
of SiF.sub.4 and WF.sub.6 down to concentrations of 10 parts per
million (ppm), and the amount of SiH.sub.4 can be correlated to the
amount of SiF.sub.4 that is produced. Typical delay tuning ranges
are from 0.7 to 1.0 second, and accuracy on the order of 0.1 second
or less is desired.
[0090] Thus, the TPIR apparatus of the invention permits real time
monitoring of gas phase nucleation by monitoring gas species
(SiF.sub.4, WF.sub.6, SiH.sub.4) in the effluent from the tungsten
CVD process. The concentration of these gases as well as their
appearance/disappearance rates, and their concentration
differences, provide measurements indicative of the types of
reactions that are taking place in the CVD chamber of the tungsten
CVD system, and an indication of whether or not gas phase
nucleation is occurring in the CVD chamber.
[0091] Although the foregoing description has been directed to a
CVD system arrangement of the TPIR apparatus in which the TPIR
apparatus is arranged for monitoring of a pump line for discharging
effluent from the CVD system, it will be appreciated that it is
possible to arrange the TPIR apparatus for monitoring of gas
delivery lines to the CVD chamber, where higher concentrations and
more accurate timing can be monitored. For example, the influent
SiH.sub.4 delivery line to the CVD chamber may be monitored, to
provide enhanced detection of silane.
[0092] The use of a multi-pass cell between the IR source and IR
sensor in the monitoring apparatus of the invention can greatly
improve the sensitivity and lower the detection limit of the
apparatus. In arrangements in which mirrors are utilized in the
TPIR monitoring apparatus and are exposed to the fluid stream in
the cell, in a corrosive environment, a corrosion-resistant coating
on the mirror, e.g., of nickel or other corrosion-resistant
material with good reflectivity characteristics, can beneficially
be employed.
[0093] FIG. 15 is a schematic representation of a multi-pass cell
according to another aspect of the invention, in which 5 passes of
the IR radiation beam is achieved. More passes can be obtained in
this apparatus by changing the beam angle of the infrared
radiation.
[0094] FIG. 16 is a schematic representation of another multi-pass
cell arrangement, in which mirrors are mounted inside a cylindrical
pipe interposed between an IR source and the TPIR detector
(sensor), to provide an extended radiation path length.
[0095] FIG. 17 is a graph of SiF.sub.4 signal to SiH.sub.4
flowrate, showing the correlation between the two, in a tungsten
CVD system including a TPIR monitoring apparatus of the
invention.
[0096] FIG. 18 is a graph of signal ratio of SiH.sub.4 signal to
WF.sub.6 signal, as a function of the ratio of the flowrate of
SiH.sub.4 to flowrate of WF.sub.6, showing the correlation between
the two, in a tungsten CVD system including a TPIR monitoring
apparatus of the invention.
[0097] The invention contemplates various approaches for
algorithmically characterizing the gas species detected by the TPIR
apparatus. Such approaches may be implemented by a central
processing unit, such as a programmable logic controller,
microprocessor, computer or server including a memory or other data
carrier that contains a program, firmware or the like, that is
executable to carry out the algorithmic detection of the gas
species of interest in the gas being sampled by the TPIR apparatus.
The gas species can include source materials, reactants, reaction
products or other species in the stream being monitored by the TPIR
apparatus. Such specially adapted machine may be embodied in a
module containing the TPIR detector, e.g., of a type shown in FIG.
5 hereof.
[0098] Although the invention is primarily described herein in
application to a gas stream containing one or more gas species of
interest, it is to be recognized that the invention is not thus
limited in applicability, and that the invention may be employed
for monitoring other species such as liquid components and/or solid
components, or of gas and/or liquid and/or solid components of a
stream containing same. In the same respect, other forms of
materials, e.g., plasma species, adsorbed species, nanoparticulate
composite materials, etc. may be monitored using the apparatus and
method of the invention.
[0099] In one aspect, directed to detection of onset of GPN and/or
Ti attack in a gas stream containing silicon tetrafluoride
(SiF.sub.4) and WF.sub.6, the TPIR monitoring apparatus may be
programmably arranged to detect peak heights of these components in
the radiation output spectra of the monitoring cell, as illustrated
in the spectra of WF.sub.6, and SiF.sub.4 in FIG. 19 hereof.
[0100] By measuring the peak heights, H.sub.WF6 and H.sub.SiF4, of
SiF.sub.4 and WF.sub.6 in such monitoring operation, the monitoring
apparatus is able to predict GPN and/or Ti attack. Such prediction
can also be derived by determining a peak height difference
(H.sub.WF6-H.sub.SiF4), or a peak height ratio
(H.sub.WF6/H.sub.SiF4) of SiF.sub.4 and WF.sub.6 to determine onset
conditions for GPN and/or Ti attack.
[0101] In another aspect, directed to detection of onset of GPN
and/or Ti attack in a gas stream containing silicon tetrafluoride
(SiF.sub.4) and WF.sub.6, the TPIR monitoring apparatus may be
programmably arranged to detect peak areas of the spectral curves
of these components in the radiation output of the monitoring cell,
as in the spectra of these components shown in FIG. 20 hereof.
