Analysis of the polishing ability of electrogenerated chemical polishing

Electrogenerated chemical polishing (EGCP) had been proved effective in improving both the smoothness and the flatness of copper surface in our previous work. In this paper the polishing ability, defined as the ratio between the material removal rate at the peak and at the valley of a rough surface, is studied theoretically and experimentally. In a mathematical model, the effects of the special wavelength L, the peak-to-valley height h of the workpiece surface profile and the working distance d between working electrode and workpiece surface on the polishing ability are studied. The results show that the polishing ability decreases with increasing the working distance and finally approaches the value (d + h)/d, if L is much larger than d. However, the effect of the working distance on polishing ability is negligible, if L is close to or less than d. The polishing ability also decreases with h decreasing. Based on the above analysis, an analytical expression of the polishing ability of EGCP is given. For validating the theoretical analysis, a copper surface is polished by EGCP and the change of the surface profile is measured and analyzed using the analytical expression. The measured polishing ability agrees well with the simulation results.     

Hydrodynamic analysis of chemical mechanical polishing process

Chemical Mechanical Polishing (CMP) refers to a material removal process done by rubbing a work piece against a polishing pad under load in the presence of chemically active abrasive containing slurry. The CMP process is a combination of chemical dissolution and mechanical action. The mechanical action of CMP involves hydrodynamic lubrication. The liquid slurry is trapped between the work piece (wafer) and pad (tooling) forming a lubricating film. For the first step to understand the mechanism of the CMP process, hydrodynamic analysis is done with a semiconductor wafer. Slurry pressure distribution, resultant forces and moments acting on the wafer are calculated in typical conditions of the wafer polishing, and then nominal clearance of the slurry film, roll and pitch angles at the steady state are obtained.     

Estimating chemical mechanical polishing pad wear with compressibility

A polishing pad is an important component in a chemical mechanical polishing (CMP) system. Few investigations have specialized in the variation of the characteristics of the pad as it undergoes wear. All of the information concerning a pad, such as compressibility and pad life, comes from the manufacturer. No acknowledged standard or instrument exists for determining a pad’s quality. This study obtained the variation of the compressibility (K) of major types of pad (single-layer pad and composite pad) with polishing time (pad wearing) by theoretical modeling and real experiments. The K of single-layer or composite pads changes due to wear, and the trends in the K values of the two types of pads are exactly opposite. A finite element method (FEM) is used here to show that the variation in K strongly affects the polishing process. Theoretically, the compressibility of a pad can be used to judge whether the pad is good for polishing or not.     

A novel method for micro-gap control in electrogenerated chemical polishing

In the electrogenerated chemical polishing (EGCP), material removal rate (MRR) is inversely proportional to the processing gap. To polish a workpiece with a large area, high and uniform MRR is necessary, which prefers a small and uniform processing gap. Based on the principle of the hydrostatic support, a novel micro-gap control method is proposed. The method uniformly controls the gap between the electrode and workpiece to a micro level over a large area. A relationship between the gap size and the inlet pressure is derived theoretically and verified experimentally. The proposed method is successfully applied to the polishing of a Cu surface with a diameter of 50 mm. Promising results are obtained that surface roughness and flatness are reduced from average roughness (Ra) 82 nm and peak-to-valley (PV) value 290 nm to Ra 4 nm and PV 120 nm, respectively.     

In-situ neural network process controller for copper chemical mechanical polishing

Process control is one of the key methods to improve manufacturing quality. This research proposes a neural network based run-to-run process control scheme that is adaptive to the time-varying environment. Two multilayer feedforward neural networks are implemented to conduct the process control and system identification duties. The controller neural network equips the control system with more capability in handling complicated nonlinear processes. With the system information provided by this neural network, batch polishing time (T) an additional control variable, can be implemented along with the commonly used down force (p) and relative speed between the plashing pad and the plashed wafer (v). Computer simulations and experiments on copper chemical mechanical polishing processes illustrate that in drafting suppression and environmental changing adaptation that the proposed neural network based run-to-run controller (NNRTRC) performs better than the double exponentially weighted moving average (d-EWMA) approach. It is also suggested that the proposed approach can be further implemented as both an end-point detector and a pad-conditioning sensor.     

Factors influencing the dressing rate of chemical mechanical polishing pad conditioning

The primary consumables in the chemical mechanical polishing (CMP) process are the polishing pad and the slurry. Among those consumables, the polishing pad significantly influences the stability of the process and the cost of consumables (CoC). Furthermore, the small holes on the pad surface will be filled by the reactant from the CMP process, and the surface of the pad will deposit hard glazing gradually. The glazing not only reduces the ability of absorbing slurry of the pad, but it also causes scratching on the work piece. In order to maintain the stability of the CMP process and return to an ideal pad surface status, we must condition the pad according to a regular time schedule. At the same time, if we use different pad conditioning factors, the dressing rate of the CMP pad will be different. Most important of all, we have to decrease the pad material abrasion due to the pad conditioning process. In conclusion, if we can understand the influence of the dressing rate and conditioning factors effectively, it will be useful for maintaining CMP process stability, extending pad life, and reducing CoC and non-processing time.     

