Improved understanding of thermally activated structural changes in Al/SiOx/p-Si tunnel diodes by means of infrared spectroscopy

Thermal treatment at temperatures well above 100 degrees C is known to lead to a degradation of the current-voltage (I-V) characteristics of Al/SiOx/p-Si metal-insulator-semiconductor (MIS) tunnel diodes. In the present work, the structural changes caused in these devices by annealing at temperatures around 300 degrees C are investigated by means of grazing internal reflection (GIR) infrared spectroscopy, I-V measurements, and scanning electron microscopy. While all previous studies attributed the structural changes to a single chemical process, we show that at least three different processes occur: the reduction of SiOx by Al, the diffusion of aluminum or oxygen through the tunnel insulator, and the formation of Al spikes through the tunnel insulator. The first two processes lead to significant changes in the Al-O and Si-O bond concentrations in the tunnel insulator, but the impact on the I-V characteristics of the MIS tunnel diode is negligible. In contrast, the third process leads to a drop of the baseline of the GIR spectra and to a significant degradation or even a complete destruction of the diode characteristics. (C) 1998 American Institute of Physics. [S0021-8979(98)01703-4].