JPH01200546A - Electron beam device - Google Patents

Abstract

PURPOSE:To reduce dependency on secondary electron emission angle and improve voltage measurement precision for a sample surface in an electron beam device for which external observation is possible for action conditions of each part of a semiconductor device by providing a collimate grid added between a pullout grid and an analyzing grid provided between a sample and a radiation beam. CONSTITUTION:A sample 3 to be observed is disposed on the underside of an aperture through the center part of an objective lens 1, and an electron beam 2 is radiated to it from the top. In this constitution are provided an analyzing grid 5 of a flat form positioned on the incident side in a beam passage in the aperture and a pullout grid 4 positioned on the sample side, and a beam passing through the grid 5 is detected by a plurality of secondary electron detectors 6, where a collimate grid 8, of a flat similarly, is disposed added between the grid 5 and 4. By composing this way, a proper positive potential is applied to the grid 8, so an orbit 7 of a secondary electron is collimated, or paralleled, thereby the inclination angle to the grid 5 is reduced to zero.

Description

[Detailed Description of the Invention] [Summary] An electron beam device that allows the operating state of each part of a semiconductor device to be observed from the outside, and is in the form of an in-lens detector with a plane grid, and is capable of reducing voltage measurement errors. The purpose of the present invention is to provide an electron beam device capable of minimizing the dependence on the secondary electron emission angle and thus reducing the voltage measurement error. In an electron beam device comprising an extraction grid for extracting secondary electrons, both of which are made of a planar mesh, and an analysis grid that decelerates the secondary electrons and analyzes their energy, the extraction grid and the analysis grid are In the middle,
at least one for collimating the extracted secondary electron stream
It is constructed by providing two collimating grids.

[Industrial application field]

The present invention relates to an electron beam device that allows the operating state of each part of a semiconductor device to be observed from the outside, and particularly relates to an electron beam device with a short WD (
This invention relates to an improvement of an in-lens analyzer in which an energy analyzer is provided within the objective lens or closer to the electron beam source than the objective lens for the purpose of improving working distance.

In a semiconductor device such as an LSI, it is generally impossible to check the operating state of the internal electronic circuits from the outside, except for parts to which input/output terminals are connected.

However, when analyzing the operation of a semiconductor device or investigating a failure, it may be necessary to know the operating state of an internal circuit. For this purpose, by utilizing the fact that secondary electrons emitted when a semiconductor device is irradiated with an electron beam have energy (velocity) corresponding to the potential of the irradiated area, the electron beam column of a scanning electron microscope is By scanning each part of the semiconductor device surface using a mechanism similar to that of , and analyzing the energy of the generated secondary electrons,
An electron beam device has been developed that measures the potential distribution of each part of the semiconductor device.

It is generally desirable to install the secondary electron energy analyzer in such an electron beam device close to the sample, but in this case, the electron beam column needs to have a short WD of the objective lens in order to achieve high magnification. Therefore, it is not possible to install an energy analyzer between the objective lens and the sample, so an in-lens analyzer is used where the energy analyzer is installed inside the objective lens or above the objective lens (closer to the electron beam source). .

To analyze the energy of secondary electrons in such an electron beam device, a deceleration grid that is applied with a voltage to decelerate the secondary electrons is provided in the path of the secondary electrons, and the secondary electrons passing through this grid are detected. carried out by For in-lens analyzers, deceleration (analysis) to perform energy analysis
There are two types of grids: one with a hemispherical grid and one with a planar grid. Those with hemispherical grids have good energy analysis accuracy, but require a large space above the lens, which poses a problem in the construction of the electron beam column.

On the other hand, those having a planar grid do not take up much space, but have the problem of poor energy analysis accuracy because secondary electrons enter the analysis grid obliquely.

Therefore, there is a need for an electron beam device with good voltage measurement accuracy even when the analysis grid used for energy analysis is planar.

[Conventional technology]

Conventionally, as this type of energy analyzer, one in which both an extraction grid for extracting secondary electrons from a sample surface and an analysis grid for energy analysis are configured in a planar shape is known.

FIG. 5 shows the configuration of a conventional energy analyzer. In the figure, reference numeral 1 indicates an objective lens with an electron beam column, and an electron beam 2 emitted from an upper electron beam source (not shown) and converged by the objective lens 1 is transmitted to the sample LSI.
It is configured to irradiate the surface of 3. An extraction grid 4 made of a mesh is provided in a portion of the objective lens 1 near the sample surface for accelerating and extracting secondary electrons emitted from the sample LSI. A suitable positive potential is applied to the extraction grid 4. The extracted secondary electrons pass through the mesh of the extraction grid 4 and head upward, reaching the analysis (deceleration) grid 5, which is also made of a mesh, and is placed above the objective lens, where the energy exceeds the deceleration electric field of the analysis grid 5. Only those having this pass through this and are captured and detected by the secondary electron detector 6. 7 shows the secondary electron orbit in this case.

