JPS6332945A - Device for testing electronic device - Google Patents

Abstract

PURPOSE:To make it possible to accurately measure the potentials of a plurality of beam irradiation positions by providing setting means for setting a reference secondary electron signal amount for measuring the potentials of beam irradiation positions in response to one or more signal amount deciding cause values. CONSTITUTION:A material designation signal (a) is input to a multiplexer 184 in a potential measuring circuit 18, voltage sources 185 for generating a reference voltage responsive to a material is connected to each channel in the multiplexer 184, the value is input as a reference secondary electron signal amount to a differential amplifier 181, an energy analysis voltage is so controlled as to bring the reference amount into coincidence with the detected secondary amount, and the potential is then measured. A current amplifier 39, a multiplier 183, the multiplexer 184 and the sources 185 constitutes setting means for setting the reference amount in response to the signal amount deciding cause. Since the potential measurement can be performed on the basis of separate reference secondary electron signal amounts responsive to the irradiation positions, the potentials can be accurately measured even when the materials are different with different S curves.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention irradiates an electronic device such as a VLSI with a charged beam, analyzes the energy of the secondary electrons emitted thereby, and analyzes the detected secondary electrons. (hereinafter referred to as "detected secondary electrons") signal amount and a set standard secondary electron signal amount are compared based on energy analysis, and based on this comparison, the potential of the irradiation position on the electronic device is measured and the electronic device is tested. The present invention relates to a test device that performs testing.

[Conventional technology]

In electronic device testing equipment such as an electron beam tester, an energy analyzer is used to measure the potential at the beam irradiation point.

Conventional energy analyzers and potential measurement methods are described, for example, in E. Menzel and E. Kubarek, "Secondary Electricity Pre-Detection System for Quantitative Potential Measurement," Scanning Vol. 1, 151-171+1983 (E. Menzel
and u, Kubalek, r secondar
yElectron Detection System
tems for QuantitativeVo
ltage Measurements J, 5CA
NNING vol, 5 +151-171 (19
83) ).

Next, the contents described in the above literature will be explained.

Secondary electrons emitted from a certain sample by irradiation with a charged beam have an energy distribution as shown in FIG. 7 depending on the material.

In FIG. 7, 1 is when the sample voltage vsp is +5V,
2 is the sample voltage VSF when it is OV, 3 is the sample voltage V3P
The case where is 15■ is shown. In this way, when the voltages V and P are applied to the sample, the energy distribution shifts to the lower energy side by the voltage. Therefore, the sample potential can be measured from the amount of shift in this energy distribution.

This will be explained using the device 5 graphs shown in FIGS. 8 and 9. In FIG. 8, 4 is an electron beam, 5 is a sample, 6 is a power source for providing a sample potential vsr, 7 is a secondary electron detector for detecting secondary electrons SE generated by irradiation with the electron beam 4, and 8 is a secondary electron detector for detecting secondary electrons SE generated by irradiation with the electron beam 4. Sample 5 to analyze energy
and a deceleration grid provided between the secondary electron detector 7 and the secondary electron detector 7;
is a power source for applying a potential VG to the deceleration grid 8.

When a negative voltage -■ is applied to the deceleration grid 8, the secondary electrons SE emitted from the sample 5 are decelerated, and only the secondary electrons with energy higher than ■ pass through the deceleration grid 8 and are detected as secondary electrons. Reach vessel 7. When the secondary electrons passing through the deceleration grid 8 are detected by changing this deceleration voltage vG, the 9th
An integral type energy distribution curve (S curve) of 11°12.13 as shown in the figure is obtained. S curves 11, 12 and 13 are sample potential v, 2 is +5V, OV and -5■
The case is shown below. As shown in FIG. 9, when the sample potential VSF changes, the S curve shifts as in the case of FIG. 7. Therefore, when a constant voltage VGI is applied to the deceleration grid 8, the amount of secondary electron signal I is detected according to the sample potential vspO value. , changes. Conversely, when the voltage V3F is applied to the deceleration grid 8, the amount of secondary electron signal becomes equal to that when the sample potential is 0. That is, if the secondary electron signal amount when the potential of the deceleration grid 8 is ■6□ and the sample potential vs-p is OV is 15EDO, even when the sample potential vsp changes, the secondary electron signal amount will be I3EDO. By controlling the potential of the deceleration grid 8 so that the sample potential v
sp can be determined from the potential of the deceleration grid 8.

