The basic semiconductor devices like diodes, transistors and resistors are all manufactured by monolithic technology during the manufacturing of integrated circuits. 'Monos' means 'single' and 'lithos' means stone, hence which means that all these components are manufactured using same technology.
Most of the semiconductor components are manufactured using silicon through fabrication process. Silicon is the most abundantly available element in sand and quartz as oxides.
Silicon is the element belonging to the group 4 in the periodic table having 4 atoms in the outermost shell.
Silicon in its purest form is used for fabrication process. The conversion of sand to silicon involves various process.
Now we are ready with the silicon. This the base for all the manufacturing process. This silicon will be the substrate for manufacturing of resistors, diodes or transistors.
Above this substrate, the doping are done suitably to form the required semiconductors.
The substrates which we use are either of p-type or n-type.The n-type semiconductor is formed by doping a pentavalent impurities like Phosphorous,Arsenic to pure silicon atom, so that the extra atom left free without any bonding will start conduction.The p-type semiconductor is formed by doping trivalent impurities like Gallium, Indium to pure silicon, so that the hole left free during bonding will start conduction.
As far as transistor is considered, there are many types, basic types includes NPN and PNP transistor.
The steps involved in fabrication of NPN transistor includes
The manufacturing of PNP transistor have similar process except that there is change in substrate, instead of P-substrate their will be N-substrate.
The fabrication process of MOS transistors involves these general steps during fabrication.
1.First deciding the type of substrate either p-type or n-type.
2.Applying a thick oxide layer over the substrate.
3.Applying a layer of photoresist over the oxide layer.
4. Applying mask over the photoresist and applying UV rays so that the desired parts are etched.
There are two types of etching process,
Soft bake and hard bake
-> in soft bake the layer which is masked will get etched by the UV rays
->in hard bake the layer which is uncovered will get etched by UV rays
General method of etching process is done by using UV rays, as an advancement nowadays Laser light is also used for etching process.
5.Now after masking and exposure to UV rays the portions not required are etched to form window.
6. A polysilicon (1-2 micrometer thickness)is diffused over the thin oxide layer.
7.Next step is the diffusion, for n-type substrate p-diffusion is made and for p-type substrate n-diffusion is made.
8.Now the contacts are taken from the diffusions and polysilicon to form gate, drain and source.
Here n-mos is illustrated
Other types of transistor involves FET, MOSFET,JFET,CMOS,PMOS all having different properties but having base as silicon substrate.
Again when fabrication of diode is considered, there are only 2 regions in diode, p and n regions.
When resistors are considered the material attains its basic resistance property through the appropriate diffusion. The diffusion of material decided the resistance of the resistor.
There are four methods available for fabrication of integrated resistors,namely
4.Thin film resistor
The fabrication type is chosen according to the application. Each type has its own advantages and disadvantages, hence chosen according to the requirement.
Most of the electronic devices are made of silicon . The manufacturing process is : sand from sea shore is purified to electrical grade silicon.later varing the doping amounts of impurity resistors of various values can be created.diodes are made by doping n type impurity with p type impurity.transistors are made by doping n impurity followed by p impurity followed by n impurity.
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