大马士革铜互连线织构的研究

采用EBSD研究了不同线宽和退火前后Cu互连线的织构和晶界特征分布.Cu互连线均具有多重织构,其中(111)织构强度最高.沉积态样品在室温下发生了自退火现象,并出现了一些异常长大的晶粒.随高宽比降低和退火处理,Cu互连线晶粒尺寸变大,(111)织构得到加强,而具有较低应变程度的织构与(111)织构强度的比例下降.沉积态样品出现了(111)<112>和(111)<231>织构组分.退火后,出现了(111)<110>组分,而且(111)<112>和(111)<231>组分得到增强.Cu互连线以大角度晶界为主,其中具有55°～60°错配角的晶界和∑3晶界比例最高,35°～40°的错配角和∑9晶界次之.随高宽比增加和退火处理,∑3晶界比例逐渐升高,∑9晶界比例下降.     

大马士革铜互连线织构的研究

采用EBSD研究了不同线宽和退火前后Cu互连线的织构和晶界特征分布.Cu互连线均具有多重织构,其中(111)织构强度最高.沉积态样品在室温下发生了自退火现象,并出现了一些异常长大的晶粒.随高宽比降低和退火处理,Cu互连线晶粒尺寸变大,(111)织构得到加强,而具有较低应变程度的织构与(111)织构强度的比例下降.沉积态样品出现了(111)<112>和(111)<231>织构组分.退火后,出现了(111)<110>组分,而且(111)<112>和(111)<231>组分得到增强.Cu互连线以大角度晶界为主,其中具有55°～60°错配角的晶界和∑3晶界比例最高,35°～40°的错配角和∑9晶界次之.随高宽比增加和退火处理,∑3晶界比例逐渐升高,∑9晶界比例下降.     

大马士革镶嵌结构对Cu膜微结构及应力的影响

通过TEM、SEM、XRD和EBSD,观察了Cu互连线和平坦Cu膜的微观结构。采用薄膜应力测试分布仪和二维面探测器XRD,测量了平坦Cu膜和Cu互连线的应力,计算了Cu薄膜热应力的理论值。凹槽侧壁成为互连线新的形核区域,并且在平行于侧壁的方向形成较弱的(111)织构。与平坦膜相比,互连线晶粒尺寸明显变小(、111)织构较弱,且存在大量Σ3和Σ9晶界。平坦膜和互连线分别表现出压应力和张应力。降温过程产生的热应力为互连线的主要应力。     

Cu互连线显微结构和应力的AFM及SNAM分析

在ULSI中采用Cu互连线代替Al以增加电子器件的传输速度和提高器件的可靠性，Cu的激活能约为1．2eV，而Al的激活能约为0．7eV,Cu互连线寿命约为Al的3－5倍。Cu大马士革互连线的制备工艺为：在硅衬底上热氧化生成的SiO2上开出凹槽，在凹槽中先后沉积阻挡层Ta和晶种层Cu，然后由电镀的Cu层将凹槽填满，最后采用化学机械抛光将凹槽外多余的Cu研磨掉，Cu互连线的尺寸为：200um长，0．5μm厚，宽度分别为0．35，0．5，1至3μm不等，部分样品分别在200℃，300℃和450℃下经过30min退火。利用原子力显微镜（AFM）和扫描近场声学显微镜（SNAM），同时获得形貌像和声像，分别了Cu大马士革凹槽构造引起的机械应力和沉积引起的热应力对Cu互连线显微结构及可靠性的影响，SNAM是在Topometrix公司AFM基础上建造的实验装置，实验采用的机械振动频率在600Hz-100kHz之间。分析测试结果如下：1．AFM和SNAM可以实现对微米和亚微米特征尺寸的Cu互连线的局域应力分布和显微结构的原位分析。2．采用AFM，TEM、XRD观察和测试了Cu互连线的晶体结构，分析了大马士革凹槽工艺 对Cu晶粒尺寸及取向的影响。平坦的沉积态Cu膜的晶粒尺寸约为100nm；而由大马士革工艺制备的凹槽中的Cu互连线的晶粒尺寸约为70－80nm，凹槽结构抑制了晶粒生长，平坦的沉积态Cu膜有较强的（111）织构；而凹槽中的Cu互连线的（111）织构减弱，（200）和其它的晶体取向分量增强。3．SNAM声阻尼信号对材料局域应力的变化敏感，SNAM声图衬底可显示出局域应力的分布，在沉积态的Cu互连线声图中，金属和SiO2介电层的界面处像衬度强，表明该处为应力较高的区域，而在退火后的Cu互连线的声图中，金属和SiO2介电层的界面处像衬度弱，表明退火后该处应力减小，我们对Cu膜进行了宏观应力的测试，退火后应力值从沉积态的661MPa减少至359Mpa，这与SNAM声成像的结果相符合。     

