Cu互连中Ta/Ta-N和Ti/Ta-N双层膜的扩散阻挡性能比较

采用磁控溅射法在SiO2/Si基底上沉积Cu/Ta/Ta-N及Cu/Ti/Ta-N薄膜,在高纯的Ar/H2气氛保护下对样品进行快速热退火处理,用XRD、SEM、EDS及四探针电阻测试仪(FPP)等分析测试方法对Ta/Ta-N和Ti/Ta-N双层薄膜的热稳定性及互扩散阻挡性能进行了比较分析。结果表明,当退火温度低于700℃时,Cu/Ta/Ta-N/SiO2/Si和Cu/Ti/Ta-N/SiO2/Si多层膜结构表面平整,方阻值均比较小(Cu/Ta/Ta-N/SiO2/Si约为0.175Ω/□,Cu/Ti/Ta-N/SiO2/Si约为0.154Ω/□);当退火温度到达700℃时,Cu/Ta/Ta-N/SiO2/Si试样开始出现Ta2O5和Cu3Si,由于Cu向基底扩散打破Si-Si和Si-O键,Si、O经扩散通道分别与Cu、Ta反应生成了Cu3Si和Ta2O5,表明Ta/Ta-N阻挡层开始失效;而Cu/Ti/Ta-N/SiO2/Si试样的Cu/Ti相界面形成了很薄的扩散溶解层——Cu4Ti、Cu4Ti3与Cu3Ti2,有力地阻断Cu向基底扩散的通道,从而提高了Ti/Ta-N双层膜的阻挡性能,使Ti/Ta-N双层膜对Cu的有效阻挡温度高达700℃。因此,Ti/Ta-N双层膜是一种良好的扩散阻挡层。     

纳米Ta-Al-N薄膜的制备及其扩散阻挡特性的研究

采用直流反应磁控溅射方法在P型（100）Si衬底上制备了Ta-Al—N纳米薄膜与Cu／Ta-Al—N复合膜，并对薄膜样品进行了卤钨灯快速热退火（RTP）。用四探针电阻测试仪（VPP）、AFM、SEM—EDS、Alpha—stepIQ台阶仪和XPd）等分析测试方法对样品的形貌结构与特性进行了分析表征。实验结果表明，本实验条件下制得的Ta-Al—N纳米薄膜表面光滑；随着Al靶溅射功率的增加，Ta-Al—N薄膜中Al含量和方块电阻相应增大，均方根粗糙度降低，而沉积速率变化不大，且Ta-Al—N膜层对Cu扩散的阻挡能力增强。但在过高的温度下退火，导致Cu通过Ta-Al—N的晶界扩散到Ta-Al—N／Si界面并形成Cu3Si，从而引起阻挡层的失效。     

真空镀膜实验中掺Al对Ta-N薄膜性能的影响

采用磁控反应共溅射法制备了Ta-Al-N纳米薄膜及Cu/Ta-Al-N/Si结构,并在氮气保护下对薄膜进行了快速热处理,用四探针电阻测试仪、台阶仪、原子力显微镜、X射线衍射、X射线光电子能谱、扫描电镜等对薄膜进行了表征。研究表明,少量Al的掺入可降低薄膜的表面粗糙度,有效提高其热稳定性和Cu扩散阻挡能力,但同时也增大了薄膜的电阻率。Al原子分数为1.7%、厚约100nm的Ta-Al-N薄膜在800℃热处理5min后仍可保持稳定和对Cu扩散的有效阻挡,其作用机制与Al填充堵塞晶界及提高薄膜的晶化温度有关。     

不同氮流量比制备纳米Ta-N薄膜及其性能

超大规模集成电路Cu互连中的核心技术之一是制备性能优异的扩散阻挡层.本文采用直流磁控反应溅射在N2/Ar气氛中制备了不同组分比的Ta-N薄膜,并原位制备了Cu/Ta-N/基底复合结构,对部分样品在N2保护下进行了快速热处理(RTA),采用台阶仪、四探针测试仪、原子力显微镜(AFM)、扫描电镜、X射线衍射(XRD)对薄膜形貌结构进行了表征.结果表明,随着N2流量比的增加,薄膜沉积速率下降,表面趋于平滑,Ta-N薄膜热稳定性能及阻挡性能随之提高,而电阻率则上升.氮流量比为0.3制备的厚度为100nm的Ta-N薄膜经600℃/5min RTA后,仍可保持对Cu的有效阻挡;在更高温度下退火,Cu将穿过阻挡层与Si发生反应,导致阻挡层失效.     

