Vision Servo Motion Control and Error Analysis of a CoplanarXXYStage for Image Alignment Motion

Abstract

In recent years, as there is demand for smart mobile phones with touch panels, the alignment/compensation system of alignment stage with vision servo control has also increased. Due to the fact that the traditional stacked-typeXYθstage has cumulative errors of assembly and it is heavy, it has been gradually replaced by the coplanar stage characterized by three actuators on the same plane with three degrees of freedom. The simplest image alignment mode uses two cameras as the equipments for feedback control, and the work piece is placed on the working stage. The work piece is usually engraved/marked. After the cameras capture images and when the position of the mark in the camera is obtained by image processing, the mark can be moved to the designated position in the camera by moving the stage and using alignment algorithm. This study used a coplanarXXYstage with 1 μm positioning resolution. Due to the fact that the resolution of the camera is about 3.75 μm per pixel, thus a subpixel technology is used, and the linear and angular alignment repeatability of the alignment system can achieve 1 μm and 5 arcsec, respectively. The visual servo motion control for alignment motion is completed within 1 second using the coplanarXXYstage.

Design of an Image-Servo Mask Alignment System Using Dual CCDs with an XXY Stage

“…Recently, a coplanar XXY stage is developed, because its coplanar design has smaller cumulative error and it can move faster than the traditional XY-Θz stage. Figure 2b shows the structure of the coplanar XXY stage, which is driven by three stepping motors, which are denoted as X1-axis motor, X2-axis motor and Y-axis motor [11]. The working stage is supported by four sub-stages; each sub-stage consists of X-translation, Y-translation and θz-rotation stages.…”

“…However, considering the rotational movement of θz, because the rotational center of the XXY stage is not fixed as the stacked XY-Θz stage, the kinematic relationship is very complicated. The kinematic of the coplanar XXY stage can be formulated as follows [11]. …”

“…Otherwise, the larger R means that the matching case is worse. The above method is called the square difference matching method [11]. Different from the above method, there is another popular method which uses the normalized correlation coefficient (NCC) between the pattern image and the searched image to determine the matching score; this method is called the NCC matching method [17].…”

Performance Characterization of an xy-Stage Applied to Micrometric Laser Direct Writing Lithography

“…Lee et al [14] propose a technique for alignment of a coplanar xy -stage. In this work, an image of a cross was selected as a fiducial mark.…”

“…Both types of stages have cumulative errors due to their mechanical assembly, those errors being smaller in the coplanar stage than in the stacked one. However, the coupling of the two motors in the same plane, as in the case of a coplanar stage, makes the command of this type of stage more difficult [ 14 , 15 , 16 ]. Moreover, those stages are less versatile than the stacked ones.…”