U.S. patent application number 11/023383 was filed with the patent office on 2005-08-25 for method and apparatus for non-invasive measurement and analysis of semiconductor process parameters.
This patent application is currently assigned to Tokyo Electron Limited. Invention is credited to Parsons, Richard.
Application Number | 20050183821 11/023383 |
Document ID | / |
Family ID | 30115543 |
Filed Date | 2005-08-25 |
United States Patent
Application |
20050183821 |
Kind Code |
A1 |
Parsons, Richard |
August 25, 2005 |
Method and apparatus for non-invasive measurement and analysis of
semiconductor process parameters
Abstract
A RF sensor for sensing and analyzing parameters of plasma
processing. The RF sensor is provided with a plasma processing tool
and an antenna for receiving RF energy radiated from the plasma
processing tool. The antenna is located proximate to the plasma
processing tool so as to be non-invasive. Additionally, the RF
sensor may be configured for wideband reception of multiple
harmonics of the RF energy that is radiated from the plasma
processing tool. Further, the RF sensor may be coupled to a high
pass filter and a processor for processing the received RF energy.
Additionally, the antenna may be located within an enclosure with
absorbers to reduce the interference experienced by the RF sensor.
Additionally, a tool control may be coupled to the processor to
provided to adjust and maintain various parameters of plasma
processing according to the information provided by the received RF
energy.
Inventors: |
Parsons, Richard; (Mesa,
AZ) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
Tokyo Electron Limited
Tokyo
JP
|
Family ID: |
30115543 |
Appl. No.: |
11/023383 |
Filed: |
December 29, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11023383 |
Dec 29, 2004 |
|
|
|
PCT/US03/19038 |
Jun 18, 2003 |
|
|
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60393101 |
Jul 3, 2002 |
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Current U.S.
Class: |
156/345.28 ;
118/723R |
Current CPC
Class: |
H01J 37/32935 20130101;
H01J 37/32174 20130101 |
Class at
Publication: |
156/345.28 ;
118/723.00R |
International
Class: |
C23F 001/00 |
Claims
What is claimed is:
1. A system for sensing parameters of plasma processing, said
system comprising: a plasma processing tool; an enclosure placed
proximate to said plasma processing tool; an antenna, located
inside said enclosure, for receiving RF energy radiated from said
plasma processing tool; and a processor coupled to said antenna for
processing said RF energy received by said antenna.
2. The system of claim 1, wherein said enclosure is attached to
said plasma processing tool.
3. The system of claim 1, further comprising: at least one absorber
provided with said enclosure for absorbing RF energy.
4. The system of claim 3, wherein said enclosure has at least one
surface adjacent to a surface of said plasma processing tool, and
said at least one surface and said surface of said plasma
processing tool are configured to pass RF energy.
5. The system of claim 1, wherein said enclosure and said tool are
adjacent and define an opening therebetween.
6. The system of claim 4, wherein said at least one absorber is
located to prevent absorption of RF energy passing through said at
least one surface of said enclosure adjacent to said plasma
processing tool.
7. The system of claim 3, wherein a first absorber is configured to
absorb a fundamental frequency of said RF energy and a second
absorber is configured to absorb a harmonic frequency of said RF
energy.
8. The system of claim 3, wherein said enclosure is rectangular and
said absorbers are provided on all sides of said enclosure except a
side located proximate to said plasma processing tool.
Description
[0001] This is a continuation of International Patent Application
No. PCT/US03/19038, filed Jun. 18, 2003, which is based on and
claims the benefit of U.S. Provisional Application No. 60/393,101,
filed Jul. 3, 2002, the entire contents of both of which are
incorporated herein by reference in their entireties.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to plasma process tools, more
particularly, the present invention relates to sensing equipment
for non-invasive measurement and analysis of parameters of plasma
process tools.
