不含抑制剂的碱性抛光液对铜布线平坦化的研究

本文提出一种碱性铜布线抛光液,其不含通用的腐蚀抑制剂,并对其化学机械抛光和平坦化 (CMP)性能进行了研究。首先研究了此抛光液对铜的静态腐蚀速率和抛光速率,并与含抑制 剂的铜抛光液做了对比实验。在静态条件下,此不含抑制剂的碱性铜抛光液对铜基本无腐蚀速率,而在动态抛光过程中对铜有较高的速率。而含抑制剂的抛光液对静态腐蚀速率略有降低,但是却大幅度降低了铜的去除速率。另外,对铜布线的化学机械平坦化研究表明,此不含抑制剂的碱性铜抛光液能够有效的去除铜布线表面的高低差,有较高的平坦化能力。此抛光液能够应用于铜CMP的第一步抛光,能够去除大量多余铜时初步实现平坦化。     

A new weakly alkaline slurry for copper planarization at a reduced down pressure

This study reports a new weakly alkaline slurry for copper chemical mechanical planarization （CMP）, it can achieve a high planarization efficiency at a reduced down pressure of 1.0 psi. The slurry is studied through the polish rate, planarization, copper surface roughness and stability. The copper polishing experiment result shows that the polish rate can reach 10032 A/rain. From the multi-layers copper CMP test, a good result is obtained, that is a big step height （10870 A） that can be eliminated in just 35 s, and the copper root mean square surface roughness （sq） is very low （〈 1 rim）. Apart from this, compared with the alkaline slurry researched before, it has a good progress on stability of copper polishing rate, stable for 12 h at least. All the results presented here are relevant for further developments in the area of copper CMP.     

Alkaline barrier slurry applied in TSV chemical mechanical planarization

We have proposed a TSV （through-silicon-via） alkaline barrier slurry without any inhibitors for barrier CMP （chemical mechanical planarization） and investigated its CMP performance. The characteristics of removal rate and selectivity of Ti/SiO2/Cu were investigated under the same process conditions. The results obtained from 6.2 mm copper, titanium and silica show that copper has a low removal rate during barrier CMP by using this slurry, and Ti and SiO2 have high removal rate selectivity to Cu. Thus it may be helpful to modify the dishing. The TSV wafer results reveal that the alkaline barrier slurry has an obvious effect on surface topography correction, and can be applied in TSV barrier CME     

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.     

磷酸和酒石酸在GSI阻挡层CMP抛光液中的应用

在阻挡层的化学机械平坦化(CMP)过程中,Cu与阻挡层去除速率的一致性是保证平坦化的关键问题之一。低k介质材料的引入要求阻挡层在低压力下用弱碱性抛光液进行CMP,这给抛光液对不同材料的选择性提出了新的挑战。研究了低压2 psi,(1 psi=6.89 kPa)CMP条件下,磷酸和酒石酸作为阻挡层抛光液pH调节剂对Cu和Ta的络合作用。实验结果表明,酒石酸对Cu和Ta有一定的络合作用,能够提高它们的去除速率;磷酸能提高Ta的去除速率,而对Cu的去除有抑制作用。最终在加入磷酸浓度为2×10-2mol/L,酒石酸浓度为1×10-2mol/L,H2O2体积分数为0.3%,pH=8.5时,Cu/Ta/SiO2介质的去除速率选择比达到了1∶1∶1,去除速率约为58 nm/min;同时,磷酸和酒石酸的加入能够有效改善Cu的表面状态。     

化学机械抛光制程中铜抛光液平坦化能力的评估

The evaluation methods of planarization capability of copper slurry are investigated.Planarization capability and material removal rate are the most essential properties of slurry.The goal of chemical mechanical polishing(CMP) is to achieve a flat and smooth surface.Planarization capability is the elimination capability of the step height on the copper pattern wafer surface,and reflects the passivation capability of the slurry to a certain extent.Through analyzing the planarization mechanism of the CMP process and experimental results,the planarization capability of the slurry can be evaluated by the following five aspects:pressure sensitivity,temperature sensitivity,static etch rate,planarization efficiency and saturation properties.     

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.     

