ABSTRACTS
The following is a list of the abstracts for papers which will be presented in INTERNATIONAL SYMPOSIUM ON SURFACE CONTAMINATION AND CLEANING. The listing is alphabetical by presenting author. This list is updated continually to add abstracts as they become available and to make appropriate corrections. This list may be conveniently searched by using the editor provided with most popular browsers (e.g. Microsoft Explorer, Netscape, ... etc.)
Slurry Removal from Blanket Wafers: a Useful Tool for Post-CMP Cleans Process Development
The use of CMP processes in the semiconductor industry continues to expand, enabling advanced manufacturing techniques such as metal damascene, shallow trench isolation, and the formation of three-dimensional capacitors. For all such processes, efficient removal of slurry is required to obtain low defect levels and high yields. Ultimately, the performance of any post-CMP cleaning process must be evaluated using real product wafers. Leading up to product tests, there are many types of experiments using blanket wafers and generic topography wafers. Blanket wafer experiments are reviewed here. Several different substrate films, contamination methods, slurry components, cleaning techniques, process parameters and metrology techniques are described and compared.
Ultrasonic Cleaning of Delicate Surfaces and Miniature Components
Ultra-cleaning of surfaces with ultrasonic requires a thorough assessment, evaluation of materials and contaminants followed by testing and validation of all process parameters.
Main process parameters include ultrasonic frequency, power intensity and component handling. Cleaning chemistry is a crucial factor in achieving high levels of cleanliness.
Surface of Silicon Chemical composition Cleaning Using Clean Solutions With Surfactants and Chelates
This paper reports a new type of semiconductor cleaning detergents and cleaning technique using clean solution with surfactants and chelates. The results of cleaning using the new type of cleaning technique and the RCA standard cleaning technique are compared. The results are the silicon surface chemical composition obtained by X-ray photoelectron spectra and infrared absorption spectra. The measurement results show that a thin layer of oxide in the act of their cleaning is grown.. Two types of cleaning technique produces organic carbon contaminants, but the new technique is significantly less than the RCA standard system. .
Contamination of Cast Iron Lapping Surfaces By Abrasive Micrograins
The high demands required today by design engineers for machine parts and tools necessitates very precise machining. The lapping process leads to a surface with low roughness and high precision. The topographical structure of the surface after lapping is very advantageous for sliding joints because of the high lubricant retention ability, as well as in non-sliding joints because of the high load - carrying ability. The range of lapped materials is very wide. This situation requires the use of natural and artificial abrasive materials and mainly such materials as micrograins of alumina, silicon carbide, boron carbide and diamond. Solid and liquid carriers distribute the micrograins on the surface of the lapping tool arid the chemical active components make the machining more intensive.
One of the main disadvantages of lapping is the contamination of machined surfaces by micrograms of the abrasive material. The rnicrograin s embedded into the machine surface during coarse lapping enter the „machining" zone during fine lapping. During service, contaminated surfaces are objected to excessive wear.
Since surface contamination is harmful and the methods of removal of the embedded micrograms are ineffective, the intensity of the contamination should be reduced as much as possible during the lapping process. The indentation of abrasive material into a machined surface should be considered as an element of general behavior of abrasive micrograins including position of the micrograins, their size, shape as well as the physical and mechanical properties of the machined material and the lapping tool. The pressure and the lapping speed are also important.
In the present investigation, surfaces contaminated by abrasive micrograins have been studied with an electron microscope and a microanalyzer. The combination of microscopy with X-ray analysis permits the study of secondary electron images and the X-ray images of the same spot on the sample. The statistical size of abrasive slurry micrograins was estimated by means of an automatic image analysis (TV image analysis).
Investigation of Modified SC-1 Solutions
The RCA clean is widely used in the semiconductor industry for many wet-chemical cleaning processes. The RCA clean consists of a particle removal step, the Standard Clean 1 or SC-1 and metallic impurity removal step, the Standard Clean 2 or SC-2 step. In this work we have investigated the addition of chelating agents in SC-1 solutions to prevent metallic deposition during the SC-1 step as well as remove metallic contamination. We also have studied the effect of surfactants in such solutions on sub-micron particle removal. This leads to the development of a very fast and efficient single step RCA replacement clean. The use of a single step cleaning strategy in a single wafer mode dramatically reduces the cycle time of cleaning.
1) ERA Systems, 50 North Crest Rd., P.O. Box 3609, Chattanooga, TN 37404-0609
2) Honeywell FM&T, Dept. 833, MS 2C43, P.O. Box 419159, Kansas City, MO 64141-6159
A New Method Using MESERAN™ Technique for Measuring Surface Contamination after Solvent Extraction
(Abstract not yet available)
Best Practices for an Aqueous Washer
This presentation will cover a broad range of discussion for an aqueous washer. The best practice design for a washer can greatly assist in meeting the cleanliness specifications in a timely fashion to meet the production volume demand. It can also enhance the performance of your washer. The best practices discussed will include the design concept, some of the major options for the washer, and critical role of operator's training along with preventive maintenance.
