JPH0122577B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring Auger electron spectroscopy.

A typical method for measuring conventional Augier electron spectroscopy spectra is to use a cylindrical mirror energy analyzer (CMA).
Written as CMA. ) by superimposing a DC sweep voltage and a minute amplitude modulation voltage, and phase-detecting only the frequency components synchronized with the modulation voltage among the secondary electrons (including Auger electrons) emitted from the sample using a lock-in amplifier. Therefore, a method of detecting Auger electron spectroscopy is adopted.

A block diagram of this conventional measuring method is shown in FIG. In FIG. 1, reference numeral 1 denotes a vacuum container which is evacuated by an ion pump 2. In FIG. The sample 4 is irradiated with primary electrons from the primary electron irradiation system 3, and the sample 4 is
The secondary electrons including Augier electrons emitted from
The energy is separated by the CMA 5, amplified by the secondary electron multiplier 6, and detected by the lock-in amplifier 7.

The output of the lock-in amplifier 7 is sent to the X-Y recorder 8.
recorded in A DC sweep voltage 9 and a minute modulation voltage 10 are applied to the CMA 5 via a transformer 11. The lock-in amplifier 7 is synchronously matched to the frequency and phase of the minute modulation voltage 10 applied to the CMA 5, and reduces noise in the input signal by amplifying only the component having the frequency and phase of the input signal. are doing.

In this measurement method, since a modulation voltage of 10 is applied to the CMA 5, all electrons passing through the CMA 5 are modulated. Most of the electrons passing through CMA 5 are secondary electrons that are emitted from sample 4 and fly directly to it, but low-energy electrons generated from sources other than sample 4, called stray electrons, also pass through CMA 5. These stray electrons include stray electrons generated from the ion pump 2,
Secondary electrons generated from the mesh 12 of the CMA opening, secondary electrons generated from the inner wall of the CMA 5, etc. are included. In the CMA 5, not only secondary electrons emitted from the sample 4 and giving a true signal but also stray electrons are simultaneously modulated. This phenomenon causes noise when detecting the Augier electron spectra, and sometimes makes it difficult to detect the Augier electron spectra in the low energy region. In particular, when studying the surfaces of elements such as metal and semiconductor devices, it is often important to measure Auger electron spectra in the low energy region. For example, carbon, oxygen, nitrogen, potassium, and other contaminant elements are problematic when investigating the state of contamination on the surface of a device, but the Auger electron spectra of most of these elements exist in the range of several 100 EV or less. Furthermore, the Auger electron spectroscopy spectrum in the low energy region is important for understanding the chemical bonding state on the surface of the device. For example, low-energy Augier electrons in silicon
Although it is 92ev, when it is oxidized, it emits Auger electrons of 76ev, which are unique to silicon oxide. In this way, in order to obtain accurate Auger electron spectroscopy in the low energy region, it is necessary to remove stray electrons from the detection system, but conventional measurement methods have the disadvantage that stray electrons cannot be removed. have

In addition, particularly in evaluating the surface of a semiconductor device, it has become important to measure the Auger electron spectroscopy spectrum in a minute region of the surface. In current semiconductor integrated circuits, it is now possible to form patterns with line widths of 1 μm or less, and unipolar FETs (Field Effect Transistors) have gate lengths of 1 μm or less to improve high frequency characteristics. Types with gate electrodes have also been developed. Measuring and evaluating such minute regions using Auger electron spectroscopy will become increasingly important in the future. In the conventional measurement method of applying a minute modulation voltage 10 to the CMA 5, it is necessary to reduce the diameter of the primary electron beam irradiated onto the sample 4 in order to detect the Auger electron spectra in a minute region.

Generally, in order to detect the Auger electron spectrometer with good sensitivity, the amount of current of the primary electron beam incident on the sample 6 needs to be about 10 ^-5 to ^{10 -7} A. In this case, the minimum beam diameter that the primary electron beam can reach is approximately
It is approximately 1 μmφ. The diameter of the primary electron beam irradiated onto the sample 4 is roughly determined by the amount of sample irradiation current, but the diameter of the primary electron beam is set to 1 μm.
In order to make it less than mφ, it is necessary to reduce the amount of current of primary electrons irradiated to the sample.

When this happens, it is difficult to obtain a good Auger electron spectroscopy spectrum, and the signal is often buried in noise, resulting in a situation where no information can be detected. Furthermore, even if the diameter of the primary electron beam could be made sufficiently thin,
It is necessary to limit fluctuations in the irradiation position of the primary electron beam. Even if a primary electron beam is irradiated onto a microscopic region to be measured, there is a risk that the irradiation position will fluctuate over time, and in this case, accurate Auger electron spectroscopy spectrum information cannot be obtained. In this way, in the conventional measurement method of applying a minute modulation voltage 10 to the CMA 5, the factor that limits the measurement of a minute area of the sample 4 is the primary electron beam irradiation system 3, and the diameter of the primary electron beam is reduced. However, it also has the disadvantage of requiring a high degree of technical precision in order to reduce fluctuations in the irradiation position.

Furthermore, as seen in Japanese Patent Application Laid-Open No. 50-54380, there is a method in which a variable delay voltage is applied to the sample, that is, a modulation voltage is superimposed on a saw-toothed sweep voltage to measure the total current flowing through the sample. However, although this method has the advantage of improved sensitivity and miniaturization of the device, it is not possible to measure different minute regions in the same sample independently and simultaneously.

