Effects of impurities on removal of polysilicon in chemical-mechanical polish

The effects of impurities on the removal of doped polysilicon in the chemical-mechanical polishing (CMP) process is discussed. It has been found that the Si-CMP is seriously retarded in the presence of boron impurities. In this paper, effects of several usually used n-and p-type impurities for polysilicon are investigated. Successive polishing was performed to reveal the correlation between the removal rate and the dopant concentration along the depth of polysilicon layer. The removal is seriously retarded for p-type samples and slightly enhanced for n-type samples. After excluding the interference from surface roughness, linear relationship was found between the resultant removal rate and the doping concentration. In this study, electrostatic interaction between the reactant ions and the ionized impurities at the silicon surface is proposed to be the primary factor to change the removal reaction rates. For p-type polysilicon etched in an alkaline aqueous solution, transport of OH⁻ anions is hindered because OH⁻ anions experience a repelling force in front of the negative-charged acceptors. Following the same principle, the removal reaction forn-type polysilicon is enhanced. However, the removal rate forn-type polysilicon is rather limited by surface reaction than by transport of reactant ions. As a consequence, the enhancement of removing n-type polysilicon is not so prominent as compated to the retardation effect found for removal of p-type polysilicon.     

Mechanical processes in chemical-mechanical planarization: Plasticity effects in oxide thin films

The role of plastic behavior of normally brittle oxide films in controlling materials removal mechanisms in chemical-mechanical planarization (CMP) is discussed. Particular attention is given to how material removal mechanisms are sensitive to fundamental changes in surface materials properties. It is suggested that the synergism between chemical and mechanical effects in CMP can be framed in the context of an environmentally sensitive fracture process. The concept of “fracture” in the case of CMP, however it is argued, occurs at the nanometric or ultimately at the atomistic scale. This type of paradigm for chemical-mechanical planarization is developed through an analysis of the different types of materials behavior associated with surface changes where environment and mechanical effects are coupled.     

基于磨粒运动轨迹的硅片化学机械抛光材料去率研究

硅片化学机械抛光（CMP）是机械作用与化学作用相结合的技术,硅片表面的化学反应层主要是由抛光液中磨料的机械作用去除,磨粒对硅片表面的摩擦和划擦对硅片表面材料的去除起着重要作用。磨粒在硅片表面上的划痕长度直接影响硅片表面的材料去除率。本文首先在实验结果的基础上分析了硅片CMP过程中磨粒的分布形式,然后根据运动学和接触力学理论,分析了硅片、磨粒及抛光垫三者之间的运动关系,根据磨粒在硅片表面上的运动轨迹长度,得出了材料去除率与抛光速度之间的关系,该分析结果与实验结果一致,研究结果可为进一步理解硅片CMP的材料去除机理提供理论指导。     

Material removal rate in chemical-mechanical polishing of wafers based on particle trajectories

Distribution forms of abrasives in the chemical mechanical polishing (CMP) process are analyzed based on experimental results.Then the relationships between the wafer,the abrasive and the polishing pad are analyzed based on kinematics and contact mechanics.According to the track length of abrasives on the wafer surface,the relationships between the material removal rate and the polishing velocity are obtained.The analysis results are in accord with the experimental results.The conclusion provides a theoretical guide for further understanding the material removal mechanism of wafers in CMP.     

Pattern evolution in shallow trench isolation chemical mechanical planarization via real-time shear and down forces spectral analyses

This study explores the transition of force spectral fingerprints of shallow trench isolation chemical mechanical planarization during early evolution of wafer topography and layer transition from silicon dioxide to silicon nitride. Polishing was done on a polisher and tribometer capable of measuring shear force and down force in real-time. Fast Fourier Transformation is performed to convert the force data from time domain to frequency domain and to illustrate the spectral amplitude distribution of the force. Such frequency spectra provide in-depth insights into the interactions among abrasive particles, pad and wafer. Shallow trench isolation patterned wafers are over-polished using cerium oxide slurry. Results show that shear force increases during polishing when the silicon dioxide layer is removed thus exposing the silicon nitride layer. Unique and consistent spectral fingerprints are generated showing significant changes in several fundamental peaks during the early evolution of wafer topography and subsequent layer transition to silicon nitride polishing. Variance of force is also plotted to show the progression of pattern evolution. Results show that a combination of unique spectral fingerprinting, coefficient of friction as well as analyses of force and its variance (based on shear and down force) can be used as to monitor in real-time the polishing progress during shallow trench isolation chemical mechanical planarization.     