[0102] By measuring the peak areas (area under the curve, or AUC)
of SiF.sub.4 and WF.sub.6 in such monitoring operation, the
monitoring apparatus is able to predict GPN and/or Ti attack. Such
prediction can also be derived by determining an AUC difference
(AUC.sub.SiF4-AUC.sub.WF6) or an AUC ratio
(AUC.sub.SiF4/AUC.sub.WF6) of SiF.sub.4 and WF.sub.6 to determine
onset conditions for GPN and/or Ti attack.
[0103] In a further aspect, directed to detection of onset of GPN
and/or Ti attack in a gas stream containing silicon tetrafluoride
(SiF.sub.4) and WF.sub.6, the TPIR monitoring apparatus may be
programmably arranged to determine the slope, S, of the spectral
curves of these components (S.sub.SiF4 and S.sub.WF6) in the
radiation output of the monitoring cell, as illustrated in the
spectra of these components shown in FIG. 21 hereof.
[0104] By measuring the slopes of the curves of SiF.sub.4 and
WF.sub.6 spectra in such monitoring operation, the monitoring
apparatus is able to predict GPN and/or Ti attack. Such prediction
can also be derived by determining a difference in slopes
(S.sub.SiF4-S.sub.WF6) or a slope ratio (S.sub.SiF4/S.sub.WF6) of
SiF.sub.4 and WF.sub.6 to determine onset conditions for GPN and/or
Ti attack.
[0105] Slopes of the WF.sub.6 and SiF.sub.4 spectral curves can be
usefully employed because they reflect the reaction rate of the
tungsten CVD process, and the spectral curves of these components
for GPN conditions are typically quite different from the spectral
curves obtained under conditions of normal (GPN-free and Ti
attack-free) deposition of tungsten on the wafer surface.
[0106] In yet another aspect, directed to detection of onset of GPN
and/or Ti attack in a gas stream containing silicon tetrafluoride
(SiF.sub.4) and WF.sub.6, the TPIR monitoring apparatus may be
programmably arranged to monitor peak heights at any specific point
in time, rather than simply the amplitude of the peaks, as shown in
the WF.sub.6 (top curve) and SiF.sub.4 (bottom curve) spectral
curves in FIG. 22. Such monitoring of peak heights at a specific
time can be quite useful in determining onset of GPN and/or Ti
attack, since relative concentrations of the gases may change at
any point in the process and cause GPN or Ti attack.
[0107] The temporal traces of the peaks of WF.sub.6 and SiF.sub.4
spectral curves also reflect the timing of the gas dispense, which
is another factor that can cause GPN and/or Ti attack.
[0108] Thus, a "time slice" of the spectrum (AH) may be obtained
for each of the WF.sub.6 and SiF.sub.4 spectral curves, and used
independently, or aggregately (e.g., as differences or ratios), to
determine correlates of the onset of GPN and/or Ti attack.
[0109] In a still further aspect, directed to detection of onset of
GPN and/or Ti attack in a gas stream containing silicon
tetrafluoride (SiF.sub.4) and WF.sub.6, the TPIR monitoring
apparatus may be programmably arranged to monitor silane
(SiH.sub.4), as in the spectral curves (top curve WF.sub.6, middle
curve SiF.sub.4, and lower curve SiH.sub.4) shown in FIG. 23.
[0110] This monitoring mode is based on the fact that SiH.sub.4 is
typically completely consumed during tungsten CVD. Any residual
SiH.sub.4 therefore can be utilized as an indicator of GPN and/or
Ti attack.
[0111] Note that in the implementation of the foregoing monitoring
arrangements, it may be desirable to construct the monitoring
detection module, e.g., as shown at the lower portion of the
apparatus illustrated in FIG. 5, so that it incorporates as part of
the module a CPU providing an output signal for modulating the CVD
process to suppress or eliminate GPN and/or Ti attack. Such CPU may
usefully incorporate or be communicatively coupled with a database
including spectra or spectral characteristics of onset of GPN and
Ti attack, against which current monitoring spectra or spectral
characteristics can be matched or otherwise correlated or
processed, for purposes of determining if onset of GPN or Ti attack
is currently occurring, and if such GPN or Ti attack is incipient,
then providing a output for modulation of the CVD process to avoid
such GPN or Ti attack behavior.
[0112] The output and resulting modulation of the CVD process may
involve any suitable changes of process conditions, e.g., pressure,
temperature, flow rate and composition of gases or individual gas
species flowed to the process chamber. Thus, in application to
tungsten CVD, the relative flow rates of silane and tungsten
hexafluoride may be adjusted in response to the monitoring sensing
of the output radiation from the sampling cell, so that the gas
phase constitution of the gas mixture in the deposition chamber is
not conductive to GPN or Ti attack, so that normal operation may be
maintained throughout the deposition process.
[0113] The modulation of the process system to suppress and avoid
GPN and Ti attack conditions may be carried out in any suitable
manner, using conventional signal processing, transmission and
control components, including for example flow control valves and
valve actuator assemblies, pressure transducers, thermocouple
sensors, etc., within the skill of the art, based on the disclosure
herein.
[0114] The TPIR monitoring system of the present invention in
another aspect embodies a system and algorithms for data analysis,
to increase the resolution of the monitoring operation and control
of the process system to avoid GPN and Ti attack conditions.
