Epitaxy or epitaxial growth is the process of depositing a thin layer (0.5 to 20 microns) of single crystal material over a single crystal substrate, usually through chemical vapor deposition (CVD). In semiconductors, the deposited film is often the same material as the substrate, and the process is known as homoepitaxy, or simply, epi. An example of this is silicon deposition over a silicon substrate.
Silicon epitaxy is done to improve the performance of bipolar devices. By growing a lightly doped epi layer over a heavily-doped silicon substrate, a higher breakdown voltage across the collector-substrate junction is achieved while maintaining low collector resistance. Lower collector resistance allows a higher operating speed with the same current.
Epitaxy has also recently been used in CMOS VLSI circuits. By fabricating the CMOS device on a very thin (3-7 microns) lightly doped epi layer grown over a heavily-doped substrate, latch-up occurrence is minimized.
Aside from improving the performance of devices, epitaxy also allows better control ofdoping concentrations of the devices. The layer can also be made oxygen- and carbon-free. The disadvantages of epitaxy include higher cost of wafer fabrication, additional process complexities, and problems associated with defects in the epi layer.
The chemical vapor deposition of silicon epitaxy is usually achieved using an epitaxial reactor (Fig. 1) that consists of a quartz reaction chamber into which a susceptor is placed. The susceptor provides two things: 1) mechanical support for the wafers and 2) an environment with uniform thermal distribution. Epitaxial deposition takes place at a hightemperature as the required process gases flow into the chamber.
Our epitaxial wafers meet the technological demands of our customers that manufacture advanced semiconductor devices. Epitaxial wafers consist of a thin, single crystal silicon layer grown on the polished surface of a silicon wafer substrate. This "epi" layer is designed to have different compositional and electrical properties from the underlying wafer, tailored to the specific demands of the device. This compositional change, among other things, can be used to improve isolation between circuit elements fabricated on the epi wafer. The epi layer is also substantially free of surface imperfections that can cause device failure. Epitaxial wafers provide for increased reliability of the finished semiconductor device, greater efficiencies during the semiconductor manufacturing process, and ultimately more complex integrated circuit devices.
Epitaxial Layer: layer grown in the course of epitaxial deposition, or epitaxy; its crystallographic structure reproduces structure of the substrate but doping level and conductivity type of epitaxial layer is controlled independently of the substrate; e.g. can be made chemically purer than the substrate; silicon substrates with epitaxial layers are commonly used in CMOS and bipolar device technology.
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