Mikhail Krishtab

Impact of plasma pretreatment and pore size on the sealing of ultra-low-k dielectrics by self-assembled monolayers.

Self-assembled monolayers (SAMs) from an 11-cyanoundecyltrichlorosilane (CN-SAM) precursor were deposited on porous SiCOH low-k dielectrics with three different pore radii, namely, 1.7, 0.7, and lower than 0.5 nm. The low-k dielectrics were first pretreated with either O2 or He/H2 plasma in order to generate silanol groups on the hydrophobic pristine surface. Subsequently, the SAMs were chemically grafted to the silanol groups on the low-k surface. The SAMs distribution in the low-k films depends on the pore diameter: if the pore diameter is smaller than the size of the SAMs precursors, the SAM molecules are confined to the surface, while if the pore diameter exceeds the van der Waals radius of the SAMs precursor, the SAMs molecules reach deeper in the dielectric. In the latter case, when the pore sidewalls are made hydrophilic by the plasma treatment, the chemical grafting of the SAM precursors follows the profile of the generated silanol groups. The modification depth induced by the O2 plasma is governed by the diffusion of the oxygen radicals into the pores, which makes it the preferred choice for microporous materials. On the other hand, the vacuum ultraviolet (VUV) light plays a critical role, which makes it more suitable for hydrolyzing mesoporous materials. In addition to the density of the surface -OH groups, the nanoscale concave curvature associated with the pores also affects the molecular packing density and ordering with respect to the self-assembly behavior on flat surfaces. A simple model which correlates the low-k pore structure with the plasma hydrophilization mechanism and the SAMs distribution in the pores is presented.

Vacuum ultra-violet damage and damage mitigation for plasma processing of highly porous organosilicate glass dielectrics

Porous organosilicate glass thin films, with k-value 2.0, were exposed to 147 nm vacuum ultra-violet (VUV) photons emitted in a Xenon capacitive coupled plasma discharge. Strong methyl bond depletion was observed, concomitant with a significant increase of the bulk dielectric constant. This indicates that, besides reactive radical diffusion, photons emitted during plasma processing do impede dielectric properties and therefore need to be tackled appropriately during patterning and integration. The detrimental effect of VUV irradiation can be partly suppressed by stuffing the low-k porous matrix with proper sacrificial polymers showing high VUV absorption together with good thermal and VUV stability. In addition, the choice of an appropriate hard-mask, showing high VUV absorption, can minimize VUV damage. Particular processing conditions allow to minimize the fluence of photons to the substrate and lead to negligible VUV damage. For patterned structures, in order to reduce VUV damage in the bulk and on feature sidewalls, the combination of both pore stuffing/material densification and absorbing hard-mask is recommended, and/or the use of low VUV-emitting plasma discharge.

Dependence of dielectric constant of SiOCH low-k films on porosity and pore size

A simple, clear, and robust numerical approach to calculate dielectric constant of porous organosilicate (SiOCH) based films with arbitrary shaped pores is proposed. The calculations are based on modified Clausius–Mossotti equation and can be applied for the films with wide range of porosity (0.01–0.96) and pore size (0.5–5 nm). The dielectric constants calculated in assumption of preferential localization of CH3 groups on pore wall are in good agreement with the experimentally measured k-values. The advantage of the proposed calculation model is ability to analyze the dependence of dielectric constant on pore size.

Selective Ru ALD as a Catalyst for Sub-Seven-Nanometer Bottom-Up Metal Interconnects

Integrating bottom-up area-selective building-blocks in microelectronics has a disruptive potential because of the unique capability of engineering new structures and architectures. Atomic layer deposition (ALD) is an enabling technology, yet understanding the surfaces and their modification is crucial to leverage area-selective ALD (AS-ALD) in this field. The understanding of general selectivity mechanisms and the compatibility of plasma surface modifications with existing materials and processes, both at research and production scale, will greatly facilitate AS-ALD integration in microelectronics. The use of self-assembled monolayers to inhibit the nucleation and growth of ALD films is still scarcely compatible with nanofabrication because of defectivity and downscaling limitations. Alternatively, in this Research Article, we demonstrate a straightforward H2 plasma surface modification process capable of inhibiting Ru ALD nucleation on an amorphous carbon surface while still allowing instantaneous nucleation and linear growth on Si-containing materials. Furthermore, we demonstrate how AS-ALD enables previously inaccessible routes, such as bottom-up electroless metal deposition in a dual damascene etch-damage free low-k replacement scheme. Specifically, our approach offers a general strategy for scalable ultrafine 3D nanostructures without the burden of subtractive metal patterning and high cost chemical mechanical planarization processes.

