Round robin test for height valuation methods, LEL and W/3, in China

In the field of optical microscopy, height valuations, or calibrations, are critical to ensure accuracy and traceability. Height assessment, however, may be controversial, particularly for measurements on large steps or narrow grooves. Thus, standard setting and instrument operations are essential. In this paper, the limited energy lost (LEL) method, which is a Chinese solution, and the well-known ISO W/3 method were both applied in a two-year round robin test to verify their theoretical compatibility and promote their corresponding applications throughout China. The results show that the LEL method successfully predicted outlier growth for progressively narrowing grooves. In addition, compared with the W/3 method, 71% of the results from 24 measurements showed improved repeatability when applying the LEL method. This paper supports the LEL method with evidence from a large sample, after its original publishing in 2016 and the subsequent publication, as a key part of China's standard on confocal microscopy, in 2017. These results indicate that dynamic model-based valuation might be the future trend for 3D optical micro-nano metrology.