U.S. patent application number 10/961572 was filed with the patent office on 2005-04-21 for system and method for cleaning semiconductor fabrication equipment parts.
Invention is credited to Tan, Samantha.
Application Number | 20050085400 10/961572 |
Document ID | / |
Family ID | 22841292 |
Filed Date | 2005-04-21 |
United States Patent
Application |
20050085400 |
Kind Code |
A1 |
Tan, Samantha |
April 21, 2005 |
System and method for cleaning semiconductor fabrication equipment
parts
Abstract
A process for cleaning semiconductor fabrication equipment parts
includes determining a definition for a clean part including
multiple maximum acceptable impurity levels; determining an initial
multiple impurity levels of a part prior to its cleaning;
determining a cleaning process to apply to the part; applying the
cleaning process to the part, wherein the cleaning process creates
reduced multiple impurity levels for the part below that of the
initial multiple impurity levels; determining the reduced multiple
impurity levels; comparing the reduced multiple impurity levels
against the multiple maximum acceptable impurities levels of the
definition; and repeating the application of the cleaning process
to the part if the reduced multiple impurity levels do not meet the
definition of a clean part. A dilute aqueous cleaning solution for
cleaning parts includes 0.5-1.5% wt. HF; 0.1-0.5% wt. HNO.sub.3;
and 1-10% wt H.sub.2O.sub.2. A method for reducing sub-surface
damage to a part includes determining how deep is the sub-surface
damage beneath a surface of a part; chemically etching said surface
of said part; and stopping said chemical etching of said surface at
about said depth of said sub-surface damage.
Inventors: |
Tan, Samantha; (Union City,
CA) |
Correspondence
Address: |
PERKINS COIE LLP
P.O. BOX 2168
MENLO PARK
CA
94026
US
|
Family ID: |
22841292 |
Appl. No.: |
10/961572 |
Filed: |
October 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10961572 |
Oct 8, 2004 |
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09927263 |
Aug 10, 2001 |
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6810887 |
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60224582 |
Aug 11, 2000 |
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Current U.S.
Class: |
510/175 ; 134/26;
134/34 |
Current CPC
Class: |
B44C 1/22 20130101; B08B
3/00 20130101; C11D 7/08 20130101; B08B 3/12 20130101; C11D 11/0047
20130101; B44C 1/227 20130101; H01L 21/67253 20130101; B08B 3/08
20130101; Y10T 436/12 20150115; C11D 3/3947 20130101; C23C 16/4407
20130101; Y10S 134/902 20130101 |
Class at
Publication: |
510/175 ;
134/026; 134/034 |
International
Class: |
B08B 003/00; C11D
001/00 |
Claims
What is claimed is:
1. A process for cleaning semiconductor fabrication equipment parts
comprising: determining a definition for a clean part including
multiple maximum acceptable impurity levels; determining an initial
multiple impurity levels of a part prior to its cleaning;
determining a cleaning process to apply to the part; applying the
cleaning process to the part, wherein the cleaning process creates
reduced multiple impurity levels for the part below that of said
initial multiple impurity levels; determining said reduced multiple
impurity levels; comparing said reduced multiple impurity levels
against said multiple maximum acceptable impurities levels of said
definition; and repeating the application of said cleaning process
to said part if said reduced multiple impurity levels do not meet
said definition of a clean part.
2. A process as recited in claim 1, further comprising testing the
part in reassembled equipment in which the part was designed to
operate.
3. A process as recited in claim 2, further comprising the
operation of repeating a cleaning process on the part if the part
does not function properly in the reassembled equipment.
4. A process as recited in claim 1, wherein at least one impurity
level is determined utilizing a surface particle test.
5. A process of claim 1, wherein at least one impurity level is
determined using a liquid particle test.
6. A process of claim 1, wherein at least one impurity level is
determined by using acid-extraction ICP-MS.
7. A dilute aqueous cleaning solution for parts comprising:
0.5-1.5% wt. HF; 0.1-0.5% wt. HNO.sub.3; and 1-10% wt
H.sub.2O.sub.2.
8. A dilute aqueous cleaning solution as recited in claim 7 wherein
the concentration of H.sub.2O.sub.2 is no greater than about 5%
wt.
9. A method for reducing sub-surface damage to a part comprising:
determining how deep is the sub-surface damage beneath a surface of
a part; chemically etching said surface of said part; and stopping
said chemical etching of said surface at about said depth of said
sub-surface damage.
10. A method for cleaning a part comprising: performing an
ultrasonication cleaning process to a surface of a part to be
cleaned; spray rinsing said part with a dilute chemical mixture;
and spray rinsing said part with deionized water.
11. A method for cleaning a part as recited in claim 10 further
comprising repeating said spray rinsing of said part with a dilute
chemical mixture and spray rinsing said part with deionized water
based upon the specification of purity for said part.
12. A method for determining contamination of an openable part
having inner surfaces comprising: introducing a part into a
controlled clean environment of at least class 1000; opening said
part in said controlled clean environment; and running
contamination analysis on said inner surfaces of said part.
13. A method for determining contamination as recited in claim 12
where running contamination analysis includes applying a known
volume of ultra pure water to a cavity of a part, extracting said
water, and analyzing contaminants found in said water.
14. A method for determining contamination as recited in claim 12
where running contamination analysis includes applying a known
volume of a high purity extraction solution to a cavity of a part,
extracting said extraction solution, and analyzing contaminants
found in said extraction solution.
15. A method for cleaning ceramic parts comprising: immersing a
ceramic part into a first chemical bath to damage contaminant
bonds; heating said ceramic part in a furnace after said
contaminant bonds are damaged; and immersing said ceramic part in a
second chemical bath to remove contaminants.
16. A method for cleaning ceramic parts as recited in claim 15
wherein said first chemical bath is a dilute chemical bath
including HF and HNO.sub.3 which is heated to about 60-80.degree.
C.
17. A method for cleaning textured quartz parts comprising:
immersing a textured quartz part into an ultrasonic chemical bath;
immersing said textured quartz part into an ultrasonication water
bath; and immersing said textured quartz part into a deionized
water bath.
18. A method for cleaning metallic impurities from textured ceramic
surfaces comprising: immersing a ceramic part having a textured
surface into a heated chemical bath; rinsing said ceramic part in
deionized water; immersing said part in a dilute acid bath and
rinsing; visually inspecting said part; and repeatedly immersing
said part in said dilute acid bath until it passes visual
inspection.
