Technology Overview

Spin coating of photoresist allows a uniform layer to be distributed on a substrate in a short amount of time, while using a small amount of liquid photoresist.

While spin coating is relatively straight forward, be aware of the following:

• Coating uniformity degrades for non-rotationally symmetric substrates (i.e. squares and rectangles)
• Evaporation forms an 'edge bead' at the substrate edges; This is more substantial for longer spin times, thicker photoresist, and less circular substrates
• Coverage of textured/patterned surface depends on the thickness of photoresist
• Photoresist adhesion will depend on the surface state of the substrate

Example of a multidispense spin (via Specialy Coating Systems):

Spinning may either proceed directly to the target RPM, or via multiple steps to more gently distribute resist. In general, thin resist layers (e.g. 2 μm of AZ1518) on a properly prepared substrate surface (e.g. BOE cleaned silicon) spin best without a low RPM dispersal step, while thicker films (e.g. 10 μm of AZ9260) on non-ideal surfaces (e.g. Piranha cleaned glass) may benefit from a dispersal step.

An example of a multistep coating cycle is seen below. Note that typically only a single low RPM dispersal step is used.

Representative Coating Cycle

Process Library

For in-depth information about photoresist properties and spin recipes, see BNC Supplied Photoresists.

Typical Recipe:
Step 0:   Values should be set to 0 or "None". Disp should be rounded up to the nearest chuck size, and Disp Time may be set to a nonzero value to avoid the "Homing" step after spinning.
Step 1:   Timed ramp and dwell at process rpm.
Step 2:   Timed ramp down to zero rpm / unload

AZ1518

Standard Spin, AZ1518, no dispersal steps

Standard Spin, AZ1518, initial dispersal spin

References

MicroChemicals: Spin Coating of Photoresist