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FrankGroup » Blog Archive » Theresa Hsu, Ph.D.

Theresa Hsu, Ph.D.

Project description: Surface Cleaning using Elastic Polymer and Surfactant Solutions.

Surface contamination is a major problem in several technology-driven industries, ranging from aerospace to pharmaceuticals. It is especially important for integrated circuit fabrication of semiconductors, where over 50 percent of yield losses result from contamination on device wafers.  Currently, the most common technology for removing contaminants on wafers is the chemical wet cleaning process. This process involves the use of strong acid and base baths containing hydrogen peroxide: environmentally harmful chemicals that produce large amounts of hazardous waste. Other physical removal processes using megasonics, shockwaves, or lasers also exist, but these protocols are energy intensive, can damage the wafer surface, and are inefficient at removing smaller particles.

Clearly, novel cleaning technologies are needed to provide greener and more energy efficient processes. The current study investigates a new approach holds such promise. In this process, a layer of aqueous polymer or surfactant solution is deposited on the contaminated substrate.  The substrate is then subjected to a simple water-rinsing procedure. This sequence has been shown to remove particles in both the micron and submicron ranges effectively. This continuous rinsing process is energy efficient, creates a limited amount of waste, and the aqueous polymer or surfactant solutions are safe to handle and environmentally friendly.

We aim to understand this particle removal process at both the macroscopic and the molecular level by combining approaches from polymer physics, fluid mechanics, surface science, and rheology.  The first component of this project involves a detailed analysis of the polymer solution as well as the flow profile of the rinse.  Instruments such as the parallel-plate rheometer and the capillary breakup extensional rheometer are currently utilized to measure the responses of the polymer solution under different forces and stress conditions. Also, an experimental setup was designed utilizing a high-speed camera (at 2000 frames per second) to image the rinsing flows.

The other aspect of this projec involves the construction of an experimental set-up to directly image particle removal in situ.  Differential interference contrast microscopy is utilized, which enables particle imaging down to the nanometer scale.  As in the rinsing flow visualizations, a high-speed camera is used to observe the process in detail.  This enables us to determine the relevant timescales for particle removal and quantify the number of particles removed as a function of time.

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