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SEMI C34-0699 © SEMI 1981, 1999 MIXED ACID ETC H ANTS 2 ready a spectrophotometer and set the wavelength to 302 nm . T ransfer t he sample solution to a 1 c m fused silica cell and measure the absorban ce of the sample s…

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MIXED ACID ETCHANTS SEMI C34-0699 © SEMI 1981, 19991
SEMI C34-0699
SPECIFICATION AND GUIDELINE FOR MIXED ACID ETCHANTS
This specification and this guideline were technically approved by the Global Process Chemicals Committee
and are the direct responsibility of the North American Process Chemicals Committee. Current edition
approved by the North American Regional Standards Committee on April 23, 1999. Initially available on
SEMI OnLine May 1999; to be published June 1999. This document replaces SEMI C2.1 and C7.19 in their
entirety. Originally published in 1981 and 1995 respectively.
1 Purpose
1.1 The purpose of this document is to standardize
requirements for mixed acid etchants used in the
semiconductor industry and testing procedures to
support those standards. Test methods have been shown
to give statistically valid results. This document also
provides guidelines for grades of mixed acid etchants
for which a need has been identified. In the case of the
guidelines, the test methods may not have been
statistically validated yet.
2 Scope
2.1 The scope of this document is all grades of mixed
acid etchants used in the semiconductor industry.
3 Limitations
3.1 None.
4 Referenced Documents
SEMI C1 — Specifications for Reagents
SEMI C2 — Specifications for Etchants
5 Terminology
mixed acid etchant — any combination of nitric,
hydrofluoric, and acetic acids with the relative
composition expressed in terms of volumes of 70%
nitric acid, 49% hydrofluoric acid, and glacial acetic
acid, respectively. In the expression, all the relative
volumes shall be reduced to a ratio of the smallest
whole numbers. For example, a 3:1:2 mixed acid
etchant would imply a mixture of 3 volumes of 70%
nitric acid, 1 volume of 49% hydrofluoric acid, and 2
volumes of glacial acetic acid. If a component is absent,
its relative volume shall be taken as zero. For example,
a 3:1:0 mixed acid etchant would imply that no acetic
acid is present.
6 Composition
6.1 The content of each of the components of a mixed
acid etchant shall be expressed on a weight/weight basis
of the 100% acids in the total mixture. For the volume-
to-weight conversion, the densities shall be taken as
1.415, 1.153 g/mL, and 1.050 g/mL for 70% nitric acid,
49% hydrofluoric acid, and glacial acetic acid,
respectively.
7 Tolerances
Nitric Acid: ± 1.0% (± 0.16 meq/g)
Hydrofluoric Acid: ± 0.5% (± 0.25 meq/g)
Acetic Acid: ± 1.0% (± 0.17 meq/g)
8 Requirements
8.1 The requirements for mixed acid etchants for
Grade 1 and Tier A are listed in Table 1.
9 Grade 1 Procedures
9.1 Total Acidity — Accurately weigh a sample
containing 30 to 40 milliequivalents of acidity in a
polyethylene weighing bottle. Transfer with water to a
250 mL polyethylene beaker and dilute to
approximately 100 mL. Add 10 drops of
phenolphthalein indicator solution and titrate with 1 N
standardized sodium hydroxide to a faint pink end
point. Calculate the total acidity (A):
Total Acidity
me
q
g
()
=
mL
×
N
of NaOH
Weight of sample g
()
=
A
9.2 Hydrofluoric Acid — Accurately weigh a sample
containing 0.3 to 0.5 g of hydrofluoric acid in a
polyethylene weighing bottle. Transfer with water to a
polyethylene beaker and dilute to approximately 100
mL. Add 10 drops of phenolphthalein indicator solution
and titrate with 1 N or stronger sodium hydroxide
solution to a faint pink endpoint. Add 25 mL of Acetate
Buffer for Hydrofluoric Acid Determination and 1 g of
Eriochrome Cyanine R indicator mixture. Mix
continuously by magnetic stirring and titrate with
standardized aluminum chloride solution to a pink-
purple endpoint.
% Hydrofluoric Acid
=
mL
×
HF factor of AlCl
3
soln.
Weight of sample g
()
9.3 Nitric Acid — Accurately weigh a sample
containing 0.9 to 1.1 g of nitric acid in a polyethylene
weighing bottle. Quantitatively transfer into a 100 mL
volumetric flask containing 50 mL of 2% boric acid
solution, dilute to volume with water, and mix
thoroughly. Following the manufacturer's direction,
SEMI C34-0699 © SEMI 1981, 1999 MIXED ACID ETCHANTS2
ready a spectrophotometer and set the wavelength to
302 nm. Transfer the sample solution to a 1 cm fused
silica cell and measure the absorbance of the sample
solution versus water. Read from a previously
established calibration curve the grams of nitric acid
present in the sample solution (see SEMI C2, Section
3.2, Determination of Nitric Acid by Ultraviolet
Absorption Spectrophotometry).
% Nitric Acid
=
grams of HNO
3
calibration curve
×
100
Weight of sample g
()
9.4 Acetic Acid — The acetic acid content is
calculated by deducting the acidity found for each of
the other components from the value for the total
acidity.
