RF Modules and MEMS

Mass loading is a technique used to tune the resonant frequency of RF filters. To successfully tune a filter with this technique, accurate metrology and frequency measurements are needed. The Echo acoustic metrology system accurately measures the mass load film which can be combined with frequency measurements from electrical test through Onto Innovation's Discover software to monitor and control the mass load process steps in filter manufacturing.

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.

Filters have become critical to managing the number of frequency bands that current mobile devices use to ensure clear communication. Filters have also become a significant portion of the overall cost of goods within RF front end modules. Reducing defectivity is critical to achieving performance and yield. Onto Innovation's advanced inspection systems are used throughout the process to highlight, track, and classify yield-robbing defects.

The ability to detect defects that are not visible on the top surface of a device is critical for many MEMS devices. Multiple angles in multiple directions further complicate the ability to properly monitor device quality and integrity. Onto Innovation uses unique illumination techniques across multiple wavelengths to create the optimal inspection capability for each unique MEMS device.

Complex MEMS manufacturing processes not only require a variety of handling solutions, but also place stringent demands on wafer handling, including limiting wafer contact to the extreme edge of a wafer, or perhaps, limit contact with the wafer completely.

A variety of handling solutions are needed to support the variety of requirements, including the ability to offer no wafer contact while also delivering wafer inversion capability for combined frontside and backside substrate inspection. Customized handling solutions can be created to meet the most demanding handling requirements.