JP2008310090A - Halftone phase shift mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a photomask with high resolution while decreasing the depth of a pattern. <P>SOLUTION: A translucent part (A) and a semi-translucent part (B) are formed on one major surface of a substrate 11 made of quartz, calcium fluoride or the like transparent to exposure light, on which phase modulation sections are respectively provided for changing phases of light propagating in a medium in contact with the pattern surface of the mask during exposure. For example, an optical film 13 provided in the translucent part (A) acts as a phase modulation section 1 having a thickness d<SB>1</SB>, while an optical film 12 provided in the semi-translucent part (B) acts as a phase modulation section 2 having a thickness d<SB>2</SB>. The phase ϕ<SB>1</SB>of transmitted light in the optical film 13 and the phase ϕ<SB>01</SB>of light propagating in the medium to the depth d<SB>1</SB>satisfy ϕ<SB>1</SB>=ϕ<SB>01</SB>+Δϕ<SB>1</SB>(wherein Δϕ<SB>1</SB>>0); while the phase ϕ<SB>2</SB>of transmitted light in the optical film 12 and the phase ϕ<SB>02</SB>of light propagating in the medium to the depth d<SB>2</SB>satisfy ϕ<SB>2</SB>=ϕ<SB>02</SB>+Δϕ<SB>2</SB>(wherein Δϕ<SB>2</SB><0). By this configuration, pattern depth can be designed by using a difference in the phase change in a plurality of optical films and a photomask with high resolution can be obtained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a halftone phase shift mask used for manufacturing a semiconductor integrated circuit or the like.

  Photomasks used in a wide range of applications including the manufacture of semiconductor integrated circuits such as ICs, LSIs, and VLSIs are, for example, photomasks in which a light-shielding film containing chromium as a main component is formed on a translucent substrate A blank is used, and a predetermined pattern is formed on the light-shielding film by a photolithography method using ultraviolet rays, electron beams or the like as exposure light. In recent years, along with market demands such as higher integration of semiconductor integrated circuits, pattern miniaturization has rapidly progressed, and the exposure wavelength has been shortened and the numerical aperture of the lens has been increased to increase the resist resolution in the exposure process. Has been addressed.

  However, there is a problem that shortening the exposure wavelength results in an increase in the cost of the apparatus and materials. In addition, while increasing the numerical aperture of the lens has the advantage of improving the resolution, it results in a decrease in the depth of focus. As a result, there is a problem in that the process stability is lowered and the product yield is adversely affected. As one of pattern transfer methods effective for solving such problems, a “phase shift method” using a “phase shift mask” as a photomask is known.

  FIG. 1 is a cross-sectional view for explaining an example of a phase shift mask (halftone type phase shift mask) used in the phase shift method. FIG. 1A is a “single layer type” in which the phase shift portion is a single layer. (For example, Patent Document 1) and FIG. 1B show a phase shift mask of “two-layer type” (for example, Patent Document 2) in which the phase shift portion has a two-layer structure of a phase adjustment film and a transmittance adjustment film. . In addition, it is known that the “two-layer type” phase shift mask is useful as a photomask for short wavelength exposure (exposure wavelength is 200 nm or less) (Patent Document 3).

In these phase shift masks, a region where the main surface of the substrate 1 is exposed (translucent portion: A) and the phase shift film 2 are patterned on one main surface of the substrate 1 that is transparent to exposure light. Region (semi-transparent portion: B) is formed, and the light transmitted through these regions is transmitted light phase (φ ₀ ) of the translucent portion A and transmitted light phase of the semi-transparent portion B ( (φ ₀ + π) and the phase difference is approximately π (180 °), and the contrast reduction due to diffraction is improved by the interference of the transmitted light between the translucent part and the semi-transparent part at the pattern boundary, and the transferred image The contrast can be improved. The “two-layer type” phase shift film 2 is formed by laminating two layers of a phase adjustment film 2a and a transmittance adjustment film 2b.

