Mask blank and manufacturing method of transfer mask

Abstract

The present application provides a mask blank capable of suppressing reduction in etching rate of the entire hard mask film while improving pattern resolution, CD in-plane uniformity, and CD linearity. The mask blank has a structure in which a pattern-forming film and a hard mask film are sequentially stacked on a light-transmissive substrate, wherein the pattern-forming film is formed of a material containing chromium, the hard mask film includes a stacked structure of a lower layer and an upper layer, the lower layer is formed of a material containing silicon and oxygen, the upper layer is formed of a material containing tantalum and oxygen, the content of the oxygen is 30 atomic % or more, and the ratio of the thickness of the upper layer to the thickness of the entire hard mask film is 0.7 or less.

Description

Technical Field

[0001] This invention relates to a mask blank and a method for manufacturing a transfer mask using the mask blank. Background Technology

[0002] Previously known mask blanks for halftone phase-shift masks included those having a structure on which a halftone phase-shift film formed of a metal silicide-based material, a light-shielding film formed of a chromium-based material, and an etching mask film (hard mask film) formed of an inorganic material were stacked on a light-transmitting substrate. When manufacturing a phase-shift mask using this mask blank, firstly, an etching resist pattern formed on the surface of the mask blank is used as a mask, and the etching mask film is patterned using dry etching with a fluorine-based gas. Next, the etching mask film is used as a mask, and the light-shielding film is patterned using dry etching with a mixture of chlorine and oxygen gases. Finally, the pattern of the light-shielding film is used as a mask, and the phase-shift film is patterned using dry etching with a fluorine-based gas.

[0003] For example, Patent Document 1 describes a problem where, when a silicon-containing inorganic film is used as a hard mask and a resist film is formed by coating the silicon-containing inorganic film, the resist has poor adhesion and peels off during the development of the resist pattern. Furthermore, it describes that, in order to improve the adhesion of the resist film, the surface of the silicon-containing inorganic film must be silanized using hexamethyldisilazane or similar substances.

[0004] Furthermore, Patent Document 2 discloses a mask blank having a structure in which an etching mask film (hard mask film) and a conductive mask film are sequentially stacked on a chromium-based light-shielding film. Both the etching mask film and the conductive mask film function as hard masks relative to the light-shielding film. SiON is cited as an example of a material for the etching mask film, and TaN is cited as an example of a material for the conductive mask film.

[0005] Furthermore, Patent Document 3 discloses a mask blank having a structure in which a hard mask film is laminated on a chromium-based light-shielding film. The hard mask film is formed of a material containing tantalum and oxygen, with an oxygen content of 50 atomic%.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 6234898

[0009] Patent Document 2: Japanese Patent No. 4989800

[0010] Patent Document 3: Japanese Patent Application Publication No. 2016-188958 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] With the further miniaturization of semiconductor devices, there is a growing demand for improved Critical Dimension (CD) accuracy of the patterns on transfer masks. When using mask blanks obtained by coating a resist film onto the surface of an existing Si-based hard mask film after silanization treatment, and then performing exposure and development processes on this resist film to create fine patterns, issues arise regarding insufficient pattern resolution, CD uniformity (CDU), and CD linearity.

[0013] It has been found that when using hard masks made of tantalum-based materials, the adhesion to the resist film is sufficiently high even without silanization. Furthermore, it has been discovered that when the resist film formed by coating is exposed and developed to create a fine pattern, the resolution, in-plane uniformity of the CD (coating density), and CD linearity of the resist pattern are higher than those of hard masks made of Si-based materials.

[0014] It is known that tantalum-based thin films are prone to oxidation. Furthermore, for hard mask films, to fully utilize their function, the film thickness is thinner compared to that used for light-shielding films. When hard mask films are formed from tantalum-based materials, overall oxidation of the film is likely to occur. Considering the compositional stability of the film after deposition, it is desirable for the mask film to contain oxygen in a certain amount (30 atomic percent or more).

[0015] Generally, both silicon-based and tantalum-based thin films can be patterned using dry etching with fluorine gases. However, tantalum-based films suffer from a slower etching rate compared to silicon-based films. The purpose of a hard mask is to reduce the thickness of the resist film; therefore, the slow etching rate is particularly problematic when a hard mask is formed from tantalum-based materials. That is, when a hard mask is formed from tantalum-based materials, the resist film must be thickened for patterning via dry etching, compared to the case of a hard mask formed from silicon-based materials. Furthermore, thickening the resist film reduces the resolution, in-plane uniformity (CD), and CD linearity of the resist pattern, thus negating the advantages over hard masks formed from silicon-based materials.

[0016] This invention was made to solve the aforementioned problems. The object of this invention is to provide a mask blank that can improve pattern resolution, in-plane uniformity of the CD (coaxial groove) and CD linearity while suppressing a decrease in the overall etching rate of the hard mask film. Furthermore, this invention provides a method for manufacturing a transfer mask capable of forming fine patterns on a pattern-forming thin film with good precision using this mask blank.

[0017] Problem Solving Methods

[0018] The present invention provides the following solution as a method for solving the above-mentioned problems.

[0019] (Option 1)

[0020] A mask blank has a structure in which a pattern-forming thin film and a hard mask film are sequentially stacked on a light-transmitting substrate, wherein...

[0021] The aforementioned film is formed from a chromium-containing material.

[0022] The aforementioned hard mask film comprises a stacked structure of a lower layer and an upper layer.

[0023] The lower layer described above is formed of a material containing silicon and oxygen.

[0024] The aforementioned upper layer is formed of a material containing tantalum and oxygen, wherein the oxygen content is 30 atomic percent or more.

[0025] The ratio of the thickness of the upper layer to the overall thickness of the hard mask film is less than 0.7.

[0026] (Option 2)

[0027] According to the mask blank described in Scheme 1, wherein...

[0028] The thickness of the aforementioned upper layer is greater than 1 nm.

[0029] (Option 3)

[0030] According to the mask blank described in scheme 1 or 2, wherein,

[0031] The thickness of the aforementioned hard mask film is greater than 4 nm and less than 14 nm.

[0032] (Option 4)

[0033] According to any one of Schemes 1 to 3, the mask blank, wherein...

[0034] The upper layer mentioned above contains boron.

