Ronald A. Carpio

Initial study on copper CMP slurry chemistries

Chemical mechanical polishing (CMP) of copper has been investigated with suspended silica and alumina abrasives using various slurry chemistries. The characteristics of these chemistries were studied by electrochemical d.c. polarization and a.c. impedance measurements. Problems and directions related to the formulation of copper CMP slurries are discussed.

Comparison and Reproducibility of H-Passivation of Si(100) with HF in Methanol, Ethanol, Isopropanol and Water by IBA, TMAFM, and FTIR'

Three different HF:alcohol solutions are investigated to etch native SiO 2 and passivate Si(100) surfaces with H which can the be desorbed at low temperature (T 2 O). After a modified RCA cleaning, Si(100) etched by HF:Methanol, HF:IPA, or HF:Ethanol, is characterized by Ion Beam Analysis (IBA), Tapping Mode Atomic Force Microscope (TMAFM), and Fourier Transform Infrared Spectroscopy (FTIR). The absolute coverage of O and C is measured by nuclear reaction analysis (NRA) combined with ion channeling at 3.05 MeV for O and 4.265 MeV for C. Hydrogen is measured via the elastic recoil detection (ERD) of 4 He 2+ at 2.8 MeV. Compared to aqueous HF, HF:alcohol passivates Si(100) leaving a lower O residue by an average factor of 0.62 and a similar C residue. H coverage is higher by an average factor of 1.43. Surface coverages are found to be reproducible in average by 1.4 × 10 14 atoms/cm 2 for C, and by 1.25 × 10 14 atoms/cm 2 for O when measured by IBA on samples identically processed. H coverage is reproducible within 5.5% when measured by ERD. Selective area analysis by TMAFM shows that an increasing number of particulates is responsible for the apparent increase in root-mean -square (rms) surface roughness when the rms is measured over a whole image. Taking this effect into account, all passivated surfaces exhibit similar roughness when compared to the original Si(100) surface with little difference between alcohols and with the reference aqueous HF solution. FTIR in the attenuation total reflection (ATR) mode detected SiH x species mostly as a dihydride. Both IBA and FTIR detected significant levels of oxygen on surfaces passivated HF in alcohol and aqueous HF. This indicates that while Si(100) exhibits more H when passivated with HF in alcohol and can be desorbed at lower temperature than when treated with aqueous HF, H is not bonded to Si only but likely bonds into a more complex surface termination, such as SiOH.

Process development for 180-nm structures using interferometric lithography and I-line photoresist

A bilayer positive I-line process, based upon the use of a bottom antireflective coating and implementable on a standard processing track, is described for the production of sub-0.2- micrometer features by interferometric lithography. Pattern collapse for small, high-aspect ratio photoresist features was found to be a significant issue. The impact of a number of processing variables on pattern collapse was investigated. These variables included resist thickness, substrate reflectivity, developer concentration, post exposure bake (PEB) time and temperature, L/S pitch differences, and development and drying methods. Using a 0.8-micrometer resist thickness, a feature width of 180 nm (360-nm pitch) was attainable without a PEB, while with a suitable PEB, 150-nm features could be obtained. A reduction of resist thickness to 0.6-micrometer enables 120 nm features to be obtained without a PEB, and 100-nm features with a PEB.

Chemical-mechanical polishing of SiO2 thin films studied by X-ray reflectivity

Specular X-ray reflectivity from SiO2 thin films prepared on silicon substrates by plasma-enhanced chemical vapor deposition showed the films to have a characteristic width of the decay in density at the free surface of 17 A, to be about three-quarters the density of α-quartz, and to have an interfacial layer at the silicon interface that was of the order of 100 A wide and less dense than the bulk of the film. After chemical-mechanical polishing the characteristic width of the decay in density at the free surface was reduced to 10 A; furthermore, the near-surface region to a depth of 30 A had a greater density than the as-deposited film. Off-specular reflectivity confirmed that the decrease in characteristic width at the free surface was due to reduced roughness upon polishing and also revealed that the lateral correlation length in the limit of long wavelengths was the same for both polished and unpolished samples. The compression of the near-surface region during polishing is believed to enhance the dissolution of SiO2 into the slurry which is necessary to achieve smooth surfaces.

Capillary electrophoresis methods for the trace cation analysis of semiconductor grades of hydrogen peroxide

Abstract Method development and applications of capillary electrophoresis to the analysis of cations in highest purity grades of hydrogen peroxide which are used for semiconductor processing are discussed. Indirect UV detection in conjunction with electromigration sampling provides a sufficient sensitivity for measurements of low ppb (v/v) levels of contaminants. In contrast to hydrostatic sample introduction, the range of signal vs. concentration proportionality is limited with electromigration sampling. However, meaningful calibration plots can be obtained over the range of 1 to 35 ppb. Examples of electropherograms are presented for two different samples of semiconductor grade hydrogen peroxide. Also given are estimates of detection limits for cations found in analysed samples.

