Nanoporous PMSSQ-based spin-on-glass films

for ultra-low-dielectric thin film applications

 

Hyun Wook Ro1, Kookheon Char2, David W. Gidley3, Hae-Jeong Lee4, Jin-Kyu Lee1,

Hee-Woo Rhee5, Christopher L. Soles4, and Do Yeung Yoon1

 

1Department of Chemistry, Seoul National University

2School of Chemical Engineering, Seoul National University

3Department of Physics, University of Michigan

4Polymers Division, National Institute of Standards and Technology

5Department of Chemical Engineering, Sogang University

 

Nanoporous films attract significant attention as candidates for the ultra-low-dielectric constant (ultra-low-k, k<2.2) insulating layers in high performance next generation integrated circuits.  In general, ultra-low-k films are generated by introducing nanometer-sized pores into a matrix material through a controlled decomposition of an added pore generation molecule or porogen.  This reduced k is, however, accompanied by undesirable changes in the mechanical properties of the material.  Therefore, there have been tremendous efforts to modify the matrix material to improve important physical properties such as elastic modulus and crack resistance.  In this work, we develop a poly(methylsilsesquioxane) (PMSSQ)-based matrix materials by a hydrolytic polycondensation of methyltrimethoxysilane (MTMS), 1,2-bis(triethoxysilyl)ethane (BTSE), and dimthoxydimethylsilane (DMDMS) at a 7:2:1 molar ratio under  controlled reaction conditions. Nanoporous films of this matrix are then prepared by incorporating commercial Tetronic* porogen into the terpolymer at loadings ranging from 0 % to 50 % by volume.  The as-spun films are annealed up to 430 oC under vacuum to remove the porogen and to generate the nanoporous structures. Critical structural characteristics are determined using X-ray porosimetry (XRP), ellipsometry and positron annihilation lifetime spectroscopy (PALS). The average film density, wall density of the material between the pores, and porosity of the nanoporous films are deduced by XRP. The porosity of the films is also calculated from the index of refraction measured by ellipsometry and compared with those of XRP. Average pore size and interconnectivity of the films are systematically investigated by PALS. As a result, 50 % by volume porogen loading film displays average pore sizes that are smaller than 3.5 nm and the percolation threshold for interconnected pores occurs at 24 % porosity.

 

*Certain commercial equipment and materials are identified in this paper in order to specify adequately the experimental procedure.  In no case does such identification imply recommendation by the National Institute of Standards and Technology nor does it imply that the material or equipment identified is necessarily the best available for this purpose.

 

 

 

 

 

 

 

Author Information

Name: Hyun Wook Ro

Guest Researcher, Polymers Division, Electronic Materials Group, National Institute of Standards and Technology,

Building #: 224

Room #: A321

tel: 301-975-4736

fax: 301-975-3928

e-mail : hyunwook.ro@nist.gov

Poster category: Materials