HiREF® (high reflectivity) wafers are non polished wafers for demanding applications. Because of their special characteristics HiREF® wafers are determined for applications for discrete devices with high surface and tight geometry requirements as well as detectors and MEMS applications. As thin wafers they are also an alternative to diffused. Furthermore HiREF® wafers are a cost competitive alternative to very thin polished and double side polished wafers for discrete applications.

Siltronic provides 125 and 150 mm HiREF® wafers with non standard thicknesses from 100 to 1,500 µm. Further general characteristics:

• Available for CZ and FZ in all resistivities and dopant ranges
• Highly reflective (> 98 %) surface on both sides
• Line width resolution in automated lithography down to 1.0 µm
• Narrow geometry tolerances
• Gate oxide quality at 650 Å equivalent to polished wafer

Comparison of wafer parameters

The surface structure of HiREF® wafers are significantly improved compared to bright etched wafers and so close the gap to polished wafers. HiREF® wafers show also a distinctive improvement in micro-roughness compared to bright etched wafers. The residual line structure on the surface of HiREF® wafers is due to a grinding step but which does not represent any mechanical damage. This is possible because the wafer is etched to be damage-free. Furthermore the global geometry capabilities are extensively improved compared to bright etched wafers. HiREF® wafers are only slightly below as-lapped wafers. The warp is not influenced.

1) AFM

2) Tencor profiler P10 / P11 (AFM and Tencor profiler (80 µm filter) data can be roughly compared)

HiREF® can be supplied in various thicknesses down to 100 µm. This provides the advantage that the thickness requirement of the final can be reflected in the thickness of the wafer. Therefore deep backside diffusions can be avoided and cost savings in device processing can be achieved. The main challenge is to handle a relative thin wafer during the device process from the beginning.