U.S. patent application number 12/417289 was filed with the patent office on 2009-08-06 for dosimetry using optical emission spectroscopy/residual gas analyzer in conjunction with ion current.
This patent application is currently assigned to APPLIED MATERIALS, INC.. Invention is credited to Seon-Mee Cho, Majeed A. Foad, Kartik Ramaswamy, Tsutomu Tanaka.
Application Number | 20090195777 12/417289 |
Document ID | / |
Family ID | 39892361 |
Filed Date | 2009-08-06 |
United States Patent
Application |
20090195777 |
Kind Code |
A1 |
Ramaswamy; Kartik ; et
al. |
August 6, 2009 |
DOSIMETRY USING OPTICAL EMISSION SPECTROSCOPY/RESIDUAL GAS ANALYZER
IN CONJUNCTION WITH ION CURRENT
Abstract
The present invention generally provides methods and apparatus
for controlling ion dosage in real time during plasma processes. In
one embodiment, ion dosages may be controlled using in-situ
measurement of the plasma from a mass distribution sensor combined
with in-situ measurement from an RF probe.
Inventors: |
Ramaswamy; Kartik; (San
Jose, CA) ; Cho; Seon-Mee; (Santa Clara, CA) ;
Tanaka; Tsutomu; (Santa Clara, CA) ; Foad; Majeed
A.; (Sunnyvale, CA) |
Correspondence
Address: |
PATTERSON & SHERIDAN, LLP - - APPM/TX
3040 POST OAK BOULEVARD, SUITE 1500
HOUSTON
TX
77056
US
|
Assignee: |
APPLIED MATERIALS, INC.
Santa Clara
CA
|
Family ID: |
39892361 |
Appl. No.: |
12/417289 |
Filed: |
April 2, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11681313 |
Mar 2, 2007 |
7531469 |
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12417289 |
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10971772 |
Oct 23, 2004 |
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11681313 |
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Current U.S.
Class: |
356/326 ;
118/708; 156/345.26; 250/281 |
Current CPC
Class: |
H01J 37/32935 20130101;
C23C 14/54 20130101; H01J 37/321 20130101; H01J 37/32412 20130101;
C23C 14/48 20130101 |
Class at
Publication: |
356/326 ;
250/281; 118/708; 156/345.26 |
International
Class: |
G01J 3/28 20060101
G01J003/28; H01J 49/00 20060101 H01J049/00; B05C 11/00 20060101
B05C011/00; H01L 21/3065 20060101 H01L021/3065 |
Claims
1. An apparatus for processing a substrate, comprising: a process
chamber defining a process volume; a conductive support pedestal
positioned in the process volume; a gas distribution assembly
connected to a gas panel and positioned parallel the conductive
support pedestal, wherein an RF plasma bias power supply is coupled
between the gas distribution assembly and the conductive support
pedestal; a first sensor configured to monitor one or more
attributes of a plasma generated in the process volume; a second
sensor configured to monitor one or more attribute of the RF plasma
bias power supply; and a controller coupled to the first and second
sensors, wherein the controller is configured to receive and
analyze signals from the first and second sensors.
2. The apparatus of claim 1, wherein the first sensor is one of an
optical emission spectrometer, a mass spectrometer and a residual
gas analyzer.
3. The apparatus of claim 2, wherein the second sensor is a RF
voltage/current probe.
4. The apparatus of claim 2, wherein the second sensor is a RF
voltage/current probe connected to the RF plasma bias power
supply.
5. The apparatus of claim 3, wherein the controller is configured
to monitor dosage of one or more ion species in the plasma
generated in the process volume using measurements from the first
sensor combined with measurements from the second sensor.
6. The apparatus of claim 1, further comprises a toroidal plasma
source in fluid communication with the process volume.
7. An apparatus for processing a substrate, comprising: a plasma
reactor having a process volume; a first sensor configured to
monitor one or more attributes of a plasma generated in the process
volume by a RF bias power supply coupled to the plasma reactor; a
second sensor configured to monitor one or more attribute of a RF
bias power supply; and a controller coupled to the first and second
sensors, wherein the controller is configured perform a process
comprising: obtaining a value of the one or more attributes of the
plasma from the first sensor; obtaining a value of the one or more
attributes of the RF bias power supply from the second sensor; and
determining a real time dose value of one or more ion species in
the plasma from the value of the one or more attributes of the
plasma and the value of the one or more attributes of the RF bias
power supply.
8. The apparatus of claim 7, wherein the one or more attributes of
the RF bias power supply comprises a value of total ion
current.