19. A method for cleaning metallic impurities as recited in claim
18 further comprising: immersing said part in an ultrasonification
overflowing bath.
20. A method for determining the cleanliness of semiconductor
fabrication equipment parts comprising: testing the parts before a
cleaning process for at least one of particles, metallic impurities
and organics; testing the parts after certain steps in the cleaning
process for at least one of particles, metallic impurities and
organics; and testing the parts after a final cleaning step for at
least one of particles, metallic impurities and organics.
21. A method for removing particles on a textured surface of a
semiconductor fabrication equipment part comprising: determining a
chemical bonding characteristic of the particles; identifying a
type of particles embedded in the textured surface; measuring a
depth of any subsurface damage; and performing a combination of
ultrasonication and chemical etching to the textured surface based
upon said chemical bonding characteristics, said type of particles
and said depth of subsurface damage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of provisional
application U.S. Serial No. 60/224/582 (Atty. Docket No.
60081-300500), filed on Aug. 11, 2001, entitled "System and Method
for Cleaning Semiconductor Fabrication Equipment Parts",
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The commercial fabrication of semiconductor chips is
performed on silicon wafer substrates, which are typically four to
twelve inches in diameter. There are often more than 100 processing
steps in the fabrication of semiconductor chips including
oxidation, diffusion, ion implantation, deposition of conductors
and insulators, photolithography, and etching. Various conducting
and insulating layers are deposited uniformly over the wafer to a
thickness of a few microns.
[0003] In critical applications, certain new parts of semiconductor
processing equipment need to be cleaned prior to installation and
use in order to remove residual contamination from the machining or
manufacturing process in order to achieve levels of cleanliness
similar to the semiconductor wafer itself. Furthermore, after many
wafers have been processed, the equipment used in the semiconductor
processing process becomes contaminated, and therefore unusable.
For example, in an etching machine, polymer deposits on the outer
circumference of electrodes or chucks supporting the wafers until
it becomes thick enough to interfere with the wafer's contact with
the electrode. This results in non-uniform etching across the wafer
as well as missed transfers due to a wafer sticking to polymer
buildup on the electrode. Non-uniformity exceeding seven percent is
beyond some specified limits, in turn affecting side wall profile
variance across the wafer. In addition, other components in the
equipment chamber e.g. roofs/domes and liners are also coated with
polymers and contaminants which contribute particles, metallic and
organic impurities to the wafers. Therefore, it is then necessary
to disassemble the parts in the equipment chamber and clean the
individual parts.
[0004] Generally, semiconductor manufacturing plants employ
specialized cleaning houses to have the semiconductor processing
equipment parts cleaned. These cleaning houses typically clean the
equipment by following "recipes," given to them by the manufacture
of the equipment. These recipes generally include information
informing the cleaning house how to clean the parts. Since, there
are many variations to the wafer processes, the polymer and
contamination levels of a used chamber part is different,
therefore, merely following one cleaning recipe does not always
result in the part being cleaned. In addition, after following the
cleaning recipe, a conventional cleaning house generally will not
test the parts to ensure its cleanliness. In general, a
conventional cleaning house has no idea as to the effectiveness of
the cleaning process provided to them in the recipe.
[0005] The result of following cleaning recipes in this manner, is
that many semiconductor parts are returned to the semiconductor
manufacturing plant still contaminated with unacceptable levels of
impurities. This results in contamination that may be transferred
onto a wafer typically in the form of high particle counts, or in
inoperable equipment that must again be disassembled for
re-cleaning, thus further increasing the down time for the
equipment.
[0006] In view of the forgoing, what is needed are methods and
systems for enhanced cleaning and certification of semiconductor
fabrication equipment. The methods should be flexible, and
consistent enough to minimize or eliminate contamination from the
equipment, to improve the mean time between cleanings (MTBC), to
improve the number of RF hours run on a chamber set of parts and to
reduce the downtime experienced by most semiconductor fabrication
equipment.
[0007] With the ability to test and verify the effectiveness of
cleaning procedures, new cleaning methods can be developed for
critical chamber parts. Critical chamber parts are usually
constructed from base materials such as ceramics (Al.sub.2O.sub.3,
SiC, AlN) and quartz (SiO.sub.2). Chamber parts manufactured from
these base materials are very expensive and are selected because of
they are non-contaminating with respect to metallics, organics and
particles. With new cleaning methods, these critical chamber parts
can be effectively cleaned and recycled to reduce manufacturing
cost.
[0008] Typically, in the prior art, relatively high concentrations
of acids and other cleaning agents were used to clean parts. For
example, a typical acid bath for quartz cleaning would include 1
part HF, 1 part HNO.sub.3, and 1 part H.sub.2O. Unfortunately, such
high concentration solutions suffer from a number of drawbacks. For
one, they can damage the surface of part being cleaned by scoring,
etching, pitting, etc. Further, these high concentration solutions
tend to be expensive, hazardous, and difficult to dispose of.
SUMMARY OF THE INVENTION
[0009] The present invention addresses these needs by providing a
process for enhanced semiconductor fabrication equipment and parts
cleaning. In one embodiment, a definition is determined that
defines the characteristics for a clean part. Next, a part to be
cleaned is tested to determine its incoming impurity levels. A
cleaning process is then determined that is capable of reducing the
incoming impurity levels for a particular part, depending on the
type of base material the part is made from, the deposits on the
part, and characteristics of adhesion, particle generation and
reactivity. The appropriate cleaning process is then applied to the
part so that it reduces the incoming level of impurities on the
part, and tested to ensure that the part is clean. There are
various types of impurities, but typically they fall into the
categories of metals, particles, and organic organics.
[0010] Advantageously, one embodiment of the present invention
reduces the cleaning defects by use of repeated testing of the
impurity levels after each pass through the cleaning process.
Moreover, by knowing the characteristics of a clean part through
testing, the process of the present invention can achieve
particular impurity level goals with increased accuracy, and the
part can be certified to meet an actual specification based on
either the need for cleanliness in the semiconductor process, or
based on statistically significant test data. Finally, the process
may be continuously optimized to further enhance the cleaning
process by direct testing of the cleanliness of the part, by
correlating to number of "added" particles and RF hours that the
parts can be used before particles increase to unacceptable limits,
and ultimately by correlating to improved wafer yield.
