JPS62282279A - Apparatus for measuring delay time of transistor gate - Google Patents

Abstract

PURPOSE:To measure the delay time of an arbitrary transistor gate in the atmosphere with sufficient time resolving power, by gradually changing the delay time of a clock determining laser generating timing at every definite time. CONSTITUTION:A laser beam source 15 irradiates the arbitrary transistor gate of an article 18 to be measured having a plurality of transistor gates with laser beam and a delay circuit 14 delays a clock determining the laser generating timing of the laser beam source 15 and gradually changes said delay time at every definite time. A control and data analyzing computer 13 drives a pattern generator 19 to supply an input signal to the article 18 to be measured in constant timing regardless of the change in the delay time of the circuit 14 and calculates the delay time of the arbitrary transistor gate on the basis of the delay time of the circuit 14 when the value of the beam exciting current generated in the arbitrary transistor gate is changed by the irradiation of laser beam.

Description

[Detailed Description of the Invention] a. Detailed Description of the Invention (Summary) The present invention provides an apparatus for measuring the delay time of a transistor gate, in which the irradiation timing of a laser to be irradiated to an arbitrary transistor gate is gradually set in a preset order. Along with changing
By measuring changes in the photoexcited current flowing through the transistor gate by laser irradiation, we can measure the delay time of any transistor gate separately from other transistor gates with sufficient time resolution. It is designed so that it can be measured while it is still installed in a StC large-scale integrated circuit.

[Industrial application field]

The present invention relates to a device for measuring delay time of a transistor gate, and more particularly to a device for measuring delay time of a transistor gate incorporated in an integrated circuit.

There are various factors that determine the performance of LSIs, but as LSIs have become faster in recent years, it has become important to accurately know the delay time of the transistor gates that make up the LSI. There is a need for a measuring device that can measure time with sufficient time resolution and high precision.

[Conventional technology]

Conventionally, the delay time of a transistor gate is measured by observing the time difference between the input signal waveform and the output signal waveform of the transistor gate using an oscilloscope, and determining 'Is. In addition, when the delay time of one transistor gate is extremely short, the time difference between the input signal waveform and the output signal waveform of multiple transistor gates connected in cascade is usually measured by 152M using an oscilloscope, and the time difference (that is, the total delay time) is calculated using an oscilloscope. By dividing by the number of transistor gates, the delay time of each transistor gate was measured.

In addition, as another method for measuring the delay time of a conventional transistor gate, EB (Electron Beam:
There is a method using an electron beam (electron beam) prober.

FIG. 5 shows a configuration diagram of an example of this EB prober.

In the figure, control data from computer 1 for υ110 is transmitted to delay unit 2. The signal is supplied to the driver 3 and the signal processing circuit 4, respectively.

The output signal of the delay unit 2 is supplied to a signal processing circuit 4, while being applied to a refractive deflector 6 via a driver 3. This refraction type deflector 6 refracts the electron beam taken out from the electron gun 5 and irradiates it onto an energy analyzer 7, where it is extracted and irradiated onto a sample (here, an IC) 8. The delay unit 2 changes the irradiation phase of the electron beam stepwise within a predetermined range. Further, in order to quantitatively measure the voltage at any part of the sample 8, a hemispherical energy analyzer with a flat mesh extraction electrode is used. The output pattern of the IC driver 9 is input to the sample 8.

Since the value of secondary electrons generated by irradiation with the electron beam changes depending on the potential of the surface of the sample 8, the secondary electrons are detected by the detector 310, and the signal processing circuit 4 converts them into secondary electron signal data. After being converted into , it is supplied to the control computer 1 .

As a result, the potential on the sample 8 is measured. Note that the measurement results are displayed on the display device 11.

This EB prober is originally a device for measuring the potential on the sample 8, but the delay time of the transistor gate also
It can be measured by measuring the time difference between the input and output signals of the transistor gate.

[Problem that the invention seeks to solve]

However, among the methods for measuring the delay time of transistor gates using an oscilloscope described above, in the case of a measurement method in which a plurality of transistors are connected in N-connection, after measuring the delay time of the entire plurality of transistor gates, the measurement time is The delay time per transistor gate is calculated by dividing by the number of gates, but since the delay time of a transistor gate is different when it is on and when it is off, the obtained delay time per transistor gate is an average value. Q: ``It wasn't accurate.

