Zener diode mfr. from silicon wafer - with poly-silicon screen serving as dopant source and metal diffusion barrier

摘要

Xener diodes are made from silicon wafers of a first conductivity type by chemical vapour deposition of a doped polysilicon layer of second conductivity type at below 700 deg.C; heat treating the wafers at not more than 950 deg.C to diffuse the dopant no more than a few dozen microns into the wafers; removing the wafers from the furnace depositing metal contact layers and encapsulation in a process involving heating the wafers to about 650 deg.C. Pref. the wafers are deoxidised prior to CVD, and are encapsulated in glass after deposition of the contacts, and the metallisation is CVD Ti and Ag formed first by CVD then by electroplating. Esp. for mfr. of Xener diodes of tension less than 3V breakdown potential, i.e. having an extremely abrupt junction. By keeping the encapsulation temp. to 650 deg.C, and using higher melting metals than Al of prior art for the metallisation, problems of short circuiting due to diffusion of metallisation metal during encapsulation are avoided. The polycrystalline Si protects the diffused layer since should the contact metallisation diffuse into the underlying semiconductor layer, it diffuses only into part of the polysilicon layer. This layer also forms a source for the dopant. The diodes can be reproduced satisfactorily on an industrial scale.