Nano-Defects Inspection in Polished Silicon Wafer Sub-Surface Using IR Evanescent Light

近年来，LSI器件的设计规则已经迅速缩小，并且现在持续进行实现比0.1微米更精细的尺度的挑战。为了实现这种下一代器件制造过程中的高生产率和可靠性，抛光硅晶片表面的纳米缺陷检测技术是必不可少的。在本研究中，我们提出了一种新的检测方法的纳米缺陷的抛光硅晶片的表面上出现的红外辐射（IR）倏逝光检测亚表面。红外倏逝光的检测使用扫描探针尖端和分辨率是独立的光波长。本文的主要研究成果如下：（1）采用时域有限差分法（FDTD）建立了严格的计算机模拟方法，并对该方法进行了数值模拟 关于我们 基于麦克斯韦方程。时域有限差分法（FDTD）不仅具有三维空间分辨率，而且具有三维时间分辨率。(2)我们已经计算了由所设计的探针针尖和硅晶片组成的模拟模型的电磁场。Si和SiO_2探针针尖以100nm的间隙靠近表面。具有s偏振高斯波的IR（1064nm波长）光束以超过临界角45.0 °的入射角到达Si晶片表面。(3)在近场区，由外部缺陷引起的倏逝光的扰动发生在缺陷周围。并且该扰动被Si探针的尖端拾取并通过探针传播。这些结果表明，Si探针可以探测到40nm左右的外部小缺陷的信息。(4)可以看出，由诸如空隙缺陷的内部缺陷引起的倏逝光的扰动也被Si探针的尖端拾取。该结果表明，即使缺陷存在于亚表面中，该方法也能够高灵敏度地检测10nm尺度的缺陷。(5)通过分析探针针尖在硅片表面扫描得到的检测信号，可以估计缺陷的位置、大小和特征，如凹坑或凸起。(6)针尖材料是实现高灵敏度探测硅表面纳米缺陷引起的倏逝光干扰的重要因素之一。在灵敏度方面，氧化硅比硅更适合作为探针针尖的材料。少

Recently, the design rule of LSI device has been shrank rapidly and challenges to achieve finer scale than 0.1 micrometer are continuously carried out now. In order to realize high productivity and reliability in the fabrication process of such next generation devices, nano-defects inspection technology for polished Si wafer surface is essential. In this research, we propose the new inspection method of nano-defects in a polished Si wafer subsurface by detecting infrared radiation (IR) evanescent light emerging on the surface. IR evanescent light is detected using scanning probe tips and the resolution is independent of light wavelength. Therefore this method makes it possible to sensitively detect the nano-defects with the size of nano meter scale and the defects in subsurface as well as on the surface can be detected also.Main results of this study are summarized as follows,(1) Rigorous computer simulation method are established by means of Finite Difference Time Domain (FDTD) method … More based on Maxwell's equations. FDTD method can analyses electro-magnetic wave propagation with not only three dimensional space resolution but also time resolution.(2) We have calculated the electromagnetic field of the simulation model consisting of the designed probe tip and the Si wafer. The Si and SiO_2 probe tip is approached towards the surface with a gap of 100nm. The IR (1064nm wavelength) light beam with s-polarized Gaussian wave reached at the Si wafer surface with incident angle at 45.0 degree exceeding the critical angle.(3) In the near field zone, the disturbance of the evanescent light resulting from the external defects occurs around the defects. And the disturbance is picked up by the tip of the Si probe and propagated through the probe. These results suggest that the information of the small external defects with the sizes of 40nm can be detected by the Si probe.(4) It can be seen that disturbance of the evanescent light resulting from the internal defect such as the voids defect is also picked up by the tip of the Si probe. This result suggests that even if the defect exists in the subsurface, this method enables the high sensitive detection of the defects with the sizes of 10nm scale.(5) Position, size and features such as pit or boss of a defect can be estimated by analyzing detection signal obtained by scanning the probe tip on Si wafer surface.(6) Material of probe tips is one of the important factors to detect the disturbance of the evanescent light resulting from a nano-defect on or below Si surface with high sensitivity. Silicon-oxide is more suitable material for the probe tip than Silicon in sensitivity. Less