Patent GB-1234894-A (GB)
Title: Process for polishing the surface of semiconductor materials
IPC: H01L21/306
Filed: 1969-04-10
Abstract: 1,234,894. Surface polishing of semi-conductor materials. WACKER-CHEMIE G.m.b.H. 10 April, 1969 [11 April, 1968], No. 18372/69. Heading B3D. [Also in Divisions C4-C5] A suspension of a precipitated metal silicate and/or a metal silicofluoride is used as a mechanically acting agent for polishing semi-conductor surfaces. The silicate may be precipitated by adding a silicate-forming metal salt or solution thereof to a solution of silicic acid or of a salt or derivative thereof. Suitable metal salts are those of the metals of the 2nd and 3rd groups of the Periodic Table, e.g. soluble salts of magnesium, calcium, strontium, barium, zinc or aluminium; salts of heavy metals, e.g. zirconium, iron, lead, nickel and cobalt may be used. The solutions of silicic acids or of their salts or derivatives are usually aqueous solutions, but organic solvents, e.g. alcohols, ketones or esters may be used. As derivatives of silicic acid there may be used silicic acid esters which may be partially or wholly hydrolyzed, e.g. partially hydrolyzed silicic acid-tetra-n-butyl ester. The silicofluoride may be precipitated by adding a silicofluoride-forming metal compound or solution thereof to a solution of fluorosilicic acid or of a salt or derivative thereof. Suitable metal compounds are oxides or hydroxides of the metals of Groups I-III of the Periodic Table, especially of sodium, potassium, magnesium, calcium barium, aluminium or zinc. The polishing suspension may be neutral or alkaline. Example 1. Silicon discs, 32 mm. diameter and 300 Á thick, obtained by sawing up a monocrystalline rod of silicon, are lapped with carborundum powder (particle size 5 Á) whereby on each side 50 Á are removed. Twelve discs are attached by beeswax to a round plane carrier plate of stainless steel, 180 mm. diameter, which is placed on the rotary table (450 mm.) of a polishing machine and is covered with a polishing cloth, the whole being loaded with 1À5 kg. pressure. The table is rotated at 90 r.p.m. Polishing suspension is dropped on to the table at 1 to 2 drops per minute, and polishing performed for 20 mins. The polishing suspension was obtained by taking 120 ml. of waterglass solution (33% SiO 2 ), diluting with 1800 ml. of deionized water and slowly adding a solution of 25 g. AlCl 3 .6H 2 O in 100 ml. of water. The precipitate has a grain size of about 20 mÁ. Example 2. Silicon discs, pretreated as in Example 1, are polished with a suspension prepared as follows: 120 ml. of sodium waterglass solution (33% SiO 2 ) are diluted with 1800 ml. of deionized water and heated to 80 C. A solution of 150 g of CaCl 2 .6H 2 O in 200 ml. of water is stirred in very slowly; the suspension is cooled before use. The precipitate has an approximate formula CaO.2SiO 2 , and a grain size of about 60 mÁ. Polishing time is 15 mins. Example 3. Discs about 300 Á thick are sawn off a rod of gallium arsenide and lapped with carborundum powder of 2-3 Á particle size removing about 30 Á on each side. Polishing is carried out as in Example 1, using an aqueous suspension of barium hexafluorosilicate prepared as follows: 560 ml. of aqueous hydrofluoric acid (38% HF) are diluted with 500 ml. of deionized water and 120 g. SiO 2  added. The SiO 2  dissolves and hexafluorosilicic acid forms. A saturated aqueous solution of 75 g. BaCl 2 .2H 2 O is slowly added, and a precipitate of BaSiF 6  settles. The strongly acidic polishing suspension is then neutralized. Polishing time is 15 mins.