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Ion Implantation Presentation Transcript
2.What shall we study? What is Ion Implantation? I. I. basics Stopping mechanisms Total stopping power I. I. Equipment Comparison with diffusion
3.University Questions Explain in terms of nuclear and electronic stopping the range theory of ion implantation. What is disadvantage of ion implantation, explain the role of RTA for recovering these damages.
4.What is Ion Implantation? I.I. provides an alternative to diffusion as a means for junction formation in semiconductor technology. It is a process by which energetic impurity atoms can be introduced into a single crystal substrate in order to change its electronic properties.
5.Ion Implantation is a random process High energy ions (1 – 1000 keV) bombard the substrate and loose energy through nuclear collisions and electronic drag forces.
6.I. I. Process In the I. I. Process a beam of ions, usually the dopant, having a desired charge-to-mass ratio are accelerated by voltage VA , and allowed to impinge on the target wafer. The wafer surface itself is suitably selectively coated such that the beam energy is sufficient to penetrate the target lattice only in selected regions.
7.Basic requirements of I.I. systems are: Ion Sources Means for their purification extraction acceleration Beam deflection Scanning Substrate holder
8.Ion tracks in the silicon crystal
9.Range Theory for I.I. The range theory covers the physics of ion collisions, its application to calculating range distributions, the effect of crystal lattice, damage and recoil distributions. This includes Ion Stopping Range Distribution Damage Channeling Recoils
11.Damage: The implanted ion displaces an atom of the lattice. The original energy is divided between the two. These two displace other atoms. The chain reaction goes on till the energy is reduced to a level that further displacement can not take place. This is called DAMAGE. This is mainly due to nuclear stopping The number of displaced atoms is N(E)
12.Channeling Effect For ions moving in certain directions, the atom rows or planes lineup so that there are long-range open spaces through which the ions can travel without significant scattering. Ions are steered down these channels by glancing collisions with the atom rows or planes, extending the final ion distribution deeper into the target. This is called channeling effect.
13.Recoils Recoil mixing can be used positively for introducing dopant atoms that can not readily be made into a source for I.I. machines but can be deposited as a thin film onto a silicon substrate. Implanting silicon through the film will push a dopant tail into silicon.
14.Damage caused by one ion
15.Disadvantage of I.I I.I. damages the target I.I. displaces many atoms for each implanted ion The electrical behavior after I.I. is dominated by deep-level electron and hole traps These traps capture carriers and make the resistivity high
16.Anneal The process of heating and then cooling slowly is called annealing. Its purpose is to remove the damage caused by I.I. Annealing is required to repair lattice damage and put dopant atoms on substitutional sites where they will be electrically active.
17.Annealing damage from implantation can be annealed by heating the wafer in a furnace to T > 900oC. Furnace anneal Rapid Thermal Annealing (RTA) Adiabatic RTA – time < 10-7 sec ; only thin surface film is affected. Thermal Flux RTA – time < 10-7 to 1 sec; heating from one side with laser, electron beam or flash lamp Isothermal RTA - > 1 sec, heating from either one side or both the sides