Fiber-optics Low-coherence Integrated Metrology for In-Situ Non-contact Characterization of Wafer Curvature for Wafers H
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Fiber-optics Low-coherence Integrated Metrology for In-Situ Non-contact Characterization of Wafer Curvature for Wafers Having Non-uniform Substrate and Thin Film Thickness Wojciech J. Walecki, Alexander Pravdivtsev, Kevin Lai, Manuel Santos II, Georgy Mikhaylov, Mihail Mihaylov, and Ann Koo Frontier Semiconductor, 1631 North 1st Street, San Jose CA 95112 Abstract. We propose novel stress metrology technique for measurement of local values stress tensor components in the coated wafers. New metrology is based on fiber-optic low coherence interferometry and can be applied to study stress not only in semicondiuctor wafers but in wide variety applications spanning from semiconductor to construction industry where measurements of plates covered by thin film encountered in flat panel displayes, solar cells, modern windows. Keywords: Thin-Film Metrology; Diagnostics; In-Situ, Real-Time Control and Monitoring, Thin Film Stress Metrology, Interferometry. PACS: 68.60.-p, 68.90.+g, 83.85.St, 95.75.Kk
INTRODUCTION Low coherence optical interferometry [1] has been proven to be an effective tool for characterization of thin and ultra-thin semiconductor silicon [2], [3], [4], compound semiconductor wafers [5], and MicroElectro- Mechanical Systems (MEMS) structures [6] [10]. In this paper we describe extension of this method to characterization of strained silicon wafers, SOI and other novel structures.
Traditional Stress Metrologies The metrology of stress and topography of silicon wafers is a mature field. Available solutions are based on large aperture optical interferometers, capacitance, and laser scanning tools. Free space optical interferometers for 300 mm wafer metrology are expensive due to high cost of large aperture optics and high cost of precision mechanical mounts. Due to large dimensions, and large mass of optical components they are rather difficult to integrate for in-situ applications, and their
integration with other complementary metrologies is usually quite cumbersome. Recently local stress metrology tool based on curvature-sensitive measurement was proposed by Rossakis et al [11]. This very interesting method allows measuring accurately curvature of the wafer when achieving very high throughput. It suffers however from the same limitations as traditional phase shifting optical interferometry – it requires use of large optics and is not capable to neither provide information on neither wafer nor film thickness. Some of the most successful tools for wafer topography measurements are based on capacitance measurements. This method however is not suitable for measuring thickness of semi-insulating and insulating materials, and does not provide insight in the internal structure of layered systems such as SOI. Laser scanning tools are offering several advantages over two earlier mentioned technologies. Laser scanning tools are easier to adapt in integrated environment, and have great potential for in-situ application. This technology does suffer however from limitations of accuracy inherent to
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