Electron beam adjustment method, electron beam apparatus, and program

Abstract

To provide an adjustment method of an electron beam capable of searching an operation point of a thermal electron gun in a route in which the electron beam emitted from the thermal electron gun does not enter a deep part of a temperature restriction region.SOLUTION: Setting a temperature of a cathode in a thermal electron gun that emits an electron beam from the cathode toward an anode to a predetermined value, changing a bias voltage applied to a Wehnelt electrode while maintaining the temperature of the cathode at the predetermined value, measuring an emission current when the bias voltage is changed while maintaining the temperature of the cathode at the predetermined value, and calculating, as a determination parameter, a value obtained by dividing a change rate of the emission current when the bias voltage is changed by a change amount of the bias voltage, the step of changing the bias voltage, the step of measuring the emission current, and the step of calculating the determination parameter are repeated until the determination parameter reaches the threshold value.SELECTED DRAWING: Figure 10

Description

[Technical Field]

[0001] One aspect of the present invention relates to an electron beam adjustment method, an electron beam apparatus, and a program, and relates to a technique for adjusting the operating conditions of a cathode of a thermionic electron gun that emits an electron beam. [Background technology]

[0002] Lithography technology, which is responsible for the advancement of miniaturization of semiconductor devices, is the only extremely important process in semiconductor manufacturing that generates patterns. In recent years, with the increasing integration density of LSIs, the circuit line width required for semiconductor devices has been getting finer year by year. Here, electron beam (EB) lithography technology has inherently excellent resolution, and mask patterns are written onto mask blanks using an electron beam.

[0003] For example, there is a lithography system that uses multiple beams. Compared to lithography using a single electron beam, using multiple beams allows for the irradiation of many beams at once, thereby significantly improving throughput. In such a lithography system, for example, an electron beam emitted from a thermal electron gun is passed through a mask with multiple holes to form multiple beams, each of which is blanked and each beam that is not blocked is reduced in size by an optical system, the mask image is reduced, and the beam is deflected by a deflector to be irradiated at the desired position on the sample.

[0004] In a thermionic gun that emits an electron beam, the operating point of the thermionic gun is often set near the boundary between the space charge limited region and the temperature limited region, but not within the temperature limited region, in order to obtain a desired emission current at the lowest possible cathode temperature. Conventionally, methods have been proposed in which the relationship between the emission current and the bias voltage is measured for each cathode temperature until the bias saturation point is reached, and the operating point is determined from the characteristics. Another method involves measuring the bias voltage required to maintain a constant emission current while changing the cathode temperature, and searching for a position where the change in bias voltage is sufficiently small relative to the change in temperature (see, for example, Patent Document 1).

[0005] However, when adjusting the electron beam using conventional methods, it is necessary to measure data over a wide range, even deep within the temperature-limited region, in the process of obtaining such an operating point. Emitting the electron beam in the temperature-limited region creates a problem in that the beam current density distribution has locally high intensity areas, which can damage the aperture substrate and other components that the electron beam impinges on. Therefore, it is necessary to search for the operating point along a path that does not penetrate deep within the temperature-limited region. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-228501 Summary of the Invention [Problem to be solved by the invention]

[0007] One aspect of the present invention provides a method and apparatus that can search for the operating point of a thermionic electron gun along a path that prevents the electron beam emitted from the thermionic electron gun from penetrating deep into a temperature-limited region. [Means for solving the problem]

[0008] A method for adjusting an electron beam according to one aspect of the present invention includes: a step of setting the temperature of a cathode in a thermionic electron gun to a predetermined value, the thermionic electron gun having a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, the thermionic electron gun emitting an electron beam from the cathode toward the anode; Varying the bias voltage applied to the Wehnelt electrode while maintaining the temperature of the cathode at a predetermined value; a step of measuring an emission current when the bias voltage is changed while the cathode temperature is maintained at a predetermined value; a step of calculating a value obtained by dividing a rate of change in emission current when a bias voltage is changed by an amount of change in the bias voltage as a judgment parameter; Equipped with The method is characterized in that, while maintaining the cathode temperature at a predetermined value, the steps of changing the bias voltage, measuring the emission current, and calculating the judgment parameter are repeated until the judgment parameter reaches a threshold value.

[0009] Also, a step of comparing the decision parameter with a threshold value; When the determination parameter reaches the threshold value, the bias voltage is decreased to the negative side by a predetermined amount; It is preferable that the device further comprises:

[0010] It is also preferable that the step of changing the bias voltage, the step of measuring the emission current, and the step of calculating the decision parameter are repeated so that the decision parameter approaches the threshold value from a state in which the decision parameter is greater than the threshold value.

[0011] It is also preferable that each step is performed at predetermined intervals.

[0012] An electron beam apparatus according to one aspect of the present invention comprises: a thermionic electron gun having a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, and emitting an electron beam from the cathode toward the anode; a temperature setting unit that sets the temperature of the cathode to a predetermined value; a bias voltage control unit that changes a bias voltage applied to the Wehnelt electrode while maintaining the temperature of the cathode at a predetermined value; an emission current measuring unit that measures the emission current when the bias voltage is changed while the cathode temperature is maintained at a predetermined value; a parameter calculation unit that calculates a value obtained by dividing a rate of change in emission current when a bias voltage is changed by an amount of change in the bias voltage as a judgment parameter; an irradiation mechanism for irradiating a sample with an electron beam emitted from a thermal electron gun; Equipped with While maintaining the temperature of the cathode at a predetermined value, repeating the operation of changing the bias voltage, the operation of measuring the emission current, and the operation of calculating the judgment parameter until the judgment parameter reaches a threshold value. It is characterized by:

[0013] A program according to one aspect of the present invention comprises: a process of setting the temperature of a cathode in a thermionic electron gun, which has a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, and which emits an electron beam from the cathode toward the anode, to a predetermined value; A process of measuring an emission current when a bias voltage applied to the Wehnelt electrode is changed while the temperature of the cathode is maintained at a predetermined value; storing the measured emission current in a storage device; A process of reading out the emission current from the storage device, and calculating a value obtained by dividing the rate of change of the emission current when the bias voltage is changed by the amount of change of the bias voltage as a judgment parameter; a process of repeating a process of changing the bias voltage, a process of measuring the emission current, and a process of calculating the judgment parameter until the judgment parameter reaches a threshold value while maintaining the cathode temperature at a predetermined value; to be executed by the computer. [Effects of the Invention]

