JPH06215715A - Electron beam device - Google Patents

Abstract

PURPOSE:To have secondary electrons incident vertically on an analysis electrode by forming a low magnetic field region, and to achieve resolution and analytical accuracy by thinning a part of the magnetic circuit of an objective lens in an annular form on the same axis of an optical axis or by enlarging the diameter of the part. CONSTITUTION:The thickness of a part 6X of a cylinder facing an optical axis L-L of a magnetic circuit 6B of an objective lens 6 is reduced, and a thick annular part is formed. Magnetic flux is leaked from the annular part, and a cylindrical part 6Y of the circuit 6B is enlarged, and an annular part of large diameter is formed. A flat low magnetic field region is formed in the range of 0.1 to 0.7%, on the peak magnetic field in the side of an electron gun, in the magnetic field distribution of the optical axis. A buffer electrode is provided on the low-magnetic field region, and primary electrons can be maintained at low abberation even when the low electric potential required for the vertical incidence of secondary electrons to an analysis electrode is achieved for the electric potential of the buffer electrode, and the resolution and the analytical accuracy of an electron beam tester can thus be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam apparatus for performing a non-contact test on an integrated circuit or the like, and more particularly to an electron lens suitable for controlling both primary electrons and secondary electrons.

[0002]

2. Description of the Related Art A so-called electron beam probe or electron beam for irradiating an operating integrated circuit chip with an electron beam and examining the potential of these parts from a secondary electron image generated from each part of the integrated circuit chip at this time A tester is used. The outline of this device will be described with reference to FIG.

An electron beam 2 (primary electron) generated by an electron gun 1 is controlled to a predetermined speed by an accelerating electrode 3, focused by a pre-lens 4 and a condenser lens 5, and an objective lens 6 at the final stage, and then a sample 7 The surface of (for example, an integrated circuit chip) is irradiated. In the meantime, electron beam 2
Is deflected by the deflector 8 and scanned on the sample 7.
In FIG. 4, reference numeral 9 is a blanker for irradiating the sample 7 with the pulsed electron beam 2.

Inside the objective lens 6, there is a set of electrodes consisting of a plane grid such as a metal mesh, ie,
An extraction electrode 11 closest to the sample 7 and a buffer electrode 12 and an analysis electrode 13 parallel to the extraction electrode 11 are arranged on the optical axis with a gap between them. These electrodes are perpendicular to the optical axis of the objective lens 6. In FIG. 4, reference numeral 15 is an analysis electrode
Reference numeral 16 is a reflection electrode for directing the trajectory of the secondary electrons 10 passing through the detector 13 to the detector 14, and reference numeral 16 is a collector electrode for focusing the secondary electrons 10 toward the detector 14.

The secondary electrons 10 generated from the sample 7 by the irradiation of the electron beam 2 are accelerated by the extraction electrode 11 and then separated into energy by the analysis electrode 13. That is, the secondary electrons with a predetermined energy are
After passing through 13, it enters the detector 14 and is converted into an electrical signal. For accurate energy analysis, the secondary electron 10
It is necessary to control the orbit so that is incident on the analysis electrode 13 perpendicularly. For this orbit control,
The potential of the buffer electrode 12 is adjusted.

[0006]

FIG. 7 (a) shows a partial cross-sectional structure of the objective lens 6 in the conventional electron beam apparatus, and FIG. 7 (b) shows the magnetic field strength along the optical axis LL of the objective lens 6. The distribution, the trajectories of the primary electron beam 2 and the secondary electron 10, and the installation positions of the extraction electrode 11, the buffer electrode 12, and the analysis electrode 13 are shown.

In FIG. 7 (a), reference numeral 6A is a coil and reference numeral
6B is a magnetic circuit made of a ferromagnetic material, and a gap 6C is provided in a part of the magnetic circuit 6B. The drawing shows a part of the coil 6A and the magnetic circuit 6B along the optical axis LL of the objective lens 6, but the coil 6A and the magnetic circuit 6B have an annular structure with the optical axis LL as the axis of symmetry. Needless to say.

Referring to FIG. 7B, the secondary electron 10 generated from the surface of the sample 7 is accelerated to about 1 KV by the extraction electrode 11. Such a relatively high accelerating voltage is necessary in order to extract the secondary electrons from the electrode or wiring to be measured on the surface of the sample 7 without being affected by the potential of the adjacent electrodes. The accelerated secondary electrons 10 are decelerated by the buffer electrode 12 and their trajectories are controlled so that they are vertically incident on the analysis electrode 13.

Under the magnetic field distribution in the conventional electron beam apparatus as shown in FIG. 7, the secondary electrons 10 must be decelerated in a relatively strong magnetic field for the above orbit control. As a result, it is necessary to lower the potential of the buffer electrode 12 to several tens of volts (specifically, about 50V).

