U.S. patent application number 10/931546 was filed with the patent office on 2005-02-10 for apparatus and method of detecting endpoint of a dielectric etch.
This patent application is currently assigned to Micron Technology, Inc.. Invention is credited to Chapman, James Malden.
Application Number | 20050029227 10/931546 |
Document ID | / |
Family ID | 22994032 |
Filed Date | 2005-02-10 |
United States Patent
Application |
20050029227 |
Kind Code |
A1 |
Chapman, James Malden |
February 10, 2005 |
Apparatus and method of detecting endpoint of a dielectric etch
Abstract
A system detects the clearing of a dielectric at a plurality of
contact sites by measuring the surface voltage of the dielectric
and comparing the surface voltage to a reference voltage set to a
value that relates to the cleared contact sites. Another system
detects the clearing of a dielectric at a plurality of contact
sites on a substrate by measuring the rate of change of a substrate
current during an etch process and ending the etch process when the
rate of change is approximately zero. Another system detects the
clearing of a dielectric at a contact site by measuring a substrate
current during an etch process and ends the etch process when the
measured substrate current exceeds a predetermined value.
Inventors: |
Chapman, James Malden;
(Boise, ID) |
Correspondence
Address: |
SCHWEGMAN, LUNDBERG, WOESSNER & KLUTH, P.A.
P.O. BOX 2938
MINNEAPOLIS
MN
55402
US
|
Assignee: |
Micron Technology, Inc.
|
Family ID: |
22994032 |
Appl. No.: |
10/931546 |
Filed: |
August 31, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10931546 |
Aug 31, 2004 |
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10328617 |
Dec 23, 2002 |
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10328617 |
Dec 23, 2002 |
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09261601 |
Feb 26, 1999 |
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6517669 |
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Current U.S.
Class: |
216/59 |
Current CPC
Class: |
H01J 37/32963 20130101;
H01J 37/32935 20130101 |
Class at
Publication: |
216/059 |
International
Class: |
H01L 021/20 |
Claims
What is claimed is:
1. A method comprising: placing a substrate in a plasma etch
chamber; etching the substrate; measuring a substrate current; and
stopping the etching when the substrate current stabilizes.
2. The method of claim 1, wherein etching the substrate includes
inducing a substrate current with plasma ions.
3. A method comprising: placing a substrate in a plasma etch
chamber; etching the substrate; measuring a substrate current
having a rate of change; stopping the etching when the rate of
change of the substrate current is substantially zero.
4. The method of claim 3, wherein etching the substrate includes
inducing a substrate current with plasma ions.
5. The method of claim 3, wherein measuring a substrate current
includes measuring the substrate current in real time while the
substrate is etched.
6. A method comprising: placing a substrate having a layer to etch
in a plasma etch chamber; etching the layer; measuring a substrate
current; and stopping the etching when the substrate current
stabilizes.
7. The method of claim 6, wherein measuring a substrate current
includes measuring the substrate current in real time while the
layer is etched.
8. The method of claim 6, wherein placing the substrate includes
placing a substrate having a dielectric layer including one of an
oxide, a nitride, borophosphosilicate, silicon-dioxides,
silicon-nitrides, and tetra-ethyl-ortho-silicates.
9. A method comprising: placing a substrate having a layer to etch
in a plasma etch chamber; etching the layer; measuring a rate of
change of a substrate current; and stopping the etching when the
rate of change of the substrate current is approximately zero.
10. The method of claim 9, wherein etching the layer includes
inducing a substrate current with plasma ions.
11. The method of claim 9, wherein measuring the rate of change of
a substrate current includes measuring a substrate current in real
time while the layer is etched.
12. A method comprising: placing a substrate having a layer to etch
in a plasma etch chamber; etching the layer; measuring a substrate
current; and stopping the etching when the substrate current
exceeds a predetermined reference value.
13. The method of claim 12, wherein stopping the etching when the
substrate current exceeds a predetermined reference value includes
setting the reference current to a value approximately equal to a
substrate current when contacts formed in the layer are cleared of
dielectric.
