SiCOH Films Research Articles

Heat transport in SiCOH thin films: an experimental and molecular dynamics study

Carbon-doped silicon dioxide (SiCOH) film is currently regarded as one of the most promising low-k materials in the integrated circuits (ICs) industry for advanced technology nodes. However, there have been limited studies on the thermal properties of SiCOH compared to its electrical and mechanical properties. In this study, we investigate the thermal conductivity of SiCOH thin films through molecular dynamics simulations (MD) and experimental characterizations. Our findings indicate that the size effect on thermal conductivity at 300 K is negligible when the thickness of SiCOH film is less than 20 nm. Additionally, we observe a contrasting temperature dependence law for the thermal conductivity of SiCOH thin films compared to crystal SiO2 thin films. Furthermore, we demonstrate a significant decrease in thermal conductivity with increasing porosity in SiCOH films; specifically, an increase in porosity from 5.35% to 42.77% results in a 60% reduction in thermal conductivity. Moreover, we validate our simulation results by characterizing the thermal conductivity of SiCOH using 3 ω method.

Study on plasma-polymerized 1-(trimethylsilyl)pyrrolidine films deposited by plasma-enhanced chemical vapor deposition for use as a Cu diffusion barrier in multilevel metallization process

As integration continues in the modern semiconductor industry, copper (Cu) is used for metal lines and low dielectric constant (low-k) films are used for intermetal dielectrics (IMD) to reduce signal delays occurring in device interconnects. A diffusion barrier is essential between the Cu metal lines and the IMD to prevent Cu diffusion, and silicon carbon-nitride (SiCN) films with relatively low dielectric constants are being widely studied. In this study, SiCN films deposited from 1-(trimethylsilyl)pyrrolidine (TSPD) precursor by plasma-enhanced chemical vapor deposition (PECVD) were investigated for use as a Cu diffusion barrier in multilevel metallization process. This plasma-polymerized TSPD (ppTSPD) monolayer film as SiCN was deposited in plasma powers ranging from 15 to 30 W. The electrical properties of ppTSPD were measured and the chemical properties were analyzed by Fourier-transform infrared spectroscopy (FTIR). The dielectric constant increased with increased plasma power. The lowest dielectric constant of 3.70 and leakage current density at 1 MV/cm of 2.27×10−8 A/cm2 were found for ppTSPD film deposited at 15 W. To verify the Cu diffusion barrier characteristics of the ppTSPD films, a ppTSPD/ppOMCTS bilayer was introduced by using plasma-polymerized octamethylcyclotetrasiloxane (ppOMCTS) as porous low-k SiCOH films. The time-dependent dielectric breakdown (TDDB) characteristic was enhanced around five times than ppOMCTS monolayer used as a reference. The ppTSPD was suggested for fabricating SiCN films for use as a Cu diffusion barrier in multilevel metallization process.

Challenges in scaling of IPVD deposited Ta barriers on OSG low‐k films: Carbonization of Ta by CHx radicals generated through VUV‐induced decomposition of carbon‐containing groups

AbstractThe effect of vacuum ultraviolet (VUV) radiation during ionized physical vapor deposition (IPVD) of tantalum barriers on various porous organosilicate glass low‐k SiCOH films is studied using advanced diagnostics and quantum chemical calculations. VUV photons break the Si–C bonds, releasing hydrocarbon radicals from the pore surfaces. These radicals, trapped in pores that are partially sealed by tantalum deposition, can either react with tantalum to form carbide‐like compounds, TaCx, or be redeposited in the pores as CHx polymers. This is evidenced by a decrease in CH3 groups that correlates with an increase in TaCx. The formation of TaCx poses a significant challenge in the back end of line (BEOL) technology when reducing the barrier thickness.

Influence of plasma parameters on low-k SiCOH film grown by plasma-enhanced chemical vapor deposition using dimethyldimethoxysilane

Here, we report the influence of the electron density and the electron temperature on the reduction of dielectric constant in the SiCOH thin film using dimethyldimethoxysilane (DMDMS) as a function of pressure. The measured electron density and electron temperature decreased as increasing the pressure. The decrease in the measured electron density with increasing pressure can be attributed to local electron kinetics. Moreover, the decreasing electron temperature is caused by increased inelastic collisions between electrons and neutral species in the chamber. It is identified that CH3 radicals are less dissociated from DMDMS molecular at higher pressure by a quadrupole mass spectroscopy. As increasing pressure, the increase of the Si–CH3 bonds in SiCOH thin films is confirmed by Fourier transform infrared spectroscopy. As a result, the dielectric constant and refractive index of the SiCOH films are reduced at low electron density and electron temperature.

