Preparation of silicon oxide by plasma-assisted chemical vapor deposition

Glossary：

WVTR: Water vapor transmission rate, the water vapor transmission rate of flexible barrier materials used in packaging/industrial applications.
HMDSO: hexamethyldisilaxane.

Figure 1. Water vapor transmission rate of various materials

Summary：

1. As can be seen from Figure 1, the WVTR of quartz glass is much lower than that of PET. Therefore, if pure SiO2 is prepared on the surface of PET, the WVTR will decrease.
2. The effect of O2/HMDSO flow ratio on WVTR, the surface element content of silicon oxide film changes with O2/HMDSO flow ratio as shown in Table 1. It can be seen that at a certain ratio, the O/Si ratio has a maximum value and does not contain C.

Table 1, O2-to-HMDSO flow rate change on the surface element content of silicon oxide film

3. The effect of O2/Ar flow ratio on WVTR, the surface element content of silicon oxide film changes with the O2/Ar flow ratio. It can be seen from Figure 2 that when the gas ratio S=1, there is the lowest WVTR value.

Figure 2. Water vapor transmission rate of silicon oxide/PET composite film prepared under different oxygen/argon mixed gas ratios

Gas flow ratio S, S=[O₂/(O₂+Ar)], the change value of S is 0, 0.25, 0.5, 0.75 and 1

(Plasma power 200W; cavity pressure 300mTorr; film thickness 100nm)

4.The effect of plasma power on WVTR, the surface element content of silicon oxide film changes with the plasma power. It can be seen from Table 2 that the plasma power is 250 watt-hours, and Si/O is closer to 1:2 than 50 watt-hours.

Table 2. Plasma power changes on the surface element content of silicon oxide film

5. The chamber cavity pressure affects WVTR, and the content of silicon oxide film surface elements changes with the chamber cavity. It can be seen from Figure 3 that in the range of chamber cavity pressure　250~450mTorr, WVTR has a tendency to decrease with vacuum value.

Figure 3. The water vapor transmission rate of the silica/PET composite film with varying chamber cavity pressure is related
(Plasma power 250W; O₂=40sccm; film thickness 100nm)

conclusion：

1. As the O2/HMDSO flow ratio increases, the purity of SiO2 increases and the barrier effect increases.
2. When the O2/Ar flow ratio is increased, the WVTR is relatively reduced, and the blocking effect is improved.
3. As the plasma power increases, the purity of SiO2 increases and the barrier effect increases.
4. When the chamber cavity pressure is reduced, the WVTR is relatively reduced, and the blocking effect is improved.

References： [1] Hui-Ling Wu,“Fabrication of SiOX Barrier Coatings Using Plasma Enhanced Chemical Vapor Deposition"(2007)

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