Magnetron sputtering technology is an important technique widely used for material surface modification and thin film deposition. As the core component of this technology, the quality and performance of magnetron sputtering targets directly determine the quality and characteristics of the prepared thin films. This article will provide a comprehensive and in-depth introduction to magnetron sputtering targets.
The requirements for magnetron sputtering targets are higher than those in the traditional materials industry, generally including size, flatness, purity, impurity content, density, N/O/C/S ratio, grain size, and defect control; High or special requirements: surface roughness, resistance value, uniformity of grain size, uniformity of composition and structure, content and size of foreign substances (oxides), magnetic permeability, ultra-high density and ultrafine grains, etc.
Magnetron sputtering target refers to a material that is sputtered with atoms or molecules by high-energy particles during the magnetron sputtering process, and then deposited onto a substrate to form a thin film. It is usually composed of substances with specific chemical compositions and crystal structures, such as metals, alloys, compounds, etc.
Principle of Magnetron Sputtering
Under the action of electric field E, electrons collide with argon atoms during their flight towards the substrate, ionizing and producing Ar positive ions and new electrons; New electrons fly towards the substrate, and Ar ions accelerate towards the cathode target under the action of an electric field, bombarding the target surface with high energy, causing sputtering of the target material.
In sputtered particles, neutral target atoms or molecules deposit on the substrate to form a thin film, and the generated secondary electrons are subjected to electric and magnetic fields, resulting in a directional drift of E (electric field) × B (magnetic field), abbreviated as E × B drift, whose motion trajectory approximates a cycloid. If it is a circular magnetic field, electrons will move in a circular motion on the target surface in an approximate cycloid form. Their motion path is not only long, but also confined in the plasma region near the target surface, and a large amount of Ar is ionized in this region to bombard the target material, thereby achieving a high deposition rate.
As the number of collisions increases, the energy of the secondary electrons is exhausted, gradually moving away from the target surface and ultimately depositing on the substrate under the action of the electric field E. Due to the low energy of the electron, the energy transferred to the substrate is very small, resulting in a lower temperature rise of the substrate.
Magnetron sputtering is a collision process between incident particles and a target. The incident particle undergoes a complex scattering process in the target, collides with the target atom, and transfers some momentum to the target atom. This target atom then collides with other target atoms, forming a cascade process. In this cascade process, certain target atoms near the surface gain sufficient momentum to move outward and are sputtered out of the target.
Magnetron sputtering is generally divided into two types: direct current sputtering and radio frequency sputtering. Among them, direct current sputtering equipment has a simple principle and a fast rate when sputtering metals. The application range of radio frequency sputtering is more extensive. In addition to sputtering conductive materials, non-conductive materials can also be sputtered. At the same time, reactive sputtering is also used to prepare compound materials such as oxides, nitrides, and carbides. If the frequency of the radio frequency is increased, it becomes microwave plasma sputtering, commonly known as electron cyclotron resonance (ECR) microwave plasma sputtering.
Classification of Magnetron Sputtering Target Materials
Metal sputtering coating target, alloy sputtering coating target, ceramic sputtering coating target, boride ceramic sputtering target, carbide ceramic sputtering target, fluoride ceramic sputtering target, nitride ceramic sputtering target, oxide ceramic target, selenide ceramic sputtering target, silicide ceramic sputtering target, sulfide ceramic sputtering target, telluride ceramic sputtering target, other ceramic targets, chromium doped silicon oxide ceramic target (Cr SiO), indium phosphide target (InP), lead arsenide target (PbAs), indium arsenide target (InAs).
Metal target materials have good conductivity and thermal conductivity, and can be used to prepare high-purity and uniform metal thin films, which are widely used in fields such as electronics and semiconductors. For example, in integrated circuit manufacturing, copper targets are used to prepare conductive lines, improving the performance and integration of circuits.
Alloy target materials combine the characteristics of multiple metals and can adjust the composition ratio according to different needs to obtain thin films with specific properties. For example, nickel chromium alloy target materials are commonly used to prepare resistive thin films, meeting the precise requirements of electronic components for resistance values.
