cassette

A cassette is a container with uniformly spaced horizontal slots that holds multiple semiconductor wafers in a vertical stack, maintaining separation between wafers during storage, transport, and batch processing. While FOUPs have largely replaced open cassettes for 300mm wafer handling in modern fabs, cassettes remain widely used in 200mm and smaller wafer fabs, in wet processing equipment (where batch immersion requires open containers), and as internal wafer staging within tools. Cassette types include: open cassettes (traditional design — wafers sit in molded or machined slots with the cassette open on front and top, used in wet benches where wafers must be accessible for batch immersion in chemical baths), H-bar cassettes (wafers rest on horizontal support bars rather than edge slots — used for fragile or warped wafers), boat cassettes (quartz boats for thermal processing — holding wafers vertically during furnace operations at temperatures up to 1200°C), and SMIF pods (Standard Mechanical Interface — enclosed cassettes with a sealed bottom-opening door, the predecessor to FOUPs used in 200mm fabs for particle protection). Cassette specifications include: wafer capacity (typically 25 wafers for 300mm, 25 for 200mm, and 25 or 50 for 150mm), slot pitch (the spacing between adjacent wafer positions — 10mm for 300mm wafers, 6.35mm for 200mm), material (polypropylene, PVDF, Teflon for wet processing chemical resistance; quartz for high-temperature furnace processing; polycarbonate for general transport), and dimensional conformance to SEMI standards (E1.9 for 200mm, E47 for 300mm). Cassette-to-FOUP transition was driven by the need for sealed micro-environments — open cassettes expose wafers to fab ambient air where molecular contamination (AMC) and particles can deposit between process steps, causing defects at advanced technology nodes. Cassettes remain essential in wet processing where batch immersion in chemical baths requires open access to the wafer stack.