Influence of Cleaning on the Surface of Model Glasses
The influence on glass of wet and dry cleaning processes impacts the glass surface composition. We probe the alteration of glass surface chemistry by wettability measurments as a function of pH. The wettability measurments are performed using the two liquid method, depositing sessile water drops under liquid octane. The measured wettabilities allow the estimation of the number of hydroxyl groups exposed at the glass/water interface. Measurements with varying pH of the water drops probe the surface charge at the glass surface and indicate the isoelectric points of predominant functional groups. The variations in glass surface composition correlate to the sensitivity of the glass surfaces to the adsorption of organic contamination. Three typical species of glass are probed: a silica surface, the surface of sodalime glass, and the surface of an aluminoborosilicate glass. The three glass species show different contamination behavior, as a function of wet or dry cleaning of the glass. The surface compositions, as probed by wettability measurments, are correlated to grazing incidence XPS data, indicating the alteration of surface chemical sites by leaching during the acidic wet cleaning process. It appears that sensitivity to organic contamination is controlled by the surface chemistry of the exposed substrate.
Qualifying a Cleaning system for Space Flight Printed Wiring Assemblies
During the last decade, the challenges of printed wiring assemblies (PWAs) have grown tremendously. Today printed wiring boards have grown more complex to meet the continuing challenges posed by the increasing uses of microdevices such as ball grid arrays and microball grid arrays. Multilayer boards with a large layer count and narrow trace widths and spaces are commonplace. The ball grid arrays, microball grid arrays, and other small devices generally have a large number of I/Os, small standoffs, and small pitches. The small standoff and small pitch, coupled with the complex circuitry needed to route such components, makes cleaning an ever more critical operation. High reliability PWAs cannot tolerate contaminants since their presence can potentially degrade the board, thus compromising the intended mission. Cleaning for high performance PWAs is normally performed as a minimum at the following stages:
1) At the bare PWB stage prior to the application of solder mask;
2) Immediately after the application of flux or paste;
3) Immediately prior to the application of conformal coating.
If the PWAs are properly stored, the second and third operation are sometimes combined. In addition to cleaning, some sort of cleanliness verification method is employed to ascertain that a certain level of cleanliness has been achieved. The most common cleanliness verification method has been ionic contamination testing using an industry-recognized device such as an Ionograph® or Omega-Meter®. Today, however, determining the amount of residual rosin (assuming that a rosin-based flux or paste was used) is often done. Another useful technique is to remove some of the components and examine for flux residues both visually and by use of a microscope.
In addition to all this, the last decade has also seen the dramatic decrease and continuing disuse of ozone-depleting solvents. The common chlorofluorocarbon solvents, such as Freon® TMS, have been discontinued, and many PWA assemblers have switched to more environmentally friendly cleaning agents, such as a wide variety of semi-aqueous and aqueous-based materials. To enhance the performance of such materials, the proper equipment selection plays a critical role.
This paper addresses a centrifugal cleaning system used in conjunction with a water-based cleaning medium to achieve optimally low levels of contaminants on PWAs. Ionograph data, ion chromatography profiling, residual rosin determination, and outgassing data are presented demonstrating the effectiveness of the centrifugal cleaning system and the cleaning agent for space flight printed wiring assemblies.
A Comparison of the Efficacy of Surface Cleaning as Monitored by Electron Spectroscopy for Chemical Analysis (ESCA) and Micro-Fourier Transform Infrared Spectroscopy (FTIR)
Two main issues in surface cleanliness are, defining how clean is clean enough and how to reproducibly measure the level of cleanliness. The degree of cleanliness required is related to the materials used in a
product, the manufacturing processes required and ultimately the final use of the product. Very different devices from sophisticated arid expensive micro electronics and surgical implements to disposable and inexpensive
razor blades, bioassay sample trays and plastic or metal foil packaging material require similarly high levels of cleanliness.
This paper discusses and compares the use of two different analytical techniques used as stand alone and in concert cleanliness rnonitoring tools. The ability of each technique to: qualitatively determine the presence of
contamination; identify it; determine how much of the contamination is present: and how thick (from monolayers to microns) it is, will be presented for a variety of materials.
How Clean Is Clean? Monitoring Cleanliness and Defining Acceptable Cleanliness Levels
Defining and maintaining a "proper" level of surface cleanliness is, at best subjective. For consistent results, it is important to define how "clean" is clean. Often the failure of surface preparation processes is not discovered until problems, such as poor adhesion, occur down stream. To assure consistent quality of surface cleanliness, it is important to: understand the types of contaminants that need to be monitored, most common cleanliness monitoring methods, their strengths and limitations and, factors to be considered in choosing appropriate cleanliness monitoring method/s, and cost impact of various cleanliness levels. . In addition, two approaches to defining acceptable levels of surface cleanliness will be discussed.
Selection of cleanliness monitoring method, as a minimum, should take into account the type of substrate and the types of contaminants to be monitored, desired level of cleanliness, speed of measurement, operator skill level required and acquisition & operating costs. In addition, it is very important that the cleanliness monitoring method be quantitative, non-destructive and readily useable.
The cost of non-conformance rate corresponding to the cost of each level of cleanliness is defined as "total cost" of cleaning. An acceptable level of cleanliness is the one that minimizes or optimizes that "total cost".
