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Pre-oxidation cleaning

The first step in oxidizing a surface of silicon is the removal of the native oxide which forms due to exposure to open air. This may seem redundant to remove an oxide only to put on another, but this is necessary since uncertainty exists as to the purity of the oxide which is present. The contamination of the native oxide by both organic and inorganic materials (arising from previous processing steps and handling) must be removed to prevent the degradation of the essential electrical characteristics of the device. A common procedure uses a H 2 O-H 2 O 2 -NH 4 OH mixture which removes the organics present, as well as some group I and II metals. Removal of heavy metals can be achieved using a H 2 O-H 2 O 2 -HCl mixture, which complexes with the ions which are formed. After removal of the native oxide, the desired oxide can be grown. This growth is useful because it provides: chemical protection, conditions suitable for lithography, and passivation. The protection prevents unwanted reactions from occurring and the passivation fills vacancies of bonds on the surface not present within the interior of the crystal. Thus the oxidation of the surface of silicon fulfills several functions in one step.

Thermal oxidation

The growth of oxides on a silicon surface can be a particularly tedious process, since the growth must be uniform and pure. The thickness wanted usually falls in the range 50 - 500 Å, which can take a long time and must be done on a large scale. This is done by stacking the silicon wafers in a horizontal quartz tube while the oxygen source flows over the wafers, which are situated vertically in a slotted paddle (boat), see [link] . This procedure is performed at 1 atm pressure, and the temperature ranges from 700 to 1200 °C, being held to within ±1 °C to ensure uniformity. The choice of oxidation technique depends on the thickness and oxide properties required. Oxides that are relatively thin and those that require low charge at the interface are typically grown in dry oxygen. When thick oxides are required (>0.5 mm) are desired, steam is the source of choice. Steam can be used at wide range of pressures (1 atm to 25 atm), and the higher pressures allow thick oxide growth to be achieved at moderate temperatures in reasonable amounts of time.

Horizontal diffusion tube showing the oxidation of silicon wafers at 1 atm pressure.

The thickness of SiO 2 layers on a Si substrate is readily determined by the color of the film. [link] provides a guidline for thermal grown oxides.

Color chart for thermally grown SiO 2 films observed under daylight fluorescent lighting.
Film thickness (μm) Color Film thickness (μm) Color
0.05 tan 0.63 violet-red
0.07 brown 0.68 "bluish"
0.10 dark violet to red-violet 0.72 blue-green to gree
0.12 royal blue 0.77 "yellowish"
0.15 light blue to metallic blue 0.80 orange
0.17 metallic to light yellow-green 0.82 salmon
0.20 light gold 0.85 light red-violet
0.22 gold 0.86 violet
0.25 orange to melon 0.87 blue violet
0.27 red-violet 0.89 blue
0.30 blue to violet blue 0.92 blue-green
0.31 blue 0.95 yellow-green
0.32 blue to blue-green 0.97 yellow
0.34 light green 0.99 orange
0.35 green to yellow-green 1.00 carnation pink
0.36 yellow-green 1.02 violet red
0.37 green-yellow 1.05 red-violet
0.39 yellow 1.06 violet
0.41 light orange 1.07 blue-violet
0.42 carnation pink 1.10 green
0.44 violet-red 1.11 yellow-green
0.46 red-violet 1.12 green
0.47 violet 1.18 violet
0.48 blue-violet 1.19 red-violet
0.49 blue 1.21 violet-red
0.50 blue green 1.24 carnation pink to salmon
0.52 green 1.25 orange
0.54 yellow-green 1.28 "yellowish"
0.56 green-yellow 1.32 sky blue to green-blue
0.57 "yellowish" 1.40 orange
0.58 light orange to pink 1.46 blue-violet
0.60 carnation pink 1.50 blue

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
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.
yes that's correct
I think
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
How we are making nano material?
what is a peer
What is meant by 'nano scale'?
What is STMs full form?
scanning tunneling microscope
how nano science is used for hydrophobicity
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
what is differents between GO and RGO?
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
analytical skills graphene is prepared to kill any type viruses .
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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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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