Film formation method and tungsten film

Abstract

To provide a film deposition method capable of simply obtaining a tungsten film having reduced film stress, and the tungsten film.SOLUTION: A film deposition method for depositing a tungsten film comprises the steps of preparing a substrate and depositing the tungsten film on the substrate. A chlorine containing tungsten film having film stress controlled by chlorine concentration in the film is deposited as at least a part of the tungsten film.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a deposition method and a tungsten film. [Background technology]

[0002] In the semiconductor manufacturing process, tungsten is used as a material for filling contact holes and via holes between wirings formed on a substrate (semiconductor wafer), as well as a material for interdiffusion barriers.

[0003] A known method for forming a tungsten film is to form the film by a CVD method using, for example, tungsten hexafluoride (WF6) and a reducing gas as source gases. Patent Document 1 describes that when forming a blanket tungsten film using WF6, the tensile stress of the film increases when the substrate temperature is low, about 400°C. To solve this problem, it describes performing pretreatment using a mixed gas of WF6 and monosilane in a predetermined ratio.

[0004] On the other hand, in recent years, design rules have become increasingly finer, and there are concerns that raw materials containing fluorine may have a negative effect on devices. Therefore, a technique for forming a tungsten film by CVD or ALD using tungsten chloride as a raw material gas has also been proposed (e.g., Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-307480 [Patent Document 2] International Publication No. 2015 / 080058 Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure provides a film formation method and a tungsten film that can easily produce a tungsten film with reduced film stress.

[0007] According to one aspect of the present disclosure Film forming method is a film formation method for forming a tungsten film, comprising the steps of preparing a substrate and forming a tungsten film on the substrate, wherein at least a portion of the tungsten film is a chlorine-containing tungsten film in which the chlorine concentration in the film is increased to more than 2 at % to adjust the film stress, and the chlorine-containing tungsten film has a tensile stress or compressive stress lower than that of a tungsten film in which the chlorine concentration in the film is 2 at % or less. The step of forming the tungsten film includes forming an initial tungsten film on the substrate, the initial tungsten film having a lower chlorine concentration than the chlorine-containing tungsten film, and then forming the chlorine-containing tungsten film thereon. . [Effects of the Invention]

[0008] According to the present disclosure, a tungsten film with reduced film stress can be easily obtained. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a state in which warpage occurs in a substrate due to tensile stress of a tungsten film. [Figure 2] 1 is a flowchart illustrating a film forming method according to an embodiment. [Figure 3] FIG. 1 is a diagram showing a model for explaining the mechanism by which a tungsten film has tensile stress. [Figure 4] FIG. 1 is a diagram showing a model for explaining the mechanism by which the tensile stress of a tungsten film containing a large amount of chlorine, 4 at % or more, decreases. [Figure 5] 1A to 1C are cross-sectional views illustrating a method for manufacturing a tungsten film according to an embodiment. [Figure 6] FIG. 1 is a cross-sectional view showing an example of a film formation apparatus used to form a tungsten film. [Figure 7] FIG. 1 is a diagram showing the structure of a sample used in an experimental example. [Figure 8] 1A and 1B are diagrams for explaining tensile stress and compressive stress of a film. [Figure 9]FIG. 10 is a diagram showing the relationship between film thickness and film stress when the substrate temperature is changed in an experimental example. [Figure 10] FIG. 10 is a diagram showing the relationship between film thickness and film stress when the H 2 gas flow rate (H 2 gas partial pressure) is changed. [Figure 11] FIG. 10 is a diagram showing the relationship between film thickness and film stress when a tungsten film is formed under Low Temp, Low H2, and normal conditions (Ref) in an experimental example. [Figure 12] FIG. 10 is a diagram showing the results of measuring the chlorine (Cl) concentration of tungsten films at Low Temp, Low H2, and Ref in an experimental example, by X-ray photoelectron spectroscopy (XPS). [Figure 13] FIG. 10 is a diagram showing the results of X-ray diffraction (XRD) performed on tungsten films at LowTemp, LowH2, and Ref in an experimental example. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments will be described with reference to the accompanying drawings.

[0011] <Summary> Tungsten films generally have tensile stress. The tensile stress of a tungsten film exhibits a high value proportional to the film thickness. Therefore, as shown in FIG. 1, when a tungsten film 201 is formed on a substrate 200 such as a semiconductor wafer, the tensile stress can cause warping of the substrate 200. Peeling of the tungsten film 201 can also occur. If the wafer 200 warps, problems such as transport errors and out-of-focus exposure may occur, and peeling can cause particles.

