A power supply circuit for an electron gun of a scanning electron microscope

Abstract

The present invention discloses a power supply circuit for an electron gun of a scanning electron microscope. A filament heating input circuit is used for transforming, isolating, and filtering the input grid voltage; a scanning electron microscope electron gun is used for obtaining the filament current output by the filament heating input circuit; an accelerating power supply, whose output terminal is connected to the grid bias voltage regulating electrode of the scanning electron microscope electron gun through a grid bias voltage regulating resistor, is used for applying a preset accelerating voltage to the scanning electron microscope electron gun; a filament power supply protection resistor is connected between the filament inflow electrode and the filament outflow electrode of the scanning electron microscope electron gun to protect the scanning electron microscope electron gun. The present invention converts low-voltage and alternating current through the filament heating input circuit to provide a stable filament direct current for the scanning electron microscope electron gun, and superimposes the preset accelerating voltage on the scanning electron microscope electron gun through the electron gun protection resistor, ensuring the safe and reliable operation of the scanning electron microscope electron gun.

Description

Technical Field

[0001] The present invention relates to the technical field of scanning electron microscope electron guns, and particularly to a power supply circuit for a scanning electron microscope electron gun. Background Art

[0002] A scanning electron microscope is an electron optical instrument that uses a focused electron beam to scan the surface of a sample line by line. When the electron beam bombards the surface of the sample, secondary electrons or backscattered electrons are generated. The position where the electron beam scans the surface of the sample and the generated secondary electrons or backscattered electrons are collected, and the position where the electron beam scans the surface of the sample and the number of generated secondary electrons or backscattered electrons are represented in the form of a two-dimensional code image, thus obtaining a secondary electron image or a backscattered electron image of the scanning electron microscope.

[0003] When a scanning electron microscope electron gun is working, first, a current needs to flow through the filament to heat the cathode. The electrons in the filament are thermally excited, and under the action of an accelerating electric field, the electrons are emitted from the tip of the filament. The filament heating current is about 2.5 A, and the accelerating electric field is generally 0 to -30 KV, with a negative polarity to the ground. At the same time, to adjust the size of the emission beam current, there is a grid in the scanning electron microscope electron gun. Compared with the accelerating voltage, a negative voltage of 0 - 2000 V is applied to the grid plate (cap) to adjust the size of the emission beam current. The scanning electron microscope electron gun requires 0 - 3 A adjustable direct current and a grid bias voltage of 0 - 2000 V, and both need to be "floating" under an accelerating voltage of 0 - 30 KV. Due to the too large accelerating voltage, it is impossible to ensure that the scanning electron microscope electron gun can generate a stable filament current and an adjustable grid bias voltage, ultimately affecting the safety of using the scanning electron microscope electron gun. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the problem in the prior art that due to the too large accelerating voltage, it is impossible to ensure that the scanning electron microscope electron gun can generate a stable filament current and an adjustable grid bias voltage, ultimately affecting the safety of using the scanning electron microscope electron gun, so as to provide a power supply circuit for a scanning electron microscope electron gun.

[0005] According to a first aspect, an embodiment of the present invention discloses a power supply circuit for a scanning electron microscope electron gun, including:

[0006] A filament heating input circuit for transforming, isolating, and filtering the input grid voltage;

[0007] A scanning electron microscope electron gun, whose filament inflow electrode is connected to the first output end of the filament heating input circuit, and whose filament outflow electrode is connected to the second output end of the filament heating input circuit, for obtaining the filament current output by the filament heating input circuit;

[0008] An accelerating power supply, whose output terminal is connected to the grid bias voltage regulating electrode of the scanning electron microscope electron gun through a grid bias voltage regulating resistor, is used to apply a preset accelerating voltage to the scanning electron microscope electron gun;

[0009] A filament power supply protection resistor, which is connected between the filament inflow electrode and the filament outflow electrode of the scanning electron microscope electron gun to protect the scanning electron microscope electron gun;

[0010] Combined with the first aspect, in an implementation manner of the first aspect, the filament power supply protection resistor includes: a first resistor and a second resistor. The first end of the first resistor is connected to the first output end of the filament heating input circuit, the first end of the second resistor is connected to the second output end of the filament heating input circuit, and the second ends of the first resistor and the second resistor are connected.

