Enhanced Thermal Stability of Low-k Ethyl-Bridged Organosilicas Using Laser Spike Annealing

Abstract

Incorporating organic bridges within porous organosilica films is a promising route to achieving required mechanical properties of ultralow-k dielectric films. To retain these critical organic bridges during thermal processing, submillisecond laser spike annealing (LSA) of sol–gel-derived, low-k, ethyl-bridged organosilica films was investigated. Structural and dielectric properties changes, as a function of the peak annealing temperature between 400 and ∼1400 °C, were determined by using a lateral-gradient LSA technique. Under LSA, the ethyl-bridged structures were found to remain stable to the highest LSA peak temperatures; in contrast, nearly 40% of the bridges were lost by 540 °C under hot plate annealing. Refining of Si–O–Si structures, and porosity generation from remnant porogens, was found to begin above ∼700 °C with densification only occurring ∼350 °C higher. This ability of LSA to retain organic bridges within a silica network during thermal processing may ultimately enable development of high-modulus, low-k films for advanced microelectronic applications.

Kinetic Insights into Bridge Cleavage Pathways in Periodic Mesoporous Organosilicas

“…The bridge cleavage can also be quantified by the rise of the Si-CH 2 CH 3 peak (Figure S4b); the fully cleaved intensity was estimated by a long-duration hotplate anneal. 40 The Si-C 2 H 5 data (Figure 3d) is consistent with the bridge loss data (Figure 3c), confirming the limited loss of bridges for short dwells. At the 0.5 ms dwell, bridge cleavage is minimal until ∼ 1000 ℃, while at 3 ms dwell the significant loss is observed even by ∼ 800 ℃.…”

“…6,8,10,39 Moreover, additional bridge con- nections within the framework provide opportunities for tuning mechanical, dielectric, and optical characteristics. 8,40 Additionally, the integration of these organic bridge motifs can tailor pore structures for surface properties at the nano-scale. 21 However, bridges in PMOs are thermally unstable and may undergo substantial undesirable cleavage during either synthesis or post heat treatment.…”

Millisecond flash lamp curing for porosity generation in thin films

“…In such a way, closed and isolated pores could be formed and porous materials with improved chemical and physical properties would be manufactured. Millisecond Laser spike annealing (LSA) was introduced to low-k processing as a fast post-curing treatment 26 , 27 . LSA has been utilized as a post-curing process in order to enhance the mechanical stability by oxidative or bond redistribution transformations 27 or by retaining the stability of ethyl bridge structures within the silica network 26 .…”

“…Millisecond Laser spike annealing (LSA) was introduced to low-k processing as a fast post-curing treatment 26 , 27 . LSA has been utilized as a post-curing process in order to enhance the mechanical stability by oxidative or bond redistribution transformations 27 or by retaining the stability of ethyl bridge structures within the silica network 26 . Prior to LSA in these studies, spin-on coated dielectric films have been cured at 400 °C for 1 h 26 or at 450 °C for 2 h 27 .…”

“…LSA has been utilized as a post-curing process in order to enhance the mechanical stability by oxidative or bond redistribution transformations 27 or by retaining the stability of ethyl bridge structures within the silica network 26 . Prior to LSA in these studies, spin-on coated dielectric films have been cured at 400 °C for 1 h 26 or at 450 °C for 2 h 27 . Despite the improved mechanical stabilities of the LSA-treated low-k films, the initial thermal curing at 400–450 °C is believed to form interconnected pores 20 with the drawbacks mentioned above.…”