14. The method of claim 13, wherein setting the reference current
includes determining the reference substrate current for a given
manufacturing step, wherein determining the reference substrate
current includes: measuring the substrate current at an end of a
manufacturing step; and verifying that the contacts are cleared of
dielectric.
15. The method of claim 13, wherein setting the reference current
includes selecting the reference current from a range of current
values related to the etching process parameters.
16. A method comprising: placing a substrate having a dielectric
layer to etch in a plasma etch chamber; etching the dielectric
layer; measuring a substrate current; and stopping the etching when
the substrate current stabilizes.
17. A method comprising: placing a substrate having a dielectric
layer to etch in a plasma etch chamber; etching the dielectric
layer; measuring a rate of change of a substrate current; and
stopping the etching when the rate of change of the substrate
current is substantially zero.
18. The method of claim 17, wherein etching the substrate includes
inducing a substrate current with plasma ions.
19. The method of claim 18, wherein measuring a rate of change of a
substrate current includes measuring the current in real time while
the dielectric layer is being etched.
20. A method comprising: placing a substrate having a dielectric
layer to etch in a plasma etch chamber; etching the dielectric
layer; measuring a substrate current; and stopping the etching
process when the substrate current exceeds a predetermined
reference value.
21. The method of claim 20, wherein etching the dielectric layer
includes forming contacts.
22. The method of claim 21, wherein stopping the etching process
when the substrate current exceeds a predetermined reference value
includes setting the reference current to a value approximately
equal to a substrate current when the contacts are cleared of
dielectric.
23. The method of claim 22, wherein setting the reference current
to a value includes selecting the value from a range of current
values related to the etching process parameters.
24. The method of claim 22, wherein setting the reference current
includes determining the reference substrate current for a given
manufacturing step, wherein determining the reference substrate
current includes: measuring the substrate current at an end of a
manufacturing step; and verifying that the contacts are cleared of
dielectric.
25. A method for etching a dielectric on a substrate, comprising:
placing the substrate having a dielectric to etch within an etching
chamber; setting a reference current to a value related to a
substrate current when a contact is cleared of the dielectric;
etching the dielectric in the etching chamber; measuring the
current in the substrate; generating an endpoint detection signal
when the measured current is greater than the reference current;
detecting the endpoint detection signal; and stopping the etching
when the endpoint detection signal is detected.
26. The method of claim 25, wherein setting the reference current
includes setting the reference current to a value approximately
equal to the substrate current when the contact is cleared of
dielectric.
27. The method of claim 25, wherein setting the reference current
includes determining the reference substrate current for a given
manufacturing step, wherein determining the reference substrate
current includes: measuring the substrate current at an end of a
manufacturing step; and verifying that the contact is cleared of
dielectric.
28. The method of claim 25, wherein the reference current is
selectable from a range of current values related to the etching
process parameters.
29. The method of claim 25, wherein placing the substrate includes
placing a semiconductor substrate.
30. The method of claim 25, wherein detecting the endpoint
detection signal includes visually detecting the endpoint detection
signal.
31. The method of claim 25, wherein detecting the endpoint
detection signal includes detecting a digital output signal.
32. The method of claim 25, wherein detecting the endpoint
detection signal includes detecting an analog signal.
33. A method comprising: placing a substrate having a dielectric
layer to etch in an etching chamber; etching the dielectric layer;
measuring a substrate current in real time while the layer is
etched; and stopping the etching process when the substrate current
exceeds a predetermined reference value.
34. The method of claim 33, wherein etching the dielectric layer
includes a substrate current increasing during the etching.
Description
[0001] This application is a Divisional of U.S. application Ser.
No. 10/328,617 filed Dec. 23, 2002 which is a Divisional of U.S.
application Ser. No. 09/261,601, filed Feb. 26, 1999, now issued as
U.S. Pat. No. 6,517,669. These applications are incorporated herein
by reference.
TECHNICAL FIELD OF THE INVENTION
[0002] This invention relates to the field of semiconductor
manufacturing, and more particularly, to the field of etching
dielectrics.
