JP2011028934A - Method and device for stabilizing electron beam of electron beam irradiation apparatus - Google Patents

Abstract

The present invention relates to an electron beam stabilization method and apparatus for an electron beam irradiation apparatus, and to an electron beam stabilization method for an electron beam irradiation apparatus capable of stabilizing an irradiation current even when a field emission electron gun is used. The object is to provide a device.
A plurality of apertures capable of detecting current are prepared, and a relationship between aperture detection currents of the plurality of apertures and corresponding electron beam irradiation currents is stored in a memory 21 as a table, and electron beam irradiation currents are stored. In a small area, the sum of the plurality of diaphragm detection currents is used as a diaphragm detection current, and in an area where the electron beam irradiation current is large, a detection current of a specific diaphragm among the plurality of diaphragms is used as a detection current. The feedback control of the electron beam irradiation current is performed.
[Selection] Figure 1

Description

  The present invention relates to an electron beam stabilization method and apparatus for an electron beam irradiation apparatus, and more particularly, an electron that requires a stable irradiation current, such as EPMA (electron beam microanalyzer), analysis SEM, analysis TEM, and electron beam drawing apparatus. The present invention relates to an electron beam stabilization method and apparatus for a beam irradiation apparatus.

  In a scanning electron microscope (SEM), a transmission electron microscope (TEM), an electron beam drawing apparatus, and the like, it is necessary to irradiate a sample with a stable irradiation current. For this reason, feedback control for stabilizing the irradiation current is performed.

  FIG. 3 is a conceptual diagram of a conventional apparatus. In the figure, 1 is a focusing lens (CL), 2 is an objective lens, 3 is an electron beam, 4 and 5 are apertures for focusing the electron beam, 6 is an aperture capable of detecting current, and a micro ammeter 8 detects the aperture. The current is detected. Reference numeral 7 denotes a target irradiated with the electron beam 3. The target 7 is a sample such as a wafer. The irradiation current increases from the left to the right in the figure. The operation of the electron beam irradiation apparatus having such a configuration will be described as follows.

  An electron beam 3 emitted from an electron source (not shown) is focused by a focusing lens (CL) 1. The focused electron beam 3 passes through subsequent apertures 4, 5, 6, is focused again by the objective lens 2, and irradiates the target 7 with the electron beam 3. Here, when the excitation current of the focusing lens 1 is changed, the amount of current passing through the diaphragm 6 changes, and the amount of irradiation current applied to the target 7 changes.

  Under the condition that the periphery of the electron beam 3 is blocked by the diaphragm 5, the current detected by the diaphragm 6 is proportional to the irradiation current amount as shown in the graph 1. Graph 1 is a diagram showing the relationship between the irradiation current to the target 7 and the aperture detection current. α represents an irradiation current-aperture detection current characteristic. This characteristic indicates the characteristic of the objective aperture 6.

  The irradiation current can be kept constant by measuring the current detected by the diaphragm 6 with the ammeter 8 and performing feedback control of the focal position of the focusing lens 1 so that the detected current becomes constant.

  As a conventional device of this type, a detector for detecting the emission current is arranged between the electron gun and the focusing lens, and the initial value of the detector at the set probe current and the excitation correction data of the focusing lens are stored. There is known a probe current stabilizing device that includes a means for correcting the focusing lens current based on excitation correction data in accordance with a change in detector output with respect to an initial value (see, for example, Patent Document 1).

  Further, an electron beam stabilizer that arranges a current detection slit below the focusing lens, detects a beam corresponding to the peripheral edge of the current detection slit, and feeds back the detected current value to the focusing lens, thereby controlling the beam current constant. The electron beam stabilizer is characterized in that the current detection slit is provided with a hole with a mesh and the beam is detected through the peripheral edge of the current detection slit and the mesh (see, for example, Patent Document 2). ).

  Further, between the converging lens and the objective lens, the first stop for electron beam shielding from the converging point of the electron beam by the converging lens to the objective lens side, and the objective lens side from the first aperture to the objective lens side. A box shape having a third aperture having an aperture larger than one aperture on the upper surface, an aperture smaller than the first aperture, and a second aperture on the lower surface for setting an opening angle of an electron beam in the objective lens Beam current measuring means and lens control means capable of changing the intensity of the converging lens based on the measured beam current detected by the beam current measuring means, and the focusing lens of the converging lens so that the measuring beam current is constant. An electron beam apparatus characterized by controlling strength is known (for example, see Patent Document 3).

