JP2011034741A - Gas analyzer, and inspection device using the same - Google Patents

Abstract

An object of the present invention is to prevent shape observation and reduction in observation resolution of dimensional accuracy due to contamination inside an inspection apparatus and to suppress contamination of an observation target.
As a means for monitoring contamination inside an inspection apparatus, a contaminated component is adsorbed on a solid surface, and the adsorbed contaminated component is heated and gasified and detected by a gas analyzer.
The inspection equipment is cleaned according to the amount of contamination monitored. Inspection equipment cleaning provides a means for generating active species of oxygen in the sample observation chamber, reduces contamination remaining in the observation chamber, and enables shape observation and dimension measurement with less degradation in observation resolution due to contamination effects And preventing contamination of the sample to be observed.
[Selection] Figure 1

Description

  The present invention relates to a technique for analyzing a gas in an inspection apparatus that inspects a semiconductor device or the like.

  When observation is performed using a scanning electron microscope, it is well known that contaminants are deposited on a portion irradiated with an electron beam, that is, an observation portion. It is considered that organic contaminants or the like existing on the sample or in the atmosphere of the apparatus cause the sample contaminant deposition. It has been reported that such organic molecules are solidified by receiving electron beam energy and are deposited on a sample. Such a sample contamination phenomenon reduces the accuracy of electron microscope shape observation.

Conventional techniques relating to the prevention of sample contaminant deposition in such a scanning electron microscope include those disclosed in Patent Document 1 and Patent Document 2.
In Patent Document 1, a cooling plate is attached to an objective lens through a heat insulator and a spring, and gas emitted from the lower surface of the objective lens and the sample itself is adsorbed and trapped by the cooling plate. The method of preventing sample contamination by cooling is the most common method at present, and traps the gas in the vicinity of the sample, that is, prevents the sample contamination by reducing the number of gas molecules present in the vicinity of the sample. It is.

  Further, in Patent Document 2, hydrocarbon gas generated from the sample by electron beam irradiation accumulates in the lens body and causes contamination of the sample. An isolation membrane is provided to prevent sample contamination.

  As a related invention, Patent Document 3 discloses a method for removing contaminants (such as hydrocarbon molecules) in an electron beam observation apparatus. Further, Patent Document 4 discloses a technique for monitoring organic molecules in a sample observation chamber using a mass spectrometer in order to efficiently clean the sample observation chamber.

JP-A-5-82062 Japanese Patent Laid-Open No. 10-64467 JP 2001-325912 A Japanese Patent Laid-Open No. 10-12173

An electron beam inspection device that scans an electron beam over an observation sample and measures and observes the pattern shape or dimensions formed on the sample by secondary electrons or reflected electrons generated from the observed sample Its role is becoming more important as it becomes more advanced.
When a contaminant is deposited on the sample surface, the observed sample surface does not represent a true shape, but represents a surface shape after the contaminant deposition. Changing dimensions and shapes during observation is a fatal problem. In addition, in an electron beam inspection apparatus that measures semiconductor pattern dimensions, not only the measurement error problem, but also the problem that the contact hole diameter becomes smaller due to the accumulation of contaminants during observation, and in some cases the contact hole is blocked. In addition, an increase in the wiring width causes a short circuit of the element, which may cause a product defect.
In recent years, semiconductors have been miniaturized, and submicron-order patterns and contact hole dimension measurement and shape observation have been performed. In many cases, the magnification is observed at a high magnification of tens of thousands to several tens of thousands of times. When observed at a high magnification, the amount of contaminants deposited may be about 10% of the pattern, for example, several tens of nanometers for a 0.5 μm pattern.

  If semiconductors are further miniaturized in the future, higher dimensional measurement accuracy will be required, and the amount of contaminants deposited must be kept below several nanometers. As semiconductor devices become more sophisticated and sophisticated, there is a concern that the adsorption of trace amounts of contaminants from the gas phase when the sample observation room is introduced will adversely affect the electrical performance and process yield of the semiconductor devices to be observed. Yes.

