WO2020073511A1 - 电子源制造方法 - Google Patents

电子源制造方法 Download PDF

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Publication number
WO2020073511A1
WO2020073511A1 PCT/CN2018/124330 CN2018124330W WO2020073511A1 WO 2020073511 A1 WO2020073511 A1 WO 2020073511A1 CN 2018124330 W CN2018124330 W CN 2018124330W WO 2020073511 A1 WO2020073511 A1 WO 2020073511A1
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WIPO (PCT)
Prior art keywords
emission
needle tip
substrate
gas molecules
field
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PCT/CN2018/124330
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English (en)
French (fr)
Inventor
王学慧
王俊听
胡贤斌
陈迪志
唐广
刘华荣
郑磊
钱庆
郑春宁
王国超
Original Assignee
中国电子科技集团公司第三十八研究所
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Application filed by 中国电子科技集团公司第三十八研究所 filed Critical 中国电子科技集团公司第三十八研究所
Priority to KR1020207022427A priority Critical patent/KR102539959B1/ko
Priority to JP2020542132A priority patent/JP6961831B2/ja
Priority to EP18936558.8A priority patent/EP3736847B1/en
Priority to US16/966,908 priority patent/US11373836B2/en
Publication of WO2020073511A1 publication Critical patent/WO2020073511A1/zh

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/30—Cold cathodes, e.g. field-emissive cathode
    • H01J1/304—Field-emissive cathodes
    • H01J1/3048—Distributed particle emitters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J3/00—Details of electron-optical or ion-optical arrangements or of ion traps common to two or more basic types of discharge tubes or lamps
    • H01J3/02—Electron guns
    • H01J3/021—Electron guns using a field emission, photo emission, or secondary emission electron source
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/065—Construction of guns or parts thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/02—Details
    • H01J37/04—Arrangements of electrodes and associated parts for generating or controlling the discharge, e.g. electron-optical arrangement, ion-optical arrangement
    • H01J37/06—Electron sources; Electron guns
    • H01J37/073—Electron guns using field emission, photo emission, or secondary emission electron sources
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/30—Cold cathodes
    • H01J2201/304—Field emission cathodes
    • H01J2201/30403—Field emission cathodes characterised by the emitter shape
    • H01J2201/30426—Coatings on the emitter surface, e.g. with low work function materials
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/30—Cold cathodes
    • H01J2201/304—Field emission cathodes
    • H01J2201/30403—Field emission cathodes characterised by the emitter shape
    • H01J2201/30438—Particles
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2201/00—Electrodes common to discharge tubes
    • H01J2201/30—Cold cathodes
    • H01J2201/304—Field emission cathodes
    • H01J2201/30446—Field emission cathodes characterised by the emitter material
    • H01J2201/30449—Metals and metal alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/063—Electron sources
    • H01J2237/06325—Cold-cathode sources
    • H01J2237/06341—Field emission
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/06—Sources
    • H01J2237/063—Electron sources
    • H01J2237/06325—Cold-cathode sources
    • H01J2237/06341—Field emission
    • H01J2237/0635—Multiple source, e.g. comb or array

Definitions

  • the present disclosure relates to the field of electron source technology, and more particularly, to a field emission electron source manufacturing method.
  • the free electrons in the metal can be emitted under certain conditions. If the cathode is made of metal and made into a very fine needle shape, and thousands of volts are applied in a vacuum, the electrons in the metal can be emitted from the cold metal of the cathode. This method of emitting electrons is called field emission and belongs to cold cathode emission.
  • the most important indicator is brightness, which directly determines its beam quality.
  • the brightness can be shown as formula (1):
  • B is the brightness
  • I is the emission current
  • S is the equivalent emission area
  • d is the equivalent diameter
  • ⁇ is the space emission angle
  • ⁇ is the emission half angle.
  • the luminance B is proportional to the acceleration voltage V a, as shown in Equation (2).
  • the most ideal electron source is cold field emission electron sources (CFE).
  • CFE cold field emission electron sources
  • the brightness of CFE is about one order of magnitude higher than that of other types of electron sources, and there is little energy dissipation ( ⁇ 0.3 eV).
  • atomic-level electron sources with low work functions have become a research hotspot, that is, the emission point is composed of only one or several atoms.
  • Schottky thermal-field emission source Schottky thermal-field emission source
  • the present disclosure provides a manufacturing method that can manufacture an electron source that is stable, has a large field emission current, and can operate under a poor vacuum.
  • An aspect of the present disclosure provides an electron source manufacturing method, including: forming one or more fixed emission points on at least one needle tip, the emission points including a reaction product formed by metal atoms on the surface of the needle tip and gas molecules. Because the formed emission point is the reaction product formed by the metal atoms fixed on the surface of the needle tip and the gas molecules rooted on the surface of the needle tip, rather than the gas molecules or free particles free on the surface of the needle tip, it will not be free like in the prior art Matters gather together to form a new emission point, which causes overcurrent burning, which effectively improves stability.
  • the formed emission point includes the reaction product formed by metal atoms and gas molecules on the surface of the needle tip, relative to metal atoms or other metal compounds (such as metal borides, etc., in the working environment (the presence of gas molecules) has better stability, such as less likely to interact or react with the working environment such as hydrogen, etc., further improving the stability of the electron source .
  • the emission point manufactured by the electron source manufacturing method provided by the present disclosure may be a reaction product formed by one or several metal atoms and gas molecules, that is, an atomic level electron with a low work function may be formed by controlling the number of emission points formed source.
  • the reaction product significantly reduces the surface work function, and the formation of surface emission point cones also significantly improves the emission ability.
  • the current value of the field emission current can be increased by preparing a larger number of emission points. In this way, a stable electron source with a large field emission current can be manufactured.
  • the metal atoms react with the gas molecules under an electric field to form the emission point. This facilitates the formation of an emission point at a specified position of the needle tip, especially at a position where the electric field has an advantage, such as the protrusion of the needle tip.
  • At least one needle tip includes a substrate and one or more high field strength structures on the substrate that are higher than the field strength of other parts of the substrate, wherein, At least one outer surface of the high-field strength structure includes metal atoms, and the metal atoms on the surface of the high-field strength structure are more likely to form reaction products with gas molecules in the same environment by virtue of the field strength to preferentially generate in the high-field strength structure Launch point.
  • at least one needle tip includes a substrate and one or more active regions on the substrate that are more reactive than other parts of the substrate, wherein at least one outer surface of the active region includes Metal atoms.
  • At least one needle tip includes a substrate and one or more high field strength structures on the substrate that are higher than the field strength of other parts of the substrate, at least one of the high field strength structures Part of the surface is an active area with high reactivity, wherein the outer surface of the active area includes metal atoms, and the metal atoms on the surface of the active area are more likely to form reaction products with gas molecules in the same environment by virtue of field strength advantages and activity advantages.
  • the active area includes metal atoms, and the metal atoms on the surface of the active area are more likely to form reaction products with gas molecules in the same environment by virtue of field strength advantages and activity advantages.
  • the high field strength structure includes protrusions.
  • the size of the protrusion is on the order of sub-nanometer to 100 nanometers.
  • the protrusion is formed by any one or more of the following methods: heat treatment, electric field application, thermal-electric field treatment, etching or nano-processing, or the following method: for example, plating a single crystal on the tip of a single crystal metal Layers of metal atoms are reshaped by heat treatment to form protrusions.
  • a tip including a protrusion in a reaction with a gas molecule under vacuum conditions, at least part of the surface of the protrusion has metal atoms that have the same or greater reaction than other surface parts of the substrate Activity, that is, at least a part of the surface of the protrusion (such as a designated area) has a metal atom with a larger reactivity than other areas.
  • the metal atoms on the surface of the active area of the substrate have a greater reactivity than other surface portions of the substrate during the reaction with gas molecules under vacuum conditions.
  • the method may further include the operation of adjusting the size and shape of the substrate and / or high field strength structure of the needle tip to adjust the size of the electron beam current angle, or, by adjusting the height
  • the field strength structure and / or the size of the active region adjust the number of emission points, or adjust the size or consistency of the voltage of the electron source emission current by adjusting the substrate structure and / or high field strength structure, or by adjusting the tip of the needle tip To adjust the direction of the emission current.
  • the emission point is formed on the needle tip protrusion formed by field etching, field evaporation, etc.
  • the voltage can be lower than -0.5KV (for example, the extraction voltage is -0.4KV), so that the structure of the electron gun is designed simpler.
  • the gas molecules include hydrogen-containing element gas molecules and any one or more of the following: nitrogen-containing element gas molecules, carbon-containing element gas molecules, or oxygen-containing element gas molecules.
  • the hydrogen-containing element gas molecules are composed of the introduced hydrogen-containing element gas molecules and / or the remaining gas molecules in the vacuum environment, and accordingly, the introduction rate of the hydrogen-containing element gas molecules can be adjusted Adjusting the formation rate of the emission point, for example, when the introduction rate of hydrogen-containing element gas molecules is at a higher rate, the formation rate of the emission point can be increased.
  • the hydrogen element-containing gas molecule may include a hydrogen molecule
  • the metal atom may be a tungsten atom
  • the emission point is a hydrogen tungsten compound.
  • the electric field is formed by applying a bias voltage; wherein the applying bias voltage includes any one or more of the following: applying a positive bias voltage, applying a negative bias voltage, or applying both positive and negative bias voltages Combined bias.
  • the way of applying the bias voltage includes, but is not limited to, directly applying a bias voltage to the needle tip or applying a bias voltage to the components near the needle tip to generate an electric field.
  • the molecules form a reaction product.
  • the formed field strength range includes 1 to 50 V / nm, which can prevent the formation of an emission point due to field-induced etching, field-induced evaporation, etc. caused by the positive bias.
  • the formed field strength ranges from 1 to 30V / nm, which can prevent the tip of the needle from being burned or the shape of the tip from changing due to excessive emission current.
  • a negative bias when a negative bias is applied to form an emission point, a negative bias may be applied to the needle tip first to generate an emission current with a magnitude of microampere, and then, to maintain the preset duration or adjust the The negative bias voltage is generated until a predetermined value of emission current is generated. Next, the negative bias voltage is adjusted so that the emission current of the electron source is less than the order of milliampere to avoid the change of tip shape or burning.
  • a positive bias voltage when a positive bias voltage is applied to form an emission point, a positive bias voltage is applied to the needle tip and maintained for a preset duration, and the value of the positive bias voltage is less than that of the field-induced evaporative bias voltage forming the protrusion value.
  • the number of emission points formed may be adjusted by adjusting the value of the applied bias voltage or the value of the preset duration. In this way, an electron source at the atomic level or an electron source with a large emission current can be realized.
  • the environment for manufacturing the electron source may include any one of the following: when the tip temperature ⁇ 1000K, the pressure ⁇ 10 -3 Pa, or, when 500K ⁇ the tip temperature ⁇ 800K, the pressure ⁇ 10 -6 Pa, or , When the tip temperature ⁇ 150K, the pressure ⁇ 10 -6 Pa. Due to the formation of the emission point and the low operating temperature, the structure of the electron source does not change. During operation, the structure of the electron source does not change, and the value of the applied voltage does not change.
  • the method may further include any one or more of the following operations: adjust the number of emission points to adjust the uniformity of the emission points, or adjust the number of emission points to adjust the magnitude of the current, Or, increase the stability of the emission current by increasing the number of emission points.
  • the method may further include the operation of: after forming one or more fixed emission points on at least one needle tip, applying an electric field to cause gas molecules to adsorb on the emission points to remove at least one emission point .
