Showing papers on "Depth of focus published in 1995"

Optical disk pickup device with focusing correction by electrostriction

Abstract: An optical pickup is adapted for recording and/or reproducing signals by radiating a light beam from a light source on an optical recording medium via an object lens. The optical pickup includes a light receiving device for receiving a return light from the optical recording medium, and a focusing error detecting unit for detecting an amount of deviation of the focal point along the optical axis. The measurement of a focusing error is based on signals from the light receiving device. The optical pickup further includes an electrostriction device arranged on a path of light outgoing from the light source to the optical recording medium and having a central section and a peripheral section exhibiting a phase difference from each other depending on an applied voltage. Focusing errors may be detected with high accuracy with the optical pickup. A focusing servo device compensates for the focusing error detected by controlling the focal point along the optical axis using a focusing servo device. Depending on error detection signals from the focusing error detection unit, a rough servo is carried out by an the object lens driving unit to the vicinity of the depth of focus, and a fine servo is carried out by the electrostriction device within the range of the depth of focus.

Feasibility study of photocathode electron projection lithography

Abstract: Photocathode electron projection is an electron lithography technique that may be used to pattern semiconductors at the deep submicron level. Using a robust gold cathode, mask features in the range of 0.11–0.54 μm have been transferred to electron resist coated wafers with adequate depth of focus (≂5 μm) and large field of view (≂2 cm2). Low accelerating voltages ∼3 keV minimize proximity effects, and with a mask to wafer spacing of a few millimeters, the necessary magnetic field is ≂0.46 T.

Multi-focus ultrasound lens

Abstract: The focal length of an acoustic ultrasound transducer is made variable by shaping the focusing element positioned over the transducer. The focusing means consists of a non-uniform focusing element whereby the transducer can be manipulated either electronically or mechanically to optimize the depth of focus for the area of interest.

Method and device for working materials using plasma-inducing laser radiation

Abstract: The invention concerns a method of working materials by means of plasma-inducing high-energy radiation, in particular laser radiation, the method calling for radiation originating in the region of the workpiece (10) to be viewed along the axis (4) of the laser radiation (12) focussed on the workpiece (10) as a function of time. In order to obtain a measure of the depth of penetration of the vapour capillary (13) into the workpiece (10), only the vapour-capillary cross-section is observed with a depth of focus covering the whole thickness (14) of the workpiece and the mean value of the intensity of the plasma radiation is used as a measure of the penetration depth.

Scanning probe microscope

Abstract: PURPOSE: To obtain a scanning probe microscope which can be aligned automatically by a method wherein an image is formed in a setting position which has been focused by an autofocus mechanism and the interval between a sample and a probe at this time is used as a setting distance CONSTITUTION: A sample 1, a probe 2 and an optical microscope 3 which is equipped with an autofocus function are set Then, when a part of the probe 2 (or the sample 1) is focused by the autofocus mechanism of the microscope 3, the image of the probe 2 is formed in the image of the microscope 3 Then, when the focal position of the microscope 3 is set in a setting position which is away by a setting distance from a focus A, the probe 3 on the position of the focus A is contained within the range of its depth of focus Then, a movement mechanism which is constituted of a sample raising-and-lowering mechanism 4, a control device 6, a driving gear 7 and the like is driven, and the sample 1 is moved to the focal position which has been aligned with the setting position Thereby, the sample 1 and the probe 2 are contained inside the depth of focus of the microscope 3, both the image of the probe 1 on the focus A and the image of the sample 1 on a focus B are formed in the image of the microscope 3, and both can be observed clearly

Multispot polygon ROS with maximized line separation depth of focus

Abstract: An apparatus for improving the depth of focus in a raster output scanner (ROS), and more particularly to a system for maximizing the line separation depth of focus of a multispot ROS while maintaining the system common depth of focus. The apparatus comprises: a source of at least two light beams (A,B; Fig. 1); a scanning polygon mirror having at least one facet (92); pre-scanning optics including a collimator (84), an aperture (86) and a cross-scan cylinder lens (88); and post-scanning optics including a dual element (94a,94b) f-theta scan lens (94) and a wobble correcting element. In a preferred design for a ROS-based system, the system common depth of focus (system common DOF) is maximized, where the system common DOF is characterized as the depth-of-focus over which all performance parameters are met. The optical system design achieves a desirable system common DOF while maintaining a line separation of 127 µm (1/200 inch).

