Method for manufacturing a hard mask

Abstract

A method for manufacturing a hard mask is provided that makes it possible to adjust the film stress according to the film thickness while making the tungsten film into a fine crystal film. The method includes a first step of forming a tungsten nitride film Ly1 on the surface of a substrate Sw to be processed by a reactive sputtering method using a tungsten target and introducing a rare gas and a nitrogen gas into a processing chamber with a vacuum atmosphere, and a second step of forming a tungsten film Ly2 on the surface of the tungsten nitride film by a sputtering method using a tungsten target and a processing chamber with a vacuum atmosphere. In the first step, the flow rate ratio of the rare gas to the nitrogen gas is set to 1.5 or less and the pressure in the processing chamber is set to 1 Pa or more, and in the second step, the stress according to the thickness of the tungsten film is adjusted by controlling at least one of the total pressure in the processing chamber and the bias power input to the substrate to be processed during film formation.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing a hard mask. [Background technology]

[0002] For example, in the manufacturing process of a semiconductor device, there is a process of performing a dry etching process on a predetermined thin film (e.g., a SiO2 film) formed on a substrate to be processed such as a substrate. At this time, for example, a (metal) hard mask is provided on the surface of the substrate to be processed to limit the processing range of the dry etching. As this type of hard mask, for example, a hard mask having a tungsten nitride film as a base layer and a tungsten film laminated on the tungsten nitride film is known in Patent Document 1. In this hard mask, in the first step, a target is made of tungsten, rare gas and nitrogen gas are introduced into a processing chamber in a vacuum atmosphere, and a tungsten nitride film is formed on the surface of the substrate to be processed by a reactive sputtering method. In the second step, a target is made of tungsten, and a tungsten film is formed on the surface of the tungsten nitride film by a sputtering method in a processing chamber in a vacuum atmosphere. Thereafter, a desired opening is patterned by, for example, lithography technology.

[0003] Here, the tungsten film formed by the sputtering method has a higher density than carbon films and has excellent resistance to dry etching, but it is known that the grain size of the tungsten film is large (100 nm or more), which may cause deterioration of the processed shape during the patterning of the opening in the later process. Therefore, it is desirable for such a tungsten film to be a fine crystal film with a grain size as small as possible, but depending on the application of the tungsten film, it is also required that the film stress be maintained within a predetermined range. For example, when sufficient focusing is required in the lithography process, it is desirable to maintain the film stress within ±300 MPa (more preferably within ±100 MPa). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-27215 Summary of the Invention [Problem to be solved by the invention]

[0005] In view of the above, an object of the present invention is to provide a method for manufacturing a hard mask that makes it possible to adjust the film stress according to the film thickness while forming a tungsten film into a fine crystal film. [Means for solving the problem]

[0006] In order to solve the above problems, a method for producing a hard mask according to the present invention includes a first step of forming a tungsten nitride film on a surface of a substrate to be processed by a reactive sputtering method using a tungsten target and introducing a rare gas and a nitrogen gas into a processing chamber with a vacuum atmosphere, and a second step of forming a tungsten film on the surface of the tungsten nitride film by a sputtering method in the processing chamber with a vacuum atmosphere, wherein the flow rate ratio of the rare gas to the nitrogen gas in the first step is set to 1.5 or less and the flow rate in the processing chamber is set to 1.5 or less. Total Pressure Set to 1 Pa or more death, In the second step, the stress according to the thickness of the tungsten film is adjusted by controlling at least one of the total pressure in the processing chamber and the bias power input to the substrate during film formation. A fine-crystal tungsten film with a grain size of 60 nm or less is formed over the entire surface of the substrate. In this case, in the second step, the total pressure in the processing chamber can be controlled by introducing argon gas so that the total pressure in the processing chamber is in the range of 0.1 Pa to 30 Pa, and the bias power applied to the processing substrate can be controlled by applying a bias power in the range of 0 W to 300 W to the processing substrate.

