JPS6258140B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for alignment in electron beam exposure.

In electron beam exposure, it is necessary to accurately know the relative positional relationship between the electron beam and the substrate, and mark detection is a technique for detecting this positional relationship. Mark detection involves forming a mark on a part of the substrate by deforming the geometrical shape of the substrate surface (forming irregularities) or using a material that is different from the substrate, and then scanning the substrate containing the mark with an electron beam. This technique obtains the positional relationship between the electron beam and the mark by detecting secondary electrons or reflected electrons emitted from the substrate and the mark during scanning.

The gist of the present invention will be explained below with reference to an example in which a variable shaped beam is used. In order to make this type of technique possible, a mark detection circuit as shown in FIG. 1 is used.

When the electron beam 3 is scanned one step at a time with respect to the mark 2 formed on the substrate 1, the electron beam 3
When the electrons reach the mark 2, they are scattered and the amount of generated secondary electrons or reflected electrons changes rapidly. This change is detected by detectors 4 and 4' and amplified. The differentiated waveform is shown in Figure 2. In FIG. 2, the horizontal axis shows time (corresponding to distance), the vertical axis shows detection signal strength, 9 is the detection signal waveform, and 10 is the threshold voltage determined by the constant voltage generator. Detection signal waveform 9 is threshold voltage 10
The position of the mark end can be detected by reading the number of beam movement steps when it exceeds . Similarly, when scanning from the opposite side, the other end position of the mark is detected, and half of the sum becomes the mark center position.

Generally, when detecting marks, the mark scanning speed may need to be slower than the normal pattern drawing speed depending on the characteristics of the secondary electron or backscattered electron detector and the detection circuit. generally scans over the mark many times. For this reason, the electron beam resist on and near the mark receives a dose of irradiation more than necessary, and in the case of a positive resist, for example, it becomes impossible to remove it by normal chemical operations. If such unremovable parts occur on or near the mark, there will be a difference between the part that was removed in the next process (etching or plating) after electron beam exposure, and when the mark is scanned again with the electron beam, A detection signal is also generated from this difference, causing problems such as being indistinguishable from the detection signal from the original mark.

In order to suppress the amount of mark irradiation within a range where the resist in the mark scanning portion during mark detection can be easily peeled off, it is conceivable to increase the mark scanning speed. However, if the mark scanning speed is increased, fewer secondary electrons or reflected electrons are generated per unit time, and the detection signal becomes less than the threshold value, making it impossible to detect the mark. Therefore, in order to increase the amount of secondary electrons or reflected electrons generated per unit time,
It is conceivable to increase the beam shape BM as shown in Figure 3b, but the generation position of the secondary electrons or reflected electrons generated by mark scanning is different from that in Figure 3a, and compared to MK in the mark. When the beam size is large, the difference between the amount of secondary electrons or reflected electrons generated from areas other than the mark and those generated from the mark area becomes smaller, and the detection signal becomes less than the threshold value as shown in Figure 4-11, making threshold judgment possible. becomes difficult. Note that in FIG. 3, the arrow indicates the scanning direction. The present invention aims to solve the above-mentioned problems, and the present invention provides a method for detecting the position of a mark formed on a substrate by electron beam scanning.
The size in the direction perpendicular to the scanning direction is larger than the size in the same direction of the beam spot during pattern exposure scanning, and the size in the scanning direction is the same as the size in the same direction of the beam spot during pattern exposure scanning. It is characterized by: In other words, as shown in Figure 3c, the beam size in the mark scanning direction
By increasing the size BM ₂ in the direction perpendicular to the scanning direction without changing BM ₁ , the amount of secondary electrons or reflected electrons generated per unit time can be kept constant even if the mark scanning speed is increased. , Furthermore, since the beam size in the mark scanning direction is the same, the mark detection accuracy remains unchanged.

In a variable-shaped electron beam exposure device in which the electron beam is shaped into a rectangle and the length of each side of the rectangle can be arbitrarily changed, when marks are scanned on orthogonal marks MK as shown in Figure 5. The beam shape BM can be changed depending on the scanning direction.

As explained above in the case of variable shaped beam,
As in the electron beam scanning method for mark detection of the present invention, by keeping the length of the side in the beam scanning direction constant and changing the length of the side in the edge forming direction of the mark according to the beam scanning speed, the mark scanning of the beam can be performed. The amount of secondary electrons or reflected electrons generated per unit time can be made constant.

Conventionally, pattern exposure and mark detection were performed using an electron beam with a mark width of 6 μm and a square beam spot of 3 μm on a side.
By doing so, it was possible to perform scanning at approximately twice the speed of the conventional method, without reducing mark detection accuracy, and without creating any portions of the resist that could not be removed.

The present invention has been explained above using an example of a rectangular beam, but even when a circular beam is used, the present invention can be applied to an ellipse by increasing the diameter in the direction perpendicular to the scanning direction without changing the diameter in the scanning direction. It can also be implemented in the form of

In addition, in the explanation of the present invention so far, a solution method has been explained in which the scanning speed is increased in order to prevent the resist from peeling off due to excessive beam irradiation on the resist, but in the present invention, it is possible to solve the problem by increasing the scanning speed For example, the same effect can be obtained by adjusting the electron beam current density by increasing the area of the beam spot.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of the mark detection device, FIG. 2 is a mark detection signal, and FIG. 3 is a, b,
Fig. 3c shows a relationship between mark width and beam size, a and b show a conventional example, and c shows an embodiment of the present invention. Figure 4 shows
A mark detection signal when the beam size is large compared to the mark width. FIG. 5 is a diagram showing the relationship between orthogonal marks and mark sizes. In FIG. 1, 1 is a substrate, 2 is a mark formed on the substrate, 3 is an electron beam, 4 and 4' are secondary electron or backscattered electron detectors, 5 is an amplifier circuit, 6 is a differential circuit, 7 is a comparator, 8 is a low voltage generation circuit, and in Figure 3, BM is a beam spot and MK is a beam spot.
indicates a mark.

Claims (1)

[Claims] 1. A method for detecting the position of a mark formed on a substrate by electron beam scanning, wherein the electron beam is shaped into a rectangle, and each side of the rectangle is arbitrary. When using a variable shaped beam that can be changed to , the beam is scanned perpendicular to the direction in which the edge of the mark to be detected is formed, and the direction of one side of the rectangular beam is parallel to the scanning direction (the other side is at right angles). In , the length of the sides of the rectangular beam in the direction parallel to the scanning direction is kept constant, and even if the rectangular area of the beam is changed by changing the length of the sides perpendicular to the scanning direction, and the beam scanning speed is changed, the beam 1. An electron beam scanning method for mark detection, characterized in that the amount of secondary electrons or reflected electrons generated by mark scanning is kept constant per unit time. 2 The length of the side of the rectangular beam in the direction parallel to the scanning direction is the same as the size of the beam spot in the same direction during pattern exposure scanning, and the length of the side in the direction perpendicular to the scanning direction is the same as the size of the beam spot during pattern exposure scanning. 2. The electron beam scanning method for mark detection according to claim 1, wherein the electron beam scanning method for mark detection is made larger than the size in the same direction. 3. The electron beam scanning method for mark detection according to claim 2, wherein the beam scanning speed during mark position detection is set higher than the beam scanning speed during pattern exposure scanning. 4. Claims characterized in that the size of the scanning beam spot in the direction perpendicular to the scanning direction and the scanning speed at the time of mark detection are set to conditions that enable chemical peeling of the electron beam resist. The electron beam scanning method for mark detection according to item 3.