Plasma electron density measurement method and plasma electron density measurement apparatus

Abstract

This invention provides a plasma electron density measurement method and a plasma electron density measurement apparatus that enable more accurate plasma electron density measurement. [Solution] The plasma electron density measurement method involves the plasma processing apparatus 1 generating plasma P, passing two electromagnetic waves E of different frequencies through the generated plasma P, obtaining the phase change Δφ of the electromagnetic waves E at each frequency, and determining the electron density η of the plasma P from the obtained phase change Δφ of the electromagnetic waves E. e It includes a step for measuring [something].

Description

[Technical Field]

[0001] This disclosure relates to a plasma electron density measurement method and a plasma electron density measurement apparatus. [Background technology]

[0002] There are devices and methods (hereinafter referred to as plasma electron density measurement devices and plasma electron density measurement methods) that measure the electron density of a plasma by utilizing the phase change of electromagnetic waves passing through the plasma of a plasma processing device. The principle is that when electromagnetic waves (microwaves, millimeter waves, terahertz waves, or laser light, depending on the electron density) generated by an electromagnetic wave generator are propagated into the plasma, the phase of the electromagnetic waves changes according to the electron density of the plasma. Then, by comparing this phase change with the phase of the original electromagnetic wave generated by the electromagnetic wave generator, the amount of phase change is determined and the plasma electron density is calculated.

[0003] As such a technology, Patent Document 1 shows that, in order to enable more accurate measurement and evaluation of plasma density, the distance variation between transmitting and receiving horn antennas is determined by a laser rangefinder, and the electron density is determined based on said distance variation. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2000-266692 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, in the technology described in Patent Document 1, distance variations are determined by a laser rangefinder installed separately from the microwave interferometer, but the distance measured is at a location different from the propagation path of the electromagnetic wave being measured. Therefore, there is a problem in that the distance of the actual propagation path of the electromagnetic wave cannot be accurately measured, and thus accurate plasma electron density measurement is not possible.

[0006] The present disclosure solves these problems, and an object thereof is to achieve more accurate plasma electron density measurement in a plasma electron density measurement method and a plasma electron density measurement apparatus. Means for Solving the Problems

[0007] The plasma electron density measurement method according to the present disclosure is a plasma electron density measurement method for measuring the electron density of plasma from a phase change of an electromagnetic wave passing through the interior of plasma generated by a plasma processing apparatus, the method comprising: a step of generating, by the plasma processing apparatus, plasma; a step of passing two electromagnetic waves having different frequencies through the interior of the generated plasma; a step of acquiring a phase change of the electromagnetic wave at each frequency; and a step of measuring the electron density of the plasma from the acquired phase change of the electromagnetic wave. Effects of the Invention

[0008] According to the present disclosure, the plasma electron density measurement method comprises: a step of generating, by the plasma processing apparatus, plasma; a step of passing two electromagnetic waves having different frequencies through the interior of the generated plasma; a step of acquiring a phase change of the electromagnetic wave at each frequency; and a step of measuring the electron density of the plasma from the acquired phase change of the electromagnetic wave. Accordingly, more accurate plasma electron density measurement can be achieved in the plasma electron density measurement method and the plasma electron density measurement apparatus. Brief Description of the Drawings

[0009] [Figure 1] FIG. 1 is a partial detailed diagram illustrating the principle of the plasma electron density measurement method according to Embodiment 1. [Figure 2] FIG. 2 is a diagram illustrating the relationship between plasma electron density and phase change of an electromagnetic wave in the plasma electron density measurement method according to Embodiment 1. [Figure 3] FIG. 3 is a diagram illustrating the measurement principle of the plasma electron density measurement method according to Embodiment 1. [Figure 4]Figure 4 shows a plasma electron density measuring device according to Embodiment 1. [Figure 5] Figure 5 shows a plasma electron density measuring device according to Embodiment 2. [Modes for carrying out the invention]

[0010] The plasma electron density measurement method and plasma electron density measurement apparatus according to the embodiments of this disclosure will be described in detail below with reference to the drawings.

[0011] Embodiment 1. (i) The plasma processing apparatus 1 generates plasma P. The plasma electron density measurement method according to the embodiment of this disclosure first involves (i) the plasma processing apparatus 1 generating plasma P.