[0011] Using the dual concepts of in-process testing of the
cleanliness of a part for improved cleaning performance, and
testing the cleaned part after the final cleaning, a cleaning
method can be customized, optimized, and validated for each
critical part.
[0012] Advantageously, dilute chemistries can be used in preferred
embodiments of the present invention. This makes the cleaning
process less expensive. Used chemicals are also easier to dispose
of because the percentage of acids is much lower which also in turn
makes it less hazardous. Additionally, there is less damage to the
product. The present invention further includes methodologies to
determine optimal chemistries which are effective, yet dilute.
[0013] These and other advantages of the present invention will
become apparent upon a study of the following descriptions and
related drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1A is a flowchart showing a general process guideline
for cleaning semiconductor fabrication equipment parts.
[0015] FIG. 1B is a flowchart showing a process for cleaning
semiconductor fabrication equipment parts, for example high purity
quartz, in accordance with an embodiment of the present
invention.
[0016] FIG. 2 is a flowchart showing a process for cleaning high
purity quartz in accordance with another embodiment of the present
invention.
[0017] FIG. 3 is a flowchart showing a surface particle test
process for impurity level testing of a new or clean part, in
accordance with one embodiment of the present invention.
[0018] FIG. 4 is a flowchart showing a liquid particle test process
of a new or clean part, in accordance with an embodiment of the
present invention.
[0019] FIG. 5 is a flowchart showing an acid extraction/ICP-MS
technique of a new or clean part, in accordance with an embodiment
of the present invention.
[0020] FIG. 6 is a flowchart showing a cleaning process 110, in
accordance with one aspect of the present invention, to remove
resistant organic polymer and metallic impurities from a high
purity ceramic dome.
[0021] FIG. 7 is a flowchart showing a cleaning process 110, in
accordance with one aspect of the present invention to remove
particle from a textured high purity quartz surface.
[0022] FIG. 8 is a flowchart showing a cleaning process 110, in
accordance with one aspect of the present invention to remove
particle and metallic impurities from a textured high purity
ceramic (>99% Al.sub.2O.sub.3) surface.
[0023] The invention, together with further advantages thereof, may
best be understood by reference to the following description taken
in conjunction with the accompanying drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0024] An invention is described herein for cleaning semiconductor
equipment parts (such as CVD and etch chamber parts) that achieve
increased effectiveness in impurity removal. In the following
description, numerous specific details are set forth in order to
provide a thorough understanding of the present invention. It will
be apparent, however, to those skilled in the art, that the present
invention may be practiced without some or all of these specific
details. In other instances, well known process steps have not been
described in detail in order not to unnecessarily obscure the
present invention. In particular, this includes most of the
analytical testing methods used to measure or confirm impurity
levels.
[0025] In accordance with one aspect of the present invention, the
aforementioned metallic impurity removal is substantially enhanced
by the use of a new chemical formula in the various cleaning
processes. This cleaning formula is particularly novel as applied
to the cleaning of polysilicon, quartz, and ceramic parts
(Al.sub.2O.sub.3, SiC and AlN) for which it has proven to be quite
effective. Specifically, the cleaning formula is a composition of
high purity hydrofluoric acid (HF), nitric acid (HNO.sub.3), and
hydrogen peroxide (H.sub.2O.sub.2), in very dilute quantities.
Preferably, the composition includes 0.5-1.5% wt. HF, 0.1-0.5% wt.
HNO.sub.3, and 1-10% wt. H.sub.2O.sub.2. This particular formula
results in a particularly efficient collector of metals on certain
materials as described in greater detail subsequently. This high
purity cleaning and collection solution has been shown to have very
high recoveries and efficiencies, especially on single crystal
silicon wafer surfaces, high purity quartz, polysilicon, and
ceramics. Previously, these materials were cleaned with
concentrated chemicals mixtures of HF/HNO.sub.3, and HCl/HNO.sub.3
at much higher concentration of 10%40% wt for each chemical. The
chemical H.sub.2O.sub.2 is not employed in these mixtures. The high
concentrations of the chemical mixtures did not improve metallic
removal and can severely etched and damaged the base materials. It
is shown that the high purity dilute chemical formula in this
invention is highly effective in removing metallic contaminants and
will not etch any of the aforementioned base materials for more
than a few hundred angstroms.
[0026] It will therefore be appreciated that a dilute aqueous
cleaning solution for parts can be made up of 0.5-1.5% wt. HF,
0.1-0.5% wt. HNO.sub.3 and 1-10% wt H.sub.2O.sub.2. The
concentration of H.sub.2O.sub.2 can also be no greater than about
5% wt.
[0027] Metallic contaminants form bonds with the surfaces of the
semiconductor fabrication equipment parts, thus bonding the metal
impurities to the surfaces of the equipment. These chemical bonds
create increased difficulty in cleaning the parts without the use
of correct chemical formulations. If the chemical formulations are
too concentrated, the semiconductor equipment parts can be
irreversibly destroyed or are not sufficiently cleaned.
[0028] The chemical formula of the present invention substantially
enhances the cleaning process by breaking the chemical bonds and
thereafter collecting the metal impurities. To elaborate further,
the hydrofluoric acid breaks silicon and aluminum bonds by
dissolving the silicon and aluminum oxides of the surface of the
semiconductor equipment. This frees the metal impurities and allows
them to be collected in the cleaning solution. It should be borne
in mind that the amount of hydrofluoric acid must be carefully
controlled, as too much hydrofluoric acid results in damage to the
surface of the equipment parts. The use of HF is critical in
semiconductor parts cleaning because silicon and aluminum oxides
are prevalent impurities in all types of parts.
[0029] The hydrogen peroxide is a strong oxidizer and is used to
convert the metals such as Cu, Au and Ag into the soluble forms.
Therefore, the presence of H.sub.2O.sub.2 greatly increases the
range of metal impurities that can be removed from a surface.
[0030] Finally nitric acid is used to stabilize and increase the
solubility of some metal impurities so that insoluble fluorides of
Ca and Mg are kept in the solution and away from the surface of the
semiconductor equipment parts. In this technique, it is preferable
to have the solution as dilute as possible, yet still effective to
clean the equipment parts to predefined specifications. The above
mentioned ranges are thus the preferred minimums needed to clean
the equipment.
