JPH0690156B2 - Fine structure measurement method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fine structure measuring method for accurately and nondestructively measuring a fine structure in a solid sample, particularly a minute composition change formed in a semiconductor sample. It is a thing.

[Prior Art] Conventionally, as a technique for observing a fine structure in a solid sample such as a semiconductor sample, a method of observing a transmission electron image of a sample cross section by a transmission electron microscope and a simpler scanning electron microscope (SE
M) There was a method of observing a secondary electron image with a device. The latter method by the SEM device is the intensity distribution of low energy electrons of about 0 to 50 eV (electron volt) among the secondary electrons emitted from the surface of the solid sample when the focused incident electron beam is applied to the solid sample. To observe. Figures 12 (a) and 12 (b) show the results of Al
_This is a measurement example of observing a cross section of a sample in which the composition x of _X Ga _1-X As is slightly changed, and FIG. 13 shows a period of 300 nm and a depth of ~ 3.
This is an example of observing a GaAs surface with a groove of nm by a conventional secondary electron image.

[Problems to be Solved by the Invention] However, the above-mentioned conventional methods for observing a fine structure have the following problems to be solved.

(1) In the method of observing a transmission electron image with a transmission electron microscope, although it has a very high spatial resolution, sufficient contrast cannot be obtained for a fine structure related to composition, and it is difficult to prepare a sample to be measured. It was a complete destructive inspection, and was not suitable for observing characteristics such as fine structure over a wide area.

(2) In the method of observing a secondary electron image by a scanning electron microscope (SEM) device, as shown in the conventional secondary electron intensity distribution diagram (a) of FIGS. 12 (a) and 12 (b), ) A large contrast is not obtained with respect to the composition change of the sample, but rather, as shown in the conventional secondary electron intensity distribution diagram for the spatial structure such as the unevenness of the sample surface in FIG. It is configured to be sensitive to slight potential changes on the surface, and since it uses low-energy electrons or secondary electrons, the secondary electrons have a depth within about 20 Å of the surface of the solid sample to be measured. It was only emitted from the sample, and only information near the sample surface could be obtained. Therefore, it is impossible to detect minute composition changes of the solid sample to be measured without being affected by the unevenness of the sample surface from the contrast of the secondary electron image. When it was attempted to observe from the deep region to the deep region, the etching and the observation of the secondary electron image were inevitably repeated, and the sample had to be destroyed.

Actual SEM devices often have a function of observing relatively high-energy electrons (referred to as backscattered electrons) emitted from the sample, but it has been considered that the measurement by these backscattered electrons has a poor spatial resolution. It is not used for observing the structure of 1 μm or less, especially for observing the fine structure of a semiconductor sample. Therefore, no attempt has been made to accurately determine the composition or composition distribution of the semiconductor sample based on the intensity distribution of the reflected electrons. Didn't.

The present invention was devised in order to solve the above-mentioned problems, and it is non-destructive, precisely and three-dimensionally, for a fine structure relating to the composition in a solid sample, particularly for a minute composition change formed in a semiconductor sample. It is an object of the present invention to provide a fine structure measuring method capable of measuring.

[Means for Solving the Problems] The structure of the fine structure measuring method of the present invention for achieving the above object is to irradiate a solid sample to be measured composed of a compound or a mixture with a finely focused high-energy incident electron beam. During the irradiation sweep, the intensities of the electrons reflected from the solid sample to be measured at the time of this irradiation sweep are equal to or almost equal to the energy of the incident electron beam are measured, and the measurement result is used to calculate the composition accurately. It is characterized in that the composition of the solid sample to be measured or the distribution of minute composition changes existing in the solid sample to be measured are evaluated by evaluation based on the measurement result of the solid sample known in the above.

[Operation] According to the present invention, among the electrons emitted from the sample to be measured when irradiated with a high-energy convergent incident electron beam, the electrons equal to or substantially equal to the high energy are affected by the unevenness of the surface of the sample to be measured. Instead, focusing on the fact that the composition at that position is reflected with a significant difference from the deeper position, the intensity of the reflected high-energy electrons is selectively measured, and the composition can be evaluated and determined. In addition, since the depth of emitted high-energy reflected electrons changes depending on the energy of the incident electron beam, it is necessary to nondestructively evaluate and determine the composition distribution in the depth direction or the three-dimensional composition distribution. To enable.

