Phase shift mask blank and phase shift mask

Abstract

The present invention provides a phase shift mask blank and a phase shift mask. The phase shift mask blank includes a substrate and a phase shift film thereon, the phase shift film is composed of a material containing silicon and nitrogen and not containing a transition metal, the phase shift film includes at least one composition gradient layer having a composition continuously varying in a thickness direction, and a refractive index n and an extinction coefficient k for an exposure light, which is a KrF excimer laser, vary in the thickness direction, a difference between a maximum refractive index n(H) and a minimum refractive index n(L) of the composition gradient layer is 0.40 or less, and a difference between a maximum extinction coefficient k(H) and a minimum extinction coefficient k(L) is 1.5 or less.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This non-provisional application claims priority under 35 U.S.C. §119(a) to Japanese Patent Application No. 2019-067065 filed on March 29, 2019 and Japanese Patent Application No. 2019-111026 filed on June 14, 2019, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present invention relates to a phase shift mask blank and a phase shift mask which are generally used for manufacturing a semiconductor integrated circuit. BACKGROUND

[0004] In a photolithography technique used for semiconductor technology, a phase shift method is used as one of resolution enhancement techniques. The phase shift method is a contrast enhancement method by forming a phase shift film pattern provided on a transparent substrate which is transparent to exposure light as a photomask substrate, and utilizing interference of light. The phase shift film pattern has a phase shift of about 180°, which is a difference between a phase passing through a portion where the phase shift film is not formed and a phase passing through the phase shift film, in other words, a phase passing through air having a length equivalent to a thickness of the phase shift film. A half tone phase shift mask is one of photomasks using this method. The half tone phase shift mask includes a transparent substrate made of quartz or the like which is transparent to exposure light, and a mask pattern of a half tone phase shift film formed on the transparent substrate and having a phase shift of about 180° with respect to a phase passing through a portion where the phase shift film is not formed and a transmittance which is substantially insufficient to contribute to exposure. As a phase shift film for the half tone phase shift mask, a film containing molybdenum and silicon is mainly used. As such a film, a half tone phase shift film composed of molybdenum silicon oxide or molybdenum silicon oxynitride is known (JP-A H07-140635 (Patent Document 1)).

[0005] LIST OF CITATIONS

[0006] Patent Document 1: JP-A H07-140635

[0007] Patent Document 2: JP-A 2007-33469

[0008] Patent Document 3: JP-A 2007-233179

[0009] Patent Document 4: JP-A-2007-241065 SUMMARY

[0010] As a phase shift film for exposure light of a KrF excimer laser (wavelength 248 nm), a phase shift film composed of a material containing molybdenum and silicon, which has a phase shift of 180° and a transmittance of about 6%, is generally used. In this case, the phase shift film has a thickness of about 100 nm. Recently, for a phase shift film using an ArF excimer laser (wavelength 193 nm) as exposure light, a phase shift film of silicon nitride has been used for the purpose of minimizing the film thickness and enhancing the washing resistance and light resistance. Although not as much as when an ArF excimer laser is used as exposure light, when a KrF excimer laser is used as exposure light, a phase shift film having high washing resistance and light resistance and being difficult to generate haze is also required.

[0011] When a phase shift film used with a KrF excimer laser as exposure light is made of silicon nitride, if the phase shift film is formed as a single layer having a single composition (uniform composition in the thickness direction) of a refractive index n and an extinction coefficient k corresponding to a phase shift of 170 to 190° and a transmittance of 4 to 8%, the film is formed under film formation conditions employing an unstable region (so-called transition mode region) in reactive sputtering, and therefore, the film has a problem that in-plane uniformity of optical characteristics is deteriorated.

[0012] Meanwhile, in order to obtain a film having high in-plane uniformity of optical characteristics, it is conceivable to configure a phase shift film composed of silicon nitride as a multilayer composed of layers having a single composition (uniform composition in the thickness direction) and formed by reactive sputtering under film formation conditions of a stable region (so-called metal mode or reaction mode). However, the refractive index n of a film that can be formed under this region is lower than the refractive index n of a film formed under the transition mode region, and therefore, it is necessary to form the film thick. In lithography, a thin phase shift film is advantageous in forming a finer pattern and further can reduce a three-dimensional effect. However, such a thick film composed of a multilayer is disadvantageous. Further, in the case of a multilayer composed of layers formed under film formation conditions of a stable region, the layer composition of each layer is significantly different. Therefore, there is a concern that the cross-sectional shape of a pattern is deteriorated due to a difference in etching rate when the film is processed.

[0013] The present application has been achieved in order to solve the above-described problems, and an object of the present application is to provide a phase shift mask blank including a thin phase shift film that satisfies the requirement for pattern miniaturization even when exposure light is a KrF excimer laser having a wavelength of 248 nm, is advantageous in patterning and reducing a three-dimensional effect while satisfying the phase shift and transmittance necessary for a phase shift film, and a phase shift mask.

[0014] The inventors have found that when a phase shift film is composed of a material containing silicon and nitrogen and not containing a transition metal and includes a composition gradient layer having a composition that continuously changes in the thickness direction and having an optical constant for an exposure light that changes in the thickness direction, a film having a phase shift amount (phase shift) of 170 to 190° and a transmittance of 4 to 8% can be formed without thickening the film of a phase shift mask blank for an exposure light of a KrF excimer laser (wavelength 248 nm), thereby obtaining a phase shift mask blank and a phase shift mask including a phase shift film having high in-plane uniformity of optical characteristics.

[0015] In one aspect, the present application provides a phase shift mask blank including a substrate and a phase shift film thereon, the phase shift film being composed of a material containing silicon and nitrogen and not containing a transition metal, wherein

[0016] The phase shift film includes at least one composition gradient layer having a composition that continuously changes in the thickness direction and having a refractive index n and an extinction coefficient k for an exposure light that change in the thickness direction, the exposure light being a KrF excimer laser,

[0017] The difference between the maximum refractive index n(H) and the minimum refractive index n(L) of the composition gradient layer is 0.40 or less, and the difference between the maximum extinction coefficient k(H) and the minimum extinction coefficient k(L) is 1.5 or less.

