Method and apparatus for increasing signal to noise ratio in a photoacoustic film thickness measurement system
US7050178B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Jul 12, 2002 |
| Grant date | May 23, 2006 |
| Priority date | — |
| Expiry date | Jun 17, 2023 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N2021/1706
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
An apparatus for improving the signal to noise ratio of measurements of the thickness of layers in a thin film stack uses a photoacoustic measurement system that includes a time differentiation system for inducing a delay in pump beam pulses. The time differentiation system uses, among other things, a birefringent element and other elements to control the polarization of pump beam pulses. Use of the apparatus involves applying a time varying voltage to an electro-optic modulator driver and setting a time differentiation step; or, in another embodiment, applying a time varying voltage to an electro-optic modulator to induce a fixed time delay delta-t between a vertically polarized pulse and a horizontally polarized pulse. The high frequency operation of the system provides for improved determinations of film thickness.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.