CN102156001A - Method for diagnosing self-biased probe of radio-frequency discharge plasma - Google Patents

Abstract

The invention relates to a radio frequency discharge plasma self-bias probe diagnosis method, which belongs to the field of plasma science and technology. It is characterized in that two probes are placed in the plasma: probe a and probe b, the probe a is in a floating state relative to the plasma discharge circuit, and the probe b is connected to the ground of the discharge circuit through a DC blocking capacitor and a sampling resistor. Measure the amplitude ΔV of the AC component of the voltage between probe a and probe b, the first harmonic amplitude |i _1ω | and the second harmonic amplitude |i _2ω | of the probe b current, using ΔV, |i _1ω | and | i _2ω | The electron temperature T _e and the ion density _ni are calculated. The beneficial effect of the invention is that it can overcome the influence of the insulation pollution on the surface of the probe, and obtain parameters such as ion density and electron temperature. There is no DC or AC bias voltage applied to the probe, which has little disturbance to the plasma discharge.

Description

A radio frequency discharge plasma self-bias probe diagnostic method

technical field

The invention belongs to the field of plasma science and technology, and relates to a radio frequency discharge plasma self-bias probe diagnosis method, which is used for diagnosing radio frequency discharge plasma, can overcome the influence of probe surface insulation pollution, and obtain ion density and electron temperature and other parameters.

Background technique

A common method for diagnosing plasma parameters is to place a probe in the plasma and apply a scanning bias voltage, measure and analyze the volt-ampere characteristic curve of the probe current changing with the scanning bias voltage to obtain various parameters of the plasma. A serious limitation of this method is that it cannot be used in reactive plasmas where the deposition of insulating films occurs, because in this case the surface of the probe will be covered with insulating products, unable to collect current and fail.

In response to this problem, Lee et al. disclosed a plasma diagnostic method for a floating probe [M.H.Lee, et al., J.Appl.Phys.v101, p033305 (2007)], adding a high-frequency AC bias to the probe Voltage, electron temperature and ion density are calculated using the fundamental and second harmonic amplitudes of the probe current. Since this kind of probe relies on displacement current to work, even if there is a certain degree of pollution on the surface of the probe, the insulation can still be used continuously. However, the disadvantage of this method is that a high-frequency AC bias voltage needs to be added to the probe, which often disturbs the plasma, changes the original state of the plasma, and makes the measurement inaccurate.

Contents of the invention

The technical problem to be solved by the present invention is to provide a radio frequency discharge plasma self-biased probe diagnosis method to solve the above-mentioned floating probe plasma diagnosis method that disturbs the plasma due to the need to add a high-frequency AC bias voltage to the probe. body, change the original state of the plasma, and make the measurement inaccurate.

Technical scheme of the present invention is:

Place two probes in the plasma: probe a and probe b. Probe a is in a floating state relative to the plasma discharge circuit, and probe b is connected to the ground wire of the discharge circuit through a DC blocking capacitor and a sampling resistor. No DC or AC bias voltage is applied to the probes.

Measure the amplitude ΔV of the AC component of the voltage between probe a and probe b, the first harmonic amplitude |i _1ω | and the second harmonic amplitude |i _2ω | of the probe b current, using ΔV, |i _1ω | and | i _2ω | Calculate the electron temperature T _e and the ion density n _i , and the calculation formulas are:

|i _1ω |/|i _2ω |＝I ₁ (eΔV/T _e )/I ₂ (ΔV/T _e )(1)

${\mathrm{<span\; class="notranslate">\; no</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}\mathrm{<span\; class="notranslate">\; \&omega;</span>}}<span\; class="notranslate">\; |</span>\sqrt{{\mathrm{<span\; class="notranslate">\; m</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}}}{\mathrm{<span\; class="notranslate">\; 1.22</span>}\mathrm{<span\; class="notranslate">\; E</span>}\sqrt{\mathrm{<span\; class="notranslate">\; k</span>}{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}}}\frac{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; e\&Delta;V</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; e\&Delta;V</span>}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; e</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the above two formulas, I ₀ , I ₁ and I ₂ are the zero-order, first-order and second-order modified Bessel functions respectively; e is the electron charge, the unit is Coulomb; A is the surface area of the probe, the unit is square meter; M _i is the mass of ions in kilograms; k=1.38×10 ^-23 J/K is Boltzmann's constant; ΔV is in volts; |i _1ω | and |i _2ω | are in amperes; _Te and _ni The units are Kelvin and units per cubic meter, respectively.

