JPS60167247A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To prevent shift of an observation visual field accompanying the acceleration voltage change-over by adding a generating means of a deflection magnetic field for correction, which forms the magnetic field in the direction negating the power to be received by electrons of an electron beam, to the secondary electron collecting means. CONSTITUTION:An electron beam 3 in a transmission imaging type electron microscope or the like is focused to irradiate a sample 6 arranged almost in the center of a magnetic pole gap of an objective 5 for detecting its secondary electrons by a secondary electron detector A including a ring-shaped electrode 11 as a secondary collecting means through a generating means 15 of a deflection magnetic field provided above the objective 5. Further, the generating means of the deflection magnetic field 15 is formed while being wounded by the coils 15a and 15b formed is saddle type on yoke 16 in order to generate a magnetic field B orthogonal to the optical axis 2. Accordingly, shift of an observation visual field can be prevented by changing the magnetic field B for correcting the deflection of the electron beam 3 when changing over the acceleration voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an improvement in a secondary electron detector of a scanning electron microscope.

[Prior art] When observing a sample such as a semiconductor using a scanning electron microscope, it is necessary to suppress damage to the semiconductor element, prevent charge-up of the sample, and reduce the penetration of incident electrons to improve the optical density near the surface. In order to extract only the red, the accelerating voltage of the electron beam that irradiates the sample is often lowered. Figure 1 shows an example of a conventional transmission imaging electron microscope equipped with a function that allows scanning electron microscope images to be observed.
is an electron gun from which an electron beam 3 is taken out along an optical axis 2, and the electron beam 3 from the electron gun 1 is focused by a focusing lens 4 to a magnetic pole piece I! of an objective lens 5. The sample 6 placed at approximately medium heat in the I gap is irradiated.

7 and 8 are deflection coils for two-dimensionally scanning the electron beam 3 on the sample 6. A secondary electron detector for detecting secondary electrons is provided above the objective lens 5, and is composed of a light pipe with a scintillator attached to its tip and a photomultiplier tube 10 disposed at its rear end. . A conductive thin film is deposited on the front surface of the scintillator at the tip of the light pipe 9, and a ring-shaped secondary electron collecting electrode 11 as a means for collecting secondary electrons is arranged around the conductive thin film. is applied at, for example, +10 KV by a DC power supply 12, and a shield tube 13 at a ground potential is provided around it. Reference numeral 14 denotes an accelerating power source that supplies an accelerating voltage for the electron beam 3 to the electron gun.

In the apparatus shown in FIG. 1, when the acceleration voltage Va for accelerating the electron beam 3 is as high as 40 KV, for example, the deflection of the electron beam 3 due to the electric field formed by the secondary electron collection electrode 11 does not pose a problem. However, when the accelerating voltage Va is lowered to about 5 KV, the speed of the electron beam becomes slower, and the time spent in the charge formed by the secondary electron collecting electrode 11 becomes longer, so the electron beam 3 is largely deflected by the electric field. It will be done. For example, trajectory 3 shown in FIG.
is when Va is 30 KV, and 3' is when Va is 5 KV. This change in the trajectory of the electron beam by switching the accelerating voltage means that the field of view of the sample image moves when switching the accelerating voltage.
This has been a major hindrance, especially in the observation of semiconductor samples.

[Purpose of the Invention] The present invention provides a secondary electron detection device (by preventing an electron beam irradiated onto a sample from being deflected by an electric field formed by a secondary electron collecting means). The purpose is to prevent movement of the observation field due to

[Structure of the Invention] The 4iQ configuration of the present invention includes a means for accelerating an electron beam taken out from an electron gun along the optical axis with an acceleration voltage Va and irradiating the sample, and a means for irradiating the sample with the electron beam taken out from the electron gun, and A device comprising: a secondary electron collecting means for forming an electric field for collecting secondary electrons; and a secondary electron detector for detecting the secondary electrons collected by the secondary electron collecting means, A correction deflection magnetic field generating means is provided for forming a magnetic field that applies a force to the electrons of the electron beam in a direction that cancels out the force that the electrons of the electron beam receive due to the electric field formed by the secondary electron collecting means. It is characterized by the following.

[Example] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 is a schematic diagram showing one embodiment of the present invention.

