JP4954470B2 - Current measuring device - Google Patents

Description

The present invention relates to a current measuring equipment. Further, the present invention utilizes an electron beam, directed to suitable current measuring equipment for performing a semiconductor device manufacturing process during the process evaluation.

  A substrate current method is known as a method for evaluating process quality of a semiconductor device using a substrate current that flows during electron beam irradiation (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3). In this method, for example, a wafer after etching is irradiated with an electron beam having a constant energy for several seconds, and the state of the process is known from the magnitude or polarity of the substrate current generated at that time. For example, 1 KeV is used as the electron beam energy, and a picoampere (pA) magnitude is used as the current amount.

  In this method, when the process result is the same, the same substrate current is generated, and when the process result is different, the process state can be grasped by generating a different current.

As described above, when knowing the relative changes in the process, the energy level of the irradiated electron beam may be single, but in order to investigate the absolute process state, it is necessary to use various acceleration voltages in combination. It is. Further, since the measurement sensitivity varies depending on the electron beam energy, it is necessary to find an optimum value for each measurement object. For this purpose, as shown in FIG. 14, the acceleration voltage (voltage of the high voltage power supply) Vh applied to the electron beam 3 emitted from the electron beam source 2 is switched and used.
Japanese Patent No. 3334750 Japanese Patent No. 3292159 Japanese Patent No. 3175765

  In order to perform precise measurement from the substrate current, it is necessary to use an electron beam having a plurality of energy levels. In other words, it is necessary to perform measurement in a state where only the energy level of the electron beam is different at the same measurement point. However, conventionally, the voltage of the high-voltage power supply of the electron beam generator has been changed in order to change the energy level of the irradiation electron beam. When the voltage of the high-voltage power supply is changed, the axis of the electron beam changes greatly, and it is difficult to accurately irradiate the electron beam at exactly the same place. Therefore, the conventional substrate current measuring method has a problem that the measurement accuracy is lowered.

  In addition, it is necessary to use an electron beam having a very low energy level in order to change the measurement sensitivity. However, an electron beam having a very low energy level can be realized only by changing the voltage of a conventional high-voltage power supply. Was difficult. As a conventional method, a method of applying a bias voltage Vb to a measurement sample 4 which is a semiconductor substrate as shown in FIG. 15 is also known. However, in this method, since the power supply 20 is turned on in parallel with the ammeter 5, a substrate current necessary for measurement flows to the ground (ground) via the power supply 20. For this reason, the current flowing through the ammeter 5 is substantially “0” and cannot be measured. In addition, when the voltage Vb of several kilovolts is applied to the measurement sample 4 by the power source 20 in order to change the energy level of the electron beam 3, there is a big problem that the ammeter 5 cannot be used practically. .

The present invention has been made to solve such problems, and an object of the present invention is to provide a current measuring device and a current measuring method capable of easily setting the energy level of an electron beam irradiated to a measurement sample such as a semiconductor substrate. It is to provide.
Another object of the present invention is to provide a current measuring apparatus and a current measuring method capable of improving the sensitivity and accuracy of measuring the current flowing through the measurement sample without damaging the measurement sample. .

The present invention has been made to solve the above problems, and the current measuring device of the present invention is a current measuring device for measuring a current generated in a measurement sample irradiated with an electron beam, and the electron beam is emitted. A chamber whose atmosphere is controlled as possible, an electron beam emission source that emits an electron beam with a set energy, and a means for irradiating a specific location of the measurement sample with the electron beam emitted from the electron beam emission source; A current measurement circuit that at least amplifies the current flowing through the measurement sample, and a voltage application unit that applies a voltage between the current measurement circuit and a ground potential.
According to the present invention, the bias voltage can be applied to the current measuring circuit by the voltage applying means. Thereby, the potential of the measurement sample can be controlled. The effective energy that the measurement sample receives by electron beam irradiation is a value obtained by subtracting the potential of the measurement sample from the energy of the electron beam. Therefore, the present invention can reduce the effective energy received by the measurement sample even when a high-energy electron beam is emitted from the electron beam emission source. Therefore, the present invention can improve the sensitivity and accuracy of measuring the current flowing through the measurement sample without damaging the measurement sample.

The current measuring device of the present invention is a current measuring device for measuring a current generated in a measurement sample irradiated with an electron beam. The current measuring device includes a chamber whose atmosphere is controlled so that the electron beam can be emitted, and an electron beam. An electron beam emission source that emits at a set energy; means for irradiating a specific location of the measurement sample with an electron beam emitted from the electron beam emission source; an electrode capacitively coupled to the measurement sample; and the electrode A current measuring circuit for amplifying at least the current flowing through the current measuring circuit, and voltage applying means for applying a voltage between the current measuring circuit and a ground potential.
According to the present invention, the potential of the measurement sample can be changed by the voltage applied to the current measurement circuit without directly applying the bias voltage to the measurement sample. The effective energy received by the measurement sample is a value obtained by subtracting the potential of the measurement sample from the energy of the irradiated electron beam. Therefore, the present invention can improve the sensitivity and accuracy of measuring the current flowing through the measurement sample without damaging the measurement sample. Further, the present invention does not require wiring connection between the measurement sample and the current measurement circuit (or electrode), facilitates installation and removal of the measurement sample at the measurement position, and can increase the practicality.

