Silicon Wafer | The Importance of Lithography Process in Circuit Fabrication

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October 28, 2019

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Lithography is a process used to pattern specific geometric shapes on a silicon wafer for circuit fabrication to produce electrical devices. Without it, no electrical device would ever function. In this article, we will discuss to you the importance of the lithography process.

What is Circuit Fabrication?

Circuit fabrication on a silicon wafer involves several different layers, each imprinted with different patterns. These patterns used in depositing layers and doping parts of specific areas on the substrate are set by a process called lithography. The lithography process consists of the following steps: A photoresist layer is spin-coated on the surface of a silicon wafer. Then, the resist layer is selectively exposed to radiation such as x-rays, ultraviolet light, or electrons, with the exposed areas outlined by mask or computer data.  After the exposure, the photoresist layer is subjected to development which helps get rid of unwanted parts of the photoresist layer, showing the equivalent parts of the underlying layer. But some resist type, during development, may destroy both the exposed or unexposed areas. The areas with no resist material left on the surface are then made to undergo subtractive or additive processes, allowing selective removal on the wafer. There are two types of photoresist: positive photoresist and negative photoresist. A positive photoresist is when the part of the photoresist that is exposed to light becomes dissolvable in a developer, while the unexposed part remains to be insoluble. A negative photoresist is when the part of the photoresist that is exposed to light becomes insoluble, while the exposed part is soluble. In most wafer fabrication, a positive photoresist is preferred because it can provide higher resolution capabilities.

Photoresist Materials are Composed of Three Things:

  • Matrix material- serves as a body for the photoresist
  • Inhibitor- considered to be the photoactive ingredient
  • Solvent- keeps the resist in the liquid until applied on the wafer
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