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Submitted on 1 Jan 1979
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METAL ATOM DENSITY BY ATOMIC ABSORPTION SPECTROSCOPY IN A D.C.
SPUTTERING DICHARGE
C. Fourrier, G. Lemperiere, J. Poitevin
To cite this version:
C. Fourrier, G. Lemperiere, J. Poitevin. METAL ATOM DENSITY BY ATOMIC ABSORPTION
SPECTROSCOPY IN A D.C. SPUTTERING DICHARGE. Journal de Physique Colloques, 1979, 40
(C7), pp.C7-819-C7-820. �10.1051/jphyscol:19797395�. �jpa-00219394�
JOURllrAL DE PHYSIQUE CoZZoque C7, suppziment au n07, Tome 4 0 , JuiZZet 1979, page ~ 7 - 819
METAL ATOM DENSITY BY ATOMIC ABSORPTION SPECTROSCOPY IN A D ~ ~ S W T T E R I N G DISCHARGE
C. Fourrier, G. Lernperiere and J.M. Poitevin.
Laboratoire de Physique CorpuscuZaire, I n s t i t u t de Physique, 2, rue de Za HoussiniDre, 44072 Nantes Cedex, Frame.
INTRODUCTION
-
At the present time, the use of ato- mic absorption spectroscopy for concentration mea- surements of a metal vapour in sputtering glow dis- charges is not widely developped. We shall present here some specific problems which arise when this method is used in a d.c. sputtering discharge,and on the base of results concerning the titanium we shall show what kind of information one can obtain.EXPERIMENTAL SET-UP
-
DISCHARGE CHARACTERISTICS.The d.c. . diode sputtering apparatus has been previously described [I]. The gap between the mo- vable electrodes is 30 m. The abnormal discharge
sustained at an argon pressure of 80 x Torr shows a well-developped cathodic glow, followed by a dark space with its boundary at s 9 m from the cathode and a negative glow (N G) spreading up to the anode (A).
Fig. I
"at
: Soectrorneter
The titanium atoms of the target (C)are ejected as a result of bombardement by gas ions from the discharge. These sputtered atoms are scattered and diffuse through the discharge chamber (0 = 370 mm) most of them being deposited on the anode-The light source is a titanium hollow cathode lamp (HCL). The
0
spectrometer has a resolving power of D.1 A.
MEASUREMENTS OF THE POPULATION DENSITIES OF THE a F LOWER STATE 3
-
We employ the method of absorp- tion of lines [2]1) A grid (G) at the anode potential limits the diffusion zone and defines the length
!
of the ab- sorbing layer.2) Ne measure the population densities Ni of the lowest triplet term a 3 ~ 2 , a F3, a3Fq (0.00 3 ; 0.021;
0.048 eV). The small excitation temperature implies that
-
Nk is negligeable for the observed transitions.Ni
We have measured
Text-0.2eV
at any discharge power P.3) ~nterferometric measurements have shown that the resonance lines have no significant hyperfine struc- ture [3]
.
4) Titanium atomic lines near the target are broa-
0
dened(%0.3A) (Most probable ejection energy=3.3 ev)
.
A narrowing of their width is observed through the dark space. Thus the metal atoms have a decreasing temperature from C to A. The reported measurements have been made on-axis,5nrm from the anode where the titanium atoms are thermalized. (T = 425 K + Vp), 5) The knowledge of a, ratio of the Doppler widths in the HCL and in the discharge is necessary for the obtention of k.!-E Because the radiation of the excited atoms close to A is proportional to the dis- charge power P [I]
,
kt4 must be proportional to p.This iaplies 1 . 4 < a < 1.6. Double path method mea- surements have shown that a > 1.2 at 15 mm from C.
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19797395
- - Fig. 2
"s -
a 3 ~ $ l e v e l 3 6 4 2 A
2
-
I'-
1
10 2 0 30 40 50 P ( W I
Fig.2 shows the results obtained from 36421 and em- phasizes the error made on the variation law and the population densities if one assumes a = 0 or a = 1.
1
Fig. 3/ " I
The results for a F4, obtained from several re- 3 sonance lines are reported on figure 3. An identi- cal work has been made for a 3 ~ = and a F3. 3
6) The values of the absolute oscillator strengths fik are widely dispersed (50 to 100%).0nly the a F- 3
3 0
y F transitions give consistent results. Using the data of Whaling 141 for these transitions we deduce other fik values from our results.
Fig. 4 gives the mean population densities. For 60W the population density of the three levels,5 mm
' 11
away from the anode reaches * 4 x 10 ~ m - ~ . ~ i g . 5 shows the concentration gradient near the anode.
The deposition rate of ground state atoms which
can be deduced is i15x 1 014cm-?s'l= 9x
1016cm-?min-l .
'*-
Fig. 4
+
N / ~ ~ F ~ ) , 3642 Ad t t l s n s e f r o m the l n o d a
Gravimetric measurements have given a deposition rate of 1 1- 13x 10. 16 .min-' [I] .For T=500K we would
have obtained 12x 1 ~'~cm-~.min-I
.
CONCLUSION
-
The foregoing example illustrates the difficulties to obtain accurate density values.More precisely the knowledge of the Doppler breadths of the emission line and the absorption line is needed if correct variation laws are to be deduced.We think that the limitation of the absorption length and the determination of the excitation temperature have allowed the obtention of satisfactory results concerning the correlation between the ground state atom density and the deposition rate.REFERENCES
[I]
J.M. POITEVIN, G. LEMPERIERE, C. FOURRIER-
J. Phys. D : Appl. Phys., Vol. 9, (1976) 1783.
[2] MITCHELL and ZEMANSKY
-
Resonance Radiation and excited atoms.Cambridge University Press,p.l22.131 H.C. WAGENAAR and L. DE GALAN
-
Spectrochimica Acta, Vo1.28 B (1973) '157.[4] W. WHALING, J.M. SCALO and L. TESTERMAN
-
TheAstrophysical Journal, 212 (1977) 581.
