Instrument Design

The UVISEL-2 spectroscopic ellipsometer is of phase modulated design, and the instrument uses a photoelastic modulator (PEM) to modulate the polarisation of the light beam at 50kHz rather than a rotating element operating at a few Hz.

The UVISEL-2 phase modulated ellipsometer has no moving parts during signal acquisition, allowing very high measurement precision and no beam rotation.

The UVISEL-2 phase modulated delivers excellent precision and sensitivity across the full range of Y and D angles, even when D is in the range 0º – 20º or 160º – 180º where rotating type ellipsometers suffer from poor performance, and when Y is close to 45º.

The reason for this is that phase modulated ellipsometers measure the quantities:

I_s =  sin(2. Y).sin(D) and I_c = sin(2. Y).cos (D)               (configuration II) or

I_s = sin(2. Y).sin(D) and I_c = cos(2. Y)                           (configuration III),

 rather than the values tan(Y) and cos(D) measured by a rotating type ellipsometer. As rotating ellipsometers measure cos(D) the precision and accuracy on D can be suspect for some parts of the angle domain. For the UVISEL-2 phase modulated ellipsometer the accuracy and precision on Y and D is excellent across the full range. Changing the configuration from configuration II to configuration III is automatic as the analyser and modulator are mounted on high precision stepper motors.

This can be very important when measuring very thin and / or highly transparent films. In addition the UVISEL-2 software will automatically take the backside reflection from a transparent sample into account when modelling the data.

Data Acquisition System

The UVISEL-2 phase modulated ellipsometer has a fully digital signal acquisition system. Every modulation cycle (50kHz = 20microsecond waveform) is sampled 16 times using a high precision analogue to digital converter and averaged numerically.

This method of measurement is far removed from electrical mains frequencies and mechanical vibrations, and the UVISEL-2 phase modulated ellipsometer may make measurements in environments that would be difficult for rotating type ellipsometers using analogue signal averaging.

The UVISEL-2 data acquisition system allows data capture rates at up to 1 millisecond per point (average of a minimum of 50 measurement cycles) allowing rapid processes to be followed with excellent signal to noise ratio.

The numerical signal acquisition system allows a simple mechanism whereby ellipsometric signals can be measured in the presence of an external perturbing field.

Spectral Range

190nm – 2100nm (150W Xe lamp with N2)

210nm – 2100nm (150W Xe lamp without N2)

Light Source

Fully stabilised 150W xenon arc source. Housing includes time counter to monitor lamp lifetime and power supply.

-     Spectral Range of Lamp : 180 - 2200nm.

-     Continous Rotating chopper.