Nondestructive Observation of Depths and Dimensions of Subsurface Microdefects in Czochralski-Grown and Epitaxial Silicon Wafers

Abstract

Evaluation of the depths and dimensions of microdefects are nondestructively studied in the subsurface region of Czochralskigrown and epitaxial silicon wafers, using a new short wavelength laser scattering tomography which was proposed in our previous paper. It has been shown experimentally that the method is capable of observing the depths and dimensions of microdefects in the subsurface region and that of their densities of silicon wafers. From these results, depth profile of size distributions of detected subsurface defects have been obtained. For epitaxial wafers, distinct boundaries between their epitaxial layers and substrates are successfully detected.One of the key factors of success for ultralarge scale integrated ͑ULSI͒ fabrication is the quality of the subsurface region ͑to a depth of a few micrometers͒ of silicon wafers. 1,2 It is very important to know information about the depth and dimension of microdefects in the region, but there are no nondestructive methods which are available for the subsurface region to a depth of a few micrometers. In our previous paper, 3 we proposed an original method of nondestructive short wavelength laser scattering tomography ͑S-LST͒ for determining the depths and dimensions of individual microdefects in the subsurface region to a depth of 5 m, utilizing the temperature dependence of the absorption coefficient of silicon at the laser wavelength. In the present paper, we apply this S-LST method, which we call the two-temperature S-LST method, to Czochralski-grown ͑CZ͒ and epitaxial silicon wafers, to clarify its capability for observing the depths and dimensions of microdefects in the subsurface region of these silicon wafers. From these results, depth profiles of size distributions of the detected defects and that of their densities are obtained. An Outline of the Two-Temperature S-LST MethodWe briefly review the outline of the two-temperature S-LST method. 3 The detected intensity I(d) of the light scattered by a defect at a depth of d decreases exponentially with d as followswhere A, which reflects the dimension of a defect, corresponds to the detected intensity of light scattered by a defect located on the surface (d ϭ 0) and ␣ is the absorption coefficient of silicon at the incident laser wavelength. Note that the scattered light is observed just above the wafer. According to the two-temperature S-LST method, d and A are calculated from the scattering intensities I 23 and I 83 which are measured at 23 and 83°C as follows d ϭ ln͑I 83 /I 23 ͒/͓Ϫ2͑ ␣ 83 Ϫ ␣ 23 ͔͒ ͓2͔A ϭ I 23 exp͑2␣ 23 d ͒ ͓3͔where ␣ 23 and ␣ 83 are the absorption coefficients at the incident laser wavelength ͑680 nm͒ in silicon at 23 and 83°C, respectively. In our study, ␣ 23 ϭ 2200 cm Ϫ1 and ␣ 83 ϭ 2905 cm Ϫ1 are used. 3 Observation of Subsurface Microdefects in a CZ-Si WaferFirst, depths and dimensions of defects in CZ wafers are studied by the two-temperature S-LST method. In CZ wafers, the size distribution and the density of microdefects at each depth should be similar over the subsurface region....

Topic Review: Application of Raman Spectroscopy Characterization in Micro/Nano-Machining

“…A new laser scattering method was also used to detect subsurface defects. Goto et al [ 13 , 14 ] measured the depth and dimension of subsurface microdefects in Czochralski-grown silicon wafers and epitaxial silicon wafers using the laser scattering method. They found out that this method could determine the depth of subsurface defects which are less than 5 μm deep, and the boundaries between the epitaxial layers and substrates were detected successfully.…”

Non-destructive evaluation methods for subsurface damage in silicon wafers: a literature review

“…Figure 14 shows a result of the number of the defects versus the penetration depth for the CZ wafer. For epitaxial wafers, distinct boundaries between their epitaxial layers and substrates were successfully detected (Satio et al, 2002). Satio et al (2002).…”

“…For epitaxial wafers, distinct boundaries between their epitaxial layers and substrates were successfully detected (Satio et al, 2002). Satio et al (2002). Sun et al (1998) have set up a two-detector laser scattering system as illustrated in Figure 15.…”