[0035] (Option 5)

[0036] According to any one of Schemes 1 to 4, the mask blank, wherein...

[0037] The aforementioned lower layer is formed of a material having a combined silicon and oxygen content of 96 atomic% or more, or a material having a combined silicon, nitrogen, and oxygen content of 96 atomic% or more.

[0038] (Option 6)

[0039] According to any one of Schemes 1 to 5, the mask blank, wherein...

[0040] The aforementioned upper layer is formed of a material having a total content of tantalum and oxygen of 90 atomic% or more, or a material having a total content of tantalum, oxygen and boron of 90 atomic% or more.

[0041] (Option 7)

[0042] According to any one of Schemes 1 to 6, the mask blank, wherein...

[0043] The aforementioned film is a light-shielding film.

[0044] (Option 8)

[0045] According to any one of Schemes 1 to 7, the mask blank, wherein...

[0046] A phase-shifting film made of a silicon-containing material is provided between the light-transmitting substrate and the light-shielding film.

[0047] (Option 9)

[0048] A method for manufacturing a transfer mask, which uses a mask blank as described in any one of claims 1 to 7, the method comprising:

[0049] The process of forming an anti-etching pattern on the hard mask film of the above-mentioned mask blank;

[0050] The process of forming a hard mask pattern by dry etching the hard mask film using fluorine gas, using the aforementioned resist pattern as a mask; and

[0051] The process of forming a thin film pattern by dry etching a thin film using a mixture of chlorine and oxygen as a mask, using the aforementioned hard mask pattern as a mask.

[0052] (Option 10)

[0053] A method for manufacturing a transfer mask, which uses the mask blank described in embodiment 8, the method comprising:

[0054] The process of forming an anti-etching pattern on the hard mask film of the above-mentioned mask blank;

[0055] The process of forming a hard mask pattern by dry etching the hard mask film using fluorine gas, using the above-mentioned resist pattern as a mask.

[0056] The process of forming a light-shielding film pattern by dry etching the light-shielding film using a mixture of chlorine and oxygen gas, using the aforementioned hard mask pattern as a mask; and

[0057] The process involves using the aforementioned light-shielding film pattern as a mask, dry etching the aforementioned phase-shifting film with fluorine gas to form a phase-shifting film pattern, and simultaneously removing the aforementioned hard mask pattern.

[0058] The effects of the invention

[0059] According to the mask blank of the present invention having the above-described embodiments, when a resist film is formed on a hard mask by coating it with a material containing tantalum and oxygen as the upper layer, and then a micro-pattern is formed by exposure drawing and development, the pattern resolution, in-plane uniformity of the etching pattern, and the etching linearity of the resist pattern can be improved. Furthermore, by making the ratio of the thickness of the upper layer to the overall thickness of the hard mask film 0.7 or less, and by forming the lower layer of the hard mask film with a material containing silicon and oxygen, the decrease in the etching rate of the hard mask film as a whole relative to fluorine gases can be suppressed. Attached Figure Description

[0060] Figure 1 This is a cross-sectional schematic diagram of an implementation method for the mask blank.

[0061] Figure 2 This is a cross-sectional schematic diagram showing the manufacturing process of a phase-shifting mask.

[0062] Figure 3 This is a graph showing the relationship between the ratio of the thickness of the upper layer to the overall thickness of the hard mask film and the ratio of the overall etching rate of the hard mask film to the etching rate of the SiON monolayer film.

[0063] Symbol Explanation

[0064] 1. Transparent substrate

[0065] 2. Phase Shifting Film

[0066] 2a Phase-shifting film pattern

[0067] 3 shading film

[0068] 3a, 3b Light-blocking film patterns

[0069] 4. Hard mask

[0070] 41 Lower level

[0071] 42 Upper level

[0072] 4a Hard mask pattern

[0073] 41a Lower layer pattern

[0074] 42a Upper layer pattern

[0075] 5a Anti-corrosion pattern

[0076] 6b Anti-corrosion pattern

[0077] 100 Mask blank

[0078] 200 phase shift mask Detailed Implementation

[0079] Hereinafter, the detailed configuration of various embodiments of the present invention will be described based on the accompanying drawings. It should be noted that in each drawing, the same constituent elements are labeled with the same symbols.

[0080] <Mask blank>

[0081] Figure 1 A schematic configuration of an embodiment of the mask blank is shown. Figure 1 The mask blank 100 shown is composed of a phase-shifting film 2, a light-shielding film 3, and a hard mask film 4 sequentially stacked on a main surface of a light-transmitting substrate 1. Alternatively, the mask blank 100 may also be composed of a resist film stacked on the hard mask film 4 as needed. The main components of the mask blank 100 will be described in detail below.

[0082] [Transparent substrate]

[0083] The light-transmitting substrate 1 is formed from a material with good transmittance to the exposure light used in the lithographic printing exposure process. Such materials can include synthetic quartz glass, aluminosilicate glass, soda-lime glass, low thermal expansion glass (SiO2-TiO2 glass, etc.), and various other glass substrates. In particular, substrates using synthetic quartz glass are suitable for use as the light-transmitting substrate 1 of the mask blank 100 due to their high transmittance to ArF excimer lasers (wavelength: approximately 193 nm).

[0084] It should be noted that the exposure process in offset printing mentioned here refers to the exposure process in offset printing using a phase-shifting mask made using the mask blank 100. Hereinafter, the exposure light refers to the exposure light used in this exposure process. As this exposure light, any light among ArF excimer lasers (wavelength: 193nm), KrF excimer lasers (wavelength: 248nm), and i-rays (wavelength: 365nm) can be used. From the viewpoint of miniaturizing the phase-shifting film pattern in the exposure process, it is preferable to use an ArF excimer laser as the exposure light. Therefore, the following description addresses the implementation of using an ArF excimer laser as the exposure light.

[0085] [Phase-shifting film]

[0086] The phase shift film 2 has a given transmittance to the exposure light used in the exposure transfer process and has the optical properties described below, such that the exposure light transmitted through the phase shift film 2 achieves a given phase difference relative to the exposure light transmitted through the atmosphere only at a distance equal to the thickness of the phase shift film 2.

