Carbon-doped Silicon Oxide Research Articles

Dependence of leakage mechanisms on dielectric barrier in Cu–SiOC damascene interconnects

Leakage mechanisms of low-dielectric constant (low-k) carbon-doped silicon oxide (SiOC) were investigated in Cu damascene structure integrated with amorphous SiC or SiN as Cu diffusion barrier at low electric fields (0–1.36 MV/cm) and various temperatures (25–250 °C). Conduction mechanisms of SiOC integrated with SiC were found to be different from that with SiN. Schottky emission over a barrier height of 0.70 eV at Ta/SiOC interface dominates in SiC–SiOC structures while Poole–Frenkel emission over a trap potential well of 0.69 eV dominates in SiN–SiOC structures. Traps in the SiN/SiOC interface are the main sources of leakage in Cu low-k damascene structures with SiN barrier.

Stability of Carbon-Doped Silicon Oxide Low-k Thin Films

The impact of and plasma treatments on the properties of low-dielectric-constant (low-k) carbon-doped silicon oxide (CDO) film, deposited by plasma-enhanced chemical vapor deposition, has been investigated. The thermal stability and the effect of moisture penetration on low-k films have also been evaluated. It is found that and plasma treatments of low-k films result in some loss of C content and increase in moisture uptake. This increases the k value and leakage current of the film. The and plasma treatments do not add any N content in the films. Therefore, it does not cause the resist contamination of chemically amplified-type photoresists. High thermal stability of the low-k CDO material is confirmed by isothermal thermogravimetric analysis of the low-k CDO powder and there is no weight loss or change of composition of the low-k CDO film after seven thermal cycles at 425°C for 1 h in ambient. A pressure cooker test of the film carried out at ∼2 atm, 120°C, and 100% relative humidity for 24 h has been found to increase the k value by 7% and leakage current by two orders of magnitude. © 2004 The Electrochemical Society. All rights reserved.

Intense blue–white luminescence from carbon-doped silicon-rich silicon oxide

The effect of carbon doping on the enhancement of visible luminescence from silicon-rich silicon oxide (SRSO), which consists of Si nanoclusters embedded inside a SiO2 matrix, is investigated. C-doped SRSO films were fabricated by electron cyclotron resonance-plasma enhanced chemical vapor deposition method using SiH4, O2, and CH4 source gases followed by a high-temperature anneal. Intense blue-white visible luminescence, visible to the naked eye under daylight conditions, was observed from the film with a nearly equal amount of C and excess Si (∼16 at. %) after an anneal at 950 °C. Furthermore luminescence could be tuned from 1.8 to 2.5 eV by controlling the C to excess Si ratio, the C content, and the anneal temperature. Taken together with the infrared absorption spectra, these results indicate that the luminescence is attributed to exciton recombination in C-incorporated Si nanoclusters.

On Distributions of Defect States in Low-k Carbon Doped Silicon Dioxide Films in Vicinity of Fermi Level

Spectrum of defect states N(E) in vicinity of Fermi level position in carbon-doped hydrogenated silicon dioxide (SiOCH) low-k films has been experimentally studied by deep level transient spectroscopy (DLTS) and space charge limited current (SCLC) techniques. The SiOCH films were deposited by CVD, using 3-methylsilane-oxygen mixture. Good correlation is found between features of defect spectrum obtained by DLTS and the SCLC techniques for the same SiOCH samples. In particular, N(E) peaks at 0.15-0.20 and 0.25-0.30 eV below E c have been detected by both techniques. These peaks are attributed to doubly negatively charged silicon vacancy in hexagonal or rhombohedral SiC-like phases.

Determination of the hardness and elastic modulus of low- k thin films and their barrier layer for microelectronic applications

This paper presents the experimental results and analysis of the elastic modulus and hardness for several thicknesses of dielectric films, namely low- k films and their barrier layer, using the nano-indentation technique. The elastic modulus and hardness of the films were determined by “normal” nano-indentation analysis. The data were then analyzed by re-arranging the load–displacement data ( P– h) obtained by nano-indentation in such a way that the applied load divided by the corresponding displacement ( P/ h) versus the displacement ( h) was obtained, which effectively differentiates the film-only mechanical properties from those of the substrate. The low- k film, carbon-doped silicon oxide (SiOC), was prepared using a parallel plate PECVD system. The dielectric constant of the low- k film was measured to be 3.09, which is much lower than that of commonly used dielectric materials such as SiO 2 ( k∼3.9). The hardness and elastic modulus of the film were measured to be approximately 2.23 and 13.98 GPa, respectively. To enhance the mechanical properties of the low- k thin film, a low- k barrier layer (SiCN:H) with better mechanical properties was deposited between the low- k film and the substrate or on top of the low- k film. It was found that the barrier layer improved the mechanical properties of the low- k film and the barrier layer stacked in certain circumstances. The effects of the arrangement of the barrier layer and the low- k film on the mechanical behavior of the bi-layer system were studied in detail.

