Photomask blank and method for manufacturing photomask

Abstract

The invention relates to a photomask blank and a method for manufacturing a photomask. Specifically, the present invention provides a photomask blank including a transparent substrate, a film formed of a chromium-containing material, and a film formed of a tantalum-containing material. The film formed by the tantalum-containing material is composed of a single layer or a plurality of layers and has a thickness of 0.5-15 nm; the tantalum-containing material contains tantalum and oxygen or contains tantalum, oxygen and nitrogen and does not contain silicon; at least the layer, farthest from the transparent substrate, in the single layer and the layers forming the multiple layers is made of a tantalum-containing material, the tantalum content of the tantalum-containing material is 40-80 at%, the oxygen content is 5-50 at%, and the nitrogen content is not larger than 50 at%; and the layer farthest from the transparent substrate has a thickness of not less than 0.5 nm.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing photomasks for manufacturing semiconductor devices, etc., and a photomask blank used as a material for manufacturing reflective photomasks. Background Technology

[0002] Recently, due to the miniaturization of semiconductor devices, especially the high integration density of large-scale integrated circuits, there is a demand for high pattern resolution in projection exposure. Therefore, phase-shifting masks have been developed as a means to improve the resolution of transferred patterns. The principle of the phase-shifting method is that, by adjusting the phase of the transmitted light passing through the opening of the phase-shifting film, the phase is reversed by approximately 180 degrees relative to the phase of the transmitted light passing through the area near the opening. The interference between the transmitted light reduces the light intensity at the boundary between the opening and the area near the opening. As a result, the resolution and depth of focus of the transferred pattern are improved. Photomasks utilizing this principle are commonly referred to as phase-shifting masks.

[0003] The most common phase-shifting mask blanks used for manufacturing phase-shifting masks have a structure in which the phase-shifting film is laminated onto a transparent substrate such as a glass substrate, and a film formed of a chromium-containing material is laminated onto the phase-shifting film. Phase-shifting films typically have a phase shift of approximately 175–185 degrees and a transmittance of approximately 6%–30% to the exposed light. The mainstream phase-shifting films are formed from materials containing molybdenum and silicon. Furthermore, films formed of chromium-containing materials are adjusted to have a thickness that, together with the phase-shifting film, provides a specified optical density. Films formed of chromium-containing materials are commonly used as light-shielding films and can also be used as hard masks for etching phase-shifting films.

[0004] An example of a method for forming a pattern of a phase-shifting film from such a phase-shifting mask blank is as follows: First, a photoresist film is formed on a film made of a chromium-containing material on the phase-shifting mask blank. A pattern is drawn on the photoresist film using light or an electron beam and then developed to form a photoresist film pattern. The photoresist film pattern is then used as an etching mask to etch the film made of the chromium-containing material to form a pattern of the film made of the chromium-containing material. Furthermore, the pattern of the film made of the chromium-containing material is used as an etching mask to etch the phase-shifting film to form a phase-shifting film pattern. Then, the photoresist film pattern and the pattern of the film made of the chromium-containing material are sequentially removed.

[0005] Furthermore, a film formed of a chromium-containing material is retained as a light-shielding film on the outer portion of the circuit pattern forming the phase-shifting film, providing a light-shielding area (light-shielding pattern) with a combined optical density of not less than 3 on the outer periphery of the phase-shifting mask. This is to prevent exposure light from being transmitted to the resist film adjacent to the portion of the circuit pattern to be exposed when transferring the circuit pattern onto the resist film using a wafer exposure apparatus, due to insufficient light shielding at the outer periphery of the phase-shifting mask. In a general method for forming such a light-shielding film pattern, after forming the phase-shifting film pattern and removing the resist film pattern, the resist film is re-formed, and a pattern is drawn on the resist film by light or electron beam and developed to form the resist film pattern. Then, using the resist film pattern as an etching mask, the film formed of the chromium-containing material is etched only in the circuit pattern portion to form the light-shielding area (light-shielding film pattern) retained on the outer periphery.

[0006] The mainstream etching method used for manufacturing photomasks requiring high-precision patterns is dry etching using gas plasma. Dry etching using chlorine-based gases is used for films formed from chromium-containing materials, while dry etching using fluorine-based gases is used for films containing molybdenum and silicon. In particular, it is known that when dry etching films formed from chromium-containing materials, applying chlorine gas (Cl2 gas) mixed with 10–25% by volume oxygen (O2 gas) as the etching gas (i.e., a chlorine-based gas) can improve chemical reactivity and etching rate.

[0007] As circuit patterns become miniaturized, phase shift mask patterns require techniques for fine pattern formation. Specifically, when transferring circuit patterns onto the resist film of a wafer using a wafer exposure apparatus, the auxiliary patterns of the line patterns that support the main pattern resolution of the phase shift mask need to be formed smaller than the main pattern to prevent the auxiliary patterns from transferring onto the resist film on the wafer. In first-generation phase shift masks where the spacing between the line and space patterns of the circuitry on the wafer is 10 nm or narrower, the linewidth of the auxiliary patterns of the line patterns on the phase shift mask needs to be approximately 40 nm. In this case, to stably manufacture phase shift masks with high-precision circuit patterns and phase change margins, the linewidth needs to be less than approximately 40 nm, and the linewidth of the auxiliary patterns needs to be approximately 36 nm.

[0008] To fabricate phase-shift masks with intricate patterns, chemically amplified resists are typically used. Chemically amplified resists consist of a base resin, an acid-generating agent, and a surfactant, and can be applied to many reactions in which the acid generated during light exposure acts as a catalyst. Therefore, chemically amplified resists can exhibit high sensitivity. They can form film patterns, such as phase-shift film patterns with linewidths no greater than 0.2 μm. However, even with chemically amplified resists, as the pattern width narrows, the resist film pattern will collapse due to the impact of the developing solution during development or the impact of pure water during rinsing, eventually reaching the resolution limit.

[0009] The typical thickness of the resist film used to fabricate phase-shift masks is about 100–150 nm. However, it is difficult to form finer auxiliary patterns in phase-shift masks with such a thickness. This is because the thick resist film formed on a film made of chromium-containing material has a high aspect ratio in the resist film pattern with narrow linewidth used to form the auxiliary patterns. Therefore, during the development process used to form the resist film pattern, the resist film pattern collapses due to the impact of the developer or the impact of pure water during rinsing.

[0010] When considering reducing the aspect ratio of the resist film pattern to minimize the impact of developer or pure water during rinsing, it is necessary to further thin the resist film. However, when the resist film is thin, if it disappears during dry etching of a film made of chromium-containing material, pinhole defects are formed in the chromium-containing film. As a result, when using a chromium-containing film pattern with pinhole defects as an etching mask for dry etching of the phase-shifting film, plasma reaches the phase-shifting film through the pinholes during etching, also forming pinhole defects in the phase-shifting film. In this case, a normal phase-shifting mask cannot be manufactured.

[0011] Therefore, to address this issue, it has been considered to further provide a silicon-containing film on top of the chromium-containing film for use as a hard mask. In this case, the silicon-containing film is a thin film with a thickness of 5–15 nm, and the thickness of the resist film formed on the silicon-containing film can be reduced to approximately 80–110 nm.

[0012] When dry etching films formed from chromium-containing materials using oxygen-containing chlorine-based gases, over-etching of 100% to 300% of the etching removal time is required, in addition to the etching removal time until the chromium-containing film disappears. This is because dry etching using oxygen-containing chlorine-based gases is a chemically-dominated isotropic etching process. Therefore, because dry etching only occurs within the etching removal time, the pattern of the chromium-containing film is not sufficiently etched at the boundary with the phase-shifted film, resulting in a trailing shape, thus preventing the stable formation of the desired pattern width.

[0013] Furthermore, since dry etching using oxygen-containing chlorine-based gases is a chemically-driven isotropic etching process, the plasma of the oxygen-containing chlorine-based gas moves to the main surface of the substrate in both vertical and horizontal directions, resulting in side etching in the pattern of the film formed from the chromium-containing material. Therefore, in order to obtain a uniform pattern linewidth CD (critical dimension) across the entire surface of the mask, an equal amount of side etching is required across the entire mask surface. This necessitates a prolonged over-etching process until the amount of side etching saturates (reaches saturation) across the entire surface of the mask and stabilizes.

[0014] Dry etching using fluorine-based gases is used for dry etching of films formed from silicon-containing materials. When dry etching of films formed from silicon-containing materials using fluorine-based gases, in addition to the etching removal time until the silicon-containing film disappears, over-etching of up to about 20% of the etching removal time is required (e.g., a short over-etching time of 1 to 6 seconds).

[0015] Short-time over-etching can be applied in dry etching of films formed from silicon-containing materials using fluorine-based gases because: dry etching using fluorine-based gases is anisotropic etching dominated by physical composition, and the pattern of the silicon-containing film does not form a trailing shape at the boundary with the film formed from chromium-containing materials. Furthermore, this is because: the plasma of the fluorine-based gas moves vertically to the main surface of the substrate, and the CD of the resist film pattern is faithfully copied onto the pattern of the silicon-containing film.

[0016] Dry etching using fluorine-based gases is anisotropic etching dominated by physical composition; therefore, the amount of resist loss in dry etching is generally greater than that in dry etching using oxygen-containing chlorine-based gases. Consequently, the resist film used to pattern films formed from silicon-containing materials must be appropriately thick. On the other hand, since the silicon-containing film serves as an etching mask when dry etching films formed from chromium-containing materials is performed using oxygen-containing chlorine-based gases, and it has sufficient resistance to dry etching using oxygen-containing chlorine-based gases, the silicon-containing film can be relatively thinned for use as a hard mask. When the silicon-containing film is thinned, the etching time for dry etching of the silicon-containing film using fluorine-based gases is shortened. As a result, the thickness of the resist film required to pattern the silicon-containing film can also be reduced.

[0017] Therefore, by using a film formed of silicon-containing material as a hard mask, the thickness of the resist film used for etching the hard mask can be reduced, i.e., the thickness of the resist film formed on and in contact with the hard mask can be reduced. By reducing the thickness of the resist film, the aspect ratio of the resist pattern is reduced, and the impact of the developer or the impact of pure water during the rinsing process is reduced, thus allowing for the formation of a better auxiliary pattern. As a result, high resolution can be achieved in pattern transfer using a phase-shift mask.

[0018] On the other hand, when dry etching is performed on a phase-shifting film formed of a molybdenum- and silicon-containing material using fluorine-based gases, in some cases, the transparent substrate in contact with the phase-shifting film is also slightly etched during dry etching, adjusting the phase shift (phase difference) to approximately 175 to 185 degrees relative to the exposure light. In this case, the phase shift (phase difference) of the phase-shifting film itself, formed of a molybdenum- and silicon-containing material, is set to, for example, approximately 175 to 179 degrees, and the transparent substrate is slightly etched through over-etching, adjusting the phase shift (phase difference) in the phase-shifting mask to approximately 175 to 185 degrees.

[0019] The general method for manufacturing a phase shift mask is as follows: a phase shift mask blank is obtained by sequentially forming a phase shift film made of a molybdenum- and silicon-containing material, a light-shielding film made of a chromium-containing material, and a hard mask made of a silicon-containing material on a transparent substrate; a phase shift film is then patterned.