[0012] 2, a film formation method according to one embodiment includes a step of preparing a substrate (step ST1) and a step of forming a tungsten film on the substrate (step ST2). In step ST2, a chlorine-containing tungsten film is formed as at least a portion of the tungsten film, with the film stress adjusted by the chlorine concentration in the film. By adjusting the chlorine concentration of the tungsten film, the tensile stress can be reduced compared to that of a normal tungsten film, and a tungsten film with reduced tensile stress can be easily obtained.

[0013] For example, when a tungsten film is formed by CVD or ALD using tungsten chloride gas and a reducing gas, the chlorine concentration in the film is typically about 2 at% and the tensile stress of the film is high, at 1700-1900 MPa, when the film thickness is about 50-100 nm. In contrast, increasing the chlorine concentration in the film can reduce the tensile stress. Furthermore, by increasing the chlorine concentration in the film to 4 at% or higher, the tensile stress can be reduced to 500 MPa or less, and the film stress can even be made compressive.

[0014] The mechanism by which tungsten films generally have tensile stress can be explained by the model shown in Figure 3. As shown in Figure 3(a), the size of the crystal lattice 211 of the tungsten crystal is smaller than the size of the crystal lattice 212 of the underlying silicon crystal. Therefore, when a tungsten film is formed on a silicon wafer substrate, the tungsten crystal lattice 211 is pulled by the silicon crystal lattice 212, resulting in tensile stress, as shown in Figure 3(b). Therefore, as shown in Figure 3(c), the tungsten film 222 formed on the silicon wafer 221 has tensile stress as a whole. This tendency remains unchanged even if the film contains approximately 2 at% chlorine as an impurity.

[0015] In contrast, the mechanism by which the tensile stress of a tungsten film containing a large amount of chlorine (e.g., 4 at% or more) decreases and even becomes compressive can be explained by the model shown in Figure 4. The crystal lattice 213 of a high-chlorine-containing tungsten crystal containing a large amount of chlorine 214 is larger than the normal crystal lattice 211. As a result, the crystal lattice 213 approaches the size of the crystal lattice 212 of the silicon crystal, and in some cases, as shown in Figure 4(a), the size of the crystal lattice 213 of the tungsten crystal becomes larger than the size of the crystal lattice 212 of the silicon crystal. When the size of the crystal lattice 213 of the high-chlorine-containing tungsten crystal approaches the size of the crystal lattice 212 of the silicon crystal, the tensile stress is alleviated. Furthermore, when the crystal lattice 213 of the tungsten crystal becomes larger as shown in Figure 4(a), the tungsten crystal lattice 213 is pulled by the silicon crystal lattice 212, resulting in compressive stress, as shown in Figure 4(b). In this case, as shown in FIG. 4(c), the high chlorine concentration tungsten film 223 formed on the silicon wafer 221 will have compressive stress as a whole.

[0016] The tungsten film may be a chlorine-containing tungsten film with an adjusted chlorine concentration as described above. However, a tungsten film with a high chlorine concentration (e.g., 4 at% or higher) is difficult to deposit on a silicon wafer or a TiN film as an underlayer using a typical CVD or ALD method. For this reason, as shown in FIG. 5(a), an initial tungsten film 233 with a low chlorine concentration and tensile stress is deposited under normal conditions on a substrate 230 having a TiN film 232 formed as an underlayer on a silicon substrate 231, so that a chlorine-containing tungsten film with a high chlorine concentration can be deposited. Then, as shown in FIG. 5(b), a chlorine-containing tungsten film 234 is deposited on the initial tungsten film 233. The initial tungsten film 233 and the chlorine-containing tungsten film 234 form a tungsten film 235. The thickness of the TiN film 232 is preferably 0.1 nm or more, more preferably in the range of 0.5 to 10 nm. The thickness of the initial tungsten film 233 is preferably 0.5 nm or more, and more preferably in the range of 1 to 15 nm. By forming the initial tungsten film 233 in this manner, it is possible to broaden the conditions under which the chlorine-containing tungsten film 234 can be formed. Furthermore, a tungsten film having tensile stress under normal conditions may be formed on the chlorine-containing tungsten film 234.

[0017] As described above, the tungsten film formed by stacking a chlorine-containing tungsten film and a tungsten film having tensile stress under normal conditions can alleviate or offset the stress of the tungsten film having tensile stress when the chlorine-containing tungsten film has compressive stress.In addition, even when the chlorine-containing tungsten film has low tensile stress, the stress of the entire film can be alleviated.

[0018] Next, an example of a method for obtaining a chlorine-containing tungsten film with a high chlorine concentration that can reduce tensile stress will be described in a typical example of forming a tungsten film by CVD or ALD using tungsten chloride gas and a reducing gas.

