Thermal evaporation
Webs are designed for capacitor and packaging applications where the vast majority have resistively heated metal boats as the coating source. Small vessels are connected in series to allow coating of wide nets (up to 2500 mm wide), and aluminum is supplied to the vessel feeder wire.
This technique is limited to the evaporation of relatively low-melting metals such as aluminum and zinc. The main advantage of this coating method is that high speeds of 8 to 10 m/s can be achieved. Due to the action of the ship array, the uniformity of the coating thickness is (slightly) wavy.
electron beam evaporation
This technique typically employs thermal electron generation where individual electron beams are accelerated to a potential of 5 to 10 volts to achieve magnetic deflection and then focused onto a target spaced apart from elements located symmetrically in front of the substrate in a water-cooled holder. Process parameters, especially accurate film stoichiometry and abrupt interfaces, are difficult to control because direct templates of individual beams near each source are difficult without interfering with the focused electron beam, thereby extinguishing the evaporation of the target material. Evaporation of elemental materials from different spatial locations involves complex hardware, often producing inhomogeneous thin films on large-area substrates.
Reliable high-power electron beam guns have opened up new potential markets for web coatings. The electron beam gun can be programmed to scan a number of spots in a large crucible containing the material to be deposited. The maximum scan width is about 1 meter, therefore, for wide web coating several parallel electron beams (usually two) are required.
Electron beam technology is probably the fastest deposition source today, reaching network speeds of over 12 m/s. In theory, this is also an economic process. However, while it has the potential to replace resistance and induction heating in the aluminum alloy market, very few of these machines are in use. Considerable investment costs, compared with conventional machines, and high technical complexity, combined with some conservatism when spraying, it is a big step.
This coating source can handle most pure metals, including those with higher melting points. As long as the vapor pressure is not too far away, for example chromium and nickel, can also vaporize, such as several oxides, nitrides, and occasionally decompose these compounds.
Applications today include magnetic storage media, clear coatings, and ultra-high speed aluminizing.
plasma sputter deposition
Sputtering involves the bombardment of a solid target of material, extracting ions from a dense cloud very close to the target surface. High energy atoms are drawn from the target surface and towards the substrate.
Sputtering is a versatile coating selection technique. It can be used on all pure metals and alloys, and even more complex materials. In addition, most oxides and nitrides can be precisely deposited.
Virtually all thin film deposition techniques utilize the effective sputtering area. It is also technically more practical to sputter surface energies in the less than 1000 eV range. This reduces complexity in power leads and insulation, as well as reduces high voltage safety risks.
Physical sputtering of energetic neutral particles is effective with sputtering ions. Since sputtering is an efficient momentum and energy transfer process, the electrical state (charge) on the incident particles is mostly irrelevant. In reality, ions are usually neutralized as they approach the surface (a few angstroms) and hit the surface as neutral. Therefore, the sputtering rates of ions and neutral ions are indistinguishable. However, the experiments used to measure the sputtering yield do not have a reliable way to measure the incident neutral flux. Therefore, this topic has been practically ignored, although in some cases it can lead to significant underestimations of sputtering or deposition rates. The energy spectrum atoms produced during sputtering are significantly different from evaporated atoms. Sputtered atoms have higher kinetic energy than evaporated atoms. As an example, a sputtered Cu atom has an average kinetic energy of 8 eV, while evaporated atoms are typically less than 1 eV. This energy difference leads to differences in film properties, especially density, microstructure and adhesion.
Coatings achieved with this technique generally exhibit excellent adhesion and a dense crystalline structure due to the inherently high particle energy. A uniform coating (approximately 2%) can be deposited over a width of more than 2.5 meters.
Despite these advantages, the process is still much slower than evaporation. In recent years, however, significant progress has been made in terms of speed. The computer-aided design of the magnet array structure is used to optimize the target utilization rate of more than 50%, and the standard planar magnetron structure is improved, and the medium target efficiency is about 25%. All these developments lead to sputtering machines with a maximum speed of 600 m/s.
