U.S. patent application number 11/060598 was filed with the patent office on 2005-12-01 for plasma processing apparatus and plasma processing method.
This patent application is currently assigned to SEMICONDUCTOR TECHNOLOGY ACADEMIC RESEARCH CENTER. Invention is credited to Kadomura, Shingo, Nishikawa, Satoshi, Samukawa, Seiji.
Application Number | 20050263247 11/060598 |
Document ID | / |
Family ID | 35423921 |
Filed Date | 2005-12-01 |
United States Patent
Application |
20050263247 |
Kind Code |
A1 |
Samukawa, Seiji ; et
al. |
December 1, 2005 |
Plasma processing apparatus and plasma processing method
Abstract
In a plasma processing apparatus which includes a chamber (1)
equipped with a wafer stage (3) for mounting thereon a substrate
(2) to be processed, and which processes the substrate (2) by
exposure to a plasma (4), a photon detection sensor (5) for
measuring an ultraviolet-light-induced current is placed on a
circumferential portion of a substrate mounting surface (3a) of the
wafer stage (3) so that the occurrence of an abnormal discharge can
be detected, in real time, from a change in the output of the
photon detection sensor (5).
Inventors: |
Samukawa, Seiji;
(Sendai-shi, JP) ; Nishikawa, Satoshi; (Tokyo,
JP) ; Kadomura, Shingo; (Yokohama-shi, JP) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
SEMICONDUCTOR TECHNOLOGY ACADEMIC
RESEARCH CENTER
Yokohama-shi
JP
|
Family ID: |
35423921 |
Appl. No.: |
11/060598 |
Filed: |
February 18, 2005 |
Current U.S.
Class: |
156/345.24 ;
216/60 |
Current CPC
Class: |
H01J 2237/0206 20130101;
G01R 31/1263 20130101; H01J 37/32935 20130101 |
Class at
Publication: |
156/345.24 ;
216/060 |
International
Class: |
C23F 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 28, 2004 |
JP |
2004-159531(PAT.) |
Claims
What is claimed is:
1. A plasma processing apparatus comprising: a chamber equipped
with a wafer stage for mounting thereon a substrate to be
processed; a means for providing plasma on said substrate mounted
on said wafer stage; and a photon detection sensor for measuring an
ultraviolet-light-induced current placed on a circumferential
portion of a substrate mounting surface of said wafer stage.
2. A plasma processing apparatus as claimed in claim 1, wherein
said photon detection sensor comprises a semiconductor substrate,
an insulating film formed over said semiconductor substrate, an
electrode layer embedded in said insulating film, a means for
applying a bias voltage to said electrode layer, and a means for
detecting a current flowing in said electrode layer.
3. A plasma processing apparatus as claimed in claim 2, wherein
said photon detection sensor further comprises a second electrode
formed on said insulating film.
4. A plasma processing apparatus as claimed in claim 1, wherein a
plurality of said photon detection sensors are arranged around the
circumferential portion of said substrate mounting surface of said
wafer stage.
5. A plasma processing method for processing a substrate,
comprising: providing a plurality of photon detection sensors, each
for measuring an ultraviolet-light-induced current, on a wafer
stage provided within a plasma chamber; providing said substrate to
be processed on said wafer stage, performing plasma processing in
said plasma chamber in which said photon detection sensors and said
substrate to be processed are placed, and monitoring an output
current from each of said photon detection sensors while said
plasma processing is being performed.
6. A plasma processing method as claimed in claim 5, wherein when a
spike-like current drop different from a steady-state current is
observed during the monitoring of said photon detection sensors,
said spike-like current drop is recognized as indicating the
occurrence of an abnormal discharge.
7. A plasma processing apparatus as claimed in claim 2, wherein a
plurality of said photon detection sensors are arranged around the
circumferential portion of said substrate mounting surface of said
wafer stage.
