U.S. patent application number 11/551739 was filed with the patent office on 2007-03-01 for method for continuously blending chemical solutions.
This patent application is currently assigned to Air Liquide America Corporation. Invention is credited to Joe G. Hoffman, John B. Thompson, Karl J. URQUHART.
Application Number | 20070047381 11/551739 |
Document ID | / |
Family ID | 23859707 |
Filed Date | 2007-03-01 |
United States Patent
Application |
20070047381 |
Kind Code |
A1 |
URQUHART; Karl J. ; et
al. |
March 1, 2007 |
METHOD FOR CONTINUOUSLY BLENDING CHEMICAL SOLUTIONS
Abstract
Provided are a method and apparatus for continuously blending a
chemical solution for use in semiconductor processing. The method
involves the step of mixing a first chemical stream with a second
chemical stream in a controlled manner to form a stream of a
solution having a predetermined formulation. The apparatus allows
one to practice the above method. The method and apparatus can
accurately provide chemical solutions of desired concentration in a
continuous manner. The invention has particular applicability in
semiconductor device fabrication.
Inventors: |
URQUHART; Karl J.; (Allen,
TX) ; Thompson; John B.; (Sherman, TX) ;
Hoffman; Joe G.; (Santa Fe, NM) |
Correspondence
Address: |
AIR LIQUIDE
2700 POST OAK BOULEVARD, SUITE 1800
HOUSTON
TX
77056
US
|
Assignee: |
Air Liquide America
Corporation
Houston
TX
|
Family ID: |
23859707 |
Appl. No.: |
11/551739 |
Filed: |
October 23, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10938570 |
Sep 13, 2004 |
|
|
|
11551739 |
Oct 23, 2006 |
|
|
|
09468411 |
Dec 20, 1999 |
6799883 |
|
|
10938570 |
Sep 13, 2004 |
|
|
|
Current U.S.
Class: |
366/152.4 ;
257/E21.219; 257/E21.223; 257/E21.228 |
Current CPC
Class: |
H01L 21/02052 20130101;
H01L 21/30604 20130101; B01F 15/0408 20130101; Y10T 137/2509
20150401; H01L 21/30608 20130101; Y10T 137/034 20150401; Y10T
137/0329 20150401; B01F 15/00227 20130101 |
Class at
Publication: |
366/152.4 |
International
Class: |
B01F 15/04 20060101
B01F015/04 |
Claims
1. A method of continuously blending a chemical solution for use in
semiconductor processing, comprising the steps of: a) mixing a
first chemical with a second chemical in a first mixing zone in a
conduit system and in a real time controlled manner to provide a
first solution having a predetermined formulation; the flowrate of
the first chemical and the flowrate of the second chemical are
continuously adjusted; the first solution formulation is
continuously monitored; b) mixing a third chemical with the first
solution in a second mixing zone in said conduit system and in a
real time controlled manner to provide a second solution having a
predetermined formulation; the flowrate of the third chemical is
continuously adjusted; second solution formulation is continuously
monitored, wherein steps (a) and (b) are performed
contemporaneously; and c) mixing a fourth chemical with the second
solution in a real time controlled manner to provide a third
solution having a predetermined formulation; the flowrate of the
fourth chemical and the flowrate of the second solution are
continuously adjusted; the third solution is continuously
monitored; and wherein step (c) is performed contemporaneously with
steps (a) and (b).
2. The method of claim 1, wherein step (a), the flowrate of the
first chemical or the second chemical is controlled in response to
a signal generated by a first sensor which monitors the first
solution, and in step (b), the flowrate of the third chemical or
the first solution is controlled in response to a signal generated
by a second sensor with monitors the second solution.
3. The method of claim 2, wherein the first sensor and the second
sensor are of the same or different types, and are selected from
the group consisting of conductivity sensors and acoustic signature
sensors.
4. The method of claim 3, wherein the first sensor and/or the
second sensor is an AC toroid coil sensor.
5. The method of claim 3, wherein the first solution and the second
solution are ionic solutions, and the first sensor and the second
sensor are conductivity sensors.
6. The method of claim 5, wherein the conductivity sensor is an
electrodeless conductivity sensor employing AC toroid coils.
