Reactive ion etching of silica structures for integrated optics applications

Abstract

Reactive ion etching of silica in a hollow cathode reactor using a CHF3/Ar gas mixture has been studied as a function of masking material, rf power, sample temperature, and O2 and CF4 additions. Etch rates in excess of 0.5 μm/min are typically obtained with a selectivity over amorphous silicon and photoresist of more than 10. The sidewall roughness for etching with an amorphous silicon mask is of the order of 0.05 μm, whereas for a photoresist mask, under similar etching conditions, the sidewall roughness is up to 0.1 μm. For the a-Si mask a further improvement in the sidewall roughness down to 0.02 μm can be obtained by adding O2 to the discharge or elevating the sample temperature, however both parameters cause lateral etching of the a-Si mask and therefore linewidth loss. Nonetheless, when using sample temperature as a control parameter, a process window was found which allows smooth sidewalls to be obtained without dimension loss. In the case of O2 additions such a process window was not found. Possible mechanisms accounting for this difference are discussed. Etching in a CHF3/Ar discharge occurs in competition with simultaneous polymer deposition. The polymer deposition rate was measured in areas shielded from ion bombardment. A phenomenological model describing the effects of polymer deposition on etch rates, sidewall slope, and roughness is proposed. This model assumes that a polymer film with different steady-state thickness can form on different etched structure surfaces, as a result of a balance between polymer etching and deposition. The model is used to explain the tendencies in etch rates, profile slope, and sidewall roughness obtained in this study.

Satistical Analysis of SiO2Contact Hole Etching in a Magnetically Enhanced Reactive Ion Etching Reactor

“…Although the slope of the left sidewall was about 3 o less than that of the right sidewall owing to asymmetry in the etch profile, both sidewall slopes show the same trend with respect to the CHF 3 /CF 4 ratio. Similar experimental results have been reported for SiO 2 contact hole etching [26]. One explanation is the effect of the CHF 3 /CF 4 ratio on the sidewall polymer deposition rate.…”

“…The DC self-bias voltage also decreases as the pressure increases, as indicated by the DC self-bias voltage model, and this could be another reason for the decrease in the etch rate. The CHF 3 flow rate affects the etch rate through changes in the densities of CHF 2 radicals and CHF 2 + ions, which have been reported to affect the deposition of polymer films [26]. Fig.…”

“…One explanation is the effect of the CHF 3 /CF 4 ratio on the sidewall polymer deposition rate. In RIE of SiO 2 wave guides with CHF 3 /CF 4 /Ar gas, the polymer deposition rate in the area shielded from ion bombardment was found to decrease with increasing CHF 3 /CF 4 ratio in the plasma [11,26]. In fluorocarbon plasmas, with an increase in the H 2 addition in the plasma, which was similar to the addition of CHF 3 , the etch rate of SiO 2 increased first and then decreased or became zero [27].…”

Reactive ion etching of quartz and Pyrex for microelectronic applications

“…This erosion of the corner, with an angle of approximately 45°in the plot, can be seen clearly in both the surface maps and the section profiles. Note that similar features with rounded corners were observed on silica structures by Bazylenko and Gross 13 although the process conditions ͑hollow cathode discharge plasma source using a mixture of CF 4 /CHF 3 , Ar or O 2 ) used were different from those in the current study. It appears that the presence of the layer of photoresist on the metal mask is responsible for a better edge profile under the conditions described in this article.…”

Modeling oxide etching in a magnetically enhanced reactive ion plasma using neural networks

“…This is mainly due to the increased ion directionality as supported by the increased dc bias at 800 W. Another possible attributor might be the polymer increasingly deposited with an increase in rf power. 20,23 This can partly be ascertained by the measurements of CF 2 intensity since it is one of major precursors for the polymer deposition. Actually, the CF 2 intensity increased from 1.905 at 300 W to 1.935 at 800 W. At 300 W rf power, the profile becomes increasingly anisotropic with a decrease in pressure.…”