Mid-Frequency AC SputteringMid-frequency AC Sputtering has become a mainstay of thin film sputtering technologies, particularly for the deposition of dielectric or non-conducting film coatings on surfaces such as solar panels, optical glass such as telescope mirrors or rolls of plastic. It is largely replacing RF Sputtering for coating dielectrics because it operates in the kHz rather than MHz range requiring less sophisticated and expensive power sources and is a process that is adaptable to large scale applications.

MF or Mid-frequency AC power supplies cover a wide range of voltage outputs between 300 V to 1200 V - generally in the 25 to 300 kW range - at frequencies between 20 to 70 kHz with 40 kHz used most commonly. It is a process frequently used with Reactive Sputtering where a reactive gas such as oxygen or nitrogen is introduced into the plasma to form oxides or nitrides on the substrate.

Two cathodes are used with an AC current switched back and forth between them which cleans the target surface with each reversal to reduce the charge build up on dielectrics that leads to arcing which can spew droplets into the plasma and prevent uniform thin film growth.

PVD Gold SputteringGold is one of the most beautifully luminescent and valuable metals on Earth because of its ability to throw light, reflect energy and resist tarnishing. PVD or Physical Vapor Deposition Gold Sputtering is commonly used in the watch and jewelry industry to produce coatings that are hard and durable and won’t rub off with constant contact with the skin or clothes and lose it sheen.

PVD Gold Sputtering is also used for coating circuit panels and electronic components due to its excellent conductivity, for coating optical fibers, batteries and high end faucets and fixtures. Gold Sputtering processes are invaluable for biomedical implants that serve as radiopaque coatings that are visible in x-rays and lifesaving procedures like coating tissue samples to make them visible for scanning under electron microscopes.

Gold Sputtering coatings are a thin film deposition process where gold or a gold alloy is bombarded with high energy ions in a vacuum chamber resulting in the gold atoms or molecules being “Sputtered” into the vapor and condensing on the substrate to be coated such as jewelry, circuit boards or medical implants.

Written By Matt Hughes - President - Semicore Equipment, Inc.

blue sonar

Pulsed DC Sputtering is a physical vapor deposition technique with a wide range of applications in the semiconductor, optical and industrial coating industries. Pulsed DC Sputtering is particularly effective for the sputtering of metals and dielectric coating – coatings which are insulating non-conducting materials that can acquire a charge.

It is most often used with Reactive Sputtering where there is a chemical reaction occurring in the plasma between the vaporized target material and ionized gases like Oxygen to form deposition molecules such as silicon oxides. Pulsed DC Sputtering has revolutionized the Reactive Sputtering of “difficult” dielectric materials like Alumina, Titania and Silica with high deposition rates that are impossible with straight DC Sputtering alone.

Written By Matt Hughes - President - Semicore Equipment, Inc.

Sputter Glow

DC or Direct Current Sputtering is a Thin Film Physical Vapor Deposition (PVD) Coating technique where a target material to be used as the coating is bombarded with ionized gas molecules causing atoms to be “Sputtered” off into the plasma. These vaporized atoms are then deposited when they condense as a thin film on the substrate to be coated.

Written By Matt Hughes - President - Semicore Equipment, Inc.

High Voltage Spark

High Power Impulse Magnetron Sputtering or HIPIMS is a relatively recent advance in sputtering technology used for the physical vapor deposition of thin film coatings based upon Magnetron Sputtering with a high voltage pulsed power source. HIPIMS utilizes a very high voltage, short duration burst of energy focused on the target coating material to generate a high density plasma that results in a high degree of ionization of the coating material in the plasma.

By pulsing the target coating material with bursts of high voltage energy – with a length of ~100 μs on the order of kW⋅cm−2 but with a relatively short duration or “Duty time” of less than 10% - allows for a large fraction of the sputtered target material to be ionized in the plasma cloud without overheating the target and other components of the system. The target has a chance to cool during the predominant “Off duty” time which results in a low average cathode power of 1–10 kW which helps maintain process stability.

Written By Matt Hughes - President - Semicore Equipment, Inc.

magnetron sputtering source

RF or Radio Frequency Sputtering is the technique involved in alternating the electrical potential of the current in the vacuum environment at radio frequencies to avoid a charge building up on certain types of sputtering target materials, which over time can result in arcing into the plasma that spews droplets creating quality control issues on the thin films – and can even lead to the complete cessation of the sputtering of atoms terminating the process.

