Pressure Waves Induced by Megasonic Agitation in a LIGA Development Tank

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Megasonic agitation is used to improve the uniformity of the LIGA{sup 1} development process. To investigate the acoustic wave fields induced by megasonic agitation, we compute wave fields for a development tank containing a submerged wafer and for a typical trench-like feature on the wafer face. This separate treatment of these two problems is advantageous, because the length scales of the tank and the feature differ by three to four orders of magnitude. A spectral method based on Green's functions is used to construct the acoustic wave field, avoiding the alternative of solving partial differential equations over the entire domain. ... continued below

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Ting, Aili August 1, 2002.

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  • Sandia National Laboratories
    Publisher Info: Sandia National Labs., Albuquerque, NM, and Livermore, CA (United States)
    Place of Publication: Albuquerque, New Mexico

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Description

Megasonic agitation is used to improve the uniformity of the LIGA{sup 1} development process. To investigate the acoustic wave fields induced by megasonic agitation, we compute wave fields for a development tank containing a submerged wafer and for a typical trench-like feature on the wafer face. This separate treatment of these two problems is advantageous, because the length scales of the tank and the feature differ by three to four orders of magnitude. A spectral method based on Green's functions is used to construct the acoustic wave field, avoiding the alternative of solving partial differential equations over the entire domain. The total acoustic wave field is obtained by superposing of the primary wave field and the first reflected wave field, which are computed in sequence without any need for iterations. The wafer interference to the wave field is treated directly by a priori recognition of shadow regions in the primary field and a concept of boundary of dependence in the reflected field. Unlike a divergent wave field produced by ultrasonic agitation, results show that the wave field in the tank becomes narrowly focused at megasonic frequencies such that the most effective agitation is confined in a region directly above the acoustic source; this numerical expectation has been verified analytically and further confirmed experimentally by Sandia's LIGA Group.{sup [13]} The amplitude of the focused wave pressure is proportional to square root of the wave frequency. The wave pattern in a feature cavity also depends strongly on the orientation of the wafer and the aspect ratio of the cavity. It is concluded that the LIGA development process will be greatly accelerated, if the orientation and the location of the immersed wafer is arranged so that the wafer spends more time in the focused wave field of high frequency agitation.

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  • Other Information: PBD: 1 Aug 2002

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  • Report No.: SAND2002-8333
  • Grant Number: AC04-94AL85000
  • DOI: 10.2172/799150 | External Link
  • Office of Scientific & Technical Information Report Number: 799150
  • Archival Resource Key: ark:/67531/metadc741021

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  • August 1, 2002

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  • Oct. 19, 2015, 7:39 p.m.

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  • April 11, 2016, 8:14 p.m.

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Ting, Aili. Pressure Waves Induced by Megasonic Agitation in a LIGA Development Tank, report, August 1, 2002; Albuquerque, New Mexico. (digital.library.unt.edu/ark:/67531/metadc741021/: accessed September 24, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.