过滤阴极真空电弧镀膜技术所制得氧化铝薄膜的结构和特性摘要摘要：：通过过滤阴极真空电弧镀膜技术制备氧化铝薄膜时，其内部结构、组成、形态、光学和机械性能被详尽的描述，这些都与制备时氧气的流量有关。
薄膜结构、组成、形态和性能都是很重要的，随着氧气流量的增加，薄膜的结构也由非晶体经过一系列变化到单晶体，随着O/Zr原子比率的增加和Z离子由低氧化作用的状态转化为Zr4+再一次形成非晶体。
形成这样的结构是由于其内部结构的变化而引起的，并且影响其形态和机械性能，以致这种非晶体薄膜表面有一些小簇，其光滑程度就像低硬度的多晶体薄膜。
当反射指数和系数相对接近最大值时，在发射率和光学带宽随着O/Zr比增加时，薄膜的组成来决其光学性能而非其密度。
1.1.说明说明在大气压力下由于三种不同温度有多种不同靶形态结构，单晶体时低于1170O C，四面体时为1170-2370O C，2370O C为立方体，知道2680O C时形成金属。
Zr有很高的反射指数，大光学带宽间距，和很低的光损失及在0.3-8范围内高透明度,所以被广泛的应用于光学领域。
此外，Zr具有很高的电介质，低泄露量等特点，最有可能代替做电解质的晶体管。
进而，由于Zr很低的传热性，它成为了装置中隔热层的首选。
Z其他的特性如：高硬度、高抗氧性也使其成为机械材料中的热门。
至今为止，已经有很多制备Z的方法，例如反应磁控溅射，离子辅助反应溅射，化学气相沉积等。
薄膜特性的优劣取决于制备过程及其参数。
过滤阴极真空电子弧镀膜技术，在低电压和高电流状态下工作。
通过磁性机械过滤器来防止微粒从阴极发射。
它提供了一种具有很高能量的沉积离子源，远大于相应的热蒸发和磁控溅射。
能有效去处宏观无用微粒，很明显能提高薄膜质量并拓展其应用。
固有的高能量提高薄膜的附着性和密度。
由于能力是离子辅助沉积中最重要的参数，这种制备的方法已经有了一些应用，已经应用于在高热平衡和高SP3状态下碳薄膜的制备，还合成了一些金属氧化物的薄膜。
然而对我们最有利的是，很少有关过滤阴极真空电子弧镀膜技术制备ZrO2薄膜的知识。
我们现在的工作是系统研究在不同O2流量与ZrO2薄膜的结构、组成、表面形态和性质之间的关系。
我们的结论表明薄膜的结构、组成特性都与O2流量有关系。
过滤阴极真空电子弧镀膜技术所制的薄膜特性与其他方法相比，更说明了该方法的优越性。
2.实验图1为制备设备。
该图已经详细反应了这个系统，各个部分都表现了出来。
该系统有一个双倍滤光器，可以使弧自身发射出微粒。
阴极Zr原子在120A电流下，阴、阳极瞬间接触点燃喷出的浆体，该浆体是从一个400mT的磁场放射出来并压缩的。
一个旋转泵和一个冷凝泵可使这个系统的压力达到4×10-6T。
O2通过一个有很多小孔的铜管进入Zr靶附近区域。
这种发射O2的方式可使O2电离到最大程度，因此增加了与浆体的接触使得Zr与O2之间发生充分的反应。
O2流量可选择10-98sccm,在制备过程中，随着O2流量的增加，靶的氧化更加充分。
O2增加使得靶材充分氧化，并且损失了冷凝粒子，使得制备的速率75nm/s降至35nm/s。
`在室温下薄膜生长在n-si和石英表面。
基片被放在制备室之中，按顺序被丙酮、酒精和未电离的水清洗。
所制得的薄膜厚度大约在200nm。
通过由CUKα做源的XRD法可得出薄膜所处阶段和晶体结构。
光谱计记录下反射率等参数，光学特性也被软件检测。
主要特征和组成分析被XPS通过ALK辐射测得到。
不可使用没有清洗过的样品溅射，以免所溅射得到的薄膜化学组成发生变化。
图13.3.结果结果3.1结构图2表明在不同O2流量ZrO2薄膜由XRD测得的结构，在10sccm时，在曲线中对应着边缘处，而系统峰值在32.4o C附近，为标准的结构。
这个高峰来自于没有完全氧化的ZrO固体。
由于类似现象可看出峰值点又是不对称的和急剧变化处。
当O2流量增加至20sccm，一个最高峰是当晶体阶段，相对弱的高峰是多晶体阶段。
氧气流量决定峰值。
我们可以检测出它是怎么影响薄膜结构的。
在35sccm时，出现了更多的弱高峰，在m(200)处峰值变得很弱，在m（-202m）变得很强。
然而当氧气的流量增加至65sccm时，薄膜由多晶体变为无定形，在弯曲处出现更宽的高峰。
结构的不同反应出02流量在薄膜结构形成中扮演了很重要的角色。
正在一定流量范围内（20-50sccm）薄膜保持在多晶体状态，而在纯单晶体阶段在不同的范围内。
3.2化学组成和化学状态通过典型的XPS光谱测量可以得到由光电离子及Zr和O转变达到高峰，在与空气接触后的抽样中经过观察C1S是主要表面组成部分。
在Zr3d和O1S处出现两个高峰。
图4中可看到常态的元素和由XPS测得的局部光谱。
频谱非常接近标准单晶体的ZrO2。
两个高峰，Zr3d5/2和Zr3d3/2时的能量分别为181.8ev和184.2ev，非常接近在中标准ZrO2，并且是对称的，在氧化状态的薄膜中只有它。
他们的强度比率和导致旋转轨道在1.5ev和2.4ev的能量间隔和其他研究是一致的。
一个不对称的高峰能分解为的529.6evLBE能量和531ev的HBE，与报告中的那些类似。
相比之下，薄膜沉积速率很低时，例如35sccm，Zr3d光谱是以某种方式不同的而O1S频率是十分类似的。
出现较低能量接近其边缘，有形式为Zr,Zr n+,(n=1,2,3)氧化物存流量的不同可转变为使得和发生充分的反应。
氧化程度的不同也被在。
可得出随着O2表明，薄膜中O和Zr的原子比率可由它们在峰值区域的灵敏度算出。
O1S的HBE是一个小片段所以高峰不能被确定。
正如预料，O/Zr比增加可导致更多氧化。
可看到在薄膜沉积速率为时，O/Zr比为1.98：1接近原子比为2：1，在65sccm及起以上，薄膜3.3表面形态五表现了在65sccm时典型的薄膜。
在薄膜表面，小簇由相同的冷凝的原子成。
这表面相当干净和光滑，RMS粗燥率小于0.1nm在1um×1um区域内。
上面提到的高能量轰击微粒使得形成干净、光滑的表面，这些微粒运动时损失粒子，或者促进原子和提供足够能量运动到生长表面相结合，再一次建议流量的边界值不影响原子的运动，与XRD测量结果一致。
流动速率XRD分析出的薄膜结构的改变有关。
有趣的是，薄膜的形态似乎也被O2在10sccm时，薄膜表面的簇会很大。
这种簇的变化可以反映出薄膜表面粗糙。
XRD分的流量有关。
换句话说，与无定型薄膜析出的薄膜结构的改变说明薄膜表面结构与O2相比较，这种多晶体薄膜在20-50sccm速率下在表面形成巨大的簇并且看起来很粗糙。
3.4机械性能薄膜的硬度是测量抵制塑性变形和确定载荷符合凹行区域的峰值。
实际上，硬度通过卸载数据所构成能量方程来表现。
薄膜的机械性能作为流量方程显示在图9，其值平均至少出现了3次，微硬度和是依赖于氧气流量。
当流量由10sccm增加到20sccm，硬度几乎维持为13.6GP,再增加流量会导致硬度急速提高。
在35。
50，硬度仍然在增加，超出50sccm后，薄膜开始变软，并且在65sccm会降至13.4GPA。
显然，硬度的改变非常接近在XRD式样中观察的。
这表明硬度是由薄膜的结构确定而非特性确定其硬度，这与KAO的报告结果不一致。
4.结论通过过滤阴极真空电弧镀膜技术制备薄膜，研究了在不同氧气流量时，薄膜的结构、组成、形态、光学性能和机械性能，最终的流量达到了98sccm。
经研究发现O2流量的增加，薄膜的结构由无的流量是薄膜结构、组成、特性的重要参数。
随着O2定型到不同氧化率的单晶体再到无定型；随着0/Zr原子比的增加，Zr原子由低氧化率到Zr。
这种与氧气流量有关的结构趋势会导致薄膜组成的改变并且决定表面形态和薄膜的机械性能。
