JPH0616406B2 - Voltage waveform measurement method using strobe electron beam - Google Patents

Description

DETAILED DESCRIPTION [Overview] The voltage waveform measurement of a sample by an electron beam apparatus includes a time error. The present invention measures the error in the delay time of the electron beam pulse with respect to the trigger pulse and corrects the irradiation timing of the electron beam pulse. Alternatively, the time axis of the obtained voltage waveform is corrected. As a result, measurement with less time error can be performed.

[Industrial application field]

The present invention relates to an electron beam apparatus for measuring a voltage of a sample by an electron beam, and in particular, a strobe electron for obtaining a voltage waveform of a sample by irradiating the sample with an electron beam pulse in synchronization with the repeating operation of the sample to measure the voltage. Beam device

[Conventional technology]

Since the voltage measurement in the electron beam apparatus, particularly the stroboscopic electron beam apparatus is non-contact, it has a feature that it can be measured without destroying a sample such as an integrated circuit. Due to this feature, a voltage waveform measurement by a strobe electron beam device, that is, an EB prober is used to analyze the internal operation of an integrated circuit such as an LSI.

Generally, voltage measurement in a stroboscopic electron beam apparatus uses a secondary electron amount generated by irradiating a sample with an electron beam pulse with a delay time provided for a trigger pulse synchronized with the repetitive periodic operation of the sample. Seeking voltage. Then, the delay time described above is made variable, and the waveform of the operation cycle of the sample is measured.

[Problems to be solved by the invention]

In the conventional strobe electron beam apparatus, if the strobe pulse generation circuit of the control circuit that controls the irradiation of strobe electron beam pulses has a temporal drift, that is, instability, fluctuations occur in the irradiation phase of the electron beam pulses,
The time resolution of the acquired voltage waveform is limited. That is, the time resolution is reduced.

For example, as is clear from the diagram for explaining the drift of the EB pulse in FIG. 8, drifts temporally before and after the phases φ _o , φ _i , and φ _n occur. If this drift occurs, especially when measuring a sharp rising pulse waveform, the results of multiple measurements to obtain a good S / N waveform are averaged to obtain the equivalent high value due to the drift. The waveform is as if a bandpass filter had been inserted. For example, when the waveform shown by the dotted line in FIG. 9 is measured, the waveform shown by the solid line in FIG. 9 results.

In addition to the fluctuation or drift, when the strobe pulse generation circuit responds to a trigger pulse to generate a strobe electron beam pulse with a specific time delay, a voltage that is found if there is an error in the target specific time delay. The same error occurs on the time axis of the waveform, and the accuracy with respect to the required time decreases.

The present invention has been made in view of the above-mentioned conventional drawbacks, and an object thereof is to provide a stroboscopic electron beam apparatus having high temporal resolution and accuracy.

[Means for solving problems]

In order to achieve the above object, the present invention delays the voltage of a sample by irradiating a sample with an electron beam pulse by sequentially providing a delay time with respect to a trigger pulse signal and performing energy analysis of secondary electrons generated by the sample. This is a method for measuring a voltage waveform by an electron beam, which is obtained corresponding to time and measures the voltage waveform of the sample.

The first invention of the present application is to obtain an error of a delay time of an electron beam pulse with respect to the trigger pulse signal in advance, measure a voltage waveform, change an address corresponding to the delay time, and store the voltage waveform. In addition, the voltage value measured by instructing the error with the corrected address is stored and corrected. In a second aspect of the invention, an error due to the drift of the delay time of the electron beam pulse with respect to the trigger pulse signal is obtained in advance before measuring the voltage waveform, and is corrected according to the error due to the drift obtained in advance when measuring the voltage waveform. And irradiating the sample with the electron beam pulse.

