The Effect Of Annealing Treatment On Reverse Breakdown Voltage Of Schottky Diodes

- Schottky Barrier Diodes (SBD) has outstanding properties, such as low power, large electronic current, high frequency, and which is widely used in the field of microwave communication and IC circuit system. Nevertheless, the reverse breakdown voltage of Silicon SBD is quite low at present. The first reason is the curvature radius of metal contact periphery is small. The strong electric field intensity results in the breakdown voltage decreasing. The second reason is the existences of surface states and interfacial layer at the interface which formed in the process of fabrication. At present, many effective solutions have been given for the first question. But, there's no any method to reduce the influence of surface states and interfacial layer on breakdown voltage. Therefore, this study gives a series researches on this problem theoretically and experimentally and the results can heighten properties of device.This study fabricated two kinds of samples on epitaxial layer which electrical resistivity is 2.85～3.15Ω·cm under the current fabrication condition of national electronics corporation. One of them has been annealed after sputtered Cr and Ni, and the other hasn't. An actual SBD is a metal-semiconductor contact with a thin film and surface states between them, which has an effect on the barrier height. At present no way can extract these two parameters, which has seriously hampered the analysis of characteristics of devices and the building of model. Based on the thermionic emission theory, a method to extract parameters of Si SBD is given in this study. Using this model, we tested the characteristics of devices and extracted the parameters of two kinds of samples. The ideality factor is 1.01 and 2.13 respectively. The zero-field barrier height is 0.70eV and 0.72eV. The surface state density is 5.5×10¹⁵cm^-2eV^-1 and 4.3×10¹²cm^-2eV^-1. The interface oxide capacitance is 9.0×10^-4F·cm^-2 and 5.4×10^-6F·cm^-2. The neutral level of the surface states is 0.81eV and 1.1eV. The reverse breakdown voltage is 101V and 56V. The results indicate that annealing treatment can heighten breakdown voltage of SBD remarkably.We observed microstructure of cross-sections of two samples using SEM and tested element distribution using energy spectrometer. The results indicate that there is a layer of silicide of Cr between Si and Cr for annealed sample, the thickness is 50nm. The interfaces of Si/ CrSi and CrSi/Cr are very flat and straight. The barrier region of unannealed sample is composed of Si contacting with Cr directly, and the interface is curve and rough. There is an oxygen-containing interface layer between two layers, the thickness is 1nm. There are alloy column crystals of NiCr in the region of metal Cr and Ni for annealed sample, but there are no crystals at the same region for unannealed sample. The experiments show that the microstructure of annealed sample is favourable to improving reverse breakdown voltage.