[0014] According to one aspect of the present invention, the operating point of the thermionic electron gun can be searched for along a path that prevents the electron beam emitted from the thermionic electron gun from penetrating deep into the temperature-limited region. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a conceptual diagram showing a configuration of a drawing device according to a first embodiment. [Figure 2]FIG. 2 is a conceptual diagram showing the configuration of a shaping aperture array substrate according to the first embodiment. [Figure 3] 2 is a cross-sectional view showing the configuration of a blanking aperture array mechanism in the first embodiment. FIG. [Figure 4] FIG. 4 is a diagram showing an example of the relationship between the emission current, the bias voltage, and the cathode temperature in the first embodiment. [Figure 5] FIG. 10 is a diagram showing an example of movement of the operating point in a first comparative example of the first embodiment. [Figure 6] FIG. 10 is a diagram illustrating an example of a method for adjusting an operating point in a second comparative example of the first embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of a method for adjusting an operating point in a third comparative example of the first embodiment. [Figure 8] FIG. 10 is a diagram illustrating an example of a method for adjusting an operating point in a fourth comparative example of the first embodiment. [Figure 9] FIG. 3 is a diagram for explaining the space charge effect in the first embodiment. [Figure 10] FIG. 3 is a flowchart showing an example of main steps of the electron beam adjusting method according to the first embodiment. [Figure 11] FIG. 4 is a diagram for explaining an example of a method for lowering the cathode temperature in the first embodiment. [Figure 12] FIG. 4 is a diagram for explaining an example of a method for increasing the cathode temperature in the first embodiment. [Figure 13] FIG. 4 is a diagram showing an example of the transition of a decision parameter in the first embodiment. [Figure 14] 10 is a diagram for explaining threshold values ​​of determination parameters when the operating conditions and cathode design conditions are different in the first embodiment. FIG. [Figure 15] FIG. 3 is a diagram showing an example of an adjustment period in the first embodiment. [Figure 16] FIG. 2 is a conceptual diagram for explaining an example of a drawing operation in the first embodiment. [Figure 17] 3 is a diagram showing an example of a multi-beam irradiation area and a pixel to be written in the first embodiment. FIG. [Figure 18] FIG. 2 is a diagram for explaining an example of a multi-beam writing method according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0016] In the following embodiments, a configuration using multiple electron beams will be described. However, the present invention is not limited to this, and a configuration using a single beam may also be used. Furthermore, a drawing apparatus will be described below as an example of an electron beam apparatus, but any apparatus other than a drawing apparatus may be used as long as it uses an electron beam emitted from a thermoelectron emission source. For example, an image acquisition apparatus, an inspection apparatus, or the like may also be used.

[0017] Embodiment 1 FIG. 1 is a conceptual diagram showing the configuration of a lithography apparatus according to the first embodiment. In FIG. 1, the lithography apparatus 100 includes a lithography mechanism 150 and a control circuit 160. The lithography apparatus 100 is an example of a multi-electron beam lithography apparatus. The lithography mechanism 150 (an example of an irradiation mechanism) includes an electron lens barrel 102 (a multi-electron beam column) and a lithography chamber 103. The electron lens barrel 102 includes an electron gun 201 (a thermionic electron gun), an illumination lens 202, a shaping aperture array substrate 203, a blanking aperture array mechanism 204, a reduction lens 205, a limiting aperture substrate 206, an objective lens 207, a detector 108, a deflector 208, and a deflector 209. The lithography chamber 103 includes an XY stage 105. A sample 101, such as a resist-coated mask blank that serves as a target substrate for lithography, is placed on the XY stage 105. The sample 101 includes an exposure mask used in manufacturing a semiconductor device, a semiconductor substrate (silicon wafer) on which the semiconductor device is manufactured, etc. A mirror 210 for measuring the position of the XY stage 105 is also placed on the XY stage 105. A Faraday cup 106 is also placed on the XY stage 105. A mark 107 is also placed on the XY stage 105.

[0018] The electron gun 201 (thermal electron gun, electron beam emission source) has a cathode 222, a Wehnelt 224 (Wehnelt electrode), and an anode 226 (anode electrode). The anode 226 is grounded (earthed). The anode 226 is controlled to have a positive potential relative to the cathode 222. The Wehnelt 224 is controlled to have a negative potential relative to the cathode 222. The electron gun 201 emits an electron beam 200 from the cathode 222 toward the anode 226.

[0019] The control system circuit 160 includes a control computer 110, a memory 112, a monitor 114, an electron gun power supply device 120, a deflection control circuit 130, digital-to-analog conversion (DAC) amplifier units 132 and 134, a current detection circuit 136, a stage position detector 139, and a storage device 140 such as a magnetic disk drive. The control computer 110, the memory 112, the monitor 114, the electron gun power supply device 120, the deflection control circuit 130, the DAC amplifier units 132 and 134, the current detection circuit 136, the stage position detector 139, and the storage device 140 are connected to one another via a bus (not shown). The deflection control circuit 130 is connected to the DAC amplifier units 132 and 134 and a blanking aperture array mechanism 204. The output of the DAC amplifier unit 132 is connected to a deflector 209. The output of the DAC amplifier unit 134 is connected to a deflector 208. The deflector 208 is composed of four or more electrodes, and each electrode is controlled by the deflection control circuit 130 via a DAC amplifier 134. The deflector 209 is composed of four or more electrodes, and each electrode is controlled by the deflection control circuit 130 via a DAC amplifier 132. The stage position detector 139 irradiates a mirror 210 on the XY stage 105 with laser light and receives the light reflected from the mirror 210. The position of the XY stage 105 is measured using the principle of laser interference and information on this reflected light. The output of the Faraday cup 106 is connected to a current detection circuit 136.

[0020] The control computer 110 includes a current density measurement unit 51, a current density determination unit 52, a current density distribution measurement unit 53, a current density distribution determination unit 54, a determination unit 55, an emission current measurement unit 56, a parameter calculation unit 58, a determination unit 59, a writing data processing unit 40, and a writing control unit 42. Each of the "units" such as the current density measurement unit 51, the current density determination unit 52, the current density distribution measurement unit 53, the current density distribution determination unit 54, the determination unit 55, the emission current measurement unit 56, the parameter calculation unit 58, the determination unit 59, the writing data processing unit 40, and the writing control unit 42 includes a processing circuit. Such a processing circuit includes, for example, an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each of the "units" may use a common processing circuit (the same processing circuit) or different processing circuits (separate processing circuits). Information input and output to and from the current density measurement unit 51, current density determination unit 52, current density distribution measurement unit 53, current density distribution determination unit 54, determination unit 55, emission current measurement unit 56, parameter calculation unit 58, determination unit 59, drawing data processing unit 40, and drawing control unit 42, as well as information being calculated, are stored in memory 112 each time.

[0021] The electron gun power supply device 120 includes a control computer 232, a memory 78, a storage device 79 such as a magnetic disk device, an acceleration voltage power supply circuit 236, a bias voltage power supply circuit 234, a filament power supply circuit 231 (filament power supply unit), and an ammeter 238. The control computer 232 is connected to the memory 78, the storage device 79, the acceleration voltage power supply circuit 236, the bias voltage power supply circuit 234, the filament power supply circuit 231, and the ammeter 238 by a bus (not shown).

[0022] The control computer 232 includes a bias voltage adding unit 60, a bias voltage reducing unit 62, a bias voltage margin reducing unit 64, a cathode temperature setting unit 70, an emission current setting unit 72, a bias voltage control unit 74, and a cathode temperature control unit 76. Each of the "units" such as the bias voltage adding unit 60, the bias voltage reducing unit 62, the bias voltage margin reducing unit 64, the cathode temperature setting unit 70, the emission current setting unit 72, the bias voltage control unit 74, and the cathode temperature control unit 76 has a processing circuit. Such a processing circuit includes, for example, an electric circuit, a computer, a processor, a circuit board, a quantum circuit, or a semiconductor device. Each of the "units" may use a common processing circuit (the same processing circuit) or different processing circuits (separate processing circuits). Information input and output to and from the bias voltage adding unit 60, bias voltage reducing unit 62, bias voltage margin reducing unit 64, cathode temperature setting unit 70, emission current setting unit 72, bias voltage control unit 74, and cathode temperature control unit 76, as well as information being calculated, are stored in memory 78 each time.

