JPS61107170A - Electron beam probing apparatus - Google Patents

Abstract

PURPOSE:To short a measuring time as a whole, by reading stored data calculated with low time resolving power and binarizing the same to detect the change time of voltage. CONSTITUTION:The electron beam in a stroscopic electron beam apparatus 1 is allowed to irradiate IC14 on an XY stage through a pulse gate 11 and the quantity of the secondary electron from IC14 is detected by an analyser 13 and converted by an A/D converter 3 and added by an addition averaging processing circuit 9 while the average value of secondary electron output at analysis voltage V1 is stored in memory M1 through a switch SW and the average value of secondary electron output at analysis voltage V2 is stored in memory M2 through said switch W. The stored data are operated with respect to the ratio thereof by a ratio operation circuit 15 and collimated with the table in a radio table circuit 16 by a collimation circuit 17 to calculate the voltage of the wiring of IC14 while said voltage is stored in memory 18 and subsequently read to be inputted to a time magnifying detection system 19. In the detection system, measured data calculated with low time resolving power is differentiated and binarized to perform the detection of a time magnifying region and not only rising start time and period but also falling start time and period, both of which show the abrupt change in voltage, are calculated to be sent to a control circuit 6 and accurate measurement is enabled.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a strobe electron beam device used for measuring the potential of RC wiring, etc., and particularly relates to a voltage measuring device using an electron beam that speeds up voltage measurement. It is something.

One way to measure the voltage waveform of XC wiring, etc. is to irradiate a sample with an electron beam in a vacuum and indirectly measure the voltage at the irradiated part from the energy distribution of secondary electrons emitted from the sample. However, it takes a long time for measurement, and there is a demand for the development of a device that can perform measurement in a short time.

[Conventional technology]

The strobe electron beam device irradiates the IC to be measured with an electron beam once per cycle in synchronization with the operating cycle of the IC to be measured.
The secondary electrons are detected and the voltage at the irradiation point is measured.

Secondary electrons are detected by a hemispherical analyzer, and then converted into digital data and processed by an A/D converter, etc. However, the output from the analyzer is minute, and is measured multiple times and averaged. This is the calculated detection voltage.

The detection voltage does not have a simple proportional relationship with the voltage at the point being measured; instead, the relationship between the analysis voltage and the detection voltage of the analyzer is determined by changing the analysis voltage applied to the analyzer during measurement, and is based on a predetermined standard. The voltage at one point at the timing of the measured point is determined by comparing it with the analytical curve.

In order to obtain the voltage waveform that changes over time at the point to be measured, use the method described above to synchronize the IC to be measured with the operating cycle and slightly delay the timing (for example, 1/32 of the IC drive pulse period). The IC to be measured is irradiated with an electron beam once per cycle, the secondary electrons are detected, and the voltage at the irradiation point is measured by the method described above. By sequentially repeating this delay operation of IT/32 32 times, the voltage waveform of the IC is obtained. If you want to observe even more precise waveforms, for example,
Shorten the delay time to IT/256 and increase the number of measurement points to 256.
The more points you have, the better.

[Problem that the invention seeks to solve]

In the above-mentioned conventional strobe electron beam device, the output of the secondary electrons is extremely small and it takes time to repeatedly measure the energy of the secondary electrons just to find the voltage at one point. Furthermore, there is a problem in that when attempting to precisely measure a voltage waveform, the number of measurement points increases and it takes a long time.

[Means for solving problems]

The present invention provides a strobe electron beam device that solves the above-mentioned problems, and includes a storage means for storing voltage waveform data obtained with low time resolution, and a digital differentiation method for reading out the stored data. The problem is solved by an electron beam probing apparatus characterized by comprising circuit means for performing binarization and detecting the start time and change time of the rise or fall of the voltage.

