In situ real-time and ex situ spectroscopic analysis of Al2O3 films prepared by plasma enhanced atomic layer deposition

Abstract

In situ real-time ellipsometry (irtE) with a very high time resolution of 24 ms was applied to monitor the inductively coupled plasma enhanced atomic layer deposition (ALD) process of Al2O3 thin films to precisely resolve each step of the ALD process and its complete cycle. The influence of plasma power, plasma pulse duration, and deposition temperature on the film growth characteristics was investigated. Ex situ ellipsometry [UV-VIS-NIR-SE (ultraviolet-visible-nearinfrared-spectroscopic ellipsometry) and IR-SE (infrared spectroscopic ellipsometry)] and x-ray photoelectron spectroscopy revealed the bulk properties (thickness, refractive index, chemical composition, and carbon incorporation) of the films, which together with the in situ results are compared to those of the films prepared by thermal ALD (T-ALD). The ICPEALD (inductively coupled plasma enhanced ALD) films were deposited at substrate temperatures between 80 and 250 °C and the role of plasma power (50–300 W) and its pulse duration (1–20 s) was investigated at 250 °C. The reference T-ALD layers were prepared at 200 °C. The ICPEALD process of Al2O3 shows an increased growth rate, and the produced films exhibit higher carbon contaminations than the T-ALD Al2O3 films. Plasma pulse times of up to 15 s further increase the content of carbon and CH species; at the same time, the refractive index decreases. The optical properties of ICPEALD deposited Al2O3 films are comparable with those of the T-ALD films for low plasma power and short plasma pulse durations. For the ICPEALD films, UV absorption is found and it is dependent on the deposition parameters. irtE resolves process effects that correlate with the bulk properties of Al2O3, such as impurities and oxygen deficiencies.