Source: http://www.google.com/patents/US5528156?dq=5,963,646
Timestamp: 2017-09-26 15:19:40
Document Index: 445560805

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Patent US5528156 - IC analysis system and electron beam probe system and fault isolation method ... - Google Patents
A stop pattern setting part 203 is provided which permits setting therein a plurality of patterns for stopping the test pattern updating operation of a test pattern generator 210, and upon each generation of the test patterns set in the stop pattern setting part 203, the test pattern generator 210 is...http://www.google.com/patents/US5528156?utm_source=gb-gplus-sharePatent US5528156 - IC analysis system and electron beam probe system and fault isolation method therefor
Publication number US5528156 A
Application number US 08/181,584
Also published as DE4403768A1, US5589780, US5633595
Publication number 08181584, 181584, US 5528156 A, US 5528156A, US-A-5528156, US5528156 A, US5528156A
Inventors Koshi Ueda, Akira Goishi, Masayuki Kuribara
US 5528156 A
A stop pattern setting part 203 is provided which permits setting therein a plurality of patterns for stopping the test pattern updating operation of a test pattern generator 210, and upon each generation of the test patterns set in the stop pattern setting part 203, the test pattern generator 210 is stopped from the pattern updating operation. Each time the test pattern stops, a stop signal is applied to an electron beam probe system 300, causing it to start an image data acquiring operation. Upon completion of the image data acquisition, a write completion signal generating part 308 generates a write completion signal, which is applied to the test pattern generator 210 to cause it to resume the pa-tern updating operation. By applying different test patterns to a device under test alternately with each other and displaying image data of the difference between resulting pieces of image data, a potential contrast image can be improved.
1. An integrated circuit analysis system sweeping and irradiating with an electron beam a surface of a device under test, said surface having quantities of secondary emissions from each irradiated point of the surface and a surface potential distribution corresponding to the quantities of secondary emissions, said integrated circuit analysis system displaying said surface potential distribution as an image, the integrated circuit analysis system comprising:
an integrated circuit tester applying a test pattern signal, comprising a plurality of test patterns, to said device under test, and sequentially updating each of the plurality of test patterns applied to said device under test, said integrated circuit tester comprising:
a test pattern generator generating said test pattern signal applied to said device under test and sequentially updating the each of the plurality of test patterns of said test pattern signal applied thereto,
stop pattern setting means for setting therein one of the plurality of test patterns of said test pattern signal as an update stopping test pattern, and
main control means for stopping said test pattern generator, when said test pattern generator generates a same test pattern as said update stopping test pattern, from updating said same test pattern and holding the test pattern generator in a state of continually outputting said same test pattern being applied to said device under test, and for outputting a pattern update stop signal representing a pause of the test pattern updating operation by said test pattern generator; and
an electron beam probe system comprising:
image data processing means for responding to said pattern update stop signal and starting, based on said pattern update stop signal, acquisition of image data comprising the surface potential distribution, and
write completion signal generating means for generating and outputting a write completion signal indicating that the acquisition of said image data by said image data processing means is completed,
said main control means for receiving said write completion signal and for controlling said test pattern generator to resume said test pattern updating operation being based thereon.
