JP3085070B2 - X-ray irradiation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray irradiation apparatus,
In particular, a wide area used for a total reflection X-ray fluorescence analyzer for elemental analysis of trace impurities on the surface of a sample such as a silicon wafer, an X-ray apparatus for crystal defect evaluation, an X-ray apparatus for precision roughness measurement, etc.
The present invention relates to an X-ray irradiation device that generates a parallel X-ray flux.

[0002]

2. Description of the Related Art In recent years, with the progress of silicon technology in the electronics field, it has become important to quickly measure information such as impurities on a wafer, various crystal defects, and surface roughness.

For example, a chemical analysis method or a fluorescent X-ray analysis method has been mainly used for analyzing impurities on the surface of a sample such as a silicon wafer.

In the former method, impurities are dissolved by hydrofluoric acid, and then the type and concentration of impurities contained in the solution are determined by an atomic absorption method.

[0005] The latter is a method of obtaining information in the range of several microns to several tens of microns from the surface in a non-destructive and non-contact manner by a fluorescent X-ray analyzer.

The latter method has the excellent characteristics of non-destruction and non-contact, but has the disadvantage that most of the information is information inside the bulk, and the signal from the surface is hidden in the signal inside the bulk. there were.

A total reflection X-ray fluorescence analyzer using total reflection of X-rays has been developed in order to solve such a drawback.

An X-ray is applied to an optically smooth plane (Optica).
When illuminated on a flat surface at a low incident angle, X-rays are totally reflected at the same angle as the incident angle without being absorbed by the irradiated material.

At this time, if the sample is placed on this plane, fluorescent X-rays emitted from the sample can be detected. This is the total reflection X-ray fluorescence analysis.

In this method, the scattered X-rays are apparently negligible because they are totally reflected except for the impact on the sample.
A spectrum measurement with a good / N ratio can be performed.

In this apparatus, not only can information on impurities and defects on the surface of a silicon wafer be obtained, but also a concentration map of impurities and a distribution state of defects on the wafer can be known.

However, in the conventional X-ray fluorescence spectrometer, for example, in the case of impurities, the detection limit of a substantial element is 10 ^11.
(Atoms / cm ² ), which is a low level of 10 ¹⁰ to 10 ⁹ (atoms / cm ² ), which is a problem in device processing, cannot be detected due to the low intensity of incident X-rays.

For this reason, conventionally, a method has been adopted in which a surface that totally reflects X-rays is divided into a plurality of regions, and impurities are quantified by individually analyzing all the divided regions.

For this reason, the measurement requires a huge amount of time,
The efficiency of the measurement was remarkably low.

In order to improve the measurement sensitivity and the measurement efficiency of such a total reflection X-ray fluorescence spectrometer, the X-ray used therein can not only have a high intensity but also irradiate a large area at a time. It is necessary to use such wide-area monochromatic parallel X-rays.

A parallel X-ray is an indispensable condition for total reflection, and a wide-area X-ray is necessary for measuring the whole area by one measurement.

That is, it is preferable that irradiation can be uniformly performed on a silicon wafer, and the absence of such an X-ray source is the biggest problem of the total reflection X-ray fluorescence analysis.

On the other hand, a rapid evaluation of crystal defects and a precise roughness measurement of a silicon wafer also require a wide range of parallel and monochromatic strong X-rays for the same reason as described above.

However, in the prior art, since the intensity of incident X-rays is insufficient and it is difficult to obtain wide-area parallel monochromatic X-rays, a long time is required for measurement and the sensitivity is low. Was.

For this reason, it has been impossible to incorporate an X-ray silicon crystal defect evaluation apparatus into a semiconductor manufacturing line.

[0021]

As described above, if high-intensity, wide-area, parallel and monochromatic X-rays can be easily obtained, the total reflection X-ray fluorescence analysis is very useful for analyzing impurities on the surface of a silicon wafer. It is thought to be a useful technique for

Further, such a light source is indispensable for a crystal defect measuring device and a surface roughness measuring device of a silicon wafer.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art described above, and has as its object to measure the concentration distribution of trace impurities on the surface of a sample such as a silicon wafer and to measure the distribution of crystal defects. Measurement or measurement of surface roughness is to be performed with higher sensitivity and higher speed than before.

That is, an object of the present invention is to provide a large-area, parallel X-ray monochromatic X-ray irradiation source which enables such X-ray analysis.

[0025]

An X-ray irradiator according to the present invention has at least an X-ray source and its X-rays which are widened and parallelized.
It is composed of a graphite monochromator for monochromating and obtaining large-area parallel X-rays.

