JPH0665193B2 - Contamination detection device for probe surface - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a probe measuring device that inserts a probe electrode into plasma to obtain various kinds of information, and is particularly contaminated by ionized substances in plasma. The present invention also relates to a probe surface contamination detection device for detecting the degree of contamination of the probe electrode surface.

(Prior Art) In the field of plasma chemistry, technological developments such as modification of solid surface using plasma, cleaning, and synthesis / decomposition of substances are being carried out. In various devices using such plasma,
In order to control the plasma with high accuracy, it is important to accurately grasp information such as ion distribution, electron density, and electron temperature in the medium, and it is already necessary to insert single or multiple probes into the plasma. A probe measuring method for measuring various parameters is known. However, since the probe installed in the plasma is constantly exposed to the ionized gas, ionization substances, sputtered substances, dissociated substances, etc. adhere to the probe surface and gradually deteriorate the cleanliness of the surface. There was a problem that various measurement results could not be obtained.

Conventionally, in order to solve the above problem, a method for detecting the degree of contamination on the probe surface as described below has been used.

FIG. 5 is a block diagram for checking the surface contamination of the probe electrode, where P ₁ and P ₂ are probe electrodes. In the single probe method, P ₁ is used as a probe electrode and P ₂ is used as a reference electrode, and in the double probe method, P ₁ and P ₂ are inserted into the plasma as the same probe for measurement. The output voltage V _P of the sweep voltage generator 1 is applied to the probe electrode, and the probe current I _P flowing at this time is detected by the current detection circuit 2 and drawn on an XY recorder or an oscilloscope. Typical examples of the probe voltage-probe current characteristics obtained by this method are shown in FIG. 4 in the case of the single probe method and in FIG. 3 in the case of the double probe method. In FIGS. 4 and 3, the curve 1 is
This is a characteristic obtained when the sweep voltage rises and falls when the probe surface is not contaminated. On the other hand, when the probe surface is contaminated, it follows the path of curve 2 when the sweep voltage rises, and the curve 3 when the sweep voltage falls. In other words, when the probe surface is clean, the characteristics are the same when the sweep voltage rises and when the sweep voltage falls, but when the probe surface is contaminated, a hysteresis loop is observed in the probe voltage-probe current characteristic. Therefore, whether or not the probe surface is contaminated is checked from the presence or absence of a hysteresis loop on these probe characteristics.

(Problems to be Solved by the Invention) Generally, in plasma processing such as forming a film of a homogeneous material on the sample surface, it is necessary to accurately monitor the parameters inside the plasma by the probe method. Depending on the type, the deposition rate of impurities adhering to the probe surface is high, so that the conventional probe surface contamination inspection method uses an expensive display device and requires time and effort for its operation. there were. For this reason, efforts are made to remove the deposits by heating the probe, etc., except when measuring the internal parameters. Even in such a case, confirmation of the degree of cleanliness of the probe surface is indispensable when evaluating the measured internal parameters, and in short, the development of a detection device that can quickly directly read the degree of contamination of the probe surface is required. Was there.

(Means for Solving the Problem) The above-mentioned problem is that the detection circuit of the probe current flowing according to the output voltage from the sweep voltage generation circuit, the output amplitude of this detection circuit, is compared with a predetermined threshold value, An amplitude discriminating circuit that generates an output pulse when it matches a threshold value, and an output voltage of the sweep voltage generating circuit, which receives an output pulse of the amplitude discriminating circuit when the voltage rises, and extracts and holds the sweep output voltage. Similarly, a sample-hold circuit, a second sample-hold circuit that receives the output pulse of the amplitude discrimination circuit when the voltage drops, and extracts and holds a sweep output voltage, and a subtraction circuit that obtains the output difference between the first and second sample-hold circuits. Can be solved by a contamination detection device on the probe surface.

That is, according to the present invention, the result detected within the period of one cycle of the sweep voltage generator is indicated on the meter or the numerical display element, and the sweep cycle of the sweep voltage generator is within a range where the probe dynamics characteristic does not occur. Therefore, the detection time can be shortened.

