DISCO Technical Review Sep. 2021

Resistivity Control of Cutting Water with CO2 Injector and Hub Blade Wear
Sales Engineering Department
Abstract
In the blade dicing process, static electricity is generated during workpiece processing/cleaning, which leads to electrostatic
discharge (ESD) in the workpiece. As one ESD countermeasure, DISCO has adopted technology that mixes CO2 into thecutting water supplied during processing using a CO2 injector, controlling the resistivity of the cutting water. While theworkpiece’s electric charge does decrease as the amount of CO2 supplied increases, wear to the hub blade tends to increase.
However, with DISCO’s standard resistivity of 0.5 M to 1.0 MΩ/cm, blade wear is comparable to that with DI water.

1. Introduction

2. Test method

As semiconductor miniaturization progresses, the2-1 Measurement of Si wafer electric charge

requirements

generated by contact with waterhave

increasedforelectrostatic

discharge anti-countermeasures in blade dicing saw
equipment (hereinafter referred to as dicers).

After a ⌀12-inch, 775 μm thick Si wafer was mounted
to a frame with SPV224 tape (Nitto), the frame was

DISCO has clarified the root cause of static electricity

mounted on the dicer spinner table. The nozzle

and has taken the following measures to control

supplied cutting water at each resistivity to the wafer

electrostatic discharge.

surface at 6 MPa, spin-dry was performed, and

1. Installed CO2 injector(1) (decreases resistivity ofDI water)
2. Installed ionizer (removes electric charge onelectric charge was measured after removal from thespinner table.
Electric charge at the time of removal was measured
using the ZJ-SD100 (OMRON) static electricityworkpiece)

sensor, which was placed in the transfer area directly
3. Controlled ascension rate of transfer arm (makesabove the wafer.

change in capacitance more gradual)
For water resistivity, three values were tested: 18(2)Details are provided in past technical reviews .

MΩ･cm (DI water, no CO2), 0.9 MΩ･cm, and 0.5

This report examines “1. Installed CO2 injector” andpresents

investigation

results

regardingMΩ･cm.

ESD

countermeasure effectiveness and hub blade wear.

Figure 1. Measurement of wafer electric charge

DISCO Technical Review Sep. 2021
2-2 Blade wear measurement

3. Measurement results and remarks

After a hub blade was installed and precut was

3-1 Measurement of Si wafer electric charge

performed, thirteen ⌀12-inch, 400 μm thick Si wafers

generated by cutting water

were processed. After the wafers were processed,
blade wear was measured with the non-contact setup
function(3) using a transmission-type sensor installed
to the equipment. After the 13 wafers were processed,
the blade was inspected by SEM. For water resistivity,
three values were tested: 18 MΩ･cm (DI water, noCO2 supply), 0.5 MΩ･cm, and 0.1 MΩ･cm.
The equipment and blade used for processing are

The electric charge of the wafers upon removal fromthe spinner table is shown in figure 2. It was
confirmed that the electric charge decreases
monotonically as the amount of CO2 supplied isincreased and water resistivity is decreased. It issuspected

that

reducedresistivitydecreases

triboelectric charging on the wafer surface when thewater makes contact.

shown in tables 1 and 2.

Table 1. Blade used and precut condition

Figure 2. Water resistivity and electric charge upon
removal from spinner table
Table 2. Processing condition

DISCO Technical Review Sep. 2021
3-2 Blade wear
Figure 3 shows trends in blade wear when wafers
were processed under each condition. No drastic
difference in blade wear was observed with theresistivity of 0.5 MΩ･cm compared to with DI water.
However, a drastic increase in blade wear wasobserved with the resistivity of 0.1 MΩ･cm. Bladewear after processing 13 wafers was 43 μm with theresistivity of 0.5 MΩ･cm but was 67 μm with theresistivity of 0.1 MΩ･cm, which was 1.5x the wear.
Figure 3. Blade wear trends

Figure 4 shows the SEM images of the blade edgebefore and after processing. Comparing to that withDI water and the resistivity of 0.5 MΩ･cm, grit on theblade edge was more exposed after 13 wafers wereprocessed with the resistivity of 0.1 MΩ ･ cm,confirming that the Ni bond that secures the diamond
grit is being eluted.
It is assumed that increasing the supply of CO2 caused
the pH of the cutting water to decrease and eluted theNi bond of the blade, leading to blade wear as a result.
CO2(aq) + H2O ⇄ H+(aq) + HCO3-(aq) ⇄ 2H+(aq) +CO32-(aq)Figure 4. SEM images before and after processing

Ni + 2H (aq) ⇄ Ni (aq) + H2+2+As reference, the relationship between water
resistivity when CO2 is dissolved in the water and pH
is shown in the figure 5. This diagram was calculated
from internal testing and measurement errors areincluded.

Figure 5. Water resistivity when CO2 is dissolved andpH

DISCO Technical Review Sep. 2021
4. Conclusion

References

Based on the test results, a workpiece’s electric(1) DISCO

charge decreases when CO2 supply is increased andwater resistivity is decreased. On the other hand, Ni
eluting reaction accelerates, leading to an increase in

website:ProductInformation/Accessory Equipment / CO₂ Injector
https://www.disco.co.jp/eg/products/accessory/co2.html

blade wear.
(2) DISCO Technical Review “Wafer ESD in dicing
At the resistivity of 0.5 MΩ･cm, a decrease in electriccharge was observed. In addition, blade wear

saws and the effect of the countermeasures(TR16-02)”

comparable to that with DI water was achieved.
https://www.disco.co.jp/eg/solution/technical_revie
For that reason, the CO2 injector at DISCO sets 0.5
M–1.0 MΩ･cm as the standard for resistivity.

w/doc/TR1602_Wafer%20ESD%20in%20dicing%20saws%20a
nd%20the%20effect%20of%20the%20countermeas*Blade wear changes depending on the bond type andenvironment, and thus, these are reference values
and are not guaranteed.

ure_20160610.pdf(3) DISCO website: Solutions / Blade Dicing / The
Advantages of Non-Contact Setup (NCS)
https://www.disco.co.jp/eg/solution/library/dicing/setup.html

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