8. A plasma processing apparatus as claimed in claim 3, wherein a
plurality of said photon detection sensors are arranged around the
circumferential portion of said substrate mounting surface of said
wafer stage.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority of Japanese Patent
Application No. 2004-159531, filed on May 28, 2004.
FIELD OF THE INVENTION
[0002] The present invention relates to a plasma processing
apparatus, and to a plasma processing method, for processing a
semiconductor wafer or the like and, more particularly, to a plasma
processing apparatus and to a plasma processing method capable of
monitoring, in real time, an abnormal discharge phenomenon that can
occur during plasma processing.
BACKGROUND OF THE INVENTION
[0003] Plasma processes such as etching, thin-film deposition, etc.
are indispensable for achieving high-quality, high-functionality
semiconductor devices. However, one problem involved with such
plasma processes is that an abnormal discharge can occur abruptly
during processing in a plasma processing apparatus. If an abnormal
discharge occurs, etching and thin-film deposition conditions
change and, as a result, the characteristics of the produced
semiconductor device substantially change. In the worst case, the
processing-apparatus may be damaged. Accordingly, in order to
produce high-reliability semiconductor devices while ensuring high
productivity, it is essential to monitor the occurrence of an
abnormal discharge, in real time, during plasma processing and to
take quick and appropriate action to deal with the abnormality.
[0004] An abnormal discharge occurs when the large electric charge
accumulated on the inside wall of the plasma chamber, etc. either
exceeds a limit or is discharged for some reason during plasma
processing. As such discharge occurs in an unpredictable manner,
and as there are no effective sensing methods for detecting the
occurrence, with a prior known plasma processing apparatus, it has
not been possible to take appropriate action by detecting the
occurrence of such an abnormal discharge in real time, and this has
led to the degradation of the productivity, as well as the
reliability, of the produced semiconductor device.
[0005] An on-wafer monitoring system has already been proposed that
measures the plasma processing state by a sensor build into a
semiconductor wafer (Japanese Unexamined Patent Publication
2003-282546). This system is one that monitors the energy
distribution, ion current, etc., for example, of the ions,
electrons, and other particles generated by the plasma, but, as
these changes manifest themselves relatively slowly on the
semiconductor wafer in contrast with an instantaneous change in the
plasma state such as an abnormal discharge, the proposed system is
not suitable for real-time monitoring of an abnormal discharge.
SUMMARY OF THE INVENTION
[0006] In view of the above situation, it is an object of the
present invention to provide a plasma processing apparatus and
plasma processing method that can monitor the plasma state in real
time during processing and, more particularly, can monitor in real
time the occurrence of an abnormal discharge.
[0007] To achieve the above object, in a plasma processing
apparatus according to the present invention which includes a
chamber equipped with a wafer stage for mounting thereon a
substrate, for example, a semiconductor wafer, to be processed, and
which processes the substrate by exposure to a plasma, a photon
detection sensor for measuring an ultraviolet-light-induced current
is placed on a circumferential portion of a substrate mounting
surface of the wafer stage.
[0008] The photon detection sensor comprises a semiconductor
substrate, an insulating film formed over the semiconductor
substrate, an electrode layer embedded in the insulating film, a
means for applying a bias voltage to the electrode layer, and a
means for detecting a current flowing in the electrode layer.
[0009] When an abnormal discharge occurs in the plasma chamber, the
plasma density appreciably drops at that instant because of the
discharge, and the generation of ions, neutral particles,
electrons, and ultraviolet light by the plasma decreases. When the
photon detection sensor is installed, during the generation of the
plasma a certain amount of current induced by the ultraviolet light
generated from the plasma is observed in a steady-state condition;
however, when the plasma density drops due to an abnormal
discharge, and the amount of ultraviolet light generation
decreases, then a spike-like current drop is observed. Accordingly,
by installing the photon detection sensor on the wafer stage in the
plasma processing apparatus, and by monitoring the sensor output in
real time, the occurrence of an abnormal discharge manifesting
itself as a spike-like current drop can be detected in real time.