[0007] Here, as a result of the intensive research of the present inventors, the following has been found. That is, when forming a tungsten nitride film on the surface of the substrate to be processed by reactive sputtering in the first step, if the flow rate ratio of nitrogen gas to rare gas and the pressure in the processing chamber are increased, the grain size of the tungsten film formed in the second step becomes smaller, while the stress (absolute value) of the tungsten film becomes larger. Based on such findings, in the present invention, the flow rate ratio of rare gas to nitrogen gas is set to 1.5 or less and the pressure in the processing chamber is set to 1 Pa or more in the first step to form a tungsten nitride film, and then in the second step, a tungsten film is formed on the surface of the tungsten nitride film, thereby forming a fine-crystal tungsten film with a small grain size (for example, 60 nm or less) over the entire surface of the substrate to be processed. Then, by controlling at least one of the total pressure in the processing chamber and the bias power input to the substrate during film formation in the second step, the stress of the tungsten film can be adjusted to a predetermined range (for example, within ±300 MPa, more preferably, within ±100 MPa) according to the film thickness.

[0008] In the present invention, when the bias power to the substrate is supplied from an AC power source connected via a matching box, the control of the bias power preferably includes the time until impedance matching by the matching box. This makes it possible to effectively adjust the stress of the tungsten film even when the pressure in the processing chamber of the second step is relatively high. [Brief description of the drawings]

[0009] [Figure 1] FIG. 2 is a schematic cross-sectional view showing a hard mask according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view of a sputtering apparatus capable of carrying out the hard mask manufacturing method of the present embodiment. [Diagram 3]4(a) to (c) are AFM images showing the results of an inventive experiment confirming the effects of the present invention, and (d) to (f) and (g) to (i) are AFM images showing the results of comparative experiment 1 and comparative experiment 2. [Figure 4] 1 is a graph showing changes in stress of a tungsten film when the argon gas flow rate is changed. [Diagram 5] 1 is a graph showing the change in stress of a tungsten film when the bias power is changed. [Figure 6] 11 is a graph showing changes in stress of a tungsten film when the time until impedance matching is achieved when bias power is applied is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, with reference to the drawings, an embodiment of the hard mask Hm of the present invention and a manufacturing method thereof will be described. The hard mask Hm is formed on the surface of a substrate Sw to limit the etching processing area when a dry etching process is performed on the substrate Sw.

[0011] Referring to FIG. 1, the hard mask Hm has a tungsten nitride (WN) film Ly1 formed on the surface of the substrate Sw, and a tungsten (W) film Ly2 laminated on the tungsten nitride film Ly1. As the substrate Sw, a substrate such as a silicon wafer or a substrate having a predetermined thin film (for example, an insulating film such as a SiO2 film (TEOS film) or a metal film such as an Al film) formed on the surface thereof can be used. The thickness of the tungsten nitride film Ly1 can be set within a range of, for example, 5 to 15 nm. The thickness of the tungsten film Ly2 can be set within a range of, for example, 100 to 500 nm. An opening Op having a predetermined outline is patterned in the hard mask Hm by a known lithography technique, and a portion of the substrate Sw exposed at the bottom of the opening Op is dry etched to be processed into a desired etching shape. Hereinafter, a method for manufacturing the hard mask Hm of this embodiment will be described.

[0012] Referring to FIG. 2, Sm is a sputtering apparatus capable of implementing the manufacturing method of the hard mask Hm of this embodiment. The sputtering apparatus Sm includes a vacuum chamber 1 capable of forming a vacuum atmosphere, and the vacuum chamber 1 defines a processing chamber Pc. An exhaust pipe 11 leading to a vacuum pump unit Pu consisting of a turbo molecular pump, a rotary pump, or the like is connected to the bottom wall of the vacuum chamber 1, and the vacuum chamber 1 can be evacuated. A conductance valve 12 is interposed in the exhaust pipe 11 so that the effective exhaust speed of the vacuum pump unit Pu can be adjusted. A gas pipe 14 with a mass flow controller 13 interposed therein is connected to the side wall of the vacuum chamber 1, and a rare gas (e.g., argon gas) and nitrogen gas can be introduced at a predetermined flow rate into the vacuum chamber 1 in the vacuum atmosphere. In the following, terms indicating directions such as "upper" and "lower" will be explained based on the installation posture shown in FIG. 2.