2. An integrated circuit analysis system sweeping and irradiating with an electron beam a surface of a device under test, said surface having quantities of secondary emission from each irradiated point of the surface and a surface potential distribution corresponding to the quantities of secondary emission, said integrated circuit analysis system displaying said surface potential distribution as an image, the integrated circuit analysis system comprising:
an integrated circuit tester applying a test pattern signal comprising a plurality of test patterns to said device under test and sequentially updating each of the plurality of test patterns applied to said device under test, said integrated circuit tester comprising:
stop pattern setting means for setting therein at least a first test pattern and a second test pattern of the plurality of test patterns of said test pattern signal as update stopping test patterns, respectively, and
main control means for stopping said test pattern generator, when said test pattern generator generates a same test pattern as one of said first test pattern and said second test pattern, from updating said same test pattern and holding the test pattern generator in a state that the test pattern generator continues to output said same test pattern being applied to said device under test, and for outputting a first pattern update stop signal representing a pause of the test pattern updating operation by said test pattern generator when said test pattern generator generates the same test pattern as said first test pattern and outputting a second pattern update stop signal representing a pause of the test pattern updating operation by said test pattern generator when said test pattern generator generates the same test pattern as said second test pattern; and
image data processing means for responding to each of said first and second pattern update stop signals and starting, based on each pattern update stop signal, acquisition of image data comprising the surface potential distribution, and
mode changeover means for switching between a first operation mode and a second operation mode, said first operation mode being a first state in which, in response to said first pattern update stop signal, said image data processing means is inhibited from acquiring said image data and concurrently said device under test is subjected to the sweeping of irradiation of the electron beam when said test pattern updating operation by said test pattern generator is temporarily stopped by generation of said first test pattern, said second operation mode being a second state in which, in response to said second pattern update stop signal, said image data processing means acquires said image data and concurrently said device under test is subjected to the sweeping of irradiation with the electron beam when said test pattern updating operation by said test pattern generator is temporarily stopped by generation of said first test pattern.
3. The integrated circuit analysis system as claimed in claim 2, wherein said electron beam probe system further comprises write completion signal generating means for outputting a write completion signal representing that the image data processing means has completed the acquisition of the image data, and the main control means for receiving said write completion signal from said electron beam probe system and for controlling said test pattern generator to resume said test pattern updating operation based thereon.
4. An electron beam probe system scanning and irradiating with an electron beam a surface of a device under test being supplied with a test pattern signal comprising a plurality of test patterns from an integrated circuit tester, said test patterns being sequentially updated by said integrated circuit tester which outputs a pattern update stop signal representing a pause of the pattern updating operation of the integrated circuits tester, said electron beam probe system measuring a quantity of secondary emission from each irradiated point on the surface, and displaying a surface potential distribution of said device as an image, said electron beam probe system comprising:
image data processing means for responding to the pattern update stop signal and starting acquisition of image data based thereon; and
write completion signal generating means for generating and outputting to said integrated circuit tester a write completion signal representing completion of the image data by the image data processing means and causing the integrated circuit tester to resume the test pattern updating operation thereof.
The present invention relates to an electron beam probe system which irradiates an IC under test with an electron beam, measures the quantity of secondary electrons emanating from each irradiated point and displays the potential distribution in the IC as a potential contrast image that is used to locate a fault, for example. The invention also pertains to an IC analysis system and a fault isolation method that utilize such an electron beam probe system.
Heretofore, there has been used an IC analysis system of the type that sweeps and irradiates (namely, irradiates while scanning) the surface of a chip of an IC under test (hereinafter also referred to generally as a device or an element under test DUT) chip with an electron beam, measures the quantity of secondary electrons emitted from the IC chip at each irradiated point as an electrical signal, processes the electrical signal as image data to display the potential distribution in the IC as a potential contrast image, and compares it with a similar potential contrast image of a non-defective IC to pinpoint a fault of the IC under test, for example.
The IC tester 200 provides a test pattern signal to an IC under test DUT placed in the electron beam probe system 300. The conventional IC tester 200 includes: a test pattern generator 210 which as a plurality of test patterns stored at addresses therein and generates a test pattern signal composed of a series of test patterns for application to the device under test DUT, hereinafter a test pattern also referred to as a pattern; a main control part 204 which controls, in accordance with a program which describes an analysis procedure, a pattern generating sequence of the test pattern generator 210 such as the start of a test pattern generation, a pause of update of the pattern, a repetition of a desired pattern sequence, the end of the pattern generation, for instance; a start switch 201 for starting the generation of a test pattern signal; a stop switch 202 for stopping the generation of the test pattern signal at an arbitrary point of time; and a stop pattern setting part 203 in which a stop pattern is set for stopping a test pattern having the same pattern as that of this stop pattern from being updated in the test pattern generator 210 when this same test pattern is generated from the test pattern generator 210. The main control part 204 can always monitor the stop pattern set in the stop pattern setting part 203 and a test pattern generated from the test pattern generator 210. Accordingly, the main control part 204 always compares the stop pattern and stops the updating operation of the test pattern generator 210 when both patterns of the stop pattern and the test pattern are identical.
