Lighting solutions with colored LEDs provide many opportunities for illumination. One of these opportunities is to
create a color tunable light source. In this way different kinds of white light (color temperature) as well as discrete colors
may be realized. This opens the field for applications as mood lighting.
But there is always a spatial separation of the distinct LEDs that might get converted into an angular separation by any
collimating optics. This angular separation causes such problems like color fringes and colored shadows that cannot be
accepted in most applications. Conventional methods to solve these problems include e.g. mixing rods or dichroic filters.
A new approach is the use of the dispersive effect of a diffractive structure to compensate the angular separation of the
different colors.
In this contribution the potential and limitations of diffractive structures in LED color mixing applications are discussed.
Ray tracing simulations were performed to analyze such important parameters like efficiency, color performance and the
cross section of the color mixing optics. New means for the estimation of color mixing performance were developed. A
software tool makes it possible to detect the color distribution within ray trace data and it provides a quality factor to
estimate the color mixing performance. It can be shown that the spectral band width has a large influence on the mixing
process.
Ray tracing simulations are compared with results of an experimental setup such that both measured as well as simulated
data is presented.
The analysis of scattered light is a well known method for the inspection of very smooth surfaces. Some new methods of data analysis have now widened its utilization to rough and very rough surfaces. Even if no generalized solutionis available it is possible to determine any surface parameter in certain applications. Especially for process control purposes, scatterometry can be a fast, contactless and reliable method to measure deviations form rated values and to detect machining errors. In this paper, the method and its application to honed, polished and turned surfaces are presented. Amplitude as well as spatial parameters of the surfaces microtopography will be determined and compared to those obtained by other methods.
Optical scatterometry, defined as the characterization of surfaces via diffracted light analysis, has been shown to be an attractive tool for the metrology of microlithographic structures. To tackle the inverse scattering problem, advanced data analysis schemes have been developed. This paper illustrates the application of light scattering to characterize developed resist lines in terms of multi- parameter measurements. Additionally, the depth prediction and the width prediction of special silicon concentration profiles, embedded in a plane resist layer, are reported. Substantial accuracy gains have been achieved by using partial least squares (PLS) regression along with quasi- nonlinear data preparation techniques, including range splitting or enhanced quadratic and cubic approaches. Moreover, a combination of PLS and minimum mean square error methods enables rapid and nearly arbitrarily accurate measurements.
Angle resolved light scatterometry along with advanced data analysis is a promising new metrology technique to meet the challenges of today's and tomorrow's submicron technology. The measurement accuracy strongly depends on the performance capabilities of the algorithms utilized for data exploration and analysis. Presently, multivariate regression methods such as inverse least squares and principal component approaches are preferred. Substantial accuracy gains may be achieved by applying quasi-nonlinear methods, i.e. nonlinear data pretreatment followed by the usual linear regression. In this way, not only were the linewidth prediction errors in measuring developed resist lines pushed to below 20 nm, but likewise more complicated tasks such as silylation profile evaluation and latent image measurement could be addressed satisfactorily.
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