JP-A-1-183044 (page 3, upper left column, line 1 to lower right column, line 8) JP-A-1-292733 (page 2, lower left column, lines 10 to 17). Japanese Patent No. 3520165 (paragraphs 0009 to 0014).

  In the case of a thermionic emission electron gun using a tungsten (W) filament or the like, since the amount of electrons (current) emitted from the light source is large, a current sufficient for feedback control by the diaphragm 6 can be obtained. On the other hand, in order to obtain an image with high brightness and high spatial resolution, it is necessary to use a field emission electron gun.

  However, since the amount of electrons (current) emitted from the field emission type electron gun is small, the radiation current irradiated to the target is under the condition of obtaining the same value as the irradiation current obtained with a thermal electron gun such as tungsten W or LBG. There is a problem that the detection current for feedback is reduced, and a current sufficient for feedback control cannot be detected by the diaphragm.

In addition, as shown in FIG. 4, when the diameter of the diaphragm 5 or 4 is increased in order to increase the current detected by the diaphragm 6, if the irradiation current irradiated to the target 7 is increased as I → II →. The peripheral portion of the electron beam 3 is not blocked by the diaphragm 5, and the current detected by the diaphragm 6 is not proportional to the irradiation current above a certain irradiation current.

  This is shown in graph 2. The characteristic shown in the graph 2 is proportional to the diaphragm detection current until the irradiation current becomes I1, but when the irradiation current exceeds I1, the characteristic α is not proportional to the diaphragm detection current.

  The present invention has been made in view of such problems, and provides an electron beam stabilization method and apparatus for an electron beam irradiation apparatus that can stabilize an irradiation current even when a field emission electron gun is used. The purpose is to do.

In order to solve the above-described problems, the present invention has the following configuration.
(1) According to the first aspect of the present invention, a plurality of apertures capable of detecting current are prepared, and the relationship between the aperture detection currents of the plurality of apertures and the corresponding electron beam irradiation current is stored in a memory as a table. In the region where the electron beam irradiation current is small, the sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the detection current of a specific aperture among the plurality of apertures is used. Each is used as a detection current, and feedback control of the electron beam irradiation current is performed.

  (2) The invention according to claim 2 uses the control device that controls the overall operation of the electron beam irradiation apparatus to determine the relationship between the aperture detection current stored in the memory and the corresponding electron beam irradiation current. In the region where the electron beam irradiation current is small, the detection current is obtained by adding a plurality of aperture detection currents. In the region where the electron beam irradiation current is large, the detection current of a specific aperture among the plurality of apertures is detected. As the current, feedback control of the electron beam irradiation current is performed.

  (3) The invention according to claim 3 is a plurality of apertures capable of detecting current, aperture detection current detecting means for detecting current flowing through each aperture, aperture detection currents of these apertures, and corresponding electron beams A memory for storing the relationship with the irradiation current as a table, and a control device for controlling the operation of each of the overall components. The control device refers to the memory, and in a region where the electron beam irradiation current is small. The sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the detection current of the specific aperture among the plurality of apertures is used as the detection current. This is characterized in that the feedback control is performed.

According to the present invention, the following effects can be obtained.
(1) According to the invention described in claim 1, in the region where the electron beam irradiation current is small, the sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the plurality of the plurality of aperture detection currents. Feedback control of the electron beam irradiation current is performed by using the detection currents of the specific diaphragms as detection currents, so that stable feedback control is always performed even when a field emission electron gun is used. be able to.

  (2) According to the invention described in claim 2, stable feedback control can always be performed even when a field emission type electron gun is used using a control device that controls the overall operation of the electron beam apparatus. .

  (3) According to the invention described in claim 3, in the region where the electron beam irradiation current is small, the sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the plurality of the plurality of aperture detection currents. Feedback control of the electron beam irradiation current is performed by using the detection currents of the specific diaphragms as detection currents, so that stable feedback control is always performed even when a field emission electron gun is used. be able to.

It is a figure which shows the structural example of this invention. It is an operation | movement conceptual diagram of this invention apparatus. It is an operation | movement conceptual diagram of a conventional apparatus. It is another operation | movement conceptual diagram of a conventional apparatus.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. The same components as those in FIG. 3 are denoted by the same reference numerals. In the figure, 3 is an electron beam, 1 is a focusing lens (CL) for focusing the electron beam 3, and 2 is an objective lens (OL) for finely focusing and irradiating the electron beam 3 onto the target.

