Chemistry Reference
In-Depth Information
1
Plasma alone
Plasma + TiO
2
Plasma + TiO
2
+ UV
UV + TiO
2
0,1
0
50
100
150
200
250
Time (ms)
FIGURE 6.15
Time evolution of C
2
H
2
concentration during a 1 000 ms plasma pulse; open
squares plasma only; solid circle plasma
+
+
TiO
2
+
TiO
2
; open triangles plasma
UV; solid
diamonds UV
TiO
2
; total pressure 210 Pa, discharge current 3 mA. (From Rousseau, A. et al.,
Appl. Phys. Lett.
, 87, 221501, 2005.)
+
the C
2
H
2
concentration was measured by TDLAS during the plasma pulse of 1s. The
combination of the nonthermal plasma with photocatalysis leads to a strong increase
(a factor 25) of the photocatalytic activity. Under the experimental conditions used,
UV generated by the plasma is not sufficient to ensure such a synergetic effect. The
main results of this study was, that UV irradiation promotes adsorption of oxidative
neutral radicals produced by the plasma as well as adsorption of C
2
H
2
; this leads
to higher oxidative species concentration on the TiO
2
surface, which enhances the
photocatalytic activity, see Figure 6.15 [233].
6.3.4.2.3 In-Situ Monitoring of Silicon Plasma Etching
During the last 40 years plasma etching has become a fundamental feature for pro-
cessing integrated circuits. The optimization of the plasma chemistry of the etching
processes includes the identification of the mechanisms responsible for plasma-
induced surface reactions combined with the achievement of uniformity in the
distribution of molecules and radicals for homogeneous wafer treatment.
In etch plasmas used for semiconductor processing, concentrations of the precur-
sor gas NF
3
and of the etch product SiF
4
were measured online and in-situ using an
experimental arrangement, designated the Q-MACS Etch System, which is based on
QCLAS. In addition, the etch rates of SiO
2
layers and of the silicon wafer were mon-
itored, including plasma etching endpoint detection. For this purpose the Q-MACS
