JPH10116580A - Sample image displaying method and semiconductor manufacturing method using the method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To observe the bottom parts of a deep hole and a groove with an aspect ratio of a depth/opening diameter is certain value or more and contribute the observation to an inspection in the process of the preparation of a semiconductor element by irradiating high energy electron beam of an optimum intensity according to the depth of the deep hole and detecting generated electron. SOLUTION: Holes and grooves of an aspect ratio 2.5 or more are irradiated with high energy primary electron beam 1. Based on the detection of tertiary electron 5 generated by generated reflection electron 2 and reflection electron 6 passing through a side wall, the bottom part of the hole or the groove is displayed. At this stage, primary electron enters the depth of a sample when energy is too high, reflection electron amount is reduced and tertiary electron is also reduced. Therefore, energy intensity is required to be optimum energy intensity that generated electron amount becomes maximum. In the detection of tertiary electron, tertiary electron is sucked in electric field made by a scintillator and tertiary electron is detected by an electron multiplying tube. Thus, an important deep hole groove can be observed/confirmed in the etching process of a semiconductor element by making it possible to observe the bottom part of a hole of the aspect ratio 2.5 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for observing a surface shape using an electron beam, and more particularly to a method for observing a shape of a bottom portion of a deep hole or a residue which is frequently used in a semiconductor process.

[0002]

2. Description of the Related Art A scanning electron microscope which scans a sample with an electron beam and detects secondary electrons generated therefrom is widely used in the fields of biology and engineering. In particular, in the semiconductor industry, as a result of high integration, inspection with an optical microscope has become impossible, and a scanning electron microscope has been used. In a scanning electron microscope used for a semiconductor, an electron beam having a low energy of 1 kV or less is generally used to avoid charging of an insulator.

[0003] The use of a scanning electron microscope in the semiconductor industry is not only a visual inspection of a completed semiconductor but also an inspection during a process. For example, it is used for appearance inspection, dimension inspection, and through hole opening inspection during the process.

[0004]

As a result of the progress of high integration of semiconductor devices, it has become impossible to inspect the opening of a through hole by a conventional method using a scanning electron microscope.

A problem in observing a deep hole with a conventional scanning electron microscope will be described with reference to FIG. FIG. 2 shows a case where the low energy primary electrons 1 irradiate the plane portion of the sample and the hole 3. Almost all of the secondary electrons 2 generated in the plane portion can be detected because there are no obstacles. Simultaneously, reflected electrons are also emitted, which can be detected as well. However, when irradiating the hole 3,
Since the generated secondary electrons 2 collide with the side wall of the hole 3, the
Can't go outside. The backscattered electrons have higher energy than the secondary electrons, but they do not have enough energy to penetrate the side wall, so they also stop at the side wall.

FIG. 3 shows the aspect ratio of a hole (depth / opening diameter).
It is the result of calculating the relationship between and the ratio of the signal that escapes from the hole. The signal on the surface (aspect ratio = 0) was set to 1. From this calculation, it is understood that it is impossible to observe a hole having an aspect ratio of more than 2: with a conventional scanning electron microscope.

[0007]

According to the present invention, in order to solve the above-mentioned problems, a deep hole having an aspect ratio of 2.5 or more is provided.
Alternatively, a method of irradiating a semiconductor element having a groove with an electron beam to display a sample image, wherein electrons generated due to irradiation of the electron beam on the deep hole or the bottom of the groove are formed on the sample. The present invention provides a method of displaying a sample image, wherein the method comprises detecting and detecting the bottom of the deep hole or groove based on the detection.

The principle of deep hole observation using primary electrons will be described with reference to FIG.

When a hole or groove having an aspect ratio of 2.5 or more is irradiated with a primary electron beam which generates electrons on a sample due to the irradiation, the hole or groove has an electron beam as shown in FIG. A higher signal intensity can be obtained as compared with the case of irradiating a primary electron beam that does not generate.

By detecting these electrons with a detector arranged on the sample, an image in the hole can be obtained.

