TW346669B - Method for improving the stability of SRAM memory unit - Google Patents

Abstract

A method for improving the stability of SRAM memory unit, which comprises the following steps: (a) forming a gate oxide layer on a P-type semiconductor substrate formed with an isolation region; (b) forming a polysilicon layer on the gate oxide layer; (c) selectively etching the polysilicon layer thereby separately forming a gate of an access transistor and a gate of a pull down transistor; (d) applying a light N-type ion implantation thereby forming a first N-type light ion diffusion region on the P-type semiconductor substrate on the both sides of the gate of the access transistor and the gate of the pull down transistor; (e) forming a photoresist thereby exposing a first N-type light ion diffusion region of the access transistor, and covering the gate and the first N-type light ion diffusion region of the pull-down transistor; (f) applying a P-type ion implantation step thereby adjusting the first N-type light ion diffusion region of the access transistor into a second N-type light ion diffusion region, in which the concentration of the second N-type light ion diffusion region is smaller than that of the first N-type light ion diffusion region; (g) forming a sidewall insulator on the sidewalls of the gate of the access transistor and the gate of the pull down transistor; and (h) applying a heavy N-type ion implantation thereby implanting a high concentration of N-type ions in the second N-type light ion diffusion region of the access transistor, and the first N-type light ion diffusion region of the pull down transistor, so as to form source/drain regions of the access transistor and the pull down transistor.