The theory of partial coherence has important applications in many fields such as optical system imaging, optical projection lithography, optical communication and speckle metrology. A tiny pinhole is essential to calibrate the wavefront error of the collimating lens when testing the wavefront error of the projection optics by using the method of Shack-Hartmann wavefront sensor. In this paper, a formulation is developed for investigating the intensity distribution in the far field diffracted by a circular tiny pinhole illuminated with partially coherent light. Assuming that aperture complex coherence is Bessel's correlation, the diffraction field far away from the pinhole is numerical calculated. The actual distribution of the field diffracted by the tiny pinhole is influenced by both the pinhole diameter and the coherence of light inside the pinhole aperture.
Compared with other non-contact displacement sensors, the chromatic confocal sensor, which based on wavelengthdisplacement modulation technique, has no special requirements on the material and texture of the measured surface, and suitable for measuring the displacement of objects whose size range from micro to macro with high precision. In this paper, the chromatic confocal method is applied to measure the micro displacement. A hyperchromats with a measurement range of 1.27mm and linear regression coefficient R2 of 0.996 has been designed by using ZEMAX optical design software. The experimental system of chromatic confocal displacement measurement is set up. Through two miniature fiber optic spectrometers, the large measurement range and high precision spectrum detection are realized. The system error is calibrated synthetically. The measurement range of 1.2mm and linear regression coefficient R2 of 0.997 is realized. The research results are of great significance for the development of micro-nanometer displacement measurement technology.
In an aberration measurement for the lithographic projection lens based on the lateral shear interferometry, stage needs move tens of nanometers to do phase motion, and move tens of millimeters to shift field points. But the stage met the both requirements is very expensive. Usually using a fine stage fold on a coarse stage to meet the both requirements. Whereas this method has a difficult to overcome since the both stages hardly keep the same motion direction. This article proposes a method to measure the angle between the stages motion direction based on the dual-frequency laser interferometer by respectively moving the both stages and flowing the 45 degrees. The measurement accuracy able reach the 0.10 mrad and meet the aberration measurement requirement.
For the rapid development need of the digital light processing (DLP), we designed a mini-projection lens applied to 0.65” DLP with ZEMAX. The mini-projection lens is composed of 9 group of 10 lenses, total length is 90mm, and the maximum aperture is 36mm. It has simple structure, small size, low processing and assembly costs, suitable for mass production. F-number is 2.4, projection ratio is 1.56, effective focal length is 22.67mm, and back working distance is 28mm. Its modulated transfer function (MTF) in all fields is higher than 0.75 at 66lp/mm, and higher than 0.6 at 100lp/mm, which has good image quality. The full field distortion is less than 0.2%, meeting the low distortion requirement of the projection lens.
The aberration inspection of Shack-Hartmann of lithographic lens has reached the nanometer inspection accuracy. Collimator as the key element of the system, the accurate positioning of itself is one important factor for the inspection accuracy. Based on the wavefront reconstruction with Zernike polynomials, in this paper, an optical alignment method for positioning adjustments of the collimator is presented. A sensitivity matrix is obtained from the equation that describes the correlation between Zernike coefficients and the multi-degree-of-freedom misalignment, and the positioning adjustments of collimator are acquired thereof. For the aberration inspection with Shack-Hartmann method, an engineering model of 193nm NA 0.75 projection lens is established in commercial simulating software (ZEMAX). For 0.5nm RMS aberration inspection accuracy, the positioning accuracy of collimator is analyzed and plotted with independent single freedom degree and mutual correlation with combined three freedom degrees. These analysis indicate the proposed method is a viable tool for aligning confocal position of collimator.
Rapid inspection of a projection optics incorporated to 193 nm excimer-exposure system is important for 90 nm node and beyond IC manufacturing. To overcome the problems of the collimator lens presented in high NA high accuracy wavefront error metrology with Shack-Hartmann wavefront sensor, a pinhole array is used as the illumination source, which produces an array of high NA and high accuracy spherical waves, and form a high brightness source. In this paper, the diffraction of the pinhole array is calculated by using finite-difference time domain method and the theory of partial coherence. The distribution of the pinhole array considered here includes square, hexagonal and random distribution. The results shown that, pinhole diameter and separation in pinhole array have significant influence on the intensity contrast of the diffracted light, and the light intensity diffracted by the random pinhole array is smoother than that diffracted by the square or hexagonal distribution pinhole array, and is preferential in high precision wavefront error metrology.
The centroid estimation, wavefront reconstruction and environment (typically temperature) are the main error sources of the Shack-Hartmann wavefront sensor (SHWS). In this paper, theoretical and experimental studies are conducted to analyze the effect of ambient temperature on the measurement accuracy of SHWS. The spot arrays corresponding to ambient temperature varied from 20.5 to 24 degrees are obtained by using the thermal analysis features in ZEMAX. The wavefronts are then reconstructed by home-made software from these spot arrays. By using the wavefront diffracted by a single mode optical fiber and the SHWS, the experiment setup is built to verify the results obtained by theoretical analysis. The results obtained by theoretical analysis and experiments are coincident well. The variation of the wavefronts measured by SHWS will be smaller than 0.06 nm RMS if the ambient temperature variation is controlled within 0.1 degree. The range of temperature within ±2 degrees, the max wavefront deviation is 2.12 nm. This research will be of guiding significance to ambient temperature control in high precision wavefront error metrology by using SHWS.
Rapid inspection of a projection optics incorporated to 193 nm excimer-exposure system is important for 90 nm node and beyond IC manufacturing. The measurement accuracy of the projection optics, which comprises of dozens of refractive mirrors and has numerical aperture (NA) of 0.75, should be reach 2.0 nm RMS. The high brightness subnanometer accuracy spherical wave with NA of 0.75 is crucial to realize such high accuracy metrology. In this paper, we introduce a new illumination source for Shack-Hartmann wavefront sensor used to measure the wavefront error of the projection optics. The new illumination source, which contains many randomly distributed pinholes etched on a metal membrane, acts as many incoherent point sources and has high brightness. The diameters of the pinholes are in the same order as the wavelength of the illumination wave. The diffraction of the pinholes is calculated based on finite difference time domain (FDTD) method, the diffractive waves can cover the whole space behind the pinholes, the wavefront error of the diffracted spherical wave is about 10-3λ RMS (λ=193 nm) within NA 0.75. The brightness is improved to N (Number of pinholes) times compared with single pinhole case.