RF sputtering is a technique that uses radio waves to create thin films. It differs from DC sputtering in voltage, system pressure, sputter deposition pattern, and target material. The process involves running an energy wave through an inert gas to create positive ions that hit the target material and form a coating on the substrate. RF sputtering requires more input power and has different effects on the sputtering system compared to DC sputtering. It is ideal for target materials with insulating qualities.
Radio frequency (RF) sputtering is a technique used to create thin films, such as those found in the computer and semiconductor industries. Like direct current (DC) sputtering, this technique involves running an energy wave through an inert gas to create positive ions. The target material, which will eventually become the thin film coating, is hit by these ions and fragmented into a fine spray that covers the substrate, the inner base of the thin film. RF sputtering differs from DC sputtering in voltage, system pressure, sputter deposition pattern, and ideal type of target material.
During the sputtering process, the target material, substrate and RF electrodes begin in a vacuum chamber. Next, the inert gas, which is usually either argon, neon, or krypton, depending on the size of the target material’s molecules, is directed into the chamber. The RF power source is then turned on, sending radio waves through the plasma to ionize the gas atoms. Once the ions begin to contact the target material, it is broken down into small pieces which travel to the substrate and begin to form a coating.
Because RF sputtering uses radio waves instead of a direct electron current, it has different requirements and effects on the sputtering system. For example, DC systems require between 2,000 and 5,000 volts, while RF systems require up to 1012 volts to achieve the same sputter deposition rate. This is largely because DC systems involve the direct bombardment of gas plasma atoms by electrons, whereas RF systems use energy to strip electrons from the outer electron shells of gas atoms. The creation of radio waves requires more input power to achieve the same effect as a current of electrons. While a common side effect of DC sputtering involves charge buildup on the target material from the high number of ions in the chamber, overheating is the most common problem with RF systems.
As a result of the different power supply method, the inert gas plasma in an RF system can be maintained at a much lower pressure, less than 15 mTorr, compared to the 100 mTorr required to optimize DC sputtering. This allows for fewer collisions between the target material particles and the gas ions, creating a more direct path for the particles to travel to the substrate material. The combination of this reduced pressure, along with the method of using radio waves instead of a direct current for the power source, makes RF sputtering ideal for target materials that have insulating qualities.
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