% Acetic Acid
=
A-
%HF
2.001
−
%HNO
3
6.302
×
6.005
9.5 Arsenic and Antimony (as As) — To 50 g of
sample in a polyfluorocarbon dish, add 5 mL of
hydrochloric acid and 5 mL of sulfuric acid. Mix gently
and evaporate in a sandbath in a hood to dense fumes of
sulfur trioxide. Cool, cautiously add 10 mL of water,
and re-evaporate to dense fumes of sulfur trioxide.
Cool, and cautiously wash into a generator flask with
water to make a volume of 35 mL. Proceed as described
in the General Method for Arsenic (and Antimony)
under SEMI C1, Section 3.4.5, starting with the
sentence which begins, "Swirl the flask…" Any red
color in the silver diethyldithiocarbamate solution of
the sample should not exceed that in the standard
containing 0.0015 mg of arsenic (As).
9.6 Trace Element Contents — Determine the levels
of specified trace elements and establish that they do
not exceed the specification limits using a suitable
emission spectrographic procedure (see SEMI C1,
Section 3.5, for Guidelines for Determination of Trace
Elements by Emission Spectrography).
10 Grade 2 Procedures
10.1 This section does not apply to this chemical.
11 Grade 3 Procedures
11.1 This section does not apply to this chemical.
12 Grade 4 Procedures
12.1 This section does not apply to this chemical.
13 Grade 5 Procedures
13.1 This section does not apply to this chemical.
14 VLSI Grade Procedures
14.1 This section does not apply to this chemical.
15 Tier A Procedures
15.1 Standardized test methods are being developed
for all parameters at the purity levels indicated. Until
standardized test methods are published, test
methodology shall be determined by user and producer.
The Process Chemicals Committee considers a test
method to be valid only if there is a documented
recovery study showing a recovery of 75 - 125%.
Recovery is for a known sample spike at 50% of the
specified level.
16 Tier B Procedures
16.1 This section does not apply to this chemical.
17 Tier C Procedures
17.1 This section does not apply to this chemical.
18 Tier D Procedures
18.1 This section does not apply to this chemical.
Table 1 Impurity Limits and Other Requirements for Mixed Acid Etchants
Previous SEMI Reference # C2.1-95 C7.19-95
Grade 1 Tier A
(Specification) (Guideline)
Aluminum (Al) 0.3 ppm max 10 ppb max
Antimony (Sb) -- 10 ppb max
Arsenic (As) -- 10 ppb max
Arsenic and Antimony (as As) 0.03 ppm max --
Barium (Ba) -- 10 ppb max
Boron (B) 0.2 ppm max 10 ppb max
SEMI C34-0699 © SEMI 1981, 19993
Previous SEMI Reference # C2.1-95 C7.19-95
Grade 1 Tier A
(Specification) (Guideline)
Cadmium (Cd) 0.3 ppm max 10 ppb max
Calcium (Ca) -- 10 ppb max
Chromium (Cr) 0.2 ppm max 10 ppb max
Cobalt (Co) -- 10 ppb max
Copper (Cu) 0.1 ppm max 10 ppb max
Gallium (Ga) -- 10 ppb max
Germanium (Ge) -- 10 ppb max
Gold (Au) 0.3 ppm max --
Iron (Fe) 0.3 ppm max 10 ppb max
Lead (Pb) 0.3 ppm max 10 ppb max
Magnesium (Mg) 0.3 ppm max 10 ppb max
Manganese (Mn) -- 10 ppb max
Molybdenum (Mo) -- 10 ppb max
Nickel (Ni) 0.1 ppm max 10 ppb max
Potassium (K) 0.3 ppm max 10 ppb max
Sodium (Na) 0.3 ppm max 10 ppb max
Strontium (Sr) 0.3 ppm max --
Tin (Sn) 0.3 ppm max 10 ppb max
Titanium (Ti) 0.3 ppm max 10 ppb max
Zinc (Zn) 0.3 ppm max 10 ppb max
Particles in bottles:
size, #/mL
≥1.0 µm ≥1.0 µm, 25 max
NOTICE: These standards do not purport to address
safety issues, if any, associated with their use. It is the
responsibility of the user of these standards to establish
appropriate safety and health practices and determine
the applicability of regulatory limitations prior to use.
SEMI makes no warranties or representations as to the
suitability of the standards set forth herein for any
particular application. The determination of the
suitability of the standard is solely the responsibility of
the user. Users are cautioned to refer to manufacturer’s
instructions, product labels, product data sheets, and
other relevant literature respecting any materials
mentioned herein. These standards are subject to
change without notice.
The user’s attention is called to the possibility that
compliance with this standard may require use of
copyrighted material or of an invention covered by
patent rights. By publication of this standard, SEMI
takes no position respecting the validity of any patent
rights or copyrights asserted in connection with any
item mentioned in this standard. Users of this standard
are expressly advised that determination of any such
patent rights or copyrights, and the risk of infringement
of such rights, are entirely their own responsibility.
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International), 3081 Zanker Road, San Jose, CA 95134. Reproduction o
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