The current measurement device of the present invention is a current measurement device for measuring a current generated by irradiating a measurement sample with an electron beam, and includes a chamber whose atmosphere is controlled so that the electron beam can be emitted, and an electron beam An electron beam emission source that emits a predetermined energy, means for irradiating the electron beam emitted from the electron beam emission source to a specific location of the measurement sample, and scattering generated by irradiation of the electron beam to the measurement sample An electrode for collecting electrons or secondary electrons, a current measuring circuit for amplifying at least a current flowing through the electrode, and a voltage applying means for applying a voltage between the current measuring circuit and a ground potential. To do.
According to the present invention, the bias voltage can be applied to the current measuring circuit by the voltage applying means. Thereby, the potential of the measurement sample can be controlled. The effective energy that the measurement sample receives by electron beam irradiation is a value obtained by subtracting the potential of the measurement sample from the energy of the electron beam. Therefore, the present invention can reduce the effective energy received by the measurement sample even when a high-energy electron beam is emitted from the electron beam emission source. Here, the electron beam having low energy can improve the secondary electron emission probability. Therefore, the present invention can improve the sensitivity and accuracy without damaging the measurement sample in the measurement of the current generated by the electron beam irradiation to the measurement sample.

In addition, the current measuring device of the present invention is characterized by having an aperture that allows a part of the electron beam emitted from the electron beam emission source to pass therethrough.
According to the present invention, it is possible to irradiate a measurement sample with an electron beam with uniform energy by passing an aperture through the electron beam. Therefore, the present invention can irradiate a desired portion of a measurement sample with a highly focused electron beam and inspect the measurement sample with high resolution.

The current measuring apparatus according to the present invention includes an acceleration electrode that accelerates the electron beam emitted from the electron beam emission source to a first energy level, an acceleration power source that applies a voltage to the acceleration electrode, and the acceleration electrode. An aperture that passes a portion of the accelerated electron beam; a deceleration electrode that converts energy of the electron beam that has passed through the aperture to a second energy level; and a deceleration power source that applies a voltage to the deceleration electrode. Features.
According to the present invention, it is possible to irradiate a measurement sample with an electron beam with uniform energy by passing an aperture through the electron beam. Furthermore, the present invention can convert the electron beam from the first energy level to the second energy level by the deceleration electrode. Therefore, no matter how much the energy of the electron beam is increased by the acceleration electrode or the like, the energy of the electron beam reaching the measurement sample can be controlled by the deceleration electrode. Thus, the present invention can irradiate a desired portion of a measurement sample with a highly focused electron beam while avoiding damage to the measurement sample, and can inspect the measurement sample with high resolution.

The current measuring device of the present invention is characterized in that the voltage applying means includes a variable power source that applies a variable voltage between the current measuring circuit and a ground potential.
According to the present invention, it is possible to change the effective energy level of the electron beam irradiated to the measurement sample only by changing the output of the variable power source without changing the setting on the electron beam emission source side. Therefore, the effective energy level can be changed very simply and quickly. Furthermore, according to the present invention, it is possible to quickly irradiate the same location in the measurement sample with electron beams having different effective energy levels, thereby improving measurement accuracy and improving measurement throughput.

In addition, the current measurement device of the present invention includes control means for controlling the voltage application timing by the voltage application means or the variable power supply in synchronization with the current measurement timing of the current measurement circuit.
According to the present invention, it is possible to synchronize the timing of applying the bias voltage to the measurement sample via the current measurement circuit and the current measurement timing. As a result, white noise or the like, which is a problem in current measurement, can be easily removed, and sensitivity and accuracy can be further improved with respect to measurement of the current flowing through the measurement sample.

The current measuring device according to the present invention is a component of the current measuring circuit, and an operational amplifier that amplifies the current flowing through the measurement sample, and applies a voltage to a positive or negative input terminal of the operational amplifier. And a bias power source.
According to the present invention, for example, a measurement sample is electrically connected to the negative input terminal of the operational amplifier, a bias voltage is applied to the positive input terminal of the operational amplifier, and a resistor is connected between the output of the operational amplifier and the negative input terminal. It can be set as the structure which has arrange | positioned the container. In this way, a bias voltage is applied to the measurement sample via the negative input terminal of the operational amplifier. Therefore, the present invention can reduce the effective energy received by the measurement sample even when a high-energy electron beam is emitted from the electron beam emission source, and can measure the current flowing through the measurement sample without damaging the measurement sample. Sensitivity and accuracy can be improved.

The current measuring device of the present invention is a component of the current measuring circuit, and an operational amplifier that amplifies the current flowing through the measurement sample, and a variable voltage at a positive or negative input terminal of the operational amplifier. A variable power supply for the operational amplifier to be applied, and a control signal generator for outputting a signal for controlling the output voltage of the variable power supply.
According to the present invention, the potential of the measurement sample can be controlled by the signal output from the control signal generator. Here, the variable voltage output from the variable power supply for the operational amplifier may be a periodic waveform such as a sine wave, a rectangular wave, or a sawtooth wave, or a trigger waveform. Thus, according to the present invention, an optimum variable voltage can be selected according to the attribute of the measurement sample and the like, and current measurement can be performed, so that process evaluation can be performed with higher accuracy.

