Plasma-assisted deposition of thin silicon oxide films in a remote PECVD reactor and characterization of films produced under different conditions☆
Introduction
The preparation of thin dielectric films plays a very important role in semiconductor development [1]. Silicon oxide films can be produced with different methods for different purposes. Sol–Gel [2] and liquid phase deposition [3] do have limitations in the minimal thickness of the films. Sputtering [4] and chemical vapor deposition [5] allow a better control of the film thickness, and doping of the films can easily be achieved by adding additional gases to the deposition process. Nowadays the plasma-assisted deposition of silicon oxide is most commonly used. For future miniaturization of microelectronics pure silicon oxide films have become questionable and silicon oxynitride SiOxNy (or, more accurately, nitrogen-doped silicon oxide) is a promising solution [6].
In this paper we present a study of the optical and electrical properties of silicon-based oxide films prepared by PECVD. Parameters, such as density, refractive index, composition and resistivity of the deposited dielectric films are estimated by analysis of the results from the XRD, IR and SE spectroscopies and capacitance–voltage (C–V) and current–voltage (I–V) measurements.
Section snippets
Deposition procedure
All depositions were performed in a downstream plasma reactor presented in Fig. 1. The plasma source is mounted above the substrate, driven by a 13.54 MHz RF generator and oxygen gas with a gas flow between 1 and 20 sccm. For all depositions, the TEOS precursor is introduced to the reactor through a nozzle near the substrate. The total pressure was about 1 Pa during deposition. The plasma power can be varied between 2 and 100 W. All depositions were performed with a substrate temperature of 200°C,
Results and discussion
Fig. 2 shows the difference in the in situ reflectivity during the deposition of 100 nm thick films on silicon wafers using TEOS in pure O2 plasma (2 sccm oxygen flow) and in a mixture between 2 sccm O2 and 4 sccm N2. In both cases the plasma power was 80 W, the substrate temperature was 200°C, the bias voltage on the sample was −120 V. The maxima for the O2/N2 sample are slightly higher, pointing to higher density of the film. This can be explained by the incorporation of nitrogen; silicon nitride
Conclusions
In this paper we have demonstrated, that with the oxygen plasma-assisted chemical vapor deposition of TEOS silicon dioxide of good quality with low surface roughness can be produced. The addition of nitrogen to the process leads to incorporation of nitrogen in the silicon oxide films. The characteristics of the silicon oxynitride films strongly depend on the bias voltage applied to the substrate during deposition. The best results were achieved with a voltage of 120 V, while no bias or a higher
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Paper presented at the 13th International Summer School on Vacuum, Electron and Ion Technologies, 15–19 September 2003, Varna, Bulgaria.