Initial brief was for the design and supply of a machine that would cut circular disks, in varying layouts, from 100 mm silicon wafers. The process needed to be automatic and capable of upgrading to 150 mm origin wafers at a later date. The customer also required qualification of edge quality of the cut as well as throughput figures based on project manufacturing requirements.
Following initial applications work, we sourced a JK Laser product that provided the cut quality and speed across the wafer thicknesses laid down by the customer. A number of different processes were considered such as multiple skimming to deal with thickness. The JK pulsed laser provided sufficient power to punch through and cut as a single cut process.
We decided that we would use the M series chassis as the basis to our design. This was then modified in order to incorporate all the necessary equipment that would be required to complete the process flow.
Started with throughput characterising, it was decided that a dual load capability would be used in order to maximise the cutting process while reducing potential delays through handling. You can see from the photo the 3 chamber configuration. Left and right doors provide access to the load unload station while the central one provides access to the cutting chamber.
Two 3 axis linear units were selected providing X-Y and Z motion control on each loading facility. These were attached a linear slide facility that joined together the 2 load stations effectively providing a six axis control capability.
Each load station comprised of a vacuum chuck to accommodate each of the wafer formats. The first wafer of each batch, once located onto the chuck, required the focal position to be configured. A small laser unit measured the focal position and set the Z height to the correct position, providing a closed loop feedback until the correct height was achieved. Once the focal position was set then the pattern needed to be addressed.
Pattern variation and location onto the chuck could not be predetermined, so a camera system was used to determine pattern recognition and then align the pattern to the lasers X and Y axis set up – the biggest issue being rotation of the pattern. The chuck, with its load, moved into the inner chamber of the loading enclosure so that the lighting could be controlled. Once the pattern had been located, measured and the appropriate coordinates sent to the controller, the chuck would sit until requested for cutting. This chuck would wait until the cutting chamber was available for loading. The chuck unit would pass through a set of side doors to the cutting chamber where it would dock onto the extraction point and lift the extraction hose. Once it had the hose, then the chuck would move to the appropriate position below the laser. At this time the laser would fire, punching through the silicon. Motion control would start the trace action for the pattern, each circle starting with a plunge cut from the outside. Once the pattern had been completed, the chuck would exit back to its load – unload position ready for the next sequence. Once the chuck had passed back through the safety doors to its load enclosure, then the second chuck from the second load enclosure moved into the cutting enclosure to continue its process sequence. While one wafer was being processed in the cutting chamber, the other one was being unloaded, then loaded. Then it would progress to the camera alignment in preparation for the cutting process. This sequencing continued until the batch size was completed or the operator stopped the process manually.
In delivering the completed unit we were able to provide a product that out-performed their previous production capability. One thinklaser product replaced 2 of the customer’s older units by providing a higher throughput capability. Westcode ordered a second unit 6 months later, and now have 2 units running European production requirements.
We went on to design a smaller unit for a second Semiconductor house – again for silicon wafer cutting. All these machines are still running production today.
If you would like further information on this laser application, or any other application, please request a call back or talk to one of our laser marking specialists on 01737 826902.
