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Resist Description

TI Spray is specifically designed to be used for spray coating, and is a positive UV photoresist with image reversal capability. It is considered to have good adhesion when wet etching.

Spray Coating

Soft Baking

Exposure

Image reversal

Typical image reversal parameters:

Reversal bake temperature: 110°C
Reversal bake time: 60-120 s
Flood exposure: 200-500 mJ/cm²

If TI Spray is baked after exposure, the exposed resist will cross-link, making it insoluble in the developer. This is called the "Reversal bake". The reversal bake activates cross-linking of the exposed areas, which "reverses" the polarity of the design.

If the substrate is flood exposed after the reversal bake, the previously unexposed areas become soluble, and will be removed in the subsequent development. The reversal procedure effectively makes TI Spray a negative resist.

The image reversal process greatly increases the sensitivity of TI Spray, and the dose of the image exposure is a critical parameter, especially if negative angled resist sidewalls are desired.
Half dose of the normal, positive process is a good starting point for optimization. Similarly, the reversal bake is also a critical step, and must be tightly controlled in order to achieve consistent results. If negative sidewalls are desired, 60-120s at 110°C is recommended (as well as a resist thickness above 2 µm), but if straight sidewalls are desired, 60-120s at 120°C can be used.

The flood exposure, on the other hand, is uncritical, and 2-5 times the normal positive process dose is generally used.

Development

Development speed:

Puddle development in 2.38% TMAH (AZ 726 MIF): ~2 µm/min