Mar. 03, 2026
A voltage is applied between the target material (cathode) and the substrate (anode) to be coated with the target material. Initial electrons from the target's surface cause cascade ionization in the chosen process gas and thus, plasma is formed. Sputtering sources are compatible with vacuum levels from a few mTorr to UHV and come in many shapes and sizes, from small 1" round type R&D cathodes to large planar production cathodes.
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Because the plasma is both electrically neutral and highly conductive, there is little voltage drop across it. The voltage drop occurs across thin "dark space" regions (areas between the plasma and each electrode). The target's negative potential attracts positive ions from the plasma's edge, which in turn hit the target with sufficient kinetic energies to eject neutral target atoms/molecules by energy transfer. While traveling from target to substrate, each ejected atom hits numerous gas atoms/molecules that deflect them and cause energy loss. By optimizing the target-substrate distance, the atoms approach the substrate's surface from partially randomized directions, producing a uniform film thickness across a textured substrate's surface.
For circular sources, the optimum throw distance between target and substrate is larger than the target's diameter to "smooth out" the source's ring-like deposition pattern. By contrast, a linear production source used to coat large area substrates moving across it has a much shorter optimum throw distance.
Similar to other techniques, the chamber pressure is brought to as low a level as possible to prevent background gases from chemically reacting with the film or sputter target. Under carefully controlled partial pressures of reactive gases, reactive sputtering can create films of a different chemical composition than that of the bulk material.
The basic configuration typically includes: a TORUS® sputtering source with a target of the desired coating material; shutters; deposition chimney and/or gas injection; and appropriately sized DC, Pulsed DC, and RF power supplies.
The evaporation temperatures of organic materials are low compared to that of most metals, typically much less than 500°C, and the evaporation rate is exceptionally sensitive to the material's temperature. To achieve satisfactory film deposition demands rigorous temperature control. For this purpose, low temperature evaporation sources designed specifically for depositing organic thin films are frequently used in sequential and co-deposition applications.
Similar to other techniques, the chamber pressure is brought to as low a level as possible to prevent background gases from chemically reacting with the film or bulk evaporant. Under carefully controlled partial pressures of reactive gases, reactive thermal evaporation can create films of a different chemical composition than that of the bulk material.
The use of a glove box to control the ambient atmosphere for loading and unloading organic evaporants is a very useful tool for this technique. Organic compounds are typically volatile and reactive in atmospheric conditions and at room temperature. Glove box integration allows creation of an inert environment to keep and control the evaporant's native properties.
The basic configuration typically includes a point source with accessory feedthroughs, cross-contamination shielding, shutters, and appropriately sized power supplies and PID controllers.
During each pulse step, chemical reactions between precursor molecules and active surface species yield new surface species that passivate the surface. Once the surface becomes fully passivated, reactions are complete and result in the formation of a limited number of new surface species. Uniformity depends primarily on the distribution of active surface species/sites and completion of surface reactions during each precursor pulse step. Subsequently, remaining precursor and/or reaction by-products are purged in preparation for the next pulse step. A complete cycle is required to obtain the desired material. Each cycle deposits a very specific amount of material onto the substrate surface and is repeated until the desired amount of material has been deposited, enabling very accurate control of film thickness.
Thermal-based methods depend on substrate heating where the range of process temperatures resulting in ideal growth is referred to as the "ALD window." Ideal growth is characterized by chemical adsorption of surface species that is irreversible, self-limiting, and complete. Outside of the ALD temperature window growth becomes non-ideal.
Plasma-Enhanced ALD (PEALD) methods utilize reactive plasma species as precursors for ALD surface reactions. Typical plasma gases include O2, N2, and H2. Benefits of PEALD include lower temperature process capability as well as new pathways for chemical reactions that would otherwise be inaccessible by purely thermal methods. Plasma treatments can also be used for substrate surface modification prior to ALD processing.
The basic configuration typically includes a sealed reaction chamber with flow characteristics suitable for entry, exit of reactive precursors, multiple precursor delivery modules, and high-speed valving and software control.
Rather than different techniques, some applications need multiple examples of the same technique. This is particularly true and very common with sputtering, where an array of cathodes and/or effusion cells for organic materials may be mounted in one chamber.
One critical aspect of multiple or combined techniques in one deposition system is cross-contamination. The "plume" of one material must not deposit on (contaminate) the material in another deposition source. This is achieved by careful design of sources, shields, and shutters.