In relation to such a phase shift mask, a structure in which a chromium film as an etching stopper is provided between a transparent substrate and a phase shift film (Patent Document 4), or the phase of light transmitted through the light shielding film is substantially zero. In order to achieve this, a configuration (Patent Document 5) in which a light shielding film is formed by laminating a phase retardation film and a phase progression film has been proposed.
JP-A-7-140635 JP-A-4-136854 Japanese Patent Laying-Open No. 2005-084682 JP 2001-337436 A JP 2006-215297 A

In a conventional halftone phase shift mask, whether it is a “single layer type” or “two layer type”, an optical for causing a phase difference between the light transmitting part and the semi-light transmitting part in the light transmitting part. Since the film is not provided and the phase adjustment is performed only by the semi-translucent portion, the pattern depth is equal to the film thickness of the phase shift film responsible for the phase adjustment. However, when the phase shift film is thick, defects such as particles and half pinholes increase during the film formation, or after patterning, a predetermined phase difference that leaks out from the side surface of the pattern during exposure. There is a problem that the amount of different light increases and it becomes difficult to cause an original phase difference in the boundary region between the translucent part and the semi-translucent part. In particular, when a material having a high transmittance such as SiO ₂ is used for phase adjustment, since the refractive index is small, it is inevitably necessary to increase the film thickness in order to obtain a predetermined phase difference. As a result, the above problem becomes serious.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to adjust the phase of propagating light in each of the light-transmitting portion and the semi-light-transmitting portion, and thereby the depth of the pattern. It is to make it possible to form the film shallowly.

In order to solve such a problem, the halftone phase shift mask of the present invention has a translucent part and a semi-translucent part on a transparent substrate, and each of the translucent part and the semi-translucent part has A phase modulation unit that changes the phase of the light propagating through the medium that is in contact with the pattern surface of the mask during exposure is provided, and one phase modulation unit of the translucent unit and the semi-translucent unit has a thickness of d ₁ . When the phase modulation unit 1 and the other phase modulation unit 2 having a thickness d ₂ are used, the phase φ _{1 of} the light transmitted through the phase modulation unit 1 is equal to the phase φ _{01 of} the light propagated through the medium by d ₁ and the following equation: The relationship: φ ₁ = φ ₀₁ + Δφ ₁ (Δφ ₁ > 0) is satisfied, and the phase φ _{2 of} the light transmitted through the phase modulator ₂ is next to the phase φ _{02 of} the light propagated through the medium by d ₂ Expression relationship: φ ₂ = φ ₀₂ + Δφ ₂ (Δφ ₂ <0) is satisfied.

  For example, the phase modulation unit 2 is provided in the semi-translucent unit, and the phase modulation unit 1 is provided in the translucent unit.

  Preferably, a transmittance adjusting film is provided in the semi-translucent portion, and the transmittance adjusting film is the phase modulating portion 2.

  Preferably, the phase difference between the light transmitted through the phase modulation unit 2 and the light transmitted through the phase modulation unit 1 is substantially π (radian).

  In the present invention, the transmittance adjusting film that is the phase modulation unit 2 may be an optical film made of at least one of silicon, molybdenum, and molybdenum silicide, and the phase modulation unit 1 may be formed of silicon oxide, silicon An optical film made of at least one of nitride and silicon oxynitride can be obtained.

  In the present invention, since the pattern depth is conventionally determined only by the design of the semi-transmissive portion, the pattern depth is designed using the difference in phase change received in a plurality of optical films. A shallow pattern can be formed, and as a result, a high-resolution photomask can be obtained.

  Hereinafter, the halftone phase shift mask of the present invention will be described with reference to the drawings.

FIG. 2 is a cross-sectional view for explaining a basic configuration example of the halftone phase shift mask of the present invention, on one main surface of a substrate 11 such as quartz or calcium fluoride that is transparent to exposure light. The translucent part A and the semi-translucent part B are formed, the phase modulating part is provided in both the translucent part A and the semi-translucent part B, and either the translucent part A or the semi-translucent part B is provided. phase modulation unit phase phi ₁ of the light transmitted through the (phase modulation unit 1 of the thickness d ₁₎ is a medium in which the pattern surface of the mask is in contact during exposure of light propagated by d ₁ phase phi ₀₁ and phi ₁ = satisfy the relationship of _{φ 01 + Δφ 1 (Δφ 1} > 0), and light-transmitting part a and the semi-light-transmitting portion other phase phi ₂ of the light transmitted through the (phase modulation unit 2 of the thickness _{d 2)} and B, It is designed for the medium so as to satisfy the relationship _{d 2} only light phase phi ₀₂ that propagates _{φ 2 = φ 02 + Δφ 2} (Δφ 2 <0) . In the example shown in FIG. 2, the optical film 13 provided in the translucent part A is the phase modulation part 1, and the optical film 12 provided in the semi-transparent part B is the phase modulation part 2.

