Photomask preform

Abstract

This invention relates to a photomask preform comprising a transparent substrate and a chromium-containing film. The chromium-containing film is composed of one or more chromium compound layers formed from a chromium compound comprising Cr, N, and optionally O, and having the following composition: Cr content ≥ 30 at%, total Cr+N+O content ≥ 93 at%, and satisfying the formula: 3Cr ≤ 2O + 3N. The thickness of the chromium compound layer satisfying the first composition is in the range of greater than 70% to 100% of the total thickness of the chromium-containing film, wherein the first composition is: N / Cr atomic ratio ≥ 0.95, Cr content ≥ 40 at%, total Cr+N content ≥ 80 at%, and O content ≤ 10 at%.

Description

[0001] This invention is a divisional application of the invention application with application number 201610791249.8, application date August 31, 2016, and invention title "Photomask Blank". Technical Field

[0002] This invention relates to a photomask blank that is processed into a photomask suitable for pattern transfer using exposure light with a wavelength below 250 nm. Background Technology

[0003] Driven by the pursuit of high operating speeds and energy efficiency in microelectronic devices, the challenge of increasing integration density in large-scale integrated circuits continues. To meet the ever-growing demand for miniaturized circuit patterns, advanced semiconductor microprocessing technologies have become crucial. For example, miniaturization techniques for circuit diagrams and contact hole patterns used to form interlayer connections have become necessary.

[0004] Advanced microprocessor technologies rely on photolithography using photomasks. Like photolithography systems and resist materials, photomasks are a crucial area of ​​miniaturization. Efforts are focused on developing techniques to form finer and more precise patterns on photomask preforms in order to obtain photomasks with fine-diameter circuit patterns or contact hole patterns.

[0005] To form high-precision photomask patterns on a photomask substrate, the primary task is to pattern the resist film on the photomask blank with high accuracy. Because photolithography for microprocessing semiconductor substrates uses shrinkage projection, the pattern size formed on the photomask is approximately four times the size of the pattern formed on the semiconductor substrate. This does not mean that the precision of the pattern formed on the photomask should be relaxed. Forming photomask patterns with high precision is still necessary.

[0006] Currently, the size of circuit patterns written on semiconductor substrates by photolithography is much smaller than the wavelength of the exposure light. If shrinkage exposure is performed using a photomask with a pattern that magnifies the circuit pattern by 4 times, the photomask pattern cannot be accurately transferred to the resist film due to exposure light interference and other effects.

[0007] Super-resolution masks that address this problem include OPC masks and phase-shift masks. In OPC masks, so-called Optical Proximity Correction (OPC), a technique used to correct the optical proximity effect that degrades transfer performance, is applied to the photomask. Phase-shift masks cause a 180° phase shift in the exposure light transmitted through the pattern, resulting in a sharp intensity distribution of the incident light. For example, in some OPC masks, OPC patterns (hammerheads, auxiliary strips, etc.) with dimensions smaller than half that of the circuit pattern are formed. Types of phase-shift masks include halftone, Levenson, and chrome-free types.

[0008] Generally, the formation of a photomask pattern begins with a photomask preform on a transparent substrate having a light-shielding film. A photoresist film is then formed on the photomask preform. This photoresist film is exposed to light or an electron beam (EB) to write the pattern, and then developed to form the photoresist pattern. This photoresist pattern is then used as an etching mask to etch or pattern the light-shielding film to form the photomask pattern. To obtain finer photomask patterns, reducing the thickness of the photoresist film (i.e., a thinner photoresist film) is effective for several reasons.

[0009] If the resist pattern is only miniaturized without reducing the resist film thickness, the resist pattern acting as an etching mask for the light-shielding film is characterized by a higher aspect ratio (the ratio of resist film thickness to feature width). Generally, due to the higher aspect ratio of the resist pattern features, the pattern outline is more prone to deterioration. This reduces the pattern transfer accuracy for the light-shielding film. In extreme cases, the resist pattern may be partially destroyed or peeled off, resulting in pattern defects. As photomask patterns are miniaturized, it is necessary to thin the resist film used as an etching mask during light-shielding film patterning to prevent the aspect ratio from becoming too high. An aspect ratio of 3 or less is generally recommended. To form a resist pattern with a feature width of 70 nm, a resist film thickness of 210 nm or less is preferred, for example.

[0010] On the other hand, in ArF lithography, which uses a photomask and an ArF excimer laser as the exposure light, the photomask pattern is transferred onto a processable substrate, typically a photoresist film on a semiconductor wafer. Based on current miniaturization advancements, the pattern width (on the wafer) of standard products is less than 100 nm, while the pattern width of advanced products is less than 20 nm. Corresponding to this reduced pattern width, the minimum width of the main pattern on the photomask is approximately 100 nm, and due to the increasing complexity of OPC (Optical Process Control), the minimum width of the auxiliary pattern is reduced to less than 100 nm (more precisely, approximately 70 nm).

[0011] Several materials have been proposed for light-shielding films used as etching masks for etching with photoresist patterns. In particular, pure chromium films and chromium compound films containing at least one of nitrogen, oxygen, and carbon and chromium are generally used as light-shielding film materials. For example, the photomask preforms disclosed in Patent Documents 1 to 3 have a chromium compound film formed therein as a light-shielding film, which has the light-shielding properties necessary for photomask preforms used in ArF excimer laser lithography.

[0012] For photomask production, electron beam (EB) exposure is the mainstream method for resist patterning. EB irradiation utilizes a high accelerating voltage of 50 keV to achieve further miniaturization. Simultaneously, there is a trend towards reducing resist sensitivity to achieve higher resolution. In EB lithography systems, from a productivity perspective, current EB irradiation densities have evolved from 40 A / cm².2 Up to 800A / cm 2 A significant leap forward.

[0013] When an electron ion (EB) is guided to an electrically levitated photomask blank, electrons accumulate on the surface of the blank, creating a negative potential. The electric field generated by these charges causes the EB's trajectory to bend, resulting in low accuracy in the write position. To avoid such errors, EB lithography systems suitable for high-energy / high-density EB writing have been designed to enable EB writing while the photomask blank is grounded. For example, Patent Document 4 discloses a grounding mechanism using a grounding pin to ground the photomask blank.

[0014] However, if the grounding resistance is significant, the potential on the photomask surface increases due to the product of the grounding current and the grounding resistance, correspondingly reducing the accuracy of the write position. If EB writing is performed under conditions of very high grounding resistance, abnormal discharge or substrate failure may occur in the imaging vacuum chamber, causing system contamination. Therefore, obtaining sufficient grounding resistance is important, and a grounding method requiring low grounding resistance is recommended in EB lithography systems, and the photomask must have sufficient conductivity.

