Sorry, your combination is currently not available. Activate your e-mail service!
WHAT ARE SEMICONDUCTORS?
Semiconductors are materials which are between insulators and conductors in terms of conduction of current. Silicon, germanium and carbon are the most common semiconductors. Semiconductors, often referred to as computer chips or integrated circuits (ICs), contain numerous electrical pathways which are capable of connecting to a number of transistors and other electronic components. The information is stored by these transistors on the semiconductors, either by holding an electrical charge or by holding little or no charge.
Due to the significant advances in the technology, semiconductor technology is continuously evolving and becoming more prevalent in our lives. Over the past 40 years there has been a tremendous decrease in the size of the individualtransistors.
Semiconductor manufacturing can be defined as the process of taking bare silicon wafers and repetitively processing them by adding layers of material which are then patterned and cut into individual chips for use in electronic system. The semiconductor manufacturing process consists of two phases: the wafer process, during which circuit patterns are formed in the wafer, and the assembly process, during which the semiconductors are tested and packaged. The fabrication of integrated circuits often referred to as fab involves a sequence of production steps, which is repeated many number of times as required depending on the complexity of the device. Most fabrication steps are carried out in clean rooms as a high level of impurity and environmental control is desirable at all phases of device manufacturing.
A typical wafer is cut from a pure silicon ingot. Silicon wafers are produced in different diameters ranging from 200 mm to 300 mm. Today almost all the computer chips are made of silicon wafers as silicon is inexpensive and highly abundant. After the preparation of the wafers, it has to undergo several processing steps which can be categorized into the following four types:
Deposition is the process of growing, coating, layering or transferring materials onto the wafer. Oxidation and Nitridation are some of the famous growing technologies. Other available technologies include physical vapour deposition (PVD), chemical vapour deposition (CVD), electrochemical deposition (ECD), molecular beam epitaxy (MBE) and atomic layer deposition (ALD). Oxidation forms a thin layer of silicon dioxide (SiO2) completely over the wafer surface which acts as a diffusion barrier covering the silicon throughout the entire processing sequence.
Patterning is also known as masking, photo masking, photo lithography etc. Photolithography is used to define patterns in the oxide layer and it is done so in the following manner: Applying photo resist as a spun coat on the wafer surface, Exposing a circuit pattern to ultra violet light using a mask or reticle (smaller masks) and Developing the Photo resist. The photoresist is exposed by a stepper, a machine that focuses, aligns, and moves the mask, exposing select portions of the wafer to short wavelength UV light. Developing the photo resist causes the soft unexposed resist to be removed and the hard photo resist to remain on the wafer surface.
Removal or Etching is the process step used to remove the non-patterned oxide layer from the wafer surface after photolithography. A specialized machine called plasma etcher is used to remove the oxide layers not covered by photo resist. Etching can be accomplished in wet or dry chemical systems. Dry etching is the most common method and utilizes gaseous species to generate reactive products that attack the surface to be etched. Wet etching involves the use of wet chemicals which react with the material to be removed.
It is defined as the process step in which controlled amounts of doper are introduced into semiconductor wafer. Dopants are electrically active ions that are added to the wafer to modify the properties of the material. Implantation can be performed before or after the etching process depending upon the desired results.
Assembly is the process of converting fabricated wafers into individually packaged integrated circuits. The assembly operation consists of the following steps:
- Sawing the wafer between die
- Packaging the die
- Bonding die pads to package leads
- Package sealing
- Making identification marks on package
A packaged die is referred to as the chip or unit. The packaged chips are re-tested to ensure that they were not damaged during packaging.
INSPECTION AND CONTROL
Physical defects are introduced during manufacturing steps due to equipment and human problems. Defects can be of several types and can cause various problems like distortion in the pattern, open or short circuit, mechanical stress. Some defects may be completely inactive while some may be dormant initially and then get activated at a later point of time which may be dangerous. Defects are identified and rectified by visual inspection and electrical tests during and after wafer fabrication. Die test is the first step carried out on the wafer testing each IC and conforming its compliance to the design specifications. Some chips are also physically damaged during assembly process which are visually recognized and scrapped after assembly.
A few of the integrated circuit manufacturing companies in the world are: TOSHIBA, Fujitsu, Freescale, Atmel, BECKHOFF, RENESAS Electronics, Infineon Technologies, Conax Technologies and ST Microelectronics.