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Evaluation of the Cu atomic density during sputter deposition process with optical emission spectroscopy
Takeo Nakano, Kouji Tanakaand Shigeru Baba
Dept. of Applied Physics,Seikei University, Japan
Outline
Optical Emissions and absorptions between low-energy levels of Cu neutral
Evaluation of copper atomic density using intensity profiles of 2 emission lines from CuI
Comparison with the atomic density deduced from a one-particle Monte-Carlo simulation
Energy levels of Cu neutral
324.8nm510.6nm
3.817eV
0eV
1.389eV
(4s 2S: g = 2)
(m 2D: g = 6)
(4p 2P: g = 4)
A=1.68x108 (s-1)A=9.46x106 (s-1)
1016 1017 101810-3
10-2
10-1
Dec
ay L
engt
h (m
)Cu atomic density (m-3)(Vacuum 59 (2000)
581.)
Sputter Plasma
200 300 400 5000
1000
2000
3000
Wavelength (nm)
Inte
nsity
(ar
b.)
200 300 400 5000
1000
2000
3000
Wavelength (nm)
Inte
nsity
(ar
b.)
1.6 Pa 16 Pa
200 300 400 5000
1000
2000
3000
Wavelength (nm)
Inte
nsity
(ar
b.)
200 300 400 5000
1000
2000
3000
Wavelength (nm)
Inte
nsity
(ar
b.)
OES measurement
OES measurement
Optical System with an iris (2.0mm ) and a plano-convex lens
Wavelength 185 ~ 525nm (with 1024 channels)
Balanced-magnetron (targetφ5cm )
DC power 50 W Ar flow-rate 10 sccm Ar pressure 1.6 ~ 16 Pa
Emission Profile (16Pa)
Computed Tomography.
(Vacuum 74 (2004) 387.)
-3 -2 -1 0 1 2 30
50
100
150
Inte
nsit
y(ar
b.)
Lateral Position (cm)
324nm510nm
0 1 2 30
10
20
30
40
50
Radial Position (cm)In
tens
ity
(arb
.)
Evaluation of Cu density: Concept
Line Profile Radial Profile
CT
510
324
A
A
absorption?
)(rk
Evaluation of Cu density: Assumptions
Radial emission profile of the 510.6 nm line can be obtained by the Computed Tomography (no absorption for 510.6 nm).
Emission profile I 324(r ) of 324.8 nm line is given by the 510.6 profile and the ratio of transition probabilities of these emissions.
Absorption coefficient k (r ) for the 324.8 nm line is determined by the density of Cu atoms at ground states.
Evaluation of Cu density: Effect of the Absorption
lt r
I(r)
V (t)
222222
324
'',
)'('exp)()(
ltrltr
rkdlrIdltVl
Radial profile of the Cu atomic density
0 1 2 3
1017
1018
1019
1.6 Pa
Radial Position (cm)
Ato
mic
Den
sity
(m
-3)
0 1 2 3
4 Pa
0 1 2 3
8 Pa
0 1 2 3
16 Pa
One-particle MC Simulation
Monte Carlo simulation of the sputtered particles treats the “life” of them through:1. Sputtering ejection from the target.2. Collision and scattering with gas atoms3.Deposition on the chamber wall.
collision &scatteirngwith gases
Sputtering
Residualtime Tpin a cell
Depositionon the wall
One-particle MC simulation (2) (Appl. Surf. Sci. 113/114 (1997) 642.)
Boundary Condition Axisymmetric Uniform gas temperature (400K) and pressure Sticking Coefficient at the boundary is unity.
Ejection of the particles Position proportional to the erosion track de
pth Energy Thompson’s formula Angle cosine law
Scattering with gas atoms Thermal motion of gas atom (Maxwellian) Elastic scattering with the Born-Mayer potential (
U (r )=A exp(-br ) )
Density evaluationby the MC simulation
Split the space into cells Count the staying time Tp of Cu atoms in e
ach cell during the simulation Compare the arrival flux of atoms (simulati
on) with the experimental deposition rate, and obtain Ts
Average atomic number in each cell is given by Tp /Ts
Atomic density profile of Cu (MC calculation)
Summary A method is proposed to evaluate the atomic d
ensity profile of copper sputter plasma using the Optical Emission Spectroscopy.
The result was agreed with the one obtained by the one-particle MC simulation in: 1017~1018 m-3 of density was obtained. The higher the pressure was, the higher the atomic
density became. The solver of the inverse problem should be im
proved.
http://surf.ap.seikei.ac.jp/~nakano/