KR101676514B1 - Phase shift mask for extream ultra-violet lithography using single-layered absorber thin film - Google Patents

Abstract

A phase inversion mask for extreme ultraviolet exposure process using a single layer absorber thin film is provided. The phase shift mask comprising: a substrate; A reflective layer disposed on the substrate and composed of a multilayer thin film that reflects extreme ultraviolet rays; And an absorber layer comprising a patterned monolayer film positioned on the reflective layer, wherein the absorber layer has a reflectance of 5 to 10% with respect to extreme ultraviolet light, and the extreme ultraviolet light reflected from the absorber layer is an extreme ultraviolet light And has a phase difference of 180 +/- 15 degrees. According to this, it is possible to simplify the mask making process, to obtain an image with high contrast ratio, and to secure high uniformity of the threshold value even for a fine pattern having a narrow line width, thereby improving the process yield.

Description

[0001] The present invention relates to a phase shift mask for extreme ultraviolet exposure using a single-layer absorber thin film,

The present invention relates to a mask for an exposure process, and more particularly, to a phase inversion mask for an extreme ultraviolet exposure process using an absorber layer composed of a single layer thin film.

EUV lithography (EUVL), unlike existing techniques using G-line (436 nm), I-line (365 nm), KrF (248 nm) or ArF (193 nm) As a technology that uses light of a very short wavelength of 22 nm or less as a key process technology for developing a semiconductor device having a line width of 22 nm or less.

Since the EUV exposure technique uses high energy light, a conventional transmission type exposure method can not be applied, and a reflective mask is used to form a pattern on the wafer. In this case, for efficient use of the reflected light, interference between the incident light and the reflected light should be prevented. For this, the incident light is incident at a constant incident angle, not perpendicular to the mask. The angle of incidence differs depending on the equipment configuration, but is generally inclined by 6 ° with respect to the axis perpendicular to the mask surface, and can be adjusted by the numerical aperture change of the optical system. A portion of the obliquely incident light is reflected in the reflective region of the exposure mask and a portion is absorbed in the absorption region of the exposure mask to form a uniform pattern on the wafer.

However, in the EUV exposure process of irradiating the incidence light obliquely, a physical phenomenon called a shadowing effect is generated, and information of light reflected from the mask is distorted to generate a pattern shift and a horizontal-vertical threshold bias (HV CD bias) and the like.

In the case of a conventional general EUV mask, a mask having a structure with a high absorption layer thickness (corresponding to the height of the absorption layer) is used to maximize the contrast ratio between the reflection area and the absorption area to increase the image resolution. For example, in the case of tantalum nitride (TaN) used as a conventional absorbing layer material, the minimum thickness of the absorbing layer required to satisfy a reflectance of less than 0.5% (contrast ratio of 100: 1 or more) is 70 nm.

However, in the case of a mask having a thick absorber layer, an increased shadow effect is caused by an increased thickness, and as a result, the CD error increases, and thus patterning becomes impossible for a line width of 20 nm or less.

For this reason, a phase shift mask (PSM) has been researched and developed to secure high image resolution even at a low thickness. To date, phase inversion masks have been used to control the phase shift and reflectivity in the absorption region of the mask A multi-layer thin film made of two or more materials is used.

1 is a perspective view showing the structure of a conventional phase inversion mask.

Referring to FIG. 1, a conventional phase inversion mask has a structure in which a reflective layer 12, a capping layer 14, a phase inversion layer 20, and an absorbing layer 30 are sequentially formed on a substrate 10.

Extreme ultraviolet rays incident on the mask are reflected by the Bragg reflection in the reflection layer 12 composed of a multilayer thin film and absorbed in the absorption layer 30 to print the mask pattern on the wafer. At this time, the light not absorbed by the absorptive layer 30 is inverted in phase in the phase inversion layer 20, and thereby the image resolution is ensured.

That is, the conventional phase inversion mask has a disadvantage in that at least two kinds of materials must be deposited on the portion corresponding to the absorption region (including the absorption layer 30 and the phase inversion layer 20) And the phase is easily changed, it is difficult to precisely control the deposition process. Further, when dry etching is performed to pattern the multilayer thin film, the patterning may not be easy depending on the etching selection ratio of the material for each layer, and there is a problem that the width of the etching gas selection becomes narrow.

