KR20070054019A - Method of retouching a extreme ultraviolet radiation mask using a atomic force microscopy lithography - Google Patents

Abstract

Provided are methods for modifying extreme ultraviolet masks using atomic force microscopy lithography techniques. The method includes forming a reflective multilayer thin film on a substrate and forming an absorber pattern on the multilayer thin film. Using an atomic force microscope, an electric field is applied between the probe and the multilayer thin film to form an oxide film that corrects defects in the absorber pattern. The multilayer thin film may include a capping layer formed of a semiconductor or a metal, and may form an oxide film at a desired position by oxidizing the semiconductor or metal capping layer by using the atomic force microscope.

AFM, extreme ultraviolet, reflective mask,

Description

METHOD OF RETOUCHING A EXTREME ULTRAVIOLET RADIATION MASK USING A ATOMIC FORCE MICROSCOPY LITHOGRAPHY}

1 and 2 illustrate atomic force microscopy lithography techniques.

3 and 4 illustrate one embodiment of the present invention to illustrate a method for local modification of an extreme ultraviolet mask.

5 and 6 are views showing another embodiment of the present invention to explain a wide area correction method of an extreme ultraviolet mask.

7 and 8 are graphs showing changes in reflectance of the oxide film thickness and line width of the pattern of the reflectance, respectively.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting a pattern of a mask for semiconductor manufacture, and more particularly to a method for correcting an extreme ultraviolet mask.

Lithography is a key process technology for semiconductors that forms circuit patterns by shining light on a substrate coated with a photoresist. A lithography process uses a laser as a light source, but optically as the fine line width is reduced. It is hitting the limit. Accordingly, new light sources such as extreme ultraviolet (EUV), electron beam, X-ray, and ion beam are being sought. Among them, extreme ultraviolet light and electron beam are spotlighted by the next-generation exposure technology.

Lithography processes currently in use or under development use KrF (248 nm) light sources or ArF (193 nm) light sources, and use transmissive masks in which light-shielding film patterns such as chromium are formed on a blank substrate. However, EUV lithography uses electromagnetic waves with wavelengths of up to 13.4 nm as light sources. EUV lithography techniques are reflective (or Mirror type photomask is used.

The reflective mask used in the extreme ultraviolet exposure process may be referred to as a reflective multilayer thin film mirror that enables Bragg reflection. The multilayer thin film mirror uses a laminated structure of Mo and Si layers having a large difference in optical properties such as refractive index, and a multilayer thin film using various materials to produce a multilayer thin film having better reflectivity than the Mo / Si multilayer thin film. Is making. For example, US Pat. No. 6,229,652 suggests a Mo2C / Be multilayer thin film structure, and US Pat. No. 6,228,512 presents a MoRu / Be multilayer thin film structure. An absorber pattern is formed on the wafer on the multilayer thin film to transfer the pattern onto the wafer using light reflected from the reflective mask.

Meanwhile, in forming an absorber pattern of an extreme ultraviolet mask, a lithography technique using atomic force microscopy (AFM) oxidation has been proposed to overcome the process limitations of the conventional electron beam lithography technique.

As shown in FIG. 1, a probe 14 of an atomic force microscope is placed close to a substrate on which an oxide capping layer 12 is formed on a silicon or metal substrate 10, and between the probe 14 and the substrate. When an electric field is applied in a state in which a water column 16 is formed, oxygen ions are induced to the substrate under the influence of an electric field, and then pass through the oxide capping layer 12 to the silicon or metal substrate 10. Oxygen ions that reach the substrate 10 react with silicon or metal to form an oxide film 12a as shown in FIG. 2. Oxidation using atomic force microscopy forms an absorber film on a multilayer thin film mirror, forms an oxide film that penetrates the absorber film, and then removes the oxide film to form an absorber pattern.

In the reflective mask, a defect may occur in the absorber pattern in the process of manufacturing the mask, similarly to the transmissive mask. The defects of the mask may be classified into a clear defect in which a portion of the absorber pattern should not be formed and a dark defect in which a pattern is formed in the portion where the absorber pattern should be absent. The dark defect is a method of removing a defect site using an ion beam, and the clear defect is a method of forming an absorber pattern by a method such as W (CO) ₆ FIB-CVD. However, this physical defect correction method may cause a problem that the underlying mirror is damaged by the ion beam, resulting in a new non-healing defect applied to the mask.

