What is OPC?
OPC is the abbreviation for Optical Proximity Correction.
This is the generic name for a number of different image enhancement techniques where additional features are included on the mask to improve the quality of the image when the mask is used.
The use of OPC becomes important when smaller feature sizes are present, especially as these sizes approach the wavelengths of the light being used in stepper and scanner systems. Some typical examples of OPC techniques are:
- Adding small rectangles, called serifs, to the corners of lines and contacts to reduce the effect of corner rounding. (Simple OPC)
- Cutting out of small rectangles, serifs, from the inside edges of angled lines to reduce the over exposure of these areas. (Simple OPC)
- Using a set of rules relating to feature types and sizes to make changes to features to compensate for the effects of the stepper or scanner. (Moderate OPC)
- Using computer modelling to make major changes to features to compensate for the effects of the stepper or scanner. (Aggressive OPC)
- Adding features such as assist bars which will generate interference effects to enhance the nearby images, with the size of the assist bars being small so that they are not being printed. (Aggressive OPC)
In all cases, the resulting mask data when using OPC will be greater than that of a mask without OPC, and will often require to be written using a smaller resolution (pixel size). As a result, OPC masks will usually take longer to expose and require more sensitive inspection, so will cost more than a mask of a similar specification with no OPC features.