Electrochemical effects in the chemical-mechanical polishing of copper for integrated circuits

Chemical-mechanical polishing of copper in ammonia based solutions has been studied using electrochemical techniques such as electrochemical potential, linear polarization resistance, and potentiodynamic polarization. A copper rotating disk electrode was used to simulate polishing conditions. Measurements made on sputter-coated wafers during polishing were used for comparison. The dissolution of copper is limited by transport of Cu(NH₃)₂ ⁺ from the surface, and the removal rate of copper during polishing is controlled in the solution by the formation of copper ammine complexes.     

Pattern density and deposition profile effects on oxide chemical-mechanical polishing and chip-level modeling

Test masks for characterizing pattern-dependent variation of the remained thickness after chemical-mechanical polishing (CMP) were designed by taking the experimentally obtained interaction distance into consideration. Polishing behaviors were characterized by taking into consideration layout pattern density and pitch variations using these masks. Deposition profile effects were also compared between plasma-enhanced tetra ethyl ortho silicate (PETEOS) and high-density plasma (HDP) oxide. Both the measured post-CMP thickness and the expected oxide pattern density after the consideration of deposition profile effects showed a good correlation with respect to the pitch variation for a constant layout pattern density. Also, the relationship between remained thickness and true layout pattern density was deduced. Chip-level CMP modeling was investigated to obtain the post-CMP thickness distributions across a die from its design layout and a few oxide film and CMP parameters. The experimental CMP results agreed well with the modeling results. The effective dummy filling results were shown to achieve a smaller pattern density variation, which resulted in better post-CMP thickness uniformity. Whether the resulting oxide thickness could be predicted for any location on a die for an arbitrary layout, if the effective pattern density distributions are calculated, was discussed.     

Effect of process conditions on uniformity of velocity and wear distance of pad and wafer during chemical mechanical planarization

The kinematics of conventional, rotary chemical mechanical planarization (CMP) was analyzed, and its effect on polishing results was assessed. The authors define a novel parameter, ζ, as a “kinematic number,” which includes the effects of wafer size, distance between rotation centers, and rotation ratio between wafer and pad. The analysis result suggests that velocity distribution, direction of friction force, uniformity of velocity distribution, distribution of sliding distance, and uniformity of sliding-distance distribution could be consistently expressed in terms of the kinematic number ζ. These results become more important as the wafer size increases and the requirement of within-wafer nonuniformity is more stringent.     

固结磨料抛光K9光学玻璃的工艺实验研究

采用一种亲水性固结磨料抛光垫(FAP),通过单因素实验法,系统地研究了抛光K9光学玻璃过程中抛光时间、偏心距、压力、转速、抛光液流量及pH值等工艺参数对材料去除速率(MRR)和表面粗糙度的影响规律,并对实验结果进行了解释。结果表明:随着抛光时间的延长,K9光学玻璃的MRR逐渐呈下降趋势;在抛光20min时,MRR达最大值310nm/min,且表面粗糙度降至最低值为2.73nm;选择较大的偏心距和碱性抛光液环境均有利于提高MRR;随着抛光盘转速的升高,MRR将显著增大。而在一定范围内,抛光压力和抛光液流量对MRR的影响不大。     

Effect of polishing pad with holes in electro-chemical mechanical planarization

Electro-chemical mechanical planarization (ECMP) process dissolves copper ions electrochemically by applying an anodic potential on the copper surface in an aqueous electrolyte, and then removes a copper (Cu) complex layer by the mechanical abrasion of a polishing pad or abrasives in the electrolyte. The ECMP process is a low pressure polishing method for metals such as copper, aluminium (Al) and tungsten (W) on dielectric materials such as silicon dioxide, low-k (LK) and ultra low-k (ULK) dielectrics, comparing to the amount of defects by the traditional Cu chemical mechanical planarization (CMP). The polishing pad used in the ECMP process is a conventional closed cell type pad (IC 1400 K-groove pad) with holes. It supplies the aqueous electrolyte to the copper surface and removes the copper complex layer. The material removal rate (MRR) and MRR profile were simulated and tested according to the changes of the wafer overhang distance (WOD) from the platen and the electric contact area (ECA). In order to derive the design rule of the system, the experimental results are compared with the simulation results. After the ECMP process, it was verified that the within wafer non-uniformity (WIWNU) was lower than 2% using the relatively uniform ECA pad (C-type) under the smallest WOD condition. The experimental results well matched the simulated results.     

