SGL offers alternatives to graphics

10/01/1998

SGL offers alternative to graphite

A carbon/carbon composite material once destined for use in rocket nozzles is now being introduced as an alternative to graphite in the CZ crystal pulling furnace market, and may help increase wafer yields by up to 7%.

Semicarb, manufactured by SGL Carbon Composites-Hitco, Gardena, CA, consists of a carbon matrix reinforced with carbon fibers. The material is manufactured using a proprietary chemical vapor infiltration process said to produce a stronger, more inert material than the conventional graphite with a lower chemical reactivity.

"Although (graphite) has proved to be relatively satisfactory in such areas as high-temperature capability, chemical inertness and initial cost, there have been significant problems involving durability, brittleness and a tendency to micro-crack when exposed to repeated temperature cycles," according to a paper published by the company. "These types of problems create excessive impurities which result in higher replacement costs and lower wafer yields."

According to SGL, Semicarb is less susceptible to impurity complications because it is a stronger material (it has demonstrated longevity three to five times longer than graphite), resulting in the ability to increase wafer yields by up to 7%. Semicarb`s thermal characteristics, with thermal conductivity of 8-28 W/m?K, allow for a 10% reduction in furnace energy use and cut cycle cooldown times by approximately 50%.

Capable of supporting its own weight, the material can be used for free-standing structures over 48 in. in diameter. In addition, furnace liners, shields tubes and crucibles can be built as direct "form, fit and function" replacements for graphite components. - C.L.