Photomask Inspection Research Articles

Preliminary study of photomask pattern inspection by beam-shaped knife-edge interferometry

This paper presents a photomask inspection and defect analysis technique to accurately measure the pattern dimensions and to detect the defects of the photomask in a convenient, fast, reliable manner. The beam-shaped knife-edge interferometry (BSKEI) was developed to collect the interferogram created by the superposition of the reference incident wave and the edge-diffracted wave while scanning the photomask. BSKEI consists of a pulsed laser diode, an aperture, an objective lens, and a fiber-coupled photodiode. The objective lens enabled the beam shaping to create a spherical wave as a new source of light, and the beam shaping was effective to enhance the spatial frequency of the interferogram. The interferograms were characterized based on a Fresnel number model, and the corresponding interferogram analysis methods were developed. BSKEI produced different interferograms according to the photomask patterns and defects while scanning the photomask. As a result, BSKEI is capable of the measurement of pattern width, opening width, line-edge quality, and opening area surface quality of the photomask, and is expected to be an alternative tool for critical dimension metrology in many semiconductor applications.

Actinic microscope for extreme ultraviolet lithography photomask inspection and review

Two dual-configuration extreme ultraviolet (EUV, 13.5nm wavelength) optical designs are described as a means to overcome principal EUV photomask metrology challenges. Semiconductor industry-wide efforts to define performance requirements and create standalone tools that can be used to discover, review, and accurately locate phase, amplitude, and mask pattern defects are described. The reference designs co-optimize low and high magnification configurations for orthogonal chief ray planes to avoid inspection and review trade-offs and emulate the aerial image of a lithography scanner.

Sub-Pixel Resolution by Die to Database Reticle Inspection

The description of the new Virtual Scanning Algorithms (VSA), providing sub-pixel resolution, is presented. VSA are developed specially for EМ-6029B and EM-6329 die-to-database reticle and photomask inspection systems of UEKBTEM-OMO Minsk, Belarus. For the effective building of these algorithms into the inspection system the special two-level dynamic model of optical image was created. This model allows to perform the precise alignment of optical image (collected from the reticle) with a reference image (generated from the design data), and to perform the analysis of optical image to get optimum mutual position of the digitization grid of the inspection system and detected defects position. VSA calculate the second level of this model. Both the VSA and the second level of dynamic model of optical image are presented the Virtual Scanning sub-System (VSS). VSS allows to increase the detection capability of automatic reticle inspection system by means of achievement sub-pixel resolution. During detection of semi-transparent defects, VSA allow to get maximum available amplitude contrast of the CCD-signals on the image model. VSA allow also the inspection system to work without using maximum sensitivity settings with the same detection capability. Result is the reduction of the risk of false or nuisance defects detection while keeping maximum sensitivity to printable defects. The VSS design and test results are discussed. Ill. 3, bibl. 5 (in English; summaries in English, Russian and Lithuanian).

Optical inspection of next generation lithography masks

For the last 5years a joint venture has pursued a research program studying and enhancing the ability of optical inspection tools to meet the inspection needs of extreme ultraviolet (EUV) and other next generation lithographies (NGLs). In this article we present a survey of results we have obtained for patterned inspection of NGL masks. The NGL technologies that we have studied include two electron projection lithographies, EUV, and step and flash imprint lithography (SFIL). We discuss the sensitivity of the inspection tools and mask design factors that affect tool sensitivity. In contrast to conventional photomask inspection, which primarily utilizes transmitted light for inspection, almost all NGL mask inspections are performed in reflected light. Much of the work has been directed towards EUV mask inspection and how to optimize the mask to facilitate inspection. Early EUV masks had an optical contrast of 40% or lower. Our partners have succeeded in making high contrast EUV masks ranging in contrast from 70% to 98%. Die to die and die to database inspections, at a wavelength of 257nm, of EUV masks have been achieved with a sensitivity that is comparable to what can be achieved with conventional photomasks, with a minimum detected defect size of 80nm square defects. We have inspected scattering with angular limitation projection electron-beam masks successfully. Electron-beam stencil masks, such as that used in projection reduction exposure with variable axis immersion lenses, pose a problem in that their high aspect ratio of mask thickness to minimum feature width results in low resolution transmission images. Reflected light images provide high-resolution images suitable for inspection, but will not be sensitive to defects below the inspection surface. We have run inspections on SFIL masks in die to die, reflected light in an effort to provide information concerning possible cumulative damage due to imprinting and to provide feedback on defect densities, types and sizes to improve the masks. Our defect sensitivity on SFIL masks is approximately 100nm, though we cannot run at the highest sensitivity due to large numbers of nonprogrammed defects. We have also used an inspection system, at a wavelength of 364nm, to inspect both unpatterned EUV substrates (no coatings) and blanks (with EUV multilayer coatings), and demonstrated a sensitivity of approximately 100nm to polystyrene latex spheres. This information has helped drive down the defect densities on EUV blanks and substrates by some three orders of magnitude. Extensions of conventional optical lithography have pushed out the introduction of NGL technology to the 33nm or possibly the 22nm node. Mask inspection technology will need substantial improvements in resolution to meet the NGL inspection requirements below the 45nm node.

