Surface Deformation of Metal Films Under Controlled Pressure for Generating Ultra-flat Metal Surfaces
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Surface Deformation of Metal Films Under Controlled Pressure for Generating Ultra-Flat Metal Surfaces Logeeswaran Vj1,2, Mei-Lin Chan3, M.Saif Islam1,2, David A. Horsley3, Wei Wu2, Shih Yuan Wang2, and R. Stanley Williams2 1 Electrical & Computer Engineering, University of California-Davis, Kemper Hall, One Shields Ave, DAVIS, CA, 95616 2 Quantum Science Research Advanced Studies, Hewlett Packard Laboratories, 1501 Page Mill Road, Palo Alto, CA, 94304 3 Mechanical & Aeronautical Engineering, University of California-Davis, Bainer Hall, One Shields Ave, DAVIS, CA, 95616 ABSTRACT We present a technique to generate ultra-smooth surfaces and direct pattern imprinting on thin metal films by flattening the bumps and spikes of a freshly vacuum deposited metal film. The technique was implemented by using a small footprint mechanical imprint press that has the capability to vary the applied pressure from 100MPa to 600MPa. The mechanical press was incorporated with a tactile force sensor that enabled direct monitoring of the applied pressure. We demonstrated the feasibility of the technique on an e-beam evaporated silver (Ag) metal film with thickness ranging from 150Å (optically thin) to 1000Å (optically thick). The film was deposited on double-polished (100)-oriented silicon surface and double-polished borosilicate glass, resulting in a varying degree of film smoothness. The surface morphology of the pressed thin film was then studied using atomic force microscopy and SEM. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.
INTRODUCTION Potential new approaches for constructing revolutionary nanoelectronic and photonic circuits involve unconventional building blocks such as molecules, DNA, carbon nanotubes, nanowires or plasmonic metamaterials. Unlike the metals commonly used for interconnecting conventional integrated circuit (IC) devices, innovative devices and circuits employing these new building blocks may require the use of noble metals such as silver (Ag), platinum (Pt) and gold (Au) [1–6]. One key issue that needs to be addressed in these applications is the requirement for a smooth noble metal interface. In interconnect and molecular electronics, rough metal surface leads to decrease in device yield due to electrical shorting [7] while in plasmonic metamaterials scattering losses dominate thus reducing the signal transmission integrity [6,8-9]. Thus efforts to realize atomically smooth uniform metal surfaces in modern electronic and photonic systems cannot be overemphasized. These noble metals are typically deposited using common thin film deposition techniques such as evaporation, ion-beam-assisted deposition and rf/dc sputtering. Analysis of these metal surfaces using atomic force microscopy reveals a rough surface topography –often rougher than the size of the desired nanoscale circuit elements [10]
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