Pad flattening ratio, coefficient of friction and removal rate analysis during silicon dioxide chemical mechanical planarization

Pad flattening ratio (PFR) was investigated as a non-destructive pad surface analysis method on the IC1000 K-groove pad during silicon dioxide chemical mechanical planarization. The PFR defines as the ratio of the bright area to the total image area. A series of marathon polishing runs were performed under ex-situ diamond disc pad conditioning, ex-situ high-pressure micro jet (HPMJ) pad conditioning and no pad conditioning methods where PFR analysis was performed to estimate the amount of pad surface flattening or glazing under these conditions. With no conditioning, PFR increased rapidly to 40% indicating severe glazing. With ex-situ diamond disc pad conditioning, PFR remained relatively constant below 12%, suggesting a rough and stable pad surface for polishing, while with ex-situ HPMJ conditioning it increased gradually and stabilized at the value of about 23%. Real-time analysis of friction force and silicon dioxide removal rate showed a clear correlation among the PFR, the coefficient of friction and the removal rate during the silicon dioxide chemical mechanical planarization.     

Surface Removal Rate in Chemical-Mechanical Polishing

Variation of the surface removal rate with down pressure, pad asperity, and relative velocity in chemical-mechanical polishing (CMP) was studied. A phenomenological model for contact of pad asperities with abrasive particles and wafer is described. The functional dependence of the polishing rate on pressure and velocity was found to be related to the distribution of pad asperities. Simple argument based on the mechanical contact theory suggests that the linear variation predicted by Preston's equation follows when the pad asperities have a random distribution. The sublinear dependence of the removal rate, however, is obtained when the pad asperities have a wavy distribution. The use of the statistical least-square method is suggested as a way to determine the relationship between the removal rate and pressure for different industrial pads used in CMP processes.

CMP polishing planarization surface removal     

固结磨料化学机械研抛K9玻璃的材料去除机理

采用失重法对固结磨料研抛K9玻璃材料去除过程中的机械与化学作用进行了分离,采用显微硬度方法分析了研抛液对K9玻璃工件表层硬度的影响.研究结果表明:研抛液能与K9玻璃发生化学反应并在其表面形成一层较基质材料软的变质层,变质层厚度随浸泡时间的延长而增加；单纯研抛液的化学作用对K9玻璃的材料去除作用有限,固结磨料研抛垫对K9玻璃的机械去除作用主要以脆性去除为主,化学与机械的交互作用是K9玻璃影响材料去除的主要方式:当研抛盘转速为200r/min时,化学作用与机械作用达到平衡,交互作用最为强烈,材料去除率达到最大值.     

Characterization of thermoset and thermoplastic polyurethane pads, and molded and non-optimized machined grooving methods for oxide chemical mechanical planarization applications

This paper systematically studies the effect of pad material, grooving method and grooving pattern on interlayer dielectric chemical mechanical planarization. The tested polishing pads consist of thermoplastic and thermoset polyurethanes synthesized using two different processes. Grooves created using a molding technique are compared with grooves formed by mechanical cutting. The concentric groove design is also compared with the logarithmic positive spiral positive grooving design. Experimental data collected include removal rate, coefficient of friction, shear force variance, pad temperature and dynamic mechanical analyzer measurements. Scanning electron microscope images are used to correlate grooving methods with coefficient of friction and shear force variance measurements. Results show that all of the pads polish wafers in boundary lubrication mode with unique friction coefficient, shear force variance and pad temperature characteristics. Simulations using a two-step removal rate mechanism are performed to estimate the chemical and mechanical rate constants. The analysis indicates that the thermoplastic pad is more mechanically controlled than the thermoset pad and that molded grooving induces a more mechanically controlled process than non-optimized machined grooving.     

