Sputtering Target Material Selection: Why Titanium Tungsten Targets Shine

Introduction

In the world of thin film deposition, the choice of sputtering target material is crucial. The material you select can significantly impact the quality, performance, and durability of the thin film you're depositing. Regarding specific applications that demand exceptional properties, titanium tungsten (TiW) sputtering targets shine as a top choice. In this article, we'll delve into why TiW targets are the preferred option for certain applications.

Understanding Sputtering Targets

Sputtering is a versatile and widely used thin film deposition technique. It involves bombarding a target material with high-energy ions in a vacuum chamber, causing atoms from the target to be ejected and deposited as a thin film on a substrate. The choice of target material is vital as it directly affects the film's properties, such as composition, thickness, and adhesion.

Why Titanium Tungsten Sputtering Targets?

Film Quality: Titanium tungsten is renowned for producing high-quality films. It offers excellent control over film thickness and composition, making it suitable for applications requiring precise and uniform films.

Adhesion: TiW sputtering targets ensure strong adhesion between the thin film and the substrate. This characteristic is particularly valuable in applications where there are other options than film delamination or peeling.

Chemical Inertness: Titanium tungsten is chemically inert, meaning it doesn't react with many substances. This makes it ideal for applications involving harsh chemical environments.

Temperature Stability: TiW sputtering targets can withstand high-temperature deposition processes, ensuring stability and integrity during film formation. This stability is crucial in various industries, including semiconductor manufacturing and aerospace.

Customizability: TiW sputtering targets are available in various compositions to meet specific application requirements. This customizability allows researchers and manufacturers to fine-tune the properties of the deposited films.

Applications of Titanium Tungsten Sputtering Targets

Now that we've discussed the exceptional properties of TiW targets let's explore where they shine:

Semiconductor Industry: In semiconductor manufacturing, TiW sputtering targets play a pivotal role in depositing thin films for integrated circuits (ICs) and microelectronics. The ability to precisely control film thickness and composition is critical to ensure the performance and reliability of these electronic components.

Optical Coatings: Titanium tungsten is widely used in optical coatings. Whether it's anti-reflective coatings for lenses, mirrors, or optical filters, TiW targets help create films that enhance optical performance.

Aerospace Applications: The aerospace industry relies on TiW sputtering targets for thermal barrier coatings and protective layers. These films help safeguard critical components in extreme conditions, such as those found in jet engines and aerospace structures.

MEMS Devices: Micro-electro-mechanical systems (MEMS) require precise and durable thin films. Titanium tungsten targets are the material of choice for producing these microcomponents found in sensors, accelerometers, and microactuators.

Conclusion

When it comes to thin film deposition, the choice of sputtering target material can make or break your application. For those demanding precise film quality, exceptional adhesion, chemical inertness, temperature stability, and customizability, titanium tungsten sputtering targets emerge as the shining star. Their significance in the semiconductor, optical, aerospace, and MEMS industries is a testament to their exceptional properties. In the quest for high-quality, reliable thin films, TiW targets are a top-tier choice. For more information, please visit https://www.sputtertargets.net/.

Five Sputtering Deposition Power Supplies

Sputter deposition is a physical vapor deposition (PVD) method of thin film deposition by sputtering. This involves spraying material from a "sputter target" as a source onto a "substrate" such as a silicon wafer.

There are mainly five sputtering powder suppliers, as listed below.

Direct Current (DC) Sputtering Power

DC Power is generally used with electrically conductive sputtering materials. It is easy to control and a low-cost option.

Radio Frequency (RF) Sputtering Power

RF Power can be used with all materials, but generally finds most use in depositing films from dielectric target materials. The deposition rate (driven by the relative duty cycle), when compared to DC, is generally quite low and the electron flux (due to the mobility difference of electrons and ions in a plasma) on the substrate is much higher and may cause significant heating. Due to the major cost considerations of RF power supplies, RF deposition is generally limited to smaller substrate sizes.

Pulsed DC Sputtering Power

Pulsed DC (variable frequency) has found broad application in reactive sputtering applications where a positive voltage spike, induced at some frequency on the power waveform can be used to clean the target face and eliminate the buildup of a thick dielectric layer which can be prone to arcing. Frequency ranges from 40 to 200 KHz are typically used. This approach is commonly referred to as unipolar pulsed sputtering. Another option known as bipolar pulsed sputtering uses two pulses, 180 degrees out of phase, that is applied to two adjacent magnetrons in which each magnetron alternates as both a cathode and anode, mitigating the effects of dielectric build-up and greatly reducing the disappearing anode effect. This technique has also found wide industrial use.

