Discuss the UV-Visible Spectrophotometric Method Development.
Photolithography: Process & Its Application
Photolithography, which is a combination photography and lithography, generates an image that can be used in a variety of applications.
Lithography is a combination of the Greek words lithos, graphia and lithography which refers to writing on stones.
This process allows for the transfer of geometric shapes to a surface, or onto a film during microfabrication.
This allows electrical properties, wires and dopants to form a circuit, which is used in most modern devices, such as smartphones, tablets, computers and sensors.
Alois Senefelder (German actor) and playwright invented lithography in order to publish his theatrical works at a low cost.
It was the first type of new printmaking technology to emerge after more than 300 years.
This is a way to print using a stone, metal, or a polyester plate on an entirely smooth surface.
It works on the principle mutual repulsion between water and oil.
The negative image will remain hydrophilic, but the image that is printed on a smooth surface with an oil-based media like wax crayon or paint plate.
When the plate is placed in contact with a compatible printing ink/water mixture, the ink sticks to the positive and water removes the negative.
Today, lithography can be used to produce posters, maps books, newspapers, and packaging.
Technically, lithography can be described as the transfer of any shapes or patters onto another surface. While photolithography directly relates to lithography within semiconductors (Sungyong Choi 2010,).
A variety of physical and chemical procedures are required to fabricate an integrated circuit.
There are three main steps to making an integrated circuit: semiconductor doping and film deposition.
Films of conductors or insulators can be used to connect and isolate transistors.
Photolithography, one of the most popular techniques for microfabrication, is also very popular.
Because of the precision of the incisions made, photolithography is very common.
It is one the most complicated processes because it requires ideal conditions to be successful.
It requires a very clean substrate. The temperature condition of the substrate should also be known.
This technique is limited to flat surfaces.
This method is widely used for integrated circuits.
Modern lithography can be summarized as:
The first step is to manufacture an integrated circuit. This represents 30% of the manufacturing cost.
The second is that lithography can be a technical constrainer in terms of advancements in feature size reduction and further impact on speed of transistors and silicon surface area.
For cost-cutting and improving efficiency, it is essential to be aware of the operating cost and competence when making a circuit using lithography.
When exposed to light, photoresist forms 3D relief images on the substrate’s surface.
The intended or designed pattern will generally be the same shape with vertical walls, regardless of how thick the substrate is in the ideal photoresist images.
The binary pattern is a complete outline of the final design. Other parts are covered in resist.
Binary pattern plays an important role in pattern transfer, as the ion-protected parts are protected (Acikgoz 2011,).
Photolithography is done in the following steps:
The Application Of Photoresist
Photoresist is a light sensitive material. When it is applied to the core of an oxidized Silicon wafer, it causes wafer acceleration to a velocity of between 3000 and 7000 rpm for 30-60 seconds.
This causes the solution to be spread into a thin, uniformly coated layer.
The excess material is then spun off (Young, 2008).
The thickness of the material generally ranges from 500 to 10000 A.
Sometimes, wafers are baked at 100° Celsius prior to applying photoresist. This is done to dry the silicon wafer surface of moisture and improve adhesion.
After photoresist has been applied, the wafers must be baked at 80°C for an hour. It will then turn into a semisolid and remove solvents. (Moreau 2017).
Exposure and alignment of wafer
After the process is complete, the silicon coated wafer should be kept in a container known as mask aligner.
It is placed right next to the photo mask.
Place the silicon wafer and mask in such a manner that they align with the reference mask (Ping 2010, 2010).
Photomask appears like a square glass plate measuring approximately 125mm in area and 2mm thick.
One side of the photomask contains a photographic emulsion.
This thin metal pattern can be used in both transparent and opaque areas.
The alignment of the wafer photomask is critical. It must be accurate to less than 1mm, or even 0.5mm in certain cases.
After the alignment has been achieved, the wafers are placed on photomask and brought into contact with each other for further processing.
The ultraviolet is then turned on and the photomask is removed so that the wafer is exposed to ultraviolet rays.
It takes around 10 seconds to expose UV radiation. This is why it is important to monitor the exposure carefully and ensure that UV radiation does not exceed required levels.
They can be divided into two types: positive and negative photoresist.
On photoresist not exposed to UV rays, the negative photoresist can be applied. This is where polymerization takes place.
The photoresist’s molecules become longer due to this process.
This makes photoresist difficult to dissolve in solution.
After that, the resisting photoresist is a copy of the photomask design with areas on photomask matching the photoresist area on the wafers.
The positive photoresist is subject to a reverse reaction.
The photoresist areas are exposed to ultraviolet radiation. This causes depolymerization.
The exposed areas of the photoresist become soluble in developer solution while the unexposed areas remain insoluble.