N含量对Ta-Si-N扩散阻挡层阻挡性能的影响

采用磁控反应溅射技术在p型Si(111)衬底上制备了Ta-Si-N薄膜与Cu/Ta-Si-N复合结构,并对样品进行了快速热处理.用四探针电阻测试仪、原子力显微镜、X射线衍射和扫描电镜等对样品的电阻、形貌、结构与特性进行了分析表征.实验结果表明,随着N含量的增加,Ta-Si-N薄膜的方块电阻单调增加,表面粗糙度则先减小后增大;Ta-Si-N阻挡层的阻挡性能随N含量的增加而有所增强,但当N含量过大时,阻挡性能的提升并不明显;沉积态的Ta-Si薄膜为纳米晶结构,掺入N后,薄膜成为非晶态,但在高温热处理后Ta-Si-N薄膜重新结晶,铜原子主要通过晶界扩散并与Si反应,导致阻挡层失效.     

Al2O3基陶瓷及玻璃基底制备Ta-N薄膜微结构与电学特性的比较研究

在N2、Ar气氛中,采用反应直流磁控溅射法在Al2O3基陶瓷及玻璃基底上制备了Ta-N薄膜,并对各样品的形貌结构、化学组分及电学特性进行了比较分析研究。结果表明,沉积于Al2O3陶瓷及玻璃基底的Ta-N薄膜分别呈团簇状生长与层状紧密堆积生长;Al2O3陶瓷基底沉积的Ta-N为单相薄膜,而玻璃基底上的Ta-N薄膜,随N2、Ar流量比增加,呈单相向多相共存转变;薄膜表面形貌和微结构与基底材料的原始形貌和微结构紧密相关,这说明基底材料对薄膜的形成有重要的影响;N2、Ar流量比相同时,玻璃基底上沉积的Ta-N薄膜电性能优于Al2O3基陶瓷基底上沉积的Ta-N薄膜。     

Si3N4陶瓷/Nb/Cu/Ni/Inconel 600界面反应层形成机制研究

观察分析了Si3N4陶瓷/Nb/Cu/Ni/Inconel600界面处反应层的形貌、元素分布、反应层中的相结构、界面反应以及反应层的生长规律,研究了Si3N4陶瓷/Nb/Cu/Ni/Inconel600界面处反应层的形成机制.研究结果表明:在连接过程中,Cu层首先熔化,Nb、Ni向液态Cu中扩散溶解形成Cu-Nb-Ni合金,液态合金中的Nb和Ni向Si3N4表面扩散聚集并与Si3N4反应形成反应层;Si3N4侧的反应层主要物相是NbN和Nb、Ni的硅化物,Ni基合金侧反应相主要是NbNi3和Cu-Ni合金;在连接温度为1403 K的条件下,随着连接时间的增加,界面反应层厚度先快速增加,再缓慢增加.     

PZT/Si薄膜的扩散反应研究

运用XPS和AES研究了PZT薄膜／Si在热处理过程中的薄膜及界面化学反应：在热处理过程中，气氛中的氧气通过PZT的缺陷通道扩散到PZT／Si界面上，并与界面上的硅发生氧化反应形成SiO2界面层。同时基底上的硅通过PZT的缺陷扩散到样品表面形成SiO2表面层。此外，在PZT／Si界面上，Ti的氧化物和Si发生还原反应，形成了TISix金属硅化物，并残留在PZT膜层和SiO2界面层中。在PZT膜层内，有机结碳和钛的氧化物发生还原反应形成了TiCx物种，并存在于PZT膜层中。     

缓冲层Ta对退火Co/Cu/Co薄膜微观结构和界面互扩散的影响

用直流磁控溅射法在Si/SiO₂基底上制备了Co/Cu/Co薄膜和加入缓冲层的Ta/Co/Cu/Co薄膜,用扫描电子显微镜、原子力显微镜、X射线衍射和俄歇电子能谱研究了薄膜的微观结构、表面形貌、织构和界面互扩散现象。结果表明:退火后薄膜中均存在{111}和{002}衍射峰,加入缓冲层Ta后,Co/Cu/Co薄膜的衍射峰强度明显增强,并存在较强的{111}纤维织构,薄膜表面孔洞及粗糙度大幅减小。退火后薄膜界面处产生互扩散现象,层状结构被破坏。缓冲层Ta提高了薄膜与基底材料间的润湿性,可有效缓解界面互扩散现象。     

