振鏡掃描式全域彩色共焦表面形貌量測系統之研發

Abstract

隨著半導體產業步入3D封裝甚至晶圓級封裝，製程中關鍵尺寸的檢測出現 前所未有的技術挑戰，目前主流的量測技術為雷射三角法等，但因其天生的遮蔽 效應，在量測密集排列的凸起結構或是高深寬比的結構具有相對劣勢，然而這些 微結構卻是如今先進封裝設計中常用之幾何特徵，使低遮蔽效應的量測技術成為 半導體三維量測必要元素。因此同軸架構且量測速度快的彩色共焦系統具有相當 大的發展潛力。 為滿足半導體製程線上高速、高解析度的量測需求，本研究以發展全域式彩 色共焦量測方法為主要目標。針對上述條件，本研究之關鍵技術主要可列為兩項， 首先，為滿足全域式的量測，所研發之光學量測系統需具遠心特性，以避免不同 軸向深度的量測範圍不一之常見問題，且保持量測視野內之光學波前的一致性。 二，為增加量測速度，採用線型照明搭配光學掃描振鏡，以達到量測範圍內快速 之全域性三維形貌的量測能力。其主要優勢在於，此光學量測架構不需透過系統 與樣品之間的相對運動，可完全避免平台移動時的震動影響且減少位移所造成的 體積誤差。此外，振鏡旋轉小角度之響應時間遠小於過去多點式彩色共焦系統所 用之空間濾波器，如數位微鏡裝置(DMD)、液晶面板(LCD)，或液晶覆矽面板 (LCoS)等等其他方式，且所提出的線型照明具備多點式特性，其光的使用效率更 佳，因此可達更快速的量測。相較於其他彩色共焦多點式策略，本研究的架構可 避免常見光譜解析與量測速度互相限制的問題，使所研發的量測系統可達到更高 量測速度的同時，維持彩色共焦系統的量測精度水準。 本研究所實現之振鏡掃描式全域彩色共焦系統，經平面鏡與標準階高塊30次量測驗證，其深度量測範圍達到190 μm，量測偏差0.239 μm，量測標準差0.126 μm，且量測速度達250 lines/s。相較於單點型共焦系統，量測速率大幅提升，且 深度量測效能維持於次微米等級，使本系統具有相當大之未來發展性。

As the semiconductor industry enters 3D packaging and even wafer-level packaging, there are unprecedented technical challenges in detecting critical dimensions in the process. The current mainstream measurement technology is laser triangulation. However, its inherent shadowing effect is not suitable for measuring high densely arranged structures or structures with a high aspect ratio. These structures are geometric features commonly used in today's advanced package design, making measurement techniques with low shadowing effects essential for three-dimensional semiconductor measurement. Therefore, a chromatic confocal system with a coaxial structure and a fast measurement speed have considerable development potential. In order to meet the high-speed, high-resolution measurement requirements of the semiconductor production line, this research aims to develop a full-field chromatic confocal system. Given the above conditions, the key technologies of this study can be listed as two points. First, the developed optical system must have telecentric characteristics to make the field of view the same in the whole depth measurement range to achieve full-field measurement. Second, in order to increase the measurement speed, line illumination is used with an optical scanning galvanometer to accomplish a fast, full-field three-dimensional surface profile measurement. The main advantage is that the optical measurement design does not need the relative movement between the system and the sample, which can avoid the impact of vibration when the platform moves and reduce the error caused by displacement. In addition, the response time of the galvanometer rotating at a slight angle is much shorter than the spatial filters used in the multi-point chromatic confocal systems, such as digital micro-mirror devices (DMD), liquid crystal panels (LCD), or liquid crystal on silicon panels (LCoS). The proposed line-type illumination has features of multi-point measurement and high light efficiency to achieve faster measurement. Compared with other multi-point chromatic confocal strategies, the proposed system can avoid the mutual trade-off between spectral resolution and measurement speed. The developed system can achieve higher measurement speed while maintaining the precision of the chromatic confocal system. Thirty measurement times of a flat mirror and the standard height step have verified the galvanometer-scan full-field chromatic confocal system of this research. The depth measurement range reaches 190 μm, the accuracy is 0.239 μm, the standard deviation is 0.126 μm, and the measurement speed can achieve 250 lines/s. Compared with the single-point confocal system, the measurement rate is significantly increased. The depth measurement performance is maintained at the sub-micron scale, which makes this system have considerable development potential.