Further, in the present invention, the monochromator may be a parabolic or rotating parabolic curved graphite crystal, a circularly curved graphite crystal, a spherically curved graphite crystal, or an asymmetrically cut graphite crystal. It is characterized by using a graphite crystal having a graphite laminated surface.

[0027]

By using the various graphite crystals according to the present invention in combination with an X-ray source, it is possible to obtain monochromatic wide-area, parallelized X-rays which are far more intense than conventional ones.

These X-ray irradiators can be used for a total reflection X-ray fluorescence analyzer for analyzing semiconductor surface impurities, an X-ray apparatus for evaluating crystal defects of silicon wafers, an X-ray apparatus for analyzing surface roughness, and the like.

[0029]

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

FIG. 1 shows a graphite crystal (single-vented parabolic crystal) 1 that is curved in a paraboloid or a paraboloid of revolution used for widening and parallelizing X-rays in the present invention.
1 (FIG. 1A), circularly curved graphite crystal (single bent type crystal) 12 (FIG. 1 (b)), spherically curved graphite crystal (double bent type crystal) 13
(FIG. 1 (c)), and a graphite crystal (asymmetric crystal) 14 having an asymmetrically cut graphite laminated surface
It is a conceptual diagram of (FIG.1 (d)).

In a crystal such as 11, 12, 13, etc., the graphite layer structure is formed parallel to the curved surface,
X-rays are strongly reflected and monochromatic by the crystal lattice having the layer structure.

This reflection is a reflection from the graphite (002) surface, and only X-rays incident at an angle satisfying the Bragg condition are reflected, so that monochromatization can be achieved.

For example, an X-ray source using Cu as a target is used, and its Kα characteristic X-ray is reflected at an angle of about 13 °.

The reflection from the graphite (002) plane has a feature that it is much stronger than the reflection from other optical crystals, which is the reason why strong characteristic X-rays can be obtained.

For example, the intensity of the reflected X-rays from the graphite (002) surface is 7 to 20 times the intensity of the reflection from the (200) surface of lithium fluoride, which is a standard fluorescent X-ray monochromator. A large reflection intensity is obtained.

The reason why the graphite crystal of the present invention has a curved surface as described above is to obtain parallel X-rays.

The reason why parallel X-rays can be obtained will be described later in detail with reference to the drawings in the case of individual graphite crystals.

The graphite monochromator is not a single crystal but a polycrystal, and has a feature that a curved surface is easily formed as compared with other optical crystals because the light is reflected from the graphite layer structure.

Conventionally, it has been very difficult to produce such a graphite crystal, but in recent years, it has become possible by a new method.

The most effective means for producing such a crystal is
This is a production method based on carbonization and graphitization of polymer film developed in recent years.

For example, such a graphite crystal is produced by the following method. First, 400 μm
Having the following thickness, from among polyoxadiazole, aromatic polyimide, aromatic polyamide, aromatic polyamideimide, polybenzimidazole, polybenzobisthiazole, polybenzoxazole, polythiazole, polyparaphenylenevinylene, etc. At least one selected polymer film is used.

The biaxial stretching of the polymer film is performed by
Effective for obtaining good quality graphite.

Next, a plurality of the polymer films are laminated, carbonized at a temperature of about 1000 ° C., and nitrogen in the polymer is removed.
Remove hydrogen, oxygen, etc.

Next, the obtained carbide was cooled to 3700 ° C.
The treatment is performed at a temperature of 000 ° C., and the graphite is formed while applying pressure.

The pressure treatment at this time is performed by a flat graphite jig, a parabolically curved graphite jig, a circularly curved graphite jig, a spherically curved graphite jig, or a rotating parabolic surface. A crystal having a desired shape can be obtained by using a curved jig.

Thus, a large area has high smoothness and (0
A highly oriented graphite is obtained, characterized in that the 0l) plane is highly oriented parallel to the substrate surface.

When a plane crystal is used in the present invention, the surface on which the graphite layer is laminated is cut asymmetrically, and that surface is used as a reflection surface.

The graphite used in the present invention must have a mosaic spread value of 0.5 ° or less, more preferably 0.2 ° or less.

FIG. 2 is an example of a configuration diagram in an embodiment of a total reflection X-ray fluorescence spectrometer. In this figure, 21 is X
Radiation source.

As the X-ray source 21, for example, a sealed X-ray generating tube targeting Mo and a rotating anti-cathode X-ray tube targeting W are used, and targets such as Cu and Fe are also used as necessary. Is done.

As described above, in order to perform highly accurate analysis in a short time, a monochromatic, high-intensity, parallel X-ray is used as the X-ray source.
A line is needed, and the present invention aims to produce such an X-ray.

