JP3259762B2 - LSI potential distribution image acquisition method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for acquiring a potential distribution image on an LSI surface by an electron beam.

[0002]

2. Description of the Related Art An electron beam tester is used as one of effective means for analyzing a failure of an LSI. By applying a test vector generated by an LSI tester or the like to a defective LSI in a vacuum chamber, irradiating the target surface of the LSI with an electron beam and measuring the amount of secondary electrons corresponding thereto,
The relative potential of each wiring near the LSI surface can be read depending on whether the amount is large (potential is relatively low) or small (potential is relatively high). In particular, in an electron beam tester, a potential distribution image representing a two-dimensional potential distribution on the LSI surface can be obtained by scanning an electron beam over a specified range on the LSI surface with a test vector of a specified address applied. This is very effective for grasping the operation inside the LSI.

However, if the irradiation of the electron beam to a certain range is continued, electrons are charged up to the protective film on the LSI surface. Irradiated electrons will be charged with a biased distribution that cancels the distribution on the surface protective film,
Therefore, the amount of secondary electrons with respect to the electron beam irradiation does not reflect the wiring potential, and the observed potential distribution image has low contrast.

As means for solving this problem, Japanese Patent Laid-Open No.
There is a method described in the specification of Japanese Patent No. 159497, in which the power supply terminal of the LSI is grounded for a certain period each time a test vector is applied for one cycle, thereby making the potential of each wiring inside the LSI uniform. LS by electron beam irradiation
Electrons can be charged in the protective film on the I surface with a uniform distribution. As a result, when the test vector is applied again, the amount of secondary electrons with respect to the irradiation of the electron beam reflects the wiring potential, and the potential of the contrast is higher than when the test vector is applied repeatedly without grounding the power supply. A distribution image can be obtained.

[0005]

In the above-described method, the control of the power supply terminal and the application of the test vector are generally performed by the same L.
Depending on the type of the LSI tester and the type of the test vector series, the test is performed by the SI tester. (1) The supply voltage to the power supply terminal of the LSI is raised from the ground state to a predetermined voltage,
It may take time between (2) starting application of test vectors and (3) sequentially applying test vector sequences from the first address to the address to be measured. Charge-up of the surface protective film by electron beam irradiation may occur in about several tens of milliseconds depending on conditions. On the other hand, the operations (1) to (3) may require several hundred milliseconds. In such a case, even in accordance with the above-described method, electrons are charged to the protective film on the surface in a distribution corresponding to the wiring potential between any of (1) to (3), and the original address of the measurement target is It is not possible to obtain a potential distribution image expressing the wiring potential for the test vector with good contrast.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for avoiding charge-up of electrons in a target LSI and obtaining a potential distribution image showing a potential distribution with respect to a test vector of an original measurement target address with good contrast. It is.

[0007]

An LSI potential distribution image acquiring method according to the present invention comprises the steps of: applying a predetermined power supply voltage to a power supply terminal of a target LSI after reducing irradiation of an electron beam to the target LSI; To sequentially apply a test vector sequence up to the address of the measurement target, and the target L of the electron beam.
The irradiation amount to the observation range of the SI is increased, and the target L is applied while the test vector of the address of the measurement target is applied while being held.
A series of operations including an operation of acquiring an SI potential distribution image and an operation of grounding the power supply terminal of the target LSI for a certain period of time thereafter is performed by one operation.
It is characterized by being repeated at least twice.

The irradiation amount of the electron beam to the target LSI during a period in which the power supply terminal of the target LSI is grounded is larger than the irradiation amount of the electron beam to the target LSI when acquiring the potential distribution image of the target LSI. Is preferred.

[0009]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a program flow chart showing each operation of an embodiment of an LSI potential distribution image acquiring method according to the present invention,
FIG. 2 is an apparatus configuration diagram for applying a test vector sequence to a target LSI by an LSI tester and forming a potential image by an electron beam tester in the embodiment, and FIG. 3 is an operation timing in the embodiment. FIG.

Referring to FIGS. 1 and 2, in this embodiment, an LSI tester 1 is used to apply a test vector sequence to a target LSI 9, and an electron beam tester 2 is used to acquire and generate a potential distribution image. An example in the case of using will be described. The target LSI 9 is mounted in the vacuum chamber 3 of the electron beam tester 2 so that the electron beam system can be observed, and electrical connection is established through a jig and a connection cable. A test program and a test vector sequence for the target LSI 9 are loaded and placed in the LSI tester 1,
The test vector generated by the SI tester 1 is the target LSI 9
To be applied.

The electron beam tester 2 irradiates the target LSI 9 with electrons generated by the electron beam source 4. When the target LSI 9 is irradiated with electrons, secondary electrons are generated in accordance with the potential on the LSI surface and detected by the secondary electron detector 7. The electron beam tester 2 generates a potential distribution image based on this. However, when the applied voltage of the beam blanker 5 is changed, the direction of the electron beam is bent, hits the blanking aperture 6 and does not pass, so that the target LSI 9 is not irradiated. The beam blanker 5 is placed so that the applied voltage can be changed in accordance with a control signal sent via the control signal cable 10.