[0087] Such a phase-shifting film 2 is preferably formed of a material containing silicon (Si). Furthermore, it is more preferable that the phase-shifting film 2 is formed of a material containing nitrogen (N) in addition to silicon. Such a phase-shifting film 2 uses a material that can be patterned by dry etching using fluorine gases and has sufficient etching selectivity for the chromium-containing light-shielding film 3 described later.

[0088] In addition, as long as the phase-shifting film 2 can be patterned by dry etching using fluorine gas, it may further contain one or more elements selected from half-metallic elements, non-metallic elements, and metallic elements.

[0089] The half-metal element, excluding silicon, can be any half-metal element. The non-metal element, excluding nitrogen, can also be any non-metal element; for example, it is preferably composed of one or more elements selected from oxygen (O), carbon (C), fluorine (F), and hydrogen (H). Examples of metallic elements include molybdenum (Mo), tungsten (W), titanium (Ti), tantalum (Ta), zirconium (Zr), hafnium (Hf), niobium (Nb), vanadium (V), cobalt (Co), chromium (Cr), nickel (Ni), ruthenium (Ru), tin (Sn), boron (B), and germanium (Ge).

[0090] Such a phase-shifting film 2 is, for example, made of MoSiN. The refractive index n, extinction coefficient k, and film thickness of the phase-shifting film 2 are selected in a way that satisfies a given phase difference (e.g., 150 [deg] to 210 [deg]) and a given transmittance (e.g., 1% to 30%) for the exposure light (e.g., ArF excimer laser). The composition of the film material and the film formation conditions are adjusted in a way that achieves the refractive index n and the extinction coefficient k.

[0091] [Light-shielding film]

[0092] In this embodiment, the mask blank 100 includes a light-shielding film 3 as a thin film for forming a transfer pattern. The light-shielding film 3 is a film formed on the mask blank 100 that constitutes a light-shielding film pattern including a light-shielding band pattern, and is a film that has light-shielding properties against the exposure light used in the exposure process of offset printing. For the light-shielding film 3, it is required that, through its stacked structure with the phase-shifting film 2, the optical density (OD) for, for example, an ArF excimer laser with a wavelength of 193 nm is greater than 2.0, preferably 2.8 or more, and more preferably 3.0 or more. In addition, in the exposure process of offset printing, in order to prevent poor exposure transfer caused by the reflection of exposure light, the surface reflectivity of the exposure light on both main surfaces is suppressed to a low level. In particular, it is desirable that the reflectivity on the surface side of the light-shielding film 3 (the surface furthest from the light-transmitting substrate 1) irradiated by the reflected light from the reduction optical system of the exposure apparatus is, for example, 40% or less (preferably 30% or less). This is to suppress stray light generated by multiple reflections between the surface of the light-shielding film 3 and the lens of the reduced optical system.

[0093] Furthermore, the light-shielding film 3 must function as an etching mask during dry etching using fluorine-based gases to form a transfer pattern (phase-shift film pattern) on the phase-shift film 2. Therefore, the light-shielding film 3 must be made of a material that exhibits sufficient etching selectivity for the phase-shift film 2 during dry etching using fluorine-based gases. The light-shielding film 3 is required to form the fine pattern to be formed on the phase-shift film 2 with good precision. The film thickness of the light-shielding film 3 is preferably 70 nm or less, more preferably 65 nm or less, and particularly preferably 60 nm or less. If the film thickness of the light-shielding film 3 is too thick, it is impossible to form the fine pattern to be formed with high precision. On the other hand, the light-shielding film 3 is required to meet the optical density requirements described above. Therefore, the film thickness of the light-shielding film 3 is required to be greater than 15 nm, preferably 20 nm or more, and more preferably 25 nm or more.

[0094] The light-shielding film 3 is formed of a chromium-containing material. The chromium-containing material can be elemental chromium or a material containing chromium and additive elements. Oxygen and / or nitrogen are preferred as such additive elements from the perspective of accelerating the dry etching process. It should be noted that, in addition to these, the light-shielding film 3 may also contain elements such as carbon, hydrogen, boron, indium, tin, and molybdenum.

[0095] The light-shielding film 3 can be formed on the phase-shift film 2 by reactive sputtering using a chromium-containing target. The sputtering method can be either DC sputtering (using a direct current (DC) power supply) or RF sputtering (using a high-frequency (RF) power supply). Alternatively, magnetron sputtering or a conventional method can be used. From the perspective of structural simplicity, DC sputtering is preferred. Furthermore, from the perspective of faster film formation rate and improved productivity, magnetron sputtering is preferred. It should be noted that the film formation apparatus can be of an inline type or a monolithic type.

[0096] The target material is not limited to elemental chromium; as long as chromium is the main component, it can be made of chromium containing any element such as oxygen and carbon, or by adding substances containing oxygen and carbon to chromium.

[0097] [Hard mask]

[0098] A hard mask 4 is disposed on the light-shielding film 3. The hard mask 4 is a film formed of a material that is resistant to etching gases used when etching the light-shielding film 3. As for the hard mask 4, as long as it has a sufficient thickness to function as an etching mask during the period until the dry etching used to pattern the light-shielding film 3 is completed, it is essentially not limited by optical properties. Therefore, the thickness of the hard mask 4 can be significantly reduced compared to the thickness of the light-shielding film 3.

[0099] The thickness of the hard mask film 4 is preferably 14 nm or less, more preferably 10 nm or less. This is because if the thickness of the hard mask film 4 is too thick, the thickness of the resist film serving as the etching mask becomes necessary during dry etching to form the light-shielding film pattern on the hard mask film 4. The thickness of the hard mask film 4 is preferably 4 nm or more, more preferably 5 nm or more. This is because if the thickness of the hard mask film 4 is too thin, according to the conditions of dry etching using oxygen-containing chlorine gas, there is a risk that the pattern on the hard mask film 4 may disappear before the dry etching to form the light-shielding film pattern on the light-shielding film 3 is completed.

[0100] Specifically, for the resist film of organic materials used as an etching mask in dry etching using fluorine-based gases to form patterns on the hard mask film 4, it is sufficient for the film to have a thickness adequate to function as an etching mask during the period until the dry etching of the hard mask film 4 is completed. Therefore, compared with the conventional configuration without the hard mask film 4, the thickness of the resist film can be significantly reduced by providing the hard mask film 4.

