JPH0363213B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an electronic device, and particularly to a potential distribution measuring device for an electronic device that measures the potential distribution of a semiconductor sample in a non-contact manner using an electron beam.

[Technical background of the invention and its problems]

BACKGROUND ART Recently, research and development has been conducted on a sample potential measuring device that measures the potential of a sample surface without contact by irradiating an electron beam onto a semiconductor sample such as an IC or LSI and detecting secondary electrons emitted from the sample. This device applies the principle that when a drive signal is applied and an electron beam is irradiated onto a sample in an operating state, the secondary electrons emitted from the sample contain information about the potential at the beam irradiation point. Therefore, in the above device, the sample potential can be detected without contact by detecting the secondary electrons emitted from the sample when the sample is irradiated with an electron beam using an appropriate detector.
Furthermore, by pulsing the electron beam and irradiating the sample with the pulsed beam only at a specific phase of the sample motion and detecting secondary electrons, it is also possible to observe the state of signal transmission. Therefore, it is extremely effective for observing high-speed motion of semiconductor samples.

By the way, when a semiconductor sample in an operating state is irradiated with an electron beam, the secondary electrons emitted from the sample not only contain information on the potential at the beam irradiation point, but also information on the composition of the sample at the beam irradiation point. It also contains a mixture of information. For example, if a beam is scanned in the direction of the arrow in the figure without applying a drive signal to a sample having regions 1, 2, and 3 with different compositions as shown in Figure 1a, the detected secondary electron current will be affected by the difference in composition. Therefore, it changes as shown in FIG. This is because the secondary electron emission efficiency differs depending on the underlying composition at the beam irradiation position, and the number of emitted secondary electrons changes. In addition, 4 in the figure
indicates a deflection plate for beam scanning.

Since the number of emitted secondary electrons differs depending on the composition, information regarding the composition must be removed from the detected secondary electron signal in order to accurately measure the potential at the beam irradiation point of a sample in an operating state. . Conventionally, the following procedure has been used to correct level fluctuations in detected secondary electron signals caused by differences in underlying composition. That is, as shown in FIG. 2, first, the application of the drive signal to the sample is stopped, the electron beam is scanned over the sample surface, and the detected secondary electron signals for all pixels in the measurement area are appropriately stored as non-application data 5. Store in the device. Next, while applying a drive signal to the sample, an electron beam is scanned over the sample surface, and the detected secondary electron signals for all pixels in the same measurement area as when obtaining the non-application data 5 are appropriately set as the application data 6. Store it in a suitable storage device. Then, the subtracter 7 extracts the data 5 and 6 from the respective storage devices and calculates the difference between them. Since the applied data 6 includes information regarding the potential and composition, by subtracting the non-applied data 5 which includes only information regarding the composition, the correction data 8 which includes only potential information is obtained.

However, this type of conventional method has the following problems. That is, a cumbersome operation is required to apply a drive signal to the semiconductor sample or to switch it to a non-applied state. Furthermore, it takes about 100 seconds to obtain the applied data 6, depending on the device and the number of pixels, and it takes twice as long to measure the non-applied data 5 and compensate for the composition information.
Unfavorable in terms of measurement efficiency. Furthermore, since the sample is dosed by beam irradiation twice as much as in normal measurement, this is not preferable from the viewpoint of protecting the sample from beam damage.

[Purpose of the invention]

An object of the present invention is to be able to remove information regarding the composition from detected secondary electron signals, and to improve the accuracy of potential measurement of electronic devices, especially semiconductor samples.
Another object of the present invention is to provide a potential distribution measuring device for an electronic device that can minimize beam damage to a sample.

[Summary of the invention]

The gist of the present invention is to create non-applied data (background data) without irradiating an electronic device with an electron beam, and to subtract this background data from the detected secondary electron signal.

That is, the present invention applies a drive signal to an electronic device, for example, a semiconductor sample, scans the sample with an electron beam using a predetermined scanning signal, detects secondary electrons emitted from the sample at this time, and scans the sample. In a sample potential measurement device that measures the potential distribution on a surface,
The pattern data of the element realized on the sample is stored in advance with information on the type of underlayer added to the data, and background data, which is a detected secondary signal when no drive signal is applied to the sample, is stored as the type of underlayer. The irradiation position of the electron beam is detected from the scanning signal of the electron beam, and the type of base formed at the beam irradiation position is determined based on the detected position data and the stored pattern data. Based on the determined background data, the stored background data is selected to determine the background data configured at the beam irradiation position, and the detected secondary electrons are detected while a drive signal is applied to the sample. The background data determined above is subtracted from the signal.

〔Effect of the invention〕

According to the present invention, it is possible to detect the beam irradiation position from the scanning signal of the electron beam, to obtain the background data configured at the beam irradiation position from the detected position data, and to obtain the background data configured at the beam irradiation position from the detected secondary electron signal. By subtracting the ground data, it is possible to automatically correct level fluctuations in the detected secondary electron signal due to differences in underlying composition. Therefore, the potential distribution of the electronic device can be measured with high precision. Further, since it is not necessary to irradiate the electronic device with a beam to obtain background data, it is possible to reduce beam damage to the electronic device.