9. The apparatus of claim 8, wherein the first sensor is one of an
optical emission spectrometer, a mass spectrometer and a residual
gas analyzer.
10. The apparatus of claim 8, wherein the second sensor is a RF
voltage/current probe connected to a feedpoint of the RF bias power
supply.
11. The apparatus of claim 10, wherein determining the real time
dose value of the one or more ion species in the plasma comprises:
determining a real time value of a ratio of the one or more ion
species over total ions in the plasma using a real time value of
the at least one attribute of the plasma measured by the first
sensor; determining a real time value of a total ion current near a
feedpoint of the RF bias power supply measured by the second sensor
coupled to the feed point of the RF bias power; calculating a
current value of the one or more ion species by multiplying the
ratio of the one or more ion species in the plasma and the total
ion current; and integrating the current value of the one or more
ion species over time.
12. The apparatus of claim 11, wherein determining real time value
of the total current comprises transforming the total ion current
near the feedpoint of the RF bias power supply to a total ion
current near a surface of the substrate.
13. The apparatus of claim 7, wherein the method performed by the
controller further comprises adjusting at least one attribute of
the plasma reactor according to the real time dosage value of the
one or more ion species in the plasma.
14. An apparatus for processing a substrate, comprising: a process
chamber defining a process volume; a conductive support pedestal
positioned in the process volume and configured to support the
substrate during processing; a gas distribution assembly positioned
parallel the conductive support pedestal; an RF plasma bias power
supply coupled between the gas distribution assembly and the
conductive support pedestal and configured to generate a plasma in
the process volume; a first sensor configured to monitor one or
more attributes of the plasma generated in the process volume; a
second sensor configured to monitor one or more attribute of the RF
plasma bias power supply; and a controller coupled to the first and
second sensors, wherein the controller is configured to apply a
desired dose of a material to the substrate.
15. The apparatus of claim 14, wherein the controller is configured
to perform a process comprising: obtaining a value of an attribute
of the ions of the material in the plasma using the first sensor;
obtaining a value of a total current of the RF bias power supply
using the second sensor; determining a real time dosage value of
the material using the value of the attribute of the ions of the
material and the value of the total current of the RF bias power
supply; and terminating the plasma when the real time dosage value
is within an error range of the desired dose.
16. The apparatus of claim 15, wherein the attribute of the ions of
the material is a ratio of the ions of the material over total ions
in the plasma.
17. The apparatus of claim 16, wherein the first sensor is one of
an optical emission spectrometer, a mass spectrometer and a
residual gas analyzer.
18. The apparatus of claim 15, wherein the second sensor is a RF
voltage/current probe coupled to a feedpoint of the RF bias power
supply and configured to measure voltage, current and phase of the
RF bias power supply.
19. The apparatus of claim 18, wherein the process performed by the
controller further comprises transforming the total current of the
RF bias power supply to a total ion current near a surface of the
substrate.
20. The apparatus of claim 19, wherein transferring the total
current of the RF bias power supply to the total ion current near
the surface of the substrate comprises: transforming the total
current of the RF bias power supply from time domain to frequency
domain; correcting the total current of the RF bias power supply in
frequency domain using calibration data of the second sensor; and
obtaining the total ion current near the surface of the substrate
by transforming corrected total current in frequency domain to time
domain.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of co-pending
U.S. patent application Ser. No. 11/681,313 (Attorney Docket No.
9615P1), filed Mar. 2, 2007, which is a continuation-in-part of
co-pending U.S. patent application Ser. No. 10/971,772 (Attorney
Docket No. 9615), filed Oct. 23, 2004, which is herein incorporated
by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention generally relate to
method and apparatus for processing a substrate. Particularly,
embodiments of the present invention relate to methods and
apparatus for monitoring dosages of one or more species during
plasma processing of semiconductor substrates.
[0004] 2. Description of the Related Art
[0005] It is important to control ion dosage during plasma
processes, such as plasma enhanced chemical vapor deposition
(PECVD) process, high density plasma chemical vapor deposition
(HDPCVD) process, plasma immersion ion implantation process (P3I),
and plasma etch process. Ion implantation processes in integrated
circuit fabrication particularly require instrumentation and
control to achieve a desired ion dose on a semiconductor
substrate.