抛光垫在蓝宝石衬底化学机械抛光中的应用研究

在分析化学机械抛光中常用抛光垫的材质、性能、表面结构基础上,研究了抛光垫对蓝宝石衬底抛光质量的影响规律:材质硬的抛光垫可提高衬底的平面度;材质软的抛光垫可改善衬底的表面粗糙度;表面开槽的抛光垫可提高抛光效率;表面粗糙的抛光垫可提高抛光效率;对抛光垫进行适当的修整可使抛光垫表面粗糙;用聚氨酯类抛光垫能够使得蓝宝石衬底的抛光面小于0.3nm的表面粗糙度.     

化学机械抛光的研究进展

化学机械抛光简称CMP技术是迄今唯一的可以提供整体平面化的表面精加工技术,可广泛用于集成电路芯片、计算机硬磁盘、微型机械系统等表面的平坦化。介绍了半导体加工领域CMP技术的特点,重点叙述了CMP技术的发展历程、设备特性、研磨抛光耗材和应用领域的技术现状,指出CMP急待解决的技术和理论问题,并对其发展方向进行展望。     

Modeling the effects of abrasive size, surface oxidizer concentration and binding energy on chemical mechanical polishing at molecular scale

No conclusive results have been proposed for the influence of the abrasive particle size on the material removal during the chemical mechanical polishing (CMP). In this paper, a mathematical model as a function of abrasive size and surface oxidizer concentration is presented for CMP. The model is proposed on the basis of the molecular-scale removal theory, probability statistics and micro contact mechanics. The influence in relation to the binding energy of the reacted molecules to the substrate is incorporated into the analysis so as to clarify the disputes on the variable experimental trends on particle size. The predicted results show that the removal rate increases sub-linearly with the abrasive particle size and oxidizer concentration. The model predictions are presented in graphical form and show good agreement with the published experimental data. Furthermore, variations of material removal rate with pressure, pad/wafer relative velocity, and wafer surface hardness, as well as pad characteristics are addressed. Results and analysis may lead further understanding of the microscopic material removal mechanism from molecular-scale perspective.     

The crystallographic change in sub-surface layer of the silicon single crystal polished by chemical mechanical polishing

The effect of the contact nominal pressure on the surface roughness and sub-surface deformation in chemical mechanical polishing (CMP) process has been investigated. The experimental results show that a better surface quality can be obtained at the lower pressure, and the thickness of sub-surface deformation layer increases with the increase of the pressure. In CMP process, polishing not only introduces amorphous transformation but also brings a silicon oxide layer with a thickness of 2–3 nm on the top surface. The atomic structure of the material inside the damage layer changes with the normal pressure. Under a higher pressure (125 kPa), there are a few crystal grain packets surrounded by the amorphous region in which the lattice is distorted, and a narrow heavy amorphous deformation band appears on the deformation region side of the interface. Under a lower pressure, however, an amorphous layer can only be observed.     

Chemical polishing of palladium for transmission electron microscopy

Chemical polishing methods for thinning palladium for TEM are reviewed. The quality of the foils produced by the different solutions is compared and the possible influence of hydrogen absorption on the microstructure is discussed.     

数控非接触式超光滑光学元件加工机床的设计

基于数控技术,提出了一种非接触式光学元件表面超光滑液体抛光方法.通过磨头中心孔为抛光表面提供抛光液,抛光液在磨头自转的带动下与光学元件表面相互作用,实现光学元件表面材料的微量去除,利用计算机控制抛光磨头的运动轨迹完成对光学元件表面的抛光.根据上述原理,设计和研制了数控非接触表面超光滑光学元件加工机床样机,样机直线运动轴最低进给速度为0.000 1 m/s,定位精度为0.008 mm;摆动轴最低转速为0.002 8 r/min,定位精度为15″.抛光实验结果表明,经过20 min的超光滑加工,熔石英材质光学元件上两点的表面粗糙度Ra值分别由加工前的1.03 nm和0.92 nm提高到加工后的0.48 nm和0.44 nm,显著提高了加工精度.     