[0018] Preferably, the composition gradient layer has a minimum refractive index n(L) of 2.3 or more and a maximum extinction coefficient k(H) of 2 or less, and includes a region satisfying a refractive index n of 2.55 or more and an extinction coefficient k of 1.0 or less, the region having a thickness of 5 to 30 nm.

[0019] Preferably, the composition gradient layer has a region in which the content ratio N / (Si+N) continuously changes in the thickness direction in the range of 0.2 to 0.57, the ratio N / (Si+N) representing the nitrogen content (at%) relative to the sum of the silicon and nitrogen contents (at%).

[0020] Preferably, the difference between the maximum silicon content (at%) and the minimum silicon content (at%) of the composition gradient layer is 30 or less.

[0021] Preferably, the phase shift film has a phase shift of 170 to 190° and a transmittance of 4 to 8%, in which the ratio of the difference between the maximum phase shift and the minimum phase shift to the average phase shift in the plane is 3% or less, the ratio of the difference between the maximum transmittance and the minimum transmittance to the average transmittance in the plane is 5% or less, and the phase shift film has a thickness of 90 nm or less.

[0022] Preferably, the material containing silicon and nitrogen and not containing a transition metal is a material composed of silicon and nitrogen.

[0023] Generally, the phase shift mask blank can include a second layer composed of a single layer or multiple layers on the phase shift film, the second layer composed of a chromium-containing material.

[0024] In another aspect, the present application provides a phase shift mask manufactured by using the phase shift mask blank.

[0025] Advantages of the Invention

[0026] According to the present application, a phase shift mask blank and a phase shift mask having a thinner phase shift film are provided, which are advantageous in patterning and exposure and have high optical characteristic in-plane uniformity while satisfying the necessary phase shift and transmittance of the phase shift film for exposure light of a KrF excimer laser. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A and 1B are cross-sectional views illustrating an exemplary phase shift mask blank and a phase shift mask of the present application.

[0028] Figure 2 A to 2C are cross-sectional views illustrating other embodiments of the phase shift mask blank of the present application. DETAILED DESCRIPTION

[0029] The phase shift mask blank of the present application includes a transparent substrate such as a quartz substrate, and a phase shift film provided on the transparent substrate. The phase shift mask of the present application includes a transparent substrate such as a quartz substrate, and a mask pattern (a photomask pattern) of a phase shift film provided on the transparent substrate.

[0030] The transparent substrate in the present application is preferably a 6-inch square, 0.25-inch thick transparent substrate, for example, referred to as a 6025 substrate, which is specified by SEMI standards, which is generally represented by a 152-mm square, 6.35-mm thick transparent substrate according to the SI unit system.

[0031] Figure 1 A is a cross-sectional view illustrating an exemplary phase shift mask blank of the present application. In this embodiment, the phase shift mask blank 100 includes a transparent substrate 10 and a phase shift film 1 formed on the transparent substrate 10. Figure 1 B is a cross-sectional view illustrating an exemplary phase shift mask of the present application. In this embodiment, the phase shift mask 101 includes a transparent substrate 10 and a phase shift film pattern 11 formed on the transparent substrate 10. The phase shift mask can be obtained by using the phase shift mask blank and forming a pattern of the phase shift film thereof.

[0032] The phase shift film in the present application having a prescribed thickness has a predetermined phase shift amount (phase shift) and a predetermined transmittance for exposure light of a KrF excimer laser (wavelength: 248 nm). The phase shift film of the present application is composed of a material containing silicon and nitrogen and not containing a transition metal. In order to improve the wash resistance of the film, it is effective to add oxygen to the phase shift film. Therefore, the material containing silicon and nitrogen and not containing a transition metal can contain oxygen in addition to silicon and nitrogen. However, when oxygen is added, the refractive index n of the film decreases, and therefore the thickness of the film tends to increase. Therefore, as the material containing silicon and nitrogen and not containing a transition metal, a material composed essentially of silicon and nitrogen (a material composed of two elements and inevitable impurities) is preferred.

[0033] The phase shift film is preferably composed of a single layer designed to satisfy the phase shift and the transmittance necessary for the phase shift film. The phase shift film can be composed of a plurality of layers designed to satisfy the phase shift and the transmittance necessary for the entire phase shift film. In each case of the single layer and the plurality of layers, the phase shift film is constructed so that the film includes at least one composition gradient layer having a composition that continuously changes in the thickness direction, and a refractive index n and an extinction coefficient k for exposure light that change in the thickness direction. In the case of the plurality of layers, although the film can be composed of a plurality of composition gradient layers or a combination of composition gradient layers and single composition layers (layers that do not change in the thickness direction), the total thickness of the composition gradient layers is preferably 30% or more, more preferably 50% or more, and most preferably 100% of the total thickness of the phase shift film.

[0034] In the composition gradient layer, the difference between the maximum refractive index n(H) and the minimum refractive index n(L) is preferably 0.40 or less, more preferably 0.25 or less, and is preferably 0.1 or more, more preferably 0.15 or more. In the composition gradient layer, the difference between the maximum extinction coefficient k(H) and the minimum extinction coefficient k(L) is 1.5 or less, more preferably 1.2 or less, and is preferably 0.3 or more, more preferably 0.6 or more. The minimum refractive index n(L) in the composition gradient layer is preferably 2.3 or more, more preferably 2.4 or more, and the maximum extinction coefficient k(H) is preferably 2 or less, more preferably 1.5 or less. In particular, in the composition gradient layer, the thickness of the region satisfying a refractive index n of 2.55 or more and an extinction coefficient k of 1.0 or less is preferably 5 nm or more and 30 nm or less.