[0020] First, a photoresist film is formed on a hard mask. Next, a pattern is drawn on the photoresist film using light or an electron beam and developed to form a photoresist film pattern. Then, using the photoresist film pattern as an etching mask, a hard mask made of silicon-containing material is dry-etched using a fluorine-based gas to form a hard mask pattern, and then the photoresist film pattern is removed. Next, using the hard mask pattern as an etching mask, a light-shielding film made of chromium-containing material is dry-etched using an oxygen-containing chlorine-based gas to form a light-shielding film pattern. Next, using the light-shielding film pattern as an etching mask, a phase-shifting film made of molybdenum and silicon-containing material is dry-etched using a fluorine-based gas to form a phase-shifting film pattern, while simultaneously removing the hard mask pattern. Finally, the light-shielding film pattern is removed by etching using an oxygen-containing chlorine-based gas.

[0021] WO2004 / 090635A1 (Patent Document 1) discloses a phase-shifting mask blank, which comprises at least a phase-shifting film, a chromium film, an etching mask film made of an inorganic material resistant to etching of the chromium film, and a resist film on a transparent substrate. The etching mask film is made of at least one material selected from molybdenum, silicon, tantalum, and tungsten, specifically elemental Mo, MoSi, MoSiO, MoSiN, MoSiON, elemental Si, SiO, SiN, SiON, elemental Ta, TaB, W, WSi, and TaSi. Furthermore, in the method for manufacturing a phase-shifting mask described in WO2004 / 090635A1 (Patent Document 1), a resist pattern is formed by exposing and developing a desired pattern on the resist film, and the resist pattern is used as a mask to dry-etch the etching mask film to form the etching mask pattern.

[0022] JP2013-238691A (Patent Document 2) discloses a phase-shift mask blank in which a phase-shift film, a light-shielding film, and a hard mask are sequentially laminated on a substrate transparent to the exposure wavelength. The phase-shift film and the light-shielding film are formed of materials that are substantially un-etchable by dry etching methods capable of etching the hard mask, and the light-shielding film is formed of materials that are substantially un-etchable by dry etching methods capable of etching the phase-shift film. For the light-shielding film, a metal compound film mainly formed of Cr oxide, Cr nitride, or Cr nitride is described, as well as a metal film or alloy film mainly formed of Cr. For the hard mask, a Ta film or a TaN film is described. Furthermore, in the method for manufacturing a phase-shift mask described in JP2013-238691A (Patent Document 2), a resist pattern is formed by applying a resist film onto a hard mask for drawing, followed by a development process. Using a resist pattern as a mask, the hard mask is patterned by oxygen-free chlorine-based dry etching (dry etching using chlorine gas as the etching gas) to form a hard mask pattern. Existing technical documents

[0023] Patent documents Patent Document 1: WO2004 / 090635A1 Patent Document 2: JP2013-238691A Summary of the Invention The problem that the invention aims to solve

[0024] Patent document WO2004 / 090635 (Patent Document 1) discloses a silicon-containing material as an etching mask film. However, when a resist film is formed on a film made of silicon-containing material, hydrophilic hydroxyl groups (OH groups) easily form on the surface of the film, which reduces the adhesion to the resist. When the adhesion between the resist film and the silicon-containing material film deteriorates, the resist film pattern is prone to collapse during the developing process of forming the resist film pattern due to the impact of the developing solution in the developing process or the impact of pure water in the rinsing process, resulting in a significant decrease in resolution.

[0025] Therefore, when forming a resist film on a film made of silicon-containing material, in order to improve the adhesion between the resist film and the film made of silicon-containing material, the surface of the film made of silicon-containing material is usually treated with HMDS (hexamethyldisilazane) before the resist is applied to the film made of silicon-containing material. This is done to replace the hydroxyl groups with hydrophobic groups, thereby improving the adhesion between the resist film and the film made of silicon-containing material.

[0026] However, while HMDS treatment improves the adhesion between the silicon-containing film and the resist film, the resist is insufficiently dissolved during the development process. As a result, the resist is not completely removed from the silicon-containing film in the spatial pattern, leaving resist residue. This residue acts as an etching mask when etching the silicon-containing film. Consequently, etchable portions of the silicon-containing film are left unetched, and ultimately, the phase-shifting film at the location of the resist residue remains unetched, becoming a defect. In the manufacturing process of photomasks such as phase-shifting masks, defects can be corrected, and the effect of correction on CD can be evaluated through wafer transfer simulation. However, defect correction affects photomask productivity, and in the presence of numerous defects, photomask manufacturing productivity deteriorates significantly.

[0027] Furthermore, WO2004 / 090635A1 (Patent Document 1) discloses elemental Ta, TaB, and TaSi as materials for etching mask films, and JP2013-238691A (Patent Document 2) discloses Ta and TaN as materials for hard masks. However, these materials readily react with oxygen, and when exposed to air, an oxide layer forms unevenly or locally on the surface of the etching mask film or hard mask. In this case, when dry etching is performed on the etching mask film or hard mask, the etching rate within the film surface is uneven, and the CD uniformity within the film surface is low and unstable.

[0028] Furthermore, both the etching mask film and the hard mask need to be formed to a sufficient thickness to prevent them from disappearing during dry etching using oxygen-containing chlorine-based gases to etch films made of chromium-containing materials. These materials exhibit relatively high etching rates for dry etching using oxygen-containing chlorine-based gases; therefore, the etching mask film and hard mask need to be formed to a relatively thick thickness. However, if the etching mask or hard mask film is too thick, a thick resist film is required. With a thick resist film, the aspect ratio of the resist film pattern with narrow linewidths becomes high, leading to resolution degradation.

[0029] This invention is proposed to solve the above-mentioned problems. The object of this invention is to provide a photomask blank and a method for manufacturing a photomask using such a photomask blank, the photomask blank comprising a film formed on a film made of a chromium-containing material, which exhibits good adhesion to the resist film even without HMDS (hexamethyldisilazane) treatment, high uniformity of the CD (critical dimension) within the film surface during etching, and low etching rate in dry etching using oxygen-containing chlorine-based gases. Methods for solving problems

[0030] The inventors conducted serious research to solve the above-mentioned problems and discovered a photomask blank comprising: a transparent substrate, a film formed of a chromium-containing material formed on the transparent substrate, and a film formed of a tantalum-containing material formed on the film formed of the chromium-containing material. Furthermore, a film formed of a silicon-containing material is also included between the transparent substrate and the film formed of the chromium-containing material. The above-mentioned problems can be solved by configuring the film formed of the tantalum-containing material to contain nitrogen and have a specified structure, composition and thickness.

[0031] Furthermore, the inventors have found that such photomask blanks are particularly suitable when the film formed from a chromium-containing material is a light-shielding film and the film formed from a tantalum-containing material is a hard mask, and even more so when the film formed from a silicon-containing material is a phase-shifting film.

[0032] Furthermore, the inventors discovered that when a photomask is manufactured from such a photomask blank, a film formed of tantalum-containing material can be etched using dry etching with a fluorine-based gas to form a resist film in contact with the film formed of tantalum-containing material. Dry etching is performed on the film formed of tantalum-containing material using a fluorine-based gas, on the film formed of chromium-containing material using an oxygen-containing chlorine-based gas, and on the film formed of silicon-containing material using a fluorine-based gas. This allows for the manufacture of photomasks that advantageously form fine auxiliary patterns in circuit patterns.

[0033] 1. In one aspect, the present invention provides a photomask blank comprising: a transparent substrate, a film formed of a chromium-containing material formed on the transparent substrate, and a film formed of a tantalum-containing material formed on the film formed of the chromium-containing material, wherein, The film formed from tantalum-containing material consists of a single layer or multiple layers. The film formed from the tantalum-containing material has a thickness of not less than 0.5 nm and not more than 15 nm. The tantalum-containing material contains tantalum and oxygen, or contains tantalum, oxygen and nitrogen, and does not contain silicon. The single layer and at least the layer furthest from the transparent substrate among the layers constituting the multilayer are formed of a tantalum-containing material, wherein the tantalum-containing material has a tantalum content of not less than 40 at% and not more than 80 at%, an oxygen content of not less than 5 at% and not more than 50 at%, and a nitrogen content of not more than 50 at%. The layer furthest from the transparent substrate has a thickness of not less than 0.5 nm. 2. Preferably, in the photomask blank, when dry etching is performed on the film formed of the chromium-containing material and the film formed of the tantalum-containing material using an oxygen-containing chlorine gas, the ratio of the etching rate of the film formed of the chromium-containing material to the etching rate of the film formed of the tantalum-containing material is not less than 50. 3. Preferably, the thickness of the film formed from the chromium-containing material is not less than 30 nm and not more than 80 nm. 4. Preferably, the photomask blank further includes a silicon-containing film between the transparent substrate and the film formed of the chromium-containing material. 5. Preferably, the film formed from silicon-containing materials is a phase-shifting film. A film formed from chromium-containing materials is a light-shielding film. A film formed from tantalum-containing materials is a hard mask. 6. Preferably, the phase shift film has a phase shift (phase difference) of not less than 175 degrees and not more than 185 degrees to the exposure light, a transmittance of not less than 6% and not more than 30%, and a thickness of not less than 60 nm and not more than 85 nm. 7. Preferably, the total optical density of the light-shielding film and the phase-shifting film to the exposure light is not less than 3. 8. Preferably, the photomask blank further includes a resist film, which contacts the side of the film formed of tantalum material away from the transparent substrate and has a thickness of not less than 40 nm and not more than 120 nm. 9. In another aspect, the present invention provides a method for manufacturing a photomask, which is a method for manufacturing a photomask having a circuit pattern of a film formed of a chromium-containing material from a photomask blank as described in any one of claims 1 to 3 above, comprising the following steps: (A) A first resist film is formed in contact with the side of the film formed of tantalum material away from the transparent substrate. (B) Patterning the first resist film to form a first resist film pattern. (C) Using the pattern of the first resist film as an etching mask, the film formed of tantalum-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the film formed of tantalum-containing material. (D) Remove the pattern of the first resist film. (E) Using the pattern of the film formed from the tantalum-containing material as an etching mask, the film formed from the chromium-containing material is patterned by dry etching with an oxygen-containing chlorine gas to form a pattern of the film formed from the chromium-containing material. (F1) The pattern of the film formed of tantalum-containing material is removed by dry etching using fluorine-based gases. 10. In another aspect, the present invention provides a method for manufacturing a photomask, which is a method for manufacturing a photomask having a circuit pattern of a film formed of a silicon-containing material from the photomask blank described in claim 4 above, comprising the following steps: (A) A first resist film is formed in contact with the side of the film formed of tantalum material away from the transparent substrate. (B) Patterning the first resist film to form a first resist film pattern. (C) Using the pattern of the first resist film as an etching mask, the film formed of tantalum-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the film formed of tantalum-containing material. (D) Remove the pattern of the first resist film. (E) Using the pattern of the film formed of the tantalum-containing material as an etching mask, the film formed of the chromium-containing material is patterned by dry etching with an oxygen-containing chlorine gas to form a pattern of the film formed of the chromium-containing material. (F2) Using the pattern of the film formed of the chromium-containing material as an etching mask, the film formed of the silicon-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the silicon-containing film including circuit patterns, while removing the pattern of the film formed of the tantalum-containing material. (G) A second resist film is formed, which, on the side of the film formed of the chromium-containing material away from the transparent substrate, contacts the pattern of the film formed of the chromium-containing material and the exposed transparent substrate. (H) The second resist film is patterned so that the second resist film pattern is formed only on the outer periphery of the transparent substrate, the outer periphery being the region excluding the circuit pattern. (I) Using the pattern of the second resist film as an etching mask, the pattern of the film formed of the chromium-containing material is removed from the portion outside the outer periphery by dry etching with an oxygen-containing chlorine gas, such that the pattern of the film formed of the chromium-containing material remains on the outer periphery. (J) Remove the pattern of the second resist film. 11. Preferably, in this method, Films formed from silicon-containing materials are phase-shifting films. The film formed from chromium-containing materials is a light-shielding film, and A film formed from tantalum-containing materials is a hard mask. Beneficial effects of the invention

[0034] The film formed from tantalum-containing material in the photomask blank of the present invention has good adhesion to the resist film without HMDS (hexamethyldisilazane) treatment. Therefore, the problem of resist residue that occurs when HMDS treatment is performed can be avoided.