g.q.yub.k.tay_z.w.zhaoStructure and propertiesof zirconium oxide thin filmsprepared by filtered cathodic vacuum arcSchool of Electrical and Electronic Engineering,Nanyang TechnologicalUniversity,Singapore,639798,SingapoReceived:19September2003/Accepted:17January2004Published online:1April2004•©Springer-Verlag2004ABSTRACT Zirconium oxide(ZrO2)thin films deposited atroom temperature by the filtered cathodic vacuum arc(FCVA)technique are detailed in terms of the film structure,composition, morphology,and optical and mechanical properties,which are tailored by the oxygen(O2)flow rate during deposition.The relationships between the film structure,composition,morphology, and properties are emphasized.With an increasing flow rate,the film evolves in structure from amorphous,through a pure monoclinic phase with varying preferential orientation,to amorphous again,accompanied by an increase in the O/Zr atomic ratio and a conversion of Zr ions from low oxidation states into Zr4+.Such a structural trend arises from the change in composition,and influences the film morphology and mechanical properties so that the amorphous films exhibit small clusters on the surface and smoother morphology as well as lower hardness compared with the polycrystalline films.Thefilm composition rather than the density dominates the optical properties,where the transmittance and the optical band gap increase with increasing O/Zr values,while the refractive index and extinction coefficients behave conversely with the lowest refractive index(2.16at550nm) approaching the bulk value(2.2).PACS68.55.Jk;78.66.Nk;68.37.Ps1.IntroductionZirconium oxide(ZrO2)has three temperature dependent polymorphic structures at atmospheric pressure.A monoclinic phase is stable at temperature below1170◦C,a tetragonal between1170and2370◦C,and a cubic from2370◦C to the melting point at2680◦C.ZrO2is widely used in optical fields[1–3],because of its high refractive index,large optical band gap,and low optical loss and high transparency in the0.3–8μm range.In addition,ZrO2is a promising candidate to replace silicon dioxide as the gate dielectric in transistors,due to its high dielectric constant(∼25),lowleakage current level,etc.[4–6].Furthermore,ZrO2has potentialas a thermal barrier coating in devices due to its low thermal conductivity[7,8].Other properties such as high hardness,large resistance against oxidation,also make it interesting as a mechanical material[9].To date,many efforts to prepare ZrO2have been made by various deposition techniques,for example,reactive magnetron sputtering[10–13],ion-assisted reactive sputtering or evaporation deposition[8,14–25],solgelmethods[26],chemical vapor deposition[4,17],and so on.The film properties are generally strongly dependent on the deposition process and parameters.The filtered cathodic vacuum arc technique(FCVA)[27–29],operated at low pressure,low voltage,and high current,effectively eliminates micro-sized(0.1–10μm)macroparticles from being emitting from cathode materials during arcing by means of mechanical,magnetic,or electrical filters,or a combination of these.It also provides an intense source of fully ionized deposition specieswith energies(50∼150eV)greater than counterparts produced in thermal evaporation or magnetron sputtering[30,31].The removal of detrimental macro-particles undoubtedly improves the resulting film quality and extends the application of the deposition technique.The inherent high-energy could increase the film adhesion and the packing density.The full ionization of the deposition species allows tailoring of the film properties with substrate bias,since kinetic energy is one of the most important parameters as in ion beam assisted deposition(IBAD)[8].This technique has been demonstrated in the preparation of a diamond-like carbon film with high thermal stability and a high sp3[32],to fill trenches[33,34],as well as the synthesisof certain metal