强共价键赋予金刚石卓越性能，如高导热、高迁移率及宽禁带，使其成为功率器件、光电、量子技术及传感器的候选材料。但实际应用仍面临挑战，如MPCVD工艺控制以实现大尺寸、平滑表面及导电性需求，以及传统加工技术的改进。本文概述了Kanazawa University针对此的三项MPCVD生长技术研究。论文引入金刚石晶片生长速率增强技术，通过优化MPCVD的反应器、电场、气体与基体定位，无氮气下实现250 μm/h的高生长速率且晶体质量优异。增添氮气并优化条件后，速率提升至432 μm/h。该技术制得0.1mm厚独立金刚石板，结晶度媲美HPHT基板，优于商用CVD基板，X射线衍射验证其高质量。但大面积基板应用仍是技术难点。The paper introduces the technology of diamond sheet growth rate enhancement. By optimizing the reactor, electric field, gas and substrate positioning of MPCVD, a high growth rate of 250 μm/h and excellent crystal quality are achieved without nitrogen. After adding nitrogen and optimizing the conditions, the rate is increased to 432 μm/h. This technology produces 0.1mm thick independent diamond plates with crystallinity comparable to HPHT substrates and better than commercial CVD substrates. X-ray diffraction verifies its high quality. However, the application of large-area substrates is still a technical difficulty.金刚石CVD生长要点：自由基生成于氢甲烷混合气微波激发；氢原子促进活性物质保存。活性物质从等离子体扩散至基体，途中碰撞生成新物质，经鞘层与金刚石表面交互。表面反应中，活性物质迁移至反应位点，形成化学键或解吸，氢原子蚀刻SP2键，碳氢化合物促进钻石生长。研究采用CVD设备与支架结构，探索(100)金刚石膜生长速率随甲烷分压变化，发现提升微波功率与总压强可增速，最大达150μm/h。高功率密度或提升甲烷转化效率，但生长速率斜率与无氮条件相当，或归因于碳自由基扩散效率低。Key points of diamond CVD growth: Free radicals are generated by microwave excitation of hydrogen-methane mixture; hydrogen atoms promote the preservation of active substances. Active substances diffuse from plasma to substrate, collide on the way to generate new substances, and interact with the diamond surface through the sheath. During the surface reaction, active substances migrate to the reaction site to form chemical bonds or desorb, hydrogen atoms etch SP2 bonds, and hydrocarbons promote diamond growth. The study used CVD equipment and support structure to explore the growth rate of (100) diamond film as a function of methane partial pressure, and found that increasing microwave power and total pressure can increase the growth rate, up to 150μm/h. High power density may improve methane conversion efficiency, but the growth rate slope is equivalent to that under nitrogen-free conditions, which may be attributed to the low diffusion efficiency of carbon free radicals.
研究报告指出，该项目已达到世界最快生长速度。与Si、SiC及GaN等功率半导体材料比较，金刚石生长率虽低于商业化Si、SiC，但与GaN相当。金刚石晶种面积扩大是最大挑战，异质外延难达大尺寸，同质外延可三维或马赛克生长。团队技术在小基片上测试成功，适用于后者。MPCVD需三维扩展等离子球增面积，但降低功率密度，限制大面积生长速率。915 MHz微波虽增面积，却降低功率利用率和物质供应效率。解决之道在于二维扩等离子体提功率密度，并探索热丝CVD及无等离子气体CVD以降低钻石生产能源成本。
The research report pointed out that the project has achieved the fastest growth rate in the world. Compared with power semiconductor materials such as Si, SiC and GaN, the growth rate of diamond is lower than that of commercial Si and SiC, but it is comparable to GaN. The biggest challenge is to expand the area of diamond seeds. Heteroepitaxial growth is difficult to reach a large size, and homoepitaxial growth can be three-dimensional or mosaic growth. The team's technology has been successfully tested on a small substrate and is suitable for the latter. MPCVD requires three-dimensional expansion of the plasma ball to increase the area, but reduces the power density and limits the growth rate over a large area. Although 915 MHz microwaves increase the area, they reduce power utilization and material supply efficiency. The solution lies in two-dimensional expansion of plasma to increase power density, and explore hot filament CVD and plasma-free gas CVD to reduce the energy cost of diamond production.研究人员通过调整生长模式，在原子层面操控金刚石表面。在同质外延（111）面，采用横向、二维岛状及三维生长模式。通过精细调控甲烷浓度与基板错位，可在高压高温（111）台面上切换生长模式。横向生长实现从微米到毫米扩展，优化后，研究人员在全基材上达成原子级平坦金刚石表面。The researchers manipulated the diamond surface at the atomic level by adjusting the growth mode. On the homoepitaxial (111) surface, lateral, two-dimensional island and three-dimensional growth modes were used. By finely controlling the methane concentration and substrate misalignment, the growth mode can be switched on the high-pressure and high-temperature (111) table. The lateral growth was extended from microns to millimeters. After optimization, the researchers achieved an atomically flat diamond surface on the entire substrate.
研究扩展至杂质掺杂技术，调控金刚石导电性。硼掺杂金刚石薄膜生长速率高达30 μm/h，为传统速度的5倍。通过调节硼掺杂，制得电阻率跨度的金刚石薄片。采用横向生长模式实现δ掺杂层，保持原子级平坦，提升载流子浓度与迁移率。结合此技术与调制掺杂，可精准掺杂于三维器件，优化电子特性。MPCVD同质外延金刚石技术已成熟应用于晶圆制造与电导率控制。针对电力电子应用，需定制晶体规格，并整合技术以展现金刚石半导体卓越性能。未来，还需解决器件制造、表面/界面控制及极致物理特性发挥等挑战。The research has been extended to impurity doping technology to regulate the conductivity of diamond. The growth rate of boron-doped diamond films is as high as 30 μm/h, which is 5 times the traditional speed. By adjusting the boron doping, diamond sheets with a resistivity span are produced. The δ-doped layer is realized using a lateral growth mode to maintain atomic-level flatness and increase carrier concentration and mobility. Combining this technology with modulation doping, it can be precisely doped in three-dimensional devices to optimize electronic properties. MPCVD homoepitaxial diamond technology has been maturely applied to wafer manufacturing and conductivity control. For power electronics applications, crystal specifications need to be customized and technologies need to be integrated to demonstrate the excellent performance of diamond semiconductors. In the future, challenges such as device manufacturing, surface/interface control, and the ultimate physical properties need to be addressed.
