Fluorine-doped Silicon Dioxide Research Articles

Characterization of fluorine-doped silicon dioxide films by Raman spectroscopy and Electron-spin resonance

We have measured Raman and Electron-spin resonance (ESR) spectra of fluorine-doped SiO 2 films deposited by two different methods. In high-density plasma (HDP) films, the Raman band at about 490 cm − 1 becomes drastically stronger as the F/Si ratio increases, whereas the Raman band from threefold ring defect is independent of the F/Si ratio. The unusual increase of the intensity of the 490 cm − 1 band in HDP films has been interpreted in terms of the existence of Si–Si clusters. From a comparison between Raman spectra of HDP film and plasma chemical vapor deposition using tetraethoxysilane (p-TEOS) film with the same F/Si ratios it has been found that HDP film has more Si–Si bonds and threefold ring defects than p-TEOS film. Furthermore, the polarized Raman spectra in the 810 cm − 1 bands indicate that inhomogeneous SiO 2 clusters of various sizes should exist in the network structure of HDP film. The result of the ESR measurement shows that HDP films have fewer dangling bonds than p-TEOS films. It is considered that many Si–Si clusters, threefold ring defects, and inhomogeneous SiO 2 cluster sizes, and the few dangling bonds in HDP films give rise to the film properties of low stress, good adhesion with Si substrate, and low water permeation.

Features of Er3+ luminescence in fluorine-doped amorphous silicon dioxide fabricated by low-temperature plasma CVD

Spectra and photoluminescence kinetics of Er3+ ions incorporated in an amorphous host of fluorine-doped silicon dioxide synthesized by surface plasma chemical vapor deposition (SPCVD) are investigated at temperatures of 27–300K. Luminescence is excited with an Ar+ laser at a wavelength of 514.5nm and with a diode laser at a wavelength of 975nm. Narrow and well-defined components of Stark manifolds with a small contribution from inhomogeneous broadening intrinsic to Er3+ ions in crystalline, but not amorphous, hosts are revealed and identified in photoluminescence spectra. The structure of the Stark manifolds is well-resolved at low temperatures. The presence of the well-resolved Stark structure in the spectra is indicative of stable anion complexes formating the Er3+ local neighborhood presumably associated with fluorine incorporation. This neighborhood is formed during the low temperature plasma chemical synthesis and is destroyed upon glass fusion.

Effects of Properties and Growth Parameters of Doped and Undoped Silicon Oxide Films on Wear Behavior During Chemical Mechanical Planarization Process

Understanding the tribological, mechanical, and structural properties of an inorganic and organic dielectric layer in the chemical mechanical planarization (CMP) process is crucial for successful evaluation and implementation of these materials with copper metallization. Polishing behaviors of different carbon- and fluorine-doped silicon dioxide (SiO2) low dielectric constant materials in CMP process are discussed in this paper. Films were deposited using both chemical vapor deposition and spin-on method. Carbon and fluorine incorporation in the Si–O network weaken the mechanical integrity of the structure and behave differently in slurry selective to SiO2 films. Mechanical properties of the films were measured using depth-sensing nanoindentation technique, and it was found that undoped SiO2 film has the highest and spin-on carbon-doped oxide films have the lowest hardness and modulus values. Wear behavior of the doped SiO2 is studied in a typical SiO2 CMP environment, and results are analyzed and compared with those of the undoped SiO2 films. Coefficient of friction and acoustic emission signals have significant effect on the polishing behavior. Surface of the films are investigated before and after polishing using atomic force microscopy. Roughness and section analysis of the films after polishing show the variation in wear mechanism. Validation of Preston’s equation is discussed in this study. Additionally, different wear mechanisms are presented, and a two body abrasion model is proposed for the softer films.

Fluorine-Doped SiO2 Films Made from Silicone and Polytetrafluoroethylene Using an F2 Laser

In the present paper, we propose a novel method which permits us to fabricate fluorine-doped silicon dioxide (F-doped SiO2) films on various substrates at room temperature. The films were selectively grown on a substrate by simultaneous 157-nm F2 laser illumination of a silicone rubber target, a polytetrafluoroethylene (PTFE) target, and the substrate. Fourier transform infrared spectroscopy (FT-IR) spectra and X-ray photoelectron spectroscopy (XPS) spectra showed that the films had a uniform fluorine concentration in the depth direction and no contaminants, such as carbon and hydrocarbon. The films were photochemically grown on the substrate in an atmosphere of gases evolved from silicone and PTFE by F2 laser illumination. The relative dielectric constant of the films was lower than that of the SiO2 films grown by F2 laser illumination without a PTFE target, namely, 3.6 at a laser fluence of 22 mJ/cm2. The F-doped SiO2 film formed at a higher a laser fluence had a lower refractive index and lower relative dielectric constant.

