U.S. patent application number 09/905025 was filed with the patent office on 2001-11-08 for vapor drying system and method.
Invention is credited to Butler, Josh, Elsawy, Tamer, Hall, R. Mark.
Application Number | 20010037822 09/905025 |
Document ID | / |
Family ID | 26800867 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010037822 |
Kind Code |
A1 |
Elsawy, Tamer ; et
al. |
November 8, 2001 |
Vapor drying system and method
Abstract
The present apparatus is a method and system for treating and
drying the surface of an object. According to the described method,
with a wet object positioned in a vessel, a drying vapor is
introduced into the vessel. The drying vapor condenses on the
surface of the object and reduces the surface tension of the
residual process fluid, causing the residual process fluid to flow
off of the surface. In one embodiment, wet processing of the object
and a subsequent evacuation of process fluid is carried out in the
vessel prior to introduction of the drying vapor.
Inventors: |
Elsawy, Tamer; (Boise,
ID) ; Hall, R. Mark; (Meridian, ID) ; Butler,
Josh; (Kuna, ID) |
Correspondence
Address: |
Stallman & Pollock LLP
Suite 290
121 Spear Street
San Francisco
CA
94105
US
|
Family ID: |
26800867 |
Appl. No.: |
09/905025 |
Filed: |
July 13, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09905025 |
Jul 13, 2001 |
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09227637 |
Jan 8, 1999 |
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60103802 |
Oct 9, 1998 |
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Current U.S.
Class: |
134/30 ; 134/28;
134/902; 134/95.2; 134/98.1 |
Current CPC
Class: |
Y10S 134/902 20130101;
H01L 21/67028 20130101 |
Class at
Publication: |
134/30 ; 134/28;
134/902; 134/95.2; 134/98.1 |
International
Class: |
B08B 007/04 |
Claims
We claim:
1. A method of treating and drying the surface of an object,
comprising the steps of: (a) providing a vessel and at least one
object having a surface; (b) immersing the object in a process
fluid in the vessel; (c) discharging the process fluid from the
vessel, leaving residual process fluid on the surface of the
object; (d) after discharging the process fluid from the vessel,
introducing a drying vapor into the vessel, the drying vapor
condensing on the surface of the object and reducing the surface
tension of the residual process fluid, causing the residual process
fluid to flow off of the surface.
2. The method of claim 1 wherein the process fluid is deionized
water.
3. The method of claim 1 wherein the process fluid is hydrofluoric
acid.
4. The method of claim 1, further including the step of introducing
a heated gas into the vessel after step (d) to volatilize condensed
drying vapor from the surface.
5. The method of claim 1, wherein the method further includes the
step of, prior to step (b), generating the drying vapor at a
location remote from the vessel; and step (d) includes the step of
using a carrier gas to carry the drying vapor from the remote
location into the vessel.
6. The method of claim 5 wherein: step (a) further provides a
chamber fluidly coupled to the vessel, the chamber positioned
remotely from the vessel; the generating step includes the step of
heating a drying compound within the chamber to produce the drying
vapor; and step (d) includes passing the carrier gas through the
chamber to cause it to carry the drying vapor into the vessel.
7. The method of claim 1, wherein the method further includes the
step of reclaiming drying vapor from the vessel and condensing the
reclaimed drying vapor to a liquid form.
8. The method of claim 1 wherein the drying vapor is formed from
isopropyl alcohol.
9. A method of treating and drying the surface of an object,
comprising the steps of: (a) providing a vessel and at least one
object having a surface; (b) immersing the object in a liquid
chemical within the vessel to treat the object; (c) introducing a
rinse fluid into the vessel to rinse the chemical from the vessel
and from the surface of the object; (e) discharging the rinse fluid
from the vessel, leaving residual rinse fluid on the surface of the
object; (f) after discharging the rinse fluid from the vessel,
introducing a drying vapor into the vessel, the drying vapor
condensing on the surface of the object and reducing the surface
tension of the residual rinse fluid, causing the residual rinse
fluid to flow off of the surfaces.
10. The method of claim 9 further including the step of introducing
a heated gas into the vessel after step (d) to volatilize condensed
drying vapor from the surface.
11. The method of claim 9, wherein the method further includes the
step of, prior to step (b), generating the drying vapor at a
location remote from the vessel; and step (d) includes the step of
using a carrier gas to carry the drying vapor from the remote
location into the vessel.
12. The method of claim 11 wherein step (a) further provides a
chamber fluidly coupled to the vessel, the chamber positioned
remotely from the vessel; the generating step includes the step of
heating a drying compound within the chamber to produce the drying
vapor; and step (d) includes passing the carrier gas through the
chamber to cause it to carry the drying vapor into the vessel.
13. The method of claim 9, wherein the method further includes the
step of reclaiming drying vapor from the vessel and condensing the
reclaimed drying vapor to a liquid form.
14. The method of claim 9 wherein the drying vapor is formed from
isopropyl alcohol.
15. The method of claim 9 wherein the rinse fluid is deionized
water.
16. The method of claim 9 wherein the method includes the step of
rinsing the objects in ozonated water.
17. The method of claim 16, including the step of rinsing the
object with ozonated rinse fluid prior to step (d).
18. A method of treating and drying the surface of an object,
comprising the steps of: (a) providing a vessel, a remote chamber
fluidly coupled to but remote from the vessel, and at least one
object having a surface; (b) treating the object using a wet
processing procedure outside the vessel, to produce a wet object
having residual process fluid thereon; (c) positioning the wet
object in the vessel; (d) generating a drying vapor in the chamber;
and (e) passing a carrier gas through the chamber into the vessel,
the carrier gas carrying the drying vapor from the chamber into the
vessel, the drying vapor condensing on the surface of the object
and reducing the surface tension of the residual process fluid,
causing the residual process fluid to flow off of the surface.
19. The method of claim 18 wherein step (d) includes heating a
drying compound within the chamber to produce the drying vapor.
20. The method of claim 19 wherein the drying compound is heated to
a temperature below its boiling point.
21. The method of claim 18, wherein: step (a) further provides a
lid for the vessel, the lid including at least one inlet; the
method further includes the step of sealing the vessel using the
lid; and in step (e) the carrier gas and drying vapor are passed
into the vessel via the at least one inlet in the lid.
22. The method of claim 19 wherein the drying compound is isopropyl
alcohol.
23. The method of claim 18, wherein the method further includes the
step of reclaiming drying vapor from the vessel and condensing the
reclaimed drying vapor to a liquid form.
24. The method of claim 18, further including the step of
introducing a heated gas into the vessel after step (e) to
volatilize condensed drying vapor from the surface.
25. A method of treating and drying the surfaces of an object,
comprising the steps of: (a) providing a vessel and at least one
object having a surface; (b) immersing the object in a treatment
solution in the vessel, the treatment solution including
hydrofluoric acid; (c) discharging the treatment solution from the
vessel; (d) after the treatment solution has been fully discharged
from the vessel and without first rinsing the object, introducing a
drying vapor into the vessel, the drying vapor condensing on the
surface of the object and reducing the surface tension of the
residual treatment solution causing the residual treatment solution
to flow off of the surfaces.
26. The method of claim 25, further including the step of
introducing a heated gas into the vessel after step (d) to
volatilize condensed drying vapor from the surface.
27. The method of claim 25, wherein: the method further includes
the step of, prior to step (b), generating the drying vapor at a
location remote from the vessel; and step (d) includes the step of
using a carrier gas to carry the drying vapor from the remote
location into the vessel.