  • the substrate material is a conductive material
  • the high field strength structure material is a conductive material
  • the substrate and / or high field strength structure surface is a metal atom
  • the high-field-strength structure material is the same as or different from the substrate material
  • the metal atomic material on the substrate and / or high-field-strength structure surface is the same or different from the high-field strength structure material, and when different, the substrate And / or metal atoms on the surface of the high-field-strength structure are formed by evaporation or electroplating
  • the material of the metal atoms on the substrate and / or the surface of the high-field-strength structure is the same as or different from the substrate material, and when different,
  • the metal atoms on the surface of the substrate and / or high-field-strength structure are formed by evaporation or electroplating.
  • the substrate material is a conductive material and the melting point is higher than 1000K
  • the high field strength structural material is a conductive material and the melting point is higher than 1000K
  • the material of the metal atoms on the surface of the high-field-strength structure is a metal material with a melting point higher than 1000K
  • the reaction product of the metal atoms and gas molecules includes the reaction product of metal atoms with a melting point higher than 1000K and gas molecules under vacuum conditions.
  • a high-field-strength structure or a region with high reactivity is located at the center of the surface of the substrate, or a high-field-strength structure is located on a substrate whose size is greater than a set threshold, or, The metal atom is located at the top of the high field strength structure or at the center of the surface of the substrate.
  • the disappearance temperature of the emission point is lower than the small value of the disappearance temperature of the substrate, the high field strength structure, and the metal atom, and the disappearance temperature of the emission point is higher than The working temperature of the electron source; or the disappearance temperature of the emission point is lower than the small value of the disappearance temperature of the substrate, the high field strength structure and the metal atom, and the disappearance temperature of the emission point is higher than The large value of the working temperature of the electron source and the desorption temperature of the gas molecules adsorbed on any needle tip.
  • the size of the emission point is on the order of nanometers or sub-nanometers; and by adjusting the operating voltage, the emission current value of the emission point of the needle tip can reach the order of 10 mA.
  • the electron source has cold field emission characteristics
  • the magnitude of the emission current is adjusted by adjusting the extraction voltage
  • FIG. 1 schematically shows a schematic diagram of a preparation process of an electron source according to an embodiment of the present disclosure
  • FIG. 2 schematically shows a schematic diagram of a preparation process of an electron source according to another embodiment of the present disclosure
  • FIG. 3A schematically shows a schematic diagram of a tip structure for forming an emission area according to an embodiment of the present disclosure
  • FIG. 3B schematically shows a schematic diagram of a high field strength structure according to an embodiment of the present disclosure
  • 3C schematically shows a schematic diagram of metal atoms on the surface of the protrusion according to an embodiment of the present disclosure
  • FIG. 4 schematically shows a schematic diagram of a tip structure for forming an emission area according to another embodiment of the present disclosure
  • FIG. 5 schematically shows a schematic diagram of a tip structure for forming an emission area according to another embodiment of the present disclosure
  • FIG. 6 schematically shows a schematic diagram of an emission point forming process according to an embodiment of the present disclosure
  • FIG. 7 schematically shows a schematic diagram of a process of applying a positive bias to form an emission point according to an embodiment of the present disclosure
  • FIG. 8 is a schematic diagram schematically illustrating the relationship between the number of emission points and the uniformity of emission patterns according to an embodiment of the present disclosure
  • FIG. 9 schematically shows a schematic diagram of adjusting the number of emission points according to an embodiment of the present disclosure.
  • FIG. 11 schematically shows a schematic diagram of an electron source using process according to an embodiment of the present disclosure.
  • the inventors conducted further research and showed that it is closely related to ion bombardment. This is because after the electrons are emitted, they will ionize the gas molecules in the surrounding space and then bombard the tip of the needle.
  • One possibility is that the surface of the needle tip is bombarded to form multiple protrusions, which are used as launch points, respectively, and eventually lead to excessive current, causing burnout.
  • the aforementioned problems become more serious at larger emission currents.
  • the total emission current that can work stably for a long time is ⁇ 10 microamperes, and the utilization rate is very low.
  • the Schottky field emission electron source Schottky thermal-field emission source dominates the field of high-brightness electron sources.
  • the current field emission electron source (generally refers to the metal needle tip) can only work in ultra-high vacuum ( ⁇ 10 -8 Pa), which severely restricts the scope of application of CFE. Further in-depth research was conducted here, and the following characteristics were found.
  • the residual gas components in the vacuum are H 2 , CO, CO 2 , and the main component is H 2 .
  • the adsorption of H 2 causes the emission ability of the clean surface to gradually deteriorate. It can be said that in this vacuum range, the influence of H 2 fundamentally determines the field emission performance of the needle tip. Therefore, how to cope with the influence of H 2 has become the key to achieving a highly stable needle point.
  • the inventor provides the manufacturing method of the electron source of the present disclosure to improve an electron source, achieve long-term stable operation, can provide a larger field emission current, and can be used in a poor vacuum environment Work under low pressure, and it is not easily interfered by gas when exposed to the atmosphere.
  • the method for manufacturing an electron source provided by the present disclosure forms one or more fixed emission points on at least one needle tip, and the emission points include a reaction product formed by metal atoms on the surface of the needle tip and gas molecules. Since the metal atom on the surface of the needle tip is used as the reaction substance, the reaction product formed with the gas molecule is rooted on the surface of the needle tip, and since the reaction product is a reaction product formed by the reaction of the metal atom and the gas molecule under similar working conditions, the reaction product The activity of reacting with gas molecules again is not great, so the stability is high. In addition, since the number of reaction products can be controlled, a larger field emission current can be provided by increasing the number of reaction products. In addition, since the reaction product is a reaction product formed by the reaction of metal atoms and gas molecules, it is not susceptible to gas interference even when exposed to the atmosphere.
  • the above-mentioned emission point can be formed by applying an electric field to react metal atoms with gas molecules.
  • the electric field is formed by applying a bias voltage; wherein, the applying bias voltage includes any one or more of the following: applying a positive bias voltage, applying a negative bias voltage, or applying a positive bias voltage and a negative bias voltage Compression combined.
  • the reaction product formed by the metal atoms on the surface of the needle tip and the gas molecules can be specifically implemented in various ways, for example, directly applying a voltage to the needle tip to form a higher field strength on the surface of the needle tip to promote the metal atoms and The reaction product formed by the reaction of gas molecules; it can also be to apply a voltage to the field strength generating structure (such as electrodes, etc.) near the needle tip to form an electric field, and then form a higher field strength on the surface of the needle tip to promote the metal atoms and gas molecules on the surface of the needle tip The reaction product formed by the reaction.
  • the field strength generating structure such as electrodes, etc.
  • the field formed on the surface of the needle tip and the formation method of the field are not limited, as long as the field can be formed on the surface of the needle tip, the field can promote the reaction of metal atoms on the surface of the needle tip with surrounding gas molecules to form a reaction product.
  • the following is an example of forming an emission point on the surface of the needle tip by applying a bias to the needle tip to form an electric field.
  • FIG. 1 schematically shows a schematic diagram of a preparation process of an electron source according to an embodiment of the present disclosure.
  • FIG. 1 From the left picture of Fig. 1, it can be seen that after the bias is applied to the needle tip, the gas molecules on the surface of the needle tip and the environment will continue to move to the high field strength, and then, the action of the high electric field Next, at least part of the metal atoms on the surface of the needle tip are caused to form a reaction product with the gas molecules, that is, an emission point.
  • the right picture is an enlarged schematic view of the image in the dashed box in the left picture, and the dashed box below the left picture is a schematic substrate.
  • the gas molecules in the environment and the gas molecules adsorbed on the surface of the needle tip will It gradually gathers toward the tip of the needle tip, which is also one of the reasons that the electron source emission ability of the tungsten single crystal in the prior art decreases.
  • a field (such as an electric field, etc.) is formed at the tip of the needle to encourage the gas molecule to form a reaction product (black dot) with the metal atoms (white dots) on the surface of the tip
  • the dot, or launch point, referred to as Ma1 the launch point will be rooted on the surface of the needle tip, rather than free on the surface of the needle tip.
  • FIG. 2 schematically shows a schematic diagram of a preparation process of an electron source according to another embodiment of the present disclosure.
  • the hatched part in the figure represents the region with large reactivity, and the emission point is formed in the above-mentioned region with large reactivity.
  • the surface of the region with large reactivity can be composed of metal atoms with high reactivity with gas molecules, so that these metal atoms can preferentially form reaction products with gas molecules under the action of an electric field, for example, to form an emission point in a designated region , As shown by the black dots in the figure.
  • FIG. 3A schematically shows a schematic diagram of a tip structure for forming an emission area according to an embodiment of the present disclosure.
  • At least one needle tip includes a substrate and one or more high field strength structures on the substrate that have higher field strengths than other parts of the substrate, wherein at least one of the high field strength structures
  • the outer surface of the metal includes metal atoms.
  • the substrate may be a portion of the needle tip near the tip, or may be a conductive material or the like formed on the surface of the needle tip.
  • FIG. 3B schematically shows a schematic diagram of a high field strength structure according to an embodiment of the present disclosure.
  • the shape of the high field strength structure may be pointed cone, mesa, ellipsoid, hemisphere, etc.
  • the number of high field strength structures may be 1, 3, 5, 10, etc., here No limitation.
  • the high field strength structure material and the substrate material may be the same or different.
  • the metal atom material on the surface of the substrate and / or high field strength structure is the same as or different from the material of the high field strength structure.
  • the metal atom on the surface of the substrate and / or high field strength structure may be Formed by evaporation or electroplating.
  • the metal atom material on the surface of the substrate and / or high field strength structure and the substrate material may be the same or different, and when different, the metal atom on the surface of the substrate and / or high field strength structure may be Formed by plating or electroplating.
  • the material of the substrate shown, the material of the high field strength structure and the material of the body of the needle tip are the same or different, and are not limited herein.
  • the high field strength structure may include a protrusion (Protrusion), corresponding to the Lo1 position in FIG. 3A.
  • the size of the protrusion may be on the order of sub-nanometer to 100 nm. Due to the advantage of high field strength at the protrusion, when a voltage is applied to the tip of the needle, under the effect of the field strength, at least part of the metal atoms on the surface of the protrusion will form a reaction product with gas molecules. In this way, the launch point can be formed at a specified position on the surface of the needle tip simply and quickly.
  • the number of emission points formed by the protrusions is controllable. For example, more emission points can be formed to increase the emission current by increasing the duration of the applied bias voltage or increasing the size of the protrusions.
  • the protrusion is formed by any one or more of the following methods: heat treatment, electric field application, thermal-electric field treatment, etching or nano-machining, etc., or the following method: for example, a layer of metal atoms is deposited on the tip of the single crystal metal needle, and the heat treatment Remodeling to form protrusions. It should be noted that any method that can form protrusions on the surface of the needle tip is applicable, and is not limited herein.
  • the substrate material is a conductive material
  • the high field strength structure material is a conductive material
  • the substrate and / or the high field strength structure surface are metal atoms.
  • the type of the metal atom is different from the type of the tip body or substrate, it may be different types of metal atoms formed on the surface of the tip by means of evaporation, electroplating, or the like.
  • the melting point of the substrate material and the high-field-strength structural material is higher than 1000K
  • the melting point of the metal atom is higher than 1000K
  • the stability is better
  • the metal material may include any one or more of the following: tungsten, tantalum, niobium, molybdenum, rhenium, hafnium, iridium, osmium, rhodium, ruthenium, platinum, palladium, gold, chromium, vanadium, zirconium, titanium, or Hexaboride metal, for example, one of the metal atoms is used alone as the metal atom on the surface of the tip, or a stack of several metal atoms, such as a stack of titanium layer ⁇ platinum layer ⁇ tungsten layer, etc., or The non-elementary metal layer formed by mixing several metal atoms is not limited herein.
  • the metal atom is a tungsten atom
  • the gas molecule includes hydrogen
  • the emission point is a hydrogen tungsten compound.
  • FIG. 3C schematically shows a schematic diagram of metal atoms on the surface of a protrusion according to an embodiment of the present disclosure.
