Etching etch gases

The etch rates were measured by a surface profiler and field emission scatming electron microscopy (FESEM), and the etch profile were observed by FESEM. In this study, a C /Ar gas chemistry was chosen to obtain high etch selectivity of Si film to niobium oxide mask since CI2 gas was known to be a good etch gas for Si films. The etch rate, etch selectivity and etch profile of niobium oxide nanopillars and Si films were explored by varying the CI2 concentration, coil RF power and dc bias voltage to substrate. 

The hydrogen was introduced both as an additive gas (CF, —mixtures) and intramolecularly by using CHFj as the etch gas. This concept has been extended by several groups and impressive SiOj-to-Si etch-rate ratios have been obtained. Ephrath , for example, using CF —mixtures in a reactive-ion etching system has observed ratios of 30 1. An example of this work is shown in Fig. 3.2. Lehmann and Widmer using CHFj gas also in a reactive ion etching mode have obtained ratios of 15 1. We have previously shown that mixtures of CF, and CjF behave similarly to CF —Hj mixtures with respect to the SiOj-to-Si etch-rate ratio. 

For systems in which is not zero, the shape of the etched profile can be controlled to a certain extent by adjusting the stoichiometry of the discharge. This is illustrated in Fig. 3-7 using an idealized Si sample. As hydrogen is added to a CF. discharge the etch rate of Si will decrease as we have seen earlier in Fig. 3.2. However, the etch rate will stop on surfaces not subjected to ion bombardment (point A in Fig. 3.7) before etching stops on surfaces which are exposed to energetic ion bombardment. This means that the lateral etch rate has been eliminated and features with vertical sidewalls can be etched if an etch gas mixture of CF. — 10% is used in this example. 

The F/C ratio model accounts for the fact that for carbon-containing gases etching and polymerization occur simultaneously. The process that dominates depends upon etch gas stoichiometry, reactive-gas additions, amount of material to be etched, and electrode potential and upon how these factors affect the F/C ratio. For instance, as described in Figure 8, the F/ C ratio of the etchant gas determines whether etching or polymerization is favored. If the primary etchant species for silicon (F atoms) is consumed either by a loading effect or by reaction with hydrogen to form HF, the F/... 

The tin oxide thin film was patterned by reactive ion etching (RIE) using either SiCl or 1% H2 in N2 as the etch gas. The polysilicon contact holes were opened by wet-chemical etching in buffered hydrofluoric acid (BHF). A double-layer metallization (Cr -50 nm plus A1 -1 pm) was done by electron beam evaporation to form the electrical interconnection (Figure 1c). 

NF3 was synthesized by Ruff et al. for the first time in 1928 by the molten salt electrolysis [22]. Unlike the fluorinated carbons, the nitrogen trifluoride is easy to decompose due to relatively low bond energy in N—F bond, and therefore can be a fluorine source. Consequently, at first, many researches were made as a rocket fuel oxidizer. The utilization as cleaning/etching gas was developed in the semiconductor industry as in the case of fluorinated carbon [23],... 

The effectiveness of chemical etching is largely dependent on the volatility of fragmented species. For instance, oxygen plasma is an effective etching gas for most... 

C for 30 minutes in a vacuum oven. Plasma development was carried out either in a barrel etcher or a planar etcher. For the barrel etcher, 02 (oxygen) was used as the etch gas. In Figure 4, the normalized film thickness remained after development vs exposure dose is plotted for two different bake temperatures. It appears from the figure that 60° bake has produced a more sensitive resist but 100° bake has produced a thicker resist at high dose. The exposed patterns were 10 micron by 500 micron rectangles. 

The deposited polymer film can be removed by ion bombardment with low energy. In the etching step, the etching gas (for instance, SFg) is dissociated by the plasma, liberating high amounts of etching species. These species are necessary to remove the polymer film at the bottom of the pattern and to effectively react with the silicon. The etching reactions involve the removal of the passivation layer... 

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