[0015] List of cited references

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

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

[0018] Patent Document 3: JP-U 3093632

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

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

[0021] Patent Document 6: JP-A 2001-312043 Summary of the Invention

[0022] Chromium-containing films, such as chromium compound films, used as light-shielding films are typically patterned using oxygen-chlorine-based dry etching. In this process, organic films, typically photoresist films, are often etched to a significant degree. If a mask made of a relatively thin photoresist film is used to dry-etch the chromium-containing film, the photoresist film can be damaged during etching, potentially deforming the photoresist pattern. This makes it difficult to accurately transfer the photoresist pattern onto the chromium-containing film.

[0023] Attempts to endow photoresists or organic films with high resolution, high patterning accuracy, and etching resistance have encountered technical barriers. Photoresist films must be thinned to achieve high resolution; however, the thinning of the photoresist film must be limited to ensure its etching resistance during chromium-containing film etching. This raises a trade-off between high resolution / patterning accuracy and etching resistance. To reduce the load on the photoresist film during chromium-containing film patterning and reduce its thickness to ultimately form a chromium-containing mask pattern with higher accuracy, the composition (including thickness and composition) of the chromium-containing film used for patterning must be improved.

[0024] Patent document 5 describes a chromium-based photomask containing light elements (oxygen and nitrogen added therein), which exhibits a high etch rate during oxychlorine-based dry etching, reducing the load on the photoresist film and ultimately forming a photomask pattern with high precision. However, the conductivity of the chromium film containing light elements decreases with increasing light element content. This is because EB lithography systems are suitable for current densities up to 800 A / cm². 2 Under certain conditions, EB is emitted, so measures are necessary to prevent charge buildup in the photomask preform during EB writing.

[0025] Regarding films based on chromium and containing light elements (oxygen and nitrogen added therein), one approach is, for example, to form the film as a multilayer structure comprising at least one metallic chromium layer to maintain conductivity. However, in this example, the etch rate of the metallic chromium layer is low, meaning that multiple layers with significant differences in etch rate are arranged along the film thickness direction. When the film is processed using dry etching, the cross-sectional profile of the pattern deteriorates due to the different side etching, leading to a deterioration in dimensional accuracy.

[0026] One of the objectives of this invention is to provide a photomask preform having electrical conductivity that allows it to be used in an EB lithography system suitable for emitting EB at high current density, and the photomask preform includes a chromium-containing film that is substantially defect-free and thin enough to be patterned with a thin photoresist film to form a fine-diameter photomask pattern with a good cross-sectional profile with high precision.

[0027] When dry etching is used to process chromium-containing films, the cross-sectional profile of the resulting pattern is significantly affected by the composition of the chromium-containing film. When dry etching is anisotropic, as shown in the schematic diagram... Figure 4 As shown, the outline linewidth of the chromium-containing film pattern 52 is a true reflection of the linewidth of the etching mask pattern 53 of the etching mask film or resist film in the film thickness direction. When dry etching is isotropic, as illustrated in the schematic diagram... Figure 5 As shown, relative to the linewidth of the etched mask pattern 53, the outline linewidth of the chromium-containing film pattern 52 tapers towards the center in the film thickness direction. Figure 4 and Figure 5 In the middle, the film or transparent substrate 51 is below the chromium-containing film.

[0028] To accurately form fine-diameter patterns on a chromium-containing film used as a light-shielding film for photomasks, the chromium-containing film must, for example, possess sufficient electrical conductivity and a high etch rate for use in imaging systems. In the case where the chromium-containing film is a light-shielding film, it must have the optical density necessary for its function as a light-shielding film relative to the exposure light. From the perspective of obtaining a sufficient cross-sectional profile pattern to provide high dimensional accuracy, it is important that the chromium-containing film exhibits minimal etch rate variation in the thickness direction.

[0029] For chromium-containing films, there exists a trade-off between the etching rate and conductivity in oxychlorine-based dry etching. Therefore, multilayer chromium-containing films, including high-metallicity chromium layers and light-element-rich chromium layers, are used depending on the desired optical properties. However, in such multilayer films composed of different layers, each layer has a different etching rate, resulting in varying degrees of etching along the width direction from the pattern sides. This different side etching results in a pattern profile where the pattern width varies along the pattern thickness direction; for example, a waist-shaped or barrel-shaped profile where the pattern width is narrower or wider at the center in the thickness direction, or a T-shaped or inverted T-shaped profile where the pattern width is wider at the top or bottom in the thickness direction. In other words, multilayer films are prone to profile errors.

[0030] In one example, the chromium-containing film 52 comprises a chromium compound layer 52a with a high etch rate, a chromium compound layer 52b with a low etch rate, and a chromium compound layer 52c with a high etch rate, stacked sequentially, as shown in the schematic diagram. Figure 6 As shown, layers with high etch rates are more prone to lateral etching, losing the perpendicularity of the cross-section. Figure 6 The mid-side etching state is exaggeratedly depicted as stepped, but actual side etching is not so extreme and becomes a continuous, moderate variation. In any case, it is difficult to accurately transfer the shape of the etched mask pattern 53 onto the chromium-containing film 52. Figure 6 In the middle, the film or transparent substrate 51 is below the chromium-containing film.

[0031] When using a chromium-containing film pattern as an etching mask to pattern a base film, such as a silicon-containing material without transition metals, a silicon-containing material with transition metals, or a transparent substrate, etching deviations can occur. This means that a substantial dimensional deviation occurs between the pattern of the film used as the etching mask and the pattern of the base film or substrate being etched, causing a deterioration in the pattern transfer effect.

[0032] Regarding photomask preforms comprising a transparent substrate and a chromium-containing film thereon, the inventors have discovered that when the chromium-containing film is constructed as a single chromium compound layer or a multilayer chromium compound layer, formed of a chromium compound containing chromium and nitrogen or containing chromium, nitrogen and oxygen, and each chromium compound layer has a chromium content of at least 30 at% and a total content of chromium, nitrogen and oxygen of 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%)) When the chromium-containing film 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 the first composition, wherein the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total chromium and nitrogen content is at least 80 at%, and the oxygen content is less than 10 at%. If the chromium-containing film is a multilayer structure film, the film includes at least one chromium compound layer that satisfies the first composition, wherein the nitrogen / chromium atomic ratio is at least 0.95, the chromium content is at least 40 at%, the total chromium and nitrogen content is at least 80 at%, and the oxygen content is less than 10 at%. The total thickness of the at least one chromium compound layer that satisfies the first composition is in the range of greater than 70% to 100% of the overall thickness of the chromium-containing film, and the others are composed of layers that do not satisfy the first composition. Thus, the conductivity necessary for use in EB lithography systems can be obtained, and the cleaning time of chlorine dry etching is shortened.

