Tungsten blanks for producing tungsten through-machined products, and a method for producing tungsten through-machined products using tungsten blanks

Abstract

To provide a tungsten blank capable of forming a through hole of diameter level of several tens μ m with high aspect ratio and manufacturing a tungsten processed product having high processing accuracy of submicron level, and to provide a method for manufacturing such a tungsten processed product.SOLUTION: Provided are a tungsten blank and a method for manufacturing a tungsten processed product using the tungsten blank trying to suppress film floating of a hard mask film caused by difference in a thermal expansion coefficient during dry etching processing, by sandwiching a buffer layer made of a material having an intermediate thermal expansion coefficient of tungsten and a hard mask film between tungsten of a blank substrate made of tungsten and the hard mask film.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a tungsten blank for producing a tungsten through-machined product, and a method for producing a tungsten through-machined product using the tungsten blank. [Background technology]

[0002] Tungsten has excellent heat resistance and radiation shielding properties, and these properties are utilized to make penetrating processed products (hereinafter simply referred to as processed products) for applications such as apertures for electron beams, X-rays, and ion beams, collimators, various orifices, various electrodes, and various filaments in scientific and chemical equipment, medical equipment, measuring and inspection equipment, and vacuum components.

[0003] For apertures and collimators, a tungsten thickness equal to or greater than the aperture diameter is required to achieve a high radiation shielding rate, so high aspect ratio processing is required. Also, for orifices used in high-pressure environments such as mass flow meters and spray nozzles, mechanical strength is required, so high aspect ratio processing with a thick film is required.

[0004] However, while tungsten has excellent mechanical properties such as high hardness, a high melting point, tensile strength, and elasticity, it is also known as a material that is generally difficult to process into high aspect ratios. The processable substrate size and thickness vary depending on the processing method, and the processing accuracy also varies accordingly, so it is necessary to select a processing method according to the required specifications.

[0005] Possible processing methods include laser processing, electrical discharge processing, cutting processing, focused ion beam processing, precision press processing, dry etching processing, and the like.

[0006] For example, ultra-short pulse laser processing uses picosecond or femtosecond laser light sources. In general laser processing, continuous application of the laser can cause defects such as deformation due to the effects of heat, but in ultra-short pulse laser processing, the effects of heat are mitigated by turning the pulse laser on and off.

[0007] With laser processing, it is possible to process through-holes with a diameter of several tens of microns at a high aspect ratio, but the processing position accuracy is around 2 to 20 microns, and it is not possible to control the processing position at the submicron level.

[0008] Dry etching is being considered as a method for achieving such high aspect ratio etching. In dry etching, a resist mask pattern is first formed with submicron-level positional and dimensional accuracy (hereinafter collectively referred to as processing accuracy) by exposure transfer using a high-precision patterning mask formed by a lithography system or by direct electron beam lithography, and then the resist mask pattern is transferred to the underlying layer by dry etching, so processing accuracy is not compromised.

[0009] As an example of processing using the dry etching method, Patent Document 1 describes a process in which resist patterning using an electron beam lithography machine, dry etching, and hard mask oxidation treatment are combined to form a pattern with a film thickness of 0.5 μm, dimensions of 0.2 to 0.5 μm, and an aspect ratio of approximately 1.

[0010] Furthermore, for high aspect ratio patterning, a method such as that described in Patent Document 2 has been studied, and according to this document, through holes with diameters on the order of several tens of μm can be formed with an aspect ratio of 10 or more. It has also been reported that it has high processing accuracy at the submicron level. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Application Publication No. 2-27713 [Patent Document 2] Patent Application No. 2020-001575 Summary of the Invention [Problem to be solved by the invention]

[0012] However, in the tungsten etching process of the previous inventions, there is a concern that the hard mask pattern may float due to the substrate temperature during dry etching, which may result in insufficient etching shielding and significant impairment of the etching shape and uniformity.

[0013] Dry etching equipment is equipped with a substrate cooling mechanism on the stage to prevent the substrate temperature from rising, but when etching tungsten, the substrate may not be cooled sufficiently due to the following reasons, resulting in film lifting.

[0014] Tungsten blank substrates are less than 1 mm thick, but vary in thickness depending on the specifications, and are generally 0.1 to 0.5 mm thick. They are usually sold on the market as square or rectangular substrates. The transport systems of typical semiconductor etching equipment are designed to transport round wafers and cannot transport square substrates.

