U.S. patent application number 12/095626 was filed with the patent office on 2009-03-12 for pulsed-continuous etching.
This patent application is currently assigned to XACTIX, INC.. Invention is credited to Kyle S. Lebouitz, David L. Springer.
Application Number | 20090065477 12/095626 |
Document ID | / |
Family ID | 38092791 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090065477 |
Kind Code |
A1 |
Lebouitz; Kyle S. ; et
al. |
March 12, 2009 |
PULSED-CONTINUOUS ETCHING
Abstract
In a system and method of etching a sample disposed in an
etching chamber, a plurality of separately stored charges of an
etching gas is discharged, one at a time, into a sample etching
chamber. The discharge of each charge of etching gas occurs such
that a momentary overlap exists in the end discharge of one charge
of etching gas with the beginning discharge of another charge of
etching gas, whereupon the desired flow of etching gas into the
etching chamber is maintained. During discharge of one charge of
etching gas, a previously discharged charge of etching gas is
recharged. The process of discharging a plurality of separately
stored charges of an etching gas, one at a time, and recharging at
least one previously discharged charges of etching gas during the
discharge of at least one charge of etching gas continues until the
sample is etched to a desired extent.
Inventors: |
Lebouitz; Kyle S.;
(Pittsburgh, PA) ; Springer; David L.;
(Pittsburgh, PA) |
Correspondence
Address: |
THE WEBB LAW FIRM, P.C.
700 KOPPERS BUILDING, 436 SEVENTH AVENUE
PITTSBURGH
PA
15219
US
|
Assignee: |
XACTIX, INC.
Pittsburgh
PA
|
Family ID: |
38092791 |
Appl. No.: |
12/095626 |
Filed: |
November 30, 2006 |
PCT Filed: |
November 30, 2006 |
PCT NO: |
PCT/US06/45879 |
371 Date: |
August 6, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60741517 |
Dec 1, 2005 |
|
|
|
Current U.S.
Class: |
216/59 ;
156/345.26 |
Current CPC
Class: |
H01L 21/3065
20130101 |
Class at
Publication: |
216/59 ;
156/345.26 |
International
Class: |
B44C 1/22 20060101
B44C001/22; C23F 1/08 20060101 C23F001/08 |
Claims
1-19. (canceled)
20. A method of etching a sample via an etching system having an
etching gas source, a main chamber where etching of a sample
occurs, a first expansion chamber, a second expansion chamber, and
means for connecting each expansion chamber to the main chamber and
the source of etching gas, the method comprising: (a) controlling
the means for connecting to charge the first expansion chamber with
a suitable amount of etching gas from the etching gas source to
sustain a constant flow of etching gas to the main chamber, and
once charged is isolated therefrom; (b) controlling the means for
connecting to connect the charged first expansion chamber to the
main chamber, whereupon the charge of etching gas in the first
expansion chamber flows to the main chamber such that the pressure
of etching gas inside the first expansion chamber decreases; (c)
while etching gas in the first expansion chamber is flowing to the
main chamber, controlling the means for connecting such that the
second expansion chamber is charged with a suitable amount of
etching gas from the etching gas source to sustain a constant flow
of etching gas to the main chamber, and once charged is isolated
therefrom; (d) following step (c), controlling the means for
connecting to isolate the first expansion chamber from the main
chamber and to connect the second expansion chamber to the main
chamber before a pressure of the etching gas in the first expansion
chamber decreases below a level sufficient to sustain a constant
flow of etching gas to the main chamber; (e) following step (d),
while etching gas in the second expansion chamber is flowing to the
main chamber, controlling the means for connecting such that the
first expansion chamber is charged with a suitable amount of
etching gas from the etching gas source to sustain a constant flow
of etching gas to the main chamber, and once charged is isolated
therefrom; and (f) following step (e), controlling the means for
connecting to isolate the second expansion chamber from the main
chamber and to connect the first expansion chamber to the main
chamber before the pressure of the etching gas in the second
expansion chamber decreases below a level sufficient to sustain a
constant flow of etching gas to the main chamber.
