ICMCTF2015 Session B2-1: CVD Coatings and Technologies

The advent of FinFETs with high-aspect-ratio 3-D geometries increases demands on conformality of SiNx films. These stringent requirements on conformality and low thermal budget can be simultaneously met usingatomic layer deposition (ALD). While there are a few reports in the literature that show that SiN_xcan beconformally deposited via ALD at <400 °C, these films are not sufficiently dense to serve as moisture oroxidation barriers. Hence, improvements in this area are needed via a fundamental understanding of the surfacereaction processes. Recently, we have developed a novel ALD processes for the growth of Si₃N₄ thin films using trisilylamine (Si(NH₃)₃, TSA) and silane precursors, and an NH₃ plasma. This ALD process with these precursors providesdense films with a conformal coverage over aspect ratios typical for the above applications; 10:1. To understand theunderlying film growth mechanism, the specific surface reactions involved during each half-reaction cycle of thisALD process were monitored with in situ attenuated total reflection Fourier transform infrared (ATR-FTIR)spectroscopy. ZnSe internal reflection crystals were used as substrates since ZnSe is transparent in the infrared upto 700 cm^-1. This spectral range, combined with the high sensitivity achieved with ATR-FTIR spectroscopy,allows us to identify and monitor in real time the different surface species generated and consumed due tosequential exposure of the growth surface to Si-containing precursors and an NH₃ plasma. The vibrational modesthat were monitored include the surface SiH_x (x = 1,2,3)and NH_x(x = 1,2)stretching modes in the 2100 and 3400 cm^-1 region, respectively, NH_x(x = 1,2)bending modes in the 1100-1600 cm^-1 region, and Si₃N₄ phonon modes, which appear in the 800-900 cm^-1 region. Further, these films were extensively characterized using a suite of ex situ diagnostic tools such as ellipsometry, transmission electron microscopy, and Rutherford backscattering.

In the present work CVD TiAlN multilayer coatings were produced on standard WC/Co cemented carbide substrates. The coatings were characterized by X-ray diffraction (XRD), scanning and trans­mis­sion electron microscopy (STEM and TEM) and energy dispersive X-ray analysis (EDX). The detailed microstructure, such as grain size, grain shape and possible twinning is reported. The texture and presence of local epitaxy between layers are described using XRD pole figures and electron diffraction techniques, such as selected area electron diffraction (SAED) and convergent beam electron diffraction (CBED). The local composition changes are described using EDX linescans and maps. The possible grain boundary changes in TiAlN due to prolonged deposition times are also investigated.

In this work, we investigated growth mechanism of amorphous phase mixed α-Al₂O₃ thin films deposited by Plasma-Enhanced Metal Organic CVD (MOCVD) using gas mixtures of trimethylaluminium, as aluminum precursor and O₂. Due to the plasma activation, high growth rate of 15μm/h for amorphous phase mixed α-Al₂O₃ and 45μm/h for amorphous-Al₂O₃ are obtained. Plasma-Enhanced MOCVD Al₂O₃ film shows unique lenticular morphology and much higher deposition rate makes more amorphous-like Al₂O₃.

[1] S. Tatsuoka, et al., ICMCTF2014, B2-12.

Hydrogenated silicon nitride (SiNx: H) films have shown many useful industrial applications. Conventionally, PECVD method offers the possibility of producing high-quality dielectrics at relatively low temperatures (200-400ºC) in comparison to thermal oxidation or low-pressure CVD, which take place at temperatures approaching several hundreds to few thousands of ºC. Due to the utilization of process gases like silane (SiH₄) and ammonia (NH₃), there is the issue of the incorporation of high content of hydrogen in the films that can affect the characteristics of the SiNx: H films, such as high residual stress, Si-H bond concentration, etc. This drawback together with the high deposition temperature can also limit the deposition of films on polymer substrates. Moreover, low temperature SiNx: Hfilm deposition with low hydrogen content by PECVD is of special interest for barrier films for flexible substrates. The deposition temperature can be reduced significantly by utilizing alternative plasma concepts to lower the reaction activation energy. Evolution in this area continues and has recently produced solutions by increasing the plasma excitation frequency from radio frequency to very high frequency (VHF) and in the range of microwave.

High quality SiNx: H films with very low content of hydrogen are prepared at low temperature using the mixture of N₂/SiH₄/NH₃, by utilizing ultrahigh frequency plasma (UHF) source at 320 MHz along with a low frequency RF CCP source at 13.56 MHz. The primary goal of the former one is to assist and enhance the dissociation of nitrogen radicals along with the RF. Thus, one of the major goals of this work is also to investigate dissociation and control of the nitrogen radicals during the deposition process and their role in the film property and structure control, using radical monitor diagnostic by vacuum ultraviolet absorption spectroscopy (VUVAS). Moreover, different operating parameters can affect deposition rates along with other physical and optical properties of the film. To investigate the radical and plasma formation and their control for the growth of the film, we have systematically used other plasma diagnostic tools like optical emission spectroscopy (OES), RF compensated Langmuir probe (LP) and ICCD camera diagnostics, at different process conditions.