[0101] The hard mask 4 comprises a stacked structure of a lower layer 41 and an upper layer 42.

[0102] The lower layer 41 is preferably formed of a material containing silicon and oxygen. As the material containing silicon and oxygen, SiO2, SiON, etc., are preferred. Preferably, the lower layer 41 is formed of a material with a total silicon and oxygen content of 96 atomic percent or more, or a material with a total silicon, nitrogen, and oxygen content of 96 atomic percent or more. This allows the content of other elements to be suppressed to less than 4 atomic percent, ensuring a good etching rate.

[0103] Furthermore, the upper layer 42 is preferably formed of a material containing tantalum and oxygen. Examples of materials containing tantalum and oxygen include those containing one or more elements selected from nitrogen, boron, and carbon in addition to tantalum and oxygen. Examples include TaO, TaON, TaBO, TaBON, TaCO, TaCON, and TaBOCN. Among these materials, the upper layer 42 is preferably a boron-containing material. Furthermore, from the viewpoint of suppressing the change in oxidation degree over time after the formation of the upper layer 42, the oxygen content of the upper layer 42 is preferably 30 atomic percent or more, more preferably 40 atomic percent or more, and even more preferably 50 atomic percent or more. On the other hand, the oxygen content of the upper layer 42 is preferably 71.4% or less. If the oxygen content of the upper layer 42 is greater than that of stoichiometrically stable Ta₂O₅, there is a risk that the surface roughness of the film will become rough.

[0104] Furthermore, the upper layer 42 is preferably formed of a material with a combined content of tantalum and oxygen of 90 atomic% or more, or a material with a combined content of tantalum, oxygen, and boron of 90 atomic% or more. This allows the content of other elements to be suppressed to less than 10 atomic%, ensuring good adhesion to the resist film, good in-plane uniformity of the CD (coating density), and CD linearity.

[0105] To ensure uniform in-plane distribution of the thickness of the upper layer 42, the thickness of the upper layer 42 of the hard mask film 4 is preferably 1 nm or more, more preferably 2 nm or more. Furthermore, the ratio of the thickness (Du) of the upper layer 42 to the overall thickness (Dt) of the hard mask film 4 (hereinafter sometimes referred to as the Du / Dt ratio) is preferably 0.7 or less, more preferably 0.5 or less, and even more preferably 0.3 or less. By fabricating a hard mask film 4 with such a configuration, it is possible to suppress the decrease in the overall etching rate of the hard mask film 4 relative to fluorine-based gases.

[0106] It should be noted that the hard mask film 4 may also have an intermediate layer formed of a material that can be patterned by dry etching using fluorine gases between the upper layer 42 and the lower layer 41. Additionally, the hard mask film 4 may also have a bottom layer formed of a material that can be patterned by dry etching using fluorine gases between the lower layer 41 and the light-shielding film 3. Furthermore, at least either the upper layer 42 or the lower layer 41 may have a structure with a tilted composition in the thickness direction.

[0107] In fact, a study was conducted on the case where a SiON film (Si:O:N = 34 atomic%: 60 atomic%: 6 atomic%) was used as the lower layer 41 of the hard mask film 4, and a TaBO film (Ta:B:O = 36 atomic%: 8 atomic%: 56 atomic%) was used as the upper layer 42. The etching rates of the SiON and TaBO films using dry etching with fluorine-based gases were measured. The results showed that the etching rate of the upper layer 42, with the TaBO film, was 2.48 times slower than that of the lower layer 41, with the SiON film. Figure 3 This paper illustrates the relationship between the ratio of the thickness (Dup) of the upper layer 42 to the thickness (Dto) of the entire hard mask film 4 (Dup / Dto ratio), and the ratio of the etch rate (Eto) of the entire hard mask film 4 to the etch rate (Esi) of a single layer of SiON film (hereinafter sometimes referred to as the Eto / Esi ratio), when the overall thickness of the hard mask film 4 is fixed at a given thickness. According to this result, by keeping the Dup / Dto ratio below 0.7, the Eto / Esi ratio can be increased by more than 0.5 times. Furthermore, it is found that by keeping the Dup / Dto ratio below 0.5, the Eto / Esi ratio can be increased by more than 0.57 times. Moreover, it is found that by keeping the Dup / Dto ratio below 0.3, the Eto / Esi ratio can be increased by more than 0.7 times.

[0108] The aforementioned tendency also applies when the lower layer 41 uses other materials containing tantalum and oxygen, and the upper layer 42 uses other materials containing silicon and oxygen. It should be noted that the hard mask film 4 preferably satisfies the following relationship (1) within the range of 0.07≤Rd≤0.92 when the Eto / Esi ratio is set to Re and the Dup / Dto ratio is set to Rd.

[0109] Equation (1) Re≥0.4047×Rd 4 -1.264×Rd 3 +1.694×Rd 2 -1.431×Rd+0.9995

[0110] [Resistant film]

[0111] In the mask blank 100, it is preferable to form an organic resist film with a thickness of 100 nm or less in contact with the surface of the hard mask film 4. In the case of fine patterns corresponding to DRAM hp32nm generation, sometimes a SRAF (Sub-Resolution Assist Feature) with a linewidth of 40 nm is provided in the light-shielding film pattern to be formed on the light-shielding film 3. However, in this case, the thickness of the resist film can be suppressed by providing the hard mask film 4 as described above, thereby reducing the aspect ratio of the resist pattern formed by the resist film to 1:2.5. Therefore, damage and detachment of the resist pattern can be suppressed during the development and washing of the resist film. It should be noted that the thickness of the resist film is more preferably 80 nm or less. The resist film is preferably a resist for electron beam tracing exposure, and more preferably a chemically amplified type.

[0112] [Mask blank manufacturing sequence]

[0113] The mask blank 100 constructed above is manufactured in the following sequence. First, a light-transmitting substrate 1 is prepared. For the light-transmitting substrate 1, the end face and the main surface are ground to a given surface roughness (for example, the root mean square roughness Rq is less than 0.2 nm in the inner region of a quadrilateral with a side length of 1 μm), and then a given cleaning and drying process is performed.

