JPH0843331A - X-ray analysis method and apparatus - Google Patents

Abstract

PURPOSE:To provide an X-ray analyzing device, which can accurately analyze a residual film of the bottom surface of a fine hole. CONSTITUTION:Electron beams 8 from an electron source 1 are accelerated and converged, and the surface of a sample 6 is irradiated with the electron beams 8, and the generated X-ray 9 is detected by a detecting head 11. Change of the irradiation position of the electron beam 8 is corrected by a deflecting coil 5', and change of the incident current quantity and incident energy of the electron beam 8 to the sample 6 can be corrected. Consequently, since electron beam irradiation position, incident current quantity, incident energy during the measurement of the X-ray can be maintained constant, analysis of 2 residual film can be accurately performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface analysis technique, and more particularly to an X-ray analysis apparatus excellent in analyzing a sample surface having fine pores.

[0002]

2. Description of the Related Art As semiconductor elements are highly integrated, highly precise fine processing techniques are required. For example, 256Mb
In manufacturing a DRAM, it is required to process a fine contact hole having a diameter of 0.2 μm and a depth of about 2 μm. In order to perform such high-precision micromachining, a measurement technique capable of inspecting and determining the accuracy of machining is required. Among the above-mentioned measurement techniques, a measurement technique capable of determining the presence or absence of a residual thin film (residual film) on the bottom surface of a fine hole such as a contact hole is particularly important. If there is a residual film on the bottom of the contact hole,
This is because the continuity failure is transferred to cause a serious device failure.

As a measuring technique for detecting the presence or absence of a residual film on the bottom surface of a micropore, an analysis method and apparatus for micropores is disclosed in Japanese Patent Application No.
No. 257789. In this analyzer,
The remaining film in the fine holes is irradiated with a finely focused electron beam, and the X-ray (or the fluorescent X-ray) generated from the remaining film by the electron beam irradiation.
Line). At the time of this X-ray observation, low energy X-rays from the residual film can be detected by installing a part or all of the X-ray receiving surface of the X-ray detector within 20 ° from the electron beam central axis. It is possible to measure the type and film thickness, that is, qualitatively and quantitatively analyze the remaining film.

[0004]

[Problems to be Solved by the Invention] In qualitative and quantitative analysis,
The reliability of the analysis is important. Taking residual film measurement as an example, it is necessary to accurately determine the type and film thickness of the residual film. For example, measurement of the remaining film thickness requires measurement accuracy of 1 to several nm. In order to perform such high-precision analysis, the irradiation position of the electron beam on the sample surface, the electron beam incident current on the sample surface, and the stability of the incident energy are indispensable.

When the irradiation position changes during electron beam irradiation,
The electron beam may be irradiated on the side wall of the fine hole. The residual film and the side wall are often made of the same material, and when the side wall is irradiated with an electron beam, X-rays of the same type as the residual film are generated. Therefore, even when the residual film does not exist on the bottom surface, the residual film is present. May be erroneously determined to be. The intensity of X-ray generation is a function of the current and incident energy of the electron beam with which the residual film is irradiated. Therefore, if these change during X-ray measurement, the measured intensity of X-ray changes, and the reliability of the remaining film thickness obtained from the X-ray intensity is significantly reduced. The change of the irradiation position and the change of the incident energy described here are particularly remarkable when observing a fine hole formed on a sample whose surface is charged, for example, an insulating sample such as a photoresist.

As described above, the stability of the electron beam irradiation position, incident current, and incident energy is indispensable for highly accurate analysis of the residual film. However, in the conventional methods and devices, since no consideration is given to these stability, the reliability of measurement is low, and highly accurate residual film analysis is difficult. An object of the present invention is to measure and correct changes in electron beam irradiation position, incident current, and incident energy during X-ray measurement, thereby minimizing these effects and reliably performing residual film analysis. It is to provide an X-ray analyzer capable of performing the above.

[0007]

In order to achieve the above object, an electron beam accelerating and converging means on a sample surface, an observing means for X-rays generated by electron beam irradiation, a sample holding means and a position control means, a sample A monitor means and a correction means for the electron beam irradiation position on the surface, and a monitor means and a correction means for the electron beam incident current and the incident energy on the sample were provided.

