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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 shows the construction of an apparatus for monitoring an electron density and electron temperature of a plasma according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of transmit/receive antennas shown in FIG. 1;

FIG. 3 is a view illustrating convey within a reaction container of an electromagnetic wave transceiver shown in FIG. 1;

FIG. 4 a is a graph illustrating cutoff frequencies measured using the monitoring apparatus according to an embodiment of the present invention;

FIG. 4 b is a graph illustrating absorption frequencies measured using the monitoring apparatus according to an embodiment of the present invention;

FIG. 5 is a graph illustrating electron density and electron temperature measured using the monitoring apparatus according to an embodiment of the present invention; and

FIG. 6 is a flowchart illustrating a method of measuring an electron temperature of a plasma according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An apparatus for monitoring an electron density and electron temperature of a plasma according to an embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

FIG. 1 shows the construction of an apparatus for monitoring an electron density and electron temperature of a plasma according to an embodiment of the present invention. FIG. 2 is a cross-sectional view of transmit/receive antennas shown in FIG. 1.

Referring to FIGS. 1 and 2, the monitoring apparatus according to the present invention is adapted to measure a corresponding characteristic value and monitor the characteristic value in real-time, by finding a correlation between the characteristics of electromagnetic wave and a plasma 100a (more particularly, an electron density, an electron temperature, and so on) and monitoring.

In order to have the correlation, the monitoring apparatus of the present invention includes an electromagnetic wave transceiver 200 for transmitting/receiving electromagnetic wave to/from the plasma 100a. For the purpose of such transmission/reception, the electromagnetic wave transceiver 200 has an antenna structure.

What is contained in a cylindrical reaction container 100 is the plasma 100a. It has been known that if electromagnetic wave of a specific band is transmitted to the plasma 100a, corresponding electromagnetic wave is cut off or absorbed. A specific electromagnetic wave of a frequency band that is cut off or absorbed as described above becomes the index of an electron density or an electron temperature of the plasma 100a. It is therefore possible to obtain an electron density and electron temperature of the plasma 100a based on a correlation between the electromagnetic wave and the plasma 100a.

The correlation is established in the electromagnetic wave transceiver 200. An electromagnetic wave generator 300 and the frequency analyzer 400 are electrically connected to the electromagnetic wave transceiver 200 in order to transmit electromagnetic wave to the electromagnetic wave transceiver 200 or to analyze received electromagnetic wave.

In this case, the electromagnetic wave transceiver 200 includes two coaxial cables 210, 220 that are disposed in parallel. Each of the coaxial cables 210, 220 is surrounded with an additional dielectric-coated layer 230 and a ground shield, for preventing the coaxial cables 210, 220 from noise, heat, etc. Accordingly, electromagnetic wave can be transmitted and received more accurately. The dielectric-coated layer 230 may be formed of alumina or quartz.

Furthermore, transmit/receive antennas 210a, 220b are connected to and projected from one ends of the coaxial cables 210, 220, respectively, on the same axial line, and transmit/receive electromagnetic wave to/from the plasma 100a.

Referring to FIG. 2, if the metal antennas 210a, 220a having a radius “b” are inserted into the plasma, a sheath 240 having a thickness “s” is formed on an outer surface of the antenna, thus surrounding the circumference of the antenna. In the present embodiment, the antennas 210a, 220a may be disposed at a distance of about 1 mm to 5 mm and may have a length of about 5 mm to 10 mm. The distance is only illustrative. The smaller the distance, the better. In addition, the length of each of the antennas 210a, 220a may be varied depending on a wavelength of electromagnetic wave used.

The electromagnetic wave generator 300 is connected to the other end of the first coaxial cable 210 and consecutively transmits electromagnetic waves of a frequency band of about 50 kHz to 10 GHz to the first coaxial cable 210 and the transmit antenna 210a. Consequently, a series of electromagnetic waves of a frequency band can be transmitted to the plasma 100a consecutively.

In this case, the cutoff frequency of the transmitted electromagnetic waves is cut off with respect to the plasma 100a. The cutoff frequency can be used to calculate and obtain an electron density of a corresponding plasma 100a. Furthermore, an electromagnetic wave of a band absorbed by the plasma 100a is an absorption electromagnetic wave, which can be used to calculate and obtain an electron temperature of a corresponding plasma 100a.