Another important aspect of multi-chamber systems is source orientation geometry. Evaporation sources are mounted with the vapor plume's axis vertically up. This avoids spillage if/when the material is molten at its evaporation temperature. Magnetron sputtering cathodes are not orientation dependent, i.e., they can be mounted at any angle. Two common arrangements for multiple sputter sources are "parallel" and "convergent." Parallel orientation is a common arrangement in large area coaters where a number of substrates are mounted on a rotating platen, and the platen moves to locate a substrate's center over each source's center in turn (this arrangement suits sequential layer deposition). Convergent sources have axes that meet at a point in space that coincides with the substrate surface's center-point, or offset slightly to achieve better uniformity. This arrangement is particularly useful when co-depositing different materials on a single substrate.
Multi-Chamber deposition systems can also be accommodated by combining chambers/modules that house different techniques. This arrangement typically avoids cross-contamination quite well. More complex combinations interconnect UHV chambers for, perhaps, MBE deposition and surface science analysis, or high vacuum chambers for plasma etching, metal deposition, organic deposition, mask storage, ALD, etc., in a cluster arrangement.
Reactive sputtering can be used with a base metal target (e.g., titanium plus oxygen gas) or to control the stoichiometry of the film from a conductive compound/ceramic target (e.g., ITO plus oxygen gas). The reactive gas partial pressure required to form a particular stoichiometric compound on the substrate usually causes the surface of the target to be partially reacted. This produces areas on the target surface with different electrical properties, resulting in varying charge accumulation and arc formation to dissipate the charge difference. These arcs are strong enough to cause local evaporation resulting in the undesirable ejection of macroparticles, unstable process parameters, and possible target damage.
KJLC utilizes our bipolar pulsed DC supply to mitigate arc formation. Instead of applying a constant negative DC voltage to the target, the potential is reversed to a positive voltage (15% of the negative voltage magnitude) for a short duration, many thousands of times a second. This positive pulse draws an electron current from the plasma and neutralizes charge build-up on the target surface, whereas the longer period of applied negative voltage sputters the target.
The duration and frequency of the positive voltage reversal are fully controllable from 1-10µs (1µs resolution) and 2-100 kHz, respectively. The full range of duty cycle allows a user to set the appropriate pulsing parameters to outpace charge build-up creating a stable reactive sputtering process while maximizing the deposition rate.
It is important to note that the DC pulse frequency is high enough to maintain a stable reactive deposition process but is not as high as the 13.56 MHz typically used in Radio Frequency (RF) processes. Pulsed DC provides advantages over RF as it does not require complicated matching networks, offers higher deposition rates, and typically has better arc control.
KJLC has pulsed DC supplies with 1 kW and 2 kW maximum single-output power, which are a good fit for 2" to 4" magnetron sputter cathodes. Figure 1 is our recommended size of power supply for the size of the sputter cathode. Additionally, the power supplies have a suitably large current range for reactive sputtering processes at 2.5 amps and 5 amps, respectively.
Target Diameter Recommended Size of Pulsed DC Supply 2 Inches 1 kW 3 Inches 1 kW 4 Inches 2 kWWhen some target materials are exposed to a reactive gas, their emission of secondary electrons increases, and the voltage required to sustain the target plasma reduces. As the voltage decreases, the current must increase to maintain a fixed power. Furthermore, it is sometimes beneficial to choose pulsing parameters that operate the target at the lowest voltage and highest current. Sputtering at lower voltages is especially useful when working with complex oxides, such as ITO, to reduce high energy neutral bombardment on the growing thin film. The high energy neutral bombardment can be detrimental by causing preferential re-sputtering of the film, driving it non-stoichiometric. As for the voltage output of these supplies, both the 1 kW and 2 kW units can output up to 800 V, which is well suited to ignite and sustain a plasma at standard operating pressures.
Nitrogen gas (N2) is commonly used for making reactively sputtered nitride films, although it is only moderately chemically reactive in its diatomic form. It may be beneficial to increase its reactivity by applying RF bias on the substrate while doing a pulsed DC sputtering process on the sputter cathode. The RF bias creates a plasma to crack the nitrogen into monoatomic form and adds energy to promote the reaction. KJLC has rigorously tested the pulsed DC supplies and verified stable operation while RF bias is applied to the substrate.