When the main control part 206 detects that the test pattern generator 210 has generated the same test pattern as the stop pattern set in the stop pattern setting part 203, the main control part 204 controls to stop temporarily the test pattern generator 210 from updating the test pattern now being generated therefrom so that the test pattern generator 210 can continue to generate the identical test pattern. At the same time, the main control part 204 supplies the image data processor 304 and the column control part 307 with a stop signal STP representing that the test pattern updating operation of the test pattern generator 210 has stopped. Upon receiving the stop signal STP, the column control part 307 effects control to emit the electron beam EB and the image data processor 305 starts to acquire image data.
Conventionally, the time for pause of the test pattern is set a little longer than the time required to write the image data into the image data processor 305 in order to afford a margin of time. On account of this, a change in the conditions for writing the image data into the image data processor 305 calls for a change in the test pattern pause time as well; hence, the prior art system has the defect of poor operability.
That is, the electron beam acceleration voltage, scanning speed and scanning area must be set for acquiring the image data, and if these conditions are changed or modified, the time for acquiring the image data will change. Consequently, when the conditions for acquiring the image data are changed, the test pattern pause time also needs to be changed accordingly. This involves operating both of the IC tester 200 and the electron beam probe system 300, and hence is troublesome.
On the other hand, the conditions for writing the image data into the image data processor 305 need to be changed in accordance with the purpose of each test. In particular, in the case of an IC chip wherein the device under test DUT is covered all over its surface with an insulating film as a protective layer, it is necessary to observe or measure potentials corresponding to those of wiring conductors underlying the insulating film. It is difficult, however, to detect, as potential contrast images, the potential distributions of the wiring conductors of the IC chip covered all over its surface with the insulating film. The quantity of secondary emission of electrons from the chip surface irradiated by the electron beam depends on the surface potential of the IC chip. When the surface potential is positive, some of the secondary electrons emitted return to the chip surface. Hence the quantity of secondary electrons that reach the sensor is small. When the surface potential is negative, the secondary electrons are readily emitted and they do not return to the chip surface, and hence a large amount of secondary electrons reach the sensor. For instance, when the surface of the insulating film has a negative potential, the surface is charged in the positive direction as the secondary emission of electrons proceeds, and the quantity of secondary emission gradually decreases. Conversely, when the surface of the insulating film has a positive potential, the potential decreases in the negative direction by electrons that are injected thereinto by the electron beam. In either case, the surface potential reaches equilibrium at a certain potential. That is, when the surface of the insulating film is irradiated with an electron beam, the potential distribution of the IC chip surface becomes gradually uniform and ultimately disappears owing to the storage of charges on the insulating film that is cause by the secondary emission of electrons in proportion to the electron beam irradiating time, and as a result, it is impossible to detect potential contrast images desired to obtain.
FIGS. 2A, 2B and 2C show how the potential distribution of the IC chip surface disappears as mentioned above. FIG. 2A shows potential contrast image of conductors L1, L2, L3 and L4 underlying the insulating film when they are supplied with L-logic, H-logic, L-logic and H-logic potentials, respectively. As shown, the application of the L-logic potential (a voltage close to zero volt or negative potential) provides a white potential contrast image (which means that the quantity of secondary electrons reaching the sensor is large). The application of the H-logic potential (a voltage above zero volt) provides a black potential contrast image (which means that the quantity of secondary electrons reaching the sensor is small). In this instance, an insulated substrate PB has a potential intermediate between the L-logic and H-logic potentials and is displayed in gray.
