What is Reactive Sputtering Coating Technology?

At present, reactive sputtering deposition is a well-established sputter coating technology and is widely used for industrial coating deposition to produce thin layers for high-added value products, such as flat panel displays, solar cells, optical components, and decorative finishes.

Definition

In the process of reactive sputtering, a target material is sputtered in the presence of a gas or a mixture of gasses that will react with the target material to prepare a compound film of a predetermined chemical ratio. Reactive sputtering is most often practiced using one or more magnetron sputtering cathodes. Therefore, it is also called reactive magnetron sputtering.

Sputtering Target

Sputtering targets can be divided into metal targets, alloy targets, ceramic targets, etc. Metal sputtering targets can be used to produce compound materials. For example, a titanium sputtering target can be used to produce coatings such as TiO2, TiN, and Ti-O-N. Apart from it, titanium targets can also be used to produce any of the aforementioned different compositions as well as boride and carbide films. Compared with the compound target, the metal target has the advantage of longer service life.

Reactive gases

In most cases, Argon is the main gas used in reactive sputtering as well as other sputter coating methods. It has to be mentioned that the amount of a reactive gas introduced into a process chamber should be strictly controlled in order to either achieve a certain amount of doping or to produce a fully reacted compound. Here is a list of other gasses used in reactive sputtering).

Gasses Uses
Oxygen (O2) deposition of oxide films (e.g. Al2O3, SiO2, TiO2, HfO2, ZrO2, Nb2O5, AZO, ITO)
Nitrogen (N2) deposition of nitride films (e.g. TiN, ZrN, CrN, AlN, Si3N4, AlCrN, TiAlN)
Carbon dioxide (CO2) deposition of oxide coatings
Acetylene (C2H2) deposition of metal-DLC, hydrogenated carbide, carbo-nitride films
Methane (CH4) similar applications as for C2H2

Several reactive gasses can be mixed in order to deposit a multi-component functional thin film. Additional reactive gas is sometimes used to enhance a certain deposition process (e.g. addition of N2 in the SiO2 reactive sputtering process).

Application

Coatings and films produced by Reactive Magnetron Sputtering can be used in a large variety of products such as OLED devices, optical antireflective coatings, and decorative coatings.

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What Will Affect The Magnetron Sputtering Voltage?

Magnetic field

Magnetic field influences inversely the sputtering voltage. In other words, when the magnetic field on the surface of the sputtering target increases, the operating voltage of magnetron sputtering will decrease. It happens because the sputter-etched surface of the target gets closer to the strong magnetic field of the permanent magnet behind the target. To be noted, when the magnetic field strength increases above 0.1T, its effect on the sputtering voltage is no longer obvious.

In order to reduce the influence of this factor, the thickness of the sputtered material is not arbitrary, but limited. In general, thicker non-magnetic targets can be used in stronger magnetic fields.

magnetron sputtering11-9-2

Material Type

Different target materials also affect the sputtering voltage. Here are examples of ITO, copper, aluminum, titanium, manganese, and chromium target.

Sputtering Target Sputtering Voltage
Indium Tin Oxide (ITO) ≈200V
Copper (Cu)
Aluminum (Al)
Titanium (Ti)
400~600V
Manganese (Mn)
Chromium (Cr)
>700V

Gas Pressure

Working gas pressure

Under the condition that various parameters (such as environmental conditions, power control panel parameters, etc.) remain unchanged, the increase of the working gas pressure will reduce the magnetic sputtering voltage.

Reactive gas pressure

On contrary, under the determined environment and constant power source, the increase of reactive gas pressure will result in the increase of magnetic sputtering voltage.

Distance Between Cathode & Anode

magnetron sputtering11-9

The distance between the cathode and anode in vacuum gas discharge can have a certain effect on the sputtering voltage. If the distance is too large, the internal resistance of the equivalent gas discharge is mainly determined by the plasma equivalent internal resistance. Conversely, if the distance is too small, the internal resistance of the plasma discharge will be small.

When the magnetron target ignited and enters the normal sputtering, if the distance between the cathode and anode is too small, although the sputtering current has reached the process setting value, the target sputtering voltage is still low.

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Magnetrons & Magnets Used in Magnetron Sputtering

The planar magnetron is an exemplary “diode” mode sputtering cathode with the key expansion of a permanent magnet cluster behind the cathode. This magnet exhibit is organized so that the attractive field on the substance of the target is ordinary to the electric field in a shut way and structures a limit “burrow” which traps electrons close to the surface of the target. This enhances the effectiveness of gas ionization and compels the release plasma, permitting higher presence at the lower gas weight and attaining a higher sputter affidavit rate for Physical Vapor Deposition (PVD) coatings.