The current measurement method of the present invention is a current measurement method for irradiating a measurement sample with an electron beam and measuring a current generated in the measurement sample, and a procedure for disposing an amplification circuit that amplifies the current generated in the measurement sample. And a procedure for applying a voltage between the amplifier circuit and a ground potential.
According to the present invention, the potential of the measurement sample can be controlled by applying a voltage between the amplifier circuit and the ground potential. Therefore, the effective energy that the measurement sample receives by electron beam irradiation can be reduced by the voltage. Therefore, the present invention can improve the sensitivity and accuracy of measuring the current flowing through the measurement sample without damaging the measurement sample.

  The present invention can improve the sensitivity and accuracy of measuring a current flowing through a measurement sample while lowering the effective energy level of an electron beam applied to the measurement sample such as a semiconductor substrate. Therefore, it is possible to improve the sensitivity and accuracy in measuring the attributes of the measurement sample without damaging the measurement sample.

  Moreover, since the effective energy level in the measurement sample irradiated with the electron beam can be lowered according to the present invention, the secondary electron emission probability can be improved and the measurement sensitivity can be increased.

  Further, according to the present invention, since the effective energy level in the measurement sample can be largely changed without changing the setting of the electron beam source or the like, the energy level can be changed very quickly. Therefore, for example, it is possible to quickly irradiate the same location in the measurement sample with electron beams of different energy levels, and to improve the measurement throughput while greatly increasing the measurement accuracy.

  Further, according to the present invention, various modes can be set on the electron beam source side and the bias power source side as modes for irradiating the measurement sample with the electron beam. Therefore, even if the effective energy level in the measurement sample is the same, various combinations can be made as the modes of electron beam irradiation and bias voltage. As a result, it is possible to adjust the energy dispersion state and spatial distribution of electron beams having the same energy on average, and it is possible to perform highly accurate measurement by selecting an optimal combination according to the application.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a diagram illustrating an overall configuration example of a current measuring device according to a first embodiment of the present invention. The current measuring apparatus of the present embodiment includes a chamber 1, an electron beam source 2, an ammeter (current measuring circuit) 5, a bias power source (voltage applying means) 6, and an XY stage 9. Yes. In FIG. 1, a measurement sample 4 is a measurement target of the current measuring device, and the measurement sample 4 is irradiated with an electron beam 3. For example, a measurement sample 4 is a wafer which is a semiconductor substrate.

  The chamber 1 is for controlling the atmosphere so that the electron beam 3 can be emitted. In the chamber 1, an electron beam source 2, a measurement sample 4, an ammeter 5, a bias power source 6 and an XY stage 9 are arranged. The electron beam source 2 emits the electron beam 3 with a set constant energy. Here, the energy of the electron beam 3 emitted from the electron beam source 2 can be changed by changing the voltage (acceleration voltage) Vh of the high-voltage power supply. Each set voltage is stored by the voltage value storage means. The XY stage 9 is a positioning mechanism for irradiating a desired location in the measurement sample 4 with the electron beam 3 emitted from the electron beam source 2, and is an example of means for irradiating a specific location of the present invention. The place where the electron beam is irradiated is also stored by the storage means.

The ammeter 5 is an example of a current measuring circuit of the present invention. That is, the ammeter 5 has a circuit that at least amplifies the current flowing through the measurement sample 4, and is for measuring the current generated when the measurement sample 4 is irradiated with the electron beam. In addition, the ammeter 5 is not actually an ammeter based on a mechanical pointer, but is composed of a current measuring circuit using an operational amplifier that converts and amplifies a minute current into a voltage signal or the like (hereinafter, referred to as an ammeter). The same for the ammeter 5). The details of the current measurement circuit will be described later.
The bias power source 6 constitutes an example of a voltage application unit of the present invention, and applies a voltage Vm between the ammeter 5 and a reference potential (ground potential).

  The current measuring device according to the present embodiment is characterized in that an ammeter 5 and a bias power source 6 for biasing the ammeter 5 are connected in series with the measurement sample 4. Here, the impedance of the ammeter 5 is very small and can be regarded as virtually zero. Therefore, although the measurement sample 4 is not directly biased, the potential of the measurement sample 4 can be changed by the bias voltage Vm applied to the ammeter 5. Therefore, according to the present embodiment, it is possible to realize electron beam irradiation having an effective energy obtained by subtracting the bias voltage Vm applied to the ammeter 5 from the electron beam irradiation energy Eir with respect to the measurement sample 4.

  Moreover, the energy level of the electron beam 3 in the measurement sample 4 can be instantaneously changed by changing the bias voltage Vm. Further, since energy conversion is performed in the vicinity of the surface of the measurement sample 4 such as a wafer, the change of the electron beam path due to the change of the electron beam energy level is very small. Therefore, for example, after performing alignment on the order of several nanometers by positioning using a pattern matching method or the like, while changing the effective energy level of the electron beam in the measurement sample 4 in various ways, the alignment is exactly the same (alignment on the order of several nanometers). (Accuracy) can be repeatedly irradiated with an electron beam.