For example, when the sample potential VSP changes from OV to +5V, if the potential of the deceleration grid 8 is set to the potential VaS at point P, the amount of secondary electron signal will be I! It remains EDO.

From vcs VG+, sample potential V, = +5
V can be found.

An energy analyzer consists of a hemispherical or planar mesh electrode (grid) placed above a measuring electronic device. As a potential measurement system using such an energy analyzer, for example, E. Menzel and M. Brunner, "Improvement of the characteristics and performance of a secondary FFL output device", J. Bank Science Chikunoroshii B. 1,
1348.1983 (E, Menzel and M
, Brunner+ rcharacterizati
onand performance improve
ment of 5secondary el-ectr
on analyzersJ, J+Vac, Sc
i, Technol, B1+1348 (1983)).

The above measurement system is shown in FIGS. 10 and 11.

FIG. 10 is a perspective view of the energy analyzer, and FIG. 11 is a system diagram showing the configuration of the potential measurement system. Figure 1O and 1
In Figure 1, 14 to 16 are three grids that make up the energy analyzer, and grid 14 is used to apply a positive voltage to alleviate the influence of potential around the wiring to be measured (local electric field effect). An extraction grid for extracting secondary electrons, grid 15 is an energy analysis grid, grid 16 is a subresolution grid, and a secondary electron detector 7
An electric field is applied to make it easier for the secondary electrons SE to go toward . Further, 17 is a linearization unit for applying feedback so that the detected secondary electron signal amount becomes equal to the reference value, and as mentioned above, the detected secondary electron signal amount is equal to the reference secondary electron signal amount. The voltage of the energy analysis grid is controlled so that it is equal, and the potential of the sample is measured from that voltage. In FIGS. 1O and 11, the same or equivalent parts as in FIG. 8 are given the same reference numerals.

On the other hand, an electron beam tester using a strobe SEM has been put into practical use, which supplies a driving voltage to an electronic device from a contact-connected terminal from the outside, causes it to operate, and measures the logic state at that time and the time change in the potential of any wiring. has been done. Devices that are measured with this type of apparatus are either finished products or semi-finished products before the passivation film is applied. In this case, the beam irradiation position at which the temporal change in potential is measured for measurement of delay time, etc. is usually the uppermost layer wiring, and the same material is often used for the plurality of measurement positions. Also,
The driving voltage is supplied externally, and an electron beam is used only for potential measurement, and the beam current is not changed during measurement. Therefore, the reference secondary electron signal amount mentioned above is kept constant during the measurement.

On the other hand, Japanese Patent Application No. 129937/1983 proposes a testing device that uses an electron beam to supply voltage to measure the electrical characteristics of an electronic device in a non-contact manner during manufacture. In this type of apparatus, in order to set the potential of the irradiation point to a target value, the beam current is changed based on the measurement result of the potential.

[Problem that the invention seeks to solve]

However, during measurements during manufacturing, the electrode material may be polysilicon at some irradiation points and aluminum at other irradiation points, and in such situations, the potential measurement described above may be In this case, the standard amount of secondary electron signal varies depending on the material, accelerating voltage, and beam current. Therefore, if you change the irradiation position,
Alternatively, there is a problem in that errors occur in potential measurement when the accelerating voltage and beam current are changed.

The purpose of the present invention is to solve various problems in the prior art, and to provide an electronic device that can measure the potential at multiple irradiation positions with high precision, and can also measure the potential with high precision even when the accelerating voltage and beam current change. The purpose is to obtain test equipment.

[Means for solving problems]

In order to achieve these objectives, the present invention analyzes the energy of secondary electrons generated by irradiation with a charged beam,
In a test device that tests an electronic device by comparing the detected amount of secondary electron signal and a set reference amount of secondary electron signal based on energy analysis, and measuring the potential at the beam irradiation position based on this comparison, A setting means is provided for setting a reference secondary electron signal amount for measuring the potential at the beam irradiation position according to the value of one or more signal amount determining factors.

