Measuring and controlling deposition on a piezoelectric monitor crystal
US5112642A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | Mar 30, 1990 |
| Grant date | May 12, 1992 |
| Priority date | — |
| Expiry date | Mar 30, 2010 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01B7/066
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
The thickness and rate of growth of a deposited film is monitored using a piezoelectric crystal sensor such as an AT-cut plano-convex crystal. The frequencies of the fundamental frequency and another resonance mode are measured prior to deposition, and the change of these two frequencies is monitored during deposition. The areal mass density of the deposited material is determined from these two resonance frequencies for the uncoated quartz crystal and for the crystal during deposition. A frequency generator provides accurate sweeps of frequency which are applied to the crystal, and the crystal response is supplied to a phase detector to identify the positions of the resonance frequencies. The acoustic impedance ratio Z of the deposited material relative to the fresh crystal is computed from the resonance frequencies for the coated and uncoated crystal, by applying the modal equations for AT-cut plano-convex quartz crystal and Lu-Lewis relation. From the frequency shifts and acoustic impedance ratio, and areal mass density can be calculated. The same crystal can be used to control the growth rate of several successive layers.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.