Furthermore, due to their characteristics, it is not possible to connect the input stage transistor gate (input buffer?) and the output stage transistor gate (output buffer) in cascade and measure the delay time with an oscilloscope.

For this reason, if you try to measure the gate delay time using an oscilloscope with the input buffer or output buffer alone, the capacitance of the measurement system such as a probe is considerably larger than that of the input buffer or output buffer. Another problem was that the delay time of the output buffer could not be measured accurately.

On the other hand, the method of measuring the gate delay time using the EB prober described above requires a special device to obtain a vacuum because the sample 8 must be placed in a vacuum, and if the sample 8 is an LSI, LSIs usually have a transparent protective film formed thereon, but measurements cannot be made unless this film is removed, resulting in poor operability.

The present invention was created in view of the above points, and an object of the present invention is to provide a transistor gate delay time measuring device that can measure the delay time of any transistor gate with sufficient temporal resolution and in the atmosphere. do.

[Means for solving problems]

The transistor gate delay time measuring device of the present invention delays a laser light source that irradiates a laser beam to an arbitrary transistor gate in an object to be measured, and a clock that determines the laser generation timing of the laser light source, and also keeps the delay time constant. A delay circuit that changes gradually over time, and a delay circuit that supplies an input signal to the object under test at a constant timing, and delays when the value of the photoexcitation current generated in an arbitrary transistor gate by laser beam irradiation changes. It consists of a measuring means for calculating the delay time based on the time.

[Effect]

The clock delayed by the delay circuit is applied to the laser light source, and the laser generation timing is changed to υl111. As a result, the timing of generation of a photoexcitation current generated by irradiating a laser beam to an arbitrary transistor gate in the object to be measured changes in synchronization with the output delay clock of the delay circuit.

On the other hand, an input signal is applied to the object to be measured by the measurement means at a constant timing, and the ON or OFF state of any transistor gate due to this input signal is detected by a change in the value of the photoexcitation current.

Therefore, the above measurement means can measure the delay time of any transistor gate based on the delay time of the delay circuit when the value of the photoexcitation current changes.

〔Example〕

FIG. 1 shows a block diagram of one embodiment of the invention.

In the figure, 13 is a data analysis computer 1i1112'0, which generates and outputs clock pulses for driving the laser light source 15 to the delay circuit 14, and also changes the delay time of the delay circuit 14 gradually at regular intervals. ff1ll
III signal is supplied to the delay circuit 14. Further, the computer 13 supplies a power supply voltage to the object to be measured 18, and
The value of the photoexcitation current from the object to be measured 18 is detected. Furthermore,
The computer 13 controls the X-Y stage 17
At the same time, the pattern generator 19 is driven.

The output delay clock pulse of the delay circuit 14 is applied to the laser light source 15 to drive it. As a result, the laser light source 15 is generated once within one cycle of the clock pulse input to the delay circuit 14 and then disappears (that is, the laser light source 15 blinks within one cycle of the input clock pulse).

). The laser beam generated by this laser light source 15 is transmitted to an object to be measured 18 in the atmosphere by an objective lens 16.
is focused and convergently irradiated onto the surface of the The diameter of the laser beam on the object to be measured 18 is determined by the magnification of the objective lens 16.

The laser beam irradiation position on the object to be measured 18 is set at an arbitrary position by the XY stage 17. Measured object 1
For example, 8 is an LSI that has many transistor gates. Even if this LSI has a protective film, the protective film is transparent, so it can be irradiated with a laser beam as it is without having to remove the protective film. .

The OA position of this laser beam is such that the transistor gate is composed of a P-channel MO3 type field effect transistor Q1 and an N-channel MOS type field effect transistor Q2, as shown in FIG. A C-MO in which an input signal is applied to both gates of transistors Q1 and Q2, and a phase inverted signal of the input signal is output from both drains of transistors Q1 and Q2 to an output terminal 31.
Assuming that it is an S inverter circuit, the transistor Q! shown by the broken line 32. and Q2 at or near the drain regions (selected as desired).

