16-10-2012, 01:25 PM
IC Fabrication – An Introduction
IC Fabrication.ppt (Size: 2.15 MB / Downloads: 84)
Types of Chips
Dynamic Random Access Memory chips (DRAMs) - serve as the primary memory for computers
Microprocessors (MPUs) - act as the brains of computers.
Application Specific Integrated Circuits (ASICs) - are custom semiconductors designed for very specific functions
Digital Signal Processors (DSPs) - process signals, such as image and sound signals or radar pulses.
Programmable memory chips (EPROMs, EEPROMs, and Flash) - are used to perform functions that require programming on the chip.
Logic Circuit Design / Layout Design
A logic circuit diagram is drawn to determine the electronic circuit required for the requested function.
Once the logic circuit diagram is complete, simulations are performed multiple times to test the circuit’s operation.
Photomask Creation
The photomask is a copy of the circuit pattern, drawn on a glass plate coated with a metallic film.
The glass plate lets light pass, but the metallic film does not.
Due to increasingly high integration and miniaturization of the pattern, the size of the photomask is usually magnified four to ten times the actual size.
Wafer Fabrication
A high-purity, single-crystal silicon called "99.999999999% (eleven-nine)" is grown from a seed to an ingot.
The wafers are generally available in diameters of 150 mm, 200 mm, or 300 mm, and are mirror-polished and rinsed before shipment from the wafer manufacturer.
Deposition
the wafer is placed in a high-temperature furnace to make the silicon react with oxygen or water vapor, and to develop oxide films on the wafer surface (thermal oxidation).
To develop nitride films and polysilicon films, the chemical vapor deposition (CVD) method is used, in which a gaseous reactant is introduced to the silicon substrate, and chemical reaction produce the deposited layer material.
The metallic layers used in the wiring of the circuit are also formed by CVD, spattering (PVD: physical vapor deposition)
Patterning: Development
The photoresist chemically reacts and dissolves in the developing solution, only on the parts that were not masked during exposure (positive method).
Development is performed with an alkaline developing solution.
After the development, photoresist is left on the wafer surface in the shape of the mask pattern.
Device Insulation Layer (Field-Oxide Film) Formation
After the oxide film and nitride film are developed, a resist pattern is formed on the regions that will become the device insulation layer.
Ion implantation is performed on the wafer, forming a p-type diffusion layer.
Next, the oxide film and nitride film on the diffusion layer are etched.
Using the nitride film pattern as the mask, the oxide film that will become the device insulation layer is developed.
Transistor Formation
A transistor is a semiconductor device with a switching function and three terminals: source, drain, and gate.
An insulation layer called "gate oxide" is first formed on the wafer surface.
A polysilicon film is deposited onto the gate oxide, and a polysilicon gate for controlling the flow of electrons between the source region and the drain region is formed by lithography and etching.
After the polysilicon gate is formed, an n-type diffusion layer consisting of both the source and the drain regions is formed by implantation of impurities