Existing photomask metrology is struggling to keep pace with the rapid reduction of IC dimensions as traditional measurement techniques are being stretched to their limits. This thesis examines the use of on-mask probable electrical test structures and measurement techniques to meet this challenge and to accurately characterise the imaging capabilities of advanced binary and phase-shifting chrome-on-quartz photomasks. On-mask, electrical and optical linewidth measurement techniques have highlighted that the use of more than one measurement method, complementing each other, can prove valuable when characterising an advanced photomask process. Industry standard optical metrology test patterns have been adapted for the direct electrical equivalent measurement and the structures used to characterise different feature arrangements fabricated on standard and advanced photomasks with proximity correction techniques. The electrical measurements were compared to measurements from an optical mask metrology and verification tool and a state-of-the-art CD-AFM system and the results have demonstrated the capability and strengths of the on-mask electrical measurement. For example, electrical and AFM measurements on submicron features agreed within 10nm of each other while optical measurements were offset by up to 90nm. Hence, electrical techniques can prove valuable in providing feedback to the large number of metrology tools already supporting photomask manufacture, which in turn will help to develop CD standards for maskmaking. Electrical test structures have also been designed to enable the characterisation of optical proximity correction to characterise right angled corners in conducting tracks using a prototype design for both on-mask and wafer characterisation. Measurement results from the on-mask structures have shown that the electrical technique is sensitive enough to detect the effect of OPC on inner corners and to identify any defects in the fabricated features. For example less than 10 (5%) change in the expected resistance data trends indicated a deformed OPC feature. Results from on-wafer structures have shown that the correction technique has an impact on the final printed features and the measured resistance can be used to characterise the effects of different levels of correction. Overall the structures have shown their capability to characterise this type of optical proximity correction on both mask and wafer level. Test structures have also been designed for the characterisation of the dimensional mismatch between closely spaced photomask features. A number of photomasks were fabricated with these structures and the results from electrical measurements have been analysed to obtain information about the capability of the mask making process. The electrical test structures have demonstrated the capability of measuring tool and process induced dimensional mismatches in the nanometer range on masks which would otherwise prove difficult with standard optical metrology techniques. For example, electrical measurements detected mismatches of less than 15nm on 500nm wide features.

No description available.

In the field of photolithography for micro-chip manufacturing, the photo-mask is used to print desired patterns on a proper photo-resist on wafer. The most common type of photo-mask is binary amplitude mask made an opaque layer of chrome. The principle and potential application of hybrid photo-mask with diffractive phase element and binary amplitude is presented in this dissertation paper from both numerical modeling and experimental research. The first important application is the characterization of aberration in the stepper system using hybrid diffractive photo-mask. By utilizing multiple diffractive illumination conditions, it is possible to characterize Zernike wave front aberration coefficients up to any desired order. And, the second application is the use of binary phase grating mask for analog micro-optics fabrication. This approach of using binary phase grating mask for fabricating analog micro-optics turned out to be a very effective alternative for gray-scale mask technology. Since this is a pure phase only mask, it doesn't cause any scattered noise light like half-tone mask and it results in smooth desired resist profile. The benefits and limitations of hybrid diffractive photo-mask approach for both applications are discussed.

No description available.

This thesis explores how the diffraction pattern in the near-field region of a chromium feature edge on a photomask gets altered for three scenarios: First, an analytical study using the Fresnel diffraction integral is performed that investigates what happens when the thin-mask approximation is omitted and the chromium layer is given a thickness. Another analytical study is performed where the edges of a test feature are altered to simulate deviations in the linewidth or a translation of the whole feature, image subtraction is then used to create a difference pattern by subtracting a reference diffraction pattern from the diffraction pattern created by the altered test feature. Lastly, a numerical study using Fourier optics is performed to investigate the effect that introducing four common defects: extrusions, intrusions, dark spots, and pinholes, around the edge will have on the diffraction pattern by subtracting the diffraction pattern from a reference half-plane and again analyzing the resulting difference pattern. Introducing a thickness to the chromium layer alters the diffraction pattern by creating a small crease around the area of the edge in reflective mode, resulting in something similar to a double edge. The high optical density of chromium nullified any effect the thickness had when viewing the system through transmission mode. A linear relation between a change in linewidth or translation of a feature and the peak intensity of the difference pattern is observed that might be used for edge detection. The defect diameter of an extrusion or intrusion seems to correlate in a quadratic way with the peak fringe intensity of the subtracted difference pattern along the x-axis as the defect is fully visible. For a dark spot or pinhole defect being translated away from a chromium edge, the central fringe along the y-axis of the difference pattern follows a sinusoidal curve as it translates further away from the edge. The amplitude of this curve is related to the defect size.

