Thin film deposition
Thin film deposition technologies are applied in order to coat a substrate surface with a very thin film of material – between a few nanometers up to 5 micrometers.
Thin film deposition procedures are manly categorized into two groups based on the nature of the processes: physical based processes and chemical based processes.
We offer our expertise to help you deciding what process fits you project best based on complex factors - more than one technique can be applied to help you reach your goals.
Physical vapor Deposition
Physical Vapor Deposition (PVD) refers to a wide range of techniques where a material is transferred from a target source and relocated on a substrate using thermodynamic, mechanical or electromechanical processes. The basic mechanism of these methods is altering the phase of the deposited target material from its solid phase to vapor phase and reconverting back to solid phase, this time on the designated substrate. Physical Vapor Deposition usually carried out under vacuum conditions in order to keep the deposited material pure. Generally the formation of thin films by physical vapor deposition consist of three main steps: (1) transformation of the target material into adequate atomic, molecular, or ionic best fit for the specific depositing species and process; (2) transportation of the transformed material from the source trget onto the substrate; (3) Condensation/rearrangement of the depositing species directly on the forming a solid deposited thin film. In the case of atomic scale processes, the solid film is created by condensation of the vapored material onto a substrate and migration to nucleation and growth sites. In order to prevent structural imperfections, the adsorbed atoms require a certain amount of energy to occupy their lowest possible energy configurations.
The most common techniques of physical vapor deposition are thermal evaporation (including e-beam) and sputtering. a material utilizes Plasma gas (mostly Argon) and – Condensation of metal vapor in under vacuum conditions onto a substrate to create thin film.
Thermal evaporation is accomplished by passing a strong current through a coil, crucible or rod containing the target material, resulting in the heating and evaporation of the material. The process usually takes place in chamber, at high vacuum environment, and as the current passing through the material starts to heat the material (as a result of its inherent resistant) the material evaporates. The material can either be heated directly, or by a crucible/boat. Even at relatively low pressure, vapor cloud can be sufficient to raise and create a thin film metal deposition. This means that the substrate needs to be face upside down to the target material. Evaporated vapors can travel without scattering by atoms collision, thanks to the vacuum conditions, which allows a free mean path. The cloud of atoms, condensing on the substrate and forms a deposited thin film.
There are two widely used process/mechanisim of heating the source metal for the Thermal Evaporation process. One is known as Filament 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 focused at the source metal located in a crusible to evaporate it and reach/fill/evaporate/stream 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.
E-beam evaporation process provides us the ability to deliver a larger amount of energy directly into the target crucible, enabling evaporation of high melting temperatures point metal such as gold, titanium and even tungsten. Not commonly used, e-beam evaporation can be also utilized to deposit layers of oxides materials. In short, it is possible to vaporize metals that cannot be deposited by resistive thermal evaporation. In addition, another advantage of e-beam evaporation process is the fact the process is considered sensitive and does not harm the substrate surface, especially when compared to sputtering. E-beam evaporation can yield significantly higher deposition rates than normal thermal evaporation - from 0.1 nm per minute to 100 nm per minute - resulting in higher density film coatings and better layer uniformity. E-beam evaporation process has a much higher material utilization efficiency than other physical vapor deposition methods, resulting in cost reduction. The focused E-Beam only heats the metal source in specific spot while the chilled crucible prevent excess material to be evaporatred, including the crucible itself, thus heat damage to the substrate and contamination are prevented. Multi layers of thin film coating and adhesion materials can be easily performed by using target magazine with a multiple crucible for E-Beam evaporation, removing the need to open the chamber for material replacements and by that breaking the chamber vacuum.
Sputtering process utilizes high energy charged particles in order to create bombardment of the target matter followed by the transportation of material atoms from the target as a direct result of the collision. The ballistic impact caused momentum to pass to the extracted atoms which trevel in straight line toward the substrate, allowing the coating process. The process is carried out under vacuum conditions and argon plasma is being used as the high energy particles for the target material bombardment and extraction of atoms. While argon plasma is frequently used due to its inert properties, reactive sputtering in oxygen gas environment is also available for the use of metal-oxide sputtering.
Magnetron sputtering deposition demands the use of magnetically confined plasma near the surface of a target material. Argon (or any noble gas) plasma is created by applying a strong magnetic field which strips electrons from the argon atom, leaving a positively charged ions. The positively charged argon ions are then accelerated by an electrical field overlying over the negatively charged plate shaped material target.Since the sputtered atoms are not charged and do react with the Ar ions, the are not effected by the electric field. As a result of the strong electric potential applied in the sputtering chamber, a bombardment process of the negatively charged target I taking place, with sufficient momentum to cause the ejection of atoms from the target. These extracted atoms travels in an opposite vactor the bombardment and will be in a cosine distribution. As the sample is positioned directly over the target, the evaporated atoms condense over the substrate, forming a nanometric-level controlled layer. Magnetron sputtering is a highly versatile thin film deposition procedure for creating thin films capable of reaching high deposition rates and high density, high-purity thin layers and can be used with most metal, alloy, or ceramic compound. The magnetron Sputtering systems t can deposit thin films of metals by a DC power supply while insulators targets require radio frequency (RF) power supply to prevent material target charging. 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.
While sputtering is considered easy to use and more conformal coating method, the kinetic energy stored in the material atoms can harm soft materials (such as resists) and can lead to lift-off complications. Yet, since there are no crucibles and less heat is involved compared to thermal Evaporation, sputtering process is a purer and more controllable thin film deposition on the atomic level.
