What is SU-8 Photolithography?

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What is SU-8 Photolithography?

If you're curious about SU-8 Photolithography, you've come to the right place. Learn about SU-8 negative photolithography wavelengthphotoresist, UV exposure, and T-topping. In this article, we'll look at SU-8's pros and cons. We'll also take a look at some of the common mistakes people make when using this photoresist. Read on to learn how to avoid them.

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SU-8 photoresist is soluble chemical-amplification photoresist with negative emission, manufactured for photo coatings and microelectronics. It's great for low-volume printing and production. And works well for making dense structures. Below are some important industry terms:

  • photo coatings
  • amplification photoresist 
  • epoxy photoresist 
  • photoresist layers 
  • photolithographic process
  • acrylic filters 
  • exposure wavelength 
  • microelectromechanical systems 
  • uv exposure #exposure light 
  • wafer cleaning 
  • uv light 
  • microfluidic applications 
  • photosensitive chemical
  • lithography precision 


Fabricating Microstructures with SU-8 Photolithography

SU-8 Photolithography uses an epoxy-based negative photoresist that allows fabrication of microstructures with high resolution and aspect ratios. It has many applications in the microelectronics industry and has been a staple material in the field of miniaturization. SU-8's properties include high chemical and thermal resistance, excellent mechanical properties, and low UV permeability. Poly(methyl methacrylate) and polyetheretherketone are both common SU-8 materials, but PEEK displays better solvent resistance and increased operating temperature.

SU-8 is very biocompatible. Neuroscientists using it to culture biological cells use it as a passivation layer on measurement electrodes. As a result, SU-8 Photolithography is an excellent choice for microfluidic devices. Marc Heuschkel, a researcher at EPFL, explains, "This material is a good choice for many applications, including microfluidics."

The transmission properties of SU-8 photoresist make it a good candidate for self-limiting exposure and polymerization depth. This allows the creation of novel microarchitectures. Examples of these structures include hollow polymers and SU-8 Photolithography. These measurements are made using the Beer-Lambert principle. For each individual photoresist layer, the SU-8 coating is exposed to UV light to produce a pattern on the surface of the substrate.

The SU-8 photoresist is very sensitive to ultraviolet light. It can't be exposed to g-line ultraviolet light. When exposed, the photoresist's long molecular chains crosslink. The SU-8 photoresists are produced using cyclopentanone or gamma-butyrolactone as the primary solvent. If the photoresist is a little too sensitive for g-line exposure, the wavelength of the PEB must be reduced to prevent it from causing cracks.

SU-8 negative photoresist

SU-8 negative photoresist is a common choice in photolithography. It was originally developed for the microelectronics industry and provides high-resolution masks for semiconductor devices. SU-8 requires careful temperature control during the baking steps. The longer the baking time, the thicker the layer of SU-8 will be. This process helps to reduce stress formation in the thick layers, which can cause cracks.

SU-8 is an epoxy-based negative photoresist from MicroChem. It is a strong, cross-linked polymer with reversible residual epoxy groups on the surface. The photopolymerized resist also contains several functionalized molecules, including a polymer molecule, and is ideal for multistep solid-phase synthesis. This material is a versatile photolithography material, allowing for precise micro and nanoscale patterns.

The SU-8 negative photoresist is an epoxy-based material with a unique cross-linking mechanism. It is made from eight epoxy groups per moiety, and exhibits excellent resistance to light. This material is widely available and suitable for various industries. There are many applications for SU-8. A few of these include semiconductor manufacturing, 3D printing, and other processes. In the case of semiconductor manufacturing, this resin is a popular choice.

To create a high-resolution film, SU-8 photoresist must be exposed to ultraviolet light at 365 nm. Its long molecular chains crosslink when exposed to high-dose ultraviolet light. A primary solvent for SU-8 negative photoresist is gamma-butyrolactone. Alternatively, pure Hydrogen is used as the precursor.

UV exposure

SU-8 Photolithography is an excellent method for etching microfluidic components. To achieve high-quality results, it's important to understand UV exposure to SU-8 in photolithography. The dielectric function of SU-8 is determined from its reflectance spectra. Using an extended Lorentz model, the dielectric function of SU-8 is calculated from the reflectance spectra of samples.

The optimum SU-8 exposure doses are presented in tabular and graphical formats based on the SU-8 thickness, surface reflectivity, and type of wafer or coating. The absorption band near 3 mm exhibits a sharp increase upon UV exposure. It suggests that SU-8 has an increased number of hydroxyl groups. The absorption band near ten and fifteen mm corresponds to aromatic C-H bends.

