JPS61124046A - Strobe electron beam apparatus - Google Patents

Abstract

PURPOSE:To measure voltages respective points of IC surface with high accuracy by alternately executing the precharge and sampling of secondary electron signal at the desired measuring points by continuous beam. CONSTITUTION:When an IC6 to be checked is irradiated with electron beam pulse 5, the secondary electrons 7 are emitted from the surface of internal wiring. It is then detected by a secondary electron detector 12 and an analog secondary electron signal 121 is output. A signal processing circuit 13 converts this secondary electron signal 121 into a digital signal. A wiring voltage of IC to be checked can be measured by giving an output of AC converter to an additional average processing circuit. Namely, a protection film cam be set quickly to the condition as having the normal charges by giving continuous electron beam to the IC for the initial N periods. The secondary electron released by the pulse electron beam in the succeeding M periods are emitted only from the wiring and relative value wiring voltage can be measured accurately.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an electron beam device that applies an electron beam to wiring inside an integrated circuit and detects wiring voltage from the intensity of secondary electrons generated therefrom. In particular, the present invention relates to a strobe electron beam device that performs precharging using a continuous beam.

[Conventional technology]

BACKGROUND OF THE INVENTION With the development of large-scale integrated circuits, it has become increasingly important to establish advanced fault detection and diagnosis techniques that can quickly check whether the internal logical operations of large-scale integrated circuits are normal. It is connected to the output of each gate in order to know the internal logic state of the integrated circuit or the change in the gate output in response to a change in the input. It is necessary to know the voltage status or voltage change of the wiring. To do this, the wire voltage can be determined by touching the wire with a voltmeter probe. However, in large-scale integrated circuits, the width of internal wiring is extremely narrow, making it difficult to contact with probes. In addition, contact may cause problems with the wiring, and the probe method has the disadvantage that each wiring is examined one after another, resulting in a very long measurement time. Therefore, an electron beam device that is attracting attention recently is an electron beam device that can detect wiring voltage without contact, and thus without removing the protective film. This electron beam device places an integrated circuit as a sample on a stage, and irradiates the IC with an electron beam from the top of the stage.
Since a secondary electron beam is emitted from the internal wiring, the wiring voltage is detected by measuring the energy of this secondary electron beam. Not only can you observe the voltage change of each wiring due to the input voltage, that is, the change over time,
It is possible to observe the voltage state of all wiring within the field where the beam is applied, that is, the spatial voltage distribution.

[Problem that the invention seeks to solve]

Conventionally, the voltage contrast of an IC with a protective film was observed by increasing the energy of the irradiated electron beam, but in the case of a MOS device, if the energy of the irradiated electron beam was made too high, the device would be destroyed. A method of observing voltage contrast using a strobe method with low beam energy and low beam current has also been proposed, but control of electron beam (EB) pulse irradiation and the like are complicated.

[Means to solve the problem]

The present invention is a voltage waveform inside an RC covered with a protective film.

In order to easily observe the voltage image, the rc repetition clock is divided into three parts, and one has a precharge timing delay,
The other two are given a delay for the EB pulse irradiation timing, first a continuous beam for precharging is given in order to quickly create a steady charge on the protective film, and then a pulse beam is given for acquiring a secondary electron signal. To provide a strobe electron beam device that can perform this alternately.

〔Example〕

The configuration of the electron beam apparatus of the present invention is shown in FIG. 1, the EB pulse gate control circuit is shown in FIG. 2, and the signal processing circuit is shown in FIG. 3.

The configuration of the strobe electron beam device of the present invention is shown in FIG. In FIG. 1, an electron beam pulse 5 projected from an electron gun through an electron beam (EB) pulse gate 3 in an electron beam column 1 is deflected in an appropriate direction by a deflection coil 4 into a sample chamber 2. It is applied to the surface of the internal wiring inside the IC 6 under test. Electron beam (EB) pulse 5
When secondary electrons 7 are projected, secondary electrons 7 are emitted from the surface of the internal wiring, which are detected by a secondary electron detector and an analog secondary electron signal 121 is output. The signal processing circuit 13 amplifies, samples, and quantizes this analog secondary electronic signal 121 to convert it into a digital signal, and at the same time transfers the digital data 131 to the control computer 14 and converts the S/N ratio under the control of the control computer. It also includes a function to add and average the digital signals near each sample point in order to increase the accuracy.

