Study of diffusion barrier properties of ternary alloy (TixAlyNz) in Cu/TixAlyNz/SiO2/Si thin film structure

The effects of aluminum (Al) incorporation on the performance of a titanium nitride (TiN) diffusion barrier were investigated up to the temperature of 1000°C in the Cu/Ti_xAl_yN_z/SiO₂/Si structure. The thermal stability of the structure was evaluated by using four-point probe, X-ray diffraction, and Rutherford Backscattering Spectroscopy. The Cu/Ti_xAl_yN_z/SiO₂/Si system retained its structure up to 1000°C. The incorporation of Al into the Ti_xN_y film modified the microstructure of the Ti_xN_y film, especially the microstructure of grain boundaries in which oxide and nitride compounds of Al and Ti were formed during thermal annealing. As a result, the fast pathways for copper (Cu) diffusion were effectively blocked by these compounds and the stability of the barrier performance was enhanced up to 1000°C.     

Electronic properties of Cu(In,Ga)Se2 solar cells on stainless steel foils without diffusion barrier

Compared with rigid glass, manufacturing of Cu(In,Ga)Se₂ (CIGS) solar cells on flexible stainless steel (SS) substrates has potential to reduce production cost because of the application of roll‐to‐roll processing. Up to now, high‐efficiency cells on SS could only be achieved when the substrate is coated with a barrier layer (e.g. SiO_x or Si₃N₄) for hindering the diffusion of impurities, especially Fe, into the CIGS layer. In this paper, the effect of these impurities on the electronic transport properties of the device is investigated. Using admittance spectroscopy, the presence of a deep defect level at around 320 meV is observed, which deteriorates the efficiency of the solar cells. Furthermore, it is shown that reducing substrate temperature during CIGS deposition is an effective alternative to a barrier layer for reducing diffusion of detrimental Fe impurities into the absorber layer. By applying a CIGS growth process for deposition at low substrate temperatures, an efficiency of 17.7%, certified by Fraunhofer Institute ISE, Freiburg, was achieved on Mo/Ti‐coated SS substrate without an additional metal‐oxide or metal‐nitride impurity diffusion barrier layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Texture evolutions of ionized metal plasma Cu seed layers on tantalum nitride barriers

Ionized metal plasma (IMP) was a favorable method for the deposition of thin barrier and seed layers due to its sufficient bottom coverage in high aspect ratio features. In this study, the texture evolution of IMP copper (Cu) seed layers on IMP tantalum nitride barriers deposited by various nitrogen flow rates were investigated. The (111)/(200) ratio of the Cu seeds was found to relate to the grain size of the tantalum nitride substrates. A proposed model revealed that the surface energy reduction of the Cu deposition was a main factor to determine the (111)/(200) ratio of the Cu seeds.     

Chemical studies of CVD Cu deposited on Ta and TaN barriers under various process conditions

Contamination in the matrix of CVD copper films and at the interface between CVD copper films and barrier layers has been characterized using XPS, SIMS, XRD and RGA. Contamination in the CVD copper matrix has been found to increase with increasing precursor flow rate and with decreasing wafer temperature. Interfacial contamination has been investigated in an attempt to quantitatively define acceptable levels of contamination and ultimately reduce the effect of these contaminants on the integrated film stack. Sputtered copper flash layers for CVD copper deposition are also shown as highly effective for reducing the levels and effects of incorporated contamination.     

Failure mechanisms of PVD Ta and ALD TaN barrier layers for Cu contact applications

PVD Ta-based and ALD TaN layers were studied as Cu diffusion barriers on poly-silicon, NiSi and CoSi₂ for Cu contact applications. The effectiveness of nanometer-thick layers, deposited in manufacturing compatible chambers on 200 and 300 mm wafers, is evaluated by detection of Cu-silicidation temperature using high temperature in situ XRD. It is found that Si diffuses into the α-Ta lattice for PVD barriers between 300 and 500 °C, and induces Ta silicidation at 600 °C. The agglomeration of TaSi₂ seems to be responsible for the damage of barrier continuity and cause subsequent Cu-silicidation. The growth of ALD TaN on different surfaces of NiSi was studied by XRF, RBS and XRR. The growth curves show excellent linearity as a function of thickness. TOF-SIMS shows closed layers after 60 ALD cycles. In situ XRD reveals that the failure temperature of 4 nm thick ALD layers is higher than 500 °C. It is found that the failure of 3 and 4 nm ALD TaN layers in Cu/barrier/NiSi stacks is a diffusion controlled process, with an activation energy Q of ∼2.2 eV and a pre-exponential factor D₀ of ∼3.8 × 10⁻³ cm²/s.     

Formation of Ti diffusion barrier layers in Thin Cu(Ti) alloy films

In order to study a formation mechanism of thin Ti-rich layers formed on the surfaces of Cu(Ti) wires after annealing at elevated temperatures, the 300-nm-thick Cu(Ti) alloy films with Ti concentration of 1.3 at.% or 2.9 at.% were prepared on the SiO₂/Si substrates by a co-sputter deposition technique. The electrical resistivity and microstructural analysis of these alloy films were carried out before and after annealing at 400°C. The Ti-rich layers with thickness of ∼15 nm were observed to form uniformly both at the film surface and the substrate interfaces in the Cu(2.9at.%Ti) films after annealing (which we call the self-formation of the layers) using Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). Both the resistivities and the microstructures of these Cu(Ti) films were found to depend strongly on the Ti concentrations. The resistivities of the films decreased upon annealing due to segregation of the supersaturated Ti solutes in the alloy films to both the top and bottom of the films. These Ti layers had excellent thermal stability and would be applicable to the self-formed diffusion barrier in Cu interconnects of highly integrated devices. The selection rules of the alloy elements for the barrier self-formation were proposed based on the present results.     

Defects properties and vacancy diffusion in Cu2MgSnS4

Cu₂Mg_SnS₄(CZTS)is a promising photovoltaic absorber material,however,efficiency is largely hindered by potential fluctuation and a band tailing problem due to the abundance of defect complexes and low formation energy of an intrinsic Cu_Zndefect.Alternatives to CZTS by group I,II,or IV element replacement to circumvent this challenge has grown research in-terest.In this work,using a hybrid(HSE06)functional,we demonstrated the qualitative similarity of defect thermodynamics and electronic properties in Cu₂Mg_SnS₄(CMTS)to CZTS.We show Sn_Mgto be abundant when in Sn-and Cu-rich condition,which can be detrimental,while defect properties are largely similar to CZTS in Sn-and Cu-poor.Under Sn-and Cu-poor chemic-al potential,there is a general increase in formation energy in most defects except Sn_Mg,Cu_Mgremains as the main contribu-tion to p-type carriers,and Sn_Mgmay be detrimental because of a deep defect level in the mid gap and the possibility of form-ing defect complex Sn_Mg+Mg_Sn.Vacancy diffusion is studied using generalized gradient approximation,and we find similar va-cancy diffusion properties for Cu vacancy and lower diffusion barrier for Mg vacancy,which may reduce possible Cu-Mg dis-order in CMTS.These findings further confirm the feasibility of CMTS as an alternative absorber material to CZTS and suggest the possibility for tuning defect properties of CZTS,which is crucial for high photovoltaic performance.     

贵金属磁控溅射镀膜技术及工艺研究

本文介绍了一种独特的贵重金属溅射靶的结构设计,并在此基础上对贵重金属磁控溅射薄膜工艺进行研究,结果表明新型靶的设计可以有效提高靶材利用率达60%以上,沉积的Au薄膜具有良好的均匀性,且附着力大于25.1 N/mm2.     

氮分压对磁控溅射制备TaN薄膜性能的影响

采用直流反应磁控溅射法制备了TaN薄膜,研究了φ(N2)对薄膜的结构和性能影响。研究发现,在N2分压(体积分数)为9%时,多相共存的TaN薄膜表现出TaN(200)面择优取向,方阻和αt达到最佳,其值为52Ω/□和–306×10–6/℃。薄膜的方阻、电阻温度系数αt和晶粒尺寸都随着N2分压的增大而增大:当N2分压高于11%时,薄膜的方阻和αt增长较快。     

Effect of sputter deposited Zn precursor film thickness and annealing time on the properties of Cu2ZnSnS4 thin films deposited by sequential reactive sputtering of metal targets

Cu₂ZnSnS₄ (CZTS) is made of earth abundant elements and also have suitable optical properties for solar cell applications. But, in phase diagram, CZTS exists in a narrow range of temperature and composition. Therefore, optimizing the elemental composition and annealing time is very important for obtaining phase pure CZTS. In this study, the effects of elemental composition and short annealing time on the structural and optical properties of reactively sputtered CZTS thin films are reported. Thin films were deposited by reactive sputtering of Cu: Sn (60:40 wt%), Sn and Zn targets sequentially in the presence of H₂S at room temperature. Amount of Zn precursor was varied by changing the sputter time for Zn. The films were rapidly annealed in inert atmosphere for varying time. The band gap of sample changed with change in the composition as well as annealing time. Sample with higher Zn content showed better crystallinity. With increase in the annealing time the crystallinity of samples improved. Sample annealed for 12 min at 550 °C was phase pure. Obtaining good quality film even for very short anneal time is the novelty of reactive sputtering method as all the elements are already mixed and short annealing is required only for crystal growth. Through detailed experiments, the optimum composition and annealing time required for the growth of phase pure CZTS has been established.     

Photoelectric properties of Cu2ZnSnS4 thin films deposited by thermal evaporation

正Sn/Cu/ZnS precursor were deposited by evaporation on soda lime glass at room temperature,and then polycrystalline thin films of Cu_2ZnSnS_4(CZTS) were produced by sulfurizing the precursors in a sulfur atmosphere at a temperature of 550℃for 3 h.Fabricated CZTS thin films were characterized by X-ray diffraction,energy dispersive X-ray spectroscopy,ultraviolet-visible-near infrared spectrophotometry,the Hall effect system,and 3D optical microscopy.The experimental results show that,when the ratios of[Cu]/([Zn]+[Sn]) and[Zn]/[Sn]in the CZTS are 0.83 and 1.15,the CZTS thin films possess an absorption coefficient of larger than 4.0 x 10~4 cm~(-1) in the energy range 1.5-3.5 eV,and a direct band gap of about 1.47 eV.The carrier concentration,resistivity and mobility of the CZTS film are 6.98 x 10~(16) cm~(-3),6.96Ω-cm,and 12.9 cm~2/(V-s),respectively and the conduction type is p-type.Therefore,the CZTS thin films are suitable for absorption layers of solar cells.     

Effect of crystallinity and thickness on the diffusion barrier behavior of electroless nickel deposit between Cu and solder

The crystallinity of electroless nickel deposit was manipulated by applying bath stabilizer including lead acetate and thiourea. A crystalline deposit and a higher deposition rate of electroless nickel were achieved with thiourea than with lead acetate. The effect of crystallinity on the diffusion barrier performance of the electroless nickel deposit was studied between solder and Cu deposit. The thickness of the electroless nickel deposit investigated includes 1, 3, and 5 /spl mu/m. It was found that both crystalline and amorphous deposits perform similarly in barrier performance except when the thickness of the deposit is as thin as 1 /spl mu/m. Cross sectional elemental analysis results indicate that a 3 /spl mu/m thickness deposit can withstand ten times of reflow without counter diffusion between Sn and Cu, although Ni-Sn intermetallic compounds were formed. The 3 /spl mu/m thickness is also adequate for barrier function after 1000 hours of aging at 150/spl deg/C.     

Effect of substrate bias on the properties of plasma deposited organosilicone (pp-HMDSN) thin films

Organosilicone thin films have been deposited by plasma polymerization (pp) in a plasma enhanced chemical vapor deposition (PECVD) system using hexamethyldisilazane (HMDSN:C6H19Si2N) as a monomer precursor, at different biases of the stainless-steel substrate holder. The substrate bias affected film thickness, surface morphology, chemical composition and photoluminescence (PL) emission. For a negatively biased substrate, it is found that the film thickness is the minimum, while the porosity and PL emission are the maximum. For a positively biased substrate, the thickness and the ratio of Si/N are the maximum which correspond to a blue shift of the PL emission in comparison with the case of non-biased grounded substrate. In addition, the characterization of the plasma using a single cylindrical Langmuir probe has been performed to obtain information about both the electron density and the positive ion energy, where it can be concluded that the ion energy plays a major role in determining film thickness.     

纳米TiO2包硅处理及其性能的研究

从紫外线的吸收能力、分散稳定性及酸溶性等方面分析包硅前后产品的性能变化。包膜改性后的TiO2分散性和酸溶性都得到明显改善,ζ电位发生了很大的变化。并且确定,要得到紫外吸收及可见光的透过能力较大的TiO2,包SiO2含量约在5%左右效果最好。     

Studies on sulfur diffusion into Cu(In,Ga)Se2 thin films

A systematic study was carried out to investigate the distribution of sulfur (S) in CuInSe₂ (CIS) and Cu(In,Ga)Se₂ (CIGS) absorbers which were exposed to an H₂S atmosphere at elevated temperature. Results demonstrated that S diffusion into CIS layers was a strong function of the original stoichiometry of the absorber before sulfurization. Sulfur inclusion into Cu‐rich CIS films was much more favorable compared to S diffusion in Cu‐poor layers. The sulfur distribution profile was also strongly influenced by the micro‐structure of the original CIS and CIGS layers, with sections of the films with smaller grains accommodating more S. Copyright © 2000 John Wiley & Sons, Ltd.     

