Silva F, Hassouni K, Bonnin X, Gicquel A
LIMHP, Université Paris 13, CNRS, Institut Galilée, 99 avenue Jean-Baptiste Clément, F-93430 Villetaneuse, France.
J Phys Condens Matter. 2009 Sep 9;21(36):364202. doi: 10.1088/0953-8984/21/36/364202. Epub 2009 Aug 19.
The unique properties of CVD diamond make it a compelling choice for high power electronics. In order to achieve industrial use of CVD diamond, one must simultaneously obtain an excellent control of the film purity, very low defect content and a sufficiently rapid growth rate. Currently, only microwave plasma-assisted chemical vapour deposition (MPACVD) processes making use of resonant cavity systems provide enough atomic hydrogen to satisfy these requirements. We show in this paper that the use of high microwave power density (MWPD) plasmas is necessary to promote atomic hydrogen concentrations that are high enough to ensure the deposition of high purity diamond films at large growth rates. Moreover, the deposition of homogeneous films on large surfaces calls for the production of plasma with appropriate shapes and large volumes. The production of such plasmas needs generating a fairly high electric field over extended regions and requires a careful design of the MW coupling system, especially the cavity. As far as MW coupling efficiency is concerned, the presence of a plasma load represents a mismatching perturbation to the cavity. This perturbation is especially important at high MWPD where the reflected fraction of the input power may be quite high. This mismatch can lead to a pronounced heating of the reactor walls. It must therefore be taken into account from the very beginning of the reactor design. This requires the implementation of plasma modelling tools coupled to detailed electromagnetic simulations. This is discussed in section 3. We also briefly discuss the operating principles of the main commercial plasma reactors before introducing the reactor design methodology we have developed. Modelling results for a new generation of reactors developed at LIMHP, working at very high power density, will be presented. Lastly, we show that scaling up this type of reactor to lower frequencies (915 MHz) can result in high density plasmas allowing for fast and homogeneous diamond deposition on up to 160 mm diameter surfaces.
化学气相沉积（CVD）金刚石的独特性能使其成为高功率电子学领域极具吸引力的选择。为了实现CVD金刚石的工业应用，必须同时实现对薄膜纯度的出色控制、极低的缺陷含量以及足够快的生长速率。目前，只有利用谐振腔系统的微波等离子体辅助化学气相沉积（MPACVD）工艺能够提供足够的原子氢来满足这些要求。我们在本文中表明，使用高微波功率密度（MWPD）等离子体对于提高原子氢浓度是必要的，该浓度要高到足以确保以高生长速率沉积高纯度金刚石薄膜。此外，在大尺寸表面上沉积均匀薄膜需要产生具有合适形状和大体积的等离子体。产生这样的等离子体需要在扩展区域上产生相当高的电场，并且需要精心设计微波耦合系统，特别是腔体。就微波耦合效率而言，等离子体负载的存在对腔体来说是一种失配扰动。这种扰动在高MWPD时尤为重要,此时输入功率的反射部分可能相当高。这种失配会导致反应器壁显著发热。因此，必须在反应器设计的一开始就予以考虑。这需要结合详细电磁模拟的等离子体建模工具的实施。这将在第3节中讨论。在介绍我们开发的反应器设计方法之前，我们还简要讨论了主要商业等离子体反应器的工作原理。将展示在LIMHP开发的新一代高功率密度反应器的建模结果。最后，我们表明将这种类型的反应器扩展到较低频率（915 MHz）可以产生高密度等离子体，从而能够在直径达160 mm的表面上快速且均匀地沉积金刚石。