  In order to solve the above problems, more strict trace contamination management is required. Contamination in the sample observation room and other vacuum vessels of the electron beam inspection equipment must be reduced to the utmost limit. In that case, high molecular weight organic molecules are particularly problematic. Due to its high molecular weight, it is difficult to exhaust with a vacuum pump, and it remains in the electron beam inspection apparatus until the end. Further, the high molecular weight organic substance is easily adsorbed on the sample surface, and even a very small amount adsorbs on the sample surface and causes surface contamination.

  For strict trace contamination control, contamination detection and monitoring means are important. Patent Document 4 describes a monitoring means based on mass analysis of a simple gas phase component. However, there is a problem in that the sensitivity is insufficient to detect a trace amount of high molecular weight organic matter.

  An object of the present invention is to provide a highly sensitive analysis technique for a small amount of a high molecular weight organic component.

  In order to solve the above-described problems, in the inspection apparatus of the present invention, an adsorbent is prepared in advance in a sample observation room that requires trace contamination control, and the components adsorbed on the adsorbent are heated and desorbed. A detection mechanism is provided.

  According to the present invention, it is possible to detect a very small amount of high molecular weight organic matter in an observation room with high sensitivity.

It is a block diagram of the electron beam inspection apparatus concerning the Example of this invention. It is a contamination monitor process flow concerning the Example of this invention. It is a mass spectrum of the detected contamination component concerning Example 1 of this invention. It is a mass spectrum of the contamination component of a sample observation room immediately after performing decontamination by the oxygen active species by Example 1 of this invention. It is a block diagram of the sample observation room concerning Example 2 of this invention. It is a block diagram of the sample observation room which uses a folding wire in Example 2 of this invention. It is a mass spectrum of the contamination component detected by the system of Example 2 of the present invention. It is a block diagram of the sample observation room concerning Example 3 of this invention. It is a mass spectrum of the contamination component detected by the system of Example 2 of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an electron beam inspection apparatus according to a first embodiment related to the present invention. In FIG. 1, an electron gun chamber 1, a condenser lens chamber 2, and a sample observation chamber 3 are arranged in the vertical direction, and an intermediate chamber 4 is provided between the condenser lens chamber 2 and the sample observation chamber 3. A preliminary exhaust chamber 5 is disposed adjacent to the sample observation chamber 3, and a sample exchange chamber 6 is provided above the preliminary exhaust chamber 5.
The electron gun chamber 1 has an electron gun 7, an extraction electrode 8, an acceleration electrode 9, and a fixed aperture 10, the condenser lens chamber 2 has a condenser lens 11, and the intermediate chamber 4 has a deflection coil 12, an objective lens 13, and an objective lens. Fixed diaphragms 14 are provided respectively. A sample holder 15 is provided in the sample observation chamber 3, and a sample 16 is installed on the sample holder 15. A gate valve 17 is installed between the sample observation chamber 3 and the preliminary exhaust chamber 5, and the sample holder moves between the sample observation chamber 3 and the preliminary exhaust chamber 5 by opening and closing the gate valve 17. A gate valve 18 is installed between the preliminary exhaust chamber 5 and the sample exchange chamber 6, and the sample holder moves between the sample exchange chamber 6 and the preliminary exhaust chamber 5 by opening and closing the gate valve 18.
A vacuum pump 19, 20 is connected to the electron gun chamber 1, and a vacuum pump 21 is connected to the condenser lens chamber 2, and the vacuum pumps 19, 20, 21 are used to obtain a stable electron beam from the electron source 7. Due to the differential evacuation, the electron gun chamber 1 and the condenser lens chamber 2 are decompressed to a pressure of 10 ⁻⁷ Pa or less.

