Soft lithography

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Soft lithography
Softlitho web.jpeg
Technology Details
Technology Lithography
Equipment List of soft lithography equipment
Solvent Bench 94
Materials SU-8, PDMS

Soft lithography refers to a technique used to create micro devices or three dimensional structures by means of molding and embossing an elastomer on a mold. The most common devices fabricated with this technique are microfluidics which are widely used in cell biology. The most common elastomer used in this technique is PDMS (polydimethylsiloxane) a soft bio-compatible elastomer that has high thermal stability, high chemical stability, low toxicity, chemically inert, insulating, is transparent to UV and visible light, low cost, easy to mold and mechanically flexible and durable. This is why the term “soft” is used. The molds used can me fabricated out of silicon, photoresist (most commonly used is SU-8), or a metal mold. Soft lithography is also well suited for polymers, gels, and organic monolayers. Soft lithography is widely use because it is an easy, reliable, and low cost process to replicate three dimensional structures (ranging from cm to microns).


Soft Lithography suite includes:
Spinner CEE Apogee ROBIN
Solvent Bench 94
SU-8 lithography
Glen 1000P Plasma Cleaner

Mold fabrication

The first step in the soft lithography process is the fabrication of the mold which will be be replicated. The most commonly used material is a photo-patternable epoxy commonly known as SU-8, this photoresist comes in a wide variety of viscosities, producing a wide variety of film thicknesses from less than a micron up to hundreds microns. SU-8 molds are fabricated with standard lithography methods. See SU-8 lithography for details. It is also common to use molds fabricated in Silicon using standard fabrication techniques: patterning and etching. PDMS can also be used as a mold material.

Release agent coating

It is necessary to apply an agent or chemical to lower the surface energy of the mold to in order to facilitate the removal of the elastomer from the mold after cured. This is essential to extend the life of the mold. Especially necessary in the case of fine features. Please see the [SOP for the application of the release agent] for more details on this process.

PDMS processing

PDMS is fabricated by mixing two compounds in the Sylgard 184 kit, the polymeric base and the curing agent in a 10:1 ratio respectively. It can be used to replicate features as small as a micron. Consult Solvent Bench 94/Processes for detailed instrctions.


Soft lithography is widely used to fabricate easily replicated, low cost devices. The main use is in the fabrication of micro-fluidics for biological applications. Usually the molds are attached and assembled on microscope glass slides, and placed under a microscope objective for examination.



The most commonly used materials used as molds are SU-8 photoresist and PDMS. SU-8 is a commonly used epoxy-based negative photoresist. As a negative photoresist, the parts exposed to UV become cross-linked, while the remainder of the film remains soluble and can be washed away during development. The SU-8 polymer derives its name from the presence of 8 epoxy groups.

The epoxy groups make SU-8 molds durable and resistant, once cured they can be re-used many times.


Polydimethylsiloxane belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones, the chemical structure can be represented as

For more details go to the PDMS page


(Tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-Trichlorosilane is chlorosilane that is used to create a fluorinated monolayer on molds for PDMS to enable easy release of the PDMS from the mold. The chlorosilane groups are highly reactive and can bind the molecule to a wide variety of materials, including polymers and metals. The chlorosilane also readily reacts with moisture to form hydrochloric acid and should be handled in a fume hood.

See also

  • SU-8 Photoresist Processing [1][PDMS]]


[1] [2]

  1. Smart Mater. Struct. 15 (2006) S112–S116
  2. Annu. Rev. Mater. Sci. 1998. 28:153–84

Further reading