J. L. Lauer

Measuring vacuum ultraviolet radiation-induced damage

During plasma processing of semiconductors, ultraviolet (UV) and vacuum ultraviolet (VUV) radiation are present, but their effects can be difficult to separate from those due to charged particles incident on the wafer. The contribution of VUV photon irradiation to gate-oxide damage, and damage to dielectric materials in general, was examined using two measurement techniques that can predict the possibility of damage. They are (1) surface potential measurements and (2) electrically erasable read-only memory transistors (CHARM-2 wafers). To isolate the radiation effects, unpatterned oxide-coated wafers and CHARM-2 wafers were exposed to VUV synchrotron radiation. VUV exposure of dielectrics and conductors results in an accumulation of positive charge due to photoemission. As a result, it can become difficult to distinguish the photoemitted from the plasma-deposited charge. In addition, it was determined that the UV monitors on CHARM-2 wafers did not respond to VUV radiation.

The effects of vacuum ultraviolet radiation on low-k dielectric films

Plasmas, known to emit high levels of vacuum ultraviolet (VUV) radiation, are used in the semiconductor industry for processing of low-k organosilicate glass (SiCOH) dielectric device structures. VUV irradiation induces photoconduction, photoemission, and photoinjection. These effects generate trapped charges within the dielectric film, which can degrade electrical properties of the dielectric. The amount of charge accumulation in low-k dielectrics depends on factors that affect photoconduction, photoemission, and photoinjection. Changes in the photo and intrinsic conductivities of SiCOH are also ascribed to the changes in the numbers of charged traps generated during VUV irradiation. The dielectric-substrate interface controls charge trapping by affecting photoinjection of charged carriers into the dielectric from the substrate. The number of trapped charges increases with increasing porosity of SiCOH because of charge trapping sites in the nanopores. Modifications to these three parameters, i.e., (1) VU...

Charge Trapping within UV and Vacuum UV Irradiated Low-k Porous Organosilicate Dielectrics

Vacuum ultraviolet (VUV) spectroscopy is used to determine the valence-band structure and location of defect states within the bandgap of porous organosilicate (SiCOH) dielectrics both before and after VUV and UV irradiation. SiCOH dielectrics have bandgap energies of about 9 eV. In addition, positive charge is trapped by defect states located 1 eV above the top of the SiCOH valence-band edge. These defect states can be populated or depopulated with electrons during UV and VUV irradiation, respectively. This is verified by measuring the magnitude and polarity of the trapped charge after VUV irradiation using two techniques: (i) capacitance vs voltage characteristics obtained with a mercury probe and (ii) surface-potential measurements obtained with a Kelvin probe. Both techniques show that the defect states are uncharged when occupied with electrons and positively charged when depleted of electrons.

Effect of vacuum ultraviolet and ultraviolet Irradiation on capacitance-voltage characteristics of low-k-porous organosilicate dielectrics

High frequency capacitance-voltage (C-V) measurements are used to determine the effects of vacuum ultraviolet (VUV) and ultraviolet (UV) irradiation on defect states in porous low-k organosilicate (SiCOH) dielectrics. The characteristics show that VUV photons depopulate trapped electrons from defect states within the dielectric creating trapped positive charge. This is evidenced by a negative shift in the flat-band voltage of the C-V characteristic. UV irradiation reverses this effect by repopulating the defect states with electrons photoinjected from the silicon substrate. Thus, UV reduces the number of trapped positive charges in the dielectric and can effectively repair processing-induced damage.

Reduced adhesion of human blood platelets to polyethylene tubing by microplasma surface modification

A hollow-cathode microplasma modified the lumenal surface of small-diameter polyethylene (PE) tubing. A microwave cavity diagnostic was used to measure the density of the microplasma. Plasma light output was observed with a monochromator at various positions along the PE tube to assess uniformity. Treatment effectiveness was evaluated by measuring the variation in capillary rise at various positions along the tubing. A correlation between the properties of the inner surface of the PE tubing and the emitted light intensity was found. A poly(ethylene oxide) surfactant was immobilized to the lumenal surface of the PE tubing with an argon microplasma discharge. To test hematocompatibility, an in vitro blood-flow loop circulated heparinized human blood through both a plasma-treated and -untreated PE tubes, simultaneously. After blood exposure, the tubes were examined with a scanning electron microscope to assess the density of adhering platelets along the length of the tubes. By modifying the plasma parameters...

Control of uniformity of plasma-surface modification inside of small-diameter polyethylene tubing using microplasma diagnostics

A hollow-cathode microplasma was used to modify the lumenal surface of small-diameter polyethylene (PE). We make use of two microplasma diagnostics to monitor the plasma properties during the treatment process. A microwave cavity was used to measure the density of the microplasma. Emitted light from the microplasma was fed into a monochromator at various positions along the PE tube to assess uniformity of the microplasma. Effectiveness of plasma treatments were evaluated using the capillary-rise method at various positions along the tubing. We show a correlation between the properties of the inner surface of the PE tubing and the light emitted from the plasma. A Poly(ethylene oxide) (PEO) surfactant was immobilized to the lumenal surface of the PE tubing using the microplasma discharge. An in vitro blood-circulation loop was constructed to test the hematocompatibility of the PE tubes. After blood exposure, scanning electron microscope images were taken to assess the density of adhering platelets along the length of the tubes. The plasma-treated tubing showed fewer blood adherents than the untreated tubing. By suitably controlling the pressure drop along the tube, the uniformity of the microplasma treatment along the tubing can be optimized.

Depletion of charge produced during plasma exposure in aluminum oxide by vacuum ultraviolet radiation

A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to vacuum ultraviolet (VUV) 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.

Surface potential measurements of vacuum ultraviolet irradiated Al/sub 2/O/sub 3/, Si/sub 3/N/sub 4/, and SiO/sub 2/

Vacuum ultraviolet radiation (VUV), generated during plasma processing of semiconductors devices can induce charge on dielectric materials. By exposing dielectric coated wafers to synchrotron radiation of varying energy, it is possible to separate the photoemission and photoconductive effects, both of which result in an increase in the surface potential of the dielectric. Maps of the surface potential induced on the dielectrics by VUV can be obtained by the use of a Kelvin probe.

Monte Carlo simulation of the effects of vacuum-ultraviolet radiation on dielectric materials

Radiation-induced damage during plasma processing of semiconductor materials can adversely affect device reliability. However, it has been shown that vacuum ultraviolet (VUV) radiation (8–20 eV) 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.

Effect of thermal annealing on charge exchange between oxygen interstitial defects within HfO2 and oxygen-deficient silicon centers within the SiO2/Si interface

We compare the charging response of rapid thermally annealed (800 and 1000 °C) 4 nm thick HfO2 to as-deposited HfO2 on Si by measuring the surface potential of the HfO2 layers after vacuum ultraviolet (VUV) irradiation with 11.6 eV photons. From VUV spectroscopy, we determined all HfO2 layers show the presence of oxygen-interstitial defects (OIDs). The electronic states of OID in HfO2 line up in energy with oxygen-deficient Si centers within the SiO2 interfacial layer. This implies charge exchange between OIDs within HfO2 and the O-deficient silicon centers within the SiO2 interfacial layer are very important for controlling the radiation-induced trapped charge in HfO2 dielectric stacks.