BAW filter process control
State-of-the-art smartphones continue to add more frequency bands and contain more than 60 RF filters. With the planned migration to 5G, the complexity of the filters is increasing several fold to enhance the user experience as well as to provide flexibility to mobile providers.
Frequency response of filters is determined by a combination of the thickness and acoustic properties of the piezoelectric layer layer. Thickness uniformity requirements for the films are beyond what process tools can offer at deposition and there are several options available to achieve such tight controls post-deposition. Metrology techniques employed for characterizing these properties must meet the sensitivity, accuracy and stringent repeatability requirements.
The Echo acoustic metrology system can simultaneously and accurately measure the piezo layer as well as the top and bottom electrode films on product wafers. Measurements from the technique are used to feed forward to the trimming process to adjust the center frequency and improve wafer to wafer variability. Also, when combined with frequency measurements through Onto Innovation's Discover software, value added SPC control is provided to improve yield.