[Work]

The sample is irradiated with an electron beam pulse having a delay time with respect to the trigger pulse signal, and the secondary electron generated from the sample is subjected to energy analysis to measure the voltage of the sample. Prior to this voltage measurement, the error in the delay time of the electron beam pulse with respect to the trigger pulse signal is obtained. Then, the address value to be stored corresponding to the delay time is corrected and stored in the storage unit that stores the voltage measurement result. Alternatively, the delay time of the electron beam irradiation is corrected according to the obtained error data.

〔Example〕

 Hereinafter, the present invention will be described in detail with reference to the drawings.

{First Correction} FIG. 1 is a circuit configuration diagram of the first embodiment of the present invention. I
The C driver 1 operates the IC 4 on the sample table 3 provided below the electron beam lens barrel. The IC 4 is repeatedly operated by the IC driver 1. IC driver 1
In addition to the repeated operation of this IC, outputs a clock pulse indicating the start of the repeated operation of the IC 4 to the delay unit 5. The delay unit 5 is a circuit that outputs a clock pulse having a delay of a time designated by delay data added from a storage circuit 6 described later.

Generally, in the voltage measurement by the electron beam, the measured portion is repeatedly operated, and the timing of irradiating the EB pulse during the repeated operation is changed by the delay unit 5 described above to obtain the voltage waveform of the measured portion in the repeated operation. ing. The same applies to the embodiment of the present invention shown in FIG. 1 as described above.
It is output with a delay of the delay data output from the storage circuit 6 with respect to the basic clock (clock pulse for starting the operation of the IC 4) output from the driver 1. Then, in response to the input of the clock pulse output from the delay unit 5, the deflector driving means 7 applies a pulsed deflection voltage to the sub deflector 8 in the electron beam lens barrel. Further, the clock pulse output from the delay unit 5 is added to the fixed delay circuit 9, is provided with a specific delay and is input to the deflector driving means 10, and a pulsed deflection voltage is applied to the main deflector 11. Since the principle of the beam device in the electron beam lens barrel 2 is general, its explanation is omitted. The sub deflector 8 and the main deflector 11 generate an electron beam pulse by deflecting an electron beam on a diaphragm plate (not shown in the figure), and a clock pulse output by the delay unit 5. An EB pulse is generated in synchronization with. A coil 12 for controlling focusing of the beam position is provided below the main deflector 11.

2 from the IC4 by the electron beam applied to the IC4
Secondary electrons are generated and detected by the secondary electron detector 14 via the energy analyzer 13. A specific voltage is applied to the energy analyzer 13 from the voltage measuring circuit 15, and 2
The secondary electron signal amount detected by the secondary electron detector 14 has a value depending on the voltage applied to the energy analyzer 13. In the embodiment of the present invention, the voltage value at the irradiation timing of the electron beam pulse irradiation point is obtained by obtaining the voltage applied to the energy analyzer 13 such that the secondary electron signal amount obtained from the secondary electron detector 14 becomes a specific value. Is calculated. Therefore, the voltage measuring circuit 15 is the fixed delay circuit 9
The amount of signal from the secondary electron detector 14 is obtained by the clock pulse output from the above, and the voltage applied to the energy analyzer 13 is controlled in clock pulse units so that the value becomes a specific value. Then, the voltage value of the sample, that is, IC4 is calculated from the voltage value of the energy analyzer 13 when the secondary electron signal amount reaches a specific value. Generally, the voltage value described above is used as the voltage value of the electron beam pulse irradiation phase at the electron beam pulse irradiation point, but in the embodiment of the present invention, it is detected whether the electron beam is irradiated to the IC 4 with a target time delay. It has a voltage waveform monitor 16 that operates.
Errors and fluctuations in the delay time are generated from the IC driver 1 delay unit 5, the fixed delay 9, and the deflector driver 10, as is clear from the circuit. The voltage waveform monitor 16 displays I
It has a function of monitoring the deflection voltage waveform by using the drive waveform for driving C4 as a trigger, and the monitor function can detect the above-mentioned delay time error and fluctuation. The delay time error data obtained here is stored in the storage circuit 6.
Join in.