28. The method of claim 27 wherein step (a) further provides a
chamber fluidly coupled to the vessel, the chamber positioned
remotely from the vessel; the generating step includes the step of
heating a drying compound within the chamber to produce the drying
vapor, and wherein step (d) includes passing the carrier gas
through the chamber to cause it to carry the drying vapor into the
vessel.
29. The method of claim 28, wherein the method further includes the
step of reclaiming drying vapor from the vessel and condensing the
reclaimed drying vapor to a liquid form.
30. The method of claim 25 wherein the drying vapor is formed from
isopropyl alcohol.
31. The method of claim 25 wherein: step (a) further provides a lid
for the vessel, the lid including at least one inlet; the method
further includes the step of sealing the vessel using the lid; and
in step (d) the carrier gas and drying vapor are passed into the
vessel via the at least one inlet in the lid.
32. A method of treating and drying an object, comprising the steps
of: (a) providing a vessel having a moveable lid, the lid formed of
a plurality of walls joined together to form a bottomless
enclosure, and further providing an object having a surface; (b)
immersing the object in a process fluid in the vessel; (c) sealing
the vessel using the lid; (d) heating at least a portion of the lid
to a temperature above that of the process fluid; (e) discharging
the process fluid from the vessel, leaving residual process fluid
on the surface of the object; and (f) after the process fluid has
been fully discharged from the vessel, introducing a drying vapor
into the vessel, the drying vapor condensing on the surface of the
object and reducing the surface tension of the residual process
fluid, causing the residual process fluid to flow off of the
surface.
33. The method of claim 32, wherein the process fluid is rinse
fluid and wherein the method further comprises the steps of: prior
to step (b) suspending the lid above the vessel, immersing the
object in a chemical bath in the vessel, then discharging the
chemical from the vessel after immersing the object, and then
sealing the vessel using the lid.
34. The method of claim 33 wherein the step of suspending the lid
above the vessel creates a hood above the vessel for minimizing
escape of fumes from the vessel into the surrounding
atmosphere.
35. The method of claim 32 wherein the lid is provided to have at
least one inlet, and wherein step (f) includes introducing the
drying vapor into the vessel via the inlet in the lid.
36. The method of claim 32, further including the step of
introducing a purging gas into the vessel prior to introducing the
drying vapor.
37. The method of claim 31, further including the step of
introducing a heated gas into the vessel after step (f) to
volatilize condensed drying vapor from the surface of the
object.
38. An apparatus for treating and drying an object, the apparatus
comprising: a vessel, the vessel including an open top portion and
a lid moveable between a closed condition sealing the open top
portion and an opened condition leaving the open top portion
exposed, a dump opening formed in a lower portion of the vessel and
a dump door moveable between an opened condition permitting
discharge of fluid through the dump opening and a closed condition
sealing the dump opening, and a fluid inlet formed in a lower
portion of the vessel; a source of rinse fluid fluidly coupled to
the inlet by a fluid line; a source of process chemical fluidly
coupled to the fluid line; a drying vapor generation chamber
fluidly coupled to the vessel; and a condenser fluidly coupled to
the dump opening.
39. The apparatus of claim 38 further comprising: control means for
causing the vessel to be filled with rinse fluid from the source of
rinse fluid, for opening the dump door after a predetermined period
of time has lapsed following filling of the vessel with the rinse
fluid, and for causing the vessel to be filled with drying vapor
from the drying vapor generation chamber after the rinse fluid has
been discharged from the vessel.
40. The apparatus of claim 39 wherein: the lid includes a plurality
of fluid manifolds formed therein and a plurality of vapor inlets
fluidly coupled to the fluid manifolds; and the drying vapor
generation chamber is fluidly coupled to the fluid manifolds.
41. The apparatus of claim 38 wherein: the drying generation
chamber includes: an enclosed chamber, a heated surface within the
chamber for receiving a liquid drying compound to create a drying
vapor; and the apparatus further comprises a carrier gas source
fluidly coupled to the enclosed chamber.
42. The apparatus of claim 41 wherein: the lid includes a plurality
of fluid manifolds formed therein and a plurality of vapor inlets
fluidly coupled to the fluid manifolds; and the drying vapor
generation chamber is fluidly coupled to the fluid manifolds.
43. The apparatus of claim 38 wherein the source of chemical
includes: a chemical storage tank fluidly coupled to a bulk
chemical supply and proportioned to contain a first volume of
chemical; a dispense tank fluidly coupled to the chemical storage
tank, the dispense tank proportioned to contain a second volume of
chemical significantly smaller than the first volume of chemical; a
first valve between the chemical storage tank and the dispense
tank; a second valve between the dispense tank and the vessel; and
control means for opening the first valve for a predetermined
period of time to dispense a predetermined quantity of chemical
from the storage tank to the dispense tank, the predetermined
quantity corresponding to an amount needed to carry out a process
in the vessel, and further for opening the second valve to dispense
the predetermined quantity from the dispense tank into the
vessel.
44. The apparatus of claim 43 further including a secondary fluid
source fluidly coupled to the dispense tank, and a third valve
positioned between the secondary fluid source and the dispense
tank, the control means being further for controlling operation of
the third valve to permit a secondary fluid to mix with the
predetermined quantity of chemical to form a process solution.
45. An apparatus for drying an object comprising: a vessel having
an opening; a lid formed of a plurality of walls joined together to
form a bottomless enclosure, the lid moveable between a first
position sealing the opening in the vessel and a second position
permitting access to the vessel via the opening; a heating element
coupled to the walls of the lid; and a source of drying vapor
fluidly coupled to the vessel.
46. The apparatus of claim 45, wherein the vessel includes an
inlet, and wherein the apparatus further comprises a source of
rinse fluid fluidly coupled to the inlet.
47. The apparatus of claim 46, further comprising a source of
process chemical fluidly coupled to the inlet.
48. The apparatus of claim 46 wherein the vessel further includes a
dump opening formed in a lower portion of the vessel and a dump
door moveable between an opened condition permitting discharge of
fluid through the dump opening and a closed condition sealing the
dump opening.
49. The apparatus of claim 46 wherein the lid includes a drying
vapor inlet and wherein the source of drying vapor is fluidly
coupled to the drying vapor inlet.
50. The apparatus of claim 46 wherein the source of drying vapor
includes: an enclosed chamber having a heated surface for receiving
a liquid drying compound, the chamber remote from but fluidly
coupled to the vessel; and a source of carrier gas fluidly coupled
to the enclosed chamber.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 60/103,802, filed Oct. 9, 1998.
FIELD OF THE INVENTION
[0002] The present invention relates generally the field of systems
for processing and cleaning objects requiring a high level of
cleanliness, and more particularly to a dryer system and drying
process for drying such objects using a drying vapor.
BACKGROUND OF THE INVENTION
[0003] In certain industries there are processes that must be used
to bring objects to an extraordinarily high level of cleanliness.
For example, in the fabrication of semiconductor wafers, multiple
cleaning steps are typically required to remove impurities from the
surfaces of the wafers before subsequent processing. The cleaning
of a wafer, known as surface preparation, has for years been
performed by collecting multiple wafers into a batch and subjecting
the batch to a sequence of chemical and rinse steps and eventually
to a final drying step. A typical surface preparation procedure
involves bathing the wafers in an etch solution of HF and HCl to
remove surface oxidation and metallic impurities. Afterwards, the
wafers are thoroughly rinsed in high purity deionized water (DI) to
remove etch chemicals from the wafers. The rinsed wafers are then
dried using one of several known drying processes.
