离子束辅助工艺中APS源偏转电压对HfO2薄膜性能的影响

 基于Leybold APS1104镀膜系统,采用离子束辅助反应沉积技术,以金属Hf粒为初始镀膜材料,APS源偏转电压为50~140 V范围内,在［100］单晶硅片和紫外石英（JGS1）基板上制备了HfO₂单层膜。分别利用Lambda 900分光光度计、X射线光电子能谱仪、X射线衍射仪以及原子力显微镜对HfO2薄膜的光谱性能、表面及纵向化学成分、晶相结构以及表面粗糙度进行了分析。结果表明：当APS源偏转电压在120~140 V及50~90 V两个范围内变化时,HfO2薄膜的紫外短波光学损耗随着偏转电压的降低而减小,而为110~90 V时紫外短波光学损耗对偏转电压的变化不敏感;偏转电压在50~140 V的范围内时,制备的HfO₂薄膜表面及纵向化学成分无明显变化;当偏转电压为100 V时,HfO₂薄膜晶粒尺寸及表面粗糙度分别达到最大值26.2 nm及5.79 nm,其后,随着偏转电压的降低,二者均逐渐减小。     

缺陷对HfO2薄膜的激光弱吸收与损伤阈值的影响

激光弱吸收是导致光学薄膜损伤的重要原因。在(5~43)mPa的氧分压下制备并测试了一组HfO2薄膜。实验发现,当氧分压小于20mPa时,薄膜弱吸收越大,损伤阈值越低;当氧分压大于20mPa时,薄膜的损伤阈值与弱吸收并不一一对应,具有较高弱吸收的薄膜可能同时具有较高的损伤阈值。建立了缺陷模型,采用有限元法模拟了缺陷对弱吸收测量和损伤阈值测量的影响,分析了缺陷尺寸、密度、吸收系数对弱吸收和损伤阈值的影响。研究结果显示,吸收系数高于薄膜1 000倍的缺陷可以降低薄膜的损伤阈值1 000倍,却并不影响薄膜的弱吸收。缺陷对HfO2薄膜的激光弱吸收与损伤阈值测试有完全不同的影响,是导致某些薄膜弱吸收与损伤阈值背离的原因。     

化学法制备的HfO2薄膜的激光损伤阈值研究

 采用化学法制备了HfO₂介质膜，研究了热处理、紫外辐照以及Al₂O₃复合对HfO₂介质膜激光损伤阈值的影响。采用红外光谱（FTIR）和X射线衍射仪对薄膜进行了表征，并用输出波长为1.064 μm、脉宽为10 ns的电光调Q激光系统测试薄膜的激光损伤阈值。实验结果表明：采用150 ℃左右的温度对薄膜进行热处理可以提高薄膜的激光损伤阈值，所获得的薄膜的激光损伤阈值高达42.32 J/cm²，比热处理前的激光损伤阈值提高了82%；无机材料Al₂O₃的适量添加能够提高薄膜的激光损伤阈值，其中HfO₂与Al₂O₃的最佳质量配比约为95∶5；另外，对薄膜进行适当的紫外辐照也可改善HfO₂ 薄膜以及HfO₂-Al₂O₃复合薄膜的抗激光损伤性能。紫外辐照对提高HfO₂-Al₂O₃复合薄膜的激光损伤阈值效果尤为显著，辐照40 min后的激光损伤阈值达到44.33 J/cm²，比紫外辐照前的激光损伤阈值提高了90%。     

金属氧化物薄膜光学常数计算物理模型应用研究

采用离子束溅射(IBS)方法制备了HfO₂和Ta₂O₅两种金属氧化物薄膜,通过测量薄膜的椭偏参数,使用非线性最小二乘法反演计算获得薄膜的光学常数。 在拟合过程中,采用L₈(27)正交表设计了8组反演计算实验,在初始选定Cauchy模型后,对HfO₂薄膜拟合影响最大的为表面层模型,对Ta₂O₅薄膜拟合影响最大的为折射率梯度模型。 确定了不同物理模型对拟合函数MSE的影响权重和拟合过程中模型选择的次序,按照确定的模型选择次序拟合,最后加入弱吸收模型反演计算两种薄膜的光学常数,反演计算的MSE相对初始MSE可下降79%和39%,表明拟合过程模型选择物理意义明确,具有广泛的应用价值。 在500 nm处,Ta₂O₅薄膜的折射率梯度大于HfO₂薄膜, 而HfO₂薄膜消光系数大于Ta₂O₅薄膜。 表明Hf金属与Ta金属相比容易氧化形成稳定的氧化物,HfO₂薄膜的吸收要高于Ta₂O₅薄膜。     

