Event
MSE Seminar-Dr. Christopher L. Soles, NIST
Friday, April 3, 2009
1:00 p.m.
Room 2108, Chemical and Nuclear Engineering Bldg.
Annette Mateus
301 405 5207
amateus@umd.edu
"The Direct Patterning of Organosilicate Materials by Nanoimprint Lithography"
Organosilicate or silsesquioxane (SSQ) films are widely used in a range applications, including nanocomposites, scratch resistant coatings, barrier coatings, biological devices, porous separation media, optical films or coatings, semiconductor interconnect insulators, and high resolution e-beam resist materials. Some of the key attributes which have lead to this widespread use includes the ease with which they can be processed into high quality films and coatings, the ability of these films and coatings to support high levels of porosity, and their intrinsic resistance to high temperatures and aggressive chemical environments. Recently there has been a growing interest in patterning nanoscale functional devices directly into SSQ materials using nanoimprint lithography (NIL). NIL is a direct patterning process whereby the material being patterned is mechanically squeezed into a rigid mold or template, essentially a nanoscale stamping process. This differs significantly from optical lithography where the pattern is first created in a sacrificial photoresist formulation and then transferred to the functional material of interest via additive and subtractive processes. In this presentation we examine the use of NIL as a high resolution process to directly pattern SSQ materials. The primary target for this work is to simplify fabrication processes and significantly reduce the manufacturing costs for semiconductor interconnect structures. However, the prospect of mechanically forging these materials, especially in their porous form, into nanoscale patterns raises concerns regarding their physical integrity and pore structure. So we have developed critical dimension small angle X-ray scattering and specular X-ray reflectivity methods to verify that an excellent fidelity of the pattern transfer process can be achieved, with minimal pattern shrinkage or distortion [1]. Furthermore, we have also developed the measurement techniques to characterize the porosity characteristics of SSQ patterns, and thus their dielectric constants that are critical to the performance of an interconnect structure. X-ray porosimetry (XRP) is used quantify the average density, the porosity, and the wall density of the material between the pores of these imprinted patterns [2]. All of these parameters characterized by XRP can be resolved as a function of vertical height through the pattern. In addition, positron annihilation lifetime spectroscopy (PALS) measurements are described to quantify the pore size distributions and the degree of pore interconnectivity in the patterned material. Finally, the porosity characteristics determined by XRP and PALS are correlated with high resolution transmission electron microscopy (TEM) images of the pattern cross section to obtain a complete picture of how the imprint process affects the porosity of these materials. Examples will be shown where the porosity level is pushed to over 50 % by volume, well into the ultralow-k regime where the expected dielectric constants will be less than 1.8. In addition to the interconnect applications, we will also show how these SSQ materials can be used to make high resolution daughter NIL molds from an imprint master or template. These daughter molds can be used to then directly imprint a range of materials, including both thermal and UV cross-linkable materials, thereby extending the life of the imprint master.
[1] HW Ro, RL Jones, H Peng, DR Hines, HJ Lee, EK Lin, A Karim, DY Yoon, DW Gidley, CL Soles, Adv. Mater. 19 (2007) 2919.
[2] HW Ro, H Peng, K Nihara, HJ Lee, EK Lin, A Karim, DW Gidley, H Jinnai, DY Yoon , CL Soles, Adv. Mater. 20 (2008) 1934.