  4 is a first aperture, 5 is a second aperture, and 6 is a third aperture. Among these stops, 5 and 6 are current-detectable stops, and 6 may also serve as an objective stop. Reference numeral 7 denotes a target (sample). 8 is an ammeter that measures the current detected by the second diaphragm 5, and 9 is an ammeter that measures the current detected by the third diaphragm 6.

  An adder 13 adds the outputs of the ammeters 8 and 9. SW is a switch that receives the output of the ammeter 9 at the contact a and the output of the adder 13 at the contact b. A control device 20 controls each component of the apparatus and controls the entire operation. For example, a personal computer is used as the control device 20. Reference numeral 21 denotes a memory connected to the computer 20 for storing various information. For example, a RAM or a hard disk device is used as the memory 21.

  An amplifier 22 receives the control signal from the control device 20 and drives the focusing lens 1. For example, a variable output power source is used as the amplifier 22. The common contact c of the switch SW is in the control device 20. As a result, the contact point of the switch SW can be selected from the control device 20 as a or b. Reference numeral 10 denotes an ammeter that measures the electron beam irradiation current, and its output is input to the control device 20.

  FIG. 2 is a conceptual diagram of the operation of the apparatus of the present invention. The same components as those in FIG. 3 are denoted by the same reference numerals. The graph 3 in the figure will be described. In graph 3, the horizontal axis represents the electron beam irradiation current, and the vertical axis represents the aperture detection current. The electron beam irradiation current indicates the current applied to the target 7, and the aperture detection current indicates the detection current of the apertures 5 and 6. α is a characteristic of the diaphragm 5, and β is a characteristic of the diaphragm 6. α + β represents a characteristic obtained by adding the characteristic α and the characteristic β.

  The characteristic α of the diaphragm 5 has a non-linear detection current characteristic since the electron beam irradiation current value is I1. The characteristic α + β is used for feedback control up to the region where the irradiation current becomes I1. In the region where the irradiation current is larger than I1, the characteristic β is used for feedback control. Therefore, the characteristic indicated by the thick solid line in the graph 3 is stored in the memory 21. The control device 20 performs feedback control using this characteristic.

  The electron beam 3 is focused by the focusing lens 1, passed through the diaphragms 4 to 6, and again focused by the objective lens 2, and the target 7 is irradiated with the electron beam 3. When the focal position of the focusing lens 1 is changed, the amount of current passing through the diaphragm 6 changes, and the amount of irradiation current applied to the target 7 changes.

  The focusing lens 1 is a magnetic lens, an electric field lens, an electromagnetic superposition lens, or the like, and can change the focal position of the electron beam 3 by changing the excitation current or the applied voltage. The diaphragms 5 and 6 are diaphragms capable of detecting current. Here, for the sake of simplicity, the description will be made assuming that there are two diaphragms capable of detecting a current, but there may be a case where a diaphragm capable of detecting a current is further provided between the diaphragm 4 and the diaphragm 6. The operation of the apparatus configured as described above will be described as follows.

Under conditions I to V where the periphery of the electron beam 3 is blocked by the diaphragm 5, the current detected by the diaphragm 6 is proportional to the entire area of the irradiation current as indicated by β in the graph 3. Similarly, under the conditions (I to II) where the periphery of the electron beam 3 is blocked by the diaphragm 4, the current detected by the diaphragm 6 is in the region on the left side of I1 in the graph 3.
Proportional to the amount of irradiation current. However, the condition that the periphery of the electron beam 3 is not blocked by the aperture 4 (II
˜V), the current detected by the diaphragm 5 is not proportional to the irradiation current as shown by the characteristic α.

  The control device 20 monitors the output of the ammeter 10, and in a region where the output does not exceed the current value I1, the common contact c of the switch SW is connected to the b contact side, and the current detected by the apertures 5 and 6 is detected. A control signal is output to the amplifier 22 so that the electron beam irradiation current becomes constant by using the characteristic α + β which is a current obtained by summing the currents. In the amplifier 22, a control signal is applied to the focusing lens 1. Here, when the focusing lens 1 is a magnetic lens, an excitation current is applied to the focusing lens 1, and when the focusing lens 1 is an electric field lens, a voltage is applied to the focusing lens 1.

