Location of image plane in a laser processing system

An apparatus for laser processing a substrate comprising:

• a laser source;
• a beam imaging system, adapted to produce, from an optical output of the laser source, a first beam of laser energy characterized by a first spatial intensity distribution having a non-circular perimeter shape at the focal point of the beam when viewed in a plane that is orthogonal to a path along which the beam of laser energy propagates and adapted to produce a second beam of laser energy to form a modulated beam of laser energy characterized by a second spatial intensity distribution different from the first spatial intensity distribution;
• a scan lens;
• a workpiece positioner adapted to support a workpiece such that the distance orthogonal from the workpiece positioner to the scan lens is variable;
• a camera adapted to capture imagery of a feature formed in the workpiece and generate image data representative of the captured imagery;
• and
• a controller communicatively connected to the camera, the workpiece positioner and the beam imaging system, wherein the controller is operative to:
• process the image data to determine if the feature has a shape that sufficiently resembles the shape of the first spatial intensity distribution;
• and
• if the shape of the feature sufficiently resembles the shape of the first spatial intensity distribution:
• set a process distance as the distance between the scan lens and the workpiece;
• control an operation of the workpiece positioner to dispose a surface of a workpiece at the process distance;
• and
• control an operation of the beam imaging system to produce, from the optical output of the laser source, second beam of laser energy.

A method of processing a workpiece using a laser processing system having a scan lens, the method, comprising:

• processing a workpiece using a first beam of laser energy, wherein the first beam of laser energy irradiates a spot on the workpiece, wherein the spot has a first shape, wherein the first shape is a non-circular shape, wherein the processing includes forming a plurality of features in the workpiece, wherein a first distance between the scan lens and the workpiece during the forming of one of the plurality of features is different from a second distance between the scan lens and the workpiece during the forming of another of the plurality of features;
• determining which of the plurality of features has a shape that most closely resembles the first shape;
• setting a process distance as the distance between the scan lens and the first workpiece during the forming of the feature having the shape that most closely resembles the first shape;
• determining an image plane as a plane at the process distance from the scan lens to a plane orthogonal to the path along which the beam of laser energy propagates;
• disposing a surface of the workpiece at least substantially at the image plane;
• and
• processing the surface of the workpiece using a second beam of laser energy, wherein the second beam of laser energy irradiates a spot on the surface that has a second shape different from the first shape.