Alkaline Electrolytic Etching Combined with Acid Chemical Etching for Ge-In Alloyed Junction Element

Studies on After-etching for Ge-In Alloyed Junction Element (Part 1)

Abstract

After-etching of semi-conductor P-N junction element is a very important process for carrying out proper action of transistor or diode upon the device, in which indium pellet is alloyed with single crystal germanium pellet.
In the alloying process, there were produced thermal stress, crystal imperfections, irregularity, and some contaminations on the boundary and around the periphery of P-N junction at the alloying temperature. These imperfections produced low inversed voltages, V_CBO and V_EBO; made increase or drift of saturation currents, I_CBO and I_EBO; made larger noise figure with low gain; made smaller amplication factor; and made the life shorter for instability in electric action.
The techniques for removing these imperfections prevailed hitherto are as follows.
(1) Electrochemical etching
(2) Chemical etching
(3) Supersonic etching
(4) Electron beam or ion spattering
The above techniques (3) and (4) were suitable for the mass production of germanium type transistor (1-10MHz class) and the studies of these techniques have been pursued as follows.
(A) Alkaline electrolytic etching
(B) Alkaline electrolytic etching combined with acid chemical etching
(C) Acid chemical etching
The above item (C) showed the best result in electric characteristics and stabilization for accelerated life test.
This paper reports the results of experiments on alkaline electrolytic etching for 10MHz class transistor and its after-treatment.
The optimum condition for the element was as follows.
Electrolyte……KOH 30%aq. solution
Current density……DC 60mA. per one element
Etching time……3s. x 4 pulses
The author got high value of V_CBO at low value of rbb' but the average value of V_EBO was much lower than V_CBO. In the testing of I_CBO and I_EBO by diode curve tracer, leakage currellt of several μA was often found out in some specimens before the avalanche break down.
The latter half of this paper describes the acid chemical etching performed after the electrolytic etching. K⁺ ion adsorbed around the periphery of P-N junction was removed and the junction element, slightly etched by acid Chemical etching, was researched by the behavior of V_EBO. The Composition of the after-acid etching. solution and the specification for the etching were as follows.
Pure water……6vol.
H₂O₂……2vol. (30% reagent)
HF……1vol. (49% reagent)
Etching temperature……room temperature
Etching time……5-20s.
As the results of experiments, the increase of V_EBO and the decrease of surface leakage current were confirmed.