  Further, according to the current measuring device of the present embodiment, since the current flowing through the measurement sample 4 is directly input to the ammeter 5, compared with the case where the power is turned on in parallel to the ammeter 5 as in the past. (Refer to FIG. 15) The minute current generated in the measurement sample 4 can be measured very accurately.

[Second Embodiment]
FIG. 2 is a circuit diagram showing a current measuring apparatus according to the second embodiment of the present invention. In FIG. 2, the same components as those in FIG. The difference between this embodiment and 1st Embodiment is a point which has the electrode 10 in this embodiment.

  That is, the current measuring device of the present embodiment is characterized in that a plate-like electrode 10 that is capacitively coupled to the measurement sample 4 is attached below the measurement sample 4. Therefore, the electrode 10 and the measurement sample 4 are connected in an alternating manner. The electrode 10 may be on the back surface of the measurement sample 4 or may be on the front surface or side surface of the measurement sample 4. When the electrode 10 is disposed on the back surface of the measurement sample 4, the electrode 10 has almost the same size as the measurement sample 4, so that a very large capacity can be formed. Here, the very large capacity means a very large capacity as compared with, for example, the parasitic capacity between the measurement sample 4 and the casing of the current measuring device.

  In the current measuring device of this embodiment, an ammeter 5 is directly connected to an electrode 10 provided under a measurement sample 4, and a bias power source 6 for applying a voltage in series to the ammeter 5 is provided. Yes. The capacitance component existing in the measurement system is mainly composed of a capacitance formed between the electrode 10 and the measurement sample 4 and a parasitic capacitance generated between the measurement sample 4 and the measurement device housing. In this, the capacity | capacitance produced between the measurement sample 4 and the electrode 10 is overwhelmingly large compared with another capacity | capacitance. Therefore, although the measurement sample 4 is not directly biased, the potential of the measurement sample 4 can be changed by the bias voltage Vm applied to the ammeter 5. Therefore, the current measuring apparatus can apply effective energy obtained by subtracting the bias voltage Vm applied to the ammeter 5 from the irradiation energy Eir of the electron beam 3 to the measurement sample 4 to be measured. Moreover, according to the current measuring device of this embodiment, it is not necessary to directly connect the ammeter 5 to the measurement sample 4, and practicality can be improved.

[Third Embodiment]
FIG. 3 is a circuit diagram showing a current measuring apparatus according to the third embodiment of the present invention. In FIG. 3, the same components as those of FIG. The difference between this embodiment and 1st Embodiment is a point which has the acceleration electrode 11, the acceleration power supply 11a, and the aperture 12 in this embodiment. The acceleration electrode 11 accelerates the electron beam emitted from the electron beam source 2. The acceleration power supply 11a applies an acceleration voltage Va to the acceleration electrode 11, and variably controls the degree of acceleration in the acceleration electrode 11. The aperture 12 allows a part of the electron beam emitted from the electron beam source 2 and accelerated by the acceleration electrode 11 to pass therethrough.

  According to the principle of optics, it has been found that the resolution serving as an index for identifying an object is comparable to the wavelength of light to be used. The electron beam is characterized by a very short wavelength. For example, even a 100 eV electron beam has a wavelength smaller than 1 angstrom. However, the electron beam that can actually be generated has a large energy dispersion and can only obtain a resolution much lower than expected from the wavelength.

  In the current measuring apparatus of the present embodiment shown in FIG. 3, the electron beam 3 that has jumped out of the electron beam source 2 using the acceleration electrode 11 and the acceleration power source 11a is once brought into a very high energy level state by the acceleration voltage Va. For example, the energy of the electron beam 3 is increased to about 5 kV by the acceleration electrode 11. In this state, a very small cylindrical aperture 12 is passed, and only the portion having the same energy level is taken out. Thereafter, the effective electron beam irradiation energy in the measurement sample 4 is lowered by the same configuration as that of the first embodiment shown in FIG.

  The aperture 12 has a size of several microns, for example, and constitutes a kind of energy filter. The electron beam emitted from the electron beam source 2 is emitted from a wide range of electron beam emission electrodes called chips. Although the emitted region is a small region of a few hundred angstroms, the energy of the electron beam varies depending on the emitted region. When this difference occurs, when the electron beam 3 is focused, an aberration occurs and the focal point is set at a different location, which causes the image to be blurred. Since these cause the measurement accuracy to be lowered, there is a demand to use only the electron beam 3 having the same energy as possible for the measurement.

  According to the present embodiment, in the aperture 12, only the central portion where the energy levels in the electron beam are uniform passes. Thereby, it has a very small dispersion compared to the energy dispersion when the electron beam is emitted from the electron beam source 2. The electron beam 3 in such a state can realize a focus that may have a low electron beam energy. Thereafter, the electron beam energy actually received by the measurement sample 4 becomes as small as 500 eV by the bias voltage Vm applied to the ammeter 5 such as 4.5 kV. However, the electron beam 3 has a very uniform energy level, and the beam is focused sharply.

  As a result, according to the current measuring device of the present embodiment, the electron beam 3 that is highly focused can be irradiated onto a desired portion of the measurement sample 4, and the measurement sample 4 can be inspected with high resolution.

