A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to vacuum ultraviolet ͑VUV͒ radiation produced by a synchrotron light source. The oxide was charged, either positively or negatively, by exposure to a nonreactive inductively coupled plasma, under typical plasma processing conditions. We show the dependence of the conductivity on the energy of the incoming radiation, and conclude that only those photons whose energy is above the band gap of the oxide are capable of producing a temporary increase in the conductivity. Two processes, photoemission and enhanced conductivity, create currents flowing across the oxide layer. A circuit model was developed to show the contributions from both processes to the total current. We conclude that VUV radiation may be used to significantly decrease plasma-induced surface charging of dielectrics.

This work investigates the vacuum ultraviolet ͑VUV͒ emission from various feed gases producing plasmas in an electron cyclotron resonance etcher. Absolute measurements of plasma VUV emission at typical pressures for processing between 0.5 and 5 mTorr, and microwave powers between 700 and 1300 W, show levels of irradiance at the wafer position of the order of tenths of mW/cm 2 and integrated photon fluxes in the 10 14 photons/cm 2 s range. The reported level of VUV emission is sufficient to induce radiation damage in typical metal-oxide-semiconductor devices in the form of flatband voltage shift and inversion of lightly doped substrates. © 1999 American Institute of Physics. ͓S0003-6951͑99͒04718-X͔ During the last decade, the problem of gate oxide damage from plasma processing of metal-oxide-semiconductor ͑MOS͒ devices has been widely studied, because it is increasingly perceived as a threat for the production of advanced integrated circuits. As gate oxide thicknesses approach 20 Å for advanced MOS processes, sources of damage considered minor in the past now hold the potential to degrade device reliability and performance, and the relative impact of different damage mechanisms may also change.Although charging of floating gates is considered to be the most important MOS damage mechanism, gate oxides may also be damaged during plasma processing by x-ray, vacuum ultraviolet ͑VUV͒, and ultraviolet irradiation. 1-3High-energy photons ͑hϾ9 eV͒ can be generated from recombination and relaxation processes in the plasma. Depending on the energy of the incident photons, two cases that may introduce damage can occur: ͑1͒ photons with energies higher than the band gap of SiO 2 ͑ϳ9 eV͒ generate electronhole pairs in the oxide, 4 and ͑2͒ photons with energies lower than the SiO 2 energy gap but greater than 4.2 eV ͑the height of the minimum energy barrier between the Si substrate valence band and the oxide conduction band͒ cause electron injection from the silicon surface into the oxide through the photoelectric effect. In case ͑1͒, it has been established that electron-hole-pair generation increases the bulk and interface trapped-charge density, which will affect device reliability accordingly. 5,6 In case ͑2͒, there is a controversy: while some studies show a similar phenomenon to the one proposed, 7,8 others report that photocarrier injection from the substrate is beneficial, proposing that it anneals the positive interface charge 9 through a recombination process. Consequently, it is apparent that characterizing the plasma VUV irradiation impinging on the wafer surface during processing both qualitatively and quantitatively is essential for understanding radiation damage in MOS devices. This is the key goal of this work.The electron cyclotron resonance ͑ECR͒ plasma etching system employed in this study incorporates a 1.5 kW microwave plasma source and a pair of magnets arranged in a vertical magnetic-mirror configuration. 10 The wafer stage is located 19 cm below the resonance region, and is provided with a radio frequen...

In this article we report a method for in situ electrical characterization of dielectric thin films under direct exposure to plasma in an electron-cyclotron-resonance etcher. This method is based on the development of a special test structure that allows for the measurement of the influence of plasma vacuum-ultraviolet ͑VUV͒ radiation on the electrical conductivity of thin dielectric layers. Results show that the measured conductivity of SiO 2 layers temporarily increases during exposure to argon and oxygen plasmas, with controlled VUV emission. Based on the measurements made through this method, a model of the VUV-induced conductivity of SiO 2 is developed. These measurements are very important for plasma processing of semiconductor devices, because the temporary increase in the conductivity of these layers upon exposure to processing plasmas can decrease the plasma-induced charging of these dielectric layers depending on the intensity of the plasma VUV emission. This can have an impact on the properties and reliability of processed devices.

A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to vacuum ultraviolet ͑VUV͒ radiation produced by a synchrotron light source. The oxide was charged, either positively or negatively, by exposure to a nonreactive inductively coupled plasma, under typical plasma processing conditions. We show the dependence of the conductivity on the energy of the incoming radiation, and conclude that only those photons whose energy is above the band gap of the oxide are capable of producing a temporary increase in the conductivity. By exposing localized regions of precharged oxide samples to the vacuum ultraviolet radiation, we produce regions of charge depletion in and around the exposed areas. We conclude that VUV radiation may be used to significantly decrease plasma-induced surface charging of dielectrics. © 2000 American Institute of Physics. ͓S0003-6951͑00͒01250-X͔During plasma processing, charging of dielectrics plays a leading role within the damage mechanisms of semiconductor devices and plasma-processed materials in general. This damage mechanism is greatly influenced by plasmaemitted x ray, vacuum ultraviolet ͑VUV͒, and ultraviolet radiation.1-3 It was determined that most processing plasmas emit radiation in the VUV energy band of 4-30 eV, with most of the radiation above 9 eV, the latter of which is approximately the energy band gap of SiO 2 , 4 and more than the energy band gap of other dielectrics used in semiconductor device manufacturing ͑e.g., 6 eV for Si x N y and 8.3 eV for Al 2 O 3 ). The radiation is absorbed in the exposed oxide layers and it results in the generation of electron-hole pairs. Although it has been established that electron-hole-pair generation in the oxide increases the SiO 2 bulk and interface trapped-charge density, which may affect device reliability, 5,6 we believe plasma VUV irradiation of oxides can have a beneficial effect by inducing a temporarily enhanced oxide conductivity. This can reduce dielectric charging, especially that induced by electron-shading effects 7 during plasma etching of high aspect-ratio devices, by providing a safe way to discharge these structures and, thus, minimize charging damage. The enhanced conductivity can also have beneficial effects on the etching properties of oxides such as reduction of notching, sidewall bowing, and trenching.It has been previously shown, by exposure to synchrotron radiation in the earlier energy range, that a temporary increase in oxide surface conductivity was produced while the oxide was exposed to VUV radiation. 8 The purpose of this work is to show the energy dependence of the surface conductivity in Al 2 O 3 and that an actual depletion of previously stored charge occurs in and around the exposed region.First, we demonstrate the dependence of the Al 2 O 3 surface conductivity on the energy of the incoming radiation and we show that the peak conductivity occurs for irradiation with photons with an energy of approximately 18 eV. Second, by exposing ...

In this work, we investigate the electrical surface conductivity that is temporarily induced in SiO 2 by exposure to monochromatic vacuum-ultraviolet synchrotron radiation for modification of plasma charging. Special preprocessed test structures were exposed to controlled fluxes of monochromatic synchrotron radiation in the range of 500-3000 Å ͑approx. 4-25 eV͒, the energy band of most plasma vacuum-ultraviolet radiation. The highest oxide surface conductivity is achieved during irradiation by photons with energies between 15 and 18 eV. This enhanced oxide surface conductivity holds the potential to discharge high-aspect ratio structures that charge up during plasma processing due to electron shading, and thus minimize plasma-processing-induced damage to semiconductor devices.