Robotics are commonly used in the semiconductor manufacturing industry to transfer semiconductor wafers, also known as substrates, throughout the fabrication area. Conventional wafer cassettes are typically used to retain a group of wafers that are commonly referred to collectively as a lot. Many times throughout the manufacturing process, the individual semiconductor wafers must be loaded into or out of the wafer cassettes. Various robotic wafer transfer systems may be used. In many cases, the wafer cassette is disposed within a transportable wafer transfer module such as a FOUP, front opening unified pod, when the transfer of semiconductor wafers into or out of the cassette takes place. The robotic systems typically utilize a blade that transfers the individual wafers into and out of slots of the wafer cassette. It is important that the semiconductor wafer is accurately and precisely aligned with respect to the slots during these transfers. If the semiconductor wafer is not aligned accurately and precisely with respect to the slots, the wafer can be scratched or shattered, dispersing particles and contaminating all of the other wafers in the lot, the cassette itself, the wafer transfer module, the wafer transfer system itself, and the associated semiconductor processing equipment.
Correct alignment is more critical and challenging as wafer sizes increase from six to eight to ten to twelve inches in diameter or greater and also when wafers are being loaded into cassettes disposed in a wafer transfer module as the relationship between the cassette and the wafer transfer module, e.g. FOUP, introduces another alignment issue. The robotics systems that provide the wafer blade to transfer wafers into and out of cassettes may consist of multiple pulleys and belts and various pneumatic systems and other positioning devices. It is therefore a challenge to assure that the multiple components of the robotics system work cohesively to produce accurate alignment. When loading a wafer into a slot of a wafer cassette, it is therefore quite challenging to ensure proper alignment of the wafer with respect to the wafer cassette in the x-direction, y-direction and z-direction.
There are conventional methods for calibrating and adjusting the alignment of a wafer transfer blade and therefore the semiconductor wafer with respect to the slots of the wafer cassette, but these calibration/alignment methods are typically time and labor intensive. Many calibration/alignment techniques require multiple measurements to be made with the wafer blade in various stages of extension. Complex algorithms are often used to evaluate the alignment based on multiple measurements. Oftentimes, the multiple measurements require at least partial disassembly of the front opening unified pod to calibrate the instruments. Typically, a side door must be opened. A plurality of data points is typically analyzed and based on the data analysis, instructions for adjusting the robot position are generated. Many recommended alignment procedures take as long as six hours to complete. In addition, many procedures also require tools and/or instrumentation from outside vendors. Moreover, when wafer transfer modules such as the FOUP are opened to check positioning and alignment, particle testing is required afterwards before the wafer transfer module can be returned to production use. The resulting unavailability of the wafer transfer robotic system carries with it an associated financial impact and significantly increases cycle time for the semiconductor devices being manufactured.
It would therefore be desirable to calibrate the alignment of a robotic wafer transfer system in a reliable, efficient and expedited manner.