JP5912835B2 - Electron gun, driving device thereof, and control method thereof - Google Patents

Description

The present invention relates to an electron gun used in a variable shaped electron beam lithography apparatus, a driving apparatus thereof, and a control method thereof, and more particularly, an electron gun which does not deteriorate current density uniformity even when the cathode shape and dimensions change, and the driving apparatus thereof And a control method thereof.

  The variable shaped electron beam drawing apparatus is an electron beam drawing apparatus using a beam having a large cross-sectional area and a variable cross-sectional shape and size. This apparatus is mainly used for drawing a photomask for manufacturing semiconductor elements. With the recent miniaturization of semiconductor elements and the like, the drawing accuracy required for the apparatus is increasing year by year.

  In order to improve the drawing accuracy of the apparatus, it is necessary to accurately control the exposure amount (product of current density and exposure time) given to the drawing material, that is, the material coated with the resist (photosensitive agent). . This is because the size of the figure transferred to the resist as a result of exposure depends on the exposure amount.

  In order to meet the above requirements, it is necessary to maintain high current density stability and uniformity of the electron beam for exposing the drawing material. This is because if the stability is lowered, the temporal variation of the dimension of the figure transferred to the resist becomes larger. If the uniformity is lowered, the dimension is caused by partial overexposure or underexposure of the figure. This is due to the increased error.

  The stability and uniformity depend on the electron gun that generates the electron beam and its control method. FIG. 1 shows a conventionally used electron gun and its driving device for a variable shaped electron beam drawing apparatus. The electron gun in the figure is a thermionic emission type electron gun. The control is based on a control method called a self-bias method.

  1 includes a cathode 1, an anode 2, a grid 3, a cathode heating power source 4, an acceleration voltage source 5, and a self (self) bias resistor 6, as shown in FIG. .

  The electron gun and the driving device generate the electron beam 7 and emit the beam from the opening of the anode 2 based on the above configuration. At that time, as shown in FIG. 1, the electron gun converges the same beam inside and ties a crossover 8 (a portion where the beam diameter is minimized).

  The above-described operation of the electron gun and the driving device is based on the operating principle of first generation of thermoelectrons from the cathode 1, second acceleration of the electron by acceleration voltage, and third limitation of emission current by bias voltage. based on. Here, the acceleration voltage and the bias voltage refer to voltages between the cathode 1 and the anode 2 and between the cathode 1 and the grid 3, respectively. The emission current refers to a current that flows from the cathode 1 to the anode 2.

  Among the above principles, first, the generation of the thermoelectrons is caused by supplying the output current of the cathode heating power source 4 to a heating element (not shown) brought into contact with the cathode 1. Second, the acceleration of the electrons is caused by applying the output voltage of the acceleration voltage source 5 between the cathode 1 and the anode 2 via the self-bias resistor 6. However, since the potential of the anode 2 is set to the ground potential in the same manner as the potential of the optical system and the drawing material thereafter, the sign of the potential of the cathode 1 is negative. Third, the emission current is limited because the voltage generated between both ends of the resistor due to the current flowing through the self-bias resistor 6 is used as the bias voltage. That is, the bias voltage in the above configuration is proportional to the emission current. However, since the sign of the emission current is negative, the potential of the grid 3 is lower than the potential of the cathode 1.

  A bias voltage depending on the emission current like the bias voltage is called a self-bias voltage. On the other hand, a bias voltage that does not depend on the emission current is called a fixed bias voltage.

  The bias voltage, that is, the self-bias voltage, provides negative feedback with respect to the emission current due to the above property. Therefore, even if any factor that can cause the current to fluctuate occurs, the fluctuation of the current can be kept small by this action of the self-bias voltage. The conventional electron beam drawing apparatus utilizes this fact to stabilize the emission current and, consequently, the current density of the electron beam.

  However, when a self-bias voltage is generated in the above configuration, as can be seen from FIG. 1, the potential on the negative side of the acceleration voltage source 4 is equal to the potential of the grid 3, but not the potential of the cathode 1. That is, as long as the emission current is not zero, the voltage between the cathode 1 and the anode 2, that is, the acceleration voltage is not equal to the output voltage of the acceleration voltage source 4 and depends on the emission current.

  Therefore, in practice, control (not shown) is performed on the above configuration so that the acceleration voltage is kept constant regardless of the emission current. Specifically, this control is based on detecting the potential of the cathode 1 and changing the output voltage of the acceleration voltage source 4 to compensate for the change.