Effect of porosity and pore size on dielectric constant of organosilicate based low-k films : an analytical approach

An analytical approach allowing to analyze effect of porosity, pore size, and interconnectivity on dielectric constant of organosilicate based low-k materials is developed. Within the framework of this approach, a good agreement between the calculated and experimentally measured dielectric constants for several porogen (template) based organosilicate glasses low-k films is demonstrated. It is shown that the best agreement between the calculated and measured k-values corresponds to low-k structure with CH3 groups localized on pore wall surface. The results also demonstrate a good agreement with recently published results of similar analysis based on numerical approach.

Effect of the C-bridge length on the ultraviolet-resistance of oxycarbosilane low-k films

The ultra-violet (UV) and vacuum ultra-violet (VUV) resistance of bridging alkylene groups in organosilica films has been investigated. Similar to the Si-CH3 (methyl) bonds, the Si-CH2-Si (methylene) bonds are not affected by 5.6 eV irradiation. On the other hand, the concentration of the Si-CH2-CH2-Si (ethylene) groups decreases during such UV exposure. More significant difference in alkylene reduction is observed when the films are exposed to VUV (7.2 eV). The ethylene groups are depleted by more than 75% while only about 40% methylene and methyl groups loss is observed. The different sensitivity of bridging groups to VUV light should be taken into account during the development of curing and plasma etch processes of low-k materials based on periodic mesoporous organosilicas and oxycarbosilanes. The experimental results are qualitatively supported by ab-initio quantum-chemical calculations.

Surface-confined activation of ultra low-k dielectrics in CO2 plasma

An approach allowing surface-confined activation of porous organosilicate based low-k dielectrics is proposed and studied. By examining the plasma damage mechanism of low-k, we came up with an initial idea that the main requirements for the surface-confined modification would be the high reactivity and high recombination rate of the plasma species. Based on this concept, CO2 plasma was selected and benchmarked with several other plasmas. It is demonstrated that a short exposure of organosilicate low-k films to CO2 plasma enables high surface hydrophilicity with limited bulk modification. CO2+ ions predominantly formed in this plasma have high oxidation potential and efficiently remove surface -CH3 groups from low-k. At the same time, the CO2+ ions get easily discharged (deactivated) during their collisions with pore walls and therefore have very limited probability of penetration into the low-k bulk. Low concentration of oxygen radicals is another factor avoiding the bulk damage. The chemical reactions de...

On the mechanical and electrical properties of self-assembly-based organosilicate porous films

The effect of the replacement of Si–O–Si by Si–CH2–Si groups on the mechanical and electrical properties of silica-based hybrid sol–gel thin films is reported. For a reliable inference, two sets of organosilica films were synthesized – one consisting of a silica matrix decorated with methyl groups (Si–CH3) while the other further incorporating bridging methylene (Si–CH2–Si) functionalities. As a result, at the film density of 0.87 g cm−3, a higher Youngs modulus of 6.6 GPa was deduced for the film containing Si–CH2–Si groups compared to 5.3 GPa for the one with Si–O–Si functionalities. Concurrently, the introduction of the methylene bridging groups leads to a dielectric constant increase from 2.12 to 2.27. Furthermore, the type of surfactant, ionic or nonionic, employed as a templating agent has a negligible effect on the electrical properties and the reliability performance of the porous organosilica films.

Plasma induced damage mitigation in spin-on self-assembly based ultra low-k dielectrics using template residues

This paper describes an approach for the reduction of plasma-induced damage in self-assembly based porous ultra low-k organosilica dielectrics. The concept is based on retention of the partially decomposed sacrificial organic phase (template) into the pores of the low-k film during plasma exposure. The amount of the template residues can be controlled by varying the hard-bake process time. It is shown that those residues are uniformly distributed throughout the film in the form of pore wall coatings. After plasma processing, the remaining residues are removed by means of a UV cure. Plasma damage to the underlying organosilica matrix was assessed by exposure of the differently hard-baked low-k films to fluorine-rich Ar/SF6 plasma. The thickest coating, estimated to be around 0.4 nm, enables a nearly damage-free etch process without any carbon depletion or k-value degradation along with limited shrinkage induced by post-etch UV-curing (<4.5%). These results highlight the efficiency of a simple and scalable ...

On-chip interconnect trends, challenges and solutions: How to keep RC and reliability under control

Interconnects pose increasing challenges as technology scaling proceeds. In order to overcome these challenges simultaneous optimization of novel metallization schemes, new materials, circuit and system level approaches are required.