Showing papers on "Aerial image published in 1989"

Focus and overlay characterization and optimization for photolithographic exposure

Abstract: The focus and overlay alignment of photolithographic exposure tools of the type wherein the location of the wafer is accurately tracked with respect to a baseline position, such as in step and repeat cameras, are evaluated by monitoring the output signal generated by a photodetector in response to the light radiated from one or more periodic test patterns carried by a re-useable calibration wafer while such a test pattern is being exposed to an aerial image of a matching calibration mask. Overlay alignment suitably is evaluated by stepping the pattern on the wafer from side-to-side and fore and aft of the aerial image while monitoring the photodetector for a peak output signal, whereby overlay alignment errors along the x-axis and y-axis of the exposure tool are determined by the displacement of the wafer positions at which such peak signals are detected from the positions at which such peak signals ae expected. Focus, on the other hand, suitably is evaluated by incrementally defocusing the imaging optics of the exposure tool while monitoring the rms width of the output signal generated by the photodetector as the wafer pattern is stepped through the aerial image of the calibration mask at each focal setting. The best focal setting minimizes the rms width of the output signal.

Automating knowledge acquisition for aerial image interpretation

Abstract: The interpretation of aerial imagery requires substantial knowledge about the scene under consideration. Knowledge about the type of scene-airport, suburban housing development, urban city-aids in low-level and intermediate level image analysis and will drive high-level interpretation by constraining search for plausible consistent scene models. Collecting and representing large knowledge bases requires specialized tools. In this paper we describe the organization of a set of tools for interactive knowledge acquisition of scene primitives and spatial constraints for interpretation of aerial imagery. These tools include a user interface for interactive knowledge acquisition, an automated knowledge compiler that transforms schemabased assertions into productions that are directly executable by our interpretation system, and a performance analysis tool that generates a critique of the final interpretation. The generality of these tools is demonstrated by the generation of rules for a new task, suburban house scenes, and the analysis of a set of imagery by our interpretation system.

Scene registration in aerial image analysis

Abstract: In this paper we discuss the importance of scene registration for several tasks in the automated interpretation of aerial imagery. These tasks are structure matching, stereo matching, and stereo visualization. While the processes of registration and matching have traditionally been treated as separate problems, particularly in the case of stereo matching, we describe techniques that may unify these processes. We also demonstrate the automatic generation and matching of control points in complex aerial imagery and show that the resulting registration is comparable to that achieved using manual control point selection. Finally, methods for the generation and visualization of stereo disparity images and stereo ground truth scene segmentations are described.

Scene Registration In Aerial Image Analysis

Abstract: In this paper we discuss the importance of scene registration for several tasks in the automated interpretation of aerial imagery. These tasks are structure matching, stereo matching, and stereo visualization. While the process of registration and matching has traditionally been treated as separate problems, particularily in the case of stereo matching, we describe techniques that may unify these processes.

Understanding Focus Effects In Submicron Optical Lithography, Part 2: Photoresist Effects

Abstract: In a previous study [1] a new method was developed to describe the effects of defocus on an optical lithographic process. The interaction of the aerial image with the photoresist was described mathematically in order to determine the features of the image which are important in determining lithographic performance. The slope of the log-image was determined to be an appropriate metric of aerial image quality. By calculating this log-slope as a function of defocus, rigorous definitions of both depth-of-focus ( DOF) and resolution were given. The DOF, for a given feature size, can be defined as the amount of defocus for which the log-slope of the aerial image remains above some minimum value. The minimum value of the log-slope which gives acceptable process latitude is determined by the properties of the photoresist process. This paper discusses the important properties of a photoresist and how these properties affect DOF. The primary parameter lithography model PROLITH [2] is used to investigate how various process parameters change the response of the lithographic system to focus. The results are compared to the log-slope defocus curve to determine the minimum acceptable log-slope for the modeled system. Finally, experimental linewidth data was collected as a function of focus and exposure using electrical linewidth measurement techniques. This data is compared with both the modeled data and the log-slope analysis.

