Measurement of novel micro bulk defects in semiconductive materials based on Mie scatter

Transcription

1 Indian Journal of Pure & Applied Physics Vol. 45, April 2007, pp Measurement of novel micro bulk defects in semiconductive materials based on Mie scatter You Zheng, Li Yingpeng & Chen Jun Department of Precision Instruments, Tsinghua University, Beijing, China Received 7 June 2006; accepted 6 February 2007 This paper introduces a new micro bulk defects measurement method in semiconductive materials, which scales the defects by analyzing scattering light distribute based on Generalized Lorenz and Mie Theory (GLMT). A method named character recognition and pick up two characters as defect criterions have been presented. Moreover, a set of experimental apparatus is built to prove the detect method and defect criterions. The micro bulk defects in semiconductive materials have been detected experimentally. Keywords: Non-destructive detection, Semiconductive material, Micro bulk defect, Generalized Lorenz, Mie Theory (GLMT), Near-infrared laser, Scattering IPC Code: B81B7/02 1 Introduction Now-a-days, non-destructive detection of micro/nano bulk defects in semiconductive materials is one of the hottest research fields in micro/nano technology. It plays very important role in the development of Very Large Scale Integrated Circuit (VLSI) and Micro Electric Mechanical Systems (MEMS). Especially, the development of high deepbroad ratio machinery superfine processing technique makes it necessary to improve uniformity of semiconductive materials. It is reported that bulk defects would affect and reduce the function of micro devices. At the same time, the study on detection bulk interior property is helpful to the research of semiconductive materials. The existing method can detect defects in materials. Ultrasonic, Transmission Electric Microscope (TEM) and optics etc, cannot satisfy the demands for nondestructive detection of micro bulk defects in semiconductive materials. It is important and imperative to develop a new method that can implement the task for material research and quality monitoring. Today, it has many examples to detect defect and granularity by using scattering signal. The application based on the detection of near infrared laser scattering signal in lange-angle is presented at the end of nineteen eighties. Laser Scanning Tomograph (LST) has been developed rapidly at the beginning of the nineteen nineties 1,2, but the research on the scattering distribution is still blank, and our work solve the problem to a certain extent 3. 2 Principle The method of measuring micro bulk defects is given based in the foundation and development of Generalized Lorenz and Mie Theory 4 (GLMT), which discuss the situation of a single spherical particle illuminated by a polarized Gauss wave. As Figure 1 shows, a spherical particle is placed at the zero of a rectangular coordination system, the incident light is along the Z-axes. The scattering light intensity at P( r, θ, ϕ ) caused by the particle can be described as Eq. (1): I0F ( θ, ϕ, q) I ( r, θ, ϕ ) = (1) 2 2 2K r In Eq. (1), I 0 is the intensity of incident light, K = 2π λ (λ is wave-length of incident light), r represents the distance between the particle and point P, F ( θ, ϕ, q) is scattering function, which can be shown as, 2 2 F (,, q) i1 sin i2 cos θ ϕ = ϕ + ϕ (2) In Eq. (2), i 1 and i 2 are called General Mie intensity index, which are the function of scatter angle θ, the relative complex refractive index m, the size parameter q and the diameter of the incident light waist ω 0. From Eqs (1) and (2), we can reason out following conclusion, (1) In the light elastic scattering, scattering waves are consisted of different order syntonic waves.

2 ZHENG et al.: NOVEL MICRO BULK DEFECTS IN SEMICONDUCTIVE MATERIALS 373 (2) The light intensity in the scattering field is determined by size parameter q, relative complex refractive index m, scattering distance r, scattering angle θ and ϕ, incident wavelength λ and the diameter of the incident waist ω 0. (3) In certain application, when r, θ, ϕ and λ are constant, the spatial distribution of the scattering light is only related to m and q, which reflect property and scale of the scattering particle. Therefore, if an optical detector is placed at the Y- axes in Fig. 1, we can scale the particle and analyze the scattering signal. The sketch of detect method based on GLMT is shown in Fig. 2, near infrared polarized Gauss beam that is transparent to silicon is first emitted from a laser. It passes through an aperture and then is focused to be a thin beam of 30 µm in diameter at the focal point. Afterwards the focused beam is incident into the measured sample which is placed on a precision three-dimensional stage, by moving the stage stepwise and collecting the scattered light with CCD in the direction vertical to the incident laser light at the same time, the sample is scanned overall. If there is a bulk defect in the sample, we can receive scattering light signal by CCD and process the signal by computer. 3 Defect Criterions Different defects have different scattering light distribution on a certain spatial area. Generally, both relative complex refractive index m and size parameter q are unknown to detect course; in order to find a criterion, numerical value calculation of scattering light distribution based on GLMT is carried out under different combinations of m and q, shown in Fig. 3. According to Fig. 3[(a)~(f)] we can find, though relative refractive index m turns from small to big, from real to complex, the change of the scattering light distribution is similar. When the radius of the scattering particle changes from 15 to 1 µm (q changes from 75 to 5 when λ=1.3 µm) or even smaller, the ripples (or the max peaks) of the scattering light distribution curve on a certain Fig. 1 Coordination of GLMT spherical particle scattering light 1.laser 2.aperture 3.lens 4.3D precision stage 5.sample 6.CCD 7.computer 1 2 Fig. 2 Sketch of detect method based on GLMT Y X Z Fig. 3 Numerical value calculation of scattering light distribution based on GLMT under different combinations of m and q (λ=1.3 µm,θ =75 ~105, ϕ =90 )