[0015] Therefore, when dry etching a tungsten substrate with the thickness described above, a dry etching device with a transport system that can accommodate square substrates must be prepared, or the square tungsten substrate must be attached to a commonly available silicon wafer, transported into the device, and processed.

[0016] Dry etching equipment for square substrates, as the former, is very expensive and therefore not common, whereas the latter, as a general silicon wafer, is a commonly used processing method in which a square tungsten substrate, i.e., a blank substrate made of tungsten, is bonded to the silicon wafer.

[0017] When the substrate is processed in the dry etching apparatus, the substrate is irradiated with plasma from above, and heat is generated on the surface of the substrate during this plasma irradiation.

[0018] The substrate is transported from outside the apparatus and placed on the stage of the dry etching apparatus, and is layered in this order from the lower stage onwards: a silicon wafer, an adhesive such as wax, and a blank substrate made of tungsten. When heat is generated on the surface side by irradiating plasma from above, even if a cooling device is provided on the lower stage of the dry etching apparatus, the cooling efficiency of the tungsten blank substrate is extremely reduced because the silicon wafer and adhesive such as wax are interposed between the tungsten blank substrate and the stage equipped with the cooling device, even if cooling from the stage is performed from the underside, resulting in a rise in temperature of the substrate and film lift due to thermal expansion.

[0019] The present invention has been made in consideration of the above problems, and aims to provide a tungsten processed product that can process tungsten with a high aspect ratio even when the film is thick, and a tungsten blank and a method for manufacturing the same that solve the problem in the manufacturing method of the tungsten blank that film floating occurs between the metals in the patterned portion due to the difference in thermal expansion coefficient between the hard mask film and the tungsten base material, which is caused by the temperature rise during dry etching. [Means for solving the problem]

[0020] As a means for solving the above problem, the present invention aims to suppress film floating of the hard mask film by sandwiching an intermediate film, which serves as a buffer layer made of a material having an intermediate thermal expansion coefficient between the tungsten and the hard mask film, between the tungsten and the hard mask film.

[0021] One aspect of the present invention is a blank substrate made of tungsten, which has an etching stopper film laminated on a first surface of the blank substrate, an intermediate film laminated on a second surface opposite to the first surface, a hard mask film laminated on the intermediate film, and a thermal expansion coefficient of the intermediate film that is intermediate between that of the hard mask and that of tungsten.

[0022] In one aspect of the present invention, a resist film is provided on the hard mask film.

[0023] One aspect of the present invention is a blank substrate made of tungsten, characterized in that an etching stopper film is laminated on a first surface of the blank substrate, an intermediate film is laminated on a second surface opposite to the first surface, a resist pattern is formed on the intermediate film, and a hard mask film is laminated on the intermediate film and the resist pattern.

[0024] In one aspect of the present invention, the hard mask film is made of any one of nickel, copper, and aluminum.

[0025] In one aspect of the present invention, the intermediate film is made of titanium.

[0026] Another aspect of the present invention is a method for producing a tungsten processed product, characterized by comprising the following steps in order: 1) A step of forming an etching stopper film on a first surface of a blank substrate made of tungsten. 2) forming an intermediate film on a second surface of the blank substrate made of tungsten opposite to the first surface; 3) forming a hard mask film on the intermediate film. 4) forming a resist pattern on the hard mask film. 5) forming a hard mask film pattern using the resist pattern as an etching mask; 6) A step of performing a penetrating process on the intermediate film and tungsten by dry etching using the hard mask film pattern as a mask and primarily using a fluorine-based gas. 7) removing the hard mask film pattern and the dry etching stopper film; Another aspect of the present invention is a method for producing a tungsten processed product, characterized by comprising the following steps in order: 1) A step of forming a dry etching stopper film on a first surface of a blank substrate made of tungsten. 2) forming an intermediate film on a second surface of the blank substrate made of tungsten opposite to the first surface; 3) A step of forming a resist pattern on the intermediate film. 4) forming a hard mask film on the intermediate film. 5) A step of removing the hard mask film formed on the resist pattern together with the resist pattern to form a hard mask film pattern. 6) A process of using the hard mask film pattern as a mask to perform dry etching using a fluorine-based gas as the main gas to penetrate the intermediate film and tungsten. 7) The hard mask film 8) A step of removing the pattern and the dry etching stopper film. [Effects of the Invention]