[0019] The usual conditions for forming a tungsten film using tungsten chloride gas and reducing gas are a substrate temperature of 400°C or higher and a flow rate of H2 gas supplied as reducing gas of 1000 to 10000 sccm (H2 gas partial pressure 3.73 to 21.36 Torr (497 to 2848 Pa)). is. The tungsten film formed under these conditions exhibits a high tensile stress of 1700 to 1900 MPa at a film thickness of about 50 to 100 nm, and the chlorine concentration in the film is low at 2 at% or less.

[0020] In contrast, lowering the substrate temperature or reducing the H gas flow rate (reducing the H gas partial pressure) can increase the chlorine concentration in the tungsten film and reduce the film stress. Specifically, by setting the substrate temperature below 380°C or the H gas flow rate below 800 sccm (H gas partial pressure below 3.03 Torr (404 Pa)), the chlorine concentration can be increased compared to tungsten films formed under normal conditions, reducing the film's tensile stress. At a substrate temperature of 380°C or an H gas flow rate (H gas partial pressure) below 800 sccm (H gas partial pressure below 3.03 Torr (404 Pa)), the chlorine concentration in the film can be increased to 4 at% or higher. Furthermore, at a H gas flow rate (H gas partial pressure) below 500 sccm (H gas partial pressure below 1.95 Torr (259 Pa)), the film's tensile stress can be reduced to 500 MPa or lower, or the film stress can be reduced to compressive stress. In order to increase the chlorine concentration in the tungsten film, both the substrate temperature and the H2 gas flow rate may be reduced.

[0021] The above-mentioned Patent Document 1 describes that when a tungsten film is formed by CVD using WF6 and a reducing gas, the tensile stress increases when the substrate temperature drops to a low temperature of about 400°C, so that the tensile stress is reduced by performing pretreatment using a mixed gas of WF6 and monosilane in a predetermined ratio. However, the method described in Patent Document 1 requires complicated processes, and there is also concern that the fluorine contained in WF6 may adversely affect the device, so a different approach is required.

[0022] In this embodiment, when a tungsten film is formed on a substrate, a chlorine-containing tungsten film in which the film stress is adjusted by adjusting the chlorine concentration in the film is used as at least a part of the tungsten film, so that a tungsten film with low tensile stress can be easily obtained without pretreatment. In particular, a tungsten film with a chlorine concentration of 4 at % or more has a low tensile stress. of 500MPa or less can be Since the stress in the film can be made compressive, the effect of reducing the stress in the entire tungsten film is significant.

[0023] <Specific embodiment> Next, a specific embodiment in which a tungsten film is formed by the ALD method will be described.

[0024] [Example of film deposition equipment] FIG. 6 is a cross-sectional view showing an example of a film formation apparatus used when forming a tungsten film by the ALD method.

[0025] The film forming apparatus 100 includes a chamber 1, a susceptor 2 for horizontally supporting a semiconductor wafer (hereinafter simply referred to as a wafer) W as a substrate within the chamber 1, a shower head 3 for supplying a process gas into the chamber 1 in a shower-like manner, an exhaust unit 4 for evacuating the inside of the chamber 1, a process gas supply mechanism 5 for supplying the process gas to the shower head 3, and a control unit 6.

[0026] The chamber 1 is made of a metal such as aluminum and has a substantially cylindrical shape. A loading / unloading port 11 is formed in the side wall of the chamber 1 for loading and unloading the wafer W, and the loading / unloading port 11 can be opened and closed by a gate valve 12. An annular exhaust duct 13 with a rectangular cross section is provided above the main body of the chamber 1. A slit 13a is formed along the inner peripheral surface of the exhaust duct 13. An exhaust port 13b is formed in the outer wall of the exhaust duct 13. A ceiling wall 14 is provided on the upper surface of the exhaust duct 13 to close the upper opening of the chamber 1. A seal ring 15 provides an airtight seal between the ceiling wall 14 and the exhaust duct 13.

[0027] The susceptor 2 has a disk shape and a size corresponding to the wafer W, and is supported by a support member 23. The susceptor 2 is made of a ceramic material such as aluminum nitride (AlN) or a metal material such as aluminum or a nickel-based alloy, and has a heater 21 embedded therein for heating the wafer W. The heater 21 generates heat when power is supplied from a heater power supply (not shown). The output of the heater 21 is controlled by a temperature signal from a thermocouple (not shown) provided near the wafer-mounting surface on the upper surface of the susceptor 2, thereby controlling the temperature of the wafer W to a predetermined value.

[0028] The susceptor 2 is provided with an outer ring 22 made of ceramics such as alumina so as to cover the outer peripheral region of the wafer mounting surface and the side surfaces of the susceptor 2 .

