Apparatus for monitoring electron density and electron temperature of plasma and method thereof

Abstract

The present invention relates to an apparatus and method for monitoring an electron density and electron temperature of a plasma. The apparatus includes an electromagnetic wave generator that continuously transmits electromagnetic wave of a series of frequency bands, an electromagnetic wave transceiver connected to a plasma within a reaction container and electrically connected to the electromagnetic wave generator so that a frequency of the transmitted electromagnetic wave is correlated to the electron density and electron temperature of the plasma, the electromagnetic wave transceiver transmitting the electromagnetic wave, a frequency analyzer electrically connected to the electromagnetic wave transceiver, for analyzing the frequency of the electromagnetic wave received from the electromagnetic wave transceivers and a computer electrically connected to the electromagnetic wave generator and the frequency analyzer, for calculating a correlation between the electron density and electron temperature, and a corresponding electromagnetic wave based on a frequency band-based transmission command of the electromagnetic wave and the analyzed data.

1 . An apparatus for monitoring an electron density and electron temperature of a plasma, comprising:
 an electromagnetic wave generator that continuously transmits electromagnetic wave of a series of frequency bands;   an electromagnetic wave transceiver connected to a plasma within a reaction container and electrically connected to the electromagnetic wave generator so that a frequency of the transmitted electromagnetic wave is correlated to the electron density and electron temperature of the plasma, the electromagnetic wave transceiver transmitting the electromagnetic wave;   a frequency analyzer electrically connected to the electromagnetic wave transceiver, for analyzing the frequency of the electromagnetic wave received from the electromagnetic wave transceiver; and   a computer electrically connected to the electromagnetic wave generator and the frequency analyzer, for calculating a correlation between the electron density and electron temperature, and a corresponding electromagnetic wave based on a frequency band-based transmission command of the electromagnetic wave and the analyzed data.   
     
     
         2 . The apparatus as claimed in  claim 1 , wherein the electromagnetic wave transceiver comprises:
 first and second coaxial cables that are electrically connected to the electromagnetic wave generator and the frequency analyzer, respectively, and are disposed in parallel; and   a transmit antenna and a receive antenna that are connected to and projected from one ends of the first and second coaxial cables, respectively, on the same axial line and are connected to the plasma in order to transmit and receive the electromagnetic wave.   
     
     
         3 . The apparatus as claimed in  claim 2 , wherein each of the first and second coaxial cables comprises a dielectric-coated layer coated/shielded at a predetermined thickness. 
     
     
         4 . The apparatus as claimed in  claim 1 , further comprising a conveyer connected to the other end of the electromagnetic wave transceiver, for causing the electromagnetic wave transceiver to be selectively conveyed within the reaction container. 
     
     
         5 . The apparatus as claimed in  claim 4 , wherein the conveyer is driven by a stepping motor. 
     
     
         6 . The apparatus as claimed in  claim 5 , wherein the electromagnetic wave transceiver is disposed along a radial direction of the reaction container. 
     
     
         7 . The apparatus as claimed in  claim 6 , wherein the conveyer is driven by an oil-pressure cylinder. 
     
     
         8 . The apparatus as claimed in  claim 7 , wherein the electromagnetic wave transceiver is disposed along a radial direction of the reaction container. 
     
     
         9 . A method of monitoring an electron density and electron temperature of a plasma using an apparatus including an electromagnetic wave generator that continuously transmits electromagnetic wave of a series of frequency bands; an electromagnetic wave transceiver connected to a plasma within a reaction container and electrically connected to the electromagnetic wave generator so that a frequency of the transmitted electromagnetic wave is correlated to the electron density and electron temperature of the plasma, the electromagnetic wave transceiver transmitting the electromagnetic wave; a frequency analyzer electrically connected to the electromagnetic wave transceiver, for analyzing the frequency of the electromagnetic wave received from the electromagnetic wave transceiver; and a computer electrically connected to the electromagnetic wave generator and the frequency analyzer, for calculating a correlation between the electron density and electron temperature, and a corresponding electromagnetic wave based on a frequency band-based transmission command of the electromagnetic wave and the analyzed data, the method comprising:
 a first step of allowing the electromagnetic wave generator to apply electromagnetic wave of a predetermined frequency to the transmit antenna;   a second step of allowing the receive antenna to analyze a frequency of the electromagnetic wave received from the transmit antenna;   a third step of measuring a cutoff frequency based on the analyzed frequency;   a fourth step of calculating an electron density of a plasma using the measured cutoff frequency;   a fifth step of allowing the electromagnetic wave generator to transmit electromagnetic wave, monitor reflected wave returned to the transmit antenna, and measure a surface wave absorption frequency; and   a sixth step of calculating an electron temperature of the plasma based on the electron density of the plasma and the absorption frequency found in the fourth step and the fifth step, respectively.   
     
     
         10 . The method as claimed in  claim 9 , wherein the electron density of the plasma in the fourth step is found according to the following Equation 1, i.e., a relational expression of a plasma frequency ω pe  (.i e., the cutoff frequency).
   ω pe   =[n   e   e   2 /ε 0   m   e ] 1/2    [Equation 1]   where ω pe  is the plasma frequency, n e  is the electron density of the plasma, ε 0  is a dielectric constant in the vacuum, and e and m e  are an electron charge and mass, respectively.   
     
     
         11 . The method as claimed in  claim 9 , wherein the electron temperature T e  of the plasma in the sixth step is found according to the following Equation 2 and Equation 3.
   [1−[ω pe /ω] 2   ]={K   m (β a ) I   m ′(β a ) K   m (β b )− K   m ′(β a ) I   m (β b )}/{ K   m ′(β a ) I   m (β a ) K   m (β b )− K   m (β a ) I   m (β b )}  [Equation 2]   where ω is the absorption frequency, ω pe  is the plasma frequency, K m , I m , K m ′, and I m ′ are modified Bessel functions, β=2π/λ, λ=2l, and l is the length of the transmit antenna, a is a radius from the center of a metal unit of the transmit antenna to the boundary of a sheath, and b is a radius of the metal unit of the transmit antenna.
   λ d =(ε 0   T   e   /n   e   e   2 ) 1/2    [Equation 3] 
   s=nλ d    
   where λ d  is a Debye length, T e  is the electron temperature, n e  is the electron density of the plasma, ε 0  is the dielectric constant in the vacuum, e is the electron charge, s is the width of the sheath wherein s=a−b, and n is a given integer.