DIODE ZENER ENTERREE ET PROCEDE DE FABRICATION

A subsurface zener diode is formed in an N- epitaxial region formed on a P type substrate. The N- epitaxial region is isolated by a P+ isolation region. An N+ buried layer region is disposed between a portion of the N- epitaxial region and the P type substrate. A first P+ region is formed in the middle of the N- epitaxial region at the same time as the P+ isolation regions. Second and third adjacent P+ regions also are formed in the N- epitaxial region adjacent to and slightly overlapping the first P+ region, all three P+ regions terminating at the N+ buried layer. An N+ region, formed during an emitter diffusion operation, has first and second opposed edges centered within the overlapping portions of the first, second, and third P+ regions. Two other opposed edges of the N+ region extend beyond the other edges of the first P+ region, forming N+N- contacts to the N- epitaxial region, enabling it to be reverse biased without an additional N+ contact region and a corresponding metal conductor. Masking alignment tolerances in the direction of the N+N- overlap are eased, increasing overall processing yields.