【作者】 张敏；

【导师】 董闯； 林国强；

【作者基本信息】 大连理工大学 ， 材料物理与化学， 2008， 博士

【摘要】 介电薄膜是应用最广泛的一类功能薄膜，在机械、电子、信息、航天等领域起着越来越重要的作用。但由于其导电性能不好，给它们的沉积制备带来了难度。比如采用最为常用的PVD技术之一即离子镀方法来制备这类薄膜时，由于薄膜表面的电荷累积会引发微弧放电效应，一方面会给薄膜带来灾难性的破坏，另一方面还给控制系统的电器元件带来安全隐患，所以普通的离子镀技术，包括应用最为广泛的电弧离子镀技术一直被认为不能用来制备这类介电功能薄膜。脉冲偏压电弧离子镀是近年来涌现出来的一种先进的薄膜制备技术，它继承了电弧离子镀的高离化率、高沉积速率等优点，还独具沉积温度低、内应力小、晶粒细化及颗粒净化等技术优势，为沉积精细功能薄膜提供了潜在条件。但实际上是否能够用脉冲偏压电弧离子镀来制备介电功能薄膜，却从未有过系统的研究来提供充分的证据来证实，这一问题的明确对于发展电弧离子镀技术和开发薄膜新材料都具有重要意义。本文采用脉冲偏压电弧离子镀，通过合理匹配脉冲偏压的频率、占空比和幅值等参数，有效地抑制了由电荷累积所导致的微弧放电效应，在玻璃、单晶硅和不锈钢等三种具有不同导电性能的基片上，成功地制备出致密平整的TiO₂、TiO_2-xN_x和AlN等介电薄膜，充分证实了脉冲偏压电弧离子镀制备介电功能薄膜的可行性。同时在0～-900V范围内改变脉冲偏压的幅值，考察了脉冲偏压对TiO₂、TiO_2-xN_x和AlN薄膜的生长形态、微观结构及其宏观性能的影响，结果表明，无论是在导电基片、半导体基片还是绝缘基片上，脉冲偏压对薄膜的色泽、沉积速率、硬度和弹性模量、膜基结合力、表面微结构和粗糙度以及光学性能等均有明显的调控能力，进一步深层次证实了用脉冲偏压电弧离子镀制备介电功能薄膜的有效性。最后利用等离子体鞘层理论模型和模拟计算结果对实验现象给出了合理解释。具体研究结果如下：（1）脉冲偏压电弧离子镀TiO₂薄膜研究在很宽的范围内（0～-900V）改变脉冲偏压的幅值，在玻璃、硅片及不锈钢三种基片上均获得均匀透明的TiO₂薄膜。薄膜表面均平整光滑，大颗粒的数量少且尺寸小，薄膜表面质量好。-300V偏压时玻璃基片上沉积态TiO₂薄膜表面达原子级平滑，R_rms约为0．1nm，薄膜的折射率n_λ=550nm最大，约为2．51，达到已有报道非晶TiO₂薄膜的最高折射率。也是在偏压为-300V时，不锈钢基片上的TiO₂薄膜的膜基结合力可高达82N。玻璃基片上沉积态TiO₂薄膜主要呈非晶态，薄膜颜色均匀但各偏压下各不相同。XPS结果表明，玻璃基片上薄膜中钛氧化学计量比约为1：2；增加基片负偏压有利于Ti-O成键。随着负偏压的增大，玻璃基片上薄膜的吸收边先红移后蓝移，沉积速率先增大后减小，薄膜的硬度先增大后减小，-100V和-300V负偏压时薄膜硬度较高，达到11GPa以上；光学带隙基本不变，约为3．27eV。硅基片上沉积态TiO₂薄膜以金红石相为主，-900V时，薄膜在（220）方向择优生长。经过空气中600℃保温1h退火处理后，薄膜的相结构随制备偏压各有不同。AFM结果表明，无偏压时薄膜平整，表面岛尺寸小且密度高，-900V时薄膜表面起伏较大，表面岛尺寸大且密度小。傅立叶红外光谱和拉曼光谱也表明负偏压对薄膜微结构和成键有明显的影响。不锈钢基片上仅-500V时所得沉积态薄膜为锐钛矿相，其余偏压时为非晶态。随负偏压的增加，沉积速率先增大后减小。不同负偏压下TiO₂薄膜的硬度均高于不锈钢基体的硬度，弹性模量与之相近，后者有利于提高膜基结合力。（2）脉冲偏压电弧离子镀TiO_2-xN_x薄膜研究利用脉冲偏压电弧离子镀通过多元气体混合法实现了N元素的置换式掺杂，N离子置换TiO₂中部分O离子，形成了N-Ti-O网络。掺杂N元素后，薄膜吸收响应起始波长蓝移至400nm。在偏压为-300V时玻璃基片上TiO_2-xN_x薄膜表面大颗粒较少，薄膜摩擦系数最小，约为0．13。不锈钢基片上，当负偏压由0V增大至-300V，薄膜的膜基结合力由45N增大至65N，提高了40％以上。（3）脉冲偏压电弧离子镀AlN薄膜研究同样通过改变脉冲偏压幅值进行制备AlN薄膜的对比实验，在玻璃、316L不锈钢和硅基片上也成功地获得了AlN薄膜，但由于Al的熔点很低致使薄膜表面存在较多的“针状”大颗粒。无偏压时Si基片上AlN薄膜无明显的择优取向，-50V时表现为六角相AlN（110）面择优取向，偏压升高至-100V和-300V，薄膜择优取向转变为面心立方相AlN（200），偏压继续升高至-500V，薄膜择优取向重新转变为六角相AlN（110）。无偏压、-100V和-300V时硅基片上AlN薄膜为面心立方相和六角相混晶结构，-50V和-500V偏压时为六方相结构，此时AlN薄膜的硬度高达33GPa。由于形成了六方相结构，-100V和-300V时316L不锈钢基片上AlN薄膜的硬度也高于30GPa。最后，本文结合脉冲偏压等离子体鞘层的物理特性对实验结果进行讨论分析，可知本实验有效避免微弧效应的根本原因源于两方面，一是等离子体鞘层厚度随脉冲偏压变化而产生动态的脉冲振荡，使积累的正电荷能及时被中和；二是通过合理调整脉冲偏压频率、占空比和幅值，使电荷累积达不到微弧击穿的强度。此外更为重要的是，脉冲偏压可使加速沉积粒子的电场始终有效，进而对介电薄膜的生长产生影响，从而能间接调控薄膜的结构与性能，这是用脉冲偏压电弧离子镀制备介电功能薄膜具有可行性的深层次原因。更多还原

【Abstract】 Dielectric films are the most widely-used functional films, which play increasing roles in the machinery, electronics, information, aerospace and other fields. But their poor conductivity brings difficulty to synthesis in some PVD processes. Take ion plating as an example, micro-arcs caused by charge accumulation not only severely degrade film quality, but also damages electrical components of the control system. Thus, ion plating, including widely-used arc ion plating, has always been considered unsuitable to fabricate dielectric films. Pulsed bias arc ion plating （PBAIP） is an advanced thin film deposition technology emerging in recent years. It inherits the advantages of arc ion plating such as high ionization rate