ArticleslgStudy

science

Soft lithography

Soft lithography is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Soft lithography rather than just read about it. In short: In technology, soft lithography is a family of techniques for fabricating or replicating structures using "elastomeric stamps, molds, and conformable photomasks". It is called "soft" because it uses elastomeric materials, most notably PDMS.

Soft lithography — main illustration
Soft lithography — illustration

Key takeaways

  • Soft lithography belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Soft lithography to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Soft lithography from memory before moving on to harder problems.

Reference excerpt

In technology, soft lithography is a family of techniques for fabricating or replicating structures using "elastomeric stamps, molds, and conformable photomasks". It is called "soft" because it uses elastomeric materials, most notably PDMS. PDMS, an amorphous polymer, is favored for the following characteristics:

Elasticity: the elasticity of PDMS is tuned by (1) adjusting curing conditions (curing agent concentration and temperature) and (2) dispersing particles throughout the polymer matrix. Its elasticity and durability allows the mold to conform to the surface of the substrate without rupture. Optical transparency: PDMS transmits ~90% of light from 390 nm to 780 nm, meaning it's optically transparent across the entire visible spectrum. The transparency of PDMS allows the direct observation of biological processes (including the observation of blood flow through the mimicked PDMS-based blood vessels). Gas-permeability: PDMS is gas-permeable which is useful in applications such as Microfluidics. Isotropic: PDMS is isotropic, meaning its physical properties are identical in every direction, and will thus perform uniformly. Chemically-inert: PDMS will not interfere chemically with the substrate. Following the molding onto the master template, PDMS is cured at high temperatures with a cross-linking agent. Soft lithography is generally used to construct features measured on the micrometer to nanometer scale. According to Rogers and Nuzzo (2005), development of soft lithography expanded rapidly from 1995 to 2005. Soft lithography tools are now commercially available.

Types PDMS stamp Microcontact printing Multilayer soft lithography Nanosphere lithography Patterning by etching at the nanoscale

Advantages

Soft lithography has some unique advantages over other forms of lithography (such as photolithography and electron beam lithography). They include the following:

Lower cost than traditional photolithography in mass production Well-suited for applications in biotechnology Well-suited for applications in plastic electronics Well-suited for applications involving large or nonplanar (nonflat) surfaces More pattern-transferring methods than traditional lithography techniques (more "ink" options) Does not need a photo-reactive surface to create a nanostructure Smaller details than photolithography in laboratory settings (~30 nm vs ~100 nm). The resolution depends on the mask used and can reach 6 nm. Nanolithography

Limitations Due to the high elasticity of PDMS (or an alternative elastomer), the stamp can undergo undesired mechanical deformations including pairing, shrinking, and sagging.

Pairing: the lateral collapse of the elastomer which can happen due to the low structural and high elasticity of the stamp. If the height of the feature is much greater than its width, adjacent structures may collapse. Sagging: If the height of the features is much less than the distance, the stamp may sag due to gravity. Shrinking: the volume of PDMS shrinks by 1% after curing. Depending on the dimensional tolerance of the design, the registered pattern may produce inaccurate patterns.

References

Further reading Xia, Y.; Whitesides, G. M. (1998). "Soft Lithography". Angew. Chem. Int. Ed. Engl. 37 (5): 551–575. doi:10.1002/(SICI)1521-3773(19980316)37:5<550::AID-ANIE550>3.0.CO;2-G. PMID 29711088.{{cite journal}}: CS1 maint: deprecated archival service (link) Xia, Y.; Whitesides, G. M. (1998). "Soft Lithography. In". Annu. Rev. Mater. Sci. 28: 153–184. Bibcode:1998AnRMS..28..153X. doi:10.1146/annurev.matsci.28.1.153. Quake, S. R.; Scherer, A. (2000). "From micro- to nanofabrication with soft materials". Science. 290 (5496): 1536–1540. Bibcode:2000Sci...290.1536Q. doi:10.1126/science.290.5496.1536. PMID 11090344. S2CID 1386132. Rogers, J. A.; Nuzzo, R. G. (2005). "February). Recent progress in soft lithography. In". Materials Today. 8 (2): 50–56. doi:10.1016/S1369-7021(05)00702-9.

Illustrations

Soft lithography: Figure 1 - "Inking" a stamp. PDMS stamp with pattern is placed in Ethanol and ODT (octadecanethiol) solution
Figure 1 - "Inking" a stamp. PDMS stamp with pattern is placed in Ethanol and ODT (octadecanethiol) solution
Soft lithography: Figure 2 - ODT from the solution settles down onto the PDMS stamp. Stamp now has ODT attached to it which acts as the ink.
Figure 2 - ODT from the solution settles down onto the PDMS stamp. Stamp now has ODT attached to it which acts as the ink.
Soft lithography: Figure 3 - The PDMS stamp with the ODT is placed on the gold substrate. When the stamp is removed, the ODT in contact with the gold stays stuck to the gold. Thus the pattern from the stamp is transferred to the gold via the ODT "ink."
Figure 3 - The PDMS stamp with the ODT is placed on the gold substrate. When the stamp is removed, the ODT in contact with the gold stays stuck to the gold. Thus the pattern from the stamp is transferred to the gold via the ODT "ink."
Soft lithography: Sarfus image of streptavidin deposited by soft lithography with PDMS stamp.
Sarfus image of streptavidin deposited by soft lithography with PDMS stamp.

Worked examples

Example 1 — a first encounter with Soft lithography

Start with the simplest possible case. Write down what Soft lithography claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Soft lithography before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Soft lithography ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Soft lithography

In research
Soft lithography appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Soft lithography in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Soft lithography is common in secondary-school and first-year university syllabi. It links to neighbouring topics Lithography (microfabrication), so understanding it makes those chapters shorter.
In everyday life
Look for Soft lithography outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Soft lithography in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Soft lithography means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Soft lithography out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Soft lithography in simple terms?

In technology, soft lithography is a family of techniques for fabricating or replicating structures using "elastomeric stamps, molds, and conformable photomasks". It is called "soft" because it uses elastomeric materials, most notably PDMS.

Why does Soft lithography matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Soft lithography?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Soft lithography.

Tags

  • Lithography (microfabrication)

Keep exploring