中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 1 頁共 13 頁 過濾陰極真空電弧鍍膜技術(shù)所制得氧化鋁薄膜的結(jié)構(gòu)和特性 摘要 ： 通過過濾陰極真空電弧鍍膜技術(shù)制備氧化鋁薄膜時，其內(nèi)部結(jié)構(gòu)、組成、形態(tài)、光學和機械性能被詳盡的描述，這些都與制備時氧氣的流量有關(guān)。薄膜結(jié)構(gòu)、組成、形態(tài)和性能都是很重要的，隨著氧氣流量的 增加，薄膜的結(jié)構(gòu)也由非晶體經(jīng)過一系列變化到單晶體，隨著 O/Zr原子比率的增加和 Z 離子由低氧化作用的狀態(tài)轉(zhuǎn)化為 Zr4+ 再一次形成非晶體。形成這樣的結(jié)構(gòu)是由于其內(nèi)部結(jié)構(gòu)的變化而引起的，并且影響其形態(tài)和機械性能，以致這種非晶體薄膜表面有一些小簇，其光滑程度就像低硬度的多 晶體薄膜。當反射指數(shù)和系數(shù)相對接近最大值時，在發(fā)射率和光學帶寬隨著O/Zr 比增加時，薄膜的組成來決其光學性能而非其密度。 1.說明 在大氣壓力下由于三種不同溫度有多種不同靶形態(tài)結(jié)構(gòu)，單晶體時低于 1170OC，四面體時為 1170-2370OC， 2370OC 為立方體，知道 2680OC 時形成金屬。 Zr 有很高的反射指數(shù)，大光學帶寬間距，和很低的光損失及在 0.3-8范圍內(nèi)高透明度 ,所以被廣泛的應用于光學領(lǐng)域。 此外， Zr 具有很高的電介質(zhì)，低泄露量等特點，最有可能代替做電解質(zhì)的晶體管。進而，由于 Zr 很低的傳熱性，它成為 了裝置中隔熱層的首選。 Z其他的特性如：高硬度、高抗氧性也使其成為機械材料中的熱門。至今為止，已經(jīng)有很多制備 Z 的方法，例如反應磁控濺射，離子輔助反應濺射，化學氣相沉積等。薄膜特性的優(yōu)劣取決于制備過程及其參數(shù)。 過濾陰極真空電子弧鍍膜技術(shù)，在低電壓和高電流狀態(tài)下工作。通過磁性機械過濾器來防止微粒從陰極發(fā)射。它提供了一種具有很高能量的沉積離子源，遠大于相應的熱蒸發(fā)和磁控濺射。能有效去處宏觀無用微粒，很明顯能提高薄膜質(zhì)量并拓展其應用。固有的高能量提高薄膜的附著性和密度。由于能力是離子輔助沉積中最重要的參數(shù)，這種 制備的方法已經(jīng)有了一些應用，已經(jīng)應用于在高熱平衡和高 SP3 狀態(tài)下碳薄膜的制備，還合成了一些金屬氧化物的薄膜。然而對我們最有利的是，很少有關(guān)過濾陰極真空電子弧鍍膜技術(shù)制備 ZrO2薄膜的知識。 我們現(xiàn)在的工作是系統(tǒng)研究在不同 O2流量與 ZrO2 薄膜的結(jié)構(gòu)、組成、表面形態(tài)和性質(zhì)之間的關(guān)系。我們的結(jié)論表明薄膜的結(jié)構(gòu)、組成特性都與 O2流量有關(guān)系。 過濾陰極真空電子弧鍍膜技術(shù)所制的薄膜特性與其他方法相比，更說明了該方法的優(yōu)中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 2 頁共 13 頁 越性。 2.實驗 圖 1 為制備設(shè)備。該圖已經(jīng)詳細反應了這個系統(tǒng)，各個部分都表現(xiàn)了出來。該系統(tǒng) 有一個雙倍濾光器，可以使弧自身發(fā)射出微粒。陰極 Zr 原子在 120A 電流下，陰、陽極瞬間接觸點燃噴出的漿體，該漿體是從一個 400mT 的磁場放射出來并壓縮的。一個旋轉(zhuǎn)泵和一個冷凝泵可使這個系統(tǒng)的壓力達到 4 10-6T。 O2通過一個有很多小孔的銅管進入 Zr 靶附近區(qū)域。這種發(fā)射 O2 的方式可使 O2電離到最大程度，因此增加了與漿體的接觸使得 Zr 與 O2之間發(fā)生充分的反應。 O2流量可選擇 10-98sccm,在制備過程中，隨著 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，并且損失了冷凝粒子，使得制備的速率 75nm/s 降至 35nm/s。 在室溫下薄膜生長在 n-si 和石英表面?；环旁谥苽涫抑?，按順序被丙酮、酒精和未電離的水清洗。所制得的薄膜厚度大約在 200 nm。 通過由 CUK做源的 XRD 法可得出薄膜所處階段和晶體結(jié)構(gòu)。光譜計記錄下反射率等參數(shù)，光學特性也被軟件檢測。主要特征和組成分析被 XPS 通過 ALK 輻射測得到。不可使用沒有清洗過的樣品濺射，以免所濺射得到的薄膜化學組成發(fā)生變化。 圖 1 3.結(jié)果 3.1 結(jié)構(gòu) 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 3 頁共 13 頁 圖 2 表明在不同 O2流量 ZrO2薄膜由 XRD 測得的結(jié)構(gòu)，在 10sccm時，在曲線中對應著邊緣處，而系統(tǒng)峰值在 32.4oC附近，為標準的結(jié)構(gòu)。這個高峰來自于沒有完全氧化的 ZrO 固體。由于類似現(xiàn)象可看出峰值點又是不對稱的和急劇變化處。當 O2流量增加至 20sccm，一個最高峰是當晶體階段，相對弱的高峰是多晶體階段。氧氣流量決定峰值。我們可以檢測出它是怎么影響薄膜結(jié)構(gòu)的。在 35sccm 時，出現(xiàn)了更多的弱高峰，在 m(200)處峰值變得很弱，在 m（ -202m）變得很強。然而當氧氣的流量增加至 65sccm時，薄膜由多晶體變?yōu)闊o定形，在彎曲處出現(xiàn)更寬的高峰。結(jié)構(gòu)的不同反應出 02流量在薄膜 結(jié)構(gòu)形成中扮演了很重要的角色。正在一 定流量范圍內(nèi)（ 20-50sccm）薄膜保持在多晶體狀態(tài)，而在純單晶體階段在不同的 范圍內(nèi)。 3.2 化學組成和化學狀態(tài) 通過典型的 XPS 光譜測量可以得到由光電離子及 Zr 和 O 轉(zhuǎn)變達到高峰，在與空氣接觸后的抽樣中經(jīng)過觀察 C1S 是主要表面組成部分。在 Zr3d 和 O1S 處出現(xiàn)兩個高峰。圖 4中可看到常態(tài)的元素和由 XPS 測得的局部光譜。頻譜非常接近標準單晶體的 ZrO2。兩個高峰， Zr3d5/2和 Zr3d3/2時的能量分別為 181.8ev 和 184.2ev，非常接近在中標準ZrO2， 并且是對稱的，在氧化狀態(tài)的薄膜中只有它。他們的強度比率和導致旋轉(zhuǎn)軌道在1.5ev 和 2.4ev 的能量間隔和其他研究是一致的。一個不對稱的高峰能分解為的529.6evLBE 能量和 531ev 的 HBE，與報告中的那些類似。 相比之下，薄膜沉積速率很低時，例如 35sccm， Zr3d 光譜是以某種方式不同的而 O1S中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 4 頁共 13 頁 頻率是十分類似的。出現(xiàn)較低能量接近其邊緣，有形式為 Zr,Zrn+,(n=1,2,3)氧化物存在?？傻贸鲭S著 O2流量的不同可轉(zhuǎn)變?yōu)槭沟煤桶l(fā)生充分的反應。氧化程度的不同也被表明，薄膜中 O和 Zr 的原子比率可由它們在峰 值區(qū)域的靈敏度算出。 O1S 的 HBE 是一個小片段所以高峰不能被確定。