【作者】 王刚；

【导师】 刘肃； 狄增峰；

【作者基本信息】 兰州大学 ， 电子科学与技术·微电子学与固体电子学， 2016， 博士

【摘要】 石墨烯(Graphene),即石墨的单原子层(厚度约为0.34 nm),是碳原子按照sp2碳-碳(C-C)键形成的以蜂窝状排列的二维晶体结构。2004年英国曼彻斯特大学的安德烈·盖姆和康斯坦丁·诺沃肖洛夫利用微机械剥离的方法发现了石墨烯材料,并于2010年获得诺贝尔物理学奖。石墨烯材料集多种优异的性能于一身,其电子迁移率高于硅材料两个数量级表明石墨烯材料有望替代半导体工业中的硅材料,使其拥有广阔的应用前景。因此,在学术界和工业界备受瞩目,掀起了物理学和材料科学等领域的研究热潮。石墨烯材料制备工艺的优化和成熟是推动后续应用的前提,针对石墨烯材料不同的应用领域,对石墨烯材料的可控制备提出了极大的挑战。目前,石墨烯材料的制备方法层出不穷,但是仍有很多问题亟待解决,所以制备工艺的优化和新方法的探索依然有着极大的发展空间,最终目标是获得大面积、高质量、免转移、易与半导体技术集成、层数可控以及带隙可控的石墨烯材料。本论文围绕石墨烯材料生长方面所遇到的难题,结合半导体技术(即半导体衬底和离子注入技术),着重从如何制备大面积、高质量、与半导体技术集成、层数可控以及掺杂可控的石墨烯材料等方面开展了全面的研究,主要取得如下重要的研究成果:1、在国际上首次提出了半导体锗衬底上直接生长石墨烯材料的方法,并采用常压化学气相沉积(APCVD)法在锗衬底上成功地制备了大面积、高质量、单层的石墨烯连续薄膜。锗是一种重要的半导体材料,相比传统的硅材料,锗材料具有极高的载流子迁移率,被认为是最具潜力取代硅的半导体材料,有望应用于未来大规模集成电路。锗基石墨烯的生长工艺实现了与半导体基底的集成,制备工艺与现有的半导体工艺相兼容。此外,在半导体锗材料上直接制备石墨烯薄膜,避免了繁琐的石墨烯材料的转移过程,减少了对石墨烯材料的破坏与污染,保证了石墨烯材料优异的性能,为石墨烯材料在微电子器件中的应用打下了良好基础,促进基于石墨烯器件的大规模推广与应用。2、针对石墨烯材料层数难于控制这一难题,结合催化金属镍(Ni)和铜(Cu)在化学气相沉积(CVD)法中制备石墨烯材料的优点,利用各自对碳溶解能力的不同。设计了Ni/Cu体系(即在25μm厚的Cu箔上电子束蒸发一层300 nm的Ni),利用半导体产业中成熟的离子注入技术将碳原子注入到Ni/Cu体系中的Ni层中,通过控制注入碳原子的剂量(即4×1015 atoms/cm2剂量对应单层的石墨烯;8×1015 atoms/cm2剂量对应双层的石墨烯),经退火后成功实现了大面积、高质量的单、双层石墨烯材料的制备。从实验结果出发,利用第一性原理(DFT)和分子动力学模拟(MD)详尽地研究了离子注入法制备层数可控石墨烯材料生长的物理机制。由于离子注入技术具有低温掺杂、精确的能量和剂量控制及高均匀性等优点,与传统的CVD法制备石墨烯材料工艺相比,采用离子注入法制备单、双层石墨烯材料仅受注入碳原子剂量的影响,与各种气体的体积比、衬底厚度以及生长温度无关,制备条件易于控制。此外,离子注入技术与现代半导体技术相兼容,有助于实现石墨烯材料作为电子材料在半导体器件领域真正的应用。3、瞄准石墨烯材料掺杂难题,结合离子注入技术和常压化学气相沉积(APCVD)法,通过“异质原子成核-促进石墨烯再生长”两步动力学路径分别制备了晶格式掺杂的P型和N型石墨烯材料。研究关键实验参数,攻克了掺杂石墨烯材料可控制备(掺杂类型可控和掺杂含量可控)的难题。并对P型和N型石墨烯材料进行表征与分析,掌握了掺杂石墨烯材料的结构和性能与离子注入的原子类型、剂量之间的关系。利用互补金属氧化物半导体(CMOS)工艺在硅基衬底上制作基于掺杂石墨烯材料的晶体管(GFETs)。使用半导体参数测试仪分析石墨烯材料的输运特性,研究了掺杂石墨烯材料作为传输层与器件匹配后的载流子迁移能力和狄拉克点位置。更多还原

