| 摘要 |
PROBLEM TO BE SOLVED: To sustain etching rate stably for silicon nitride film and silicon oxide film while exhibiting a high etching select ratio for both of them. SOLUTION: Etching liquid is produced by dissolving a compound containing silicon into phosphoric acid through a solvent until the concentration of silicon ion becomes 20-500 ppm. At the time of conditioning the etching liquid, TEOS (tetraethoxy silane), or the like, is previously dissolved into a solvent, e.g. ethanol, especially alcohol compatible with phosphoric acid before a compound containing silicon, e.g. TEOS, is added to phosphoric acid liquid thus dissolving the compound. A silicon nitride film is etched by raising the temperature of the etching liquid in the range of 145-170 deg.C. According to the method, the silicon nitride film can be overetched while leaving the silicon oxide film even if a pad oxide film underlying a nitride film mask for forming an LOCOS film is as thin as 5 nm.
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