Modification of Porous Ultralow-k Film by Vacuum Ultraviolet Emission

Modification of spin-on-deposited porous PMO (periodic mesoporous organosilica) ultralow-k (ULK) SiCOH films (k = 2.33) containing both methyl terminal and methylene bridging groups by vacuum ultraviolet (VUV) emission from Xe plasma is studied. The temporal evolution of chemical composition, internal defects, and morphological properties (pore structure transformation) is studied by using Fourier transform infrared spectroscopy, in situ laser ellipsometry, spectroscopic ellipsometry, ellipsometric porosimetry (EP), positron-annihilation lifetime spectroscopy (PALS), and Doppler broadening positron-annihilation spectroscopy. Application of the different advanced diagnostics allows making conclusions on the dynamics of the chemical composition and pore structure. The time frame of the VUV exposure in the current investigation can be divided into two phases. During the first short phase, film loses almost all of its surface methyl and matrix bridging groups. An increase of material porosity due to removal of methyl groups with simultaneous matrix shrinkage is found by in situ ellipsometry. The removal of bridging bonds leads to an increase of matrix intrinsic porosity. Nevertheless, when the treated material is exposed to the ambient air, the sizes of micro- and mesopores and pores interconnectivity decrease with the VUV exposure time according to PAS and EP data. The last is the result of the additional film shrinkage caused by atmosphere exposure. During the second phase the increase of mesopore size is detected by both EP and PAS. The increase of mesopore size goes all the time as it is expected from in situ ellipsometry, but it is masked by the air exposure.

Simultaneous distillation-extraction for manufacturing ultra-high-purity electronic-grade octamethylcyclotetrasiloxane (D4)

Ultra-high-purity (UHP) electronic-grade octamethylcyclotetrasiloxane (D4) is the key precursor of low-dielectric constant (low-k) SiCOH films to manufacture integrated circuits (IC), meeting the stringent requirements of the rapidly developing semiconductor industry. Commonly, metallic impurities in D4 were removed by multiple unit operations of adsorption, filtration, and distillation, which could reduce the concentration of a single metallic impurity below 1 ppb. However, D4 with higher purity is required by semiconductor production due to an increase in transistor density. Herein, a novel method based on the integrated simultaneous distillation–extraction (SDE) was developed for manufacturing UHP electronic-grade D4. The lab and pilot scale experiments showed that the purity of water and D4 has a positive correlation. Based on the experimental data, a double-column process, consisting of azeotropic/extractive distillation column and precision distillation column with UNIQUAC method, was established to access the feasibility of scaling up the SDE process. According to the simulation results, D4 with the purity > 99.999 wt.% and total metallic impurities (TMI) content below 1 ppb could be obtained using ultra-pure water.

Investigation of Structure Modification of Underlying SiCOH Low-kDielectrics with Subsequent Hardmask Deposition Process Conditions

Device miniaturization requires the use of hardmasks in the IC manufacturing process, and employing an amorphous carbon layer (ACL) hardmask over a low-kdielectric is a well-known technology. An elevated temperature causes a dielectric constant shift owing to structural changes and methyl group desorption in the deposited SiCOH films. In this study, the structural change of the SiCOH film, which varies depending on the ACL deposition condition, was analyzed. Structural changes in SiCOH after ACL deposition were analyzed using Fourier transform infrared spectroscopy (FTIR). From 900 to 1300 cm−1wavenumber, changes of methyl group and structure of the SiCOH film were identified. As a result, we found that the structure and methyl content of the low-kfilm changes during the hardmask deposition due to the heat and plasma. In particular, the SiCOH film is richer in methyl group at higher temperatures. A high-density hardmask was deposited at higher temperatures. It was deduced that a high-density ACL hardmask was deposited on SiCOH because of the higher temperature, and the ACL hardmask on low-kacts as a capping layer.

