science

Maskless lithography

Maskless 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 Maskless lithography rather than just read about it. In short: Maskless lithography (MPL) is a photomask-less photolithography-like technology used to project or focal-spot write the image pattern onto a chemical resist-coated substrate (e.g. wafer) by means of UV radiation or electron beam. In microlithography, typically UV radiation casts an image of a time constant mask onto a photosensitive emulsion (or photoresist).

Key takeaways

Maskless 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 Maskless lithography to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Maskless lithography from memory before moving on to harder problems.

Reference excerpt

Maskless lithography (MPL) is a photomask-less photolithography-like technology used to project or focal-spot write the image pattern onto a chemical resist-coated substrate (e.g. wafer) by means of UV radiation or electron beam. In microlithography, typically UV radiation casts an image of a time constant mask onto a photosensitive emulsion (or photoresist). Traditionally, mask aligners, steppers, scanners, and other kinds of non-optical techniques are used for high speed microfabrication of microstructures, but in case of MPL, some of these become redundant. Maskless lithography has two approaches to project a pattern: rasterized and vectorized. In the first one it utilizes generation of a time-variant intermittent image on an electronically modifiable (virtual) mask that is projected with known means (also known as laser direct imaging and other synonyms). In the vectored approach, direct writing is achieved by radiation that is focused to a narrow beam that is scanned in vector form across the resist. The beam is then used to directly write the image into the photoresist, one or more pixels at a time. Also combinations of the two approaches are known, and it is not limited to optical radiation, but also extends into the UV, includes electron-beams and also mechanical or thermal ablation via MEMS devices. Maskless lithography's advantages have included "resolution and flexibility." However, low through-put and integration difficulties delayed high-volume adoption.

Forms Currently, the main forms of maskless lithography are electron beam and optical. In addition, focused ion beam (FIB) systems have established an important niche role in failure analysis and defect repair. Also, systems based on arrays of mechanical and thermally ablative probe tips have been demonstrated.

Electron beam (e-beam) The most commonly used form of maskless lithography today is electron beam lithography. Its widespread use is due to the wide range of electron beam systems available accessing an equally wide range of electron beam energies (~10 eV to ~100 keV). This is already being used in wafer-level production at eASIC, which uses conventional direct-write electron beam lithography to customize a single via layer for low-cost production of ASICs. Most maskless lithography systems currently being developed are based on the use of multiple electron beams. The goal is to use the parallel scanning of the beams to speed up the patterning of large areas. However, a fundamental consideration here is to what degree electrons from neighboring beams can disturb one another (from Coulomb repulsion). Since the electrons in parallel beams are traveling equally fast, they will persistently repel one another, while the electron lenses act over only a portion of the electrons' trajectories.

Optical Direct laser writing is a very popular form of optical maskless lithography, which offers flexibility, ease of use, and cost effectiveness in R&D processing (small batch production). The underlying technology uses spatial light modulating (SLM) micro-arrays based on glass to block laser pathway from reaching a substrate with a photoresist (in similar manner to digital micromirror devices). This equipment offers rapid patterning at sub-micrometer resolutions, and offers a compromise between performance and cost when working with feature sizes of approximately 200 nm or greater. Direct laser writing for microelectronics packaging, 3D electronics and heterogeneous integration were developed in 1995 at the Microelectronics and Computer Technology Corporation (or MCC) in Austin, Texas. The MCC system was fully integrated with precision control for 3D surfaces and artificial intelligence software with real-time machine learning and included laser wavelengths for standard i-line resist and DUV 248nm. The MCC system also included circuit editing capabilities for isolating circuits on a programmable wafer design. In 1999, the MCC system was advanced for use in MEMS manufacturing. Interference lithography or holographic exposures are not maskless processes and therefore do not count as "maskless", although they have no 1:1 imaging system in between. Plasmonic direct writing lithography uses localized surface plasmon excitations via scanning probes to directly expose the photoresist. For improved image resolution, ultraviolet light, which has a shorter wavelength than visible light, is used to achieve resolution down to around 100 nm. The main optical maskless lithography systems in use today are the ones developed for generating photomasks for the semiconductor and LCD industries. In 2013, a group at Swinburne University of Technology published their achievement of 9 nm feature size and 52 nm pitch, using a combination of two optical beams of different wavelengths. DLP technology can also be used for maskless lithography.

Focused ion beam Focused ion beam systems are commonly used today for sputtering away defects or uncovering buried features. The use of ion sputtering must take into account the redeposition of sputtered material.

Proton beam writing Proton beam writing (or p-beam writing) is a direct-write lithography process that uses a focused beam of high energy (MeV) protons to pattern resist material at nanodimensions. The process, although similar in many ways to direct writing using electrons, nevertheless offers some interesting and unique advantages.

Probe-tip contact

IBM Research has developed an alternative maskless lithography technique based on atomic force microscopy. In addition, Dip Pen Nanolithography is a promising new approach for patterning submicrometer features.

Research

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with Maskless lithography

Start with the simplest possible case. Write down what Maskless 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 Maskless 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 Maskless 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 Maskless lithography

In research: Maskless 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 Maskless 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: Maskless 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 Maskless 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.

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How to study Maskless lithography in 20 minutes

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

Frequently asked questions

What is Maskless lithography in simple terms?

Why does Maskless 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 Maskless 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 Maskless lithography.