The Effect of Porogen on Physical Properties in MTMS-BTMSE Spin-on Organosilicates
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The Effect of Porogen on Physical Properties in MTMS-BTMSE Spin-on Organosilicates B.R. Kim*, J. M. Son, J.W. Kang, K.Y. Lee, K.K. Kang, M.J. Ko LG Chem. Ltd./Research Park, Corporate R & D, Daejeon Korea D.W. Gidley University of Michigan, Department of Physics, Ann Arbor, MI. 48109
Abstract Decreasing the circuit dimensions is driving the need for low-k materials with a lower dielectric constant to reduce RC delay, crosstalk, and power consumption. In case of spin-on organosilicate low-k films, the incorporation of a porogen is regarded as the only foreseeable route to decrease dielectric constant of 2.2 or below by changing a packing density. In this study, MTMS-BTMSE copolymers that had superior mechanical properties than MSSQ were blended with decomposable polymers as pore generators. While adding up to 40 wt % porogen into MTMS:BTMSE=100:50 matrix, optical, electrical, and mechanical properties were measured and the pore structure was also characterized by PALS. The result confirmed that there existed a tradeoff in attaining the low dielectric constant and desirable mechanical strength, and no more pores than necessary to achieve the dielectric objective should be incorporated. When the dielectric constant was fixed to approximately 2.3 by controlling BTMSE and porogen contents simultaneously, the thermo-mechanical properties of the porous films were also investigated for the comparison purpose. Under the same dielectric constant, the increase in BTMSE and porogen contents led to improvement in modulus measured by the nanoindentation technique but deterioration of adhesion strength obtained by the modified edge lift-off test.
Introduction As integrated circuit-feature dimensions continue to shrink, there is a strong need for new low-k materials to be in use with copper as the metal line [1]. In parallel with an effort to seek a homogeneous alternative to incorporate atoms and bonds with lower polarizability, the introduction of porosity into base matrix materials has been attempted to reduce a dielectric constant. The porous films are generally synthesized by blending a thermally labile porogen with a thermally stable matrix resin. However, one of the fundamental dilemmas for developing low-k dielectrics is the fact that a low dielectric constant is incompatible with high mechanical stability, particularly for porous materials where the mechanical properties are generally deteriorated further by the presence of pores. Therefore, no more porosity than necessary to achieve the dielectric objective should be incorporated to survive the harsh semiconductor fabrication processes. In the previous works [2], MTMS-BTMSE copolymers with five different compositions were synthesized and their physical properties were characterized. Network formation enhanced as the amount of BTMSE increased, which led to the improvement of mechanical properties and the increase in the dielectric constant. In the present study, the MTMS-BTMSE copolymers were added with sacrificial porogens. At first, MTMS:BTMSE=100:50 matrix w
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