The design of thin-film polysilicon resistors for analog IC applications

The authors describe the design of thin LPCVD polysilicon resistors based on their desired electrical performance (sheet resistance, temperature coefficient, voltage nonlinearity, and matching and uniformity). Based on measured data and an understanding of polysilicon carrier transport phenomena, it is shown how resistor processes can be designed for a wide variety of analog IC (integrated circuit) applications, requiring only ion implantation and standard polysilicon deposition and patterning processes. For a ±500 p.p.m./°C temperature coefficient of resistance range, the available sheet resistance lies between 2400 and 40 Ω/sq. for a polysilicon thickness ranging from 50-600 nm. Matching and nonlinearity (in a 10-V range) to better than 0.06% has been achieved from a process designed as described. Thus it is demonstrated that performance comparable to thin sputtered resistor films can be achieved without the requirement of a long development time and specialized knowledge