[0035] In the compositionally-graded layer of the present application (in the entire compositionally-graded layer when the phase shift film is composed of a single layer; in each layer when the phase shift film is composed of a plurality of compositionally-graded layers), the compositionally-graded range of the silicon content is preferably in the range of 40 at% or more, particularly 45 at% or more, and 70 at% or less, particularly 60 at% or less, and the compositionally-graded range of the nitrogen content is preferably in the range of 30 at% or more, particularly 40 at% or more, and 60 at% or less, particularly 55 at% or less.

[0036] In particular, the compositionally-graded layer preferably includes a region in which the content ratio N / (Si+N) representing the nitrogen content (at%) with respect to the sum of the contents of silicon and nitrogen (at%) continuously changes, the content ratio N / (Si+N) being in the range of preferably 0.2 or more, more preferably 0.3 or more, and preferably 0.57 or less, more preferably 0.55 or less. The difference between the maximum silicon content (at%) and the minimum silicon content (at%) in the compositionally-graded layer is preferably 30 or less, more preferably 15 or less. In the case where the compositionally-graded layer contains oxygen, the oxygen content is preferably 30 at% or less, more preferably 10 at% or less, most preferably 5 at% or less.

[0037] As a result of the phase shift due to the interference of the exposure light passing through each region, the phase shift of the exposure light passing through the phase shift film in the present application can be sufficient to be able to increase the contrast at the boundary between the region having the phase shift film (phase shift region) and the region not having the phase shift film. The phase shift can be 170° or more and 190° or less. Meanwhile, the transmittance of the phase shift film in the present application with respect to the exposure light can be 4% or more and 8% or less. The phase shift film in the present application can have the phase shift and the transmittance with respect to the KrF excimer laser (wavelength: 248 nm) controlled in the above-described ranges.

[0038] The phase shift film is configured to include at least one compositionally-graded layer having a composition continuously varying in the thickness direction, and a refractive index n and an extinction coefficient k with respect to the exposure light varying in the thickness direction. According to the phase shift film of the present application, the variation range of the phase shift, which is the ratio between the difference between the maximum and minimum phase shifts and the average phase shift in the plane of the phase shift film (for example, in a 135 mm square area in the center of the substrate surface of a 6025 substrate), can be 3% or less, particularly 1% or less, and the variation range of the transmittance, which is the ratio between the difference between the maximum and minimum transmittances and the average transmittance in the plane of the phase shift film, can be 5% or less, particularly 3% or less.

[0039] When the entire thickness of the phase shift film is thin, a fine pattern can be easily formed. Therefore, the entire thickness of the phase shift film in the present application is 90 nm or less, preferably 85 nm or less. Meanwhile, the lower limit of the thickness of the phase shift film can be set as long as a desired optical property can be obtained for the exposure light, and is generally 50 nm or more, but is not limited thereto.

[0040] The phase shift film in the present application can be formed by a publicly known film forming method. The phase shift film is preferably formed by sputtering, by which a highly homogeneous film can be easily obtained, and the sputtering can be DC sputtering or RF sputtering. The target and the sputtering gas are appropriately selected depending on the kind and composition of the layer to be formed. Examples of the target include a silicon target, a silicon nitride target, and a target containing both silicon and silicon nitride. These targets can contain oxygen. The nitrogen content and the oxygen content can be controlled by reactive sputtering using any one of reactive gases as the sputtering gas, such as a nitrogen-containing gas, an oxygen-containing gas, and a gas containing both nitrogen and oxygen, with the supply amount being appropriately controlled. In particular, nitrogen gas (N2 gas), oxygen gas (O2 gas), and nitric oxide gas (N2O gas, NO gas, and NO2 gas) can be used as the reactive gas. A rare gas such as helium, neon, and argon can also be used as the sputtering gas.

[0041] In order to suppress a change in the properties of the phase shift film, the phase shift film composed of a plurality of layers can include a surface oxidation layer formed as an outermost layer on the top surface (on the side away from the transparent substrate). The surface oxidation layer can have an oxygen content of 20 at% or more, preferably 50 at% or more. Examples of the method for forming the surface oxidation layer specifically include atmospheric oxidation (natural oxidation); a forced oxidation treatment such as a sputtered film treatment with an ozone gas or ozone water, or heating in an oxygen-containing atmosphere such as an oxygen gas atmosphere at 300°C or more by heating in an oven, lamp annealing, or laser heating. The surface oxidation layer preferably has a thickness of 10 nm or less, more preferably 5 nm or less, and most preferably 3 nm or less. The effect of the surface oxidation layer is generally obtained with a thickness of 1 nm or more. Although the surface oxidation layer can be formed by sputtering with an increased amount of oxygen gas, it is more preferable to form the surface oxidation layer by the aforementioned atmospheric oxidation or oxidation treatment in terms of obtaining a layer with fewer defects.

[0042] The phase shift mask blank of the present application can include a second layer composed of a single layer or a plurality of layers, which is formed above the phase shift film. The second layer is generally provided adjacent to the phase shift film. The second layer is specifically exemplified as a light shielding film, a combination of a light shielding film and an antireflection film, and a process assist film that functions as a hard mask in the process of patterning the phase shift film. In the case where a third layer is employed as described below, the second layer can function as a process assist film that functions as an etching stopper layer (etching stopper film) in the process of patterning the third layer. The material of the second layer is preferably a chromium-containing material.

[0043] This embodiment is specifically exemplified asFigure 2 The phase shift mask blank described in A. Figure 2 A is a cross-sectional view illustrating an exemplary phase-shifting mask blank of the present invention. In this embodiment, the phase-shifting mask blank 100 includes a transparent substrate 10, a phase-shifting film 1 formed on the transparent substrate 10, and a second layer 2 formed on the phase-shifting film 1.

