JPH073775B2 - Strobe electronic beam device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a data string for each time with respect to a voltage measured value data string at a predetermined irradiation point of an integrated circuit under test, which is obtained by repeating phase scanning of an electron beam pulse a plurality of times. Has a means for performing the averaging process by shifting the phase so that the correlation between them becomes maximum, and thereby the observed voltage caused by the drift of the electron beam pulse irradiation phase control circuit or the drive circuit of the integrated circuit under test, etc. It is a strobe electron beam device capable of preventing a decrease in time resolution of a waveform.

[Industrial application field]

The present invention relates to a strobe electron beam device capable of obtaining a voltage measurement value data string with high time resolution.

[Prior art]

Strobe electron beam devices are attracting attention in order to analyze internal operations of ICs, LSIs, and the like. The stroboscopic electron beam device is used for a specific position of an integrated circuit that repeatedly operates.
An electron beam pulse of various phases is irradiated with a variable delay in synchronism with the operation clock, and the voltage at the specific position in each irradiation phase is measured from the obtained secondary electron signal. Therefore, by changing the irradiation phase very finely with respect to the voltage change and measuring the voltage, the voltage change at each position of the integrated circuit operating at high speed can be accurately observed with high time resolution.

In order to enable the above operation, a control circuit that finely changes the irradiation phase of the electron beam pulse has been realized.

[Problems to be solved by the invention]

In the above-mentioned conventional method, first, with respect to the sample voltage waveform at a predetermined position which changes with time as shown in FIG. 5 (a) by one phase scan, φ _o , ... φ _i ,. φ _n
In this way, electron beams are emitted in each phase to obtain each voltage measurement value data string. Since one measurement is easily affected by noise, the above phase scanning is performed a plurality of times (for example, 10 times).
(00 times) repeatedly to increase the S / N by performing the averaging process for each phase.

However, even when trying to change each phase with high precision in the above method, the phenomenon that the irradiation phase of the electron beam fluctuates in a certain direction appears as the phase control circuit is affected by drift etc. (Fig. 5 (a)
51). This also applies to the drive circuit system of the integrated circuit, and the phase of the sample voltage waveform itself with respect to the EB pulse may fluctuate. In such a state, when the averaging process is performed for each phase on the voltage measurement value data string obtained by each phase scan, the time resolution of the voltage measurement value decreases due to the fluctuation of the phase, and FIG. As shown in (b), there is a problem that the measured waveform becomes blunt with respect to the sample voltage waveform.

In order to eliminate the above-mentioned problems, the present invention shifts the phase so that the correlation between the voltage measurement value data strings for each phase scan becomes maximum, and performs the averaging process to obtain an observation voltage with a high time resolution. An object is to provide a strobe electronic device capable of obtaining a waveform.

[Means for solving problems]

In order to eliminate the above problems, the present invention eliminates the above-mentioned problems by measuring the voltage measurement value data string ({S _i }) obtained for each phase scan and the voltage measurement value data string ({{S _i }) obtained by a predetermined number of times (for example, the first time). W _i}) and the correlation function value of the (Rl) calculates the maximum value (the phase deviation amount calculating means for calculating a phase shift amount (n) corresponding to R _n) (141), said voltage measurement data string Voltage measurement value data string addition storage for adding and storing a data string ({S _{i + n} }) obtained by shifting each phase of ({S _i }) by the phase shift amount (n) to the corresponding address for each phase Means (14
3) and have.

[Action]

In the above means, the voltage measurement value data string ({S _i }) obtained for each phase scan is, for example, the voltage measurement value data string ({W _{i by} the first phase scan in the phase shift amount calculating means (141). _i )), the phase shift amount (n) is determined so as to maximize the correlation with the voltage measurement value data string addition storage as a data string ({S _{i + n} }) shifted by the phase shift amount (n). It is added to the means (143). As a result, even if a phase fluctuation occurs in each phase scan, the phase shift amount (n) corresponding to the fluctuation is detected, the data is shifted, and then the averaging process is performed. Can be prevented.

〔Example〕

Hereinafter, examples of the present invention will be described in detail. {Structure and Operation of Strobe Electron Beam Device (FIG. 2)} FIG. 2 is a block diagram of a strobe electron beam device according to the present invention. Inside the electron beam column 1, a sub-deflector 2, a main deflector 3, an energy analyzer 4, a sample IC 5, a secondary electron detector 6 and the like are configured. Although the electron gun, the deflection lens and the like are shown in the drawing, they are not directly related to the present invention and their explanation is omitted. First, the sample IC5 is driven by the IC drive voltage signal 71 from the IC driver 7. On the other hand, in synchronization with this, the clock 72 is output to the delay unit 9. The delay unit 9 applies a variable delay to the clock 72 according to the delay unit control data 1402 from the arithmetic storage circuit 14, and the sub deflector 2 via the sub deflector driver 11, the fixed delay 10, the main deflector driver 12 The electron beam pulse is phase-scanned by the main deflector 3 via the
Irradiate a specific point above. As a result, the secondary electrons emitted from the irradiation point are subjected to energy analysis by the energy analyzer 4 according to the energy analyzer control signal 81 from the electronic measuring circuit 8 and detected as the secondary electron signal 61 by the secondary electron detector 6. After that, the voltage is input to the voltage measuring means 8 and the voltage is measured and converted into the waveform data string 82. The voltage measurement operation at this time is controlled by the voltage measurement circuit control data 1403 from the arithmetic storage circuit 14, and the sampling timing of the secondary electronic signal 61 is controlled by the strobe 101 from the fixed delay 10.

