Carbon nanotubes (CNTs) have been proposed as electrical interconnects, due to their excellent properties. However, the current nanotube growth techniques suffer from several drawbacks. One of the main challenges for applying CNTs to the circuitry is the high growth temperature (>600°C). Such temperatures are incompatible with microelectronic processes. The other issue is the poor adhesion between CNTs and the substrates, which will result in long term reliability issues and high contact resistance. To overcome these disadvantages, we have successfully demonstrated a methodology that we term “CNT transfer technology”. The distinctive CNT-transfer-technology features are separation of CNT growth and CNT device assembly at solder reflow temperature. In this paper, we combined our expertise in growth of well-aligned open-ended CNT bundles with the CNT transfer process to assemble CNT bundles for fine-pitch interconnects applications. To demonstrate the feasibility of transfer process to assemble the fine-pitch CNT bundles, the CNT bundles with diameter, aspect-ratio and pitch of 25 μm, 4, and 80 μm, respectively, were assembled on the copper substrates. The measured resistivity of the long CNTs is ∼2.3×10−4 Ω-cm. The CNT-solder alloy interfaces were observed by the SEM. The results indicated that molten SnPb solder form strong mechanical bonding with open-ended CNTs, suggesting the superior CNT/solder interfacial properties by solder reflow process.

We present a technique to generate ultra-smooth surfaces and direct pattern imprinting on thin metal films by flattening the bumps and spikes of a freshly vacuum deposited metal film. The technique was implemented by using a small footprint mechanical imprint press that has the capability to vary the applied pressure from 100MPa to 600MPa. The mechanical press was incorporated with a tactile force sensor that enabled direct monitoring of the applied pressure. We demonstrated the feasibility of the technique on an e-beam evaporated silver (Ag) metal film with thickness ranging from 150Å (optically thin) to 1000Å (optically thick). The film was deposited on double-polished (100)-oriented silicon surface and double-polished borosilicate glass, resulting in a varying degree of film smoothness. The surface morphology of the pressed thin film was then studied using atomic force microscopy and SEM. Our demonstration with the e-beam evaporated silver thin film exhibits the potential for applications in decreasing the scattering-induced losses in optical metamaterials, plasmonic nanodevices and electrical shorts in molecular-scale electronic devices.

UV curing of low-k dielectrics presents a unique challenge in that the cure process is expected to do the impossible – increase hardness, modulus, cohesive strength, adhesion and reliability, decrease water absorbtion and dielectric constant, remove porogens (for porogen containing films), improve dielectric breakdown and chemical stability, all while minimizing shrinkage and contributions to film stress. Achieving this, in general, requires optimization of all of the cure parameters, such as UV spectral intensity, temperature, time, pressure, background gas, and process sequence, as well as the formulation of the low-k material itself. The spectral dependence of many of these important parameters will be discussed. A good figure of merit for modulus and k-value is the ratio of modulus/k-value. If one plots the spectral response of this ratio, one finds it peaks at a specific wavelength range. In principle it is possible to measure the UV spectral response of all of the critical parameters (not just modulus and k-value) and by overlaying these responses together determine what the proper UV exposure wavelength ranges should be. An example of this will be shown for an idealized porogen containing low-k material, for modulus, k-value, porogen removal and porogen crosslinking. A real low-k dielectric system has many more wavelength parameters to consider and the problem of bulb spectral intensity optimization becomes complex. It is also found that the relative intensity of the important wavelength bands also plays a significant role, requiring a great deal of spectral optimization experiments.

UV cure performance is also dependent on cure temperature, time, background gases and ironically, the deposition or post-deposition bake temperature. Most cure parameters such as modulus, hardness, leakage, adhesion, etc, have a strong and generally exponential dependence on cure temperature. As a result, most UV cures are performed at the highest temperature allowable as defined by thermal budget constraints and copper voiding thresholds. Background ambient can also play a critical role in the UV cure, especially for porous low-k materials and those containing porogens. Changes in composition of the background gases can alter interface. The ultimate in performance is obtained when the low-k material formulation itself is included as a key parameter in the cure optimization. By optimizing the material, UV spectrum, and cure parameters together, significant improvements can be made.

In conclusion, UV curing cannot be implemented without serious consideration to the wavelength dependence on many critical process factors. The interdependence of all components that makeup the optical system such as the wavelengths employed, light source technology, chamber design and ironically, the dielectric film itself must be considered. Only with these factors in mind, can the full benefit of UV curing be realized.

We investigated effects of thermal annealing on Ru films deposited on the 8 inch Si substrates using a volatile liquid-phase Ru precursor, tricarbonyl-1,3-cyclohexadienyl ruthenium (Ru(CO)3(C6H8)) by an atomic layer deposition (ALD) technique. Structural and electrical properties of the films were characterized by scanning probe microscopy, X-ray diffractometry, sheet resistance. Grazing incidence X-ray diffraction (GIXRD) patterns show typical Ru hexagonal polycrystalline peaks as annealing temperature was increased. At the highest annealing temperature condition, Ta = 700 °C electrical resistivity become 6 times less than in as-deposited films.

