Minimum feature size
Minimum Critical Dimension (CD):
The minimum feature size, also known as the half pitch size, is one of the most important parameters for measuring the performance of lithography machines.
Among them, is a constant that varies in different lithography schemes, where λ is the wavelength of the input light source and NA is the numerical aperture of the lithography machine optical system. For constants, currently ASML's DUV lithography machine in the Netherlands can achieve a maximum of around 0.25, while EUV is still around 0.35. The smaller the wavelength of the input light source, the smaller the actual photolithography process that can be performed. For the numerical aperture NA, the upper limit of this value is generally 1.0 for non wetting DUV schemes and around 1.35 for wetting DUV schemes. Compared to non immersion lithography, immersion lithography machines use additional liquid for refraction during lithography, usually pure water with a refractive index of about 1.33. This is also the reason why immersion lithography machines have a larger NA.
Engraving accuracy
Overlay accuracy: The alignment accuracy between the mask and wafer patterns.
The basic meaning refers to the alignment accuracy of the patterns between the two photolithography processes. If the alignment deviation is too large, it will directly affect the yield of the product.
Exposure tolerance
Exposure Latitude: Exposure latitude, also known as exposure margin, is one of the important parameters of the process window. Optical exposure systems can form an exposure energy range that meets the design layout requirements. It is usually defined by the exposure energy selection range within ± 10% of the change in CD value detected by the exposure result. If the line width of the exposed pattern changes relatively little when the photoresist deviates from the optimal exposure dose, it indicates that the photoresist has a large exposure tolerance. The greater the exposure tolerance, the greater the development tolerance.
Exposure tolerance and projection image contrast are closely related. If the feature size of the projected image has poor image contrast, it will be too sensitive to dose changes