[Effect]

The voltage waveform does not necessarily change greatly over the entire measurement range, and it is not necessary to precisely measure parts with small changes.
- Measure the voltage waveform at coarse intervals by increasing the delay time, and store the data at each measurement point in memory. This is read out and digitally differentiated (difference from the previous value) to determine the amount of change, using a certain standard; The total measurement time can be shortened by remeasuring only that part at finer intervals if necessary.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a strobe electron beam device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram showing waveforms of various parts. An electron beam emitted from an electron gun (not shown) in the strobe electron beam device 1 passes through a pulse gate 11 to an X-Y beam that can move in the X-axis direction and the Y-axis direction.
The object to be measured, that is, the IC 14 placed on the stage 12
is irradiated.

By the irradiation, secondary electrons are emitted from the IC 14, and the amount thereof is detected by the analyzer 13.

The output is amplified by detector 2 and converted into a secondary electron signal by A/
It is added to the D converter 3 and converted into digital data.

Since the detected output is minute, the above-described operation is repeated for multiple cycles and the output is integrated. Note that this control is performed by a control circuit 6 described below.

The IC 14 is driven by a driver 4, and the operation period is determined by the driver 4 and applied to the delay circuit 5 as a repetitive signal. For example, multiple times in synchronization with the operating cycle.
Since the analysis is performed 32 times at the same analysis voltage, the delay circuit 5 outputs a delay pulse proportional to the amount of delay applied by the control circuit 6, for example. Note that the delay pulse outputted here corresponds one-to-one to the repetitive signal applied from the driver 4. The delayed pulse is then applied to the pulse generator 7.

The pulse generator 7 receives frequency data input by the control circuit 6, such as 1/n cycle of the operating cycle (in the waveform diagram of FIG. 2 of this embodiment, one pulse is set within the operating cycle T, that is, n=1, Accordingly, n clocks starting from a delay pulse are output to the gate circuit 8 based on data instructing n pulses to be inserted within the operation period T.

FIG. 2(a) shows the repetition signal, and FIG. 2(b) shows the output of the pulse generator 7. For example, when the pulse generator 7 generates pulses in one cycle and measures 32 points of the waveform within one cycle (one cycle is divided into 32), the delay circuit 5 described above is connected to the control circuit 6. A delay amount that changes in units of 1/32 of the repetitive operation period T is added. Note that, of course, in order to measure one point of the signal under test, measurement is performed multiple times (for example, N times) in order to add minute outputs. Therefore, the above-mentioned delay amount changes in units of N cycles.

The output of the pulse generator 7 mentioned above is applied to a gate circuit 8. This gate circuit 8 connects the pulse gate driver 0 to the pulse generator 7 by a control signal applied from the averaging circuit 9.
Outputs more added pulses. This gate circuit 8 inputs the strobe electron beam when the averaging process, etc. is completed.
This is a circuit to prevent C14 from being irradiated. If measurement is in progress, this input pulse is applied to the pulse gate 11 via the pulse gate driver 10 to turn on and off the pulse gate 11 that irradiates the electron beam.

As a result, the object to be measured is irradiated with a strobe electron beam as shown in FIG. 2(C).

On the other hand, sampling signals are outputted from the pulse gate driver 10 to the A/D converter 3 in one-to-one correspondence to the strobe pulses applied to the pulse gate driver 10.

The A/D converter 3 starts sampling with this (1) and converts the secondary electronic signal shown in FIG. 2(d) output from the detector 2 into digital data.

The averaging processing circuit 9 is a circuit that performs addition processing on the digital signals applied from the A/D converter 3 in correspondence with pulses within the operating cycle, and has a register that stores the addition results. The averaging processing circuit 9 clears the contents of the register and starts addition processing in response to the start signal from the control W1 circuit 6. Furthermore, when the addition processing of the number of averages added by the control circuit 6 is performed, an end signal is sent to the control circuit 6. At the same time, the average result is output to the memory M via the switch SW. In the case of Fig. 2 1d), a, +a, +a, ・
..., b, +b! +b, . . . is an addition of 1 grade.

The memory M stores the average value of the secondary electron output at the analysis voltage V, that is, the detection voltage, and the memory M2 stores the average value of the secondary electron output at the analysis voltage V2.
The average value of the secondary electron output at the time, that is, the detected voltage is memorized. Note that the switch SW is a digital switch that is switched when the analysis voltage (V+, Vt) applied from the control circuit 6 changes.

