In the era of 2-inch wafers, these were handled manually using tweezers and held manually for the time required for a given process. Tweezers were replaced by vacuum wands as they generate fewer particles which can contaminate the wafers. Wafer carriers or cassettes, which can hold several wafers at once, were developed to carry several wafers between process steps, but wafers had to be individually removed from the carrier, processed and returned to the carrier, so acid-resistant carriers were developed to eliminate this time consuming process, so the entire cassette with wafers was dipped into wet etching and wet cleaning tanks. When wafer sizes increased to 100 mm, the entire cassette would often not be dipped as uniformly, and the quality of the results across the wafer became hard to control. By the time 150 mm wafers arrived, the cassettes were not dipped and were only used as wafer carriers and holders to store wafers, and robotics became prevalent for handling wafers. With 200 mm wafers manual handling of wafer cassettes becomes risky as they are heavier.
In the era of 2-inch wafers these were handled manually using tweezers and held manually for the time required for a given process Tweezers were replaced by vacuum wands as they generate fewer particles which can contaminate the wafers Wafer carriers or cassettes which can hold several wafers at once were developed to carry several wafers between process steps but wafers had to be individually removed from the carrier processed and returned to the carrier so acid-resistant carriers were developed to eliminate this time consuming process so the entire cassette with wafers was dipped into wet etching and wet cleaning tanks When wafer sizes increased to 100 mm the entire cassette would often not be dipped as uniformly and the quality of the results across the wafer became hard to control By the time 150 mm wafers arrived the cassettes were not dipped and were only used as wafer carriers and holders to store wafers and robotics became prevalent for handling wafers With 200 mm wafers manual handling of wafer cassettes becomes risky as they are heavier