[0044] The phase-shift mask blank of the present invention may include a light-shielding film disposed above the phase-shift film as a second layer, or an etching mask film that acts as a hard mask when a pattern is formed on the phase-shift film. Alternatively, the light-shielding film may be combined with an anti-reflection film to form a second layer. The second layer including the light-shielding film can provide an area in the phase-shift mask that completely blocks the exposure light. The light-shielding film and the anti-reflection film can also be used as processing aid films in etching. There are many reports on the film structures and materials of the light-shielding film and the anti-reflection film (e.g., JP-A2007-33469 (Patent Document 2), JP-A 2007-233179 (Patent Document 3)). A preferred film structure having a combined light-shielding film and an anti-reflection film is exemplified by a structure in which a light-shielding film composed of a chromium-containing material is disposed and an anti-reflection film composed of a chromium-containing material is further disposed, the anti-reflection film being used to reduce reflection from the light-shielding film. The light-shielding film and the anti-reflection film may be composed of a single layer or multiple layers. Examples of chromium-containing materials for light-shielding and antireflective films include elemental chromium and chromium compounds such as chromium oxide (CrO), chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride (CrON), chromium carbonoxylate (CrOC), chromium carbonitride (CrNC), and chromium carbonitride oxide (CrONC). It is important to note that the chemical formula representing a chromium-containing material indicates only the constituent elements, not the composition ratio of the constituent elements (this also applies to chromium-containing materials below).

[0045] For the second layer, which is either a light-shielding film or a combination of a light-shielding film and an anti-reflective film, the chromium content of the chromium compound in the light-shielding film is preferably 40 at% or more, more preferably 60 at% or more, and preferably less than 100 at%, more preferably 99 at% or less, and most preferably 90 at% or less. The oxygen content is preferably 60 at% or less, more preferably 40 at% or less, and preferably 1 at% or more. The nitrogen content is preferably 50 at% or less, more preferably 40 at% or less, and preferably 1 at% or more. The carbon content is preferably 20 at% or less, more preferably 10 at% or less, and preferably 1 at% or more if the etching rate needs to be adjusted. In this case, the total content of chromium, oxygen, nitrogen, and carbon is preferably 95 at% or more, more preferably 99 at% or more, and most preferably 100 at%.

[0046] For the second layer as a combination of a light-shielding film and a reflection-reducing film, the reflection-reducing film is preferably composed of a chromium compound, and the chromium content of the chromium compound is preferably 30 at% or more, more preferably 35 at% or more, and 70 at% or less, more preferably 50 at% or less. The oxygen content is preferably 60 at% or less, and preferably 1 at% or more, more preferably 20 at% or more. The nitrogen content is preferably 50 at% or less, more preferably 30 at% or less, and preferably 1 at% or more, more preferably 3 at% or more. The carbon content is preferably 20 at% or less, more preferably 5 at% or less, and preferably 1 at% or more if necessary to adjust the etching rate. In this case, the total content of chromium, oxygen, nitrogen, and carbon is preferably 95 at% or more, more preferably 99 at% or more, most preferably 100 at%.

[0047] For the second layer as a light-shielding film or a combination of a light-shielding film and a reflection-reducing film, the second layer has a thickness of generally 20 to 100 nm, preferably 40 to 70 nm. The total optical density of the phase shift film and the second layer for exposure light is preferably 2.0 or more, more preferably 2.5 or more, most preferably 3.0 or more.

[0048] Above the second layer of the phase shift mask blank of the present application, a third layer composed of a single layer or multiple layers can be provided. The third layer is generally provided adjacent to the second layer. The third layer is specifically exemplified as a process assist film that functions as a hard mask in patterning the second layer, a light-shielding film, and a combination of a light-shielding film and a reflection-reducing film. The material constituting the third layer is preferably a silicon-containing material, particularly a chromium-free silicon-containing material.

[0049] This embodiment is specifically exemplified as Figure 2 A phase shift mask blank as described in B. Figure 2 B is a cross-sectional view illustrating an exemplary phase shift mask blank of the present application. In this embodiment, the phase shift mask blank 100 includes a transparent substrate 10, a phase shift film 1 formed on the transparent substrate 10, a second layer 2 formed on the phase shift film 1, and a third layer 3 formed on the second layer.

[0050] For the second layer as an optical absorption film or a combination of an optical absorption film and an antireflection film, a process assist film (etching mask film) that functions as a hard mask in patterning the second layer can be provided as a third layer. In the case where a fourth layer is employed as described below, the third layer can function as a process assist film that functions as an etching stopper (etching stopper film) in patterning the fourth layer. The process assist film is preferably composed of a material that is different from the second layer in etching characteristics, such as a material that is resistant to chlorine-based dry etching of a chromium-containing material, particularly a silicon-containing material that is etchable by a fluorine-containing gas such as SF6and CF4. Examples of the silicon-containing material include silicon (elemental) and silicon compounds such as a material containing silicon and either or both of nitrogen and oxygen, a material containing silicon and a transition metal, and a material containing silicon and either or both of nitrogen and oxygen and a transition metal. Examples of the transition metal include molybdenum, tantalum, and zirconium.

[0051] For the third layer as a process assist film, the process assist film is preferably composed of a silicon compound. The silicon content of the silicon compound is preferably 20 at% or more, more preferably 33 at% or more, and preferably 95 at% or less, more preferably 80 at% or less. The nitrogen content is preferably 50 at% or less, more preferably 30 at% or less, and preferably 1 at% or more. The oxygen content is preferably 70 at% or less, more preferably 66 at% or less, and preferably 1 at% or more, more preferably 20 at% or more, if necessary to adjust the etching rate. The third layer can or can not contain a transition metal. When the transition metal is contained, the content of the transition metal is preferably 35 at% or less, more preferably 20 at% or less. In this case, the total content of silicon, oxygen, nitrogen, and the transition metal is preferably 95 at% or more, more preferably 99 at% or more, most preferably 100 at%.

[0052] For the second layer as an optical absorption film or a combination of an optical absorption film and an antireflection film, and for the third layer as a process assist film, the second layer has a thickness of generally 20 to 100 nm, and preferably 40 to 70 nm, and the third layer generally has a thickness of generally 1 to 30 nm, and preferably 2 to 15 nm. The total optical density of the phase shift film and the second layer for exposure light is preferably 2.0 or more, more preferably 2.5 or more, most preferably 3.0 or more.

