In recent years, with the increased adoption of IC cards, RFID tags, and SIP (system in package)
for cellular phones and other mobile products, the market for finished semiconductor die 100 µm thick or
less has grown rapidly. This high demand has in turn made the processing of thin wafers
an essential competence for many device manufacturers. To provide the processing results
that these companies require, DISCO continuously researches and develops the machines,
blades, and applications that make thin wafer dicing a reality.
Blades
As a workpiece grows thinner, backside chipping caused during the dicing process also tends
to increase. Photos 1 and 2 show backside chipping in a 25 µm-thick silicon wafer, the backside of which was
dry polished prior to dicing. For the workpiece in Photo 1, a #2000 blade was employed, typical for standard-thickness
dicing; backside chipping, however, is substantial. For the workpiece in Photo 2, a #4800 blade (much finer grit)
was employed; backside chipping has been greatly reduced. In general, as Graph 1 indicates, a finer-grit blade imparts
less of a shock to the workpiece, thereby reducing backside chipping.
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Photo 1: Typical Grit Size (#2000)
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Photo 2: Small Grit Size (#4800)
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Graph 1: Effect of Grit Size on Processing Quality |
Processing Conditions
Graph 2: Effect of Feed Speed on Processing Load |
As stated above, it is generally advisable to dice thin wafers with an extremely fine-grit
blade. But because these blades have reduced cutting power, they can be affected by films, TEGs, and other elements
of the wafer frontside. Clogging can result, in turn compromising processing quality on the wafer backside. In such
a case, the use of a step cut (instead of single-pass dicing) often solves the problem. Further, when performing
blade dicing with a view to stable, long-term processing, it is essential to maintain a consistent processing load
and preserve the self-sharpening mechanism of the blade.
In the case of thin wafer dicing, the volume of material being ground by the blade does not contribute significantly to the
processing load; therefore, this load must be raised by adjusting the processing conditions themselves. Graph 2 displays
the relationship between feed speed and processing load. Grit size, feed speed, and spindle speed are closely interrelated
processing factors that require knowledge and experience to adjust. DISCO performs careful and detailed experiments that
allow a perfect match between dicing processing conditions and customers’ thin semiconductor workpieces.
DISCO Short Kerf Check Function (Patent Pending)
In the typical kerf check function, spindles Z1 and Z2 cut in separate areas with kerfs checked
individually (it is difficult to check both kerfs simultaneously, as the Z2 kerf becomes hard to measure). In the case
of a step cut, however, the Z2 blade, which does not normally cut the surface of the wafer, can encounter films, TEGs,
etc., and incur damage. This damaged Z2 blade may then cause backside chipping and other problems.
DISCO's Short Kerf Check function can help solve this problem. In this function, the Z2 blade cuts with a shortened
stroke; the kerf is then measured and the information processed. Because of the shortened stroke, the Z2 blade incurs
minimal damage and does not become a cause of increased backside chipping. Through the proper blade, processing conditions,
and the DISCO Short Kerf Check function, it is possible to dice thin wafers with extremely high processing quality.
Please contact your DISCO representative for further details about thin wafer dicing and DISCO's premier applications
support. |
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