Porogen Approach Research Articles

Porogen Approach for the Fabrication of Plasma-Polymerized Nanoporous Polysiloxane Films

Nanoporous polysiloxane films were fabricated by plasma polymerization of hexamethyldisiloxane mixed with cyclohexane under different conditions. The pores were generated through the elimination of carbonaceous aggregates (porogen) by annealing at 600 degrees C. Results of spectroscopic ellipsometry, Fourier transform infrared spectroscopy, and positron annihilation lifetime spectroscopy suggest that not only film porosity but also average pore size depends on the amount of the decomposable porogen. The pore size was controllable in a range between 0.6 and 1.0 nm in radius by proper selection of the substrate temperature and precursor composition.

Porogen Approach for the Fabrication of Carbon-Containing Nanoporous Silicon Oxide Films

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Characterization of porous low-k films using variable angle spectroscopic ellipsometry

Variable angle spectroscopic ellipsometry (VASE™) is used as a tool to characterize properties such as optical constant, thickness, refractive index depth profile, and pore volume fraction of single and bilayer porous low-k films. The porous films were prepared using sacrificial pore generator (porogen) approach. Two sets of porous films with open- and closed-pore geometries were measured. Three models were used for data analysis: Cauchy, Bruggeman effective medium approximation (BEMA), and graded layer. Cauchy, a well-known model for transparent films, was used to obtain thickness and optical constant, whereas BEMA was utilized to calculate the pore volume fraction from the ellipsometric data. The Cauchy or BEMA models were then modified as graded layers, resulting in a better fit and a better understanding of the porous film. The depth profile of the porous film implied a more porous layer at the substrate-film interface. We found 3%–4% more porosity at the interface compared with the bulk for both films. This work shows that VASE™, a nondestructive measurement tool, can be used to characterize single- and multigraded layer porous films quickly and effectively.

PECVD Versus Spin-on to Perform Porous ULK for Advanced Interconnects: Chemical Composition, Porosity and Mechanical Behavior

AbstractPorosity introduction in a-SiOCH matrix is a main research field in microelectronic. Two techniques are used to deposit these dielectric thin films: spin-on or Plasma Enhanced Chemical Vapor Deposition (PECVD). In this work, different porous a-SiOCH thin films (k close to 2.2 – 2.3) are studied. Several synthesis ways are used to deposit these a-SiOCH layers: by porogen approach, self assembling or nanoclustering techniques for spin-on, and using a porogen approach for PECVD. Impact of deposition process and curing on material crosslinking are investigated. The skeleton structure is correlated to the elastic properties whatever the deposition technique used. Finally, porosity and pore interconnectivity are studied and the results show that barrier diffusion is less pronounced in case of small pores size such as those obtained by PECVD.

Precursor chemistry for ULK CVD

Deposited thin silicon-based films used for electronic devices as insulators in interconnections should have low and ultra low permittivity (ULK) to be acceptable to the future integration requirements, especially for the advanced technology (45 nm and below). Diffusion dielectric barrier should have also low permittivity to limit the increase of the effective global constant and should be also acceptable for etch selectivity. After an explanation of the different factors that can increase the dielectric permittivity as a function of the working frequency and the chemical bonds and atoms present in silicon-based materials, examples of plasma-polymerised materials a-SiOC:H obtained by plasma enhanced chemical vapour deposition are presented, starting with different single precursor vapours and mixed vapours. A way to get a low dielectric constant is to decrease the weight density of the bulk material, keeping the same material family, by choosing complex precursors. Voids inside the bulk material could be obtained with macropores or larger (air gap), mesopores (xerogels, SOD) or micropores up to free volume. In that case, cyclic chain precursors and/or a porogen approach can be selected in agreement with plasma experimental conditions to synthesise low density plasma-polymers with intrinsic free volume or with microporosity revealed by a post treatment.

Mechanical Properties of Porous MSQ Films: Impact of the Porogen Loading and Matrix Crosslinking.

AbstractSemiconductor industry needs a continuously improvement of integrated circuits performance and an increase of integrated density on silicon. The 2004 ITRS Roadmap underlines the need of dielectric material for ILD with dielectric constant (k) lower than 3 for the 90 nm node and than 2.4 for the 45 nm node. In this work, porous films with k value lower than 2.2 were processed using a porogen approach. Firstly, a material composed of a methylsilsesquioxane (MSQ) matrix and of organic nanoparticles (called porogen) is deposited and baked. Then, this composite is thermally cured to allow the porogens degradation and matrix crosslinking. Different k values were obtained by varying the porogen loading in the composite. Mechanical properties of composite and porous films (before and after porogen removal respectively) were investigated using nanoindentation and FTIR analysis for different porogen loadings (between 0 and 40 %). The composite modulus is higher than the porous film modulus for high porogen loading. This result is interpreted in term of matrix crosslinking. Mechanical properties were also modelized using foam mechanical models. For high porosity level, the best Young modulus fitting is obtained with tetrakaidecaedric cells, which seems in good agreement with porosity morphology.

Ultra low κ PECVD Porogen Approach: Matrix Precursors Comparison and Porogen Removal Treatment Study

AbstractThe introduction of new dielectrics into silicon chip interconnection technology is necessary to increase electrical performance. Sub-65nm technologies need κ values below 2.5 and the main way to reduce the dielectric constant is to introduce porosity. This work reports results concerning a two steps PECVD porogen approach to perform Ultra Low κ (κ <2.5). The first step is an hybrid material deposition: i.e. an a-SiOC:H matrix containing organic sacrificial inclusions (porogen phase). In the second step, the porogen is removed by a suitable curing to generate porosity. Two siloxane precursors (decamethylcyclopentasiloxane and diethoxymethylsilane) were evaluated as matrix precursors. Their influences, as well as O2 addition in plasma gas feed, in terms of cross-linking and incorporation were evaluated by FTIR analysis. Thermal anneal and UV treatment (thermally assisted) were evaluated as a curing second step. It allows to better understand this critical step which combines porogen removal and material cross-linking. By optimizing deposition and curing parameters, κ value lower than 2.4 were obtained.

Porous extreme low κ (EL κ) dielectrics using a PECVD porogen approach

The introduction of new dielectrics into silicon chip interconnection technology, to improve the electrical performance of ultra large-scale integration (ULSI), is marked by continuous revisions to meet the International Technology Roadmap for Semiconductors (ITRS) projection. Amorphous a-SiOC:H ( κ = 2.9 ) deposited by plasma-enhanced chemical vapor deposition (PECVD) from linear precursors is now in scale up towards production. Using other precursors like cyclic siloxanes, κ value is reduced to 2.5 at least. The main way to reduce the dielectric constant is to introduce porosity into the film. In this work, a two-step porogen approach is followed to perform extreme low (EL) κ ( κ < 2.5 ) deposition. Firstly, a dual-phase thin film is deposited by PECVD using two advanced precursors: decamethylcyclopentasiloxane (D5) to create a a-SiOC:H matrix and a sacrificial organic precursor. Within the matrix, the organic precursor generates organic inclusions. In a second step, the organic phase is removed by a suitable curing to induce porosity. Various types of organic precursors are investigated and thin films are then characterized. Incorporation and removal of organic molecules from a-SiOC:H material are closely studied using infrared spectroscopy. Using cyclohexene oxide as organic precursor (porogen), κ value of the porous dielectric is measured at 2.2. Nitrogen adsorption isotherms measurements prove the cured material porosity. This work clearly demonstrates the ability of achieving an EL κ with a PECVD porogen approach using D5 as matrix precursor and new organic precursors as porogen.