In this paper, we investigated the role of ultra-violet light (UV) curing on the molecular structure and fracture properties of a porous organosilicate glass (OSG) dielectric with k∼2.5. A correlation between material properties, including fracture toughness, and molecular structure was found. Multiple analytical techniques including Fourier Transform IR (FTIR) Spectroscopy, x-ray photo-emission spectroscopy (XPS) and x-ray reflectivity were used to investigate changes in the molecular bonding and material properties with UV curing. Overall, UV seems to be highly penetrating leading to uniform composition and density changes in the low k film to improve its properties. The decrease of methyl and hydrogen content relative to the Si-O-Si bonding structures led to increasing density and dielectric constant with UV exposure. UV curing increases the critical fracture toughness, while the sub-critical fracture toughness is insensitive to UV cure. The correlation between critical fracture toughness and material properties is discussed.

Extended abstract to Symposium B

The use of proteins and peptides to deposit and pattern metallic nanoparticles is becoming increasingly important. This method provides an inexpensive procedure to produced patterned and continuous metallic nanoparticles on variety of substrates such as silicon dioxide, silicon nitride, and polyimide. In this work, we explore the use of proteins and peptides for patterning and depositing gold nanoparticles. We used two different peptides or proteins for this experiment. One is 3XFLAG peptide from Sigma-Aldrich and the other one is bovine serum albumin (BSA). To pattern the peptides on the substrates we used two different methods, photolithography and micro-transfer molding. In photolithography, S1813 photoresist was patterned on the substrates through clean room process. In the micro-transfer molding process, a PDMS mold was made out of photoresist pattern. Polypropylmethacrylate (PPMA) was spin coated on the PDMS mold and stamped on the substrate in a high temperature. The proteins were adsorbed on the surface either physically or covalently. To deposit gold nanoparticles, the substrates with adsorbed proteins were covered with aqueous HAuCl4 solution. The proteins catalyze gold nanoparticles reduction from the solution. To characterize nanoparticles we used SEM and Electron Beam Induced Current (EBIC).

We are reporting here on the current status of our investigations on the time evolution of nanoscale surface morphology of thermally evaporated tungsten carbide coatings on silicon carbide substrates. The purpose of the study is to develop a recipe for creating thermally and chemically stable electrical contacts on silicon carbide electronic devices able to work at elevated temperatures (up to 800 °C) in oxidizing environments. We used thermal evaporation and tungsten carbide (WC) powder as a starting material to produce the thin layer deposition on semi-insulating silicon carbide (6H). Our intended applications are for devices working at 800 °C; therefore, our investigations are carried out at 1 hr intervals of time the samples spent at this temperature, in air at atmospheric pressure. We used Rutherford Backscattering Spectrometry (RBS) for measuring the stoichiometry and depth profile, and Atomic Force Microscopy (AFM) to monitor the surface morphology change.

The prevention of charge-induced corrosion of tungsten vias after metal etch has been stud-ied with several types of commonly used wet chemical solutions and two kinds of dielectric film materials, silicon dioxide and silicon oxynitride. It was found that one of the solutions, leaving essentially no polymer residue on metal lines, could effectively prevent corrosion of tungsten vias. Other solutions either produced minor residues or severe sidewall erosion on metal lines. This study has shown that the combination of wet treatment with oxynitride as the dielectric charge shielding film was as effective as other conventional methods for preventing tungsten vias corrosion. However, for metal lines capped with silicon dioxide, significant sidewall ero-sion, surface roughness, and polymer residue were observed. Chemical reaction mechanisms are proposed for the preservation of tungsten vias after metal etch.

Back End of Line (BEOL) cleaning of copper based structures requires chemical formulations that can remove copper oxide selectively without corroding copper and etching the dielectric. Many commercially available semi-aqueous and all aqueous formulations claim to meet these criteria. These include semi-aqueous fluoride strippers (SAF) and all- aqueous ammonium phosphate based chemical systems.

This paper will report the results from a fundamental study undertaken to evaluate the performance of a semi-aqueous fluoride formulation in removing copper oxide films of controlled thickness grown on copper. The thickness and composition of the oxide films were determined electrochemically using cathodic reduction technique. Electrochemical impedance spectra of samples immersed in the formulation have been measured as a function of time to follow copper oxide dissolution and the data have been analyzed to detect the transition of copper oxide to copper.

Next-generation microelectronic interconnects require the use of dielectrics with continuously lower permittivity (k) to overcome limitations induced by crosstalk parasitic signal delay. Using PECVD, Ultralow-k film (ULK, k ≤ 2.5) can be developed by creating pore inclusions within an organosilicate matrix through porogen approach. Both ULK deposition and subsequent curing process has to be adjusted in order to achieve optimized mechanical and electrical properties and maintain stability during integration. For this concern, the attention was recently focused on ultraviolet (UV) radiation to sustain the thermal curing. In the present work, a fundamental understanding of structural transformations occurring during porogen extraction from as-deposited ULK materials when exposed to thermal-assisted UV radiation is proposed. This thermal-assisted UV cure technique is very efficient in porogen removal since in a few minutes the desired porosity is reached. During the first stage of curing, the film shrinks strongly whereas the porosity is created. After porogen removal step, the porous film continues shrinking under UV radiation leading to an increase of SiOSi bonds concentration (film densification). The normalized FTIR SiOSi peak increase during UV curing (related in literature to an improvement of mechanical properties) is mainly due to the film densification, in addition to the SiOSi bridging bond creation. In this case, correlation is found between shrinkage and elastic modulus.