JP-A-2005-26241

  In order to increase the current density stability of the electron beam in the conventional variable shaped electron beam drawing apparatus, that is, the electron beam 7 generated by the electron gun and the driving device of FIG. 1, as described above, However, control based on the self-bias method may be performed. On the other hand, in order to increase the current density uniformity for the beam, it is required to appropriately set the bias voltage for the electron gun. This is because the uniformity depends on the depth of the bias. Here, the depth of the bias represents the degree to which the bias voltage limits the emission current. That is, when the bias is deep, the emission current is strongly limited and decreases.

  The current density uniformity of the electron beam 7 depends on the bias depth. When the emission current is limited by the bias voltage in the above configuration, the emission region (thermionic emission region) in the cathode 1 is limited by the voltage. By. This region is localized near the tip of the cathode 1 in the normal use state of the electron gun.

  However, the size of the region depends on the tip diameter of the cathode 1. As can be seen from FIG. 1, the tip of the cathode 1 is processed flat. The reason why the tip is made flat in this way is that the cross-sectional area of the electron beam 7 on the material to be drawn, that is, the exposure area is as large as possible (the irradiation area of the shaped aperture plate described below is increased).

  The current density distribution of the electron beam 7 is shown in FIG. 2A shows the current density distribution when the bias is too shallow with respect to the electron gun of FIG. 1, FIG. 2B shows the current density distribution when the bias is too deep, and FIG. 2C shows the current density when the bias is appropriate.

  However, these current densities are the current density distribution of the electron beam 7 on the shaped aperture plate. Here, the molded aperture plate refers to a plate-like member having an aperture (a stop) for determining the shape and size of an exposure region by the same beam on the drawing material. Moreover, the area | region limited between two broken lines in each figure is equivalent to opening of the opening plate. That is, the current density distribution in the same region is reflected in the exposure amount distribution on the drawing material.

  When the bias is too shallow with respect to the electron gun, the current density distribution becomes concave as shown in FIG. In this case, the emission region in the cathode 1 is large and extends from the flat part of the cathode to the region on the root side. On the other hand, when the bias is too deep, a convex shape is formed as shown in FIG. In this case, the emission region in the cathode 1 is small and is located near the center of the flat portion. In any of these cases, the current density uniformity is low.

  However, when the bias is appropriate, such unevenness is neutralized, and the current density distribution becomes flat as shown in FIG. That is, the current density uniformity is increased. Strictly speaking, the distribution is not completely flat, but can be regarded as substantially flat in the above-mentioned region, ie, the opening of the shaped aperture plate.

  The current density uniformity of the electron beam 7 is increased by making the bias appropriate in this way, but the uniformity can change with time. This is because the cathode 1 is consumed over time as a result of the heating, and changes its shape and dimensions. Therefore, even if the bias is appropriate and the current density uniformity of the electron beam 7 is high at the start of use of the electron gun, the uniformity can subsequently decrease with the use time of the electron gun.

  FIG. 3 shows how the cathode 1 changes its shape and dimensions as it is consumed. FIG. 3A shows a change in shape and dimensions when the tip angle of the cathode 1 is large, and FIG. 3B shows a change in shape and dimensions when the tip angle is small.

  As can be seen from FIG. 3, as the cathode 1 is consumed, the tip of the cathode 1 retreats (moves toward the base side), and at the same time, the tip diameter decreases. In FIG. 3, t represents the retreat amount of the tip of the cathode, and d and d 'represent the tip diameters before and after the cathode is consumed.

  When the tip of the cathode 1 moves backward in this way, the distance from the tip of the cathode to the opening of the grid 3 increases. As a result, the potential near the tip of the cathode 1 decreases, and the emission region becomes smaller. This corresponds to a deeper bias.

  However, when the tip diameter of the cathode 1 becomes smaller at the same time, the bias becomes shallower accordingly. This is because as the tip diameter decreases, the emission region in the cathode 1 becomes smaller and the emission current decreases (self-bias becomes shallower).

  The bias change based on the latter mechanism becomes significant when the tip angle of the cathode 1 is small (FIG. 3B). This is because when the tip angle is small, the ratio of the tip diameter reduction amount Δd = d−d ′ to the tip retraction amount t is increased.

