Inkjet printing system and method for processing wafers

An inkjet printing system configured to inkjet patterns of liquid material on wafers that are supplied in a high volume and that each have a wafer edge that extends in at least two different directions, the inkjet printing system including:

• at least one chuck on which a wafer can be placed;
• at least one inkjet printing head that includes at least one nozzle that is configured to discharge liquid when the nozzle is fired by a control signal;
• a printing motion assembly that supports at least one of the at least one chuck and the at least one inkjet printing head so that a two dimensional printing area on the at least one chuck can be covered with liquid discharged by the at least one printing head;
• an electronic controller assembly configured to produce control signals to fire the at least one nozzle and configured to control the printing motion assembly for positioning the at least one printing head relative to the at least one chuck so that the positioning variation with which the liquid is deposited relative to the chuck is less than a first threshold value;
• each chuck of the at least one chuck being associated with a single associated camera that is directed to the associated chuck, each camera having a two dimensional matrix of camera pixels, each pixel having a pixel coordinate;
• each chuck including a placement area extending within a boundary;
• each chuck including a 2-dimensional visual reference provided directly on each chuck, within a periphery of each chuck and outside of the boundary;
• wherein the controller assembly is configured:
• to control a said camera that is associated with a said chuck to take a single image each instance a wafer has been placed on that chuck, wherein the image includes the wafer edge and the 2-dimensional visual reference of the chuck;
• to determine from each said single image:
• the position of the chuck relative to the camera by detecting the position of the 2-dimensional visual reference with respect to the camera pixel coordinates;
• and
• the position of the wafer relative to the camera by detecting the position of the wafer edge of the wafer with respect to the camera pixel coordinates;
• to use these two position determinations to calculate, for each said single image, the wafer position relative to the 2-dimensional visual reference and thus relative to the chuck with an accuracy of less than a second threshold value and, based on that relative position, subsequently time the firing of the at least one nozzle of the at least one printing head and control the movement of the printing motion assembly so that the liquid discharged by the inkjet printing head is positioned on the wafer with a positioning variation which is less than the sum of the first and the second threshold values, and
• wherein each camera has an associated ring light source that has a central axis that is collinear with a camera axis of the associated camera, wherein the ring light source directs light to the associated chuck.