Effect of deposition temperature on thermal stability in high-density plasma chemical vapor deposition fluorine-doped silicon dioxide

Thermal stability of fluorine-doped silicon dioxide films deposited by high-density plasma chemical vapor deposition as a function of deposition temperature were investigated in this study. Both thermal desorption spectrum and annealing test results show that SiOF films deposited above 400 °C have better thermal stability. Furnace annealing data indicate that non –Si–F– bonding fluorine does exist in low-deposition-temperature SiOF films. Furthermore, secondary-ion mass spectrometer results also reveal that the fluorine in SiOF films with a lower-deposition temperature is easily diffused out and turned into the underlayer, which results in less thermally stable SiOF films. Moreover, short-loop simulation results have been subsequently tested and it was concluded that the deposition temperature of the SiOF film is extremely important for thermal stability.

FTIR Characterization of Fluorine Doped Silicon Dioxide Thin Films Deposited by Plasma Enhanced Chemical Vapor Deposition

Fluorine doped silicon dioxide (SiOF) thin films have been prepared by plasma enhanced chemical vapor deposition. The Fourier transform infrared spectrometry (FTIR) spectra of SiOF films are deliberated to reveal the structure change of SiO2 and the mechanism of dielectric constant reduction after doping fluorine. When F is doped in SiO2 films, the Si-O stretching absorption peak will have a blue-shift due to increase of the partial charge of the O atom. The FTIR spectra indicate that some Si-OH components in the thin film can be removed after doping fluorine. These changes reduce the ionic and orientational polarization, and result in the reduction in dielectric constant of the film. According to Gaussian fitting, it is found that the Si-F2 bonds will appear in the SiOF film with increase of the fluorine content. The Si-F2 structures are liable to react with water, and cause the same increase of absorbed moisture in the film.

Structural Analyses of Fluorine-Doped Silicon Dioxide Dielectric Thin Films by Micro-Raman Spectroscopy

AbstractFluorine-doped silicon dioxide, a dielectric material compatible with copper integration, has received considerable attention for applications requiring a k value in the 3.5 to 4.0 range. Given the influence of structure on desired properties, convenient experimental structural probes of this type of material are of widespread interest. This work focuses on Raman spectroscopic analyses of ring defects in fluorine-doped silicon dioxide films prepared by plasma enhanced chemical vapor deposition (PECVD) as well as high density plasma methods (HDP). These measurements are complemented by ab initio computational simulations of the ring defects in these films and the impact of nearby fluorine on their stability. The impact of aging on these structures and correlations of observed trends with experimental techniques such as X-ray fluorescence are also described.

Metal/fluorinated-dielectric interactions in microelectronic interconnections: Rapid diffusion of fluorine through aluminum

Rather surprising behavior has been observed when aluminum (Al) is in contact with fluorine-doped silicon dioxide (FSG). With Al deposited onto FSG, x-ray photoelectron spectroscopy shows that there is only a very minor reaction at the interface, producing a small amount of AlF3. No fluorine is observed in the bulk of the Al film, but fluorine diffuses readily through the Al even at room temperature and reacts at the free metal surface. On the other hand, with FSG deposited onto Al, the native aluminum oxide provides quite good protection against fluorine diffusion. By contrast, when pure Cu is in contact with FSG, there is almost no interaction or fluorine diffusion. Various approaches to reducing fluorine diffusion into a metal are also discussed, including using a diffusion barrier (TiN, Ta, TaN) or a suitable plasma treatment of the FSG before metal deposition.

Thermal stability enhancement of Cu/WN/SiOF/Si multilayers by post-plasma treatment of fluorine-doped silicon dioxide

The effect of a post-plasma treatment on the dielectric property and reliability of fluorine doped silicon oxide (SiOF) film was studied. Also, the thermal stability of the Cu/WN interconnect system with SiOF interlayer dielectrics was examined by rapid thermal annealing. The surface roughness of SiOF films increased with increasing plasma treatment power due to ion bombardment effect during the plasma treatment. As the plasma treatment power increased, the dielectric constant increased from 3.16 to 3.43, while the change in the relative dielectric constant of the plasma treated films decreased in magnitude after treatment at 100 °C for 30 min in boiling water. Furthermore, the chemical properties of the plasma treated SiOF layers near the top surface tend to resemble those of thermal oxides after plasma treatment with sufficient plasma power, apparently due to the reduction in the Si–F bonding in the films. In the case of a Cu/WN/SiOF/Si multilayer structure, surface oxidation and densification due to the plasma treatment seemed to play an important role in suppressing the interdiffusion between SiOF and metal interconnects.

PECVD of Low Dielectric Constant Fluorine-Doped SiO2 Using TICS/O2/TFAA with In-Situ Annealing

AbstractA 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.

