JP2002151472A - Method and apparatus for measuring side etching amount of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring the side etching amount wherein the side etching amount in a semiconductor device can be measured. SOLUTION: The apparatus for measuring the side etching amount comprises a section 21 for irradiating the surface of a semiconductor device W being etched with laser light from a direction inclining against a direction perpendicular to the surface of the semiconductor device W; a section 23 for scanning the surface of the semiconductor device W with the laser light; a section 22 for measuring the laser light reflected on the surface of the semiconductor device W; and an operating section 24 for measuring the side etching amount in the semiconductor device, by comparing the correlation characteristics of the scanning position of laser light and the quantity of measured laser light, with the correlation characteristics of the scanning position of laser light and the quantity of measured laser light at that time for a preset known side etching amount in the semiconductor device. Side etching amount in the semiconductor device can thereby be measured with high accuracy and a suitable failure analysis of the semiconductor device can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for analyzing a failure of a semiconductor device, and more particularly to a method and an apparatus for measuring a side etching amount in a semiconductor substrate in a dry etching process for the semiconductor substrate.

[0002]

2. Description of the Related Art Recent advances in the field of semiconductor device technology have made the structure of LSIs more complicated, and at the same time, are increasing the number of layers by a multilayer wiring structure and the like. Such LSI
In particular, when performing a failure analysis of a multi-layer LSI,
It is necessary to etch the insulating film in order to specify the failure location in the lower layer. In the etching of such an insulating film, if the aluminum wiring in the upper layer is damaged, it is impossible to reproduce the defect of the LSI, and there is a possibility that a failure location cannot be specified. Therefore, the insulating film is etched without damaging the aluminum wiring. This is very important. Therefore, in such etching, dry etching with high anisotropy is used so as not to etch the insulating film immediately below the aluminum wiring in the upper layer. That is, by dry-etching the insulating film by a self-alignment method using the aluminum wiring in the upper layer, the insulating film in a region other than the aluminum wiring can be etched without etching the aluminum wiring in the upper layer and the insulating film immediately thereunder. Etching is performed to analyze the failure by exposing the underlying aluminum wiring and device electrodes.

However, it is difficult to make the anisotropy 100% even by dry etching, and the insulating film immediately below the upper aluminum wiring is etched in a direction horizontal to the surface of the semiconductor substrate, that is, It is difficult to completely prevent side etching. Therefore, it is required to measure the side etching amount of the insulating film immediately below the aluminum wiring in the upper layer portion and manage the side etching amount so as not to exceed a preset etching amount.

However, a technique for measuring the amount of side etching has not been proposed so far, and it is difficult to satisfy such requirements. As a technique for monitoring the etching amount, for example, Japanese Patent Application Laid-Open No. 62-299032
In Japanese Patent Application Laid-Open Publication No. H11-157, a technique for detecting the depth of the dry etching amount is described, and the surface of a semiconductor substrate is irradiated with laser light from an oblique direction, and the position where the reflected light of the laser light is received is the etching depth. Is used to detect the etching depth. Patent No. 2
Japanese Patent No. 6553017 discloses a technique of irradiating a substrate to be etched with light and measuring an etching depth based on an intensity vibration generated by a change in interference between each reflected light between the substrate surface and the etched surface as the etching proceeds. ing.

[0005]

However, in any of the techniques, it is possible to measure the etching depth in a direction perpendicular to the surface of the semiconductor substrate. Measuring the etching amount is theoretically difficult, and cannot satisfy the above-described requirement of measuring the side etching amount, which is a problem in realizing failure analysis of a semiconductor device.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method and a device for measuring a side etching amount capable of measuring a side etching amount in a semiconductor device.

[0007]

According to the method of measuring the amount of side etching of the present invention, a surface of a semiconductor device is irradiated with laser light from a direction inclined with respect to a direction perpendicular to the surface of the semiconductor device to be etched. At the same time, the laser light is scanned along the surface of the semiconductor substrate, the laser light reflected on the surface of the semiconductor device is measured, and a correlation characteristic between the scanning position of the laser light and the measured light amount at that time is obtained. In addition, the obtained correlation characteristic is compared with a correlation characteristic between a scanning position of a laser beam with respect to a known side etching amount set in advance in the semiconductor device and a measured light amount at that time, thereby obtaining a side etching amount in the semiconductor device. Is calculated.

