JP2016225358A - Cathode sorting method and electron beam drawing apparatus - Google Patents

Abstract

Provided is a method for selecting a cathode in which no abnormality occurs in the periphery of an electron emission surface. An acceleration voltage is applied between a measurement target cathode and an anode electrode while maintaining the temperature of the measurement target cathode at a preset temperature using a measurement target cathode whose electron emission surface is limited to a flat surface by a cover member. In step S110, the bias voltage applied to the Wehnelt electrode is adjusted to start the operation of the measurement target cathode in the temperature limited region, and the emission current value when the operation of the measurement target cathode is started for a predetermined period. Step S112 for controlling the bias voltage so as to be maintained, Step S114 for determining whether or not the amount of fluctuation of the bias voltage during a predetermined period is smaller than a preset threshold value, and using the measurement target cathode as a result of the determination. If the amount of fluctuation in the bias voltage is smaller than the threshold value, the measurement target cathode is selected as a usable cathode. Comprising the step S116 that, the. [Selection] Figure 7

Description

  The present invention relates to a cathode selection method and an electron beam drawing apparatus, and, for example, relates to a cathode selection method for a beam source used in an electron beam apparatus.

  In the electron beam apparatus, an electron gun serving as a beam source is used. There are various types of electron beam apparatuses such as an electron beam drawing apparatus and an electron microscope. For example, when it comes to electron beam drawing, it has an essentially excellent resolution and is used for the production of high-precision original picture patterns.

  In recent years, with the high integration of LSI, the circuit line width of a semiconductor device has been further miniaturized. As a method for forming an exposure mask (also referred to as a reticle) for forming a circuit pattern on these semiconductor devices, an electron beam (EB) drawing technique having excellent resolution is used.

  FIG. 15 is a conceptual diagram for explaining the operation of the variable shaping type electron beam drawing apparatus. The variable shaping type electron beam drawing apparatus operates as follows. In the first aperture 410, a rectangular opening 411 for forming the electron beam 330 is formed. Further, the second aperture 420 is formed with a variable shaping opening 421 for shaping the electron beam 330 having passed through the opening 411 of the first aperture 410 into a desired rectangular shape. The electron beam 330 irradiated from the charged particle source 430 and passed through the opening 411 of the first aperture 410 is deflected by the deflector, passes through a part of the variable shaping opening 421 of the second aperture 420, and passes through a predetermined range. The sample 340 mounted on a stage that continuously moves in one direction (for example, the X direction) is irradiated. That is, the drawing area of the sample 340 mounted on the stage in which the rectangular shape that can pass through both the opening 411 of the first aperture 410 and the variable shaping opening 421 of the second aperture 420 is continuously moved in the X direction. Drawn on. A method of creating an arbitrary shape by passing both the opening 411 of the first aperture 410 and the variable shaping opening 421 of the second aperture 420 is referred to as a variable shaping method (VSB method).

  In electron beam drawing, with the miniaturization of integrated circuits, the shot size is reduced and the number of shots is increased. As a result, the drawing time becomes longer. Therefore, it is desired to shorten the drawing time, in other words, to improve the throughput of the drawing apparatus. In order to improve the throughput of the drawing apparatus, it is necessary to increase the current density of the electron beam. In order to increase the current density, it is necessary to increase the brightness of the cathode of the electron gun serving as the beam source. In order to cope with higher luminance of the cathode, a cathode is used in which the inclined surface of the truncated cone is covered with a cover material and the electron emission surface is limited to a flat surface (for example, see Patent Document 1). When manufacturing such an emission surface limited type cathode, among the plurality of manufactured cathodes, there is a mixture of cathodes that cause a phenomenon that the current density of the shaped beam fluctuates greatly during use in the drawing apparatus. There was a problem such as. If such a cathode continues to be used as it is, the periphery of the electron emission surface will be corroded by chemical reaction, so some abnormality occurring in the periphery of the electron emission surface will cause fluctuations in the current density of the shaped beam. It seems to be the cause. When a cathode having such an abnormality is mounted on a drawing apparatus, the current density of the shaped beam fluctuates during use, and the dimensions of the drawn pattern deteriorate. Therefore, it is required to eliminate in advance the cathode in which such a problem occurs.

JP 2005-228741 A

  Accordingly, an object of the present invention is to provide a method for selecting a cathode that does not cause an abnormality in the periphery of the electron emission surface.

