Alkaline cleaning of silicon wafers: additives for the prevention of metal contamination

The paper presents a new strategy for cleaning of silicon wafers. A novel class of chelating agents added to alkaline cleaning mixtures provides promising performance without negative effects such as metal redeposition due to residual metal contamination of the cleaning solution. The superior capability of the new cleaning process is confirmed by the results obtained from wafer surface metal analysis as well as from minority carrier lifetime and diffusion length measurements and gate oxide integrity tests. Particle densities and surface roughness are not influenced by the presence of the chelating agents in the cleaning solution. TOF–SIMS measurements do not indicate any deposition of chelating agent on the wafer surface. With this type of modified SC-1 cleaning procedure the acid SC-2 step used in conventional RCA cleans to remove the metals deposited in the preceding SC-1 step is unnecessary resulting in substantial cost savings with respect to chemicals, waste, equipment and space.     

Chemical analysis of metallic contamination on a wafer after wetcleaning

The chemical analysis of trace metallic contamination on a wafer can be achieved by using total reflection X-ray fluorescence (TRXRF) with HF condensation and with poly silicon encapsulation secondary ion mass spectroscopy (PC-STMS). HF condensation can concentrate almost all atoms, such as Fe, Cr, and Ni, within 10 mm of the center of a wafer, which leads to lower detection limits. Poly silicon encapsulation eliminates the surface problems that tend to occur with normal SIMS, which results in good reproducibility. A combination of both methods is suitable for analyzing lower-level contaminations up to 10⁸ atoms/cm² level for many elements such as transient metals and lightly elemental metals. The application of the analyses to wet cleaning reveals the contamination removal and adhesion effects for various solutions and cleaning procedures, as well as variation between experimental cleaning batches     

半导体硅片金属微观污染机理研究进展

综述了近10年来国内外在半导体硅片金属微观污染研究领域的进展.研究了单金属特别是铜的沉积、形成机理和动力学以及采用的研究方法和分析测试手段,包括对电化学参数和物理参数等研究.指出了随着科学技术的不断发展,金属污染金属检测手段也得到了丰富,为金属微观污染的研究提供了有力的工具.     

Megasonic free single wafer cleaning using ozone jet without pattern damage and with minimum substrate etching

A newly developed single wafer cleaning process using gaseous ozone and very dilute chemistries at room temperatures shows high particle removal performance without the use of megasonics. The process utilizes the strong oxidative properties of ozone with the oxide etching property of HF and zeta potential advantages of NH/sub 4/OH for particle removal. Alumina, silica, ceria, and nitride particles on silicon wafers were removed with 95% or greater particle removal efficiency with about 0.2 /spl Aring/ of oxide and 0.4 /spl Aring/ silicon loss. The physical force of the ozone gas stream effectively reduces the boundary layer thickness enhancing particle removal with very dilute chemistries and without damaging patterns. Therefore, improved particle removal efficiencies can be achieved with significant cost advantages when compared with a batch type cleaning process. The process can be applied to FEOL and BEOL cleans.     

金刚石膜电化学清洗硅片表面有机沾污的研究

采用金刚石膜电极的电化学方式在专用水基清洗剂中不断产生强氧化剂过氧焦磷酸根离子(P2O4-8),并将此方式作为金刚石膜电化学清洗工艺步骤的第一步,用于氧化去除硅片表面的有机沾污.通过与RCA清洗进行对比实验,并应用X射线光电子谱和原子力显微镜进行清洗效果的检测,结果表明,本清洗工艺处理后的硅片表面有机碳含量更少,微粗糙度小,明显优于现有的RCA清洗工艺.     

Low pressure chemical vapor deposition from TEOS–NH3 mixtures: thermochemical study of the process considering kinetic data

A calculational thermodynamic investigation of the chemical vapor deposition (CVD) of SiO₂ films from TEOS/NH₃ mixtures has been performed, by minimizing the Gibbs energy of the C–H–N–O–Si chemical system. Calculations are based on an upgraded thermodynamic data bank which includes silicon containing complex gaseous compounds. The obtained results illustrate the influence of temperature, of pressure, and of initial gas composition on the formation of stable phases. Partial equilibrium calculations were also performed, in order to investigate the predominant mechanisms for deposition. These calculations have been conducted (a) by excluding the solid phases from the calculations, and (b) by assuming a partial striping and elimination of the ethoxy ligands in the gas phase before reaching the growing surface. Finally, the supersaturation of the gas phase relative to silicon dioxide and the corresponding driving force for the deposition have been evaluated in different processing conditions. A direct relation between driving force and the growth rate of the deposits has thus been evidenced.The aim of this research is to contribute to the definition of optimum conditions for the processing of materials which can be used as dielectrics in integrated circuits, and as waveguides in optoelectronics.     