[0031] The chemical formula of the present invention is used to
perform various cleaning processes for semiconductor equipment
parts and other high purity material applications. In one
embodiment, this formula has been shown to be quite effective in
cleaning metal ions from high purity quartz, as is commonly found
as rods, tubes, crucibles, domes, chambers and bell jars. In
another embodiment, this formula has been shown to be quite
effective in cleaning metal ions from high purity polysilicon and
single crystal silicon surface, as is commonly found in chamber
roofs, source rings, collars and wafers respectively. In another
embodiment, this formula has been shown to be quite effective in
cleaning metal ions from high purity ceramic materials
Al.sub.2O.sub.3 as found in chamber domes, bell jars, rings, gas
nozzle assemblies and wafer chucks; SiC as found in chamber roofs,
domes, rings and collars; and AlN as is commonly found in wafer
chucks.
[0032] In accordance with another aspect of the present invention,
the aforementioned particle impurities are removed from the
semiconductor equipment surface by chemical treatments. Most
semiconductor equipment parts fabricated from the aforementioned
critical base materials are textured by grit blasting in order to
improve process polymer adhesion. After machining and texturing,
the parts are cleaned to remove particles. There are two categories
of particles on the textured surface. The first type is surface
particles that are loosely adhering. These particles can be removed
physically by a short ultrasonication step. The origin of the
second category of particles is less obvious. These particles
originated from the weakened base material surface caused by
texturing. In the process chamber, sub-surface damages are often
exaggerated during wafer processing causing particle shedding.
[0033] The chemical formula of the present invention significantly
reduces the particles from textured equipment parts by etching off
a layer of damaged base materials without affecting the desired
surface roughness. First, the depth of the subsurface damage is
determined using any one of a number of well-known techniques.
Using concentrated basic solutions such as 10-30% wt KOH and NaOH
in water, base materials such as polysilicon base materials can be
etched off to a predetermined depth (i.e. to about the depth of the
measures subsurface damage) by controlling temperature and time to
remove all the sub-surface damages. Using concentrated acidic
solutions such as H.sub.2SO.sub.4/H.sub.2O.sub.- 2 and
H.sub.2SO.sub.4/H.sub.3PO.sub.4 in the range of 10-50% wt for each
chemical, ceramic materials (Al.sub.2O.sub.3, SiC and AlN) can be
etched off to a predetermined depth by controlling temperature and
time to removed all the sub-surface damages. In another application
with quartz, the use of HF/HNO.sub.3, 20-40% wt for each chemical
in water, used with ultrasonic energy (27-120 kHz) for 10-20 mins
is found to effectively etched off damaged quartz material
resulting from grit-blasting and particle counts can thereby be
drastically decreased.
[0034] In accordance with another aspect of the present invention,
the aforementioned organic polymer deposited on semiconductor
equipment surface during wafer processing can be removed from all
type of critical materials surface by a thermal decomposition step.
Organic polymers are often found in etch equipment parts. These
organic polymers can be efficiently removed by submitting dirty
quartz and Al.sub.2O.sub.3 parts to a high temperature of
600-800.degree. C. for 1-10 hours depending on how thick or
resistance the organic polymer to cleaning. A high temperature
muffle furnace is used for this purpose.
[0035] In another embodiment, disassembled semiconductor
fabrication equipment parts are subjected to cleaning processes and
testing to achieve enhanced impurity removal, as described in
greater detail subsequently.
[0036] FIG. 1A is a flowchart showing a general process guideline 5
for cleaning semiconductor fabrication equipment parts. The process
starts at operation 10 and proceeds to operation 20 where a
baseline chemistry is developed for cleaning the part. In operation
30, the part is cleaned with the baseline chemistry. In operation
40, the effectiveness of the cleaning process is tested. If it is
not sufficient, operation 50 is performed where the chemistry is
adjusted to improve the cleaning ability and the part is re-cleaned
at operation 30. If the first cleaning was effective, the process
ends at operation 60.
[0037] In operation 50, the chemistry can be adjusted in various
ways. For example, the chemistry can be changed by adding or
deleting acids, oxidizers, etc. It can also be adjusted by
increasing the concentration of the solution, or by making the
solution more dilute. The purpose of operation 50 is, therefore, to
optimize the chemistry to provide the most effective, least
damaging, most economical, and least hazardous solution to cleaning
the part.
[0038] FIG. 1B is a flowchart showing a process 100 for cleaning
semiconductor fabrication equipment parts, for example high purity
quartz, in accordance with an embodiment of the present invention.
In an initial operation 102, pre-process operations are performed.
Pre-process operations include preparing and testing facility
configurations and other pre-process operations that will be
apparent to those skilled in the art. In particular, pre-process
operations can include establishing environmental controls (e.g.
particles and metals in the environment), qualifying RO/DI high
purity water, establishing "new" handling protocols, and setting up
fixturing process.
[0039] In a specification operation 104, the specification for what
constitutes a clean part is determined. As indicated previously,
conventional cleaning houses generally follow a recipe given to
them by a manufacturer. For example, a cleaning recipe from a
manufacturer may include rinsing a part in deionized water,
immersing it in a particular chemical mixture, etc. In the present
invention, instead of merely following a cleaning recipe, a
specification for a clean part is determined. The specification
characterizes what the minimum parameters are for a particular part
to be considered clean enough to achieve the required wafer
performance.
[0040] A specification may be obtained from another party, such as
the party owning the part to be cleaned, or the specification may
be determined by testing. There are three ways to create a
specification through testing. In the first approach a part is
first obtained that is already known to be clean, i.e., has the
minimum parameters to be considered clean, for example a new part.
The part is then tested and characterized with respect to
particles, metals, organics, or any combination thereof. When
characterizing with respect to particles, the surface of the part
is examined with respect to particles using several different
analytical techniques which may include the Dryden QIII surface
particle counter, a liquid particle counter (LPC), or Scanning
Electron Microscopy (SEM) or SEM with Energy Dispersive X-ray
detection (SEM/EDX). When characterizing with respect to metals,
the surface is examined through sophisticated analytical chemistry
testing methods with respect to surface metal contamination, bulk
metal contamination, or both. When examining the part with respect
to bulk metal contamination, a portion of the material is digested
in a solution to measure the impurities within the material. With
respect to surface metal contamination, metals are extracted from
the surface, normalized to the surface area, and measured by
spectroscopic techniques such as inductively coupled plasma-mass
spectrometry (ICP-MS). When characterizing the part with respect to
organics, surface extractions may be made using DI and solvents
that are then analyzed by a total organic carbon analyzer (TOC) and
Gas Chromatography (GC) or Gas Chromatography with Mass
Spectrometry (GCMS) respectively. Alternately or additionally, the
entire material may be outgassed at a high temperature with the
resulting gasses being analyzed by dynamic head space GC-MS or ATD
GC-MS.
