JPH01296598A - Potential sensing device for space in probe characteristic - Google Patents

Abstract

PURPOSE:To enhance the accuracy of a sensing device and quicken the operation by sweeping the probe voltage from positive ion current saturation region toward the electron current saturation region, and determining the bent point in the extent from the electron current repulsive region till the electron current saturation region about the obtained probe characteristic curve from secondary differential signals of a curve after the current makes zero intersection. CONSTITUTION:A probe electrode P is inserted in plasma to sense the probe current Ip flowing in compliance with a signal Vp in a sweep voltage generator circuit 1 using a current sensor circuit 2. This sensing of probe current Ip yields the probe characteristic, and the current detection signal is subjected to second order differentiation by a second order differentiation circuit 3. In this second order differentiation signal, particularly, the point of intersection with the zero potential in the boundary of the electron current saturation region from the electron current repulsive region is the space potential Vs, and No.1 zero point is sensed by No.1 zero sensor circuit 4 while floating potential Vf is sensed by No.2 zero sensor circuit 5 so as to specify the regions besides the positive ion current saturation region, followed by processing by a gate circuit 6 and a sample hold circuit 7.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a device for detecting the space potential of plasma.
In particular, the present invention relates to a device that detects space potential at high speed and with high reliability by inserting a probe into plasma.

(Prior art and problems) Figure 3 shows a typical example of probe voltage (V,) current (l,) characteristics, but determining the space potential directly from the same characteristics will lead to errors, so it is usually As shown in FIG. 4, a method has been adopted in which the same characteristic is rewritten using a single logarithmic current, and the intersection of the extended line of the electron current repulsion region and the extended line of the electron current saturation region is set as the space potential. However, this method requires measurement time and human judgment, its applicability is limited to low-temperature plasma, the detection temperature range is narrow, and there are also problems in its application to reactive plasma, which tends to deposit impurities on the probe surface. was there.

(Problem to be solved by the invention) In general, space potential is important in knowing the state of plasma, but it is also an essential physical quantity when calculating electron density. This is the standard value when calculating. Obtaining this from a graph according to the conventional method not only has a narrow scope of application, but also cannot improve accuracy.

An object of the present invention is to provide an apparatus capable of detecting space potential at high speed and with high precision for various plasmas ranging from low to high temperatures and reactive plasmas with a wide range of industrial applications.

(Means to Solve the Problem) The above-mentioned problem can be solved by accurately detecting, using an electronic circuit, a curved point that occurs at the boundary between the electron current repulsion region and the electron current saturation region on the probe characteristic curve. . Specifically, it includes a probe current detection circuit, a second-order differential circuit for obtaining a second-order differential signal of the detected probe current signal, and a first differential circuit for detecting the point at which this second-order differential signal crosses zero potential. a zero point detection circuit, a second zero point detection circuit for detecting the point at which the detected probe current signal crosses zero potential, and a sample sensor for extracting the probe voltage from the output signals of both of the zero point detection circuits. This problem is solved by the space potential detection device of the present invention including a halt circuit.

(Operation and Effects of the Invention) In the present invention, the probe voltage is swept from the positive ion current saturation region to the electron current saturation region, and the obtained probe characteristic curve is particularly focused from the electron current repulsion region to the electron current saturation region. The bending point that occurs during the probe current is determined from the second-order differential signal of the above characteristic curve after the probe current crosses the zero point.The detection method itself is highly reliable, highly accurate, fast, and widely applicable. We have developed a plasma space potential detection device that has applicability.

(Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the block diagram in FIG. 1 and the operation waveforms of each part in FIG. 2.

A probe electrode P is inserted into the plasma, and a probe current 1p flowing in response to a signal Vp from a sweep voltage generation circuit 1 is detected by a current detection circuit 2.

As a result, the probe characteristics shown in FIG. 2a) are obtained.

This current detection signal is second-order differentiated by the second-order differentiation circuit 3, resulting in the second-order differentiation signal shown in b) of the same figure.In this signal, especially at the boundary between the electron current repulsion region and the electron current saturation region, The point where the zero potential intersects is the space potential Vs, and the first zero point detection circuit 4 detects this point Vs as shown in FIG. However, since noise usually exists, the second-order differential signal in the positive ion current saturation region crosses the zero potential. Therefore, the second zero point detection circuit 5
As shown in d) of the same figure, the floating potential Vf is detected using the method, and a region other than the positive ion current saturation region is specified. As a result, the gate circuit 6 generates the output shown in e) of the same figure, and at the time of the rise of the output, the sample-and-hold circuit 7 generates the output of the sweep voltage generating circuit, which is the manual input, as shown in f) of the same figure. Extract and hold. From the above, the sample-and-hold circuit 7 outputs the following information every time the probe voltage is swept:
An output Vs representing the spatial potential is obtained.

As is clear from the above explanation, the probe voltage (total voltage) when the output signal of the second zero point detection circuit is obtained after the output signal of the first zero point detection circuit is obtained can be calculated. In this case, that value becomes the space potential. Therefore, it goes without saying that those skilled in the art can easily conceive of various other types of circuits in addition to the circuit shown in FIG.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a detection device for space potential in probe characteristics based on the present invention, Fig. 2 a) to f) are operational waveform diagrams of each part in the above block diagram, and Figs. 3 and 4 are , graphs showing the probe characteristics and its logarithmic characteristics, respectively. (Explanation of symbols) P... Probe electrode. 1...Sweep voltage generation circuit. 2...Current detection circuit. 3...Second order differential circuit. 4. First zero point detection circuit. 5...Second zero point detection circuit. 6...Gate circuit. 7...Sample/halt circuit.

Claims (1)

[Claims] a probe current detection circuit; a second-order differential circuit for obtaining a second-order differential signal of the detected probe current signal; a first zero point detection circuit for detecting a point at which this second-order differential signal crosses zero potential; A space equipped with a second zero point detection circuit for detecting the point at which the detected probe current signal crosses zero potential, and a sample and hold circuit for extracting the probe voltage from the output signals of both of the zero point detection circuits. Potential detection device.