BACKGROUND OF THE INVENTION
[0003] Types of dielectrics used in semiconductor manufacturing
include oxides, nitrides, borophosphosilicate glasses (BPSG),
silicon-dioxides, silicon-nitrides, and tetra-ethyl-ortho-silicates
(TEOS). During an integrated circuit manufacturing process, these
dielectrics are often etched. For example, insulating oxides are
etched, protective oxides are etched, and sacrificial oxide masks
are etched. Dielectrics sometimes function as insulators to isolate
one level of conductors and devices from another. However, the
conductors and devices on different levels must be interconnected
in order to have a working integrated circuit. This is accomplished
by etching holes in the dielectric layers in order to connect one
layer to another. In the art of integrated circuit manufacturing,
these etched holes are referred to as contacts or vias. In this
document, all holes etched in a dielectric are referred to simply
as contacts.
[0004] A long standing problem in the art of manufacturing
integrated circuits is that of completing a process step and not
knowing whether the process step completed successfully. If the
step did not complete successfully, and the processing of the
integrated circuit continues, then it is likely that at the end of
the manufacturing process the circuit will not work as designed.
Thus, continued processing after a failed process step results in
wasting the costs of processing after the failed step.
[0005] In the etching of dielectrics, a problem that can cause a
processing step to fail is the failure of the process to completely
etch the dielectric at a contact location. This failure prevents
devices from being connected. One approach to solving this problem
is to design the etching process to over etch, i.e., to run the
process longer than necessary for etching some contacts in order to
completely etch all contacts on the substrate. One difficulty with
this approach is that over etching results in some contacts being
etched to dimensions larger than necessary, and this interferes
with the important goal of integrated circuit manufacturing of
increasing the density of the devices on a substrate.
[0006] For these and other reasons, there is a need for the present
invention.
SUMMARY OF THE INVENTION
[0007] The present invention provides a system and method for
overcoming the problems as described above and others that will be
readily apparent to one skilled in the art from the description of
the present invention below.
[0008] A system in accordance with one embodiment of the present
invention for use in identifying the successful completion of a
dielectric etching process on a semiconductor substrate includes a
voltage probe for measuring the surface voltage of the dielectric,
a selectable reference voltage, and a comparator. The selectable
reference voltage is set to a value related to the surface voltage
of the dielectric when the contacts are cleared of the dielectric.
The comparator is coupled to the selectable reference voltage and
the voltage probe. The comparator compares the measured voltage to
the selectable reference voltage and produces an endpoint detection
signal.
[0009] In one embodiment of the system, the voltage probe is a
non-contact probe. In another embodiment of the system, the
selectable reference voltage is set to a value approximately equal
to the surface voltage of the dielectric when the contacts are
cleared of the dielectric. In still another embodiment, the
comparator is an analog comparator, and in yet another embodiment,
the comparator is a digital comparator.
[0010] A method in accordance with one embodiment of the present
invention for identifying the completion of a dielectric etching
process on a semiconductor substrate includes the steps of setting
a selectable reference voltage to a value related to the surface
voltage of the dielectric when a contact is cleared of the
dielectric, measuring the surface voltage of the dielectric,
comparing the measured voltage to the selectable reference voltage,
and identifying the successful completion of the dielectric etching
process by noting when the measured voltage is less than the
selectable reference voltage.
[0011] In one embodiment of a method of the present invention, the
selectable reference voltage is set to a value of approximately
equal to the surface voltage of the dielectric when the contacts
are cleared of the dielectric. In another embodiment, measuring the
surface voltage of the dielectric consists of averaging multiple
measurements of the surface voltage of the dielectric.
[0012] A method for etching a dielectric on a semiconductor
substrate in a plasma etch system is also described. The method
includes placing a substrate with a dielectric to etch within a
plasma etch chamber, setting a selectable reference voltage to a
value related to the surface voltage of the dielectric when the
contact is cleared of the dielectric, etching the dielectric in the
plasma etch chamber, measuring the surface voltage of the
dielectric, generating an endpoint detection signal when the
measured voltage is less than the selectable reference voltage,
detecting the endpoint detection signal, and stopping the etching
when the endpoint detection signal is detected.
[0013] In one embodiment of this method, the selectable reference
voltage is set to a value approximately equal to the surface
dielectric voltage when the contact is cleared of the
dielectric.