[0029] A support member 23 that supports the susceptor 2 extends from the center of the bottom surface of the susceptor 2 to below the chamber 1, passing through a hole formed in the bottom wall of the chamber 1, and its lower end is connected to an elevation mechanism 24, which enables the susceptor 2 to be raised and lowered via the support member 23 between a processing position shown in Fig. 6 and a transfer position shown by a dashed line below that position where a wafer can be transferred. In addition, a flange 25 is attached to the support member 23 below the chamber 1, and a bellows 26 is provided between the bottom surface of the chamber 1 and the flange 25 to separate the atmosphere inside the chamber 1 from the outside air, and which expands and contracts as the susceptor 2 is raised and lowered.

[0030] Three wafer support pins 27 (only two shown) are provided near the bottom surface of the chamber 1, protruding upward from a lift plate 27a. The wafer support pins 27 can be raised and lowered via the lift plate 27a by a lift mechanism 28 provided below the chamber 1, and are inserted into through holes 2a provided in the susceptor 2 at the transfer position, so that they can be protruded and retracted relative to the upper surface of the susceptor 2. By raising and lowering the wafer support pins 27 in this manner, the wafer W is transferred between a wafer transfer mechanism (not shown) and the susceptor 2.

[0031] The showerhead 3 is made of metal, is disposed opposite the susceptor 2, and has approximately the same diameter as the susceptor 2. The showerhead 3 has a main body 31 fixed to the ceiling wall 14 of the chamber 1, and a shower plate 32 connected below the main body 31. A gas diffusion space 33 is formed between the main body 31 and the shower plate 32.

[0032] A plurality of distribution blocks 46 are provided within the gas diffusion space 33. A plurality of gas discharge holes are formed around the periphery of the distribution block 46, and are configured to distribute the gas. The distribution block 46 is connected to one end of each of a plurality of gas supply paths 47 provided in the main body 31. The other ends of the gas supply paths 47 are connected to a diffusion section 45 formed in the center of the upper surface of the main body 31. In addition, a gas introduction hole 36 is provided in the center of the main body 31, penetrating from the upper surface to the diffusion section 45.

[0033] A downwardly protruding annular protrusion 34 is formed on the periphery of the shower plate 32, and gas ejection holes 35 are formed on the flat surface inside the annular protrusion 34 of the shower plate 32.

[0034] When the susceptor 2 is in the processing position, a processing space 37 is formed between the shower plate 32 and the susceptor 2, and the annular protrusion 34 and the upper surface of the cover member 22 of the susceptor 2 are close to each other to form an annular gap 38.

[0035] The exhaust unit 4 includes an exhaust pipe 41 connected to the exhaust port 13b of the exhaust duct 13, and an exhaust mechanism 42 having a vacuum pump, an APC (Adjustable Pressure Control Valve), etc., connected to the exhaust pipe 41. During processing, gas inside the chamber 1 reaches the exhaust duct 13 through the slit 13a, and is exhausted from the exhaust duct 13 through the exhaust pipe 41 by the exhaust mechanism 42 of the exhaust unit 4.

[0036] The process gas supply mechanism 5 includes a WCl5 gas supply mechanism 51 that supplies WCl5 gas as tungsten chloride, which is a tungsten source gas, an H2 gas supply source 52 that supplies H2 gas as a reducing gas, a first N2 gas supply source 54 and a second N2 gas supply source 55 that supply N2 gas as a purge gas, a WCl5 gas supply line 61 extending from the WCl5 gas supply source 51, an H2 gas supply line 62 extending from the H2 gas supply source 52, a first N2 gas supply line 64 extending from the first N2 gas supply source 54 to supply N2 gas to the WCl5 gas supply line 61 side, and a second N2 gas supply line 65 extending from the second N2 gas supply source 55 to supply N2 gas to the H2 gas supply line 62 side. Note that the tungsten chloride is not limited to WCl5, and WCl4 or WCl6 may also be used.

[0037] The first N2 gas supply line 64 branches into a first continuous N2 gas supply line 66, which constantly supplies N2 gas during film formation by the ALD method, and a first flush purge line 67, which only supplies N2 gas during the purge process. The second N2 gas supply line 65 branches into a second continuous N2 gas supply line 68, which constantly supplies N2 gas during film formation by the ALD method, and a second flush purge line 69, which only supplies N2 gas during the purge process. The first continuous N2 gas supply line 66 and the first flush purge line 67 are connected to a first connection line 70, which is connected to the WCl5 gas supply line 61. The second continuous N2 gas supply line 68 and the second flush purge line 69 are connected to a second connection line 71, which is connected to the H2 gas supply line 62. The WCl5 gas supply line 61 and the H2 gas supply line 62 join together at a joining pipe 72, which is connected to the gas inlet hole 36 described above.

