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The Photoresist Coat Process

For decades, the process of spin coating has been used to apply a resist film over a silicon wafer as a part of the broader process of microcircuit fabrication necessary to produce high yielding silicon wafers. 

A typical spin coating process involves depositing a small quantity of liquid polymer at the center of a substrate while rotating at a relatively low speed, then spinning the substrate at high speed (~3000 rpm). Centripetal acceleration will cause the polymer to spread to the edge and eventually fall off, leaving a thin film of polymer on the surface. Final film thickness and other properties will depend on the nature of the polymer (viscosity, drying rate, surface tension, etc.) and the parameters chosen for the spin process.

There are several major factors affecting the coating process:

  • Spin Speed
  • Acceleration
  • Spin Time
  • Exhaust

The careful control of the wafer’s spin speed and acceleration during coating, the precise application and positioning of resist, and the controlled ambient and exhaust conditions all contribute S-Cubed’s ability to coat wafers quickly and with great uniformity and minimal waste. 

Coating Uniformity

Because of the precise and careful control of spin and acceleration in S-Cubed Coat and Develop tools, coating uniformity is consistently optimal.

When using our Flexi or Scene tools, coating uniformity varies by less than .5% (BCB).

The Photoresist
Develop Process

The develop process will be either aqueous based or solvent based, depending on the photoresist polymer chemistry. As the aqueous develop is essentially an etch, it is important that corrosion rather than erosion occurs so that develop “hot spots” can be avoided. Hot spots will very adversely affect develop uniformity. A “zero impact” dispense nozzle rapidly builds a puddle without creating hot spots, followed by agitation of the wafer itself. Agitation during a puddle develop step provides the refreshment of reactant at the photoresist/developer boundary layer, which leads to shorter develop time, less consumption of resources, and better uniformity.

For solvent based develop in which a gel like material is created, a needle like programmable stream provides the desired removal while maintaining control of the fluid.

For more information on our Semiconductor Photoresist Coater/Developer processors, call the S-Cubed engineering team today.

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