金刚石膜电化学清洗硅片表面有机沾污的研究

采用金刚石膜电极的电化学方式在专用水基清洗剂中不断产生强氧化剂过氧焦磷酸根离子(P2O4-8),并将此方式作为金刚石膜电化学清洗工艺步骤的第一步,用于氧化去除硅片表面的有机沾污.通过与RCA清洗进行对比实验,并应用X射线光电子谱和原子力显微镜进行清洗效果的检测,结果表明,本清洗工艺处理后的硅片表面有机碳含量更少,微粗糙度小,明显优于现有的RCA清洗工艺.     

Optimization of Selective Epitaxial Growth of Silicon in LPCVD

Selective epitaxial growth (SEG) of silicon has attracted considerable attention for its good electrical properties and advantages in building microstructures in high‐density devices. However, SEG problems, such as an unclear process window, selectivity loss, and nonuniformity have often made application difficult. In our study, we derived processing diagrams for SEG from thermodynamics on gas‐phase reactions so that we could predict the SEG process zone for low pressure chemical vapor deposition. In addition, with the help of both the concept of the effective supersaturation ratio and three kinds of E‐beam patterns, we evaluated and controlled selectivity loss and nonuniformity in SEG, which is affected by the loading effect. To optimize the SEG process, we propose two practical methods: One deals with cleaning the wafer, and the other involves inserting dummy active patterns into the wide insulator to prevent the silicon from nucleating.     

Effects of size, humidity, and aging on particle removal from Si wafers

The effects of particle size, humidity, and aging time on particle removal from silicon wafers were investigated with a laser shock wave at a constant removal force. Particle adhesion force, shock wave cleaning force, and the removal moment ratio were calculated and related to particle removal efficiency (PRE). The presence of capillary forces and particle deformation significantly increased the adhesion force. In order to control the humidity and magnitude of deformation, humidity and aging time were varied during particle removal tests. PRE decreased rapidly for particle sizes below 1 μm as the humidity and contact area increase. The calculations of removal moment ratios agreed well with the experimental observations. Both humidity and process time should be controlled to avoid the aging of particles and to achieve high PRE for particles smaller than 1 μm.     

微腐蚀去除硅衬底表面损伤及污染物研究

硅片CMP工艺会引入表面缺陷和沾污,通常采用NaOH和KOH作为腐蚀溶液,利用微腐蚀法将硅片表面的损伤污染层剥离,以免导致IC制备过程中产生二次缺陷,但会不可避免地引入金属离子。制备了一种用螯合剂和表面活性剂复配的新型清洗液,利用螯合剂对硅片表面损伤层进行微腐蚀,同时采用表面活性剂去除硅片表面吸附的微粒。经台阶仪和原子力显微镜检测,该清洗液能有效去除硅片表面损伤层和颗粒,同时螯合剂本身不含金属离子,并且对金属离子有螯合作用,可有效避免传统腐蚀液中金属离子带来的二次污染。     

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.     

Condensed phase equilibria in the metal-In-P systems

Ternary phase diagrams have proven valuable for understanding the reactions between a metal contact and a compound semiconductor, as well as for choosing thermally stable electrical contacts in thermodynamic equilibrium with the semiconductor. Since InP is important for both optoelectronic and electronic devices, the metal-In-P systems are of particular interest. In this work, new portions of isothermal sections of the (Rh, Ir, Ru, Os)-In-P diagrams are presented. Then, since no compilation of the published metal-In-P phase diagrams is available, the diagrams are reviewed here. The features of these diagrams are discussed in terms of the thermodynamics of the metal-In-P systems, particularly the considerable thermodynamic stability of many of the transition metal phosphides. Finally, some of the phases in thermodynamic equilibrium with InP, particularly PdIn and Ni₂P, are highlighted for their potential for high-temperature contacts to InP.     

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.     

