JP2000074649A - Inspecting apparatus and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To excel the limit of inspection of a hole which is caused by a secondary electron image and a reflected electron image, and realize the quantitative measurement of a fine hole, by detecting an X-ray radiated when a substrate to be inspected is irradiated with an electron beam. SOLUTION: A substrate to be inspected in which one or a plurality of apertures are formed on an A layer 41 is scanned and irradiated with electron beams 45, 45'. Radiated X-rays are detected with an X-ray detector. On the basis of the detected signal, X-ray spectrum is calculated. The ratio of X-ray spectrum radiated from the A layer 41 to X-ray spectrum radiated from a B layer 42 is obtained. Thereby the area or the diameter of the aperture part formed in the A layer is calculated. In the spectrum of characteristic X-ray 46 when the A layer 41 is irradiated with the electron beam 45, peaks exist at, e.g. energy S1, S3, S4. In the spectrum of characteristic X-ray when the B layer 42 is irradiated with the electron beam 45', peaks exist at, e.g. energy S1, S2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus and a recording medium for inspecting one or a plurality of openings reaching from an upper layer to a lower layer on a substrate to be inspected. The present invention relates to an inspection apparatus for inspecting the quality of processing of a through hole (so-called contact hole) for wiring between layers in a processed circuit pattern. Inspection of the contact hole basically measures the diameter from the image of the optical microscope or the electron microscope,
It is to determine whether or not the diameter falls within a target allowable range. However, as the diameter becomes smaller, the resolution (clearness) of the image becomes lower, so that the inspection becomes difficult.

[0002]

2. Description of the Related Art With the progress of LSI technology, the pattern of a wafer has become finer and the processing size of a contact hole has been reduced to 0.1 mm in diameter.
Since the resolution is 5 μm or less and the resolution of the optical microscope has become insufficient, a scanning electron microscope (hereinafter referred to as SEM) has come to be used even in inspection after processing in a mass production factory. In recent years, further miniaturization has been promoted by advances in processing technology, and it is expected that the diameter of the contact hole will be 0.2 μm or less.

The SEM scans the surface of a wafer to be observed with a high-speed electron beam, detects secondary electrons generated from the surface, modulates the brightness, and forms and displays an image.
The inspection of the contact hole is performed by observing the secondary electron image and measuring whether the hole penetrates to the lower layer or measuring the diameter of the through hole. Since the thickness of the film to be penetrated by the contact hole is about 1 μm, the aspect ratio (depth with respect to the diameter) of the hole having a diameter of 0.2 μm is 5 or more, and the bottom portion of the hole is scanned with a high-speed electron beam. Sometimes, it becomes difficult for secondary electrons generated at the bottom to escape from the holes. Unless secondary electrons can be detected, information on that portion (the bottom portion of the hole) cannot be obtained. In such a case, there is a method of detecting backscattered electrons instead of conventional secondary electrons. This is because the backscattered electrons have a higher kinetic energy than secondary electrons and can escape from the bottom of a deep hole, but in reality, a hole of 0.2 μm or less is insufficient. Further, the image due to the backscattered electrons is blurred compared to the secondary electrons, and the measurement of the bottom of the hole is inaccurate.

[0004]

Basically, neither the secondary electrons nor the backscattered electrons indicate information for directly identifying the hole bottom. It merely interprets the intensity distribution of the emitted electrons based on the effect of the shape and regards the information as the hole bottom. Therefore, there is a problem that when the S / N of the detection signal is reduced, the reliability of information is rapidly lost.

As described above, it has become clear that there is a limit to the method using a conventional SEM for measuring a contact hole of 0.2 μm or less. The present invention
In order to solve these problems, an object of the present invention is to realize a quantitative measurement of a fine hole beyond the limit of inspection of a hole having a large aspect ratio by a secondary electron image or a reflected electron image by the SEM.

[0006]

Means for solving the problem will be described with reference to FIG. In FIG. 1, electron beams 45 and 45 'irradiate an A layer (upper layer) 41 and a B layer (lower layer) 42 formed on a substrate to be inspected.

