154_lecture_6 - 10/24/2011 Lecture-6 Sputtering Yield...

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10/24/2011 1 Lecture-6 Sputtering yield & depth profiles Lee Chow Institute of Electro-Optics Chang Gung University 10/01/2011 Lecture 6 2 Sputtering Yield (Phenomenology) The impact of an atom or ion on a surface produces sputtering from the surface as a result of the momentum transfer from the incoming particle. Both neutral atoms, charged ions and electrons can be emitted into free space. 10/01/2011 Lecture 6 3 Number of atoms(ions) ejected per incident ion: Important factor in sputter deposition processes typically, range 1-30. Primarily depends on three major factors: Target material Mass of the bombarding particles Energy of bombarding particles Sputtering Yield ) 1 ( # # ions incident of particles ejected of Y Low energy (0<E<20-50ev) Too little energy to eject atoms Moderate energy (50ev <E< 1000ev) Known as “knock on sputtering regime” Used for PVD thin film deposition High energy (1Kev <E< 50Kev) Focused Ga + ion beam (10-30 keV) Very high energy ( 50Kev <E) Ion penetrates deep into target Used in ion implantation Sputtering yield depending on energy: 10/01/2011 Lecture 6 5 (a) Energy dependence of the Ar ion sputtering yield of Silicon. (b) Incident ion dependence of the silicon sputtering yield. The solid line represents the theory developed by Sigmund. 10/01/2011 Lecture 6 6 Several possible sputtering mechanisms (a)Sputtering off the surface atoms, (b)Sputtering through a thermal spike, (c)Sputtering through a collision cascade
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10/24/2011 2 10/01/2011 Lecture 6 7 Basic concept of sputtering yield Primary ion penetrates surface, energy lost through collision cascade, primary ion implanted into solid, secondary particles(including ions) leave surface at low energy 10/01/2011 Lecture 6 8 Sputtering yield as a function of primary ion mass 10/01/2011 Lecture 6 9 Sputtering Yield of silicon substrate 10/01/2011 Lecture 6 10 Sputtering yield of different targets as function of angle Calculated using SRIM. 10/01/2011 Lecture 6 11 Sputtering yield of different elements (13<Z<30) Calculated from SRIM. 10/01/2011 Lecture 6 12 For medium mass (20 < Z < 50) and keV energy, the sputtering yield is 0.5 ~ 10. For comparison, the sputtering yield of light ions (H or He) are of the order of 0.001. Therefore, for FIB process, the Ga + ions at 15 keV, sputtering is the most important process of ion-solid interaction, while in RBS, we ignore the sputtering process due to MeV, particles. In general, the sputtering yield is proportional to the number of displaced or recoil atoms, this quantity is proportional to the energy deposited per unit depth; ) 2 ( ) ( o D E F Y where ------ contains material properties F D (E o ) is the density of deposited energy at the surface
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10/24/2011 3 10/01/2011 Lecture 6 13 ) 3 ( ) ( ) ( o n o D E NS E F Where S n ----- nuclear stopping cross-section N ----- number density of the target ------ a correction factor n o n dx dE E NS ) ( and has been discussed before(equation (1) of lecture #4.
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154_lecture_6 - 10/24/2011 Lecture-6 Sputtering Yield...

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