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This module is based upon the Connexions module entitled Photolithography by Bill Wilson.

Actually, implants (especially for moats) are usually done at a sufficiently high energy so that the dopant(phosphorus) is already pretty far into the substrate (often several microns or so), even before the diffusion starts. Theanneal/diffusion moves the impurities into the wafer a bit more, and as we shall see also makes the n-region grow larger.

"The n-region"! We have not said a thing about how we make our moat in only certain areas of the wafer. Fromthe description we have so far, is seems we have simply built an n-type layer over the whole surface of the wafer. This would bebad! We need to come up with some kind of "window" to only permit the implanting impurities to enter the silicon waferwhere we want them and not elsewhere. We will do this by constructing an implantation "barrier".

To do this, the first thing we do is grow a layer of silicon dioxide over the entire surface of the wafer. Wetalked about oxide growth when we were discussing MOSFETs but let's go into a little more detail. You can grow oxide in eithera dry oxygen atmosphere, or in a an atmosphere which contains water vapor, or steam. In [link] , we show oxide thickness as a function of time for growth with steam. Dry O 2 does not behave too much differently, the rate is just somewhat slower.

A plot of oxide thickness as a function of time.

On top of the oxide, we are now going to deposit yet another material. This is silicon nitride, Si 3 N 4 or just plain "nitride" as it is usually called. Silicon nitride is deposited through a method calledchemical vapor deposition or "CVD". The usual technique is to react dichlorosilane and ammonia in a hot walled low pressurechemical vapor deposition system (LPCVD). The reaction is:

Silicon nitride is a good barrier for impurities, oxygen and other things which do not want to get into the wafer. Take alook at [link] and see what we have so far. A word about scale and dimensions. The silicon wafer is about250 μm thick (about 0.01") since it has to be strong enough not to break as it is being handled. The two deposited layersare each about 1 μm thick, so they should actually be drawn as lines thinner than the other lines in the figure. This wouldobviously make the whole idea of a sketch ridiculous, so we will leave things distorted as they are, keeping in mind that thedeposited and diffused layers are actually much thinner than the rest of wafer, whichreally does not do anything except support the active circuits up on top.

Initial wafer configuration.

Now what we want to do is remove part of the nitride, so we can make our n-well, but not put inphosphorous where do not want it. We do this with a processes called photolithography and etching respectively. First thing we do is coat the wafer with yetanother layer of material. This is a liquid called photoresist and it is applied through a processcalled spin-coating. The wafer is put on a vacuum chuck, and a layer of liquid photoresist is sprayed uncap of thewafer. The chuck is then spun rapidly, getting to several thousand RPM in a small fraction of a second. Centrifugal forcecauses the resist to spread out uniformly across the wafer surface. The solvent for thephotoresist is quite volatile and so the layer of photoresist dries while the wafer is still spinning, resulting in a thin,uniform coating across the wafer [link] .

Questions & Answers

how can chip be made from sand
Eke Reply
is this allso about nanoscale material
Almas
are nano particles real
Missy Reply
yeah
Joseph
Hello, if I study Physics teacher in bachelor, can I study Nanotechnology in master?
Lale Reply
no can't
Lohitha
where is the latest information on a no technology how can I find it
William
currently
William
where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
learn
Google
da
no nanotechnology is also a part of physics and maths it requires angle formulas and some pressure regarding concepts
Bhagvanji
hey
Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
revolt
da
Application of nanotechnology in medicine
has a lot of application modern world
Kamaluddeen
yes
narayan
what is variations in raman spectra for nanomaterials
Jyoti Reply
ya I also want to know the raman spectra
Bhagvanji
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
nanocopper obvius
Alexandre
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
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Source:  OpenStax, Chemistry of electronic materials. OpenStax CNX. Aug 09, 2011 Download for free at http://cnx.org/content/col10719/1.9
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