CN1157103C - Composite probe for plasma diagnosis - Google Patents

Abstract

The present invention relates to a novel composite probe used for high-precision and real-time measurement with spatial resolution for plasma parameters, which belongs to the technical field of plasma diagnosis. The present invention is characterized in that a Langmuir single probe and a difference emission probe are integrated and installed into the same probe tube so as to form the novel composite probe. The present invention realizes the high-precision and real-time measurement of plasma parameters by combining a Langmuir single probe scanning circuit, an automatic tracking circuit of the space electric potential for the difference emission probe, a pulse generating circuit of square waves, a computer interface circuit and a computer software for automatically collecting and analyzing data. The present invention has the characteristics of high measuring precision and high measuring speed, and besides, the present invention can obtain time and spatial distribution information of plasma parameters as well as observe a voltampere (V-I) characteristic curve of the Langmuir single probe in real time. The present invention is widely suitable for the scientific research and the industrial application of plasmas.

Description

Composite Probes for Plasma Diagnostics

technical field

The invention belongs to the technical field of plasma diagnosis. It is a new composite probe diagnostic technology based on the combination of Langmuir single probe and differential emission probe, which involves accurate determination, real-time monitoring and space-time distribution measurement of plasma parameters.

Background technique

At present, the Langmuir (Langmuir) electrostatic probes used for plasma diagnosis include single probes, double probes, emission probes and differential emission probes. The structure of the single probe is shown in Figure 1. The front end (i.e. the probe) is a thin metal wire with a high melting point (or a small metal disc, or a small metal ball), which is covered with an insulating sleeve ( or inner insulated metal sleeve) to connect the probe to an adjustable power source. When in use, place the probe part in the plasma, connect one end of the adjustable power supply to the probe lead, and connect the other end to the plasma chamber wall (the chamber wall should have good contact with the plasma), and the chamber wall and Laboratory ground connection. And connect the potentiometer and ammeter according to the figure. Assuming that the plasma is in a stable state, adjust the adjustable power supply to apply different potentials to the probe, corresponding to each potential of the probe (read by the potentiometer), and read the current flowing through the probe by the ammeter. Taking the measured probe potential as the abscissa and the probe current as the ordinate to plot, the volt-ampere (VI) characteristic curve of the Langmuir single probe is obtained (accompanying drawing 2). By analyzing the volt-ampere characteristics of a single probe, information such as electron temperature, electron density (parallel ion density), space potential, levitation potential, and electron energy distribution function of the measured plasma can be obtained. It is worth pointing out that here, the plasma space potential is generally read from the inflection point of the single-probe volt-ampere characteristic curve, commonly known as the inflection point method. In principle, the inflection point of the single-probe volt-ampere characteristic curve is the point at which the scanning voltage is equal to the plasma space potential, the probe current reaches the electron saturation current, the scanning voltage continues to increase, and the probe current remains unchanged. That is, the single-probe volt-ampere characteristic curve should remain a horizontal straight line after passing the scanning voltage value corresponding to the plasma space potential, as shown by the dotted line in Figure 2, which means that when the abscissa is the plasma space potential, There will be a very obvious inflection point; in fact, due to the edge effect of the probe and other reasons, when the probe potential is higher than the plasma space potential, the probe current still continues to increase slightly, as shown in the solid line in Figure 2 As shown, the position of the inflection point becomes inaccurate, which means that there will be an error in the positioning of the inflection point, so that the plasma space potential obtained by the single-probe inflection point method has a large error. Not only that, because the abscissa value corresponds to the plasma space potential, its ordinate value is the electron saturation current I _e0 ; and the electron saturation current will be used to solve the electron density (and ion density). Therefore, a large error in the plasma space potential will also cause a large error in the electron density (and ion density). It can be seen that it is very important to accurately measure the plasma space potential. For this reason, launch probes and differential launch probes have been invented successively. As shown in Fig. 3, the differential emission probe can directly indicate the plasma space potential at the position of the probe in real time. Unfortunately, emission probes or differential emission probes can only provide information on the space potential of the plasma; however, information on other parameters is often desired. In this case, people have to use two kinds of probes at the same time: differential emission probe (or emission probe) and single probe. The space potential of the plasma is obtained by differential emission probes, and then the position of the inflection point is more accurately found on the volt-ampere characteristic curve of the single probe according to the space potential value, so as to find out the electron saturation current value more accurately, and then obtain Electron density (and ion density). Things have improved, but problems still exist. Please imagine the actual application situation: if two kinds of probes are installed in the same plasma device at the same time, one is that the insertion of the two probes will inevitably increase the disturbance of the plasma; The space potential is not necessarily the value of the position of the single probe, it can only be an approximation, which has errors. If two kinds of probes are used successively at the same position, it will be more troublesome and the error will be larger.