7. The method of claim 3, wherein one of the first solution and the
second solution is a non-ionic solution and the other of the first
solution and the second solution is an ionic solution.
8. The method of claim 1, wherein the first chemical or the second
chemical is deionized water.
9. The method of claim 1, wherein the second solution having a
predetermined formulation is directly introduced into a
semiconductor processing tool.
10. The method of claim 1, wherein the second mixing zone is
arranged downstream from the first mixing zone.
11. A method of continuously blending a chemical solution on-site
at a semiconductor manufacturing facility, comprising the steps of:
a) mixing a first chemical with a second chemical in a first mixing
zone in a conduit system and in a real time controlled manner to
provide a first solution having a predetermined formulation; the
flowrate of the first chemical and the flowrate of the second
chemical are continuously adjusted; the first solution formulation
is continuously monitored; b) mixing a third chemical with the
first solution in a second mixing zone in said conduit system and
in a real time controlled manner to provide a second solution
having a predetermined formulation; the flowrate of the third
chemical is continuously adjusted; the second solution formulation
is continuously monitored; wherein steps (a) and (b) are performed
contemporaneously; c) introducing at least part of the second
solution having a predetermined formulation into a semiconductor
processing tool; and d) mixing a fourth chemical with at least part
of the second solution in a real time controlled manner to provide
a third solution having a predetermined formulation; the flowrate
of the fourth chemical is continuously adjusted; the third solution
formulation is continuously monitored, and wherein step (d) is
performed contemporaneously with steps (a) and (b).
12. The method of claim 11, wherein the second solution having a
predetermined formulation is directly introduced into a
semiconductor processing tool.
13. The method of claim 11, wherein at least part of the third
solution having a predetermined formulation is directly introduced
into a semiconductor processing tool.
Description
[0001] This application is a continuation of application Ser. No.
10/938,570, filed on Sep. 13, 2004, which is a divisional of
application Ser. No. 09/468,411, filed on Dec. 20, 1999.
BACKGROUND
[0002] The present invention relates to novel methods and apparatus
for continuously blending a chemical solution for use in
semiconductor processing and, more particularly, to their on-site
use at a semiconductor manufacturing facility.
[0003] In the semiconductor manufacturing industry, extensive use
is made of liquid chemicals, for example, in wafer cleaning and
etching processes. Accurate mixing of reagents at desired ratios is
particularly important because variations in concentration of the
chemicals introduce uncertainty in etch rates and, hence, are a
source of process variation.
[0004] Conventionally used chemicals in the semiconductor
manufacturing industry which are formed by mixing together two or
more chemicals include, for example, hydrofluoric acid (HF),
ammonium fluoride (NH.sub.4F), hydrochloric acid (HCl), ammonium
hydroxide (NH.sub.4OH) and nitric acid (HNO.sub.3). On-site
preparation of such chemicals in ultrapure form is described, for
example, in U.S. Pat. Nos. 5,785,820, 5,722,442, 5,846,387,
5,755,934 and in International Publication No. WO 96/39263, the
contents of which documents are herein incorporated by
reference.
[0005] Conventionally, the blending of chemicals is performed by
chemical suppliers off-site from the semiconductor manufacturing
facility. The chemicals are typically blended through the use of
load cells and mixing tanks, with analytical verification. The use
of load cells, however, is undesirable for various reasons. For
example, piping, which is attached to the weighed mixing vessel,
exerts an unpredictable force. This can lead to inaccuracies in
measuring the weight of the fluid in the vessel resulting in
chemical blends of imprecise formulation.
[0006] In addition, expensive electronic equipment is typically
required for such known blending processes. The exposure of this
equipment to corrosive chemical environments often leads to
corrosion and premature failure thereof. Moreover, load cells
require the use of additional laboratory instrumentation to
determine incoming chemical assay as well as program adjustments to
compensate for assay variability.
[0007] Upon obtaining a desired chemical formulation, the chemicals
are conventionally packaged in totes or drums for shipment to the
semiconductor manufacturing facilities. Packaging and storage of
the chemicals in this manner is undesirable in that the process of
packaging the chemicals and the containers themselves are sources
of contamination.
