| 摘要 |
PURPOSE:To form an element isolation region which has a small bird's beak shift (a bird's beak shaped unnecessary oxide film region), a fine structure and a high breakdown strength by a method wherein a silicon nitride layer which has a required pattern with a tapered side wall part is formed on a silicon substrate with a silicon oxide layer therebetween. CONSTITUTION:A silicon oxide layer 2 is formed on a silicon substrate 1 by a thermal oxidation method and a silicon nitride layer 3 and an undoped silicate glass (N-type) layer 4 are built up on the silicon oxide layer 2 by a CVD method. Then the layers 2, 3 and 4 are etched to form a required pattern by a photolithography method and a silicon oxide layer 2a, a silicon nitride layer 3a and an N-type SG layer 4a are left. Then a silicon oxide layer 2b is again formed on the silicon substrate 1 by a thermal oxidation method and a silicon nitride film is built up on the silicon oxide layer 2b by a CVD method and the silicon oxide layer 2b and the silicon nitride layer are etched by a reactive ion etching(RIE) method to form a tapered side wall part 5. Then the silicon substrate 1 is subjected to isotropic ethcing by a plasma etcher to form a trench 6 with an offset, boron ions are implanted into the surface and the substrate 1 is subjected to an oxidation treatment by a LOCOS method to form a silicon oxide element isolation region 7.
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