Si衬底上Ta-N/Cu薄膜性能研究

对Si衬底上Ta-N/Cu薄膜进行了电学和热学分析，结果发现500℃以下薄膜电随几乎不变，600-690℃下的退火引起的电阻率降低是由于Ta-N电阻的热氧化和Cu熔化扩散引起的，而690℃以上的电阻率增加是由于Cu引线传输能力减弱所致，为0.18μm以下的超大规模集成电路中的Cu引线和电阻薄膜的制作提供了有益的借鉴。     

Barrier capability of Zr–N films with titanium addition against copper diffusion

Zr–Ti–N film prepared by sputtering deposition has been employed as a potential diffusion barrier for Cu metallization. It is thought that the existing states of Ti and Zr in the films are Ti–N and Zr–N phase in Zr–Ti–N films. Material analysis by XRD, XPS and sheet resistance measurement reveal that the failure of Zr–N film is mainly due to the formation of Cu₃Si precipitates at the Zr–N/Si interface by Cu diffusion through the grain boundaries or local defects of the Zr–N barrier layer into Si substrate. In conjunction with sheet resistance measurement, XRD and XPS analyses, the Cu/Zr–Ti–N/Si contact system has high thermal stability at least up to 700 °C. The incorporation of Ti atoms into Zr–N barrier layer was shown to be beneficial in improving the thermal stability of the Cu/barrier/Si contact system.     

Tantalum and niobium as a diffusion barrier between copper and silicon

The efficiency of Ta and Nb films as diffusion barriers between thin Cu film and Si substrate has been studied using Auger electron spectroscopy, X-ray diffraction, optical microscopy, scanning electron microscopy and sheet resistance measurements. Two kinds of system were prepared by electron-beam evaporation: Cu/Ta (or Nb)/Si and Cu/Ta (or Mb) SiO₂/Si. The samples were annealed at temperatures from 400 to 800C in a vacuum of 1 × 10^–7 torr (13 Pa) for 30 min. In the Cu/Ta (or Nb)/Si system, the thermal stability was determined by interdiffusion at local sites, forming suicides, whereas the Cu/Ta (or Nb)/SiO₂/Si system degraded by interdiffusion at the interface between Ta (or Nb) and Cu. It appears that Ta is a more effective diffusion barrier than Nb for both kinds of system. This difference in the barrier effect of the transition metals is attributed to differences between oxygen segregation at grain boundaries of barrier layers and differences between diffusion coefficients through barrier layers. It is suggested that the driving force for interdiffusion may play a major role in the reaction that determines the thermal stability of a given contact system; this suggestion is based on the fact that the interdiffusion in Cu/barrier/Si systems is suppressed by interposing an SiO₂ layer in the Si substrate.     

Investigations of failure mechanisms at Ta and TaO diffusion barriers by secondary neutral mass spectrometry

One of the most important processes in Cu metallization for highly integrated circuits is to fabricate reliable diffusion barriers. Recently, thin films made of refractory metals and their compounds have been widely used in solid-state electronics as barriers because of their good electric properties, favourable thermal properties and chemical stability. Thermal stability of Tantalum (Ta) and Tantalum-oxide (TaO_x) layers as a diffusion barrier in Si/Ta/Cu, Si/TaO_x/Cu and Si/Ta-TaO_x/Cu systems have been investigated. Si/Ta (10 nm)/Cu (25 nm)/W (10 nm), Si/TaO_x (10 nm)/Cu (25 nm)/W (10 nm) and Si/Ta (5 nm)TaO_x (5 nm)/Cu (25 nm)/W (10 nm) thin layers were prepared by DC magnetron sputtering. A tungsten cap layer was applied to prevent the oxidation of the samples during the annealing process. The samples were annealed at various temperatures (473 K-973 K) in vacuum. Transmission Electron Microscopy, X-ray diffraction, X-Ray Photoelectron Spectroscopy and Secondary Neutral Mass Spectrometry were used to characterize the microstructure and diffusion properties of the thin films. Our results show that at the beginning phase of the degradation of the Si/Ta/Cu system Ta atoms migrate through the copper film to the W/Cu interface. In the Si/TaO_x/Cu system the crystallization of TaO and the diffusion of Si through the barrier determine the thermal stability. The Ta-TaO bilayer proved to be an excellent barrier layer between the Si and Cu films up to 1023 K. The observed outstanding performance of the combined film is explained by the continuous oxidation of Ta film in the TaO_x-Ta bilayer.     