Memory MI by changing the delay of the operation described above.

Each data as shown in FIG. 3 is stored in M2.

The memory Ml at this analysis voltage V,,Vt.

The data of M2 is input to the ratio calculation circuit 15 and analyzed voltage V
Find the analyzer output S+ and StO ratio at , ,V,
Furthermore, the wiring voltage and analysis-output ratio (S.

/S+).

It is compared by the table circuit 16 and the matching circuit 17, and the IC 14
The voltage of the wiring is found. (The method of obtaining this is described in detail in Japanese Patent Application No. 198818/1982 by the present inventors, so it is omitted here.) The voltage of the wiring of the IC 14, which is obtained by being verified by the verification circuit 17, is stored in the memory 18. Stored. As mentioned above, this data was delayed little by little with respect to the reference drive pulse (
Here, the voltage values are obtained by a pulse (1/32) of the operating period T, and the voltage values of 32 points of the voltage waveform of the IC 14 are sequentially stored in the memory 18, and are read out and used in the next time expansion detection system. 19 is input.

FIG. 4 is a block diagram for explaining the function of the time expansion detection system, and FIG. 5 is an output voltage diagram of each circuit.
0. The signal is input to a time expansion detection system 19 composed of a disulfide circuit 21 and a time expansion area detection circuit 22. Low time resolution (for example, the delay time of one pulse is 1/3 of the operating period T)
The data in FIG. 5 (al) measured at 32 points (measured at 32 points as 2) and stored in the memory 18 is input to the digital differentiation circuit 20, and the difference with the previous value is taken, and the data is converted into the digital differentiation shown in FIG. 5(b). value is obtained.

This digital differential value is then binarized by a binarization circuit 21 based on a constant reference value as shown in FIG. 5(C). However, the absolute value of the digital differential value shall be taken. The output of the binarization circuit 21 is input to the time expansion area detection circuit 22, and the start time t of the rise indicating a steep change in voltage, the period Δtl+the start time 1t of the fall, and the period Δtt are determined and sent to the control circuit 6. is input.

The rise start time t and period Δ determined in this way
Regarding tI+ falling start time Lffi+ and period Δt2, if you measure only those parts again with high time resolution (for example, measure the pulse delay time at 1/256 of the operating period T at 256 points), you will be able to see the parts that have large changes in a short time. Can be measured precisely.

〔Effect of the invention〕

As explained above, according to the present invention, parts of the voltage waveform with little change can be measured quickly with low time resolution, and at the same time, sections with large changes can be detected, and only that part can be precisely measured again with high time resolution. This has the effect of shortening the overall measurement time.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the configuration of a strobe electron beam device according to an embodiment of the present invention, Fig. 2 is a waveform diagram showing waveforms of each part, and Fig. 3 shows each data stored in memories M+ and Mz. 4 is a block diagram for explaining the function of the time expansion detection system, and FIG. 5 is an output voltage diagram of each circuit. In the figure, 4 is a driver, 5 is a delay circuit, 6 is a control circuit, and 7 is a control circuit. Pulse generator, 8 is a gate circuit,
9 is an averaging processing circuit, 10 is a gate pulse driver, 11 is a pulse gate, 12 is an X-Y stage, 13
is an analyzer, 14 is an IC115 is a ratio calculation circuit,
16 is a ratio table circuit, 17 is a collation circuit,
Reference numeral 18 indicates a memory 19, a time expansion detection system, 20, a digital differentiation circuit, 21, a binarization circuit, and 22, a time expansion area detection circuit.

Claims (1)

[Claims] In a strobe electron beam device equipped with an energy analyzer, a storage means for storing voltage waveform data of a part to be measured determined with low time resolution, a circuit for reading out the stored data and digitally differentiating it, and a circuit for digitally differentiating it by reading out the stored data and converting it into binary values. 1. An electron beam probing apparatus, comprising: a circuit for detecting a start time and a change time of a rise or fall of the voltage waveform.