CN106413237A - Plasma diagnostic method of multi-amplitude AC bias probe based on data acquisition card - Google Patents

Abstract

The invention belongs to the field of plasma technology, and relates to a multi-amplitude AC bias probe plasma diagnosis method based on a data acquisition card. The invention generates an AC bias signal based on a data acquisition card, which is driven by a power amplifier and then added to the Placed on the probe in the plasma, at the same time, the differential analog input port of the data acquisition card commanded by the computer collects the voltage signal on the sampling resistor and sends it to the computer, which is converted into a current signal by the computer; after the spectrum analysis, the least square method is carried out Fitting and further calculations yield accurate electron temperature values and ion density values. The invention solves the problem of inaccurate measurement of electron temperature and ion density by the existing fixed-amplitude AC bias probe diagnostic technology, can diagnose plasma, especially plasma in insulating deposition environment, and can automatically complete the plasma diagnosis process, output Accurate electron temperature values and ion density values.

Description

A Multi-amplitude AC Biased Probe Plasma Diagnosis Based on Data Acquisition Card method

technical field

The invention belongs to the field of plasma technology, and relates to a multi-amplitude AC bias probe plasma diagnosis method based on a data acquisition card, which is used for diagnosing plasma, especially plasma in an insulating deposition environment, and obtaining electron temperature and ion density.

Background technique

Existing probe technologies for diagnosing plasma parameters are of various types. The most commonly used single probe is to place a small metal electrode, the probe, in the plasma, apply a scanning bias voltage between the probe and the plasma ground electrode, and then measure the change of the probe current with the scanning bias voltage , to obtain the volt-ampere characteristic curve, and then obtain the plasma parameters by analyzing the volt-ampere characteristic curve. In addition, there are double-probe, three-probe and other types. A common feature of these probe technologies is that they all need to add a DC bias voltage to the probe, and the problem that this brings is: when the diagnosed When insulating deposition occurs in a plasma environment, the surface of the probe will be covered by deposited substances, which will lose its conductivity and fail to work.

A prior art for solving the above-mentioned problem is to use a signal generator to generate an AC bias voltage with a fixed amplitude V ₀ to add to the probe, measure the probe current signal, and then use a spectrum analyzer to analyze the probe current signal to obtain the First harmonic amplitude i _1ω and second harmonic amplitude i _2ω , then use the formula i _1ω /i _2ω =I ₁ (eV ₀ /T*)/I ₂ (eV ₀ /T*) to calculate T* as the electron temperature , and then use the formula Calculate n* as the ion density. In the above two formulas, e is the electron charge, and I ₀ (eV ₀ /T*), I ₁ (eV ₀ /T*) and I ₂ (eV ₀ /T*) are eV The zero-order, first-order and second-order imaginary volume Bessel functions of ₀ /T*, A and M are the probe surface area and ion mass, respectively. Since alternating current can pass through the insulating layer on the probe surface in the form of displacement current, this technique can be used even when the probe surface is covered with insulating substances, thus enabling the diagnosis of plasmas in insulating deposition environments.

However, T* and n* obtained by the above prior art are not accurate electron temperature and ion density. This is because the theoretical basis of the above-mentioned existing fixed-amplitude AC bias probe diagnostic technology is an infinite planar electrode model. It cannot be regarded as an infinite planar electrode, and the amplitude of the current signal is related to the amplitude of the AC bias voltage. This makes the electron temperature and ion density values obtained by the existing technology vary with the selected AC bias voltage amplitude, and the existing fixed-amplitude AC bias probe diagnostic technology cannot accurately obtain the plasma electron temperature and ion density. Ion density value.

On the other hand, the existing fixed-amplitude AC bias probe diagnosis technology uses signal generators and spectrum analyzers, which cannot automatically complete the plasma diagnosis process and output results.

Contents of the invention

The invention provides a multi-amplitude AC bias probe plasma diagnosis method based on a data acquisition card to solve the problem of inaccurate measurement of electron temperature and ion density by the existing fixed-amplitude AC bias probe diagnostic technology, and can Automatically complete the plasma diagnosis process, and output accurate electron temperature values and ion density values.

Technical scheme of the present invention is:

(a) The computer instructs the analog output port of the data acquisition card to successively generate AC bias signals with the amplitudes of V=V _j (j=1,2,...), which are driven by the power amplifier, and then added to the set by the sampling resistor On the probe in the plasma, at the same time, the computer instructs the differential analog input port of the data acquisition card to collect the voltage signal on the sampling resistor and send it to the computer, and the computer converts it into a current signal.

(b) The computer performs frequency spectrum analysis on the probe current signals under each amplitude AC bias voltage V=V _j (j=1,2,...), and obtains the first harmonic amplitude i _1ωj (j=1,2, . . . ) and the second harmonic amplitude i _2ωj (j=1,2,...) and calculate their ratio P _j =i _1ωj /i _2ωj (j=1,2,...).

(c) The computer uses the function I ₁ (eV _j /T)/I ₂ (eV _j /T) for the data points (P _j , V _j ) (j=1, 2,...) with T as the variable Least squares fitting (where e is the electron charge, I ₁ (eV _j /T) and I ₂ (eV _j /T) are the first-order and second-order virtual parity Bessel functions of eV _j /T, respectively), The output satisfies the T value T=T _e fitted by the least square method, and T _e is an accurate electronic temperature value.