[0011] Combined with the first aspect, in another implementation manner of the first aspect, the grid bias voltage regulating resistor, its first end is connected to the second ends of the first resistor and the second resistor, its second end is connected to the grid bias voltage regulating electrode of the scanning electron microscope electron gun, and its third end is connected to the output terminal of the accelerating power supply through a third resistor.

[0012] Combined with the first aspect, in another implementation manner of the first aspect, the grid bias voltage regulating resistor is used to adjust the preset accelerating voltage applied by the accelerating power supply to the scanning electron microscope electron gun.

[0013] Combined with the first aspect, in another implementation manner of the first aspect, the scanning electron microscope electron gun includes: a tungsten filament scanning electron microscope electron gun or a lanthanum hexaboride scanning electron microscope electron gun.

[0014] Combined with the first aspect, in another implementation manner of the first aspect, the filament heating input circuit includes: a first transformer, a second transformer, a rectifier bridge, and an LC filter circuit connected in sequence.

[0015] Combined with the first aspect, in another implementation manner of the first aspect, the LC filter circuit includes: an L filter inductor and a filter capacitor connected to each other.

[0016] Combined with the first aspect, in another implementation manner of the first aspect, the preset accelerating voltage is 0 - 30 KV.

[0017] The technical solution of the present invention has the following advantages:

[0018] The present invention discloses a power supply circuit for an electron gun of a scanning electron microscope. A filament heating input circuit is used to transform, isolate, and filter the input grid voltage. A scanning electron microscope electron gun is used to obtain the filament current output by the filament heating input circuit. An accelerating power supply, whose output terminal is connected to the grid bias voltage regulating electrode of the scanning electron microscope electron gun through a grid bias voltage regulating resistor, is used to apply a preset accelerating voltage to the scanning electron microscope electron gun. A filament power supply protection resistor is connected between the filament inflow electrode and the filament outflow electrode of the scanning electron microscope electron gun to protect the scanning electron microscope electron gun. The present invention converts low-voltage alternating current through the filament heating input circuit to provide a stable filament direct current for the scanning electron microscope electron gun, and superimposes the preset accelerating voltage on the scanning electron microscope electron gun through the electron gun protection resistor to ensure the safe and reliable operation of the scanning electron microscope electron gun. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0020] Figure 1 It is a structural block diagram of the power supply circuit for the electron gun of the scanning electron microscope in the embodiment of the present invention;

[0021] Figure 2 It is a circuit schematic diagram of the power supply circuit for the electron gun of the scanning electron microscope in the embodiment of the present invention;

[0022] Reference Numerals:

[0023] 11 - Filament heating input circuit; 12 - Scanning electron microscope electron gun; 13 - Accelerating power supply;

[0024] 14 - Filament power supply protection resistor; 15 - Grid bias voltage regulating resistor; 110 - First transformer;

[0025] 111 - Second transformer; 112 - Rectifier bridge; 113 - LC filter circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will clearly and completely describe the technical solutions of the present invention with reference to the drawings. Obviously, the described embodiments are some embodiments of the present invention, rather than all embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0027] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0028] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected", "connected to" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and can also be the communication inside two elements. It can be a wireless connection or a wired connection. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0029] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present invention discloses a power supply circuit for the electron gun of a scanning electron microscope, as Figure 1 shown, including: a filament heating input circuit 11, a scanning electron microscope electron gun 12, an acceleration power supply 13, a filament power protection resistor 14, and a grid bias voltage adjustment resistor 15.

[0031] In Figure 1 , among them, the filament heating input circuit 11 is used to transform, isolate, and filter the input grid voltage. Therefore, the filament heating input circuit 11 includes: a first transformer 110, a second transformer 111, a rectifier bridge 112, and an LC filter circuit 113 connected in sequence. The first transformer 110 is used to transform the 220V AC voltage into an AC voltage of 0 - 10V, then isolate the voltage through the second transformer 111, and then filter it through the LC filter circuit 113, and then transform it into a smooth DC voltage, which is transmitted to the filament inflow electrode and the filament outflow electrode for use when the scanning electron microscope electron gun 12 is heated. The LC filter circuit 113 in the filament heating input circuit 11 includes: an LC filter inductor and a filter capacitor connected to each other. As Figure 2 shown, the filter inductor is L1, and the filter capacitor is C1.

