What Is Thin Film Deposition? Deposition Equipment Types

Thin Film Deposition is the technology of applying a very thin film of material onto a “substrate” surface to be coated, or onto a previously deposited coating to form layers. Thin Film Deposition equipment and  manufacturing processes are at the heart of today’s semiconductor industry, solar panels, CDs, disk drives, medical implants and optical devices industries.

What is the Thickness of a Thin Film?

Between a few nanometers to about 100 micrometers, or the thickness of a few atoms.

What is the Difference Between PVD and CVD?

Thin Film Deposition techniques are usually divided into two broad categories – Physical Vapor Deposition Coating Systems and Chemical Deposition.

Physical Vapor Deposition refers to a wide range of technologies where a material is released from a source and deposited on a substrate using mechanical, electromechanical or thermodynamic processes. The two most common techniques of Physical Vapor Deposition or PVD are Sputtering and Thermal Evaporation.

Chemical Vapor Deposition is when a volatile fluid precursor produces a chemical change on a surface leaving a chemically deposited coating.  One example is Chemical Vapor Deposition or CVD used to produce the highest-purity, highest-performance solid materials in the semiconductor industry today. Plasma Enhanced Chemical Vapor Deposition or PECVD is another commonly used thin film deposition technique or process.

Sputtering

Sputtering involves the bombardment of a target material with high energy particles that are to be deposited on a substrate like a silicon wafer or solar panel.  The substrates to be coated are placed in the thin film deposition equipment in a high vacuum chamber containing an inert gas – usually Argon – and a negative electric charge is placed on the target material to be deposited causing the plasma in the chamber to glow.

Atoms are “Sputtered off” the target by collisions with the Argon gas atoms, carrying these particles across the vacuum chamber and are deposited as a thin film.  Several different methods of plasma vapor deposition coating systems are widely used, including ion beam assisted deposition, reactive sputtering in an Oxygen gas environment, gas flow and magnetron sputtering.

Magnetron Sputtering

Magnetron sputtering equipment uses magnets to trap electrons over the negatively charged target material so they are not free to bombard the substrate, preventing the object to be coated from overheating or being damaged, and allowing for a faster thin film deposition rate.

Magnetron Sputtering systems are typically configured as In-line where the substrates travel by the target material on some type of conveyor belt, or circular for smaller applications. They use several methods of inducing the high energy state including direct current (DC), alternating current (AC) and radio frequency (RF) magnetron sources.

Compared to Thermal Evaporation that utilizes more conventional heating temperatures, Sputtering takes place in the plasma “Fourth state of nature” environment with much higher temperatures and kinetic energies allowing a much purer and more precise thin film deposition on the atomic level.

Thermal Evaporation

Thermal Evaporation involves heating a solid material that will be used to coat a substrate inside a high vacuum chamber until it starts to boil and evaporates producing vapor pressure. Inside the vacuum deposition chamber, even a relatively low vapor pressure is sufficient to raise a vapor cloud.  This evaporated material now constitutes a vapor stream which the vacuum allows to travel without reacting or scattering against other atoms. It traverses the deposition equipment chamber and hits the substrate, sticking to it as a coating or thin film.

There are two primary methods of heating the source material during Thermal Evaporation.  One is known as Filament or Resistive Evaporation, as it is achieved with a simple electrical heating element or filament. The other common heat source is an electron beam or E-Beam Evaporation where an electron beam is aimed at the source material to evaporate it and enter the gas phase.

Thin Film Evaporation systems can offer the advantages of relatively high deposition rates, real time rate and thickness control, and (with suitable physical configuration) good evaporant stream directional control for processes such as Lift Off to achieve direct patterned coatings.

Which approach is the right choice for your specific thin film deposition coating system needs can depend upon many complex factors – and more than one approach can be taken to reach similar ends.

Main Processes that Control the Growth of Thin Films

Nucleation: The first stage of film growth is when atoms or molecules become absorbed onto the substrate and form clusters known as nuclei around which films begin to grow.

Growth: Once nuclei begin to form further deposition leads to the growth of continuous films. Growth occurs through several mechanisms that can influence the characteristics of the film.

These include what is known as island growth, where the coating materials at the nucleation stage are initially more bonded to each other than to the substrate. Layer-by-layer growth is formed by depositing alternating layers of oppositely charged materials. This can be achieved using methods like electrostatic self-assembly or Langmuir-Blodgett deposition. The positively and negatively charged materials attract each other, resulting in a controlled and ordered multilayer structure.

Another method is Mixed-Mode Growth where a combination of different deposition techniques or processes to create a more complex film structure for a specific outcome. These thin film deposition techniques are controlled by parameters such as deposition rate, temperature and surface kinetics to create a stunning variety of useful applications.

Surface Kinetics: Include processes like absorption and desorption of how effectively the film bonds to the substrate material.

Surface Diffusion: Refers to the movement of atoms or molecules on the surface of the substrate. At the initial stages of nucleation atoms and molecules spread or diffuse across the surface to find suitable binding sites. Surface diffusion can play a crucial role defining the thin film’s morphology, grain size and microstructures.

Substrate Surface: The surface roughness, crystal structure and lattice can determine the nucleation and growth process.

Epitaxy: The underlying crystal structure of the substrate can provide an initial pattern for creating the preferred crystal orientation of the microstructures. This makes possible many desirable improvements being able to be tailored for electronic, optical and mechanical components when the film adopts the same crystal structure and orientation as the underlying substrate.

Stress and Strain: When thermal expansion coefficients differ between substrates and the thin films bonding to them, it can introduce stress and strain in the thin film during the high temperatures of many thin film deposition processes. This can lead to film deformations, delamination and cracking that is important to control for strength and integrity of the coatings.

You always want to get the help of a competent PVD vacuum engineering expert to assess your exact Thin Film machine needs and offer you the optimum outcome at the best price.

Semicore’s CAPOS All-in-one Sputtering & Thermal Evaporation System

Semicore’s breakthrough CAPOS thin film deposition system is the PVD Industry’s first cost effective “Open-platform” design, ideal for both precision R&D and batch production.

Flexible enough that it can be used for either sputtering or thermal evaporation coatings, this platform is also used for Semicore’s CAPOS-CT series, as a highly versatile “Cluster Tool” platform that can be configured with multiple Process Modules (PM) and cassette-to-cassette operation.

For more detailed information on these units’ specifications please download the PDF.

Matt Hughes is President of Semicore Equipment Inc, a leading worldwide supplier of sputtering equipment for the electronics, solar energy, optical, medical, military, automotive, and related high tech industries. Please let our helpful support staff answer any questions you have regarding “What is Thin Film Deposition?” and how to implement the best techniques for your specific Thin Film Vapor Deposition Equipment needs by contacting us at sales@semicore.com or by calling 925-373-8201.