Advanced BEOL integration using porous low-k (k=2.25) material with charge damage-less electron beam cure technique

Abstract

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 Young's 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. IntroductionPropagation speed of signals in the multi-level interconnections of semiconductor devices is determined by the parasitic capacitance and wiring resistance. The low dielectric constant material is used as an interlayer dielectric (ILD) to decrease parasitic capacitance. We used NCS as an ILD that has a dielectric constant (k) of 2.25 (See Table 1 and Fig. 1). The Young's modulus of NCS is higher than that of the other porous low-k materials with almost the same dielectric constant. This is because constituent silica of NCS has nano-size cluster in the film [1,2]. We applied NCS as a homogeneous ILD into intermediate layers of 45-nm node process and excellent integration technology has been established [3].For further improvement of reliability of Cu wirings with NCS ILD for applying 32-nm node, more mechanical strength of NCS, such as high endurance to the mounting stress, and better adhesion between diffusion barrier and NCS, and also between NCS and cap insulation layers, are requested. NCS solution contains pre-composed silica clusters. After spin coating on a wafer, the silica clusters are baked and thermally cured in order to evaporate solvents and form cross-linked structure between clusters [1]. It means that physical properties of the silica clusters in the NCS solution is difficult to change by the baking and thermal curing, and other curing method should be considered. Although broadband ultraviolet (UV) sources have been widely applied for curing low-k materials [4], it has disadvantage of being unable to separate wavelengths suitable for low-k curing. On the other hand, in the case of e-beam, the irradiation energy is tunable by changing an acceleration voltage of e-beam. Therefore we expect that the most suitable irradiation energy can be applied for curing NCS by e-beam.In this paper, we compared several curing method for NCS hardening and found that the mechanical strength of NCS can be improved by the e-beam cure without degradation of low-k dielectric. In addition, we also discuss the reliability of wiring and MOS gate oxide.

Improving mechanical robustness of ultralow-k SiOCH plasma enhanced chemical vapor deposition glasses by controlled porogen decomposition prior to UV-hardening

“…Moreover, UV-curing spin-on occurs in a ͑or alternatively e-beam curing or thermal curing͒ separate process step. 24 On the contrary, the PECVD approach realizes the final film hardening and the organic porogen removal in one UV-curing process that results in PR-creation. 16 Therefore, a possible solution to avoid PR-creation ͑which has negative effect on YM͒ is to remove the organic part ͑porogen͒ from the PECVD film matrix before the regular UV-curing, similar to the spin-on deposition approach.…”

The Mechanical Property, Microstructure, and Pore Geometry of a Methyltrimethoxysilane Modified Silica Zeolite (MSZ) Film

“…The same trend was found in the film thickness variation, where most of the shrinkage occurred at 150-160 • C, and there was little change in the film thickness between 160 and 400 • C. Overall, MSZ film shrank 32% from 440 nm to 299 nm in the 150-400 • C temperature range, a shrinkage that is much larger than that of NCS2.3 (<15%) in 25-400 • C range. 38 To sum up, the porous structure was formed upon the decomposition of TPOAH at 160 • C. It is postulated that, at this temperature, the large film shrinkage in MSZ film results in high compressive stress and then the collapse of the matrix skeleton, The matrix skeleton of MSZ film cured at 400 • C, especially the actual MTMS (or CH 3 ) amount in the MSZ low-k film can be measured by 29 Si NMR spectroscopy. Figure 7 shows a predominant T-structure [(SiO) 3 Si(CH 3 )] and a minor Q-structure [(SiO) 4 Si] in the MSZ samples.…”

Porous Dielectrics in Microelectronic Wiring Applications

“…The preceding observations involve UV-assisted processes but e-beam curing raises similar concerns and a particular one with regard to electrical degradation of semiconductor devices. Owada et al [ 53 ] have reported a K = 2.25 e-beam cured film free of this issue, however.…”