Post-CMP cleaning using acoustic streaming

Noncontact surface cleaning is a desirable process in post-chemical mechanical polishing cleaning. High-frequency megasonic cleaning utilizes acoustic streaming as the dominant particle removal mechanism. It is widely used in the semiconductor industry for the removal of particulate contamination. This paper introduces recent results that involve the removal of silica slurry using megasonic cleaning. A noncontact (megasonic) cleaning process for the removal of slurry residues from dipped and polished wafers is presented. Complete particle removal (100%) was achieved using megasonics with deionized water with 1% NH₄OH using wafers dipped in silica slurry. The optimum conditions for megasonic cleaning (power, temperature, and time) were determined for the removal of the silica slurry. Up to 99% particle removal from polished wafers was accomplished using noncontact megasonic cleaning with 1% ammonia for 15 min.     

The influence of silicon heat treatments on the minority carrier generation and the dielectric breakdown in MOS structures

The minority carrier lifetime of Si and the dielectric breakdown of SiO₂ on Si has been investigated as a function of various high temperature treatments preceding the formation of the SiO₂ layer. Annealing wafers in H₂ or certain H₂ -containing ambients prior to oxidation lea to a dramatic decrease in the number of breakdown defects found in capacitors. The higher the temperature the more effective is the defect removal. Using this process the defect density could be reproducibly controlled at ≤10 defects/cm , and in some cases wafers with no defects were found. The defects appear to be related to some airborn contamination and can be increased by exposure to air and to certain aqueous cleaning steps. By “soaking≓ the Si wafers in an equilibrium gas mixture containing SiH₄ as well as HCl, it was possible to prevent etching of the Si but yet expose the wafer to approximately 4% HC1 for longer times and at higher temperatures, 12 75‡C, than is possible with the well known HCl-oxidation process. It was found that this treatment will remove Au, Fe, and Cu from intentionally contaminated wafers but at rates much slower than would be expected from bulk-diffusion, rate-limited transport. Soaking at 1275‡C led to minority carrier lifetimes comparable but not significantly better than for HCl-oxidized wafers.     

硅片清洗研究进展

综述了清洗液的组成、特点、清洗机理、对硅片表面质量的影响以及清洗技术和理论的发展;着重指出了,改进的RCAI对颗粒度、微粗糙度和金属沾污作用的机理,讨论了它与清洗顺序的关系,极度稀释的RCA2能使金属沾污降至10∧10原子/cm∧2以下,且不易使颗粒重新沉淀;最后介绍了清洗工艺的最新进展。     

新型抛光后晶片表面金属离子清洗工艺

本文提出了一种新型的利用金刚石膜电极电化学氧化进行抛光后晶片金属离子污染的清洗方法。金刚石膜电极电化学氧化,可以制备氧化性强的过氧焦磷酸盐,过氧焦磷酸盐可以有效的氧化表面有机物,同时过氧焦磷酸盐被还原成的焦磷酸盐具有很强的配合力,它能与铜等金属离子络合。将三块晶片在0.01mol/L的CuSO4溶液中进行金属离子污染后进行清洗对比实验。对比实验有三部分,一是采用金刚石膜电化学氧化制备的过氧焦磷酸盐进行清洗,二是传统的RCA清洗方法,三是去离子水清洗。XPS测试结果表明,过氧焦磷酸盐清洗与RCA清洗方法对金属离子的去除效果均小于ppm级。过氧焦磷酸盐清洗对有机物的清洗效果优于传统的RCA清洗方法。因此金刚石膜电化学氧化清洗方法可以有效去除有机污染以及金属离子污染,实现了一剂多用,减少清洗步骤,达到节能环保的目的。     

A new cleaning process for the metallic contaminants on a post-CMP wafer's surface

This paper presents a new cleaning process using boron-doped diamond(BDD) film anode electrochemical oxidation for metallic contaminants on polished silicon wafer surfaces.The BDD film anode electrochemical oxidation can efficiently prepare pyrophosphate peroxide,pyrophosphate peroxide can oxidize organic contaminants,and pyrophosphate peroxide is deoxidized into pyrophosphate.Pyrophosphate,a good complexing agent,can form a metal complex,which is a structure consisting of a copper ion,bonded to a surrou...     