Traditional DC Sputtering is a cost effective way of applying metal target coatings that are electrical conductors like gold. However, DC Sputtering is limited when it comes to dielectric target materials – coatings which are non-conducting insulating materials that can take on a polarized charge. Examples of common dielectric coating materials used in the semiconductor industry include Aluminum Oxide, Silicon Oxide and Tantalum Oxide.

Electron-Beam Evaporation Equipment

E-Beam or Electron Beam Evaporation is a form of Physical Vapor Deposition in which the target material to be used as a coating is bombarded with an electron beam from a charged tungsten filament to evaporate and convert it to a gaseous state for deposition on the material to be coated. Taking place in a high vacuum chamber, these atoms or molecules in a vapor phase then precipitate and form a thin film coating on the substrate.

E-Beam Evaporation, which is a Thermal Evaporation process, and Sputtering are the two most common types of Physical Vapor Deposition or PVD. Of these two processes, The E-Beam Deposition technique has several clear advantages for many types of applications.

Thin Film DepositionThin Film Deposition is the technology of applying a very thin film of material – between a few nanometers to about 100 micrometers, or the thickness of a few atoms – onto a “substrate” surface to be coated, or onto a previously deposited coating to form layers. Thin Film Deposition manufacturing processes are at the heart of today’s semiconductor industry, solar panels, CDs, disk drives, and optical devices industries.

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

Chemical 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.

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 Thermal Evaporation and Sputtering.

abstract sputtering  glow

There are several methods of Thin Film Deposition which is a vacuum technology for applying coatings of pure materials to the surface of various objects. The coatings are usually in the thickness range of angstroms to microns and can be a single material, or multiple materials in a layered structure.

The object to be coated is referred to as the substrate, and can be any of a wide variety of things such as: semiconductor wafers, solar cells, optical components, or many other possibilities. The materials to be applied can be pure atomic elements including both metals and non metals, or can be molecules such as oxides and nitrides.

Thin Film Semiconductor Wafers

One of the common methods of Physical Vapor Deposition (PVD) is Thermal Evaporation. This is a form of Thin Film Deposition, which is a vacuum technology for applying coatings of pure materials to the surface of various objects. The coatings, also called films, are usually in the thickness range of angstroms to microns and can be a single material, or can be multiple materials in a layered structure.

The materials to be applied with Thermal Evaporation techniques can be pure atomic elements including both metals and non metals, or can be molecules such as oxides and nitrides. The object to be coated is referred to as the substrate, and can be any of a wide variety of things such as: semiconductor wafers, solar cells, optical components, or many other possibilities. 


Thermal Evaporation involves heating a solid material inside a high vacuum chamber, taking it to a temperature which produces some vapor pressure. Inside the vacuum, even a relatively low vapor pressure is sufficient to raise a vapor cloud inside the chamber. This evaporated material now constitutes a vapor stream, which traverses the chamber and hits the substrate, sticking to it as a coating or film.

inline sputtering system

An "In Line" PVD Sputtering System is one in which substrates pass linearly beneath one or more Sputter cathodes to acquire their Thin Film coating. Normally the substrates are loaded onto a carrier or pallet in order to facilitate this motion, and some smaller systems handle just one pallet per batch run. Larger systems may have the capability of handling multiple pallets through the use of end station pallet handlers that send and receive one pallet after another in a continuing convoy passing through the transport subsystem, the tip of each following behind the tail of the prior one.

The most common, and least complex, configuration is to have the pallets and cathodes horizontal with cathodes on top and substrates on the bottom in a sputter down orientation. In this mode, gravity is usually the only thing holding the substrates onto the pallets, and also the only thing holding the pallets onto the transport mechanism, which can just be chains running along side rails through the vacuum chamber.

lift offThin Film Coatings are sometimes applied to entire surfaces of substrates, "wall to wall" so to speak, in a continuous unbroken film. But many times the final form of whatever particular material is being applied is patterned so that it is coated in certain specific areas and bare in others.

There are two principal ways to achieve this effect:

1) Subtractive, or Etch Back process - the entire surface is coated, and then select portions are removed, leaving the desired pattern. The pattern generating step normally involves some form of physical masking agent and then an appropriate type of etching to remove what should be removed and not damage anything else.