The present invention provides a method for modifying an extreme ultraviolet mask in which no damage is applied to a lower substrate other than a defective part.

Another technical problem to be achieved by the present invention is to provide a mask correction method that can increase the pattern uniformity of each region as well as the local defect of the mask.

In order to achieve the above technical problem, the present invention provides a method of modifying an extreme ultraviolet mask by forming an oxide film using an atomic force microscope. The method includes forming a reflective multilayer thin film on a substrate and forming an absorber pattern on the multilayer thin film. Using an atomic force microscope, an electric field is applied between the probe and the multilayer thin film to form an oxide film that corrects defects in the absorber pattern.

The multilayer thin film may include a capping layer formed of a semiconductor or a metal, and may form an oxide film at a desired position by oxidizing the semiconductor or metal capping layer by using the atomic force microscope.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed subject matter is thorough and complete, and that the spirit of the present invention to those skilled in the art will fully convey. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. In addition, where a layer is said to be "on" another layer or substrate, it may be formed directly on the other layer or substrate, or a third layer may be interposed therebetween. Portions denoted by like reference numerals denote like elements throughout the specification.

3 and 4 are views for explaining a local pattern correction method of the extreme ultraviolet mask according to the present invention.

Referring to FIG. 3, a reflective multilayer thin film 50 is formed on a substrate. The multilayer thin film 50 may be formed using a laminated structure of a Mo layer and a Si layer having a large difference in optical characteristics such as refractive index, or using a laminated structure of Mo 2 C / Be or MoRu / Be. A capping layer 52 formed of a semiconductor or a metal is formed on the multilayer thin film 50. For example, the capping layer 52 may be formed of a metal or a semiconductor such as silicon (Si), chromium (Cr), tantalum (Ta), titanium (Ti), gallium arsenide (GaAs), and aluminum (Al). An oxide capping layer 54 may be formed on the upper portion thereof to protect the lower layer.

An absorber film is formed on the capping layers 52 and 54, and the absorber film is patterned using a pattern technique such as an electron beam lithography technique to form an absorber pattern 56. The absorber pattern 56 may be formed of a tantalum (Ta) or chromium (Cr) layer, and a ruthenium (Ru) or silicon oxide layer (SiO ₂ ) buffer layer is further formed on the lower layer to remove dark defects. It may also serve to prevent damage.

At this time, a clear defect may occur in which a part 56a of the absorber pattern is not formed. The clear defect may occur in various forms such as a line break in a line-shaped pattern or a shape deformed in a complex structure.

Referring to FIG. 4, a cantilever of an atomic force microscope is positioned on an upper portion of a capping layer 52 of a desired portion, and a voltage is applied to the probe 58 while a water column is formed. At this time, the oxygen ions pass through the oxide capping layer 54 by the electric field applied between the probe 58 and the capping layer 52, and the oxidation reaction occurs. As a result, an oxide film 60 having a predetermined thickness and width is formed on the capping layer 52.

Using this method, it is possible to form a fine oxide film 60 of about 20 nm by adjusting the voltage, the oxide film 60 serves to correct the defect of the absorber pattern 56 by reducing the reflectance of the exposure light. . Furthermore, since the thickness and line width of the oxide film 60 can be arbitrarily adjusted, the oxide film 60 is formed in a portion of the mask where the dose reduction of the reflected light is required to reduce the reflectance, thereby reducing the dose of reflected light for each region. You can get different effects.

5 and 6 are views for explaining a method for correcting a wide area of an extreme ultraviolet mask that can improve the uniformity of a pattern formed on a wafer by using an effect of differently setting doses of reflected light.

