Homogeneity qualification of GaAs substrates for large scale integration applications

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Abstract
A novel procedure is used to qualify the homogeneity of GaAs substrates for large scale integration (LSI) circuit applications. This procedure is particularly well adapted for assessing the electrical variations of densely packed field-effect transistors (FET’s) used in GaAs LSI circuits. Threshold voltage nonuniformity due to crystal inhomogeneity and surface effects is measured for both conventional and In-alloyed, dislocation-free, slightly Cr-doped, semi-insulating liquid encapsulated Czochralski substrates. The average value of the threshold voltage standard deviation of about 300 dense rows over a 2-in.-diam wafer (30 FET’s over 300 μm for each row) is 20 mV using dislocation-free substrates which is much smaller than in conventional substrates (50–100 mV). These data show the importance of this qualification test with the highest ever reported resolution of 10 μm suitable for the evaluation of fabrication yield of LSI circuits.