1) Evans East, 104 Windsor Center, Suite 101, East Windsor, NJ 08520
2) Evans PHI, 6509 Flying Cloud Drive, Eden Prairie, MN 55344
3) Charles Evans & Associates, 810 Kifer Road, Sunnyvale, CA 94086
Submicron Particle Analysis on Surfaces by Raman and Auger Spectroscopies
Historically, particle analysis has been accomplished by direct analysis using microprobe techniques such as Energy dispersive x-ray spectroscopy (EDS) and micro Fourier Transform Infrared Spectroscopy (m-FTIR), or by indirect analysis using a variety of bulk methods after dissolving or digesting the particles. These methods generally require particles larger than several microns or many smaller particles. Advances in the aerospace, optical, and semiconductor industries have pushed the critical defect size below one micron, thus necessitating the use of alternative methods. This paper will demonstrate the use of Raman Spectroscopy and Auger Electron Spectroscopy (AES) for particles having at least one submicron dimension. In Raman spectroscopy one typically employs the 488 nm (blue) and 515 nm (green) lines of an argon ion laser as the molecular probe. This permits fingerprint analysis of particles as small as 0.5-1.0 mm in comparison with m-FTIR which requires particles 10-15 mm. The surface sensitivity (< 100Å) and high spatial resolution (100-200Å) of AES results in a small analysis volume relative to EDS. Consequently AES provides far superior sub-micron elemental analysis. Both of these methods benefit from the ability to handle large samples in tack thereby limiting contamination due to sample preparation.
Improve Efficiency with CO2 Blasting
Surface cleaning by carbon dioxide blasting is becoming more prevalent and advantageous in many industries. From a Scientific curiosity to a work-horse industrial cleaning solution, CO2 Clean blasting is the optimum method for many surface cleaning applications. This paper will discuss the important areas of greatest efficiency as well as some of the promising areas that have not survived the test of application.
Microdenier Fabrics for Cleanroom Wipers
Advancing microelectronics technology continues to require improvements in cleanroom techno!ogy. In Europe and Asia adoption of microdenier cleanroom Wipers has progressed more rapidly than in North Arnerica. Microdanier fibers are much smaller than the fibers used in conventional cleanroom wipers. Simple analyses of scale can demonstrate some of the reasons to prefer microdenier fabrics. These finer fabrics have a greater affinity for water than do the less fine. In some cases , they are more porous than would be expected from simple scaling arguments. Some microdenier fibers have angular rather than rounded profiles, which could enhance wiping effectiveness. Scale considerations also indicate a much larger surface area for microdenier wipers, which may require enhanced laundering. Current microdenier technology is best combined with effective laundering to produce cleanroom cleaning materials that can take advantage of the fine features of the wipers without having cleanliness issues. Data are presented to illustrate the importance of laundering microdenier fabrics.
Cleaning Particles from Parts by Adding Soil!
Recent work in continuous cleaning with ultrasonics has shown the power of a concept called "sacrificial soil." This is not cleaning with cavitation bubbles. Rather pressure waves from a transducer produce a mechanical emulsion of organic soils and water on the parts. The emulsion scavenges particles from the part surface. In industrial cleaning, this has been shown to be a very effective technique in removing both larger particles [>10 micron], metal scales, and carbonized organic materials.
Flo-Matic [Bellvidere, IL] have applied for a patent of this technology. This paper is about their initial application of it to removal of small (< 1 micron] particles from critical surfaces.
The key concept is that through use of a removable emulsion, we can affect conditions beneath a boundary layer and on a part surface. Normally, this is very difficult by flow-based means.
This paper will describe the results of the application, including: construction of a new apparatus, methodology behind selection of various sacrificial soils, nature of the rinsing equipment, preliminary testing of the apparatus at a manufacturer of surfaces which must be particle-free, and results of those tests.
Characterization of Surface Free Energies and Surface Chemistry of Solids
(Abstract not yet available)
Fine Particle Detachment Studied by Reflectometry and Atomic Force Microscopy
Optical Reflectometry was used to study the attachment and subsequent detachment of silica particles (diameter 25 nm) from the surface of titanium dioxide wafers under well-defined hydrodynamic conditions. The rate of detachment and maximum detached amount was studied as a function of both pH and added linear polyphosphate concentration. The latter has the general formula [PnO3n+1](n+2)- where n is the number of phosphate atoms in the molecule. The maximum detached amount increased with pH. The maximum detached amount also increased with both polyphosphate concentration and n.
Atomic Force Microscopy was used to measure the interaction between silica spheres (diameter 7mm) and titanium dioxide wafers under the same solution conditions. The detachment force needed to separate the surfaces decreased with increasing pH and with n in direct agreement with the Reflectometry data. It was shown that, in addition to repulsive electrical double layer forces, adsorbed polyphosphates provide a short-ranged steric layer that reduces the lateral interaction between the surfaces. The use of these two complementary techniques has given valuable insight into the processes responsible for fine particle detachment and has particular application to surface cleaning.
1) Engineering Sciences Center, Sandia National Laboratories, Albuquerque, NM 87185
2) Lithography, SEMATECH, Austin, TX 78741
Reduction of Lens Contamination in the Exitech 157 Nm Lithography Tool Through Transport Control
For the last few generations of lithography tools, there have been problems of fouling of the optics due to material outgassing from photoresist on the wafer. The deposition of the outgas material has either degraded the performance of the tool or required frequent cleanings or replacement of optical elements at great cost both in equipment and lost production. In order to expedite development of a 157 nm lithography process, SEMATECH, in collaboration with Exitech, has been developing a test stand to investigate outgassing from possible 157 nm photoresists. In order to get the most use out of the test stand and develop technology for production lithography tools, we studied the gas phase transport of outgas material from the photoresist to the final optical element with the goal of both understanding the mechanisms which control contaminant transport and reducing the fouling of optical elements in the SEMATECH tool. Assuming a constant generation of outgas material and diffusion controlled deposition on the lens, a model for the purge gas flow and material transport in the tool was developed. The fluid mechanics were solved using FIDAP, a finite element fluid dynamics package available from Fluent Int. Factors studied included purge gas flow rate, material diffusivity, aperture size, and height of nose cone. The results indicated that for many of the parameters there was an optimum operating range for which the transport of contaminant to the lens was minimized. Based on the numerical simulations, improvement of several orders of magnitude can be achieved, and early testing at SEMATECH has shown promising results.