Chemical mechanical planarization operation via dynamic programming

In this paper, the impact on non-planarization index by the down force and rotational speed during a SiO₂ or Cu CMP process was investigated. Since the magnitudes of down force and rotational speed have limits, we choose the dynamic programming approach because of its ability to achieve constrained optimization by the down force and rotational speed. The duration and the amount of input were computed based on the chemical mechanical polishing model by Luo and Dornfeld [J. Luo, D.A. Dornfeld, IEEE Trans. Semiconduct. Manufact. 14(2) (2001) 112-132.] when the other parameters were fixed. Experiments done for blanket wafers based on dynamic programming operation and conventional constant removal rate operation was compared with each other. The non-planarization index could be improved consistently by dynamic programming operation versus constant removal rate operation. The improvement ranges from 2% to 39% improvement over the base recipe of constant removal rate in all experiments as shown in Table 3 and Table 6. The thickness removal error is consistently smaller by constant removal rate operation versus dynamic programming operation in all experiments as shown in Table 3 and Table 6. To get the best performance of both planarization and thickness removal, it is recommended that planarization step and overpolish step in SiO₂ and Cu CMP should use different mode of operation, i.e., dynamic programming operation during planarization step for minimizing non-planarization index and constant removal rate operation during overpolish step for minimizing thickness removal error. The incremental time calculation for eliminating thickness removal error during overpolish step can be done using the thickness error and removal rate derived from Luos’ removal rate model based on constant wafer pressure and platen speed at the end of planarization step.Our contribution is a new approach for CMP. Standard CMP uses constant removal rate operation in both planarization step and overpolish step. Our new approach uses dynamic programming operation during planarization step and constant removal rate operation during overpolish step.     

Cu CMP过程中背压对膜厚一致性影响

在极大规模集成电路Cu布线的化学机械平坦化过程中,抛光后表面薄膜厚度的一致性是检验平坦化能力的重要参数。从抛光过程中晶圆所受背压方面着手,研究了在不同背压参数情况下抛光后表面薄膜的一致性,得出了在工作压力为103 mdaN/cm2(1 kPa=10 mdaN/cm2)时,最佳的背压参数为108 mdaN/cm2。采用此工艺参数进行抛光后得到的晶圆表面薄膜非均匀性为5.04%,即一致性可以达到94.96%,而且此时表面粗糙度为0.209 nm,从而得到了良好的抛光效果,为极大规模集成电路Cu布线化学机械平坦化的进一步发展提供了新的途径。     

Mechanical and tribological properties of interlayer films for the damascene-Cu chemical-mechanical planarization process

Chemical-mechanical planarization (CMP) has emerged as the most preferred method to achieve excellent global and local planarity in the damascene-Cu process. As the feature sizes shrink, understanding the fundamentals of CMP is critical for successful implementation of the CMP process in sub 0.35-μm technology. It is also important to understand the effects of mechanical and tribological properties of the interlayer films on the CMP process to conduct successful evaluation and implementation of these materials. In this paper, we present the mechanical and tribological properties of various interlayer films (SiO₂, SiC, low-k B, low-k C, Ta, and Cu) and discuss the CMP process of the films in an alumina-based Cu slurry. Mechanical properties were evaluated using a nanoindentation technique. A micro-CMP tester was used to study the fundamental aspects of the CMP process. The coefficient of friction (COF) was measured during the process and was found to decrease both with downward pressure and with platen rotation. An acoustic sensor, attached to the substrate carrier, was used to monitor the process, and the signal was recorded to examine the difference in polishing behavior of these films. The acoustic emission (AE) signal was found to increase with the increase in platen velocity and pressure. Effects of machine parameters on the polishing behavior of the interlayer films and the correlation of mechanical properties with tribological properties have been discussed.     

在铜CMP过程中降低抛光压力与磨料的机械作用

Chemical mechanical planarization(CMP) is a critical process in deep sub-micron integrated circuit manufacturing. This study aims to improve the planarization capability of slurry, while minimizing the mechanical action of the pressure and silica abrasive. Through conducting a series of single-factor experiments, the appropriate pressure and the optimum abrasive concentration for the alkaline slurry were confirmed. However, the reduced mechanical action may bring about a decline of the polishing rate, and further resulting in the decrease of throughput.Therefore, we take an approach to compensating for the loss of mechanical action by optimizing the composition of the slurry to enhance the chemical action in the CMP process. So 0.5 wt% abrasive concentration of alkaline slurry for copper polishing was developed, it can achieve planarization efficiently and obtain a wafer surface with no corrosion defect at a reduced pressure of 1.0 psi. The results presented here will contribute to the development of a “softer gentler polishing” technique in the future.     

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.     

