High-throughput and fully automated system for molecular-beam epitaxy

Abstract

A new high‐throughput and fully automated system for molecular‐beam epitaxy was developed by employing multiple substrate mount pallets and automatic pallet transfer mechanisms. The geometrical configuration between pallet and effusion cells was optimized to achieve the uniformity of thickness and carrier concentration of epitaxial layer better than ±2% within a pallet. The throughput was more than 70 2‐in. wafers per day for the growth of AlGaAs/GaAs two‐dimensional electron gas structure. In a typical two‐dimensional electron gas structure with a 6‐nm spacer layer, the variation of sheet electron mobility closed in 7.5 to 10×104 cm2 /V s at 77 K over growth run to run. By improving the heater structure of the Ga effusion cell, the Ga‐related oval defect density was found to be reduced <1 cm −2. The total surface defect density was reduced to <50 cm−2 by preventing the particulate contamination on the growth surface. Moreover, unintentionally doped GaAs layer was dominated by a donor, whose concentration was lower than 1×1014 cm−3, and electron mobility was 145 000 cm2 /V s at 77 K.