[0004] Currently, there are several types of tools and methods used
in industry to carry out the surface preparation process. The tool
most prevalent in conventional cleaning applications is the
immersion wet cleaning platform, or "wet bench." In wet bench
processing, a batch of wafers is dipped into a series of process
vessels, where certain vessels contain chemicals needed for clean
or etch functions, while others contain deionized water ("DI") for
the rinsing of these chemicals from the wafer surface. Megasonic
energy may be imparted to the wafers using piezoelectric
transducers coupled to one or more of the vessels in order to more
thoroughly clean the wafer surfaces. In the final process vessel,
the rinse fluid is removed from the wafer surface using a solvent
such as isopropyl alcohol (IPA). IPA is an organic solvent known to
reduce the surface tension of water.
[0005] In one IPA drying method, described in U.S. Pat. No.
5,226,242 (Schwenkler), wet substrates are moved into a sealed
vessel and placed in the processing region of the vessel. An IPA
vapor cloud is generated in a vapor-generating region of the vessel
and is directed into the processing region, where it removes water
from the wafers. This drying technology is highly effective in
removing liquid from the wafers, but is not easily adaptable to
single vessel systems in which chemical processing, rinsing, and
drying can be carried out in a single vessel.
[0006] Environmental concerns have given rise to efforts to improve
drying technology in a manner that minimizes IPA usage. One such
improved drying technology is the Marongoni technique, which is
illustrated schematically in FIG. 1. In one application of the
Marongoni technique, an IPA vapor is condensed on top of the rinse
water containing the wafers while the wafers are slowly lifted from
the processing vessel. The concentration of the dissolved vapor is
highest at the wafer surfaces S and lower at regions of the rinse
fluid that are spaced from the wafer surfaces. Because surface
tension decreases as IPA concentration increases, the surface
tension of the water is lowest at the wafer surface where the IPA
concentration is highest. The concentration gradient thus results
in "Marongoni flow" of the rinse water away from the surfaces of
the wafers as indicated by arrow A. Rinse water is thereby stripped
from the wafer surfaces, leaving the wafer surfaces dry.
[0007] Another application of the Marongoni technique is described
in U.S. Pat. No. 4,911,761 (McConnell), which describes a single
chamber system for cleaning, rinsing and drying wafers. As
described in the patent, a batch of wafers is placed into a single
closed vessel, and process fluids are passed from top to bottom
sequentially through the vessel. The method further employs a
process called "direct displacement drying" to dry the wafers after
the final rinse. The drying step is accomplished using an IPA
drying vapor introduced into the vessel as the rinse fluid is
slowly drained. The IPA vapor displaces the receding rinse water
and condenses on the surface of the rinse water in the vessel,
creating Marongoni flow from the wafer surfaces into the receding
rinse water and resulting in dry wafers.
[0008] While providing satisfactory drying results and reducing IPA
usage, the direct displacement drying method leaves further room
for improvement. For example, because this process relies in part
on the pulling (or surface tension) by the descending rinse fluid
in the process vessel, it is not adaptable to systems in which
rinsing is carried out in a separate vessel and then transferred
into a drying vessel. Moreover, the rate at which the deionized
water is drained from the vessel must be closely controlled to
achieve full benefit of the Marongoni effect.
[0009] In a cleaning and drying process described in U.S. Pat. No.
5,571,337 (Mohindra), wafers within a vessel are exposed to process
chemicals and subsequently rinsed in DI water to remove residual
chemicals. After rinsing, an IPA cleaning step is carried out which
utilizes Marongoni flow to remove remaining particles from the
wafer surface. This cleaning step involves directing an IPA vapor
into the vessel while the DI rinse water is slowly drained,
creating Marongoni flow from the wafer surfaces into the receding
rinse water. According to the patent, if the rate at which the
rinse water recedes is carefully controlled, this flow can be made
to carry residual particles away from the wafer surfaces and
results in cleaner wafers. In addition to cleaning particles from
the wafers, the Marongoni flow during the IPA step removes a
substantial amount of rinse water from the wafers. However, water
droplets remain on the wafer surfaces at the end of the IPA step,
and so hot nitrogen gas is directed onto the wafers to evaporate
the residual water droplets. While this process is desirable in
that it reduces IPA usage over conventional drying processes, the
residual water droplets are problematic in that they may leave
impurities on the wafer surfaces.
[0010] An object of the present invention is thus to provide an
improved drying method and apparatus which is thorough, which
minimizes solvent usage, and which is highly adaptable for use in a
variety of surface preparation systems and processes.
SUMMARY OF THE INVENTION
[0011] The present apparatus is a method and system for treating
and drying the surface of an object. According to the described
method, with a wet object positioned in a vessel, a drying vapor is
introduced into the vessel. The drying vapor condenses on the
surface of the object and reduces the surface tension of the
residual process fluid, causing the residual process fluid to flow
off of the surface. In one embodiment, wet processing of the object
and a subsequent evacuation of process fluid is carried out in the
vessel prior to introduction of the drying vapor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a side elevation view of a wafer schematically
illustrating Marongoni flow from a wafer surface during Marongoni
drying processes.
[0013] FIG. 2 is a schematic representation of a first embodiment
of a drying system in accordance with the present invention.
[0014] FIG. 3 is a flow diagram illustrating examples of process
steps which may be carried out using the drying systems of FIGS. 2
and 8 during an HF last (etch), rinse, and dry process.
[0015] FIG. 4A is a cross-sectional front view of a drying vessel
in accordance with the present invention, together with a schematic
illustration of drying system components.
[0016] FIG. 4B is a cross-sectional end view of the drying vessel
of FIG. 4A.
[0017] FIG. 4C is a bottom perspective view of the vessel, in which
the lid and dump door components are not shown.
[0018] FIG. 5 is an exploded view of the drying vessel of FIG. 4A,
showing the lid in the closed position.
[0019] FIG. 6 is an exploded view of the drying vessel of FIG.
4A.
[0020] FIG. 7 is an exploded view of the lid for the drying vessel
of FIG. 4A.
[0021] FIGS. 8A-C are side elevation views of a wafer schematically
sequentially illustrating the process of removing rinse water and
condensed IPA from the surface of the wafer as described with
respect to the first and second embodiments.
[0022] FIG. 9A is a schematic representation of a chemical
injection system useful in connection with the first and second
embodiments, the figure includes a front elevation view of the
chemical storage vessel.
[0023] FIG. 9B is a side elevation view of the chemical storage
vessel of the chemical injection system of FIG. 9A.
[0024] FIG. 10 is a schematic representation of a chemical
injection system useful in connection with the first and second
embodiments, and particularly for use in dispensing a drying
compound into drying vapor generation chamber.
DETAILED DESCRIPTION OF THE DRAWINGS
[0025] The present invention is a vapor drying system and method
that is highly adaptable to use with various processing methods.
For example, the system and method may be used for drying alone, in
which case wet objects may be transferred from a separate wet
treatment vessel into the vessel of the drying system. As another
example, the vessel of the drying system may be used for surface
passivation processes that precede drying, such as etch, ozone
rinse, and DI rinse processes use in wafer processing, as well as
for the subsequent drying process.
[0026] The system and method according to the present invention
will be described in the context of surface preparation for
semiconductor substrates. This is done for purposes of illustration
only and is not intended in a limiting sense. The system and method
of the present invention are equally suitable for use on other
objects for which a high level of cleanliness is needed. Examples
of such other objects include, but are not limited to flat panel
displays, optical and magnetic recording disks, and photomasks. It
should also be noted that, although referred to as a "drying system
and method" the system and method of the present invention are
adaptable for use in a variety of applications, which may or may
not include chemical processing and rinse steps.
