Silicon Wafer Processing
Silicon Wafer Processing
Silicon Wafer Processing
Contents
1. Introduction---------------------------------------------------------------------------------------2 1.1 1.2 2 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 History of Integrated Circuits -----------------------------------------------------------2 What are Wafers??? ----------------------------------------------------------------------3 Wafer Preparation ------------------------------------------------------------------------- 4 Oxidation ------------------------------------------------------------------------------------ 4 Diffusion ------------------------------------------------------------------------------------- 4 Ion Implantation ---------------------------------------------------------------------------5 Chemical Vapor Deposition--------------------------------------------------------------5 Metallization---------------------------------------------------------------------------------5 Photolithography---------------------------------------------------------------------------5 Packaging ------------------------------------------------------------------------------------ 6
References ----------------------------------------------------------------------------------------------7
1. Introduction
Integrated circuits ( IC ) consists of several layers of patterned material to form FETS and interconnections. Nowadays in modern silicon processing minimum feature size is less than 0.12 m and there are chips present having more than 100 million FETs. Different techniques have been developed for chip-making.
Figure 1
Robert Noyce came up with his own idea for the integrated circuit. He did it half a year later than Jack Kilby. Noyce's circuit solved several practical problems that Kilby's circuit had, mainly the problem of interconnecting all the components on the chip. This was done by adding the metal as a final layer and then removing some of it so that the wires needed to connect the components were formed. This made the integrated circuit more suitable for mass production. Besides being one of the early pioneers of the integrated circuit, Robert Noyce also was one of the cofounders of Intel. Intel is one of the largest manufacturers of integrated circuits in the world. (1)
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Figure 2
The location of the IC on the wafer is known as Die site and these are the programmable locations. The Flat part of the wafer is used as a reference plane to form a grid for die placement.
2 IC Fabrication Steps
The basic steps of IC fabrication are described in this document , some of these steps may be done repeatedly with different combinations and under different conditions during a complete fabrication process. The basic steps of IC fabrication are as follows:
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2.2 Oxidation
The chemical process in which Oxygen reacts with Silicon to produce Silicon dioxide is called Oxidation. The oxygen used in oxidation is used as a high purity gas or it is introduced in the form of steam.
2.3 Diffusion
The movement of the atoms from high concentration region to the low concentration region through a semiconductor is known as Diffusion.
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2.6 Metallization
The process of connecting the components with the integrated circuit is done by using different metal layers and the process is known as Metallization. In this process firstly a metal layer is deposited over the surface of the semiconductor.
2.7 Photolithography
This is the most important step of the fabrication of the integrated circuits, in this process using ultra violet light we project a bigger circuit to a much smaller surface. Thus this process enables us to develop microscopically small circuits on the silicon wafers. It further consists of two main steps i. ii. Making a photographic mask Photo etching
Figure 3
This process requires the most expensive equipment in fabrication. The circuits can be printed with the fine resolution of 50nm.
2.8 Packaging
After finishing a silicon wafer may have hundreds of circuits or chips and each chip may have billions of transistors present in it. These circuits and chips are firstly checked electrically and bad chips are marked for the recognition of the defected chips. After all the testing and marking then these circuits or chips are separated from each other and the good circuits and chips are mounted in packages and we get our desired IC. A sample IC is shown in figure below:
Figure 4
References
1. The History of the Integrated Circuit. Nobelprize.org. [Online] May 5, 2003. [Cited: September 3, 2012.] http://www.nobelprize.org/educational/physics/integrated_circuit/history/. 2. Barron, Andrew R. Formation of Silicon and Gallium Arsenide Wafers. cnx.org. [Online] November 24, 2010. [Cited: September 03, 2012.] http://cnx.org/content/m16627/latest/.