  • the material of the substrate, the high field strength structure and the body of the needle tip may be metallic materials, or not metallic materials (such as conductive materials), when the electron source does not include high field strength In the structure, it is only necessary to ensure that the surface of the substrate includes highly reactive metal atoms, and the substrate can introduce current; when the electron source includes a high-field strength structure, as long as the surface of the high-field strength structure is ensured It includes metal atoms, and the high-field-strength structure can introduce current.
  • the high field strength structure is located at the center of the surface of the substrate, or the high field strength structure is located on a substrate with a size greater than a set threshold, such as a substrate with a larger size, or,
  • the metal atom is located at the center of the surface of the top of the high field strength structure.
  • the size and shape of the substrate and / or high field strength structure of the needle tip can be adjusted to adjust the beam angle of the electron beam, and the emission point can also be adjusted by adjusting the size of the high field strength structure and / or active region
  • the amount of the electron beam can also be adjusted by adjusting the structure of the substrate and / or the structure of the high field strength, or the consistency of the voltage of the electron source emission current, and the shape of the tip of the needle tip can be adjusted to adjust the direction of the emission current.
  • the lead-out voltage may be lower than -0.5KV, for example, the lead-out voltage is -0.4KV.
  • FIG. 4 schematically shows a schematic diagram of a tip structure for forming an emission area according to another embodiment of the present disclosure.
  • At least one needle tip includes a substrate and one or more active regions on the substrate that are more reactive than other parts of the substrate, corresponding to the Lo2 position, wherein at least one of the active regions
  • the surface includes metal atoms.
  • the active area is shown in the shaded area of Figure 4.
  • the number of active regions may be 1, 3, 5, 10, etc., which is not limited herein, and the emission point may be preferentially formed in the active region located in the top region of the needle tip.
  • the metal atoms on the surface of the active area of the substrate have greater reactivity than other surface portions of the substrate during the reaction with gas molecules under vacuum conditions .
  • the material of the substrate and the material of the body of the needle tip may be the same or different.
  • the metal atoms in the active region may be formed by evaporation or electroplating, for example, a metal atom layer of a certain area is formed at the intersection of the axis of the needle tip and the surface by electroplating, and the material of the metal atom layer is compared with that of the substrate Materials on other surfaces have higher reactivity with gas molecules. Accordingly, in the reaction with gas molecules under vacuum conditions, the metal atoms on the surface of the active area of the substrate have a greater reactivity than other surface portions of the substrate.
  • the region with high reactivity is located at the center of the surface of the substrate, or the metal atom is located at the center of the surface of the substrate.
  • At least one needle tip includes a substrate and one or more active regions on the substrate that are more reactive than other parts of the substrate, wherein at least one outer surface of the active region includes metal Atoms, the metal atoms on the surface of the active area are more likely to form reaction products with gas molecules in the same environment by virtue of the activity advantage, so as to preferentially generate emission points in the active area.
  • FIG. 5 schematically shows a schematic diagram of a tip structure for forming an emission area according to another embodiment of the present disclosure.
  • At least one needle tip includes a substrate and one or more high field strength structures on the substrate that are higher than the field strength of other parts of the substrate, at least part of the surface of the high field strength structure It is an active area with high reactivity, corresponding to the Lo3 position, wherein the outer surface of the active area includes metal atoms.
  • the metal atoms on at least part of the surface of the protrusion have the same or greater reactivity than other surface parts of the substrate in the reaction with the gas molecule under vacuum conditions In this way, it is possible to more accurately control the emission point to be formed on the specified area of the protrusion, such as the shadow area on the protrusion of FIG. 5 to form the emission point.
  • the method of forming metal atoms on the surface of the active region reference may be made to the method of forming the active region in the previous embodiment, which will not be described in detail here.
  • At least one needle tip includes a substrate and one or more high field strength structures on the substrate that are higher than the field strength of other parts of the substrate, at least part of the high field strength structure
  • the surface is an active area with high reactivity, wherein the outer surface of the active area includes metal atoms, and the metal atoms on the surface of the active area are more likely to form reaction products with gas molecules in the same environment by virtue of the field strength advantage and the activity advantage. Priority is given to generating emission points in the active area.
  • FIG. 6 schematically illustrates a process of forming an emission point according to an embodiment of the present disclosure.
  • the emission point Ma1 is formed, and the formation of Ma1 proceeds at a certain temperature.
  • the formation process of the emission point is based on the preparation method determined after in-depth study of the hydrogen adsorption behavior in a small area on the surface of the needle tip.
  • a negative bias voltage when a negative bias voltage is applied to form an emission point, the following operations may be included: first, a negative bias voltage is applied to the needle tip to generate an emission current with a microampere level, and then, the preset duration is maintained Or adjust the negative bias voltage until an emission current of a predetermined value is generated, and then adjust the negative bias voltage so that the emission current of the electron source is less than the order of milliamps to avoid the change or burnout of the tip shape.
  • a positive bias when a positive bias is applied to form the emission point, a positive bias is applied to the needle tip and maintained for a preset duration, the value of the positive bias is less than that of the field-induced evaporative bias forming the protrusion value.
  • a needle tip of tungsten single crystal (111) can be provided, and a protrusion is formed on the needle tip by the method described above, such as after flash treatment (heating to 1200K for 3 s, it can also be supplemented by bias voltage, etc.), which can A nano-level protrusion is formed in the middle of the surface of the needle tip, and its surface is clean.
  • FIG. 6a when a negative pressure is applied to the needle tip to -2KV, a field electron emission mode is formed. To avoid the impact of ion bombardment, the formation temperature of Ma1 is ⁇ 50K.
  • the emission current (I E ) has been controlled within 5 nA and the vacuum degree is 10 -7 Pa throughout the formation of the emission point.
  • the gas adsorption first causes the emission capability to decrease, the emission pattern on the display interface of the fluorescent screen assembly 103 gradually becomes darker, and the emission current gradually decreases, that is, the emission capability of the existing clean surface of tungsten gradually decreases.
  • the emission point described in the present disclosure begins to form, and the composition of the emission point at this time is different from the previous emission substance.
  • the previous emission The substance is a tungsten atom of a tungsten single crystal, and the emission point at this time is a reaction product of tungsten atoms and gas molecules on the surface of the needle tip, such as tungsten atoms and hydrogen molecules, and the reaction product is fixed on the surface of the needle tip.
  • the gas such as H 2
  • the gas undergoes adsorption, dissociates under the electric field, and further combines with the surface metal atoms to form a certain HW reaction product (compound), which belongs to a type of Ma1.
  • the compound seems to bond directly with the surface and does not move.
  • similar materials can be formed at other locations, but they do not move, and have always been a stable launch point.
  • the launch capability of a single launch point can reach more than 30uA, far exceeding the single-point launch capability of the existing CFE ( ⁇ 10 microamperes). If a dense launch area is formed, the launch map becomes One piece, the total current can reach the order of 100uA. If the emission area is increased, the mA emission current can be achieved.
  • the emission current is large at high vacuum, and the maximum emission current rapidly decays at low vacuum.
  • the tip of the formed emission point (The tip terminated by emission site) has field emission consistency, that is, the voltage of the emission current is consistent, for example, when the emission current is 1 microampere, the voltage is -1.2 ⁇ 0.1KV.
  • the emission point is a reaction product that generates metal atoms and gas molecules on the surface of the needle tip under the action of an electric field in a vacuum environment and in a certain temperature range.
  • the electric field may be an electric field formed by applying a positive bias voltage or a negative bias voltage.
  • the field strength should be 1-50V / nm; when applying a negative bias voltage, the field strength should be 1-30V / nm. .
  • the manufacturing equipment may include a vacuum chamber, a cooling head (the cooling head may include a heating device), a sample stage, a heating plate, a power supply, a gas introduction device, and a fluorescent screen assembly, wherein the background vacuum degree of the vacuum chamber is ⁇ 10 -3 Pa (generally should be better than 10 -6 Pa).
  • the cooling head may include a heating device
  • the sample stage may include a heating plate
  • a power supply may include a sample stage
  • a power supply a gas introduction device, and a fluorescent screen assembly
  • the background vacuum degree of the vacuum chamber is ⁇ 10 -3 Pa (generally should be better than 10 -6 Pa).
  • a heating device (such as a heating sheet and a heating rod) can be set on the sample holder, and the temperature can be adjusted between 10 and 500K.
  • the pre-treated needle tip (such as a tungsten single crystal needle tip, which can be a needle tip with protrusions, the size of the protrusion is nm or sub-nm, or it can be a needle tip with a larger reactive area)
  • a voltage is applied to the needle tip, and the voltage can be a positive high voltage V P or a negative high voltage V N.
  • the power supply can be a dual output high voltage power supply with an output range of ⁇ 0 to 30kv.
  • the gas introduction device is used to introduce reaction gas molecules, such as H 2 , or other reaction gases, such as H element-containing gas, water, CH 4, etc.
  • the gas flow rate can be dynamically adjusted, and the vacuum degree is generally less than 10 -4 when introduced Pa (It should be noted that the residual gas molecules in the strong chamber can also be used directly, and the main component is hydrogen).
  • the gas molecules include hydrogen-containing gas molecules and any one or more of the following: nitrogen-containing gas Molecule, carbon-containing gas molecule or oxygen-containing gas molecule.
  • the formation rate of the emission point can be adjusted by adjusting the introduction rate of gas molecules containing hydrogen elements.
  • the fluorescent screen assembly is used to convert the particle beam image into a light image. When the signal is small, the fluorescent screen-multi-channel plate assembly can be used to amplify the signal.
  • the particle beam When a voltage is applied to the needle tip, the particle beam can be drawn out, and the applied voltage can be positive pressure or negative pressure; when the positive pressure is, there is an imaging gas, the positive ion beam is output; when the negative pressure, the electron beam . Due to the formation of the emission point and the low operating temperature, the structure of the electron source does not change during operation, the applied voltage value does not change, and the stable voltage value makes the design of the electron gun simpler.
  • First form a high field strength structure The process of forming a high field strength structure may include the following operations.
  • a region with a strong field strength is formed on the surface of the needle tip.
  • a protrusion is formed in the center of the needle tip.
  • the material of the protrusion may be the same as the substrate, or it may be heterogeneous.
  • the material of the protrusion is a conductor, and the one or several layers of atoms on the outermost surface of the protrusion are metal atoms.
  • the size of the protrusion is nm or sub-nm.
  • the protrusion can be subjected to electrochemical etching, field ion etching, heat treatment, and electric field application. , Nano-machining and other methods or a combination of several methods, or the following methods: For example, a layer of metal atoms is plated on the tip of a single crystal metal needle, and the protrusion is formed by heat treatment and reshaping.
  • a gas which can be H 2 , N 2 , or a gas containing H element, such as H 2 or a gas containing H element.
  • the gas may also be a gas remaining in the vacuum chamber, such as H 2 , H 2 O, CO, CO 2 and the like.
  • the vacuum of the chamber should be less than 10 -3 Pa. Preferably, the vacuum can be less than 10 -6 Pa.
  • the temperature of the needle tip can be adjusted before applying the bias.
  • the tip temperature should be lower than 1000K; preferably, the low temperature is lower than 150K, and the high temperature is in the range of 500-800K; when the tip temperature is higher than 1000K, the formed emission point will be removed. As shown in Table 1, it is the formation condition of the emission point.
  • the structure of the electron source does not change.
  • the structure of the electron source does not change, and the value of the applied voltage does not change.
  • the applied bias voltage can be positive or negative, or a combination of the two.
  • the applied positive bias voltage when a positive bias is applied, the applied positive bias voltage should be lower than the field-induced evaporation voltage, and the field strength should be 1-50V / nm; when a negative bias is applied, the applied negative bias voltage should be lower than Burnout voltage, the field strength should be 1 ⁇ 30V / nm, in addition, the voltage should be adjusted in time when a negative bias is applied, so as to prevent the needle tip shape change or burn out due to excessive current, in general, the needle tip current should be controlled to less than mA level.
