What is SU-8 Lithography?

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Silicon Wafers Used for SU-8 Lithography

A scientist from a European University asked for the following quote for silicon wafers:

Can you send me a quote for silicon wafer suitable for
SU-8 lithography. I want totally 50 wafers. I want 4" wafer suitable for SU-8 lithography. Also, I may want a few 6" wafer for AZ positive photoresist lithography.

UniversityWafer, Inc. Quoted:

4" wafer suitable for SU-8 lithography SSP Exw price $Contact Us

 6" wafer SSP $Contact us

Please reference #268687 for specs/pricing.

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These are Key Research Terms Used in SU-8 Lithography

  • microelectromechanical systems (MEMS)
  • microfluidics manufacturing 
  • microfluidic applications
  • microelectronics applications
  • uv light    
  • microfluidic chips    
  • photoresist film    
  • photosensitive chemical    
  • microfluidic features    
  • microelectronics industry    
  • wafer mold    
  • thermal organic    
  • photography equipment   
  • film thickness 
  • cured structures    



What is SU-8 Lithography?

SU-8 is an epoxy-based negative photoresist that contains portions that are crosslinked and portions that are soluble. This is a good mix of acidity and cationicity, and SU-8 is called such for its characteristic chemistry. To get the best results, SU-8 materials should be stored in a dark box. The dark box helps the materials dry properly and prevent them from becoming sticky or brittle. It takes around 3 days for SU-8 to cross-link completely, though the final time can vary from batch to batch.

SU-8 lithography

SU-8 lithography involves writing multiple layers of information on a thin film. The writing process is carried out with interacting reflected beams, which result in the formation of polymer microstructures at the different layers. The photoresist's thermal expansion coefficient and solvent content will determine the ultimate microstructure. Superfine, free-standing tall structures are typically collapsed due to the high vapour pressure of the developer. High vapour pressure will also cause cracking.

SU-8 film has a high crosslink density and glass transition temperature of 230degC. As a result, the film does not change much after processing. Maximum shrinkage occurs before 270degC, while 5% of the film's thickness is reached at 364degC. The highest temperature required for SU-8 film chars at 900degC. The temperature of the SU-8 film is controlled to reduce the amount of stress and cracking in the SU-8 layer.

Before removing the SU-8 photoresist, the wafer should be cleaned. Acetone or piranha solution can be used to clean the surface. Wafers must be heated to remove any moisture from the surface. The recommended time is 15 minutes at 120degC. This helps the SU-8 to stick to the surface better. The development time of SU-8 lithography is based on the thickness of the layer.

The SU-8 thin-film has a nSU-8 value of 1.66 and mm units. The maximum intensity occurs at the silicon-SU-8 interface. Multiple reflection is also possible and allows for the creation of pyramidal microstructures in the silicon-photoresist interface. As a result, SU-8 is an excellent choice for microlithography. So, what do you need to know about SU-8?

SU-8 has been used in various applications for 15 years. Most commonly, it is used to fabricate micro and sub-micron structures. Because of its high aspect ratio and low glass transition temperature, it is often preferred over other photoresists. Despite the difficulties that SU-8 faces, the technique can produce micro and sub-micron structures in silicon-free glass. There are some advantages to PMMA lithography, and this method has many applications.

SU-8 is an epoxy-based negative photoresist that has portions that crosslink and parts that are soluble. The cationic and acid nature of SU-8 contributes to its name. SU-8 photoresist is best stored in a dark box to avoid brittleness and sticky materials. The final cross-linkage time varies based on the batch. The process can take up to three months for a single image.

SU-8 microtowers were coated with copper at 30 um thickness. Copper is typically used for electroplating, so the resulting image may appear larger than 30 um. The 100-turn toroidal inductors were coated with the copper layer. This process yields a high aspect ratio and benefits microdevice performance. The SU-8 mold is also used for the fabrication of the bottom, vertical, and top windings.

SU-8 photoresist

SU-8 is one of the most commonly used photoresists for lithography. It is a grayscale photoresist with a maximum elevation of 0.5 mm. It is typically fabricated in two steps, with low speed and low acceleration used to spread the photoresist over the wafer. During the exposure, the photomask makes contact with the bugle, which results in decreased resolution. It is important to note that the size of the bugle is dependent on the viscosity of the photoresist. For example, if you use 100um SU-8, you'll probably end up with a bugle several micrometers wide.

