Nondestructive Wafer Level MEMS Piezoelectric Device Thickness Detection.

Area of Science:

• Materials Science
• Nondestructive Testing
• Acoustics

Background:

• Traditional thin film thickness inspection methods face limitations in wafer-scale applications and with opaque materials.
• Accurate thickness measurement is crucial for micro-electromechanical systems (MEMS) devices like PMUT, FBAR, and SAW devices.

Purpose of the Study:

• To introduce a novel, nondestructive, wafer-scale thin film thickness measurement method.
• To demonstrate the method's effectiveness on scandium doped aluminum nitride (AlScN) and molybdenum (Mo) layers.
• To validate the method by comparing in-situ measurements with Scanning Electron Microscope (SEM) data.

Main Methods:

• Utilizing picosecond ultrasonic waves to detect reflected waves between interfacial layers.
• Employing a 515 nm laser for measurements.
• Characterizing single Molybdenum (Mo) electrode layers (100-300 nm), single AlScN piezoelectric layers (600-1000 nm), and combined stacking layers.
• Measuring a standard piezoelectric composite structure (Mo/AlScN/Mo).

Main Results:

• The method successfully measured individual Mo and AlScN layers within specified thickness ranges.
• Accurate thickness characterization of the Mo/AlScN/Mo piezoelectric composite structure was achieved.
• In-situ 8-inch wafer scale measurements showed good agreement with off-line SEM data.

Conclusions:

• The developed picosecond ultrasonic wave method offers an efficient and accurate approach for nondestructive wafer-scale thin film thickness measurement.
• This technique is suitable for opaque materials and various piezoelectric stacking layers used in MEMS.
• The method provides a reliable alternative to traditional inspection techniques for advanced material characterization.