The process takes place inside a vacuum chamber containing a small amount of an inert process gas, usually argon (Ar). A negative voltage is applied to the target, which serves as the cathode, creating an electric field between the cathode and the anode. Free electrons are accelerated by this field and collide with argon atoms. These collisions ionize the gas, producing more electrons and positively charged ions that form a plasma.

Positive ions move toward the target and strike its surface. With sufficient energy, they eject individual atoms from the target — a process known as sputtering. The ejected atoms travel through the vacuum and condense on the glass substrate, gradually building up a dense film. Unlike evaporation, the target does not need to melt or evaporate during sputtering. Because the deposited material comes directly from the target, the composition and thickness of the resulting film can be precisely controlled.

With an electric field alone, electrons are accelerated rapidly toward the anode, reducing their chances of colliding with gas atoms. As a result, gas ionization is limited, and maintaining a stable discharge at low pressure becomes difficult. In magnetron sputtering, magnets behind the target create a magnetic field near the target surface. This field traps electrons in longer circulating paths, increasing the probability of collisions with gas atoms. The more efficient ionization allows the plasma to remain stable at lower gas pressures, resulting in a higher sputtering rate and less thermal load on the substrate.

The design of the magnetic field distribution has a direct impact on coating results. It affects the target’s erosion pattern, target utilization, and film uniformity across the glass width. As the target is consumed during production, its surface profile and coating uniformity change gradually. With a well-designed magnetic field and adjustment system, these changes can be compensated for, maintaining film uniformity over longer production runs.

Depending on how the substrate moves in relation to the sputtering source, magnetron sputtering can use either a dynamic or static coating process.

• Dynamic coating
  The substrate moves continuously past the sputtering source. The thickness of the film is determined by the sputtering rate and the speed at which the substrate moves through the coating area.
• Static coating
  The substrate stays in front of the sputtering source for a set period of time. The thickness of the film depends on how long the deposition lasts.

The TH Series Low-E glass coating system uses a continuous dynamic coating process. Glass passes through the vacuum chambers in sequence, with each process chamber depositing a different layer of the multilayer film stack. Film thickness is controlled by sputtering power, process gas flow, and glass transport speed. Process recipes are used to manage these parameters and ensure consistent production batches. This continuous configuration is well suited to high-volume production of large-format coated glass.

Magnetron sputtering can deposit a wide range of metallic and compound materials. The target is selected according to the required coating and process.

• Metallic materials
  Silver, titanium, chromium, nickel-chromium, aluminum and copper are among the commonly used materials. Silver forms the functional low-emissivity layer in a Low-E coating stack. Other metals can be used in reflective, conductive, decorative and functional coatings.
• Compound materials
  Oxides, nitrides and other compound films can serve as dielectric and protective layers in Low-E coating stacks. They are also used for anti-reflective, wear-resistant, colored and other functional coatings.

The thickness of each film layer can differ from just a few nanometers to several hundred nanometers. Even small changes in thickness on large pieces of glass can affect the color or how the glass performs optically. It is therefore important to keep the thickness consistent across both the width and length of the glass. Uniformity for a single film layer can be controlled within 1.6%.

A multilayer coating forms as the glass moves through each coating chamber, with each layer added one at a time. The optical properties that result depend on the thickness and state of each layer. To ensure consistent results in industrial production, it is important to keep the coating process repeatable.

Magnetron sputtering systems use two types of cathodes, selected according to the target shape. Rotary and planar cathodes can both be used in the same coating line, with each type chosen to suit the specific material and film layer required.

• Rotary Cathode
  Uses a tubular target that rotates slowly around its axis during sputtering. This produces more uniform target erosion and higher target utilization, making it suitable for long production runs and large-area coating.
• Planar cathode
  Uses a flat target with a relatively simple structure that is easy to install, remove and maintain. It is commonly used for the deposition of specific metallic layers.

Target length is configured according to the width of the glass to maintain coating coverage across the full substrate.
We develop and manufacture our planar cathodes in-house. Target dimensions and target-to-substrate distance can be configured for different coating system specifications. Several magnetic-field adjustment options are available, including adjustment at atmospheric pressure, manual adjustment under vacuum and online adjustment under vacuum. This gives operators different ways to fine-tune film uniformity for different coating stacks. For key components such as rotatable cathodes, we work with established international brands on jointly developed, customized solutions.

Compound films are typically produced by reactive sputtering from metallic targets or direct sputtering from ceramic targets. In reactive sputtering, sputtered atoms react with oxygen or nitrogen during deposition to form a compound film on the glass. Typical applications include dielectric layers such as zinc oxide, silicon nitride, and titanium oxide, as well as certain colored coatings.

The challenge in reactive sputtering is keeping the process stable. Even a small change in reactive gas flow can shift the target surface between metallic and oxidized states. This can change the discharge conditions, the deposition rate, and the resulting film properties. The process therefore requires continuous monitoring of the process and closed-loop adjustment of reactive-gas flow to maintain the required operating point.

Our sputtering systems use three control methods for different materials and coating stacks: voltage control, oxygen partial-pressure control (λ probe) and PEM control. Each provides a different way to monitor the sputtering state and keep the process within the required operating range.

We have developed our magnetron sputtering capabilities around both the coating process and the equipment required to run it at production scale.

• In-house planar cathodes
  In-house development and production of planar cathodes allow us to configure target dimensions, target-to-substrate distance and magnetic-field adjustment to suit different coating system specifications.
• Customized rotatable cathodes
  Key components such as rotatable cathodes are jointly developed and customized in cooperation with established international technology brands.
• TH120 test coating system
  The compact TH120 magnetron sputtering system is available for coating-stack development and process validation. This coating equipment has already been supplied to Xinyi Glass.
• 20+ Low-E coating lines delivered
  We have been developing and manufacturing vacuum coating equipment since 2009, with more than 20 Low-E coating lines delivered for single-, double- and triple-silver coating production.
• Complete line integration
  Cathodes, power supplies, vacuum systems, gas control and inspection systems are integrated and validated at complete-line level. The same technical scope extends from process development and equipment manufacturing through installation, commissioning and mass-production support.

This continuous coating process supports large-scale production of coated glass, including energy-saving glass, decorative glass and functional coated glass.

For more information on the equipment behind these processes, see the TH series continuous magnetron sputtering low-E glass coating system or contact CNBM to discuss your coating requirements.