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

近年来，LSI器件的设计规则迅速缩小，实现0.1微米以上的更精细尺寸的挑战正在不断进行。为了在此类下一代器件的制造过程中实现高生产率和可靠性，抛光硅片表面的纳米缺陷检测技术至关重要。在这项研究中，我们提出了一种通过检测表面出现的红外辐射 (IR) 倏逝光来检测抛光硅片表面纳米缺陷的新方法。使用扫描探针尖端检测红外倏逝光，分辨率与光波长无关。因此，该方法使得灵敏地检测纳米级尺寸的纳米缺陷成为可能，并且可以检测地下和表面的缺陷。本研究的主要结果概括如下：（1）基于麦克斯韦方程组，采用时域有限差分（FDTD）方法建立了严格的计算机模拟方法。 FDTD方法不仅可以以三维空间分辨率而且可以以时间分辨率来分析电磁波传播。(2)我们计算了由所设计的探针尖​​端和硅片组成的仿真模型的电磁场。 Si 和 SiO_2 探针尖端以 100 nm 的间隙接近表面。具有s偏振高斯波的IR（波长1064nm）光束以超过临界角45.0度的入射角到达硅片表面。（3）在近场区，缺陷周围发生由外部缺陷引起的倏逝光的扰动。干扰被硅探针的尖端拾取并通过探针传播。这些结果表明，尺寸为40nm的微小外部缺陷的信息可以被Si探针检测到。(4)可以看出，由于内部缺陷（例如空洞缺陷）引起的倏逝光的干扰也被Si探针的尖端拾取。这一结果表明，即使缺陷存在于亚表面，该方法也能够对10nm尺度的缺陷进行高灵敏度检测。(5)通过分析探针针尖在Si晶片表面上扫描所获得的检测信号，可以估计缺陷的位置、大小和特征，如凹坑或凸台。(6)探针针尖的材料是高灵敏度检测Si表面或下方纳米缺陷引起的倏逝光干扰的重要因素之一。就灵敏度而言，氧化硅是比硅更适合用作探针尖端的材料。较少的

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