Masafumi Nakaishi

Effects of Etch Rate on Plasma-Induced Damage to Porous Low-

We investigated the effects of etch rate on low-k damage induced by dry etching under CF4, CF4/O2, and C4F6/O2/Ar chemistry conditions. The amount of damage increases with decreasing etch rate in all chemistries. This is because the amount of fluorine or oxygen radical diffusion increases with plasma exposure time. These radicals extract CH3 groups from the low-k film or oxidize the film. To reduce damage to the lowest level possible, it is necessary to suppress the effect of the damage diffusion using etching conditions where the etching speed is higher than the diffusion speed of the damage.

k

The addition of an atom having different bonding radii to a matrix film is an effective method for changing the stress of the film. In a plasma-enhanced CVD of BN, it is difficult to obtain tensile stress except for extremely boron-rich films. The controllability of tensile stress in BN film was improved by introducing a small amount of carbon into the BN matrix, using plasma-enhanced CVD between 400{degrees} and 500{degrees}C. The authors have obtained transparent films with high Youngs modulus and tensile stress. They report that the radiation resistance of BNC deposited at 400{degrees}C was improved five times better than that of BN deposited by low-pressure CVD at similar temperatures.

Films

45 nm-node multilevel Cu interconnects with porous-ultra-low-k have successfully been integrated. Key features to realize 45 nm-node interconnects are as follows: 1) porous ultra-low-k material NCS (nano-clustering silica) has been applied to both wire-level and via-level dielectrics (what we call full-NCS structure), and its sufficient robustness has been demonstrated; 2) 70-nm vias have been formed by high-NA 193 nm lithography with fine-tuned model-based OPC and multi-hard-mask dual-damascene process - more than 90% yields of 1 M via chains have been obtained; 3) good TDDB (time-dependent dielectric breakdown) characteristics of 70 nm wire spacing filled with NCS has been achieved. Because it is considered that the applied-voltage (Vdd) of a 45 nm-node technology will be almost the same as that of the previous technology, the dielectrics have to endure the high electrical field. NCS in Cu wiring has excellent insulating properties without any pore sealing materials which cause either the k/sub eff/ value or actual wire width to be worse.

Improvements of stress controllability and radiation resistance by adding carbon to boron-nitride

We studied the relationship between Ta crystal structures and the stress stability of Ta under heating. The stress in Ta which was sputter deposited on SiC was unstable and changed more than 2×109 dyn/cm2 to the compressive side during heating at 200 °C for 30 min in air. In contrast, the stress in Ta which was sputter deposited on SiC whose surface was modified by Ar sputtering was very stable, and the stress change was less than 1.5×108 dyn/cm2 even after 6 h of heating at 200 °C. The x‐ray diffraction patterns of the Ta revealed that stable Ta was strongly (002) oriented β‐Ta, and that unstable Ta was randomly oriented β‐Ta with some α‐Ta. We found that amorphizing the SiC surface or inserting a thin amorphous interlayer enhanced growth of strongly (002) oriented β‐Ta.

45 nm-node BEOL integration featuring porous-ultra-low-k/Cu multilevel interconnects

Ta is easily etched by chlorine plasmas in spite of the low vapor pressure of the reaction product, i.e. Ta-chloride. In order to clarify the etching mechanism of Ta in relatively low temperature conditions below 25°C, optical emissions were monitored. Contrary to the case of Al etching, the emission intensity of atomic chlorine, which is assumed to be an active etching species, becomes stronger during Ta etching as if it is a reaction product itself. This suggests that molecular chlorine reacts with Ta as strong as atomic chlorine, and that the reaction, especially the desorption process of the reaction product, is strongly assisted by ion bombardment, and that the reaction product, TaCl x , is sputtered off the surface to form partly as decomposed TaCl x−1 and atomic chlorine

Stress stabilization of β‐tantalum and its crystal structure

According to the 45 nm BEOL technology node, we demonstrated that a homogeneous interlayer dielectric with dielectric constant of 2.25 has a substantial advantage in terms of RC delay reduction compared to other potential architectures such as hybrid and tri-level dielectrics. Combination of the homogeneous interlayer dielectric and ultra-thinned barrier metal lowered the RC delay to 86 % compared to that listed in the ITRS 2006 update.

An Etching Mechanism of Ta by Chlorine‐Based Plasmas

Abstract We have developed an X-ray mask using Ta as the X-ray absorber and heteroepitaxially grown SiC as the X-ray membrane. Ta was reactive ion etched with a Cl 2 /CCl 4 gas mixture. Because of the high etching selectivity of Ta to a resist, 0.15 μm line and space patterns could be made using a single layer resist as an etching mask. SiC was heteroepitaxially grown on off-axis Si (111) substrates at 1,000°C with a gas mixture of SiHCl 3 /C 3 H 8 /H 2 . The properties were nearly the same as bulk values. The radiation durability was greater than 100 MJ/cm 3 . This combination of Ta and SiC is an excellent candidate for use in future X-ray lithography.

Strategies of RC Delay Reduction in 45 nm BEOL Technology

We investigated the reactive ion etching (RIE) of the Ta absorber on X-ray masks using a mixture of chlorine (Cl2) and chloroform (CHCl3) gases. To improve the pattern profiles, we used a gas mixture of chlorine (Cl2) and chloroform (CHCl3) which enhances deposition and protects side wall. We consistently obtained vertical side walls (90°±3°) with a Ta-to-resist etch-rate ratio (selectivity) of 7 and pattern edge roughness below 0.02 µm. The transfer accuracy was 0.00±0.04 µm (3 sigma) using 40% CHCl3 and Cl2 with a gas pressure of 0.2 Torr and power density of 0.8 W/cm2.

An X-ray mask using Ta and heteroepitaxially grown SiC

Abstract We measured the distortion of 0.8 μm thick Ta absorbers patterned on 2 μm thick SiC membranes. The maximum membrane diameter was 60 mm, and the largest field-window was 40 × 40 mm. This paper describes the relationship between the distortion and the shape of the blocker pattern. We got a distortion less than 0.10 μm using a parallel-cross blocker and filling the area outside the blocker pattern with dummy patterns with the same pattern density as the cell region.

Precise Reactive Ion Etching of Ta Absorber on X-Ray Masks

As a practical curing technique of low-k material for 32-nm BEOL technology node, we demonstrated that electron beam (e-beam) irradiation was effective to improve film properties of nano-clustering silica (NCS). We confirmed that by using optimized e-beam cure condition, NCS was successfully hardened without degradation of dielectric constant and the Youngs modulus increased by 1.7 times compared with that of thermally cured NCS. We fabricated two-level Cu wirings layers with NCS cured by optimized e-beam cure technique. The e-beam cure dramatically enhanced the lifetime of time-dependent dielectric breakdown (TDDB) of interlayer dielectrics. We also examined the influence of the charge damage to the MOSFETs under e-beam cured NCS layer and confirmed that there was no e-beam charge damage to the Ion-Ioff characteristics and reliability of MOSFETs with the optimized e-beam cure.