[0027] According to the present invention, it is possible to provide a tungsten blank that can be used to produce a tungsten processed product having through holes with diameters of several tens of μm and an aspect ratio of 10 or more, and high processing accuracy at the submicron level, and a method for producing such a tungsten processed product. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 2 is a schematic cross-sectional view showing (a) a tungsten blank according to a first embodiment of the present invention, and (b) a modified example of the tungsten blank according to the first embodiment. [Figure 2] 1A is a schematic cross-sectional view showing a tungsten blank according to a second embodiment of the present invention, and FIG. 1B is a schematic cross-sectional view showing a modified example of the tungsten blank according to the second embodiment of the present invention. [Figure 3] 1A to 1C are schematic cross-sectional views showing a part of a process for manufacturing a tungsten product using the tungsten blank of the first embodiment of the present invention in the order of steps. [Figure 4] 4A to 4C are schematic cross-sectional views showing the manufacturing process following FIG. 3 in the order of steps. [Figure 5] 5A to 5C are schematic cross-sectional views showing a part of a process for manufacturing a tungsten product using a tungsten blank according to a second embodiment of the present invention in the order of steps. [Figure 6] 6A to 6C are schematic cross-sectional views showing the manufacturing process following FIG. 5 in the order of steps. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following describes the manufacturing method of tungsten blanks and tungsten processed products according to the embodiments of the present invention with reference to the drawings. The same components are designated by the same reference numerals unless otherwise specified for convenience. In each drawing, the thickness and proportions of the components may be exaggerated for clarity, and the number of components may be reduced. Furthermore, the present invention is not limited to the following embodiments as they are, and can be embodied by appropriate combinations and modifications without departing from the spirit of the invention.

[0030] [Tungsten blanks] 1(a) is a schematic cross-sectional view showing a tungsten blank 100 according to a first embodiment of the present invention. The tungsten blank 100 according to the first embodiment of the present invention includes a blank substrate 1 made of tungsten, a dry etching stopper film 2 on a first surface thereof, and an intermediate film 3 on a second surface opposite to the first surface.

[0031] Although tungsten does not necessarily mean pure tungsten, but may be any tungsten-based material, hereinafter it will be referred to simply as "tungsten."

[0032] Here, in order to achieve a high etching selectivity and a high aspect ratio after etching, the etching stopper film 2 is characterized in that the boiling point of the chloride or oxychloride in the etching stopper film 2 is lower than the boiling point of the fluoride, and the boiling point of the fluoride in the etching stopper film 2 is higher than the boiling point of the fluoride of tungsten, which is the blank substrate 1. The reason for this will be described later. 1(b) is a schematic cross-sectional view showing a modified example 100a of the tungsten blank of the first embodiment of the present invention. The modified example 100a of the tungsten blank of the first embodiment is provided with an intermediate film 3 and a resist layer 4 on the second surface of the tungsten blank 100 of the first embodiment, which is opposite to the first surface having the etching stopper film 2. Here, the reason why both the form not having the resist layer 4 and the form having the resist layer 4 are referred to as blanks is that they are generally used in photomasks. Regarding blanks, both the form with and without a resist layer are referred to as blanks.

[0033] 2(a) is a schematic cross-sectional view showing a tungsten blank 200 according to a second embodiment of the present invention. Similar to the tungsten blank 100 according to the first embodiment, the tungsten blank 200 according to the second embodiment of the present invention has a dry etching stopper film 2 on a first surface of a blank substrate 1, and an intermediate film 3 and a hard mask film 5 on a second surface opposite the first surface.

[0034] Here, the hard mask film 5 is characterized in that the boiling point of the fluoride thereof is higher than that of the tungsten fluoride of the blank substrate 1, and the boiling point of the chloride or oxychloride of the hard mask film 5 is lower than that of the fluoride, the reason for which will be described later.

[0035] The intermediate film is characterized by a material property in that its thermal expansion coefficient is greater than that of tungsten but smaller than that of the hard mask film. The reason for this is that in order to solve the problem of film lift-up occurring between the metals in the patterned portion due to the difference in thermal expansion coefficient between the hard mask film and the tungsten substrate caused by the temperature rise during dry etching, a buffer layer made of a material having an intermediate thermal expansion coefficient is sandwiched between the tungsten and the hard mask film to suppress film lift-up of the hard mask film, and the intermediate film corresponds to this.