The formation of acid diffusion wells in acid catalyzed photoresists

Abstract This paper describes the use of two step post-exposure-bakes for improving the lithographic performance of the chemically amplified resist, UVIIHS TM from the Shipley Company. With this process, post-exposure-baking at a low temperature allows the deprotection reaction to go to completion, with minimal acid diffusion into unexposed portions of the resist; and the high temperature PEB makes it possible to average out the standing waves. This study examines various two step post-exposure-bakes and provides evidence for the existence of the formation of a diffusion well. For 250nm nominal features, conventional single bake processes yield +40nm for the isolated to grouped line bias and in excess of −20nm for the isofocal region bias. Using a double PEB, processes were found that reduced both the isolated line to grouped line bias and the isofocal region bias to 0nm. Finally the kinetics of the double PEB process is studied using FTIR.

Investigation of deep-ultraviolet photoresists on TiN substrates

The problem of deep ultraviolet (DUV) resist footing on titanium nitride (TiN) substrates has been studied using three different photoresists and TiN films of various stoichiometries. Multiple characterization techniques have been used to characterize the TiN films including auger electron spectroscopy, atomic force microscopy, Rutherford backscattering and reflectivity measurements. Resist footing was compared for process delay experiments, softbake temperature changes, and pretreatments to the TiN substrates. Based on these results and information previously published, it is concluded that detrimental surface and interface states exist on the TiN substrate which are principally reasonable for the footing.

Bath Additive and Current Density Effects on Copper Electroplating Fill of Cu Damascene Structures

Copper electroplating has become the leading technology for gap fill of damascene structures on advanced interconnects. A key to developing a robust electroplating process that produces deposits free of voids and seams is understanding the role of the additive components, i.e., levelers, brighteners and wetting agents, and their relative diffusion/adsorption characteristics. Additionally, obtaining insight about the cathodic current/potential relationship is critical for maximizing the effectiveness of the additive components. Our results indicate that bath additive composition and the plating parameters (plating pulse frequency, and current density) play critical roles in the outcome of the Cu fill. SEM cross sectional analysis of timed partial electroplating fill studies show two types of fill, 1) conformal and 2) bottom-up. Conformal fill of features smaller than 0.25 μm with an aspect ratio (AR) of 4.0 tends to form seam voids in the center of the structure. These seam voids can lead to early electromigration failures. On the other hand, bottom-up fill leads to a void free Cu deposit within the feature.

Contamination monitoring for ammonia, amines, and acid gases utilizing ion mobility spectroscopy (IMS)

The effect of ammonia (NH3) and n-methyl pyrrolidinone (NMP) contamination on chemically amplified DUV resists is well documented. Other amines and related compounds are under suspicion as well. In addition, the concentration levels that are of concern have steadily decreased from approximately 10 ppbv down to levels as low as 0.1 ppbv. While some techniques such as ion chromotagraphy (IC) have been demonstrated to have limits of detection at these levels, the analysis times are rather long and cumbersome. This paper describes the use of IMS to perform these measurements, in a totally automated, continuous instrument. IMS is a simplified time-of-flight technique that requires no liquid reagents and has been demonstrated to be a reliable method for monitoring for ammonia and NMP in cleanrooms. This paper demonstrates the ability of the technique to monitor for amines such as dimethylamine, methylamine, methanolamine, ethanolamine, diethanolamine, butylamine and others. Detection limits of 0.1 ppbv and below are clearly demonstrated. Also discussed are methods of monitoring multiple points with a single analyzer. Ability to detect corrosive gases such as hydrogen fluoride (HF), hydrogen chloride (HCl), sulfur dioxide (SO2), sulfur trioxide (SO3), nitrogen dioxide (NO2), chlorine (Cl2), bromine (Br2), phosphoric acid (H3PO4) are also demonstrated.

New model for the effect of developer temperature on photoresist dissolution

The effects of developer temperature on dissolution behavior for eight g-line and i-line resists, ranging from first- generation to state-of-the-art formulations, are characterized using development rate measurements. Using the RDA-790 development rate measurement tool, dissolution rates as a function of dose and depth into the resist were measured. Each data set was analyzed and the basic performance of rate versus photoactive compound concentrations was fit to appropriate models. The variation of these results with temperature of the developer solution has led to temperature-dependent characterization of the dissolution modeling parameters. Two such parameters, the maximum dissolution rate Rmax and the dissolution selectivity parameter n, are shown to exhibit an Arrhenius behavior with well defined activation energies.