Low-k SiOCH Films Research Articles

Impact of Barrier Metal Sputtering on Physical and Chemical Damages in Low-k SiOCH Films with Various Hydrocarbon Content

Impact of barrier metal sputtering on physical and chemical damages in the low-k SiOCH films is investigated. In RF sputtering system, the potential drop across the anode sheath accelerates the ion in the plasma toward the wafer surface, inducing damages in the low-k SiOCH dielectrics. High DC bias on the target reduces the anode sheath voltage to suppress the process-induced damage in the SiOCH films. For conventional rigid and porous SiOCH films with methyl (–CH3) additives, the accelerated ions break the Si–CH3 bond, pushing up the dielectric constants. A new type of SiOCH film such as a molecular-pore-stacking (MPS) SiOCH, which is consisted of hexagonal silica ring with a large amount of hydrocarbon groups surrounding the core silica structure, exhibits high endurance to the sputtering-induced damages. The long side-chains of the hydrocarbon prevent the direct ion bonberdment to the core Si–CH3 bonds by sacrificing the C–C bond in the chains, keeping the low dielectric constant in the MPS SiOCH.

Plasma damage mechanisms for low-k porous SiOCH films due to radiation, radicals, and ions in the plasma etching process

Low dielectric constant (low-k) films have been widely used as insulating materials in ultra-large-scale integrated circuits. Low-k films receive heavy damage during the plasma processes of etching or ashing, resulting in an increase in their dielectric constant. In order to realize damage-free plasma processes for low-k films, it is essential to determine the influence of radiation, radicals, and ions emitted in the plasma process on the characteristics of low-k films. We have developed a technique to evaluate the influence of radiation, radicals, ions, and their synergies on films in real plasma processes and have named it pallet for plasma evaluation (PAPE). Using the PAPE, plasma-induced damage on porous SiOCH films were investigated in dual-frequency capacitively coupled H2∕N2 plasmas. The damage was characterized by ellipsometry, Fourier-transform infrared spectroscopy, and thermal desorption spectroscopy. On the basis of the results, the damage mechanisms associated with vacuum ultraviolet (VUV) and UV radiation, radicals, and ions were clarified. The damage was caused not only by ions and radicals but also by VUV and UV radiation emitted by the plasmas. Moreover, it was found that the synergy between the radiation and the radicals enhanced the damage.

Plasma Modification Of Si-O-Si Bond Structure in Porous Sioch Films

ABSTRACTPlasma modification of SiOCH low-k films is analyzed by means of Molecular Mechanics. It is shown that the most probable mechanism of SiOCH modification in He plasma is removal of hydrogen atoms from CH3 groups. The change of Si–O–Si bond angles depends on the amount of the formed –CH2* (CHx) groups. During the followed exposure in NH3 plasma, NH2* radicals bind CHx groups with Si forming a –CH2– Si–O–Si–O–Si–O–Si– chain. The end of this chain gets bound to its beginning through NH2. This process is the reason of pore sealing.

Plasma Etching Technology for Low-k Porous SiOCH Films

An environmental friendly gas, C5F10O, has been proposed for etching low-k SiOCH films using dual frequency (60MHz/2MHz) capacitively coupled plasma. The main ion produced is CF3+, as compared to CF+ produced by the conventional c-C4F8 gas. The advantage of CF3+ over CF+ is the much higher etching rate. With the new etching gas, a high etching rate of about 1000 nm/min with a vertical profile pattern can be achieved. The damage to SiOCH films induced by light, radicals and ions were systematically evaluated. It was found that the most severe damage was caused by ions, followed by VUV. The resist materials can be selectively removed with respect to SiOCH with less damage by employing an O2/Ar surface wave excited plasma. An advanced plasma etching technology with controlled radicals has thus been introduced.

Low-k SiOCH Film Etching Process and Its Diagnostics Employing Ar/C5F10O/N2 Plasma

We proposed an environmental harmonic etching gas of C5F10O (CF3CF2CF2OCFCF2), and demonstrated the etching of low-k SiOCH films employing a dual-frequency capacitively coupled etching system. Dissociative ionization cross sections for the electron impact ionizations of C5F10O and c-C4F8 gases have been measured by quadrupole mass spectroscopy (QMS). The dissociative ionization cross section of CF3+ from C5F10O gas was much higher than those of other ionic species, and 10 times higher than that of CF3+ from C4F8 gas. CF3+ is effective for increasing the etching rate of SiO2. As a result, the etching rate of SiOCH films using Ar/C5F10O/N2 plasma was about 1000 nm/min, which is much higher than that using Ar/C4F8/N2 plasma. The behaviours of fluorocarbon radicals in Ar/C5F10O/N2 plasma, which were measured by infrared diode laser absorption spectroscopy, were similar to those in Ar/C4F8/N2 plasma. The densities of CF and CF3 radicals were markedly decreased with increasing N2 flow rate. Etching rate was controlled by N2 flow rate. A vertical profile of SiOCH with a high etching rate and less microloading was realized using Ar/C5F10O/N2 plasma chemistry.

Channel Cracking Technique For Toughness Measurement Of Sioch Low-K Films

AbstractThe technique of channel cracking is used to study the crack growth in SiOCH low-k films. Various film thicknesses are produced using consecutive PECVD deposits on silicon substrates in up to the critical thickness for which spontaneous cracks appear. After determining mechanical properties and residual stresses of these films, samples are cleaved, and subjected to four-point bending tests. During the loading in ambient environment, cracks propagate from defects due to cleavage. Propagation of these cracks is observed in situ in order to correlate crack growth velocities to film thickness and total stress in the film. These results allow plotting crack growth rate versus stress intensity factor for crack velocity varying from 10-9 to 10-4 m/s for a stress intensity factor about 0.1 MPa√m. Moreover, in this range of velocities a model is proposed for this material to determine the film stress required to produce channel cracking, for a given film thickness.

