31 March 2020
ALLOS reports wavelength uniformity and reproducibility of 200mm GaN-on-Si epiwafers for micro-LEDs
To address the wafer size mismatch and to tackle the yield challenge in micro-LED production, IP licensing & technology engineering firm ALLOS Semiconductors GmbH of Dresden, Germany has applied its unique strain-engineering to show what is said to be outstanding uniformity and reproducibility for 200mm gallium nitride on silicon (GaN-on-Si) epiwafers. The company has also reported its success on the roadmap to 300mm.
Yield plays a crucial role in making micro-LED displays successful, since it has a direct impact on the manufacturing complexity and cost. To enable the necessary cost reductions, large wafer diameters are essential. This is particularly true for micro-LED applications in which wafers from CMOS lines are integrated with LED epiwafers, e.g. by bonding. Here the matching wafer diameter even has an enabling role compared with the smaller diameters available from GaN-on-sapphire. ALLOS has already used its unique strain-engineering technology to push the wavelength uniformity further, in February 2019 demonstrating 200mm GaN-on-Si LED epiwafers on Veeco’s Propel metal-organic chemical vapor deposition (MOCVD) system with standard deviation (STDEV) of as little as 0.6nm.
Figure 1: Reproducibility of wavelength uniformity on 200mm GaN-on-Si epiwafers for micro-LED application.
With its latest results, ALLOS can now show what it says is excellent reproducibility for this technology, with a wavelength uniformity consistently below 1nm STDEV for 200mm. “At the same time we achieve all other production requirements, like bow of <40µm and SEMI-standard thickness of 725µm. These parameters are very important when bonding CMOS wafers to LED epiwafers,” says Alexander Loesing, a co-founder of ALLOS. “These results are particularly impressive because our technical team is really pushing the boundaries of GaN technology only with very limited time and resources available for this work,” he adds.
“Already our predecessor company AZZURRO had been first in the market with commercial 150mm and later 200mm GaN-on-Si epiwafer products. Making 300mm was the next natural challenge,” says co-founder & chief technology officer Dr Atsushi Nishikawa. “When the first reactor designed for such large wafers, the Veeco ImPulse, became available we proceeded to tackle the challenge.”
Figure 2: 300mm GaN-on-Si epiwafer for micro-LED.
ALLOS has now confirmed that its technologies scale successfully to 300mm on this new reactor. In particular, the firm’s unique technologies for strain-engineering and superior crystal quality work on 300mm as expected.
“Being among the first to push III/nitride technology to 300mm is very exciting for us,” says Nishikawa. “It proves how robust our strain-engineering technologies are and we are looking forward to establish this technology for micro-LED customers.”
Figure 3: Scaling wafer dimensions: additional cost benefit by better area utilization due to matching rectangular shape of display or transfer stamp to circular shape of wafer.
Scaling up from 100mm diameter – the typical wafer dimension for GaN-on-sapphire – has an even bigger business impact for micro-LEDs than in other parts of the LED industry, notes ALLOS. Beside the well-known effects of lower cost per area when using larger diameters, the jump to 200mm and 300mm GaN-on-Si for micro-LED production enables the usage of CMOS facilities that have a much lower cost and additionally higher production accuracy than conventional LED lines. A further effect arises because most micro-LED manufacturing concepts include either mass transfer technologies that are using large-area transfer-stamps or monolithically integrated displays.
“For micro-LED displays the better area utilization of larger wafer sizes can easily account for 40% cost advantage from 300mm epiwafers for this step alone,” summarizes Loesing. “Together with the other cost advantages and the production benefits offered by CMOS lines, this results in leading industry players evaluating micro-LED displays based on 300mm GaN-on-Si.”