SU-8 photoresist for sputtering is another common technique for lithography. After spin-coating, the SU-8 photoresist is exposed to UV radiation. This UV exposure will produce a pattern that is roughly two microns in size, with a peak thickness of about three microns. However, some researchers prefer to use mechanical grade wafers for photolithography.

The material adhesion of SU-8 is generally satisfactory. It varies with the type of substrate. Gold, for example, shows poor adhesion while silicon nitride and silicon with native oxide are good. It also depends on the chemical. HF or KOH helps lift off the photoresist, while immersion in water makes it stick. This issue is also related to substrate cleanliness. However, MCC claims that the new SU-8 2000 series has improved adhesion due to a change in the solvent.

The UV exposure of SU-8 photoresist causes variation in transparency during the photoexposure process. The UV exposure of the film produces a photoacid, which acts as a catalyst that causes crosslinking when the film is heated. The post-exposure bake process also causes partial crosslinking of SU-8. This effect can occur with long UV exposure or with heat accumulation during the UV exposure.

In order to prevent cracks in SU-8 photoresists, the exposure time should be as low as possible. The time between exposure and developing depends on the thickness of the sample and the SU-8 layer. Increasing the exposure time increases the risk of cracks. To avoid this, you should keep the exposure time low and increase the exposure dose. Then, rinse the sample with isopropyl alcohol. Finally, the SU-8 pillar is ready to be used.

SU-8 photoresist is a negative epoxy-based photoresist with eight epoxy groups in a single molecule. SU-8 resists light well and is suitable for wide-ranging industrial processes. The film can be cut and pasted onto metal surfaces. It is highly versatile and is widely available. It is also biocompatible. Once it has been cured, the surface is a slick, shiny object.

SU-8 is often used in combination with HMDS. Before using this photoresist, you should first clean your wafer with a cleaning solution. In a clean room, piranha solution is recommended. If your work space isn't clean, you can try using acetone instead. After cleaning, you'll need to heat the wafer for a few minutes at 120degC. This will remove any moisture on the surface and make the SU-8 adhere to the surface better.

SU-8 lithography protocol

The SU-8 photoresist is a negative-tone negative-nuclear material that has proven popular in multiple-photon interference lithography. This technique has enabled the fabrication of deep sub-microns and periodic structures. Recent advances in the SU-8 lithography protocol have led to unprecedented capabilities for creating a variety of unique microstructures. The following paragraphs will discuss the basic steps required for SU-8 lithography.

The process utilizes a negative photoresist that has a 365-nm peak wavelength. It is exposed to a UV light source that contains the SU-8 photoresist. The UV exposure time depends on the thickness of the layer and the power of the lamp. The SU-8 lithography protocol requires a photomask to reduce the amount of UV reflection. However, it has several advantages.

To develop the SU-8 image, the wafer should be cleaned. For clean rooms, this can be done with piranha solution. However, if a non-clean room is involved, acetone can be used. The wafer should be heated for a short period of time to remove any excess moisture. The recommended heating time is 15 minutes at 120degC. This will ensure a greater adhesion between the SU-8 and the wafer.

After preparing the SU8 film, it is exposed. The exposure time depends on the thickness of the film. After the exposure, the film is baked again to complete the polymerization. The baking time is slow and controlled. The SU-8 layer is now ready for development using 1-methoxy-2-propanol acetate. The SU-8 layer is then exposed to a UV radiation between 350 and 400 nm.

The SU-8 polymerization process begins after the photoactivation of the photoacid generator, post-exposure baking, and photoacid exposure. SU-8 polymerization is a cationic chain growth mediated by ring-open polymerization of epoxide groups. A variety of different mesh thicknesses can be obtained for different applications. The SU-8 spin speed calculator can help determine the optimal RPM for the appropriate thickness.

Following the exposure phase, SU-8 layers must be heated again. The SU-8 post-exposure baking (PEB) protocol is almost identical to that of the soft-baking step. However, the temperatures and baking time are different. In addition, the cross linking process of SU-8 generates considerable residual stress, which is a major source of cracks. Therefore, it is imperative to avoid rapid cooling of the SU-8 layer after the PEB at 95 degrees Celsius.

In addition to this, SU-8 photoresists must be prepared for a non-uniform process. Generally, SU-8 samples should be completely cross-linked before processing. However, the SU-8 photoresist must be exposed to sulfuric acid for only a short time before the exposure time is reached. Because the SU-8 photoresist reacts with sulfuric acid, it must be exposed under very short time intervals in order to minimize the risk of forming dendrites.

Video: Learn about SU-8 Lithography