Effect of polishing parameters on abrasive free chemical mechanical planarization of semi-polar(11$\bar{2}$2) aluminum nitride surface

An abrasive free chemical mechanical planarization(AFCMP) of semi-polar(11$\bar{2}$2) AlN surface has been demonstrated. The effect of slurry pH, polishing pressure, and platen velocity on the material removal rate(MRR) and surface quality(RMS roughness) have been studied. The effect of polishing pressure on the AFCMP of the(11$\bar{2}$2) AlN surface has been compared with that of the(11$\bar{2}$2) AlGaN surface. The maximum MRR has been found to be ~562 nm/h for the semi-polar(11$\bar{2}$2) AlN surface, under the experimental conditions of 38 kPa pressure, 90 rpm platen velocity, 30 rpm carrier velocity, slurry pH 3 and 0.4 M oxidizer concentration. The best root mean square(RMS) surface roughness of ~1.2 nm and ~0.7 nm, over a large scanning area of 0.70×0.96 mm², has been achieved on AFCMP processed semi-polar(11$\bar{2}$2) AlN and(AlGaN) surfaces using optimized slurry chemistry and processing parameters.     

碱性抛光液中纳米SiO_2磨料在Cu CMP中的作用

GLSI多层铜互连线的平坦化中,抛光液中的SiO2磨料对铜的平坦化效率具有重要的作用。研究了碱性纳米SiO2质量分数对300 mm铜去除速率和300 mm铜布线平坦化作用的影响。结果表明,随着磨料质量分数的增大,铜的去除速率增大,晶圆的均匀性变好,但磨料质量分数过高时,铜的去除速率略有降低,可能由于纳米SiO2表面硅羟基吸附在金属铜表面,导致质量传递作用变弱,引起速率降低。通过对图形片平坦化实验研究表明,随着磨料质量分数的增大,平坦化能力增强,这是因为磨料的质量分数增大使得高低速率差增大,能够有效消除高低差,实现平坦化。     

Effect of polishing parameters on abrasive free chemical mechanical planarization of semi-polar(1122) aluminum nitride surface

An abrasive free chemical mechanical planarization(AFCMP) of semi-polar(1122) AlN surface has been demonstrated. The effect of slurry pH, polishing pressure, and platen velocity on the material removal rate(MRR) and surface quality(RMS roughness) have been studied. The effect of polishing pressure on the AFCMP of the(1122) AlN surface has been compared with that of the(1122) AlGaN surface. The maximum MRR has been found to be ~562 nm/h for the semi-polar(1122) AlN surface, under the experimental conditions of 38 kPa pressure, 90 rpm platen velocity, 30 rpm carrier velocity, slurry pH 3 and 0.4 M oxidizer concentration. The best root mean square(RMS) surface roughness of ~1.2 nm and ~0.7 nm, over a large scanning area of 0.70×0.96 mm², has been achieved on AFCMP processed semi-polar(1122) AlN and(AlGaN) surfaces using optimized slurry chemistry and processing parameters.     

CMP中抛光垫的性质研究

以IC1000/Suba IV抛光垫为例,综述了影响抛光垫性能的各种因素,以文献相关数据为依据,着重分析了抛光温度和修整力对抛光垫性能的影响。从分析结果可以得出:IC1000/Suba IV比单层结构IC1000具有更好的抛光效果;新旧抛光垫性能在0~40°C基本相当;新、旧和没有黏合剂抛光垫的正常工作温度为-2.02~103.64°C,且玻璃过渡温度随着抛光垫厚度的减小而增加;抛光垫在0~50°C具有最小的外形变化。定性得出修整力与抛光精度成反比关系,明确了较小修整深度具备较好的平坦化效果。     