Effect of Si target sputtering power on diffusion barrier properties of Ta–Si–N thin films

Abstract

Ta–Si–N thin films and Cu/Ta–Si–N thin films were deposited on p type Si(111) substrates by magnetron reactive sputtering. Then the films were characterised by four point probe sheet resistance measurement, AFM, SEM and XRD respectively. According to the XRD results, the authors found that the crystallisation of Ta nitrides in Ta–Si–N/Si thin films is suppressed effectively when fabricated by a high Si target sputtering power. As the Si target power varies, the failure temperature of Cu/Ta–Si–N/Si is changed. The sample fabricated by the Si target power of 200 W fails after 800°C rapid thermal annealing and it has the highest failure temperature. The investigation of failure mechanism shows that Cu atoms diffuse through grain boundaries or amorphous structure of the Ta–Si–N barrier, and react with Si to form Cu–Si phase. And it causes the failure of the barrier.     

Investigation of diffusional intermixing in Si/Co/Ta system by Secondary Neutral Mass Spectrometry

Low temperature analysis of diffusion and intermixing of Co-Si systems are very important in applications for microelectronics and Ultra Large Scale Integration (ULSI). In this communication a comprehensive report has been given on degradation and diffusion processes in the Si(substrate)/Co(150 nm)/Ta(10 nm) system. The samples were prepared by DC magnetron sputtering and were annealed in argon ambient at several temperatures ranging from 400 to 623 K for various times. The composition of the samples was investigated by Secondary Neutral Mass Spectrometry (SNMS). The degradation/intermixing starts with fast (grain boundary (GB)) diffusion of the Si into the Co layer. After some incubation time Si atoms appear and spread over the Co/Ta interface. This amount of Si accumulated at the Co/Ta interface acts as a reservoir for back-diffusion into the Co layer from the Co/Ta interface through the slower grain boundaries. At higher temperatures the formation of a Co-Si phase was detected at the Co/Si and Co/Ta interface. Three different diffusion coefficients were calculated from the SNMS concentration-depth profiles using “Central-gradient” (CG) and “First-appearance” methods. The observed intermixing was interpreted as a mixture of different “C-type” grain boundary diffusion processes. Furthermore, the experimental results are also compared with computer simulations modelling the grain-boundary diffusion through different grain-boundary paths. From the SNMS profiles measured at different temperatures the activation energy of the GB interdiffusion coefficients was deduced using the “CG method”.     

Investigations of diffusion kinetics in Si/Ta/Cu/W and Si/Co/Ta systems by secondary neutral mass spectrometry

Proper understanding of the degradation mechanisms and diffusion kinetics of copper and cobalt interconnections for advanced microelectronics is important from the point of view of fundamental research and technology as well. In this paper Si(substrate)/Ta(10 nm)/Cu(25 nm)/W(10 nm) and Si(substrate)/Co(150 nm)/Ta(10 nm) samples, prepared by DC magnetron sputtering, were in investigated. The samples were annealed at several temperatures ranging from 423 K to 823 K for various times. The composition distributions were detected by means of Secondary Neutral Mass Spectrometry (SNMS). Microstructural characterization of samples was carried out by means of Transmission Electron Microscopy (TEM). It is shown that the changes in the composition profiles were mainly caused by grain boundary, GB, diffusion and the effective GB diffusion coefficients of Ta in Cu were determined both by the “first appearance” and “centre-gradient” methods. The activation energy is 100 kJ/mol. The importance of the Ta penetration into the Cu and its accumulation at the Cu/W interface can lead to an increase of the Ta content in the copper film. This can be an important factor in the change/degradation of the physical parameters (e.g. the electrical resistance) of interconnects. Furthermore a Ta segregation factor in Cu was evaluated. Preliminary results in the Si(substrate)/Co(150 nm)/Ta(10 nm) indicate fast (GB) diffusion of the Si into the Co layer, formation of a cobalt silicide layer at the Co/Si interface and Si accumulation first at the Ta/Co interface and later a retarded accumulation at the free Ta surface.     