[0036] 2(b) is a schematic cross-sectional view showing a modified example 200a of the tungsten blank according to the second embodiment of the present invention. The modified example 200a of the tungsten blank according to the second embodiment includes a resist layer 4 on a hard mask film 5 formed on the second surface of the tungsten blank 200 according to the second embodiment.

[0037] In the present invention, a dry etching method is used to fabricate a tungsten processed product.

[0038] Therefore, in order to achieve the goal of forming through holes with diameters of several tens of μm with an aspect ratio of 10 or more and producing tungsten processed products with high processing accuracy at the submicron level, the tungsten blank of the first embodiment is provided with a dry etching stopper film (hereinafter referred to as etching stopper film) 2, and the tungsten blank of the second embodiment is further provided with a hard mask film 5.

[0039] As will be described later in the manufacturing method of a tungsten processed product, the tungsten blank 100 according to the first embodiment of the present invention shown in FIG. 1 and its modified example 100a do not have a hard mask film. However, this is because a hard mask film pattern is formed by lift-off after a resist pattern is formed on the second surface of the blank substrate 1. The first and second embodiments, as well as their modified examples, all share the common practice of dry etching tungsten using a hard mask film pattern as an etching mask. Using a hard mask film pattern as an etching mask is a requirement for producing a tungsten processed product having through holes with diameters on the order of several tens of microns and aspect ratios of 10 or more, which cannot be obtained by simply using a resist pattern as an etching mask.

[0040] In dry etching tungsten using the tungsten blanks of the present invention, a necessary condition for achieving a high aspect ratio and high processing accuracy is that the dry etching selectivity of tungsten to the hard mask film, which is the etching mask (=etching rate of tungsten / etching rate of hard mask film) is high.

[0041] If the etching selectivity is not sufficient, the thickness of the hard mask film, which is the etching mask, will be reduced. This inevitably leads to a thicker resist pattern when the hard mask film is patterned by dry etching, which in turn leads to a poorer resolution of the resist pattern, resulting in a loss of precision in the final tungsten processed product.

[0042] In general, dry etching occurs when introduced gas collides with electrons in the plasma, generating active radicals and reactive ions dissociated into various forms, which then cause etching. It is known that the lower the boiling point of volatile products formed on the etching surface, the easier the etching process will be. The boiling point and vapor pressure of the reaction products between the material to be etched and the introduced gas are indicators of this. In other words, reaction products with lower boiling points tend to vaporize, resulting in higher vapor pressures and easier exhaust.

[0043] Dry etching is usually performed using halogen gas, especially fluorine-based or chlorine-based gas, as the main gas, which is inexpensive and easy to use. In order to improve the etching rate and etching shape, oxygen (O2) gas or reducing gases such as hydrogen (H2) may be added.

[0044] Taking the above into consideration, the boiling points of representative fluorides, chlorides, and oxychlorides of metal elements that are potential candidates for hard mask film materials in dry etching of tungsten (W) are compared with those of W. The values ​​in Table 1 are compiled from non-patent literature (CRC Handbook of Chemistry and Physics, 78th Edition) and various websites.

[0045] [Table 1]

[0046] The boiling point is an indicator of the ease of dry etching, but it is not proportional to the etching rate. The actual etching rate and etching selectivity vary depending on the gas flow rate, pressure, power density, dry etching conditions of the added gas, and the temperature of the object to be etched. Therefore, it is necessary to optimize the etching conditions according to the required specifications of the processed product.

[0047] According to Table 1, W undergoes the reaction W + 6F → WF6 with fluorine-based gases, and since the boiling point of WF6 is low, it can be seen that W is easily etched by fluorine-based gases. On the other hand, with chlorine-based gases, the reaction W + 6Cl → WCl6 occurs, but since the boiling point of WCl6 is high, it is difficult to etch with chlorine-based gases.

[0048] Since it has been found that fluorine-based gases are used as the main gas for dry etching of tungsten, it is clear that in order to increase the dry etching selectivity (= etching rate of tungsten / etching rate of hard mask film), the hard mask film must be made of a material whose boiling point of fluoride is higher than the boiling point of tungsten fluoride and that is difficult to etch with fluorine-based gases.