[0008] Furthermore, the cost per unit volume of transporting
ultrapure chemicals is high. This cost can be especially
prohibitive if chemicals of all requisite concentrations are to be
shipped. In this regard, the conventionally used chemicals, such as
hydrofluoric acid, are often employed at various dilutions in the
semiconductor manufacturing process. Chemical shipment is
particularly inefficient with very dilute acids.
[0009] Once at the semiconductor manufacturing site, the chemicals
are stored until used. Such storage, however, is not particularly
desirable, as considerable space is required and costs are incurred
due to storage and management of the totes in the manufacturing
facility.
[0010] In addition, the chemicals are often unstable and therefore
have limited shelf lives. High purity water ("deionized" or "DI"
water), typically employed in the manufacture of chemicals,
exhibits organic growth after short periods of time. Hence, it is
not uncommon for the shelf life of a chemical to expire prior to
use. The unused chemical must therefore be disposed of, resulting
in economic loss as well as environmental issues associated with
waste disposal.
[0011] To address the problems associated with the processing of
chemicals off-site from the point-of-use, on-site blending methods
and apparatus have been proposed for semiconductor applications. An
on-site blending method is described, for example, in International
Publication No. WO 96/39651, the contents of which are incorporated
herein by reference. An exemplified embodiment of that document
involves a batch-type process, with mixing of the components taking
place in a single blender tank. After mixing two chemicals in the
blender tank to a desired endpoint, those chemicals are shut off. A
third chemical is next introduced into the tank to a desired
endpoint.
[0012] One of the disadvantages associated with such a batch-type
process is that it is difficult to achieve steady state conditions
and the desired chemical formulation in a small amount of time. In
addition, it is necessary with the batch-type process that a supply
of the blended chemical be stored in a tank or other container to
avoid production down time if the chemical should become depleted.
The use of a storage container, however, is undesirable at least
due to its space and management requirements.
[0013] To meet the requirements of the semiconductor manufacturing
industry and to overcome the disadvantages of the related art, it
is an object of the present invention to provide novel methods for
continuously blending a chemical solution. The invention allows for
real time, precise control of chemical formulations by continuous
monitoring and flowrate adjustment of the chemicals employed. The
desired formulations can be achieved in a fast and facile manner
from startup based on calibration data stored in one or more
controllers.
[0014] Furthermore, total cost associated with the chemicals can be
significantly reduced since only concentrated acids, and not dilute
solutions, need be shipped to the end user's site. This renders
unnecessary the need to inventory and handle large volumes of
dilute chemicals. In addition, the costs and time associated with
laboratory analytical verification can be avoided or minimized,
since the process is calibrated to analytical analysis at the time
the process is set up and only periodically thereafter to ensure
continued calibration accuracy.
[0015] It is a further object of the invention to provide methods
of continuously blending a chemical solution on-site at a
semiconductor manufacturing facility.
[0016] A further object of the present invention is to provide a
novel apparatus for continuously blending a chemical solution.
[0017] It is a further object of the invention to provide an
apparatus for continuously blending a chemical solution on-site at
a semiconductor manufacturing facility.
[0018] Other objects and aspects of the present invention will
become apparent to one of ordinary skill in the art on a review of
the specification, drawings, and claims appended hereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The objects and advantages of the invention will become
apparent from the following detailed description of the preferred
embodiments thereof in connection with the accompanying drawings,
in which:
[0020] FIG. 1 is a process flow diagram of an apparatus for
continuously blending solutions in accordance with one exemplary
aspect of the invention;
[0021] FIG. 2 is a process flow diagram of an apparatus for
continuously blending solutions connected to supply the blended
solution to a semiconductor processing tool, in accordance with a
further exemplary aspect of the invention;
[0022] FIG. 3 is a graph of weight assay percent of EDA versus
conductivity in a accordance with Example 1 of the invention.
[0023] FIG. 4 is a graph of weight assay percent of EDA versus
conductivity at process set-up in accordance with Example 1 of the
invention.
[0024] FIG. 5 is a graph of conductivity versus time to exhibit the
length of time need to bring the EDA component to specification in
accordance with Example 1 of the invention.
[0025] FIG. 6 is a graph of weight assay percent of KOH versus
conductivity in a accordance with Example 1 of the invention.
[0026] FIG. 7 is a graph of weight assay percent of KOH versus
conductivity at process set-up in accordance with Example 1 of the
invention.