[0027] It is also noteworthy that, while isopropyl alcohol ("IPA")
is identified herein as the preferred drying compound/vapor
utilized in the system, the present invention is equally suitable
for use with other drying compounds/vapors now known or developed
in the future. Such alternatives are considered to lie within the
scope of the present invention. Examples include other polar
organic compounds like IPA, as well as methane, HFE, other alcohols
and other substances that are substantially free of polar organic
compounds, including argon and nitrogen.
[0028] Structure--First Embodiment
[0029] One embodiment of a system according to the present
invention is illustrated schematically in FIG. 2. Generally
speaking, system 10 includes a rinse/dry vessel 12, a moveable lid
14, a drying vapor generation chamber 16 remote from the vessel, a
chemical injection component 68, an exhaust and reclamation
component 70, and various drains and inlets described in greater
detail below.
[0030] The rinse/dry vessel 12 is a process vessel of any size and
shape suitable for receiving and processing a batch of
semiconductor wafers. Vessel 12 preferably has an inner tank
section 18 surrounded at its side, front and rear walls by an
overflow weir 20. The weir 20, which is of a type found on many
conventional rinse tanks, allows processing fluids to cascade over
the vessel walls during certain applications. An overflow drain 22
is formed in the weir 20, and a process drain 24 is formed in the
base of the inner tank section 16. Valve 26 controls the opening
and closing of the drain 24. A separate drain 28 and valve 30 are
used for IPA drainage. A condenser 32 is provided for condensing
exhausted IPA into a disposable form.
[0031] A source of rinse fluid 34 is fluidly coupled to a rinse
fluid inlet 36 in the base of the vessel 12. The system may be
provided with a filter for filtering the rinse fluid as it flows
towards the vessel, although many fabrication facilities come
equipped with separate filtering systems that yield rinse fluid of
the appropriate level of purity. During use, rinse water flows into
the vessel, passes through the vessel and cascades over the
interior vessel walls to the overflow weir 20. The rinse fluid
exits the weir via drain 22 for disposal.
[0032] Lid 14 is formed of a top wall 40 and four side walls 42
descending from the top wall 40 to form a bottomless enclosure. The
lid 14 is moveable by a robotic system 44 between a lowered
position and an elevated position. In the lowered position, side
walls 42 extend into the interior tank section 18 and make sealing
contact with the tank bottom, while the top wall 40 extends across
the opening at the top of the vessel. When fully lowered the top
wall 40 preferably makes sealing contact with the sidewalls forming
the vessel interior and overflow weir sections. This arrangement
prevents vapors from escaping from the vessel during processing,
and it also prevents any gases or particulate matter that may be in
the surrounding environment from passing into the vessel.
[0033] In the elevated position, the lid 14 is spaced from the
vessel 12 by a sufficient distance to allow wafers W on a wafer
cassette 46 to be lowered into and removed from the vessel 12.
Robotics system 44 may be configured to move the lid 14 along a
vertical axis between the lowered and raised positions. It may
alternatively be configured for multi-axis movement, so as to
position the lid above and to one side of the vessel opening for
movement of wafers into and out of the vessel.
[0034] As with the vessel 12, the lid 14 is formed of a material
that is inert to the process chemicals that will be used in the
system. The lid is further equipped with a heating system that
maintains the lid walls 40, 42 at an elevated temperature. As will
be discussed in greater detail with respect to FIG. 2, heating the
lid is beneficial in that it minimizes drying vapor condensation on
the lid, and thus leaves more of the drying vapor available for
condensing on the cool wafer surfaces. This allows drying to be
carried out using a minimum of IPA or other drying solvent.
[0035] Naturally, many systems may be conceived of for heating the
lid. One system found useful for this purpose relies upon a system
of heating elements embedded in the walls 40, 42. In a preferred
system, these heating elements are fluid conduits 48 coupled to a
source 50 of hot fluid, such as heated deionized water. The heated
fluid is circulated through the conduits in the walls 40, 42,
heating the walls and keeping them at an elevated temperature
(which is preferably selected to be above the temperature of the
rinse fluid used to rinse the wafers). Naturally, the specific
arrangement of the conduits 48 within the walls 40, 42 is not
critical, so long as the arrangement is adequate to circulate the
heated liquid through the walls in a manner which maintains the
walls at or above the desired elevated temperature. As another
alternative, the lid may be heated by heated nitrogen directed onto
the surfaces of the lid.
[0036] Top wall 40 of the lid is equipped with one or more inlets
51 that are used to introduce vapors into the vessel. These inlets
provide the N.sub.2 gas used to purge the vessel of air so as to
prevent oxidation of wafers inside the vessel, as well as the
drying vapors used to effect drying.
[0037] In one embodiment of the present invention, drying is
carried out using an initial IPA step in which IPA vapor is carried
into the vessel by heated N.sub.2 gas. The IPA step is followed by
the step of introducing heated N.sub.2 into the vessel to
volatilize condensed IPA remaining on the wafers and cassette. The
N.sub.2 used for both purposes is heated by an N.sub.2 heater 52,
which receives the nitrogen from an N.sub.2 source 54. Plumbing is
provided for flowing the heated N.sub.2 into the IPA chamber 16
when needed for the N.sub.2/IPA drying step, and for flowing the
heated N.sub.2 directly into the vessel when needed for the second,
heated N.sub.2, drying step. Valve 56 allows N.sub.2 flow into the
IPA chamber to be stopped and started, and valve 58 similarly
controls N.sub.2 flow directly into the vessel via the bypass
plumbing. When opened, an N.sub.2/IPA outlet valve 59 allows
N.sub.2/IPA to flow from the chamber 16 into the vessel 12.
[0038] IPA chamber 16 is preferably an electropolished high purity
stainless steel chamber having a bottom wall 60 and a heating
element 61 adjacent to the bottom wall 61 for heating the bottom
wall. During use, a pre-measured quantity of liquid IPA is fed from
IPA reservoir 62 onto the bottom wall of chamber 16.
[0039] A source of room temperature N.sub.2 66 is connected to lid
14 and is configured to allow gas from source 66 to flow into the
vessel via inlets 51.
[0040] If the system is to be utilized for chemical processes such
as cleaning and/or etching, it may further be provided with a
chemical dispensing component 68 which measures process chemicals
and injects them into the DI water stream, which carries them into
vessel 12.
[0041] Operation--First Embodiment
[0042] The system of FIG. 2 is adaptable for use in a variety of
applications, including those which involve chemical processing and
rinse steps carried out within or external to the vessel 12. FIG. 3
is a simplified flow diagram illustrating one use of the drying
system of FIG. 2, in which surface oxidation is removed using an
HF/HCl etch, and in which the wafers are subsequently rinsed, and
dried.
[0043] IPA vapor generation is preferably carried out in the early
stages of the process, but in any event prior to the moment at
which the wafers are ready for drying. Step 200. IPA vapor is
created within the IPA chamber 16 by injecting a pre-measured
quantity of IPA liquid onto surface 60 of chamber, which is heated
by heating element 61. The IPA is heated on surface 60 to a
temperature preferably less than the boiling point of IPA (which is
82.4.degree. C. at 1 atmosphere). Heating the IPA increases the
rate at which IPA vapor is generated and thus expedites the
process, creating a dense IPA vapor cloud.
[0044] The process preferably begins with lid 14 positioned away
from the opening in the vessel, and with heated DI circulating
within fluid conduits 48 to heat the walls 40, 42 of the lid to a
temperature that will promote IPA vapor condensation on the wafer
surfaces rather than on the lid. DI flow into the vessel is
initiated, while etch chemicals (for example, HF and HCl) are
simultaneously injected into the DI stream as it flows into the
vessel, to fill the vessel with an etch solution having the desired
concentration. Step 204.
