JPS63210751A - Glow discharge emission spectral analyzer - Google Patents

Abstract

PURPOSE:To stabilize an analysis by providing a feedback system which detects the internal resistance of a glow discharge tube using a sample as a cathode and maintains the internal resistance of the glow discharge tube at approximately a constant level and maintaining a sputtering rate automatically at a constant value. CONSTITUTION:Gaseous argon is admitted through an inflow port 5 into the glow discharge tube G and is discharged from outflow ports 6 and 7. A flow rate control valve V is otherwise inserted into, for example, a gaseous argon supply pipe and the voltage drop generated across a resistor (r) connected in series to the discharge tube G is detected by a current detector D to control a valve driving device P via a comparator C, thereby opening and closing the valve V. The internal resistance of the discharge tube G increases and the tube current increases when the sputtering rate of the sample is low. The valve V is then opened to increase the gaseous argon pressure, by which the internal resistance is decreased and the sputtering rate is maintained constant. The stable analysis is thereby executed.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a glow discharge device used in glow discharge emission spectroscopy or as a constant rate sputtering light source in a mass spectrometer.

Conventional technology A glow discharge tube used in luminescence analysis has a structure as shown in FIG. In this figure, 1 is a cylindrical anode, 2 is a sample, and the left end opening of the anode is closed with a quartz window 3 so that light can be extracted. The right end of the anode is covered with a sample 2 via an insulator 4, and argon gas is introduced into the anode through a gas inlet 5 and sucked and discharged through an outlet 6 by an exhaust pump. In the anode, the end face of the right tubular part 1a is close to the surface of the sample 2, and a narrow gap g of about 0.2 mm is formed between it and the sample. The second gas outflow lower is connected to a vacuum pump.

With this structure, the argon gas pressure inside the cylindrical anode is 1
The pressure is maintained at about 0 to 10 Torr, and a large pressure gradient is formed in the gap g, so that the outside of the tubular portion 1a is in a high vacuum state. Since the gap g is narrow in this state, there is almost no chance for the charged particles to collide with other gas molecules in this part, and therefore no air discharge occurs, and a glow discharge region is formed in the inner space of the tubular part 1a. Ru. The surface of sample 2 is bombarded with argon ions due to glow discharge, and constituent atoms are ejected (cathode sputtering). The ejected atoms are excited within the plasma and emit light. Qualitative and quantitative analysis of the elements is performed by extracting this light through the window 3 and performing spectroscopy.

C.9 Problems to be Solved by the Invention In the above-mentioned emission spectroscopic analysis using a glow discharge tube, the sputtering rate (volatilization rate) of the element to be measured differs depending on the type of matrix element constituting the sample. There's a problem. When the sputtering rate is different, even if the concentration of the target element in the sample is the same a, the vapor concentration of the target element in the glow discharge region will be different, and the emission intensity of that element will be different. In other words, even if the concentration of the target element in the sample is the same, if the matrix element is different, the luminescence intensity will be different, so it is not possible to perform quantitative determination using a single calibration curve for various samples. In the case of homogeneous samples, it is possible to create a calibration curve using samples of the same type with different concentrations of the target element, but it is also possible to create a calibration curve using samples of the same type with different concentrations of the target element. When analyzing a sample in the depth direction while etching the surface, the types and concentrations of coexisting elements change in the depth direction, making it impossible to obtain a calibration curve that can be used commonly for all samples. Quantitative analysis is almost impossible with discharge emission spectrometry. Glow discharge emission spectroscopy is characterized by the ability to proceed in the depth direction from the surface while removing the surface of the sample through the action of cathode sputtering, making quantitative analysis difficult when analyzing the surface layer. This is an important drawback.

The present invention uses glow discharge optical emission spectrometry to solve the problem that the sputtering rate of a target element changes depending on the coexisting elements.

21 Means for Solving Problems A means was provided to detect the internal resistance of a glow discharge tube whose cathode is a sample and to control the electric power injected into the discharge tube to keep it constant. To keep the power injected into the discharge tube constant, it is necessary to adjust the gas pressure inside the glow discharge tube, connect a variable impedance circuit in series with the glow discharge tube, or intermittent the discharge tube current and change its intermittent ratio. Various means can be used.

The tube current of a glow discharge tube is the sum of the argon ions and the sample element ions sputtered from the sample, and since the argon ions are considered to be constant, if the sputtering rate of the sample differs, The amount of current changes depending on the sample element. This change is observed as a change in the internal resistance of the glow discharge tube. On the other hand, to perform ternary sputtering of a sample, either increase the number of ion bombardments per hour on the sample surface, that is, increase the tube current, or increase the energy of the bombarded ions to increase the probability of ejecting sample atoms, that is, increase the tube voltage. The basic operation is to increase the sputtering rate, and the sputtering rate can be increased by increasing the product of voltage and current supplied to the discharge tube. On the other hand, for samples with a low sputtering rate, the internal resistance of the glow discharge tube increases, and under a constant voltage power supply, the current decreases and the absorbed energy of the discharge tube decreases, so a feedback system is required to keep the absorbed energy of the discharge tube constant. By configuring this, the sputtering rate can be kept constant regardless of the sample. Since the internal resistance decreases when the sputtering rate is increased, it is sufficient to configure a feedback system that keeps the internal resistance constant.

