JPH03252508A - Alignment method - Google Patents

Abstract

PURPOSE:To improve the SN ratio of an alignment signal and decrease the half-value width and to improve the alignment accuracy by providing a light fading material layer as a filter in front of a photodetector. CONSTITUTION:An He-Ne laser light source 3 is provided above a base body which has a projection type alignment mark 2 formed on a substrate 1 and the photodetector 4 for detecting reflected light is provided nearby the light source 3. Then the light fading filter 5 which has the light fading material layer is set on the optical path extending from the mark 2 to the photodetector 4. A light fading compound such as a photochromic compound which absorbs and fades alignment light is used for the light fading material layer. An inorganic photochromic compound such as Hg3S2I2 and TiO2 or biimidazole, nitron or spiropyrane organic photochromic compound, e.g. spiro benzothiopyran coloring matter is used as the photochromic compound by being applied on a glass plate.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alignment method for aligning a mask with high precision in a photolithography process in the field of manufacturing semiconductor devices.

[Summary of the invention]

The present invention provides an alignment method in which a photodetector detects alignment light reflected from an alignment mark formed on a substrate to align a mask, and the present invention provides a photobleaching material layer sensitive to the wavelength region of the alignment light. By receiving the alignment light through the optical fiber, the SN ratio of the alignment signal generated according to the intensity of the received light is improved.

[Conventional technology]

In recent years, as semiconductor devices have become more highly integrated, design rules have become increasingly finer, and along with this, there has been a demand for improved accuracy in mask positioning, that is, alignment.

Generally, alignment is performed by irradiating an alignment mark formed on a wafer with an alignment light beam and detecting the reflected light with a photodetector. The light sources for the alignment light at this time include g-line (wavelength 436 nm), h-line (wavelength 405 nm), i
A light source common to the exposure light source for photolithography, such as a line (wavelength: 365 nm), or a light source different from the exposure light source, such as a He-Ne laser (wavelength: 632.8 nm), is used. The alignment accuracy requires 1/1 of the design rule.
Approximately 3 to 1/4 degree of severity is required. Therefore, S
It is extremely important to sensitively detect alignment signals with a high N ratio.

Generally, the intensity distribution of alignment light (reflected light) detected by a photodetector shows a pattern as shown in FIG. In the figure, the vertical axis represents the light intensity, and the horizontal axis represents the angle of incidence of the alignment light on the photodetector (all scales are arbitrary).The main peak in the center is the detected signal component corresponding to the light reflected from the alignment mark. , that is, an alignment signal. As an alignment mark, a diffraction grating pattern is usually used, such as several fine patterns (for example, 7 squares) arranged in a line at equal intervals, so what the main peak above actually represents is This is the synthesis of diffracted light by the pattern. Moreover, the small peaks appearing on both sides are noise components caused by diffused reflection from the periphery of the alignment mark. Here, if the peak value of the noise component does not exceed 50% of the peak value of the alignment signal, detection can be performed with practical accuracy.

[Problem to be solved by the invention]

However, in the conventional alignment-7 method,
The problem is that the signal-to-noise ratio decreases due to the condition of the underlying surface of the alignment mark circumference 4υ and the height of the alignment mark itself.

For example, when detecting alignment marks on a substrate with an aluminum film deposited on the entire surface as a wiring layer, noise components increase due to diffused reflection caused by the uneven surface of the aluminum film, and the target alignment signal cannot be detected. is relatively easy to weaken.

Further, since the alignment mark is formed at the same time as patterning the material layer for forming each part of the device, the height may be insufficient depending on the thickness of the material layer. In such a case, the intensity of the diffracted light from the alignment mark becomes weak, so the SN
In addition to the decrease in the ratio, the half-width of the main peak also increases, resulting in a decrease in detection accuracy.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems and improve alignment accuracy by improving the S/N ratio of an alignment signal and decreasing the half-width.

[Means to solve the problem]

The inventor of the present invention conducted studies to achieve the above-mentioned object, and found that a photobleachable compound that fades when irradiated with alignment light is held on a suitable base material, and this is placed in front of the light receiving part of a photodetector. The inventors discovered that the photobleachable compound fades in color depending on the intensity of the alignment light, and thus the above substrate can function as a kind of noise-cutting filter, leading to the completion of the present invention.

