Method for fabricating double-diffused, lateral transistors

A method for fabricating a double-diffused, lateral transistor structure comprising the steps of:

• a. oxidizing a p-type silicon substrate;
• b. forming an opening in the silicon dioxide layer formed by step (a);
• c. predepositing an n.sup.+-type impurity in the portion of the substrate exposed by said opening and heating said substrate to thermally drive said n.sup.+-type impurity into said substrate to form a buried layer;
• d. removing the remaining silicon dioxide formed by step (a) from the surface of said substrate;
• e. epitaxially forming a layer of p-type conductivity;
• f. forming a mask on the surface of said p-type epitaxial layer;
• g. applying a thick silicon dioxide layer to mask against implanted high-energy ions;
• h. removing said thick silicon dioxide applied by step (g) everywhere except over a portion of the active transistor structure to be formed;
• i. applying a photoresist mask to define a base opening;
• j. implanting an n-type impurity in said substrate through said base opening and through said mask formed by step (f);
• k. removing said photoresist mask;
• l. applying a thermal oxidation masking material to said mask formed by step (f) over said active transistor structure to be formed;
• m. etching the portion of the epitaxial layer not covered by said thermal oxidation masking material to approximately one-half the depth of said epitaxial layer;
• n. heating said epitaxial layer to thermally oxidize said etched portion of said epitaxial layer so that the surface of the isolation-forming, thermally-grown silicon dioxide corresponds approximately to the plane of the original surface of said epitaxial layer and so that said implanted n-type impurities diffuse to meet said buried layer;
• o. removing said thermal oxidation material applied by step (1);
• p. reoxidizing said substrate to form a thin protective oxide layer;
• q. defining said protective silicon dioxide layer formed by step (p) to form emitter and collector contact openings;
• r. predepositing a p-type impurity in said epitaxial layer through said emitter and collector contact openings and heating said epitaxial layer to thermally drive said p-type impurities into said epitaxial layer to form emitter and collector regions, said emitter region stopping short of the diffusion front associated with said base region;
• and
• s. forming metal contacts to said emitter, base and collector regions.