Subquarter micron optical lithography with practical superresolution technique

Abstract: Practical resolution, which is defined as the minimum geometry for a 1.0 micrometers depth of focus, in conventional krypton fluoride (KrF) excimer laser (248 nm) lithography is 0.30 micrometers . A new illumination technique, which uses a weak quadruple effect to enhance the depth of focus and to solve the current problems in the off-axis illumination techniques, has been developed. This new illumination technique is suitable for use with the attenuated phase shifting mask. With this combination technique, a 1.8 micrometers depth of focus using a 0.45 NA KrF excimer laser stepper can be achieved without a secondary peak in the distribution of light intensity for the various duties 0.30 micrometers space patterns. Even for hole patterns, a 2.0 micrometers common depth of focus can be achieved. These results indicate that KrF excimer laser lithography is a powerful candidate for beyond 0.25 micrometers -rule devices. It is also confirmed that i-line lithography is an expectable candidate for the second generation of 0.35 micrometers -rule devices.

Study of optical proximity effects using off-axis illumination with attenuated phase shift mask

Abstract: The global proximity effects of densed line, semi-isolated line are studied for conventional illumination, off-axis illumination, and finally off-axis illumination in combination with attenuated phase shift masks which have transmittance of 4% and 8%, respectively, by experiments and simulations. To analyze the behavior of proximity effects, the lithographic performances of the super resolution technique are investigated comparing the cross-sectional view of resist pattern profile, useful depth of focus, and the curves of linewidth vs. defocus for 0.30 micrometers , 0.35 micrometers , and 0.40 micrometers pattern size, respectively. The global proximity effect is quantitatively analyzed by fitting the curve for densed line and isolated line to 2nd order polynomials. Off- axis illumination with attenuated phase shift mask is very effective to minimize the proximity effects for the pattern size less than 0.40 micrometers , and have useful depth of focus of 1.0 micrometers for 0.30 micrometers patterns.

Camera having a depth priority operation mode

Abstract: A camera having a depth priority operation mode calculates a stop value and perform photography such that multiple objects at different distances all enter into the photographic depth of field. When the calculated stop value is less than the smallest possible stop value of a photographic lens attached to the camera, the photographic lens is driven so that the closest object is placed on the photographic lens side of the focal surface, when the closest object is focused into the photographic depth of field.

Camera including a zoom lens having simultaneous focusing and zooming

Abstract: A camera having a zoom lens in which the zoom lens includes: first and second lens components for focusing the light from an object on the focal plane; a lens barrel for guiding movements of the first and the second lens components, in which the lens barrel includes a first guide portion for guiding movement of the first lens component and a second guide portion for guiding movement of the second lens component; and a moving driver for moving the first lens component along the first guide portion and for moving the second lens component along the second guide portion so that the first and the second lens components focus the light on the focal plane at plural focal lengths, and a focal point adjustment, including focusing and focusing compensation, is conducted continuously from the first focal length to the second focal length of the plural focal lengths.