As a result, quick and appropriate action can be taken to deal with
the abnormal discharge.
[0010] The photon detection sensor further comprises a second
electrode formed on the insulating film. With the provision of this
electrode, the influence of only the ultraviolet light can be
observed by eliminating the influence of particles other than the
vacuum ultraviolet light, such as ions and electrons. This serves
to enhance the accuracy in detecting the occurrence of an abnormal
discharge.
[0011] Further, a plurality of sensors, each identical to the
above-described photon detection sensor, are arranged spaced apart
from each other on the wafer stage. With this arrangement, it
becomes possible to know the spatial distribution indicating the
extent to which the effect of the abnormal discharge has spread,
thus making it easier to determine, for example, which devices on
the semiconductor wafer are affected.
[0012] To achieve the above object, a plasma processing method
according to the present invention comprises the steps of: placing
a plurality of photon detection sensors, each for measuring an
ultraviolet-light-induced current, on a wafer stage provided within
a plasma chamber; placing the substrate to be processed on the
wafer stage; performing plasma processing in the plasma chamber in
which the photon detection sensors and the substrate to be
processed are placed; and monitoring an output current from each of
the photon detection sensors while the plasma processing is being
performed.
[0013] The plasma processing method further comprises a step in
which, when a spike-like current drop different from a steady-state
current is observed in the monitoring step of the photon detection
sensors, the spike-like current drop is recognized as indicating
the occurrence of an abnormal discharge.
[0014] According to the above method, the current induced by the
ultraviolet light generated from the plasma is detected by the
photon detection sensor mounted on the wafer stage while the plasma
processing of the substrate is being performed; in this way, any
abnormal discharge occurring in the plasma chamber can be detected
in real time in the form of a change in current value. Accordingly,
quick action can be taken to deal with the abnormality, offering
the effect of enhancing the reliability and productivity of
semiconductor devices.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a diagram showing in simplified form the
configuration of a plasma processing apparatus according to one
embodiment of the present invention;
[0016] FIG. 2 is a plan view of a wafer stage in the plasma
processing apparatus shown in FIG. 1;
[0017] FIG. 3 is a diagram showing the result of the measurement of
an electric current value of a photon detection sensor;
[0018] FIG. 4 is a diagram showing a first embodiment of the photon
detection sensor used in the plasma processing apparatus of the
present invention;
[0019] FIG. 5A is a diagram for explaining one fabrication step for
the photon detection sensor shown in FIG. 4;
[0020] FIG. 5B is a diagram for explaining another fabrication step
for the photon detection sensor shown in FIG. 4;
[0021] FIG. 5C is a diagram for explaining a further fabrication
step for the photon detection sensor shown in FIG. 4;
[0022] FIG. 5D is a diagram for explaining a still further
fabrication step for the photon detection sensor shown in FIG.
4;
[0023] FIG. 6A is a cross-sectional view in one fabrication step
for the photon detection sensor shown in FIG. 4;
[0024] FIG. 6B is a plan view of the photon detection sensor shown
in FIG. 6A;
[0025] FIG. 7 is a diagram showing a second embodiment of the
photon detection sensor used in the plasma processing apparatus of
the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] FIG. 1 is a diagram showing, in simplified form, the
configuration of a plasma processing apparatus according to one
embodiment of the present invention. Reference numeral 1 is a
chamber for performing a plasma process therein; the chamber 1 is
equipped with a wafer stage 3 for mounting thereon a substrate to
be processed, i.e., a semiconductor wafer 2. A gas excited into a
plasma state (hereinafter simply referred to as the plasma) 4 is
introduced into the chamber 1, and a plasma process such as etching
or thin-film deposition is performed on the semiconductor wafer 2.
