JPS61193443A - How to detect alignment marks - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an alignment mark detection method used in detecting the position of a mark attached to a material to be drawn in an electron beam drawing device or the like.゛[Conventional technology] Electron beam lithography! ! When direct writing is performed on a wafer using an i-position, the wafer and the electron beam must be aligned prior to the writing. That is, alignment marks 1 to 1 are placed on the wafer, the stage on which the wafer is placed is moved so that the mark portion is placed on the optical axis, and then the electron beam is moved around the mark portion, Reflected electrons or secondary electrons from the wafer rice mark are detected, and this detection signal is processed to detect the positional shift of the wafer. This detected positional deviation is corrected during the actual writing process, for example, by deflecting the electron beam.

[Problems to be solved by the invention] -11 In the process of aligning the wafer and the electron beam described above,
After first moving the stage so that the mark part is placed on the optical axis, even if the electron beam is moved on the wafer, the mark may not be placed on the predetermined part of the wafer.
Alternatively, if the position of the wafer on the stage is greatly deviated, the mark may not be detected even if the electron beam moves. In this case, since the drawing process is automated, the wafer is treated as a defective product without any drawing being performed, and if the wafer has already gone through the above process, would result in huge waste.

The present invention has been made in view of the above-mentioned points, and even if the mark part and the optical axis of the electron beam are far apart and the mark on the monthly rate is not detected, the mark part is automatically moved to the optical axis. The purpose of this positioning is to provide a method for detecting marks by moving the J: sea urchin stage placed above and detecting the mark position.

Means for Solving Problem L] The method for detecting alignment marks based on the present invention is as follows:
It is characterized by consisting of each stage of [.

A. Moving an electron beam in a mark detection mode with a mark marked with an arrow, and detecting a signal from a mark based on an information signal from the material; B. An electron beam in the mark detection mode. To move,
If the signal from the mark cannot be obtained, the electron beam is scanned two-dimensionally in a predetermined area on the monthly interest rate, the information signal from the monthly interest rate is detected, and the detected signal is transferred to the second part of the electron beam. Storing it in an image memory without being related to dimensional scanning; Selectively extracting only the signal of a relatively narrow small area from among the signals stored in the image memory, and using the pre-stored standard of the central part of the mark. D. Based on the comparison, move the stage on which the material is placed so that the optical axis of the electron beam and the center of the mark on the material coincide; After the movement of the material, the electron beam is moved in a mark detection mode over the material, and the signal from the mark is detected based on the information signal from the material.

[Operation] The monthly stage is moved so that the mark placed on the wafer or the like is placed on the optical axis of the electron beam, and then the electron beam is moved to cross the mark at the marked part of the material. be done. For example, foul electrons obtained from the mark portion as the electron beam moves are detected. The center position of the mark is determined based on the backscattered electron detection signal, but if the electron beam does not cross the mark even after the movement of the electron beam, the electron beam covers a relatively wide desired range of the material in two dimensions. scan. For example, secondary electrons obtained based on the scanning are detected, and the detection signal is stored in the image memory. On the other hand, the reference pattern for the center portion of the mark is created and stored in advance. The signals stored in the image memory are read out for each predetermined small area and compared with a reference pattern centered on the mark. As a result of the comparison, the stage is moved so that a portion of the small area is located on the electron beam optical axis based on the coordinates of the small area that matches the M quasi-pattern, and then the stage is moved across the mark.
;Uni electron beam is moved on monthly basis.

[Example] An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an example of an electron beam lithography apparatus in which the present invention is implemented, and 1 is an electron gun. The accelerated electron beam generated from the electron gun 1 is passed through the converging lens 2 to the stage 3.
is focused on the material 4 placed at . The electron beam is further deflected by an electrostatic deflector 7 to which a deflection signal is supplied from the computer 5 via a DA converter 6, and the material-L
The electron beam irradiation position of is moved. Core material F3I/
The return port 4 electrons generated from the material by irradiation of the electron beam to the material I are detected by the detector 8, and the nuclear material F31.4
Secondary electrons generated from the detector 9 are detected by the detector 9.

The reflected electron signal detected by the detector 8 is amplified by an amplifier 10 and then supplied to a signal processing circuit 12 via an AD converter 11. The secondary electron detection signal detected by the detector 9 is amplified by an amplifier 13, and then supplied via a Δ-D converter 14 to an image memory 15 to which a reference signal is supplied from the computer 5, and is stored therein. be done. The controller 5 supplies a control signal to a control device 17 for a motor 16 that drives the stage 3, and also has a memory 1 in which a predetermined mark pattern is stored in advance.
8 is connected.

