铜抛光液对片内非均匀性影响的研究

对于低介电常数材料和铜互连结构在低压化学机械抛光中,研发新的抛光液和调整工艺参数是非常必要的。抛光液的研发是减少抛光表面划伤和解决磨料剩余的关键。抛光液组成由片内非均匀性和铜抛光去除速率特性来优化。氧化剂浓度1Vol%;磨料浓度0.8Vol%;螯合剂浓度2Vol%。工作压力1kPa。抛光后表面缺陷减小并且表面干净无污染。去除速率289nm/min,片内非均匀性0.065。化学机械抛光后用原子力测量粗糙度为0.22 nm。     

不同压力下螯合剂浓度在碱性Cu CMP中的影响

We propose the action mechanism of Cu chemical mechanical planarization(CMP) in an alkaline solution.Meanwhile,the effect of abrasive mass fraction on the copper removal rate and within wafer non-uniformity(WIWNU) have been researched.In addition,we have also investigated the synergistic effect between the applied pressure and the FA/O chelating agent on the copper removal rate and WIWNU in the CMP process.Based on the experimental results,we chose several concentrations of the FA/O chelating agent,which added in the slurry can obtain a relatively high removal rate and a low WIWNU after polishing,to investigate the planarization performance of the copper slurry under different applied pressure conditions.The results demonstrate that the copper removal rate can reach 6125 °/min when the abrasive concentration is 3 wt.%.From the planarization experimental results,we can see that the residual step height is 562 ° after excessive copper of the wafer surface is eliminated.It denotes that a good polishing result is acquired when the FA/O chelating agent concentration and applied pressure are fixed at 3 vol% and 1 psi,respectively.All the results set forth here are very valuable for the research and development of alkaline slurry.     

新型碱性抛光液各组分对铜化学机械平坦化性能的影响

随着集成电路特征尺寸的减小、晶圆尺寸的增大以及布线层的逐渐增多,加工晶圆过程中实现较高的材料去除速率、较小的片内非一致性(WIWNU)及较小的表面粗糙度已经成为铜化学机械抛光工艺的几大难点.采用正交实验法选取5组抛光液进行Cu CMP实验,系统研究了含有双氧水、脂肪醇聚氧乙烯醚(AEO)、FA/O Ⅰ型螯合剂与苯骈三氮唑(BTA)的碱性抛光液化学组分对铜去除速率、WIWNU的影响,并对铜CMP的各种变化规律做出机理分析.结果表明:采用pH值约为8.6,体积分数为3％的H202,质量分数为0.08％的非离子表面活性剂AEO与体积分数为1.5％的螯合剂的碱性抛光液,在12英寸(1英寸=2.54 cm)铜镀膜片抛光后有助于去除速率达到629.1 nm/min,片内非一致性达到4.7％,粗糙度达到1.88 nm.     

低磨料浓度的碱性铜抛光液平坦化性能的研究

A novel alkaline copper slurry that possesses a relatively high planarization performance is investigated under a low abrasive concentration.Based on the action mechanism of CMP,the feasibility of using one type of slurry in copper bulk elimination process and residual copper elimination process,with different process parameters,was analyzed.In addition,we investigated the regular change of abrasive concentration effect on copper and tantalum removal rate and within wafer non-uniformity(WIWNU) in CMP process.When the abrasive concentration is 3 wt%,in bulk elimination process,the copper removal rate achieves 6125 °/min,while WIWNU is 3.5%,simultaneously.In residual copper elimination process,the copper removal rate is approximately 2700°/min,while WIWNU is 2.8%.Nevertheless,the tantalum removal rate is 0 °/min,which indicates that barrier layer isn’t eliminated in residual copper elimination process.The planarization experimental results show that an excellent planarization performance is obtained with a relatively high copper removal rate in bulk elimination process.Meanwhile,after residual copper elimination process,the dishing value increased inconspicuously,in a controllable range,and the wafer surface roughness is only 0.326 nm(sq < 1 nm) after polishing.By comparison,the planarization performance and surface quality of alkaline slurry show almost no major differences with two kinds of commercial acid slurries after polishing.All experimental results are conducive to research and improvement of alkaline slurry in the future.     

300mm铜膜低压CMP速率及一致性

随着铜互连结构中低k介质的应用,要求CMP抛光过程中必须将压力减小到6.89 kPa以下,传统的化学机械抛光已不符合当前的工艺要求,如何兼顾超低压力下抛光速率和速率一致性成为关键问题.对300 mm Blanket铜膜进行了低压化学机械抛光实验,分析研究了碱性抛光液组分及抛光工艺参数对铜膜去除速率及其一致性的影响.通过...     

