Study the Effect of Composition and Preparation Process of Precursor Solution on the Properties of Porous Low-k Silica Thin Films
Date Issued
2005
Date
2005
Author(s)
Huang, Qi-Da
DOI
zh-TW
Abstract
The pH values of precursor solutions and the effect of preparation processes for precursor solutions on the properties of porous low-k silica thin film were studied in this research. Porous silica thin film has been widely studied; for it can possess low dielectric constant under appropriate preparation conditions. The increasing number of pores can effectively lower dielectric constant; however, the insufficient mechanical strength is sequential shortcoming. It was found that the composition of precursor solution and the process for preparing precursor solution would have great influence on mechanical strength of porous silica thin film. Therefore, the properties improvement of porous silica thin film was carried out by observing pH values of precursor solutions and by altering the processes for preparing the precursors.
From observing the variation of pH values through reflux process and comparing the pH values among different solutions during reflux process, it was found that the added basic organic salt not only reacted with HCl but also with the micelles that formed from the template, Tween80. Furthermore, when the basic organic salt, TPAOH, was added along with Tween 80 into the coating (precursor) solution after the reflux, there were apparent silica particles formed on the spin-on thin film. They came from the local higher basic region in the solution, because TPAOH could not be dissolved in the coating solution immediately.
By altering the process for preparing precursor solution, it was found that the thin films possessed lower dielectric constant and higher mechanical strength from the precursor solution, which contained more HCl and went through the reflux process; however due to imperfect SiO2 structure, the film was observed with more trapped charges from C-V curve. When Tween80 was used as the template, the thin films possessed lower dielectric constant. And the mechanical strength was slightly improved by adding organic salt, TBAOH (with a molecule size larger than TPAOH), to the precursor solution. When Brij56 was used as the template in the precursor containing HCl/TEOS=0.25, which did not go through the reflux process, the resulting thin films possessed better properties. The timing for adding organic salt was not an apparent factor for changing the properties of thin films. However, the dielectric constants of thin films were increased after the precursor solution aged for 6 days.
In this research it was found that the most significant factor affecting the properties of SiO2 film was the amount of HCl added in the precursor solution. When the precursor solutions are fresh (before aging), the thin films with the best performance among those tested in this study are produced under the following conditions: non-reflux, non-adding organic salt, and HCl/TEOS=0.25 in the precursor solution. The resulting properties are the followings: dielectric constant= 1.94, leakage current density= 2.23E-07 A/cm2, hardness= 0.758 GPa and elastic modulus= 8.034 GPa.
Subjects
低介電
孔洞材料
薄膜
旋轉塗佈
界面活性劑模板法
模板
low dielectric constant
low-k
porous material
thin film
spin coating
surfactant-templated method
template
Type
thesis
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