[0045] A wafer cassette 46 (FIG. 2) carrying wafers W is lowered
into the vessel and positioned on the wafer support 47. Step 204.
Lid 14 is next moved into a position suspended above the vessel
(such as the position shown in FIG. 2). N.sub.2 gas from a source
66 (which may, but need not be, the same as source 54) is
introduced into the vessel via inlets 50 to purge the system of
air.
[0046] The wafers remain immersed in the process chemicals for a
predetermined period of time as needed to complete etching. Step
208. At the end of the etch period, rinse fluid is pumped into the
vessel 12 via inlet 36, and cascades into the overflow weir 20 and
out the overflow drain 22. Step 210. If an ozone rinse is desired,
the wafers are next rinsed using ozonated DI water. Step 212. This
may be carried out by injecting ozone into the rinse water via a
separate inlet in the vessel 12, or into the DI stream using
chemical dispensing component 68. After the ozone rinse, pure DI
rinsing continues for a sufficient period of time to thoroughly
rinse the wafers and cassette, Step 214, after which time the
process drain 24 is opened to quickly drain the rinse fluid from
the vessel ("quick dump"). Step 216. While the rinse water is being
discharged, lid 114 is moved by robotics system 44 into its lowered
position within the vessel. Preferably, N.sub.2 gas from ambient
temperature source 66 flows out of inlet(s) 51 as the lid is
lowered in order to maintain the purged environment within the
vessel.
[0047] As discussed, generation of IPA vapor is initiated within
the IPA chamber 16 early in the process. Shortly before the drying
step, valve 56 is briefly opened, permitting heated N.sub.2 gas to
fill the chamber 16. Once the vessel has been drained and the lid
fully lowered, valve 59 is opened, causing the heated N.sub.2 to
carry the IPA vapor into the vessel. Step 218.
[0048] As is typical of hot vapors, the IPA vapor condenses on the
cool surfaces with which it comes into contact. Because the lid's
walls are heated, the hot IPA vapor condenses on the relatively
cool wafer surfaces rather than on the lid walls. It should be
appreciated that this use of heated walls to promote condensation
on the wafers allows IPA usage to be minimized, since there is
little IPA "wasted" due to condensation on vessel surfaces.
[0049] The vapor condenses on the wafers, breaking the surface
tension of water on the wafers and thus shearing the rinse water
from the wafer surfaces.
[0050] At the end of the IPA drying step, valve 59 is closed, and
bypass valve 58 is opened, causing heated N.sub.2 to flow directly
into the vessel. Step 220. It should be noted that additional gas
inlets 51a (FIG. 2) may be positioned within the vessel 12 and
oriented to direct the gas onto the cassette to facilitate drying
during this step. The heated gas completes the drying process by
volatilizing condensed IPA that remains on the wafer and cassette
surfaces.
[0051] The heated N.sub.2 gas removes the condensed IPA by
evaporation and exhausts the IPA through IPA drain 28 into
condenser 32. Condenser 32 condenses the IPA to a liquid form
suitable for disposal.
[0052] Afterwards, lid 14 is withdrawn by robotics system 44, and
the fully dried wafers and cassette are removed from the vessel.
Step 222.
[0053] As discussed, the system 10 is useful for other processes,
as well. For example, the system 10 may be utilized as a component
of a larger system in which wafers are processed and rinsed in a
separate vessel. For an operation of that type, use of the system
10 might begin just after the rinse steps, with wet wafers being
lowered into the vessel 12 for drying. Steps 224, 226, 216, 218,
220, 222. As another example, for certain surfaces it may be
desirable to skip the HF last step and to use the system to carry
out an ozone rinse/rinse/dry process. Steps 212, 214, 216, 218,
220, 222. An ozone rinse produces a hydrophilic surface on the
wafer, whereas the HF last process described above produces a
hydrophobic surface. The drying process described herein is
beneficial in that it works well regardless of whether the wafer
surface is a hydrophilic or hydrophobic.
[0054] Structure--Second Embodiment
[0055] FIGS. 4A through 7 illustrate a second embodiment of a
drying system utilizing concepts in accordance with the present
invention. The second embodiment is similar to the first
embodiment, and differs from the first embodiment primarily in the
structure and use of the lid.
[0056] Referring to FIGS. 4A and 4B, the second embodiment includes
a vessel 112 of any size and shape suitable for receiving and
processing a batch of semiconductor wafers, and a lid 114 used to
seal the interior of the vessel from the external environment.
Vessel 112 and lid 114 are formed of materials, such as PVDF or
PFA, which are inert to chemicals used in the process
environment.
[0057] A vessel having the general characteristics of vessel 112 is
the Dynaflow.TM. rinse tank available from SCP Global Technologies,
Boise Id. Vessel 112 is preferably formed of an inner tank section
118 surrounded at its side, front and rear walls by an overflow
weir 120 for use with processes requiring process or rinse fluids
to cascade over the vessel walls. Its walls are preferably serrated
along their top edges to minimize fluid accumulation on the edges.
Weir 120 has an interior bottom surface angled from the horizontal
so as to facilitate flow of fluids towards a drain 122 positioned
at one end of the weir 120. A conventional fill sensor (not shown)
may be located within the vessel for use in confirming that liquid
levels within the inner tank 118 are sufficiently high to
completely immerse the wafers during use.
[0058] Pluralities of fluid inlets 136 are spaced longitudinally
and laterally along the vessel bottom. A fluid line 134 connects a
deionized water source to cavities 135 beneath the inlets. Fluid
flowing from fluid line 134 into cavities 135 pressurizes the
cavities, resulting in high pressure fluid flow through inlets 136
into vessel 112. The bottom wall of inner tank 118 preferably
includes beveled side sections as shown in FIG. 4A to promote
uniform fluid flow through the vessel from inlets 136.
[0059] As described with respect to the first embodiment, a
chemical dispensing component is connected to the fluid line 134 to
allow process chemicals to be injected into the DI stream when
needed.
[0060] An elongate opening 123 is formed in the bottom wall of the
inner tank section 118. Opening 123 extends longitudinally along
the bottom wall from an area adjacent to the front of the tank to
an area adjacent to the back of the tank. A dump door 124 seals the
opening 123. An automatic dump door assembly 126 controls movement
of the dump door 124 away from opening 123 to quickly empty inner
section 118, and further controls movement of dump door 124 back
into the opening 123 to re-seal the tank. A sensor of a type
conventionally used with dump door assemblies may be provided to
verify that the dump door has been opened or closed in accordance
with instructions from the system controller.
[0061] When opened, the dump door permits quick discharge of fluids
from the vessels into a catch basin 72 beneath the vessel. The
system includes an exhaust and reclamation component that includes
a waste line 74 that flows from the catch basin to an acid waste
site within the foundry. A separate IPA disposal outlet 128 is
positioned in an upper region of the discharge tank 72. During use,
IPA vapor is exhausted (by N.sub.2 gas flowing from inlet 150,
through dump opening 123 and into the catch vessel 72) through
outlet 128 to a condenser 132 where it is condensed for
disposal.
[0062] The components of the system used to generate N.sub.2 gas
and drying vapor for delivery into the vessel are similar to those
described above with reference to the first embodiment and so they
will not be described again. These components are labeled in FIG.
4A using numbering that is consistent with their counterparts shown
in FIG. 3 in connection with the first embodiment.
