III-V Dry Etching by CCD-controlled in situ Interferometry
Wilfred John, Leonhard Weixelbaun, Harald Wittrich, Gottfried Frankowski, Joachim Wurfl
Ferdinand-Brawn-Institut fur Hochstfrequenztechnik im Forschungsverbund Berlin e. V.
A novel method for in situ depth and reflectivity measurements during dry etching is presented in this paper. The method is based on laser interferometry with a CCD chip as the detecting element. This allows for a process alignment to typical critical layout structures using optical markers. The full in depth resolution of about 3 nm is available immediately after starting the etching process (no extrapolation of data). The lateral resolution of depth measurement is determined by the marker size (about 150x10 mm2). Using the same arrangement in the reflectivity mode (thin film interference), the lateral resolution is given by the pixel density of the CCD image and the optics itself. In the present case the lateral resolution is about 1 mm2. The method is now routinely applied for dry etch process control in MESFET, HBT and diode laser technology.