Improved On-Wafer Probing of High-Frequency Components Based on Optical Recognition of the Probe Positions

This article describes a novel method for on-wafer probing of high-frequency components based on optical recognition of probe skating and positions. The method enables a more accurate automatic probing of on-wafer structures and is developed to increase precision and accuracy in radio frequency (RF) measurements. The presented real-time optical recognition of the probe touchdown enables an estimated probe skating precision of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm ~3~\mu $</tex-math> </inline-formula>m on the evaluated probe system. Optical identification of the probes’ position is used for verification of the measurement distance. Wafer mapping of S-parameters conducted on microstrip (MS) lines on a GaN wafer are evaluated with regard to accuracy and precision in the 0.5–50 GHz range using metrology software for S-parameter analysis. The developed probing method is verified by comparing it to a standard procedure with fixed <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i>-height probing and to a bow-compensated method, with all measurements conducted on the same setup and the same device. It is shown that the optically recognized probe skating and position detection can improve the accuracy of S-parameter measurements by up to 50% for devices positioned across a wafer, assuming a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5\sigma $</tex-math> </inline-formula> acceptance margin for the probe distance.