Thus, while simplifying the process, it exhibits high image resolution even at a thickness lower than that of conventional tantalum nitride-based materials, and minimizes the horizontal-vertical threshold number bias on the wafer, in particular, by reducing the pattern distortion occurring in a mask pattern with narrow line width A mask for an EUV exposure process is required.

Korean Patent No. 10-0879139 Korean Patent No. 10-1054746

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above-mentioned problems, and it is an object of the present invention to provide an ultraviolet ray exposure process capable of forming a single layer thin film using a material having suitable optical properties, Phase inversion mask.

According to an aspect of the present invention, there is provided a phase reversal mask for an extreme ultraviolet exposure process.

The phase shift mask comprising: a substrate; A reflective layer disposed on the substrate and composed of a multilayer thin film that reflects extreme ultraviolet rays; And an absorber layer comprising a patterned monolayer film positioned on the reflective layer, wherein the absorber layer has a reflectance of 5 to 10% with respect to extreme ultraviolet light, and the extreme ultraviolet light reflected from the absorber layer is an extreme ultraviolet light And has a phase difference of 180 +/- 15 degrees.

Wherein the absorber layer comprises _{PdO, PdO 2, Pd 2 O} 3, RhO, RhO 2, Rh 2 O 3, Tc 2 O 7, Nb 2 O 5, OsO 2, Os 2 O 3, ReO 2, ReO 3, Re 2 O ₅ , Re ₂ O ₇ , WO ₂ , WO ₃ , W ₂ O ₃ , VO ₂ F, V ₂ O ₅ , MnSO ₄ , CrN, TaBON, IrCl ₂ and IrO ₂ .

The absorber layer may be formed to a thickness of 40 nm or less, preferably 10 nm to 30 nm.

The pattern of the absorbent layer may have a half pitch of 22 nm or less.

The extreme ultraviolet ray may have a wavelength selected from the range of 10 nm to 20 nm, and preferably have a wavelength of 13.5 nm.

The phase shift mask may further include a capping layer disposed between the reflection layer and the absorption layer and covering the surface of the reflection layer.

INDUSTRIAL APPLICABILITY As described above, according to the present invention, it is possible to simplify the mask fabrication process and obtain a high contrast ratio image by forming an absorbing layer having appropriate reflectivity and phase difference from a single layer thin film.

In addition, since the absorber layer is formed using a single absorber, it is possible to realize an absorber layer structure having a very low thickness, thereby minimizing the shadow effect and ensuring high uniformity of the threshold value even for a fine pattern having a narrow line width. Can be improved.

However, the effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned can be clearly understood by those skilled in the art from the following description.

1 is a perspective view showing the structure of a conventional phase inversion mask.
2 is a perspective view showing a phase inversion mask for an EUV exposure process according to an embodiment of the present invention.
3 is a graph showing the reflectivity and the phase difference of the IrO ₂ absorption layer measured according to the thickness of the absorption layer.
Figures 4A and 4B illustrate the results of a < _{RTI ID =} 4A) and HVM (FIG. 4B), respectively, for the line width of the absorption layer and the TaN absorption layer.
Figures 5a and 5b illustrate the results of a < _{RTI ID =} 5A) and the HVM (FIG. 5B) for the line width of the absorption layer and the TaN absorption layer, respectively.
Figs. 6 to 8 are graphs comparing the contrast ratio of linewidths with respect to the absorption layer and the TaN absorption layer made of the materials shown in Table 1. Fig.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. It is to be understood, however, that the present invention is not limited to the embodiments described herein but may be embodied in other forms and includes all equivalents and alternatives falling within the spirit and scope of the present invention.

When a layer is referred to herein as being "on" another layer or substrate, it may be formed directly on another layer or substrate, or a third layer may be interposed therebetween. In the present specification, directional expressions of the upper side, upper side, upper side, and the like can be understood as meaning lower, lower, lower, and the like according to the standard. That is, the expression of the spatial direction should be understood in the relative direction and should not be construed as limiting in the absolute direction.

In the drawings, the thicknesses of the layers and regions may be exaggerated or omitted for the sake of clarity. Like reference numerals designate like elements throughout the specification.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

2 is a perspective view showing a phase inversion mask for an EUV exposure process according to an embodiment of the present invention.

2, the phase shift mask according to the present embodiment has a structure in which a reflection layer 12, a capping layer 14, and an absorption layer 40 are sequentially formed on a substrate 20.

The substrate 10 serves to support the mask structure and may be made of a material having a low coefficient of thermal expansion such as glass.