A first object of the present invention is to provide an electron beam probe system which permits enhancement of its operability and an IC analysis system using such an electron beam probe system.
According to a first aspect of the present invention, the IC tester comprises a test pattern generator which generates test patterns while updating them one after another, a stop pattern setting part which sets a test pattern for stopping the updating of the test patterns, and a main control part which controls the test pattern generator to stop its test pattern updating operation but keep the generation of the test pattern set in the stop pattern setting part and outputs a pattern stop signal representing the suspension of the test pattern updating operation. When supplied with a write completion signal representing the completion of acquiring image data from the electron beam probe system, the main control part causes the test pattern generator to resume the pattern updating operation. The electron beam probe system comprises an image data processor which starts to write thereinto image data when receiving the pattern stop signal from the main control part, and a write completion signal generator for generating the write completion signal which indicates that the image data processor has written thereinto required image data.
According to a second aspect of the present invention, the IC tester comprises a test pattern generator which generates test patterns while updating them one after another, a stop pattern setting part which sets at least first and second test patterns for temporarily stopping the updating of the test patterns, and a main control part which controls the test pattern generator to stop its test pattern updating operation but keep the generation of one of the test patterns set in the stop pattern setting part and outputs a pattern stop signal representing the suspension of the test pattern updating operation. The electron beam probe system comprises an image data processor which starts to write thereinto image data when receiving the pattern stop signal from the main control part, and a mode switching part which is switchable between a first operation mode in which the first test pattern is generated, the test pattern updating operation is suspended, the acquisition of image data is inhibited in response to the pattern stop signal and the IC under test is irradiated with a scanning electron beam, and a second operation mode in which the second test pattern is generated, the test pattern updating operation is suspended and image data is acquired while at the same time the IC under test is irradiated with a scanning electron beam.
According to a third aspect of the present invention, the IC tester comprises a test pattern generator which applies test patterns to the device under test while updating them one after another, a stop pattern setting part which sets at least two test patterns for suspending the pattern updating operation of the test pattern generator, and a main control part which controls the test pattern generator to stop its updating operation whenever it generates each test pattern set in the stop pattern setting part, and outputs a pattern stop signal upon each suspension of the test pattern updating operation. The electron beam probe system comprises at least two image data processors which write thereinto image data in response to the pattern stop signals that the main control part outputs upon generation of the two stop patterns, a calculating part which calculates the difference between the image data written acquired into the two image data processors, and a monitor for displaying image data corresponding to the difference calculated by the calculating part.
With the construction according to the first aspect of the invention, when the image data processor has acquired or written thereinto required image data, the write completion signal generator generates the write completion signal indicating the completion of acquisition of the image data. The test pattern generator responds to the write completion signal to start its test pattern updating operation. Hence, there is no need of setting a test pattern stop or suspension time in the IC tester, and the acquisition of image data and the start and stop of the test pattern can automatically be repeated. Moreover, by setting the test pattern generation in a repeated generation mode, it is possible to repeatedly obtain image data from the device under test supplied with the same test pattern.
FIGS. 9A-I are waveform diagrams for explaining another example of operation of the FIG. 7 embodiment;
FIGS. 13A-E are waveform diagrams for explaining the formation of the potential contrast images shown in FIG. 12;
FIGS. 15A-H are waveform diagrams for explaining an example of operation of the FIG. 14 embodiment;
FIG. 18 is a table showing the relationship of differential contrast images of an non-defective IC and a defective IC for each logic combination of the patterns r and n;
FIG. 3 illustrates, in block form, an embodiment of the IC analysis system employing the electron beam probe system 300 according to the first aspect of the present invention. The parts corresponding to those in FIG. 1 are identified by the same reference numerals. The structural feature according to the first aspect of the invention is the provision of a write completion signal generator part 308 in the electron beam probe system 300. The write completion signal generating part 308 generates a write completion signal WCMP when detecting that the image data processor 305 having an internal memory has completed the acquisition of image data. The write completion signal WCMP is input into the main control part 204 of the IC tester 200.
