JP2548834B2 - Electron beam dimension measuring device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an electron beam dimension measuring apparatus for measuring the line width and the like of a fine pattern formed on a semiconductor wafer, and more particularly to improving the accuracy thereof. .

[Conventional technology]

FIG. 2 (a) is a schematic diagram showing a conventional electron beam size measuring device disclosed in, for example, Japanese Patent Publication No. 58-24726, in which 1 is an electron beam generator and 2 is an electron beam focusing device. A lens, 3 is a deflection coil or electrode, and 4 is an electron beam. Further, 5 is a sample stage, 6 is a sample mounted on the sample stage 5, 7 is signals such as backscattered electrons, secondary electrons, and X-rays generated by the electron beam 4, 8 is a detector of the signal 7, and 9 is It is an amplifier of the signal detected by the detector 8. Ten
Is a scanning signal generator for scanning the electron beam 4 on the sample 6 by deflecting the electron beam 4 by the deflector 3.

Next, referring to FIGS. 2B to 2D, the operation principle of this conventional technique will be described. FIG. 2B shows a cross section of a scene where the electron beam 4 is incident on the sample 6. Sample 6
In order to measure the line width of the pattern 11 formed on the electron beam 4, the electron beam 4 is scanned as indicated by 12. At this time, when the generated signal is displayed according to the scanning signal, a waveform as shown in FIG. 2 (c) is obtained. The waveform signal (c) is subjected to edge detection processing such as threshold processing and maximum inclination processing to determine the pattern edge and the line width. When this scanning 12 is two-dimensionally performed on the pattern and the signal 7 is two-dimensionally displayed, a pattern image 15 as if the pattern was seen from the beam incident direction is shown in the scanning region 13 as shown in FIG. Can be seen in. The line width 14 is determined by performing similar edge detection processing from this two-dimensional pattern signal image. The reason why the electron beam 4 is scanned in two dimensions instead of one dimension is that
This is because if the edges of the pattern have irregularities due to processing, it is possible to obtain the results of averaging these and to improve the accuracy of length measurement reproduction. This two-dimensional scanning signal is to be generated by the scanning signal generator 10 of FIG. 2 (a), and the scanning area is the rectangular area 13 shown in FIG. 2 (d).

[Problems to be Solved by the Invention]

In the conventional apparatus, the sample stage 5 is positioned perpendicular to the incident direction of the electron beam 4, and the pattern 11 to be measured shown in FIG.
There is an advantage that an image as shown in FIG. 7D can be obtained and the pattern to be measured can be measured correctly. However, in recent years, as the pattern formed on the semiconductor wafer becomes finer, the measurement width becomes smaller, and high precision measurement is required. Further, not only the pattern width but also the pattern film thickness tends to be thin, and the signal intensity is also small, which tends to deteriorate the measurement accuracy. For this reason, it is necessary to have a signal strength higher than that, and it has become difficult to perform measurement with a conventional device.

The present invention has been made in order to solve the above problems, and an electron beam capable of increasing the signal intensity of reflected electrons, secondary electrons, X-rays, etc. from a sample, and performing highly accurate length measurement. The purpose is to obtain a dimension measuring device.

A further object of the present invention is to obtain an electron beam dimension measuring device capable of performing highly accurate length measurement by irradiating a tilted sample with a rectangular electron beam.

[Means for solving the problem]

An electron beam size measuring apparatus according to a first aspect of the present invention increases a signal emission efficiency of reflected electrons, secondary electrons, X-rays, etc. by inclining a sample stage on which a sample is placed with respect to an incident axis of a focused electron beam. The signal strength of the sample image is increased to measure the length.

Furthermore, in the second invention, since the sample is tilted,
A deflection signal is generated to correct the trapezoidal change in the rectangular area of the electron beam to be scanned on the sample.

[Action]

In the first aspect, by tilting the sample, signals such as backscattered electrons, secondary electrons, and X-rays are increased, and the signal-to-noise ratio of the pattern image on the sample is improved. As a result,
The visibility of the pattern is improved, and the edges of the pattern are easily recognized.

In the second aspect, the deflection signal is corrected by the deflection signal generation circuit, so that the tilted sample is correctly irradiated with the electron beam in a rectangular shape. As a result, more accurate length measurement can be performed.

