Maskless lithography (ML2) with a scanning high-density spot array has been applied to pattern writing of flat panel displays (FPDs) and printed circuit boards (PCBs). In a ML2 system, spot array diagnostics is necessary to calibrate spot position deviations to achieve exposure pattern uniformity. However, it takes time for the diagnostic including the throughfocus spot profile measurement of a large number of spots (~ 1M spots). Therefore, a high throughput spot diagnostic system is required. We have proposed an alignment-free, high-throughput and cost-effective diagnostic technique with a scanning linear image sensor. Through-focus spot profiles were reconstructed with through-focus scanning signals and response functions of the image sensor pixels. This technique can realize a cost-effective on-machine spot diagnostic system compared to conventional micro-slit scanning systems. We have demonstrated this spot diagnostic with the proofof- concept system. We have confirmed the feasibility in measurements and achieved a lateral position variance of σ < 0.1 μm, (7% of spot size 1.5 μm), an axial position variance of σ < 0.2 μm, (2% of DOF 10 μm) and a telecentricity variance of σ < 1.0 mrad. These variances are then correlating with the level of positioning variances in the stage repeatability. In addition, we also have demonstrated an estimation of low-order wavefront aberrations with a focal spot profile. This onmachine laser spot diagnostic tool could contribute to improve the pattering quality and monitor the optical performance for various focus-spot laser processing systems.
In this paper, we suggested an alignment mark measurement system for die-to-wafer bonder. The system consisted of a vision system to measure the positions of alignment marks on die and wafer opposite to each other, and a height measurement system to detect the heights of the die and wafer to the vision system. Besides them, a tilt measurement system was also attached to check the parallelism between the die and wafer for exact measurement and bonding. For high precision measurement, the vision system used a special prism structure which minimized the distance between the die and wafer and measured alignment marks on both sides simultaneously. A focus tunable lens was also applied to control a focus position without changing the height of the system. We have designed and built the optical system in a compact size and presented some preliminary results here.
Advances in the semiconductor industry have led the wafer inspection technology to the limit of nanometer-scale defect detection, which is far beyond the diffraction limit. In this regime, the signal-to-noise ratio (SNR) is the figure-of-merit to determine whether the optical system can detect a single nanometer-scale defect. In this paper, we investigated the SNR properties of various line defects using the dark-field inspection with tailored polarized illumination by simulation and experiment. Conventional crossed Nicols configuration with linear polarized illumination and crossed analyzer can minimize background scattering noise and maximize line defect signal only for a specific kind of line defect such as gap or bridge due to strong polarization dependence on a line and space (L/S) pattern. The nulling elliptically polarized illumination is optimized to suppress background scattering noise moderately and maintain defect signal intensity at the same time. We confirmed SNR improvement for both 10 nm open and bridge defects on 40 nm line and space silicon pattern with 40 nm depth. There was a good agreement between our simulation results and experimental results. We experimentally confirmed SNR ~ 4 for both line gap and bridge defect detection on 40 nm L/S patterned wafer with the fixed nulling illumination.
We present a novel optical device which interchanges two orthogonal directions in the cross-section of a beam. The optical prism is composed of six flat faces and has particular edge angles. The beam passing through the component is totally reflected at right angles inside the prism and flipped diagonally at the exit with respect to the entrance. When a line beam is incident to the device, the beam is segmented step by step at the first side face and combined on the other side. The overall shape of the line beam is maintained at the exit, but the segments of the line beam are flipped. The narrow axis of the line beam at the exit has the divergence angle corresponding to the long axis at the entrance. The component is also useful to focus beams from linear laser diode array with asymmetric divergence angles. Compared to the other beam transformation systems, the suggested device has advantages of easy fabrication, coating-free and no energy loss on reflective surfaces.
One of the most popular methods for high precision lens assembly of an optical system is using an autocollimator and a rotation stage. Some companies provide software for calculating the state of the lens along with their lens assembly systems, but the calculation algorithms used by the software are unknown. In this paper, we suggest a calculation method for lens alignment errors using ray transfer matrices. Alignment errors resulting from tilting and decentering of a lens element can be calculated from the tilts of the front and back surfaces of the lens. The tilt of each surface can be obtained from the position of the reticle image on the CCD camera of the autocollimator. Rays from a reticle of the autocollimator are reflected from the target surface of the lens, which rotates with the rotation stage, and are imaged on the CCD camera. To obtain a clear image, the distance between the autocollimator and the first lens surface should be adjusted according to the focusing lens of the autocollimator and the lens surfaces from the first to the target surface. Ray propagations for the autocollimator and the tilted lens surfaces can be expressed effectively by using ray transfer matrices and lens alignment errors can be derived from them. This method was compared with Zemax simulation for various lenses with spherical or flat surfaces and the error was less than a few percent.
In the performance evaluation of phase-shifting interferometers for figure metrology, the height response, or height transfer function, is rarely taken into consideration, because in most applications smooth surfaces are measured and only the lowest spatial frequencies are of interest. For measurements with low uncertainty it is important to understand the height response as a function of the spatial-frequency content of a surface under test, in particular when it contains form-error components with frequencies at the high end of an interferometer's spatial-frequency passband. A mirror with a patterned area of 140-mm diameter, consisting of several subpatterns with varying spatial frequency, was used to evaluate the spectral response. Our goal was to develop a method for efficient mapping of the spectral response over the circular field of view of a phase-shifting interferometer. A new way of representing the dependence of the spectral response on the field of view of an interferometer is described.
In characterizing the performance of a phase-shifting interferometer, the dependence of the measured height on the
spatial frequency is rarely considered. We describe a test mirror with a special height relief that can be used to measure
the height transfer function for the interferometer in a fashion analogous to the measurement of the modulation transfer
function for the optical imaging system. We fabricated the test mirror at the National Institute of Standards and
Technology (NIST) using a lithography-based process. The test mirror has several patterns (reminiscent of moth
antennae) with variable spacing in radial direction. We describe the fabrication of the test mirror and its application to
test the performance of the interferometer.
We describe a novel interferometric scheme that attempts to measure the absolute distance of a three-dimensionally moving target with respect to a reference station. The target transmits two orthogonal pairs of lateral-shearing interferograms generated using four near-perfect spherical waves emitted from single-mode fibers by means of point diffraction. The interferograms are modulated with varying amounts of phase shifting and monitored by the reference station holding a 2-D array of photodetectors. Captured interferograms are analyzed by use of a modified version of the Rimmer-Wyant technique and reconstructed as the spherical wavefront emitted form the center of four fibers in the target. The absolute distance of the target is then determined by fitting the reconstructed wavefront into Zernike polynomials. Experimental results are discussed to verify that the proposed method is capable of measuring the absolute distance along not only the optical axis, but also out of the axis.
We describe a novel method of measuring absolute distances by using a two-point diffraction source specially devised to
generate two high quality spherical waves simultaneously with a small lateral offset. Interference of the generated two
spherical waves produces a unique ellipsoidal phase distribution in the measurement space. A partial map of the resulted
interference phase field is sampled and fitted to a geometric model of multilateration that allows absolute-distance
measurements to be performed without 2π-ambiguity. The partial phase map may be obtained by use of either homodyne
or heterodyne phase measuring technique. Test results demonstrate that high precision with 1 part in 106 uncertainty can
be achieved over 1 meter distance range.
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