[0041] In the second approach, new or used parts are cleaned using
the best known cleaning methods based on historical or theoretical
considerations. After the cleaning process is applied, the part is
tested for impurities. The part is then assembled into the
semiconductor process equipment and chamber process data is
collected. Process data may include 1) particles added ("adders")
to a silicon wafer surface after being in contact with the process
equipment containing the clean part; 2) metal impurities
transferred onto a silicon wafer surface after being processed in
the semiconductor equipment containing the clean part; 3) mean
number of wafers between cleanings; etc. Such chamber process data
can then be correlated to analytical impurity test data from the
cleaned part itself. In this way cleaning methods and formulas can
be developed or improved based on the correlation between the test
data from the analytical impurity testing on the part and the data
generated after running a wafer in the process chamber. Moreover, a
specification can be set after evaluation of the chamber process
performance parameters.
[0042] In the third approach, specifications can be set by
collecting impurity test data on a statistically significant number
of parts that has proven to perform well in the semiconductor
process. Control limits can also be established by collecting test
data on a statistically significant number of parts.
[0043] Next, in an operation 106, the incoming impurity level for
the part is determined. In this operation, a part is tested to
determine the current impurity level of the part with respect to
metals, particles, or organics. For particles, this determination
is made by performing either a surface particle test or a liquid
particle count test, as described in greater detail subsequently.
Depending on the type of test utilized to determine the particle
level, the particle impurities are described as either particles
per cm.sup.2 or particles per volume of solution. The incoming
trace metal impurities are typically measured using acid extraction
ICP-MS technique, the metallic levels are described as
atoms/cm.sup.2 or ng/cm.sup.2. The incoming impurity levels for
organics are measured using GC, GCMS, or ATD GCMS and the organic
levels are described as atoms/cm.sup.2 or ng/cm.sup.2 for trace
concentration or % surface concentration for major concentration.
SEM/EDX maybe used semi-quantitatively for the determining of major
elements such as those present in the process polymers, the
elements being C, F, Cl, Al Si and O.
[0044] In a surface determination operation 108, the surface of the
part is characterized. Generally, this operation determines the
characteristics of the material. These characteristics include the
desired surface finish as well as surface roughness.
[0045] Referring next to operation 110, a mechanical and chemical
process that will meet the clean specification of the part is
determined. Depending on the material, size, condition, and
specification of the part being cleaned, a mechanical and chemical
process is determined that will clean the part to the predefined
clean specification of operation 104. For example, a process for
cleaning a quartz part is disclosed subsequently. Once determined,
the chemical and/or mechanical processes are applied to the
part.
[0046] After cleaning, the part is again tested to determine the
impurity level of the part, in operation 112. This operation is
performed much the same as operation 106, the difference being that
operation 112 is carried out after the part is cleaned.
[0047] A determination is then made as to whether the clean
specification has been met, in operation 114. Essentially, the
results of the impurity level determination operation 112 are
compared to the specification, determined in operation 104. If the
specification has been met, the process continues with an equipment
testing operation 116. However, if the specification is not met,
the process continues with another process determination operation
110.
[0048] Thus, the present invention, with respect to metal
impurities, utilizes a sequential approach to cleaning
semiconductor equipment parts. In this manner, the cleaning process
is repeated until the impurity level is brought down to an
acceptable level. Essentially, the impurity levels are brought down
by orders of magnitude in a stepwise fashion. In addition, the
cleaning processes can be optimized with each pass through the
process, based on the measurement of the impurity levels.
[0049] In an equipment test operation 116, the clean equipment part
is installed and operated with the process for manufacturing
semiconductor devices and the wafers are measured for contaminants
after being run in the process as an indication of the purity of
the materials in the chamber. Particularly, the number of particles
added to the wafer after running the process and the impurities on
the wafers are considered indicies.
[0050] A decision is then made as to whether the part functions
properly in its related equipment, in operation 118. If the part
functions properly, the process is completed in a finishing
operation 120. Otherwise, the process continues with another
process determination operation 110.
[0051] Finally, in a finishing operation 120, the cleaning process
is completed and the cleaned part may be put back into production.
Advantageously, the present invention reduces cleaning defects by
repeated testing of the impurity levels after each pass through the
cleaning process. Moreover, by knowing the characteristics of a
clean part, the process of the present invention can achieve
specified results with increased accuracy. Finally, the cleaning
process may by continuously optimized to achieve a cleaning process
that cleans close to 100% of the parts from a particular
process.
[0052] An important feature of the present invention is the use of
analytical testing. As described previously, conventional cleaning
is done with little or no testing of the part itself. The most
testing typically done in conventional cleaning is testing of the
resistivity of the rinse water used in a conventional cleaning
process or of the concentrations of the acid baths. In contrast,
the present invention consistently test the impurity levels of the
semiconductor parts after being cleaned, as described in greater
detail with respect to FIG. 3.
[0053] In view of the foregoing, it will be appreciated that a
process for cleaning semiconductor fabrication equipment parts
includes determining a definition for a clean part including
multiple maximum acceptable impurity levels, determining an initial
multiple impurity levels of a part prior to its cleaning,
determining a cleaning process to apply to the part, applying the
cleaning process to the part, wherein the cleaning process creates
reduced multiple impurity levels for the part below that of the
initial multiple impurity levels, determining the reduced multiple
impurity levels, comparing the reduced multiple impurity levels
against the multiple maximum acceptable impurities levels of said
definition, and repeating the application of the cleaning process
to the part if said reduced multiple impurity levels do not meet
the definition of a clean part.
[0054] The process can also include testing the part in reassembled
equipment in which the part was designed to operate and repeating a
cleaning process on the part if the part does not function properly
in the reassembled equipment.
[0055] Also the process can include at least one impurity level
which is determined utilizing a surface particle test. The impurity
level can also be determined by using a liquid particle test. Also,
one or more impurity levels can be determined by using
acid-extraction ICP-MS technique.