Next, the waveform data string 82 from the voltage measuring circuit 8 is input to the arithmetic storage circuit 14, where the correlation function with the first waveform data string is calculated, and the phase shift amount corresponding to the maximum value is shifted. Then, the addition process is performed. After repeating the above operation for the required number of times, voltage waveform data obtained by averaging 14
01 is output to the control computer 15. The arithmetic storage circuit 14
Is the calculation memory circuit control data 151 from the control computer 15.
Controlled by. Further, the voltage waveform data 1401 can be arbitrarily displayed on the display device 16.

{Arrangement of Arithmetic Storage Circuit (FIG. 1)} Next, FIG. 1 shows the arrangement of the arithmetic storage circuit 14 directly related to the present invention. First, the waveform data string 82 from the voltage measuring circuit 8 (FIG. 2) is temporarily stored in the waveform data string storage unit 144. The waveform data string {W _i } obtained by the first phase scan is stored in the waveform data string storage unit 145 of FIG. 1 and set in the waveform data string addition storage unit 143 as an initial value. Next, the waveform data string {S _i } from the second and subsequent phase scans and the FIG. 1 waveform data string {W _i } from the FIG. 1 waveform data string storage unit 145 are input to the phase shift amount calculation unit 141. Then, the correlation function value of the one data string is calculated here, and the phase shift amount n corresponding to the maximum value is output to the waveform data string shift unit 142. Waveform data string shift unit 142
Then, the phase of the waveform data string {S _i } from the waveform data string storage unit 144 is shifted by the phase shift amount n to correspond to each phase of the waveform data string addition storage unit 143 as a data string {S _{i + n} }. The address is added and stored. After the above operation is repeated for a plurality of phase scans, the averaged voltage waveform data 1401 is output from the waveform data string addition storage unit 143 to the control computer 15. At this time, the arithmetic control unit 146 outputs the delay unit control data 1402 and the voltage measurement circuit control data 1403 to the delay unit 9 and the voltage measurement circuit 8 according to the arithmetic storage circuit control data 151 from the control computer 15. Further, the phase shift amount calculation unit 141, the waveform data string shift unit 142, the waveform data string addition storage unit 143, the waveform data string storage unit 144, and the first waveform data string storage unit 145.
Are controlled by respective control signals 1401-1405.

{Operation of Operation Memory Circuit (FIGS. 1, 3, and 4)} Next, the operation of the operation memory circuit will be described with reference to the operation flowchart of FIG. 3 and the operation explanatory diagram of FIG. I do.

First, the arithmetic storage circuit control data 15 from the control computer 15
By 1, the arithmetic control unit 146 starts the operation flowchart of FIG. 3 (T1).

The arithmetic and control unit 146 thereby determines the variable I indicating the number of phase scans.
Is set to 1 (T2) and the delay unit control data 14
The delay unit 9 is controlled by 02 to scan the irradiation phase of the electron beam pulse (EB pulse), and the voltage measurement circuit 8 is controlled by the voltage measurement circuit control data 1403 to perform the voltage measurement. Waveform data string 82 corresponding to the second phase scan, that is, {S _i } (i = 1, 2, ... K)
Is acquired and stored in the waveform data string storage unit 144 (T3).
Next, as shown in FIG. 4, the operation storage unit 146 cuts out arbitrary N pieces (deviation amount = k from the start point) from the data string {S _i } of K phase points, and The waveform data string {W _i } = {S _{i + k} } (i = 1, 2, ... N) is stored in the first waveform data string storage unit 145, and the addition of the waveform data string addition storage unit 143 is performed. Waveform data string {A _i } (i = 1,2,
Set as initial value of (N) (T3 → T4 → T5 → T6
→ T7). The operation of these control signals 1403, 1404, 14
It is controlled by 05 (Fig. 1).

Next, the arithmetic storage unit 146 performs the second phase scan of the EB pulse in the same manner as described above, performs the voltage measurement, and outputs the K waveform data strings 82 of the second time and thereafter shown in FIG. _i } (i =
1, 2, ... K) are acquired and stored in the waveform data string storage unit 144 (T8 → T3). After that, the arithmetic and control unit 146 outputs the control signal 1
The phase shift amount calculation unit 141 is activated by 401, and the correlation between the waveform data string {S _i } of the waveform data string storage unit 144 and the first waveform data string {W _i } of the first waveform data string storage unit 145 is correlated. Calculate the function (T3 → T4 → T5 → T9).