(Operation and Effect of the Invention) In general, when the probe surface is contaminated, it is estimated to be higher than the true value of the internal parameter of plasma, especially the electron temperature. It also makes the determination of the plasma potential and the evaluation of the electron density ambiguous. Therefore, in the measurement of the plasma internal parameter by the probe method, the cleanliness of the probe surface must be guaranteed. In contrast to this, the conventional method uses an oscilloscope for several seconds or longer, and an XY recorder for the inspection. It takes a few minutes or longer, and there is a possibility that the probe surface may be contaminated during the inspection period with the high density reactive plasma. However, according to the detection apparatus of the present invention, when the plasma ion vibration frequency is high, it is easy to set the detection time to 1/1000 second or less,
Surface contamination during the detection period is negligible. Further, in any of the inspection methods, if contamination of the probe surface is detected, it is necessary to remove contaminants and re-inspect, and the effect of the present invention is further enhanced in the case of such re-inspection. It is demonstrated.

(Embodiment) A detailed description will be given below with reference to the block diagram of FIG. 1, which is an embodiment of the present invention.

The sweep voltage generator 1 applies a probe voltage V _P to the probe electrodes P ₁ and P _2, and the probe current I _P flowing at this time is detected by the current detection circuit 2 and sent to the amplitude discrimination circuit 12. In the amplitude discrimination circuit, preset threshold current I _PS and detected current output I
_P is compared, and a pulse is generated at the time when both are equal (I _P = I _PS ). The two sample and hold circuits 14 and 15 are both for holding the output voltage of the sweep voltage generator at a certain time. The output pulse of the amplitude discrimination circuit is sampled and held by the gate circuit 13 when the sweep voltage rises. It becomes the sampling signal of the circuit 14, and becomes the sampling signal of the sample hold circuit 15 when the sweep voltage falls. FIG. 2 shows the relationship between the hysteresis characteristic generated when the probe surface is contaminated and the threshold value of the amplitude discrimination circuit. When the sweep voltage rises and the probe current I _P increases to reach the threshold P _PS , the sample and hold circuit 14 outputs the sweep output at this time.
When V _P1 is held, and when the threshold value is reached again during the fall, the sample hold circuit 15 holds the sweep output V _P2 at this time. The subtraction circuit 16 gives the difference (V _P2 −V _P1 ) between the outputs of these sample and hold circuits. As described above, when the probe surface is contaminated and the hysteresis of the probe characteristic appears, a detection signal (V _P2 −V _P1 ) is generated.

[Brief description of drawings]

FIG. 1 is a blog circuit diagram showing an embodiment of the present invention, and FIG. 2 is a curve diagram showing the relationship between the hysteresis characteristic and the threshold value of the amplitude discrimination circuit when the probe surface is contaminated. Fig. 5 is a probe voltage vs. probe current characteristic curve diagram using a double probe in the probe measurement of Fig. 5, Fig. 4 is a probe voltage vs. probe current characteristic curve diagram using a single probe in the probe measurement of Fig. 5, FIG. 5 is a block circuit diagram for inspecting the surface contamination of the probe electrode by the conventional method. (Explanation of symbols) P ₁ ... probe electrode, P ₂ ... reference electrode or probe electrode, 1 ... sweep voltage generator, 2 ... current detection circuit, 3 ... XY recorder or oscilloscope, 12 ... Amplitude discrimination circuit, 13 …… Gate circuit, 14,15 …… Sample hold circuit, 16 …… Subtraction circuit.

Claims (1)

[Claims] 1. A sweep voltage generation circuit, a detection circuit of a probe current flowing according to this output voltage, and an output amplitude of this detection circuit are compared with a predetermined threshold value, and an output is generated when they match the threshold value. An amplitude discriminating circuit, a first sample-hold circuit that receives the output of the amplitude discriminating circuit and extracts and holds the sweep output voltage when the output voltage of the sweep voltage generating circuit rises, and also the amplitude discriminating circuit when it descends. Of the probe surface, which includes a second sample hold circuit for receiving and outputting the output of the sweep output voltage and a subtraction circuit for obtaining the difference between the outputs of the first and second sample hold circuits.