JPH06310075A - Scanning electron microscope - Google Patents

Abstract

(57) [Summary] [Object] To provide an observation device for a semiconductor wafer in a semiconductor manufacturing process. [Structure] A sample 4 is irradiated with an electron beam 3, and electrons 5 emitted from the surface of the sample 4 by the electron beam irradiation are absorbed by a scintillator 6
And using the detector 7. The energy of the electron beam 3 can be arbitrarily set within the range of 0.5 to 100 keV. [Effect] Since the energy of the electron beam can be set according to the observation object or the purpose, the observation object can be easily found and the inside of the hole or groove can be observed in detail. Moreover, damage to the sample can be minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an observation technique using an electron beam, and more particularly to an apparatus capable of observing a finely processed shape of a semiconductor wafer and a residue.

[0002]

2. Description of the Related Art A scanning electron microscope (S) that scans a sample surface with an electron beam and detects secondary electrons generated by this scanning.
EM) is widely used in the field of engineering. Particularly, in the semiconductor industry, it is an indispensable device for observing processed shapes and residues. In such observation, an electron beam having an energy of 2 keV or less is often used in order to avoid charging of the insulator.

A large number of holes (or grooves) typified by contact holes are formed on the surface of a wafer used in a semiconductor process. For example, in a 16Mb DRAM which will be the mainstream semiconductor device in the future, the diameter of the hole will be 0.5μ.
m and the depth is 1.5 to 2 μm. In the scanning electron microscope (low-acceleration SEM) using the low-energy electron beam described above, the secondary electrons generated in the hole by the electron beam irradiation are blocked by the inner wall of the hole, so that the secondary electron reaches the detector. However, it was difficult to observe the inside of the hole. On the other hand, in recent years, by increasing the electron beam energy to 50 keV or more and detecting backscattered electrons and tertiary electrons formed by the backscattered electrons, a scanning electron microscope (high-acceleration SEM ) Was proposed. For the principle of this method,
For example, it is disclosed in detail in JP-A-4-149944.

[0004]

Taking the observation of the contact hole 15 shown in FIG. 2 as an example, a low acceleration SEM and a high acceleration SEM are used.
Organize the usage of. With the low-acceleration SEM, the shape of the surface 10 can be observed in detail without charging the sample. But this S
In the EM, the secondary electrons 16 from the bottom surface 12 are blocked by the inner wall 17 and cannot be detected, and it is difficult to observe the bottom surface 12. On the other hand, in the high acceleration SEM, the backscattered electrons 13 reflected on the bottom surface 12
Have sufficient energy to penetrate through the inner wall 17 and jump out of the surface 10. This reflected electron 13
Electrons (tertiary electrons 14) are generated again when passing through. The backscattered electrons 13 and the tertiary electrons 14 have information on the bottom surface 12, and the bottom surface 12 can be detected by detecting these electrons.
(Or the residue attached to the bottom surface 12) can be observed. Until now, the observation of the surface 10 was a low-acceleration SEM.
The observation of the bottom surface 12 was performed separately by using a high acceleration SEM.

As described above, the bottom surface of the hole can be observed with the high-acceleration SEM. However, in this device, the front surface 10 and the bottom surface 12 are simultaneously displayed on the monitor screen with substantially the same contrast. Further, as is clear from the observation principle, not only the surface but also the lower metal wiring and the like are simultaneously observed and displayed on the monitor screen. For this reason, the image displayed on the monitor screen becomes complicated, it is difficult to determine the vertical relationship of the displayed image, and it is difficult to understand what is observed by observing only the high-acceleration SEM. .
As a result, it is difficult to compare with the design pattern of the device, and even if a residue is detected inside the hole or groove, it takes time to identify the defective portion. Further, since it is necessary to observe the observation object for a long time as described above, there is a problem that the sample is likely to be damaged by the long-time irradiation with the high-energy electron beam.

There is also a method of observing the sample surface with a low acceleration SEM first and then observing the inside of the hole with a high acceleration SEM, as opposed to the method using a high acceleration SEM. However, in this method, since two different devices are used, it takes time to move the sample between the devices, introduce the sample into each device, evacuate the device, and search for the same observation region. Therefore, 2
The method using one device is extremely inconvenient as a method used in a semiconductor manufacturing process.

[0007]

In order to solve the above problems, according to the present invention, the energy of the electron beam with which a sample is irradiated is set to 0.5 according to the object to be observed or the purpose.
It can be arbitrarily switched in the range of up to 100 keV.