[0013] A stage 2 is disposed at the bottom of the vacuum chamber 1. The stage 2 includes a base 21 made of a thermally conductive metal (e.g., SUS) and disposed on the bottom wall of the vacuum chamber 1 via an insulator I1, and a chuck plate 22 disposed on the base 21. An output from a high-frequency power source as a bias power source Pb is connected to the base 21 via a matching box Mb, and a predetermined bias power can be applied to the substrate Sw by applying high-frequency power of a predetermined frequency (e.g., 13.56 MHz) to the base 21 during sputtering. Since the chuck plate 22, bias power source Pb, and matching box Mb can be publicly known, further explanation is omitted. Although not shown or described, a heater and a coolant circulation path are assembled to the base 21, and the substrate Sw can be controlled to a predetermined temperature by thermal conduction from the base 21 by applying electricity to the heater from an external power source or circulating a coolant from a chiller unit not shown in the figure in the coolant circulation path.

[0014] A cathode unit Cu is attached to the ceiling of the vacuum chamber 1. The cathode unit Cu has a tungsten target 3 arranged opposite the substrate Sw, and a magnet unit 4 arranged above the target 3. The target 3 has a shape (circular in plan view) corresponding to the contour of the substrate Sw, and is attached to the lower surface of a backing plate 31 attached to the vacuum chamber 1 via an insulator I2. An output from a sputtering power source E such as a DC power source is connected to the target 3, so that a predetermined power can be input to the target 3 during film formation. The magnet unit 4 can be one having a known structure that generates a magnetic field in the space below the sputtering surface 3a of the target 3, captures electrons ionized below the sputtering surface 3a during sputtering, and efficiently ionizes sputtered particles scattered from the target 3, so a detailed description will be omitted here.

[0015] Although not shown, the sputtering apparatus Sm has a known control means including a microcomputer, a sequencer, or the like, which controls the operation of the sputtering power supply E and the bias power supply Pb, the aperture of the conductance valve 12, the operation of the mass flow controller 13, the operation of the vacuum pump unit Pu, the operation of the magnet unit 4, etc. Hereinafter, a method for manufacturing the hard mask Hm of this embodiment using the above-mentioned sputtering apparatus Sm will be specifically described.

[0016] The substrate Sw is placed on the upper surface of the stage 2 arranged in the vacuum chamber 1, the inside of the vacuum chamber 1 is evacuated to a predetermined pressure, and when the predetermined pressure is reached, argon gas is introduced into the vacuum chamber 1 at a flow rate of 150 to 300 sccm and nitrogen gas is introduced at a flow rate of 100 sccm or more (at this time, the flow rate ratio of argon gas to nitrogen gas is set to 1.5 or less and the pressure in the vacuum chamber 1 is set to 1 Pa or more), and DC power having a negative potential (for example, 2 kW to 6 kW) is input from the sputtering power supply E to the target 3. As a result, a plasma atmosphere is formed in the vacuum chamber 1, and the tungsten target 3 is reactively sputtered, and a tungsten nitride film Ly1 is formed on the surface of the substrate Sw (first step). When the flow rates of argon gas and nitrogen gas are set so that the flow rate ratio of argon gas to nitrogen gas is 1.5 or less and the pressure in the vacuum chamber 1 does not reach 1 Pa, the effective pumping speed of the vacuum pump unit Pu is adjusted by adjusting the opening of the conductance valve 12 to maintain the pressure in the vacuum chamber 1 at 1 Pa or more. However, if the pressure in the vacuum chamber 1 becomes, for example, 30 Pa or more, it becomes difficult to adjust the stress of the tungsten film in the second step described below. In the first step, a bias power (for example, 50 W to 300 W) may be input from the bias power supply Pb to the substrate Sw during film formation.