[0056] FIG. 2 is a flowchart showing a process for cleaning high
purity quartz in accordance with another embodiment of the present
invention. FIG. 2 shows a process 200 that progresses through the
following acts or operations. In 210 the part is degreased with
solvents such as IPA/acetone and is sprayed rinse with DI water or
alternately ultrasonicated in DI water. In 212 the part is cleaned
by either a spray or squirt rinse with the aforementioned high
purity cleaning formula. In 214 the cleaning solution used in 212
is discarded. In 216 the acts or operations of 212 and 214 are
repeated, where the number of repeats is a function of
specification level of purity. In 218 another DI water
ultrasonication and spray rinse of the quartz part is performed. In
220 the part is allowed to dry under heat lamps within a controlled
HEPA/ULPA filtration cleanhood located in a cleanroom. In 222
testing is performed for surface metals and/or surface particles.
In 224 impurity data is collected. And in 226 the quartz part is
packaged in a cleanroom or similar controlled environment.
[0057] It will therefore be appreciated that a method for reducing
sub-surface damage to a part includes determining how deep is the
sub-surface damage beneath a surface of a part, chemically etching
the surface of the part and stopping the chemical etching of the
surface at about the depth of the sub-surface damage.
[0058] Also, a method for cleaning a part includes performing an
ultrasonication cleaning process to a surface of a part to be
cleaned, spray rinsing the part with a dilute chemical mixture and
spray rinsing the part with deionized water. The method can also
include repeating the spray rinsing of the part with a dilute
chemical mixture and spray rinsing the part with deionized water
based upon the specification of purity for the part.
[0059] FIG. 3 is a flowchart showing a surface particle test
process 300 for impurity level testing of a new or clean part, in
accordance with one embodiment of the present invention. In an
initial operation 301, pre-process operations are performed.
Pre-process operations include determining the specification of
characteristics for a clean part, and other pre-process operations
that will be apparent to those skilled in the art. This process is
applicable, for example, to operations 1-6 and 112 of FIG. 1.
[0060] Next, in a cleanroom operation 302, the semiconductor
equipment part to be measured is opened in a class 1000 cleanroom
or better (1000 particles per cubic centimeter). Upon being
disassembled, semiconductor equipment part is packaged for delivery
to the cleaning center. To avoid further contamination of a new or
clean part, it is preferable to open the part in a controlled clean
environment. In 304 the input of the particle counter is scanned
over the part over a specified distant. In 306 an analysis of the
part is begun using clean handling techniques. In 308 impurity data
is collected after stabilization, and in 310 the data is processed.
The process is completed in 312.
[0061] FIG. 4 is a flowchart showing a liquid particle test process
400 of a new or clean part, in accordance with an embodiment of the
present invention. In an initial operation 401, pre-process
operations are performed. Pre-process operations include
determining the specification of characteristics for a clean part,
and other pre-process operations that will be apparent to those
skilled in the art. This process is applicable, for example, to
operations 1-6 and 112 of FIG. 1.
[0062] Next, in a cleanroom operation 402, the semiconductor
equipment part to be cleaned is opened in a cleanroom. Upon being
disassembled, semiconductor equipment is packaged for delivery to
the cleaning center. To avoid further contamination of the part, it
is preferable to open the part in a controlled clean
environment.
[0063] In a UPW control operation 404, the particles currently
present in the ultra pure water are measured. The liquid particle
test process 400 uses ultra pure water (UPW) as the carrier medium
to determine the impurity level for a particular semiconductor
equipment part. As a control, the level of particles present in the
UPW is determined before the part is placed in the water.
Subsequently, the new part can be ultrasonicated to dislodge
particles that are adhered to its surface into the UPW. The UPW can
then be retested, with the particle count difference being
attributable to the part itself.
[0064] In a UPW application operation 406, a known volume of the
UPW is applied to a cavity of the part to be analyzed. The cavity
of the part is essentially the area of the part which provides the
best test area for analyzing the impurity level of the part.
[0065] Next, in a UPW extraction operation 408, the UPW is
extracted from the part and introduced into a liquid particle
counter. After introducing the UPW to the cavity of the part, the
UPW gathers particles from the surface of the part. Thus, by
knowing the particle level of the UPW before being introduced into
the cavity of the part, and then measuring the amount of particles
in the UPW after being introduced into the cavity of the part, the
impurity level of the part can be determined.
[0066] The analysis of the impurity level for the part is then
begun, in an analysis operation 410.
[0067] Then, after the liquid particle counter stabilizes, the
impurity level data is collected, in a data collection operation
412. Initially, the data is collected in particle size. Thereafter,
the data is normalized over the surface area of the semiconductor
part being analyzed.
[0068] The impurity level data is then processed in a data
processing operation 414. The particles are measured both in terms
of size distribution and quantity. The quantity could be in
thousands of counts down to single digits. The distribution can be
as low as about 0.05 microns up to about 10 microns. Preferably,
the particle counts are "bucketed" into specified size ranges of
interest to assist in analysis. The result is the number of
particles per volume of solution or particles per cm.sup.2.
[0069] Finally, post-process operations occur in operation 416.
Post-process operations include using the impurity level
information to aid in further processing of the part and other
post-process operations that will be apparent to those skilled in
the art.
[0070] In view of the foregoing, a method for determining
contamination of an openable part having inner surfaces includes
introducing a part into a controlled clean environment of at least
class 1000, opening the part in the controlled clean environment
and running contamination analysis on the inner surfaces of the
part.
[0071] The method can also include applying a known volume of ultra
pure water to a cavity of a part, extracting the water, and
analyzing contaminants found in the water. The method can
additionally include applying a known volume of a high purity
extraction solution to a cavity of a part, extracting the
extraction solution, and analyzing contaminants found in the
extraction solution.
[0072] FIG. 5 is a flowchart showing an acid extraction/ICP-MS
technique 500 of a new or clean part, in accordance with an
embodiment of the present invention. In an initial operation 501,
pre-process operations are performed. Pre-process operations
include determining the specification of characteristics for a
clean part, and other pre-process operations that will be apparent
to those skilled in the art. This process is applicable, for
example, to operations 1-6 and 112 of FIG. 1.
[0073] Next, in a cleanroom operation 502, the semiconductor
equipment part to be cleaned is opened in a cleanroom. Upon being
disassembled, semiconductor equipment is packaged for delivery to
the cleaning center. To avoid further contamination of the part, it
is preferable to open the part in a controlled clean
environment.