The side-etching amount measuring apparatus according to the present invention further comprises: means for irradiating the surface of the semiconductor device with laser light from a direction inclined with respect to a direction perpendicular to the surface of the semiconductor device to be etched; A means for scanning the surface of the semiconductor substrate with laser light irradiated along the surface, a means for measuring the laser light reflected on the surface of the semiconductor device, a scanning position of the laser light by the scanning means, The correlation characteristic between the light amount measured by the means for measuring the laser light at that time and the correlation characteristic between the scanning position of the laser light with respect to a known side etching amount in the semiconductor device set in advance and the light measurement amount at that time is calculated. Computing means for measuring the amount of side etching in the semiconductor device by comparison.

Here, in the present invention, the correlation characteristic is obtained based on the measured light amount obtained by irradiating the laser beam from a plurality of angle directions in which the inclined directions are set to different angles, and The side etching amount may be measured based on a correlation characteristic obtained in advance corresponding to each of the angles.

According to the present invention, the amount of side etching in a semiconductor device can be measured with high accuracy. In particular, the amount of side etching in an insulating film immediately below aluminum wiring in a semiconductor device can be measured, and the side etching amount of the semiconductor device can be measured. By managing the etching amount so as not to exceed the preset etching amount, it becomes possible to realize a suitable failure analysis of the semiconductor device.

[0011]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an apparatus for measuring the amount of side etching according to the present invention. The dry etching apparatus 10 includes a chamber 11 and a pair of upper and lower units arranged in the chamber and forming a plasma of a reactive gas. And a gas supply pipe 14 for supplying a reactive gas for etching a semiconductor substrate as an object to be etched, ie, a semiconductor wafer W constituting an LSI, and an exhaust pipe 15 for exhausting the gas. ing. The semiconductor wafer W as the object to be etched is placed on the lower electrode 13 of the electrodes, and at a position on the surface of the semiconductor wafer W in the chamber 11 according to the present invention. The side etching amount measuring device 20 is provided.

The side etching amount measuring device 20 includes:
As shown in FIG. 2, a laser beam irradiator that irradiates a laser beam from a required angle direction with respect to a direction perpendicular to the surface of the semiconductor wafer W and scans the laser beam on the surface of the semiconductor wafer W 21; a laser light metering unit 22 for measuring the amount of the laser light reflected on the surface or the etched surface of the semiconductor wafer W; and the laser beam irradiating unit 21 and the laser light metering unit 22 integrated with the semiconductor wafer. A scanning unit 23 including a moving mechanism for scanning the laser light on the surface of the semiconductor wafer W while moving along the surface of W, and side etching based on the amount of laser light measured by the laser light metering unit 22 And an arithmetic unit 24 for calculating the quantity. Here, the laser beam irradiating unit 21 is configured by a laser diode that emits a laser beam, and the laser beam metering unit 22 is configured by a photodiode. A beam splitter 25 that reflects the laser light reflected along the optical axis of the laser diode 21 in a direction perpendicular to the laser diode 21 is arranged, whereby the photodiode 22 is optically arranged on the same optical axis as the laser diode 21. You. Further, the laser diode 21 and the photodiode 22 are integrally built in a casing 26, and are tilted together with the casing 26 by an angle adjusting mechanism (not shown) to change an angle direction with respect to a direction perpendicular to the surface of the semiconductor wafer W. It is configured such that it can be changed and adjusted to a plurality of different angles. In addition, as will be described later, the arithmetic unit 24 scans the laser diode, that is, the scanning position of the laser light in the laser light irradiation unit 21, and measures the light at the scanning position by the photodiode, that is, the laser light measuring unit 22. The configuration is such that the side etching amount of the semiconductor wafer W is calculated by comparing the correlation characteristic with the laser light amount with a reference correlation characteristic obtained in advance based on a reference side etching amount.

