The Meaning and Measure of Vertical Resolution in Optical Surface Topography Measurement

• Published in: Applied sciences Vol. 7; no. 1; p. 54
• Main Author: de Groot, Peter J
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.01.2017
• Subjects: Data acquisition; Equivalence; instruments; interferometry; metrology; Noise; Noise levels; Noise measurement; Phase modulation; Pixels; Repeatability; Reproducibility; resolution; Specifications; Topography
• ISSN: 2076-3417; 2076-3417
• DOI: 10.3390/app7010054

Vertical resolution is the most widely quoted and most frequently misunderstood performance specification for equipment that measures surface topography. Here I propose to use internationally standardized terms and definitions for measurement noise and surface topography repeatability as more meaningful quantifiers for measurement performance. A specific example is an interference microscope operating with a 100 Hz, 1 k × 1 k pixel camera, and a sinusoidal phase modulation to convert intensity data to a height map. The measurement noise is found experimentally to be 0.072 nm for a 1 s data acquisition using a surface topography repeatability test, which determines the random height-equivalent noise level for an individual pixel in the areal surface topography map. Under ideal conditions, the measured noise is equivalent to the instrument noise that may be published in a performance specification in place of the more common, but poorly defined, vertical resolution specification.