Study on Effects of Carrier Gas Flow Rate on Properties of Low Dielectric Constant Film Deposited by Plasma Enhanced Chemical Vapor Deposition Using the Octamethylcyclotetrasiloxane Precursor.

In semiconductor industry, low-dielectric-constant SiCOH films are widely used as inter-metal dielectric (IMD) material to reduce a resistance-capacitance delay, which could degrade performances of semiconductor chips. Plasma enhanced chemical vapor deposition (PECVD) system has been employed to fabricate the low-dielectric-constant SiCOH films. In this work, among various parameters (plasma power, deposition pressure, substrate temperature, precursor injection flow rate, etc.), helium carrier gas flow rate was used to modulate the properties of the low-dielectric-constant SiCOH films. Octamethylcyclotetrasiloxane (OMCTS) precursor and helium were injected into the process chamber of PECVD. And then SiCOH films were deposited varying helium carrier gas flow rate. As helium carrier gas flow rate increased from 1500 to 5000 sccm, refractive indices were increased from 1.389 to 1.428 with enhancement of mechanical strength, i.e., increased hardness and elastic modulus from 1.7 and 9.1 GPa to 3.3 and 19.8 GPa, respectively. However, the relative dielectric constant (k) value was slightly increased from 2.72 to 2.97. Through analysis of Fourier transform infrared (FTIR) spectroscopy, the effects of the helium carrier gas flow rate on chemical structure, were investigated. It was thought that the increase in helium carrier gas flow rate could affect the density with changes of chemical structure and composition. In conclusion, regulation of helium carrier gas flow rate can effectively modulate k values and mechanical strength, which is needed for IMD material in semiconductor fabrication possess.

Plasma Polymerized SiCOH Films from Octamethylcyclotetrasiloxane by Dual Radio Frequency Inductively Coupled Plasma Chemical Vapor Deposition System.

We have fabricated porous plasma polymerized SiCOH (ppSiCOH) films with low-dielectric constants (low-k, less than 2.9), by applying dual radio frequency plasma in inductively coupled plasma chemical vapor deposition (ICP-CVD) system. We varied the power of the low radio frequency (LF) of 370 kHz from 0 to 65 W, while fixing the power of the radio frequency (RF) of 13.56 MHz. Although the ppSiCOH thin film without LF had the lowest k value, its mechanical strength is not high to stand the subsequent semiconductor processing. As the power of the LF was increased, the densities of ppSiCOH films became high, accordingly high in the hardness and elastic modulus, with quite satisfactory low-k value of 2.87. Especially, the ppSiCOH film, deposited at 35 W, exhibited the highest mechanical strength (hardness: 1.7 GPa, and elastic modulus: 9.7 GPa), which was explained by Fourier transform infrared spectroscopy. Since the low-k material is widely used as an inter-layer dielectric insulator, good mechanical properties are required to withstand chemical mechanical polishing damage. Therefore, we suggest that plasma polymerized process based on the dual frequency can be a good candidate for the deposition of low-k ppSiCOH films with enhanced mechanical strength.

Enhanced Thermo-Mechanical Reliability of Ultralow-K Dielectrics with Self-Organized Molecular Pores.

This paper reported the enhancement in thermo-mechanical properties and chemical stability of porous SiCOH dielectric thin films fabricated with molecularly scaled pores of uniform size and distribution. The resulting porous dielectric thin films were found to exhibit far stronger resistance to thermo-mechanical instability mechanisms common to conventional SiCOH dielectric thin films without forgoing an ultralow dielectric constant (i.e., ultralow-k). Specifically, the elastic modulus measured by nano-indentation was 13 GPa, which was substantially higher than the value of 6 GPa for a porous low-k film deposited by a conventional method, while dielectric constant exhibited an identical value of 2.1. They also showed excellent resistance against viscoplastic deformation, as measured by the ball indentation method, which represented the degree of chemical degradation of the internal bonds. Indentation depth was measured at 5 nm after a 4-h indentation test at 400 °C, which indicated an ~89% decrease compared with conventional SiCOH film. Evolution of film shrinkage and dielectric constant after annealing and plasma exposure were reduced in the low-k film with a self-organized molecular film. Analysis of the film structure via Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) indicated an increase in symmetric linear Si–O–Si molecular chains with terminal –CH3 bonds that were believed to be responsible for both the decrease in dipole moment/dielectric constant and the formation of molecular scaled pores. The observed enhanced mechanical and chemical properties were also attributed to this unique nano-porous structure.