and deposition rate and brings in new features such as low deposition temperature and residual stress, grain refinement and droplet reduction. These favorable features make PBAIP a potential technique to fabricate fine functional films. However, whether PBAIP can be used to fabricate dielectric films has not been extensively attempted. The clarification of this issue is of great significance to the development of arc ion plating technique and new film materials.Micro-arcs due to charge accumulation have been effectively suppressed by properly matching pulse frequency, duty cycle and bias voltage. Dense and smooth dielectric films such as TiO₂, TiO_2-xN)x and AlN have been successfully synthesized by using pulsed bias arc ion plating technique on glass, Si（100） and 316L stainless steel substrates, which represent respectively insulator, semiconductor and conductor. It has been sufficiently proven by our experiments that PBAIP can be used to synthesize dielectric films. The influence of pulsed bias on growth morphology, microstructure and properties of TiO₂, TiO_2-xN_x and AlN films has been investigated by varying the bias voltage from 0V to -900V. The results show that on whatever substrates, pulsed bias exhibits good regulation and control ability on film color, deposition rate, hardness and elastic modulus, adhesion force, microstructure, surface roughness and optical properties, which has further proven the feasibility of using PBAIP to fabricate dielectric films. The experiment results have been rationally interpreted by using a plasma sheath model and numerical simulations. Detailed results are listed as follows.（1） Synthesis of TiO₂ filmsUniform and transparent TiO₂ films have been deposited on three kinds of substrates with pulsed bias voltage varying in a fairly wide range from 0V to -900V. Droplets on film surface are few and small, film surface quality is good. As-deposited TiO₂ films on glass deposited at -300V are atomically smooth with RMS roughness of 0.113nm, which results in a high refractive index 2.51 at 550nm, closed to the maximum reported in the literatures. Deposited at the same bias, -300V, and TiO₂ films on 316L stainless steel substrates have a high adhesion force of 82N.Most of the as-deposited TiO₂ films on glass are in amorphous state. The film colors are uniform and different with the substrate bias. XPS results show that stoichiometric proportion of Ti and O is 1:2 and high bias voltage helps bonding between Ti and O. With the increase of bias voltage, absorption edge of the TiO₂ films red-shifts first, and then blue-shifts. Meanwhile deposition rate and film hardness increase first and then decrease. The hardnesses of the films deposited at -100V and -300V are at above 11GPa. Optical band gap is nearly constant, 3.27eV.Most of the as-deposited TiO₂ films on Si substrates consist of the Rutile phase, and the films deposited at -900V show a preferred orientation along the （220） direction. Film phase changes with the bias voltages after annealing at 600℃for 1h in air. AFM results show that