[0017] When the tungsten nitride film Ly1 is formed on the surface of the substrate Sw with a predetermined thickness (after the first step), the introduction of only the nitrogen gas is stopped, and only argon gas is introduced into the vacuum chamber 1 with a flow rate of 150 to 300 sccm (at this time, the pressure in the vacuum chamber 1 is 0.1 Pa to 30 Pa), and the power input from the sputtering power source E to the target 3 is changed to, for example, a range of 4 kW to 12 kW. As a result, the tungsten target 3 is sputtered, and a tungsten film Ly2 is formed (laminate) on the surface of the tungsten nitride film Ly1 with a predetermined thickness (second step). In the second step, as in the first step, a bias power (for example, 50 W to 300 W) may be input from the bias power source Pb to the substrate Sw. Then, after the formation of the tungsten film Ly2 is completed, an opening Op is patterned and formed in the tungsten film Ly2 and the tungsten nitride film Ly1 using a known lithography technique or the like. If the pressure inside the vacuum chamber 1 exceeds 30 Pa in the second step, it becomes difficult to adjust the stress of the tungsten film.

[0018] As described above, in the first step, the flow rate ratio of the rare gas to the nitrogen gas is set to 1.5 or less and the pressure in the vacuum chamber 1 is set to 1 Pa or more, and then in the second step, a tungsten film Ly2 is formed on the surface of the tungsten nitride film Ly1, thereby making it possible to form a fine-crystalline tungsten film Ly2 having a small grain size (e.g., 60 nm or less) over the entire surface of the substrate Sw.

[0019] In order to confirm the above effect, the following experiment was carried out using the sputtering device Sm. In the invention experiment, a substrate Sw was prepared by depositing a SiO2 (TEOS) film of 100 nm on the surface of a silicon wafer of Φ300 mm, and argon gas was introduced into the vacuum chamber 1 at a flow rate of 300 sccm and nitrogen gas at a flow rate of 200 sccm (the flow rate ratio of argon gas to nitrogen gas was 1.5), while adjusting the aperture of the conductance valve 12 so that the pressure in the vacuum chamber 1 was maintained at 1 Pa. Then, 3 kW of DC power was applied to the tungsten target 3, and 300 W of bias power was applied to the substrate Sw, to deposit a tungsten nitride film Ly1 of 5 nm (first step). After that, argon gas was introduced into the vacuum chamber 1 at a flow rate of 150 sccm, and 6 kW of DC power was applied to the tungsten target 3, to deposit a tungsten film Ly2 of 195 nm (second step). The results of observation (AFM images) of the surface of the tungsten film Ly2 in the center (FIG. 3(a)), periphery (FIG. 3(b)), and intermediate region (FIG. 3(c)) of the substrate Sw on which the tungsten film Ly2 was formed by an atomic force microscope (AFM) are shown in FIGS. 3(a) to 3(c). As a result, it was confirmed that the tungsten film Ly2 was a fine crystal with a small grain size over the entire in-plane surface of the substrate Sw, as compared with those in Comparative Experiment 1 (FIGS. 3(d) to 3(f)) and Comparative Experiment 2 (FIGS. 3(g) to 3(i)), which will be described later. Furthermore, when the surface of this tungsten film Ly2 was observed by a scanning transmission electron microscope (STEM), the grain size was 60 nm or less.

