JP3474082B2 - Electron beam equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an electron beam apparatus capable of high-resolution observation even in a low acceleration voltage region.

[0002]

2. Description of the Related Art In recent years, with the dramatic increase in the integration of semiconductor integrated circuits, there is an increasing demand for high resolution observation with a scanning electron microscope at a low accelerating voltage of about 1 kV which causes less charge-up and electron beam damage.

Up to now, in response to this demand, Japanese Patent Laid-Open No. 1-13
6557 (FIG. 4), the magnetic field of the electromagnetic lens is mainly generated on the sample side to bring the lens main surface as close as possible to the sample, and as disclosed in JP-A-62-256352 (FIG. 5). That the electric field and the magnetic field are superimposed, or a kind of Einzel lens is formed by applying a positive bias voltage between the grounded magnetic pole and the sample as shown in FIG. We have dealt with this by reducing the aberration coefficient by applying a negative bias to the sample of the primary electron beam that has run at high energy and decelerating it just before the sample.
When the sample is not tilted, a high resolution is obtained by the above structure, but when the sample is tilted at a large angle, the type in which a magnetic field is generated on the sample side as shown in FIG. High resolution cannot be obtained because it can only be used with. In the case of using a deceleration electric field by applying a negative bias to the sample as shown in FIG. 6 or by using a deceleration electric field, an asymmetric electric field is generated due to the tilt and astigmatism is increased, so that a good image cannot be obtained, or the tilt is taken into consideration. With such a shape, in the electric field and magnetic field superposition type of FIGS. 5 and 6, there is a problem that the main surface of the electrostatic lens is moved away from the sample and is used with a bad aberration coefficient, and high resolution observation cannot be performed.

In addition, it takes time to change the working distance for observation, which is not preferable for achieving high throughput, and there is a problem that the observation place is displaced due to backlash of the sample stage.
There has been a demand for a technique capable of performing high-resolution observation with the working distance fixed while performing elemental analysis by X-ray.

[0005]

[Problems to be Solved by the Invention]

According to the present invention, an asymmetric electric field is generated when the sample is tilted by the electromagnetic lens of the type shown in FIG. 4 for generating a magnetic field on the sample side, the objective lens of the electric field and magnetic field superposition type of FIGS. The objective is to enable high-resolution observation at a low working voltage with a fixed working distance.

[0007]

[Means for Solving the Problems]

1) As shown in FIG. 1, if an electrode having a tiltable shape is arranged between the electromagnetic lens and the sample and the sample and the electrode are used at the same potential, the magnetic field of the electromagnetic lens and the potential difference between the electrode and the magnetic pole form the electrode. The generated electric field can reduce the aberration coefficient, especially the chromatic aberration coefficient that is dominant at low accelerating voltage, compared to the electromagnetic lens alone. In addition, the potential of the sample and the electrode are the same, so that the increase in astigmatism even when tilted. No asymmetric electric field is generated.

2) When the electrode of FIG. 1 is not tilted to the sample, if the potential is switched to the same potential as the magnetic pole, the main surface of the electrostatic lens will be brought closer to the sample, and a long working distance that allows elemental analysis by X-rays but a short working distance. High-resolution observation comparable to distance becomes possible.

3) By disposing two tiltable electrodes between the electromagnetic lens and the sample as shown in FIG. 2, the set potential of the two electrodes and the set potential of the magnetic poles are controlled so that the A potential lens or a bipotential lens can be formed and can be used as an electromagnetic field compound objective lens having a low aberration coefficient. In particular, when the magnetic pole and the lower electrode are used at the same potential as the sample, an asymmetric electric field is not generated even at the time of tilting, and there is no fear of discharge because the magnetic pole and the sample have the same potential even at a high tilt. Of course, 1) and 2) above
If the upper electrode is made to have the same electric potential as the magnetic pole and the lower electrode and the sample are made to have the same electric potential, an asymmetric electric field does not occur even when tilted, and the electrostatic lens main surface is closer to the sample than in 1). Chromatic aberration can be reduced by that much, enabling high-resolution observation.

[Operation] In FIG. 1, electrons accelerated by a relatively high voltage of about several kV are focused by the convex lens effect of the magnetic field of the electromagnetic lens, and the ground potential of the magnetic pole and the negative bias applied to the electrode and the sample. 1k due to the combined effect of the convex and concave lenses of the deceleration electric field formed by the voltage
It is decelerated and focused to about V and irradiated onto the sample. Due to the combination of the magnetic field and the deceleration electric field, a kind of achromatic effect is produced and the aberration coefficient is reduced. Secondary electrons generated by the irradiation of the electron beam are detected by a secondary electron detector installed above the electromagnetic lens to form a secondary electron image. Since the electrode has a shape capable of tilting the sample and the sample and the electrode have the same potential, an asymmetric electric field does not occur and astigmatism does not occur even when tilted.

In FIG. 2, the magnetic pole and the lower electrode are set to the ground potential,
1 kV when a positive bias potential is applied to the upper electrode
The electron beam accelerated by a certain acceleration voltage is focused by the magnetic field of the electromagnetic lens, then accelerated by the positive potential of the upper electrode, and then decelerated and focused again by the ground potential of the lower electrode to irradiate the sample. . Secondary electrons generated by irradiating with an electron beam are detected by the secondary electron device in the same manner as described above to form a secondary electron image. Since both the upper electrode and the lower electrode have a shape that does not hinder sample tilting, sample tilting is possible. At this time as well, since the sample and the lower electrode have the same potential, the astigmatism does not occur due to the asymmetric electric field due to the sample inclination. Further, when the large sample is tilted by a large angle, the magnetic pole and the sample come close to each other, but there is no fear of causing discharge because the magnetic pole and the sample have the same potential.