直流和脉冲电镀Cu互连线的性能比较

针对先进纳米Cu互连技术的要求,比较了直流和脉冲两种电镀条件下Cu互连线的性能以及电阻率、织构系数、晶粒大小和表面粗糙度的变化.实验结果表明,在相同电流密度条件下,脉冲电镀所得Cu镀层电阻率较低,表面粗糙度较小,表面晶粒尺寸和晶粒密度较大,而直流电镀所得镀层(111)晶面的择优程度优于脉冲.在超大规模集成电路Cu互连技术中,脉冲电镀将有良好的研究应用前景.     

低碳冲压钢板静态再结晶行为的研究

利用背散射电子衍射(EBSD)技术和X射线衍射(XRD)对SPCD冷轧钢板缓慢升温退火工艺下的再结晶取向特征、织构的形成规律及与形变织构的关系进行研究,并与快速加热退火工艺下的IF钢再结晶取向特点进行对比。结果表明:宏观织构显示冷轧态下{111}〈112〉形变织构稳定存在,随后的再结晶过程中γ线上存在{111}〈112〉与{111}〈110〉织构的竞争,其中再结晶初期{111}〈112〉织构占主导,后期{111}〈110〉吞食{112}〈110〉和{001}〈110〉织构进而取代{111}〈112〉作为γ线织构的主导取向;不同取向新晶粒具有不同的再结晶形核地点:{111}〈110〉新晶粒主要在{112}〈110〉和{111}〈112〉形变晶粒的晶界处形核;{111}〈112〉新晶粒主要在相同取向的形变晶粒内形核;而{110}〈001〉新晶粒主要在{111}〈112〉形变晶粒的形变带内形核。     

一种低成本的硅垂直互连技术

采用KOH刻蚀工艺制作硅垂直互连用通孔,淀积SiO2作为硅垂直互连的电绝缘层,溅射Ti和Cu分别作为Cu互连线的黏附层/扩散阻挡层和电镀种子层.电镀10μm厚的Cu作为硅垂直互连的导电层.为实现金属布线的图形化,在已有垂直互连的硅片上试验了干膜光刻工艺.采用化学镀工艺,在Cu互连线上沉积150～200 nm厚的NiMoP薄膜作为防止Cu腐蚀和Cu向其上层介质扩散的覆盖层.高温退火验证了Ti阻挡层和NiMoP覆盖层的可靠性.     

退火温度对铝互连线热应力的影响

采用二维面探测器X射线衍射(XRD)测量1μm和0.5μm厚Al互连线退火前后的残余应力.沉积态Al线均为拉应力,且随膜厚的增加而减小.沿长度方向的应力明显高于宽度方向的应力,表面法线方向应力最小.250℃退火2.5h后,互连线在各方向上的应力都减弱,其中1μm Al线应力减弱幅度高于0.5μm互连线.采用电子背散射衍射(EBSD)方法,测量退火前后Al互连线(111),(100),(110)取向晶粒的IQ值.退火后平均IQ值提高,互连线残余内应力随之减小.EBSD分析结果与XRD应力测试结果相符合.     

退火温度对铝互连线热应力的影响

采用二维面探测器X射线衍射(XRD)测量1μm和0.5μm厚Al互连线退火前后的残余应力.沉积态Al线均为拉应力,且随膜厚的增加而减小.沿长度方向的应力明显高于宽度方向的应力,表面法线方向应力最小.250℃退火2.5h后,互连线在各方向上的应力都减弱,其中1μm Al线应力减弱幅度高于0.5μm互连线.采用电子背散射衍射(EBSD)方法,测量退火前后Al互连线(111),(100),(110)取向晶粒的IQ值.退火后平均IQ值提高,互连线残余内应力随之减小.EBSD分析结果与XRD应力测试结果相符合.     

