JP3379160B2 - Beam current measuring device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a beam current measuring apparatus capable of accurately measuring a beam current by reducing the influence of a noise component. 2. Description of the Related Art An ion implantation apparatus grasps an irradiation amount of an ion beam to an ion irradiation object based on a beam current generated when the ion beam is irradiated to the ion irradiation object or Faraday. It has become. This dose is
Since it greatly affects the physical properties of the ion irradiation target, it is desired to perform the data processing of the beam current with high accuracy. [0003] The above-mentioned beam current is usually measured by an instantaneous value or an integrated value by a beam current measuring device. As shown in FIG. 2, a conventional beam current measuring apparatus includes an amplifying circuit 1
1, integration circuit 12, voltage / frequency conversion circuit (V /
F) 13, frequency / light conversion circuit (F / O in the figure) 14,
An optical / frequency conversion circuit (O / F in the figure) 15 and a pulse counter 16 are provided. In this beam current measuring device, an input beam current is amplified by an amplifier circuit 11 at a predetermined amplification factor, the current is converted into a voltage, and then integrated by an integrating circuit 12. The output voltage of the integration circuit 12 is converted to a frequency by a voltage / frequency conversion circuit 13. This frequency is converted into a pulse train of light by the frequency / light conversion circuit 14. [0005] The pulse train is transmitted to the optical / frequency conversion circuit 15 through a transmission path, where it is returned to a frequency.
The converted frequency is pulse-counted by the pulse counter 16 to obtain a count signal serving as a beam current integrated signal. This signal is used for data processing such as dose calculation and beam current display. Meanwhile, the beam current is a signal shown in FIG. 3A and includes a noise component such as a high-frequency electromagnetic noise shown in FIG. 3B. For this reason, the beam current actually becomes as shown in (c) of the figure, and an error occurs in the beam current measurement due to the above-described noise component. Therefore, in order to improve the measurement accuracy, it is necessary to avoid the influence of noise. On the other hand, in the above-described beam current measuring device, for example, a subtractor (not shown) is provided at the next stage of the pulse counter 16 so as to remove noise from the integrated beam current signal. . This noise data is the current value of the noise component measured under the same conditions as the measurement of the beam current without the beam current. However, in the beam current measuring device described above, the conversion by the voltage / frequency conversion circuit 13 cannot convert the negative voltage to the frequency. Therefore, for example, in the beam current, the negative part of the noise component indicated by the broken line in FIG. In addition, since the noise component is measured in the same manner as the beam current, only the positive portion is converted into a frequency as shown in FIG. Therefore, when the noise data of such a positive portion is subtracted from the beam current integrated signal, only the noise component is present in the originally flat portion having no signal portion, so that the noise in that portion can be removed. become. However, in the signal portion, only the positive noise component is removed, and the negative noise component is not removed. As described above, in the above-mentioned method, there is a problem that an error generated in the measurement of the beam current cannot be removed because the noise component is not sufficiently removed. SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and is capable of measuring a beam current of an ion implanter with high accuracy without being affected by the above-mentioned noise components. It is intended to provide a current measuring device. In order to solve the above-mentioned problems, a beam current measuring apparatus according to the present invention converts a beam current into a voltage.
The beam current of the ion implanter
And to convert the negative voltage to frequency
Voltage / frequency conversion means and voltage / frequency conversion
The output frequency of the means is counted and counted for each scanning cycle.
Count to measure as a current signal according to the value of the beam current
And means, usually aging that is part of the above beam current
Is a noise component without
It can take a negative level based on 0V of the
From conversion to voltage to measurement by the counting means
Measured under the same conditions as the above beam current without beam current
The measured current value of the counting means according to the noise component determined
Is subtracted from the current signal corresponding to the value of the beam current.
A beam current measuring device having noise subtraction means
Current / voltage conversion for converting the beam current into a voltage
Means and the current range or energy used by the ion implanter.
Even if the above noise component changes due to injection conditions such as energy.
Voltage / frequency conversion means converts all input voltage to frequency
The noise of the output of the current / voltage conversion means is
Positive bias voltage greater than the negative maximum of the component.
Bias adding means for adding, and the bias adding means
The product that integrates the output and enters the voltage / frequency conversion means.
And a dividing means . In the above configuration, the input beam current of the ion implantation apparatus is converted into a voltage by the current / voltage conversion means, and the voltage on the negative side cannot be converted into a frequency.