[0035] Furthermore, the film formed from tantalum-containing material in the photomask blank of the present invention is not easily oxidized in air, and therefore, it is not easy for an oxide layer to form on the surface of the film. Thus, it avoids the following problems: uneven or localized formation of an oxide layer on the surface of the film, and deterioration and instability of the CD uniformity on the film surface due to uneven etching rates within the film surface.

[0036] Furthermore, the film formed from tantalum-containing material in the photomask blank of the present invention has a low etching rate when dry etching is performed using an oxygen-containing chlorine gas. Therefore, by forming a thinner film formed from tantalum-containing material, a thin resist film in contact with the film formed from tantalum-containing material can be formed on the film formed from tantalum-containing material.

[0037] Furthermore, the photomask blank of the present invention has high resolution. By manufacturing a photomask using the photomask blank of the present invention, a thin resist film in contact with a film formed of tantalum material can be formed, exhibiting good adhesion. Even when the resist film pattern has a narrow linewidth, a low aspect ratio can be achieved. Therefore, the problem of resist film pattern collapse due to the impact of the developer solution or the impact of pure water in the rinsing process can be avoided during the developing process for forming the resist film pattern.

[0038] Therefore, the photomask blank of the present invention can effectively form auxiliary patterns with narrow linewidths as auxiliary patterns for line patterns formed in circuit patterns. In particular, when the photomask blank has a film formed of silicon material between the transparent substrate and the film formed of chromium material, especially in the case of a phase-shifting photomask blank in which the film formed of silicon material is a phase-shifting film, for example, even when the auxiliary pattern has a linewidth of about 40 nm, and further about 36 nm, the auxiliary pattern can be formed well, and a photomask with a circuit pattern having high CD uniformity and few defects can be obtained. Attached Figure Description Figure 1 This is a cross-sectional view showing an example of a first embodiment of the photomask blank of the present invention. Figure 2 This is a cross-sectional view showing an example of a second embodiment of the photomask blank of the present invention. Figure 3 This is a cross-sectional view showing an example of a third embodiment of the photomask blank of the present invention. Figure 4 This is a cross-sectional view showing an example of the fourth embodiment of the photomask blank of the present invention. Figure 5 This is a cross-sectional view showing an example of a first embodiment of the photomask of the present invention. Figure 6 This is a cross-sectional view showing an example of a second embodiment of the photomask of the present invention. Figure 7 A to 7F are cross-sectional views illustrating the process of manufacturing a reflective photomask of the first embodiment from a reflective photomask blank of the first embodiment or the third embodiment. Figure 8 A~ Figure 8 J is a cross-sectional view illustrating the process of manufacturing a reflective photomask of the second embodiment from a reflective photomask blank of the second or fourth embodiment. Detailed Implementation

[0039] The present invention will now be described in more detail.

[0040] [Photomask preform] The photomask blank of the present invention includes a transparent substrate, a film formed of a chromium-containing material, and a film formed of a tantalum-containing material. The film formed of the chromium-containing material is formed on the substrate directly or through other films. Another film may be formed between the film formed of the chromium-containing material and the film formed of the tantalum-containing material; however, the film formed of the tantalum-containing material is preferably formed in contact with the film formed of the chromium-containing material.

[0041] The photomask blank and photomask of the present invention are preferably made of exposure light, which is light with a wavelength of no more than 250 nm, especially light with a wavelength of no more than 200 nm, such as ArF excimer laser (wavelength: 193 nm) and F2 laser (wavelength: 157 nm), but are not particularly limited thereto.

[0042] The invention will now be described with reference to the accompanying drawings. Identical parts may be given the same reference numerals (figure marks), and repeated descriptions of them may be omitted. Furthermore, for convenience, the drawings may be enlarged or reduced, and the dimensions of each part may differ from the actual proportions.

[0043] Figure 1 This is a cross-sectional view showing an example of a first embodiment of the photomask blank of the present invention. The photomask blank 101 includes a film 3 formed in contact with the transparent substrate 1 and a film 4 formed in contact with the film 3 formed in contact with the film 3 formed in the transparent substrate and a film 4 formed in contact with the film 3 formed in the transparent substrate and a film 4 formed in contact with the film 3 formed in the transparent substrate and a film 4 formed in contact with the film 3 formed in the transparent substrate. In the photomask blank of the first embodiment, the film formed in the chromium-containing material and the film formed in the tantalum-containing material are sequentially formed on the transparent substrate from the transparent substrate side.

[0044] Preferably, the photomask blank of the present invention further includes a film formed of a silicon-containing material between the transparent substrate and the film formed of a chromium-containing material. The photomask blank of the present invention may include a transparent substrate, a film formed of a silicon-containing material, a film formed of a chromium-containing material, and a film formed of a tantalum-containing material. The film formed of the silicon-containing material is formed directly on the substrate or in between another film. Furthermore, another film may be formed between the film formed of the silicon-containing material and the film formed of the chromium-containing material; however, the film formed of the silicon-containing material is preferably formed in contact with the film formed of the chromium-containing material.

[0045] Figure 2 This is a cross-sectional view illustrating an example of a second embodiment of the photomask blank of the present invention. The photomask blank 102 includes, on a transparent substrate 1, a film 2 formed of a silicon-containing material and formed in contact with the transparent substrate 1, a film 3 formed of a chromium-containing material and formed in contact with the film 2 formed of the silicon-containing material, and a film 4 formed of a tantalum-containing material and formed in contact with the film 3 formed of the chromium-containing material. In the photomask blank of the second embodiment, the film formed of the silicon-containing material, the film formed of the chromium-containing material, and the film formed of the tantalum-containing material are sequentially formed on the transparent substrate from the transparent substrate side.

[0046] The photomask blank of the present invention may further include a resist film that contacts the side of the transparent substrate away from the film formed of a tantalum-containing material.

[0047] Figure 3This is a cross-sectional view illustrating an example of a third embodiment of the photomask blank of the present invention. The photomask blank 103 includes, on a transparent substrate 1, a film 3 formed of a chromium-containing material and formed in contact with the transparent substrate 1, a film 4 formed of a tantalum-containing material and formed in contact with the film 3 formed of the chromium-containing material, and a photoresist film 5 formed in contact with the film 4 formed of the tantalum-containing material. In the photomask blank of the third embodiment, the film formed of the chromium-containing material, the film formed of the tantalum-containing material, and the photoresist film are sequentially formed on the transparent substrate from the transparent substrate side.

[0048] Figure 4 This is a cross-sectional view illustrating an example of a fourth embodiment of the photomask blank of the present invention. The photomask blank 104 includes, on a transparent substrate 1, a film 2 formed of a silicon-containing material and in contact with the transparent substrate 1; a film 3 formed of a chromium-containing material and in contact with the film 2 formed of the silicon-containing material; a film 4 formed of a tantalum-containing material and in contact with the film 3 formed of the chromium-containing material; and a photoresist film 5 formed in contact with the film 4 formed of the tantalum-containing material. In the photomask blank of the fourth embodiment, the film formed of the silicon-containing material, the film formed of the chromium-containing material, the film formed of the tantalum-containing material, and the photoresist film are sequentially formed on the transparent substrate from the transparent substrate side.

[0049] [Transparent substrate] There are no particular restrictions on the material or size of the transparent substrate. Preferred substrates are those that are transparent to exposure light, used for transmissive photomask blanks and transmissive photomasks, especially quartz substrates, such as synthetic quartz substrates. A suitable transparent substrate is the 6025 substrate defined in the SEMI standard, which has a size of 6 square inches and a thickness of 0.25 inches. In the SI unit system, a 6025 substrate is typically represented as a substrate with a size of 152 square millimeters and a thickness of 6.35 millimeters.

[0050] [A membrane formed from silicon-containing materials] Films formed from silicon (Si) materials can consist of a single layer or multiple layers (e.g., films consisting of 2 to 5 layers). Single layers and the layers constituting multiple layers can have a single composition or a gradient composition.

[0051] The film formed from silicon-containing materials is preferably formed from a material that is resistant to dry etching using oxygen-containing chlorine gases and can be removed by dry etching using fluorine gases.

[0052] In this invention, as a typical dry etching method using fluorine-based gases, dry etching using fluorine-containing gases such as CF4 and SF6 as etching gases is exemplified. In this invention, as a typical dry etching method using oxygen-containing chlorine-based gases, dry etching using a mixture of chlorine (Cl2 gas) and oxygen (O2 gas) is exemplified. Preferably, the mixture of chlorine and oxygen is a gas in which chlorine is mixed with oxygen at a volume percentage of 10–25% relative to chlorine.

[0053] The silicon-containing material is preferably a material containing silicon and free of transition metals, or a material containing a transition metal (Me) other than chromium and silicon but free of chromium (Cr). Examples of silicon-containing materials free of transition metals include: elemental silicon (Si) or silicon compounds containing silicon and at least one selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such silicon compounds include: materials composed of silicon and oxygen (SiO), materials composed of silicon and nitrogen (SiN), materials composed of silicon, oxygen, and nitrogen (SiON), materials composed of silicon and carbon (SiC), materials composed of silicon, oxygen, and carbon (SiOC), materials composed of silicon, nitrogen, and carbon (SiNC), and materials composed of silicon, oxygen, nitrogen, and carbon (SiONC).

[0054] On the other hand, examples of materials containing a transition metal (Me) other than chromium and silicon but without chromium include transition metal (Me) silicon compounds containing a transition metal (Me) and silicon (Si), or transition metal (Me) silicon compounds containing a transition metal (Me), silicon (Si), and at least one selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such transition metal (Me) silicon compounds include: materials composed of a transition metal and silicon (MeSi), materials composed of a transition metal, silicon, and oxygen (MeSiO), materials composed of a transition alloy, silicon, and nitrogen (MeSiN), materials composed of a transition metal, silicon, oxygen, and nitrogen (MeSiON), materials composed of a transition element, silicon, and carbon (MeSiC), materials composed of a transition element, silicon, oxygen, and carbon (MeSiOC), materials composed of a transition element, silicon, nitrogen, and carbon (MeSiNC), and materials composed of a transition element, silicon, oxygen, nitrogen, and carbon (MeSiONC).