That is, in the alignment method according to the present invention, a photobleaching material layer sensitive to the wavelength region of the alignment light is disposed midway on the optical path from the alignment mark formed on the substrate to the photodetector, and the alignment light is It is characterized by detecting.

In the present invention, a photobleaching material layer is provided as a filter before the photodetector, and this photobleaching material layer uses a photobleaching compound that absorbs alignment light and fades the color. Here, fading means becoming optically transparent to alignment light. Therefore, photobleachable compounds are not limited to those whose original absorption spectrum exists in the visible light range and whose color fading can be confirmed with the naked eye;
It may be such that the absorption maximum wavelength λ1.8 is shifted due to absorption of the alignment light. However, the former is widely known as a so-called photochromic compound and is considered to be particularly practical.

The photochromic compound is Hg5Silz.

Inorganic photochromic compounds such as TiOt+ZnS, biimidazolyl, nitrone, spiropyran, dihydroindolizine, and fulgide.

Organic photochromic compounds such as aromatic polycyclic compounds, thioindigo compounds, viologen compounds, etc. are known, but among these, one that is sensitive to the wavelength range of the alignment light used and that fades should be appropriately selected and used. . It is practically preferable that the light transmittance of the photobleaching material layer increases by about 30% due to color fading.

The photobleaching material layer is formed by holding the above photobleaching compound on a suitable base material. Such a base material may be in various forms, such as a rigid substrate or a flexible film, but it must be optically transparent to the alignment light used. For example, when ultraviolet light is used as alignment light, quartz, borosilicate glass,
Acrylic resin, polystyrene, etc. are used. Furthermore, in order to retain the photobleaching compound in the base material, it may be dispersed in the base material, or it may be coated or vapor-deposited on the base material.

It may be formed into a thin film by a method such as sputtering.

In the present invention, especially when a photochromic compound is used, since photochromism is a reversible reaction, the photobleaching material layer can be used reversibly within a range where reliability and durability are guaranteed. In this case, heating or irradiation with light at a wavelength different from that of the alignment light makes it possible to quickly regenerate the faded state to the colored state.

[Effect]

The present invention applies the photobleaching phenomenon of a photobleaching material to an optical filter. Here, the degree of color fading of the photobleaching material depends on the amount of incident light.

Therefore, for example, when light with a certain intensity distribution is incident on a photobleaching material layer containing a photochromic compound,
In a region where the amount of incident light is large, the degree of fading within a unit time is large, and the transmittance of the photobleaching material layer in that region can be increased. However, since the photochromic compound does not fade much in areas where the amount of incident light is small, it is not possible to sufficiently increase the transmittance of the photobleaching material layer.

When such a photobleaching material layer is applied to alignment, when a strong reflected light component from the alignment mark and a weak diffusely reflected light component from the peripheral area are simultaneously incident, the photobleaching material layer selectively transmits the reflected light component and diffuses the reflected light component. It will function as a filter to block out the components. therefore,
The intensity distribution pattern of light detected by the photodetector has a steep main peak and a noise component suppressed to a low level, as shown in FIG. 4, for example. This greatly improves alignment accuracy.

Note that the technology for using a photobleachable material layer in the field of manufacturing semiconductor devices is disclosed in, for example, Japanese Patent Application Laid-Open No. 63-272.
As described in No. 030, this technique aims to improve optical contrast by performing exposure through a photobleaching material layer when transferring a mask pattern to a photoresist, and the purpose of the present invention is to and have different effects.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

This example uses a He-Ne laser (wavelength: 632.8 nm) as the alignment light and a photobleaching filter made of a glass plate coated with a spirobenzothiobilane dye as the photobleaching material layer.

The spirobenzothiobilane dye used in this example was 6
-Nitro-1°,3',3°-trimethylspiro[2H
-1-benzothiobilane-2,2''-indoline 1, which is a colorless spiropyran type and a colored one (maximum absorption wavelength λwrsx) by heating or light irradiation, as shown by the following formula.
It is a photochromic compound that undergoes a reversible structural change with the merocyanine type (= 680 nm).