[0008]

When the surface 10 of FIG. 2 is observed (for example, the analysis position is identified), the energy of the electron beam is set low. In this case, just like the low-acceleration SEM, only the sample surface can be observed, so the image displayed on the monitor screen becomes simple, and it is possible to easily know which place is being observed. Also, since the energy of the electron beam is low,
No sample damage occurs. After observing the hole or groove to be observed in this way, when observing the inside, the energy of the electron beam is switched to a high energy for observation. After observing the surface and the inside with a high-energy electron beam at the same time by changing the order of these observations, the observation location may be identified from the image of the sample surface obtained by the low-energy electron beam. The essence of the present invention is to provide an apparatus that has an observation function having both the functions of a low-acceleration SEM and a high-acceleration SEM and can perform observation by switching between low acceleration and high acceleration according to demand.

Next, the energy of the electron beam used in this observation will be described. The minimum size of a semiconductor device is already sub μm
Is in the area of. High (spatial) resolution is required to observe such elements. Various materials are used in the semiconductor element manufacturing process. When an insulating film such as an oxide or a nitride, or a resist or the like is irradiated with an electron beam, these materials may be charged depending on the energy of the electron beam, and the image quality of the obtained secondary electron image may be significantly reduced. Considering these facts, it can be concluded that the factors that determine the lower limit of the energy value of the electron beam are the resolution and the charged state of the sample.

FIG. 3 shows the measurement results of the electron beam energy dependence of the SEM resolution. The broken line shows the resolution of the normal SEM, and the solid line shows the resolution of the in-lens system high resolution SEM. In general, application of SEM to a semiconductor manufacturing process requires a resolution of 1/10 or less of the minimum dimension of an observation target. Considering that the minimum element size of DRAMs after 16 Mb, which is the mainstream of semiconductor devices, is 0.5 μm or less, the resolution of SEM must be at least 0.05 μm or less. It can be seen from FIG. 3 that the electron beam energy required to obtain this resolution may be about 0.5 keV.

From the measurement using the insulator sample, it was also found that the surface of the sample was rapidly charged when the energy of the electron beam was 2 keV or more. That is, in order to reduce the influence of electrification and observe the insulator sample, the energy of the electron beam must be 2 keV or less. From the above, it can be concluded that the electron beam energy should be set to 0.5 to 2 keV in order to observe an insulator sample with high resolution without charging. Of course, this conclusion is that the sample is an insulator, and in the case of a semiconductor or a metal sample, the sample is not charged, so that an electron beam of higher energy can be used.

The upper limit of the electron beam energy is determined as follows. As shown in Japanese Patent Laid-Open No. 4-149944, secondary electrons from the bottom surface 12 of the tertiary electrons from the surface 10
The ratio of the electron beam to the secondary electron is 50 to 10
It becomes maximum at 0 keV. Therefore, when detecting a signal from the bottom surface 12 (that is, observing the bottom surface 12), the upper limit of the energy of the electron beam is 100 keV. Furthermore, by setting the upper limit of the energy of the electron beam to 100 keV, it is possible to further reduce the damage given to the sample as compared with the case of using the electron beam having the energy of 100 keV or more.

From the above, it can be concluded that the electron beam energy switching in the present invention is best at 0.5 to 100 keV.

According to the present invention, since one apparatus can perform observation, which conventionally requires two different apparatuses, all of the above-mentioned problems of the prior art can be solved. That is, by changing the energy of the electron beam in accordance with the object to be observed or the purpose, not only the surface but also the inside of the hole or groove can be observed, and the processed shape and the residue can be observed quickly and easily. Moreover, comparison with the design pattern of the element can be easily performed in a short time. As a result, less energy is applied to the sample, and damage to the sample can be minimized.

[0015]

【Example】

<Example 1> The most basic example of the present invention is shown in FIG. Electrons from the electron source 1 are accelerated and focused by the electron lens 2 to generate an electron beam 3 having a predetermined energy.
Electrons 5 (2
Secondary electrons, tertiary electrons, etc.) are converted into light by the scintillator 6 and detected by the detector 7. In order to collect the electrons 5 efficiently, the scintillator 6 receives a high voltage (1 to 10
kV) is supplied.

When observing the surface of the sample 4, the energy of the electron beam 3 is set to 2 keV or less and the surface of the sample 4 is scanned with the electron beam 3. This scanning can also be performed using the electronic lens 2. Here, when the sample 4 is other than an insulator, no charging occurs, so that an electron beam having higher energy can be used. By observing these surfaces, it is possible to find holes and grooves to be observed in detail.