Ultralow dielectric constant SiCOH films by plasma enhanced chemical vapor deposition of decamethylcyclopentasiloxane and tetrakis(trimethylsilyloxy)silane precursors

In semiconductor industry, SiCOH films with low dielectric constant (relative dielectric constant k ≤ 4.0) have been widely used as inter-metal dielectric (IMD) materials in the interconnects of semiconductor chips, to reduce a resistance-capacitance delay. In this study, copolymerized SiCOH films were deposited using the plasma enhanced chemical vapor deposition of decamethylcyclopentasiloxane (DMCPS) and tetrakis(trimethylsilyloxy)silane (TTMSS) precursors. The chemical structure and materials performances of the SiCOH films strongly depended on the flow rate ratios (FRRs) of DMCPS/TTMSS. The chemical bonds and compositions of the SiCOH films were investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The peak area ratios of methyl groups (CH3)x (x=1,2,3) in the spectra varied with the FRRs, affecting the k values and mechanical strengths of the films. The SiCOH films with the FRR of 1.0 showed the elastic modulus of 8.27 GPa and hardness of 0.96 GPa, which are acceptable values for semiconductor devices manufacturing. Ultralow-k values below 2.5 were achieved, along with the leakage current density below 10−6 A•cm−2 at 1 MV•cm−1. The enhanced mechanical and electrical performance with the appropriate FRR of DMCPS/TTMSS suggest the possibility of applying the copolymerized SiCOH films as IMD materials.

Characterization of Flexible Low-k Dielectric SiCOH Films Prepared by Plasma-Enhanced Chemical Vapor Deposition of Tetrakis(trimethylsilyloxy)Silane Precursor.

SiCOH thin films were deposited on rigid silicon (Si) wafers and flexible ITO/PEN substrates via plasma-enhanced chemical vapor deposition at room temperature using a tetrakis(trimethylsilyloxy)silane (TTMSS) precursor. Different chemical compositions of hydrocarbon and Si-O bondings were obtained depending on substrate types and deposition conditions. The main chemical compositions of the as-deposited films were observed as C-Hx (x = 2, 3) stretching, Si-CH₃ bending, Si-O-Si stretching, and H-Si-O bending/Si-CH₃ stretching modes. With regard to the as-deposited films, the dielectric constant increased from 1.83 to 3.45 when the plasma power increased from 20 to 80 W and the lowest leakage current of 1.76×10-4 A/cm² was obtained at the plasma power of 80 W. After bending tests with 1000, 5000, and 10000 bending cycles, the dielectric constants of the SiCOH films increased and leakage currents decreased. The structures of the SiCOH films after the bending tests were highly complicated with a variety of chemical bonding combinations. Higher peak intensity and peak area of main chemical bonding were obtained with the increased bending cycles, resulting in the increase in dielectric constants. It should be noted that the film with small changes in peak area fractions of the bending and stretching modes showed good electrical and mechanical stabilities after bending tests.

Effects of He/H₂ Plasma Treatment on Properties of SiCOH Films Deposited with the 1,1,1,3,5,7,7,7- Octamethyl-3,5-Bis(Trimethylsiloxy) Tetrasiloxane Precursor.

