The industry is strongly interested in integrating low-κ dielectrics with Damascene copper. Otherwise, with conventional materials, interconnects cannot continue to scale without limiting circuit performance. Integration of copper wiring with silicon dioxide (oxide) requires barrier encapsulation since copper drifts readily in oxide. An important aspect of integrating copper wiring with low-κ dielectrics is the drift behavior of copper ions in these dielectrics, which will directly impact the barrier requirements and hence integration complexity.

This work evaluates and compares the copper drift properties in six low-κ organic polymer dielectrics: parylene-F; benzocyclobutene; fluorinated polyimide; an aromatic hydrocarbon; and two varieties of poly(arylene ether). Copper/oxide/polymer/oxide/silicon capacitors are subjected to bias-temperature stress to accelerate penetration of copper from the gate electrode into the polymer. The oxide-sandwiched dielectric stack is used to overcome interface instabilities occurring when a low-κ dielectric is in direct contact with either the gate metal or silicon substrate. The copper drift rates in the various polymers are estimated by electrical techniques, including capacitance-voltage, current-voltage, and current-time measurements. Results correlate well with timeto-breakdown obtained by stressing the capacitor dielectrics. Our study shows that copper ions drift readily into fluorinated polyimide and poly(arylene ether), more slowly into parylene-F, and even more slowly into benzocyclobutene. A qualitative comparison of the chemical structures of the polymers suggests that copper drift in these polymers may possibly be retarded by increased crosslinking and enhanced by polarity in the polymer.

As technology progresses, the need for thinner Cu diffusion barrier caps is becoming more important, and it is advantageous if these barriers have low dielectric constants (κ). Towards this end, we characterized Cu penetration in several thin (35 nm to 70 nm) dielectrics, including silicon nitrides, silicon oxynitrides, an amorphous hydrogenated carbon film, and a methyl silsesquioxane layer. Metal Insulator Silicon (MIS) structures were used as the test vehicle. The barrier dielectrics were deposited on 100 nm thermal oxide which was grown on 2 Ω-cm, n-type Si wafers. After the deposition of 50 nm TEOS capping layers, both Al and Cu dots were evaporated on each wafer through a mask. Both Al and Cu dot samples were stressed at +2.7 MV/cm at 300°C for 10 minutes. For Cu dots, the applied stress pushed Cu ions into the dielectric stack. Stressing Al dots characterized the effects of the stress on the dielectric stacks and the quantity of Na ions in the films. Since C-V shifts are subject to stress-related instabilities in the interfaces as well as within the dielectrics themselves, triangular voltage sweep (TVS) was used after the applied stress to measure the concentration of Cu which reached the underlying thermal oxide film. The sensitivity of the TVS test with the structures used is about 5×109/cm2. Secondary ion mass spectroscopy (SIMS) analyses were performed on some of these samples to verify the electrical results.

The fluorinated low-k dielectrics SiO:F and Teflon AF were investigated for process integration with aluminum and copper interconnects. To minimize fluorine diffusion, several potential barrier materials were deposited onto the fluorinated dielectrics and characterized after heat treatment at temperatures up to 450°C. The barrier layers studied include conventional materials such as Ta, TaN, and TiN, in addition to several novel materials. Barrier layer materials were deposited using evaporation, and sputtering. The materials were characterized using nuclear reaction analysis (NRA) to determine the fluorine concentration profile. A reaction zone was noted at the dielectric-barrier interface on several samples, corresponding to the formation of a fluoride complex. In some instances, this fluoride layer was self-limiting and prevented further fluorine diffusion through the remainder of the barrier layer.

In order to achieve better performance of devices, the interconnects RC delay time, the limiting factor of the device speed today, must be reduced. This calls for a new interconnect stack: lower resistivity Copper and low k materials (k<3) as dielectrics.

Fluorinated amorphous carbon (a-F:C) prepared by HDP- CVD is an attractive candidate as a low-k material. In this work we have studied the film, its stability and its interface with Copper metallization. The high density plasma CVD process resulted in a film which contains C and F at a ratio of 1:0.6 as determined by Nuclear Reactions Analysis. XPS analysis of the Cls transition indicated four types of bonds: C-C, C-CF, CF, and CF2. X-ray diffraction as well as high resolution TEM analyses proved that the film was amorphous at least up to 500°C anneal. For various applications, the advantage of adding a thin bi-layer of a-SiC/SiOx for adhesion promotion purposes was demonstrated. In addition, the interface of a-F:C and the adhesion promoter layer with Ta, TaN and Cu was studied. No interdiffusion was observed by SIMS after 400°C annealing. 500°C annealing caused F outdiffusion from the film and Cu diffusion into the adhesion promoter layer.

Due to its low dielectric constant, high porosity SiO2 is a potential intermetal dielectric (IMD) film for sub-half micron devices. High porosity SiO2 xerogels with a low dielectric constant were prepared by a sol-gel method. Basic and mixtures of SiO2 sols (acid/base) aqueous particulate suspensions were employed using TEOS as a precursor.