[0038] On the most downstream sides of the WCl5 gas supply line 61, the H2 gas supply line 62, the first continuous N2 gas supply line 66, the first flush purge line 67, the second continuous N2 gas supply line 68, and the second flush purge line 69, opening / closing valves 73, 74, 76, 77, 78, and 79 for switching gases during ALD are provided, respectively. Furthermore, on the upstream sides of the opening / closing valves of the H2 gas supply line 62, the first continuous N2 gas supply line 66, the first flush purge line 67, the second continuous N2 gas supply line 68, and the second flush purge line 69, mass flow controllers 82, 84, 85, 86, and 87 are provided, respectively, as flow rate controllers. Furthermore, the WCl5 gas supply line 61 and the H2 gas supply line 62 are provided with buffer tanks 80 and 81, respectively, to enable the required gas supply in a short time.

[0039] The WCl5 gas supply mechanism 51 has a film-forming raw material tank 91 that stores WCl5. WCl5 is solid at room temperature, and solid WCl5 is stored in the film-forming raw material tank 91. A heater 91a is provided around the film-forming raw material tank 91, and heats the film-forming raw material in the tank 91 to an appropriate temperature to sublimate the WCl5. The above-mentioned WCl5 gas supply line 61 is inserted into the tank 91 from above.

[0040] The WCl5 gas supply mechanism 51 also includes a carrier gas pipe 92 inserted from above into the film-forming raw material tank 91, a carrier N2 gas supply source 93 for supplying N2 gas as a carrier gas to the carrier gas pipe 92, a mass flow controller 94 as a flow rate controller connected to the carrier gas pipe 92, on-off valves 95a and 95b downstream of the mass flow controller 94, and on-off valves 96a and 96b and a flow meter 97 provided on the WCl5 gas supply line 61 near the film-forming raw material tank 91. In the carrier gas pipe 92, the on-off valve 95a is provided directly below the mass flow controller 94, and the on-off valve 95b is provided on the insertion end side of the carrier gas pipe 92. The on-off valves 96a and 96b and the flow meter 97 are arranged in this order from the insertion end of the WCl5 gas supply line 61.

[0041] A bypass pipe 98 is provided to connect a position between on-off valves 95a and 95b of the carrier gas pipe 92 and a position between on-off valves 96a and 96b of the WCl5 gas supply line 61, and an on-off valve 99 is interposed in the bypass pipe 98. By closing the on-off valves 95b and 96a and opening the on-off valves 99, 95a, and 96b, N2 gas from the carrier N2 gas supply source 93 can be supplied to the WCl5 gas supply line 61 via the carrier gas pipe 92 and the bypass pipe 98, thereby purging the WCl5 gas supply line 61.

[0042] One end of an evacuated piping 101 is connected to a position downstream of the flow meter 97 on the WCl5 gas supply line 61, and the other end of the evacuated piping 101 is connected to the exhaust piping 41. Open / close valves 102 and 103 are provided on the evacuated piping 101 near the WCl5 gas supply line 61 and near the exhaust piping 41, respectively. In addition, an open / close valve 104 is provided on the WCl5 gas supply line 61 downstream of the connection position of the evacuated piping 101. The inside of the film-forming raw material tank 91 can be evacuated to a vacuum by the exhaust mechanism 42 by opening the open / close valves 102, 103, 96a, and 96b while keeping the open / close valves 104, 99, 95a, and 95b closed.

[0043] The control unit 6 is configured by a computer and includes a main control unit with a CPU, an input device, an output device, a display device, and a storage device (storage medium). The main control unit controls, for example, the opening and closing of valves, the gas flow rate controlled by a flow rate controller, the opening of a pressure control valve (APC), and the output of a heater that heats the wafer W.

[0044] [Film forming method] Next, a method for forming a tungsten film on a wafer W using the film forming apparatus of FIG. 6 will be described.

[0045] First, a wafer W, which is a substrate, is loaded into chamber 1 through loading / unloading port 11 and placed on susceptor 2 heated to a predetermined temperature by heater 21. Then, susceptor 2 is raised to a processing position. Then, chamber 1 is evacuated to a predetermined vacuum level, and on-off valves 104, 95a, 95b, and 99 are closed. On-off valves 102, 103, 96a, and 96b are opened. The film-forming source tank 91 is also evacuated via evacuator piping 101. Then, on-off valves 76 and 78 are opened, and on-off valves 73, 74, 77, and 79 are closed. N gas is supplied from first N gas supply source 54 and second N gas supply source 55 through first continuous N gas supply line 66 and second continuous N gas supply line 68 into chamber 1 to increase the pressure and stabilize the temperature of wafer W on susceptor 2.