  By performing such feedback control, it is possible to perform control such that the electron beam irradiation current becomes constant. Further, the control device 20 that has monitored the electron beam irradiation current with the ammeter 10 connects the common contact c to the a side when the electron beam irradiation current exceeds I1, and uses the characteristic β to Feedback control is performed so that the irradiation current becomes constant.

As described above, according to the present invention, feedback control can be performed so that the electron beam irradiation current becomes constant using the linear aperture detection current characteristic in the entire region from the electron beam irradiation current regions I to V. In particular, when feedback control is performed using α + β as the electron beam irradiation current, feedback control is performed in a region where the aperture current value is large, so that control with a good SN ratio can be performed. In such a series of feedback control, the control device 20 refers to the value stored in the memory 21. If α + β or β exceeds the data value stored in the memory 21 or does not reach the data value, it is possible to carry out an abnormality process assuming that the feedback control is abnormal. In the present invention, feedback control is performed using the characteristic indicated by the thick solid line in the graph 3.

  According to the present invention, in the region where the electron beam irradiation current is small, the sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the specific aperture among the plurality of apertures. Therefore, even when a field emission electron gun is used, stable feedback control can always be performed.

  In the above-described embodiment, the case where the electron beam irradiation current is monitored and the feedback is switched depending on whether the electron beam irradiation current exceeds I1 has been described as an example. However, the present invention is not limited to this. When the common contact c of the switch SW is connected to the contact a or b, and in the region A where the aperture detection current is small, the common contact c of the switch SW is connected to the b contact and feedback control is performed using the characteristic of α + β. . When the control device 20 refers to the characteristics of the graph 3 stored in the memory 21 and detects that α + β which is the output of the adder 13 has reached the maximum value, the control device 20 sends a selection signal to the switch SW, and the common contact c may be switched to the a contact, and feedback control may be performed using the characteristic of β. When such control is used, the ammeter 10 is not necessary.

  As described above in detail, according to the present invention, a plurality of apertures capable of detecting current are used, and at each irradiation current value, the current detected by the aperture having a proportional relationship between the irradiation current and the detected current. Can be used for feedback control of the focusing lens. According to the present invention, even with an electron gun that emits a small amount of electrons from a light source such as a field emission electron gun, a detection current sufficient for feedback control of the focusing lens can be obtained regardless of the magnitude of the irradiation current.

DESCRIPTION OF SYMBOLS 1 Focusing lens 2 Objective lens 3 Electron beam 4 Aperture 5 Aperture 6 Objective aperture 7 Target 8 Ammeter 9 Ammeter 10 Ammeter 13 Adder 20 Controller 21 Memory 22 Amplifier SW switch

Claims (3)

Prepare multiple apertures that can detect current,
The relationship between the aperture detection current of these multiple apertures and the corresponding electron beam irradiation current is stored in a memory as a table,
In the region where the electron beam irradiation current is small, the sum of the plurality of aperture detection currents is used as the aperture detection current, and in the region where the electron beam irradiation current is large, the detection current of a specific aperture among the plurality of apertures is detected. An electron beam stabilization method for an electron beam irradiation apparatus, wherein feedback control of an electron beam irradiation current is performed as an electric current.   In a region where the electron beam irradiation current is small, using the control device that controls the overall operation of the electron beam irradiation device, the relationship between the aperture detection current stored in the memory and the corresponding electron beam irradiation current. In the region where the electron beam irradiation current is large, the sum of the plurality of diaphragm detection currents is used as the detection current, and feedback control of the electron beam irradiation current is performed using the detection current of the specific diaphragm among the plurality of diaphragms as the detection current. The method of stabilizing an electron beam of an electron beam irradiation apparatus according to claim 1, wherein the method is performed. Multiple apertures capable of detecting current,
Aperture detection current detection means for detecting the current flowing through each aperture;
A memory for storing the relationship between the aperture detection currents of these multiple apertures and the corresponding electron beam irradiation current as a table;
A control device for controlling the operation of each of the overall components;
Comprising
The control device refers to the memory, and in a region where the electron beam irradiation current is small, a sum of the plurality of diaphragm detection currents is used as a diaphragm detection current, and in a region where the electron beam irradiation current is large, the plurality of diaphragms Among them, an electron beam stabilizing device for an electron beam irradiation apparatus, wherein feedback control of an electron beam irradiation current is performed using a detection current of a specific aperture as a detection current.

Images