MEI semiconductor wet process tools built to prevent contamination

April 27, 2012 — MEI makes batch immersion equipment for cleaning, etching, and developing microelectronics wafers, including silicon and gallium arsenide, as well as process control equipment and automation software. The PVC materials used to make process tools influence tool performance, safety in the fab, and chip quality. Semiconductor and solar are two of the most materials-/contamination-sensitive manufacturing sectors. MEI uses Vycom Flametec PVC-C for chemical rinse tanks and other wafer-contacting elements of its process tools, reducing tool-based contamination and protecting fab workers.

Figure 1. The dual robots of the MEI Advancer Gemini, dual robot semi-auto wet bench.

Many MEI wet bench tools take dry wafers and move them — using robotic arms (see Figure 1) — through chemical and rinse tanks, then to an IPA-style dryer. MEI uses Vycom Flametec PVC-C, a fire-retardant, chemical and moisture-resistant material, to build the housing (shell) of its wet process systems, the robotic arm ends, chemical rinse tanks, and conveyances for automated dry-to-dry wet bench acid process immersion tools. “We use some non-4910 material, called Protec, for tanks and valve boxes, but for the bulk of our batch immersion wet benches for acid type process we rely on PVC-C,” said Bill McGinty, MEI operations manager.

Figure 2. MEI’s Advancer Micro semi-automated wet bench. Detail: the back of the Advancer Micro.

Wet process chemicals can be punishing to the equipment and its internal components. Older bench-construction materials were brittle, difficult to weld, and had color matching issues, said McGinty. An inherently clean material, PVC-C is resistant to bacteria, reducing contamination opportunities. It is abrasion resistant and easy to clean, reducing particulate contamination created from internal tool components rubbing together. Tool-created contamination can compromise the wafer bath and enable corrosion or contamination of tool components from wafer-processing chemicals.

Flametec PVC-C is also ANSI FM-4910 compliant, passing the Factory Mutual test for fire propagation and smoke density. Contamination from smoke particulates and toxicity can damage chips and endanger workers in the fab.

To build its automated wet processing systems housings and tanks, MEI starts with 5 x 8 and 5 x 10 PVC-C sheets, using multiple CNC router tables up to 10 feet long to cut and shape them according to designs made in SolidWorks. MEI obtains its PVC-C raw material — tens of thousands of pounds per year — through a stocking program with Vycom’s distributors.

Figure 3. MEI’s flagship MEI Evolution fully automated wet processing system.

Thermoplastic welds must be strong and precise to prevent leaks and contamination in the fab tool. PVC welders complete an apprentice program at MEI to learn timing, technique, pressure, and angle skills. After a year of training, welders are qualified to build the wet plenum — the tank area below the tool where chemicals and water drain — the most sensitive wet bench tool component.

Figure 4. MEI Revolution rotary, semi-auto wet processing system. Photos courtesy of Garry Myers, MEI LLC.

MEI is a semiconductor process tool supplier. The company also develops process control equipment and automation software, and provides field service, repair, and retrofits on used equipment. Learn more at

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