A vacuum pump 22 is connected to the sample observation chamber 3 and is evacuated to 10 ⁻³ Pa or less. Further, a vacuum pump 23 is connected to the preliminary exhaust chamber 5, and the preliminary exhaust chamber 5 is evacuated to 10 ⁻² Pa or less.
The intermediate chamber 4 has a reflected electron / secondary electron detector 24 for detecting secondary electrons or reflected electrons B2 from the surface of the sample 16 when the sample 16 is irradiated with the electron beam B1 from the electron gun 7. It is attached. Reference numeral 25 denotes an exhaust bypass connecting the sample observation chamber 3 and the intermediate chamber 4.
When transporting to the sample observation chamber 3 for observing the sample 16, the following procedure is performed. The sample exchange chamber 6 is evacuated with a roughing pump. Next, the sample holder 15 is lowered and lowered to the preliminary exhaust chamber 5. After the inside of the preliminary exhaust chamber 5 is evacuated to 10 ⁻² Pa or less, the gate valve 17 is opened, and the sample holder 15 is placed on the upper surface of the sample holder 15 via the gate valve 17. Transport to. In the sample observation chamber 3, the sample holder 15 is positioned almost directly below the electron gun 7. Thereafter, the gate valve 17 is closed, and the inside of the sample observation chamber 3 is evacuated to 10 ⁻³ Pa or less by the vacuum pump 22.
When the inside of the sample observation chamber 3 is evacuated to 10 ⁻³ Pa or less, the electron beam B 1 is extracted from the electron gun 7 by the voltage applied to the extraction electrode 8, and the extracted electron beam B 1 is applied to the acceleration electrode 9. The desired energy is adjusted by the applied acceleration voltage. Further, after passing through the fixed aperture 10, the electron beam B 1 is converged on the sample 16 by the condenser lens 11 and the objective lens 13. The converged electron beam B 1 is scanned on the sample 16 by the change coil 12. At this time, secondary electrons and reflected electrons B2 are generated from the surface of the sample 16, and these secondary electrons and reflected electrons B2 are detected by the reflected electron / secondary electron detector 24 to obtain a sample image.

  When the sample 16 is introduced into the sample observation chamber 3, adsorption of the residual gas component mainly composed of organic substances to the sample occurs. By irradiating the electron beam B 1 there, the adsorbed residual gas component receives energy from the electron beam and is gradually deposited on the surface of the sample 16. Deposition occurs with the contribution of both incident residual gas from the gas phase and surface diffusion of adsorbed components. In any case, the amount of deposition increases as the residual gas component increases. As the deposition amount increases, the dimensional measurement error increases and accurate measurement becomes impossible. Therefore, in order to realize accurate measurement, it is necessary to accurately reduce organic residual gas molecules.

  There is a problem that the gas in the electron gun chamber 1 or the sample observation chamber 3 exists. Examples of the gas existing in the electron gun chamber 1 and the sample observation chamber 3 include a gas released due to adhesion to the inner wall of the sample observation chamber 3, a gas released from components constituting the sample observation chamber, , There is a gas released from the sample surface or the back surface. Naturally, as the number of measurement samples increases, the gas generated from the sample accumulates in the sample observation chamber.

  When the sample 16 is introduced into the sample observation chamber 3, the gas components accumulated in the sample observation chamber 3 by the above process are adsorbed on the sample 16 and cause a problem. In order to suppress this, it is necessary to provide some cleaning means. However, for accurate cleaning, a mechanism for detecting and monitoring the gas component in the sample observation chamber 3 and cleaning it at an optimal timing is essential.

  In this case, a problem in monitoring the gas component is detection of a high molecular weight organic substance having a molecular weight of 200 or more. High molecular weight organic substances are adsorbed on the wafer surface even in a very small amount. Therefore, the potential for causing problems is high. Nevertheless, high molecular weight organic matter is difficult to evacuate with a turbo molecular pump and tends to remain in the vacuum chamber.

  On the other hand, high molecular weight organic substances are difficult to detect by simple gas phase mass spectrometry, which is a conventional monitoring means. This is because the vapor pressure is extremely low and the amount in the gas phase is very small.

  In this embodiment, the gas components present in the sample observation chamber 3, the electron gun chamber 1, the sample exchange chamber 6 and the preliminary exhaust chamber 5 are monitored by detecting the components adsorbed on the substrate.

  A first embodiment in which the monitoring method of this embodiment is applied to a gas component monitor in the sample observation chamber 3 will be described with reference to FIG.

  In the first embodiment, a monitor substrate 100 is provided inside the sample observation chamber 3. The monitor substrate 100 is a conductor, a wire 101 is welded, and the wire is connected to a power supply 102 installed outside the sample observation chamber 3. A mass spectrometer 103 is provided in the sample observation chamber.

