Multicenter comparison of alpha particle measurements and methods typical of semiconductor processing

Alpha counting measurement methods have been widely used in the semiconductor industry for many years to assess the suitability of materials for semiconductor production and packaging applications. Although a number of published articles describe aspects of this counting, a multicenter, comparative trial has not been carried out to assess the methodological accuracy of current methods. This paper reports on experience with a 9 center, international, round-robin style trial using a shared set of samples to quantify variability in alpha emission measurements. Four samples representing low and ultralow alpha materials were counted by each participating lab in a blinded trial. The consensus mean emissivity for low alpha material was estimated as 30.9 khr-1-cm-2 with a range from 20.2 to 45.5, less than half of which can be attributed to counting uncertainty or other known sources of error. A strong correlation for replicate measurements within a lab was also observed supporting the conclusion that there are systematic variations in equipment or calibration among labs. Eleven of 23 measurements of ultralow alpha materials were within 1 standard deviation of the consensus mean and 7 were at or below background. The high level of counting uncertainty for these measurements is thought to be sufficient to mask any systematic variation similar to the low alpha observations. Comparison of the reported values with a standard calculation demonstrates that there are also differences in the interpretation of the values reported for emissivity and error, underscoring the need for careful interpretation of results.