Here, the plasma 4 can also be formed within the chamber 1 by
applying high-frequency energy from outside the chamber to a gas
introduced into the chamber 1. Usually, an insulating film for
preventing the discharge of the plasma 4 is formed on the inside
wall of the chamber 1.
[0027] FIG. 2 is a plan view of the wafer stage 3. As shown, one or
more photon detection sensors 5 are arranged on the surface 3a of
the wafer stage 3 on which the semiconductor wafer 2 is to be
mounted. The structure of the photon detection sensor and its
sensor mechanism will be described later. As shown, the photon
detection sensors 5 are arranged at equally spaced intervals around
the circumferential portion of the surface 3a of the wafer stage 3.
A data processing apparatus 6, which performs data processing by
detecting a change in an electric current being output from each
photon detection sensor 5, is connected to the photon detection
sensors 5.
[0028] The plasma processing apparatus shown in FIG. 1 detects a
change in the electric current value of each of the plurality of
photon detection sensors 5 while performing processing of the
semiconductor wafer 2 by exposing it to the plasma. The present
inventor has discovered that when an abnormal discharge occurs
within the chamber 1, the output, i.e., the electric current value,
of the photon detection sensor 5 drops in a spike-like manner.
Accordingly, by observing the output of each photon detection
sensor 5 during the processing of the semiconductor wafer 2, any
abnormal discharge occurring in the chamber 1 can be detected.
Further, by simultaneously monitoring the outputs of the plurality
of photon detection sensors 5, it becomes possible to detect the
spatial distribution of the abnormal discharge, which shows which
portions of the semiconductor wafer 2 are affected by the abnormal
discharge.
[0029] FIG. 3 shows one example of how the output of the photon
detection sensor 5 changes. In the figure, the ordinate represents
the ultraviolet-light-induced current value of the photon detection
sensor 5 measured in arbitrarily chosen units, and the abscissa
represents the time. In the photon detection sensor 5, a current 8
induced by the ultraviolet light generated from the plasma is
constantly observed in accordance with a mechanism to be described
later and, during that process, a spike-like drop 7 in the electric
current value is observed. The present inventor has discovered that
the spike-like drop 7 is caused by an abnormal discharge occurring
in the chamber 1.
[0030] Accordingly, the time of occurrence, the magnitude, and the
spatial distribution of the abnormal discharge in the chamber 1 can
be deduced from the detected occurrence of the drop 7, its
magnitude, and the position on the wafer stage 3 of the photon
detection sensor 5 whose output exhibited the drop.
[0031] Next, the structure of the photon detection sensor 5 used in
the present invention, its operating principle, and the mechanism
by which an abnormal discharge is detected using the photon
detection sensor will be described with reference to FIGS. 4 and
5.
[0032] FIG. 4 shows a first embodiment of the photon detection
sensor 5. In FIG. 4, for convenience of explanation, the photon
detection sensor 5 is shown as being mounted directly on the bottom
of the chamber, but in practice, the sensor is mounted on the wafer
stage 3 on which the semiconductor wafer is to be held, as shown in
FIG. 1. In the figures hereinafter given, the same reference
numerals as those in FIGS. 1 and 2 designate the same or similar
component elements, and the description of such elements will not
be repeated here.
[0033] In the photon detection sensor 5 shown in FIG. 4, reference
numeral 10 is a Si semiconductor substrate, 11 is a first
insulating film formed from SiO.sub.2 or the like, 12 is an
electrode formed from Al, and 13 is a second insulating film formed
from SiO.sub.2 or the like. A portion of the second insulating film
13 is removed by suitable means such as etching to expose a portion
of the electrode 12. A wiring line 14 is connected to the exposed
portion, and the current flowing in the electrode 12 is measured by
an ammeter 15. Reference numeral 16 is a power supply for applying
a bias voltage to the electrode 12.
