Photolithography is a key process in the manufacturing of semiconductor devices, integrated circuits, and microelectromechanical systems (MEMS). It is a photomechanical process used to transfer geometric patterns from a photomask or reticle to a photosensitive chemical photoresist on a substrate, typically a silicon wafer.
The basic steps of photolithography include:
Cleaning the substrate: The substrate, often a silicon wafer, is cleaned to remove any contaminants from its surface.
Coating with photoresist: A thin layer of photosensitive material called photoresist is spin-coated onto the substrate. The photoresist can be positive or negative, depending on whether it becomes more or less soluble upon exposure to light.
Soft bake: The coated substrate is subjected to a low-temperature bake to evaporate any solvent and make the photoresist layer more uniform.
Exposure: The photoresist-coated substrate is exposed to UV light through a photomask or reticle. The mask contains the pattern that needs to be transferred to the substrate. Exposure causes a chemical change in the photoresist, creating a latent image of the pattern.
Development: The substrate is then immersed in a developer solution. In positive photoresist, the exposed areas become soluble and are washed away during development, leaving the unexposed areas. In negative photoresist, the exposed areas remain after development.
Hard bake: The developed photoresist is subjected to a high-temperature bake to harden it and make it more resistant to subsequent processing steps.
Etching or deposition: The patterned photoresist serves as a mask for subsequent processes such as etching (removing material from exposed areas) or deposition (adding material to exposed areas), depending on the desired outcome.
Photoresist stripping: The remaining photoresist is typically removed to reveal the final pattern on the substrate.
Photolithography is a crucial technology for the semiconductor industry, allowing the creation of intricate patterns on a microscopic scale, which is essential for the fabrication of integrated circuits and other miniaturized electronic components. It enables the mass production of complex electronic devices with high precision.