An Ultra-precision Measurement System for Next Generation 400 mm Silicon Wafers

本研究的目的是为直径达400mm的大型硅片开发一套精确的平面度测量系统。该系统由二维（2D）坡度传感器单元、晶圆轴和传感器架组成。晶圆样品垂直安装在真空吸盘上，可通过主轴旋转。二维坡度传感器单元由两个二维坡度传感器组成。2D坡度传感器单元放置在传感器架上。它检测晶圆表面上一点的二维局部斜率（x和y方向的局部斜率）。2D斜率传感器由传感器架沿x方向移动，以在晶圆片旋转时扫描晶圆表面。在这种基于角度的测量系统中，传感器的横向误差运动（直线度误差运动）和晶圆轴的横向误差运动（轴向误差运动）不会影响传感器的输出。基于误差分离的概念，利用斜率传感器的二维输出，可以将晶圆表面的二维局部斜率与传感器小车（偏航、滚转）和晶圆主轴（角误差运动）的角误差分离开来。通过对晶圆表面x向局部斜率积分，可以得到晶圆表面沿径向的截面高度分布；通过对y向局部斜率积分，可以得到晶圆表面沿同心圆方向的截面高度分布。因此，整个晶圆表面的高度轮廓可以通过结合这两个方向的截面轮廓来评估。利用自准直原理，研制了二维坡度传感器来实现测量系统。利用位置传感装置检测物镜焦平面上反射光斑对应的二维位置，得到二维局部斜率（角度）。为了使传感器体积更小，选择合适的位置传感装置比使用较大焦距的物镜更有效地提高角度检测的灵敏度。结果表明，四象限光电二极管是高灵敏度二维斜率检测的最佳选择。紧凑的原型坡度传感器被证实具有大约0.01角秒的分辨率。对大型硅片进行了平面度测量实验，验证了该系统的可行性。少

The purpose of this study is to develop an accurate flatness measuring system for large silicon wafers with diameters of up to 400 mm. The system consists of two-dimensional (2D) slope sensor unit, a wafer spindle, and a sensor carriage. The wafer sample is mounted on a vacuum chuck vertically and can be rotated by the spindle. The 2D slope sensor unit consists of two 2D slope sensors. The 2D slope sensor unit is placed on the sensor carriage. It detects the 2D local slopes (X-and Y-directional local slopes) at a point on the wafer surface. The 2D slope sensor is moved by the sensor carriage along X-direction to scan the wafer surface while the wafer is rotating. In this angle-based measuring system the transnational error motions of the sensor carriage (straightness error motions) and the wafer spindle (axial error motion) will not affect in the sensor outputs. Based on the concept of error separation, the 2D local slopes of the wafer surface can be separated from the angular error mo … More tions of the sensor carriage (yaw, roll) and the wafer spindle (angular error motion) using the 2D outputs of the slope sensors. The cross-sectional height profiles of the wafer surface along radial directions can be obtained through integrating the X-directional local slopes of the wafer surface, and the cross-sectional height profiles along concentric circles can be obtained through integrating the Y-directional local slopes. The height profile of the entire wafer surface can thus be evaluated from combining the sectional profiles in these two directions. Two-dimensional slope sensors, which utilizes the principle of autocollimation, were developed to realize the measuring system. The two-dimensional local slopes (angles) are obtained through detecting the corresponding two-dimensional positions of the reflected light spot on the focal plane of the object lens using position-sensing devices. To make the sensor compact in size, it is more effective to improve the sensitivity of angle detection by selecting proper position-sensing devices than using an objective lens with a larger focal distance. It was shown that a quadrant photodiode is the best for highly sensitive two-dimensional slope detection. The compact prototype slope sensors were confirmed to have a resolution of approximately 0.01 arc-seconds. Flatness measurement experiments of large silicon wafers have been conducted to indicate the feasibility of the developed system. Less