Wafer Cleaning Research Articles

Evaluation of Very Dilute Alkaline Solutions for Wafer Cleaning with Megasonic Irradiation

In the semiconductor wafer cleaning, ammonium hydroxide based APM (ammonium peroxide mixture) has been widely used to remove particles and organic contaminants [. However as the film thickness and line width of semiconductor structure scales down rapidly, the material losses by etching reaction of alkaline chemicals can cause serious problem in yield loss due to electric failure. The presence of H2O2 could enhance the material loss on silicon wafer. Very dilute alkaline chemicals might be of interest since it could minimize any possible ionic contamination or chemical residues from chemicals as long as we control the surface roughness and particle removal efficiency. Also the characterization of these very dilute alkaline chemicals will be very useful for particle removal in gas dissolved DI water.

Novel Cleaning Method of SiC Wafer with Transition Metal Complex

In this article, we report a new cleaning method for silicon carbide (SiC) wafers. We found that the dipping treatment in hydrogen fluoride (HF) solution damages the SiC in the “RCA cleaning process”, so we have designed a new cleaning method that does not use HF and reduced the cleaning process to three steps. The characteristic factor of this new method is using a transition metal complex. Generally, no metals have been used for wafer cleaning, but we deliberately used metal and found it could clean the wafer surface very well. After cleaning, the atomic force microscope (AFM) and “Candela” images showed that the particles on most parts of the SiC surface had been removed and the contact angle for ultra-pure water became very low.

Static Charge Induced Damage during Lightly Doped Drain (LDD) by Single Wafer Cleaning Process

The present work reports some approaches to reduce the static charge defects induced during single wafer cleaning process. Increase conductivity of DIW with CO2, adding backside rinse and IPA drying sequence optimization were evidenced to be effective by surface potential difference with Quantox tool. TEM and EELS were also used for analysis of volcano-like discharge defects.

High Efficiency Single Wafer Cleaning for Wafer Bonding-Based 3D Integration Applications

Current work describes development, testing and verification of a single wafer megasonic cleaning method utilizing a transducer design that meets the extreme particle neutrality, Particle Removal Efficiency (PRE), and repeatability requirements of production scale wafer bonding and other applications requiring extremely low particle levels.

Optimum design of reverse osmosis systems for hydrogen peroxide ultrapurification

AbstractThis work is focused on the optimization of a reverse osmosis network proposed for the ultrapurification of chemicals, from technical grade to semiconductor grades demanded in electronic applications that require the use of high‐purity wet chemicals in the semiconductor manufacturing, as it is the case of hydrogen peroxide that is commonly used in the wafer cleaning and surface conditioning processes. An industrial installation able to produce simultaneously the five different Semiconductor Equipment and Materials International Grades of hydrogen peroxide is represented by a simplified superstructure configuration formulated as a nonlinear programming problem. The network integrates reverse osmosis membrane modules, mixers, and split functions, defined by the equations of mass balances and the Kedem–Katchalsky transport model for the description of the permeate flux and the metal rejection coefficients at each membrane stage. The objective of the design is to maximize the daily profit obtained from the sale of the electronic grades of hydrogen peroxide produced by the ultrapurification system. © 2012 American Institute of Chemical Engineers AIChE J, 2012

Study of Bubble Activity in a Megasonic Field Using an Electrochemical Technique

In the megasonic cleaning of wafers, size and motion of cavitating bubbles and fluid flow due to acoustic streaming play a very important role. In this paper, chronoamperometric technique has been used to seek information on acoustic streaming and bubble activity in a 1 MHz sound field. Specifically, current transients during reduction of potassium ferricyanide were recorded. Data collected at 1-6 MHz sampling rate using a 25 μm platinum electrode show current “peaks” indicative of the approach of oscillating bubbles to the electrode and current “valleys” due to blocking of the electrode by bubbles. Acoustic streaming velocity ( ~ 1.5 cm/s) and bubble size (maximum radius of ~ 1 μm for oscillating bubbles) have been estimated from local current transients caused by bubble activity near the electrode.

