SOURCES OF ASYMMETRY IN IONIZED METAL PVD REACTOR

UNIVERSITY OF ILLINOISOPTICAL AND DISCHARGE PHYSICS

SOURCES OF ASYMMETRYIN IONIZED METAL PVD REACTOR+

AVS98_TITLE

Junqing Lu*, and Mark J. Kushner**

*Department of Mechanical and Industrial Engineering

**Department of Electrical and Computer Engineering

University of Illinois at Urbana-Champaign

November 1998

+Supported by SRC, TAZ, NSF


AGENDA

AVS98_AGENDA

• Introduction to Ionized Metal Physical Vapor Deposition (IMPVD)

• Overview of Hybrid Plasma Equipment Model

• Symmetric excitation

• Asymmetric excitation for two aspect ratios

• Sputtering from two irregular targets

• Concluding remarks


IONIZED METAL PHYSICAL VAPOR DEPOSITION (IMPVD)

GEC98_IMPVD_REACTOR

• In IMPVD, a second plasma source is used to ionize a large fraction of the the sputtered metal atoms prior to reaching the substrate.

• Typical Conditions: • 10-30 mTorr Ar buffer • 100s V bias on target • 100s W - a few kW ICP • 10s V bias on substrate

TARGET(Cathode)

MAGNETS

ANODESHIELDS

PLASMA ION

WAFER

INDUCTIVELYCOUPLEDCOILS

SUBSTRATE

SECONDARYPLASMA

BIAS

e + M > M+ + 2e

NEUTRALTARGET ATOMS

+


IMPVD DEPOSITION PROFILES

GEC98_IMPVD_PROFILE

• In IMPVD, a large fraction of the atoms arriving at the substrate are ionized.

• Applying a bias to the substrate narrows the angular distribution of the metal ions.

• The anisotropic deposition flux enables deep vias and trenches to be uniformly filled.

SiO2

METALATOMS

METALIONS

METAL


ASYMMETRIC EXCITATION IN IONIZED METAL PVD

GEC98_IIMPVD_EXCITE

• IMPVD is an antenna excited system in which transmission-line effects can produce azimuthally asymmetric excitation rates.

• IMPVD differs, to some degree, from conventional etching and deposition systems because the two dominant species, a rare gas and a metal, have markedly different ionization potentials.

• IMPVD systems may also have a “positive feedback” character in that asymmetries in ionization produce asymmetries in metal sputtering rates, which can feed back by generating more low ionization potential atoms.

• In this paper, we will investigate the consequences of asymmetric excitation of IMPVD reactors on ion densities and fluxes in rare gas-metal vapor discharges.

V(Applied)

V(termination)

Coil length

Coil length

Conduction

Capacitive


SCHEMATIC OF 3-D HYBRID PLASMA EQUIPMENT MODEL

HPEM_3D SCHEMATIC

• HPEM-3D combines modules which address different physics or different timescales.

ELECTRONENERGY

EQUATION /BOLTZMANN

MODULE

IONTRANSPORT(CONTINUITY,MOMENTUM)

ELECTRONTRANSPORT

(CONTINUITY)

POISSONSOLUTION

SURFACEKINETICS

Te(r,z,θ),

S(r,z,θ),µ(r,z,θ)

E(r,z,θ)

N(r,z,θ) φ(r,z,θ)P(r,z,θ)

σ(r,z,θ)

CIRCUITMODULE

ELECTRO-MAGNETICS

MODULE

I,VE(r,z,θ)

σ(r,z,θ)

MAGNETO-STATICSMODULE

B(r,z,θ)

AMBIPOLARTRANSPORT/

SHEATH

NEUTRALTRANSPORT(CONTINUITY,MOMENTUM)

LONG MEANFREE PATHSPUTTER

TRANSPORT


DESCRIPTION OF SPUTTERING MODEL

GEC_DESCRIP

• The HPEM has been applied to analysis of IMPVD tools in which sputtered metal atoms are treated using a kinetic Monte Carlo approach.

• Energy of the emitted atoms (E) obeys the cascade distribution, an approximation to Thompson’s law for Einc ≈ 100’s eV:

f(E) ~ EbE/(Eb+E)3

where Eb is the surface binding energy.

