3.9 Wafer Thinning Technique
After the major device fabrication steps are complete, the wafer is often thinned from the bottom to ensure maximum heat conduction during device operation. It is also important for scribing very small devices.
The front of the wafer is covered with a thick photoresist (3 mm) and hard baked to protect the devices from any mechanical damage. It is then gently turned upside down and pasted on a cylindrical aluminium chuck (2 cm diameter) with wax. The surface to be lapped faces outward.
The reverse side is then polished using a mechanical polisher covered with fine grained sand paper. Once the required thickness has been removed, the sample is recovered by a soak in TCE to remove the wax. The photoresist from the front surface is removed in the usual way using acetone.
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