Photomask blank

Abstract

The present invention relates to a photomask blank comprising a transparent substrate and a chromium-containing film. The chromium-containing film consists of a chromium compound layer formed of a chromium compound comprising Cr, N and optionally O and having a composition with a Cr content of > 30 at%, a total content of Cr + N + O of > 93 at% and fulfilling the formula: 3Cr ≤ 2O + 3N. The first composition is: an atomic N / Cr ratio of > 0.95, a Cr content of > 40 at%, a total content of Cr + N of > 80 at% and an O content of ≤ 10 at%.

Description

[0001] The present application is a divisional application of the application with application number 201610791249.8, filed on August 31, 2016, and entitled "Photomask blank". TECHNICAL FIELD

[0002] The present application relates to a photomask blank processed into a photomask suitable for pattern transfer with exposure light having a wavelength of 250 nm or less. BACKGROUND

[0003] The challenge for large scale integrated circuits to higher integration continues for the purpose of, for example, high operation speed and energy saving of microelectronic devices. To meet the increasing demand for circuit pattern miniaturization, advanced semiconductor microprocessing technology becomes important. For example, miniaturization technology of line pattern constituting a circuit and contact hole pattern for interlayer connection of a constituting unit becomes necessary.

[0004] Advanced microprocessing technology relies on photolithography technology using a photomask. Like a photolithography system and a resist material, a photomask is an important field of microfabrication technology. To obtain a photomask having a fine line pattern or a fine contact hole pattern, technology for forming a finer and more accurate pattern on a photomask blank is being developed.

[0005] To form a high-precision photomask pattern on a photomask substrate, the first task is to pattern a resist film on a photomask blank with high precision. Since photolithography for microprocessing of a semiconductor substrate employs a reduction projection, the pattern size formed on a photomask is about 4 times the pattern size formed on a semiconductor substrate. This does not mean that the precision of the pattern formed on a photomask is thus relaxed. It is necessary to form a photomask pattern with high precision.

[0006] Currently, the size of a circuit pattern written on a semiconductor substrate by photolithography is much smaller than the wavelength of exposure light. If a reduction exposure is performed using a photomask having a pattern that enlarges a circuit pattern by 4 times as is, the photomask pattern cannot be faithfully transferred to a resist film due to exposure light interference and other influences.

[0007] Super-resolution masks that solve this problem include OPC masks in which a so-called optical proximity correction (OPC), that is, a technique for correcting optical proximity effects that degrade transfer performance, is applied to a photomask, and phase shift masks that cause 180° phase shift of exposure light transmitted by a pattern to make the intensity distribution of incident light sharp. For example, in some OPC masks, an OPC pattern (hammerhead, assist bar, etc.) having a size smaller than half of a circuit pattern is formed. Phase shift mask types include half tone, Levenson, and chromeless types.

[0008] Generally, the formation of a mask pattern starts with a photomask blank having a light-shielding film on a transparent substrate, a photoresist film is formed on the photomask blank, the photoresist film is exposed under light or an electron beam (EB) to write a pattern, and the photoresist film is developed to form a photoresist pattern. Then, the photoresist pattern is used as an etching mask, and the light-shielding film is etched or patterned to form a photomask pattern. To obtain a fine photomask pattern, reducing the thickness of the photoresist film (i.e., a thinner photoresist film) is effective for the following reasons.

[0009] If the thickness of the photoresist film is not reduced and only the photoresist pattern is shrunk, the photoresist pattern features that function as an etching mask for the light-shielding film are characterized by a higher aspect ratio (the ratio of the thickness of the photoresist film to the width of the features). Generally, as the aspect ratio of the photoresist pattern features becomes higher, the profile of the pattern is more likely to deteriorate. Thus, the accuracy of pattern transfer to the light-shielding film is reduced. In the extreme case, the photoresist pattern is partially destroyed or peeled off, resulting in pattern defects. As the photomask pattern is shrunk, it is necessary to make the photoresist film that functions as an etching mask during patterning of the light-shielding film thinner to prevent the aspect ratio from becoming too high. It is generally recommended that the aspect ratio be 3 or less. To form a photoresist pattern having a feature width of 70 nm, for example, it is preferable that the thickness of the photoresist film be 210 nm or less.

[0010] In another aspect, in ArF photolithography using a photomask and an ArF excimer laser as an exposure light, the photomask pattern is transferred to a processable substrate, typically a photoresist film on a semiconductor wafer. According to the current progress in miniaturization technology, the pattern width (size on the wafer) of a standard product is less than 100 nm, while the pattern width of an advanced product is less than 20 nm. The minimum width of the main pattern on the photomask corresponding to the reduced pattern width is about 100 nm, and the minimum width of the auxiliary pattern is reduced to less than 100 nm (to be exact, about 70 nm) due to the complication of OPC.

[0011] Some materials have been proposed for the light-shielding film for which the photoresist pattern functions as an etching mask. In particular, a pure chromium film and a chromium compound film containing at least one of nitrogen, oxygen, and carbon and chromium are generally used as a light-shielding film material. For example, the photomask blanks disclosed in Patent Document 1 to Patent Document 3 in which a chromium compound film formed as a light-shielding film has light-shielding properties necessary for a photomask blank for ArF excimer laser photolithography.

[0012] For the production of photomasks, a method of exposure with an electron beam (EB) is the mainstream of resist patterning. For EB irradiation, a high acceleration voltage of 50 keV is employed to achieve further miniaturization. At the same time, there is a tendency for the resist to be reduced in sensitivity to achieve higher resolution, and the current EB irradiation density is undergoing a transition from 40 A / cm2 to 800 A / cm 2 a remarkable leap.

[0013] When the EB is directed to the electrostatically suspended photomask blank, the electrons accumulate on the surface of the photomask blank to form a negative potential. The electric field due to the charge generation causes the orbit of the EB to bend, resulting in low accuracy of the writing position. In order to avoid such errors, an EB lithography system suitable for high-energy / high-density EB writing is designed so that the EB writing is performed while the photomask blank is grounded. For example, Patent Literature 4 discloses a grounding mechanism using a grounding pin for grounding the photomask blank.

[0014] However, if the grounding resistance is significant, the potential on the surface of the photomask blank increases due to the product of the grounding current and the grounding resistance, and the accuracy of the writing position decreases accordingly. If the EB writing is performed in a state where the grounding resistance is very high, abnormal discharge or substrate failure occurs in the imaging vacuum chamber, causing system contamination. Therefore, it is important to obtain sufficient grounding resistance, and a grounding method requiring low grounding resistance is suggested in the EB lithography system, and the photomask blank must have sufficient electrical conductivity.

[0015] List of Incorporated References

[0016] Patent Literature 1: JP-A 2003-195479

[0017] Patent Literature 2: JP-A 2003-195483

[0018] Patent Literature 3: JP-U 3093632

[0019] Patent Literature 4: JP-A 2014-216407

[0020] Patent Literature 5: JP-A 2007-033470

[0021] Patent Literature 6: JP-A 2001-312043 SUMMARY

[0022] A chromium-containing film such as a chromium compound film as a light shielding film is generally dry-etched with an oxygen-chlorine-based etchant, and in this case, an organic film, typically a photoresist film, is often etched to a significant extent. If a mask made of a relatively thin resist film is used to dry-etch a chromium-containing film, the resist film can be damaged during etching so that the resist pattern can be deformed. It is thus difficult to accurately transfer the resist pattern to the chromium-containing film.