(Margin below) Here, the change from spiropyran type to merocyanine type,
That is, color development progresses by ultraviolet irradiation (360 nm). The opposite change, that is, fading, can be achieved by heating to about 80 to 100°C, or by utilizing the fact that the absorption spectrum of merocyanine-type compounds exists broadly from around 550 nm to the near-infrared region.
The progress can be made by irradiating light with a laser or the like.

In this example, the initial state of the photobleaching material layer corresponds to the merocyanine type, and the state where the color fades due to absorption of alignment light corresponds to the spiropyran type.

To create a photobleaching filter using the spirobenzothiopyran dye, a solution of the dye dissolved in a cyclohexanone-tetrahydrofuran mixed solvent was applied onto a quartz substrate and dried.

Thereafter, the entire surface was irradiated with ultraviolet light to develop a green color.

This filter was applied to the actual alignment. 1st
As shown in the figure, He-Ne was placed above the substrate (1) on which convex alignment marks (2) were formed.
A laser light source (3) is provided, and the He-
In a device configuration in which a photodetector (4) for detecting reflected light is disposed near the Ne laser light source (3), a light beam is placed in the middle of the optical path from the alignment mark (2) to the photodetector (4). The photobleaching filter (5) prepared as described above was set. When irradiated with He-Ne laser in this state, the color fading progressed most strongly in the area on the photobleaching filter (5) where the incident light intensity was highest, and the light transmittance increased significantly, but other areas The degree of discoloration was small. As a result, the apparent contrast of the transmitted light increases, and the alignment signal generated based on the detection result of the photodetector (4) has a steep S
A pattern with a high N ratio was shown. The above photobleaching filter (
5) returned to its original hue by batch irradiation with ultraviolet rays using a high-pressure mercury lamp.

By the way, in the present invention, continuous processing and repeated use can be made possible by devising the form and installation mode of the photobleaching material layer.

For example, the photobleaching filter (11) shown in Fig. 2 shows a method of continuously and repeatedly using a used part while regenerating it by irradiating it with ultraviolet rays.
Appropriate guide members and transport mechanisms (none of which are shown)
), etc., between the pair of reproduction mechanisms (12a) and (12b) disposed at both ends of the photobleaching filter (11) along the direction perpendicular to the optical path of the alignment light (direction of arrow X in the figure). It is held in a state where it can reciprocate. Now, when the photobleaching filter (11) is at the position shown by the solid line, the right end in the figure is on the optical path of the alignment light, and fading occurs here along with the alignment work. Thereafter, this photobleaching filter (11) is moved to the position shown by the dotted line in the figure and the used right end is stored inside the regeneration mechanism (12b), where ultraviolet irradiation is performed using a high-pressure mercury lamp or the like. , the colored state is restored. Similar operations are performed alternately within the regeneration mechanisms (12a) and (12b) every time one alignment operation is completed, making continuous operation possible and making it possible to repeatedly use the photobleaching filter (11). Become.

Alternatively, as shown in FIG. 3, a flexible film made of polystyrene or the like is used as a base material for the photobleaching material layer to constitute a photobleaching tape (21), and a suitable guide member (21) is constructed.
2) and the side of the first recycler (23) may be used to sequentially remove the used parts from the optical path while the machine is running.In this case as well, the used photofading tape (21) is irradiated with ultraviolet light while being rewound. If you do this, you can reuse it.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, the rise of the alignment signal and the S/N ratio are significantly improved due to the filter effect of the photobleaching material layer, so that extremely sensitive and highly accurate alignment is possible. Therefore, if the present invention is applied to, for example, the manufacture of highly integrated semiconductor devices, reliability, productivity, yield, etc. will be significantly improved.

1

[Brief explanation of drawings]

FIG. 1 is a schematic diagram explaining the alignment method of the present invention,
FIG. 2 is a schematic diagram illustrating an example of how the photobleaching material layer can be recycled, and FIG. 3 is a schematic diagram illustrating another example of how the photobleaching material layer can be recycled. FIG. 4 is a graph showing the intensity distribution of alignment light in the alignment method of the present invention, and FIG. 5 is a graph showing the intensity distribution of alignment light in the conventional alignment method.・・・ Photobleaching tape

Claims (1)

[Claims] An alignment characterized in that a photobleaching material layer sensitive to the wavelength region of the alignment light is disposed midway on the optical path from the alignment mark formed on the substrate to the photodetector to detect the alignment destination. Method.