Zsolt Tőkei

Influence of absorbed water components on SiOCH low-k reliability

We investigated plasma treatment induced water absorption in a SiOCH low-k dielectric and the influence of the absorbed water components on the low-k dielectric reliability. By using thermal desorption spectroscopy (TDS), water absorption in SiOCH was evidenced for N2/H2 plasma treatments. Based on these TDS results, two anneal temperatures were selected to separate and quantify the respective contributions of two absorbed water components, physisorbed (α) and chemisorbed (β) water, to low-k dielectric reliability. With the physisorbed water desorbed by an anneal at 190 °C, the low-k dielectric shows reduced leakage currents and slightly improved time-dependent dielectric breakdown (TDDB) lifetimes. However, the observed failure mechanism represented by the TDDB thermal activation energy (Ea) does not change until the chemisorbed water component was desorbed by an anneal at 400 °C. The close similarity between Ea and the bond energy associated with the β water component demonstrates that the β bond is amo...

Direct observation of the 1/E dependence of time dependent dielectric breakdown in the presence of copper

Time dependent dielectric breakdown (TDDB) lifetime model study has been performed on a metal-insulator-semiconductor capacitor structure with copper directly deposited on silicon dioxide without a barrier material. The structure generates a low electric field acceleration of time-to-failure, which makes it possible to measure TDDB over a wide range of electric fields from 3.5 to 10 MV/cm and experimentally validate TDDB lifetime model without any assumption and data extrapolation. The experimental results are in good agreement with the so called 1/E model and do not support the E, √E, or power-law model.

Role of copper in time dependent dielectric breakdown of porous organo-silicate glass low-k materials

The role of copper in time dependent dielectric breakdown (TDDB) of a porous low-k dielectric with TaN/Ta barrier was investigated on a metal-insulator-metal capacitor configuration where Cu ions can drift into the low-k film by applying a positive potential on the top while they are not permitted to enter the low-k dielectric if a negative potential is applied on the top. No difference in TDDB performance was observed between the positive and negative bias conditions, suggesting that Cu cannot penetrate TaN/Ta barrier to play a critical role in the TDDB of porous low-k material.

Synchrotron measurement of the effect of linewidth scaling on stress in advanced Cu/Low-k interconnects

The stress of Cu/low-k interconnects with linewidths scaled to 50 nm was determined using precision lattice parameter measurement at an advanced light facility. Grazing incidence and θ-2θ diffraction geometries were used to gain a direct measurement of the strain tensor, showing an increase in stress as the linewidth is reduced an order of magnitude from 500 to 50 nm. This increase in stress contrasts existing predictions of finite element simulations, which predict a decrease in stress as the line aspect ratio increases above one. Our simulations, considering the low-k stack, have shown this decrease should occur at lower aspect ratios; however, neither trend is reflected in the measured data. All of the lines showed a strong [111] texture suggesting their stiffness was not affected at the scaled dimensions. The narrower lines show a more bamboolike structure compared to a more polycrystalline structure in the wider lines. In the narrow lines, the grains become pinned in the linewidth reducing stress rel...

1/f noise measurements for faster evaluation of electromigration in advanced microelectronics interconnections

The use of 1/f noise measurements is explored for the purpose of finding faster techniques for electromigration (EM) characterization in advanced microelectronic interconnects, which also enable a better understanding of its underlying physical mechanisms. Three different applications of 1/f noise for EM characterization are explored. First, whether 1/f noise measurements during EM stress can serve as an early indicator of EM damage. Second, whether the current dependence of the noise power spectral density (PSD) can be used for a qualitative comparison of the defect concentration of different interconnects and consequently also their EM lifetime t50. Third, whether the activation energies obtained from the temperature dependence of the 1/f noise PSD correspond to the activation energies found by means of classic EM tests. In this paper, the 1/f noise technique has been used to assess and compare the EM properties of various advanced integration schemes and different materials, as they are being explored ...

