Semiconductor Manufacturing

Semiconductors

In general, semiconductors are inorganic or organic materials that can control their conduction depending on chemical structure, temperature, illumination, and the presence of dopants. The name semiconductor comes from the fact that these materials have electrical conductivity between a metal, like copper, gold, etc., and an insulator, like glass. They have an energy gap of less than 4eV (about 1eV). In solid-state physics, this energy gap or band gap is an energy range between the valence band and conduction band where electron states are forbidden. In contrast to conductors, semiconductors’ electrons must obtain energy (e.g., from ionizing radiation) to cross the band gap and reach the conduction band. The properties of semiconductors are determined by the energy gap between valence and conduction bands.

Semiconductor Manufacturing

Semiconductors are typically made using a process called semiconductor fabrication or “semiconductor manufacturing.” Here are the basic steps involved in the process:

1. Crystal Growth: The first step in semiconductor manufacturing is growing a pure crystal of silicon, which will serve as the substrate for the rest of the process.
2. Wafer Preparation: After growing the crystal, it is sliced into thin wafers. These wafers are polished to remove any surface defects or impurities.
3. Photoresist Coating: A thin layer of photoresist material is applied to the surface of the wafer.
4. Photo Masking: A photo mask is placed over the wafer, and the entire assembly is exposed to ultraviolet light. The photoresist material reacts to the light, creating a pattern on the surface of the wafer.
5. Etching: The wafer is etched using a chemical solution or plasma, which removes the silicon material from the areas not protected by the photoresist.
6. Ion Implantation: Ions are implanted into the exposed areas of the wafer to alter its electrical properties.
7. Thermal Processing: The wafer is heated in a furnace to activate the implanted ions and anneal the silicon crystal structure.
8. Deposition: Layers of thin-film materials are deposited onto the wafer using chemical vapor deposition or other methods.
9. Photolithography: The photoresist is removed, and the wafer is coated with a new layer of photoresist. This process is repeated to create additional layers of patterned materials on the wafer.
10. Dicing and Packaging: Once all the layers are complete, the wafer is cut into individual chips and packaged for use in electronic devices.

The entire semiconductor manufacturing process is highly automated and precise, with many of the steps being repeated hundreds or thousands of times to create a single chip.

Types of Semiconductors

Semiconductors can be classified into two basic types based on their electronic properties:

1. Intrinsic Semiconductors: These are pure semiconductors that are made up of a single element (e.g., Silicon, Germanium) and have no intentional doping with impurities. Intrinsic semiconductors have a specific number of electrons in their valence band and conduction band. They conduct electricity when they are heated, and some electrons gain sufficient energy to break free from their bonds and become free electrons in the conduction band.
2. Extrinsic Semiconductors: These are impure semiconductors that are intentionally doped with impurities to change their electronic properties. Extrinsic semiconductors can be further classified into two types:
   1. p-type semiconductors: In p-type semiconductors, impurity atoms such as boron are introduced into the semiconductor material. These impurities have fewer valence electrons than the semiconductor material, which results in “holes” (absence of electrons) being created in the valence band. These holes can conduct current like positive charge carriers, which gives the material its p-type designation.
   2. n-type semiconductors: In n-type semiconductors, impurity atoms such as phosphorus are introduced into the semiconductor material. These impurities have more valence electrons than the semiconductor material, which creates excess electrons in the conduction band. These excess electrons can conduct current like negative charge carriers, which gives the material its n-type designation.