Reticle Plane Research Articles

Adaptive visual servo control law for finite-time tracking to land quadrotor on moving platform using virtual reticle algorithm

This paper proposed an image-based visual servoing (IBVS) control law for a quadrotor that is equipped with a single monocular camera attached to its bottom. For control purposes virtual reticle plane (VRP) algorithm is used to track the relative 3D position of the quadrotor to the tilting and moving target landing platform within the range of the camera’s field of view (FOV). In this article, the landing platform’s tilting motion is considered sinusoidal type oscillatory motion for the overhead camera. For control purposes, an adaptive finite-time control (AFTC) is proposed, based on the finite-time control (FTC) and adaptive approximation of uncertainties. A constructive combination of FTC and adaptive approximation inherits benefits of both to overcome each other’s limitations. The task of the controller is to regulate the position error to zero in time calculated by VRP. The experimental results confirmed the effectiveness of the VRP algorithm to track the desired parameters of the moving target. Finally, simulations are performed to illustrate the effectiveness and improved performance of the proposed AFTC in response time, robustness, and tracking accuracy.

Real time extraction of tracking error signal in IR seeker with a plus stationary reticle

In non-imaging IR seekers, the reticle will modulate the received radiation from the target. The modulation signal contains the tracking error signal (TES), which is the main signal in IR seeker. In IR seeker with a plus stationary reticle, the accuracy of TES extraction may be affected by several items, such as noise from engines, shine background, jamming and changes in the radius of target image spot (TIS). These reasons will decrease the accuracy of target positioning and may push the target to the nonlinear region. In the nonlinear region, the target will be lost although it remains in the field of view (FOV). In this paper, we introduce a new algorithm to extend the linear region, and then, we use the cross-correlation function to decrease the undesirable effects of noise and changes in the radius of TIS. All algorithms have been simulated in Matlab and implemented in Raspberry Pi 3 Model B+. The simulation results showed that the new algorithm with cross-correlation extend the region more than 100 times on the reticle plane, where the error in phase less than 2° compared with other algorithms in this field, especially in the presence of noise. The implementation using Raspberry Pi was in real time because the total execution time for one period was less than 3 ms, which is less than strict timing window in our problem.

A novel telecentricity measuring method for illumination system in lithography based on pinhole imaging

A methodology for measuring the telecentricity of illumination system in lithography tool based on the pinhole imaging is proposed. Illumination light goes through the pinhole located on the reticle plane and forms the pupil-fill image in CCD image sensor. Based on the Fresnel diffraction theory, the image intensity of source in CCD photosurface and the optimization of pinhole size are discussed. By simulating, effects of the stability of telecentricity measuring from non-uniformity of light field and pinhole defocus in different illumination patterns are analyzed respectively. Simulation results prove the effectiveness of this new method.

Vectorial imaging of deep subwavelength mask features in high NA ArF lithography

As silicon processes scale toward the 45-nm node using conventional 0.25-magnification, the feature sizes on the photomask are below the ArF (193.3 nm) laser wavelength. At these scales, traditional scalar and paraxial approximations used for optical image modeling are no longer valid. Thick-mask and vector-based rigorous models are equired to account for mask topographic effects and large incident angles at the reticle plane in ultra-high numerical aperture (NA) systems. Experimental depolarization measurements through advanced optical reticles at 193 nm are compared to rigorous finite-difference timedomain vector-based electromagnetic simulations. The validated simulation model is extended to explore the impact of polarization purity, mask absorber profile, mask film properties, and Fresnel effects through the pellicle on the imaging process window and requirements for optical proximity correction (OPC) in immersion imaging. The model has shown that line-end pullback has a strong correlation with mask shadowing under TE-polarized off-axis illumination (OAI).