[0012] Figure 1 is a detailed diagram showing the principle of the plasma electron density measurement method according to Embodiment 1. The plasma processing apparatus 1 is a device for plasma etching a substrate 2. Inside the apparatus, the substrate 2 is placed between electrodes 3 located at the top and bottom. A reaction gas is introduced into the apparatus from the top of the electrodes 3 via a reaction gas inlet pipe 4, and plasma P is generated between the electrodes 3 by electrical processing by the electrodes 3. The generated plasma P etches the surface of the substrate 2. After that, the reaction gas and reaction products generated during the etching process are discharged outside the apparatus through an exhaust gas outlet pipe 5.

[0013] (ii) The step of passing two electromagnetic waves E of different frequencies through the generated plasma P. The plasma electron density measurement method according to the embodiment of this disclosure then performs the step of passing two electromagnetic waves E of different frequencies into the generated plasma P.

[0014] While plasma P is generated between electrodes 3, electromagnetic waves E are generated by an electromagnetic wave generator 6. Then, electromagnetic waves E are transmitted from a transmitting horn antenna 7 located on the side of the plasma processing device 1, and the electromagnetic waves E are received by a receiving horn antenna 8 located on the opposite side of the plasma processing device 1. As a result, electromagnetic waves E propagate by passing through the plasma P generation area.

[0015] (iii) Step of obtaining the phase change Δφ of the electromagnetic wave E at each frequency. The plasma electron density measurement method according to the embodiment of this disclosure then performs the step of (iii) acquiring the phase change Δφ of the electromagnetic wave E at each frequency. For example, as shown in Figure 2, the phase change Δφ of the electromagnetic wave E is acquired for the case of a frequency of 60 GHz and for the case of 120 GHz.

[0016] When comparing the electron density η of plasma P before and after propagation, electromagnetic wave E is e Accordingly, the phase changes due to the influence of plasma P. By comparing this phase change Δφ with the phase of the original electromagnetic wave E immediately after it is generated by the electromagnetic wave generator 6, the phase change Δφ is determined, and the plasma electron density η is calculated. e Calculate.

[0017] The plasma electron density measurement method according to the embodiment of this disclosure utilizes this phenomenon. With this method, the electron density η of the plasma P can be measured without disturbing the plasma P. e It can measure [something].

[0018] Here, the plasma electron density η is obtained from the phase change Δφ of the electromagnetic wave. e We will explain the principle for determining the electron density η. e (x)[pcs / m 3 Let ] be the mass of the electron m e If the weight is [kg], the elementary charge of an electron is e[C], the permittivity of vacuum is ε0[F / m], and the speed of light is c[m / s], then the plasma angular frequency is ω pe (x) is, TIFF2026147802000002.tif13166 , which gives:

[0019] The refractive index n(x) at the angular frequency ω(=2πf) of an electromagnetic wave propagating in plasma is: TIFF2026147802000003.tif13166 and the phase change Δφ of the electromagnetic wave E having a plasma length L is: TIFF2026147802000004.tif11166 From the above, substituting equation (2): TIFF2026147802000005.tif14166 , which gives:

[0020] m e , e, ε0, and c are constants (m e =9.11×10 -31 [kg], e=1.60×10 -19 [C], ε0=8.85×10 -12 [F / m], c=3.00×10 8 [m / s]). By substituting these values into equation (1) and solving equation (4), the phase change Δφ of plasma electron density η e (x) is: TIFF2026147802000006.tif11166 , which gives: the phase change Δφ at the angular frequency ω of the electromagnetic wave E is a function of the plasma electron density η e (x). In this way, the plasma electron density η e can be obtained from the phase change Δφ of the electromagnetic wave E.

[0021] Figure 2 is a diagram showing the relationship between plasma electron density η e and the phase change Δφ of the electromagnetic wave E in the plasma electron density measurement method according to the first embodiment. The diagram shows the relationship between the electron density η e of the plasma P in a plasma processing apparatus 1 and the phase change Δφ of the electromagnetic wave E for two cases where the frequency of the electromagnetic wave E is 60 GHz and 120 GHz. In both cases, the electron density ηe 10 17 [m -3 When the value becomes larger than 0 [rad.], the phase change Δφ becomes larger than 0 [rad.], meaning that a phase change Δφ appears.