Effect of Pump Pulsation on Particle Contamination on Wafer Surface in Wet Cleaning System

The effects of pumping method on wafer cleaning were investigated. Two types of pump such as diaphragms and centrifugal were used for circulation and supply of DI water for wafer cleaning in both wet bath and single wafer tool. The cleaning studies show that the pumping methods have a great influence on cleaning performance. The experimental investigations reveal that the number of added particles on the wafer during wafer cleaning is much lesser in MLC pump (non-pulsation flow) than the both diaphragm pumps (pulsation flow).

Ultrasound Cleans with a Twist

A rapidly expanding and collapsing microbubble in a fluid exerts forces strong enough to roll submerged particles stuck to a solid surface, which may explain how ultrasonic cleaning of jewelry and silicon wafers in a liquid removes dirt.

Effects of Ultrasonic Cleaning on Carrier Lifetimes and Photovoltage in Monocrystalline Silicon

Effects of a kHz-frequency ultrasonic cleaning of silicon wafers on free carrier lifetimes and the photovoltage magnitude are addressed. It is found that the initial photovoltage decay, taken before ultrasonic treatments, can be fitted to a double-exponent form, exhibiting the involvement of shorter- and longer time recombination and trapping centers. The decay speeds up remarkably due to the treatment, and the rapid component of the decay grows at the expense of the slow component. It is also found that, before the treatment, the decay time is markedly non-uniform over the wafer surface, implying the existence of distributed sites affecting carrier lifetimes. The cleaning causes an overall smoothening of the lifetime distribution, which is accompanied by the above shortening. A likely explanation of the effects is based on two facts: (i) the cavitating bubbles are capable of locally removing the surface oxide layer affecting the dangling bonds on the bare Si surface, and (ii) the oxygen and hydrogen, decomposed in water at elevated pressures and temperatures occurring inside a cavitating bubble, can micro-precipitate the Si wafer thus affecting the recombination rate.

Plasma-aided fabrication in Si-based photovoltaic applications: an overview

Plasma-aided fabrication has been largely employed in the photovoltaic industry and widely reported in the literature for the growth of Si-based solar cells and the dry etching of Si substrates. This paper reviews the current status of plasma technologies for the synthesis of Si-based thin films (including silicon nitride: SiN) and solar cells, removal of phosphorus silicate glass or parasitic emitters, wafer cleaning, masked or mask-free surface texturization and the direct formation of a p–n junction by means of p-to-n type conductivity conversion. The plasma physics and chemistry involved in these processes and their fundamental mechanisms are briefly discussed. Some examples of superior performance and competitive advantages of plasma processes and techniques are selected to represent a range of applications for solar cells. Finally, an outlook in the field of plasma-aided fabrication for photovoltaic applications is given.

초음파장내 파괴적인 기포의 운동 가시화

The bubble oscillations play an important role in ultrasonic cleaning processes. In the ultrasonic cleaning of semiconductor wafers, the cleaning process often damages micro/nano scale patterns while removing contaminant particles. However, the understanding of how patterns in semiconductor wafers are damaged during ultrasonic cleaning is far from complete yet. Here, we report the observations of the motion of bubbles that induce solid wall damage under 26 kHz continuous ultrasonic waves. We classified the motions into the four types, i.e. volume motion, shape motion, splitting or jetting motion and chaotic motion. Our experimental results show that bubble oscillations get unstable and nonlinear as the ultrasonic amplitude increases, which may exert a large stress on a solid surface raising the possibility of damaging microstructures.

Plasma Cleaning Effect on Automotive Devices

In today's semiconductor market of the growing automotive industry, reliability of the devices becomes a major concern as all these devices require an extremely low stress and high thermal condition. This paper will discuss the critical characteristics that are responsible for the die top corner delamination and focuses mainly on a few key areas such as molding compound, wafer and plasma cleaning process so as to enable the achievable of reliable and robust package for automotive products. The devices are to be characterized with scanning acoustic tomography (SAT) and various package level reliability tests. From the study, it has been found that plasma cleaning process plays an important role in resolving the reliability issue by totally eliminating die top corner delamination, and which has improved tremendously in the life span of the devices and also the reliability of the packages.