the films deposited at 0V are smooth, surface islands are small and their density is high; The surface of the films at -900 V is wavy, surface islands are large and their density is low. FT-IR and Raman spectra also show that pulsed bias has apparent effects on film microstructure and bonding.Only the TiO₂ films deposited at -500V on stainless steel substrates are composed of Anatase phase, those deposited at other biases are amorphous. Deposition rate of the films on stainless steel first increases, and then decreases with the increase of bias voltage. Film hardness is higher than that of the substrates, while elastic modulus is similar to that of the substrates, which results in higher adhesion force.（2） Synthesis of TiO_2-xN_x filmsN substitutional doping has been realized by using PBAIP in a mixed atmosphere. N ions substitute some O ions in TiO₂, forming an N-Ti-O structure. The wavelength threshold for optical absorption of the films blue-shifts to 400nm after N doping. Droplets on the surface of TiO_2-xN_x films deposited at -300V on glass substrates are scarce, resulting in a low friction coefficient of 0.13. With the bias voltage increasing from 0 to -300V, adhesion force of TiO_2-xN_x films on 316L stainless steel substrates increases by 40%, from 45N to 65N.（3） Synthesis of AlN filmsAlN films have also been successfully synthesized on glass, Si（100） and 316L stainless steel substrates by PBAIP with bias voltage varying from 0 to -500V. Many "needle-like" droplets appear on the film surface due to the low melting point of Al. AlN films deposited at 0V on Si substrates show no preferred orientation. AlN films at -50V show a preferred orientation along the hexagonal A1N （110） direction. At -100V and -300V, the preferred orientation changes to fcc-AlN （200）. As the bias voltage further increases to -500V, the preferred orientation changes back to hexagonal AlN （110）. AlN films on Si substrates deposited at 0V, -100V and -300V are composed of the fcc and hexagonal phases, and the films at -50V and -500 V consist of the hexagonal phase, resulting in a higher film hardness of 33GPa. Hardness of A1N films on 316L stainless steel substrates at -100V and -300V is higher, above 30GPa, due to thr formation of the hexagonal phase.Finally, the experimental results have been discussed within the framework of pulse plasma sheath. The fundamental reasons for the suppression of micro-arcs lie in two aspects. One is that plasma sheath thickness shows a dynamical oscillation in step with the pulsed bias. The accumulated positive charge is neutralized instantly. Accumulated charge quantity cannot meet the intensity for micro-arc breakdown by matching pulse frequency, duty cycle and bias voltage. More importantly, pulsed bias is always effective in accelerating the deposition ion species and influences the film growth. Thus pulsed bias can indirectly regulate and control film microstructure and properties. This is the unique feature in the synthesis of dielectric functional films using pulsed bias arc ion plating technique.更多还原