RECENT PROGRESS IN MOVPE FOR HEMT LSIS

An MOVPE technique capable of mass-producing selectively doped AlGaAs/GaAs heterostructure has been developed for HEMT LSI applications. A barrel-type reactor developed has a load capacity of twelve 3-inch wafers. Wafer rotation resulted in extremely uniform epitaxial layers. The variations in both layer thickness and carrier concentration of a Si-doped AlGaAs layer are less than ±1% across a 3-inch wafer. The wafer-to-wafer variations among the twelve wafers are ±1.1% for layer thickness and ±1.8% for carrier concentration. The reactor routinely produces high-quality AlGaAs/GaAs selectively doped heterostructures. A mobility of 121,000 cm2/V ·s with a sheet carrier concentration of 6.46×1011 cm-2 was obtained at77 K for the heterostructure having a 7-nm spacer layer. The total particle density on an epitaxial layer was reduced to less than 10 cm-2. The fabricated HEMTs showed excellent uniformity of the threshold voltage. The standard deviations were as small as 10.1 mV for E-HEMTs and 16.1 mV for D-HEMTs over an entire 3-inch wafer. © 1990.