By Pieter Burggraaf
Technical Editor WaferNews
A new technology dubbed “resistive quartz” shows promise of providing advantages over conventional methods of heating fluids used in wafer processing without contaminating them. In addition, this technology is better able to handle changing process flow demands reliably.
The technology is a GE 214 semiconductor-grade quartz tube with a ridged interior wall and an intimately compliant, thin, resistive film on the exterior. The effect is a piece of quartz tubing that heats up as if it were a heating element. As fluid passes through the tube there is a minimal amount of thermal resistance between the heat source and the fluid. The low thermal resistance allows the element to operate under 300 degrees C. Resistive quartz is a proprietary product made by Trebor International, West Jordan, UT, with multiple patents issued and other patents pending.
Conventionally, wafer processing has used PTFE Teflon-coated immersion or IR lamp heaters. With immersion style, the element is immersed in a process fluid, and runs a risk of breaching the tube if the element fails due to extreme temperatures. To minimize this risk these units are typically run at a low watt density that results in a large, sluggish thermal mass that can trap particles.
IR heaters are sluggish due to a large thermal resistance between the heat source and the fluid, often causing the element to operate over 1000 degrees C. In addition, IR quartz vessels are often complex, expensive, and fragile designs. The sluggishness of these conventional technologies often required control via complex algorithms to maximize performance (i.e., an attempt to compete against the laws of physics).
The most impressive application advantages of the resistive quartz technology comes from its cleanliness, heating characteristics, and robustness. For example, resistive quartz will not contaminate in the event of a heating element failure. In addition, the coefficient of thermal expansion for quartz is 1/200th that of PTFE, so as a heater made with resistive quartz cycles it will not move and generate particles.
Compared to immersion and IR style elements, resistive quartz responds rapidly to process changes because of low thermal resistance and low thermal mass combined with high power densities. In addition, the simple quartz construction eliminates mechanical stress concentrations to provide a rugged heating package, virtually free of broken quartz.