The cathode sorting method of one embodiment of the present invention includes:
Using a measurement target cathode that is attached with a cover member and whose electron emission surface is limited to a flat surface by the cover member, the temperature of the measurement target cathode is maintained at a preset temperature, and faces the measurement target cathode and the measurement target cathode. By adjusting the bias voltage applied to the Wehnelt electrode arranged between the cathode to be measured and the anode electrode with the acceleration voltage applied to the anode electrode, the operation of the cathode to be measured is controlled in the temperature limited region. Starting the process;
Controlling the bias voltage so as to maintain the value of the emission current flowing between the measurement target cathode and the anode electrode when the operation of the measurement target cathode is started for a predetermined period;
Determining whether the amount of variation in bias voltage during a predetermined period is smaller than a preset threshold;
As a result of the determination, when the variation amount of the bias voltage when the measurement target cathode is used is smaller than a threshold, the measurement target cathode is selected as a usable cathode; and
It is provided with.

  Further, it is preferable to further include a step of obtaining a relationship between the emission current and the bias voltage in the space charge limited region and the temperature limited region in a state where the temperature of the measurement target cathode is maintained at the above-described preset temperature. .

  In addition, it is preferable that the temperature of the cathode to be measured during a predetermined period is set to a temperature used for electron emission in an electron beam apparatus used after sorting.

  Moreover, it is preferable that carbon is used as the material of the cover member.

An electron beam drawing apparatus according to one embodiment of the present invention includes:
An electron gun equipped with a measurement target cathode selected as a cathode usable by the cathode selection method described above;
A drawing unit for drawing a pattern on a sample using an electron beam emitted from an electron gun;
It is provided with.

  According to one aspect of the present invention, it is possible to select a cathode that does not cause an abnormality in the periphery of the electron emission surface. Therefore, it is possible to eliminate a cathode in which an abnormality occurs in the peripheral portion of the electron emission surface before being mounted on a device to be used. As a result, it is possible to suppress fluctuations in current density due to abnormalities in the periphery of the electron emission surface.

3 is a cross-sectional view illustrating an example of a cathode in Embodiment 1. FIG. 2 is a conceptual diagram illustrating an apparatus configuration of an example of a cathode sorting measurement apparatus according to Embodiment 1. FIG. 6 is a diagram showing an example of a time chart of a change in current density of a shaped beam in the first embodiment. FIG. FIG. 3 is a conceptual diagram for explaining a temperature limited region and a space charge limited region in the first embodiment. FIG. 3 is a diagram illustrating an example of a relationship between an emission current and a bias voltage in the first embodiment. 6 is a diagram illustrating an example of measurement points in a relationship between an emission current and a bias voltage in the first embodiment. FIG. FIG. 3 is a flowchart showing main steps of the cathode selection method in the first embodiment. 6 is a diagram for explaining a method for obtaining a relationship between an emission current and a bias voltage in the first embodiment. FIG. FIG. 10 is a diagram for explaining a method for acquiring another example of the relationship between the emission current and the bias voltage in the first embodiment. FIG. 3 is a cross-sectional view showing an abnormal part of the cathode in the first embodiment. 3 is an electron micrograph showing an abnormal portion of the cathode in the first embodiment. FIG. 4 is a diagram showing another example of the cathode in the first embodiment. FIG. 3 is a conceptual diagram showing a configuration of a drawing apparatus equipped with a selected cathode in the first embodiment. FIG. 5 is a conceptual diagram showing a device configuration of a measuring device in a second embodiment. It is a conceptual diagram for demonstrating operation | movement of a variable shaping type | mold electron beam drawing apparatus.

Embodiment 1 FIG.
FIG. 1 is a cross-sectional view showing an example of the cathode in the first embodiment. In FIG. 1, a cathode 10 (measurement target cathode) is processed into a truncated cone shape in which, for example, a lower portion of a cylindrical LaB ₆ crystal 20 is tapered and a lower surface 11 is processed into a flat surface. For example, a carbon film 30 (cover member) is disposed (attached) on the entire side surface including at least the tapered lower portion. As will be described later, since the upper portion of the LaB ₆ crystal 20 is covered with a heater or the like, only the lower surface 11 formed in a plane is exposed when heated, and the carbon (carbon) film 30 exposes the exposure. The lower surface 11 can be limited to the electron emission surface.

It should be noted that the crystalline material of the cathode 10 is generally a single crystal and may be formed from any of several suitable types of crystalline materials that may or may not be sintered. Or may include such materials. Typical materials that may be used include single crystal lanthanum hexaboride (LaB ₆ ), single crystal cerium hexaboride (CeB ₆ ), single crystal hafnium carbide (HfC), sintered LaB ₆ , sintered Examples include, but are not limited to, CeB ₆ , sintered HfC, sintered tungsten-barium-oxygen-Al (W—Ba—Al—O), sintered scandate (Ba—Sc—W—O), and the like. . A “sintered” material is a material formed from particles that are combined by exposure to heat and / or pressure. As the material of the cathode cover, for example, a carbon material is preferably used as a material that is a conductor and has a work function larger than that of the crystal material of the cathode 10. Therefore, in the cathode 10 of Embodiment 1, the electron emission surface is limited to a plane (lower surface) orthogonal to the optical axis direction. Therefore, the uniformity of the current density can be maintained in the electron emission stage.