The characteristic X-rays 46 and 46 ′ correspond to the electron beam 4
Characteristic X-rays emitted by irradiating the A layer 41 or the B layer 42 with 5, 45 ′. Next, the operation will be described.

The electron beams 45, 45 ′ are applied to an A layer (upper layer) 4.
Scanning and irradiating a substrate to be inspected having one or a plurality of apertures in 1 and detecting the emitted X-rays with an X-ray detector, and X-ray spectrum based on the detected signal After calculating the calculated X-ray spectrum,
The ratio between the X-ray spectrum emitted from the A layer (upper layer) 41 and the X-ray spectrum emitted from the B layer (lower layer) 42 is obtained, and the area of one or more openings in the A layer 41 or When the opening is a circle, the diameter is calculated.

At this time, characteristic X-rays emitted only from one or more openings or a predetermined range including the openings on the surface of the A layer (upper layer) 41 are detected, and the X-rays of the detected characteristic X-rays are detected. The ratio of the X-ray spectrum emitted from the A layer (upper layer) 41 to the X-ray spectrum emitted from the B layer (lower layer) 42 is determined to obtain one or more of When the area of the opening or the opening is a circle, the diameter is calculated.

The electron beams 45 and 45 'scan the A layer 41 and the B layer 42 on the substrate to be inspected,
2 formed based on secondary electrons, reflected electrons or absorbed electrons
A layer 41 on the secondary electron image, reflected electron image or absorbed electron image
X-rays emitted from only one or a plurality of apertures in the space are detected, and an X-ray spectrum of the detected X-rays is obtained. The ratio with the X-ray spectrum emitted from the layer (lower layer) 42 is obtained, and the area of one or a plurality of openings in the A layer 41 or the diameter when the openings are circular is calculated. .

Therefore, beyond the limit of inspection of a hole having a large aspect ratio by a secondary electron image or a backscattered electron image by SEM, the characteristic X-ray ratio between the upper layer (A layer 41) and the lower layer (B layer 42) is also reduced. At the same time, it becomes possible to quantitatively measure the area or diameter of an extremely small fine hole (for example, a fine hole having a diameter of 0.2 μm and an aspect ratio of about 5 or more) formed in the upper layer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment and operation of the present invention will be described in detail with reference to FIGS.

FIG. 1 is an explanatory view (part 1) of the present invention. This means that a wafer 9 is attached as a substrate to be inspected to a wafer holder 10 under the system configuration of FIG.
This is a view for explaining a state in which the electron beams 45 and 45 ', which are narrowed down, are scanned from top to bottom in FIG. 1 and irradiated.

In FIG. 1, an A layer 41 is a layer formed on a B layer 42.
4 is a layer to be formed. The B layer 42 is for electrically connecting to a layer above the A layer 41 via a contact hole 44 formed in the A layer 41.

Here, the contact hole 44 is a hole formed in the A layer 41. In the present invention, the contact hole 44 is very fine, for example, a diameter of 0.2 μm, a depth of about 1 μm, and a very deep aspect ratio of about 5. It is a hole.

The electron beam 45 is an electron beam narrowed down by the system configuration shown in FIG. 5 which will be described later. Here, the surface of the A layer 41 without the contact hole 44 is scanned and irradiated, and This is for emitting characteristic X-rays corresponding to the element (excitation source).

The electron beam 45 'is an electron beam narrowed down by the system configuration shown in FIG.
This is for scanning and irradiating the surface of the B layer 42 through the contact hole 44 to emit a characteristic X-ray corresponding to the element of the B layer 42 (excitation source).

The characteristic X-ray 46 is a characteristic X-ray having a specific wavelength specific to an element contained in the region of the A layer 41 irradiated with the electron beam 45. The characteristic X-ray 46 ′ is a characteristic X-ray having a specific wavelength specific to an element included in the region of the B layer 42 irradiated with the electron beam 45 ′.

FIG. 1A is a schematic sectional view of a portion of the wafer where the contact hole 44 is located. Here, the electron beam 45 irradiates the surface of the A layer 41 to emit characteristic X-rays 46. The electron beam 45 'irradiates the surface of the B layer 42 to emit a characteristic X-ray 46'.