/ Frequency conversion means the current range used by the ion implanter
The noise component changes depending on the injection conditions such as energy.
Current / power so that all input voltages are converted to frequency.
The output of the pressure conversion means is subjected to noise
Positive bias voltage greater than the negative maximum
Is calculated. As a result, the output voltages of the bias adding means are all present on the positive side. Biasing
The output voltage of the calculating means is integrated by the integrating means. Next, the voltage after the addition is converted to a frequency corresponding to the voltage value by the voltage / frequency conversion means. Then, the frequency is counted by the counting means for each scanning cycle, and a current signal corresponding to the value of the beam current is output. Further, a value corresponding to the noise component is subtracted from the current signal by the noise subtracting means. [0015] This noise component is included in the beam current.
A noise component that does not change over time and is converted to voltage.
Then, the negative level based on 0V of the beam current voltage
Possible, from conversion to voltage to measurement by counting means.
Measured under the same conditions as beam current without beam current
You. As described above, according to the above configuration, the output voltages of the current / voltage conversion means including the signal measurement and the noise measurement are all present on the positive side by the addition of the bias voltage by the bias addition means. Voltage / period
The wave number conversion means can convert all input voltages to frequencies.
Will be able to do it . Thereby, all the noise components can be removed by the subtraction by the noise subtraction means. An embodiment of the present invention will be described below with reference to FIG. As shown in FIG. 1, the beam current measuring apparatus according to the present embodiment includes an amplifying circuit 1, an adder 2, an integrating circuit 3,
Voltage / frequency conversion circuit (V / F in the figure) 4, frequency / light conversion circuit 5 (F / O in the figure), light / frequency conversion circuit (O / F in the figure) 6, pulse counter 7, and subtraction A vessel 8 is provided. Amplifier circuit 1 as current / voltage conversion means
Is a circuit that amplifies the input beam current and converts it into a voltage. The adder 2 serving as a bias adding unit is a circuit that adds a DC bias voltage to the output voltage of the amplifier circuit 1. The bias voltage is set to a value larger than the maximum negative value of the noise component included in the beam current. The noise component, which does not normally change with time such as high-frequency electromagnetic noise, changes depending on the injection conditions such as the current range used by the ion implanter and the energy. An integrating circuit 3 as integrating means includes an adder 2
Is a circuit that integrates the output voltage of. The voltage / frequency conversion circuit 4 as a voltage / frequency conversion means is a circuit for converting the output voltage of the integration circuit 3 into a frequency according to the voltage value. The frequency / light conversion circuit 5 is a circuit for converting the output frequency of the voltage / frequency conversion circuit 4 into a pulse train light signal. The optical / frequency conversion circuit 6 is a circuit that converts an optical signal transmitted from the frequency / optical conversion circuit 5 into a frequency. Frequency / light conversion circuit 5 and light / frequency conversion circuit 6
Are connected by an optical transmission line, and are configured so as to be hardly affected by noise or the like even if the transmission line becomes long by performing transmission using an optical signal. The pulse counter 7 as a counting means counts the output frequency of the light / frequency conversion circuit 6 for each scanning cycle, and uses the counted value as a beam current integration signal (current signal) corresponding to the beam current value. This is the output circuit. The beam current integration signal is obtained by integrating the beam current with respect to time (total amount of charge flowing in within a certain time). A subtractor 8 as a noise subtracting means is a circuit for subtracting a value (noise data) corresponding to a noise component from the above-mentioned integrated beam current signal. The value is a value measured by the above-described configuration with no beam current and with a bias voltage applied to all the DC and AC noise components in the same manner as the beam current. In the beam current measuring device configured as described above, the input beam current is amplified by the amplifier circuit 1 at a predetermined amplification rate, the current is converted into a voltage, and the output of the amplifier circuit 1 is output by the adder 2. A bias voltage is added to the voltage. The output voltage of the amplifier circuit 1 is all present on the positive side due to the addition of the bias voltage. Next, the output voltage of the adder 2 is integrated by the integration circuit 3, and the output voltage of the integration circuit 3 is converted to a frequency by the voltage / frequency conversion circuit 4. Then, this frequency is converted into an optical signal by the frequency / optical conversion circuit 5. The optical signal is transmitted to the optical / frequency conversion circuit 6 through a transmission line, where it is returned to a frequency. The pulse counter 7 counts the converted frequency for each scanning cycle, thereby obtaining a beam current integrated signal. Further, the subtractor 8 subtracts noise data from the beam current integrated signal. This noise data is measured in the same manner as the beam current, and a bias voltage is added. Therefore, the beam current integrated signal is also subtracted by the value corresponding to the bias voltage by the subtraction. As a result, a true beam current value is obtained. The beam current integrated signal thus obtained is used for data processing such as dose calculation and beam current display. As described above, the beam current measuring device according to the present embodiment performs the addition of the bias voltage before integrating the voltage converted from the beam current, so that all the voltages exist on the positive side. Let it. Similarly, the noise component can be measured without missing the portion existing on the negative side. Accordingly, when the noise data is subtracted by the subtracter 8, the noise component originally existing on the negative side can also be removed. Therefore, it is possible to accurately measure the beam current by removing the noise component. As described above, the beam current measuring apparatus according to the present invention has a beam current converted into a voltage by the ion implantation apparatus.
