本文介紹一款新型四維偏光散射量測儀，可量測晶圓表面粗糙度與螺紋的表面規格。為了達到精確及快速測量，該機被設計成有四個旋轉的機構，可用在二維及三維量測。光學機構必須具備結構穩定性，以保持光學元件間的相對位置，以維持系統的整體性能品質。本文以有限元素進行整體結構分析，檢測結構的性能。應用拓樸結構最佳化方法，解得重量輕及滿足剛度需求的轉動平板結構改良型態。為考慮最佳拓樸型態之可加工性，分別使用拓樸最佳化及參數最佳化的循環計算，再進行尺寸最佳化，增進結構性能。 本文敘述全程最佳化設計方法，去除偏光散射儀原有含滾輪之轉動平板裝置，成功改良為懸臂樑型式，可有0.0814mm的靜位移量。並於懸臂樑提出新的三角支撐滑軌之懸臂樑結構設計，可有0.0722mm的靜位移量，皆優於原來兩端支持結構的0.12mm。 A new four-axis polarized scattering instrument is presented and the critical structure of influencing the whole system is improved by optimium design methodology. This new type instrument can be conveniently and rapidly operated to achieve satisfying results including the function of three and two axis measuring requirement. For further enhance the performance of the current instrument , a systematic structural analysis is applied to determine the critical member. So that it can be modified to be a better performance . The common rotating plate where the detector is sliding on that plate is found to be the most critical member. The design task is to remove the existing supporting roller that is replaced by a cantilever moving arm, however the primary sizes and required performance must be maintained. This work apply topological structural optimization to obtain the initial layout of such a common moving arm. Three models are presented to improve the original slide way, long cantilever arm and static displacement. The first kind is directly modified from original slideway. The second kind is a simplified modification to the first kind structure. The third kind is a triangle slide way structure. All of them went through topological optimization , man-made shape design and parameter optimization. The result of first kind design can achieve static the displacement of 0.0814mm that is less than required 0.12mm . The third kind design can reach to 0.0722mm .