JPH03180044A - Electron beam apparatus - Google Patents

Abstract

PURPOSE:To shorten the time of measurement by providing an edge-timing measuring part, and performing both the observation of a measured waveform and the measurement of timing at the same time. CONSTITUTION:A specified test vector is down-loaded to an LSI driving circuit 9. A multiple-stroboscope measuring system, i.e., a projecting means 31 including an EB-pulse driver 12 and the like, and a measuring means 32 are initialized. Then test patterns are repeatedly generated with the LSI driving circuit 9 in accordance with the test vector. A trigger signal for indicating the start timing of the test pattern and the lock signal for driving an IC 4 under test are supplied to the IC 4 under test. Thereafter, sampling of the secondary electron signals is performed in synchronization with the pulse signal of the clock signal with the trigger signal as a reference in the projecting means 31. The signal voltage of the IC 4 under test is measured based on the result of the sampling. The edge timing is measured with an edge-timing measuring part 19. Thus the measuring time can be shortened.

Description

[Detailed Description of the Invention] [Summary] The purpose of the present invention is to provide an electron beam device that can simultaneously perform both measurement waveform observation and timing measurement to shorten measurement time. For the measurement location,
An electron beam device in which an irradiation means irradiates the sample with an electron beam pulse synchronized with an operation signal in a phase-controlled manner, and a measurement means detects secondary electrons emitted from the measurement point to measure the voltage at the measurement point, edge approximate detection means for determining an approximate value of edge timing at which the voltage measurement waveform crosses a predetermined threshold from the waveform data of the measurement location; and voltage waveform data near the approximate value of edge timing determined by the edge approximate detection means. and edge measuring means for determining the edge timing of the measured waveform based on the slope of the measured waveform.

[Industrial application field]

The present invention relates to an electron beam device for measuring the operating voltage of LSIs and the like, and particularly to an electron beam device called an electron beam tester for determining the timing at which the operating voltage crosses a threshold voltage with high precision.

2. Description of the Related Art As LSIs become more highly integrated and operate at higher speeds, techniques for performing operation analysis, failure analysis, operation tests, etc. of LSIs using electron beams have become important.

In this LSI operation analysis, for example, one of the basic measurements is to measure the time difference between two waveforms, such as gate delay time.

As a means of measuring the voltage inside an IC that operates at high speed,
A strobe electron beam device that repeatedly operates an IC and irradiates the surface of the IC with a pulsed electron beam in synchronization with the repeated operation to obtain a secondary electron signal is attracting attention. According to this, it is possible to create a voltage distribution image at any phase during the repeated operation cycle of the IC, and a temporal change waveform of the voltage at a specific point on the IC line.

[Conventional technology]

The operating concept of a conventional strobe electron beam device is as follows. First, when an electron beam pulse (hereinafter referred to as an EB pulse) is irradiated onto a specific portion of an IC wiring that is in a certain voltage state, secondary electrons are emitted from the surface portion. And the secondary electronic signal obtained thereby,
The amount is large if the specific portion is in a low voltage state, and small if the specific portion is in a high voltage state. Therefore, by measuring the amount of secondary electron signals, the IC at the moment of irradiation with the BB pulse can be determined.
The voltage state of a particular part of the surface can be measured.

Furthermore, when the IC is operated with a specific clock (for example, a TMHz clock), the 1c becomes 10
Assuming that a series of operations is performed at 0 clock, each part of the IC repeats the same voltage state every 100 clocks as the clock advances. Therefore, in order to measure the time change of the voltage state of a specific part of the IC wiring due to the clock using the EB pulse, we use the fact that the IC repeats the same operation every one repetition operation period, and use the EB pulse for each repetition operation period. By gradually shifting the irradiated tie straw, it is possible to measure changes in the voltage state over time (this is called waveform mode).

In addition, in order to measure the voltage distribution image on the IC surface at a specific timing during the repetitive operation cycle (this is called an image mode), for example, first, the EB pulse is identified at a specific phase on the first cycle of the repetitive operation. Irradiate the area and measure the voltage at that area.