[0006] The dose in ion implantation generally refers to the total
number of ions per unit area passing through an imaginary surface
plane of a substrate being processing. The implanted ions
distribute themselves throughout the volume of the substrate. The
principal variation in implanted ion density (number of ions per
unit volume) occurs along the direction of the ion flux, usually
the perpendicular (vertical) direction relative to the substrate
surface. The distribution of ion density (ions per unit volume)
along the vertical direction is referred to as the ion implantation
depth profile. Instrumentation and control systems for regulating
ion implant dose (ions per unit area) is sometimes referred to as
dosimetry.
[0007] Ion implantation may be performed in ion beam implant
apparatus and in plasma immersion ion implantation apparatus. Ion
beam implant apparatus, which generate a narrow ion beam that must
be raster-scanned over the surface of the substrate, typically
implant only a single atomic species at one time. The ion current
in such an apparatus is precisely measured and integrated over time
to compute the actual dose. Because the entire ion beam impacts the
substrate and because the atomic species in the beam is known, the
ion implant dose can be accurately determined. This is critical in
an ion beam implant apparatus, because it employs a D.C. ion
source, which is subject to significant drift in its output
current, and the various grids and electrodes employed in the beam
implant machine drift as well (due to the susceptibility of a D.C.
source to accumulation of deposited material on component
surfaces). Accordingly, precise dosimetry is essential in an ion
beam implant apparatus. The precisely monitored ion beam current is
integrated over time to compute an instantaneous current implant
dose, and the process is halted as soon as the dose reaches a
predetermined target value.
[0008] In contrast, plasma immersion ion implantation reactors
present a difficult problem in dosimetry. Typically, the atomic
weight of the ions incident on the substrate cannot be precisely
determined because such a reactor employs a precursor gas
containing the desired ion implantation species as well as other
species. For example, since pure boron is a solid at room
temperature, plasma immersion ion implantation of boron must employ
a multi-species gas such as B.sub.2H.sub.6 as the plasma precursor,
so that both boron and hydrogen ions are incident on the substrate.
As a result, determining the boron dose from a measured current is
difficult. Another difficulty in implementing dosimetry in a plasma
immersion ion implantation reactor is that the plasma ions impact
the entire substrate continuously, so that it is difficult to
effect a direct measurement above the substrate of the total ion
current to the substrate. Instead, the dose must be indirectly
inferred from measurements taken over a very small area. This is
particularly true of reactors employing RF (Radio Frequency) plasma
source power or RF plasma bias power.
[0009] Plasma immersion ion implantation reactors employing D.C.
(or pulsed D.C.) plasma source power are susceptible to drift in
the plasma ion current due to deposition of material on internal
reactor components from the plasma. Such reactors therefore require
precise real-time dosimetry. This problem has been addressed by
providing a small orifice in the wafer support pedestal or cathode
outside of the substrate periphery, for plasma ions to pass through
into the interior volume of the cathode. An electrode sometimes
referred to as a Faraday cup faces the orifice and is biased to
collect the ions passing through the orifice. The interior of the
cathode can be evacuated to a slightly lower pressure than the
plasma chamber to ensure efficient collection of ions through the
orifice. A current sensor inside the cathode interior measures the
current flowing between the ion-collecting electrode and its bias
source. This current can be used as the basis of a dosimetry
measurement. One problem with such an arrangement is that the
current measurement cannot distinguish between different atomic
species, and therefore cannot provide an accurate measurement of
the species of interest (e.g., boron). Another problem is that the
transmission of the measured current from the current sensor inside
the cathode interior to an external controller or processor can be
distorted by the noisy electromagnetic environment of the plasma
reactor.
[0010] Another problem is that the orifice in the cathode
constitutes an intrusion upon the ideal plasma environment, because
the orifice can distort the electric field in the vicinity of the
substrate periphery. Furthermore, plasma passing through the
orifice can cause problems by either sputtering the orifice
surfaces or by depositing on the orifice interior surfaces,
requiring the periodic cleaning of the orifice interior.
[0011] In plasma immersion ion implantation reactors employing RF
plasma source power, precise or real-time dose measurement
typically was not critical. This is due in part to the fact that an
RF plasma is relatively impervious to deposition of material on
internal chamber components, so that the ion flux at the wafer
surface does not drift significantly, compared to a reactor
employing a D.C. plasma source. Moreover, real-time dose
measurement in such a reactor is difficult. For example, the harsh
RF environment of such a reactor would distort an ion current
measurement taken inside the cathode (as described above) as it is
conveyed to an external controller or processor. To avoid such
problems, implant dose can be reliably controlled based upon the
predicted or estimated time required to reach the target implant
dose. However, a real-time does control is more and more in need as
the feature size becomes smaller and smaller in the semiconductor
devices.