[0008]

As described in Japanese Patent Application No. 4-257789, in order to detect X-rays from the residual film on the bottom surface of the micropores, the X-rays are observed within a range of 20 ° from the electron beam central axis. Is essential. In the X-ray observing means of the present invention, a part or the whole of the X-ray receiving surface is installed in this area. As the X-ray observing means, any observing means may be used as long as it is a means capable of X-ray energy analysis. For example, a solid (semiconductor) X-ray detector such as Si (Li), or a combination of a multilayer film reflecting mirror or a diffraction grating and an X-ray detector may be used. When a spectroscopic element such as a multi-layered film reflecting mirror or a diffraction grating is used, part or all of the X-ray receiving surfaces of these spectroscopic elements or a part of the X-ray receiving surface of an optical element that guides X-rays to these spectroscopic elements. Alternatively, it is assumed that the spectroscopic element and the optical element are installed so that all of them fall within the range of 20 ° from the electron beam central axis.

In the present invention, the electron beam irradiating position monitoring means and the correcting means on the surface of the sample are used to irradiate the residual film on the bottom surface of the micropores with the electron beam with high positional accuracy (for example, even when the surface of the sample is charged). It is possible to As this monitoring means, for example, a method of observing an SEM image (electron beam scanning image) of the sample surface and obtaining the image movement amount (that is, the amount of change in the electron beam irradiation position) by comparing the observed images is considered. To be Further, as a means for correcting the electron beam irradiation position,
A deflection coil for electron beam may be used. Specifically, the X-ray measurement is interrupted, the electron beam is scanned on the sample surface, and the SEM image of the sample surface is observed during the measurement of the X-ray by the fixed irradiation of the convergent electron beam on the bottom surface of the micropore. Next, this SEM
The image is compared with the SEM image observed one time before to obtain the image movement amount, the electron beam is deflected by a distance corresponding to the movement amount (that is, the electron beam irradiation position is corrected), and fixed irradiation is performed,
The X-ray measurement is performed again. By performing such comparison with the SEM image observation and automatically correcting the electron beam irradiation position a required number of times during the X-ray measurement, the electron beam can be always irradiated to a desired position on the bottom surface of the micro hole, and the side wall of the micro hole can be constantly irradiated. It is possible to prevent deterioration of analysis accuracy due to unnecessary electron beam irradiation to the.

In the above description, the SEM image is used to grasp the image movement amount, but the image movement amount can be grasped even by observing and comparing the X-ray images obtained from the X-ray mapping accompanying the electron beam scanning. It is possible. When the amount of image movement is large, the sample itself is slightly moved using the sample holding means and the position control means (for example, an electrically controlled sample stage) instead of the electron beam deflection, and the electron is moved. The line irradiation position can also be corrected.

Further, according to the present invention, it is possible to correct the incident current and the incident energy of the electron beam on the sample during the X-ray measurement by using the automatic monitor means and the automatic correcting means of the electron beam incident current and the incident energy. . The simplest method of monitoring and correcting the electron beam incident current is to electrically float the holding means of the sample, measure the current incident on the sample using, for example, an ammeter, and measure the electron current so that the incident current is constant. This is to automatically control the filament current of the source and the electron extraction voltage. This method is effective for conductive samples.

When the sample is an insulator, it is difficult to measure the sample current as described above. Therefore, for example, an aperture is installed in the electron beam path from the electron source to the sample, and the current flowing therethrough is measured. do it. In this case, the total incident current to the sample is not measured, but it is possible to know the relative change of the incident current. Based on this relative change, the incident current can be kept constant by using the same method as described above.

