Precise online auto-focus system in high speed laser micromachining applications

Maintaining constant quality is challenging in laser processes where a small focal point down to few micrometers is necessary, because the beam focus must be kept within the limits of narrow depth of focus in the entire working area. We demonstrated the importance of the focus control in sapphire scribing and silicon surface material removal processes. With an online auto-focus system micromachining was made up to 1000 mm/s processing speed with a precision of +/- 2 mu m. According to the test results, the auto-focus system significantly improved the process quality and reliability and allowed using high processing speeds and large wafer sizes with high precision. (C) 2012 Published by Elsevier B.V. Selection and/or review under responsibility of Bayerisches Laserzentrum GmbH