FIG. 1B shows that the A layer 41 is irradiated with the electron beam 4.
5 shows the energy when the characteristic X-ray 46 at the time of irradiation is detected and the spectrum is analyzed. The horizontal axis represents energy (wavelength), and the vertical axis represents the number of counts (intensity) at that time.
Represents In this example, three of energy S1, S3, and S4
It can be seen that there are peaks at three times (there are three peaks of characteristic X-rays of energies S1, S3, and S4 emitted from the elements existing in the region of the A layer 41 irradiated with the electron beam). .

FIG. 1C shows that the B layer 42 is irradiated with the electron beam 4.
The figure shows the energy when the characteristic X-ray 46 ′ when irradiated at 5 ′ is detected and the spectrum is analyzed. The horizontal axis represents energy (wavelength), and the vertical axis represents the count number (intensity) at that time. In this example, a peak exists at each of two energies S1 and S2 (two of characteristic X-rays of energies S1 and S2 emitted from an element existing in the region of the B layer 42 irradiated with the electron beam). Peak is present).

As described above, the A layer 41 is irradiated with the electron beam 45.
Is scanned to emit a characteristic X-ray 46 and spectrum analysis is performed to obtain FIG. 1 (b). The B layer 42 is scanned with an electron beam 45 ′ to emit a characteristic X-ray 46 ′ and spectrum analysis is performed. FIG. 1C can be obtained. These are A
Electron beam 45 for layer 41 and B layer 42 individually,
It can be obtained by irradiating 45 ′ and analyzing the characteristic X-ray at that time by spectrum analysis.

FIG. 2 is an explanatory view (part 2) of the present invention. FIG. 2A shows a contact hole 44 of the A layer 41.
Shows a state in which is processed normally.

FIG. 2A-1 shows the A layer 4 shown in FIG.
1 shows a pattern as viewed from above by SEM. 4 in the figure
Two circles represent the contact holes 44, respectively. FIG. 2A-2 shows an energy distribution obtained by spectral analysis of characteristic X-rays 46 and 46 'generated by scanning the entire electron beam in FIG. 2A-1. Here, the energy S1 described in FIG. 1B and FIG.
Peaks are obtained at S2, S3 and S4. This is because the characteristic X-rays 4 emitted from the A layer 41 shown in FIG.
6, and the characteristic X-rays 46 'emitted from the B layer 42 of FIG. 1C are obtained by spectral analysis, and the characteristic X-rays are added to the area ratio between the former (A layer) and the latter (B layer). This is the sum of the lines 46 and 46 '. Therefore, the A layer 41
Energy S1, S3 and S4 are detected from the
2, the energies S1 and S2 are detected, and when these are added by the area ratio, the energies S1 and S2 are
2, S3 and S4.

FIG. 2B shows a state in which the contact hole 44 of the A layer 41 is not optimally processed and is processed to have a small diameter. FIG. 2B-1 shows a pattern viewed from above the A layer 41 of FIG. 1A by SEM. The four circles in the figure represent the contact holes 44, respectively, and are smaller than the normal case of FIG. 2A.

FIG. 2B-2 shows characteristic X-rays 46, 4 generated by scanning the entire electron beam in FIG. 2B-1.
6 shows the energy distribution displayed by analyzing the spectrum of 6 ′. Here, the energies S1, S2, S3, and S4 described in FIGS. 1B and 1C are obtained. This is a result of spectral analysis of the characteristic X-rays 46 emitted from the A layer 41 in FIG. 1B and the characteristic X-rays 46 ′ emitted from the B layer 42 in FIG. The characteristic X-rays 46 and 46 'are added to the area ratio of the former (layer A) and the latter (layer B). Therefore,
The B layer 4 has a smaller through hole than that of FIG.
2 shows that the energy S1 and S2 emitted from the second layer 2 are reduced in accordance with the area (in particular, the energy S2 emitted only from the B layer 42 is smaller than that in FIG. 2A-2). (B-2), the area ratio of the contact holes 44 is small).

