Photomask manufacturing steps
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Chrome On Glass (COG) or Binary Interface Mask (BIM)
This type of mask is the most common type and consists of an opaque layer (chrome) on a glass substrate.
Prior to exposure, the mask is also coated with a layer of resist, which will be sensitive to the wavelength of the exposure system being used to pattern the mask.
To see the processing steps for Conventional Binary Masks in more detail download Conventional Masks
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More advanced masks, i.e. Phase Shift masks
These are required to expose smaller feature sizes, and use optical interference techniques to improve the resolution that can be achieved from the mask.
The simplest of these are the masks used to make an Attenuated Phase Shift mask, which has one additional layer present between the chrome layer and the quartz glass.
To see the processing steps for Attenuated Phase Shift Masks in more detail download Phaseshift Masks