[0020] As a comparative experiment 1 for the above-mentioned invention experiment, a substrate Sw on which a tungsten film Ly2 was formed was obtained in the same manner as the above-mentioned invention experiment, except that the flow rate of the argon gas introduced into the vacuum chamber 1 in the first step was 150 sccm, the flow rate of the nitrogen gas was 70 sccm (the flow rate ratio of the argon gas to the nitrogen gas was 2.1), and the pressure in the vacuum chamber 1 was maintained at less than 1 Pa. Also, as in the above-mentioned invention experiment, the surface of the tungsten film Ly2 in the center (FIG. 3(d)), the periphery (FIG. 3(e)), and the intermediate region (FIG. 3(f)) of the substrate Sw on which the tungsten film Ly2 was formed was observed by AFM. As a result, it was confirmed that the tungsten film Ly2 was a crystalline film with a large grain size over the entire surface of the substrate Sw compared to that of the above-mentioned invention experiment. Also, when the surface of this tungsten film Ly2 was observed by STEM, the grain size was 100 nm or more.

[0021] In Comparative Experiment 2, a substrate Sw on which a tungsten film Ly2 was formed was obtained in the same manner as in the above-mentioned inventive experiment, except that the flow rate of the argon gas introduced into the vacuum chamber 1 in the first step was 132 sccm, the flow rate of the nitrogen gas was 88 sccm (the flow rate ratio of argon gas to nitrogen gas was 1.5), and the pressure inside the vacuum chamber 1 was maintained at less than 1 Pa. In addition, as in the above-mentioned inventive experiment, the surface of the tungsten film Ly2 in the center (FIG. 3(g)), peripheral portion (FIG. 3(h)), and intermediate region (FIG. 3(i)) of the substrate Sw on which the tungsten film Ly2 was formed was observed by AFM, and it was confirmed that the center and intermediate regions were fine crystals with small grain sizes, while the peripheral region was a crystalline film with large grain sizes.

[0022] Next, an experiment was conducted to form a tungsten film Ly2 on the surface of the tungsten nitride film Ly1 using a substrate Sw on which a tungsten nitride film Ly1 had been formed under the conditions of the first step of the above-mentioned invention experiment (i.e., the flow rate ratio of argon gas to nitrogen gas was 1.5 and the pressure in the vacuum chamber 1 was 1 Pa). In this case, the input power (DC power) to the tungsten target 3 was set to 6 kW. Then, in the second step, the flow rate of the argon gas introduced into the vacuum chamber 1 was changed in the range of 150 to 300 sccm, and the tungsten film Ly2 was formed to a thickness of 195 nm (at this time, the pressure in the vacuum chamber 1 was in the range of 0.1 Pa to 30 Pa). The stress (MPa) of the tungsten film Ly2 formed by changing the argon gas flow rate was measured by a thin film stress measurement device, and the results are shown in FIG. 4. According to this, it was confirmed that when the flow rate of the argon gas introduced into the vacuum chamber 1 in the second step, i.e., the pressure (total pressure) in the vacuum chamber 1, increases, the stress of the tungsten film Ly2 changes from the compression direction to the tensile direction via the zero point, and then increases in the tensile direction. It was also confirmed that the tungsten film Ly2 formed by changing the argon gas flow rate was also fine crystal with a small grain size over the entire in-plane surface of the substrate Sw.

[0023] In addition, the substrate Sw on which the tungsten nitride film Ly1 was formed under the conditions of the first step of the invention experiment was used, and in the second step, the input power (DC power) to the tungsten target 3 was set to 6 kW, and the flow rate of the argon gas introduced into the vacuum chamber 1 was set to 300 sccm. Then, the bias power input from the bias power supply Pb to the substrate Sw was changed in the range of 0 to 300 W, and the tungsten film Ly2 was formed to a thickness of 195 nm. The stress (MPa) of the tungsten film Ly2 formed by changing the bias power was measured by a thin film stress measurement device, and the result is shown in FIG. 5. According to this, it was confirmed that when the input bias power increased, the stress of the tungsten film Ly2 changed from the tensile direction to the compressive direction via the zero point, and further increased in the compressive direction. It was confirmed that the tungsten film Ly2 formed by changing the bias power was also a fine crystal with a small grain size over the entire surface of the substrate Sw.

