A new type of electroless deposition monitor has been constructed from a monolithic acoustic wave device utilizing plate modes with shear displacement components. This device, which operates at 158 MHz, provides a highly accurate means of measuring mass changes (1 ng sq cm) accompanying electrochemical reactions. The acoustic wave, in the form of a plate mode, is launched by applying a radio frequency signal to an interdigital transducer on one face of a piezoelectric substrate. Electroless deposition is carried out on the opposite face of the quartz in the path of the wave. The acoustic plate mode, which propagates along the quartz plate to the receiving transducer, has components of displacement at the surface/electrolyte interface. Changes in mass at the quartz/electrolyte interface affect the acoustic wave velocity, which is monitored with high accuracy by utilizing the device as the feedback element of an oscillator circuit. The electroless deposition of Cu at a rate of 2 to 3 angstons per second from aqueous Cu (2+) formaldehyde was monitored with sub-angstrom resolution.
Presented at the 172nd Meeting of the Electrochemical Society
- Pub Date:
- Electroless Deposition;
- Sound Waves;
- Rayleigh Waves;
- Instrumentation and Photography