• There is a risk of breaking wafers when measuring.
• Since the sensor measures the height including the BG tape, if the thickness of the tape changes, there is an error of that amount.
• Very hard to align the optical axes of two sensors.
• Since the sensors measure the thickness including the BG tape, if the thickness of the tape changes, that creates error.
• The sensor can easily make measurements just by being positioned 80 mm (3.15") from wafers.
• Non-contact so wafers are not damaged.
• The sensor can directly measure just wafer thickness, so measurements are not influenced by BG tape thickness.
• With a small head that can be installed 80 mm (3.15") from the wafer, wafer thickness can be constantly monitored inside equipment while polishing.