Investigation of electrical conduction in carbon-doped silicon oxide using a voltage ramp method

Electrical conduction in carbon-doped silicon oxide (SiOC) is investigated over the electric field range of 0 MV/cm to the breakdown field at 300 K. Below 1.4 MV/cm, the dominant conduction mechanisms are electron hopping (<0.2 MV/cm) and Schottky emission (0.2 to 1.4 MV/cm). Poole–Frenkel emission at higher fields (>1.4 MV/cm) confirms the presence and role of electron traps in the conduction of SiOC. Near breakdown field (1.7 to 2.08 MV/cm), Fowler–Nordheim tunneling occurs and this is the major cause of dielectric breakdown in SiOC. The effective dielectric constant of SiOC in an integrated Cu damascene structure is derived from both experimental data and emission modeling.

The influence of carbon content in carbon-doped silicon oxide film by thermal treatment

Carbon-doped silicon oxide (SiOC) low- k dielectric film was deposited on a p-type Si(100) substrate with mixture of bis-trimethylsilylmethane (BTMSM) and oxygen by inductively coupled plasma chemical vapor deposition (ICPCVD). Electron density and electron temperature of ∼10 12 cm −3 and 1.6 eV, respectively, were obtained at low pressure (<300 mTorr) and radio frequency (RF) power of approximately 300 W. Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the bonding configurations, porosity and atomic concentrations within the films. The carbon content increased and the film density decreased in films annealed at 400 °C in vacuum. SiOSi and SiOC bonds were separately identified in the bonding structure of SiOC composite films. We can deduce the existence of caged SiO bonds and enhanced porosity of the film from these results. The dielectric constant of the SiOC composite film depends on the relative carbon content and the pore density. The porosity calculated is 68% when the dielectric constant is approximately 2.1.

Thickness dependent dielectric breakdown of PECVD low-k carbon doped silicon dioxide dielectric thin films: modeling and experiments

The experimental results obtained on the dielectric strength EB of carbon doped silicon dioxide thin films for various film thicknesses using I–V measurements with metal–insulator–semiconductor structures suggest a new relationship between the film thickness d and the dielectric strength EB, i.e. EB∝(d−dc)−n. This inverse power law relationship indicates the existence of a critical thickness dc which may correspond to an ultimate thickness limit below which the rate of detrapping of electron charges exceeds the rate of trapping and no dielectric breakdown can be observed. The newly obtained inverse power law relationship appears to be general since it is also supported by other published dielectric strength data for both amorphous and polycrystalline polymer thin films.

Reduction of Oxygen Plasma Damage by Postdeposition Helium Plasma Treatment for Carbon-Doped Silicon Oxide Low Dielectric Constant Films

The low dielectric constant (low k) carbon doped silicon oxide (CDO) films are obtained by plasma-enhanced chemical vapor deposition. The impact of oxygen plasma treatment on the properties of low k films has been investigated and it is found that O 2 plasma treatment damages the CDO film by removing C and part of Si contents in the film. This results in the loss of film thickness and increase in k value of the film. Postdeposition He plasma treatment has been confirmed to be effective in reducing the O 2 plasma damage on the CDO films significantly. With He plasma pretreatment, the thickness loss after O 2 plasma is reduced, and k value remains the same as the as-deposited CDO film compared to the film without the He plasma pretreatment. Also analysis of film properties by Fourier transform infrared spectroscopy. secondary ion mass spectrometry, atomic force microscopy, and scanning electron microscopy indicates that there is no obvious change of the properties of low k CDO films after O 2 plasma for postdeposition He plasma pretreated films.

The Study of Modified Layers in SiCOH Dielectrics using Spectroscopic Ellipsometry

AbstractThe current challenge in designing new low-k dielectrics is realizing sufficient mechanical and chemical stability such that the material can be integrated into current damascene schemes. The material of interest in this study is a nonporous SiCOH composite (carbon-doped silicon oxide, also known as organosilicate glass “OSG”) for use as an intermetal dielectric (IMD). During integration of this IMD, processing steps such as etch, resist strip and chemicalmechanical polishing for planarization may chemically alter the outer layer of the dielectric. Here, spectroscopic ellipsometry is used to characterize the modified layer of SiCOH films after exposure to different resist strip plasmas. The data are analyzed based on a 2-layer model, consisting of a carbon-deficient layer on the surface of the low-k SiCOH dielectric. This model is supported by XPS and FTIR data. The effects of two types of plasma etch chemistry on the formation of this modified layer were studied, and differences between the two chemistries were found. The 2-layer model accurately describes the modifications produced by the oxidizing plasma, but its description of the modified layer formed by the plasma involving nitrogen is not complete. A 3-layer model with an additional nitrogen-doped layer is suggested.