[0053] For the second layer as a processing assist film, a light-shielding film can be provided as the third layer. A light-shielding film combined with a reflection-reducing film can be provided as the third layer. In this case, the second layer can function as a processing assist film (etching mask film) that functions as a hard mask in patterning the phase shift film and a processing assist film (etching stop film) in patterning the third layer. The processing assist film is exemplified by a film composed of a chromium-containing material such as disclosed in JP-A-2007-241065 (Patent Document 4). The processing assist film can be composed of a single layer or multiple layers. Examples of the chromium-containing material of the processing assist film include chromium (elemental) and chromium compounds such as chromium oxide (CrO), chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromium carbonitride (CrNC), and chromium oxycarbonitride (CrONC).

[0054] For the second layer as a processing assist film, the chromium content of the chromium compound in the second layer is preferably 40 at% or more, more preferably 50 at% or more, and preferably 100 at% or less, more preferably 99 at% or less, most preferably 90 at% or less. The oxygen content is preferably 60 at% or less, more preferably 55 at% or less, and preferably 1 at% or more if it is necessary to adjust the etching rate. The nitrogen content is preferably 50 at% or less, more preferably 40 at% or less, and preferably 1 at% or more. The carbon content is preferably 20 at% or less, more preferably 10 at% or less, and preferably 1 at% or more if it is necessary to adjust the etching rate. In this case, the total content of chromium, oxygen, nitrogen, and carbon is preferably 95 at% or more, particularly 99 at% or more, most preferably 100 at%.

[0055] The light-shielding film and the reflection-reducing film as the third layer are preferably composed of a material different from the second layer in etching characteristics, such as a material resistant to chlorine-based dry etching of the chromium-containing material, particularly a silicon-containing material etchable by a fluorine-containing gas such as SF6and CF4. Examples of the silicon-containing material include silicon (elemental) and silicon compounds such as a material containing silicon and either or both of nitrogen and oxygen, a material containing silicon and a transition metal, and a material containing silicon and either or both of nitrogen and oxygen and a transition metal. Examples of the transition metal include molybdenum, tantalum, and zirconium.

[0056] For the third layer which is a light shielding film or a combination of a light shielding film and an antireflection film, the light shielding film and the antireflection film are preferably composed of a silicon compound. The silicon content of the silicon compound is preferably 10 at% or more, more preferably 30 at% or more, and is preferably less than 100 at%, more preferably 95 at% or less. The nitrogen content is preferably 50 at% or less, preferably 40 at% or less, most preferably 20 at% or less, and is preferably 1 at% or more if it is necessary to adjust the etching rate. The oxygen content is preferably 60 at% or less, more preferably 30 at% or less, and is preferably 1 at% or more if it is necessary to adjust the etching rate. The transition metal content is preferably 35 at% or less, preferably 20 at% or less, and is preferably 1 at% or more. In this case, the total content of silicon, oxygen, nitrogen, and transition metal is preferably 95 at% or more, more preferably 99 at% or more, most preferably 100 at%.

[0057] For the second layer which is a process assist film, and for the third layer which is a light shielding film or a combination of a light shielding film and an antireflection film, the second layer has a thickness of generally 1 to 20 nm, preferably 2 to 10 nm, and the third layer has a thickness of generally 20 to 100 nm, preferably 30 to 70 nm. The total optical density of the phase shift film, the second layer, and the third layer for exposure light is preferably 2.0 or more, more preferably 2.5 or more, most preferably 3.0 or more.

[0058] A fourth layer composed of a single layer or multiple layers can be provided above the third layer of the phase shift mask blank of the present application. The fourth layer is generally provided adjacent to the third layer. The fourth layer is specifically exemplified as a process assist film which functions as a hard mask in patterning the third layer. The material of the fourth layer is preferably a chromium-containing material.

[0059] This embodiment is specifically exemplified as Figure 2 the phase shift mask blank explained in C. Figure 2 C is a cross-sectional view illustrating an exemplary phase shift mask blank of the present application. In this embodiment, the phase shift mask blank 100 includes a transparent substrate 10, a phase shift film 1 formed on the transparent substrate 10, a second layer 2 formed on the phase shift film 1, a third layer 3 formed on the second layer 2, and a fourth layer 4 formed on the third layer 3.

[0060] For the third layer as a light shielding film or a combination of a light shielding film and an antireflection film, a process assist film (etching mask film) that functions as a hard mask in patterning the third layer can be provided as a fourth layer. The process assist film is preferably composed of a material that is different from the third layer in etching characteristics, such as a fluorine-based dry etching-resistant material, particularly a chromium-containing material that is etchable by an oxygen-containing chlorine-based gas. The chromium-containing material is exemplified by chromium (elemental) and chromium compounds such as chromium oxide (CrO), chromium nitride (CrN), chromium carbide (CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromium carbonitride (CrNC), and chromium oxycarbonitride (CrONC).

[0061] For the fourth layer as a process assist film, the chromium content of the fourth layer is preferably 40 at% or more, more preferably 50 at% or more, and preferably 100 at% or less, more preferably 99 at% or less, most preferably 90 at% or less. The oxygen content is preferably 60 at% or less, more preferably 40 at% or less, and preferably 1 at% or more if necessary to adjust the etching rate. The nitrogen content is preferably 50 at% or less, more preferably 40 at% or less, and preferably 1 at% or more if necessary to adjust the etching rate. The carbon content is preferably 20 at% or less, more preferably 10 at% or less, and preferably 1 at% or more if necessary to adjust the etching rate. In this case, the total content of chromium, oxygen, nitrogen, and carbon is preferably 95 at% or more, more preferably 99 at% or more, most preferably 100 at%.

[0062] For the second layer as a process assist film, for the third layer as a light shielding film or a combination of a light shielding film and an antireflection film, and for the fourth layer as a process assist film, the second layer has a thickness of typically 1 to 20 nm, preferably 2 to 10 nm, the third layer has a thickness of typically 20 to 100 nm, preferably 30 to 70 nm, and the fourth layer has a thickness of typically 1 to 30 nm, preferably 2 to 20 nm. The total optical density of the phase shift film, the second layer, and the third layer for exposure light is preferably 2.0 or more, more preferably 2.5 or more, most preferably 3.0 or more.