A Simple And Calibratable Method For The Determination Of Optimal Focus

Abstract: Achieving a proper focus setting in sub-micron optical lithography is extremely important A technique has been developed for the determination of optimal focus setting on production lots Using aerial image simulation the dimensions of the test structure studied have been optimized With a simple optical microscope a judgement can be made about the focus setting As the depth of focus becomes comparable to the resist thickness, it was observed that different methods of focus determination do not give the same results

ANKAN : Simulator for Resist Exposure and Etching

Abstract: In this paper, we report the results of ANKAN, a computer program written for the exposure and development of positive photoresist using matrix formulation. Exposure process is modelled using diffraction limited optics and partially coherent light source with a wavelength λ. The program uses string model for resist development. The results of theoretical computations are reported and are found to be in good agreement with those of previous workers. In addition, the program can also be used for computing edge threshold for linewidth measurement and predicting the shape of aerial image for two dimensional objects.

Focus Effects In Submicron Optical Lithography, Optical And Photoresist Effects

Abstract: This paper gives a review of previous work [1-3] describing a new method to characterize the effects of defocus on an optical lithographic process. The interaction of the aerial image with the photoresist is described mathematically in order to determine the features of the image which are important in determining lithographic performance. The slope of the log-image is determined to be an appropriate metric of aerial image quality. By calculating this log-slope as a function of defocus, rigorous definitions of both depth-of-focus (DOF) and resolution are given. The DOF, for a given feature size, can be defined as the amount of defocus for which the log-slope of the aerial image remains above some minimum value. The minimum value of the log-slope which gives acceptable process latitude is determined by the properties of the photoresist process. The primary parameter lithography model PROLITH [4] is used to investigate how various process parameters change the response of the lithographic system to focus. The results are compared to the log-slope defocus curve to determine the minimum acceptable log-slope for the modeled system. Finally, experimental linewidth data was collected as a function of focus and exposure using electrical linewidth measurement techniques. This data is compared with both the modeled data and the log-slope analysis.

An Analytical Model For The Aerial Image Simulation Of 2-D Mask Structures. Optimization Of The ODB Tapering Method

Abstract: An analytical model for 2-D non periodic aerial image simulation is proposed for rectangular and circular mask structures. As applications we demonstrate that better resolution in contact opening is acheivable if near circular pattern are designed at mask level. Examples of optimized aerial image for ODB tapering method are shown. Influence of defects on the reticle are considered.

Grating Moire Effects With Partially Coherent Illumination And Detection

Abstract: We present an analysis of the imaging of a linear grating with an extended illuminating source and of the moire effect with a second grating in the image plane. The light transmitted by the moire grating is captured by a detector with finite angular extent. The amplitude and the phase shift of the moire signal are calculated in the presence of both symmetrical and asymmetrical aberrations of the imaging lens; the influence of both the source and the detector size are taken into account. A comparison is made between the axial and transverse position of imaged features (e.g. the position of an imaged edge) and the position of the grating as predicted by the phase and the maximum modulation depth of the moire signal. The offset between the aerial image position and the detected grating position should be known when one uses the moire signal for the testing of the lens in a lithographic projection system. Numerically calculated values of this offset are given for a number of practical situations.

Focusing display device for optical equipment of camera or the like

Abstract: PURPOSE:To confirm an object image at the time of focus matching by providing a liquid crystal plate which has dynamic light scattering effect to a finder optical system and changing the liquid crystal plate from a 1st state to a 2nd state with a focus matching detection signal. CONSTITUTION:When a photographic lens 39 is moved for focusing, a light measurement optical system operates correspondingly to change light incident on a focus sensor 36, which sends a distance measurement information signal to an arithmetic circuit 37. The liquid crystal plate 33 forms a map surface by being fed with electricity from a drive circuit 38 until the circuit 37 judges the point of time of focus matching, so an object image formed on the liquid crystal plate 33 can be observed through a finder. When the circuit 37 judges the focus matching, the movement of the lens 39 is stopped according to the output signal and the circuit 38 stops feeding the electricity to the liquid crystal plate 33. Consequently, the liquid crystal plate 33 becomes transparent to display the state of the focus matching. In this case, an aerial image of the object can be observed through the finger.