In other words, it becomes possible to observe the bottom of a hole or groove having an aspect ratio of 2.5 or more, which has been impossible so far.

[0012]

FIG. 4 shows an aspect ratio of about 3,
The ratio of the signal from the bottom to the signal from the surface when observing a 1.5 μm deep SiO ₂ hole was measured by changing the energy of the primary electron beam. That is, the ratio of tertiary electrons to secondary electrons is measured. It can be seen that the electron beam energy is maximum around 100 kV.
When the primary electrons have low energy, tertiary electrons are not generated because reflected electrons are absorbed by the side walls. As the energy of the primary electrons increases, the number of reflected electrons penetrating the side wall increases, and the number of tertiary electrons also increases gradually. However, when the energy is further increased, the primary electrons penetrate deep into the sample, and the amount of reflected electrons decreases, and as a result, tertiary electrons decrease. That is why we have this maximum. The electron beam energy showing this maximum value depends on the hole depth and the material. Deeper holes, denser materials require higher energy.

FIG. 5 shows an example using 100 keV energy.
This is the relationship between the aspect ratio and the signal ratio when observing a deep hole. The relationship of 1 keV is also shown for reference,
In eV, it can be seen that the signal ratio does not decrease even if the aspect ratio exceeds 3, and that a hole with a higher aspect ratio can be observed.

The energy of a conventional scanning electron microscope is 50
No high energy below 50 kV and above 50 kV is used. That is because there was no observation concept of the principle as shown here. Here, the effectiveness of high-energy primary electrons enabling deep hole observation was shown for the first time.

FIG. 6 shows a method for detecting tertiary electrons generated by high-energy reflected electrons. Scintillator 10
And a method using the secondary electron multiplier 12. A high voltage of 10 kV is supplied to the scintillator 10 from a high voltage power supply 13. Tertiary electrons generated on the surface of the sample 8 are detected by the attractive electric field 9 generated by the high voltage. The sample 8 contains primary electrons 4 having sufficient energy to generate the above-mentioned tertiary electrons.
Are converged and irradiated by the objective lens 7. In this figure, the scanning of the primary electron beam, the display circuit of the scanned image, and the like are omitted.

FIG. 7 shows an example of detecting not the tertiary electrons but the reflected electrons transmitted through the side wall. A backscattered electron detector 15 having a large viewing angle with respect to the sample 8 is provided between the objective lens 7 and the sample 8. The backscattered electron detector 15 may be a PN-junction or Schottky-junction semiconductor detector or a method of emitting and detecting a phosphor (in the embodiment, an example using a semiconductor). Since the energy of the backscattered electrons is high, the surface layer of the semiconductor detector is made thick (1-10 μm) to prevent a decrease in detection efficiency. The thickness of the phosphor is similarly increased. The thickness of the phosphor depends on the energy, but is 10-100 μm.

FIG. 8 shows an example in which both reflected electrons and tertiary electrons are detected. A suction electrode 16 is provided through the center of the objective lens. The three-dimensional electrons generated in the sample 8 are drawn into the magnetic field of the objective lens 7 by the suction electrode 16 and are pulled upward. The tertiary electrons pulled upward are accelerated by the attraction electric field 9 created by the scintillator 10, collide with the scintillator 10, and cause the scintillator 10 to emit light.
The emitted light is guided to a light guide 11, amplified by a secondary electron multiplier 12, and converted into an electric signal. Since the backscattered electrons generated by the sample 8 have high energy, they are hardly deflected by the electric field generated by the suction electrode 16, travel substantially linearly, and enter the backscattered electron detector 15. By this method, reflected electrons themselves and tertiary electrons can be distinguished and detected. Since the scanned images created by the two are slightly different, select the one with good contrast. Alternatively, processing such as addition and subtraction to improve contrast can be performed.