Impact of substrate temperature and film thickness on the interfacial evolution during atomic layer deposition of HfO2 on InP

The effects of both the deposition temperature and the HfO₂ film thickness on the interfacial layer (IL) evolution were studied when tetrakis(ethylmethylamino)hafnium and H₂O based atomic layer deposition (ALD) was performed on InP substrates. While the self‐cleaning effect resulted in an IL‐free structure after formation of ～2 nm thick HfO₂ at 200 °C and 250 °C, substantial IL growth occurred at 300 °C, probably due to simultaneous InP oxidation. Following further growth to ～8 nm at 300 °C, the IL was almost removed and, in particular, a significant In incorporation into the HfO₂ film was observed, which was attributed to IL decomposition and subsequent out‐diffusion of the constituent elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reduction of charge trapping in HfO2 film on a Ge substrate by trimethylaluminum pretreatment

Trimethylaluminum pretreatment prior to HfO₂ deposition is introduced for native oxide reduction. It is identified that the trimethylaluminum pretreatment could effectively reduce native oxide, which is transformed to an aluminum oxide interfacial layer. Formation of the thin aluminum oxide layer suppresses Ge diffusion into HfO₂, reducing hysteresis in the ca‐ pacitance–voltage curve. Moreover, the device reliability of the trimethylaluminum pretreated sample is improved in a constant current stress test. This work indicates that trimethylaluminum pretreatment is an effective in‐situ method for the gate dielectric stack formation to reduce charge trapping in the HfO₂ film on a Ge substrate. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermal instability of HfO2 on InP structure with ultrathin Al2O3 interface passivation layer

We studied the thermal stability of HfO₂ on an InP structure when an Al₂O₃ interface passivation layer (PL) was introduced. In contrast to the thick (～4 nm) Al₂O₃‐PL, an almost complete disappearance of the thin (～1 nm) Al₂O₃‐PL was observed after a post‐deposition anneal at 600 °C. Based on various chemical and electrical analyses, this was attributed to the intermixing of the thin Al₂O₃‐PL with HfO₂, which might have been accompanied by the out‐diffusion of a substantial amount of substrate elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

沉积温度对HfO2薄膜残余应力的影响

 用电子束蒸发方法制备了HfO₂薄膜，根据镀膜前后基片曲率半径的变化，用Stoney公式计算了薄膜应力，讨论了沉积温度对薄膜残余应力的影响。结果发现，HfO₂薄膜的残余应力均为张应力，应力值随沉积温度的升高先增大后减小，在280 ℃左右出现极大值。对样品进行了XRD测试，从微观结构上对实验结果进行了分析，发现微结构演变引起的内应力变化是引起薄膜残余应力改变的主要因素，HfO2薄膜在所选沉积温度60~350 ℃内出现了晶态转变，堆积密度随温度升高而增大。     

两种后处理方法对HfO2薄膜性能的影响

利用电子束蒸发和光电极值监控技术制备了氧化铪薄膜,并分别用两种后处理方法(空气中退火和氧等离子体轰击)对样品进行了处理.然后,对样品的透过率、吸收和抗激光损伤阈值进行了测试分析.实验结果表明,两种后处理方法都能不同程度地降低了氧化铪薄膜的吸收损耗、提高了抗激光损伤阈值.实验结果还表明,氧等离子体轰击的后处理效果明显优于热退火,样品的吸收平均值在氧等离子体后处理前后分别为34.8 ppm和9.0 ppm,而基频(1 064 nm)激光损伤阈值分别为10.0 J/cm2和21.4 J/cm2.     

Influence of different oxidants on the band alignment of HfO2 films deposited by atomic layer deposition

Based on X-ray photoelectron spectroscopy （XPS）, influences of different oxidants on band alignment of HfO2 films deposited by atomic layer deposition （ALD） are investigated in this paper. The measured valence band offset （VBO） value for H2O-based HfO2 increases from 3.17 eV to 3.32 eV after annealing, whereas the VBO value for O3-based HfO2 decreases from 3.57 eV to 3.46 eV. The research results indicate that the silicate layer changes in different ways for H2O-based and O3-based HfO2 films after the annealing process, which plays a key role in generating the internal electric field formed by the dipoles. The variations of the dipoles at the interface between the HfO2 and SiO2 after annealing may lewd the VBO values of H2O-based and O3-based HfO2 to vary in different ways, which fits with the variation of fiat band （VFB） voltage.     

