Time-resolved plasma characterization in modulated pulse ...zpulser.com/assets/2012/01/AN-Cloud-et-al-AVS-2009.pdf•Quartz crystal microbalance •Used to determine deposition rate

AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California

a Department of Materials Science and Engineeringb Department of Nuclear, Plasma, and Radiological Engineering

Contact: [email protected]

Time-resolved plasma characterization in modulated pulse plasma (MPP)

magnetron sputtering

A.N. Clouda, R.E. Flautab, M.J. Neumannb, S.L. Rohdeb, and D.N. Ruzicb

mailto:[email protected]


Overview

• Introduction and motivation

• Experimental apparatus and diagnostics

• Vacuum system and magnetron

• Triple Langmuir probe

• Gridded energy analyzer (GEA)

• Quartz crystal microbalance (QCM)

• Results

• Time-resolved electron temperature and density

• Growth rate dependence on plateau current and repetition rate

• Time-resolved ion current at the substrate level

• Conclusions

2


Introduction and motivation

3


Modulated Pulse Plasma (MPP)

• Relatively new method of applying the basic principles of HPPMS / HIPIMS

• Allows the generation of an arbitrary voltage waveform

• Most studies of discharges produced by this technology have been inherently time-averaged.• Time-averaged plasma diagnostics• Film properties

• In order to intelligently apply this technology and create improvement, the underlying physics must be understood.

• We are conducting time-resolved diagnostics of this interesting type of discharge.

4


Multi-step power delivery of MPP

• Step 1 – Ignition• Step 2 – Low power (DC-like) discharge• Step 3 – Current ramp• Step 4 – High power discharge

5

Voltage

Current

Power


Experimental apparatus and diagnostics

6


Magnetron sputtering tool 7

MRC Galaxy

• Planar circular rotating magnetron

• Designed for 20kW DC sputtering

14” (36 cm) diameter sputtering

targets

• 1000 cm2

• <150 W/cm2 power density


Triple probe theory and setup8

From T.K. Gray

• Probe 2 is allowed to float in the plasma.

• Probes 1 and 3 are biased using a floating voltage source.

Probe 1 is held above floating potential while probe 3 is held

below Vf. While ΔV13 remains constant, the exact values for V1

and V3 are dependant on the need to satisfy Kirchhoff’s current

law.

• Determining electron temperature (t):

• To determine the electron density (t), the following

relation is solved for ne:

•Assumptions:

• Maxwellian electron energy distribution function

• Collisionless thin sheath

• No interaction between probe tips

From S. Chen and T. Sekiguchi.

Instantaneous direct-display system of

plasma parameters by means of triple probe.

J. Appl. Phys., 26(8):2363{2375, 1965.

Probe tips


Gridded energy analyzer

• Gridded Energy Analyzer

• Custom built at CPMI

• Can be used as an ion collector and ion energy discriminator

• Schematic:

• Quartz crystal microbalance

• Used to determine deposition rate

• Also can be used in conjunction with the GEA to determine ionization fraction

• Previous work at CPMI has shown ~6% metal ionization at the substrate level in this sputtering tool.

9

Range of voltage to measure energy


Results

10


0.00E+00

5.00E+10

1.00E+11

1.50E+11

2.00E+11

2.50E+11

3.00E+11

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

ne (

eV

)

0

5

10

15

20

25

30

35

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

kTe

(eV

)

Triple probe results (1)11

• Pressure: 2 mTorr

• Distance from target:~12.5 cm (far)

• Plateau “temperature” is ~20 eV.

• Peak density is 0.9 x 1011 cm-3

.

• Density tracks Z-pulser current on target.

• High energy electrons are present, likely responsible for ionizing the metal atoms.

Voltage

Current

Power

Electron “Temp.”

Electron Density


-5.00E+10

0.00E+00

5.00E+10

1.00E+11

1.50E+11

2.00E+11

2.50E+11

3.00E+11

3.50E+11

4.00E+11

4.50E+11

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

n e (c

m-3

)

0

5

10

15

20

25

30

35

40

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

kTe

(eV

)



• Distance from target:~6.3 cm (near)


• Peak density is 1.4 x 1011 cm-3

.

• Density is higher near the target as expected.

Voltage

Current

Power


Electron Density


-5.00E+10

0.00E+00

5.00E+10

1.00E+11

1.50E+11

2.00E+11

2.50E+11

3.00E+11

3.50E+11

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

n e (c

m-3

)



• Distance from target:~12.5 cm (far)


• Peak density is 1.3 x 1011 cm-3.

• Higher pressure of process gas leads to higher density as expected (compared to the density at same distance, lower pressure).

Voltage

Current

Power


Electron Density

0

5

10

15

20

25

30

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

kTe

(eV

)


0.00E+00

1.00E+11

2.00E+11

3.00E+11

4.00E+11

5.00E+11

6.00E+11

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

n e (c

m-3

)

0

5

10

15

20

25

30

35

40

45

50

-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006

t (s)

kT

e (

eV

)



• Distance from target:~6.3 cm (near)

• Plateau “temperature” ~22 eV.

• Peak density is 1.6 x 1011 cm-3.

• Again, density is slightly higher near the target.

Voltage

Current

Power


Electron Density


Growth rate behavior• Lower pressure

gives higher deposition rate.

• Deposition rate not proportional to current plateau value

• Deposition rate not constant with power

15

Deposition rate versus time as deposition conditions are altered.

Pressure (mTorr)

Peak Current (A)

Deposition Rate (Å/s)

30 230 1.86

2 160 3.92

2 125 4.52

2 40 5.13

Pressure (mTorr)

Peak Current (A)

Deposition Rate (Å/s)

2 172 2.55

2 135 2.20

2 122 2.02

2 54 1.60

Constant average power (2.0 kW)Constant repetition rate (39 ±1 Hz)


Time-resolved ion current at the substrate

• When do the ions arrive at the substrate?

• At 2mTorr, 160A plateau current:

• Note that these are not necessarily metal ions; most likely Ar+.

16

-0.2

-0.15

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

-0.0015 -0.001 -0.0005 0 0.0005 0.001 0.0015 0.002

t (s)

Ion

Curr

ent (

mA)

Ion current follows the shape of

plasma density curves found

with triple probe.

Voltage

Current

Power

ion current to grid


Energy of time resolved ion current17

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

0.3

0.4

-6 -5 -4 -3 -2 -1 0 1 2 3

Stopping potential (V)

Cu

rren

t (m

A)

2 mTorr

30 mTorr

At 30 mTorr ions have less than 1 eV

of energy at substrate.

At 2 mTorr ions have less than 3 eV

of energy at substrate.


Conclusions

• The plasma is very hot during the pulse.

• 20 eV and greater.

• Likely a non-Maxwellian electron energy distribution

• Density is on the order of 2 x 1011 cm-3 and follows input current.

• Density increases with pressure and falls off with distance from target.

• Deposition rates are not strictly a function of power or plateau current.

• Energy of ions reaching substrate is very low (< 3eV), though we are not measuring metal ions at this point.

18


Thank you for your attention.

Andrew N. CloudPhD candidate, Department of Materials Science and Engineering

University of Illinois at Urbana-Champaign

Acknowledgements:

19

Graduate student support provided by the National Defense Science and Engineering Graduate research fellowship program (NDSEG).

This research was funded in part by a grant from the National Science Foundation, under Grant #CMMI09-53057.

Documents

Time-resolved plasma characterization in modulated pulse ...zpulser.com/assets/2012/01/AN-Cloud-et-al-AVS-2009.pdf•Quartz crystal microbalance •Used to determine deposition rate