The primary X-rays emitted from this X-ray source 21 pass through a slit 22 and are reflected by a monochromator crystal 23 before being irradiated on a sample 24 (for example, the surface of a silicon semiconductor wafer).

The incident angle θ on the surface of the wafer as the sample 24
Is set to an angle at which the primary X-ray is totally reflected.

On the wafer, a secondary X-ray detector 26
Is provided, and the fluorescent X-rays from the wafer surface are detected by the detector 26.

The X-rays totally reflected pass through the slit 27 and enter the scintillation counter 28.

Although not shown, the output from the detector 28 is processed by a processing circuit including a pre-main amplifier, an A / D converter, a multi-channel analyzer, and the like. It is to be calculated.

FIG. 3 is an example of a configuration diagram in an embodiment of a crystal defect measuring apparatus for a silicon wafer.

In FIG. 3, reference numeral 31 denotes an X-ray source. X-rays from the X-ray source are split in both the vertical and horizontal directions by a two-crystal, three-crystal, or four-crystal monochromator 32 to form a wide-area parallel / monochromatic display. The obtained X-ray flux is obtained.

In this case, the X-ray source 31
X-rays emitted from the X-ray tube are used, but other than that, for example, synchrotron radiation (SOR light) can also be used.

The SOR light is a continuous X-ray, and this X-ray is made monochromatic by a monochromator crystal.

As monochromators used for such purposes, Si, Ge, InSb, InAs, CdS,
CdTe, graphite, lithium fluoride, α-quartz,
NaCl, calcite CaCO ₃ , pentaerythritol,
Etc. The present invention uses the graphite crystal of the present invention as at least one of the crystals as the monochromator.

The X-rays are guided onto a silicon wafer 33 placed on a rotatable sample stage 34, and the reflected X-rays are set at a position at a rotation angle twice the rotation angle of the sample stage (not shown). Guided to the scintillation counter.

An X-ray irradiator according to the present invention which can be used in the above-described analyzers and analyzers will be described.

FIG. 4 is a configuration diagram of an X-ray irradiator of the present invention using a single vent type parabolic crystal.

As the X-ray source 41 in this case, for example,
X-rays of the filament radiated from the tube are used.

Normally, when the X-rays emitted from the X-ray generating tube are converted into parallel beams, the slits are turned into narrow parallel X-rays. However, this operation has a drawback that the intensity of the X-rays is significantly reduced. there were.

In the present invention, such an operation is not necessarily required, and a divergence slit 43 for restricting the divergence angle and a solar slit 42 for restricting the divergence of the diffraction line in the vertical direction may be used.

This solar slit is formed by stacking thin metal plates at equal intervals. X obtained by the above method
The line is then incident on the graphite crystal according to the invention.

The single-vent parabolic graphite crystal 44 used for increasing the area and parallelizing the X-rays used in the present invention can also be used for the purpose of monochromaticizing X-rays. Is not always necessary.

Further, by using two graphite crystals of the present invention, the divergence of diffraction lines in the vertical and horizontal directions can be suppressed, so that the above-mentioned slit can be eliminated.

It should be noted that the above-mentioned spectral crystal other than graphite is used for X-rays after completion of widening and collimation by the graphite crystal (that is, for the X-ray collimated by the graphite crystal of the present invention). Is very effective.

Examples of such an X-ray spectral crystal include Si,
Ge, InSb, InAs, CdS, CdTe, lithium fluoride, α-quartz, NaCl, calcite CaCO ₃ , pentaerythritol and the like are used.

This is because the effect of the monochrome conversion by the graphite crystal is not always sufficient because the mosaic spread value of the graphite crystal is larger than that of other spectral crystals.

What is important in such an X-ray optical system is that the reflection angle β is set so as to satisfy the Bragg reflection condition. Is set at a position that satisfies various conditions.

The incident angle β formed by the parabolic crystal plane X-ray light source
Is always constant, and in such a crystal, strong reflection satisfying the Bragg reflection condition can be obtained from the entire crystal plane.

FIG. 5 is a configuration diagram of an X-ray irradiator according to an embodiment of the present invention using a single bent crystal (circularly curved crystal).

The X-ray source 51 in this case is, for example, X-ray source.
Linear X-rays emitted from the X-ray tube are used, and the generated X-rays are restricted by a divergence slit 52 and a solar slit 53 in a divergence angle and a vertical divergence of diffraction lines.

Normally, X-rays are monochromatized by diffracting X-rays from the X-ray source 51 with various X-ray spectral crystals, but the X-rays used in the present invention have a large area. The single vent type graphite crystal 54 used for parallelization can also be used for such a monochromatic purpose.