<p>The project has been carried out at, and in association with, Micronic Laser Systems AB in Täby, Sweden. Micronic Laser Systems, manufacture laser pattern generators for the semiconductor and display markets. Laser pattern generators are used to create photomasks, which are a key component in the microlithographic process of manufacturing microchips and displays. </p><p>An essential problem to all modern semiconductor manufacturing is the constantly decreasing sizes of features and increasing use of resolution enhancement techniques (RET), leading to ever growing sizes of datasets describing the semiconductors. When sizes of datasets reach magnitudes of hundreds of gigabytes, visualisation, navigation and editing of any such dataset becomes extremely difficult. As of today this problem has no satisfying solution. </p><p>The project aims at the proposal of a geometry engine that effectively can deal with the evergrowing sizes of modern semiconductor lithography. This involves a new approach to handling data, a new format for spatial description of the datasets, hardware accelerated rendering and support for multiprocessor and distributed systems. The project has been executed without implying changes to existing data formats and the resulting application is executable on Micronics currently existing hardware platforms. </p><p>The performance of the new viewer system surpasses any old implementation by a varying factor. If rendering speed is the comparative factor, the new system is about 10-20 times faster than its old counterparts. In some cases, when hard disk access speed is the limiting factor, the new implementation is only slightly faster or as fast. And finally, spatial indexing allow some operations that previously lasted several hours, to complete in a few seconds, by eliminating all unnecessary disk-reading operations.</p>

Large area flat displays are nowadays considered being a commodity. After the era of bulky CRT TV technology, LCD and OLED have taken over as the most prevalent technologies for high quality image display devices. An important factor underlying the success of these technologies has been the development of high performance photomask writers in combination with a precise photomask process. Photomask manufacturing can be regarded as an art, highly dependent on qualified and skilled workers in a few companies located in Asia. The manufacturing yield in the photomask process depends to a great extent on several steps of measurements and inspections. Metrology, which is the focus of this thesis, is the science of measurement and is a prerequisite for maintaining high quality in all manufacturing processes. The details and challenges of performing critical measurements over large area photomasks of square meter sizes will be discussed. In particular the development of methods and algorithms related to the metrology system MMS15000, the world standard for large area photomask metrology today, will be presented. The most important quality of a metrology system is repeatability. Achieving good repeatability requires a stable environment, carefully selected materials, sophisticated mechanical solutions, precise optics and capable software. Attributes of the air including humidity, CO2 level, pressure and turbulence are other factors that can impact repeatability and accuracy if not handled properly. Besides the former qualities, there is also the behavior of the photomask itself that needs to be carefully handled in order to achieve a good correspondence to the Cartesian coordinate system. An uncertainty specification below 100 nm (3σ) over an area measured in square meters cannot be fulfilled unless special care is taken to compensate for gravity-induced errors from the photomask itself when it is resting on the metrology tool stage. Calibration is therefore a considerable challenge over these large areas. A novel method for self-calibration will be presented and discussed in the thesis. This is a general method that has proven to be highly robust even in cases when the self-calibration problem is close to being underdetermined. A random sampling method based on massive averaging in the time domain will be presented as the solution for achieving precise spatial measurements of the photomask patterns. This method has been used for detection of the position of chrome or glass edges on the photomask with a repeatability of 1.5 nm (3σ), using a measurement time of 250 ms. The method has also been used for verification of large area measurement repeatability of approximately 10 nm (3σ) when measuring several hundred measurement marks covering an area of 0.8 x 0.8 m2. The measurement of linewidths, referred to in the photomask industry as critical dimension (CD) measurements, is another important task for the MMS15000 system. A threshold-based inverse convolution method will be presented that enhances resolution down to 0.5 µm without requiring a change to the numerical aperture of the system. As already mentioned, metrology is very important for maintaining high quality in a manufacturing environment. In the mask manufacturing industry in particular, the cost of poor quality (CoPQ) is extremely high. Besides the high materials cost, there are also the stringent requirements placed on CD and mask overlay, along with the need for zero defects that make the photomask industry unique. This topic is discussed further, and is shown to be a strong motivation for the development of the ultra-precision metrology built into the MMS15000 system. / <p>QC 20130515</p>

The project has been carried out at, and in association with, Micronic Laser Systems AB in Täby, Sweden. Micronic Laser Systems, manufacture laser pattern generators for the semiconductor and display markets. Laser pattern generators are used to create photomasks, which are a key component in the microlithographic process of manufacturing microchips and displays. An essential problem to all modern semiconductor manufacturing is the constantly decreasing sizes of features and increasing use of resolution enhancement techniques (RET), leading to ever growing sizes of datasets describing the semiconductors. When sizes of datasets reach magnitudes of hundreds of gigabytes, visualisation, navigation and editing of any such dataset becomes extremely difficult. As of today this problem has no satisfying solution. The project aims at the proposal of a geometry engine that effectively can deal with the evergrowing sizes of modern semiconductor lithography. This involves a new approach to handling data, a new format for spatial description of the datasets, hardware accelerated rendering and support for multiprocessor and distributed systems. The project has been executed without implying changes to existing data formats and the resulting application is executable on Micronics currently existing hardware platforms. The performance of the new viewer system surpasses any old implementation by a varying factor. If rendering speed is the comparative factor, the new system is about 10-20 times faster than its old counterparts. In some cases, when hard disk access speed is the limiting factor, the new implementation is only slightly faster or as fast. And finally, spatial indexing allow some operations that previously lasted several hours, to complete in a few seconds, by eliminating all unnecessary disk-reading operations.