The invention according to claim 1 is a cathode for emitting electrons,
An anode for accelerating electrons emitted from the cathode;
A grid for connecting a crossover of electron beams generated from the cathode and limiting an emission current Ie flowing from the cathode;
A cathode heating power source for heating the cathode;
A bias voltage generator for applying a bias voltage Vb between the grid and the cathode, comprising a self-bias resistor and a fixed bias voltage applying means for applying a fixed bias voltage;
The product of the resistance of the self-bias resistor, that is, the self-bias resistor and the emission current Ie is a self-bias voltage,
A bias voltage generation unit in which the sum of the self-bias voltage and the fixed bias voltage is the bias voltage Vb ;
An electron gun and a driving device thereof,
The value of the bias voltage Vb to the maximum current density uniformity of the electron beam emanating from the cross-over to the optimum value of the bias voltage Vb,
The value of the emission current Ie flowing through the bias voltage Vb when fitted to the said optimum value and the optimum value of the emission current Ie,
The regression line Ie = Vb / C−D / C, that is, Vb = C · Ie + D, the first order term coefficient C, the constant term D, the self-bias resistance, An electron gun and a driving device thereof, wherein the fixed bias voltages are made to coincide with each other.

  The invention according to claim 2 is the electron gun and the driving device thereof according to claim 1, wherein the self-bias resistor and the fixed bias voltage are variable.

The invention described in claim 3 is a control method for the electron gun and the driving device thereof according to claim 2,
A first step of measuring current density uniformity of the electron beam at a plurality of time points with different degrees of consumption of the cathode;
A second step of identifying optimum values of the bias voltage Vb and the emission current Ie at the plurality of times and storing the optimum values;
A third step of determining the regression line for the optimal value;
A fourth step of causing the self-bias resistor and the fixed bias voltage to coincide with the coefficient C and the constant term D of the primary term,
And a method for controlling the driving device thereof.

  According to the first aspect of the present invention, with respect to an electron gun using a cathode having a predetermined shape and size, the current density uniformity of the electron beam generated by the electron gun is kept high regardless of the consumption of the cathode. Can do.

  According to the second aspect of the present invention, even if the shape and dimensions of the cathode used are changed, and the values of the coefficient C and the constant term D of the primary term of the regression line are changed accordingly, the self-bias resistance is changed to these values. And the fixed bias voltage can be matched. That is, it is possible to deal with cathodes having different shapes and dimensions.

  According to the third aspect of the present invention, the values of the self-bias resistor and the fixed bias voltage to be adopted in the first or second aspect of the invention can be determined.

It is a figure showing the general electron gun used for the conventional variable shaping | molding electron beam drawing apparatus. 3 is a diagram illustrating a current density distribution of an electron beam 7. FIG. It is a figure showing the change of the shape and dimension accompanying consumption of the cathode 1. FIG. It is a figure of the typical form for implementing this invention. It is a flowchart showing the flow of the setting of a self-bias resistance and a fixed bias voltage. It is a figure showing a mode that the 1st shaping | molding aperture plate 12 is scanned by the electron beam 7. FIG. It is a figure explaining transition of the optimum value of bias voltage Vb and emission current Ie accompanying consumption of cathode 1. FIG. It is a figure explaining the regression line Vb = C * Ie + D with respect to the optimal value of the bias voltage Vb and the emission current Ie in several time points from which the degree of consumption of the cathode 1 differs.

  Hereinafter, an example of a variable shaped electron beam drawing apparatus to which the present invention is applied will be described as a typical form for carrying out the present invention. The configuration of this apparatus is shown in FIG.

  As shown in FIG. 4, the apparatus includes an electron gun according to the present invention, a driving apparatus for the electron gun, an irradiation optical system (from the anode 2 to the first molded aperture plate 12), and a molded optical system (from the first molded aperture plate 12). (Up to the second shaping aperture plate 19), a reduction projection optical system (from the second shaping aperture plate 19 to the drawing material 16), and a control system for these.

  As shown in FIG. 4, the electron gun and its driving device of this apparatus include a cathode 1, an anode 2, a grid 3, a cathode heating power supply 4, an acceleration voltage source 5, a self-bias resistor 6, a fixed bias voltage source 9, and It consists of an emission ammeter 10.

  Among the above components, the cathode 1, the anode 2, the grid 3, the cathode heating power source 4, the acceleration voltage source 5, and the self-bias resistor 6 are the same as those in the electron gun and driving device of FIG. However, the resistance of the self-bias resistor 6 is variable.