[0004] 2. Description of Background Information
[0005] Plasma processing systems are of considerable use in
material processing, and in the manufacture and processing of
semiconductors, integrated circuits, displays, and other electronic
devices, both for etching and layer deposition on substrates, such
as, for example, semiconductor wafers. Generally, the basic
components of the plasma processing system include a chamber in
which a plasma is formed, a pumping region which is connected to a
vacuum port for injecting and removing process gases, and a power
source to form the plasma within the chamber. Additional components
can include, a chuck for supporting a wafer, and a power source to
accelerate the plasma ions so the ions will strike the wafer
surface with a desired energy to etch or form a deposit on the
wafer. The power source used to create the plasma may also be used
to accelerate the ions or different power sources can be used for
each task.
[0006] To insure an accurate wafer is produced, typically, the
plasma processing system is monitored using a sensor to determine
the condition of the plasma processing system. Generally, in such a
system, the sensor is placed within the plasma to monitor certain
parameters or in the transmission line coupled to an electrode
within the processing chamber.
SUMMARY OF THE INVENTION
[0007] The present invention provides a novel method and apparatus
for measurement and analysis of plasma process parameters.
[0008] A RF sensor for sensing parameters of plasma processing is
provided with a plasma processing tool and an antenna for receiving
RF energy radiated from the plasma processing tool. The antenna is
located proximate to the plasma processing tool so as to be
non-invasive. The antenna may be a broadband mono-pole antenna.
[0009] In an aspect of the invention, a RF sensor may be located in
an enclosure and the enclosure may be provided with a plurality of
absorbers for absorbing RF energy. The enclosure can reduce the
amount of interference seen by the antenna by attenuating RF energy
originating from another nearby source and reducing the distortion
of the desired RF energy. The absorbers reduce the backscattering
of incident RF energy to the antenna.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 is an illustration of a RF sensor in accordance with
an embodiment of the present invention;
[0011] FIG. 2 is a simplified block diagram of an antenna and
processor in accordance with an embodiment of the present
invention;
[0012] FIG. 3 is a simplified block diagram of an antenna in
accordance with an embodiment of the present invention;
[0013] FIG. 4 is a simplified block diagram of a plasma processing
system in accordance with an embodiment of the present invention;
and
[0014] FIG. 5 is a simplified graph of expected harmonic data in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0015] The present invention will be described in more detail below
with reference to the illustrative embodiments disclosed.
[0016] FIG. 1 is an illustration of a RF sensor in accordance with
an embodiment of the present invention. A plasma processing tool
includes a chamber 110. The plasma processing tool is generally
powered by an RF power source (not shown). RF energy 120 from the
RF power source creates and maintains a plasma 130 in the chamber
110 of the plasma processing tool that is generally used in the
processing of substrates. The plasma processing tool can be
assembled in any of a variety of known configurations, all of which
contain a chamber 110 where a plasma 130 is present for processing.
Some of these configurations include, for example, an inductively
coupled plasma (ICP) source, an electrostatically shielded radio
frequency (ESRF) plasma source, a transformer coupled plasma (TCP)
source, and a capacitively coupled plasma (CCP) source. Regardless
of the source of the RF energy, the plasma 130 inside of the
chamber 110 is excited by the RF energy that is generated by the RF
power source. Accordingly, RF energy radiates from the chamber 110
at the fundamental RF frequency and at harmonics of the fundamental
RF frequency. The harmonic frequencies are generated in the plasma
130. The magnitude and the phase of the harmonic frequencies
provide information on the state of the plasma 130 and the chamber
110. For example, experiments at various power, pressure, and flow
rates indicate a high degree of correlation between the radiated
energy and the process parameters. Specifically, analysis indicates
that the first and second harmonics relate to the electron density
of the plasma with better than a 99% match.
