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Automated Surface Profile and Film Thickness Analyzer

IP.com Disclosure Number: IPCOM000039244D
Original Publication Date: 1987-May-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 4 page(s) / 67K

Publishing Venue

IBM

Related People

Chastang, JC: AUTHOR [+3]

Abstract

1. INTRODUCTION Current surface profile measuring techniques are accurate, but most require a direct contact between a probe and the sample. There are instruments and techniques for accurate measurement of film thickness (such as ellipsometers and film thickness analyzers) which use optical techniques for measuring in the micrometer range. Thick films are not measured by such instruments due to wavelength ambiguity in the results. A light section microscope is not accurate and requires a skilled operator. No currently available instruments automatically and easily measure films whose thicknesses lie beyond the range of interferometric techniques and below the range of simple optomechanical devices. (Image Omitted) 2.DESCRIPTION OF INSTRUMENT 2.1 General Principle The instrument in Fig.

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Automated Surface Profile and Film Thickness Analyzer

1. INTRODUCTION Current surface profile measuring techniques are accurate, but most require a direct contact between a probe and the sample. There are instruments and techniques for accurate measurement of film thickness (such as ellipsometers and film thickness analyzers) which use optical techniques for measuring in the micrometer range. Thick films are not measured by such instruments due to wavelength ambiguity in the results. A light section microscope is not accurate and requires a skilled operator. No currently available instruments automatically and easily measure films whose thicknesses lie beyond the range of interferometric techniques and below the range of simple optomechanical devices.

(Image Omitted)

2.DESCRIPTION OF INSTRUMENT

2.1 General Principle The instrument in Fig. lA consists of a microscope objective MO, a beam splitter BS, a light source LS and a photodiode PD. MO is stationary, while BS, LS and PD are mounted on a linear translation stage whose motion is parallel to the optical axis xx' of MO. As represented in Fig. lA, the instrument is focused on a point P of sample S. This means the image of LS given by MO is coincident with P and that the image P' of P given by MO is coincident with PD. Assume now that the sample S is translated in a direction orthogonal to xx'. Let Q be the new intersection of xx' and S dx is the projection of PQ on xx' (i.e., dx is the surface height variation between P and QP. The image Q' of Q lies at a distance dx' from the previous image P' of P dx', which is given by the relationship. (Fig. 1B): dx' = m2 x dx (l) where m is the linear transversal magnification of MO. Q' and PD are not coincident. To measure dx', focusing is necessary, accomplished by translating the stage so Q' and PD are coincident. The translation is equal to dx'.

See Fig. lC. Measuring is carried out in image space using the tremendous "leverage" afforded by the m2 term in Eq. (l). 2.2 Practical Considerations The measurements are made in object space, and LS, BS, PD and MO are displaced as an integral unit to perform the focusing operations. However, this image space measuring (ISM) technique has an advantage over the object space measuring (OSM) technique. The ISM instrument has an accuracy of the order of 0.2 mm over a range of tens of micrometers (in object space naturally). The OSM instrument can have the same range, but at great cost. For example, an OSM instrument equipped with an electronic linear measurement gauge to monitor its displacement has a gauge accuracy that is excellent over small ranges. An alternate approach is to use a glass-scale-based linear measuring device; however, though the range is enormous, the accuracy is mediocre. The use of an interferometer-based measuring device is accurate, but the range is not practical because of high cost. Returning to Eq. (l), assuming m is about 32, the amplification factor is about l000 between th...