Methods and apparatus for irradiating a substrate to avoid substrate edge damage

Abstract

Methods and apparatus () for scanning a surface () of a substrate () with an obliquely incident radiation beam () over a select scan path () to avoid damage () to the curved edge () of the substrate. The methods and apparatus allow for the substrate edge to be irradiated with the full intensity of the radiation beam, provided that the edge crossing positions avoid a region where the polar angle is less than a scan path critical (SPC) polar angle (φ). At the SPC polar angle the temperatures produced by scanning the beam on the substrate surface and on the edge are the same. The scan path is arranged so the edge crossing positions are located where the polar angle corresponding to each meets or exceeds the SPC polar angle. Ensuring that the substrate edge temperature (T) remains at or below the substrate surface temperature (T). The invention has particular utility in laser thermal processing (LTP) of circular silicon substrates when forming transistor-based integrated circuits.