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For different purposes and demands, a lot of preparing silicon dioxide films have been developed and applied, mainly are chemical vapor deposition, physical vapor deposition, thermal oxidation method, a sol-gel method and a liquid phase deposition method. 

1. Chemical vapor deposition (CVD) 

In 1969, the Colette first use of photochemical reactions deposited Si3N4 film, from application opens up a photochemical vapor deposition method in microelectronics. Chemical vapor deposition is a way of chemical reaction, in the reaction chamber, the reaction (usually gas) to generate a solid-state product, and is deposited on the silicon surface of a thin film deposition techniques. Because it involves a chemical reaction, also known as CVD (Chemical Vapour Deposition). CVD method is divided into atmospheric chemical vapor deposition (APCVD), low pressure chemical vapor deposition (LPCVD), plasma enhanced chemical vapor deposition (PECVD), photochemical vapor deposition. Additionally CVD Preparation of silicon dioxide available in the following reaction system: SiH4-O2, SiH4-N2O, SiH2Cl2-N2O, Si (OC2H5) 4 and the like. Various preparation methods and different reaction systems required for the growth of SiO2 equipment and process conditions are not the same, and each has different uses and advantages and disadvantages. The most commonly used is a plasma enhanced chemical vapor deposition method.

1.1 Plasma enhanced chemical vapor deposition

This technology uses a glow discharge, high frequency electric field in the rare gas plasma ionization, the ions are accelerated in an electric field and gain energy, deposition of SiO2 films can be achieved at a lower temperature. Characteristic of this method is the deposition temperature can be reduced, and can be reduced from 700 ℃ LPCVD in to 200 ℃, and the fast growth rate, can accurately control the deposition rate (about 1nm Park s), the resulting dense film structure; drawback is vacuum It is low, so that the content of impurities in the film (Cl, O) is high, low film hardness, film deposition rate too fast and cause serious columnar crystals and the presence of voids and so on.

1.2 Chemical vapor deposition method

This method is to use uv mercury lamp (UV2Hg) as a radiation source, using mercurial sensitizing principle, in SiH4 + N2O gas mixture of photochemical reaction. SiH4 and O2 in 2 road into the reaction chamber, under ultraviolet light vertical irradiation, the reaction equation is the following 3 O 2 O 2, 3 (< 195 nm)

O. O. 3 + 2 O (200 ~ 300 nm)

Total reactive SiH4 + 2 o the SiO 2 + 2 gas by-products (N 2 discharge)

PCVD preparation of silicon dioxide(SiO2) thin films can be applied to the surface modification of gas sensor, so as to improve the selectivity of the sensor. The main characteristic of the method is that the film forming temperature is low (50 ~ 200 ℃). In addition, as a result of the photon energy is not enough.



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