As described above, the delay data for delaying the clock pulse by the designated time is added to the delay unit from the storage circuit 6, and the voltage measurement value corresponding to each delay data is added to the storage circuit 6 from the voltage measurement circuit 15.
The memory circuit 6 stores in the memory in the memory circuit 6 in consideration of the delay time error output from the voltage waveform monitor 16.
The output of the fixed delay circuit 9 is added to the voltage measuring circuit 15, and the voltage measuring circuit samples the secondary electronic signal data by the clock pulse from this output.

FIG. 2 is a voltage waveform diagram showing a waveform (main deflection voltage waveform) for driving the main deflector obtained by the voltage waveform monitor 16. The broken line is the main deflection voltage waveform when the delay unit 5 is designated with a delay time φ _o at the start of the voltage waveform measurement, and the solid line is the main deflection voltage waveform when the delay time φ _i during the measurement is designated. Since the electron beam pulse is generated at the moment when the rising portion of the main deflection voltage crosses 0 V, the electron beam pulse generation timing for each designated delay time is found to be t _o , t _i. If there is no error or fluctuation in time, φ _i −φ ₀
= T _i −t _o should hold exactly. In other words, even if the delay time φ _i is specified, φ _o + (t _i −t _o ) = φ
_{If j} is satisfied, it is detected that the delay actually added to the clock pulse is φ _j due to an error or fluctuation.

As described above, the memory circuit 6 stores the voltage measurement value in the memory in consideration of this error, but this consideration, that is, the error correction is performed by changing the address position stored in the memory. This is because a series of voltage measurement data obtained while changing the designated delay time is stored in the memory at the address position corresponding to the actual delay time detected by the monitor means. That is, the delay time φ _o ,
, Φ _i , ..., φ _j , ..., φ _n , ... As shown in FIG. 3, data S _o ... S _i ... S _j ... S are assigned to addresses o ... i ... j ... n. _n ... is stored, but the voltage value data measured for the specified delay time φ _i is the address i
The error of the delay time is corrected by storing the data in the address corresponding to the actual delay time φ _j detected by the monitor means, instead of storing it in the memory.

In order to reduce the variation of the voltage measurement value due to the noise included in the secondary electron signal, the voltage measurement circuit 15 performs the voltage measurement a plurality of times for the same designated delay time, and the obtained voltage data is stored in the storage circuit 6. Add average with.

That is, to explain together with the above correction, the delay time φ _i
The measured voltage value data obtained by specifying is added to the addition data S _j up to the last time of the address j corresponding to the actual delay time φ _j detected by the monitor means and stored at the address j. The content of the data addition number counter for the address j is incremented by one. This series of operations is repeated with the same designated delay time φ _i , and the designated delay time is sequentially changed.

According to the above operation, the number of data added at each address is not uniform. Therefore, in the present invention, as shown in FIG. 4, voltage measurement is performed for addresses 0, ..., N corresponding to respective delay times φ _{o to} φ _n. When the number of added data becomes larger than A, the addition for the address is finished, and the obtained added value is divided by the number A of added data to obtain the voltage value.

The control computer 17 and the storage circuit 6 are connected to each other, and the data stored in the memory of the storage circuit 6 is read from the control computer 17 in the order of addresses, thereby reading the data in which the delay error is corrected. become. For example, even if the voltage waveform is displayed on the display device 18 connected to the control computer 17, the voltage waveform displayed on the display device is a waveform in which the time delay error is corrected.

By the above operation, the influence of the error of the delay unit and the influence of the drift due to the instability of the electric circuit can be removed, and the voltage waveform data with high accuracy on the time axis can be obtained.

{Second Correction} In the first embodiment of the present invention, the time error is calculated,
The correction is performed by changing the address value in which the result is stored. FIG. 5 is a circuit configuration diagram of the second embodiment of the present invention. In this case, as will be described later, the signals applied to the main deflector and the sub deflector are delayed to perform the correction. The same circuits as those in FIG. 1 are designated by the same reference numerals and the description thereof is omitted.

