Quality monitoring of PZT

From experience, much information on the quality of PZT, including uniformity, is learned from visual observations of the deposited thin film on the wafers. In addition for qualitative assessment, the quality must also be monitored for less obvious characteristics such as film thickness, and determining the correct crystallite phase and quality by x-ray diffraction. Tables of specifications have been worked out to aid the quantitative assessment of the quality of the PZT. The ultimate characteristic of the film is the (electromechanical) performance of the piezoMEMS device.

The use of test-wafers that follow production batches is likely to be the preferred solution for production process monitoring and early-stage verification of the key piezoelectric thin film properties. Non-destructive tests are of course preferred as routine controls, using e.g. aixACCT equipment, in particular for whole, completed wafers and batch-testing during production. The aixACCT Systems TF Analyzer 2000 E is the most versatile and sophisticated analyzer of electroceramic materials and devices, and is used widely for determining key characteristics such ferroelectric hysterisis, impedance, leakage current and fatigue, with recent capability for batch-to-batch testing.

Ideally, tests should be performed across whole wafers, and not be restricted to the use of statistical analysis as for point testing. Wafer mapping-techniques were developed and used extensively for the development of the high volume deposition tools in the piezoVolume project. More information on the double beam laser interferometer tool (aixDBL)is available on the aixACCT web-site.The rapid, accurate mapping and characterization of simple test patterns across wafers reveals the true film quality, and in particular enables the user to determine the most critical thin film performance uniformity (on wafer-level) from batch-to-batch and to do this before the most complex and costly micromachining steps are performed on the device production batch.


8inch Wafer map of AlN wafer for reference measurement

8inch Wafer map of AlN wafer for reference measurement

Published April 22, 2010