  That is, the electron gun and its driving device of the present apparatus are obtained by adding a fixed bias voltage source 9 and an emission ammeter 10 to the electron gun and driving device of FIG.

  Among these, the fixed bias voltage source 9 applies a fixed bias voltage between the cathode 1 and the grid 3 separately from the bias voltage by the self-bias resistor 6, that is, the self-bias voltage. That is, the bias voltage in the electron gun of this apparatus is the sum of the self-bias voltage by the self-bias resistor 6 and the fixed bias voltage by the fixed bias voltage source 9. However, the output voltage of the same voltage source is variable. On the other hand, the emission ammeter 10 measures the emission current flowing in the above configuration.

  In the above configuration, the fixed bias voltage is generated by providing a current source between both ends of the self-bias resistor 6 or between the cathode 1 side end of the resistor and the ground instead of using the fixed bias voltage source 9. The output current of the source may be passed through the resistor together with the emission current. By doing so, a sum of a self-bias voltage and a fixed bias voltage is generated as a bias voltage between both ends of the resistor.

  The operation of the electron gun of this device and its driving device is basically the same as those of FIG. 1 except that the bias voltage is the sum of the self-bias voltage and the fixed bias voltage as described above. . That is, as a result of the electrons generated from the cathode 1 being accelerated by the acceleration voltage, the electron beam 7 is emitted from the opening of the anode 2. At that time, the emission current is limited by the bias voltage.

  The irradiation optical system of this apparatus converges the electron beam 7 supplied from the electron gun by the irradiation lens 11 and irradiates the first shaping aperture plate 12 with the beam. At that time, the irradiation lens 11 forms an image (not shown) of the first light source under the aperture plate.

  In addition to the above components, the optical system includes a blanker 13 and an irradiation aligner 14. Among these, the blanker 13 is an electrostatic deflector. The blanker controls the exposure time. A blanker power source (not shown) is connected to the blanker. When the same power source applies a voltage to the blanker, the electron beam 7 is deflected by the blanker and blocked by the non-opening portion of the blanking aperture plate 15. As a result, the electron beam 7 does not reach the drawing material 16. On the other hand, the irradiation aligner 14 is a magnetic field type deflector. The aligner controls the incident position of the electron beam 7 with respect to the opening of the first molded aperture plate 12. An aligner driving amplifier 17 is connected to the aligner. The amplifier supplies current to the aligner as needed.

  The shaping optical system of this apparatus projects an image of the opening of the first shaping aperture plate 12 irradiated by the electron beam 7 onto the second shaping aperture plate 19 by the shaping lens 18. At that time, the molded lens 18 forms an image (not shown) of the second light source at the height position of the blanking aperture plate 15.

  In addition to the above components, the optical system includes a shaping deflector 20. The deflector is an electrostatic deflector. The deflector moves the image of the opening with respect to the opening of the second shaping aperture plate 19, thereby controlling the shape and size of the figure generated by the overlap (logical product) of the image and the opening. A deflector drive amplifier (not shown) is connected to the deflector. The amplifier applies a voltage as necessary to the deflector.

  The optical system further has a function of measuring the current of the electron beam 7 incident on the second shaping aperture plate 19. For the measurement, a first electron beam ammeter 21 is connected to the second shaped aperture plate 19.

  The reduction projection optical system of the present apparatus uses the reduction lens 22 and the objective lens 23 to convert an image of the above-mentioned figure generated by the overlap of the opening image of the first shaping aperture plate 12 and the opening of the second shaping aperture plate 19. Project onto the drawing material 16. As a result, the drawing material 16 is exposed. At that time, the reduction lens 22 forms an image (not shown) of the third light source at the height position of the objective lens 23.

  In addition to the above components, the optical system is provided with an objective deflector 24. The deflector is an electrostatic deflector. The deflector draws a desired figure on the material by moving the figure image to an arbitrary position on the drawing material 16. A deflector drive amplifier (not shown) is connected to the deflector. The amplifier applies a voltage as necessary to the deflector.

  However, since the range in which the image is moved by the objective deflector 24 is limited (generally about 1 mm square), in order to draw a desired figure over a wide range on the drawing material 16, The material stage 25 is used together.