21. The method of claim 20, further including repeating steps
(c)-(f).
22. The method of claim 20, wherein, in steps (d) and (f), the
means for connecting is controlled to simultaneously connect the
first and second expansion chambers to the main chamber.
23. The method of claim 22, wherein the first and second expansion
chambers are simultaneously connected to the main chamber
momentarily.
24. The method of claim 22, wherein: the etching system includes
means for preventing etching gas from flowing from the first
expansion chamber to the second expansion chamber, and vice versa,
when the first and second expansion chambers are simultaneously
connected to the main chamber; in step (d), the means for
preventing is operative for preventing the flow etching gas from
the second expansion chamber into the first expansion chamber when
the first and second expansion chambers are simultaneously
connected to the main chamber; and in step (f), the means for
preventing is operative for preventing the flow etching gas from
the first expansion chamber into the second expansion chamber when
the first and second expansion chambers are simultaneously
connected to the main chamber.
25. The method of claim 20, wherein, at least one of step (a), step
(c) and step (e) includes controlling the means for connecting to
charge the corresponding expansion chamber with an inert gas from
an inert gas source coupled to the means for connecting.
26. The method of claim 25, wherein the inert gas is nitrogen,
helium, argon, xenon or some combination thereof.
27. A vapor etching system comprising: a source of etching gas; a
main chamber where etching of a sample occurs; a first expansion
chamber; a second expansion chamber; means for connecting each
expansion chamber to the main chamber and the source of etching
gas; and a controller operative for performing the steps of: (a)
controlling the means for connecting to connect the first expansion
chamber to the source of etching gas to be charged with a suitable
amount of etching gas to sustain a constant flow of etching gas to
the main chamber when connected thereto, and once charged to be
isolated therefrom; (b) controlling the means for connecting to
connect the charged first expansion chamber to the main chamber,
whereupon the charge of etching gas in the first expansion chamber
flows to the main chamber and the pressure of etching gas inside
the first expansion chamber decreases, and to connect the second
expansion chamber to the source of etching gas to be charged with a
suitable amount of etching gas to sustain a constant flow of
etching gas to the main chamber when connected thereto, and once
charged to be isolated therefrom; and (c) following step (b),
controlling the means for connecting to connect the charged second
expansion chamber to the main chamber, whereupon the charge of
etching gas in the second expansion chamber flows to the main
chamber and the pressure of etching gas inside the second expansion
chamber decreases, and to connect the first expansion chamber to
the source of etching gas to be charged with a suitable amount of
etching gas to sustain a constant flow of etching gas to the main
chamber when connected thereto, and once charged to be isolated
therefrom.
28. The system of claim 27, wherein the controller is further
operative for repeating steps (b) and (c).
29. The system of claim 28, wherein: step (c) includes the second
expansion chamber being connected to supply etching gas to the main
chamber before the pressure of the etching gas in the first chamber
decreases below a level sufficient to sustain a constant flow of
etching gas to the main chamber; and when an instance of step (b)
follows an instance step (c), step (b) includes the first expansion
chamber being connected to supply etching gas to the main chamber
before the pressure of the etching gas in the second chamber
decreases below a level sufficient to sustain a constant flow of
etching gas to the main chamber.
30. The system of claim 29, wherein: step (c) includes the first
and second expansion chambers being both momentarily connected to
the main chamber; and when an instance of step (b) follows an
instance step (c), step (b) includes the first and second expansion
chambers being both momentarily connected to the main chamber.
31. The system of claim 30, further including means for preventing
etching gas from flowing from the first expansion chamber to the
second expansion chamber, and vice versa, when the first and second
expansion chambers are both connected to the main chamber.