In the embodiments described above, tertiary electrons and reflected electrons generated on the primary electron incident side are detected. However, when the sample is thin, tertiary electrons generated by transmitted electrons or transmitted electrons are detected. It may be detected. FIG. 9 shows an embodiment for detecting tertiary electrons and transmitted electrons generated on the side opposite to the primary electrons. The detection method on the primary electron side is the same as in the above-described embodiment. Tertiary electrons 2 generated on the lower surface of the sample by electrons transmitted through the sample 8
0, the tertiary electrons 21 generated by the collision of the transmitted electrons 19 with the reflection plate 22 are detected by the scintillator 10, the light guide 11, and the secondary electron multiplier 12. 200k of primary electron energy
At V, the range of electrons becomes 200 μm, so that it can pass through a Si wafer used in the semiconductor industry. That is, by detecting transmitted electrons and tertiary electrons from the lower surface of the sample, it becomes possible to observe holes on the surface of the sample 8. In this detection method, the distance from the bottom of the hole to the lower surface is shorter, so that the signal at the bottom of the hole is larger than that at the surface.

FIG. 10 shows a scanning electron microscope using the above-described observation principle and detection method. The electron source is LaB ₆
Is used, and electrons emitted by heating the single crystal are used. The emission electrons are controlled by the Wehnelt 24. The emitted electrons are accelerated by the acceleration electrode 25. The maximum acceleration voltage (energy) in this embodiment is 200 kV. An accelerating voltage is applied to the uppermost accelerating electrode 25, and each accelerating electrode 25
, A voltage divided by the dividing resistor 34 is applied. Here, cables, power supplies, and the like for applying an acceleration voltage are omitted. The accelerating part including the accelerating electrode 25 is a high voltage shield 3
5 shielded. The accelerated primary electrons 4
It is reduced by the condenser lens 26, the second condenser lens 27 and the objective lens 7. If an objective lens having a focal length of 30 mm is used, a resolution of 3 nm can be obtained at 200 kV.
The aperture of the electron beam is determined by the aperture 36 placed on the second condenser lens. The scanning of the electron beam is performed by the scanning coil 28. It is composed of two-stage coils so that the scanned electron beam passes through the center of the objective lens 7. The backscattered electrons reflected by the sample are reflected by the backscattered electron detector 15.
The tertiary electrons are guided by the suction electrode 16 above the objective lens 7 and are detected by a detector composed of the scintillator 10, the light guide 11, and the secondary electron multiplier 12.

The sample is placed on an XY fine movement stage 29 with a wafer of 4 inches or more. The sample tilt fine movement 30 can tilt ± 15 degrees in an arbitrary direction. The sample tilt fine movement is composed of three columns, and the length of each column is controlled by a computer. The wafer to be observed is stored in a special cassette 32 in a spare room 33. When observing, the valve 42 is opened and mounted on the XY fine movement stage 29 using an exchange mechanism (not shown). The height can be measured by observing the same portion of the sample at different inclination angles (stereo measurement).

It has already been mentioned that in a highly integrated semiconductor device, an etching step for processing a deep hole having a high aspect ratio is important. It is very difficult to etch a deep hole having a high aspect ratio, and it is necessary to observe the bottom of the deep hole and check the progress of the etching to determine the etching conditions. FIG. 11 shows a flow of this confirmation, and feedback such as re-etching is performed according to the result of the confirmation, thereby completing the process. The etching conditions determined in this way are continued in the subsequent steps. By performing this check at regular intervals, the process can be further stabilized. The scanning electron microscope is very effective in confirming this etching, and can contribute to the improvement of the production yield of highly integrated devices. In particular, the high-energy scanning electron microscope utilizing tertiary electrons described above is effective.

FIG. 12 shows an apparatus for simplifying the above-mentioned confirmation step. The sample chambers of the microwave etching apparatus 38 and the high-energy scanning electron microscope 37 are made common, and the sample is transferred from the etching apparatus sample table 39 to the scanning electron microscope. Etching and inspection can be performed alternately simply by moving to the microscope XY fine movement stage. The degree of vacuum of the microwave etching apparatus is 10 ^-4 Torr, which is ^{almost the} same as that of the scanning electron microscope. However, since an active gas is used, the intermediate chamber 41 is provided in this embodiment, and the valve 40 for the intermediate chamber is provided. By alternately opening and closing, the active gas is prevented from flowing into the scanning electron microscope apparatus. In this figure, the exhaust system is omitted.

