Soft lithography

From LNF Wiki
Jump to navigation Jump to search
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 mode. 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).

Equipment

Soft Lithography suite includes:
Solvent Bench 94
MJB 45S
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 the use of molds fabricated in Silicon using standard fabrication techniques: patterning and etching.

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.

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. Consult Solvent Bench 94/Processes for detailed instrctions

Applications

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.

Materials

SU-8

Optional description of materials that can be processed by technology. I thinknk the best example of where this comes in handy would be with LPCVD describing the difference between HTO and LTO.

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

PDMS

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

See also

Slides from Workshop??
  • SU-8 Photoresist Processing [1][PDMS]]

References

[1] [2]

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

Further reading