JP2868595B2 - Current control circuit in electron beam equipment - Google Patents

Description

The present invention relates to a current control circuit for controlling a current supplied to a load coil such as a lens coil and a deflection coil used in an electron beam device such as an electron microscope. More particularly, the present invention relates to a current control circuit in an electron beam apparatus that changes a current supplied to a load coil by switching control of a reference resistor.

[Prior Art] Conventionally, a current control circuit in an electron microscope or the like having a configuration as shown in FIG. 6 has been known.

In FIG. 6, reference numeral 1 denotes a signal generation source. Output signal V _ref of the signal source 1 is supplied to the D-A converter 12, the output Vi output resistor R _i, feedback resistor R _f, an operational amplifier 2 and the load coil, for example a lens coil 3, a plurality Reference resistor
It is applied to the input section A of the constant current circuit 4 composed of R _{1 to} R _n . The reference resistor R ₁ to R _n is, for example, different resistors of resistance value _{(R 1 <R 2 <......} <R n) is composed of each relay switch RY ₁ to Ry _n in the said resistor Is connected. The relay switches RY _{1 to} RY _n are turned on / off based on a control signal from the switch switching circuit 5.

By selecting a resistor R ₁ to R _n is turned on / off the relay switch RY ₁ to Ry _n by switching the switching circuit 5 is a current control circuit having such a configuration, the current I ₀ flowing through the lens coil 3 Can be changed. Therefore, keep the change in the output signal of the signal source 1 to a constant variation width by D-A converter 12, continuously over several orders of magnitude the resistor by switching the relay switch RY ₁ to Ry _n to R ₁ to R _n The current flowing through the lens coil 3
I ₀ can be continuously varied from the maximum value to the minimum value.

[Problems to be Solved by the Invention] Now, in the current control circuit having the configuration described above,
Output current with the maximum value of the output current I ₀ of the lens coil as 1
I ₀ is linearly changed from the maximum value with time to 10 ⁻¹ , 10 ⁻² ,.
When changing the ^-n, first, with the reference resistor R ₁ is connected varies Figure 7 (b) to indicate such a certain variation (for example, from 1 to 0 in absolute value display) DA
When the output signal Vi of the converter 12 is supplied to the operational amplifier via an input resistor R _i, the output current I ₀ as shown in FIG. 7 (a)
Decreases from a maximum of 1 to 10 ^-1 . In conjunction to the decrease of the output current, at the same time RY ₂ when the relay switch RY ₁ is turned off based on a control signal from the switch switching circuit 5 at time t ₁ as shown in FIG. 7 (c) is turned on Resistor
R ₂ is selectively connected. Also, as shown in FIG. 3B, the output signal Vi of the DA converter 12 is returned to the maximum value simultaneously with the generation of the control signal from the switch switching circuit 5.

However, the response of this relay switch is actually several milliseconds.
From the control signal shown in FIG. 7C, it takes Δt ₁ (about 8 msec) until RY ₂ is turned on as shown in FIG. It takes time Δt ₂ (about 5 msec) before RY ₁ is turned off. Therefore, RY ₁ is not actually turned off between t ₁ and Δt ₁ ,
In order to RY ₂ also not turned on, the output signal Vi of the switching circuit at the same time the generation and control signals from the 5 D-A converter 12 is returned to the maximum value, the FIG. 7 (a) As shown, during the period of Δt ₁ , an excessive current flows through the lens coil. In addition, RY at the time of Δt ₁ has elapsed from t _1
1 is turned off, but at this time RY ₂ is not turned on yet,
No current flows during the period Δt ₂ ′ shown in the figure.

Therefore, in order to remove the influence of the residual magnetism and the hysteresis of the lens having the yoke having the hysteresis characteristic, the current control circuit as described above is gradually reduced from the maximum excitation value to a target excitation current value over a certain period of time. In such a case, since an excessive current flows through the coil in the middle, there arises a problem that complete residual magnetic erasure cannot be performed.

When the signal generation source 1 of such a current control circuit is used as a scanning signal generation source and the load is used as a deflection coil of the scanning electron microscope to control the scanning magnification of the scanning electron microscope, the above-mentioned excessive current is generated when the magnification is switched. When the current flows through the coil, a shift of the scanned image occurs due to the influence of residual magnetism and hysteresis.

The present invention considering the above problems, eliminating the transient current generated when switching the reference resistor, the current control circuit of the output current I ₀ of the current control circuit in the electron beam apparatus capable of linearly changing from the maximum value It is intended to provide.