2) Additive, or Lift Off process - the pattern generating step, which again will normally involve some sort of physical masking agent, comes first. This is followed by the coating process, which is similar to using a stencil. Only the desired pattern gets applied through the openings in the deposition mask onto the actual substrate. The excess ends up on top of the mask and is removed when the deposition mask is lifted off. This type of Thin Film Deposition Lift Off process will be the subject of this article.

wafer patternedPhysical Vapor Deposition (PVD) is a common class of techniques for applying very pure coatings usually in the thickness of angstroms to microns onto substrates, and includes Thermal Evaporation from a heated source. This paper discusses principles of Advanced Thin Film Deposition thickness and rate control by use of quartz crystal monitoring. In particular it will go beyond the basics into topics including co-deposition and multi crystal systems for PVD by Thermal Evaporation.

Key to understanding the basis of how quartz crystals are used to measure and control the deposition rate is that as the thin film is being deposited on the crystal in real time in the vacuum chamber, the crystal’s oscillation frequency drops as the crystal’s mass increases from the material being deposited on it. To complete the monitoring system, an electronic instrument continuously reads the frequency converting that frequency data to Thin Film Deposition thickness data, both the instantaneous rate and cumulated thickness.

Reactive Sputtering EquipmentSputtering is a common technique for Physical Vapor Deposition (PVD), one of the methods of producing Thin Film Coatings. Standard Sputtering uses a target of whatever pure material is desired, and an inert gas, usually argon. If the material is a single pure chemical element, the atoms simply come off the target in that form and deposit in that form.


However, it is also possible to use a non inert gas such as oxygen or nitrogen either in place of, or (more commonly) in addition to the inert gas (argon). When this is done, the ionized non inert gas can react chemically with the target material vapor cloud and produce a molecular compound which then becomes the deposited film. For example, a silicon target reactively sputtered with oxygen gas can produce a silicon oxide film, or with nitrogen gas can produce a silicon nitride film.

conforcal cathode sputteringAn introduction to the confocal method of magnetron sputtering that allows serial and co-sputtering of materials in the production of thin films.

INTRODUCTION

Confocal sputtering is the technique of arranging magnetrons within a vacuum chamber in such a way that multiple materials can be applied onto the substrate without breaking vacuum.  Confocal sputtering also allows the user to co-sputter, or to create a film of two or more materials at once.  This method is popular for research and development tools and for small scale batch productions.


BENEFITS OF CONFOCAL SPUTTERING

For conventional top down sputtering, only one material will be able to be sputtered at a time.  This is because of the geometric relation that the magnetron has with the substrate.  Generally when sputtering in this way, the target material must be larger than the substrate to yield acceptable film uniformity. 

Thin Film Deposition is a vacuum technology for applying coatings of pure materials to the surface of various objects. The coatings, also called films, are usually in the thickness range of angstroms to microns and can be a single material, or can be multiple materials in a layered structure. This paper discusses the basic principles of thickness and rate control by use of quartz crystal monitoring.

One major class of Physical Vapor Deposition (PVD)  techniques is Thermal Evaporation, which involves heating a solid material inside a high vacuum chamber, and taking it to a temperature which produces some vapor pressure. Commonly used techniques include Electron Beam (E-beam) and Resistive Evaporation. Inside the vacuum. even a relatively low vapor pressure is sufficient to raise a vapor cloud inside the vacuum deposition chamber. This evaporated material condenses on surfaces in the chamber as a coating or "Thin film". This method, including the general type of chamber designs commonly used for it, is an excellent candidate for successful control of rate and thickness through the use of quartz crystals.

sc250 tnOne popular method of Physical Vapor Deposition (PVD) is Sputtering, which has numerous product applications. Whereas commercial Sputter systems are often geared to large scale production volume of established processes, there is also a need for smaller scale sputtering systems for research and development where versatility is generally more important than volume throughput. These same smaller sputtering systems can also serve for lower volume initial production.

This paper will discuss some of the features and capabilities that can be available in smaller Sputter systems geared to low volume work such as research and development, in particular the use of a confocal arrangement of multiple targets around the perimeter of a circular rotating substrate stage, all angled in toward it.

magnetron sputtering in PVD coatingsThe Planar Magnetron is, in essence, a classic "diode" mode sputtering cathode with the addition of a permanent magnet array behind the cathode. This magnet array is arranged so that the magnetic field is normal to the electric field in a closed path and forms a boundary "tunnel" which traps electrons near the surface of the target. This electron trapping improves the efficiency of gas ion formation and constrains the discharge plasma, allowing higher current at lower gas pressure and achieves a higher sputter deposition rate for PVD (Physical Vapor Deposition) coatings.

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