The bond distance is slightly smaller than the sum of the conventional covalent "radii" of the atoms: Si (0.11 nm) O(0.066 nm) = 0.18 nm.
The water can migrate through the deposited materials to the gate oxide, there causing drifts in performance of transistors under bias, impairing hot electron reliability, also known as gate oxide integrity or GOI.
The water molecules can, however, be consumed by the reactions with Si-H groups: this is the basis of the use of silicon-rich oxides as water getters or barriers.
Deposited silicon dioxide, almost always by CVD approaches, is almost as old as thermal growth on the substrate, and has been employed in various ways in IC fabrication due to its familiarity, versatility, and reliability. Si O is formed by strong, directional covalent bonds, and has a well-defined local structure: four oxygen atoms are arrayed at the corners of a tetrahedron around a central silicon atom: (click link for an animated version)Si O2The oxygen atoms are electronegative, and some of the silicon valence electron density is transferred to the oxygen neighbors, but it is incorrect to regard the material as a salt of a Si[ 4] ion with O[-2] ions, as is sometimes seen in the literature: the directionality of the bonds is essential to the observed structures.
The bond angles around O-Si-O are essentially the tetrahedral angle, 109 degrees; the Si-O distance is 1.61 Å (0.16 nm) with very little variation.
Thus, addition of phosphorus or boron (PSG, BSG, and BPSG) is used.