[Means for Solving the Problems] A first invention supplies an output from a signal generation source to a current control circuit including a DA converter, a resistor, an amplifier, a load coil, and a plurality of reference resistors. In the current control circuit in the electron beam device for varying the current supplied to the load coil by controlling the switching of the reference resistor, the output signal of the DA converter is switched during the switching control of the reference resistor. It is characterized in that the switch is temporarily set to zero or a minimum value during the response delay period of the switch.

According to a second aspect of the present invention, an output from a signal generation source is supplied to a current control circuit including a DA converter, a resistor, an amplifier, a load coil, and a plurality of reference resistors, and the reference resistor is switched. In a current control circuit in an electron beam device that varies a current supplied to the load coil by control, a switching signal is generated prior to switching control of the reference resistor by a response delay period of a switching switch. It is characterized by.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram for explaining one embodiment of the first and second embodiments of the present invention, and FIGS. 2A to 2D are diagrams for explaining the operation of the current control circuit according to the first embodiment of the present invention. FIGS. 3, 3 and 5 are tables for explaining codes generated by the control signal generator, and FIGS. 4 (a) to 4 (d) show the operation of the current control circuit according to the second invention. It is a figure for explaining.

1, the same components as those in FIG. 6 are denoted by the same reference numerals, and description thereof will be omitted. The embodiment of the present invention shown in FIG. 1 is different from the conventional example in that a control signal generator 10, a decoder 11, and a DA converter 12 are provided, and a code generated by the control signal generator 10 is transmitted through a decoder. During the switching control of the reference resistor, the output voltage Vi of the DA converter temporarily becomes zero or a minimum value based on the output signal from the decoder during the switching control of the reference resistor. It is the point which did so.

An output voltage V _i of the control signal generating unit 10 in the D-A converter 12 from the ratio of absolute value 1 (maximum value) and code for continuously changed in a range of up to one-tenth, the switch RY ₁ RY _n is switched to generate a code for changing the output current I ₀ by one digit. The code is supplied to a DA converter 12 and a switch switching circuit 5 via a decoder 11. The D
The -A converter 12 and the voltage V _ref from the signal generating source 1 is supplied, the output voltage V _ref divided by the output voltage V _i of the signal source 1 based on a signal from the decoder 11 is formed Is done. A switch selection signal is supplied to the switch switching circuit 5 simultaneously with the supply of the voltage setting signal Vi to the DA converter 12, and for example, as shown in FIG. Vi data from 1.0 (maximum value)
When up to 0.1, is supplied to the circuit 5 changeover switch of the selection signals switch RY ₁ is selected. Then, the setting signal Vi of the voltage value, for example, RY ₁ the switch RY ₂ is turned on before returning to the initial value 1.0 is supplied to the circuit 5 changeover switch of the selection signal is turned off. The voltage setting signal Vi at this time is set to 0 or a minimum value, and this state is maintained for a preset stop time Δt as shown in FIG. 2A (from the control signal generator 10). The output voltage Vi of the DA converter 12 is set to 0 V or the minimum value by stopping the data output of FIG.
The switching of the switch is completed as shown in FIG. Here, the stop time Δt is determined by experimentally measuring the on-state switching characteristic from the on-state to the off-state or from the off-state to the on-state of the switching element used, and is set to a slightly longer time than either of the slower ones. Is preferred. Later, the setting signal Vi of the voltage value from 1.0 to 0.1, the output current is selected switch RY ₂ is so that order of magnitude lower than the previous switch connection state, the switch R
Signal for selecting a Y ₂ is supplied persist switching circuit.

Thus, the transient current is not generated at the time of switching of the switches, comprising an output current I ₀ of the current control circuit can be varied linearly from a maximum value to a minimum value.

Next, the operation of the second present invention will be described with reference to FIGS.

According to the second aspect of the present invention, when the output current I ₀ is continuously changed over several digits over a certain period of time, that is, when the change sequence of the output current I ₀ is fixed, the switching control of the resistor is performed. The switching signal is generated in advance of the response time Δt _OFF from the ON state to the OFF state of the switching element and the response time Δt _ON from the OFF state to the ON state.