正如預料， O/Zr 比增加可導致更多氧化?？煽吹皆诒∧こ练e速率為時， O/Zr 比為 1.98： 1 接近原子比為 2： 1，在 65sccm 及起以上，薄膜 3.3 表面形態(tài) 五表現(xiàn)了在 65sccm 時典型的薄膜。在薄膜表面，小簇由相同的冷凝的原子成。 這表面相當干凈和光滑， RMS 粗燥率小于 0.1nm 在 1um 1um 區(qū)域內(nèi)。上面提到的高能量轟擊微粒使得形成干凈、光滑的表面 ，這些微粒運動時損失粒子，或者促進原子和提供足夠能量運動到生長表面相結(jié)合，再一次建議 流 量的邊界值不影響原子的運動，與 XRD 測量結(jié)果一致。 有趣的是，薄膜的形態(tài)似乎也被 O2流動速率 XRD 分析出的薄膜結(jié)構(gòu)的改變有關(guān)。在 10sccm 時，薄膜表面的簇會很大。這種簇的變化可以反映出薄膜表面粗糙。 XRD 分析出的薄膜結(jié)構(gòu)的改變說明薄膜表面結(jié)構(gòu)與 O2的流量有關(guān)。 換句話說，與無定型薄膜相比較，這種多晶體薄膜在 20-50sccm 速率下在表面形成巨大的簇并且看起來很粗糙。 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 5 頁共 13 頁 3.4 機械性能 薄膜的硬度是測量抵制塑性變形和確定載荷符合凹行區(qū)域的峰值。實際上，硬度通過卸載數(shù)據(jù)所構(gòu)成能量方程來表現(xiàn)。薄膜的 機械性能作為流量方程顯示在圖 9，其值平均至少出現(xiàn)了 3次，微硬度和是依賴于氧氣流量。當流量由 10sccm 增加到 20sccm，硬度幾乎維持為 13.6GP,再增加流量會導致硬度急速提高。在 35。 50，硬度仍然在增加，超出 50sccm 后，薄膜開始變軟，并且在 65sccm 會降至 13.4GPA。顯然，硬度的改變非常接近在 XRD 式樣中觀察的。這表明硬度是由薄膜 的結(jié)構(gòu)確定而非特性確定其硬度，這與 KAO 的報告結(jié)果不一致。 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 6 頁共 13 頁 4.結(jié)論 通過過濾陰極真空電弧鍍膜技術(shù)制備薄膜，研究了在不同氧氣流量時，薄膜的結(jié)構(gòu)、組成、 形態(tài)、光學性能和機械性能，最終的流量達到了 98sccm。經(jīng)研究發(fā)現(xiàn) O2的流量是薄膜結(jié)構(gòu)、組成、特性的重要參數(shù)。隨著 O2 流量的增加，薄膜的結(jié)構(gòu)由無定型到不同氧化率的單晶體再到無定型；隨著 0/Zr 原子比的增加， Zr 原子由低氧化率到 Zr。這種與氧氣流量有關(guān)的結(jié)構(gòu)趨勢會導致薄膜組成的改變并且決定表面形態(tài)和薄膜的機械性能。 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 7 頁共 13 頁 g.q. yu b.k. tay_ z.w. zhao Structure and properties of zirconium oxide thin films prepared by filtered cathodic vacuum arc School of Electrical and Electronic Engineering, Nanyang Technological University,Singapore, 639798, Singapo Received: 19 September 2003/Accepted: 17 January 2004 Published online: 1 April 2004 Springer-Verlag 2004 ABSTRACT 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. The film 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 (2.16 at 550 nm) approaching the bulk value (2.2). PACS 68.55.Jk； 78.66.Nk； 68.37.Ps 1. Introduction Zirconium oxide (ZrO2) has three temperature dependent polymorphic structures at atmospheric pressure. A monoclinic phase is stable at temperature below 1170 C, a tetragonal between 1170 and 2370 C, and a cubic from 2370 C to the melting point at 2680 C. ZrO2 is widely used in optical fields 13, because of its high refractive index,large optical band gap, and low optical loss and high transparency in the 0.38 m range. In addition, ZrO2 is a promising candidate to replace silicon dioxide as the gate dielectric in transistors, due to its high dielectric constant ( 25), lowleakage current level, etc. 46. Furthermore, ZrO2 has potential as 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 ZrO2 have been made by various deposition techniques, for example, reactive magnetron sputtering 1013, ion-assisted reactive sputtering or evaporation deposition 8, 1425, solgelmethods 26, chemical vapor deposition 4, 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 8 頁共 13 頁 17, and so on. The film properties are generally strongly dependent on the deposition process and parameters. The filtered cathodic vacuum arc technique (FCVA) 2729, operated at low pressure, low voltage, and high current, effectively eliminates micro-sized (0.110 m) 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 (50150 eV) 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 ZrO2 synthesis by the (FCVA) technique.In the present work, we systematically investigate the structural, chemical composition, optical, and mechanical properties of ZrO2 films 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 O2 flow rate. The variation in composition induces 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 crosscompared with those of films prepared by other methods to highlight the FCVA features. 