Optical lithography (also known as photolithography) is a technique used in integrated circuit manufacturing that uses light to produce minutely detailed patterns on a surface. It involves transferring a pattern from a mask to the surface using a radiation source, such as ultraviolet light. The fundamental limit of optical lithography is determined by the wavelength of the radiation source and the numerical aperture of the imaging system.
The lithography process involves creating an image on a photoresist, which is then etched or ion implanted into the surface. This process can be optimized and controlled through various techniques, such as adjusting the exposure dose and focus of the radiation source.
Photolithography Process
The optical lithography process involves manipulating light to etch desired features onto a surface of a wafer or a substrate. This process involves transferring the pattern from a mask onto a photosensitive emulsion (photoresist) coated onto a substrate such as a silicon wafer or Sapphire in Compound Semiconductor. Photolithography shares some fundamental principles with photography in that the pattern in the photoresist is created by exposing it to light – either directly or through a mask. Patterned surfaces can be created using photolithography, which involves coating the substrate with photoresist, exposing it to light, and then developing the exposed areas. The history of lithography dates back to 1796 when Alois Senefelder invented the printing technique.
Limitations
The primary limitation of optical lithography is the resolution, which depends on the wavelength used. Additionally, local geometry of the resist layer can affect the fabricated structure’s geometry. Practical drawbacks include the cost and complexity of photolithography equipment, as well as resolution limits due to Rayleigh’s scaling laws of resolution and depth-of-focus. Finally, optical lithography is now reaching its physical limits due to diffraction effects.