Thin film deposition is the process of creating and depositing thin film coatings onto a substrate material. These coatings can be made of many different materials, from metals to oxides to compounds. Thin film coatings also have many different characteristics which are leveraged to alter or improve some element of the substrate performance. For example, some are transparent; some are very durable and scratch-resistant; and some increase or decrease the conductivity of electricity or transmission of signals.
Thin film deposition is an important manufacturing step in the production of many opto-electronic, solid state and medical devices and products, including consumer electronics, semiconductor lasers, fiber lasers, LED displays, optical filters, compound semiconductors, precision optics, microscopy & microanalysis sample slides, and medical implants. There are a few different technologies and methods that can be used to apply thin film coatings, and an array of tools and equipment that can be used to streamline or enhance the thin film deposition process.
There is no one-size-fits-all, perfect thin film deposition system or method. Your technique and configuration of choice depends on the performance and production requirements that are unique to your application.
Physical vapor deposition (PVD) describes a group of thin film deposition techniques that involve vaporizing a solid material in a vacuum, then depositing that material onto a substrate. Coatings created in this manner are highly durable, and resistant to scratching and corrosion. PVD is useful in the production of devices ranging from solar cells to eyeglasses to semiconductors.
The benefits of PVD are numerous, and include the creation of a hard coating that is resistant to corrosion and scratching. PVD also creates thin films that can tolerate high temperatures. Denton’s PVD systems can be integrated with in-situ controls that allow for feedback and stability throughout the process.
Potential drawbacks of PVD include cost, as these methods may require a larger investment than other thin film deposition processes. The cost can also vary among PVD methods themselves. For example, evaporation is a lower-cost type of PVD, while ion beam sputtering is a rather costly option. Magnetron sputtering is more expensive than other methods, but has better scalability.
A variety of techniques fall under the PVD umbrella. For a comparison of these method types, read: Which PVD Method to Use: Magnetron Sputtering v. Evaporation.
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Chemical vapor deposition (CVD) describes a group of thin film deposition techniques in which a substrate is placed into a vacuum chamber, two chemical precursors are heated, which causes them to vaporize. When they meet on the substrate surface, a chemical reaction occurs to form a high-performance thin film coating. CVD is useful in creating coatings for a wide variety of applications including medical devices, automotive components and silicon wafers.
Benefits of CVD methods include the ability to use these processes on a wide variety of substrates, as well as the ability to coat intricate or complex topographies. Thin films created through CVD also typically maintain their bonds well in high-stress environments.
Some drawbacks may include limitations in size, which is dependent on the size of the vacuum chamber, as well as that most methods typically require a higher temperature to drive the chemical reactions. It can also be difficult to mask the surface of the coating.
There are a variety of CVD methods:
In this process, which takes place at normal, or atmospheric, pressure and a lower temperature than other methods, the substrate is exposed to at least one volatile precursor. The precursor(s) react on the surface of the substrate to deposit the thin film. It can be used to deposit doped and undoped oxides, and the deposition is fairly quick. Thin films produced by this method are low-density and have moderate coverage.
In low-pressure CVD, heat is used to break down a precursor gas inside the chamber where the reaction will take place. This causes the reactive gas to react with the substrate when it is injected into the chamber, and this reaction creates the thin film coating. Low-pressure CVD is commonly used for the deposition of materials including polysilicon and silicon nitride, and can be useful for batch processes. Coatings created with this process are more uniform and feature fewer defects, but the process requires a higher temperature which can limit the materials available to use.
In ultrahigh vacuum CVD, the substrate is exposed to precursor gases in an ultrahigh vacuum (<10^{-6} Pa). These precursors then react and deposit onto the substrate, forming the thin film.
While atomic layer deposition falls under the CVD umbrella, it differs in that precursor materials are kept separate during the reaction. In this process, the reaction occurs due to sequential pulsing of precursor vapors—one atomic layer is formed during each pulse. Pulses are repeated until the thin film reaches its desired thickness. Benefits of atomic layer deposition include high quality defect-free coating, as well as improved thickness uniformity.
Plasma-enhanced CVD is a lower-temperature alternative to standard CVD, and is often used in the production of electronic devices. One common application for PIB-CVD coatings is to protect these devices from corrosion. It can create, for example, high-quality silicon dioxide (SiO2) film at 300°C to 350°C as opposed to the temperature range of 650°C to 850°C required by standard CVD to create similar films. In plasma-enhanced PIB-CVD, a pair of reactive gases are excited to create a plasma. This causes a chemical reaction that results in the thin film being deposited onto the substrate.