[0023] The cathode (-) side of the acceleration voltage power supply circuit 236 is connected to both electrodes of the cathode 222 in the electron microscope column 102. The anode (+) side of the acceleration voltage power supply circuit 236 is grounded (connected to ground) via an ammeter 238 connected in series. The cathode (-) of the acceleration voltage power supply circuit 236 is also branched and connected to the anode (+) of the bias voltage power supply circuit 234. The cathode (-) of the bias voltage power supply circuit 234 is electrically connected to the Wehnelt 224, which is arranged between the cathode 222 and the anode 226. In other words, the bias voltage power supply circuit 234 is arranged so as to be electrically connected between the cathode (-) of the acceleration voltage power supply circuit 236 and the Wehnelt 224. The filament power supply circuit 231, controlled by the cathode temperature control unit 76, passes a current between both electrodes of the cathode 222 to heat the cathode 222 to a predetermined temperature. In other words, the filament power supply circuit 231 supplies filament power W to the cathode 222. A fixed relationship can be defined between the filament power W and the cathode temperature T, and the cathode can be heated to a desired cathode temperature T by the filament power W. Therefore, the cathode temperature T is controlled by the filament power W. The filament power W is defined as the product of the current flowing between the two electrodes of the cathode 222 and the voltage applied between the two electrodes of the cathode 222 by the filament power supply circuit 231. The acceleration voltage power supply circuit 236 applies an acceleration voltage between the cathode 222 and the anode 226. The bias voltage power supply circuit 234, controlled by the bias voltage control unit 74, applies a negative bias voltage to the Wehnelt 224.

[0024] Furthermore, drawing data is input from outside the drawing device 100 and stored in the storage device 140. The drawing data usually defines information on a plurality of graphic patterns to be drawn. Specifically, for each graphic pattern, for example, the coordinates of the vertices that make up the graphic are defined in the order in which the graphic is formed. Alternatively, for each graphic pattern, for example, a graphic code, reference position coordinates, size, etc. are defined.

[0025] 1 shows the configuration necessary for explaining the first embodiment. The drawing device 100 may also include other configurations that are normally required.

[0026] FIG. 2 is a conceptual diagram showing the configuration of a shaping aperture array substrate 203 according to the first embodiment. In FIG. 2, holes (openings) 22 are formed in a matrix of p columns (x direction) by q columns (y direction) (p, q≧2) at a predetermined pitch on the shaping aperture array substrate 203. In FIG. 2, for example, 512×512 columns of holes 22 are formed in the x and y directions. Each hole 22 is formed as a rectangle of the same size and shape. Alternatively, they may be circles of the same diameter. The shaping aperture array substrate 203 (beam forming mechanism) forms multiple beams 20. Specifically, multiple beams 20 are formed by portions of an electron beam 200 passing through each of the multiple holes 22. The arrangement of holes 22 is not limited to the grid-like arrangement shown in FIG. 2. For example, the holes in the kth column and the k+1th column in the y direction may be offset by a dimension a in the x direction. Similarly, the holes in the k+1th column and the k+2th column in the vertical direction (y direction) may be arranged with a shift of dimension b in the horizontal direction (x direction).

[0027] FIG. 3 is a cross-sectional view showing the configuration of the blanking aperture array mechanism 204 according to the first embodiment. In the blanking aperture array mechanism 204, as shown in FIG. 3, a semiconductor substrate 31 made of silicon or the like is placed on a support base 33. The central portion of the substrate 31 is removed, for example, from the backside, to form a membrane region 330 (first region) with a thin film thickness h. The area surrounding the membrane region 330 is a peripheral region 332 (second region) with a thick film thickness H. The upper surfaces of the membrane region 330 and the peripheral region 332 are formed to be at the same height position or substantially at the same height position. The substrate 31 is held on the support base 33 at the backside of the peripheral region 332. The central portion of the support base 33 is open, and the membrane region 330 is located in the open region of the support base 33.

[0028] In the membrane region 330, passage holes 25 (openings) for passing through each beam of the multibeam 20 are opened at positions corresponding to the holes 22 of the shaping aperture array substrate 203 shown in FIG. 2. In other words, a plurality of passage holes 25 for passing through corresponding beams of the multibeam 20 using electron beams are formed in an array in the membrane region 330 of the substrate 31. A plurality of electrode pairs, each having two electrodes, are arranged on the membrane region 330 of the substrate 31 at positions facing each other across a corresponding passage hole 25 among the plurality of passage holes 25. Specifically, on the membrane region 330, as shown in FIG. 3, pairs of a control electrode 24 for blanking deflection and a counter electrode 26 (blankers: blanking deflectors) are arranged in positions near each passage hole 25 on either side of the corresponding passage hole 25. Furthermore, a control circuit 41 (logic circuit) for applying a deflection voltage to the control electrode 24 for each passage hole 25 is arranged inside the substrate 31 and near each passage hole 25 on the membrane region 330. The counter electrode 26 for each beam is connected to ground.

[0029] The control circuit 41 includes an amplifier (an example of a switching circuit, not shown), such as a CMOS inverter circuit. The amplifier output line (OUT) is connected to the control electrode 24. On the other hand, a ground potential is applied to the counter electrode 26. A control signal is applied to the input (IN) of the amplifier, either an L (low) potential (e.g., ground potential) that is lower than the threshold voltage, or an H (high) potential (e.g., 1.5 V) that is equal to or higher than the threshold voltage. In the first embodiment, when an L potential is applied to the input (IN) of the amplifier, the output (OUT) of the amplifier is at a positive potential (Vdd). The corresponding beam is deflected by an electric field due to a potential difference with the ground potential of the counter electrode 26, and is controlled so that the beam is turned OFF by being blocked by the limiting aperture substrate 206. On the other hand, when an H potential is applied to the input (IN) of the amplifier (active state), the output (OUT) of the amplifier is at ground potential. Since the potential difference with the ground potential of the counter electrode 26 disappears, the corresponding beam is not deflected, and the beam is controlled so that it is turned ON by passing through the limiting aperture substrate 206.

[0030] The pairs of control electrode 24 and counter electrode 26 individually blank and deflect the corresponding beams of multi-beam 20 by the potentials switched by the amplifiers that serve as the corresponding switching circuits. In this way, the multiple blankers perform blanking deflection of the corresponding beams of multi-beam 20 that have passed through the multiple holes 22 (openings) of shaping aperture array substrate 203.

[0031] Next, the operation of the drawing mechanism 150 in the drawing apparatus 100 will be described. An electron beam 200 emitted from an electron gun 201 (electron emission source) illuminates the entire shaping aperture array substrate 203 via an illumination lens 202. A plurality of rectangular holes 22 (openings) are formed in the shaping aperture array substrate 203, and the electron beam 200 illuminates an area including all of the holes 22. Portions of the electron beam 200 irradiated onto the positions of the holes 22 pass through the holes 22 in the shaping aperture array substrate 203, thereby forming a plurality of electron beams (multibeams 20), each having a rectangular shape, for example. The multibeams 20 pass through corresponding blankers (first deflectors: individual blanking mechanisms) in a blanking aperture array mechanism 204. Each blanker individually deflects the passing electron beam (performs blanking deflection).