Characterization and application in XRF of HfO_2-coated glass monocapillary based on atomic layer deposition

Coating a glass monocapillary x-ray optics with high-density film is a promising way to improve transmission characteristics. For a long time, it has been a challenge to coat a high-density film in the inside of monocapillary with an extremely high length-to-diameter ratio. In this work, Hf O2 film is deposited on the inner wall of a tapered glass monocapillary with length 9.9 cm, entrance diameter 596.4 μm, and exit diameter 402.3 μm by atomic layer deposition. The coated and uncoated monocapillaries are studied by the transmission process of x-rays with energy from 5 ke V to 100 ke V and the x-ray fluorescence(XRF) spectra of a Mo sample are detected. Improved transmission characteristics have been obtained for the Hf O_2-coated monocapillary. The energy upper limit of focused x-rays increases from 18.1 ke V to 33.0 ke V and the ‘penetration halo' is suppressed to some extent. The XRF spectrum presents two stronger peaks at ～ 17.4 ke V and～ 19.6 ke V which are considered as the characteristic x-rays of Mo K_α and Mo K_β. These results reveal that more higher energy x-rays from the W x-ray tube are totally reflected on the inner wall of the Hf O_2-coated glass monocapillary due to the increase of total reflection critical angle. This work is significant for more applications of monocapillary in higher energy x-ray field.     

电子束蒸发制备HfO2高k薄膜的结构特性

使用高真空电子束蒸发在p型Si（100）衬底上制备了高k HfO2薄膜.俄歇电子能谱证实薄膜组分符合化学配比；x射线衍射测量表明刚沉积的薄膜是近非晶的，高温退火后发生部分晶化；原子力显微镜和扫描电子显微镜检测显示在高温退火前后薄膜均具有相当平整的表面，表明薄膜具有优良的热稳定性；椭偏测得在600?nm处薄膜折射率为2.09；电容电压测试得到的薄膜介电常数为19.这些特性表明高真空电子束蒸发是一种很有希望的制备作为栅介质的HfO2薄膜的方法. 关键词： 高k薄膜 HfO2 电子束蒸发     

Influence of different oxidants on the band alignment of HfO₂ films deposited by atomic layer deposition

Based on X-ray photoelectron spectroscopy(XPS),influences of different oxidants on band alignment of HfO2 films deposited by atomic layer deposition(ALD) are investigated in this paper.The measured valence band offset(VBO) value for H2 O-based HfO2 increases from 3.17 eV to 3.32 eV after annealing,whereas the VBO value for O 3-based HfO2 decreases from 3.57 eV to 3.46 eV.The research results indicate that the silicate layer changes in different ways for H2 O-based and O3-based HfO2 films after the annealing process,which plays a key role in generating the internal electric field formed by the dipoles.The variations of the dipoles at the interface between the HfO2 and SiO2 after annealing may lead the VBO values of H2 O-based and O 3-based HfO2 to vary in different ways,which fits with the variation of flat band(VFB) voltage.     

采用HfO2/SiO2溶胶-凝胶薄膜制备衍射光栅

采用溶胶-凝胶方法制备了具有光敏性的HfO2/SiO2溶胶-凝胶薄膜,并利用其光敏性制备了衍射光栅.采用XPS分析了薄膜的成份,证实了Hf元素的存在.并用椭偏仪测试了薄膜的折射率,结果证实了HfO2的加入确实提高了体系的折射率.利用其光敏性,采用X射线作曝光光源通过掩模进行曝光,利用曝光部分与未曝光部分的溶解度差,在薄膜上制备了高为0.8 μm、周期为1 μm的衍射光栅.     

HfO2中ZrO2含量对266nm HfO2/SiO2多层膜反射率的影响

用两种不同纯度的HfO2材料与同一纯度的SiO2材料组合,沉积Λ／4规整膜系(HL)^11H形成266nm的紫外反射镜,发现反射率相差0．7％左右。用X光电子能谱法分析了高反膜中表层HfO2中的成分,发现ZrO2的含量相差一个数量级左右。为确定形成这种差别的原因,用辉光放电质谱法测定了这两种HfO2材料中锆(Zr)及其钛(Ti)、铁(Fe)的含量,发现Zr是其中的最主要的杂质,两种HfO2材料中Zr含量有一个数量级的差别。说明在266nm波段,HfO2中ZrO2的含量会对HfO2／SiO2高反膜的反射率造成影响。根据HfO2单层膜的光谱曲线,推算出了这两种材料的消光系数的差别,并用Tfcalc膜系设计软件进行理论和镀制结果的模拟,得到与实验测试一致的结果。     

