DISCO Technical Review Mar. 2023

Die Strength After Ultrashort Pulse Laser Processing
Sales Engineering Department
Abstract
Adoption of interlayer dielectrics (Low-K film) has been increasing recently due to miniaturization ofsemiconductor devices. Generally speaking, as the mechanical strength of the Low-K film is low, full cut
using the blade dicing process after removing the film using the laser grooving process is common. When
compared to the blade dicing process alone, one of the challenges of this process is decline in die strength
due to heat damage from the laser. Here, die strength improvement results were verified by controllingthe heat damage using an ultrashort pulse laser.
This report shows that the die strength after using an ultrashort pulse laser followed by blade dicing ishigher than that after blade dicing alone.

1. Introduction
With the purposes of high-speed and energy-saving,semiconductors are becoming miniaturized andhighly integrated. As the distance between wirings
becomes narrower due to miniaturization, thewiring capacitance increases, leading to signal
delay. In order to prevent this, interlayer

In this process, water-soluble resin is coated on
the wafer surface prior to laser grooving, the LowK film is removed using the laser grooving process,and then the wafer is cleaned on the spinner table,
preventing debris adhesion. As the blade dicing
process is performed after the Low-K film isremoved, high-quality singulation is possible.

dielectrics (Low-K film) started to be adopted. Low-Demands for die thinning have been increasing

K film has low mechanical strength, and film

for the purpose of high integration. Die strength

peeling (delamination) occurs when processing

declines as the wafer becomes thinner, and thus

with the blade dicing process. For this reason, thereliability of the product also declines. For thismainstream process for this is to remove the film

reason, die strength improvement is an importantusing the laser grooving process and then singulatetheme. When the laser process is used, decline ininto die using the blade dicing process (Fig. 1).

die strength due to the heat effect is a challenge. In
order to resolve this, laser processing using an
ultrashort pulse (USP) laser, which controls theheat damage to the die by irradiating the laser
instantaneously, is being proposed.

Fig. 1: Laser Grooving + Blade Dicing Process

In this report, the die strength after laser
grooving using a conventional laser will becompared to the die strength after using an
ultrashort pulse laser followed by the blade dicing
process.

DISCO Technical Review Mar. 2023
2. Test Method
Wafers were singulated into die using each of thefollowing processes: a conventional laser + blade
dicing, and a USP laser + blade dicing, and thendie strength was measured using the 3-point
bending die strength measurement method.
In addition, in order to measure the laser
processing effect more accurately, bare Si
wafers without Low-K film were used in thisinvestigation.
The 3-point bending die strength measurement
method is a type of material test. As shown in Fig.

Fig. 2: 3-Point Bending Die Strength Measurement

2, both edges of the die have simple supports andare not fixed. In this state, load is applied in theperpendicular direction, and the maximum load up

3. Measurement Results and Remarks

until the die breaks is measured. Compressive

The processing results of the conventional laser +stress is generated on the front side of the die, andblade dicing and the USP laser + blade dicing are

tensile stress on the backside. In this test,

shown in Table 1. Comparing the results of the two

breakage strength due to the tensile stress on theprocesses, melting at the bottom of the groove isbackside of the die is observed. The maximum load

less with the USP laser, indicating that the heatup until the die breaks can be calculated as theeffect is lower.

bending stress value per unit area using equation(1).
Table 1: Processing Results
32 ℎRegarding

diestrength

1measurement,

thecantilever bending test is also standardized in theSpeed[mm/s]SEMI standard. In this investigation, the morecommon 3-point bending method is used.
Upper
surfaceConventional laser＋
Blade dicing

USP laser＋
Blade dicing

350800DISCO Technical Review Mar. 2023
Next, die strength comparison is shown in Table
2. Although the die strength after the conventionallaser + blade dicing is lower than that after blade
dicing alone, the die strength after the USP laser +Reference Materials[1]Highly purified water-soluble protective film
for semiconductor processes (TR21-02)

blade dicing is higher than that after blade dicing[2]Silicon wafer thinning, the singulation process,alone. The reason for these results could be due toand die strength (TR16-03)

the fact that the heat damage from the USP laser
is lower than the head damage from theconventional laser and the physical damage fromblade dicing alone.
Table 2: Comparison of Die Strength

4. Summary
By using the USP laser + blade dicing process, diestrength can be improved compared to theconventional laser + blade dicing process or blade
dicing alone. USP laser processing can be expected
to be applied not just in Low-K film removal, butalso to process a wide range of materials other thanSi such as SiC and GaN.
Please contact DISCO to request test cuts using
our USP laser.

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DISCO Corporation
Tel：03-4590-1115