JPS6142408B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an alignment method in an electron beam exposure apparatus that forms fine patterns on integrated circuits, etc., and particularly to a method for measuring the relationship between a sample and the projection position of an electron beam with high precision. The present invention relates to an alignment method and device that enable alignment.

FIG. 1 is a schematic diagram showing a conventional electron beam optical projection mechanism. A conventional positioning method will be explained based on this figure. The electron beam is electron gun 1
0 and directed through a series of electromagnetic lenses forming an electron optics system. This electron optical system includes a first focusing lens 11, a second focusing lens 12,
It is composed of a mask irradiation lens 13, a first projection lens 14, and a second projection lens 15. When forming a fine pattern such as an integrated circuit, a parallel electron beam is formed using the mask irradiation lens 13, and the pattern formed on the mask 20 is projected onto the sample 21 using the first and second projection lenses 14 and 15. image on the surface of In the manufacture of integrated circuits and the like by electron beam exposure, it is extremely important that the imaging position of the mask pattern and the sample 21 be aligned with high precision. In the prior art shown in the figure, a pair of orthogonal X deflection coils 22 and Y deflection coils 23 are installed in front of the mask irradiation lens 13 to increase the effect of the mask irradiation lens 13.
The electron beam is focused on a predetermined position on the mask 20. An alignment pattern is formed in a predetermined area of this mask 20. The electron beam that has passed through the mask 20 is focused by the first and second projection lenses 14 and 15, and is focused on the surface of the sample 21. Marks for positioning are provided on the surface of the sample 21. Under such conditions, the electron beam is scanned over the positioning pattern of the mask 20 by the X deflection coil 22 or the Y deflection coil 23, and the reflected electrons or secondary electrons from the sample 21 are detected by the detection element. Detected at 25. The detected signal can be viewed as an image on the display 26, as is well known in the field of electron microscopy. As a result, an image 27 of the mark on the sample 21 and an image 28 of the alignment pattern on the mask 20 are displayed on the display 26.
is displayed. Then, alignment is performed by overlapping the mark image 27 and the pattern image 28.

However, the conventional alignment method performed in this manner has the following drawbacks.

Since it is necessary to increase the beam deflection angle compared to a normal scanning electron microscope, the aberration of the electron optical system increases.

In order to obtain the effect of the mask irradiation lens, the position of the deflection coil is uniquely determined, which imposes restrictions on the design of the electron optical system.

Productivity decreases because it is necessary to switch the excitation current of the electromagnetic lens between alignment and pattern formation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an alignment method and apparatus that can eliminate the drawbacks of the prior art described above, improve productivity, prevent a decrease in the resolution of projected images, and provide extremely high alignment accuracy. This method is characterized in that an electron beam projected on or near a mark placed on a sample surface is vibrated, and the frequency components of a detection signal of reflected electrons or secondary electrons from the sample surface are analyzed.

Hereinafter, the alignment method and apparatus of the present invention will be explained in detail based on the drawings. FIG. 2 is a schematic diagram showing an embodiment of an electron beam optical projection mechanism used to carry out the alignment method of the present invention. Note that the electron optical system includes a first focusing lens 31, a second focusing lens 32, and a second focusing lens 32, as shown in FIG.
It is composed of a mask irradiation lens 33, a first projection lens 34, and a second projection lens 35, and the electron beam is emitted by an electron beam source such as an electron gun 30. The electron beam is turned into a beam parallel to the optical axis by the mask irradiation lens 33. When forming a fine pattern such as an integrated circuit, the pattern of the mask 40 can be projected onto the surface of the sample 42 by removing the shutter 41 provided above the mask 40. Projected image of electron beam and sample 42
When performing alignment, the shutter 41 is set so that one of the alignment patterns formed on the mask 40 is irradiated with an electron beam. As a result, as shown in FIG.
The projected image 43 of the alignment pattern above is the sample 4.
The image is projected onto or near the mark 44 placed on the image sensor 2. Next, as shown in FIG. 2, a set of an X deflection coil 50 and a Y deflection coil 5 are arranged orthogonally between the first projection lens 34 and the second projection lens 35.
1 is installed to detect reflected electrons or secondary electrons from the surface of the sample 42. First, when detecting the amount of deviation in the X direction between the projected image 43 and the mark 44, the projected image 43 is vibrated in the X direction at a constant frequency by the X deflection coil 50. At this time, the electric signal detected by the detection element 52 has a frequency and a frequency of 2
The waveform will include, etc. When the frequency signal component of this electrical signal is detected by a filter or the like, the relationship between the amount of positional deviation between the projected image 43 and the mark 44 in the X direction and the output of the frequency signal component is as shown in FIG. . In measurement using light, an example of obtaining the relationship shown in Figure 4 by vibrating a slit-shaped light can be found in a well-known publication, ``Optical Measurement of Patterns'' by Shoichiro Yoshida. Precision Machinery, Volume 40, No. 9, Pages 754~
761, 1974)” and 0.1 μm for light.
It can be detected with an accuracy within and wavelength of light
4000-5000Å, whereas the wavelength of an electron beam is usually 1
Å or less. Therefore, in the present invention that uses an electron beam with a short wavelength, the projected image 43 and the mark 44
The positional deviation in the X direction can be detected with an accuracy of within 0.1 μm. The detected positional shift amount can be corrected by applying a constant current to the X deflection coil 50 to shift the projected image 43, or by slightly moving the sample 42 in the X direction. In this way, alignment in the X direction is performed. On the other hand, the alignment in the Y direction is similar to the alignment in the X direction.
3 by vibrating it at a frequency in the Y direction.