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

1 (a) and 1 (b) are diagrams showing a schematic configuration example of an apparatus for carrying out the method of the present invention, wherein (a) is a side view,
(B) is a plan view. An incident electron 1 is an incident electron with energy Vi that is focused in a spot shape by an electron lens (not shown) or the like and can be swept by a deflection electrode, and is irradiated and swept onto the measured solid sample 2. The sample 2 to be measured is rotatably supported so that the incident angle of the incident electron beam 1 can be changed.
Reference numeral 3 denotes a backscattered electron detector arranged on the circumference so that backscattered electrons at various angles can be detected. In order to prevent information such as irregularities on the surface of the sample 2 from entering the backscattered electron detector 3 due to the influence of the secondary electrons, the secondary electrons are collected in the secondary electron detector 4 by a weak electric field, while the backscattered electron detector is collected. Three
In front of the shield net 5, a voltage of 0.5 to 0.9 × Vi is applied to the shield net 5 so that the secondary electrons of weak energy are reflected by the shield net 5, and the backscattered electron detector 3 receives incident electrons. Almost the same as the beam (0.8 to 0.9 x Vi in the example of Fig. 1)
Only the backscattered electrons of the above energy are detected. Reference numeral 6 denotes an electronic computer, which has a memory to record the measurement data and stores the measurement result of the sample whose composition is known in advance and the composition of which is previously known. Then, data processing for evaluating the composition and composition distribution in the fine structure is performed. Even if the backscattered electron detector 3 is configured to be movable on the circumference, the same effect can be obtained.

With such a configuration, the energy and angle of the incident electrons were changed, and multiple data were measured by changing the average depth at which the electrons were reflected. By analyzing these data, the composition distribution was accurately evaluated three-dimensionally. can do.

It is ideal to evaluate the energy change and the angle change of the incident electrons by configuring the apparatus as shown in FIG. 1, for example, to evaluate the three-dimensional composition distribution. ,
As mentioned above, there is a need for multiple detectors or moveable detectors to change the angle. Further, the change in incident electron energy may be accompanied by a change in focus condition due to an electron lens or the like.

FIG. 2 is a diagram showing another schematic configuration example of an apparatus for carrying out the method of the present invention. While the shield network in the device example of FIG. 1 is mainly used to shield secondary electrons, this device device positively utilizes this to protect only a certain energy component of the reflected electrons. The intensity data can be detected. In this device example, the accuracy is lower than that of the configuration shown in FIG. 1, but the composition distribution can be evaluated more easily. 1 is the incident electron beam with energy Vi,
2 is a solid sample to be measured, 3 is a reflection detector, 5 is bias Vb
A shield net to which a voltage in which the _AC component V _AC is superimposed is applied, 7 is the AC component V _AC detected by the reflection detector 5.
By detecting the AC component corresponding to the above with a lock-in system, the reflected electron intensity with an energy of ΔV = Vi-Vb is measured, and the same data processing as in the apparatus example of FIG. 1 is performed on this measurement data. A data processing device. In this device example, the reflected electron intensity of the incident electron energy Vi can be evaluated with higher selectivity. Since the reflected electrons have a higher energy as they are reflected from the surface of the sample 2 at a shallower position, the depth of the sample 2 at which the reflected electrons are reflected can be evaluated from the energy of the reflected electrons. If the backscattered electron intensity of a specific energy Vi can be measured with high selectivity as in this device example, the composition distribution at a specific depth can be evaluated nondestructively. This device example and first
By using a configuration in which the apparatus examples shown in the figure are combined, the accuracy of composition distribution observation, particularly the accuracy of three-dimensional observation, can be further improved.

Next, an example of a method for measuring a fine structure using the apparatus configured as described above will be described.

