NOR or NAND type mask ROM - has two transistors of high and low threshold respectively, with two impurity atom regions and common impurity atom region, all of opposite conductivity to that of substrate

摘要

The ROM includes Gate electrodes (7) formed in a main surface of a p-conductivity substrate (1), with an intermediate gate insulating film (6). Low concentration impurity atom regions (8) are formed using the gate electrodes as a mask. Then spacers (10) are formed at the electrode side walls. High concentration impurity atom regions are formed, using the side wall spacers as a mask. After the spacer removal, n-conductivity impurity atoms with low energy are applied by ion implantation to form through-implantation layers (60), using the gate electrodes and spacers as a mask. ADVANTAGE - Reduced prodn. time without affecting characteristics of transistors. ROM data can be written at low energy without special equipment.