  When a plurality of such cathodes 10 are manufactured, a number of defective cathodes are mixed. In the defective cathode, an abnormality that the current density of the shaped beam fluctuates greatly occurs.

  If a defective cathode that causes an abnormality among the plurality of manufactured cathodes 10 can be eliminated, the phenomenon that the current density of the shaped beam fluctuates greatly during use in the drawing apparatus can be avoided. Therefore, in the first embodiment, a cathode that does not have such an abnormality is selected from a plurality of manufactured cathodes 10. In other words, defective cathodes that cause abnormalities are eliminated.

  FIG. 2 is a conceptual diagram showing an apparatus configuration of an example of the cathode sorting measurement apparatus according to the first embodiment. In FIG. 2, the measuring apparatus 300 includes a vacuum container 50 and an electron gun power supply 60. In the electron gun power source 60, an acceleration voltage power source 62, a Wehnelt power source 64, a heater power source 66, and a control circuit 65 are arranged. The cathode (−) side of the acceleration voltage power supply 62 is connected to the cathode 10 in the vacuum vessel 50. The anode (+) side of the acceleration voltage power supply 62 is connected to the anode electrode 54 in the vacuum vessel 50 and grounded. An ammeter 70 is connected in series between the anode (+) of the acceleration voltage power supply 62 and the anode electrode 54. The cathode (−) of the acceleration voltage power source 62 is also branched and connected to the anode (+) of the Wehnelt power source 64 (bias voltage power source). The cathode (−) of the Wehnelt power source 64 is connected to the cathode 10 and the anode. It is connected to a Wehnelt electrode 56 disposed between the electrodes 54. In the vacuum vessel 50, the heater 59 covers a side surface covered with a carbon cover different from the electron emission surface of the cathode 10. The heater power supply 66 is connected to the heater 59. The Wehnelt electrode 56 is formed with an opening through which electrons emitted from the electron emission surface of the cathode 10 pass to the anode electrode 54 side. In a state where a negative Wehnelt voltage (bias voltage) is applied from the Wehnelt power source 64 to the Wehnelt electrode 56, a constant negative acceleration voltage is applied to the cathode 10 from the acceleration voltage power source 62. When heated to a temperature, electrons (electron group) are emitted from the cathode 10, and the emitted electrons (electron group) are accelerated by an acceleration voltage to become an electron beam 40 and travel toward the anode electrode 54. Here, the Wehnelt power source 64 is set so that the total emission current I (emission current) measured by the ammeter 70 maintains a constant value for a predetermined period in a state where the acceleration voltage and the temperature are set to a constant value. The control circuit 65 measures the bias voltage variably controlled by the control circuit 65.

  As a cause of the phenomenon that the current density of the shaped beam fluctuates greatly while the cathode 10 is used in a drawing apparatus, the work function in the peripheral part of the electron emission surface is increased compared to the central part. . It is presumed that the increase in work function is affected by a chemical reaction occurring in the periphery of the electron emission surface. For example, a chemical reaction between the crystal 20 of the cathode 10 and the carbon film 30, or a chemical reaction between the rest of a polymer material such as a resist used when the carbon film 30 is processed and the crystal 20 is assumed. In the drawing apparatus, the bias voltage is controlled so as to keep the emission current constant under a constant temperature condition. However, as the work function increases, the emission current varies. Therefore, in order to keep the emission current constant under a constant temperature condition, the bias voltage varies according to the variation of the emission current.

  FIG. 3 is a diagram showing an example of a time chart of a change in the current density of the shaped beam in the first embodiment. When the cathode 10 is mounted on an electron gun of a drawing apparatus and an electron beam is emitted, the current density of the shaped beam is kept uniform as shown in FIG. 3 when the cathode 10 is initially heated. However, when time elapses, for example, about several tens of minutes (for example, 30 minutes) elapses and time t1 is reached, the current density of the shaped beam changes greatly. After reaching the maximum at time t2, it gradually decreases and returns to the original state at time t3. After the current density of the shaped beam changes greatly and becomes maximum, for example, it returns to the original uniform current density in about one hour. On the other hand, as shown in FIG. 3, the bias voltage greatly decreases at time t1, reaches a minimum at time t2, gradually increases, and returns to the original state at time t3. Also, the emission current is kept constant. Such a phenomenon is that the work function of the cathode 10 increased from time t1 to time t2 when the current density of the shaped beam changes greatly, and thus the emission current should decrease accordingly. However, the bias voltage tries to keep the emission current constant. As a result of the control, the emission current is kept constant as shown in FIG.