低碳冲压钢板静态再结晶行为的研究

利用背散射电子衍射(EBSD)技术和X射线衍射(XRD)对SPCD冷轧钢板缓慢升温退火工艺下的再结晶取向特征、织构的形成规律及与形变织构的关系进行研究,并与快速加热退火工艺下的IF钢再结晶取向特点进行对比.结果表明:宏观织构显示冷轧态下{111}〈112〉形变织构稳定存在,随后的再结晶过程中γ线上存在{111}〈112...     

Microstructural characterization of inlaid copper interconnect lines

The microstructure of inlaid Cu lines has been quantified as a function of annealing conditions, post-plating, and post-CMP. The grain size distribution was measured using the median intercept method, crystallographic texture was characterized by pole figure analysis, and mechanical stress was determined using x-ray diffraction. The median grain size and mechanical stress level increase with increasing anneal temperature. The crystallographic texture is independent of the anneal temperature and is predominantly (111) with a small fraction of sidewall-nucleated (111) grains. The (111) grains nucleated from the trench bottom have a preferred in-plane orientation. The grain growth in the trench is independent of that in the overburden.     

Electromigration-Induced Plasticity: Texture Correlation and Implications for Reliability Assessment

Plastic behavior has previously been observed in metallic interconnects undergoing high-current-density electromigration (EM) loading. In this study of Cu interconnects, using the synchrotron technique of white-beam x-ray microdiffraction, we have further found preliminary evidence of a texture correlation. In lines with strong (111) textures, the extent of plastic deformation is found to be relatively large compared with that of weaker textures. We suggest that this strong (111) texture may lead to an extra path of mass transport in addition to the dominant interface diffusion in Cu EM. When this extra mass transport begins to affect the overall transport process, the effective diffusivity, D _eff, of the EM process is expected to deviate from that of interface diffusion only. This would have fundamental implications. We have some preliminary observations that this might be the case, and report its implications for EM lifetime assessment herein.     

Analysis of copper grains in damascene trenches after rapid thermal processing or furnace anneals

The microstructures of Cu lines in damascene trenches annealed at temperatures from room temperature to 425°C using both rapid thermal processing (RTP) and furnace annealing were investigated using an array of characterization techniques including transmission electron microscopy (TEM), focused ion beam, scanning electron microscopy (SEM), and electron backscatter diffraction-orientation-imaging microscopy (EBSD-OIM). It was found that the final grain sizes strongly depend on the annealing process used; RTP generated larger grains than furnace annealing. The Cu line electrical resistance correlated with grain size differences observed for RTP and furnace anneals. The ramping rate, not the annealing time, played the critical role in the grain growth process. In either case, a high density of Σ3 coincident site lattice (CSL) twin boundaries was observed in the Cu lines. Forty-five percent of the grain boundaries measured were found to be Σ3 CSL twins, which are differentiated from random high-angle boundaries by having preferred electrical and diffusion properties. The minimum feature dimension of width or height of the damascene trenches limited the average grain size. Prior to the trench height limitation, the average grain size increased linearly with the trench width. The Cu (111) texture became stronger as the trench width increased up to 0.5 μm; for wider trenches, the texture did not increase further.     

Microstructure and electromigration in copper damascene lines

Grain sizes and crystallographic orientations of Cu were analyzed versus linewidth in damascene Cu interconnects. Pure bamboo lines were not obtained because grain size decreased as linewidth was reduced. Comparison of electromigration results, for wide line Chemical vapor deposition-Cu (3 μm) polycrystalline structure, and narrow lines (0.5 μm) quasi-bamboo structure, provided almost the same activation energy E_a0.65 eV, even though the poor (2 0 0) texture has rotated in the film plane for the narrow damascene lines. These results are in agreement with copper diffusion involving surface diffusion. Besides, even with a polycrystalline crystallographic orientation, PVD-Cu samples showed a better activation energy value E_a=1.02 eV.     