Effective cleaning process and its influence on surface roughness in anodic bonding for semiconductor device packaging

Wafer cleanliness and surface roughness play a paramount role in an anodic bonding process. Impurities and the roughness on the wafer surface result in unbonded areas which lead to fringes and Newton׳s rings. With an augment in surface roughness, lesser area will be in stroke thus making more pressure and voltage to be applied onto the wafers for better bonding. Eventually it became mandatory to choose the best cleaning process for the bonding technology that can substantially reduce the impurities and surface roughness. In this paper, we investigate the bonding of silicon/oxidized silicon on Pyrex (CORNING 7740) glass with respect to surface roughness and cleanliness of the wafers by performing three renowned cleaning processes such as degreasing, piranha, RCA 1& 2 (SC‐Standard Cleaning 1 and 2) and found that RCA compromises the best between the roughness and cleanliness. Studies were also extended to find out the effects of applied voltage and load on the bonded surface. It was observed for samples cleaned with RCA, an increase of 45% in maximum current and decrease of 75% in total bonding time with the applied load and voltage among all the cleaning techniques used. Three dimensional structures for pressure sensor application were successfully bonded by selecting the appropriate load and cleaning process. Atomic force microscopy analysis was done to investigate the surface roughness on silicon/oxidized silicon and Pyrex glass for different cleaning processes. Scanning electron microscopy and optical imaging were performed on the interface for the surface integrity of the bonded samples.     

非离子表面活性剂在阻挡层CMP后清洗中去除颗粒作用的研究

本文对非离子表面活性剂在阻挡层CMP后清洗中对颗粒的去除作用进行了研究。实验过程中,通过改变活性剂的浓度,在12inch多层铜布线片上进行了一系列的实验来确定最佳的清洗效果。然后对活性剂在缺陷控制、颗粒去除,以及活性剂在清洗过程中所起的负面作用等方面进行了讨论。实验结果表明,非离子表面活性剂在阻挡层CMP后清洗中根据浓度的不同所起的正面、负面作用不同,从而为阻挡层CMP后清洗过程中非离子表面活性剂的加入起到一定的指导作用。     

PIND试验中水溶胶清洗方法研究

国内PIND试验室对水溶胶的清除方法普遍存在诸多弊端，导致元件表面胶体残留过多，给后续试验带来质量隐患。在探讨了多种在用的清洗方法后，提出了“喷淋一循环”一站式清洗方案，在满足元器件的温度、表面保护、静电防护等要求的同时，清洗质量和清洗效率也有了极大的提高，最终研制出新型水溶胶清洗机。试验证明，新方法具有耗费低廉、使用方便、易于维护、可靠性高等显著优点，可极易推广至相似需求的中、小型PIND试验环境中。     

The cleaning at a back surface and edge of a wafer for introducingCu metallization process

Cu metallization has been introduced in high-speed complementary metal-oxide-semiconductor (CMOS) large scale integration (LSI) in order to achieve low electrical resistivity. This means Cu contamination can be spread all over semiconductor equipment by the wafers, even though Cu has been thoroughly eliminated from semiconductor manufacturing for a long time. To protect the other wafers without Cu from Cu cross-contamination, we have demonstrated a method that can clean the back surface and selectively clean the edge of a wafer simultaneously without any masks. This method performs the cleaning by optimizing the overhang of chemicals in the single-wafer system with the Bernoulli chuck. We have also demonstrated a new edge extractor that can be used to perform the quantitative evaluation of Cu contamination at the wafer edge. The combination of the edge cleaning and the edge evaluation is useful for introducing not only Cu, but also new exotic materials such as Ta₂O₅ and BST     

The influence of vapor phase cleaning on the composition and the surface roughness of rapid thermal oxides and nitrided oxides