Plasmas provide an in situ source of "activated" gases and energetic ionic species that can be used to enhance various physical and chemical processes that affect the growth and properties of deposited films. One motivating factor for the use of plasma activation processes is the low temperature requirements encountered in various applications. Plasma-assisted processes offer the possibility of deposition at lower substrate temperatures. The main role of plasmas in various plasma-assisted processes is related to activation and enhancement of the reactions required to deposit composite films, as well as changes in growth kinetics and modification of deposit structure and morphology.
Due to the above considerations, plasmas are used in various physical and chemical vapor deposition processes.
The commonly used techniques of plasma-assisted PVD are: (1) sputtering including DC, RF, triode, magnetron structure and reactive sputtering of DC, RF, triode or magnetron source; (2) activation reaction evaporation.
The presence of plasma in the source-substrate space significantly affects the processes that occur at each step in the film deposition process, including species generation, transport from source to substrate, and film growth on the substrate.
Furthermore, the effect of plasma on the above three steps varies significantly between different processes. This difference manifests itself in the type and concentration of metastable species, ionized species, and energetic neutral species, which in turn affect the reaction pathways or steps in the reaction process and the physical location and physical location of these reaction sites. In addition, it should be noted that in the range of 50-60 eV, the ionization probability of electrons is the largest and decreases with the increase of energy. Therefore, it is advantageous to favor low-energy electrons to ionize gas and vapor species.
1. Diode plasma
A DC diode plasma setup is a simple form of plasma used for sputtering and sputter deposition. The system consists of cathode, anode, DC power supply and housing. The correlation between gas density, electrode spacing, and applied voltage for gas breakdown to generate plasma is required by the Paschen curve. 17 Only a small fraction (about 0.01%) of the gas atoms are ionized - most are neutral. The electrons in the plasma are relatively hot, with Maxwell energy distribution and equivalent thermal temperature 10000 K to 50000 K. The electron temperature is usually related to the energy unit (EV), and 1 EV is about 11600 K.
Because the plasma is conductive, the plasma itself has almost no potential gradient. All electric fields occur at the edge of the plasma in a region called the sheath. Due to the large ratio of neutral gas atoms to ions, ions and gas atoms (by collision) are in a state of thermal equilibrium, and the temperature is only in the range of 100-1000°C. Due to the high temperature and low mass of electrons, electrons are around the plasma Move quickly. This last effect leads to the appearance of several different potentials in the system.
The plasma potential is the apparent voltage on the plasma away from the sheath. Floating potential is the potential attained by an electrically insulating object immersed in a plasma. It is also the potential (conducting or not) on any surface under equal flux of ions and electrons arriving. The floating potential is always negative of the plasma potential, typically 3 times the electron temperature.
For objects that are electrically floating in the plasma, the energy is typically less than 20 eV, resulting in little sputtering. For a surface like a cathode, the ion energy is equal to the difference between the plasma potential (a few volts more than the anode voltage) and the cathode voltage. These energies can reach hundreds of eV and cause significant sputtering of the cathode surface. Thus, a sample surrounded by a thin film of sputtered atoms can be located on the surface of the anode, or almost anywhere in the chamber.
DC diode plasmas are characterized by low etch and deposition rates. The reason for the low rate is that the plasma density is low and is rather small due to the electron impact ionization intersection point. Therefore, in order to obtain higher plasma densities and hence, high ion bombardment rates, the gas pressure needs to be increased to a pressure close to 133 Pa. Also, the voltage required for medium currents is quite high, several thousand volts. The resulting sputtered atoms are rapidly dispersed by the background gas, and the net deposition rate on the sample surface is rather low.

DC diode sputtering is also limited by the requirement that the electrodes need to be metallic conductors. If one of the electrodes is insulated, it will charge quickly and hold back additional current. This effect can occur when a reactive gas, such as oxygen or nitrogen, is introduced into the plasma, causing oxidation of the electrodes on the metal surface. Therefore, DC diode sputtering is not a suitable technique for the deposition of most compounds and dielectrics.
These problems can be overcome by operating the plasma diode with an AC potential instead of DC (Figure 32.1). At a commonly used frequency of 13.6 MHz, there is almost no voltage drop across the insulating electrodes or layers. The electrodes will not be charged, therefore, it is possible to sputter media or react to sputter metals. There is an additional degree of ionization with RF powered plasma due to the additional energy delivered to the plasma electrons in the oscillating sheath. The net result is a higher plasma density and the ability to operate at lower system pressures (0.5 to 120 MPa) than DC powered plasmas.
