JP3479924B2 - Mark position detection method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mark position detecting method, and more particularly to a mark position detecting method for an electron beam exposure apparatus used for exposure in forming a photomask or for exposing a semiconductor wafer. is there.

[0002]

2. Description of the Related Art In recent years, as the degree of integration of semiconductor integrated circuits has improved, finer patterns have been required, and electron beam exposure has been used in the lithography process for this purpose. And in this electron beam exposure process,
With the miniaturization, it is necessary to improve the pattern placement accuracy, and therefore the accuracy of mark position detection has been improved. The pattern placement accuracy means connection accuracy between a field deflected by the main deflector and a field deflected by the sub deflector in an electron beam exposure apparatus having a main deflector and a sub deflector, or , Means the accuracy of stacking the front and rear layers in the multi-layer process.

In the conventional mark position detecting process, four photodiode chips are attached to a detector base, and the detection outputs of these four photodiodes are simply added to perform position detection. This state is shown in FIG.

As shown in FIG. 4A, a Ta mark 11 for position detection provided on a mark chip 10 made of a silicon chip is irradiated through an electron beam passage hole 13 provided in a detector base (not shown). Four photodiode chips 12A and 12B which are scanned by the electron beam 8 and whose reflected electrons 14 are mounted on a detector base
(The figure shows two of four), and the mark position is detected by simply adding the detection signals.

[0005]

However, in the conventional mark position detecting method, the level of the backscattered electrons is different between the GO scanning and the RETURN scanning depending on the arrangement position of each photodiode chip. There was a mistake. This is because a part of the reflected electrons is further reflected at the step portion of the Ta mark and the direction is changed, as shown in FIG.
The photodiode chip that should be detected (1 in the case of the figure)
This is because 2B) cannot take in the reflected electrons and the detection output decreases.

This state is shown in FIG. 4 (b). In the figure, A represents the detection output of the photodiode chip 12A, and B represents the detection output of the photodiode chip 12B.

Referring to FIGS. 4A and 4B, first, when the electron beam 8 is GO-scanned in the direction of a → b → c → d in the figure, the photodiode chip 12A is normally reflected between a → b. Although the electrons 14 are detected, the photodiode chip 12B changes the direction because the reflected electrons 15 that should originally be detected are obstructed by the step portion (mark edge) of the Ta mark 11 and change the direction. An undershoot-like waveform shown in the circle is output. Then, between b and c, a large amount of backscattered electrons from the surface of the Ta mark 11 having a high electron reflectance can be detected without being disturbed, so that the photodiode chips 12A and 12B have the same accuracy. The backscattered electrons are detected to form a flat peak.

Next, between c and d, this time the photodiode chip 12A and the photodiode chip 1
The relationship with 2B is reversed and the photodiode chip 12
A cannot capture some of the backscattered electrons and an abnormal output is obtained. The photodiode chip 1
2B is not disturbed by the step difference of the Ta mark, so that a flat Low output can be obtained. Next, this time, the scanning direction is reversed and the RETURN scanning is performed in the direction of d → c → b → a. In this case, the photodiode chip 1
The output relationship between 2A and the photodiode chip 12B is reversed.

In any case, if the simple sum of the detection outputs of the respective photodiode chips is taken, the total sum will be inaccurate because one of the photodiode chips has an abnormal detection output, so it is correct. The mark position could not be detected, and as a result, the pattern placement accuracy was degraded.

Therefore, an object of the present invention is to eliminate the abnormal detection output of the photodiode chip to enable the correct mark position detection and improve the pattern placement accuracy.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a mark provided on a mark chip is scanned with an electron beam (8 in FIG. 1) and a backscattered electron is detected by a photodiode to detect the position of the mark. In the position detecting method, the photodiodes are sequentially switched so as to select the photodiode arranged at a position where the backscattered electrons are normally taken in with respect to the scanning direction of the electron beam (8 in FIG. 1), and the selected photodiode is detected. A mark position detecting method for judging a mark position by using an output, wherein a positional relationship between a scanning direction of an electron beam (8 in FIG. 1) and a photodiode arranged at a position where a backscattered electron is normally taken in is controlled in advance. Means (Fig. 1
No. 6), and the control means (6 in FIG. 1) automatically selects the photodiode that can obtain a normal output according to the scanning direction of the electron beam (8 in FIG. 1). To do.

[0012]

Further, according to the present invention, a differential waveform is formed by differentiating normal detection output data, an average value of peak values of the obtained differential waveform is obtained, and a component above the average value is invalidated and effective. It is characterized in that the mark position is judged based on the position of the peak.