[0063] Vessel 112 includes a hinged lid 114. A pair of arms 116
extends from the lid 114. Each arm is coupled to a cylinder 117
having a lower end mounted to the stage or other support structure
(not shown) used to hold the vessel in a process platform.
Cylinders 117 are operative with arms 116 to pivot the lid between
opened and closed positions. When in the closed position, lid seals
against a flange 119 mounted on vessel 112 to prevent migration of
fumes from the vessel and to further prevent particles from the
surrounding environment from entering the vessel during use. To
optimize sealing between the lid and the flange, one or more seals
121 (FIG. 6) formed of a suitable sealing material such as
Teflon.RTM. or Chemraz, are positioned on lid 114 and/or flange
119.
[0064] A fitting 150 extends from the top of lid 114 and provides
the inlet through which N.sub.2 gas and IPA vapor enter the vessel.
Lid 114 is provided with manifolding that promotes uniform flow of
gas/vapor into the vessel and onto wafers situated within the
vessel. This manifolding will be best understood with reference to
FIG. 7. As shown, lid 114 is formed of a top plate 170, middle
plate 172 and bottom plate 174. Formed in the underside of the top
plate 170 are a pair of grooves 176 (see also FIG. 4A) that
intersect to form an X-shaped pattern. Fitting 150 is fluidly
coupled to the grooves, preferably at their intersection point, to
direct gas/vapor passing through the fitting into the grooves.
[0065] Bottom plate 174 has a system of grooves 178, 180 on its
upper surface. In one embodiment, the grooves include three
longitudinal grooves 178 and a pair of lateral grooves 180.
Longitudinal grooves 178 are lined with a plurality of small holes
which are the entry points for N.sub.2 and IPA vapor flowing from
the lid 114 into the vessel 112.
[0066] Middle plate 172 is sandwiched between the top and bottom
plates 170, 174. As can be seen in FIG. 4A, middle plate 172 forms
a series of channels with the grooves 176, 178, 180 of the upper
and lower plates. In other words, the arrangement of the plates
creates a pair of channels (intersecting to form an X-shape)
between the top and middle plates, and another series of channels
between the middle and lower plates.
[0067] Middle plate includes throughholes 182 that extend between
its upper and lower surfaces. Throughholes 182 provide a path
through which N.sub.2 gas and IPA vapor flow from the X-shaped
channel system, through the middle plate, and into the series of
channels formed between lower plate grooves 178, 180.
[0068] To facilitate distribution of N.sub.2 and IPA vapor through
lid 114, throughholes 182 may be aligned with the four corners of
the "X" formed by the two grooves of the top plate and with the
intersection points between longitudinal channels 178 and lateral
channels 180 on lower plate 174. During use, the gas/vapor flows
through fitting 150 into the X-shaped channels formed between the
top and middle plates, then through throughholes 182 into the
system of channels formed between the middle and bottom plates.
Ultimately, the gas/vapor flows into the vessel through the small
openings formed in the longitudinal grooves 180.
[0069] A process controller 184 is electronically coupled to the
lid robotics, dump door assembly 126, chemical injection component
68 and the various valves and sensors associated with operation of
the system. Controller 184 is programmed to govern control and
timing of these components to automatically open and close the
valves, activate the lid and dump door, and regulate flow of fluids
and gases etc. in accordance with a process recipe appropriate for
the treatment process being carried out. A controller suitable for
this purpose is a MCS microprocessor controller available from
Preco Electronics, Inc. Boise, Id. However, any suitable process
control computer can be used. It should be noted that the
electronic coupling between the controller and associated
components is not represented in the drawings only for reasons of
clarity.
[0070] A chemical injection system 300 useful as the chemical
injection component 68 for the system of the first and second
embodiments in shown in FIGS. 9A and 9B. Chemical injection system
300 is a desirable one in that it permits precise measurement of
process chemicals despite the variations in pressure that are
inherent to the bulk chemical supplies typically used at foundries.
Timing and control of the various valves utilized by the chemical
injection system is governed by process controller 184 or by a
separate controller.
[0071] Referring to FIG. 9A, chemical injection system 300 includes
a chemical storage vessel 302 coupled to a bulk chemical supply
304. Chemical storage vessel includes a main chamber 306 and a side
chamber 308 extending from the main chamber. The interiors of the
main and side chambers are contiguous with one another. In
addition, a fluid line 310 extends between the main and side
chambers. A liquid level sensor 312 is positioned to monitor the
liquid level in fluid line 310 and to provide feedback concerning
the liquid level to system controller 184 (FIG. 4A). A vent 314
extends from a wall of the primary vessel.
[0072] A dispense vessel 316 is coupled to chemical storage vessel
302 by line 318, which includes reduced flow orifice 320. A valve
322 is positioned downstream of orifice 320, and a DI line joins
line 318 further downstream of valve 322. A valve 324 governs flow
of DI water from DI source 326 into vessel 316.
[0073] An outlet line 328 extends from dispense vessel 316 and
includes a valve 330 and a reduced flow orifice 332. Liquid level
sensor 336 is positioned in line 328 to detect when fluid is
present in line 328 (i.e. once valve 330 has been opened).
[0074] A side branch 334 connects outlet line 328 with an upper
section of vessel 316. Further downstream of side branch 334 is a
dispensing line 338 fluidly coupled with the vessel 112.
[0075] There are four general steps involved during operation of
chemical injection system 300. The first is the bulk fill step, in
which chemical storage vessel 302 is filled with chemical from bulk
supply 304. The second is timed secondary fill step, in which the
amount of chemical needed to treat a batch of wafers is passed from
chemical storage vessel 302 into dispense vessel 316. The secondary
fill step is accomplished by opening valve 322 for a period of time
predetermined to cause the desired volume to be dispensed into
vessel 316. Third, valve 330 is opened to allow the chemical from
vessel 316 into line 338. As will be discussed in detail, this step
is timed and utilizes sensor 336 to verify the accuracy of the
secondary fill step. Finally, a dispensing step is carried out in
which the chemical is carried from line 338 into the process tank
by a DI stream passing into and through vessel 316.
[0076] The bulk fill step is typically carried out when the volume
of the chemical storage vessel 302 has decreased to a predetermined
minimum level. Valve 303 which lies between vessel 302 and bulk
supply is opened, causing chemical to flow from the bulk supply
into vessel 302. All other valves in the system remain closed
throughout the bulk fill step.
[0077] Fill sensor 312 is configured to provide feedback to
controller 184 indicating that the fluid level in chemical storage
vessel 302 has reached a predetermined level. The level will
preferably be selected to correspond to the volume of chemical
needed to treat a predetermined number of wafer batches in vessel
112.
[0078] Once fill sensor 312 detects that chemical storage vessel
302 has been filled to the desired volume, valve 303 is closed.
Next, valve 322 is opened to initiate the secondary fill step into
vessel 316. The system allows an accurate fill of vessel 316 by
monitoring the time for which valve 322 has been opened. For
example, the flow rate of the system may be such that it takes four
minutes to dispense 200 ml into the vessel 316. Once valve 322 has
been opened for the required duration, it is closed, thereby
halting fluid flow into vessel 316. Reduced flow orifice 320 causes
fluids dispensed into dispense vessel 316 to flow slowly, so as to
insure a high level of accuracy during the secondary fill step by
minimizing the effect of the split second delay between issuance of
the "close" control signal to valve 322 and the actual closing of
the valve. It should be noted that the system is useful for
applications in which successive runs of the system require
different dispense volumes. Simply changing the amount of time for
which valve 322 will be opened during the secondary fill step can
change the volume of chemical that will be dispensed.