[0012] Therefore, there is a need for precise real-time dosimetry
in a plasma processing chamber, such as an RF plasma immersion ion
implantation reactor.
SUMMARY OF THE INVENTION
[0013] The present invention generally provides methods and
apparatus for controlling ion dosage in real time during plasma
processes.
[0014] One embodiment of the present invention provides a method
for processing a substrate comprising positioning the substrate in
a plasma reactor configured to perform a plasma process, generating
a plasma in the plasma reactor to start the plasma process by
supplying a RF bias to the plasma reactor, obtaining a value of the
at least one attribute of the plasma using a first sensor
configured to monitor at least one attribute of a plasma generated
in the plasma reactor, obtaining a value of the at least one
attribute of the RF bias power using a second sensor configured to
monitor at least one attribute of a RF bias power configured to
supply the RF bias to the plasma reactor, and determining a real
time dose value of one or more ion species in the plasma from the
value of the at least one attribute of the plasma and the value of
the at least on attribute of the RF bias power.
[0015] Another embodiment of the present invention provides an
apparatus for processing a substrate comprising a process chamber
defining a process volume, a conductive support pedestal positioned
in the process volume, a gas distribution assembly connected to a
gas panel and positioned parallel the conductive support pedestal,
wherein an RF plasma bias power supply is coupled between the gas
distribution assembly and the conductive support pedestal, a first
sensor configured to monitor one or more attributes of a plasma
generated in the process volume, a second sensor configured to
monitor one or more attribute of the RF plasma bias power supply,
and a controller coupled to the first and second sensors, wherein
the controller is configured to receive and analyze signals from
the first and second sensors.
[0016] Yet another embodiment of the present invention provides a
method for implanting a desired dose of a material into a substrate
comprising positioning the substrate in a plasma reactor having a
RF bias power configured to generate a plasma in the plasma
reactor, generating a plasma comprising the material in the plasma
reactor using the RF bias power, obtaining a value of the attribute
of the material in the plasma using a first sensor configured to
monitor an attribute of the plasma in the plasma reactor, obtaining
a value of the at least one attribute of the RF bias power using a
second sensor configured to monitor at least one attribute of the
RF bias power, determining a real time dosage value of the material
using the value of the attribute of the material and the value of
the at least one attribute of the RF bias power, and terminating
the plasma when the real time dosage value is within an error range
of the desired dose.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0018] FIG. 1 schematically illustrates an isometric
cross-sectional view of a plasma chamber in accordance with one
embodiment of the present invention.
[0019] FIG. 2 schematically illustrates an isometric top view of
the plasma chamber of FIG. 1.
[0020] FIG. 3 schematically illustrates an exemplary method for
monitoring real time dosage using a mass distribution sensor in
conjunction with a current sensor.
[0021] FIG. 4 schematically illustrates a method for transforming
current/voltage values from a feedpoint to a substrate surface
positioned adjacent the plasma.
[0022] FIG. 5 illustrates a flow chart of a method for endpoint
detection for a plasma processing in accordance with one embodiment
of the present invention.
DETAILED DESCRIPTION
[0023] Embodiments of the present invention provide methods for
controlling ion dosages in real time during plasma processes and
apparatus for performing the methods.
[0024] FIG. 1 schematically illustrates an isometric
cross-sectional view of a plasma chamber 1 in accordance with one
embodiment of the present invention. The plasma chamber 1 may be
configured for a plasma enhanced chemical vapor deposition (PECVD)
process, a high density plasma chemical vapor deposition (HDPCVD)
process, an ion implantation process, an etch process, and other
plasma processes.
[0025] The plasma chamber 1 comprises a toroidal plasma source 100
coupled to a body 3 of the plasma chamber 1. The body 3 comprises
sidewalls 5 coupled to a lid 10 and a bottom 15, which bounds an
interior volume 20. Other examples of the plasma chamber 1 may be
found in U.S. Pat. No. 6,939,434, filed Jun. 5, 2002 and issued on
Sep. 6, 2005 and U.S. Pat. No. 6,893,907, filed Feb. 24, 2004 and
issued May 17, 2005, both of which are incorporated by reference
herein in their entireties.
[0026] The interior volume 20 includes a processing region 25
formed between a gas distribution assembly 200 and a substrate
support 300. A pumping region 30 surrounds a portion of the
substrate support 300. The pumping region 30 is in selective
communication with a vacuum pump 40 through a valve 35 disposed in
a port 45 formed in the bottom 15. In one embodiment, the valve 35
is a throttle valve adapted to control the flow of gas or vapor
from the interior volume 20 and through the port 45 to the vacuum
pump 40. In one embodiment, the valve 35 operates without the use
of o-rings, and is further described in U.S. Patent Publication No.