The cathode of a typical RF diode system is usually powered through an impedance matching device called a matchbox. The function of the matchbox is to flow as much power as possible from the RF generator, which has an output impedance of 50 ohms, to the plasma, which has complex impedances generally in the range of 1000 ohms. A series capacitor is included in the matchbox to allow the formation of a DC bias at the cathode. This is a result of higher electron mobility and negative DC potential at up to half the RF peak voltage to half the powered electrodes. The ions in the plasma accelerated to the cathode were too large to respond to the 13.6 MHz magnetic field, only to a DC bias.
射频二极管溅射常见的应用是沉积介质膜。通常,样品表面稍微偏在沉积过程中提供某种程度的离子轰击导致变化的电影和一些程度重复飞溅导致增加平面密度和微观结构。
2、磁增强等离子体
在磁场中的电子受到的劳伦斯力,这在均匀磁场垂直于电子运动产生的电子在一个半径的圆形轨迹移动,称为拉莫尔半径。在磁场方向,没有净磁力,所以电子是无约束的。最终的结果是电子在螺旋路径上倾向于沿着磁场衬垫螺旋。通过限制电子对这一运动,电子的有效路径长度显著增加,因此电离电子-原子碰撞的概率增大。对于给定的外加功率,磁场的作用是降低等离子体阻抗,从而在较低的电压下产生更高的放电电流。密度的增加也使得背景压力显著降低,使得磁增强等离子体可以在10到2 Pa范围内的压力下工作。

磁控管是磁增强等离子体的常见形式。在该装置中,磁场被配置为与阴极表面平行。有一个电子的漂移,通过电场和磁场的交叉产品引起的(称为e-cross–b-drift)倾向于靠近阴极表面电子陷阱。漂移运动是定向的,在磁控管中,它被配置为关闭自身。一个常见的例子如图32.2所示,它是圆形几何体,称为圆形平面磁控管。在这种情况下,磁场被配置为径向磁极和周长或环形磁极。
磁控装置,它被定义为具有闭环E×B漂移路径的次级电子,已在多个几何发展。18也许常见的替代方法是使用矩形配置,称为“赛道”磁控管(图32.3)。这种几何形状在零件的自动化处理方面有一些固有的优点。


磁控管等离子体有一个独特的特点,即二次电子强烈地限制在阴极表面附近的区域。这会导致稠密等离子体在漂移环区域的阴极附近形成。稠密的等离子体导致阴极表面的离子轰击非常高,因此溅射率很高。率高的离子轰击阴极直接定位在E×B路径下。由此产生的溅射原子也被局限,这意味着沉积均匀性通常不好。因此,对于大多数沉积系统,需要移动样品或改变磁控管位置以获得良好的沉积均匀性。此外,阴极的侵蚀也本地化,导致阴极材料利用率低下、深槽侵蚀成在电子×B漂移路径的阴极表面附近。宽槽称为“蚀刻径迹”,是磁控溅射的典型特征,只有10到15%的阴极材料可在槽开始蚀刻阴极背面之前使用。
