High-pressure phase equilibria for chlorosilane+carbon dioxide mixtures

Surface Modification of Porous Silicon-Based Films Using Dichlorosilanes Dissolved in Supercritical Carbon Dioxide

“…The dielectric constant showed that as the alkyl groups increased in size, the treatment was less effective at modifying the p -MSQ electrical properties. Electrical measurements of MISCAP structures on untreated samples found a dielectric constant of 3.5 ± 0.1, which is significantly degraded compared to the 2.4 ± 0.1 measured before the samples were exposed to the oxygen plasma (Xie, Choate et al 2005). After the dichlorosilane treatments, the dielectric constant values were 2.49 ± 0.24, 2.99 ± 0.09, and 3.39 ± 0.13, using DMDCS, DEDCS, and DBDCS, respectively.…”

“…This additional layer has three possible formation mechanisms: (1) van der Waals interaction, (2) selfcondensation in the fluid phase producing physisorbed moieties, and (3) covalent extension of the film via siloxane bond formation. 28 The first two mechanisms would explain how additional thickness (Figure 2) was added to the films in the absence of a polymerization reaction, but, as shown by Xie et al, 28,36 X-ray photoelectron spectroscopy (XPS) studies of ashed p-MSQ surfaces treated with similar halosilanes found no residual halogens, suggesting the deposited layer is the covalently bonded product of a chemical reaction that eliminates Cl atoms, independently of the Cl atom source (physisorbed, chemisorbed, or HCl). Both Cl atoms on a dichlorosilane molecule are active sites; the reaction of water with one of the sites forms a silanol (Si cs −OH), or reaction between a silanol (surface hydroxyl) and a Cl atom will form a siloxane linkage (−Si−O−Si−).…”

“…This work identified DMDCS as being more effective for surface modification of MSQ films than dichlorosilanes with longer alkyl chains. Previous results identified trimethylchlorosilane (TMCS) as an effective silylating agent that tends to create thin deposited films, and methyltrichlorosilane (MTCS) as an effective pore capping treatment. ,, DMDCS displayed intermediate capabilities. The varying results achieved by each methyl-chlorosilane tested suggest that processes using combinations or sequences of these reactants can be chosen to achieve specific requirements for treated surfaces.…”

“…This would seem to indicate that dichlorosilanes preferentially react with isolated/geminal hydroxyl groups. However, it has been shown that DMDCS can react with hydrogen-bonded hydroxyl groups, 36 meaning the apparent preference of dichlorosilanes for isolated/geminal hydroxyl groups could also be the result of rapid water incorporation during the brief ambient exposure after surface modification.…”

“…Xie et al ,, used supercritical CO 2 to deliver chlorosilanes with one, two, or three methyl groups to porous silicon-based films. This work extends the study using diactive chlorosilanes with increasing lengths of the alkyl groups: dimethyldichlorosilane (DMDCS), diethyldichlorosilane (DEDCS), and dibutyldichlorosilane (DBDCS), allowing the effect of alkyl chain length on specific film characteristics (thicknesses of deposited films, surface hydrophobicity, structure of the films deposited, physical and chemical adsorption) to be investigated.…”