2006/0237136, filed Apr. 26, 2005, which is incorporated by
reference in its entirety.
[0027] A toroidal plasma source 100 is disposed on the lid 10 of
the body 3. In one embodiment, the toroidal plasma source 100
comprises a first conduit 150A having a general "U" shape, and a
second conduit 150B having a general "M" shape. The first conduit
150A and the second conduit 150B each include at least one antenna
170A and 170B respectively. The antennas 170A and 170B are
configured to form an inductively coupled plasma within an interior
region 155A/155B of each of the conduits 150A/150B, respectively.
As shown in FIG. 2, each antenna 170A/170B may be a winding or a
coil coupled to a power source, such as a RF plasma power source
171A/172A. An RF impedance matching systems 171B/172B may also be
coupled to each antenna 170A/170B. Process gases, such as helium,
argon, and other gases, may be provided to an interior region 155A,
155B of each of the conduits 150A, 150B, respectively. In one
embodiment, the process gases may contain a dopant containing gases
that is supplied to the interior regions 155A/155B of each conduit
150A/150B. In one embodiment, the process gases may be delivered to
the toriodal plasma source 100 from a gas panel 130B. In another
embodiment, the process gases may be delivered through the gas
distribution assembly 200 from a gas panel 130A connected to a port
55 formed in the body 3 of the plasma chamber 1.
[0028] In one embodiment, each opposing end of the conduits
150A/150B are coupled to respective ports 50A-50D (only 50A and 50B
are shown in this view) formed in the lid 10 of the plasma chamber
1. During processing, a process gas is supplied to the interior
region 155A/155B of each of the conduits 150A/150B, and RF power is
applied to each antenna 170A/170B, to generate a circulating plasma
path that travels through the ports 50A-50D and the processing
region 25. Specifically, in FIG. 1, the circulating plasma path
travels through port 50A to port 50B, or vise versa, through the
processing region 25 between the gas distribution assembly 200 and
the substrate support 300. Each conduit 150A/150B comprises a
plasma channeling means 400 coupled between respective ends of the
conduit 150A/150B and the ports 50A-50D. In one embodiment, the
plasma channeling means 400 is configured to split and widen the
plasma path formed within each of the conduits 150A/150B.
[0029] The gas distribution assembly 200 comprises an annular wall
210 and a perforated plate 220. The annular wall 210, the
perforated plate 220 and the lid 10 define a plenum 230. The
perforated plate 220 includes a plurality of openings 221 formed
therethrough in a symmetrical or non-symmetrical pattern or
patterns. In one embodiment, the dopant containing process gases
may be delivered to processing region 25 from the gas distribution
assembly 200 connected to the gas panel 130A. The process gases,
such as dopant-containing gases, may be provided to the plenum 230
from the port 55. Generally, the dopant-containing gas is a
chemical consisting of the dopant impurity atom, such as boron (a
p-type conductivity impurity in silicon) or phosphorus (an n-type
conductivity impurity in silicon) and a volatile species such as
fluorine and/or hydrogen. Thus, fluorides and/or hydrides of boron,
phosphorous or other dopant species such as arsenic, antimony,
etc., can be dopant gases. For example where a boron dopant is used
the dopant-containing gas may contain boron trifluoride (BF.sub.3)
or diborane (B.sub.2H.sub.6). The gases may flow through the
openings 221 and into the processing region 25 below the perforated
plate 220. In one embodiment, the perforated plate 220 is RF biased
to help generate and/or maintain a plasma in the processing region
25.
[0030] The substrate support 300 comprises an upper plate 310 and a
cathode assembly 320. The upper plate 310 has a smooth substrate
supporting surface 310B configured to support a substrate thereon.
The upper plate 310 comprises an embedded electrode 315 which is
connected to a DC power source 306 to facilitate electrostatic
attraction between a substrate and the substrate supporting surface
310B of the upper plate 310 during process. In one embodiment, the
embedded electrode 315 may also be used as an electrode for
providing capacitive RF energy to the processing region 25. The
embedded electrode 315 may be coupled to a RF plasma bias power
305A via an RF impedance matching circuit 305B.
[0031] The substrate support 300 may also include a lift pin
assembly 500 that contains a plurality of lift pins 510 configured
to transfer one or more substrates by selectively lifting and
supporting a substrate above the upper plate 310 and are spaced to
allow a robot blade to position therebetween.