[0017] An antenna 140 is provided outside of the plasma chamber 110
to receive the RF energy that is radiated from the plasma 130 and
converts the RF energy to an RF signal. In FIG. 1, antenna 140 is
illustrated outside of chamber 110. Alternatively, it can be
located within chamber 110, but outside of the processing area of
plasma 130. In this configuration, the antenna has the benefit of
being non-intrusive to the plasma 130 since invasive sensors are
known to change the process parameters. The antenna 140 is coupled
to a processor 150. The processor 150 receives the RF signal from
the antenna 140 and accordingly, is configured to process the RF
signal to provide the desired information on the state of the
plasma. Additionally, since the fundamental frequency of the energy
source may be in the order of megahertz, the antenna 140 may be a
broadband, mono-pole antenna so it is capable of receiving the
large bandwidth of the RF energy that is radiated. For example, an
Antenna Research Model RAM-220 can be used as a broadband mono-pole
antenna.
[0018] FIG. 2 is a simplified block diagram of an antenna and
processor in accordance with an embodiment of the present
invention. In the illustrated embodiment, the antenna 140 is
coupled to a high pass filter 210. Alternatively, antenna 140 can
be coupled to another type of filter such as a bandreject, a
bandpass, or a lowpass filter. The output of the high pass filter
210 is coupled to a low noise amplifier (LNA) 220 and the amplified
signal is then input to the processor 230. The high pass filter may
be utilized to remove the fundamental frequency from the received
signal since conventionally, there may not be useful information
contained in the fundamental frequency but rather the useful
information is contained within the harmonics of the RF energy. Of
course, data concerning the fundamental frequency can be collected
by eliminating or adjusting the cut-off frequency of the high pass
filter 210. Typical attenuation of the signal below the cutoff of
the high pass filter may be in the range of 40 dB. The LNA 220
amplifies the RF signal provided from the high pass filter so the
signals can be appropriately processed by the processor 230.
Typical gains of the LNA may be in the range of 20-30 dB.
[0019] The processor 230 may be configured to support multiple
inputs as shown in FIG. 2. In this case, several processes may be
monitored independently and processed by a single processor 230.
The processor 230 may include an analog to digital (A/D) converter
for converting the received analog signal into digital samples. The
sampling rate of the signal may be determined in a variety of
methods. If, for example, the fundamental frequency of the RF
energy was 13.56 MHz, then a bandwidth of 125 MHz would be suitable
to measure 8 harmonics (the 8.sup.th harmonic having a frequency of
122.04 MHz). In this case, if the sampling interval the AID
converter is 100 ms and a frequency bin of 10 KHz is chosen, the
sampling rate would be calculated as at least 250 MS/s by the
Nyquist criterion and the sample size would be 25,000.
[0020] Coupled to the processor 230 are a user interface 240, an
external computer 250, and a network 260. The user interface 240
can comprise a variety of known components with the purpose of
allowing a user to interact with the processor 230. For example, if
the processor, after sampling, were to perform a FFT (Fast Fourier
Transform) of the sampled data, the results could be displayed on a
touch screen that would allow the user to interface with the
system. The external computer 250 can serve a variety of purposes
including real time control of the processing parameters and the
chamber 110. The network 260 serves to allow remote access to and
from the processor by a user. For example, the FFT information can
be made available to the external computer 250 or to the network
260.
[0021] In an example of such an antenna and processor, the chamber
parameters can be characterized during a calibration state and the
data collected by the antenna 140 can be applied to a model that
relates various parameters of the chamber and plasma. For example,
some of the parameters may include, electron density, assembly
cleanliness, electron temperature, and endpoint detection. The use
of such a model may permit the use of an antenna without regard to
the absolute calibration of the antenna that may simplify sensor
design parameters.