Next, repeat the operation 2 cycles to other parts with the same phase of the mouth.
Apply B pulse and measure the voltage at that part. As described above, by fixing the EB pulse irradiation timing to a specific phase and scanning the EB pulse over the tC surface, it is possible to obtain a voltage distribution image on the IC surface at the specific phase during the repetitive operation cycle.

Next, to talk specifically about gate delay time measurement, conventionally, when measuring edge timing to obtain the gate delay time of an LSI using an electron beam device, an electron beam pulse synchronized with an operating signal is placed at the measurement location. The voltage waveform is measured by detecting the secondary electron signal emitted by irradiation, and the phase at which this voltage waveform matches the threshold voltage is determined. High-accuracy timing measurement is necessary for testing a large number of high-speed LSIs, but this requires increasing the accuracy of the measured waveform, which increases the measurement time and makes it difficult to perform 100% testing. It's inappropriate. For this reason, electron beam devices have been devised that perform timing measurements at high speed through phase convergence operations.

[Problem to be solved by the invention]

However, with such conventional electron beam equipment, operation tests often require not only measurement of delay time but also observation of measured waveforms, and it is often necessary to measure waveforms and also make highly accurate timing measurements. If you also wanted to do this, the only way to do it was to do both in sequence. For this reason,
There was a problem that the operation test required a lot of time and was inefficient.

In other words, in order to obtain the edge timing from the measured waveform with high precision using conventional equipment, it is necessary to improve the accuracy of the measured waveform by adding several times as many times as when the purpose is to observe the waveform. Therefore, the measurement time will be long.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an electron beam device that can simultaneously perform both measurement waveform observation and timing measurement to shorten measurement time.

[Means for Solving the Four Problems] In order to achieve the above object, the electron beam device according to the present invention uses an irradiation means to phase-control an electron beam pulse synchronized with an operation signal of the sample to a measurement location on the sample. irradiate,
In an electron beam device that measures the voltage at a measurement point by detecting secondary electrons emitted from the measurement point by a measuring means, an outline of the edge timing at which the voltage measurement waveform crosses a predetermined threshold value based on the waveform data of the measurement point. edge measuring means 19 for determining the edge timing of the measured waveform based on the voltage waveform data near the approximate value of the edge timing obtained by the edge rough detecting means and the slope of the measured waveform; It is set up.

[Effect]

In the present invention, the approximate value of the edge timing at which the measured waveform crosses the threshold value is determined from the waveform data, and the edge timing of the measured waveform is determined based on the voltage waveform data near the approximate timing value and the slope of the measured waveform. be done.

Therefore, accurate edge timing is calculated from the voltage waveform data measured with coarse accuracy and the slope of the measured waveform. In this method, several waveform data points in the vicinity of the edge timing are used for calculation. Therefore, the number of additions can be reduced to just a few minutes, and measurement time can be shortened by simultaneously performing both measurement waveform observation and timing measurement.

〔Example〕

Hereinafter, the present invention will be explained based on the drawings.

1 to 4 are diagrams showing an embodiment of an electron beam device according to the present invention, and FIG. 1 is a diagram showing the overall configuration thereof. In FIG. 1, 1 is a strobe electron beam device, 2 is an electron beam column, and a sample chamber 3 is connected to the electron beam column 2. A test IC (sample) 4 is placed inside the sample chamber 3 . An EB pulse 5 is irradiated from the electron beam column 2 to the XC4 to be tested, and secondary electrons 6 are obtained. The secondary electrons 6 are detected by a secondary electron detector 7 connected to the sample chamber 3, and the output thereof is input to a voltage measuring circuit 8 as a secondary electron signal. Further, the IC 4 to be tested is operated by an LSI drive circuit 9 consisting of a pattern generator PG or an LSI tester, and the LSI operation clock from the LSI drive circuit 9 is input to a phase control circuit 10. The phase control circuit 10 takes in the LSI operation clock and controls the phase of the operation clock in order to pulse the electron beam 5a irradiated from the electron gun 11.The output of the phase control circuit 10 is E.
It is manually powered by the B pulse driver 12. The EB pulse driver 12 is an EB pulse driver disposed inside the electron beam column 2.
Connected to pulse gate 1-13, EB pulse gate 13
By applying an electrical pulse to the electron beam 5a
is shaken and pulsed to form EB pulse 5.