The amplitude transmittance t of the light transmitted through the phase modulation unit can be expressed as t = t ₀ exp (−iδ). The energy transmittance T is T = t · t ^* . Here, assuming that the phase change δ ₀ when light of wavelength λ propagates in the medium (refractive index n ₀ ) having a length corresponding to the film thickness (d) of the phase modulation portion is δ ₀ = φ ₀ , φ ₀ = _{2πn 0 d / λ} and becomes, in the present invention, a phase change when it passes through the phase modulation unit δ (= φ) is, when the Δφ = φ-φ _0, the phase modulation unit 1 [Delta] [phi > 0, and the phase modulation unit 2 satisfies Δφ <0.

  The phase modulation unit may be any as long as it satisfies the above relationship, and may be a single layer structure or a multilayer structure when it is formed of a film. Further, the composition may be changed in the film. For example, in the case where the phase modulation unit is configured by a single layer film having a uniform composition, the transmittance t of the film is given by the following equation.

(Equation 1)
t = t ₀・ exp (-i ・ φ)
= t _S1 t ₁₀・ exp (-i ・ 2πdn ₁ ) / λ) / (1 + r _S1 r ₁₀・ exp (-4πi ・ dn ₁ / λ)

Here, i is an imaginary unit, d is a film thickness, n ₁ is a complex refractive index of the film (refractive index n ₁ = n−ik (n: refractive index, k: extinction coefficient), and t _S1 is a relationship between the substrate and the film. Amplitude transmittance at the interface (energy transmittance T _S1 = t _S1 · t _S1 ^* ), t ₁₀ is an amplitude transmittance at the interface between the film and the medium (energy transmittance T ₁₀ = t ₁₀ · t ₁₀ ^* ), r _S1 is the amplitude reflectance at the interface between the substrate and the film, and r ₁₀ is the amplitude reflectance at the interface between the film and the medium.

In the present invention, the phase change when light propagates through the medium having a length corresponding to the film thickness (d) of the phase modulation portion is set to φ ₀ as described above, and when Δφ = φ−φ ₀ The modulation unit 1 may satisfy Δφ> 0, and the phase modulation unit 2 may satisfy Δφ <0.

In general, a dielectric film having a refractive index of the film larger than that of the medium and having an absorption coefficient close to 0 functions as the phase modulation unit 1, and functions as the phase modulation film 2 if a film having a refractive index smaller than that of the medium is selected. However, a film having a large absorption coefficient has a function as the phase modulation unit 2 when the above formula is satisfied as the phase modulation unit 2 even if the refractive index of the film is larger than the refractive index of the medium. For example, when multiple reflections in the film can be ignored, the refractive index of the substrate is n _S , the refractive index of the film is n ₁ = n−ik, the film thickness is d, and the refractive index of the medium is n _0. , The phase φ of the transmitted light t = t ₀ · exp (−i · φ) is φ = 2πnd / λ + ε (where ε = −tan ⁻¹ [k (n ² −n _S n ₀ ) / {n ( n _S + n) (n ₀ + n) + k ² (n _S + n ₀ + n)}].

The phi functions as the phase modulator 2 is smaller than phi _0. That is, in order to become the phase modulation unit 2, Δφ = φ−φ ₀ = 2π (n−n ₀ ) d / λ + ε <0 may be satisfied.

  In the above equation (Equation 1), for example, even if the refractive index of the film is larger than that of the medium, if the film has a certain absorption coefficient, it functions as the phase modulation unit 2 by selecting the film thickness. In other words, as the film becomes thicker, Δφ in the above equation is negative and the absolute value increases, becomes an extreme value at a certain film thickness, then Δφ is negative and the absolute value decreases, and finally becomes positive. Value. If the phase change amount is selected so that the phase change amount is smaller than that propagating in the medium, it functions as the phase shift film 2, and the phase change amount is larger than that propagating in the medium. If selected, it functions as the phase shift film 1.

Although the case where the phase modulation unit is configured by a single layer has been described as an example, the same applies to the case where the phase modulation unit is configured by a plurality of layers. For example, when multiple reflections can be ignored, even if the refractive index of each film is larger than that of the above medium, the total phase change at each film interface becomes a negative value, and the magnitude constitutes a multilayer. If the absolute value is larger than the difference between the phase change when propagating in the film and the phase change when propagating through the medium having the same thickness, it functions as the phase modulation unit 2, and vice versa. Function as. When the complex refractive index (n _f = n−ik) difference of the film in contact with the medium or the substrate is large and multiple reflection in the film cannot be ignored, it is necessary to consider the multiple reflection in the film. Further, when the absorption coefficient is not 0, it is necessary to consider the phase change at the interface.

