Abstract
The least square circle method calculating shifts of center coordinates of concentric circles was developed in order to evaluate an overlay error for 3D microfabrication technology. This method consists of (1) SEM image capture of a truncated cone structure fabricated by multiple stacking of concentric circle patterns, (2) edge extraction of the circles and (3) calculation of the center coordinates by the least square fitting using matrix calculation software. The repeatability of the measurement method was examined by calculating the center coordinates of an identical SEM image for five times and that was better than 1 pixel in 3σ deviation. The calculation time was 5 min. for edge extraction for 80 points in 10 circles and less than 2 sec. for the calculation. This method was applied to evaluate the fabrication accuracy of FORMULA technology, which is our original 3D microfabrication technology using surface-activated bonding. The results showed that this method enables us to distinguish the random error from the systematic error of the fabrication.
