Method of producing a semiconductor device

Abstract

In a case where a semiconductor device is produced comprising at least one semiconductor element, an isolation region surrounding the semiconductor element and a thick silicon oxide layer lying on and around the semiconductor element, the thick oxide layer is formed by thermally-oxidizing the epitaxial layer having a buried layer and, at the same time, the isolation region is formed in the epitaxial layer by heating for thermal oxidation. Prior to a step of introducing impurities into the epitaxial layer, a patterned thin silicon oxide layer is formed. This thin silicon oxide layer is varied into the thick oxide layer by the thermal-oxidation treatment.

We claim: 
     
       1. A method of producing a semiconductor device comprising at least one bipolar transistor and an isolation region which are formed in an epitaxial layer formed on a semiconductor substrate having a buried layer, said method comprising, in sequence, the steps of: forming an anti-oxidation masking layer on said epitaxial layer,   selectively removing said masking layer by etching to expose portions of said epitaxial layer,   thermally oxidizing said exposed portions of the epitaxial layer to form a thin oxide layer,   introducing a first impurity into a first predetermined portion of said epitaxial layer corresponding to said isolation region by using a first patterned resist layer as a mask,   introducing a second impurity through said masking layer into a second predetermined portion of said epitaxial layer corresponding to a collector-connecting-region of the bipolar transistor by using a second patterned resist layer as a mask,   thermally oxidizing said epitaxial layer by using the remaining anti-oxidation masking layer as to mask to form a thick oxide layer, while at the same time diffusing said introduced first and second impurities into said epitaxial layer to form said isolation region and said collector-connecting-region coming into contact with said buried layer, respectively, and   forming a base region and an emitter region of the bipolar transistor in a portion of said epitaxial layer above said buried layer.   
     
     
       2. The method of claim 1, wherein said substrate has the conductivity type of said first impurity type. 
     
     
       3. The method of claim 1 or 2, comprising the step of etching said exposed portions of the epitaxial layer prior to the formation of the thin oxide layer. 
     
     
       4. The method of claim 1 or 2, wherein said first impurity for said isolation region is introduced through a selected remaining portion of said masking layer. 
     
     
       5. The method of claim 1 or 2, wherein said first impurity for said isolation region is directly introduced into the respective portion of said epitaxial layer, after a portion of said masking layer on said respective portion of the epitaxial layer is removed by etching by using said first resist layer as a mask. 
     
     
       6. The method of claim 1 or 2, comprising the step of removing said thin oxide layer prior to said forming of the thick oxide layer and subsequent to said introducing of said second impurity. .Iadd. 7. A method of producing a semiconductor device comprising at least one semiconductor element and an isolation region, which are formed in an epitaxial layer formed on a semiconductor substrate having a buried layer, comprising the steps of; forming an anti-oxidation masking layer on the epitaxial layer;   selectively removing the masking layer by etching to uncover portions of the epitaxial layer;   thermal-oxidizing the exposed portions of the epitaxial layer to form a thin oxide layer;   forming a patterned resist layer to selectively cover said masking layer;   introducing impurities into a predetermined portion of the epitaxial layer which is not under the resist layer;   removing the patterned resist layer; and   thermal-oxidizing the epitaxial layer by using the remaining anti-oxidation masking layer as a mask to form a thick oxide layer, at the same item the introduced impurities are diffused into the epitaxial layer to form the isolation region. .Iaddend.