  The optical film 12 shown in FIG. 2 gives the exposure light propagating through the film a phase change of “−β” with respect to the light propagating through the medium, and adjusts the light transmittance to a predetermined value. It also serves as a transmittance adjusting film. The light transmittance of the semi-translucent portion B may be about 1 to 50% of the translucent portion A, and more preferably adjusted to be about 3 to 30%. By adjusting the light transmittance as described above, the exposure light after passing through the semi-translucent portion B is adjusted so as to have an intensity lower than the sensitivity of the resist.

The optical film 13 gives the exposure light propagating in the film a phase change of “+ α” with respect to the light propagating in the medium. As a result, the phase of the transmitted light (φ ₀₎ + Α) and a phase adjustment film for making a phase difference a predetermined value (generally π (180 °)) between the phase (φ ₀ −β) of the transmitted light of the semi-translucent portion B, It is a film having a higher transmittance than the transmittance adjusting film.

  For example, when the exposure wavelength is 193 nm, these optical films 12 (phase modulation films constituting the phase modulation unit 2) can be made of silicon, molybdenum, molybdenum silicide films, and satisfy the above formula. By selecting the thickness, it functions as the phase modulation unit 2. The optical film 13 (phase modulation film constituting the phase modulation unit 1) is a film of silicon oxide, silicon nitride, silicon oxynitride, or a film containing a metal such as Mo, Ta, or Zr in these films. It can be.

  If the light-transmitting part A and the semi-light-transmitting part B are configured in this way, the depth of the pattern can be reduced, and as a result, a high-resolution photomask can be obtained. Note that the phase modulation unit may be formed by digging a substrate in the light-transmitting part or the semi-light-transmitting part, or both the substrate digging and the phase adjusting film may be used.

  3 and 4 are diagrams for explaining the principle of the present invention. In the phase modulation unit, the effect of the interface between the phase modulation unit and the medium or the substrate or the multiple reflection in the phase modulation part is not necessarily propagated as shown in this figure, but the light entering the phase modulation part and Since the emitted light changes as shown in the drawings, the light propagates as if shown in these drawings at the phase modulation portion.

  3 (A) and 3 (B) show how the phase change is caused when propagating through the “phase modulation unit 2” and “phase modulation unit 1” of thickness t placed in the medium, respectively. It is a figure for demonstrating.

While propagating through the “phase modulation unit 2”, the phase change becomes small, while when propagating through the “phase modulation unit 1”, the phase change becomes large. A substrate for a phase shift mask can be obtained by designing the optical film so that the phase difference of transmitted light from these media is π (180 °). For example, if the optical film is designed so that the phase difference is π (180 °) and the thickness of the “phase modulation unit 2” is equal to the thickness of the “phase modulation unit 1”, in principle the pattern depth Thus, a phase shift mask having a “zero” thickness (a step between the light-transmitting portion and the semi-light-transmitting portion) can be obtained, and a photomask with extremely high resolution can be obtained.

  On the other hand, as illustrated in FIG. 4, a conventional phase shift mask in which phase adjustment is performed only by a phase shift film provided in a semi-translucent part without providing a special optical film in the translucent part. In this case, when the phase shift film is formed of “phase modulation film 1” (FIG. 4B), the phase to be compared with the phase of transmitted light is the same distance as the thickness t of these optical films. It is the phase of light propagating through the inside. For this reason, the depth of the pattern (the step between the translucent portion and the semi-transparent portion) can be formed shallow only by reducing the thickness of the phase shift film so that the phase difference is π (180 °). .

  In other words, in the present invention, the difference in phase change received by the phase modulation unit of the transmissive part and the semi-transmissive part, which has conventionally been possible to reduce the pattern depth only by the design of a single film, This makes it possible to make the pattern depth shallower, and greatly expands the design freedom of the phase shift mask.

  In general, the medium in contact with the mask pattern surface during exposure is a medium having a refractive index of 1, such as air or nitrogen gas. However, the mask pattern is placed in a medium having a refractive index greater than 1. The present invention can also be applied to a case where exposure is performed (for example, by immersion in a liquid having a high refractive index). In such a case, in the conventional configuration in which only the semi-transmission part is provided with a phase modulation part having a refractive index larger than that of the medium, the difference in refractive index between the phase modulation part and the medium becomes small, and a predetermined phase change occurs. However, in the case of the present invention, such inconvenience can be improved.