Investigations of diffusion kinetics in Si/Ta/Cu/W and Si/Co/Ta systems by secondary neutral mass spectrometry

Proper understanding of the degradation mechanisms and diffusion kinetics of copper and cobalt interconnections for advanced microelectronics is important from the point of view of fundamental research and technology as well. In this paper Si(substrate)/Ta(10 nm)/Cu(25 nm)/W(10 nm) and Si(substrate)/Co(150 nm)/Ta(10 nm) samples, prepared by DC magnetron sputtering, were in investigated. The samples were annealed at several temperatures ranging from 423 K to 823 K for various times. The composition distributions were detected by means of Secondary Neutral Mass Spectrometry (SNMS). Microstructural characterization of samples was carried out by means of Transmission Electron Microscopy (TEM). It is shown that the changes in the composition profiles were mainly caused by grain boundary, GB, diffusion and the effective GB diffusion coefficients of Ta in Cu were determined both by the “first appearance” and “centre-gradient” methods. The activation energy is 100 kJ/mol. The importance of the Ta penetration into the Cu and its accumulation at the Cu/W interface can lead to an increase of the Ta content in the copper film. This can be an important factor in the change/degradation of the physical parameters (e.g. the electrical resistance) of interconnects. Furthermore a Ta segregation factor in Cu was evaluated. Preliminary results in the Si(substrate)/Co(150 nm)/Ta(10 nm) indicate fast (GB) diffusion of the Si into the Co layer, formation of a cobalt silicide layer at the Co/Si interface and Si accumulation first at the Ta/Co interface and later a retarded accumulation at the free Ta surface.     

Investigation on preparation and diffusion barrier properties of W-Ti thin films

An W-10 wt.%Ti alloy target was prepared by the W-Ti ball-milled powders, and W-Ti thin ?lms were deposited by dc magnetron sputtering on Si substrates. Then Cu/W-Ti/Si structures were prepared after Cu films were deposited on the W-Ti/Si structures. The results show that W-Ti alloy has a single phase structure with fine grain size. The structures of W-Ti thin films evolved from an amorphous film to a dual phase structure with bcc W and hcp Ti, followed by W-Ti solid solution with increasing sputtering powers. W-Ti thin ?lms can effectively block against Cu diffusion and maintain good adhesion strength with Cu ?lms at 600 °C. The failure mechanism of the crystal W-Ti films is related to the grain boundary which provides fast diffusion paths for Cu and Si atoms, while the amorphous W-Ti diffusion barrier layer is directly related to the thermal stress and interface reaction.     

集成电路Cu金属化中的扩散阻挡层

阐述了集成电路Cu互连中的技术难题,重点讨论了Cu的扩散问题,综述了扩散阻挡层的研究发展进程,重点介绍了当今研究较多的难熔金属、难熔金属氮化物及其三元结构阻挡层的最新进展情况.研究表明,阻挡层的阻挡性能与制备工艺、薄膜组分及微观结构密切相关,其失效机制多为高温下阻档层晶化所产生的晶界为Cu扩散提供了快速通道,掺入Si或其它原子的难熔金属氮化物由于其较高的晶化温度和良好的阻挡性能正成为研究热点.     

Improvement of Ta-based thin film barriers on copper by ion implantation of nitrogen and oxygen

Magnetron sputtered polycrystalline Ta and Ta(Si) barriers for copper metallization schemes were modified by nitrogen as well as oxygen high dose ion implantation to improve their thermo-mechanical stability. Ion bombardment changed the initial polycrystalline microstructure to amorphous-like. In contrast to pure Ta, Ta(Si) layers were already amorphous or nanocrystalline after deposition. In this case, the annealing temperature at which formation of a well crystallized structure occurs increased by approximately 100 K as a result of the implantation. In order to demonstrate the improvement in the barrier properties of the implanted Ta films, the intermixing of Ta and Cu at the interface of corresponding layer structures was measured as a function of the annealing temperature by depth profiling using Auger electron spectroscopy (AES). The thermal stability of Ta and Ta(Si) barriers increased from 600 °C/1 h for the non-implanted layers up to 750 °C/1 h after implantation of nitrogen or oxygen.