The purpose of the present invention is to avoid the detection of stray electrons that cause noise in the Auger electron spectra in the above-mentioned low energy region, and to eliminate the need to sufficiently reduce the diameter of the primary electron beam incident on the sample. The object of the present invention is to provide a measurement method that can accurately analyze different regions in a sample at the same time.

According to the present invention, the modulation voltage is the same for each region of a plurality of regions of the sample, and Auger electron spectroscopy spectrum analysis is performed by applying a DC bias voltage of a different voltage to each region superimposed on the modulation voltage. multiplexing is possible.

FIG. 2 shows a block diagram for explaining the principle of the present invention. Only a DC sweep voltage 9 is applied to the CMA 5, and only a minute current voltage 11 is applied to the sample 4. However, the ground on the CMA5 side and the ground on the sample 4 side are the same. If the sample 4 is a conductor, a high resistance 13 is inserted between the sample 4 and the ground to prevent the modulated voltage 10 from shorting with the ground. By doing this,
When the primary electron beam is incident on the sample 4 from the irradiation system 3, only the secondary electrons (including Auger electrons) emitted from the sample are modulated by the alternating current voltage 10. At this time, stray electrons generated from sources other than sample 4 are not modulated. The electrons passing through the CMA 5 are secondary electrons from the sample 4 that have been modulated and stray electrons that have not been modulated. By detecting and amplifying only the signal, only the modulated secondary electron signal from the sample 4 is detected. At this time, since no signal due to stray electrons is detected, the Augier electron spectroscopic spectrum in the low energy region has very little noise. Furthermore, if the AC voltage 10 is applied only to a minute region to be measured, only the secondary electrons emitted from that region will be modulated. Therefore, sample 4
Even if the diameter of the primary electron beam incident on the secondary electron beam is greater than or equal to the microscopic region, the secondary electrons emitted from outside the microscopic region are not detected by the lock-in amplifier 7 because they are not modulated. In other words, this corresponds to making the diameter of the primary electron beam incident on the sample 4 equal to the microscopic area that is effectively being measured. In this way, the diameter of the primary electron beam can be effectively reduced without reducing the amount of current in the primary electron beam.

If the frequency of the AC voltage applied to a minute area in the sample is the same, and the value of the DC voltage applied superimposed on this AC voltage is different, the emitted secondary electrons will have a higher kinetic energy by the amount of this DC voltage. Because of this, it is possible to separate and detect secondary electron signals from each region.

Examples will be described below with reference to the drawings.
FIG. 3 is a diagram showing an embodiment of the present invention, which is a method of applying mutually different DC biases to a plurality of mutually insulated minute regions. Micro areas 31, 32,
33 are insulated from each other. Micro area 31, 3
2 and 33 as DC bias current, respectively.
Volts, V volts, and 2V volts are applied by the DC power supply 34. By doing this, the micro area 3
Secondary electrons emitted from 2 (including Augier electrons)
is supplied with kinetic energy by V volts more. Similarly, the secondary electrons emitted from the minute region 33 are supplied with an extra kinetic energy of 2 V volts. However, the DC bias voltage is selected so that the Auger electron spectra detected from each micro region do not overlap with each other. The Auger electron spectroscopic spectrum obtained from the microscopic region 32 is detected on the higher energy side by V volts compared to the case where no DC bias is applied, and similarly the Augier electron spectroscopic spectrum obtained from the microscopic region 33 is detected on the high energy side by 2 V volts. Detected. As described above, according to the method shown in FIG. It is possible to detect the Auger electron spectra from the regions 31, 32, and 33 independently of each other.

As described above, the present invention reduces noise signals caused by stray voltages by applying an alternating current voltage to a sample, and generates an Auger electron spectroscopy spectrum of only a minute region to be measured without considering the diameter of the primary electron beam irradiating the sample. It has various advantages, such as being able to detect and multiplexing Auger electron spectroscopic analysis.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a conventional method for measuring an Augier electron spectroscopic spectrum, and FIG. 2 is a schematic diagram showing a measuring method according to the present invention. Figures 1 and 2
In the figure, 1 is a vacuum vessel, 2 is an ion pump, and 3
is the primary electron irradiation system, 4 is the sample, 5 is the CMA, 6 is the secondary electron multiplier, 7 is the lock-in amplifier, and 8 is the X
-Y recorder, 9 is a DC sweep voltage, 10 is a minute modulation voltage, 11 is a transformer, 12 is a mesh of the CMA opening, and 13 is a resistor. FIG. 3 is a diagram showing an embodiment of a method for multiplexing Auger electron spectroscopy by applying a DC bias to each mutually insulated micro region, and 31, 32, and 33 are micro regions. , 34 is a DC bias voltage, 35 is a modulation voltage, 36 is a transformer, and 37 is a lock-in amplifier.

Claims (1)

[Claims] 1 In the Auger electron spectroscopy method, in which a sample to be measured is irradiated with primary electrons and the secondary electrons emitted from the sample are detected by energy analysis, a The same modulation voltage is applied, and DC bias voltages of different voltages are superimposed on the modulation voltage and applied to each of the plurality of regions, and excess energy is generated by the amount of the DC bias voltage generated from the plurality of regions. and detecting secondary electrons synchronized with the modulated voltage frequency using a single energy analyzer.