[0022] The shaded area in the figure represents the electron density range (10) of plasma P in an ICP (Inductively Coupled Plasma) etcher. 17 ~10 18 [m -3 This shows the phase change Δφ of the electromagnetic wave E in this range is more pronounced at a frequency of 60 GHz than at 120 GHz. In this disclosure, the difference in phase change Δφ between the two is used to determine the plasma electron density η e We will measure this. The method will be described later.

[0023] (iiii) From the phase change Δφ of the acquired electromagnetic wave E, the electron density η of the plasma P is obtained. e Steps to measure The plasma electron density measurement method according to the embodiment of this disclosure then proceeds to (iii) determine the electron density η of the plasma P from the phase change Δφ of the acquired electromagnetic wave E. e Perform the step of measuring.

[0024] Figure 3 shows the measurement principle of the plasma electron density measurement method according to Embodiment 1. As shown in Figure 3, the distance between the transmitting horn antenna 7 and the receiving horn antenna 8 is defined as the inter-antenna distance L1, and assuming that a plasma of plasma length L is generated between these antennas, the propagation length L between the transmitting and receiving antennas is... c teeth, TIFF2026147802000007.tif11166 This is the result.

[0025] Here, we assume that the refractive index of the plasma P generation area is 1. Now, the electron density of plasma P at angular frequency ω1 is η e Assuming that the region is uniform and uniform at refractive index n1, the phase change Δφ1 is given by equation (3): TIFF2026147802000008.tif35166

[0026] Even at angular frequency ω², the phase change Δφ² is similarly given by equation (3): TIFF2026147802000009.tif10166 This is the result.

[0027] Here, dividing equation (7) by ω1 and equation (8) by ω2, and eliminating L1, we get the following: TIFF2026147802000010.tif11166 If we multiply both sides by ω1ω2, TIFF2026147802000011.tif10166 Substituting equation (2) into equation (9)', TIFF2026147802000012.tif9166 This is the result.

[0028] e in equation (1) 2 / ε0m e Since is a constant, let's set it to k and substitute it into equation (10): TIFF2026147802000013.tif11166 Therefore, since ω1, ω2, and L are known, measuring Δφ1 and Δφ2 will give the plasma electron density η e You will be asked to do so.

[0029] Furthermore, by determining it in this way, the propagation length L of the electromagnetic wave E can be calculated. c However, plasma electron density η eThis eliminates the need to calculate the current value. Therefore, it is possible to reduce the phase change, i.e., noise, caused by the thermal expansion of the plasma chamber and the distance fluctuations between the transmitting and receiving antennas due to mechanical vibrations such as the exhaust pump or exhaust valve, thereby enabling more accurate plasma electron density measurement.

[0030] Figure 4 shows a plasma electron density measuring device 10 according to Embodiment 1. The plasma electron density measuring device 10 consists of a plasma processing device 1, a transmitting unit 11, a receiving unit 12, a control unit 13, and a signal processing unit 14.

[0031] The transmitting unit 11 consists of an electromagnetic wave generator 6, an amplifier 15, a frequency multiplier 16, and a transmitting horn antenna 7. The control unit 13 transmits output control signals of two different frequencies to the electromagnetic wave generator 6. The electromagnetic wave E generated by the electromagnetic wave generator 6 is first amplified by the amplifier 15.

[0032] The amplified electromagnetic wave E is then multiplied by a constant frequency by the frequency multiplier 16 to become an electromagnetic wave E with a constant frequency. This electromagnetic wave E is then transmitted from the transmitting horn antenna 7 towards the inside of the plasma processing device 1.

[0033] The receiving unit 12 includes a receiving horn antenna 8, a frequency multiplier 17, and a phase comparator 18. The phase change Δφ of the electromagnetic wave E received by the receiving horn antenna 8 is recorded by the phase comparator 18. At this time, the electromagnetic wave E is directly acquired as a reference signal from the electromagnetic wave generator 6 of the transmitting unit 11, and its phase is compared with that of the electromagnetic wave E that has passed through the frequency multiplier 17.

[0034] Once the phase change Δφ is determined by the phase comparator 18, it is processed as a complex amplitude signal in the signal processing unit 14, and the electron density η e This is measured. For this measurement, the frequency switching synchronization signal transmitted from the control unit 13 to the signal processing unit 14 is used as the comparison target.

