Note: real time three-dimensional topography measurement of microfluidic devices with pillar structures using confocal microscope.

Miniature pillars are three-dimensional (3D) features commonly found in microfluidic device. These features are usually employed as filters. Non-confocal profilometers have difficulties in measuring 3D topography of pillar structures in transparent microfluidic devices. Confocal sensors can be used to measure the 3D topography of pillar structures but they are usually time consuming due to the scanning process. We have developed a technique to measure 3D topography using a modified confocal microscope with a spinning Nipkow disk and chromatic confocal technique. Experimental results on a microfluidic device with pillar structures demonstrate the feasibility of the proposed technique. Our technique is suitable for in situ, real time measurement of microfluidic device at production speed since it requires only one confocal image to complete a measurement.

Note: development of high speed confocal 3D profilometer.

A high-speed confocal 3D profilometer based on the chromatic confocal technology and spinning Nipkow disk technique has been developed and tested. It can measure a whole surface topography by taking only one image that requires less than 0.3 s. Surface height information is retrieved based on the ratios of red, green, and blue color information. A new vector projection technique has developed to enhance the vertical resolution of the measurement. The measurement accuracy of the prototype system has been verified via different test samples.

Method for real-time critical dimensions signature monitoring and control: sensor, actuator, and experimental results.

We present in this paper a system and method for real-time monitoring and control of critical dimensions (CD) signature profile in lithography. The proposed system involves the development and integration of a scatterometry system, a programmable multi-zone thermal processing system, and control system software. Based on scatterometry, the intensity and phase of the reflected light from the resist film are measured at a fixed incident angle and across multiple wavelengths. A programmable thermal processing system is then used to adjust the processing temperature during post-exposure baking in lithography to achieve the desired CD signature profile. Experimental results demonstrate the feasibility of the proposed approach. An improvement of CD signature control of 85% is achieved in terms of the mean square error with and without control.

Data compression for speckle correlation interferometry temporal fringe pattern analysis.

Temporal fringe pattern analysis is gaining prominence in speckle correlation interferometry, in particular for transient phenomena studies. This form of analysis, nevertheless, necessitates large data storage. Current compression schemes do not facilitate efficient data retrieval and may even result in important data loss. We describe a novel compression scheme that does not result in crucial data loss and allows for the efficient retrieval of data for temporal fringe analysis. In sample tests with digital speckle interferometry on fringe patterns of a plate and of a cantilever beam subjected to temporal phase and load evolution, respectively, we achieved a compression ratio of 1.6 without filtering out any data from discontinuous and low fringe modulation spatial points. By eliminating 38% of the data from discontinuous and low fringe modulation spatial points, we attained a significant compression ratio of 2.4.

Fourier-transform method of data compression and temporal fringe pattern analysis.

Temporal fringe pattern analysis is invaluable in studies of transient phenomena but necessitates large data storage for two essential sets of data, i.e., fringe pattern intensity and deformation phase. We describe a compression scheme based on the Fourier-transform method for temporal fringe data storage that permits retrieval of both the intensity and the deformation phase. When the scheme was used with simulated temporal wavefront interferometry intensity fringe patterns, a high compression ratio of 10.77 was achieved, with a significant useful data ratio of 0.859. The average root-mean-square error in phase value restored was a low 0.0015 rad. With simulated temporal speckle interferometry intensity fringe patterns, the important paremeters varied with the modulation cutoff value applied. For a zero modulation cutoff value, the ratio of data points and the compression ratio values obtained were roughly the same as in wavelength interferometry, albeit the average root-mean-square error in the phase value restored was far higher. By increasing the modulation cutoff value we attained significant reduction and increase in the ratio of data points and the compression ratio, respectively, whereas the average root-mean-square error in the restored phase values was reduced only slightly.

Temporal fringe pattern analysis with parallel computing.

Temporal fringe pattern analysis is invaluable in transient phenomena studies but necessitates long processing times. Here we describe a parallel computing strategy based on the single-program multiple-data model and hyperthreading processor technology to reduce the execution time. In a two-node cluster workstation configuration we found that execution periods were reduced by 1.6 times when four virtual processors were used. To allow even lower execution times with an increasing number of processors, the time allocated for data transfer, data read, and waiting should be minimized. Parallel computing is found here to present a feasible approach to reduce execution times in temporal fringe pattern analysis.