A model for wafer scale variation of removal rate in chemical mechanical polishing based on elastic pad deformation

It is well known that within wafer non-uniformity (WIWNU), due to the variation in material, removal rate (MRR) in the whole wafer plays an important role in determining the quality of a wafer planarized by CMP. Various material removal models also suggest that the MRR is strongly influenced by the interface pressure. In the present work, an analytical expression for pressure distribution at the wafer and pad interface is developed. It is observed that depending on the wafer curvature and polishing conditions, the interface pressure may exhibit significant variation. The analytical model predictions are first verified against finite element method (FEM) simulations. The predicted analytical pressure profiles are then utilized in Preston's equation to estimate the MRR, and these MRR predictions are also compared to experimental observations. The analytical results suggest, that for a specified wafer curvature there exists a certain polishing condition (and vice versa) that will enable holding the WIWNU within a specified tolerance band. The proposed model facilitates the design space exploration for such optimal polishing conditions.     

阴离子对铜化学机械抛光的影响

在化学机械抛光过程中,抛光液的组成对抛光速率和表面质量有重要影响。利用自制抛光液,研究了在过硫酸铵体系抛光液中不同阴离子(硝酸根离子、溴离子、氯离子)对抛光速率的影响;采用动电位极化扫描技术对各抛光液在金属表面的成膜性能进行分析。结果表明,硝酸根离子的加入加快了阳极溶解反应,低浓度硝酸根离子的加入对抛光速率影响的波动性较大,随着浓度的增加抛光速率逐渐趋于初始值;随着氯离子(≥1mmol/L)或溴离子浓度的增加,抛光液的氧化性能降低,抛光速率不断降低;当溴离子浓度为0.1mmol/L时,Icorr值最小,抛光时对金属铜表面腐蚀程度较小。     

Optimization of slurry components for a copper chemical mechanical polishing at low down pressure using response surface methodology

Copper replaced aluminium and the low-dielectric constant material (low-k dielectrics) served as a better isolator, which has become the inevitable developing trend of IC technology. Due to the low compression resistance of low-k material, the mechanical strength must be reduced in order to ensure the functional integrity, which is a challenge for the traditional chemical-mechanical polishing (CMP) technology. To solve this issue, it is necessary to develop a chemically dominant CMP process at low down pressure. It is generally known that the implementation of optimum slurry composition is one of the important issues. To achieve a high removal rate (RR) and minimal WIWNU (Within-Wafer Non-Uniformity) at a down pressure of 0.63 psi, the response surface methodology (RSM) was applied to optimize slurry composition which contains silica sols, H₂O₂ and FA/O chelating agent. A central composite design, which is the standard design of RSM, was used to evaluate the effects and interactions of three factors. The optimal conditions obtained from the compromise of the two desirable responses, RR and WIWNU, were silica sols concentration of 13.88 vol.%, H₂O₂ concentration of 16.13 ml/L and FA/O chelating agent concentration of 20.22 ml/L, respectively. The RSM was demonstrated as an appropriate approach for the optimization of the slurry components by confirmation experiments.     

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.     

A model for wafer scale variation of material removal rate in chemical mechanical polishing based on viscoelastic pad deformation

It is well known that within-wafer nonuniformity (WIWNU) due to the variation in material removal rate (MRR) in chemical mechanical polishing (CMP) significantly affects the yield of good dies. The process control for a batch CMP operation is further complicated by wafer-to-wafer nonuniformity (WTWNU) caused by MRR decay when a number of wafers are polished with the same unconditioned pad. Accordingly, the present work focuses on modeling the WIWNU and WTWNU in CMP processes. Various material removal models suggest that the MRR is strongly influenced by the interface pressure. It is also well known that the viscoelastic properties of the pad play an important role in CMP. In the present work, an analytical expression for pressure distribution (and its associated MRR) at the wafer-pad interface for a viscoelastic pad is developed. It is observed that under constant load, which is typical during main polishing in CMP, the spatial distribution of the interface pressure profile may change with time from edge-slow to edge-fast, depending on the combination of wafer curvature, down pressure, and pad properties. For constant displacement operations, the pressure profile retains its edge-slow or edge-fast characteristics over time. The analytical model predictions of MRR based on viscoelastic pad properties also correlate very well to existing experimental observations of MRR decay when an unconditioned pad is used to polish a number of wafers. Based on these observations, it may be conjectured that the viscoelastic material properties of the pad play a primary role in causing the observed MRR decay. The analytical results obtained in the present work can also provide an estimation of evolution of thickness removal distribution over the entire wafer. This may be used for determining the optimum thickness of the overburden material and its polishing time, and for effective control of CMP processes.     

