【作者】 吴炳俊；

【导师】 王海千；

【作者基本信息】 中国科学技术大学 ， 凝聚态物理， 2010， 博士

【摘要】 太阳能电池、平板显示和触摸屏等技术的出现与快速发展对透明导电氧化物薄膜材料提出了越来越多且越来越高的需求。ZnO：Al(简称AZO)透明导电薄膜因其优异的光电学性能、丰富廉价的原材料来源以及环境友好等特点引起了业界的广泛关注,被公认为是取代In203：Sn(简称ITO)透明导电薄膜材料的最佳候选者。随AZO薄膜在薄膜型太阳能电池上的实用化以及金属铟作为ITO薄膜原材料的供需缺口的日益增大,AZO薄膜逐渐步入工业化生产的阶段。本文使用AZO陶瓷靶、金属锌靶、铝靶及锌铝合金靶等靶材在日本Shincron公司生产的RAS-1100C大型自由基辅助磁控溅射设备上溅射制备Zn0及AZO薄膜,研究薄膜的电学、光学、微结构、应力、禁带宽度、折射率等物理性能随溅射参数的变化；针对AZO陶瓷靶溅射过程中靶材前方固定衬底上溅射沉积的AZO薄膜中电阻率等多项物理性能出现空间分布不均匀的现象展开了系统的研究,发现溅射过程中产生的高能氧负离子的轰击注入效应是使AZO薄膜物理性能出现空间分布不均匀的根本原因；针对金属靶溅射过程的复杂性研究了金属锌靶溅射制备锌氧化物薄膜过程中薄膜的微结构形貌及结晶性能随溅射功率以及氧化区氧气流速的变化,并对比研究了溅射区内的高能氧负离子轰击造成的反溅射现象；同时本文还结合薄膜在空气及氢气气氛下的退火实验结果对薄膜中各种缺陷的状态展开了讨论,力图揭示薄膜中各种缺陷的状态对薄膜性能的影响,从而为溅射制备性能更加优良的AZO薄膜打下基础。通过对比性实验研究,本文主要得到了以下结论和成果：l、通过对AZO陶瓷靶溅射参数的优化在RAS圆鼓上沉积得到电阻率达2.4×10-3Ω·cm,载流子浓度为2.49×1020 cm-3,迁移率为10.5cm2V-ls-1,550nm波长处的透过率为85%的AZO薄膜样品；2、观察到靶前不同区域处固定衬底上沉积的AZO薄膜的电阻率、载流子浓度、迁移率等多项物理性能出现明显的空间分布现象；靶材溅射沟道正前方沉积的AZO薄膜电阻率最高达2.2×10-2Ω·cm,而两块靶材中间非溅射区域前方沉积的AZO薄膜的电阻率则可低至4.9×10-4Ω·cm,两者相差达45倍左右。3、通过XPS、XRD等表征发现高能氧负离子轰击注入效应是靶前电阻率空间分布不均匀的根源。氧负离子源于溅射过程中晶格氧以负离子的形式析出,在靶材负电压电场加速下获得很高的能量轰击到衬底上面,造成薄膜中的晶粒损伤,抑制薄膜沿(0002)方向上的高度取向生长,并且在薄膜中引入大量氧填隙缺陷。大量的氧填隙缺陷俘获薄膜中的自由电子载流子,并造成晶格畸变,增加薄膜中的中性杂质散射,从而引起薄膜载流子浓度及迁移率降低、电阻率升高。4、RAS圆鼓上沉积的薄膜的性能是各区域沉积薄膜性能的平均结果。溅射参数主要通过影响氧负离子轰击注入效应的强弱以及薄膜的结晶状况好坏而影响在圆鼓上制备的AZO薄膜的性能。5、通过对RAS金属锌靶溅射制备锌氧化物薄膜过程中的正向及反向沉积薄膜的研究观察了锌氧化物薄膜形貌及结晶状态随氧化程度的演化,得到了薄膜微结构随溅射功率及氧化区氧气流速分布的相图,分析了RAS金属靶的典型溅射过程中溅射区内发生的物理过程,为溅射制备结晶性能优良的AZO透明导电薄膜提供了物理依据。6、对比研究了各种金属靶溅射过程中溅射区内生成的氧负离子造成的反溅射效应。研究表明反溅射效应不完全等同于高能氧负离子轰击效应,还受到溅射区沉积薄膜薄层氧化程度的影响。反溅射效应降低了靶材的利用率并影响薄膜中的铝含量,应该尽量予以避免。7、通过对比实验研究了ZnO及AZO薄膜在空气和氢气中的退火效应并分析了氧填隙缺陷行为对薄膜性能的影响,进一步阐明了氧负离子轰击注入效应影响薄膜物理性能的机制。另外还通过对比实验分析、讨论了RAS金属锌、铝靶共溅射制备AZO薄膜性能受限的原因。8、通过氢气500℃退火获得电阻率为4.5×104Ω.cm、载流子浓度为5.15×1020cm-3、迁移率为24.6 cm2V-1s-1、550 nm波长处透射率为89%的AZO薄膜。退火后的AZO薄膜性能稳定,具备实用价值。更多还原