[0032] The multi-beams 20 that pass through the blanking aperture array mechanism 204 are reduced by the reduction lens 205 and travel toward the central hole formed in the limiting aperture substrate 206. Here, among the multi-beams 20, the electron beams that are deflected by the blankers of the blanking aperture array mechanism 204 are positioned away from the central hole of the limiting aperture substrate 206 and are blocked by the limiting aperture substrate 206. On the other hand, the electron beams that are not deflected by the blankers of the blanking aperture array mechanism 204 pass through the central hole of the limiting aperture substrate 206, as shown in FIG. 1. Blanking control is performed by turning on / off these individual blanking mechanisms, and the on / off of the beams is controlled. Then, the beams that are formed for each beam from when the beam is turned on until when the beam is turned off and that pass through the limiting aperture substrate 206 form a beam for one shot. The multibeams 20 that have passed through the limiting aperture substrate 206 are focused by the objective lens 207 to form a pattern image with the desired reduction ratio, and the individual beams that have passed through the limiting aperture substrate 206 (the entire multibeams 20 that have passed through) are deflected collectively in the same direction by the deflectors 208 and 209, and each beam is irradiated onto its respective irradiation position on the sample 101. Ideally, the multibeams 20 that are irradiated at one time are aligned at a pitch obtained by multiplying the arrangement pitch of the plurality of holes 22 in the shaping aperture array substrate 203 by the desired reduction ratio described above.

[0033] As described above, in an electron gun that emits an electron beam, in order to obtain a desired emission current at as low a cathode temperature as possible, the operating point of the thermionic electron gun is often set near the boundary between the space charge limited region and the temperature limited region, but not within the temperature limited region.

[0034] FIG. 4 is a diagram showing an example of the relationship between emission current, bias voltage, and cathode temperature in the first embodiment. The vertical axis represents the emission current, and the horizontal axis represents the bias voltage. FIG. 4 shows characteristic curves of emission current and bias voltage for each cathode temperature. The cathode temperatures T have the relationship T3>T2>T1. The boundary between the space charge limited region and the temperature limited region is indicated by a dotted line. The bias voltage value at the boundary between the space charge limited region and the temperature limited region varies depending on the cathode temperature. Generally, the lower the cathode temperature, the smaller the negative bias voltage at the boundary. The operating point for driving the electron gun 201 is set near the boundary between the space charge limited region and the temperature limited region, but not within the temperature limited region.

[0035] When an electron beam is emitted in the temperature-limited region, the beam current density distribution becomes steep and nonuniform, resulting in localized high-intensity regions. On the other hand, when an electron beam is emitted in the space-charge-limited region, the beam current density distribution becomes highly uniform. For the same emission current, the locally high intensity of the beam current density distribution in the temperature-limited region is higher than the uniform intensity of the beam current density distribution in the space-charge-limited region. Furthermore, the locally high intensity of the beam current density distribution in the temperature-limited region when the emission current is small may be higher than the uniform intensity of the beam current density distribution in the space-charge-limited region when the emission current is large. Therefore, emitting an electron beam in the temperature-limited region can potentially damage the aperture substrate and other components that the electron beam impinges on. Therefore, it is necessary to search for an operating point along a path that does not penetrate deep into the temperature-limited region.

[0036] FIG. 5 is a diagram showing an example of the movement of the operating point in Comparative Example 1 of Embodiment 1. The characteristic curve in FIG. 5 is the same as that in FIG. 4. For example, when changing the cathode temperature from an operating point of cathode temperature T2, if there is an error in obtaining the coefficients for automatic adjustment in the cathode operating temperature adjustment method described in Japanese Patent No. 6166910, an adjustment other than the intended one may be made. For example, as shown in FIG. 5, when lowering the operating point from cathode temperature T2 to cathode temperature T1, the cathode operating conditions (operating point) may fall deep into the temperature restriction region. Even if limitations are placed on the emission current value or bias voltage value to avoid such a phenomenon, this is not a 100% solution.

[0037] FIG. 6 is a diagram showing an example of a method for adjusting the operating point in Comparative Example 2 of Embodiment 1. In FIG. 6, the vertical axis represents the emission current, and the horizontal axis represents the bias voltage. The example in FIG. 6 shows an example of a method for measuring the relationship between the emission current and the bias voltage for each cathode temperature until the bias saturation point is reached, and determining the operating point from the characteristics. In the method shown in FIG. 6, the characteristics of the emission current and the bias voltage are measured at a constant temperature, and the intersection of the lines obtained from the low bias voltage side and the high bias voltage side is defined as the boundary between the temperature-limited region and the space charge-limited region. However, this method requires measuring data over a wide range, even deep within the temperature-limited region. Furthermore, determining the line is difficult. In particular, there is a problem that the way the line on the space charge-limited region side is defined results in a large calculation error for the boundary between the temperature-limited region and the space charge-limited region.

[0038] Fig. 7 is a diagram showing an example of a method for adjusting the operating point in Comparative Example 3 of Embodiment 1. In Fig. 7, the vertical axis represents bias voltage V, and the horizontal axis represents cathode temperature T. In the method of Fig. 7, bias voltage V is measured while changing the temperature with the emission current kept constant. The measurement points are fitted with an appropriate function, and the area where σ drops from the asymptote of the fitting curve is defined as the temperature-limited region and the space-charge-limited region.

[0039] Fig. 8 is a diagram showing an example of a method for adjusting the operating point in Comparative Example 4 of Embodiment 1. In Fig. 8, the vertical axis represents the amount of change dV in bias voltage V relative to the amount of change dT in cathode temperature T, and the horizontal axis represents cathode temperature T. In the method of Fig. 8, the amount of change (dV / dT) in bias voltage V is calculated while changing cathode temperature T, with the emission current kept constant. Then, the point where the value of dV / dT reaches a certain threshold is defined as the boundary between the temperature-limited region and the space-charge-limited region.

[0040] 7 and 8, the bias voltage V is measured each time the cathode temperature is changed to maintain a constant emission current, and the operating point is searched for at a position where the change in bias voltage V is sufficiently small relative to the change in cathode temperature T. In either of these methods, data must be measured over a wide range, even deep within the temperature-limited region, in the process of finding the operating point.

[0041] FIG. 9 is a diagram illustrating the space charge effect in the first embodiment. The space charge effect is formed by the emission current itself. Here, for ease of understanding, it is assumed that the space charge effect is also halved when the emission current is halved. As shown in the upper diagram of FIG. 9, when the electron gun is driven at a cathode temperature T1 with an emission current of, for example, 100 μA, the space charge effect is significantly reduced if the emission current is changed to 50 μA. On the other hand, as shown in the lower diagram of FIG. 9, when the electron gun is driven at a cathode temperature T3 with an emission current of, for example, 1000 μA, the space charge effect is not significantly reduced even if the emission current is reduced by 50 μA. In this way, the strength of the space charge effect varies depending on the rate of change, not the amount of change, of the emission current. In the first embodiment, the operating point is adjusted by focusing on the strength of the space charge effect. This will be explained in detail below.

[0042] Fig. 10 is a flowchart showing an example of main steps of the electron beam adjusting method according to the embodiment 1. In Fig. 10, a series of steps are performed: a current density and current density distribution measuring step (S100), a current density determining step (S102), a current density distribution determining step (S104), a determining step (S106), a bias voltage reducing step (S110), a cathode temperature reducing step (S112), a cathode temperature adding step (S120), an emission current measuring step (S130), a bias voltage adding step (S132), an emission current measuring step (S134), a parameter calculating step (S136), a determining step (S138), a bias voltage reducing step (S140), and a bias voltage margin reducing step (S142).