The photoresist’s exposed areas or depolymerized are removed from the developer solution, and the unexposed areas remain on the wafer.
The process of replication is repeated again, but this time the photomasks are created on the wafer.
After the development and rinse, the wafers can be baked for another hour at 150°C to harden the silicon resist.
This is done to make the adhesion more resilient to the acid HF, which is later used for engraving of oxide.
The photoresist, which is still there, has been hardened. It acts as a mask from which the oxide layer could possibly be engraved to expose the semiconductor areas.
Now, this surface is ready for impurity diffusion.
Engraving oxide is done by either submerging the wafer in a solution of hydrofluoric acids or spraying it over the wafer.
The solution’s ratio is usually 10 to 1 (water: Hydrofluoric Acid) or 10 to 1 (NH4F/hydrofluoric Acid).
This causes silicon dioxide to be dissolved, but does not damage the photoresist or silicon layer.
The solution can also be used to clean silicon wafers.
It is important to monitor the duration of the process so that any oxide remaining in the photoresist is not removed.
It is possible to increase the oxide opening if the process is extended.
This process is known as wet-etching, as the reagents used in it are liquid.
Plasma etching, ion-milling, and other dry processes are also available.
This is where the resist is removed with H2SO4/H2O2 followed by abrasion.
This cleaning and drying process helps to open up the oxide layer.
It is more difficult to remove negative photoresist than positive photoresist. These are easy to dissolve in organic solvents, such as acetone.
Organic strippers that are phenol-based are preferred because it does not create slums.
The most common wet strippers for positive photoresist are those that are inorganic acid-based and normally use at high temperatures.
There are many issues that can arise during wet stripping.
To remove any resist residues left on wafers, it is important to use plasma descum following the wet process.
It is not uncommon to see photoresist that has had to undergo extreme processing and hardening make it almost impossible for the chemicals to be removed.
For these reasons, plasms stripping is a common method used in semiconductor processing.
It’s a method of lithography that creates geometric patterns on tiny surfaces.
The photolithography process allows for the production of integrated circuits as well internal parts of computers (Minseok 2015).
It can also be used for producing microscopic computer system and nanomachines.
It is used in patterning at laboratory levels and for the manufacturing of various MEMS devices.
Projection printing is used to produce both commercial products as well as advanced electronic components such ICs or CPU chips.
Electronic beam lithography can be used to pattern in research and design, including channels for nanofluidics or photonics.
In bio sensors, nano electronics, and nano wires, the Nanoimprint lithography method is used.
All of these technologies are available.
For bio electronic sensors, sensors for gas, and other applications, dip-pen is used.
It can also engrave any pattern in Integrated circuit that requires ultraviolet light. This is one of the major advantages of this technique.
This process does not require any additional materials.
Because it makes very small incisions on a surface or film, it is the most economical and cost-effective technique.
It can also control the shape and size the substrate.
UV- Visible Meter
The UV Visible Spectrometer is an analytical instrument for UV-Vis analysis.
UV-VIS spectroscopy allows us to measure the absorption of visible and ultraviolet radiation via an analayte.
An analayte’s molecular absorption corresponds both to excitations of valance electrons as well as excitations of electrons within various atomic orbitals.
UV-Vis provides both quantitative and qualitative analysis of both organic and nonorganic compounds. It is extremely efficient and simple.
It’s an established technique that is used in most industries such as food, beverage and pharmaceutical.
It’s based on Lambert-Beer principle. According to this principle, absorbance of solution is proportional to its concentration (c), and its pathlength(l) when the wavelengths of the incidence light remain constant.
This equation sums it all:
Here is the equation for molarity adsorbtivity:
There are many types of spectrometers. The most common configuration can be divided into single beam, split-beam or double beam depending upon the design of the optical system.
Monochromator, light source and detector are the most common components in these instruments. Cell compartment and signal processing system are also important.
A single-beam spectrometer uses a single cuvette. This allows for the simultaneous measurement of both control and treatment group samples (R S Shah (2015)).
Double beam UV Vis spectrometers can simultaneously measure both the treatment and control groups.
Because we don’t need to calibrate the instrument again to measure the second group, the double-beam spectrometer gives us more accuracy.
The diagram illustrates that when a ray from a source of incident light falls on a prism, it is separated into several wavelengths.
The monochromatic beam splits into two equal beams of the same intensity via a half-mirror.
A tiny container containing compound solution and transparently encloses the sample beam.
Secondary beam, also called reference beam, enters via a similar cuvette that only contains the blank solvent.
The intensity of each beam is measured using a detector.
The reference beam will be denoted Io while the sample beam will be denoted I.
