Uniform Illumination at Tilted Surface for Inspection and Metrology Tools

Most of the detection tools for analysing surface properties have to be located perpendicular to the inspected surface. Furthermore, it is necessary to illuminate this surface homogenously. Now a new kind of asymmetric homogenizer is introduced. This is a micro-lens array consisting of micro- lenses with different profiles. Free form surface of every individual microlens enables a uniform illumination at the tilted surface. Limo’s standard illumination tool for tilted homogenization generates 300 x 340 mm2 field at the angle of 55°, in a working distance of 1.5 m and with inhomogeneity less than 5 %. Compared to traditional methods, the tilted illumination affords obvious advantages for the process. Since only one illumination device is needed instead of two, the cost can almost be reduced half. Furthermore, the efficient signal detection can simplify and accelerate the whole progress.