磁流体辅助抛光工件表面粗糙度研究

给出了磁流体辅助抛光的机理,以及依据Preston方程建立的磁流体辅助抛光的数学模型。并通过实验详细研究了磁流体辅助抛光后工件的抛光区形状,以及抛光区内表面粗糙度情况。最终加工出了表面粗糙度为0.76 nm(rms值)的光学元件,其高频表面粗糙度达到0.471 nm(rms值),满足了对一定短波段光学研究的要求。结果表明:磁流体辅助抛光可以用于对光学元件进行超光滑加工;在磁流体辅助抛光过程中,较大粒度的磁流体抛光液有利于工件表面粗糙度快速降低,较小粒度的磁流体抛光液可以获得更加光滑的光学表面。     

中等口径光学非球面的高效研抛技术

介绍了一种弹性模抛光与小磨头修正抛光相结合的两步研抛法实现中等口径光学非球面表面的快速抛光。利用弹性模预抛光来保证小工具抛光模型的准确稳定,并采用补偿的方法减小弹性模抛光对面形精度的破坏作用。然后利用优化的小磨头修正残留的表面误差来提高抛光精度。应用上述方法加工非球面,在较短的抛光周期中,获得的面形P-V精度达0.35μm。     

High precision chemical mechanical polishing of highly-boron-doped Si wafer used for epitaxial substrate

The surface waviness with concentric circular pattern is generated on highly-boron-doped Si wafer by chemical–mechanical polishing (CMP) with amine system polishing slurry. To investigate the generation mechanism of the waviness, the mechanical and chemical characteristics were clarified using the silicon crystal samples with various boron concentration level ranging from 2.9 × 10¹⁷ cm⁻³ to 1.3 × 10²⁰ cm⁻³. The conventional silicon substrate used as epitaxial wafer has boron concentration of about 2.5 × 10¹⁸ cm⁻³, a region at which the radical change of etching rate is induced with amine system chemical reagent. The mechanical micro-hardness of highly-boron-doped Si is 30% higher than that of lightly-doped Si. It is found that SiB bond in crystal lattice is firmed up and stabilized for mechanical stress and chemical reaction. To cancel the difference in CMP rate based on boron concentration deviation, increasing the mechanical action in CMP was proposed and performed. The precision CMP was performed using the harder polishing pad and a smooth surface without waviness was obtained.     

A neural-Taguchi-based quasi time-optimization control strategy for chemical-mechanical polishing processes

Besides the major factors such as the down force, back pressure and the rotating speed of wafer carrier, effect of polishing time is also an important issue in CMP processes. In this study, a neural-Taguchi method based on a cost-effective quasi time-optimisation technique for chemical-mechanical polishing (CMP) processes is developed. The key concept of this new technique is that an optimal process parameter set is obtained through a neural-network-simulated CMP process model. Under such an optimal parameter set, the desired material removal rate within-wafer-nonuniformity can be reached with the optimal polishing time. It has been proved by experiment that the proposed method can offer a better polishing performance while reducing the polishing time by 1/3.     

Damage-free tribochemical polishing of diamond at room temperature: a finishing technology

Polished surfaces are characterized by a geometric shape and a surface finish, the latter being defined by surface roughness (smoothness) and subsurface damage. In general, mechanically polished surfaces have a high geometric precision and are optically smooth, but they are subjected to surface and subsurface damage. Tribochemical polishing gives smooth surfaces and damage-free subsurfaces, but the surface geometric precision is often poor at the submicron level. Diamond is the hardest material known, and the standard polishing technique for such hard materials is mechanical polishing, causing surface and subsurface damage. In this paper a novel method of tribochemical polishing of natural and synthetic monocrystalline diamond at room temperature is described, which gives very smooth surfaces of, at least, (100) planes, free from surface and subsurface damage within the instrumental detection limits. Such diamond surfaces are van der Waals bondable to other materials. With this novel technology only low material removal rates can be achieved. Therefore, it is mostly adapted as a finishing technique. The described polishing technology can be applied to other (hard) materials as well.     

气囊抛光技术及其研究现状

气囊抛光能够获得稳定的材料去除特性和高质量的抛光表面。回顾了气囊抛光的工作原理、特点和发展现状,对气囊抛光的关键技术进行了比较分析,包括抛光工具,进动抛光,脉动抛光,磁流体抛光,驻留时间,边缘控制和过程控制,抛光轨迹规划,磨粒场及气囊抛光应用等。研究结果表明,气囊抛光是一种值得关注的自由曲面高效精密抛光方法。     

Modelling of delamination of ultra low-k material during chemical mechanical polishing

Two sets of experiments are performed to examine the delamination mechanism of ultra low-k material during chemical mechanical polishing (CMP): (i) a macro-scale polishing test using a metallographic polisher and (ii) a micro-scale scratch test on a micro-tribometer. Delamination has been observed at higher pressures in both sets of experiments and the relationship between delamination rate and pressure has been established. Contact mechanics models are proposed to correlate results from the two sets of experiments, combining a Weibull model of failure with a statistical asperity contact model. Results confirm the usefulness of the combined testing procedure in predicting safe polishing pressures during CMP.