[0027] FIG. 8 is graph of conductivity versus time to exhibit the
length of time need to bring the KOHS blender to specification in
accordance with Example 1 of the invention.
[0028] FIG. 9 is a graph of weight percent KOH and weight percent
EDA in a blended solution, formed in accordance with an exemplary
aspect of the invention, versus sample number.
[0029] FIG. 10 is a graph of weight assay percent of NH.sub.4OH
versus conductivity in a accordance with Example 2 of the
invention.
[0030] FIG. 11 is a graph of weight assay percent of surfactant
versus conductivity at process set-up in a accordance with Example
2 of the invention.
[0031] FIG. 12 is graph of weight percent assay versus sonic
velocity ranges to exhibit the length of time need to bring the
block cleaning solution to specification in accordance with Example
2 of the invention.
SUMMARY
[0032] In accordance with the present invention, innovative methods
and apparatus for continuously blending chemical solutions are
provided. The invention finds particular applicability in the
semiconductor manufacturing industry, wherein chemical solutions of
desired formulations can be generated on-site, with the resulting
chemical being introduced directly into one or more semiconductor
processing tools. Of course, the resulting chemical employed can be
in the form of aqueous solutions.
[0033] According to a first aspect of the invention, a method of
continuously blending a chemical solution for use in semiconductor
processing is provided. The method comprises the step of mixing a
first chemical stream with a second chemical stream in a controlled
manner, to form a stream of a solution having a predetermined
formulation.
[0034] According to a further aspect of the invention, a method of
continuously blending a chemical solution for use in semiconductor
processing is provided. The method comprises the steps of: [0035]
(a) mixing a first chemical with a second chemical in a controlled
manner to provide a first solution having a predetermined
formulation; and [0036] (b) mixing a third chemical with the first
solution in a controlled manner to provide a second solution having
a predetermined formulation. Steps (a) and (b) are performed
contemporaneously.
[0037] In accordance with a further aspect of the invention, a
method of continuously blending a chemical solution on-site at a
semiconductor manufacturing facility is provided. The method
comprises the steps of: [0038] (a) mixing a first chemical with a
second chemical in a controlled manner to provide a first solution
having a predetermined formulation; and [0039] (b) mixing a third
chemical with the first solution in a controlled manner to provide
a second solution having a predetermined formulation; and [0040]
(c) introducing the blended solution into a semiconductor
processing tool, wherein steps (a) and (b) are performed
contemporaneously.
[0041] In accordance with yet a further aspect of the invention, an
apparatus for continuously blending a chemical solution for use in
semiconductor processing is provided. The apparatus comprises a
first chemical source, a second chemical source and a third
chemical source connected by a conduit system to allow a stream of
the first chemical to be mixed with a stream of the second chemical
to form a first solution, and a stream of the first solution to be
mixed with a stream of the third chemical to provide a second
solution. The first and second solutions are provided
contemporaneously. Means for controlling the formulations of the
first and second solutions are provided.
[0042] In accordance with a further aspect of the invention, an
apparatus for continuously blending a chemical solution on-site at
a semiconductor manufacturing facility is provided. The apparatus
comprises a first chemical source, a second chemical source and a
third chemical source connected by a conduit system to allow a
stream of the first chemical to be mixed with a stream of the
second chemical to form a first solution, and a stream of the first
solution to be mixed with a stream of the third chemical to provide
a second solution. The first and second solutions are provided
contemporaneously. Means for controlling the formulations of the
first and second solutions are provided. A semiconductor processing
tool is connected to receive the blended solution.
[0043] In accordance with a further aspect of the invention, an
apparatus for continuously blending a chemical solution for use in
semiconductor processing is provided. The apparatus comprises a
first chemical source and a second chemical source connected by a
conduit system to allow a stream of the first chemical to be mixed
with a stream of the second chemical to form a solution, and means
for controlling the formulation of the solution.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0044] The invention will be described with reference to FIG. 1,
which illustrates a process flow diagram of a system 100 for
continuously blending chemical solutions in accordance with one
exemplary aspect of the invention. The chemical solution is formed
by mixing together any number of chemicals in a controlled manner
to achieve a final solution of desired concentration.
