DISCO Technical Review March 2022

Highly purified water-soluble protective film for semiconductor processes
Sales Engineering Department
Abstract
Laser ablation is a process that can cut brittle materials and difficult-to-machine materials while maintaining
productivity and quality. Miniaturized and highly integrated semiconductor die are singulated through thecutting of the silicon substrate using blade dicing after removal of the wiring layer using laser irradiation.
However, during processing, laser ablation produces debris, which adheres to the workpiece surface and isdifficult to remove. To resolve this issue, DISCO developed HogoMax, a water-soluble protective film foruse in laser processing. This review describes HogoMax’s characteristics and explains its importance inlaser ablation processing.

substrate is cut using blade dicing. For devices that

1. Background
With efforts to achieve better performanceuseacompoundsemiconductor

substrate,

through improved integration, the miniaturization

singulation is sometimes performed using onlyof semiconductor devices has progressed. Because

laser ablation.

the distance between wires has decreased due toLaser ablation is a processing method thatdevice miniaturization, parasitic capacitance has

focuses laser energy on a small area for a very shortbecome greater, leading to concerns about signal

time, causing the workpiece material to sublimate

delay. To lower parasitic capacitance, low-k

or evaporate.

material is used as interlayer dielectrics. However,
the mechanical strength of this material is low, andHowever, if the molten material (debris)

film peeling may occur if the workpiece isdispersed by laser ablation adheres to theprocessed using standard blade dicing. In addition,

electrodes on the workpiece surface, it will be

due to the low feed speed needed to achieve highdifficult to remove using only DI water cleaning

processing quality, it was difficult to obtain highand may cause electrical property defects in theproductivity using blade dicing for compound

wire or bump bonding (figure 1).

semiconductors such as red LEDs (light emitting

To resolve this issue, DISCO developed

diodes), for which demand has been increasing in

HogoMax, a water-soluble protective film for use

recent years, and gallium arsenide (GaAs), whichin laser processing.

is used as a substrate for high-frequency devices.
To cut these materials with both high quality andproductivity, laser ablation is used for dicing.
For example, for semiconductor devices that use
low-k material, the wiring layer on the surface isremoved using laser ablation, and then the silicon
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DISCO Technical Review March 2022

Figure 1. Schematic drawing of laser grooving process; Top, conventional laser grooving process without
protective film; Bottom, laser grooving process with water-soluble protective film

2. HogoMax usage
If HogoMax is spin coated onto the workpiecesurface before laser ablation processing, debris
will accumulate on the protective film instead ofmaking direct contact with the workpiece surface.
As HogoMax is water soluble, when it is removed
during DI water cleaning, the debris that has
accumulated is removed as well. As a result, laser
processing without debris adhesion to theworkpiece surface becomes possible (figure 2).
Figure 2. Comparison of ablation processing
with and without HogoMax, using a GaAs
mirror wafer2

DISCO Technical Review March 20222.0

3. Physical properties of HogoMax
Coating thickness [μm]The major physical properties of HogoMax are
listed in table 1. One feature is its metallic impurity
concentration of 50 ppb or less, which minimizes
impact on the semiconductor device, enablingprocessing in which heat is applied locally, such as
laser ablation.
Table 1. Major physical properties
Material properties

HogoMax103

Viscosity (cP)

235

pH

3.3

Surface tension (mN/m)

50.2

Specific gravity

1.012

1.58
1.5
0.99
1.0

0.82

0.5

0.0
01000
2000
3000
Rotation speed [rpm]Figure 3. Film thickness at different rotation speeds

Absorbance
0.019(undiluted @ 420 nm)
Metal impurity concentration

Figure 4. Differences in coated film thickness based ontype of protective film

<50Na, K, Fe, Cu @ ppb

In addition, depending on the type, commercial
4. HogoMax coating performanceprotective films may leave some areas uncoatedVariation in coated film thickness caused byduring spin coating due to the workpiece surface

spin coating rotation speed was measured using apattern (figure 5). Because it optimizes thesilicon mirror wafer (figure 3). It was discovered

wettability of the wafer, HogoMax can be coatedthat protective film thickness can be controlled toonto the entire surface of the workpiece throughbetween 0.82 and 1.58 µm using rotation speed.

spin coating without liquid accumulating on areas

Maximum coated film thickness variation, 0.04 μmof the workpiece surface with a different shape or

at 1,000 rpm, was minor with excellent uniformity.

materials.

In addition, when film is coated onto an unevensurface, such as ball bumps, deviation typicallyoccurs near the uneven area due to surface tension,
causing thin sections in the coating (figure 4).
HogoMax is composed of materials thatsuppress surface tension, achieving uniform film
thickness even in areas near the street or densely
covered with ball bumps.
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DISCO Technical Review March 2022

Figure 5. Different protective films coated onto wafers with bumps; Top, debris adhesion when protective
film manufactured by another company was used; Bottom, debris adhesion when HogoMax was used

5. Processing performance with HogoMax
With protective films made of high-polymer
material, the constituent material may coagulate on
the surface due to cross-linking during laser
Figure 6. Comparison of protective film
coagulation due to heat generated by ablation
processing; (a) product without countermeasures,(b) HogoMax

ablation, which makes it difficult to remove
through cleaning (figure 6).
Because HogoMax is manufactured for use withlaser processing, materials are optimized to100

Tansmittance [%]prevent cross-linking. Thus, no coagulation due toheat was observed, even after laser ablation
processing.

ー Coated806040-- After 30 sec washingー Non-coating20

6. HogoMax cleaning residue
To measure HogoMax residue after cleaning,

03500

the workpiece surface was measured with FT-IR

2500

1500500

Wavenumber [cm-1]

Figure 7. FT-IR spectrum on the wafer surface
after protective film coating and DI water
spinner cleaning.

after coating and after DI water cleaning. In thesample that had been coated, the spectrum clearly
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DISCO Technical Review March 2022

Figure 8. Comparison of coated film thickness on the wafer surface after protective film coating and after DI
water spinner cleaningshows the presence of HogoMax on the workpiece.
The measurement results after 30 seconds of DI

References(1) M. Kumagai, N. Uchiyama, E. Ohmura, R.
Sugiura, K. Atsumi and K. Fukumitsu,"Advanceddicing
technology
forsemiconductor wafer -Stealth Dicing," 2006
IEEEInternational
Symposiumon
Semiconductor Manufacturing, 2006, pp.
215-218, doi: 10.1109/ISSM.2006.4493065.

water cleaning were similar to those before
HogoMax was coated (figure 7).
In addition, figure 8 shows a visualization andcomparison results for HogoMax coating. As
shown, HogoMax, which had been evenly coatedonto the workpiece surface, was removed with 30

Inquiries regarding DISCO Technical Review

seconds of DI water cleaning. These results show

Sales Engineering Department

thatitispossibletoremove

DISCO CorporationHogoMax

Tel: 03-4590-1115

satisfactorily through only DI water cleaning.

7. Conclusion
This review shows that using HogoMax can
prevent debris adhesion caused by laser ablation
processing. With the combined use of laser
ablation processing and HogoMax, it is possible toprocess

difficult-to-machinematerials

andcompound semiconductors, such as low-k film,
while achieving both high productivity and quality.

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