Conventional ash strippers can easily damage most porous low-k materials, causing increased dielectric constants and decreased film thicknesses. This effect is more prominent in carbon containing porous low-k materials such as methylsilsesquioxane (MSQ). Ashed MSQ films exhibit increased water adsorption and dielectric constants due to the removal of methyl groups and structural damage caused by interaction with plasma species. Supercritical carbon dioxide (SC-CO2), has attracted considerable attention due its low cost, low critical point temperatures and pressures, and environmentally benign nature. This work describes the effects of SC-CO2 in combination with silylating agents on O2 ash-damaged MSQ films. FTIR, sessiledrop goniometric contact angle measurements, and SEM were used to monitor changes in the films' chemical bonding, composition, and microstructure.

The continued shrink of interconnect structures is requiring new materials to be introduced into back-end of the line (BEOL) devices at an increasing rate. These new materials must provide a performance benefit from the previous generation with the recent focus on reducing the effective dielectric constant of the integrated structures. This reduction may occur not only by changing the intralevel dielectric but also by changing the capping layer/diffusion barrier on the chemicalmechanically polished (CMP'd) Cu surface. However, changing this material may alter the reliability of the device structure due to a change in the Cu/cap interface bonding. Another consequence of the decrease in minimum feature size in interconnects is that commonly practiced techniques, such as sputtered liner and Cu seed, may not be extendable to future generations. Accordingly, the focus of this paper is on identifying basic relationships between interfacial chemistry and interfacial adhesion and illustrating how those relationships can be used to address some of the issues that may pose problems in future technologies.

Recrystallization, grain growth and crystallographic texture evolution in Cu films is an area of importance for IC interconnect fabrication as the film characteristics influence the resulting line microstructure. This study examines Cu films deposited by partially ionized beam deposition onto a sublayer of tantalum nitride and additionally onto alpha- C:H. The films were annealed in-situ in the SEM chamber and intermittent orientation imaging was used to characterize the grain growth and crystallographic texture evolution in the films. Both initial and final textures are weak in each of the films analyzed, but are a function of sublayer material and thickness. Grain size in the Cu films is significantly smaller for the tantalum nitride sublayer than for the á-C:H sublayer.

The MIM capacitors with HfO2 and HfAlOx are investigated for Si RF and analog applications. The results show that both the capacitance density and voltage coefficients of capacitance (VCCs) increase with decreasing the HfO2 thickness. A high capacitance density of 13 fF/μm2with a low leakage current and a VCC of 607 ppm/V is obtained for 10 nm HfO2 MIM capacitor, which can meet the requirement of the ITRS roadmap by 2007 for silicon RF application. On the other hand, it was found that both the capacitance density and voltage coefficients of capacitance (VCC) values of the HfAlOx MIM capacitors decrease with increasing Al2O3 concentration. The results show that HfAlOx MIM capacitor with an Al2O3 mole fraction of 0.14 is optimized. It provides a high capacitance density of 3.5 fF/μm2 and a low VCC of μ140 ppm/V2. Also, small frequency dependence, low leakage current, and low loss tangent are obtained. Thus, the HfAlOx MIM capacitor with an Al2O3 mole ratio of 0.14 is very suitable for use in silicon analog applications.

Adhesion strength in sputter-deposited Cu thin films on various types of barrier layers was investigated by scratch test. The barrier layers were Ta1-xNx with varied nitrogen concentration of 0, 0.2, 0.3, and 0.5. Microstructure observation by TEM indicated that each layer consists of mixed phases of β;-Ta, bcc-TaN0.1, hexagonal-TaN, and fcc-TaN, depending on the nitrogen concentration. A sulfur- containing amorphous phase was also present discontinuously at the Cu/barrier interfaces in all samples. Scratch test showed that delamination occurred at the Cu/barrier interface and that the overall adhesion strength increased with increasing the nitrogen concentration. A good correlation was found between the measured adhesion strength and the composing phases in the barrier layer.

A new method of lowering the dielectric constant (k) of a low k polyimide thin film by plasma hydrogenation has been studied. The influence of the plasma process to the material properties, such as the composition, binding energies, and bond types, and dielectric characters, such as k and leakage current, were investigated. The result showed that after hydrogenation, the film's chemical and physical structures were changed. The film's k value could be lowered to 2.3 or less and the leakage current was only slightly increased. The mechanism of the process, which is responsible for the film's material and electrical property changes, is discussed. This is an effective method in preparing dielectrics with very low k values, which is critical for the success of the multilevel interconnection structure.

Conventional, dense dielectrics serve as structural elements in Cu/low-k interconnect structures, and a full understanding of their thermo-mechanical properties is desired to help optimize device fabrication and avoid mechanical failure. Wafer curvature measurements were made on plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films during thermal cycling to explore the large, irreversible, tensile stress developed. Spectroscopic techniques were used to probe the composition and structure of the films after annealing steps and indicate that reaction of hydrogen-containing defects provides the mechanism for stress change. A simple kinetic model, modified by the inclusion of an equilibrium function of hydrogen defects, is proposed and is found to adequately describe stress development.

