SiGen vFinal DR 2/9/09 11:15 Page 33
MANUFACTURINGISSUES
silicon ingots or bricks as shown in figure 1. This not only adds costs but fundamental limitations in
process is based on a hydrogen assisted cleaving reducing kerf loss and wafer thickness.
principle. The first step is to define a cleaving
plane at the desired thickness under the brick top The SiGen cleaving manufacturing addresses
surface using high energy hydrogen (proton) beam multiple issues of current wafering technology and
irradiation. The incident mono energetic protons market conditions. With a focus on cost savings
lose their energy as they traverse a silicon through reduction of silicon usage, the company
thickness to form a stressed End-Of-Range (EOR) has developed an approach to counter the
layer. In silicon, ~1-4MeV proton energy is technical barriers to wafer thickness reduction. The
required to form a cleave layer at the desired depth wafering production steps are dramatically
of 20-150mm below the brick surface. simplified by the cleaving approach as shown in
figure 2.
The wafering process is the final step of a wafer
formation within a series of steps in the PV value The additional steps required by the wire saw, as Figure 3. Wafer comb
chain, denoted as upstream. The wafering step shown in figure 2 involve both equipment usage from wire saw and
itself however, is not a single process but again a and material handling that are prime sources for 150um as-cleaved
series of processes after the wire saw cuts the breakage. In addition, all the used slurry and wire
ingot into bricks. have limited recycling options, adding costs and
causing potential contamination to the
Wire saw and cleaving manufacturing environment.
The upstream steps of wire saw based
manufacturing consist of growing the silicon Figure 3 shows an example of wafer comb from
ingots, cropping top and tail, squaring, surface wire saw after pre-cleaning and the 150um as-
grinding, cropping into bricks, wire sawing, pre- cleaved wafer that does not require any additional
cleaning, separation, final cleaning, sorting and steps.
33
packing. For the wire sawing process itself, the
brick is glued and mounted onto a holder and The cleaving approach represents a clean
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placed into the wire saw. The saw consists of a technology that eliminates the waste in the
.solar
spool of wire within a suspension of grit particles of wafering process. The technology is a non-contact
SiC in a slurry mixture. The wire is guided onto the process, it should be emphasized that the wafers
-pv-management.com
brick by a threading unit that spaces the wires at exhibit improved characteristics in terms of:
intervals along the brick. The wire spacing and the reduced/eliminated micro-cracks, improved Total
wire diameter determine the wafer thickness and Thickness Variation (TTV), improved strength and
the kerf loss. It is a complex set of processes that improved handling capabilities.
Issue IV 2009
Figure 4. PolyMax
Manufacturing Factory
Layout
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