The Difference Between Positive and Negative Photoresist

As semiconductor suppliers, photoresist is a material that is continuously worked with. This light sensitive material has two types, positive and negative, that react very differently when exposed to UV light; therefore, it is essential to understand each reaction in order to produce the best results in the semiconductor manufacturing industry.

Positive Photoresists

With positive photoresists, UV light strategically hits the material in the areas that the semiconductor supplier intends to remove. When the photoresist is exposed to the UV light, the chemical structure changes and becomes more soluble in the photoresist developer. These exposed areas are then washed away with the photoresist developer solvent, leaving the underlying material. The areas of the photoresist that aren’t exposed to the UV light are left insoluble to the photoresist developer. When working with positive photoresists in the semiconductor manufacturing industry, you receive an identical copy of the pattern, which is exposed as a mask on the wafer.

Negative Photoresists

With negative resists, exposure to UV light causes the chemical structure of the photoresist to polymerize, which is just the opposite of positive photoresists. Instead of becoming more soluble, negative photoresists become extremely difficult to dissolve. As a result, the UV exposed negative resist remains on the surface while the photoresist developer solution works to remove the areas that are unexposed. This leaves a mask that consists of an inverse pattern of the original, which is applied on the wafer.

Both positive and negative photoresists are still used in the semiconductor manufacturing industry today, but many semiconductor suppliers opt for positive photoresists due to their higher resolution capabilities. Positive photoresists are able to maintain their size and pattern as the photoresist developer solvent doesn’t permeate the areas that have not been exposed to the UV light. With negative resists, both the UV exposed and unexposed areas are permeated by the solvent, which can lead to pattern distortions.

While positive photoresists seem to have the advantage, negative photoresists aren’t necessarily a thing of the past. Negative resists are a great material to use for those semiconductor supplies that don’t require such high resolutions. As opposed to positive photoresists, negative resists have a faster photo speed, wider process latitude and a significantly lower operating cost. Negative photoresists also have better adhesion capabilities to certain substrate materials.

Both positive and negative photoresists have their place in the semiconductor manufacturing industry, and help to produce a range of high quality products. At Shin-Etsu MicroSi in Phoenix, we specialize in developing and manufacturing materials for the semiconductor industry. We are dedicated to our customers, and seek to provide only the best products and customer service. For more information on Shin-Etsu MicroSi, a world class semiconductor supplier, please call (480) 893-8898 or contact us online.