**6. Conclusions**

72 Dielectric Material

[53](figure 7).

porogens.

**Figure 7.** Introduction of POSS moiety by sol-gel method

**5.4. Porous Network polymer by subtraction of porogen** 

final material to satisfy the required mechanical property.

Efforts to further decrease the dielectric constant without decreasing mechanical strength, POSS skeletons have been introduced in MSQ. To suppress the phase separation, incompletely condensed methyl functionalized POSS precursors have been used to form chemical bonds with oligomeric sol precursors. These incompletely condensed POSS moieties functioned as coupling agents while expanding the free volume of the final sol after curing which was accomplished to 4 GPa of modulus and 2.3 of dielectric constant.

Numerous methods of introducing subtractive porosity into spin-on deposited materials exist. Conventional methods of substractive porosity involve the addition of molecular or supramolecular particles called 'porogens' with tailored thermal stability to the dielectric precursor[54]. The stability of these particles is such that they are not affected by the coating drying step, and they are removed by pyrolysis during final film sintering or cure at temperatures typically in the range from 300 to 400 °C. An example of a material for which the pore size and porosity, or the pore size and porogen load can be controlled independently. [55] However, it should be noted that the use of porogens should only be applied to dense materials having a k less than 2.5 and modulus over 5 GPa in order for the

In organic materials, the SilK matrix has been the only known material to provide the thermal and mechanical properties at temperature up to 500oC for use in combination with porogens. C.E. Mohler et al. [56] reported on porous SiLK dielectric film properties such as pore volume, porosity, size distribution, and showed a 2.2 dielectric constant at 30% load of

In comparison with organic porous dielectric material, inorganic porous dielectric materials have been more rigorously investigated because of their superior mechanical properties. Representative studies have used polymethylsilsesquioxane (PMSQ) as matrix for the The search for materials with low dielectric constant in the microelectronics industry has and will continue feverishly into the future as the demand of faster processing speeds increases. Reduction of the dielectric constant of a material can be accomplished by selecting chemical bonds with low polarizability and introducing porosity. Integration of such materials into microelectronic circuits, however, poses a number of challenges, as the materials must meet strict requirements in terms of properties and reliability. The introduction of low-k materials in microelectronics research and development is a good example of how industrial needs drive new fundamental and applied research topics in science. Examples include pore structure characterization, deposition of thin films on porous substrates, mechanical properties of porous films, and conduction mechanisms in these materials. The substantial efforts made by materials and IC researchers to integrate the lowk films and continue historical device performance improvements have contributed to, and are still leading to, innovative fundamental and applied science.
