Thermal Stability of a-C:F,H Films Deposited by Electron Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition

Abstract

Amorphous carbon films grown with fluorohydrocarbons can be grown to have dielectric constant values around 2.0. The behavior of these films when subjected to thermal excursion is studied. We have investigated material deposited in an ECR plasma, and find that the F:H ratio of the gas mixture is a good guide to material properties. Films deposited at 5°C were placed in a vacuum chamber at 400°C as long as 60 minutes. The film thickness, dielectric constant, and infrared absorption spectrum change with the F:H ratio of the incoming gas and thermal cycling. It was found that the dielectric constant and loss tangent decrease upon heating and that there is an apparent increase in C=C groups. As expected, as the F:H ratio increases, the dielectric constant and thermal stability decrease. Good thermal stability is shown for F:H ratios of 1.5, which result in films with a dielectric constant of ∼2.4 after heating.

Fluorinated amorphous carbon films for low permittivity interlevel dielectrics

“…shows the effect of gas mixture on for HDPCVD and PECVD films. 3,27 For electron cyclotron resonance ͑ECR͒ HDPCVD films, the dielectric constant for the films decreases monotonically from 3.3 for an F:H ratio of 1.5 to 2.0 for an F:H ratio of 3.0. 3 For PECVD films using CF 4 /CH 4 gas mixtures, on the other hand, only decreases from 3.8 with an F:H ratio of 0 down to 3.4 with an F:H ratio of 3.…”

“…With respect to lowering the dielectric constant, many materials have been examined such as fluorinated SiO 2 , fluorinated amorphous carbon ͑a-C:F,H͒, spin-on organic films, spin-on glasses, parylenes, organo-silane/H 2 O 2 chemical vapor deposition ͑CVD͒, liquid-deposited glasses, xerogels, aerogels, and phase-separated materials. [1][2][3][4][5][6][7][8][9][10][11][12][13][14] A few of these materials are already being used in manufacturing, but they tend to provide small improvements in . The more advanced materials ͑Ͻ3.5͒, are not yet in volume production.…”

“…It has been shown that these films can achieve as low as 2.0, and that it appears to be controlled by composition and film density. 3 Because these are plasma-deposited films, they have an extremely high crosslink density with respect to spin-on organic films, and hence do not have a detectable glass transition temperature. They have structural similarities to hydrogenated amorphous carbon ͑a-C:H͒, giving them the potential to have higher thermal conductivity than SiO 2 .…”

“…11 Finally, there is PACVD of fluorinated organic films, which is the subject of this article (ϳ2.0-3.2). 3,4 Many different approaches have been applied to producing a-C:F,H films using plasmas, but the two most common types employed are capacitively coupled glow discharges ͓plasma enhanced CVD ͑PECVD͔͒, and high-density plasmas ͑HDP͒. Capacitively coupled glow discharges typically operate in the range of 100 mTorr-20 Torr, with plasma density between 10 9 and 10 11 cm Ϫ3 , and T e between 3 and 10 eV.…”

Effect of deposition temperature on thermal stability in high-density plasma chemical vapor deposition fluorine-doped silicon dioxide

“…The HDP-CVD technique has been demonstrated to have good gap-filling capability and film stability. 2,3 Moreover, in 1998, Yang et al 4 produced SiOF films in 0.18 m logic devices. As a consequence, SiOF films are considered a suitable and a manufacturable low dielectric constant ͑low-k͒ IMD for devices below 0.25 m.…”