Chemical Vapor Deposition of Diffusion Barriers for Microelectronics

微电子扩散势垒的化学气相沉积

• 批准号: 9975504
• 负责人: Roy Gordon
• 金额: $ 25万
• 依托单位: Harvard University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-07-01 至 2002-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9975504&HistoricalAwards=false
• 关键词: Chemical; Vapor; Deposition; Diffusion; Barriers

9975504GordonIn microelectronic devices, barrier layers must be placed between the semiconductor silicon and the metal wiring connecting different parts of its surface. The barrier keeps the metal from diffusing into the silicon and ruining its transistor characteristics. Aluminum and tungsten are the metals commonly used for these circuits. In the near future, copper will also be used because of its lower electrical resistance and better durability against electro-migration. In the absence of a barrier layer, aluminum would alloy with the silicon, producing etch pits that can short out the electrical circuits; tungsten would peel off of the silicon dioxide insulating layers; or copper would diffuse into the silicon and provide deleterious recombination centers for the electrons and holes. The barrier layers must cover the sidewalls and bottom of the etched features with a film thickness about the same as on the outer surface. In other words, the barrier layer should have step coverage close to one.Titanium nitride is the material that is usually used as the barrier layer. The titanium nitride is ordinarily formed by the process of reactive sputtering of a titanium target in a low pressure of nitrogen gas. The sputtered material has been satisfactory for the production of computer chips with feature sizes down to about one-quarter of a micron. As the industry tries to make the circuits operate faster and store more information, the feature sizes are being reduced. For feature sizes less than about one-quarter of a micron, sputtering does not cover adequately the sides and bottoms of the narrow holes and trenches that are etched a micron deep into the substrates. Thus a critical need is perceived for barrier layers deposited by a process that has better step coverage than sputtering can provide. Another problem for the use of titanium nitride in future generations of computer chips is that it may not be an effective diffusion barrier for thicknesses below about 30 nm. For features below 0.25 micron, thinner diffusion barriers will be needed, so that the barrier material does not take up too much of the hole. Titanium nitride films have a microcrystalline structure that allows diffusion of copper through thin titanium nitride barriers along boundaries between the microcrystalline grains.Amorphous diffusion barriers are expected to perform better than microcrystalline ones, because amorphous materials lack intergranular pathways for diffusion. Amorphous tantalum nitride or niobium nitride form the most conductive known thin barriers to diffusion of copper. Unfortunately, the sputtering processes commonly used to make amorphous tantalum nitride or niobium nitride do not provide adequate step coverage.Under a previous NSF grant, the PI discovered a process for CVD of amorphous niobium nitride with excellent step coverage at temperatures below 400 oC. In order to gain commercial acceptance for this new CVD process, a pure precursor with completely reproducible properties is needed, not the currently available mixture with unpredictable proportions. Analytical methods need to be established to verify the composition and purity of the precursor. The chemical properties of the precursor must be studied, including its reactivity to materials of construction, air and water, and its stability in storage. Various physical properties, such as vapor pressure, density and viscosity, must also be measured. The composition and quantities of the CVD reaction byproducts must be determined, so that they can be neutralized and disposed of properly. Finally, the kinetics and reaction mechanism must be understood so that proper chemical engineering of the reactor can be accomplished and rational control of the reaction conditions can be practiced. The proposed research will establish this fundamental knowledge base needed for commercialization of CVD niobium nitride barriers in the microelectronics industry.***

9975504 Gordon在微电子器件中，必须在半导体硅和连接其表面不同部分的金属布线之间放置阻挡层。 阻挡层防止金属扩散到硅中并破坏其晶体管特性。 铝和钨是这些电路常用的金属。 在不久的将来，铜也将被使用，因为它的电阻较低，对电迁移的耐久性较好。 在没有阻挡层的情况下，铝会与硅合金化，产生可以使电路短路的蚀坑;钨会从二氧化硅绝缘层剥离;或者铜会扩散到硅中，为电子和空穴提供有害的复合中心。 阻挡层必须覆盖蚀刻特征的侧壁和底部，其膜厚度与外表面上的膜厚度大致相同。 换句话说，阻挡层应该具有接近1的台阶覆盖率。氮化钛是通常用作阻挡层的材料。 氮化钛通常通过在低压氮气中反应溅射钛靶的方法形成。 溅射的材料已经令人满意地用于生产特征尺寸低至约四分之一微米的计算机芯片。 随着业界试图使电路运行得更快并存储更多信息，特征尺寸正在缩小。 对于小于约四分之一微米的特征尺寸，溅射不能充分覆盖蚀刻到衬底中一微米深的窄孔和沟槽的侧面和底部。 因此，认为迫切需要通过具有比溅射可以提供的更好的台阶覆盖的工艺沉积阻挡层。 在未来几代计算机芯片中使用氮化钛的另一个问题是，对于低于约30 nm的厚度，它可能不是有效的扩散阻挡层。 对于小于0.25微米的特征，将需要较薄的扩散阻挡层，使得阻挡层材料不会占据太多的孔。 氮化钛薄膜具有微晶结构，允许铜沿着微晶晶粒之间的边界沿着扩散通过薄的氮化钛阻挡层。 无定形氮化钽或氮化铌形成已知的对铜扩散的最导电的薄阻挡层。 不幸的是，通常用于制造非晶氮化钽或氮化铌的溅射工艺无法提供足够的台阶覆盖。在之前的NSF资助下，PI发现了一种在400 oC以下温度下具有出色台阶覆盖的非晶氮化铌CVD工艺。 为了使这种新的CVD工艺获得商业认可，需要具有完全可再现特性的纯前体，而不是目前可用的具有不可预测比例的混合物。 需要建立分析方法来验证前体的组成和纯度。 必须研究前体的化学性质，包括其对建筑材料、空气和水的反应性及其储存稳定性。 还必须测量各种物理特性，如蒸汽压、密度和粘度。 必须确定CVD反应副产物的组成和数量，以便它们可以被中和和适当地处理。 最后，必须理解动力学和反应机理，以便可以完成反应器的适当化学工程，并且可以实施反应条件的合理控制。 拟议的研究将建立微电子工业中CVD氮化铌屏障商业化所需的基础知识基础。