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SEMI C37-0699 © SEMI 1981, 1999 PHOSPHORIC ETC H ANTS 2 SEMI C2, Section 3.2, Determination of Nitric Acid by Ultraviolet Absorption Spectrophotometry). % Nitric Aci d = grams of HNO 3 calibratio n curve × 100 Weight of …

PHOSPHORIC ETCHANTS SEMI C37-0699 © SEMI 1981, 19991

SEMI C37-0699

SPECIFICATION FOR PHOSPHORIC ETCHANTS

This specification was technically approved by the Global Process Chemicals Committee and is 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 C2.3 in its entirety. Originally published in 1981.

1 Purpose

1.1 The purpose of this document is to standardize

requirements for phosphoric 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 phosphoric 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

phosphoric 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

5.1 phosphoric etchant — any combination of phos-

phoric, nitric, and acetic acids with the relative compo-

sition expressed in terms of 85% phosphoric acid, 70%

nitric 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

16:1:2 phosphoric etchant would imply a mixture of 16

volumes of 85% phosphoric acid, 1 volume of 70%

nitric acid, and 2 volumes of glacial acetic acid. If a

component is absent, its relative volume shall be taken

as zero. For example, a 16:1:0 phosphoric etchant

implies that no acetic acid is present.

6 Composition

6.1 The content of each of the components of a

phosphoric etchant shall be expressed on a weight/

weight basis of the 100 percent acid in the total mix-

ture. For the volume-to-weight conversion, the densities

shall be taken as 1.695, 1.415, and 1.050 g/mL for 85%

phosphoric acid, 70% nitric acid, and glacial acetic

acid, respectively.

7 Tolerances

7.1 The tolerances allowed for the absolute percentage

of each of the components of a phosphoric etchant shall

be:

Phosphoric Acid: ± 1.0% (± 0.20 meq/g)

Nitric Acid: ± 0.5% (± 0.08 meq/g)

Acetic Acid: ± 0.5% (± 0.08 meq/g)

8 Requirements

8.1 The requirements for phosphoric etchants for

Grade 1 are listed in Table 1.

9 Grade 1 Procedures

9.1 Total Acidity — Weigh accurately 2.5 to 3.0 g of

sample in a tared weighing bottle. Transfer with water

to a 25 mL beaker and dilute to approximately 100 mL.

Add 10 drops of thymolphthalein indicator solution and

titrate with standardized 1 N sodium hydroxide solution

to the blue endpoint. Calculate the total acidity (A):

Total Acidit

meq

()=

of NaOH

Weight of sample g

()

9.2 Phosphoric Acid — Weigh accurately 2.5 to 3.0 g

of sample in a tared weighing bottle. Quantitatively

transfer the sample with 40 to 60 mL of water into a

platinum or polyfluorocarbon dish. Evaporate the

solution on a steam bath in a hood (1 to 2 hours). Rinse

down the inner sides of the dish with 10 to 15 mL of

water and re-evaporate for 1 hour. Cool and dilute with

50 mL of water. Add 10 drops of thymolphthalein

indicator solution and titrate with standardized 1 N

sodium hydroxide solution to the blue endpoint.

% Phosphoric Acid

of NaOH

4.900

Weight of sample g

()

9.3 Nitric Acid — Weigh accurately a sample

containing 0.9 to 1.1 g of nitric acid in a tared 100 mL

volumetric flask. Dilute to volume with water and mix

thoroughly. Following the manufacturer's directions,

ready a spectrophotometer and set the wavelengh to 302

nm. Transfer the sample solution to a 1 cm fused silica

cell and measure the absorbance versus water. Read

from a previously established calibration curve the

grams of nitric acid present in the sample solulion (see

SEMI C37-0699 © SEMI 1981, 1999 PHOSPHORIC ETCHANTS2

SEMI C2, Section 3.2, Determination of Nitric Acid by

Ultraviolet Absorption Spectrophotometry).

Nitric Aci

grams of HNO

calibration curve

100

Weight of sample g

()

9.4 Acetic Acid — The acetic acid content is calcu-

lated by deducting the acidity found for each of the

other components from the value for the total acidity.

% Acetic Acid

−

4.900

−

%HNO

6.302

[

]

6.005

9.5 Heavy Metals (as Pb) — Dilute 6 g of sample to

30 mL with water. For the standard, add 0.02 mg of

lead ion (Pb) to a 5 mL aliquot of this solution and

dilute to 25 mL with water. For the sample, use the

remaining 25 mL portion. Adjust the pH to between 3

and 4 (using a pH meter) with 1 N acetic acid or dilute

ammonium hydroxide (10% NH

), dilute to 40 mL with

water, and mix. Add 10 mL of freshly prepared hydro-

gen sulfide water to each and mix. Any color in the

solution of the sample should not exceed that in the

standard.

