etching – part 2 - folk.ntnu.nofolk.ntnu.no/jonathrg/fag/tfe4180/slides/ch16 etching (part...

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TFE4180 Semiconductor Manufacturing TechnologyTFE4180 Semiconductor Manufacturing Technology

Etching – Part 2Chapter : 16 Semiconductor Manufacturing Technology by M. Quirk & J. Serda

Spring Semester 2014

Saroj Kumar PatraTFE4180 Semiconductor Manufacturing Technology,

Norwegian University of Science and Technology ( NTNU )

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TFE4180 Semiconductor Manufacturing Technology

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

• Requirements• Reaction chamber• RF• Gas• Vacuum

F2 SiO2

Cl, F2 AlBr2, Cl, F2 SiO2 Photoresist

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Barrel reactor

• 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 O2

Vacuum pump

Gas in

RF electrode

RFgenerator

Wafers

Quartz boat

WafersReaction chamber

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Parralel plate (planar) reactor

• 0.1-1 Torr• Direct contact with plasma/energetic ions• High-energy ion bombardment• Early reactor

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Downstream etch systems

• 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

Plasma chamberDiffuser

Wafer chuck

Heat lampTo vacuum system

Microwave energy Microwave source 2.45 GHz

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Triode planar reactor

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Ion beam milling

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Hot filament emits electrons

Gas inlet(Argon)

To vacuum system

Neutralizing filamentAccelerating gridScreen grid

Electromagnet improves ionization

Plasma chamber(+anode repels +ions)

Wafer can be tilted to control etch profile

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Reactive ion etch (RIE)

RF generator

Wafer

Powered electrode(cathode)

Grounded electrode

(anode)

Ar+

(physical etch t)F

(chemical etch)

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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)

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Electron cyclotron resonance (ECR)• Introduced in early 1980s• Microwave excitation• Magnetic field parallel to reactant flow• Electron cyclotron resonance• Both physical and chemical etch

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Inductively-coupled plasma (ICP)

Electromagnet

Dielectric window/ quartz tube

Inductive coil

Biased wafer chuck

RF generator

Bias RF generator

Plasma chamberPlasma

chamber

• 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

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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

Decoupled plasma chamber

Turbo pump

Lower chamber

Cathode

Wafer

Capacitively-coupled RF generator (bias power)

Inductively-coupled RF generator (source power)

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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)

13.56 MHz

Biased wafer chuck

WaferWafer

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Etch system reviewConfigurations Activity Pressure

(Torr) Arrangement High

Density Plasma

Biasing Bias Source Profile

Barrel Reactive 10-1 to 1 Coil or electrodes outside vessel No In cassette (bulk) RF Isotropic

Parallel Plate (Plasma) Reactive 10-1 to 1 Planar diode (two electrodes) No On powered electrode (anode) RF Anisotropic

Downstream Plasma Reactive 10-1 to 1 Coil or electrodes outside vessel No

In cassette (bulk) downstream of plasma

RF or Microwave Isotropic

Triode Planar Reactive 10-3 Triode (three electrodes) No On platform electrode Anisotropic

Ion Beam Milling Inert 10-4 Planar triode No On powered electrode (anode) Anisotropic

Reactive Ion Etch (RIE) Reactive < 0.1 Planar or cylindrical diode No On cathode Anisotropic

Electron Cyclotron Resonance (ECR) Reactive

10-4 to 10-

3 (low)

Magnetic field in parallel with plasma flow Yes On cathode RF or DC Anisotropic

Distributed ECR Reactive (low) Magnets distributed around central plasma Yes On cathode RF or DC Anisotropic

Inductively Coupled Plasma (ICP) Reactive (low) Spiral coil separated from

plasma by dielectric plate Yes On cathode RF or DC Anisotropic

Helicon Wave Reactive (low)

Plasma generated by electromagnets and plasma density maintained at wafer by magnetic field

Yes On cathode RF or DC Anisotropic

Dual Plasma Source Reactive (low) Independent plasma and wafer biasing Yes On cathode RF or DC Anisotropic

Magnetically Enhanced RIE (MERIE)

Reactive (low) Planar diode with magnetic field confining plasma Yes On cathode RF or DC Anisotropic

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Endpoint detectionEndpoint detectionNormal etch Change in etch

rate - detection occurs here.

Endpoint signal stops the etch.

Time

Etch

Par

amet

er

Material Etchant Gas Emitting Species of some Products Wavelength (nm)

Silicon CF4/O2 Cl2

SiF SiCl

440; 777 287

SiO2 CHF3 CO 484

Aluminum Cl2 BCl3

Al AlCl

391; 394; 396 261

Photoresist O2 CO

OH H

484 309 656

Nitrogen (indicating chamber vacuum leak)

N2

NO 337 248

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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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etching – part 2 - folk.ntnu.nofolk.ntnu.no/jonathrg/fag/tfe4180/slides/ch16 etching (part...

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