U.S. patent application number 10/141969 was filed with the patent office on 2002-10-03 for method and apparatus for etching a workpiece.
Invention is credited to Boman, Lee Campbell, McQuarrie, Andrew Duncan.
Application Number | 20020142599 10/141969 |
Document ID | / |
Family ID | 10812209 |
Filed Date | 2002-10-03 |
United States Patent
Application |
20020142599 |
Kind Code |
A1 |
McQuarrie, Andrew Duncan ;
et al. |
October 3, 2002 |
Method and apparatus for etching a workpiece
Abstract
An XeF.sub.2 source includes an XeF.sub.2 source chamber having
a tray or ampoule for XeF.sub.2 crystals, a reservoir coupled to
the XeF.sub.2 source chamber via a valve, a flow controller fed by
the reservoir and a valve between the reservoir and the flow
controller. Pressure sources are provided respectively to maintain
the reservoir and the source chamber at the sublimation pressure of
XeF.sub.2. The arrangement allows for a steady supply of XeF.sub.2
to an etching chamber.
Inventors: |
McQuarrie, Andrew Duncan;
(San Jose, CA) ; Boman, Lee Campbell; (Belmont,
CA) |
Correspondence
Address: |
VOLENTINE FRANCOS, PLLC
SUITE 150
12200 SUNRISE VALLEY DRIVE
RESTON
VA
20191
US
|
Family ID: |
10812209 |
Appl. No.: |
10/141969 |
Filed: |
May 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10141969 |
May 10, 2002 |
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09065622 |
Apr 24, 1998 |
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6409876 |
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Current U.S.
Class: |
438/689 ;
438/690 |
Current CPC
Class: |
H01J 37/3244
20130101 |
Class at
Publication: |
438/689 ;
438/690 |
International
Class: |
H01L 021/302; H01L
021/461 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 1997 |
GB |
9709659.8 |
Claims
1. A method of etching a workpiece using XeF.sub.2, comprising
allowing solid XeF.sub.2 to subliminate into its gaseous state into
a reservoir of sufficient volume to provide gas at a pre-determined
flow rate for a pre-determined etch period, supplying the gas at
the desired flow rate to an etching chamber containing the
workpiece and etching the workpiece.
2. A method as claimed in claim 1 wherein XeF.sub.2 gas is mixed
with an inert carrier gas prior to its introduction into the etch
chamber.
3. A method as claimed in claim 1 or claim 2 wherein the XeF.sub.2
source continues to subliminate going outward flow from the
reservoir.
4. A method as claimed in any one of claims 1 to 3 including
recharging the reservoir between etches.
5. A method as claimed in any one of the preceding claims wherein
the flow rate is controlled on a pressure basis.
6. Apparatus for etching a workpiece comprising an etch chamber, a
XeF.sub.2 source, a reservoir, valve means for connecting the
source to the reservoir to allow sublimination of the source into
XeF.sub.2 gas, a flow control of the feeding of the etch chamber
and valve means for connecting the reservoir to the flow
controller.
7. Apparatus as claimed in claim 6 further including pressure
control means for maintaining the reservoir at approximately
sublimination pressure of XeF.sub.2 when there is no outward flow
from the reservoir.
8. Apparatus as claimed in claim 6 or claim 7 further comprising
means for mixing the XeF.sub.2 gas with an inert carrier gas prior
to its introduction into the process.
9. Apparatus as claimed in any one claim 6 to 8 when the flow
controller is a pressure based flow controller.
Description
[0001] This invention relates to methods and apparatus for etching
a workpiece using Xenon Difluoride (XeF.sub.2) Xenon Difluoride is
a dry isotropic gas phase etchant, which provides a gentle etch for
silicon at low temperature. Xenon Difluoride is usually supplied in
the form of colourless crystals which sublime without
decomposition. The sublimation pressure for XeF.sub.2 is
approximately 4 Torr.
[0002] Present attempts to use XeF.sub.2 for etching have been
essentially experimental and have taken place using a pulsed supply
of XeF.sub.2 which requires the etch to be stopped and started with
the etch chamber being pumped down between each etch step. Such an
arrangement is impracticable for production processes. Direct flow
has been attempted unsuccessfully.
[0003] From one aspect the invention consists in a method of
etching a workpiece using XeF.sub.2, comprising allowing XeF.sub.2
in its solid phase to sublimate into its gaseous state into a
reservoir of sufficient volume to provide gas at a predetermined
flow rate for a pre-determined etch period, supplying the gas at
the desired flow rate to an etching chamber containing the
workpiece and etching the workpiece.
