Question about surface area of faraday cage

In summary, the conversation discusses the use of a faraday cage in reactive ion etching of silicon. The size and surface area of the cage do not have a significant impact on its effectiveness, but the mesh size, material used, and grounding can affect its performance. The cage can act as an antenna and emit radio waves, so measures must be taken to prevent resonance and limit parasitic capacitance. The cage is being used to do angled etching on the silicon wafer and can affect the flow of plasma. However, the ions impacting the silicon can emit photons, which can be addressed by reinjecting missing electrons.
  • #1
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Hi,

I am making a faraday cage to be used in reactive ion etching of silicon. I was wondering if the size of the cage, or the surface area has any impact on it's effectiveness or how it works?

I know the size of the mesh and the material I use, as well as whether or not it is grounded all have an effect on it. I can't seem to find any information on the effect of size though.
 
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  • #2
No size does not matter, although I don't know about ridiculously large cages. There are big cages for sale and for example at CERN they routinely enclose big objects in tin foil or similar material. It's the quality of the seal that matters.
 
  • #3
I'm going to disagree with Antti.

Since you seem to be talking about a manufacturing process I'm going to assume the ions are on the inside of the cage. In that case the cage could act as a microwave chamber. That could lead to problems. You will need to consider a way to prevent resonance.

More generally a cage can act as an antenna. High frequencies can slip through the holes. But I think you've considered these effects already.
 
  • #4
I would think that in an RIE system you would need to limit parasitic capacitance between electrodes and shield in order to not disturb the geometry of the field. If the shield were too small (too close in proximity to the electrodes), it would disturb the geometry of the field and the plasma flow.
 
  • #5
Thanks for your answers; I will definitely look into all of those things.

I think I should clarify that the cage is going inside an RIE etcher, to shield the silicon wafer. The cage is a triangular prism, and it is being used to do angled etching on the silicon wafer, so it is actually supposed to affect the flow of plasma.

(If the cage works, the potential gradient in the etching process will build up over the face of the cage and accelerate the ions perpendicular to the cage's surface. Since there is no field inside, the ions continue traveling in that direction. The surface of the cage is angled, so the ions hit the wafer at an angle.
Source: http://nano-optics.seas.harvard.edu/publications/Mike_freestanding.pdf [Broken])
 
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  • #6
DKhosla said:
Thanks for your answers; I will definitely look into all of those things.

I think I should clarify that the cage is going inside an RIE etcher, to shield the silicon wafer. The cage is a triangular prism, and it is being used to do angled etching on the silicon wafer, so it is actually supposed to affect the flow of plasma.

(If the cage works, the potential gradient in the etching process will build up over the face of the cage and accelerate the ions perpendicular to the cage's surface. Since there is no field inside, the ions continue traveling in that direction. The surface of the cage is angled, so the ions hit the wafer at an angle.
Source: http://nano-optics.seas.harvard.edu/publications/Mike_freestanding.pdf [Broken])
Be aware that accelerating (and more importantly in your case, decelerating) charges emit photons. Basically the ions impacting the silicon will act as an antenna spewing radio waves all over the place -- inside your cage. This effect is called Bremsstrahlung.

One way to reduce this potential problem might be to reinject the missing electrons just before passing the cage. Of course you might want the extra energy of the photons to break substrate molecular bonds.
 
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1. What is a Faraday cage?

A Faraday cage, also known as a Faraday shield, is an enclosure made of conductive material that blocks external electric fields and prevents electromagnetic radiation from entering or leaving the space inside the cage.

2. How does a Faraday cage work?

A Faraday cage works by redistributing the electric charge on its surface in response to an external electric field. This redistribution creates an equal and opposite electric field inside the cage, canceling out the external field and preventing it from reaching the inside of the cage.

3. What is the surface area of a Faraday cage?

The surface area of a Faraday cage depends on its size and shape. In general, the surface area should be large enough to encompass the object or space that needs to be protected from external electric fields.

4. How is the surface area of a Faraday cage calculated?

The surface area of a Faraday cage can be calculated by adding the area of each individual surface, including the top, bottom, and sides. For more complex shapes, the surface area can be calculated using mathematical formulas or calculated through experimentation.

5. Does the surface area of a Faraday cage affect its effectiveness?

Yes, the surface area of a Faraday cage can affect its effectiveness. A larger surface area provides more coverage and can better block external electric fields. However, the material and thickness of the cage also play a significant role in its effectiveness.

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