[0049] Therefore, in order to achieve a high aspect ratio and high processing accuracy, the hard mask film provided in the second embodiment of the tungsten blank of the present invention and the hard mask film used when manufacturing a tungsten product using the first embodiment must have a boiling point of fluoride higher than that of tungsten fluoride, and a boiling point of chloride or oxychloride lower than that of fluoride. Here, the boiling point of chloride or oxychloride is lower than that of fluoride so that the hard mask film can be peeled off with a chlorine-based gas without damaging the tungsten after piercing the tungsten.

[0050] The tungsten blanks of the present invention, including the tungsten blanks of the first and second embodiments and their modifications, are characterized in that they have an etching stopper film on the surface (first surface, lower surface) of the tungsten blank substrate that faces the stage.

[0051] The etching stopper film must literally have the function of stopping the etching of tungsten or slowing down the processing speed of the blanks. Therefore, the etching stopper film is preferably made of a material that has a low dry etching selectivity ratio of the etching stopper film to tungsten (=etching rate of etching stopper film / etching rate of tungsten), or conversely, a material that has a high dry etching selectivity ratio of tungsten to the etching stopper film (=etching rate of tungsten / etching rate of etching stopper film).

[0052] Therefore, the dry etching selectivity required for the etching stopper film of the tungsten blank of the present invention is the same as that of the hard mask film, and is characterized in that the boiling point of the fluoride is higher than that of the tungsten fluoride, and the boiling point of the chloride or oxychloride is lower than that of the fluoride. Here, the reason why the boiling point of the chloride or oxychloride is lower than that of the fluoride is that after piercing the tungsten, the etching stopper film can be stripped off with a chlorine-based gas without damaging the tungsten.

[0053] As described above, the hard mask film candidates listed in Table 1 can be used as etching stopper film candidates as they are. The difference is that the hard mask film remains after tungsten penetration processing and is not etched in the planar direction, so that the through-hole diameter is not enlarged. Therefore, the material of the etching stopper film should have a low dry etching selectivity to tungsten (=etching rate of etching stopper film / etching rate of tungsten).

[0054] On the other hand, in general, over-etching is performed in dry etching to remove etching residues and to adjust the etching shape. However, if the etching selectivity ratio of the etching stopper film to tungsten is too low, there is a possibility that side etching in the lateral direction will occur in the tungsten during over-etching. Therefore, it is preferable that the selectivity is not too low, and that the dry etching will stop midway through the etching stopper film 2.

[0055] In view of the above, it is preferable that the material whose fluoride has a boiling point higher than that of tungsten fluoride and whose chloride or oxychloride has a boiling point lower than that of the fluoride be any of nickel, copper, and aluminum.

[0056] Additionally, nickel, copper, or aluminum is preferable because it is an inexpensive material that does not use rare metals, can be removed using chemicals such as acid, and has excellent thermal conductivity and rapid heat dissipation.

[0057] Furthermore, since the tungsten blank of the present invention has a thick tungsten film thickness of several tens of micrometers, there is a concern that the etching time will be long and the temperature will rise. Therefore, there is a concern that cracks, chips, and distortions will occur due to the difference in thermal expansion coefficient between the hard mask film and the etching stopper film as the temperature rises. Therefore, it is desirable that the thermal expansion coefficients of the hard mask film and the etching stopper film be close to that of tungsten.

[0058] For the same reason, it is preferable to cool the tungsten blanks during tungsten dry etching. Usually, the object to be etched in a dry etching apparatus is cooled by flowing cooling water or cooling gas on the backside of the stage on which the object to be etched is placed. Another method is to apply cool grease or the like to the backside of the object to be etched.

[0059] Furthermore, the etching stopper film is preferably made of a material with high thermal conductivity in order to smoothly transmit the cooling effect from the stage side to the tungsten blank during dry etching. Table 2 shows the thermal conductivity of the materials listed in Table 1 along with their thermal expansion coefficients.

[0060] [Table 2]

[0061] As mentioned above, when dry etching a tungsten substrate with the thickness described above, a dry etching device with a transport system compatible with square substrates must be prepared, or the square tungsten substrate must be attached to a commonly available silicon wafer and processed.

[0062] Dry etching equipment for square substrates, as the former, is very expensive and therefore not common, whereas the latter, as a general silicon wafer, is a commonly used processing method in which a square tungsten substrate, i.e., a blank substrate made of tungsten, is bonded to the silicon wafer.