The reflective layer 12 is formed of a multilayer thin film that reflects incident extreme ultraviolet rays using Bragg reflection. For example, the reflective layer 12 may be a different layer such as Mo / Si, Mo / Be, MoRu / Be, or Ru / ) Material can be formed by repeated lamination.

The capping layer 14 may be formed using a material such as Ru, Mo, C, or Si as a layer that covers the surface of the reflective layer 12 and prevents oxidation and impurity penetration of the reflective layer 12. However, the capping layer 14 may be omitted if necessary.

On the other hand, the absorbing layer 40 is an absorbing extreme ultraviolet absorbing layer which is located on the reflective layer 12 (when it includes the capping layer 14, it is located on the capping layer 14) Layer thin film.

The absorption layer 40 is patterned into a predetermined shape so that a part of the surface of the reflection layer 12 is exposed to the light source and the light is absorbed by the absorption layer 40 and the light reflected from the reflection layer 12, The pattern is printed.

At this time, the absorption layer 40 is formed of a single layer thin film using a single material, unlike the light absorption region of the conventional mask structure.

The absorbing layer 40 has a reflectivity of 5 to 10% with respect to the extreme ultraviolet ray and the extreme ultraviolet ray reflected from the absorbing layer 40 is 180 ± 15 ° (that is, 165 To < RTI ID = 0.0 > 195). ≪ / RTI >

That is, in the conventional phase shift mask, the absorption region is formed in the form of a multilayer thin film using two or more materials in order to satisfy the out of phase condition. However, in the case of the present invention, the optical characteristics (reflectivity and phase difference) The absorption layer is formed in the form of a single layer thin film using a single absorber.

The refractive index (n) of the extreme ultraviolet region can be expressed by n = 1 -? + I? (?: Refraction index or refraction index,?: Extinction coefficient). Since the absorption coefficient of the absorber is directly proportional to the extinction coefficient Materials with high extinction coefficients can effectively absorb extreme ultraviolet radiation at lower thicknesses. In addition, the phase of the light is transited while the extreme ultraviolet ray passes through the absorber medium. The contrast ratio is highest at a thickness where the phase difference between the light reflection area and the light absorption area becomes near 180 °, But it is in the form of a fluctuation in a half wavelength period of the light source and reaches a saturation state.

The phase difference ?? can be expressed by ?? = (2 ?? / ??) *? R, where? R is the distance at which the light propagates in the medium, i.e., the thickness of the absorption layer, lambda denotes the wavelength of the irradiated light source. When the wavelength of the irradiated light source is fixed at a certain value, the phase reversal effect can be determined by the refractive index and the absorptive layer thickness.

Therefore, if an absorbing layer is formed of a material having a high extinction coefficient for extreme ultraviolet wavelength and a high refraction coefficient, a very thin single layer film can exhibit a high absorption (low reflectivity) and a phase reversal effect.

Material of the absorbent layer that satisfies the above optical properties are _{PdO, PdO 2, Pd 2 O} 3, RhO, RhO 2, Rh 2 O 3, Tc 2 O 7, Nb 2 O 5, OsO 2, Os 2 O 3, ReO 2 , which is _{ReO 3, Re 2 O 5,} Re 2 O 7, WO 2, WO 3, W 2 O 3, VO 2 F, V 2 O 5, MnSO 4, selected from the CrN, TaBON, IrCl ₂ and IrO ₂ One or two or more compounds.

The absorbing layer 40 may be formed to a thickness of 40 nm or less, preferably 10 nm to 30 nm. The lower the thickness of the absorber layer 40, the less the shadow effect and the horizontal-vertical threshold bias. However, when the thickness of the absorbing layer 40 is too low, sufficient light absorption may not occur. Therefore, it is necessary to set the thickness appropriately in consideration of the specific material to be used.

On the other hand, the wavelength of the extreme ultraviolet ray used in the phase shift mask according to the present invention can be selected in the range of 10 nm to 20 nm. The shorter the wavelength of the light used, the finer the pattern can be formed on the wafer, but in consideration of compatibility, an extreme ultraviolet ray having a wavelength of 13.5 nm is preferably used.

As described above, according to the present invention, since the absorption layer can impart a phase reversing effect to extreme ultraviolet rays reflected by the absorption layer while having a slight reflectance, the contrast ratio of an image can be increased.

In addition, the shadow effect can be minimized by using a thin layer of a single layer of absorber layer, without the additional step of introducing a separate phase inversion layer into the absorber layer.