  Therefore, if such a defective cathode whose bias voltage fluctuates can be eliminated, a phenomenon that the current density of the shaped beam fluctuates greatly can be avoided. However, in the drawing apparatus, when the pattern is actually drawn on the sample, the cathode 10 is operated in a state where the operating point (use operation setting) of the cathode 10 is controlled to be located in the space charge limiting region.

  FIG. 4 is a conceptual diagram for explaining the temperature limited region and the space charge limited region in the first embodiment. In the temperature limited region, as shown in FIG. 4A, all the electrons emitted from the cathode 52 travel toward the anode electrode 54. In such a state, the number of electrons emitted (corresponding to the emission current) varies greatly with changes in the work function and temperature of the cathode. In other words, the Richardson Dashman equation holds. In the Richardson Dashman equation, the number of electrons emitted (corresponding to the emission current) increases as the temperature increases, and decreases as the work function increases. On the other hand, in the space charge limited region, an electron cloud called space charge 82 is formed on the front surface of the cathode 52 as shown in FIG. The space charge 82 has a negative feedback effect on the electron emission phenomenon from the cathode 52. In such a state, the number of electrons emitted (corresponding to the emission current) hardly depends on the work function or temperature of the cathode. Whether the state is the temperature limit region or the space charge limit region is determined by the relationship (combination) of the cathode temperature, the bias voltage, and the emission current. For example, in the temperature limited region, in order to maintain the emission current at a predetermined value, when the cathode temperature is increased, the bias voltage needs to be increased (in the negative direction) accordingly. However, when the cathode temperature increases and exceeds the limit value, the bias voltage becomes almost constant thereafter. In other words, the emission current becomes independent of temperature. Such a state is a space charge limited region.

FIG. 5 is a diagram showing an example of the relationship between the emission current and the bias voltage in the first embodiment. In FIG. 5, the vertical axis represents the emission current, and the horizontal axis represents the bias voltage. In a state where the cathode temperature is kept constant, as shown in a graph 501 in FIG. 5, in the temperature limited region, the emission current gradually decreases as the bias voltage increases (in the negative direction). When the bias voltage increases (in the negative direction) and exceeds the limit value, the emission current decreases greatly as the bias voltage increases (in the negative direction) thereafter. Such a state is a space charge limited region. In the space charge limited region, the emission current stops flowing when the bias voltage is further increased. Here, since the emission current decreases as the work function of the cathode 10 increases, the graph 501 changes like a graph 503. As described above, in the drawing apparatus, when a pattern is actually drawn on a sample, the cathode is operated in a state in which the operating point of the cathode is controlled to be located in the space charge limiting region. In the example of FIG. 4, for example, the operating point 502 is set in the space charge limited region. When the work function of the cathode 10 increases in this state, the bias voltage is changed to maintain the emission current value at the operating point 502. As a result, the operating point 502 shifts to the operating point 504. As shown in FIG. 5, in the space charge limited region, the fluctuation of the bias voltage is very small as the work function of the cathode 10 increases. Specifically, for example, the amount of change in the bias voltage with respect to the bias voltage is about 1 × 10 ⁻⁵ . Therefore, in order to detect a change in bias voltage with respect to an increase in work function, it is necessary to reduce the control resolution of the Wehnelt power supply 64. This makes the circuit expensive and is not realistic.

  FIG. 6 is a diagram illustrating an example of measurement points in the relationship between the emission current and the bias voltage in the first embodiment. As described above, since the emission current decreases as the work function of the cathode 10 increases, the graph 501 changes like the graph 503. However, it is difficult to detect fluctuations in the bias voltage even when the operating point 502 is shifted to the operating point 504 in the space charge limited region. Therefore, in the first embodiment, a change in the bias voltage is detected not in the space charge limited region but in the temperature limited region. In the example of FIG. 6, for example, the operating point 701 is set in the temperature limited region. When the work function of the cathode 10 increases in such a state, the bias voltage is changed in order to maintain the emission current value at the operating point 701. As a result, the operating point 701 is shifted to the operating point 702. As shown in FIG. 6, in the temperature limited region, the fluctuation of the bias voltage is very large as the work function of the cathode 10 increases. This is based on the fact that the correlation between the emission current and the bias voltage is different between the temperature limited region and the space charge limited region. In the space charge limited region, the change in the emission current is large with respect to the change in the bias voltage. In other words, the slope of the graph 501 is steep. On the other hand, in the temperature limited region, the change in the emission current is small with respect to the change in the bias voltage. In other words, the slope of the graph 501 is small. Therefore, in the first embodiment, the cathode 10 is intentionally operated in the temperature limited region to detect a defective cathode.

