Fabrication of teflon-like ultra thin plasma polymer films on silicon wafer surfaces

Research area: Nanomaterials, polymer science
Degree: Honours
Supervisors: Prof Naba Dutta and Prof Namita Roy Choudhury
Aim: Visualization and characterization of plasma polymer thin film using micro thermal analysis 

Many crucial material properties such as adhesion, biocompatibility, hydrophobicity and friction are governed by the molecular state of the topmost surface. Tailoring surface by plasma modification and polymerization is an emerging technology and revolutionized the thin film forming process.

The technology is versatile and can be used for deposition of conducting/semiconducting organic films, controlling the tribology, hydrophobic/hydrophilic and biocompatible nature of the surface, modifying the transport properties of the membranes, improving adhesion, wettability, dye uptake and other technologically important surface characteristics.1,2 Poly (tetrafluroethylene) (Teflon, PTFE) has many desirable properties including chemical inertness, thermal stability, low coefficient of friction, low dielectric constant (1.9-2.1), low surface energy, ultrahydrophobicity, and relatively low permeability for most of the gases, which can hardly be matched by any other polymers.

Due to the combination of outstanding properties they are ideal materials for many crucial applications, which place stringent demand on materials performance. These include passivation layer on electronic devices (to avoid deterioration in the operating environment), and interlayer dielectrics for next generation of multilevel integrated circuits. However, due to their insolubility and infusible nature, conventional production technology do not allow the deposition of thin layer Teflon material. 

In this project a promising alternative, plasma polymerization technique will be used and optimized for deposition of flawless ultra-thin fluorocarbon polymers film on smooth silicon wafer surface. Different type of per-fluoro monomers including paraffinic, vinyl, aromatic and cyclic will be employed to engineer the plasma polymer thin film.

Besides the classical techniques, such as FTIR and XPS, the film surface morphology, thickness and physical properties (transitions, degradation etc.) will be examined using a Micro Thermal Analyzer ('TA'). 'TA' is essentially an atomic force microscopy (AFM), where a tiny resistive thermal probe is mounted within an AFM in place of the usual Si probe.3-5. The thermal probes can raster the surface as an AFM tip and collect the images related to the sample topography and thermal conductivity. Using the image as a guide, points on the film can be selected for further examination of the physical properties by local thermal analysis (LTA).

In this technique the probe is positioned at the selected points and the temperature is ramped from a start to a final temperature at very high ramp rate (5-250 oC/s) of the plasma engineered coating. The topographic images will be used to determine the nanoscale morphology, film thickness and roughness (including fractal analysis) in details. LTA is a local technique, it analyzes only a few cubic micrometers of the experimental surface, and the changes in properties, laterally, over the surface will be employed to evaluate the uniformity of the film. 

References 
1) Handbook of 'Advanced Plasma Processing Techniques', Shul, R.J.and Pearton, S.J., Eds., Springer, Berlin, 2000. 
2) Inagaki N., 'Plasma Surface Modification and Plasma Polymerization', Technomic, Lancaster, 1996 
3) Hammiche et al., J. Vac. Sci. Technol. B, 1996, 14,1486. 
4) Hammiche et al., Rev. Sci. Instrum., 1996, 67, 4268. 
5) Price, D.M., Reading, M., Hammiche, A. and Pollock, H.M., Journal of Thermal Analysis and Calorimetry, 2000, 60, 723.

Areas of study and research

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