We report the results of a comparative study of the damage induced in boron-doped Si by contact etching. The two approaches compared are conventional reactive ion etching and magnetically enhanced reactive ion etching (MERIE). The two structure-chemistry combinations used are SiO2/Si with CHF3/O2 plasmas, and bare Si wafers with CHF3/Ar plasmas. The damage examined in the Si substrates of both structures is that of electronic states in the band gap, the permeation into Si of hydrogen, and the deactivation of boron acceptors. These types of damage are explored by means of deep level transient spectroscopy and capacitance-voltage measurements on Ti/Si Schottky diodes fabricated on the etched substrate surfaces. The gap states induced by these contact etches are ascribed to interstitial-atom-related defects which are proposed to be formed as a result of interactions involving self interstitials. During etching these defects are observed to be both generated by the etching process itself as well as electrically passivated by permeating hydrogen. The hydrogen permeation of the substrate, monitored via acceptor deactivation, is seen to be enhanced for MERIE with increasing magnetic field intensities.

Reactive ion etching and magnetically enhanced reactive ion etching with CHF3/O2 are employed to remove SiO2 from boron-doped Si substrates. Etch-induced gap states in the substrate are monitored using deep-level transient spectroscopy. The dominant state is found to be a donor with a hole binding energy of 0.36 eV. The state has been identified as that of the carbon-interstitial oxygen-interstitial pair. The depth profile of the pair is determined by two competing mechanisms: the pair generation and its electrical deactivation by atomic hydrogen. The latter process is especially prevalent in the presence of a magnetic field.

In this study we explore the silicon substrate damage produced by CI 2-and HBr-based reactive ion polycrystalline silicon overetches used in the definition of polycrystalline Si / SiO, [ single-crystal Si structures. The damage-caused traps, examined by means of deep-level transient spectroscopy, in the p-type Si are found to have concentrations that can exceed one tenth that of the boron dopant, and are detectable as far as -10 pm from the SiO, / Si interface. The concentration and depth of these traps are shown to depend on the polycrystalline Si overetch selectivity, initial oxide thickness, and on the magnetic field strength as well as the presence of hydrogen.

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New experimental results are presented which provide evidence for hydrogen passivation and depassivation of plasma-charging-induced defects in gate oxides and at oxide/silicon interfaces. The devices used in this study were 0.5 μm n-channel metal–oxide–semiconductor field-effect transistors fabricated on 200 mm boron-doped silicon substrates. The processing included Cl2/HBr-based chemistries for the polycrystalline silicon gate definition etch, and CHF3/CF4-based chemistries for the contact etch. Plasma-charging defects resulting from the processing are shown to have the following properties: (i) plasma-induced charging defects are latent (electrically inactive) directly after our processing and before postmetallization annealing (PMA); (ii) these defects continue to be latent after N2 and Ar anneals done at temperatures T in the range 200 °C≤T≤400 °C; (iii) these defects are also latent after our standard PMA done in forming gas at 400 °C; (iv) these defects are electrically activated by room-temperature Fowler–Nordheim stress, and (v) equivalently these defects are electrically activated by annealing below 400 °C in hydrogen-rich ambients. We show hydrogen passivation/depassivation is responsible for this behavior. This passivation/depassivation has been previously suggested to occur for defects at SiO2/Si interface; here it is also proposed to describe defect–hydrogen interactions in the bulk gate oxide for defects caused by plasma-charging damage.