[0115] The TPIR monitor utilizes a hot filament infrared source and
a thermopile infrared detector. Due to the character of the
thermopile detector, as functioning to measure temperature change,
the infrared detector is sensitive not only to incident infrared
light but also to ambient temperature changes in the environment of
the CVD process. Additionally, white noise from ambient light and
electronics, such as power supplies, also operate to potentially
adversely affect the signal-to-noise level in the infrared
monitoring operation.
[0116] The present invention in such additional aspect therefore
utilizes an algorithmic approach for calibrating signals from the
TPIR monitoring system, which may be implemented by a monitoring
and control system programmably arranged to carry out the
monitoring, data analysis, and control functions, using the data
analysis algorithm, e.g., as contained in a memory unit, such as a
RAM, ROM, PROM device in which the data analysis algorithm and
associated monitoring and control operational instructions are
stored, which may be associated with a processor and other
components of a monitoring and control system, wherein the
processor is arranged to access and execute the data analysis
algorithm and associated monitoring and control operational
instructions. Alternatively, the data analysis algorithm and
associated monitoring and control operational instructions may be
stored on a computer-readable medium, such as a disc, memory stick,
or other data carrier device, to be used in a computer system
adapted to carry out the monitoring, data analysis and control
functions stored on the data carrier device.
[0117] It will be appreciated that any of the methods and
techniques described hereinabove or hereafter for TPIR monitoring
and/or control are contemplated as being likewise able to be
implemented within the broad practice of the invention as above
described, e.g., by memory units and/or data carrier devices, with
associated processors and other components of a monitoring and
control system.
[0118] This algorithmic approach for calibrating signals from the
TPIR monitoring system is illustrated below with respect to an
exemplary application.
[0119] The radiation output signal of the monitoring cell may have
spikes due to ambient radio frequency noise. Such ambient noise can
be readily removed, since most of the spikes are significantly
larger than the fundamental monitoring signal. FIG. 24 shows a
graph of raw data for a radiation output signal of a monitoring
cell in a CVD process system, and FIG. 25 shows the corresponding
signal output with the spikes removed. The output signals include
spectra for silicon tetrafluoride, tungsten hexafluoride, silane
and a reference signal ("REF").
[0120] The corresponding code for the spike removal process is as
follows:
[0121] Code:
TABLE-US-00001 if (Signal (n)>~40000) Then Signal (n) = Signal
(n-1)
[0122] After such removal of spikes from the output, the data are
still noisy, primarily because of so-called "short noise" from the
associated electronics of the monitoring and CVD process systems.
To smooth the data, a binomial smoothing algorithm is employed with
a smoothing term of 50. The corresponding code is:
[0123] Code:
[0124] Smooth_binomial_n_50 (Signal)
[0125] This data smoothing operation was employed to smooth the
data shown in FIG. 26, with the corresponding smoothed data being
shown in FIG. 27, for the same spectral components and reference
shown in FIGS. 24 and 25 (silicon tetrafluoride, tungsten
hexafluoride, silane and "REF" reference signal).
[0126] As indicated, the TPIR detector is sensitive to ambient
temperature change, and temperature corrective operations are
advantageously employed to compensate for such variable
temperature. The ambient temperature can introduce large baseline
change of the output signal of the monitoring cell, and render
subsequent analysis difficult. The TPIR may, for example, have four
channels, for the illustrative case of monitoring of silicon
tetrafluoride, tungsten hexafluoride and silane, together with a
reference channel, wherein the reference channel is employed to
calibrate the remaining chemical reagent channels.
[0127] The ambient temperature change experienced by the TPIR
monitoring system should introduce a same trend of signal changes
on all four channels of the detector. Insofar as detector settings
remain the same, signal changes on channels 2, 3 and 4 (silicon
tetrafluoride, tungsten hexafluoride and silane, respectively)
should be proportional to channel 1 (the reference channel). If the
slopes and offsets of channels 2, 3 and 4 are calculated against
channel 1, then the results can be employed for temperature
correction of the monitoring system. The corresponding code is as
follows:
[0128] Code:
TABLE-US-00002 Plot Ch2, 3, 4 vs. Ch1 Linear Fit Ch2, Ch3, Ch4 vs.
Ch1 Output (a2, b2; a3, b3; a4, b4) (wherein a2, a3, a4 are slopes
and b2, b3, b4 are offsets)
wherein Ch=channel.
[0129] FIG. 28 illustrates a linear fitting of channel 3 to channel
1 to calculate slope and offset.
[0130] Next, temperature correction is effected, utilizing the
following code:
[0131] Code:
TABLE-US-00003 Ch2 = Ch2 - a2 * Ch1 - b2 Ch3 = Ch3 - a3 * Ch1 - b3
Ch4 = Ch4 - a2 * Ch1 - b4
[0132] FIG. 29 shows a plot of the spectra for the four channels
before temperature correction. FIG. 30 shows the corresponding
spectra after temperature correction. It is seen that the baseline
still has some curvature after temperature correction, but such
curvature should not affect further data analysis.