Upon receiving the write completion signal WCMP, the main control part 204 provides to the test pattern generator 210 a command for cancelling the pause state of the test pattern updating operation thereof. Thus, the test pattern generator 210 is released from the stopped state of the test pattern updating operation and resumes the test pattern updating operation. That is, according to the first aspect of the present invention, assuming that a stop pattern n, for example, has been set in the stop pattern setting part 203 (n is a positive integer and "pattern n" denotes that n-th pattern in the test pattern generating sequence from the test pattern generator 210. In this embodiment, the setting of the stop pattern n means that when the n-th test pattern having the same pattern as that of the stop pattern n is generated from the test pattern generator 210, the n-th test pattern is not updated in the test pattern generator 210), the main control part 204 controls to stop the test pattern generator 210 from performing the updating operation of the n-th test pattern each time the n-th test pattern is generated from the test pattern generator 210 and to hold the test pattern generator 210 in the state that the n-th test pattern is continuously generated therefrom. Generally, since a series of test patterns are stored at respective addresses in the test pattern generator 210, a stop command which specifies only an address of the test pattern generator 210 may be set in the stop pattern part 203 instead of a stop pattern. In such case, each time the test pattern stored at the address specified by the stop command is generated, the main control part 204 controls to stop the test pattern generator 210 from performing the updating operation of this test pattern. FIGS. 4A-B show examples of its operation. FIG. 4A, FIG. 4B shows a start signal and Row B a test pattern signal which is composed of a series of test patterns 1, 2, . . . , n, . . . , LST where LST denotes the last, and "pattern LST" represents the test pattern generated last in the test pattern generating sequence. When the n-th pattern of the test pattern signal is generated from the test pattern generator 210, the main control part 204 causes the test pattern generator 210 to stop its pattern updating operation and holds the test pattern generator 210 in the state that the pattern n is continually generated therefrom, and at the same time the main control part 204 outputs the stop signal STP representing that the test pattern updating operation has stopped. The stop signal STP is applied to the image data processor 305 to cause it to start the acquisition of image data. FIG. 4D shows an image data acquisition period during which the n-th test pattern is continuously applied to the IC under test DUT.
The write completion signal generating part 308 can identify the completion of the acquisition of image data, for example, by detecting a vertical blanking signal representing that the sweep of the electron beam EB on the surface of the IC under test DUT has completed one frame. If the write completion signal generator 308 is adapted to generate the write completion signal WCMP when it detects one or a desired number of vertical blanking signals representing the above-mentioned condition, respectively, it is possible to generate the write completion signal WCMP when the electron beam EB has scanned one or desired number of frames. FIG. 4E shows the write completion signal WCMP.
When the write completion signal WCMP is applied to the main control part 204, the main control part 204 causes the test pattern signal generator 210 to be released from the pause state of the test pattern updating operation so that the test pattern generator 210 resumes generation and updating operation of test patterns following the test pattern n, namely, from the test pattern last pattern LST as shown in FIG. 4B. In the case where the generation of a series of test patterns that is, the test pattern signal is set to once, the test pattern generator 210 stops to generate the test pattern signal after generating the last pattern LST.
In the case where the test pattern generator 210 is set to repeat the generation of a test pattern signal composed of a series of test patterns, it automatically stops to effect its test pattern updating operation upon each generation of the test pattern n, restarts after the completion of the acquisition of image data and returns to the first test pattern namely, "the test pattern 1" after the generation of the last pattern LST, thereafter repeating the generation of the test pattern signal under control of the main control part 204, as shown in FIGS. 5A-F. Incidentally, it is also possible to return the operation of the test pattern generator 210 to the generation of the first test pattern after acquisition of image data as shown in FIGS. 6A-F. At any rate, the IC analysis system according to the present invention can acquire, a plurality of times, image data on the surface of the IC under test DUT to which the specified test pattern n is continuously applied. The pattern generator 210 can be stopped by the stop switch 202.