  • an example of forming an emission point under the action of a negative bias voltage will be described.
  • the pre-treated needle tip such as a needle tip with a protrusion and a clean surface
  • the degree of vacuum is 1E -7 Pa.
  • the temperature of the needle tip should be lower than 1000K.
  • the temperature of the needle tip is preferably a low temperature below 150K or a high temperature in the range of 500-800K. When the temperature of the needle tip is higher than 1000K, the formed emission point will be removed.
  • a negative bias is applied to the tip of the needle.
  • gas molecules or ions adsorbed on the surface of the needle continuously move to a specific area of the tip.
  • the specific area may be a high-field-strength structure area and / or a region with a large reactivity .
  • the gas molecules react with the metal atoms (such as tungsten) on the surface of the needle tip to form an emission point, generating a small emission current, such as less than 1 ⁇ A, as the emission point continues to form, the emission
  • a small emission current such as less than 1 ⁇ A
  • the emission current increases sharply to hundreds of ⁇ A ⁇ 1mA, and the negative bias voltage should be quickly reduced or cut off in time to avoid burning the needle tip.
  • the control current is less than the order of mA, and passes many times Slowly apply negative high voltage to obtain a predetermined emission current.
  • the needle tip includes the protrusion structure as shown in FIG. 3B (such as a super needle structure obtained by applying a positive bias to the needle tip and performing field etching, that is, the needle tip is applied with a positive bias)
  • the negative bias voltage is added to a certain value (such as -1.2KV)
  • gas molecules react with metal atoms (such as tungsten) on the surface of the needle tip to form an emission point, generating a small emission current, for example, less than 1 ⁇ A; the voltage can be increased to make the emission point continue to form ,
  • the emission current grows to tens of ⁇ A (such as 30 ⁇ A); after continuous waiting or increasing the voltage, the field emission point continues to form; the number of field emission points gradually increases, and the total emission current gradually increases.
  • the protruding structure is a super needle structure obtained by applying a positive bias to the needle tip and performing field etching.
  • the voltage of the field etching is consistent, the voltage of the emission current can be made uniform, for example, the field etching voltage is + 8KV, forming Protruding, then the voltage for stable emission current is -1KV.
  • the process of forming the emission point on the clean surface of the protrusion of the W needle tip (111) is as follows, the temperature of the needle tip is ⁇ 50K, and the vacuum degree is 10E -7 Pa; applying a negative bias to the needle tip, the W needle tip (111)
  • the field emission pattern of the clean surface of the protrusion is shown in FIG. 6a.
  • the test is maintained. Under the action of the electric field, the gas molecules move to the position of the protrusion; due to the gas adsorption, the field emission pattern continues to darken or disappear completely, as shown in FIGS. 6a-6g .
  • the negative bias under the action of a certain electric field, the gas molecules react with the metal atoms on the surface of the protrusion to form an emission point rooted in the surface.
  • an example of forming an emission point under the action of a positive bias voltage will be described.
  • a vacuum environment preferably, the degree of vacuum is 1E -7 Pa; the needle tip has a clean surface, adjust the temperature of the needle tip, the needle tip temperature should be below 1000K, when the needle tip temperature is above 1000K At this time, the formed emission point will be removed.
  • a positive bias voltage such as + 8KV
  • the value of the positive bias voltage should be less than the field evaporation voltage.
  • the gas molecules continue to move to a specific area of the needle tip, and the reaction forms a reaction product as an emission point.
  • the positive bias and the negative bias have the same effect, all to form a certain field strength.
  • the value of the positive bias voltage can be adjusted or the holding time can be adjusted to adjust the number of emission points formed.
  • FIG. 7 schematically shows a schematic diagram of a process for forming an emission point by applying a positive bias voltage according to an embodiment of the present disclosure.
  • FIG. 6 when a positive bias is applied, the processes of the cleaning surface emission shown in FIG. 6 a and the cleaning surface emission pattern shown in FIGS. 6 a to 6 f are darkened may not be observed, and only FIG. 6 g to 61 can be observed.
  • FIG. 7 for example, in the embodiment in which the emission point is formed on the surface of the protruding structure shown in FIG. 3B, after applying a positive bias, the emission point is directly formed.
  • a negative bias is applied to the tip of the needle, and when it is added to a certain value, such as -1.2KV, the field emission point that has been formed will emit current.
  • the compound seems to be directly combined with the surface of the needle tip and does not move.
  • similar materials can be formed at other positions of other needle tips, but it does not move and has always been a stable launch point.
  • the vacuum is high, the current is large, and when the vacuum is low, the maximum emission current quickly decay.
  • FIG. 8 schematically illustrates a relationship between the number of emission points and the uniformity of emission patterns according to an embodiment of the present disclosure.
  • the number of emission points is more uniform.
  • the uniformity of the emission pattern can be increased by increasing the number of emission points.
  • the protrusions can accommodate more emission points. For example, when the protrusions have the same surface area: the number of emission points is small, the emission current is small, and the pattern is uneven; the number of emission points is large, and the emission current is large , The pattern is even.
  • the electron source manufactured by the electron source manufacturing method provided by the present disclosure has an emission point with high emission capability, and has the advantages of small emission point, small energy dissipation, and stability.
  • a single emission point is at the nm or sub-nm level.
  • the tip of the point (The tip terminated by emission site) is a field emission electron source that can draw and control the current by adjusting the voltage.
  • the emission current of a single emission point can reach more than 30uA. If a dense emission area is formed, the emission points are connected together, and the total current can reach the order of 100uA. If the formation area is increased, a current of mA level can be realized. Under different vacuum degrees, it has different launch capabilities.
  • the method can also include the following operations: after forming one or more fixed launch points on at least one needle tip, pass The electron source applies an electric field so that gas molecules are adsorbed on the emission point to remove at least one emission point. For example, by applying a voltage to the electron source to form an electric field, gas molecules are adsorbed on the emission point under the action of the electric field, so that at least one emission point does not emit current.
  • FIG. 9 schematically shows a schematic diagram of adjusting the number of emission points according to an embodiment of the present disclosure.
  • the number of emission points can be adjusted by adjusting the size of the protrusions, because the protrusions are nano-scale, the emission points can also be nano-scale, each protrusion can accommodate a limited number of emission points, therefore, small The number of emission points that can be formed on the protrusions will be less.
  • the size of the tip protrusion is increased, more emission points can be formed by adjusting the voltage, thereby increasing the emission current.
  • FIG. 10 schematically shows a schematic diagram of adjusting a beam angle according to an embodiment of the present disclosure.
  • the size of the beam angle can be adjusted by adjusting the size of the substrate and / or the size of the protrusions. For example, when the protrusion sizes are the same, the smaller the substrate size, the larger the beam angle ⁇ . Conversely, when the protrusion sizes are the same, the larger the substrate size, the smaller the beam angle ⁇ . In addition, when the substrate sizes are the same, the higher the protrusion height h1, the larger the beam angle ⁇ 1. Conversely, when the protrusion sizes are the same, the lower the protrusion height h2, the smaller the beam angle ⁇ 1.
  • the beam angle can be reduced by increasing the size of the substrate and / or reducing the height of the field evaporation protrusion.
  • the shape of the substrate can also be adjusted to change the direction of the emission current.
  • the direction of the emission current of the substrate that does not coincide with the axis of the needle tip is different from the direction of the emission current of the substrate that coincides with the axis of the needle tip.
  • controlling the structure of the tip protrusion and the substrate can make the voltage of the emission current consistent (such as the protrusion formed by field-induced etching, the etching voltage is V1 ⁇ 0.5KV, Then the voltage for stable emission current is V2 ⁇ 0.1KV).
  • FIG. 11 schematically shows a schematic diagram of an electron source using process according to an embodiment of the present disclosure.
  • an electron gun including the electron source prepared by the method as described above, and a cooling device, a heating device, and a gas introduction device.
  • the electron source is used to emit electrons
  • the cooling device is used to dissipate heat to the electron source
  • the electron source is fixed on the cooling device through an electrically insulated thermal conductor
  • the heating device is used to The electron source is heated to adjust the temperature
  • the gas introduction device is used to introduce a gas containing hydrogen element. Because the formation temperature and working temperature of the emission point on the electron source surface of the electron gun are low, the structure of the electron source does not change during operation, the applied voltage value does not change, and the voltage value is also more stable, making the design of the electron gun simpler.

