DISCO Technical Review Mar. 2016

Dicing technologies for SiC
Sales Engineering Department
Abstract
SiC, which is expected to be the new material for power devices, is a difficult material to process withregular blade dicing due to its hardness. Ultrasonic dicing and stealth dicing are being suggested forprocessing SiC wafers. In this review, we introduce each feature of these dicing technologies andcompare the quality and productivity.
electrode. During the dicing of metals, burr tends
to occur because of their ductility. Thus, a dicing
technology capable of suppressing this problem isrequired.

1. Introduction
Power devices are used in various fields such as
consumer electronics, automobiles, railways, andgenerators. The market for these devices isexpected to expand further. Conventionally,silicon (Si) was used as the material for powerdevices. However, silicon carbide (SiC) is thesubject of attention at present, and some SiC
power devices are already commerciallyavailable.

2. Dicing technologies for SiC
Application of ultrasonic-wave dicing and stealthdicing (SD) is effective in solving the problems
associated with the dicing of SiC power devices.

Using SiC in power devices provides numerous
advantages owing to its capability to withstandhigher breakdown voltage, reduce the power loss
due to high-speed operation, and minimize thesize of cooling system due to its high heatdissipation. However, it is difficult to process SiC
at high speed while maintaining high quality
because of its hardness.

2.1
Ultrasonic-wave dicing
Ultrasonic-wave dicing is a technology capable ofreducing the processing load by applying
ultrasonic vibrations in the blade radial direction(Fig. 2).
Fig. 3 shows the processing loads with andwithout the application of ultrasonic vibrations.
The graph clearly indicates that the processing
load is greatly reduced by applying ultrasonicvibrations. This is because water flow to theprocessing point is improved, thereby suppressing
blade glazing and loading.

Fig. 1 shows the results of processing Si and SiC
with standard blade dicing. These picturesindicate that blade dicing could process Si withoutcausing any problem whereas blade dicing of SiC
caused chipping. Chipping and cracks can besuppressed by lowering the processing speed,
however, the market demands high quality
processing of this material while maintaining highproductivity.
Further, a power device typically has a verticalcurrent flow structure, and there is a metallic filmon the wafer backside, which acts as an

Fig.1 Examples of Si and SiC blade dicing

Fig. 2 Ultrasonic-wave dicing

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DISCO Technical Review Mar. 2016

Fig. 3 Processing load during dicing
Fig. 5 Stealth dicing process

Lower processing load in ultrasonic-wave dicing
enables the selection of a blade with smaller gritsize, thereby improving the processing quality.
This technology also makes it possible to increase
the processing speed.

of laser passes required for dicing differs
depending on the chip thickness. Since this dicing
technology achieves a processing speed as high as
350 mm/s or more per pass, it is particularly
effective for high volume production.

Fig. 4 shows examples processed by standard
blade dicing and ultrasonic-wave dicing. SiC
could be processed by blade dicing at a low speed.
However, at a higher processing speed, dicing
caused chipping and cracks. On the other hand,when ultrasonic-wave dicing was applied,chipping and cracks could be prevented even at aprocessing speed of 10 mm/s. Thus, this dicing
technology enables high quality processing while
maintaining high productivity.

In the example shown in Fig. 6, a 350 µm thickchip was processed by SD. Since the workpiece isdivided into chips from the modified layer as astarting point, this layer remains at the side of thechip. However, in terms of productivity, SDachieves a processing speed equal to or greaterthan five times the processing speed ofultrasonic-wave dicing even when a large numberof laser passes is required (six passes when thethickness is 350 µm).

Fig. 4 Examples processed by standard blade andultrasonic-wave dicing

Fig. 6 SD processing example

2.2
Stealth dicing
SD is a technology that forms a modified layer byfocusing a laser beam below the surface of aworkpiece[1] and then separates the workpiece intochips by breaking (Fig. 5).

3. Comparison of the dicing technologies
The qualities and productivities achieved byultrasonic-wave dicing and SD are compared. In
the vertical structure of power devices, the chip
thickness determines their withholding voltage
and power loss. Chips with thicknesses of 110 µm
and 350 µm were selected for comparison. Inorder to verify the influence of dicing on themetallic layer, a 5 µm thick nickel-titanium

SD is capable of processing SiC at a speed higher
than that of ultrasonic-wave dicing. The number2

DISCO Technical Review Mar. 2016

(Ni-Ti) alloy layer was formed on the wafer
backside. Since the number of laser pulses needed
to divide a wafer into chips differs depending on
the chip thickness, the 110 and 350 µm chips
were irradiated by three and six passes,
respectively.

in strength between this technology and SD isonly approximately 10 % on average. In SD, thesignificant reduction in die strength is a concern
because the modified layer remains on the side ofthe chip. However, this comparison revealed thatthe modified layer did not cause any significant
deterioration of die strength.

3.1
Appearance inspection
Fig. 7 shows the appearance of the diced chips.
For ultrasonic-wave dicing, the roughness at theside of the chip is low. On the other hand, SD
forms a modified layer to divide the chips, andtherefore, the roughness on the side of chips tends
to be higher. Both dicing technologies did notcause burr, which indicates that the metallic layeron the backside did not influence the processing.

110 µm thickness

Fig. 8 Die strength comparison

3.3
Productivity
Fig. 9 shows the comparison of the units per hour(UPH) required by both the dicing processes.
UPH was compared not only for the chip
thickness but also for the chip size. Disregarding
the chip thickness and size, SD achieved higher
productivity. SD especially excels in the region
where the chip is thin, which requires less laserpasses per line, and in small chips with larger
number of lines per wafer.

350 µm thickness
Fig. 7 Comparison of appearance inspection results

3.2
Die strength
The results of the comparison of the die (chip)
strength are shown in Fig. 8. Ultrasonic-wave
dicing produces stronger dies, but the difference

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DISCO Technical Review Mar. 2016

Fig. 9 UPH comparison

4. Conclusion
In this review, two dicing technologies for SiC,
namely the ultrasonic-wave dicing and SD, werecompared and their characteristics were presented.
Disregarding chip thickness, ultrasonic-wave
dicing is effective when quality is emphasized,
whereas SD is preferable when high productivity
is required.

References[1]DISCO Technical Review TR16-04

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