A Novel Fabrication Technique for Developing Metal Nanodroplet Arrays
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0940-P13-12
A Novel Fabrication Technique for Developing Metal Nanodroplet Arrays Christopher Edgar, Chad Johns, and M. Saif Islam Electrical and Computer Engineering, University of California, Davis, One Shields Avenue, 1207 Kemper, Davis, California, 95616 INTRODUCTION Metal in particle form is useful in fabrication of silicon nanowires [1], superlattice nanowires [2], colloidal solutions, biomedical applications [3,4], photonics [5] and sensors [6]. Incorporation of such research into manufacturing processes requires new research in fabrication processes for scalable and reproducible low cost arrays of nanoparticles. Exploiting known metallurgical sciences, new approaches in fabrication technology are constantly approaching a goal for the fabrication of oriented arrays of nanoparticles [7,8]. At present these existing processes are not capable of wide-scale deployment and selective array fabrication. In this paper, we demonstrate a novel process for ultimately developing well-defined arrays of metal nanodroplets that can be incorporated into most microfabrication processes. EXPERIMENTAL DETAILS First, a common silicon wafer was cleaned, dried, and soft-baked at 110°C for 60 seconds to remove residual water from the substrate. Photoresist (Shipley Corporation) was next applied and spun on and baked at 110°C to stabilize the photoresist for further processing. The photoresist was next exposed by a mask aligner (Karl-Suss) to produce patterned arrays of microstructures. The exposed substrate was then developed for 50 seconds, and then rinsed in de-ionized water and nitrogen dried. Metal deposition was performed in an electron-beam evaporation chamber (CHA) to control the thickness of the metal pattern lines. Our experiments also used angular deposition in the e-beam to produce smaller width metal patterned lines. Liftoff was performed and the sample was once again washed and nitrogen dried. The annealing process was carried out using a Vacuum Tube Furnace (MTI Crystal, GSL-1600X) at a temperature range of 400°C to 1000°C under the flow of argon gas. Characterization was performed by using a scanning electron microscope (FEI XL30-SFEG), and a digital camera optical microscopy station.
Figure 1 Schematic of ideal metal patterned lines that experience transformation from linear metal patterned lines into uniform isolated droplets in place of the original metal.
DISCUSSION Figure 1 shows a schematic representation of the process that is used to develop metal nanodroplet arrays. Metal when exposed to an elevated temperature becomes unstable and break down into metal clusters that eventually form into droplets. In our experiments, we have gold metal lines on a silicon substrate and the heating of the metal lines on the substrate causes diffusion of the silicon substrate atoms into the gold metal bulk, and gold atoms into the silicon substrate. The mixing of silicon atoms into the gold patterns allows for our method for the formation of droplet arrays. The melting temperature of the original bulk gold droplet decreases
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