32. The system of claim 31, wherein the means for preventing
includes at least one of: a sensor for measuring a flow direction
of etching gas between the first and second expansion chambers,
said sensor coupled to the controller which is responsive thereto
for controlling the means for connecting to prevent the flow
etching gas from the first expansion chamber into the second
expansion chamber and vice versa; or at least one check valve
between the first and second expansion chambers.
33. The system of claim 27, further including at least one of:
means for controlling a rate of flow of gas into the main chamber;
or means for controlling a pressure of gas in the main chamber.
34. The system of claim 27, further including a source of mixing
gas(es), wherein the controller is operative for controlling the
means for connecting to selectively connect each expansion chamber
to the source of mixing gas(es).
Description
[0001] Vapor etching of semiconductor materials and/or substrates
is accomplished using gases such as xenon difluoride. Specifically,
in xenon difluoride etching, the xenon difluoride gas reacts with
solid materials such as silicon and molybdenum such that the
materials are converted to a gas phase and removed. This removal of
these materials is known as etching.
[0002] Adding non-etching gases have been described by Kirt Reed
Williams, "Micromachined Hot-Filament Vacuum Devices," Ph.D.
Dissertation, UC Berkeley, May 1997, p. 396.sup.1, U.S. Pat. No.
6,409,876, and U.S. Pat. No. 6,290,864, to the xenon difluoride can
offer improvements to the etch process. The advantages of using
non-etchant gases to xenon difluoride etching gas are noted in U.S.
Pat. No. 6,290,864 which include improved selectivity, which is the
ratio of etching of the material to be etched versus those
materials that are intended to remain and uniformity. Increases in
both of these parameters ultimately lead to improved yield. .sup.1
Kirt Reed Williams, "Micromachined Hot-Filament Vacuum Devices,"
Ph.D. Dissertation, UB Berkeley, May 1997, p. 396.
[0003] A common approach to xenon difluoride etching is through the
pulsed method of etching..sup.2 In this mode, xenon difluoride is
sublimated from a solid to a gas in an intermediate chamber,
referred to as an expansion chamber, which can then be mixed with
other gases. The gas(es) in the expansion chamber can then flow
into an etching chamber to etch the sample, referred to as the
etching step. The main chamber is then emptied through a vacuum
pump and this cycle, including the etching step, is referred to as
an etching cycle. These cycles are repeated as necessary to achieve
the desired amount of etching. .sup.2 Chu, P. B.; J. T. Chen; R.
Yeh; G. Lin; J. C. P. Huang; B. A. Warneke; K. S. J. Pister
"Controlled PulseEtching with Xenon Difluoride"; 1997 International
Conference on Solid State Sensors and Actuators--TRANSDUCERS '97,
Chicago, USA, June 16-19, p. 665-668
[0004] Alternatively, xenon difluoride etching can be accomplished
using a continuous method such as that described in McQuarrie et
al., U.S. Pat. No. 6,409,876 where single reservoir is connected to
a flow controller to provide a constant flow of xenon difluoride
gas to the sample to be etched. In addition, a means of mixing an
additional, inert, gas to the etch gas between the outlet side of
the flow controller and the inlet of the chamber is described.
[0005] Adding an additional gas, typically an inert or minimally
reacting gas, such as nitrogen, to the etching process, must be
accomplished keeping in mind the sublimation pressure of xenon
difluoride. Often, the partial pressure of the additional,
non-etching gas is higher than the sublimation pressure, which is
the pressure below which that xenon difluoride is a gas and above
which is a solid, of the xenon difluoride. At 25 C, the sublimation
pressure of xenon difluoride is approximately 4 torr. It is not
uncommon during pulsed etching to mix in high pressures of other
gases, such as nitrogen, into the expansion chamber, after the
expansion chamber has been filled with a few torr of xenon
difluoride, to high pressures such as 30 torr. However, in a
continuous process, such as that described in U.S. Pat. No.