The LSI tester 1 applies the LSI power supply voltage and ground, generates a test vector sequence, and generates a beam suppression control signal at the timing shown in FIG. First, L
In the SI tester 9, the voltage of the beam blanker 5 is changed based on the beam irradiation amount control signal so as to reduce the beam irradiation amount. And
The LSI tester 1 applies a predetermined power supply voltage to a power supply terminal of the LSI, and sequentially applies a test vector sequence to an address to be measured. When the address of the measurement target is reached, the beam irradiation control signal is switched so as to increase the beam irradiation amount. As a result, in the electron beam tester 2, the target LSI 9
Irradiation of the electron beam to is started. The LSI tester 1 continues to apply the test vector at the address to be measured, and the electron beam tester 2 acquires and generates a potential distribution image based on the amount of secondary electrons. After a certain period of time, the LSI tester 1
Ground the power supply terminal.

According to such a procedure, the beam irradiation amount can be reduced from the time when a predetermined voltage is applied to the power supply terminal of the LSI to the time when the test vector of the target address is applied, and electrons are biased on the LSI surface. Charge up can be avoided.

Next, a second embodiment will be described.

FIG. 4 is a timing chart of the operation in the second embodiment.

In the case of this embodiment, the irradiation amount of the electron beam to the target LSI during the period in which the power supply terminal of the target LSI is grounded is determined by the amount of the electron beam applied to the target LSI when acquiring the potential distribution image of the target LSI. It is larger than the irradiation amount.

By doing so, the effect during the period when the power supply terminal of the LSI is grounded, that is, the potential of each wiring inside the LSI is made uniform, similarly to the effect in the above-mentioned prior art JP-A-5-159497. In this state, the effect of charging electrons can be enhanced, and the contrast is improved. Further, the effect of charging electrons with a uniform distribution in the protective film on the LSI surface is also accelerated, so that the time required for obtaining a certain effect is shortened. On the other hand, in the above-mentioned prior art method, originally,
In order to obtain a sufficient effect, it is necessary to make the period during which the power supply terminal of the LSI is grounded sufficiently longer than other periods. As described above, in the case of the present embodiment, in particular, the period during which the power supply terminal of the LSI is grounded can be reduced, and the image acquisition time can be reduced.

[0019]

As described above, according to the present invention, the object LS
After a predetermined power supply voltage is applied to I and before the test vector address to be measured is applied, the amount of electron beam irradiation on the surface protective film is reduced. In this way, a potential distribution image with good contrast with respect to the test vector at the address of the original measurement target can be obtained. By increasing the irradiation dose to
In particular, there is an effect that it is possible to provide an LSI potential distribution image acquisition method that shortens the period during which the power supply terminal of the LSI is grounded, and thus shortens the image acquisition time.

[Brief description of the drawings]

FIG. 1 is a program flow chart showing each operation of an embodiment of an LSI potential distribution image acquiring method according to the present invention.

FIG. 2 is a configuration diagram of an apparatus for applying a test vector sequence to a target LSI by an LSI tester and forming a potential image by an electron beam tester in the embodiment.

FIG. 3 is a timing chart of an operation in the embodiment.

FIG. 4 is a timing chart of an operation in the second embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 LSI tester 2 Electron beam tester 3 Vacuum chamber 4 Electron beam source 5 Beam blanker 6 Blanking aperture 7 Secondary electron detector 8 Connection cable 9 Target LSI 10 Control signal cable 11 Beam irradiation amount reduction 12 LS power supply voltage application 13 Apply test vector sequence 14 Increase beam irradiation 15 Apply test target address Test vector 16 Acquire potential distribution image 17 LS power supply terminal ground

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/66 G01R 31/302

Claims (2)

(57) [Claims] An electron beam irradiating the surface of the LSI;
In an LSI potential distribution image acquiring method for acquiring a potential distribution image of an SI surface, while maintaining the irradiation amount of the electron beam smaller than the irradiation amount of the electron beam when acquiring the potential distribution image of the LSI surface, A first step of applying a predetermined power supply voltage to the LSI and sequentially applying a test vector sequence up to the address of the measurement target; and, after the test vector sequence reaches the address of the measurement target, the address of the measurement target. A second step of increasing the irradiation amount of the electron beam onto the LSI surface while acquiring the test vector and acquiring a potential distribution image of the LSI surface; Third to ground
An LSI potential distribution image acquiring method, wherein the first step and the second step are sequentially and continuously repeated one or more times. 2. An irradiation amount of the electron beam to the LSI surface during a period in which a power supply terminal of the target LSI is grounded, the amount of the electron beam applied to the LSI surface when acquiring the potential distribution image on the LSI surface. 2. The method according to claim 1, wherein the amount of irradiation is larger than the irradiation amount.