Therefore, another spectral crystal is not always necessary. It is extremely effective to use various types of spectral crystals for X-rays after completion of the widening and parallelization of graphite crystals.

What is important in such an X-ray optical system is that a convex surface of a single vent type crystal is used as a reflecting surface.

Also in this optical system, the reflection angle β between the X-ray source 51 and the single bent graphite is set so as to satisfy the Bragg reflection condition.

The curvature of such an optical crystal is determined by the reflection angle β
It is determined by the size of the light source and the distance between the light source and the crystal, and can be obtained by a simple calculation.

In such a single vent type crystal, unlike the parabolic crystal (FIG. 4), strictly speaking, the X-ray source and the incident angle satisfy the Bragg reflection condition at one point in the graphite crystal. is there.

Therefore, theoretically, such a crystal cannot provide a wide range of perfectly parallel X-rays.

However, since there is a crystal which satisfies Bragg's reflection condition slightly deviated from perfect parallel at another place of the graphite crystal, reflection from the crystal is obtained.

Therefore, a wide range of parallel X-rays can be obtained from such a crystal. FIG. 6 is a configuration diagram of an X-ray irradiator according to an embodiment of the present invention using a double bent type (spherical curved type) crystal.

The X-ray source 61 in this case is, for example, X-ray source.
A point-like X-ray source radiated from a tube is used.

As the X-ray generating tube, a sealed X-ray generating tube targeting Mo and a rotating anti-cathode X-ray tube targeting W are used.

In the present invention, a divergence slit 62 for limiting the divergence angle may be used.

The X-rays passing through the divergence slit 62 are then led to the double bent graphite crystal 63 of the present invention.

The double bent graphite crystal 63 used in the present invention can be used not only for increasing the area and parallelizing the X-rays but also for the purpose of making the X-rays monochromatic.

Therefore, a normal spectral crystal is not always necessary, but it is extremely effective to use such a spectral crystal for X-rays after completion of widening and parallelization by a graphite crystal.

What is important in such an X-ray optical system is that the convex surface of the double vent type crystal is used as a reflecting surface.

Also in this optical system, the reflection angle β between the X-ray source 61 and the double bent graphite is graphite (0
02) It is set so as to satisfy the Bragg reflection condition from the surface.

The curvature of such an optical crystal is determined by the reflection angle β
Is determined by the size of the light source and the distance between the light source and the crystal, and can be obtained by a simple calculation.

FIG. 7 shows an X-ray irradiating apparatus characterized in that the X-ray irradiating apparatus is composed of an X-ray generating source and a crystal using an asymmetrically cut graphite laminated surface as a reflecting surface.

X-rays radiated from the X-ray generating tube 71 are used as a radiation source. As the X-ray generating tube, a sealed X-ray generating tube targeting Mo and a rotating cathode X targeting a W target are used. A wire tube is used. Further, targets such as Cu and Fe are also used as needed.

Normally, when the X-ray emitted from the X-ray generating tube is converted into a parallel beam, it is converted into a narrow parallel X-ray by a slit.

Incidentally, synchrotron radiation (SOR light) can be used as the X-ray source. Since the SOR light is a continuous X-ray, Si, Ge, InSb, InAs, CdS,
CdTe, graphite, lithium fluoride, α-quartz,
NaCl, calcite CaCO3, pentaerythritol,
Are monochromated by such crystals.

[0100] The X-rays thus converted into narrow parallel light are as follows.
Next, the light is reflected by the graphite crystal 73 having the asymmetrically cut graphite laminated surface, and the area is widened.
Silicon (511) is used as such an asymmetric cut crystal.
A device utilizing silicon (111) reflection on a cut surface is known.

However, the asymmetric cut crystal of graphite has a feature that a stronger reflection intensity can be obtained than the asymmetric cut crystal of silicon, and therefore, strong parallel X-rays can be generated.

Of course, it is also possible to form a two-crystal, three-crystal, or four-crystal X-ray optical system by combining the graphite crystals having the above structures.

(Example 1) An X-ray irradiator shown in FIG. 4 was manufactured using an enclosed generator tube using Mo as an X-ray source, and the graphite crystal according to the present invention was evaluated. went.

FIG. 4A is a perspective view, and FIG. 4B is a top view thereof. The primary X-rays emitted from this X-ray source 41 pass through a solar slit 42 for restricting divergence in the vertical direction, and are incident on a single vent type parabolic crystal 44 through a divergence slit 43 for restricting divergence. I let it.