[0043] In the current density and current density distribution measurement step (S100), the current density measurement unit 51 measures the current density J of the multibeam 20 reaching the sample 101. First, the XY stage 105 is moved to a position where the multibeam 20 can be incident on the Faraday cup 106. Then, the Faraday cup 106 detects the overall current value of the multibeam 20, which is formed from the electron beam 200 emitted from the electron gun 201 and reaches the sample surface position. The signal detected by the Faraday cup 106 is output to the current detection circuit 136, converted into digital data, and output to the control computer 110. Within the control computer 110, the current density measurement unit 51 calculates the overall current density J of the multibeam 20. The current density J can be calculated by dividing the measured current value by the sum of the opening areas of the multiple holes 22 in the shaping aperture array substrate 203.

[0044] The current density distribution measurement unit 53 also measures the current density distribution U of the multibeam 20 reaching the sample 101. The multibeam 20 is divided into multiple beam array groups, and the Faraday cup 106 detects the current value for each beam array group. Beams other than the target beam array group can be turned off by the blanking aperture array mechanism 204. The signal detected by the Faraday cup 106 is output to the current detection circuit 136, converted into digital data, and output to the control computer 110. Within the control computer 110, the current density distribution measurement unit 53 calculates the current density j for each beam array group. The current density j can be calculated by dividing the measured current value by the sum of the opening areas of the multiple holes 22 for each beam array group in the shaping aperture array substrate 203. The current density distribution measurement unit 53 calculates the current density distribution U using the current density j for each beam array group.

[0045] The current density measuring unit 51 may calculate the current density J of the entire multi-beam 20 by summing up the current densities j for each beam array group.

[0046] When starting up the device, the cathode temperature setting unit 70 sets a predetermined initial value for the cathode temperature, and the emission current setting unit 72 sets a predetermined initial value for the emission current. The bias voltage V is set to a sufficiently small value (a value on the negative side). Adjustment can be started from this state. By starting the bias voltage V from a sufficiently small value on the negative side, it is possible to start in the space charge limited region.

[0047] In the current density determination step (S102), the current density determination unit 52 determines whether the measured current density J of the entire multi-beam 20 is the desired current density J0 or whether it is within an allowable range centered on the desired current density J0. If the current density J is the desired current density J0 or is within an allowable range centered on the desired current density J0, the process proceeds to a current density distribution determination step (S104). If the current density J is not the desired current density J0 or is not within an allowable range centered on the desired current density J0, the process proceeds to a determination step (S106).

[0048] In the current density distribution determination step (S104), the current density distribution determination unit 54 determines whether the uniformity of the measured current density distribution U is equal to or greater than the desired uniformity U0. If the uniformity of the current density distribution U is equal to or greater than the desired uniformity U0, no beam adjustment is necessary, and the electron beam adjustment ends. If the uniformity of the current density distribution U is not equal to or greater than the desired uniformity U0, the process proceeds to the determination step (S106).

[0049] In the determination step (S106), the determination unit 55 determines whether the measured current density J of the entire multi-beam 20 is greater than the desired current density J0. The current density J increases as the emission current Emi increases. Conversely, the current density J decreases as the emission current Emi decreases. It is desirable to operate the electron gun 201 at the lowest possible cathode temperature T that can obtain the emission current Emi required to obtain the desired current density J0. Therefore, if the current density J is greater than the desired current density J0, the cathode temperature T is lowered. Conversely, if the current density J is smaller than the desired current density J0, the emission current Emi is insufficient, so the cathode temperature T is raised. This determination is made here. If the current density J is greater than the desired current density J0, the process proceeds to the bias voltage reduction step (S110). If the current density J is greater than the desired current density J0 (in this case, smaller), the process proceeds to the cathode temperature addition step (S120).

[0050] In the bias voltage reduction step (S110), the bias voltage control unit 74 controls the bias voltage power supply circuit 234 so as to sufficiently reduce the current bias voltage V.

[0051] FIG. 11 is a diagram illustrating an example of a technique for lowering the cathode temperature in the first embodiment. In FIG. 11, the vertical axis represents the emission current, and the horizontal axis represents the bias voltage. The example in FIG. 11 shows a characteristic curve of the emission current versus bias voltage at cathode temperature T2 and a characteristic curve of the emission current versus bias voltage at cathode temperature T1. In the characteristic curves, the solid line indicates the space-charge-limited region, and the dotted line indicates the temperature-limited region. T2>T1. If the cathode temperature is lowered from T2 to T1 while maintaining the bias voltage unchanged while operating at the operating point at cathode temperature T2, the operating point will enter the temperature-limited region. Therefore, before lowering the cathode temperature, the bias voltage control unit 74 lowers the bias voltage to the negative side by a value sufficient to maintain the operating point in the space-charge-limited region even when the cathode temperature is lowered from T2 to T1 (operation a in FIG. 11). The sufficient value may be set empirically.

[0052] In the cathode temperature reduction step (S112), the cathode temperature setting unit 70 (temperature setting unit) sets the temperature of the cathode 222 to a predetermined value. Specifically, the operation here is as follows: The cathode temperature setting unit 70 subtracts ΔT from the current cathode temperature T and sets the cathode temperature reduced by ΔT from the current cathode temperature T as the new cathode temperature T. The cathode temperature control unit 76 controls the filament power supply circuit 231 so that the cathode temperature becomes the set cathode temperature T. As a result, the cathode temperature is controlled to the newly set cathode temperature T that is reduced by ΔT (operation b in FIG. 11). ΔT is preferably set in the range of 5 to 50°C, for example. For example, it is set to 10°C.

[0053] In the cathode temperature addition step (S120), the cathode temperature setting unit 70 sets the temperature of the cathode 222 to a predetermined value. Specifically, the operation here is as follows: The cathode temperature setting unit 70 adds ΔT to the current cathode temperature T and sets the cathode temperature increased by ΔT from the current cathode temperature T as the new cathode temperature T. The cathode temperature control unit 76 controls the filament power supply circuit 231 so that the cathode temperature becomes the set cathode temperature T. As a result, the cathode temperature is controlled to the newly set cathode temperature T that is increased by ΔT. As shown in FIG. 4, even if the cathode temperature T is increased while maintaining the bias voltage, the operating point does not enter the temperature limited region, and the space charge limited region can be maintained.

[0054] FIG. 12 is a diagram illustrating an example of a method for increasing the cathode temperature in the first embodiment. In FIG. 12, the vertical axis represents the emission current, and the horizontal axis represents the bias voltage. The example in FIG. 12 shows a characteristic curve of the emission current versus bias voltage at cathode temperature T2′ and a characteristic curve of the emission current versus bias voltage at cathode temperature T3′. In the characteristic curves, the solid line indicates the space charge limited region, and the dotted line indicates the temperature limited region. T3′>T2′. Even if the cathode temperature is increased from T2′ to T3′ while maintaining the bias voltage unchanged while operating at the operating point at cathode temperature T2′, the operating point will not enter the temperature limited region. Therefore, the cathode temperature setting unit 70 sets a new cathode temperature T that is increased by ΔT from the current cathode temperature T while maintaining the current bias voltage (operation B in FIG. 12).

[0055] In the emission current measurement step (S130), the emission current measurement unit 56 measures the current emission current Emi(0). The value of the emission current Emi can be obtained as a current value detected by the ammeter 238. The obtained emission current Emi(0) is stored in the storage device 140 or the like.

