Frank B. Kaufman

Chemical‐Mechanical Polishing for Fabricating Patterned W Metal Features as Chip Interconnects

Interconnect features of W metal, recessed in an dielectric, can be formed using a novel chemical‐mechanical polish process. Mechanical action, to continually disrupt a surface passivating film on W, and chemical action, to remove W, appear to be requirements for workability of the process. A trial process chemistry using a ferricyanide etchant is described. Removal of the W is discussed in terms of competition between an etching reaction which dissolves W and a passivation reaction to reform on the surface of the W. This novel processing technology is compared with earlier methods of fabricating metal interconnect structures.

Copper Corrosion With and Without Inhibitors

The utility of copper interconnects may ultimately depend on the ability to protect copper from corrosion. We have studied the capacity of lH-benzotriazole (1H-BTA) to provide a protective and stable surface film able to withstand harsh chemical and thermal environments. The film was characterized with electrochemical techniques, in situ ellipsometry, ex situ time-of-flight static secondary ion mass spectrometry, high-temperature mass spectrometry, and accelerated temperature and humidity tests. Several important passivating film properties (thickness, degree of polymerization, thermal stability, corrosion resistance) depend critically on the details of the film preparation conditions. The best corrosion protection is offered by the thin film formed on an oxidized Cu surface. This film has also shown the slowest growth kinetics and the highest degree of polymerization in the Cu-BTA structure. With more aggressive performance requirements for multilevel interconnections, higher conductivity metals, such as copper, are finding their way into a number of products. Copper is a relatively noble metal. Nevertheless, it reacts easily in ordinary, oxygen containing, environments (1). In view of the limited passivation offered by Cu-oxides, we have studied the effectiveness of organic azoles, such as lH-benzotriazole (1H-BTA), as a general method of controlling Cu degradation. For over 40 years 1H-BTA has been successfully used in the prevention of atmospheric Cu corrosion (2), in packaging, storage and transport, in the reduction of thermal oxidation and, in particular, in the protection of copper under immersed conditions (Ref. (3) and references within). The relevant literature is abundant but not unified in its teaching about bonding, thickness, composition and structure of the resulting film and the nature of its protection. Recent work from our laboratory, based on a combination of electrochemical, ellipsometric, and XPS data, has shown that the spontaneous reaction of Cu and 1H-BTA under a variety of conditions leads to the formation of Cu-BTA (4, 5), with copper being Cu +1 , as reported elsewhere (6-12). The formation of a Cu-N bond was clearly identified from the Cu LMM Auger lines. The film was formed both on an oxidized and an oxide-free Cu surface, in contrast to reports suggesting that the presence of Cu2O is a prerequisite for the buildup of CuBTA (8, 14). The thickness of the film was determined to be 0.5-4 nm in the pH range from 3 to 12, reaching 25 nm only under harsh conditions, i.e., in pH 2. Several recent studies of ultrahigh vacuum deposited 1H-BTA have indeed detected 1H-BTA adsorption on clean Cu metal (14-16). An electrochemical equivalent of such a film was formed in our laboratory at Cu 0 kept in

The influence of polymer morphology on polymer film electrochemistry

Abstract The electrochemical behavior of functionalized polystyrene-coated electrodes shows a marked dependence on the nature of the electrolyte ions. Scanning electron microscope and surface profile measurements are presented which show that changes in polymer film volume and morphology accompany electrochemical oxidation. Changing polymer morphology by doping the films with soluble monomers during preparation is shown to produce large changes in electrochemical response. Diffusion coefficients were determined for a neutral organic dye dopant in each of the polymer films investigated, and these correlate very well with the oxidation overpotentials observed electrochemically. The nature of polymer film/solvent interactions and the mechanism by which counter ions penetrate the polymer phase is discussed and is related to other physical properties of amorphous polymers in terms of free volume concepts.