[0023] Attempts to impart high resolution, high patterning accuracy and etch resistance to a photoresist or organic film have encountered technical barriers. A photoresist film must be reduced in thickness to achieve the goal of high resolution, however the degree of thinning of the photoresist film must be limited for the purpose of ensuring etch resistance of the photoresist film during etching of a chromium-containing film. This gives rise to a trade-off between high resolution / patterning accuracy and etch resistance. In order to reduce the load on the photoresist film during patterning of a chromium-containing film and to reduce the thickness of the chromium-containing film and ultimately to form a mask pattern of the chromium-containing film with higher accuracy, the constitution of the chromium-containing film used for patterning (including thickness and composition) must be improved.

[0024] Patent Document 5 describes a light-shielding film based on chromium and containing light elements (oxygen and nitrogen added thereto) which exhibits a high etching rate during oxygen-chlorine-based dry etching and is capable of reducing the load on a photoresist film and ultimately forming a photomask pattern with high accuracy. However, the electrical conductivity of the light element-containing chromium film decreases as the light element content increases. Since EB lithography systems are adapted to radiate EBs at a current density of up to 800 A / cm 2 under the condition, measures for preventing the accumulation of electric charges on a photomask blank during EB writing are necessary.

[0025] With respect to a film based on chromium and having light elements (oxygen and nitrogen added thereto), for example, one measure is to form the film as a multilayer structure film including at least one metal chromium layer to maintain the electrical conductivity. However, in this example, the etching rate of the metal chromium layer is low, which means that a plurality of layers having a significant difference in etching rate are arranged in the film thickness direction. When the film is processed with dry etching, the cross-sectional profile of the pattern deteriorates due to different side etching, giving rise to deterioration in dimensional accuracy.

[0026] One of the objects of the present invention is to provide a photomask blank having an electrical conductivity that enables the photomask blank to be used in an EB lithography system adapted to radiate EBs at a high current density, and the photomask blank including a chromium-containing film that is substantially defect-free and thin enough to be patterned with a thin photoresist film to form a fine-pitch photomask pattern with a good cross-sectional profile with high accuracy.

[0027] When a chromium-containing film is processed with dry etching, the cross-sectional profile of the resulting pattern is greatly affected by the composition of the chromium-containing film. When the dry etching is anisotropic, as shown in the schematic view Figure 4 , the profile line width of the chromium-containing film pattern 52 is faithfully reflected in the line width of the etching mask pattern 53 of the etching mask film or resist film in the film thickness direction. When the dry etching is isotropic, as shown in the schematic view Figure 5 , the profile line width of the chromium-containing film pattern 52 is contracted in the center with respect to the line width of the etching mask pattern 53 in the film thickness direction. In Figure 4 and Figure 5 , a film or a transparent substrate 51 is present under the chromium-containing film.

[0028] In order to accurately form a fine pattern on a chromium-containing film serving as a light shielding film of a photomask, for example, the chromium-containing film must have sufficient electrical conductivity and a high etching rate for an imaging system. In the case of the chromium-containing film being a light shielding film, it must have a necessary optical density with respect to exposure light as a light shielding film. It is important for the chromium-containing film to have a minimum variation in etching rate in the thickness direction from the viewpoint of obtaining a sufficient cross-sectional profile pattern to provide high dimensional accuracy.

[0029] For a chromium-containing film, there is a trade-off relationship between the etching rate and the electrical conductivity of oxygen-containing chlorine dry etching. Thus, a multilayer structure chromium-containing film including a high-metallicity chromium-containing layer and a light-element-rich chromium-containing layer is applied in accordance with the required optical properties. However, in such a multilayer film composed of layers having different compositions, the layers have different etching rates, and thus the extent of etching in the width direction from the pattern side varies for each layer. As a result of the different side etching, the pattern forms a profile in which the pattern width varies in the thickness direction of the pattern, such as a waist-shaped or barrel-shaped profile in which the pattern width is narrower or wider in the center in the thickness direction, or a T-shaped or inverted T-shaped profile in which the pattern width is wider at the top or bottom in the thickness direction. That is, the multilayer film is susceptible to profile errors.

[0030] In one example, the chromium-containing film 52 includes a chromium compound layer 52a having a high etching rate, a chromium compound layer 52b having a low etching rate, and a chromium compound layer 52c having a high etching rate, which are sequentially stacked, as shown in the schematic view Figure 6 The layer having a high etching rate is more susceptible to side etching, losing the perpendicularity of the cross section. In Figure 6 the side etching state is exaggeratedly depicted as a step, but actual side etching does not become so extreme and becomes a continuously moderate variation. In any case, it is difficult to accurately transfer the shape of the etching mask pattern 53 to the chromium-containing film 52. In Figure 6 In this case, a film or transparent substrate 51 is present below the chromium-containing film.

[0031] When a chromium-containing film pattern is used as an etching mask to pattern a base film, such as a film of a material containing silicon and no transition metal or a material containing silicon and a transition metal, or a transparent substrate, etching deviation occurs. That is, substantial dimensional deviation occurs between the pattern of the film used as the etching mask and the pattern of the base film or substrate to be etched, causing deterioration of the effectiveness of pattern transfer.

[0032] With respect to a photomask blank including a transparent substrate and a chromium-containing film thereon, the present inventors have found that when the chromium-containing film is constructed of a single chromium compound layer or a multilayer structure chromium compound layer formed of a chromium compound containing chromium and nitrogen or chromium, nitrogen, and oxygen, and the chromium content of each chromium compound layer is at least 30 at% and the total content of chromium, nitrogen, and oxygen is at least 93 at% and satisfies formula (1):

[0033] 3Cr < 2O + 3N (1)

[0034] (where Cr is the chromium content (at%), O is the oxygen content (at%), and N is the nitrogen content (at%)) has the highest etching rate and is resistant to cleaning; if the chromium-containing film is a single chromium compound layer, the chromium compound layer satisfies a first composition in which the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total content of chromium and nitrogen is at least 80 at%, and the oxygen content is 10 at% or less; if the chromium-containing film is a multilayer structure film, the film includes at least one chromium compound layer satisfying the first composition in which the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total content of chromium and nitrogen is at least 80 at%, and the oxygen content is 10 at% or less, and the total thickness of the at least one chromium compound layer satisfying the first composition is in the range of more than 70% to 100% of the entire thickness of the chromium-containing film, the other being composed of layers not satisfying the first composition, whereby the necessary electrical conductivity for use in an EB lithography system is obtained, and the cleaning time of chlorine dry etching is shortened.

[0035] All or most of the chromium-containing film is composed of layers satisfying the first composition, which ensures that the thickness of the chromium-containing film is reduced while the necessary electrical conductivity of the photomask blank is maintained. As a result, the thickness of the photoresist film can be reduced. Even when the chromium-containing film is a multilayer structure, the difference in side etching between the chromium compound layers is minimized, resulting in an etched pattern with a satisfactory cross-sectional profile. A chromium-containing film pattern with high resolution and high precision is obtained. Even in a photolithography process in which a resist pattern with a line width of not more than 0.1 μm is formed on a processable substrate using exposure light with a wavelength of 250 nm or less, the chromium-containing film can be processed to form a high-precision required photomask pattern necessary even in the case of a fine photomask pattern.

[0036] Accordingly, the present application provides a photomask blank processed into a photomask suitable for pattern transfer using exposure light with a wavelength of 250 nm or less, which comprises a transparent substrate and a chromium-containing film disposed on the substrate directly or through an optical film. The chromium-containing film is composed of a single chromium compound layer or at least two chromium compound layers, each of which is formed of a chromium compound containing chromium and nitrogen, or chromium, nitrogen and oxygen, having a composition in which the chromium content is at least 30 at% and the total content of chromium, nitrogen and oxygen is at least 93 at%, and satisfying formula (1):

[0037] 3Cr < 2O + 3N (1)

[0038] where Cr is the chromium content (at%), O is the oxygen content (at%), and N is the nitrogen content (at%). When the chromium-containing film is composed of a single chromium compound layer, the chromium compound layer satisfies a first composition: the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total content of chromium and nitrogen is at least 80 at%, and the oxygen content is 10 at% or less. When the chromium-containing film is composed of at least two chromium compound layers, the chromium compound layers include at least one chromium compound layer satisfying the first composition: the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total content of chromium and nitrogen is at least 80 at%, and the oxygen content is 10 at% or less, and the total thickness of the at least one chromium compound layer satisfying the first composition is in a range of more than 70% to 100% of the entire thickness of the chromium-containing film. The sheet resistance of the chromium-containing film is 10,000 Ω / D or less.