[0046] After the pressure inside the chamber 1 reaches a predetermined level, the on-off valves 102 and 103 are closed, and the on-off valves 104, 95a, and 95b are opened to increase the pressure inside the film forming raw material tank 91 so that WCl5 gas, which is a tungsten raw material, can be supplied.

[0047] In this state, WCl5 gas as a film-forming source gas, H2 gas as a reducing gas, and N2 gas as a purge gas are supplied in the following sequential manner to form a tungsten film.

[0048] First, with the on-off valve 76 and the on-off valve 78 open, N2 gas continues to be supplied from the first N2 gas supply source 54 and the second N2 gas supply source 55 via the first continuous N2 gas supply line 66 and the second continuous N2 gas supply line 68, and by further opening the on-off valve 73, WCl5 gas is supplied from the WCl5 gas supply mechanism 51 via the WCl5 gas supply line 61 to the processing space 37 in the chamber 1. At this time, the WCl5 gas is temporarily stored in the buffer tank 80 and then supplied into the chamber 1. As a result, the WCl5 gas is adsorbed onto the surface of the wafer W.

[0049] Next, while continuing to supply N2 gas via the first continuous N2 gas supply line 66 and the second continuous N2 gas supply line 68, the on-off valve 73 is closed to stop the WCl5 gas, and the on-off valves 77 and 79 are opened to supply N2 gas (flash purge N2 gas) from the first flush purge line 67 and the second flush purge line 69 as well, and excess WCl5 gas and the like in the processing space 37 is purged with a large flow rate of N2 gas.

[0050] Next, the on-off valves 77 and 79 are closed to stop the supply of N gas from the first flush purge line 67 and the second flush purge line 69, and while continuing to supply N gas via the first continuous N gas supply line 66 and the second continuous N gas supply line 68, the on-off valve 74 is opened to supply H gas as a reducing gas from the H gas supply source 52 through the H gas supply line 62 to the processing space 37. At this time, the H gas is temporarily stored in the buffer tank 81 and then supplied into the chamber 1. As a result, WCl adsorbed on the wafer W is reduced.

[0051] Next, while continuing to supply N2 gas via the first continuous N2 gas supply line 66 and the second continuous N2 gas supply line 68, the on-off valve 74 is closed to stop the supply of H2 gas from the H2 gas supply line 62, and the on-off valves 77 and 79 are opened to supply N2 gas (flash purge N2 gas) from the first flash purge line 67 and the second flash purge line 69 as well, and the excess H2 gas in the processing space 37 is purged with a large flow rate of N2 gas.

[0052] By performing the above steps once in a short period of time, a thin tungsten unit film is formed, and by repeating these steps multiple times, a tungsten film of the desired thickness can be obtained.

[0053] For example, as shown in FIG. 5, when forming an initial tungsten film 233 on a substrate 230 and then forming a chlorine-containing tungsten film 234 thereon to form a tungsten film 235, the following procedure is followed.

[0054] 5(a), a substrate 230 is used in which a TiN film 232 is formed as an undercoat on a silicon substrate 231, and an initial tungsten film 233 is formed thereon by the ALD method using the above-described procedure under normal conditions. The conditions in this case are as follows: Pressure: 10 to 60 Torr (1333 to 7998 Pa) Temperature: 400~600℃ WCl5 gas flow rate: 0.5 to 40 sccm (Carrier gas flow rate: 100 to 5000 sccm) H2 gas flow rate: 1000 to 10,000 sccm (H2 gas partial pressure: 3.73 to 21.36 Torr (497 to 2848 Pa)) Continuous supply N2 gas flow rate: 10 to 5000 sccm Flash purge N2 gas flow rate: 500 to 5000 sccm Raw material tank temperature: 50~200℃ However, when forming a film by the ALD method, the H2 gas partial pressure is the H2 gas partial pressure for one entire ALD cycle.

[0055] Next, as shown in FIG. 5(b), a stress-adjusting chlorine-containing tungsten film 234 is formed on the initial tungsten film 233 by the ALD method described above. In this case, the chlorine concentration in the film is increased by lowering the substrate temperature or reducing the H gas flow rate compared to the normal conditions described above. Specifically, the substrate temperature is set to 380°C or lower or the H gas flow rate is set to 800 sccm or lower (H gas partial pressure 3.03 Torr (404 Pa) or lower), and the chlorine concentration in the film is set to 4 at% or higher.

[0056] In this way, by lowering the substrate temperature or reducing the H gas flow rate (reducing the H gas partial pressure), the chlorine concentration in the film increases, and the tensile stress of the film can be reduced. In particular, by setting the substrate temperature to 380°C or less or the H gas flow rate to 500 sccm or less (H gas partial pressure to 1.95 Torr (259 Pa) or less), the tensile stress of the film can be reduced to 500 MPa or less, or the film stress can be made compressive.