Embodiment FIG. 1 shows a first embodiment of the present invention. G is a glow discharge tube, U is a constant voltage power source for lighting the glow lamp G, and M is a spectrometer. The structure of the glow discharge tube G is the same as the one shown in FIG. The right end of the anode is covered by the sample 2 with an insulator 4 in between. Argon gas is supplied from the inlet 5 and suctioned and discharged from the outlet 6 by a pump, and is also suctioned and discharged from the outflow lower outside the anode tubular portion 1a by a pump.

The feature of this embodiment is that there is a flow control valve V in the argon gas supply pipe.
is inserted, and this is controlled by a tube current detector. r is a current detection resistor connected in series with the glow discharge tube G, and a voltage drop proportional to the tube current occurring across this resistor r is detected by a tube current detector, which is a voltmeter. The output of the detector is compared with a reference value by a comparator C, and the valve driving device P is controlled by the output of the comparator C. If the sputtering rate of the sample is low, the internal resistance of the glow discharge tube will increase, and in this example, since it is lit with a constant voltage power supply, the tube current will decrease. Then, the valve V opens and the argon gas pressure inside the glow discharge tube G is increased, thereby reducing the internal resistance. Therefore, the tube current is maintained at its original level, and the power absorbed by the glow discharge tube is also maintained at its original level.

FIG. 2 shows a second embodiment of the invention. Components corresponding to those in the example of FIG. 1 are given the same reference numerals, and their explanation will be omitted. Points that are different from the embodiment shown in FIG. 1 will be explained. The lighting power supply U is a constant voltage power supply. In this embodiment, the gas pressure inside the glow discharge tube G is kept constant. discharge tube G
A variable resistor R is connected in series with the tube current, and the tube current is detected by the current detector, and the detection signal is sent to the comparator C.
is compared with the reference level at C, and the variable resistor R is
is operated to keep the tube current constant. In this case, when the tube current becomes lower than the standard depending on the sample, the resistance value of the variable resistor R is decreased, so the tube voltage becomes high by the decrease in voltage drop in R, and the tube current is kept constant. , the power supplied to the tube will increase, but as the tube voltage increases, the sputtering rate will increase and the internal resistance of the tube will decrease, so in the actual dynamic equilibrium state, the power supplied to the tube will be approximately at the reference value. In other words, when changing the sample, if the internal resistance of the tube is ΔR larger than the standard, then instead of reducing the variable resistance R by ΔR, if you reduce it by a smaller value Δr, the internal resistance of the tube will be kept at ΔR. By increasing the sputtering rate of , the internal resistance of the tube decreases by Δρ, and in the parallel state, Δr=ΔR−Δρ.

FIG. 3 shows a third embodiment of the invention. In this embodiment, the lighting power supply Q for the glow lamp G is a constant power pulse generator,
A pulse number control circuit N per unit time is controlled by the output of a glow lamp lighting current detector, and the number of supplied pulses is increased when the tube current decreases.

In emission analysis using a glow discharge as a light source, the sputtering rate of the sample differs depending on the matrix element of the sample, but according to the present invention, the sputtering rate is automatically kept constant, so a single calibration curve Element quantification is now possible regardless of the element, and since the sputtering rate is kept constant, only the fluctuations in the spectrometer and photometry system need to be checked, so equipment calibration can be performed using a constant light source for the spectrometer and photometry system. I should go (
, stable analysis becomes possible. In addition, when analyzing the sample surface in the depth direction, the sputtering rate is always kept constant even if the main elements of the sample change in the depth direction, so the time axis of the analysis record corresponds to the depth from the sample surface. This makes it much easier to examine the analysis records.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of the first embodiment of the present invention, Fig. 2 is a block diagram of the second embodiment, Fig. 3 is a block diagram of the third embodiment, and Fig. 4 is a glow analyzer for luminescence analysis. FIG. 3 is a longitudinal side view of the discharge tube. G... Glow discharge tube, U... Constant voltage power supply, D...
Current detector, ■...Flow control valve, P...Valve drive device, C...Comparator, M...Spectrometer.

Claims (6)

[Claims] (1) A glow discharge optical emission spectrometer characterized by being provided with a feedback system that detects the internal resistance of a glow discharge tube whose cathode is a sample and keeps the internal resistance of the glow discharge tube substantially constant. (2) The glow discharge tube emission spectrometer according to claim 1, wherein the internal resistance detection means of the glow discharge tube is means for detecting the tube current of the tube. (3) The glow discharge optical emission spectrometer according to claim 1, wherein the internal resistance detection means of the glow discharge tube is a tube voltage detection means of the tube. (4) The glow discharge optical emission spectrometer according to claim 1, wherein the control object of the feedback system that keeps the internal resistance of the glow discharge tube substantially constant is gas pressure regulating means within the discharge tube. (5) The glow discharge optical emission spectrometer according to claim 1, wherein the controlled object of the feedback system that keeps the internal resistance of the glow discharge tube substantially constant is a variable resistor connected in series with the glow discharge tube. (6) The glow discharge optical emission spectrometer according to claim 1, wherein the control object of the feedback system that keeps the internal resistance of the glow discharge tube substantially constant is an output power adjustment means of a power source of the glow discharge tube.