[0114] Next, a phase-shifting film 2 is formed on the transparent substrate 1 by sputtering. After the phase-shifting film 2 is formed, an annealing treatment is performed at a given heating temperature. Next, the light-shielding film 3 is formed on the phase-shifting film 2 by sputtering. Then, the hard mask film 4 having an upper layer 42 and a lower layer 41 is formed on the light-shielding film 3 by sputtering. When forming each layer by sputtering, a sputtering target containing the materials constituting each layer in a given composition ratio and a sputtering gas are used. Furthermore, a mixture of the aforementioned inert gas and reactive gas is used as the sputtering gas as needed. Then, a resist film is formed on the surface of the hard mask film 4 by a coating method such as spin coating, thereby completing the mask blank 100.

[0115] <Method for Manufacturing Phase Shift Masks>

[0116] Next, it was used Figure 1 The manufacturing method of the phase shift mask in this embodiment will be described using the manufacturing method of a halftone phase shift mask with the mask blank 100 shown as an example.

[0117] First, a resist film is formed on the hard mask film 4 of the mask blank 100 by spin coating. Next, the resist film is exposed by an electron beam to draw a first pattern (phase shift film pattern) to be formed on the phase shift film 2. Then, the resist film is subjected to given treatments such as PEB treatment, development treatment, and post-baking treatment to form a resist pattern 5a (see reference) on the hard mask film 4 of the mask blank 100. Figure 2 (a)).

[0118] Next, using the resist pattern 5a as a mask, the hard mask film 4 is dry-etched using fluorine gas to form a hard mask pattern 4a containing an upper pattern 42a and a lower pattern 41a (see reference). Figure 2 (b) Then the resist pattern 5a is removed. It should be noted that the resist pattern 5a can also be left intact and the light-shielding film 3 can be directly dry-etched. In this case, the resist pattern 5a disappears during the dry etching of the light-shielding film 3.

[0119] Next, using the hard mask pattern 4a as a mask, dry etching is performed using a mixture of chlorine and oxygen gas to form a light-shielding film pattern 3a, which serves as the thin film pattern, on the light-shielding film 3 used for pattern formation (see reference). Figure 2 (c)).

[0120] Next, using the light-shielding film pattern 3a as a mask, dry etching with fluorine-based gases is performed, forming the phase-shifting film pattern 2a on the phase-shifting film 2 while removing the hard mask pattern 4a (see reference). Figure 2 (d) Next, a resist film is formed on the light-shielding film pattern 3a by spin coating. The light-shielding film pattern to be formed on the light-shielding film 3 is drawn by electron beam exposure of the resist film. Then, given treatments such as development are performed to form a resist film with the resist pattern 6b (see reference). Figure 2 (e)).

[0121] Next, using the resist pattern 6b as a mask, dry etching was performed using a mixture of chlorine and oxygen gases to form the light-shielding film pattern 3b on the light-shielding film 3 (see reference). Figure 2 (f)). Further, the resist pattern 6b is removed, and after given processing such as cleaning, a phase-shift mask 200 is obtained (see reference). Figure 2 (g)).

[0122] It should be noted that there are no particular restrictions on the chlorine gases used in the dry etching process of the above-mentioned manufacturing steps, as long as they contain Cl. Examples of chlorine gases include Cl2, SiCl2, CHCl3, CH2Cl2, CCl4, and BCl3. Similarly, there are no particular restrictions on the fluorine gases used in the dry etching process of the above-mentioned manufacturing steps, as long as they contain F. Examples of fluorine gases include CHF3, CF4, C2F6, C4F8, and SF6. In particular, fluorine gases that do not contain C exhibit a lower etching rate on the glass substrate, thus further reducing damage to the glass substrate.

[0123] The phase-shifting mask 200 manufactured through the above process has a structure in which a phase-shifting film pattern 2a and a light-shielding film pattern 3b are sequentially stacked on a light-transmitting substrate 1 from the side of the light-transmitting substrate 1.

[0124] In the phase-shifting mask manufacturing method described above, the method utilizes... Figure 1 The phase-shift mask 200 is manufactured using the mask blank 100 described herein. The mask blank 100 used in manufacturing this phase-shift mask has the following characteristic configuration: the hard mask film 4 comprises a stacked structure of a lower layer 41 and an upper layer 42. The lower layer 41 is formed of a material containing silicon and oxygen, and the upper layer 42 is formed of a material containing tantalum and oxygen, with an oxygen content of 30 atomic percent or more. The thickness of the upper layer 42 is 0.7 or less relative to the overall thickness of the hard mask film 4. Therefore, while improving pattern resolution, in-plane uniformity of the CD (cutoff plane), and CD linearity, it is possible to suppress the decrease in the overall etching rate of the hard mask film 4, thereby manufacturing the phase-shift mask 200. Through the above effects, a phase-shift mask 200 with excellent pattern accuracy can be manufactured.

[0125] It should be noted that in this embodiment, the mask blank used to make the phase shift mask 200 as a transfer mask is described, but the present invention is not limited thereto. For example, it can also be applied to the mask blank used to make binary masks or Levenson-type phase shift masks.

[0126] Example

[0127] The embodiments of the present invention will be described in more detail below with reference to examples.

[0128] <Example 1>

[0129] [Mask blank manufacturing]

[0130] Reference Figure 1A light-transmitting substrate 1 made of synthetic quartz glass with a main surface size of approximately 152 mm × approximately 152 mm and a thickness of approximately 6.35 mm was prepared. The end face and main surface of the light-transmitting substrate 1 were ground to a given surface roughness (less than 0.2 nm in terms of Rq), and then a given cleaning and drying process was performed.

[0131] Next, a high-transmittance layer (Si:N = 44 atomic%:56 atomic%) of phase-shifting film 2 was formed on the transparent substrate 1 with a thickness of 8.0 nm. Specifically, the transparent substrate 1 was disposed in a monolithic RF sputtering apparatus, and the high-transmittance layer was formed by reactive sputtering (RF sputtering) using a silicon (Si) target and a mixed gas of krypton (Kr), helium (He), and nitrogen (N2) as the sputtering gas. It should be noted that the composition of the high-transmittance layer was obtained by measurement based on X-ray photoelectron spectroscopy (XPS). The same applies to other films below.