  When the monitor substrate 100 is exposed to the atmosphere in the sample observation chamber 3, the gas component is adsorbed on the surface thereof. After being exposed for a certain time, the monitor substrate 100 is energized from the power source 102 through the wire 101. By energizing, the monitor substrate 100 is rapidly heated, the adsorbed components are desorbed, released into the sample observation chamber, and detected by the mass spectrometer 103. Thereafter, the monitor substrate 100 is naturally cooled and returned to room temperature. By repeating this cycle, the time change of the gas component in the sample observation chamber is monitored. That is, the temperature rise of the monitor substrate 100 and the measurement of the mass spectrometer 103 are performed in synchronization.

  FIG. 2 shows the cycle. The monitor substrate 100 is exposed to the evacuated gas in the sample observation chamber 3 at room temperature (step 201). During this time, gas molecules in the sample observation chamber 3 are physically adsorbed on the surface of the monitor substrate 100 by van der Waals force. Then, analysis of the gas in the sample observation chamber 3 is started when a predetermined time has elapsed or according to an instruction from the outside. In the analysis, the monitor substrate 3 at room temperature is energized to be heated to about 1000 ° C. (step 202). At this time, gas molecules physically adsorbed on the monitor substrate 100 are desorbed by thermal energy, and the gas density in the sample observation chamber 3 (particularly around the monitor substrate 100) temporarily increases. At this time, the mass analyzer 103 detects a gas (step 203). After the gas is detected, the heating of the monitor substrate 100 is stopped, whereby the monitor substrate 100 is cooled to room temperature and becomes a temperature at which gas is easily adsorbed (step 204).

  The point here is that the temperature of the monitor substrate 100 is rapidly raised to about 1000 ° C. in about several seconds (7 seconds in this embodiment). As a result, the adsorbed high molecular weight organic matter is instantaneously released into the sample observation chamber 3, and the partial pressure of the high molecular weight organic matter inside the sample observation chamber 3 is instantaneously increased to facilitate detection by the mass spectrometer 103. That is, the temperature can be rapidly increased by disposing the monitor substrate 100 away from the wall of the sample observation chamber. The rapid temperature rise here is sufficient if the temperature rises from room temperature (100 ° C. or lower) to 800 ° C. or higher within 60 seconds.

  As the exposure time of the monitor substrate 100 is longer, the amount of adsorption increases, and as a result, the sensitivity is improved. However, the number of monitoring times per unit time is reduced. In this example, the exposure time was 30 minutes to 1 hour.

  In addition, as a material for the surface of the monitor substrate, nickel, tungsten, tantalum, copper, gold, silicon, or the like is suitable in consideration of ease of gas adsorption and desorption and ease of heating.

  FIG. 3 shows the measurement results as an example. The horizontal axis indicates the mass of ions of the detected molecule, and the vertical axis indicates the detected amount. Here, a mass number 149 caused by dioctyl phthalate (hereinafter referred to as DOP) which is a high molecular weight organic substance, which is difficult to detect by ordinary gas phase mass spectrometry, is clearly observed. This DOP, for example, adheres to the surface of a semiconductor that is a measurement target of an electron beam inspection apparatus, resulting in performance degradation. In addition, a peak that appears to be organic silicon is observed at mass numbers 73 and 221. None of these could be detected by normal gas phase mass spectrometry.

  Further, in the electron beam inspection apparatus according to the embodiment of the present invention, an oxygen active species generation apparatus 104 is attached to the sample observation chamber 3. Here, the means for generating the oxygen active species is generated, for example, by introducing oxygen through the leak valve 150 into the sample observation chamber 3 and then generating plasma in this embodiment, but also by other methods. Good. The generated oxygen active species acts on the binding of the organic matter and decomposes the organic matter. This makes it possible to remove the organic matter in the sample observation chamber 3.

  However, since the electron beam inspection apparatus cannot be operated during the introduction of the oxygen active species, it is important that the number of introductions be the minimum necessary and performed at an appropriate timing. In the present embodiment, it is possible to appropriately grasp the amount of organic matter in the sample observation chamber 3 by monitoring the organic matter by the method using the monitor substrate 100. Thereby, it is possible to perform cleaning at an optimal timing.