Inspection of templates for imprint lithography

Masks of any next generation lithography (NGL), such as imprint lithography, must eventually achieve and maintain the very low defect counts of current production masks. This requires typically fewer than 10 or even no defects over the entire field. We describe an inspection methodology and how it can be applied to the imprint template. Special test patterns etched onto the template enable both a die to die comparison, to find nuisance defects, and also calibration of sensitivity to different types of preprogrammed defects. A state of the art deep ultraviolet photomask inspection system (KLA-Tencor model 526) can detect these rare events with about 70nm threshold for imprint masks with reflection mode contrast. Initial scans are made at various stages of the imprint process: the newly processed mask, after dicing, and after several imprints. The scans show mostly isolated point defects at a density of ∼10–100permm2. This is an encouraging start for a new NGL, and reductions are expected from better processes, equipment, and handling. In the future viable mask inspection at the 45–22nm node will be very demanding for these 1× masks and will require sensitivities approaching 10–20nm defect size. To this end, special masks suitable for electron (e)-beam inspection are being made and show good contrast and immunity to e-beam charging.

Photomask dimensional metrology in the scanning electron microscope, part II: High-pressure/environmental scanning electron microscope

Binary and phase-shifting chromium on quartz optical photomasks have been successfully investigated with high-pressure/environmental scanning electron microscopy (SEM). The successful application of this methodology to semiconductor photomask metrology is new because of the recent availability of high-pressure SEM instrumentation equipped with high-resolution, high-signal, field emission technology in conjunction with large chamber and sample transfer capabilities. The high-pressure SEM methodology employs a gaseous environment to help diminish the charge buildup that occurs under irradiation with the electron beam. Although very desirable for charge reduction, this methodology has not been employed in production photomask or wafer metrology until now. This is a new application of this technology to this area, and it shows great promise in the inspection, imaging and metrology of photomasks in a charge-free operational mode. This methodology also holds the potential of similar implications for wafer metrology. For accurate metrology, high-pressure SEM methodology also affords a path that minimizes, if not eliminates, the need for charge modeling. This paper presents some new results in high-pressure SEM metrology of photomasks.

High-speed two-dimensional pattern generator using multi-DSPs' parallel processing for pattern inspection of PCB photomasks.

A high-speed design pattern generating method and its hardware for pattern inspection of printed circuit board (PCB) photomasks are described.PCB photomask patterns consist of some ten kinds of aperture patterns and straight and arc lines by scanning the aperture. Remarking that these patterns are categorized into aperture stop parts and its transfer parts, we developed a new method which generates aperture stop parts by referring stored pattern elements in memories and the transfer parts by high-speed approximation of straight and arc lines.64 digital signal processors (DSPs) calculate start and end addresses of each pattern in each scanning line in parallel, but in preceding to each raster scanning of a linear image sensor for photomask pattern detection. Input/output buffers of the DSPs are owned commonly and equal services are realized by patrolling to detect requests from each DSP.Pattern generating speed as fast as 0.1μs/pixel has been achieved. 220 pattern elements can be generated in a scanning line in maximum. Scale of the hardware of this parallel, asynchronous pattern generator is about a half of conventional synchronous ones.