[0133] In order to extract meaningful information from the data,
peaks of silicon tetrafluoride and tungsten hexafluoride
corresponding to CVD processing of each individual wafer have to be
identified. The location of the peak for the wafer can be
accomplished utilizing any suitable peak search algorithm. For
example, a simple peak search algorithm can be used involving the
histograph of Signal (n+A)-Signal(n) where A is the pre-defined
parameter. Either channel 2 (silicon tetrafluoride) or channel 3
(tungsten hexafluoride) can be used for the search. The
corresponding code is as follows:
[0134] Code:
TABLE-US-00004 Num_peak = 0 A = 100 Peak_threshold = 50 For (I = 0
to Num_Data_Points-A) If (Signal (I+A)-Signal(I) >
Peak_threshold) Num_peak = Num_peak + 1 Peak_Position = I+A Endif
EndFor
[0135] A graph of the peak search results obtained by searching the
tungsten hexafluoride signal is shown in FIG. 31.
[0136] Peak height of silicon tetrafluoride and tungsten
hexafluoride then is calculated by a minimum search. Because the
baseline may sometimes still retain curvatures, it is necessary to
do a baseline correction to obtain correct peak heights. The
corresponding code is as follows:
[0137] Code:
TABLE-US-00005 Range = 70 Left_limit = 80 Right_limite = 80
Base_range = 50 Peak_height = Max (Peak_position - range,
Peak_position + range) Base_left = Average (Peak_position -
left_limit - base_range, Peak_position - left_limit + base_range)
Base_right = Average (Peak_position - right_limit - base_range,
Peak_position - right_limit + base_range) Peak_height = Peak_height
- 1/2 (Base_left + Base_right)
[0138] A resulting graph of peak heights of silicon tetrafluoride
and tungsten hexafluoride are shown in FIG. 32.
[0139] After peak heights are extracted from the TPIR monitoring
system data, the system can determine whether or not to output a
GPN warning based on the difference of the silicon tetrafluoride
and tungsten hexafluoride signals. Typically, if the SiF.sub.4
signal is larger, it means that silane is in excess and GPN is very
likely to occur under such conditions. Accordingly, a warning or
termination of wafer processing is necessary. The corresponding
code for such operation is as follows:
[0140] Code:
TABLE-US-00006 Warning_Flag = 0 If (Peak_SiF4 - Peak_WF6 < 0)
(Keep in mind, all the peak heights are negative) Warning_Flag = 1
Endif
[0141] FIG. 33 shows a graph of peak height difference between
SiF.sub.4 and WF.sub.6, together with the individual silicon
tetrafluoride and tungsten hexafluoride output signals. The system
for which data is shown in FIG. 33 does not have a GPN issue.
[0142] The foregoing algorithmic data analysis process has been
illustratively described in respect of GPN monitoring of a tungsten
hexafluoride CVD system. Such algorithmic process, however, is not
limited to GPN monitoring applications, and the baseline and
temperature correction procedures, as well as peak search and peak
height (area) calculation, may be utilized in other TPIR monitoring
applications. For example, the data analysis algorithmic process
may be employed to calculate effluent concentrations, and temporal
profiles can be used to calculate kinetic rates or other time
sensitive information in chemical process monitoring or other
applications.
[0143] The foregoing algorithmic data analysis process permits
thermopile infrared detection systems to be calibrated and
corrected for ambient radio frequency noise, short noise from
electronics, and ambient temperature fluctuations.
[0144] In one embodiment, the data analysis process includes:
generating a TPIR monitoring output from a monitoring cell;
removing ambient radio frequency noise spikes to produce a first
refined data output; smoothing the first refined data output using
a binomial smoothing algorithm to produce a second refined data
output; calculating slope and offset values for signals of output
components monitored in the gas cell; utilizing the slopes and
offsets for the monitored components to temperature correct the
second refined output and produce a third refined output;
conducting a peak search algorithm of the third refined output and
calculating peak heights of output components, to generate peak
heights of such output components, and determining from peak height
differences of such output components whether processing associated
with the monitoring is within a predetermined operating regime; and
correspondingly modulating the process by adjustment of one or more
operating parameters thereof.
[0145] For example, the predetermined operating regime in the case
of tungsten CVD may be a regime free of GPN and/or Ti attack,
arranged so that process conditions determined to be outside of
such predetermined regime cause an output alarm to be generated, in
addition to effecting control steps for the process to reestablish
the desired operating regime.
[0146] Thus, the invention contemplates a process for controllably
maintaining a process within a predetermined operating regime,
using a TPIR monitoring and control system including a monitoring
cell adapted to receive material from the process, wherein the
material in the monitoring cell interacts with infrared radiation
generated by the monitoring system and infrared radiation resulting
from such interaction is detected by a TPIR detector of the TPIR
monitoring and control system as a TPIR monitoring output from the
monitoring cell, said process comprising:
generating a TPIR monitoring output from the monitoring cell;
removing ambient radio frequency noise spikes from TPIR monitoring
output to produce a first refined data output; smoothing the first
refined data output using a binomial smoothing algorithm to produce
a second refined data output; calculating slope and offset values
for signals of material components monitored in the monitoring
cell; utilizing the slopes and offsets for the monitored material
components to temperature correct the second refined output and
produce a third refined output; conducting a peak search algorithm
of the third refined output and calculating peak heights of the
monitored material components, to generate peak heights of such
monitored material components, and determining from peak height
differences of such monitored material components whether
processing associated with the monitoring is within a predetermined
operating regime; and correspondingly modulating the process by
adjustment of one or more operating parameters thereof, to maintain
the process within the predetermined operating regime.