[Fourth Embodiment]
FIG. 4 is a circuit diagram showing a current measuring apparatus according to the fourth embodiment of the present invention. 4, the same components as those in FIGS. 1 to 3 are denoted by the same reference numerals. The difference between this embodiment and 3rd Embodiment is a point which has the electrode 10 in this embodiment.

  That is, the current measuring device of the present embodiment is characterized in that a plate-like electrode 10 that is capacitively coupled to the measurement sample 4 is attached below the measurement sample 4. Therefore, the electrode 10 and the measurement sample 4 are connected in an alternating manner. The electrode 10 has substantially the same size as the measurement sample 4 and forms a very large capacitance compared to other parasitic capacitances. An ammeter 5 is directly connected to the electrode 10 provided under the measurement sample 4. A bias voltage Vm is applied to the ammeter 5 by a bias power source 6.

  With such a configuration, although the measurement sample 4 is not directly biased, the potential of the measurement sample 4 can be changed by the bias voltage Vm applied to the ammeter 5. Therefore, the current measuring apparatus can apply effective energy obtained by subtracting the bias voltage Vm applied to the ammeter 5 from the irradiation energy Eir of the electron beam 3 to the measurement sample 4 to be measured. Moreover, according to the current measuring device of this embodiment, it is not necessary to directly connect the ammeter 5 to the measurement sample 4, and practicality can be improved.

  Further, according to the current measuring device of the present embodiment, the energy filter for reducing the energy dispersion of the electron beam 3 is configured by the acceleration electrode 11 and the aperture 12. Therefore, it is possible to irradiate the electron beam 3 that is highly focused on a desired portion of the measurement sample 4 and to inspect the measurement sample 4 with high resolution.

[Fifth Embodiment]
FIG. 5 is a circuit diagram showing a current measuring apparatus according to the fifth embodiment of the present invention. In FIG. 5, the same components as those in FIGS. 1 to 4 are denoted by the same reference numerals. The difference between this embodiment and 3rd Embodiment is a point which has the deceleration electrode 13 and the deceleration power supply 13a in this embodiment. The deceleration electrode 13 converts the energy level of the electron beam 3 that has passed through the aperture 12. The deceleration power supply 13 a applies a voltage to the deceleration electrode 13.

  That is, in the current measuring device of this embodiment, the electron beam is accelerated by the acceleration electrode 11 and the energy rises. The electron beam 3 passes through the aperture 12 and is filtered. The electron beam 3 is decelerated by the deceleration electrode 13 and the energy level is lowered before irradiating the measurement sample 4.

  For example, the acceleration voltage Va applied to the acceleration electrode 11 is set to 100 kV, and the deceleration voltage Vd applied to the deceleration electrode 13 is set to 99 kV. Then, an electron beam having an energy of 1 keV is effectively obtained on the surface of the measurement sample 4. Furthermore, by applying a bias voltage Vm of, for example, 900 V to the ammeter 5 in this state, an electron beam having an energy of 100 eV can be realized effectively. In order to realize energy of several hundred eV suddenly from a high acceleration state exceeding 5 kV, it has conventionally been necessary to apply a very large bias voltage Vm to the ammeter 5, which is practically difficult.

  According to the current measuring device of this embodiment, no matter how high the energy level of the electron beam 3 is due to the acceleration electrode 11 or the like, the energy level can be controlled using the deceleration electrode 13. Therefore, the bias voltage Vm applied to the ammeter 5 can be set small.

[Sixth Embodiment]
FIG. 6 is a circuit diagram showing a current measuring apparatus according to the sixth embodiment of the present invention. In FIG. 6, the same components as those in FIGS. 1 to 5 are denoted by the same reference numerals. The difference between the present embodiment and the fifth embodiment is that the electrode 10 is provided in the present embodiment.

  That is, the current measuring device of the present embodiment is characterized in that a plate-like electrode 10 that is capacitively coupled to the measurement sample 4 is attached below the measurement sample 4. Therefore, the electrode 10 and the measurement sample 4 are connected in an alternating manner. The electrode 10 has substantially the same size as the measurement sample 4 and forms a very large capacitance compared to other parasitic capacitances. An ammeter 5 is directly connected to the electrode 10 provided under the measurement sample 4. A bias voltage Vm is applied to the ammeter 5 by a bias power source 6.

  With such a configuration, although the measurement sample 4 is not directly biased, the potential of the measurement sample 4 can be changed by the bias voltage Vm applied to the deceleration electrode 13 and the ammeter 5. Therefore, effective energy obtained by subtracting the deceleration voltage Vd and the bias voltage Vm from the irradiation energy Eir of the electron beam 3 can be applied to the measurement sample 4. Moreover, according to the current measuring device of this embodiment, it is not necessary to directly connect the ammeter 5 to the measurement sample 4, and practicality can be improved.

[Seventh Embodiment]
FIG. 7 is a circuit diagram showing a current measuring apparatus according to the seventh embodiment of the present invention. In FIG. 7, the same components as those in FIGS. 1 to 6 are denoted by the same reference numerals. The difference between the present embodiment and the fifth embodiment is that the present embodiment does not include the bias power source 6 but includes the variable power source 7 and the control signal generator 8. The variable power source 7 applies a variable voltage between the ammeter 5 and the ground potential. The control signal generator 8 outputs a voltage control signal for controlling the operation of the variable power source 7.