Further, according to the present invention, the interval between the positive peak value and the negative peak value of the peak value of the differential waveform is calculated and compared with the width of the mark to invalidate the non-coincident peak value and to determine the effective peak value. It is characterized in that the mark position is judged based on the position.

Further, according to the present invention, a plurality of photodiodes are attached to a detector base provided with an electron beam passage hole for passing an electron beam, and four photodiodes are arranged so as to be point-symmetric with respect to the center of the electron beam passage hole. It is characterized by being arranged.

[0016]

The photodiode arranged at the position where the reflected electrons can be accurately taken in is selected, and the mark position is detected by using the output of the selected photodiode. Even if the reflected electrons are redirected, abnormal data will not be mixed in the detection output.

Further, since the positional relationship between the scanning direction of the electron beam and the photodiode arranged at the position where the backscattered electrons are normally taken in can be easily estimated, by storing the relationship in the control means in advance, the scanning time can be improved. Simplifies the selection of photodiodes. Furthermore, by using the differential output of the output data, even if unexpected spike noise is mixed, such spike noise can be easily removed.

Further, by arranging the four photodiodes substantially in point symmetry with respect to the center point of the electron beam passage hole, it is possible to accurately detect the position of the mark for scanning in each direction with a small number of photodiodes. You can

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described with reference to FIGS. 1 is a diagram schematically illustrating the principle configuration of the present invention, FIG. 2 is a diagram illustrating a detailed configuration of a mark detection unit of the electron beam exposure apparatus, and further, FIG.
FIG. 6 is a diagram for explaining a method of analyzing a detection output.

Referring first to FIG. 1, the structure of the present invention will be briefly described. An electron beam scanning signal for detecting a Ta mark is output from the control system 6 to the column system 1 and a photodiode chip is sent to the video amplifier 5. The selection signal of is output. In the column system 1, the electron beam 8 is emitted from the electron gun 2 and
The mark chip placed on the wafer holder 4 is moved to the electron beam 8 by the electron beam scanning signal applied to the column system 1.
To scan by.

Next, the reflected electrons from the mark chip are detected by the four photodiode chips attached to the detector base 3, and the detection output is output to the video amplifier 5, and the video amplifier 5 selects from the detected outputs. The detection output of the photodiode chip previously selected by the selection signal of the control system 6 is selected and output to the control system 6.

Next, the control system 6 differentiates the detection output from the selected photodiode chip, sends the obtained differential waveform to the computer 7, analyzes the differential output in the computer 7, and detects the Ta mark on the mark chip. Determine the position. The computer 7 obtains the deflection position deviation of the main deflector and the sub-deflector of the electron beam exposure apparatus based on the obtained Ta mark detection data, corrects the deviation, and exposes the semiconductor to be exposed stored in the wafer holder 4. Start exposure of the wafer or the like.

Next, the detailed structure of the mark detection unit of the electron beam exposure apparatus will be described. 2A, the detection mark 11 made of Ta is formed on the substrate made of silicon.
The mark chip 10 provided with is scanned by the electron beam 8 that has passed through the electron beam passage hole 13 provided in the detector base 3, and the reflected electrons 14 from the silicon substrate and the Ta mark 11 are scanned by the four photodiode chips 12. To detect.

Referring to FIG. 2B, this mark chip 10 is obtained by patterning a Ta mark 11 having a predetermined shape on a silicon wafer for each chip.
This mark chip 10 is divided into chips.
Is a wafer holder 4 for accommodating a semiconductor wafer 9 to be exposed.
It is attached to the periphery of.

Next, the scanning direction of the electron beam and the selection of the photodiode chip will be described. See FIG. 3. First, as shown in FIG.
When GO scanning is performed in the → c → d direction, the photodiode chip 12A normally operates the backscattered electron 1 between a → b.
4 can be detected, but the photodiode chip 12B changes the direction because the backscattered electrons 15 that should originally be detected are obstructed by the stepped portion (mark edge) of the Ta mark 11 and change the direction. In the scanning of, the photodiode chip 12A is selected in advance as the photodiode chip that obtains an effective detection output.

Next, between b and c, both of the photodiode chips have Ta mark 1 with high electron reflectance.
Although a large amount of backscattered electrons from one surface can be properly detected without being disturbed, the relationship between the photodiode chip 12A and the photodiode chip 12B is reversed during the next c → d, and the photodiode chip 12B is normal. Although the backscattered electrons 14 can be detected in the photo diode chip 12A, the photo diode chip 12A cannot normally detect the photo diode chip 12A from the photo diode chip 12A to the photo diode chip 12B. Switch.

