Framework for uncertainty evaluation in optical surface topography measurement using a virtual instrument

• Challenges in uncertainty evaluation using metrological characteristics. • Using a virtual instrument for uncertainty evaluation in optical surface metrology. • Introducing a framework to quantify the uncertainty contribution of error sources. • Employing a tilted optical flat for continuous scanner non-linearity measurement. Uncertainty evaluation in the measurement of surfaces with complex topography using optical techniques remains a challenge due to the complex interaction between light and the surfaces. The ISO 25178 part 600 specification standard simplifies uncertainty evaluation by introducing a set of agreed metrological characteristics that can be propagated through a mathematical model. To complement this, we developed a virtual coherence scanning interferometer to model error sources and provide task-specific uncertainty evaluation. This paper presents a framework for evaluating measurement uncertainty of areal surface texture parameters, using both the metrological characteristics approach and the virtual instrument method. We demonstrate this framework by assessing the uncertainty of the Sq parameter, which represents the root-mean-square of surface heights, for sinusoidal and quasi-random surfaces. By comparing the combined standard uncertainty from both approaches, we quantify the contribution of topography fidelity, a key but difficult-to-evaluate characteristic. The proposed method offers a comprehensive understanding of uncertainty in optical surface measurement, leading to improved tolerancing in manufacturing.