【Abstract】 The demand of transparent and conductive oxide (TCO) films has been highly stimulated by the appearance of fast growing solar voltaic、flat panel display and touch panel techniques. Transparent and conductive ZnO:Al (AZO) films has attracted lots of research interests and is considered as one of the best candidates for substitution of the traditional In2O3:Sn (ITO) films because of its excellent electrical and optical properties and cheap、abundant and non-toxic raw materials. Practical utilization of AZO films on thin film solar cells together with the aggravation of supply deficiency of In, which is the main raw material of ITO films, have provided the best opportunity for the industrialization and commercialization of AZO films.ZnO and AZO films were prepared by a large radical assisted magnetron sputtering apparatus RAS-1100C (Shincron Co.,Ltd.) with AZO ceramic targets, metallic zinc targets and aluminum targets and zinc-aluminum alloy targets. The relation between physics properties of these films, such as electrical and optical properties, microstructures, film stress, energy bandgap and reflective index were systematically studied. In the sputtering process of AZO ceramic targets, several physics quantities including resistivity were found to exhibit significant spatial distributions. Detail works were conducted to disclose the origins of these spatial distributions and find out that a bombarding implantation effect by negative oxygen ions was mainly responsible for these spatial inhomogeneities. As for the situation of sputtering processes of metallic targets, a detail observation of the microstructures and crystallinity evolution of the deposited zinc oxide films related to the sputtering powers and oxygen flow rates were carried out with a extra comparative study on re-sputtering phenomena which was caused also by energetic negative oxygen ions bombardments. Besides, a discussion on the defects states, behaviors and their influences on the properties of deposited films were given base on comparative experimental results of post annealing treatments of the deposited ZnO and AZO films under air or hydrogen atmospheres. We endeavored to shed lights on the deep mechanisms on the influences of sputtering parameters and deposition mode, which are beneficial for improvements of the properties of sputtering prepared AZO films.The main results and conclusions in this thesis are:1、We obtained AZO films with resistivity of 2.4x 10-3Ω·cm, carrier concentration of 2.49×1020 cm-3, mobility of 10.5cm2V-1s-1 and transmittance (at wavelength of 550nm) of 85% through optimizing sputtering parameters with AZO ceramic targets;2、The resistivity, carrier concentration, mobility, energy bandgap and reflective index for AZO films deposited on substrates fixed in different regions in front of the AZO ceramic targets were found to exhibited significant spatial distributions. The resistivity of AZO films deposited on substrates facing the erosion areas of targets were found to be high with maximum resistivity of 2.2×10-20Ω·cm while those deposited in the regions facing the non-sputtered areas were relatively much lower, with a minimum resistivity of 4.9×10-4Ω·cm. The gap between the resistivity maximum and minimum was as high as 45 times or more.3、We confirmed implantation effect by the bombardments of energetic negative oxygen ions as the main cause of resistivity (and other physics quantities) spatial distribution. The negative oxygen ions originated from the liberation of targets’O anions in the form of negative ions and obtained high energy under the acceleration by electrical field in the cathode fall. The bombardment of O" brought damages to crystalline grains and deteriorated the (0002) preferred oriented growth and introduced lots of oxygen interstitial defects in the deposited AZO films. The oxygen interstitial defects was mainly responsible for the degradation of electrical properties as they can trapped free electron carriers and cause lattice distortions and increase the neutral impurity scattering in AZO films, which ultimately led to decrease in carrier concentration and mobility and thus increased the resistivity of AZO films.4、AZO films deposited on the drum of RAS possess average physics properties as compared to those deposited on fixed substrates in different regions in front of the targets. Properties of AZO films were influenced by sputtering parameters through affecting the degree of bombardments by energetic negative oxygen ions and through changing of the thin film crystallinity.5、We have studied the microstructure and crystallinity evolution of zinc oxide films in detail in the sputtering process of metallic zinc targets with observation of both forward and backward deposited films. Microstructure zone models for both forward and backward deposited films related to sputtering power and oxygen flow rate have been obtained, which helps to further understand what is going on in the sputtering zone in typical sputtering process of RAS-1100C and helps to determine the suitable working parameters area for preparation of AZO transparent and conductive films by sputtering of metallic targets.6、We comparatively studied re-sputtering effect caused by the generation of energetic negative oxygen ions in the sputtering zone through different sputtering processes with several kinds of metallic targets. It was pointed out that although the re-sputtering effect was caused from the energetic negative oxygen ions bombardments, the two effects was not equal, as the former was simultaneously affected by the oxidation degree of the thin layers deposited in sputtering zone. Re-sputtering effect lowers the targets utilization efficiency and affects the aluminum content in the deposited AZO films. It was suggested that the re-sputtering effect should be intentionally avoid.7、Investment of the defects states and the influence of their behavior on the properties of AZO films were carried out through comparative post annealing experiments of ZnO and AZO films both in air and hydrogen gas ambient. The experimental results supported the interpretation of implanted oxygen interstitial defects as the main factors which determined the properties of the as-deposited AZO films. Meanwhile the reason for the limitation of properties of AZO films prepared by co-sputtering process with metallic zinc and aluminum targets were analyzed and discussed.8、The properties (both resistivity and visible light transmittance) of the deposited AZO films were found to be further improved with post-annealing treatments in hydrogen ambient. AZO films with resistivity of 4.5×10-4Ω·cm, carrier concentration of 5.15×1020cm-3, mobility of 24.6 cm2V-1s-1 and transmittance (at wavelength of 550nm) of 89% was obtained through 500℃annealing treatment for 2h in hydrogen ambient. The improved properties of AZO films are stable under storage in air conditions and thus are valuable for practical applications.更多还原