Thereafter, scanning is performed up to the position of d with the photodiode chip 12B selected as effective, and this time, RETURN scanning is performed in the direction of d → c → b → a. In this case, the relationship is reverse to that of GO scanning, and the photodiode chip 12B is selected as effective from d to the middle of c → b, and the photodiode chip that obtains effective detection output between b → c is used as the photodiode. The chip 12B is switched to the photodiode chip 12A, and scanning is performed up to the position a with the photodiode chip 12A selected as valid.

Next, the detection output detected by the photodiode chip and the method of analyzing its waveform will be described. A in the reference diagram of FIG. 3 (b) shows a composite output waveform obtained by switching the photodiode chips. As in the conventional detection output waveform obtained by simple summation, a portion corresponding to the Ta mark edge is non-existent. The normal waveform disappears.

Next, the composite output is differentiated in the control system to obtain a differential waveform output shown in B of the figure. The peak position in the obtained differential waveform corresponds to the Ta mark edge.

If spike noise occurs in the differentiated output waveform for some reason, a peak larger than the normal peak value will be detected. Therefore, by averaging the absolute values of the peak values, the average value is calculated. The larger peak value is excluded as invalid spike noise, and the mark position is determined by the valid peak. Further, since the width of the Ta mark is fixed, by storing and inputting this value in advance, the distance between the positive peak value and the negative peak value is calculated, and the calculation result and the memory input are compared. If they do not match, they are excluded as spike noise.

Then, based on the obtained Ta mark position data, the deviation of the deflection position between the main deflector and the sub deflector of the electron beam exposure apparatus is obtained, the deviation is corrected, and the electron beam exposure is started.

In the above description, two photodiode chips 12A and 1A are provided to simplify the description.
Although 2B has been described, four photodiode chips are actually used, and in this case, the switching of the photodiode chips is performed by the control system according to the scanning direction of the electron beam.

[0033]

According to the present invention, when the Ta mark is scanned by the electron beam, the effective photodiode chip is switched according to the scanning direction to detect the reflected electrons, thereby improving the mark position detection accuracy and the pattern. It is possible to improve the placement accuracy of.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a principle configuration of the present invention.

FIG. 2 is a diagram illustrating details regarding a Ta mark of an apparatus used for implementing the present invention.

FIG. 3 is an explanatory diagram of a mark position detecting method of the present invention.

FIG. 4 is an explanatory diagram of a conventional mark position detecting method.

[Explanation of symbols]

1 column system 2 electron gun 3 detector stand 4 Wafer holder 5 video amplifier 6 control system 7 computer 8 electron beam 9 Exposed semiconductor wafer 10 mark chips 11 Ta mark 12 Photodiode chip 12A Photodiode chip A 12B Photodiode chip B 13 Electron beam passage hole 14 Backscattered electrons 15 Backscattered electrons obstructed by mark

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A 61-177719 (JP, A) JP-A 61-207017 (JP, A) JP-A 3-167819 (JP, A) JP-A 58- 125 (JP, A) JP 57-42129 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 504 G03F 7/20 521

Claims (4)

(57) [Claims] 1. A mark position detection method for scanning a position detection mark with an electron beam, detecting reflected electrons with a plurality of photodiodes to detect the position of the position detection mark, in the scanning direction of the electron beam. Is a mark position detecting method in which the photodiodes are sequentially switched so as to select a photodiode arranged at a position where the backscattered electrons are normally taken in, and the mark position is determined using the detection output of the selected photodiode. Te effectively test the scanning direction of the electron beam, the reflected electrons
The positional relationship with the photodiode that can be output is controlled beforehand.
In the electron beam of the electron beam by the control means.
Photodiode that can obtain normal output depending on the scanning direction
A mark position detection method characterized by automatically selecting . 2. Differentiating the valid mark detection data.
The differential waveform is formed by and the peak of the obtained differential waveform
Calculate the average value of the values, invalidate the components above the average value, and enable
Characterized by determining the mark position based on the position of various peaks
The mark position detecting method according to claim 1. 3. A positive peak value of the peak value of the differential waveform
And the negative peak value are calculated, the calculated result and position detection
Peaks that do not match by comparing with the width of the peak
Invalidate the value and set the mark position according to the position of the valid peak.
The mark position detection according to claim 2, wherein the mark position is detected.
How to get out. 4. The plurality of photodiodes are the electrons
Detector stand with electron beam passage hole for passing the beam
Attached to the center of the electron beam passage hole
The feature is that 4 pieces are arranged so as to be point-symmetric with respect to
The mark position according to any one of claims 1 to 3.
Position detection method.