[0035] The chromium-containing film is composed entirely or mostly of layers satisfying a first composition, which ensures that the thickness of the chromium-containing film is reduced while the necessary conductivity of the photomask preform 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 photoetching processes where fine photomask patterns are necessary to form resist patterns with a linewidth of no more than 0.1 μm on a processable substrate using exposure light with wavelengths below 250 nm, the chromium-containing film can be processed to form a high-precision, compliant photomask pattern.

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

[0037] 3Cr≤2O+3N (1)

[0038] Wherein, Cr is the chromium content (at%), O is the oxygen content (at%), and N is the nitrogen content (at%). When the chromium-containing film consists of a single chromium compound layer, the chromium compound layer satisfies the first composition: a nitrogen / chromium atomic ratio of at least 0.95, a chromium content of at least 40 at%, a total chromium and nitrogen content of at least 80 at%, and an oxygen content of less than 10 at%. When the chromium-containing film consists of at least two chromium compound layers, each chromium compound layer includes at least one chromium compound layer satisfying the first composition, which is: a nitrogen / chromium atomic ratio of at least 0.95, a chromium content of at least 40 at%, a total chromium and nitrogen content of at least 80 at%, and an oxygen content of less than 10 at%. The total thickness of the at least one chromium compound layer satisfying the first composition is in the range of greater than 70% to 100% of the overall thickness of the chromium-containing film. The sheet resistance of the chromium-containing film does not exceed [amount missing].

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

[0040] In a preferred embodiment, the chromium-containing film is disposed on a transparent substrate via an optical film, and the optical film comprises a phase-shifting film formed of a silicon-containing material without transition metals or a silicon-containing and transition metal-containing material.

[0041] The photomask preform may further include an etch mask film disposed on the substrate-remote side of a chromium-containing film, the etch mask film being formed of a silicon-containing material.

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

[0043] In a preferred embodiment, the sum of the optical densities of the chromium-containing film and the phase-shifting film relative to the exposure light is 2.5 to 3.5.

[0044] In a preferred embodiment, the sum of the optical density of the chromium-containing film, the phase-shifting film, and the etch mask film relative to the exposure light is 2.5 to 3.5.

[0045] In a preferred embodiment, the chromium-containing film is disposed on a transparent substrate via an optical film, and the optical film comprises a light-shielding film formed of a silicon-containing material without transition metals or a silicon-containing and transition metal-containing material.

[0046] Beneficial effects

[0047] The photomask preform of the present invention comprises a chromium-containing film that meets the required optical density, exhibits a high etch rate in dry etching, and is effective in reducing the load on the photoresist film used as the etching mask when forming a chromium-containing film pattern using dry etching, thus contributing to a reduction in the photoresist film thickness. Because the chromium-containing film maintains electrical conductivity, it effectively prevents charge buildup on the photomask preform in the EB lithography system, achieving high write accuracy. Because the chromium-containing film is thin and substantially defect-free with minimal etch rate variation in the thickness direction, the etched pattern has an improved cross-sectional profile, resulting in high transfer efficiency of the photomask pattern. As a result, using the photomask preform of the present invention, fine-diameter photomask patterns can be formed with high precision. This achieves improved photomask productivity and a reduction in pattern size formed by pattern transfer using a photomask on a processable substrate. Attached Figure Description

[0048] Figure 1A and Figure 1B This is a cross-sectional view of the photomask blank according to the first embodiment of the present invention. Figure 1A It shows a single-layer chromium-containing film, while Figure 1B The chromium-containing film with a multilayer structure is shown.

[0049] Figure 2A and Figure 2B This is a cross-sectional view of the photomask blank in the second embodiment of the present invention. Figure 2A It shows a single-layer chromium-containing film, while Figure 2B The chromium-containing film with a multilayer structure is shown.

[0050] Figure 3A and Figure 3B This is a cross-sectional view of the photomask blank according to the third embodiment of the present invention. Figure 3A It shows a single-layer chromium-containing film, while Figure 3B The chromium-containing film with a multilayer structure is shown.

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

[0052] Figure 5 This is a schematic diagram of the cross-sectional outline of a pattern formed by isotropic dry etching.

[0053] Figure 6 This is a cross-sectional view of a chromium-containing film formed by stacking three chromium compound layers with different etching rates after dry etching. Detailed Implementation

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

[0055] The photomask preform includes a transparent substrate (typically a quartz substrate) and a chromium-containing film disposed thereon, either 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 (multilayer structure) and is formed of a material that can be etched using an oxychlorine-based dry etching process.

[0056] The etching rate of chromium-containing materials in oxychlorine-based dry etching (commonly used for etching chromium-containing materials) can be improved by adding light elements to the chromium-containing material. The addition of light elements enables high-speed etching of chromium-containing films, resulting in a reduced burden on the photoresist film when etching the chromium-containing film through a pattern of photoresist film used as an etching mask (typically a chemically magnified photoresist film written for EB imaging). In some cases, using a silicon-containing etching mask as a hard mask to etch chromium-containing films allows for a reduction in the thickness of the etching mask film due to its high etching rate. This leads to a direct improvement in etching deviation and an indirect reduction in the thickness of the photoresist film used as the etching mask.

[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 the "common composition"): a chromium content of at least 30 at%, a total chromium, nitrogen and oxygen content of at least 93 at%, and satisfies formula (1):

[0058] 3Cr≤2O+3N (1)

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

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

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

[0062] As mentioned above, the addition of nitrogen and / or oxygen to chromium-containing materials is effective in improving their etching rate. Specifically, when light elements are added to metallic materials, their resistivity increases with the amount of light element added, indicating a loss of conductivity. When a film made of a material with increased resistivity is placed on the photomask preform side away from the transparent substrate, specifically on the formation side of the resist film used for EB lithography, charge buildup occurs during EB exposure, inducing unsatisfactory write accuracy degradation. In particular, when oxygen is added as a light element, it induces a significant increase in resistivity, resulting in a high-resistivity film.

