JPH0820212B2 - Positioning method for fine pattern - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] When aligning a mask with a substrate to be processed, a laser for converging a Fresnel zone plate to irradiate the substrate to be processed is used as a method of improving measurement accuracy of diffracted light used for alignment. A method in which the wavelength of light is changed and only light of the corresponding wavelength is detected.

[Industrial applications]

The present invention relates to a fine pattern alignment method with improved measurement accuracy.

In order to meet the demand for information processing technology that processes a large amount of information at high speed, semiconductor devices, which are the main components of information processing devices, are being integrated.

In other words, although the maximum area of the semiconductor chip remains almost unchanged, the number of elements that make up it is increasing.
In addition, high integration is progressing from LSI to VLSI.

Here, the integration is performed by miniaturizing the unit element, but this miniaturization largely depends on the progress of the photolithography technology (photolithography or electron beam lithography) together with the semiconductor layer forming technology, the thin film forming technology and the like.

Here, in the photo-etching technique, a substrate to be processed is coated with a photosensitive resist, which is irradiated with light or ionizing radiation to be selectively exposed. The exposed portion and the non-exposed portion are exposed to a developing solution. A resist pattern is formed by utilizing the difference in solubility.

Then, by using this resist pattern as a mask, dry etching or wet etching is performed to selectively etch the substrate to be processed to form a fine pattern.

Now, as semiconductor integrated circuits become highly integrated, it is necessary to form a so-called sub-micron pattern having a pattern width of 1 μm or less. However, in the conventional pattern formation method using ultraviolet rays as a light source, the wavelength is limited to 1 μm. It is limited to the above line width, and it is difficult to form a fine pattern below this.

On the other hand, the wavelength of the electron beam is 0.1 Å depending on the acceleration voltage.
Since it is about 4 digits or more shorter than the wavelength of light, a large resolving power can be expected, and a pattern with a width of 0.1 μm can be formed.

However, this method requires a large amount of time to draw a pattern by sequentially scanning an electron beam. "Since electrons have a negative charge, charge accumulation occurs on the resist surface,
Therefore, there is a problem that the position of the pattern is displaced.

In addition, the photo-etching technology that uses X-rays has a wavelength of 5 to 15Å
This is a method of exposing the resist through a mask by using soft X-rays instead of light, and it is possible to expose the entire area at once compared to electron beam exposure, the exposure time is short, and electron scattering like electron beams occurs. It has various advantages such that a fine pattern with good sharpness can be formed without using a special vacuum.

However, in this case, a mask is required as in the case of ultraviolet exposure, and it is necessary to perform highly accurate mask alignment with a tolerance of submicron or less.

The present invention is not limited to such X-ray exposure,
The present invention relates to an improvement in a fine pattern alignment method that requires high accuracy.

[Conventional technology]

In the case of forming a fine three-dimensional circuit by repeating thin film formation and photolithography a plurality of times on a substrate to be processed as in the VLSI manufacturing process, it is necessary to perform mask alignment with the substrate with high accuracy.

As a method, a plurality of Linear-Fresnel-zone-plates are abbreviated as LFZ on the mask.
P) on the other hand, while a diffraction grating is patterned on the substrate to be processed, the FLZP is irradiated with laser light and condensed by diffraction to form a bright line, and this bright line is applied to the diffraction grating on the substrate to be processed. A method of diffracting light, detecting the diffracted light, and aligning the position is known.

(Alignment mechanism for X-ray lithography "Optical al
ignment system for submicron x-ray lithography "BF
ay, J.Trotel, and A.Frichet J.Vac.Sci.Technol.16
(6), Nov / Dec.1979) FIG. 1 is a perspective view of a mask alignment mechanism to which the present invention is applied, and FIG. 2 is a perspective view showing a method of aligning an LFZP and a diffraction grating. Since it is the same as the conventional method, the alignment method will be described with reference to this drawing.

In FIG. 1, a fine pattern 2 to be transferred, such as an electrode or a conductor pattern, is formed on a mask 1 made of a material such as boron nitride (BN) or a polyimide thin film having a thickness of several μm that allows X-rays to pass therethrough. Multiple (three in this example) LFZP3 are made of gold (Au) as in the fine pattern using the gap.
It is made by a vacuum deposition method, a sputtering method, or the like using a metal thin film that absorbs X-rays.

A diffraction grating 5 is formed on the substrate 4 to be processed. For example, when the substrate 4 to be processed is made of a silicon (Si) wafer, the diffraction grating etches silicon dioxide (SiO ₂ ) formed on the substrate. It is made by.

FIG. 2 is an enlarged view of the LFZP3 corresponding to a laser beam having a wavelength of 7800Å and the diffraction grating 5. The LFZP3 is formed by etching the Au vapor-deposited film and the pattern width of the central portion 6 is as wide as about 3 μm. The width is narrow and the outermost part 7 is formed as narrow as about 0.5 μm, while the Fresnel zone having a long length of about 150 μm is formed.