FIG. 3 shows an example of comparison of the calculation results of the aberration coefficient of the present invention (FIG. 2) and the conventional example (FIG. 4). From the figure, with a long working distance (17 mm) that allows a large tilt, the chromatic aberration coefficient that greatly contributes to resolution at low acceleration voltage is about 1 / for tilt correspondence (upper electrode is ground, lower electrode is the same bias voltage as the sample). It can be seen that it is reduced to about 1/3 in the case of 2 (planar correspondence (both upper electrode and lower electrode are ground, bias voltage for sample)).

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, a primary electron beam 1 emitted from an electron source is accelerated to 3 kV, passes through a hole provided in an axisymmetric secondary electron detector 2, and then a unipolar type electromagnetic lens 3
Is focused by the magnetic field of. Further, it is decelerated to about 1 kV by a decelerating electric field created by a negative bias voltage of about 2 kV of the conical electrode 4 and the earth potential of the magnetic pole so as not to disturb the inclination of the sample, and at the same time, it is focused and irradiated onto the wafer 5. It The focused electron beam is scanned on the wafer surface by a deflection coil (not shown in FIG. 1), and the generated secondary electrons 6 move upward due to the superposition of the magnetic field of the monopole lens and the electric field between the magnetic pole and the electrode. The secondary electron detector is efficiently guided to form a secondary electron image.
The secondary electron detector 2 is composed of a scintillator or a micro channel plate. Since the wafer 5 and the electrode 4 have the same electric potential, a high-resolution observation can be performed without causing an asymmetric electric field due to the tilt and without changing the asymmetry due to the tilt angle and increasing the astigmatism even when tilted. And

If the electrode 4 is also set to the ground potential when the sample is not tilted, the above-mentioned decelerating electric field is formed near the wafer 5, so that the electric field / magnetic field superimposing effect works more efficiently and higher resolution observation is possible. To

In FIG. 2, two electrodes, an upper electrode 4a and a lower electrode 4b, are formed in a conical shape so as not to obstruct the inclination of the wafer 5, and the voltage is controlled together with the wafer 5 to widen the range of application. It is a thing.

1) When the upper electrode 4a is at the ground potential and the lower electrode 4b is at the same potential as the wafer 5, the observation can be performed with higher resolution even when the main surface of the electrostatic lens is tilted as much as the main surface approaches the wafer 5.

2) When the wafer 5 is not tilted,
Both the upper electrode 4a and the lower electrode 4b are set to the ground potential,
If a negative bias voltage is applied to only the wafer 5 and used, high-resolution observation comparable to observation at a short working distance as in FIG. 1 is possible.

3) If the magnetic pole, the lower electrode 4b, and the wafer 5 are all set to the ground potential and a positive voltage is applied to the upper electrode 4a to form the Einzel lens, the aberration coefficient is reduced by the electric field / magnetic field superimposing action. Not only that, since the wafer 5 and the lower electrode 4b have the same potential, an asymmetric electric field does not occur even if the wafer is tilted, and the observed image is not deteriorated due to astigmatism. Moreover, even if the wafer 5 is tilted at a large angle to approach the magnetic pole, the magnetic pole and the wafer are at the same potential, so that there is no fear of occurrence of discharge.

Since both FIG. 1 and FIG. 2 can be used with a long working distance, they can be fixed and used with the working distance used in elemental analysis by X-ray.

[0020]

As described above, by inserting a small electrode between the electromagnetic lens and the sample and optimally controlling the voltage, the sample can be tilted greatly with a low accelerating voltage that causes less charge-up and electron beam damage. However, no asymmetric electric field is generated, and when the sample is not tilted, the main surface of the electrostatic lens can be lowered to perform high-resolution observation. Since it can be used with a fixed working distance, there is no visual field shift due to a change in working distance, and observation / measurement time can be shortened.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of an embodiment of the present invention.

FIG. 3 is a diagram showing an example of comparison of aberration coefficients of the present invention and a conventional example.

FIG. 4 is an explanatory diagram of a conventional example in which a magnetic field is generated on the sample side to reduce an aberration coefficient.

FIG. 5 is an explanatory diagram of a conventional example in which an electric field and a magnetic field are superposed to reduce an aberration coefficient.

FIG. 6 is an explanatory diagram of a conventional example in which an electric field and a magnetic field are superposed to reduce an aberration coefficient.

[Explanation of symbols]

1 primary electron beam 2 Secondary electron detector 3 electromagnetic lens 4 electrodes 5 wafers 6 Secondary electron 7 Variable voltage power supply

Continuation of the front page (56) Reference JP-A-8-185823 (JP, A) JP-A-9-17369 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37 / 12-37/145 H01J 37/28 H01J 37/244

Claims (2)

(57) [Claims] The electron beam apparatus comprising a magnetic lens for focusing the claim 1 Electron beam source and the electron beam, is arranged a small electrode in the form capable of tilting of the sample between the electromagnetic lens and the sample, the sample the so asymmetrical electric field due to the inclination of the sample by the voltage of the sample and the electrode at the same potential does not occur when the inclined, the when not tilting the sample
Switching the magnetic pole of the electromagnetic lens and the electrode to the same potential
An electron beam device that enables high-resolution observation with . Wherein a second <br/> electrodes between the electromagnetic lens and the electrode, and wherein the magnetic pole, to control the electrode and the second electrode <br/> potential respectively The electron beam apparatus according to claim 1.