[Embodiments of the invention]

FIG. 3 is a schematic diagram showing an embodiment of the present invention. 11 in the figure is an electron gun, and this electron gun 11
The electron beam emitted from the beam chopper is pulsed by a beam chopping deflection plate 12 and a chopper driver 13. The pulsed beam is deflected by a beam scanning deflection coil 14 and a deflection driver 15, and is two-dimensionally scanned over a semiconductor sample 16. The sample 16 is placed on a sample stage 17 that is movable in a direction perpendicular to the beam irradiation direction, and a drive signal generator 18 is attached to the sample 16.
A drive signal is applied from

Secondary electrons emitted from the sample 16 by the beam irradiation are detected by a secondary electron detector 19 , and this detected secondary electron signal is amplified via an amplifier 20 and then sent to an A/D converter 21 . Here, in order to increase the SN ratio of the detected secondary electron signal, the secondary electron detector 19 may perform sampling multiple times to obtain one piece of data. An analog integrator may be provided in
The detected secondary electron signal is digitized by the A/D converter 21, and this digital signal is sent to the subtracter 22.

On the other hand, the scanning signal from the deflection driver 15 is supplied to the position calculation section 23. The position calculation unit 23 calculates the position of the beam irradiation point on the sample 16 from the scanning signal and coordinate values in the X and Y directions up to the deflection center in the chip coordinate system inputted from the outside. This situation will be explained with reference to FIG. Fourth
When the chip area P and the deflection area Q have the relationship as shown in the figure with respect to the chip coordinate system shown in the figure, the coordinates (x _c , y _c ) are input from the outside at the center of the deflection area, that is, the deflection center point. Ru. This value is read from, for example, a length measurement system that measures the sample stage position and is input by the operator. The coordinates (x _d , y _d ) are the distance from the deflection center to the pulse beam irradiation point R, and when the deflection driver 15 is composed of, for example, a D/A converter and an amplifier, the deflection driver 1
5, the input signal of the D/A converter is sent as a scanning signal to the position calculation unit 23, and the position calculation unit 23 calculates (x _d , y _d ) is calculated. Further, the coordinates (x _c +x _d , y _c +y _d ) of the beam irradiation point R in the chip coordinate system are determined, and this coordinate information is sent to the base determining section 25 connected to the pattern data memory 24 .

The pattern data memory 24 stores pattern data created by a CAD system corresponding to ICs, LSIs, etc. realized on the sample 16, which have been subjected to the following preprocessing. First, the coordinate origin of the pattern data is moved so that it coincides with the coordinate origin when calculating the beam irradiation point position in the position calculation section 23, that is, the coordinate origin of the chip coordinate system. Next, the coordinate units are converted so that the scale of the pattern data matches the scale of the IC, LSI, etc. on the sample 16. Finally, underlying information, such as Al or SiO ₂ information, is added to the pattern data. After these pre-processes, the pattern data is stored in the pattern data memory 24. The base determination unit 25 receives the position coordinates of the beam irradiation point from the position calculation unit 23, searches the pattern data in the pattern data memory 24 based on these coordinates, and determines the type of base at the position of the beam irradiation point. For example, if it is determined from the search of the pattern data memory 24 that the beam irradiation point position (x _c +x _d , y _c +y _d ) shown in FIG. . This background data is stored in the background compensation data memory 2.
6 is connected to the base compensation data determination unit 27.

The base compensation data memory 26 stores data in which secondary electrons emitted from the sample 16 are detected by the secondary electron detector 19 when a pulse beam is irradiated onto the base area without applying a drive signal to the sample 16. A secondary electronic signal is passed through an amplifier 20 to an A/D converter 21
digitized data (background data) is stored. The measurement conditions at this time, such as beam acceleration voltage, beam current, beam diameter, beam pulse width, and number of samplings, are as follows:
It is preferable to set the conditions to be the same as the conditions for actually performing the measurement, that is, the conditions for applying a drive signal to the sample 16 and performing the measurement. If the measurement conditions are changed midway through, it is better to not apply a drive signal to the sample 16 and remeasure the data in the underlying region. However, if there are items for which the measurement conditions change frequently during measurement, the underlying data may be collected without applying a drive signal for several types of items expected in advance and stored in the underlying compensation data memory 26. Then, when selecting background data from the background compensation data memory 26 later, it may be taken out with matching conditions. For example, if you want to perform measurements with three different beam pulse widths: 0.5nS, 1nS, and 2nS, collect data in advance under these three conditions with no drive signal applied, and store it in the base compensation data memory 26. Just leave it there. Note that in order to obtain compensation data when no voltage is applied, instead of actually irradiating the sample 16 with a beam, various types of bases are placed at the sample position, and secondary electrons due to beam irradiation are detected in this state. Desired. Base compensation data determination unit 2
At step 7, background compensation data is selected from the background compensation data memory 26 based on the background data determined by the background determination section 25, and thereby background data of the base formed at the position to be irradiated with the beam is determined. This background data is then sent to the subtracter 22.