[0023]

As described above, according to the observation principle of the present invention, it is possible to observe deep holes having an aspect ratio of 2.5 or more, which could not be observed conventionally. This means that, for example, in-line inspection can be performed in the process of manufacturing a semiconductor device, and this effect is very large.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an observation principle of the present invention.

FIG. 2 is a diagram illustrating a conventional observation method.

FIG. 3 is a diagram showing a relationship between a signal intensity from a hole and an aspect ratio according to a conventional method.

FIG. 4 is a diagram showing a measurement result of an increase in a signal from the bottom of a hole by increasing an acceleration voltage (energy).

FIG. 5 is a diagram showing a relationship between signal intensity and aspect ratio when the present invention is used.

FIG. 6 is a diagram illustrating a method for detecting tertiary electrons generated by reflected electrons from the bottom of a hole.

FIG. 7 is a view for explaining a method of observing reflected electrons from the bottom of a hole.

FIG. 8 is a view for explaining a method for simultaneously observing both reflected electrons and tertiary electrons.

FIG. 9 is a diagram for detecting electrons transmitted through a sample.

FIG. 10 is a view for explaining an embodiment of the present invention so that observation can be performed in a wafer state by the observation principle and the detection method of the present invention.

FIG. 11 is a diagram showing a flow of determining an etching condition using a scanning electron microscope.

FIG. 12 is a conceptual diagram of an apparatus that facilitates determination of etching conditions by using a common sample chamber for microwave etching and a scanning electron microscope.

[Explanation of symbols]

1 ... primary electron (low energy), 2 ... secondary electron, 3 ... hole,
4: Primary electrons (high energy), 5: Tertiary electrons, 6: Reflected electrons, 7: Objective lens, 8: Sample, 9: Attraction electric field, 10
... Scintillator, 11 ... Light guide, 12 ... Secondary electron multiplier, 13 ... High voltage power supply, 15 ... Backscattered electron detector, 16
... suction electrode, 17 ... suction power supply, 18 ... ground electrode, 19
... Transmitted electrons, 20: Tertiary electrons due to transmitted electrons, 21: Tertiary electrons formed by a reflector, 22 ... Reflector, 24 ... Wehnelt, 25 ... Accelerator electrode, 26 ... First condenser lens, 27 ... Second condenser lens, 28 scanning coil,
29 ... XY fine movement stage, 30 ... Sample tilt fine movement, 31 ...
Sample chamber, 32 cassette, 33 preliminary chamber, 34 divided resistance, 35 high voltage shield, 36 aperture.

Claims (5)

[Claims] 1. A method for irradiating a semiconductor element having a deep hole or a groove having an aspect ratio of 2.5 or more with an electron beam to display a sample image, wherein the method comprises the steps of: A sample image display method, comprising: detecting electrons generated due to irradiation with an electron beam on the sample; and displaying the bottom of the deep hole or groove based on the detection. 2. The method according to claim 1, wherein the electron beam is scanned in a region including the deep hole, the groove, or both, and the electron beam is generated due to the irradiation of the electron beam to the bottom of the deep hole, the groove, or both. And displaying the scanning area based on electrons generated and secondary electrons or reflected electrons generated from portions other than the deep hole or the groove. 3. The sample according to claim 1, wherein the electrons generated by the irradiation of the bottom of the deep hole or the groove with the electron beam pass through the inside of the sample from the side wall of the deep hole or the groove. A method for displaying a sample image, characterized by including electrons penetrating upward. 4. The sample according to claim 1, wherein electrons generated by irradiation of the bottom of the deep hole or groove with an electron beam pass through the inside of the sample from a side wall of the deep hole or groove, and A method of displaying a sample image, wherein the electrons penetrating upward include secondary electrons generated on the sample. 5. In a semiconductor device manufacturing process which requires a deep hole etching process having an aspect ratio of 2.5 or more, an inspection is performed by a scanning electron microscope after the etching process, and the etching condition is determined based on the result. Device manufacturing method.