Atomic contrast transfer in annular darkfield images

Abstract: SUMMARY We examine some of the assumptions underlying the standard optical equation as used for modelling high-resolution annular darkfield (Z-contrast) images of thin specimens. The validity of the approximations (i) that scattering occurs as spherical waves (atoms are point potentials) and (ii) that the depth of focus is infinite is found to be resolution-dependent. The correction to the optical equation for non-spherical wave scattering is found to be important when the probe size is of the order of 0·1 nm or smaller, and does not vanish in the ideal case of a large annular detector with no hole. Depth of focus becomes an important consideration at 100 kV for probes smaller than about 0·2 nm when the specimen thickness exceeds 10 nm. Both corrections can significantly degrade the effective point-to-point resolution of high-resolution Z-contrast images relative to that predicted by the standard optical equation.

LED printbars with depth of focus enhancement

Abstract: A printbar assembly comprised of an array of light emitters, and array of gradient index lenses, and a light control film. The light control film, which is comprised of a plurality of microlouvers, is disposed such that it limits the angle at which light from the light emitters can enter the gradient index lenses. The light control film increases the depth of focus of the gradient index lens array without significantly reducing the effective radiometric efficiency.

Depth of Focus

Abstract: The effect of focus on a projection lithography system (such as a stepper) is a critical part of understanding and controlling a lithographic process As feature sizes decrease, their sensitivity to focus errors increases dramatically Many people would say that this focus sensitivity is the main limitation of the use of optical lithography for smaller and smaller features This column will address the importance of focus by providing a definition of depth of focus

Automatic focus device

Abstract: PURPOSE: To fast perform the automatic focus control of a TV camera. CONSTITUTION: This device includes at least an evaluation value calculation part which extracts the horizontal frequency component out of a specific image area of the image signal received from an image pickup device, a signal processing part which calculates the control value to control a photographic lens drive part of the image pickup device in response to the evaluation value calculated by the evaluation value calculation part, and an output part which sends the calculated control part to the photographic lens drive part. Then the evaluation value is calculated while the focal position of a photographic lens 30 is moved, and the focal point of the lens 30 is moved by a prescribed multiple of depth of focus from the point where the maximum evaluation value is obtained. The evaluation value of this moved position is compared with the maximum evaluation value. When the former value is smaller than the latter value, the latter value is defined as an in-focus point. Then the position of the lens 30 is controlled and set at the in-focus point. COPYRIGHT: (C)1997,JPO

Depth of focus and the moment expansion.

Abstract: We introduce the so-called moment expansion of a defocused image as a tool for analyzing and improving the depth of focus in optical imaging. It is shown that a number of previously noted defocus phenomena can be readily derived or explained in terms of moment expansion. Some potential applications of the moment expansion to phase-shifting mask and pupil filter design for optical lithography are also briefly noted.

Optical system with reduced focus spot size

Abstract: A toroidal lens has a first surface comprised of a convex curve rotated about a central axis and a second surface comprised of a concave curve rotated about the central axis. The toroidal lens receives a radiation beam and produces an annular or halo shaped radiation beam. This resulting annular beam is focussed by a focussing lens to a reduced focus spot size without sacrificing depth of focus.

Image processing method for microscope

Abstract: PROBLEM TO BE SOLVED: To improve the depth of focus by a sufficient increase in focal length and to obtain a sharp image of the whole sample by processing an integrated image of plural microscope images which differ from each other in focus position by Fourier transformation and finding a two-dimensional spectrum, and processing the two-dimensional spectrum after higher harmonic emphasis by inverse Fourier transformation and finding a microscope image subjected to higher harmonic emphasis. SOLUTION: The optical microscope consists of an optical microscope 1, an image pickup means 2, a sample stage 3, a sample stage control means 4, an image processing means 5, and a display means 6. The image processing means 5 outputs a stage driving signal to the sample stage control means 4 to control the movement of the sample stage 3 and the input of an image signal. And, the microscope images which differ from each other focus position are integrated by image processing to find the integrated image, which is processed by Fourier transformation to find the two-dimensional spectrum; and the higher harmonic components of the found two-dimensional spectrum are emphasized and the higher-harmonic-emphasized two-dimensional spectrum is processed by inverse Fourier transformation to find the higher-harmonic-emphasized microscope image.