Microstructure control of copper films by the addition of molybdenum in an advanced metallization process

The effect of annealing on the resistivity, morphology, microstructure, and diffusion characteristics of Cu(Mo)/SiO₂/Si and Ti/Cu(Mo)/SiO₂/Si multilayer films has been investigated in order to deterine the role of Mo. In the case of a Cu(Mo)/SiO₂/Si multilayer, most of the Mo diffused out to the free surface to form MoO₃ at temperatures up to 500 C, and complete dissociation of Mo occurred at higher temperatures. The segregation of Mo to the external surface leads to Mo-free Cu films with extensive grain growth up to 20 times the original grain size and strong (111) texture. In the case of a Ti/Cu(Mo)/SiO₂/Si multilayer, a thin Ti film prohibits Cu agglomeration, out-diffusion of Mo, and diffusion of Cu into SiO₂ at temperatures up to 750 C. Cu(Mo) grain growth was less extensive, but (111) fiber texturing was much stronger than in the case of Cu(Mo)/SiO₂/Si. In the current study, significant changes in microstructure, such as a strong (111) texture and abnormal grain growth, have been obtained by adding Mo to Cu films when the films are annealed.     

Electromigration in sputtered copper film on plasma-treated hydrogen silsesquioxane dielectric

Electromigration (EM) damage is one of the major causes for the failure of interconnects. Plasma treatment, such as dry etching, is frequently employed in the fabrication of multilevel interconnection patterns. This work investigates the hydrogen silsesquioxane (HSQ) and copper integrated systems and the effect of H₂ plasma treatment on the EM of Cu. Hydrogen plasma bombardment induces a rough HSQ surface and results in a coarse morphology of the Cu film deposited on HSQ. The crystallographic texture of Cu is also affected by the plasma treatment. A decrease in the Cu I(111)/I(200) peak ratio is observed for a specimen treated with H₂ plasma. The activation energy for EM in Cu and the EM lifetime of the Cu interconnect decreases with an increased degree of plasma treatment. The activation energies obtained, ranging from 0.76 eV to 0.94 eV, suggest that the electromigration in copper proceeds via an interfacial diffusion path. Possible mechanisms for the effects of plasma treatment are explored. The rough surface and the retarded Cu (111) orientation induced by H₂ plasma bombardment are the major causes for the decrease of activation energy and EM lifetime.     

Electromigration failure in ultra-fine copper interconnects

This paper presents experimental evidence suggesting that electromigration (EM) can be a serious reliability threat when the dimension of Cu interconnects approaches the nanoscale range. To understand the failure mechanism prevailing in nanoscale Cu interconnects, single-level, 400-μm long interconnects with various effective widths, ranging from 750 nm to 80 nm, were made, EM tested, and characterized in this investigation. The results indicate that interface EM (Cu/barrier) may be the predominant EM mechanism in all line widths. The evidence supporting the active Cu/barrier interface EM includes the fact that the EM lifetime is inversely proportional to the interface area fraction. Microscopic analysis of the failure sites also supports the conclusion of interface EM because voids and hillocks are found at the ends of the test strip, which is not possible if lines fail by grain-boundary EM in the test structure used in this study. In addition, our study finds evidence that failure is assisted by a secondary mechanism. The influence of this factor is particularly significant when the feature size is small, resulting in more uniform distribution of failure time in narrower lines. Although limited, evidence suggests that the secondary factor is probably attributed to pre-existing defects or grain boundaries.     

Effects of deposition conditions of Al and Ti underlayer on electromigration reliability for deep-submicron interconnect metallization

We have studied the effects of Ti underlayer (collimated Ti vs. standard Ti) and Al deposition power (12 KW vs. 6 KW) on the electromigration (EM) lifetime of bottom-Ti/Al-0.5wt.%Cu/Ti/TiN-top stack. The (002) texture of standard Ti (s-Ti) was stronger than that of collimated Ti (c-Ti). The Al stack prepared with s-Ti underlayer, which had the stronger Al (111) texture and more uniform grain size distribution, showed better EM lifetime than the same with c-Ti underlayer, independent of the Al deposition power. The Al stack prepared with an Al deposition power of 6 KW was also found to show better EM lifetime than the same with a 12 KW deposition power, independent of the type of Ti underlayer. Longer deposition time for low power sputtering resulted in the stronger Al (111) texture, larger median grain size, and more uniform Ti−Al reaction layer. Finally, the effects of Ti underlayer and Al deposition power on the EM lifetime of Al-0.5%Cu films could be well explained by the grain size distribution and Al (111) texture, which is closely related to the underlying-Ti (002) texture.