Photoresist

The semiconductor process begins with photolithography. Forming semiconductor circuits in the photolithography step requires the use of a special material: Photoresist. Just what is photoresist, and how does the semiconductor process make use of it?

Photoresist

Photoresist is a light-sensitive material used in photolithography processes, particularly in the fabrication of semiconductor devices, integrated circuits, and microelectromechanical systems (MEMS). It is a crucial component in the patterning of semiconductor wafers during the manufacturing process.

The primary function of photoresist is to undergo a chemical or physical change when exposed to light, making it selectively soluble or insoluble in a subsequent development step. The general process involving photoresist includes the following steps:

Coating: A thin layer of photoresist is applied to the surface of a substrate, often a silicon wafer. The substrate is typically cleaned before coating.

Exposure: The photoresist-coated substrate is exposed to UV light through a photomask or reticle. The photomask contains the pattern that needs to be transferred to the substrate. The exposed areas of the photoresist undergo a chemical change.

Development: The substrate is immersed in a developer solution. In positive photoresist, the exposed areas become soluble and are removed during development, leaving the unexposed areas. In negative photoresist, the exposed areas remain, and the unexposed areas are dissolved.

Pattern Transfer: The remaining patterned photoresist serves as a mask for subsequent processes such as etching or deposition. The pattern is transferred to the underlying layers of the substrate.

There are two main types of photoresist: positive and negative.

Positive photoresist: In positive photoresist, exposure to light increases solubility. The exposed areas are removed during development, leaving the unexposed areas as the desired pattern.

Negative photoresist: In negative photoresist, exposure to light decreases solubility. The unexposed areas are removed during development, leaving the exposed areas as the pattern.

The choice between positive and negative photoresist depends on the specific requirements of the fabrication process.

Photoresists play a critical role in the semiconductor manufacturing industry, enabling the creation of intricate patterns with high precision on the nanoscale, which is essential for the production of modern electronic devices.

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