Application of Ice Particles For Precision Cleaning of Sensitive
Surfaces
Entrainment of the ice particles by the waterjet and particles formation within the water stream was investigated. FIDAP package was used to determine probability of particles surviving in the course of the jet formation. Another part of the study was concerned with the use of the ice-air jet. It was demonstrated that at the optimal range of process conditions this jet constitutes a precision tool for selective material removal operations. Number of experiments was carried out in order to demonstrate this technology. Various electronic devices (computers, calculators, electronic games and watches) were disassembled and electronic boards were contaminated by grease and metal powder. Then the boards were cleaned and reassembled. The computer, calculators and watches worked normally. Other experiments involved degreasing, depainting and deicing of liquid crystals, polished metals, optical glass, fabric, removal emulsion from a film, etc. The feasibility of the damage free and pollution free decontamination of highly sensitive, highly countered surfaces was demonstrated. A low cost of ice-air cleaning will enable us to use it for processing large surfaces at a high rate. On-line degreasing of metal in the course of rolling or prior to machining illustrates this application. A generic environmentally friendly surface processing technology is emerging as the result of the presented study.
Newark, NJ 07102-1982
Development of a Technology For Fabrication of Ice Abrasives
The mission of this project was to develop a practical technology for formation of ice abrasive. In our previous works we demonstrated the effectiveness of the use of ice-air mixture as a cleaning media. However a practical technology for fabrication of ice particles of desired size and at a desired temperature in necessary for process implementation into industrial practice. The physical properties of ice (tendency to agglomerate, change of the size due to absorption of water and melting, etc.) make development of this technology extremely difficult. We developed a process for controllable generation of ice particles using a rotational crusher embedded into a heat exchanger. Water is supplied at the bottom of the heat exchanger and as it moves along the rotating auger ice particles are formed. Then the generated particles are entrained in the air stream. A refrigerant and liquid nitrogen were used as a cooling media. In the course of the operation the flow rate and the temperature of the of the refrigerant and speed of the auger rotation were kept constant while the rate of the water supply was changed. The temperature and the form of the particles were monitored in the course of this experiment. Further, we investigated the temperature distribution along the heat exchanger and the corresponding distribution of the particle size. The process phenomenology was developed and the design of a system for formation of the ice abrasive was suggested
Modeling of the Waterjet Cleaning
A practical procedure for modeling of the waterjet cleaning was presented. The procedure enables us to utilize all available information, both numerical and linguistic, for identification of the operational conditions. Several Neural Networks based prediction models were constructed using previously available information. Then a single parameter, the erosion strength was determined experimentally or by the use of an expert knowledge. The fuzzy logic technique enabled us to determine weight of each preliminary constructed model for the process in question. Thus the first approximation of the operational conditions are determined. In the course of further operation the developed model is improved. The developed procedure will assist a practitioner in the selection of a decontamination technology for an unknown surface.
Experimental and Numerical Investigtion of Waterjet Rust Removal Process
The study is concerned with development of effective technology for rust removal from a steel surface. We have investigated the surface derusting process using high-speed waterjet and determined the optimal operational conditions. The study involved topographical and metallographical examination of the surfaces of selected samples and subsequent classification of the substrates with respect to the degree of the rust development. Then rust was removed by the jet impact and the generated surfaces were examined. Soft computing techniques were used to select operational conditions of rust removal. Due to extremely chaotic and fuzzy nature of input information the advanced numerical procedure based on the method of the Neural Network Driven Fuzzy Reasoning was employed. As the result the realistic procedure of steel derusting was presented and practical technique of process design was suggested.
Methods for Pharmaceutical Cleaning Validations
There are many techniques that can be used for measuring residues in pharmaceutical cleaning validations. Choosing the appropriate "tool" to use depends on what residue is being measured, the way the sample was collected, and the level at which it is being determined. The available state-of-the art testing techniques will be described in detail along with the pros and cons of each. Comparisons of a variety of methods will be given as an example of choosing the most effective technique. The application of these techniques for actives, excipients, and cleaner residue analyses will be presented. The newest and established analytical techniques will be presented along with choosing the most appropriate method. Specific and non-specific techniques will be compared as will direct and indirect testing. Examples of validating methods will be given.
Decontamination of Sensitive Equipment
Most of the electronic and electro-optic equipment fielded by the military is incompatible with the standard aqueous based decontamination solutions, such as DS 2. ESI has developed a nondestructive decontamination process for such sensitive equipment. In this process, the components to be decontaminated are immersed in an ultrasonic bath filled with either HFE-7100, a hydrofluoroether, if they are contaminated with chemical warfare agents (CWA), or in a solution of a highly fluorinated surfactant in HFE-7100, followed by an HFE-7100 rinse, if they are contaminated with biological agents or radioactive particles.