Automated visual inspection: 1981 to 1987

This bibliography lists journal publications, conference papers, research technical reports, and articles from trade journals on automated visual inspection for industry which were published during the years from 1981 to 1987. More than 600 references are included. References are organized into 13 categories according to subject matter. The categories are (1) books, (2) conferences and workshops, (3) general discussions and surveys, (4) inspection of printed circuit patterns, (5) inspection of solder joints, (6) inspection of microcircuit photomasks, (7) inspection of integrated circuits and hybrids, (8) inspection of other electrical and electronics components, (9) surface inspection, (10) X-ray inspection, (11) other inspection applications, (12) system components, and (13) inspection algorithms. References listed in each category are arranged in chronological order. The purpose is primarily to provide a complete bibliography for those interested in automated visual inspection. Some general observations have been made for the above areas of activity summarizing the advances that have taken place and the problems that remain to be solved.

Inspection of Integrated Circuit Photomasks using Optical Data Processing Techniques

AbstractThe application of optical signal processing techniques for the inspection of integrated circuit photomasks, could prove to be a fast and cheap means of photomask inspection. In this paper we discuss two possible optical inspection techniques and their suitability for use as a practical inspection tool.

DKG 160 photomask inspection equipment localizes defects in IC patterns: Eberhard Degenkolbe, Manfred Heinze and Gerhard Kirmse Jena Rev.2, 83 (1982)

DKG 160 photomask inspection equipment localizes defects in IC patterns: Eberhard Degenkolbe, Manfred Heinze and Gerhard Kirmse Jena Rev.2, 83 (1982)

DKG 160 photomask inspection equipment localizes defects in IC patterns : Eberhard Degenkolbe, Manfred Heinze and Gerhard Kirmse. Jena Rev.2, 83 (1982)

DKG 160 photomask inspection equipment localizes defects in IC patterns : Eberhard Degenkolbe, Manfred Heinze and Gerhard Kirmse. Jena Rev.2, 83 (1982)

Automated equipment for 100% inspection of photomasks : Kenneth Levy. Solid St. Technol. p. 60 (May 1978)

Automated equipment for 100% inspection of photomasks : Kenneth Levy. Solid St. Technol. p. 60 (May 1978)

Automated photomask inspection : Donald B. Novotny and Dino R. Ciarlo. Solid St. Technol. p. 59 (June 1978)

Automated photomask inspection : Donald B. Novotny and Dino R. Ciarlo. Solid St. Technol. p. 59 (June 1978)

Automated photomask inspection : Donald B. Novotny and Dino R. Ciarlo. Solid St. Technol. p. 51 (May 1978)

Automated photomask inspection : Donald B. Novotny and Dino R. Ciarlo. Solid St. Technol. p. 51 (May 1978)

Integrated circuit photomask inspection by spatial filtering : L. S. Watkins, Solid St. Technol., September (1969), p. 29

Integrated circuit photomask inspection by spatial filtering : L. S. Watkins, Solid St. Technol., September (1969), p. 29

Inspection of periodic patterns with intensity spatial filters

This reports the application of spatial filtering to integrated circuit photomask inspection. Experiments were performed that used intensity filters and took advantage of the grating effect of the periodic array. A stop filter corresponding to the periodic distance was placed at the diffraction plane. The transmitted image showed tip the nonperiodic errors, i.e., contamination pinholes, scratches, missing or extra features and incorrectly registered patterns.

Inspection of integrated circuit photomasks with intensity spatial filters

Spatial filtering is shown to be an effective method for integrated circuit photomask inspection. Results show that errors of 0.2 mils can be detected using f/9.5 lenses and that the use of f/2.0 lenses detects errors of below 0.1 mil. Contamination, missing and added features, and step and repeat errors are all displayed. The method allows the observation of nonperiodic errors and can be used immediately for contamination inspection with very little increase in sensitivity. The procedure only needs alignment of the mask in rotation, and means that the mask can be totally inspected by scanning it through a laser beam.