FIG. 2C shows a state where the processing conditions of the contact hole 44 of the A layer 41 are shifted and the contact hole does not reach the B layer 42 below. (C- of FIG. 2)
1) shows a pattern viewed from above the A layer 41 of FIG. 1A by SEM. The four dotted circles in the figure are the contact holes 44 but do not reach the B layer 42 and do not form holes.

FIG. 2C-2 shows characteristic X-rays 46, 4 generated by scanning the entire electron beam in FIG. 2C-1.
6 shows the energy distribution displayed by analyzing the spectrum of 6 ′. Here, only the energies S1, S3, and S4 described with reference to FIG. 1B are obtained, and it is clear that the contact hole 44 does not reach the lower B layer 42.

As described above, the contact hole 44 having the optimum diameter is formed in the upper A layer 41 in FIG.
The energy S1 in the state of 2) (the state of adding the area ratio of the characteristic X-rays 46 of the A layer 41 and the characteristic X-rays 46 'of the B layer 42),
Peaks P1, P2, P3, S2, S3, S4 respectively
P4), small diameter contact hole 44
(B-2) of FIG. 2 (where the energies S1, S2, S3, and S4 of the state where the area ratio of the characteristic X-ray 46 of the A layer 41 and the characteristic X-ray 46 'of the B layer 42 are added). The state having the peaks P1, P2, P3, and P4 respectively, and the state of FIG. 2C-2 in which the contact hole 44 does not reach the lower B layer 42 and has no hole (the state of the A layer 41). It is possible to obtain peaks P1, P3, and P4 at the energies S1, S3, and S4 of the characteristic X-ray 46, respectively. Accordingly, the characteristic X-ray energy Si (i = 1) corresponding to the area of the entire contact hole 44 is obtained.
4) and the respective peaks (intensities) Pi (i = 1 to 4), it is possible to calculate the area (the diameter in the case of a circle) of the contact hole 44 with respect to the whole by calculating backward from these. Become.

Further, an upper A layer 41 and a lower B layer 42
The peak P1 of the common energy S1 with respect to each other (the peak P1 is set to 1.00), and the other energy S
The relative values of the peaks P2, P3, and P4 of 2, S3, and S4 may be obtained, and the relative values of the peaks P2, P3, and P4 may be used to calculate the area of the contact hole 44 (the area of the B layer) with respect to the entire area (FIG. Will be described later).

FIG. 3 is an explanatory view (3) of the present invention. This is based on the above-mentioned peak P1 of the energy S1 as a reference (1.00), and the other energies S2, S3, S4
7 is a curve for obtaining the contact hole area at the time of FIG. The horizontal axis represents the area of the contact hole, and the vertical axis represents the count ratio. The peaks P2, P3, and P4 in FIG.
The relative intensity at 2, S3, and S4 (the relative intensity when the peak P1 of the energy S1 is 1.00 (count ratio in the figure)). It is clear from the curve of FIG. 3 that the relationship between the contact hole area and the characteristic X-ray intensity ratio (relative intensity) can be quantified. In FIG. 3, Xs represents an area when the contact hole 44 is completely opened.
c represents an opening area of the contact hole 44 which is regarded as a permissible limit at which there is no problem in the function of the element (if it is larger than Xc, it represents an opening area for which the shape of the contact hole 44 is determined to be acceptable).

As described above, the upper A layer 41 and the lower B layer 42 appearing when the contact hole 44 is opened.
The relative intensity ratio of the characteristic X-ray is measured, and on a curve as shown in FIG. 3, when the contact hole area is larger than a preset contact hole area Xc, the shape of the contact hole 44 is inspected as acceptable. Can be inspected as failed.

FIG. 4 is an explanatory view (part 4) of the present invention. This shows a secondary electron image generated by scanning an electron beam from the upper A layer 41 of FIG. 1A, collecting secondary electrons emitted at that time, and modulating the intensity thereof. here,
The solid line represents a secondary electron image of the edge of the contact hole 44 on the surface of the A layer 41. The dotted line represents a circular region including the edge of the contact hole 44 of the secondary electron image on the surface of the A layer 41.