[0055] As a transition metal (Me) other than chromium, it is suitable to be at least one selected from molybdenum (Mo), tungsten (W), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf), with molybdenum being particularly suitable from the viewpoint of processability in dry etching. Furthermore, the material of the film formed from silicon-containing materials may contain hydrogen (H), etc.

[0056] The thickness of the film formed from silicon-containing materials is preferably not less than 50 nm, more preferably not less than 60 nm, more preferably not more than 90 nm, and more preferably not more than 85 nm.

[0057] Films formed from silicon-containing materials are suitable for use as optical films in photomask preforms (e.g., transmissive photomask preforms) and photomasks (e.g., transmissive photomasks), particularly phase-shifting films. When the film formed from silicon-containing materials is a phase-shifting film, the photomask preform is a phase-shifting mask preform, and a phase-shifting mask with a phase-shifting film pattern is manufactured from the phase-shifting mask preform. When the phase-shifting film is a halftone phase-shifting film, the phase-shifting mask preform and the phase-shifting mask are respectively a halftone phase-shifting mask preform and a halftone phase-shifting mask.

[0058] When the film formed from silicon-containing material is a phase-shifting film, the phase-shifting film preferably has a phase shift of not less than 175 degrees and not more than 185 degrees to the exposure light. When the film formed from silicon-containing material is a phase-shifting film, the transmittance of the phase-shifting film to the exposure light is preferably not less than 4%, more preferably not less than 6%, more preferably not more than 50%, and more preferably not more than 30%. However, more preferably, it has a transmittance of not less than 6% and not more than 30% that significantly improves the resolution and depth of focus of the transferred pattern due to the phase-shifting effect depending on the exposure conditions. When the film formed from silicon-containing material is a phase-shifting film, the phase-shifting film preferably has a thickness of not less than 50 nm, more preferably not less than 60 nm, and more preferably not more than 90 nm, and more preferably not more than 85 nm, to set the phase shift and transmittance within a specified range.

[0059] [A film formed from chromium-containing materials] Films formed from chromium (Cr)-containing materials can consist of a single layer or multiple layers (e.g., films consisting of 2 to 5 layers). Single layers and multiple layers can have a single composition or a gradient composition.

[0060] The film formed from chromium-containing materials is preferably formed from materials that are resistant to dry etching using fluorine-based gases and can be removed by dry etching using oxygen-containing chlorine-based gases.

[0061] The chromium-containing material is preferably free of silicon (Si). The chromium-containing material is also preferably free of tantalum (Ta). Examples of chromium-containing materials include elemental chromium (Cr), or chromium compounds containing silicon and at least one selected from oxygen (O), nitrogen (N), and carbon (C). Examples of such chromium compounds include: materials composed of chromium and oxygen (CrO), materials composed of chromium and nitrogen (CrN), materials composed of chromium, oxygen, and nitrogen (CrON), materials composed of chromium and carbon (CrC), materials composed of chromium, oxygen, and carbon (CrOC), materials composed of chromium, nitrogen, and carbon (CrNC), and materials composed of chromium, oxygen, nitrogen, and carbon (CrONC). In particular, materials composed of chromium, oxygen, and nitrogen (CrON) and materials composed of chromium, oxygen, nitrogen, and carbon (CrONC) are suitable as chromium-containing materials.

[0062] The thickness of the film formed from the chromium-containing material is preferably no greater than 86 nm, more preferably no greater than 80 nm, even more preferably no greater than 70 nm, and preferably no less than 30 nm, more preferably no less than 32 nm.

[0063] When the film formed from chromium-containing materials is too thick, the removal time becomes longer during dry etching using oxygen-containing chlorine gases. As described later, when a pattern of a film formed from tantalum-containing materials is used as an etching mask to etch the film formed from chromium-containing materials using dry etching with oxygen-containing chlorine gases, the film formed from tantalum-containing materials is also etched bit by bit using dry etching with oxygen-containing chlorine gases. In the case where the film formed from tantalum-containing materials disappears, pinhole defects appear in the film formed from chromium-containing materials.

[0064] Therefore, depending on the thickness of the film formed from the chromium-containing material, the film formed from the tantalum-containing material also needs to have a certain thickness. To reduce the thickness of the resist film formed in contact with the film formed from the tantalum-containing material, it is preferable to make the film formed from the tantalum-containing material thinner, and it is also preferable to make the film formed from the chromium-containing material thinner. From this perspective, the thickness of the film formed from the chromium-containing material is preferably no greater than 80 nm, more preferably no greater than 70 nm.

[0065] Films formed from chromium-containing materials are suitable for optical films used in photomask blanks (e.g., transmissive photomask blanks) and photomasks (e.g., transmissive photomasks), particularly light-shielding films.

[0066] When the film formed from silicon-containing material is a phase-shifting film and the film formed from chromium-containing material is a light-shielding film, especially when the light-shielding film is retained as a light-shielding part (light-shielding film pattern) on the outer periphery of the transparent substrate (the outer periphery is the area where the circuit pattern of the phase-shifting film is not formed), the phase-shifting film and the light-shielding film are formed by setting a predetermined total optical density (OD) (e.g., greater than 2, especially not less than 2.5). However, the phase-shifting film and the light-shielding film preferably have a total optical density (OD) of not less than 3.

[0067] For example, when the transmittance of the phase-shift film to the exposure light is not less than 6% and not more than 30% (optical density not less than 0.53 and not more than 1.22), in order to obtain a total optical density of not less than 3 for the phase-shift film and the light-shielding film, the optical density of the light-shielding film to the exposure light must be not less than 1.78. Therefore, the thickness of the light-shielding film is preferably not less than 30 nm, and more preferably not less than 32 nm.

[0068] [A film formed from tantalum-containing materials] Films formed from tantalum (Ta)-containing materials can consist of a single layer or multiple layers (e.g., films consisting of 2 to 5 layers). Single layers and multiple layers can have a single composition or a gradient composition.

[0069] The film formed from the tantalum-containing material is preferably formed from a material that is resistant to dry etching using oxygen-containing chlorine gases and can be removed by dry etching using fluorine gases. When the film formed from the tantalum-containing material is formed from a material that can be removed by dry etching using fluorine gases, the pattern of the film formed from the tantalum-containing material can be removed simultaneously when the film formed from the silicon-containing material is etched by dry etching using fluorine gases to form a pattern of the film formed from the silicon-containing material.

[0070] Typically, during photomask fabrication, a film formed from tantalum-containing material comes into contact with a resist film and with a cleaning solution during the cleaning of the photomask blank before the resist film is formed. Therefore, the film formed from tantalum-containing material is required to have high adhesion to the resist film and high chemical resistance to the cleaning solution. Furthermore, the film formed from tantalum-containing material is usually the film furthest from the transparent substrate in the photomask blank. Therefore, the film is required to have low reflectivity to light used for inspection (e.g., defect inspection of the photomask blank).

[0071] In this invention, the tantalum-containing material used for the film formed from the tantalum-containing material is a material containing tantalum and oxygen (O) or containing tantalum, oxygen (O) and nitrogen (N) (materials containing tantalum and oxygen, or materials containing tantalum, oxygen and nitrogen), and is a silicon-free (Si) material. Furthermore, in this invention, the tantalum-containing material used for the film formed from the tantalum-containing material is preferably a chromium-free (Cr) material. Examples of materials containing tantalum and oxygen or containing tantalum, oxygen and nitrogen and not containing silicon include tantalum oxide or tantalum oxynitride, particularly materials composed of tantalum and oxygen (TaO), and materials composed of tantalum, oxygen and nitrogen (TaON). ​​Furthermore, in this invention, the tantalum-containing material used for the film formed from the tantalum-containing material may also contain boron (B).

[0072] When the film formed from tantalum-containing material is composed of multiple layers, each layer constituting the multiple layers is formed from tantalum-containing material. In the case where the film formed from tantalum-containing material is composed of multiple layers, at least one layer constituting the multiple layers is formed from a material containing tantalum and oxygen (O), or containing tantalum, oxygen (O), and nitrogen (N) and not silicon (Si). In such a case, the tantalum-containing material forming the other layers constituting the multiple layers can be elemental tantalum (Ta), a material composed of tantalum and nitrogen (TaN), etc. Preferably, when the film formed from tantalum-containing material is composed of multiple layers, each material forming the multiple layers is a material containing tantalum and oxygen (O), or containing tantalum, oxygen (O), and nitrogen (N), and is a material that does not contain silicon (Si).

[0073] Compared to silicon-containing materials, tantalum-containing but silicon-free materials, especially those composed of tantalum and oxygen (TaO) and those composed of tantalum, oxygen, and nitrogen (TaON), are less likely to form hydroxyl groups (OH groups) as hydrophilic groups on their surfaces. Therefore, even without HMDS treatment, films formed from tantalum-containing but silicon-free materials exhibit good adhesion to resist films and avoid the resist residue problems that occur when HMDS treatment is applied to films formed from silicon-containing materials.

[0074] Compared to tantalum-containing but oxygen-free materials (e.g., elemental tantalum (Ta) and materials composed of tantalum and nitrogen (TaN), materials containing tantalum and oxygen, particularly those composed of tantalum and oxygen (TaO) and those composed of tantalum, oxygen, and nitrogen (TaON), exhibit higher chemical stability in air. They are less likely to react with oxygen in the air and less likely to form oxide layers on the film surface. Therefore, during etching, films formed from tantalum-containing and oxygen-containing materials exhibit a uniform etching rate within the film surface and maintain good CD uniformity. Thus, films formed from tantalum-containing and oxygen-containing materials can avoid the problem of uneven etching rates within the film surface caused by uneven or localized formation of oxide layers, which leads to reduced CD uniformity and instability within the film surface.

[0075] When the tantalum-containing material used in the film formed from the tantalum-containing material is a single layer, or when the film formed from the tantalum-containing material is a multilayer, the tantalum-containing material is formed in at least the layer furthest from the transparent substrate in the multilayer. Preferably, the tantalum-containing material forming two or more layers constituting the multilayer preferably satisfies the following content ranges for tantalum, oxygen, and nitrogen.

[0076] <Content range of tantalum, oxygen, and nitrogen> Tantalum content: preferably not less than 40 at%, more preferably not less than 42 at%, and preferably not more than 80 at%, more preferably not more than 70 at%. Oxygen content: preferably not less than 5 at%, more preferably not less than 10 at%, and more preferably not more than 50 at%, even more preferably not more than 45 at%. Nitrogen content (in the case of nitrogen content): preferably not more than 50 at%, more preferably not more than 40 at%.

[0077] When a pattern of a film formed from tantalum-containing material is used as an etching mask, and a film formed from chromium-containing material is etched using dry etching with an oxygen-containing chlorine gas, the tantalum-containing film is also gradually etched away bit by bit using the dry etching with the oxygen-containing chlorine gas. When the tantalum-containing film disappears, pinhole defects appear in the chromium-containing film.

[0078] Therefore, in dry etching using oxygen-containing chlorine-based gases, it is preferable that the etching rate of the film formed from tantalum-containing materials is sufficiently low relative to the etching rate of the film formed from chromium-containing materials. Under certain conditions, the ratio of the etching rate of the film formed from chromium-containing materials in dry etching using oxygen-containing chlorine-based gases to the etching rate of the film formed from tantalum-containing materials in dry etching using oxygen-containing chlorine-based gases under the same conditions is preferably not less than 50, more preferably not less than 100. This ratio is generally not greater than 3000, but is not particularly limited thereto.