When the test IC 6 is supplied with a power supply voltage and an input voltage as well as a clock signal by the IC driver 8, the output of each gate changes according to the input logic or input change given in each clock period of the clock signal. , its changing state or steady logic state will be propagated to the wiring connected to its gate output.

The 2B pulse gate control circuit 9 receives an IC repetition clock signal 81, which is the same as the clock signal supplied to the IC 6 under test, from the IC driver 8, decodes the frequency division over-setting signal 141 from the control computer 14, and processes the signal as described below. For this reason, this circuit creates a frequency-divided clock signal for the clock signal and branches the frequency-divided clock signal into three signals: one for precharging, one for EB pulse irradiation, and one for sampling enable.

And in this EB pulse gate control circuit 9.

The IC periodic clock is divided into three. three delay circuits 9
4.95.96 respectively, and the input 98 given to the three delay circuits is connected to the gate signal 132 and the AND circuit 810 in order to give the IC repetition clock 81 for M+N+1 periods as shown in FIG. This is an output frequency-divided clock 98 that can be given to the output. One of the delays is provided from the control computer 14 to the first delay circuit 94 for setting the EB pulse irradiation timing for acquiring strobe data (141-1). The output 100 is obtained by gating φ0 of the IC repetition clock 81 with the gate signal 132 and AND81 as shown in (100) in FIG.
φ2, which is slightly delayed from φ0 of the frequency divided clock 98 outputted from 0, becomes a pulse control signal for forming the pulsed strobe EB. The second is for setting the precharge timing by continuous beam (141- 2) from the control computer to the second delay circuit 9
5, and its output 99 is (99
), the gate signal 1 is slightly behind φ0 of the frequency divided clock 98 and slightly ahead of φ2.
φ N cycles after the first φ1 triggered at 32
The signal is continuously high level up to 1.

The other one is for sampling enable (141-3) and is given to the third delay circuit 96 from the control computer, and its output 93 is as shown in (93) in FIG.
The first φ1 triggered by the gate signal 132
This signal is continuously at a high level from 1 to φ1, which is one clock period longer than the continuous EB (99) (N+1) period. The delay amounts φ1-φ0 given to (141-2, 3) are the same and are kept constant even when φ2 due to the signal (141-1) is changed.

Continuous EB signal 99. Pulse signal 100 for strobe EB
are integrated by an OR circuit to form an EB pulse gate driver drive signal (91). As shown in (91) in FIG. 4, this EB pulse gate driver drive signal 91 has a φ slightly delayed from the first φ0 triggered by the gate signal 132.
The continuous waveform is at high level during the 1st to N cycle period, and after that, the variable φ2 is slightly delayed from φ1.
This is a pulse signal. Therefore, when a signal in which this continuous signal and a pulse signal are mixed is given to the EB pulse gate driver 10 in FIG. The period is a continuous beam, and the subsequent M period is a pulsed beam synchronized with φ2.

Such a beam will be applied to the IC 5 to be tested with a protective film. The analog secondary electron signal 121 emitted as a result has a pulse-like waveform that is continuous for the first N cycles and slightly delayed from φ2 for the subsequent M cycles, as shown in (121) in Fig. 4. becomes. At this time, as shown in Figure 1, the fall of the continuous waveform after N cycles and the first secondary electron signal pulse emitted with a slight delay from φ2, which is slightly delayed from φ1, may interfere. many. Therefore, at this time, it is necessary to ignore the detection of the first secondary electronic signal pulse, and for this purpose, the third delay circuit 9
The sampling enable signal 93, which has a continuous waveform for N÷1 period, which is the output of 6, is inverted by an inverter 930, and the strobe timing signal 100 and the sampling enable signal 93 are inverted by an AND circuit 93.
Enter 1. As shown in the strobe signal (92) in FIG. 4, the output 92 of the AND circuit is a pulse signal in which there is no waveform in the first N+1 period, and M φ2 clocks are output from the N+2 clock. This signal 92, as shown in FIG.
4-1 to the delay circuit 134 controlled by
The output 135 is a sampling signal 1 of an AD converter 136 which inputs an analog secondary electronic signal via an amplifier.
It is 35. Therefore, as shown in FIG. 4, since the sampling signal (135) reliably captures M secondary electron pulses after N+1 cycles, the output of AD conversion is given to the signal processing circuit 137, and the cycles are added there. If you try to average it.