[Effect]

In the present invention, a separate reference secondary electron signal amount is set for each measurement point made of different materials. Further, the reference secondary electron signal amount is changed in accordance with changes in the acceleration voltage and beam current irradiation conditions. Potential measurement is performed by comparing the reference secondary electron signal amount and the detected secondary electron signal amount.

〔Example〕

FIG. 1 is a system diagram showing an embodiment of an electronic device testing apparatus according to the present invention. Electron beam 2 coming out of the lens barrel
3 is irradiated onto the electronic device 34 on the stage 35, and the energy of the secondary electrons generated at this time is analyzed by the energy analyzer 36 and detected by the secondary electron detector 37. The output of this secondary electron detector 37 is amplified by an amplifier 38. 18
is a potential measuring circuit that measures the potential, and the differential amplifier 18
1. Energy analysis voltage control circuit 1822 multiplication circuit 18
3. Multiplexer 184. It is composed of a voltage source 185. 24 is an accelerating voltage source that accelerates the electron beam; 25
is an aligner. 26 is a condenser lens, and 27 is a lens power supply. The beam current is changed by controlling the lens power supply 27. 28 is a blanker for turning on and off the beam, 29 is a blanking power supply, and 30 is a blanking aperture. 31 is a deflector for deflecting the beam, and 32 is a deflection power source.

Although only one set of deflector and aligner is shown in FIG. 1, there are two sets of deflectors and aligners in the x and y directions. 33 is an objective lens, and the focus is adjusted by changing the voltage of an objective lens power source (not shown).

Reference numeral 20 denotes an irradiation position control circuit, which specifies a deflection amount to the deflection control circuit 19 according to the irradiation position of the beam. The deflection control circuit 19 changes the irradiation position by changing the voltage applied to the deflection power source 32 according to the amount of deflection. Further, the irradiation position control circuit 20 tabulates the material of each irradiation position with reference to design data and the like. That is, a table is prepared in which the amount of deflection and surface material are set for each irradiation position, and at the same time the amount of deflection is specified to the deflection control circuit 19, a signal specifying the material is sent to the potential measuring circuit 18. This material designation signal a is, for example, 1 for aluminum. Polysilicon is coded as 2.

This material designation signal a is input to the multiplexer 184 in the potential measurement circuit 18 and is used to designate a channel therein. A voltage source 185 that generates a reference voltage depending on the material such as aluminum or polysilicon is connected to each channel in the multiplexer 184, and by selecting a channel, the value can be set as the reference secondary electron signal amount. The voltage is input to the differential amplifier 181, and the potential is measured after controlling the energy analysis voltage so that the reference secondary electron signal amount and the detected secondary electron signal amount match. Also,
Even if the material is irradiated at the same position, the amount of secondary electron signal increases in proportion to the beam current. Therefore, it is necessary to also change the reference secondary electron signal amount in proportion to the beam current. In the apparatus shown in FIG. 1, a current amplifier 39 converts the beam current into a voltage proportional to the current, and a multiplier circuit 1 in the potential measuring circuit 18 converts the beam current into a voltage proportional to the current.
83, and the product of a voltage proportional to this current and a reference voltage input from a multiplexer 184, which varies depending on the material, is input to the differential amplifier 181 as a reference voltage.

Here, the beam current is measured by the current amplifier 39, but it is also possible to detect reflected electrons on the electronic device 34 and input a voltage proportional to the amount to the multiplication circuit 183. Alternatively, the beam current may be measured midway inside the lens barrel and that value may be used. In the device of FIG. 1, the current amplifier 391
Multiplier circuit 183, multiplexer 184. voltage source 185
constitutes a setting means for setting the reference secondary electron signal amount according to the signal amount determining factor.

With the device shown in Figure 1, potential can be measured based on separate reference secondary electron signal amounts depending on the irradiation position, so even if the materials are different and the S curves are different, the potential can be measured accurately. can.

Furthermore, since the reference secondary electron signal amount is changed in proportion to the beam current, potential measurement can be performed with high accuracy even when the potential is set by changing the beam current.