[0132] Next, a low-transmission layer (Si:N = 62 atomic%:38 atomic%) of phase-shifting film 2 is formed on the high-transmission layer with a thickness of 3.5 nm. Specifically, a light-transmitting substrate 1 with a high-transmission layer is disposed in a monolithic RF sputtering apparatus, and a low-transmission layer is formed by reactive sputtering (RF sputtering) using a silicon (Si) target and a mixed gas of krypton (Kr), helium (He) and nitrogen (N2) as the sputtering gas.

[0133] Next, following the same sequence, a stacked structure of four sets of high-transmittance layers and low-transmittance layers is formed by grounding the surface of the low-transmittance layer 21 on the transparent substrate 1, which has a stacked structure of one set of high-transmittance layers and low-transmittance layers stacked sequentially. Furthermore, under the same film-forming conditions as when forming the high-transmittance layer, a top layer with a thickness of 8.0 nm is formed by grounding the surface of the low-transmittance layer furthest from the transparent substrate 1. Through the above sequence, a phase-shifting film 2 with a total of 11 layers, including a stacked structure of five sets of high-transmittance layers and low-transmittance layers and a top layer, is formed on the transparent substrate 1 with a total film thickness of 65.5 nm.

[0134] Next, a heat treatment was performed to reduce the film stress of the phase-shifting film 2 on the transparent substrate 1 to which the phase-shifting film 2 is formed, and to form an oxide layer on the surface. Specifically, a heat treatment was performed in an electric furnace at atmospheric temperature for 1 hour. The transmittance and phase difference of the phase-shifting film 2 after heat treatment for light with a wavelength of 193 nm were measured using a phase shift measurement device (Lasertec MPM193). The results showed a transmittance of 5.9% and a phase difference of 175.9 degrees (deg).

[0135] Next, a transparent substrate 1 with a phase-shifting film 2 formed thereon was placed in a monolithic DC sputtering apparatus, and reactive sputtering (DC sputtering) was performed in a mixed gas atmosphere of argon (Ar), carbon dioxide (CO2), and helium (He) using a chromium (Cr) target. As a result, a light-shielding film composed of chromium, oxygen, and carbon (CrOC film Cr:O:C = 55 atomic%:30 atomic%:15 atomic%)3 was formed with a thickness of 43 nm in contact with the phase-shifting film 2.

[0136] Next, the transparent substrate 1 on which the light-shielding film (CrOC film) 3 is formed was subjected to heat treatment. Specifically, a heating plate was used in the atmosphere, and the heating temperature was set to 280°C and the heating time was set to 5 minutes. After the heat treatment, the optical density of the laminated structure of the phase-shifting film 2 and the light-shielding film 3 was measured at the wavelength (approximately 193 nm) of ArF excimer laser light using a spectrophotometer (Cary4000 manufactured by Agilent Technologies). The result was confirmed to be 3.0 or higher.

[0137] Next, a lower layer (SiON film Si:O:N = 34 atomic%:60 atomic%:6 atomic%) 41 of a hard mask film 4 was formed on the light-shielding film 3 with a thickness of 5.5 nm. Specifically, a transparent substrate 1 with a phase-shifting film 2 and a light-shielding film 3 stacked on it was disposed in a monolithic DC sputtering apparatus, and the lower layer 41 was formed by DC sputtering using a silicon (Si) target and argon (Ar) gas, oxygen (O2) gas, and nitrogen (N2) gas as sputtering gases.

[0138] Next, an upper layer (TaBO film, Ta:B:O = 36 atomic%:8 atomic%:56 atomic%) 42 was formed on the lower layer 41 with a thickness of 2 nm. Specifically, a light-transmitting substrate 1, in which a phase-shifting film 2, a light-shielding film 3, and a lower layer 41 are stacked, is disposed in a monolithic DC sputtering apparatus. A mixed target of tantalum (Ta) and boron (B) (Ta:B = 4:1 atomic ratio) is used, and argon (Ar) and oxygen (O) gases are used as sputtering gases to form the upper layer 42 by DC sputtering. The thickness of the upper layer 42 is 0.27 relative to the overall thickness of the hard mask film 4, satisfying the condition of 0.7 or less. The given cleaning process is further performed to manufacture the mask blank 100 of Example 1.

[0139] Under the same film-forming conditions as in Example 1, hard mask films 4, comprising a lower layer 41 and an upper layer 42, were formed on multiple other transparent substrates 1, thus fabricating multiple substrates with hard mask films. Then, a resist film was formed on the hard mask film 4 of each substrate with a hard mask film thickness of 80 nm. Next, test patterns (design linewidth 200 nm) were exposed and drawn on the resist films on the three substrates with hard mask films by varying the drawing density. The drawing densities were set to 10%, 50%, and 90%. The resist films on the three substrates with hard mask films were developed, forming resist patterns on the hard mask film 4. The CD value of all test patterns on the resist patterns of each substrate with hard mask films was measured using a CD-SEM (Critical Dimension-Scanning Electron Microscope). Based on the measured CD values, the in-plane uniformity of the resist pattern on each substrate with a hard mask was calculated using 3σ (three times the standard deviation σ). The average 3σ of the resist pattern on each of the three transparent substrates 1 was further calculated. The average 3σ of this in-plane uniformity of CD was 1.42 nm, which is a good value.

[0140] On the other hand, test patterns with different designed linewidths were exposed and depicted on the resist films on the remaining substrates with hard mask films. Then, the resist films were developed, forming resist patterns on the hard mask film 4. Using CD-SEM, the CD values ​​of all test patterns formed on the substrate with the hard mask film were measured. Based on the measured CD values, the correlation between the designed linewidth and the CD value, i.e., the tendency of CD linearity, was examined. The results showed that the increase in CD value as the designed linewidth decreases is smaller, achieving a good trend. Furthermore, it was found that test patterns with small linewidths (40 nm) could be resolved with high precision. Based on these results, it can be concluded that by adopting the configuration of the hard mask film 4 of Example 1, good pattern resolution, in-plane CD uniformity, and CD linearity can be obtained when resist patterns are formed on it.