Point spread function and coherent line response in optical systems with non-uniform transmission pupils: application to photolithography

Abstract: The three-dimensional (3D) coherent line and the 3D point response functions of optical systems with non-uniform pupils are discussed for possible applications of these filters in photolithography. In this case, filters that are hyper-resolving in the transverse direction and apodizing in the axial direction are of special interest. For both line- and point-like objects, we analyse the resulting image intensities and show that the resolution, the heights of the side lobes (pseudostructures) and the depth of focus differ in dependence on the pupil filter.

Optical device for condensing and optical additive device to be added thereto as well as measuring apparatus using the same

Abstract: PURPOSE:To expand an effective range of depth of focus by providing the optical device with a phase control means for dividing a luminous flux to an inner disk-shaped part and an outer ring band part and imparting a specific phase difference to the light beams transmitted respectively through these parts. CONSTITUTION:For example, a vapor deposited thin film 2 is added to the disk-shaped central part which is enclosed by a radius (r) (r=a/2 ) of a lens system 1 for condensing having an exit pupil of a radius (a) and allows the transmission of >=50% of total incident energy in such a manner that the phase difference of half the wavelength is generated in the light passing the central part and the peripheral ring band part. The total sum of the amplitude of the part where the phase difference is given and the part where the phase difference is not given acts to negate each other in the position of the focus F and, therefore, the concentration of the light at the focus F attenuates. On the other hand, the ring band phase difference generated by the misalignment of the focus and the phase difference given by the vapor deposited thin film 2 act to negate each other at the point D deviated by 2f lambda/a the optical axis direction from the focus of this optical system and the diffractecl light distribution as if the focus moves to the point D is generated.

Automatic focus adjusting device

Abstract: PURPOSE:To obtain an automatic focus adjusting device capable of an effective focusing operation by enabling a high speed focusing and also reducing power consumption accompanied with the focusing operation. CONSTITUTION:This device has a photographic system having a diaphram means mounting selectively plural apertures and one aperture in an optical path with a diaphram changeover means 9, a photoelectric converting element 2 and a focus lens driving means 8 and performs the focusing operation by setting previously conditions relating to a photographing at the time of performing the focus detection of the photographic system while using two focus detecting systems in the order of, so-called, an autocorrelation system and a mountain climbing system and by using the signal based on the focusing operation with only the autocorrelation system when the conditions are satisfied. The conditions are values relating to a focus distance, stop values, the depth of focus and also a high speed mode changeover switch 13.

Four-mirror imaging system (magnification +1/5) for ArF excimer laser lithography

Abstract: Research was conducted on the axially symmetric four-mirror system (magnification +1/5) for use in optical lithography using an ArF excimer laser beam. The initial design is derived from an extensive numerical calculation that makes the sum of the third-order aberration coefficients very small ∑j=IV|Sj|<10-6. Using an optimization method (damped least-squares method) the finite aberrations are reduced; then, to obtain the diffraction-limited performance, three surfaces are aspherized. The final system has NA=0.38 for the ArF excimer laser line (λ=0.193 μm) and depth of focus of 1.2 μm over a 2.6×2.6 cm2 object field. Nearly all rays fall within the Airy disk in the image plane. The resolution is 540 cycles mm-1 at MTF=0.5 level for axial object point. We consider that the present four-mirror system may be further refined for use in soft x-ray lithography.

Resolution Enhancement by Oblique Illumination Optical Lithography Using a Transmittance-Adjusted Pupil Filter

Abstract: This paper describes the resolution enhancement by oblique illumination optical lithography using a transmittance-adjusted pupil filter that has a conjugate shape to the secondary light source. The resolution enhancement depends on the amplitude transmittance distribution of the pupil filter in the lens aperture. Thus, the optimum transmittance distribution attaining the highest resolution at a practical depth of focus is investigated, and superior performance is verified experimentally using an actual i-line stepper, that is, the actual resolution improvement is comparable to the simulation results. Despite this improvement, two problems must be addressed. Pattern profiles degrade at the ends of periodical patterns, and the opaque pattern widths of middle-pitch patterns become a little narrow. These two problems are solved by optimizing the transmittance distribution of the filter such that there is no significant deterioration in the high-resolution performance.

