SEMI C37-0699 SPECIFICATION FOR PHOSPHORIC ETCHANTS.pdf.pdf

PHOSPHORIC ETCHANTSSEMI 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 semiconductorindustryandtestingproceduresto 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 2.1The 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 6.1The 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 8.1The 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 Acidity meqg ()= mL N of NaOH Weight of sample g ( ) =A 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 polyfluorocarbondish.Evaporatethe 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= mLN of NaOH4.900 Weight of sample g ( ) 9.3Nitric Acid Weigh accuratelyasample 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 manufacturers 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, 1999PHOSPHORIC ETCHANTS2 SEMI C2, Section 3.2, Determination of Nitric Acid by Ultraviolet Absorption Spectrophotometry). % Nitric Acid= grams of HNO3calibration curve100 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 = A %H3PO4 4.900 %HNO3 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% NH3), 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 wi