Analysis for manufacturing technology of micro LED- Optimization of laser transfer conditions In the manufacturing process of micro LED displays, the laser process is very effective for accurate and fasttransfer of micro chips. However, it is necessary to select the appropriate laser wavelength and energy
for high-precision transfer. We introduce analysis methods that can evaluate surface contaminations anddamage in order to select optimal process conditions.

RAP-LLO Toray Engineering Co., Ltd.
Toray Engineering Co., Ltd. supplies a wide variety of equipment related to the micro LED manufacturing process, and has
developed a new technology, RAP-LLO (Random Access Patterned - Laser Lift Off). The new technology, RAP-LLO is capable oftransferring only selected chips at a high speed of 10,000 chips per second, and is expected to become an indispensable technology
for the widespread use of micro LED displays in the market. We will introduce examples of analysis related to this new technology.

Chip

Release layer

Laser（ Polyimide-type ）DonorCatch layer（ Silicone-type ）TargetDaring to experiment
under inappropriate
condition

Condition of laser transferLaserWavelength

WavelengthAB

Morphological observation (SEM)
Chip cracks are observed under inappropriate condition.
High resolution SEM observation is effective in determining
the cause of defects and can contribute to yield improvement.
NormalLow energy

Transferred

Not released

High energy

Transferred

Cracking

Crack

30um
Wavelength A, Low energy

5um
Wavelength B, High energy

Surface-contamination evaluation (TOF-SIMS)

Damage evaluation (Cathodoluminescence)

TOF-SIMS can obtain chemical structure of organic materials
with high sensitivity and high spatial resolution. It is an idealmethod to evaluate the matching of laser conditions withrelease materials and catch materials.

Cathodoluminescence (CL) can evaluate damage (defects) on
the surface of semiconductor chips with high sensitivity andhigh spatial resolution, and is a very effective method forevaluating micro-sized LEDs.

100100

Wavelength A, High energy
80

7Wavelength A, Low energy

6d80
5a60

4020・

4・b36040

220100μm 04080・・c・ ・f

5Confirmation of dark spotsthat cannot be seen with SEM.

Defect types canbe identified fromspectra.

14232e10μm 0Wavelength A, High energy

6040

380Intensity

Polyimide residue

Distribution of polyimide residue

45.00E‐02
4.00E‐02
3.00E‐02
2.00E‐02
1.00E‐02
1.00E‐05

56abcdPositionef

Contamination were found on the top surface of the chip even in thenormal transfer process, and the distribution of the contamination
varied among the conditions. TOF-SIMS is an important method forselecting appropriate laser conditions.

CL image5um

CL spectrum

Many dark spots were observed under all the normal transferconditions. It is conceivable that these could have occurred during
the lift-off process of the LED chip from the sapphire substrate. CL
method can evaluate residual defects in chips with high sensitivity,
it can be used for process improvement.

Toray Research Center will contribute to accelerate the development of micro-LEDs by utilizing thelatest analysis techniques and the more than 40 years of experience we have accumulated.
P02252海外営業部(滋賀)20210331