oxide films[35,36].However,to the best of our knowledge,little work has been reported on ZrO2synthesis by the(FCVA)technique.In the present work,we systematically investigate the structural,chemical composition,optical,and mechanicalproperties of ZrO2films deposited at different oxygen(O2)flow rates by FCVA.The emphasis is placed on the relationships between structure,composition,surface morphology,and properties of the films.Our results disclose that the structural and compositional properties of the films are considerably influenced by the O2flow rate.The variation in compositioninduces structural transformation from amorphous through a pure monoclinic phase to amorphous again,and determines the optical properties,whereas the change in structure controls the mechanical properties and affects the surface morphology.The properties of the films are also crosscomparedwith those of films prepared by other methods to highlight the FCVA features.2ExperimentalA schematic diagram of the FCVA deposition system is shown in Fig.1.The details regarding the main principles of the system have been described elsewhere[37].Briefly,the system incorporates an off-plane double bendfilter,which effectively removesmacro-particles originating from the arc itself.A Zr cathode(99.98%pure)operated at120A dc current is ignited through instant contact between cathode and anode to obtain the plasma,which is steered out by a toroidal magnetic field fixed at40mT to condense on a substrate.The base pressure of the system, evacuated by a rotary pump and a cryo-pump,can reach4×10−6Torr.O2gas(99.99%pure)is led into the region near the Zr target through a copper tube on which many tiny holes are distributed.This way of introducing O2is expected to maximize O2ionization due to its relatively increased collision with the plasma,possibly promoting a chemical reaction between O2and Zr. The O2flow rate chosen here is varied from10to98sccm corresponding to1×10−4to4.6×10−4Torr.During deposition,the deposition rate decreases from75to35nm/min with an increasing O2flow rate as a result of increased.oxidization of the target,and collision-induced loss of condensing particles.The films are grown on n-Si(100)and quartz substrates at room temperature.All the substratesare sequentially cleaned in acetone,alcohol,and de-ionizedwater prior to being loaded into the deposition chamber.All the films being investigated are generally around200nm thick.The film phase and crystal structure are identified by Xray diffraction(XRD)with a Cu Kαsource at1.54Å.Transmittance and reflectance are recorded from200to1100nm with a spectrometer.Optical constants are obtained by fitting optical spectra with Scout software[38]. Core level spectra and compositional analysis areand compositional analysis are carried out by X-ray photoelectronspectroscopy(XPS)with monochromatic Al Kαradiation(1486.6eV).No sputter cleaning of the samples is performed to avoid changes in chemical compositions induced by preferential sputtering.The spectrum obtained iscorrected by an adventitious C1s peak at284.6eV.Surface morphology is measured by atomic force microscopy(AFM)in tapping mode(Dimension3000scanning probe microscope from Digital Instruments).The mechanical properties on a nano-scale are obtained by a nanoindentation techniqueapparatus(Hysitron Inc.)attached to the above AFM equipment.Nanoindentations were made using a Berkovich diamond indenter and the maximum loads applied were500μN.The indenter was loaded at100μN/s,held at peak load for5s and then finally unloaded at100μN/s.3Results3.1StructureFigure2shows theXRDpatterns for ZrO2films deposited at differentO2flowrates.At10 sccm,a broad but symmetric peak centered at around32.4◦is observed in curve(a),indicative of an amorphous structure.The peak is believed to come from an oxygen-deficient Zr-O solidsolution[40].Wong et al.