As mentioned above, according to the first aspect of the present invention, start of a pattern generating operation and stop of a pattern updating operation of the test pattern generator 210 in the side of the IC tester 200 are interlocked with the image data acquiring operation in the side of the electron beam probe system 300 only by setting in the stop pattern setting part 203 a test pattern which is continuously applied to the surface of the IC under test DUT the potential contrast image of which at that time is desired to observe, or an address in the test pattern generator 210 at which the above test pattern is stored; hence, even if the conditions for acquiring the image data are changed, the setting of the IC tester 200 need not be changed.
FIG. 7 illustrates, in block from, embodiments of the electron beam probe system and the IC analysis system using the same according to the second aspect of the present invention. In the FIG. 7 embodiment, the stop pattern setting part 203 is adapted to permit setting therein of first and second test patterns r and n and a mode changeover part 309 is provided in the electron beam probe system 300. Upon each generation of either of the first and second test patterns r and n by the pattern generator 210, the main control part 204 controls the pattern generator 210 to temporarily stop its pattern updating operation and, at the same time, generates stop signals STP1 and STP2, respectively. As is the case with the FIG. 3 embodiment, the pattern generator 210 resumes the pattern updating operation when the write completion signal WCMP (or a sweeping irradiation completion signal) is output from the write completion signal generator 308. Alternatively, it is possible to omit the write completion signal generating part 308 and resume the pattern updating after a predetermined period of time so long that it can be judged that the sweeping irradiation by the electron beam in the electron beam probe system has been completed after the generation of the stop signals STP1 and STP2 by the main control part 204.
FIGS. 8A-H and 9A-I show examples of the execution of the first and second operation modes in different pattern generating sequences. FIGS. 8A-H show the case of generating the test pattern continuously from the leading address to the last address LST and executing the first and second operation modes for the patterns r and n that are generated in that while. FIGS. 9A-I show the case of returning the operation to the leading address upon each execution of the first and second operation modes. In either case, the write completion signal generating part 308 is provided. By acquiring the image data in the second operation mode after the first operation mode, it is possible to eliminate the influence of decreased potential contrast in the surface (the insulating film) of the device under test DUT.
FIGS. 10 through 13A-E show how a clear potential contrast image is formed. FIG. 10 shows potentials that are applied to the conductors L1, L2, L3 and L4 when the first test pattern r is applied. The FIG. 10 example shows the state of applying L-logic to the conductor L1, H-logic to the conductor L2, L-logic to the conductor L3 and H-logic to the conductor L4. FIG. 11 shows potentials that are applied to the conductors L1 through L4 when the second test pattern n is applied. The FIG. 11 example shows the state of applying L-logic to the conductors L1 and L2 and H-logic to the conductors L3 and L4.
In the state of FIG. 10 the area containing the conductors L1 through L4 is subjected to sweeping irradiation with the electron beam EB but no image data is acquired, after which the test pattern is updated and when the second pattern n is reached, the pattern updating operation is temporarily stopped. By sweeping and irradiating the above-said area with the electron beam EB in the state of FIG. 11 wherein the second test pattern n is being applied and by acquiring the image data at that time, it is possible to obtain such potential contrast images as shown in FIG. 12. As shown in FIG. 12, only those conductors of potentials which are reversed in logic by the application of the first test pattern r and the second test pattern n appear as potential contrast images. In this example, the conductors L2 and L3 appear as potential contrast images, whereas the conductors L1 and L4 are each supplied with the same potential, and hence are not displayed as potential contrast images.
The reason for it will be given using FIGS. 13A-E. Incidentally, assume that the sweeping irradiation with the electron beam EB has already been repeated for the pair of patterns r and n. Since the conductors L1 and L4 are supplied with L-logic and H-logic, respectively, in both cases of the patterns r and n, their surface potentials remain Vs in either case as shown in FIG. 13B. When the first test pattern r is applied, the conductors L2 and L3 are supplied with H-logic and L-logic potentials which are reverse in logic from those when the previous pattern n was applied, hence the potentials of the insulating film covering these conductors L2 and L3 are biased positively and negatively in excess of the equilibrium potential Vs (equivalent to the potential of the surrounding insulator) indicated by the broken lines.