电荷俘获存储器的过擦现象

基于密度泛函理论的第一性原理平面波超软赝势方法和VASP软件对电荷俘获存储器过擦现象进行了分析研究.通过形成能的计算,确定了含有氮空位缺陷的Si3N4和含有间隙氧缺陷的Hf O2作为研究的对象;俘获能的计算结果表明两种体系对电子的俘获能力比对空穴的大,因而对两体系擦写载流子确定为电子.分别计算了Hf O2和Si3N4擦写前后的能量、擦写前后电荷分布变化、吸附能和态密度,以说明过擦的微观机理.对能量和擦写电荷变化的研究,表明Si3N4相比于Hf O2,其可靠性较差,且Si3N4作为俘获层,在一个擦写周期后,晶胞中电子出现减少现象;界面吸附能的研究表明,Si3N4相比于Hf O2在缺陷处更容易与氧进行电子交换;最后,通过对态密度的分析表明Si3N4和Hf O2在对应的缺陷中均有缺陷能级俘获电子,前者为浅能级俘获,后者为深能级俘获.综上分析表明,Si3N4在氮空位的作用下,缺陷附近原子对电子的局域作用变弱,使得Si3N4作为俘获层时,材料本身的电子被擦出,使得擦操作时的平带偏移电压增大,导致存储器发生过擦.本文的研究结果揭示了过擦的本质,对提高电荷俘获存储器的可靠性以及存储特性有着重要的指导意义.     

A comparison of FePt thin films with HfO2 or MnO additive

The influence of oxide additives on the magnetic and structural properties of FePt L1₀ thin films has been studied. FePt films with HfO₂ additive grown on a 5 nm MgO buffer showed a primarily random texture for both as-deposited and annealed samples. The average grain size was limited to 10 nm and the perpendicular coercivity was 1.3 kOe for a 10 nm thick FePt +20% HfO₂ film annealed at 650°C for 10 min. In direct contrast, MnO additive neither limited grain size nor L1₀ ordering in annealed FePt films. A 10 nm thick FePt+20% MnO film grown on a 5 nm MgO buffer showed a unique discontinuous microstructure composed of clusters of (0 0 1) textured L1₀ grains after being annealed at 650°C for 10 min. The average size of the grains making up these clusters was 50 nm and the perpendicular coercivity of the film exceeded 7 kOe.     

Growth and characterization of MOMBE grown HfO2

HfO₂ dielectric layers were grown directly on the p-type Si (1 0 0) by metalorganic molecular beam epitaxy (MOMBE). Hafnium tetra-butoxide was used as a Hf precursor and pure oxygen was introduced to form an oxide layer. The properties of the layers with different thicknesses were evaluated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), and capacitance–voltage (C–V) and current–voltage (I–V) analyses. XRD and HRTEM results showed that the HfO₂ films thinner than 12 nm were amorphous while the films thicker than 12 nm began to crystallize in the tetragonal and the monoclinic phases. The XPS spectra of O 1s show that the O---Si binding energies shifted to the lower binding energy with increasing the HfO₂ layer thickness. Moreover, the snap back phenomenon is observed in accumulation capacitance. These changes are believed to be linked with the decomposition of SiO and the crystallization of HfO₂ layer during the film growth.     

Distribution of electron traps in SiO_2/HfO_2 nMOSFET

In this paper, the principle of discharge-based pulsed I–V technique is introduced. By using it, the energy and spatial distributions of electron traps within the 4-nm HfO_2 layer have been extracted. Two peaks are observed, which are located at ?E ~-1.0 eV and-1.43 eV, respectively. It is found that the former one is close to the SiO_2/HfO_2 interface and the latter one is close to the gate electrode. It is also observed that the maximum discharge time has little effect on the energy distribution. Finally, the impact of electrical stress on the HfO_2 layer is also studied. During stress, no new electron traps and interface states are generated. Meanwhile, the electrical stress also has no impact on the energy and spatial distribution of as-grown traps. The results provide valuable information for theoretical modeling establishment, material assessment,and reliability improvement for advanced semiconductor devices.     

Charge transport and bipolar switching mechanism in a Cu/HfO_2/Pt resistive switching cell

Bipolar resistance switching characteristics are investigated in Cu/sputtered-HfO_2/Pt structure in the application of resistive random access memory(RRAM).The conduction mechanism of the structure is characterized to be SCLC conduction.The dependence of resistances in both high resistance state(HRS) and low resistance state(LRS) on the temperature and device area are studied.Then,the composition and chemical bonding state of Cu and Hf at Cu/HfO_2 interface region are analyzed by x-ray photoelectron spectroscopy(XPS).Combining the electrical characteristics and the chemical structure at the interface,a model for the resistive switching effect in Cu/HfO_2/Pt stack is proposed.According to this model,the generation and recovery of oxygen vacancies in the HfO_2 film are responsible for the resistance change.