[0014] In another embodiment, a method for etching a dielectric on
a semiconductor substrate in a plasma etch system includes placing
a substrate with a dielectric to etch within a plasma etch chamber,
setting a selectable reference current to a value related to the
substrate current when the contact is cleared of the dielectric,
etching the dielectric in the plasma etch chamber, measuring the
substrate current, generating an endpoint detection signal when the
measured current is greater than the selectable reference current,
detecting the endpoint detection signal, and stopping the etching
process when the endpoint detection signal is detected.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a block diagram of a system in accordance with the
present invention in which the contact dielectric etching is
incomplete.
[0016] FIG. 2 is a block diagram of a system in accordance with the
present invention in which the contact dielectric etching is
complete.
[0017] FIG. 3A is a graph showing the relationship between the
dielectric surface voltage and the selectable reference voltage for
an area of a semiconductor substrate that has not been completely
etched and an area of the semiconductor substrate that has been
completely etched.
[0018] FIG. 3B is a graph showing the endpoint detection signal in
an unetched area and an etched area.
[0019] FIG. 4 is a general flow diagram of the endpoint detection
process of the present invention.
[0020] FIG. 5 is a general flow diagram of a second embodiment of
the endpoint detection process of the present invention.
[0021] FIG. 6 is a general flow diagram of a method for real time
detection of the endpoint of a dielectric etching process in a
plasma environment of the present invention.
[0022] FIG. 7 is an illustration of a measurement system for
measuring the surface voltage of a semiconductor substrate in a
plasma etch chamber using a voltage probe.
[0023] FIG. 8A is an illustration of a system for sensing a
substrate current in a substrate having partially etched
contacts.
[0024] FIG. 8B is an illustration of a system for sensing a
substrate current in a substrate having etched contacts.
[0025] FIG. 8C is a graph of a substrate current versus time for a
plasma etch process of a substrate.
DETAILED DESCRIPTION OF THE INVENTION
[0026] In the following detailed description, reference is made to
the accompanying drawings which form a part hereof, and in which is
shown by way of illustration specific embodiments in which the
invention may be practiced. These embodiments are described in
sufficient detail to enable those skilled in the art to practice
the invention, and it is to be understood that other embodiments
may be utilized and that structural, logical and electrical changes
may be made without departing from the spirit and scope of the
present invention. The following detailed description is,
therefore, not to be taken in a limiting sense, and the scope of
the present invention is defined by the appended claims.
[0027] Embodiments of systems and methods in accordance with the
present invention shall be described with reference to FIGS. 1-8.
The embodiments of the systems and methods of the present invention
for identifying the completion of a dielectric etching process on a
semiconductor substrate are useful whenever contacts are etched in
a dielectric, and determining whether the contacts are cleared of
the dielectric is desired. Embodiments of the present invention can
also be used in connection with processes that make use of
protective oxides, sacrificial oxides, nitrides,
borophosphosilicate glasses (BPSG), silicon-dioxides,
silicon-nitrides, and tetra-ethyl-ortho-silicates (TEOS).
[0028] As shown in FIG. 1, in one embodiment of the present
invention system 100 comprises voltage probe 110, selectable
reference voltage 120, and comparator 130.
[0029] Voltage probe 110 measures surface voltage 140 of dielectric
150 on semiconductor substrate 155 after a dielectric etching
process. As one skilled in the art will recognize, any device that
can sense surface voltage 140 of dielectric 150 is suitable for use
in the present invention. In one embodiment, a non-contact Kelvin
Probe is used to sense surface voltage 140. A Kelvin Probe is a
non-contact, non-destructive vibrating capacitor device used to
measure the work function difference, or for non-metals, the
surface potential, between a conducting specimen and a vibrating
tip. Kelvin Probes are known to practitioners in the art of
integrated circuit manufacturing.
[0030] A reference voltage, such as selectable reference voltage
120 is set to a value that corresponds to surface voltage 140 of
dielectric 150 when contact site 160 is cleared of the dielectric
during an etching process. The precise value for a given
manufacturing step can be determined by measuring surface voltage
140 of dielectric 150 at the completion of a dielectric etching
process and then verifying that contact site 160 is cleared of the
dielectric using a scanning electron microscope. The precise value
of the selectable reference voltage can depend on the physical
parameters of the etching process, such as the initial depth of
dielectric 150, the number of contact sites 160 in dielectric 150,
and the aggressiveness of the etching process. In a typical
process, with a dielectric thickness of one thousand angstroms,
selectable reference voltage 120 can have a value of between
one-half volt and two volts.