  FIG. 4 shows the effect of reducing contamination when oxygen-activated species by plasma is used as an embodiment of the present invention. In the example of FIG. 3 described above, the decontamination treatment is not performed, but it can be seen that the hydrocarbon gas in the atmosphere is clearly reduced as compared with this example.

  In this embodiment, the mass spectrometer is used to analyze the gas. However, the present invention is not limited to this, and an ionization vacuum gauge or a B-A gauge may be used.

  Next, another embodiment of the second embodiment will be described. Although the basic configuration is the same as that of the first embodiment, a feature is that a wire 105 is used instead of the monitor substrate 100.

  FIG. 5 shows a case where the monitoring method of the second embodiment is applied to a gas component monitor in the sample observation chamber 3. In the second embodiment, a linear wire 105 for monitoring is provided inside the sample observation chamber 3. The linear wire 105 is an electric conductor, and the wire is connected to a power source 102 installed outside the sample observation chamber 3. In addition, a mass spectrometer 103 is provided inside the sample observation chamber 3.

  The following procedure is almost the same as in the first embodiment. When the wire 105 is exposed to the atmosphere in the sample observation chamber 103, a gas component is adsorbed on the surface thereof. After being exposed for a certain time, the wire 105 is energized from the power source 102. By energizing, the wire 105 is rapidly heated, the adsorbed components are desorbed, released into the sample observation chamber, and detected by the mass spectrometer 103. Thereafter, the wire 105 is naturally cooled and returned to room temperature. By repeating this cycle, the time change of the gas component in the sample observation chamber is monitored.

  Since the second embodiment uses a linear wire 105 without preparing a special monitor substrate, it has advantages that it is easy to make and has high reliability. On the other hand, with a simple wire. There is a possibility that the surface area is insufficient and the amount of adsorption cannot be obtained. In this regard, it is effective to increase the surface area of the folded wire 106 as shown in FIG.

  FIG. 7 shows a spectrum monitored in the sample observation chamber 2 with the configuration of the second embodiment. As in Example 1, a peak originating from DOP siloxane is clearly observed.

  Next, another embodiment of Example 3 will be described. Although the basic configuration is the same as that of the first embodiment, a feature is that a porous body having a large surface area is used instead of the monitor substrate 100 as an adsorbent that adsorbs atmospheric components.

  Embodiment 3 will be described with reference to FIG. FIG. 9 shows a case where the monitoring method of Example 3 is applied to the gas component monitor in the sample observation chamber 3.

  In Example 3, the sample observation chamber 3 includes a porous body 107, a support body 108 that supports the porous body 107, and a heater 109 that heats the porous body 107. A wire 110 for energizing the heater is connected to a power source 102 installed outside the sample observation chamber 3. In addition, a mass spectrometer 103 is provided inside the sample observation chamber 3.

  The following procedure is almost the same as in the first embodiment. When the porous body 107 is exposed to the atmosphere in the sample observation chamber 103, a gas component is adsorbed on the surface thereof. After being exposed for a certain time, the heater 109 is energized from the power source 102. By energizing, the heater 109 is rapidly heated, and the adsorbed component is desorbed and released into the sample observation chamber and detected by the mass spectrometer 103. Thereafter, the porous body 107 is naturally cooled and returned to room temperature. By repeating this cycle, the time change of the gas component in the sample observation chamber is monitored.

  Since the porous body 107 having a large surface area is used in Example 3, it is possible to adsorb more gas components in the atmosphere. As the porous material, activated carbon, silica gel, porous polymer, or fine particles can be used.

  FIG. 9 shows a spectrum monitored in the sample observation chamber 2 with the configuration of the third embodiment. As in Examples 1 and 2, peaks originating from DOP and siloxane are clearly observed. Moreover, the detection sensitivity was about 10 times, and more sensitive detection was possible.

  In each embodiment, the sample observation chamber 3 is described as an example. However, the problem of contamination is not only the sample observation chamber 3, but also the electron gun chamber 1, the sample exchange chamber 6, and the preliminary exhaust chamber 5. The means shown in each embodiment can be applied to any of the electron gun chamber 1, the sample exchange chamber 6, and the preliminary exhaust chamber 5.

