Akinori Nakano

Highly thermal-stable, plasma-polymerized BCB polymer film

A new plasma-enhanced organic monomer-vapour polymerization (plasma polymerization) method has been developed. It was used to make a divinyl siloxane bis-benzocyclobutene (DVS-BCB) polymer film for Cu dual-damascene interconnects that had high thermal stability and a low dielectric constant, k = 2.6. The method consists of the vaporization of organic monomers, transportation of monomers in the gas phase, and polymerization by plasma to make the polymer film. The method eliminates polymer oxidation of DVS-BCB during the polymerization in high vacuum, which improves the films thermal stability. The thermal stability of plasma-polymerized BCB (p-BCB) exceeded 400°C because of the higher deposition temperature, and the film had a high resistance to Cu diffusion at 400°C annealing. The narrow-pitched Cu/BCB damascene lines showed a 35% reduction in line capacitance compared with Cu/SiO2 ones. The p-BCB is shown to be a strong candidate for Cu/low-k interconnects.

Plasma enhanced ALD pore sealing for highly porous SiOCH films with k = 2.0

In order to implement highly porous PECVD SiOCH films with k = 2.0 in ILD integration, the UV-assisted restoration to remove plasma damages related with dry etch and pore sealing by plasma enhanced ALD (PEALD)-SiN formation to prevent the metal penetration into the film during subsequent metallization process was investigated. Sequential application of the restoration and pore sealing processes was proved to be the best solution enabling successful sealing capability with preserving pristine k-value of the porous SiOCH films.

Plasma-enhanced co-polymerization of organo-siloxane and hydrocarbon for low-k/Cu interconnects

A plasma-enhanced co-polymerization technique was developed for low-k/Cu damascene integration on 300 mm wafers. This technique enables us to control dielectric film properties by introducing organo-siloxane and hydrocarbon into a He-plasma. The growth rate of the low-k film derived from divinyl siloxane–benzocyclobutene (DVS–BCB) as a matrix monomer is increased by adding C2H2 as a deposition acceleration monomer and the Youngs modulus was enhanced by adding diisopropenylbenzene (DIPB) or divinylbenzene (DVB) as a reinforcement monomer. Cu damascene interconnects with plasma polymerized low-k films were successfully fabricated on 300 mm wafers.

Impact of Hydrocarbon Control in Ultraviolet-Assisted Restoration Process for Extremely Porous Plasma Enhanced Chemical Vapor Deposition SiOCH Films with k = 2.0

We investigated the effects of UV-assisted restoration on porous plasma-enhanced chemical vapor deposition (PECVD) SiOCH films with k = 2.0 and 2.3 having high porosities. By applying the UV-assisted restoration to O2-plasma-damaged films with k = 2.0 and 2.3, the recovery of the k-value was observed on the k = 2.3 film in proportion to –OH group reduction. However, the k = 2.0 film did not show recovery in spite of –OH group reduction. We found that hydrocarbon content in the k = 2.0 film was significantly increased by the UV-assisted restoration compared with the k = 2.3 film. According to these findings, we optimized the UV-assisted restoration to achieve improved controllability of the hydrocarbon uptake in the k = 2.0 film and confirmed the recovery of the k-value for O2-plasma-damaged film. Thus, adjusting the hydrocarbon uptake was crucial for restoring extremely porous SiOCH film.

An Organic Low-k Film Deposited by Plasma-Enhanced Copolymerization

A plasma-enhanced copolymerization technology has been developed in which organic precursors are designed and synthesized to form polymerized films with low dielectric constants. In order to lower the dielectric constant, a tricyclodecane (TCD) group is introduced as an organic precursor molecule because TCD is a large aliphatic hydrocarbon group, which contributes to lowering the film density. The TCD precursors are liquid at room temperature and they have a sufficient saturated vapor pressure to be applicable to the vapor phase deposition. The optimized dielectric constant of the TCD polymer was less than 2.5. A solid 13 C nuclear magnetic resonance spectrum showed that the TCD moiety in the precursor was included in the polymer without changing the structure. The effect of the substrate temperature on the film structure was studied by analyzing Raman spectra. It was revealed that the dielectric constant was associated with sp 2 carbon content in the TCD-based polymer films.