Referring to FIG. 5, similarly to the first embodiment, a capping layer 52, an oxide capping layer 54, and an absorber pattern 156 are formed on the multilayer thin film 50. The wide area correction method of the mask can be effectively applied to an exposure mask in which the same pattern is formed at a predetermined pitch. Although the absorber pattern 156 is formed on the mask at the same line width and the same pitch in the inspection process after the absorber pattern 156 is formed, it may have scattering for each region. For example, in some regions, the line width of the absorber pattern 156 is thinner than the designed line width so that not only the line width of the line pattern transferred to the wafer is thinned but also the dose of reflected light increases proportionally to be transferred to the wafer. The line width can be even thinner. This results in an increase in the area-by-region dispersion of the pattern line width formed on the wafer, causing a problem of property dispersion or increase. In addition, when the pitch and pattern density of the pattern for each region are different, the dose of light reflected in a region having a low pattern density is high, and the dose of light reflected in a region having a high pattern density is relatively low. Even when a pattern of the same line width is transferred onto the wafer, the line width varies depending on the dose of light to be irradiated. For this reason, the line width is reduced in the region having a low pattern density because of high dose of light, and the line width is increased in the region having high pattern density because of low dose of light. For this reason, a problem may arise that the pattern designed on the mask is not transferred identically on the wafer. The change in line width according to the dose of light may be solved through design correction by predicting it to some extent, but it is difficult to accurately predict it before performing the actual exposure process.

Referring to FIG. 6, according to the present invention, an oxide film is formed on a reflective mask using atomic force microscopy, thereby reducing the reflectance of the reflected light to lower the dose of light irradiated onto the wafer. That is, the oxide film 160 is formed in a region where the absorber pattern 156 is thinner than the required line width or in a region having a low pattern density to lower the reflectance. As a result, light having a lower dose is irradiated to a region on the wafer to which the region where the oxide film 160 is formed is transferred, and light of a normal dose is irradiated to a region on the wafer where the region where the oxide film 160 is not formed is transferred. .

As shown in Fig. 7, the dose of exposure light irradiated on the wafer affects the line width of the pattern. For example, in the positive exposure process of the line-space pattern, the width of the space increases in proportion to the dose of the exposure light, and the width of the space increases as the dose of the exposure light increases. In the reflective mask, the dose of exposure light may be changed according to the reflectance of the light reflected by the mask. Therefore, as shown in FIG. 8, as the reflectance of the reflective mask is higher, the spacer width between the linear patterns formed on the wafer increases, and when the reflectance increases by about 1%, the spacer width increases by about 1.42 nm. It can be seen that. In this case, since the dose of light irradiated onto the wafer can be changed by adjusting the reflectance, and the line width of the pattern can be adjusted by adjusting the dose, the portion where the line width of the absorber pattern 156 is thinned is transferred to the pattern. The line width is further increased, and the dose of exposure light irradiated onto the wafer is reduced in scattering due to the pattern density, thereby correcting pattern defects.

As shown in Fig. 8, the reflectance is changed depending on the thickness of the oxide film. Since the thickness of the oxide film can be adjusted by the voltage applied between the probe and the substrate, it is easy to adjust the oxide film thickness to obtain a desired reflectance. Therefore, the wide area correction of the reflective exposure mask may be possible by forming an oxide film having a thickness suitable for correcting the scattering of patterns formed on the wafer.

As described above, according to the present invention, when the pattern is not formed at the portion where the absorber pattern is to be formed, the pattern may be modified by reducing the reflectance of light by forming an oxide film.

In addition, when the absorber pattern is scattered in the line width due to some cause, an oxide film is formed in the region where the line width of the pattern is thinned to decrease the reflectance, thereby increasing the line width of the pattern transferred to the wafer, thereby reducing the spread.

Furthermore, since an oxide film is formed on the mask to adjust the reflectance to prevent the dose deviation of the light irradiated onto the wafer according to the pattern density, scattering and pattern deformation according to the pattern density can be reduced.

Claims (6)

Forming a reflective multilayer thin film on the substrate; Forming an absorber pattern on the multilayer thin film; Applying an electric field between the probe and the multilayer thin film using an atomic force microscope to form an oxide film for correcting defects in the absorber pattern. The method according to claim 1, The multilayer thin film includes a semiconductor or metal capping layer, And oxidizing the semiconductor or metal capping layer using the atomic force microscope to form an oxide film. The method according to claim 1, The method of modifying the extreme ultraviolet mask, characterized in that for determining the thickness and width of the oxide film by adjusting the voltage applied between the probe and the multilayer thin film. The method according to claim 1, And forming the oxide film in a predetermined region of the multilayer thin film to correct partial defects in the absorber pattern. The method according to claim 1, And forming the oxide film in a predetermined region of the multilayer thin film to reduce the reflectance of the region where the oxide film is formed. The method according to claim 5, The absorber pattern includes a line pattern disposed at a predetermined pitch, and the oxide film is formed between the line patterns constituting the absorber pattern to reduce the reflectance of the extreme ultraviolet mask.

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