In this paper, we present some results of the newly developed on-wafer photothermal measurement. To study thermal anisotropy, the out-of-plane thermal diffusivity measured from this technique is compared with the in-plane thermal diffusivity by measured by ISTS [1]. In addition to the thermal properties, the agreement with mechanical [2] and optical properties are also shown. The significance of different thermal performance between low K dielectric medium materials and SiO2 suggests that greater attention should be paid to thermal properties for integrated devices with low K materials.

Spin-on glasses are candidates in the microelectronics industry as low dielectric constant insulating layers. Spin-on glasses are very brittle materials. This paper discusses measurement problems as relevant to the characterization of a brittle material by the indentation technique. As for all polymeric materials curing temperature is the most important preparation parameter. There is a correlation between hardness, Young's modulus, the onset of cracking with curing temperature. This dependence on curing temperature is also expressed by the change in Si-H bond density as shown by FTIR data. Life expectancy or aging characteristics were also investigated for these features. As an example results on silsesquioxane spin -on glasses are presented.

We have carried out a comparative study of the dielectric losses in some complex perovskites with both 1:1 and 1:2 compositions of the B ions, namely, SrAl1/2Nb1/2O3 (SAN), SrAl1/2Ta1/2O3 (SAT) and BaMg1/3Ta2/3O3 (BMT). The samples were prepared in two forms, viz. ceramics and single-crystal fibers, the latter were grown by laser heated pedestal growth technique (LHPG). All of these materials possess low dielectric constants, low losses and high Q values. In contrast to relaxor ferroelectrics, that as a rule exhibit broad features in their Raman spectra, SAN, SAT and especially BMT have very narrow phonon lines in the Raman spectra. A linear correlation is found between the microwave dielectric losses and the width of first order phonon lines in a sequence of BMT → SAT → SAN ceramics with increasing phonon damping. Moreover, the phonon damping decreases in materials with non-close-packed structure where there is enough space for undisturbed phonon vibrations. The problem of charge compensation in compounds with the Bsite disorder is also discussed.

The crack-velocity behavior of silsesqioxane spin-on glass thin films exposed to moist environments is examined. An absolute reaction-rate model is used to predict crack velocity using a deleted-bond model and fused silica as a basis, and compared with observed steady-state crack velocities as a function of film thickness and variations in the curing process. An implication is that, on curing, the driving force for film fracture, determined by thermal expansion mismatch, increases less rapidly than the fracture resistance, determined by polymerization.

Recent experimental results based on x-ray reflectivity[1, 2], and ellipsometry[3] have demonstrated that physical properties of polymer films thinner than one micron may deviate significantly from bulk values[4]. The mechanical properties of the ultra-thin films (sub-micron) are experimentally difficult to determine with precision. The quartz crystal microbalance is an established technique for measuring properties of polymer thin films of a few microns thick. [5–7] Recently this quartz crystal microbalance technique has been modified for measuring the mechanical properties of sub-micron polymer films with high precision. The details and preliminary results from this recently modified quartz crystal microbalance technique will be presented.

Polymer thin films (less than 20 ltm) are widely used as coatings and inter-level dielectrics in microelectronic applications. In multi-layer structures, stresses generated in the films due to interaction with adjacent layers and solvent evaporation induced shrinkage, cause the polymer chains to orient in the plane of the film resulting in anisotropic film properties. Characterization of properties in all directions is essential for accurate electrical and mechanical design and modeling.

A new technique has been developed to measure, in-situ, the through-plane (z) properties of thin polymer films. A parallel plate capacitor device and an interdigitated electrode structure were used as sensors to detect changes in dielectric constant and thickness of thin polymer films under thermal or mechanical loading. The through-plane compression modulus and coefficient of thermal expansion were calculated and results are reported for benzocyclobutene (BCB) films.