[0034] Ions, neutral particles, electrons, and ultraviolet light
are generated in the plasma. In this ultraviolet radiation, there
is radiation that has large energy and cannot pass through the
insulating films 12 and 13. Such ultraviolet radiation is absorbed
by the insulating films 12 and 13 and forms electron-hole pairs in
the films. The holes, whose mobility is lower than the electrons,
are trapped by defects formed in the insulating films 12 and 13,
and thus form positive fixed charges. Here, when a bias voltage is
applied to the electrode 12, these charges can be detected as a
hole current by the ammeter 15.
[0035] At the interface between the Si semiconductor substrate and
the insulating film, for example, the SiO.sub.2/Si interface, there
exist many defects formed by so-called dangling bonds of Si. The
holes formed in the SiO.sub.2 film by absorbing high-energy light
such as vacuum ultraviolet light are trapped by such defects formed
at the SiO.sub.2/Si interface, and thus form positive fixed
charges. Accordingly, the electric current value measured by the
ammeter 15 during plasma processing has correlation with the amount
of fixed charge at the SiO.sub.2/Si interface.
[0036] It is presumed that the steady-state current value 8 shown
in FIG. 3 has a relationship with the current generated based on
the positive fixed charges. In a MOS transistor or the like, the
number of positive fixed charges greatly affects the device
characteristics. Accordingly, the characteristics of the
semiconductor device being produced can be predicted to a certain
extent from the measured electric current value.
[0037] It is known that the energy of the plasma 4 fluctuates in
cyclic fashion based on its generation process. This fluctuation of
the plasma is observed as a fluctuation in the steady-state current
value, as shown by reference numeral 9 in FIG. 3, when measuring
the electric current value of the photon detection sensor 5.
Accordingly, by detecting the fluctuation of the electric current
value of the sensor 5, the fluctuation of the plasma can be
observed, which has not been possible with the prior art.
[0038] Usually, the inside surface of the plasma chamber 1 is
treated with an insulating film to prevent contact with the
high-energy plasma 4 and thereby prevent discharge of the plasma
energy. Accordingly, as the plasma process progresses, a large
electric charge is accumulated on the insulating film. When the
charge accumulation exceeds a limit, or when the accumulated charge
is discharged for some reason, an abnormal discharge occurs in the
chamber 1.
[0039] When an abnormal discharge occurs, the energy of the plasma
4 is released, and the plasma density thus drops. As a result, the
ultraviolet light generated by the plasma 4 substantially
decreases, and the number of electron-hole pairs to be formed in
the insulating layers 12 and 13 substantially decreases in a
corresponding manner. This decrease is observed by the ammeter 15
as a spike-like drop in the current value, as shown in FIG. 3.
[0040] Therefore, when a spike-like drop is detected in the current
value, it can be determined that an abnormal discharge has occurred
in the chamber 1. Here, when an abnormal discharge occurs, the
density of the plasma 4 appreciably drops at that instant, and this
greatly affects the plasma process in progress such as insulating
film etching or thin-film deposition. This can significantly
degrade or damage the characteristics of the semiconductor device
being produced. Therefore, in order to improve the reliability and
productivity of semiconductor devices, it is extremely important to
detect the occurrence of an abnormal discharge during plasma
processing, the magnitude of the abnormal discharge, and the
spatial distribution of the abnormal discharge that occurred.
[0041] FIGS. 5 and 6 are diagrams showing a fabrication process for
the ultraviolet-light-induced current measuring photon detection
sensor 5 having the structure shown in FIG. 4. As shown in FIG. 5A,
first the Si substrate 10 is subjected to wet thermal oxidation for
30 minutes at 1000.degree. C., to form the SiO.sub.2 film 11. The
thickness of the film 11 is 3 .mu.m. Next, as shown in FIG. 5B, Al
as the electrode material is deposited (Al film thickness of 100
nm) to form an electrode layer 12'. Then, the electrode layer 12'
is etched by phosphoric acid (H.sub.3PO.sub.4), to form the
electrode 12 of the desired shape as shown in FIG. 5C.
