Technique and Analaysis of Spin Coating

Spin coating is one of general processing which always used to coat disc, plate or other solids. Before making process for coating on the disc or plate, we have to know basic principle for refractive index, ellipsometry, Brewster angle and etc. Here are little bit some general informations or theory used to in analysis layer by layer between substrate and substrate. Actually, this technique is really important in Chemical and manufacture Industries. The true process and technique will have a role to get good result.

The principle of the technique and the theoretical basis

The measurement refractive index with symbol (n) has function to describe and understand how such a slower and a faster velocity could come about. Mathematically we can illustrate refractive index by equation 1 which there is ratio between speed light in vacuum (c) and speed light in substrate (v) then we can get value of refraction index (n).

In particular, we should try to see what the relation is to some physical assumptions, or statements, we made earlier, which were the following some procedure:

a. That the total electric field in any physical circumstance can always be represented by the sum of the fields from all the charges in the universe.

b. The acceleration evaluated can be retarding the field from a single charge by the speed (c).[1]

We should know the important of the process to measure refractive index comes about. The refractive index can be measured by understanding how the apparent wave velocity in different materials. The measurement of refractive index can be described by the process in figure1.

Figure1. The correlation of refraction, velocity, wavelength, angle of incident and angle of reflection [1]

From figure 1 then we can get the equation (2). The equation is very familiar name with Snell’s law.

Brewster's angle (also known as the polarization angle) is an angle of incidence at which light with a particular polarization is perfectly transmitted through a transparent dielectric surface, with no reflection. When unpolarized light is incident at this angle, the light that is reflected from the surface is therefore perfectly polarized. Correlated with Brewster’s angle

When light encounters a boundary between two media with different refractive indices, some of it is usually reflected as shown in the figure above. The fraction that is reflected is described by the Fresnel equations (we can see the equations (4) and (5)), and is dependent upon the incoming light's polarization and angle of incidence. [2]

These equations are called “Ellipsometry equation” by measurement of Null Ellipsometry. The measurement we get the value following the equations:

The compensator is a -plate which is rotated by against the p-direction. By the equations (6 and 7), we can measure the angle dan to know the Fresnel coefficients in equations (8, 9 and 10).

The Fresnel equations predict that light with the p polarization (electric field polarized in the same plane as the incident ray and the surface normal) will not be reflected if the angle of incidence is. These are the name of parameter of the symbols in equations above:

In another part of this experiment before measuring ellipsometry, we have to prepare thin of film of polystyrene by spin coating technique. Actually the spin coating has four basic step, they are deposition, spin up, sin off and evaporation.

Experimental Part

In this experiment, we have to prepare the ellipsometer before measure refractive index (n) of the water and another substrate (SiO2/Si). Before measuring some parameters we have to set up the ellipsometer parts such as the orientation of laser light, compensator, polarisator, and analysator. The last step of preparing ellipsometer was checking the laser light by accurate stave. We could see detail about part by part of the ellipsometer in figure2.

Figure2. Setup parts of an ellipsometer[2]

After preparing the ellipsometer we have to measure the important parameter in this experiment such as Brewster angle of water, reflectivity for s- and p- polarized, refractive index of water, analyzer, polarizer values by setting angle of incident at 45o, 50o, 60o and 65o.

Spin Coating Process

In the last section of this experiment, we have to make thin of film of Polystyrene on SiO2/Si Substrate by spin coating process following figure3.  We made 11 samples by different speed of spin which the speeds are 150, 100, 90, 80, 70, 60, 50, 40, 30, 20 and 10 (rps).

Figure3. Process of Spin coating[3]

After finishing spin coating process we have to measure the thickness of film of Polystyrene by null ellipsometry to get some parameter such as polarizer, analyzer, ∆, .  Actually in the last section of this experiment, we have same step with the first step before.

References

[1] Ellipsometry and polarized light, R.M.A. Azzam and N.M. Bashara, Elsevier Science, Amsterdam, 1987

[2] Optics (3rd edition), E. Hecht, Addison Wesley Longman, Reading, 1998

[3] http://homepages.rpi.edu/~plawsky/Research/images/Spinning.jpg

This is a little bit information and technique for all Indonesian people. I hope this information can be useful for us. I am sorry that I wrote my article in English because I think English is very important language now. If you want detail about other technique related to polymer science and chemical engineering you can ask me at hardiyantoputra@gmail.com or www.facebook.com/hardiyanto.wijaya . You can use Bahasa Indonesia, Jawanese or English what you want to.

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