JP3248504B2 - Inspection method for semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for inspecting a semiconductor device, and more particularly to a method for inspecting a semiconductor device with less defect information.

[0002]

2. Description of the Related Art In a commercially available image inspection type defect inspection apparatus using an SEM (scanning electron microscope) image, a number of irregular irregularities (about 30 nm) that can be resolved by an SEM are used. In the case of inspecting a pattern having a period of about 100 nm, an irregular structure is superimposed on an intentionally created periodic structure. For this reason, even if an image shifted in each cycle is obtained, a random fine structure existing in a periodically formed structure is recognized as a defect.
In such a case, an abnormal load is imposed on the image processing system, so that the time required for the defect inspection becomes long, and the obtained defect information becomes enormous. Further, even if the storage capacity is increased, there is no means for determining whether the detected defect is a defect that does not affect device characteristics or a defect that actually affects device characteristics such as dust and that is to be detected.

[0003]

As described above, the conventional method for inspecting a semiconductor device has a problem that the time required for defect inspection is long and the amount of obtained defect information is enormous.

Another problem is that there is no means for determining whether a defect affects device characteristics or not.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for inspecting a semiconductor device in which the time required for defect inspection is shortened and the obtained defect information is reduced in order to solve the above-mentioned problem.

Another object of the present invention is to provide a method of inspecting a semiconductor device, which can determine whether or not it affects device characteristics.

[0007]

In order to achieve the above object, a method for inspecting a semiconductor device according to the present invention uses a scanning electron microscope (SEM) image to detect a defect in a fine structure having irregularities in a periodic structure. In a method of inspecting a semiconductor device by an image comparison method for inspecting a sample, when an inspection is performed on a sample using a secondary electron image by a scanning electron microscope, an offset is applied to an objective lens current value, and a fine structure having irregularities is applied. An inspection method of a semiconductor device for inspecting by deteriorating image quality ,
If the sample has a shape caused by a grain boundary in one direction,
When using an astigmatism correction lens, resolution in only one direction
To prevent microstructure detection
Characterized in that that.

A step of converging an electron beam emitted from the electron gun by a condenser lens, a step of restricting a scattering angle of the electron beam by a diaphragm, passing the electron beam through a deflection coil, and scanning by a scanning deflector; Focusing the focused electrons on the sample by the objective lens, detecting and amplifying secondary electrons generated by the electrons radiated on the sample by the secondary electron detector, and scanning provided to the scanning deflector. Capturing a signal from the secondary electron detector into a computer in synchronization with the signal to obtain a scanned image.

Further, it is preferable that the resolution be degraded so that an irregular fine structure of 1/10 or less of the period of the periodic structure does not affect the inspection.

Further, in a state where a difference between the current value of the objective lens and the current value of the objective lens at which a positive focus can be obtained, the stage on which the sample is placed is shifted for every pattern repetition cycle. It is preferable to take in a comparative test.

[0011]

Further, when the sample has a fine structure only in a specific region, a region to be offset at the time of electron beam scanning is newly designated, and only the region where the fine structure exists is registered in advance, and the intended region is registered. It is preferable to apply an offset only to.

[0013]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic diagram showing a configuration of a scanning electron microscope in an embodiment of a semiconductor device inspection method according to the present invention. In this method, the electron beam 2 emitted from the electron gun 1 is
After being converged by the condenser lens 3, the divergence angle is restricted by the diaphragm 4, the light passes through the polarizing coil 5, and passes through the scanning deflector 6.
Is scanned by The scanned electrons are supplied to the objective lens 7
Converges on the sample 9. Secondary electrons generated by the electrons irradiated on the sample 9 are detected and amplified by the secondary electron detector 9. At this time, a signal from the secondary electron detector 8 is taken into the computer 11 in synchronization with a scanning signal given to the scanning deflector 6 to obtain a scanned image.

FIG. 2 is a block diagram showing a scanning image processing system according to the present invention. Generally, a pattern of a semiconductor device has a periodic structure. First, a scanning electron image by the scanning electron microscope 26 is recorded in the image storage unit 21. Next, the stage 10 is moved by one cycle, and a scanning electronic image of the next cycle is obtained and recorded in the image storage unit 22. These images are processed by the control processing unit 23 to obtain a difference image between them, and the difference image storage unit 24
To accumulate. The position of the obtained defect on the wafer can be calculated from the position of the stage and the SEM image.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS.

FIG. 3 is a flow chart for explaining a semiconductor device inspection method according to the present invention. FIG. 4 is a schematic view showing an example of an image having a fine structure to which the present invention is applied. FIG. 3 is a schematic diagram illustrating an example of an image shifted from a normal focus. Generally, when performing a defect inspection using two or more images, a difference image between the two images is obtained,
A flow is used in which a portion corresponding to a pixel having a value equal to or greater than a certain value among the pixels in the difference image is recognized as a defect. Before the series of operations shown here, the optical axis of the SEM is adjusted or adjusted so as to obtain a positive focus image. First, a level (threshold) T recognized as a defect and a change rate (step) S of the objective lens are given. This is set as a threshold T and a step S input. These values are obtained empirically and may be optimized if there is a problem later (step A1). Next, images of adjacent cycles are obtained by the image storage unit 21 and the image storage unit 22. As the SEM image at this time, an image artificially confirmed that no abnormal portion to be detected during the inspection is included is used. As an example of an image having a fine structure as the object of the present invention, as shown in FIG. 4, there is an image having a structure of 0.5 μm and a random structure of about one tenth thereof. Next, the difference image is calculated by the control processing unit 23 (steps A2 and A3). The value of the pixel in the difference image obtained here is compared with the threshold T already set, and the number of pixels having a value equal to or larger than the threshold T is set to n (step A4). However, since the image used in this process is an image in which it is artificially confirmed that no abnormality is included, n must be zero in the first place. Then, next, n
Is determined to be 0 (step A5). Then n
Is not 0, it is artificially determined that there is no abnormality, but the apparatus recognizes it as a defect. This is because a difference in the fine structure that does not need to be detected is detected even though it is not abnormal because the SEM image is used. Then, the objective lens current value is changed by S so that n becomes 0 (step A6). An image is acquired using the changed objective lens current value, and steps A2 to A6 are performed until n = 0. The image when n = 0 is shifted from the focus position as shown in FIG. The difference between the objective lens current value at this time and the objective lens current value at which a positive focus is obtained will be referred to as an offset current value. At the time of the image comparison inspection, the stage 10 is shifted by the offset current value obtained by this series of operations from the current value at which the correct focus can be obtained by shifting the stage 10 for each repetition period of the pattern, and the image is taken in and the comparative inspection is performed. Image comparison inspection without recognizing the image as a defect. Further, for abnormalities appearing in portions other than the periodic pattern (41 in FIG. 4), the deterioration of the detection sensitivity can be suppressed by adjusting the threshold value T.

