Thermal Evaporation VS Magnetron Sputtering
When considering the two primary physical vapor deposition (PVD) methods employed by Mueller, it is crucial to understand the advantages and disadvantages of each technique before determining the most suitable approach for your specific application. PVD can be achieved through sputtering, which involves the use of energetic ions colliding with a target material to dislodge or sputter atoms, or through evaporation, which relies on heating a solid source material until it reaches its vaporization temperature. In this article, we will delve into the technical benefits, drawbacks, and typical applications of these PVD techniques.
Resistive thermal evaporation is a physical vapor deposition technique that involves the application of thermal energy from a resistive heat source to a solid-state material within a vacuum chamber. This process causes the material to evaporate, and the resulting vapor condenses on a substrate, forming a thin film of the source material. It is considered one of the most common and straightforward methods of physical vapor deposition.
Advantages of Thermal Evaporation:
- Compatible with both metals and nonmetals, including aluminum, chrome, gold, and indium, making it suitable for applications requiring electrical contacts
- Well-suited for materials with low melting points, such as alloys containing mercury or gallium
- Exhibits excellent uniformity when using planetary substrate fixturing and uniformity masks (though poor uniformity without them)
- Offers a high deposition rate of less than 50 Angstroms per second (Å/s)
- Demonstrates good directionality
- Relatively low cost compared to other physical vapor deposition methods
- Represents the least complex process among PVD methods
- Compatible with ion-assist sources
Disadvantages of Thermal Evaporation:
- Exhibits the highest impurity levels among PVD methods
- Film quality has low density, but this can be improved with ion-assist
- Moderate film stress
Typical thermal evaporation applications include decorative applications such as cosmetic closures, sporting goods, displays and more. thin-film devices such as OLEDs, solar cells, and thin-film transistors that require the deposition of metallic contact layers. Other thermal evaporation applications include EMI/RFI Shielding, light reflectors for Automotive, Medical, Aerospace and more.
Magnetron sputtering is a plasma-based coating technique that involves the collision of positively charged energetic ions from a magnetically confined plasma with a negatively charged target material. This collision results in the ejection, or “sputtering,” of atoms from the target, which are then deposited onto a substrate. This process takes place within a closed magnetic field, which traps electrons and enhances efficiency. By creating plasma at lower pressures, gas incorporation in the film is reduced, and energy losses in the sputtered atoms are minimized. Magnetron sputtering is known for its ability to produce high-quality films and its exceptional scalability compared to other physical vapor deposition (PVD) methods.
Advantages of Magnetron Sputtering:
- Well-suited for metals and dielectrics
- Offers good uniformity, leading to improved yield (though achieving uniformity enhancements can be challenging and costly)
- Exhibits low levels of impurity
- Yields films with high density, ranging from moderate to high stress
- Provides a high deposition rate, particularly for metals, making it suitable for high-throughput applications
- Offers the highest level of scalability, with automation options available
Disadvantages of Magnetron Sputtering:
- Demonstrates a poor deposition rate for dielectrics (1-10 Å/s)
- Involves high system cost and complexity
- The energetic target material can cause substrate heating
- Applications of magnetron sputtering include multi-layer metal coatings for EMI/RFI shielding, vapor barriers, heat shielding, antenna paths, decorative metallic finishes in more.
- Ideal for producing very dense films that require strong adhesion.
- Suitable for depositing metallic or insulating coatings with specific optical and electrical properties.
- Well-suited for applications that demand high levels of automation.
Differences between magnetron sputtering and aluminum evaporation can be observed in the following aspects:
Metal Effect: Magnetron sputtering excels in depositing metal materials, resulting in a delicate and flat object surface with excellent adhesion. The metal effect achieved through sputtering appears more realistic, and light transmission is uniform.
In contrast, evaporated aluminum, due to the relatively weaker energy of the evaporator, produces a film with a less crystalline structure. As a result, the metal effect is not as pronounced, and the adhesion of the metal film is weaker, leading to a higher risk of detachment. This can result in a relatively poorer deposition effect, causing uneven brightness in light transmission.
Color Options: Magnetron sputtering offers greater color versatility through modulation, allowing for 12 different colors such as champagne gold, rose gold, gold, purple blue, amethyst, and bright silver. Some manufacturers have even achieved a fog matte effect, meeting various customer demands.
Evaporated aluminum, as the name suggests, is limited to the true color of aluminum. To apply other colors, additional spray painting is required, which presents technical challenges and can result in color variations. Moreover, sputtering achieves real colors through true metals, while the colors obtained through aluminum evaporation involve chemical coating mixing.
The two coating principles differ significantly: Magnetron sputtering involves bombarding the target material with high-energy ions, causing atoms on the target surface to sputter away. Controlled by a magnetic field, sputtered atoms or secondary electrons move in a cycloidal form, allowing for sustained glow and sputtering.
The adhesion and bonding effects of the metal film also differ. Evaporation coatings exhibit relatively weaker adhesion but superior film uniformity. Sputtered films, formed through high-energy processes, exhibit better substrate adhesion but may contain particles, resulting in slightly lower uniformity.
Evaporation coatings often employ crystal oscillators for precise control, achieving thicknesses below 10nm. In contrast, sputtered films may contain particles, and achieving precise and controllable thicknesses of 10nm can be challenging.
In summary, magnetron sputtering represents a more advanced technology than thermal evaporation. However, selecting the ideal method depends on the specific products and application requirements. Sputtered metal films partially penetrate the plastic, resulting in better contact and suitability for challenging environments. It is worth noting that sputtering is a more expensive technology, necessitating careful consideration when choosing the appropriate machine for production purposes.
At Mueller Corporation, we take immense pride in offering a comprehensive suite of services and equipment for vacuum metalized physical vapor deposition (PVD) techniques. Our commitment to excellence is driven by our mission to serve a wide range of industries, including medical, space and defense, cosmetics, and more. With expertise in both magnetron sputtering and thermal evaporation, we provide tailored PVD solutions to meet the unique requirements of each industry, delivering exceptional thin film coatings that fuel innovation and success.