Next, a method of measuring the side etching amount in the side etching amount measuring apparatus will be described. FIGS. 3 and 5 show a cross-sectional state of the semiconductor wafer W as the etching progresses, and a state (a) illustrating a state in which the semiconductor wafer W is scanned while being irradiated with laser light from the laser light irradiation unit 21. FIG. 4B shows a characteristic diagram (b) of the measured light amount of the laser light obtained by measuring the irradiated laser light in the laser light measuring unit 22. In this embodiment, in order to simplify the description, as a structure of the semiconductor wafer W, a lower insulating film 32 is formed on a semiconductor substrate 31, and a lower aluminum wiring 33 is formed thereon in a required pattern. ing. It is also assumed that an upper insulating film 34 is formed thereon, and an upper aluminum wiring 35 is formed thereon in a required pattern.

First, FIG. 3 shows a state in which etching is not performed. As shown in FIG. 3A, a required angle θ1 ( Scanning is performed in one direction from a scanning position t1 to t6 at an angle with respect to a direction perpendicular to the LSI surface (the same applies hereinafter), and the amount of laser light reflected on the surface of the semiconductor wafer W is measured by the laser light measuring unit 22. At this time,
In FIG. 3B, the horizontal axis represents the scanning position, and the vertical axis represents the light intensity,
The light intensity of the laser beam measured by the laser beam meter 22 is shown. Here, the surface of the upper insulating film 34 and the surface of the upper aluminum wiring 35 of the surface of the semiconductor wafer W are substantially flat in the horizontal direction, and the laser light is irradiated at an angle of θ1, so that the laser light is reflected to the laser light measuring unit 22. The light amount of the laser light measured by the above becomes extremely small. At the boundary portion t6 of the upper aluminum wiring 35, a part of the reflected light is
Is the degree of light reception.

Next, FIG. 4A shows a state where the upper insulating film 34 of the semiconductor wafer W has been etched to a substantially intermediate thickness. Similarly to FIG. 3, a laser beam is irradiated at an angle of θ1. Scan while scanning. The laser light metering unit 22 at this time
FIG. 4 (b) shows the characteristics of the light intensity measured by the method described in FIG. In this case, due to the etching of the upper insulating film 34, side etching occurs immediately below the upper aluminum wiring 35, and the side surface of the upper insulating film 34 has a shape that is slightly concave in a horizontal direction due to the side etching. To be
The amount of light reflected toward the optical axis direction of the laser beam irradiating unit 22 at a scanning position slightly later than the scanning position t5 at which the side-etched surface is perpendicular to θ1 at a scanning position at which the laser beam is irradiated. That is, the laser light metering unit 22
, The photometric light intensity measured at the maximum is obtained. Before and after the position near the scanning position t5 where the measured light amount becomes the maximum, the measured light amount of the laser beam gradually increases or decreases from an extremely small state. When the laser beam reaches the scanning position t6 at which the upper aluminum wiring 35 is irradiated with the laser beam, the amount of the laser beam is extremely reduced.

FIG. 5A shows a state where the lower insulating film 32 of the semiconductor wafer W has been etched to a substantially intermediate thickness. Similarly, scanning is performed while irradiating a laser beam at an angle of θ1. FIG. 5B shows the characteristic of the light amount measured by the laser light metering unit 22 at this time. In this case, the upper insulating film 3
4 and the lower insulating film 33, side etching occurs immediately below the upper aluminum wiring 35 and immediately below the lower aluminum wiring 33, respectively. The side etching causes the upper insulating film 34 and the lower insulating film 3 to be etched.
2 has a shape that is slightly concave in a horizontal curved surface, the side-etched surface has a surface region orthogonal to θ1 near the scanning position t2 where the laser beam is irradiated, In each area of the scanning position slightly before the scanning position t5, the light measurement amount measured by the laser light measurement unit 22 becomes the maximum. Here, the scanning position of the upper insulating film 34 at which the light intensity is maximized is a position slightly different from the case of FIG. Then, before and after each of the regions near the scanning positions t2 and t5 where the light intensity is maximum, the light intensity of the laser beam is gradually increased or decreased from an extremely small state. Further, the laser light is applied to the lower aluminum wiring 33,
Alternatively, at the scanning position where the upper aluminum wiring 35 is irradiated, the light amount of the laser light is extremely reduced.