When an insulator sample is irradiated with an electron beam, the surface of the sample is charged and the surface potential changes, so that the effective energy of the electron beam incident on the sample changes (in a normal electron beam irradiation apparatus, the electron beam is accelerated). The voltage or incident energy is
The sample surface is set to be at ground potential). In the present invention, this electron beam incident energy can be automatically measured and corrected. The means for monitoring the incident energy may be any means capable of measuring the surface potential of the sample. For example, if a surface electrometer is installed in the vicinity of the electron beam irradiation area, the potential due to the charging of the sample surface can be easily measured (the incident energy on the sample changes by this surface potential). Furthermore, the surface potential can be estimated from the highest energy value of the bremsstrahlung part in the observed X-ray spectrum. The maximum value of the energy of the bremsstrahlung light (X-ray) generated from the sample by the electron beam irradiation is equal to the incident energy value of the electron beam on the sample. Therefore, by reading the maximum energy value of the bremsstrahlung light from the X-ray spectrum, the incident energy of the electron beam on the sample surface can be obtained. The maximum energy value can be easily read by incorporating the necessary electronic circuit or computer program in the control device of the X-ray spectrum observation means. The electron beam incident energy (effective acceleration voltage) is automatically measured during the X-ray measurement using the above-described means, the difference from the initial setting value of the acceleration voltage is obtained, and the electron beam acceleration / focusing means is fed back. By doing so, the incident energy on the sample surface can always be kept constant.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> An example of the most basic embodiment of the present invention is shown in FIG. In the figure, the electron beam 8 from the electron source 1 passes through the electrode 2, the condenser lens 3, and the objective lens 4, and is irradiated onto the sample 6. Here, the electrode 2 imparts a desired acceleration energy to the electron beam 8 and, at the same time, is combined with the condenser lens 3 and the objective lens 4 to form a series of electron lens systems, and serves to form a fine electron beam. The X-ray 9 generated from the sample 6 by the irradiation of the electron beam 8 enters the detection head 11 (X-ray receiving surface) of the X-ray detector 10 controlled by the controller 14 and is detected.
As described above, regarding the installation of the detection head 11,
Inserting the X-ray detector 10 into the electron lens system (mirror body) so that a part or all of the detection head 11 is installed within 20 ° (that is, α ≦ 20 °) from the central axis of the electron beam 8.
Installation is devised.

The procedure for measuring the residual film using this apparatus is as follows.
This will be described using the sequence shown in FIG. First, in order to determine the analysis position on the surface of the sample 6, the SEM image of the surface of the sample 6 is observed (A). In this observation, the deflection coil 5 is controlled by the control circuit 13 based on the electron beam scanning signal from the control device 15, the surface of the sample 6 is scanned by the electron beam 8, and the secondary generated by the electron beam irradiation. The electrons are detected by the detector 12. The controller 15 can obtain the SEM image of the surface of the sample 6 by performing mapping using the secondary electron detection signal corresponding to the irradiation position of the electron beam 8.

An example of the obtained SEM image is shown in FIG.
FIG. 3 is an SEM image of the surface of the sample 6 displayed on the screen 21 of the display device 17 connected to the control device 15. As shown in FIG. 3A, on the screen 21, the cursor line 23 is aligned with the center of the fine hole 22 for measuring the residual film, and the irradiation position of the electron beam 8 (that is, analysis position, point P) is determined. (FIG. 2 (B)), fixed irradiation of the electron beam 8 is started,
X-ray measurement is performed using the X-ray measuring means described above (C). Here, the irradiation position of the electron beam 8 is stored in the storage device 16 connected to the control device 15. X for a certain time
After performing the X-ray measurement, the controller 14 controls the X-ray detector 10 to interrupt the X-ray measurement (D), and determine whether the X-ray measurement is continued or finished. For this determination, for example, the number of times the X-ray measurement is repeated may be input in advance to the control device 15 and the determination may be made by comparison with this number. X
When the line measurement is continued, the surface of the sample 6 is scanned again with the electron beam 8 and SEM observation of the surface of the sample 6 is performed (E). Next, this SEM image is the SEM image most recently obtained in time (for example, in FIG. 2, SEM image (B),
Or if the X-ray measurement has already been repeated multiple times,
By comparing with the SEM image (E) one time before, the amount of image movement during that period (that is, the amount of change in the irradiation position of the electron beam 8)
Can be obtained (F).

A method of obtaining the movement amount will be specifically described with reference to FIG. FIG. 2B is an SEM image of the surface of the sample 6 after the X-ray measurement was stopped. Before the fixed irradiation of the electron beam 8 (FIG. 2A), the fine hole 22 in the center of the screen 21 is
After the electron beam irradiation, it moves to the lower left of the screen 21 (the cause is, for example, the charging of the surface of the sample 6). The setting of the cursor line 23 at the center (point P) of the fine hole 22 is automatically performed based on the pattern information stored in advance in the storage device 16. Further, the center position of the fine hole 22 after the image movement is stored in the storage device 16. The controller 15 obtains the image movement amount 1 and the movement direction (arrow in FIG. 3B) after the fixed irradiation of the electron beam 8 by comparing with the previously stored center position of the fine hole 22. (Fig. 2 (F)). The deflection coil 5'is controlled via the control circuit 13 based on a signal from the control device 15 so as to correct the movement amount and the movement direction, that is, the fine hole 22 is located at the center of the screen 21. , The irradiation position of the electron beam 8 is automatically corrected (G). After that, the fixed irradiation of the electron beam 8 is restarted and the X-ray measurement is performed. By repeating the above operation a desired number of times, X-ray measurement can be performed while always reliably irradiating the desired position with the electron beam 8. Here, the positions of the deflection coils 5 and 5 ′ can be freely changed as needed as long as they do not interfere with the measurement of the X-ray 9.

