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Photoresist Coating

Photoresists are light sensitive materials used in photolithography to produce a patterned coating on a substrate.   Photoresists are widely used in the electronics industry including the fabrication of multi-layer high density interconnects for advanced packaging.  In the case of wafer-level and panel-level packaging photoresist is used to create the intra-layer horizontal connections.  The photoresist must be applied in a uniform layer at a specified thickness to ensure that these connections can be properly formed.  Traditionally, photoresists are applied to wafers by spin coating.  However, with the advent of the panel-level process, spin coating is not practicable for achieving a uniform coating on a large rectangular panel.  Additionally, these panels are often warped which poses serious challenges for application methods like slot-die coating.

 In order to demonstrate the efficacy of using tCAT to apply photoresist for the creation of high density interconnects a study comparing tCAT with spin coating was conducted.  In this study the USI Prism 800 system was used to produce 2 micron line/space pattern in a 7 micron thick layer of photoresist using a  300 mm diameter copper seeded silicon wafer as the test substrate.  

Spin Coated Wafer Thickness Uniformity

The photoresist layer thickness was measured across the surface of a 300 mm diameter wafer for the spin coating process.

Spin Coated Wafer Uniformity Data

A statistical analysis of the photoresist film thickness data for the spin coated wafer is shown above.

Spray Coated Wafer Thickness Uniformity

The photoresist layer thickness was measured across the surface of a 300 mm diameter wafer for the spray coating process.

Spray Coated Wafer Uniformity Data

A statistical analysis of the photoresist film thickness data for the spin coated wafer is shown above.

 

The photoresist thickness uniformity of the wafer coated with tCAT is significantly better than for the spin coated wafer.

The next step is to demonstrate that the imaging performance is not adversely impacted by the tCAT spray coating process.

Spin Coated Wafer Imaging Performance

A 2 micron line/space pattern is achieved in a 7 micron thick layer of photoresist applied with the spin coating process.  

Spray Coated Wafer Imaging Performance

A 2 micron line/space pattern is achieved in a 7 micron thick layer of photoresist applied with the tCAT spray coating process with no adverse impact on performance.

The same results have also been achieved on panel size substrates up to 650 mm x 650 mm.  Please contact us directly to receive a detailed technical presentation and paper on this promising new process.

Contact us to discuss your coating process requirements.

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