AVS2017 Session EL-TuP: Spectroscopic Ellipsometry Poster Session

As a comprehensive manufacturer of metrology tools and deposition tools, ULVAC developed an innovative ultra high-speed spectroscopic ellipsometer for many deposition applications, such as PVD, CVD, ALD and others.

This novel spectroscopic ellipsometry can measure the thickness and optical constants of thin films at a dramatically fast speed. Its data acquisition time is as short as 10 ms. It does not require any active components for polarization-control, such as a rotating compensator or an electro-optical modulator.

It created great opportunities for new applications of the spectroscopic ellipsometry in which the compactness, the simplicity and the rapid response are extremely important. It can be integrated into the deposition tool and successfully measured thin films in-situ and ex-situ. Obviously, PVD, CVD and ALD are some promising applications for this novel spectroscopic ellipsometry.

This paper describes the principle, system configuration and our creative efforts on developing a series of ultra high-speed spectroscopic ellipsometers. Some of the novel applications will be also introduced, such as the PVD, CVD, ALD, EUV, OLED, MEMS and some measurement data of thin films from the semiconductor, flat panel display and other industries.

Germanium based photonic devices attract a lot of interest due to the fact that its band structure is easily influenced by strain and alloying with tin. A direct bandgap group IV semiconductor will show an improvement in efficiency in optoelectronic devices. Utilizing a germanium-on-insulator (GOI) substrate is a key feature for future silicon compatible germanium based devices, allowing for easier integration by the microelectronics industry. [1]

Here, we analyzed the optical response of a GOI bonded wafer via spectroscopic ellipsometry. The ellipsometric angles, psi and Delta, and the depolarization were acquired from 0.5 to 6 eV in 0.01 eV increments using a J.A. Woollam variable angle spectroscopic ellipsometer (VASE) and from 0.1 to 0.8 eV using a Fourier transform infrared (FTIR) ellipsometer, allowing high precision measurements in the mid-infrared range. The measurements in both ranges were performed at angles of incidence from 60 to 75 degrees in 5 degree increments.

The optical response of the GOI wafer was modeled with four layers (Si, buried oxide, Ge, native oxide). As expected, strong interference oscillations were observed below the E1 critcal point of Ge. For Ge, we used the parametric semiconductor oscillator model and compared it to our previously determined optical constants of bulk germanium. We are particularly interested in differences near the direct band gap. The infrared phonon vibrations of the buried oxide were also visible in the measurements. The same measurement procedure was performed on the GOI wafer before and after cleaning the sample to observe the optical effects of a native surface oxide. While the pseudo-dielectric function of the GOI sample appeared different from that of a bulk Ge sample due to interference effects, the optical constants of the germanium layer only showed small differences. We did not find any differences in the electronic structure of bulk Ge and a thin bonded Ge layer.

References:

[1] B.Y. Nguyen, M. Sadaka, G. Gaudin, W. Schwarzenbach, K. Boudele, C. Figuet, C. Maleville