Technological Progress Path of Gem-Quality Synthetic Diamond by MPCVD
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摘要:
微波等离子体法(MPCVD)是目前CVD合成钻石较为优选技术,具有能量输入稳定、工艺可控性高、生长质量好等显著优势,该技术可生长晶体颗粒大、净度高和颜色好的优质宝石级金刚石,快速发展为宝石级合成金刚石商业化生产应用的主流技术之一,成为反哺并提升整体MPCVD法制备高质量工业应用领域合成金刚石的重要动力[1-3]。
MPCVD法在合成宝石级金刚石领域的应用重点关注晶体大小、晶体净度、晶体颜色和生长速度四个方面的表现。本文对近三年来MPCVD法的生长机制、方法及相关结果的进展进行了综述。为了获得尽可能大的晶体,目前的重点是关注籽晶筛选处理和生长方法的选择[1],包括优选具有易加工、外延能力强的(100)晶向的Ⅱa型HPHT基板或者CVD基板作为生长籽晶;利用金刚石的自然表面特性,在三个维度上培养大尺寸单晶金刚石的三维生长法、通过多次连续生长循环获得大厚度晶体的重复生长方法,以及通过拼接多个抛光的籽晶基板[4],实现大面积单晶金刚石生长的马赛克生长法[1, 5]。技术上,可通过优化甲烷浓度、氢气浓度等生长参数,提高气源纯度和生长系统的真空度,可减少非金刚石相的产生[1]。通过多次生长循环,每次生长后去除多晶金刚石,然后继续生长单晶金刚石,可以有效避免多晶相的形成和裂纹的产生,从而提高晶体的净度;此外,在每次循环生长之间以及生长后,对晶体进行机械抛光,去除表面缺陷和多晶相,可显著提高晶体的净度和光学质量[1, 5];在颜色研发方向,通过降低生长速度和降低氮浓度,或者通过生长后处理(如高温退火),可以减少氮相关的光吸收缺陷所导致的光吸收,从而获得趋于无色的晶体[4, 6]。CVD法合成宝石级彩色金刚石主要是通过掺入NV色心,退火辐照后获得红色、粉红色和黄色[4-8];另外通过硼掺杂直接获得蓝色,也可在生长后通过高能电子辐照处理,改变金刚石晶格缺陷获得浅蓝色金刚石[4, 6]。
生长速度与晶体质量的平衡,是合成金刚石晶体生产成本的重要指标,目前主要是通过调节生长温度区间、适当的功率密度和压力等生长参数,同时协调籽晶布置与气流分布,可实现较高的生长速度和生长质量的平衡[1, 4];通过优化甲烷浓度,可以实现高速度沉积碳相金刚石;氢气的浓度也对金刚石生长速率和晶体质量有显著影响;通过对上述一系列生长参数的调节,影响等离子体状态、解离、活化和活性基团的分布,从而有效控制生长表面的物理和化学反应,在提高晶体生长速度的同时保障晶体生长质量[1, 4, 9]。有研究人员开发出一种基于等离子体诊断技术,利用等离子体成像和光谱分析对微波等离子体进行定量诊断、选择工艺参数,对不同的单晶金刚石生长进行有效的等离子体控制和工艺优化[10]。提高晶体生长体积和生长速度,保证净度质量,实现无色或者可控的彩色,仍然是降低晶体生产成本、提高晶体价值的关键,推动了MPCVD技术整体发展,并将有助于进一步扩大工业领域应用的研究和实现。
Abstract:MPCVD is favored for its stable energy input, high process control, and excellent growth quality, demonstrating high performance in growing large, high-purity, well-coloured gem-quality diamonds. Reviewing the development in growth mechanism, methods and related results of MPCVD technology in recent three years, we noted advancements focus on producing large single-crystal diamonds, reducing non-diamond phase, enhancing purity, optical quality and color-performance, and achieving balances between growing speed and quality by adjusting the growth parameters. The development of MPCVD technology of growing gem-quality diamonds has promoted the overall development of MPCVD technology and will help to further expand the research and implementation of industrial applications.
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Keywords:
- MPCVD /
- gem-quality diamond /
- technological path
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