EFFECTS OF POLYSILICON GATE ON CHARACTERISTICS OF ONO CAPACITORS

Abstract

Electrical characteristics of oxide/nitride/oxide(ONO) capacitors using two polysilicon gates deposited by low pressure chemical vapor deposition (LPCVD) at two different temperatures (560-degrees-C, 620-degrees-C) were investigated and compared. It was found that the quality of polysilicon is important for the electrical characteristics of ONO capacitors. The as-deposited film deposited at 560-degrees-C is amorphous, whereas the film deposited at 620-degrees-C is polycrystalline. After heat treatment, the film deposited at 560-degrees-C demonstrates a preferred orientation along (111), which is different from the (220) preferred orientation of the film deposited at 620-degrees-C. Better electrical characteristics, including lower sheet resistance, higher mobility and dopant activation were observed on the films deposited at 560-degrees-C after heat treatment. With a higher quality polysilicon gate, the electrical characteristics of ONO capacitors using a low temperature deposited polysilicon gate doped by phosphorus implantation are superior to those of ONO capacitors using a POCl3 doped low temperature (560-degrees-C) deposited gate or a POCl3 doped high temperature (620-degrees-C) deposited gate.