  That is, the current measuring device of the present embodiment is characterized in that the bias voltage Vm applied to the ammeter 5 can be variably controlled by the voltage control signal output from the control signal generator 8. The control signal generator 8 may be a self-oscillating AC signal generator or a device that generates a voltage control signal based on a digital or analog signal from an external computer (not shown).

  For example, an external computer has a program for automatically controlling the current measuring device of the present invention, and the current flowing through the measurement sample 4 is measured based on a certain sequence. For example, the measurement target wafers constituting the measurement sample 4 are first taken out from the wafer cassette one by one and loaded into the current measurement device by a robot. The loaded wafer is accurately positioned by an alignment mechanism, and further transferred to a chamber having a precise mechanical stage.

  The wafer transferred to the chamber is accurately positioned by optical and electron beam means. Since the part of the wafer to be measured is recorded in advance in the sequence, the machine stage operates according to the sequence, and the position where the electron beam 3 is irradiated is determined. If necessary, pattern matching using an electron beam is performed to accurately determine the measurement target position.

  The first electron beam irradiation is performed with the bias voltage Vm1 on the determined position. Next, the second electron beam irradiation is performed with a bias voltage Vm2. The currents obtained at these two bias voltages are measured and stored. The measured current value is appropriately corrected and then substituted into a predetermined equation to be converted into a material thickness or the like.

[Eighth Embodiment]
FIG. 8 is a circuit diagram showing a current measuring apparatus according to the eighth embodiment of the present invention. In FIG. 8, the same components as those in FIGS. 1 to 7 are denoted by the same reference numerals. The difference between the present embodiment and the seventh embodiment is that the electrode 10 is provided in the present embodiment.

  That is, the current measuring device of the present embodiment is characterized in that a plate-like electrode 10 that is capacitively coupled to the measurement sample 4 is attached below the measurement sample 4. Therefore, the electrode 10 and the measurement sample 4 are connected in an alternating manner. The electrode 10 has substantially the same size as the measurement sample 4 and forms a very large capacitance compared to other parasitic capacitances. An ammeter 5 is directly connected to the electrode 10 provided under the measurement sample 4. A bias voltage Vm is applied to the ammeter 5 by a variable power source 7. Moreover, the electron beam source 2, the acceleration electrode 11, the aperture 12, the deceleration electrode 13, etc. are provided like the current measuring device of 7th Embodiment.

  In the current measurement device of the present embodiment, the electron beam 3 emitted from the electron beam source 2 is accelerated by the acceleration voltage Va applied to the acceleration electrode 11 as in the current measurement device of the seventh embodiment. The accelerated electron beam 3 passes through the aperture 12 and only the electron beam 3 forming the electron beam axis center is taken out. The energy of the electron beam 3 that forms the axis center is much more uniform than the energy dispersion of the electron beam 3 when emitted from the electron beam source 2. The electron beam 3 having the same energy is decelerated in accordance with the deceleration voltage Vd applied to the deceleration electrode 13 and has a low energy before the measurement sample 4. The surface potential of the measurement sample 4 is controlled by a bias voltage Vm applied to the ammeter 5. Therefore, the surface of the measurement sample 4 is converted into the electron beam 3 having energy lower than that obtained by the deceleration electrode 13.

  The measurement sample 4 is capacitively connected to the ammeter 5. However, the capacitance generated between the measurement sample 4 and the electrode 10 is very large as compared with the capacitance generated between the measurement sample 4 and the electron beam source 2. Therefore, the bias voltage Vm applied to the ammeter 5 is substantially applied between the electron beam source 2 and the measurement sample 4.

[Ninth Embodiment]
FIG. 9 is a circuit diagram showing a current measuring apparatus according to the ninth embodiment of the present invention. 9, the same components as those in FIGS. 1 to 8 are denoted by the same reference numerals. The difference between the present embodiment and the seventh embodiment is that the control signal generator 8 outputs a measurement timing signal. That is, the control signal generator 8 serves as a control unit that controls the timing of applying the bias voltage Vm by the variable power source 7 in synchronization with the current measurement timing of the ammeter 5.

  In other words, the current measuring device of the present embodiment is configured to synchronize the timing at which the bias voltage Vm is applied to the ammeter 5 from the variable power source 7 and the timing at which the ammeter 5 measures current. There are features.

  In a normal state where no measurement is performed, the bias voltage Vm is not applied or is maintained at a globally set voltage. Then, the bias voltage Vm is applied to the ammeter 5 in synchronization with the timing at which the measurement is actually performed by the ammeter 5. The timing at which the bias voltage Vm is applied may be an alternating signal with a very short period or a relatively long on / off signal.

  According to the current measurement device of the present embodiment, the timing of applying the bias voltage Vm to the measurement sample 4 via the ammeter 5 can be synchronized with the current measurement timing. As a result, white noise or the like, which is a problem in current measurement, can be easily removed, and sensitivity and accuracy can be further improved with respect to measurement of the current flowing through the measurement sample 4.