  By taking the measures shown in the above-mentioned embodiments, not only observing the contamination state of the electron beam inspection apparatus, but also removing contamination according to the contamination state, the measurement trouble is always reduced as much as possible. It is possible to provide a measurement environment.

DESCRIPTION OF SYMBOLS 1 ... Electron gun chamber, 2 ... Condenser lens chamber, 3 ... Sample observation chamber, 4 ... Intermediate chamber, 5 ... Preliminary exhaust chamber, 6 ... Sample exchange chamber, 7 ... Electron gun, 8 ... Extraction electrode, 9 ... Acceleration electrode, DESCRIPTION OF SYMBOLS 10 ... Fixed aperture, 11 ... Condenser lens, 12 ... Deflection coil, 13 ... Objective lens, 14 ... Objective lens movable aperture, 15 ... Sample holder, 16 ... Sample, 17, 18 ... Gate valve, 19-23 ... Vacuum pump, 24 ... backscattered electron / secondary electron detector, 25 ... exhaust bypass, 100 ... monitor substrate, 101 ... wire, 100 ... monitor substrate, 102 ... power source, 103 ... mass spectrometer, 104 ... oxygen active species generator, 105 ... wire, 106 ... folding wire, 107 ... porous body, 108 ... support, 109 ... heater, 110 ... wire.

Claims (20)

A sample observation room;
An exhaust means for evacuating the sample observation chamber;
Inspection means for inspecting the sample stored in the sample observation room;
In an inspection apparatus comprising a gas analyzing means for analyzing a gas component in the sample observation chamber,
Adsorption means provided in the sample observation chamber;
An inspection apparatus provided with heating means capable of heating the adsorption means. In claim 1,
2. The inspection apparatus according to claim 1, wherein the adsorption means is provided apart from the wall of the sample observation chamber. In claim 1,
The adsorption means is a metal;
The said heating means heats by the electricity supply to the said metal, The inspection apparatus characterized by the above-mentioned. In claim 1,
The inspection apparatus characterized in that heating of the adsorption means by the heating means and inspection of the gas analysis means are performed in synchronization. In claim 3,
The inspection apparatus according to claim 1, wherein the metal is nickel, tungsten, tantalum, copper, or gold. In claim 1,
With cleaning means,
An inspection apparatus, wherein the cleaning means is operated based on an analysis result of the gas analysis means. In claim 3,
The inspection device, wherein the adsorption means is a plate-like metal. In claim 3,
2. The inspection apparatus according to claim 1, wherein the suction means is wire-shaped. In claim 1,
The adsorption means adsorbs the gas in the observation chamber,
The adsorbed gas is desorbed by heating the heating means,
The gas analyzer is configured to analyze the desorbed gas. In claim 1,
An inspection apparatus comprising a mass spectrometer as the gas analyzing means. In claim 1,
An inspection apparatus using an ionization vacuum gauge as the gas analyzing means. In claim 1,
An electron beam inspection apparatus using a BA gauge as the gas analysis means. In claim 1,
The electron beam inspection apparatus, wherein the adsorption means is a porous body. In claim 6,
2. The electron beam inspection apparatus according to claim 1, wherein the cleaning means is means for introducing oxygen active species. In claim 10,
An inspection apparatus characterized in that the means for introducing oxygen active species is plasma. In the analyzer that analyzes the gas in the sample observation chamber of the inspection device held in vacuum,
Adsorption means for adsorbing gas;
Heating means for heating the adsorption means;
An analysis device comprising an analysis means for analyzing a gas. In claim 16,
The adsorbent desorbs the adsorbed gas by the heating,
The analyzing device analyzes the desorbed gas. In claim 16,
The heating apparatus and the analysis are performed in synchronization with each other. Exposing the adsorbent to the gas to be analyzed;
Heating the adsorbent;
A gas analysis method including an analysis step of analyzing a gas in synchronization with the heating. In claim 19,
The adsorbent adsorbs the gas to be analyzed,
A gas analysis method, wherein the adsorbed gas is desorbed by the heating.

Images