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Semiconductor Manufacturing and Fabrication

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Semiconductor Manufacturing and Fabrication Review

Semiconductor manufacturing and fabrication is the process industry uses to create an integrated circuit for use in electronic devices. The steps required to create a semiconductor are chemical and photographic techniques to create what is termed a wafer. The wafer may be composed of semiconductor material, such as Silicon (made primarily from sand), gallium arsenide, germanium and other materials.

When a wafer is made from purified silicon, it is grown from crystalline ingots using the Czochralski process. After the wafers have been grown into a cylinder, they are cut to create an optimal thin flat shape (thin and circular). On the cut wafer piece, many more steps are employed to create a final product. A typical first step may be that a p-type (epi-layer) layer is grown on the cut wafer (silicon substrate) by a process called chemical vapor deposition. The next layer may be nitride, then the silicon substrate is masked and etched as required to expose areas on p-type layer. These etched areas are then masked again, then processed by diffusion or ion implantation to create dopants such as phosphorus to form n-wells.

The Ion implantation require equipment that consists of a controlled and directed ion source, where the ions are electrostatically accelerated by a high energy which are then directed onto the substrate. Where the ions are targeted on the substrate, the ion implantation cause a chemical change on the substrate surface. Following this step, many more layers and masking steps may be utilized to ultimately create many multilayer integrated circuits on the same circular wafer. Following testing, each integrated circuit is cut from the wafer using a precision diamond saw. Each integrated circuit is assembled into a protective and final package. The final semiconductor integrates circuit, is then tested again to verify performance.

The steps outlined are one of many possible processes used within industry for manufacturing a semiconductor. In reality, there may be more than 250 very high technology steps required to manufacture a semiconductor.

Processing

In semiconductor device fabrication, the various processing steps fall into four general categories: deposition, removal, patterning, and modification of electrical properties.

  • Deposition is any process that grows, coats, or otherwise transfers a material onto the wafer. Available technologies include physical vapor deposition (PVD), chemical vapor deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and more recently, atomic layer deposition (ALD) among others.
  • Removal is any process that removes material from the wafer; examples include etch processes (either wet or dry ) and chemical-mechanical planarization (CMP).
  • Patterning is the shaping or altering of deposited materials, and is generally referred to as lithography . For example, in conventional lithography, the wafer is coated with a chemical called a photoresist ; then, a machine called a stepper focuses, aligns, and moves a mask , exposing select portions of the wafer below to short wavelength light; the exposed regions are washed away by a developer solution. After etching or other processing, the remaining photoresist is removed by plasma ashing .
  • Modification of electrical properties has historically entailed doping transistor sources and drains (originally by diffusion furnaces and later by ion implantation ). These doping processes are followed by furnace annealing or, in advanced devices, by rapid thermal annealing (RTA); annealing serves to activate the implanted dopants. Modification of electrical properties now also extends to the reduction of a material's dielectric constant in low-k insulators via exposure to ultraviolet light in UV processing (UVP).

Modern chips have up to eleven metal levels produced in over 300 sequenced processing steps.

Terms defined:

Etch - Process used to remove selected portions of material from the wafer.

Ions - Atoms which have an electrical charge. The ions cause the required chemicals changes on the surface of the wafer.

Masks - Masks are used on wafers and printed circuit boards on selected areas to prevent material removal from subsequent manufacturing processes.

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