The light projected on this is diffracted and condensed as shown by a broken line 8 to form a long and narrow bright line.

On the other hand, in this example, on the substrate 4 to be processed, a diffraction grating 5 is formed which is composed of spots 9 having a size of 2 μm square and linearly arranged at intervals of about 3 μm.

Then, as shown in FIG. 1, the laser light 10 is projected on the LFZP 3 by the mirror 11, and the laser light 10 is condensed by diffraction to become a bright line. This bright line is the diffraction grating 5 of the substrate 4 to be processed. When the light is projected on, the light is diffracted, and the reflected light again passes through the LFZP3, is reflected by the mirror 12, and is detected by the photodetector 13.

Therefore, in order to align the mask, the substrate 4 to be processed is moved and a plurality of (three in this case) photodetectors 13 are attached to the diffraction grating 5.
It suffices that the diffracted light in 1 can be detected with the maximum sensitivity.

Here, the reason for providing three or more combinations of the LFZP 3 and the diffraction grating 5 is that the rotation of the substrate 4 to be processed with respect to the mask 1 can be corrected by this.

However, since the laser light 10 used for the conventional alignment is projected from the same light source, the wavelengths thereof are all the same, so that the scattered light from the mask 1 or the substrate 4 to be processed corresponds to the light detection. There was a problem that the light was incident on the photodetectors other than the device 13 and the S / N of the signal was significantly lowered.

[Problems to be solved by the invention]

As described above, when alignment of the mask with respect to the substrate to be processed is performed by using a combination of a plurality of LFZPs and a diffraction grating, conventionally, since the wavelength of the laser light is the same, the scattered light from the mask or the substrate to be processed is Is incident on a photodetector other than the corresponding photodetector, and the S / N of the signal is significantly reduced, which is a problem.

[Means for solving problems]

The above problem is caused by irradiating a mask provided with a plurality of Fresnel zone plates with laser light, projecting each bright line condensed by the plates onto a corresponding diffraction grating provided on the substrate to be processed, and diffracting the diffraction lines. In detecting the light and performing the alignment, as the laser light projected on the diffraction grating, the light of the different wavelength is used, and the alignment method of the fine pattern detects only the diffracted light of the corresponding wavelength. Can be resolved.

[Action]

The present invention is a method for improving the S / N of the signal incident on the photodetector by changing the wavelengths of the laser light 10 projected on the plurality of diffraction gratings 5 formed on the substrate 4 to be processed. By providing a filter for each of the photodetectors 13 corresponding to the plurality of diffraction gratings 5, only the corresponding laser beam can be detected, thereby improving the S / N.

〔Example〕

FIG. 1 is a perspective view of a mask aligning mechanism to which the present invention is applied. The difference from the conventional method is that the wavelength of the laser light 10 is different, and the corresponding LFZP3 and diffraction grating 5 correspond to the wavelength. The pitch is to be formed.

Further, the photodetector 13 corresponding to this must also be provided with an interference filter that selectively passes only light of that wavelength.

In the case of this embodiment, the center wavelength is 7800Å as three light sources.
And used 8300Å and 13000Å laser diodes.

As a result of the measurement, since the S / N is low in the past, if minute dust is present on the mask 1 and the substrate 4 to be processed, it is greatly affected, and it is difficult to perform simultaneous alignment of three points. The laser light 10 projected onto the LFZP3 had to be narrowed so as to enter the Fresnel zone in order to prevent unnecessary scattering at, but the implementation of the present invention facilitates the simultaneous alignment of three points, and the diameter of the laser light is Even if it exceeds the Fresnel zone, there is no hindrance, which greatly improves work efficiency.

Although it seems to be difficult to use different laser light sources, even if laser diodes with the same center wavelength are used and the injection current is changed to oscillate in different wavelength modes, light with different wavelengths will be emitted. Can be obtained.

〔The invention's effect〕

As described above, the practice of the present invention facilitates the alignment of the mask, which requires accuracy of sub-micron or less, and thus can significantly improve the work efficiency.

[Brief description of drawings]

FIG. 1 is a perspective view of a mask alignment mechanism to which the present invention is applied, and FIG. 2 is a relational diagram between LFZP on a mask and a diffraction grating on a substrate to be processed. In the figure, 1 is a mask, 2 is a fine pattern, 3 is LFZP, 4 is a substrate to be processed, 5 is a diffraction grating, 10 is a laser beam, 11 and 12 are mirrors, 1
3 is a photodetector.

Claims (1)

[Claims] 1. A laser beam is applied to a mask having a plurality of Fresnel zone plates, and the respective bright lines collected by the plates are projected onto a corresponding diffraction grating provided on a substrate to be processed to be diffracted. In detecting the diffracted light and performing alignment, light of different wavelengths is used as each laser light projected on the diffraction grating, and only the diffracted light of the corresponding wavelength is detected. Pattern alignment method.