Effect of wavelength and incident angle in the laser removal of particles from silicon wafers

As semiconductor and microelectronic devices are becoming increasingly smaller, surface contamination of these devices is becoming an increasing problem for manufacturers due to the adverse effects that micron and sub micron particles have on the device performance. As a result of this there proves to be a continual need to develop effective techniques for the removal of small particles in the semiconductor industry. Recently, a non-contact dry laser cleaning technique, using a short-pulse (in the order of ns) laser irradiation on the surface, has been demonstrated as a potential solution for the removal of particles from critical surfaces. In this paper the removal of small copper particles with a diameter of 1 µm from silicon wafers has been carried out over a range of different wavelengths, since wavelength is one of the most crucial parameters for successful laser cleaning. Moreover it has been found that a dramatic improvement of cleaning efficiency in terms of number of particles removed is produced when using the laser at glancing angle of incidence as compared with normal incidence. The process mechanism is discussed by considering the adhesion and the laser-induced cleaning forces for different incident angles.