(1) Here, only the inside of the edge of the contact hole 44 of the secondary electron image on the surface of the A layer 41 in FIG. 4 is scanned with an electron beam and the characteristic X emitted at that time is scanned. The extracted characteristic X of the line (or the position inside the edge)
The area (diameter) of the contact hole 44 may be determined based on the line (line), and the pass / fail may be checked. For example, when the count ratio of the peak P2 of the energy S2 on the curve shown in FIG. 3 is equal to or greater than Xc, the area of the opening of the contact hole 44 is equal to or greater than a specified value, and the inspection is performed as pass.

(2) A layer 4 indicated by a solid line in FIG.
The electron beam is scanned only at a portion such as a predetermined circle including the edge of the contact hole 44 of the secondary electron image of the surface of the surface 1 to extract the characteristic X-ray emitted at that time (or to extract the position inside the edge). Based on the characteristic X-ray), the area (diameter) of the contact hole 44 may be determined, and the pass / fail may be checked. For example, when the count ratio of the peaks P2, P3, P4 of the energies S2, S3, S4 on the curve of FIG.
The area of the opening of No. 4 is equal to or more than the specified value, and it is judged as pass.

(3) In addition, the characteristic X is divided into the inside of the solid line (contact hole 44) and the outside
Based on the line, the area (diameter) of the contact hole 44
May be obtained, and a pass / fail check may be performed. For example, when the count ratio of the peaks P2, P3, and P4 of the energies S2, S3, and S4 on the curve of FIG. 3 described above is each equal to or greater than Xc, the area of the opening of the contact hole 44 is equal to or greater than a specified value. I do.

The description has been given using the secondary electron image. Similarly, a reflected electron image (reflected electron whose luminance is modulated by irradiating the electron beams 45 and 45 'and detecting the reflected electron beam at that time) Image) or absorption electron image (electron beam 45,
Inspection can be performed by using an electron beam 45 ′ irradiated, and detecting an electron beam absorbed by the wafer at that time, and using an intensity-modulated absorbed electron image).

FIG. 5 shows a system configuration diagram of the present invention.
In FIG. 5, an electron gun 2 generates an electron beam. The lens 3 focuses the electron beam generated from the electron gun 2.

The aperture 4 cuts off unnecessary off-axis portions of the electron beam focused by the lens system 3. The beam alignment system 5 adjusts the axis of the electron beam focused by the lens 4 to a lens system (objective lens system) 7.
The axis is aligned with the axis.

The beam scanning system 6 scans the electron beam narrowly focused on the wafer 9 in the X and Y directions. The lens system 7 narrows the electron beam focused by the lens system 3 onto the wafer 9, and is usually
This is called an objective lens.

The secondary electron detector 8 collects and detects secondary electrons emitted from the wafer 9. Wafer 9
Is an object to be scanned by irradiation with an electron beam, and is a sample to be inspected.

The wafer holder 10 is a holder for holding the wafer 9. The sample moving stage 11 is a mechanism for moving the wafer holder 10 in the X direction and the Y direction.

X-rays 21 are characteristic X-rays emitted when the wafer 9 is irradiated with an electron beam. X-ray detector 22
Is for detecting characteristic X-rays emitted from the wafer 9. Regarding the signal detected by the X-ray detector 22,
Energy analysis is performed to count peaks (intensities) Pi for each energy (wavelength) Si.
In order to improve the S / N ratio, the device is usually used after being cooled by the cooler 23.

The power supply 30 includes the electron gun 2, the lens systems 3, 7,
A predetermined power supply is supplied to the beam alignment system 5 and the like, and a finely controlled power supply is supplied.

The deflection power supply 31 supplies power of a predetermined signal for beam scanning to the beam scanning systems 6, 6 '. The signal image system 32 amplifies a signal from the secondary electron detector 8 or the like to display a scanned image, or stores an image and reproduces and displays the image when necessary.

The calculation processing system 33 counts the pulse signals from the X-ray detector 22 and stores them as spectrum data. The data processing system 34 performs various calculations, noise removal, graphing, and the like on the stored data as necessary.

