JP4545284B2 - High voltage power circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-voltage power supply circuit that supplies a high-voltage current to an electron beam apparatus such as an electron beam exposure apparatus.
[0002]
[Prior art]
Conventionally, in an electron beam exposure apparatus that performs fine processing by irradiating an electron beam, an electron beam apparatus as shown in FIG. 3 has been used.
[0003]
Such an electron beam apparatus includes an electron gun having a cathode 1 connected to a negative electrode of a high-voltage power supply (not shown), a Wehnelt 2 connected to a bias power supply (not shown), and an anode 3 connected to a positive electrode of a high-voltage power supply. I have. As the high-voltage power source, a Cockcroft Walton circuit is used, and the positive electrode side is grounded.
[0004]
Here, the electrons jumping out from the cathode 1 are drawn out by the anode 3 and become an electron beam 4 accelerated after passing through holes provided in the Wehnelt 2 and the anode 3, and further converged by the electromagnetic lenses 7 and 8. A point on the sample 9 is irradiated. Further, by adjusting the bias voltage applied between the cathode 1 and the Wehnelt 2, the intensity of the electron beam can be adjusted. Furthermore, the electron beam 4 normally passes through the aperture 6 aperture. However, during the period when the sample 9 is not irradiated, a current is passed through the blanking coil 5 to deflect the electron beam 4 so that the aperture 6 The electron beam 4 can be blocked by preventing the electron beam 4 from passing through the hole.
[0005]
Such an electron beam exposure apparatus can perform fine processing by exposing the resist applied to this portion to light when the electron beam 4 is irradiated to one point on the sample 9 and developing the resist. Therefore, it is often used for processing of a wafer that becomes an LSI substrate, for example.
[0006]
In order to process a wafer or the like, it is necessary to accurately know the origin position drawn on the wafer or the like. For this purpose, when the electron beam 4 irradiates the origin on the sample 9 and when it irradiates other portions, the state of secondary electrons jumping out from the sample 9 is different. The electron beam 4 was scanned, the secondary electrons jumping out from the sample 9 were detected by the secondary electron detector 24, and the origin position was obtained by obtaining an image from the detection signal by the observation system.
[0007]
In order to amplify the detection signal, the lock-in amplifier 27 is used in order to reduce the change in the operating state of the amplifier due to the influence of the power supply voltage, temperature, or the like, that is, to reduce the drift or to make it strong against noise. A lock-in amplifier takes out only the target input signal from the input signal buried in noise by multiplying the AC input signal by a signal synchronized with the same frequency as the input signal, and narrows the vicinity of this frequency. It amplifies the band. The detection signal from the secondary electron detector 24 is blocked by the capacitor 25 so as to have only a direct current component, is amplified by the preamplifier 26, and is input to the lock-in amplifier 27.
[0008]
Therefore, in order to operate the lock-in amplifier 27, conventionally, a high-frequency rectangular wave or sine wave is applied from the oscillator 22 to the blanking coil 5 and the lock-in amplifier 27. Then, when no current flows through the blanking coil 5, the electron beam 4 goes straight and passes through the hole of the aperture 6, irradiates the sample 9, causes secondary electrons to jump out of the sample 9, and the blanking coil 5. When an electric current flows through the electrode 9, the electron beam 4 is deflected and cannot pass through the hole of the aperture 6, and does not irradiate the sample 9, so that secondary electrons do not jump out of the sample 9. Therefore, the secondary electron detector 24 generates a high frequency detection signal synchronized with the same frequency as the high frequency output from the oscillator 22. The lock-in amplifier 27 multiplies the detection signal from the secondary electron detector 24 by the high-frequency output from the oscillator 22 synchronized with the same frequency as the detection signal, thereby detecting the detection signal buried in noise. Amplify and output only the target detection signal. An image can be obtained from the output of the lock-in amplifier 27 by the observation system, and the origin position drawn on the wafer or the like can be accurately obtained.
[0009]
However, when the electron beam 4 is shaken, the origin position is also shaken, and the accuracy of the origin position is limited. Moreover, if the electron beam 4 is deflected and blocked by the aperture 6, the aperture 6 is heated by the electron beam 4 and melted. In order to solve such a problem, the present applicant has disclosed the following invention (hereinafter referred to as the prior invention) in Japanese Patent Application No. 11-347623.
