science

Reactive-ion etching

Reactive-ion etching 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 Reactive-ion etching rather than just read about it. In short: Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching.

Key takeaways

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

Reference excerpt

Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching. RIE uses chemically reactive plasma to remove material deposited on wafers. The plasma is generated under low pressure (vacuum) by an electromagnetic field. High-energy ions from the plasma attack the wafer surface and react with it.

Equipment A typical (parallel plate) RIE system consists of a cylindrical vacuum chamber, with a wafer platter situated in the bottom portion of the chamber. The wafer platter is electrically isolated from the rest of the chamber. Gas enters through small inlets in the top of the chamber, and exits to the vacuum pump system through the bottom. The types and amount of gas used vary depending upon the etch process; for instance, sulfur hexafluoride is commonly used for etching silicon. Gas pressure is typically maintained in a range between a few millitorr and a few hundred millitorr by adjusting gas flow rates and/or adjusting an exhaust orifice. Other types of RIE systems exist, including inductively coupled plasma (ICP) RIE. In this type of system, the plasma is generated with a radio frequency (RF) powered magnetic field. Very high plasma densities can be achieved, though etch profiles tend to be more isotropic. A combination of parallel plate and inductively coupled plasma RIE is possible. In this system, the ICP is employed as a high density source of ions which increases the etch rate, whereas a separate RF bias is applied to the substrate (silicon wafer) to create directional electric fields near the substrate to achieve more anisotropic etch profiles. The RF power given to the substrate is often a tunable parameter called 'platen power', and controls the energy of ions bombarding the surface.

Method of operation

Plasma is initiated in the system by applying a strong RF (radio frequency) electromagnetic field to the wafer platter. The field is typically set to a frequency of 13.56 Megahertz, applied at a few hundred watts. The oscillating electric field ionizes the gas molecules by stripping them of electrons, creating a plasma. In each cycle of the field, the electrons are electrically accelerated up and down in the chamber, sometimes striking both the upper wall of the chamber and the wafer platter. At the same time, the much more massive ions move relatively little in response to the RF electric field. When electrons are absorbed into the chamber walls they are simply fed out to ground and do not alter the electronic state of the system. However, electrons deposited on the wafer platter cause the platter to build up charge due to its DC isolation. This charge build up develops a large negative voltage on the platter, typically around a few hundred volts. The plasma itself develops a slightly positive charge due to the higher concentration of positive ions compared to free electrons. Because of the large voltage difference, the positive ions tend to drift toward the wafer platter, where they collide with the samples to be etched. The ions react chemically with the materials on the surface of the samples, but can also knock off (sputter) some material by transferring some of their kinetic energy. Due to the mostly vertical delivery of reactive ions, reactive-ion etching can produce very anisotropic etch profiles, which contrast with the typically isotropic profiles of wet chemical etching. Etch conditions in an RIE system depend strongly on the many process parameters, such as pressure, gas flows, and RF power. A modified version of RIE is deep reactive-ion etching, used to excavate deep features.

See also Deep RIE (Bosch Process) Plasma etcher

References

External links BYU Cleanroom – RIE Etching Bosch Process Reactive Ion Etching Systems Plasma RIE Fundamentals and Applications

Illustrations

Worked examples

Example 1 — a first encounter with Reactive-ion etching

Start with the simplest possible case. Write down what Reactive-ion etching 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 Reactive-ion etching 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 Reactive-ion etching 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 Reactive-ion etching

In research: Reactive-ion etching 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 Reactive-ion etching 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: Reactive-ion etching is common in secondary-school and first-year university syllabi. It links to neighbouring topics Etching (microfabrication), Plasma processing, Semiconductor device fabrication, so understanding it makes those chapters shorter.
In everyday life: Look for Reactive-ion etching 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 Reactive-ion etching in 20 minutes

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

Frequently asked questions

What is Reactive-ion etching in simple terms?

Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching.

Why does Reactive-ion etching 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 Reactive-ion etching?

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 Reactive-ion etching.