The display device 35 displays a secondary electron image, a characteristic X-ray image, and the like. Next, the operation of the configuration of FIG. 5 will be described. The electron beam emitted from the electron gun 2 is converged by the lens system 3 and irradiates the wafer 9 by being narrowed down by the lens system 7, and is scanned in the X and Y directions by the beam scanning systems 6 and 6 ′. Secondary electrons emitted from the surface of the wafer 9 irradiated with the electron beam are displayed as a secondary electron image on a display device 35 which is collected and amplified by the secondary electron detector 8. The characteristic X-rays emitted from the wafer 9 are detected by the X-ray detector 22 and analyzed for energy, and the area (diameter) of the contact hole 44 is equal to or larger than the specified value Xc as described above with reference to FIGS. Is determined to be acceptable when?, And rejected when the following is true.

[0048]

As described above, according to the present invention,
Exceeding the limit of inspection of holes with a large aspect ratio by secondary electron image or backscattered electron image by SEM, the upper layer (A
Based on the characteristic X-rays of the layer 41) and the lower layer (B layer 42), the area or diameter of an extremely small fine hole (for example, a fine hole having a diameter of 0.2 μm and an aspect ratio of about 5 or more) opened in the upper layer is quantitatively determined. It becomes possible to measure at once. Thus, the conventional inspection using images such as a secondary electron image and an optical image requires observation at a high magnification, and thus damage to the sample is inevitable. The area (diameter) of the opening can be inspected based on the line.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram (part 1) of the present invention.

FIG. 2 is an explanatory view (No. 2) of the present invention.

FIG. 3 is an explanatory view (No. 3) of the present invention.

FIG. 4 is an explanatory view (No. 4) of the present invention.

FIG. 5 is a system configuration diagram of the present invention.

[Explanation of symbols]

 2: electron gun 8: secondary electron detector 9: wafer 22: X-ray detector 41: A layer (upper layer) 42: B layer (lower layer) 44: contact hole 45, 45 ': electron beam 46, 46': Characteristic X-ray

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F067 AA22 AA57 BB05 BB16 CC17 HH06 JJ03 JJ05 KK02 KK04 KK06 KK08 LL15 RR01 UU02 5C033 PP05 UU04 UU05 UU08

Claims (4)

[Claims] An inspection apparatus for inspecting one or more openings from an upper layer to a lower layer on a substrate to be inspected, wherein an electron beam is formed on the substrate to be inspected in which one or more openings are formed from an upper layer to a lower layer. Means for irradiating with an electron beam; an X-ray detector for detecting X-rays emitted when irradiated with the electron beam; means for calculating an X-ray spectrum based on a signal detected by the X-ray detection; Means for calculating the area or diameter of the one or more openings based on the calculated X-ray spectrum and the X-ray spectrum emitted from the upper layer and the X-ray spectrum emitted from the lower layer. An inspection device characterized by comprising: 2. An X-ray emitted from only one or a plurality of openings or a predetermined range including the openings on the surface of the upper layer, and an X-ray spectrum of the detected X-rays is obtained. 2. The inspection apparatus according to claim 1, wherein an area or a diameter of said one or a plurality of openings is calculated based on an X-ray spectrum emitted from the substrate and an X-ray spectrum emitted from said lower layer. . 3. A secondary electron image, a reflected electron image or an absorbed electron image formed based on secondary electrons, reflected electrons or absorbed electrons emitted by scanning the substrate under inspection with the electron beam. X-rays emitted from the one or more openings or a predetermined area including the openings are detected, and an X-ray spectrum of the detected X-rays is determined to obtain X-rays emitted from the upper layer. 2. The inspection apparatus according to claim 1, wherein an area or a diameter of the one or more openings is calculated based on a spectrum and an X-ray spectrum emitted from the lower layer. 4. A means for irradiating an inspected substrate having one or a plurality of openings from an upper layer to a lower layer with an electron beam, and an X-ray for detecting X-rays emitted when irradiated with the electron beam. Means for controlling a detector; means for calculating an X-ray spectrum based on the detected signal; and for the calculated X-ray spectrum, an X-ray spectrum emitted from the upper layer and an X-ray emitted from the lower layer. A computer-readable recording medium in which a program that functions as means for calculating the area or diameter of the one or more openings based on the line spectrum is recorded.