[0010]
The electron beam apparatus of the prior invention will be described with reference to FIG. In FIG. 4, the portions denoted by the same reference numerals as those in FIG. 3 are the same as those in the conventional electron beam apparatus, and thus the description thereof is omitted.
[0011]
In the invention of the prior application, in order to change the intensity of the electron beam in synchronism with the high frequency output from the oscillator 22, the high frequency alternating voltage output from the oscillator 22 is applied between the cathode 1 and Wehnelt 2. The application circuit is different from the conventional electron beam apparatus shown in FIG.
[0012]
In the prior application invention, the negative electrode of the high-voltage power supply 11 is connected to the cathode 1 via the bias resistor 13, and the positive electrode of the high-voltage power supply 11 is grounded. The positive electrode of the bias power source 12 and one end of the bypass capacitor 14 are coupled to both ends of the bias resistor 13. The negative electrode of the bias power source 12 and the other end of the bypass capacitor 14 are connected to one end of the secondary winding of the step-up transformer 15. Are connected. The other end of the secondary winding of the step-up transformer 15 is connected to the Wehnelt 2. The bias resistor 13 has a function of stabilizing the intensity of the electron beam 4 by generating a self-bias voltage by a current flowing therethrough and applying the self-bias voltage to a fixed bias voltage by the bias power source 12.
Both ends of the primary winding of the step-up transformer 15 are connected to both ends of a core wire 17 of a coaxial cable that is a secondary winding of the insulating transformer 16. The insulation transformer 16 is obtained by bending a single coaxial cable inserted into the ring-shaped core 21 into a substantially U shape, the shield 19 is a primary winding, and the core wire 17 is a secondary winding. ing. An insulator 18 is interposed between the shield 19 and the core wire 17, and the outside of the shield 19 is covered with an insulating cover 20. By changing the number of the ring-shaped cores 21, the mutual inductance of the insulating transformer 16 can be changed. Both ends of the shield 19 that is the primary winding of the insulating transformer 16 are connected to the oscillator 22.
[0013]
Here, the frequency of the alternating voltage applied between the cathode 1 and the Wehnelt 2 is a high frequency of about 1 MHz, and the step-up ratio required for the insulation transformer 16 is a small value of about 1, so that even with such an insulation transformer 16. Work well. The step-up transformer 15 has a step-up ratio of about several tens to 100 and is disposed close to the cathode 1 and the Wehnelt 2. Then, the secondary side wiring portion of the step-up transformer 15 through which a large amplitude high frequency (about 50-100 V) flows becomes as short as possible, and the primary side wiring portion of the step-up transformer 15 having a relatively long wiring has a small amplitude high frequency. Therefore, the high frequency output from the oscillator 22 hardly affects the acceleration voltage of the electron beam 4 and can perform a stable operation.
[0014]
One end of the primary winding of the step-up transformer 15 connected to the core wire 17 that is the secondary winding of the insulating transformer 16 is connected to the cathode 1, and one end of the shield 19 that is the primary winding of the insulating transformer 16 is grounded. Has been. For this reason, a high voltage is applied between the core wire 17 of the insulating transformer 16 and the shield 19. However, since the insulator 18 of the coaxial cable used for the insulating transformer 16 has a very good insulating property even at a high voltage, it can sufficiently withstand such a high voltage between the core wire 17 and the shield 19. Therefore, the oscillator 22 can be completely insulated from the high-voltage power supply 11 and high voltage can be prevented from being applied between the primary winding and the secondary winding of the step-up transformer 15, and the special step-up transformer 15 and the oscillator 22 are used. There is no need to use the inexpensive step-up transformer 15 and the oscillator 22.
