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information about electrical characteristics of materials

Discussing how p-n junctions work

Describing the processing and properties of semiconductors

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FIGURE 1 : Resistivity chart

resistance

resistivity ,f(T)

conductor

insulator

semiconductor

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have electrical properties between a conductor and insulator

do not conduct as well as conductors

do not insulate as well as insulators

their atoms are closely , have a crystal structure

electronic devices, computers, telephones made from semiconductors

conductivity can be controlled by doping

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FIGURE 2: structure and lattice of pure crystal of Silicon

Most common semiconductor material

four valence electron

covalent bond ,very stable

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introduce an impurity such as phosphorus, arsenic, aluminum,gallium

can be exist unbounded electron

can exist a hole

pure silicon electrical conductor by adding impurity

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With elements that have three valence electrons

Such as B, Al and Ga

Fourth bond cannot be formed

Positive charge

Not a complete connection

There is a empty place ‘hole’

Hole movement will existBy diffusion of B2H6

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Electron leave the covalent bond and move into hole

Therefore, another hole will be existed

Holes will move

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These elements have five valence electrons to share with other atoms

Such as Sb, P and As

Fifth electron cannot form a bond

Negative charge

Greatly increasing the conductivityBy diffusion of PH3

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A single type (p or n ) semiconductor material is not very useful

For useful applications, semiconductor crystal must contain both P-type and N-type

PN junction can only be created by inserting different impurities into different parts of a single crystal

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N region will has positive charge after missing some electrons

Those electrons will fill the holes in the P region, which will therefore has a negative charge.

So there will be potential difference and electrical current

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p-type n-type

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p-type n-type

Semiconductors p-type and n-type are brought together

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p-type n-type

Electrons and holes migrate across the junction

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p-type n-type

The depletion layer is formed

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p-type n-type

A potential difference is set up across the depletion layer

Electric field

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Higher dopant concentration, more carriers

(electrons or holes)

Higher conductivity, lower resistivity

Electrons move faster than holes

N-type silicon has lower resistivity than P-type

silicon at the same dopant concentration

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Resistor

Transistors

Capacitors

Diode

www.made-in-china.com/.../Resistor-Capacitor.jpg

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Resistors are made by doped silicon or polysilicon on an IC chip.

Resistance is determined by length, line width,height, ana dopant concentration

V=I*R ( Ohm law)

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Charge storage device

The capacitor's function is to store electricity, or electrical energy.

The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC).

blogs.courant.com/.../capacitor.jpg

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P-N Junction(transistor),electron tube with anode ana cathode

Allows electric current go through only in one direction

Used commonly in bridge form to convert AC to DC voltage.

“Rectification”

Various types of Bridge Rectifiers

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PNP or NPN

Switch

Amplifier

Anolog,digital circuit

Fast, high power device

www.ehobbycorner.com/images/trn_type.jpg

injection

collection

diffusion

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Metal-oxide semiconductor

Also called MOSFET( MOS Field Effect Transistor)

Simple, symmetric structure

Switch, good for digital, logic circuit

Most commonly used devices in the semiconductor industry

www.doitpoms.ac.uk/.../images/mosfet.jpg

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NPN-PNP configuration

Market share reducing rapidly

Still used for anolog systems

power devices

TV,Cellar phone, etc.

A standard bipolar transistor static.howstuffworks.com/gif/amplifier-transi...

Advantages

Switch signal high speed

Handle large circuit(high power amplifier)

Wireless transmitter

Not effective weak signaal amplification

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1.Silicon Manufacturing a) Wafer Manufacturing

b) Crystal structure

2.Photolithography a) Photoresists

b) Photomask and Reticles

c) Patterning

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3.Oxide Growth & Removal a) Oxide Growth & Deposition

b) Oxide Removal

c) Other effects

d) Local Oxidation

4. Diffusion & Ion Implantation a) Diffusion

b) Other effects

c) Ion Implantation

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Czochralski Process is a Technique in Making Single-Crystal Silicon

A Solid Seed Crystal is Rotated and Slowly Extracted from a Pool of Molten Si

Requires Careful Control to Give Crystals Desired Purity and Dimensions

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The Silicon Crystal is Sliced by Using a Diamond-Tipped Saw into Thin Wafers

Sorted by Thickness

Damaged Wafers Removed During Lapping

Etch Wafers in Chemical to Remove any Remaining Crystal Damage

Polishing Smoothes Uneven Surface Left by Sawing Process

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Photolithography is a technique that is used to define the shape of micro-machined structures on a wafer.