The material stage 25 is provided with a Faraday cup 26. A second electron beam ammeter 27 is connected to the Faraday cup 26. Accordingly, if the Faraday cup 26 is moved by the material stage 25 and the electron beam 7 is made incident thereon, the current of the electron beam 7 incident on the drawing material 16 can be measured during drawing. The current density of the beam can be calculated from the current and the cross-sectional area of the electron beam 7 on the drawing material 16, and the required exposure time can be calculated from the current density and the required exposure amount.

  The control system of this apparatus includes a control device 28, a storage device 29, and an arithmetic device 30. The control device 28 sets and controls the self-bias resistor 6 and the fixed bias voltage source 9 in addition to the lens, the deflector, and the aligners, and reads the measured values of the ammeters including the emission ammeter 10. The storage device 29 stores setting values, measured values, and calculation results related to the above elements. The computing device 30 performs computations necessary for the setting and control using the measured values and the data stored in the storage device 29.

  The flow of setting the self-bias resistor and the fixed bias voltage in the electron gun of this apparatus and its driving apparatus will be described below. Therefore, a flowchart showing the same flow is shown in FIG.

  First, the main routine (FIG. 5A) will be described. The control of the routine is performed by the control device 28, the numerical values related to the routine are stored in the storage device 29, and the calculation related thereto is performed by the arithmetic device 30.

Step M1: Set the self-bias resistance to the minimum value for use.
Step M2: The loop variable i is initialized. That is, i = 0.
Step M3: A subroutine is executed. The routine measures the current density unevenness U while swinging the fixed bias voltage, and specifies the optimum value of the fixed bias voltage, that is, the value of the fixed bias voltage that minimizes the current density unevenness U.

  Step M4: When the fixed bias voltage is set to the optimum value, it is determined whether the current density uniformity U is less than the reference ε, that is, whether U <ε can be satisfied. If this is not satisfied, the main routine is terminated, but if it is satisfied, the process proceeds to step M5.

Step M5: a fixed bias voltage is set to the optimum value Vf _i. At this time, the current density uniformity is the highest.

Step M6: The emission current Ie _i is measured and stored. Hereinafter, Ie _i is the optimum value of the emission current.

Step M7: Calculate and store the optimum bias voltage Vb _i = Rb _i · Ie _i + Vf _i . Here, Rb _i represents the value of the self-bias resistance, but at this point it is not yet the optimum value.

  Step M8: Determine if i = 0. If i = 0, the process proceeds to Step M16, but if i = 0, the process proceeds to Step M9.

  Step M9: A timer provided in the control device 28 is initialized.

  Step M10: Operate this apparatus for its original purpose. That is, drawing is performed on the drawing material 16. At that time, the current of the electron beam 7 is appropriately measured by the Faraday cup 26, and the necessary exposure time is calculated each time.

  Step M11: When the step M10 is completed, the timer is referred to and it is determined whether a predetermined time (for example, one week) has elapsed. If the predetermined time has not elapsed, the process returns to step M10, and the operation of the apparatus is continued. If it has elapsed, the process proceeds to step M12.

  Step M12: The distribution of current density J is measured. Therefore, a deflection signal is sent to the aligner driving amplifier 17, the electron beam 7 is deflected by the irradiation aligner 14 through the amplifier, and the first shaped aperture plate 12 is scanned by the beam as shown in FIG. At that time, the electron beam 7 that has passed through the opening of the first shaping aperture 12 is made incident on the non-opening portion of the second shaping aperture plate 19, and the current of the beam is measured by the first electron beam ammeter 21. To do. (If necessary, the beam is deflected by the shaping deflector 20 so that the beam does not pass through the opening of the second shaping aperture plate 19). This is stored together with the deflection amount of the electron beam 7 by the irradiation aligner 14.

Step M13: Current density unevenness U is calculated. The unevenness U is defined as Jmax as the maximum value of the current density obtained in step M12, and Jmin as the minimum value.
U = | (Jmax−Jmin) / Jmax | (Formula 1)
Calculate according to

  Step M14: It is determined whether the current density uniformity U is less than the reference ε, that is, whether U <ε is satisfied. If this is satisfied, the process returns to Step M9, but if not satisfied, the process proceeds to Step M15.

  Step M15: Increase the value of the loop variable i by 1.

Step M16: Unless i = 0 in Step M8, the optimum values Rb _i and Vf _i of the self-bias resistor and the fixed bias voltage are calculated. The optimum values Rb _i and Vf _i are
Vb _i-1 = Rb _i · Ie _i-1 + Vf _i-1 (Formula 2)
Vb _i = Rb _i · Ie _i + Vf _i (Formula 3)
To solve the problem. That is, two points _{(Vb i-1, Ie i} -1) and _{(Vb i,} Ie i) determining a linear _{Vb = Rb i · Ie + Vf} i that passes through the.

