Masataka Shiba

Automatic Inspection Of Contaminants On Reticles

Wafer steppers require contaminant-free reticles to assure high yield. This paper describes a new particle detection technique. A linearly polarized He-Ne laser beam scans obliquely across the reticle surface and only scattering light produced by the particles is detected by the detectors, which consist of analyzers, collection lenses, slits, and PMTs (photomultipliers). On the other hand, scattering light produced by the pattern edges on the reticle is cut off by the analyzers. Using this technique, particles as small as 2 1im on the surface of pellicle-installed reticles can be detected.

Relative Alignment By Direct Wafer Detection Utilizing Rocking Illumination Of Ar Ion Laser

A new alignment system for micron and submicron lithography has been developed by Hitachi. Ar ion laser and charge coupled devices (CCD) are used in this system to detect the relative position of wafer and reticle. Each wafer mark on the scribe lines is directly detected through the reduction lens and kept in position till exposure is completed. Direct wafer detection has been realized by using a chrome surface on the reticle as a reflector for the detection optics arranged under the reticle. This construction permits TTL on axis alignment to be performed without movement of the detection optics and does not obstruct the exposure light. As Ar ion laser light can transmit through the multi-layer resist, the mark under the resist can be detected. Laser rocking illumination of the wafer mark and the storage type light detector (CCD) allow highly accurate detection of grainy wafers. By chromatic aberration of the reduction lens for Ar ion laser light, the image of the wafer mark is presented below the reticle after reflection. This phenomena has prevented the detection of the relative position between the wafer and reticle using single detection optics. However this problem has been eliminated by using a hyperbolic grating on reticle. The hyperbolic grating illuminated by the Ar ion laser beam projects a line shape image on the image plane of the wafer mark, and the position of the line represents the position of the reticle. The alignment system achieves overlay accuracy (3σ) of less than 0.2 μm for process wafers and stable offset (for five days) of less than 0.05 μm. The alignment time is about 0.3 seconds.