The first step in the photolithography process is to develop a mask, which will be typically be a chromium pattern on a glass plate.

Next, the wafer is then coated with a polymer which is sensitive to ultraviolet light called a photoresist.

Afterward, the photoresist is then developed which transfers the pattern on the mask to the photoresist layer.

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There are two basic types of Photoresists Positive and Negative.

Positive resists

Positive resists decomposes ultraviolet light. The resist is exposed with UV light wherever the underlying material is to be removed.

Negative resists

Exposure to the UV light causes the negative resist to become polymerized, and more difficult to dissolve. Therefore, the negative resist remains on the surface wherever it is exposed, and the developer solution removes only the unexposed portions.

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Photomask

This is a square glass plate with a patterned emulsion of metal film on one side. The mask is aligned with the wafer, so that the pattern can be transferred onto the wafer surface. Each mask after the first one must be aligned to the previous pattern.

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When a image on the photomask is projected several time side by side onto the wafer, this is known as stepping and the photomask is called a reticle.

A common reticle is the 5X

The patterns on the 5X reticle are reduced 5 times when projected onto the wafer. This means the dies on the photomask are 5 times larger than they are on the final product. There are other kinds of reduction reticles (2X, 4X, and 10X), but the 5X is the most commonly used. Reduction reticles are used on a variety of steppers, the most common being ASM, Canon, Nikon.

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The last stage of Photolithography is a process called ashing. This process

has the exposed wafers sprayed with a mixture of organic solvents that dissolves portions of the photoresist .

Conventional methods of ashing require an oxygen-plasma ash, often in combination with halogen gases, to penetrate the crust and remove the photoresist.  Usually, the plasma ashing process also requires a follow-up cleaning with wet-chemicals and acids to remove the residues and non-volatile contaminants that remain after ashing.  Despite this treatment, it is not unusual to repeat the "ash plus wet-clean" cycle in order to completely

remove all photoresist and residues.

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Dry oxide - Pure dry oxygen is employed Disadvantage

- Dry oxide grows very slowly. Advantage

- Oxide layers are very uniform.

- It has especially low surface state charges and thus make ideal dielectrics for MOS transistors.

Wet oxide - In the same way as dry oxides, but steam is injected Disadvantage

- Hydrogen atoms liberated by the decomposition of the water molecules produce imperfections that may degrade the oxide quality.

Advantage

- Wet oxide grows fast.

- Useful to grow a thick layer of field oxide

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Diffusion

--A uniformly doped ingot is sliced into wafers.

--An oxide film is then grown on the wafers.

--The film is patterned and etched using photolithography exposing specific sections of the silicon.

Diffusion is a cheaper and more simplistic method, but can only be performed from the surface of the wafers. Dopants also diffuse unevenly, and interact with each other altering the diffusion rate.

Ion Implantation

--A particle accelerator is used to accelerate a doping atom so that it can penetrate a silicon crystal to a depth of several micron

Ion implantation is more expensive and complex. It does not require high temperatures and also allows for greater control of dopant concentration and profile.

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Semiconductors; materials, conductivity between conductor

and insulator

Its conductivity can be controlled by dopant concentration and applied

voltage

Silicon, germanium, and gallium arsenate

Silicon most popular: abundant and stable oxide

Boron doped semiconductors is p-type, majority carriers are holes

P, As or Sb doped semiconductor is P-type, the majority carriers are

electrons

Higher dopant concentration, lower resistivity

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R=g *l / A

C=KA/d

Capacitors are mainly used in DRAM

Bipolar transistors can amplify electric signal, mainly used for analog systems

MOSFET electric controlled switch, mainly used for digital systems

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http://www.play-hookey.com/semiconductors/pn_junction.html

http://rel.intersil.com/docs/lexicon/manufacture.html