Components that are the same as those in FIG. 1 are given the same numbers and their explanations will be omitted. In FIG. 2, reference numeral 15 denotes a correction deflection located near the secondary electron detector for the purpose of correcting the deflection of the electron beam 3 due to the electric field formed by the secondary electron collecting electrode 11 of the electron beam 3. The correcting deflection magnetic field generating means 15 is a magnetic field generating means, and the correcting deflection magnetic field generating means 15 includes saddle-shaped coils 15a and 15b for forming a correcting magnetic field B in a direction perpendicular to the optical axis 2, as shown in FIG. It is composed of a yoke 1G.

The coils 15a and 15b are wound around a yaw 916 that also serves as a winding frame, and in this embodiment, a third coil is provided between the opposing coils.
A uniform correction magnetic field B is formed in the direction shown by the arrow in the figure.

Further, a window 16a is bored in the yoke 16, and a secondary electron detector is arranged in the window portion. 17 is coil 1
5a and 15b, and the excitation FI 11 power supply 17 is connected to the acceleration power supply 14,
Switching of the acceleration voltage of the acceleration power source 14 [The excitation current supplied to the coils 15a and 15b is changed in conjunction with this.

In FIG. 3, for example, assuming that the distance between the ground potential part A and the secondary electron collecting electrode 11 is 20 cm and the electric field is uniformly distributed, the secondary electron collecting electrode 11 is
When applying a voltage of 0KV, there is a voltage of 10KV near the optical axis.
10.2m=5X104V/m electrodes are formed. Therefore, the electron beam 3 becomes F+ = eE due to the electric field.
The electron beam is deflected like the electron beam 3' in FIG. 1 by the force, and the sample irradiation position moves. Here, e is the amount of charge of the electron, and E is the strength of the electric field.

Therefore, in order to correct the deflection of the electron beam 3 due to the electric field formed by the secondary electron collecting electrode 11, the present invention provides a force F due to the electric field of the secondary electron collecting electrode 11 that the electron beam 3 receives.
1 is canceled out by the deflection magnetic field generated by the newly provided corrective pot direction magnetic field generating means 15. Second
Magnetic field B formed by correction deflection magnetic field generating means 15 shown in the figure
Therefore, the electrons of the electron beam 3 are subjected to a force F2 = eVo B in the opposite direction to Fl. Here, VO is the velocity of the electron beam 3, B is the strength of the magnetic field, Vas is the acceleration voltage of the electron beam 3, is the mass of the electron, and is mo
Vo 2= 2 e Va Vo= 26Va/n-, therefore, F2=ezu] ";σ]- and 1-0x8.

Further, a secondary electron collection electrode 11 receives the electrons of the electron beam 3.
In order to cancel out F+ by the newly added magnetic field, it is sufficient to create a magnetic field that makes F+=F2 '+fJ'45f:' and cancel it out.

That is, it is sufficient if e[=eF'5/rTIQX3 holds true. Therefore, if E=5X104V/m and Va=1KV, in this example, by forming a magnetic field of about 26.7 Gauss, electrons can be It is possible to correct the deflection of the beam 3 due to the electric field.Here, assuming that the voltage applied to the secondary multiplex collecting electrode 11 is constant, if the accelerating voltage Va of the electron gun 1 is avoided, this voltage will change. The excitation of the corrective deflection magnetic field generating means 15 in conjunction with the change in the current i!magnetic field B
By changing the strength of the electron beam, it is possible to always correct the deflection of the electron beam by the electrode 11, regardless of the acceleration voltage. Note that the excitation coil and yoke in the correction deflection magnetic field generating means 15 are arranged in a direction perpendicular to the direction in which the secondary electrons e2 from the sample 6 go toward the secondary electron detector.
The excitation coil and yoke 16 do not obstruct passage of secondary electrons.

Furthermore, since the secondary electrons e2 emitted from the sample 6J travel in the opposite direction to the electron beam 3, they receive a force from the correction magnetic field B in a direction opposite to the force received by the electron beam 3. That is, since the direction is toward the secondary electron collection electrode 11, this newly added correction magnetic field B also contributes to secondary electron collection. By forming +F4 in this manner, the deflection of the electron beam 3 due to the electric field of the secondary electron collecting electrode 11 can be corrected.