[0031] Comparator 130, in one embodiment, is coupled to voltage
probe 110 and selectable voltage reference 120 for the purpose of
generating endpoint detection signal 170 shown as a time-voltage
magnitude graph. Comparator 130, in one embodiment, is an analog
device with an analog output, and compares the voltage measured by
voltage probe 110 with selectable reference voltage 120. Endpoint
detection signal 170 indicates whether the voltage measured by
voltage probe 110 is greater than or less than selectable reference
voltage 120. In an alternate embodiment, comparator 130 is an
analog integrated circuit comparator. In another embodiment,
comparator 130 is a digital comparator. In still another
embodiment, comparator 130 is a person who compares the surface
voltage indicated by voltage probe 110 to selectable voltage
reference 120. The digital comparator can be implemented in a
microprocessor, as a combination of hardware and software, or
strictly in hardware. An analog comparator is preferable when
voltage probe 110 and selectable reference voltage 120 generate
analog voltage output signals, a digital comparator is preferable
when selectable reference voltage 120 and voltage probe 110
generate digital output signals, and a human comparator is
preferable when voltage probe 110 provides a visual displays of the
voltages or a visual display of the relationship between the
voltages.
[0032] FIG. 2 shows the system of FIG. 1 with like components
labeled with like reference numerals. A difference between FIG. 1
and FIG. 2 is that in FIG. 1 contact site 160 is not cleared of the
dielectric, while in FIG. 2 contact site 260 is cleared of the
dielectric. Another difference is that surface voltage 240 of FIG.
2 has a value different from the value of surface voltage 140 of
FIG. 1. Still another difference is that FIG. 2 shows endpoint
detection signal 270 as a time-voltage magnitude graph assuming a
positive voltage level, which indicates that contact 260 is cleared
of the dielectric. Whereas, FIG. 1 shows endpoint detection signal
170 assuming a low voltage level, indicating that contact 160 is
not cleared of the dielectric.
[0033] FIG. 3A shows in graphical form the relationship between
surface voltage 140 of FIG. 1 and selectable reference voltage 120
in an area of a semiconductor substrate that has not been
completely etched, unetched area 180, and the relationship between
surface voltage 240 of FIG. 2 and selectable reference voltage 120
in an area of a semiconductor substrate that has been completely
etched, etched area 190. In the unetched area 180, which is related
to FIG. 1, the etching process has not cleared dielectric 150 from
contact site 160. As shown in FIG. 3A, in the unetched area 180,
surface voltage 140 is greater than selectable reference voltage
120, and as shown in FIG. 3B, endpoint detection signal 170 is at a
low level. In etched area 190, which is related to FIG. 2, the
etching process has cleared dielectric 250 from contact site 260.
Also, as shown in FIG. 3A, in etched area 190, surface voltage 240
is less than selectable reference voltage 120, and as shown in FIG.
3B endpoint detection signal 270 is at a high level. Endpoint
detection signal 170 may be implemented in positive logic as in
FIG. 3B or in negative logic, in which case the polarity of
endpoint detection signal 170 is complemented.
[0034] In operation, surface voltage 140 and surface voltage 240
stabilize after the etching process completes. In some
manufacturing process environments, stabilization occurs a few
minutes after completion of the etching process, while in other
environments stabilization may not occur for an hour or more after
completion of the etching process. The actual stabilization time is
determined empirically for each process etch step in the
manufacturing of a particular product and may depend on
environmental factors. After stabilization, system 100 measures
surface voltage 140 as shown in FIG. 1 or surface voltage 240 as
shown in FIG. 2. After the measurement is taken, system 100
compares the measured value to selectable reference voltage 120.
