Influence of Salicide Block Oxide and Key Process Parameters on P+ Polysilicon Resistor Performance

Polysilicon resistors are extensively used in integrated circuits due to their superior linearity, lower temperature coefficient, enhanced process compatibility, higher sheet resistance, and reduced chip area. This paper presents an indepth analysis of the effects of various processes on P+ poly resistors, focusing on poly film thickness, poly grain size, source-drain doping, spike annealing temperature, refractive index (RI) of Salicide block (SAB) film, stress of the contact etch stop nitride layer, clean reworks, and process resequencing. For the first time, we report on the impact of the PECVD SAB oxide film RI on P+ poly sheet resistance. The PECVD deposition process parameters, such as bias power and the spacing between the showerhead and wafer, can be adjusted to change the RI of the film and thus the sheet resistance. Our findings reveal that the SAB film RI is the most sensitive parameter for P+ poly resistors and can be independently tuned with minimal impact on other devices. SIMS analysis confirmed that the RI of the film influences the boron diffusion from silicon to SAB oxide. This study provides a novel and efficient method for process tuning and control of P+ poly resistors, offering valuable insights into optimizing resistance values through precise adjustment of deposition process parameters.