Contents of the invention

The purpose of the present invention is to take into account the advantages of both Langmuir (Langmuir) single probe and differential emission probe, combined with microcomputer data acquisition and analysis technology, to provide a new high-precision, automatic acquisition and analysis of data and Probe system for convenient experimental observation.

The technical solution of the present invention is to integrate Langmuir (Langmuir) single probe and differential emission probe into the same probe tube to form a composite probe, and the distance between the single probe and the differential emission probe is 0.6 mm to 2.0 mm; the composite probe circuit includes a single probe scanning circuit, a differential emission probe space potential tracking circuit, a rectangular wave pulse generating circuit and a computer interface circuit. The single-probe scanning circuit converts the probe current signal relative to the virtual ground into a signal relative to the laboratory ground through an isolated operational amplifier, so that the computer can collect the signal; the rectangular wave pulse generation circuit is used for single-probe offline continuous scanning , so that the oscilloscope can observe the volt-ampere characteristic curve of a single probe. When connected to a microcomputer, the software automatically collects the data of the V-I characteristic curve of the Langmuir single probe and the plasma space potential tracked by the differential emission probe, and then the software uses the plasma provided by the differential emission probe The space potential analyzes and processes the data of the Langmuir single-probe V-I characteristic curve, so as to obtain the plasma space potential, electron density and ion density, suspension potential, electron temperature and electron energy distribution functions, etc.; When the machine is running, the scanning of the V-I characteristic curve is continuously triggered by the rectangular wave pulse generator, so that the V-I characteristic curve can be observed with an oscilloscope, and the plasma space potential can be read from the voltmeter at any time.

The effect and benefit of the present invention are that the detection accuracy and speed of the plasma parameters are significantly improved, and the plasma parameters can be measured in real time; combined with the dynamic sealing mechanism, the spatial distribution of the plasma parameters can be measured; the V-I characteristics can also be directly observed with an oscilloscope The curve is convenient for debugging the plasma generator.

Description of drawings

Accompanying drawing 1 is a schematic circuit diagram of a single probe.

Accompanying drawing 2 is single probe V-I characteristic curve diagram.

Accompanying drawing 3 is a schematic circuit diagram of a differential emission probe.

Accompanying drawing 4 is the principle circuit diagram of compound probe.

In the figure, 1 plasma, 2 quartz tube, 3 tungsten probe, 4 isolation ring, 5 chamber wall, 6 flange, 7 nickel wire, 8 dynamic seal, 9 probe tube, 10 vacuum sealing plug, 11 ammeter, 12 Potentiometer, 13 potentiometer, 14 battery pack, 15 differential emission probe plasma space potential automatic tracking circuit, 16 differential emission probe, 17 rectangular pulse generator, 18 trigger sawtooth wave generator with power amplification, 19 isolation Operational amplifier, 20 dual-channel oscilloscope, 21 computer interface.

Although the compound probe has the functions of Langmuir single probe and differential emission probe, it is inserted into the plasma only as a probe. In this way, it is not only ensured that the information acquired by the two is the same point in the plasma space, but also the interference to the plasma is reduced.

The compound probe has the functions of Langmuir single probe and differential emission probe at the same time, but it is not a simple addition of the two, but an organic combination of the two. The two are not only at the same point in the plasma space, but also can provide the plasma parameter information at the position of the probe at the same time through the control of the computer (the so-called "same time" here is related to the scanning voltage rate and data sampling rate, currently can be done on the order of microseconds). Therefore, using the plasma space potential accurately measured by the differential emission probe at the same position and at the same time to analyze the volt-ampere characteristic curve of a single probe will significantly improve the accuracy and reliability of the obtained plasma parameters.