In the above-described embodiment, the current value of the objective lens is changed in only one direction. However, it is also possible to change the current value of the objective lens alternately.

Next, another embodiment of the present invention will be described with reference to FIG.

FIG. 6 is a schematic diagram showing an Al wiring pattern in another embodiment of the method for inspecting a semiconductor device according to the present invention. In the present embodiment, the fine structure cannot be detected by lowering the resolution only in one direction using an astigmatism correction lens. This method uses Al as shown in FIG.
This is particularly effective when the wiring pattern has a shape due to a crystal grain boundary in one direction such as a wiring pattern. The same effect can be obtained by changing the condenser lens current value to increase the beam diameter.In this case, the axis of the electron optical system may be shifted.
It is necessary to add a function of storing the optimum value of each lens for each condenser lens current value in the control system and reproducing it.

Next, another embodiment of the semiconductor device inspection method of the present invention will be described. As shown in FIG. 4, when a fine structure is provided only in a specific region, it is necessary to add a function for newly designating a region to be offset during electron beam scanning. There is also a method of registering only in advance and applying an offset only to an intended area.

[0022]

As described above, the present invention suffices in the same data processing process as in the normal inspection except that the current value of the objective lens during the inspection is offset. Therefore, if the offset is obtained before the inspection, there is an effect that no load is applied to the data processing system for data processing such as averaging between pixels during the inspection.

In addition, the resolution is optimized by offsetting the current value at which the focus can be obtained. Therefore, it is possible to drastically reduce the frequency of recognizing as a defect a difference in shape that cannot be regarded as a structural defect due to inspection at an unnecessary resolution. As a result, there is an effect that only the shape abnormality to be detected can be detected.

Furthermore, the above-described effect eliminates unnecessary detection defects, so that the entire time can be reduced by the time required to process these data. Therefore, there is an effect that the inspection speed can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a scanning electron microscope according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a scanning image processing system according to the embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the embodiment of the present invention.

FIG. 4 is a schematic view showing an SEM image photographed with a right focus.

FIG. 5 is a schematic diagram showing an SEM image taken with an offset.

FIG. 6 is a schematic diagram showing an Al wiring pattern.

[Explanation of symbols]

 1 electron gun 2 electron beam 3 condenser lens 4 stop 5 deflection coil 6 scanning deflector 7 objective lens 82 secondary electron detector 9 sample 10 stage 11 computer 21 image storage unit 22 image storage unit 23 control processing unit 24 difference image storage unit 25 Electron optical system adjustment unit 26 scanning electron microscope

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/66 H01J 37/22 502

Claims (5)

(57) [Claims] An inspection method of a semiconductor device by an image comparison method for inspecting a defect of a fine structure having irregularity in a periodic structure using an image of a scanning electron microscope, wherein a secondary electron image by a scanning electron microscope is used. when inspecting the sample Te, means offsets the objective lens current value, the method of inspecting a semiconductor device inspecting and degrade the image quality of the microstructure with irregularities, crystal the sample in one direction Fields with shapes due to grain boundaries
When using an astigmatism correction lens, resolution in only one direction
To prevent microstructure detection
A method of inspecting a semiconductor device, characterized in that that. 2. A step of converging an electron beam emitted from an electron gun by a condenser lens, a step of restricting a scattering angle of the electron beam by a stop, passing the electron beam through a deflection coil, and scanning by a scanning deflector; Converging the scanned electrons on the sample by the objective lens; detecting and amplifying secondary electrons generated by the electrons irradiated on the sample by a secondary electron detector; characterized in that it comprises the steps of: obtaining a scanning image by scanning signals applied to the vessel and by synchronizing capturing signal from the secondary electron detector to the computer, the semiconductor device according to claim 1 Inspection methods. 3. The semiconductor device according to claim 1, wherein the resolution is degraded so that an irregular fine structure of 1/10 or less of the period of the periodic structure does not affect the inspection. Inspection method. 4. A stage on which the sample is mounted is shifted for each pattern repetition period in a state where a difference is provided between the current value of the objective lens and the current value of the objective lens for obtaining a positive focus. The method for inspecting a semiconductor device according to any one of claims 1 to 3, wherein an image is taken and compared and inspected. If wherein said sample has only the microstructure particular region, a region subjected to offset when the electron beam scans the newly specified, it may be registered only in advance region present in the microstructure, intended The method for inspecting a semiconductor device according to claim 1 , wherein an offset is applied only to a region.