Colorful Nanowire Arrays Imprinted on Semiconductor Wafers Enable Metrology at High Speeds

Achievement date: 
2016
Outcome/accomplishment: 

Researchers at the Nanomanufacturing Systems for Mobile Computing and Mobile Energy Technologies (NASCENT) center, an NSF-funded Nanosystems Engineering Research Center (NERC) headquartered at The University of Texas at Austin, have fabricated nanowire arrays that exhibit vibrant colors visible to the naked eye on wafers, producing colors that correspond to a specific wavelength.

Impact/benefits: 

TheCenter observed how modifying the nanowires’ diameter shifted the reflection peaks toward shorter or higher wavelengths. Understanding this relationship enables spectrophotometry that characterizes nanoscale geometry of the arrays at high speeds. While electron microscopy only measures several nanowires at a time, this research enables metrology at wafer-scale production levels.

Explanation/Background: 

Silicon (Si) nanowire arrays have been shown to exhibit interesting interactions with light that produce observable optical effects that are often visible to the naked eye, and are certainly measurable by a spectrophotometer. The study of these interactions and others at nano-scale is known as nanophotonics or nano-optics.

In the case of the Si nanowire arrays, the nanophotonic effects manifest themselves by altering the reflectivity spectrum of bare polished Si. The reflectivity spectrum is measureable with a spectrophotometer and is a function of the dimensions (height, diameter, and pitch) of the nanowires, as the researchers at NASCENT observed.

The research team observed that decreasing the diameter of the Si nanowires shifted the reflection peak towards shorter wavelengths, with the resulting color appearing bluer to the naked eye, and increasing the height of the Si nanowires increased the height of the reflectivity peak while hardly affecting the position of the peak.