[Tenth embodiment]
FIG. 10 is a circuit diagram showing a current measuring apparatus according to the tenth embodiment of the present invention. 10, the same components as those in FIGS. 1 to 9 are denoted by the same reference numerals. The difference between this embodiment and 8th Embodiment is a point which has the electrode 10 in this embodiment.

  That is, the current measuring device of the present embodiment is characterized in that a plate-like electrode 10 that is capacitively coupled to the measurement sample 4 is attached below the measurement sample 4. Therefore, the electrode 10 and the measurement sample 4 are connected in an alternating manner. The electrode 10 has substantially the same size as the measurement sample 4 and forms a very large capacitance compared to other parasitic capacitances. An ammeter 5 is directly connected to the electrode 10 provided under the measurement sample 4. Other components and operations are the same as those of the current measuring device of the ninth embodiment shown in FIG.

[Eleventh embodiment]
FIG. 11 is a circuit diagram showing a current measuring apparatus according to the eleventh embodiment of the present invention. In FIG. 11, the same components as those in FIGS. 1 to 10 are denoted by the same reference numerals. The present embodiment shows a current measurement circuit 5a as a specific example of the ammeter 5 in the current measurement device of each of the above embodiments.

  The current measurement circuit 5 a includes an operational amplifier 14, a bias power source 6 that applies a bias voltage Vm to the positive input terminal of the operational amplifier 14, and a high resistor disposed between the output terminal and the negative input terminal of the operational amplifier 14. R1. The measurement sample 4 is electrically connected to the negative input terminal of the operational amplifier 14.

  As a result, the current measurement circuit 5a constitutes a current-voltage conversion circuit using the operational amplifier 14. The current to be measured is introduced into the negative input terminal of the operational amplifier 14. The negative input terminal is internally connected to the gate of the FET transistor that constitutes the operational amplifier 14 and serves as an original signal for operational amplification. The operational amplifier 14 operates so that the voltage difference between the two input terminals is zero volts. Therefore, the high resistor R1 is biased so as to have the same magnitude as the current input to the negative input terminal. The voltage necessary for this bias becomes the output of the operational amplifier 14.

  On the other hand, when the operational amplifier 14 is operating normally, the voltage between the positive input terminal and the negative input terminal of the operational amplifier 14 is controlled to be zero volts. Therefore, when the bias voltage Vm is applied to the positive input terminal of the operational amplifier 14, the bias voltage Vm and the voltage at the negative input terminal are the same. Therefore, the potential of the measurement sample 4 can be substantially changed by applying a voltage to the positive input terminal of the operational amplifier 14 without applying a voltage directly to the measurement sample 4. Therefore, the measurement sample 4 is irradiated with an electron beam corresponding to energy obtained by subtracting the bias voltage Vm applied to the positive input terminal of the operational amplifier 14 from the electron beam irradiation energy Eir.

  Therefore, the current measurement apparatus of the present embodiment can reduce the effective energy received by the measurement sample 4 even when a high-energy electron beam is emitted from the electron beam source 2, without damaging the measurement sample 4. Sensitivity and accuracy can be improved in measuring the current flowing through the measurement sample 4.

[Twelfth embodiment]
FIG. 12 is a circuit diagram showing a current measuring apparatus according to the twelfth embodiment of the present invention. In FIG. 12, the same components as those in FIGS. 1 to 11 are denoted by the same reference numerals. The difference between the present embodiment and the eleventh embodiment is that the present embodiment does not include the bias power source 6 but includes the variable power source 7 and the control signal generator 8. The variable power source 7 constitutes a variable power source for an operational amplifier that applies a variable voltage to the positive input terminal of the operational amplifier 14. The control signal generator 8 outputs a voltage control signal for controlling the output voltage of the variable power source 7.

  That is, the current measuring device of this embodiment is characterized in that the bias voltage Vm applied to the operational amplifier 14 is variable by the voltage control signal from the control signal generator 8. The control signal generator 8 can vary the substantial energy level of the electron beam in the measurement sample 4 by outputting a voltage control signal. Here, the bias voltage Vm variably controlled by the voltage control signal may be a periodic signal such as a sine wave, a rectangular wave, or a sawtooth wave, or may be a trigger one-shot signal.

  As a result, the current measuring apparatus according to the present embodiment can perform current measurement by selecting an optimum application mode of the bias voltage Vm according to the attribute of the measurement sample 4 and the like, and can perform process evaluation with higher accuracy. can do.

[Thirteenth embodiment]
FIG. 13 is a circuit diagram showing a current measuring apparatus according to the thirteenth embodiment of the present invention. In FIG. 13, the same components as those in FIGS. 1 to 12 are denoted by the same reference numerals. The difference between the present embodiment and the twelfth embodiment is that the control signal generator 8 outputs an irradiation timing control signal to the aperture 12. More specifically, the irradiation timing of the electron beam is determined by applying a voltage to the blanking electrode existing above the aperture so that the electron beam does not pass through the aperture. Or you may use the mechanism in which the magnitude | size of an aperture itself changes with an electrical signal.

