The quality requirements for the epitaxial process used to manufacture micro LEDs for displays are significantly higher than in general lighting. The two most important parameters are the variation of the peak emission wavelength over all LEDs of an epiwafer and the number of defects. General lighting typically requires 10 nm and 1 defect/cm². For the economical production of micro LED displays, manufacturers are aiming for an upper limit of 5 nm and 0.1 defects/cm².
More homogeneous emission wavelength and fewer defects
The German semiconductor supplier Aixtron has come quite close to these values. In a paper that the company submitted in the course of the »Micro LED Technology Research Contest« organized by TrendForce, the technical development of a current production system type (AIX G5+C) that processes eight 150 mm sapphire wafers in parallel is described.
According to the paper, a more uniform emission wavelength was achieved with a retrofitted individual temperature control for each wafer and is now 5 nm. The average defect density was reduced to 0.14/cm² per epiwafer by replacing manual wafer loading with automatic cassette loading and combining it with in-situ cleaning.
First place in research competition for micro LED technology
The jury awarded the paper first place. Second and third place went to the US start-up Uniquarta with a laser-based transfer technology for the assembly of micro LED displays and the US company Tesoro Scientific, founded in 2017, with an in-line test method for micro LED chips.