A Double Diffused Silicon High-Frequency Switching Transistor Produced by Oxide Masking Techniques

Abstract

The relative merits of two double diffused transistor structures are discussed, one of which employs a localized emitter. A process for producing the localized emitter structure is described employing the masking property of SiO2 against the subsequent phosphorus diffusion. The dimensions of each emitter are controlled closely by etching away this oxide mask from only those regions not protected by a specially prepared photo resist coating. Transistors have been produced which switch 30 ma with a gain of 12, in times in which the sum of the turn‐on, storage, and turn‐off time is less than 0.1 µsec. Small signal alphas of 0.97, and alpha cut‐off frequencies in the common base connection in excess of 300 mc have been achieved.

Introduction to the History of Semiconductors

“…Gallium diffusion into n-type Si substrate was performed to form p-type base. (Note: This is similar to Aschner et al 1959. 48 ) This was a blanket diffusion into the whole Si substrate and so there was no base mask.…”

“…(Note: This is similar to Aschner et al 1959. 48 ) This was a blanket diffusion into the whole Si substrate and so there was no base mask. (Note: Silicon dioxide cannot be used to mask gallium diffusion into silicon.…”

“…47 Aschner et al published a paper "A double diffused silicon high-frequency switching transistor produced by oxide masking techniques" in 1959. 48 Theuerer et al published a famous paper on "Epitaxial diffused transistors" in 1960. 49 For discrete silicon transistors, the double diffused epitaxial transistor eventually becomes the standard structure.…”

“…63 Figure 1.3 shows the cross-sections of 2 double diffused silicon npn transistors according to Aschener et al (Bell Laboratories). 48 The area of the collector-base junction was defined by a mesa etch process. (Note: The mesa transistor structure was probably developed by engineers in Texas Instruments.…”

“…48 Figure 1.4 shows the detailed diffusion and masking process according to Aschener et al in 1959. 48 Gallium was used as the p-type dopant to form the p-type base while phosphorus was used as the n-type dopant to form the n-type emitter. Aschner et al did not mention that the masking oxide was removed.…”