2 Experimental A 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 at 120 A 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 at 40 mT to condense on a substrate. The base pressure of the system, evacuated by a rotary pump and a cryo-pump, can reach 4 106 Torr. O2 gas (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 O2 is expected to maximize O2 ionization due to its relatively increased collision with the plasma, possibly promoting a chemical reaction between O2 and Zr. The O2 flow rate chosen here is varied from 10 to 98 sccm corresponding to 1 104 to 4.6 104 Torr. During deposition, the deposition rate decreases from 75 to 35 nm/min with an increasing O2 flow 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. 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 9 頁共 13 頁 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 around 200 nm thick. The film phase and crystal structure are identified by Xray diffraction (XRD) with a Cu K source at 1.54 . Transmittance and reflectance are recorded from 200 to 1100 nm with a spectrometer. Optical constants are obtained by fitting optical spectra with Scout software 38. Core level spectra and compositional analysis are and compositional analysis are carried out by X-ray photoelectron spectroscopy (XPS) with monochromatic Al K radiation (1486.6 eV). No sputter cleaning of the samples is performed to avoid changes in chemical compositions induced by preferential sputtering. The spectrum obtained is corrected by an adventitious C1s peak at 284.6 eV. Surface morphology is measured by atomic force microscopy (AFM) in tapping mode (Dimension 3000 scanning probe microscope from Digital Instruments). The mechanical properties on a nano-scale are obtained by a nanoindentation technique apparatus (Hysitron Inc.) attached to the above AFM equipment. Nanoindentations were made using a Berkovich diamond indenter and the maximum loads applied were 500 N. The indenter was loaded at 100 N/s, held at peak load for 5 s and then finally unloaded at 100 N/s. 3 Results 3.1 Structure Figure 2 shows theXRDpatterns for ZrO2 films deposited at differentO2 flowrates.At 10 sccm, a broad but symmetric peak centered at around 32.4 is observed in curve (a), indicative of an amorphous structure. The peak is believed to come from an oxygen-deficient Zr-O solid 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 10 頁共 13頁 solution 40. Wong et al. 13 also reported a similar phenomenon, where, however, the peak was unsymmetric and sharp. As the O2 flow rate increases to 20 sccm (Fig. 2b) ), one peak at 33.7 assigned to (200) planes of monoclinic phase (denoted as m(200) is predominant, accompanied by the appearance of other weak peaks also from the monoclinic phase. This rapid occurring of diffraction peaks shows that so much oxygen is incorporated that sufficient ZrO2 crystallite forms which can be detected. The easy combination between Zr and O is possibly related to charged and therefore active emitted species, as well as further stimulated by energetic Zr particles bombarding the surface as in IBAD. At 35 sccm, in addition to more weak peaks, them(200) peak becomes weaker while the m(-202) peak gets stronger. When the O2 flow rate goes up to 50 sccm, the dominant peak is changed to m(-111) while many more monoclinic peaks are produced. 