[0079] Compared to tantalum-containing but oxygen-free materials (e.g., elemental tantalum (Ta) and materials composed of tantalum and nitrogen (TaN), materials containing tantalum and oxygen, particularly materials composed of tantalum and oxygen (TaO) and materials composed of tantalum, oxygen, and nitrogen (TaON), exhibit higher resistance to dry etching using oxygen-containing chlorine gases, and the etching rate using oxygen-containing chlorine gases is lower. Therefore, thin films formed from materials containing tantalum and oxygen can be formed.

[0080] The thickness of the film formed from the tantalum-containing material (the thickness of a single layer when the film is composed of a single layer, or the total thickness of all layers when the film is composed of multiple layers) is preferably not greater than 15 nm, more preferably not greater than 12 nm, and preferably not less than 0.5 nm, more preferably not less than 1 nm, further preferably not less than 4 nm, and particularly preferably not less than 6 nm.

[0081] Furthermore, when the film formed from tantalum-containing material is composed of multiple layers, the thickness of the layer furthest from the transparent substrate is preferably not less than 0.5 nm, more preferably not less than 1 nm, even more preferably not less than 2 nm, and particularly preferably not less than 4 nm. Among the multiple layers, the total thickness of the layers satisfying the above-mentioned content ranges of tantalum, oxygen, and nitrogen is preferably not less than 0.5 nm, more preferably not less than 1 nm, even more preferably not less than 2 nm, particularly preferably not less than 4 nm, and preferably not more than 15 nm, more preferably not more than 12 nm.

[0082] When the film formed from tantalum-containing materials is too thick, the removal time becomes longer during dry etching using fluorine-based gases. As described later, when the film formed from tantalum-containing materials is etched using a chlorine-based gas dry etching method with a resist film pattern as an etching mask, the resist film is also etched bit by bit by the chlorine-based gas dry etching. When the resist film disappears, pinhole defects appear in the film formed from tantalum-containing materials.

[0083] Therefore, depending on the thickness of the film formed from the tantalum-containing material, the resist film also needs to have a certain or greater thickness. To reduce the thickness of the resist film formed in contact with the film formed from the tantalum-containing material, the film formed from the tantalum-containing material is preferably thinner. If the film formed from the tantalum-containing material is too thick, high resolution cannot be provided because the resist film cannot be thinned. From this point of view, the thickness of the film formed from the tantalum-containing material is preferably no greater than 15 nm, more preferably no greater than 12 nm.

[0084] On the other hand, when the film formed from tantalum-containing materials is too thin, sufficient inspection sensitivity may not be obtained for light used in inspections such as defect inspection of photomask blanks; for example, defects with a size no larger than 100 nm may not be detected. From this perspective, the thickness of the film formed from tantalum-containing materials is preferably not less than 4 nm, and more preferably not less than 6 nm.

[0085] Films formed from tantalum-containing materials are suitable for processing aids used in photomask preforms (e.g., transmissive photomask preforms) and photomasks (e.g., transmissive photomasks), particularly hard masks.

[0086] [Resist film] The resist film can be an electron beam resist drawn with an electron beam or a photoresist drawn with light, with chemically amplified resists being particularly preferred. Chemically amplified resists can be positive or negative. Examples of resists include resists containing a base resin (e.g., hydroxystyrene-based resins or (meth)acrylic resins, etc.) and an acid-generating agent, and optionally containing a crosslinking agent, quencher, surfactant, or other components. The thickness of the resist film is preferably no greater than 120 nm, more preferably no greater than 100 nm, further preferably no greater than 90 nm, and particularly preferably no greater than 70 nm, to prevent the resist film pattern from collapsing during the developing and post-developing rinsing processes in the case of forming fine patterns. There is no limitation on the thickness of the resist film, as long as the resist film can be formed with a uniform thickness; however, the thickness typically has a lower limit of not less than 40 nm.

[0087] [Film Formation Method] Films formed from silicon-containing materials (constituting layers of the film), films formed from chromium-containing materials (constituting layers of the film), and films formed from tantalum-containing materials (constituting layers of the film) are preferably formed by sputtering, which offers good controllability and allows for the easy formation of films with predetermined properties, but is not particularly limited thereto. DC sputtering or RF sputtering can be used as the sputtering method, but is not particularly limited thereto.

[0088] When forming films from silicon-containing materials, particularly when the films are formed from silicon-containing materials that do not contain transition metals, silicon targets can be used as sputtering targets. On the other hand, when films formed from silicon-containing materials are formed from materials containing transition metals (Me) other than chromium and silicon, particularly from materials containing transition metals (Me) other than chromium and silicon and not containing chromium, targets appropriately selected from those containing transition metals (Me) other than chromium, silicon targets, and targets containing transition metals (Me) other than chromium and silicon and not containing chromium can be used as sputtering targets. If necessary, two or more targets can be used for co-sputtering. As targets containing transition metals (Me) other than chromium and silicon and not containing chromium, two or more targets with different compositions (partial or complete differences in constituent elements, or the same constituent elements but different contents) can be used.

[0089] When forming films from chromium-containing materials, especially when the films are formed from chromium-containing materials and do not contain either or both of silicon and tantalum, chromium targets can be used as sputtering targets.

[0090] When forming films from tantalum-containing materials, especially when the films are formed from tantalum-containing materials and do not contain silicon or silicon and chromium, tantalum targets can be used as sputtering targets. Furthermore, when the films formed from tantalum-containing materials are formed from materials containing tantalum and boron, targets made of tantalum and boron (TaB targets) can be used as sputtering targets.

[0091] The power supplied to the sputtering target should be appropriately set according to the target's size, cooling efficiency, and the controllability of film formation. The power per unit area of ​​the sputtering surface of the target is typically 0.1–10 W / cm². 2 Rare gases such as helium (He), neon (Ne), and argon (Ar) can be used as sputtering gases. When forming a film containing only the elements that constitute the target material, only rare gases can be used as sputtering gases.

[0092] When the film is formed from a material containing at least one light element selected from oxygen (O), nitrogen (N), carbon (C), and hydrogen (H), reactive sputtering is preferred. In reactive sputtering, rare gases such as helium (He), neon (Ne), and argon (Ar) and reactive gases are used as sputtering gases.

[0093] As reactive gases, for example, when the membrane is formed from an oxygen-containing (O) material, oxygen gas (O2 gas) can be used; when the membrane is formed from a nitrogen-containing (N) material, nitrogen gas (N2 gas) can be used; when the membrane is formed from a material containing both nitrogen (O) and nitrogen (N), nitrogen oxide gases such as nitric oxide gas (NO gas), nitrogen dioxide gas (NO2 gas), and nitrous oxide gas (N2O gas) can be used; when the membrane is formed from a material containing carbon (C) and oxygen (O), carbon oxide gases such as carbon monoxide gas (CO gas) and carbon dioxide gas (CO2 gas) can be used; and when the membrane is formed from a material containing carbon (C) and hydrogen (H), hydrocarbon gases such as methane gas (CH4 gas) can be used.

[0094] In particular, when the membrane is formed of a material containing oxygen (O) and nitrogen (N), a gas appropriately selected from nitrogen oxide gases such as oxygen (O2 gas), nitrogen (N2 gas), nitric oxide (NO gas), nitrogen dioxide (NO2 gas), and nitrous oxide (N2O gas) can be used, and if necessary, two or more gases can also be used.

[0095] The pressure used to form each membrane can be appropriately set taking into account membrane stress, chemical resistance, and cleaning resistance. In particular, chemical resistance can be improved by setting the pressure to preferably not less than 0.01 Pa, more preferably not less than 0.03 Pa, and preferably not more than 1 Pa, more preferably not more than 0.3 Pa. Furthermore, the flow rates of each gas can be appropriately set to obtain the desired composition, typically from 0.1 to 100 sccm.

[0096] In the manufacturing process of photomask blanks, heat treatment can be performed on the transparent substrate and the film formed on the transparent substrate before the resist film is formed. Infrared heating, resistance heating, etc., can be used as heat treatment methods, and the processing conditions are not particularly limited. For example, heat treatment can be performed in an oxygen-containing gas atmosphere such as air. In the case of oxygen (O2 gas), the concentration of the oxygen-containing gas is, for example, 1 to 100% by volume, but is not particularly limited thereto. The heat treatment is preferably performed at a temperature not lower than 200°C, more preferably not lower than 400°C.

[0097] In the photomask preform manufacturing process, before forming the resist film, the film formed on the transparent substrate, especially the film formed of chromium-containing materials, can be subjected to ozone treatment or plasma treatment, and the treatment conditions are not particularly limited. Each treatment can be performed to increase the oxygen concentration on the film surface. In such cases, the treatment conditions can be appropriately adjusted to obtain a predetermined oxygen concentration. Furthermore, when the film is formed by sputtering, the oxygen concentration on the film surface can also be increased by adjusting the ratio of rare gases and oxygen-containing gases (oxidizing gases) such as oxygen (O2 gas), carbon monoxide gas (CO gas), and carbon dioxide gas (CO2 gas) in the sputtering gas.

[0098] Furthermore, during the manufacturing process of the photomask blank, before the formation of the resist film, a cleaning process can be performed to remove particles present on the surface of the transparent substrate or the film formed on the transparent substrate. Cleaning can be performed using one or both of ultrapure water and functional water, where the functional water is ultrapure water containing ozone gas, hydrogen, or other gases. Alternatively, cleaning can be performed by washing with ultrapure water containing surfactants, followed by further washing with one or both of ultrapure water and functional water. If necessary, cleaning can be performed simultaneously with ultrasonic irradiation or in combination with ultraviolet light irradiation.

[0099] There are no particular restrictions on the method of forming a resist film (coating resist), and known methods such as spin coating can be used.

[0100] [Photomask] The photomask blank of the present invention can be used to manufacture a photomask having a circuit pattern (photomask pattern) of a film formed of a chromium-containing material. In the case of a circuit pattern (photomask pattern) having a film formed of a chromium-containing material, the film formed of the chromium-containing material is preferably a light-shielding film. In such a case, the photomask blank and the photomask can be a binary photomask blank and a binary photomask, respectively.

[0101] Figure 5This is a cross-sectional view showing an example of a first embodiment of the photomask of the present invention. The photomask 111 includes a pattern (circuit pattern) 3a of a film formed of a chromium-containing material and formed in contact with the transparent substrate 1 on the transparent substrate 1. The photomask of the first embodiment can be manufactured from the photomask blank of the first embodiment or the photomask blank of the third embodiment.

[0102] The photomask blank of the present invention can be used to manufacture a photomask having a circuit pattern (photomask pattern) of a film formed of a silicon-containing material. When the circuit pattern (photomask pattern) has a film formed of a silicon-containing material, the film formed of the silicon-containing material is preferably a halftone phase-shifting film or a phase-shifting film, and the film formed of a chromium-containing material is preferably a light-shielding film. In this case, the photomask blank and the photomask can be respectively a halftone phase-shifting mask blank and a halftone phase-shifting mask.

[0103] In particular, a photomask can be manufactured from the photomask blank of the present invention, wherein, in the film formed of silicon-containing material, in the portion of the film without a circuit pattern of the film formed of silicon-containing material (i.e., the portion outside the area with a circuit pattern (effective area)), that is, in the portion located at the outer periphery of the transparent substrate, a pattern of a film formed of chromium-containing material (light-shielding portion (light-shielding pattern)) is formed and in contact with the film formed of silicon-containing material.

