TITLE: Comparing Optical Profilometer Measurement Modes

CONTRIBUTOR: Simeona Hein, Graduate Student at the University of Pittsburgh

DESCRIPTION: I was interested in evaluating the various measurement modes on our white-light optical profilometer. Specifically, after using the STC samples to verify my training on a stylus profilometer, I began seeing differences across modes the various modes: phase-shifting interferometry (PSI), vertical scanning interferometry (VSI), or a combination technique called “VXI”. We wanted to know which mode was giving us the most accurate measurement, so I decided to use the smooth STC surface and its published consensus data as a reference.

OVERALL PROCESS: I measured the smooth STC surface using all three modes: (PSI, VSI, VXI), keeping constant the other factors like tool, sample, location, and magnification. I uploaded the data to contact.engineering, where I downloaded the average PSD for each dataset. I then compared the three PSDs to the STC results, specifically the published consensus PSD and its variability. Because each mode was measuring the same reference surface, this gave us a straightforward way to evaluate how the choice of measurement mode affected our results.

DETAILS: Here is the same standard operating procedure (SOP) that I used in the prior Use Case.

RESULT: As shown in the figure, there were discrepancies between the various modes when applied to this STC Smooth sample. It appears that VSI mode showed the best overall agreement with the STC consensus data, while PSI and VXI showed greater deviation, especially at the smaller length scales. This suggested VSI as our preferred mode for measuring samples similar to these, but it also showed us that selecting the best-performing mode was only part of the solution. There was still some deviation between the VSI measurement and the consensus data, reinforcing the STC recommendation to combine measurements from multiple techniques for reliable surface characterization.