[0015]
Here, the operation of the electron beam apparatus according to the invention of the prior application will be described. The high frequency output from the oscillator 22 is applied to the Wehnelt 2 and the negative electrode of the bias power source 12 through the insulating transformer 16 and the step-up transformer 15. Then, a voltage obtained by adding a bias voltage and a high-frequency alternating voltage output from the step-up transformer 15 is applied between the cathode 1 and the Wehnelt 2. Then, since the voltage applied between the cathode 1 and the Wehnelt 2 fluctuates with the same waveform as the high frequency output from the oscillator 22, the intensity of the electron beam 4 and the secondary that jumps out of the sample 9 due to the irradiation of the electron beam 4. The number of electrons and the detection output from the secondary electron detector 24 are modulated by the high-frequency alternating voltage output from the oscillator 22. Accordingly, since the lock-in amplifier 27 receives the detection output from the secondary electron detector 24 and the high frequency output from the oscillator 22 synchronized with the same frequency as the detection output, the lock-in amplifier 27 can input the target signal from the input signal buried in noise. Only the detected output can be amplified and extracted. At this time, since the electron beam 4 is not shaken as in the conventional case, the image obtained by the secondary electron detection is not shaken, the origin position drawn on the sample 9 or the like can be accurately detected, and high-precision processing is performed. Can do. The structure of the conventional electron beam apparatus is not changed, and the aperture 6 is not melted because the electron beam 4 does not irradiate the aperture 6.
[0016]
[Problems to be solved by the invention]
By the way, in the electron beam apparatus according to the invention of the prior application shown in FIG. 4, the electron beam 4 is turned on and off by applying an alternating voltage between the cathode 1 and the Wehnelt 2. For example, if a pulsed electron beam 4 of 1.6 mA from a cathode 1 having a potential of 100 kV is emitted in a period of 600 μs including a blanking period of 60 μs, the electron beam 4 is emitted for 540 μs. The electron beam 4 is turned off for 60 μsec.
[0017]
Here, the internal resistance of the high-voltage power supply 11 is 180 kΩ, the bias resistance is 100 kΩ, and the capacitance of the cathode-side wiring portion 31 of the high-voltage power supply 11 is 3000 pF for the cable itself and 1300 pF in addition, and 4300 pF as a whole. 5, an equivalent circuit such as that shown in FIG. 5 comprising the high-voltage power supply 11, the resistor R, the capacitor C, and the load L (electron beam 4) is obtained.
[0018]
When the electron beam 4 is ON and the cathode current is 1.6 mA and the cathode potential is −100 kV, a voltage drop of 448 V occurs in the resistor R, and the potential of the negative electrode of the high-voltage power supply 11 is −100.448 kV. Become. If the electron beam 4 is suddenly turned off from this state, the capacitor C is charged by the high voltage power supply 11 via the resistor R due to the potential difference E = 448 V between the negative electrode of the high voltage power supply 11 and the negative electrode side of the capacitor C. The cathode potential changes. The change ΔE in cathode potential t seconds after the electron beam 4 is turned off is
ΔE = E * (1−exp (−t / (CR))) (1)
Therefore, if E = 448, t = 60 * 10 ⁻⁶ , R = 280 * 10 ³ , and C = 4300 * 10 ⁻¹² are substituted into the equation (1), ΔE = 22.4V is obtained.
[0019]
Thus, every time the electron beam 4 is turned on and off, the potential of the cathode 1 changes by about 22 V. However, if the potential of the cathode 1 fluctuates, the energy width of the electron beam 4 becomes wider. There is a problem that when a wafer or the like is irradiated by the apparatus, defocusing occurs and it becomes impossible to draw a fine pattern.
[0020]
In view of this, a high voltage power supply circuit is provided in which an electron beam device is turned on and off so that the cathode potential does not fluctuate even when current is interrupted.
[0021]
[Means for Solving the Problems]
In order to solve the above problems, in the invention according to claim 1, in a high-voltage power supply circuit having a cathode-side wiring section for supplying a high-voltage current from a high-voltage power supply to the cathode of the electron beam apparatus, a capacitor is provided in the cathode-side wiring section. The current source is connected to the cathode side wiring portion when the electron beam is turned off, and the current source is caused to flow backward from the cathode side wiring portion when the electron beam is turned on. The electric potential of was kept constant.
In the invention according to claim 2, in the invention according to claim 1, the current source is a differential amplifier, and one end of the input side of the differential amplifier is connected to the cathode side wiring section via a capacitor. The other end of the input side is connected to the reference potential generator.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
First, the principle of the present invention will be described with reference to the circuit shown in FIG. In order to prevent the potential of the cathode 1 from fluctuating, a constant current always flows through the resistor R in FIG. 2 so that the voltage drop at the resistor R is always constant. For this reason, the circuit of FIG. 2 is provided with a current source 52 ′ for supplying current to the cathode side wiring portion 31. The cathode side wiring section 31 is divided into a capacitor 56 corresponding to the electrostatic capacity of the cable itself and a capacitor 54 corresponding to other electrostatic capacity, and the current source 52 ′ is connected to the cathode side wiring via the capacitor 54. Connected to the unit 31. The capacitor 54 prevents high-voltage direct current from flowing directly into the current source 52 '. The rest is the same as the circuit of FIG.