The SU-8 chemical removal and photolithographic pattern definition are dependent on the correct ultraviolet light exposure. Gaudet et al. determined that a critical exposure dose of 49.4 mJ cm-2 is necessary for SU-8 polymerization. This dose must be adjusted for thickness, as the SU-8 absorbs light at 38 cm-1 at 365 nm, increasing to 49 cm-1 at higher exposure levels. For this experiment, a hundred-u-hole photomask was used to expose the SU-8 array under twenty-five J of UV light.

The SU-8 photoresist is composed of a polymer based on silica. Its physical properties are similar to those of silicon. The SU-8 photoresist has good mechanical and electromagnetic properties. It has been shown to have larger aspect ratios than 1:50, although this may pose a problem of repeatability. In addition, SU8 photolithography can produce gray tones, enabling a high aspect ratio.


SU-8 photolithography is an excellent tool for fabrication of Fresnel zone plate arrays. MPL has used SU-8 for Fresnel zone plate arrays, and this technique has excellent parallelization capabilities. In addition to SU-8's photo-response, SU-8 also exhibits a high crosslinking density and has a low temperature change.

To fabricate spatially variant photonic crystals, MPL in SU-8 is used. The spatially varying photonic crystals (SVPCs) are shown in yellow. The blue ribbons show the relative intensity exiting the SVPC faces and represent light introduced by optic fiber. The intensity of a SU-8 structure is measured by using vertically and horizontally polarized light. The intensity measurements are compared to simulations of beam bending.

The process is very effective and produces thin-film layers that are difficult to remove. The process of IP-L diffusion is an important consideration for SU-8 photolithography. The process of photolithography is a critical step in manufacturing a specialized device. In this process, IP-L resin diffuses into the SU-8 layer, thereby forming a diffusion barrier. However, the polymerized "skin" on the SU-8 layer makes the removal of the mask more difficult, so ultrasonication is required to remove the mask.

This technique is effective for making layered optical structures and can be used to fabricate complex objects. The SU-8 material has a high refractive index, and the maximum aspect ratio is limited by the photolithography equipment. The SU-8 process uses a narrow band of UV with a peak at 405 nm, making it a perfect material for T-topping. This method requires a specialized UV exposure machine and UV lamp.

Glass transition temperature

SU-8 is a negative type photoresist. It is fabricated by a single spin-coating process. During exposure, the film undergoes a cross-linking process. The film undergoes a glass transition temperature (GTT) of 230degC. This value correlates to the exposure depth. The film undergoes a significant amount of shrinkage when the first glass mask is exposed at UV1 for ten seconds. Once exposed, the film undergoes a rapid transformation, resulting in a negative area with a cross-linked exposed area. The film is completely soluble at temperatures above 230degC. However, once processed, the film undergoes a rapid change in temperature.

The SU-8 process has a wide range of exposure energies. The exposure energy should be optimized for small patterns. The lower exposure energy of 20 mJ/cm2 has been used in conventional research. However, Esch et al. report that it is necessary to use a thickness of 0.5 to 2.5 mm to hold the structure. The higher the exposure energy, the less precise the pattern can be.

One important thing to keep in mind is that a high dose increases the surface temperature. It is therefore important to maintain this temperature during the SU-8 application to avoid the formation of a thin solid crust. In addition, a slow spin rpm is needed for high aspect ratio features. A stir rod is needed to suspend the wafer in the developer. A stir rod is also helpful in clearing out deep vias and trenches.

Effects of exposure time

This study aimed to investigate the effect of exposure time on the crosslinking behavior of SU-8. To determine the effects of exposure time on SU-8 photolithography, we fabricated multiple samples with varying thicknesses. The i-line intensity was most attenuated near the 1-mm thickness, whereas the h-line was only 65% attenuated. This research highlights the importance of exposure time for SU-8 lithography.

Optimal exposure time is critical for the definition of SU-8 patterns and the chemical removal of SU-8. Gaudet et al. have determined the critical exposure dose for polymerization to be 49.4 mJ cm-2, although this value needs to be adjusted for surface reflectivity. The absorption coefficient at 365 nm is 38 cm-1, but increases to 49 cm-1 after high exposures. For the purpose of this article, the authors assumed that SU-8 exposure time should be 43 cm-1, which is the average of exposure times.

To reduce the shrinkage of SU-8, it is possible to increase the exposure time. In this case, the mask's design should be optimized to reduce shrinkage. In the event that the mask is adapted to reduce shrinkage, the shrinkage problem will disappear. Another important factor affecting stress is the PEB temperature. The PEB temperature of 55 degrees Celsius may reduce shrinkage, but a lower exposure time will increase adhesion.

Video: SU-8 Photolithography Explained