JPS5591164A - Junction collapsible type programmable rom - Google Patents

Abstract

PURPOSE:To improve a collector to base withstand voltage and a collector to emitter withstand voltage and increase the integration degree of a junction collapsible type programmable ROM by expanding the periphery of a base layer in an epitaxial layer on a substrate divided via V-shaped grooves. CONSTITUTION:An n-type epitaxial layer 3 is formed on the n<+>-type buried layer 2 of a p-type silicon substrate 1, and divided via V-shaped grooves 4 reaching the layer 2. The grooves 4 are buried with polycrystalline silicon 7 through insulating films to thus form insulating films 6 on the surface thereof. Then, ions are selectively implanted through the film 6 on the substrate 1 to thereby form p-type base layers 9 in predetermined depth in the substrate. Then, a resist mask 15 is formed on the substrate, and ions are implanted to the substrate to thereby form p<->-type base spreading layers 16. Dosage is so determined that the layer 16 may be depleted when a voltage is applied to collapse the pn-junction. Thereafter, an emitter layer 11, a collector layer 17 and further electrodes are provided according to the convertional process after removing the mask 15 and annealing the substrate. Since the layer 16 is depleted in this configuration, the withstand voltage VCBO is increased, and since the volume of the base layer 9 is increased, the withstand voltage VCEO is increased even if the interval L among the V-shaped grooves is reduced.