在高压下,由于气体散射和沉积均匀性的增加,溅射原子的分布变得模糊,但溅射原子的动能和薄膜性能的潜在变化确实降低了溅射的成本。对于不均匀性有两种明显的解决方法。第一种方法是以某种方式移动样品,使样品表面的沉积平均化。圆形平面磁控管,这需要一个相当复杂的行星运动。另一种方法是使用传统的旋转样品运动,在阴极和样品之间使用沉积屏蔽,有效地收集了溅射通量。然而,这一过程将整个样品的净沉积速率降低到原始分布的最低水平。
矩形或其它细长管,提高均匀性的解决方案是将样品经过垂直于阴极磁控管“长”的方向。一个例子如图32.4所示,它显示了一端观看的矩形磁控管系统,其中样品从系统一端移动到另一端。这些系统在制造业规模上的规模可能相当大。一个共同的尺寸使用阴极2米长的溅射系统,总长度超过20米。
对于某些工业应用,特别是那些污染是一个关键问题的应用,在沉积过程中移动样品可能不太称心。在这种情况下,磁控管已经开发出来,一个移动的蚀刻径迹。21,随着时间的推移,腐蚀区域相当均匀,在大的固定衬底上沉积薄膜时,可以获得高度的均匀性。通过将磁体组件旋转到阴极面后面的冷却水中来设置移动蚀刻径迹。这种设计的工业阴极直径为25厘米,额定功率为25千瓦。这些磁控管的第二个重要的优势是,阴极的利用是非常有效的:高达80%的阴极材料可用于溅射,相比15%的非旋转磁控。这将导致更好的效率和更长的时间间隔之间的阴极变化。由于这种固有的效率,这种类型的磁控管正在变得越来越普遍,并被用于在各种不同的应用,如硬涂层和辊或网涂层。
3、非平衡磁控溅射沉积
平衡磁控溅射有一个特点。随着磁控靶衬底距离的增加,衬底离子电流急剧下降。它限制了在沉积过程中激活基底的可能性。
在原则上,有两种可能的方法来增加磁控溅射衬底上的离子电流密度,即:(1)额外的气体电离,例如,由热阴极电子束或空心阴极作为源,或(2)等离子体的磁约束,例如不平衡磁控管。
在非平衡磁控管中,常规磁控管故意配置有磁性块或线圈的阵列,在阴极的磁场中增加附加垂直分量。图32.5显示了三种常见配置。第一个配置(图32.5a图32.5b)是基于在磁控阴极极片配置额外的长久磁铁。在第一种情况下,中心极片比周边极片强得多,从而产生一个附加的轴向磁场。在第二种情况下,周长杆变得更坚固,从而产生一个额外的圆柱形部件。在第三种情况下(图32.5c),电磁铁已添加外部磁控管提供一个简单的轴向磁场。
不平衡磁控管是由磁场线不再约束中央和周边的磁控极片之间加入。额外的磁力线离开磁控管的区域并与样品区域相交。电子运动沿着这些磁力线是由E×B诱捕效果阴极附近的约束实际上是由于电子的漂移高强度磁场强度较低的地区加强区域。结果,电子可以从近阴极区泄漏出去。这会产生一个很弱的电位,使离子从阴极区引出到近样品区。正是这些离子可以用来形成增强锡反应所需的样品偏压的基础。
氮化钛在硬装饰涂料中有着广泛的应用。非平衡磁控法已成功应用于生产锡及其相关化合物的生产规模。大量的部分覆盖,或者覆盖不寻常的形状的大型部件,系统往往设置多个磁控管在单室。24一个简单的例子如图32.6所示,其中两个不平衡磁控管已配置,彼此相望,与放置在中间的样品。磁控管可以配置连接或排斥,导致在样品中观察到的偏置电流密度差异显著。
设有不平衡磁控管溅射系统中,高的离子电流密度可以运到基板,这是比磁控电流更大。如果到达衬底的非平衡磁控管的磁场足够强(几米),放电与弱磁场中的磁场有很大的不同。这种放电可以在磁控管和衬底上维持,因此称为双点持续放电。
双站点持续放电溅射系统允许密集的,紧凑的生产,明亮的金色TiN薄膜的显微硬度大于2200公斤毫米–2和良好的附着力(高临界负载高达64 N)甚至在压力高达5 Pa和衬底电压U≈–40 V和在目标范围内基距200 mm。后者与低能电子束或电弧蒸发源离子镀系统的典型距离比较。然而,用于溅射的压力和偏置范围在电子束和电弧技术中并不常见。
反应溅射沉积
反应溅射广泛用于合成化合物涂层。溅射金属会从一个单纯的目标,和足够的反应气体的过程中加入了在基板上形成所需的复合(图32.7)。反应溅射通常是在空气泄漏或高背景水压的情况下溅射的不希望发生的工件。在每一种情况下,通过加入气体种类将薄膜从期望的纯度改变。
