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MICRONANOSYSTEMS
Fig. 4. Microscopic image of diced wafer Fig. 5. Microscopic image of kerf cut in
low-k silicon wafer
cuts in both thin and thick materials, producing oxides, metals and low-k silicon. Use of a diamond
perfectly parallel kerf walls. This is especially blade saw requires a dramatic reduction in cutting
important with very small die geometry, as the chip speed (down to 2 to 3 mm/s) and even then less
yield will improve with the increased surface area than optimum results are obtained.
becoming available, due to the reduced dicing The LMJ, however, can dice low-k materials,
street width requirements. (200 µm thick in this example) at high speed as
Dicing thin silicon wafer is another process at shown in Fig. 5, where it can be seen that no
which the LMJ excels. A good example is the chipping of the glass passivation layer has
dicing of 75 µm thick silicon wafer with a 7 µm occurred, nor has there been any delaminating of
metal top layer. This was carried out a with a 25 the metal layers. The wafer was diced with a 50
µm nozzle installed on the LMJ. The results after µm nozzle fitted at an overall speed of 100 mm/s.
dicing are shown in Fig. 4. The actual kerf width is A final example of the flexibility of the LMJ is
~22 µm allowing for a large margin in the 40 µm the cutting of large and sophisticated x-ray optical
wide dicing street. elements from 250 µm thick silicon wafer, which
demand perfectly parallel and clean cut surfaces.
Material science The ‘comb’ shaped structure shown in Fig. 6,
As mentioned earlier, devices made from low consisted of 40*400 µm wide and 125 mm long
Fig. 6. ‘Comb’ k-wafer pose additional difficulties for dicing, ‘fingers’. Each cut was made in four passes at 100
structure cut from which revolve around the material brittleness and mm/s. The quality of the chip free cutting is
250µm silicon wafer the fragility of the top layers, consisting mainly of demonstrated in the insert, which shows the ‘comb
finger’ tips after separation. The resulting parts
exhibited no micro cracking, no thermal
deformation but high fracture strength.
Conclusion
To conclude this brief article describing the
advantages of using the LMJ technology, should be
added that it is also ideally suited to many other
semiconductor manufacturing processes that have
not been covered here.
These include the edge isolation of photovoltaic
(PV) cells, where the LMJ is finding an increasing
number of customers, for cutting the narrow and
shallow grooves on either the front or back surface
of the wafer, to provide electrical isolation between
the cells active layers. Wafer edge grinding and
chamfering for the relief of stresses resulting from
blade saw cutting or surface grinding, is another
process, where the LMJ has been successfully
applied to manufacturing.
www.micronanosystems.info July 2008
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