In both cases, the contaminants are dissolved or suspended in the decontamination liquid in the bath. The contaminants are removed from the decontamination liquid by circulating it through a filtration train. In the case of CWA, the filtration train consists of an activated carbon filter, a particulate pre-filter, and a membrane filter. In the case of biological or nuclear contaminants, the circulating liquid bypasses the activated carbon beds.
It has further been found that substrates contaminated with biological species such as bacteria, bacterial spores, or fungi, can be sterilized by sonication in HFE-7100/fluorocarbon solutions, much in the same manner that radioactive particles are quantitatively removed from substrates by such solutions.
A prototype decontamination system has been built and operated to demonstrate the process. In this campaign, a wide range of sensitive equipment was contaminated with a fluorescent CWA simulant. This equipment tested included night vision binoculars, a digital camera, multi-meters, calculators, a notebook computer, a GPS receiver, and an automatic pistol. The contaminated equipment was immersed and sonicated in flowing HFE-7100, which recirculated around a purification loop, until the fluorescent simulant could no longer be detected (i.e. at a concentration level of less than 100 ppt), and dried. The decontaminated equipment was then functionally tested. In all cases:
a. no traces of simulant were found on the processed pieces, and
b. the processed items were fully functional
The process equipment that is required to operate the process also has a dual use, in that it could be used to clean and maintain this type of sensitive equipment on a routine basis, which could carry most of the cost of amortizing this process equipment.
Particle Removal Using Resonant Laser Desorption
A new photonic cleaning process that minimize system cost and exposure of the substrate to excess laser fluences is introduced. The unique Resonant Laser Desorption (RLD) technology is described. The RLD process uses a laser light source with frequency intensity modulation to remove sub-micron contamination particles from a substrate. Unlike other laser removal methods, which launch the particle from the surface with a single high-intensity laser pulse, RLD uses a continuous series of low-intensity laser pulses. The timing and shape of these laser pulses are engineered to exploit certain kinematic properties of the particle-surface system and laser-material interactions. Early theoretical and experimental data suggest a correlation between system resonant frequency and the particle separation mechanism. The projected result is an efficient particle removal mechanism that imparts minimum stress and heat loading to the underlying substrate
Surface Contamination and Precision Cleaning in Hard Disk Drive Fabrication
Minimizing contamination of rigid disk drive components is critical to obtaining high yields. Both particle and thin film contamination can cause drive failures due to events such as thermal asperities or stiction. Despite contamination-free manufacturing practices, particle contamination continues to be the leading cause of drive failures. As capacities increase and feature sizes shrink to 0.05 p,m or smaller, removal of contaminant submicron particles and films throughout the manufacturing process will become critical to drive fabrication and performance. These particles adhere very strongly to the surface and can be removed only by physical contact. Aqueous cleaning with ultrasonic and megasonic agitation is a well established cleaning method. However, the inherent physical limitations of water with high viscosity and surface tension make aqueous cleaning less effective for removing submicron particles from parts with complex geometries. To overcome these limitations of aqueous cleaning, several non-aqueous precision cleaning techniques have been developed for removing small particles and/or contaminant films. Other techniques are in pre-commercialization or research and development stages. These alternative methods can help meet the current and future cleaning needs of the drive industry. The advantages and limitations of these techniques for precision cleaning will be discussed.
The Impact of Ultrasonic Frequency on Particle Removal
(Abstrtact not yet available)
Safer and Greener Solvents in Surface Cleaning
Traditional solvent-based cleaning and degreasing agents pose well-established environmental, health and safety hazards. Finding effective, environmentally-friendlier cleaning methods, however, has proven to be no easy task.
This presentation chronicles five years of laboratory research into organo/chlorinated solvent substitution and offers a systematic approach, the first of its kind to cover a wide range of manufacturing applications in such specificity. It theorizes that a test data/ material's information methodology will assist governments, companies, scientists and cleaning practitioners in their quest for more sustainable cleaning chemicals and processes. A proposed web-based tool to support environmental decision-making will be described. This interactive matrix is (1) rooted in actual performance testing of existing commercial products and (2) capable of expanding to include new technologies for continuous improvement. Use of this computer-enhanced program may advance the search for safer cleaning solvents within the burgeoning field of Green Chemistry.
Based on the cornerstones of pollution prevention and cleaner production, pursuit of this vision minimizes or eliminates risks associated with many of today's industrial cleaning applications. Specifically, reductions in ozone depletion, global warming and VOC emissions as well as decreases in exposures to flammable, carcinogenic and other toxic substances such as endocrine disrupters are sought: valuable goals for workers, consumers and communities alike.
Corrosive Effect of Microcontaminants from Plastic and Polymeric Components in Hard-Disk Drives
Plastics, adhesives, and polymeric foams are often used as seals, gaskets and viscoelastic dampers for constraining moving mechanism and damping vibration in hard-disk drives(HDDs). However, some of these materials produces volatile organic compounds that can be corrosive to the important thin film magnetic disk-media and the sensitive magnetic recording heads in addition to being potentially detrimental to the head-disk interface tribology. The surfaces of these components may also contain ions that, though non-volatile, can also contribute to corrosion. The corrosion susceptibility of heads and media are particularly heightened by the extremely thin protective overcoat ( < 5nm) of the disk-media and the ultrathin (few nm) multilayer structure of the very sensitive sensors, such as those in GMR heads, necessary for good playback signal in today's ultrahigh areal density hard-disk drives. Hence the selection of materials with very low outgas, high temperature and chemical stability, and surface cleanliness for these components are all very critical to the reliability and durability of the HDDs. In this study we looked at the effect of outgas and ionics species from disk-drive plastic and polymeric components with adhesives on the corrosion of copper foil in the presence of humidity and elevated temperature in an environmental chamber. The corroded copper surfaces were analyzed using field-emission SEM and the corrosion products were identified by surface sensitive chemical tools like the X-ray Photoelectron Spectrometer (XPS). The outgas species and ions found on selected disk-drive materials, determined using gas chromatography followed by mass spectroscopy/atomic emission spectroscopy and by ion chromatography, respectively, were correlated to the corrosion products to determine possible corrosion mechanisms and corrossivity of the outgas and ionic species.