The spectrometer scans all wavelengths automatically while the reference beam is denoted as Io.
If the sample compound cannot absorb light, I is Io. If the sample compound can absorb light, I is Io.
This absorption can either be expressed as transmittance (where T is equal to I/Io) or absorbance (A= log Io/I).
If there is no absorption then T=1 and I =0.
The vertical axis of the spectrometer displays absorbance ranges between 0 and 2.
The maximum wavelength of the spectrometer is denoted as lmax.
Absorbance maxima and absorbances can vary depending on the compound.
Because it allows the detector to receive enough light, it is easier to see compounds that are dilute. It also requires transparent solvents that have non-absorbing properties.
Common solvents are hexane, ethanol and water (Behera (2012).
Single bonds are preferable.
Two groups can be categorized for the UV Vis spectrometer:
Application of structural principles
Chemical Application Of UV- Vis Spectrumtry:
(i) Identification an unknown substance: UV-Vis spectrometry is a useful tool for identifying various compounds in biological preparations or pure form.
You can do this by plotting the absorption spectrum lines that correspond to specific classes of compounds. This helps you identify any substance.
The substances which are not absorbed between 220-280nm and alicyclic or aliphatic hydrocarbons, or their derivatives, are, for example, alicyclic or aliphatic hydrocarbons.
Even complex systems can produce absorption curves with different maxima. Every curve has its own characteristic range and form that identifies the presence of a certain functional group.
(iii). Identification of concentration in cases of unknown substance: A similar spectrometry technique can be used to identify concentration of unknown substances. To do this, first choose the absorption spectrum where measurement of absorbance is possible.
If the sample was previously studied, the sample’s interest absorbance spectrum can be determined.
A double beam spectrometer, however, can be used to identify the spectrum band of the sample and determine where it lies.
The best absorption is determined this way.
Most organic compounds absorb in the visible area of the ultraviolet spectrum. Therefore, the majority of biological substances can be measured by an ultraviolet-visible scope.
iii. Measurement enzyme activity: The enzyme’s activity can easily be measured if the substrate is colored or absorbs UV visible light.
A spectrometer measures the rate at which a substance or product appears or disappears.
The structural application of UV Vis is spectrometers:
i) Identify the purity a compound: This is the most important application of spectrometer.
If a compound does not have its characteristic spectrum, then it is easy to identify any impurities.
This can be used to identify benzene found in absolute alcohol (Oskam, 2010).
Because benzene absorbs at 280nm while alcohol spectrum absorbs at 210nm.
ii. Study of trans Isomer and cis Isomer: The trans isomer has a shorter length, and the structural difference can be seen in absorbance spectrum.
The trans-isomer absorbs maximum at higher wavelengths.
iii. When determining molecular mass, let’s suppose that a compound is react with a chemical to produce a derivative having a specific absorption spectrum.
The extinction coefficient of derivative will be similar to the reagent’s. This is because the derivative has an absorbance band that is very intense and long enough for the compound not to absorb it.
Although the extinction ratio of the derivative and the reagent are identical, their optical density differs with different compounds.
Where, a = absorption coefficient
w = the weight of compound
b = length of the path
iv). Turbidimetry: The solution appears turbid because of any specific matter or bacteria present in it.
This is due to the tyndall phenomenon in which colloidal particles in the solution scatter light and makes solution appear turbid.
The solution absorbs a certain wavelength of light and scatters it.
After this happens, the wavelength radiation that is not absorbed is passed to a suspension. The existing solution will only be due to the scattering of light.
The light that is transmitted has a lower intensity relative to the incident.
This can be used to measure the intensity and count the particles in the solution.
This phenomenon is known by turbidimetry.
For fabrication of nanostructures, polymers can be used in both conventional and alternative lithography.
European Polymer Journal, 47 (11), pp.
UV-visible simultaneous UV-visible spectrum spectrophotometric estimation of paracetamol, nabumetone and combined tablet dosage form.
UV-Visible Scopemetric Method Development and Validation for Paracetamol Tablet Formulation.
Journal of Analytical & Bioanalytical Techniques.
Cracking-assisted photography for mixed-scale patterning.
Springer International Publishing. pp.
Semiconductors and Metal oxides, and composites: Metallization or Electrodeposition of Thin Films or Nanostructures.
:The Electrochemical Society.
Alignment for Double Side Deep-exposure Lithography.
R. S. Shah R. R. S. R. B. P. 2015
INTERNATIONALJOURNAL OF INSTITUTIONALPHARMACEY & LIFE SCIENCES.
Two-step photolithography for multilevel microchannels.
UV-VIS absorption spectroscopy.
A Simulation Model to Characterize Photolithography in Semiconductor Wafer Manufacturing, s.l.
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