technology MOCVD
rhombus4
Larger wafers can spur further
growth of the LED industry
LEDs are making inroads into the backlighting of LCD TVs and general
illumination. Further success hinges on reducing the cost per lumen, and this can
be realized through a move to growth on larger sapphire or silicon substrates,
argues Aixtron’s Rainer Beccard.
T
oday, the high-brightness LED market is enjoying This cost reduction can be achieved by various means.
its strongest boom since the market first emerged. One route is to develop MOCVD reactors that
After initially being used for mobile phone illumination, it is accommodate even more wafers of the same size, thus
now appearing in the back light units (BLUs) required for increasing the throughput. This is precisely what has been
notebook PCs and, more recently, it is being deployed in done in terms of reactor development since the early
large area LCD TVs, which will shortly become the 1990s. As a result, each new reactor generation has been
dominant application for the market. Furthermore, even the significantly larger than the previous one while the
holy grail of lighting applications appears at long last to purchased cost has increased only moderately. However,
be becoming accessible, thanks to the rapid improvement there are some practical limitations to this scale-up
of white LED efficacies. process that encourage MOCVD reactor manufacturers to
look for other, more intelligent ways, to reduce the LED
The continuation of this success story, however, still production costs.
requires significant improvements of LED cost (or, to be
more precise, an improvement of cost per lumen). To understand the anticipated future development of the
Consequently, LED manufacturing processes have to be III-V industry - and in particular the LED part of it – it is
continuously improved in order to reduce the production helpful to take a look at the history of the silicon industry.
cost and related to that need, MOCVD development also In that industry larger and larger wafer sizes have played a
has to focus on reducing the operating cost when crucial role in reducing the manufacturing cost of silicon
growing LED structures. devices and fundamentally this should be very similar in
LED manufacturing.
What could be the benefits of moving to larger wafers in
LED processes? First of all, using larger wafers in
MOCVD reactors results in an increase in the usable
wafer area per run. Looking at the typical geometry of an
MOCVD reactor, it becomes obvious that a bigger part of
the available reactor area can be better utilized when
switching to large wafers. Furthermore, a relative
reduction of the unusable edge area that has to be
excluded from further processing is also achieved. The
costly metal organics and hydrides would also be better
Fig. 1: AIX utilized and finally all the subsequent process steps
2800G4 beyond the MOCVD process will enjoy improved yields.
HT reactor
in 6x6-inch The advantage of employing large wafers can be revealed
configuration with some simple calculations (Table 1). Looking at one of
30
www.compoundsemiconductor.net January/February 2010
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