Thermal loading of laser induced plasma shockwaves on thin films in nanoparticle removal

Abstract

Damage concerns, such as substrate/film material alterations, damage, and delamination of thin films, have become a central problem in sub-100 nm particle removal applications. In the laser induced plasma (LIP) removal technique both LIP shockwave and radiation heating are potential sources of thermomechanical damage. The specific objective of current study is to conduct a computational investigation of the LIP shockwave effect on the thermoelastic response of a thin chromium (Cr) film deposited on a quartz substrate and to identify the conditions leading to the onset of plastic film deformations. The experimentally characterized shockwave pressure and temperature (approximated from gas dynamic relations) were prescribed as boundary conditions in the computational analysis. From the shockwave arrival times for different travel distances, the shockwave radius as well as the velocity were obtained as a function of the shockwave propagation time. Radial (and circumferential) stresses, caused by thermal expansion of the Cr film, were most dominant and, hence, of damage concern. It is determined that the resultant temperature rise utilizing a 1064 nm Nd:yttrium-aluminum-garnet (YAG) laser (450 mJ) due to the film-shockwave interactions was not sufficiently high to initiate film and/or substrate damage. No material alteration/damage of the Cr film is predicted due to the temperature and pressure of LIP shockwaves at the firing distance of 2 mm, with a high strain rate gain factor of two (minimum), though damage was observed experimentally for 1064 nm Nd:YAG laser at the pulse energy of 370 mJ. Reported results indicate that the leading cause of observed thin film damage during nanoparticle removal is almost certainly radiation heating from the LIP core.

Onset of Material Alterations Due to Laser-Induced Plasma Exposure in Nanofilms Deposited on Photomasks

“…1 for the experimental setup). Various shockwave characteristics [29]- [33] (the location of the shockwave front as a function of the arrival time) along with the obtained experimental results compared in [18] indicate slight offsets due to the different laser pulse energies utilized.…”

“…1. A dynamic pressure transducer [27], [28] with a resonant frequency of 500 kHz (i.e., a rise time of 1 s), a surface diameter of 5.54 mm (Kistler 603B1), and a Spectra Physics Nd:YAG INDI-series pulsed-laser (450 mJ rated pulse energy, 5-8 ns pulse width, 10 Hz repetitive rate, 8.5-10 mm beam diameter, and 1064 nm wavelength) were utilized for the transient pressure measurement experiments [29] (see inset of Fig. 1 for the experimental setup).…”

Transient Thermoelastic Response of Nanofilms Under Radiation Heating From Pulsed Laser-Induced Plasma

“…From the results of the previous FE simulations it can be concluded that the surface stresses induced due to surface temperature were dominating the stresses induced due to shock pressure loading. However, the induced stresses, radial (a peak level of approximately 650 MPa), shear ( 120 kPa), and axial ( 200 kPa) stress components with both thermal and mechanical loadings, were within the damage limits of the material when the effect of the level of dynamic strain rate is taken into consideration [7]. It is then concluded that the substrate damage could be caused by the radiation heating generated by the LIP.…”

“…The pressure levels are typically too low to result in any mechanical substrate damage, as the strength of the substrate is often three orders of magnitude higher than the shock pressure. The effect of shock temperature and pressure on a film bonded to a substrate is determined by a computational analysis based on the finite-element (FE) method and it is reported in [6] and [7]. From the results of the previous FE simulations it can be concluded that the surface stresses induced due to surface temperature were dominating the stresses induced due to shock pressure loading.…”

Thermal-Induced Stress of Plasmonic Magnetic Nanocomposites

“…The radial stress is long-ranged and simply inversely proportional to the distance r. The manner definitely changes when the surrounding medium is supercooled liquids or solids. Laser-induced thermal stresses on nanoparticle removal from thin films 32) and due to metal nanoparticles in silica matrices 33) are compelling evidence.…”