Silicon etching oxygen addition

Fig. 43. Silicon relative etch rate and relative intensity of the 703.7 nm F-atom emission as a function of oxygen additions to a CF4 discharge. After [219].

Figure 11 shows an RBS spectrum of a PBTMSS film after O2 RIE (1 min, —800 V, 20 mTorr). The substrate signal in this and other spectra is markedly lower and it is similar to the simulated spectrum which indicates that oxygen plasma treatment makes the film more radiation resistant. In addition, the surface layer of plasma treated films does not contain measurable amounts of sulfur. The thickness of this sulfur-free layer, estimated by comparison with simulated spectra, is about 50 A after RIE and SME and 25 A after the barrel etching. The data also show that the same layer is enriched in oxygen and silicon which was confirmed by simulation. These results compare favorably with those obtained from AES spectra. 

Finally silicon can be etched in fluorocarbon plasmas (e.g., CF4). The addition of oxidation (oxygen) or reducing (hydrogen) agents to these plasmas has been used to control polymer formation and thereby affect the etch rate and selectivity. Fig. 43... 

Fig. 44. Etch rate of polysilicon, oxide, and photoresist as a function of hydrogen addition to a CF4 discharge. Etch rate stops on non-oxide materials due to polymer build up at high % H - Oxide continues to etch due to polymer removal by the available oxygen. This yields high selectivity of etching oxide over silicon. After [220].

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