As shown in FIG. 4 (a), the output current I ₀ of the lens coil
Is 10 ^-1 , 10 ^-2 , ... 10 ^-n at a constant speed with the maximum value as 1
The operation will be described for the case where the setting is changed. First, when RY ₁ is turned on and the reference resistor R ₁ is connected, the D− that changes with a certain change width (for example, from 1 to 0.1 in absolute value display) as shown in FIG. the output signal Vi a converter 12 is supplied to the operational amplifier 2 via an input resistor R _i. At this time, as shown in FIG. 4A, the output current I ₀ decreases from the maximum value 1 to 10 ⁻¹ .
In conjunction to the decrease of the output current, at the same time RY ₂ when the relay switch RY ₁ is turned off based on a control signal from the switch switching circuit 5 at time t ₁ as shown in the figure is turned on resistor R ₂ As shown in FIG. 4C, the control signal of the switch switching circuit 5 is changed to a time (t ₁ −Δ) before the time t ₁ of the resistor switching control as shown in FIG.
t _ON ), the ON signal of the switching element is supplied at time (t ₁ −Δt)
_OFF ) to generate an OFF signal. That is, as shown in FIG. 5, the data of the voltage setting signal Vi is 1.0
Before reaching (maximum value) to 0.1, switch R first
Outputs selection data for turning on the Y _2, followed by outputting the data for turning off the switch RY _1, Figure 4 the switches at time t ₁ as shown at (d) is at substantially the same time on or off I am trying to be. Thus, the transient current is not generated at the time of switching of the switches, changed linearly without FIG. 4 (a) the output current I ₀ of the current control circuit as shown in to the minimum value from the maximum value dead time Will be able to do it.

Note that the above-described embodiment is merely an embodiment of the present invention,
The present invention can be implemented with various modifications. For example, in the above-described embodiment, the case where the relay switch is used as the changeover switch has been described. However, the changeover switch has various switching elements, such as a semiconductor switch, which has a stable switching response time. If so, it can be applied.

In the present invention, the case where the current is decreased with time has been described. However, the present invention can also be applied to the case where the current is increased with time, and the hysteresis elimination that reduces the hysteresis loop by changing the current amplitude from the maximum to the minimum. Can also be applied.

[Effects of the Invention] As is clear from the above description, according to the first aspect, the output from the signal generation source is configured by the DA converter, the resistor, the amplifier, the load coil, and the plurality of reference resistors. The current control circuit in the electron beam device that supplies a current to the current control circuit and changes the current supplied to the load coil by controlling the switching of the reference resistor. by the only such that at one time to zero or minimum value response delay period of the switch to switch the output signal of the transducer, since not a transient current generated when switching of the switch, the maximum output current I ₀ of the current control circuit Since it is possible to change linearly from the value to the minimum value or from the minimum value to the maximum value, the effects of residual magnetism and hysteresis can be reduced. Wear.

According to the second aspect of the present invention, the output from the signal generation source is supplied to a current control circuit including a DA converter, a resistor, an amplifier, a load coil, and a plurality of reference resistors,
In a current control circuit in an electron beam device that varies a current supplied to the load coil by switching control of the reference resistor, a switching signal is generated by a response delay period of a switch prior to switching control of the reference resistor. Since the transient current does not occur when the switch is switched, the output current I ₀ of the current control circuit is linearly changed from the maximum value to the minimum value or from the minimum value to the maximum value without any dead time. Since it can be changed, it is possible to complete the removal of the influence of the residual magnetism and the hysteresis in a short time.

[Brief description of the drawings]

FIG. 1 is a block diagram for explaining one embodiment of the first and second embodiments of the present invention, and FIGS. 2A to 2D are diagrams for explaining the operation of the current control circuit according to the first embodiment of the present invention. FIGS. 3, 3 and 5 are tables for explaining codes generated by the control signal generator, and FIGS. 4 (a) to 4 (d) show the operation of the current control circuit according to the second invention. It is a figure for explaining. 6 and 7 are diagrams for explaining a conventional example. 1: signal source, 2: operational amplifier 3: lens coil, 4: constant current circuit 5: switch switching circuit 10: control signal generator, 11: decoder 12: DA converter _Ri : input resistor, R _f: feedback resistor R ₁ to R _n: reference resistor RY ₁ ~RY _n: relay switch

Claims (2)

(57) [Claims] An output from a signal generation source is supplied to a current control circuit including a DA converter, a resistor, an amplifier, a load coil, and a plurality of reference resistors. In a current control circuit in an electron beam device that varies a current supplied to the load coil, during switching control of the reference resistor, the output signal of the DA converter is temporarily reduced to zero for a response delay period of a switching switch. Alternatively, a current control circuit in the electron beam device, wherein the current control circuit is set to a minimum value. 2. An output from a signal generation source is supplied to a current control circuit including a DA converter, a resistor, an amplifier, a load coil, and a plurality of reference resistors, and the switching of the reference resistors is controlled. In a current control circuit in an electron beam device that varies a current supplied to the load coil, a switching signal is generated before a switching control of the reference resistor by a response delay period of a switching switch. Current control circuit in the electron beam device.