Dai Ishikawa

Extended Scalability of HfON/SiON Gate Stack Down to 0.57 nm Equivalent Oxide Thickness with High Carrier Mobility by Post-Deposition Annealing

We discuss scaling the equivalent oxide thickness (EOT) of Hf-based high-k gate dielectrics by post-deposition annealing (PDA). Thin HfON/SiON gate stacks with EOT=0.57 nm were successfully formed by repeating ultra thin (0.6 nm) HfO2 deposition and high-temperature (950 °C) PDA on a previously formed SiON interfacial layer. Physical and electrical analyses revealed that the reduction in EOT was due to crystallization of HfON to the tetragonal phase which has a higher dielectric constant than the amorphous and other crystalline phases. It was also found that Hf diffusion in the SiON interfacial layer was induced by the high-temperature PDA treatment. This also improved the k-value of the interfacial layer and enabled aggressive scaling even when using a SiO2-based interfacial layer. The electron mobility of the gate stack is higher than those in the previous reports, indicating that a high quality interface is realized using this approach. The reduction in EOT together with the excellent interfacial quality demonstrated in the present study shows that this technique is a promising solution for the 22-nm-node and beyond.

Study of a Negative Threshold Voltage Shift in Positive Bias Temperature Instability and a Positive Threshold Voltage Shift the Negative Bias Temperature Instability of Yttrium-Doped HfO2 Gate Dielectrics

We have studied unusual Vth shifts in the positive bias temperature instability (PBTI) and negative bias temperature instability (NBTI) of yttrium-doped HfO2 gate dielectrics. Both positive and negative stress conditions introduce shifts in opposite directions for yttrium-doped HfO2 in the low stress region. That is, a negative shift under a positive bias and a positive shift under a negative bias were observed. This is due to yttrium-related defects, with electron detrapping for PBTI and electron trapping for NBTI. Such defect formation can be suppressed by incorporating nitrogen into HfO2.

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.

Impact of In situ Postnitridation Annealing for Successful Fabrication of HfSiON Thin Film

For the successful integration of high-k gate dielectrics into advanced complementary metal–oxide–semiconductor (CMOS) processes, it is important to determine the stability of high-k materials during exposure to an ambient atmosphere. In this work, we investigated the effect of exposure to air on the nitrogen concentration in HfSiON films formed by sequentially combining HfSiO chemical vapor deposition (CVD), plasma nitridation, and postnitridation annealing (PNA). We observed that exposure to air after the nitridation step reduces the nitrogen concentration due to a reaction between the HfSiON surface and the constituents of atmospheric air. We also found that exposure to air for even a short time between nitridation and PNA leads to a significant loss of nitrogen concentration, indicating that in situ PNA is critical for achieving precise control of the nitridation. These results confirmed the importance of using clustered multichamber platforms for successful high-k fabrication.

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.

Pore-sealing process initiated by self-assembled layer for extreme low-k SiOCH (k=2.0)

A pore sealing process by Plasma-enhanced ALD (PEALD) with an amino-silane precursor has been developed, which enabled simultaneous restoration and pore-sealing film formation on damaged low-k film with k = 2.0. The precursor adsorbed preferentially at OR termination on the low-k surface to form self-assembled (SA) SiOC layer, which simultaneously recovered low-k damage. It is suggested that the SA-SiOC layer narrowed the pore opening at the low-k surface, and was followed by hermetic SiCN layer formation by PEALD. Sealing of pores against wet chemical was confirmed by forming 1.3 nm SiCN. Leakage current after pore-sealing formation was reduced by more than one magnitude compared to the pristine low-k. The current process will pave the way for enabling extremely thin diffusion barrier <;2nm at IX nm node Cu interconnect.

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.

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.