Effect of Chemical Solutions and Surface Wettability on the Stability of Advanced Porous Low- k Materials
- PDF / 444,535 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 6 Downloads / 203 Views
Effect of Chemical Solutions and Surface Wettability on the Stability of Advanced Porous Low-k Materials Q. T. Le1, G. Vereecke1, A. Bertha2, E. Kesters1, M. Lux1, and H. Struyf1 1 Imec, Kapeldreef 75, 3001 Leuven, Belgium. 2 University of Antwerp, Belgium. ABSTRACT This study focuses on the impact of chemical solutions (hydrogen fluoride and tetramethylammonium hydroxide) on the change in properties of advanced porous low-k films. It was shown that there is no preferential removal of methyl groups during the dissolution process. With regard to wetting agents, the presence of isopropyl alcohol or surfactant (polyoxyethylene ether and alkoxylated diol type) in HF solution slowed down low-k film etching. Complete removal of surfactant residual usually requires an additional rinsing step using a low-molecular weight alcohol such as isopropyl alcohol. INTRODUCTION The past ten years have seen dielectric materials evolve from silicon dioxide (k ~ 3.9), through dense silica-based films (k ~ 3.0), to the current porous low-k dielectrics (k < 2.5), which are required for the 45 nm technology node and beyond. The decrease in material density (i.e. introduction of high-porosity materials) presents new challenges and issues for processing. For instance, it has been shown in literature that porous materials are extremely sensitive to plasma processes (patterning of porous low-k layer) and to post-etch treatment and subsequent wet cleaning (e.g. for removal of photoresist layer and post-etch residues). Damages induced by a wet clean using chemical solutions or mixtures may lead to film etching, densification, and/or to major changes in the properties of the low-k material. These effects result in an increase in dielectric constant and degraded electric reliability of the low-k material. This study first focuses on the impact of hydrogen fluoride (HF), and to some extent, tetramethylammonium hydroxide (TMAH) solutions on the change in properties of advanced porous low-k films. Another important characteristic of low-k dielectrics is surface hydrophobicity. However, good cleaning requires reasonable surface wettability. The use of additives was considered to enhance surface wettability by means of two different approaches: (a) isopropyl alcohol, a polar organic solvent and (b) surfactants. We will show that the degree of modification and etching caused by chemical solutions can be substantially different depending on the type of porous low-k films (of similar k-value) and of additives used. EXPERIMENT The low-k films used in this study were silica-based porous materials with open porosity ranging from 25 to 46%. One of them was spin-on (ULK 2.3), and the other three materials were made using chemical vapor deposition (OSG 2.5, ULK1 2.0, and ULK2 2.0, where numbers give nominal k-values). The film thicknesses were targeted at about 180-200 nm after hotplate bake and UV cure. A plasma treatment was carried out at room temperature (RT) on one selected film, ULK1 2.0, to study the effect of wet clean solution on the modified layer ind
Data Loading...
