SWHL: Main Features
Compared to the projection photolithography, there are some distinguishing features of SWHL imaging:
Comparison with projection photolithography
Projection photolithography with a deep ultraviolet light source (known as "DUVL") is based on geometrical optics concept:
- pattern to be printed ("IC topology layer") is the essential part of projection photomask ("mask") layout;
- every mask layout element corresponds to an IC layout element;
- light diffraction (on mask) produces harmful effects and has to be corrected and overcome by additional measures and labor-consuming technological procedures.
SWHL is based on light wave optics concept:
- the sub-wavelength holographic mask (SWHM) generates an image itself without any projection lens, as a result of the mask illumination by specified optical wave;
- every point of a holographic mask diffracts the illumination light and interference of all the waves diffracted from the whole mask generates an image;
- there is no resemblance between the mask and the printed image (IC layer); there is no one-to-one correspondence between the mask elements and the printed image elements, as every element of the mask contains the information about the whole image;
- defects on a holographic mask do not affect printed image elements;
- SWHM physical structure does not change from node to node at the same wavelength.
SWHL is able to generate any kind of images that common projection lithography generates, and those that projection lithography cannot. All the RET (Resolution Enhancement Technologies) of common photolithography (i.e. OPC, Phase-Shift, Multi-Patterning, SMO, etc.) are successfully performed in SWHL as a method of HoloOptimization.