Is converted to a frequency corresponding to that value, and the voltage on the negative side is
Voltage / frequency converter that cannot convert
Stage and the output frequency of the voltage / frequency conversion means for one scanning cycle.
Current for each beam is calculated according to the beam current value
Counting means for measuring as a signal;
Noise component that does not change over time
When converted to pressure, the beam current voltage of 0 V
The conversion from voltage to voltage
In the absence of the beam current, the beam
Depending on the noise component measured under the same conditions as the
The measured current value of the counting means depends on the value of the beam current.
Noise subtraction means for subtracting from the current signal
In the beam current measuring device, the beam current is converted to a voltage.
Current / voltage conversion means for converting,
Depending on the injection conditions such as current range and energy
Even if the noise component changes, the above voltage / frequency conversion means inputs
The above current / voltage conversion so that all voltages are converted to frequency
The output of the means is greater than the maximum negative value of the noise component
Bias adding means for adding a positive bias voltage having a value,
The output of the bias adding means is integrated to calculate the voltage / frequency.
And an integrating means for inputting to the number converting means . As described above, by adding the bias voltage by the bias adding means, all the output voltages of the current / voltage converting means are present in the positive part.
As a result, the voltage / frequency conversion means circulates all input voltages.
It can be converted to wave numbers . Therefore, all the noise components can be removed by the subtraction by the noise subtraction means. Therefore, if the present beam current measuring apparatus is employed, the beam current can be accurately detected without being affected by noise components.
This has the effect that the beam current of the on-injection device can be measured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a configuration of a beam current measuring device according to one embodiment of the present invention. FIG. 2 is a block diagram showing a configuration of a conventional beam current measuring device. FIG. 3 is a waveform diagram showing a signal portion of a beam current, a noise component, and a beam current on which the noise component is superimposed. FIG. 4 is a waveform diagram showing a positive-side noise component and a beam current that can be converted into a frequency by a voltage / frequency conversion circuit. [Description of Signs] 1 Amplifying circuit (current / voltage converting means) 2 Adder (bias adding means) 3 Integrating circuit (integrating means) 4 Voltage / frequency converting circuit (voltage / frequency converting means) 7 Pulse counter (counting means) 8. Subtractor (noise subtraction means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01J 37/04 H01J 37/317

Claims (1)

(57) [Claims] [Claim 1] A beam of an ion implanter converted into a voltage
The current is converted to a frequency corresponding to that value and the negative side
Voltage / frequency conversion that cannot convert voltage to frequency
Conversion means and the output frequency of the voltage / frequency conversion means for one scan
Counted for each cycle and determined according to the value of the beam current
Counting means for measuring as a current signal;
Noise components that do not normally change over time
When converted to voltage, the voltage of the beam current
It can take a negative level as a reference,
Without the above beam current until measurement by the counting means
It responds to the noise component measured under the same conditions as the above beam current.
The measured current value of the counting means is calculated as the beam current value.
Noise subtraction means for subtracting from a current signal corresponding to
In it are the beam current measuring device, a current / voltage converting means for converting the beam current into a voltage
And the current range and energy used by the ion implanter
Even if the noise component changes due to injection conditions such as
Pressure / frequency conversion means converts all input voltage to frequency
As described above, the noise component is added to the output of the current / voltage conversion means.
Positive bias voltage greater than the maximum negative value of
Bias adding means for performing the operation, and an output of the bias adding means.
And integrates the voltage into the voltage / frequency conversion means.
And a beam current measuring device.
Place.