[0056] In the bias voltage addition step (S132), the bias voltage control unit 74 changes the bias voltage V applied to the Wehnelt 224 while maintaining the cathode temperature T at a predetermined set value. Specifically, the operation is as follows: First, the bias voltage addition unit 60 adds ΔV to the current bias voltage V and sets it as a new bias voltage V (for example, operation c in FIG. 11 or operation C in FIG. 12). The bias voltage control unit 74 applies the new bias voltage V to the Wehnelt 224. Here, the bias voltage V indicates the potential difference between the negative potential applied to the cathode 222 and the negative potential applied to the Wehnelt 224. ΔV may be, for example, 10 to 50 V. For example, 20 V is used.

[0057] In the emission current measurement step (S134), the emission current measurement unit 56 measures the emission current Emi(1) when the bias voltage V is changed while the cathode temperature T is maintained at a predetermined set value. The value of the emission current Emi can be obtained as a current value detected by the ammeter 238. The obtained emission current Emi(1) is stored in the storage device 140 or the like.

[0058] In the parameter calculation step (S136), the parameter calculation unit 58 divides the rate of change in the emission current when the bias voltage V is changed by the amount of change in the bias voltage ΔV, and calculates the result as a judgment parameter A. The rate of change ΔE (%) in the emission current can be defined by the following equation (1), which divides the amount of change ΔEmi in the emission current by the emission current Emi(0) before the change. (1) ΔE(%)=(Emi(1)-Emi(0)) / Emi(0) =ΔEmi / Emi(0)

[0059] The judgment parameter A can be defined by the following equation (2). (2) A=ΔE(%) / ΔV =(ΔEmi / Emi(0)) / ΔV =((Emi(1)-Emi(0)) / Emi(0)) / ΔV

[0060] In the determination step (S138), the determination unit 59 compares the determination parameter A with a threshold value Ath. Specifically, it determines whether the determination parameter A is smaller than the threshold value Ath. If the determination parameter A is smaller than the threshold value Ath, the process proceeds to the bias voltage return step (S140). If the determination parameter A is not smaller than the threshold value Ath, the process returns to the emission current measurement step (S130), and the steps from the emission current measurement step (S130) to the determination step (S138) are repeated until the determination parameter A becomes smaller than the threshold value Ath. In other words, while maintaining the cathode temperature T at a predetermined value, the step of changing the bias voltage V, the step of measuring the emission current, and the step of calculating the determination parameter A are repeated until the determination parameter A reaches the threshold value Ath (for example, operation c in FIG. 11 or operation C in FIG. 12).

[0061] Fig. 13 is a diagram showing an example of the transition of the decision parameter in the first embodiment. In Fig. 13, the vertical axis represents the decision parameter A, and the horizontal axis represents the bias voltage. In the first embodiment, the process of changing the bias voltage V, the process of measuring the emission current, and the process of calculating the decision parameter A are repeated so that the decision parameter A approaches the threshold value Ath from a state in which it is greater than the threshold value Ath. Therefore, it is possible to prevent the decision parameter A from entering the temperature restricted region until it reaches the threshold value Ath.

[0062] The threshold Ath is set to a value between 0.5 and 0.9, for example, Ath=0.9.

[0063] Fig. 14 is a diagram for explaining threshold values ​​of the decision parameters when the operating conditions and cathode design conditions are different in embodiment 1. Fig. 14 shows a case where a VI characteristic curve of the bias voltage V and the emission current I is converted into a VA characteristic curve of the bias voltage V and the decision parameter A obtained by dividing the rate of change ΔE (%) of the emission current by the amount of change ΔV in the bias voltage.

[0064] The left diagram in Figure 14 shows a case where the emission current differs at the boundary between the space charge limited region and the temperature limited region. The emission current I1 at the boundary is obtained at cathode temperature T1. The emission current I2 at the boundary is obtained at cathode temperature T2. The bias voltages required to obtain these emission currents are different. When this VI characteristic curve is converted into a VA characteristic curve, it can be seen that the determination parameter A at the inflection point corresponding to the boundary between the space charge limited region and the temperature limited region shows the same value for cathode temperature T1 and cathode temperature T2.

[0065] The diagram on the right side of FIG. 14 shows cases where the design of cathode 222 is different. Emission current I1 at the boundary position between the space charge limited region and the temperature limited region is obtained by design 1. Emission current I2 at the boundary position is obtained by design 2. The bias voltages required to obtain these emission currents are different. When such a VI characteristic curve is converted into a VA characteristic curve, it can be seen that the determination parameter A at the inflection point corresponding to the boundary position between the space charge limited region and the temperature limited region shows the same value for design 1 and design 2. It can also be seen that this value is the same as the value shown in the diagram on the left side of FIG. 14.

[0066] The value of this inflection point can be set as the threshold value Ath. In other words, the same behavior is exhibited regardless of design conditions such as the dimensions of the cathode 222, changes in characteristics due to wear and tear of the cathode 222, and operating conditions of the cathode 222. This indicates that it is possible to compare and determine the judgment parameters using the same standard (the same threshold value Ath) regardless of design conditions such as the dimensions of the cathode 222, changes in characteristics due to wear and tear of the cathode 222, and operating conditions of the cathode 222.

[0067] In the bias voltage return step (S140), when the decision parameter A reaches the threshold value Ath, the bias voltage reducer 62 subtracts ΔV from the bias voltage V at that time, thereby returning the bias voltage V to the previous state. The bias voltage controller 74 applies a new bias voltage V to the Wehnelt 224 (for example, operation d in FIG. 11 or operation D in FIG. 12). This causes the decision parameter A to return from a state where it has shallowly entered the temperature-limited region to the space-charge-limited region near the boundary position. In other words, the operation of the electron gun 201 returns from an operation shallowly entered the temperature-limited region to an operation in the space-charge-limited region near the boundary position. In the first embodiment, the decision parameter A operates so as to approach the threshold value Ath (the boundary between the space-charge-limited region and the temperature-limited region) from a state where it is larger than the threshold value Ath (the space-charge-limited region), thereby preventing the decision parameter A from entering the temperature-limited region deeply.

[0068] In the bias voltage margin reducing step (S142), the bias voltage margin reducing unit 64 reduces the bias voltage on the negative side by a preset amount when the decision parameter A reaches the threshold value Ath. Specifically, the bias voltage margin reducing unit 64 sets a new bias voltage V as the bias voltage V obtained by subtracting the bias voltage margin Vm from the bias voltage V on the space charge limited region side near the boundary position. The bias voltage control unit 74 applies the new bias voltage V to the Wehnelt 224. This state is then set as the operating point of the electron gun 201 at the currently set cathode temperature T.

[0069] The bias voltage margin Vm may be set appropriately according to the adjustment period, which will be described later. The longer the adjustment period, the more likely drift will occur, so the bias voltage margin Vm should be set large. The bias voltage margin Vm may be set to, for example, about 5 to 10% of the bias voltage V. For example, it may be set in the range of 100V to 20V. For example, if the bias voltage V is -700V, the bias voltage V is reduced by 50V on the negative side as the bias voltage margin Vm. In other words, 50V is subtracted from the bias voltage V (-50V is added to the bias voltage V). In this example, the bias voltage V at the operating point is, for example, -750V.

