Planarization Processes and Applications III. As-Deposited and Annealed Film Properties

Abstract

In Parts I 1 and II 2 of this paper, it has been shown that both undoped and boron/phosphorus-doped germanosilicate thin films can be planarized over structures at significantly lower temperatures than other glasses, such as borophosphosilicate glass. However, variations in several film properties based on composition, such as water solubility, electrical leakage, and mechanical stress, must also be addressed. For instance, it is well known that germanium dioxide and germanosilicates rich in germanium oxide are water soluble. 3-6 Germanium dioxide is also reported to have high leakage currents when functioning as an insulator. 7-10 Mechanical stress is also an issue, since the thermal coefficient of expansion (TCE) of GeO 2 is greater than that of silicon, 11,12 while the TCE of SiO 2 is less than that of silicon. 13 Therefore, changes in the germanosilicate composition may have a profound effect on stress, or at least on the extrinsic (thermal expansion) component of stress.This paper examines the water solubility, electrical leakage, breakdown characteristics, and the mechanical stress of both the undoped and boron/phosphorus-doped germanosilicate glasses in both the as-deposited and the argon annealed states. Moreover, these properties are to be examined following the "composition changing" forming gas and steam anneals, as discussed in Parts I and II, to ascertain the benefits or disadvantages incurred by the forming gas, steam, or argon-steam two-step processes. ExperimentalSample preparation.-Germanosilicate films were deposited on single-crystal silicon substrates by the plasma-enhanced chemical vapor deposition (PECVD) method reported elsewhere. 14 Following deposition, reflow experiments were conducted in either argon, steam, forming gas, or a two-step process with argon and either steam or forming gas. These experiments were all conducted at atmospheric pressure. Temperatures for argon treatments ranged from 550 to 1050ЊC. Steam treatments were conducted with stoichiometric combinations of hydrogen and oxygen in a 2:1 ratio as well as with 10% excess oxygen. Excess oxygen was used to consume any excess hydrogen in the steam pyrolysis reaction. Steam treatments were limited to temperatures at and above 750ЊC to ensure complete combustion of the hydrogen/oxygen mixtures. Experiments were actually performed at both 750 and 800ЊC. Forming gas experiments were conducted with 3.4, 8.9, and 9.6% H 2 with the balance being N 2 . Various percentages of hydrogen were used to study the effects of different partial pressures of hydrogen on the films during the anneals. Forming gas reflow experiments were also performed at 750 and 800ЊC for direct comparison with the steam treatment results.Samples for water solubility tests were cleaved into 1 ϫ 1 cm dies prior to thermal treatments. Wafers for electrical testing were left whole in the undoped experiments, but they were cleaved into quarters prior to thermal treatment in the doped experiments. Stress measurement wafers were left intact, as required by the stress me...

Thermally poled germanosilicate films with high second-order nonlinearity

“…We mostly relate these observations to an increase in the film electrical conductivity as the Ge concentration increased, which has been previously confirmed. [7] On the other hand, the built-in field of the 33-sccm sample is higher than that of the 0-sccm sample (pure SiOi), although the latter has a lower electrical conductivity. This points out that there should be an optimum electrical conductivity range for a given set of poling conditions.…”

Engineering UV-photosensitivity in planar lightwave circuits by plasma enhanced chemical vapour deposition

“…In theoretical work [22], it was shown that quenching at high temperatures resulted in low-density silica. Local heating due to thermal spikes, produced upon impact, results in local surface diffusion and causes the tensile stress (therefore decrease of compressive stress) to rise as the micro-voids collapse [6]. Furthermore, ion and energetic neutral bombardment increases the surface mobility of chemically active species and increases the active sites on the substrate.…”

“…The net stress in a material system consists of two components: the intrinsic stress (incorporated into the film during deposition, pertaining to composition, microstructure and particle bombardment [5]) and the extrinsic stress generated during cooling from the deposition temperature (∼300˚C) to room temperature due to the differences in thermal expansion coefficients between the film and substrate. It is known that the amount of stress in a film can be varied through addition of dopants [6]. The extrinsic stress level in a material system is set by using different dopants and varying their concentrations (e.g.…”

Characterization of thermally poled germanosilicate thin films

“…We mostly relate these observations to an increase in the film electrical conductivity as the Ge concentration in the film is increased, which has been previously confirmed. [26] On the other hand, the built-in field of the 33-sccm sample is higher than that of the 0-sccm sample (pure SiO 2 ), although the latter has a lower electrical conductivity. This points out that there exists an optimum electrical conductivity range for a given set of poling conditions.…”