Megasonic cleaning, cavitation, and substrate damage: an atomistic approach

Kapila, Vivek; Deymier, Pierre A.; Shende, Hrishikesh; Pandit, Viraj; Raghavan, Srini; Eschbach, Florence O.

doi:10.1117/12.681771

Cited by 17 publications

(10 citation statements)

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“…Still, pressures may be of the order of 10 3 -10 4 bars. The range of driving pressures analysed here is the typical operating range of megasonic cleaning devices (Kapila et al 2006;Holsteyns et al 2008;Minsier & Proost 2008;Ahn et al 2009;Keswani et al 2009). An uncontrolled radiation by cavitation bubble fields will result in mechanical failure, when the high peak energies of the radiated sound containing highfrequency components drive unwanted mechanical oscillations.…”

Section: Discussionmentioning

confidence: 99%

Acoustic energy radiated by nonlinear spherical oscillations of strongly driven bubbles

Holzfuss

2010

Proc. R. Soc. A.

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Based on the theory of F. Gilmore (Gilmore 1952 The 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 mm for the lower frequency driving and 1-3 mm 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.

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Section: Discussionmentioning

confidence: 99%

Acoustic energy radiated by nonlinear spherical oscillations of strongly driven bubbles

Holzfuss

2010

Proc. R. Soc. A.

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“…As the SC1 part of this process is the same for all substrates, the additional added pits may be contributed to the cleaning steps which contain ozonated water with megasonic. In this case, the presence of ozone in the water during megasonic cleaning will lead to increased cavitation activity [7], which could be responsible for the additional cleaning induced pits observed during this cleaning process.…”

Section: Mechanism Of Pit Creation By Cleaningmentioning

confidence: 99%

Sub 50 nm cleaning-induced damage in EUV mask blanks

Rastegar¹,

Eichenlaub²,

Kapila³

et al. 2008

SPIE Proceedings

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Defects are still one of the main challenges of extreme ultraviolet (EUV) mask blanks. In particular, a majority(~75%) of substrate defects are nanometer size pits. These pits are usually created during final surface polishing of the synthetic, quartz glass substrates. This study presents data that indicates cleaning may also induce pits in the substrate surface. These pits are typically 20 nm and larger, and are contained in a circular area on the surface, which is scanned by a megasonic nozzle during cleaning. Concentrated collapse of cavitation bubbles in the areas scanned by megasonic is expected to be one of the main mechanisms of pit creation. The data indicates the existence of a hard surface layer with an estimated thickness of approximately 30 to 60 nm, which is resistive to pit creation. After this layer is removed, the number of pit defects present on the substrate increases dramatically with megasonic cleaning. It is also demonstrated that, within the detection limits of the atomic force microscope (AFM), the size of a pit does not change due to cleaning.

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“…It is a well-known phenomenon that both acoustic cavitation and acoustic streaming play some critical roles in the megasonic cleaning. 1,2 Kapila et al 2,3 reported that acoustic streaming does not induce the force strong enough to damage the substrates or patterns. However, excessive cavitation energy should cause extensive surface damage, particularly to tiny surface features such as SRAFs.…”

Section: Introductionmentioning

confidence: 98%

“…3,4 Furthermore, it has been reported that cavity size has a wider distribution at fixed megasonic conditions, and SRAFs damages caused by large cavity sizes with large cavitation energy would occur at a certain probability. 3,5 Therefore, it is important to control the distribution of the cavitation energy and cavity size on photomask surface within an adequate range to achieve maximum cleaning efficiency without SRAFs damage. However, a correlation between cavity size distribution, cavitation energy distribution and SRAFs damage still remains much to be explored.…”

Section: Introductionmentioning

confidence: 99%

The effect of puddle megasonic cleaning for advanced photomask with subresolution assist features (SRAFs)

Chen¹,

Yang²,

Tseng³

2012

SPIE Proceedings

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Sub-resolution assist features (SRAFs) damage-free cleaning by use of megasonic nozzle becomes main challenge in photomask industry. Using non-sulfate cleaning tool, the effect of key performance parameters of 1 MHz puddle megasonic nozzle such as megasonic power, and the gap between puddle nozzle and cleaned surface were investigated for opaque SRAFs sizes of 107 nm, 93 nm, 81nm, 71 nm, 63 nm, and 56 nm. Damage-free and high efficiency on particle removal cleaning for SRAFs size down to 71 nm for 38 nm technology node (MPU/ASIC ½ pitch, as outlined in ITRS 2010) has been demonstrated on advanced photomask with MoSi layer in this paper. Furthermore, conducting atomic force microscopy (CAFM) was employed to investigate the nanoscale surface electrical properties of chrome binary blanks cleaned by 1 MHz puddle megasonic nozzle. The results show that highly conducting regions on chromium oxide surfaces can be considered as "cavitation-rich and/or cavitation energy-strong" regions. And their sizes range from 15 to 100 nm, which are comparable to the sizes of SRAFs damage. Finally, in the future, CAFM may be a useful tool to inspect intrinsic defects on advanced photomasks at nanoscale, such as EUV blanks.

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Megasonic cleaning, cavitation, and substrate damage: an atomistic approach

Cited by 17 publications

References 0 publications

Acoustic energy radiated by nonlinear spherical oscillations of strongly driven bubbles

Acoustic energy radiated by nonlinear spherical oscillations of strongly driven bubbles

Sub 50 nm cleaning-induced damage in EUV mask blanks

The effect of puddle megasonic cleaning for advanced photomask with subresolution assist features (SRAFs)

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