A coherence scanning tomographic imaging system with an innovative signal correction method is presented for a critical dimension (CD) measurement of thin film transistor liquid crystal display patterns having multiple focus positions within a single field of view. To facilitate the analyzing of coherence signals, a simulation model based on fast Fourier transform method is proposed, and its simulated result is compared with the coherence signals from the actual experiments. The comparison shows that the majority of frequency characteristics from simulation modeling results are matched with the experimental results. However, in many edge regions, discrepancies in frequency characteristics between the two results are observed. For the interpretation of signals, those are different from the simulation modelling, in that the intensity of its pixels has been corrected by an innovatively proposed connected neighborhoods window method with multiple window sizes. By using this combination of tomographic imaging and edge correction methods, the repeatability of the CD measurement of multiple focus position samples is significantly enhanced compared to the results with a plain two-dimensional optics. The proposed method is also compared with the autofocus methods including gradient magnitude method and frequency domain method and other tomographic imaging methods, including the phase shift method and the Hilbert transform method to show the advantages in the processing time.
We report a system for performing critical-dimension (CD) measurements of glass panels that uses a substepping system to generate a sequence of lower-resolution images and a fast, edge-directed image reconstruction algorithm to combine these images into a higher-resolution image. A large working distance and large aperture of microscope objective is required in glass panel manufacturing, to measure very small distances at high-level repeatability in a short time, which in turn allows only low magnification objectives. Low-resolution images are obtained when the camera of the CD measurement system is moved at step intervals smaller than the normal pixel size of the camera sensor. We propose a fast, edge-directed image registration (IR) algorithm to find the subpixel accuracy information for full-size images to be registered. The number of processed pixels is only about 5% to 10% of the number of pixels in the image, and the algorithm runs noniteratively. Thus, the subpixel IR algorithm is faster than other methods. In addition, a weighting calculation method for fast and robust edge-directed image interpolation algorithm is proposed to form a high-resolution image. Our experimental results prove that the proposed method offers faster processing time than the standard process and acceptable repeatability of CD measurements.
We report experimental studies on laser scribing of thin film solar cells using various types of short pulsed lasers
(nanosecond, picosecond, and femtosecond temporal pulse widths), aiming to determine the optimum laser parameters
for the scribing of multilayer structures of amorphous silicon (a-Si) and copper indium diselenide (CIS) based solar cells.
Detailed laser scribing parameters such as repetition rate of the laser pulses, scanning speed of the sample and laser
beam, individual pulse energy, laser wavelength, and direction of laser illumination (either from film side or from
substrate side) are examined. Characteristics of each scribing conditions are evaluated in terms of morphology by atomic
force microscopy (AFM) and scanning electron microscopy (SEM), chemical species analysis by Energy Dispersive X-ray
Spectroscopy (EDS), and electrical conductance of interconnects by conductive AFM (c-AFM) and contact
resistance measurement to determine the optimal laser scribing conditions. Further issues on defects in the films such as
re-deposited debris, elevated molten rim and delamination, thermal damage to surrounding and/or underlying layers and
inter-diffusion of materials at the interface are discussed on the basis of thermal/mass diffusion, thermal stress, and
ablation-induced plasma formation, in order to demonstrate an efficient laser scribing of P1/P2/P3 of thin film solar
cells.
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