Low-k SiOCH Film Deposited by Plasma-Enhanced Chemical Vapor Deposition Using Hexamethyldisiloxane and Water Vapor

We have developed low dielectric constant SiOCH films by plasma-enhanced chemical vapor deposition (PE-CVD) using hexamethyldisiloxane (HMDSO) containing a siloxane structure and water vapor (H2O) gases. Although the film was deposited using H2O vapor, the content of H2O is very small and the k value can be reduced to the order of 2.5. The leakage current is small and on the order of 10-9 to 10-10 A/cm2 at 1 MV/cm2. The hardness and Young's modulus are larger than 2 and 10 GPa, respectively at the k value of 2.8. However the values decrease abruptly with decreasing k value. The mechanism in which the structure and Young's modulus of PE-CVD low-k film decrease with changing k value and deposition conditions is discussed.

Porosity in low dielectric constant SiOCH films depth profiled by positron annihilation spectroscopy

The 3γ annihilation of orthopositronium and the Doppler broadening of the positron annihilation line have been measured by implanting low energy positrons in low dielectric constant (low-k) SiOCH films. The evolution and stability of film porosity with thermal treatments in the 400–900 °C temperature range has been studied. The films have been produced by plasma enhanced chemical vapor deposition and after annealing in N2 atmospheres at 480 °C have been treated in N2+He plasma. The minimum free volume of the pores in the as-produced samples has been estimated to correspond to that of a sphere with radius r=0.6 nm. The treatment in the N2 plasma was found to seal the pores up to 45 nm depth. Both the composition of the films (as obtained by Rutherford backscattering spectroscopy and elastic recoil detection analysis) and the chemical environment of the pores probed by positrons were found to be very stable up to 600 °C thermal treatment. Above such a temperature a reduction of the hydrogen content accompanied by a change in the structure and in the chemical environment of the pores has been observed. In the samples thermal treated at 800–900 °C, the positronium formation is reduced by one-third respect with the as produced sample. In the annealed and as-produced films, a natural aging of 30 days in air was enough to contaminate the porosity, as pointed out by a strong reduction of the 3γ annihilations. The effect of contamination and the distribution of the pores were completely recovered after a thermal treatment at 400 °C. Artificial aging of SiOCH films in controlled atmospheres of H2, O2, H2O has shown that H2O is the more efficient contaminant in reducing the effective volume of the pores.

Comparative study of SiOCH low-k films with varied porosity interacting with etching and cleaning plasma

The interaction between conventional and highly porous SiOCH with CF4, O2, and H2 plasma has been investigated. The highly porous SiOCH film has porosity about 40% and a k value about 2.2. The pristine SiOCH film has 19% of porosity and k value of 2.7. All experiments were performed at room temperature in a downstream plasma reactor. It was found that (i) the CF4 plasma etches the SiOCH film without bulk material modification (however, the etch rate was higher in the case of the SiOCH film with increased porosity); (ii) the O2 plasma oxidizes the SiOCH film converting the top layer to a hydrophilic SiO2-like porous material, the SiOCH film with increased porosity suffers more severely from this kind of plasma; (iii) the CF4/O2 plasma mixture has an optimal O2 concentration at which the etch rate is maximal; and (iv) the H2 plasma does not interact with the SiOCH film and can be a promising candidate for the resist stripping.

Comparative study of PECVD SiOCH low-k films obtained at different deposition conditions

Four CVD SiOCH films deposited at various conditions were used for comparative evaluation. The films were evaluated by RBS, spectroscopic ellipsometry, and ellipsometric porosimetry. Oxygen plasma resistance was studied by spectroscopic ellipsometry and TOF-SIMS analysis after exposure of the films to downstream oxygen plasma. The different deposition conditions result in different carbon content and different porosity. The film with the highest carbon content has the lowest porosity and vice versa. As carbon content of films increases and their porosity decreases, the SiOCH films become more resistant to oxygen plasma.

Nano-Scale Morphology and Electron Spectrum of Defect States in Low-k SiOCH Films

ABSTRACTResults of experimental investigations on the relationship between nanoscale morphology of carbon doped hydrogenated silicon-oxide (SiOCH) low-k films and their electron spectrum of defect states are presented. The SiOCH films have been deposited using trimethylsilane (3MS) - oxygen mixture in a 13.56 MHz plasma enhanced chemical vapor deposition (PECVD) system at variable RF power densities (from 1.3 to 2.6 W/cm2) and gas pressures of 3, 4, and 5 Torr. The atomic structure of the SiOCH films is a mixture of amorphous-nanocrystalline SiO2-like and SiC-like phases. Results of the FTIR spectroscopy and atomic force microscopy suggest that the volume fraction of the SiC-like phase increases from ∼0.2 to 0.4 with RF power. The average size of the nanoscale surface morphology elements of the SiO2-like matrix can be controlled by the RF power density and source gas flow rates.Electron density of the defect states N(E) of the SiOCH films has been investigated with the DLTS technique in the energy range up to 0.6 eV from the bottom of the conduction band. Distinct N(E) peaks at 0.25 - 0.35 eV and 0.42 - 0.52 eV below the conduction band bottom have been observed. The first N(E) peak is identified as originated from E1-like centers in the SiC-like phase. The volume density of the defects can vary from 1011 - 1017 cm-3 depending on specific conditions of the PECVD process.