When sweeping and irradiating the device under test DUT with the electron beam EB in this state, the potentials of those portions of the insulating film overlying the conductors L2 and L3 gradually vary toward the equilibrium potential Vs. On the other hand, the potentials of those portions of the insulating film overlying the conductors L1 and L4 remain at Vs. During the irradiation with the electron beam EB the potential of the insulating film undergoes a change, but when the irradiation is stopped, the potential change does not occur. Although several test patterns are applied in the interval between the first and second test patterns r and n, potentials Va, Vb, Vc and Vd reached as the result of irradiation with the electron beam EB during the application of the pattern r are held unchanged to a time immediately prior to the application of the pattern n.
When the irradiation with the electron beam EB is resumed in the state in which the second test pattern n is generated and applied to the conductors L1 through L4, the potentials of those portions supplied with potentials reverse in logic from those supplied previously (the conductors L2 and L3) are shifted to potentials Ve and Vf far apart from the equilibrium potential Vs and start to vary therefrom, but the potentials of those portions supplied with the potentials of the same logic as before remain at the equilibrium potential Vs. Hence, in the state wherein the second test pattern n is being applied, the portions of the conductors L1 and L4 are displayed as potential contrast images in the same gray color as the surrounding areas, whereas the portions of the conductors L2 and L3 are displayed as bright and dark potential contrast images, respectively, as depicted in FIG. 12.
As described above, according to the second aspect of the present invention, by applying the second test pattern n after the first test pattern r, it is possible to obtain, at all times, a potential contrast image on the conductor which, at the time of application of the second test pattern n, was supplied with a voltage reverse in logic from that supplied at the time of application of the first test pattern r. Hence, by acquiring this potential contrast image as image data upon each generation of the second test pattern n, image data can be accumulated. Moreover, a clear potential contract image of improved SN ratio can be obtained by averaging image data acquired a plurality of times for the test pattern n through repetition of such a procedure. By changing the first test pattern r to new ones in a sequential order, the conductors whose logic is reversed at the time of applying the test pattern n can be changed one after another. This permits observation of-the conditions of almost all the conductors.
When detecting that either the image data processing part 305A or 305B has completed the acquisition of image data, the write completion signal generating part 308 generates the write completion signal WCMP, which is applied to the main control part 204 provided in the IC tester 200. The main control part 204 responds to the write completion signal WCMP to supply the test pattern generator 210 with a command for resuming the pattern updating operation. Thus, the test pattern generator 210 is released from the stopped stat and resumes the pattern updating operation.
According to the third aspect of the invention, assuming that the stop patterns r and n, for example, are set in the stop pattern setting part 203, whenever the stop pattern r or n is generated, the main control part 204 controls the test pattern generator 210 to stop it from the test pattern updating operation, holding it in the state of outputting the test pattern r or n. FIGS. 15A-H shows this. In FIG. 15A shows a start signal and Row B a test pattern signal. When the pattern of the test pattern signal reaches r or n, the main control part 204 causes the test pattern generator 210 to stop the pattern updating operation and holding it in the state of outputting the pattern r or n. At the same time, the main control part 204 yields the stop signal STP1 or STP2, which is applied to the image data processing part 305, causing it to start the acquisition of image data. FIG. 15F shows the image data acquisition period.
By the application of the write completion signal WCMP to the main control part 204, the test pattern generator 210 is released from the stopped state and updates the test pattern to r+1, r+2, . . . , or n+1, n+2, . . . and outputs the last pattern LST as shown in FIG. 15B. In the case where the generation of a series of test patterns (1 through LST) is set to once, the test pattern generator 210 stops in the state of outputting the last pattern LST.
