Comprehensive Study of the Chemical, Physical, and Structural Evolution of Molecular Layer Deposited Alucone Films during Thermal Processing

Abstract

Thermal processing of molecular layer deposited (MLD) hybrid inorganic−organic alucone thin films produced porous and low-k materials. Alucone films were deposited by MLD using trimethyl aluminum and ethylene glycol at 120 °C. Changes in the film density and thickness during annealing were monitored using in-situ X-ray reflectivity and were compared to atomic layer deposited (ALD) alumina films. The chemical evolution of the as-deposited and annealed alucone films during post-deposition heating with and without UV was probed using infrared spectroscopy, Rutherford backscattering, nuclear reaction analysis, and 15 N spectroscopy, providing a detailed understanding of the induced changes. The concentration of OH groups decreased after depositing 1 nm of alumina capping layer as a barrier to moisture uptake, which also decreased the etch rate in CF 4 /O 2 plasma. The lowest dielectric constant of the processed alucone films (k min = 4.75) was 25% lower than the lowest values measured in ALD alumina counterparts (k min = 6.7). Large thickness decreases for alucone films were observed at ∼200 °C of anneal temperatures. Removal of retained organic components by thermal processing of MLD films is demonstrated to be a promising and versatile route to porous thin films for a wide range of applications including low dielectric constant materials.

Chemical, Structural, and Electrical Changes in Molecular Layer-Deposited Hafnicone Thin Films after Thermal Processing

“…Peaks observed at 2860, 2920 cm −1 correspond to −CH 2 and at 1090 cm −1 correspond to C− O/C−C species. 32 These peaks are consistent with the presence of metal−alkoxide bonds. The broad feature at 3330 cm −1 corresponds to the hydrogen bond between Hf− OH and Hf−OH species.…”

“…Turning to the hafnicone films (Figure b), the as-deposited hafnicone films displayed absorption peaks consistent with the inclusion of EG. Peaks observed at 2860, 2920 cm –1 correspond to –CH 2 and at 1090 cm –1 correspond to C–O/C–C species . These peaks are consistent with the presence of metal–alkoxide bonds.…”

“…The rapid increase in density from 3.7 to 7 g/cm 3 and the decrease in thickness for hafnicone films were observed during 250–350 °C annealing, indicating removal of some organics and densification. This decrease in thickness and the increase in density in this temperature range could be a result of mass loss due to the removal of organics like CO, CO 2 , and CH 4 in the form of volatile products, which are released due to the cleavage of C–C and C–H bonds from the EG species (HO–CH 2 –CH 2 –O–Hf) inside the film causing film collapse and densification. ,, …”

“…By thermally processing the hafnicone films, the etch rate becomes similar to the ALD hafnia films while the dielectric constant remains lower and the crystallization temperature is increased, proving that the MLD hafnicone films may be useful in low- k etch stops layers. MLD hybrid films were recently examined as potential candidates for negative EUV resists. , Through our work, we show that the MLD films are highly tunable via processing conditions according to the application requirements . Hence, this study further supports the evidence that the thermal processing of hybrid MLD films provides an approach to design porous and/or low density materials.…”

“…Molecular layer deposition (MLD) is an analogue of ALD where molecular fragments are included in the resulting films and may be a route to porous and/or low-k materials. 31,32 In prior studies, chemical changes in MLD metalcone films were observed with UV, thermal, and/or ambient exposure, indicating the removal of organics and changes in physical properties. 33−38 Previously, aluminum oxide-based materials were developed for low-k etch stop applications motivating us to explore the applicability of hafnium-based MLD films for the low-k applications and to better understand the synthesis− structure−composition−property relationships in these materials.…”