[0032] FIG. 2 schematically illustrates an isometric top view of
the plasma chamber 1 shown in FIG. 1. The sidewall 5 of the plasma
chamber 1 have a substrate port 7 that may be selectively sealed by
a slit valve (not shown). Process gases are supplied to the gas
distribution assembly 200 by the gas panel 130A coupled to the port
55. One or more process gases may be supplied to the toroidal
sources 150A, 150B through the gas panel 130B.
[0033] The plasma chamber 1 further comprises a controller 600
configured to monitor and control processes performed in the plasma
chamber 1. The controller 600 may be connected with one or more
sensors and configured to sampling, analyzing and storing sensor
data. In one embodiment, the controller 600 may have the capacity
to perform control tasks for different processes. The controller
600 may be connected to operating parts of the plasma chamber 1 and
send control signals to the operating parts. The controller 600 may
perform a closed loop control task by adjusting process parameters
according to sensor data to achieve desired process result. In one
embodiment of the present invention, the controller 600 may be
configured to perform dosage control of one or more species, end
point detection, and other control tasks.
[0034] In one embodiment, a RF probe 606 is positioned on a
feedpoint 607 between the RF impedance matching circuit 305B and
the embedded electrode 315. The RF probe 606 may be a
voltage/current coupler or a directional coupler. The RF probe 606
may be replaced by individual instruments, such as a voltage probe
and a current probe. The RF probe 606 is capable of simultaneously
or nearly simultaneously measuring RF voltage, RF current and an
instantaneous impedance angle between the RF voltage and the RF
current.
[0035] Total current or real part of current (product of total
current and cosine of impedance angle, or quotient of absorbed bias
power with respect to bias voltage), may be measured directly or
calculated from indirect measurements from the RF probe 606. The
measured current many be the RMS (root means squared) current, the
peak current or the peak to peak current. The measured current may
be used to estimate ion dose rate and/or dose, which may be used to
control dosage or determine an endpoint. The measured current may
be used to control dose-rate.
[0036] During a plasma processing, the RF current measured by the
RF probe 606 substantially reflects a total current of radials
flowing from a ground electrode, such as the perforated plate 220,
to a RF biased electrode (or the substrate disposed on the biased
electrode), such as the embedded electrode 315. In one embodiment
of the present invention, a transformation may be computed to
transform a RF voltage/current value at the feedpoint 607 to a RF
voltage/current value at a substrate positioned on the embedded
electrode 315. The transform is described in detail in accordance
of FIG. 4.
[0037] In one embodiment, ion current may be the RF current value
corresponding to the minimum RF voltage value. Detailed explanation
of determining ion current value using the minimum value of RF
voltage can be found in "Measuring the Ion Current in High-density
Plasma Using Radio Frequency Current and Voltage Measurements", by
Mark A. Sobolewski, Journal of Applied Physics, Volume 90, No. 6,
pp. 2660-2671, 2001.
[0038] Current value obtained from the RF probe 606, however, is
usually not equal to a current of one or more ion species intended
to conduct the plasma process because, at least in part, there are
other ion species in the plasma. For example, Boron ion is intended
to be implanted into a substrate during a plasma implantation using
B.sub.2H.sub.6 as the plasma precursor. The plasma may include ion
species B.sup.3+ and H.sup.+ and both boron and hydrogen ions may
incident on the substrate. The current value obtained from the RF
probe 606 may include current of both boron and hydrogen ions. To
obtain desired dosage of Boron, it is necessary to obtain a ratio
of the boron current relative to the total ion current measured by
the RF probe.
[0039] In one embodiment of the present invention, ratio of one or
more ion species of interest may be obtained in-situ using a mass
distribution sensor configured to monitor a plasma generated in the
plasma reactor. The mass distribution sensor may be an optical
emission spectrometer, a residual gas analyzer, a ground side mass
spectrometer, or any suitable sensor.
[0040] In one embodiment, as shown in FIG. 1, an optical emission
spectrometer 601 is disposed adjacent a quartz window 6 formed on
the body 3. The optical emission spectrometer 601 is configured to
quantitatively measure optical emissions from excited species in
the plasma generated inside the plasma chamber 1. Excited species
in a plasma may decay back from the excited energy level to the
lower energy level of emitting light. Since the transition is
between distinct atomic energy levels, wavelength of the emitted
light may be used to identify the excited species. In one
embodiment, intensity of the emitted lights may reflect
concentration or distribution of different species in a plasma
including one or more species. Plasma generally generate
electromagnetic radiation that includes emissions having
wavelengths in the optical spectrum, i.e., from about 180 nm to
about 1100 nm. A portion of these emissions can be detected by a
spectrometer, such as the optical emission spectrometer 601, or
other suitable devices such as a monochromator of a spectral filter
equipped with one or more photodiodes.