Mid-Frequency AC Sputtering Power

MF Sputtering is typically used to deposit non-conductive materials. Two cathodes in a dual configuration are used and the AC current is switched between each cathode allowing the target surface to be cleaned with each reverse of the cycle. This reduces arcing by charge build-up and eliminates the need for anode cleaning which provides long term process stability. MF sputtering is widely used in many inline production systems today.

High Power Impulse Magnetron Sputtering (HIPIMS)

High Power Impulse Magnetron Sputtering is a emerging process which uses a high current pulse to greatly increase the ionization of the sputtering material. These ionized atoms have much higher energies than sputtered atoms in conventional magnetron sputtering and have been found to yield very dense and stable films.
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Will the grain size and crystal orientation affect the quality of the sputtering targets?

Among the sputtering targets of the same composition, the targets having a smaller grain size have a faster deposition rate than those having a larger grain size.

In addition to affecting the sputtering rate, the grain size also affects the quality of the obtained film. If the grain size is too large and the sputtering time is short, the film layer may be poorly densified, resulting in oxidative release of the surface of the coated product.

The grain size has a smaller effect on uniformity. Studies have shown that for the four metal materials of the same material prepared by the same preparation process, changing the grain size from 0.5 to 3.3 mm through different heat treatment times does not change the uniformity of the film layer. Therefore, the grain size has little or no effect on the uniformity of film formation, but the uniformity of grain size can directly affect the uniformity of film formation.

In view of the constant consumption of the sputtering target, in addition to considering the uniformity of the same layer of the target, uniformity in the direction of the thickness of the target should also be considered. The grain size of different cross-sections is required to be as uniform as possible to ensure the uniformity of sputtering at different times.

The image below is a comparison of the microstructure of NiCr sputtering targets from different manufacturers. It can be seen from the photo of the crystal phase that the grain size and uniformity of the target a are better than that of the target b, so that the target a corresponds to a higher quality of the sputtering deposition film.

According to research by Energy Research of Japan, if the grain size of the titanium sputtering target is controlled to be less than 100 lm and the change in grain size is kept within 20%, the quality of the film obtained by sputtering can be greatly improved.

For polycrystals, the crystal grains of the crystal are arranged to some extent along certain special orientations. During the sputtering process of the sputtering target, the target atoms are easily sputtered along the direction in which the atoms are most closely arranged. The crystal orientation of the material has a great influence on the sputtering rate and film thickness uniformity. Therefore, the sputtering rate and film forming quality can be improved by changing the crystal structure of the sputtering target. 

For example, by controlling the processing process of the silicon sputtering target to make the crystal grains have a certain preferred orientation, the film thickness deviation of the film layer can be reduced from 10% to 5%.

Different materials have different crystal structures, so different molding and heat treatment methods should be used to make the target have grain orientation, thereby increasing the film formation rate and film quality of sputtering deposition.

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What is the mechanism of pulsed laser deposition?

Although the equipment of pulsed laser deposition (PLD) system is simple, its working mechanism is related to many complicated physical phenomena. It includes all physical interactions between the laser and the substance when the high-energy pulsed radiation strikes the solid target, the formation of plasma plumes and the transfer of the molten material through the plasma plume to the surface of the heated substrate. Therefore, PLD can generally be divided into the following three stages:

Interaction between laser radiation and the target

In this stage, the laser beam is focused on the surface of the target. When sufficient high energy flux and short pulse width are achieved, all elements of the target surface are rapidly heated to the evaporation temperature. At this point, the material in the target will be sputtered from the target. The instantaneous melting rate of the target is highly dependent on the flow of laser light onto the target. The melting mechanism involves many complex physical phenomena such as collisions, heat, excitation with electrons, delamination, and fluid mechanics.

Dynamics of molten matter

In the second stage, according to the law of aerodynamics, the sputtered particles have a tendency to move toward the substrate. The space thickness varies with the function cosn θ, and n>>1. The area of the laser spot and the temperature of the plasma have an important influence on the uniformity of the deposited film. The distance between the target and the substrate is another factor that affects the angular extent of the molten material. It has also been found that placing a baffle close to the substrate narrows the angular extent.

Deposition of molten material on the substrate

The third stage is the key to determining the quality of the film. The high-energy nuclides emitted hit the surface of the substrate and may cause various damages to the substrate. The high energy nuclide sputters some of the atoms on the surface, and a collision zone is established between the incident stream and the sputtered atoms. The film is formed immediately after the formation of this thermal energy zone (collision zone), which is the best place to condense particles. As long as the condensation rate is higher than the release rate of the sputtered particles, the heat balance condition can be quickly reached, and the film can be formed on the surface of the substrate due to the weakened flow of the molten particles.

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Related: The development of Pulsed Laser Deposition