  FIG. 5 is a diagram for explaining a manufacturing process of the phase shift mask of the present invention. First, on a substrate 11 made of transparent quartz, a silicon target is sputtered with Ar to form a silicon film 20 having a thickness of 17 nm (FIG. 5A). This silicon film 20 functions as a transmittance adjusting film, and is a film that becomes the phase modulation section 2 at an exposure wavelength of 193 nm. The reason why the thickness of the silicon film 20 is 17 nm is that the transmittance of this film is about 6%, and the film thickness is appropriately set according to the value of the set transmittance.

  A chemical amplification type positive resist for electron beam is applied to the silicon film and a predetermined pattern is formed by photolithography (FIG. 5B), and the silicon film 20 is etched using the resist pattern 21 as a mask (FIG. C)).

  On the patterned silicon film 20 and the resist 21, a 140 nm-thickness silicon oxide film 22 constituting the phase modulation unit 1 and serving as a phase adjustment layer is formed (FIG. 5D). This film formation is performed by sputtering a silicon target with Ar gas and oxygen gas. The thickness of this silicon oxide film of 140 nm is such that the phase difference from the transmitted light of the above-described silicon film 20 (17 nm) is π (180 °) in the air that is the medium in contact with the mask pattern surface during exposure. Is the result of selection for.

  Next, the silicon oxide film 22b on the resist 21 is removed by lift-off, and a “transmission portion” including the optical film 13 which is the “phase modulation portion 1” made of the silicon oxide film 22a and the “phase modulation portion” made of the silicon film 20. A semi-transparent portion including the optical film 12 that is “2” is formed (FIG. 5E).

  The phase shift mask obtained in this example has a pattern depth (step difference between the light-transmitting portion and the semi-light-transmitting portion) of 123 nm (140 nm-17 nm), and the transmittance of the semi-light-transmitting portion with respect to incident light of 193 nm is 6 %, A phase shift film having a phase difference of 180 ° can be made shallower by about 70 nm than when a conventional method is used (about 190 nm).

It is sectional drawing for demonstrating the structural example of the phase shift mask used by the phase shift method, (A) is a "single layer type" with a single phase shift part, (B) This is a “two-layer type” phase shift mask. It is sectional drawing for demonstrating the basic structural example of the halftone type phase shift mask of this invention. In the drawings for explaining the principle of the present invention, (A) and (B) are respectively shown when propagating through a “phase modulation unit 2” and a “phase modulation unit 1” having a thickness t placed in a medium. It is a figure for demonstrating what kind of phase change it receives. It is a figure for demonstrating the phase change in the phase shift film in the case of a conventional phase shift mask. It is a figure for demonstrating the example of a manufacturing process of the phase shift mask of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Board | substrate 12 Optical film which is "phase modulation part 2" 13 Optical film which is "phase modulation part 1" 20 Silicon film 21 Resist 22a, 22b Silicon oxide film

Claims (7)

A halftone phase shift mask having a translucent part and a semi-translucent part on a transparent substrate,
Each of the translucent part and the semi-translucent part is provided with a phase modulation part that changes the phase with respect to the light propagating through the medium with which the mask pattern surface is in contact during exposure,
When _one of the light transmitting part and the semi-light transmitting part is a phase modulating part 1 having a thickness d 1 and the other is a phase modulating part 2 having a thickness d ₂ , the phase of the light transmitted through the phase modulating part 1 φ ₁ satisfies the relationship between the phase φ _{01 of} the light propagated through the medium by d ₁ and the following formula: φ ₁ = φ ₀₁ + Δφ ₁ (Δφ ₁ > 0), and the light transmitted through the phase modulator 2 phase phi ₂ the relation between the phase phi ₀₂ and the formula of the light propagating in the medium by _{d 2: φ 2 = φ 02} + Δφ 2 (Δφ 2 <0) the phase shift mask, characterized by satisfying the.   The halftone phase shift mask according to claim 1, wherein the phase modulation unit 2 is provided in the semi-translucent unit, and the phase modulation unit 1 is provided in the translucent unit.   The halftone phase shift mask according to claim 1, wherein a transmittance adjusting film is provided on the semi-translucent portion.   The halftone phase shift mask according to claim 3, wherein the transmittance adjusting film is the phase modulation unit 2.   5. The phase difference between the light transmitted through the phase modulation unit 2 and the light transmitted through the phase modulation unit 1 is substantially π (radian). 6. Halftone phase shift mask.   The halftone phase shift mask according to claim 1, wherein the phase modulation unit 2 is an optical film made of at least one of silicon, molybdenum, and molybdenum silicide.   The halftone phase shift mask according to claim 1, wherein the phase modulation unit 1 is an optical film made of at least one of silicon oxide, silicon nitride, and silicon oxynitride.

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