Post CMP Cleaning by a Developed Wet Process on Matton's OMNI™ System
To get a good cleanness on silicon wafers after CMP (chemical mechanical polish) has been a challenge for wet cleaning, especially at small particle size. A cleaning process for this purpose has been developed on matton's OMNI™ system and the results turn out very well.
The OMNI™ system is designed with a closed chamber. Chemicals are the fresh mixture of SC1 (ID, H2O2 and NH4OH) with a surfactant (Valtron SP2200) by injected together (co-inject) into the system. The wafers after CMP are cleaned briefly by SC1 followed by N2 dry in a wet bench for the purposes of storage and transportation.
The process sequence is initial rinse, co-inject SC1 with the surfactant, soaking with megsonics, displacement by DI, DI rinse and IPA dry. LPD (low point defect) count is cleaned by this process from more than fifty thousands at 0.08 micron down to below two thousands. The most of the remaining LPD are surface defects. By using this cleaning, it is able to get the lowest of LPD count, in regard of other cleaning processes. It helps the CMP engineers to find the correlation between the post LPD count and its CMP parameters. It is also found that this clean process works on other applications, e.g., post mask clean, photoresist removal, etc. This paper is going to present the detail information on the process, results and conclusions.
1) AEG of IDEA, LLC, 3715 Felda Street, Cocoa, FL 32926
2) DL-ICD-A, Kennedy Space Center, FL 32899
3) DYN-4, Kennedy Space Center, FL 32899
Qualitative and Automated Monitoring of Particle Levels in Cleanroom Environments
(Abstract not yet available)
Dust Removal from Solar Panels and Spacecraft on Mars
In Lunar or Martian habitat systems it is impossible to avoid contact with dust. Martian dust storms containing submicron to 20micron particles, are an environmental threat to solar cells, spacecraft, and spacesuits. Because of the high electrostatic charge of the dust and its strong adhesive properties, its deposition on life support equipment could damage or degrade equipment, reducing the mission duration and endangering personnel. The inhalation of electrostatically charged airborne dust is also a health hazard to astronauts inside the habitat. The potential hazards caused by charged particles on space life support equipment are discussed and ways to minimize or eliminate them are presented. Specifically, the following topics will be discussed: (1) the design of a sensor to measure particle size and electrostatic charge distributions of Mars dust on a single particle basis and in real-time, (2) an experimental plan to minimize deposition of charged particles on solar cells and life support equipment, and (3) methods for removing deposited dust particles.
Micro-Contamination and Particulate Cleaning Using HFC Formulations
This paper will discuss several new environmentally friendly HFC formulations as replacements for ozone depleting and global warming CFC's. The presentation will include theoretical considerations of particle removal and fluid dynamics as well as properties of these formulations such as their physical, thermodynamic, heat transfer and cleaning properties and performance in various cleaning applications. Some case studies will be included where these formulations have successfully replaced global warming CFC solvents and energy intensive aqueous cleaning processes with improved shorter cleaning cycles and reduced capital investment.
The Application of Excimer Lamps in the Cleaning and Conditioning of Surfaces
A new monochromatic lamp system that operates at reduced temperature for cleaning and treatment of wafers, reticles and other materials in the semiconductor industry has been developed. Originally proven to allow the production of defect free flat panel displays, studies underway with SemaTech, Intel and MIT utilizing this new source of 172 nm light show it to have superior characteristics to other methods in cleaning soft defects and organic materials from surfaces without utilizing wet processes. With application studies ongoing in other areas such as soft ashing and the improvement of coating performance and adhesion, the light source achieves success through the simultaneous enabling of two separate and unique processes. The 172 nm UV light energy breaks the organic contaminant bond energies and the direct production of Ozone that is generated assists in the cleaning and removal process. The performance of this wavelength system is compared to equivalent excimer laser systems and the results from published scientific studies within the industry are presented.
1) AEG of IDEA, LLC, 3715 Felda Street, Cocoa, FL 32926
2) DL-ICD-A, Kennedy Space Center, FL 32899
Development Of An Automated Particle Fallout Detection Instrument Using Surface Image Analysis
(CANCELLED)
1) University of Konstanz, Department of Physics, Center of Modern Optics, Fach M6767, 78457 Konstanz, Germany
2) Johannes-Kepler-University of Linz, Institute of Applied Physics, 4020 Linz, Austria
3) Optics Institute, CSIC, Serrano 121, 28006 Madrid, Spain
Laser Cleaning of Particles on Surfaces: Prospects and Problems
In nanotechnology the preparation of extremely clean surfaces free of particle contaminants is of utmost importance for a further increase of the integration densities of devices. The cleaning of silicon wafers, the key material for micro- and nanoelectronics, therefore is of considerable interest and different cleaning strategies are tested currently.
