| 摘要 |
PURPOSE:To improve junction breakdown strength between a gate electrode and a substrate, in a nonvolatile memory of one polySi layer type, by forming diffused layers beneath a floating gate by ion implantation steps and heat treatments by a plurality of times. CONSTITUTION:Low concentration P ions are projected on an Si substrate, which is patterned with a resist layer 3 on a wafer 1, through an oxide film 2, and the ions for forming a gate in a diffused layer 4 are implanted. After the layer 3 is removed, annealing is performed, and a diffused layer 6 is formed. Then high concentration As ion beams 8 are projected on the substrate 1, which is patterned with a resist layer 7, again through the film 2, and the ions are implanted. Finally the layer 7 is removed. Junction breakdown strength largely depends on the concentrations of the diffused layers, which are formed with the P-type impurities and the N-type impurities in the wafer 1. Therefore, when the concentration of the impurities is made low, the junction breakdown strength becomes high. Since the N-type impurity region can be formed at low concentration, the junction breakdown strength becomes high.
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