• Collisions of the emitted atoms with the gas atoms are tracked, and locations where they slow to thermal speeds are recorded, formulating a Green’s function.

• The transport of thermalized atoms are modeled by fluid equations.

• The above approach generates metal atom sputtering sources in the plasma region, and the metal flux to the wafer.

ion flux

fast neutral flux

θ

ArAl Al

Target

wafer


IMPVD REACTOR

GEC98_REACTOR

• An IMPVD reactor utilizing a Faraday shield and having external coils is examined.

• Process conditions:

• Ar, 10 mTorr, Al Target• 600 W (inductive),

• -100 V target, -20 V substrate• 200 G (at target)

SUBSTRATE (-20 V)

Al TARGET (-100 V)

RING MAGNET

FARADAY SHIELD

QUARTZ

COIL(TYPICAL)

ABOVE WAFER

BELOW TARGET

MID-REACTOR


IMPVD REACTOR-UNIFORM AZIMUTHAL EXCITATION:ELECTRIC FIELD AND ELECTRON TEMPERATURE

GRC98M03

• The “traverses” of the coil from one level to another produce small asymmetries in the electric field, electron temperature and electron source. These asymmetries quickly “diffuse” away with few consequences on ion densities.

MID-REACTOR

BELOWTARGET

ABOVEWAFER

E-MAG

5.6E0

2.8E0

1.4E0

6.8E-1

3.4E-1

1.7E-1

8.3E-2

4.1E-2

2.0E-2

1.0E-2

• Inductive Electric Field (V/cm) • Electron Temperature (eV)

MID-REACTOR

BELOWTARGET

ABOVEWAFER

TE

4.07

3.64

3.21

2.79

2.36

1.93

1.50

1.07

0.64

0.21

• Ar, 10 mTorr, Al target, 600 W, H/R = 0.5


IMPVD REACTOR-UNIFORMAZIMUTHAL EXCITATION:

ION AND Al DENSITIES

GRC98M04

• Al Density (cm-3)

MID-REACTOR

BELOWTARGET

ABOVEWAFER

AL

1.9E11

1.2E11

7.0E10

4.2E10

2.5E10

1.5E10

9.2E9

5.5E9

3.3E9

2.0E9

MID-REACTOR

BELOWTARGET

ABOVEWAFER

AR

3.6E11

2.2E11

1.3E11

8.0E10

4.8E10

2.9E10

1.8E10

1.1E10

6.6E9

4.0E9

MID-REACTOR

BELOWTARGET

ABOVEWAFER

AL

6.0E11

3.7E11

2.3E11

1.4E11

8.6E10

5.3E10

3.3E10

2.0E10

1.2E10

7.6E9

• Ar+ Density (cm-3)

• Al+ Density (cm-3)

• Ar, 10 mTorr, Al target, 600 W, H/R = 0.5


IMPVD REACTOR-ASYMMETRIC EXCITATION:ELECTRIC FIELD AT TWO ASPECT RATIOS

AVS98_E-MAG_ASPE

• The electric field peaks at mid-reactor due to the coil location, and peaks on the right edge of the plasma due to the transmission line effects (Cterm = 100 pF).

• The electric field for H/R = 0.75 below the target and above the wafer is smaller than that for H/R = 0.5 due to skin depth effects.

• Height/Radius = 0.5

ABOVEWAFER

BELOWTARGET

MID-REACTOR

E-MAG

3.2E0

1.3E0

5.3E-1

2.2E-1

8.8E-2

3.6E-2

1.5E-2

6.0E-3

2.5E-3

1.0E-3

BELOWTARGET

MID-REACTOR

ABOVEWAFER

E-MAG

5.6E0

2.8E0

1.4E0

6.8E-1

3.4E-1

1.7E-1

8.3E-2

4.1E-2

2.0E-2

1.0E-2

E-field (V/cm)

• Ar, 10 mTorr, Al target, 600 W

• Height/Radius = 0.75

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SOURCES OF ASYMMETRY IN IONIZED METAL PVD REACTOR

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