Comparative behavior of electrodes coated with thin films of structurally related electroactive polymers

Abstract General methods are described for the synthesis of electroactive polymers and the preparation of uniform, stable, polymer-coated electrodes. The electrochemical behaviour of thin films of eight different functionalized polystyrenes, differing in the identity and amount of attached electroactive species, and polyvinylferrocene is presented. A wide range of electrochemical properties can be observed by varying parameters such as film thickness, nature of the bound redox couple, extent of polymer functionalization and oxidation state. The deviations from ideal surface behavior are investigated in detail. These are shown to be consequences of cooperative electronic interactions, structural reorganization or uncompensated resistance within the film, depending upon the material. The film resistance varies greatly among the polymer films studied and is shown, in some cases, to be a sensitive function of the extent of oxidation and prior treatment of the film. This variable resistance is shown to be a consequence of slow ion transport through the film. The mechanism of electron transport in such materials is considered and a model of the metal/polymer/electrolyte interface is proposed.

X‐ray photoelectron spectroscopy and ellipsometry studies of the electrochemically controlled adsorption of benzotriazole on copper surfaces

Adsorption of the corrosion inhibitor benzotriazole (BTA) from solution has been studied on well‐characterized electrochemically prepared Cu surfaces. In situ ellipsometry and ex situ x‐ray photoelectron spectroscopy (XPS) have been used to probe both the nature of the Cu surfaces prior to BTA adsorption and to determine the stoichiometry, thickness, and chemical composition of the Cu–BTA overlayer films. The films grown on Cu2O and on Cu0 under oxidizing conditions are generally 5–40 A thick and best described as Cu+1 BTA. Uptake of BTA is also observed on CuO and reduced Cu0 surfaces where the adsorbed film is limited at close to a monolayer. Therefore, Cu2O does not appear to be a prerequisite for uptake of BTA. The thickness of the inhibitor overlayer was calculated from the N 1s/ Cu 3p core level XPS data and was in good agreement with independent ellipsometric measurements on similar samples. Roughening of the Cu surface is observed for samples treated at low pH. Differing amounts of oxygen are foun...

A Model of Copper CMP

A model of copper chemical mechanical polishing (CMP) based on methods of chemical kinetics is presented which includes both chemical and mechanical processes. This CMP model explains observed patterns in removal rates for peroxide and nonperoxide-based slurries as a function of oxidizer concentration, polishing pressure and speed, etchant concentration, and pH.

Polymer‐modified electrodes: a new class of electrochromic materials

A new class of organic polymeric thin‐film electrochromic materials is described. We show that the new polymer‐modified electrodes change color reversibly in permanent thin‐film form without the electrodeposition characteristics of organic liquid state systems such as the viologens. The polymer films exhibit good switching speeds (τ⩽100 ms), possess intrinsic memory, and show no chemical degradation or adhesion loss in preliminary life tests (104 cycles). It is demonstrated that several important electrochromic parameters can be varied by chemical modification of the polymeric material.

Electrochemistry of tetrathiafulvalene polymers, anion effects on charge transport through donor substituted thin polymer films

Thin polymer films prepared from a series of tetrathiafulvalene (TTF) substituted polystyrenes in contact with acetonitrile solutions of tetraethylammonium electrolytes (TEAX, X=ClO4−, PF6−, CH3C6H4SO3−) have been studied using cyclic voltammetric, chronocoulometric and absorption photometry techniques. Reduction of the oxidized films, which proceeds via an intermediate mixed-valence state, was markedly affected by the nature of the supporting electrolyte anion. After allowance for uncompensated resistance, the reduction process could be treated by Fickian diffusion with anion dependent diffusion coefficients for charge transport through the polymer film. Chronocoulometric Cottrell slopes, nD1/2C, increased in the order: p-CH3C6H4SO3−

New high‐resolution charge transfer x‐ray and electron beam negative resist

A new class of polymeric negative x‐ray and electron beam resists is described. Polystyrene‐tetrathiafulvalene films doped with a halocarbon acceptor show good sensitivity to x‐rays (D1/2=44 mJ/cm2) and electron beams (D1/2=6 μC/cm2), with high contrast values γ≳2.5, and with no evidence for the classical swelling phenomena. In electron beam exposures at 10 μC/cm2, parallel wall patterns are produced with pattern resolution of 1000 A or better. Reasons for the improvement in lithographic parameters relative to previous negative resists are briefly discussed.

Electrochemistry of tetrathiafulvalene polymers, electron spin resonance of polymer film electrodes

Etude par RPE de polymeres TTF electroactifs adsorbes sur des electrodes de platine en utilisant a la fois la generation externe et la technique electrochimique simultanee-RPE (SEESR) de Goldberg et Bard