Electron shading, or topography-dependent charging, occurs during plasma exposure of wafers with high-aspect-ratio features due to an imbalance between the electron and ion currents that reach the feature bottoms. High-aspect-ratio pit structures were exposed to an electron cyclotron resonance plasma. The surface potential of the structures after plasma exposure was measured with scanning surface-potential microscopy (SSPM). The results show that SSPM can be used to measure the differential charging in a high-aspect-ratio pit. In situ depletion of the plasma-induced charge with ultraviolet radiation was time resolved using SSPM. A circuit model is used to explain the experimental results.

Radiation-induced damage during plasma processing of semiconductor materials can adversely affect device reliability. However, it has been shown that vacuum ultraviolet ͑VUV͒ radiation ͑8-20 eV͒ can beneficially deplete previously deposited charge on the surface of dielectrics by temporarily increasing their conductivity. Incident VUV photons can cause photoemission and form electron-hole pairs in the dielectric thus producing the desired increased conductivity. To verify this, statistical information obtained from a Monte Carlo simulation is used to model VUV exposure of dielectrics. The simulation calculates the surface potential on the dielectric produced by electron photoemission, which compares favorably with experimental surface-potential measurements made using a Kelvin probe.

A hollow capillary array is examined as a coupling window between an electron cyclotron resonance plasma vacuum ultraviolet ͑vuv͒ source and a separate processing chamber. The transmission of vuv through the capillary array as a function of wavelength is measured and shown to agree with theoretical calculations. A silicon wafer with a dielectric surface is then placed in the processing chamber and exposed to vuv, both with and without the capillary array. A Kelvin probe is used to measure the surface charge induced on the wafer by photoemission in both cases, which confirms the previously measured transmission values. The results show that a capillary array can efficiently couple vuv radiation from a source to a processing chamber without significant modification in the spectrum and its resulting effects on a material.

Vacuum ultraviolet (vuv) emitted during plasma processing degrades dielectrics by generating electron-hole pairs. VUV-induced charging of SiO2∕p-Si and HfO2∕SiO2∕p-Si dielectric stacks are compared. For SiO2∕p-Si, charging is observed for photon energies >15eV by ionization of dielectric atoms from photoinjected electrons. In HfO2∕SiO2∕p-Si, charging is observed for photon >10eV and is due to ionization by photoinjected electrons and by H+ trapping in the HfO2∕SiO2 bulk. Hydrogen appears during annealing at the Si–SiO2 interface forming Si–H, which, during irradiation, is depassivated by photoinjected electrons. The authors conclude that dielectric charging in thin oxides (<10nm) occurs more easily in HfO2∕SiO2 than in SiO2.

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