The frequency analyzer 400 is also connected to the other end of the second coaxial cable 220. The frequency analyzer 400 serves to analyze an amplitude from a frequency of electromagnetic wave, which is received and obtained by the receive antenna 220a and the second coaxial cable 220.

If the transmitted electromagnetic wave is cut off, however, the receive rate of the electromagnetic wave in the receive antenna 220a is very weak. Accordingly, the electromagnetic wave of the weakest receive rate can be analyzed as the cutoff frequency. The frequency analyzer 400 can identify the weakest frequency by analyzing a frequency, an amplitude, and so on of the obtained electromagnetic wave. It is therefore possible to analyze/obtain the cutoff frequency.

Furthermore, if there is electromagnetic wave absorbed by the plasma 100a, the electromagnetic wave is weakly reflected from the transmit antenna 220a and the first coaxial cable 220. It causes to generate resonance in the sheath space between the plasma 100a and the transmit antenna 220a by way of a kind of a cavity, resulting in a strong absorption of the electromagnetic wave. Therefore, a signal of the reflected electromagnetic wave becomes the weakest. That is, it is meant that a ratio in which the electromagnetic wave is reflected from the transmit antenna again is low. It is possible to obtain/acquire a corresponding frequency band of the absorbed electromagnetic wave by analyzing a frequency band, amplitude, etc. of the weakly reflected electromagnetic wave. Accordingly, there is provided a structure capable of analyzing/acquiring an absorption frequency band.

A computer 500 is provided to calculate an electron density and an electron temperature based on the occurrence of a series of the electromagnetic waves, a received command, and analyzed frequency data. The computer 500 is electrically connected the electromagnetic wave generator 300 and the frequency analyzer 400.

Therefore, if the electromagnetic wave transceiver 200 is connected to the plasma 100a within the reaction container 100 and transmits electromagnetic wave, a frequency band, etc. is obtained from a weakly received electromagnetic wave and data of a cutoff frequency and an absorption frequency are transmitted to the computer 500. Calculation equations capable of calculating an electron density and/or an electron temperature based on a frequency are programmed into the computer 500. Accordingly, a structure that can calculate and acquire an electron density and electron temperature of a corresponding plasma 100a can be provided.

FIG. 3 is a view illustrating convey within the reaction container 100 of the electromagnetic wave transceiver 200 shown in FIG. 1.

As shown in FIG. 3, the monitoring apparatus according to the present invention includes a conveyer 600. To the other end of the electromagnetic wave transceiver 200 is connected the conveyer 600.

In the present invention, the conveyer 600 may have a power structure that allows for a straight-line convey, such as a stepping motor structure or an oil-pressure cylinder structure. The conveyer 600 is constructed to convey the electromagnetic wave transceiver 200, which is disposed to move along a radial direction within the cylindrical reaction container 100, in a straight line forward and backward.

As described above, the conveyer 600 is constructed to convey the electromagnetic wave transceiver 200 in the straight line. Therefore, the electromagnetic wave transceiver 200 can transmit/receive electromagnetic wave while moving in the straight line within the plasma 100a. Furthermore, there is provided a structure capable of analyzing, measuring, and monitoring spatial distributions of an electron density and electron temperature of a corresponding plasma 100a.

FIG. 4 a is a graph illustrating cutoff frequencies measured using the monitoring apparatus according to an embodiment of the present invention, and FIG. 4b is a graph illustrating absorption frequencies measured using the monitoring apparatus according to an embodiment of the present invention.

Referring to FIG. 4a, the X axis denotes a frequency band (Hz) and the Y axis denotes an amplitude of electromagnetic wave (au.), which is received by the receive antenna 220a. From FIG. 4a, it can be seen that as the frequency increases, the amplitude increases, then decreases at about 1.5×10⁹ Hz, and then becomes the lowest at a frequency of about 2.5×10⁹ Hz (indicated by an arrow in the drawing). A portion indicating the lowest amplitude, of ones in which the electromagnetic wave received as described above is indicated as the frequency band versus the amplitude, is the cutoff frequency.

The cutoff frequency is a frequency of a band that does not transmit the plasma 100a when the transmit antenna 210a transmits the electromagnetic wave to the plasma 100a as mentioned earlier. Accordingly, a very weak signal is received by the receive antenna 220a. The cutoff frequency serves as an index to detect an electron density of the plasma 100a.