[0024] Furthermore, a substrate Sw on which a tungsten nitride film Ly1 was formed under the conditions of the first step of the invention experiment was used, and in the second step, the power (DC power) input to the tungsten target 3 was set to 6 kW, the flow rate of argon gas introduced into the vacuum chamber 1 was set to 150 sccm, the pressure in the vacuum chamber 1 was set to 10 Pa or more, and the bias power input from the bias power supply Pb to the substrate Sw was set to 800 W. Then, the time until impedance matching by the matching box Mb was changed in the range of 0.5 to 2.0 s, and a tungsten film Ly2 was formed to a thickness of 195 nm. The stress (MPa) of the tungsten film Ly2 formed by changing the time until impedance matching was measured by a thin film stress measurement device, and the results are shown in FIG. 6. According to this, it was confirmed that the stress of the tungsten film Ly2 decreased in the compression direction when the time until impedance matching was extended. It was also confirmed that the tungsten film Ly2 formed by changing the time until impedance matching was made up of fine crystals with small grain sizes over the entire in-plane surface of the substrate Sw.

[0025] Based on the above findings, by controlling at least one of the total pressure in the vacuum chamber 1 and the bias power input to the substrate Sw during film formation in the second step, the stress of the tungsten film Ly2 can be adjusted to a predetermined range (for example, within ±300 MPa, more preferably, within ±100 MPa) according to its film thickness. In addition, when the bias power to the substrate Sw is input from a bias power supply Pb connected via a matching box Mb, by controlling the time until impedance matching by the matching box Mb, the stress of the tungsten film Ly2 can also be adjusted to a predetermined range according to its film thickness even when the pressure in the vacuum chamber 1 in the second step is relatively high (for example, 10 Pa or higher).

[0026] Although the embodiment of the present invention has been described above, various modifications are possible without departing from the scope of the technical concept of the present invention. In the above embodiment, the total pressure in the vacuum chamber 1, the bias power input to the substrate Sw during film formation, and the time until impedance matching are changed individually to adjust the stress of the tungsten film Ly2, but two or more of these conditions can be changed simultaneously to adjust the stress of the tungsten film Ly2. [Explanation of symbols]

[0027] Mb...matching box, Ly1...tungsten nitride film, Ly2...tungsten film, Pb...bias power supply (AC power supply), Pc...processing chamber, Sw...substrate (substrate to be processed), 3...target.

Claims

1. a first step of forming a tungsten nitride film on a surface of a substrate to be processed by a reactive sputtering method using a tungsten target and introducing a rare gas and a nitrogen gas into a processing chamber with a vacuum atmosphere; a second step of forming a tungsten film on the surface of the tungsten nitride film by a sputtering method in a processing chamber in a vacuum atmosphere using a tungsten target, In the first step, the flow rate ratio of the rare gas to the nitrogen gas is set to 1.5 or less and the pressure in the processing chamber is set to 1 Pa or more; A method for manufacturing a hard mask, comprising the steps of: adjusting a stress according to a thickness of a tungsten film by controlling at least one of a total pressure in the processing chamber and a bias power input to a processing substrate during film formation in a second step;

2. The method for manufacturing a hard mask as described in claim 1, characterized in that in the second step, argon gas is introduced so that the total pressure in the processing chamber is in the range of 0.1 Pa to 30 Pa.

3. A method for manufacturing a hard mask as described in claim 1 or 2, characterized in that in the second step, a bias power in the range of 0 W to 300 W is applied to the processed substrate.

4. A method for manufacturing a hard mask as described in claim 1 or 2, characterized in that the stress according to the thickness of the tungsten film is adjusted to within ±300 MPa.

5. 2. The method for producing a hard mask according to claim 1, wherein bias power to the substrate is supplied from an AC power source connected via a matching box, The method for manufacturing a hard mask, wherein the control of the bias power includes a time required for impedance matching by a matching box.

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