Selectable reference voltage 120, of FIG. 2, is set to a value that
can be obtained empirically and is related to the surface voltage
240 of the dielectric 250 when the contact site 260 is cleared of
the dielectric. If the contact site 160, of FIG. 1, is not cleared
of the dielectric, then, as illustrated in FIG. 1, the endpoint
detection signal is maintained at a low level. If the contact site
260, of FIG. 2, is cleared of the dielectric, then, as illustrated
in FIG. 2, the endpoint detection signal 270 assumes a high level,
indicating that the dielectric etching process completed
successfully. An advantage of system 100 is that at the completion
of the dielectric etching process, system 100 makes determining the
success or failure of the process relatively easy.
[0035] An embodiment of a method in accordance with the present
invention is shown in FIG. 4. Method 400 for identifying the
completion of a dielectric etching process includes setting 410,
measuring 420, comparing 430, and identifying 440 operations. In
the setting 410 operation, a selectable reference voltage is set to
a surface voltage value, which indicates that the dielectric at the
contacts is cleared. In the measuring 420 operation, a voltage
probe measures the surface voltage of the dielectric after the
dielectric etching process in order to obtain the value of the
surface voltage prior to the comparing 430 operation. The measuring
420 operation is preferably performed after the surface voltage has
stabilized following the etching process. The surface voltage,
after the etching process, is an indicator of whether the etching
process completely etched the dielectric at the contact site. In
the comparing 430 operation, the measured surface voltage is
compared to the selectable reference voltage. And in the
identifying 440 operation, when the measured voltage is less than
the selectable reference voltage, an indicator of whether the
dielectric etching process completed successfully is generated.
[0036] An advantage of this embodiment is that it can be tailored
to dielectric etching steps at any point in the manufacturing
process. This is accomplished by determining the reference voltage
for a given process through measuring the surface voltage after the
completion of the process and stabilization of the surface voltage,
and by verifying that the contact site is cleared. One method of
verifying that the contact site is cleared is to observe the
contact site using a scanning electron microscope.
[0037] An alternate embodiment of the present invention is shown in
FIG. 5. The method includes setting 510, measuring 520, averaging
545 comparing 530, and identifying completion 540 operations. As
will be recognized by those skilled in the art, it is possible for
a single measurement to be in error. So, for the purpose of
increasing the accuracy and reliability of the measurement of the
surface voltage, the embodiment shown in FIG. 5 adds the averaging
545 operation for averaging multiple surface voltage measurements.
The number of measurements to average may be determined empirically
using methods known in the art.
[0038] In another embodiment of the present invention, a further
improvement in the surface voltage dielectric measurement process
is achieved when the measurements are made at multiple locations on
the dielectric. As will be appreciated by those skilled in the art,
local process variations in the semiconductor manufacturing process
are common and can be accounted for by making multiple measurements
at different locations on the surface of the substrate.
[0039] FIG. 6 shows a general flow diagram of method 600, a real
time embodiment of the present invention. An advantage of the
embodiment of method 600 is that time is not wasted making
measurements after completion of the dielectric etching process.
Method 600 comprises placing 610, setting 620, etching 630,
measuring 640, generating 650, detecting 660, and stopping 670
operations.
[0040] Referring to FIG. 6, the placing 610 operation requires
placing a substrate having a dielectric to etch within a plasma
etch chamber. The setting 620 operation requires setting a
selectable reference voltage as described in the previous
embodiments of the invention. In one embodiment of the present
invention, the selectable reference voltage is set to a value
approximately equal to the surface voltage of the dielectric when a
contact site is cleared of the dielectric. The etching 630
operation requires etching the dielectric in the plasma etch
chamber. The measuring 640 operation requires measuring the surface
voltage of the dielectric. Any method known to those skilled in the
art for measuring a surface voltage in real time is suitable for
use in connection with the present invention. The generating 650
operation requires generating an endpoint detection signal when the
measured surface voltage is less than the selectable reference
voltage. The endpoint detection signal is generated by a comparator
as described in the previously described embodiments of the
invention. The detecting 660 operation requires detecting the
endpoint detection signal. In a positive logic system, the endpoint
detection signal is detected by identifying the time when the
endpoint detection signal goes positive. The stopping 670 operation
requires stopping the etching process when the endpoint detection
signal is detected. Purging the plasma chamber or removing the
substrate from the plasma etch chamber stops the etching
process.