In the apparatus shown in FIG. 1, a multiplier circuit 183 is used, but the value obtained by converting the beam current into a voltage proportional to the current by the current amplifier 39 is inputted to the difference amplifier 181 as a reference secondary electron signal amount via the amplifier. Good too. In this case, in order to change the gain of the amplifier depending on the material, the gain adjustment resistor is switched by a multiplexer using the material designation signal a.

FIG. 2 shows a second embodiment of the present invention, and the same or equivalent parts as in FIG. 1 are given the same reference numerals. The differences between the device configuration in FIG. 2 and the device configuration in FIG. 1 will be described. The beam current control circuit 40 controls the value of the voltage of the lens power supply 27 (hereinafter referred to as "lens voltage") that changes the beam current. To do this, a table is prepared that shows how much lens voltage should be set for the required beam current, and the lens voltage is set based on that value. At this time, the value of the beam current is simultaneously input to the reference voltage control circuit 186 of the potential measurement circuit 18. Further, the value of the acceleration voltage is determined by controlling the acceleration voltage source 24 with the acceleration voltage control circuit 41. At this time, the value of the acceleration voltage is set by the reference voltage control circuit 186.
send to Further, the reference voltage control circuit 186 is sent data encoding the material of the irradiation position from the irradiation position control circuit 20 . Based on these data, the reference voltage control circuit 186 sets the output voltage of the reference voltage generation source 187 so that the value of the reference secondary electron signal amount varies depending on the acceleration voltage and material and is proportional to the beam current. In the device shown in FIG. 2, the reference voltage control circuit 186 and the reference voltage generation R
187 constitutes a setting means.

FIG. 3 shows a third embodiment of the invention. In FIG. 3, 50 is a control computer, 51 is an AD converter, and 52 to 5
5 is a DA converter. In FIG. 3, the same or equivalent parts as in FIG. 1 are given the same reference numerals. This device has a configuration in which the voltage corresponding to the reference secondary electron signal amount of the potential measuring circuit 18 is directly set from the control computer 50 by the DA converter 55 in accordance with changes in the acceleration voltage/beam current and changes in the irradiation position. I'm taking it. In addition to this, the control computer 50 also supplies a lens power source 2 that changes the beam current.
7 is set by the DA converter 53, the voltage value of the deflection power source for changing the irradiation position is set by the DA converter 52, and the voltage value of the acceleration voltage source 24 is set by the DA converter 54. Further, the reference voltage Vr of the potential measurement circuit 18 is set by the DA converter 55. The reference voltage VrO value at this time is kl
It becomes the shape of p. Here, Ip is a beam current, and k is a constant determined by the accelerating voltage and material. For the value of k, prepare a table in advance of how much it should be for materials such as aluminum and polysilicon and accelerating voltage.
Normally, the secondary electron emission ratio has a peak when the accelerating voltage is several hundred volts, and decreases with accelerating voltage at higher accelerating voltages. The value of k may be set from this functional form.

There is a table on the control computer 50 that shows how many lens voltages should be set in order to set the beam current to a certain value. Set with . Further, the beam irradiation position is set by the DA converter 52, and the material of that part is known from the design data. therefore,
The value of k is determined at the time when the irradiation position and acceleration voltage are set using the DA converter. In addition, the beam current is also determined when setting the lens voltage, and the product of both is calculated and the value is set as DA.
The settings are made using the converter 55. In the apparatus shown in FIG. 3, the control computer 50 and the DA converter 55 constitute setting means.

FIG. 4 shows a fourth embodiment of the present invention, and is an example of a test apparatus having two lens barrels. In FIG. 4, the same or equivalent parts as in FIG. 3 are given the same reference numerals. Although the lens barrel that generates the electron beam 21 has the same structure as the lens barrel that generates the electron beam 22, it does not necessarily have to be the same lens barrel. The electron beams 21 and 22 are irradiated onto the electronic device 34 on the stage 35, and the energy of the secondary electrons generated at this time is analyzed by the energy analyzer 36 and detected by the secondary electron detector 37. Next, the output of the secondary electron detector 37 is amplified by an amplifier 38. The output potential of the potential measurement circuit 18 is read into the control computer 50 by the AD converter 51. From the control computer 50, the DA converter 52,
53 controls the deflection amount and beam current of each beam. Further, the reference voltage of the potential measurement circuit 18 is also D.
It is set by the A converter 55.

