Photoresist

Thickness of SU-8 Photoresist

One of the challenges in the development and manufacture of MEMS and other devices is the measurement of the thickness of SU-8 and other thick photoresists. Though simple and quick, spin coating SU-8 can be an inaccurate method for yielding a desired thickness. Since exposure time is dependent on resist thickness, an accurate measurement must be taken. Moreover, since positive and negative photoresists can be used in conjunction to create complex multilayer structures, knowing the thicknesses of each layer becomes extremely important.

The Filmetrics Advantage

Filmetrics offers a wide range of solutions for measuring the thickness of SU-8 and other photoresists. The F20 family can measure both freestanding and multilayer films, and can measure SU-8 thicknesses from less than 0.1 to 100s of microns. All F20 models measure thickness (and even index) by accurately modeling spectral reflectance. Special propriety algorithms allow robust “one-click” analysis, with results typically available in less than a second. Whether you are involved in basic research or manufacturing of MEMS, Filmetrics can deliver the capabilities that you need.

Measure Thickness of SU-8

♦   Single Layers and Multilayers


Measure Thickness and Index of Process Films

♦   SiO2, Si3N4 – virtually all dielectrics

♦   Other positive and negative photoresists

♦   Parylene and other encapsulating films

How it Works

Filmetrics’ tools are based upon spectral reflectance where light is reflected off the sample and then analyzed over a range of wavelengths. Light reflected from the top and bottom interfaces of the film can be in-phase so that reflections add, or out-of-phase so reflections subtract. The result is characteristic intensity oscillations in the reflectance spectrum. Simply put, the thicker the film, the more oscillations that will be present in the reflectance spectrum.

Fig 1: The main F20-XT screen, showing the meaurement of an SU-8 layer of 69 µm nominal thickness on silicon.

Fig 1: The main F20-XT screen, showing the meaurement of an SU-8 layer of 69 µm nominal thickness on silicon.