Correlations Between Structural Characteristics and Process Conditions of HSQ Based Porous Low-k Thin Films
- PDF / 255,221 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 82 Downloads / 195 Views
Correlations between Structural Characteristics and Process Conditions of HSQ Based Porous Low-k Thin Films Hae-Jeong Lee1, Eric K. Lin1, Howard Wang1, Wen-li Wu1, Wei Chen2, and Thomas A. Deis2 1 National Institute of Standards and Technology, Polymers Division, Gaithersburg, MD, 20899, USA 2 Semiconductor Fabrication Materials KCI, Dow Corning, Midland, MI, USA
ABSTRACT A novel methodology using a combination of ion scattering, x-ray reflectivity (SXR), and small angle neutron scattering was used to characterize the structure and properties of a hydrogen silsesquioxane (HSQ) based porous low-k dielectric films after varying process conditions. The dielectric constant and the remaining Si−H fraction (degree of cure) of the samples were varied from 1.5 to 2.2 and from 30 % to 52 %, respectively, by controlling the mass ratio of the solvent and the HSQ resin in the initial solutions and the wet ammonia treatment time. We determined the density depth profile, average mass density, wall density, porosity, average pore size, average wall thickness, pore connectivity and atomic composition. The chemical bond structures were also measured using Fourier transform infrared (FTIR) spectroscopy. The density profile of each porous low-k film was uniform and only two layers were required to fit the experimental SXR data. Higher dielectric constant films show significantly higher wall densities and lower porosities and pore sizes. The measured increases in the wall density with lower Si-H fractions are consistent with the FTIR results. INTRODUCTION One of the biggest challenges in semiconductor processing is to reduce RC delay, a limiting factor in improving the performance of next generation devices. One way to reach this goal is to lower the dielectric constant of inter-layer dielectric material. In particular, there is a strong push to develop new porous films with a dielectric constant below 2.2 [1]. Among several candidates of porous materials, hydrogen silsesquioxane (HSQ) based porous materials are considered on excellent choice because of their potential compatibility with conventional Si technology [2]. Although these porous low-k materials can improve device performance, the detailed structure of the porous network more seriously affects properties crucial to the integrated chip than non-porous low-k materials. The semiconductor industry would like to precisely control structural characteristics such as porosity, pore size, and pore connectivity of the porous low-k thin films. It is therefore essential to have methods to characterize the on-wafer structure of these porous thin films and to understand correlations between processing conditions and the resulting physical properties. Currently, there are few experimental techniques able to characterize the structural properties of thin films as prepared on a silicon substrate [3]. In this work, we provide unique on-wafer measurements of structural properties of HSQ based porous films (Dow Corning XLK) [4] prepared with a wide range of processing conditions using combinat