[0079] After valve 322 has been closed, valve 330 is opened to
permit chemical to flow from dispense vessel 316 into dispense
plumbing 338, which is preferably large enough to contain the
entire dispense volume. Once line 328 has been emptied, sensor 336
turns off, indicating that vessel 316 has been completely
evacuated. The system registers the time lapsed between the opening
of valve 330 and the turning off of sensor 336, which is the amount
of time taken to empty vessel 316. The measured time is compared by
the system to a value saved in the system's software correlating to
the amount of time that it should take for the desired dispense
volume to exit vessel 316 given the known rate at which fluid will
flow from vessel 316. This step is done in order to verify the
initial time dispense into vessel 316. If the comparison reveals a
possible error in the amount of chemical dispensed, remedial
measures are taken before wafers are transferred into vessel 112.
Such remedial measures may include disposing of the chemical via
drain valve 339 and repeating the secondary fill step.
[0080] Shortly afterwards, when it is time to dispense chemical
into the vessel 112, valve 324 is opened, causing DI water to flow
from source 326, into dispense vessel 316, and then into plumbing
338 via lines 328 and 334. Because of the positioning of reduced
flow orifice 332 in line 328, only a small portion of the DI water
flows through line 328 where it serves to rinse chemical from the
line. A larger percentage of the DI fills the vessel 316 and flows
through side branch 334 into line 338, pushing the chemical in line
338 into tank 112 while also rinsing vessel 316 and lines 334 and
338. Control over the volume of DI water dispensed can be carried
out by keeping valve 324 opened for a predetermined amount of time
known to result in dispensing of the desired volume, or by closing
valve 324 in response to feedback from a liquid level sensor in the
vessel 340.
[0081] FIG. 10 shows a chemical injection system 400 useful for
dispensing drying compound (such as IPA or another suitable
compound) into the drying vapor generation chamber (chamber 16,
FIGS. 2 and 4A). Chemical injection system 400 includes a chemical
storage vessel 402 coupled to a bulk supply of drying compound 404.
A fluid line 410 extends between upper and lower portions of vessel
402. A liquid level sensor 412 is positioned to monitor the liquid
level in fluid line 410 and to provide feedback concerning the
liquid level to system controller 184 (FIG. 4A). A vent 414 extends
from a wall of vessel 402.
[0082] A dispense vessel 416 is coupled to chemical storage vessel
402 by a system of plumbing formed of line 417, reservoir 418a, and
lines 418b through 418f. A reduced flow orifice 420 is positioned
in line 417 and a valve 422 is positioned downstream of orifice
420.
[0083] The opening in reservoir 418a at its connection with line
418c is significantly smaller than the diameter of the pipe forming
line 418c. For example, reservoir 418a may include a 1/2-inch
diameter opening leading to a 1-inch diameter line 418c. Lines 418d
and 418f have vents at their upper ends. A sensor 436 is located in
line 418d and a valve 437 is positioned below sensor 436.
[0084] Vessel 416 and its associated plumbing 418a-f are
proportioned to contain and precisely dispense the entire quantity
of chemical needed for a single dispense operation. They are
arranged such that detection of a fluid level by sensor 436 occurs
when dispense vessel 416 and its associated plumbing has been
filled with slightly more than the required volume of chemical for
the process. Dispense vessels and plumbing of different volumes may
be used to replace vessel 416 and its plumbing when different
dispense volumes are needed.
[0085] A dispensing line 428 extends from dispense vessel 416 and
includes a valve 430. Dispensing line 428 is fluidly coupled with
drying vapor generation chamber 16 for dispensing a drying compound
into the chamber for vaporization.
[0086] There are three general steps involved during operation of
chemical injection system 400. The first is the bulk fill step, in
which chemical storage vessel 402 is filled with chemical drying
compound from bulk supply 404. The second is a secondary fill step,
in which the amount of chemical needed for use in drying a batch of
wafers is passed from storage vessel 402 into dispense vessel 416
and its plumbing.
[0087] Third, valve 430 is opened to allow the chemical from vessel
416 and its plumbing into chamber 16.
[0088] The bulk fill step is typically carried out when the volume
of the chemical storage vessel 402 has decreased to a predetermined
minimum level. Valve 403 is opened, causing chemical to flow from
the bulk supply into the vessel. Valve 422 remains closed
throughout the bulk fill step.
[0089] Fill sensor 412 is configured to provide feedback to
controller 184 indicating that the fluid level in chemical storage
vessel 402 has reached a predetermined level. The level will
preferably be selected to correspond to the volume of chemical
needed to carrying out a predetermined number of drying
procedures.
[0090] Once fill sensor 412 detects that chemical storage vessel
402 has been filled to the desired volume, valve 403 is closed.
Next, valve 422 is opened to initiate the secondary fill step into
vessel 416. It should be noted that valve 437 in line 418d remains
closed during the secondary fill.
[0091] During the secondary fill, fluid flows through orifice 420,
filling the portion of line 428 that lies upstream of valve 430,
then filling vessel 416, line 418b and then reservoir 418a. Next,
fluid cascades from reservoir 418a into line 418c and into the
portion of line 418d that sits above closed valve 437. Fluid also
rises from vessel 416 into the portion of line 418d that lies below
valve 437, and flows into lines 418e and 418f. When sensor 436
detects a fluid level, the calibrated fluid volume has been
achieved. In response, valve 422 is closed, thereby halting fluid
flow into vessel 416. Shading in FIG. 10 represents the calibrated
volume of fluid at the end of the secondary fill step.
[0092] After valve 422 has been closed, valve 430 is opened to
permit chemical to flow from dispense vessel 416 into chamber 16.
It should again be noted that at this stage valve 437 remains
closed.
[0093] After valve 430 has been opened for a predetermined amount
of time known to dispense the calibrated volume of chemical, it is
closed. Because valve 437 remains closed during the secondary fill,
a small volume of fluid remains in line 418c and in the portion of
line 418d that is above valve 437. Valve 437 is next opened to
allow this small volume of fluid to flow into vessel 416 where it
will form a portion of the calibrated volume measured during the
following secondary fill step. This small volume corresponds to the
amount of volume over the required process volume that will enter
the system as a result of the inability of valve 422 to close
instantaneously when sensor 436 detects a liquid level.
[0094] Operation--Second Embodiment
[0095] Operation of the second embodiment will next be described
with reference to FIG. 3 and in the context of a process in which
oxidation is removed using an HF/HCl etch, and in which the wafers
are subsequently rinsed, and dried. In a preferred embodiment, the
described sequence of steps occurs automatically in accordance with
a process recipe pre-programmed into controller 184. In other
words, management of the chemical processing times, rinse times,
vessel evacuation times, flow rates, waste disposal, chemical
measurement, dispensing and injection etc. is governed by process
controller 184.
[0096] IPA vapor generation is preferably carried out in the early
stages of the process, but in any event prior to the moment at
which the wafers are ready for drying. IPA vapor is created within
the IPA chamber 16 by injecting a premeasured quantity of IPA
liquid onto heated surface 60 of chamber in the manner discussed
with reference to chemical injection system 400 (FIG. 10). In one
embodiment, the amount of IPA utilized for a batch of fifty 200-mm
diameter wafers is approximately 50-150 ml. The IPA is heated on
surface 60 to a temperature preferably less than the boiling point
of IPA (which is 82.4.degree. C. at 1 atmosphere). Heating the IPA
increases the rate at which IPA vapor is generated and thus
expedites the process, creating a dense IPA vapor cloud.
Maintaining the IPA temperature below boiling prevents impurities
in the IPA liquid from becoming airborne where they are apt to be
carried into contact with the wafers.