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Abstract

一种电子源制造方法，该方法包括：在至少一个针尖上形成一个或多个固定的发射点，所述发射点包括针尖表面的金属原子与气体分子形成的反应产物。

Description

电子源制造方法 技术领域
本公开涉及电子源技术领域，更具体地，涉及一种场发射的电子源制造方法。
背景技术
金属中的自由电子在特定条件下可以发射出来，若用金属构成阴极并做成极细的针尖状，在真空中施以数千伏电压，金属中的电子即可从阴极冷金属中发射，这种发射电子的方法称为场发射，属于冷阴极发射。
对于电子源而言，最重要的指标就是亮度，直接决定了其束流品质。在引出电压V0下，亮度可如公式(1)所示：
Figure PCTCN2018124330-appb-000001
其中，B为亮度，I为发射电流，S为等效发射面积，d为等效直径，Ω为空间发射角，α为发射半角。此外，亮度B正比于加速电压V a，如公式(2)所示。
B∝V a   (2)
由公式(1)可知，为得到高亮度，需要尽可能得提升I，以及减小α和d。此外，获得一定的发射电流所需要的引出电压V0越低越好，而这需要针尖的发射面具有较低的功函数以及较尖锐的头部结构。另外，电子源的另外一个关键指标就是单色性，可用能散δE表示。
综合上述考虑，最理想的电子源就是冷场发射电子源(cold field emission electron sources，简称CFE)，CFE的亮度高过其它种类电子源约一个量级以上，且有很小的能散(～0.3eV)。此外，为了尽量追求极限直径，近年来具有低功函数的原子级电子源成为研究热点，即发射点仅有一个或者数个原子组成。
在实现本公开构思的过程中，发明人发现现有技术中CFE至少存在如下问题：第一，CFE稳定性往往很差，需在极高真空下(10 -9～10 -8Pa)才能工作，这严重限制了其使用范围。而即使在该环境下，也需定期处理以获得较稳定的工作状态。第二，受离子轰击的影响，CFE较容易烧毁。第三，前述问题在较大发射电流下变得更为严重，现有的CFE一般可长时间稳定工作的总发射电流为～10微安，且利用率很低。鉴于前述弊端，在高亮度电子源领域占据主导地位的是肖特基式场发射电子源(Schottky thermal-field emission  source)。
发明内容
有鉴于此，本公开提供了一种可以制造出稳定的、具有较大的场发射电流、可以在较差真空度下工作的电子源的制造方法。
本公开的一个方面提供了一种电子源制造方法，包括：在至少一个针尖上形成一个或多个固定的发射点，所述发射点包括针尖表面的金属原子与气体分子形成的反应产物。由于形成的发射点是固定在针尖表面的金属原子与气体分子形成的反应产物根植于针尖表面，而非游离在针尖表面的气体分子或游离颗粒物等，不会如现有技术中的游离状的物质聚集在一起形成新的发射点而导致过电流烧毁，有效提升了稳定性，此外，形成的发射点包括针尖表面的金属原子与气体分子形成的反应产物，相对于金属原子或其它金属化合物(如金属硼化物等)而言，在工作环境中(存在气体分子)具有更好的稳定性，如更加不容易与工作环境中的例如氢气等发生作用或反应，进一步提升了电子源的稳定性。另外，本公开提供的电子源制造方法制造的发射点可以为一个或数个金属原子与气体分子形成的反应产物，即可以通过控制形成的发射点的数量来形成具有低功函数的原子级电子源。此外，该反应产物使表面功函数显著降低，表面发射点尖锥的形成也使发射能力显著提高。另外，可以通过制备更多数量的发射点来提升场发射电流的电流值。这样就可以制造出稳定的、具有较大的场发射电流的电子源。
根据本公开的实施例，在电场下使所述金属原子与所述气体分子反应形成所述发射点。这样便于在针尖的指定位置，尤其是具有电场优势的位置形成发射点，如针尖的突起处。
根据本公开的实施例，在一个具体实施例中，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，其中，至少一个所述高场强结构的外表面包括金属原子，该高场强结构表面的金属原子凭借场强优势在相同的环境中更容易与气体分子形成反应产物，以优先在高场强结构生成发射点。在另一个具体实施例中，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其他部位反应活性大的活性区域，其中，至少一个所述活性区域外表面包括金属原子，该活性区域表面的金属原子凭借活性优势在相同的环境中更容易与气体分子形成反应产物，以优先在活性区域生成发射点。在另一个具体实施例中，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，所述高场强结构的至少部分表面是反应活性大的活性区域，其中，所述活性区域外表面包括金属原子，该活性区域表面的金属原子凭借场强 优势和活性优势在相同的环境中更容易与气体分子形成反应产物，以优先在活性区域生成发射点。
根据本公开的实施例，所述高场强结构包括突起。
根据本公开的实施例，所述突起的尺寸为亚纳米至100纳米量级。
根据本公开的实施例，所述突起通过以下任意一种或多种方法形成：热处理、施加电场、热-电场处理、刻蚀或者纳米加工，或者如下方法：例如在单晶金属针尖上面镀一层金属原子，通过热处理重塑形成突起。
根据本公开的实施例，对于包括突起的针尖，在真空条件下与气体分子的反应中，所述突起的至少部分表面的金属原子比所述衬底的其他表面部分具有相同或更大的反应活性，即突起表面至少部分区域(如指定区域)上有反应活性相对其他区域大的金属原子。对于不包括突起的针尖，在真空条件下与气体分子的反应中，所述衬底的活性区域的表面的金属原子比所述衬底的其他表面部分具有更大的反应活性。
根据本公开的实施例，所述方法还可以包括如下操作：通过调节所述针尖的衬底和/或高场强结构的尺寸和形状以调节电子束束流角的大小，或者，通过调节高场强结构和/或活性区域的尺寸调节发射点的数量，或者，通过调节衬底的结构和/或高场强结构调节电子源发射电流的电压的大小或一致性，或者，通过调节针尖顶部的形状以调节发射电流方向。这样便于制造出能满足用户各种需求的电子源。例如通过场致刻蚀、场蒸发等方法形成的针尖突起上形成发射点，发射电流为1微安时，电压可以低于-0.5KV(例如引出电压为-0.4KV)，从而使电子枪结构设计更简单。
根据本公开的实施例，所述气体分子包括含氢元素气体分子以及以下任意一种或多种：含氮元素气体分子、含碳元素气体分子或者含氧元素气体分子。
根据本公开的实施例，所述含氢元素气体分子由引入的含氢元素气体分子构成和/或由真空环境中残存的气体分子构成，相应地，可以通过调节含氢元素气体分子的引入速率调节所述发射点的形成速率，如含氢元素气体分子引入速率处于较高速率时可以提升所述发射点的形成速率。
根据本公开的实施例，所述含氢元素气体分子可以包括氢气分子，所述金属原子可以为钨原子，相应地，所述发射点为氢钨化合物。这样可以在现有的钨针的基础上制造出稳定的、具有较大的场发射电流的电子源，且与现有技术的兼容度较高。
根据本公开的实施例，所述电场为通过施加偏压形成的；其中，所述施加偏压包括以下任意一种或多种：施加正偏压、施加负偏压或者施加正偏压和负偏压相结合。其中，施 加偏压的方式包括但不限于直接给针尖施加偏压或者给针尖附近的部件施加偏压以产生电场，该电场作用与针尖上形成一定的场强以使针尖表面的金属原子与气体分子形成反应产物。
根据本公开的实施例，对于施加正偏压，形成的场强的范围包括1～50V/nm，这样可以避免由于正偏压引起的场致刻蚀、场致蒸发等导致无法形成发射点。对于施加负偏压，形成的场强的范围包括1～30V/nm，这样可以避免发射电流过大导致针尖被烧毁或针尖的形貌发生改变。
根据本公开的实施例，当施加负偏压形成发射点时，可以首先给所述针尖施加负偏压，产生电流值为微安量级的发射电流，然后，维持预设时长或调节所述负偏压直至产生预定值的发射电流，接着，调节负偏压使得所述电子源的发射电流小于毫安量级，避免针尖形貌改变或烧毁。
根据本公开的实施例，当施加正偏压形成发射点时，给所述针尖施加正偏压并维持预设时长，所述正偏压的值小于形成所述突起的场致蒸发偏压的值。
根据本公开的实施例，可以通过调节所述施加偏压的值或者调节预设时长的值来调节形成的发射点的数量。这样就可以实现原子级别的电子源或者大发射电流的电子源。
根据本公开的实施例，制造电子源的环境可以包括以下任意一种：针尖温度≤1000K时，压强≤10 -3Pa，或者，500K≤针尖温度≤800K时，压强≤10 -6Pa，或者，当针尖温度≤150K时，压强≤10 -6Pa。由于发射点形成和工作温度较低，电子源结构不改变，在工作时电子源结构不改变，施加电压值不发生变化。
根据本公开的实施例，所述方法还可以包括如下任意一种或多种操作：通过调节发射点的数量以调节发射点的均匀性，或者，通过调节发射点的数量以调节电流的大小，或者，通过增加发射点的数量来增加发射电流的稳定性。
根据本公开的实施例，所述方法还可以包括如下操作：在至少一个针尖上形成一个或多个固定的发射点之后，通过施加电场使得气体分子吸附在发射点上，以去除至少一个发射点。
根据本公开的实施例，所述衬底材料是导电材料，或者，所述高场强结构材料是导电材料，或者，所述衬底和/或高场强结构表面是金属原子，或者，所述高场强结构材料与衬底材料相同或者不同，或者，所述衬底和/或高场强结构表面的金属原子材料与高场强结构材料相同或者不同，当不同时，所述衬底和/或高场强结构表面的金属原子通过蒸镀或者电镀等方式形成，或者，所述衬底和/或高场强结构表面的金属原子材料与衬底材料 相同或者不同，当不同时，所述衬底和/或高场强结构表面的金属原子通过蒸镀或者电镀等方式形成。
根据本公开的实施例，可选地，所述衬底材料是导电材料并且熔点高于1000K，或者所述高场强结构材料是导电材料并且熔点高于1000K，或者所述衬底和/或高场强结构表面的金属原子的材料为熔点高于1000K的金属材料，以及所述金属原子与气体分子的反应产物包括在真空条件下熔点高于1000K的金属原子与气体分子的反应产物。
根据本公开的实施例，可选地，高场强结构或者反应活性大的区域位于所述衬底的表面中心位置，或者，高场强结构位于尺寸大于设定阈值的衬底上，或者，所述金属原子位于所述高场强结构顶端或者所述衬底的表面中心位置。
根据本公开的实施例，所述发射点的消失温度低于所述衬底、所述高场强结构和所述金属原子的消失温度的小值，且所述发射点的消失温度高于所述电子源的工作温度；或者所述发射点的消失温度低于所述衬底、所述高场强结构和所述金属原子的消失温度的小值，且所述发射点的消失温度高于所述电子源的工作温度和吸附于任一针尖上的气体分子的脱吸附温度的大值。
根据本公开的实施例，所述发射点的尺寸为纳米级或亚纳米级；以及通过调节工作电压，针尖发射点发射电流值可达10mA量级。
根据本公开的实施例，其中，所述电子源具有冷场发射特点，通过调节引出电压调节发射电流大小。
附图说明
通过以下参照附图对本公开实施例的描述，本公开的上述以及其他目的、特征和优点将更为清楚，在附图中：
图1示意性示出了根据本公开实施例的电子源的制备过程示意图；
图2示意性示出了根据本公开另一实施例的电子源的制备过程示意图；
图3A示意性示出了根据本公开实施例的用于形成发射区域的针尖结构的示意图；
图3B示意性示出了根据本公开实施例的高场强结构的示意图；
图3C示意性示出了根据本公开实施例的突起表面金属原子的示意图；
图4示意性示出了根据本公开另一实施例的用于形成发射区域的针尖结构的示意图；
图5示意性示出了根据本公开另一实施例的用于形成发射区域的针尖结构的示意图；
图6示意性示出了根据本公开实施例的发射点形成过程的示意图；
图7示意性示出了根据本公开实施例的施加正偏压形成发射点的过程示意图；
图8示意性示出了根据本公开实施例的发射点数量和发射图案均匀性的关系的示意图；
图9示意性示出了根据本公开实施例的调节发射点的数量的示意图；
图10示意性示出了根据本公开实施例的调节束流角的示意图；以及
图11示意性示出了根据本公开实施例的电子源使用过程的示意图。
具体实施方式