〔Example〕

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

In FIG. 1A, 1 is an electron beam generation source, 2 is an electron beam focusing lens, 3 is a deflection coil or electrode, and 4 is
Indicates an electron beam. Further, 5 is a sample stage, 6 is a semiconductor wafer mounted on the sample stage 5, 17 is a mechanism for rotating the sample stage, 7 is a signal such as backscattered electrons, secondary electrons, X-rays generated by the electron beam 4, Reference numeral 8 is a detector for the signal 7, 9 is an amplifier for the signal detected by the detector 8, and 10 is a scanning signal for deflecting the electron beam 4 by the deflector 3 to scan the electron beam on the sample 6. Further, in FIG. 1 (b), 4 is an electron beam incident on the sample, 6 is an inclined sample, and 7 is signals such as backscattered electrons, secondary electrons, and X-rays generated by the electron beam 4. Further, FIG. 1 (c) is a view showing an inclined pattern image obtained by two-dimensionally scanning a sample, in which 13 is a scanning region, 14 is a pattern line width, 15 is a pattern, and 16 is another. The pattern line width in the direction is shown.

Next, the operating principle of the first invention will be described. First
FIG. 1 (b) is an enlarged view of the sample portion of FIG. (A). However, when the sample of FIG. 1 (b) is tilted and the tilt angle of the sample is θ, the signal amount is 1 / It is well known that the ratio of cos θ becomes large (for example, L. Reimer “Scanni
ng Electron Microscopy ", 1985 p.145, etc.), which has the effect of improving the visibility of the pattern image. The pattern image thus obtained becomes an inclined image as shown in FIG. Compared with Fig. 2 (d), the image has more contrast.
Of the patterns arranged in both Y directions, FIG. 1 (c)
The pattern width as shown by 14 of FIG. 1 can be measured by the conventional method, but the pattern width shown by 16 cannot be measured correctly. Therefore, the stage rotating mechanism of FIG. 1 is used. Then, the length can be measured by rotating the sample pattern by 90 ° or 270 °.

According to such an embodiment of the first invention, the visibility of the pattern image can be improved by inclining the sample stage with respect to the electron beam. Further, on this, among the patterns arranged in both the X and Y directions like a semiconductor, the pattern width as shown by 14 in FIG. 1 (c) is
The length can be measured by the conventional method, and the pattern width indicated by 16 is shown in Fig. 1.
By rotating the sample pattern by 90 ° or 270 ° by using the stage rotating mechanism of 17, it is possible to measure the pattern on the sample with good contrast.

Next, an embodiment of the second invention will be described with reference to FIGS.

FIG. 1 (d) is a diagram showing how the scanning area of the electron beam changes when the sample is tilted, and FIG. 1 (e) shows an example of a deflection signal generating circuit for correcting it. First
FIG. 6F is a diagram showing that the scanning area on the inclined surface corrected by the deflection signal generating circuit is correctly scanning the rectangular area.

In FIG. 1 (d), reference numeral 20 denotes a region which is correctly scanned in a rectangular shape when the sample is arranged perpendicular to the electron beam. Reference numeral 22 is a sample tilt angle θ, 21 is a scanning region of an electron beam when the sample is tilted at a tilt angle θ, 23D is a working distance for deflection of the electron beam, and 24 is a deflection working point.
Further, in FIG. 1 (e), 30 is a rectangular scanning signal generating circuit, 31 is its scanning area, and 32 is A generation circuit, 33 is a sin θ generation circuit, 34 is a cos θ generation circuit, 35 is a multiplier, 36 is a divider, and 37 is a corrected trapezoidal scanning area. Further, in FIG. 1 (f), 20 is a scanning area on the sample vertical plane generated in the circuit as shown in FIG. 1 (e), and 21 is a sample plane tilted at an inclination angle θ of 22, which is correctly rectangular. Scanned area, 23 is working distance of electron beam deflection, 24
Indicates the deflection operating point.

Next, the operating principle of the second invention will be described. In the first invention, the signal intensity was improved and the visibility of the pattern image could be improved, but the image in the two-dimensional scanning region looks like a projection as shown in FIG. 1 (c), Depending on the part to be measured, the length cannot be measured correctly. As shown in FIG. 1 (d), this is an inverted trapezoidal shape like 21 on the inclined surface if a deflection signal is generated so as to correctly scan a rectangle when the sample is placed perpendicular to the electron beam. Area will be scanned. If it is displayed two-dimensionally, a projected image will be seen as shown in FIG. 1 (c).

Therefore, in FIG. 1 (d), the coordinates (X,
If the relationship between Y) and the coordinates (x, y) on the inclined surface projected on the inclined surface is calculated correctly, Met. Here, D represents the working distance, and θ represents the tilt angle.

In order to correctly scan the (x, y) point on the inclined surface into a rectangle, a rectangular scan signal is given to (x, y) and the corrected deflection is calculated while calculating (X, Y) according to equation (1). It is possible if a signal is given. As an example thereof, the circuit of FIG. 1 (e) is shown. A rectangular scan signal (x, y) is given at 30. This may be a conventional deflection scanning circuit. Then, from the y signal, the working distance D, and the data of the inclination angle θ, Through the circuit 32 that calculates The X signal is output through the divider 36 which divides by. Also, after multiplying the y signal by cos θ by the multiplier 35, Then, the Y signal is output. This gives 3 for X and Y.
A signal for scanning a trapezoidal shape as shown in 7 is generated.