[0063] Therefore, according to the present invention, the chromium-containing film is formed from a chromium compound containing chromium and nitrogen or containing chromium, nitrogen, and oxygen, and satisfies the common composition as defined above, and includes at least one chromium compound layer satisfying the first composition, preferably one or two chromium compound layers, most preferably one chromium compound layer, wherein the first composition is: an atomic ratio of nitrogen to chromium of at least 0.95, a chromium content of at least 40 at%, a total chromium and nitrogen content of at least 80 at%, and an oxygen content of less than 10 at%. The total thickness of the chromium compound layer satisfying the first composition is greater than 70% of the overall thickness of the chromium-containing film, preferably at least 90%, and less than 100%. 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 too large.

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

[0065] In a multilayer chromium-containing film, the remaining chromium compound layers, except for the chromium compound layer satisfying the first composition, are formed of chromium compounds containing chromium and nitrogen or chromium, nitrogen, and oxygen, and consist of at least one layer, preferably one or two layers, particularly one layer, satisfying the common composition but not the first composition. The layers not satisfying the first composition are preferably formed of chromium compounds containing chromium, nitrogen, and oxygen. When the layers not satisfying the first composition are used as the remaining layers besides the layers satisfying the first composition, the overall chromium-containing film has a high etch rate. Furthermore, the layers not satisfying the first composition are suitable for use as layers with antireflective properties.

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

[0067] Light elements other than nitrogen, or oxygen and nitrogen, can be added to the chromium compound layer. These other light elements include carbon, hydrogen, and fluorine. For example, the addition of carbon is effective in enhancing the etching rate. However, if too much carbon is added, the etching rate becomes too high, and dry etching becomes more isotropic, making it difficult to control the cross-sectional profile. When carbon-added chromium compound layers are stacked on top of carbon-free chromium compound layers, the etching rates of these layers can differ significantly. If this is the case, the lateral etching of these layers will differ during dry etching, potentially deteriorating the cross-sectional profile. Furthermore, the addition of carbon to the chromium compound layer reduces the photomask's chemical resistance to sulfuric acid peroxide mixtures or ozone peroxide mixtures (used to periodically clean the photomask during the photomask preform fabrication and exposure steps). Thus, it may be possible to adjust dry etching conditions to prevent cross-sectional profile deterioration, but the profile will still be deteriorated by chemical cleaning. Therefore, when other light elements besides nitrogen and oxygen, such as carbon, are added to the chromium compound layer, the content of these other light elements 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, especially 2 at% or less.

[0068] In the photomask preform of this invention, the sheet resistance of the chromium-containing film should not exceed 10,000 ohms / square. Preferably not exceeding 8,000 ohms / square meter When a single-layer or multi-layer chromium-containing film is composed of one or more chromium compound layers that meet the above compositional requirements, the overall sheet resistance of the chromium-containing film is within this range. Especially when the layer meeting the first composition is the only layer, the sheet resistance of that layer should preferably not exceed 10,000 ohms / square. More preferably, not exceeding 8,000 ohms / square meter When the film comprises two or more layers satisfying the first composition, the sheet resistance of each layer satisfying the first composition may fall within or outside this range. In either case, the sheet resistance of the overall chromium-containing film should not exceed 10,000 ohms / square. Preferably not exceeding 8,000 ohms / square meter This is effective in preventing any charge buildup during the writing of the resist pattern EB.

[0069] Chromium-containing films can be films with any desired function, such as optical films like light-shielding films, anti-reflective films, or phase-shifting films (e.g., halftone phase-shifting films), or auxiliary processing films like etch mask films or etch stop films. In some cases, optical films include auxiliary processing films that function as etch mask films or etch stop films, provided that such films are left on the photomask after the photomask preform has been processed into a photomask so that it can function as an optical film. It should be noted that although an etch stop film is a typical film left on the photomask after the photomask preform has been processed into a photomask, the etch mask film can be either left on the etch mask or completely removed from the photomask after the photomask preform has been processed into a photomask (referred to as a sacrificial film).

[0070] The materials constituting the optical film and auxiliary processing film of the photomask preform can be selected from transition metals, metals, their alloys, and compounds of these metals or alloys, depending on the required optical and etching properties, as well as electrical properties such as 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); suitable compounds include oxides, nitrides, carbides, oxynitrides, carbon oxides, carbonitrides, and carbonoxynitrides of metals or alloys. Among these metals, chromium (Cr), molybdenum (Mo), and silicon (Si) are preferred.

[0071] The photomask preform of the present invention is best suited as a photomask preform comprising a chromium-containing film, wherein the chromium-containing film is patterned by using a photoresist film (typically a chemically amplified resist film) as an etching mask during the processing of the photomask preform into a photomask, and the pattern is formed by oxychlorine-based dry etching.

[0072] The first embodiment of the photomask blank of the present invention is a photomask blank having a chromium-containing film directly disposed on a transparent substrate. Figure 1A and1B Each of these is a cross-sectional view of a typical photomask preform in a first embodiment. The photomask preform 101 includes a transparent substrate 1 and a chromium-containing film 2 thereon. Figure 1A In the process, the chromium-containing film 2 consists of a single layer that satisfies the first composition. Figure 1B In this embodiment, the chromium-containing film 2 is a three-layer structure comprising a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 sequentially stacked from the substrate 1 side. One or two of these layers satisfy the first composition, while the remaining two or one layers do not satisfy the first composition. Typically, the photomask preform 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. In the first embodiment, the photomask preform can be a binary photomask preform; in this case, the chromium-containing film is preferably a light-shielding film.

[0073] In the first embodiment of the photomask preform, when the chromium-containing film is a light-shielding film, the optical density of the chromium-containing film relative to the exposure light should preferably be at least 2.5, more preferably at least 2.8 and less than 3.5, and more preferably less than 3.2.

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

[0075] In a second embodiment of the photomask preform of the present invention, the photomask preform includes a chromium-containing film and is a photomask preform on a transparent substrate through one or more optical films. The chromium-containing film is patterned by an oxychlorine-based dry etching process using a mask pattern of a photoresist film (typically a chemically amplified photoresist film) as an etching mask when the photomask preform is processed into a photomask. The photomask preform of the second embodiment is particularly advantageous when the chromium-containing film pattern functions as a hard mask in the etching of the optical film, 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. Combinations of the chromium-containing film and the optical film include combinations of light-shielding films and phase-shifting films (e.g., halftone phase-shifting films) and combinations of etching mask films and light-shielding films.