In FIG. 4, 42 is a hold circuit, and 43 is a differential amplifier, which is used to separate the secondary electrons generated from two irradiation positions and measure the potential at each irradiation position. When multiple beams are used, secondary electrons are generated simultaneously from multiple irradiation positions, so it is necessary to separate them and detect the potential at each point. A method for separating secondary electrons caused by the first beam and secondary electrons caused by the second beam will be described below. First, when the first beam is turned on and the second beam is turned off, the output of the amplifier 38 is input to the hold circuit 42 by the switch S1, and the detected secondary electron signal amount Sa at this time is held. I'll keep it. Next, while keeping the first beam on, turn on the second beam.
When irradiated with a beam of 1. Secondary electrons from the second beam are simultaneously detected by a secondary electron detector 37. At this time, the secondary electron detector 37 is connected to the differential amplifier 43 by the changeover switch S1. After the detected secondary electron signal amount output from the secondary electron detector 37 is amplified by the amplifier 38, it is input to the differential amplifier 43, and the secondary electron signal amount due to the first beam is held in the hold circuit 42. Sa
This difference is input to the potential measuring circuit 18 to measure the potential. This makes it possible to separate a plurality of secondary electrons generated from a plurality of irradiation positions and measure the potential at each irradiation position. At this time, the reference voltage of the potential measuring circuit 18 is set by the D, A converter 55. This value is the material 'ff at the irradiation position of the first beam, acceleration 1
! It is set to a value obtained by multiplying the value of pressure k by the beam current of the first beam. When the first beam and the second beam are exchanged, the reference voltage is set to a value obtained by multiplying the material and accelerating voltage k at the irradiation position of the second beam by the beam current of the second beam.

In the apparatus shown in FIG. 4, the control computer 50 and the DA converter 55 constitute setting means.

The apparatus shown in FIG. 4 is an apparatus that can be used to measure transistor characteristics of a device. For an example of the use of this device, MO3I-transistor It+-■. A method for measuring characteristics, threshold voltage, etc. will be explained using FIGS. 5 and 6 as an example. In FIGS. 5 and 6, 21 and 22 are electron beams, G is a gate portion, D is a drain portion, S is a source portion, 60 is an oxide film of SiO, and 61 is a silicon substrate.

First, the electron beam 21 is irradiated onto the gate part G of the transistor, and while measuring the potential of this part, the beam current is adjusted by changing the lens voltage using the DA converter 53 so that the potential becomes a desired value. At this time, the reference voltage of the potential measuring circuit 18 is changed by the DA converter 55 in accordance with the change in the beam current, and the potential is measured. Generally, the potential is beam current 1p, secondary electron emission ratio δ, and leakage current ■.

Then, it is saturated at a potential where I, = (δ-1)Ip. Since the leakage current IL is a function of potential, the saturation potential can be changed by changing the beam current. First, the gate voltage is set so that the transistor turns off. This setting is possible by changing the beam current while measuring the potential.

Next, the eleventh beam 22 is irradiated onto the drain portion of the transistor. At this time, the DA converter 55 sets a reference voltage for potential measurement to a value obtained by multiplying the value of k of the material of the drain portion by the beam current of the electron beam 22. Due to this beam irradiation, the potential at the drain portion gradually increases.

This potential rise is measured. The potential at the drain part is ■. ,
The capacitance of this part is 00, and the amount of charge stored in this capacitance is QD.