  FIG. 7 is a flowchart showing the main steps of the cathode selection method in the first embodiment. In FIG. 7, the cathode selection method in the first embodiment includes a cathode arrangement step (S104), a cathode heating step (S106), a correlation acquisition step (S108), a cathode operating point setting step (S110), a bias A series of steps of a voltage measurement step (S112), a determination step (S114), a selection step (S116), and a determination step (S118) are performed.

First, the cathode to be selected is manufactured. As shown in FIG. 1, the manufactured cathode 10 is formed by the carbon film 30 in a shape in which the electron emission surface (lower surface 11) is flat and the emission area is limited. In other words, an emission area limited type cathode having a flat electron emission surface (lower surface 11) is manufactured. The cathode is manufactured by, for example, a mass of LaB ₆ crystals by a zone melting method or the like. Then, such a lump is processed to produce a plurality of cathodes 10. Here, the manufactured cathode 10 may be formed of the same crystal or may be formed of different crystals.

  As the cathode arrangement step (S104), one of the plurality of cathodes 10 is arranged in the vacuum container 50 of the measuring apparatus 300 shown in FIG. In the vacuum vessel 50, the upper side surface covered with the carbon film 30 (carbon cover) different from the electron emission surface of the cathode 10 is held so as to be covered with the heater 59.

  In the cathode heating step (S <b> 106), a current is passed through the heater 59 by the heater power supply 66, and the cathode 10 is heated by the heater 59. At that time, the temperature of the cathode 10 to be measured is set to a temperature used for electron emission in a drawing apparatus (an example of an electron beam apparatus) used after selection. For example, it is preferable to set to 1700-1900K.

  In the correlation acquisition step (S108), the relationship between the emission current and the bias voltage in the space charge limited region and the temperature limited region is acquired while maintaining the temperature of the measurement target cathode 10 at the preset temperature. Specifically, the temperature of the measurement target cathode 10 is maintained at a preset temperature, and an acceleration voltage is applied between the measurement target cathode 10 and the anode electrode 54 facing the measurement target cathode 10. Then, a sufficiently large bias voltage is applied to the Wehnelt electrode 56 on the negative side with respect to the cathode 10 potential. When the bias voltage is sufficiently large on the negative side with respect to the cathode 10 potential, no emission current flows. When the bias voltage is gradually lowered to the positive side, an emission current starts to flow.

  FIG. 8 is a diagram for explaining a method for obtaining the relationship between the emission current and the bias voltage in the first embodiment. In FIG. 8, the vertical axis represents the emission current, and the horizontal axis represents the bias voltage. As shown in FIG. 8, when the bias voltage is gradually lowered to the positive side from the case where the bias voltage is sufficiently large on the negative side with respect to the cathode 10 potential, the emission current starts to flow. As the bias voltage is lowered to the positive side, the emission current greatly increases. When the bias voltage is lowered to the positive side to a certain limit value, the rate of increase in the emission current is reduced. As the bias voltage is further lowered to the positive side, the emission current gradually increases. The emission current may be measured by an ammeter 70, and the bias voltage may be a desired voltage applied by the Wehnelt power source 64 controlled by the control circuit 65. The measurement result is stored as data associated with the bias voltage in a storage device (not shown) in the control circuit 65. The control circuit 65 may plot the measurement data by a plot circuit (not shown) and output the data to the outside. Thereby, the graph 801 showing the relationship between the emission current and the bias voltage can be acquired. An intersection 804 of a straight line 803 that approximates a measurement point in a region where the emission current flows and the emission current greatly increases, and a straight line 802 that approximates a measurement point in a region where the increase rate of the emission current is small is a space charge. It can be regarded as a branch point between the restriction region and the temperature restriction region. A region where the emission current greatly increases is the space charge limited region, and a region where the increase rate of the emission current is small is the temperature limited region.

