Wavelength Dependence of Photon-Induced Interface Defects in Hydrogenated Silicon Nitride/Si Structure during Plasma Etching Processes

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The wavelength dependence of SiN<inf>x</inf>:H/Si interface defect generation caused by vacuum ultraviolet (VUV)/UV radiation from plasma etching processes was investigated. VUV radiation (\lambda < 200 nm) had almost no impact on the generation of defects at the SiN<inf>x</inf>:H/Si interface, since all the radiation in this wavelength range was absorbed in the upper SiN<inf>x</inf>:H film. However, UV radiation (200 < \lambda < 400 nm) was able to reach the underlying SiN<inf>x</inf>:H/Si interface and damage the interface. Direct UV radiation reaching the SiN<inf>x</inf>:H/Si interface dissociated the chemical bonds at the interface and generated interface-trapped charges. The estimated total energy of absorbed photons (E_{\text{total}}; 200 < \lambda < 400 nm) at the interface layer seems to be proportional to the interface-trapped charge density (D_{\text{it}}) measured by capacitance--voltage measurement. However, the mechanism underlying the relationship between E_{\text{total}} and D_{\text{it}} is not yet clear. Visible radiation (\lambda > 400 nm) had no influence on damage generation on the SiN<inf>x</inf>:H/Si structure, since the visible radiation was transmitted through upper SiN<inf>x</inf>:H film and underlying interface layer. The results revealed that UV radiation transmitted through the upper dielectrics can cause the electrical characteristics of underlying metal--oxide--semiconductor (MOS) devices to fluctuate.
2013-05-25