Electronics from the inside (Day 125)

What does a two hundred year old printing process, a mobile phone and chemical engineering have in common?

At first glance not a lot, but there is an interesting story to tell to illustrate why chemical engineering matters so much in today’s world.

Firstly, let’s head back to the 1790s when a printing process called lithography was discovered. Encyclopaedia Britannica describe lithography as ‘planographic printing process that makes use of the immiscibility of grease and water’.

In its early days, lithography was used by fine artists as a medium and later evolved to become a mainstay of commercial printing, especially packaging and publishing.

Remarkably, the phrase lithography is also the name used in the electronics industry to make integrated circuits, microprocessors and memory chips. Without it mobile phones, computers and a whole host of gadgets wouldn’t be possible.

I’m sure even the discoverer of lithography, German Alois Senefelder, couldn’t have foreseen just how important the principle that oil and water don’t mix could be helping to improve quality of life over two centuries later.

In the semiconductor industry, lithography is used to print two-dimensional patterns onto silicon wafers using a light-sensitive polymer called a photoresist.

Patterns are transferred into the silicon wafer with different unit operations, like deposition or etching, to build up the conductors, insulators and circuits that form the final device.

Though the lithography process might sound simple, it requires a variety of very complex physical and chemical processes in the photoresist to form the pattern.

The semiconductor industry relies on the lithography process to produce nearly all electronic device components – yet, very little is understood about the science underlying the complex chemical reactions required for semiconductor patterning.

The chemical engineering part of this story concerns Gila Stein, who is the Ernest J. and Barbara M. Henley assistant professor of chemical and biomolecular engineering at the University of Houston Cullen College of Engineering.

Gila is currently researching and developing models that can explain the complex physical and chemical reactions that take place in lithography systems used for device fabrication.

In particular, Gila will be looking at materials called chemically amplified resists, which are systems wherein a polymer is blended with a catalyst and then a chemical reaction is used to form the patterns for semiconductor devices.

Gila describes the importance of her investigative work into the lithography materials: “These are the materials that are used to pattern semiconductor devices, like the chips in your computer.

“As computers become faster and faster, it’s because you’re shrinking the size of all the little devices that go into those integrated circuits, like the microprocessors and memory chips,”

“So, if you want to be able to pattern things that are very, very small, you need to have really good control over the reactions that create those patterns.”

Gila’s hope is to develop a model that factors in the interaction of the polymer with the catalysts, temperature and the possible plasticizing of the polymer film.

If the model proves successful, it is hoped it can be implemented into semiconductor manufacturing processes, taking out much of the guesswork with semiconductor patterning at the nanoscale.

The next time a non-chemical engineering friend is thinking of buying a new phone, remember to tell them that it is our profession that is helping to improve issues like battery life, and in Gila’s case their performance, size and reliability as well.