The influence of different annealing conditions on the electrical resistivity of copper damascene interconnects with lateral dimensions down to sub-50 nm was studied. Different thermal treatments after copper plating as well as annealing processes in addition to the final anneal step were carried out in order to study the microstructural change of copper damascene lines. It was found that rapid thermal annealing (RTA) at high temperatures (600°C) leads to an enlargement of the Cu grains by a factor of 2 for wide lines, whereas a significant impact of annealing on the median grain size of ultrafine lines was not observed. This is attributed to the geometrical limitation of the grain growth process. As a result, the size effect in Cu nano-interconnects which is mainly determined by grain boundaries acting as scattering sites for electrons cannot be reduced significantly by using thermal treatments.

This study reports low temperature chemical vapor deposition of amorphous boron carbonitride films on SiO2 using a dimethylamine borane complex at temperatures ranging from 360 to 500°C and with varying NH3 flow at 360°C. The dielectric constant, k, of the films ranged from 4.11 to 4.83, and increased with temperature while the addition of nitrogen using NH3 decreased k. The index of refraction changed correspondingly with k, ranging from 1.826 to 2.226. Higher substrate temperature caused nitrogen and carbon content to increase with additional bonding to boron. The addition of ammonia increased the N:B ratio to as high as 0.64 and reduced k to 4.11. The higher nitrogen incorporation displaced both boron and carbon in the film, leaving boron bonded primarily to nitrogen and other boron atoms. These films were amorphous with smooth surfaces of RMS roughness ranging from 0.30 nm to 0.53 nm.

The mechanism for cleaning Cu surfaces using the vapor from organic acids was studied by infrared reflection-absorption spectroscopy (IR-RAS) and by analysis of products collected using a cold-trap placed downstream of a reactor. When formic acid vapor was exposed to oxidized Cu samples heated to about 200°C for about a half an hour, the oxides were reduced. The surface seemed to have a shiny metallic appearance but no Cu-containing volatile products were collected, and the decomposition of formic acid molecules into CO2 was observed. In contrast, using acetic acid vapor, Cu-containing etching products were collected and identified as a dinuclear Cu (II) acetate complex. The vapor treatment using formic and acetic acids can be reduced Cu oxides to have metallic Cu surfaces. Furthermore, controlling temperature and choice of organic acids enabled the advantageous establishment of a control for the reduction in, and etching of, the Cu oxides.

Black DiamondTM. (BD) is one of the primary candidates for use in copper-low k integration. Although BD is SiO2 based, it is vastly different from oxide in terms of dielectric strength and reliability. One of the main reliability concerns is the drift of copper ions under electric field to the surrounding dielectric layer and this is evaluated by voltage ramp (V-ramp) and time dependent dielectric breakdown (TDDB). Metal 1 and Metal 2 intralevel comb structures with different metal widths and spaces were chosen for dielectric breakdown studies. Breakdown field of individual test structures were obtained from V-ramp tests in the temperature range of 30 to 150°C. TDDB was performed in the field range 0.5 – 2 MV/cm. From the leakage between combs at the same level (either metal 1 or metal 2) Cu drift through SiC/BD or SiN/BD interface was characterized. It was found that Cu/barrier and barrier/low k interfaces functioned as easy paths for copper drift thereby shorting the lines. Cu/SiC was found to provide a better interface than Cu/SiN.

The compatibility of ALD and CVD metal deposition with mesoporous and microporous carbon-doped organosilicate glass (OSG) films was examined. Blanket film studies using TEM, TOF-SIMS, and positron lifetime spectroscopy demonstrate that ALD Wand TaN penetrate deep into the mesoporous film via the film's connected pore structure. In contrast, metal penetration into microporous OSG films was not observed. He and NH3 plasma pretreatments to the mesoporous OSG film surface did not seal the mesopores to ALD metal penetration, but the plasmas did damage the bulk of the mesoporous OSG film with varying severity. The results indicate that porosity, pore size, and/or pore structure regulate ALD/CVD precursor diffusion and that ALD metal deposition is a good probe of pore sealing strategies.

As the need for low-k dielectrics in the ULSI technology becomes urgent, the research primarily focuses on the deposition of novel materials with appropriate electrical properties and on the challenges concerning their integration with subsequent processing steps. In this framework we introduce the expanding thermal plasma as a novel remote technique for the deposition of low-k carbon-doped silicon dioxide films from argon/hexamethyldisiloxane/oxygen mixtures. We have obtained k values in the range 2.9-3.4 for films characterized by acceptable mechanical properties (hardness of 1 GPa).

The electronics industry, in a continual drive for improved integrated device performance, is seeking increasingly lower dielectric constants (k) of the insulators that are used as interlayer dielectric (ILD) for advanced logic interconnects. As the industry continually seeks a stepwise reduction of the “effective” dielectric constant (keff), simple extendibility, leads to the consideration of the highest performance possible, namely air bridge technology. In this paper we will discuss requirements, integration schemes and properties for a novel class of materials that has been developed as part of an advanced technology probe into air bridge architecture. We will compare and contrast these potential technology offerings with other existing dense and porous ILD integration options, and show that the choice is neither trivial nor obvious.