In addition, the horizontal-vertical threshold number bias can be minimized in the pattern of the absorption layer having a half pitch of 22 nm or less, and the process yield can be improved

Hereinafter, preferred examples for the understanding of the present invention will be described. It should be understood, however, that the following examples are intended to aid in the understanding of the present invention and are not intended to limit the scope of the present invention.

<Experimental Example 1>

In order to confirm the effect of the absorbing layer having a single layer thin film structure and having a reflectance of 5 to 10% and a retardation of 180 ± 15 °, the characteristics of the absorbing layer were measured using an EUV lithography computer simulation program.

(PPT, NA = 0.25, σ = 0.8) and High Volume Manufacturing (HVM, NA = 0.33, σ = 0.9) using a reflective layer composed of 40 pairs of Mo / Si multilayer films and a 2 nm Ru capping layer. We calculated the image contrast for the half pitch to be implemented in accordance with the equipment.

3 is a graph showing the reflectivity and the phase difference of the IrO ₂ absorption layer measured according to the thickness of the absorption layer.

Referring to FIG. 3, IrO ₂ It can be confirmed that the absorption layer has a reflectance of 8.36% at a thickness of 19 nm and a phase difference of 166.9 °.

Figures 4A and 4B illustrate the results of a &lt; _{RTI ID =} 4A) and HVM (FIG. 4B), respectively, for the line width of the absorption layer and the TaN absorption layer.

Referring to FIGS. 4A and 4B, although the thinner IrO ₂ absorption layer (19 nm thick) than the conventional TaN absorption layer (70 nm thick) is applied, the contrast ratio has a further improved value for a pattern having a narrower line width than the TaN absorption layer .

<Experimental Example 2>

Using the computer simulation program, IrO ₂ The horizontal-vertical threshold bias (HV CD bias) for the absorber layer was calculated.

Figures 5a and 5b illustrate the results of a &lt; _{RTI ID =} 5A) and the HVM (FIG. 5B) for the line width of the absorption layer and the TaN absorption layer, respectively.

The horizontal-vertical threshold number bias value generated by the shadow effect increases sharply as the line width of the pattern to be printed is narrowed. Referring to FIGS. 5A and 5B, when a TaN absorption layer having a thickness of 70 nm is applied, a very high horizontal-vertical threshold number bias value is obtained for a line width of 2 x nm or less, which is a result of improving resolution such as optical proximity correction It is difficult to implement by technology. Also, in the case of a mask having a high-thickness absorption layer (TaN), sufficient resolution is not achieved in realizing a line width of less than 20 nm half pitch, and patterning itself becomes impossible. However, in the case of a mask having a thin structure absorption layer (IrO ₂ ), it can be seen that patterning is possible because the mask has a low horizontal-vertical threshold value as a whole and a high resolution even for a narrow line width.

The most effective way to reduce this shadow effect is to lower the thickness of the absorbent layer. Therefore, a material having a high extinction coefficient capable of effectively absorbing ultraviolet rays even at a low thickness and using a material having a high refraction coefficient can have a very low horizontal-vertical threshold number bias. In addition, when a lens having a high collection ratio of first-order diffracted light is used, it is possible to uniformly distribute a pattern within a range of 1 nm deviation with respect to almost all the line width patterns.

<Experimental Example 3>

In addition to IrO ₂ , an experiment was conducted on a material capable of satisfying the optical properties (5 to 10% reflectance and 180 ± 15 ° phase difference) of the absorption layer of the phase inversion mask according to the present invention.

Table 1 summarizes the materials obtained from this experiment.

matter Absorbing layer thickness Reflectivity (%) Phase difference (°) PdO 20 nm 7.505839 171.8322 PdO ₂ 25 nm 7.597039 194.6588 Pd ₂ O ₃ 24nm 7.023466 170.8784 Rho 23nm 9.848818 166.4602 RhO ₂ 23nm 5.822356 177.7466 Rh ₂ O ₃ 21 nm 7.587705 183.7603 Tc ₂ O ₇ 21 nm 8.158349 170.9819 Nb ₂ O ₅ 36nm 9.641769 183.3935 OsO ₂ 25 nm 6.430403 190.883 Os ₂ O ₃ 25 nm 7.397975 181.6308 ReO ₂ 25 nm 7.309107 178.9433 ReO ₃ 25 nm 5.770558 194.5457 Re ₂ O ₅ 25 nm 6.512397 187.4299 Re ₂ O ₇ 19 nm 8.002601 181.7422 WO ₂ 26 nm 6.413254 173.7115 WO ₃ 25 nm 7.278294 176.4576 W ₂ O ₃ 32nm 6.213847 179.8921 VO ₂ F 39nm 5.075664 182.6345 V ₂ O ₅ 40nm 5.050895 190.6375 MnSO ₄ 38 nm 5.358442 183.2283 MnO ₂ 52nm 5.367143 177.8674 CrN 39nm 5.761201 180.4795 TaBON 32nm 5.465626 179.3855 IrCl ₂ 31nm 6.388977 186.2066 IrO ₂ 19 nm 8.357470 166.9024

