Views: 0 Author: Site Editor Publish Time: 2023-05-26 Origin: Site
Sputtering is a phenomenon in which microscopic particles of a solid material are ejected from its surface after the material itself has been bombarded by energetic particles of a plasma or gas.It occurs naturally in outer space and can be an unwelcome source of wear in precision components.However, the fact that it can act on extremely fine material layers is exploited in science and industry - where it is used to perform precise etching, perform analytical techniques, and deposit thin-film layers in the manufacture of optical coatings, semiconductor devices and nanotechnology products.It is a physical vapor deposition technique.When energetic ions collide with atoms of a target material, a momentum exchange occurs between them.These ions are called "event ions" and initiate a collision cascade in the target.This cascade can take multiple paths; some recoil to the target surface.If the collision cascade reaches the target surface with a residual energy greater than the target's surface binding energy, an atom is ejected.This process is called "sputtering".If the target is thin (on the atomic scale), the collision cascade can reach its backside; atoms ejected in this way are said to escape surface binding energy "in transport".
The average number of atoms ejected from the target per incident ion is called the "sputter yield".The sputtering yield depends on several factors: the angle at which the ions collide with the material surface, the energy with which they strike the material, their mass, the mass of the target atoms, and the surface binding energy of the target.If the target has a crystalline structure, the orientation of its axes relative to the surface is an important factor.The ions that cause sputtering come from a variety of sources they can come from plasmas, specially constructed ion sources, particle accelerators, outer space (such as the solar wind) or radioactive substances (such as alpha radiation).Thompson's analytical model is a model describing sputtering in cascaded regions of amorphous planar targets.An algorithm for simulating sputtering based on quantum mechanical processing including energetic electron stripping is implemented in the program TRIM.
Another mechanism of physical sputtering is called "thermal spike sputtering".This happens when the solid is dense enough and the incoming ions are heavy enough that the collisions happen in very close proximity to each other.In this case, the binary collision approximation is no longer valid, and the collision process should be understood as a many-body process.The intense collisions cause a heat spike (also known as a heat spike), which actually melts a small portion of the crystal.If the part is close enough to its surface, large numbers of atoms may be ejected due to liquid flow towards the surface and/or micro-explosions.Thermal spike sputtering is most important for the bombardment of dense but soft metals (Ag, Au, Pb, etc.) with low melting points by heavy ions (such as Xe or Au or cluster ions) with energies in the keV–MeV range.Thermal spike sputtering typically increases non-linearly with energy and can result in sputter yields on the order of 10,000 per cluster for small cluster ions.For an animation of such a process, see "Re: Displacement Cascade 1" in the External Links section.
Physical sputtering has a well-defined minimum energy threshold equal to or greater than the ion energy at which the maximum energy transfer from the ion to the target atom is equal to the binding energy of the surface atoms.That is, it can only happen if the ion is able to transfer more energy into the target than is needed for the atom to detach from its surface.This threshold is usually in the range of ten to one hundred eV.Preferential sputtering can occur initially when a multicomponent solid target is bombarded and there is no solid-state diffusion.If the energy transfer to one of the target components is more efficient, or if it binds to the solid less strongly, it will sputter more efficiently than the other.If component A is preferentially sputtered in AB alloys, the solid surface will be enriched in component B during long bombardment, increasing the probability of B being sputtered, so that the composition of the sputtered material will eventually return to AB.
The term electron sputtering can denote sputtering caused by energetic electrons (such as in a transmission electron microscope), or sputtering due to the loss of energy from very high energy or highly charged heavy ions to a solid, mainly by stopping the power of the electrons, where Electron excitation causes sputtering.Electron sputtering produces high sputtering rates from insulators because the electron excitations that cause sputtering are not immediately extinguished as they are in conductors.An example of this is Jupiter's snow-covered moon Europa, where MeV sulfur ions in Jupiter's magnetosphere can eject as many as 10,000 H2O molecules.
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