OPTIMIZATION OF PULSE DIODE MANUFACTURING TECHNOLOGY

Abstract

Modern pulse diodes have, as a rule, a small base thickness and small active areas of structures. This provides small capacitances of p-n junctions, a high cut-off frequency and rather steep pulse fronts in the switching mode. But in switching circuits, pulse diodes operate in the saturation mode, for which it is very important to have a minimum time for the distribution of the accumulated charge, which is related to the lifetime of current carriers. The lifetime of current carriers can be reduced by introducing impurities into the thickness of the diode structure crystal that have a large cross section for capturing current carriers. One of such impurities is gold. The paper investigates the process of gold diffusion in the technological process of manufacturing a silicon pulse diode. It is shown that the reason for the increase in the level of reverse current of a pulsed diode after gold diffusion (T=1100°C) is associated with an increase in the density of generation-recombination centers in the space charge region of the p-n junction due to the introduction of gold atoms into the interstitials of the silicon crystal lattice and the presence of structural defects in silicon. It is established that additional annealing of diode structures in an inert environment at a temperature of 950°C, i.e. lower compared to the temperature of gold diffusion, makes it possible to reduce the level of reverse currents of the diode and increase the percentage of suitable devices. It is shown that one of the reasons for the high level of reverse current in diode structures after gold diffusion is the presence of oxidative packing defects in their active regions. Experimental results of the study of the influence of gettering, carried out by pre-oxidative high-temperature annealing of plates in vacuum, on the parameters of diodes are presented. Experimental results of the study of the influence of additional annealing of diode structures after gold diffusion on the reverse current of diode structures are presented, and possible mechanisms of this influence are analyzed. The effectiveness of using additional annealing of diode structures after the gold diffusion process and getter annealing of epitaxial structures before thermal oxidation in reducing the level of reverse currents of diodes and increasing the yield of usable devices is shown.