Pressure amplification of laser induced plasma shockwaves with shock tubes for nanoparticle removal

Abstract

A method using shock tubes for amplifying the dynamic pressure of Laser Induced Plasma (LIP) shockwaves for removing sub-100-nm nanoparticles is introduced and demonstrated. The higher the amplitude of the pressure generated, the smaller the particles that can be removed and, thus the more useful for a variety of applications. Constraining the expansion of the LIP core with a shock tube is a non-contact approach to increase pressure amplitude by an order of magnitude for removal of particles without damaging the substrate through shockwave and LIP radiation heating effects. Heat transfer to the substrate increases as the distance from the LIP core to the substrate (gap distance d) decreases. LIP shockwaves in air, however, demonstrate a pressure decrease on an order of magnitude per every 5 mm in the reported experimental set-up. The shock tube technique allows for higher pressures at distances significantly further from the core of LIP. In the current investigation, the effect of a set of shock tubes to amplify the transient pressure of the LIP-generated shockwave fronts has been studied to evaluate their pressure amplification performances. The effectiveness of a shock tube is quantified in terms of its pressure amplification factor. Through experimental data from several shock tube geometries examined, pressure amplification factors of 11.00 have been experimentally verified which is a ratio of shock-tube-generated transient pressure of 523 kPa to in-air LIP transient pressure of 47.5 kPa at the same gap distance d = 10 mm. The potential advantages of shock tubes as an amplification approach are discussed.

Laser-Induced Plasma Exposure on Extreme Ultraviolet Lithography Masks: Damage Analysis

“…Based on [14], a minimum diameter of D min = 59 nm PSL is calculated as the smallest particle that can be removed from Ru film (compared to 46 nm for Cr film at d cr = 2.5 mm) utilizing the LIP shockwave pressure of 93.5 kPa in air for a single laser shot without any material alterations of EUVL mask blank at critical clearance distance d cr = 3.6 mm. So it is concluded that, in order to achieve the particle removal requirement according to the ITRS 2010 update [2], pressure amplification techniques utilizing LIP, such as shock tubes [29], wet-LIP [30], and submerged shock-tubes [31], or film design approaches creating stressed films are required.…”

“…It was predicted that damage-free cleaning of 59-nm and 46-nm standard PSL particles were possible utilizing LIP shockwaves from Ru and Cr films, respectively. Removal of sub-50-nm particles from EUVL masks required utilization of LIP pressure amplification techniques [29]- [31]. It was reported that pressure amplitude can be increased from the same LIP source by using varies types of shocktubes [29].…”

“…Removal of sub-50-nm particles from EUVL masks required utilization of LIP pressure amplification techniques [29]- [31]. It was reported that pressure amplitude can be increased from the same LIP source by using varies types of shocktubes [29]. It was determined that if/when dynamic yield stress is exceeded, the Ru film surface radial stress component σ rr was the critical damage concern for the thermomechanical LIP radiation heating (∼ 9.33 × σ rr of LIP shockwave loading).…”

Enhancement of cleaning efficiency by geometrical confinement of plasma expansion in the laser-shock cleaning process for nanoscale contaminant removal

“…Among various techniques to remove sub-100 nm particles from solid substrates, the laser shock cleaning (LSC) process based on laser-induced breakdown (LIB) of air and plasma formation has attracted substantial attention as the process demonstrated strong potential to remove nanoscale particles from silicon wafers [5][6][7][8]. Recently, removal of polystyrene (PS) particles as small as 10 nm in diameter was reported [8]. The LSC method is not only a dry but also a non-contact technique without exposure of the surface to direct mechanical contact.…”

“…Concerning the first limitation, Dunbar et al proposed a method to enlarge the shock wave intensity using shock tubes [8]. The LIP is generated in a cylindrical tube in the proposed method, leading to propagation of a near-planar shock wave with small diffraction at the exit of the tube.…”