Note that the electron beam 5a from the electron gun 11 is transmitted through the electron lens 1.
4, passes through the EB pulse gate 13 and becomes E
The B pulse 5 is then electromagnetically deflected by the scan coil 15 to scan the wiring of the IC 4 to be tested.

The voltage measurement circuit 8 measures the operating voltage of the IC 4 to be tested based on the output (secondary electron signal) of the secondary electron detector 7, and analyzes the measurement results with the voltage control circuit 16 and the waveform data buffer 1.
Output to 7. The analysis voltage control circuit 16 is the voltage measurement circuit 8
The energy analyzer 18 controls the voltage applied to the energy analyzer 18 based on the output of the analysis voltage control circuit 16. The supplied voltage is applied. The energy analyzer 18 is provided because it is difficult to quantitatively measure voltage from a simple voltage contrast signal. This is because the voltage measurement is quantified by using a voltage measurement method (energy analysis method) that uses development that moves with a voltage at a point.

On the other hand, the waveform data buffer 17 buffer-amplifies the waveform data of the measured voltage based on the output of the voltage measurement circuit 8 and outputs it to the edge timing measurement section 19 and the display device 20. The edge timing measuring section 19 measures, from the waveform data, an approximate value of the edge timing at which the measured waveform crosses a predetermined threshold based on the output of the waveform data buffer 17;
The display device 20 displays waveform data necessary for voltage measurement and the like at measurement points of the IC 4 to be tested.

The phase control circuit 10, the electron gun 11SEB pulse driver 12, the EB pulse gate 13, the electron lens 14, and the scan coil 15 collectively constitute an irradiation means 31, and the secondary electron detector 7, voltage measurement circuit 8, and waveform Data buffer 17 and display device 20 constitute measuring means 32 . Further, the edge timing measurement section 19 has functions as an edge rough detection means and an edge measurement means.

Next, the effect will be explained.

The measurement sequence is as follows. First, a predetermined test vector is downloaded to the LSI drive circuit 9, and the multi-strobe measurement system, that is, the irradiation means 31 and measurement means 32 including the EB pulse driver 12 and the like are initialized.

Next, the LSI drive circuit 9 repeatedly generates a test pattern according to the test vector, and without indicating the start timing of the test pattern, the trigger signal and the IC 4 under test (i.e.
The clock signal for driving the DUT (device under test) is
Supply to C4.

Thereafter, the irradiation means 31 samples the secondary electron signal in synchronization with the pulse signal of the clock signal using the trigger signal as a reference, and based on the sampling result, the
The signal voltage of C4 is measured, and the edge timing is also measured by the edge timing measuring section 19 according to the program shown in FIG.

FIG. 2 is a flowchart of edge timing measurement. The first half of the flowchart is an operation for measuring a waveform, and as in the conventional case, the voltage is measured while scanning the phase, and the results are averaged. That is, first, in 5t (Si refers to a step; the same applies hereinafter), the loop indicator i corresponding to the number of voltage measurement additions is set to i=1 (initialization), i is incremented in S2, and then the loop indicator is incremented in S3. A reference value N corresponding to a predetermined number of additions of indicator i
Compare with w. Initially, i<N, so proceed to S4,
Number of phase points of measurement voltage (number of points to pick up the phase)
Set the loop indicator j to 1-0 (initialization),
S, increments j, and S, further compares the loop indicator j with a reference value N, corresponding to a predetermined number of phase points. When j≦NP, the phase t (j
), the measured value at this time is set as V (j) =V (j) +V, and the process returns to S5. In S5, j is incremented, and then the process returns to S6. Then, when j>N in Sh, the process returns to 82, and the process further advances to S3. i>N in S3
When the voltage becomes H, the average of the voltage data of all phases is calculated using the following equation in S8.

N.