[0076] Figure 2A and 2B Each of these is a cross-sectional view of a typical photomask preform in the second embodiment. The photomask preform 102 includes a transparent substrate 1, an optical film 3, and a chromium-containing film 2 sequentially stacked thereon from the substrate 1 side. Figure 2AIn pattern 2B, the chromium-containing film 2 consists of a single layer satisfying the first composition. In pattern 2B, the chromium-containing film 2 is a three-layer structure comprising a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 sequentially stacked from the substrate 1 side, wherein one or two layers satisfy the first composition, while the remaining two or one layers do not satisfy the first composition. Typically, the photomask preform 102 is processed into a photomask by forming a resist film for EB lithography on the chromium-containing film 2 and performing EB imaging writing. In the second embodiment, the photomask preform can be a phase-shifting photomask preform, in which case the optical film is preferably a phase-shifting film and the chromium-containing film is preferably a light-shielding film.

[0077] The photomask preform in this invention is preferably a photomask preform comprising a chromium-containing film, wherein the chromium-containing film is patterned by etching the mask pattern of the etched mask film as a hard mask during the processing of the photomask preform into a photomask using an oxygen-chlorine-based dry etching process. A third embodiment is a photomask preform comprising a transparent substrate, a chromium-containing film, and an etched mask film disposed on the side of the chromium-containing film away from the substrate, preferably adjacent to the chromium-containing film.

[0078] Figure 3A and 3B Each of these is a cross-sectional view of a typical photomask preform according to a third embodiment. The photomask preform 103 includes a transparent substrate 1, an optical film 3, a chromium-containing film 2, and an etched mask film 4, sequentially stacked from the substrate 1 side. Figure 3A In the process, the chromium-containing film 2 consists of a single layer that satisfies the first composition. Figure 3B In this embodiment, the chromium-containing film 2 is a three-layer structure comprising a first chromium compound layer 21, a second chromium compound layer 22, and a third chromium compound layer 23 sequentially stacked from the substrate 1 side, wherein one or two layers satisfy the first composition, and the remaining two or one layers do not satisfy the first composition. Typically, the photomask preform 103 is processed into a photomask by forming a photoresist film for EB lithography on the photoresist mask film 4 and performing EB imaging writing. In the third embodiment, the photomask preform can be a phase-shifting photomask preform, in which case the optical film is preferably a phase-shifting film and the chromium-containing film is preferably a light-shielding film.

[0079] In the first to third embodiments of the photomask preform, when the chromium-containing film is an optically functional film such as a light-shielding film, the film must possess high resolution, high pattern transfer accuracy, and optical functionality. In this sense, the chromium-containing film must meet the required optical functions such as optical density, high etching rate in oxychlorine-based dry etching, and form a mask pattern with an improved cross-sectional profile and minimal linewidth 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, which functions as an antireflective layer, is adjusted to meet the required reflectivity, from the viewpoint of minimizing the impact of increasing the thickness of the chromium-containing film, the thickness is preferably less than 20 nm, more preferably less than 10 nm, and at least 0.7 nm. If the thickness of the antireflective layer is below this range, such a thin layer may have a poor reflectivity suppression effect and be unstable for deposition.

[0084] In the second embodiment of the photomask preform, when the optical film is a phase-shifting film (typically a halftone film), the phase-shifting film is suitable for being formed from a silicon-containing material without transition metals or a material containing both silicon and transition metals. Preferably, the transition metal does not include chromium, and molybdenum is particularly preferred. Such materials include elemental silicon, compounds containing silicon and light elements such as oxygen, nitrogen, or carbon, especially compounds containing one or both of oxygen and nitrogen, and these compounds have a further added transition metal, preferably excluding chromium, specifically molybdenum, tantalum, tungsten, zirconium, or titanium, particularly molybdenum. Especially when the phase-shifting film is a halftone phase-shifting film, it also has optical density, and compared to a photomask preform without a halftone phase-shifting film, the thickness of the chromium-containing film can be reduced.

[0085] In the photomask preform of the second embodiment, when the chromium-containing film is a light-shielding film and the optical film is a halftone phase-shifting film, the chromium-containing film preferably has an optical density relative to the exposure light of at least 1.5, more preferably at least 1.8 and less than 2.6, more preferably less than 2.5, and even more preferably less than 2.4. The sum of the optical densities of the chromium-containing film and the phase-shifting film relative to the exposure light is preferably at least 2.5, more preferably at least 2.8 and less than 3.5, and more preferably less than 3.2. The desired light-shielding performance is obtained by adjusting the optical densities of the chromium-containing film and the halftone phase-shifting film to this range.

[0086] In the second embodiment of the photomask preform, when the chromium-containing film is a light-shielding film and the optical film is a halftone phase-shifting film, the thickness of the chromium-containing film is preferably 50 nm or less, more preferably 47 nm or less, even more preferably 44 nm or less and at least 35 nm when the exposure light is an ArF excimer laser; or when the exposure light is a KrF excimer laser, the thickness is preferably 80 nm or less, more preferably 70 nm or less, even more preferably 65 nm or less and at least 50 nm.

[0087] On the other hand, the halftone phase shift film is configured to have a transmittance of at least 2% relative to the exposure light, more preferably at least 5%, further more preferably at least 10%, most preferably at least 11% and below 40%, more preferably below 30%, and further more preferably below 20%. When the exposure light is an ArF excimer laser, the thickness of the halftone phase shift film is preferably 80 nm or less, more preferably 70 nm or less, and at least 50 nm, more preferably at least 60 nm; or when the exposure light is a KrF excimer laser, the thickness is preferably 110 nm or less, more preferably 100 nm or less, and at least 70 nm, more preferably at least 80 nm.

[0088] Similar to the third embodiment of the photomask preform, an etched mask is provided as a hard mask used in the etching of the chromium-containing film, thereby enabling the photoresist film to be thinned to accommodate further pattern miniaturization. This etched mask typically serves as a sacrificial film for the chromium-containing film. Often, this etched mask is completely removed during the photomask manufacturing process. Sometimes, the etched mask is partially left in the photomask manufacturing process, rather than being completely removed.

[0089] The etching mask can be formed from a material that is rapidly etched using fluorine-based dry etching but exhibits an extremely slow etching rate (i.e., no substantial etching) in oxychlorine-based dry etching. Suitable materials are silicon-containing materials, such as elemental silicon, compounds containing silicon and light elements (such as oxygen, nitrogen, or carbon), and such compounds have a transition metal further added thereto, preferably excluding chromium, specifically molybdenum, tantalum, tungsten, zirconium, or titanium.

[0090] In the third embodiment of the photomask preform, when the optical film is a phase-shifting film (typically a halftone phase-shifting film), the phase-shifting film is preferably formed of a silicon-containing material without transition metals or a material containing both silicon and transition metals. Preferably, the transition metal does not include chromium, and molybdenum is particularly preferred. Suitable materials are as described in the second embodiment of the photomask preform above. Especially when the phase-shifting film is a halftone phase-shifting film, it also possesses optical density, and compared to a photomask preform without a halftone phase-shifting film, the thickness of the chromium-containing film can be reduced.

