Abstract
The measurement accuracy of an interferometer is largely affected by the refractive index of air. Compared with the direct compensation method, the indirect compensation method is more suitable for compensation for an ultra-precision motion platform using an interferometer. However, the indirect compensation method depends on the air refractive index’s formula, which is empirical and not entirely accurate. It seems that the application of the indirect compensation method in a high-precision measured object is hampered. Considering that the repeat positioning accuracy of some application objects such as lithography’s ultra-precision platform is the highest requirement while the positioning accuracy is less demanding, this means that repeat measuring accuracy is the main factor. For these objects, this paper proposed a hypothesis of Birch and Downs’s revised Edlén’s formula firstly and derived the relation between the repeat measuring accuracy and the repeatability of environmental parameters on this basis when an indirect compensation method was used. An example on the analysis of the difference between Bonsch and Potulski’s further revised formula and Birch and Downs’s revised Edlén’s formula explains the rationality of the hypothesis. In addition, a simulation result on the lithography mask stage’s flow field showed that the indirect compensation method can achieve sub-nanometer repeat measuring accuracy and it meets repeat positioning accuracy’s requirement in lithography.
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