In the present embodiment, the electromagnetic wave generator 300 generates electromagnetic waves. The generated electromagnetic waves are consecutively transmitted to the transmit antenna 210a through the first coaxial cable 210 on a frequency basis and are then transmitted to the plasma 100a.

The electromagnetic waves that have been transmitted and have been cut off and weaken in the plasma 100a as described above are continuously received by the receive antenna 220a. The electromagnetic waves are then transmitted to the frequency analyzer 400 connected to the second coaxial cable 220 and are then analyzed on a frequency-band basis.

The analyzed data are transmitted to the computer 500 and are then indicated as the graph as shown in FIG. 4a. Furthermore, what is indicated as a frequency band of the lowest amplitude in the graph is the cutoff frequency. Therefore, there is provided a structure in which the computer 500 can calculate/acquire an electron density of a corresponding plasma 100a based on the cutoff frequency acquired through the above operation.

In addition, referring to FIG. 4b, an X axis denotes a frequency band (Hz) and a Y axis denotes a predetermined reflection coefficient (dB). Accordingly, in the case where electromagnetic waves are transmitted to a corresponding plasma 100a, an absorption frequency can be acquired by analyzing electromagnetic wave of a corresponding frequency having the lowest reflection coefficient through a process in which the electromagnetic wave is reflected and received.

Analyzed data of the absorption frequency obtained as described above are transmitted to the computer 500. Accordingly, there is provided a structure in which the computer 500 can measure an electron temperature of a corresponding plasma 100a based on the analyzed data.

FIG. 5 is a graph illustrating electron density and electron temperature measured using the monitoring apparatus according to an embodiment of the present invention.

Referring to FIG. 5, an X axis denotes a pressure (mTorr) of the plasma 100a within the reaction container 100, and a Y axis on the right side denotes an electron density (cm⁻³) of the plasma 100a on a pressure basis and a Y axis on the left side denotes an electron temperature (eV) of the plasma 100a on a pressure basis.

From FIG. 5, it can be seen that in the case where argon (Ar) plasma is used in the present invention, the electron density of the plasma 100a increases as the gas pressure increases, but the electron temperature of the plasma 100a decreases as the discharge gas pressure increases.

Therefore, FIG. 5 shows that the slope of the graph of the electron density indicated by a straight line and triangles is opposite to the slope of the graph of the electron temperature indicated by a straight line and squares.

It has been illustrated above that the apparatus for monitoring an electron density and electron temperature of a plasma according to an embodiment of the present invention has a structure in which one electromagnetic wave transceiver 200 in which the conveyer 600 is connected to one end of the reaction container 100 is mounted. However, the present invention can be applied to a structure in which respective electromagnetic wave transceivers 200 are mounted in the other side, and upper and lower sides of the reaction container 100, and the conveyers 600 are connected to the respective electromagnetic wave transceivers 200 and measure three-dimensional spatial distributions of an electron density and electron temperature of the X-Y-Z axis while moving within the reaction container 100 in the respective axial directions.

Furthermore, the transmit antenna 210a and the receive antenna 220a of the straight-line type have been illustrated above as means for transmitting and receiving electromagnetic wave. It is however to be noted that a loop antenna, a superturnstile antenna, an excitation antenna, a parabola antenna or the like may be selectively used as the means for transmitting and receiving electromagnetic wave.

FIG. 6 is a flowchart illustrating a method of measuring an electron temperature of a plasma according to an embodiment of the present invention.

Referring to FIG. 6, a method of monitoring an electron temperature using the electron temperature monitoring apparatus of the present invention includes a first step (S1) of allowing the electromagnetic wave generator 300 to apply electromagnetic wave of a predetermined frequency to the transmit antenna 210a, a second step (S2) of allowing the receive antenna 220a to analyze a frequency of the electromagnetic wave received from the transmit antenna 210a, a third step (S3) of measuring a cutoff frequency based on the analyzed frequency, a fourth step (S4) of calculating an electron density of a plasma using the measured cutoff frequency, a fifth step (S5) of allowing the electromagnetic wave generator 300 to transmit electromagnetic wave, monitor reflected wave returned to the transmit antenna 210a, and measure a surface wave absorption frequency, and a sixth step (S6) of calculating an electron temperature based on the plasma density and the absorption frequency found in the fourth step (S4) and the fifth step (S5), respectively.