Low-dielectric-constant SiCOH films fabricated using plasma enhanced chemical vapor deposition (PECVD) are widely used as inter-metallic dielectric (IMD) layers in interconnects of semiconductor chips. In this work, SiCOH films were deposited with 1,1,1,3,5,7,7,7-octamethyl-3,5-bis(trimethylsiloxy)tetrasiloxane (OMBTSTS), and plasma treatment was performed by an inductively coupled plasma (ICP) system with mixture of He and H₂. The values of relative dielectric constant (k) of the as-deposited SiCOH films ranged from 2.64 to 4.19. The He/H₂ plasma treatment led to a reduction of the k values of the SiCOH films from 2.64-4.19 to 2.07-3.94. To investigate the impacts of the He/H₂ plasma treatment on the SiCOH films, the chemical compositions and structures of the as-deposited and treated the SiCOH films were compared by Fourier transform infrared spectroscopy. The experimental results indicate that the k value of the SiCOH films was decreased, there was a proportional increase in pore-related Si-O-Si structure, which is commonly called the cage structure with lager angle than 144°, after He/H₂ plasma treatment. The He/H₂ plasma treatment was considered to have reduced the k value by forming pores that could be represented by the cage structure. On the other hand, the leakage current density of the SiCOH films was slightly degraded by He/H₂ plasma treatment, however, this was tolerable for IMD application. Concludingly the He/H₂ plasma treated SiCOH film has the lowest relative dielectric constant (k~2.08) when the most highly hydrocarbon removal and cage structure formation increased.

Low-k SiCOH Films Deposited with a Single Precursor 1,1,1,3,5,7,7,7 Octamethyl-3,5-Bis(trimethylsiloxy) Tetrasiloxane by Plasma Enhanced Chemical Vapor Deposition.

Low-dielectric-constant SiCOH films were deposited by plasma-enhanced chemical vapor deposition using 1,1,1,3,5,7,7,7-octamethyl-3,5-bis(trimethylsiloxy)tetrasiloxane (OMBTSTS) as a single precursor, and the characteristics were investigated. The relative dielectric constant (k) of the SiCOH films declined gradually from 3.57 to 1.90 with decreasing plasma power. The film with the lowest k, deposited at the lowest power of 10 W, showed the lowest leakage current density, with adequate mechanical strength (hardness: 0.98 GPa and elastic modulus: 8.56 GPa) for application in multilevel semiconductor interconnects. The chemistry of the OMBTSTS films was characterized by Fourier transform infrared spectroscopy to study the relation between the chemical and dielectric properties. The dielectric properties, such as the k value and leakage current density, could be explained by a quantitative relation between the Si-O stretching bond and hydrocarbon-related bonds, such as CH₃ and Si-CH₃ bonds, with lower polarizability in the SiCOH film. The refractive index, which is directly linked to the density of the film, was also investigated by ellipsometry. We consider OMBTSTS a promising candidate as a single precursor for fabricating low-k SiCOH films in the plasma-enhanced chemical vapor deposition system.

Relation of Dielectric Constants and Chemical Structures of Low Dielectric Constant SiCOH Films Deposited by Using Octamethylcyclotetrasiloxane and Tetraethylorthosilicate Precursors.

In case of the conventional SiCOH films, a post-deposition process was used to make pores by vaporization of porogen (e.g., hydrocarbon) for decreasing the dielectric constant. However, the authors intended the deposition of the SiCOH films, which does not need the post-deposition process to form the pores by using the dual precursors having different structures. The octamethylcy-clotetrasiloxane (OMCTS) and tetraethylorthosilicate (TEOS) have different structures which were of the ring shape and the linear shape, respectively. The OMCTS and TEOS were used to fabricate the plasma polymerized low dielectric constant SiCOH film by using the plasma enhanced chemical vapor deposition system in this work. A ratio of OMCTS and TEOS was adjusted by controlling flow rates of precursor carrier gases into the process chamber. The SiCOH films, which were deposited with dual precursors, showed the very low dielectric constants (relative dielectric constant k 2.06 and 2.09) at plasma power of 10 W. All the fabricated SiCOH films showed the proper leakage current densities below 10-6 A/cm-2 at 1 MV/cm as the intermetallic dielectric material. The SiCOH films were investigated to study the relations between dielectric constants and chemical structures by using Fourier transform infrared spectroscopy. The formation of pores inside the SiCOH films was studied through the relation between Si-O-Si peaks, including network, suboxide and cage peaks, and the dielectric constant.

