Semiconductor Etching With Light
September 29, 2012

Faster, Less Expensive Semiconductor Etching Method Developed

redOrbit Staff & Wire Reports - Your Universe Online

Researchers at one US university have developed a new, low-cost method of etching minute features onto semiconductor wafers while monitoring the process as it happens.

University of Illinois electrical and computer engineering professor Gabriel Popescu and colleagues say that their method allows chipmakers to use a special microscope that uses two beams of light to precisely measure the topography. Their technique allows researchers and manufacturers to watch the process in real time with nanometer resolution, according to Liz Ahlberg, the university news department's physical sciences editor.

"Chip makers and semiconductor researchers need to very precisely control the dimensions of their devices. The dimensions of the components affect performance, speed, error rate and time to failure," Ahlberg said. "Semiconductors are commonly shaped by etching with chemicals. Etching errors, such as residual layers, can affect the ability to further process and etch as well as hamper device performance. Thus, researchers use time-consuming and costly processes to ensure precise etching -- for some applications, to within a scant few nanometers."

"The idea is that the height of the structure can be determined as the light reflects off the different surfaces," said Lynford Goddard, who, like Popescu, is an electrical and computer engineering professor at the university and was involved in the research. "Looking at the change in height, you figure out the etch rate. What this allows us to do is monitor it while it´s etching. It allows us to figure out the etch rate both across time and across space, because we can determine the rate at every location within the semiconductor wafer that´s in our field of view."

According to Ahlberg, this new method is less expensive, quicker, and quieter than the more commonly used methods of atomic force microscopy or scanning tunneling microscopy. Neither of those techniques allow semiconductor developers to monitor the process as it happens, and the Illinois technique also has the advantage of being contact-free, which means the entire wafer can be seen at all times. In fact, Popescu called that last point the primary advantage of their innovative etching method.

"In addition to monitoring the etching process, the light catalyzes the etching process itself, called photochemical etching," Ahlberg said. "Traditional chemical etching creates features in steps or plateaus. For curved surfaces or other shapes, semiconductor researchers use photochemical etching."

"Usually, light shines though very expensive glass plates called masks that have distinct patterns of gray to let light through by degrees. A researcher must purchase or make a mask for each tweak of a pattern until the correct pattern of features is achieved," she added. "By contrast, the new method uses a projector to shine a grayscale image onto the sample being etched. This allows the researchers to create complex patterns quickly and easily, and adjust them as needed."

Their research was sponsored by the National Science Foundation (NSF), and was published Friday in the journal Light: Science and Applications.