Material deposition refers to the process of adding or depositing material onto a substrate or surface. This can be achieved through various techniques and methods, each suited to different applications. For many of these applications, vacuum is an essential requirement to achieve the required quality.

Material deposition or thin-film deposition can be achieved through Plasma Vapour Deposition (PVD) Molecular Beam Epitaxy (MBE), Atomic Layer Deposition (ALD) and Chemical Vapour Deposition (CVD); and more. These variations in material deposition techniques allow for different profiles of material to be deposited onto a substrate or sample surface, building up complex material structures. Material Deposition is successfully utilised in applications such as microelectronics, material science and research, optics, coatings and semiconductor production; where the style of deposition required can depend on the nanoscale and complexity of the surface, chip or node which is being fabricated.

In this article we’ll look at some of the techniques used in material deposition and how these are utilised in advancing science and industry. We’ll also look at some real-life applications such as semiconductor wafer fabrication and why vacuum is a fundamental aspect in creating a successful environment for deposition.

Chemical Vapour Deposition (CVD)

Chemical Vapour Deposition (CVD) is a materials processing technique used for the deposition of thin films onto a substrate surface. In CVD, the chemical reactions take place at the surface of a substrate to produce a thin layer of material. Gaseous reactants, typically in the form of volatile precursor gases, are introduced into a reactor chamber, where they undergo chemical reactions to form a solid material. Substrates are placed within a vacuum chamber and often heated to a specific temperature to facilitate the chemical reaction and promote adhesion of the deposited material. Plasma-Enhanced CVD involves the use of plasma to enhance the chemical reactions and promote the deposition of thin films. This technique is widely used in various industries, including semiconductor manufacturing, optics and coatings. The control over film composition, thickness and uniformity in production of coatings for optical components, solar cells and various other applications is critical for specialised components to operate successfully. CVD allows for the deposition of thin films with excellent conformity to complex shapes and high aspect ratios.

Atomic Layer Deposition (ALD)

ALD is a thin film deposition technique used in various industries, particularly semiconductor manufacturing, electronics and material science. A highly controlled process that allows for the precise deposition of an atomic uniform layer of material onto a substrate surface. The vacuum chamber in which this happens, must be extremely clean and maintain a consistent level of high vacuum to prevent contamination. These specialised vacuum chambers offer precise control over temperature and gas flows. The equipment used for ALD is designed to facilitate the sequential exposure of precursors and ensure precise control over the deposition process. Atomic Layer Deposition is characterised by its layer-by-layer growth mechanism. It involves sequentially exposing the substrate to alternating precursors, typically in a gas phase. Each exposure results in the formation of a single atomic layer. Offering exceptional control over film thickness, this precision is crucial for applications in nanotechnology and semiconductor devices, where thin films with specific properties are required.

Physical Vapour Deposition (PVD)

PVD processes generally involve the vaporisation of a solid material (the target or source) and its subsequent condensation onto a substrate to form a thin film. This is typically done in a vacuum environment to minimise interference from gases and achieve better film quality. Unlike chemical processes, PVD methods involve the physical transfer of material from a source to a substrate. Two common PVD techniques include Sputtering and Evaporation: Sputtering: This method involves bombarding the target material with energetic ions (usually argon ions) to eject atoms or molecules, which then deposit onto the substrate. Evaporation: In this process, the target material is heated to a high temperature, causing it to evaporate and form a vapour. The vapour then condenses on the substrate to create the thin film. PVD allows for precise control over the properties of the deposited films, including thickness, composition, and microstructure. PVD coatings often exhibit high adhesion, hardness, and wear resistance. They can also enhance the corrosion resistance of materials. Common PVD coatings include metallic coatings (e.g., titanium nitride, chromium), decorative coatings (e.g., gold, silver), and functional coatings (e.g., anti-reflective coatings, barrier coatings). PVD is a versatile and widely used technology in manufacturing and research, offering control over film properties and enabling the deposition of thin films with specific characteristics tailored to different applications.

Why Vacuum is Necessary?

Vacuum conditions provide a stable and predictable environment for controlling the deposition rates. This is crucial for achieving uniform film thickness and desired properties. Some other factors include contamination prevention, improving adhesion and purity, reducing oxidisation rates and enhancing thin film properties.

Prevention of Contamination: In many deposition processes, maintaining a vacuum helps prevent contamination of the deposited material. Contaminants such as gases and particles in the air can affect the quality and properties of the deposited layer.

Controlled Environment: Vacuum environments allow for better control over the deposition process. Removing air and other gases helps in achieving a more uniform and controlled deposition of materials.

Improved Adhesion and Purity: Vacuum environments can enhance adhesion between the substrate and the deposited material. Additionally, a vacuum minimises the presence of impurities, leading to higher purity in the deposited layers.

Reduced Oxidation: Some materials are sensitive to oxidation, and a vacuum helps in reducing or eliminating the presence of oxygen, ensuring that the material deposited retains its desired properties.

Enhanced Film Properties: Vacuum conditions can influence the microstructure and properties of the deposited films, leading to improved mechanical, electrical, or optical characteristics.