Fluorinated silicon oxide films were prepared in a plasma enhanced chemical vapor deposition reactor using TEOS, O2, and either C2F6 or NF3. Properties such as deposition rate, film refractive index, dielectric constant, density, and fluorine concentration were investigated as a function of experimental conditions. Based on nuclear reaction analysis (NRA) and Fourier Transform Infrared (FTIR) measurements, no single linear relationship was found between fluorine concentration or film density and dielectric constant. Special attention was paid to the interaction of fluorine with metals. NRA and X-ray photoelectron spectroscopy (XPS) depth profiles showed that fluorine diffuses rapidly through aluminum and piles up at the free surface. The effect of various plasma treatments was investigated to passivate the surface of fluorinated silicon oxide. CF4 - O2 plasma treatment of the fluorinated oxide before aluminum deposition produced significant improvement in inhibiting fluorine diffusion into aluminum without increasing the dielectric constant.

Considerable effort has been expended in recent years in the development, evaluation, and integration of new low Kc dielectric materials for IC applications. Many film properties must be measured before a film can be selected for integration into an interconnect process flow. Among them are glass transition temperature, thermal stability, Young's modulus, adhesion, stress, coefficient of thermal expansion, dielectric constant, breakdown voltage, solvent resistance, dry etch characteristics, and gap fill performance. These properties must in turn be considered when developing interconnect process modules and selecting the associated equipment set. The properties of these materials differ from those of the commonly used (PE)CVD silicon dioxides to varying extents, depending upon the nature of their composition and structure. This has often resulted in substantial modifications to the modules that comprise interconnect process flows, sometimes compromising manufacturability. This paper will address some of the issues associated with the integration of low K materials into interconnect process flows and how they are related to the properties of these materials.

With a tunable ultra low dielectric constant, porous silica xerogel is an attractive dielectric material for ULSI interconnect applications and is potentially extendable to multiple future technology nodes. Porous silica xerogel films have been processed and integrated into device test structures as ultra low k intermetal dielectrics. A fully automated thin film deposition process is recently developed and gives high throughput and good repeatability. A surface modification technique is used to make the films hydrophobic. The film dielectric constant is measured to be less than 2, depending on porosity. Because of the small pore sizes, the films display high dielectric break down strength. With proper shrinkage control, porous silica xerogel shows excellent gapfill capabilities. Integration of the porous silica xerogel material into CMP planarized double level metal (DLM) test structures with both Al and W plugs in a gapfill scheme is successful. Porous silica xerogel structures provide 14% and 35% total capacitance reduction compared to structures with hydrogen silsesquioxane (HSQ) and high density plasma (HDP) oxide respectively. Reliability and current leakage data of porous silica xerogel are comparable to that of HSQ. Feasibility of integrating porous silica xerogel into Cu damascene structures is also demonstrated. Cu/xerogel damascene structures exhibit improvements in both resistance and capacitance compared with convention Al/Oxide gapfill structures.

Hydrogenated “diamondlike” carbon (DLC) is a potential candidate as a low k material for the back end interconnect (BEOL) dielectric for VLSI chips. The DLC material is an attractive dielectric due to its isotropic properties and the ability to deposit the films by CVD techniques, such as PECVD or HDP systems. Under suitable preparation conditions such materials can reach dielectric constant values below 2.8, even as low as 2.4. While the as-deposited films are not stable to exposure to subsequent processing temperatures of about 400 C, it appears that they can be stabilized, in terms of dimensional stability and material loss, by an initial anneal.

The integration of DLC films in the BEOL structure further requires good adhesion with the materials in contact with the DLC dielectric, such as silicon nitride or silicon oxide, and liner metallurgy. As the potential application of the DLC films will be in Cu based damascene structures the behavior of the films under CMP conditions is also important.

The talk will discuss the evaluation of DLC films and of integration issues such as adhesion under processing conditions, patterning, CMP behavior. Blanket and patterned structures built with DLC films will be presented.