[0070] Then, the process returns to the current density determination step (S102), and in the current density distribution determination step (S104), the steps from the current density determination step (S102) to the bias voltage margin reduction step (S142) are repeated until the uniformity of the measured current density distribution U becomes equal to or greater than the desired uniformity U0.

[0071] FIG. 15 is a diagram showing an example of an adjustment period in the first embodiment. In FIG. 15, each of the above-described steps is performed at a predetermined period S. In the writing apparatus 100, the current density J and the current density distribution U are measured when the apparatus is started up. Furthermore, the current density J and the current density distribution U are measured at each predetermined period S while the apparatus is in operation. For example, the measurements are made once a week or once a month. Then, the electron beam is adjusted each time, in other words, the driving operating point of the electron gun 201 is adjusted.

[0072] Next, the method of the writing process will be described. The writing data processing unit 40 reads out the writing data stored in the storage device 140 and generates writing time data for writing with multiple beams. The writing control unit 42 rearranges the irradiation time data in shot order according to the writing sequence. Then, the irradiation time data is transferred to the deflection control circuit 130 in shot order. The deflection control circuit 130 outputs a blanking control signal to the blanking aperture array mechanism 204 in shot order, and also outputs a deflection control signal to the DAC amplifier units 132 and 134 in shot order. The writing mechanism 150 (irradiation mechanism) controlled by the writing control unit 42 irradiates the sample 101 with the beam-adjusted electron beam emitted from the electron gun 201. For example, here, the writing mechanism 150 writes a pattern on the sample 101 using the beam-adjusted electron beam emitted from the electron gun 201.

[0073] FIG. 16 is a conceptual diagram illustrating an example of the writing operation in the first embodiment. As shown in FIG. 16, the writing region 30 on the sample 101 is virtually divided into a plurality of stripe regions 32, each having a predetermined width in the y direction. First, the XY stage 105 is moved to adjust the irradiation region 34 that can be irradiated with one shot of the multi-beam 20 to be located at the left end of the first stripe region 32 or further to the left, and writing begins. When writing the first stripe region 32, the XY stage 105 is moved, for example, in the −x direction to relatively write in the x direction. The XY stage 105 is moved continuously, for example, at a constant speed. After writing the first stripe region 32, the stage position is moved in the −y direction to adjust the irradiation region 34 to be located at the right end of the second stripe region 32 or further to the right in the y direction. Then, the XY stage 105 is moved, for example, in the x direction to similarly write in the −x direction. The writing time can be reduced by alternately changing the writing direction, such as writing in the x direction in the third stripe region 32 and writing in the -x direction in the fourth stripe region 32. However, writing is not limited to alternately changing the writing direction, and writing in each stripe region 32 may proceed in the same direction. In one shot, multiple shot patterns, up to the same number as the number of holes 22 formed in the shaping aperture array substrate 203, are formed at once by the multi-beams formed by passing through each hole 22 in the shaping aperture array substrate 203. Furthermore, while the example in FIG. 12 shows a case where each stripe region 32 is written once, this is not limiting. Multiple writing, in which the same region is written multiple times, is also suitable. When performing multiple writing, it is suitable to set the stripe regions 32 for each pass while shifting their positions.

[0074] FIG. 17 is a diagram showing an example of a multibeam irradiation area and target pixels for writing in the first embodiment. In FIG. 17, a stripe area 32 is set with a plurality of control grids 27 (design grids) arranged in a grid pattern at a beam size pitch of the multibeams 20 on the surface of the sample 101. For example, an arrangement pitch of approximately 10 nm is preferable. These control grids 27 are the designed irradiation positions of the multibeams 20. The arrangement pitch of the control grids 27 is not limited to the beam size, and may be any size that can be controlled as the deflection position of the deflector 209 regardless of the beam size. A plurality of pixels 36 are virtually divided into a mesh shape with the same size as the arrangement pitch of the control grids 27, centered on each control grid 27. Each pixel 36 is an irradiation unit area for one beam of the multibeams. The example of FIG. 16 shows a case where the writing area of ​​the sample 101 is divided into a plurality of stripe areas 32, for example, in the y direction, with a width substantially equal to the size of the irradiation area 34 (writing field) that can be irradiated by one irradiation of the multibeams 20. The x-direction size of the irradiation area 34 can be defined by the inter-beam pitch of the multibeam 20 in the x-direction multiplied by the number of beams in the x-direction. The y-direction size of the irradiation area 34 can be defined by the inter-beam pitch of the multibeam 20 in the y-direction multiplied by the number of beams in the y-direction. Note that the width of the stripe area 32 is not limited to this. It is preferable that the size be n times (n is an integer greater than or equal to 1) the size of the irradiation area 34. In the example of FIG. 17, for example, a 512×512 array of multibeams is simplified to an 8×8 array of multibeams. Furthermore, within the irradiation area 34, a plurality of pixels 28 (beam drawing positions) that can be irradiated with one shot of the multibeam 20 are shown. In other words, the pitch between adjacent pixels 28 is the pitch between each beam of the multibeam in the design. In the example of FIG. 17, one sub-irradiation area 29 is formed by an area surrounded by the inter-beam pitch. In the example of FIG. 17, each sub-irradiation area 29 is formed by 4×4 pixels.

[0075] FIG. 18 is a diagram illustrating an example of a multi-beam writing method according to the first embodiment. FIG. 18 illustrates a portion of the sub-irradiation region 29 written by the beams at coordinates (1,3), (2,3), (3,3), . . . , (512,3) in the third row in the y direction among the multiple beams that write the stripe region 32 shown in FIG. 16 . The example in FIG. 18 illustrates a case in which, for example, four pixels are written (exposed) while the XY stage 105 moves a distance equivalent to eight beam pitches. While writing (exposing) these four pixels, the entire multi-beam 20 is deflected collectively by the deflector 208 to prevent the relative position of the irradiation region 34 with respect to the sample 101 from shifting due to the movement of the XY stage 105, thereby causing the irradiation region 34 to follow the movement of the XY stage 105. In other words, tracking control is performed. The example in FIG. 18 illustrates a case in which one tracking cycle is performed by writing (exposing) four pixels while shifting the pixel 36 to be irradiated with the beam in the y direction for each shot while moving a distance equivalent to eight beam pitches.

[0076] Specifically, the writing mechanism 150 irradiates each control grid 27 with a corresponding ON beam of the multi-beam 20 for a writing time (irradiation time or exposure time) corresponding to each control grid 27 within the maximum irradiation time Ttr among the irradiation times of each beam of the multi-beam in the shot. The maximum irradiation time Ttr is set in advance. In reality, the shot cycle is the maximum irradiation time Ttr plus the settling time of beam deflection. However, here, the settling time of beam deflection is omitted and the maximum irradiation time Ttr is shown as the shot cycle. Then, when one tracking cycle is completed, the tracking control is reset and the tracking position is swung back to the start position of the next tracking cycle.

[0077] Since drawing of the first pixel row from the right in each sub-irradiation area 29 has been completed, after tracking reset, in the next tracking cycle, the deflector 209 first deflects the beam so as to align (shift) the drawing position of the corresponding beam with the control grid 27 of the pixel in the first row from the bottom and second from the right in each sub-irradiation area 29.

