Process for producing a semiconductor device using purified phosphoric acid

• US 5,910,257 A
• Filed: 04/25/1996
• Issued: 06/08/1999
• Est. Priority Date: 04/27/1995
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Nakanishi, Takashi, Fukuda, Hiroyuki, Hirose, Mitsuru
• Primary Examiner(s): Breneman, Bruce
• Assistant Examiner(s): ALANKO, ANITA KAREN
• Application Number:
  US08/637,432
• Time in Patent Office: 1,139 Days
• Field of Search: 156/626.1, 156/642.1, 156/654.1, 156/657.1, 252/79.2, 210/682, 205/43, 205/771, 423/321.1, 438/426, 438/791, 438/787, 438/904, 438/928, 438/953, 438/745, 257/297, 257/660, 257/921, 216/93
• US Class Current: 216/93
• CPC Class Codes: C01B 25/234 Purification; Stabilisation; Concentration purification concomitant with preparation C01B25/22; preparation involving solvent-solvent extraction C01B25/46
• CPC Class Codes: H01L 21/31111 by chemical means
• CPC Class Codes: Y10S 438/904 Charge carrier lifetime control
• CPC Class Codes: Y10S 438/953 Making radiation resistant device
• CPC Class Codes: Y10T 436/15 Inorganic acid or base [e.g. , hcl, sulfuric acid, etc. ]
• CPC Class Codes: Y10T 436/25 including sample preparation
• CPC Class Codes: Y10T 436/25375 Liberation or purification of sample or separation of material from a sample [e.g., filtering, centrifuging, etc.]
• CPC Class Codes: Y10T 436/255 including use of a solid sorbent, semipermeable membrane, or liquid extraction

Abstract

A process for the preparation of an analytical sample characterized by depositing and separating solely the impurity to be analyzed from phosphoric acid; a process for analysis of the impurity characterized by depositing and separating solely the impurity from phosphoric acid and applying the separated material to analysis; a process for preparation of high grade phosphoric acid characterized by depositing and separating solely the impurity from phosphoric acid to be purified; a process for the fabrication of a semiconductor device characterized by using phosphoric acid, the impurity content of which is not more than 10^-3 Bq/mL, defined by the concentration of a contained radioactive element selected from the group consisting of Pb, Bi and Po, as a processing solution.

Claims

1. In a process for producing a semiconductor device wherein a substrate is processed using a phosphoric acid processing solution, the improvement comprising using as said processing solution a purified phosphoric acid which is prepared by heating phosphoric acid, dipping a semiconductor base, which is different from the substrate, into said resultant heated phoshoric acid so as to deposit impurities therein on said semiconductor base, and then removing said semiconductor base therefrom, and has an impurity content at a level of not more than 10^-3 Bq/mL, as defined by the concentration of a contained radioactive element selected from the group consisting of Pb, Bi and Po, and applying a protective film of Si₃ N₄ or SiO₂ for preventing adsorption of the impurities to an unprocessed back surface area of said substrate, said purified phosphoric acid being used to process other areas of said substrate.

2. A process of producing a semiconductor device according to claim 1, in which said processing of said substrate is by etching to selectively remove a thin film formed on said substrate.

3. A process for producing a semiconductor device according to claim 1 in which said protective film is formed on said unprocessed back surface area of said substrate in earlier processing of said substrate or is newly formed thereon prior to processing with said purified phosphoric acid.