1. Field
Embodiments of the present invention relate to a method for manufacturing a device and to a lithographic apparatus.
2. Background
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging with a radiation beam with a radiation beam mode onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
U.S. Appl. Publ. No. 2007/081138 A1, incorporated herein by reference in its entirety, describes a device manufacturing method using a lithographic apparatus in which, during an alignment calibration process in the lithographic apparatus using a sensor to detect a property of a projected image at substrate level, a diffuser is inserted into the radiation beam to increase the range of angles of radiation incident on the substrate. Thereby it can be ensured that sufficient radiation enters the sensor even when there is a mismatch between the radiation beam mode used and the acceptance NA of the sensor.
It may be a disadvantage of the known apparatus and the known method that the diffuser is to be physically moved from a first position outside the path of the radiation beam to a second position inside the radiation beam. This movement requires some time to complete and may negatively effect the through-put time of the apparatus.
It may be a further disadvantage of the known apparatus and the known method that they may not function well with any possible illumination mode, i.e. the radiation beam mode used for illumination of the substrate. For example, for an illumination mode with a very steep illumination profile in one or more very narrow angular ranges, such as a steep quadrupole profile filling only a small portion of the pupil, the mismatch between the illumination mode and the sensor acceptance range may be too large to allow to be compensated for by the diffuser. In particular, as the form of the diffuser will depend on the degree and nature of the mismatch between the illumination mode and the sensor acceptance range, it may be needed to use a diffuser of a form that is not available.
It may be a further disadvantage of the known apparatus and the known method that the mechanical movement of the diffuser over quite a significant distance may result in disturbances to the illumination beam, e.g. to mechanical vibrations.
It may be a further disadvantage of the known apparatus and the known method that the resulting diffuse beam may not be compatible with a measurement and/or alignment system of the lithographic apparatus. For example, a diffuse beam may conflict with performing an interferometric measurement on the beam quality or using an interferometric alignment method.
It may be a further disadvantage of the known apparatus and the known method that the effect of the diffuser is limited to increasing the range of angles at which radiation of the illumination beam is incident on a marker on the patterning device.