[0041] FIG. 7 shows a measurement system 700 for measuring the
surface voltage or a substrate current of substrate 715 in plasma
etch chamber 705 using probe 710. The present invention can be
practiced in connection with a variety of embodiments of probe 710.
For example, in one embodiment, probe 710 is a voltage probe, in
another embodiment probe 710 is a circuit capable of sensing
current or the rate of change of a current signal, in still another
embodiment probe 710 is an ammeter or a calibrated ammeter, and in
yet another embodiment probe 710 is a computer system capable of
measuring current or the rate of change of a current signal.
[0042] Various embodiments of processes and systems for measuring
the surface voltage have been described above. Some of these
processes and methods can be used in connection with the
measurement of a surface voltage of semiconductor substrate 715.
Measurement system 700 has the advantage that semiconductor
substrate 715 is not removed from plasma etch chamber 705 before
making a surface voltage measurement, and therefore reduces the
overall manufacturing time for the substrate.
[0043] Referring to FIG. 8A, in current sensing system 800, plasma
ions 803 are capable of inducing a current 806 in substrate 809.
Substrate 809 is not limited to a particular material. In one
embodiment, substrate 809 is a semiconductor, such as silicon. In
an alternate embodiment, substrate 809 is gallium arsenide. As long
as the plurality of contacts, such as contact 812 and contact 815,
are not cleared of material 818, current 806 is likely to be
relatively small, in the range of picoamperes. Current 806 is
sensed by current sense device 821, which can assume a variety of
embodiments. For example, current sense device 821 can be a
circuit, an ammeter, a calibrated ammeter, or a computer system
capable of sensing current. Material 818 is generally a dielectric.
Types of dielectrics suitable for use in connection with the
present invention include oxides, nitrides, borophosphosilicate
glasses (BPSG), silicon-dioxides, silicon-nitrides, and
tetra-ethyl-ortho-silicates (TEOS).
[0044] Referring to FIG. 8B, in current sensing system 823, as
contacts 827 and 830 are cleared, substrate current 833, which is
induced by plasma ions 836, increases to a relatively large value
in the range of microamperes or milliamperes. This current can be
measured using current sense device 839. In one embodiment, current
sense device 839 is a circuit. In another embodiment, current sense
device 839 is an ammeter. In yet another embodiment, current sense
device 839 is a computer system capable of sensing current.
[0045] Referring to FIG. 8C, a substrate current versus time graph
841 shows the increase in current along line 844 as time changes
from the beginning of an etch process at time zero 847 until etch
finish time 850. At etch finish time 850, the rate of change of the
current approaches zero. In one embodiment of the present
invention, this rate of change is detected to identify etch finish
time 850. In an alternate embodiment, etch finish time 850 is
detected by empirically determining the current value at which the
etch process is complete. Substrate current at etch process time
zero 847 is on the order of picoamperes and at etch finish time 850
substrate current is on the order of microamperes or milliamperes.
As described above, the substrate current value at etch finish time
850 is determined by etching a substrate, measuring the substrate
current, and verifying that the contacts are cleared using a
scanning electron microscope.
[0046] It is to be recognized that the above description is
intended to be illustrative, and not restrictive. Many other
embodiments will be apparent to those of skill in the art upon
reviewing the above description. The scope of the invention should,
therefore, be determined with reference to the appended claims,
along with the full scope of equivalents to which such claims are
entitled.
Conclusion
[0047] The identification by the applicant of the relationship
between the dielectric etching process and the surface voltage, and
the real time relationship between the dielectric etching process
and the substrate current, permits the above described embodiments
of the present invention. The embodiments exploit the process
insight that as a contact site is cleared of dielectric, the
surface voltage of the dielectric decreases, and that in real time
as a contact site is cleared of dielectric, the substrate current
increases.
[0048] Although specific embodiments have been illustrated and
described herein, it will be appreciated by those of ordinary skill
in the art that any arrangement which is calculated to achieve the
same purpose may be substituted for the specific embodiment shown.
This application is intended to cover any adaptations or variations
of the present invention. Therefore, it is manifestly intended that
this invention be limited only by the claims and the equivalents
thereof.
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