Wafer-Level Correlations of EL2, Dislocation Density, and FET Saturation Current at Various Processing Stages

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The neutral deep-donor density [EL2]0, and dislocation density, ρ D, are measured on adjacent, semi-insulating GaAs wafers, grown by both high-pressure (HP) and low-pressure (LP) liquid-encapsulated Czochralski (LEC) techniques; also, other nearby wafers from each boule are used for low-noise, field-effect-transistor (FET) fabrication. Dense data maps (at least 3500 points per wafer per parameter) are then visually and mathematically compared for [EL2]0, ρ D, I u, Ir, and Ig where the latter three quantities rep-resent the unrecessed-ungated, recessed-ungated, and gated saturation currents, respectively, for ion-implanted, 0.5 µm × 300 µm FET’s. For the particular wafers and processing used in this study, the following conclusions can be drawn: (1) on all of the wafers, materials (EL2 and ρ D) non-uniformities are correlated with at least some of the I u non-uniformities; (2) on some of the wafers, materials non-uniformities follow all the way through to I g, but on others, the gate-recess step itself introduces much stronger non-uniformities; (3) the HP-LEC wafers give slightly higher I u’s than the LP-LEC wafers; and (4) [EL2] 0 is a better predictor of I u than is ρ D.