Ultralow k using a plasma enhanced chemical vapor deposition porogen approach: Matrix structure and porogen loading influences

To improve integrated circuit performance, microelectronic chip interconnections need dielectric materials with ultralow k (ULK) values. Porous a-SiOCH, an ULK material, can be created using a two step strategy called a porogen approach. The first step consists of a hybrid film deposition, which is an a-SiOCH matrix containing an organic sacrificial phase. Afterwards, the organic phase is removed during a post-treatment to generate the porosity. In this work, hybrid deposition was performed by plasma enhanced chemical vapor deposition and the post-treatment was a thermal annealing. Firstly, hybrid films with different a-SiOCH matrix structures were created using two matrix precursors [decamethylcyclopentasiloxane (DMCPS) and diethoxymethylsilane (DEMS)] and an O2 addition in a plasma gas feed. For the same porogen loading, the shrinkage behavior during the porogen removal is correlated to the matrix structure. Fourier transform infrared spectroscopy and Si29 solid nuclear magnetic resonance are both used to determine the structure. The O3SiMe1 is favorable to prevent high film shrinkage and the O2SiMe2 leads to high film shrinkage and absence of porosity generation. To prevent the existence of this type of structure, DEMS+O2 appears more appropriate as a matrix precursor than DEMS only or DMCPS. Secondly, using the appropriate matrix structure, the influence of the porogen loading on the porosity creation is studied. Hybrids with different porogen loadings are achieved by changing the porogen precursor ratio in the plasma gas feed. The porogen conversion into porosity is studied for different porogen loadings and the results indicate the existence of a porogen loading threshold. Above it, there is no more porosity generation because of the too high film shrinkage during the porogen removal. This behavior is explained by a too low matrix ratio in the hybrid film. For the high porogen loadings, the matrix skeleton (mainly constituted by SiOSi bridging bonds) is not in sufficient quantity to prevent such film shrinkage. The porous a-SiOCH created with the most favorable matrix structure and porogen loading has the ultralow k value of 2.3.