SPUTTERING is a widely used and highly versatile vacuum coating system used for the deposition of a variety of coating materials. Plasma at higher pressure is used to “knock “metal atoms out of a “target”. These energetic atoms deposit on a wafer located near the target. The higher pressure produces better step coverage due to more random angled delivery. The excess energy of the ions also aids in increasing the surface mobility (movement of atoms on the surface). First discovered in 1852, and developed as a thin film deposition technique by Langmuir in 1920.
Magnetron sputtering is a versatile technique extensively used for the deposition of a wide range of materials such as insulators, metals, semiconductors. One or more magnetron cathodes of several sizes can be used in a system for deposition of multi layers of different materials or for code position. Both RF and DC generators are available for plasma excitation depending upon the application. The system is normally equipped with a turbo molecular pump of suitable pumping speed to evacuate the chamber to the high vacuum or ultra-high vacuum range.
A sputtering chamber can be readily integrated as one of the process chambers of a multi chamber system.
Application of Sputtering System
Mainly Sputtering System is used for the deposition of various films on the different metal, semiconductor and insulator substrate. Except of the deposition there are few more applications of the sputtering system, as discussed below…
- Film Deposition- Sputtered atoms are ejected into the gas phase but are not in their thermodynamic equilibrium state, and tend to deposit on all surfaces in the vacuum chamber. A substrate (such as a wafer) placed in the chamber will be coated with a thin film. Sputtering deposition usually uses argon plasma because argon, a noble gas, will not react with the target material.
- Etching- In the semiconductor industry sputtering is used to etch the target. Sputter etching is chosen in cases where a high degree of etching anisotropy is needed and selectivity is not a concern. One major drawback of this technique is wafer damage.
- For Analysis- Another application of sputtering is to etch away the target material. One such example occurs in secondary ion mass spectrometry (SIMS), where the target sample is sputtered at a constant rate. As the target is sputtered, the concentration and identity of sputtered atoms are measured using mass spectrometry. In this way the composition of the target material can be determined and even extremely low concentrations (20 μg/kg) of impurities detected. Furthermore, because the sputtering continually etches deeper into the sample, concentration profiles as a function of depth can be measured.
- In Space- Sputtering is one of the forms of space weathering, a process that changes the physical and chemical properties of airless bodies, such as asteroids and the Moon. On icy moons, especially Europa, sputtering of photolysis water from the surface leads to net loss of hydrogen and accumulation of oxygen-rich materials that may be important for life. Sputtering is also one of the possible ways that Mars has lost most of its atmosphere and that Mercury continually replenishes its tenuous surface-bounded exosphere.
Advantages of Sputtering System
- Use large-area-targets which give uniform thickness over the wafer.
- Control the thickness by Deposition time and other parameters.
- Even materials with very high melting points are easily sputtered.
- Sputtered films typically have a better adhesion on the substrate.
- Sputtering can be performed top-down.