[0039] In one preferred embodiment, the optical density of the chromium-containing film with respect to exposure light is 2.5 to 3.5.

[0040] In one preferred embodiment, the chromium-containing film is disposed on the transparent substrate through an optical film, and the optical film includes a phase shift film formed of a material containing silicon and no transition metal or a material containing silicon and a transition metal.

[0041] The photomask blank can further include an etching mask film formed of a material containing silicon disposed on the far side of the chromium-containing film from the substrate.

[0042] In one preferred embodiment, the optical density of the chromium-containing film with respect to exposure light is 1.5 to 2.6.

[0043] In one preferred embodiment, the sum of the optical densities of the chromium-containing film and the phase shift film with respect to exposure light is 2.5 to 3.5.

[0044] In one preferred embodiment, the sum of the optical densities of the chromium-containing film, the phase shift film, and the etching mask film with respect to exposure light is 2.5 to 3.5.

[0045] In one preferred embodiment, the chromium-containing film is disposed on the transparent substrate through an optical film, and the optical film includes a light shielding film formed of a material containing silicon and no transition metal or a material containing silicon and a transition metal.

[0046] Advantageous effects

[0047] The photomask blank of the present application includes a chromium-containing film which satisfies the required optical density, has a high etching rate in dry etching, and is effective for reducing the load on a photoresist film used as an etching mask when a pattern of the chromium-containing film is formed by dry etching, contributing to reduction in the thickness of the photoresist film. Since the chromium-containing film maintains electrical conductivity, it is effective in preventing charge accumulation of the photomask blank in an EB lithography system, achieving high writing accuracy. Since the chromium-containing film is thin and substantially defect-free and has a minimum variation in etching rate in the thickness direction, the pattern after etching is an improved cross-sectional profile, leading to high transfer efficiency of the photomask pattern. As a result, using the photomask blank of the present application, it is possible to form a fine-pitch photomask pattern with high accuracy. This realizes improvement in photomask productivity and reduction in the size of a pattern formed by pattern transfer with a photomask on a processable substrate. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1A and Figure 1B is a cross-sectional view of a photomask blank in a first embodiment of the present application, Figure 1A shows a chromium-containing film of a single-layer structure, while Figure 1B shows a chromium-containing film of a multi-layer structure.

[0049] Figure 2A and Figure 2B is a cross-sectional view of a photomask blank in a second embodiment of the present application, Figure 2A shows a chromium-containing film of a single-layer structure, while Figure 2B shows a chromium-containing film of a multi-layer structure.

[0050] Figure 3A and Figure 3B is a cross-sectional view of a photomask blank in a third embodiment of the present application, Figure 3A shows a chromium-containing film of a single-layer structure, while Figure 3B shows a chromium-containing film of a multi-layer structure.

[0051] Figure 4 is a schematic view of a cross-sectional profile of a pattern formed by anisotropic dry etching.

[0052] Figure 5 is a schematic view of a cross-sectional profile of a pattern formed by isotropic dry etching.

[0053] Figure 6 is a cross-sectional view of a chromium-containing film in which three layers of chromium compounds having different etching rates are laminated after dry etching. DETAILED DESCRIPTION

[0054] The photomask blank of the present application is used to process a photomask suitable for pattern transfer with exposure light having a wavelength of 250 nm or less, particularly 200 nm or less, typically a KrF excimer laser of 248 nm, an ArF excimer laser of 193 nm or an F2 laser of 157 nm. For a photomask suitable for pattern transfer with exposure light having a wavelength of 250 nm or less, for example, light having a wavelength of 257 nm is used for defect inspection, and light having a wavelength of 405 nm (solid-state laser diode) is used for read-out of alignment marks.

[0055] The photomask blank includes a transparent substrate (typically a quartz substrate) and a chromium-containing film disposed thereon directly or through one or more optical films. The chromium-containing film consists of a single chromium compound layer or at least two chromium compound layers (a multilayer structure) and is formed of a material that can be etched with an oxygen-chlorine-based dry etching.

[0056] The etching rate of the chromium-containing material in an oxygen-chlorine-based dry etching, which is generally used for etching of chromium-containing materials, can be increased by adding a light element to the chromium-containing material. The addition of the light element makes it possible to etch the chromium-containing material film, i.e., the chromium-containing film, at a high speed, resulting in the advantage that the burden on a photoresist film used as an etching mask can be reduced when etching the chromium-containing film through a pattern of the photoresist film (typically a chemically amplified resist film written by EB imaging). In some cases, the chromium-containing film is etched with an etching mask film of a silicon-containing material as a hard mask, and the chromium-containing film having a high etching rate is able to reduce the etching mask film in thickness. This leads to a direct improvement in etching bias and an indirect reduction in the thickness of a photoresist film used as an etching mask of the etching mask film.

[0057] The chromium-containing film consists of a single chromium compound layer or at least two chromium compound layers. Each chromium compound layer is formed of a chromium compound containing chromium and nitrogen or containing chromium, nitrogen and oxygen, and has the following composition (hereinafter referred to as "common composition"): a chromium content of at least 30 at%, a total content of chromium, nitrogen and oxygen of at least 93 at%, and satisfies formula (1):

[0058] 3Cr ≤ 2O + 3N (1)

[0059] where Cr is the chromium content (at%), O is the oxygen content (at%), and N is the nitrogen content (at%). Formula (1) means that the average valence number of chromium in the chromium compound layer is at least 3.

[0060] Each chromium compound layer is a layer that satisfies all of the chromium content, the total content of chromium, nitrogen and oxygen, and formula (1) defined by the common composition. In each chromium compound layer, the chromium content is preferably at least 33 at% and 52 at% or less, more preferably 50 at% or less, and further more preferably 48 at% or less; and the total content of chromium, nitrogen and oxygen is preferably at least 95 at%, more preferably at least 97 at%, and further more preferably at least 98 at%.

[0061] The chromium compound layer is formed of a chromium compound containing chromium and nitrogen or chromium, nitrogen and oxygen, examples of which include chromium nitride (CrN), chromium oxynitride (CrON), chromium carbonitride (CrNC), and chromium oxycarbonitride (CrONC), with chromium nitride (CrN) and chromium oxynitride (CrON) being preferred.

[0062] As described above, the addition of nitrogen and / or oxygen to the chromium-containing material is effective in increasing the etching rate thereof. Specifically, when a light element is added to a metallic material, the resistivity thereof increases with the amount of the added light element, indicating a loss of electrical conductivity. When a film made of a material having an increased resistivity is provided on the side of the photomask blank away from the transparent substrate, particularly on the side of the resist film used for EB lithography, charge accumulation occurs during EB exposure, inducing an undesirable decrease in writing accuracy. Especially when oxygen is added as a light element, it induces a significant increase in resistivity, resulting in a high-resistance film.

