Exploring the Advantages and Disadvantages of Sputtering

Introduction

Sputtering is a cornerstone of physical vapor deposition (PVD) and stands at the forefront of materials science and advanced manufacturing. This versatile technique plays a pivotal role in the deposition of thin films onto substrates with plenty of advantages and limitations. In this article, we will delve into the world of sputtering, uncovering its principles, strengths, and areas where it faces challenges

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What Is Sputtering?

Sputtering is a fundamental process in materials science and manufacturing that involves the deposition of thin films onto surfaces. It works by bombarding a target material with high-energy ions, typically using an inert gas like argon in a vacuum chamber. When the ions collide with the target, they dislodge atoms or molecules from the surface, which then condense on a substrate to form a thin film.

Figure 1. The Sputtering Process

This technique offers several advantages, including precise control over film thickness, high material purity, and the ability to deposit a wide range of materials. It is widely used in industries such as microelectronics, optics, and coating technology to create thin films with specific properties for various applications. Sputtering plays a crucial role in producing everything from semiconductor devices to optical coatings on lenses and mirrors. Its versatility and ability to deposit high-quality films make it a valuable tool in modern manufacturing and research.

Advantages of Sputtering

Indeed, sputtering is a technique that brings a multitude of advantages to the realm of thin film deposition. Here are some notable examples.

1. High Purity Deposition: It allows for the deposition of high-purity thin films since it does not involve chemical reactions. This makes it suitable for applications where material purity is critical, such as in microelectronics.
2. Controlled Film Thickness: It provides precise control over the thickness of the deposited film, enabling the production of thin films with specific thickness requirements.
3. Uniform Coating: Sputtering typically results in uniform film deposition across the entire substrate surface, ensuring consistency in film properties.
4. Wide Material Compatibility: Sputtering can be used with a wide range of materials, including metals, semiconductors, ceramics, and even some polymers, making it versatile for various applications.
5. Excellent Adhesion: Sputtered films often exhibit strong adhesion to the substrate, reducing the risk of delamination or peeling.
6. High-Density Films: The high packing densities of high-density films can lead to improved mechanical and electrical properties.

Disadvantages of Sputtering

However, sputtering is not without its challenges, and a comprehensive understanding of both its strengths and limitations is crucial for harnessing its full potential.

1. Low Deposition Rate: Sputtering generally has a slower deposition rate compared to other techniques like chemical vapor deposition (CVD) or atomic layer deposition (ALD). This can be a limitation for high-volume production.
2. Target Erosion: During sputtering, the target material gradually erodes, reducing its lifespan and necessitating frequent target replacement.
3. Line of Sight Deposition: Sputtering is a line-of-sight process, which means that areas not directly exposed to the sputtered material may receive limited deposition. This can be a limitation for coating complex shapes.
4. High Equipment Cost: Sputtering equipment can be expensive to purchase and maintain, which may be a barrier to entry for some facilities. This process typically requires the use of argon gas, which can add to operational costs.
5. Heat Sensitivity: Some materials are sensitive to the heat generated during sputtering, which can limit their use with this technique.

Related reading: Advantages and Disadvantages of Ion Beam Sputtering.

Conclusion

In summary, sputtering is a versatile and widely used thin film deposition technique with several advantages, including high purity, precise control, and uniformity. Yet, it also has limitations, such as slower deposition rates, high equipment costs, and heat sensitivity. The choice of deposition technique depends on the specific requirements of the application and the properties of the materials involved.

Stanford Advanced Materials (SAM) is a leading supplier of a variety of sputtering targets and evaporation materials. Customization is also welcome. Send us an inquiry if you are interested.

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Reference:

[1] Pujahari, R. (2021, June 8). Solar cell technology. ScienceDirect. Retrieved September 8, 2023, from https://www.sciencedirect.com/topics/chemical-engineering/sputter-deposition

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Performance and versatility can be greatly improved by using them in combination with a primer. The combination of hardcoat and primer are often referred to as a hardcoating system. The primer provides adhesion to multiple substrates, impact resistance and tintability. The hardcoat provides abrasion and scratch resistance, as well as a host of other features. For the lab and manufacturer, working closely with the hardcoating supplier, one can carefully select both primer and topcoat, and thereby optimize performance of the hardcoating system.

Thermal vs. UV: Most coatings are cured by either UV light or heat (thermal) exposure. The choice of cure method depends on the chemistry of the coating. Each of these two types of coatings has their advantages and disadvantages. The following is a summary of the general pros and cons of each. These are typical attributes of each of these classes of coatings—not all coatings in each class are alike.

Thermally Cured Coatings: Thermally cured coatings were traditionally used only by lens manufacturers and referred to as factory coatings or the front side coating on a semi-finished lens blank. They have good to excellent abrasion resistance and AR compatibility. They allow the option of using primers to achieve better adhesion, tintability and impact enhancement. Most thermally cured coatings are designed for adhesion to a single substrate. This makes them ideal in the lens manufacturing environment. The use of a primer, however, allows the same coating to be used on multiple substrates or even as an overcoat (more details below). This has resulted in increased usage of thermally cured coatings at labs and retailers. Thermally cured coatings are generally thought to be more compatible with AR and mirror coatings. Thermally cured coatings can be spin or dip coated. Thermally cured coatings have longer cure times (typically one to four hours) and have limited substrate compatibility.

UV Cured Coatings: UV cured coatings are traditionally used in the laboratory environment and at some lens manufacturers. The advantages of UV cure coatings are quick cure time and multiple substrate compatibility. This makes them ideal for the laboratory or retailer where multiple substrates are used and quick turnaround times are expected. UV cured coatings can be applied by spin coating, dip coating or in-mold coating. Spin coating is the most typical method of application. UV cured coatings are typically lower in abrasion resistance and often less compatible with AR and mirror coatings. UV cure coatings often have good steel wool abrasion resistance, but do not perform as well as thermally cured coatings in the Bayer Abrasion Test (more on test methods below).

Hybrid Coatings: This is a new category of coatings. The goal is to combine the "best of both worlds." These coatings are cured by first exposing them to UV light, followed by a short thermal cure. This results in a coated surface with the abrasion resistance and AR compatibility of thermally cured coatings and the quicker cure time of UV cured coatings.

Overcoating: Overcoating is the technique of applying a hardcoat over an existing hardcoat. This is used to apply the same coating on the front and back surface of a lens that already has a factory coating on the front surface or both sides of the lens. This allows the lab or retailer to apply a premium hardcoat with consistent performance on both surfaces and on all substrates. A primer is used to achieve adhesion on a variety of factory coatings, as well as a variety of bare substrates. A thermally cured coating is then applied over the primer. Using this process, the lab or retailer can produce lenses with premium abrasion resistance, optics and AR compatibility on both surfaces and on all substrates. Some coating systems require that lenses have the factory hardcoat etched off with an acid wash before overcoating.

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