When the leakage current is II and o, the following equation holds true.

dVo/dt# (dQti/dt)/Cn= ((δ
−10+1 ILD IJ・・・・・(1) At the gate voltage at which the transistor turns off, i,=o. The beam current 1p can be determined from the set value of the lens voltage or can be directly measured using a Faraday cup. Further, CIl can be determined from the area of the electrode and the thickness of the insulating film. Further, the secondary electron emission ratio δ is determined from a table of values previously measured for each material. Using the above values, the leakage current ILD can be determined from the time change in potential dVn/dt, and ■LI, -■. characteristics are obtained. next,
A similar measurement is performed by changing the set value of the gate voltage to a voltage that causes the drain current to flow. At this time, the setting of the reference voltage for potential measurement is as described above. After this measurement is completed, by similar calculation, IL
D+I. Find the value of Here, the ILDO value is It, o
Since Vo characteristics have been obtained, drain current ■ can be obtained by subtracting this value. can be found. From this, the ID-V+ characteristic is obtained. Also, if you measure the gate voltage by changing it sequentially and plot the drain current when the drain voltage is a certain value, you can see that the drain voltage V
II for D, -V. The characteristics can be obtained and the dark value of the transistor can be determined.

〔Effect of the invention〕

As explained above, in the case of measuring the potential of a plurality of beam irradiation positions, the present invention sets a separate reference secondary electron signal amount in advance for each measurement point of different materials, and sets this reference secondary electron signal amount and By measuring the potential by comparing the amount of detected secondary electron signals, even if there are differences due to the material, it is possible to compensate for the differences, making it possible to measure the potential at multiple points with high precision. effective.

In addition, when the accelerating voltage and beam current change, the reference secondary electron signal amount is changed in accordance with the change in the accelerating voltage, and the reference secondary electron signal amount is also changed in proportion to the beam current. Even when measuring the potential at the irradiation position while changing the conditions, it is possible to eliminate the influence of changes in the irradiation conditions, which has the effect of enabling highly accurate potential measurement.

Therefore, the gate of the transistor before the wiring process.

This method has the advantage that the electrical characteristics of a transistor can be measured in-process even when the drain material is different.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing one embodiment of an electronic device testing apparatus according to the present invention, FIG. 2 is a system diagram showing a second embodiment of the present invention, and FIG. 3 is a system diagram showing a third embodiment of the present invention. FIG. 4 is a system diagram showing a fourth embodiment of the present invention, FIGS. 5 and 6 are connection diagrams and cross-sectional views of transistors for explaining the test method, and FIGS. Fig. 9 is a graph showing the principle and method of potential measurement using an energy analyzer, Fig. 8 is a conceptual diagram thereof, and Figs. 10 and 11 are perspective views showing an example of an energy analyzer and potential measurement. FIG. 2 is a system diagram showing the configuration of the system. 21-23... Electron beam, 24... Accelerating voltage source,
25... Aligner, 26... Condenser lens, 2
7...Lens power supply, 28...Blanker, 29...
Blanking power supply, 30... Blanking aperture, 31... Deflector, 32... Deflection power supply, 33...
Objective lens, 34... Electronic device, 35... Stage, 36... Energy analyzer, 37... Secondary electron detector, 38... Amplifier, 39... Current amplifier,
40... Beam current control circuit, 41... Acceleration voltage control circuit, 42... Hold circuit, 43,181...
Differential amplifier, 50... Computer, 51... AD converter, 52-55... DA converter, 60... S
iO□ oxide film, 61... silicon substrate, 182...
Energy analysis voltage control circuit, 183... multiplication circuit,
184... Multiplexer, 185... Voltage source, 1
86... Reference voltage control circuit, 187... Reference voltage generation source.

Claims (4)

[Claims] (1) Analyze the energy of secondary electrons generated by irradiation with a charged beam, compare the detected secondary electron signal amount and a set reference secondary electron signal amount based on the energy analysis, and make this comparison. A test device for testing an electronic device by measuring the potential at a beam irradiation position, comprising a setting means for setting the reference secondary electron signal amount according to the value of one or more signal amount determining factors. An electronic device testing device characterized by: (2) The signal amount determining factors are the material of the irradiation position, acceleration voltage,
2. The electronic device testing apparatus according to claim 1, wherein the beam current is one to three of the three factors of the beam current. (3) The electronic device testing apparatus according to claim 1, wherein the signal amount determining factors have values arranged in a table. (4) The electronic device testing apparatus according to claim 1, wherein the reference secondary electron signal amount is set in proportion to the secondary electron emission ratio or the beam current.