[0063] The substrate is transported from outside the dry etching apparatus and placed on the stage, and is made up of a silicon wafer, an adhesive such as wax, and a blank substrate made of tungsten, stacked in this order from the lower stage. When heat is generated on the surface side by irradiating plasma from above, even if a cooling device is provided on the lower stage of the dry etching apparatus, the cooling efficiency of the tungsten blank substrate is extremely reduced because the silicon wafer and adhesive such as wax are interposed between the tungsten blank substrate and the stage equipped with the cooling device, even if cooling from the stage is performed from the underside.

[0064] Even if the adhesive, such as wax, has a high thermal conductivity, such as cool grease, the cooling efficiency will still be drastically reduced.

[0065] Therefore, this thermal expansion has conventionally caused a problem in that the interface between the hard mask film pattern and tungsten peels off, resulting in film floating.

[0066] Here, we have discovered that this problem can be solved by sandwiching a material between the hard mask film and tungsten, the material having a thermal expansion coefficient intermediate between the thermal expansion coefficients of the two materials.

[0067] Considering that the hard mask film is made of nickel, copper, or aluminum, it has been discovered that titanium is optimal as a material that exhibits intermediate material properties that are not too close to those of tungsten and are smaller than those of any of the above materials, i.e., nickel, copper, or aluminum.

[0068] In addition, the material properties of the hard mask film are such that the boiling point of the fluoride is higher than that of the tungsten fluoride, and the boiling point of the chloride or oxychloride is lower than that of the fluoride. Here, titanium has similar properties to tungsten, so it is preferable that it can be simultaneously etched under the same etching conditions as tungsten.

[0069] [Manufacturing method for tungsten processed products] FIG. 3 is a schematic cross-sectional view showing a part of the process for manufacturing a tungsten processed product using the first embodiment of the tungsten blank of the present invention in the order of steps, and FIG. 4 is a schematic cross-sectional view showing the manufacturing process following FIG. 3 in the order of steps.

[0070] First, an etching stopper film 2 having a thickness of 1 to 5 μm is formed on a first surface of a blank substrate 1 (thickness 50 to 400 μm, FIG. 3(a)) made of tungsten. The etching stopper film 2 is appropriately selected from materials other than W and Ti (tungsten, titanium) in Table 1, depending on the specifications of the processed product (tungsten thickness, through-hole diameter, processing accuracy, etc.), taking into consideration the etching conditions and etching temperature.

[0071] Possible methods for forming the etching stopper film 2 include chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD), and among these, plasma CVD, vacuum deposition, ion plating, sputtering, etc. can be preferably used.

[0072] Next, an intermediate film 3 having a thickness of 0.2 to 1 μm is formed on a second surface of the blank substrate 1 opposite to the first surface, to form a tungsten blank 100 (FIG. 3(c)).

[0073] Possible methods for forming the intermediate film 3 include chemical vapor deposition (CVD), physical vapor deposition (PVD), and atomic layer deposition (ALD), and among these, plasma CVD, vacuum deposition, ion plating, sputtering, and the like can be preferably used.

[0074] A resist layer 4 having a thickness of 1 to 10 μm is applied onto the intermediate film 3 to form a tungsten blank 100a (FIG. 3(d)). As a resist coating method, for example, general spin coating can be used.

[0075] The produced blank 100a is processed by a resist patterning device such as an exposure device or a drawing device and a process device such as a baking device or a developing device, to form a resist pattern 4a on the blank substrate 1 (FIG. 3(e)).

[0076] Next, a hard mask film 5 having a thickness of 1 to 5 μm is formed on the formed resist 4a and on the blank substrate 1 where no resist 4a is present (FIG. 4(a)). The film formation method may be the same as the film formation method for the etching stopper film 2 in FIG. 3(b) as long as it does not affect the shape of the resist pattern 4a.

[0077] Next, the hard mask film 5 on the resist pattern 4a is selectively removed simultaneously with the resist pattern 4a by a lift-off method using a chemical treatment, to form a hard mask film pattern 5a that is the reverse of the resist pattern 4a (FIG. 4(b)).

