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Semiconductor silicon carbide technology

Special Design and Technology Bureau with Pilot Production ISP NASU

Description
The porous SiC of semiconductor purity has been around of a number of years as an object of interest for many investigators. Due to low thermal expansion coefficient, small value of the relative density, high thermal conductivity, mechanical strength, high chemical inertness, oxidation and corrosion resistance, porous SiC has a great application potential in many industrial applications such as light ultrastrong material in aerospace and motor-car industry, medicine and as well as heat insulation material. The possible use of porous silicon carbide as a biocompatible material suitable for orthopedic and dental implants was also proven.
The technical silicon carbide (SiC) is well known since XIX century. It is made by Achesson method and also is widely used in industry as abrasive. Besides this stuff is applied to deposition of protective coatings, manufacturing of aggregates and goods from 100% SiC.
The semiconductor silicon carbide has large width of a forbidden region, chemical stability, high stability to heightened temperatures and ionizing radiations, capability of doping by its acceptor and donor impurities. It finds a use in solid-state electronics engineering. On the majority of the main physic-chemical properties the silicon carbide considerably surpasses conventional semiconductor materials. The devices on the SiC basis are capable to work at the temperatures up to 1200 °C, at very high levels of irradiation and current densities.
Many explorers designed different technologies of single-crystal silicon carbide of semiconductor purity obtaining. As a rule, it is possible to discharge three main types of these methods; the truth, combined technologies are often used. The maiden type of technologies is known as a method of a chemical deposition from a gas phase. The following methods use increase from melt silicon. And at last, one of the earliest and developed ways is cultivation of chips by sublimation. Sponge SiC obtained by direct synthesis of carbon and silicon powder of high purity in inert (Ar) atmosphere at 1900 - 2000 °C in resistive furnace for 2-3 hours. The ground reactor graphite of high purity with the granule size of 20-80 mm was used as the source of the carbon. The silicon charge was obtained by powdering of n-type Si monocrystal with the specific resistance of 250 Wcm. The Si granule size was of about 2-3 mm³. The mixture of components with the ratio Si:C= 1:2 were charged into the tight graphite crucible. The synthesis of carbon and silicon powder in resistive furnace in inert (Ar) atmosphere as was shown in Fig. 1 was performed in a few steps. The first step includes the annealing for 4-5 hours in inert (Ar) atmosphere at T = 1200 °C.

Fig.1. The process of C and Si powder synthesis

During the second step the temperature was slowly increased up to the temperature higher than Si melting 1600 °C. Within the third step the composition was exposure at the temperature ranging between 1900 °C and 2200 °C. The phase composition and density of sponge SiC is governed by exposure time and temperature of the third step of the process. The material being removed from graphite crucible, the carbon excess was burn out in oxygen atmosphere at 800-900 °C. The relative density of SiC sponge is 1.5 - 1.7 g/sm³.
 

Fig.2. Image of SiC sponge macrostructure.

Area of Application

The sponge SiC has a great application potential in many industrial applications such as light ultrastrong material in aerospace and motor-car industry, medicine and as well as heat insulation material.