Excimer lasers use a mixture of gases to provide pulsed emission at a series of discrete wavelengths in the UV region. The word excimer comes from the term excited dimer. A dimer is a diatomic molecule that is electronically bound in its excited state, but is not or only very weakly bound in ground state.

At a general level, excimer lasers work on the following principle:

i)       Halogen gas (“H”) and inert gas (“N”) atoms are excited by an electrical discharge

ii)      Excited atoms form a metastable excited dimer (HN^*)

iii)     Dimer relaxes to ground state with the emission of a UV photon

iv)     Dimer dissociates rapidly (<10^-13s)

For excimer lasers the spatial distribution, or profile of the laser beam, is said to be a “top- hat” or have a flat-top intensity profile which is two dimensional in shape. This refers to how the laser energy varies in axes orthogonal to the direction in which the laser propagates. The system is designed for fabrication of surface features (micro-machining, micro-milling) on polymer surfaces, semiconductor microlithography and marking and precision drilling of polymers. Its short wavelength allows ’cold processing’ to occur and sub-micron resolution features can be produced with little or no heat-affected zones (HAZ) and clean, precisely defined shapes.

Technical Specifications

Wavelength: 193 nm
Pulse Duration: 3 - 7 ns
Pulse Energy: 20 mJ
Average Power: up to 200 mW
Pulse Repetition Rate: 300 Hz

Optec Micromaster machining centre consists of:-

Mask –The beam illuminates a mask, whose image is then projected onto the part at selected demagnification.

Vision system - The system uses TTL (through the lens) vision over the demagnification range. There is also an independent vision system, the off-axis camera, providing an overall view of the process area.

Stage - this can be displaced in X, Y and theta directions and is controlled by the ProcessPower software system

ATL ATLEX SPI excimer system in NCLA

SEM image of nanopits produced on a acrylic polymer (Pits have a periodicity of approximately 400 nm)

SEM image of grooves produced on a 50 µm diameter polymer fibre