Ebrahim Andideh

Influence of phonon, geometry, impurity, and grain size on Copper line resistivity

The authors report on the resistivity of submicron copper lines ranging from 75to500nm linewidths as a function of temperature in the 10Kto380K interval. Their estimate of the contributions to electron scattering at 20K for the narrowest line (75nm linewidth) is 29% from copper surfaces, 25% from grain boundaries, and 30% from impurities, with the bulk resistivity making up the remaining 16%. It should be noted that at 300K, the contribution of electron-phonon scattering is about 60% illustrating the benefit of studying different scattering mechanisms at cryogenic temperatures.

Compositional effects on electrical and mechanical properties in carbon-doped oxide dielectric films: Application of Fourier-transform infrared spectroscopy

Organosilicate glasses, also known as carbon-doped oxides (CDO), have been studied for application as interlayer dielectrics in microprocessors. Fourier-transform infrared (FTIR) spectroscopy is used here to monitor CDO film compositions prepared by plasma-enhanced chemical vapor deposition of dimethyldimethoxysilane. The Si–CH3/Si–O peak area ratios represent the relative content of these functional groups within the films, and indicate compositional changes in the films produced. Additionally, a close inspection of the C–H stretching modes shows a large peak at 2962 cm−1 due to the CH3 asymmetric stretch and a smaller shoulder to the right, made up of up to three other C–H stretching modes. The shoulder intensity divided by the asymmetric stretch intensity provides another metric that tracks compositional changes in the film. Product compositions indicated by FTIR also correlate well with physical properties such as dielectric constant, hardness, bulk modulus, and cohesive strength.

Interfacial adhesion of copper-low k interconnects

Adhesion energies of Cu-low k dielectric interfaces, measured with the technique of four-point bending, show a correlation to chemical mechanical polish results. A limit of 5 J/m/sup 2/ is established, below which thin film delamination and cracking are observed. In general, spin-on polymer dielectrics exhibit better adhesion to barrier films than carbon-doped oxide dielectrics. PVD barriers exhibit better adhesion to low k dielectric films than CVD barriers. Surface treatments of the dielectric film before barrier deposition are found to strongly modulate CVD barrier to spin-on polymer adhesion.

Transient enhanced diffusion after laser thermal processing of ion implanted silicon

The effect of laser thermal processing (LTP) on implantation-induced defect evolution and transient enhanced diffusion (TED) of boron was investigated. A 270-A-thick amorphous layer formed by 10 keV Si+ implantation was melted and regrown using a 20 ns ultraviolet laser pulse. Transmission electron microscopy revealed that recrystallization of the amorphous layer following LTP results in a high concentration of stacking faults and microtwins in the regrown region. Also, the end-of-range loop evolution during subsequent 750 °C furnace annealing, is different in a LTP sample compared to a control sample. Secondary ion mass spectroscopy of a boron marker layer 6000 A below the surface showed that LTP alone produced no enhanced diffusion. However, during subsequent furnace annealing, the boron layer in the LTP sample experienced just as much TED as in the control sample which was only implanted and furnace annealed. These results imply that laser melting and recrystallization of an implantation-induced amorph...

Optical pump and probe measurement of the thermal conductivity of low-k dielectric thin films

We report on measurements of the thermal conductivity of a number of amorphous materials, including fluorinated silicate glass and carbon-doped oxides. These materials are of interest to the microelectronics industry for use as insulators in microprocessors. The samples measured were in the form of thin films deposited onto silicon substrates. Measurements were made using an optical technique in which the film is heated with a picosecond light pulse, and a time-delayed, probe light pulse is used to measure the temperature of the film as a function of time. We find that the thermal conductivity of these low-k dielectrics is reduced by as much as a factor of 5 with respect to amorphous SiO2. Most measurements were made at room temperature, but for two samples we additionally report on measurements for the temperature range 150–375 K. Results for the thermal conductivity for these materials are compared to theories of heat flow in amorphous solids.

Effects of amorphizing species’ ion mass on the end-of-range damage formation in silicon

The effects of preamorphizing ion mass on the end-of-range (EOR) damage and subsequent enhanced diffusivity have been investigated. Amorphizing silicon with implants of 22 keV 28Si+, 32 keV 73Ge+, 40 keV 119Sn+, and 45 keV 207Pb+ provided the mass comparisons. Cross-sectional transmission electron microscopy analysis showed that the amorphous layer depths were approximately 400 A. After postimplantation annealing at 750 °C for 30 min, plan-view transmission electron microscopy (PTEM) revealed that increasing the ion mass decreased the defect size and density. Quantitative analysis of PTEM results also showed that increasing ion mass decreased the population of interstitials trapped in the EOR. Secondary ion mass spectrometry depth profiles of grown-in boron marker layers showed that increasing the ion mass decreased the time average diffusivity enhancements of boron (〈DB〉/DB*).

Cohesive strength characterization of brittle low-k films

The cohesive strength of low k dielectric films is an important property in predicting thermomechanical integrity of the Cu/low k interconnect structure. An approach to measure the cohesive strength of brittle low k films is presented, in which residual stress, elastic modulus and film thickness, are considered. The importance of residual film stress in cohesive failures is demonstrated.

Measurements of the thermal conductivity of amorphous materials with low dielectric constants

Abstract We report on measurements of the thermal conductivity of a number of amorphous materials, including several that have a low dielectric constant and which are of current interest for use as insulators in computer chips. The samples are thin films deposited onto Si substrates. Measurements are made using an optical technique in which the film is heated with a picosecond light pulse, and a time-delayed probe light pulse is used to measure the temperature of the film as a function of time. The measured thermal conductivity of these thin films is compared with the Cahill–Pohl theory of the thermal conductivity of amorphous solids.

Detection of plasma-induced, nanoscale dielectric constant variations in carbon-doped CVD oxides by electrostatic force microscopy

Electrostatic force microscopy was used to detect nanoscale dielectric constant variations in two different, carbon-doped oxide low-k dielectrics deposited by plasma-enhanced chemical vapour deposition and subjected to oxidizing isotropic plasmas and inert gas isotropic plasmas. Samples were polished at 10\r{} to the sample normal to enhance the through-the-thickness spatial resolution. We observed that the technique was able to detect k{}~{}0.1 variations of dielectric constant with ~10 nm spatial resolution. We also observed that the oxidizing isotropic plasma caused damage to a depth of approximately 10-50 nm and that one of the carbon-doped oxides was more susceptible to plasma-induced damage. The estimated increase of dielectric constant from the oxidizing plasma was from k~2.5-3 to k>4-5. The damage from the inert gas plasma was observed to be deeper but less severe.

Use of electric force microscopy to detect process-induced, nanoscale dielectric damage of low k oxides

There is some concern that processing (ash/reactive ion etch) may increase the dielectric constant of the etched structures and thereby diminish or remove the advantage of the low k dielectric. We proposed that electric force microscopy (EFM) should be able to resolve dielectric constant variations with approximately 50 nm spatial resolution in properly prepared samples. This report presents preliminary results that show that EFM is able to detect damage and that processing does indeed cause damage.