[0032] In Figure 2Among them, for the scanning electron microscope electron gun 12, the filament inflow electrode is connected to the first output end of the filament heating input circuit 11, and the filament outflow electrode is connected to the second output end of the filament heating input circuit 11, which is used to obtain the filament current output by the filament heating input circuit 11; the acceleration power supply 13, whose output end is connected to the grid bias voltage regulating electrode of the scanning electron microscope electron gun 12 through the grid bias voltage regulating resistor 15, is used to apply a preset acceleration voltage to the scanning electron microscope electron gun 12, and the preset acceleration voltage is 0 - 30 KV. Therefore, this acceleration power supply 13 is a high-voltage acceleration power supply, and the scanning electron microscope electron gun 12 includes 3 electrodes, namely the filament inflow electrode, the filament outflow electrode, and the grid bias voltage regulating electrode. When the scanning electron microscope electron gun 12 is working, a heating current needs to flow through the filament inflow electrode and the filament outflow electrode, and a grid bias voltage is provided to make the filament current and the grid bias voltage of the scanning electron microscope electron gun float on the preset acceleration voltage.

[0033] In a preferred embodiment, for the power supply circuit of the scanning electron microscope electron gun in the embodiment of the present invention, the scanning electron microscope electron gun includes: a tungsten filament scanning electron microscope electron gun or a lanthanum hexaboride scanning electron microscope electron gun. For example: when the scanning electron microscope electron gun in the embodiment of the present invention is a tungsten filament scanning electron microscope electron gun, when the tungsten filament scanning electron microscope electron gun is working, first, a current needs to flow through the filament to heat the cathode end. Then, the electrons in the tungsten filament are thermally excited, and under the action of the accelerating electric field, the electrons are emitted from the tip of the filament. The tungsten filament heating current is about 2.5 A, and the accelerating electric field is generally 0 - 30 KV, which is the negative electrode end with respect to the ground. At the same time, to adjust the size of the emission beam current, there is a grid electrode end in the tungsten filament electron gun. Compared with the accelerating voltage, a negative voltage of 0 - 2000 V is applied to the grid electrode end to adjust the size of the emission beam current. That is to say, the tungsten filament electron gun needs 0 - 3 A adjustable direct current and a grid bias voltage of 0 - 2000 V, and both need to float on the accelerating voltage of 0 - 30 KV.

[0034] In Figure 2 it can be seen that the input end of the filament heating input circuit is 0 - 10 V alternating current, and this alternating current can be obtained through the first transformer 110 of 220 V / 110 V. Because the scanning electron microscope electron gun needs to work in an environment of up to tens of thousands of volts, the 0 - 10 V alternating current must be electrically isolated through the second transformer 111. After the 0 - 10 V alternating current leaves the secondary side of the second transformer 111, it enters the rectifier bridge 112 to convert the alternating current into direct current. The LC filter inductor and the filter capacitor form the filter circuit 113, and this filter circuit can effectively filter out the alternating current components. When the scanning electron microscope electron gun 12 is a tungsten filament scanning electron microscope electron gun, the resistance value of the cathode end of the tungsten filament scanning electron microscope electron gun is very small, usually about 0.5 Ω, and the filament current generally does not exceed 3 A. Therefore, the withstand voltage of the filter capacitor does not need to be very high.

[0035] In a preferred embodiment, Figure 1 In the electron gun protection circuit according to the embodiment of the present invention, the filament inflow electrode is connected to the first output end of the filament heating input circuit 11, and the filament outflow electrode is connected to the second output end of the filament heating input circuit 11, for obtaining the filament current output by the filament heating input circuit. The filament power protection resistor 14 is connected between the filament inflow electrode and the filament outflow electrode of the scanning electron microscope electron gun to protect the safe operation of the scanning electron microscope electron gun, and further protect the scanning electron microscope electron gun.

