Silicon-on-Insulator (SOI) has emerged as promising material choice for various integrated optoelectronic devices. Two
issues make SOI attractive for complex optical systems: the cost reduction due to compatibility with CMOS technology
and high refractive index contrast between core and cladding, which is an important property for good confinement of
light and efficient guiding and coupling in sub-micron waveguides. However, for those devices that are intended to be
part of broadband optical networks, for example multiplexers and de-multiplexers, it is desirable to demonstrate a high
selectivity and a tunable response. Thus, it is necessary to provide wavelength selective elements with the ability to filter
input data streams producing a large Free Spectral Range (FSR), a small Full Width at Half Maximum (FWHM), and a
high quality factor (Q), all conditions set by communication standards. Owing to the generic and adaptable operation,
ring-resonator-types of filters in SOI are often considered as candidates to meet these demands. Herein two different
designs are investigated from both experimental and modelling standpoints in order to tailor the filter transfer function.
These are mutually coupled (Vernier) resonators and cascaded resonators based on small SOI photonic wires. Fabricated
filters designed to provide a large FSR and a polarisation independent (PI) response are analysed and improvements
proposed. Issues associated with temperature control of the transfer function have also been addressed.
The transfer function of a photonic filter is significantly influenced by the profile of the waveguides forming the device. In this work we discuss requirements for devices based on two geometries, rib and wire shaped waveguides in Silicon-on-Insulator, from both the modal and polarisation standpoints. General guidelines and recommendations for the design of single-mode and polarisation-independent ring resonator filters with large Free Spectral Range (>30nm) are given, together with supportive experimental results.
We report Photonic Crystal (PhC) designs fabricated in silicon-on-insulator wafers (SOI) using 248 nm & 193 nm DUV lithography. Emphasis was on demonstrating unique PhC effects through the use of standard CMOS equpiment and process development of an optical test chip using a high-volume manufacturing facility. Most of the planar 2-D PhCs waveguides were designed using a triangular lattice of holes. An extensive range of test structures were also designed, including W1 and W3 waveguides in both triangular and square lattices. The use of optical proximity correction (OPC) and variations of pitch and hole dimensions allowed for a large design-of-experiment not practical using the more conventional e-beam direct-write approach. Smart Cut SOI wafers with a thin epitaxial Si layer on a 2μm buried SiO2 layer were first processed and characterized using 248 nm lithography. Preliminary pitch/hole patterning requirements were 400nm/200nm. Resist was changed from high- to low-contrast resist to compensate for the high sensitivity of critical hole dimension to exposure dose. Optical characterization data of PhC test structures were used to map band structure calculations and more accurately determine the PhC effective index; results were used to model more accurate pitch/hole values. Successful processing results were also obtained using 193nm lithography to resolve PhC pitch/hole dimensions of ~280/180nm. Optical characterization data are being used to refine next-generation PhC designs.
The bulk stability of the lens material in Deep-UV lithography (Fused Silica and Calcium Fluoride), as well as the susceptibility of the lens anti-reflection coating to a thin layer of chemical contamination during laser irradiation over long period of time, are the keys for advanced lithography systems lifetime.
Lens degradation impacts laser-based exposure systems’ performance and therefore affects the product quality. There is a need for careful monitoring and prediction of lens lifetimes. This paper describes a method to calculate the degradation rate of optics and the lifetime prediction of these systems, along with some possible mechanisms for imaging degradation and factors that accelerate the degradation process. Currently, 'Pulse count' methods are used for such calculation; here we describe a new 'Energy based' method equal to 'Cumulative energy' through the projection lens. The paper compares the two methods using actual cases and shows the benefits of using the proposed method. We also suggest some new ways to deal with the problem. In addition, we report the learning from a project which entails developing a software application for automatic continuous tracking of degradation rates as well as the lens lifetime prediction across all Intel's laser based lithography tools.
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