In this paper, the influence of various pre-oxidation cleanings on the Si/SiO₂ interface and the oxide surface roughness is investigated. Different types of Vapor Phase Cleanings (VPC) are performed in an integrated STEAG AST cluster module and are compared to a standard wet cleaning process. The VPC uses Anhydrous Hydrogen Fluoride (AHF) and additional ozone cleaning. Directly after the cleaning, oxidation in pure oxygen (O₂) is carried out in an integrated STEAG AST Rapid Thermal Processing (RTP) cluster module. Nitrided oxides are formed by annealing in pure nitric oxide (NO) gas directly after the oxidation. The nitrogen incorporation and distribution in the oxide is investigated using secondary ion mass spectroscopy (SIMS). The nitrogen concentration at the Si/SiO₂ interface depends on the time and/or temperature of the NO annealing. For a 900°C annealing, the nitrogen incorporation varies from 0.5 at.% for a 5 s anneal to 2.5 at.% for a 60 s anneal. The nitrogen concentration of the oxides can be correlated with the different types of precleaning sequences which seems to be an effect of the different fluorine contents obtained after various cleaning procedures. The surface roughness of oxide layers formed after different pre-cleaning sequences is analyzed by Atomic Force Microscopy (AFM). A decrease in surface roughness is measured for oxidation performed at higher temperature. and for rapid thermal oxides produced after a cleaning procedure using AHF and ozone.     

Influence of initial wafer cleanliness on metal removal efficiencyin immersion SC-1 cleaning: limitation of immersion-type wet cleaning

When contaminated silicon wafers are immersed in an ultra-pure cleaning solution of an NH₄OH/H₂O₂/H ₂O mixture known as the RCA Standard Clean 1 (SC-1), in which the impurity concentration is negligibly low, the level of wafer-surface metallic contamination after the cleaning treatment depends on the amount of metallic impurities brought into the solution by the to-be-cleaned wafers themselves. Even if the chemicals are disposed of after each wafer cleaning, the surface metallic contamination is still dominated by the amount of impurities brought into the fresh solution by the wafers themselves. In the past, purer chemicals have been sought to improve metal removal efficiency, but after reasonably purer chemicals are obtained the efficiency is not governed by the initial chemical purity but by the initial wafer cleanliness. Because of this, scrubbing of dirty wafers-both the backand front-surfaces-before immersion-type wet cleaning is recommended. However, to meet future stricter wafer cleanliness requirements, new cleaning methods in which fresh chemicals are continuously supplied, such as single-wafer spin cleaning, will have to be employed     

Influence of dry and wet cleaning on the properties of rapid thermal grown and deposited gate dielectrics

Various silicon surface cleaning processes for rapid thermal in-situ polysilicon/ oxide/silicon stacked gate structures have been evaluated. Metal-oxide-semiconductor capacitors were fabricated to assess the effects of cleaning on the quality of gate oxide structures produced by both rapid thermal oxidation (RTO) and rapid thermal chemical vapor deposition (RTCVD). Excellent electrical properties have been achieved for both RTO and RTCVD gate oxides formed on silicon wafers using either an ultraviole/zone (UV/O₃) treatment or a modified RCA clean. On the contrary, poor electrical properties have been observed for RTO and RTCVD gate oxides formed on silicon wafers using a high temperature bake in Ar, H₂, or high vacuum ambient. It has also been found that the electrical properties of the RTCVD gate oxides exhibit less dependence upon cleaning conditions than those of RTO gate oxides. This work demonstrates that initial surface condition prior to gate oxide formation plays an important role in determining the quality of RTO and RTCVD gate oxides.     

A lubrication model between the soft porous brush and rigid flat substrate for post-CMP cleaning

A 3D lubrication model between a soft porous brush and rigid flat surface in the post-CMP (chemical mechanical polishing) cleaning process for wafer or hard-disc surface is set up in this article. The mesh porous structure of the brush and the kinematic relations between the brush and the surface are taken into account. The flow governing equations for cleaning process are deduced with Newtonian fluids between the brush nodule and the substrate. The distributions of fluid pressure and hydrodynamic removal moment are calculated. The simulation results show that the fluid pressure has negative regions in inlet area. The removal force is depended on system parameter, location, time and particle size. The load and hydrodynamic moment increase with the increase of brush velocity and deflection of brush nodule, which is effective for cleaning. A low wafer rotation speed is recommended to keep the cleaning uniformity. The removal moment is increasing during the cleaning process. The hydrodynamic drag force decreases rapidly with decreasing of particle size. The models are coincident with the actual process and can be used as reference for designing a higher level cleaning process and the analysis of the formation of particle defect.     

