G. A. Antonelli

Measurement of bandgap energies in low-k organosilicates

In this work, experimental measurements of the electronic band gap of low-k organosilicate dielectrics will be presented and discussed. The measurement of bandgap energies of organosilicates will be made by examining the onset of inelastic energy loss in core-level atomic spectra using X-ray photoelectron spectroscopy. This energy serves as a reference point from which many other facets of the material can be understood, such as the location and presence of defect states in the bulk or at the interface. A comparison with other measurement techniques reported in the literature is presented.

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...

Plasma damage effects on low-k porous organosilicate glass

Damage induced in low-k porous organosilicate glass (SiCOH) dielectric films by exposure to an electron cyclotron resonance (ECR) plasma was investigated. The effects of charged-particle bombardment and vacuum ultraviolet radiation were separated. Flux measurements showed that the ECR plasma has a greater photon flux in the vacuum ultraviolet (VUV) range than in the UV range. Damage was measured by examining the surface potential and capacitance-voltage characteristics after exposure. It was found that during argon ECR plasma processing, 75% of the charge accumulation comes from ions at the surface, while 25% of the charge accumulation occurs from charge trapped within the bulk of the dielectric film. The charge accumulation can be modified by changing the bias voltage of the wafer chuck. UV exposure was shown to repair both sources of damage. Fourier transform infrared (FTIR) spectroscopy results showed no significant change except for Si–(CH3)x bonds. It was found that both charged-particle bombardment ...

Time-dependent dielectric breakdown of plasma-exposed porous organosilicate glass

Time-dependent dielectric breakdown (TDDB) is a major concern for low-k organosilicate dielectrics. To examine the effect of plasma exposure on TDDB degradation, time-to-breakdown measurements were made on porous SiCOH before and after exposure to plasma. A capillary-array window was used to separate charged particle and vacuum ultraviolet (VUV) photon bombardment. Samples exposed to VUV photons, and a combination of VUV photons and ion bombardment exhibited significant degradation in breakdown time. The samples exposed to VUV photons and ion bombardment showed more degradation in breakdown time in comparison to samples exposed to VUV photons alone.

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.

Defects in low-k organosilicate glass and their response to processing as measured with electron-spin resonance

Defect concentrations in low-k organosilicate glass films deposited on high-resistivity silicon were measured with electron-spin resonance. Bulk dangling bonds were detected. Both plasma exposure and ultraviolet exposure were used. During argon electron cyclotron resonance plasma exposure, ion and photon bombardment increased the measured defect concentrations. Ultraviolet lamp exposure was also shown to increase the defect concentrations. Dielectric samples with various dielectric constants were examined showing that as the value of the dielectric constant was lowered, the defect concentrations were shown to increase significantly.

Effects of vacuum ultraviolet radiation on deposited and ultraviolet-cured low-k porous organosilicate glass

The authors compare the effects of vacuum ultraviolet (VUV) irradiation on pristine and UV-cured low-k porous organosilicate glass (SiCOH). The authors find that during VUV irradiation, more trapped charges are generated in UV-cured SiCOH as compared to pristine SiCOH. VUV is also used as a tool to investigate effects of UV curing. From comparison of VUV spectroscopy and photoinjection current of the two samples, the authors find that UV curing reduces the number of defect states in SiCOH. The authors also find that UV-cured SiCOH has higher photoconductivity and intrinsic conductivity from VUV spectroscopy and trapped-charge decay rate, respectively.

Surface potential due to charge accumulation during vacuum ultraviolet exposure for high-k and low-k dielectrics

The surface potential due to charge accumulation during vacuum ultraviolet irradiation of high-k and low-k thin dielectric films is measured. Measurement of the substrate current, which is the sum of the charge-accumulation and photoinjection currents, allows an in situ monitoring of the charge accumulation during irradiation. The relationship between the substrate current and the calculated in situ surface potential is also found, eliminating the need for a separate surface-potential measurement. With a high photon dose, the surface potential and substrate current reach a steady-state value with no further net charge accumulation.

Effect of vacuum ultraviolet and ultraviolet irradiation on mobile charges in the bandgap of low-k-porous organosilicate dielectrics

Capacitance-voltage (C-V) measurements are used to determine the effect of vacuum ultraviolet (VUV) and ultraviolet irradiation on mobile charges in porous low-k organosilicate (SiCOH) dielectrics. Hysteresis in the C-V characteristics shows that VUV irradiation increases the number of mobile charges in the dielectric. This is because VUV photons excite the trapped electrons from defect states to make them mobile carriers. Conversely UV reverses this effect by reducing the mobile charges through photoemission of free electrons and repopulation of trap states. Thus UV irradiation can be used to improve the electrical properties of plasma-processed dielectrics that are subjected to VUV irradiation.