1. 12.00.012.08.9 7.18 9.20 8.60 6.40 6.20 6.40 6.80 6.20 5.00 Infineon Technologies Dresden Advanced Data Processing Combining full IEP spectrum with an interferometric signal for depth etch endpoint detection Frank Hoffmann, Infineon Technologies Dresden GmbH & Co. OHG Knut Voigtländer, Advanced Data Processing GmbH Motivation In absence of a stop layer, etch process and equipment control is typically done by depth monitoring using an interferometric endpoint system. The state-of-the-art method of a single UV/VIS wavelength approach has to balance between appropriate signal-to-noise ratio and interference frequency. State-of-the-Art Approach Fig. 1: Process Scheme, shallow recess etch with no stop layer. 8th European Advanced Equipment Control / Advanced Process Control (AEC/APC) Conference Dresden - Germany, April 18 - 20, 2007 Method Description This approach uses full spectra time signals to form the interferometric reference trace by combining the individual wavelengths. Fig. 2: Set of reference measurements containing the full spectra; the time behavior even of the shortest available wavelength has long signal period and is not suited for exact endpoint control. A PCA (principle component analysis) based method is used to decompose the full spectra into its linear independent components. A nonlinear optimization is used for a suited superposition of these components providing the final combined interferometric time signal. Fig. 3: With PCA decomposition the independent signals can be discovered. A Modeling procedure is used to try to superimpose these signals to fit a given fast oscillating target signal. Model quality depending on target signal period and phase: - blue – very good modeling possible with large signal period. - green – sufficient modeling with fast oscillating target - red –too fast oscillating target – no good modeling possible modeling not possible for 5s target period very good modeling for 20s target period for 10s target modeling is just possible Fig. 4 The resulting inter- ferometric refe- rence signal has shorter periods (more frequent Min/Max features), less noise and more clear inter- ference information. Results The full OES and IEP spectrum is collected by a standard EyeD endpoint system from Applied Materials, Inc. (spectral range 200 … 800 nm, time resolution 0.1 sec). The incoming IEP spectra is multiplied by the weighting vector during etch. The final interferometric time-based signal is generated by summing up all weighted spectral intensities within a relevant spectral range. Fig. 5: Weighting vector for online calculation of the interferometric reference signal. Fig. 6: Interferometric reference signal obtained by single wavelengths and by the PCA method. Final IEP trace with pattern (t1 … t4) detection. blue: Interferometric reference signal provided by the pca method (smoothing over 5 data points) red/green: Interferometric reference signal obtained by a typical single wavelength (280/229 nm, smoothing over 5 data points) The final interferometric time signal was used for in situ depth calculation using standard methods for endpoint algorithms. Using this method for endpoint detection a more reliable depth control for these shallow recesses is achieved in high volume production. Fig. 7: Depth distribution (productive data) with single wavelength (left) and pca algorithm (right). 5s 10s 20s