  In the cathode operating point setting step (S110), the temperature of the measurement target cathode 10 is maintained at a preset temperature, and an acceleration voltage is applied between the measurement target cathode 10 and the anode electrode 54 and applied to the Wehnelt electrode 56. By adjusting the bias voltage to be operated, the operation of the measurement target cathode 10 is started in the temperature limited region. For example, the bias voltage V2 at the operating point in the temperature limited region is preferably set to nV1, which is n times the bias voltage V1 at the branch point (emission current I1) described above. The coefficient n is preferably about 0.5 <n <0.9. In the vicinity of the intersection 804 in FIG. 8, there is a possibility of being affected by both the space charge limited region and the temperature limited region. By setting n <0.9, the cathode 10 can be reliably operated within the temperature limited region. Further, by setting 0.5 <n, the minimum value of the bias voltage when the bias voltage fluctuates can be reliably measured.

  As the bias voltage measurement step (S112), the Wenelt value is maintained so as to maintain the value of the emission current Ie flowing between the measurement target cathode 10 and the anode electrode 54 when the operation of the measurement target cathode 10 is started for a predetermined period. The power source 64 controls the bias voltage. During such a period, the value of the emission current Ie measured by the ammeter 70 is fed back to the Wehnelt power supply 64, and the Wehnelt power supply 64 controls the bias voltage so as to maintain the value of the emission current. Information on the bias voltage value to be applied is output to the control circuit 65. In the control circuit 65, the bias voltage value during this period is stored in the storage device. In other words, the variation of the bias voltage during such a period is stored. As the predetermined period, for example, about 1 to 2 hours is preferable. However, it is not limited to this and may be longer.

  As a determination step (S114), a determination unit (not shown) in the control circuit 65 determines whether the variation amount ΔVb of the bias voltage during a predetermined period is smaller than a preset threshold value Vth. The determination result is output to the outside.

  As a selection step (S116), the selection unit (not shown) in the control circuit 65 determines the measurement target cathode 10 when the bias voltage variation ΔVb when the measurement target cathode 10 is used is smaller than the threshold value Vth. The cathode is selected as a usable (OK) cathode in the drawing apparatus. Conversely, when the bias voltage variation ΔVb is not smaller than the threshold value Vth, the cathode 10 to be measured is selected as an unusable (NG) cathode in the drawing apparatus.

  As a determination step (S118), a determination unit (not shown) in the control circuit 65 determines whether all of the plurality of produced cathodes have been selected. If there is a cathode that has not yet been selected, the process returns to the cathode arrangement step (S104), from the cathode arrangement step (S104) to the determination step (S118) until all of the plurality of prepared cathodes are selected. Repeat these steps.

  FIG. 9 is a diagram for explaining a method for obtaining another example of the relationship between the emission current and the bias voltage in the first embodiment. In the correlation acquisition step (S108), solid differences occur for a plurality of fabricated cathodes, so that the bias voltage V1 and the emission current I1 at the branch point vary. Therefore, as shown in FIG. 9, the emission current on the vertical axis is defined by the emission current ratio Ie / I1 which is a relative value. Similarly, the bias voltage on the horizontal axis is defined by a bias voltage ratio Vb / V1 which is a relative value. As a result, the bias voltage V2 that is the operating point in the temperature limited region in the cathode operating point setting step (S110) can be set at a certain distance from the branch point.

  Alternatively, a plurality of cathodes made from rods of the same material often have generally similar characteristics. Therefore, the correlation acquisition process (S108) for the remaining cathodes may be omitted on the assumption that the correlation is acquired for one cathode and the remaining is approximate.

  FIG. 10 is a cross-sectional view showing an abnormal portion of the cathode in the first embodiment. If the defective cathode is continuously used in the drawing apparatus, a groove is formed around the electron emission surface of the cathode as shown in FIG.

FIG. 11 is an electron micrograph showing an abnormal portion of the cathode in the first embodiment. In FIG. 11, the electron emission surface of the LaB ₆ crystal 20 indicated by LaB ₆ is shown. As shown in FIG. 11, it can be seen that the outer peripheral portion of the electron emission surface covered with the carbon film 30 is corroded.

  Before the cathode 10 shown in FIGS. 10 and 11 is formed, in the first embodiment, the cathode that can cause the abnormality shown in FIGS. 10 and 11 can be excluded in advance.