[0057] In this way, when the chlorine-containing tungsten film 234 is laminated on the initial tungsten film 233 having tensile stress formed under normal conditions, the chlorine-containing tungsten film 234 has low tensile stress, which can reduce the stress of the entire tungsten film 235. Furthermore, when the chlorine-containing tungsten film 234 has compressive stress, it can reduce or offset the stress of the initial tungsten film 233 having tensile stress.

[0058] <Experimental Example> Next, an experimental example will be described. First, a bare silicon substrate with a 1-nm-thick TiN film was prepared, as shown in Figure 7. Using the deposition system shown in Figure 6, a 3-nm-thick initial tungsten film was deposited on the TiN film. Then, a main tungsten film was deposited on the initial tungsten film under various conditions and thicknesses to create samples, and the film stress was measured. The film stress is shown in Figure 8(a) for tensile stress and in Figure 8(b) for compressive stress. The initial tungsten film was deposited using the conditions for the initial tungsten film described above. Then, tungsten films with thicknesses of 10 to 130 nm were deposited by varying the substrate temperature between 350 and 440°C and the H gas flow rate between 500 and 5000 sccm. The H gas flow rate of 500 to 5000 sccm corresponds to a H gas partial pressure of 1.95 to 14.00 Torr (259 to 1867 Pa).

[0059] Figure 9 shows the relationship between film thickness and film stress when the substrate temperature is changed. As shown in Figure 9, when the substrate temperature is 440°C, the film stress is a large tensile stress of 1700 to 1900 MPa at a film thickness of 40 to 90 nm. In contrast, when the substrate temperature is 380°C or lower, the tensile stress is relaxed to 500 MPa or lower at a film thickness of 10 to 130 nm, and it is confirmed that as the film thickness increases, the tensile stress changes to compressive stress.

[0060] Figure 10 shows the relationship between film thickness and film stress when the H gas flow rate (H gas partial pressure) is changed. As shown in Figure 10, when the H gas flow rate is 900 to 5000 sccm (H gas partial pressure is 3.38 to 14.00 Torr (451 to 1867 Pa)), the film thickness is 40 to 90 nm and the film stress is a large tensile stress of 1500 to 2000 Pa. In contrast, when the H gas flow rate is 800 sccm (H gas partial pressure is 3.03 Torr (404 Pa)), the tensile stress is relaxed to 1300 MPa, and at 500 sccm (1.95 Torr (259 Pa)), the tensile stress is confirmed to be relaxed to 500 MPa or less.

[0061] Next, we further investigated the film stress at a substrate temperature of 380°C (Low Temp) and an H2 gas flow rate of 500 sccm (Low H2). Figure 11 shows the relationship between film thickness and film stress when tungsten films are formed under Low Temp, Low H2, and normal conditions (Ref). As shown in Figure 11, similar to the results in Figures 9 and 10, Ref results in a large tensile stress of 1700 to 1900 MPa, while Low Temp and Low H2 result in a tensile stress of 500 MPa or less, or a slight compressive stress in the thick film region.

[0062] The chlorine (Cl) concentrations of the tungsten films at Low Temp, Low H2, and Ref were measured using X-ray photoelectron spectroscopy (XPS). Figure 12(a) shows the XPS spectra, and Figure 12(b) shows the chlorine concentrations determined from the XPS spectra. As shown in these figures, the tungsten films at Low Temp and Low H2, which have low film stress, have higher chlorine concentrations than the tungsten film at Ref, at chlorine concentrations of 4 at% or higher. In other words, it was confirmed that the decrease in tensile stress corresponds to an increase in the chlorine concentration in the film, and this tendency becomes more pronounced at chlorine concentrations of 4 at% or higher.

[0063] Next, we performed X-ray diffraction (XRD) on the LowTemp, LowH2, and Ref tungsten films. The diffraction intensity near the (110) plane was shown in Figure 13(a). Figure 13(b) shows the angles of the diffraction peaks for these (110) planes, and Figure 13(c) shows the full width at half maximum (FWHM) of the diffraction peaks for these (110) planes. As shown in these figures, the diffraction peaks for LowTemp and LowH2, which have low film stress, are shifted from those for Ref. Furthermore, the peaks become broader and the FWHM deteriorates. This confirms that the size and arrangement of the crystal lattice in the LowTemp and LowH2 tungsten films change as the Cl concentration increases, resulting in changes in stress according to the mechanisms described in the models shown in Figures 3 and 4.

