Inductively Coupled Plasma

Product details


Inductively Coupled Plasma

Working principle    

The working principal of inductively coupled plasma (ICP): Plasma is generated by RF circulator discharge. When RF current passes inductance coil, an alternating magnetic field is excited in the vacuum chamber (discharge tube); the alternating magnetic field in turn induces an electric field, and the electrons in the gas obtains energy from the electromagnetic field and ionized to generate a plasma of higher density. ICPs are anisotropic.

ICPs can be roughly divided into high-pressure ICP and low-pressure ICP. The former, which is achieved by igniting a plasma torch at atmospheric pressure, is mainly applied in spectroscopy. The latter generates discharge at a lower pressure (1–100 mTorr); in this process there is a large temperature difference between electrons and ions in the formed plasma, which are in a non-thermal equilibrium state.

     

ICP has the following characteristics:

(1) Higher plasma density. The electron density of ICP is generally greater than  which is much higher than that of traditional capacitively coupled plasma sources and rivals other high-density plasma sources such as electron cyclotron resonance plasma sources.

(2) Simple equipment structure. Other high-density plasma sources require magnetic field coils which are huge and expensive. ICP, however, does not require an external magnetic field. Therefore, the equipment has low cost and is an economical and practical low-temperature high-density plasma source.

(3)It features good plasma uniformity and ion flux direction selectivity, low and controllable ion energy, separately controllable ion energy and plasma density, and ease of large-area and directional etching.

(4)Operation at low pressure. As high-density plasma can be generated at low pressure (1–100 mTorr), the bombardment damage from high-energy particles in the plasma source to the substrate can be greatly reduced.

     

ICP source is a complex discharge system. The characteristics of plasma produced by ICP source depend on many factors, such as discharge mechanism, coil geometry, structure of discharge container and so on. The geometry of the inductor can significantly influence plasma uniformity. Several typical inductor devices are shown in Figure 1. Both type (a) and type (b) are multi-turn inductor. In practical application, their larger inductance comes with several defects, such as reduced ICP efficiency, undermined plasma uniformity and discharge stability, etc., making it impossible to further expand processing area. Type (c) is a built-in single-turn inductor. A single-turn inductor coil has relatively better plasma radial uniformity. Additionally, it does not need an external magnetic field, thus avoiding the impact of the use of magnetic field constraints on plasma uniformity.


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Figure:Several Typical Inductor Coil Shapes and Coupling Modes


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