The two giants of the thin film world: An analysis of the core differences between magnetron sputtering and ion plating

The essence of magnetron sputtering is the "collaborative effect of high-energy ion bombardment + magnetic field constraint". Its working principle can be summarized into three key steps: Firstly, inert argon gas is introduced into the vacuum chamber, and plasma is formed through an electric field excitation; then argon ions are accelerated by the electric field and bombard the surface of the target material, "sputtering" the target material atoms away; the most crucial point is that the magnetic field behind the target will bind electrons near the target surface to perform a spiral motion, significantly improving the ionization efficiency of argon gas, and ultimately allowing the sputtered target material atoms to uniformly deposit on the substrate surface to form a film. This "electric field acceleration + magnetic field constraint" design solves the pain points of slow production rate and high substrate temperature in traditional sputtering, becoming the core technology for industrial mass production.

Ion plating is a composite process of "evaporation / sputtering + ionization + electric field acceleration", known as the "combination of vacuum evaporation and sputtering". Its core process is: first, the target material forms gas particles through evaporation or sputtering, then these particles are ionized by glow discharge to high-energy ions; subsequently, under the action of a strong electric field, these ions are accelerated towards the substrate, not only cleaning the impurities on the substrate surface, but also forming a strong bond with the substrate with high kinetic energy. This ionization deposition method enables a leap in the bond strength between the film layer and the substrate.

Adhesion is the core indicator for measuring the durability of the film layer. Experimental data shows that the adhesion of magnetron sputtered film layers is usually between 3-10N/cm, while ion plating can reach 5-15N/cm, and some hard coatings even higher. For example, in the test of aluminum film deposition on glass substrates, the adhesion of ion plating reaches 12N/cm, which is more than 5 times that of traditional evaporation. Even after repeated friction, it does not fall off easily. This advantage stems from the sputtering effect of ions on the substrate, which can form a 1-5nm mixed transition layer, achieving "atomic-level bonding" between the film layer and the substrate.

Deposition rate directly affects production efficiency. The metal film deposition rate of magnetron sputtering is 10-100nm/min, and that of compound films is 5-30nm/min; while the rate of ion plating is generally slower, only 5-50nm/min. For example, in the case of ITO film used in display screens, magnetron sputtering can complete a 200nm thick coating in 1 hour, while ion plating requires 2-3 hours. This is because the ionization process consumes part of the energy, resulting in a reduction in the number of effectively deposited particles.

In large-scale coating scenarios, the uniformity advantage of magnetron sputtering is particularly obvious. With the help of "planetary turntable" and "multi-target symmetrical layout", magnetron sputtering can control the film thickness deviation of large-area substrates within ±1%-5%, while the uniformity of ion plating is usually ±3%-7%. The production data of a display panel manufacturer shows that for the 6th-generation line with a glass substrate (1500mm * 1800mm), the ITO film is deposited by magnetron sputtering, with the thickness uniformity reaching within ±1%. The yield of continuous production of 500 pieces is as high as 97%, far exceeding the 85% of ion sputtering.

Base temperature is a key parameter determining the adaptability of the process. Magnetron sputtering reduces the direct bombardment of ions on the substrate through magnetic field confinement, and the base temperature can be controlled within room temperature to 300℃, and some processes can even maintain room temperature; while ion sputtering due to ion bombardment generates heat, the base temperature is generally in the range of 150-500℃. This difference enables magnetron sputtering to adapt to heat-sensitive materials such as PET flexible films and MEMS devices - when depositing Au electrodes on a 2μm thick MEMS cantilever, magnetron sputtering only raises the base temperature to 80℃, and the deflection of the cantilever changes by only 0.1μm; while the 350℃ high temperature of ion sputtering will cause the cantilever to directly bend and fail.

Magnetron sputtering supports various modes such as co-sputtering and reactive sputtering, and can prepare various types of films, including ITO transparent conductive films, TiN hard films, etc., and complex materials such as ITO and TiN. Ion sputtering is more proficient in preparing metal and ceramic hard coatings, such as TiAlN and CrN, and has limitations in the coating of organic materials and low-melting-point alloys. For example, when coating Cu film on the flexible circuit board of the mobile phone screen, magnetron sputtering can be completed at 60℃, and the cantilever deflection changes by only 0.1μm; while the high temperature of 350℃ of ion sputtering will cause the PET film to shrink and deform, and is not applicable.

The greatest advantage of magnetron sputtering lies in its stable production and low-temperature adaptability. Its closed-loop control system can monitor parameters such as film thickness and gas composition in real time, with a film thickness error controlled within ±0.1nm, and the yield can still maintain over 99% for 30 consecutive days of continuous operation. At the same time, the target utilization rate can reach 60%-80%, saving 20% more material costs than traditional sputtering. However, this technology also has limitations: poor filling hole performance and weak step coverage ability, and it is not as uniform as ion sputtering on complex curved surfaces; and the equipment structure is complex, with a higher initial investment cost.

The outstanding feature of ion sputtering is its super strong adhesion and surface adaptability. The ion bombardment effect allows the film layer to penetrate into the tiny pores of the substrate, even if the substrate shape is complex (such as the cutting edge of a knife or the mold cavity), it can achieve uniform coverage. In the wear resistance test, the TiN coating (2μm thick) of ion sputtering (2μm thick) under a 1kg load friction for 100,000 times has a wear amount of only 0.2μm, which is half of that of the similar coating of magnetron sputtering. However, the shortcomings of ion sputtering are also very obvious: slow deposition rate resulting in low production efficiency, high temperature prone to damage sensitive substrates, and complex process parameter control, with a higher risk of gas impurity introduction than magnetron sputtering.

Due to its large-area uniformity and low-temperature deposition advantages, magnetron sputtering is widely used in electronics, optics, and new energy fields:

• Electronic industry: ITO transparent conductive films for display screens, hard disk magnetic head electrodes, Cu films for flexible circuit boards;
• Optical industry: Anti-reflection films for eyeglass lenses, anti-reflective films for mobile phone glass covers;
• New energy industry: Aluminum backfield for solar cells, coating for battery electrode tabs. The mass production case of a certain hard disk manufacturer shows that the Ni-Fe alloy film (20nm thick) prepared by magnetron sputtering, with the component deviation controlled within ±0.5%, meets the high-precision requirements of the magnetic head.

The super strong adhesion of ion plating makes it the preferred choice for hard coatings and complex workpiece plating:

• Machining: TiN, TiAlN ultra-hard coatings for cutting tools and molds, can extend the service life by 3-10 times;
• Decoration industry: Wear-resistant decorative films for bathroom hardware and high-end watches, combining beauty and durability;
• Aerospace: High-temperature protective coatings for engine blades and gears, capable of withstanding temperatures above 800℃.

In the automotive mold field, the TiAlN coating of ion plating has a hardness of 3200HV, allowing the mold to continuously stamp 100,000 times or more without obvious wear.