Although some distinctive magnetron cathode/target shapes have been utilized in magnetron sputtering processes, the most widely recognized target types are circular and rectangular. Circular magnetrons are all the more regularly found in littler scale “confocal” cluster frameworks or single wafer stations in group instruments. Rectangular Magnetrons are frequently found in bigger scale “in line” frameworks where substrates examine straightly past the focus on some type of carpet lift or transporter.

Color-online-Upper-Illustrations-of-circular-and-rectangular-planar-magnetron
Color-online-Upper-Illustrations-of-circular-and-rectangular-planar-magnetron. Greene, J.. (2017). Review Article: Tracing the recorded history of thin-film sputter deposition: From the 1800s to 2017. Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. 35. 05C204. 10.1116/1.4998940.

Most cathodes – including practically all circular and rectangular ones – have a straightforward concentric magnet design with the middle being one shaft and the edge the inverse. For the circular magnetron, this would be a generally little adjusted magnet in the middle, and an annular ring magnet of the inverse extremity around the outside with a hole in the middle. For the rectangular magnetron, the core one is typically a bar down the long hub (however short of the full length) with a rectangular “wall” of the inverse extremity and the distance around it with a hole in the middle. The crevice is the place the plasma will be, a roundabout ring in the circular magnetron or a lengthened “race track” in the rectangular.

The magnetron works with either an attractive arrangement – the middle could be north and the border might be south, or the other way around. Notwithstanding, in most sputter frameworks, there are various cathodes in reasonably close vicinity to one another, and you don’t need stray north/ south fields structured in the middle of the targets.

Those N/S fields ought to just be on the targets’ confronts, structuring the coveted attractive shafts there. Hence, it is completely attractive to verify all the cathodes in one framework are adjusted the same way, either all north on their borders or all south on their edges. What’s more, for offices with numerous sputter frameworks, it is similarly alluring to make all of them the same so cathodes can securely be traded between the frameworks without agonizing over magnet arrangement.

There are extra contemplations and choices in regard to the magnets. Most target materials are nonmagnetic and in this manner don’t meddle with the obliged attractive field quality. However, in the event that you are sputtering attractive materials, for example, iron or nickel, you will require either higher quality magnets, more slender targets, or both with a specific end goal to abstain from having the surface attractive field adequately shorted out by the attractive target material.

Past that, the magnet’s subtle elements, for example, attractive quality and crevice measurements, might be intended to enhance target material usage or to enhance consistency along the vital pivot of a rectangular target. It is even conceivable to utilize electromagnets rather than perpetual magnets, which can manage the cost of some level of programmable control of the attractive field, yet does, obviously, build many-sided quality and expense.

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Metal Molybdenum Target Used in Mobile Phone LCD Screen

Nowadays, mobile phones have become the most indispensable thing for the masses. Mobile phone displays are also becoming more and more high-end, such as full-screen designs, small bang designs, and so on.

One of the most important steps in making a mobile phone LCD screen is thin film coating, using magnetron sputtering to sputter the molybdenum target onto the liquid crystal glass to form a Mo thin film. Molybdenum thin films have the advantages of high melting point, high electrical conductivity, low specific impedance, good corrosion resistance and good environmental performance. Compared with the chromium film, the specific impedance and film stress of the molybdenum film are only half of that.

As an advanced film material preparation technology, sputtering has two characteristics of “high speed” and “low temperature”. It concentrates ions into a high-speed ion stream in a vacuum to bombard a solid surface. The kinetic energy exchange between the ions and the atoms on the solid surface causes the atoms on the solid surface to leave the target and deposit on the surface of the substrate to form a nano (or micro) film. The bombarded solid is a material for depositing a thin film by sputtering, which is called a sputtering target.

mobile phone lcd screen

In the electronics industry, molybdenum sputtering targets are mainly used for flat panel displays, electrodes and wiring materials for thin film solar cells, and barrier materials for semiconductors. These are based on its high melting point, high electrical conductivity, low specific impedance, good corrosion resistance, and good environmental performance.

Molybdenum used in components of LCDs can greatly improve the brightness, contrast, color, and life of the LCD. One of the major applications for molybdenum sputtering targets in the flat panel display industry is in the TFT-LCD field.

In addition to the flat panel display industry, with the development of the new energy industry, the application of molybdenum sputtering targets on thin film solar photovoltaic cells is also increasing. The molybdenum sputtering target mainly forms a CIGS (Copper Indium Gallium Selenide) thin-film battery electrode layer by sputtering. Among them, molybdenum is at the bottom of the solar cell, and as a back contact of the solar cell. It plays an important role in the nucleation, growth, and morphology of the CIGS thin film crystal.

For more information, please visit https://www.samaterials.com/.

Solar Thin Film and Its Technical Advantages

Thin-film solar cells refer to thin films with thicknesses ranging from a few nanometers to tens of microns attached to the solar surface, which make thin-film cells lighter in weight. Thin-film solar cells are used in building-integrated photovoltaics as translucent photovoltaic glass materials that can be laminated to windows.

As a second-generation solar technology, thin-film technology is more affordable than the traditional first-generation c-Si technology, but is less efficient. Therefore, in recent years, people have also paid more attention to the development of sputtering materials and thin film coating technology, and are committed to improving the efficiency of thin film technology. And now it has improved significantly. Laboratory cell efficiencies for CdTe and CIGS are now over 21%, better than polysilicon, the main material currently used in most solar photovoltaic systems. And the life expectancy of thin-film solar cells is also extended to 20 years or more.

Thin film solar cells are made by depositing one or more thin layers or thin films of photovoltaic materials on a substrate such as glass, plastic or metal. In the deposition process, the coating source material used are usually sputtering targets or evaporation materials. Commonly used thin-film solar cell categories include cadmium telluride (CdTe) thin films, copper indium gallium selenide (CIGS) thin films, and gallium arsenide (GaTe) thin films.

The target materials corresponding to the three thin films mentioned above are important materials for the thin film coating of solar cells. Among them, cadmium telluride targets account for 50% of the solar market. On a life cycle basis, CdTe PV has the smallest carbon footprint, lowest water usage, and shortest energy payback time of all solar technologies. With an energy payback period of less than a year, CdTe can reduce carbon emissions faster without short-term energy shortages.

The CIGS sputtering target is composed of four metal elements, namely copper (Cu), indium (In), gallium (Ga) and selenium (Se), and it is also one of the representatives of commonly used targets in the solar industry. CIGS thin film has the advantages of strong light absorption, good power generation stability and high conversion efficiency, which can enable solar cells to generate electricity for a long time during the day and generate a large amount of electricity. CIGS has great advantages in photovoltaic building-integrated applications. At the same time, with the improvement of CIGS conversion efficiency, the self-sufficiency rate of CIGS as a photovoltaic building power supply built with glass curtain walls is also increasing.

GaAs thin-film solar cells have an efficiency of up to 28.8%, which is considered the highest efficiency of all thin films. Gallium arsenide is also resistant to damage from moisture, radiation and UV light. These properties make GaAs thin films an excellent choice for aerospace applications with increased UV and radiation.

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Classification of Molybdenum Target Materials

Molybdenum sputtering targets perform the same as their source material (pure molybdenum or molybdenum alloy). Molybdenum is a metallic element mainly used in steel, where it improves the strength, hardness, weldability and toughness of alloys, as well as high temperature and corrosion resistance. Molybdenum targets are one of the important sputtering materials and are used in aerospace, semiconductor, solar and many other applications.

Different Shapes of Sputtering Target
Different Shapes of Sputtering Target

Classify by Shape of Molybdenum Target

According to the shape of the target, the molybdenum target can be divided into square molybdenum target, circular molybdenum target, molybdenum plate target, rotatory molybdenum target, and molybdenum tube target.

The square molybdenum target has the characteristics of high melting point, high electrical conductivity, low impedance, good corrosion resistance and good environmental performance. It is the most widely used planar molybdenum target.

The circular molybdenum target, or the disc molybdenum target, also has a wide range of applications, which can form films on various types of substrates, and these films can be widely used in electronic components and electronic products.

Molybdenum plate target common thickness is 0.09 inch ~ 3 inch and the surface shows silver-gray metallic luster. Common Specifications (mm) is BCM = 9.9 (0.3-10) (60-400) 800 or bigger.

The rotatory molybdenum target is a rotatable sputtering target that is usually cylindrical and has a fixed magnet so that it will rotate at a low speed during operation.

The length of the molybdenum tube target is generally ≤3000mmm, and the outer diameter is ≤250mm. The wall thickness is 3-25 mm and the flatness is 0.1 mm. In addition, its shape is tubular and the surface shows a silver metallic luster.

Classify by Applications of Molybdenum Target

According to its application, the molybdenum target can be divided into the X-ray molybdenum target, the coated molybdenum target, and etc. Stanford Advanced Materials offers a wide range of high performance, high quality molybdenum targets.

Coated molybdenum target has good properties, including excellent high temperature performance, high temperature physical strength, high elastic modulus, excellent thermal conductivity and corrosion resistance and other properties, so commonly used in the field of coatings, as coating materials.

X-ray molybdenum targets are commonly used in the medical field for breast examination of women. X-ray mammography as a non-invasive method can more fully and accurately reflect the structure of the entire breast.

If you have any interest in molybdenum metal targets, please visit our website at https://www.sputtertargets.net/.

Study on Preparation Methods of Magnesium Film Materials

Thin-film is a rapidly developing material in the field of modern material science and technology, and there are many methods for its preparation. This article introduces several methods for preparing thin films, focusing on magnetron sputtering and ion beam sputtering deposition, and using magnesium sputtering targets as raw materials to prepare magnesium thin films.

Magnesium is in a diagonal position with lithium in the periodic table of the elements, has similar chemical properties to lithium, and has some electrochemical properties better than lithium, which can meet the needs of power batteries. Magnesium batteries have many advantages such as low cost, non-toxicity, no pollution, stable discharge voltage, high specific energy, high specific power, rich resources, and renewable. However, magnesium batteries have not been widely used. One of the main reasons is that magnesium is severely polarized and corroded in the electrolyte, making it unable to meet the applicable standards and difficult to meet the actual requirements. Research on magnesium thin-film materials can help improve this defect of magnesium batteries.

Principle of magnetron sputtering coating

Sputter deposition is the process whereby particles of sputtering materials are sputtered out and deposited on a substrate to form a film. Since ions are charged particles, we can add magnetic fields to control their speed and behavior. And that’s how its name “magnetron sputtering” comes from.

Under the action of an electric field of several hundred to several thousand electron volts, the plasma is accelerated and obtained sufficient force to bombard the cathode, causing the atoms of the solid sputtering target to be ejected in a typical line-of-sight cosine distribution. These atoms will condense on the surface of the substrate to form a thin film.

Ion beam sputtering coating

Ion beam sputtering (IBS), or ion beam deposition (IBD), is a thin film deposition technology that uses an ion source to deposit a sputtering target onto a substrate to produce the highest quality films with excellent precision. Compared to other PVD technologies, ion beam sputtering is more accurate and can accurately control the thickness of the substrate. As shown below, an IBS system usually includes the ion source, the target material, and the substrate. The ion beam, usually generated by the ion gun, is focused on the sputtering target, and the sputtered target material finally deposits onto the substrate to create a film.

Preparation of magnesium film material

In the preparation of magnesium-thin films, magnetron sputtering is a very good choice. This method has the advantages of high speed, low temperature and low damage. The deposited layer is uniform, dense, has small pinholes, high purity, and has strong adhesion. These advantages are the key to the quality of magnesium films. The selected targets are high-purity powder-pressed magnesium sputtering targets and magnesium alloy sputter targets.

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Seven Sputtering Targets and Their applications

Tantalum is used as a barrier layer on silicon wafers for semiconductor production, and tantalum is used in all modern electronic products. Mobile phones, DVD and Blu-ray players, laptops, etc. Car electronics and even game consoles contain tantalum.

Niobium is commonly used in electronic products and its properties are similar to tantalum. Niobium has corrosion resistance due to its oxide film and is considered a superconductor.

Titanium has the characteristics of light weight and corrosion resistance, and can be used in various conventional products including watches, notebook computers and bicycles. Titanium is commonly used for wear resistance and aesthetic design, but can also be used for semiconductor and optical coatings.

Read more: Everything You Need to Know About Titanium Sputtering Target

Tungsten film is a decorative coating, due to its thermal, physical and mechanical properties (such as high melting point
And thermal conductivity) and widely used.

Molybdenum has a lower density and a consistent price, and can be used to replace tungsten. It is usually used to coat solar panel cells.

black and white solar panels

It is often used as an insulator for semiconductors, as well as surface hardness and protective layer. As an element with a high dielectric constant, it can improve the performance of certain electronic devices.

