Improvement of Temperature Coefficient of Resistance by Co-Implantation of Argon or Xenon or Fluorine in Boron Implanted Polysilicon Resistors

Abstract

This paper proposes a new method to decrease the absolute value of temperature coefficient of resistance (TCR) in P-type boron implanted polysilicon resistors, at a given intermediate sheet resistance values, by selecting an optimized combination of boron doping implant conditions with co-implantation conditions. The co-implantation ion species that were investigated are fluorine, argon and xenon. Each of the co-implantation species was studied at three different co-implantation conditions and two different boron doping implant conditions of dose and energy. The stopping and range of ions in matter (SRIM) Monte Carlo simulation and thermawave measurements were used in order to set the experimental conditions and to evaluate the crystal damage and the amorphous layer depth created by the co-implantation. Amorphous layer is defined in this work as highly disordered material with vacancies concentration above 10% of the crystal density. Electrical measurements show that co-implantation causes a remarkable change in sheet resistance and TCR. Deeper co-implanted amorphous layer increases TCR and decreases sheet resistance. Typical polysilicon TCR is negative, while the TCR of a single crystal is positive. An improvement of TCR is defined at this work as minimum TCR in absolute values, which is lower sensitivity of sheet resistance to operational temperatures. Co-implantation that created deep amorphous layer in the polysilicon, decreases the TCR absolute values by up to ~75 % at the lower boron doping implant samples. Deep co-implanted amorphous layer also decreases sheet resistance by up to ~40% in both of the boron doping implants. Co-implanted xenon and fluorine exhibit similar effect on sheet resistance and TCR, while the co-implanted argon effect is weaker in comparison to samples without co-implantation. The increase of TCR and the decrease of sheet resistance are attributed to grains regrowth during the rapid thermal anneal (RTP). The regrowth of the co-implanted amorphous layer creates larger grains with less grain boundaries and less defects in comparison to the polysilicon samples without co-implantation. Analysis by X-ray diffractometer (XRD) and atomic force microscope (AFM) supports the suggested model.