The digital data from the A/D converter 21 is input to the subtracter 22 together with the background data, and the subtracter 22 subtracts the background data from the digital data. In other words, the background data containing only information on the base composition is subtracted from the digital data containing information on the sample potential and the base composition, and the output data of the subtracter 22 is only potential information without mixed base composition information. The data is based on Then, data based only on this potential information is sent to the display 28, and the potential contrast image and potential waveform of the sample 16 are displayed on the display 28.

Thus, according to the present apparatus, level fluctuations in the detected secondary electron signal based on the underlying composition are automatically corrected at any position on the semiconductor sample 16. Therefore, the accuracy of potential measurement of the semiconductor sample 16 can be significantly improved. Furthermore, since there is no need to irradiate the sample 16 with an electron beam when creating the background data, there are advantages such as minimizing beam damage to the sample 16 and shortening measurement time.

Next, other embodiments of the present invention will be described.
This embodiment differs from the previously described embodiments in the following points:
A length measurement system consisting of a position detector 31 for measuring the position of the sample stage 17 and a table position length measurement section 32 is provided, and the signals (coordinates) obtained by this system are directly input to the position calculation section 23. This is what I did. If X and Y shown in Figure 5 are sample system coordinates, and the chip arrangement in this coordinate system is as shown in the figure, the coordinate values (X _l , Y _l ) from the sample coordinate system origin 0 are the table position measurement. The output from the long section 32 is sent to the position calculation section 32 . Position calculation unit 23
Now, coordinates (x _c , y _c ) in the chip coordinate system are determined from the X-direction pitch P _x , Y-direction pitch P _y of the chip arrangement, and if necessary, the chip layout. When the chip playout is as shown in FIG. 5, it can be determined by the simple formula x _c =X _l - [X _l /P _x ].X _l y _c = Y _l - [X _l /P _{x ]} . However, in the above formula, [ ] is a Gauss symbol. From this point on, the deviation (x _d , y _d ) from the deflection center to the beam irradiation point is calculated in the same manner as in the previous embodiment.

With this configuration, not only can the same effects as in the previous embodiment be obtained, but also it is possible to measure the potential at any arbitrary point of a large sample such as a semiconductor wafer with high precision. I can do it.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and may be modified without departing from the scope of the invention.
Various modifications can be made.

[Brief explanation of drawings]

Figures 1a and b are for explaining the level fluctuations of the detected secondary electron signal caused by the underlying composition, a is a schematic diagram, b is a signal waveform diagram, and Figure 2 is a diagram for correcting the level fluctuations mentioned above. FIG. 3 is a schematic diagram for explaining the conventional method, FIG. 3 is a schematic configuration diagram showing an embodiment of the present invention, FIG. 4 is a schematic diagram for explaining the operation of the above embodiment, and FIG. 5 is a diagram for explaining another embodiment. It is a schematic diagram for demonstrating the effect|action of an example. 11... Electron gun, 12... Deflection plate for beam chop, 13... Chipper driver, 14... Deflection coil for beam scanning, 15... Deflection driver, 1
6... Semiconductor sample, 17... Sample stage, 18
... Drive signal generator, 19 ... Secondary electron detector,
20...Amplifier, 21...A/D converter, 22...
...Subtractor, 23...Position calculation unit, 24...Pattern data memory, 25...Base determining unit, 26...
Base compensation data memory, 27... Base compensation data determination section, 28... Display, 31... Position detector,
32...Table position measuring section.

Claims (1)

[Claims] 1. Applying a drive signal to an electronic device, scanning an electron beam over a sample using a predetermined scanning signal, detecting secondary electrons emitted from the electronic device at this time, and irradiating the beam with the electron beam. A potential distribution measuring device for an electronic device that measures the potential of a surface, comprising: a pattern data storage means for storing pattern data of an element realized on the electronic device by adding information about the type of substrate to the data; and the electron beam. beam irradiation position detection means for detecting the irradiation position of the beam from the scanning signal of the beam irradiation, and the beam irradiation position is configured based on the position data detected by this means and the pattern data from the pattern data storage means. a base determination means for determining the type of base; a background data storage means for storing background data, which is a detected secondary electronic signal in a state in which no drive signal is applied to the electronic device, for each type of base; background data determining means for selecting and determining background data of a base formed at the position to be irradiated with the beam from the background data storage means based on the base data determined by the determining means; 1. A potential distribution measuring device for an electronic device, comprising: subtraction means for subtracting the background data determined by the background data determination means from the detected secondary electron signal in the applied state. 2. The electronic device is placed on a sample stage movable in a direction perpendicular to the irradiation direction of the electron beam, and the beam irradiation position detection means detects the stage position information indicating the position of the sample stage and the sample stage. The potential distribution measuring device for an electronic device according to claim 1, wherein the device detects the irradiation position of the shaped electron beam based on the scanning signal.