Michael C. Burrell

XPS, Auger study of Cu3Si and its reaction with oxygen

Abstract The copper silicon alloy Cu 3 Si (η phase) was investigated by XPS and Auger analysis. XPS binding energies of Si2p 3 2 = 99.4 eV and Cu2p 3 2 = 932.7 eV were found, identical to their values in pure elemental Si or Cu, respectively. The X-ray induced Cu LMM Auger peak was observed at kinetic energy of 914.1 eV, again similar to that found for pure copper metal. In the electron excited N ( E ) Auger spectrum the Si LVV for η phase displays a shoulder at 92.3 eV on the main Si peak (89.0 eV). This shoulder causes the derivative spectrum to split into two negative excursions at 90.3 and 94.3 eV. Cu 3 Si was found to react readily with oxygen. The oxidation state of Cu in η phase was stable with respect to O 2 exposure. Silicon however, was preferentially oxidized to SiO 2 with a decrease in the surface Cu/Si ratio with exposure to O 2 and air. Exposure of Cu 3 Si to air for two weeks produced oxide layers 3600 A deep.

Interfacial reactions at copper surfaces coated with polyimide films prepared from poly(amide–acid) precursors

Thin films of polyimide were prepared by spin coating the poly(amide–acid) precursor onto copper and aluminum substrates, followed by the usual heat treatment to promote imidization (curing) of the film. Films prepared on aluminum substrates were completely cured during the heat treatment, as shown by x‐ray photoelectron spectroscopy and infrared measurements. On copper substrates, the thinnest films (2000 A or less) showed considerable intermixing of copper ions in the polymer layer. This prevented the films from curing completely during heat treatment. The formation of a copper carboxylate at the acid site in the polyimide precursor is postulated.

Characterization of reactive areas in the direct process for the production of methylchlorosilanes

Abstract The surface of silicon reacting with methyl chloride in a laboratory fluidized bed via the direct process is characterized at several stages. In the first activation stage, the CuCl catalyst reacts with the Si, resulting in a decrease in the Cu surface concentration. Once reaction with methyl chloride has begun the Cu catalyst, the promoters (Zn, Sn) are found only on reactive sections of the silicon. The regions where reaction occurred had high Cu levels with Cu Si ratio near 1. XPS determined the oxidation state of Cu on the surface to be zero. Zn is found to remain at higher surface concentrations than those of Cu during the course of reaction.

STOICHIOMETRY AND THICKNESS OF THE INITIAL OXIDE FORMED ON CLEAN TITANIUM SURFACES DETERMINED BY QUANTITATIVE AUGER ELECTRON SPECTROSCOPY, ELECTRON ENERGY LOSS SPECTROSCOPY, AND MICROGRAVIMETRY.

The initial oxidation of a clean polycrystalline titanium film was studied by Auger electron spectroscopy (AES) and electron energy loss spectroscopy (ELS), while simultaneously monitoring the total oxygen uptake using the quartz crystal microbalance (QCM). Quantitation of the O KLL and Ti LMM AES intensities reveals that the surface stoichiometry at the initial stages of oxidation (<100 L O2 at 1×10−5 Torr) corresponds to that expected for Ti2O3, and the ELS results also suggest the presence of the lower oxidation states of titanium (+2,+3) on the surface. The microgravimetric results indicate that the oxidation is not confined to the region sampled by the electron spectroscopic methods, and a surface layer of Ti2O3 whose thickness is ∼40 A is consistent with the observed combination of results.

Interfacial reactions at copper surfaces coated with polymer films

Polymeric coatings on copper surfaces are known to degrade at a faster rate than identical materials on other metals such as aluminum, particularly during thermal aging. We have studied the interfacial reactions occurring at copper surfaces coated with poly(esterimide) and polyimide wire enamels. Thin coatings (100 A–1 μm) were heat treated at temperatures from 200 to 240 °C. Interfacial reactions were studied by x‐ray photoelectron spectroscopy (XPS), Auger profiling, and reflectance infrared spectroscopy. In addition to copper oxide growth at the interface, thermal oxidative degradation of the polymer leads to thinning of the coating. This reaction is catalyzed by the copper (oxide) surface and material loss occurs primarily at the polymer/copper (oxide) interface. Migration of mobile copper species into the bulk of the coating is observed by its appearance at the surface and by depth profiling. For polyimide films prepared from poly(amide‐acid) precursors, an interfacial reaction occurs during initial ...