[0074] In an acidic extraction control operation 504, the
analytical test process 500 uses a high purity extraction solution
(e.g. 1.25% wt HF, 3% wt H.sub.2O.sub.2 and 0.125% wt HNO.sub.3) to
determine the metallic impurity level for a particular
semiconductor equipment part. As a control, the level of metallic
impurities present in the extraction solution is determined by
ICP-MS. Subsequently, a selection area of the new part is extracted
with the high purity extraction solution. The extract is then
retested, with the metallic level difference being attributable to
the part itself.
[0075] In a operation 506, a known volume of the high extraction
solution is applied to a cavity of the part to be analyzed. The
cavity of the part is essentially the area of the part which
provides the best test area for analyzing the impurity level of the
part.
[0076] Next, in a operation 508, the high purity extraction
solution is extracted from the part and introduced into an ICP-MS.
After introducing the high purity extraction solution to the cavity
of the part, the extraction solution gathers metallic impurities
from the surface of the part. Thus, by knowing the metallic level
of the extraction solution before being introduced into the cavity
of the part, and then measuring the amount of particles in the
extraction solution after being introduced into the cavity of the
part, the impurity level of the part can be determined. The acid
extraction/ICP-MS technique is then completed with operation
510.
[0077] The analysis of the impurity level for the part is then
begun, in an analysis operation 510.
[0078] Then, after the ICP-MS stabilizes, the impurity level data
is collected, in a data collection operation 512. Initially, the
data is collected in ppbw (parts per billion wt). Thereafter, the
data is normalized over the surface area of the semiconductor part
being analyzed.
[0079] The impurity level data is then processed in a data
processing operation 514. The metallic impurities are measured both
in terms of concentration in ppbw for each type of trace metals.
The area of the part that is extracted is calculated and the result
is normalized atoms per cm.sup.2 or ng/cm.sup.2.
[0080] Finally, post-process operations occur in operation 516.
Post-process operations include using the impurity level
information to aid in further processing of the part and other
post-process operations that will be apparent to those skilled in
the art.
[0081] FIG. 6 is a flowchart showing a cleaning process 600, in
accordance with one aspect of the present invention, to remove
resistant organic polymer and metallic impurities from a high
purity ceramic dome (>99% Al.sub.2O.sub.3). In an initial
operation 601, pre-process operations are performed. Pre-process
operations include determining the particular characteristics of
the part to be processed and other pre-process operations that will
be apparent to those skilled in the art.
[0082] In operation 602, the ceramic dome is DI water sprayed rinse
to remove loose polymers, particles and metallic impurities.
Initially, the ceramic dome is unpacked, recorded, and photographed
to record the initial condition of the dome. The ceramic dome is
then placed in a chemical bath 603 for about 2 hours. The chemical
bath is preferably an dilute HF/HNO.sub.3 chemical bath, which is
heated to about 60-80.degree. C. The concentration of HF is less
than 5% wt and HNO.sub.3 is less than 10% wt. The hot acid
dissolves Si--O and Al--O bonds and breaks other metallic bonds.
Thereafter it is removed from the chemical bath, DI spray rinsed
and dried with a cleanroom wipe or with a heat lamp until no
moisture is observed on the inside or outside of the dome. It has
been found to be very important to do the pre-treatment step 603
before putting the part into the furnace in order to dissolve the
Si--O and Al--O bonds. This advantageously reduces the amount time
the part has to be in the furnace of the next operation.
[0083] In a heating operation 604, the dome is heated in a furnace.
In this operation, the dome is placed in a furnace and heated to
about 700-800.degree. C. for about 6-12 hours. After about 6-12
hours, the furnace is turned off. To avoid damage to the dome, the
furnace should generally not be opened until the temperature
reaches below 200.degree. C. Opening the furnace earlier may result
in the dome being cracked. After the temperature reaches below
200.degree. C., the furnace may be opened and allowed to cool to
below 80.degree. C. The dome is then withdrawn from the furnace
when the temperature reaches below 80.degree. C.
[0084] Next, in a bath operation 606, the dome is placed in another
chemical bath. The chemical bath is also an HF/HNO.sub.3 chemical
bath, which is heated to about 80.degree. C. The concentration of
HF and HNO.sub.3 is the same as the first bath but is kept clean
and is prepared from higher purity chemicals. The dome is placed in
the chemical bath for about 6-8 hours to dissolve any residual
carbon and silicon/aluminum oxides and any other metallic
impurities. After this step, it is placed in an acid waste tank and
rinsed with deionized water to remove any residual acids.
Thereafter, the dome is preferably visually inspected 607 to
determine the cleanliness of the part. If organic polymer is still
observed, the operations 604/606 are repeated.
[0085] In an ultrasonication operation 608, the dome is
ultrasonicated in deionized water. Once a visual inspection has
been made of the dome, it is ultrasonicated in a fresh overflowing
deionized water bath for about two hours. In the operation 610, the
dome is tested by LPC technique. As stated previously, this
impurity testing operation helps in determining whether the part
has been cleaned to have characteristics in accordance with the
predetermined clean specification. If the particle level as
measured by LPC technique is less than 400,000 particle per
cm.sup.2, the dome is then rinsed in deionized water approximately
10 times, and thereafter purged dry with filtered N.sub.2 and
further under a heat lamp 611 for at least 1 hour. The process 608
can be repeated if the dome has not attained the specified levels
of impurity.
[0086] The part is then further tested for impurities, in a testing
operation 612. Preferably, a surface particle test is performed on
the dome using a Dryden QIII particle counter. After testing
adequately to the predetermined specification, the part is packaged
with cleanroom double bags in the cleanroom.
[0087] Finally, in operation 614, various post-process operations
are performed. Post-process operations include testing the dome in
fully assembled semiconductor fabrication equipment, and other
post-process operations that will be apparent to those skilled in
the art. After the post-process operations are completed, process
600 is completed with operation 616.
[0088] It will therefore be appreciated that a method for cleaning
ceramic parts includes immersing a ceramic part into a first
chemical bath to damage contaminant bonds, heating the ceramic part
in a furnace after the contaminant bonds are damaged and immersing
the ceramic part in a second chemical bath to remove contaminants.
Also, the first chemical bath can be a dilute chemical bath
including HF and HNO.sub.3 which is heated to about 60-80.degree.
C.
[0089] FIG. 7 is a flowchart showing a cleaning process 700, in
accordance with one aspect of the present invention to remove
particle from a textured high purity quartz surface. In an initial
operation 701, pre-process operations are performed. Pre-process
operations include determining the particular characteristics of
the part to be processed and other pre-process operations that will
be apparent to those skilled in the art.