Next, in the phase shift amount calculation unit 141, the value of the variable l is changed from 0 to K−N. Therefore, as shown in FIG. 4, N pieces of data are selected from K waveform data strings {S _i }. Column (S _{i + l} )
(I = 1,2, ..., N) are sequentially cut out, multiplied by the first waveform data string {W _i } for each phase point as shown in the following equation, and the sum is taken. The correlation functions Rl are sequentially calculated (T9 → T10 → T11 → T12 → T9).

▲ ▼ = average value of {S _{i + l} } = average value of {W _i } δ _sl ² = variance of {S _{i + l} } δ _w ² = variance of {W _i } l = K-N),
Find the largest of the correlation functions Rl (T11 → T1
3). Now, when the target waveform data string has no phase shift from the first waveform data string, the two correlation waveforms almost overlap when l = k, and the correlation function Rk at that time is the maximum. Becomes However, the delay unit 9
Assuming that the phase is shifted by m points as shown in FIG. 4 due to the drift of the electric circuit system (see FIG. 2), the two waveforms are well overlapped when 1 = Rk + m,
The correlation function R _n = R _{Rk + m} at that time becomes maximum. Therefore, the phase shift amount n = Rk + corresponding to the value R _n that maximizes the correlation function.
N waveform data strings {S _{i + n} } (i = 1,
2, ..., N) are extracted and added to eliminate the phase fluctuation due to drift.

When the phase shift amount n is found as described above, the arithmetic control unit 146 uses the control signal 1402 to shift the waveform data string shift unit 142.
Is started, and the waveform data string {S _i } (i = 1,2,
..., K), N data strings {S _{i + n} } (i = 1, 2, ... N) are cut out with the phase shift amount n as the head, and each of the waveform data string addition storage units 143 is cut out. Addition Add to the waveform data string A _i . That is, A _i = A _i + S _{i + n} (i = 1,2, ... N) (T13 → T14 → T8).

Then, the arithmetic control unit 146 repeats the above-mentioned addition processing by the required number of times Ima.
After repeating x times, the average of the added waveform data strings in the waveform data string addition storage unit 143 is calculated as A _i = A _i / Imax (i = 1,2, ... N) (T4 → T
15) The voltage waveform data 1401 is output to the control computer 15 and displayed on the display device 16 (T16).

As described above, when calculating the average of waveform data strings for each phase scan, even if a phase shift occurs due to the drift of the phase control circuit system, the phase shift amount is automatically detected and corrected. Since it can be performed, it is possible to acquire the waveform data string with high time resolution.

[Advantages of the Invention] According to the present invention, due to the influence of drift of the electron beam pulse irradiation phase control circuit or the drive circuit of the integrated circuit under test, it is possible to automatically detect the phase shift generated in each phase scan, Since it becomes possible to correct, it is possible to prevent deterioration of the time resolution of the observed voltage waveform.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an arithmetic storage circuit, FIG. 2 is a configuration diagram of a strobe electron beam apparatus according to the present invention, FIG. 3 is an operation flowchart of the arithmetic storage circuit, and FIG. 4 is an explanation of the operation of the present invention. FIGS. 5 (a) and 5 (b) are explanatory views of conventional problems. 5 ... Sample IC, 8 ... Voltage measurement circuit, 9 ... Delay unit, 14 ... Calculation memory circuit, 61 ... Secondary electronic signal, 14
1 ... Phase shift amount calculation unit, 143 ... Waveform data string addition storage unit, S _i ... Waveform data string, W _i ... First waveform data string.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Okubo 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa, Fujitsu Limited (72) Inventor Yoshiro Goto 1015, Kamikodanaka, Nakahara-ku, Kawasaki, Kanagawa (56) References JP-A-59-220940 (JP, A)

Claims (1)

[Claims] 1. A variable delay for generating an electron beam pulse by applying a variable delay to a clock (72) synchronized with a repeating period operation of an integrated circuit (5) to be inspected and irradiating the integrated circuit (5) to be inspected. A stroboscopic electron beam device comprising means (9) and voltage measuring means (8) for measuring a voltage at an irradiation point from a secondary electron signal (61) obtained by each irradiation, wherein the irradiation phase of the electron beam pulse is The voltage measurement value data string ({S _i }) obtained by the voltage measuring means (8) by performing the phase scanning while sequentially changing it by the delay varying means (9) and the voltage measurement obtained by the predetermined phase scanning Phase shift amount calculation means (141) for calculating a correlation function value (Rl) with the value data string ({W _i }) and calculating a phase shift amount (n) corresponding to the maximum value (R _n ), Voltage measurement Data sequence ({S _i}) each phase of the phase shift amount (n) shifted by the data string ({S _{i + n})} of the voltage measurement data string to be added and stored in the address corresponding to each phase of And an adding / storing operation of the voltage measurement value data string ({S _i }) and the corresponding corrected voltage measurement value data string ({S _{i + n} }). Strobe electron beam device characterized by being repeated a plurality of times.