Comparison of dicarboxylic acids as complexing agents for abrasive-free chemical mechanical planarization of copper

Abrasive particles used in chemical mechanical planarization (CMP) of copper often agglomerate and cause scratches on the finished surface. Abrasive-free CMP offers a feasible solution to this problem, and our present work examines four dicarboxylic acids (oxalic, malonic, succinic and glutaric, with increasing carbon chain lengths) as possible complexing agents for such a chemically dominated CMP process. At pH 3.0-4.0, oxalic and malonic acids are most effective for abrasive-free Cu removal. The rates of Cu dissolution and polish (with or without abrasives) are correlated with pH dependent distributions of mono-anionic (for oxalic and malonic) and neutral (for succinic and glutaric) acid species. The surface morphologies of a Cu wafers obtained by abrasive-free CMP in these acids also are more defect free and flat compared to those obtained using abrasives.     

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.     

用于铜的化学机械抛光液的研究

文中介绍了一种以碱性抛光液对铜进行全局平面化的方法 ,讨论了以 Si O2 水溶胶为磨料的抛光液在Cu-CMP过程中的化学 (络合 )作用及反应机理 ,并给出了抛光液的配比及上机实验结果。结果表明 :该抛光液用于对带有阻挡层和介质层的铜抛光 ,达到了对铜层的高去除速率和高选择比 ,取得了较好的全局平面化效果     

Cu CMP抛光液对速率的影响分析及优化

在超大规模集成电路多层Cu布线CMP工艺中,抛光液是决定抛光速率、抛光表面状态和平坦化能力的重要因素。采用Plackett-Burman(PB)筛选实验对抛光液成分(磨料、氧化剂、活性剂、螯合剂)进行显著性因素分析,得出磨料、FA/O螯合剂Ⅱ型和氧化剂为显著性因素,并采用响应曲面法对其进行优化并建立了模型,最终得到以去除速率为评价条件的综合最优抛光液配比,为Cu抛光液配比优化及对CMP的进一步发展提供了新的思路与途径。     

Characterization and optimization of copper chemical mechanical planarization

The feature scale planarization of the copper chemical mechanical planarization (CMP) process has been characterized for two copper processes using Hitachi 430-TU/Hitachi T605 and Cabot 5001/Arch Cu10K consumables. The first process is an example of an abrasive-free polish with a high-selectivity barrier slurry, while the second is an example of a conventional abrasive slurry with a low-selectivity barrier slurry. Copper fill planarization has been characterized for structures with conformal deposition as well as with bumps resulting from bottom-up fill. Dishing and erosion were characterized for several structures after clearing. The abrasive-free polish resulted in low sensitivity to overpolish and low saturation levels for dishing and erosion. Consequently, this demonstrated superior performance when compared to the International Technology Roadmap for Semiconductors (ITRS) 2000 roadmap targets for planarization. While the conventional slurry could achieve the 0.13-μm technology node requirements, the abrasive-free polish met the planarization requirements beyond the 0.10-μm technology node.     

Inverse analysis of material removal data using a multiscale CMP model

This paper describes a mechanical model for a representative dual axis rotational chemical mechanical planarization (CMP) tool. The model is three-dimensional, multiscale and includes sub-models for bulk pad deformation, asperity deformation, lubrication based slurry flow, carrier film deformation, wafer compliance and material removal by abrasive particles in the slurry. With the model, material removal rate (MRR) can be determined as a function of stress applied to the wafer, relative sliding speed, and material and geometric parameters of the pad and slurry. Experimental material removal rate profiles obtained from Cu polishing experiments performed on a wafer without rotation are analyzed as an inverse problem. We use MRR data to predict local CMP conditions such as fluid film thickness, fluid pressure and contact pressure. The results are consistent with available experimental and analytical information. This inverse technique offers promise as an improved method of CMP model verification.     

新型碱性阻挡层抛光液对铜布线化学机械平坦化的评估研究

化学机械平坦化(CMP)是铜互连制备过程中唯一的全局平坦化技术。但是由于互连线铜与扩散阻挡层物理及化学性质上的差异,在阻挡层的化学机械平坦化过程中将加剧导致碟形坑的产生。目前,国际上抛光液以酸性为主,但是其存在固有的问题,如酸性气体挥发,腐蚀严重等。本论文研发出一种新型碱性阻挡层抛光液,与商用的阻挡层抛光液做对比,评估了其抛光性能。实验结果表明,新型碱性阻挡层抛光液抛光后表面状态好,粗糙度较低。另外,碟形坑及电阻测试结果表明,新型碱性阻挡层抛光后铜布线的表面形貌好,碟形坑小,能够应用于铜布线阻挡层的CMP中。     

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.