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Optoelectronic Signature Technique and Associated Measurement System for Defect Characterization on Rigid Surfaces

IP.com Disclosure Number: IPCOM000046289D
Original Publication Date: 1983-Jun-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 4 page(s) / 70K

Publishing Venue

IBM

Related People

Hamaker, RW: AUTHOR [+3]

Abstract

It is well known that certain types of microscopic surface defects on rigid magnetic storage media are directly related to loss of magnetic storage performance. To detect such defects, several types of laser scanning optoelectronic techniques have been developed by Hopkins IBM Technical Disclosure Bulletin 20, llB, 4939 (April 1978)) and by Martin and Williams NASA Technical Briefs 4, (March l979)), the latter being initially utilized for defect detection on semiconductor wafer surfaces. Both types of system provide rapid defect detection capability over large surface areas; hence they are ideal for product screening applications. Furthermore, both techniques employ electronic pulsesampling comparator features to permit defect-size discrimination.

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Optoelectronic Signature Technique and Associated Measurement System for Defect Characterization on Rigid Surfaces

It is well known that certain types of microscopic surface defects on rigid magnetic storage media are directly related to loss of magnetic storage performance. To detect such defects, several types of laser scanning optoelectronic techniques have been developed by Hopkins IBM Technical Disclosure Bulletin 20, llB, 4939 (April 1978)) and by Martin and Williams NASA Technical Briefs 4, (March l979)), the latter being initially utilized for defect detection on semiconductor wafer surfaces. Both types of system provide rapid defect detection capability over large surface areas; hence they are ideal for product screening applications. Furthermore, both techniques employ electronic pulsesampling comparator features to permit defect-size discrimination.

The aforementioned optoelectronic techniques have provided significant product cost-saving potential for rigid magnetic disk media processes through their rapid sampling/defect screening features. However, because of the qualitative nature of defect detection in both techniques, an additional technique is required to quantitatively identify such defects as to shape and type as well as size.

Described herein is an optoelectronic technique that will provide the required defect identification/ characterization sensitivity, while having the capability of operating in a rapid scan mode. This technique utilizes the basic principle of non-isotropic light scattering from illuminated microscopic defects of different materials and geometries. Defect size, shape and type can be derived directly from the resultant radiated light patterns.

Specifically, by projecting a narrow beam of incident light onto a flat medium surface in the vicinity of a defect, a characteristic angular distribution of radiated light intensity will be emitted from the object (optical signature). This radiated intensity pattern is considered to be due to two independent, fundamental physical effects: light scattering and diffuse reflection.

The former effect is caused by induced molecular electric dipole moments within an object after interacting with an incident light beam. The resultant dipole radiation will be a function of both the molecular structure and size of the object. For molecular size particles, this effect is known as Rayleigh scattering (Lord Rayleigh, (J. W. Strutt), Phil . Mag . 41, 107 (1871); Ibid., 47, 375 (1899)). For larger particles, the effect is known as Mie scattering (G. Mie, Ann . Physik . 25, 37 (l908); also, T. Allen, Particle Size Measurement, Chapman and Hall Publ., London, l975.)

The latter effect, diffuse reflection, is based on light reflection from an object having either strong surface curvature or a high degree of roughness. If each element on the exposed surface of a defect reflects an incident light beam according to the laws of regular (specular) reflection, the resultant r...