[0004] The XeF.sub.2 gas may be mixed with an inert carrier gas
prior to its introduction into the etch chamber. It is particularly
preferred that the XeF.sub.2 source continues to sublimate during
the outward flow of XeF.sub.2 from the reservoir. Additionally or
alternatively the reservoir may be recharged between the etching of
separate workpieces.
[0005] From a further aspect the invention consists in apparatus
for etching a workpiece comprising, an etched chamber, a XeF.sub.2
source, a reservoir, valve means for connecting the source to the
reservoir to allow sublimination of the source into XeF.sub.2 gas,
a flow controller for feeding the etch chamber and valve means for
connecting the reservoir to the flow controller.
[0006] Preferably the apparatus includes pressure control means for
maintaining the reservoir at approximately the sublimination
pressure of XeF.sub.2 when there is no outward flow from the
reservoir. Means may be provided for mixing the XeF.sub.2 gas with
an inert carrier gas prior to its introduction into the process
chamber. It is particularly preferred that the flow controller is a
pressure-based flow controller.
[0007] A chamber will normally be provided for the solid XeF.sub.2
and conveniently the reservoir may have a volume which is
approximately three times the volume of the XeF.sub.2 chamber.
[0008] Although the invention has been described above, it is to be
understood that it includes any inventive combination of the
features set out above or in the following description.
[0009] The invention may be performed in various ways and a
specific embodiment will not be described, by way of example,
reference to the accompanying drawing, which is a schematic view of
etching apparatus.
[0010] Etching apparatus is generally indicated at 10 and comprises
at etch chamber 11, a XeF.sub.2 supply generally indicated at 12, a
flow controller 13, a roughing pump assembly, generally indicated
at 14, and a carrier gas supply 15.
[0011] The XeF.sub.2 supply comprises a XeF.sub.2 source chamber
16, which includes a tray or ampoule 17 for the XeF.sub.2 crystals
17a. The source chamber 16 is connected to a reservoir 18 via a
valve 19, which in turn is connected to the flow controller 13 by a
valve 20. Pressure sources 21 and 22 are provided to respectively
maintain the reservoir 18 and source chamber 16 at approximately 4
Torr which is the sublimination pressure of XeF.sub.2. Downstream
of the controller 13 is a valve 23 which connects the flow
controller to a supply line 24 between valves 25 and 26. Valve 25
controls the flow of the carrier gas from supply 15 into the supply
line 24, whilst valve 26 controls the supply of gases in the supply
line 24 to an etch chamber 27 of the etching apparatus 11. As is
conventional the roughing pump installation 14 is connected
downstream of the etch chamber 27, but it is also connected to the
source chamber 16 via bypass 28. A line 29 and valve 30 allows
carrier gas to be supplied to this region for purging purposes.
[0012] In this the XeF.sub.2 crystals are placed in the ampoule or
tray 17 with the valve 19 closes and valve 30 open. Carrier gas is
used to purge the chamber and the roughing pump assembly 14 pumps
the source down to the sublimination pressure. The roughing pump
assembly and carrier gas are then isolated and valve 19 is opened
allowing XeF.sub.2 gas to expand or diffuse into the reservoir
18.
[0013] A wafer is then loaded into the etch chamber 27 using
conventional apparatus and valves 20, 23, 25 and 26 open
sequentially to allow XeF.sub.2 and the carrier gas into the etch
chamber where etching occurs spontaneously. The pressure within the
chamber is controlled by the roughing pump assembly 14 and its
automatic pressure control valve 14a. On certain occasions carrier
gas may not be required in which case valve 25 remains closed.
[0014] Valve 19 may be open or closed, depending on the process and
production levels which are required. A optical detector generally
indicated at 31 determines when the etch has been completed or
alternatively a time basis may be used. Upon completion of the etch
valves 20, 23, 25 and 26 are shut and the wafer is removed. By the
time a new wafer is introduced into the chamber for etching the
reservoir 18 is re-charged and thus not only can each water be
fully etched in one process, continuous etching of wafers is
achieved. Continuous delivery of XeF.sub.2 also enhances uniformity
and the use of a pressure based flow control mechanism 13 is
considerably beneficial over say mass flow measurement. It will be
noted that the process chamber pressure control is independent of
the flow control mechanism for XeF.sub.2.
* * * * *