[0064] <Other applications> Although the embodiments have been described above, the disclosed embodiments should be considered to be illustrative and not restrictive in all respects. The above embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0065] For example, in the above embodiment, the tungsten film is formed by the ALD method or the CVD method using tungsten chloride and a reducing gas, but the method for forming the tungsten film is not limited to this.

[0066] Furthermore, in the above embodiment, a semiconductor wafer is used as an example of the substrate, but the substrate is not limited to a semiconductor wafer and may be other substrates such as a glass substrate or a ceramic substrate. [Explanation of symbols]

[0067] 1; Chamber 2; susceptor 3. Shower head 4. Exhaust section 5. Gas supply mechanism 6; Control unit 51: WCl5 gas supply mechanism 52;H2 gas supply source 61: WCl5 gas supply line 62; H2 gas supply line 73, 74, 76, 77, 78, 79, 102, 103; Opening and closing valves 91: Film forming material tank 100; Film deposition equipment 201,222;Tungsten film 211;Crystal lattice of tungsten crystal 212;Crystal lattice of silicon crystal 213;High chlorine concentration tungsten film 221;Silicon wafer 231: Silicon substrate 232;TiN film 233; Initial tungsten film 234; Chlorine-containing tungsten film W: Semiconductor wafer (substrate)

Claims

1. A method for forming a tungsten film, comprising: providing a substrate; forming a tungsten film on the substrate; and At least a portion of the tungsten film is a chlorine-containing tungsten film in which a chlorine concentration in the film is increased to more than 2 at % to adjust film stress, and the chlorine-containing tungsten film has a tensile stress or compressive stress lower than that of a tungsten film having a chlorine concentration of 2 at % or less in the film, The step of forming the tungsten film includes forming an initial tungsten film on the substrate, the initial tungsten film having a lower chlorine concentration than the chlorine-containing tungsten film, and then forming the chlorine-containing tungsten film thereon.

2. 2. The film forming method according to claim 1, wherein the chlorine-containing tungsten film has a chlorine concentration of 4 at % or more and a tensile stress or compressive stress of 500 MPa or less.

3. 3. The film forming method according to claim 1, wherein the initial tungsten film has a thickness of 0.5 nm or more.

4. 4. The film forming method according to claim 1, wherein the substrate has a base body and a TiN film formed on the base body, and the initial tungsten film is formed on the TiN film.

5. A method for forming a tungsten film, comprising: providing a substrate; forming a tungsten film on the substrate; and The step of forming the tungsten film includes forming the tungsten film by a CVD method or an ALD method using tungsten chloride and a reducing gas as source gases, At least a portion of the tungsten film is a chlorine-containing tungsten film in which a chlorine concentration in the film is increased to more than 2 at % to adjust film stress, and the chlorine-containing tungsten film has a tensile stress or compressive stress lower than that of a tungsten film having a chlorine concentration of 2 at % or less in the film, The film formation method includes forming an initial tungsten film on the substrate, the initial tungsten film having a lower chlorine concentration than the chlorine-containing tungsten film, and then forming the chlorine-containing tungsten film on the initial tungsten film.

6. The tungsten film forming step is performed by the ALD method, and H is used as the reducing gas. ２ The film forming method according to claim 5 , wherein a gas is used.

7. When forming the chlorine-containing tungsten film, H ２ 7. The film forming method according to claim 6, wherein the partial pressure of the gas is set to 404 Pa or less.

8. When forming the chlorine-containing tungsten film, H ２ 8. The film forming method according to claim 7, wherein the partial pressure of the gas is set to 259 Pa or less and / or the substrate temperature is set to 380[deg.] C. or less.

9. 9. The film forming method according to claim 8, wherein the chlorine-containing tungsten film has a chlorine concentration of 4 at % or more and a tensile stress or compressive stress of 500 MPa or less.

10. The initial tungsten film is formed by setting the substrate temperature at 400° C. or higher and ２ The film forming method according to any one of claims 5 to 9, wherein the film is formed by an ALD method with a gas partial pressure of 497 to 2848 Pa.

11. 11. The film forming method according to claim 10, wherein the initial tungsten film has a thickness of 0.5 nm or more.

12. 12. The film forming method according to claim 5, wherein the substrate has a base body and a TiN film formed on the base body, and the initial tungsten film is formed on the TiN film.

13. A tungsten film formed on a substrate, At least a portion of the tungsten film is a chlorine-containing film having a chlorine concentration of 4 at% or more and a tensile stress or compressive stress of 500 MPa or less, A tungsten film comprising an initial tungsten film formed on the substrate and having a lower chlorine concentration than the chlorine-containing tungsten film, the chlorine-containing tungsten film being formed on the initial tungsten film.

14. 14. The tungsten film according to claim 13, wherein the initial tungsten film has a thickness of 0.5 nm or more.

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