Expanding thermal plasma for low-k dielectrics deposition

AbstractAs 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).

Optical properties of PECVD dielectric thin films: thickness and deposition method dependence

Low-k dielectric carbon doped silicon dioxide films 105–1255nm in thickness, prepared by plasma-enhanced chemical vapor deposition (PECVD) in a six-station sequential deposition system and in a single deposition station, have been investigated for their optical properties using an optical spectrometer coupled with a hot stage. A decrease in refractive index, n, for films with six sub-layers compared with films with a single layer of similar thickness has been observed. This decreased refractive index is thought to be caused by the different effect of crystallinity of the substrate, as a film interface effect is introduced due to the different deposition methods. Both types of PECVD thin films show an increasing refractive index with increasing thickness, which could be attributed to the increased effective density with the increased thickness indicated from Fourier transform infrared spectroscopy microstructure analysis. Cauchy dispersion function is found to be valid for films within all the thickness range and with different deposition methods from visible spectrum to IR spectrum. The refractive index is found to decrease as the temperature increases from 25 to 450°C at a fixed wavelength for all the films.

Thickness dependent glass transition temperature of PECVD low-k dielectric thin films: effect of deposition methods

Low-k dielectric carbon-doped silicon dioxide films created by Plasma Enhanced Chemical Vapor Deposition (PECVD) using a six-station sequential deposition system exhibit different glass transition behavior from films created by PECVD in a single deposition station. The enhanced glass transition temperature (Tg) for the PECVD thin films of a layer consisting of six sub-layer deposited in a six-station sequential deposition system to the Tg for films of a single layer deposited in a single deposition system is traced back to the introduced film interface effect inherent to the different deposition methods. Both types of PECVD thin films range in thickness from 50 to 1255nm and show an increasing Tg with decreasing film thickness. The observed glass transition behavior for films with six sub-layers can be well explained by a theoretical model of thickness dependent Tg for multiple sub-layers obtained by modifying the currently existing theoretical model for the single layer thickness dependent Tg behavior, which explains the observed thickness dependent Tg for single layer PECVD thin films.

Adhesion measurement of thin films to a porous low dielectric constant film using a modified tape test

In the microelectronics industry, a simple tape test (ASTM 3359) is typically used to qualitatively study the adhesion of dielectric films. In this work, a novel approach to conduct the tape test is proposed. This new method eliminates the inconsistency in the results encountered in the traditional tape test, and, at the same time, it provides both qualitative and quantitative results. This approach employs a spring-loaded mechanism and eliminates the subjective interpretation of the results of the traditional tape test. It also provides quantitative measures of the peel rate and force, factors that are relevant in the characterization of the interfacial strength of thin films. We illustrate the use of this new, modified tape test (MTT) in the study of the adhesion of multi-layered thin film structures. This study is of significance to the understanding of the damascene interconnect process integration. Thus, the adhesion of various films (e.g. oxide, insulator and metallic films) on the spun-on porous carbon-doped silicon dioxide low dielectric constant (k) material is examined. Also, the effects of surface treatments (ion implantation and N2 plasma) and curing temperature of the porous low-k films on the adhesion of the overlying oxide films are also described. An explanation of the adhesion strength with respect to the thickness of the cap layer (overlayer) is presented as well.

Impact of substituting SiO 2 ILD by low k materials into AlCu RIE metallization

The impact of introducing a low k dielectric for gap fill into standard process flow of AlCu RIE metallization with SiO 2 ILD is described. The low k material is a carbon-doped silicon oxide deposited by CVD. Standard oxide treatment is used for further processing of the material, i.e. CMP, contact etch, resist strip and contact clean. The CMP polish rate and the via hole profiles are investigated. The capacitive coupling is reduced by 15% compared to a standard HDP oxide gap fill.

Study of SiH4-based PECVD Low-k Carbon-doped Silicon Oxide

AbstractIn previous studies, low-k carbon-doped silicon oxide (SiOC) films were deposited using organosilicon precursor: (CH3)xSiH4−x. In this paper, we present the properties of PECVD low-k SiOC films produced by using conventional SiH4 based gas precursors. The SiH4 based SiOC films have similar gross physical and electrical characteristics to those of (CH3)xSiH4−x based SiOC. Since the precursors are inexpensive, commercially available and convenient to operate for existing tools, the process should not require additional cost as compared with that of PECVD silicon dioxide. We demonstrate the feasibility of integrating Cu with SiOC on damascene interconnection. The evaluation on electrical performance of the Cu/SiOC based damascene structure will be discussed.