Potential thermo-mechanical substrate damage in nanoparticle removal with pulsed lasers

Abstract

Difficulties associated with the removal of nanoparticles with traditional cleaning methods have been widely discussed and reported in the literature. It has been projected that the minimum feature sizes of semiconductor devices by the year 2008 will be reduced to 70 nm. Laser cleaning as an emerging technique has been gaining momentum in recent years. The two main features of the laser methods: its dry and non-contact nature, make it particular attractive. However, as damage in pulsed laser processing has been an issue in micro-manufacturing applications, so concerns about damage in laser cleaning applications must also be adequately addressed. In laser cleaning, detachment often is achieved by creating a normal inertial force exerted on the particle due to the normal surface acceleration under a rapid laser thermal loading. The value of the required detachment acceleration is proportional to 1/D ² (D: particle diameter). In this study, the onset of thermal and mechanical substrate damage in nanoparticle removal has been computationally studied for silicon and copper substrates. The maximum and minimum values of the components of the acceleration vector and axisymmetric stress tensor as well as the temperature are computed at various points on the substrate surface and in the interior of the substrate. The minimum and maximum values of the thermoelastic quantities along the radial and axial directions have been reported. It is computationally determined and demonstrated that the type of first-damage depends on the substrate and particle material properties as well as particle diameter.

Keywords:

• Nanoparticles
• thermo-mechanical damage
• laser cleaning
• particle removal
• laser ultra-sonics
• micro-manufacturing
• nano-manufacturing.