Step M17: setting a self-bias resistor and a fixed bias voltage to the optimum values Rb _i and Vf _i.

  The above is the entire process of the main routine. By these steps, the current density unevenness of the electron beam 7 can be reduced, that is, the current density uniformity can be kept high regardless of the consumption of the cathode.

  Next, the subroutine (FIG. 5B) will be described. The control of the routine is performed by the control device 28, the numerical values related to the routine are stored in the storage device 29, and the calculation related thereto is performed by the arithmetic device 30.

  Step S1: A fixed bias voltage is set to a maximum value in use.

  Step S2: The distribution of the current density J is measured. The measurement is performed by the same method as in step M12.

  Step S3: The current density unevenness U is calculated from the above distribution and stored together with the value of the fixed bias voltage. The calculation is performed by the same method as that in step M13.

  Step S4: Determine whether the fixed bias voltage is the minimum value in use. If it is not the minimum value, the process proceeds to step S5. If it is the minimum value, the process proceeds to step S6.

  Step S5: Decrease the fixed bias voltage by one step.

  Step S6: The optimum value of the fixed bias voltage, that is, the value of the fixed bias voltage that minimizes the current density unevenness U is specified from the data of the current density unevenness U and the fixed bias voltage stored in Step S3.

  The above is the whole process of the subroutine. Through these steps, the current density unevenness U of the electron beam 7 is measured while swinging the fixed bias voltage, and the optimum value of the fixed bias voltage, that is, the value of the fixed bias voltage that minimizes the current density unevenness U of the beam is specified. be able to.

  FIG. 7 shows how the bias voltage Vb and the emission current Ie change due to the execution of the main routine and subroutine. However, for convenience, the signs of the bias voltage Vb and the emission current Ie are positive. That is, when the value of the bias voltage Vb is large in the positive direction, the bias is deep.

In FIG. 7, the three points (Vb ₀ , Ie ₀ ), (Vb ₀ ′, Ie ₀ ′), and (Vb ₁ , Ie ₁ ) are points (Vb, The coordinates of Ie) immediately after the step M5 (i = 0), immediately before the step M17 (i = 1), and immediately after the step M17 (i = 1) are represented. A straight line passing through the two points (Vb ₀ , Ie ₀ ) and (Vb ₁ , Ie ₁ ) corresponds to the straight line Vb = Rb ₁ · Ie + Vf ₁ determined in step M16. This straight line can be interpreted as representing the sum of the optimum value Rb ₁ · Ie of the self-bias voltage and the optimum value Vf ₁ of the fixed bias voltage.

The point (Vb, Ie) is first point with consumption of the cathode 1 _{(Vb 0,} Ie 0) from point _{(Vb 0 ', Ie 0'} ) moves in. As can be seen from FIG. 7, since Vb ₀ ′ <Vb ₁ , the bias is shallow at the point (Vb ₀ ′, Ie ₀ ′). Therefore, the current density distribution at this point is concave (see FIG. 2A).

Next, the point (Vb, Ie) moves from the point (Vb ₀ ′, Ie ₀ ′) to the point (Vb ₁ , Ie ₁ ) as a result of setting the self-bias resistor and the fixed bias resistor to the optimum values. However, the movement follows the broken line on the left side in FIG. The broken line in the figure represents the bias voltage dependence of the emission current.

The above point (Vb ₀ ′, Ie ₀ ′) does not coincide with the point (Vb ₁ , Ie ₁ ) because the values of the self-bias resistance and the fixed bias voltage are respectively optimum from step M1 to immediately before step M17. This is because the values Rb ₁ and Vf ₁ do not match.

However, if Rb ₀ coincides with Rb ₁ before the process M5, the movement of the point (Vb, Ie) accompanying the consumption of the cathode 1 is approximately the straight line Vb = Rb ₁ · Ie + Vf ₁ Should be along. This should also apply to step M15 and subsequent steps. This is the reason why the values Rb ₁ and Vf _{1 of the} self-bias resistance and the fixed bias voltage determined in step M16 are the optimum values.