[0045] If the chemical solution is to be used in the manufacture of
electronic devices, the starting materials are preferably of
ultrapure quality, preferably less than 1 ppb impurities. This will
help to ensure a final chemical purity which also is ultrapure, and
thus not detrimental to the devices being formed. The starting
chemicals are typically in liquid form. However, gases may be
employed, for example, by bubbling the gas into a liquid
chemical.
[0046] Typical combinations of chemicals used in semiconductor
fabrication which may be applied to the invention include, for
example, the following: deionized water, hydrofluoric acid (HF),
nitric acid (HNO.sub.3) and acetic acid (CH.sub.3COOH); deionized
water, hydrofluoric acid and ammonia (NH.sub.3), to form ammonium
fluoride (NH.sub.4F); deionized water, potassium hydroxide (KOH)
and ethylene diamine (EDA); and deionized water, ammonium hydroxide
(NH.sub.4OH) and a surfactant, to form a block cleaning solution
(BCS). Other combinations of the above or different chemicals or
gases that are soluble in solution, would be understood by persons
of ordinary skill in the art to be within the scope of the
invention.
[0047] A partial list of conventional chemicals that can be
generated on-site at the semiconductor fabrication facility
includes at least the hydrofluoric acid, buffered hydrofluoric
acid, hydrochloric acid, and ammonia.
[0048] For purposes of the present invention, it is convenient to
classify the chemicals being mixed into two groups, i.e., ionic and
non-ionic chemicals. This allows for the selection of an
appropriate concentration sensor for the chemicals being blended.
For concentration measurement of an ionic solution, a conductivity
sensor, such as an electrodeless conductivity sensor employing AC
toroid coils, or an acoustic signature sensor can be employed.
Concentration measurement in non-ionic solutions can be
accomplished with an acoustic signature sensor.
[0049] Electrodeless conductivity systems measure the conductance
in a solution by inducing an alternating current in a closed loop
and measuring its magnitude. An electric current may be caused to
flow in an electrolyte by means of induction. The electrodeless
system contains an electrolyte which flows in an electrically
insulating tube that surrounds two coils in a fashion that the
electrolyte forms a closed loop linking the flux in both cores.
These coils serve as a primary and secondary winding, and they are
toroidal. Additionally, both windings are housed in the same
encapsulation. The first toroidal coil serves as a single turn
secondary winding in which an alternating voltage is induced. The
second toroidal coil serves as a single turn primary winding in
which the loop forms. This provides a means for measuring the
resulting current, which is directly proportional to the specific
conductance of the electrolyte comprising the loop. Suitable AC
toroid coil sensors are commercially available from, for example, a
model 3700 series electrodeless sensor provided by GLI
International.
[0050] Acoustic signature sensors are commercially available, for
example, from Mesa Laboratories, Inc., Nusonics Division, Colo.,
and are described generally in International Publication No. WO
96/39263. Such sensors include an ultrasonic generator and a
transducer. An acoustic sound wave or pulse is propagated through
the solution and its velocity, i.e., the time of flight, is
measured. The sound velocity through the solution is directly
related to the solution temperature and to the concentration of the
chemicals in the solution or, more appropriately, the volume ratio
of the chemicals.
[0051] The system includes a conduit system interconnecting the
various components of the system. A first chemical source 102, a
second chemical source 104, and a third chemical source 106 are
provided. The first, second and third chemicals are introduced into
the system through conduits 108, 115 and 117, respectively. As
illustrated, the first chemical can be deionized water which is
conventionally produced by a central generation system. The flow
rate of first chemical 102 into the system can be controlled by a
regulation device (not shown) or pneumatic valve 114. The second
and third chemicals are typically stored in a reservoir (not
shown), and are fed into storage tanks 160, 162 through conduits
115, 117 which include valves 119, 121. These second and third
chemicals which are dosed in to the main stream include a
backpressure regulator (not shown) disposed between the metering
pump and the stream. The storage tanks can include vents 118, 120
for exhausting the headspace under a nitrogen blanket so as not to
contaminate the ultrapure chemicals therein.
