Semiconductor wet processing equipment is absolutely necessary for the manufacturing of semiconductor components. The slightest error, contamination, or poor process control during fabrication can result in semiconductor devices that perform unreliably or even fail during normal use. Wet process equipment is used by manufacturers to work on a sensitive Silicon wafer during production whilst ensuring it remains contaminant free and all processes are carefully controlled. Find out what the wet process steps are, the equipment used, and their various functions.
What Is The Semiconductor Wet Process?
Semiconductor manufacturing involves many complex processes that will eventually produce the tiny integrated circuits or microchips that make most modern appliances run. It starts at the fabrication plant where cylindrical blocks of crystalline silicon called ‘ingots’ are artificially grown. These ingots are then sliced into thin disk-shaped layers that we call ‘semiconductor wafers’. Each semiconductor wafer is about 160-300 μm in thickness.
Next is the wet processing stage which is also called ‘wafer processing’. In wet processing, photoresist materials are deposited on the wafer surface based on the circuit layout needed for the final product. Afterward, the wafers are either submerged or exposed to liquids or vapors that will etch the exposed parts of the wafer that is not covered by photoresist. This etching process is followed by wafer cleaning to remove the photoresist as well as any contaminants that may have been introduced.
These wet process steps are conducted in carefully controlled environments called ‘semiconductor cleanrooms’ to avoid the risk of contamination from particles like dust. To learn more, read What Is a Semiconductor Clean Room and What Is It For?
Finally, the wafer is inspected carefully for any manufacturing defects, through highly sophisticated semiconductor imaging techniques before sending it to the next stage of production. While the wet processing steps like etching and cleaning of semiconductors are a small part of the manufacturing process, they are nevertheless extremely important. This is because wet wafer processing is how the entire industry can ensure the manufacture of semiconductor wafers to an exact specification. The performance, reliability, and device lifetime of semiconductor equipment depends on it.
What Are Semiconductor Wet Process Equipment?
Wet wafer processing requires specialized equipment called ‘wet benches’ or wet processing equipment. They are also known as ‘wet chemistry benches’ since these wet process equipment are meant to handle various chemicals that will deposit, mask, etch, clean, wash, and dry the wafers as required at different stages of fabrication.
Wet process equipment is often modular in nature, offering a variety of functions. These modular equipment have multiple tanks called ‘baths’. They contain either cleaning or etching solutions. Deionized water is kept in separate rinse tanks. In addition to all of these,
temperature controllers, spray guns, circulators, dryers, and other modules used for process control may also be present in wet process equipment.
The Design Of Modular Wet Process Equipment
Wet processing equipment has to be designed to handle chemicals like Sodium Hydroxide and Nitric Acid. Polypropylene is the design material when acids or bases are handled, while stainless steel is used for solvents. Modular design means that manufacturing companies can select and customize which capabilities they require for their processes.
A cleaning station is made from Polypropylene and comes equipped with sinks, Nitrogen spray guns, faucets, and deionized water. The surface of the cleaning station is perforated to allow any chemical spill to run off and be collected safely for disposal. On every wet process station, there are overhead lighting and filter units called ‘fume scrubbers’ to remove dangerous exhaust fumes.
Solvent Spray Module
The solvent spray modules are made from stainless steel to handle chemicals that are corrosive or even flammable. Fire sprinklers can also be equipped with lighting systems that are designed to be resistant to explosions. Solvents are used for rinsing while Nitrogen is used for drying the wafer. There are specially-made valves, faucets, and sinks to deliver and drain chemicals as required.
Chemical Delivery And Waste Disposal
Wet processing equipment is connected to chemical delivery systems and pneumatic foot pedals are used by the engineers to precisely control the pressure, flow, and delivery of the chemicals. The chemicals that run off into the draining can be directed toward special waste disposal systems to be safely collected, neutralized, and disposed of.
Types of Semiconductor Wet Process Equipment
Wafers are normally loaded in batches or lots of 25 at a time for processing. The sequence of wet wafer processing can be pre-programmed into the equipment. The industry utilizes manual, semi-automated, and innovative fully-automated systems that rely on intelligent technologies.
Manual Wet Benches
At these wet benches, a human operator is required to handle the wafers at each step. They do not include the sophisticated robotics used in more expensive models. Apart from their relatively low cost, they are perfect for the production of prototypes.
Semi-Auto Wet Benches
The semi-automated models have servo-based robotics for precise motion-controlled handling of the wafers. They can be programmed and monitored using a touchscreen interface. Semi-auto models also offer data logging. Process uniformity is guaranteed, providing high throughput and better efficiency. These models are more expensive than manual wet benches.
Fully-Auto Wet Benches
The fully automated stations provide the best process yields in the industry by further reducing the human element from the equation. Process times are reduced and chemical dosage is more carefully calculated by the onboard computer using chemical analyzers. This reduces the chance of error at all stages of wet processing, ensuring a consistent level of quality.
Naturally, fully-auto wet benches are very expensive and can also come with advanced simulation software that allows users to further improve their etch rates and throughput without compromising on quality.
Standards For Semiconductor Wet Process Equipment
All semiconductor manufacturing equipment has to be designed according to the safety and ergonomic guidelines laid out in the Semiconductor Equipment and Materials International (SEMI) S8-0712 standard. Furthermore, there are additional standards like UL508a for industrial control panels, NFPA 70/NEC for fire/electrical protection, and NFPA 79 for safety involving industrial-grade machinery. Customers looking to purchase wet process equipment should pay attention to these standards and ensure the equipment they purchase are fully compliant.
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Wet processing is the phase in semiconductor production where Silicon wafers are exposed to chemicals for depositing, etching, cleaning, rinsing, and various other processes.
Wet benches are the workstations where Silicon wafers are handled during the wet processing stage.
Wet benches can be manually operated by an engineer, semi-auto with robotic servo-controlled handling systems overseen by an engineer, or fully-auto systems that monitor and precisely control chemical dosage without requiring a human operator.