Here, the reason why the scanning position at which the measured light amount at the time of etching shown in FIG. 4 and FIG. 5 becomes maximum is different will be described with reference to FIG. A of FIG. 6A shows a side etching state at the time of etching of FIG. 4, and B shows a side etching state at the time of etching of FIG. As can be seen from the figure, when the side etching progresses, an area of the etching surface orthogonal to the irradiation angle θ1 of the laser light, that is, a state where the irradiated laser light is reflected toward the optical axis direction of the laser light measuring unit 22. It can be seen that the scanning position where the measured light amount of the laser beam is maximized gradually moves toward the scanning position side. FIG. 6B shows a comparison between the measured light amounts of the laser light at that time, and the scanning position at which the maximum measured light amount is different in each side etching state.

Therefore, in the arithmetic unit 24, the semiconductor wafer, that is, the LSI product or the LS
The correlation characteristic between the side etching amount and the scanning position at which the maximum light intensity is obtained for each process I is determined, and the scanning position at which the maximum light intensity is actually determined based on the light intensity measured by the laser light metering unit 22 Is detected, and the scanning position is applied to the correlation characteristic, whereby the amount of side etching can be measured. In addition, as a method of obtaining the above-described correlation characteristics, a semiconductor device having various side etching amounts is formed as a material, and laser light irradiation at an irradiation angle θ1 is performed on each semiconductor device to obtain data of a light measurement amount. Thereafter, the amount of side etching of the semiconductor device can be obtained by a technique such as performing dimension measurement using an optical microscope or the like. Then, at the time of etching with the etching apparatus 10 shown in FIG.
The upper or lower aluminum wirings 33 and 35 are formed by side etching of the upper insulating film 34 or the lower insulating film 32.
If the amount of side etching that may cause damage to the side etching is obtained, and the etching process is terminated before the side etching amount is exceeded, the failure analysis of the LSI can be appropriately performed.

Here, in the above embodiment, the irradiation angle of the laser beam for irradiating the LSI is θ1, but when it is required to measure the etching amount in more detail,
It is preferable to add measurements at different irradiation angles. For example, as shown in FIG. 6, by performing laser beam irradiation and scanning at an irradiation angle θ2 larger than the irradiation angle θ1, a correlation characteristic of a scanning position with respect to an etching amount as shown in FIG. 6C can be obtained. . In this case, the irradiation angle θ2 is θ1
Is different from the case where the area of the etching surface orthogonal to the irradiation angle θ2 of the laser light is the irradiation angle θ1, and accordingly, the scanning position at which the measured light amount of the laser light becomes maximum is also different. Therefore, the calculation unit 24 also determines the irradiation angle θ2 in advance for each LSI product or LSI.
The correlation characteristic between the side etching amount and the scanning position at which the maximum light intensity is measured at each process is determined in advance, and the actual measurement value is applied to the correlation characteristic to obtain the LS.
It becomes possible to measure the side etching amount of I.
Then, using the side etching amounts obtained at the irradiation angles θ1 and θ2, for example, by performing a process such as averaging the two, a more accurate measurement of the side etching amount becomes possible.

In the above embodiment, the reflected laser light is measured by scanning the laser beam with the irradiation angle kept constant. However, the irradiation angle is continuously changed without scanning the laser light. , Measuring the reflected laser light,
The side etching amount may be obtained from the obtained light intensity.