Vapor phase reactions in polymerization plasma for divinylsiloxane-bis-benzocyclobutene film deposition

Vapor phase reactions in plasma polymerization of divinylsiloxane-bis-benzocyclobutene (DVS-BCB) low-k film depositions on 300mm wafers were studied using mass spectrometry, in situ Fourier transform infrared, and a surface wave probe. Polymerization via Diels-Alder cycloaddition reaction was identified by the detection of the benzocyclohexene group. Hydrogen addition and methyl group desorption were also detected in DVS-BCB monomer and related large molecules. The dielectric constant k of plasma polymerized DVS-BCB with a plasma source power range up to 250W was close to ∼2.7 of thermally polymerized DVS-BCB, and increased gradually over 250W. The electron density at 250W was about 1.5×1010cm−3. The increase of the k value at higher power was explained by the decrease of both large molecular species via multistep dissociation and incorporation of silica components into the polymer. It was found that the reduction of electron density as well as precursor residence time is important for the plasma polymeri...

Plasma-Enhanced Atomic Layer Deposition Sealing Property on Extreme Low-k Film with k = 2.0 Quantified by Mass Metrology

We have investigated plasma-enhanced atomic layer deposition (PEALD) SiN pore-sealing film formation and diffusion behavior on highly porous SiOCH films. Mass measurement revealed the diffusion of the precursor used in PEALD into pores of SiOCH films, which was enhanced for higher-porosity SiOCH films. The diffusion of the precursor into the pores was reduced by applying UV-assisted restoration treatment before the pore-sealing process, which helped the formation of hermetic pore-sealing films. The results indicated that a 1-nm-thick SiN film was sufficient to seal the surface of the restored SiOCH film with k = 2.0. It was found that the decrease in k due to the pore-sealing deposition was as small as 0.02. The results indicated that the sequential application of UV-assisted restoration and PEALD-SiN pore sealing is a promising method of introducing the use of highly porous SiOCH films with k = 2.0 into interconnect integration.

Effect of Bridging Groups of Precursors on Modulus Improvement in Plasma-Enhanced Copolymerized Low-k Films

The mechanical strength of an organic silica low dielectric constant film was enhanced by introducing a reinforcement monomer into a matrix monomer under plasma polymerization deposition. The modulus improvement mechanism was investigated by using pyrolysis gas chromatography and mass spectrometry. Incorporation of a reinforcement monomer in the film matrix through copolymerization reactions was confirmed. Compositional analysis of the films showed that the extent of reinforcement was associated with the copolymerization ratio and the monomer content in the film. It is also found that the modulus enhancement depends on the content of three-dimensional aromatic bridged structure.

Effect of bridging groups of precursors on modulus improvement in plasma co-polymerized low-k films

We have demonstrated that the mechanical strength of organic silica low-k films can be enhanced by introducing a reinforcement monomer in a matrix monomer under plasma excitation. The modulus improvement mechanism was investigated by analyzing the film structure. Pyrolysis gas chromatography / mass spectrometry (Py-GC/MS) revealed incorporation of a reinforcement monomer in the matrix through co-polymerization reactions. Compositional analysis of the films showed that the extent of reinforcement is associated with co-polymerization ratio or the monomer content in the film. It is also indicated that the modulus enhancement depends on the content of 3D aromatic bridge structure, which is affected by the chemical structure of the reinforcement monomers.

Plasma-enhanced CVD low-k process enabling global planarity by controlling flowability

Plasma-enhanced CVD (PECVD) flowable low-k process compatible with the conventional UV cure process has been developed. Reduction of shrinkage by the UV cure was critical to ensure gap-filling capability with planarity, which was achieved by deposition condition tuning to reduce hydro-carbon constituent in the film and enhancement of dehydration by applying post-deposition treatment. Complete filling of 45-nm-space trench was achieved with excellent global planarity. The present results suggest applicability of the process for future pre-metal dielectric (PMD) or inter-layer dielectric (ILD) for aggressively scaled devices.