[0042] Next, plasma TEOS (tetraethoxysilane,
Si(OC.sub.2H.sub.5).sub.4) is deposited to a thickness of 200 nm to
form the oxide film 13, as shown in FIG. 5D, after which a portion
of the oxide film 13 is etched off by hydrofluoric acid
(HF:H.sub.2O=1:50) to expose a portion 12" of the electrode 12, as
shown in FIG. 6A. Finally, a current measuring lead wire (not
shown) is connected to the exposed portion 12" of the electrode 12.
After the lead wire is connected, the device is covered with an
insulating film (not shown) to prevent charged particles from
entering the device through the periphery of the lead wire.
[0043] FIG. 6B is a plan view showing the device shown in FIG. 6A
as viewed from the top; here, the electrode 12 is shown through the
overlying SiO.sub.2 film 13, with the portion 12" of the electrode
exposed through the opening formed in the SiO.sub.2 film 13.
[0044] When the photon detection sensor 5 is formed as described
above, the sensor is mounted on the wafer stage 3 in the plasma
chamber 1, and connected to the power supply 16 and the ammeter 15
outside the chamber 1 via a current lead terminal (not shown)
connected to the electrode 12, and the ammeter 15 measures the
electric current value when a bias voltage of 0 to 30 V is applied
from the power supply 16. The electric current value when the
plasma is not applied is about 10 to 20 pA, which means that
virtually no current is flowing. The measured sensor output is
processed by the data processing apparatus 6 and monitored by the
user.
[0045] FIG. 7 is a diagram showing a second embodiment of the
photon detection sensor used in the plasma processing apparatus of
the present invention. The photon detection sensor 50 of this
embodiment differs from the photon detection sensor 5 of the
structure shown in FIG. 4 in that the SiO.sub.2 film 13 is covered
with an Al film 17 about 100 nm in thickness. Reference numeral 12a
indicates the lead terminal of the electrode 12.
[0046] Ions, neutral particles, electrons, and ultraviolet light
are generated in the plasma. Therefore, in the photon detection
sensor 5 of FIG. 4, the SiO.sub.2 film 13 is affected by charged
particles such as ions and electrons, causing a variation in the
measured current value. In the photon detection sensor 50 shown in
FIG. 7, the film 13 is covered with the Al thin film 17 to prevent
such particles from penetrating into the film 13. It is known that
ultraviolet light with wavelengths of about 17 nm to 90 nm passes
through the Al film. Therefore, by depositing the Al film 17 over
the SiO.sub.2 film 13, the influence only of vacuum ultraviolet
light of 90 nm and shorter wavelengths that pass through can be
observed by eliminating the influence of ions and electrons. The Al
film 17 is grounded during plasma exposure.
[0047] In the photon detection sensors 5 and 50 described with
reference to FIGS. 4 and 7, the insulating film has been formed
from SiO.sub.2, but the present invention is not limited to this
particular material; for example, the insulating film can be
equally achieved by using, for example, a nitride film or the like.
The insulating film need only be formed using the same material as
the insulating film formed on the semiconductor wafer or to be
formed thereon and processed by etching.
[0048] As described above with reference to the various
embodiments, in the plasma processing apparatus of the present
invention, with the ultraviolet-light-induced current measuring
photon detection sensor mounted on the wafer stage, any abnormal
discharge phenomenon occurring in the plasma chamber can be
detected in real time during the processing of the semiconductor
wafer. Accordingly, when an abnormal discharge occurs, corrective
action can be taken quickly, and as a result, semiconductor devices
having high reliability can be produced while ensuring high
productivity. Further, by arranging a plurality of photon detection
sensors on the wafer stage, it becomes possible to know the spatial
distribution of the abnormal discharge, so that more appropriate
action can be taken to deal with the abnormal discharge.
* * * * *