STUDY OF THE EFFICIENCY OF HETEROGENEITY OF STRUCTURAL DEFECTS BY DIFFUSION DOPING IN THE PRODUCTION OF SILICON DIODES

Abstract

A varicap is a semiconductor diode whose operation is based on the use of the dependence of the capacitance on the reverse voltage and which is intended for use as an element with an electrically controlled capacitance. The barrier (charge) capacity of the p – n junction is used as the controlled capacity. Diffusion capacitance is not suitable for this purpose, as it manifests itself in the direct bias of the p-n junction, when the level of direct current through the diode is large, therefore, to control the value of diffusion capacitance, it is necessary to spend significant power of the power source. At the same time, changing the value of the barrier capacity when the varicap is turned on in reverse consumes very little power from the power source. However, despite the wide application, the cost of varicaps remains relatively high due to the low yield of suitable varicaps, which is determined by the significant dependence of the inverse characteristics of varicaps on the density of structural defects and heavy metal impurities in their active regions. The article discusses the causes and mechanisms of degradation of the reverse characteristics of the varicap. It was established that the main reason for the low percentage of yield of suitable investigated varicaps is the oxidation defects of the packaging formed in silicon structures during high-temperature technological operations. In order to prevent the formation of ODEs, which were detected in epitaxial structures after thermal oxidation, or to reduce their density, it was necessary to choose an effective method of heterization. Since ODUs are formed starting with the first high-temperature technological operation – thermal oxidation, it is obvious that heterization should be used at the very beginning of the technological route of varicap production. The conducted studies showed that the most effective method of preventing the formation of structural defects in epitaxial layers is the creation of a heterogenous region on the reverse side of the substrates by diffusion of boron to the non-working side of the plates before their thermal oxidation. The work is devoted to the study of the comparative efficiency of using the heterization method by carrying out additional diffusion of boron to the non-working side of the plates: the standard method, which is carried out after thermal oxidation of the plates, and the modernized method, which is carried out before thermal oxidation of the plates, on the level of reverse current of varicap structures and the percentage of output of suitable devices. The experimental results of the study of the influence on the inverse characteristic of the varicap of each of the researched heterogenization processes are presented, as well as the possible mechanisms of this influence are analyzed.