As is the case with FIGS. 10 and 11, let it be assumed that the potentials L, H, L and H are applied to the wiring conductors L1, L2, L3 and L4 in the device under test DUT when the test pattern r is applied and that the potentials L, L, H and H are applied to the conductors L1, L2, L3 and L4 when the test pattern n is applied.
FIGS. 17A and 17B show potential contrast images obtained during the application of the test patterns r and n after the repetition of the electron beam irradiation therefor. These potential contrast images are available during the application of the patterns r and n shown in FIGS. 13A-E, and hence the images in FIG. 17B are the same as those shown in FIG. 12. Of the potential contrast images depicted in FIGS. 17A and 17B, the potential contrast images of the conductors L1 and L4 both disappear and only the potential contrast images of the conductors L2 and L3 are left remaining. The reason for this is that the conductors L1 and L4 are each supplied with the same potential when the test pattern r is applied and when the test pattern n is applied, as mentioned previously. On the other hand, since the logic of the potential that is applied to the insulating film overlying the conductors L2 and L3 is reversed each time the test patterns r and n are applied, potential contrast images reverse in logic are formed upon each application of the test patterns r and n.
Thus, according to the third aspect of the present invention, the potential contrast of each of the conductors L2 and L3 is emphasized as shown in FIG. 17C, by obtaining with the calculating part 310 the difference between the pieces of image data taken into the image data processing parts 305A and 305B for the patterns r and n. By displaying the difference image data on the monitor 306, the quality of the display image is increased and its resolution is also enhanced.
In Table I of FIG. 18 there are shown the presence or absence of the difference between difference contrast images of a non-defective IC and a defective IC and the presence or absence of a fault isolation problem in connection with all possible combinations of logical patterns of corresponding wiring conductors of the both ICs. In items No. 3, No. 8, No. 9 and No. 14, the logical signals to the corresponding wiring conductors of the both ICs are the same, and hence the difference contrast images naturally become the same. A fault isolation problem is presented in items No. 2 and No. 11. That is, although the test patterns for the corresponding wiring conductors of the non-defective and defective ICs have different logical levels, the difference contrast images do not differ. A description will be given of a solution to this problem according to the present invention.
With reference to FIGS. 19A-I, the method according to the present invention will be described as being applied to the embodiment of FIG. 14. According to this method, the power supply to the device under test DUT is held OFF, the state of no test pattern being applied is regarded as if the first test pattern r of all L-level is applied, the surface of the device under test DUT is swept and irradiated with the electron beam EB in the power OFF period and then image data is taken into the image data processing part 305A. The main control part 204 effects ON/OFF control of the power supply to the device under test DUT and outputs the stop signal STP1 upon initiation of the power OFF period. During the power OFF period all wiring conductors of the device under test DUT are at the L-logic level. When the column control part 307 performs the sweeping irradiation of the device under test DUT with the electron beam in the power OFF period and the image data processing part 305A completes the data acquisition, the write completion signal generating part 308 generates the write completion signal WCMP. The main control part 204 responds to the signal WCMP to turn ON the power supply to the device under test DUT and starts the test pattern generator 210. When the test pattern n is generated, the power supply is in the ON state and the pattern n is applied as described previously with reference to FIG. 14 and in that the state the image data of the potential contrast images of the device under test DUT is taken into the image data processing part 508B. The difference between the pieces of image data read out of these image data processing part 508A and 508B is calculated by the calculating part 310 and provided as difference contrast image data to the monitor 306. In Table II of FIG. 20 there are shown respective difference contrast images of the non-defective and defective ICs obtained by this method, the presence or absence of a difference between the contrast images and the fault isolation capability.
U.S. Classification 324/754.22, 850/10, 850/9, 324/754.19, 324/762.02
International Classification G01Q60/30, G01R31/307, G01Q30/02, G01Q30/04
European Classification B82Y15/00, G01R31/307
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:UEDA, KOSHI;GOISHI, AKIRA;KURIBARA, MASAYUKI;REEL/FRAME:006855/0814