(d) The computer uses V _j (j=1,2,...), i _1ωj (j=1,2,...) and T _e data to substitute into the formula Calculate n _j (j=1,2,...), where A and M are the probe surface area and ion mass, respectively, and I ₀ (eV _j /T _e ) is the zero-order virtual parameter of eV _j /T _e Measure the Bessel function, then perform linear fitting on the data points (n _j ,V _j )(j=1,2,...) and extend to V=0, and output the value of the fitted line at V=0 n ₀ , n ₀ is the exact ion density value.

The beneficial effects of the present invention are:

It can diagnose plasma, especially the plasma in insulating deposition environment, automatically complete the plasma diagnosis process, and output accurate electron temperature and ion density values.

Description of drawings

Fig. 1 is a schematic diagram of plasma diagnosis using the method of the present invention.

Fig. 2 is the data point (P _j , V _j ) (j=1,2,...) obtained by the method of the present invention and its function I ₁ (eV _j /T)/I ₂ (eV _j /T) Carry out the result of least square method fitting, and utilize the data point (n _j , V _j ) (j=1,2,...) obtained by the method of the present invention and carry out linear fitting to it and extend to V=0 the result of.

In the figure: 1 probe; 2 argon plasma; 3 computer; 4 instruction data acquisition card; 5 analog output port; 6 power amplifier; 7 sampling resistor; 8 differential analog input port.

detailed description

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

In Fig. 1, the probe 1 is a metal wire with an area of 0.15 cm ² placed in the argon plasma 2. The computer 3 instructs the analog output port 5 of the data acquisition card 4 to successively generate AC bias signals whose amplitudes are respectively V=V _j (j=1, 2,...), driven by the power amplifier 6, and then added by the sampling resistor 7. On the probe 1 placed in the plasma 2, at the same time, the computer 3 instructs the differential analog input port 8 of the data acquisition card 4 to collect the voltage signal on the sampling resistor 7 and send it to the computer 3, which converts it into a current signal.

In Fig. 2, P _j =i _1ωj /i _2ωj (j=1,2,...) is the AC bias voltage V=V _j (j=1,2,...) for each amplitude of the computer 3 The ratio of the first harmonic amplitude i _1ωj (j=1,2,...) to the second harmonic amplitude i _2ωj (j=1,2,...) obtained by spectrum analysis of the probe current signal. Each P _j and the corresponding V _j constitute a data point (P _j , V _j ) (j=1, 2, . . . ) indicated by a mark "○" in the figure.

The computer 3 uses the function I ₁ (eV _j /T)/I ₂ (eV _j /T) with T as the variable to _perform the least _square Multiplicative fitting (where e is the electron charge, and I ₁ (eV _j /T) and I ₂ (eV _j /T) are the first and second order imaginary parity Bessel functions of eV _j /T, respectively). When T=2.35eV, the function I ₁ (eV _j /T)/I ₂ (eV _j /T) (solid curve in Fig. 2) satisfies the data point (P _j , V _j ) (j=1,2 ,...) by the least square method fitting, the output T _e =2.35eV is the accurate electron temperature value.

In Fig. 2, n _j (j=1,2,...) is the computer using V _j (j=1,2,...), i _1ωj (j=1,2,...) data and T _e = 2.35eV into the formula Calculated results (where A=0.15 cm ² is the surface area of the probe and M=6.68×10 ⁻²⁶ kg is the mass of argon ions). Each n _j and the corresponding V _j constitute a data point (n _j , V _j ) (j=1, 2, . . . ) indicated in the figure by a mark "Δ".

The computer performs linear fitting on the data points (n _j , V _j ) (j=1,2,...) and extends them to V=0 (dashed straight line in Figure 2), and the value of the fitted straight line at V=0 n ₀ =9.1×10 ⁹ cm ^-3 , output n ₀ =9.1×10 ⁹ cm ^-3 as the accurate ion density value.

Claims (1)

1. a kind of many amplitude AC bias probe plasma diagnostic method based on data collecting card is it is characterised in that include Following steps：

A the simulation output port of the data collecting card of () computer instruction gradually produces amplitude and is respectively V=V_j(j=1,2 ...) AC bias signal, drive through power amplifier, then be added on the probe being placed in plasma through sample resistance, with When, the voltage signal that the difference analogue input port of the data collecting card of computer instruction gathers on sample resistance sends into calculating Machine, and current signal is converted into by computer；

B () computer is to each amplitude AC bias voltage V=V_jProbe current signal under (j=1,2 ...) carries out frequency spectrum and divides Analysis, obtains first harmonic amplitude i_1ωj(j=1,2 ...) and second-harmonic amplitude i_2ωj(j=1,2 ...) and calculate the two Ratio P_j=i_1ωj/i_2ωj(j=1,2 ...)；

C () computer is to data point (P_j,V_j) (j=1,2 ...) in order to T for variable function I₁(eV_j/T)/I₂(eV_j/ T) enter Row least square fitting, wherein e are electron charges, I₁(eV_j/ T) and I₂(eV_j/ T) it is eV respectively_jThe single order of/T and second order are empty Argument Bessel function, output meets the T value T=T of least square fitting_e, T_eIt is accurate electron temperature value；

D () computer utilizes V_j(j=1,2 ...), i_1ωj(j=1,2 ...) and T_eData substitutes into formulaIt is calculated n_j(j=1,2 ...), in formula, A and M is that detecting probe surface amasss respectively And mass of ion, I₀(eV_j/T_e) it is eV_j/T_eZeroth order Bessel function of imaginary argument, then to data point (n_j,V_j) (j=1, 2 ...) carry out Linear Quasi merging continuation to V=0, export value n in V=0 for the fitting a straight line₀, n₀It is accurate ion concentration Value.