Investigation into doping of silica glasses with fluorine by modified chemical vapor deposition

Abstract

The equilibrium observed during modified chemical vapor deposition (MCVD) of silica glasses doped with fluorine is investigated by chemical thermodynamics. The influence of the flow rate of Freon-12 and sulfur hexafluoride on the efficiency of the incorporation of fluorine into the condensed phase is analyzed. It is revealed that, at very low flow rates of fluorinating reactants, more than 50% of fluorine can be incorporated into the glass. The refractive index and the efficiency of the conversion of SiCl 4 into the fluorine-doped silica glass are studied as functions of the vapor-gas phase composition.

Thermodynamics of fluorine incorporation into silica glass

“…3-5, using only two adjustable parameters, verifies the validity of an equilibrium approach in general, and of our simplified model. In Table 1, we find a good agreement of our K1 with the pioneering work of Walker et al [16] and with recent results of Andreev et al [26]. A detailed consideration also shows good agreement with experimental results of other authors, which do not explicitly state equilibrium values or thermodynamical data [22,25].…”

“…The D f G 0 values in parenthesis are not directly specified in [16,26] and have been calculated from the equilibrium constants in the same manner as in the present work, using data of [36].…”

“…Several authors have already investigated thermally activated fluorine incorporation via gas phase [11][12][13][14] and have discussed the mechanisms of fluorine incorporation and the influence of fluorine on the deposition efficiency of silica (it is reduced in general) with different fluorine source compounds [15][16][17][18][19][20][21][22][23][24][25][26]. Most authors agree that the mechanism of the fluorine chemistry is based on the existence of chemical equilibria in the gas phase and between the gas and condensed phase, based on the original ideas and investigations of Walker et al [16].…”

Investigation of the modified chemical vapor deposition in preparation of glasses in the SiO2-GeO2-F system

“…x GeO 2 The change in the refractive index due to the incorporation of fluorine into the silica glass can be represented in the from [17] ( 10) where P is the gas pressure (atm).…”

Fluorine incorporation in silica glass by the MCVD process: Study of fluorine incorporation zone, evaluation of optical properties and structure of the glass

“…Several fluorinated reagents such as SF 6 , SiF 4 , CF 4 and CCl 2 F 2 are used for this purpose [2][3][4][5][6]. Fluorine incorporation into silica glass using chlorofluoromethane (CCl 2 F 2 -12) as a source of fluorine has been studied under different deposition conditions and methods [7][8][9][10][11][12][13]. Fluorine incorporation into silica glass specifically using CCl 2 F 2 -12 does not show any fixed deposition condition.…”