Richard H. Krukar

Reactive ion etching profile and depth characterization using statistical and neural network analysis of light scattering data

As device design rules continue to shrink for the manufacturing of integrated circuits, unprecedented challenges for process inspection appear. No longer is optical microscopy adequate for determining if process results meet specifications. On the other hand, the alternative—scanning electron microscopy—is time consuming, destructive, and costly. Another approach is to measure scattered light intensity as a function of scattering angle, as opposed to imaging, to obtain distinct signatures for submicron structures. In this work, a set of Si wafers with photolithographically defined lines and spaces are reactively ion etched. By varying process conditions, a range of depths and sidewall profiles is generated and then inspected by detecting visible scattered laser light over 180°. The resultant scattergrams are then analyzed both by using discriminant analysis and by training a neural network to catalog the microstructures according to depth and profile. We find that this approach is a viable alternative to ...

Wafer examination and critical dimension estimation using scattered light

We have applied optical scatter techniques to improve several aspects of microelectronic manufacturing. One technique involves characterizing light scattered from two dimensional device structures, such as those from VLSI circuitry etched on a wafer, using a frosted dome which is imaged by a CCD camera. Previously, limited dynamic range available from affordable digital imaging systems has prevented the study of two dimensional scatter patterns. We have demonstrated a simple technique to increase the dynamic range by combining multiple images taken at different intensities. After the images have been acquired, image processing techniques are used to find and catalog the diffraction orders. Techniques such as inverse least squares, principal component analysis, and neural networks are then used to evaluate the dependence of the light scatter on a particular wafer characteristic under examination. Characterization of surface planarization over a VLSI structure and measurement of line edge roughness of diffraction gratings are presented as examples.

Analyzing simulated and measured optical scatter for semiconductor process verification

We describe an experiment in which the etch depth of a diffraction grating is measured. A simulated experiment is used to develop and calibrate the measurement technique. A scatterometer was used to measure the diffraction patterns of a set of 5 wafers at 14 die locations. The estimator already developed is then used to find the etch depths at the 70 measured locations. Finally, a scanning force microscope is used as a reference method to validate the scatterometer measurements.

Grating parameter estimation using scatterometry

The trend towards smaller design geometries for microelectronics devices places unprecedented demands on the measurement of these small structures. Two sample problems are considered. In the first case we predict the shape of developed photoresist gratings from diffraction data obtained from an angle scanning scatterometer in which a detector tracks a particular diffraction order as the angle of incidence is varied. The second problem we consider is the prediction of depths of cylindrical cells etched into Silicon. A dome scatterometer is used to collect the 2-D diffraction signal and in this case the experimental data is used to construct a data base of scatter signals.

First Principle Simulation of Diffraction based Metrology Techniques

This report is a summary of the work performed by SNL in regards to light diffraction techniques.

Polynomial Multiplication And Filter Design Via Fourier Transforms

The convolution property of the Fourier Transform is used for solving the problem of substituting one polynomial into another, as with the BLT (bilinear transform). Using transform techniques, first a BLT is computed and then a bandpass filter is designed using the substitution s=/spl alpha/(z/sup 2/-2/spl alpha//spl beta/z + 1)/(z/sup 2/ - 1_, where /spl alpha/ and /spl beta/ are real numbers that are determined by the passband.