MT2-Review - Midterm 2 Review Sputtering In sputtering, the...

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Midterm 2 Review
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Sputtering In sputtering, the target material and the substrate is placed in a vacuum chamber. A voltage is applied between them so that the target is the cathode and the substrate is attached to the anode. A plasma is created by ionizing a sputtering gas (generally a chemically inert, heavy gas like Argon). The sputtering gas bombards the target and sputters off the material we’d like to deposit. -V Target (cathode) Substrates Anode Sputtering gas Plasma
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Generating and Controlling the Plasma Ions can be generated by the collision of neutral atoms with high energy electrons. The interaction of the ions and the target are determined by the velocity and energy of the ions. Since ions are charged particles, electric and magnetic fields can control these parameters. The process begins with a stray electron near the cathode is accelerated towards the anode and collides with a neutral gas atom converting it to a positively charged ion. The process results in two electrons which can then collide with other gas atoms and ionize them creating a cascading process until the gas breaks down. The breakdown voltage depends on the pressure in the chamber and the distance between the anode and the cathode. At too low pressures, there aren’t enough collisions between atoms and electrons to sustain a plasma. At too high pressures, there so many collisions that electrons do not have enough time to gather energy between collisions to be able to ionize the atoms. ±² ² ±o ± AeAe 2 V B Pd
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How Ions Sputter Atoms When ions collide with surface atoms on the target, the energy transfer can knock some of these atoms off the surface. The key principle is energy and momentum conservation. In any collision, momentum is conserved. If the collision is elastic, kinetic energy is also conserved. The energies required for sputtering are much higher than lattice bonding or vibrational energies (which are the causes of inelastic interactions), therefore sputtering collisions can be considered elastic.
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Various Sputtering Regimes Single Knock-On The initial ion-surface collision sets target atoms in motion. If enough energy is transferred, binding forces can be overcome. Typical threshold energies are in the 10 - 30 eV range. Linear Collision Cascade At higher ion energies (100 eV - 10 keV) recoil is minimal and a cascading effect produces sputtering.
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Sputter Yield S depends on type of target atom binding energy of target atoms relative mass of ions and atoms incident ion energy angle of incidence of ions S can range from 0.1 to 10 ions incident of Number atoms sputtered of Number S T ions S T 90 0 60-70 S E (eV) ~1000
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Deposition Sputtered atoms from the target make their way on to the substrate through diffusion.
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MT2-Review - Midterm 2 Review Sputtering In sputtering, the...

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