Structural Transformation in PECVD Ultralow-k Material during Porogen Removal by UV Assisted Thermal Curing
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0990-B02-04
Structural Transformation in PECVD Ultralow-k Material during Porogen Removal by UV Assisted Thermal Curing Aziz Zenasni1, Vincent Jousseaume1, Olivier Gourhant2, Laurent Favennec2, Patrick Maury2, and Lucile Mage1 1 D2NT, CEA-LETI, 17 rue des martyrs, Grenoble, 38054, France 2 STMicroelectronics, 850 rue Jean Monnet, Crolles, 38390, France Abstract Next-generation microelectronic interconnects require the use of dielectrics with continuously lower permittivity (k) to overcome limitations induced by crosstalk parasitic signal delay. Using PECVD, Ultralow-k film (ULK, k ≤ 2.5) can be developed by creating pore inclusions within an organosilicate matrix through porogen approach. Both ULK deposition and subsequent curing process has to be adjusted in order to achieve optimized mechanical and electrical properties and maintain stability during integration. For this concern, the attention was recently focused on ultraviolet (UV) radiation to sustain the thermal curing. In the present work, a fundamental understanding of structural transformations occurring during porogen extraction from as-deposited ULK materials when exposed to thermal-assisted UV radiation is proposed. This thermal-assisted UV cure technique is very efficient in porogen removal since in a few minutes the desired porosity is reached. During the first stage of curing, the film shrinks strongly whereas the porosity is created. After porogen removal step, the porous film continues shrinking under UV radiation leading to an increase of SiOSi bonds concentration (film densification). The normalized FTIR SiOSi peak increase during UV curing (related in literature to an improvement of mechanical properties) is mainly due to the film densification, in addition to the SiOSi bridging bond creation. In this case, correlation is found between shrinkage and elastic modulus. Introduction Next-generation microelectronic interconnects require the use of insulating thin films with continuously decreasing permittivity (k) to overcome limitations induced by crosstalk parasitic and signal delay. One of the most mature realizations is obtained with the pore inclusions into the dielectric skeleton. The resulted porous film takes benefit of bulk + vacuum mixture and shows a further decrease of the dielectric constant, according to the porosity rate. However, several material properties suffer from this porosity introduction such as mechanical strength, moisture uptake, chemistry diffusion and thus affect drastically the circuit integrity during integration processes. Several deposition processes have been evaluated to perform this kind of material. The co-deposition process, based on addition of couple of precursors is one of them. During ULK elaboration, the film is deposited as hybrid and treated in additional step which is an adequate curing process. Consequently, the properties of final porous film are doubly dependant on the hybrid film elaboration and the final curing process conditions. In this concern, the attention was recently focused on the ultraviolet
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