以下，将参照附图来描述本公开的实施例。但是应该理解，这些描述只是示例性的，而并非要限制本公开的范围。在下面的详细描述中，为便于解释，阐述了许多具体的细节以提供对本公开实施例的全面理解。然而，明显地，一个或多个实施例在没有这些具体细节的情况下也可以被实施。此外，在以下说明中，省略了对公知结构和技术的描述，以避免不必要地混淆本公开的概念。
在此使用的术语仅仅是为了描述具体实施例，而并非意在限制本公开。在此使用的术语“包括”、“包含”等表明了所述特征、步骤、操作和/或部件的存在，但是并不排除存在或添加一个或多个其他特征、步骤、操作或部件。
在此使用的所有术语(包括技术和科学术语)具有本领域技术人员通常所理解的含义，除非另外定义。应注意，这里使用的术语应解释为具有与本说明书的上下文相一致的含义，而不应以理想化或过于刻板的方式来解释。
在使用类似于“A、B和C等中至少一个”这样的表述的情况下，一般来说应该按照本领域技术人员通常理解该表述的含义来予以解释(例如，“具有A、B和C中至少一个的操作”应包括但不限于单独具有A、单独具有B、单独具有C、具有A和B、具有A和C、具有B和C、和/或具有A、B、C的操作等)。在使用类似于“A、B或C等中至少一个”这样的表述的情况下，一般来说应该按照本领域技术人员通常理解该表述的含义来予以解释(例如，“具有A、B或C中至少一个的操作”应包括但不限于单独具有A、单独具有B、单独具有C、具有A和B、具有A和C、具有B和C、和/或具有A、B、C的操作等)。本领域技术人员还应理解，实质上任意表示两个或更多可选项目的转折连词和/或短语，无论是在说明书、权利要求书还是附图中，都应被理解为给出了包括这些项目之一、这些项目任一方、或两个项目的可能性。例如，短语“A或B”应当被理解为包括“A”或“B”、或“A和B”的可能性。
以下首先对现有技术中的场发射行为进行说明以便更好地理解本公开的技术方案。
现有的电子源，如钨(310)单晶针尖的电子源在使用过程中会经历如下三个阶段，首先，是较清洁的电子源，随着气体的吸附，进入稳定期(Stability)，然而，随着气体的进一步吸附，电流噪声逐渐出现，进入不稳定期(Instability)，电子源稳定性变差，需Flash处理(短时间加热至约2000℃)，以重新回到稳定状态。如不及时处理，表面会逐渐出现污染物，发射电流开始剧烈波动，最终导致烧毁。
关于上述烧毁，发明人进一步的研究，表明其与离子轰击密切相关。这是由于电子发射后会电离周围空间的气体分子，进而轰击到针尖。一个可能就是针尖表面被轰击形成多个突起，多个突起分别作为发射点，最后导致过多电流，造成烧毁。还有一种机制，就是吸附到针尖表面的气体分子或其和其它物质的结合物，在电场作用下不断移动，最终在一个表面的缺陷点(如由离子轰击产生)汇集成一个纳米级突起作为发射点，发射点的迅速长大导致了过流，最终导致了针尖的烧毁。
进一步地，前述问题在较大发射电流下变得更为严重。一般可长时间稳定工作的总发射电流为～10微安，且利用率很低。鉴于前述弊端，在高亮度电子源领域占据主导地位的是肖特基式场发射电子源(Schottky thermal-field emission source)。
本质上讲，对CFE而言，任何材料都不能避免气体吸附和离子轰击的影响。但是，如工作在大电流下(＞10微安)，电子激励脱气(特别在电子轰击引出极)，就会进一步劣化真空度，使得针尖发射稳定性很差，波动幅度极大，更加无法长期稳定工作。因而，如何提供出稳定的、较大的场发射电流，一直是冷场发射电子源发展历程中最主要的挑战。
为了避免上述气体吸附和离子轰击的影响，当前场发射电子源(一般指金属针尖)仅能在超高真空中工作(＜10 -8Pa)，这严重制约了CFE的适用范围，发明人针对于此又进行了进一步深入研究，发现以下特点，真空中残留气体成分有H 2，CO，CO 2，而主要成分则是H 2。H 2的吸附会导致清洁表面的发射能力逐渐变差。可以说在该真空范围，H 2的影响从根本上决定了针尖的场发射性能。因此，如何应对H 2的影响成为实现高稳定度针尖的关键。现有技术中也存在一些技术方案可以缓解气体吸附的问题，例如，通过进一步提高腔体真空度至1×10 -9Pa量级，Keigo Kasuya等发明了一种技术(mild flashings at 700℃)，使得W(310)面一直处于一个较清洁的发射状态，延长了其使用时间并获得了高发射能力。该专利的技术方案目前已广泛应用于Hitachi的电子显微镜产品中。
此外，还存在一些技术方案直接利用一些针尖表面游离颗粒物(atomic clusters)作为发射点，也是尝试的一种解决方式。这些游离颗粒物，可以是通过在较差真空度下长时间放置形成的污染物，电场作用使得这些游离颗粒物可以移动到针尖某处。这种发射点发射角很小(～5°)，引出电压极低，亮度可以达到传统W(310)的10倍以上。尽管不能够形成较大的发射电流(一般可以稳定地给出～10nA)，但是展现出了极好的稳定性(＜1×10 -7Pa)。一个可能推论就是，极小的束流角和发射面积可以有效降低离子轰击的影响。然而，如前所述，这种游离颗粒物是不固定的，发明人发现，在电流较大时(＞1uA)，这种电子源容易烧毁，且在工作工程中，还会有这种物质不断出现，逐渐改变其发射状态，很难长时间维持。另外一个问题就是暴露大气时，由于这种物质的尺寸和气体分子可以比拟，极易受到气体的干扰。
基于以上种种分析、推理及实验，发明人提供了本公开的电子源制造方法以提高一种电子源，实现可长期稳定的工作，能提供较大的场发射电流，能在较差的真空环境下工作，且在暴露在大气中时也不易受到气体的干扰。
本公开提供的电子源制造方法，在至少一个针尖上形成一个或多个固定的发射点，所述发射点包括针尖表面的金属原子与气体分子形成的反应产物。由于利用针尖表面的金属原子作为反应物质，其与气体分子形成的反应产物根植于针尖表面，且由于该反应产物是金属原子与气体分子在类似于工作条件下反应形成的反应产物，该反应产物再次与气体分子反应的活性不大，因此稳定性较高，此外，由于可以控制反应产物的数量，因此，可以通过增加反应产物的数量来实现提供较大的场发射电流。另外，由于反应产物是金属原子与气体分子反应形成的反应产物，即使暴露在大气中也不易受气体的干扰。
上述发射点可以通过施加电场使金属原子与气体分子进行反应的方式形成。
在一个实施例中，所述电场为通过施加偏压形成的；其中，所述施加偏压包括以下任意一种或多种：施加正偏压、施加负偏压或者施加正偏压和负偏压相结合。通过施加电场而使得针尖表面的金属原子与气体分子形成的反应产物，具体可以采用多种实现方式，例如，直接给针尖施加电压在针尖表面形成较高的场强以促使针尖表面的金属原子和气体分子发生反应形成的反应产物；也可以是给针尖附近的场强产生结构(如电极等)施加电压形成电场，进而在针尖表面形成较高的场强以促使针尖表面的金属原子和气体分子发生反应形成的反应产物。总之，在针尖表面形成的场，及该场的形成方式不做限定，只要能在针尖表面形成场，该场能促使针尖表面金属原子与周围气体分子反应形成反应产物即可。
以下以在针尖施加偏压形成电场的方式在针尖表面上形成发射点为例进行说明。
图1示意性示出了根据本公开实施例的电子源的制备过程示意图。
如图1所示，从图1的左图中可以看到，在针尖上施加偏压之后，针尖表面和环境中的气体分子会不断的向高场强处移动，接着，在高电场的作用下，促使针尖表面的至少部分金属原子与气体分子生成反应产物，即发射点。右图是对左图中虚线框中图像的放大示意图，左图下方的虚线框为示意性的衬底。从左图可以看到，在给针尖施加偏压后，由于针尖顶端，如突起处的场强最强，环境中的气体分子和针尖表面吸附的气体分子(左图中的灰色小点)会逐渐向针尖顶端聚集，这也是造成现有技术中的钨单晶的电子源发射能力下降的原因之一。从右图可以看出，随着气体分子聚集到电子源的针尖处，通过在针尖处形成场(如电场等)以促使气体分子与针尖表面的金属原子(白色小点)形成反应产物(黑色圆点，即发射点，简称Ma1)，该发射点会根植于针尖表面，而非游离在针尖表面。
图2示意性示出了根据本公开另一实施例的电子源的制备过程示意图。
如图2所示，图中的阴影部分表示具有大反应活性的区域，发射点形成在上述大反应活性的区域。具体地，大反应活性的区域的表面可以为与气体分子反应活性大的金属原子组成，这样使得这些金属原子可以在如电场的作用下优先与气体分子形成反应产物，以在指定区域形成发射点，如图中黑色圆点所示。
图3A示意性示出了根据本公开实施例的用于形成发射区域的针尖结构的示意图。
如图3A所示，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，其中，至少一个所述高场强结构的外表面包括金属原子。衬底可以为针尖接近顶端的部分，也可以是在针尖表面另外形成的导电材料等。
图3B示意性示出了根据本公开实施例的高场强结构的示意图。
如图3B所示，高场强结构的形状可以为尖锥形、台形、椭球形、半球形等，高场强结构的数量可以为1个、3个、5个、10个等，在此不做限定。
需要说明的是，所述高场强结构材料与衬底材料可以相同或者不同。此外，所述衬底和/或高场强结构表面的金属原子材料与高场强结构材料相同或者不同，当不同时，所述衬底和/或高场强结构表面的金属原子可以是通过蒸镀或者电镀方式形成。另外，所述衬底和/或高场强结构表面的金属原子材料与衬底材料可以相同或者不同，当不同时，所述衬底和/或高场强结构表面的金属原子可以是通过蒸镀或者电镀方式形成。此外，所示衬底的材料、所述高场强结构的材料与所述针尖的本体的材料相同或不同，在此不做限定。
如图3B所示，所述高场强结构可以包括突起(Protrusion)，对应图3A中的Lo1位置。其中，所述突起的尺寸可以为亚纳米至100纳米量级。由于突起处具有高场强优势，当给 针尖施加电压时，在场强的作用下，突起表面的至少部分金属原子会与气体分子形成反应产物。这样就可以简单快捷地在针尖表面的指定位置处形成发射点。此外，突起形成的发射点的数量可控，例如，可以通过增加施加的偏压的时长或者增大突起的尺寸来形成更多的发射点以增大发射电流等。
所述突起通过以下任意一种或多种方法形成：热处理、施加电场、热-电场处理、刻蚀或者纳米加工等，或者如下方法：例如在单晶金属针尖上面镀一层金属原子，通过热处理重塑形成突起。需要说明的是，只要能在针尖表面形成突起的方法都适用，在此不做限定。
可选地，所述衬底材料是导电材料，所述高场强结构材料是导电材料，所述衬底和/或高场强结构表面是金属原子。其中，当所述金属原子的种类和针尖本体或衬底的种类不相同时，可以是通过蒸镀、电镀等方式在针尖表面形成的不同种类的金属原子。优选地，所述衬底材料、高场强结构材料熔点高于1000K，该金属原子熔点高于1000K，稳定性更好，且便于利用Flash(短时高温加热)技术等进行热处理以对针尖进行清洁。例如，该金属材料可以包括以下任意一种或多种：钨、钽、铌、钼、铼、铪、铱、锇、铑、钌、铂、钯、金、铬、钒、锆、钛、或者六硼化金属，例如，其中某一种金属原子单独作为针尖表面的金属原子，或者其中几种金属原子形成的叠层，如钛层\铂层\钨层形成的叠层等，又或者其中几种金属原子混合形成的非单质的金属层，在此不做限定。在一个优选的实施例中，所述金属原子为钨原子，所述气体分子包括氢气，相应地，所述发射点为氢钨化合物。
图3C示意性示出了根据本公开实施例的突起表面金属原子的示意图。
需要强调的是，所述衬底、所述高场强结构和所述针尖的本体的材料都可以是金属材料，或不是金属材料(如导电材料即可)，当电子源不包括高场强结构时，只要保证所述衬底的表面包括反应活性大的金属原子，且所述衬底可以引入电流即可；当电子源包括高场强结构时，只要保证所述高场强结构的表面包括金属原子，且所述高场强结构可以引入电流即可。
在一个优选的实施例中，高场强结构位于所述衬底的表面中心位置，或者，高场强结构位于尺寸大于设定阈值的衬底上，如尺寸较大的衬底上，或者，所述金属原子位于所述高场强结构顶端的表面中心位置。
此外，可以通过调节所述针尖的衬底和/或高场强结构的尺寸和形状以调节电子束束流角的大小，还可以通过调节高场强结构和/或活性区域的尺寸调节发射点的数量，也可 以通过调节衬底的结构和/或高场强结构调节电子源发射电流的电压的大小或一致性，并且可以通过调节针尖顶部的形状以调节发射电流方向。例如，增大衬底尺寸，则束流角减小；场蒸发使突起高度降低，则束流角减小；突起的尺寸越小，则发射点数量减少越少等。其中，引出电压可低于-0.5KV，如引出电压为-0.4KV。