3 (a) and 3 (b) are graphs showing the backscattered electron intensity of the sample to be measured measured by this example. The image A based on the intensity of the reflected electrons is a finely focused incident electron beam with an energy (for example, 10 KeV) of several KeV to several tens KeV,
The semiconductor sample 2 made of l, gallium Ga, and arsenic As is scanned in the direction B (direction on the cross section) to perform irradiation sweep (b), and among the electrons reflected from the solid sample 2 to be measured at this time. It is obtained by measuring the intensity of backscattered electrons which is almost the same as the incident electron energy (a). Sample 2 in the figure is Al _X Ga
_It shows a cross section in which x of _1-X As is gradually changed and crystal is grown, and the thickness of each layer is 0.1 μm. Further, the backscattered electron intensity measured in the figure is shown with the backscattered electron intensity of GaAs as a reference (= 1) (the same applies hereinafter unless otherwise specified). Compared with the secondary electron image of the same sample already observed in Fig. 12, the contrast with respect to the composition was significantly improved, and the composition of Al _0.03 Ga _0.97 As was distinguished from GaAs. It can be seen that a linearly monotonically changing contrast is obtained.

FIG. 4 is a standard backscattered electron intensity distribution chart showing changes in backscattered electron intensity due to Al composition with GaAs as a reference. The backscattered electron intensity distribution map of the above criteria is GaAs or AlAs or Al _X G
It can be obtained by measuring the backscattered electron intensity with a sample of known composition such as a1 _-X , As. In this example, after measuring the backscattered electron intensity in a sample with a known composition above to obtain the standard backscattered electron intensity distribution data, the composition to be measured whose composition adjacent to the sample is unknown is measured. By measuring, the measurement data is evaluated based on the above-referenced backscattered electron intensity distribution, and the Al composition distribution is evaluated and determined.

The operation of the embodiment configured as described above will be described. FIGS. 5 (a) and 5 (b) are examples in which the composition distribution in a sample in which the composition was periodically changed was measured by the measuring method of the above-described example. (A) is the actually obtained backscattered electron intensity distribution, and (b) shows the profile of the Al content obtained by converting it using the data of the backscattered electron intensity distribution map of the standard of FIG. It is a figure. As is clear from the figure, the Al composition distribution in the sample can be precisely measured with an accuracy of Al composition of 0.03 or less.

FIG. 6 is a diagram showing a backscattered electron image obtained by measuring a sample having unevenness on the surface but no change in composition as in the case of FIG. 13 in this example. It can be seen that, unlike the conventional secondary electron image, the backscattered electron image of this example does not show a striped pattern corresponding to minute irregularities on the surface of the sample.
As is clear from this result, the method of measuring the composition distribution by the reflected electrons of the present example has an effect that it is hardly affected by the minute irregularities on the surface of the sample and the surface condition.

FIGS. 7A and 7B show the spatial resolution of this embodiment as Ga
It is a backscattered electron intensity distribution diagram checked using a superlattice of As (8 nm) -AlAs (8 nm). It has been thought that the conventional backscattered electron measurement has poor spatial resolution, but it is clear from this figure that 8 nm fine structures can be sufficiently identified. This is
It is considered that the incident electrons penetrate deep into the sample, but a large amount of electrons with sufficient energy are reflected, when the electron of 10 KeV is incident, it is limited to the region within the depth of 30 nm at most.

The above results show that the method for measuring the fine structure according to the present embodiment,
The spatial resolution is about 10 nm or less, and the composition resolution is 0.03 or less in terms of Al composition, which is a significant improvement over the conventional method.

8 (a), (b), (c), (d) and (e) are Al
The reflected electron intensity is shown when the incident electron beam is scanned for a sample having a GaAs structure embedded in _0.5 Ga _0.5 As by changing the incident electron energy Vi, the incident angle θ ₀ , and the reflected electron measuring direction θ b. It is a figure. FIG. 9 is a diagram showing the above measurement conditions. FIG. 10 is an embedded structure diagram assumed by the measurement. The profile of the intensity of the reflected electrons in the above changes considerably depending on the incident electron energy Vi, the incident angle θ ₀ , and the measurement direction θb of the reflected electrons, and if these data are combined to assume a three-dimensional composition distribution,
As shown in Fig. 10, a three-dimensional fine structure can be understood.