The composite probe adopts a dynamic seal and is installed on the chamber wall of the plasma device, so the position of the probe in the plasma can be changed conveniently, creating conditions for the measurement of the spatial distribution of the plasma parameters.

In this composite probe circuit, the setting of the oscilloscope interface is convenient for observing the volt-ampere characteristic curve of the single probe at any time during the experiment, which provides an effective and convenient way to monitor the state of the plasma in real time, especially when debugging the plasma generator. it works.

The composite probe software includes the control of the probe system, data collection and data processing. Various parameters of a certain position and a certain moment in the plasma space can be obtained within sub-milliseconds and displayed or printed.

Detailed ways

Embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in FIG. 4 , the compound probe is simultaneously loaded with a single probe 3 and a differential emission probe 16 in a probe tube. The composite probe circuit includes a single probe scanning circuit, a differential emission probe space potential tracking circuit 15 , a rectangular wave pulse generating circuit 17 and a computer interface circuit 21 . The single-probe scanning circuit further includes a trigger-type sawtooth wave generator 18 with power amplification, an isolated operational amplifier 19, probe voltage dividing sampling resistors R1 and R2, and probe current sampling resistor R3. Here, the isolated operational amplifier 19 converts the probe current signal relative to the virtual ground (ie, IxR3 ) into a signal relative to the laboratory ground, so as to facilitate computer acquisition. S1 to S5 are 5 pole double throw switches. When S1 to S5 are placed in the dotted line position, it is offline, and the system is used to observe the V-I characteristic curve of a single probe. At this time, the rectangular wave generator 17 generates a series of rectangular waves, thereby triggering the sawtooth generator 18 to generate a series of sawtooth waves. These sawtooth waves are applied to single probe 3 via R3. Corresponding to each sawtooth wave, its voltage amplitude is divided by R1 and R2 and sent to channel 1 (CH1) of the oscilloscope; while the probe current signal (I) is sampled by sampling resistor R3 (IxR3), and sent to To channel 2 (CH2) of the oscilloscope. In this way, the oscilloscope displays the V-I characteristic curve of a single probe in X-Y mode. Corresponding to a series of sawtooth waves, the V-I characteristic curve of a single probe can be repeatedly displayed, making it easy to observe. At this time, the plasma space potential can be read from the voltmeter (Vp) in the differential emission probe circuit 15 at any time. When S1 to S5 are placed at the positions of the solid lines, the system is connected to the computer, which is the online state, and the computer controls the collection of the plasma space potential and the V-I characteristic curve of the single probe. The steps are as follows: first, the software controls to output a rectangular wave on the D/A output line to trigger the sawtooth wave generator 18 to output a sawtooth wave to add to the single probe 3 . During this sawtooth wave period, the software collects the probe voltage (V) and probe current (I) signals cyclically through the data lines A/D(1) and A/D(2), that is, to obtain the V-I characteristic curve data of a single probe ; After the sawtooth wave, read the plasma space potential Vp through the data line A/D (3). Then, the computer uses the plasma space potential Vp obtained from the differential emission probe to process the V-I characteristic curve of the single probe to obtain a series of plasma parameters, namely, the plasma space potential, electron temperature, electron density, and ion density , Levitation potential and electron energy distribution function, etc.

The composite probe is installed on the chamber wall of the plasma device with a dynamic seal, so the position of the probe in the plasma can be changed conveniently, creating conditions for the measurement of the spatial distribution of plasma parameters, and the spatial resolution can reach millimeters class. When the composite probe is at a certain position in the plasma space, the above-mentioned plasma parameters can be obtained at different times, and the time resolution depends on the A/D conversion speed of the computer interface 21. The A/D conversion time is set to 1 microsecond, and the acquisition With 100 pairs of V-I data, the time resolution can reach 0.25 milliseconds.

Claims (1)

1. combined probe that is used for plasma diagnostic, it is characterized in that: constitute combined probe with single probe and integrated being installed in the same probe tube of difference emitting probe, cooperate the combined probe circuit, the combined probe circuit comprises that single probe scanning circuit, difference emitting probe space potential tracking circuit, square wave pulse generating circuit and computer interface circuit and computer software measure the various parameters of plasma in real time.

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