Ultralow-k silicon containing fluorocarbon films prepared by plasma-enhanced chemical vapor deposition

Abstract

Low dielectric constant materials as interlayer dielectrics (ILDs) offer a way to reduce the RC time delay in high-performance ultra-large-scale integration (ULSI) circuits. Fluorocarbon films containing silicon have been developed for interlayer applications below 50-nm linewidth technology. The preparation of the films was carried out by plasma-enhanced chemical vapor deposition (PECVD) using gas precursors of tetrafluorocarbon as the source of active species and disilane (5 vol.% in helium) as a reducing agent to control the ratio of F/C in the films. The basic properties of the low dielectric constant (low-k) interlayer dielectric films are studied as a function of the fabrication process parameters. The electrical, mechanical, chemical, and thermal properties were evaluated including dielectric constant, surface planarity, hardness, residual stress, chemical bond structure, and shrinkage upon heat treatments. The deposition process conditions were optimized for film thermal stability while maintaining a relative dielectric value as low as 2.0. The average breakdown field strength was 4.74 MV/cm. The optical energy gap was in the range 2.2-2.4 eV. The hardness and residual stress in the optimized processed SiCF films were, respectively, measured to be in the range 1.4-1.78 GPa and in the range 11.6-23.2 MPa of compressive stress.

Study and optimization of PECVD films containing fluorine and carbon as ultra low dielectric constant interlayer dielectrics in ULSI devices

“…2-4). Our data therefore not only correlate well with increased shrinkage rates observed by several authors with increasing flow rate ratio (FRR), attributed to F outgassing, 12,15,17 but also confirms that the extended 40 300 120 5 530 50 500 140 10 540 100 700 160 12.5 550 150 -180 16.67 600 200 -200 20 840 ---24 1000 ---25 1040 ---30 treatment does not significantly modify the annealing mechanism or film structure. An interesting deduction is that at FRR 12.5, film densification results in higher residual thickness 6 when process power is increased from 50 to 100 W. Standard forming gas anneal (NH 3 /H 2 ) done at 400 C for 1 h resulted in film degradation via blister formation.…”

“…Absorption coefficient exhibits a nonlinear region related to disorder in the network at a < 10 4 cm À1 and linear Tauc region at a > 10 4 cm À1 . 15 Optical energy gap increases from 2.4 to 3.4 with increasing FRR and from 2.2 to 2.4 with increasing pressure. F. X-ray diffraction XRD data confirm that the ULK film is completely amorphous with none of the crystallinity or ordered CF 2 bonds found in PTFE [ Fig.…”

“…Previously we have demonstrated the applicability of a:C-F films deposited using CF 4 and Si 2 H 6 for low-k applications. 15 In this work, film properties are changed by substantially modifying the reactor chamber configuration to allow for the use of larger gas volumes and gas flow rates (by almost a factor of 10) while maintaining similar operating pressures. Residence time of radicals is given by…”

“…The CF 4 -Si 2 H 6 plasma system comprising the scheme of Yasuda et al 17 modified to include the role of fluorine trapping agents and deposition mechanisms has been detailed elsewhere. 15 Some possible reactions for the interaction of electrons with CF 4 include e À þ CF n ! CF n à þ e À ;…”

“…29 The principal band splits into nine absorbance bands of which four are attributed to CF type bonds, two to CF 2 , and the others to CF 3 , CF-CH 3 , and CH 3 , respectively. 15,22,24 Of significance in the bonding configuration is the absence of a sharp peak at 1100 cm À1 that is an overlap of C-O/Si-O stretching mode and C-F x group 15 signifying the resulting lack of detectable oxygen incorporation into the film. Both complementary techniques of XPS and IR confirm that CF 2 is the primary monomer in the ULK film.…”