【Abstract】 Graphene is one-atom-thick planar film of sp2-bonded carbon atoms densely arranged in a honeycomb crystal lattice. In 2004, Andre Geim and Kostya Novoselov first obtained graphene by micromechanical exfoliation of highly oriented pyrolytic graphite(HOPG), and in 2010 won the Nobel Prize in physics. The electron mobility of graphene has two orders of magnitude higher than that of silicon materials so that graphene is expected to replace silicon materials in semiconductor industry. It has attracted enormous scientific and technological interest due to the outstanding electrical, mechanical, and chemical properties as well as large potential in a multitude of applications. Graphene has the potential to be great useful in diverse technological application, In view of the different application field of graphene, controllable preparation of graphene challenges are put forward. At present, synthesis of graphene emerge in endlessly, but there are still many problems remain to be solved, so the optimization of preparation technology and the exploration of new method still has a huge space for development. However, it is quite challenging to obtain the graphene with large-scale, high-quality, free-transfer, easy to integration with semiconductor technology, well-controllable thickness and controllable doping. This paper around graphene growth has encountered problems, conducted a comprehensive research, mainly the following important research results:1. For the first time in the world, by ambient-pressure chemical vapor deposition(APCVD), large-scale and uniform depositon of high-quality graphene have been demonstrated directly on a germanium(Ge) substrate which is considered a promising channel material to replace conventional silicon in next-generation high-performance metal-oxide-semiconductor field-effect transistors(MOSFETs) due to its higher carrier mobility and process compatibility with Si-based microelectronics processes. Moreover, our technique bypass transfer step which may introduce defects, impurities, wrinkles, and cracks, thus potentially degrading the performance of graphene-based devices. Our technique is compatible with modern microelectronics technology thus allowing integration with high-volume production of complementary metal-oxide-semiconductors(CMOS).2. For the precise control of the thickness of graphene remains a major challenge, by taking advantage of the dual metal substrate of the Ni-coated Cu foils, the precise control of layer number of graphene by ion implantation has been demonstrated and the layer number of graphene strictly corresponds to the implantation fluence as expected. For instance, uniform monolayer graphene can be produced using a fluence of 4×1015 atoms/cm2, and a fluence of 8×1015 atoms/cm2 produces a bilayer graphene film. The formation mechanism is explored and confirmed by theoretical calculation. Superior to CVD method, our approach is less sensitive to the processing conditions, especially the thermal history, since the carbon content is solely determined by the implantation fluence. Given that the ion implantation is a mature technology in the current integrated circuit manufacturing, we believe that graphene synthesized by this strategy can expedite the industrial application of graphene.3. Because of its zero bandgap, graphene is highly limited in application as material of optical or electronic devices. Doping is considered as an efficient method to modulate the graphene bandgap, which breaks the symmetry structure of graphene with heteroatom to realize the modulation. Aims to overcome the difficulty of controllable graphene doping including doping type and content, we propose a method combined with implantation and CVD, by “heteroatom nucleation-promoting graphene regrowth” two-step dynamics way to fabricate doping-controllable lattice substitution graphene, study the mechanics of formation and evolution of heteroatom and graphene lattice, and research the relationship between structure and physical properties of doped graphene, to develop our research accordingly on some basic problem of doped grapheme, which will greatly improve the application of graphene in semiconductor device field.更多还原