In the above routine, Rb ₀ is the minimum value for use of the self-bias resistor (step M1), but instead, it may be an empirically obtained optimum value of the self-bias resistor. By doing so, the point (Vb ₀ ′, Ie ₀ ′) approaches the point (Vb ₁ , Ie ₁ ). That is, after the step M5, a state with high current density uniformity continues for a long time.

Such an optimum value of the self-bias resistor includes a regression line Ie = Vb / for the optimum values Vb _i and Ie _i (i = 0, 1, 2,...) Of the bias voltage and emission current obtained in the past. C−D / C, that is, Vb = C · Ie + D (Formula 4)
The coefficient C of the first-order term may be selected. This is because the first and second terms of (Equation 4) correspond to the optimum value of the self-bias voltage and the optimum value of the fixed bias resistor, respectively. The straight line is shown in FIG. 8 together with the optimum values Vb _i and Ie _i (i = 0, 1, 2,...) Of the bias voltage and the emission current. However, for convenience, the signs of the bias voltage Vb and the emission current Ie are positive.

If the number of samples of the optimum value is limited to 2, the above method is the method of step M16, that is, a straight line Vb = Rb passing through two points (Vf _i−1 , Ie _i−1 ) and (Vf _i , Ie _i ). _This is equivalent to the method of determining _i · Ie + Vf _i . That is, the straight line determined in step M16 is a special example of the regression line.

  As described above, in the present invention, the self-bias resistor and the fixed bias voltage are set to the optimum values obtained from the regression lines with respect to the optimum values of the bias voltage and the emission current at a plurality of time points with different degrees of consumption of the cathode 1. Set. Therefore, the current density uniformity of the electron beam 7 can be kept high regardless of the consumption of the cathode 1.

DESCRIPTION OF SYMBOLS 1 ... Cathode 2 ... Anode 3 ... Grid 4 ... Cathode heating power supply 5 ... Acceleration voltage source 6 ... Self bias resistor 7 ... Electron beam 8 ... Crossover 9 ... Fixed bias voltage source 10 ... Emission ammeter 11 ... Irradiation lens 12 ... 1st shaping | molding aperture plate 13 ... Blanker 14 ... Irradiation aligner 15 ... Blanking aperture plate 16 ... Drawing material 17 ... Aligner drive amplifier 18 ... Molding lens 19 ... 2nd shaping aperture plate 20 ... Molding deflector 21 ... 1st Electron beam ammeter 22 ... reduction lens,
DESCRIPTION OF SYMBOLS 23 ... Objective lens 24 ... Objective deflector 25 ... Material stage 26 ... Faraday cup 27 ... Second electron beam ammeter 28 ... Control device 29 ... Storage device 30 ... Arithmetic device

Claims (3)

A cathode that emits electrons;
An anode for accelerating electrons emitted from the cathode;
A grid for connecting a crossover of electron beams generated from the cathode and limiting an emission current Ie flowing from the cathode;
A cathode heating power source for heating the cathode;
A bias voltage generator for applying a bias voltage Vb between the grid and the cathode, comprising a self-bias resistor and a fixed bias voltage applying means for applying a fixed bias voltage;
The product of the resistance of the self-bias resistor, that is, the self-bias resistor and the emission current Ie is a self-bias voltage,
A bias voltage generation unit in which the sum of the self-bias voltage and the fixed bias voltage is the bias voltage Vb ;
An electron gun and a driving device thereof,
The value of the bias voltage Vb to the maximum current density uniformity of the electron beam emanating from the cross-over to the optimum value of the bias voltage Vb,
The value of the emission current Ie flowing through the bias voltage Vb when fitted to the said optimum value and the optimum value of the emission current Ie,
The regression line Ie = Vb / C−D / C, that is, Vb = C · Ie + D, the first order term coefficient C, the constant term D, the self-bias resistance, An electron gun and a driving apparatus thereof, wherein the fixed bias voltages are made to coincide with each other. The electron gun and its driving device according to claim 1, wherein the self-bias resistor and the fixed bias voltage are variable. A control method for the electron gun and its driving device according to claim 2,
A first step of measuring current density uniformity of the electron beam at a plurality of time points with different degrees of consumption of the cathode;
A second step of identifying optimum values of the bias voltage Vb and the emission current Ie at the plurality of times and storing the optimum values;
A third step of determining the regression line for the optimal value;
A fourth step of causing the self-bias resistor and the fixed bias voltage to coincide with the coefficient C and the constant term D of the primary term,
And an electron gun control method.

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