X-ray of High Order Planes, Pathway for HBT Control

High volume HBT (Heterojunction Bipolar Transistor) production benefits from non-destructive measurement techniques to verify the quality of every product wafer. X-ray diffraction is non-destructive and sensitive to layer thicknesses and compositions. The thin layers typical of HBT designs yield weak diffraction intensity, which are overwhelmed by the signal from the substrate in the conventional (004) orientation. We have found that by diffracting from the (117) planes, much more information can be obtained. As the HBT layer peaks move away from the substrate signal this enables the in-line measurement of HBT product wafer characteristics, such as base doping. In this paper, we develop a new curve fitting methodology, and demonstrate the precise measurement of the base doping of HBT wafers in the production line for the first time. This technique is demonstrated to measure base doping changes in production as small as 1.8%.