What is Soft Lithography?

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Soft Lithography

In the last decade, soft lithography has been developed as a method for the chemical production of micro- and nanostructured surfaces. Over the years, it has become a popular method, with many research groups producing high-resolution, high-quality, and cost-effective parts. In fact, mass production costs for these parts are significantly lower than for photolithography. Various advantages make it very attractive, one of which is noticed by researchers who want to access this cheap lithography. In order to achieve a reasonable resolution, for example, no cleanroom equipment is required, although special devices are still required. [Sources: 4, 7, 10]

PDMS has one of the most serious technical problems that can be solved by using soft lithography to form complex patterned structures (Figure 6). [Sources: 13]

The first step in soft lithography is to create a mould that replicates the shape of the patterned structure using standard manufacturing techniques such as pattern etching. It is also common to produce the mould using a standard etching technique and it is common to produce this mould with the most commonly used PET-based soft mould to balance the rigidity of hard moulds and prevent deformation during the process. [Sources: 5, 8]

However, there are a number of existing and emerging applications of soft lithography in manufacturing that utilize and require the properties of this technique. One of these techniques is Soft Interference Lithographic (SIL), which is used in a new and interesting way to draw patterns [5]. [Sources: 6, 10]

The material has a flat, rough surface that it profiles when used with soft lithography and is therefore deformable, but it is limited because the design of stamps and shapes must take into account non-planar surfaces. To obtain precise micropatterns (nanopatterns) on both planar and non-planar surfaces, the structure must be patterned [5]. Conventional embossing 56 requires the use of a large number of layers as required for the structure of the patterns [7]. [Sources: 0, 5, 6, 10]

Soft lithography thus offers the possibility of forming certain types of test patterns [6, 7]. Similar to lithography printing, it is also very cheap and allows to model a very large area in a short time [8]. In particular, the fusion of self-assembly techniques with the use of high-quality, cost-effective and high-quality materials will enable more innovative developments than any other [9]. [Sources: 3, 6, 13]

A key element of soft lithography is the use of high-quality, cost-effective materials such as silicon and metals. The stamps used to define the patterns can be made from hard materials such as silicon or metals, using only a small amount of high quality and low cost materials. If low costs are required, it can also represent curved substrates [8, 9] or flat surfaces [10]. [Sources: 0, 6]

The most commonly used material is photographic art printing - patterned epoxy, commonly known as SU-8, a material commonly used in micro-contact printing, but difficult to produce due to its high cost. Its main purpose is to create a polymer that moves more easily than it can and is used for soft molded parts. Photoresists are available in two types, which are made of BPAPC or PDMS block copolymers or polymers of the same chemical composition as the polymer. The resulting BPapC and PD MSM blocks or copolems differ in their properties depending on length and load. When the chain moves from a rigid vitreous state and begins to move into a soft, flexible state, it moves from a rigid state to a flexible state, which it then moves back and forth. [Sources: 1, 5, 8, 12]

The 184 PDMS can extend the possibilities of soft lithography to the 50 - 100 nm regime44. A composite die consists of a flexible layer supported by a rigid layer and a thin layer of polymers with the same chemical composition as the polymer. [Sources: 6]

One of the reasons soft lithography can produce high quality patterns and structures is that it has many excellent properties of PDMS. In contrast to conventional nanoimprint moulds, a mould suitable for electrochemical nanoIMprint lithography requires good conductivity. The PD MSM shape can be used to temperature a wide range of materials such as ceramics, polymers and other materials due to the low modulus and low surface energy of PDMS, resulting in compliant contact and easy release. [Sources: 2, 11, 13]

PDMS can also be used as a stamping resin, making it one of the most common materials for the flow conveyance of microfluidic chips. It is essentially a soft form of PDMS, which is coated with a chemical solution, the ink, during the printing process and then brought into physical contact with the substrate after the ink has dried. [Sources: 1, 4]

When optimizing technical issues, it is also possible to extend the concept to cell replication, for example by using nanoelectrode shapes, for which conductive silicon etching processes are also used. Methods of casting and hardening are often used together with soft lithography to create patterns on silicon substrates. UCP catalytic demonstration to demonstrate double-layer patterns of silicon refined with h-EB lithography and to prepare a PDMS membrane for microfluidic chips. Frequently used soft lithographic techniques are microform capillaries, solvent-assisted micronolding or the application of a chemical solution to the surface of the substrate. [Sources: 4, 5, 9, 12]

 

 

Sources:

[0]: https://www.intechopen.com/books/micro-nanolithography-a-heuristic-aspect-on-the-enduring-technology/micro-nano-patterning-on-polymers-using-soft-lithography-technique

[1]: https://csantander.com/hjr1/pdms-tg.html

[2]: https://www.hindawi.com/journals/ijps/2018/6365096/

[3]: http://lafsi.fisica.unipd.it/soft-lithography.html

[4]: http://www.nanolithography.org/2018/07/18/soft-lithography/

[5]: https://www.universitywafer.com/silicon-soft-lithography.html

[6]: https://www.nature.com/articles/nprot.2009.234

[7]: https://www.fz-juelich.de/ibi/ibi-3/EN/Research-old/04-MolecularBioelectronics/03-4-SoftLithography/_artikel.html

[8]: http://lnf-wiki.eecs.umich.edu/wiki/Soft_lithography

[9]: https://jnanobiotechnology.biomedcentral.com/articles/10.1186/s12951-014-0060-6

[10]: http://soft-matter.seas.harvard.edu/index.php/Soft-lithography

[11]: https://www.sciencedirect.com/topics/engineering/soft-lithography

[12]: http://screens.aviator.eu/nvotej6/pdms-yield-strength.html

[13]: https://www.intechopen.com/books/lithography/application-of-soft-lithography-for-nano-functional-devices