[0104] Figure 6 This is a cross-sectional view illustrating an example of a second embodiment of the photomask of the present invention. The photomask 112 includes a pattern 2a of a film formed of a silicon-containing material and a pattern 3b of a film formed of a chromium-containing material, both formed in contact with the transparent substrate 1. The 3b is formed on a portion located at the outer periphery of the transparent substrate 1 (this portion is the area where the circuit pattern 2a of the silicon-containing material film is not formed) and is in contact with the pattern 2a of the silicon-containing material film. The photomask of the second embodiment can be manufactured from the photomask blank of the second embodiment or the photomask blank of the fourth embodiment.

[0105] [Methods for manufacturing photomasks] The photomask of the first embodiment can be manufactured, for example, by the following method. Figure 7 A to 7F are cross-sectional views illustrating the process of manufacturing a reflective photomask of the first embodiment from a reflective photomask blank of the first embodiment or the third embodiment.

[0106] In this case, when using the photomask of the first embodiment, firstly, as... Figure 7As shown in step (A), a first resist film 5 is formed that contacts the side of the film 4 made of tantalum material away from the transparent substrate 1, forming the photomask blank 101 (step (A)). When using the photomask blank of the third embodiment, step (A) can be replaced by step (A0) for preparing the photomask blank 103.

[0107] The resist film formed in step (A) can be the same as the resist film in the photomask blank of the third or fourth embodiment. The thickness of the resist film formed in step (A) is preferably not greater than 120 nm, more preferably not greater than 100 nm, even more preferably not greater than 90 nm, particularly preferably not greater than 70 nm, and generally not less than 40 nm.

[0108] Next, as Figure 7 As shown in B, the first resist film pattern 5a is formed by patterning the first resist film 5 (step (B)).

[0109] Next, as Figure 7 As shown in step (C), the first resist film pattern 5a is used as an etching mask, and the film 4 formed of tantalum material is patterned by dry etching with fluorine gas to form the pattern 4a of the film formed of tantalum material (step (C)).

[0110] Next, as Figure 7 As shown in step D, the first resist film pattern 5a is removed (step (D)). Step (D) can be performed after the subsequent step (E).

[0111] Next, as Figure 7 As shown in E, the pattern 4a of the film formed of tantalum material is used as an etching mask, and the film 3 formed of chromium material is patterned by dry etching with oxygen-containing chlorine gas to form the pattern 3a of the film formed of chromium material (process (E)).

[0112] Next, as Figure 7 As shown in F, the pattern 4a of the film formed from tantalum-containing material is removed by dry etching using a fluorine-based gas (process (F1)). This yields the photomask 111 of the first embodiment.

[0113] The photomask of the second embodiment can be manufactured, for example, by the following method. Figure 8 A~ Figure 8 J is a cross-sectional view illustrating the process of manufacturing a reflective photomask of the second embodiment from a reflective photomask blank of the second or fourth embodiment.

[0114] In this case, when using the photomask of the second embodiment, firstly, as... Figure 8As shown in step (A), a first resist film 5 is formed in contact with the side of the film 4 made of tantalum material away from the transparent substrate 1, forming the photomask blank 102 (step (A)). When using the photomask blank of the fourth embodiment, step (A) can be replaced by step (A0) for preparing the photomask blank 104.

[0115] The resist film formed in step (A) can be the same as the resist film in the photomask blank of the third or fourth embodiment. The thickness of the resist film formed in step (A) is preferably not greater than 120 nm, more preferably not greater than 100 nm, even more preferably not greater than 90 nm, particularly preferably not greater than 70 nm, and generally not less than 40 nm.

[0116] Next, as Figure 8 As shown in B, the first resist film pattern 5a is formed by patterning the first resist film 5 (step (B)).

[0117] Next, as Figure 8 As shown in step (C), the first resist film pattern 5a is used as an etching mask, and the film 4 formed of tantalum material is patterned by dry etching with fluorine gas to form the pattern 4a of the film formed of tantalum material (step (C)).

[0118] Next, as Figure 8 As shown in step D, the first resist film pattern 5a is removed (step (D)). Step (D) can be performed after the subsequent step (E).

[0119] Next, as Figure 8 As shown in E, the pattern 4a of the film formed of tantalum material is used as an etching mask, and the film 3 formed of chromium material is patterned by dry etching with oxygen-containing chlorine gas to form the pattern 3a of the film formed of chromium material (process (E)).

[0120] Next, as Figure 8 As shown in F, the pattern 3a of the film formed of chromium-containing material is used as an etching mask, and the film 2 formed of silicon-containing material is patterned by dry etching with fluorine gas to form the pattern 2a of the film formed of silicon-containing material including circuit pattern, while the pattern 4a of the film formed of tantalum-containing material is removed (step (F2)).

[0121] After performing steps (A) to (F2), the pattern 3a of the film formed of chromium-containing material can be removed by dry etching using an oxygen-containing chlorine gas to create a photomask having a pattern (circuit pattern) of a film formed of silicon-containing material formed on and in contact with the transparent substrate. On the other hand, by further performing the following steps (G) to (J), a photomask having a pattern of a film formed of chromium-containing material on the portion located on the outer periphery of the transparent substrate can be obtained.

[0122] After process (F2), firstly, as Figure 8 As shown in G, a second resist film 6 is formed on the side of the pattern 3a of the film formed of chromium-containing material that is away from the transparent substrate, and in contact with the pattern 3a of the film formed of chromium-containing material and the exposed transparent substrate 1 (process (G)).

[0123] The resist film formed in step (G) can be the same as the resist film in the photomask blank of the third or fourth embodiment, or a resist film for laser drawing can be used. The thickness of the resist film formed in step (G) is preferably not less than 200 nm, more preferably not less than 300 nm, and preferably not more than 1000 nm, more preferably not more than 800 nm.

[0124] Next, as Figure 8 As shown in H, by patterning the second resist film 6, the second resist film pattern 6a is formed only on the outer periphery of the transparent substrate (i.e., the area where no circuit pattern is formed (the area other than the effective area 7)) (process (H)).

[0125] Next, as Figure 8 As shown in Figure 1, the second resist film pattern 6a is used as an etching mask, and the pattern 3a of the film formed of chromium-containing material outside the outer periphery (in the effective area 7) is removed by dry etching with oxygen-containing chlorine gas, so that the pattern (light-shielding part) 3b of the film formed of chromium-containing material is retained on the outer periphery of the transparent substrate.

[0126] Next, as Figure 8 As shown in step J, the second resist film pattern 6s is removed (step (J)). This yields the photomask 112 of the second embodiment, which has a pattern (light-shielding portion) 3b of a film formed of a chromium-containing material formed on its outer periphery, but no pattern of a film formed of a chromium-containing material formed in the effective region 7.

[0127] The photomask of the present invention is particularly effective in photolithography for forming patterns with a half-pitch preferably not greater than 50 nm, more preferably not greater than 30 nm, further preferably not greater than 20 nm, and especially preferably not greater than 10 nm on a substrate to be processed, in exposure of a photoresist film formed on a substrate to be processed, and in exposure of a pattern transferred by an exposure light with a wavelength not greater than 200 nm, such as an ArF excimer laser (wavelength: 193 nm) or an F2 laser (wavelength: 157 nm).

[0128] Using the photomask of the present invention, a photomask pattern can be exposed onto a photoresist film formed on a substrate to be processed, the photoresist film being the exposure target of the photomask pattern. In the pattern exposure method using the photomask of the present invention, the photomask pattern can be transferred onto the photoresist film formed on the substrate to be processed by irradiating an exposure light with a photomask manufactured from a photomask blank. The exposure light can be applied under dry conditions or by immersion exposure, and the photomask is particularly suitable for exposing photomask patterns by immersion exposure using a wafer with a size of not less than 300 mm as the substrate to be processed. Example

[0129] The embodiments of the present invention are given below by way of illustration rather than limitation.

[0130] [Examples 1-10 and Comparative Examples 1-6] A photomask blank (halftone phase-shifting mask blank) is manufactured by sequentially laminating a phase-shifting film (halftone phase-shifting film) formed of silicon material, a light-shielding film formed of chromium material, and a hard mask formed of tantalum material on a transparent quartz substrate with dimensions of 152 mm square and a thickness of about 6 mm.

[0131] First, on a transparent substrate, a molybdenum target and a silicon target are used as targets. While adjusting the power applied to the targets, argon and nitrogen are used as sputtering gases. Sputtering is performed in the atmosphere of these gases to form a phase-shifting film (thickness: 70 nm) with a single-layer structure on the transparent substrate. As a film formed of silicon-containing material, the phase-shifting film is composed of MoSiN (Mo content: 3 at%, Si content: 52 at%, N content: 45 at%), which has a phase shift of 177 degrees and a transmittance of 6% (optical density of 1.22) for light with a wavelength of 193 nm.

[0132] Next, on the phase-shifted film, a chromium target is used as the target, and argon, oxygen and carbon dioxide gases are used as sputtering gases. The power applied to the target and the flow rate of the sputtering gases are adjusted to perform sputtering, so as to form a light-shielding film with a single-layer structure (thickness: 40 nm) on the phase-shifted film. As a film formed of chromium-containing material, the light-shielding film is composed of CrOC (Cr content: 60 at%, O content: 20 at%, C content: 20 at%), which has a transmittance of 1.4% (optical density of 1.85) for light with a wavelength of 193 nm.

[0133] Next, in Examples 1-10 and Comparative Examples 3-6, a tantalum target was used as the target on the light-shielding film, and argon and oxygen or argon, oxygen and nitrogen were used as sputtering gases. The power applied to the target and the flow rate of the sputtering gas were adjusted to perform sputtering. As a film formed of tantalum-containing material, a hard mask with a single-layer structure was formed on the light-shielding film in Examples 1-7 and Comparative Examples 3-6, and a hard mask with a double-layer structure of a first layer and a second layer was formed in Examples 8-10, thereby obtaining a photomask blank.

[0134] On the other hand, in Comparative Examples 1 and 2, a silicon target was used as the target on the light-shielding film, and argon and oxygen were used as sputtering gases. The power applied to the target and the flow rate of the sputtering gas were adjusted to perform sputtering, so as to form a hard mask with a single-layer structure of silicon oxide (SiO) on the light-shielding film, thereby obtaining a photomask blank.

[0135] The composition and thickness of each layer of the hard mask, as well as the thickness of the hard mask itself, are shown in Table 1. In Table 1, layer 2 is the layer furthest from the transparent substrate. In the embodiments and comparative examples, the composition of the films (layers) was measured using X-ray photoelectron spectroscopy. The thickness of the films (layers) was measured using X-ray diffraction.

[0136] [Table 1]

[0137] [Evaluation 1: Etching clear time of dry etching of the light-shielding film using oxygen-containing chlorine-based gas] For the evaluation sample in which only a light-shielding film (a film formed of a chromium-containing material) was formed on a transparent substrate, the time until the light-shielding film disappeared by dry etching with an oxygen-containing chlorine gas was evaluated (removal time). The removal time was the time until the end point was detected when the light-shielding film was etched under the following conditions (condition 1). As a result, the removal time was 140 seconds, and therefore the etching rate was 0.286 nm / s.