[0141] [Phase-shifting mask fabrication]

[0142] Next, using the mask blank 100 of Example 1 described above, a halftone phase shift mask 200 of Example 1 was manufactured in the following order. First, a resist film with a thickness of 80 nm was formed by spin coating with the surface of the hard mask film 4 to form a chemically amplified resist for electron beam tracing. Next, the resist film was electron beam traced to form a phase shift film pattern, i.e., a first pattern, to be formed on the phase shift film 2, and given development and cleaning processes were performed to form a resist pattern 5a having the first pattern (see reference). Figure 2(a)). The first pattern comprises line and space patterns with a line width of 200 nm and patterns of minute size (line width of 30 nm).

[0143] Next, using the resist pattern 5a as a mask, dry etching with CF4 gas was performed, forming a hard mask pattern 4a containing the upper pattern 42a and the lower pattern 41a on the hard mask film 4 containing the upper layer 42 and the lower layer 41 (see reference). Figure 2 (b) The resist pattern 5a, formed after the hard mask pattern 4a, remains with sufficient film thickness. The in-plane uniformity and linearity of the CD plane of the hard mask pattern 4a were examined using CD-SEM, confirming good results. Furthermore, it was confirmed that all patterns containing the aforementioned minute dimensions of the resist pattern 5a were formed with high precision on the hard mask film 4. It should be noted that the overall etch rate (Eto) of the hard mask film 4 at this point was reduced by a factor of 0.76 compared to the etch rate (Esi) of a single-layer SiON film of the same thickness.

[0144] Next, the resist pattern 5a is removed. Then, using the hard mask pattern 4a as a mask, dry etching is performed using a mixture of chlorine (Cl2) and oxygen (O2) gas (gas flow ratio Cl2:O2 = 13:1), forming a light-shielding film pattern 3a on the light-shielding film 3 (see reference). Figure 2 (c)).

[0145] Next, using the light-shielding film pattern 3a as a mask, dry etching with fluorine-based gas (SF6+He) was performed to form the first pattern, namely the phase-shifting film pattern 2a, on the phase-shifting film 2, while simultaneously removing the hard mask pattern 4a (see reference). Figure 2 (d)).

[0146] Next, a resist film with a thickness of 150 nm was formed on the light-shielding film pattern 3a using a spin-coating method with a chemically amplified resist for electron beam mapping. Next, a second pattern (including a pattern containing a light-shielding strip pattern) was exposed and drawn on the resist film as a pattern to be formed on the light-shielding film, and further processed by given treatments such as development, to form a resist pattern 6b having the light-shielding film pattern (see reference). Figure 2 (e)). Next, using the resist pattern 6b as a mask, dry etching was performed using a mixed gas of chlorine (Cl2) and oxygen (O2) (gas flow ratio Cl2:O2 = 4:1), forming a light-shielding film pattern 3b on the light-shielding film 3 (see reference). Figure 2 (f)). Further, the resist pattern 6b is removed, and after given processing such as cleaning, a phase-shift mask 200 is obtained (see reference). Figure 2 (g)).

[0147] Using CD-SEM, the in-plane uniformity and CD linearity of the phase shift film pattern 2a of the phase shift mask 200 of Example 1, fabricated in the above sequence, were examined, and the results were confirmed to be good. Furthermore, it was confirmed that all patterns including the aforementioned minute-sized patterns of the resist pattern 5a were formed with high precision on the phase shift film 2. In addition, for the phase shift mask 200 of Example 1, a simulation of the transfer image when the resist film was exposed to a semiconductor device using an AIMS193 (manufactured by Carl Zeiss) with exposure light at a wavelength of 193 nm was performed. The results of verifying the simulated exposure transfer image fully met the design specifications.

[0148] <Comparative Example 1>

[0149] [Mask blank manufacturing]

[0150] For the mask blank of Comparative Example 1, except for the hard mask film 4, it was manufactured in the same order as in Example 1. The hard mask film 4 of Comparative Example 1 is a single-layer structure formed of silicon and oxygen, with a thickness of 15 nm. Specifically, a light-transmitting substrate 1 with a phase-shifting film 2 and a light-shielding film 3 formed thereon was disposed in a monolithic DC sputtering apparatus. Using a silicon (Si) target, argon (Ar), oxygen (O2), and nitrogen (N2) were used as sputtering gases, and a single-layer hard mask film 4 (SiON film Si:O:N = 34 atomic%:60 atomic%:6 atomic%) was formed on the light-shielding film 3 by DC sputtering.

[0151] Under the same film-forming conditions as Comparative Example 1, single-layer hard mask films were formed on several other transparent substrates 1, thus fabricating multiple substrates with hard mask films. Then, the average 3σ values ​​of the resist patterns on the three substrates with hard mask films were calculated in the same order as in Example 1. The average 3σ value of the in-plane uniformity of CD was 1.78 nm, which is a relatively large value (i.e., the in-plane deviation of CD is relatively large). Furthermore, the correlation between the design linewidth and CD value of the resist pattern formed on the substrate with hard mask film, i.e., the tendency of CD linearity, was examined in the same order as in Example 1. As a result, the increase in CD value, which varies with decreasing design linewidth, tends to be relatively large. Furthermore, it was found that the resolution of the test pattern with the small linewidth was low. Based on these results, it can be concluded that if the hard mask film 4 of Comparative Example 1 is used, the pattern resolution, in-plane uniformity of CD, and CD linearity when forming resist patterns on it will all decrease.

[0152] [Phase-shifting mask fabrication]

[0153] Next, using the mask blank from Comparative Example 1, the surface of the hard mask film 4 was silanized using hexamethyldisilazane, and a resist film was formed by coating. Otherwise, the phase-shifting mask of Comparative Example 1 was manufactured in the same order as in Example 1. The resist pattern 5a, formed after the hard mask pattern 4a, remained with sufficient film thickness. On the other hand, the in-plane uniformity and linearity of the CD plane of the hard mask pattern 4a were examined using CD-SEM, and the results showed that both were lower than in Example 1. In particular, the aforementioned small-sized patterns could not be formed within the hard mask pattern 4a.