光伏太阳能硅片清洗工艺的探索

对两种不同清洗方法的工作原理、清洗效果和适用范围等特点进行了分析。不同的工艺应采用不同的清洗方法才能获得最佳效果。介绍了硅片清洗机的清洗工艺和腐蚀工艺。指出了硅片清洗工艺的发展趋势。     

多结化合物电池用p型Ge抛光片清洗技术研究

对多结化合物太阳电池用的p型Ge抛光片的清洗技术做了研究.Ge抛光片的清洗可以采用酸性清洗液和碱性清洗液相结合的方式.酸性清洗液的主要作用是去除晶片表面的有机物;碱性清洗液的主要作用是去除晶片表面的颗粒.清洗液的温度和组分影响着抛光片的清洗效果.通过实验结果确定了p型Ge抛光片的清洗方案,采用这一清洗方案清洗的Ge抛光片,表面质量可以达到"开盒即用"的水平.运用晶片清洗机理分析了各种清洗液的功能和作用.     

激光清洗工艺的发展现状与展望

综述了激光清洗技术的作用机理和发展现状,展望了该技术的应用前景。     

Belief based data cleaning for wireless sensor networks

Wireless sensor network (WSN) data is often subjected to corruption and losses due to wireless medium of communication and presence of hardware inaccuracies in the nodes. For a WSN application to deduce an appropriate result it is necessary that the data received is clean, accurate, and lossless. WSN data cleaning systems exploit contextual associations existing in the received data to suppress data inconsistencies and anomalies. In this work we attempt to clean the data gathered from WSN by capturing the influence of changing dynamics of the environment on the contextual associations existing in the sensor nodes. Specifically, our work validates the extent of similarities among the sensed observations from contextually (spatio‐temporally) associated nodes and considers the time of arrival of data at the sink to educate the cleaning process about the WSN's behavior. We term the data cleaning technique proposed in this work as time of arrival for data cleaning (TOAD). TOAD establishes belief on spatially related nodes to identify potential nodes that can contribute to data cleaning. By using information theory concepts and experiments on data sets from a real‐time scenario we demonstrate and establish that validation of contextual associations among the sensor nodes significantly contributes to data cleaning. Copyright © 2010 John Wiley & Sons, Ltd.     

锈蚀表面的激光清洗及其元素组成分析

采用波长1064 nm高重频高能量激光清洗设备,研究了激光清洗碳钢表面锈蚀时工艺参数对除锈效果的影响,分析了激光清洗锈蚀表面、微区、线和点处的元素组成以及相对含量。结果发现:脉冲激光在优化参数下能将碳钢表面的锈蚀完全清洗干净,激光清洗锈蚀表面、微区、线和点处都没有发现氧元素的存在,表明脉冲激光不仅能将碳钢表面的锈蚀完全清洗干净,而且在激光清洗锈蚀过程中不会发生铁元素和氧元素的化学反应,生成氧化铁膜。     

Megasonic cleaning of wafers in electrolyte solutions: Possible role of electro-acoustic and cavitation effects

Investigations have been conducted on the feasibility of removal of particles from silicon wafers in electrolyte solutions of different ionic strengths irradiated with megasonic waves. Cleaning experiments have been performed using potassium chloride (KCl) as a model electrolyte and silica particles as model contaminant particles. Particle removal efficiency (PRE) increases with KCl concentration and transducer power density and much lower power densities may be used at higher KCl concentration for a comparable level of cleaning. Enhanced cleaning in KCl solutions has been explained as due to two types of electro-acoustic potentials, namely, ionic vibration potential (IVP) and colloidal vibration potential (CVP) that arise when the sound wave propagates through the electrolyte solution. Theoretical computations have shown that the removal forces due to CVP are much larger in magnitude than those due to IVP and are comparable to van der Waals adhesion forces.The effect of ionic strength on cavitation has been investigated through the measurement of acoustic pressure in solutions using a hydrophone. Using Fourier transformation of time dependent pressure data, the size distribution of stable bubbles in KCl solutions of different concentration has been obtained.     

离心清洗技术在印制电路板清洗中的应用

焊接属电子设备生产过程中的一个关键步骤.焊接后必须进行清洗才能确保电子设备的可靠性,延缓其工作寿命.本文重点介绍了一种离心清洗技术,清洗洁净度高,能有效去除PCB残留物.