9.6 Antimony — Dilute 20 mL (20 g) of stock solution

to volume with water in a 100 mL volumetric flask and

mix. For the standard, dilute 0.4 mg of antimony ion

(Sb) to volume with water in a second 100 mL

volumetric flask and mix. Following the manufacturer's

directions, ready an atomic absorption spectrometer,

use an air-acetylene flame, position the antimony

hollow cathode lamp, and set the monochromator to the

antimony resonance line of 217.6 nm. Employ

deuterium lamp correction. Aspirate water and set to

zero absorbance. Then aspirate, in succession, the

standard, water, and sample. The absorbance of the

sample should not exceed that of the standard. (see

SEMI C1, Section 3.6, Guidelines for Determination of

Trace Elements by Atomic Absorption Spectrometry.)

9.6.1 Stock Solution for Sections 9.6 through 9.9 —

To 200 g of sample in a 400 mL beaker, add 100 mL of

water. Heat to boiling on a hot plate in a hood, and boil

off approximately 100 mL. Cool slightly, add 100 mL

of water, and again boil off about 100 mL. Cool,

transfer to a 200 mL volumetric flask, and dilute to

volume with water. One mL contains 1 gram of sample.

9.7 Arsenic — To 10 mL (10 g) of stock solution in a

125 mL arsine generator flask, add 30 mL of water 10

mL of ferric ammonium sulfate reagent solution, and

then 2% potassium permanganate reagent solution

dropwise to a permanent pink color. Add 1.5 g of

sodium chloride and mix to dissolve. Heat nearly to

boiling, remove from heat, and add 1 mL of stannous

chloride reagent solution. Dilute to 60 mL and cool to

25°C ± 3°C. For the standard, add 20 mL of dilute

sulfuric acid (1 + 4) to 0.005 mg of arsenic ion (As) in a

second arsine generator flask and treat as above.

Assemble the arsenic test apparatus (see SEMI C1,

Section 3.4.2). Pack each scrubber tube with two

pledgets of lead acetate-impregnated glass wool

previously moistened with lead acetate solution, freed

from excess solution by squeezing, and dried in a

vacuum. Allow a small space between the two pledgets.

Place 3.0 mL of silver diethyldithiocarbamate solution

in each absorber tube and 10 g of zinc (granular) in

each generator flask. Immediately connect the scrubber

absorber assemblies to the sample and standard

generator flasks. Place the flasks in a water bath

maintained at 25°C ± 3°C. Swirl each flask

occasionally. After 30 minutes disconnect the tubing

from the generator flasks and transfer the silver

diethyldithiocarbamate solutions to separate 1 cm

photometer cells. Measure both sample and standard

absorbances at 540 nm using the silver diethyldithio-

carbamate solution as a blank. The absorbance of the

sample should not exceed that of the standard.

9.8 Manganese — Add 25 mL (25 g) of stock solution

to 100 mL of dilute sulfuric acid (1 + 9). For the

standard, add 5 mL (5 g) of stock solution and 0.01 mg

of manganese ion (Mn) to 100 mL of dilute sulfuric

acid (1 + 9). To each solution, add 20 mL of nitric acid,

heat to boiling, and continue boiling gently for 5 min-

utes. Cool slightly, add 0.25 g of potassium periodate,

and again boil for 5 minutes. Any pink color in the

sample solution should not exceed that in the standard.

9.9 Copper, Iron, and Nickel — Dilute 1 mL (1 g) of

stock solution with 50 mL of water in a 100 mL beaker.

Add 0.5 mL of ammonium hydroxide and cool. For the

three-element standard, add 0.002 mg of copper ion

(Cu), 0.01 mg of iron ion (Fe), and 0.003 mg of nickel

ion (Ni) to 50 mL of water in a second 100 mL beaker.

9.9.1 Treat each solution as follows: Adjust the pH to

2.5 (using a pH meter) with dilute ammonium hy-

droxide (10% NH

) or 10% hydrochloric acid. Transfer

to a polyfluorocarbon-stoppered 250 mL separatory

funnel. Rinse the beaker with water adjusted to pH 2.5

and add the rinsings to the funnel (the final volume

should not exceed 100 mL). Add 10 mL of freshly

prepared 1% ammonium 1-pyrrolidinecarbodithiolate

solution and mix thoroughly. Add 10.0 mL of water-

saturated methyl isobutyl ketone (that is, 4-methyl-2-

pentanone), stopper, and shake vigorously for 3

minutes. Allow the layers to separate. Drain and discard

the lower, aqueous layer; save the upper, organic layer.

9.9.2 Following the manufacturer's directions, ready

the atomic absorption spectrometer for measurements in

the absorbance mode and with the air-acetylene flame

adjusted for aspiration of an organic solvent. For

copper, align the copper hollow cathode lamp, set the

wavelength to 324.7 nm, and zero the absorbance while

PHOSPHORIC ETCHANTS SEMI C37-0699 © SEMI 1981, 19993

aspirating methyl isobutyl ketone. Then aspirate the

extract of the standard solution, solvent, and the extract

of the sample solution. Record the absorbances.

