Electrical and mechanically robust, porous, ultra-low dielectric constant materials

随着对集成电路(IC)运算速度性能要求的不断提高，需要新的纳米制造技术和新材料。IC行业最引人注目的最新发展之一是在线路后端结构中部署了铜互连和超低介电常数(ULK)材料。互连线是用于将晶体管连接在一起的纳米级金属线。为了避免这些纳米线之间的电气短路，并为IC器件提供机械支撑，使用ULK材料对这些金属线进行绝缘。铜/ULK技术从过时的铝/二氧化硅技术中迁移出来，是为了通过互连线的电阻和互连线之间的电容串扰来减少信号延迟。在未来，特征晶体管栅长小于22 nm(22 nm工艺节点)的IC技术将由目标介电常数小于2.1的ULK材料组成。为了实现这一目标，ULK将加入纳米级的空洞或孔洞。这类新材料通常被称为多孔ULK，可以通过造孔剂-减法生产。采用等离子体增强化学气相沉积(PECVD)技术将有机模板剂(致孔剂)引入硅酸盐基质材料中。随后，它们将通过在超高真空室中使用高温紫外线辐射的汽化过程来去除。根据PECVD过程中使用的致孔剂的量，多孔-ULK膜的最终孔隙率可以在20%到40%的范围内。然而，这种技术存在一些缺点，限制了它的应用。这包括制造直径小于2 nm的孔的困难，这是22 nm技术节点的要求。紫外光固化可以通过改变其分子结构来提高多孔ULK的介电常数。最后，正如预期的那样，在硅酸盐薄膜中引入孔洞降低了其机械强度和断裂强度。这项研究的目的是了解这些降解的原因，并通过发明新的制造技术提供解决方案。

With the increasing demand of integrated circuits (IC) computational speed performance, new nano-fabrication techniques and novel materials are needed. One of the most noticeable recent developments in the IC industry is the deployment of copper interconnects and ultra-low dielectric constant (ULK) materials in back-end-of-line structures. Interconnect lines are nanometer-scale metal wires used to connect transistors together. To avoid electrical shorts between these nano-wires and to provide mechanical support for the IC devices, ULK materials are used to insulate these metal wires. The migration of copper/ULK from the out-dated aluminum/silicon dioxide technology is to reduce signal delay by the resistances of interconnect line and the capacitance cross-talks between them. In the future, IC technology with the characteristic transistor gate length smaller than 22 nm (22 nm technology node) will consist of ULK materials with target dielectric constants less than 2.1 To achieve this objective, the ULK will be incorporated with nanometer-scale empty voids or pores. This new class of material is commonly referred to as porous-ULK and can be produced by using the porogen-subtraction method. Organic template agents (porogen) are introduced into the silicate matrix material by using the plasma-enhanced chemical vapor deposition (PECVD) techniques. They will be subsequently removed by a vaporization process using UV radiation at high temperature in an ultra-high-vacuum chamber. Depending on the amount of porogen used during the PECVD process, the final porosity in the porous-ULK film can be in the range of 20% to 40%. However, this technique has drawbacks which limit its application. This includes the difficulty of producing pores with diameters smaller than 2 nm which is the 22 nm technology node requirement. The UV cure process may increase the dielectric constant of the porous-ULK by modifying its molecular structures. Finally, as expected, the introduction of porosity into the silicate film reduces its mechanical and fracture strength. It is the goal of this research to understand the causes of these degradations and provide solutions by inventing new fabrication techniques.