Planar diffusion method for an I2 L circuit including a bipolar analog circuit part

Claim 1

A planar diffusion method for the monolithic integration of an I 2 L circuit of the type including a bipolar analog circuit part including the steps of diffusing highly doped intermediate layers into a substrate, depositing an epitaxial layer on the surface of said substrate and said intermediate layers, producing an isolation region for insulating an I 2 L circuit part from a bipolar analog circuit part and depositing a diffusion masking layer on the surface of said epitaxial layer and said insulating region, comprising: opening windows in said masking layer over the base and injector regions of said I 2 L part and the base region of said bipolar analog circuit part; depositing a second masking layer in the windows over the base and injector regions of said I 2 L circuit part of such a thickness that during following treatment with an etching agent, the semiconductor material below said base and injector window is again exposed; prediffusing a first doping material of a first concentration into the remaining opening in said bipolar analog circuit part for forming a prediffused base region; removing excessive doping material from the diffusion masking layer and simultaneously exposing said substrate in the I 2 L circuit part base and injector regions; depositing a second doping material having a concentration of smaller than said first concentration on the exposed regions of said epitaxial layer; and simultaneously diffusing the base and injector regions of said I 2 L circuit part and the base region of said bipolar analog circuit part prior to emitter diffusion.