[0147] In such process, the TPIR monitoring and control system can
comprise a memory unit in which a data analysis algorithm and
associated monitoring and control operational instructions for the
process are stored, and from which the instructions are able to be
accessed and executed by a monitoring and control system
processor.
[0148] The process in one specific embodiment comprises a tungsten
CVD process, and the predetermined operating regime comprises a
process operating regime that is free of GPN and/or Ti attack.
[0149] The process can further comprise outputting an alarm when
the process is determined to be outside the predetermined operating
regime.
[0150] In another specific embodiment, the process comprises a
chemical process producing an effluent, wherein the material from
the process comprises effluent material, and the predetermined
operating regime comprises effluent concentration below a
predetermined value.
[0151] The invention in another aspect relates to a TPIR monitoring
and control system, comprising:
a monitoring cell adapted to receive material for monitoring; an
infrared source arranged to emit radiation that interacts with
material in the monitoring cell to produce output infrared
radiation resulting from such interaction; a TPIR detector arranged
to detect the output infrared radiation and responsively generate a
TPIR monitoring output for material monitored in the monitoring
cell; a computational module arranged for: [0152] generating a TPIR
monitoring output from the monitoring cell; [0153] removing ambient
radio frequency noise spikes from TPIR monitoring output to produce
a first refined data output; [0154] smoothing the first refined
data output using a binomial smoothing algorithm to produce a
second refined data output; [0155] calculating slope and offset
values for signals of material components monitored in the
monitoring cell; [0156] utilizing the slopes and offsets for the
monitored material components to temperature correct the second
refined output and produce a third refined output; [0157]
conducting a peak search algorithm of the third refined output and
calculating peak heights of the monitored material components, to
generate peak heights of such monitored material components, and
determining from peak height differences of such monitored material
components whether processing associated with the monitoring is
within a predetermined operating regime; and a controller coupled
with the computational module for correspondingly modulating the
process by adjustment of one or more operating parameters thereof,
to maintain the process within a predetermined operating
regime.
[0158] The TPIR monitoring and control system in a specific
embodiment comprises a memory unit in which a data analysis
algorithm and associated monitoring and control operational
instructions are stored, and a processor arranged to access and
execute such instructions.
[0159] Although the discussion herein has been primarily directed
to tungsten CVD processes, many other CVD processes, e.g., for epi
layer formation, polysilicon deposition, formation of SiN layers,
and oxide formation, have associated process control and particle
formation issues, in which monitoring in accordance with the
present invention can be of value.
[0160] Other processes in which the monitoring apparatus and
methodology of the invention can be beneficially employed include
monitoring of the following specific deposition reactions:
SiH.sub.4+NH.sub.3.fwdarw.SiN
TEOS+O.sub.2.fwdarw.SiO.sub.2
TDMAH(Hf)+TMA(Al)+O.sub.3.fwdarw.HfO.sub.2
wherein TEOS is tetraethylorthosilicate, TDMAH(Hf) is
tetrakis(dimethylamino)hafnium, and TMA(Al) is
trimethylaluminum.
[0161] A further aspect of the invention relates to another
infrared radiation monitoring technique for detecting occurrence of
GPN in tungsten CVD systems.
[0162] Consistent with the earlier discussion herein, the chemistry
of tungsten CVD involves two primary deposition reactions,
SiH.sub.4+WF.sub.6.fwdarw.SiF.sub.4+W+HF and
WF.sub.6+H.sub.2.fwdarw.W+HF.
[0163] The reaction of SiH.sub.4 and WF.sub.6 can occur in the gas
phase if the SiH.sub.4 concentration is much higher than the
WF.sub.6 concentration. Instead of deposition of tungsten on the
surface of wafer, the gas phase reaction (gas phase nucleation,
GPN) produces fine particles of tungsten (several nm to several
hundred nm in size) that threaten the wafer quality. Therefore, the
timing of introducing SiH.sub.4 and WF.sub.6 into the deposition
chamber is critical for tungsten CVD to be efficiently conducted.
In production facilities, wafers may be processed in batches of 50
or more.
[0164] The occurrence of GPN can result in such entire batches of
wafers being rendered deficient or even useless for their intended
purpose. When GPN occurs, a "cloud" of fine particles is typically
created in the deposition tool chamber.
[0165] The invention contemplates monitoring the deposition chamber
with an infrared radiation diode laser arranged at a window of the
chamber to transmit IR radiation into the gas volume in the
interior of the chamber during tungsten CVD operation. The laser
beam radiation when encountering a GPN "cloud" is scattered, and
the resulting burst of back-scatter IR radiation can be detected by
an appropriately positioned photodiode detector.
[0166] Alternatively, the CVD chamber may be arranged with
opposedly facing windows, one being arranged for incident
transmission of IR radiation therethrough from the laser diode, and
the other window being arranged for transmission of exiting
radiation to an in-line or otherwise appropriately positioned
photodiode detector (e.g., when a mirror/lens arrangement is
employed to conduct exiting radiation to the detector). In such
transmissivity detection arrangement, the occurrence of GPN will
act to attenuate the incident radiation beam and the detected
signal will therefore be correlative of such occurrence of GPN.
[0167] The above-discussed IR laser and photodiode detector
arrangement can be integrated with an existing control system of a
tungsten CVD installation, and may be constructed to stop the
deposition operation to facilitate establishment of non-GPN
conditions. Alternatively, the IR source and detector apparatus may
be adapted to provide an output signal indicative of the presence
or absence of GPN conditions, with such output signal being
utilized to control the CVD process equipment so that non-GPN
conditions are established without cessation of CVD operation.