On the other hand, when the potential of the buffer electrode 12 is lowered in the structure shown in FIG. 4, the beam diameter of the primary electron beam 2 is increased due to the increase of aberration. This state is shown in FIG. In the figure, the horizontal axis is the potential (Vb) of the buffer electrode 12, and the vertical axis is the chromatic aberration coefficient (Cc) representing the magnitude of aberration. The increase of aberration means the decrease of resolution of electron beam probe. In Fig. 6, the parameter Zb
Is the distance of the buffer electrode 12 from the surface of the sample 7. From the figure, it can be seen that aberration can be reduced by disposing the buffer electrode 12 away from the sample 7. For each Zb,
The optimum Vb for vertically injecting the secondary electrons to the analysis electrode is only one marked with *, and such Vb is in the region of relatively low potential of several tens of V as described above.

The present invention provides a contradiction regarding the potential of the buffer electrode 12, that is, a low potential required from vertical incidence of secondary electrons on the analysis electrode 13 and a high potential required to reduce aberration of primary electrons. The purpose is to eliminate the disagreement with. In other words, it aims to achieve both high-precision secondary electron energy analysis and electron beam probing.

[0012]

The above object is an apparatus for measuring the voltage of a surface of a sample irradiated with primary electrons by analyzing the energy of secondary electrons generated from the surface of the sample. An electron gun for generating a primary electron beam, an electromagnetic lens for focusing the primary electron beam and irradiating the surface with the electron gun, each having a lattice-like structure perpendicular to the optical axis of the electromagnetic lens and having a mutual structure. A pair of electrodes arranged on the optical axis in the electromagnetic lens with a gap therebetween, that is, an extraction electrode arranged closest to the sample for accelerating the secondary electrons and the accelerated secondary electrons An electron beam device comprising a buffer electrode for making parallel to the optical axis of the electromagnetic lens and an analyzing electrode for analyzing the energy of the secondary electrons made parallel, in which the optical axis of the electromagnetic lens The magnetic field distribution above , 0.1% to 0 of its peak magnetic field.
The present invention is characterized in that it has a substantially flat region in the range of 7% on the electron gun side with respect to the position of the peak magnetic field, and the buffer electrode is arranged in the flat region. This is achieved by such an electron beam device.

[0013]

FIG. 1 shows the distribution of the magnetic field along the optical axis LL of the objective lens in the electron beam apparatus of the present invention, the trajectories of the primary electron beam and secondary electrons, and the installation of the extraction electrode 11, the buffer electrode 12 and the analysis electrode 13. Indicates the position. As shown in the figure, there is a wide region of low magnetic field, and the buffer electrode 12 is arranged in this region. This low magnetic field is
It is about 0.1% to 0.7%. Secondary electron is the analysis electrode
It is decelerated in this region so that it is vertically incident on 13. If the magnetic field strength in this region deviates from the range of the above value, secondary electrons do not vertically enter the analysis electrode 13.

Since the above-mentioned region has a low magnetic field, it does not significantly affect the aberration of the primary electron beam. Also,
This low magnetic field region is located on the opposite side of the sample with respect to the peak of the magnetic field strength. Therefore, the distance Zb between the sample and the buffer electrode is larger than that of the conventional electron beam apparatus shown in FIG. 7 (b). As a result, it can be seen from FIG. 6 that the aberration can be kept small even if the buffer electrode is set to a lower potential than before.

[0015]

FIG. 2 is an explanatory view of an embodiment of the present invention, showing a partial sectional structure of an objective lens 6 in the electron beam apparatus shown in FIG. 2 (a) corresponds to claim 2, and FIG. 2 (b)
Corresponds to the other general cases. The same parts as those in FIG. 7 are designated by the same reference numerals.

In the objective lens 6 shown in FIG. 2 (a),
The thickness of the cylindrical portion 6X facing the optical axis LL in the magnetic circuit 6B is smaller than that of the other portions. This part 6X is
It forms a thin annular part that is arranged coaxially with the optical axis LL. In the objective lens 6 shown in FIG. 2 (b), similarly,
The diameter of the cylindrical portion 6Y facing the optical axis LL in the magnetic circuit 6B is made larger than that of the other portions. This part 6Y is
It forms an annular part with a large diameter that is arranged coaxially with the optical axis LL.

Objective lens 6 shown in FIGS. 2 (a) and 2 (b)
The magnetic field distribution on the optical axis in Fig. 3 (a) and
Shown in (b). Further, the magnetic field strength distribution on the optical axis in the conventional objective lens 6 shown in FIG. 7 (a) is shown in FIG. 5 for comparison. The horizontal axis in FIGS. 3 and 5 is the distance on the optical axis LL with reference to the sample 7 (see FIG. 4), and the vertical axis is the magnetic field strength (gauss) on the optical axis LL.

