Laser Lift-off

Laser Lift Off (LLO) is a technique to selectively remove

one material from another. It utilizes a process whereby

the laser passes through a transparent  base material

and couples strongly with a second material. LLO

is widely used in LED manufacturing to separate

the GaN semiconductor from the Sapphire host

wafer, and has application in other processes

that involve transparent and absorbing films,

such as the separation of polymers from

glass in flex display and AMOLED

applications.

The basic concept behind laser lift off is the difference in absorption of the laser light by one layer, typically a host substrate, and the filmstack being separated. In the case of LEDs for example, the GaN epi layer has a bandgap of about 3.3 eV whereas the sapphire bandgap energy is ~ 9.9 eV. Short wavelength laser light passes through the sapphire, and ablates the 

 

interface when it couples with the GaN, thereby releasing the two materials.  In order to achieve successful lift off beam quality and control are important. At IPG, innovative and patented beam delivery techniques are implemented to achieve high-speed, high-yielding production processes.


Laser Lift Off

A laser light source is projected through a transparent material and is absorbed in an adjacent material on the backside, such as GaN on Sapphire.  Confined plasma at the interface results in lift-off or separation of the materials

Figure shows an exposed wafer after Laser Lift Off

System: IX-255-LLOIX-6655

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Laser Lift Off of Polymer on Glass

 

Transfer of 3D wafer-based electronic device structures and polymer-based active matrix display panels such as AMOLED for smartphones (polymer backplane). Figure shows separation of 15 µm thick polyimide using a 355nm scanned laser.

System: Micromachining Workstation (IX-280-ML)

Lasers: UV ns pulsed lasers

 

 LLO polymer on glass


Monolithic Advanced Lift Off in GaN

Shorter wavelengths/higher energy photons are better absorbed, resulting in shallower optical penetration depth in certain materials such as GaN.  UV pulses can be used for separation of thin film semiconductor materials when the heat penetration depth needs to be minimal.

System: Micromachining Workstation (IX-280-ML)

Lasers: UV ns pulsed lasers

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