Repetition: Practical Aspects

Transcription

1 Repetition: Practical Aspects Reduction of the Cathode Dark Space! E x 0 Geometric limit of the extension of a sputter plant. Lowest distance between target and substrate V Cathode (Target/Source) - + d Cathode Fall: Ions will no more be neutralized by electrons. They are subjected to a high electric field and are accelerated towards the target. Anode x

2 Repetition: Technical Modifications Aims: a) Reduction of the cathode dark space b) Increase of the ion current to increase erosion rate c) Reduction of working gas pressure (purity) d) Extension of the material palette (Semicunuctors/Insulators) Methods: RF-sputtering: c/d Triode sputtering: a-c Magnetron sputtering a-c RF-Magnetron: a-d Ion beam sputtering: c; free choice of ion energy

3 Repetition: RF-Sputtering f = 13,56 MHz (free industry frequency) * Higher electron density * Sputtering of insulators possible * Lower working gas pressure * Different plasma characteristics (EEDF, plasma potential)

4 Repetition: Magnetron-Sputtering Permanent magnets below the target concentrate the plasma in the vicinity of the target. * Smaller dark space * Higher ion density * Reduction of working gas pressure

5 Repetition: Target Erosion

6 Repetition: Ion Gun Advantages of the ion gun: 1. Ion source 2. Target 3. Sputtered species 4. Substrate * Control of ion energy * Control of ion impingement angle * No working gas, i. e. UHV-capable

7 Repetition: Sputter-Cleaning Substrat HV Working gas, ionized or neutral Magnetic field assistance (optional) Sputtering can also be used to clean surfaces, if the substrate, which then acts as "target", is biased with negative high voltage.

8 Ion Plating: Fundamentals I Substrate HV (bis ca. 1kV) Optional + + ionization system Source + Ionized filling gas + Source material, ionized or neutral

9 Ion Plating: Fundamentals II Separated ion source 1. Ion probe 2. Substrate holder 3. Shutter 4. Pumps 5. Ion source 6. Evaporator Ions from gas discharge 1. Substrate holder 2. RF-coil 3. RF-generator 4. Evaporator 5. Pumps 6. Gas inlet

10 Ion Plating: Electron Activated Plasma 1. Substrate 2. Ring electrode 3. Differentially pumped region 4. Electron gun 5. Pumps 6. Gas inlet

11 Ion Plating: Hollow Cathode Arc Discharge 1. Substrate holder 2. Cooling water 3. Hollow cathode discharge (longitudinal magnetic field) 4. Pumps 5. Cooled crucible 6. Reactive gas 7. Electron ray

12 Ion Plating: Low Voltage Arc Discharge

13 Ion Plating: Thermionic Arc

14 Ion Plating: Cluster-Beam

15 Pulsed Magnetron Techniques Pulsed Magnetron Sputtering: Ignition of a short term (µs - ms) magnetron discharge with extremly high power density; due to the short duration of the discharge the average power corresponds to that of a conventional magnetron discharge. Disadvantage: only 30% deposition rate when compared to a conventional magnetron. Modulated Pulse Technique: Igniton of a conventional magnetron discharge; Intentionally introduced voltage peak ignites high power discharge which can be sustained for ms to 0.01 s. Advantage: Average deposition rate is equal or even higher when compared to conventional magnetron.

16 PVD-Methods: Power Densities Method Sputtering Evaporation Electron gun Pulsed Magnetron Low Voltage Arc Discharge Arc-Evaporation Power Density [Wcm -2 ]

17 PVD-Methods: Ionization Degrees Method Evaporation Electron Gun Sputtering Low Voltage-Arc Discharge Arc-Evaporation Pulsed Magnetron Ionization Degree [%] <0.1 < >50 bis 100 Reason of Ionization Therm. excitation Therm. excitation Collisions High Power density High Power density Average Power density

18 Ion Bombardement and Film Growth I Ion Bombardement leads to good adhesion small grains dense films high internal stresses

19 Ion Bombardement and Film Growth II Bombardement with externally generated ions: Evaporation Electron gun Sputtering Reason: low ionization degree Bombardement with ions of the coating material: Low Voltage Arc Discharge Arc-Discharge Reason: high ionization degree

20 Ion Bombardement and Film Growth III Advantages of high ionization degrees (ions of coating material): 1. Manipulation of the energy introduction by substrate bias 2. Manipulation of the directionality of the impinging coating particles (collimation in the case of comlexely shaped bodies, all side coating by particles which impinge permanently parallel to the substrate normal, trench-filling)

21 Chemical Vapor Deposition (CVD) Reaction types 1. Chemosynthesis (Reactions with Gases) TiCl 4 (g) + 1/2N 2 (g) + 2H 2 (g) C mbar 2. Pyrolysis (thermal decomposition) SiH 4 (g) <650 C Si(s) + 2H 2 (g) 3. Disproportionation 2GeJ 2 (g) Ge(s) + GeJ 4 (g) 4. Photopolymerization TiN(s) + 4HCl(g)

22 CVD: Typical Plant Schematic

23 Pasma Assisted CVD (PACVD) Reduction of growth temperature

24 PACVD: Reactor Types Parallel plate reactor Multi level chamber

25 Plasma Polymerization: Elementary Processes After monomer introduction the following processes are present within the RF-plasma: 1. Reactions in the gas phase: Formation of reactive species as excited and ionized Molecules and molecule fragments. Formation of free radicals and coagulation to chains and clusters. 2. Species formed in phase 1 are adsorbed at the substrate surface. 3. Polymerization of particles and fragments at the substrate surface.

26 Plasma Polymerization: Reactor Schematic Monomers: Hexamethyldisiloxane (HMDSO), C 6 H 18 OSi 2 Tetraethylorthosilikate (TEOS) Deposited material: mostly SiO 2