Porosity values up to 55% could be obtained for the silica xerogels calcined at 250°C. The porosity values were estimated by means of nitrogen adsorption (BET). The dielectric constant was directly measured using an impedance analyzer and also calculated from the nitrogen adsorption measurements. Both techniques were in good agreement and resulted in a dielectric constant value of 2.32 for xerogels having the highest porosity.

The oxygen plasma via resists strip process cause significant damage to organic SOP, thus limiting its inter-level dielectric application. A simple treatment technology using reactive ion is proposed to reform the SOP surface. The reactive ion modification of the SOP can improve the resistance towards oxygen plasma. This is owing to the carbon atom absence in the SOP's surface area. The measurements of Fourier transform infrared (FTIR) spectroscopy, x-ray photoelectron spectroscopy (XPS), stress, thickness variation, Scanning Electron Microscope (SEM) cross-sectional view for gap filling and dielectric constant show that SOP with reactive ion treatment (RIT) has better quality for non-etch-back process than SOP without RIT.

A new TFT-LCD panel with an air-bridge type gate to data line inter-crossing has been proposed and its characteristics have been measured. The proposed structure has air-gap between gate and data line intercrossing. This air-bridge TFT-LCD panel has very small amount of capacitance between gate and data line. The new panel structure achieves 9 times faster signal delay compared with conventional panel, which enables to have enough design margin of over 20-inch diagonal size UXGA panel. We have examined thermal and mechanical durability of new panel to verify capability for commercial AMLCD application.

A fluorine-doped silicon dioxide (SiO2:F) film with dielectric constant as low as 3.0 was deposited by introducing trifluoroacetic anhydride ((CF3CO) 2O TFAA) into our hydrogen-free SiO2 PECVD system using tetraisocyanatesilane (Si(NCO)4 TICS) and O2. The film was deposited at 100°C and 0.5 Torr. It was annealed by in-situ, 0.2 Torr O2 plasma treatment at 400°C for 1 hour, as well as post-metallization annealing in N2 ambient at 400°C for 1 hour. The refractive index and the ratio of infrared absorbance of Si-F/Si-O-Si peak intensity were 1.37 and 11.7%, respectively. No peak related to water absorption was clearly observed in its infrared spectrum even after contact-holes opened and dipped into boiling water for 2 hours.

The mechanical properties and thermal stresses of FOx thin films at different thickness and cured at different temperatures have been investigated by a nanoindentor and a profilometer. In this study, the correlation between structure change, thickness, Si-H/Si-O ratio, modulus, hardness, and calculated coefficient of thermal expansion (CTE) of FOx films have been established. The results show that the modulus of 400°C cured FOx film decreases with increasing film thickness while the hardness slightly varies with increasing film thickness. The calculated CTE of FOx film increases with increasing film thickness. In addition, both the modulus and hardness of FOx films increase with increasing curing temperature. However, the calculated CTE of FOx film decreases with increasing curing temperature. The Si-H/Si-O ratio increases with increasing film thickness but decreases with increasing curing temperature. These results indicate that the increase in modulus and hardness and the decreases in CTE for FOx films are either due to the remaining of Si-H bonds in FOx film at different film thickness or the conversion of Si-H into Si-O when forming the network structure in the FOx film at higher curing temperatures.

Polysilsesquioxanes PSSQ as a candidate of coatings for interlayer low dielectric films were synthesized by acid and base catalyzed hydrolytic polycondensation of RSi(OMe)3 (R=methyl, vinyl, 3-methacryloxypropyl). Dip and spin coating of PSSQ on organic and inorganic substrates followed by curing at 100 °C, 400 °C, and 450 °C provided transparent and tough coating films of thickness 2000–9000 A. Polysilsesquioxanes adhered strongly to the substrates to form coating films of which the adhesion strength and hardness were 10 and 9H based on JIS K5400 comparable to ISO standard, as heating time and molecular weight increase. On curing at the elevated temperatures, they provided the films with a very smooth surface and the dielectric constants of 3.2∼3.6 (R=3-methacryloxypropyl), 3.8∼4.0 (R=vinyl), and 2.5∼2.7 (R=methyl) depending on film thickness and molecular weight of PSSQ. The films from PSSQ (R=methyl) were found to be porous compared with those from PSSQ (R=vinyl).

Low dielectric constant F-doped silicon oxide films (SiO:F) can be prepared by adding fluorine source, like as CF4 to the conventional PECVD processes. We could obtain SiO:F films with dielectric constant as low as 2.6 from the reaction mixture of SiH4/N2 O/CF4. The structural changes of the oxides were sensitively detected by Raman spectroscopy. The three-fold ring and network structure of the silicon oxides were selectively decreased by adding fluorine into the film. These structural changes contribute to the decrease ionic polarization of the film, but it was not the major factor for the low dielectric constant. The addition of fluorine was very effective to eliminate the Si-OH in the film and the disappearance of the Si-OH was the key factor to obtain low dielectric constant. A kinetic analysis of the process was also performed to investigate the reaction mechanism. We focused on the effect of gas flow rate, i.e. the residence time of the precursors in the reactor, on growth rate and step coverage of SiO:F films. It revealed that there exists two species to form SiO:F films. One is the reactive species which contributes to increase the growth rate and the other one is the less reactive species which contributes to have uniform step coverage. The same approach was made on the PECVD process to produce low-k C:F films from C2F4, and we found ionic species is the main precursor to form C:F films.

