Advanced Lifetime Killing in Silicon Power Devices by High Energy Particle Irradiation

The aim of the project develop novel method for optimization of silicon power device parameters using lifetime killing techniques based on high energy particle irradiation. We investigated the effect of sloping lifetime reduction in the power chip P-iN diode using 500 keV electron and high energy proton irradiation and compared it with local lifetime killing by high energy alphas. The device under test was a planar 100A/1200V P-iN chip diode produced on the low-doped <100>-oriented FZ n-type silicon substrate. The reference local lifetime reduction was done by irradiation with alphas at fluences ranging from 2×10 10 to 2×10 11 cm-2. The alpha's range was set into three qualitatively different regions (anode emitter, anode space charge region and n-base space charge region) covering the most important locations from the point of application. Irradiation with low-energy (500 keV) electrons was used to produce the gradual sloping profile. The sharp sloping profile was introduced by a high-energy (7.35 MeV) proton irradiation with fluences from 1.4×10 10 to 2×10 12 cm-2. Different sets of aluminum foils were placed in the front side of irradiated diodes. This allowed us to place the back side of the wide Gaussian radiation defect peak produced by high energy protons to desired locations in the diode (comparable to those irradiated by alphas). Defects produced by irradiation were characterized by capacitance deep level transient spectroscopy, high-voltage current transient spectroscopy, I-V and C-V profiling. Static and dynamic parameters of modified diodes were recorded and compared to those measured before irradiation. Results show, that the gradually decreasing profile of recombination centers produced by low-energy electrons cannot substitute for local lifetime reduction in diodes with base thicknesses below 500µm. The sloping lifetime control by defects produced in the end-of-range region of high energy protons provides identical trade-off between the ON-state and turn-off loses as a traditional local lifetime killing by alpha-particles. However, it provides lower increase of leakage compared to the local lifetime reduction by alphas, if we compare irradiations leading to the equivalent reduction of turn-off losses.