碱性Cu抛光液中非离子表面活性剂和氧化剂作用的研究

化学机械抛光是集成电路制造工艺中十分精密的技术。在本文中,为了改善抛光效果,分表讨论了非离子表面活性剂和氧化剂在CMP过程中作用。我们主要分析了非离子表面活性剂对片内非均匀性和表面粗糙度的影响。同时,我们从静态腐蚀速率、电化学曲线和剩余高低差的角度,讨论了在不加BTA条件下,不同氧化剂浓度的抛光液的钝化特性。实验结果明显地表明：加入了非离子表面活性剂的抛光液,更有利于改善抛光后的片内非均匀性和表面粗糙度,并确定2vol%体积分数是比较合适的浓度。当抛光液中氧化剂浓度超过3vol%,抛光液拥有较好的钝化能力,能够有效减小高低差,并有助于获得平整和光滑的表面。根据这些实验结果,非离子表面活性剂和氧化剂的作用进一步被了解,将有助于抛光液性能的改善。     

硒化镉晶片的化学机械抛光

硒化镉(CdSe)的表面加工质量对CdSe基器件的性能至关重要.化学机械抛光(CMP)是一种获得高质量晶体加工表面的常用方法.为改善CdSe晶片的表面加工质量,以SiO2水溶胶配制抛光液,研究了抛光液磨料质量分数、抛光液pH值、氧化剂NaClO的质量分数、抛光盘转速和抛光时间等因素对CdSe晶片抛光去除速率和表面质量的影响,优化了CdSe的CMP工艺参数.结果表明,在优化工艺条件下,CdSe的平均去除速率为320 nm/min,晶片的抛光表面无明显划痕和塌边现象.原子力显微镜(AFM)测量结果表明,抛光后的CdSe晶片表面粗糙度为0.542 nm,可以满足器件制备要求.     

硬盘基板化学机械粗抛光的实验研究

针对硬盘NiP/Al基板粗抛光,采用SiO2作为抛光磨料的碱性抛光液,在不同压力、转速、pH值、磨料浓度和活性剂体积浓度下,对硬盘基板粗抛光的去除速率和表面粗糙度的变化规律进行研究,用原子力显微镜观察抛光表面的微观形貌。最后对5个关键参数进行了优化。结果表明:当压力为0.10 MPa,转速为80 rad/min,pH值为11.2,磨料与去离子水体积比为1∶0.5,表面活性剂体积浓度为9 mL/L时,硬盘基板的去除速率为27 mg/min,粗抛后表面粗糙度为0.281 nm,获得了高的去除速率和较好的表面粗糙度,这样会大大降低精抛的时间,有利于抛光效率的提高。     

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.     

Polishing of silicon by the cupric ion process

This paper describes a newly developed chem-mech polishing process for silicon wafers. This polishing process, without using any abrasives, can produce a silicon surface free of work damage. A solution composed of cupric nitrate, ammonium fluoride, and nitric acid is used on a conventional polishing wheel. The rate of stock removal is controlled primarily by the composition of the solution and the polishing wheel temperature. Highly polished surfaces have been obtained with stock removal rates as high as 20 mils per hour. At higher removal rates, the process is difficult to control and surface quality suffers.     

磨料对硒化锌雾化施液化学机械抛光的影响

采用雾化施液化学机械抛光（CMP）的方法,以材料去除速率和表面粗糙度为评价指标,选取最适合硒化锌抛光的磨料,通过单因素实验对比CeO2、SiO2和Al2O3三种磨料的抛光效果。结果显示:采用Al2O3抛光液可以获得最高的材料去除率,为615.19nm/min,而CeO2和SiO2磨料的材料去除率分别只有184.92和78.56nm/min。进一步分析磨料粒径对实验结果的影响规律,表明100nm Al2O3抛光后的表面质量最佳,粗糙度Ra仅为2.51nm,300nm Al2O3的去除速率最大,达到1 256.5nm/min,但表面存在严重缺陷,出现明显划痕和蚀坑。在相同工况条件下,与传统化学机械抛光相比,精细雾化抛光的去除速率和表面粗糙度与传统抛光相近,但所用抛光液量约为传统抛光的1/8,大大提高了抛光液的利用率。     

