JPH0820237B2 - Image measurement and inspection device for electron microscope - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for measuring and inspecting the shape of a fine pattern, and particularly to an apparatus suitable for automatic measurement and inspection of a semiconductor wafer pattern that is remarkably miniaturized. .

[Conventional technology]

Conventionally, pattern defect inspection is performed by comparing a non-defective pattern with a pattern to be inspected, but in the case of defect inspection using an electron microscope image, the DC component of the sample surface changes greatly due to a charge jump. , For example, as discussed in the Japan Society for the Promotion of Science, 132nd Committee 93rd Workshop Material, pages 18 to 23, the image is immediately spatially differentiated to reduce the influence of the drift of the DC component,
It was necessary to devise such as comparing images.

[Problems to be solved by the invention]

If the image is spatially differentiated, it is possible to reduce the influence of direct current fluctuations in which the image becomes brighter or darker as a whole. However, when spatial differentiation is performed, in general, fine random noise included in an image is emphasized and is likely to be erroneously recognized as a defect, and large defects in which light and shade vary spatially are easily overlooked. It was hot.

An object of the present invention is not to use an image processing technique for spatially differentiating input image data, but in principle to provide a method capable of ignoring the influence of electron beam charge-up and various density level drifts. However, it is to realize a highly reliable and highly sensitive measuring / inspecting apparatus for electron beam images.

[Means for solving problems]

The above object is achieved by precisely controlling the irradiation time of the electron beam onto the sample surface at the time of image input.

In the automatic inspection of pattern defects, a plurality of similar patterns on the sample are successively input while moving the sample table to perform inspection. Therefore, when moving to a new pattern area, the electron beam is set to the non-irradiated state at 1 and the image input is controlled to be executed after a fixed time each time the irradiation is started. By doing so, it can be expected that the state of charge adjustment on the sample will be exactly the same, and image input in almost the same situation can be performed every time. At this time, in general, the state of charge-up on the sample depends on the surface material and the accelerating voltage of the electron beam, and therefore a means for determining the constant time in the previous period is also necessary.

[Action]

By doing so, the images at the respective inspection positions on the wafer can be input under exactly the same conditions. Therefore, even in the inspection apparatus which compares the same kind of patterns and identifies the defective portion based on the difference between them, the images are almost the same except the defective portion, so that only the defective portion can be easily extracted from the difference signal of the images. As a result, the non-defective part is less likely to be mistaken for a defect, and as a result, an appearance inspection device having high detection sensitivity can be realized.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First
The figure is a block diagram of a semiconductor wafer pattern appearance inspection apparatus according to the present invention. The electron beam 1 of the scanning electron microscope is deflected by the current flowing in the deflection coil 3, and scans the upper surface of the semiconductor wafer 5 as a sample. At that time, the secondary electron signal is detected by the detector 4, and the video signal S1 is sent to the video processing circuit 6.
Is entered as. Reference numeral 2 denotes a beam blanking deflection coil, which has a function of causing a current to flow by a signal S2 from the signal generation circuit 7 and largely deflecting the direction of the electron beam. Therefore, ON / O of electron beam irradiation on the wafer 5
The FF can be controlled by a signal. The image processing circuit 6 is
The signal S1 from the electron microscope is input, and the pattern signal portion therein is extracted by comparing the image signal with a previously stored reference image signal. The result is transferred to the control computer 8 by the signal S5 for each video input,
In the control computer 8, the defect data of the inspected wafer 5 is totaled. The signal generation circuit 7 is a time parameter signal.
Receives S6 and video input request signal S7 from the control computer 8,
This is a circuit for generating a deflection scanning signal S4 for the electron beam, an electron beam blocking signal S2, and a video input activation request signal S3. At this time, if the time from the signal generation of S2 to the video input start of S3 is kept at a constant time T,
It is possible to always input electron microscope images under the same imaging conditions, and stable pattern defect inspection becomes possible.

FIG. 2A shows a more detailed embodiment of the signal generating circuit 7. The synchronization signal generation circuit 20 generates a deflection signal S4 for raster-scanning a two-dimensional area on the wafer regardless of whether or not the electron beam is irradiated. At the same time, the vertical sync pulse VD and clock signal CLOC similar to the sync signal of the television
Is generating K. At this time, when the input request signal S7 is input and the flip-flop 9 is set, the AND gate 1
When 0 is open, the flip-flop 11 is set at the falling edge of the first VD pulse. Flip Flop
When 11 is set, AND gates 12 and 16 are open. Therefore, the pulse of the clock signal CLOCK before that is counted by the counter 17, and at the same time, the VD pulse is counted by the counter 13. At this time, if the values corresponding to the time parameters have been set in the registers 14 and 18 by the S6 signal in advance, the values of the counters 13 and 17 are set in the register 1
When the contents of 4, 18 match, the signals S2, S3 are output as the output signals of the match detection circuits 15, 19. FIG. 2 (b) shows the timing of these signals with the horizontal axis as the time axis. That is, when the overdrive request pulse is input as the S7 signal, the S2 signal is output after a fixed time t ₁ from the falling point of the first VD pulse as a starting point. Separately, the S3 signal is output at the falling edge of the VD pulse after a fixed time t ₂ . At this time, by properly setting t ₁ and t ₂ , the time T from the start of electron beam irradiation to the start of image input
(= T ₁ −t ₂ ) can be kept exactly constant, and the video input can be started from the head of the raster scan video plane by setting the start time of the video input as the falling time of the VD pulse. When the video input is completed, the flip-flops 9, 11 and the counters 13, 1 are connected by a signal line (not shown).
7. All the coincidence detection circuits 15 and 19 are reset so that the next video input request signal is generated.

