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

近年来，大规模集成电路器件的设计规则迅速缩小，要求达到0.1微米以下的尺寸的挑战也在不断进行。为了在下一代器件的制造过程中实现高生产率和高可靠性，抛光硅片表面的纳米缺陷检测技术是必不可少的。在这项研究中，我们提出了一种新的检测抛光硅片亚表面纳米缺陷的方法，即通过检测出现在表面的红外辐射(IR)消失光。红外消逝光是用扫描探头检测的，分辨率与光波长无关。本文的主要研究成果如下：(1)利用时域有限差分方法…建立了严格的计算机模拟方法更多的是基于麦克斯韦方程。FDTD方法可以分析三维空间分辨率和时间分辨率的电磁波传播。(2)计算了由设计的探头尖端和硅片组成的仿真模型的电磁场。Si和SiO_2探针针尖向表面靠近，间距为100 nm。采用S偏振高斯波的红外(1064 Nm)光束到达硅片表面，入射角为45.0度，超过临界角。(3)在近场区域，外部缺陷引起的逝去光的扰动发生在缺陷周围。并且扰动被硅探头的尖端拾取并通过探头传播。这些结果表明，硅探针可以探测到尺寸为40 nm的微小外部缺陷的信息。(4)可以看出，由内部缺陷如空洞缺陷引起的逝去光的扰动也被硅探针的尖端所拾取。这一结果表明，即使缺陷存在于亚表面，该方法也能够实现对尺寸为10 nm的缺陷的高灵敏度检测。(5)通过分析扫描硅片表面上的探头尖端获得的检测信号，可以估计缺陷的位置、大小和凹坑、凸台等特征。(6)探头尖端的材料是高灵敏度检测硅表面上或以下纳米缺陷引起的逝去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头尖端的材料。较少

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