6,409,876, the pressures of the additional gas mixed into the xenon
difluoride would have to be less than the pressure of the supplied
xenon difluoride gas. The reason for this limitation is that
additional gas pressures higher than the xenon difluoride pressure
between the outlet of the flow controller and inlet to the chamber
would cause the xenon difluoride to stop flowing through the
controller.
[0006] We herein describe a process sequence to allow the
continuous flowing of xenon difluoride gas with mixture of high
pressures of additional gases. To maintain long duration,
continuous etches, it uses multiple expansion chambers, which
allows one expansion chamber to be used for etching while the other
is being prepared.
[0007] The gases can be any inert gas such as helium, nitrogen, or
argon. Mixtures of inert gases are also possible. Note that the
term inert is used to refer to any gas that minimally reacts with
the etching chemistry and is also referred to as a non-etching
gas.
[0008] In addition, other vapor phased etching gases, such as
bromine trifluoride, could be used in addition to or in place of
xenon difluoride.
DETAILED DESCRIPTION OF THE INVENTION
[0009] Shown in FIG. 1, a vapor etching gas source 120, which is
usually a cylinder of gas, such as xenon difluoride, is connected
to a shutoff valve 1118. Shutoff valves 112 and 114 are connected
to expansion chambers 106 and 108 which are used as an intermediate
chamber to regulate the quantity of etching gas in each cycle. The
expansion chambers 106 and 108 can be optionally independently
evacuated through shutoff valves 111 and 115. The expansion
chambers 106 and 108 also have pressure sensors 105 and 107 which
are typically capacitance diaphragm gauges. In addition, the
expansion chambers have additional connections to shutoff valves
116 and 117 to allow mixing gases such as nitrogen to be mixed with
the xenon difluoride in the expansion chambers. In series with
shutoff valves 116 and 117 can also be a needle valve and
additional shutoff valves to provide additional control of the flow
of the incoming mixing gases.
[0010] The expansion chambers 106 and 108 are connected to the main
chamber 123 via a flow path that includes shutoff valves 109 and
110 which then split into two paths, one through a flow controller
101 with additional shutoff valves 100 and 102 or another which
bypasses the flow controller 101 via shutoff valve 104. The flow
controller is one that is designed for controlling flow with low
pressure drops such as those designed for SDS, or Safe Delivery
Systems, like those provided by Celerity.
[0011] Xenon difluoride gas can also be introduced into the main
chamber 123 without flowing through the expansion chambers 106 or
108 by flowing directly through shutoff valve 113.
[0012] The main chamber can be vented, or filled with an inert gas
to raise the pressure to atmosphere for opening, via shutoff valve
103. This shutoff valve could alternatively be located on the flow
path to the chamber on the other side of shutoff valve 104.
[0013] The main chamber pressure is monitored using a pressure
sensor 122 which is preferably a capacitance diaphragm gauge. The
pressure in the main chamber 123 is controlled using an automatic
pressure controller 124 which adjusts the conductance between the
main chamber 123 and the vacuum pump 126. Such pressure controllers
are available from MKS Instruments. The vacuum pump is preferably a
dry vacuum pump. In addition, the connection between the chamber
123 and the vacuum pump 126 can be fully isolated using vacuum
valve 125.
[0014] Not shown in the figures is that the system is controlled
using either a computer or other similar controller, such as a
programmable logic controller. Manual operation is possible but is
difficult.
[0015] Other modifications to the aforementioned system design are
envisioned such as those described in U.S. Pat. No. 6,887,337
(assigned to XACTIX) including, but not limited to, variable volume
expansion chambers, more than two expansion chambers, and multiple
gas sources. The addition of multiple gas sources is shown in FIG.
2 where additional gas source 121 and valve 119 have been added.
Additional gas sources could be added in a similar fashion.
[0016] In addition, the use of other noble gas fluorides, such as
krypton difluoride or halogen fluorides, such as bromine
trifluoride, are also considered for etching. In addition,
combinations of these gases are also considered.
