• Login
    View Item 
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    •   Home
    • UA Graduate and Undergraduate Research
    • UA Theses and Dissertations
    • Dissertations
    • View Item
    JavaScript is disabled for your browser. Some features of this site may not work without it.

    Browse

    All of UA Campus RepositoryCommunitiesTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournalThis CollectionTitleAuthorsIssue DateSubmit DateSubjectsPublisherJournal

    My Account

    LoginRegister

    About

    AboutUA Faculty PublicationsUA DissertationsUA Master's ThesesUA Honors ThesesUA PressUA YearbooksUA CatalogsUA Libraries

    Statistics

    Most Popular ItemsStatistics by CountryMost Popular Authors

    CONTROL OF CAVITATION USING DISSOLVED CARBON DIOXIDE FOR DAMAGE-FREE MEGASONIC CLEANING OF WAFERS

    • CSV
    • RefMan
    • EndNote
    • BibTex
    • RefWorks
    Thumbnail
    Name:
    azu_etd_11852_sip1_m.pdf
    Size:
    23.00Mb
    Format:
    PDF
    Download
    Author
    Kumari, Sangita
    Issue Date
    2011
    Keywords
    Damage
    Megasonic
    Semiconductor
    Wafer
    Materials Science & Engineering
    Carbon Dioxide
    Cleaning
    Advisor
    Raghavan, Srini
    
    Metadata
    Show full item record
    Publisher
    The University of Arizona.
    Rights
    Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
    Embargo
    Embargo: Release after 05/24/2012
    Abstract
    This dissertation describes the finding that dissolved carbon dioxide is a potent inhibitor of sonoluminescence and describes the implications of the finding in the development of improved megasonic cleaning formulations. Megasonic cleaning, or the removal of contaminants particles from wafer surfaces using sound-irradiated cleaning fluids, has been traditionally used in the semiconductor industry for cleaning of wafers. Recently however, advancing technology and miniaturization has made wafer features increasingly susceptible to damage by megasonic energy. International Technology Roadmap for Semiconductors (ITRS) 2011 predicts the critical particle diameter, critical particle count and killer defect numbers to be 22 nm, 113 #/wafer and 4.3 #/mm², respectively, on a 300 mm wafer for 45 nm technology node. A critical challenge in the field, therefore, is to achieve removal of small particles (22 nm to 200 nm) without causing damage to fine wafer features. The work described here addresses this challenge by identifying sonoluminescence and solution pH as two key factors affecting damage and cleaning efficiency, respectively and establishing novel means to control them using CO₂(aq) release compounds in the presence of acids and bases. Sonoluminescence (SL) behavior of the major dissolved gases such as Ar, Air, N₂, O₂ and CO₂ was determined using a newly designed Cavitation Threshold Cell (CT Cell). SL, which is the phenomenon of release of light in sound-irradiated liquids, is a sensitive indicator of cavitation, primarily transient cavitation. It was found that all the tested dissolved gases such as Ar, Air, N₂ and O₂, generated SL signal efficiently. However, dissolved CO₂ was found to be completely incapable of generating SL signal. Based on this interesting result, gradual suppression of SL signal was demonstrated using CO₂(aq). It was further demonstrated that CO₂(aq) is not only incapable but is also a potent inhibitor of SL. The inhibitory role of CO₂(aq) was established using a novel method of controlled in-situ release of CO₂ from NH₄HCO₃. ~130 ppm CO₂(aq) was shown to be necessary and sufficient for complete suppression of SL generation in air saturated DI water. The method however required acidification of solution for significant release of CO₂, making it unsuitable for the design of cleaning solutions at high pH. Analysis of the underlying ionic equilibria revealed that the loss of released CO₂(aq) upon increase in pH can be compensated by moderate increase in added NH₄HCO₃. Using this method, simultaneous control of SL and solution pH was demonstrated in two systems, NH₄HCO₃/HCl and NH₄OH/CO₂, at two nominal pH values; 5.7 and 7.0. Damage studies were performed on wafer samples with line/space patterns donated by IMEC and FSI International bearing Si/metal/a-Si gate stacks of thickness ~36 nm and Si/Poly-Si gate stacks of thickness ~67 nm, respectively. A single wafer spin cleaning tool MegPie® was used for the generation of megasonic energy for inducing damage to the structures. It was demonstrated that CO₂ dissolution in DI water suppresses damage to the gate stacks in a dose-dependent manner. Together, these studies establish a systematic and strong correlation between CO₂(aq) concentration, SL suppression and damage suppression. Significant damage reduction (~50 % to ~90 %) was observed at [CO₂(aq)] > ~300 ppm. It was also demonstrated that CO₂(aq) suppresses damage under alkaline pH condition too. This demonstration was made possible by the successful design of two new cleaning systems NH₄HCO₃/NH₄OH and CO₂/NH4OH that could generate CO₂(aq) under alkaline conditions. Damage suppressing ability of the newly designed cleaning systems were compared to the standard cleaning system NH₄OH at pH 8.2 and it was found that NH₄HCO₃/NH₄OH and CO₂/NH₄OH systems were 80 % more efficient in suppressing damage compared to the standard NH₄OH cleaning system. Finally, megasonic cleaning studies were conducted in the same single wafer spin cleaning tool MegPie®, using SiO₂ particles (size 185 nm) deposited on 200 mm oxide Si wafers, as the contaminant. It was found that the standard cleaning chemical, NH₄OH, pH 8.2, was effective in achieving > 95 % particle removal for 2 min irradiation of megasonic energy at power densities > 0.7 W/cm². Based on these results, a new system, NH₄HCO₃/NH₄OH, was designed with an aim to release ~300 ppm CO₂ at pH 8.2. It was demonstrated that newly designed system NH₄HCO₃/NH₄OH, allowed significant suppression of damage in comparison to NH₄OH while maintaining > 90 % cleaning efficiency that was comparable to NH₄OH solution, at the same acoustic power densities. Taken together, these studies establish a potent and flexible means for the inhibition of SL generation over a wide pH range and acoustic power densities and demonstrate its use in suppression of wafer damage without compromising megasonic cleaning efficiency.
    Type
    text
    Electronic Dissertation
    Degree Name
    Ph.D.
    Degree Level
    doctoral
    Degree Program
    Graduate College
    Materials Science & Engineering
    Degree Grantor
    University of Arizona
    Collections
    Dissertations

    entitlement

     
    The University of Arizona Libraries | 1510 E. University Blvd. | Tucson, AZ 85721-0055
    Tel 520-621-6442 | repository@u.library.arizona.edu
    DSpace software copyright © 2002-2017  DuraSpace
    Quick Guide | Contact Us | Send Feedback
    Open Repository is a service operated by 
    Atmire NV
     

    Export search results

    The export option will allow you to export the current search results of the entered query to a file. Different formats are available for download. To export the items, click on the button corresponding with the preferred download format.

    By default, clicking on the export buttons will result in a download of the allowed maximum amount of items.

    To select a subset of the search results, click "Selective Export" button and make a selection of the items you want to export. The amount of items that can be exported at once is similarly restricted as the full export.

    After making a selection, click one of the export format buttons. The amount of items that will be exported is indicated in the bubble next to export format.