[0168] The use of an infrared radiation laser source in the
above-discussed monitoring systems will avoid ambient light
interference with the IR radiation, and is readily retrofitted to
an existing CVD installation.
[0169] The features and advantages of the invention are more fully
shown by the following non-limiting example.
Example 1
[0170] Real-time detection of gas phase nucleation by monitoring
the tungsten chemical vapor deposition (WCVD) reaction gases was
conducted, using an NDIR (non-dispersive infrared) spectrometer
with a built-in analog/digital (A/D) data acquisition system
installed in the foreline of a commercial WCVD tool. The device was
installed within a process gas flow segment of the reactor where a
clear and direct optical path existed between the IR light source
and the detector unit.
[0171] A TPIR system of the type shown in FIG. 3 was used,
comprising a) a broadband IR source, b) a variable pathlength
sampling region and c) a 4-channel thermopile detector unit. The
system was capable of monitoring and recording four (4) separate
and discrete gas species, simultaneously. A narrow band-pass filter
was selected for each thermopile channel that directly correlated
to the IR absorption band for a specific gaseous species. When
multiple absorption wavelengths existed for a specific gas, a
wavelength was selected that did not overlap with the absorption of
the other gases present in the system, in order to minimize
interferences observed from the specific gases.
[0172] The thermopile detector measured the temporal temperature
change on the sensor element and was directly correlated to the
incident IR intensity resulting from the absorption of that
specific gas. The spectrometer was calibrated with pre-mixed gases
of known concentrations.
[0173] FIG. 34 shows spectra collected for WCVD process gases and
by-products involved in the WCVD nucleation stage, including IR
absorption bands for SiH.sub.4, WF.sub.6 and SiF.sub.4. The
corresponding IR bandpass filters were specifically selected to
match the v3 (W--F stretch at 712 cm-1), v3 (Si--H stretch at 2191
cm-1) and v3 (Si--F stretch at 1032 cm-1) bands for WF.sub.6,
SiH.sub.4 and SiF.sub.4, respectively. The v3 band of SiF.sub.4
overlaps with (v1+v2) combination band of SiH.sub.4 at -1060 cm-1.
Since the SiH.sub.4 reactant was largely consumed during the
nucleation step of the WCVD reaction and the combination band
intensity is usually orders of magnitude weaker at room
temperature, the contribution from (v1+v2) band of SiH.sub.4 to the
v3 band of SiF.sub.4 was negligible. The fourth detector channel
was blanked off and used as a reference channel.
[0174] FIG. 35 is a schematic representation of the deposition
system, the TPIR system and the data acquisition system. This
arrangement provides three potential, but distinct set-ups for use
in collecting the TPIR analytical data: (a) TPIR monitoring across
the actual wafer processing chamber and (b) TPIR monitoring across
the fore-line pumping region, downstream from the actual wafer
processing region and (c) TPIR monitoring at the outlet of the gas
mixing manifold region prior to the wafer processing chamber, near
the actual gas entry zone. Due to space and optical path
considerations, the TPIR system was implemented within region (b),
downstream from the wafer processing chamber and in the exhaust
foreline segment.
[0175] The IR source and the detector units were mounted on each
side of a spool piece on the foreline, with the spool flange used
as the gas sampling region. The IR light entered and exited the
spool flange through a pair of ZnSe windows. A voltage signal from
the thermopile detector was digitized with a built-in A/D converter
and sent to a laptop computer (PC) for data collection and analysis
using software developed by ATMI, Inc., Danbury, Conn., USA. A
feedback-control-loop-system was arranged to send an automated
command to the process tool, both to control the process and to
automatically stop the tool when gas phase nucleation (GPN) was
detected.
[0176] Two sets of experiments were performed to correlate visual
GPN observations with infrared analysis. The first set of tests was
carried out using a single pass configuration for the TPIR
spectrometer with a sampling pathlength of 0.33 meters. The second
set of tests used a multi-pass configuration with a total sampling
pathlength of 2.0 meters. The factors that were identified as
causing GPN included substrate temperature, total pressure, and
SiH.sub.4/WF.sub.6 ratio. Wafer temperature was precisely
controlled and monitored by the manufacturing tool.
[0177] The major cause of GPN relates to poorly functioning gas
delivery systems, including clogging of gas filters, clogging of
mass-flow controllers, changing response times of mass flow
controllers and pneumatic valve failures or delays. Each of these
malfunctions can cause a change of delivery timing of SiH.sub.4 and
WF.sub.6 and/or their respective partial pressures and
concentrations. To confirm this, different valve delays and
SiH.sub.4/WF.sub.6 flow rates were tested experimentally to
demonstrate a correlation to GPN.
[0178] The TPIR system was used to measure the gas-phase
concentrations of SiF.sub.4, WF.sub.6, and SiH.sub.4 at a 4 Hz
sampling rate. The change in observed peak intensity, between
WF.sub.6 and SiF.sub.4, directly correlates to GPN and was used to
determine the onset of GPN. The TPIR data were also compared to a
visible inspection method used to control the WCVD process.
