Dependence on the stripping efficiency to irradiating beam size was investigated in an advanced laser resist stripping method. The beam size on the resist surface was changed from 0.3 mm to 3.0 mm. An intensity shape of the laser beam was Gaussian shape. At a beam diameter of 0.3mm, the stripped resist area in a beam was 15 % of 0.01 mm 2 . In the case of beam diameter of 3.0 mm, the stripped resist area in a beam was 5 % of 0.38 mm 2 . The stripped area improves 38 times for scale-up of the beam area of 100 times. The resist stripping efficiency was thought to depend on the heat stress due to a temperature gradient between the beam center and the regions without laser irradiation. Irradiation with multiple laser beams by small beam diameter was confirmed as one of the methods for improvement of a resist stripping rate with high efficiency.

Removal by using laser irradiation was investigated in Poly-Vinyl Phenol (PVP). The laser irradiation in the water can improve the PVP stripping effect as compared with that of normal atmosphere irradiation. The surface laser damage threshold of Si wafer was 0.13 J/cm 2 , and the PVP stripping threshold was 0.06 J/cm 2 . The PVP stripping threshold decreased to approximately 50 % of the surface laser damage threshold. The PVP strips from the Si wafer just as shown in a positive-tone DNQ / novolak resist. However, removal efficiency decreased at a large irradiation beam diameter. The stripped area decreases at the beam diameter of 1.5mm or more. Irradiation with multiple laser beams with a small beam diameter could improve the PVP stripping rate with high efficiency.

Resist stripping phenomenon with laser irradiation was observed by using a time-resolved analysis. The time change of the resist stripping phenomenon by a probe laser irradiation was observed from the viewpoint of the intensity change of the probe laser. As for the laser irradiation in the water, the probe laser intensity arrived at the maximum after around 40 μs. During the pump laser irradiation of 8 ns, a large compressive stress of -10 MPa was confirmed inside the resist from the FE analysis results. The generation of this compression stress is important for starting the resist stripping process, and is thought to improve the resist removal efficiency.

Resist removal phenomenon with laser irradiation was analyzed by using a finite element (FE) method. Laser irradiation in the water can improve the resist removal effect as compared with that of normal atmosphere irradiation. A two-dimensional (2-D) micro-FE model was constructed based on the boundary surface between the Si wafer, resist and water during laser radiation. In the normal atmosphere, any effective stress did not occur along the x-axis direction in the resist. In contrast, for the laser irradiation in the water, large compressive stress was confirmed along the x-axis direction in the resist. This compressive stress in the resist is thought to improve the resist removal efficiency.