First, referring to FIG. 5, a conventional objective lens 6
, The peak magnetic field strength is 600 gauss, and
A buffer electrode (not shown) is arranged at a position where b is about 15 mm. The magnetic field strength at this position is about 200 Gauss. On the other hand, in the objective lens 6 of FIG. 3 (a), when the peak magnetic field strength is 600 gauss, the low magnetic field strength region of about 1 gauss is tailed to the right side of the peak, that is, the electron gun (not shown) side. ing. In the objective lens 6 of FIG. 3 (b), when the peak magnetic field strength is 600 Gauss,
An area with a low peak of about 4 gauss is tailed to the right of the peak. 3 (a) and 3 (b), the thin annular portion 6X or the large diameter annular portion 6Y represents the magnetic circuit 6B.
The magnetic field distribution when not provided, that is, the distribution corresponding to the magnetic field distribution in the conventional objective lens 6 (see FIG. 5) is also enlarged and shown.

As shown in FIGS. 3 (a) and 3 (b), when a thin annular portion 6X or a large diameter annular portion 6Y is provided in a part of the magnetic circuit 6B, magnetic flux leaks from these parts. As a result, a wide area with a low magnetic field is formed. The buffer electrode is arranged in this low magnetic field region.

The annular portion 6X in FIG. 2 (a) or FIG.
Instead of deforming the shape of the magnetic circuit 6B in the objective lens 6 as in the annular portion 6Y in (b), the area corresponding to these portions 6X or 6Y in the magnetic circuit 6B is an annular portion made of a low magnetic permeability material. May be replaced with. As a result, a low magnetic field region is formed due to the leakage of magnetic flux from the annular portion of low magnetic permeability.

By the way, when the annular portion 6X or 6Y or the annular portion having a low magnetic permeability is provided at the position where the magnetic field is strongest in the magnetic circuit 6B (6P in FIG. 7 (a)), the low magnetic field region is slightly deformed. Can be created. On the other hand, such an annular portion may be provided outside the position 6P where the magnetic field is maximum. In this case, there is an advantage that deformation processing for creating a low magnetic field region does not require high accuracy.

[0022]

According to the present invention, the buffer electrode in the electron beam tester can be installed farther from the sample than the conventional one, and the potential of the buffer electrode can be set to a low potential necessary for vertical incidence of secondary electrons on the analysis electrode. Even in the above, the primary electron can be maintained at a low aberration, and as a result, there is an effect that it contributes to the improvement of the resolution and analysis accuracy of the electron beam tester.

[Brief description of drawings]

FIG. 1 is an explanatory view of the principle of the present invention.

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

FIG. 3 is a magnetic field distribution in the electromagnetic lens of the electron beam apparatus of the present invention.

FIG. 4 is a schematic configuration diagram of an electron beam device to which the present invention is applied.

FIG. 5: Magnetic field distribution in an electromagnetic lens of a conventional electron beam apparatus

FIG. 6 is a relation between the potential of the buffer electrode and the aberration in the electron beam tester.

FIG. 7 is an explanatory diagram of an electromagnetic lens of a conventional electron beam device.

[Explanation of symbols]

 1 electron gun 2 primary electron beam 3 acceleration electrode 4 pre-lens 5 condenser lens 6 objective lens 6A coil 6B magnetic circuit 6C gap 6X, 6Y annular part 7 sample 8 deflector 9 blanker 10 secondary electron 11 extraction electrode 12 buffer electrode 13 analysis electrode 14 Detector 15 Reflective electrode 16 Collector electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication H01J 37/28 A H01L 21/66 C 7630-4M

Claims (4)

[Claims] 1. A device for measuring the voltage of a surface of a sample irradiated with primary electrons by analyzing the energy of secondary electrons generated from the surface, the electron gun generating the primary electron beam. An electromagnetic lens for converging the primary electron beam and irradiating the surface with the electromagnetic lens, each having a lattice structure perpendicular to the optical axis of the electromagnetic lens and having a gap between them Of a pair of electrodes disposed on the optical axis of the electromagnetic field, that is, an extraction electrode disposed closest to the sample for accelerating the secondary electrons, and the accelerated secondary electrons being parallel to the optical axis of the electromagnetic lens. In the electron beam apparatus comprising a buffer electrode for analyzing and an analysis electrode for analyzing the energy of the secondary electrons collimated, the electromagnetic lens has a magnetic field distribution on its optical axis,
A region having a size in the range of 0.1% to 0.7% of the peak magnetic field in the distribution and being substantially flat is provided on the electron gun side with respect to the position of the peak magnetic field, and the buffer electrode is arranged in the region. An electron beam device characterized by being provided. 2. A part of a cylindrical portion facing the optical axis in a magnetic circuit forming the electromagnetic lens is formed of an annular portion having a reduced thickness and arranged coaxially with the optical axis. The electron beam apparatus according to claim 1, which is characterized in that. 3. A part of a cylindrical portion facing the optical axis in a magnetic circuit forming the electromagnetic lens is made of a material having a low magnetic permeability and an annular portion arranged coaxially with the optical axis. The electron beam apparatus according to claim 1, wherein: 4. The region in which the magnetic field is substantially flat is provided at a position corresponding to a region having the highest magnetic flux density in the magnetic circuit forming the electromagnetic lens. Electron beam device.