CMP pad wear and polish-rate decay modeled by asperity population balance with fluid effect

An important task in chemical-mechanical polishing (CMP) is to determine when the pad should be changed or reconditioned. A model which can predict the pad asperity probability distribution function (PDF) during polishing and conditioning is valuable for this purpose. Previous work has been done without incorporating fluid mechanics into the model in L.J. Borucki, J. Eng. Math. 43 (2002) 105-114, but that will overestimate the pad wear because the fluid reduces the load applied on the individual asperities. This work models the wear of pad asperities and polish-rate decay in CMP by coupling the population balance model with fluid mechanics. Modeling results with and without fluid effect are compared. Polish-rate model results are compared with experimental data in D. Stein et al., J. Electron. Mater. 25 (10) (1996) 1623-1627, and the results agree with experimental results for both cases by using different wear rate coefficients to fit experimental data. A lesser wear rate coefficient must be used to fit Stein’s data for the fluid case compared to the case without fluid. The wear rate of the pad is calculated from the rate of change of the pad-wafer separation distance during polishing because only asperities above this distance will be in contact and worn down and that portion will be piled up at the pad-wafer separation distance on the PDF curve of the pad asperities. The PDF evolution model results with fluid show much less pad wear compared to the case without fluid. Also if fluid is neglected, pad-wafer separation distance will continue to drop until it is zero, while for the fluid case, it will eventually reach a dynamic steady-state with no pad wear indicating that the load is entirely supported by the fluid. Accurate predicting the interface gap (pad wear) is critical for controlling both mechanical and chemical removal rate and within wafer non-uniformity (WIWNU). These results show that fluid is an important factor which needs to be included into the model in predicting the interface gap and surface profile evolution of the pad during polishing and conditioning.     

碱性铜精抛液中表面活性剂ADS对平坦化效果的影响

研究了阴离子表面活性剂十二烷基硫酸铵(ADS)在弱碱性铜抛光液中对晶圆平坦化效果的影响.对不同质量分数的阴离子表面活性剂ADS下的抛光液表面张力、铜去除速率、抛光后铜膜的碟形坑高度、晶圆片内非均匀性和表面粗糙度进行了测试.实验结果表明,当阴离子表面活性剂ADS的质量分数为0.2％时,抛光液的表面张力降低,铜的去除速率为202.5 nm·min-1,去除速率片内非均匀性减小到4.15％,抛光后铜膜的碟形坑高度从132 nm降低到68.9 nm,表面粗糙度减小到1.06 nm.与未添加表面活性剂相比,晶圆表面的平坦化效果得到改善.     

CMP工艺对Co/Cu去除速率及速率选择比的影响研究

化学机械抛光(CMP)工艺中,选用了固定的抛光液组分,即3%体积百分比的FA/O型螯合剂、3%体积百分比的FA/O I型非离子表面活性剂、5% SiO₂。首先研究了不同抛光工艺参数,包括抛光压力、抛光头/抛光盘转速、抛光液流量等,对Co/Cu去除速率及选择比的作用机理。然后采用4因素、3水平的正交试验方法对抛光工艺进行优化实验,得到了较佳的工艺参数。在抛光压力为13.79 kPa、抛光头/抛光盘转速为87/93 r/min、抛光液流速为300 mL/min的条件下,Co/Cu的去除速率选择比为3.26,Co和Cu的粗糙度分别为2.01 、1.64 nm。     

Mechanical interactions and their effects on chemical mechanicalpolishing

Mechanical interactions, such as contact stress and fluid pressure are of extreme importance in silicon wafer polishing, especially for the wafer-scale planarity of the finished surfaces. In this paper, the measurements of interfacial fluid pressure and friction, as well as their dependence on some major process variables, are presented. A nonuniform subambient fluid pressure was measured, and the resulting wafer/pad contact stress, obtained by combining the effects of both applied normal load and interfacial fluid pressure, is determined. An analytical model was developed to predict the magnitude and distribution of the interfacial fluid pressure. The results of polishing experiments show good evidence of the effects of this subambient fluid pressure on with in-wafer nonuniformity (WIWNU). By properly designing the polishing process variables, the fluid pressure may be tailored, and a relatively uniform material removal can be achieved