[0017] A typical etching sequence is to load the sample into the
main chamber 123. The main chamber 123 is then evacuated through
opening vacuum valve 125 which connects the vacuum pump 126 to the
main chamber 123. Typically, the main chamber is pumped down to 0.3
Torr. The main chamber 123 may be further purged of atmosphere by
first closing vacuum valve 125, opening shutoff valves 103 and 104,
and flowing the venting gas, which is typically nitrogen, into the
chamber to approximately 400 Torr (anywhere from 1 Torr to 600 Torr
would be useful, though). These pumps and purges are repeated
typically three or more times to minimize moisture and undesired
atmospheric gases in the chamber 123. Most critically, moisture can
react with xenon difluoride and other etching gases to form
hydrofluoric acid which will attack non-silicon materials.
[0018] The etching sequence then proceeds generally as described in
FIG. 3. Expansion chamber one (106) is evacuated through shutoff
valve 111, typically to around 0.3 torr as monitored by 105, and is
then filled to the desired pressure of etching gas as monitored by
105 by opening and then closing shutoff valves 118 and 112.
Expansion chamber one can then be further filled with the
additional mixing gas to a specific pressure as monitored by 105 by
opening and then closing shutoff valve 116. The second expansion
chamber 108 can then be similarly prepared for use through the
control of shutoff valves 115, 118, 114, and 117 using 107 to
monitor the pressure.
[0019] The preparation of the second expansion chamber 108 can be
executed while the first expansion chamber 106 is being used for
etching. To use the first expansion chamber 106 for etching, the
flow controller 101 is set to a given flow rate, typically in the
range of a few standard cubic centimeters (sccm) of flow. The
pressure controller 124 is also set to reach a specified pressure,
typically around one torr. Etching commences by opening shutoff
valves 109, 100, 102, and 125. During this time, the flow of the
gas mixture will be controlled to the setpoint and the pressure in
the chamber will also rise to its setpoint. As the etch progresses,
the pressure in the expansion chamber 106 will fall and the flow
controller 101 will need to continue to open its control valve.
Once the valve is nearing approximately 90% of fully open, there is
sufficiently likelihood that the flow rate through the flow
controller 101 will begin to drop below the setpoint.
[0020] After the indication that the flow is about to drop below
the setpoint, shutoff valve 109 is then closed and shutoff valve
110 is then opened so that the etching gas mixture is coming from
expansion chamber two 108. Immediately following this change
between expansion chambers, expansion chamber one 106 is then
evacuated and refilled so that it is ready for use when expansion
chamber two 108 can no longer support sufficient etching gas
mixture flow. This cycle of alternating between expansion chambers
106 and 108 continues until the end of the desired etching time has
been reached.
[0021] It should be noted that although the valve position in the
flow controller 101 is one way to measure the capacity of an
expansion chamber to support a given flow, other means including
examining the pressure in the expansion chamber via sensors 105 or
107 is also possible. In the case of examining the expansion
chamber pressure, determinations from look-up tables, previous
results, or analytical models can be used to decide at what
pressure to switch between expansion chambers during an etch.
[0022] It should also be noted that during the switch between
expansion chambers that the pressure on the inlet side of the flow
controller will rapidly increase. To counteract this sudden
pressure jump, it may be necessary to make a preemptive adjustment
to the valve position in the flow controller 101 when switching
between expansion chambers. As described in U.S. Pat. No.
6,887,337, variable volume expansion chambers can be used which can
be collapsed in a continuous fashion to maintain a constant
pressure at the inlet of the flow controller 101. However, in this
case, it would be necessary to incorporate the percent that the
expansion chamber has been collapsed to decide when to switch
between expansion chambers. Specifically, when one expansion
chamber is nearing fully collapsed, the other expansion chamber
should be used. It should be noted that the pressure at the inlet
of the flow controller can be controlled by the speed at which the
expansion chamber is collapsed during the etch.
* * * * *