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The Picometer Ellipsometer
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The Picometer Ellipsometer is a very sensitive and fast single-wavelength or spectroscopic research ellipsometer. In contrast to conventional ellipsometers based on the nulling technique, the Picometer Ellipsometer uses phase modulation to achieve a higher sensitivity and lower noise under almost any measurement condition. Phase modulation makes the instrument insensitive to small variations in the measurement conditions which are inevitably introduced by glass windows, sample cells, or variations in the sample surface itself such as waves on a liquid.
The ellipsometer uses a Photoelastic Birefringence Modulator to modulate the polarisation of the incident light beam at a high, well defined frequency. Lock-in detection of the modulated detector signal eliminates most sources of noise to achieve the high sensitivity. The sensitivity is usually shot noise limited, and typically is equivalent to an ellipticity of about 10-5, or to a polarisation angle of 10-3 degrees at a time constant of 1 s. This is equivalent to a detection limit of less than 10-12Êm of oxide on the silicon surface (about 1/100 of a monolayer).
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| Instead of a rotating polariser, a Photoelastic Birefringence Modulator is used to analyze the ellipticity of the reflected beam with a response time of up to 1Êms. Beaglehole Instruments' unique modulator features a three element design that makes it independent of temperature variations. |
The response time can be as short as 1 ms. The ellipsometer is then fast enough to follow most dynamic situations in real time. In its standard configuration, the Picometer Ellipsometer operates at a single fixed wavelength. It can be modified with components from our Modular System at any time - for example, the instrument can be fitted with a monochromator and white light source for spectroscopic measurements, or can be converted into an Imaging Ellipsometer. The Picometer Ellipsometer is more than just an ellipsometer: it is a base system that can be configured for a variety of optical measurements.
Applications
In addition to the standard applications of a conventional ellipsometer, the short response time makes the Picometer Ellipsometer ideal for watching the dynamics of adsorption, and for in-situ monitoring of the growth of thin films. For these uses the ellipsometer can be set to automatically seek the Brewster angle, a feature which makes it very easy to set up - special cells with high precision windows are not needed. The phase modulated technique is also ideal for studying liquid surfaces, where conventional instruments are often disturbed by surface waves.
When operated at normal incidence the Picometer Ellipsometer becomes a fast and highly sensitive instrument for studying reflectance anisotropy. This allows the study of small surface effects by suppressing the bulk ellipsometry signal.
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© beaglehole instruments 1998-2001 All material on this page is copyright. Last updated: Thursday, 5 April 2001 |