Thermally induced improvements on SiNx:H/InP devices

Abstract

The influence of rapid thermal annealing treatments on the interface characteristics of Al/SiNx:H/InP devices was analyzed. The insulator was obtained by an electron cyclotron resonance plasma method at a 200 °C-deposition temperature. The films were deposited in a single deposition run but in two steps: first, we deposited the bottom layer with a film composition of x=1.55 and then the top layer with x=1.43. Total film thickness was 500 Å in one set of samples and 200 Å in the other one. Annealings were conducted in Ar atmosphere for 30 s in a temperature range between 400 and 800 °C. To characterize the electrical behavior of these devices, capacitance–voltage (C–V) and deep level transient spectroscopy (DLTS) measurements have been performed on each sample. This last characterization shows the presence of features in the spectra at Ec−0.2 eV, Ec−0.25 eV, Ec−0.38 eV. The last one is due to phosphorus vacancies, VP. Devices with 200-Å-thick insulator present the minimum interface trap densities. According to the DLTS analysis, this minimum (3×1011 cm−2 eV−1) is achieved on the 400 °C-annealed samples. A tentative explanation of these results is given in terms of a possible InP surface passivation due to the fact that nitrogen atoms coming from the insulator can fill phosphorus vacancies, giving rise to a low defective insulator/semiconductor interface. This process is enhanced by rapid thermal annealing treatments at moderate temperatures (400–500 °C).