[Problem to be solved by the invention]

The energy analyzer shown in FIG.
A planar grid is used as the analysis grid 5. The secondary electron trajectory 7 generally has a shape as shown in FIG. 5, and since it is incident obliquely to the analysis grid 5, it is affected by the local electric field distribution on the surface of the sample LSI 3, and energy measurement This will cause an error.

FIG. 6 explains the effect of a local electric field on secondary electron orbits, and 101 and 102 indicate LSI wiring, and the interval between them is usually about 1 μm. Now wiring 10. The potential of the wiring 102 is O■, and the potential of the wiring 102 is +5V.
, and if the inclination (emission angle) of the secondary electrons emitted vertically upward from the wiring 10 t with respect to the LS ■ normal is α1, then the secondary electrons emitted vertically upward from the wiring 102 The electron trajectory 1)2 is bent under the influence of the adjacent wiring potential and has an emission angle α2 (α1 × α2), which causes an energy detection error.

FIG. 7 illustrates secondary electron trajectories and energy analysis errors in a conventional energy analyzer.

In FIG. 7, (a) shows the magnetic field distribution of the objective lens,
The magnetic flux density BZ on the objective lens axis with respect to the distance Z(1,) taken from the sample surface toward the electron beam source has a shape as shown in the figure. By traveling through a space in which the lens magnetic field and the electrostatic field generated based on the respective potentials of the extraction grid and the analysis grid are superimposed, the secondary electrons (b
) Draw the secondary electron orbit as shown. (b) exemplifies the orbit for a 5 eV secondary electron, and is shown for the case α = 0° to 80', and the inclination angle β with respect to the normal to the direction of incidence to the analysis grid is in this range of α, 15
It is about °.

As is clear from Figure 7 (bl), the inclination angle β when the secondary electrons enter the analysis grid changes depending on the secondary electron emission angle α from the sample surface, and therefore the vertical velocity component with respect to the analysis grid changes. Therefore, if the emission angle α of the secondary electrons changes depending on the configuration of the LSI as shown in FIG. 6, an error will occur in the energy analysis results.

In Fig. 7, (C) shows an example of energy analysis characteristics, and when the deceleration voltage VRT (V) is changed, ideally the quadratic While an electronic signal output is obtained, this analyzer causes a large deviation in the analysis characteristics as the emission angle α increases.In this case, the voltage measurement error on the LSI surface is the error voltage δVRT in the IC). approximately 3
■It has been shown that it can reach.

The present invention seeks to solve these problems of the prior art by minimizing the dependence of the voltage measurement error on the secondary electron emission angle in the form of an in-lens analyzer with a planar grid. An object of the present invention is to provide an electron beam device that can reduce voltage measurement errors.

[Means to solve the problem]

As an embodiment of the present invention is shown in FIG. 1, an electron beam apparatus is provided which includes an extraction grid 4 and an analysis grid 5 inside an objective lens 1 through which an electron beam 2 is incident on the surface of a sample 3. , at least one collimating grid 8 is provided between the extraction grid 4 and the analysis grid 5.

The extraction grid 4 is made of a planar mesh and performs a secondary electron extraction function.

The analysis grid 5 is made of a planar mesh and decelerates the extracted secondary electrons to analyze their energy.

The collimating grid 8 functions to collimate (parallelize) the extracted secondary electron flow.

[For production]

When an electron beam from an electron beam source is incident on the surface of an LSI sample through an objective lens, secondary electrons are emitted from various circuit parts such as wiring on the surface of the LSI in response to the electron beam irradiation. In this case, the emitted secondary electrons have energy (velocity) corresponding to the potential of that part, so by analyzing this secondary electron energy, the potential distribution in each part of the LSI under test can be investigated from the outside.

At this time, in an in-lens analyzer type electron beam device in which a planar secondary electron extraction grid and an analysis grid are provided inside the objective lens, the secondary electron flow is obliquely incident on the analysis grid. Under the influence of the emission angle α based on the local electric field of the electron emission site, the vertical velocity component with respect to the analysis grid changes, causing an energy analysis error.

Therefore, by providing a collimating grid between the extraction grid and the analysis grid to collimate the secondary electron flow, the vertical velocity component is made uniform regardless of the change in the emission angle α, thus reducing the energy analysis error. You will be able to do this. The position of the collimating grid in this case is:
In order to reduce energy analysis errors, it is particularly preferable to provide it between the extraction grid and the point where the magnetic flux density of the objective lens decreases to 50% of its peak value on the objective lens side from the sample.

〔Example〕

FIG. 1 shows one embodiment of the present invention.
The same parts as in the figure are designated by the same numbers, and 8 is a collimating grid.