[0063] According to the present application, therefore, the chromium-containing film is formed of a chromium compound containing chromium and nitrogen or chromium, nitrogen and oxygen, and satisfies the common composition as defined above, and includes at least one chromium compound layer, preferably one or two chromium compound layers, most preferably one chromium compound layer, satisfying the first composition, which is: an atomic ratio of nitrogen to chromium of at least 0.95, a chromium content of at least 40 at%, a total content of chromium and nitrogen of at least 80 at%, and an oxygen content of 10 at% or less. The total thickness of the chromium compound layer satisfying the first composition is greater than 70%, preferably at least 90%, and 100% or less, relative to the overall thickness of the chromium-containing film. If the total thickness of the chromium compound layer satisfying the first composition is less than 70% of the overall thickness of the chromium-containing film, there is a risk that the overall thickness of the chromium-containing film necessary to provide the required optical density becomes large.

[0064] The layer satisfying the first composition is a layer that fully satisfies the atomic ratio of nitrogen to chromium, the chromium content, the total content of chromium and nitrogen, and the oxygen content defined in the first composition described above. In the preferred layer satisfying the first composition, the atomic ratio of nitrogen to chromium is 1.1 or less. In the layer satisfying the first composition, the chromium content is preferably at least 43 at% and 52 at% or less, preferably 50 at% or less, more preferably 48 at% or less; the total content of chromium and nitrogen is preferably at least 90 at%, more preferably at least 93 at%; the nitrogen content is preferably at least 43 at%, more preferably at least 46 at%, and 55 at% or less, more preferably 53 at% or less. In the layer satisfying the first composition, the oxygen content is preferably 10 at% or less, more preferably 5 at% or less. When two or more layers satisfying the first composition are included, these layers can have different compositions or some or all of these layers can have the same composition.

[0065] In the chromium-containing film where the film is a multilayer structure, the remaining layers other than the layer satisfying the first composition are formed of a chromium compound containing chromium and nitrogen or chromium, nitrogen and oxygen, and are composed of at least one layer, preferably one or two layers, particularly one layer, and satisfy the common composition but not the first composition. The layer not satisfying the first composition is preferably formed of a chromium compound containing chromium, nitrogen and oxygen. When the layer not satisfying the first composition is used as the remaining layers other than the layer satisfying the first composition, the entire chromium-containing film has a high etching rate. Also, the layer not satisfying the first composition is suitable for use as a layer having a function of a reduction of reflection.

[0066] In the layer not satisfying the first composition, the chromium content is preferably at least 30 at%, more preferably at least 33 at% and 40 at% or less, more preferably 37 at% or less; the nitrogen content is preferably at least 5 at%, more preferably at least 8 at% and 35 at% or less, more preferably 30 at% or less; and the oxygen content is preferably at least 30 at%, more preferably at least 35 at% and 57 at% or less, more preferably 54 at% or less. When two or more layers not satisfying the first composition are included, these layers can have different compositions or some or all of these layers can have the same composition.

[0067] A light element other than nitrogen or oxygen can be added to the chromium compound layer, and such other light element is carbon, hydrogen, fluorine, etc. For example, the addition of carbon is effective for enhancing the etching rate. However, if the amount of carbon is too much, the etching rate becomes too high and dry etching becomes more isotropic, resulting in a difficulty in controlling the cross-sectional profile. When the chromium compound layer with carbon is laminated on the chromium compound layer without carbon, there is a large difference in the etching rate between these layers. If so, the side etching of these layers differs during dry etching, so that the cross-sectional profile can be deteriorated. Further, the chemical resistance of a photomask to a mixture of sulfuric acid peroxide or a mixture of ozone peroxide (used for periodically cleaning the photomask in the step of processing the photomask blank into a photomask and in the step of exposing through the photomask) is reduced due to the addition of carbon in the chromium compound layer. Thus, it is possible to adjust the dry etching conditions so as to prevent the cross-sectional profile from being deteriorated, but the cross-sectional profile can be deteriorated by chemical cleaning. Thus, when an other light element, such as carbon, is added to the chromium compound layer in addition to nitrogen and oxygen, the content of such other light element is preferably controlled to a low amount, specifically 7 at% or less, more specifically 5 at% or less, even more specifically 3 at% or less, particularly 2 at% or less.

[0068] The sheet resistance of the chromium-containing film in the photomask blank of the present application should be no more than 10,000 ohms / square (Ω / □), preferably no more than 8,000 ohms / square (Ω / □). When the single layer or multilayer structure of the chromium-containing film is composed of one or more layers of a chromium compound satisfying the above composition requirement, the sheet resistance of the entire chromium-containing film falls within this range. Especially when the layer satisfying the first composition is the only layer, the sheet resistance of this layer should preferably be no more than 10,000 ohms / square (Ω / □), more preferably no more than 8,000 ohms / square (Ω / □). When two or more layers satisfying the first composition are included, the sheet resistance of each layer satisfying the first composition can fall within or outside this range, but in either case, the sheet resistance of the entire chromium-containing film should be no more than 10,000 ohms / square (Ω / □), preferably no more than 8,000 ohms / square (Ω / □), so as to be effective in preventing any charge accumulation during EB writing of the resist pattern.

[0069] The chromium-containing film can be a film having any desired function, for example, an optical film such as a light-shielding film, an antireflection film, or a phase shift film (e.g., a half-tone phase shift film), or an auxiliary processing film such as an etching mask film or an etching stop film. In some cases, the optical film includes an auxiliary processing film that functions as an etching mask film or an etching stop film, provided that such a film is left on the photomask after the photomask blank is processed into a photomask so as to function as an optical film. Note that, while an etching stop film is a typical film that is left on the photomask after the photomask blank is processed into a photomask, an etching mask film can be a film that is left on the etching mask or a film that is completely removed from the photomask (referred to as a sacrificial film) after the photomask blank is processed into a photomask.

[0070] The materials constituting the optical film and the auxiliary processing film of the photomask blank can be selected from transition metals, metals, alloys thereof, and compounds of these metals or alloys, depending on the necessary optical properties and etching properties, as well as electrical properties such as electrical conductivity. Suitable transition metals include chromium (Cr), zirconium (Zr), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), iron (Fe), nickel (Ni), and cobalt (Co); suitable metals include silicon (Si), germanium (Ge), and aluminum (Al); and suitable compounds include oxides, nitrides, carbides, oxynitrides, oxycarbides, carbonitrides, and oxycarbonitrides of the metals or alloys. Of these metals, chromium (Cr), molybdenum (Mo), and silicon (Si) are preferred.

[0071] The photomask blank of the present application is most suitable as a photomask blank including a chromium-containing film that is patterned by dry etching with an oxygen-containing chlorine-based gas using a mask pattern of a photoresist film (typically a chemically amplified resist film) as an etching mask when the photomask blank is processed into a photomask.

[0072] The first embodiment of the present application is a photomask blank having a chromium-containing film provided directly on a transparent substrate. Figure 1A and 1B Each is a cross-sectional view of a typical photomask blank in the first embodiment. The photomask blank 101 includes a transparent substrate 1 and a chromium-containing film 2 thereon. In Figure 1A In the first embodiment, the chromium-containing film 2 is composed of a single layer satisfying the first composition. In Figure 1B In the first embodiment, the chromium-containing film 2 is a three-layer structure including a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 stacked in this order from the substrate 1 side, one or two of which is a layer satisfying the first composition, and the remaining, i.e., the remaining two or one, is a layer not satisfying the first composition. Typically, the photomask blank 101 is processed into a photomask by forming a resist film for EB lithography on the chromium-containing film 2 and performing EB imaging writing. The photomask blank of the first embodiment can be a binary mask blank, in which case the chromium-containing film is preferably an optical blocking film.

[0073] In the first embodiment of the photomask blank, in the case where the chromium-containing film is an optical blocking film, the optical density of the chromium-containing film with respect to the exposure light should preferably be at least 2.5, more preferably at least 2.8 and 3.5 or less, more preferably 3.2 or less.