  That is, the current measuring device of this embodiment is characterized in that the bias voltage Vm applied to the operational amplifier 14 is synchronized with the electron beam irradiation timing. The control signal generator 8 controls the intermittent operation of the electron beam at the aperture 12 and the bias voltage Vm at the variable power source 7 in synchronization with the timing of measuring the current flowing through the measurement sample 4.

  According to the current measurement device of this embodiment, by synchronizing the on / off timing of the electron beam and the measurement timing in the current measurement circuit 5a, asynchronous noise (white noise or the like) entering the measurement system from the outside can be easily obtained. It can be removed.

  As described above, in the current measuring device of the present invention, measurement can be performed using an electron beam having very low energy. An electron beam having a low energy can improve the secondary electron emission probability and increase the measurement sensitivity. Further, the electron beam having low energy does not damage the measurement sample.

  Further, according to the present invention, the energy level of the electron beam can be changed greatly without changing the setting of the electron beam source, so that the energy level of the electron beam can be changed at high speed. For this reason, since the electron beam can be irradiated to the same place after changing the energy level of the electron beam, the measurement accuracy can be remarkably improved and the throughput can be improved when measuring using the electron beam of a plurality of energy levels. be able to.

  Further, according to the present invention, when one electron beam energy is set, various combinations of conditions can be made on the electron beam source side and the current measurement circuit side. For example, the waveforms of the high voltage power supply Vh, acceleration voltage Va, deceleration voltage Vd, bias voltage Vm, bias voltage Vm, and the like applied to the electron beam source can be combined. As a result, it is possible to adjust the energy dispersion state and the spatial distribution of electron beams having the same energy on average, so that an optimal combination of electron beam irradiation forms can be selected and used according to the application.

  Although the embodiments of the present invention have been described above, the current measuring device and the current measuring method of the present invention are not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the present invention. Of course, it can be added.

  For example, in the above-described embodiment, the current flowing through the measurement sample is measured by irradiating the measurement sample with the electron beam. However, the present invention is not limited to this, and is generated by irradiating the measurement sample with the electron beam. An electrode for collecting the scattered electrons or secondary electrons may be provided, and the current flowing through the electrode may be measured in the same manner as in the above embodiment.

  The present invention improves the sensitivity and accuracy of the measurement without damaging the measurement sample when measuring the current flowing through the measurement sample such as a semiconductor substrate by irradiation with an electron beam. Is useful for various current measuring devices and current measuring methods.

It is a figure which shows the electric current measurement apparatus which concerns on 1st Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 3rd Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 4th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 5th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 6th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 7th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 8th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 9th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 10th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 11th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 11th Embodiment of this invention. It is a figure which shows the electric current measurement apparatus which concerns on 11th Embodiment of this invention. It is explanatory drawing about an electric current measurement. It is a figure which shows an example of the conventional electric current measurement apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Chamber, 2 ... Electron beam source, 3 ... Electron beam, 4 ... Measurement sample, 5 ... Ammeter, 5a ... Current measurement circuit, 6 ... Bias power supply, 7 ... Variable power supply, 8 ... Control signal generation part, 9 ... XY stage, 10 ... electrode, 11 ... acceleration electrode, 11a ... acceleration power source, 12 ... aperture, 13 ... deceleration electrode, 13a ... deceleration power source, 14 ... operational amplifier

Claims (6)

A current measuring device for measuring a current generated in a measurement sample irradiated with an electron beam,
A chamber whose atmosphere is controlled so that an electron beam can be emitted;
An electron beam emission source that emits an electron beam at a set energy;
Means for irradiating a specific location of a measurement sample with an electron beam emitted from the electron beam emission source;
An electrode capacitively coupled to the measurement sample;
A current measurement circuit that at least amplifies the current flowing through the electrode;
Bias voltage applying means for applying a bias voltage to the measurement sample by applying a voltage between the current measuring circuit and a ground potential;
Control means for controlling the timing of bias voltage application to the measurement sample by the bias voltage application means in synchronization with the current measurement timing of the current measurement circuit;
A current measuring device comprising:   The current measuring apparatus according to claim 1, further comprising an aperture that allows a part of the electron beam emitted from the electron beam emission source to pass therethrough. An accelerating electrode for accelerating the electron beam emitted from the electron beam emission source to a first energy level;
An acceleration power source for applying a voltage to the acceleration electrode;
An aperture for passing a portion of the electron beam accelerated by the acceleration electrode;
A deceleration electrode that converts the energy of the electron beam that has passed through the aperture to a second energy level;
The current measuring device according to claim 1, further comprising a deceleration power source that applies a voltage to the deceleration electrode.   4. The current measuring device according to claim 1, wherein the voltage applying unit includes a variable power source that applies a variable voltage between the current measuring circuit and a ground potential. 5. . An operational amplifier that constitutes a component of the current measurement circuit and amplifies the current flowing through the measurement sample;
5. The current measuring device according to claim 1, further comprising a bias power supply that applies a voltage to a positive or negative input terminal of the operational amplifier. An operational amplifier that constitutes a component of the current measurement circuit and amplifies the current flowing through the measurement sample;
A variable power supply for an operational amplifier that applies a variable voltage to a positive or negative input terminal of the operational amplifier;
5. The current measuring device according to claim 1, further comprising: a control signal generation unit that outputs a signal for controlling an output voltage of the variable power source.

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