FIGS. 11 (a) and 11 (b) show a GaAs well with a thickness of 6 nm at a depth of 30 nm (both sides are sandwiched by Al _0.5 Ga _0.5 As) by a focused ion beam scan. 2 is a backscattered electron image obtained by observing backscattered electrons in a pattern in which a mixed crystal is formed at a period of 300 nm in this example. When the incident electron energy is 10 KeV as shown in (a), reflected electrons are obtained almost from 30 nm on the surface of the sample, so that the average composition change of the mixed crystal part and the non-mixed part becomes large, and the mixed crystal occurs. The region with a width of about 80 nm clearly appears as a bright line, but when the energy of the incident electron is increased to 15 KeV as shown in (b), the region where the reflected electron is obtained expands in the depth direction, and the average composition This indicates that the change is rather reduced and the region where mixed crystallization occurs is thin. This result shows that in the backscattered electron image, information in the depth direction can be obtained nondestructively by changing the incident energy.

The present invention can be applied as a field of application to non-destructive evaluation of semiconductor structures that are becoming more and more miniaturized in the future, for example, embedded structures formed by ion implantation or the like. Particularly, it can be applied to easily evaluate the uniformity of the structure over a wide area. In addition to semiconductors, it can be applied to the evaluation of sintered powder containing many grains.
As described above, the present invention can be variously applied and various embodiments can be taken according to the gist thereof.

[Effects of the Invention] As is clear from the above description, according to the fine structure measuring method of the present invention, the composition or composition change in the solid sample is determined based on the backscattered electron intensity distribution and the backscattered electron intensity distribution of the reference sample. There is an advantage that the evaluation can be performed easily over a wide range without being affected by the unevenness of the sample surface, easily and with considerably good resolution.
Further, the microstructure in the depth direction of the sample can be measured nondestructively, which has an advantage of enabling three-dimensional measurement.

[Brief description of drawings]

1 (a) and 1 (b) are diagrams showing a configuration example of an apparatus for carrying out the measuring method of the present invention, FIG. 2 is a diagram showing a configuration example of another apparatus, and FIG. 3 (a). , (B) is a backscattered electron intensity distribution chart of a sample showing a measurement example by the measurement method of the present embodiment, FIG. 4 is a standard backscattered electron intensity distribution chart, and FIG. 5 is (a),
(B) is a diagram showing a measurement example of the present embodiment for explaining the operation of the present invention, FIG. 6 is a diagram showing a measurement example of the present embodiment, which corresponds to the conventional example of FIG. 13, and FIG. FIGS. 8A, 8B, 8C, 8D, and 8D show the backscattered electron intensity distribution chart in which the spatial resolution of this embodiment is checked using a superlattice.
(E) is a diagram showing a three-dimensional measurement example for a sample having a buried structure, FIG. 9 is an explanatory diagram of the measurement conditions of FIG. 8,
FIG. 10 is a diagram showing a buried structure assumed from the measurement example of FIG. 8, and FIGS. 11 (a) and 11 (b) are diagrams showing backscattered electron images when the incident electron energy is changed, and FIG. FIGS. (A), (b) and FIG. 13 are diagrams showing conventional secondary electron intensity distributions. 1 ... Incident electron beam, 2 ... Solid sample to be measured, 3 ... Reflected electron detector, 4 ... Secondary electron detector, 5 ... Shield net, 6 ... Electronic calculator.

Claims (1)

[Claims] 1. A finely focused high-energy incident electron beam is irradiated and swept onto a measured solid sample composed of a compound or mixture, and during the irradiation sweep, the energy of electrons reflected from the measured solid sample is The electron intensity equal to or almost equal to the incident electron beam energy is measured, and the measurement result is evaluated based on the measurement result of the solid sample whose composition is known in advance. Alternatively, a microstructure measuring method characterized by evaluating the distribution of minute composition changes existing in the measured solid sample.