X-Ray Reflectivity and FTIR Measurements of N[sub 2] Plasma Effects on the Density Profile of Hydrogen Silsesquioxane Thin Films

Abstract

The density depth profile and chemical bond structure of hydrogen silsesquioxane ͑HSQ͒ thin films treated with an N 2 plasma with varying power and exposure time were measured using specular X-ray reflectivity ͑SXR͒ and Fourier transform infrared ͑FTIR͒ spectroscopy. The SXR data indicated that the density profile of an untreated HSQ film is not uniform. At least four layers with different electron densities were required to fit the SXR data. For HSQ films treated with either increasing plasma power or plasma exposure time, the film roughness increased and a densified layer was observed at the film/air interface. The thickness of the densified layer increased with both plasma power and plasma exposure time. In the FTIR spectra of the plasma-treated films, the intensities of the Si-O peaks due to the network structure and the Si-OH peak due to water absorption increased and the intensities of the Si-H peaks decreased. The FTIR data show that the plasma converts the HSQ structure into a SiO 2 -like structure and are consistent with the densification observed in the SXR measurements. In general, the HSQ film is more sensitive to increasing plasma power than to increasing plasma exposure time.

Integration of Low‐ k Dielectric Films in Damascene Processes

“…Microporous low-k SiOC materials (i.e., a pore diameter smaller than 2 nm) have been shown to seal upon exposure to plasmas through reconstruction or densifi cation of the low-k surface, creating a dense SiO 2 -line layer [154][155][156]. The densifi cation can also be denoted as plasma damage, leading to an increase of the k value and to a degradation of the electrical properties (see Section 5.3.5).…”

“…A good knowledge and control of these plasma processes is therefore essential in providing a scalable solution. Nevertheless, for microporous dielectric fi lms, the densifi cation can be confi ned into a few nanometers of the surface, provided the appropriate choice of plasma power [155]. Higher plasma power/bias were found to be necessary to seal as the porosity of the low-k material increased [154].…”

“…With the appropriate choice of plasma power, the densifi cation can be confi ned into a few nanometers of the top layers of microporous dielectric fi lms [172]. In this way, fi lm properties, such as k value, are not dramatically affected.…”

“…In this way, fi lm properties, such as k value, are not dramatically affected. The newly formed densifi ed 'skin' layer can be even benefi cial (as discussed under 'plasma sealing' in Section 5.3.4), since it can act as a protection or barrier to further damage to the fi lm bulk [158,172]. This is however not the case for mesoporous dielectric fi lms.…”

Damage minimized plasma pore sealing of microporous low k dielectrics

“…Pore sealing to prevent penetration may become a requirement for the integration of porous dielectrics in sub-90 nm interconnects [5]. Microporous low k materials (<2 nm diam pores) have been shown to seal upon exposure to plasmas through reconstruction or damage of the surface creating a dense SiO 2 -like layer [4,[6][7][8]. It has been shown that plasma damage to the low k films degrades electrical properties [9].…”