Improving the backend focus budget for 0.5-um lithography

Abstract: One of the biggest challenges for printing 0.6 micrometers metal lines (1.3 micrometers pitch) over 1.1 micrometers of topography is the shallow depth of focus. Total random errors, or, Built In Focus Errors (BIFE) for the class of steppers used in this study was determined to be 0.48 micrometers . When topography, and field curvature/astigmatism, are factored in, the required depth of focus to print the metal lines is approximately 2.18 micrometers . However, the 'Available' DOF (as determined from PROLITH simulations) is only 1.8 micrometers . The deficit between available DOF and required DOF grows bigger when there are multiple steppers. To overcome this deficiency, various techniques have been studied. Topography reduction by 0.4 micrometers was achieved by the use of Reverse Well technology. Effect of different resist chemistries, off-axis illumination, variation in numerical aperture and partial coherence, on the focus latitude are shown.

Attenuated phase-shifting mask specification with modified beam illumination

Abstract: Recently, attenuated phase-shifting masks (att-PSMs) with advanced illumination technology of a modified beam illumination (MBI) become a pioneer to expand applications of i-line and KrF lithography. This technology can enhance a depth of focus even for a dense pattern layout by eliminating an undesirable secondary peak intensity which is found in att-PSMs with a normal illumination. In order to extract appropriate performance of att-PSMs with the MBI, a new systematic evaluation method using exposure-defocus and mask fabrication latitude (EDM) methodology in which all sorts of process parameters can be considered is proposed for setting att-PSM specifications. Mask transmittance and biasing are the parameters that essentially contribute to the optimum att-PSM characteristics. In this paper, first the evaluation flow using EDM methodology is explained in detail. Next, feasible ranges of mask transmittance and bias are discussed. Finally, it is shown that the mask line width uniformity significantly affects lithography performance with the att-PSMs and mask specifications of transmittance and bias.

Surface position detector and fabrication of semiconductor employing it

Abstract: PURPOSE:To locate the entire exposing region within the allowable depth of focus of a projection optical system even if the wafer surface is inclining by varying the information relating to the heights of a plurality of measuring points in the exposing region on the surface of a wafer according to the size of the exposing region while retaining the similarity in the relative position of the plurality of measuring points. CONSTITUTION:Correction optical systems 12-16 are provided for respective measuring point 19-23 and the projective magnifications on the detection planes 17 thereof are substantially equalized. The position of a pinhole image incident to the detection plane 17 is varied depending on the position of the measuring points 19-23 on the surface of a wafer 2. The measuring points 19-23 on the surface of wafer are conjugated with the detection plane of a photoelectric converting means SC through a projection means SB. Consequently, the position of pinhole image on the detection plane 17 is varied depending on the height of the measuring points 19-23. The photoelectric converting means SC detects information relating the incident position of pinhole image on the detection plane 17 and delivers the information to a focus control means 18.

Characterization of 5X stepper lenses to improve depth of focus

Abstract: In the fabrication of integrated circuits, device pattern size determines electrical performance characteristics. Variations in the size of lines, trenches, contacts, straps, etc. result in electrical device performance differences. When the variations occur from chip to chip or wafer to wafer, we find that entire chips function differently (e.g. impacts clock speeds). This paper discusses within-chip variations that can produce undesirable effects which, when severe enough, can kill an entire chip because portions of it have incompatible electrical performance. The modeling and characterization of image-size variations caused by lens aberrations of 5X photolithography steppers with lens field sizes from 15 mm2 to 22 mm2 are also discussed.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.