Determination of thin film topography (Technion)
Interferometry is a method which allows the measurement of very small distances and thicknesses by way of transmitting two beams and using the interference principle (i.e., how they reinforce or neutralize each other) to determine the difference. A problem with interferometry is that it is usually limited to dimensions of the order of one-tenth of the light wavelength. An alternative technique, ellipsometry, also helps determine the dielectric properties of materials (e.g. semiconductors, metals, liquids) both in bulk and in films, from the characteristics of light reflected from their surface, but requires bulky equipment because of the oblique incidence angles required.This invention demonstrates an optical technique for thin film topography-determination and thickness measurement down to dimensions less than one percent of the wavelength.
Three beams are transmitted onto a specimen, with the first two being reflected – one from the front surface and the other from the back surface. The third beam is for reference purposes; it is transmitted in such a fashion which allows acquisition of topographical information which cannot be acquired using contemporary appliances fed by two reflected beams alone.
• No limitation on substrate opacity
• Particularly superior to existing methods in cases of specimens thinner than 50nm.
• Measures depths as thin as 2nm. Thickness measurement accuracy < 0.5nm
• Non-destructive measurement-taking (no contact with the specimen)
• Our invention constitutes a strong alternative to ellipsometry in that
o It is compact – which is particularly advantageous in the context of process lines (it works at
normal incidence with respect to a measured specimen)
o It is low-cost (it operates with wide-band light, requiring no spatial coherence)
o It captures thickness variations in a single imaging frame (our system is implemented using a
standard imaging system)
This invention has potential uses in thin and ultra-thin film metrology (50nm and down to 20Å) at a low cost. It may be used in QA, inspection and process control procedures of various industries (e.g. the semiconductors industry). Also, it captures thickness variations in a single imaging frame.
CHM-0676
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