Spectroscopic ellipsometry – measurements at up to 1000 °C
Spectroscopic ellipsometry at room temperature provides a lot of important information about layer structure and optical constants. However, since these parameters change at higher temperatures, these types of applications require temperature-dependent measurements.
For this purpose, our ex-situ ellipsometers like the M-2000 or RC2 can be equipped with heat stages which can easily be mounted on the sample holder. Up to now, our Linkam heat stage has provided measurements in the temperature range from -70 °C (by liquid nitrogen cooling) to +600 °C. The new TS1000 cell now permits measurements up to 1000 °C. TS1000 has been specially designed for our M-2000 and RC2 ellipsometers, which both use CCD technology. This allows running temperature ramps. Furthermore, the entire spectrum is recorded simultaneously for each point in time and thus for each temperature.
Fig. 2: Temperature profile (red) and SiO2 thickness (blue) measured during the temperature change
Fig. 3: Refractive index of Si as a function of wavelength, determined at room temperature, 300°C, 600°C and 1000°C
Fig. 4: Extinction coefficient of Si as a function of wavelength, determined at room temperature, 300°C, 600°C and 1000°C
In the measuring example, a silicon sample was heated to 1000 °C with the TS1000 cell and the M-2000DI ellipsometer (spectral range 193 - 1700 nm) to determine the increase of the oxide thickness and the changes of the optical constants. While the temperature is being raised, thermal SiO2 grows, with a slight time delay, to a thickness of approx. 90 nm.
The optical constants of Si change significantly with temperature, as the pronounced structures of the electronic transitions „smear out“.
The TS1000 is available as a separate option or in a combined package together with the standard Linkam stage (-70 °C to +600 °C). Both heating units use the same controller, which may be used with either of the two. The stages are supplied with a coolable lid and fused silica windows for measurements at an angle of incidence of 70°. They are also equipped with connections for gas purging. Thanks to quick-lock holders, the standard sample holder may easily be exchanged with the heat stage, including sensors for detecting the mounted unit, so that the measuring program directly copies the corresponding system settings.