Abrasive electrochemical multi-wire slicing of solar silicon ingots into wafers

To meet the growing demands of the global photovoltaic (PV) industry, preparing large scale and ultra-thin solar wafers becomes one of the key issues. This paper presents the preparatory investigations of slicing solar silicon ingot into wafers by an abrasive electrochemical method based on a multi-wire saw system. The anodic passivation on silicon can be controlled by applying an anodic potential during the mechanical slicing process, which improves the surface integrity and material removal rate remarkably. This new hybrid machining method has no influence on subsequent cleaning of wafers and preparing the solar cells, and the average photoelectric transformation efficiency is >17.5%.

Control of sonoluminescence signal in deionized water using carbon dioxide

Megasonic cleaning is routinely employed in semiconductor industry for cleaning of wafers. However, the method also results in damage to wafer features and such damage has been proposed to arise from transient, imploding cavities formed during megasonic processing. Transient cavitation is associated with the release of light, a phenomenon called sonoluminescence (SL) and the extent of damage has been shown to correlate with the intensity of SL. Control of sonoluminescence may therefore allow control of damage during megasonic processing of wafers. In this study, the ability of carbon dioxide to quench sonoluminescence generation in deionized water exposed to megasonic field of varying power density and duty cycle has been systematically investigated. It has been found that CO 2 is not only incapable but also a potent inhibitor of sonoluminescence, providing a potential means for selective alleviation of the violent effects of transient cavitation in process fluids. A novel chemical method has been established for in situ release of CO 2 from NH 4HCO 3 through a pH induced shift in the carbonic acid equilibria in deionized water. Using this method, a precisely controlled, progressive decrease in SL of air saturated deionized water through addition of NH 4HCO 3 has been demonstrated. It has been determined that 130 ppm of released CO 2 is sufficient for complete inhibition of sonoluminescence generated in air saturated deionized water.

Analysis of Impact on the Wafer Surface Performance of Supercritical CO<sub>2</sub> Extraction

The surface of the wafer is easy to be polluted by the organic pollution material. The supercritical fluid extraction technology works well in extracting organic pollution material. Whether the extraction process influences the surface performance of the wafer can be determined through the SEM(scanning electron microscope), AFM (atomic force microscope), and XPS (X-ray photoelectron spectroscopy). Compare the feature and the electronic structure of the wafer before and after supercritical CO2 extraction to get how supercritical CO2 extraction process influences the wafer surface performance. The conclusion helps to determine whether the extraction technology can be applied in the wafer surface cleaning technology. Tests show that supercritical CO2 extraction process almost does not influence the surface performance of the wafer, and, the supercritical CO2 extraction technology has a good prospect in the wafer cleaning.

Meniscus-Shear Particle Detachment in Foam-Based Cleaning of Silicon Wafers with an Immersion/Withdrawal Cell

New experimental data collected at Lam Research Corporation and theoretical analyses are presented for aqueous-foam cleaning of silicon wafers contaminated with strongly adhered 90 nm Si 3 N 4 particles (Freer et al. 2010). We analyze the distribution of contaminant removal along the wafer surface and the influence of foam quality in a vertical rectangular slot upon wafer immersion/withdrawal. At zero foam quality, particle removal along the wafer surface is uniform. Increased foam quality leads to improved overall removal. Removal, however, is no longer uniform with larger detachment rates toward the bottom of the wafer. To explain the observed nonuniform particle removal, we adopt a binary-collision model that demands a linear dependence of removal rate on the surface shear rate. Perturbation analysis provides the distribution of the wall shear rate along the wafer surface in an unfoamed solution. Calculations show that the wall shear rate on the wafer surface is strongly peaked in the meniscus just above the liquid-filled slot. Thus, with no foam present, removal in the meniscus zone dominates the overall removal process. Because the time of exposure to this high shear is the same for all parts of the surface, we obtain uniform cleaning. With foam bubbles present, the wall shear rate in the slot is enhanced, leading to significant removal in the bulk of the slot. Because the residence time of a wafer in the bulk cleaning solution varies for different parts of the wafer, contaminant removal in the bulk of the slot depends on the vertical position. Combined particle removal in the meniscus zone and in the slot leads to the observed nonuniform distribution of contaminant particles remaining on the wafer surface. Increasing foam quality increases the slot wall shear rate and, hence, the removal rate inside the immersion/ withdrawal cell.