[0097] To begin processing, vessel 112 is filled with an etch
solution of DI water and etch chemicals (for example, HF and HCl).
For more even mixing, the etch chemicals may be injected into the
DI stream as it flows into the vessel as discussed in connection
with the chemical injection system 300 (FIGS. 9A and 9B).
[0098] With lid 114 opened, a wafer cassette carrying wafers W is
lowered into the vessel and positioned on a wafer support within
the vessel. Lid 114 is next pivoted into a closed position, causing
the vessel to be sealed by seal 121. N.sub.2 gas (preferably at
room temperature) from a source 66 (which may, but need not be, the
same as source 54) is introduced into the vessel via fixture 150 to
purge the system of air. Ambient N.sub.2 continues to flow into the
vessel at a low flow rate until drying begins as later
described.
[0099] After the wafers have been etched, rinse fluid is pumped
into the vessel 112 via DI inlets 136, and cascades into the
overflow weir 120 and out the drain 122. If an ozone rinse is
desired, the wafers are next rinsed using ozonated DI water. This
may be carried out by injecting ozone into the rinse water via a
separate inlet in the vessel 112, or directly into the DI stream by
the chemical dispensing component. Rinsing continues for a
sufficient period of time (for example, 3-5 minutes, but will vary
with applications) to thoroughly rinse the wafers and cassette.
After the desired rinse time, the dump door assembly quickly is
activated to move the dump door 124 to its opened position to
quickly discharge the rinse fluid from the vessel ("quick dump").
Preferably complete evacuation of the fluid in the vessel occurs in
a very short time, and preferably in less than 5 seconds. The
discharged fluid moves into catch basin 72, then drains from catch
basin 72 into the foundry's acid waste disposal via waste line 74.
Low flow ambient N.sub.2 continues flowing into the vessel during
the quick dump step.
[0100] Just prior to the drying step, valve 56 is briefly opened,
permitting heated N.sub.2 gas to fill the IPA generation chamber
16, which already contains the rich IPA vapor cloud as discussed
above. Once the liquid in the vessel has been fully discharged,
valve 59 is opened, causing the heated N.sub.2 (having a
temperature of typically 80-90.degree. C.) to carry the IPA vapor
into the vessel. The IPA and nitrogen utilized in the process are
preferably high purity, such as "ppb" or parts per billion quality
or 99.999% pure.
[0101] The N.sub.2/IPA flows into the vessel at a rate of
approximately 25-100 standard liters per minute (slpm) for an IPA
drying period preferably 2-5 minutes. The lower end of this range
is preferred in that is leads to lower IPA emissions. The manifold
arrangement in the lid 114 promotes even distribution of IPA vapor
through the channels in the lid and consequently an even flow of
vapor through the inlets and onto the wafers.
[0102] The IPA vapor condenses on the wafers, forming a uniform
concentration of IPA in the liquid adhering to the wafer surface.
The condensed IPA breaks the surface tension of water on the wafers
and causes the rinse water to shear off of the wafer surfaces. By
the end of the IPA drying period, the rinse water will have been
completely removed from the waters, cassette, and vessel walls, and
will have been replaced by a layer of condensed IPA. The
N.sub.2/IPA exits the vessel through dump opening 123 into catch
basin 72, where it is exhausted through line 128, passed through
condenser 132, and disposed of.
[0103] The quick dump and IPA vapor steps as described herein
provide several advantages over the prior art. One advantage
provided over conventional vapor dryers is that the wafers remain
in a purged environment within vessel 112 throughout the entire
process, rather than being exposed to oxygen and particles as they
are moved from a rinse vessel to a drying vessel. Other advantages
will be appreciated with reference to FIGS. 8A-8C. Referring to
FIG. 8A, after the quick dump is performed, a carry over layer of
water remains on the wafer surface. When IPA vapor begins to enter
vessel 112, it condenses on the surface of this carryover layer and
diffuses into the water layer. As more IPA condenses on the water,
it gradually decreases the surface tension of the water until the
water eventually falls from the wafer surface. IPA vapor continues
to enter the vessel 112 and condenses on the wafer surface, leaving
a layer of condensed IPA on the wafer surface (FIG. 8B).
[0104] This method of water removal is particularly beneficial for
wafers having high aspect ratios or severe topography, where many
tight spaces exist within the wafer surface. Capillary forces are
high in such tight spaces and it is thus difficult to remove water
from them. The method of condensing IPA onto the carry over layer
of water where it can work its way into the water and then into the
wafer's tight geometries (and continuing to condense onto the wafer
surface after the carryover layer has fallen from the wafer)
facilitates drying even in those deeply or tightly-patterned
regions.
[0105] Moreover, the flow of condensed water and condensed IPA from
the wafer surfaces promotes IPA/water rinsing of the wafer surfaces
which facilitates removal of any particles that may remain on the
wafers.
[0106] Another advantage lies in that the quick dump step is
performed so as to completely evacuate the vessel 112 (or at least
to drain fluid in the vessel to below the wafers) in a very short
period of time, preferably under five seconds. This high velocity
draining of the liquid is beneficial to stripping water (and any
particles in the water) off the surfaces of the wafers. It thus
facilitates water removal even before the IPA vapor step is
initiated.
[0107] Returning to FIGS. 3 and 4A, at the end of the IPA drying
period, valve 59 is closed, and bypass valve 58 is opened, causing
heated N.sub.2 (preferably 80.degree.-90.degree. C.) to flow
directly into the vessel at a higher flow rate of preferably
150-250 slpm. As with the first embodiment, additional gas inlets
may be positioned within the vessel and oriented to direct the gas
onto the cassette to facilitate drying during this step.
[0108] The heated N.sub.2 gas removes the condensed IPA from the
wafers, cassette and vessel walls by evaporation (FIG. 8C). This
IPA evaporation step is preferably carried out for approximately
2-5 minutes. The evaporated IPA is exhausted through IPA drain 128
into condenser 130. Condenser 130 condenses the IPA to a liquid
form suitable for disposal. The heated N.sub.2 gas additionally
purges any IPA vapor remaining in the vessel into catch basin 72
and through condenser 132 via line 128.
[0109] At the end of the IPA evaporation step, a low flow
(preferably 20 slpm) of N.sub.2 gas is resumed to maintain a clean
environment within the vessel during removal of the wafers. Lid 114
is opened and the fully dried wafers and cassette are removed from
the vessel.
[0110] As discussed, the system 110 is useful for other processes,
as well. For example, the system 110 may be utilized as a component
of a larger system in which wafers are processed and rinsed in a
separate vessel. For an operation of that type, use of the system
110 might begin just after the rinse steps, with wet wafers being
lowered into the vessel 112 for drying. As another example also
illustrated in FIG. 8, for certain surfaces it may be desirable to
skip the HF last step and to use the system to carry out an ozone
rinse/rinse/dry process. An ozone rinse produces a hydrophilic
surface on the wafer, whereas the HF last process described above
produces a hydrophobic surface. The drying process described herein
is beneficial in that it works well regardless of whether the wafer
surface is hydrophilic or hydrophobic.
[0111] As yet another example, immersion of the wafers in HF may be
immediately followed by a quick dump of the HF solution into the
catch basin. The chemical quick dump is followed by the IPA vapor
drying step (step 218) and, if needed, the subsequent hot N.sub.2
step to remove condensed IPA from the wafers and cassette.
[0112] While the subject invention has been described with
reference to preferred embodiments, various changes and
modifications could be made therein, by one skilled in the art,
without varying from the scope and spirit of the subject invention
as defined by the appended claims.
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