Chemistry Reference
In-Depth Information
HMDSO dissociation is reported by charge exchange reactions with Ar
+
ions
Ar
+
CH
3
)
2
(
+
(
CH
3
)
3
SiOSi
(
CH
3
)
3
−→
(
CH
3
)
3
SiOSi
(
147
)
+
CH
3
+
Ar [349]
Si
2
OC
4
H
11
(
also
−→
131
)
+
(
2C,7H
)
+
Ar
SiC
3
H
9
(
−→
73
)
+
(
Si,O,3C,9H
)
+
Ar [345].
Ion-molecule reactions between HMDSO fragment ions and HMDSO molecules
could be identified, which lead to ions with higher mass (first step of formation of
oligomers), e.g., [345], see also [347]
Si
2
OC
5
H
15
(
Si
3
O
2
C
7
H
21
(
147
)
+
(
CH
3
)
3
SiOSi
(
CH
3
)
3
−→
221
)
+
(
Si,4C,12H
)
,
Si
4
O
2
C
11
H
33
(
−→
309
)
.
Besides the fragment ions of HMDSO, ions with mass numbers 163, 207, 221,
281, 295, 309, 353, 369, and 383 were observed in HMDSO RF discharges. ToF
SIMS spectra [317,318] and pyrolysis spectra measured by a high-resolution double
focusing mass spectrometer [347] of the plasma deposit show siloxane ions with mass
numbers up to 295, (CH
3
)
3
Si (OSi(CH
3
)
2
)
3
. Deposit formation will be essentially
determined by ion molecule reactions.
Solubility of plasma polymers decrease with increasing energy input. Investiga-
tion using the positive column of dc glow discharge feeded by a mixture Ar/HMDSO
show decreasing solubility in organic solvents of the deposit in relation to the
residence time of the monomer in the active plasma (see Figure 8.51 [350]).
0.5
1.0
1.5
2.0
2.5
3.0
3.5
10
10
1
1
0,1
0.1
0.5
1.0
1.5
2.0
2.5
3.0
3.5
t
res
[s]
FIGURE 8.51
Relative solubility
R
soluble
/
R
insoluble
of HMDSO films deposited in the positive
column of an Ar HMDSO dc discharge (HMDSO-flow 0.9
·
10
−
3
mol/h) for discharge currents
of 30 mA (
) and 40 mA (
•
).
