System and method for correcting the focus of a laser beam

摘要

Focus of a laser optical system can be corrected using a variable radius mirror having a focusing cavity and a separate cooling cavity. Pressure of a focusing material at a sufficiently low mass flow in the focusing cavity deforms a reflective surface mounted to the focusing cavity, changing its radius. Cooling material provided to the cooling cavity cools the variable radius mirror. A laser beam is reflected by the deformed reflecting surface to focusing optics, focusing the reflected laser beam on an EUV-emitting target, and minimizing a laser focus error by one or more of: maximizing a measured EUV power or minimizing a measured laser beam divergence. Providing focusing material at a deformation pressure and at a sufficiently low mass flow, and providing a separate cooling cavity, avoids perturbations in the reflective surface which would otherwise affect laser beam focus.

主权项

1. A system comprising:
a variable radius mirror having a deformable reflective surface and configured to receive and reflect a laser beam at the reflective surface, the variable radius mirror having:
a cooling cavity configured to pass a cooling material to cool the variable radius mirror; anda focusing cavity configured to receive a focusing material and deform the reflective surface as a function of a deformation pressure of the received focusing material; a cooling controller configured to provide the cooling material to the cooling cavity; and a pressure controller configured to provide to the focusing cavity the focusing material with the deformation pressure where the pressure controller is configured to adjust the deformation pressure of the focusing material to minimize a laser focus error by being further configured to adjust the deformation pressure of the focusing material to maximize a measured EUV power from an EUV-emitting target droplet provided to a focal point.