[0023]
When the capacitance of the capacitor 54 is set to 1300 pF and a current i of 1.6 mA is caused to flow from the current source 52 ′ to the cathode side wiring portion 31 through the capacitor 54, the capacitor 54 is charged by the current i. The increase ΔE in the potential difference across the capacitor t seconds after the current i starts to flow into the capacitor of the capacitance C
ΔE = i * t / C (2)
Therefore, substituting i = 1.6 * 10 ⁻³ , t = 60 * 10 ⁻⁶ , and C = 1300 * 10 ⁻¹² into the expression (2), the capacitor after 60 μsec from the expression (2) Therefore, the potential difference between both ends of 54 increases by 73.85V.
[0024]
However, such a potential difference cannot be continuously increased every blanking. Therefore, the capacitor 54 is discharged during 540 μsec when the electron beam 4 is turned on, that is, the current flows backward from the cathode side wiring section 31 to the current source 52 ′ so that the potential difference between both ends of the capacitor 54 is reduced by 73.85 V. That's fine. At this time, the output current of the current source 52 ′ is set to have an inverse ratio of the ON and OFF times of the electron beam 4 when the electron beam 4 is ON and OFF, respectively. That is, when the output current of the current source 52 ′ when the electron beam 4 is OFF is i, the output current of the current source 52 ′ when the electron beam 4 is ON is −i / 9. Now, assuming that the output current of the high-voltage power supply 11 is I and the cathode current is I ′,
When the electron beam 4 is ON I = I′−i / 9 (3)
When the electron beam 4 is OFF I = i (4)
Because
I ′ = (10/9) * i = (10/9) * I (5)
It becomes. Here, if the output current I of the high voltage power supply 11 is 1.6 mA, the output current i of the current source 52 ′ is 1.6 mA when the electron beam 4 is OFF, and the output of the current source 52 ′ is when the electron beam 4 is ON. The current −i / 9 may be −0.18 mA, and the cathode current I ′ at this time is 1.78 mA.
[0025]
Thus, when the current source 52 'supplies current, a constant output current I always flows through the high-voltage power supply 11 and the resistor R, and the voltage drop due to the resistor R is constant, so that the potential of the cathode 1 is also always constant. Can be kept in. As such a current source 52, any current source having constant current characteristics may be used, but an amplifier is particularly suitable. The reason is that the ON / OFF of the electron beam 4 is detected by an appropriate sensor, and a signal from this sensor is input to the amplifier, so that the output current of the amplifier is increased at a high speed according to the ON / OFF of the electron beam 4. It is because it can switch to. The various numerical values described above are merely given as examples, and it goes without saying that in an actual electron beam apparatus, these numerical values change depending on the specifications.
[0026]
A preferred embodiment of the high-voltage power supply device of the present invention is shown in FIG. In this embodiment, a differential amplifier 52 is used as the current source 52 ′ in the circuit of FIG. The differential amplifier 52 has a voltage amplification unit 60 and an output stage 64 including two transistors 61 and 62 having complementarity and a load resistor 63, and the output stage 64 is connected to the cathode side via a capacitor 54. In addition to being connected to the wiring section 31, it is connected to a + power supply V + and a -power supply V-. One of the input sides of the differential amplifier 52 is connected to the cathode-side wiring section 31 via the capacitor 51, and the other input side of the differential amplifier 52 is connected to the reference potential generator 58. Similarly to the capacitor 54, the capacitor 51 is also for preventing a high-voltage direct current from flowing directly from the cathode side wiring portion 31 to the differential amplifier 52, and allowing a sufficiently lowered voltage to be input to the differential amplifier 52. The rest of the configuration is the same as that of the prior application invention shown in FIG.