Several requirements have to be fulfilled by such a cleaning strategy: it should remove particles with diameters larger than 50 nm, damage of the substrate surface either in topography or in the electronic structure has to be strictly avoided and the process should be environmentally friendly and cost-effective.
One promising cleaning method that may fulfill these requirements is called "laser cleaning". Two general concepts have been developed. The first one is called "Dry laser cleaning" (DLC). Here the surface to be cleaned is irradiated by a short laser pulse. So far it was assumed that thermal expansion of the substrate surface or of the particle due to the absorption of the laser energy is the only physical process responsible for particle removal. However we have shown very recently that also local ablation of the substrate plays an important role due to the enhancement of the incident laser pulse in the near field of the particles. [1]. This local ablation will cause damage of the substrate. In the second concept, "Steam laser cleaning" (SLC), a liquid is condensed onto the surface just before the laser pulse. Its explosive evaporation after illumination of the sample by a short laser pulse provides the forces necessary for particle lift off. Explosive evaporation of a liquid is important not only in SLC but also in DLC if performed in ambient conditions. Humidity from the air condenses around the particle-surface contact and its evaporation supports the particle removal process.
In our experiments we removed spherical polystyrene and SiO2 particles with diameters ranging from 110-2000nm (DLC) and 60-800nm (SLC). The experiments were carried out in ambient conditions (DLC, SLC) and vacuum (DLC) and clarify which of the cleaning mechanisms (thermal substrate expansion, local substrate ablation, explosive evaporation of adsorbed humidity) is mainly responsible for particle removal depending on the particle size. We will discuss the prospect as well as the problems of laser cleaning against the background of the obtained experimental and theoretical results. In addition the extension of laser cleaning to the cleaning of polymeric substrates, a possible future substrate material for IC devices, will be presented.
[1] M. Mosbacher, H.-J. Muenzer, J. Zimmermann, J. Solis, J. Boneberg and P. Leiderer: "Optical Field Enhancement Effects in Laser-Assisted Particle Removal", Appl. Phys. A 72, 41-44 (2001).
Electronic Assembly Cleanliness Studies, Correlating Ion Chromatography Results with Electrical Performance Testing
This paper will explore the correlation between Ion Chromatography results of electronic assemblies and the electrical performance testing of SIR (surf ace insulation resistance testing) under elevated humidity arid temperature conditions. The ionic and organic analysis of component areas on electronic
assembles will have a specific amount of flux and processing residues detected, but determining good from bad levels and species must come from an electrical evaluation of the same areas. We have developed a large database as to general levels of cleanliness, but are constantly adjusting to the newer component packages. These packages are faster smaller, closer to the board and more sensitive ,to the residual effects. Through this paper we will report cleanliness levels required for typical flux and cleaning technology of today.
Tracking Surface Ionic Contamination by Ion Chromatography
Surface ionic contamination can cause device failures. In order to find the source of the contamination many questions must be answered first. Are the failures due to incoming materials that are not clean? Has there been a change in the process that is introducing contamination? What is the exact nature of the contaminant, ionic, particular, metallic etc? Is there a training issue that needs to be addressed. Can the failure be tested for or is it a long term reliability problem? These are just a few of the questions that must be answered as part of the troubleshooting process. This presentation will address how ion chromatography can be used to troubleshoot a manufacturing or cleaning process and assuring the quality and reliability of electronic devices. Presentation content will include:
1. What is ion chromatography.
2. How does it differ from other cleanliness testing methods.
3. How can ion chromatography be used to troubleshoot a cleaning process.
4. Real life examples will be presented showing how the use of ion chromatography has improved cleaning processes.
Spatial and Temporal Scales in Wet Processing of Deep Submicron Features
Liquid-phase processing is commonplace in manufacturing of thin films. Most of the time the surface processed surface has distinct topological features such as trenches and vias. A typical process cycle starts with a dry surface and consists of the following steps: (1) wetting of the surface, (2) dispencing a mix of chemical reagents, (3) rinsing the surface, and (4) drying the surface. Step 2 may consist of a sequence of chemical reagents either with or without a rinse in between. Each of the steps is governed by different physical processes which may have distincly different spatial and temporal scales. These scales are addressed in the paper. A trench is used as a representative feature.
1) Sandia National Laboratories, PO Box 969, Livermore, CA 94551-0969
2)Naval Facilities Engineering Service Center, Code ESC63, 1100 23rd Avenue, Port Hueneme, CA 93043-1074
Mapping of Surface Contaminants by Tunable Infrared-Laser Imaging
Sandia National Laboratories/CA is developing a sensitive, on-line monitor to detect the presence of residual organic contaminants on Department of Defense component surfaces following cleaning procedures. The monitor employs a novel tunable-laser source using an optical parametric oscillator based on quasi-phasematching technology to illuminate the surface being inspected. Images derived from grazing-angle infrared reflectance are then used to detect the presence of residual organic material. We have developed a method based on multispectral imaging to quantitatively determine the spatial distribution of organic residues on both flat and curved surface using absorption bands of the organic molecular species in the mid-infrared 3-micrometer wavelength range. This approach minimizes interference from other molecular species and surface treatments that may be present. Results will be presented along with a comparison of comparable Fourier Transform infrared reflectance data that were used to calibrate and quantify the laser-imaging measurements.
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This work is supported under the pollution prevention thrust area of the Strategic Environmental Research and Development Program (SERDP).