[0052] Chemical levels in the storage tanks can be maintained
within predefined limits by known methods and apparatus, which can
include maximum and minimum level sensors 122, 124, 156, 158 and
one or more controllers which operate valves 119, 121 on inlet
conduits 115, 117. The controllers are pre-programmed with minimum
and maximum set-point levels with which the actual measured levels
are compared. If the liquid level reaches the minimum set-point
level, valve 119 or 121 is opened, allowing more of the chemical to
be introduced into the storage tank. The flow of the chemical into
the storage tank is shut off by closing valve 119 or 121 when the
maximum set-point level in the tank is reached. Other variations to
control liquid level are known to those skilled in the art.
[0053] The storage tanks 160, 162 are each connected to main
conduit 108 by a conduit 110, 112. To regulate the flow of the
second and third chemicals into the main conduit 108 and through
the system, dosing pumps 130, 132 are provided in conduits 110, 112
downstream from the storage tanks. Dosing pumps 130, 132 are
preferably electromagnetic drive pumps with a variable signal to
increase and decrease the pump stroke frequency. The dosing pumps
are connected to a control system described below which controls
the flowrate of the second and third chemicals into the system.
Among the commercially available controllers, computers or
proportional integral derivative instruction devices with a
feed-back or feed-forward control algorithm are preferred.
[0054] The first chemical 102 and second chemical 134 contact each
other and are mixed in a mixing zone 136 in the conduit system. The
mixing zone preferably includes mixing means, which can include,
for example, stirrers, baffles, a vortex breaker or the like,
sufficient to mix the chemicals such that a homogeneous solution is
obtained. In the case in which a gas is to be bubbled into a
liquid, the mixing means can include, for example, a sparger.
[0055] Following the mixing step, the homogeneous first solution is
directed to first concentration sensor 140. As described above, the
sensor can be a conductivity or acoustic signature sensor for an
ionic solution, or an acoustic signature sensor for a non-ionic
solution. Based on the measurement obtained with the first sensor,
the flowrate of the first chemical or second chemical is
automatically adjusted and controlled such that the proper
formulation of the first solution is obtained.
[0056] Preferably, the system comprises a closed-loop control
system, in which a signal from the sensor 140 based on the
measurement is directed to a controller 142. The controller 142
then sends a signal to the flow control valve 114 or dosing pump
130 to control the flow of the first or second chemical via a
feed-back algorithm to arrive at the requisite concentration of the
first solution. To minimize the number of runs and time required to
reach the desired concentration, controller 142 can be programmed
to retain the process settings from the previously formed
solution.
[0057] Contemporaneous with the introduction of the first and
second chemicals into main conduit 108, the third chemical is
continuously introduced into the main conduit 108 via line 112,
downstream of first sensor 140. The third chemical is mixed with
the first solution in a second mixing zone to form a second
solution. To ensure homogeneity of the second solution, the second
mixing zone preferably includes mixing means as described above
with reference to the first mixing zone.
[0058] Following the mixing step, the homogeneous, second solution
is directed to second concentration sensor 146. As described above,
the sensor can be a conductivity or acoustic signature sensor for
an ionic solution, or an acoustic signature sensor for a non-ionic
solution. Based on the measurement obtained with the second sensor
146, the flowrate of the first solution or the third chemical is
adjusted such that the proper formulation of the second solution is
obtained.
[0059] The flowrate of the first solution can be controlled via
control valve 148 disposed downstream from the first sensor and
upstream from the point at which the first solution and third
chemical are mixed. If the flowrate of the third chemical is to be
controlled, the controller 142 can automatically regulate the
output dosing pump 132. The control system described above with
reference to the blending of the first solution is equally
applicable to the second solution, and the same or a different
controller from that used for blending the first solution can be
employed.
[0060] Until the predetermined formulation is obtained for both the
first and second solutions, valve 152 which connects the blending
system to the point of use remains closed, and valve 150 which
connects the blending system to waste is opened. Upon arriving at
the desired concentration of the second solution, valve 150 is
closed and valve 152 is opened, allowing the blended solution to be
directed to the point of use, for example, to a semiconductor
processing tool.
[0061] Prior to performing the blending method in accordance with
the invention, the first and second sensors are calibrated for the
specific chemicals and solutions being blended. Conductivity
sensors are calibrated in a manner well known in the industry.