[0090] In an operation 702, the high purity quartz part is DI water
spray rinsed to remove loose polymers, particles and metallic
impurities. Initially, the quartz part is unpacked, recorded, and
photographed to record the initial condition of the dome. The
quartz part is then placed in a chemical bath 703 and
ultrasonicated for 15 min. The chemical bath is preferably a
concentrated HF/HNO.sub.3 chemical bath. The concentration of HF is
about 25% wt and HNO.sub.3 about 35% wt. The concentrated acid in
the presence of ultrasonication energy dissolves a layer of damaged
quartz to lower the particle counts on the quartz part surface.
Thereafter it is removed from the chemical bath and DI spray rinsed
in an operation 704.
[0091] Next, in a DI ultrasonication operation 706, the quartz is
ultrasonicated in deionized water to further remove particles. Once
a visual inspection 707 has been made of the quartz part, it is
ultrasonicated in a fresh deionized water bath 707A for 15 min. If
the part does not pass the visual inspection test, the part goes
back to operation step 703 for additional cleaning. In the
operation 708, the quartz is tested by LPC technique. As stated
previously, this impurity testing operation helps in determining
whether the part has been cleaned to have characteristics in
accordance with the predetermined clean specification. If the
particle level as measured by LPC technique is less than 200,000
particle per cm.sup.2, the quartz part is then rinsed in deionized
water approximately 10 times, and thereafter purged dry with
filtered N.sub.2 and further under a heat lamp for at least 1 hour
in an operation 710. The process 706 can be repeated if the dome
has not attained the specified levels of impurity.
[0092] The part is then further tested for impurities, in a testing
operation 712. Preferably, a surface particle test is performed on
the dome using a Dryden QIII particle counter. After testing
adequately to the predetermined specification, the part is packaged
with cleanroom double bags in the cleanroom.
[0093] Finally, in operation 714, various post-process operations
are performed. Post-process operations include testing the dome in
fully assembled semiconductor fabrication equipment, and other
post-process operations that will be apparent to those skilled in
the art. After the post-process operations are completed, process
700 is completed with operation 716.
[0094] FIG. 8 is a flowchart showing a cleaning process 800, in
accordance with one aspect of the present invention to remove
particle and metallic impurities from a textured high purity
ceramic (>99% Al.sub.2O.sub.3) surface. In an initial operation
801, pre-process operations are performed. Pre-process operations
include determining the particular characteristics of the part to
be processed and other pre-process operations that will be apparent
to those skilled in the art.
[0095] In an operation 802, the ceramic dome is DI water sprayed
rinse to remove loose polymers, particles and metallic impurities.
Initially, the ceramic dome is unpacked, recorded, and photographed
to record the initial condition of the dome. The ceramic dome is
then placed in a chemical bath 803 for about 2 hours. The chemical
bath is preferably a concentrated H.sub.2SO.sub.4/H.sub.2O.sub.2 or
H.sub.2SO.sub.4/H.sub.3PO.- sub.4 chemical bath, which is heated to
about 140-180.degree. C. The concentration of H.sub.2SO.sub.4 is
about 50% wt, H.sub.2O.sub.2 is about 15% wt and H.sub.3PO.sub.4
about 40% wt. The hot concentrated acid dissolves a layer of
damaged alumina to lower the particle counts on the dome surface.
Thereafter it is removed from the chemical bath and DI spray rinsed
in an operation 804.
[0096] Next, in a bath operation 806, the dome is placed in another
chemical bath. The chemical bath is a dilute HF/HNO.sub.3 chemical
bath. The concentration of HF and HNO.sub.3 is less than 5% wt and
10% wt respectively to remove metallic impurities. After this step,
it is placed in an acid waste tank and rinsed with deionized water
to remove any residual acids. Thereafter, the dome is preferably
visually inspected 807 to determine the cleanliness of the part. If
the part still needs more cleaning, operation 806 is repeated.
[0097] In an ultrasonication operation 808, the dome is
ultrasonicated in deionized water. Once a visual inspection has
been made of the dome, it is ultrasonicated in a fresh overflowing
deionized water bath for about two hours. In the operation 810, the
dome is tested by LPC technique. As stated previously, this
impurity testing operation helps in determining whether the part
has been cleaned to have characteristics in accordance with the
predetermined clean specification. If the particle level as
measured by LPC technique is less than 500,000 particle per
cm.sup.2, the dome is then rinsed in deionized water approximately
10 times, and thereafter purged dry with filtered N.sub.2 and
further under a heat lamp for at least 1 hour in an operation 812.
The process 808 can be repeated if the dome has not attained the
specified levels of impurity.
[0098] The part is then further tested for impurities, in a testing
operation 814. Preferably, a surface particle test is performed on
the dome using a Dryden QIII particle counter. After testing
adequately to the predetermined specification, the part is packaged
with cleanroom double bags in the cleanroom.
[0099] Finally, in operation 816, various post-process operations
are performed. Post-process operations include testing the dome in
fully assembled semiconductor fabrication equipment, and other
post-process operations that will be apparent to those skilled in
the art.
[0100] In view of the foregoing it will be appreciated that a
method for cleaning textured quartz parts includes immersing a
textured quartz part into an ultrasonic chemical bath, immersing
the textured quartz part into an ultrasonication water bath and
immersing said textured quartz part into a deionized water bath.
The method can also include immersing the part in an
ultrasonification overflowing bath.
[0101] It will further be appreciated that a method for determining
the cleanliness of semiconductor fabrication equipment parts
includes testing the parts before a cleaning process for at least
one of particles, metallic impurities and organics. The parts are
tested after certain steps in the cleaning process for at least one
of particles, metallic impurities and organics. The parts are
tested a final time after a final cleaning step for at least one of
particles, metallic impurities and organics.
[0102] Also, a method for removing particles on a textured surface
of a semiconductor fabrication equipment part includes determining
a chemical bonding characteristic of the particles, identifying a
type of particles embedded in the textured surface, measuring a
depth of any subsurface damage and performing a combination of
ultrasonication and chemical etching to the textured surface.
[0103] While the present invention has been described in terms of
several preferred embodiments, there are many alterations,
permutations, and equivalents which may fall within the scope of
this invention. It should also be noted that there are many
alternative ways of implementing the methods and apparatuses of the
present invention. It is therefore intended that the following
appended claims be interpreted as including all such alterations,
permutations, and equivalents as fall within the true spirit and
scope of the present invention.
* * * * *