  FIG. 12 is a diagram illustrating another example of the cathode according to the first embodiment. In FIG. 1, the outer peripheral portion covering the cathode 10, the conical side surface and the cylindrical side surface, which is a combination of a cylindrical upper portion and a conical top portion cut horizontally and a truncated cone-shaped lower portion having a flat bottom surface. Although the cylindrical cathode cover (carbon film 30) is shown, the present invention is not limited to this. FIG. 12A shows a case where the cylindrical cathode crystal 20a and the curved surface on the side surface of the cylinder are covered with a cathode cover (carbon film 30a). Further, the lower surface (plane) of the cylindrical crystal 20a becomes the electron emission surface S. In FIG. 12B, the shape of the crystal 20b is the same as that in FIG. The shape which became conical like the side is shown. In FIG. 12 (c), two-stage cylindrical crystals 20b having different diameters, in which a cylindrical lower member having a small diameter is connected to a cylindrical upper member having a large diameter, are formed on the side surfaces of the two cylinders. The case where the curved surface is covered with the carbon film 30b is shown. In addition, the lower surface (plane) of the cylinder with a small diameter of the crystal 20b becomes the electron emission surface S. In FIG. 12D, the shape of the crystal 20d is the same as that of FIG. 1, but in the carbon film 30d, the crystal 20d and the carbon film 30d are formed on the slope portion that is the conical side surface of the carbon film 30 shown in FIG. The shape which formed the gap | interval G between these is shown. In such a configuration, electrons are also emitted from the conical side surface of the crystal 20d, but the ratio of the area of the electron emission surface S of the lower surface (plane) is larger than the area of the gap G on the lower surface (plane). If it is sufficiently large, the influence on the current density distribution can be ignored. About this ratio, what is necessary is just to adjust suitably.

  FIG. 13 is a conceptual diagram showing a configuration of a drawing apparatus equipped with a selected cathode in the first embodiment. Here, an electron beam drawing apparatus is shown as an example of an electron beam apparatus on which the selected cathode is mounted. In FIG. 13, the drawing apparatus 100 includes a drawing unit 150 and a control circuit 160. The drawing apparatus 100 is an example of an electron beam drawing apparatus. In particular, it is an example of a variable shaping type drawing apparatus. The drawing unit 150 includes an electron column 102 and a drawing chamber 103. In the electron column 102, there are an electron gun 201, an illumination lens 202, a first aperture 203, a projection lens 204, a deflector 205, a second aperture 206, an objective lens 207, a main deflector 208, and a sub deflector 209. Has been placed. An XY stage 105 is disposed in the drawing chamber 103. On the XY stage 105, a sample 101 such as a mask to be drawn at the time of drawing is arranged. The sample 101 includes an exposure mask for manufacturing a semiconductor device. Further, the sample 101 includes mask blanks to which a resist is applied and nothing is drawn yet. The cathode 10 selected as the usable cathode in the first embodiment is mounted (mounted) on the electron gun 201. Then, the drawing unit 150 draws a pattern on the sample 101 using the electron beam 200 emitted from the electron gun 201. Specifically, it operates as follows.

  The electron beam 200 emitted from the electron gun 201 (emission unit) illuminates the entire first aperture 203 having a rectangular hole by the illumination lens 202. Here, the electron beam 200 is first shaped into a rectangle. Then, the electron beam 200 of the first aperture image that has passed through the first aperture 203 is projected onto the second aperture 206 by the projection lens 204. The deflector 205 controls the deflection of the first aperture image on the second aperture 206, and can change (variably shape) the beam shape and dimensions. The electron beam 200 of the second aperture image that has passed through the second aperture 206 is focused by the objective lens 207, deflected by the main deflector 208 and the sub deflector 209, and continuously moved. The desired position of the sample 101 arranged in the above is irradiated. FIG. 1 shows a case in which multi-stage deflection of main and sub two stages is used for position deflection. In such a case, the electron beam 200 of the corresponding shot is deflected while following the stage movement to the reference position of the sub-field (SF) where the stripe region is further virtually divided by the main deflector 208. What is necessary is just to deflect the beam of the shot concerning each irradiation position.

  Since the cathode 10 that does not cause the selected abnormality is mounted, the drawing process can be performed at a desired current density.

  As described above, according to the first embodiment, it is possible to select a cathode that does not cause an abnormality in the periphery of the electron emission surface. Therefore, it is possible to eliminate a cathode in which an abnormality occurs in the peripheral portion of the electron emission surface before being mounted on a device to be used. As a result, it is possible to suppress fluctuations in current density due to abnormalities in the periphery of the electron emission surface.

Embodiment 2. FIG.
In the first embodiment, the configuration is such that only one cathode 10 can be arranged in the measuring apparatus 300, but this is not a limitation. In the second embodiment, an example in which a plurality of cathodes are simultaneously arranged will be described. The contents other than those described in particular are the same as those in the first embodiment.

