Plasma-charging damage to gate SiO2 and SiO2/Si interfaces in submicron n-channel transistors: Latent defects and passivation/depassivation of defects by hydrogen

Abstract

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.

Optical and Electrical Characterization of Hydrogen-Plasma-Damaged Silicon Surface Structures and Its Impact on In-line Monitoring

“…However, H-terminated Si bond can easily desorb hydrogen, and thus, become an electrical defect under a specific condition of annealing in the following manufacturing processes. 30,55) Therefore, H 2 -plasma damage may induce more serious device performance degradation. Fig.…”

Plasma processing damage in etching and deposition

“…For example, damage from dielectric current flow can be passivated by hydrogen. However, it has been shown that such damage is only rendered latent; it can subsequently be activated by another current stress or even by some forms of thermal cycling [9]. The layout of device edges on active area can also affect dielectric current flow damage.…”

A New Electrically Reversible Depassivation/Passivation Mechanism in Polycrystalline Silicon

“…However, to the best of our knowledge, degradation mechanisms tied to hydrogen in the poly-Si film have not been reported. In single crystal transistors, hydrogen has been thought to create instabilities in thermal silicon dioxide and at the oxide/silicon interface [9] and in amorphous silicon, it has long been implicated in the metastability of the material [10]. However, in the case of poly-Si T~lrs, the role of hydrogen has primarily been considered to be beneficial in the poly-Si itself.…”