Chemical Wet Etching: Basic Function

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Из курса от партнера Duke University

Nanotechnology: A Maker’s Course

236 оценки

Duke University

Nanotechnology: A Maker’s Course

236 оценки

How can we create nano-structures that are 10,000 times smaller than the diameter of a human hair? How can we “see” at the nano-scale? Through instruction and lab demonstrations, in this course you will obtain a rich understanding of the capabilities of nanotechnology tools, and how to use this equipment for nano-scale fabrication and characterization. The nanoscale is the next frontier of the Maker culture, where designs become reality. To become a Nanotechnology Maker pioneer, we will introduce you to the practical knowledge, skills, and tools that can turn your nanotechnology ideas into physical form and that enable you to image objects at the nano-scale. This course has been developed by faculty and staff experts in nano-fabrication, electron beam microscopy, and nano-characterization through the Research Triangle Nanotechnology Network (RTNN). The RTNN offers training and use of the tools demonstrated in this course to schools and industry through the United States National Nanotechnology Coordinated Infrastructure program. The tools demonstrated in this course are available to the public through the RTNN.

Из урока

Nanofabrication: Etching

In this module, you will learn to describe and compare wet and dry etching processes. These processes are used to selectively remove material in nanofabrication.

Chemical Wet Etching: Basic Function3:46

Chemical Wet Etching: Demonstration4:20

Познакомьтесь с преподавателями

Nan M. Jokerst
J. A. Jones Professor of Electrical and Computer Engineering
Electrical and Computer Engineering, Duke University
Carrie Donley
Director of CHANL (Chapel Hill Analytical and Nanofabrication Laboratory)
Applied Physical Sciences, UNC Chapel Hill
James Cahoon
Assistant Professor
Chemistry, UNC Chapel Hill
Jacob Jones
Professor
Materials Science and Engineering, North Carolina State University

Hi, I'm Steve Shannon,

Associate Professor in the Department Nuclear Engineering at NC State University.

Today, we'll be talking about chemical wet etching.

Wet etching uses liquid etchings to remove undesired material.

The substrates are placed directly into a bath containing an etching solution.

These etchings are often strong acids or bases.

Because the wafers are submerged in the bath,

both sides of the substrate will be exposed to the etching and can be etched.

The exposed material is etched by chemical processes.

The reaction products are typically soluble in the bath solution or gaseous.

As can be seen in this image,

the user works directly with the etching.

As these are harsh chemicals,

the user works in a fume hood to protect themselves from harmful fumes.

The user also wears the appropriate personal protective equipment including;

safety glasses, a face shield,

chemical resistant gloves, and a chemical apron to

avoid direct contact with etch chemicals.

A chemical reaction between the reactant in the film etches the surface of the film.

Depending on the reactant in the film,

the reaction can be very selective,

only etching the film.

However, wet etching is isotropic leading to pattern under-cutting.

One common process uses

the reactant hydrofluoric acid to etch the thin film silicon dioxide.

Buffering agents are also often added to etch solutions to

maintain PH and keep a consistent chemical reaction over time.

In the case of HF etching,

ammonium fluoride is used as the buffering agent to

prevent depletion of the floride ions and maintain PH.

The etch rate can also be controlled to some degree by the user.

For example, we can add more HF

to increase the number of reactants that reach the surface.

We can also increase the reaction rate by increasing the temperature.

And we can remove the reaction products by stirring,

which will also increase the reaction rate.

After etching, imaging by scanning electron microscopy or

profilometry measurements should be conducted to validate the etching process.

The sample should also be characterized prior to etching.

Here, we can see a list of common material and etchant pairs for wet etching.

It is important to consider all of

the material components when you are selecting an etchant.

For example, if you want to etch

titanium and you are using photo resist as a protective layer,

you may not want to select an etchant like

hydrogen peroxide because it will also etch the photo resist.

One of the main advantages of wet etching when properly done,

is that it uses simple equipment.

The process is straightforward and it also has high throughput.

Wafers can be loaded into the container called the boat.

Boats hold multiple wafers which allow

simultaneous etching of several wafers at one time.

Due to the chemical reaction that occurs during the etching,

the process is highly selective.

One of the main disadvantages of wet etching,

is that the reactions in most cases are isotropic.

This makes etching small geometries very difficult.

It also requires large amounts of chemicals which

can be costly to purchase and dispose of.

The etchants used are also typically very dangerous chemicals.

So safety can be a concern as users work directly with these chemicals.

Further, find process control in these systems is difficult.

This can make reproducibility hard.

When selecting an etching process,

It is important to take these pros and cons under consideration.

This concludes our overview of chemical wet etching. Thank you for joining us today.

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