DETERMINATION OF OPTIMUM MODES FOR PHOSPHORUS ADDITIONAL DISTRIBUTION IN THE PRODUCTION OF DRIFT N-P-N TRANSISTORS

Abstract

There are several types of bipolar transistor technologies, with drift n-p-n transistor technologies occupying the majority. One of the main characteristics of bipolar transistors is the current gain in a common emitter circuit, and it depends on the thickness of the base. Due to the permissible technological variation in the depth of the diffusion layers, different batches of wafers have different base thicknesses, which significantly affects the current gain of the transistors. Even when using the same technological modes, the variation of the obtained gain on different batches of wafers can differ by a factor of 7–9. In high-quality products, the variation in parameters and characteristics is minimal. When using discrete elements, this simplifies the debugging of electronic equipment at the consumer’s site, as it does not require individual adjustment of each device. When bipolar transistors are used in microcircuits, reducing the spread of gain makes it possible to reduce the resistivity and thickness of epitaxial layers, which leads to an increase in frequency-pulse properties, and also reduces both the size of individual transistors and the size of crystals. In order to obtain drift n-p-n transistors with a small spread of gain, it was proposed to apply an additional technological operation – phosphorus doping. In the technological process, after the diffusion of phosphorus to form the emitter, reduced values of the gain are obtained, and after measuring them, the phosphorus is re-accelerated at temperatures lower than the diffusion temperature during the formation of the emitter. The process time is determined by the dependence graphs based on experiments. Different modes of diffusion layer formation are used for different types and types of bipolar transistors. The modes of formation of the base regions differ in dopant doses, time and temperature of the diffusion process, and parameters of the resulting diffusion layers. As a result, the optimal modes of the technological operation of phosphorus recovery will differ.