[0041] The optical emission spectrometer (OES) 601 may comprise a
lens 602 disposed next to the quartz window 6. The lens 602 may be
configured to collimate radiation of the plasma passes through the
quartz window 6 in to an optical fiber cable 603 connected to the
spectrometer 604. The spectrometer 604 spectrally separates the
radiation based on wavelength and generates detection signals for
one or more spatially separated wavelengths. A data acquisition
device in the controller 600 may be used to collect data
representing separated wavelength, hence properties of the ion
species in the plasma, at a periodic sampling rate. The collected
data may be processed and analyzed for generating control singles
to the RF plasma bias power 305A, the RF plasma source powers
171A/172A, the gas panels 130A/130B, the pump 40, or any other
controllable components of the plasma chamber 1 to adjust process
parameters, for example pressure, power intensities, flow rates,
process duration.
[0042] In one embodiment, a residual gas analyzer 608, shown in
FIG. 1, may be disposed on the sidewalls 5. The residual gas
analyzer 608 is in fluid communication with the process region 25
so that the residual gas analyzer 608 can separate, identify and
measure the quantity of all species in the process region 25. The
residual gas analyzer 608 can monitor real time plasma behavior and
provide data to compute ratio of different ion species in the
plasma. The residual gas analyzer 608 is connected to the
controller 600 which may process and analyze measurements from the
residual gas analyzer 608 to generate control singles to the RF
plasma bias power 305A, the RF plasma source powers 171A/172A, the
gas panels 130A/130B, the pump 40, or any other controllable
components of the plasma chamber 1 to adjust process parameters,
for example pressure, power intensities, flow rates, or process
duration.
[0043] In another embodiment, a mass spectrometer 605 configured to
measure distribution of different species in the plasma may be
positioned in the gas distribution assembly 200. Similar to the
residual gas analyzer 608 or the optical emission spectrometer 601,
the mass spectrometer 605 may monitor the plasma in real time and
provide measurement to the controller 600 which may perform a
closed loop control to achieve desired result during a plasma
process.
[0044] In one embodiment of the present invention, a mass
distribution sensor, such as the optical emission spectrometer 601,
the residual gas analyzer 608, the mass spectrometer 605, or any
other suitable devices, may be used in conjunction with a plasma
current sensor, such as the RF probe 606, to monitor real time
dosage of one or more ion species of interest, to detect an
endpoint, or to achieve desired processing result. FIG. 3
schematically illustrates an exemplary method 700 for monitoring
real time dosage using a mass distribution sensor in conjunction
with a current sensor.
[0045] As shown in FIG. 3, a substrate 703 is processed by a plasma
702 generated between an electrode 704 and a grounded electrode
701. The electrode 704 is connected with a bias power supply 707
through an impedance matching circuit 706 at a feedpoint 714. The
plasma 702 is generated by an RF power supplied by the bias power
supply 707.
[0046] An RF probe 705 is connected to the electrode 704 at the
feedpoint 714. The RF probe 705 is configured to monitor the real
time voltage, current and phase of the RF bias power supplied to
the electrode 704. A mass distribution sensor 710 is positioned to
monitor the real time mass distribution of one or more ion species
in the plasma. The mass distribution sensor 710 may be one of an
optical emission spectrometer, a residual gas analyzer, or a mass
spectrometer. Both of the mass distribution sensor 710 and the RF
probe 705 are connected to a processor 720 configured to calculate
dosage values in real time according to the measurements from the
mass distribution sensor 710 and the RF probe 705.
[0047] The processor 720, in one embodiment, may be programmed to
estimate the ion implantation dose. This may be accomplished as
illustrated in the flow diagram inside the processor 720 shown in
FIG. 3. The processor 720 may track the incoming stream of
instantaneous current values from the RF probe 705. A total ion
current may be calculated in block 709 from the input of the RF
probe 705. This total ion current may be obtained by multiplying
each value of current by the cosine of the impedance angle from the
RF sensor 705. For more accurate performance, the voltage, current
and impedance angle measurements of the RF probe 705 may be
transformed, in block 708, from the feedpoint 714 to the surface of
the substrate 703, in accordance with a feature that is discussed
later in this specification.
