The previous report, Part 1, described the merits of alkaline electrolytic etching combined with acid chemical etching for Ge-In alloyed junction element. However, this technique needed a lot of processes in after-etching. On the other hand, acid chemical etching deteriorated the mechanical structure of P-N-P alloyed junction element for high frequency use. But, the above demerits could be eliminated by mixing of water, hydrogen peroxide, and hydrofluoric acid in proper ratios. The technique of acid chemical etching is used for the production of high frequency transistor. The results of experiments showed high inversed voltages, V_CBO and V_EBO, and stability of other electric characteristics.
The specifications of the etchants for experiments were as follows.
Etchant group Composition (in vol. ratio)
154 etchant H₂O:H₂O₂:HF 1:5:4
253 etchant H₂O:H₂O₂:HF 2:5:4
433 etchant H₂O:H₂O₂:HF 4:3:3
By the improved acid etching with 154 etchant (in etching for 40s), the best results were obtained in electric characteristics and mass production.