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Overview

Photomasks are high-purity glass plates with precise images of integrated circuit designs (semiconductor chips). Photomasks are used as masters to optically transfer these images onto silicon wafers.

Current advanced lithographic tools such as deep-UV (DUV) scanners and steppers project light through the photomask by using a high-aperture lens system. The intensity profile of the light generates an image of the design on the wafer coated with a light-sensitive material called photoresist. When negative photoresist is used, the unexposed portion of this material is removed, so the wafer can either be etched to form channels or other materials can be deposited.

Semiconductor chips are manufactured layer by layer, hence the described deposition or removal steps are repeated until the final circuit is completed. The current generation of semiconductor chips consists of 25 to 70 layers, each of which requires a unique photomask.

The following methods are used for the production process:

  • E-beam writing                                                                              
  • Laser writing                                                                                   
  • Resist development dry etch                                                                            
  • Optical, AFM and SEM measurements                                 
  • Inspection laser and ion beam repair                                          
  • Ion induced gas deposition repair                                          
  • Pellicle mounting