[0091] In the third embodiment of the photomask preform, where the chromium-containing film is a light-shielding film and the optical film is a halftone phase-shifting film, the light density of the chromium-containing film relative to the exposure, the sum of the light densities of the chromium-containing film and the phase-shifting film relative to the exposure light, the thickness of the chromium-containing film, the transmittance of the halftone phase-shifting film, and the thickness of the halftone phase-shifting film are preferably within the same range as in the second embodiment.

[0092] In the third embodiment of the photomask preform, where the chromium-containing film is a light-shielding film, the optical film is a halftone phase-shifting film, and the etched mask film is a film that is partially left rather than completely removed during the photomask manufacturing process (i.e., a film that remains on the photomask and functions as an optical film), the sum of the optical densities of the chromium-containing film, the phase-shifting film, and the etched mask film relative to the exposure light is preferably at least 2.5, more preferably at least 2.8 and less than 3.5, and even more preferably less than 3.2. The thickness of the etched mask film is preferably at least 3 nm, more preferably at least 5 nm and less than 15 nm, and even more preferably less than 10 nm.

[0093] In another embodiment of the second implementation, the photomask preform may be a binary photomask preform. In this case, the optical film is a light-shielding film and the chromium-containing film is an etching mask film.

[0094] In the second embodiment of the photomask preform, where the chromium-containing film is an etch mask film, the film must possess high resolution, high pattern transfer accuracy, and optical functionality. In this sense, the chromium-containing film must meet the required optical functions, exhibit a high etching rate in oxychlorine-based dry etching, and form a mask pattern with an improved cross-sectional profile exhibiting minimal linewidth variation in the thickness direction.

[0095] Chromium-containing materials are commonly used in photomask preforms that are processed into photomasks suitable for pattern transfer using exposure light with wavelengths below 250 nm. Among chromium-containing materials, high-metallicity chromium-based materials are preferred as materials for forming low-resistivity conductive layers. When a chromium-containing film is formed to include a conductive layer composed of a high-metallicity chromium-based material, the chromium-containing film is endowed with conductivity.

[0096] On the other hand, low-chromium-based materials are effective in adjusting the optical and etching properties of chromium-containing films. They are also effective in improving transmittance. Although films formed from high-chromium-based materials have high reflectivity, they are sometimes detrimental in defect detection of photomask preforms or photomasks; therefore, low-chromium-based materials are preferred as materials for forming antireflective layers used in such cases.

[0097] In the photomask preform of the present invention, the chromium-containing film is composed of a multilayer structure, including layers that satisfy a first composition and layers that do not satisfy the first composition. In a second embodiment of the photomask preform, where the chromium-containing film is an etch mask film, the chromium compound layer preferably 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 antireflection layer. Here, 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 preferred that the chromium compound layer primarily functioning as an antireflection layer is formed on one or both of the chromium-containing film surface closest to the substrate and the chromium-containing film surface furthest from the substrate; more preferably, the chromium compound layer primarily functioning as an antireflection layer is formed adjacent to the chromium compound layer primarily functioning as a conductive layer. Specifically, regarding... Figure 2B In the chromium-containing film 2, the second chromium compound layer 22 is preferably a chromium compound layer whose main function is a conductive layer, while the first chromium compound layer 21 and the third chromium compound layer 23 are chromium compound layers whose main function is an anti-reflection layer.

[0098] Although the thickness of the chromium compound layer, whose primary function is antireflection, is adjusted to meet the required reflectivity, the thickness is typically below 30 nm, preferably below 20 nm, more preferably below 10 nm, and at least 0.7 nm. If the antireflection layer thickness is below this range, such a thin layer may provide poor reflection suppression and be unstable for deposition.

[0099] In the second embodiment of the photomask preform, when the optical film is a light-shielding film, the light-shielding film is preferably formed of a silicon-containing material that does not contain transition metals or a material containing both silicon and transition metals. Preferably, the transition metal does not include chromium, and molybdenum is particularly preferred. Suitable materials are shown in the phase-shifting film described above.

[0100] In the second embodiment of the photomask preform, when the optical film is a light-shielding film, the light-shielding film is set to have an optical density relative to the exposure light that is typically at least 2.5, preferably at least 2.8 and less than 3.5, and more preferably less than 3.2. When the exposure light is an ArF excimer laser, the thickness of the light-shielding film is preferably less than 80 nm, more preferably less than 70 nm, even more preferably less than 65 nm, and at least 50 nm, more preferably at least 55 nm; or when the exposure light is a KrF excimer laser, the thickness is preferably less than 100 nm, more preferably less than 90 nm, even more preferably less than 80 nm, and at least 55 nm, more preferably at least 60 nm. On the other hand, when 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 less than 20 nm, and more preferably less than 10 nm.

[0101] In a further embodiment of the photomask preform, another optical film may be formed on the surface of the chromium-containing film disposed away from the transparent substrate, preferably adjacent to the chromium-containing film. This other optical film is preferably a light-shielding film, for example, formed of a silicon-containing material without transition metals or a material containing both silicon and transition metals. When such a light-shielding film is introduced, the chromium-containing film may be an etch-stop film or a phase-shifting film such as a halftone phase-shifting film.

[0102] The preferred method for depositing chromium-containing films, optical films (e.g., phase-shifting films or light-shielding films), and auxiliary processing films (e.g., etch mask films or etch stop films) on photomask blanks is by sputtering, because films with high in-plane uniformity and few defects with optical properties 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 reaction gases such as nitrogen (N2), oxygen (O2), nitrogen oxides (N2O, NO2), hydrocarbon gases (e.g., CH4), and carbon oxides (CO, CO2) according to the desired composition. Rare gases such as argon (Ar) can be selected and used in conjunction with the reaction gas. Film deposition can be performed by introducing sputtering gas into the sputtering vacuum chamber and adjusting the power applied to the target and the flow rate of the sputtering gas so that each chromium compound layer that becomes the chromium-containing film can become a layer that satisfies the first composition or a layer that does not satisfy the first composition.