A laser beam irradiated to this position 32 generates an optically excited@flow, and for example, a source with 90 transistors (C
- When the photoexcitation current flowing through the drain of the MOS inverter) is measured, its value shows a value corresponding to the on/off state of the transistors (h, Q2).Therefore, from the value of this photoexcitation current, it can be determined whether the transistors Q+, Q2 are on or off. You will understand.

The pattern generator 19 described above is connected to the object to be measured (here, the LS
I) Generate a predetermined pattern of input signals and supply them to the device under test 18 to test whether the device 18 performs the logical operation as installed. This input signal causes the object to be measured 18 to
Detecting whether the transistor gate in the middle is turned on or off by measuring the value of the photoexcitation current caused by the laser beam irradiation using the computer 13,
The gate delay time can be measured by using the computer 13 to measure the time from when the input signal is input to when the arbitrary transistor gate is turned on or off.

The above-mentioned gate delay time measurement can be performed without contact using an oscilloscope without the need for a probe, so the capacitance of the measurement system can be reduced, and the capacitance of the transistor gate itself is small, resulting in delay It can be done accurately even when the time is short.

By the way, since the above-mentioned detection of the value of the photoexcitation current is performed every cycle of the clock pulse for driving the laser light source 15, it is not possible to measure a signal that changes faster than the repetition frequency of this clock pulse. In other words, the time resolution of this snowmaking is limited by the repetition frequency of the above-mentioned overflow pulse.

When trying to measure the delay time of a transistor gate, a fairly high time resolution (for example, several hundred ps) is required, but the repetition frequency of the clock pulse to obtain that level of time resolution is, for example, about several GHz. Since the frequency is extremely high, it is difficult to realize it as is.

However, according to this embodiment, by providing the delay circuit 14 and gradually changing the timing of laser generation (irradiation), it is substantially the same as driving the laser light source 15 with a clock pulse with a high repetition frequency. A uniquely high time resolution can be obtained.

This will be explained in more detail. For example, as shown in FIG. 2, the delay circuit 14 includes a switch 22 and four delay lines 23 to 26 having mutually different delay times. The delay time is approximately proportional to the quality of the delay lines 23 to 26, and the delay time of the shortest delay line 23 is the shortest, and the delay time increases successively in the order of delay lines 24, 25, and 26.

In FIG. 2, the clock pulse from the computer 13 that enters the input terminal 21 of the delay circuit 14 is transferred to the switch 2.
2, the signal is selectively inputted to one of the delay lines 23 to 26, and after being delayed there, it is outputted as a driving clock pulse to the laser beam ll1ii15 via the output terminal 27. The switch 22 sequentially and cyclically switches and connects the contacts 22a to 22d based on a control signal from the computer 13.

Here, if the common clock pulse of each circuit in FIG. 1 including the pattern generator 19 and the like is indicated by a in FIG. 3, when the output delay pulse of the delay 823 is applied to the laser light source 15, As shown by b in FIG. 3, the laser light source 15 generates high-level llllSiI with almost no time delay with respect to the common clock pulse a. Similarly, when the output delay pulse with a delay of 1!24 is applied to the laser light source 15, the output delay pulses of the delay lines 25 and 26 are applied at the timing shown by C in FIG. 3 with respect to the clock pulse a. When applied to the laser light source 15, a laser beam is generated and output during the high level period of the waveform at the timings shown as d and e in FIG. 3, respectively.

Here, the delay time of an arbitrary transistor gate in the device under test 18 is determined from the time when the input signal supplied from the pattern generator 19 to the input terminal of the device under test 18 is input to the transistor gate. This is the time required for the input signal to actually turn on or off. Among these, the input signal is generated at a constant timing in synchronization with the clock pulse a of about 20 MHz, for example, so that the input time of the input signal to the sleeve measurement object 18 is at the third point.
This corresponds to, for example, the rising time of each predetermined period of the clock pulse a shown in the figure.

