In the manufacture of various semiconductor devices wherein an oxide coating is formed on a semiconductor substrate, it is often required to remove selected portions of the oxide coating. This is done conventionally by applying a photoresist film to the oxide coating, exposing the photoresist to light through a photomask which is patterned in the desired configuration, developing the exposed photoresist with a solvent to form a relief pattern and etching to remove the oxide layer not still protected by the photoresist. Positive photoresists become more soluble in the regions exposed to the light and negative photoresists become less soluble in the regions exposed to the light. After etching, the remaining photoresist is stripped from the oxide layer.
As integrated circuits and other semiconductor devices become smaller, the requirements for the photoresist become more stringent. Good photoresists should have good adherence to the oxide substrate; should have a high contrast to light so that very fine patterns can be developed; should have a relatively high solubility difference between the exposed and nonexposed areas; should be resistant to the etching solution employed so that they do not lift off or curl at the edges during etching; should be non-tacky so that they do not adhere or distort on contact with a photomask; and finally, should be able to be removed from the oxide layer rapidly and cleanly. Thus, there is a continuing search for new photoresists with improved sensitivity and effectiveness.
A major problem with existing photoresists is poor adherence to the substrate. This results in undercutting of the photoresist during the etching step and leads to reduced edge definition of the pattern obtained. Prior art workers have attempted to improve known photoresists by prebaking or postbaking to improve the adhesion of the photoresist to the oxide substrate, but these steps add to processing time and expense and are not wholly effective. Other workers have added reagents to improve this adhesion, but these reagents reduce photoresist sensitivity and some reagents cause difficulties in removal of the resist layer after etching.