Semiconductor fabrication
From Freepedia
Semiconductor device fabrication is the process used to create chips, the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is the most commonly used semiconductor material today, although gallium arsenide, germanium, and many other materials are used in special applications.
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Wafers
A typical wafer is made out of extremely pure silicon that is grown into mono-crystalline cylindrical ingots (boules) up to 12" (300 mm) in diameter using the Czochralski process. These ingots are then sliced into wafers about 0.75mm thick and polished to obtain a very regular and flat surface.
Once the wafers are prepared, many process steps are necessary to produce the desired semiconductor integrated circuit. In general the steps can be grouped into four areas:
- Front end processing
- Back end processing
- Test
- Packaging.
Processing
Front End Processing refers to the most crucial steps in the fabrication. In this stage the actual devices, including transistors and resistors are created. A typical front end process includes the following: preparation of the wafer surface, growth of silicon dioxide (SiO2), patterning and subsequent implantation or diffusion of dopants to obtain the desired electrical properties, growth or deposition of a gate dielectric, and growth or deposition of insulating materials to isolate neighboring devices.
Once the various semiconductor devices have been created they must be interconnected to form the desired electrical circuits. This "Back End Processing" involves depositing layers of metal and insulating material and etching it into the desired patterns. Typically the metal layers consist of aluminium or more recently copper. The insulating material was traditionally a form of SiO2 or a silicate glass, but recently new low dielectric constant materials are being used. The various metal layers are interconnected by etching holes, called "vias," in the insulating material and depositing tungsten in them.
Wafer test and device test
Once the Back End Processing has been completed, the semiconductor devices are subjected to a variety of electrical tests to determine if they function properly. The proportion of devices on the wafer found to perform properly is referred to as the yield.
Finally, the wafer is cut into individual dice, which are then packaged in ceramic or plastic packages with pins or other connectors to the outside world.
The packaged chips are then retested to ensure that they were not damaged during packaging and that the die-to-pin interconnect operation was performed correctly.
List of steps
- Wafer fabrication
- Wet cleans
- Photolithography
- Ion implantation (in which dopants are embedded in the wafer creating regions of increased ( or decreased ) conductivity)
- Dry Etching
- Wet Etching
- Plasma ashing
- Thermal treatments
- Chemical vapor deposition (CVD)
- Physical vapor deposition(PVD)
- Molecular beam epitaxy (MBE)
- Electroplating
- Chemical mechanical polish (CMP)
- Wafer testing (where the electrical performance is verified)
- Wafer backgrinding (to reduce the thickness of the wafer so the resulting chip can be put into a thin device like a smartcard or PCMCIA card.)
- Die preparation
- IC packaging
- IC testing
Hazardous materials note
Many toxic materials are used in the fabrication process. These include:
- poisonous elemental dopants such as arsenic, boron, antimony and phosphorus
- poisonous compounds like arsine, phosphine and silane
- highly reactive liquids, such as hydrogen peroxide, fuming nitric acid, sulfuric acid and hydrofluoric acid
It is vital that workers are not directly exposed to these dangerous substances. The high degree of automation common in the IC fabrication industry helps to reduce the risks of exposure of this sort.
History
When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacture. But as the devices became more integrated the cleanrooms became even cleaner. Today, the facilities, known as fabs, are pressurized with filtered air, to remove even the smallest particles which could come to rest on the wafers and contribute to defects. The workers in a semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination.
In an effort to increase profits, semiconductor device manufacture spread from Texas and California in the 1960s to the rest of the world, such as Japan, Taiwan, Korea, Singapore and China, and is a global business today.
Semiconductor manufacturing is still strong in the United States, but the world's market leaders are in Taiwan and Korea, represented by major companies such as Taiwan Semiconductor Manufacturing Company (see TSMC web site), United Microelectronics Corporation (see UMC web site), Samsung and Hynix. Singapore is also a significant semiconductor manufacturer and is home to Chartered Semiconductor Manufacturing.
See also
- SEMI — The semiconductor industry trade association
External links
- Semiconductor Manufacturing
- Intel's Animated step-by-step process
- Semiconductor Manufacturing and Fabrication