Highly crosslinked a-F:C films can undergo a significant change after thermal annealing, where the film expands by ∼3%, the density reduces by ∼10% and the internal stress changes from compressive to tensile. The loss of fluorine concentration and the reduction of CF. are accompanied by the transition of (C-C, sp3) to (C=C, sp2) groups. After annealing, the dielectric constant is reduced and the leakage current increases slightly. Most importantly, these changes occur only at the initial stage of annealing. After the initial annealing, the a-F:C film tends to be thermally stable and retains reasonably good electrical properties as a low-k interlayer dielectric. The profound impact of these results on Cu/a-F:C integration will be briefly discussed.

The continued miniaturization towards sub-quarter micron feature size mandates the search for low dielectric constant interlayer dielectric materials. A large number of materials and processing techniques has been suggested, but so far none of the proposed dielectric materials as well as processing techniques have been integrated into standard integrated circuit processing. In this paper, a new approach has been formulated for integration of low-k dielectric materials for future integrated circuits.

The etch characteristics of the low-k dielectrics DVS BCB (BCB hereafter) and SILK in oxygen/fluorine plasmas are studied. In an O2/NF3 plasma afterglow, the etch rate of both polymers first increase linearly with increasing NF3 concentration, then decreases monotonously. A fluorine plasma afterglow does not etch either BCB nor SILK but strongly changes their chemical and optical properties. Reactive ion etching (RIE) of the polymers shows a different behaviour. The etch rate of SILK in a pure oxygen plasma is maximal, but BCB is etched slowly. The fluorine additives increase the etch rate of BCB. The etch rate of SILK decreases with increasing fluorine concentration. RIE in a pure SF6 plasma shows good etch characteristics and can be used for some practical applications. Mechanisms of the reactions are discussed.

CF4 plasma etching of hydrogen-silsesquioxane films on bare silicon substrates was conducted. An increase in average etching rate and a decrease in dielectric constant from 2.9 to 2.7 were observed after a top layer was removed from the surface of the film, indicating that a negative density depth gradient in the film was developed during the cure processing, A small part of the reduction in dielectric constant may be attributed to structural change resulting from the plasma interaction with the films since a small amount of Si-F bonds were identified in the surface layer of the film after plasma etching. There are indications in the x-ray photoelectron spectroscopy (XPS) spectra that traces of fluorocarbon polymer residue have been generated during the plasma etching. The results of this study also indicate a possibility of obtaining a lower dielectric constant HSQ film by plasma etching.

Recently, we reported the deposition of fluorinated amorphous carbon (FlAC) from hexafluorobenzene (C6F6) under parallel plate (PP) and inductively coupled plasma (ICP-HDP) conditions. Based on initial materials testing, these two platforms generated comparable materials with low dielectric constants (2.4 – 2.8), low weight loss/shrinkage (< 1.5 %/hr. at 425° C), hardness (2–3 Gpa) and adhesion (4–9 kpsi). Here we attempt to answer a basic integration question: FIAC compatibility with other materials used in the interconnect scheme. Investigations of adhesion of F1AC to, and capped by, silicon oxide, silicon nitride and various metals shows generally greater stability of the ICP generated material vs. PP-FIAC. Failures appeared to occur primarily at the FIAC/film interface at 400 and 300 °C for ICP and PP respectively. Although thickness-loss and weight-loss measurements indicate good thermal stability, TDS spectra show low-level outgassing of fluorine-based molecules and fragments even in samples annealed for 4 hours at 400 °C, resulting in interface failures. Plasma treatments and anneals of the F1AC were found to have a minimal effect but liner/cap composition and processing has a strong influence on the adhesion of other films to the fluorocarbon.

