PURPOSE: To inhibit the unreliability of the controllability of a breakover voltage by a method wherein the field strengths of the sidewall parts of an etching region are increased by a voltage lower than a breakdown strength and an avalanche breakdown is generated.
CONSTITUTION: An etching region is provided in a semiconductor layer, on which a P-N junction for bearing a breakdown strength is formed, from the main surface of the layer and the etching region is constituted of a shallow etching region of a large diameter and a deep region, which is inhered in the etching region and has a small diameter. The total amount of an impurity concentration per unit area as seen from one main surface of the semiconductor layer, in which a depletion layer is formed, is precisely controlled by a technique, such as an ion implantation or the like, for increasing the field strengths of the sidewall parts of the etching region by a voltage lower than the breakdown strength to generate an avalanche breakdown. Thereby, a current which is made to flow by the avalanche breakdown is used as a trigger current and a pilot thyristor can be made to ignite.
SHIMIZU YOSHITERU
MURAKAMI SUSUMU
HONMA HIDEO
YOKOTA TAKESHI
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