X-ray photoelectron and static secondary-ion mass spectroscopic studies of segmented block copoly(ether-ester)s

X-ray photoelectron spectroscopy (x.p.s.) and static secondary-ion mass spectroscopy have been applied to study the surface composition and structure of copoly(ether-ester) elastomers. These materials are multiblock copolymers containing repeat units that are capable of crystallization (hard segments) and amorphous blocks (soft segments). The hard segments in the samples examined were based on poly(butylene terephthalate) (PBT) and the soft block was poly(tetramethylene oxide) (PTMO). The results indicate that the surfaces of these copoly(ether-ester)s are always enriched in the soft segment and this enrichment is driven by the surface energy difference between the hard and soft segments. The surface enrichment is shown to vary with composition and molecular weight. For a copoly(ether-ester) containing 60% w/w PTMO in the bulk, average surface composition in the top 40 A is seen to change from ∼ 66% w/w for PTMO of Mn = 1000, to ∼ 85% for PTMO of Mn = 2900. Differential scanning calorimetry studies in conjunction with x.p.s. studies suggest that the surface enrichment is reduced by an increase in the bulk crystallinity of the material. Addition of poly(hexamethylene terephthalate) to the PBT hard segment reduces the bulk crystallinity of the copoly(ether-ester)s and results in a surface that is more enriched in the PTMO soft segment. The process by which the sample is prepared is also shown to affect the extent of surface enrichment. The angle-dependent x.p.s. data have been fitted by a continuous profile, which shows an enriched soft-segment region at the air/copolymer interface and a depleted region adjacent to the preferentially enriched surface layer.

Charge correction of the binding energy scale in XPS analysis of polymers using surface deposition of PDMS

A method is described for correcting the binding energy scale for specimen charging that occurs during XPS analysis of insulating samples. A small quantity of polymeric poly (dimethyl silicone) (PDMS) is deposited from solution onto the surface of a series of polymers. After XPS analysis, the binding energy scale is then adjusted to align the Si 2p signal of the adsorbed PDMS to the value observed on conducting samples. A model is proposed that shows that the binding energies of insulating specimens are measured with respect to the sample Fermi level. Using this method, the C 1s binding energy for aliphatic hydrocarbon (CH2)x in polyethylene is measured at 284.97 eV, in excellent agreement with previously reported values based on other correction schemes. Measured energies for 12 other materials are also presented. Copyright

Study of the enhanced oxidative degradation of polymer films at polymer/copper (oxide) interfaces using depth profile and inert marker techniques

The degradation of poly(ester imide) films on metal substrates was monitored by determining the changes in polymer film thickness using x‐ray photoelectron spectroscopy combined with ion sputter depth profiling. Thin films (1000–7000 A) of poly(ester imide) wire enamel were spin coated onto metal substrates and aged in air at 200 °C for several hours. For films on copper substrates, thermal oxidative degradation of the polymer led to thinning of the film (2.5–3 A/min), whereas films on aluminum substrates did not exhibit a decrease in thickness. The catalytic effect of copper upon the degradation of the polymer occurs primarily at the copper (oxide)/polymer interface, as revealed by the location of an inert gold marker layer within the polymer film before and after aging.

Surface chemistry of polycarbonate film and adhesion of ultraviolet‐cured inks

One of the primary uses of polycarbonate film is in screen‐printing applications, with ultraviolet (UV)‐cured inks becoming increasingly popular due to environmental concerns. During multicolor printing operations, regions of the polycarbonate film surface are unavoidably exposed to UV irradiation during the cure of adjacent regions. Subtle changes in the polycarbonate surface chemistry affect subsequent printing on the UV‐exposed surface, primarily manifest as a decrease in the ink adhesion level. In this study, static secondary‐ion‐mass spectroscopy (SIMS), x‐ray photoelectron spectroscopy (XPS), and contact angle measurements were used to show that the surface becomes oxidized and water wettable. The degree of photo‐oxidation, nature of the photoproducts, and ink adhesion characteristics were measured as a function of the UV wavelength window. Filtering out the short wavelengths (λ<300 nm) from a medium pressure Hg lamp resulted in significantly less photo‐oxidation compared to identical exposures from the unfiltered UV. The ink/polymer interfaces were also examined by transmission electron microscopy (cross section) and by peeling followed by XPS and static SIMS analysis. Based on these results, mechanisms for ink/polycarbonate interface adhesion are proposed.

Copper deposition onto polyetherimide: Interface composition and adhesion

The chemical composition and adhesion of the interface between copper (applied via an electroless bath or by vacuum evaporation) and polyetherimide substrates are investigated. Electroless copper deposition requires a chemical pretreatment to ensure final adhesion values of 180–220 g/mm, whereas comparable adhesion is obtained for evaporated copper without pretreatment. Both metallization methods require a postdeposition heat treatment to maximize the copper/polyetherimide adhesion. The interface side of the metal deposits are exposed by a substrate dissolution technique and analyzed using x‐ray photoelectron spectroscopy. A thin (∼30 A) insoluble polymer layer remains which is believed to chemically interact with the metal. In addition, interfacial oxidation of the metal deposit increases with the application of the heat treatment. The role of this interfacial chemistry on copper/polyetherimide adhesion is discussed.