When the trapezoidal deflection signal of FIG. 1E is applied to the vertical surface 20 for the electron beam of FIG. 1F, it can be seen that the inclined surface 21 has a correct rectangular scanning area. Thus, in FIG. 1 (a), if the circuit of the embodiment as shown in FIG. 1 (e) is used for the scanning signal generator shown by 10, the scanning on the inclined surface is made into a correct rectangular shape. When the pattern image is displayed two-dimensionally, the edges of the pattern can be displayed in parallel and the length can be measured correctly.

According to such an embodiment of the second invention, the deformation of the scanning region on the inclined surface caused by the inclination of the sample is
In the figure (a), the scanning signal generator designated by 10
By using the circuit of the embodiment as shown in FIG. (E), the sample on the inclined surface can be scanned in a correct rectangular area, and the edges of the two-dimensional pattern image can be correctly parallel. This has the effect of enabling high precision length measurement.

〔The invention's effect〕

As described above, according to the first aspect of the invention, the sample stage is tilted with respect to the electron beam, and the stage can be rotated so that the pattern in the desired direction can be measured. The length can be measured by contrast, and the desired pattern can be measured correctly.

Further, according to the second aspect of the invention, since the scanning signal generating circuit for correcting the deformation of the scanning region on the inclined surface caused by the inclination of the sample is provided, the scanning signal generating circuit is correct for the sample on the inclined surface. The rectangular area can be scanned, the edges of the two-dimensional pattern image can be taken in parallel, and highly accurate length measurement can be performed.

[Brief description of drawings]

FIG. 1 (a) is a diagram showing an electron beam size measuring apparatus according to an embodiment of the present invention, FIG. 1 (b) is an enlarged view of the vicinity of a sample showing its effect, and FIG. 1 (c) is a tilted sample. The figure which shows the two-dimensional pattern image which is obtained by doing, Figure 1 (d) the figure which explains that the scanning territory in the inclined surface is deformed by inclining the sample, Figure 1 (e) the inclined surface FIG. 1F is a diagram showing a scanning signal generating circuit for correcting the deformation of the scanning region, and FIG. 1F is a diagram showing that the electron beam is corrected and the inclined surface is correctly rectangular-scanned. FIG. 2 (a) is a diagram showing an electron beam dimension measuring device according to a conventional example, FIG. 2 (b) is an enlarged view of the vicinity of a sample to show its principle, and FIG. 2 (c) shows an example of a one-dimensional signal. FIG. 2D is a diagram showing a two-dimensional pattern image in the conventional example. In the figure, 1 is an electron beam generation source, 2 is an electron beam focusing lens, 3 is a deflection coil or electrode, 4 is an electron beam, 5 is a sample stage, 6 is a sample, 7 is a signal, 8 is a detector, and 9 is Amplifier, 10 is a scanning signal generator, 17 is a stage rotating mechanism,
13 is a two-dimensional scanning area, 14 is a measurement line width, 16 is another measurement width,
15 indicates a pattern. The same reference numerals in the drawings indicate the same or corresponding parts.

Claims (2)

(57) [Claims] 1. An electron beam optical system comprising an electron beam generation source, a lens for focusing the electron beam, a deflecting means for deflecting the focused electron beam, a sample stage on which a sample is mounted, The scanning signal generating means for controlling the deflecting means so as to irradiate the pattern on the sample with the electron beam while scanning it two-dimensionally, and the means for detecting the signal generated from the pattern, the two-dimensional pattern signal In the electron beam dimension measuring apparatus that determines the pattern edge from the image and measures the pattern dimension, the sample stage can rotate about the normal line direction of the surface of the portion on which the sample is placed as a rotation axis. At the same time, it can be tilted about the rotation axis in a direction perpendicular to the normal direction, and when measuring the pattern of the mounted sample, the voltage is two-dimensionally scanned. The sagittal line rotates about the normal direction as a rotation axis so that the required width of the pattern can be measured, and the vertical direction is set so that the pattern has a required angle with respect to the incident electron beam. An electron beam dimension measuring device characterized by being inclined as a rotation axis. 2. The scanning signal generating means for applying a scanning signal to the deflecting means sets the coordinates on the tilted sample to (x, y),
If the sample tilt angle is θ and the deflection working distance is D, The electron beam size measuring apparatus according to claim 1, wherein a scanning signal represented by the following is generated and a rectangular scan is performed on an inclined sample.