Maskless photolithography was proposed to achieve the conventional and low-cost micro and nano fabrication, the pivotal of such technology was the application of digital micro-mirrors devices (DMD). Based on maskless photolithography, we designed a specific bifocal compound eyes (BCE) which made up of an array of two superimposed microlens. However, during our experiments, we found the existence of nonlinear relationships among gray levels, exposure intensity and development depths. To precise control the surface profiles, we did several tests and interpolations were used on the data we gathered. Finally, we ascertained the development depth of each grayscale, a gray mask was designed and filled to 1024*768 to fit the size of DMD.
Three-dimensional measurement and inspection is an area with growing needs and interests in many domains, such as integrated circuits (IC), medical cure, and chemistry. Among the methods, broadband light interferometry is widely utilized due to its large measurement range, noncontact and high precision. In this paper, we propose a spatial modulation depth-based method to retrieve the surface topography through analyzing the characteristics of both frequency and spatial domains in the interferogram. Due to the characteristics of spatial modulation depth, the technique could effectively suppress the negative influences caused by light fluctuations and external disturbance. Both theory and experiments are elaborated to confirm that the proposed method can greatly improve the measurement stability and sensitivity with high precision. This technique can achieve a superior robustness with the potential to be applied in online topography measurement.
White-light scanning interferometry plays an important role in precise profile metrology of microstructure. However, applying this approach may also be limited because of the optical reflection behavior of the surface. While there is a thin film on the surface, the reflection behavior of top and bottom of the thin-film will cause severer phase errors. Recently, the method by combining both reflectometry and white-light scanning interferometry is proposed to measure the film thickness and surface profile. This article firstly explains the principle of the proposed method and then verifies the feasibility of the thickness-measurement method for transparent film on a Silicon surface. Both of the algorithm and the experiment system have been optimized to measure the film thickness with high precision.
Dimensional metrology for micro structure plays an important role in addressing quality issues and observing the performance of micro-fabricated products. Different from the traditional white-light interferometry approach, the modulation-based method is expected to measure topography of micro structure by the obtained modulation of each interferometry image. Through seeking the maximum modulation of every pixel respectively in Z direction, the method could obtain the corresponding height of individual pixel and finally get topography of the structure. Owing to the characteristic of modulation, the proposed method which is not influenced by the change of background light intensity caused by instable light source and different reflection index of the structure could be widely applied with high stability. The paper both illustrates the principle of this novel method and conducts the experiment to verify the feasibility.
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