[0074] In the first embodiment of the photomask blank, in the case where the chromium-containing film is an optical blocking film, the thickness of the chromium-containing film is preferably 75 nm or less, more preferably 70 nm or less, further more preferably 65 nm or less, and at least 50 nm when the exposure light is an ArF excimer laser; or the thickness is preferably 90 nm or less, more preferably 80 nm or less, further more preferably 75 nm or less, and at least 55 nm when the exposure light is a KrF excimer laser.

[0075] In the second embodiment of the photomask blank of the present application, the photomask blank includes a chromium-containing film and is a photomask blank in which the chromium-containing film is provided on a transparent substrate through one or more optical films, and the chromium-containing film is patterned by oxygen-containing chlorine-based dry etching using a mask pattern of a photoresist film (typically, a chemically amplified resist film) as an etching mask when the photomask blank is processed into a photomask. The photomask blank in the second embodiment is advantageous, for example, because the pattern can be formed from the chromium-containing film with high precision and the pattern can also be formed with high precision when the optical film is patterned using the chromium-containing film pattern as a hard mask, especially when the chromium-containing film pattern functions as a hard mask in etching of the optical film. Combinations of the chromium-containing film and the optical film include combinations of an optical blocking film and a phase shift film (e.g., a half-tone phase shift film) and combinations of an etching mask film and an optical blocking film.

[0076] Figure 2A and 2BEach is a cross-sectional view of a typical photomask blank in the second embodiment. The photomask blank 102 includes a transparent substrate 1, an optical film 3, and a chromium-containing film 2 which are sequentially stacked from the substrate 1 side. In the second embodiment, the chromium-containing film 2 is a single layer which satisfies the first composition. In the pattern 2B, the chromium-containing film 2 is a three-layer structure including a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 which are sequentially stacked from the substrate 1 side, one or two of which is a layer which satisfies the first composition, and the remaining, i.e., the remaining two or one, is a layer which does not satisfy the first composition. Typically, the photomask blank 102 is processed into a photomask by forming a resist film for EB lithography on the chromium-containing film 2 and performing EB image writing. The photomask blank in the second embodiment can be a phase shift mask blank, in which case the optical film is preferably a phase shift film and the chromium-containing film is preferably a light shielding film. Figure 2A

[0077] The photomask blank in the present application is also preferably a photomask blank including a chromium-containing film which is patterned by oxygen-chlorine-based dry etching using a mask pattern of an etching mask film as a hard mask when the photomask blank is processed into a photomask. The third embodiment is a photomask blank including a transparent substrate, a chromium-containing film, and an etching mask film which is provided on the chromium-containing film side away from the substrate, preferably immediately adjacent to the chromium-containing film.

[0078] Figure 3A and 3B Each is a cross-sectional view of a typical photomask blank in the third embodiment. The photomask blank 103 includes a transparent substrate 1, an optical film 3, a chromium-containing film 2, and an etching mask film 4 which are sequentially stacked from the substrate 1 side. In the third embodiment, the chromium-containing film 2 is a single layer which satisfies the first composition. In the pattern 3B, the chromium-containing film 2 is a three-layer structure including a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 which are sequentially stacked from the substrate 1 side, one or two of which is a layer which satisfies the first composition, and the remaining, i.e., the remaining two or one, is a layer which does not satisfy the first composition. Typically, the photomask blank 103 is processed into a photomask by forming a resist film for EB lithography on the etching mask film 4 and performing EB image writing. The photomask blank in the third embodiment can be a phase shift mask blank, in which case the optical film is preferably a phase shift film and the chromium-containing film is preferably a light shielding film. Figure 3A Figure 3B

[0079] In the first to third embodiments of the photomask blank, in the case where the chromium-containing film is a film having an optical function such as a light shielding film, the film must have high resolution and high pattern transfer precision as well as the optical function. In this sense, the chromium-containing film must satisfy the required optical function such as optical density, have a high etching rate in oxygen-chlorine-based dry etching, and form a mask pattern having a cross-sectional profile with a minimum line width variation in the thickness direction. ​​​

[0080] Chromium-containing materials are used in photomask preforms that are processed into photomasks suitable for pattern transfer using exposure light with wavelengths below 250 nm. Among these chromium-containing materials, elemental chromium and chromium compounds with low content of light elements such as oxygen, nitrogen, or carbon are preferred as light-shielding films because they exhibit significant light-shielding effects. Among these light-shielding film forming materials, elemental chromium and chromium compounds with low content of light elements such as oxygen, nitrogen, or carbon (hereinafter referred to as "high metallicity chromium-based materials") have low resistivity and are suitable as materials for forming a conductive providing layer (conductive layer). When the chromium-containing film is constructed to include a conductive layer composed of high metallicity chromium-based materials, the chromium-containing film is endowed with conductivity.

[0081] On the other hand, chromium compounds with high content of light elements such as oxygen, nitrogen, or carbon (hereinafter referred to as "low-metallic chromium-based materials") are effective in adjusting the optical or etching properties of chromium-containing films. Low-metallic chromium-based materials are also effective in improving transmittance. Although films formed from high-metallic chromium-based materials have high reflectivity, they are sometimes detrimental in the defect detection of photomask blanks or photomasks, and low-metallic chromium-based materials are preferred as materials for forming antireflection-providing layers (antireflection layers) in such cases. Furthermore, when only a high-metallic chromium-based material layer provides insufficient light-shielding performance, a low-metallic chromium-based material film can be formed to compensate for the lack of light-shielding performance.

[0082] In the photomask preform of the present invention, the chromium-containing film is composed of multiple layers, including layers that satisfy a first composition and layers that do not satisfy the first composition. In the first to third embodiments of the photomask preform, when the chromium-containing film is a light-shielding film, it is preferable that the chromium compound layer includes two types of layers: one chromium compound layer primarily functions as a conductive layer, and the other chromium compound layer primarily functions as an antireflective layer, wherein the former is a layer that satisfies the first composition and the latter is a layer that does not satisfy the first composition. For example, it is preferable that a chromium compound layer primarily functioning as an antireflective layer is formed on one or both of the chromium-containing film surface disposed closest to the substrate and the chromium-containing film surface disposed furthest from the substrate, and it is particularly preferable that the chromium compound layer primarily functioning as an antireflective layer is formed adjacent to the chromium compound layer primarily functioning as a conductive layer. Specifically, regarding Figure 1B The chromium-containing film 2 shown in 2B or 3B preferably has a second chromium compound layer 22 that is a chromium compound layer whose main function is to conduct electricity, and a first and third chromium compound layer 21 and 23 that are chromium compound layers whose main function is to reduce reflection.

[0083] Although the thickness of the chromium compound layer functioning as an antireflection layer is adjusted to satisfy the required reflectance, from the viewpoint of minimizing the effects of increasing the thickness of the chromium-containing film, the thickness is preferably 20 nm or less, more preferably 10 nm or less, and at least 0.7 nm. If the thickness of the antireflection layer is lower than this range, such a thin layer can exert a poor reflectance suppressing effect and is unstable for deposition.

[0084] In the case where the optical film is a phase shift film (typically a half tone film) in the photomask blank of the second embodiment, the phase shift film is preferably formed of a material containing silicon and not containing a transition metal or a material containing silicon and a transition metal, preferably the transition metal does not include chromium, and particularly preferably is molybdenum. Such a material includes silicon simple substance, a compound containing silicon and a light element such as oxygen, nitrogen or carbon, particularly a compound containing oxygen and nitrogen one or both of which, and such a compound has further added a transition metal, preferably the transition metal does not include chromium, specifically molybdenum, tantalum, tungsten, zirconium or titanium, particularly molybdenum. Especially when the phase shift film is a half tone phase shift film, the half tone phase shift film also has optical density, and compared with the photomask blank without the half tone phase shift film, the thickness of the chromium-containing film can be reduced.