In this embodiment, it is possible to automatically measure and correct changes in the incident current and incident energy of the electron beam 8 during X-ray measurement. The sample stage 7 on which the sample 6 is installed is electrically insulated, and the current value of the electron beam 8 incident on the sample 6 can be measured by the ammeter 18.
The current measurement signal from the ammeter 18 is input to the controller 15. When the incident current to the sample 6 changes, the controller 19 controls the filament current or the electron extraction voltage in the electron source 1 based on the signal from the control device 15 to keep the incident current to the sample 6 constant. Can be kept at

As a method for keeping the incident energy of the electron beam 8 on the sample 6 constant, the following method is adopted. In the present embodiment, the effective incident energy of the electron beam 8 on the sample 6 can be measured from the maximum energy value of the bremsstrahlung light of the X-ray spectrum measured by the X-ray detector 10. The electronic circuit and computer program necessary for this measurement are included in the controller 14 and the control device 15.
Based on the measured value of this incident energy, for example, by controlling the controller 20 to change the voltage applied to the electrode 2, the incident energy to the sample 6 during X-ray measurement can be kept constant. Here, the electrode 2 constitutes an electron lens system together with the condenser lens 3 and the objective lens 4. Therefore, when the voltage applied to the electrode 2 is changed, the image resolution of the entire apparatus (or the beam diameter of the electron beam 8) or the incident current to the sample 6 may change. In such a case, the controller 15 is used to control the exciting current of the condenser lens 3 and the objective lens 4 and the electron source 1 at the same time (not shown), but the image resolution and the incident current do not change. Thus, the entire device can be controlled.

According to this embodiment, a change in the irradiation position of the electron beam 8 during X-ray measurement can be automatically measured and corrected. Furthermore, changes in the incident current and incident energy of the electron beam 8 on the sample 6 can also be automatically measured and corrected. Therefore, the influence of these changes can be minimized, and the residual film analysis on the bottom surface of the micropores can be performed with high accuracy.

<Embodiment 2> Another embodiment of the present invention is shown in FIG. In FIG. 4, the irradiation position of the electron beam 8 can be corrected by the deflection coil 5 ′ and the sample stage 30.
A moving mechanism 31 controlled by the control device 15 is installed on the sample stage 30 to enable minute movement on the order of nm. By using the deflection coil 5 ′ and the sample stage 30, it is possible to deal with a case where the correction amount of the irradiation position is large.

In <Example 1>, the current flowing in the sample 6 was directly measured, and the electron source 1 was controlled so that the incident current to the sample 6 was constant. However, this method is limited to the case where the sample 6 is a conductive sample and cannot be applied when the sample 6 is made of an insulating material. In this embodiment, in order to solve this drawback, the amount of current of the electron beam 8 is measured using the aperture plate 32. This method is not a method of measuring the total amount of current of the electron beam 8 but a method of measuring the amount of (partial) current flowing into the aperture plate 32. However, since the amount of current flowing through the aperture plate 32 is proportional to the amount of current of the electron beam 8, it is possible to measure the change in the amount of current of the electron beam 8 by this method. By using such a measuring method, the change in the current amount of the electron beam 8 can be measured regardless of the material of the sample 6, and X
The incident current of the electron beam 8 on the sample 6 during the line measurement can be kept constant. In the present embodiment, the aperture plate 32 is installed below the condenser lens 3, but it goes without saying that the installation position can be arbitrarily selected as long as it does not interfere with X-ray measurement. Further, in order to suppress the change in the incident current value during the X-ray measurement, the electron source 1 can be a TFE (thermal field emission type) electron source. Since the TFE electron source is extremely stable as compared with other electron sources, highly accurate X-ray measurement is possible. Even if this TFE electron source is adopted,
As in the first embodiment, it is assumed that the control device 15 can control the electron source 1 via the controller 19. Other parts are the same as in the first embodiment.

Also in this embodiment, the same effects as those in the first embodiment can be obtained.

<Example 3> In Examples 1 and 2, the incident energy of the electron beam 8 on the sample 6 was determined from the maximum energy value of the bremsstrahlung light in the X-ray spectrum. However, as described above, it is also possible to obtain this incident energy from the surface potential of the sample 6. The present embodiment is an example of such an embodiment.

