In layman's terms, the photolithography process is to cover the wafer with a layer of photoresist. Since the photoresist contains photosensitive materials, the material properties will change after being exposed to specific light. Therefore, light can be allowed to pass through the mask with a designed circuit pattern and shine on the photoresist. The solubility of the illuminated photoresist will change and become easier to dissolve (taking positive photoresist as an example). The exposed photoresist on the wafer is then dissolved and cleaned, and then the circuit is formed through processes such as etching, deposition, and ion implantation. Finally, the remaining photoresist is cleaned away.
Just like light passes through the film (mask) to print a photo on the screen (silicon wafer), the photoresist is like a layer of photosensitive protective film. The part of the film that is hit is easily dissolved, and the photoresist in the area that needs to be etched is washed away, and the photoresist in the reserved area is retained. Then the entire screen is placed in a corrosive liquid, and finally the photoresist is washed away. Then, the pattern of the photo (circuit) can be engraved on the screen (silicon wafer). This is the general principle of semiconductor lithography.
Composition of photoresist：
Photoresist is mainly composed of resin, photoinitiator, solvent, monomer and other additives. Resin is mainly used as an adhesive to hold different materials in photoresist together, giving photoresist mechanical and chemical properties. Photoinitiator, also known as photosensitizer or photocuring agent, is the photosensitive component in photoresist material. After absorbing ultraviolet light or visible light energy of a certain wavelength, it can be decomposed into free radicals or cations and can initiate chemical cross-linking reactions in monomers. Therefore, resin and photoinitiator are the most important components.
According to the different chemical reaction mechanisms, photoresists can be divided into positive and negative photoresists. The simplest way to distinguish them is that positive photoresists become "soft" after being exposed to light, while negative photoresists become "hard" after being exposed to light. The "soft" part will be dissolved, while the "hard" part will be retained. Therefore, for the same mask, the patterns of positive and negative photoresists after being exposed to light and dissolved are opposite.
Since the photoresist process needs to be washed with corrosive liquid at the end, the resin selected for the photoresist must be a resin with strong chemical resistance. Our company's T-7133 resin has the performance of strong acid and alkali resistance, especially hydrofluoric acid, and is very suitable for use as the main resin of the photoresist. We also have corresponding matching photoinitiators and other products.
