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

• Main Author: Peter J. de Groot
• Format: Article
• Language: English
• Published: MDPI AG 2017-01-01
• Series: Applied Sciences
• Subjects: topography; metrology; instruments; standards; interferometry; resolution
• Online Access: http://www.mdpi.com/2076-3417/7/1/54

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.