When observing the inside of these, the energy of the electron beam 3 may be increased to 50 keV or more. This increase in energy is performed by changing the high voltage supplied from the control power supply 8 to the electron lens 2. The energy range of the electron beam 3 in the present invention is 0.5 to 100 keV. The electron lens 2 is an electron lens system capable of generating a focused electron beam having energy in this range.

According to the present invention, the energy of the electron beam with which the sample is irradiated can be set according to the object to be observed or the purpose, so that the object to be observed can be easily identified and the inside of the hole or groove can be easily observed. As a result, the observation pattern and the design pattern can be easily compared, and the defective portion can be quickly grasped.

<Embodiment 2> An image of the surface of the sample or the inside of the sample can be formed also by using backscattered electrons. FIG. 4 shows an example of the embodiment.

When the energy of the electron beam 3 is low, the surface of the sample 4 is irradiated with the electron beam, so that 2
Secondary electrons 21 are generated. The secondary electrons 21 are detected using the detector 18. The configuration of the detector 18 may be a combination of the scintillator 6 and the detector 7 as described in the first embodiment. An image of the sample surface can be obtained by detecting the secondary electrons. On the other hand, when the energy of the electron beam 3 is increased to observe the inside of the hole, the backscattered electron detector 19 or the detector 18 is used. Alternatively, both detectors may be used. As the backscattered electron detector 19, a semiconductor detector using a pn junction or a Schottky junction, or a detector using fluorescence such as a scintillator is used. Reference numeral 20 is a power source for the detector 19. Further, in order to efficiently guide the secondary electrons and the tertiary electrons, which are not shown in the figure, to the detector 18, an electrode for attracting electrons is installed inside or under the electron lens 2. The energy of the electron beam 3 is changed by using the control electrode 8 as in the first embodiment. The energy variable range of the electron beam 3 is the same as that in the first embodiment.

According to this embodiment, since the backscattered electrons can also be used for image formation, observation with a better S / N can be performed.

[0022]

According to the present invention, the energy of the electron beam with which the sample is irradiated is 0.5 to 0.5 depending on the object to be observed or the purpose.
Since it can be set within the range of 100 keV, the sample surface can be observed with high resolution without charge, and the inside of the hole or groove can also be observed. As a result, the observation pattern and the design pattern can be easily and quickly compared with each other, and the defective portion can be easily found. In addition, damage to the sample can be minimized.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between an electron beam applied to a sample and generated electrons.

FIG. 3 is a characteristic diagram showing electron beam energy dependence of SEM resolution.

FIG. 4 is a block diagram of an apparatus showing another embodiment of the present invention.

[Explanation of symbols]

1 ... Electron source, 2 ... Electron lens, 3 ... Electron beam, 4 ... Sample,
5 ... Electronics, 6 ... Scintillator, 7 ... Detector, 8 ... Control power supply, 9 ... Power supply.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Tokoro, 882 Ichimo, Ichigo, Katsuta-shi, Ibaraki Hitachi, Ltd. Measuring Instruments Division (72) Inventor Sadao Terakado, 882, Ichimo, Katsuta, Ibaraki Hitachi, Ltd. Measuring Instruments Division (72) Inventor Fumio Mizuno 2326 Imai, Ome City, Tokyo, Hitachi Device Development Center (72) Inventor Satoru Yamada 2326 Imai, Ome City, Tokyo Hitachi, Ltd. Device Development Center

Claims (4)

[Claims] 1. A scanning electron microscope which irradiates a sample with an accelerated and convergent electron beam, detects electrons generated by the irradiation, and observes the sample, and the electron beam energy is 0.5 k.
A scanning electron microscope provided with means for arbitrarily setting within a range from eV to 100 keV. 2. The electron beam energy as set forth in claim 1, wherein the energy of the electron beam when observing the inside of the groove or hole when observing the sample having the groove or hole formed on the surface thereof is the electron beam when observing the sample surface. Scanning electron microscope with more than the energy of. 3. A signal for forming a scan image according to claim 1 or 2, wherein a secondary electron generated by the irradiation of the electron beam, a reflected electron, or a tertiary electron generated by the reflected electron, or these electrons. Scanning electron microscope which is a combination of. 4. A scanning electron microscope which observes the sample by irradiating a sample having grooves or holes formed on its surface with an accelerated and convergent electron beam, and detecting the electrons generated by the irradiation to observe the sample. If the observation area of contains an insulator, the energy of the electron beam when observing the sample surface is 0.
A scanning electron microscope, which is 5 keV or more and 2 keV or less, and has an electron beam energy of 50 keV or more and 100 keV or less when observing the inside of a groove or a hole.