Bead Blast Media Contamination and Removal from Stainless Steel
(Abstract not yet available)
Avoidance of Contamination by Humans in Class Level Clean Rooms
(Abstract not yet available)
Surface Contaminations of The Space Station "Mir"
About 60 samples of various materials from the surfaces of space station "Mir" were studied by various methods of surface analysis in order to determine the properties of layers of contamination forming during their exposition in low Earth orbit (LEO) conditions. These samples include: pieces of aluminum sheet with enamel coating "EP 140 white", polyimide films of Kapton H and PM (Russian analog of Kapton H); Teflon FEP films and its Russian analog; glass-cloth TSON-SOTM and beta-glass cloth. These samples were exposed to LEO conditions in various parts of surface of space station "Mir" during 997 calendar days (2400 equivalent solar hours). Altitudes of flight were from 385 to 415 km. As a result of this exposition the sample contamination deposits covered surfaces. These contamination layers are seen as rather irregular ones. They consist of stripes and spots with various tints of yellow and brown color. The dimensions of stripes and spots tend to vary from several centimeters to several tens of centimeters. The structure and chemical composition of contamination layers were studied by following techniques: optical and scanning electron microscopy, local X-ray microanalysis, SIMS, ESCA, thermodesorption mass spectrometry, spectral reflectance, solar absorptance and relative emittance measurements. The possible sources of contaminations and their chemical transformations (induced by solar radiation and atomic oxygen attack) during deposition are discussed.
Cleaning with Solid C02 Particle Blasting
(Abstract not yet avaialble)
1) Xaar Jet AB, Box 516, S-17526 Jarfalla, SWEDEN
2) IBM, Almaden Research Center, 650 Harry Road, San Jose, Ca 95193
3) Fachhochschule Kaiserslautern / Zweibruecken, Amerikastrasse 1,
D-66482 Zweibruecken, GERMANY
4) Infineon Technologies AG, Balanstraße 73, DE-81541 Munich, GERMANY
Steam Laser Cleaning of Silicon Membrane Stencil Masks
Laser Cleaning was earlier demonstrated to remove sub-micrometer particles from solid surfaces. High cleaning efficiencies at reduced laser fluence can be achieved with Steam Laser Cleaning SLC, i.e. by applying a thin liquid layer (eg water, or a mixture of water and alcohol) to the surface at the instant of the pulsed laser irradiation. The laser pulse induces an explosion of the liquid film, which transfers momentum to the particles on the surface and ejects them from the surface.
Excite-and-probe experiments with two excimer lasers were conducted to visualize the explosion process of the liquid film on a silicon surface. It was observed that the pulsed laser irradiation propelled the liquid film in form of a disk vertically up from the surface. Lift-off velocity of the disk was of the order 50 m/s.
Steam Laser Cleaning was used to study particle removal from silicon wafers and from silicon stencil masks. Threshold for particle removal was observed at KrF-excimer laser fluences of 135 mJ/cm2 at 20 ns pulse length disregarding the shape and type of particulate contamination. The influence of the doping level of silicon wafers on the cleaning threshold was studied.
Surface Cleaning of Inorganic Materials from Thin Organic Films by Ion Bombardment in Glow Discharge
It is well known that final treatment of substrate in glow discharge permits to clean the surface and to obtain strong alhesion of vacuum deposited films. But type of contamination and its initial and final thickness were very seldom determined and discussed; investigation had qualitative character.
As a substrate we used soda lime glass 4 x 6 cm, which was thoroughly washed by chemical means. Afterwards it was put in negative glow for ion treatment.
As a contamination we have chosen palmitine acid and a definite number of monomolecular layers (from 1 to 13) were transfered onto glass from water surfaace by Langmuir-Blodgett method. Molecules of first layer were oriented with carboxyle group to glass. According to the authors of this method the thickness of one layer is approximatelv 22 angstrom.
To obtain quantitative results of cleaning process we used radioisotope method which is quite sensitive. Acid was traced with carbon 14 (Beta emitter). We also obtained proportional relation between speed of count - and number of layers (400 imp/min for each layer).
We also interested in how ion treatment influence the adhesion. For thispurpose films of aluminum were deposited in high vacuum at room temperature. Adhesion was measured by scratch method and it was considered to be strong if at load of 0.5 kg along the scratch there was no rupture, or was transparent track much thinner than the width of scratch itself. Change in surface energy was estimated by contact angle of water.
First we studied the kinetics of the cleaning process: connection between rate of count and contact angle with time. They shorn that most intensive removal of contamination takes place ,within first 10-15 seconds, no matter how thick the acid film.
Secondly we determined the shortest time of treatment that provides strong adhesion of aluminum at definite initial number of layers. It has been established that this time (t) depends upon the number of contamination layers (n) as
t = (1.41)n2 sec. (n >1).
Absence of linear function points that nature of contamination changes during treatment (because of polymerisation) and this makes process of cleaning more difficult.
Analysis of data shows that it is not necessary to reach complete removal of contamination to reach strong adhesion. For example, for initial contamination of 5 monolayers strong adhesion is reached sifter 35 sec of treatment, but counter gives the number of impulses equivalent to one monolayer. This proves that contamination turns into new phase which is difficult to remove but it does not prevent strong adhesion of deposited metal, because it is highly joined to glass and has highly active surface (small contact angle of water). In case of only one initial monolayer full removal of contamination is accomplished prior to the polymerization process.