On the other hand, the ON or OFF operation of the transistor gate is detected based on whether the value of the photoexcitation current reaches a predetermined value as described above. For measurement of photoexcitation current, a third
It takes a time longer than one cycle of the clock pulse a from the rising edge of the laser generation timing waveform shown by b to e in the figure (the laser generation start point), and the integral value of the optically excited 'yl flow during that measurement time is On or off operation of the transistor gate is detected.

In this way, when the measurement with the delay time is completed, the delay time of the delay circuit 14 is switched, and the same input signal as above is supplied to the device under test 18 again in synchronization with the rising edge of the clock pulse a. and the laser beam strikes the object to be measured 1 at a timing corresponding to the delay time of the delay circuit 14.
The transistor gate of No. 8 is irradiated, and measurement of the photoexcitation current is started again at the same time.

Thereafter, in the same manner as above, the delay time of the delay circuit 14 was gradually switched for each measurement time, the value of the photoexcitation current in the laser irradiation phase was measured based on the delay time, and the measured value was changed. The delay time of the transistor gate is calculated based on the delay time of the delay circuit 14 at that time.

As a result, the gate delay time can be measured with substantially the same high time resolution as when the delay time of a transistor gate is measured using a high repetition frequency high-speed pulse.

This time resolution is limited by the pulse width of the laser generation timing waveform shown by b-e in FIG. 3 and the accuracy of the delay circuit, and a high time resolution of several hundred ps, for example, can be obtained.

According to this embodiment, high temporal resolution can be obtained, and
Since the gate delay time can be measured without contacting the transistor gate, is it an input buffer? Alternatively, the gate delay time of a single transistor gate constituting the output buffer can be accurately measured separately from other transistor gates.

Note that since the input signal is supplied only to the input terminal of the device under test 18, the delay time of the transistor gate that constitutes the output buffer 7, for example, is the delay time of all the transistors from the input terminal of the device under test 18 to the output terminal of the output buffer sofa. From the total delay time of the gate, it is determined that the output buffer 7 is
It can be obtained by subtracting the delay time of the plurality of transistor gates up to just before the input stage.

〔Effect of the invention〕

As described above, according to the present invention, since the laser irradiation phase is gradually changed, the high repetition frequency
The delay time of any transistor gate can be measured with substantially the same high time resolution as when the delay time of a transistor gate is measured using a pulse. It is possible to separate the time from other internal transistor gates and accurately measure the delay time of the transistor gate, and it is also possible to measure the delay time of the transistor gate when the LSI is assembled, so it is possible to more accurately measure the delay time of the transistor gate, including the delay due to wiring. Delay time can be measured.

Further, according to the present invention, the delay time of a transistor gate can be measured in the atmosphere without the need to place the object to be measured in a vacuum, and furthermore, the delay time of a transistor gate can be measured in the atmosphere without removing the protective film of the LSI. It has many features such as being able to measure the delay time of transistor gates and being easy to operate.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an embodiment of the present invention, Fig. 2 is a configuration diagram showing an embodiment of the delay circuit in the block shown in Fig. 1, and Fig. 3 explains the laser generation timing in the present invention. 4 is a diagram for explaining the laser irradiation position in the present invention, and FIG. 5 is a block diagram showing the configuration of an example of an EB blower. In the figure, 13 is a l1ll/data analysis combination 1-2, 14 is a delay circuit, 15 is a laser light source, 18 is an object to be measured, 19 is a pattern generator, 22 is a switch, 23 to 26 are delay lines, 32 is the laser irradiation position. This section 4β is in charge of 1st grade 1 2 eco・Article 92 1st figure 1 late payment return sanction--rent-#! L91 Tank Seal Figure 2

Claims (1)

[Claims] A laser light source (15) that irradiates a laser beam to an arbitrary transistor gate in an object to be measured (18) having a plurality of transistor gates; a delay circuit (14) that delays a clock that determines the laser generation timing and gradually changes the delay time at regular intervals; In addition to supplying an input signal to (18), the arbitrary transistor is selected based on the delay time of the delay circuit (14) when the value of the photoexcitation current generated in the arbitrary transistor gate by irradiation with the laser beam changes. Measuring means (13) for calculating gate delay time
, 19) A transistor gate delay time measuring device characterized by comprising the following.