Dry plasma processing for industrial crystalline silicon solar cell production

This paper gives an overview on the standard crystalline silicon solar cell manufacturing processes typically applied in industry. Main focus has been put on plasma processes which can replace existing, mainly wet chemical processes within the standard process flow. Finally, additional plasma processes are presented which are suited for higher-efficient solar cells, i.e. for the “passivated emitter and rear cell” concept (PERC) or the “heterojunction with intrinsic thin layer” approach (HIT). Plasma processes for the deposition of thin dielectric or semiconducting layers for surface passivation, emitter deposition or anti-reflective coating purposes are presented. Plasma etching processes for the removal of phosphorus silicate glass or parasitic emitters, for wafer cleaning and masked and mask-free surface texturisation are discussed.

Influence of Cr+ ion implantation and pulsed ion-beam annealing on the formation and optical properties of Si/CrSi2/Si(111) heterostructures

The effect of pulsed ion-beam annealing on the surface morphology, structure, and composition of single-crystal Si(111) wafers implanted by chromium ions with a dose varying from 6 × 1015 to 6 × 1016 cm−2 and on subsequent growth of silicon is investigated for the first time. It is found that pulsed ion-beam annealing causes chromium atom redistribution in the surface layer of the silicon and precipitation of the polycrystalline chromium disilicide (CrSi2) phase. It is shown that the ultrahigh-vacuum cleaning of the silicon wafers at 850°C upon implantation and pulsed ion-beam annealing provides an atomically clean surface with a developed relief. The growth of silicon by molecular beam epitaxy generates oriented 3D silicon islands, which coalesce at a layer thickness of 100 nm and an implantation dose of 1016 cm−2. At higher implantation doses, the silicon layer grows polycrystalline. As follows from Raman scattering data and optical reflectance spectroscopy data, semiconducting CrSi2 precipitates arise inside the silicon substrate, which diffuse toward its surface during growth.

Silicon Wafer Cleaning Using New Liquid Aerosol with Controlled Droplet Velocity and Size by Rotary Atomizer Method

A liquid aerosol, which sprays cleaning liquid with a carrier gas, is widely used for cleaning semiconductor devices. The liquid aerosol using a conventional two-fluid nozzle may cause pattern damage on the wafer. To resolve this problem, we have made a prototype new rotary atomizing two-fluid cleaning nozzle (RAC nozzle), which can control the velocity distribution and size distribution of flying liquid droplets separately. It was confirmed by measuring flying liquid droplets using a shadow Doppler particle analyzer system that the mean volumetric diameter of the droplets could be atomized to 20 µm or less at a rotational speed of the air turbine of 50,000 min-1 and that the mean velocity of the flying liquid droplets could be controlled in the range under 65 m/s independently. It was confirmed in a cleaning experiment using polystyrene latex (PSL) particles on a wafer that particle removal efficiency increased when shaping air pressure increased. Also, the particle removal efficiency was improved with the finer atomization promoted by a higher rotational speed of the air turbine.

Acoustic energy radiated by nonlinear spherical oscillations of strongly driven bubbles

Based on the theory of F. Gilmore (Gilmore 1952The growth or collapse of a spherical bubble in a viscous compressible liquid) for radial oscillations of a bubble in a compressible medium, the sound emission of bubbles in water driven by high-amplitude ultrasound is calculated. The model is augmented to include expressions for a variable polytropic exponent, hardcore and water vapour. Radiated acoustic energies are calculated within a quasi-acoustic approximation and also a shock wave model. Isoenergy lines are shown for driving frequencies of 23.5 kHz and 1 MHz. Together with calculations of stability against surface wave oscillations leading to fragmentation, the physically relevant parameter space for the bubble radii is found. Its upper limit is around 6 μm for the lower frequency driving and 1–3 μm for the higher. The radiated acoustic energy of a single bubble driven in the kilohertz range is calculated to be of the order of 100 nJ per driving period; a bubble driven in the megahertz range reaches two orders of magnitude less. The results for the first have applications in sonoluminescence research. Megahertz frequencies are widely used in wafer cleaning, where radiated sound may be implicated as responsible for the damage of nanometre-sized structures.