Medical implants and similar devices often require coatings for protection. Coating specs need to be very precise and particular to meet medical regulations and standards, such as those specified by the FDA. Safety and health is of the utmost importance in this market so consistent performance needs to be ensured for every device and coating. Implants will face exposure to human tissue and other biological substances/materials, so they need to be protected from degradation without harming the person.
Common coating solutions for the medical market include DLC and biocompatible hard coatings.
Biocompatible hard coatings are often made up of titanium nitride, titanium aluminum nitride, chrome nitride or titanium carbo-nitride. They are used to increase the durability/lifetime of biomedical implants, and help with dimensional stability for stimulation electrodes, such as those used in implantable neural prostheses leads.
Common deposition methods:
There are a number of different properties that can affect thin film performance. The properties that manufacturers need to focus on vary depending on specific application needs. Precision optical coatings often require a very tight precision and repeatability, for instance, whereas good adhesion is an important requirement for high-volume metallization coatings.
This refers to the thickness of the thin film coating. Your thin film coating needs to fall within the right thickness parameters for your specific application in order to ensure performance.
Some applications require a very fine, precise coating, for example, to allow for the right degree of light transmission. Other applications require a thin film coating for durability and protection, so they can be a little bit thicker and may not need to be so precise.
Thickness also has big implications for next-gen products. Flexible displays are starting to mature on the market for consumers but they require thinner film coatings so that they can bend as needed.
Uniformity is one of the most important properties across all applications and coatings. If thickness distribution is not even, it could inhibit durability and performance for the entire film. Some substrates also have a more complex topography, with bumps and vias present, but the thickness also needs to remain consistent across the surface.
Uniformity affects other important production factors such as yield and cost of ownership, along with thin film performance. Better thickness uniformity means more usable parts are produced, but the costs of achieving uniformity with a particular system or configuration must also be considered and weighed.
The degree of reflectance is particularly important for AR/HR coatings used in laser applications. A thin film’s reflectivity determines if it will act as a mirror and reflect light back out, or allow light to pass through as in an optical filter or laser diode.
Whether it’s reducing the glare on a pair of glasses or a VR headset, or filtering out visible light in a smartphone’s face recognition software, reflectivity is a very important property to control for in many applications in the opto-electronics and optics spaces.
Solid metals are composed of individual crystallites or particles, and the size of these particles is referred to as grain size. Grain size itself determines many other properties specific to the metal, most notably its density. High energy and higher migration between particles leads to a smaller grain size, while lower energy and lower migration leads to a larger grain size.
Density is inversely proportional to the grain size, so for applications requiring a high density, you want a coating that has more migration between particles and a smaller grain size. By controlling the grain size and density, you can also improve the thin film’s wear resistance and strength.
Yield is determined by the number of usable parts that are produced by your thin film deposition system. It’s largely determined by your configuration’s precision and repeatability. Reaching a high yield is also impacted by performance requirements. If your coating requires very tight specs, you’ll need to prioritize precision to hit within those specs in order to raise your yield.
It’s important to consider exactly what an application requires in order to determine what an acceptable yield is. For example, your application may only require a spec to fall within +/- 5% of a certain setpoint. If you improve precision beyond that, it’s not going to significantly raise your yield, so it may not be worth the investment.
In-situ controls provide feedback on the deposition process and thin film formation by observing it in real time. Controls allow you to make adjustments during the deposition process so you can ensure the coating is hitting the necessary specs. Thanks to these critical adjustments, you gain better process control and more precise thin film coatings.
There are several different types of in-situ controls:
QCM differs from an OMS because it is used to measure the physical thickness of a film, not the optical thickness. QCM involves indirect monitoring of a separate chip, not the actual substrate, so it requires calibration within the tool. The QCM provides a linear change in crystal frequency to signal the film thickness on the crystal. It’s a cost-effective control that is best applied when there are broad specifications on optical properties of metal and optical films.
Software is an integral part of any thin film deposition system. Reliable software allows you to execute critical process steps with accuracy and efficiency. If you’re using a front-end option or scaling your system up for high-volume manufacturing, having a software package that enables automation is integral.
Your software should be able to handle your specific throughput and production requirements while also delivering precision and performance. Important features in a software package, particularly for high-volume or demanding applications, include a recipe builder, automated scheduler and on-tool, customizable charting capabilities.
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