Proceed similarly for iron and nickel with measure-

ments at 248.3 and 232.0 nm, respectively. For each of

the three elements the absorbance of the sample extract

should not exceed that of the standard extract (see

SEMI C1, Section 3.6, Guidelines for Determination of

Trace Elements by Atomic Absorption Spectrometry).

9.10 Sodium, Lithium, Potassium, Calcium, Strontium,

and Magnesium

9.10.1 Sample Solutions for the Determination of

Sodium, Lithium, Potassium, Calcium, Strontium, and

Magnesium by Atomic Absorption Spectrometry —

Thoroughly clean four 100 mL volumetric flasks and

label them 1, 2, 3, 4, respectively. Transfer 20 mL (20

g) samples of stock solution into the four volumetric

flasks. Add the quantities of cations as listed as follows:

CATION FLASK FLASK FLASK FLASK

1234

Milligrams of Cation

Sodium Ion (Na) 0.00 0.15 0.30 0.60

Lithium Ion (Li) 0.00 0.01 0.02 0.04

Potassium Ion (K) 0.00 0.10 0.20 0.40

Calcium Ion (Ca) 0.00 0.20 0.40 0.80

Strontium Ion (Sr) 0.00 0.05 0.10 0.20

Magnesium Ion (Mg) 0.00 0.05 0.10 0.20

9.10.2 General Instructions — Dilute each solution to

volume with water and mix thoroughly. Following the

manufacturer's directions, ready the atomic absorption

spectrometer for measurements in the absorbance mode

(see SEMI C1, Section 3.6, Guidelines for

Determination of Trace Elements by Atomic

Absorption Spectrometry). Determine each of the

elements, using the conditions specified in Sections

9.10.3 through 9.10.8.

9.10.2.1 For each element plot on linear coordinate

paper the absorbance versus the added quantity in

milligrams of the cation added. Draw a straight line

through the four points and extrapolate to zero

absorbance. This intercept corresponds to the absolute

amount, in milligrams, of the element being determined

in Solution 1.

ppm element

mg foun

1000

Weight of Sample g

()

9.10.3 Sodium — Using an air-acetylene flame and a

sodium hollow cathode lamp, set the wavelength to

589.0 nm and zero the absorbance with water. Aspirate,

and record the absorbances of each of the solutions,

zeroing the absorbance with water between aspiration

of the solutions. Calculate the amount of the sodium ion

(Na) in Solution 1; this should not exceed 0.30 mg.

9.10.4 Potassium — Using an air-acetylene flame and

a potassium hollow cathode lamp, set the wavelength to

766.5 nm and zero the absorbance using water.

Aspirate, and record the absorbances of each of the four

solutions, zeroing the absorbance with water between

aspiration of the solutions. Calculate the amount of

potassium ion (K) in Solution 1; this should not exceed

0.20 mg.

9.10.5 Lithium — Using an air-acetylene flame and a

lithium hollow cathod lamp, set the wavelength to

670.8 and zero the absorbance with water. Aspirate and

record the absorbances of each of the four solutions,

zeroing the absorbance with water between aspiration

of the solutions. Calculate the amount of lithium ion

(Li) in sample Solution 1; this should not exceed 0.02

mg.

9.10.6 Strontium — Using a nitrous oxide-acetylene

flame and a strontium cathode lamp, set the wavelength

to 460.7 nm and zero the absorbance with water.

Aspirate, and record the absorbances of each of the four

solutions, zeroing the absorbance with water between

aspiration of the solutions. Calculate the amount of

strontium ion (Sr) in Solution 1; this should not exceed

0.10 mg.

9.10.7 Calcium — Using a nitrous oxide-acetylene

flame and a calcium hollow lamp, set the wavelength to

422.7 nm and zero the absorbance with water. Aspirate,

and record the absorbances of each of the four solu-

tions, zeroing the absorbance with water between aspir-

ation of the solutions. Calculate the amount of calcium

ion (Ca) in Solution 1; this should not exceed 0.40 mg.

9.10.8 Magnesium — Thoroughly clean four 50 mL

volumetric flasks and label them 1a, 2a, 3a, and 4a.

Transfer 20 mL (4 g) from each of the four 100 mL vol-

umetric flasks into the corresponding 50 mL flasks. Di-

lute each to volume and mix thoroughly. Using an air-

acetylene flame, background corrections, and a magnes-

ium hollow lamp, set the wavelength to 285.2 nm and

zero the absorbance with water. Aspirate, and record

the absorbances of each of the four solutions, zeroing

the absorbance with water between aspiration of the

solutions. Calculate the amount of magnesium ion (Mg)

in Solution 1a; this should not exceed 0.02 mg.

10 Grade 2 Procedures

10.1 This section does not apply to this chemical.