[PYE] Semiconductor Processing

What is a silicon wafer?

A thin, flat piece of silicon that serves as the base material on which semiconductor devices and integrated circuits are fabricated.

What is oxidation in semiconductor processing?

Oxidation is the process of growing a silicon dioxide SiO_2 layer on the surface of silicon.

Silicon dioxide is an electrical insulator that can be used for electrical isolation and oxide layers in semiconductor structures.

What is photolithography?

Photolithography is the process of transferring a pattern onto selected areas of a wafer using photoresist, a mask, light exposure, and development.

What is photoresist and how does it protect areas of a wafer?

Photoresist is a light-sensitive material placed on the wafer. After exposure and development, some photoresist is removed while some remains. The areas where photoresist remains are protected, while the uncovered areas can be worked on.

Positive photoresist:
Exposed to light → removed during development.

Negative photoresist:
Exposed to light → remains after development.

What is etching in semiconductor processing?

Etching removes material from the areas left uncovered after the photoresist has been patterned and developed.
Wet etching: Uses liquid chemicals and can remove material sideways and downward.
Dry etching: Uses reactive gases/plasma and can provide more directional, precise removal.

What is doping in semiconductor processing?

Doping is intentionally adding specific atoms to a semiconductor to change its electrical properties and create N-type or P-type regions.

What are dopant atoms?

Dopant atoms are the specific impurity atoms intentionally added to a semiconductor to change its electrical properties.

Examples include phosphorus and boron.
*Impurity Atom: It is an atom that is different from the main atoms making up the material.

How are dopants introduced into silicon during fabrication?

Ion implantation: Dopant ions are accelerated into selected areas of silicon.
Diffusion: Heat allows dopant atoms to diffuse into silicon.

Purpose: Create controlled N-type and P-type regions.

What is annealing in semiconductor processing?

Annealing is heating the wafer after processes such as ion implantation to repair crystal damage and electrically activate the dopants.

What is deposition in semiconductor processing?

The process of adding a thin layer of material onto the surface of a wafer.

(These thin layers can serve different purposes depending on the material, such as insulation, conducting electricity, or helping form parts of the device.)

What is the difference between Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD)?

CVD uses chemical reactions to form a layer. PVD physically transfers material onto the wafer.

What are interconnects in a semiconductor chip?

Conductive paths that electrically connect transistors and other components on a chip.

What is metallization?

The process of forming conductive layers and connections on a semiconductor chip

What do vias do?

They create an electrical connection between different conductive layers.

What is a via?

A via is a small conductive path used to create that electrical connection between different conductive layers.

What is Chemical Mechanical Planarization (CMP) in semiconductor processing?

Chemical Mechanical Planarization (CMP) is a process used to flatten and smooth an uneven surface on the wafer. Chemicals help remove material while a polishing pad physically smooths the surface.

What is process variation?

Refers to small differences that occur during manufacturing from one device, wafer, or lot to another. These differences can change the physical or electrical properties of a device, which may cause some devices to fail testing and decrease yield.

How can process variation affect yield?

Process variation can change a device's physical properties or structure, which can change its electrical behavior. This may cause the device to fail testing and lower yield.

Examples:
Doping variation → electrical properties change
Etching variation → wrong dimensions
Deposition variation → layer too thick/thin
Photolithography misalignment → structures in wrong location

What is yield in semiconductor manufacturing?

Yield is the percentage of manufactured devices that pass testing and meet the required specifications compared with the total number of devices produced.

Yield = # of good devices/total devices produced