1 Etching Part 2 Chapter : 16 Semiconductor Manufacturing Technology by M. Quirk & J. Serda Spring Semester 2014 Saroj Kumar Patra, Norwegian University of Science and Technology ( NTNU )
2 Introduction Plasma dry etch reactors Barrel plasma etcher Parallel plate etcher Downstream etcher Triode planar reactor Ion beam milling Reactive ion etch High-density plasma etchers F 2 SiO 2 Cl, F 2 Al Br 2, Cl, F 2 Si Photoresist O 2 Requirements Reaction chamber RF Gas Vacuum
3 Barrel reactor RF electrode Wafers Gas in Reaction chamber Wafers RF generato r Quartz boat Vacuum pump 0.1-1torr Almost purely chemical process Isotropic etching High selectivity Wafers parallell to E-field Minimal plasma-induced damage Typically used for photoresist stripping with O 2
4 Parralel plate (planar) reactor 0.1-1 Torr Direct contact with plasma/energetic ions High-energy ion bombardment Early reactor
5 Downstream etch systems Microwave energy Microwave source 2.45 GHz Plasma chamber Diffuser Wafer chuck 0.1-1 Torr Plasma in separate chamber Transfered to reaction chamber Uniformly distribution of plasma on surface Chemical etching Isotropic 2.45 GHz source Heat lamp To vacuum system
6 Triode planar reactor
7 Ion beam milling Electromagnet improves ionization Screen grid _ Accelerating grid Neutralizing filament Plasma chamber (anode repels ions) Hot filament emits electrons Gas inlet (Argon) To vacuum system Wafer can be tilted to control etch profile
8 Reactive ion etch (RIE) Grounded electrode (anode) Ar (physical etch t) F (chemical etch) Wafer Powered electrode (cathode) RF generator
9 High-density plasma etchers Predominant dry etching methodology. Difference from standard plasma etching: Better for small geometries (>0.25µm) Lower pressure (1-10 mtorr) Higher degree of ionization (10%) Electron Cyclotron Resonance (ECR) Inductively-Coupled Plasma (ICP) Dual Plasma Source (DPS) Magnetically Enhanced Reactive Ion Etch (MERIE)
10 Electron cyclotron resonance (ECR) Introduced in early 1980s Microwave excitation Magnetic field parallel to reactant flow Electron cyclotron resonance Both physical and chemical etch
11 Inductively-coupled plasma (ICP) Simple reactor that is widely used in the US. Plasma is generated from a spiral coil separated by a dielectric window/quartz tube Both physical and chemical etch RF generator Inductive coil Plasma chamber Dielectric window/ quartz tube Electromagnet Biased wafer chuck Bias RF generator
12 Dual plasma source (DPS) RF power applied to both coil (source) and wafer electrode (bias) Lower chamber is clean Upper chamber exposed to process gasses. Key aspect, decoupling of the source plasma power from the bias. Decoupled plasma chamber Wafer Inductivelycoupled RF generator (source power) Turbo pump Cathode Lower chamber Capacitivelycoupled RF generator (bias power)
13 Magnetically enhanced RIE (MERIE) Similar to reactive ion etch (RIE) Magnetic field holds plasma away for chamber walls. Increase in plasma density Electromagnet (1 of 4) Wafer Biased wafer chuck 13.56 MHz
14 Etch system review Configurations Activity Pressure (Torr) Barrel Reactive 10-1 to 1 Arrangement Coil or electrodes outside vessel High Density Plasma Parallel Plate (Plasma) Reactive 10-1 to 1 Planar diode (two electrodes) No Downstream Plasma Reactive 10-1 to 1 Coil or electrodes outside vessel Triode Planar Reactive 10-3 Triode (three electrodes) No Ion Beam Milling Inert 10-4 Planar triode No Reactive Ion Etch (RIE) Electron Cyclotron Resonance (ECR) Biasing Bias Source Profile No In cassette (bulk) RF Isotropic No On powered electrode (anode) In cassette (bulk) downstream of plasma On platform electrode On powered electrode (anode) RF RF or Microwave Anisotropic Isotropic Anisotropic Anisotropic Reactive < 0.1 Planar or cylindrical diode No On cathode Anisotropic Reactive 10-4 to 10-3 (low) Distributed ECR Reactive (low) Inductively Coupled Plasma (ICP) Reactive (low) Helicon Wave Reactive (low) Dual Plasma Source Reactive (low) Magnetically Enhanced RIE (MERIE) Reactive (low) Magnetic field in parallel with plasma flow Magnets distributed around central plasma Spiral coil separated from plasma by dielectric plate Plasma generated by electromagnets and plasma density maintained at wafer by magnetic field Independent plasma and wafer biasing Planar diode with magnetic field confining plasma Yes On cathode RF or DC Anisotropic Yes On cathode RF or DC Anisotropic Yes On cathode RF or DC Anisotropic Yes On cathode RF or DC Anisotropic Yes On cathode RF or DC Anisotropic Yes On cathode RF or DC Anisotropic
15 Endpoint detection Etch Parameter Normal etch Endpoint detection Change in etch rate - detection occurs here. Endpoint signal stops the etch. Material Etchant Gas Emitting Species of some Products CF 4 /O 2 SiF 440; 777 Silicon Cl 2 SiCl 287 SiO 2 CHF 3 CO 484 Aluminum Photoresist Nitrogen (indicating chamber vacuum leak) Cl 2 BCl 3 O 2 Al AlCl CO OH H N 2 NO Wavelength (nm) 391; 394; 396 261 484 309 656 337 248 Time
16 Vacuum for etch chambers Critical for the plasma parameters Has a set of predefined specifications High removal rate May require special designs
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