High-resistance voltage dividers fabricated by thin polysilicon films in silicon drift detectors

Abstract

In this paper we propose a method of fabricating high-resistance voltage dividers by thin polysilicon films and apply it in silicon drift detectors. Amorphous silicon films are firstly deposited on oxide layers by atmospheric pressure chemical vapor deposition (APCVD), and then the films are doped by boron implantation and post annealing. Deposition time and annealing temperature are two key parameters used to adjust the sheet resistance of the polysilicon films. By changing the deposition time and annealing temperature, a large sheet resistance value range from 2.5 to 36.5 kΩ/□ is achieved and it is very convenient to adjust the sheet resistance precisely by controlling these two parameters. In addition to that, the polysilicon resistors have very low temperature coefficients and resistance values remain unchanged until the largest voltage of 200 V that the equipment can apply. The width of the polysilicon film strips can reach 2 µm and the uniformity of the polysilicon films is 6.14% on the whole 2 in. wafer, which makes polysilicon films very suitable for fabricating high-resistance voltage dividers in silicon drift detectors. Beyond that, the ion implantation and annealing process can be used to dope the silicon films and fabricate the drift rings at the same time, which significantly simplify the fabrication of the silicon drift detectors.