The Laser Thickness Monitor (LTM) is designed to perform an in-situ control of thin film growth by a non destructive optical method. LTM measures the interference pattern intensity during film growth as a function of the elapsed deposition time.The Laser Thickness Monitor (LTM) is designed to perform an in-situ control of thin film growth by a non destructive optical method. LTM measures the interference pattern intensity during film growth as a function of the elapsed deposition time.

The laser intensity is measured by detector a (Fig.1a). Detector b is monitoring the reflected intensity which is modulated by interference between the top and the bottom interface of the thin film and depends on the thickness of the growing film on the substrate.

While the reflection from the substrate is constant, the variation is due to interference of the two interfaces (substrate/sample and sample/vacuum). The signal depends on the refractive index of the sample and, in turn, on the laser wavelength (lambda) and eventually on the refractive index of the material (n). It also depends on the laser beam incidence angle with respect to the normal of the sample plane (alpha).

Compared to ordinary thickness monitors (i.e. quartz balance thickness monitors) the LTM provides the following advantages:

• in–situ measurement system

• real optical thickness measurement during film growth

• installation outside the vacuum chamber

• insensitive to electromagnetic radiation (plasma, RF noise, etc.)

• extremely sensitive to thickness growth (depending on the refractive index; few nm for n=2).

• can be set at any distance from the film (remote)

• no part substitution required.

The benefits are:

• Excellent stability due to the dual beam detection

• Fully proprietary control system software

• Available with different laser wavelength for refractive response optimisation