[0078] Next, using the hard mask film pattern 5a as an etching mask, the tungsten constituting the intermediate film 3 and the blank substrate 1 is dry-etched using a fluorine-based gas as the main gas to penetrate the intermediate film and the tungsten, resulting in the shapes indicated by the symbols 3a and 1a (FIG. 4(c)). Through this process, the hard mask film pattern 5a becomes a thinned hard mask film pattern 5a', and the intermediate film also becomes an intermediate film pattern 3a that follows the hard mask film pattern.

[0079] The etching gas is primarily a fluorine-based gas, but in order to finish the through-hole more vertically and improve the dimensional accuracy of the diameter depending on the specifications of the processed product (tungsten thickness, through-hole diameter, processing accuracy, etc.), it is preferable to add an oxygen-containing gas or a reducing gas containing at least hydrogen, such as H2, hydrocarbon gas, alcohol gas, hydrogen halide, or ammonia (NH3), to a fluorine-based gas such as CF4, C2F6, or SF6, and etch so as to form a sidewall protective film.

[0080] The etching stopper film 2 is made of a material that is difficult to etch with fluorine-based gases because the boiling point of fluoride is higher than the boiling points of tungsten and titanium fluorides. Therefore, the dry etching time can be set so that the etching is over-etched to the extent that no etching residue or side etching occurs in the through-hole, and the dry etching stops halfway through the etching stopper film 2.

[0081] Finally, the reduced hard mask film pattern 5a', intermediate film pattern 3a, and etching stopper film 2 are removed sequentially or simultaneously to complete the tungsten processing, resulting in a tungsten processed product 10 (FIG. 4(d)). Because the hard mask film pattern 3a' and etching stopper film 2 are made of materials whose chloride or oxychloride boiling points are lower than those of fluorides, they can be removed by dry etching using chlorine-based gases such as Cl2 and BCl3. To avoid damaging the tungsten, it is preferable to perform soft etching at a low power and low rate, and to detect the end point of the removal using optical emission spectroscopy.

[0082] Alternatively, after removing the reduced hard mask film pattern 5a' and the etching stopper film 2 by the above-mentioned dry etching, the intermediate film pattern 3a can be peeled off by a chemical treatment that does not attack tungsten.

[0083] FIG. 5 is a schematic cross-sectional view showing a part of a process for manufacturing a tungsten product using a tungsten blank according to the second embodiment of the present invention in the order of steps, and FIG. 6 is a schematic cross-sectional view showing the manufacturing process following FIG. 5 in the order of steps.

[0084] When using the tungsten blank of the second embodiment of the present invention, the process sequence is only partially different from when a tungsten product is manufactured using the tungsten blank of the first embodiment, and the materials, methods, apparatus, and film thickness used are the same, so a description of those same parts will be omitted.

[0085] In the method for manufacturing a tungsten processed product using the tungsten blank of the second embodiment, first, an etching stopper film 2 is formed on a first surface of a blank substrate 1 (Figure 5(a)) made of tungsten, and a tungsten film 3 and a hard mask film 5 are formed on a second surface opposite to the first surface, to form a tungsten blank 200 (Figure 5(d)).

[0086] Next, a resist layer 4 is applied onto the hard mask film 5 on the second surface to form a tungsten blank 200a (FIG. 5(e)).

[0087] Next, the fabricated blank 200a is processed by a resist patterning device such as an exposure device or a drawing device and a process device such as a baking device or a developing device, to form a resist pattern 4b on the hard mask film 3 (FIG. 5(f)).

[0088] Next, the hard mask film 3 is dry-etched using the resist pattern 4b as a mask to form a hard mask film pattern 5b (FIG. 6(a)).

[0089] Next, using the resist pattern 4b and the hard mask film pattern 5b, or the hard mask film pattern 3b obtained by peeling off the resist pattern 4b, as an etching mask, the tungsten film 3 and the tungsten constituting the blank substrate 1 are dry-etched using a fluorine-based gas as the main gas, in the same manner as in the process of FIG. 4(c), to penetrate the tungsten and form the shape indicated by the reference numeral 1a (FIG. 6(b)). As a result, the hard mask film pattern 5b becomes a hard mask film pattern 5b' with a reduced thickness. At this time, even when the resist pattern 4b and the hard mask film pattern 5b are used as an etching mask, the resist pattern 4b usually disappears during the dry etching of the tungsten.