[0085] In the case where the chromium-containing film is a light shielding film and the optical film is a half tone phase shift film in the photomask blank of the second embodiment, the optical density of the chromium-containing film with respect to exposure light is preferably at least 1.5, more preferably at least 1.8 and 2.6 or less, more preferably 2.5 or less, and further more preferably 2.4 or less. The sum of the optical densities of the chromium-containing film and the phase shift film with respect to exposure light is preferably at least 2.5, more preferably at least 2.8 and 3.5 or less, more preferably 3.2 or less. By adjusting the optical densities of the chromium-containing film and the half tone phase shift film to this range, the required light shielding performance is obtained.

[0086] In the case where the chromium-containing film is a light shielding film and the optical film is a half tone phase shift film in the photomask blank of the second embodiment, the thickness of the chromium-containing film is preferably 50 nm or less, more preferably 47 nm or less, and further more preferably 44 nm or less and at least 35 nm when the exposure light is an ArF excimer laser; or the thickness of the chromium-containing film is preferably 80 nm or less, more preferably 70 nm or less, and further more preferably 65 nm or less and at least 50 nm when the exposure light is a KrF excimer laser.

[0087] In another aspect, the half-tone phase shift film is preferably set to a transmittance of at least 2% with respect to the exposure light, more preferably at least 5%, further more preferably at least 10%, most preferably at least 11% and 40% or less, more preferably 30% or less, further more preferably 20% or less. The half-tone phase shift film has a thickness of preferably 80 nm or less, more preferably 70 nm or less, and at least 50 nm, more preferably at least 60 nm, when the exposure light is an ArF excimer laser; or a thickness of preferably 110 nm or less, more preferably 100 nm or less, and at least 70 nm, more preferably at least 80 nm, when the exposure light is a KrF excimer laser.

[0088] As in the third embodiment of the photomask blank, the etching mask film is provided as a hard mask used in etching of the chromium-containing film, thereby enabling the photoresist film to be thinned to correspond to further pattern miniaturization. This etching mask film is typically used as a sacrificial film for the chromium-containing film. Many times, the etching mask film is completely removed in the photomask production process. Sometimes, the etching mask film is partially left in the photomask production process, rather than being completely removed.

[0089] The etching mask film can be formed of a material that is etched rapidly in fluorine-based dry etching, but has an extremely slow etching rate (i.e., no substantial etching) in oxygen-containing chlorine-based dry etching. A suitable material is a silicon-containing material, for example, silicon simple substance, a compound containing silicon and a light element (such as oxygen, nitrogen, or carbon), and such a compound with further addition of a transition metal, preferably a transition metal excluding chromium, particularly molybdenum, tantalum, tungsten, zirconium, or titanium.

[0090] In the third embodiment of the photomask blank, in the case where the optical film is a phase shift film (typically a half-tone phase shift film), the phase shift film is preferably formed of a silicon-containing material excluding a transition metal or a silicon-containing material with a transition metal, preferably a transition metal excluding chromium, particularly preferably molybdenum. A suitable material is as shown in the second embodiment of the photomask blank above. Especially when the phase shift film is a half-tone phase shift film, the half-tone phase shift film also has optical density, and enables the thickness of the chromium-containing film to be reduced, as compared with the photomask blank without the half-tone phase shift film.

[0091] In the third embodiment of the photomask blank, in the case where the chromium-containing film is a light-blocking film and the optical film is a half-tone phase shift film, the optical density of the chromium-containing film with respect to the exposure light, the sum of the optical densities of the chromium-containing film and the phase shift film with respect to the exposure light, the thickness of the chromium-containing film, the transmittance of the half-tone phase shift film, and the thickness of the half-tone phase shift film are preferably in the same ranges as in the second embodiment.

[0092] In the third embodiment of the photomask blank, the chromium-containing film is the light-blocking film, the optical film is the half-tone phase shift film, and in the case where the etching mask film is a film that is partially left and not entirely removed in the photomask production process (i.e., a film that is left on the photomask and functions as the optical film), the sum of the optical densities of the chromium-containing film, the phase shift film, and the etching mask film with respect to the exposure light is preferably at least 2.5, more preferably at least 2.8 and below 3.5, more preferably 3.2 or lower. The thickness of the etching mask film is preferably at least 3 nm, more preferably at least 5 nm and below 15 nm, more preferably 10 nm or lower.

[0093] In another embodiment of the second embodiment, the photomask blank can be a binary mask blank. In this case, the optical film is the light-blocking film and the chromium-containing film is the etching mask film.

[0094] In the second embodiment of the photomask blank, in the case where the chromium-containing film is the etching mask film, the film must have high resolution and high pattern transfer precision as well as optical functionality. In this sense, the chromium-containing film must satisfy the required optical functionality, have a high etching rate in oxygen-containing chlorine-based dry etching, and form a mask pattern with a cross-sectional profile that has a minimum line width variation improved.

[0095] In a photomask blank processed into a photomask suitable for pattern transfer with exposure light having a wavelength of 250 nm or less, a chromium-containing material is often used. Among the chromium-containing materials, a high-malleability chromium-based material is preferable as a material for forming a low-resistivity conductive layer. When the chromium-containing film is constituted so as to include a conductive layer composed of a high-malleability chromium-based material, the chromium-containing film is imparted with conductivity.

[0096] On the other hand, a low-malleability chromium-based material is effective for adjusting the optical properties and etching properties of the chromium-containing film. A low-malleability chromium-based material is also effective for improving the transmittance. Although a film formed of a high-malleability chromium-based material is a film with high reflectance, it is sometimes detrimental in defect detection of the photomask blank or photomask, and a low-malleability chromium-based material is also preferable as a material for forming an antireflection layer applied to such a case.

[0097] In the photomask blank according to the present application, the chromium-containing film is composed of a multilayer structure including a layer satisfying the first composition and a layer not satisfying the first composition. In the second embodiment of the photomask blank, in the case where the chromium-containing film is an etching mask film, it is preferable that the chromium compound layer include two types of layers, one chromium compound layer mainly functioning as a conductive layer and one chromium compound layer mainly functioning as an antireflection layer, where the former is a layer satisfying the first composition and the latter is a layer not satisfying the first composition. For example, it is preferable that a chromium compound layer mainly functioning as an antireflection layer be formed on one or both of the surface of the chromium-containing film disposed closest to the substrate and the surface of the chromium-containing film disposed farthest from the substrate, and more preferably that a chromium compound layer mainly functioning as an antireflection layer be formed immediately adjacent to a chromium compound layer mainly functioning as a conductive layer. Specifically, with respect to the chromium-containing film 2 in Figure 2B

[0098] Although the thickness of the chromium compound layer mainly functioning as an antireflection layer is adjusted to satisfy the required reflectance, the thickness is typically 30 nm or less, preferably 20 nm or less, more preferably 10 nm or less, and at least 0.7 nm. If the thickness of the antireflection layer is lower than this range, such a thin layer can not function to suppress reflection well and can be unstable for deposition.

[0099] In the second embodiment of the photomask blank, in the case where the optical film is a light-blocking film, the light-blocking film is preferably formed of a material containing silicon and not containing a transition metal or a material containing silicon and a transition metal, preferably not containing chromium as the transition metal, and particularly preferably containing molybdenum. Suitable materials are as described above for the phase shift film.

[0100] In the second embodiment of the photomask blank, in the case where the optical film is a light-blocking film, the light-blocking film is preferably set to have an optical density of at least 2.5, preferably at least 2.8 and 3.5 or less, preferably 3.2 or less, with respect to the exposure light. The thickness of the light-blocking film is preferably 80 nm or less, more preferably 70 nm or less, further more preferably 65 nm or less, and at least 50 nm, more preferably at least 55 nm, when the exposure light is an ArF excimer laser; or the thickness of the light-blocking film is preferably 100 nm or less, more preferably 90 nm or less, further more preferably 80 nm or less, and at least 55 nm, more preferably at least 60 nm, when the exposure light is a KrF excimer laser. In another aspect, in the case where the chromium-containing film is an etching mask film, the thickness of the chromium-containing film is preferably at least 3 nm, more preferably at least 5 nm, and 20 nm or less, more preferably 10 nm or less.

[0101] ​In a further embodiment of the photomask blank, another optical film can be formed on the surface of the chromium-containing film provided on the transparent substrate, preferably immediately adjacent to the chromium-containing film. The other optical film is preferably a light-shielding film, for example, formed of a material containing silicon and not containing a transition metal or a material containing silicon and a transition metal. When such a light-shielding film is introduced, the chromium-containing film can be an etching stop film or a phase shift film such as a half-tone phase shift film.

[0102] A preferred method of depositing the chromium-containing film, the optical film (e.g., a phase shift film or a light-shielding film) and the auxiliary processing film (e.g., an etching mask film or an etching stop film) on the photomask blank is to perform the deposition of the films by sputtering because a film having high in-plane uniformity of optical properties and few defects can be obtained.

[0103] The chromium-containing film is deposited by sputtering. For example, a chromium target is used as the target material. The sputtering gas is selected from among reactive gases such as nitrogen gas (N2), oxygen gas (O2), nitric oxide gas (N2O, NO2), hydrocarbon gas (e.g., CH4) and carbon oxide gas (CO, CO2) according to the desired composition. A rare gas such as argon gas (Ar) can be optionally used together with the reactive gas. The film deposition can be performed by inputting the sputtering gas into a sputtering vacuum chamber and adjusting the power applied to the target material and the flow rate of the sputtering gas so that each chromium compound layer of the chromium-containing film becomes a layer satisfying the first composition or a layer not satisfying the first composition.

[0104] When the phase shift film or the light-shielding film is deposited from a material containing silicon and not containing a transition metal or a material containing silicon and a transition metal, or when the etching mask film is deposited from a silicon-containing material, for example, the target material is selected from among a silicon target, a transition metal target and a transition metal-silicon target according to the desired composition. The sputtering gas is selected from among reactive gases such as nitrogen gas (N2), oxygen gas (O2), nitric oxide gas (N2O, NO2), hydrocarbon gas (e.g., CH4) and carbon oxide gas (CO, CO2) according to the desired composition. A rare gas such as argon gas (Ar) can be optionally used together with the reactive gas. The film deposition can be performed by inputting the sputtering gas into a sputtering vacuum chamber and adjusting the power applied to the target material and the flow rate of the sputtering gas so that a film of the desired composition is formed.

[0105] The photomask can be prepared from the photomask blank by a standard method. For example, a resist film composed of a chemically amplified resist is formed on the photomask blank, and then EB writing is performed. Using the resist pattern as an initial etching mask, the base film including the chromium-containing film, the optical film (e.g., a phase shift film, a light-shielding film), the auxiliary processing film (e.g., an etching mask film, an etching stop film) and the transparent substrate is sequentially etched by a dry etching technique, which can be selected from among oxygen-containing chlorine-based dry etching and fluorine-based dry etching according to the material to be etched. By this method, a photomask pattern is formed, i.e., a photomask is obtained. When this chromium-containing film is processed by dry etching, for example, the chromium-containing film is etched by fluorine-based dry etching. Figure 4The resulting pattern is a cross-sectional profile close to the anisotropic dry etching product as shown in the schematic view. Note that an organic conductive film can be formed on the resist film to further suppress the charge accumulation in EB writing.

[0106] Examples

[0107] The present application is more specifically explained using the following examples and comparative examples, but the present application is not limited to these examples.

[0108] Example 1

[0109] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 30 seem of N2 gas as sputtering gas to the sputtering chamber.

[0110] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 45 seem of N2 gas and 2 seem of O2 gas as sputtering gas to the sputtering chamber. A 46 nm thick CrON layer was formed on the half-tone phase shift film. A photo mask blank having a single layer structure of a chromium-containing film as a light shielding film was obtained. The optical density of the chromium-containing film was 2.1 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.0 with respect to an ArF excimer laser (wavelength 193 nm).

[0111] Example 2

[0112] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 30 seem of N2 gas as sputtering gas to the sputtering chamber.

[0113] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 45 seem of N2 gas and 2 seem of O2 gas as sputtering gas to the sputtering chamber. A 46 nm thick CrON layer was formed on the half-tone phase shift film. A photo mask blank having a single layer structure of a chromium-containing film as a light shielding film was obtained. The optical density of the chromium-containing film was 2.1 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.0 with respect to an ArF excimer laser (wavelength 193 nm).

[0114] Example 3

[0115] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 30 seem of N2 gas as sputtering gas to the sputtering chamber.

[0116] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 45 seem of N2 gas as sputtering gas to the sputtering chamber. A 44 nm thick CrN layer was formed on the half-tone phase shift film as an electrically conductive layer. Next, DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 10 seem of Ar gas, 30 seem of N2 gas and 15 seem of O2 gas as sputtering gas to the sputtering chamber. A 1 nm thick CrON layer was formed as an antireflection layer on the side away from the substrate. In this way, a photomask blank was obtained which had a two-layer structure and a 45 nm thick chromium-containing film as a light shielding film. The optical density of the chromium-containing film was 2.1 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.0 with respect to an ArF excimer laser (wavelength 193 nm).

[0117] Example 4

[0118] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 30 seem of N2 gas as sputtering gas to the sputtering chamber.

[0119] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 45 seem of N2 gas and 1 seem of CH4 gas as sputtering gas to the sputtering chamber. A 46 nm thick CrNC layer was formed on the half-tone phase shift film. A photomask blank was obtained which had a single-layer structure and a chromium-containing film as a light shielding film. The optical density of the chromium-containing film was 2.1 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.0 with respect to an ArF excimer laser (wavelength 193 nm).

[0120] Example 5

[0121] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 45 nm thick MoSiN film was deposited as a light shielding film on the substrate by sputtering a target material containing molybdenum and silicon (molar ratio 1:2) and a silicon target and inputting 30 seem (flow rate) of Ar gas and 5 seem of N2 gas as sputtering gas to the sputtering chamber.

[0122] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 45 seem of N2gas as a sputtering gas to a sputtering chamber. A 10 nm-thick CrN layer was formed on the light shielding film. A chromium-containing film having a single layer structure was obtained as a photomask blank of the etching mask film.

[0123] Comparative Example 1

[0124] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 61 nm-thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 32 seem of N2gas as a sputtering gas.

[0125] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 9 seem of Ar gas, 30 seem of N2gas and 14 seem of O2gas as a sputtering gas to a sputtering chamber. A 20 nm-thick CrON layer mainly functioning as a substrate-side antireflection layer was formed on the half-tone phase shift film. Next, DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 20 seem of Ar gas, 2 seem of N2gas and 2 seem of O2gas as a sputtering gas to a sputtering chamber. A 4 nm-thick CrON layer mainly functioning as a conductive layer was formed. Further, DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 12 seem of Ar gas, 30 seem of N2gas and 14 seem of O2gas as a sputtering gas to a sputtering chamber. A 22 nm-thick CrON layer mainly functioning as an antireflection layer away from the substrate side was formed. In this way, a chromium-containing film having a three-layer structure and 46 nm thick was obtained as a photomask blank of the light shielding film. The optical density of the chromium-containing film was 2.0 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.1 with respect to an ArF excimer laser (wavelength 193 nm).