Effect of Post Plasma Treatment on Reliability of Electron Cyclotron Resonance Chemical Vapor Deposited SiOF Films

Fluorine doped silicon dioxide (SiOF) films have a low dielectric constant. Unfortunately, the drawback of regarding SiOF is its low resistance to moisture which causes the increment of dielectric constant with time. Also, fluorine desorption of SiOF film during the postmetallization process causes degradation of metal interconnections. In this study, oxygen postplasma treatments are applied to as-deposited SiOF films for improving their dielectric properties and thermal stabilities. It has been observed that the postplasma treatment of SiOF films is quite an efficient method for blocking moisture and for the stabilization of the dielectric constant. Furthermore, the O2 postplasma treatment of Cu/W–N/SiOF/Si stacks by suppressing interdiffusion improved the thermal stability between SiOF and metal interconnections.

Characterization of fluorine-doped silicon dioxide film by Raman spectroscopy

We have measured Raman spectra of fluorine-doped SiO 2 (SiOF) films and quartz glass. From a comparison between Raman spectra of the SiO 2 film and quartz glass, it has been found that the SiO 2 film is under compressive stress and that it has more threefold ring defects than quartz glass. Raman bands from threefold and fourfold ring defects in SiOF films become week as the fluorine/oxygen (F/O) ratio increases and as the stress decreases. The decrease of intensities of these Raman bands shows that ring defects in SiOF films decrease as the F/O ratio increases and as the stress decreases. The triply degenerated ω 4 mode at 460 cm −1 becomes sharp as the F/O ratio increases and as the stress decreases. Furthermore, the peak-frequency of ω 1 mode around 820 cm −1 decreases with a decrease of stresses whereas that of ω 3 mode around 1065 cm −1 increases. These results can be well understood in terms of a decrease of O-Si-O bonding angle caused by relaxation of stresses.

Deposition of stable, low κ and high deposition rate SiF 4-doped TEOS fluorinated silicon dioxide (SiOF) films

Fluorine doped silicon dioxide (SiOF) is recognized as a potential intermetal dielectric (IMD) film for sub-half micron devices, due to its low dielectric constant ( κ) and good gap-fill capabilities. For the first time, physically stable and high deposition rate (1550 nm/min) SiOF films were deposited using a parallel-plate plasma CVD–single wafer DxZ reactor, involving SiF 4/TEOS/O 2 chemistry. The analytical results indicate that these SiOF films, having a F concentration up to 3.0%, contain only Si–F bonding, do not absorb moisture and show stable dielectric constants. A typical highly stable SiOF film has F concentration and dielectric constant values of 2.4% and 3.5, respectively. This film is thermally stable up to 600°C and can be used as a low cost cap layer for HDP–CVD oxides and other low κ spin-on-glass materials, as well as an IMD layer for damascene applications.

Deposition and surface modification of SiOf films with low dielectric constant

Low dielectric constant fluorine-doped silicon dioxide (SiOF) films were deposited using electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECRPECVD) with SiF4 and O2 as source gases. The effect of fluorine addition on the dielectric properties of the film as a function of the SiF4/O2 gas flow ratio is described in this paper. Also, the effect of post-plasma treatment on the moisture absorption of SiOF films for IMD materials in multilevel interconnections of ultra-large scale integrated circuits (ULSIs) was investigated. The SiOF film deposited at an SiF4/O2 gas flow ratio of 1.0 exhibited a fluorine content of 11.8 at.% and a dielectric constant of 3.14. When the duration time of post-plasma treatment increased, the following results were obtained: The etch rate of SiOF films decreased from 80 A/sec to 10 A/sec, and surface roughness of the plasma-treated SiOF films increased in relation to the ion bombardment effect of the plasma. The refractive index and relative dielectric constant increased from 1.391 to 1.461 and from 3.14 to 3. 90, respectively, due to the changes of surface chemistry in post-plasma treatment. The leakage current density of SiOF films prepared by ECRPECVD using SiF4 and O2 was less than 1 x 10-9 A/cm2 and the breakdown field strength increased from 3.5 MV/cm to 8 MV/cm.

Plasma Enhanced Chemical Vapor Deposition and Characterization of Fluorine Doped Silicon Dioxide Films

Fluorine-doped silicon dioxide films were deposited using a dual frequency (DF) multi-station sequential deposition plasma enhanced chemical vapor deposition (PECVD) reactor. Fluorine-doped silicon dioxide films with various Si–F content were deposited using mixture of vaporized tetraethylorthosilicate (TEOS), O2 and C2F6. The Si–F content, physical properties and gap filling capability of the F-doped films were characterized. The physical properties and gap filling capability were found to be dependent upon wafer temperature, pressure, gas phase reactant concentrations and rf power, but is predominantly dependent on Si–F content. Aspect ratios (AR) up to 1.64:1 with 0.5 µm spacing were filled with no observable seams and voids.