The sample 4 or IC is repeatedly driven by the IC driver 1, and a clock pulse representing the initial point of the repeated driving is applied to the delay unit 5 and the voltage waveform monitor 16. The delay unit 5 is a circuit for delaying a clock pulse applied corresponding to the delay data output from the control computer 17 '. The clock pulse 5 delayed by the target time is further corrected by the delay unit 19 for correction.
In addition, a clock pulse is added to the deflector driver 7 and the fixed delay circuit 9 with a delay of the correction time. The subsequent voltage measuring operation is similar to that of the first embodiment, and the voltage data measured by the voltage measuring circuit 15 is added to the memory circuit 6 '.
In the embodiment of the present invention shown in FIG. 1, the time is corrected by the storage address of the memory in the memory circuit 6, but in the embodiment of the present invention shown in FIG. 5, no correction is made here. , The measurement results are sequentially stored in an address corresponding to a designated delay time of the memory in the storage circuit 6 '. The voltage waveform can be read by reading the contents of the memory circuit 6'with the control computer 17 '. On the other hand, the voltage waveform monitor 16 'has the clock pulse output of the IC driver 1 as a trigger and the output of the amplifier 10 as a monitor waveform. The output from the main deflector driver 10 is added with a target time delay to the clock pulse output from the driver 1 by the control signal from the control computer 17 ', and this time delay is added to the voltage waveform monitor 16'.
And is added to the control computer 17 '. The control computer determines whether or not the delay time data is the target delay time, and changes the correction delay data added to the correction delay unit 19 by the difference value so that the delay time becomes the target value. To do.

By the above-described operation, the drift of the delay time due to the error of the delay unit 5 and the instability of the electric circuit system is detected and corrected by the correction delay unit 19. Therefore, the data measured by the voltage measuring circuit 15 and stored in the memory circuit 6'becomes a voltage value for a target time delay. That is, highly accurate waveform data can be obtained when the contents of the memory circuit 6'are read by the control computer 17 '.

As shown in FIG. 6, the electron beam pulse generation timing with respect to the designated delay time φ ₀ at the start of waveform data measurement is t ₀ , and the electron beam pulse generation timing with respect to the designated delay time φ _i in the middle of measurement is t _i . The main deflection voltage waveform for the former is shown by a broken line, and the main deflection voltage waveform for the latter is shown by a solid line.

If there is an error or drift even if the designated delay time is φ _i , φ
_i −φ ₀ = t _i −t ₀ does not hold. In other words, φ _i
The generation timing of the electron beam pulse (the moment when the main deflection voltage crosses 0 V) when t is specified is t ₀ + (φ _i −φ ₀ ).
In this case (the main deflection voltage waveform is shown by the alternate long and short dash line), delay without error is performed.

Therefore, in the second embodiment of the present invention, the necessary correction amount = t ₀ +
(Φ _i −φ ₀ ) −t _i is calculated, and this correction is performed by the correction delay unit 19.

FIG. 7 is a circuit configuration diagram of the correction delay unit described above. The output of the delay unit 5 is added to the coaxial line 21 via the amplifier 20, and is further output to the fixed delay circuit 9 and the deflector driver 7 via the amplifier 22. A varicap 23 is connected to the connection point between the coaxial line 21 and the amplifier 22, and the delay time of the pulse applied to the amplifier 20 is adjusted according to the change in the capacitance of the varicap 23. The capacity of the Paris cap 23 is determined by the output voltage of the digital-analog conversion circuit DAC, and since the correction digital data from the control computer 17 'is added to the digital-analog conversion circuit, the delay is caused by this digital data. Time can be changed. In the second embodiment of the present invention, the delay time in the circuit shown in FIG. 7 is preferably set near the center of the delay time adjustment range in the initial state of waveform measurement. Because the correction delay unit 19
This is because a negative correction (to reduce the delay time) may be specified for.

