梁 gtliang@creating-nanotech.com 奈 年 1
力 狀, 了 量粒, 利, O 2,H 2,CF 4,N 2 離,, 粒,,,,, 2
Gas reaction 3
Plasma reaction E Ea A+B C+D H N 離 E ACT E 4
Introduction to Plasma Principles (Kinetic Energy) gained F d q q (V/d e ) Electron with small volume has large free path than other species in plasma mean free path electric field d e electrode distance V electrode voltage 5
Electron and ion temperatures 6
Elastic and Inelastic Collision 7
Elastic and Inelastic Collision 不 particles 若 particle 量 particle 8
Inelastic collision Excitation Electron Attachment e - +Ar Ar*+e - e-+sf 6 SF - 6 Relaxation e-+sf 6 SF 5- +F Ar* Ar+ hν Ion-neutral collision & Neutral-neutral collision Ionization A+A+ A++A e - +Ar 2e - +Ar + B++C B+C+ hν+ar Ar*+e-, Metastable collision Recombination Ar*+G G + +Ar+e - e-+ar + +M Ar+M e-+ar + Ar+ hν Dissociation e - +O 2 e-+2o e - +CF 4 e-+cf 3 +F (dissociation) e - +CF 4 2e-+CF 3+ +F (dissociative ionization) 9
Plasma ions (positive and /or negative), electron and neutrals. Net total charge is neutral. The degree of ionization is typically only 10-4. In the absence of electric filed, the charge in plasma move around as free particles, similar to conduction electrons in solids. 10
Introduction to plasma principles Plasma Cleaning Principles Two cleaning mechanisms: Chemical reactions by free radicals Physical sputtering by high energy ions 11
Introduction to plasma principles Chemical reactions by free radicals e- + H 2 2H e- + O 2 2O O + O2 O 3 Highly reactive free radicals generated in plasma may react with the hydrocarbon contaminants or surface oxide. Both H and O can react with grease or oil on surface to form volatile hydrocarbons. H (g) + CnH2n+2(s) CH4(g) O (g) + CnH2n+2(s) CO(g) + CHxOy (g) + H2O (g) O is more reactive than H. But O may also react with surface metal to form oxide, deteriorating the material properties. And, H can also reduce metal oxide back to metal. H + MeO Me + H2O O + Me MeO 12
Introduction to plasma principles Chemical reactions by free radicals Advantages: Stable gas products are formed. There is no redeposition problem. High etching selectivity can be obtained. Disadvantages: Higher concentration of H2 or O2 is required to ensure an appropriate etching rate. H2 safety or O2 strong oxidation ability needs to be monitored. Operation: The effect of chemical reactions is increased as the pressure increases. 13
Introduction to plasma principles Physical sputtering by high energy ions Ions generated in plasma can be accelerated toward the substrate to physically bombard away the atoms of contaminants. The physical sputtering rate increases as the plasma density, acceleration voltage or the mass of bombardment atoms increases. Physical sputtering is also enhanced by lowering the pressure to increase the ion energy. Therefore, a high cathode bias will enhance the sputtering rate. H+ or H2+ will have little physical sputtering effect. Ar+ will have strong sputtering effect. 14
Introduction to plasma principles Physical sputtering by high energy ions Advantages: Highly efficient cleaning effect can be achieved. Gas consumption rate can be very low. Disadvantages: Non - selective etching by physical sputtering may induce over etching problems. The products sputtered out may be highly unstable and tend to deposit again downstream, inducing the redeposition problem. Operation: The effect of physical sputtering is increased as the pressure decreases or as the cathode bias and Ar concentration increase. 15
Plasma Cleaning Principles Physical sputter and/or Chemical etching can be chosen 16
Plasma Cleaning Theory 17
IC wire bond 路 sputter IC IC ( ) 18
Plasma Cleaning for Improving Wire Bonding 19
ICP RF DC 20
2.45GHz Electrode-free Down stream plasma Non Uniform Low pressure high density 21
ICP 13.56MHz Electrode-free Uniform Low pressure 22
高周波電漿清潔器 13.56MHz Electrode Uniform High pressure Hollow cathode 23
Low pressure plasma (cold plasma) non-equilibrium system T e T i T n High pressure plasma (thermal plasma):pseudo-equilibrium system T e =T i =T n High Pressure T Ar T Ar Ar* Ar 2 Ar (hot) e Ar Ar 2 Ar (hot) m e 5 5 m i 10 P 10 10 5 10 5 1 24
Arcing 25
(Kinetic Energy) gained q (V/de) In atmospheric pressure, is small V V 便 連 度, 理 度 Plasma jet (spot type) DBD Corona Gliding Arc Plasma torch (thermal plasma) 26
Palsma jet Spot type Small area High efficiency Without ozone Low electro static charge No Arcing Application: for small area or scanning for large issue 27
DBD 狀 度 UV Large area Low efficiency Ozone No Arcing 28
Corona Discharge Spot type 利 度 省 理量 arcing Line type 度 省 理量 arcing 29
Gliding Discharge 30
Plasma Torch 量 流 離率 理量 率 度 31