Atomic structure impacts on the dielectric and mechanical properties of hydrogen-silsesquioxane (HSQ) were investigated to determine the sensitivity of HSQ to Si-H bond degradation during thermal processing. It was demonstrated that the dielectric properties of HSQ films are not sensitive to Si-H bond degradation up to 50 % if polar silanol or water species are not induced during thermal processing at a temperature of ≤ 450 °C. However, as the Si-H bond density is reduced, the mechanical properties are changed due to the increasingly formed Si-O-Si networks. This provides an opportunity for tuning mechanical properties per application requirements by process optimization.

Low dielectric constant hydrogen silsesquioxane films were achieved by rapid thermal cure processing with production viable equipment. A reduced dielectric constant of k = 2.5–2.6 is demonstrated by optimizing rapid thermal cure process conditions to produce low density hydrogen silsesquioxane thin films. This is a significant reduction relative to production proven furnace cure processed hydrogen silsesquioxane with k = 2.9. Concurrent with reduced k performance is a characteristic film expansion which contributes to formation of a low density structure. A mechanism for film expansion and relevance to low k performance is described; and issues relative to integration of rapid thermal processed low k hydrogen silsesquioxane are discussed.

Spin-on-glass (SOG) solution has been prepared from methyltriethoxysilane and dimethoxymethyl-3,3,3-trifluoropropylsilane. Trifluoropropyl groups attached to silicon are thermally decomposed by curing at 450°C in nitrogen. Since the overall methylsiloxane network is maintained without a significant shrinkage upon the thermal decomposition of trifluoropropyl groups, vacant spaces whose sizes are comparable to those of trifluoropropyl groups are introduced into the methylsiloxane network, leading to the low-density film with the Brunauer, Emmet and Teller (BET) surface area of 270 m2/g. The film shows the dielectric constant of 2.3, heat stability, low moisture uptake, good planarization property and no corrosion toward aluminum conducting lines.

In situ observation of the plasma properties during deposition of fluorinated amorphous hydrogenated carbon (FLAC) and unfluorinated amorphous hydrogenated carbon are performed. The relationship between film properties and impinging ion energy and incident ion momentum is discussed within the framework of existing models of diamond-like carbon (DLC) formation. The DLC films are deposited in a low pressure radio frequency discharge operating at 13.57 MHz with methane and carbon tetra-fluoride as the source gases. Thermostability, stress, and mechanical properties are investigated. The films are elevated to 400 degrees C in order to investigate thermostability. Thin film stress and nano-hardness are also studied. The film density is investigated by gravimetric methods. The fluorinated film stoichiometry is explored with x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

We have succeeded to prepare high resistivity and rather low dielectric constant amorphous carbon nitride films a-CNx (0.52<x<0.86) by the reactive radio frequency magnetron sputtering of a graphite target using nitrogen molecules as a sputter gas.

The resistivity of a-CNx are 5×1016 to 1017 Ω-cm and be estimated to 1020 Ω-cm, when the ratio of the carbon and nitrogen becomes chemically stoichiometry 3 to 4, i.e. C3N4. The resistivity of a-CNx films prepared by a layer-by-layer method, LL-a-CNx, is 1018 Ω -cm for x=0.6. The layer-by-layer method is a cyclic process of a deposition by the sputtering and an etching by atomic hydrogen. The sample LL-a-CNx made by a layer-by-layer method are compared with that of usual method a-CNx. The dielectric constant of a-CNx films calculated from the refractive index n are 3.6 to 2.8 corresponds to nitrogen contents, 0.52<x<0.86. The dielectric constants ε of a-CNx films decrease with the content of nitrogen x. At an ultimate component of a-CNx, at x=4/3, the dielectric constant is estimated to 1.8.

A study of temperature-induced crystallinity changes in fluorinated and nonfluorinated parylene thin films using differential scanning calorimetry, thermal stress and wide angle x-ray diffraction measurements is presented. The nonfluorinated parylene (ppx-N) is shown to undergo two phase transitions between 200°C and 300°C. Both transitions show at least some degree of reversibility. The high temperature (β1 -β2) transition is accompanied by a sudden shift in stress, which is attributed to a contraction of the polymers chains. A single, reversible phase transition, occurring between 360°C and 400°C, is observed for fluorinated parylene (ppx-F). This transition is likewise marked by a significant shift in stress, and is apparently due to a similar chain contraction.