[0138] [Conditions for dry etching using oxygen-containing chlorine-based gases (Condition 1)] Instrument: ICP (Inductively Coupled Plasma) system Etching gases: Cl2 and O2 Gas pressure: 3.0 mTorr (0.40 Pa) ICP power: 350W

[0139] [Evaluation 2: Reduction in hard mask size when using oxygen-containing chlorine-based gases for dry etching of the light-shielding film] Using photomask blanks manufactured in the same manner as in Examples 1-10 and Comparative Examples 1-6, an over-etching time (560 seconds) was added to the etch clearance time obtained in Evaluation 1 for dry etching of the light-shielding film (a film formed of a chromium-containing material) using an oxygen-containing chlorine gas. Dry etching of the hard mask (a film formed of a tantalum-containing material or a film formed of silicon oxide (SiO)) of the photomask blanks was performed using an oxygen-containing chlorine gas, and the reduction in hard mask thickness was evaluated. The results are shown in Table 2.

[0140] As shown in Table 2, the photomask blank in Comparative Example 5, formed from a tantalum-containing material, completely disappeared within an etching time (560 seconds) when exposed to dry etching using an oxygen-containing chlorine gas. This etching time was the etching removal time for dry etching of the photomask using an oxygen-containing chlorine gas, plus an over-etching etching time of 300%.

[0141] Furthermore, the etching rate was calculated based on the reduction in hard mask thickness, and the ratio of the etching rate of the light-shielding film to the etching rate of the hard mask obtained in Evaluation 1 was calculated. The results are shown in Table 2.

[0142] As shown in Table 2, the ratio of the etch rate of the light-shielding film to the etch rate of the hard mask (film formed of tantalum-containing material) of the photomask blanks in Comparative Examples 4 and 5 is relatively low. This is believed to be because the films formed of tantalum-containing material in the photomask blanks of Comparative Examples 4 and 5 do not contain oxygen, and therefore have high etch rates in dry etching using oxygen-containing chlorine-based gases. In particular, the photomask blank of Comparative Example 5 has a higher nitrogen content, and therefore has an even higher etch rate in dry etching using oxygen-containing chlorine-based gases.

[0143] [Evaluation 3: Etch removal time for dry etching of hard masks using fluorine-based gases] Using photomask blanks manufactured using the same method as in Examples 1-10 and Comparative Examples 1-6, the time it took for the hard mask (a film formed of tantalum-containing material or a film formed of silicon oxide (SiO)) to disappear by dry etching with a fluorine-based gas (removal time) was evaluated. The removal time was the time until the endpoint was detected when the hard mask was etched under the following conditions (condition 2). The results are shown in Table 2.

[0144] [Conditions for dry etching using fluorine-based gases (Condition 2)] Instrument: ICP (Inductively Coupled Plasma) system Etching gases: SF6 and He Gas pressure: 4.0 mTorr (0.53 Pa) ICP power: 400W

[0145] As shown in Table 2, the photomask blank in Comparative Example 3, formed from a tantalum-containing material, has a longer removal time. This is because the photomask blank in Comparative Example 3, formed from a tantalum-containing material, has a thicker film. Furthermore, the photomask blank in Comparative Example 6, formed from a tantalum-containing material, also has a longer removal time. This is believed to be because the photomask blank in Comparative Example 6, formed from a tantalum-containing material, has a high oxygen content.

[0146] [Evaluation 4: Reduction in resist film when using fluorine-based gases for dry etching of hard masks] Using photomask blanks manufactured by the same method as in Examples 1-10 and Comparative Examples 1-6, the reduction in resist film thickness was evaluated when dry etching was performed on hard masks (films formed of tantalum-containing materials or films formed of silicon oxide (SiO)) using fluorine-based gases.

[0147] First, a positive chemical amplification electron beam resist is spin-coated onto a hard mask to form a resist film with a thickness of 100 nm on the hard mask. During the formation of the resist film, only the photomask blank of Comparative Example 1 is subjected to HMDS treatment on the surface of the film formed from silicon oxide (SiO) to form the resist film.

[0148] Next, an electron beam lithography apparatus was used at 100 μC / cm. 2 The dosage was used to create a total of 20 isolated line patterns with a long side of 100,000 nm and a short side of 60 nm. Next, a heat treatment (PEB: post-exposure baking) was performed at 115°C for 14 minutes. Following this, a 42-second water-pit (swirling immersion) development was performed to form the resist film pattern.

[0149] Next, using the resist film pattern as an etching mask, the etching time, as shown in Table 2, was calculated by adding 50% over-etching to the etching removal time obtained in Evaluation 3 for dry etching of the hard mask using fluorine-based gas. Dry etching of the hard mask of the photomask blank was performed under condition 2 above using fluorine-based gas to form the hard mask pattern. Afterwards, the thickness of the resist film remaining on the hard mask pattern was measured to evaluate the amount of resist film reduction. The resist film thickness was measured using atomic force microscopy (AFM) over a square area of ​​200 nm × 200 nm. The results and etching times are shown in Table 2.

[0150] Furthermore, based on the reduction in the obtained resist film, an additional 50% over-etching time was added to the etch-clearing time for dry etching of the hard mask using fluorine-based gas. Dry etching of the resist film was then performed using fluorine-based gas, and the required resist film thickness to remain at 20 nm was calculated. This thickness is the minimum thickness of the resist film for dry etching using fluorine-based gas. If the resist film is too thin, the fluorine plasma reaches the hard mask, resulting in pinhole defects. Therefore, the residual thickness of the etched resist film pattern was set to 20 nm. The results are shown in Table 2.

[0151] As shown in Table 2, in each photomask blank in Comparative Examples 3 and 6, the required minimum thickness of the resist film is thicker because the film formed from the tantalum-containing material has a longer removal time.

[0152] [Table 2]

[0153] [Photomask fabrication] A photomask (halftone phase-shifting mask) was manufactured using individual photomask blanks (halftone phase-shifting mask blanks) manufactured in the same manner as in Examples 1-10 and Comparative Examples 1-6.

[0154] First, a positive chemical amplification electron beam resist is spin-coated onto a hard mask (a film formed of tantalum-containing material or a film formed of silicon oxide (SiO)) to form a first resist film on the hard mask. During resist film formation, as in Evaluation 4, only the photomask blank of Comparative Example 1 undergoes HMDS treatment on the surface of the film formed of silicon oxide (SiO) before the resist film is formed (process (A)).

[0155] In the fabrication of the photomask used for evaluating the CD uniformity (evaluation 5) of the photomask, as described later, a resist film with a thickness of 100 nm was formed in each of Examples 1-10 and Comparative Examples 1-6. In the fabrication of the photomask used in the evaluation of the resolution limit of the photomask (evaluation 6) and the evaluation of the defects of the photomask (evaluation 7), as described later, resist films with the thicknesses shown in Table 3 were formed, respectively. In Examples 1-10 and Comparative Examples 3, 5, and 6, the necessary thickness of the resist film shown in Table 2 was not less than 40 nm, and therefore the resist was formed with the necessary thickness shown in Table 2. On the other hand, if the thickness of the resist film is less than 40 nm, it may be impossible to form a resist film with a uniform thickness. In Comparative Examples 1, 2, and 4, the necessary thickness of the resist film shown in Table 2 was less than 40 nm, and therefore the resist film was formed with a thickness of 40 nm.

[0156] Next, the first resist film is patterned to form a first resist film pattern (step (B)). Different resist film patterns are formed when manufacturing each photomask blank used in evaluations 5-7.

[0157] In manufacturing the photomask used in Evaluation 5, firstly, an electron beam lithography apparatus was used at 100 μC / cm. 2 Within a 12cm × 12cm square area centered at the intersection of the diagonals of the substrate's main surface, isolated spatial patterns with a long side dimension of 100,000 nm and a short side dimension of 200 nm are drawn at 1cm intervals, starting from one vertex of the square area. There are 13 rows along one side of the square area and 13 rows in the opposite direction perpendicular to that direction, for a total of 169 patterns. Next, a heat treatment (PEB: post-exposure baking) is performed at 115°C for 14 minutes. Following this, a 60-second water-pit (swirling immersion) development is performed to form the resist film pattern.

[0158] In manufacturing the photomask used in Evaluation 6, firstly, an electron beam lithography apparatus was used at 100 μC / cm. 2 The dosage was adjusted to serve as a test pattern, equivalent to the auxiliary pattern for the line pattern, and a total of 200,000 isolated line patterns with different short side dimensions were drawn. Their long side dimensions were 80 nm, and their short side dimensions ranged from 20 nm to 80 nm, i.e., the short side dimensions varied in 1 nm increments. Next, a heat treatment device was used to perform a 14-minute heat treatment at 115°C (PEB: post-exposure baking). Following this, a 60-second water-pit (swirling immersion) development was performed to form the resist film pattern.

[0159] In manufacturing the photomask used in Evaluation 7, firstly, an electron beam lithography apparatus was used at 100 μC / cm. 2 At a given dosage, lines and spatial patterns (with a long side dimension of 6 cm and a short side dimension of 200 nm) are drawn across the entire area of ​​a 6 cm × 6 cm square region centered at the intersection of the diagonals of the main surface of the substrate. The lines and spatial patterns are then 200 nm wide. Next, a heat treatment (PEB: post-exposure baking) is performed at 115°C for 14 minutes. Following this, a 60-second water-pit (swirling immersion) development process is performed to form the resist film pattern.

[0160] Next, using the resist film pattern as an etching mask, the etching time is the etching time shown in Table 2, which is 50% over-etched on top of the etching removal time obtained in Evaluation 3 for dry etching of the hard mask using fluorine-based gas. Under the above conditions 2, the hard mask of the photomask blank is dry etched using fluorine-based gas to form the pattern of the hard mask. (Process (C)).

[0161] Next, the resist film pattern is removed by washing with a sulfuric acid-hydrogen peroxide mixture (SPM) (a mixture of sulfuric acid and hydrogen peroxide in a volume ratio of 3:1 (the sulfuric acid-hydrogen peroxide mixture is also defined in the following)).

[0162] Next, using the pattern of the hard mask as an etching mask, an over-etching time of 300% is added to the etching removal time obtained in Evaluation 1 for dry etching of the light-shielding film (a film formed of chromium-containing material) using oxygen-containing chlorine gas, as the etching time (560 seconds), and dry etching is performed using oxygen-containing chlorine gas under the above conditions 1 to form the pattern of the light-shielding film (process (E)).

[0163] Next, using the pattern of the light-shielding film as an etching mask, in the dry etching using fluorine gas, an over-etching time of about 3% is added to the etching removal time (72 seconds) of the dry etching of the phase shift film (a film formed of silicon-containing material) using fluorine gas as the etching time (74 seconds). Under the above conditions 2, the dry etching using fluorine gas is performed to pattern the phase shift film and form a pattern of the phase shift film including the circuit pattern, while removing the pattern of the hard mask (step (F2)).

[0164] Next, a resist for laser drawing is spin-coated to form a second resist film (thickness: 360 nm) on the side of the light-shielding film pattern away from the substrate, which is in contact with the light-shielding film pattern and the exposed transparent substrate (step (G)).