Gradation Stitching Exposure Performance in the Improvement of Dose Uniformity and Continuity at the Field Stitching Boundaries

The effectiveness of gradation stitching exposure is demonstrated using a laboratory-built exposure system. After investigating convenient slit shapes, trapezoidal slits with an apex angle of 80° were adopted. From the viewpoints of ease of preventing corner rounding of exposure light flux and slit fabrication, trapezoidal slits were determined to be better than pentagonal slits. As the first experimental stage, exposure dose uniformity and continuity of the stitched parts are evaluated at the reticle plane in order to eliminate the complicated influence of the projection optics on patterns printed on wafers. Exposure and development of a special resist the dissolved depth of which after development changes almost linearly with the exposure dose is utilized for detecting partial irregular dose distribution in the narrow stitched parts. It is clarified that the dose inequality in the stitched parts is improved by adopting the gradation stitching exposure method. Moreover, by observing the line-and-space test pattern profiles and measuring the line pattern widths in the stitched parts, it is proved that the changes of top-view profiles and line widths are also very small and negligible. It will become difficult to develop a high-resolution projection optics with a large field for shorter wavelengths hereafter. Applying the gradation stitching exposure, large LSI chips will be replicated favorably by stitching two small scan fields. If a small field size is admissible, resolution and/or depth of focus will also be considerably improved.

MODELING AND EVALUATION OF INFRARED TRACKING SYSTEMS

The mathematical model of an infrared (IR) tracking system is developed. The system considered has a gyro-stabilized IR optical eye with rotating optical chopper. The dynamical equations of the gyro-mass assembly are derived. The equations that describe the signal processing in the electronic section of the system are obtained.Thus, the transfer functions that relates the precessional motion of the gyro assembly to the location of the IR-spot relative to the gyro spin axis are established. A physical simulation of the invloved system is then presented. A digital controller is employed to control the operation of the simulated tracking loop. The control is achieved via the parallel interface bus (HP-IB). The chopping action of the,tyro rotating reticle is physically simulated by placing an enlarged reticle in the front ,of an oscilloscope screen. The oscilloscope inputs are adjusted such that the oscilloscope,Spot traces a circle with angular frequency given by the gyro spinning speed. The electrimic part of the tracking system is inserted in the simulation loop. This hardware-in the loop procedure ensures that the simulation results are very close to reality. Via this simulation setup it is possible to develop and design the critical components of the system. In addition, the performance of the designed system can be tested. Simulation results show that the steady state tracking errors and the behavior of the tracking loop in: the transient period are affected by the IR spot intensity and size in the reticle plane.

Focus tracking system for direct projection cameras

A focus tracking system for direct wafer steppers has been tested and its operation simulated on computer to account for transducer fabrication limitations. The focus condition of the projection lens was determined by sensing the contrast level in the backprojected image of a test grating object mounted in a plane conjugate to the reticle plane. To permit continuous focus tracking, the test grating was illuminated with red light from a solid-state light emitting diode to prevent exposure of UV-sensitive photoresists. The contrast sensor consisted of a pair of large area silicon photodiodes with grating windows arranged so that the diodes viewed complementary space and bar projected fields of the test grating. The projection lens used in these tests was a 40× microscope objective having a numerical aperture of 0.95. The focus sensing range was found to be better than 1.6 μm, and the focus sensitivity was <0.1 μm.

Shiva Target Alignment And Viewing Instrument

To view and align Shiva laser targets, two telemicroscopic instruments have been designed; one is a single field instrument and the other a multiple field instrument. Each instrument is integral with a TV camera and HeNe laser illuminator. The common feature of the instruments is the capability of imaging both the large surrogate target (5 mm diameter) and the laser fusion target (0.250 mm diameter) with the same resolution (better than 7 um). Both instruments have an optical relay which images the targets on a fixed reference reticle so that both the surrogate target and the fusion target can be centered on the same reference point. The single field instrument reimages the reticle plane onto the TV detector using a zoom arrangement. The TV camera zoom assembly can be translated in three axes and is thereby capable of exploring an object-space volume of 1cm3 without moving either the relay optical train or the reference reticle. In the multiple field instrument the reticle plane is reimaged by a zoom lens and this enlarged image is relayed to the TV detector by a cluster of five lenses. Four lateral lenses image the periphery of the surrogate target and the reticle for coincidence. The central objective images the center of the reticle and the fusion target when it is centered.