JPH01136332A - Electron beam lithography method - Google Patents

Abstract

PURPOSE:To improve layer inquiring accuracy and field connecting accuracy, by using marks, which are provided on the outside of a sample subjected to lithography, measuring the amount of deflected distortion in the field, obtaining correcting coefficients of the deflected distortion, detecting the positions of the marks around the field in the sample subjected to lithography, correcting said coefficients, and performing the lithography. CONSTITUTION:Twenty-five gold cross marks 31 in a field 30 at the outside of a sample subjected to lithography are detected by deflecting an electron beam. The amount of deflected distortion is measured. Thus the correcting coefficient of deflected distortion is obtained. Then, a wafer 21 is mounted on a stage, and two wafer marks 22 and 23 are detected. The rotary angle of the wafer with respect to the moving direction of the stage and a distance between chips are measured. Then the positions of a chip mark and correcting marks for deflected distortion are detected with the electron beam by moving the stage and moving marks 24-29 to the center of the deflection of the electron beam. Then, the stage is moved to the center of a field f5. The electron beam is deflected and the marks 28, 24 and 29 are detected. Parts of the correcting coefficients for the deflected distortion are corrected. Thus the lithography of the pattern of a chip A is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electron beam lithography method and the structure of an alignment mark used therein, and more particularly to an improved deflection distortion correction method and a mark used therein.

[Conventional technology]

The following two types of alignment methods in electron beam lithography are known. First, as shown in Fig. 2, one chip consists of one field, and alignment marks 2, 3, and 4 are arranged around the chip 1.
, 5 are detected by deflecting the electron beam with the stage stopped. (This is called fixed stage mark detection method.) An example of this is IBM Journal of Research A. Development November (1977) pp. 498-505
Page (IBM Journal ofJasearch
andDavslopment, November
1977, pp. 4.98-505). The advantage in this case is marks 2, 3, and 4.5 positions a
Since the m constant is measured while including the deflection distortion of the electromagnetic lens system, deflection distortion correction is automatically performed. However, when writing a chip that exceeds the field size, a problem arises in that a mark must be placed at the center of the chip. Another method is as shown in FIG.
It is composed of gf4 and has a mark of 7.8, 9゜1.
0 is placed in the fourth even position of the chip. In this case, mark detection is performed by moving the stage to place each mark near the center of deflection of the electron beam6 (referred to as moving stage mark detection).At this time, the stage position is precisely measured using a laser interferometer. be done. An example of this is Journal of Vacuum Science and Technology 19(4) 1981, pages 927-931.
and 5science and Technology
19(4) 1981 pp927-931). The advantage in this case is that the chip size is not limited by the field and can be made large.

However, the deflection distortion must be precisely set in advance using marks outside the sample to be drawn, and coefficients for correction must be determined. The method of determining the correction coefficient is, for example, by using nine marks 12 to 12 whose coordinates within the field 11 are accurately measured as shown in Fig. 4.
By detecting 20 by deflecting the electron beam, the following coefficients can be determined by the method of least squares.

Equation (1) where ao ”as, be-bs are deflection distortion correction coefficients,
Xm'j is the electron beam drawing position when there is no distortion.

x' and y' are the electron beam lithography positions after correction of deflection distortion.

The latter method, which has no chip size limitations, is currently mainly used.

[Problem that the invention seeks to solve]

In the conventional technique described above, a correction coefficient for deflection distortion is determined before drawing, and the same correction coefficient is used during drawing. Therefore, when there is a change in deflection strain over time, there is a problem in that misalignment between layers occurs in the field periphery or deviation in the drawing pattern occurs in the field connection area.

An object of the present invention is to provide an electronic drawing method and an alignment mark structure that reduce layer interrogation deviations and field connection deviations due to changes in deflection strain over time, even in a stage-moving mark detection method in which alignment marks are detected at the center of deflection. There is a particular thing.

[Means for solving problems]

In order to achieve the above objective, first, before electron beam lithography, marks for deflection distortion correction made outside the sample to be drawn (referred to as standard marks) are precisely measured and the zero-order distortion correction coefficient is determined. Before pattern writing is performed, a part of the previously determined deflection distortion is corrected by detecting alignment marks placed in at least one field within the sample to be drawn by deflecting the electron beam. Perform electron beam drawing.

[Effect]

Determining the deflection distortion correction coefficient by measuring the standard mark described above requires a time of several 10 seconds to several minutes, so it is disadvantageous to perform this frequently during writing due to changes over time, as this will greatly reduce the throughput. However, according to experiments conducted by the present inventors, it has been found that changes in deflection distortion over time are not large for all deflection distortion correction coefficients. In Equation (1) mentioned above, the factors that have large changes over time are the zero-order term and the first-order term, aoe a1* any bow b, eb2. Of these, the shift amount terms ao and bo have the largest changes. This can also be corrected in the stage moving mark detection method by detecting four marks around the chip.

