M.R. Baklanov

Determination of pore size distribution in thin films by ellipsometric porosimetry

We show that ellipsometric porosimetry can be used for the measurement of the pore size distribution in thin porous films deposited on top of any smooth solid substrate. In this method, in situ ellipsometry is used to determine the amount of adsorptive, which is adsorbed/condensed in the film. Changes in refractive index and film thickness are used to calculate the quantity of adsorptive present in the film. Room temperature porosimetry based on adsorption of vapor of organic solvents has been developed. In this article, a method of calculation of pore size distribution and results of measurements on mesoporous and microporous xerogel films is discussed. Examination of the validity of the Gurvitsch rule for various organic adsorptives (toluene, heptane, and carbon tetrachloride) is carried out to assess the reliability of measurements of pore size distributions by ellipsometric porosimetry.

Enhancement of ALCVD TM TiN growth on Si-O-C and α-SiC:H films by O 2 -based plasma treatments

In advanced interconnection technologies, Atomic Layer Chemical Vapour Deposition (ALCVDTM) is a promising technique to deposit very conformal thin barriers on low-k dielectrics. To enhance the ALCVD growth, we have modified Si-O-C and α-SiC:H dielectric films by O2-based plasma treatments. This paper discusses the effect of the plasma on the growth of ALCVD TiN and the modifications induced at the surface and in the bulk of the dielectrics. The O2-based plasma enriches the dielectric surface with the OH group, improving the quality of the TiN films. Further optimisation of the surface treatments is needed to prevent undesired modification of the dielectric bulk.

Properties of porous HSQ-based films capped by plasma enhanced chemical vapor deposition dielectric layers

This article presents a study on Dow Corning® XLK™, an inorganic porous material with about 50% porosity and a dielectric constant of 2.0. It focuses on matters linked to sealing the porous film by depositing a plasma enhanced chemical vapor deposition (PECVD) dielectric cap layer. The study shows that the material can be modified during cap deposition due to the fast diffusion of reactants and radicals through the porous network, and acquire totally new properties which can be either beneficial or detrimental, depending on the chosen process. In particular, it is found that cap deposition processes on XLK in an oxidizing ambient, as used for SiO2 deposition, should be avoided. On the other hand, a beneficial modification of the dielectric film has been observed after SiC:H capping. It is also shown that there exists a critical thickness of capping material below which the cap layer reveals the presence of pinholes. The critical thickness value for a PECVD SiC:H cap layer on top of an XLK film is around 2...

Low temperature oxidation and selective etching of chemical vapor deposition a-SiC : H films

Chemical vapor deposition silicon carbide films are considered as a perspective hard mask and stop layer in advanced dry etch technology because of the high chemical and plasma stability. However the a-SiC:H film should be etched away after technological use. In this case the high chemical stability of the a-SiC:H films troubles the solution of this problem. A new approach for the selective removal of the a-SiC:H films is discussed. The basic idea is low-temperature oxidation of the a-SiC:H film and selective removal of the reaction products by wet and/or dry etching. Fourier transform infrared, x-ray photoelectron spectroscopy, and ellipsometry were used for the characterization of the a-SiC:H oxidation and etching of the reaction product. As an example of the practical application, the a-SiC:H films were tested as a dry contact etch stop layer in a 0.18 μm complimentary metal–oxide–semiconductor technology. Results of the electrical evaluation of test structures prepared by this technology are discussed...

SELECTIVE REMOVAL OF HIGH-K GATE DIELECTRICS

Continuous downscaling of integrated circuits brought an end to the era of SiO2. In gate dielectrics, it is being replaced by materials with high dielectric constant, so-called high-k dielectrics. One of the challenges in the integration of the high-k material is removal of those materials selectively over the substrate. This work is one of the first attempts to review current state of the art of the high-k removal. Two main approaches are discussed: dry (plasma) removal and wet removal. First, the fundamentals and limitations of both approaches are presented, then an overview of the existing experimental data is given. It is concluded that the best results could be obtained by combining the dry and wet approaches.

Effects of He Plasma Pretreatment on Low-k Damage during Cu Surface Cleaning with NH3 Plasma

In this study, the effect of the sequential He and NH3 plasma treatments on a chemical vapor deposition SiOC:H low-k dielectric is evaluated in the wide range of experimental conditions. Results show that the active NH3 plasma radicals penetrate the porous low-k bulk and remove the hydrophobic Si–CH3 groups, which leads to hydrophilization and results in the degradation of dielectric properties. The implementation of He plasma pretreatment reduces the damage imposed by the NH3 plasma by a stimulation of the surface recombination of active radicals from NH3 plasma. He plasma causes a surface modification of 10–20 nm presumably due to the energy transfer from the extreme UV photons and the 2 1

Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

High-resolution electron spin resonance analysis of ion bombardment induced defects in advanced low-κ insulators (κ = 2.0-2.5)

Electron spin resonance analysis of defects generated by ion bombardment in different low-permittivity (low-κ) SiO2-based insulating films reveals common types of encountered defects: The EX center (g = 2.0025) and a broad line centered at g = 2.0028 tentatively associated with dangling bonds of carbon atoms backbonded to C or Si atoms. The efficiency of defect generation varies, depending on the type of bombarding ions and the technology of insulator synthesis. However, the two identified defects are observed in all studied cases, suggesting that these defects correspond to the most stable atomic configurations resulting from the network damage of the low-κ materials.

Damage free integration of ultralow-k dielectrics by template replacement approach

Cu/low-k integration by conventional damascene approach is becoming increasingly difficult as critical dimensions scale down. An alternative integration scheme is studied based on the replacement of a sacrificial template by ultralow-k dielectric. A metal structure is first formed by patterning a template material. After template removal, a k = 2.31 spin-on type of porous low-k dielectric is deposited onto the patterned metal lines. The chemical and electrical properties of spin-on dielectrics are studied on blanket wafers, indicating that during hard bake, most porogen is removed within few minutes, but 120 min are required to achieve the lowest k-value. The effective dielectric constant of the gap-fill low-k is investigated on a 45 nm ½ pitch Meander-Fork structure, leading to keff below 2.4. The proposed approach solves the two major challenges in conventional Cu/low-k damascene integration approach: low-k plasma damage and metal penetration during barrier deposition on porous materials.

Characteristics of low-k and ultralow-k PECVD deposited SiCOH films.

We have shown previously that the dielectric constants of PECVD prepared SiCOH dielectrics can be extended to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by adding an organic precursor to the tetramethylcyclotetrasiloxane (TMCTS) used for the preparation of the SiCOH dielectric and annealing the films to remove the thermally less-stable organic CHx fractions from the films, thereby adding porosity and reducing the density of the films. To assess the effects of the reduction of the dielectric constant on other physical properties of the material, the density and composition of the films have been determined by RBS and FRES and the porosity has been measured by PAS/PALS, SAXS and ellipsometric porosimetry. In addition the films have been characterized structurally and topologically by TEM and AFM. It has been found that addition of the organic precursor reduces the Si fraction in the films, however, there is no direct correlation between dielectric constant and film composition. The dielectric constant and density decrease with increasing porosity in the films, which reaches values of 30-39% for k values of 2.05. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05. This is significantly smaller than the pore size typically found in porous spin-on films and may provide an integration advantage compared to spin-on films having similar k values.