| 摘要 |
PURPOSE:To keep the etching rate approximately constant, by bubbling nitrogen gas including a large amount of moisture in aqueous solution of phosphoric acid, in etching a silicon nitride film by using the aqueous solution of the boiled phosphoric acid. CONSTITUTION:Wet nitrogen gas including moisture is introduced into a water tank 8 through a pipe 7 and bubbled in the water tank. The gas is introduced to an etching tank 1 through a pipe 9 from the water tank. The gas is bubble in solution of phosphoric acid. The supplied amount of the moisture included in the nitrogen gas is balanced with the evaporated amount of the moisture in the aqueous solution of the phosphoric acid. Thus the concentration of the phosphoric acid becomes constant, and the etching rate becomes approximately constant. |