[0078] As described above, during the same tracking cycle, the deflector 208 controls the irradiation region 34 so that its relative position with respect to the sample 101 remains the same, and the deflector 209 shifts the irradiation region 34 by one control grid 27 (pixel 36) to perform each shot. After one tracking cycle is completed, the tracking position of the irradiation region 34 is returned, and then, as shown in the lower part of Figure 18, the first shot position is adjusted to a position shifted by, for example, one control grid (one pixel), and each shot is performed while the deflector 209 shifts the irradiation region 34 by one control grid (one pixel) while performing the next tracking control. By repeating this operation during the writing of the stripe region 32, the position of the irradiation region 34 moves sequentially from 34a to 34o, as shown in the lower diagram of Figure 16, and the stripe region is written.

[0079] Which beam of the multi-beam irradiates which control grid 27 (pixel 36) on the sample 101 is determined by the drawing sequence. If the sub-irradiation area 29 is an area of ​​n×n pixels, n control grids (n pixels) are drawn in one tracking operation. In the next tracking operation, n pixels are drawn in the same way using a beam different from the beam described above. In this way, n pixels are drawn in n tracking operations, each with a different beam, and all pixels in one n×n pixel area are drawn. Similar operations are performed at the same time on other n×n pixel sub-irradiation areas 29 within the multi-beam irradiation area, and drawing is performed in the same way.

[0080] The beam adjustment described above is performed when writing is not being performed on the sample 101. For example, it is performed after writing on one sample is completed and before writing on the next sample is started. Alternatively, it is performed after writing on the sample is started or before it is completed, for example, after writing on a stripe 32 is completed and before writing on the next stripe region 32 is started.

[0081] As described above, according to the first embodiment, the operating point of the electron gun 201 can be searched for along a path that prevents the electron beam emitted from the electron gun 201 (thermal electron gun) from penetrating deep into the temperature limited region.

[0082] Although the embodiments have been described above with reference to specific examples, the present invention is not limited to these specific examples.

[0083] Furthermore, the processing functions described in embodiment 1 may be executed by a computer, and a program for causing a computer to execute such processing functions may be stored in a non-transitory, tangible readable recording medium such as a magnetic disk device.

[0084] Although the description of the device configuration, control method, and other parts not directly necessary for the explanation of the present invention have been omitted, the required device configuration and control method can be appropriately selected and used. For example, the description of the control unit configuration that controls the drawing device 100 has been omitted, but it goes without saying that the required control unit configuration can be appropriately selected and used.

[0085] In addition, all electron beam adjustment methods, electron beam writing apparatuses, and programs (or readable recording media on which programs are non-temporarily recorded) that include elements of the present invention and that can be appropriately modified by a person skilled in the art are included in the scope of the present invention. [Explanation of symbols]

[0086] 20 Multibeam 22 holes 24 control electrode 25 Passing hole 26 Counter electrode 27 Control Grid 28 pixels 29 Sub-irradiation area 30 drawing area 32 stripe area 31 PCB 33 Support stand 34 Irradiation area 36 pixels 40 Drawing data processing unit 41 Control circuit 42 Drawing control unit 51 Current density measurement section 52 Current density determination section 53 Current density distribution measurement section 54 Current density distribution determination section 55 Judgment section 56 Emission current measurement section 58 Parameter calculation unit 59 Judgment section 60 Bias voltage adder 62 Bias voltage reduction section 64 Bias voltage margin reduction section 70 Cathode temperature setting unit 72 Emission current setting section 74 Bias voltage control section 76 Cathode temperature control unit 78 memory 79 Storage device 100 drawing device 101 Sample 102 Electron Telescope 103 Drawing room 105 XY stage 106 Faraday Cup 107 marks 108 detectors 110 Control computer 112 memory 114 Monitor 120 Electron gun power supply 130 Deflection control circuit 132,134 DAC amplifier unit 136 Current detection circuit 139 Stage Position Detector 140 Storage device 150 Drawing mechanism 160 Control Circuits 200 electron beam 201 Electron Gun 202 Lighting lens 203 Shaped Aperture Array Substrate 204 Blanking Aperture Array Mechanism 205 Reduction Lens 206 Limiting Aperture Substrate 207 Objective Lens 208,209 Deflector 210 Mirror 222 cathode 224 Wehnelt 226 Anode 231 Filament power supply circuit 232 Control Computer 234 Bias voltage power supply circuit 236 Accelerating voltage power supply circuit 238 Ammeter 330 Membrane Region 332 Outer area

Claims

1. a step of setting the temperature of a cathode in a thermionic electron gun, the thermionic electron gun having a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, the thermionic electron gun emitting an electron beam from the cathode toward the anode, to a predetermined value; Varying a bias voltage applied to the Wehnelt electrode while maintaining the temperature of the cathode at the predetermined value; a step of measuring an emission current when the bias voltage is changed while the temperature of the cathode is maintained at the predetermined value; a step of calculating a value obtained by dividing a rate of change of the emission current when the bias voltage is changed by an amount of change of the bias voltage as a determination parameter; Equipped with A method for adjusting an electron beam, characterized in that, while maintaining the temperature of the cathode at the predetermined value, a step of changing the bias voltage, a step of measuring the emission current, and a step of calculating the judgment parameter are repeated until the judgment parameter reaches a threshold value.

2. comparing the decision parameter with a threshold; When the determination parameter reaches the threshold value, the bias voltage is decreased to a negative side by a preset amount; 2. The method of claim 1, further comprising:

3. 3. The electron beam adjusting method according to claim 1, wherein the steps of changing the bias voltage, measuring the emission current, and calculating the judgment parameter are repeated so that the judgment parameter approaches the threshold value from a state where the judgment parameter is greater than the threshold value.

4. 3. The electron beam adjusting method according to claim 1, wherein each of said steps is performed at predetermined intervals.

5. a thermionic electron gun having a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, the thermionic electron gun emitting an electron beam from the cathode toward the anode; a temperature setting unit that sets the temperature of the cathode to a predetermined value; a bias voltage control unit that changes a bias voltage applied to the Wehnelt electrode while maintaining the temperature of the cathode at the predetermined value; an emission current measuring unit that measures an emission current when the bias voltage is changed while the temperature of the cathode is maintained at the predetermined value; a parameter calculation unit that calculates, as a determination parameter, a value obtained by dividing a rate of change of the emission current when the bias voltage is changed by an amount of change of the bias voltage; an irradiation mechanism for irradiating a sample with the electron beam emitted from the thermal electron gun; Equipped with repeating an operation of changing the bias voltage, an operation of measuring the emission current, and an operation of calculating the judgment parameter until the judgment parameter reaches a threshold value while maintaining the temperature of the cathode at the predetermined value; Electron beam device characterized by:

6. a thermionic electron gun having a cathode, an anode electrode controlled to have a positive potential relative to the cathode, and a Wehnelt electrode disposed between the cathode and the anode electrode and controlled to have a negative potential relative to the cathode, the thermionic electron gun emitting an electron beam from the cathode toward the anode, a process of setting the temperature of the cathode to a predetermined value; a process of measuring an emission current when a bias voltage applied to the Wehnelt electrode is changed while the temperature of the cathode is maintained at a predetermined value; storing the measured emission current in a storage device; a process of reading out the emission current from the storage device, and calculating a value obtained by dividing a rate of change of the emission current when the bias voltage is changed by an amount of change of the bias voltage as a judgment parameter; a process of repeating a process of changing the bias voltage, a process of measuring the emission current, and a process of calculating the judgment parameter until the judgment parameter reaches a threshold value while maintaining the temperature of the cathode at the predetermined value; A program that causes a computer to execute the following.

Images