[0154] The in-plane uniformity and linearity of the phase shift film pattern 2a of the phase shift mask 200 of Comparative Example 1 were examined using CD-SEM (Critical Dimension-Scanning Electron Microscope). The results showed that both were lower than those of Example 1. Furthermore, the aforementioned small-sized patterns could not be formed within the phase shift film pattern 2a. In addition, for the phase shift mask of Comparative Example 1, a simulation of the transfer image during exposure transfer of the resist film on the semiconductor device using exposure light at a wavelength of 193 nm was performed using an AIMS193 (Carl Zeiss). Verification of the simulated exposure transfer image confirmed transfer defects. It can be inferred that the low CD linearity and uniformity of the phase shift film pattern, and the failure to form the aforementioned small-sized patterns, are the main reasons for the transfer defects.

[0155] <Comparative Example 2>

[0156] [Mask blank manufacturing]

[0157] For the mask blank of Comparative Example 2, except for the hard mask film 4, it was manufactured in the same order as in Example 1. The hard mask film 4 of Comparative Example 2 is a single-layer structure formed of tantalum, boron and oxygen, with a thickness of 9.5 nm. Specifically, a light-transmitting substrate 1 with a phase-shifting film 2 and a light-shielding film 3 formed thereon was disposed in a monolithic DC sputtering apparatus, and a mixed target of tantalum (Ta) and boron (B) (Ta:B = 4:1 atomic ratio) was used. Argon (Ar) gas and oxygen (O) gas were used as sputtering gases, and the hard mask film 4 was formed by DC sputtering.

[0158] Under the same film-forming conditions as Comparative Example 2, single-layer hard mask films were formed on several other transparent substrates 1, thus fabricating multiple substrates with hard mask films. Then, the average 3σ of the resist patterns on the three substrates with hard mask films was calculated in the same order as in Example 1. The average 3σ of the in-plane uniformity of CD was 1.43 nm, which is a good value. Furthermore, the correlation between the design linewidth and CD value of the resist pattern formed on the substrate with hard mask film, i.e., the tendency of CD linearity, was examined in the same order as in Example 1. The results showed that the increase in CD value as the design linewidth decreased was small, achieving a good tendency. It was also found that the test patterns with the aforementioned small linewidths could be resolved with high precision. Based on these results, it can be concluded that by adopting the configuration of the hard mask film 4 of Comparative Example 2, good characteristics of pattern resolution, in-plane uniformity of CD, and CD linearity can be obtained when resist patterns are formed on it.

[0159] [Phase-shifting mask fabrication]

[0160] Next, using the mask blank of Comparative Example 2, the phase-shifting mask of Comparative Example 2 was fabricated in the same order as in Example 1. It was confirmed that the resist pattern 5a, after the hard mask pattern 4a was formed, disappeared in a certain area (including the aforementioned small-sized pattern). In addition, the in-plane uniformity and CD linearity of the hard mask pattern 4a were examined using CD-SEM, and the results showed that both were lower than those in Example 1. It should be noted that the overall etching rate (Eto) of the hard mask film 4 at this time was 2.48 times lower than the etching rate (Esi) of a single-layer SiON film of the same thickness, which is a significant reduction.

[0161] [Evaluation of Pattern Transfer Performance]

[0162] The in-plane uniformity and linearity of the phase-shifting film pattern 2a of the phase-shifting mask 200 of Comparative Example 2 were examined using CD-SEM (Critical Dimension-Scanning Electron Microscope). The results showed that both were lower than those of Example 1. Furthermore, for the phase-shifting mask of Comparative Example 2, a simulation of the transfer image during exposure and transfer of the resist film on the semiconductor device using exposure light at a wavelength of 193 nm was performed using an AIMS193 (Carl Zeiss). Verification of the simulated exposure and transfer image confirmed transfer defects. This suggests that the low in-plane uniformity of the CD, low CD linearity, and failure to form the aforementioned small-sized pattern are the main causes of transfer defects in the phase-shifting film pattern 2a.

Claims

1. A mask blank comprising a structure in which a pattern-forming thin film and a hard mask film are sequentially stacked on a light-transmitting substrate, wherein, The film is formed from a chromium-containing material. The hard mask film comprises a stacked structure of a lower layer and an upper layer. The lower layer is formed of a material containing silicon and oxygen. The upper layer is formed of a material containing tantalum and oxygen, wherein the oxygen content is 30 atomic percent or more. The ratio of the thickness of the upper layer to the overall thickness of the hard mask film is less than 0.

7.

2. The mask blank according to claim 1, wherein, The thickness of the upper layer is greater than 1 nm.

3. The mask blank according to claim 1 or 2, wherein, The thickness of the hard mask film is greater than 4 nm and less than 14 nm.

4. The mask blank according to claim 1 or 2, wherein, The upper layer contains boron.

5. The mask blank according to claim 1 or 2, wherein, The lower layer is formed of a material having a combined silicon and oxygen content of 96 atomic% or more, or a material having a combined silicon, nitrogen, and oxygen content of 96 atomic% or more.

6. The mask blank according to claim 1 or 2, wherein, The upper layer is formed of a material having a total content of tantalum and oxygen of 90 atomic% or more, or a material having a total content of tantalum, oxygen and boron of 90 atomic% or more.

7. The mask blank according to claim 1 or 2, wherein, The film is a light-shielding film.

8. The mask blank according to claim 7, wherein, A phase-shifting film made of a silicon-containing material is provided between the light-transmitting substrate and the light-shielding film.

9. A method for manufacturing a transfer mask, comprising using the mask blank according to any one of claims 1 to 7, the method comprising: The process of forming an anti-etching pattern on the hard mask film of the mask blank; The process of forming a hard mask pattern by dry etching the hard mask film using fluorine gas, using the resist pattern as a mask; and The process of forming a thin film pattern by dry etching a thin film using a mixture of chlorine and oxygen gas, with the hard mask pattern as a mask.

10. A method for manufacturing a transfer mask, comprising using the mask blank as described in claim 8, the method comprising: The process of forming an anti-etching pattern on the hard mask film of the mask blank; The process of forming a hard mask pattern by dry etching the hard mask film using fluorine gas as a mask, using the resist pattern as a mask. The process of forming a light-shielding film pattern by dry etching the light-shielding film using a mixture of chlorine and oxygen gas as a mask, using the hard mask pattern as a mask. as well as The process involves using the light-shielding film pattern as a mask, dry etching the phase-shifting film with fluorine gas to form the phase-shifting film pattern, and simultaneously removing the hard mask pattern.

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