Photo Resist Removal
Photo Resist can be removed quite easily with a plasma process, usually with microwave excitation. This combination offers the best combination of high stripping rates and low device damage.
Batch processing has of course the advantages of low cost per wafer and the removal of resist from either side of the wafer, however the down side of this processing technique is the limitations of achievable uniformity. However, since the selectivity of a pure oxygen process is infinite to inorganic materials, the lack of uniformity has no influence on the process result.
Since a higher temperature of the wafer during process leads to a faster stripping rate, we have developed an advanced process control, which allows processing the wafers at a pre-set temperature. The wafer temperature is measured using an IR- spectrometer and the processing power is controlled such that the wafer temperature is kept at the programmed value. The advantage of this process control is to maintain the maximum stripping rate while not exceeding the temperature limit for the device in the process.
For advanced device requirements and 300mm wafers, processing in single wafer mode is preferred. This processing mode provides better and more flexible process control for uniformity and end point detection at the expense of higher cost per wafer.
Most commonly the process is based on oxygen plasma, sometimes in combination with specialty gasses for special applications and requirements. Some devices may not be subjected to the high temperatures commonly achieved in pure oxygen plasma. On the other hand, productivity requires a high stripping rate. A small amount of special etching gas increases the removal rate even at low wafer temperature, which is the perfect solution for resist removal after high-dose implantation. In case of substrate layers, which are sensitive to oxidation, hydrogen can be used as alternative process gas to prevent oxidation.