The patterning of several novel low dielectric constant (K) materials has been studied in a high-density plasma (HDP) tool. Recent results obtained on oxide-like materials, such as fluorinated oxide, hydrogen silsesquioxane (HSQ), and methyl silsesquioxane (MSQ), are reviewed. These materials can be successfully patterned using a fluorocarbon etching chemistry. The etching is in this case controlled by a thin fluorocarbon film at the surface. The patterning of polymer dielectrics can be performed in an oxygen etching chemistry. As an example, the patterning of Parylene-N in an oxygen chemistry is discussed. In this case, the ion and the oxygen radical flux need to be properly controlled to obtain a directional etching process. After the dielectric etch, either in a fluorocarbon or oxygen based chemistry, fluorocarbons and oxygen contamination remain at the exposed metal surfaces. We recently demonstrated how a plasma treatment following the dielectric etch reduces these contaminants. The results of this treatment on copper surfaces and the resulting modification to the dielectric are reviewed.

Low dielectric constant polymers are being investigated for application as interlayer dielectrics with copper as the metal in a multilevel interconnect scheme. Processing of such structures willrequire the use of chemical-mechanical planarization (CMP) technologies for both the metal and the dielectric. Polymers are comparatively quite soft. They are not readily attacked by chemicals thus requiring more mechanical component dependency compared to the chemical component in the CMP. Polymers are thus prone to scratching during CMP which may lead to reliability problems both from materials and electrical points of view. In this presentation we will discuss the use of chemical engineering and chemistry principles to optimize the polishing process to minimize or eliminate the scratching and other mechanical damages. The role of CMP parameters such as velocity, pressure, particle size, viscosity, and chemistry will be discussed to elucidate the emerging “scratch-free”-CMP-concept.

We have developed a new interconnect technique using a low-k (εt,=2.5) organic interlayer (fluorinated amorphous carbon: a-C:F) and a low-resistivity metal line (copper). The new technique attains a duction in both the capacitance of the interlayer and the resistance of the metal line. We found that a-C:F on Cu reduces reflection to 10% for Kr-F line lithography. However, a-C:F cannot act as a protection layer for oxidation even at 200°C in atmospheric ambient annealing. Cu diffusion into a-C:F is about 100 nm at the annealing temperature of 450°C. The resistivity of the Cu line is 2.3–2.4 μΩ · cm for the 0.5-μm line width. Although the leakage current of the a-C:F ILD is one order higher than that of the SiO2 ILD, electrical isolation is acceptable at < 20 V when annealing is carried out at 350°C in a vacuum.

Carbon-Silicon polymeric films have been formed by electron beam bombardment (500eV) of molecularly adsorbed vinyl silane precursors under ultra-high vacuum (UHV) conditions. Temperature programmed desorption (TPD) studies show that polymerization is occurring via the vinyl groups, while Auger spectra show that the polymerized films have compositions very similar to the starting precursors; vinyltrichlorosilane (VTCS) or vinyltrimethylsilane(VTMS). VTCSderived films ˜ 100 Å thick show no reaction with Cu substrates and no diffusion of Cu until temperatures greater than 700 K, while Cu deposited on VTMS films on Al substrates show no diffusion prior to Al reaction/decomposition at 600 K. Auger and TPD studies also show that fluorocarbon precursors, such as perfluorobenzene can be incorporated into the films by e-beaminduced reactions, a first step in the controlled growth of adherent polymer films on unreactive substrates such as Cu.

The materials, process integration, and reliability issues in the development of multilevel electroplated Cu/polyimide on-chip interconnections are described. A combination of: good diffusion/adhesion barrier layers consisting of a metal liner plus the insulator Si3N4, and W stud/Si contacts resulted in a highly reliable IC chip. Electromigration of Cu damascene lines in both SiO2 and polyimide structures was investigated. Similar void growth was observed at the cathode ends of both the interconnect systems. However, the shapes of protrusions at the anode ends of the lines were different. Although the activation energies for both near bamboo-like Cu/SiO2 and Cu/polyimide were both 1.1 eV, the electromigration lifetime of the former was significantly longer. The difference is largely attributable to the poorer thermal conductivity of polyimide.