Referring to Table 1, it can be seen that the above-described materials satisfy the optical characteristics (reflectance and phase difference) required in the absorption layer of the phase shift mask according to the present invention at a considerably lower thickness than the conventional TaN-based absorption layer (70 nm thick) have.

Particularly, in addition to IrO ₂ , PdO, PdO ₂ , Pd ₂ O ₃ , RhO, RhO ₂ , Rh ₂ O ₃ , Tc ₂ O ₇ , Nb ₂ O ₅ , OsO ₂ , Os ₂ O ₃ , ReO ₂ , ReO ₃ , In the case of Re ₂ O ₅ , Re ₂ O ₇ , WO ₂ , WO ₃ , W ₂ O ₃ , VO ₂ F, V ₂ O ₅ , MnSO ₄ , CrN, TaBON and IrCl ₂ , It can be confirmed that it is in conformity with the characteristics. Therefore, the reduced shadow effect and the improved uniformity of the threshold number can be secured as compared with the conventional TaN-based absorption layer.

<Experimental Example 4>

The absorber layer was formed using the materials shown in Table 1 and the contrast ratio of the linewidth was calculated using HVM equipment.

Figs. 6 to 8 are graphs comparing the contrast ratio of linewidths with respect to the absorption layer and the TaN absorption layer made of the materials shown in Table 1. Fig.

6 to 8, although the absorber layers made of the materials shown in Table 1 were formed to be thinner than the conventional TaN absorber layer (70 nm thick), the contrast ratio was lower than that of the TaN absorber layer It can be confirmed that all the values are improved.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, Change is possible.

10: substrate 12: reflective layer
14: capping layer 20: phase inversion layer
30, 40: Absorbent layer

Claims (10)

Board;
A reflective layer disposed on the substrate and composed of a multilayer thin film that reflects extreme ultraviolet rays; And
An absorber layer formed on the reflective layer and consisting of a patterned monolayer film,
Wherein the absorption layer has a reflectance of 5 to 10% with respect to the extreme ultraviolet ray, and the extreme ultraviolet ray reflected from the absorbing layer has a phase difference of 180 +/- 15 with the extreme ultraviolet ray reflected from the reflection layer,
Wherein the absorber layer has IrO _{2. The} phase inversion mask for extreme ultraviolet exposure process. delete The method according to claim 1,
Wherein the absorber layer has a thickness of 40 nm or less (provided that the thickness is not 0). The method according to claim 1,
Wherein the absorber layer has a thickness in the range of 10 nm to 30 nm. The method according to claim 1,
Wherein the pattern of the absorber layer has a half pitch of 22 nm or less. The method according to claim 1,
Wherein the extreme ultra-violet ray has a wavelength selected from the range of 10 nm to 20 nm. The method according to claim 1,
Further comprising a capping layer disposed between the reflective layer and the absorber layer and covering the surface of the reflective layer. In a phase shift mask for an exposure process using light having a wavelength of 13.5 nm,
A reflective layer disposed on the substrate and composed of a multilayer thin film that reflects the light;
A capping layer disposed on the reflective layer and covering the surface of the reflective layer; And
An absorber layer disposed on the capping layer and consisting of a patterned monolayer film,
Wherein the absorption layer has a thickness of 40 nm or less and has a reflectivity of 5 to 10% with respect to the light, and the light reflected from the absorption layer has a phase difference of 180 +/- 15 degrees with the light reflected from the reflection layer,
Wherein the absorber layer has IrO _{2. The} phase inversion mask for extreme ultraviolet exposure process. delete 9. The method of claim 8,
Wherein the pattern of the absorber layer has a half pitch of 22 nm or less.

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