EVAPORATION SOURCE

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Evaporation source

Evaporation distribution is known that it has the distribution of cosine function shown in [ Picture 1 ] and < Formula 1 >as suggested by L.
Holland, W. Steckelmacher. et al. In < Formula 1 > m() is the amount of material that is randomly evaporated in the vertical line of evaporation
source and m0 is the amount that is evaporated at 0. In < Formula 1 >. n is the constant dependent on type and evaporation condition of point
evaporation source, showing the degree of anisotropy of evaporated material.

When point evaporation source is used, the evaporation speed and type may be different by n value. Therefore, it is possible to estimate the
thickness of evaporation film and the efficiency of evaporation by calculating the n value correctly. The n value can be calculated via < Formula 2 >
by measuring the thickness distribution of film that is evaporated in point evaporation source experimentally.

If you know the n value of point evaporation source and the position of evaporation source, Q, in [Picture 2], the thickness in evaporation plane, P,
is expressed by cosine function. In [Picture 2], l and β are the distance from the center of substrate and the angle between the line from the center
of substrate to evaporation source and the line from the center of substrate to measuring point. h, q and b are the height between substrate and
evaporation source, the distance from center and titling angle between evaporation sources. In [Picture 2], the random position on substrate and
the film thickness in P are expressed as <Formula 3>.

In <Formula 3>, the thickness, t, can be expressed through the function of l, h and q, Because the solution of equation does not exist,
it is possible to find the solution of equation through computer simulation. <Formula 3> related with the film thickness can be expressed as the
relative thickness formula t(l & B )/t0 as shown in <Formula 4>.

If point evaporation source is used, the area to secure the evenness of film thickness is small. Therefore, it is possible to get even thickness in wide
area by turning substrate. In this case, the thickness distribution is expressed as shown in <Formula 5>. If linear evaporation source or several point
evaporation sources are used, it can be expressed like <Formula 6>. In <Formula 5> and <Formula 6>, T(l.) is the film thickness when distance(l) and
angle are given on substrate and To is the film thickness when they are 0 respectively.

On the basis of the evaporation theory above, the evaporation
evenness of point evaporation source can be simulated as below

Here, the distance between substrate and evaporation source is
530mm The substrate is turned in the condition that n factor is 4 and
the distance between evaporation source and center of substrate(q) is 310mm. .
At this time, the evenness of evaporation simulation is less than ± 5%.