George O. Reynolds

A Concept For A High Resolution Optical Lithographic System For Producing One-Half Micron Linewidths

This paper describes a concept for developing an optical printer having a one-half micron linewidth capability to meet the pro-jected needs of future Integrated Circuit (IC) production facilities. Our approach for meeting this objective is to combine the appro-priate features of the current 1:1 reflective optical printers with the stepping characteristic of the 10:1 refractive optical systems. The proposed, very deep, UV step and repeat system has the potential of reaching a one-half micron linewidth production goal entirely with optical technology. The key subsystem elements necessary to achieve these goals are discussed. These subsystems include a reflective optical system, a 10:1 stepper configuration having a linearity limit of 0.5 microns and an FOV of 15 mm, a deep UV laser source, photoresists having the required sensitivity, an alignment capability of 500 Å , a focal sensor having a 500 Å tolerance and the associated mechanical, electronic and environmental controls compatible with a produc-tion throughput of 60-four inch wafers/hour.

A Review Of Partially-Filled, Synthetic-Aperture, Imaging Systems

Large optical apertures can be synthesized by utilizing a phased array of smaller elements. The phasing is realized by ensuring that the individual elements are made from the same lens or mirror and properly positioned. The synthesis of MTF for various geometrical arrays (Cross, Covington-Drane, Golay Six, Thin Annulus, etc.) of such partially filled apertures has been demonstrated experimentally with incoherent illumination. Post processing techniques were used to remove the deleterious effect in the image due to auto-correlation of the individual elements. The results demonstrated that the resolution of the equivalent full aperture is achievable by the MTF synthesis which arises from cross correlation of the various elements. The limitations due to misalignment of the various elements in six degrees of freedom were investigated theoretically, and experimentally verified for both refractive and reflective elements. The experimental verification of these tolerances required interferometric measurements in the focal plane. Systems Analysis showed that the aperture must be designed so that the synthesized MTF has a modulation higher than the detector noise threshold at all spatial frequencies (AIM curve). In general, the technique does not work unless the radiation is spatially incoherent. To illustrate this, experiments were performed with laser illumination. The aperture did not synthesize unless the laser was rendered incoherent by utilizing moving diffusers or scanning techniques. Synthesis with laser illumination was achieved in a non-partially filled mode by phasing with holographic arrays. Finally, some experimental results on super-resolving pupils are shown and discussed.

Phase Measurements With Image Holography

Phase compensation of an aberrating medium can be achieved with image holography and a rotating diffuser in the recon-struction beam to average speckle noise. We show that the image hologram can also be used in the object plane to achieve the same result. Both amplitude and phase holograms can be used in these experiments. The results were achieved with a three-dimensional phase aberration so that longitudinal magnification and depth-of-focus effects limited the quality of the reconstructed image. With three-dimensional aberrators, one must be careful of the exact location of the image plane when recording the hologram and its placement in the reconstruction process.

Holographic Fringe Linearization Interferometry (FLI) For Defect Detection: Part II - Comparison Of Observation With Prediction

We present results from our program on fringe linearization for double exposure holographic interferometry for the detection of defects in large areas of metal structures. A model is developed to simulate the expected holographic results, and its predictions are compared to the observations as an aid in refining this nondestructive evaluation procedure. The test specimens are aluminum plates containing circular holes and supported on three sides. Between holographic images a bending moment is applied across the hole. The specimens contain either a through cut or a part-through cut designed to approximate through and part-through cracks respectively. The interference holograms are created by double exposure. Between the first and second exposures the bending moment is applied, and the incident beam is rotated creating fringes which result from specimen deformation and beam rotation. The degree of beam rotation controls the extent to which the fringes are linearized. The supporting finite element modeling and analysis is performed using the ANSYS computer code and plate elements. Fringe linearization is accomplished by adding a rigid body deformation to the deformation field. We will discuss the excellent agreement between experimental FLI results and the finite element predictions for the case of a specimen with a part-through crack in the back surface and not optically visible.

Holographic Fringe Linearization Interferometry (FLI) For Defect Detection Part I The Basic Concept

In normal double exposure holography with impulse loading it is very difficult to locate defects because the fringe clutter, due to random motion between exposures, often swamps the fringe shifts caused by the presence of sub-surface defects (cracks, debonds, etc.). We attempted to simplify the defect location problem by developing a concept more amenable to automatic readout techniques. Our approach to incorporate this change is quite simple. We swing the object beam between the two exposures which adds a linear fringe to the reconstructed image. Proper selection of the fringe frequency (angle of object beam swing) and the loading force creates a recon-structed image laced with linear fringes with fringe shifts at the defect locations which are highly visible. We will describe the theory of the process. Experiments performed with a static load illustrate that the defect is seen as fringe shifts on a linear carrier. Both through cuts and rear surface cuts in a metal test plate were used to simulate defects. We further show that the defects have characteristic Fourier signatures different from those of the carrier.

Holographic Fringe Linearization Interferometry (Fli) For Defect Detection Part Iii Load Desensitization With Moire Techniques

Holographic FLI technique provides a means of reducing fringe clutter noise. Holographic interferometry measures position changes of the order of the wavelength of the light used. Moire techniques provide a means of desensitizing holographic interferometry. Moire techniques may be employed with FLI with the objective of automating the defect detection process. It may be necessary to employ a spatial frequency filtering step to remove fringe clutter noise.

Novel Image Duplication Technique Utilizing Fourier Optics

In the normal process of duplicating Photographic images from original negatives, resolutions of 200 cycles/mm have been neasured. lie will present a new duplication technique which has the capability of reducing this resolution loss to a few Percent at resolutions between 300 and 500 cycles/mm while simultaneously maintaining the continuous-tone quality and dynamic range of the original. The technique creates a modulated phase image dupe which produces a high resolution, continuous-tone, speckle free, image when observed through a white light Fourier optical viewing system. Plastic phase relief images with 70mm formats were made by this technique. Resolution transfers of nearly 100% at 228 cycles/mm were measured in images having excellent continuous-tone quality. The dynamic range of the retrieved images is comparable with that achieved in conventional photographic duplicates. Diffraction efficiencies greater than 20% in one diffracted order of the viewing system were also measured in the system.