Investigation of X-ray induced radiation damage at the Si-SiO2 interface of silicon sensors for the European XFEL

TL;DR

This study investigates how high-dose X-ray radiation damages the Si-SiO2 interface in silicon sensors for the European XFEL, focusing on oxide charges, interface traps, and surface currents, with effects depending on crystal orientation, vendor, and applied voltage.

Contribution

It provides detailed analysis of dose-dependent radiation effects on silicon sensors, including the influence of crystal orientation, manufacturing vendor, and gate voltage during irradiation.

Findings

Surface densities of oxide charges vary with dose and crystal orientation.

Gate voltage during irradiation significantly affects oxide charge accumulation.

Annealing reduces oxide charges and surface currents over time.

Abstract

Experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors which can withstand X-ray doses up to 1 GGy. For the investigation of X-ray radiation damage up to these high doses, MOS capacitors and gate-controlled diodes built on high resistivity n-doped silicon with crystal orientations <100> and <111> produced by two vendors, CiS and Hamamatsu, have been irradiated with 12 keV X-rays at the DESY DORIS III synchrotron light source. Using capacitance/conductance-voltage, current-voltage and thermal dielectric relaxation current measurements, the surface densities of oxide charges and interface traps at the Si-SiO2 interface, and the surface-current densities have been determined as function of dose. Results indicate that the dose dependence of the surface density of oxide charges and the surface-current density depend on the crystal orientation and producer. In addition, the influence of the voltage applied to the gates of the MOS capacitor and the gate-controlled diode during X-ray irradiation on the surface density of oxide charges and the surface-current density has been investigated at doses of 100 kGy and 100 MGy. It is found that both strongly depend on the gate voltage if the electric field in the oxide points from the surface of the SiO2 to the Si-SiO2 interface. Finally, annealing studies have been performed at 60 and 80 degree C on MOS capacitors and gate-controlled diodes irradiated to 5 MGy and the annealing kinetics of oxide charges and surface current determined.