[0048] Simultaneously, a mass distribution data may be input to the
processor 720 from the mass distribution sensor 710. Instantaneous
ratios of one or more ion species of interest in the plasma 702 may
be calculated, in block 711, from the measurements of the mass
distribution sensor 710.
[0049] The ion ratio and the total ion current is then combined
together to obtain an actual ion current of the one or more ion
species of interest, in block 712 of FIG. 3. In one embodiment, the
actual ion current of one ion species may be obtained by
multiplying the ion ratio, the total ion current, the reciprocal of
the electron charge of the ion species, and the reciprocal of
surface area of the substrate 703.
[0050] A real time dosage value of the ion species of interest may
be obtained by integrating the actual ion current over time, in
block 713.
[0051] FIG. 4 schematically illustrates a method 800 for
transforming current/voltage values from a feedpoint to a substrate
surface positioned adjacent the plasma. The method 800 may be used
in the block 708 of FIG. 3.
[0052] As shown in FIG. 4, voltage/current input from a RF probe
802 positioned at a feedpoint is first digitized in a digitizer 804
to discrete values in time domain. A fast Fourier Transformation
maybe performed in step 806 to transform the voltage/current
measurement into the frequency domain. In step 808, correction may
be added to the voltage/current measurement using calibration data
810 for the RF probe. Detailed description of calibrating the RF
probe may be found in co-pending U.S. patent application Ser. No.
10/971,772 (Attorney Docket No. 9615), filed Oct. 23, 2004, which
is herein incorporated by reference.
[0053] In step 812, a feedpoint to substrate surface transformation
may conducted to the corrected voltage/current measurement in the
frequency domain. In step 814, an inverted Fourier transform may be
performed to the transformed voltage/current value in the frequency
domain. The instantaneous voltage/current value on the substrate
surface in the time domain is then obtained in step 816 and may be
used in a precise process monitoring and controlling. Detailed
description of this feedpoint to substrate surface transformation
may be found in co-pending U.S. patent application Ser. No.
10/971,772 (Attorney Docket No. 9615), filed Oct. 23, 2004, which
is herein incorporated by reference.
[0054] FIG. 5 illustrates a flow chart of a method 900 for endpoint
detection for a plasma processing in accordance with one embodiment
of the present invention.
[0055] In step 910, a substrate to be processed may be positioned
in a plasma reactor.
[0056] In step 920, the plasma process may be started. This step
may include pumping down the plasma chamber, flowing in processing
gases, and/or generating a plasma.
[0057] In step 930, total ion current of the plasma in the plasma
reactor may be monitored using a RF probe. For example, an RF probe
connected to a RF bias power supply near a feed point. In one
embodiment, a feedpoint to substrate surface transformation may be
performed to obtain total ion current near the substrate
surface.
[0058] In step 940, mass distribution of the plasma in the plasma
reactor may be monitored using a mass distribution sensor, such as
an optical emission spectrometer, a residual gas analyzer, or a
mass spectrometer. Ratio of one or more ion species of interest may
be calculated instantaneously from the measurement of the mass
distribution sensor.
[0059] In step 950, the real time dose value of the one or more ion
species of interest may be calculated using the ration of the one
or more ion species calculated in step 940 and the total ion
current calculated in step 930. Calculation of the real time dose
value may comprise calculating actual ion current of the ion
species and integrating the actual ion current over time.
Calculation the actual ion current may comprise multiplying the
ratio of the ion species, the total ion current, the reciprocal of
the electron charge of the ion species, and the reciprocal of
surface area of the substrate.
[0060] In step 960, the real time dose value may be compared to a
desired dose value. if the real time dose value is within an error
limit of the desired dose value, the process may be terminated in
step 980. Alternatively, the process may be continued with
repeating steps of 930, 940, 950 and 960. In one embodiment, step
970 may be performed to adjust operating parameters to according to
the real time dose value to achieve a close loop control.
[0061] While the ion implantation of Boron (B) is described in the
present application, the method and apparatus of the present
invention may be used to monitor and control dosage of Arsenic
(As), Phosphorus (P), Hydrogen (H), Oxygen (O), Fluorine (F),
Silicon (Si), and other species used in a plasma process.
[0062] While method and apparatus of the present invention is
described in accordance with a plasma immersion ion implantation
process, persons skilled in the art may find it suitable to other
plasma processes, such as a plasma enhanced chemical vapor
deposition (PECVD) process, a high density plasma chemical vapor
deposition (HDPCVD) process, an ion implantation process, and an
etch process.
[0063] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *