Surface qualities after chemical–mechanical polishing on thin films

Demands for substrate and film surface planarizations significantly increase as the feature sizes of Integrated Circuit (IC) components continue to shrink. Chemical Mechanical Polishing (CMP), incorporating chemical and mechanical interactions to planarize chemically modified surface layers, has been one of the major manufacturing processes to provide global and local surface planarizations in IC fabrications. Not only is the material removal rate a concern, the qualities of the CMP produced surface are critical as well, such as surface finish, defects and surface stresses. This paper is to examine the CMP produced surface roughness on tungsten or W thin films based on the CMP process conditions. The W thin films with thickness below 1000 nm on silicon wafer were chemical–mechanical polished at different down pressures and platen speeds to produce different surface roughness. The surface roughness measurements were performed by an atomic force microscope (DI D3100). Results show that the quality of surface finish (R_a value) is determined by the combined effects of down pressures and platen speeds. An optimal polishing condition is, then, possible for selecting the down pressures and platen speeds.     

Chemical/mechanical polishing of diamond films assisted by molten mixture of LiNO3 and KNO3

Chemical/mechanical polishing can be used to polish the rough surface of diamond films prepared by chemical vapor deposition (CVD). In this paper, a mixture of oxidizing agents (LiNO₃ + KNO₃) has been introduced to improve the material removal rate and the surface roughness in chemical/mechanical polishing because of its lower melting point. It had been shown that by using this mixture the surface roughness R_a (arithmetic average roughness) could be reduced from 8-17 to 0.4 μm in 3 h of polishing, and the material removal rate can reach 1.7-2.3 mg/cm²/h at the temperature of 623 K. Pure aluminium is compared with cast iron as the contact disk material in the polishing. Although the material removal rate of aluminiumdisk is lower than that of cast iron, it can eliminate the carbon contamination from the contact disk to the surface of diamond films, and facilitate the analysis of the status of diamond in the chemical/mechanical polishing. The surface character and material removal rate of diamond films under different polishing pressure and rotating speed have also been studied. Graphite and amorphous carbon were detected on the surface of polished diamond films by Raman spectroscopy. It has been found that the oxidization and graphitization combined with mechanical cracking account for the high material removal rate in chemical/mechanical polishing of diamond films.     

Effect of argon and substrate bias on diamond thin film surface morphology

Nanocrystalline materials are of high interest, because mechanical and physical properties of such materials are different from those or coarse-grained type. Continuous and smooth nanocrystalline diamond (NCD) thin films were successfully grown on mirror polished silicon substrates, using double bias plasma-enhanced hot filament chemical vapour deposition technique. A gas mixture of Ar:CH₄:H₂ and CH₄:H₂ was used as the precursor gas. The effect of the gas composition, flow rate and substrate bias during deposition on diamond crystallite size was investigated. Changing the growth parameters facilitates control of grain size of polycrystalline diamond thin films from microcrystalline to nanocrystalline. The structure of fine-grained NCD films has been studied with scanning electron microscopy and Raman spectroscopy.     

Chemical mechanical polishing characteristics in (Bi,La)Ti3O12 damascene process for high-density ferroelectric memories

Ferroelectric thin films such as Pb(Zr,Ti)O₃, SrBi₂Ta₂O₉, and Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films have been widely investigated for non-volatile ferroelectric memories. BLT thin films show advantages such as highly fatigue resistance, low processing temperature, and large remanent polarization. The patterning of these ferroelectric thin films with a vertical sidewall and without plasma damage is strongly required. Chemical mechanical polishing (CMP) process was investigated for the vertical sidewall patterning of BLT thin films. Removal rate and within-wafer non-uniformity (WIWNU%) were examined by change of process parameters. Potential of hydrogen (pH) in slurry was varied for an improvement of the removal rate and WIWNU%. Surface roughness of BLT thin films after CMP process for the improvement of densification was inquired into by atomic force microscopy. The excellent performance such as 188.4 nm/min of removal rate, 2.61% of WIWNU%, 0.95 nm of root mean square roughness, and 6.94 nm of peak-to-valley roughness was obtained. This result will lead the CMP process to pattern the BLT thin films for the vertical sidewall without plasma damage.     

Thermal stability of nanocrystalline diamond films grown by biased enhanced microwave plasma chemical vapor deposition

The thermal stability of nanocrystalline diamond (NCD) films grown on mirror-polished silicon substrates by biased enhanced microwave plasma chemical vapor deposition was investigated. Different pieces of a NCD sample were annealed for 1 h in an ambient argon atmosphere at 200, 400, 600, and 800 degrees C. The structural and mechanical properties of as-grown and annealed samples were assessed. The surface roughness and high hardness of the samples remained fairly constant with annealing temperature.     

铝化学机械抛光中1,2,4-三唑和苯并三氮唑的缓蚀机制

揭示铝低压力化学机械抛光(CMP)中的弱缓蚀机制是铝CMP研究的关键问题。采用CMP试验,研究了1,2,4-三唑(TAZ)和苯并三氮唑(BTA)对铝表面去除率的影响规律;通过接触角和表面原子力显微镜(AFM)试验,分析了TAZ和BTA薄膜在铝表面的亲水性能,发现由TAZ作用形成的缓蚀薄膜比由BTA形成的缓蚀薄膜更厚,更易渗透与去除。结合摩擦磨损试验和Arrhenius公式,探讨了TAZ和BTA在CMP过程中对铝表面化学反应活化能的影响。结果显示:TAZ的活化能小于BTA,更容易形成弱缓蚀薄膜,机械促进化学作用的效果更明显。     

基于磨损行为的单晶硅片化学机械抛光材料的去除特性

为了掌握化学机械抛光（CMP）过程中硅片表面材料的去除行为,根据CMP过程中硅片表面材料的磨损行为,建立了硅片CMP时的材料去除率构成成分模型,设计了不同成分的抛光液并进行了材料去除率实验,得出了机械、化学及其交互作用所引起的材料去除率.结果显示,机械与化学的交互作用率为85.7%～99.1%.磨粒的机械作用率为69.5%～94.0%,磨粒的机械与化学交互作用率为55.1%～93.1%.由此可见,磨粒的机械作用是化学机械抛光中的主要机械作用,磨粒与抛光液的机械化学交互作用引起的材料去除率是主要的材料去除率.研究结果可为进一步研究硅片CMP时的材料去除机理提供理论参考依据.     

Passivation layer effect on surface integrity induced by Cu-CMP

To achieve efficient Cu-Chemical-Mechanical Polishing planarization at miniaturized device dimensions, there is a need for a better understanding of the surface integrity induced by the process. Surface quality and stresses are the two selected indices in this article to evaluate the Cu-CMP process induced surface integrity. The thickness of the passivation layer and the penetration depth of abrasives are considered as the main effects for the generations of surface qualities and residual stress. Experimental validation on copper films on silicon wafer was performed by CMP with different pads and slurries to generate varied residual stresses and surface qualities. Depth of scratches and surface roughness were measured by the atomic force microscope. The stress measurements of the thin films were performed by a Grazing Incident X-ray diffraction instrument with its principles based upon modified sin²Ψ method. Accordingly, the surface roughness and stress were related to the thickness of the passivation layer and the CMP process conditions. When the penetration depth is larger than the passivation layer thickness, the roughness values are mainly decided by the selection of pads and the resultant penetration depth. In addition, the residual stress profiles are dependent on the CMP process conditions which include the slurries and pad parameters. The stress profile obtained for the slurry SDK with soft pad Politex composed smallest maximum tensile stress below the surface and a steady transition of stress profile compared to the stress profile obtained at the initial condition. At the condition for the same slurry SDK, but with a hard pad of IC1000, the CMP process induced larger maximum stress and sharper profile transition.     

CVD diamond films with hydrophilic micro-patterns for self-organisation of human osteoblasts

Nanocrystalline diamond (NCD) films were prepared by microwave plasma-enhanced chemical vapour deposition (CVD) on Si substrates of different roughness (1 and 500 nm). Diamond nano-crystals are up to 50 nm in size and RMS surface roughness is less than 20 nm. The NCD films were cleaned chemically and terminated by hydrogen using plasma treatment (800 °C, 10 min) to generate a hydrophobic surface. Photolithography mask and oxygen plasma (300 W r.f. power, 3 min) were used to generate O-terminated (hydrophilic) patterns (30-200 μm wide) separated by a H-terminated (hydrophobic) surface. Osteoblast-like human cells were seeded on the patterned flat and rough NCD films in McCoy's 5A medium supplemented with 15% fetal bovine serum (FBS). After two days incubation the cells preferentially adhered on the O-terminated stripes. This phenomenon is not suppressed by the surface roughness and is general for other cell types (fibroblast and cervical carcinoma cells), too. The data are discussed with view to further application of NCD thin films in biotechnology and bio-electronics applications.     