作为反应气体加入到这个过程中,气体原子沉积薄膜的原子结合形成不同的化学计量化合物薄膜。此时,即使在腔室中加入额外的气体,腔室压力也不会升高,因为所有的气体原子都被薄膜吸收了。随着反应气体流量的增加,薄膜的反应越来越大,最终,在足够高的反应气体流量下,薄膜达到了“最终”反应状态。这通常是一个稳定的或“终端”的化合物。一旦达到这一点,额外的反应气体原子就不能被沉积膜吸收。现在,任何附加的反应气体流动都会在阴极表面形成反应的复合膜。这种化合物几乎总是低于纯金属阴极的溅射率,这导致阴极溅射金属原子速率的降低。降低金属沉积速率降低了薄膜吸收反应气体的速率,进一步增加了反应物的残留背景。这,反过来,在阴极表面产生额外的反应,这进一步减少了金属溅射率。实际上,阴极经历了从金属到复合态的转变,沉积过程急剧减慢。这在图32.8中可以看出,其沉积率绘制的增加反应气体流量的功能(图32.8a),和腔室的压力是绘制在图32.8b。
通过提高泵的抽速,可以减小滞后效应的严重程度,使泵排出的气体量大大超过化学耗量。这样,当目标从金属转变为复合模式时,目标的失稳压力波动大大减小。提高泵的转速可以消除磁滞现象,但在增加泵容量和增加耗气量方面成本高昂。增加气体流量有减少污染的容器放气泄漏通过稀释的优势。
通过对反应气体的分压控制,尽管有滞后效应,但仍有可能产生所有的材料组分。如果反应气体分压保持不变,同时保持溅射靶材的功率不变,则维持反应气体消耗和可用性之间的平衡。分压使气体原子在每一表面上的通量。如果控制分压,则可控制该气体的有效性。如果有一个过程扰动,如目标上的电弧,一个分压控制器将瞬间减少流量,以维持恒定的分压。一旦等离子体(电弧熄灭后重建)和金属被溅射在全速率,流量将再次增加以保持所需的压力。在分压控制中,存在着固有的稳定性。除去物体中的物质几乎是恒定的,除了像电弧这样的扰动,在衬底上,金属原子和气体原子以适当的比例到达,产生化学计量化合物。
分压控制需要一种有选择的方法实时监测过程室中的气体。常用的设备是四极质量分析器,它有能力分离气体的质量比,通常为每个气体提供一个独特的信号。良好的分压控制是当分析仪在足够短的时间内获得足够的信噪比时,在固有的过程不稳定性使部分压力远离平衡之前,流量可以被调节。
形成化学计量化合物,金属原子的到达率需要由合适的所需的反应气体原子在衬底匹配适当的到达率。如果这些到达率不平衡,所得到的胶片将不是所需的组合物。通过控制反应气体在衬底区域的分压,保持气体原子的到达率是可能的,这样当它们与到达的金属原子结合时,就会产生适当的物质相。
应严密控制反应气体的分压,使压力不存在较大的变化。即使是短时间的气赤字会产生丰富的金属组成的几个单层低压力的结果,而短期的过多会导致较低的沉积速率和不希望的相形成的可能。这些非化学计量组成的地区将降低镀层的性能,一般来说,是早期的涂层可能部分失败的原因。
保持恒定的金属到达率并不总是容易的。一个条件良好的金属靶在纯氩气氛中将有一个恒定的金属去除率,如果磁控管溅射靶的功率是恒定的。这种恒定的金属去除率在阴极转化为恒定的输运率,基板和恒定的可用金属通量。
有不同的方法来增加到达原子的能量。简单的方法是在沉积过程中将样品偏压到负电压。偏压使等离子体中的离子加速到样品中,在近表面区域沉积额外的能量。沉积速率对离子轰击尺度的要求。对于高速沉积(高达μm / min左右),所需的偏置电流密度接近2 mA / cm 2。遗憾的是,在上面考虑的传统沉积系统中,很难实现高偏置电流。等离子体被限制在阴极附近,这是阴极高速溅射所需要的,但这导致无法将离子吸引到许多厘米以外的样品区域。
阴极电弧沉积
阴极电弧沉积技术是一种重要的PVD方法,主要用于制备工具、机械零件的硬耐磨涂层。28,29具有许多良好的性能,如形状复杂的基材的高电离和均匀性好的涂料,但它也存在一些缺点。它的主要缺点是颗粒的形成,导致恶化所沉积的涂层的质量。
