Optimizing Polysilicon Resistor Fabrication via BF2 + F Co-Implantation: A Manufacturing-Compatible Approach for Low Resistance and High Reliability in MOS Devices

This study investigates the impact of BF ${}_{2} {+}$ F co-implantation at various energies on the electrical and structural characteristics of Polysilicon resistors in MOS devices. The introduction of Fluorine effectively reduces the Polysilicon sheet resistance by 10.13% while also optimizing the Temperature Coefficient of Resistance (TCR) at higher energy implantation. A grain-boundary passivation model is used to explain the reduction in sheet resistance caused by the addition of Fluorine. This is supported by evidence of grain size enhancement and surface roughness reduction, attributed to an increased concentration of Si-F bonds as observed through FTIR analysis. Furthermore, the incorporation of Fluorine results in a decrease in Gate capacitance and an increase in Gate breakdown voltage. A novel mechanism is proposed to explain the impact of Fluorine on Gate capacitance by the formation of a low-k SiOF layer. Additionally, higher Fluorine implantation energy improves the reliability of Polysilicon resistors by mitigating sheet resistance drift under constant 40 V electrical and thermal stress at various temperatures.