US Patent 7339220 Memory device with surface-channel peripheral transistors

A method of forming a memory device (e.g., a DRAM) including array and peripheral circuitry. A plurality of undoped polysilicon gates 58 are formed. These gates 58 are classed into three groups; namely, first conductivity type peripheral gates 58p, second conductivity type peripheral gates 58n, and array gates 58a. The array gates 58a and the first conductivity type peripheral gates 58n are masked such that the second conductivity type peripheral gates 58p remain unmasked. A plurality of second conductivity type peripheral transistors can then be formed by doping each of the second conductivity type peripheral gates 58p, while simultaneously doping a first and a second source/drain region 84 adjacent each of the second conductivity type peripheral gates 58p. The second conductivity type peripheral gates 58p are then masked such that the first conductivity type peripheral gates 58n remain unmasked. A plurality of first conductivity type peripheral transistors are formed by doping each of the first conductivity type peripheral gates 58n, while simultaneously doping a first and a second source/drain region 82 adjacent each of the first conductivity type peripheral gates 58n.