Preferred orientation of Cu(In,Ga)Se2 thin film deposited on stainless steel substrate

The influences of process parameters and Fe diffusing into Cu(In,Ga)Se₂ (CIGS) films on the orientation of CIGS absorbers grown on the stainless steel (SS) foils are investigated. The structural properties, morphology, and elemental profiles are characterized using X‐ray diffraction, scanning electron microscopy, and second ion mass spectroscopy, respectively. The orientation of CIGS thin films on the SS substrates strongly depends on the texture of the (In,Ga)₂Se₃ precursor, determined by the substrate temperature at the first stage (Ts1) and the flux ratio of Se to (In + Ga). Among these factors, Ts1 is the prerequisite to achieve [300]‐oriented IGS layer, which will yield [200]‐oriented CIGS thin film in the later process. The results indicate that through the comparison of CIGS thin films on the Mo/SS substrates and on the Mo/ZnO/SS substrates and combined with simply calculation, Fe diffusing into the CIGS layer will hinder the growth of the CIGS grains along [112] orientation. The grazing‐incidence X‐ray diffraction results suggest that the surface of the [220]‐textured CIGS thin film on the SS substrate still has [220] predominance, whereas the surface texture of the [220]‐texture CIGS thin film on the Mo/soda‐lime glass substrate became [112] predominant, which is due to the different compensation ability between Fe and Na elements. Finally, the relations between the device parameters and the degrees of the preferred orientation of CIGS absorbers are investigated. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural,optical and electrical properties of Cu2FeSnSe4 and Cu(In,Al)Se2 thin films

Cu-based semiconductors Cu₂FeSnSe₄ (CFTSe) and Cu(In, Al)Se₂ (CIAS) have been fabricated using radio-frequency magnetron sputtering combined with rapid thermal selenization processing. For CFTSe, the heating rate ranging from 60 to 150 °C/min results in a difference in structure, morphology and optical properties. Thin film exhibits a pure phase structure, smooth surface and a band gap of 1.19 eV as the heating rate elevated to 90 °C/min. Furthermore, the CFTSe thin film selenized at 90 °C/min own the smallest value of cell volume compared with the others samples, which represents a more stable structure. In terms of the other Cu-based material CIAS, three different selenization pressures, i.e., 1, 5 and 10 Torr, have been employed for CIAS preparation. Thin film transforms into single phase with dense morphology along with the pressure of 1 Torr. The diverse band gap of CIAS thin films from 1.34 to 2.18 eV attribute to two reasons: (i) the various Al content will affect the hybridization degree of Al–Se, and finally tunes the band structure, (ii) amounts of CuSe has a certain degree of effect on the band gap of the CIAS. In addition, the electrical properties of CFTSe and CIAS are also researched with the open circuit voltage (V_oc) of 94 and 365 mV, respectively, signifying potential applications of CFTSe and CIAS for the thin film solar cells.     

AlCoNi十次准晶与金属铜间扩散机制分析

本文利用扫描电镜和透射电镜分析了粉末冶金法制备的Al72Co20 Ni8十次准晶颗粒与Cu基体之间的扩散行为与反应机制.研究发现700℃下,Cu原子沿两个方向扩散进入准晶颗粒,一是沿着准晶晶粒的晶界,二是垂直于准晶周期轴方向扩散进入其晶粒内部.Al72 Co20 Ni8准晶由于Al原子向外扩散先转变为片层状Al(Co,...     

Curing of polyimide and the effect of the TEOS SiO2 barrier layer on the electromigration of sputtered Cu with polyimide passivation

The curing process of polyimide and the electromigration of copper films with polyimide (PI) passivation are studied. Thermal analysis of polyimide suggests that imidization completes at ∼200°C with an endothermic reaction associated with the breaking of the C-OH and N-H bonds as revealed by Fourier transformation infrared spectroscopy (FTIR). Although there is 89.8% weight loss when PI is heated from 20°C to 200°C, outgassing of PI passivation is still observed at higher temperatures. Carbon, nitrogen, and oxygen atoms diffuse into Cu during thermal processing of PI/Cu films. The tetraethyl orthosilicate (TEOS) SiO₂ films are used as the barrier layer between PI and Cu to retard the poisoning of Cu. The effect of TEOS SiO₂ film on electromigration of Cu is investigated.     

铜CMP中SiO2抛光液的凝胶及其消除实验

SiO2在不同的pH值抛光液中容易产生凝胶现象而使抛光液失效。通过控制实验时抛光液的pH值及加入适量的添加剂而使SiO2抛光液的凝胶问题得到解决。结果表明,当SiO2抛光液pH≤8时,产生凝胶;当SiO2抛光液pH≥9时,在抛光液中加入适量的活性剂和螯合剂,消除了SiO2凝胶现象,得到较好的抛光结果。