LEDmanufacturing industry
In more quantitative terms, the throughput of the AIX G5 HT is more than double that of the previous MOCVD tool generation, thanks to the combination of larger capacity, large wafers and shorter cycle time
short times associated with the non-growth processes that form part of the production run.
These gains stem predominantly from the introduction of the graphite ceiling. As noted before, this ceiling plate does not have to be frequently exchanged to ensure thermal stability, because there is absolutely no thermal drift. What’s more, the process conditions used for the ceiling mean that any deposits create a very solid film. This is stable, does not peel off and never generates particles, so there is no need whatsoever to exchange or clean the ceiling between LED growth runs. Additionally, there is no need for in situ bakes, conditioning runs, or exchange of any reactor parts.
The upshot of all of this is that growth runs can be performed continuously, without interruption. This slashes “downtime” associated with cleaning and maintenance. In more quantitative terms, the throughput of the AIX G5 HT is more than double that of the previous MOCVD tool generation, thanks to the combination of larger capacity, large wafers and shorter cycle time.
Avoiding human contact The features associated with the G5 will appeal to many of the bigger LED manufacturers, including those having a history in the silicon or display business environment. Many of these firms will lead the transition from small wafer sizes to 6-inch wafers, and are likely to view automation as a pre-requisite for unlocking the full potential of large substrates.
From a yield point of view, manual wafer handling carries an inherent risk of error. Over time this diminishes yield, with larger wafers leading to bigger losses than smaller ones. Consequently, the advantages associated with automation for manufacturing on 6-inch wafers heavily outweigh any downsides, especially once the cut in the non-productive cycle time of the MOCVD tool is accounted for.
Our incorporation of automation on the G5 tool has been realized without making any compromise to the performance of the MOCVD reactor or its processes. The transfer module, which provides automated loading, is very reliable and simple to use. A robotic system accesses the reactor through a gate valve, picks up a satellite disk together with the wafer, and then replaces it
with another satellite disk housing a fresh substrate. It only takes a few minutes to exchange a complete reactor load, a process that is performed after only a short cooling phase (hot load capability). The satellites housing the epiwafers are taken away and unloaded and reloaded while the G5 starts its next MOCVD growth run.
It is possible to operate a single G5 reactor with a transfer system. However, to cut overall capital expenditure and save space, if an LED chipmaker has several of these MOCVD units, they can share transfer systems.
The light ahead Over the next few years there will be major changes in LED manufacturing. The emergence of solid-state lighting will encourage many leading LED chipmakers to increase production capacity, and prompt heavyweights in other industries to enter this sector. This will lead to bigger LED fabs, which will start to resemble the silicon foundries.
These bigger fabs will focus efforts on rapidly improving throughput and productivity, which will include the introduction of 6-inch LED processes. Sapphire substrates of that size are already available, and are complemented by the latest MOCVD tools, such as our AIX G5 HT. Whether this is configured as an automated tool or as an MOCVD cluster tool, it will easily meet the foreseeable throughput, cost, performance and yield requirements of the coming years.
Figure 2.
Photoluminescence map of
a typical LED multi- quantum well. Standard deviation across the entire 6-inch wafer (no edge-exclusion) is 0.9 nm
November / December 2010
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