〔The invention's effect〕

As described above, according to the present invention, the voltage waveform monitor first corrects the correct delay by correcting the address position corresponding to the time to be stored in the memory when a time error occurs in the voltage measurement of the delay time to be obtained. A waveform for time is stored in a memory, and secondly, a time error of irradiating an electron beam is corrected. According to the present invention, time resolution and accuracy are high. A strobe electron beam device can be obtained.

[Brief description of drawings]

 FIG. 1 is a circuit configuration diagram of an embodiment of the present invention, FIG. 2 is a voltage waveform diagram, FIG. 3 is a memory configuration diagram, FIG. 4 is a diagram explaining the number of measurement data, and FIG. FIG. 6 is a circuit configuration diagram of a second embodiment of the present invention, FIG. 6 is a voltage waveform diagram, FIG. 7 is a compensation delay unit circuit configuration diagram, and FIG. 8 is a diagram illustrating drift of an EB pulse, FIG. 9 is a voltage waveform diagram of a conventional circuit. 6 ... Storage circuit, 15 ... Voltage waveform monitor, 16, 16 '... Voltage waveform monitor, 19 ... Correction delay unit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Okubo 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Toshihiro Ishizuka 1015, Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (56) References JP-A-60-143644 (JP, A)

Claims (7)

[Claims] 1. A sample pulse is irradiated with an electron beam pulse while sequentially providing a delay time with respect to a trigger pulse signal, and secondary electrons generated by the sample are subjected to energy analysis to obtain a sample voltage corresponding to the delay time. In the voltage waveform measuring method using an electron beam for measuring the voltage waveform of the sample, the error of the delay time of the electron beam pulse with respect to the trigger pulse signal is obtained in advance, the voltage waveform is measured, and the address is changed according to the delay time. A voltage waveform measuring method using a stroboscopic electron beam, characterized in that when the voltage waveform is stored by storing the voltage waveform, the voltage value measured by designating the error is specified and stored. 2. The error of the delay time is obtained by monitoring the electron beam pulse generation timing at the initial stage of the observation of the voltage waveform, and the corrected address is the error amount of the delay time obtained by the monitor, the delay time. The method for measuring a voltage waveform by a strobe electron beam according to claim 1, wherein the advance of the address with respect to is corrected. 3. The error in the delay time is obtained by monitoring the electron beam pulse generation timing at the initial stage of the observation of the voltage waveform, and the voltage value is stored in the address corrected for the error or in the address. The voltage waveform measuring method using a strobe electron beam according to claim 2, wherein the voltage waveform measuring method is addition to data. 4. The voltage by the stroboscopic electron beam according to claim 1, wherein the storage of the voltage value is an accumulation until the number of added data for each stored address reaches a specific value. Waveform measurement method. 5. A sample pulse is irradiated with an electron beam pulse while sequentially providing a delay time with respect to a trigger pulse signal, and secondary electrons generated by the sample are subjected to energy analysis to obtain a sample voltage corresponding to the delay time. In the voltage waveform measuring method using an electron beam for measuring the voltage waveform of the sample, an error due to the drift of the delay time of the electron beam pulse with respect to the trigger pulse signal is obtained in advance before measuring the voltage waveform, and at the time of measuring the voltage waveform, A method for measuring a voltage waveform by a stroboscopic electron beam, which comprises irradiating a sample with the electron beam pulse after performing a correction according to an error due to a drift obtained in advance. 6. The voltage by the strobe electron beam according to claim 5, wherein the correction according to the error is delayed separately from the delay for providing the sequential delay time of the trigger pulse signal. Waveform measurement method. 7. The delay error is obtained by monitoring the electron beam pulse generation timing, and the correction is obtained from voltage waveform data for a specific delay in the initial state of observation and voltage waveform data for each delay during observation. 7. The voltage waveform measuring method using a stroboscopic electron beam according to claim 6, wherein the delay is a necessary correction amount for each delay.