[0022] FIG. 3 is a simplified block diagram of an antenna in
accordance with an embodiment of the present invention. The chamber
110, plasma 130, antenna 140, and processor 150 can be the same as
those disclosed in FIGS. 1 and 2. The antenna 140 is placed in an
enclosure 340 that is connected to the chamber 110 via the
connecting wall 310. The connecting wall 310 is designed to pass
the RF energy that is radiated from the plasma 130, and may be
quartz, alumina or any other suitable material. Alternatively, a
hole may be provided in the connecting wall 310 to allow the RF
energy to pass therethrough. Absorbers 320 and 330 are utilized to
absorb the RF energy from unwanted sources as well as to reduce the
distortion caused by the resonance of the enclosure 340, i.e.,
without the absorbers 320 and 330, the antenna may receive unwanted
resonance, distorting the signal that should be received. In
general, the absorber can comprise material that absorbs energy at
discrete or broadband frequencies.
[0023] Although shown on the back of the enclosure 340, the
absorbers 320 and 330 may be placed around the enclosure 340 on
five of the sides (if the enclosure is considered to be a
rectangular box). This arrangement for the absorbers allows the RF
energy to radiate from the plasma 130 through the connecting wall
310 and in the enclosure while the absorbers are on the other five
sides of the box.
[0024] In embodiments, the absorbers 320 and 330 may be chosen such
that absorber 320 is selected to absorb the fundamental frequency
and absorber 330 is selected to absorb the first harmonic. A
quarter wave arrangement can provide the maximum attenuation of the
selected frequencies. Additionally, additional absorbing layers can
be utilized as desired. Although specific arrangements of absorbers
have been described above, any configuration of absorbers that
reduce unwanted interference may be utilized.
[0025] FIG. 4 is a simplified block diagram of a plasma processing
system in accordance with an embodiment of the present invention.
For the purpose of description, the chamber 110 is shown as a
capacitively coupled chamber with upper electrode 125, however, any
type of system could be similarly utilized. The plasma 130, the
antenna 140 and the processor 150 can be the same as described
above. As previously described, the plasma 130 is excited by a RF
generator 420. The RF generator 420 may be directly coupled to the
chamber 110 or, as shown in FIG. 4, coupled to the chamber 110 via
a match network 410 or 440. In FIG. 4, two RF generators are shown
for the purpose of illustration, however, it may be possible to
utilize a single RF Generator 420 depending on the configuration of
the chamber 110. The Upper ELectrode (UEL) match network 410 is
coupled to the upper electrode 125 and the Lower ELectrode (LEL)
match network 440 is coupled to the lower electrode 450. The plasma
130 is excited by the RF generator(s) 420. Accordingly, the plasma
130 radiates RF energy at a fundamental frequency and at harmonics
of the fundamental frequency. The RF energy is radiated out of the
chamber 110 and is received by antenna 140, which is located
exterior of the plasma 130. The antenna 140 is coupled to a
processor 150, which has been described, in part, earlier. As
described with respect to FIG. 1, the above-described arrangement
provides a non-invasive method of receiving plasma processing
parameters.
[0026] The processor 150 receives the RF energy and converts the
analog signal to a digital signal via an analog to digital (AID)
converter. Typically, the sampling rate of the analog signal
depends on the bandwidth of interest (i.e., the bandwidth is a
function of the fundamental frequency and the harmonics of
interest). For example, a 500 MHz bandwidth may typically be
sampled at a rate of 1 billion samples per second. Of course, the
sampling rate can be determined as desired and should not be
limited to the example above. The magnitude and the phase of the RF
energy, including the harmonics, may provide information about the
state of the plasma 130 and accordingly on the state of the chamber
1 10. The data may then be processed by the processor 150 and
operations such as a Fast Fourier Transform (FFT) and a Principle
Component Analysis (PCA) can typically be used to gather
information from the RF signal. The information that is acquired by
the processor 150 can provide insight into parameters such as
assembly cleanliness, plasma density, electron temperature, and
endpoint detection.
[0027] In one embodiment of the processor, trace data of the
received RF energy can be converted into a frequency domain output
signal by using conventional techniques including the FFT. The
information at the harmonic frequencies can then be extracted and
multiplied by coefficients which are obtained during a calibration
of the plasma processing system and determined by PCA. PCA may be
useful for determining the coefficients because it allows a large
set of correlated values to be converted to a smaller set of
principal values. The reduction in the size of the set can be
achieved be converting the original set of values into a new set of
uncorrelated linear combinations of the original (larger) set.