电弧沉积技术是基于电弧的物理,可以在很大范围的环境气体压力下维持,从真空到数条。According to阴极电弧电子的发射类型,放电定义为加热阴极、热离子阴极、空心阴极、阴极斑点或分布电流。电弧放电的电极暴露于高能粒子的高通量中。因此,电弧放电可用于电极材料的蒸发。
阴极可以在阴极点(带有“冷”阴极的电弧放电)或宽的活性阴极区(分布式电弧)中蒸发。在这种情况下,电弧形成了一种导电介质,通过阴极材料的强烈蒸发来维持放电。
金属阴极上的斑点是不同类型的,取决于时间、阴极材料及其纯度等因素。静止状态(10~100μm直径)的斑点具有自发衰变的倾向,它们在阴极表面上的混沌运动速度约为1~10米/秒,并且它们的灭绝。在小电流(约1至100 A),所有电弧电流集中在一个地方。在较高的电流下,光斑分为两个或更多个斑点。
外加磁场对阴极点电弧放电行为有很大的影响。它增加了放电稳定性,也影响阴极点的方向和速度。磁场可用来定位阴极表面的阴极斑点,控制阴极斑点轨迹的形状。
在阴极斑点的物质蒸发产生的后果大局部阴极表面温度而形成的小熔池由于浓度很高的功率密度(10 10 WCM–2)。蒸发的物质与电子发生碰撞电离,由于不均匀的电势分布和等离子体膨胀而加速离开阴极。稠密等离子体的通量(约10至10 - 14厘米- 3)包含电子,离子,原子和微粒(0.1到100μm),以小滴的形式存在。蒸发材料的流量和各个组分的含量取决于许多参数,如阴极材料及其纯度、阴极表面温度、总电弧电流、工作气体的组成和压力。
粒子的空间分布,这是非常重要的因为它决定了人的涂层大面积衬底上的均匀性,有很大的不同。大颗粒主要是在阴极面发射,离子发射主要垂直于阴极表面,并从阴极高熔点材料发射粒子的空间分布是接近余弦分布。
每个阴极点产生高电离阴极材料的高速射流。等离子体射流中的离子电流分量约占电弧电流的7~12%。离子主要向阴极方向运动,定向运动的速度比混沌热运动的速度大得多。蒸发通量中的高离子含量有时被用来构造有效的大电流金属离子源。离子的能量在1~100电子伏特的范围内。然而,由于气体颗粒碰撞,气体的能量随气体压力的增加而减小。蒸发材料的通量也包含多个带电离子。
大颗粒的产生是阴极斑点的运作的一个组成部分。有几个过程,可能会导致和加速颗粒的形成:焦耳加热伴随着爆炸蒸发;由热应力断裂;驱逐弱粘结材料的局部高电场;排材料的离子和等离子体的压力。
一旦产生,大颗粒被加热、加速,并由他们与阴极斑点等离子体射流接触带负电荷。
而大颗粒夹杂物在大多数微电子和光学应用显然是有害的,他们可以在其他应用程序中是中性的或甚至可能是有益的。大颗粒的产生可以用磁感应的阴极斑点运动减少,降低阴极电流密度,并减少在阴极附近的阴极表面温度的有效冷却,并通过反应气体形成高熔点的表面层上的阴极的存在。大颗粒喷雾可以过滤从血浆流量使用正确的几何位置,衬底偏压,和等离子流磁准直和方向。最后一种方法已经在季度将形成一批人员轮流,和高质量的顺利实施,大颗粒的涂料金属,陶瓷,和类金刚石碳已经产生。
颗粒从等离子体流分离是基于存在显著差异以离子、原子的基本参数,和大颗粒,如速度或荷质比。According to电荷与质量比的分离是基于离子在磁场中运动的控制。和电场,可以在不同的系统中实现。阴极电弧蒸发具有以下重要特征:金属的高电离粒子(高达100%),发射离子动能高(40~100 eV),蒸发效率高。反应气体对蒸发速率的影响很小。
这些特点,加上操作和用户的好处,如简单的蒸发器结构,简单的低压电源装置,蒸发器在任何方向的操作,和高。阴极材料的利用是这种沉积技术的主要优点。衬底可以通过辐射、从基板保持器的热传导、或加速加热。
