chemistry

Selective area epitaxy

Selective area epitaxy is a chemistry 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 Selective area epitaxy rather than just read about it. In short: Selective area epitaxy is the local growth of epitaxial layer through a patterned amorphous dielectric mask (typically SiO2 or Si3N4) deposited on a semiconductor substrate. Semiconductor growth conditions are selected to ensure epitaxial growth on the exposed substrate, but not on the dielectric mask.

Key takeaways

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

Reference excerpt

Selective area epitaxy is the local growth of epitaxial layer through a patterned amorphous dielectric mask (typically SiO2 or Si3N4) deposited on a semiconductor substrate. Semiconductor growth conditions are selected to ensure epitaxial growth on the exposed substrate, but not on the dielectric mask. SAE can be executed in various epitaxial growth methods such as molecular beam epitaxy (MBE), metalorganic vapour phase epitaxy (MOVPE) and chemical beam epitaxy (CBE). By SAE, semiconductor nanostructures such as quantum dots and nanowires can be grown to their designed places.

Concepts

Mask The mask used in SAE is usually amorphous dielectric such as SiO2 or SiN4 which is deposited on the semiconductor substrate. The patterns (holes) in the mask are fabricated using standard microfabrication techniques lithography and etching. Variety of lithography and etching techniques can be implemented to SAE mask fabrication. Suitable techniques depend on the pattern feature size and used materials. Electron beam lithography is widely used due to its nanometer resolution. The mask should withstand the high temperature growth conditions of semiconductors in order to limit the growth to the patterned holes in the mask.

Selectivity Selectivity in SAE is used to express the growth on the mask. The selectivity of the growth is originated from the property that atoms don't favor sticking to the mask i.e. they have low sticking coefficient. Sticking coefficient can be reduced by the choice of mask material, having lower material flow and having higher growth temperature. High selectivity i.e. no growth on the mask is desired.

Growth mechanism Epitaxial growth mechanism in SAE can be divided in to two parts: Growth before the mask level and growth after the mask level.

Growth before mask level Before the mask level, the growth is confined to occur only in the hole in the mask. The growth starts to exceed the crystal of the substrate crystal following the pattern of the mask. The grown semiconductor has the structure of the pattern. This is employed in template assisted selective area epitaxy (TASE), where deep patterns in the mask are used as a template for the whole semiconductor structure and the growth is stopped before the mask level.

Growth after the mask level After the mask level, the growth can exceed to any direction, because the mask is no longer limiting the growth direction. The growth continues to the direction which is energetically favorable for crystal to expand in existing growth conditions. The growth is referred as faceted growth, because it is favorable for crystal to form facets. Therefore, in SAE grown semiconductor structures, clear crystalline facets are seen. The growth direction, or more precisely, the growth rates of different crystal facets can be tuned. Growth temperature, V/III ratio, orientation of the pattern and shape of the pattern are properties that affect to the growth rates of facets. By adjusting these properties, the structure of grown semiconductor can be engineered. SAE grown nanowires and epitaxial lateral overgrown structures (ELO) are an example of structures that are engineered by SAE growth conditions. In nanowire growth, the growth rate of lateral facets is suppressed and the structure grows only in vertical direction. In ELO, the growth is initiated in the mask openings, and after mask level the growth proceeds laterally on the mask, eventually joining the grown semiconductor structures together. The main principle in ELO is to reduce the defects caused by lattice mismatch of the substrate and the grown semiconductor.

Factors that affect to SAE Temperature of growth V/III ratio Choice of mask material Orientation of window Mask to window ratio Quality of mask Shape of the pattern

Techniques SAE can be achieved in various epitaxial growth techniques, which are listed below.

Metalorganic vapour-phase epitaxy Molecular beam epitaxy Chemical beam epitaxy Liquid phase epitaxy

Applications Nanowires Quantum dots III/V-Silicon integration Topological quantum computer

References

Worked examples

Example 1 — a first encounter with Selective area epitaxy

Start with the simplest possible case. Write down what Selective area epitaxy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, 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 Selective area epitaxy 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 Selective area epitaxy 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 Selective area epitaxy

In research: Selective area epitaxy appears in chemistry 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 Selective area epitaxy 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: Selective area epitaxy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Chemical vapor deposition, Semiconductor device fabrication, so understanding it makes those chapters shorter.
In everyday life: Look for Selective area epitaxy 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 Selective area epitaxy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Selective area epitaxy 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 Selective area epitaxy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Selective area epitaxy in simple terms?

Why does Selective area epitaxy matter?

Because it connects several chemistry 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 Selective area epitaxy?

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 Selective area epitaxy.