Andreas Bich

Advanced mask aligner lithography: new illumination system

A new illumination system for mask aligner lithography is presented. The illumination system uses two subsequent microlens-based Köhler integrators. The second Köhler integrator is located in the Fourier plane of the first. The new illumination system uncouples the illumination light from the light source and provides excellent uniformity of the light irradiance and the angular spectrum. Spatial filtering allows to freely shape the angular spectrum to minimize diffraction effects in contact and proximity lithography. Telecentric illumination and ability to precisely control the illumination light allows to introduce resolution enhancement technologies (RET) like customized illumination, optical proximity correction (OPC) and source-mask optimization (SMO) in mask aligner lithography.

Fabrication and characterization of linear diffusers based on concave micro lens arrays

We present a new approach of beam homogenizing elements based on a statistical array of concave cylindrical microlens arrays. Those elements are used to diffuse light in only one direction and can be employed together with flys eye condensers to generate a uniform flat top line for high power coherent light sources. Conception, fabrication and characterization for such 1D diffusers are presented in this paper.

Multifunctional Micro-Optical Elements for Laser Beam Homogenizing and Beam Shaping

Refractive, diffractive and reflective micro-optical elements for laser beam shaping and homogenizing have been manufactured and tested. The presented multifunctional optical elements are used for shaping arbitrary laser beam profiles into a variety of geometries like, a homogeneous spot array or line pattern, a laser light sheet or flat-top intensity profiles. The resulting profiles are strongly influenced by the beam properties of the laser and by diffraction and interference effects at the micro-optical elements. We present general design rules for beam shaping and homogenizing. We demonstrate the application of such multifunctional micro-optical elements for a variety of applications from micro-laser machining to laser diagnostic systems.

Refractive statistical concave 1D diffusers for laser beam shaping

Certain high power laser applications require thin homogeneous laser lines. A possible concept to generate the necessary flat-top profile uses multi-aperture elements followed by a lens to recombine separated beamlets. Advantages of this concept are the independence from entrance intensity profile and achromaticity. However, the periodic structure and the overlapping of beamlets produce interference effects especially when highly coherent light is used. Random optical elements that diffuse only in one direction can reduce the contrast of the interference pattern. Losses due to undesired diffusion in large angles have to be minimized to maintain a good quality and high efficiency of beam shaping. We have fabricated diffusers made of fused silica for a wide range of wavelengths that diffuse only in one direction. Structures are based on an array of concave cylindrical microlenses with locally varying size and position following a well defined statistical distribution. The scattering angle can be influenced by process parameters and is typically between 1° and 60°. To predict the influence of process parameters on the optical properties, a simplified model for the fabrication process and geometrical optics have been used. Characterization of the fabricated devices was done by stylus measurements for the surface shapes, microinterferometry to measure phase profiles and high resolution goniometry to obtain far field distribution of light. The simulated data compare very well to measured optical properties. Based on our simulation tool we discuss limits of our fabrication method and optimal fabrication parameters.

Flexible beam shaping system using fly’s eye condenser

Normally, flys eye condensers are used to homogenize light. However, in the case of fully coherent light, a flys eye condenser, in connection with some simple optical elements, such as a diffractive axicon, a grating, and a telescope, can be used as a quite flexible beam shaping system, forming arrays of rings, parts of rings, or other structures with varying diameters. We present the principle, some simulation results, and some first experimental results.

Mask aligner process enhancement by spatial filtering

Mask Aligners are used in the Semiconductor Industry to transfer structures with moderate resolution requirements onto substrates. With the casting of the shadow a photochemical reactive resist is exposed. As diffraction appears at the mask structures the exposure wavelength and the proximity gap between mask and wafer influence the quality of the image in the resist. As both parameters are very often not changeable for processes there is a big need to find another way to improve the resist image. In this paper a new approach to enhance the exposure result will be presented. MO Exposure Optics, a novel illumination system for Mask Aligners, uses a combination of two microlens Köhler Integrators. MO Exposure Optics decouples the illumination system in a Mask Aligner from the lamp and ensures a uniform angular spectrum over the whole mask plane. Spatial filtering of the illumination light allows to reduce the diffraction effects at the mask structures and to improve the lithographic process in a Mask Aligner.

Shaping Light with MOEMS

Shaping light with microtechnology components has been possible for many years. The Texas Instruments digital micromirror device (DMD) and all types of adaptive optics systems are very sophisticated tools, well established and widely used. Here we present, however, two very dedicated systems, where one is an extremely simple MEMS-based tunable diffuser, while the second device is complex micromirror array with new capabilities for femtosecond laser pulse shaping. Showing the two systems right next to each other demonstrates the vast options and versatility of MOEMS for shaping light in the space and time domain.

Dynamically deformable reflective membrane for laser beam shaping and smoothing

We show a laser beam shaping device made of a deformable continuous reflective membrane fabricated over a scanning stage. The combination of two actuator schemes enables shaping and smoothing of a laser beam with a unique compact device. It is designed to shape an input laser beam into a flat top or Gaussian intensity profile, to support high optical load and to potentially reduce speckle contrast. One single electrode is needed to deform the whole membrane into multiple sub-reflecting concave elements. The scanning stage is used simultaneously to smooth out the remaining interference patterns. The fabrication process is based on SOI wafer and parylene refilling to enable the fabrication of a 100 % fill factor 5 by 5 mm2 deformable membrane. Applications for such device are laser machining and laser display.

Dynamically deformable micromirror array for defined laser beam shaping and homogenizing

We present a dynamic laser beam shaper than can generate smooth flat top and gaussian intensity profiles. It consists of a 100% fill factor membrane, supported by beams or posts, that deforms in a shape similar to a concave linear or 2D microlens array. The dynamic and tunable focal lengths allow to change the diffusion angle or to switch between flat top or gaussian output optical profiles. The whole array is fabricated over a rotating stage that enables the averaging of the interference effects caused by the array. Experiments showed that an angle of only 0.18° smooth the interferences to a contrast of 0.04. Optical simulations were performed to design the device. A first prototype using a magnetic scanner was tested to validate the simulations. Fabrication of the rotating stage and the membrane was accomplished using surface and bulk micromachining using parylene trench refilling.

Tunable optical diffusers for high-power laser applications based on magnetically actuated membranes

A dynamic laser beam shaper based on MEMS technology is presented. A magnetically actuated deformable single crystal silicon micromembrane is deformed in resonance to diffuse and homogenize laser beams. The large aperture mirror shows line generation with angles up to 1° and line smoothing capabilities. High power density handling is demonstrated up to 140 W/cm2.