In the apparatus shown in FIG. 5, a surface electrometer 40 capable of measuring the surface potential of a minute area is installed near the irradiation area of the electron beam 8 on the surface of the sample 6. Specifically, the probe probe 41 of the surface electrometer 40 is in contact with the surface of the sample 6 near the electron beam irradiation region. The probe 41 can measure the surface potential of the electron beam irradiation region, and the measurement result is output to the control device 15. Controller 15
Then, based on this measurement result, the effective incident energy of the electron beam 8 on the surface of the sample 6 is calculated (that is, the effective incident energy is changed by the potential of the surface of the sample 6), and the change amount of the incident energy is calculated. The controller 20 can be controlled to correct the. Other parts are the same as those in the other embodiments.

Also in this embodiment, the same effects as those of the first and second embodiments can be obtained.

[0028]

According to the present invention, it is possible to automatically measure and correct the change in the electron beam irradiation position or the incident current to the sample or the change in the incident energy of the electron beam during X-ray observation. . As a result, the influence of these changes on the X-ray measurement can be minimized, and the residual film on the bottom surface of the micropores can be analyzed with high accuracy.

[Brief description of drawings]

FIG. 1 is a device configuration diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing an X-ray measurement sequence in the present invention. .

FIG. 3 is a diagram showing an SEM image of micropores displayed on the screen of the display device.

FIG. 4 is a device configuration diagram showing an embodiment of the present invention.

FIG. 5 is a device configuration diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 ... Electron source 1, 2 ... Electrode, 3 ... Condenser lens, 4 ...
Objective lens 5, 5 '... Deflection coil, 6 ... Sample, 7 ... Sample stage, 8 ... Electron beam, 9 ... X-ray, 10 ... X-ray detector, 11 ... Detection head, 12 ... Detector, 13 ... Control Circuit, 14 ... Controller, 15 ... Control device, 16 ... Storage device, 17 ... Display device, 18 ... Ammeter, 19, 20 ... Controller, 21 ... Screen, 22 ... Micropore, 23 ... Cursor line, 30 ... Sample stage , 31 ... Moving mechanism, 32 ... Aperture plate, 33 ... Ammeter, 40 ... Surface electrometer, 41 ...
Probe.

Claims (11)

[Claims] 1. An electron beam accelerating means, an electron beam converging means and an irradiating means on a sample surface, a sample minute moving means, and an X-ray generated by electron beam irradiation within a range of 20 ° from a central axis of the electron beam. An X-ray analysis apparatus comprising: an X-ray measuring means capable of measuring in a region defined by, an automatic monitoring means of an electron beam irradiation position on the sample surface, and an automatic correcting means. 2. The X-ray analysis apparatus according to claim 1, wherein the automatic correction means acts in a direction of correcting a change in electron beam irradiation position measured by the automatic monitor means. 3. The X-ray analysis apparatus according to claim 2, wherein the change in the electron beam irradiation position is obtained by comparing the secondary electron image of the sample surface before and after the X-ray measurement. 4. The X-ray analysis apparatus according to claim 2, wherein the automatic correction means is a controlled electron beam deflection means or a controlled sample minute movement means. 5. An automatic measuring means and an automatic correcting means for the electron beam incident current to the sample, and an automatic measuring means and an automatic correcting means for the electron beam incident energy to the sample are provided. The X-ray analyzer described. 6. The X-ray analysis apparatus according to claim 5, wherein the electron beam incident current automatic correcting means acts in a direction of correcting a change in the incident current measured by the automatic measuring means. 7. The automatic measuring means for the electron beam incident current is a current measuring means electrically connected to the sample, or an aperture installed in the electron beam path and a current measuring means connected thereto. The X-ray analyzer according to claim 6. 8. The X-ray analyzer according to claim 6, wherein the incident current automatic correction means is a means for adjusting a filament current of the electron source or an electron extraction current inside the electron source. 9. The X-ray analysis apparatus according to claim 5, wherein the electron beam incident energy automatic correction means acts in a direction of correcting a change in the incident energy measured by the automatic measurement means. 10. The means for automatically measuring the electron beam incident energy is a means for measuring the surface potential of a sample or a means for analyzing the maximum energy value of bremsstrahlung light in an X-ray spectrum. The X-ray analysis apparatus described in 1. 11. The X-ray analysis apparatus according to claim 9, wherein the automatic correcting means for the incident energy of the electron beam is a control electrode installed in the electron beam path.