[13]also reported a similar phenomenon,where,however,the peak was unsymmetric and sharp.As the O2flow rate increases to20sccm(Fig.2b)),one peak at33.7◦assigned to(200) planes of monoclinic phase(denoted as m(200))is predominant,accompanied by the appearanceof other weak peaks also from the monoclinic phase.This rapid occurring of diffraction peaks shows that so much oxygen is incorporated that sufficient ZrO2crystallite forms which can be detected.The easy combination between Zr and O is possiblyrelated to charged and therefore active emitted species,as well as further stimulated by energeticZr particles bombarding the surface as in IBAD.At35sccm,in addition to more weak peaks,them(200)peak becomes weaker while the m(-202) peak gets stronger.When the O2flow rate goes up to50sccm,the dominant peak is changed tom(-111)while many more monoclinic peaks are produced.3.2Chemical compositions and chemical statesIt was concluded from a typical XPS survey spectrum(not shown)that besides the peaks contributed by photoelectrons and Auger transitions of Zr and O,C1s is observed as well,which is mainly from surface contamination after exposure of the sample to air.The two strong peaks at 185.9and533.2eV are identified as Zr3d and O1s,respectively.Fig.4presents the normalizedZr3d(a)and O1s(b)XPS local spectra for the film prepared at50sccm.The spectra closely resemble those observed in standard monoclinic ZrO2[42].Two peaks,Zr3d5/2and Zr3d3/2 observed at binding energies of181.8and184.2eV,very near to the values of Zr4+in ZrO2[42], are symmetrical,denoting that only one oxidation state of Zr exists in the film.Their intensityratio(I3d5/2/I3d3/2)and energy interval(∆3d5/2–3d3/2)resulting from spin-orbit splitting are1.5 and2.4eV,in agreementwith other studies[20,42].An asymmetric O1s peak can be decomposed into two components peaked at a low binding energy(LBE)of529.6eV and high binding energy(HBE)of531.6eV, quite comparable with reported ones[14,43].It has been accepted that the LBE peak is assignedto the oxygenin zirconia[14,20,43]while the HBE is attributed to oxygen present in the hydroxide and/or adsorbed oxygen or carbonates or higher-valent oxides[14,42,44,45].Matsuoka et al.[20]ascribed it to oxygen possibly bound to Zr.In contrast,for the film deposited at the low flow rate, i.e.,35sccm,the Zr3d spectrum is somehow different whereas the O1s spectrum is very similar.A shoulder of the Zr3d5/2clearly appears at the lower binding energy side(Fig.4c),indicating that other oxidation states of Zr(Zrn+,n=1,2,3)occur.This shoulder is attributed to Zr suboxides[14,20].It can be concluded from this discrepancy that with increasingflow rate,Zrn+(n≤3)will convert into Zr4+due to a full reactionbetween Oand Zr in the films.This consistent variation in the oxidation state of Zr ions with the film composition was also reported in[20].The atomic ratio of Oto Zr(O/Zr)in the films can be calculated with their respective peak areas cali-brated by their sensitivity factors(0.66,2.1,0.66 forO1s and Zr3d).For the calculation,theO1s HBE peak is not includeddue to its small fraction.As expected,theO/Zr ratio increases with more addition of oxygen(not shown).Note that for the film deposited at50sccm,the O/Zr ratio obtained is approximately1.98: 1,near to the ideal stoichiometric ratio