Ceramic target materials have important applications in optical coatings, protective coatings, and other fields due to their excellent insulation, wear resistance, and optical properties. For example, titanium oxide ceramic targets can be used to prepare thin films with anti reflection and self-cleaning functions.
1.Metal target materials: including pure metal target materials (such as copper, aluminum, nickel, etc.) and alloy target materials (such as stainless steel, aluminum alloy, etc.).
2. Compound target materials: such as oxide target materials (such as silicon dioxide, aluminum oxide, etc.), nitride target materials (such as silicon nitride, aluminum nitride, etc.), carbide target materials (such as silicon carbide, tungsten carbide, etc.), etc.
3. Semiconductor target materials: such as silicon target materials, germanium target materials, etc.
Classified by target material structure:
1. Flat target material: It has a simple planar structure and is commonly used in conventional magnetron sputtering equipment.
2. Rotating target material: It can achieve continuous rotation, improve the utilization rate of the target material and the uniformity of the deposited film.
Performance requirements for magnetron sputtering targets:
1. Purity: High purity target materials can ensure the purity and performance of deposited thin films. Generally, the purity of the target material is required to be above 99.9%.
2. Density: High density target materials can reduce particle contamination during sputtering and improve the quality and uniformity of thin films.
3. Chemical composition uniformity: The chemical composition of the target material should be evenly distributed to ensure the stability of the deposited film.
4. Crystal structure: A suitable crystal structure helps improve the sputtering efficiency of the target material and the performance of the thin film.
5. Size and shape accuracy: The size and shape of the target material should meet the equipment requirements to ensure good installation and sputtering effect.
6. Thermal stability: During the sputtering process, the target material is subjected to high temperatures and high-energy particles, so it needs to have good thermal stability.
7. Corrosion resistance: The target material should have a certain degree of corrosion resistance to extend its service life.
The deposition rate or film formation rate is an important parameter for measuring the efficiency of magnetron sputtering machines.
There are many factors that affect sedimentation rate, including the type of working gas, the pressure of the working gas, the temperature of the sputtering target, and the magnetic field strength. But today, we will talk about three important factors that affect the deposition rate of magnetron sputtering target coatings: sputtering voltage, current, and power.
Sputtering voltage (V)
The effect of sputtering voltage on film formation rate follows a pattern: the higher the voltage, the faster the sputtering rate, and this effect is gentle and gradual within the energy range required for sputtering deposition. Among the factors affecting the sputtering coefficient, the discharge voltage is indeed important after sputtering the target material and sputtering gas. Generally speaking, in a normal magnetron sputtering process, the higher the discharge voltage, the greater the sputtering coefficient, which means that the incident ions have higher energy. Therefore, atoms in solid target materials are more easily sputtered and deposited on the substrate to form a thin film.
Sputtering current (I)
The sputtering current of a magnetron target is directly proportional to the ion current on the surface of the sputtering target material, and is therefore an important factor affecting the sputtering rate. Magnetron sputtering has a universal rule that the deposition rate is fastest at the optimal pressure (depending on different sputtering targets and sputtering projects). Therefore, it is appropriate to consider the optimal value of gas pressure from the perspective of sputtering yield without affecting the quality of the film and meeting customer requirements. There are two methods to change the sputtering current: changing the working voltage or changing the working gas pressure.
Sputtering power (P)
The effect of sputtering power on deposition rate is similar to sputtering voltage. Generally speaking, increasing the sputtering power of magnetron targets can improve the film formation rate. However, this is not a universal rule. In the case of low sputtering voltage (such as around 200 volts) and high sputtering current of magnetron targets, although the average sputtering power is not low, ions cannot be sputtered or deposited. The prerequisite is that the sputtering voltage applied to the magnetron target material is high enough to ensure that the energy of the working gas ions in the electric field between the cathode and anode is sufficiently greater than the "sputtering energy threshold" of the target material.
High quality magnetron sputtering targets require high purity, high density, uniform microstructure, and good thermal stability. It is crucial to strictly control the purity of raw materials, processing techniques, and quality testing during the preparation process. Advanced production technologies such as powder metallurgy and vacuum melting can effectively improve the performance of target materials.