[0035] Using the plasma electron density measuring device 10 described above, the plasma electron density ηe The measurement is performed by following the steps (1) to (24) in order.

[0036] Initial value acquisition step (1) The electromagnetic wave generator 6 generates an electromagnetic wave E with angular frequency ω1. (2) The transmitting horn antenna 7 emits electromagnetic waves E. (3) When plasma P is not being generated, the electromagnetic wave E with angular frequency ω1 is acquired by the receiving horn antenna 8. (4) Initial phase value φ when plasma P is not generated 10 Get (5) Stop electromagnetic waves E with angular frequency ω1. (6) The electromagnetic wave generator 6 generates an electromagnetic wave E with angular frequency ω2. (7) Electromagnetic waves E are emitted from the transmitting horn antenna 7. (8) When plasma P is not being generated, the electromagnetic wave E with angular frequency ω2 is acquired by the receiving horn antenna 8. (9) Initial phase value φ when plasma P is not generated 20 Get (10) Stop electromagnetic waves E with angular frequency ω2.

[0037] Measurement steps (11) Generate plasma P (12) The electromagnetic wave generator 6 generates an electromagnetic wave E with angular frequency ω1. (13) Electromagnetic waves E are emitted from the transmitting horn antenna 7 to the plasma P. (14) The electromagnetic wave E with angular frequency ω1 that has passed through the plasma P is acquired by the receiving horn antenna 8. (15) Obtain the phase value φ1, and Δφ1 = φ1 - φ 10 To find (16) Stop electromagnetic waves E with angular frequency ω1. (17) The electromagnetic wave generator 6 generates an electromagnetic wave E with angular frequency ω2. (18) Electromagnetic waves E are emitted from the transmitting horn antenna 7 to the plasma P. (19) The electromagnetic wave E with angular frequency ω2 that has passed through the plasma P is acquired by the receiving horn antenna 8. (20) Obtain the phase value φ2, and Δφ2 = φ2 - φ 20 To find (21)Calculate the plasma electron density η from Δφ1 and Δφ2 using the above formula (10)'. e To find (22) Return to step (12)

[0038] End step (23) Stop Plasma P (24) Measurement complete

[0039] Embodiment 2. The plasma electron density measuring device 20 according to Embodiment 2 of this disclosure will be described with reference to Figure 5. Components having the same functions as those described in Embodiment 1 above are denoted by the same reference numerals, and their descriptions are omitted.

[0040] The plasma electron density measuring device 10 according to Embodiment 1 generated two electromagnetic waves E with different frequencies separately. In contrast, the plasma electron density measuring device 20 according to Embodiment 2 allows two electromagnetic waves E with different frequencies to pass through simultaneously, and simultaneously acquires the phase change Δφ of the electromagnetic waves E at each frequency. The two electromagnetic waves E with different frequencies are, for example, 60 GHz and 120 GHz.

[0041] Figure 5 shows a plasma electron density measuring device 20 according to Embodiment 2. The plasma electron density measuring device 20 is composed of a plasma processing device 1, a transmitting unit 11, a receiving unit 12, a control unit 13, and a signal processing unit 14, similar to the plasma electron density measuring device 10 according to Embodiment 1.

[0042] The transmitting unit 11 is equipped with two electromagnetic wave generators 6 and 21 to transmit two electromagnetic waves E of different frequencies. The control unit 13 transmits separate output control signals to each of the electromagnetic wave generators 6 and 21. The electromagnetic waves E generated by the electromagnetic wave generators 6 and 21 are first amplified by amplifiers 15 and 22.

[0043] The amplified electromagnetic wave E is then multiplied by a constant by frequency multipliers 16 and 23 to become an electromagnetic wave E with a constant frequency. The electromagnetic waves E that have passed through frequency multipliers 16 and 23 are combined in a multiplexer 24. The combined electromagnetic wave E is then transmitted from the transmitting horn antenna 7 towards the inside of the plasma processing device 1.

[0044] The receiving unit 12 first separates the electromagnetic wave E received by the receiving horn antenna 8 into two electromagnetic waves E with different frequencies using a demultiplexer 25. For each of the separated electromagnetic waves E, the phase change Δφ is recorded by phase comparators 18 and 27. At this time, the electromagnetic wave E is directly acquired as a reference signal from the electromagnetic wave generators 6 and 21 of the transmitting unit 11, and its phase is compared with that of the electromagnetic wave E that has passed through frequency multipliers 17 and 26.