磨料对蓝宝石衬底去除速率的影响

蓝宝石晶体已经成为现代工业,尤其是微电子及光电子产业极为重要的衬底材料,提高其化学机械抛光效率是业界无法回避的问题。在CMP系统中,磨料是决定去除速率及表面状态的重要因素。分析了化学机械抛光过程中抛光液中磨料的作用以及抛光机理,在确保表面状态的基础上,研究了抛光液中磨料体积分数、粒径和抛光液的黏度对速率的影响,指出纳米磨料是蓝宝石衬底抛光的最佳磨料。选用合适的磨料体积分数、粒径及抛光液黏度,不仅获得了良好的去除速率,而且有效地解决了表面状态方面的问题。     

镍包覆率对固结金刚石磨料研磨垫加工性能的影响

通过化学镀镍的方法,在金刚石磨粒表面包覆一层Ni-P 合金层;采用不同包覆率的金刚石磨料制备固结磨料研磨垫;通过SEM 观察分析金刚石的微观形貌;研究了磨料包覆率对研磨垫加工K9 玻璃过程中的摩擦系数和声发射信号的影响;采用马拉松式试验方法,比较了不同包覆率磨料的研磨垫加工K9 的材料去除速率及研磨后工件的表面粗糙度。结果表明:化学镀镍可以显著改变磨料的表面形貌;研磨过程中的摩擦系数、材料去除速率和工件表面粗糙度均随着包覆率的提高呈现出先增大后减小的趋势;包覆率50%时的金刚石磨料对工件的摩擦力和切入深度最大,研磨垫的磨粒保持与自修整性平衡,加工效率及其稳定性最高。     

FA/O阻挡层抛光液在铜布线中的去除速率的选择性优化

在阻挡层平坦化的过程中,由于不同材料去除速率的要求,所以有必要研发一种阻挡层抛光液来改善Cu/barrier/TEOS(SiO2)速率的选择性来减小蚀坑和碟形坑,。本次实验中,研发了一种不含腐蚀抑制剂BTA的FA/O碱性阻挡层抛光液。它包含了20mL/L的FA/O螯合剂,5mL/L的表面活性剂,磨料浓度为1:5,pH值为8.0。通过控制抛光液的成分,有效的控制了不同材料的去除速率。最后,考察FA/O阻挡层抛光液对介电层材料的影响。在进行完CMP过程后,检测介电层材料的性能。结果显示,漏电流在皮安级,电阻2.4 kΩ,电容2.3pF,碟形坑和蚀坑都在30nm以下。介质层的各项指标完全满足工业化生产的需要。     

Influence of slurry components on uniformity in copper chemical mechanical planarization

Many researchers studying copper chemical mechanical planarization (CMP) have been focused on mechanisms of copper removal using various chemicals. On the basis of these previous works, we studied the effect of slurry components on uniformity. Chemical mechanical planarization of copper was performed using citric acid (C₆H₈O₇), hydrogen peroxide (H₂O₂), colloidal silica, and benzotriazole (BTA, C₆H₄N₃H) as a complexing agent, an oxidizer, an abrasive, and a corrosion inhibitor, respectively. As citric acid was added to copper CMP slurry (pH 4) containing 3 vol% hydrogen peroxide and 3 wt% colloidal silica, the material removal (MRR) at the wafer center was higher than its edge. Hydrogen peroxide could not induce a remarkable change in the profile of MRR. Colloidal silica, used as an abrasive in copper CMP slurry containing 0.01 M of citric acid and 3 vol% of hydrogen peroxide, controlled the profile of MRR by abrading the wafer edge. BTA as a corrosion inhibitor decreased the MRR and seems to control the material removal around the wafer center. All the results of in this study showed that the MRR profile of copper CMP could be controlled by the contents of slurry components.     

GLSI钨插塞CMP碱性抛光液组分优化的研究

钨插塞化学机械平坦化(CMP)是极大规模集成电路(GLSI)铜互连多层布线的关键工艺之一。首先研究了钨在碱性条件下化学机械抛光机理;接着采用单因素实验方法分析了抛光液组分中纳米SiO2水溶胶磨料、氧化剂、有机碱(pH调节剂)和表面活性剂对W-CMP速率的影响。最后通过正交优化实验,确定抛光液最优配比为V(纳米SiO2水溶胶)∶V(去离子水)=1∶1,氧化剂体积分数为20 mL/L,pH调节剂体积分数为4 mL/L,表面活性剂体积分数为20 mL/L时,此时抛光液的pH值为10.36,获得的去除速率为85 nm/min,表面粗糙度为0.20 nm。