Initially, a zero point of the electrodeless conductivity sensor or
acoustic signature sensor is attained by exposing the sensor to air
until the sensor is entirely dry and the offset is adjusted until a
0.000 mS/cm conductivity is attained. Of course, the measure of
conductivity may be expressed in other units such as S/cm or
S/cm.
[0062] Upon attaining the zero point, the sensor is placed in a
solution of know concentration and the conductivity is measured at
a series of different temperatures. The solutions' concentration
may be verified by standard titration methods. Resulting
concentration values are entered into controller or analyzer 142
employed to continuously monitor and adjust dosing pumps 130,
132.
[0063] Alternatively sensors 140, 146 may be calibrated by the
"Grab Sample Method." The sensors are placed on the main conduit
108 and a solution of known conductivity and assay is passed
therethrough. Conductivity readings that are calibrated are taken
and stored into controller 142.
[0064] Subsequent to calibrating the concentration sensors, the
conductivity of each solution to be run through the system is
calibrated in part. Each individual solution to be transmitted in
the system is conveyed through a concentration sensor and a
correlation between the sensor reading and the actual solution is
carried out. To ensure correct readings the solution is verified by
titration or other methods. From this data a plot of sensor reading
versus actual concentration is generated. Temperature variations in
the solution are accounted for, and a corresponding correction may
be made by controller 142.
[0065] Following the first and second solution calibration
conductivity data points are entered into controller 142, and
employed to adjust the metering of pumps 130 and 132, to arrive at
the conductivity desired. As explained above, the conductivity
correlates to the percent weight assay of the chemicals
introduced.
[0066] While the exemplary embodiment described above with
reference to FIG. 1 involves at least two chemicals and a blending
step, the present invention is in no way limited thereto. The
invention can readily be applied to the blending of as few as two
chemicals in a single blending step, or with a single sensor any
number of additional chemicals in the manner described above. For
each additional chemical introduced into the mixture, an additional
blending step and sensor are required.
[0067] FIG. 2 illustrates a system 200 which includes one or more
apparatuses 202 as described above for continuously blending
solutions, as well as one or more semiconductor processing tools
connected to receive the blended solutions. Starting chemicals 204
are introduced into blending apparatus 202, which forms blended
solution 206.
[0068] The processing tools can include, for example, one or more
wet processing stations for cleaning and/or etching semiconductor
wafers, as well as auxiliary stations, for example, a drying
station. As illustrated, the treatment stations include a cleaning
station 208, a first rinse station 210, a deglaze station 212, a
final rinse station 214 and a dryer 216.
[0069] Cleaning station 208 is connected by a conduit to receive
the blended solution formed by blending apparatus 202. This
solution can be, for example, a dilute hydrofluoric acid cleaning
solution, formed by blending deionized water with concentrated
hydrofluoric acid to form a first solution, and blending the first
solution with a surfactant to form the cleaning solution. First and
second rinse stations 210, 214 contain ultrapure deionized water,
and deglaze station 212 contains, for example, a buffered
hydrofluoric acid cleaning solution.
[0070] The one or more semiconductor wafers 218 are held on a wafer
support or in a cassette 220. The wafers together with the support
or cassette are conveyed between the workstations by a robotic
transfer mechanism 222 or other conventional means of conveying
such objects between the stations. While wafer transfer can be
performed manually, the means for conveyance is preferably totally
or partially automated.
[0071] First, the wafers are introduced into cleaning station 208
to remove contaminants from the wafers. The wafers are then removed
from cleaning station 208 and transferred into first rinsing
station 210 wherein the wafers are rinsed with deionized water to
remove residual cleaning solution from the wafer surfaces. The
wafers are next transferred into deglaze station 212 for the
removal of native or other oxide films from the wafer surface. The
wafers are then introduced into final rinse station 214 and finally
to dryer 216. The wafers are removed from the dryer and sent to
subsequent processes to complete the device fabrication
process.
[0072] It should be noted that the number or types of blending
systems and treatment stations, as well as the types of chemicals
employed, are not limited in any way to those discussed above with
reference to the exemplary embodiment. In general, wet treatment
operations in semiconductor manufacturing processes may vary widely
from that illustrated in FIG. 2, either by eliminating one or more
of the units shown or by adding or substituting units not shown.
Persons of ordinary skill in the art can readily adapt the present
invention to any such operations.