Resistivity scaling and electron relaxation times in metallic nanowires

We study the resistivity scaling in nanometer-sized metallic wires due to surface roughness and grain-boundaries, currently the main cause of electron scattering in nanoscaled interconnects. The resistivity has been obtained with the Boltzmann transport equation, adopting the relaxation time approximation (RTA) of the distribution function and the effective mass approximation for the conducting electrons. The relaxation times are calculated exactly, using Fermis golden rule, resulting in a correct relaxation time for every sub-band state contributing to the transport. In general, the relaxation time strongly depends on the sub-band state, something that remained unclear with the methods of previous work. The resistivity scaling is obtained for different roughness and grain-boundary properties, showing large differences in scaling behavior and relaxation times. Our model clearly indicates that the resistivity is dominated by grain-boundary scattering, easily surpassing the surface roughness contribution by a factor of 10.

Thickness dependence of the resistivity of platinum-group metal thin films

We report on the thin film resistivity of several platinum-group metals (Ru, Pd, Ir, and Pt). Platinum-group thin films show comparable or lower resistivities than Cu for film thicknesses below about 5 nm due to a weaker thickness dependence of the resistivity. Based on experimentally determined mean linear distances between grain boundaries as well as ab initio calculations of the electron mean free path, the data for Ru, Ir, and Cu were modeled within the semiclassical Mayadas–Shatzkes model [Phys. Rev. B 1, 1382 (1970)] to assess the combined contributions of surface and grain boundary scattering to the resistivity. For Ru, the modeling results indicated that surface scattering was strongly dependent on the surrounding material with nearly specular scattering at interfaces with SiO2 or air but with diffuse scattering at interfaces with TaN. The dependence of the thin film resistivity on the mean free path is also discussed within the Mayadas–Shatzkes model in consideration of the experimental findings.

Impact of carbon-doping on time dependent dielectric breakdown of SiO2-based films

Impact of carbon-doping on time dependent dielectric breakdown (TDDB) of three SiO2-based films was investigated under two different breakdown mechanisms, one involving Cu ion injection and the other caused by intrinsic dielectric degradation without Cu injection. In the case of breakdown dominated by dielectric degradation, an undoped SiO2 film shows better TDDB performance than the two other carbon-doped SiO2 or organo-silicate glass films, suggesting that carbon-doping makes the films weaker for dielectric breakdown. In contrast, in the case of breakdown involving Cu ion injection, the two carbon-doped films show better TDDB performance than the undoped SiO2, suggesting that the presence of the carbon slows down Cu ion injection and therefore leads to less TDDB degradation.

Ultra Low-k Materials: Challenges of Scaling

Ultra low-k materials with dielectric constant value down to 2.0 are under research and development for potential applications in advanced interconnects of 22 nm node and beyond. These materials are typically based on carbon doped silicon dioxide and fabricated either by Plasma Enhanced Chemical Vapor Deposition (PECVD) or Spin-on Glass (SOG) techniques. In order to achieve lower k values, a higher porosity and/or more carbon doping are required. Some of the key characteristics of ultra low-k materials are high porosity, large pore size, and presence of porogen residues. Those characteristics impose great challenges to the integration of ultra low-k materials in interconnect systems. Many of those challenges will be discussed in this paper.

Evaluation of via density and low-k Young's modulus influence on mechanical performance of advanced node multi-level Back-End-Of-Line

Abstract Utilizing Design Of Experiments (DOE) and a decision making procedure, the mechanical performance of different advanced node Back-End-Of-Line (BEOL) configurations is evaluated, where the average peel stress in metal vias is considered as the critical parameter, and is identified with mechanical performance. The goal is to guide the design of the BEOL in its conceptual phase, with respect to the via densities and low-k Youngs modulus. The first section of the paper discusses an exploration of the design space X , using the orthogonal method as a selected DOE with which 16 different BEOL configurations are evaluated. The DOE is used to generate regression equations which allow to evaluate the influence of individual design parameters on mechanical performance. Low-k Youngs modulus was proved to have dominant effect on reducing the stresses in the vias, and while the influence of the via density is lower, it is still possible to reduce the stresses by increasing the via density. In the second part, a decision making procedure is introduced, with the objective of choosing the optimal design out of a number of existing designs. Designs that are defined in the design space are mapped to the attribute space Y , and to the metric space M , which allows for comparison of individual designs in respect to the stress levels in different BEOL via layers. In this part, all designs are sorted in the metric space, and are ready to be evaluated. Finally, different distance norms (metrics) are introduced as value functions to evaluate individual designs. Based on these norms, an optimal design with high low-k Youngs modulus and via 0 density has been identified, along with a number of other designs which show good mechanical performance.