Laser Machining processes - Excimer Laser Machining or Excimer Mask Laser Ablation Process

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Excimer lasers produce relatively wide beams of ultraviolet laser light. One interesting application of excimer lasers is their use in micro-machining organic materials (plastics, polymers, etc). This is because the excimer laser doesn't remove material by burning or vaporising it, unlike other types of laser such as CO2, so the material adjacent to the area machined is not melted or distorted by heating effects.

When machining organic materials the excimer laser is pulsed on and off, removing material with each pulse. The amount of material removed is dependent on the material itself, the length of the pulse, and the intensity (fluence) of the laser light. Below a certain threshold fluence, dependent on the material, the laser light has no effect. As the fluence is increased above the threshold, the depth of material removed per pulse is also increased. It is possible to accurately control the depth of the cut by counting the number of pulses. Quite deep cuts (hundreds of microns) can be made using the excimer laser.

The shape of the structures produced is controlled by using a chrome on quartz mask, like the masks produced for photolithography. In the simplest system the mask is placed in contact with the material being machined, and the laser light is shone through it. A more sophisticated and versatile method involves projecting the image of the mask onto the material. Material is selectively removed where the laser light strikes it.

With excimer laser ablation, nano-structures with vertical sides can be created. By adjusting the optics it is possible to produce structures with tapered sidewalls

Typical applications for excimer laser mask machining are the production of micro-fluidic channels for process control sensors, ‘cutting out’ of delicate, micro structures in sheet metals, drilling of small holes and vias, machining of micro-circuitry onto PCBs.

Excimer lasers have a number of applications beyond those mentioned here. One area of application many would be familiar with is in machining the cornea of the eye to change its optical properties; correcting for short sightedness.