Optimization of Polishing Parameters with Taguchi Method for LBO Crystal in CMP

Chemical mechanical polishing(CMP)was used to polish Lithium triborate(LiB3O5 or LBO)crystal.Taguchi method was applied for optimization of the polishing parameters.Material removal rate(MRR)and surface roughness are considered as criteria for the optimization.The polishing pressure,the abrasive concentration and the table velocity are important parameters which influence MRR and surface roughness in CMP of LBO crystal.Experiment results indicate that for MRR the polishing pressure is the most significant p...     

用于高频声表面波器件的CVD金刚石衬底的研究

使用纳米金刚石粉研磨工艺预处理硅片衬底抛光面,在低气压成核的条件下,以丙酮和氢气为反应物,采用传统的热丝辅助化学气相沉积法,制备了自支撑金刚石膜;通过射频磁控溅射法沉积氧化锌薄膜在自支撑金刚石膜的成核面,形成氧化锌/自支撑金刚石膜结构.通过光学显微镜、扫描电镜及原子力显微镜测试自支撑金刚石膜成核面的表面形貌.研究结果表明:成核期的低气压有助于提高成核密度,成核面表面粗糙度约为1.5 nm;拉曼光谱显示1334 cm-1附近尖锐的散射峰与金刚石SP3键相对应,成核面含有少量的石墨相,且受到压应力的作用;ZnO/自支撑金刚石膜结构的XRD谱显示,氧化锌薄膜有尖锐的(002)面衍射峰,是c轴择优取向生长的.     

Surface polishing of 6H-SiC substrates

The surface polishing for silicon carbide （SIC） substrates was investigated and results were presented for mechanical polishing （MP） and chemo-mechanical polishing （CMP）. High quality surfaces were obtained after CMP with colloidal silica. The removal mechanism of scratches in MP and detailed physical and chemical process during CMP were analyzed. The effects of MP and CMP on the surface roughness were assessed by optical microscopy （OM）, atomic force microscopy （AFM） and step profilometry. KOH etching and high resolution X-ray diffractometry （H RXRD） were applied to evaluate the subsurface damage of 6H-SiC substrates.     

Effect of rapid thermal annealing treatment on the field-emission characteristics of nanocrystalline diamonds grown on various metal/silicon substrates

In this study, nanocrystalline diamond (NCD) films were deposited on various metal/silicon substrates using a microwave plasma chemical vapor deposition system. Metal layers used are chromium, titanium, aluminum and were used as the electron source for field emitters. These NCD/metal/silicon structures were subsequently annealed at 500 °C in a rapid thermal annealing (RTA) furnace. After RTA treatment, the surface of NCD films becomes flat and the grain boundaries can no longer be clearly seen. The intensity of graphitic peak is substantially decreased and the sp³ content of NCD films is increased. The chemical composition of NCD film remains unchanged after RTA treatment, but the sp³/sp² ratio in C 1s has been increased. It is found that the field-emission characteristics of diamond emitter not only can be effectively controlled by the metal used in the metal/NCD/Si structure, but also can be further enhanced by the improved microstructure of the NCD film obtained after RTA treatment.     

Chemical factors for chemical–mechanical and electrochemical–mechanical planarization of silver examined using potentiodynamic and impedance measurements

Ag may eventually replace Cu (like Cu has replaced Al) in sub-micron interconnects used for integrated circuits. Fabrication of such Ag lines would typically involve damascene structures patterned by chemical–mechanical planarization (CMP). Our present work focuses on certain chemical aspects of CMP of Ag in alkaline polishing slurries. Specifically, we study the oxidation and dissolution reactions of Ag that are relevant for CMP of this metal in KOH (pH 10) solutions, and we investigate the role of O₂ in these reactions. The surface reactions are probed with Fourier transform electrochemical impedance spectroscopy in combination with potentiodynamic measurements. The reaction steps are discussed in terms of circuit models, and the possibility of incorporating electro-activated reactions in CMP through electrochemical–mechanical planarization (ECMP) of Ag is briefly discussed.     

LBO晶体的超精密加工工艺研究

采用Logitech PM5精密研抛机,通过机械抛光和化学机械抛光方法超精密加工LBO晶体;详细研究了LBO晶体的超精密加工工艺,并观察研磨和抛光等加工过程后的晶体表面形貌;研究抛光液和抛光垫在抛光中对LBO晶体表面微观形貌的影响.使用Wkyo激光干涉仪测量平面度,光学显微镜观察表面宏观损伤,原子力显微镜测量表面粗糙度和观察微观形貌.通过实验,实现高效率、高精度、高质量的LBO晶体的超精密加工,得到了LBO晶体的超精密加工工艺;超精密加工后晶体的表面粗糙度＜0.2nm RMS,表面平面度＜氇/10(氇=633nm),微观损伤少.     

Chemical polishing of aluminum coupons in support of vacuum chambers

Success of third and fourth generation light sources is highly dependent upon the smoothness of internal surfaces in small aperture undulators. The ratio of the undulator length to the chamber aperture is very large, making mechanical polishing difficult to implement. Chemical polishing is a viable alternative option. This study investigates the effectiveness of a chemical polishing step as a finishing treatment in lieu of mechanical polishing. Limited to no quantitative data exists in the literature that links specific chemical polishing processes to profilometer-measured surface roughness. This study examines the effectiveness of using two chemical solutions at various temperatures to treat the surfaces of aluminum coupons and reduce their surface roughness. Results indicate that certain chemical polishing steps can reduce the root mean square roughness of the surface by as much as 40%; however, careful control of the solution temperature, composition, and immersion time is critical.     

CVD金刚石膜高效超精密抛光技术

CVD金刚石膜作为光学透射窗口和新一代计算机芯片的材料,其表面必须得到高质量抛光,但是现存方法难以满足既高效又超精密的加工要求.本文提出机械抛光与化学机械抛光相结合的方法.首先,采用固结金刚石磨料抛光盘和游离金刚石磨料两种机械抛光方法对CVD金刚石膜进行粗加工,然后采用化学机械抛光的方法对CVD金刚石膜进行精加工.结果表明,采用游离磨料抛光时材料去除率远比固结磨料高,表面粗糙度最低达到42.2 nm.化学机械抛光方法在CVD金刚石膜的超精密抛光中表现出较大的优势,CVD金刚石膜的表面粗糙度为4.551 nm.     

Preparation of porous Fe2O3/SiO2 nanocomposite abrasives and their chemical mechanical polishing behaviors on hard disk substrates

Abrasives play an important role in chemical mechanical polishing (CMP) processes. Compact solid silica particles, which have been widely used as abrasive in CMP slurries, may cause surface defects because of their high hardness. Porous silica abrasive exhibits better surface planarization and fewer scratches than traditional solid silica abrasive during the polishing of hard disk substrates. However, the improvement in material removal rate (MRR) was not significant. Therefore, porous Fe₂O₃/SiO₂ nanocomposite abrasives were prepared and their CMP performances on hard disk substrates were investigated. Experiment results indicate that the MRR of slurry containing porous Fe₂O₃/SiO₂ nanocomposite abrasives is obviously higher than that of slurry containing pure porous silica abrasive under the same testing conditions. MRR increases with the increase of the molar content of iron in porous Fe₂O₃/SiO₂ nanocomposite abrasives. Moreover, surfaces polished by slurries containing the porous Fe₂O₃/SiO₂ nanocomposite abrasives exhibit lower surface roughness, fewer scratches as well as lower topographical variations than that by pure porous silica abrasive.     

Evolution of hillocks in Bi thin films and their removal upon nanoscale mechanical polishing

Bismuth thin films were grown on oxidized Si substrates by electron beam evaporation. The films showed clear tendency to form hillocks inducing large surface roughness. The evolution of hillocks with film thickness and deposition rate was studied. In order to improve the surface quality of the Bi films a nanoscale mechanical polishing was performed. Upon polishing, hillocks-free Bi thin films were obtained without influencing the crystalline structure and the resistivity of the films. The achieved film surface quality allows to prepare high quality Bi Hall probes with an active area down to the nm² range promising for advanced device performance.     

Chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer for obtaining atomically flat defect-free surface

Due to its high mechanical hardness and excellent chemical inertness, SiC single-crystal wafer is extremely difficult to realize effectively removed total planarization. Owing to crystalline polarity and anisotropy, material removal rate (MRR) on Si-face (0001) of SiC wafer is significantly lower than C-face (000 $ \bar{1} $ ) for a defect-free surface. In the paper, the slurry containing hydrogen peroxide (H₂O₂), potassium hydroxide and abrasive colloidal silica, is introduced to chemical mechanical polishing (CMP) of on-axis Si-face 6H-SiC wafer, resulting in acquiring high MRR with 105 nm/h, and atomically flat defect-free surface with atomic step-terrace structure and roughness of 0.0667 nm by atomic force microscope (AFM), in order to satisfy further demands of electronic device fabrication towards substrate wafer performance. The effects of the three ingredients in the slurry towards MRR of SiC wafer, polished surface quality and coefficient of friction in polishing process are studied. Optical microscope, optical interferometry profiler and AFM are used to observe the polished surface. In addition, the CMP removal mechanism of SiC wafer and the formation of ultra-smooth surface are discussed.