Method of manufacturing semiconductor device utilizing outdiffusion and epitaxial deposition

A method of manufacturing a semiconductor device comprising the steps of:

• selectively forming at least one high first impurity concentration region of a conductivity type opposite to the conductivity type of a semiconductor substrate and having a desired depth in said substrate along the principal surface thereof, depositing a first epitaxial layer of the same conductivity type as said substrate on the entire principal surface of said semiconductor substrate, selectively forming at least one second high impurity concentration region of the opposite conductivity type to said substrate in said first epitaxial layer along a surface portion thereof not corresponding to said first high impurity concentration region, selectively forming a low impurity concentration region of the opposite conductivity type to said substrate in said first epitaxial layer along a surface portion thereof corresponding to said first high impurity concentration region, the diffusion rate of the low impurity region being higher than that of the first and second high impurity concentration regions, depositing a second epitaxial layer on the entire surface of said first epitaxial layer, thermally treating the resultant intermediate device to cause diffusion of the impurities in the first and second high impurity concentration regions into the respective first and second epitaxial layers and also causing diffusion of the impurity in the low impurity concentration region into the entire portion of the first epitaxial layer corresponding to the first high impurity concentration region, forming an element isolation region of the same conductivity type as said first epitaxial layer in a portion of said second epitaxial layer between said first and second high impurity concentration regions such that said isolation layer reaches the surface of said first epitaxial layer, and forming at least one high breakdown voltage semiconductor element in said second epitaxial layer in a portion thereof corresponding to said first high impurity concentration region and at least one low breakdown voltage semiconductor element in said second epitaxial layer in a portion thereof corresponding to said second high impurity concentration region.