High-performance ultra-low-k fluorine-doped nanoporous organosilica films for inter-layer dielectric

Development of low-k materials is critical for further improving the performance of integrated circuits. In this work, a novel type of fluorine-doped ultra-low-k porous SiCOH films has been produced. The chemical composition and bond configurations of the nanometer-scale porous films were determined using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. A low dielectric constant of 2.15 was achieved with an elastic modulus of 4.84 GPa which is significantly larger than the minimum requirement of 4 GPa for ultra-large-scale integrated circuit inter-layer dielectric applications. The cage/net Si–O–Si ratio method has been proposed to elucidate the influence of molecular structure on the mechanical properties of the film. The breaking and remaking of certain bonds under UV irradiation results in the formation of increased amounts of the net Si–O–Si molecular configuration which plays a major role in increasing the elastic modulus of the film. Furthermore, it was found that increase in elastic modulus is proportional to the duration of irradiation and an increase of 20% can be achieved after 4 h of UV irradiation. The methodology and approach described in this paper can be further followed to study the mechanical properties of ultra-low k materials under various annealing and porosity conditions, and to use fluorine-doping and UV irradiation processes for optimum ultra-low k materials in application.

Low-k protection from F radicals and VUV photons using a multilayer pore grafting approach

Polymer grafting was studied in porous low-k SiCOH films as a protection against plasma damage. Pores of low-k films were covered by a plasma damage management polymer. A multistep deposition approach was applied to increase the polymer layer thickness that helped avoid pore stuffing, nonuniform deposition and polymer overburden. To study polymer protection, low-k films were exposed to F radicals and VUV photons, separately and simultaneously, at temperatures from −45 °C to +10 °C. Effective polymer protection at room temperatures was demonstrated. Lowering the temperature decreases degradation by F radicals while VUV damage, which is temperature independent, became dominant. Low-k damage protection was also significant under simultaneous exposure to F radicals and VUV photons. In the tested temperature range damage under simultaneous exposure to F radicals and VUV photons was higher than the sum of separate F and VUV damage due to a synergistic effect. To decrease the material k-value after etching, the polymer was removed from the pore walls using UV cure. It was shown that almost complete polymer removal was achieved after UV treatment. The described approach was applied to low-k etching in RF CCP CF4, CF4/Ar plasmas and exposure to Ar plasma. Significant improvement of the film k-value after the plasma treatment was confirmed.

Measurement of the vacuum-ultraviolet absorption spectrum of low-k dielectrics using X-ray reflectivity

During plasma processing, low-k dielectrics are exposed to high levels of vacuum ultraviolet (VUV) radiation that can cause severe damage to dielectric materials. The degree and nature of VUV-induced damage depend on the VUV photon energies and fluence. In this work, we examine the VUV-absorption spectrum of low-k organosilicate glass using specular X-ray reflectivity (XRR). Low-k SiCOH films were exposed to synchrotron VUV radiation with energies ranging from 7 to 21 eV, and the density vs. depth profile of the VUV-irradiated films was extracted from fitting the XRR experimental data. The results show that the depth of the VUV-induced damage layer is a function of the photon energy. Between 7 and 11 eV, the depth of the damaged layer decreases sharply from 110 nm to 60 nm and then gradually increases to 85 nm at 21 eV. The maximum VUV absorption in low-k films occurs between 11 and 15 eV. The depth of the damaged layer was found to increase with film porosity.

Effects of cesium ion implantation on the mechanical and electrical properties of porous SiCOH low-k dielectrics

In this work, the authors report an investigation of the effects of cesium (Cs) ion implantation on both porogen-embedded and ultraviolet (UV)-cured (porous) SiCOH films. For porogen-embedded SiCOH, it was found that Cs ion implantation can greatly improve the elastic modulus. It can also increase the time-zero dielectric breakdown (TZDB) strength. It also leads to an increase in the k-value for medium and high Cs doses, but for low Cs doses, the k-value decreased compared with its pristine counterpart. For UV-cured SiCOH, it was found that Cs-ion implantation does not improve the elastic modulus. It also leads to lower TZDB field strength and much higher k-values than its pristine counterpart. These effects can be understood by examining the changes in chemical bonds. This treatment is shown to have the potential to help solve the problem of the demand for lower k-values and the concomitant weak mechanical strength of SiCOH.

Characterization of Low-k SiCOH Film Etching in Fluorocarbon Inductively Coupled Plasmas

Characterization of Low-<i>k</i> SiCOH Film Etching in Fluorocarbon Inductively Coupled Plasmas