In the embodiment of FIG. 1, a collimating grid 8 is provided between the extraction grid 4 and the analysis (deceleration) grid 5. The collimating grid 8 collimates the secondary electron orbit 7 by applying an appropriate positive potential to it.
parallelization) and bring the above-mentioned inclination angle β of the secondary electrons with respect to the analysis grid 5 close to 0, thereby reducing the influence of the secondary electron emission angle α.

FIG. 2 explains the secondary electron trajectory and energy analysis error in the embodiment shown in FIG.

In Fig. 2, (al indicates the magnetic field distribution of the objective lens,
The distribution of the magnetic flux density BZ on the objective lens axis with respect to the distance Z(n) taken from the sample surface toward the electron beam source has the same shape as that in FIG. In the figure, ZE indicates the position of the extraction grid, and zC indicates the position of the collimating grid.

Secondary electrons are generated by this Yozuna lens magnetic field and the extraction grid 4.
The collimating glyph 182 travels through a space in which electrostatic fields generated based on the respective potentials of the analysis grid 5 are superimposed, thereby drawing a secondary electron trajectory as shown in FIG. The peak) exemplifies the orbit for secondary electrons at 5 eV.

As shown in Figure 2), by controlling the energy (velocity) of the secondary electrons using the collimating grid 8, the trajectory of the secondary electrons with an emission angle α=0° to 80'' is collimated, and the analysis grid 5 At the position, the inclination angle β becomes approximately 0°, and the secondary electrons are incident perpendicularly to the analysis grid 5. Therefore, the energy (velocity) of the secondary electrons with respect to the analysis grid 5 becomes −-like, and the voltage measurement error is reduced.

In FIG. 2, (C) shows an example of energy analysis characteristics, and the voltage measurement error voltage δV RT on the LSI surface is 0.5 V, which is different from the case of the conventional technology shown in FIG. In comparison, it is reduced to about 1/6.

In this case, the voltage (collimating voltage) Vc applied to the collimating grid 8 has an optimal value at which the error voltage δVRT is minimized. Figure 3 shows an example of the optimal collimating voltage. When the distance between the sample surface and the collimating grid is %Iit Z + = IQwmO, the optimal collimating voltage is approximately 150μ, and in this case, the voltage measurement error voltage is It is shown that a minimum value δV RTmin #0°5■ is obtained.

FIG. 4 shows the relationship between the collimating grid position and the voltage measurement error voltage minimum value δV RTIIIin (thick line). Generally, the closer the collimating grid position is to the extraction grid, the lower the error voltage minimum value δV RTm.
in decreases. However, the magnetic flux density BZ (thin line) from the sample surface to the electron beam source is 1/2 of the peak value.
The change is small between the point Zo where the voltage decreases to zero and the extraction grid (ZE), and by arranging the collimating grid within this range, the voltage measurement error can be kept small in the same way.

〔Effect of the invention〕

As explained above, according to the present invention, in an electron beam device for energy analysis equipped with a flat extraction grid and an analysis grid, a collimating grid is placed between the two grids and an appropriate voltage is applied. When performing energy analysis of secondary electrons emitted from the sample surface, it is possible to reduce the dependence on the emission angle of secondary electrons from the sample surface, thus improving the accuracy of voltage measurement at the sample surface. can.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment of the present invention, FIG. 2 is a diagram explaining the secondary electron trajectory and energy analysis error in the embodiment shown in FIG. 1, and FIG. 3 is a diagram showing the optimum collimating voltage. A diagram showing an example, Fig. 4 shows the collimating grid position and the voltage measurement error voltage minimum value δV RTmin
Figure 5 is a diagram showing the configuration of a conventional energy analyzer, Figure 6 is a diagram explaining the effect of a local electric field on secondary electron orbits, and Figure 7 is a diagram showing the structure of a conventional energy analyzer. FIG. 2 is a diagram illustrating secondary electron orbits and energy analysis errors in FIG. 1-Objective lens 2-Electron beam 3...Sample LSI 4-Extraction grid 5-Analysis (deceleration) grid 6-Secondary electron detector 7...-Secondary electron trajectory 8-Collimating grid

Claims (2)

[Claims] (1) Inside the objective lens (1) that makes the electron beam (2) incident on the surface of the sample (3), there is an extraction grid (4) for extracting secondary electrons, both of which are made of a planar mesh, and In the electron beam device, the extracted secondary electron stream is collimated between the extraction grid (4) and the analysis grid (5). An electron beam device characterized in that it is provided with at least one collimating grid (8). (2) The collimating grid (8) is located between the point where the magnetic flux density of the objective lens (1) decreases to 50% of the peak value on the objective lens (1) side from the sample (3) and the extraction grid (4). Claim 1 characterized in that it is provided between
Electron beam device as described in section.