[0027]
Here, the operation of the electron beam apparatus of the present embodiment will be described. When the electron beam 4 is ON, the potential of the cathode 1 is higher than the negative electrode of the high voltage power source 11 by a voltage drop due to the bias resistor 13 and the internal resistance of the high voltage power source 11. The reference potential input from the reference potential generator 58 to the differential amplifier 52 is equal to the potential input from the cathode side wiring unit 31 to the differential amplifier 52, and the potential of the cathode 1 is accurately set to the set value. It is assumed that
[0028]
Here, when the electron beam 4 is turned off and the cathode current is interrupted, the voltage drop due to the internal resistance of the bias resistor 13 and the high-voltage power supply 11 is reduced, and the potential of the cathode 1 approaches the potential of the negative electrode of the high-voltage power supply 11. Lower. Then, on the input side of the differential amplifier 52, the potential input from the cathode side wiring portion 31 becomes lower than the reference potential, and the differential amplifier 52 sends a current to the cathode side wiring portion 31 in accordance with the potential difference therebetween. Let it flow. When the potential input from the cathode side wiring section 31 to the differential amplifier 52 becomes equal to the reference potential, the differential amplifier 52 does not output current, so that the potential of the cathode 1 can be controlled to the set value.
[0029]
Next, when the electron beam 4 is turned on and a cathode current flows, a voltage drop due to the internal resistance of the bias resistor 13 and the high-voltage power supply 11 increases, and the potential of the cathode 1 rises. Then, on the input side of the differential amplifier 52, the input from the cathode side wiring portion 31 becomes larger than the reference potential, and the differential amplifier 52 causes the current to flow backward from the cathode side wiring portion 31 according to the potential difference between the two. When the potential input from the cathode side wiring section 31 to the differential amplifier 52 becomes equal to the reference potential, the differential amplifier 52 does not output current, so that the potential of the cathode 1 can be controlled to the set value.
[0030]
As described above, in this embodiment, the feedback circuit composed of the differential amplifier 52 and the capacitors 51 and 54 can always keep the potential of the cathode 1 stably at the set value. The spread of energy width can be eliminated. Therefore, by using the high-voltage power supply circuit of this embodiment, an electron beam exposure apparatus capable of drawing a fine pattern without causing blurring when a wafer or the like is irradiated by the electron beam apparatus can be obtained at low cost.
[0031]
The high-voltage power supply circuit of the present invention can be widely used not only for the electron beam device of the prior invention but also for electron beam devices using electron beams such as electron microscopes as well as conventional electron beam devices.
[0032]
【The invention's effect】
As is apparent from the above description, according to the first aspect of the invention, since the output current from the high-voltage power supply does not change between when the electron beam is turned on and off, the cathode potential is always kept constant. And the spread of the energy width of the electron beam due to the fluctuation of the cathode potential can be eliminated. Therefore, the electron beam apparatus equipped with the high-voltage power supply circuit of the present invention does not generate blur when a wafer or the like is irradiated, and a fine pattern can be drawn.
According to the second aspect of the present invention, since the feedback circuit including the differential amplifier and the capacitor is provided, the cathode potential can be more stably maintained at the set value.
[Brief description of the drawings]
FIG. 1 shows a preferred embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating the principle of the present invention.
FIG. 3 is a diagram showing a main part of a conventional electron beam generator.
FIG. 4 is a diagram showing a main part of an electron beam generator of the prior invention of the present applicant.
FIG. 5 is a diagram showing an equivalent circuit of the electron beam generator shown in FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Cathode 2 Wehnelt 4 Electron beam 11 High voltage power supply 31 Cathode side wiring part 51 Capacitor 52 Differential amplifier 52 'Current source 54 Capacitor

Claims (2)

In a high voltage power supply circuit having a cathode side wiring section for supplying a high voltage current from the high voltage power supply to the cathode of the electron beam device,
A current source connected to the cathode-side wiring part via a capacitor; the current source flows current into the cathode-side wiring part when the electron beam is off; and from the cathode-side wiring part when the electron beam is on A high-voltage power supply circuit characterized in that a current flows backward to keep the cathode potential constant. The current source is a differential amplifier, and the differential amplifier has one end on the input side connected to the cathode side wiring section via a capacitor and the other end on the input side connected to a reference potential generator. The high-voltage power supply circuit according to claim 1, wherein

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