of2:1.At65sccm and above,the films areover-stoichiometric(∼2.2:1).3.3Surface morphologyFigure5a presents a typical top-view AFM image of the film at65sccm.On the film surface, the clusters composed of many condensing adatoms are uniformly distributed.The surface is quite clear and smooth,with its rootmean-square(RMS)roughness less than0.1nmover the area of1μm×1μm.This clearness and smoothness is associated with the above-mentioned high energy of bombarding particles,which possibly removes loose particles(so-called“self-sputtering”)or promotes bonding between adatoms andoffers the adatoms enough lateral mobility on the growing surface[39,46],again suggesting that the flow rate range selected does not greatly affect the adatoms mobility,in accordance with the XRD results.Interestingly,the film morphology seems to be affected by the O2flow rate as well. At10sccm,the clusters distributed on the film surface are similar in size to that forthe film at65sccm.However,in the range of20to50sccm,larger clusters are present on the surface.This change in cluster size is also reflected in the curve of roughness versus the O2flow rate(Fig.5b)the O2flowrate(Fig.5b),where the roughness is larger for a20–50sccm flow rate range.The flowrate-dependent surface morphology could be correlated with the film structural change as drawn from XRD analysis.In other words,compared with the amorphous films,the polycrystalline films formed in a20–50sccm flowexhibit larger clusters on the surface and look relatively rougher.3.4Mechanical propertiesThe film hardness is a measure of resistance to plastic deformation and defined as the peak load divided by the corresponding indentation area.Practically,the hardness is obtained by fitting the unloading data with a power law equation[39].The mechanical properties of the films as a function of flow rate are displ ayed in Fig.9,where the v alues are averaged at least three times. Both the microhardness and Young’s modulus are apparently dependent upon the O2flow rate. When flow rate increases from10to20sccm,the hardness almost stays at about13.6GPa.Further increasing the flow rate leads to an abrupt increase in hardness.At35and50sccm,the increase is pronounced.However,beyond50 sccm,the film starts to become soft and at65sccm drops to13.4GPa in hardness.Clearly,thechange in hardness is very similar to the structural variation observed in the XRD patterns.This signifies that the film structure rather than the composition determines the film hardness,which is not in agreement with the result reported by Kao[19].4ConclusionsThe structure,composition,morphology,optical,and mechanical properties of ZrO2films deposited by the filtered cathodic vacuum arc(FCVA)technique have been investigated at varyingO2flowrates,up to98sccm.TheO2flow rate is found to be an important parameter in controlling the film structure,composition,and properties.With increasing O2flow rate,ZrO2 film evolves in structure from amorphous,through to a pure monoclinic phase with varying preferential orientation,to amorphous again,concurrent with an increase in the O/Zr atomic ratio, and a conversion of Zr ions from lowoxidation states into Zr4+.Such a trend in the structure with the O2flow rate is a result of a change in the film composition,and determines the surface morphology and the mechanical properties of the film.The film composition instead of the film density,dominates the optical properties,where transmittance and optical band gap increase with increasing O/Zrvalue,whereas the refractive index and extinction coefficients behave inversely.。