FIG. 3 is a more detailed embodiment of the video processing circuit 6. In the figure, 21 is a memory circuit for storing a video signal, 22
Is a difference circuit, 23 is a binarization circuit, 24 is a defect position detection circuit,
Reference numeral 25 denotes a result storage circuit, respectively. In the defect inspection of the pattern, the image of the reference pattern is input in advance and stored in the storage circuit 21, and then the reference image signal stored in the storage circuit 21 is input while inputting the image signal S1 of the pattern to be inspected. The difference circuit 22
To detect. The detected signal is a "defect image signal" in which a portion having a difference, that is, a portion which is considered to be a defect is emphasized. The defective video signal is binarized by the binarization circuit 23, and further, it is "1" by the defect position detection circuit 24.
Is detected, that is, the coordinates of the defective portion are detected. The detection of the coordinates of the "1" portion can be easily realized by holding the position data of the scanning signal at the time when the signal is "1" by a circuit (not shown). The detection result is successively written in the result storage circuit 25 every time a defect occurs. The written result is read out by an external control computer after all the processing of the input video signal is completed, and is aggregated as pattern defect data.

As described above, the present invention can be completely implemented by producing such a circuit.

In this embodiment, the input image is processed as it is. However, since a large random noise is usually superimposed on the image signal of the electron microscope, the averaging of a plurality of subsequent input images is taken. The processing can reduce the influence of noise and perform stable measurement inspection. It is readily possible in the prior art to make such modifications of the embodiment described above.

[Advantages of the Invention] The output image signal of an electron microscope has a property that its DC component is rapidly changed after being irradiated with an electron beam, and gradually approaches a stable state. The stabilization time constant varies greatly depending on the surface of the sample and the state of the charger inside the mirror body.In particular, when directly inspecting a semiconductor wafer pattern during manufacturing, the surface is made of a non-conductive material. Since there are many cases, the influence of the charge shock is large, and the time constant is generally much longer than the time allowed in terms of destruction of the semiconductor element due to electron beam irradiation.

According to the present invention, it is possible to avoid sudden image changes immediately after electron beam irradiation and always input images in the same change state, so that even if an unstable electron microscope image is used, it is always reproduced. It is possible to realize a good image input, for example, a stable pattern inspection device based on the pattern comparison principle.

Further, since the irradiation time of the electron beam can be shortened, it is possible to prevent the destruction of the semiconductor element which is the sample and increase the overall inspection speed, thereby making it a practical inspection apparatus.

As a result, it is possible to realize an automatic inspection apparatus for an extremely fine pattern that is difficult to inspect optically, and for example, it is extremely effective in evaluating a semiconductor pattern manufacturing process that is becoming finer.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an embodiment of the present invention. FIG. 2 is a more detailed embodiment of the signal generating circuit 20 which is a constituent element of FIG. 1, and FIG. 3 is a more detailed embodiment of the video processing circuit 6 which is another constituent element. 1 ... Electron beam, 2 ... Deflection coil, 4 ... Detector, 6 ...
… Video processing circuit, 7… Signal generation circuit, 8… Control computer, 13,17… Counter, 14,18… Register, 15,19…
... Match detection circuit, S7 ... video input request signal, S2 ... electron beam cutoff signal, S3 ... video input activation signal, VD ... vertical sync pulse, S4 ... deflection scanning signal.

Front page continuation (72) Inventor Yozo Ouchi 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) Reference JP 62-31931 (JP, A) JP 62-56807 (JP, A)

Claims (3)

[Claims] 1. In a measuring / inspecting apparatus for processing a video signal of a scanning electron microscope, first means for controlling irradiation / non-irradiation of an electron beam on a sample, surface material of the sample, and electron beam acceleration. Second means for selecting a fixed time determined by the voltage, and an instruction to input a video signal after a fixed time has passed after starting irradiation of the sample with an electron beam, and when the input is completed, the electron beam is transferred onto the sample. A third means for instructing to terminate the irradiation of the image, and at least holding a reference image or a threshold value,
And a fourth means for automatically measuring appearance defects, dimensions, etc. included in the input video signal according to the instruction of the means. Measuring / inspecting equipment. 2. The third means uses, as a reference, a reference pulse synchronized with a vertical synchronizing signal of a scanning signal of an electron microscope, and gives an instruction to start electron beam irradiation after a fixed time from one reference pulse, and further the reference. The image measuring / inspecting apparatus for an electron microscope according to claim 1, further comprising means for instructing to start inputting an image when a certain number of pulses after the pulse are generated. 3. The fourth means comprises means for storing as a reference image one pattern in a sample in which a plurality of similar patterns are formed, and another same type pattern for inputting the same pattern as the reference image. The image measuring / inspecting apparatus for an electron microscope according to claim 1, further comprising: a means for comparing and a means for detecting the different portion as a defect candidate.