3.2 Chemical compositions and chemical states It 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 185.9 and 533.2 eV are identified as Zr 3d and O1s, respectively. Fig. 4 presents the normalized Zr 3d (a) and O1s (b) XPS local spectra for the film prepared at 50 sccm. The spectra closely resemble those observed in standard monoclinic ZrO2 42. Two peaks, Zr 3d5/2 and Zr 3d3/2 observed at binding energies of 181.8 and 184.2 eV, 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 intensity ratio (I3d5/2/I3d3/2) and energy interval (3d5/23d3/2) resulting from spin-orbit splitting are 1.5 and 2.4 eV, in agreement with other studies 20, 42. An asymmetric O1s peak can be decomposed into two components peaked at a low binding energy (LBE) of 529.6 eV and high binding energy (HBE) of 531.6 eV, quite comparable with reported ones 14, 43. It has been accepted that the LBE peak is assigned to the oxygen in zirconia 14, 20, 43 while the HBE is attributed to oxygen present in the hydroxide and/or 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 11 頁共 13頁 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., 35 sccm, the Zr 3d spectrum is somehow different whereas the O1s spectrum is very similar. A shoulder of the Zr 3d5/2 clearly 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 increasing flow rate, Zrn+ (n 3) will convert into Zr4+ due to a full reaction between 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 for O1s and Zr 3d). For the calculation, theO1s HBE peak is not included due to its small fraction. As expected, theO/Zr ratio increases with more addition of oxygen (not shown). Note that for the film deposited at 50 sccm, the O/Zr ratio obtained is approximately 1.98 : 1, near to the ideal stoichiometric ratio of 2 : 1. At 65 sccm and above, the films are over-stoichiometric ( 2.2 : 1). 3.3 Surface morphology Figure 5a presents a typical top-view AFM image of the film at 65 sccm. 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 than 0.1 nmover the area of 1 m 1 m. 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 and offers 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 O2 flow rate as well. At 10 sccm, the clusters distributed on the film surface are similar in size to that for the film at 65 sccm. However, in the range of 20 to 50 sccm, larger clusters are present on the surface. This change in cluster size is also reflected in the curve of roughness versus the O2 flow 中北大學 2005 屆本科畢業(yè)設(shè)計說明書 第 12 頁共 13頁 rate (Fig. 5b) the O2 flow rate (Fig. 5b), where the roughness is larger for a 2050 sccm flow rate range. The flow rate-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 a 2050 sccm flowexhibit larger clusters on the surface and look relatively rougher. 3.4Mechanical properties The 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