There has been a great demand for improved end point detection techniques for advanced etching of III-V ternary multi stack layers. Current etch rate and end point monitoring techniques are based on three methods. The first is to use timed or a blind etch as it is known, this offers no monitoring of the etch process. The second is to use optical emission spectroscopy (OES) which is a secondary measurement of the process and requires a large open area, fast etch rate, and a detectable emission line from the etch products. The third is laser interferometry, a primary measurement, based on light interference of reflected beams from several layers in the stack. Up to now the use of commercially available interferometric techniques has not permitted the measurement of etch rates and end point the etch processes due to the absorption of the wavelengths of light available in current process control systems. A new in-situ end point system utilizing a 905 nm laser interferometer will be described that allows the ability to follow dry etching of III-V ternary multi stack layers. End point detection techniques on various AlxGa1-xAs layers on GaAs with varying compositions (i.e. X equals 0.3 - 0.92) and different types (n- or p- AlGaAs) are examined.
A new interferometric method for trench depth monitoring in micromachining applications is presented. As compared to other interferometric techniques, this new method uses a Wollaston prism to generate two linearly polarized beams, which are recombined after reflection on the sample. This differential method, by taking advantage of the polarization properties of the light allows an accurate monitoring of the trench depth. New insights on interferometry are given, in particular it is shown that an optical model taking into account the effect of the mask evolution and its etching during the process leads to an improvement of the precision of the measurements. The application of this new interferometric method to two different processes is presented. This will show that real time Twin-Spot interferometry appears as a powerful technique for deep trench monitoring in micromachining applications.
Optical raytrace analysis of instrument performance offers a powerful tool for evaluating the optical design of instruments utilizing a spectrograph and multichannel array detectors. Methods for collecting light from a source, projecting the light to the sample, collecting the light from the sample, and projecting it to a spectrograph for analysis can be evaluated. The consequences of various design options on spectrograph performance can be used to optimize overall system performance by choosing the best solution for the application. Five optical systems using different methods for light collection from a sample and projection to a spectrograph are compared. The benefits and drawbacks with respect to spectrograph optical performance are compared for both one dimensional and two-dimensional array detectors. The five optical systems being compared utilize elliptical collection optics, a single lens, a lens pair, no collection optics, and an improved lens pair option.
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