In the case of a process employing common plasma, the plasma itself includes a unique plasma frequency whose state is changed. The plasma frequency is directly related to the plasma density. Therefore, the electron density of the plasma can be measured directly by measuring the plasma frequency.

In the event that a frequency of common electromagnetic wave corresponds to the plasma frequency, the frequency has a property that if the electromagnetic wave is incident on the plasma, it is cut off and does not transmit the plasma. Therefore, if the electromagnetic wave generating apparatus transmits a frequency of 50 kHz to 10 GHz to the transmit antenna, the electromagnetic wave output from the transmit antenna can be received by the receive antenna.

At this time, electromagnetic wave having the plasma frequency decided according to the plasma density does not pass through the plasma. Accordingly, the electromagnetic wave is not received by the receive antenna or only a very weak signal is received by the receive antenna.

That is, as shown in FIG. 4a, the cutoff frequency of the lowest value can be found from the frequency spectrum through the frequency analyzer 400. The cutoff frequency is a plasma frequency (ω_pe). The electron density of the plasma can be found based on the plasma frequency (ω_pe) in accordance with the following Equation 1.

μ_p2=[n_ee²/ε₀m_e]^1/2   [Equation 1]

where ω_pe is the plasma frequency, n_e is the electron density of the plasma, ε₀ is the dielectric constant in the vacuum, and e and m_e are the electron charge and mass, respectively.

Meanwhile, if the electromagnetic wave generator 300 transmits electromagnetic wave and the transmit antenna 210a monitors returned reflected wave, a surface wave absorption frequency of the transmit antenna 210a can be measured.

In other words, the spectrum of the electromagnetic wave reflected from the transmit antenna 210a of FIG. 1 is shown in FIG. 4b. A dispersion equation of the surface wave can be expressed in the following Equation 2.

[1−[ω_pe/ω]²]={K_m(βa)I_m′(βa)K_m(βb)−K_m′(βa)I_m(βb)}/{K_m′(βa)I_m′(βa)I_m(βa)K_m(βb)−K_m(βa)I_m(βb)}  [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 the radius from the center of a metal unit of the transmit antenna to the boundary of the sheath, and b is the radius of the metal unit of the transmit antenna.

Furthermore, an electron temperature T_e can be found using the surface wave dispersion equation of the above-mentioned Equation 2, a Debye length λ_d defined by the following Equation 3, and the width s of the sheath. FIG. 2 shows the relationship between the sheath width s of the transmit antenna, and “a” and “b”.

λ_d=(ε₀T_w/n_ee²)^1/2   [Equation 3]

s=nλ_d

where λ_d is the Debye length, T_e is the electron temperature of the plasma, n_e is the electron density of the plasma, ε₀ 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.

Therefore, the cutoff frequency is the plasma frequency ω_pe and other parameters are constants corresponding to a structural antenna size. Accordingly, the electron temperature T_e can be found by measuring the absorption frequency ω.

In accordance with an apparatus and method for monitoring an electron density and electron temperature of a plasma according to the present invention, an electron density and electron temperature of a plasma can be measured by detecting an eigenfrequency. Therefore, the present invention is advantageous in that it can be applied to a thin film plasma chemical deposition method of a semiconductor fabrication process, a plasma process apparatus in a dry etch process, and so on.

Furthermore, the apparatus of the present invention can be used as a plasma real-time monitoring apparatus. Therefore, there is an advantage in that the apparatus of the present invention can be utilized as a reliable process equipment since it can check a current status of a process equipment.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.

Claims

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; anda 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; anda 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; anda 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 ωpe (.i e., the cutoff frequency). ωpe=[nee2/ε0me]1/2   [Equation 1]where ωpe is the plasma frequency, ne is the electron density of the plasma, ε0 is a dielectric constant in the vacuum, and e and me are an electron charge and mass, respectively.

11. The method as claimed in claim 9, wherein the electron temperature Te of the plasma in the sixth step is found according to the following Equation 2 and Equation 3. [1−[ωpe/ω]2]={Km(βa)Im′(βa)Km(βb)−Km′(βa)Im(βb)}/{Km′(βa)Im(βa)Km(βb)−Km(βa)Im(βb)}  [Equation 2]where ω is the absorption frequency, ωpe is the plasma frequency, Km, Im, Km′, and Im′ 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. λd=(ε0Te/nee2)1/2   [Equation 3]s=nλd where λd is a Debye length, Te is the electron temperature, ne is the electron density of the plasma, ε0 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.