静电自组装制备复合磨粒及其 对铜的抛光特性研究

研究苯代三聚氰胺甲醛（BGF）微球与阳离子型聚电解质聚二烯丙基二甲基氯化铵（PDADMAC）、阴离子型聚电解质聚4－苯乙烯璜酸钠（PSS）之间的吸附特性,利用静电自组装技术改变和控制BGF微球的荷电特性,制备出不同形式的PEi BGF/SiO2复合磨粒,以Zeta电位、透射电子显微镜（TEM）和热重分析（TG）等手段对复合磨粒进行了表征,并利用这些复合磨粒制备了铜片抛光用的复合磨粒抛光液。抛光试验表明,吸附在聚合物微球表面和游离于抛光液中的SiO2磨粒在抛光中均起到材料去除作用。传统单一SiO2磨粒抛光液的铜材料去除率为264 nm/min,PE0 BGF/SiO2混合磨粒抛光液的铜材料去除率为348 nm/min,PE3 BGF/SiO2复合磨粒抛光液的铜材料去除率为476 nm/min。经上述3种抛光液抛光后的铜表面,在5 μm×5 μm范围内,表面粗糙度Ra从0.166 μm分别降至3.7 nm、2.6 nm和1.5 nm,峰谷值Rpv分别小于20 nm、14 nm和10 nm,复合磨粒抛光液对铜片有良好的抛光性能。     

亲水性固结磨料研磨垫自修整机理探索

自修整特性是亲水性固结磨料研磨垫(FAP)的重要性能之一.为了探究其自修整的实现机理,使用PHL-350型平面高速研磨抛光机对K9玻璃圆片进行马拉松式实验.研究了研磨压力和孔隙对研磨垫自修整性能的影响.实验表明:研磨压力从0.15 MPa提高到0.20 MPa,研磨垫的自修整效果显著提高,经过一段时间后,1#研磨垫和2#研磨垫的材料去除速率分别保持在10μm/min和8μm/min以上.同时,成孔剂的加入使基体砂浆磨损率提高了近7倍,提高了固结磨料研磨垫的材料去除速率的稳定性.因此,提高压力和适当弱化基体有助于实现固结磨料研磨垫的自修整过程.     

Modeling and calculation of slurry-chemistry effects on chemical–mechanical planarization with a grooved pad

During chemical–mechanical planarization (CMP), a rotating wafer is pressed against a rotating pad, while a slurry is dragged into the pad–wafer interface. Here, taking into account the dependence of local material removal rate (MRR) on the slurry’s chemical activity, the effects of pad groove geometry and various other process parameters on the spatial average and non-uniformity of MRR are examined. Technically, the slurry flow is calculated by following an existing approach that integrates two-dimensional fluid-film lubrication theory and contact-mechanics models. A slurry impurity transport equation is then used to calculate the impurity concentration that determines the slurry’s chemical activity and hence the local MRR. The numerical results obtained here indicate that the presence of pad grooves generally decreases the average slurry impurity concentration, and increases the average contact stress on the pad–wafer interface. However, as a grooved pad has less contact area for effective interaction with the wafer surface, the average MRR may or may not be increased, depending upon the specific setting of process parameters. Meanwhile, it appears that the retaining ring generally used to keep the wafer in place also plays an important part in reducing the MRR non-uniformity.     

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.     

Static and dynamic removal rates of a new hydrodynamic polishing tool

A new tool for hydrodynamic radial polishing, HyDra, allows for the local polishing of optical surfaces with a controllable wear rate. The results of the removal rate for different polisher types and sizes, applied air pressures for slurry expulsion, and tool height with respect to the working surface, are reported. We present a numerical analysis of the volumetric removal rate for the dynamic experiments as well as a comparison with a similar technique.     

A chemical mechanical polishing model incorporating both the chemical and mechanical effects

A comprehensive model for the material removal in a chemical mechanical polishing (CMP) process is presented in which both chemical and mechanical effects are taken into consideration. The chemical effects come into play through the formation of chemically modified surface layer on the wafer surface that, in turn, is removed mechanically by the plastic deformation induced by slurry particles. This model describes the influence of most, if not all, variables involved in the CMP process including slurry characteristics (solid loading, particle size and distribution, modulus), pad properties (modulus, hardness, asperity sizes and distribution) and processing conditions (down-pressure, velocity). Although more elaborate experimental verification of the model is yet to follow, this model appears to be capable of explaining many experimental observations on both oxide and metal CMP that, otherwise, could not be explained properly.