A study on the porogen and pore size/distribution and aggregation behavior in spin-on porous ultra-low k dielectrics modified by ionic surfactants
|關鍵字:||超低介電材料;離子型界面活性劑;分散機制;ultra-low k dielectrics;ionic surfactants;dispersion mechanism|
|摘要:||後22 奈米元件的製程需引進超低介電材料（k ≤2.2），其關鍵技術是將大量的起
試圖增加porogen 含量，並改變porogen 與溶劑種類或性質，期望能提出一套完整的「陰
For ultra-low k dielectrics (ULK, k . 2.5) used as inter-layer dielectrics (ILD) for 22 nm node and beyond, large porosity is necessitated. Porosity can be incorporated into low-k materials matrix using pore generators (porogens), which are burned out immediately after dielectrics deposition or after completion of a Cu/low-k layer in a post-integration porogen removal scheme, to further reduce the k-value of dielectrics. For a mechanically robust low-k film with better reliability, it is highly desirable to have small and well-dispersed pore sizes (<5-10 nm) with tight distribution. However, the aggregation of porogens will occur in the solution, even in the hybrid film during the curing step, resulting in large pore size and wide distribution and possibly making such low-k materials inadequate for use as ILD. Earlier research indicated the aggregation of porogen in the solution or hybrid film could be constrained by using rapid curing rate or grafting a reactive porogen onto the low-k matrix. Yet, the rapid curing rate may affect the thin-film properties, while the synthesis of reactive porogen is complicated cost prohibitive. Therefore, this proposal will focus on the dispersion of porogen in the solution and hybrid film by controlling its surface potential to limit porogen aggregation under the conventional curing rate. In addition, this proposal is intended to establish an easy and effective method for controlling the porogen/pore size and tight distribution. In order to disperse the nano-particles of porogen, we plan to select appropriate anionic and cationic surfactants, to modify the surface potential of porogen in the beginning of the 1st year. The surface potential of porogen in the solution will be studied as the function of surfactant type. Then, the non-modified/modified porogen will be added in the hybrid low-k film and spun onto a silicon substrate. The interactions between porogen and low-k matrix and the porogen aggregation behavior (variation of porogen size) during the curing step will be further studied to understand the surfactant effect on the dispersion of porogens by the in situ grazing incidence small angle X-ray scattering (GISAXS) technique. In the 2nd year, the dispersion of porogen in hybrid system will be further studied as function of porogen (loading/ type/molecular weight) and solvents (ex. pH-value) to complete the model for porogen dispersion mechanism. Subsequently, the porogen will be removed to obtain the porous low-k material. We will focus on extending the dielectric constant to the lowest (k < 2.5) limit by exploring maximum porosity (>50 vol%) without interconnected pores (i.e. tight pore size distribution) or film collapse. The pore morphology and size/distribution for films with large porosity will be also investigated to examine any aggregation issue. Finally, the dielectric constant, mechanical strength and leakage behavior of the porous low-k film will be further investigated and discussed.