Ben S. Routley

Mapping chemical concentration in binary thin organic films via multi-wavelength scanning absorption microscopy (MWSAM)

The composition and thickness of binary thin organic films is determined by measuring the optical absorption at multiple wavelengths across the film surface and performing a component analysis fit to absorption standards for the materials. The multiple laser wavelengths are focused onto the surface using microscope objectives and raster scanned across the film surface using a piezo-electric actuator X–Y stage. All of the wavelengths are scanned simultaneously with a frequency division multiplexing system used to separate the individual wavelength response. The composition values are in good quantitative agreement with measurements obtained by scanning transmission x-ray microscopy (STXM). This new characterization technique extends quantitative compositional mapping of thin films to thickness regimes beyond that accessible by STXM.

A nonlinear programming approach to exposure optimization in scanning laser lithography

Laser scanning lithography is a maskless method for exposing films of photoresist during semiconductor manufacturing. In this method a focused beam is scanned over a surface with varying intensity to create features in the photoresist. Given the shape of a desired feature, an exposure pattern must be found that approximates this shape in the developed photoresist. This can be cast as an optimization problem, which is complicated by the non-negative nature of the exposure function and the non-linear photochemistry of the film. In this article, a nonlinear programming approach is described that results in a tractable optimization problem which accounts for all of the practical constraints encountered in laser scanning lithography.

A closed-loop phase-locked interferometer for wide bandwidth position sensing

This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interferogram. In this configuration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics, it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has an effectively unlimited bandwidth. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instrument is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, Ultrasonic devices, and sensors such as surface acoustic wave detectors.

Optimization of near-field scanning optical lithography

This article describes two- and three-dimensional optical simulations for determining optimal conditions for near-field scanning optical lithography. It was found that a combination of 30-nm thick photoresist and 50-nm thick anti-reflective coating will yield optimal results with 405 nm incident light and a hollow-cantilever probe with 100-nm aperture width. In addition to identifying the optimal conditions, the sensitivity of the resolution with respect to each parameter is explored and plotted. The mechanisms behind each trend are described with supporting simulation data.

A closed-loop phase-locked interferometer for wide bandwidth position sensing.

This article describes a position sensitive interferometer with closed-loop control of the reference mirror. A calibrated nanopositioner is used to lock the interferometer phase to the most sensitive point in the interferogram. In this configuration, large low-frequency movements of the sensor mirror can be detected from the control signal applied to the nanopositioner and high-frequency short-range signals can be measured directly from the photodiode. It is demonstrated that these two signals are complementary and can be summed to find the total displacement. The resulting interferometer has a number of desirable characteristics: it is optically simple, does not require polarization or modulation to detect the direction of motion, does not require fringe-counting or interpolation electronics, and has a bandwidth equal to that of the photodiode. Experimental results demonstrate the frequency response analysis of a high-speed positioning stage. The proposed instrument is ideal for measuring the frequency response of nanopositioners, electro-optical components, MEMs devices, ultrasonic devices, and sensors such as surface acoustic wave detectors.

Modelling and control of nitrogen partial pressure for prophylaxis and treatment of air embolism

This article describes a model for the absorption of a cerebral gas embolism. It is also shown that by controlling the ambient pressure and partial pressure of nitrogen, an air embolism can be absorbed at an accelerated rate. At ambient pressure, a breathing gas of 100% Oxygen will triple the rate of absorption. With an ambient pressure of 6 atmospheres, a 1-mm bubble is eliminated in 10 minutes instead of 12 hours.

Exposure Optimization in Scanning Laser Lithography

Scanning laser and probe-based exposure offers an attractive alternative to standard lithographic methods for prototyping and low volume production. As the speed of nanopositioning systems increases, these methods will become increasingly competitive. Simple devices can already be exposed in less than a second and current research aims to create millions of features in a similar time frame. This article focuses on the problem of finding an exposure pattern which optimizes the geometrical fidelity of the developed features. The solution is based on a nonlinear programming approach that can be solved with a gradient based method. By changing the beam profile function, this method is applicable to all forms of serial lithography including e-beam, probe-based, and scanning laser. Current research includes adapting the algorithm to handle images with a massive number of features and/or ultra-high resolution. It is also necessary to consider uncertainty in the optical and photoresist models, for example, variations in film thickness and photoresist constants, among others. Although technical challenges still exist, the development of this technology will dramatically improve access to a low-cost, ultrahigh resolution lithographic process. We hope that this will stimulate the development of new fabrication processes and myriad new technologies and devices that rely on them.

High sensitivity interferometer for on-axis detection of AFM cantilever deflection

A homodyne path stabilised Michelson based interferometer displacement sensor was developed. This sensor achieved a noise floor of 100 fm/√Hz, for frequencies higher than 100 KHz. A prototype AFM that integrated this sensor was developed. Using tapping mode, topography maps of an AFM test grid were produced.