[0036] In Figure 2 The filament power protection resistor includes: a first resistor and a second resistor. The first end of the first resistor is connected to the first output end of the filament heating input circuit, and the first end of the second resistor is connected to the second output end of the filament heating input circuit. The second ends of the first resistor and the second resistor are connected. In Figure 2 In, the first resistor is R1 and the second resistor is R2. The first end of the first resistor R1 is connected to the first end of the filter capacitor C1, the second end of the first resistor R1 is connected to the first end of the second resistor R2, and the second end of the second resistor R2 is connected to the second end of the filter capacitor C1. In Figure 2 In, the second input end of the rectifier bridge 112 of the filament heating input circuit is connected to the first resistor R1 through the filter inductor L1, and the second input end of the rectifier bridge 112 is connected to the second end of the filter capacitor C1 and the second end of the second resistor R2.

[0037] The power supply circuit of the scanning electron microscope electron gun according to the embodiment of the present invention converts low-voltage alternating current through the filament heating input circuit to provide a stable filament direct current for the scanning electron microscope electron gun, and superimposes a preset acceleration voltage on the scanning electron microscope electron gun through the electron gun protection resistor to ensure the safe and reliable operation of the scanning electron microscope electron gun.

[0038] In an alternative embodiment, Figure 2 In the power supply circuit of the scanning electron microscope electron gun according to the embodiment of the present invention, it further includes: a grid bias adjustment resistor 15 for adjusting the preset acceleration voltage applied to the scanning electron microscope electron gun by the acceleration power supply. Its input end is connected to the second ends of the first resistor and the second resistor, its second end is connected to the grid bias adjustment pole of the scanning electron microscope electron gun, and its third end is connected to the output end of the acceleration power supply 13 through a connection with a third resistor. In Figure 2 In, the grid bias adjustment resistor 15 is an adjustable resistor R3. In Figure 2 In, the third resistor is R4. The first end of the grid bias adjustment resistor R3 is connected to the second ends of the first resistor R1 and the second resistor R2, its second end is connected to the grid bias adjustment pole of the scanning electron microscope electron gun, and its third end is connected to the output end of the acceleration power supply 13 through a connection with a third resistor.

[0039] Obviously, the above embodiments are merely examples given for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A power supply circuit for an electron gun of a scanning electron microscope, characterized in that, Comprising: A filament heating input circuit for transforming, isolating, and filtering the input grid voltage; A scanning electron microscope electron gun, where the filament inflow electrode of the electron gun is connected to the first output terminal of the filament heating input circuit, and the filament outflow electrode is connected to the second output terminal of the filament heating input circuit, for obtaining the filament current output by the filament heating input circuit; An acceleration power supply, whose output terminal is connected to the grid bias voltage adjustment electrode of the scanning electron microscope electron gun through a grid bias voltage adjustment resistor, for applying a preset acceleration voltage to the scanning electron microscope electron gun; A filament power supply protection resistor connected between the filament inflow electrode and the filament outflow electrode of the scanning electron microscope electron gun to protect the safe operation of the scanning electron microscope electron gun; The filament power supply protection resistor includes: a first resistor and a second resistor. The first end of the first resistor is connected to the first output terminal of the filament heating input circuit, the first end of the second resistor is connected to the second output terminal of the filament heating input circuit, and the second ends of the first resistor and the second resistor are connected; The grid bias voltage adjustment resistor, its first end is connected to the second ends of the first resistor and the second resistor, its second end is connected to the grid bias voltage adjustment electrode of the scanning electron microscope electron gun, and its third end is connected to the output terminal of the acceleration power supply through a third resistor.

2. The power supply circuit for the electron gun of a scanning electron microscope according to claim 1, wherein The grid bias voltage adjustment resistor is used to adjust the preset acceleration voltage applied by the acceleration power supply to the scanning electron microscope electron gun.

3. The power supply circuit for the scanning electron microscope electron gun according to any one of claims 1 to 2, wherein the scanning electron microscope electron gun comprises: A tungsten filament scanning electron microscope electron gun or a lanthanum hexaboride scanning electron microscope electron gun.

4. The power supply circuit for the electron gun of a scanning electron microscope according to claim 1, characterized in that, The filament heating input circuit includes: a first transformer, a second transformer, a rectifier bridge, and an LC filter circuit connected in sequence.

5. The power supply circuit for the electron gun of a scanning electron microscope according to claim 4, characterized in that, The LC filter circuit includes: an L filter inductor and a filter capacitor connected to each other.

6. The power supply circuit for the electron gun of the scanning electron microscope according to claim 1, wherein The preset acceleration voltage is 0 - 30 KV.

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