This target material is most commonly used in the production of silicon solar cells.

Preparation of Molybdenum Sputtering Targets by Powder Metallurgy

Molybdenum film has many advantages such as good electrical conductivity and thermal stability, chemical resistance, and low thermal expansion coefficient. It has been widely used in solar power generation, computer circuits, flat panel displays, storage media, and other aspects.

The magnetron sputtering technology has many advantages such as densely rented thin films, low surface roughness, good film-base bonding force, high deposition rate, low substrate temperature, and convenient deposition of thin films with high melting points. It is currently the main method for preparing molybdenum films using molybdenum sputtering targets.

Previous studies have shown that the choice of different magnetron sputtering equipment and process parameters (target current, target power, gas pressure, sputtering time, etc.) should also have a close relationship with the differences in the structure and performance of the sputtered thin films.

molybdenum target powder metallurgy

The electronic display industry’s technical requirements for sputtering targets mainly include indicators such as chemical purity, density, grain size and size distribution, grain orientation and orientation distribution. Recent studies have shown that the smaller the grain size of the target, the higher the sputtering rate; the more uniform the grain size distribution of the target, the easier it is to obtain a sputtered film with uniform thickness.

Since molybdenum is a high melting point (2620 ° C) metal. Powder metallurgy is the main method for preparing molybdenum targets. The process mainly includes the steps of milling, pressing, and sintering.

The powder metallurgy method is a technical method in which metal powders, alloy powders or mixed powders of metals and non-metals are directly made into various products through pressing, sintering and other processes. The main feature of this method is that it can produce special material products that are difficult to achieve or cannot be manufactured by conventional metallurgical methods or material processing methods, such as parts of machines made of refractory tungsten and molybdenum metals.

The main features of powder metallurgy are: the raw materials can be directly manufactured into qualified products according to the shape and size requirements of parts and components without mechanical cutting or slight cutting; suitable for mass production and high efficiency; Less waste during production and high utilization of raw materials. This method has been widely used in the automotive industry, energy industry, chemical industry, national defense industry, and aviation and aerospace industries.

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Advantages of Sputtering Deposition and Vacuum Evaporation

For all devices, there is a need to go from semiconductor to metal. Thus we need a means to deposit metals, also called film coating. There are currently several methods for depositing metal thin film layers, and many of these techniques for metal deposition can also be used to deposit other materials.

1.) Physical Vapor Deposition (PVD)

2.) Electrochemical techniques

3.) Chemical Vapor Deposition (CVD)

This passage will talk about the advantages of two PVD methods: Sputtering and evaporation.

Sputtering Deposition

magnetron-sputtering-system
Magnetron Sputtering System

The plasma under high pressure is used to “sputter” metal atoms out of the “target”. These high-energy atoms are deposited on a wafer near the sputtering target material. Higher pressures result in better step coverage due to more random angular delivery. The excess energy of the ions also helps increase surface mobility (the movement of atoms on the surface).

Advantages: Better step coverage, less radiation damage than E-beam evaporation, easier to deposit alloys.

Disadvantages: Some plasma damage including implanted argon. Good for ohmics, not Schottky diodes.

Vacuum Evaporation

Evaporation (PVD)
Evaporation (PVD)

Evaporation is based on the concept that there exists a finite “vapor pressure” above any material. The material either sublimes (direct solid to vapor transition) or evaporates (liquid to vapor transition).

Advantages: Highest purity (Good for Schottky contacts) due to low pressures.

Disadvantages: Poor step coverage, forming alloys can be difficult, lower throughput due to low vacuum.

PVD Film Morphology

The three zone model of film deposition as proposed by Movchan and Demchishin
The three zone model of film deposition as proposed by Movchan and Demchishin

1.) Porous and/or Amorphous —> Results from poor surface mobility =low temperature, low ion energy (low RF power/DC bias or higher pressures=less acceleration between collisions).

2.) “T-zone”: Small grain polycrystalline, dense, smooth and high reflectance (the sweet spot for most metal processes) Results from higher surface mobility =higher temperature or ion energy

3.) Further increases in surface mobility result in columnar grains that have rough surfaces. These rough surfaces lead to poor coverage in later steps.

4.) Still further increases in surface mobility result in large (non-columnar) grains. These grains can be good for diffusion barriers (less grain boundary diffusion due to fewer grains) but pose problems for lithography due to light scatter off of large grains, and tend to be more rigid leading to more failures in electrical lines.

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