Quality monitoring of PZT
In piezoVolume attention is paid to the development of in-line quality monitoring right from the beginning. The throughput of one such in-line quality monitoring tool is expected to be 10 wafers/h. For latest results, see Project results.

For latest results, please see Project results.

Today there are no available tools or procedures for quality monitoring industrial deposition of PZT thin films. For piezoMEMS, complete devices have to be fabricated and then tested. For cost effective production it is essential to evaluate the film quality at an early stage in production, before more costly process steps like e.g. back side etching are performed.

Quality monitoring can be split into methods that are related to the quality of the morphology, e.g. in-situ XRD or ellipsometry and electrical and electromechanical test methods that are related to the ferroelectric and piezoelectric properties of the PZT. The first group of test equipment gives excellent feedback on the crystallinity, film thickness and the refraction index, whereas the second group would monitor the essential properties directly related to the device performance, e.g. d33, dielectric constant and displacement.

For in-line quality monitoring of the PZT deposition process in a production facility the piezoelectric coefficients must be monitored directly in high throughput at wafer level. This has never been done before. piezoVolume will rely on the DBLI technology, as it is known for high resolution (less than 1 pm), speed and good repeatability for small sample sizes. Hence, aixACCT will develop a tailored DBLI tool for quality control suitable for 150 mm and 200 mm wafers in high volume production.

The DBLI tool will be developed to meet the following testing needs:

  • Early stage elimination of wafers with inferior quality films: In a production process the film quality needs to be determined at an early stage of the process to decide if a certain wafer should proceed in production. This is managed by monitoring the piezoelectric coefficient d33,f.
  • Wafer level e31,f “estimation”: For most MEMS applications the effective transverse piezoelectric coefficient e31,f  is the most important, but this parameter cannot yet be monitored on wafer level. Therefore the correlation between e31,f and the longitudinal coefficient, d33,f, which can be monitored on wafer level will be investigated in detail.
  • Accelerated life time testing: It is worthwhile to find accelerated lifetime testing procedures in order to reduce testing time and therefore cost. No procedures exist today to extrapolate life time. Our aim is to transform and apply the knowledge from bulk ceramics, multilayer actuator, and FeRAM testing to thin film applications.
  • Device quality testing: Within the micro-manufacturing process chains the device quality needs to be monitored to evaluate performance and reliability.

Published April 22, 2010

aixACCT

DBLI tool from aixACCT

The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2010-2013) under grant agreement n° 229196