摘要
过渡族金属氮化物由于具有高强度、高硬度、耐高温,耐磨损以及良好的导电性、导热性等一系列优点,并可通过化学气相沉积(CVD),物理气相沉积(PVD)原子层沉积(ALD)等方法制备,与硅器件工艺兼容,可以被广泛的应用于微电子工艺中等,从而引起了广泛的关注。TiN,TaN便是其中重要的两种材料。
TiN由于其功函数大约在4.5电子伏特左右,与硅的功函数接近,从而是一种很好的金属栅极候选材料而被广泛研究,但对TiN不同表面的功函数、表面能等性质进行全面的计算分析还较少见到。作为可能出现的情况本文使用基于第一原理的密度泛函理论计算了TiN材料各个表面(100面、110面、111-N面、111-Ti面)的功函数,态密度,分波态密度,表面能,并与体相材料的相应数据作了比较。分析了在钨表面生长TiN择优取向为(111)面的原因,并得到了在SiO2和HfO2基底上生长的TiN薄膜可能是(111)面Ti端面的结论。由于在TiN的制备过程中, (111)方向为择优生长方向,因此着重分析了(111)晶面的表面电子结构。计算得到的晶格常数与试验值吻合的很好。计算结果表明在各个表面中111-Ti面的功函数与试验值最接近,而其他表面的功函数与试验值都有较大的差距。各个表面的表面能从小到大顺序为:100<110<111-N<111-Ti,各个表面都是导体,其中111-Ti面的导电性最强。
本文第二部分又采用第一原理于的密度泛函理论计算了扩散阻挡层材料的TaN材料各个相的晶体结构和电子结构,分析比较了不同相的稳定性。计算表明六角密堆结构由于在费米能级附近有赝隙的存在,要比立方结构更稳定。CoSn结构是所有结构中的基态。WC结构有最大的弹性模量。所有的结构都是导电的,其中NaCl结构的导电性最强。
The transition metal nitrides represent a technologically important series of materials and owns a wide interest because it can be deposed by Chemical Vapor Deposition (CVD),Physical Vapor Deposition(PVD) and Atom Layer Depostion (ALD) and others which are also used in IC process .TiN and TaN are two kind of important transitions nitrides.
The work function of TiN is about 4.5eV, near that of Silicon, which allows it to be used as a potential metal gate material. Although it has been widely studied, the analysis about the work function ,surface energy and electronic structure of different surfaces are not reported to the best of our knowledge. The present work calculated the work function ,surface energy and electronic structure of different surfaces employing density functional theory (DFT) with in the local density approximation (LDA). The study show that the preferred orientation is (111) on W substrate. And we find that the TiN film deposed on SiO2 and HfO2 should be the (111) surface terminated by Ti. Considering (111) surface is the preferred orientation, we analysed the electronic structure of (111) surface. The calculated lattice constant agrees with the experimental value. The result show that the work function of (111-Ti) surface agree well with the experimental value, while the other surfaces with a considerable different. The calculated surface energy from low to high is: 100<110<111-N<111-Ti. All the calculated surface has a metallic nature, and the (111-Ti) surface has the highest conductivity.
In the second part of this thesis, Using the plane wave pseudopotential method within the generalized gradient approximation, we have studied the structural and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetics stability of phase structures of TaN from low to high is: CsCl< ZnS-B3< NaCl< WC< CoSn. The higher stability of TaN in the CoSn and WC structures is due to the formation of pseudogap around the Fermi level and the stronger hybridization between N-2p states and Ta-5d states. TaN in all structures studied has metallic nature,while the NaCl structure has the highest conductivity. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressibility material.
引文
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