[0063] The film composed of a chromium-containing material for the second layer and the fourth layer can be formed by using a target such as a chromium target or a chromium-containing target to which one or more elements selected from oxygen, nitrogen, and carbon are added, and reactive sputtering using a sputtering gas containing a rare gas such as Ar, He, and Ne to which a reactive gas selected from an oxygen-containing gas, a nitrogen-containing gas, and a carbon-containing gas is appropriately added in accordance with the composition of the film to be formed.

[0064] Meanwhile, the film composed of a silicon-containing material for the third layer can be formed by reactive sputtering using a target such as a silicon target, a silicon nitride target, a target containing both silicon and silicon nitride, a transition metal target, and a composite target of silicon and a transition metal, and a sputtering gas containing a rare gas such as Ar, He, and Ne to which a reactive gas selected from an oxygen-containing gas, a nitrogen-containing gas, and a carbon-containing gas is added as appropriate in accordance with the composition of the film to be formed.

[0065] The phase shift mask of the present application can be manufactured from a phase shift mask blank by any conventional method. In general, a phase shift mask can be manufactured from an exemplary phase shift mask blank including a film composed of a chromium-containing material formed as a second layer on a phase shift film by the following process.

[0066] First, an electron beam resist film is formed on the second layer of the phase shift mask blank, a pattern is drawn by electron beam lithography, followed by a predetermined development operation to obtain a resist pattern. Next, the obtained resist pattern is used as an etching mask, and the resist pattern is transferred to the second layer by chlorine-based dry etching containing oxygen to obtain a second layer pattern. Next, the obtained second layer pattern is used as an etching mask, and the second layer pattern is transferred onto the phase shift film by fluorine-based dry etching to obtain a phase shift film pattern. In the case where a portion of the second layer is required to be left, then another resist pattern is formed on the second layer to protect the portion to be left, and the portion of the second layer not protected by the resist pattern is removed by chlorine-based dry etching containing oxygen. The resist pattern is then removed by a conventional method to obtain a phase shift mask.

[0067] In general, a phase shift mask can be manufactured from an exemplary phase shift mask blank including a light shielding film composed of a chromium-containing material or a combination of a light shielding film and an antireflection film as a second layer on a phase shift film, and a process assist film composed of a silicon-containing material as a third layer on the second layer by the following process.

[0068] First, an electron beam resist film is formed on the third layer of the phase shift mask blank, a pattern is drawn by electron beam lithography, followed by a predetermined development operation, to obtain a resist pattern. Next, the obtained resist pattern is used as an etching mask, and the resist pattern is transferred to the third layer by fluorine-based dry etching to obtain a third layer pattern. Next, the obtained third layer pattern is used as an etching mask, and the third layer pattern is transferred to the second layer by oxygen-containing chlorine-based dry etching to obtain a second layer pattern in which the portion of the phase shift film to be removed has been removed. Then, the resist pattern is removed. Next, another resist pattern that protects the portion of the third layer to be retained is formed on the third layer, and the second layer pattern is transferred to the phase shift film by fluorine-based dry etching using the obtained second layer pattern as an etching mask to obtain a phase shift film pattern while removing the portion of the third layer not protected by the resist pattern. Then, the resist pattern is removed by a conventional method to obtain a phase shift mask.

[0069] Meanwhile, a phase shift mask can generally be manufactured from an exemplary phase shift mask blank including a process assist film composed of a chromium-containing material as a second layer on a phase shift film, a light shielding film composed of a silicon-containing material as a third layer on the second layer, or a combination of the light shielding film and an antireflection film, by the following process.

[0070] First, an electron beam resist film is formed on the third layer of the phase shift mask blank, a pattern is drawn by electron beam lithography, followed by a predetermined development operation, to obtain a resist pattern. Next, the obtained resist pattern is used as an etching mask, and the resist pattern is transferred to the third layer by fluorine-based dry etching to obtain a third layer pattern. Next, the obtained third layer pattern is used as an etching mask, and the third layer pattern is transferred to the second layer by oxygen-containing chlorine-based dry etching to obtain a second layer pattern in which the portion of the phase shift film to be removed has been removed. Then, the resist pattern is removed. Next, another resist pattern that protects the portion of the third layer to be retained is formed on the third layer, and the second layer pattern is transferred to the phase shift film by fluorine-based dry etching using the obtained second layer pattern as an etching mask to obtain a phase shift film pattern while removing the portion of the third layer not protected by the resist pattern. Then, the resist pattern is removed by a conventional method to obtain a phase shift mask.

[0071] Further, a phase shift mask can generally be manufactured from an exemplary phase shift mask blank including a process assist film composed of a chromium-containing material as a second layer on a phase shift film, a light shielding film composed of a silicon-containing material as a third layer on the second layer, or a combination of the light shielding film and an antireflection film, and a process assist film composed of a chromium-containing material as a fourth layer on the third layer, by the following process.

[0072] First, an electron beam resist film is formed on the fourth layer of the phase shift mask blank, a pattern is drawn by electron beam lithography, followed by a predetermined development operation, to obtain a resist pattern. Next, the obtained resist pattern is used as an etching mask, and the resist pattern is transferred to the fourth layer by oxygen-containing chlorine-based dry etching to obtain a fourth layer pattern. Next, the obtained fourth layer pattern is used as an etching mask, and the fourth layer pattern is transferred to the third layer by fluorine-based dry etching to obtain a third layer pattern. Then the resist pattern is removed. Next, another resist pattern is formed on the fourth layer to protect the portion of the third layer to be retained, and the obtained third layer pattern is used as an etching mask, and the third layer pattern is transferred to the second layer by oxygen-containing chlorine-based dry etching to obtain a second layer pattern, and at the same time, the portion of the fourth layer not protected by the resist pattern is removed. Next, the second layer pattern is used as an etching mask, and the second layer pattern is transferred to the phase shift film by fluorine-based dry etching to obtain a phase shift film pattern, and at the same time, the portion of the third layer not protected by the resist pattern is removed. Then the resist pattern is removed by a conventional method. Further, the portion of the second layer exposed in the portion of the third layer which has been removed and the portion of the fourth layer exposed in the portion of the resist pattern which has been removed are removed by oxygen-containing chlorine-based dry etching to obtain a phase shift mask.