Experimental study of the process dependence of Mo, Cr, Ti, and W silicon Schottky diodes and contact resistance

This paper reports on the process dependence and electrical characterization of Schottky diodes and ohmic contacts fabricated on p- and n-type silicon wafers. Four metals are systematically studied using identical test structures and characterization methods: Mo, Ti, W, and Cr. The choice of these metals is motivated by their midgap barriers and compatibility with an integrated circuit technology. For these, a thorough investigation of the variation in Schottky-barrier height and contact resistance is carried out for the following process parameters: 1) predeposition wafer preparation, 2) deposition method (sputtering and e-beam evaporation), 3) deposition temperature for the sputtered samples, and 4) annealing. It is found that RF etching previous to metal deposition increases the contact resistance and the barrier height for diodes on p-type silicon. This is of great importance, since RF etching is a very common in situ cleaning process in microelectronic and microelectromechanical systems technologies. Annealing can be used to restore the values of barrier height and contact resistance on wafers exposed to the RF etching.     

Large-Area Direct Hetero-Epitaxial Growth of 1550-nm InGaAsP Multi-Quantum-Well Structures on Patterned Exact-Oriented (001) Silicon Substrates by Metal Organic Chemical Vapor Deposition

We employ a simple two-step growth technique to grow large-area 1550-nm laser structures by direct hetero-epitaxy of III–V compounds on patterned exact-oriented (001) silicon (Si) substrates by metal organic chemical vapor deposition. Densely-packed, highly uniform, flat and millimeter-long indium phosphide (InP) nanowires were grown from Si v-grooves separated by silicon dioxide (SiO₂) stripes with various widths and pitches. Following removal of the SiO₂ patterns, the InP nanowires were coalesced and, subsequently, 1550-nm laser structures were grown in a single overgrowth without performing any polishing for planarization. X-ray diffraction, photoluminescence, atomic force microscopy and transmission electron microscopy analyses were used to characterize the epitaxial material. PIN diodes were fabricated and diode-rectifying behavior was observed.     

纳秒激光去除铝板表面漆膜热力学过程分析

为了研究并分析纳秒脉冲激光去除金属表面漆膜的机理,采用1064nm的纳秒激光对涂有漆膜的铝板样品进行了单脉冲辐照实验。依据热传导理论分别模拟出作用过程中漆膜以及铝板表层的温度分布,计算出漆膜与铝板界面处由于铝板基底热膨胀而产生的分离力,并分析了等离子体冲击波对去除漆膜的影响。结果表明,纳秒激光去除漆膜时力的作用为主导,其中热膨胀产生的分离力为漆膜的去除提供必要条件,漆膜对激光等离子体的约束最终导致其自身断裂和剥落。采用热力学理论对纳秒激光去除金属表面漆膜机理进行分析是可行的。     

采用ECR-PEMOCVD方法进行立方和六方GaN单晶薄膜生长的准热力学模型和相图

基于热力学平衡理论,对在电子回旋共振等离子体增强金属有机化学气相沉积系统中的GaN薄膜生长给出了一个化学平衡模型.计算表明,GaN生长的驱动力Δp是以下生长条件的函数:Ⅲ族输入分压,输入Ⅴ/Ⅲ比,生长温度.计算了六方和立方GaN的生长相图,计算结果和我们的实验结果显示出一定的一致性.通过分析,解释了高温和高Ⅴ/Ⅲ比生长条件适合六方GaN的原因.上述模型可以延伸到用于GaN单晶薄膜生长的类似系统中.     

对抛光片清洗技术的研究

研究了一种新颖的添加了表面活性剂和HF的RCA的改进工艺,并和标准RCA工艺与目前被广泛采用的稀释RCA工艺进行了比较后指出,改进工艺对金属沾污和表面颗粒的有效去除能力,使0.18um以上的颗粒能够控制在15颗以内,金属沾污能够有效降至109原子cm-2以下(Al略高小于1010cm-2).     

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     

Characterization of oxide etching and wafer cleaning using vapor phase anhydrous hydrofluoric acid and ozone

A cleaning process using anhydrous hydrofluoric acid/methanol (AHF) and ozone was carried out in a vapor phase cleaning module (VPC). The dependence of the AHF vapor phase etch rate of thermally grown silicon dioxide on different process parameters, such as etch time, AHF-flow and temperature was studied. The optimized etch process is attained at a temperature of 40°C and a pressure of 50 mbar. To demonstrate the feasibility of this cluster tool for advanced gate dielectric formation, investigations on surface properties after AHF vapor cleaning, such as contact angle measurement and atomic force microscopy (AFM) were carried out. Using XPS, the surface binding states of HF-vapor treated silicon surfaces were studied. Traces of fluorine and low oxygen coverage were monitored. An ozone treatment immediately after AHF cleaning increases significantly the fluorine concentration on the silicon surface. A beneficial impact of AHF and ozone on the electrical characteristics of 4 nm oxide films grown in oxygen by RTP in a cluster tool immediately after cleaning without breaking the vacuum was found.