In the configuration as described above, when the material 4 is placed on the stage 3, the stage receives a control signal from the computer 5 so that the mark 4-J previously provided on the material 4 is placed on the optical axis of the electron beam. will be moved based on At this stage, ideally the center of the mark on the material and the optical axis will coincide, but there may be a positional error when marking the material, or when material 4 is placed on stage 3. Due to factors such as positional deviation and stage movement error, the center of the mark does not coincide with the optical axis. Therefore, the computer first issues an instruction to detect the positional deviation of the mark. Specifically, the computer 5 supplies a deflection signal to the deflector, and the "-"-shaped mark M provided on the material 4 shown in FIG. Move the electron beam over a large distance. As a result, the reflected electron signal detected by the detector 8 is supplied to a signal processing circuit 12, and the rough center coordinates of the mark M are determined by the circuit 12 using the deflection signal from the computer as a reference signal. Next, the computer 5 calculates a second mark based on the determined center coordinates of the mark.
As shown by dotted lines X2 and Y2 in the figure, the electron beam is scanned near the center of the mark. The reflected electron signal detected based on this scanning is supplied to the signal processing circuit 12, and the positional deviation between the optical axis and the center of the mark M is detected in the circuit 12. The amount of deviation of this position is determined by the amount of deviation of the material F3
1.4, it is superimposed on the deflection signal as a position correction signal, for example.

Next, as shown in FIG. 3, in the first stage of mark detection, if the signal from the mark M is not detected even if the electron beam is moved as shown by X+ and Y+ in the figure, the computer 5 A scanning signal is supplied to the deflector 7 in order to two-dimensionally scan a relatively wide range (area surrounded by a dashed line in the figure) on the electron beam 4 with the electron beam. Note that point C in the figure is the expected position of the center of the mark. At this time, the signal from the secondary electron detector 9 is supplied to the image memory 15, and is stored in the image memory in accordance with the scanning signal 81. On the other hand, the memory 18 stores in advance a video signal of the center portion of the mark M as shown in FIG. 4 as a reference pattern. Of the signals stored in the image memory 15, the computer 5 selects a small area A in the same range as the range of the N quasi-patterns.
The signal is read out and compared with the reference pattern. The small area A is read out while being shifted slightly in the X and Y directions, and each time it is compared with the reference pattern. When the small area is shifted and the small area AO including the center of the mark M is read out, the mark pattern of the small area Ao and the reference pattern match. At this time, since the coordinates of the small area AO can be known by the computer, the computer 5 knows the coordinates of the small area A.

The difference between the center coordinates of the mark and the expected position IC of the center of the mark is calculated. Since this difference corresponds to the amount of deviation between the electron beam optical axis and the mark center position, the computer 5 controls the motor control device 17 so that the distance stage moves according to the difference.
A control signal is supplied to the After this stage movement, the electron beam is moved over the material in the first mark detection mode shown in FIG. At this time, since the optical axis and the center of the mark are close to each other with considerable precision, the scanning of the electron beam is not limited to the scanning of X2 and Y2 shown in FIG. By scanning this electron beam, the center position of the mark M can be detected accurately.

Although the present invention has been described in detail above, the present invention is not limited to the embodiments described above and can be modified in many ways. For example, the mark may be not only in the shape of a cross but also in the shape of a single character. Further, it is also possible to detect illegal electrons and lζ to detect secondary electrons as a mark detection signal, or conversely, a backscattered electron detection signal may be used as a video signal without using a secondary electron signal.

[Effect] As detailed above, in the present invention, even if a mark is not detected in the mark detection mode, the stage is moved so that the mark is automatically detected. If the present invention is used in the manufacture of LSIs and the like, it will have a great effect on improving the yield, since it will not be easily disposed of as a defective product.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of an electron beam lithography apparatus for carrying out the present invention, and FIGS. 2 and 3 are for explaining the mark on the monthly interest rate and how the electron beam moves on the monthly interest rate. The diagram used in FIG. 4 is a diagram showing a reference pattern. 1... Electron gun 2... Converging lens 3...
Stage 4... Material to be drawn 5... Computer 6... D-A converter 7... Electrostatic deflector
12... Signal processing circuit 8.9... Detector 15.
...Image memory 10.13...Amplifier 16...Motor 11.14...A-D converter

Claims (2)

[Claims] (1) A method for detecting alignment marks consisting of the following steps: A. Moving an electron beam in a mark detection mode over a material on which marks are attached, and detecting signals from the marks based on information signals from the material. B. If no signal from the mark is obtained by moving the electron beam in the mark detection mode, scanning the electron beam two-dimensionally over a predetermined area on the material to detect information signals from the material; and storing the detected signal in an image memory in association with the two-dimensional scanning of the electron beam; C. Of the signals stored in the image memory, only signals in a relatively narrow small area; D. Based on the comparison, the material is adjusted so that the optical axis of the electron beam and the center of the mark on the material coincide. E. After moving the stage, move an electron beam over the material in a mark detection mode, and detect signals from the marks based on information signals from the material. (2) In stage A, the electron beam has a relatively wide range;
is moved in mark detection mode, and in stage E,
2. A method for detecting alignment marks according to claim 1, wherein the electron beam is moved in a mark detection mode over a relatively narrow range.