Electronic Circuits and Diagram-Electronics Projects and Design

In this post, we shall discuss, the fabrication of a standard, junction- isolated bipolar IC.  Of course, many devices can be formed at a time over the surface of the water if appropriate patterns are provided. We shall show only one device, that is, a bipolar transistor as an example. The major steps in the IC bipolar process are listed in the diagram below. The starting material is a p-type single crystal silicon wafer having 5 to 20 ohm-cm resistivity and thickness of approximately several hundred micrometers. The diameter can be 50, 75, 100, 125, or 150 mm. The most…

The figure below shows a diagram of gallium arsenide (GaAs) MESFET (metal-semiconductor field-effect transistor). MESFET is nothing but a JFET fabricated in GaAs which employs a metal-semiconductor gate region (a Schottky diode). The device operates in essentially the same way as does a junction-gate FET, except that instead of a gate-channel on junction there is a gate-channel Schottky barrier. The depletion region associated with this barrier will control the effective height of the conducting channel and can thereby control the drain-to-source current of the device. The width of this depletion region will increase with increasing gate voltage so that we…

Junction Characteristics Before describing the fabrication sequences for ICs, it will be useful to provide insight into the use of epitaxial structures for devices. A reverse-biased p-n junction can be considered to be a parallel-plate capacitor with the depletion region being the insulator or dielectric as shown in the figure below. The depletion or space-charge region is the region adjacent to the p-n junction that is essentially depleted (or devoid) of all mobile charges (that is, free electrons and holes), so that it acts like an insulator. For almost all diffused p-n junctions the doping on the diffused layer side…

To know about the different IC fabrication techniques, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES Metallization is the final step in the wafer processing sequence. Metallization is the process by which the components of IC’s are interconnected by aluminium conductor. This process produces a thin-film metal layer that will serve as the required conductor pattern for the interconnection of the various components on the chip. Another use of metallization is to produce metalized areas called bonding pads around the periphery of the chip to produce metalized areas for the bonding of wire leads from the…

To know about the different IC fabrication techniques, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES ION IMPLANTATION Ion Implantation is an alternative to a deposition diffusion and is used to produce a shallow surface region of dopant atoms deposited into a silicon wafer. This technology has made significant roads into diffusion technology in several areas. In this process a beam of impurity ions is accelerated to kinetic energies in the range of several tens of kV and is directed to the surface of the silicon. As the impurity atoms enter the crystal, they give up…

To know about the different IC fabrication techniques, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES Diffusion of Dopant Impurities The process of junction formation, that is transition from p to n type or vice versa, is typically accomplished by the process of diffusing the appropriate dopant impurities in a high temperature furnace. Impurity atoms are introduced onto the surface of a silicon wafer and diffuse into the lattice because of their tendency to move from regions of high to low concentration. Diffusion of impurity atoms into silicon crystal takes place only at elevated temperature, typically…

To know more about lithographic process and it’s basic types, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES TAKE A LOOK : PHOTOLITHOGRAPHY Electron-beam lithography provides better resolution then photolithography. This is possible because of small wavelength of the 10-50 KeV electrons. The resolution of electron-beam lithography system is not limited by diffraction, but by electron scattering in the resist and by the various aberrations of the electron optics. The electron-beam exposure system (EBES) machine has proved to be the best photomask pattern generator. However, the pattern writing is in serial form. Therefore, the throughput is…

To know more about lithographic process and it’s basic types, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES TAKE A LOOK : PHOTOLITHOGRAPHY The photolithography has its resolution limited by diffraction effects. To improve the resolution, therefore, the diffraction effects are reduced by reducing the wavelength. However, if the wavelength is reduced further, all optical materials become opaque because of the fundamental absorption, but transmission increases again in the X-ray region. This led to the requirement of X-rays for lithography purpose. In X-ray lithography an X-ray source illuminates a mask, which casts shadows on to a…

To know more about lithographic process and it’s basic types, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES TAKE A LOOK : PHOTOLITHOGRAPHY Ion-Beam Lithography Ion-beam lithography, when used to expose resist, provides higher resolution than that possible with an electron-beam because of less scattering. Also, resists are more sensitive to ions than to electrons. A unique feature of ion-beam is that there is the possibility of wafer processing without resists if it is used to implant or sputter selected areas of the wafer. The most important application is repair of photomask, a task for which…

To know more about the basics, click on the link below. TAKE A LOOK : IC FABRICATION TECHNIQUES When a sample of crystalline silicon is covered with silicon dioxide, the oxide-layer acts as a barrier to the diffusion of impurities, so that impurities separated from the surface of the silicon by a layer of oxide do not diffuse into the silicon during high-temperature processing. A p-n junction can thus be formed in a selected location on the sample by first covering the sample with a layer of oxide [oxidation step] removing the oxide in the selected region, and then performing…