[0045] Once the phase change Δφ is determined by the phase comparators 18 and 27, both complex amplitude signals are processed as two complex amplitude signals in the signal processing unit 14, and the electron density η e This is measured.

[0046] Using the plasma electron density measuring device 20 described above, the plasma electron density η e The measurement is performed by following the steps (1) to (11) in order.

[0047] Initial value acquisition step (1) In the electromagnetic wave generator 6, the angular frequency ω 1、 Generates an ω2 electromagnetic wave E. (2) The transmitting horn antenna 7 emits electromagnetic waves E. (3) ω when plasma is not being generated 1、 The ω2 electromagnetic wave E is acquired by the receiving horn antenna 8. (4) Initial phase value φ 10 , φ 20 Get

[0048] Measurement steps (5) Generate plasma P (6) ω that has passed through plasma P 1、 The ω2 electromagnetic wave E is acquired by the receiving horn antenna 8. (7) Obtain the phase value φ1, and Δφ1 = φ1 - φ 10 To find (8) Obtain the phase value φ2, and Δφ2 = φ2 - φ 20 To find (9)Calculate the plasma electron density η from Δφ1 and Δφ2 using the above formula (10)'. e To find

[0049] End step (10) Stop Plasma P (11) Measurement complete

[0050] The plasma processing apparatus 1 does not necessarily have to be an ICP etcher; any apparatus that uses plasma P for processing is acceptable. Also, lenses or the like may be used instead of the transmitting and receiving horn antennas 7 and 8. Furthermore, the electromagnetic wave E can be any of the following: microwave, submillimeter wave, millimeter wave, terahertz wave, infrared, visible light, ultraviolet, X-ray, or laser light.

[0051] Furthermore, the propagation path of electromagnetic wave E does not have to be in space; a conductor such as a coaxial cable or a waveguide may be used. In addition, a quadrature detector, interferometer, port type reflectometer, etc., can be used as the phase comparator 18, 27. [Explanation of Symbols]

[0052] 1. Plasma processing equipment 2 circuit boards 3 electrodes 4. Reaction gas inlet pipe 5. Exhaust gas outlet pipe 6.21 Electromagnetic wave generator 7. Transmitting horn antenna 8. Receiving horn antenna 10, 20 Plasma electron density measuring device 11 Transmitter 12 Receiver 13 Control Unit 14 Signal Processing Unit 15, 22 Amplifier 16, 17, 23, 26 frequency multiplier 18, 27 Phase comparator 24 Multiplexer 25 Duplexer E electromagnetic waves P Plasma

Claims

1. A plasma electron density measurement method for measuring the electron density of a plasma generated by a plasma processing device, based on the phase change of electromagnetic waves passing through the plasma, The plasma processing apparatus includes the steps of generating the plasma and The steps include passing two electromagnetic waves of different frequencies through the generated plasma, A step of acquiring the phase change of the electromagnetic wave at each frequency, The method includes a step of measuring the electron density of the plasma from the phase change of the acquired electromagnetic wave. A plasma electron density measurement method characterized by the following.

2. In the step of passing two electromagnetic waves of different frequencies through the plasma generated, The two electromagnetic waves of different frequencies are allowed to pass through simultaneously, and the phase change of the electromagnetic waves at each frequency is acquired simultaneously. The plasma electron density measurement method according to claim 1, characterized by its features.

3. The electromagnetic wave is one of the following: microwave, submillimeter wave, millimeter wave, terahertz wave, infrared, visible light, ultraviolet, X-ray, or laser light. A plasma electron density measurement method according to claim 1 or 2, characterized by the features described above.

4. A plasma electron density measuring apparatus for performing the plasma electron density measuring method according to claim 1 or claim 2, A plasma processing apparatus that generates the aforementioned plasma and performs plasma processing on a substrate, An electromagnetic wave generator that generates the aforementioned electromagnetic waves, An amplifier for amplifying the generated electromagnetic waves, Within the plasma processing apparatus, a transmitting and receiving horn antenna for transmitting and receiving electromagnetic waves is provided, such that the amplified electromagnetic waves pass through the interior of the plasma. The system comprises a phase comparator for measuring the phase change of the electromagnetic wave, A plasma electron density measuring device characterized by the following features.

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