[0073] The following examples are provided to illustrate generation
of an ultrapure solution formed by combining deionized water,
ethylene diamine (EDA) and potassium hydroxide (KOH) according to
one aspect of the invention and an ultrapure solution formed by
combining deionized water with ammonium hydroxide and surfactant
according to another aspect of the invention.
EXAMPLE 1
[0074] A continuous blending apparatus as described above with
reference to FIG. 1, configured with two AC toroid coils, was
employed to blend a solution made up of deionized water, ethylene
diamine (EDA) and potassium hydroxide (KOH). Prior to mixing the
chemicals, the sensors were calibrated to a "zero point" as
described above.
[0075] The operating parameters are established for the requisite
first solution as shown in FIG. 3, where the conductivity is
determined at different weight percent assay of EDA mixed with
deionized water. The concentration values obtained are verified by
titration and the conductivity values are entered on display 154 of
controller 142. As the first solution of EDA is passed through
conduit 108 to sensor 140 an assay weight percent vs. conductivity
correlation chart is generated showing the EDA range to be run. See
FIG. 4. Thus, to obtain a flow rate of 0.40% by weight of ethylene
diamine assay in the first solution a conductivity of 0.551 mS/cm
must be attained. A signal is sent from controller 142 adjusts the
flow of dosing pump 130 based on conductivity. As illustrated in
FIG. 5, the solution is brought to specification in approximately
60 seconds.
[0076] Subsequently, the operating parameters for a solution of KOH
and deionized water is carried out in the same manner, as described
above with respect to the first solution. Note FIGS. 6-8.
[0077] Thereafter, the first and second solution concentration is
derived by an equation in controller 142, which proportionally
increases or decreases the amount of second or third chemical 134,
136 injected into the first chemical stream 102 based on the
conductivity value set point. The amount of either chemical
injected by dosing pump 130, 132 is adjusted by controller 142 in
response to the conductivity value obtained from the sensors. Thus,
a second solution having 0.50 weight percent potassium hydroxide
assay is added to a first solution having 0.40 weight percent
ethylene diamine establishes a conductivity 21.98 mS/cm. It is
noted that this conductivity value is less than in the second
solution having 0.50 weight percent of potassium hydroxide in
water. Therein, the conductivity measurement is 22.03 mS/cm.
[0078] FIG. 9 is a graph of weight percent KOH in the first
solution and weight percent EDA in the second solution versus
sample number. It can be seen that the solution reached the target
concentrations by the seventh sample run, and thereafter the
process runs were easily reproduced. The product solution was found
to be very stable, with little adjustment of the dosing pumps being
required thereafter.
EXAMPLE 2
[0079] A continuous blending of ionic and non-ionic chemicals is
performed with reference to FIG. 1, wherein sensor 140 is a toroid
coil conductivity sensor and sensor 146 is an acoustic signature
sensor. An ionic ammonium hydroxide chemical is added to a
deionized water chemical to form a first solution. The solution is
calibrated as mentioned above in regard to Example 1, by
correlating the percentage weight assay with the conductance of the
solution. Note FIG. 10. Subsequently, a similar procedure is
carried out with respect to a non-ionic surfactant solution. The
values obtained are depicted in FIG. 11.
[0080] A second, product block cleaning solution is formed by
adding a third non-ionic surfactant to the first solution. Dosing
pump 132 is adjusted by an equation determined by controller 142 to
reach a set point value. Thus, controller 142 proportionally
increases or decreases the amount of chemical 136 added based on
the conductivity reported by sensor 146. As a result, a desired
third chemical assay is attained in the second solution based on
the ratio of the third chemical component to that of the first two
chemical components as determined through conductance. See FIG.
12.
[0081] The assay of the product is verified by analytical analysis
for verification of the process. Process assay trends are monitored
on display 154 of controller 142 and are actively adjusted based on
the concentration desired. On entering the requisite ionic
concentration for a certain application, and based on the
conductivity reading of the concentration sensors, controller 142
adjusts the flow of the dosing pumps thereby calibrating the assay
of each component to maintain the desired concentration.
[0082] While the invention has been described in detail with
reference to specific embodiments thereof, it will be apparent to
one skilled in the art that various changes and modifications can
be made, and equivalents employed without departing from the scope
of the claims.
* * * * *