Use of fresnel zone plates for material processing

DETAILED DESCRIPTION It is an advantage of the present invention to provide a system which uses diffractive optics techniques to form an arbitrary pattern for machining and material processing.
It is a further advantage of the present invention to permit the simultaneous processing of multiple areas within the field of view using approximately parallel beams of uniform power, and without having to step or scan the stage on which the workpiece is mounted.
It is another advantage of the present invention to permit highly accurate alignment of the diffractive optic with the workpiece to assure correct location of the beams.
In an exemplary embodiment the apparatus for drilling vias or holes in a circuit board includes an excimer laser and a Fresnel zone plate (FZP) positioned parallel to the circuit board, with the distance between the FZP and the circuit board being the focal length of the FZP.
For each via to be formed in the circuit board a corresponding FZP is patterned onto an FZP array.
Each FZP may be patterned directly centered over the desired via location or in high density patterns it may be located off-center from the via with deflection being accomplished by the formation of finer circular arcs on the side of the FZP opposite the desired direction of deflection.
General Plate Construction In the following description, certain terms will be used.
Although reflection is a candidate for the apparatus and process here set forth, transmission is preferred.
Reflection requires angularity between the plate producing working images and the workpiece.
A transmission mode of operation generally leads to simpler opto-mechanical arrangements and is therefore preferred.
Accordingly, and in the remainder of the text, where transmission is included, substitution of reflection will be understood.
As in the example above, it is the object of the method and apparatus to produce and describe optical plates.
Each plate will be divided into subapertures.
Each of these subapertures will produce one working image for incidence on a workpiece, typically for machining