[0021]

As described above, the present invention irradiates a laser beam while scanning it from a direction inclined with respect to a direction perpendicular to the surface of the semiconductor device to be etched, and reflects the laser light on the surface of the semiconductor device. The laser light is measured, and a correlation characteristic between the scanning position of the laser light and the measured light amount at that time is obtained, and the obtained correlation characteristic is converted to a predetermined side etching amount of the laser light with respect to a known side etching amount in the semiconductor device. By performing the measurement by calculating the side etching amount in the semiconductor device by comparing the correlation characteristic between the scanning position and the measured light amount at that time, the side etching amount in the semiconductor device can be measured with high accuracy. In particular, by measuring the side etching amount in the insulating film immediately below the aluminum wiring in the semiconductor device,
By managing the amount of side etching of the semiconductor device so as not to exceed the preset etching amount, it becomes possible to realize a suitable failure analysis of the semiconductor device.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an etching apparatus provided with a side etching amount measuring apparatus of the present invention.

FIG. 2 is a schematic configuration diagram of an apparatus for measuring a side etching amount according to the present invention.

3A and 3B are diagrams illustrating a method of measuring a side etching amount before performing etching, wherein FIG. 3A is a cross-sectional view of an LSI,
(B) is a correlation characteristic diagram between the measured light amount and the scanning position.

4A and 4B are diagrams illustrating a method of measuring a side etching amount in a state where etching is performed to an intermediate position of an upper insulating film, where FIG. 4A is a cross-sectional view of an LSI, and FIG. It is a correlation characteristic figure.

5A and 5B are diagrams illustrating a method of measuring a side etching amount in a state where etching is performed to an intermediate position of a lower insulating film, wherein FIG. 5A is a cross-sectional view of an LSI, and FIG. It is a correlation characteristic figure.

FIG. 6 is a diagram for explaining a difference in the correlation characteristic between the measured light amount and the scanning position according to the degree of progress of the side etching amount, and a difference in the correlation characteristic between the measured light amount and the scanning position due to the difference in the irradiation angle.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Dry etching apparatus 11 Chamber 12, 13 electrode 14 Gas supply pipe 15 Gas exhaust pipe 20 Side etching amount measuring apparatus 21 Laser light irradiation part 22 Laser light measurement part 23 Scanning part 24 Operation part 25 Beam splitter 31 Semiconductor substrate 32 Lower insulating film 33 Lower aluminum wiring 34 Upper insulating film 35 Upper aluminum wiring W Semiconductor wafer (LSI)

Claims (4)

[Claims] 1. A method for irradiating a surface of a semiconductor device with laser light from a direction inclined with respect to a direction perpendicular to a surface of the semiconductor device to be etched, and scanning the laser light along the surface of the semiconductor substrate. Measuring the laser light reflected by the surface of the semiconductor device to obtain a correlation characteristic between the scanning position of the laser light and the measured light amount at that time, and converting the obtained correlation characteristic to a preset semiconductor Calculating a side etching amount in the semiconductor device by comparing a correlation characteristic between a scanning position of the laser beam with respect to a known side etching amount in the device and a measured light amount at that time; Measuring method. 2. The method according to claim 1, wherein the inclination directions are set to different angle directions, and the correlation characteristic is obtained based on a measured light amount obtained by irradiating the laser light from the plurality of angle directions. 2. The method of measuring a side etching amount of a semiconductor device according to claim 1, wherein the side etching amount is measured based on a correlation characteristic obtained in advance for each of them. Means for irradiating the surface of the semiconductor device with laser light from a direction inclined with respect to a direction perpendicular to the surface of the semiconductor device to be etched; A means for scanning along the surface, a means for measuring the laser light reflected on the surface of the semiconductor device, a scanning position of the laser light by the scanning means, and a means for measuring the laser light at that time. The amount of side etching in the semiconductor device is compared with the correlation characteristic between the measured light intensity and the correlation between the scanning position of the laser beam with respect to a predetermined side etching amount in the semiconductor device and a predetermined amount of light measurement at that time. An apparatus for measuring a side etching amount of a semiconductor device, comprising: an arithmetic unit for measuring. 4. The laser beam irradiating unit and the laser beam metering unit are configured to set the angles of the inclined directions of the laser beam irradiating the semiconductor device to different angles, respectively, and the arithmetic unit 4. The semiconductor device according to claim 3, wherein the side etching amount is measured based on a correlation characteristic between a measured light amount and a scanning position obtained in advance corresponding to the different angles. Equipment for measuring the amount of etching.