The Difference Between Positive & Negative Photoresist

Photoresist is a material that semiconductor suppliers are constantly working with. This light-sensitive material is divided into two types: negative and positive, which react in very different ways when exposed to UV light. It is therefore essential to understand each reaction in order to produce the best results in the semiconductor manufacturing industry.

Positive Photoresist:

UV light is used to expose the resist where the fundamental material is to be detached. Contact with UV light changes the chemical structure of these resists, making them more soluble in the developer. The developer solution then washes away the exposed resist, separating the windows from the base material. The mask thus covers an accurate copy of the shape that will be left on the wafer as a stencil for further processing.

Negative Photoresist:

A negative photoresist works in the opposite direction. When the negative resist is exposed to UV light, it polymerises and becomes more difficult to dissolve in the developer. As a result, the negative resist remains on the exposed surface of the substrate, and the developer solution only removes the unexposed areas. The negative photoresist masks contain the opposite negative of the pattern to be transferred. The diagram above illustrates the pattern differences caused by the use of positive and negative resist.

Both positive and negative photoresists are still used in the semiconductor manufacturing industry today, but positive photoresists are preferred by many semiconductor suppliers because of their higher resolution capabilities. Because the solvent in the photoresist developer does not penetrate areas that have not been exposed to UV light, positive photoresists retain their size and pattern. The solvent penetrates both the non-UV exposed areas and the exposed areas of the negative resists, resulting in pattern distortions.

Both positive and negative photoresists have their place in the semiconductor manufacturing industry and contribute to the production of a wide range of high quality products. While positive photoresists seem to have the upper hand, negative photoresists are not necessarily on the way out. Negative photoresists are an excellent material for semiconductor supplies that do not require such high resolution. Negative photoresists, as opposed to positive photoresists, have a faster photo speed, greater process latitude and a significantly reduced operating budget. Negative photoresists are also more adherent to certain substrate materials.

A-GasElectronic Materials specialises in the development and manufacture of semiconductor materials. A-Gas is committed to providing only the best products and services to its customers. Contact A-Gas for more information on positive and negative photoresist and more.