[0165] Next, the second resist film is patterned to form a second etch-resistant film pattern (step (H)). First, the second resist film is patterned using a laser lithography apparatus, and a pattern is drawn such that the second etch-resistant film is not retained in the area where the circuit pattern has been formed (the effective area), and the second etch-resistant film pattern is only retained on the outer periphery of the transparent substrate, which is the area where no circuit pattern has been formed. Next, a heat treatment apparatus is used to perform a heat treatment at 110°C for 20 minutes (PEB: post-exposure baking). Next, a spray development is performed for 200 seconds to form the resist film pattern.

[0166] Next, using the second resist film pattern as an etching mask, an over-etching time of 300% is added to the etching removal time obtained in Evaluation 1 for dry etching of the light-shielding film using oxygen-containing chlorine gas as the etching time (560 seconds). Under the above conditions 1, dry etching is performed using oxygen-containing chlorine gas to remove the pattern of the light-shielding film except for the outer periphery, so that the pattern of the light-shielding film is retained on the outer periphery (step (I)).

[0167] Next, the resist film pattern is removed by washing with a mixture of sulfuric acid and hydrogen peroxide (step (J)), and then a photomask is obtained.

[0168] [Evaluation 5: CD uniformity of the photomask] The CD uniformity (uniformity of pattern linewidth) is evaluated within the surface of the phase-shift film (a film formed of silicon-containing material) of the obtained photomask (halftone phase-shift mask).

[0169] The linewidths of 169 isolated spatial patterns in the phase-shift film (a film formed of silicon-containing material) of the obtained photomask were measured using critical-size scanning electron microscopy (CD-SEM), and the 3σ (three times the standard deviation) of the 169 linewidths was calculated. The results are shown in Table 3.

[0170] As shown in Table 3, the photomasks of Comparative Examples 4 and 5 have a larger 3σ, and the CD uniformity within the film surface of the phase-shifting film is lower. It is believed that this is because the film formed from the tantalum-containing material of the photomask blanks of Comparative Examples 4 and 5 is a tantalum nitride (TaN) film, which does not contain oxygen. Due to the reaction with oxygen in the air, TaO is formed unevenly or locally on the surface away from the substrate. The etching rate in the dry etching using fluorine-based gas becomes uneven within the film surface, and the CD uniformity within the film surface decreases, resulting in poor CD uniformity within the film surface of the phase-shifting film.

[0171] [Review 6: The resolution limit of photomasks] The resolution limit was evaluated for the phase-shifting film (a film formed of silicon-containing material) of the obtained photomask (halftone phase-shifting mask).

[0172] For all 200,000 isolated patterns in the phase-shift film (a film formed of silicon-containing material) of the obtained photomask, pattern disappearance, pattern collapse, and pattern shape defects were evaluated by visual inspection. An isolated pattern exhibiting any of the pattern disappearance, pattern collapse, or pattern shape defects detected by the visual inspection device was considered a defect, and the resolution limit was evaluated as the minimum short side dimension of an isolated pattern without defects. The results are shown in Table 3.

[0173] As shown in Table 3, the photomask of Comparative Example 2 has a wider resolution limit (wider width of the auxiliary pattern that can be formed) and a lower resolution. This is because the hard mask of Comparative Example 2 is not a film formed of tantalum-containing material, but a film formed of silicon oxide (SiO), and HMDS treatment is not performed, so the adhesion between the hard mask and the resist film is smaller.

[0174] Furthermore, as shown in Table 3, although it does not reach the level of Comparative Example 2, the resolution limit of the photomask in Comparative Example 3 is wider (the width of the auxiliary pattern that can be formed is wider), resulting in lower resolution. It is believed that this is because the film formed by the tantalum-containing material in Comparative Example 3 is thicker, requiring a thicker resist film. Therefore, due to the impact of the developing solution during the developing process of forming the resist film pattern or the impact of pure water during rinsing, the resist film pattern with a high aspect ratio collapses.

[0175] Furthermore, as shown in Table 3, although it does not reach the level of Comparative Example 2, the photomask of Comparative Example 6 has a wider resolution limit (wider width of the auxiliary pattern that can be formed) and a lower resolution. It is believed that this is because the film formed from tantalum-containing material in Comparative Example 6 has a high oxygen content and a low etching rate (long etching removal time) in dry etching using fluorine-based gases, requiring a thick resist film. Therefore, due to the impact of the developing solution during the development process of forming the resist film pattern or the impact of pure water during rinsing, the resist film pattern with a high aspect ratio collapses.

[0176] [Review 7: Defects of photomasks] The defects in the phase-shifting film (a film formed of silicon-containing material) of the obtained photomask (halftone phase-shifting mask) were evaluated.

[0177] As an evaluation of the appearance quality of the obtained photomask, protrusion defects, missing defects, and pinhole defects in the pattern of the phase-shift film (a film formed of silicon-containing material) and pinhole defects on the transparent substrate and the phase-shift film were counted using a photomask appearance inspection device. The results are shown in Table 3.

[0178] As shown in Table 3, the photomask of Comparative Example 1 has a large number of defects. This is because the hard mask in Comparative Example 1 is a film formed of silicon oxide (SiO) and HMDS treatment is performed. When the film formed of silicon oxide (SiO) is etched, the resist residue on the film acts as an etching mask. The parts of the film formed of silicon oxide (SiO) that should be etched are not etched and remain. Finally, the phase shift film at the location of the resist residue is not etched and remains, becoming a defect, especially as pinpoint defects on the transparent substrate or phase shift film.

[0179] Furthermore, as shown in Table 3, the photomask of Comparative Example 5 has a large number of defects. This is because, as shown in Table 2, by using dry etching with an oxygen-containing chlorine gas, the film (thickness: 15 nm) formed of tantalum-containing material in Comparative Example 5 completely disappeared (the reduction was 15 nm in Evaluation 2), and the light-shielding film (the film formed of chromium-containing material) was etched in the exposed portion, becoming defects, especially pattern defects or pinhole defects.

[0180] [Table 3]

[0181] Explanation of reference numerals in the attached figures 1 transparent substrate 2. Films formed from silicon-containing materials 2a Pattern of a film formed from silicon-containing material 3. Films formed from chromium-containing materials 3a Pattern of a film formed from chromium-containing material 3b Pattern of a film formed from chromium-containing material (light-shielding area) 4. Films formed from tantalum-containing materials 4a Pattern of a film formed from a tantalum-containing material 5. First resist film 5a First resist film pattern 6. Second resist film 6a Second resist film pattern 7. Effective Area 101, 102, 103, 104 Photomask blanks 111, 112 Photomasks.

Claims

1. A photomask blank, comprising: A transparent substrate, a film formed of a chromium-containing material formed on the transparent substrate, and a film formed of a tantalum-containing material formed on the film formed of the chromium-containing material, wherein, The film formed from tantalum-containing material consists of a single layer or multiple layers. The film formed from the tantalum-containing material has a thickness of not less than 0.5 nm and not more than 15 nm. The tantalum-containing material contains tantalum and oxygen, or contains tantalum, oxygen and nitrogen, and does not contain silicon. The single layer and at least the layer furthest from the transparent substrate among the layers constituting the multilayer are formed of a tantalum-containing material, wherein the tantalum-containing material has a tantalum content of not less than 40 at% and not more than 80 at%, an oxygen content of not less than 5 at% and not more than 50 at%, and a nitrogen content of not more than 50 at%. The layer furthest from the transparent substrate has a thickness of not less than 0.5 nm.

2. The photomask blank according to claim 1, wherein, When dry etching is performed on the film formed of chromium-containing material and the film formed of tantalum-containing material using oxygen-containing chlorine gas, the ratio of the etching rate of the film formed of chromium-containing material to the etching rate of the film formed of tantalum-containing material is not less than 50.

3. The photomask blank according to claim 1, wherein, The thickness of the film formed from the chromium-containing material is not less than 30 nm and not more than 80 nm.

4. The photomask blank according to any one of claims 1 to 3, wherein a film formed of a silicon-containing material is further included between the transparent substrate and the film formed of the chromium-containing material.

5. The photomask blank according to claim 4, wherein, The film formed from silicon-containing material is a phase-shifting film. The film formed from the chromium-containing material is a light-shielding film, and The film formed from tantalum-containing material is a hard mask.

6. The photomask blank according to claim 5, wherein, The phase-shifting film has a phase shift of not less than 175 degrees and not more than 185 degrees for the exposure light, a transmittance of not less than 6% and not more than 30%, and a thickness of not less than 60 nm and not more than 85 nm.

7. The photomask blank according to claim 6, wherein, The total optical density of the light-shielding film and the phase-shifting film for the exposure light is not less than 3.

8. The photomask blank according to claim 1, further comprising a resist film, the resist film being in contact with the side of the film formed of tantalum material away from the transparent substrate, and having a thickness of not less than 40 nm and not more than 120 nm.

9. A method for manufacturing a photomask, comprising the following steps: manufacturing a photomask having a circuit pattern of a film formed of a chromium-containing material from a photomask blank according to any one of claims 1 to 3. (A) A first resist film is formed in contact with the side of the film formed of tantalum material away from the transparent substrate. (B) Patterning the first resist film to form a first resist film pattern. (C) Using the pattern of the first resist film as an etching mask, the film formed of tantalum-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the film formed of tantalum-containing material. (D) Remove the pattern of the first resist film. (E) Using the pattern of the film formed from the tantalum-containing material as an etching mask, the film formed from the chromium-containing material is patterned by dry etching with an oxygen-containing chlorine gas to form a pattern of the film formed from the chromium-containing material. (F1) The pattern of the film formed of tantalum-containing material is removed by dry etching using fluorine-based gases.

10. A method for manufacturing a photomask, comprising the steps of manufacturing a photomask having a circuit pattern of a film formed of a silicon-containing material from a photomask blank according to any one of claims 4 to 7: (A) A first resist film is formed in contact with the side of the film formed of tantalum material away from the transparent substrate. (B) Patterning the first resist film to form a first resist film pattern. (C) Using the pattern of the first resist film as an etching mask, the film formed of tantalum-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the film formed of tantalum-containing material. (D) Remove the pattern of the first resist film. (E) Using the pattern of the film formed of the tantalum-containing material as an etching mask, the film formed of the chromium-containing material is patterned by dry etching with an oxygen-containing chlorine gas to form a pattern of the film formed of the chromium-containing material. (F2) Using the pattern of the film formed of the chromium-containing material as an etching mask, the film formed of the silicon-containing material is patterned by dry etching with fluorine-based gases to form a pattern of the silicon-containing film including circuit patterns, while removing the pattern of the film formed of the tantalum-containing material. (G) A second resist film is formed, which, on the side of the film formed of the chromium-containing material away from the transparent substrate, contacts the pattern of the film formed of the chromium-containing material and the exposed transparent substrate. (H) The second resist film is patterned so that the second resist film pattern is formed only on the outer periphery of the transparent substrate, the outer periphery being the region excluding the circuit pattern. (I) Using the pattern of the second resist film as an etching mask, the pattern of the film formed of the chromium-containing material is removed from the portion outside the outer periphery by dry etching with an oxygen-containing chlorine gas, such that the pattern of the film formed of the chromium-containing material remains on the outer periphery. (J) Remove the pattern of the second resist film.

11. The method according to claim 10, wherein, The film formed from silicon-containing material is a phase-shifting film. The film formed from the chromium-containing material is a light-shielding film, and The film formed from tantalum-containing material is a hard mask.

Images