[0104] When the phase-shifting film or light-shielding film is deposited from a silicon-containing material without transition metals or a silicon-containing and transition metal-containing material, or when the etching mask film is deposited from a silicon-containing material, for example, the target material is selected from silicon targets, transition metal targets, and transition metal-silicon targets depending on the desired composition. The sputtering gas is selected from reactive gases such as nitrogen (N2), oxygen (O2), nitrogen oxides (N2O, NO2), hydrocarbon gases (e.g., CH4), and carbon oxides (CO, CO2) depending on the desired composition. Rare gases such as argon (Ar) can be selected and used in conjunction with the reactive gas. Film deposition can be performed by introducing sputtering gas into the sputtering vacuum chamber and adjusting the power applied to the target and the flow rate of the sputtering gas to form a film of the desired composition.

[0105] Photomasks can be prepared from photomask preforms using standard methods. For example, a resist film composed of a chemically amplified resist is formed on the photomask preform, followed by EB writing patterning. Using the resist pattern as the initial etch mask, the base film includes a chromium-containing film, optical films (e.g., phase-shifting films, light-shielding films), auxiliary processing films (e.g., etch mask films, etch stop films), and a transparent substrate. These are sequentially etched using a dry etching technique, where the dry etching technique can be selected from oxychlorine-based dry etching and fluorine-based dry etching depending on the material being etched. In this way, the photomask pattern is formed, i.e., the photomask is obtained. When the chromium-containing film is processed by dry etching, such as... Figure 4 As shown in the schematic diagram, the resulting pattern has a cross-sectional profile that closely resembles that of anisotropic dry etching products. It should be noted that, to further suppress charge accumulation during EB writing, an organic conductive film can be formed on the resist film.

[0106] Example

[0107] The invention is illustrated more specifically by means of the following embodiments and comparative examples, but the invention is not limited to these embodiments.

[0108] Example 1

[0109] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 30 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0110] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing N2 gas at 45 sccm into the sputtering chamber. A 45 nm thick CrN layer was formed on the halftone phase-shift film. The resulting chromium-containing film with a monolayer structure served as a photomask preform for the light-shielding film. The optical density of this chromium-containing film relative to the ArF excimer laser (wavelength 193 nm) was 2.1, and the sum of the optical densities of the chromium-containing film and the halftone phase-shift film was 3.0.

[0111] Example 2

[0112] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 30 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0113] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 45 sccm of N2 gas and 2 sccm of O2 gas into the sputtering chamber. A 46 nm thick CrON layer was formed on the halftone phase-shift film. The resulting chromium-containing film with a monolayer structure served as a photomask preform for the light-shielding film. The optical density of this chromium-containing film relative to the ArF excimer laser (wavelength 193 nm) was 2.1, and the sum of the optical densities of the chromium-containing film and the halftone phase-shift film was 3.0.

[0114] Example 3

[0115] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 30 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0116] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 45 sccm of N2 gas into the sputtering chamber. A 44 nm thick CrN layer, primarily functioning as a conductive layer, was formed on the halftone phase-shift film. Next, DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 10 sccm of Ar gas, 30 sccm of N2 gas, and 15 sccm of O2 gas into the sputtering chamber. A 1 nm thick CrON layer, primarily functioning as an antireflection layer away from the substrate, was formed. This method yielded a 45 nm thick chromium-containing film with a two-layer structure, serving as a photomask preform for use as a light-shielding film. The optical density of this chromium-containing film relative to the ArF excimer laser (wavelength 193 nm) was 2.1, and the sum of the optical densities of the chromium-containing film and the halftone phase-shift film was 3.0.

[0117] Example 4

[0118] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 62 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 30 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0119] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 45 sccm of N2 gas and 1 sccm of CH4 gas into the sputtering chamber. A 46 nm thick CrNC layer was formed on the halftone phase-shift film. The resulting chromium-containing film with a monolayer structure served as a photomask preform for the light-shielding film. The optical density of this chromium-containing film relative to the ArF excimer laser (wavelength 193 nm) was 2.1, and the sum of the optical densities of the chromium-containing film and the halftone phase-shift film was 3.0.

[0120] Example 5

[0121] DC magnetron sputtering deposition was performed on a quartz substrate with a cross-section of 152 mm and a thickness of 6 mm. A 45 nm thick MoSiN film was deposited on the substrate as a light-shielding film by sputtering a target containing molybdenum and silicon (molar ratio of 1:2) and a silicon target, and by introducing 30 sccm (flow rate) of Ar gas and 5 sccm of N2 gas into the sputtering chamber.

[0122] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing N2 gas at 45 sccm into the sputtering chamber as the sputtering gas. A 10 nm thick CrN layer was formed on the light-shielding film. The resulting chromium-containing film with a monolayer structure was used as a photomask preform for etching.

[0123] Comparative Example 1

[0124] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 61 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 32 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0125] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 9 sccm of Ar, 30 sccm of N2, and 14 sccm of O2 as sputtering gases into the sputtering chamber. A 20 nm thick CrON layer, primarily functioning as a substrate-side antireflection layer, was formed on the halftone phase-shift film. Next, DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 20 sccm of Ar, 2 sccm of N2, and 2 sccm of O2 as sputtering gases into the sputtering chamber. A 4 nm thick CrON layer, primarily functioning as a conductive layer, was formed. Furthermore, DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 12 sccm of Ar, 30 sccm of N2, and 14 sccm of O2 as sputtering gases into the sputtering chamber. A 22 nm thick CrON layer, primarily functioning as an antireflection layer away from the substrate side, was formed. Through this method, a photomask preform with a three-layer structure and a thickness of 46 nm, serving as a light-shielding film, was obtained. Compared to the ArF excimer laser (wavelength 193nm), the optical density of the chromium-containing film is 2.0, and the sum of the optical densities of the chromium-containing film and the halftone phase-shifting film is 3.1.

[0126] Comparative Example 2

[0127] DC magnetron sputtering deposition was performed on a 152 mm square and 6 mm thick quartz substrate. A 61 nm thick SiN film was deposited on the substrate as a halftone phase shift film by sputtering a silicon target and introducing 15 sccm (flow rate) of Ar gas and 32 sccm of N2 gas as sputtering gases into the sputtering chamber.

[0128] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 10 sccm of Ar, 50 sccm of N2, and 5 sccm of CH4 gas into the sputtering chamber. A 45 nm thick CrNC layer, primarily functioning as a substrate-side antireflection layer, was formed on the halftone phase-shift film. Next, DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 30 sccm of Ar and 35 sccm of N2 gas into the sputtering chamber. A 3 nm thick CrN layer, primarily functioning as a conductive layer, was formed. Furthermore, DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 10 sccm of Ar, 50 sccm of N2, and 10 sccm of O2 gas into the sputtering chamber. A 3 nm thick CrON layer, primarily functioning as an antireflection layer away from the substrate side, was formed. Through this method, a photomask preform with a three-layer structure and a thickness of 51 nm, serving as a light-shielding film, was obtained. Compared to the ArF excimer laser (wavelength 193nm), the optical density of the chromium-containing film is 1.9, and the sum of the optical densities of the chromium-containing film and the halftone phase-shifting film is 3.0.