Metals available for coating by e-beam and thermal evaporation are: Pt, Ru, Pd, Au, Ag, Co, Ti, Cu, Al, Ta, Cr, Sn, Fe, Mo, W, In and Ni. Layers up to 50000nm thickness can be achieved.
Substrate maximum size up to 5-inch.
Materials available for sputtering deposition are: Au, Ag, Al, C, Co, Cr, Cu, Fe, In, Nb, Ni, Mo, Pd, Pt, Sn, Ta, Ti, W, AlN, Al2O3, CF2, Cu:Al(96:4), ITO, Ni:Cr(80:20), MgF, SiC, SiO2, SiNx, TaN, Ta2O5, TiN, TiO2, ZnO and more. Layers up to 50000nm thickness can be achieved.
Substrate maximum size up to 6-inch.
Chemical based Deposition
Chemical based coating such as Chemical Vapor Deposition (CVD) and Atomic Layer Deposition (ALD) are coating processes performed by placing a substrate in the presence of one or more volatile precursors, which either react in a chamber or decompose over the substrate surface and produce ultrathin film. Chemical based coatings are commonly used across many field in the industry and can be found in many commercial products. Chemical based deposition are durable, environmental friendly thin film surface and require a small amount of material to cover large samples. Products which combine CVD or ALD during their production process can be found in fields such as machine tools, wear components, electrical components, optical equipment and many other areas demanding high quality thin film. While classic CVD coating is usually performed at extremely high temperatures (800⁰<) using plasma in order to decompose the supplied precursor is can dramatically reduce the heating to less then 100⁰. This process is called Plasma Enhanced Chemical Vapor Deposition (PECVD).
Plasma Enhanced Chemical Vapor Deposition (PECVD) is a single step process in which various materials are gradually deposited as thin films on samples and substrates at significantly lower temperature than that of a classic Chemical Vapor Deposition (CVD) precess.
PECVD deposition is achieved by inserting reactive gases between parallel electrodes—one electrode is grounded and the other electrode is RF-energized. The strong electric field existing between the electrodes induce the reactive gases into a plasma, which causes a chemical reaction and results in the deposited layer, over the substrate, based on the reaction of the gases. The substrate is placed on the grounded electrode and is normally heated to 250°C to 350°C, depending on the requirements of the requested film. Since not all substrates can withstand the minimal 600°C to 800°C of a typical CVD process, PECVD is an excellent option for conformal or anisotropic coating.
The lower deposition temperatures are critical in many applications where CVD temperatures could damage the devices being fabricated.
PECVD is typically used to deposit silicon dioxide (SiO2), silicon nitride (SixNy), silicon oxy-nitride (SiOxNy), silicon carbide (SiC), and amorphous silicon (α-Si). The main gas used in the process is Silane (SiH4), as the source of the silicon atoms, and is combined with oxygen source gas (O2/NO2) to form silicon dioxide/silicon oxy-nitride or a nitrogen gas source (Ammonia) to produce silicon nitride.
Silicon dioxide and silicon nitride are used as insulating (dielectric) materials commonly applied in the fabrication process of transistors in electronic devices in order to isolate different conductive layers, capacitors, and for surface passivation for MOSFET. These films can be also used for encapsulation of metallic devices and protect them against corrosion damages caused moisture and oxygen.
Deposition of Silicon Oxide and Silicon Nitride layers at low growth temperatures
down to 80°C can be performed. SiO2 and SixNy layers up to 500nm thickness.
Substrate maximum size up to 6-inch.
Atomic layer deposition (ALD) is a multistep chemically based technique for depositing a high-quality conformal thin coating films for a wide range of applications. ALD is a step based layer-by-layer process, controlled by the decomposition of the molecules immobilized on the substrate surface by the previous step, resulting in the formation of single films.
Atomic layer deposition (ALD) process involves precursors and reactants at gas phase which flow into the reaction chamber. Each step of the ALD process adds a reaction group over the surface of the substrates and responsible for the addition of a single atom type. An ALD cycle mainly consists of two saturating alternating pulses and is self-terminated as it only forms a single sequential layer each time.
There are usually two chemical precursor, which are introduced via inert high purity nitrogen gas to the reaction chamber one at a time. Each precursor saturates the volume of the ALD reaction chamber, creating a monolayer of material over the substrate surface, while releasing the reactive group responsible for the bonding. The excess gasses are then vacuumed by nitrogen purge, followed by repeatable cycle.
The successive, surface reactions enables the controlled self-limiting growth of the desired material. The ALD extraordinary self-limiting growth process results in exceptional uniformity, 3D complex conformity, even when applied over nano-size pores, and atomic level thickness.
ALD reaction chamber is operation temperature is in the range of 50°C to 400°C and many coating recipes can be performed between 50°C-200°C which allowing use of photolithographic lift-off procedures. ALD processes can create metal-oxides, nitrides, carbides, fluorides, certain metals, II–VI and III–V compounds.
Deposition of various metal-oxide layers of great uniformity and conformity can be performed on flat, as well as on 3D curved, substrates. Deposition is done at the temperature range of 50°C-250°C, allowing thus the use of photolithographic lift-off procedures. Ultrathin films down to 1 nm and up to100-200nm can be achieved with great uniformity.
Metal Oxides such as ZrO, HfO (high K dielectrics) ZnO, Al2O3, TiO2 and more are available.
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