Lasers: a sustainable wafer heating solution

Lasers, in particular diode lasers, are an attractive and sustainable option for future chipmaking needs.

By Iurii Markushov, Kazunari Miyata and Harlon O. Neumann and Toby Strite, IPG Photonics Corporation

The journey to a sustainable fab requires closer examination of how silicon wafers are heated during chip making. Elevated wafer temperature is required for annealing, epitaxial and etch processes. A sustainable heating solution must minimize energy consumption and consumables, while providing excellent temperature uniformity and competitive thermal rise time. Heating by infrared laser has proven itself in other industries to be just such a silver bullet. Here we describe heating experiments on a 200 mm silicon wafer utilizing a commercially available 975 nm diode laser. An empirical thermal model enables extrapolation to 300 mm wafer heating scenarios. The experimental and theoretical findings coupled with the mature state of diode laser technology suggest that heating silicon wafers by laser is an attractive path forward.

Our experimental apparatus (Figure 1) projects an 11kW near infrared (975 nm) diode laser over a thermally isolated 200 mm polished silicon wafer in regular atmosphere. The projection optics uniformly illuminate a ~213 mm square fully covering the wafer surface with minimal energy overspill onto the heatsink beneath. Wafer temperature is measured using a Chino model IP-CZP0JL pyrometer positioned about one meter above the wafer. Our experiments operate the laser at constant output power until steady state temperature is reached. After laser power is shut off, the cooling curve is also recorded.