[0028] Using the magnitude of the fundamental frequency and the
harmonic frequencies of the received RF energy, it is possible to
perform several different analyses including, power analysis, flow
analysis, and pressure analysis. By processing the information
obtained from the magnitude values, it is further possible to
determine between which of the harmonics, the largest correlation
exists and as a result, determine acceptable coefficients for each
frequency component. Dependence analysis is also possible to
determine if changes in one parameter effect other parameters in
the system, however, initial results indicate that the parameters
may be adjusted independently.
[0029] Further, endpoint detection may be possible from an analysis
of the trace data. Once plotted, it becomes apparent that there is
a significant shift in a harmonic of the received RF energy. More
particularly, it is possible that the major harmonic contribution
may change at the time of process completion.
[0030] For example, as shown in FIG. 5 which illustrates
simplified, expected data, a change in the 3.sup.rd harmonic is
apparent at T1 an a change in both the fundamental an 3.sup.rd
harmonic is apparent at T2. Analysis of the process indicates that
these changes are due to completion of the process. Such a method
of endpoint detection may be an accurate and cost effective method
of endpoint detection.
[0031] The processed data is then sent to a tool control 430. The
tool control 430 may be configured to perform several tasks. Some
of the tasks that the tool control 430 can perform include end
point determination, power control, and gas control (flow,
pressure, etc.). As shown in FIG. 4, the tool control 430 is
coupled to the chamber 110, and the RF generators 420. In this
manner, it is possible for the tool control to adjust parameters of
these devices according to the data that is received from processor
150 so that a repeatable process can be maintained within the
chamber 110.
[0032] As described above, PCA is a multivariate statistical
procedure that permits a large set of correlated variables to be
reduced to a smaller set of principal components. Therefore, during
a calibration phase, PCA can be utilized to first generate a
covariance matrix from a data set comprising the data of various
harmonics. Next, an eigensolution can be obtained from the
covariance matrix and accordingly a set of eigenvectors can be
calculated. From the eigensolution, the percentage contribution of
each principal component can be calculated. Using the percentages,
coefficients can be selected accordingly by a weighted sum of the
eigenvector with the percentages obtained. This calculation can be
performed for various parameters including, power, gas flow, and
chamber pressure. Once the calibration is complete and the various
coefficients are determined, the tool control can utilize the
information in control loops as would be apparent to an individual
skilled in the art. In this type of a feed back loop a reproducible
process may be maintained.
[0033] The processor 150 may be coupled to several devices as shown
in FIG. 2. Some of the devices that are of importance in the
present embodiment include the user interface 240 and the external
computer 250. Additionally, it is possible that both the user
interface 240 and the external computer 250 are a single device,
for example, a personal computer.
[0034] Lastly, as can be appreciated by an individual skilled in
the art, the amount of data that is processed by the processor 150
may be significantly large. To this regard, it may be required that
an external storage device (not shown) be utilized. One possible
configuration for connecting the storage device may be directly to
the processor 150. Alternatively, it may be beneficial to use the
remote storage via the network 260 (shown in FIG. 2). However, any
method of storing the data is acceptable. One benefit of storing
the data is for future processing and analysis. Additionally, the
archived data can be utilized to model an acceptable control system
for operating the tool control 430 and, accordingly, control the
plasma processing.
[0035] The foregoing presentation of the described embodiments is
provided to enable any person skilled in the art to utilize the
present invention. Various modifications to these embodiments are
possible and the generic principle of a RF sensor for measurement
of semiconductor process parameters presented herein may be applied
to other embodiments as well. Thus, the present invention is not
intended to be limited to the embodiments shown above, but rather
to be accorded the widest scope consistent with the principles and
novelty of the features disclosed in any fashion herein.
* * * * *