Abstract of the Disclosure

A method for forming a high frequency transistor forming the emitter-base and collector-base junctions by diffusions through the same hole in the device oxide coating. The first diffusion is in a reducing atmosphere. The base is formed by diffusing through the hole into and through the collector region below the coating; then the emitter is diffused into the base forming a narrow base region between parallel junctions.

• Figure 1 shows a portion of a silicon dioxide coated wafer of P-type silicon with holes etched in the silicon dioxide for selective diffusion process.
• Figure 2 shows a cross section of the wafer of Figure 1.
• Figure 3 shows in cross section one-half of the same wafer as shown in Figure 2, but following a solid state diffusion of N impurity into the wafer through the open regions of the silicon dioxide.
• Figure 4 is another cross sectional view of the same portion of the wafer with a hole etched in the region of the glass film which was formed during the diffusion of the N impurity in the silicon and after a P-type diffusion through the hole in the oxide has been completed.
• Figure 5 shows the same cross sectional view after an N diffusion has been selectively performed through the same hole in the oxide.
• Figure 6 shows an isometric view of the device after openings in the silicon dioxide have been prepared for metallizing the collector and emitter.
• Figure 7 shows a sectional view of Figure 6 taken along line 7-7.

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