  FIG. 14 is a conceptual diagram showing a device configuration of the measuring device according to the second embodiment. In FIG. 14, the measuring apparatus 300 according to the second embodiment simultaneously arranges a plurality of cathodes 10 in a vacuum vessel 50. The Wehnelt electrodes 56 (56a to 56c) are arranged for each cathode 10 (10a to 10c). Further, the anode electrode 54 may be common. The electron gun power supply 60 (60a to 60c) may be arranged for each cathode 10 (10a to 10c). An acceleration voltage power source (not shown) in the electron gun power source 60 (60a to 60c) and the cathode 10 are connected in parallel to the common anode electrode 54. An accelerating voltage power source (not shown) in the electron gun power source 60, the cathode 10, the anode electrode 54, and the current between the series circuits connected to the accelerating voltage power source are measured by the respective ammeters 70. The emission current I (emission current) can be measured simultaneously. Further, the fluctuation of the bias voltage during a predetermined period may be recorded by a control circuit (not shown) in each electron gun power supply 60. And what is necessary is just to batch-process each process shown in FIG. 7 with the number of cathodes which can be mounted in the measuring apparatus 300 of FIG.

The embodiments have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. The electron beam apparatus on which the selected cathode is mounted is not limited to the drawing apparatus, and can be applied to other electron beam apparatuses such as an electron microscope. The drawing apparatus is not limited to the variable shaping type drawing apparatus using a single beam, and may be suitably applied to, for example, a raster beam drawing apparatus and a multi-beam drawing apparatus. Further, as the cathode material has been described as an example LaB ₆ crystal, a tungsten (W), such as cerium hexaboride (CeB _6), it can be applied to other thermionic emission material. Further, although a carbon film is used to limit the electron emission surface of the cathode, it is not limited to carbon. In addition, any material such as rhenium (Re) having a higher work function than the electron emission material may be used.

  In addition, although descriptions are omitted for parts and the like that are not directly required for the description of the present invention, such as a device configuration and a control method, a required device configuration and a control method can be appropriately selected and used. For example, although the description of the control unit configuration for controlling the drawing apparatus 100 is omitted, it goes without saying that the required control unit configuration is appropriately selected and used.

  In addition, all cathode selection methods, cathode selection measuring devices, electron beam drawing apparatuses, and methods that include elements of the present invention and can be appropriately modified by those skilled in the art are included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Cathode 11 Lower surface 20 Crystal 30 Carbon film 50 Vacuum vessel 54 Anode electrode 56 Wehnelt electrode 59 Heater 60 Electron gun power supply 62 Accelerating voltage power supply 64 Wehnelt power supply 65 Control circuit 66 Heater power supply 70 Ammeter 100 Drawing apparatus 101,340 Sample 102 Electron column 103 Drawing chamber 105 XY stage 150 Drawing unit 160 Control circuit 200 Electron beam 201 Electron gun 202 Illumination lenses 203 and 410 First aperture 204 Projection lens 205 Deflectors 206 and 420 Second aperture 207 Objective lens 208 Main deflection 209 Sub deflector 300 Measuring device 330 Electron beam 411 Aperture 421 Variable shaping aperture 430 Charged particle source

Claims (5)

Using a measurement target cathode having a cover member attached and having an electron emission surface limited to a flat surface by the cover member, the temperature of the measurement target cathode is maintained at a preset temperature, and the measurement target cathode and the measurement target are maintained. By adjusting the bias voltage applied to the Wehnelt electrode arranged between the cathode to be measured and the anode electrode in the state where the acceleration voltage is applied between the anode electrode facing the cathode and the anode electrode facing the cathode, Starting the operation of the cathode to be measured;
Controlling the bias voltage so as to maintain a value of an emission current flowing between the measurement target cathode and the anode electrode when the operation of the measurement target cathode is started for a predetermined period;
Determining whether the amount of fluctuation of the bias voltage during the predetermined period is smaller than a preset threshold;
As a result of the determination, when the variation amount of the bias voltage when the measurement target cathode is used is smaller than the threshold, the measurement target cathode is selected as a usable cathode; and
A cathode sorting method characterized by comprising:   The method further comprises the step of obtaining a relationship between the emission current and the bias voltage in the space charge limited region and the temperature limited region in a state where the temperature of the cathode to be measured is maintained at the preset temperature. The cathode selection method according to claim 1.   The cathode selection method according to claim 1 or 2, wherein the temperature of the measurement target cathode during the predetermined period is set to a temperature used for electron emission in an electron beam apparatus used after the selection.   The cathode selection method according to claim 1, wherein carbon is used as a material of the cover member. An electron gun equipped with the measurement target cathode selected as a cathode usable by the cathode selection method according to claim 1,
A drawing unit for drawing a pattern on a sample using an electron beam emitted from the electron gun;
An electron beam drawing apparatus comprising: