利用離子型界面活性劑探討旋塗性多孔超低介電薄膜中起孔洞劑與孔洞尺寸及其分散行為之研究

Abstract

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 孔洞劑（porogen）加入低介電基材中，然後藉由熱處理將其移除後得到多孔性低介電薄 膜。然而porogen 在溶液或薄膜中會發生團聚現象，使最後孔洞尺寸在升溫後或在高孔 隙率下，形成大孔洞且分佈不均。但實際應用上，超低介電材料卻需要分佈均勻的奈米 級孔洞。迄今雖有研究利用改變升溫速率或合成接枝的方式限制porogen 的團聚行為， 但改變升溫速率可能會影響薄膜性質，接枝方法又較繁瑣。故本計畫在不改變後段製程 的升溫速率下，利用控制porogen 表面電位的方式限制其在低介電基材中的團聚行為， 以達到控制孔洞大小的目的。 本計畫第一年將利用陰/陽離子型界面活性劑改變porogen 的表面電位，達到奈米粒 子間分散的效果。探討升溫過程中，改質前後porogen 與基材間的交互行為和自身團聚 之現象，以瞭解不同界面活性劑對porogen 在低介電基材中分散的影響；第二年計畫將 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 /陽離子型界面活性劑對起孔洞劑分散機制模型」，並製備出孔隙率>50%、孔洞分散效 果佳且尺寸均一的多孔性超低介電薄膜。此外，探討多孔型低介電材料之介電常數、機 械性質及漏電行為等關鍵性質。

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.