非平行光干涉照明显微镜三维形貌检测研究

为实现表面微观形貌快速而较简单的检测,一种使用非平行光干涉照明的光学显微三维形貌检测方法被提出。该方法使用空间光调制器对激光光束进行衍射,选取光强相近的2个衍射级通过显微物镜,双光束干涉可得到周期接近图像分辨率、相位可精确调节的照明条纹,被测样本的三维形貌可通过拍摄4帧等相位差的条纹照明图像来计算得到。该方法不需借助干涉物镜产生条纹,不需要轴向扫描装置记录条纹变化,相位调节精确,成像直观。此外,该方法所产生干涉条纹的相位随坐标线性变化,不需对条纹周期进行修正。因为照明条纹参数调节光路独立于显微成像光路,系统装置具有光路简洁、易于调节的优点。为验证所提出三维检测精度,以粗糙度100 nm的粗糙度对比模块和硅片为被测样品进行了三维轮廓重建实验,实验结果显示,所提出方法轴向重复性测量精度为8.6 nm(2σ)。

Research on three-dimensional detection of microscopy using nonparallel light interference illumination

In order to realize rapid and simple measurement on micro-topography, an optical detection method using interference illumination of nonparallel light was proposed. In this method, a spatial light modulator is used to diffract the laser beam, and two diffracted beams with similar intensity are selected to pass through the objective. Fringe which has accurate phase and period approximately equal to resolution can be obtained by dual-beam interference. The surface topography is detected by calculating four fringe images with equal phase difference. This method neither need interferometric objective to produce fringes nor axial scanning device to record fringe changes, therefore the phase adjustment is accurate, and the imaging is intuitive. In addition, because the phase varies linearly with the pixel coordinates, the fringe period does not need to be modified. The adjustment path of fringe parameters is separated from imaging path, hence the system is simple and easy to adjust. To verify the accuracy of the proposed micro-topography method, a module (Ra=100 nm) and a silicon wafer were used as the samples for three-dimensional reconstruction experiments. The results show that the proposed method can achieve a repeatability measurement accuracy of 8.6 nm (2σ) in axial direction.