SAW resonator-based wafer processing control

The electrical performance of SAW devices is impacted most strongly by metal thickness (h), line width (w) and, at high h/λ, electrode shape. For liftoff processes these key parameters are controlled in the photolithographic and metallization steps. For etching processes the metal etching step also has an impact on the parameters. Controlling the manufacturing process requires an accurate, repeatable method of measuring these parameters. A test mask developed to determine these key parameters and their corresponding uniformity over the entire substrate through electrical measurement will be presented. The mask incorporates resonators with 0.5 μm linewidths, which are used to measure the key parameters of the wafer processing. All of the required resonator parameters are derived from wafer probe measurements within the stopband thereby minimizing interaction with adjacent resonators. A liftoff process is evaluated by wafer probing quartz wafers processed with the test mask and with 0.10 to 0.12 μm aluminum metallization. The wafer probe measurements of the resonators are used to determine h and w variations across the wafer. A 2D mapping of the parameters across the wafer is made to assist in adjusting the manufacturing process.