The beneficial effect of the invention is that it can overcome the influence of the insulation pollution on the surface of the probe, and obtain parameters such as ion density and electron temperature. There is no DC or AC bias voltage applied to the probe, which has little disturbance to the plasma discharge.

Description of drawings

The accompanying drawing is a schematic diagram of the diagnostic method of the present invention.

In the figure: 1 probe a, 2 probe b, 3 plasma, 4 DC blocking capacitor a, 5 DC blocking capacitor b,

6 amplifier a, 7 amplifier b, 8 spectrum analyzer, 9 discharge loop ground, 10 sampling resistor.

Detailed ways

Specific embodiments of the present invention will be described in detail below in conjunction with technical solutions and accompanying drawings.

In Figure 1, 1 probe a and 2 probe b are located in 3 plasma, 1 probe a is in a floating state relative to the plasma discharge circuit, 2 probe b is connected to 9 through 5 DC blocking capacitor b and 10 sampling resistor Discharge circuit ground; 1 probe a and 2 probe b are respectively connected to the positive and negative input terminals of 6 amplifier a through 4 DC blocking capacitors and 5 DC blocking capacitors, and the voltage AC component between 1 probe a and 2 probe b is passed through 6. Amplifier a amplifies and rectifies and filters the output amplitude ΔV; 2. The current of probe b is converted into a voltage signal by 10 sampling resistors, and then sent to 8 spectrum analyzer after being amplified by 7 amplifier b. After being analyzed by 8 spectrum analyzer, it outputs the primary harmonic wave amplitude |i _1ω | and second harmonic amplitude |i _2ω |; put the output ΔV, |i _1ω | and |i _2ω | data into formula (1) and formula (2) to calculate the electron temperature T _e and ion density n _i .

Claims (1)

1. rf (discharge) plasma automatic biasing probe diagnostics method, it is characterized in that: in plasma, place two probes: probe a (1) and probe b (2), probe a (1) is in quick condition with respect to the plasma discharge loop, and probe b (2) is connected discharge loop ground (9) by capacitance (5) with sample resistance (10); Do not add direct current or AC bias voltage on the probe;

Voltage alternating component amplitude Δ V between measuring probe a (1) and the probe b (2), the first harmonic amplitude of probe b (2) electric current | i _{1 ω}| and the second harmonic amplitude | i _{2 ω}|, utilize Δ V, | i _{1 ω}| and | i _{2 ω}| calculate electron temperature T _eWith ion concentration n _i

Computing formula is respectively:

|i _1ω|/|i _2ω|＝I ₁(eΔV/T _e)/I ₂(eΔV/T _e)(1)

$n_i=\frac{\left|i_{1\mathrm{\&omega;}}\right|\sqrt{M_i}}{1.22\mathrm{eA}\sqrt{k{T}_e}}\frac{I_0(\mathrm{e\&Delta;V}/T_e)}{I_1(\mathrm{e\&Delta;V}/T_e)}---\left(2\right)$

Above in two formulas, I ₀, I ₁And I ₂Be respectively zeroth order, single order and second order modified Bessel function; E is an electron charge, and unit is a coulomb; A is that detecting probe surface is long-pending, and unit is square metre; M _iBe the quality of ion, unit is a kilogram; K=1.38 * 10 ^-23J/K is a Boltzmann constant; Δ V unit is a volt; | i _{1 ω}| and | i _{2 ω}| unit is an ampere; T _eAnd n _iUnit is respectively Kelvin and every cubic metre.