[0073] Embodiment

[0074] Embodiments of the present application will be given below by way of example, not by way of limitation.

[0075] Embodiment 1

[0076] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering device, and a single layer phase shift film consisting of SiN which is a compositionally graded layer having a composition which continuously changes in the thickness direction and has optical properties which vary in the thickness direction was formed on the quartz substrate by using a silicon target as a sputtering target, argon and nitrogen as sputtering gases, under conditions of a discharge power of 1.9 kW, an argon flow rate of 28 seem, a nitrogen flow rate which continuously varied from 20 to 44 seem.

[0077] With respect to a KrF excimer laser (wavelength 248 nm), the compositionally graded layer had a maximum refractive index n(H) of 2.61, a minimum refractive index n(L) of 2.33, a difference between the refractive indices n of 0.28; and had a maximum extinction coefficient k(H) of 1.4, a minimum extinction coefficient k(L) of 0.05, a difference between the extinction coefficients k of 1.35; and had a region in which the refractive index n was in the range of 2.55 or more, the extinction coefficient k was in the range of 1.0 or less, and the thickness was about 15 nm.

[0078] The film had a continuously varying silicon content of 58.5 at% to 46.8 at% in the thickness direction from the quartz substrate side analyzed by XPS (X-ray photoelectron spectroscopy, the same applies hereinafter), the difference between the contents being 11.7. The film had a continuously varying content ratio N / (Si+N) of 0.41 to 0.52 in the thickness direction. The phase shift film had a thickness of 87 nm, a phase shift of 177.5° for a KrF excimer laser (wavelength 248 nm), a transmittance of 5.9%. The phase shift and the transmittance in the in-plane varied in the ranges of 0.4% and 1.9%, respectively, which was satisfactory.

[0079] Example 2

[0080] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering device, and a single layer phase shift film consisting of SiN (it is a composition gradient layer) having a continuously varying composition in the thickness direction and having optical properties varying in the thickness direction was formed on the quartz substrate by using a silicon target as a sputtering target, argon and nitrogen as sputtering gases, under conditions of a discharge power of 1.9 kW, an argon flow rate of 28 seem, a continuously varying nitrogen flow rate of 19 to 43 seem.

[0081] The composition gradient layer had a maximum refractive index n(H) of 2.61, a minimum refractive index n(L) of 2.33, a difference between the refractive indices n of 0.28; and had a maximum extinction coefficient k(H) of 1.5, a minimum extinction coefficient k(L) of 0.05, a difference between the extinction coefficients k of 1.45; and had a region in which the refractive index n was in the range of 2.55 or more, the extinction coefficient k was in the range of 1.0 or less, and the thickness was about 15 nm, for a KrF excimer laser (wavelength 248 nm).

[0082] The film had a continuously varying silicon content of 59.1 at% to 46.5 at% in the thickness direction from the quartz substrate side analyzed by XPS, the difference between the contents being 12.6. The film had a continuously varying content ratio N / (Si+N) of 0.40 to 0.53 in the thickness direction. The phase shift film had a thickness of 85 nm, a phase shift of 176.1° for a KrF excimer laser (wavelength 248 nm), a transmittance of 5.8%. The phase shift and the transmittance in the in-plane varied in the ranges of 0.9% and 1.7%, respectively, which was satisfactory.

[0083] Example 3

[0084] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering apparatus, and by using a silicon target as a sputtering target, argon gas, oxygen gas, and nitrogen gas as sputtering gases, under conditions of a discharge power of 1.9 kW, an argon gas flow rate of 28 seem, an oxygen gas flow rate of 1.0 seem, a nitrogen gas flow rate continuously varied from 19 to 43 seem, a single-layer phase shift film consisting of SiON (which is a composition gradient layer) having a composition continuously varied in the thickness direction and having optical characteristics varied in the thickness direction was formed on the quartz substrate.

[0085] For a KrF excimer laser (wavelength 248 nm), the composition gradient layer had a maximum refractive index n(H) of 2.59, a minimum refractive index n(L) of 2.30, a difference between the refractive indices n of 0.29; and had a maximum extinction coefficient k(H) of 1.4, a minimum extinction coefficient k(L) of 0.05, a difference between the extinction coefficients k of 1.35, and had a region in which the refractive index n was in the range of 2.55 or more, the extinction coefficient k was in the range of 1.0 or less, and the thickness was about 14 nm.

[0086] The film had a continuously varied silicon content of 56.7 at% to 45.4 at% in the thickness direction from the quartz substrate side by XPS analysis, a difference between the contents of 11.3. The film had a continuously varied content ratio N / (Si+N) of from 0.42 to 0.52 in the thickness direction. The film had an oxygen content of substantially constant 2 at% in the thickness direction. The phase shift film had a thickness of 88 nm, a phase shift of 177.5° for a KrF excimer laser (wavelength 248 nm), a transmittance of 6.0%. The phase shift and the transmittance in the in-plane varied in the ranges of 0.4% and 0.8%, respectively, which was satisfactory.

[0087] Comparative Example 1

[0088] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering apparatus, and by using a silicon target as a sputtering target, argon gas, oxygen gas, and nitrogen gas as sputtering gases, under conditions of a discharge power of 1.9 kW, an argon gas flow rate of 28 seem, an oxygen gas flow rate of 1.0 seem, a nitrogen gas flow rate continuously varied from 19 to 43 seem, a single-layer phase shift film consisting of SiON (which is a composition gradient layer) having a composition continuously varied in the thickness direction and having optical characteristics varied in the thickness direction was formed on the quartz substrate.