3 374 INDIAN J PURE & APPL PHYS, VOL 45, APRIL 2007 acquired plane monotonously decrease from many to one at the same time (θ = 75 ~105, ϕ = 90 ) as shown in Table 1. Therefore, we extract ripple as character I, and can use it scale the size of a defect by computer from several ten to several microns. Further, analyze Fig. 3[(a)~(f)] thoroughly, it can be found that character I are always 1 when the defects sizes are smaller than 1 µm, and at this time we can only draw a conclusion that the defect is smaller than 1 µm by use character I. However, symmetry of the scattering light distribution changes monotonously and markedly under this condition as Table 1 Character I of varying defects m=0.4 m=0.6 R Ripple R Ripple 15 µm 7 15 µm 8 10 µm 6 10 µm 7 5 µm 4 5 µm 4 1 µm 1 1 µm 1 m=0.8 m=(0.4+i8.7)/3.5 15µm µm 7 5 µm 4 5 µm 6 1 µm 1 1 µm 2 m=(0.2+i7.8)/3.5 m=(1.2+i10.2)/3.5 5 µm 5 5 µm 6 1 µm 2 1 µm 2 shown in Table 2. So, it is extracted as character II by Eq. (3) to scale defect from hundreds to tens of namometers, [ I( x = 0, z = 15) I( x = 0, z = 15)] X = I( x = 0, z = 0) (3) Thus, two characters are extracted to characterize the scattering light distribution, which provide a theoretical basis in deciding the size scale of micro bulk defect. 4 Experimental Details A set of experimental apparatus is built to prove the detect method and defect criterions. It s schematic drawing is shown in Figure 4, In Fig. 4, a infrared CCD line array is used as detector, for it s phototonus is very sensitive, it will be saturated while the scattering light comes from a Table 2 Character II of varying defects m=0.4 m=0.6 R Symmetry R Symmetry 1 µm µm µm nm µm nm 0.06 m=0.8 m=(0.4+i8.7)/3.5 1 µm nm nm nm nm m=(0.2+i7.8)/3.5 m=(1.2+i10.2)/ nm nm nm nm Infrared CCD Power Supply CCD Power Supply Storage Oscillograph XYZ 3D Image Board Monitor Adjust Setting Plane Monochrome CCD Infrared Line CCD Computer refrigerator Laser Microscope Field Lens Drive Power Supply Fig. 4 Schematic drawing of experimental apparatus

4 ZHENG et al.: NOVEL MICRO BULK DEFECTS IN SEMICONDUCTIVE MATERIALS 375 big bulk defect. Therefore, we use a monochrome CCD besides the infrared CCD, when the signal is strong, we use monochrome CCD, and when the signal is weak, use infrared CCD. In the detect course, signals come from monochrome CCD are saved as bite grayscale data corresponding to CCD pixels. In order to use the two extracted characters, we select 512 signals of the center line as the result of experiment. Signals come from infrared CCD are saved as 1024 data. A set of GaAs samples demarcated by infrared microscope are studied, the demarcated property are shown in Table 3. After filtering, detection results are shown in Fig. 5. Table 3 Demarcated property of GaAs samples Sample number I II III IV V Size of micro bulk defect 3 10 µm 2 10 µm 1 10 µm Several micron Not find Compare character I and II with the extracted criterions, the detect result are shown in Table 4. 5 Conclusion A character recognition method has been developed to detect micro/nano bulk defects semiconductive materials and an experiment has testified it. The experiment results are up to samples preferable in defects size scaling. So, we can draw a conclusion that the method based on the detection of near infrared laser scattering signal can scale the size of Table 4 Character I and II with the extracted criterions Sample number Character I Character II Criterion Defect size in sample I 8 I about 30 µm II 7 I about 20 µm III 5 I about 10 µm IV 3 I several µm V II Several hundred nm Fig. 5 Detection results of a set of GaAs samples

5 376 INDIAN J PURE & APPL PHYS, VOL 45, APRIL 2007 defects by light distribution analyzing. This method has many advantages in comparing with the method using scattering light intensity signal, the disturbance of the exterior decreases markedly and the detect precision improves to 0.1 µm, more than these, this recognition method makes it possible to detect micro bulk defects automatically. So, it is useful in microstructure processing and has great apply value. References 1 Fillard J P, Montgomery P C, Gall P, etc, J Crystal Growth, 103 (1990) Moriya Kazuo & Hirai Katsuyuki, J Appl Phys, 66(11) (1989) Jun Chen, Zheng You, Zhaoying Zhou & Xingzhan Liu, Proceedings of the China-Japan Joint Workshop on Micromachine/MEMS, (Beijing, China), (1997) 134, Gouesbet G, Maheu B & Grehan G, J Optical Society of American A, 5(9) (1988) 1427, 1443.