Abstract
The use of a multiple-sensor control system to regulate in real-time the growth of thick, lattice-matched epitaxial films of InGaAs and InAlAs on InP substrates is described. The application of transmission-mode absorption-edge spectroscopy for in situ substrate temperature sensing, and spectroscopic ellipsometry for epilayer composition and thickness are discussed, and examples are given demonstrating precision and accuracy consistent with the fabrication of devices such as heterojunction bipolar transistors that require thick (>1.5 μm) InGaAs layers. Feedback regulation of substrate temperature to ±1°C and epilayer composition (alloy fraction) to ±0.002 are demonstrated using a cascade-PID control scheme in which the sensor is used in a software-based outer control loop. Growth of a complete HBT using sensor-based feedback control of substrate temperature, composition and epilayer thickness is described.
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