[0089] For the KrF excimer laser (wavelength 248 nm), the lower layer has a refractive index n of 2.45, the upper layer has a refractive index n of 2.38, the difference between the refractive indices n is 0.07; the lower layer has an extinction coefficient k of 1.5, the upper layer has an extinction coefficient k of 0.07, the difference between the extinction coefficients k is 1.43, and there is no region in which the refractive index n is in the range of 2.55 or more and the extinction coefficient k is in the range of 1.0 or less.

[0090] The film has a silicon content of 59.2 at% in the lower layer and a silicon content of 46.5 at% in the upper layer, the difference between the contents being 12.7, by XPS analysis. The film has a content ratio N / (Si+N) of 0.40 in the lower layer and a content ratio N / (Si+N) of 0.53 in the upper layer. The phase shift film has a phase shift of 177.0° and a transmittance of 6.2% for the KrF excimer laser (wavelength 248 nm). The ranges of variation in the phase shift and the transmittance in-plane are 0.9% and 3.6%, respectively, however, the thickness of the film is 91 nm, and the film is formed as a thick film.

[0091] Comparative Example 2

[0092] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering device, and a single layer phase shift film composed of SiN having a constant composition in the thickness direction and optical properties that do not change in the thickness direction was formed by using a silicon target as a sputtering target, argon and nitrogen as sputtering gases, under conditions of a discharge power of 1.9 kW, an argon gas flow rate of 28 seem, and a nitrogen gas flow rate of 27 seem.

[0093] For the KrF excimer laser (wavelength 248 nm), the layer has a refractive index n of 2.60 and an extinction coefficient k of 0.7, and the entire layer satisfies the range in which the refractive index n is 2.55 or more and the extinction coefficient k is 1.0 or less.

[0094] The film has a silicon content of 50.4 at% by XPS analysis. The film has a content ratio N / (Si+N) of 0.49. The phase shift film has a thickness of 79 nm, a phase shift of 177.2°, and a transmittance of 4.5% for the KrF excimer laser (wavelength 248 nm). However, the ranges of variation in the phase shift and the transmittance in-plane are 0.5% and 11.1%, respectively, and the range of variation in the transmittance is disadvantageous.

[0095] Comparative Example 3

[0096] A 152 mm square, 6.35 mm thick 6025 quartz substrate was placed in the chamber of a sputtering apparatus, and a single-layer phase shift film composed of MoSiON having a constant composition in the thickness direction and optical characteristics that do not change in the thickness direction was formed by using a molybdenum silicon (MoSi) target and a silicon target as sputtering targets, argon, nitrogen, and oxygen as sputtering gases, under conditions of 1.2 kW of MoSi target discharge power, 8 kW of silicon target discharge power, 5 seem of argon flow rate, 65 seem of nitrogen flow rate, 2.5 seem of oxygen flow rate.

[0097] For a KrF excimer laser (wavelength 248 nm), the layer had a refractive index n of 2.25, an extinction coefficient k of 0.52, and there was no region in which the refractive index n was in the range of 2.55 or more and the extinction coefficient k was in the range of 1.0 or less.

[0098] The film had a molybdenum content of 14 at%, a silicon content of 35 at%, a nitrogen content of 45 at%, and an oxygen content of 6 at% by XPS analysis. The phase shift film had a phase shift of 175.1° and a transmittance of 6.2% for a KrF excimer laser (wavelength 248 nm). The phase shift and the transmittance in the in-plane direction varied by 0.3% and 1.7%, respectively, however, the thickness of the film was 99 nm, and the film was formed as a thick film.

Claims

1. A phase-shifting mask blank comprising a substrate and a phase-shifting film thereon, said phase-shifting film being composed of a material containing silicon and nitrogen but free of transition metals, wherein... The phase-shifting film, relative to the exposure light from a KrF excimer laser, has a phase shift of 170 to 190° and a transmittance of 4 to 8%, as well as a thickness of 85-90 nm. The phase-shifting film comprises at least one composition-gradient layer having a composition that varies continuously in the thickness direction and refractive index n and extinction coefficient k that vary in the thickness direction relative to the exposure light. The difference between the maximum refractive index n(H) and the minimum refractive index n(L) of the gradient layer is less than 0.40, and the difference between the maximum extinction coefficient k(H) and the minimum extinction coefficient k(L) is less than 1.

5.

2. The phase-shifting mask blank according to claim 1, wherein, The constituent gradient layer has a minimum refractive index n (L) of 2.3 or more and a maximum extinction coefficient k (H) of 2 or less, and the constituent gradient layer includes a region that satisfies a refractive index n of 2.55 or more and an extinction coefficient k of 1.0 or less, and the region has a thickness of 5 to 30 nm.

3. The phase-shifting mask blank according to claim 1, wherein, The gradient layer has a region in which the content ratio N / (Si+N) changes continuously in the thickness direction within the range of 0.2 to 0.57, where the ratio N / (Si+N) represents the nitrogen content relative to the sum of silicon and nitrogen content, expressed in at%.

4. The phase-shifting mask blank according to claim 1, wherein, The difference between the maximum and minimum silicon content of the gradient layer is less than 30, expressed in at%.

5. The phase-shifting mask blank according to claim 1, wherein... In the phase-shifting film, the ratio of the difference between the maximum and minimum phase shift to the average phase shift in the plane is less than 3%, and the ratio of the difference between the maximum and minimum transmittance to the average transmittance in the plane is less than 5%.

6. The phase-shifting mask blank according to claim 1, wherein, The material containing silicon and nitrogen but without transition metals is a material composed of silicon and nitrogen.

7. The phase-shifting mask blank according to claim 1, further comprising a second layer on the phase-shifting film, the second layer being composed of a single layer or multiple layers, the second layer being composed of a chromium-containing material.

8. A phase-shifting mask manufactured using the phase-shifting mask blank of claim 1.

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