图4示意性示出了根据本公开另一实施例的用于形成发射区域的针尖结构的示意图。
如图4所示，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其他部位反应活性大的活性区域，对应Lo2位置，其中，至少一个所述活性区域外表面包括金属原子。活性区域如图4的阴影区域所示。活性区域的个数可以为1个、3个、5个、10个等，在此不做限定，发射点可以优先形成在位于针尖顶部区域的活性区域中。
需要说明的是，对于不包括突起的针尖，在真空条件下与气体分子的反应中，所述衬底的活性区域的表面的金属原子比所述衬底的其他表面部分具有更大的反应活性。衬底的材料和所述针尖的本体的材料可以相同或不同。所述活性区域的金属原子可以是通过蒸镀或者电镀等方式形成，例如，通过电镀在针尖的轴线与表面相交处形成一定面积的金属原子层，该金属原子层的材料相较于衬底的其它表面的材料与气体分子具有更高的反应活性。相应地，在真空条件下与气体分子的反应中，所述衬底的活性区域的表面的金属原子比所述衬底的其他表面部分具有更大的反应活性。
在一个优选的实施例中，反应活性大的区域位于所述衬底的表面中心位置，或者，所述金属原子位于所述衬底的表面中心位置。
本公开提供的电子源，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其他部位反应活性大的活性区域，其中，至少一个所述活性区域外表面包括金属原子，该活性区域表面的金属原子凭借活性优势在相同的环境中更容易与气体分子形成反应产物，以优先在活性区域生成发射点。
图5示意性示出了根据本公开另一实施例的用于形成发射区域的针尖结构的示意图。
如图5所示，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，所述高场强结构的至少部分表面是反应活性大的活性区域，对应Lo3位置，其中，所述活性区域外表面包括金属原子。
在本实施例中，对于包括突起的针尖，在真空条件下与气体分子的反应中，所述突起的至少部分表面的金属原子比所述衬底的其他表面部分具有相同或更大的反应活性，这样可以更加精准的控制发射点在突起的指定区域上形成，如在图5的突起上的阴影区域形成发射点。活性区域表面的金属原子的形成方式可以参考上一实施例中形成活性区域的方式， 在此不再详述。
本公开提供的电子源，至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，所述高场强结构的至少部分表面是反应活性大的活性区域，其中，所述活性区域外表面包括金属原子，该活性区域表面的金属原子凭借场强优势和活性优势在相同的环境中更容易与气体分子形成反应产物，以优先在活性区域生成发射点。
图6示意性示出了根据本公开实施例的发射点形成过程的示意图。
通过在强电场作用下的气体分子和表面原子的化学反应实现形成发射点Ma1，Ma1的形成在一定温度下进行。发射点的形成过程是基于对针尖表面的一个小区域内氢气吸附行为的深入研究后确定的制备方法。
在一个实施例中，当施加负偏压形成发射点时，可以包括如下操作：首先，给所述针尖施加负偏压，产生电流值为微安量级的发射电流，然后，维持预设时长或调节所述负偏压直至产生预定值的发射电流，接着，调节负偏压使得所述电子源的发射电流小于毫安量级，避免针尖形貌改变或烧毁。
在另一个实施例中，当施加正偏压形成发射点时，给所述针尖施加正偏压并维持预设时长，所述正偏压的值小于形成所述突起的场致蒸发偏压的值。
例如，可以提供一个钨单晶(111)的针尖，经过如上所述的方法在针尖上形成突起，如经过Flash处理(加热至1200K，持续3s，期间还可以辅以偏压等)，这样可以在针尖的表面中间位置形成一个纳米级的突起，其表面是清洁的，参考图6a所示，当对针尖加负压至-2KV时，形成了场发射模式(field electron emission mode)。为避免离子轰击的造成的影响，Ma1形成温度在～50K。在发射点形成的全程，发射电流(I E)一直控制在5nA以内，真空度在10 -7Pa。
如图6b至图6e所示，气体吸附首先导致发射能力下降，荧光屏组件103的显示界面上的发射图案逐渐变暗，发射电流逐渐降低，即现有的钨清洁表面的发射能力逐渐下降。
如图6f所示，随着时间推移，发射图案近乎完全消失，此时，传统的钨清洁表面发射能力几乎全部消失。
如图6g所示，随着继续给电子源施加偏压，本公开所述的发射点开始形成，此时的发射点和之前的发射物质的构成不同，以钨为例进行说明，之前的发射物质为钨单晶的钨原子，此时的发射点为针尖表面的钨原子与气体分子，如钨原子与氢气分子的反应产物，该反应产物固定在针尖表面。
如图6h至图6k所示，随着继续给电子源施加偏压或者持续等待，最终该发射点变得更亮。
如图61所示，最终，形成高发射能力的发射点，发射电流进一步电流增大，通过对比图6a和图61，可以清楚看到，发射点的发射能力明显提升，且发射点更加集中在中间突起位置。
在上述过程中，由于电流一直控制的很小，且荧光屏与针尖离得很远，且真空度很好，可排除离子轰击的影响。另外，加正高压可以形成相同的场发射特性的物质。而此时完全没有发射电流，说明，离子轰击导致的游离的原子级颗粒物没有参与发射点Ma1的形成过程。
在发射点Ma1的形成过程中，气体(如H 2)经过了吸附，在电场下离解，进一步与表面金属原子产生结合，形成某种H-W反应产物(compound)，属于Ma1的一种，这种compound似乎直接与表面结合，并不移动。如其它位置也可以形成类似物质，但是其并不发生移动，一直是位置稳定的发射点。
与发射能力相关的参数中，单个发射点的发射能力可以达到30uA以上，远远超过现有的CFE的单点发射能力(～10微安)，若是形成一个密集的发射区域，发射图连成一片，总电流可达100uA量级。若增大发射面积，可以实现mA的发射电流。
在不同的真空度下，具有不同的发射能力。一般来说，高真空时，发射电流大，低真空时，最大发射电流迅速衰减。形成的发射点的针尖(The tip terminated by emission site)具有场发射一致性，即发射电流的电压具有一致性，例如，发射电流为1微安时，电压为-1.2±0.1KV。
以下以一个完整的制造流程进行示例性说明。
(一)关于制造条件
发射点是在真空环境且处于一定温度范围中，在电场作用下促使针尖表面的金属原子与气体分子生成的反应产物。其中，电场可以为施加正偏压或负偏压形成的电场，例如，施加正偏压时，场强应为1～50V/nm；施加负偏压时，场强应为1～30V/nm。
具体地，制造设备可以包括真空腔、制冷头(该制冷头可以包括加热装置)、样品台、加热片、电源、气体引入装置和荧光屏组件，其中，真空腔的本底真空度≤10 -3Pa(一般应优于10 -6Pa)。制冷头cold head上有一个绝缘的样品台(sample holder)，可以实现在sample holder上设置一加热装置(如加热片、加热棒)，温度可以在10～500K之间调整。将预处理好的针尖(如钨单晶针尖，该钨单晶针尖可以是具有突起的针尖，突起的尺寸是nm或 亚nm级，也可以是具有较大反应活性的区域的针尖)放置在样品台上，对该针尖加电压，电压可以是正高压V P，也可以是负高压V N。电源可以为双路输出高压电源，输出范围±0～30kv。气体引入装置用于引入反应气体分子，如H 2，也可以是其它反应气体，例如含H元素气体，水，CH 4等，气体通入量可以动态调整，一般引入时真空度＜10 -4Pa(需要说明的是，也可以直接利用强室内残余气体分子，其主要成分为氢气)，具体地，所述气体分子包括含氢元素气体分子以及以下任意一种或多种：含氮元素气体分子、含碳元素气体分子或者含氧元素气体分子。此外，可以通过调节含氢元素气体分子的引入速率调节所述发射点的形成速率。荧光屏组件用于将粒子束图像转换成光图像，当信号很小时，可以采用荧光屏-多通道板组件将信号进行放大。当对针尖加电压时，可以引出粒子束，该施加的电压可以是正压、也可以是负压；当正压时，有成像气体时，输出正离子束；当负压时，输出电子束。由于发射点形成和工作温度较低，在工作时电子源结构不改变，施加电压值不发生变化，电压值稳定使电子枪的设计更简单。
(二)关于制造过程
1、首先形成高场强结构，形成高场强结构的过程可以包括如下操作。
在针尖表面形成场强较强的区域，例如突起，优选地，在针尖正中心形成突起。
其中，突起的材料可以和衬底相同，也可以是异质的。例如，突起的材料是导体，突起最表面的一层或者几层原子是金属原子，突起的尺寸是nm级或亚nm级，突起可以通过电化学刻蚀、场离子刻蚀、热处理、施加电场、纳米加工等方法或者几种方法的组合形成，或者如下方法：例如在单晶金属针尖上面镀一层金属原子，通过热处理重塑形成突起。
2、使得针尖处于合适的真空环境中，其中，真空环境中包含指定的元素，具体可以包括如下操作。
将针尖置于真空腔室后进行抽真空，然后，通入气体，可以是H 2、N 2、含H元素的气体，例如主要是H 2或含H元素气体，通过调节气体分子的数量，可以影响发射点的形成速度。此外，气体也可以是真空腔室中残余的气体，例如H 2、H 2O、CO、CO 2等。腔室的真空度应当小于10 -3Pa，较优地，真空度可以小于10 -6Pa。
3、在施加偏压之前可以调整针尖的温度。针尖温度应低于1000K；优选地，低温低于150K，高温位于500～800K范围；针尖温度高于1000K时，形成的发射点会被去除。如表1所示，为发射点的形成条件。
表1发射点形成条件表
Figure PCTCN2018124330-appb-000002
例如，针尖温度≤1000K时，压强≤10 -3Pa，或者，500K≤针尖温度≤800K时，压强≤10 -6Pa，或者，当针尖温度≤150K时，压强≤10 -6Pa。由于发射点形成和工作温度较低，电子源结构不改变，在工作时电子源结构不改变，施加电压值不发生变化。
4、给针尖施加偏压。在电场的作用下，气体分子和高场强结构(如突起)表面金属原子进行反应，形成根植于表面的发射点，施加的偏压可以是正偏压或者负偏压，或者两者组合。
其中，当施加正偏压时，施加的正偏压的电压应低于场致蒸发的电压，场强应为1～50V/nm；当施加负偏压时，施加的负偏压应低于烧毁电压，场强应为1～30V/nm，此外，施加负偏压时要及时调节电压，以免电流过大导致针尖形状改变或烧毁，一般地，应当控制针尖的电流小于mA量级。
在一个具体实施例中，以负偏压作用下形成发射点为例进行说明。首先，将预处理好的针尖(如具有突起且表面清洁的针尖)放置在真空环境中，优选地，真空度为1E -7Pa。对针尖的温度进行调节，针尖温度应低于1000K，针尖温度优选地为低于150K的低温或者为500～800K范围的高温，当针尖温度高于1000K时，形成的发射点会被去除。
然后，对针尖施加负偏压，在电场的作用下，气体分子或吸附在针表面的离子不断向针尖的特定区域移动，特定区域可以为高场强结构区域和/或具有较大反应活性区域。
接着，当负偏压加至一定值(如-3KV)，气体分子与针尖表面的金属原子(例如钨)反应形成发射点，产生微小发射电流，例如小于1μA，随着发射点持续形成，发射点数量逐渐增多，总发射电流逐渐增大，例如1μA～数十(tens of)μA。
然后，持续等待或调节电压，发射电流剧烈增大至数百(hundreds of)μA～1mA，要及时快速降低或切断负偏压，以免针尖烧毁，一般地，控制电流小于mA数量级，通过多次缓慢施加负高压，以获得预定的发射电流。
需要说明的是，上述施加负偏压过程中，如果针尖包括如图3B所示的突起结构(如对针尖施加正偏压进行场刻蚀得到的超级针结构，即针尖施加过正偏压)，当负偏压加至一定值(如-1.2KV)，气体分子与针尖表面的金属原子(例如钨)反应形成发射点，产生微小发射电流，例如小于1μA；可以提高电压使发射点持续形成，发射电流长至tens of μA (如30μA)；之后持续等待或提高电压，场发射点持续形成；场发射点数量逐渐增多，总发射电流逐渐增大。其中，突起结构是对针尖施加正偏压进行场刻蚀得到的超级针结构，当场刻蚀的电压一致时，可以使发射电流的电压具有一致性，例如场刻蚀电压为+8KV，形成了突起，那么稳定发射电流的电压为-1KV。