FIG. 4 is a schematic diagram of another embodiment of the present invention, and the same components as those in FIG. 2 are designated by the same numbers and their explanations are omitted. In FIG. 4, 18a and 18b are a pair of secondary electron deflection electrodes for forming an electric field E in a direction perpendicular to v11 B formed by the correction deflection magnetic field generating means 15, and one electrode 18a is The electrode 18b is a flat metal electrode, and the other electrode 18b is configured in the form of a metal mesh. or,
A DC voltage of Lee V/2 (for example, -500V) is applied to the electrode 18a from the DC power source 19, and a DC voltage of 10V/2 is applied to the electrode 18b.
A DC voltage of 2 (for example, +500V) is applied from a DC power supply 20. In the device configured in this way, secondary electron collection of the electron beam 3 (cell 11 and electrodes 18a, 1
Since the deflection caused by the electric field 8b is corrected by the correction deflection magnetic field generating means 15, the sample irradiation position of the electron beam 3 does not move, and therefore the field of view is also prevented from moving. Further, the secondary electrons e2 from the sample 6 were deflected by the secondary electron deflection electrode 18b to which +500V was applied, passed through a mesh-like gap formed of metal, and were further applied to the secondary electron collection electrode 11. Since the secondary electrons are detected while being accelerated by a voltage of +10 KV, the efficiency of collecting secondary electrons can be improved. By arranging the electrodes 18a and 18b, it is possible to form a substantially uniform electric field, which has the advantage that the force exerted by the electrons of the electron beam 3 can be more easily offset by the correcting pan direction magnetic field generating means 15. Furthermore, the secondary electron e2 coming up from below
Since both the force due to the electric field E and the force due to the magnetic field B are directed toward the secondary electron detector, the secondary electron detection efficiency can be improved. Furthermore, a ring-shaped ferromagnetic yoke and a coil wound thereon are used as correction deflection magnetic field generating means, and a similar-shaped window 16b is provided in the yoke at a position axially symmetrical to the window for inserting the detector. By providing this, the internally generated magnetic field can be brought close to a uniform magnetic field, so that the deflection forces of the electric field E and the Il field B on the electron beam can be canceled more accurately.

[Effects] As described above, the present invention includes a means for accelerating an electron beam taken out from an electron gun along an optical axis with an accelerating voltage Va and irradiating the sample, and a means for irradiating the sample with an electron beam that is provided closer to the electron gun than the objective lens. A device comprising: a secondary electron collecting means for forming an electric field for collecting secondary electrons; and a secondary electron detector for detecting the secondary electrons collected by the secondary electron collecting means, The present invention provides a scanning electron microscope that prevents movement of the field of view due to switching of accelerating voltage by correcting the deflection of the electron beam due to the electric field formed by the secondary electron collecting means.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a conventional device, Fig. 2 is a schematic diagram of an embodiment of the present invention, Fig. 3 is a diagram for explaining the embodiment device of Fig. 2, and Fig. 4 is another embodiment. FIG. 5 is a schematic diagram for explaining another embodiment. 1: Electron gun, 3: Electron beam, 4: Focusing lens. 5: Objective lens, 7. s: a-direction coil, 9 nirite pipe, 10: secondary electron multiplier, 11: secondary electron collecting electrode,
13: Seal 1 to cylinder, 14: Acceleration power source. 15: Correction dose direction magnetic field generating means, 16: Yoke. 17: Excitation power supply, 18a, 18b: Secondary electron collection electrodes, 19.20: DC power supply. Patent applicant JEOL Ltd. Representative 9 Fuji - Husband

Claims (1)

[Scope of Claims] (1) A means for accelerating an electron beam emitted from an electron gun along an optical axis by an accelerating voltage Va and irradiating the sample; 43. A device comprising a secondary electron collecting means for forming an electric field for collecting secondary electrons, and a secondary electron detector for detecting the secondary electrons collected by the secondary electron collecting means. , further comprising a correction deflection magnetic field generating means for forming a magnetic field that applies a force to the electrons of the electron beam in a direction that cancels the force exerted on the electrons of the electron beam by the electric field formed by the secondary electron collecting means. A scanning electron microscope characterized in that: (2) The scanning electron microscope according to claim 1, wherein the excitation intensity of the correction deflection magnetic field generating means is controlled in conjunction with switching of the acceleration voltage Va. (3) As the correction deflection magnetic field generating means, a yoke made of a ferromagnetic material having a window for passage of secondary electrons and a window of the same shape at a position axially symmetrical with the window, and a yoke on the yoke. A scanning electron microscope according to claims 1 to 2, comprising a wound coil. (4) The secondary electron collecting means is a voltage of 1 V/2 arranged approximately symmetrically with respect to the optical axis. A scanning electron microscope according to any one of claims 1 to 3, characterized in that a metal plate-like electrode to which a voltage of +V/2 is applied and a metal mesh-like electrode to which a voltage of +V/2 is applied are used.