[0179] Single-Pass Gas Analysis
[0180] Designed experiments were conducted to examine the effect of
specific variables on the onset of GPN and to examine related TPIR
responses using a single pass gas cell configuration. The first set
of designed experiments consisted of a 3
factor-full-factorial-design and replication tests, as shown in
Table 1 below. Also shown in Table 1 are the TPIR responses and
complimentary results from visual inspection of the process. TPIR
responses showed excellent agreement with the visual inspection
results.
TABLE-US-00007 TABLE 1 VALVE SiH.sub.4 WF.sub.6 TPIR RUN DELAY FLOW
FLOW detection VISUAL RESULT 1 1.4 40 300 0 No GPN Observed 2 1.8
40 300 300 Heavy GPN Observed 3 1 40 300 0 No GPN Observed 4 1.4 50
300 0 No GPN Observed 5 1.4 30 300 0 No GPN Observed 6 1.4 40 250
200 Medium GPN Observed 7 1.4 40 350 0 No GPN Observed 8 1.5 40 300
0 No GPN Observed 9 1.6 40 300 320 Heavy GPN Observed 10 1.7 40 300
200 Medium GPN Observed 11 1.4 30 350 0 No GPN Observed 12 1.4 50
250 300 Heavy GPN Observed
[0181] Since the TPIR spectrometer was installed on the exhaust
foreline region of the process tool, it was possible to monitor the
reaction effluents, after gases underwent chemical reaction within
the CVD process chamber, including both un-reacted gases and
reaction by-products. The expected IR active gases within the
reaction effluent were WF.sub.6 and SiF.sub.4. Little or no
SiH.sub.4 was observed, since most of the SiH.sub.4 was consumed in
the CVD reaction, being readily converted to SiF.sub.4, and
displaying a relatively small IR cross-section. Given that
SiF.sub.4 was a major reaction by-product of the SiH.sub.4
reduction, the [SiH.sub.4] concentration was extrapolated from the
[SiF.sub.4] signal. The SiH.sub.4/WF.sub.6 ratio is proportional to
the SiH.sub.4/WF.sub.6 ratio, thereby allowing an indirect measure
of the reaction ratio that induces GPN. The concentration of
SiF.sub.4/SiHF.sub.3 during WCVD reactions varied depending on the
flow ratios of reactants and the extent of GPN. The SiF.sub.4
infrared data included both SiF.sub.4 and SiHF.sub.3 since they
share similar IR absorbance regions.
[0182] FIG. 7, previously described, and FIG. 36 are graphs of
spectral data collected with the TPIR system during monitoring of
the WCVD process. Five spectral peaks are shown, separated
temporally (from left to right) and associated with the WCVD
manufacturing process. The first peak is associated with a
pre-coating process, while the following three (3) peaks result
from the actual WCVD process. The last peak on the right of each
figure (intense red peak) was associated with the tool venting step
after completion of the WCVD process. During the actual WCVD
process steps, the intensity of the SiF.sub.4 peak (blue line) was
higher than the intensity of the red line (WF.sub.6), as shown in
FIG. 36. These spectral characteristics were noted when gas-phase
nucleation occurred, as confirmed by visual inspection.
[0183] As shown in FIG. 36, when the spectral intensities of
WF.sub.6 and SiF.sub.4 were similar, no gas-phase nucleation was
observed. The ratio of WF.sub.6 to SiF.sub.4 provided a strong
correlation to GPN during the WCVD process, as confirmed by visual
inspection of both scenarios.
[0184] The results of the designed experiments were analyzed both
quantitatively and qualitatively. Based upon the collection of
numerous spectra and comparison to visual inspection of the WCVD
process, a mathematical algorithm was developed to account for the
probability that GPN would occur during the WCVD process. By
examining the intensities and relative ratio of [WF.sub.6] to
[SiF.sub.4] concentrations, it was calculated when GPN would
occur.
[0185] FIG. 8, previously described, shows IR spectral data
obtained during the WCVD process with the TPIR system, with the
relative position of the processed spectral data and gas
concentration ratio providing a direct correlation to the absence
or presence of GPN. A line that delineates the presence or absence
of GPN during the WCVD process, is shown in FIG. 8, and equals the
arbitrary value of -15. Above this value, no GPN was observed,
while below this value corresponds to GPN. Further, the greater the
difference between -15 and the actual calculated run value, the
more intense was the formation of GPN.
[0186] The invention therefore contemplates a predictive model for
determining when GPN will occur in the WCVD process. Alternatively,
direct integration of the TPIR monitoring capability with the
deposition tool enables arrangements to be implemented in which the
reactor settings are altered, or WCVD process is stopped, to avoid
the occurrence of GPN. In either scenario, the performance of the
process tool can be optimized, thereby reducing waste and
increasing yield of product devices manufacturable by the CVD
system.
[0187] These observations provided the basis for the following
general equations for the absence or presence of GPN, based on the
single-pass, in-situ spectroscopic analysis of the WCVD
process:
If ([WF.sub.6]-[SiF.sub.4]) relative difference was >-15:No GPN
was observed
If ([WF.sub.6]-[SiF.sub.4]) relative difference was <-15:GPN was
observed
[0188] FIG. 37 shows the spectral data obtained by continuous
monitoring of product wafers by a single-pass TPIR system installed
on a WCVD tool for an extended period of continuous wafer
processing time. The variability in spectral intensity during the
manufacturing process was noted by comparing the relative
intensities of WF.sub.6 (red) to SiF.sub.4 (blue). Even though the
spectral intensity levels fluctuated throughout these runs, the
relative ratios indicated no strong presence of GPN during the
entire wafer processing sequence. Throughout a marathon run of over
12,000 wafers, the feasibility of using the TPIR diagnostic
technology for the in-situ monitoring of the WCVD process, was
demonstrated.