参考图6所示，W针尖(111)的突起的清洁表面形成发射点过程如下所示，针尖温度为～50K，真空度为10E -7Pa；对针尖施加负偏压，W针尖(111)突起清洁表面的场发射图案如图6a所示，维持测试，在电场的作用下，气体分子向突起位置移动；由于气体吸附，场发射图案不断变暗甚至完全消失，如图6a～6g所示。继续维持负偏压，在一定电场作用下，气体分子与突起表面金属原子进行反应，形成根植于表面的发射点。
在另一个具体实施例中，以正偏压作用下形成发射点为例进行说明。首先，将预处理好的针尖放置在真空环境中，优选地，真空度为1E -7Pa；针尖具有清洁表面，对针尖的温度进行调节，针尖温度应低于1000K，当针尖温度高于1000K时，形成的发射点会被去除。
然后，对针尖施加正偏压(例如+8KV)，维持一定时间(例如2分钟)；正偏压的值应小于场蒸发电压。在电场的作用下，气体分子不断向针尖特定区域移动，反应形成反应产物作为发射点，正偏压与负偏压的所起作用相同，都是为了形成一定的场强。其中，可以调节正偏压的值或者调节维持时间来调节发射点的形成数量。
图7示意性示出了根据本公开实施例的施加正偏压形成发射点的过程示意图。
参考图6所示，当施加正偏压时，图6a所示的清洁表面发射和图6a～6f所示的清洁表面发射图案变暗的过程可能观察不到，只能观察到图6g～61所示的发射点的形成过程。如图7所示，例如在如图3B所示的突起结构表面形成发射点的实施例中，施加正偏压后，直接形成发射点。使用时，对针尖施加负偏压，加至一定值时，例如-1.2KV，已经形成的场发射点会发射电流。
需要说明的是，场发射点形成过程中，由于电流一直控制的很小，且荧光屏与针尖离得很远，且真空度很好，可排除离子轰击的影响。另外，加正高压同样可以形成相同的场发射特性的物质，而此时完全没有发射电流，这就说明，离子轰击导致的游离原子级颗粒物没有参与发射点的形成。因此，在发射点形成过程中，气体分子(如H 2)经过了吸附，在电场下离解，进一步与表面金属原子(如钨原子)产生结合，形成某种H-W反应产物(compound)。该compound似乎直接与针尖表面结合，并不移动，例如，其它针尖的其它位置也可以形成类似物质，但是其并不发生移动，一直是位置稳定的发射点。一般来说，高真空时，电流大，低真空时，最大发射电流迅速衰减。
图8示意性示出了根据本公开实施例的发射点数量和发射图案均匀性的关系的示意图。
从图中可以看到，发射点的数量与发射图案均匀性存在对应关系，当发射点越多时，发射图案越均匀。可以通过增加发射点的数量来增加发射图案的均匀性。具体地，可以通过增加突起的尺寸来使得突起可以容纳更多的发射点，例如，突起具有相同的表面积时：发射点数量少，发射电流小，图案不均匀；发射点数量多，发射电流大，图案均匀。
本公开提供的电子源制造方法制造的电子源，形成的发射点具有高发射能力，具有发射点小、能散小和稳定的优点，其中，单个发射点在nm或亚nm级别，形成的发射点的针尖(The tip terminated by emission site)是场发射电子源，可以通过调节电压来引出和控制电流。例如，单个发射点的发射电流可以达到30uA以上，若是形成一个密集的发射区域，发射点连成一片，总电流可达100uA量级。若增大形成面积，可以实现mA级的电流。在不同的真空度下，具有不同的发射能力。
此外，在大电流下，单个发射点会在同一位置闪烁(重复消失再出现)，因此可通过增加发射点数量来增加电流的稳定性。刚反应形成的发射点表面清洁，未吸附气体，具有最大的发射能力，维持工作，由于气体会继续吸附在发射点上，发射能力会下降甚至几乎消失。这种特性可用于去除不需要的发射点，例如，周围的一些发射点，因此，所述方法还可以包括如下操作：在至少一个针尖上形成一个或多个固定的发射点之后，通过给所述电子源施加电场使得气体分子吸附在发射点上，以去除至少一个发射点。例如，通过给所述电子源施加电压以形成电场，在电场的作用下使得气体分子吸附在发射点上，以使得至少一个发射点不发射电流。
以上示例是以具有高场强结构的电子源为例进行说明，但是，上述发射点的形成过程同样适用于具有反应活性大的区域的电子源，在此不再赘述。
图9示意性示出了根据本公开实施例的调节发射点的数量的示意图。
如图9所示，可以通过调节突起的尺寸来调节发射点的数量，这是由于突起为纳米级，发射点也可以是纳米级，每个突起能容纳的发射点的数量有限，因此，小的突起上可以形成的发射点的数量会少一些。当增大针尖突起尺寸时，可以通过调节电压形成更多的发射点，从而增大发射电流。
图10示意性示出了根据本公开实施例的调节束流角的示意图。
如图10所示，其中，α和β分别表示束流角，h1和h2分别表示突起的高度。可以通过调整衬底的尺寸和/或突起的尺寸来调节束流角的大小。例如，突起尺寸相同时，衬底 尺寸越小，束流角α越大，相反的，突起尺寸相同时，衬底尺寸越大，束流角β越小。此外，当衬底尺寸相同时，突起的高度h1越高，束流角α1越大，相反的，突起尺寸相同时，突起的高度h2越低，束流角β1越小。
综述，可以通过增大衬底的尺寸和/或降低场蒸发突起的高度，可以减小束流角。
此外，还可以调节衬底的形状，来改变发射电流方向，例如，与针尖轴线不重合的衬底的发射电流的方向，和与针尖轴线重合的衬底的发射电流的方向不同。另外，控制针尖突起和衬底的结构(例如通过场蒸发或场刻蚀)，可以使发射电流的电压具有一致性(如经过场致刻蚀形成的突起，刻蚀电压为V1±0.5KV，那么稳定发射电流的电压为V2±0.1KV)。
图11示意性示出了根据本公开实施例的电子源使用过程的示意图。
如图11所示，当给电子源施加负偏压发射电流时，针尖表面的游离物和环境中的气体分子会逐渐吸附在针尖表面使得电子源发射能力下降。由于发射点固定在针尖表面，且发射点消失温度高于上述气体分子的脱吸附温度，因此，可以通过加热使得上述游离物或气体分子从针尖表面脱离，进而恢复电子源的发射能力。
本公开的另一个方面提供了一种电子枪，包括如上所述的方法制备的电子源，以及冷却装置、加热装置和气体引入装置。其中，所述电子源用于发射电子，所述冷却装置用于给所述电子源散热，所述电子源通过电绝缘热导体固定在所述冷却装置上，所述加热装置用于给所述电子源加热调节温度，所述气体引入装置用于引入包含氢元素的气体。由于该电子枪的电子源表面的发射点的形成温度和工作温度较低，在工作时电子源结构不改变，施加电压值不发生变化，电压值也更加稳定，使电子枪的设计更简单。
本领域技术人员可以理解，本公开的各个实施例和/或权利要求中记载的特征可以进行多种组合或/或结合，即使这样的组合或结合没有明确记载于本公开中。特别地，在不脱离本公开精神和教导的情况下，本公开的各个实施例和/或权利要求中记载的特征可以进行多种组合和/或结合。所有这些组合和/或结合均落入本公开的范围。
以上对本公开的实施例进行了描述。但是，这些实施例仅仅是为了说明的目的，而并非为了限制本公开的范围。尽管在以上分别描述了各实施例，但是这并不意味着各个实施例中的措施不能有利地结合使用。本公开的范围由所附权利要求及其等同物限定。不脱离本公开的范围，本领域技术人员可以做出多种替代和修改，这些替代和修改都应落在本公开的范围之内。

Claims (19)

  1. 一种电子源制造方法，包括：
    在至少一个针尖上形成一个或多个固定的发射点，所述发射点包括针尖表面的金属原子与气体分子形成的反应产物。
  2. 根据权利要求1所述的方法，其中，在电场下使所述金属原子与所述气体分子反应形成所述发射点。
  3. 根据权利要求1所述的方法，其中：
    至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，其中，至少一个所述高场强结构的外表面包括金属原子，并且/或者
    至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其他部位反应活性大的活性区域，其中，至少一个所述活性区域外表面包括金属原子，并且/或者
    至少一个针尖包括衬底和所述衬底上的一个或多个比所述衬底其它部位的场强高的高场强结构，所述高场强结构的至少部分表面是反应活性大的活性区域。
  4. 根据权利要求3所述的方法，其中，所述高场强结构包括突起。
  5. 根据权利要求4所述的方法，其中，所述突起的尺寸为亚纳米至100纳米。
  6. 根据权利要求4所述的方法，其中，所述突起通过以下任意一种或多种方法形成：热处理、施加电场、热-电场处理、刻蚀或者纳米加工。
  7. 根据权利要求4所述的方法，其中：
    对于包括突起的针尖，在真空条件下与气体分子的反应中，所述突起的至少部分表面的金属原子比所述衬底的其他表面部分具有相同或更大的反应活性；以及
    对于不包括突起的针尖，在真空条件下与气体分子的反应中，所述衬底的活性区域的表面的金属原子比所述衬底的其他表面部分具有更大的反应活性。
  8. 根据权利要求3所述的方法，还包括：
    通过调节所述针尖的衬底和/或高场强结构的尺寸和形状以调节电子束束流角的大小；并且/或者
    通过调节高场强结构和/或活性区域的尺寸调节发射点的数量；并且/或者
    通过调节衬底的结构和/或高场强结构的结构调节电子源发射电流的电压的大小或一致性；并且/或者
    通过调节针尖顶部的形状以调节发射电流方向。
  9. 根据权利要求2所述的方法，其中，所述气体分子包括含氢元素气体分子以及以下任意一种或多种：含氮元素气体分子、含碳元素气体分子或者含氧元素气体分子。
  10. 根据权利要求9所述的方法，其中：
    所述含氢元素气体分子由引入的含氢元素气体分子构成和/或由真空环境中残存的气体分子构成；以及
    通过调节含氢元素气体分子的引入速率调节所述发射点的形成速率。
  11. 根据权利要求9所述的方法，其中：
    所述含氢元素气体分子包括氢气分子；
    所述金属原子为钨原子；
    所述发射点为氢钨化合物。
  12. 根据权利要求2所述的方法，所述电场为通过施加偏压形成的；其中，所述施加偏压包括以下任意一种或多种：施加正偏压、施加负偏压或者施加正偏压和负偏压相结合。
  13. 根据权利要求12所述的方法，其中：
    对于施加正偏压，形成的场强的范围包括1～50V/nm；以及
    对于施加负偏压，形成的场强的范围包括1～30V/nm。
  14. 根据权利要求12所述的方法，其中：
    当施加负偏压形成发射点时，给所述针尖施加负偏压，产生电流值为微安量级的发射电流；
    维持预设时长或调节所述负偏压直至产生预定值的发射电流；
    调节负偏压使得所述电子源的发射电流小于毫安量级，避免针尖形貌改变或烧毁。
  15. 根据权利要求12所述的方法，其中，当施加正偏压形成发射点时，给所述针尖施加正偏压并维持预设时长，所述正偏压的值小于形成所述突起的场致蒸发偏压的值。
  16. 根据权利要求12所述的方法，其中，
    通过调节所述施加偏压的值或者调节预设时长的值来调节形成的发射点的数量。
  17. 根据权利要求2所述的方法，其中：
    针尖温度≤1000K时，压强≤10 -3Pa；或者
    500K≤针尖温度≤800K时，压强≤10 -6Pa；或者
    当针尖温度≤150K时，压强≤10 -6Pa。
  18. 根据权利要求2所述的方法，还包括：
    通过调节发射点的数量以调节发射点的均匀性；并且/或者
    通过调节发射点的数量以调节电流的大小；并且/或者
    通过增加发射点的数量来增加发射电流的稳定性。
  19. 根据权利要求1所述的方法，还包括：
    在至少一个针尖上形成一个或多个固定的发射点之后，通过施加电场使得气体分子吸附在发射点上，以去除至少一个发射点。
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KR102539959B1 (ko) 2023-06-05
EP3736847A1 (en) 2020-11-11
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