Here, the reason why the relationship shown in FIG. 4 is obtained will be explained. The current density distribution of the electron beam is (x), the reflectance distribution of the mark with respect to the electron beam is d(x), and (x) and g(x) are x=0.
Suppose that it is symmetric with respect to . Let d be the deviation between the center of the electron beam and the center of the mark. electron beam
Asinωt (where ω: angular frequency (ω=2π
), t: time), and if the signal amount of reflected electrons from the mark is E(d, t), then E(d, t)=∫ ^∞ _−∞ (x+d+Asinωt) ・g(x)dx ( 1) It is expressed as

(x) and g(x) are even functions, so is Fourier expanded.

Substituting equations (2) and (3) into equation (1), we get becomes.

Here, the range where the mark exists is [-h, h]
In other cases, the electron reflectance is assumed to be 0.
Equation (4) becomes as follows.

however, cos(lAsinωt) is the corner function of ωt, sin(lAsinωt)
ωt) is an odd function of ωt, so is Fourier expanded. Substituting equations (6) and (7) into equation (5), get.

Expression (1) is Fourier expanded with respect to ωt, shall be.

Comparing equations (8) and (9), we get becomes.

It can be proven that B _l1 =0 holds, and B ₁ =0. Also, since (x) and g(x) are physically existing distribution shapes, equations (2) and (3) can be expressed using a sufficiently large integer N. It can be expressed as Furthermore, if |d|≪1, it can be approximated as sinld≒ld. Therefore, equation (10)
Than That is, we obtain A ₁ =K·d (K is a constant) (12).

From the above, the functions A ₁ =K·d and B ₁ =0 are established, and the output of the frequency signal component is proportional to the "shift" d. In FIG. 4, it is shown that the output is proportional to the "shift" in the vicinity of 0 positional shift.

As a means to extract the component of A ₁ sinωt (however, ω=2π) from the mark detection signal,
As is well known, there is a method of using a lock-in amplifier. In the embodiment of the present invention, the mark detection signal is used as the input of the lock-in amplifier, and the beam deflection signal is used as the external reference input of the lock-in amplifier. As a result, the lock-in amplifier outputs a voltage value of the same frequency component as the beam deflection signal, including phase information. That is, the value of A ₁ in equation (12) can be measured including its positive and negative values. The measurement results are shown in FIG.

As described above, according to the alignment method and apparatus of the present invention, it is possible to apply vibration to the electron beam projected near the mark on the sample surface and analyze the frequency components of the detection signal of reflected electrons or secondary electrons. Since the projected image and the sample are aligned, the following remarkable effects can be achieved.

The excitation state of each electromagnetic lens of the electron optical system is the same during alignment and during pattern exposure, resulting in improved productivity associated with alignment.

In positioning, the resolution of the projected image does not decrease.

It becomes easy to automate the processing of detection signals of reflected electrons or secondary electrons.

Positioning can be performed with high precision.

Note that the alignment method according to the present invention can also be applied to a scanning electron beam exposure apparatus that uses an electron beam shaped into a square or rectangle.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing a conventional electron beam optical projection mechanism, and FIG. 2 is a configuration schematic diagram showing an embodiment of an electron beam optical projection mechanism used to implement the alignment method of the present invention. , FIG. 3 is a perspective view showing the projected image of the mask pattern and the mark during alignment, and FIG. 4 shows the relationship between the amount of deviation between the projected image and the mark position and the output of the frequency detection signal component. It is an explanatory diagram. 30...Electron gun (electron beam source), 40...Mask, 42...Sample, 43...Projected image of alignment pattern, 44...Mark, 50...X deflection coil, 51...Y deflection coil , 52...detection element.

Claims (1)

[Claims] 1. A position in an electron beam exposure device that optimally aligns the imaging position of a mask pattern and the sample by detecting the relationship between the projection position of the electron beam and the mark position provided on the sample. In the alignment method, an electron beam is projected on or near the mark, the electron beam is vibrated, reflected electrons or secondary electrons from the mark and the area around the mark are detected, and the frequency components of this detection signal are detected. A positioning method in an electron beam exposure apparatus characterized by analyzing and detecting a relationship between an electron beam projection position and a mark position. 2. An electron beam source, a sample having alignment marks, an electron beam deflection mechanism that vibrates the electron beam projected onto the sample surface at a predetermined frequency, and detects reflected electrons or secondary electrons from the sample surface. What is claimed is: 1. An alignment device for an electron beam exposure apparatus, comprising: a detection element for detecting a signal from the detection element; and means for analyzing a frequency component of a detection signal from the detection element.