The next largest changes are in the gain ring, at and b2, and the slope terms ax and bx. Therefore, by detecting marks for each chip (or every few chips) using the stage movement mark detection method, placing marks with known position coordinates around the field, and detecting them by deflecting the electron beam, the first-order term a
1. ax, b1. bx can be found. Since the time required for this mark detection is several seconds, there is no need to worry about reducing throughput even if it is performed in the middle of writing one wafer.
Therefore, by correcting only the low-order terms of the precise correction coefficients determined before drawing by measuring the marks in the sample to be drawn, the decline in field connection accuracy and glabella alignment accuracy due to changes in deflection distortion over time can be greatly improved. be done.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
Figure (a) shows the chip arrangement in the well when the electron beam lithography method of the present invention is applied.The wafer 21 has a chip A with an alignment mark (chip mark) around the chip and a chip A with a size of 300 μmD. A chip B having a wafer mark of 1 is placed. FIG. 1(b) is a diagram showing the arrangement of chip marks within the chip. The size of 1 chip is 1
10, with chip marks 24°25.2 on the four corners of the chip.
6, 27 are placed. The field size (the range that can be drawn by moving the stage) of the electron beam lithography system used here is 510, so the two broken lines Q in Fig. 1(b)
Four fields f5. with field boundaries denoted 1 and Q2. f6゜f7. It is divided into f8 and drawn. Mark 2 for deflection distortion correction is placed in one field f5.
8.29 is placed.

In this embodiment, first, as shown in FIG. 1(Q), 25 cross-engraved marks 31 whose positions in the field 30 of the 5th intestine orifice have been measured in advance are detected by deflecting an electron beam.
The amount of deflection distortion was measured, and the deflection distortion correction coefficient was determined by the least squares method. This gold mark row is a part of the stage where the wafer is not placed.
1 was attached to the stage. First, by detecting the two wafer marks 22 and 23 placed on the left and right sides of the wafer, the rotation angle of the wafer with respect to the stage movement direction and the distance between the chips are measured.The positions of the zero-order chip marks and the deflection distortion correction mark. A detection has been made.

This is done by moving the stage to each mark 24
, 28, 25, 26, 27, 29 are moved to the center of deflection of the electron beam and detected by the electron beam. From the coordinates of the stage at this time and the detection position by the electron beam, each mark 24-
The exact coordinates of 29 can be found by moving the stage to the center of the first field f5 shown in FIG. 1(b) and deflecting the electron beam to detect marks 28, 24, and 29. Some correction coefficients for deflection distortion have been corrected. After that, the pattern of chip A was drawn. Mark detection for correcting this correction coefficient is performed twice per 1 wafer immediately after the start of writing to increase the frequency, and 2 sheets are written, and from the third sheet onwards, it is performed once per wafer.Table 1 Correction Coefficients Initial pricing was carried out and five wafers were drawn in succession.

Table 1 shows the correction coefficients for deflection distortion obtained before drawing five images, and Table 2 shows the coefficients corrected during the drawing process. ""as and b
o=be is a correction coefficient. Among these, the coefficients modified during drawing are aOs a is a 21bo, bx, bl
There are 6 pieces. By modifying these six coefficients, the alignment accuracy between layers was improved from the conventional 3σ20.15 μm to 3σ20.09 μm.

In this embodiment, a mark for correcting the deflection distortion correction coefficient is provided on each chip, but the above-mentioned changes are also possible.

(i) A self-correction mark is attached only to the chip on which the wafer mark is installed, and the correction coefficient is corrected only once per wafer.

(5) The correction coefficient is corrected by detecting only the 241 chip marks shown in FIG. During correction, the stage is moved to the periphery of the field and then detection is performed using an electron beam. In this case, correction coefficients can be corrected without preparing new marks.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to correct the change in deflection distortion over time by simple mark detection during electronic drawing, so the frequency of correction of deflection distortion can be reduced, thereby improving throughput. In addition, the accuracy of layer alignment and field connection accuracy can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, in which (a) is a diagram showing chip writing in a wafer, (b) is a diagram showing a mark arrangement in a chip, and (c) is a diagram showing deflection distortion correction. FIG. 2 is a diagram showing a conventional stage stop mark detection method, and FIG. 3 is a diagram showing a conventional stage movement mark detection method. FIG. 4 is a diagram showing a complete string of nine cross marks for determining the deflection distortion correction coefficient. 1...A chip in which one chip consists of one field.

Claims (1)

[Claims] 1. In an electron beam lithography system that performs drawing with the stage stopped, when the field is the range that can be drawn without moving the stage, the amount of deflection distortion in the field is determined using marks placed outside the sample to be drawn. After measuring several coefficients for correction of deflection distortion, some of the above coefficients are determined using the results of detecting the positions of marks placed around the field in the sample to be drawn by deflecting the electron beam. An electron beam drawing method characterized by performing drawing by correcting the .