[0090] Finally, in the same manner as in the first embodiment, the reduced hard mask film pattern 5b', intermediate film pattern 3b, and etching stopper film 2 are removed sequentially or simultaneously to complete the tungsten processing, resulting in a completed tungsten processed product 10 (FIG. 6(c)). The reduced hard mask pattern 5b', intermediate film pattern 3b, and dry etching stopper film 2 can be removed using the same etching gas used to strip the hard mask film pattern 3a'. In this case, it is also preferable to detect the etching endpoint using optical emission spectrometry.

[0091] Alternatively, after removing the reduced hard mask film pattern 5b' and the etching stopper film 2 by the above-mentioned dry etching, the intermediate film pattern 3b can be peeled off by a chemical treatment that does not attack tungsten.

[0092] In both embodiments 1 and 2, an intermediate film with a thermal expansion coefficient intermediate between the thermal expansion coefficients of the hard mask film and the tungsten substrate was sandwiched between them. This solved the problem of the interface between the hard mask film pattern and tungsten peeling off, which would cause film lifting, and made it possible to obtain tungsten processed products with extremely high pattern dimensional accuracy and positional accuracy.

[0093] As explained above, the manufacturing method of the tungsten blanks and tungsten processed products of the present invention can provide tungsten processed products with high processing accuracy at the submicron level, which meets the demands for high aspect ratio processing and high precision processing of thick films that are impossible to achieve with laser processing or the like, and which have through holes with diameters on the order of several tens of μm and aspect ratios of 10 or more, as well as tungsten blanks for such products. [Explanation of symbols]

[0094] 1. Tungsten (blank substrate) 1a Etched tungsten 2. Dry etching stopper film 3. Interlayer 3a, 3b... Interlayer film pattern 4. Resist layer 4a, 4b: Resist pattern 5. Hard mask film 5a, 5b...Hard mask film pattern 5a', 5b': Hard mask film pattern with reduced thickness 10. Tungsten processed products 100 Tungsten blank according to the first embodiment of the present invention 100a: Modified example of the tungsten blank according to the first embodiment of the present invention 200 Tungsten blank according to the second embodiment of the present invention 200a: Modified example of tungsten blank according to the second embodiment of the present invention

Claims

1. A tungsten blank substrate made of tungsten, characterized in that an etching stopper film is laminated on a first surface of the blank substrate, an intermediate film is laminated on a second surface opposite to the first surface, and a hard mask film is laminated on the intermediate film.

2. 2. The tungsten blank according to claim 1, further comprising a resist film on the hard mask film.

3. A tungsten blank substrate comprising a tungsten substrate, characterized in that an etching stopper film is laminated on a first surface of the blank substrate, an intermediate film is laminated on a second surface opposite the first surface, a resist pattern is formed on the intermediate film, and a hard mask film is laminated on the intermediate film and the resist pattern.

4. 4. The tungsten blank according to claim 1, wherein the hard mask film is made of nickel, copper, or aluminum.

5. 5. A tungsten blank according to any one of claims 1 to 4, wherein the intermediate film is made of titanium.

6. A method for producing a tungsten processed product, comprising the following steps in sequence: 1) A step of forming an etching stopper film on a first surface of a blank substrate made of tungsten. 2) forming an intermediate film on a second surface of the blank substrate made of tungsten opposite to the first surface; 3) forming a hard mask film on the intermediate film; 4) forming a resist pattern on the hard mask film. 5) forming a hard mask film pattern using the resist pattern as an etching mask; 6) A step of performing a penetrating process on the intermediate film and tungsten by dry etching using the hard mask film pattern as a mask and primarily using a fluorine-based gas. 7) Step of removing the hard mask film pattern and the etching stopper film.

7. A method for producing a tungsten processed product, comprising the following steps in sequence: 1) A step of forming a dry etching stopper film on a first surface of a blank substrate made of tungsten. 2) forming an intermediate film on a second surface of the blank substrate made of tungsten opposite to the first surface; 3) forming a resist pattern on the intermediate film 4) forming a hard mask film on the intermediate film; 5) A step of removing the hard mask film formed on the resist pattern together with the resist pattern to form a hard mask film pattern. 6) A step of performing a penetrating process on the intermediate film and tungsten by dry etching using the hard mask film pattern as a mask and a fluorine-based gas as the main gas. 7) A step of removing the hard mask film pattern and the dry etching stopper film.

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