| 摘要: | 本研究提出一種「空間平均法」，並結合陰影疊紋技術之量測系統，將其應用於 12 吋未拋光矽晶圓之表面形貌量測。系統主要由 LED 白光光源、線性光柵及相機所組成，整體架構簡單，僅需單張陰影疊紋影像即可完成晶圓表面三維形貌之重建。此外，透過本研究所提出之空間平均法，可有效重建光柵形貌，並進一步對本系統量測所得之晶圓形貌進行補償，以降低光柵形貌所引入之系統性誤差。
該技術乃基於陰影疊紋(Shadow Moiré)原理，當斜向入射的白光通過線性光柵照射至晶圓表面時，光柵與其投射陰影相互疊合形成疊紋圖樣。晶圓表面的高度變化將造成光柵陰影相對位移，使條紋相位分佈包含表面形貌資訊。透過快速傅立葉轉換(FFT)擷取疊紋影像的相位分佈，便可重建晶圓的三維形貌。
另一方面，本研究發現光柵在重力作用下易產生變形，進而對晶圓形貌之重建造成干擾。此變形主要源於光柵採邊緣支撐方式，使未受支撐之區域產生下陷，進而導致系統性誤差。為降低上述影響，本研究提出一種「空間平均法」，可有效重建光柵形貌，並自量測結果中予以扣除，以提升晶圓形貌量測之精度與穩定性。
經一系列實驗驗證，本系統與商用儀器進行比對後，其重建形貌之相似度具有良好表現，皮爾森相關係數可達 0.8 以上。晶圓翹曲值之量測精度可控制於1.5 µm以內，且刻痕方位角之量測偏差可維持在0.25°以內。上述結果證實本系統已具備大面積、全域性且一次性量測晶圓表面形貌之能力，並能於 1 分鐘內完成單片晶圓的量測。此外，本研究亦針對光柵變形對量測結果之影響提出相應補償策略—空間平均法。透過此方法重建光柵形貌並進行補償，可有效消除光柵變形所造成之干擾，使本系統能正確重建並呈現晶圓之實際形貌。
綜合而言，本研究所提出之大尺寸陰影疊紋式量測系統，結合空間平均法之補償策略，能有效克服光柵變形對量測結果之影響，並準確重建晶圓之實際表面形貌。
;This study proposes a spatial averaging method integrated with a shadow moiré–based measurement system and applies it to the surface topography measurement of 12-inch unpolished silicon wafers. The system mainly consists of an LED white-light source, a linear grating, and a camera. Owing to its simple configuration, the three-dimensional surface topography of a wafer can be reconstructed using only a single shadow moiré image. Furthermore, the proposed spatial averaging method enables effective reconstruction of the grating profile, which is subsequently used to compensate the measured wafer topography, thereby reducing the systematic errors introduced by grating deformation.
The measurement principle is based on the shadow moiré technique. When obliquely incident white light passes through the linear grating and illuminates the wafer surface, the grating and its projected shadow overlap to form a moiré fringe pattern. Variations in the wafer surface height induce relative displacements of the grating shadow, causing phase shifts in the fringe pattern that encode surface height information. By applying a fast Fourier transform (FFT) to extract the phase distribution of the moiré image, the three-dimensional surface topography of the wafer can be reconstructed.
On the other hand, this study observes that the grating is susceptible to deformation under gravitational loading, which interferes with accurate wafer topography reconstruction. This deformation primarily arises from the edge-supported configuration of the grating, leading to sagging in unsupported regions and resulting in systematic measurement errors. To mitigate this effect, a spatial averaging method is proposed to reconstruct the grating profile and subtract it from the measurement results, thereby improving the accuracy and stability of wafer topography measurements.
Through a series of experimental validations, the reconstructed wafer topography obtained using the proposed system was compared with that measured by a commercial instrument. The results demonstrate a high degree of similarity, with Pearson correlation coefficients exceeding 0.8. The measurement error of wafer warpage can be controlled within 1.5 µm, and the deviation in notch orientation angle measurement remains within 0.25°. These results confirm that the proposed system is capable of large-area, full-field, and single-shot wafer surface topography measurement, completing the measurement of a single wafer within one minute. In addition, this study introduces a compensation strategy—namely, the spatial averaging method—to address the influence of grating deformation on measurement results. By reconstructing and compensating for the grating profile, the interference caused by grating deformation can be effectively eliminated, allowing the system to accurately reconstruct and represent the actual wafer surface topography.
In summary, the proposed large-area shadow moiré measurement system, combined with the spatial averaging–based compensation strategy, effectively overcomes the adverse effects of grating deformation and enables accurate reconstruction of the actual wafer surface topography. |