This means that the wiring voltage of the IC to be tested can be measured. In other words, continuous beam irradiation is performed for N clock periods from phase φ1 in this way, and after one period, the secondary electron signal is sampled M times and signal addition processing is required L times. In some cases, by repeating one or more processes L/M times, it becomes possible to acquire a voltage waveform and a voltage image through the protective film.

In this way, in the present invention, by applying a continuous electron beam to the IC for the first N cycles, the protective film can quickly be brought to a state where it has a steady charge. Since the secondary electrons emitted by are emitted only from the wiring, it is possible to accurately measure the relative value of the wiring voltage.

Next, the signal processing circuit 13 will be explained in detail with reference to FIG. The signal processing circuit 13 detects the secondary electrons 7 emitted from the IC 6 to be tested by the EB pulse 5 . The analog secondary electronic signal 121 output from the detector 12 is amplified by an amplifier 133.

The output is input to the AD converter 136. AD converter 1
36 converts the amplified analog secondary electronic signal into a digital signal. At this time, in order to specify the timing of sampling the analog signal, a signal 135 is generated by appropriately delaying the strobe signal 92 of the EB'' pulse irradiation signal φ1 generated in the EB pulse gate control circuit 13 by the delay circuit 134. It is input as a sampling signal to the AD converter 136.The AD-converted digital secondary electronic signal is input to the averaging processing circuit 137.Here, the EB pulse is inputted while keeping the phase of the EB pulse irradiation signal φ1 fixed. An average of digital secondary electron signals obtained by irradiation is calculated and becomes data for phase φ1.

By averaging in this way, the S/N (signal-to-noise ratio) of the signal will improve.

This signal processing circuit I3 is used for control calculation #! i14, inputs a start signal 144-3 from the computer 14 to start signal processing, and sends data (144-1) specifying the delay time of the strobe signal 92 to the delay circuit 134.
) and data (144-2) specifying the number of additions are given to the averaging processing circuit 137, and the calculated averaging 5, that is, the digital data 131 corresponding to the wiring voltage of the IC under test is subjected to the averaging processing. The data is transferred from the circuit 137 to the control computer 14, where it is appropriately digitally processed and displayed.

(7) Effects of the Invention As described above, the present invention provides an electron beam device equipped with a strobe function, by providing means for alternately precharging with a continuous beam and sampling a secondary electron signal at an arbitrary measurement phase. The wiring voltage of an IC with a protective film can be quickly precharged and then measured, and with an extremely simple structure, the temporal change in voltage and the voltage state of each part in a two-dimensional space on the IC surface can be observed with high precision. The effect is that it can be done.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. FIG. 2 is a concrete block diagram of the EB pulse control circuit in the above embodiment. FIG. 3 is a concrete block diagram of the signal processing circuit in the above embodiment. FIG. 4 is a timing chart showing the relationship between the EB pulse and the analog secondary electronic signal. 5...Electron beam pulse. 6...Test IC. 7...Secondary electron. 9...EB pulse gate control circuit. 13...Signal processing circuit. 14...Control computer. Figure 1 Figure 2 Figure 3

Claims (2)

[Claims] (1) In an electron beam device equipped with a strobe function,
An electron beam device comprising means for alternately performing precharging with a continuous beam and sampling a secondary electron signal at an arbitrary measurement phase. (2) The end phase of the precharge is constant regardless of the measurement phase.
The strobe electron beam device described in Section 1.