[0129] Comparative Example 3

[0130] DC magnetron sputtering deposition was performed on a quartz substrate with a cross-section of 152 mm and a thickness of 6 mm. A 45 nm thick MoSiN film was deposited on the substrate as a light-shielding film by sputtering a target containing molybdenum and silicon (molar ratio of 1:2) and a silicon target, and by introducing 30 sccm (flow rate) of Ar gas and 5 sccm of N2 gas into the sputtering chamber.

[0131] DC magnetron sputtering deposition was performed by sputtering a chromium target and introducing 20 sccm of Ar gas and 5 sccm of N2 gas into the sputtering chamber. A 10 nm thick CrN layer was formed on the light-shielding film. A photomask preform with a monolayer chromium-containing film structure was obtained and used as an etching mask.

[0132] For the photomask preforms of the Examples and Comparative Examples, the composition of each chromium compound layer of the chromium-containing film was analyzed by X-ray photoelectron spectroscopy (XPS). The results, along with whether equation (1) is satisfied, are shown in Table 1. Thin-film resistance evaluation samples were prepared individually by directly forming each chromium-containing film of the Examples and Comparative Examples on an insulating quartz substrate. The electrical properties of the samples were measured using a four-probe method, from which the thin-film resistance of the chromium-containing film was calculated. The results are shown in Table 1.

[0133] In the photomask preforms of the embodiments and comparative examples, the film thicknesses required to achieve a predetermined optical density were compared. The thickness of the film was designated as the standard thickness for optical density when it was adjusted to an optical density of 2.0 relative to the ArF excimer laser (wavelength 193 nm). This film thickness was determined according to the formula: (chromium-containing film thickness) × {2 / (chromium-containing film optical density)}. The results are shown in Table 1. Regarding the standard thickness, a lower thickness indicates better transfer performance when used as a photomask; ideally, a thickness below 50 nm is preferred, and particularly ideally, a thickness below 47 nm is preferred.

[0134] The chromium-containing film was peeled from the photomask preforms of the examples and comparative examples using an oxygen-chlorine-based dry etching process. The time required for peeling, i.e., the etching removal time, was measured. The etching removal time based on an optical density standard was determined according to the following formula, which is equivalent to an optical density of 2.0 relative to an ArF excimer laser (wavelength 193 nm): (measured etching removal time) × {2 / (optical density of the chromium-containing film)}. The results are shown in Table 1. Shorter times are more effective for patterning at high resolution relative to the standard etching removal time; ideally, times below 135 seconds are preferred, and particularly ideally, times below 130 seconds are preferred.

[0135] Next, a 100 nm thick resist film for EB lithography was deposited on the chromium-containing film of each photomask preform in the examples and comparative examples. The resist film was exposed to the EB lithography system to form a line-spacer pattern with a linewidth of 100 nm, and developed to form the resist pattern. When the resist pattern was used as an etching mask, the chromium-containing film was etched by an oxychlorine-based dry etching process under 75% over-etch conditions, i.e., the etching time was equivalent to 175% of the etch removal time calculated from the etching rate of each chromium-containing film, thereby transferring the line-spacer pattern to the chromium-containing film. The resist pattern was stripped off, and the line-spacer pattern was cut in cross-section. The cross-sectional profile of the etched walls of the lines in the chromium-containing film pattern was observed. The evaluation results of the cross-sectional profile are shown in Table 1.

[0136] For the cross-sectional profile of the line, the linewidth variation in the thickness direction is required to be zero and the cross-sectional profile to be completely perpendicular. The evaluation is performed using a pre-defined plane that is coplanar with both ends of the resist pattern in the width direction and perpendicular to the chromium-containing film surface. This plane is used as a reference plane. When the actual cross-section of the chromium-containing film line is concave inward from the reference plane, the chromium-containing film pattern is considered negative; when the actual cross-section of the film line is convex outward, it is considered positive. This is used to evaluate the linewidth variation of the chromium-containing film pattern in the thickness direction. If the chromium-containing film thickness is uniform (1), a value between -0.05 and +0.05 is considered good (○), a value between -0.1 and less than -0.05, or greater than +0.05 and +0.1 is considered medium (△), and a value between less than -0.1 and greater than +0.1 is considered poor (×).

[0137] Table 1

[0138]

[0139] Although the invention has been described and illustrated with reference to typical embodiments, this does not mean that the invention is limited to these details. Various embodiments, additions, modifications, and deletions will be conceived by those skilled in the art. All such embodiments are within the spirit and scope of the invention as long as the effects and benefits of the invention are achieved.

Claims

1. A photomask preform, processed into a photomask 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 directly disposed on the substrate, wherein, The chromium-containing film consists of one chromium compound layer or at least two chromium compound layers, each chromium compound layer being formed of a chromium compound containing chromium, nitrogen and carbon, or containing chromium, nitrogen, oxygen and carbon, and having the following common composition: a chromium content of at least 30 at%, a total chromium, nitrogen and oxygen content of at least 93 at%, and a carbon content of at most 3 at%, and satisfying equation (1). Where Cr is the chromium content, O is the oxygen content, and N is the nitrogen content, the units for chromium, oxygen, and nitrogen content are atomic percentages. When the chromium-containing film is composed of a chromium compound layer, the chromium compound layer satisfies the following first composition: the atomic ratio of nitrogen to chromium 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 less than 10 at%. When the chromium-containing film is composed of at least two chromium compound layers, each chromium compound layer comprises at least one chromium compound layer satisfying a first composition, wherein the first composition is that the atomic ratio of nitrogen to chromium 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 less than 10 at%, and the total thickness of the at least one chromium compound layer satisfying the first composition is in the range of greater than 70% and less than or equal to 100% of the total thickness of the chromium-containing film. The exposure light is an ArF excimer laser, the optical density of the chromium-containing film relative to the exposure light is 2.8~3.5, and the thickness of the chromium-containing film is at least 50 nm. The resistivity of the chromium-containing film is below 10,000 Ω / □.

2. The photomask preform according to claim 1, wherein, The thickness of the chromium-containing film is less than 75 nm.

3. The photomask preform according to claim 1, wherein, The chromium-containing film has a multilayer structure consisting of two or more layers of chromium compounds.

4. The photomask preform according to claim 1, wherein, The first component has a carbon content of less than 7 at%.

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

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