Patent ID: 7714992

Claim:
Equipment for monitoring an immersion lithographic device equipped with a main light source ( 20 ) and an optical projection device ( 25 ) for printing images on a chip ( 4 ), the propagation medium going from the optical projection device to the chip consisting of a liquid ( 3 ), characterised in that it comprises: a chamber ( 51 ), adapted to receive at least some of said liquid ( 3 ), a diffraction grating ( 50 ) immersed in the chamber, a secondary light source ( 271 ) adapted to send a secondary incident beam ( 202 ) towards the grating so as to obtain a diffracted beam, angle measuring means ( 57 ) capable of measuring at least one diffraction angle corresponding to an intensity peak of an order of diffraction of the beam diffracted by the grating ( 500 ), and computing means ( 505 ) adapted to calculate an estimate of a magnitude relating to the refractive index of the liquid.