Next, a phase boundary, in other words, a range T, where the difference 1v(j)-Vl between the voltage data V (j) averaged by S and the predetermined threshold voltage vLh is equal to or less than a predetermined specified voltage. == (T,,T,) is determined and this region is defined as the edge timing vicinity region. Here, the specified voltage is determined by the required accuracy of measurement.

As shown in FIG. 3(a), the phase boundary range (region near the edge timing) is Ts, T, with the threshold V as the center.
The zone is represented by , . The specific method for determining this zone is shown in Figure 4. If the specified voltage is set so that the absolute value of the voltage data is (amplitude x ),
Engineering at this time.

The region near the timing is the range represented by hunting in FIG. Therefore, it is preferable to change the magnitude of the absolute value of the voltage data depending on the required accuracy of measurement. In addition, the range represented by Tl and Tn in FIG. 4 is a set zone for edge measurement.

Next, the SIO calculates edge timing candidate values for all voltage data in the area near the edge timing. The candidate value is the formula t'(j)=α(Vi-V(j))
Defined by α is the slope of the waveform (see FIG. 3(a)). Further, when the hatched part in FIG. 3(a) is enlarged, it is shown as in FIG. 3(b). t'(j) is the threshold value v within the hunting part as shown in FIG. 3(b).
These are multiple points existing at the th level. Next, an additive average is obtained for all t'(j) at S, and the average value is set as the edge timing Tedge (see FIG. 3(b)).

In this way, in this example, the approximate value of the edge timing at which the measured waveform crosses the threshold value is obtained from the waveform data, and the edge timing calculated from the voltage waveform data near the approximate timing value and the slope of the measured waveform is added. The average value is used as the edge timing. That is,
Accurate edge timing is calculated from voltage waveform data measured with coarse accuracy and the slope of the measured waveform. In this method, several points of waveform data in the vicinity of the edge timing are used for calculations, so the number of additions can be reduced to a fraction of the conventional method, and both observation of the measured waveform and timing measurement can be reduced. The measurement time can be shortened by performing the measurements simultaneously.

Note that the accuracy of the timing obtained is determined by the S/N of the measured waveform.
This is determined by the number of data points in the region near the edge, and the number of data points in the region near the edge can be controlled by the specified voltage value and phase step width, so it can be changed depending on the required precision. At this time, since the phase step size is directly related to the measurement time, it is preferable to control the accuracy using a specified voltage.

〔Effect of the invention〕

According to the present invention, both measurement waveform observation and timing measurement can be performed simultaneously, and measurement time can be shortened.

[Brief explanation of drawings]

1 to 4 are diagrams showing one embodiment of the electron beam device according to the present invention. FIG. 1 is an overall configuration diagram thereof, FIG. 2 is a flowchart of its edge timing measurement, and FIG. 3 is its edge timing measurement diagram.・A diagram for explaining the method of timing measurement. FIG. 4 is a diagram for explaining the method for determining the area near the edge. 1... Strobe electron beam device, 2...
・Electron beam column, 3...Sample chamber, 4...Test IC. 5...EB pulse, 6...Secondary electron, 7...Secondary electron detector, 8...Voltage measurement circuit, 9... ... LSI drive circuit, 10 ... Phase control circuit, 12 ... EB pulse driver, 16 ...
...Analysis voltage control circuit, 17... Waveform data buffer, 18...
・Energy analyzer, 19... Edge timing measuring section (edge rough detection means, edge measuring means), 20... Display device, 31... Irradiation means, 32... ...Measurement means.

Claims (1)

[Scope of Claims] Measurement means: irradiating a measurement point of a sample (4) with an electron beam pulse (5) synchronized with an operation signal of the sample (4) by means of an irradiation means (31) in a controlled phase; In an electron beam device that measures the voltage at a measurement point by detecting secondary electrons (6) emitted from the measurement point according to (32), the voltage measurement waveform crosses a predetermined threshold based on the waveform data of the measurement point. An approximate edge detecting means (19) for obtaining an approximate value of edge timing, and an approximate edge detecting means (19)
); edge measuring means (19) for determining the edge timing of the measured waveform based on the voltage waveform data near the approximate value of the edge timing obtained by and the slope of the measured waveform;
An electron beam device characterized by being provided with.