[0189] Multi-Pass Gas Analysis
[0190] To further improve the signal-to-noise ratio (S/N) of the
spectral data obtained during the process, a multi-pass optical
system was designed, implemented and tested within the same
configuration as the single-pass system. Similar designed
experiments were then performed specifically to monitor the WCVD
process and test the previously developed GPN methodology. The
results of the designed experiments, using the multi-pass optical
configuration, are summarized in Table 2 below, for the set of 3
full factorial designed experiments, along with results of the
visual inspection method.
TABLE-US-00008 TABLE 2 VALVE SiH.sub.4 WF.sub.6 IR RUN DELAY FLOW
FLOW detection VISUAL RESULT 1 0.8 40 300 0 No GPN Observed 2 1.0
40 300 320 Heavy GPN Observed 3 0.7 50 300 320 Heavy GPN Observed 4
0.7 30 300 0 No GPN Observed 5 0.7 40 250 0 No GPN Observed 6 0.8
40 350 0 No GPN Observed 7 0.6 50 300 200 Medium GPN Observed 8 1.0
50 300 320 Heavy GPN Observed 9 1.0 30 300 0 No GPN Observed
[0191] FIG. 38 shows the IR spectral data that were obtained during
the WCVD process using the multi-pass TPIR system and that were
processed to indicate conditions that specifically result in GPN,
based upon the analysis of measured WF.sub.6 and SiF.sub.4 signal
intensities and ratios. It is noted that the relative position
designating the onset of GPN has changed with the multi-pass
optical design when compared to the single-pass system.
[0192] When reviewing all of the designed experimental data, in
light of the measured in-situ spectral data, it is clear that two
WCVD factors are critical and therefore, must be accurately
controlled. To avoid random GPN during WCVD, the valve delay time
(time delay prior to the introduction of WF.sub.6 into the
deposition chamber) and the SiH.sub.4 flow rate were both observed
to be critical. Each of these factors can cause a high ratio of
SiH.sub.4/WF.sub.6 within an extremely short time period. Less than
0.3 sec change in the valve delay time, or less than 20 sccm in
SiH.sub.4 flow rate variation, was enough to completely change the
WCVD process, transitioning from the absence of GPN to the onset of
GPN. It was not surprising that the flow rate of WF.sub.6 appeared
to have the most negligible effect on GPN, since WF.sub.6 was
usually in excess when compared with SiH.sub.4 and was introduced
later. In most cases, the SiH.sub.4 introduced was quantitatively
consumed and directly converted to SiF.sub.4. Excess WF.sub.6
during the WCVD process may negatively affect the contact
resistance of the TiN barrier film.
[0193] Concerning the operative GPN mechanism, the spectral
observations were consistent with GPN proceeding through an initial
decomposition of SiH.sub.4 to form Si (y>=2) centers or small
clusters. The silicon clusters, once formed, can act as nuclei for
particle growth through subsequent reactions, as noted below:
2SiH.sub.4.fwdarw.Si(s)
xWF.sub.6+Si(y).fwdarw.W.sub.xSi.sub.y+SiF.sub.4
W.sub.xSi.sub.y+zSiH.sub.4.fwdarw.W.sub.xSi.sub.(y+z)+H.sub.2
The short delay time allows SiH.sub.4 to form silicon clusters and
bypass the surface nucleation step. The higher ratio of
SiH.sub.4/WF.sub.6 also causes excess SiH.sub.4 to form silicon
clusters.
[0194] In summary, WCVD has two significant process failure modes,
gas-phase nucleation and Ti barrier attack. Titanium barrier attack
is affected by excessive WF.sub.6 reactant, whereas GPN is more
clearly related to excessive SiH.sub.4 reactant and the relative
ratio of WF.sub.6 to SiH.sub.4.
[0195] In-situ process monitoring utilizing thermopyroelectric
infrared (TPIR) spectroscopy enables effective control of the WCVD
process to be achieved. Real-time GPN monitoring, using TPIR
spectrometry, provided excellent correlation between the WCVD
effluent concentrations, their relative ratios and GPN, as
confirmed by visual observations. The spectrometer is capable of
detecting and predicting GPN, and is a useful diagnostic in
manufacturing operations, as well as being capable of minimizing
the titanium barrier attack by measuring the WF.sub.6 reactant gas
during the process.
[0196] The TPIR system and method of the invention deliver
reliable, real-time detection of GPN that is superior to visual
inspection methods. The TPIR system and method of the invention are
highly flexible, providing real-time feedback for both gas-blending
and process monitoring. Both single-pass and multi-pass systems can
be utilized effectively for optimization of the WCVD process. The
spectroscopic technique of the invention can be extended to other
processes where chemical control and reaction sequencing are
critical. It will be understood that in application to WCVD
applications, the TPIR system can be readily integrated with the
WCVD manufacturing process tool, to achieve effective real time
communication and process control.
* * * * *