[0126] Comparative Example 2

[0127] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 61 nm-thick SiN film was deposited as a half-tone phase shift film on the substrate by sputtering a silicon target and inputting 15 seem (flow rate) of Ar gas and 32 seem of N2gas as a sputtering gas.

[0128] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 10 seem of Ar gas, 50 seem of N2gas and 5 seem of CH4gas as sputtering gas to the sputtering chamber. A 45 nm-thick CrNC layer, which functions as a substrate-side antireflection layer, was formed on the half-tone phase shift film. Next, DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 30 seem of Ar gas and 35 seem of N2gas as sputtering gas to the sputtering chamber. A 3 nm-thick CrN layer, which functions as a conductive layer, was formed. Further, DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 10 seem of Ar gas, 50 seem of N2gas and 10 seem of O2gas as sputtering gas to the sputtering chamber. A 3 nm-thick CrON layer, which functions as an antireflection layer away from the substrate side, was formed. In this way, a photomask blank having a three-layer structure and a 51 nm-thick chromium-containing film as a light-blocking film was obtained. The optical density of the chromium-containing film was 1.9 and the sum of the optical densities of the chromium-containing film and the half-tone phase shift film was 3.0 with respect to an ArF excimer laser (wavelength 193 nm).

[0129] Comparative Example 3

[0130] DC magnetron sputter deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 45 nm-thick MoSiN film as a light-blocking film was deposited on the substrate by sputtering a target containing molybdenum and silicon (molar ratio 1:2) and a silicon target and inputting 30 seem (flow rate) of Ar gas and 5 seem of N2gas as sputtering gas to the sputtering chamber.

[0131] DC magnetron sputter deposition was performed by sputtering a metal chromium target and inputting 20 seem of Ar gas and 5 seem of N2gas as sputtering gas to the sputtering chamber. A 10 nm-thick CrN layer was formed on the light-blocking film. A photomask blank having a single-layer structure chromium-containing film as an etching mask film was obtained.

[0132] The composition of each chromium compound layer of the chromium-containing film of the photomask blanks of the examples and comparative examples was analyzed by X-ray photoelectron spectroscopy (XPS). The results are shown in Table 1 together with whether or not the formula (1) was satisfied. Separately, thin layer resistance evaluation samples were prepared by directly forming each chromium-containing film in the examples and comparative examples on an insulating quartz substrate. The sample electrical properties were measured by a four-probe method, from which the thin layer resistance of the chromium-containing film was calculated. The results are shown in Table 1.

[0133] In the photomask blanks of the examples and comparative examples, the film thickness necessary to obtain a predetermined optical density was compared. When the film was adjusted to an optical density of 2.0 with respect to an ArF excimer laser (wavelength 193 nm), its thickness was designated as the standard thickness of the optical density. The film thickness was determined according to the formula: (thickness of the chromium-containing film) x {2 / (optical density of the chromium-containing film)}. The results are shown in Table 1. With respect to the standard thickness, the lower the thickness, the better the transfer efficiency when used as a photomask, and a thickness of 50 nm or less is desirable, and a thickness of 47 nm or less is particularly desirable.

[0134] The chromium-containing film was peeled from the photomask blanks of the examples and comparative examples by oxygen-chlorine-based dry etching. The time required for peeling, that is, the etch removal time, was measured. The etch removal time based on the optical density standard, which corresponds to an optical density of 2.0 with respect to an ArF excimer laser (wavelength 193 nm), was determined according to the formula: (measured etch removal time) x {2 / (optical density of the chromium-containing film)}. The results are shown in Table 1. With respect to the standard etch removal time, a shorter time is more effective for forming a pattern with high resolution, and a time of 135 seconds or less is desirable, and a time of 130 seconds or less is particularly desirable.

[0135] Next, a resist film for EB lithography with a thickness of 100 nm was deposited on the chromium-containing film of each photomask blank in the examples and comparative examples. The resist film was exposed to an EB lithography system to become a line-space pattern with a line width of 100 nm, and developed to form a resist pattern. When the resist pattern was used as an etching mask, the chromium-containing film was etched by oxygen-chlorine-based dry etching under 75% over-etching conditions, that is, the etching time was equivalent to 175% of the etch removal time calculated from the etching rate of each chromium-containing film, so that the line-space pattern was transferred to the chromium-containing film. The resist pattern was peeled off, and the line-space pattern was cut in cross section. The cross-sectional profile of the etching wall of the line of the chromium-containing film pattern was observed. The results of the evaluation of the cross-sectional profile are shown in Table 1.

[0136] With respect to the cross-sectional profile of the line, it was required that the line width change in the thickness direction be zero and the cross-sectional profile be completely vertical. The line width change in the thickness direction of the chromium-containing film pattern was evaluated using a predetermined plane that is coplanar with both ends of the resist pattern in the width direction and is perpendicular to the surface of the chromium-containing film as a reference plane, and was judged to be negative when the actual cross section of the line of the chromium-containing film was recessed inward from the reference plane, positive when the actual cross section of the film line was protruded outward. Assuming that the thickness of the chromium-containing film was uniform (1), it was evaluated as good (O) when the maximum value of the line width change in the thickness direction was in the range of -0.05 to +0.05, as intermediate (Δ) when the maximum value was in the range of -0.1 to less than -0.05, or in the range of more than +0.05 to +0.1, and as poor (X) when the maximum value was in the range of less than -0.1 or more than +0.1.

[0137] Table 1

[0138]

[0139] While the present application has been illustrated and described with respect to exemplary embodiments, it is not intended to be limited to these details. Various modifications, additions and deletions from the details described can be made without departing from the spirit and scope of the application. All such modifications, additions and deletions are intended to fall within the scope of the application.

Claims

1. A photomask preform, fabricated to be suitable for pattern transfer using exposure light with a wavelength below 250 nm, the photomask preform comprising a transparent substrate and a chromium-containing film, the chromium-containing film being disposed on the substrate via a halftone phase-shifting film serving as an optical film, wherein, The chromium-containing film consists of a chromium compound layer formed from a chromium compound containing chromium, nitrogen, and carbon or a chromium compound containing chromium, nitrogen, oxygen, and carbon, and has the following composition: a chromium content of at least 40 at%, a total chromium and nitrogen content of at least 80 at%, an atomic ratio of nitrogen to chromium of at least 0.95, an oxygen content of less than 10 at%, a total chromium, nitrogen, and oxygen content of at least 93 at%, a carbon content of less than 7 at%, and satisfies formula (1). 3Cr ≤ 2O + 3N(1) Where Cr is the chromium content, O is the oxygen content, and N is the nitrogen content, the units for chromium content, oxygen content, and nitrogen content are at%, respectively. The exposure light is an ArF excimer laser. The optical density of the chromium-containing film relative to the exposure light is 1.5~2.6, and the optical density of the chromium-containing film and the halftone phase-shifting film relative to the exposure light is 2.5~3.

5. The thickness of the chromium-containing film is 35nm-47nm. The resistivity of the chromium-containing film is below 10,000 Ω / □.

2. The photomask preform according to claim 1, wherein, It further includes an etching mask film disposed on the side of the chromium-containing film away from the substrate, the etching mask film being formed of a silicon-containing material.

3. The photomask preform according to claim 2, wherein, The sum of the optical density of the chromium-containing film, the phase-shifting film, and the etching mask relative to the exposure light is 2.5 to 3.

5.

4. The photomask preform according to claim 1, wherein, The thickness of the chromium-containing film is at least 45 nm.

5. The photomask preform according to claim 1, wherein, The optical film is formed from a silicon-containing material but without transition metals, or a material containing both silicon and transition metals.

6. The photomask preform according to claim 1, wherein, The composition has a carbon content of 3-7 at%.

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