In the experiment, the focal length was 20 mm and the conductor position was 2
The parabolic surface designed at 0 mm was used.
It is not necessarily required to be constant depending on the size of the device.

In the actual experiment, the adjustment was made according to the arrangement of the X-ray source. As a result, it was confirmed that in such a parabolic crystal, strong monochromatic parallel X-rays were obtained from the entire surface by setting the incident angle so as to satisfy the Bragg reflection condition.

The intensity of the X-ray was 10 times that in the case of using the LiF crystal, and the irradiation area of the X-ray was 8 times that in the case of using the flat graphite crystal.

As a result, impurities on the surface of the semiconductor sample,
The measurement time for crystal defects can be greatly reduced.

Example 2 Using the same apparatus shown in FIG. 5 as in Example 1, single-vent type graphite crystals (circularly curved crystals) were evaluated.

A convex surface having a curvature of R225 was used as a single bent type (circularly curved crystal) crystal.

By using such a reflective crystal having a convex surface, it is possible to form a parallel line having a higher degree of parallelism than in the prior art.

As a result, the irradiation area was six times that of the flat crystal. Example 3 An apparatus having a point light source shown in FIG. 6 instead of the linear X-ray light source of Example 1 was used to evaluate a double bent type (spherical curved type) crystal.

The evaluation was performed using a convex spherical curved type having a curvature of R225. The spherical curved type did not change the irradiation area as compared with the above-described single vent crystal, but the reflection intensity was quadrupled.

Example 4 An asymmetric cut graphite crystal was evaluated using an X-ray irradiator shown in FIG. 7 using SOR light as an X-ray source.

The emitted light was first reflected by the silicon crystal cut on the (111) plane, and then reflected by the asymmetric cut graphite crystal.

This graphite crystal is obtained by cutting out a plane inclined by 63 ° from the (002) plane of the graphite crystal.

A parallel line was formed by reflecting the SOR light from the surface. As a result, a parallel X-ray flux having a reflection intensity eight times larger than that of a conventional asymmetrical cut crystal of silicon was obtained.

[0118]

In the X-ray irradiator comprising at least an X-ray source and a graphite monochromator for broadening, parallelizing and monochromaticizing the X-rays to obtain large-area parallel X-rays, a parabolic surface is used as a monochromator. By using a graphite crystal that is curved in the shape of a paraboloid or a paraboloid of revolution, a graphite crystal that is curved in a circular shape, a graphite crystal that is curved in a spherical shape, or a graphite crystal that has an asymmetrically cut graphite laminated surface, A much stronger wide-area, collimated monochromatic X-ray can be obtained. These X-ray irradiation apparatuses can be used for a total reflection X-ray fluorescence analyzer for analyzing semiconductor surface impurities, an X-ray apparatus for evaluating a crystal defect of a silicon wafer, an X-ray apparatus for analyzing surface roughness, and the like.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of various graphite crystals of the present invention.

FIG. 2 is a configuration diagram of a total reflection X-ray fluorescence spectrometer of the present invention.

FIG. 3 is a configuration diagram of a crystal defect measuring apparatus according to the present invention.

FIG. 4 is a configuration diagram of an embodiment of an X-ray irradiation apparatus according to the present invention.

FIG. 5 is a configuration diagram of an embodiment of an X-ray irradiation apparatus according to the present invention.

FIG. 6 is a configuration diagram of an embodiment of the X-ray irradiation apparatus of the present invention.

FIG. 7 is a configuration diagram of an embodiment of the X-ray irradiation apparatus of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 Single vent type parabolic crystal 12 Single vent type crystal 13 Double vent type crystal 14 Asymmetric crystal 21 X-ray source 22 Slit 23 Monochromator crystal 24 Sample 25 Sample table 26 Secondary X-ray detector 27 Slit 28 Scintillation counter 31 X In the source 324 crystal monochromator 33 silicon wafer 34 sample stage 41 X-ray source 42 solar slit 43 slit 44 parabolic graphite crystal 51 X-ray source 52 divergence slit 53 solar slit 54 single vent type graphite crystal 61 X-ray Source 62 Divergent slit 63 Double bent graphite crystal 71 X-ray source 72 Silicon monochromator 73 Graphite crystal with asymmetrically cut graphite laminated surface

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G21K 1/06 G01N 23/20 G01N 23/223

Claims (2)

(57) [Claims] 1. An asymmetrically cut graphite crystal
An X-ray irradiator that generates a parallel X-ray flux using the cut surface as a reflection surface. Wherein the graphite crystals, by laminating a plurality of polymer films, is obtained under pressure, it is thermally sintered 請
Motomeko 1 X-ray irradiation apparatus as claimed.