粒子(电子、气相和金属离子)。阈上能级加速离子溅射(10~25 eV)的能量使生长薄膜的衬底表面溅射。这意味着沉积与生长薄膜的离子轰击同时发生。溅射速率取决于离子能量、离子类型和衬底材料。通常,离子能量由负衬底偏压提供,约为0.2至2千伏。气相和金属离子溅射存在显著差异。
气相离子溅射包括溅射、粒子俘获或注入、混合和粒子扩散(热或辐射增强,例如离子氮化)。金属离子溅射包括金属自溅射、注入、混合和扩散。当溅射率不同时,多组分基板的溅射会出现一些问题。这导致溅射表面的成分、形貌和粗糙度的变化。阴极电弧等离子体沉积系统的示意图如图32.9所示。
沉积膜的性能取决于所有撞击粒子(金属和气相原子和离子)、衬底材料和衬底沉积温度的能量和通量。

高密度的钛膜无微孔可以轰击50 eV的离子在离子中性粒子通量比F I / F n约0.2或更高的过程中产生的。这种方法很容易满足阴极电弧沉积技术的要求,因此适用于高密度薄膜的沉积。反应气体压力(反应气体F的流量)影响阴极表面化合物的形成和薄膜的化学计量,主要取决于f/f r比值,即金属与反应气体流量。
薄膜的均匀性主要取决于不同取向衬底表面金属离子m和离子i的流量的均匀性。在工作气体压力低,当平均自由程大于基体阴极距离(碰撞政权),通量F M和F我强烈不均匀。在工作压力较高的情况下,蒸发原子和离子与气体粒子的碰撞起主导作用(扩散状态),可以提高沉积均匀性。
电弧蒸发已成功用于如氮化物和碳化物硬质涂层的钛、锆沉积,钼和铬、Al 2 O 3薄膜、类金刚石薄膜。电弧蒸发沉积薄膜的性能主要受两个因素的影响:金属粒子的高电离、高能和高通量,以及阴极中粒子的发射。
薄膜的微观结构主要取决于撞击粒子的能量,这首先由负偏压V决定。对于v=0,TiN涂层结构为粗晶和柱状。这是由于低离子轰击和低衬底温度引起的。在v =
- 400 V,部分外延生长已被观察到。TiN涂层的表面结构由大量的凹形凹陷组成,其形成原因尚不完全清楚。凹陷的数量和大小对沉积参数有很强的敏感性,它们的形成可能与撞击离子的通量和穿透深度有关。
薄膜的择优取向也可以通过偏压得到很好的修正。实验表明,在低离子能量下形成了随机取向的TiN薄膜。在中等能量(100至500 eV),薄膜有一个强大的(111)纹理,在高能量(1千电子伏和更高的),(220)方向是显性的。
关于反应沉积过程制备的薄膜的组成,很难确保在大的涂布体积和复杂形状的衬底上保持f/f r比值恒定。
这实际上排除了所有与衬底相同成分的化学计量的电影创作的表面。因此,工业沉积系统通常工作在饱和状态(含大量的反应气体),薄膜几乎是化学计量的。实验表明,在较宽的氮气分压范围内(0.4~6 Pa),TiN薄膜的化学计量比为1~0.06。这可以通过与钛基底表面上由于高活化能的入射离子和优惠resputtering的生长中的膜中的过量的氮提供氮的高反应性的解释。
电弧蒸发制备的硬质涂层具有很高的附着力,能在高速钢上达到10 N的临界载荷。这可能是由于离子刻蚀过程中界面的形成所致。
虽然锡薄膜常用的硬质涂层,其他氮化物和碳化物进行了研究,例如,ZrN 30为钛合金,HfN切割、31和TiCN。32电弧蒸发可用于合金的蒸发,如TiAl、钛锆,和TiHf。33蒸发通量组成阴极合金相同,但膜的组合物可以是不同的由于优惠重复飞溅。
Grain getting into more and more films will be a serious problem. Large particles affect many properties of coatings, such as friction, wear and corrosion resistance, reflectivity, therefore, the number of applications for coatings deposited by cathodic arc deposition techniques, so far, is relatively low.
