“electrolithography”- A Novel Nano Patterning Technique Using Electric Field Induced Material Transport
Project Description :

In this work, we introduce electrolithography — a new nano patterning technique based on electric field induced material transport. electrolithography can be used for drawing patterns having dimensions from a few nanometres to a few hundred micrometres. it does not need any uv or e-beam sources like existing lithography techniques, and can be performed in ambient condition. electric field can induce flow of liquids such as electroosmotic flow, electrokinetic flow, etc. we discovered that electric current assisted by joule heating can induce long range flow of material on thin metal films also, such as cr. in case of cr thin film deposited on an insulating substrate, application of high electric-field between two point electrodes results in liquefaction and subsequent flow of the liquefied material in a radially symmetric fashion away from the cathode. electrolithography uses this phenomenon for writing patterns, as described below. in electrolithography, we use thin cr film as a masking layer and a polymer layer beneath it as a pattern transfer layer. a negatively biased scanning probe is used to perform electromigration on the metal film. we have customized an existing atomic force microscope (afm) to serve this purpose. the conducting tip is moved on the cr layer in a predefined path to etch metal according to the desired pattern. once the metal is etched, the polymer layer below it gets exposed. the pattern drawn on the metal layer is transferred to the polymer layer by etching the polymer with an appropriate solvent. hence, the substrate gets exposed in the desired pattern. subsequently, the pattern is transferred to the desired material layer using a standard film deposition technique, followed by conventional lift-off process. same pattern can be transferred to the substrate by etching it also. using this technique, best resolutions achieved are of 9 nm on the polymer, and 40 nm on transferring the pattern to another material. depending on the probe diameter and speed, throughput for this process has been achieved in the range 10^6 to 10^9 µm^2/h, which is considerably higher than the conventional scanning probe lithography (spl) techniques. in common spl techniques, the depth of the patterns drawn on the polymer layer are often very small. thus, transferring those patterns to other materials becomes very difficult. however, in electrolithography process, etch depth in the polymer is same as the polymer layer thickness (usually ~ 200 nm). therefore, patterns are easily transferrable and final patterned structures can be as thick as 100 nm, enabling their usage in microelectronic devices. in electrolithography, polymer is used only to transfer the patterns. hence, any polymer and corresponding developer can be used in this process thereby, removing need of costly and toxic chemicals from lithography processes. we also demonstrate direct writing or resist less patterning for making mask using this technique. besides electrolithography, we have also used this electromigration driven material transport process to create periodic ripple patterns (to be used as optical grating) and multi-dimensional (1-d, 2-d and 3-d) patterns (e.g. metallic beads, which are used in plasmonic and nanowire growth applications) which are very difficult to fabricate using conventional lithography techniques. considering the complexity, cost and energy consumption of the lithography tools, this technique is far better than the e-beam lithography or ultra-violet based photolithography, which require high energy e-beam or uv sources, ultra-high vacuum and very expensive instrumentation to reach nano-scale resolutions.

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Project Details :
  • Date : Nov 25,2016
  • Innovator : Santanu Talukder
  • Team Members : Santanu Talukder,Dr. Praveen Kumar,Prof. Rudra Pratap
  • Guide Name : Prof. Rudra Pratap And Dr. Praveen Kumar
  • University : Indian Institute of Science
  • Submission Year : 2017
  • Category : Nano Science and Engineering
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