Stress reduction methods

Abstract

To provide a stress reduction method, capable of simply reducing the tensile stress of a tungsten film deposited on a chamber inner material when depositing the tungsten film on a substrate by using tungsten material gas and reduction gas.SOLUTION: A stress reduction method comprises the steps of: preparing a film deposition apparatus for supplying tungsten material gas and reduction gas to a chamber to form a tungsten film on a substrate in a chamber; and using at least a part of the tungsten film deposited on a chamber inner material as a chlorine containing tungsten film having film stress reduced by controlling chlorine concentration when depositing the tungsten film on a pre-coating and / or a substrate in the chamber using the tungsten material gas and the reduction gas.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to stress reduction methods. [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 for interdiffusion barriers.

[0003] Known methods for depositing tungsten films include CVD using tungsten hexafluoride (WF6) and a reducing gas as source gases (see, for example, Patent Document 1). In recent years, design rules have become increasingly finer, raising concerns about the adverse effects of fluorine-containing sources on devices. Therefore, a technique has been proposed for depositing tungsten films using tungsten chloride as a source gas through CVD or ALD (see, for example, Patent Document 2).

[0004] The above-mentioned Patent Document 1 describes that when a blanket tungsten film is formed using WF6, the tensile stress of the film increases when the substrate temperature drops to a low temperature of around 400°C, resulting in warping of the substrate. When forming a tungsten film using the CVD method or the ALD method, a tungsten film is also formed on the walls and components (e.g., the substrate stage) inside the chamber used for film formation during pre-coating and film formation, raising concerns that similar problems may arise in these components. Patent Document 1 also describes that the tensile stress of the film can be eliminated by performing pre-treatment using a mixed gas of WF6 and monosilane in a predetermined ratio. [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 stress reduction method that can easily reduce the tensile stress of a tungsten film deposited on a chamber interior member when forming a tungsten film on a substrate using a tungsten source gas and a reducing gas.

[0007] A stress reduction method according to one embodiment of the present disclosure includes the steps of: preparing a film formation apparatus that supplies a tungsten source gas and a reducing gas into a chamber to form a tungsten film on a substrate in the chamber; and, when using the tungsten source gas and the reducing gas to perform pre-coating in the chamber and / or to form a tungsten film on the substrate, reducing stress in the deposited tungsten film by converting at least a portion of the tungsten film deposited on a chamber internal member present in the chamber into a chlorine-containing tungsten film having a chlorine concentration of 4 at% or more. When the pre-coating and film formation on the substrate are performed, an initial tungsten film having a lower chlorine concentration than the chlorine-containing tungsten film is deposited on the surface of the chamber interior member, and the chlorine-containing tungsten film is then deposited thereon. . [Effects of the Invention]

[0008] According to the present disclosure, there is provided a stress reduction method that can easily reduce the tensile stress of a tungsten film deposited on a chamber interior member when forming a tungsten film on a substrate using a tungsten source gas and a reducing gas. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing an example of a chamber internal member in a chamber of a film forming apparatus. [Figure 2] This is a cross-sectional view that shows a state in which a crack occurs in the substrate stage due to the tensile stress of a tungsten film deposited during pre-coating and actual film formation, taking the case where the chamber interior member is a substrate stage made of ceramic as an example. [Figure 3]This is a cross-sectional view showing a state in which the coating film has peeled off due to the tensile stress of the tungsten film deposited during pre-coating and actual film formation, taking as an example the case where the chamber internal component is a shower plate with a coating film formed on a metal substrate. [Figure 4] 1 is a flowchart illustrating a method for reducing stress according to one embodiment. [Figure 5] FIG. 1 is a diagram showing a model for explaining the mechanism by which a tungsten film has tensile stress. [Figure 6] 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 7] 1 is a cross-sectional view illustrating a stress reduction method according to an embodiment. [Figure 8] FIG. 1 is a cross-sectional view showing an example of a film formation apparatus used to form a tungsten film. [Figure 9] FIG. 1 is a diagram showing the structure of a sample used in an experimental example. [Figure 10] 1A and 1B are diagrams for explaining tensile stress and compressive stress of a film. [Figure 11] 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 12] 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 13] 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 14] 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 15] 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> When depositing a tungsten film on a substrate using CVD or ALD, a pre-coating process is performed on the chamber of a deposition apparatus, and then the substrate is loaded into the chamber to deposit the tungsten film on the substrate. As shown in FIG. 1, the chamber contains components such as a substrate stage (susceptor) 201, an outer ring 202, and a shower head 203. The shower head 203 has a shower plate 203a and a distribution block 203b. During pre-coating and deposition, a tungsten film is deposited on the chamber walls and these components, i.e., the components inside the chamber.

[0012] Tungsten films generally have tensile stress, which increases with film thickness. Therefore, if a tungsten film is deposited on components inside the chamber during pre-coating or actual deposition on a substrate, the following problems may occur.

[0013] For example, as shown in FIG. 2(a), when the chamber interior component is a substrate stage (susceptor) 202 made of ceramics such as AlN, tensile stress is generated in the direction of the arrow when a tungsten film 205 is deposited thereon during pre-coating or actual film deposition on the substrate. As shown in FIG. 2(b), as the tungsten film 205 becomes thicker, the tensile stress increases, which may cause cracks 206 in the substrate stage 202. As shown in FIG. 3(a), when the chamber interior component is a shower plate 203a with a ceramic coating film 208 formed on a metal substrate 207 such as aluminum, tensile stress is also generated when the tungsten film 205 is deposited thereon. As shown in FIG. 3(b), as the tungsten film 205 becomes thicker, the tensile stress also increases, which may cause the coating film 208 to peel off.

[0014] Therefore, in one embodiment, the stress of a tungsten film deposited on a chamber interior member during pre-coating in the chamber and deposition of the tungsten film on a substrate is reduced. Specifically, a stress adjustment method is provided, including steps ST1 and ST2 shown in FIG. 4 . In step ST1, a film formation apparatus is prepared that supplies a tungsten source gas and a reducing gas to the chamber to form a tungsten film on a substrate in the chamber. In step ST2, at least a portion of the tungsten film deposited on the chamber interior member during pre-coating in the chamber and deposition of the tungsten film on a substrate using the tungsten source gas and the reducing gas is converted into a chlorine-containing tungsten film with reduced film stress by adjusting the chlorine concentration. Adjusting the chlorine concentration of the deposited tungsten film makes it easy to reduce the tensile stress of the tungsten film deposited on the chamber interior member.

[0015] 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% or less, and this is also true for tungsten films deposited on chamber interior components. The tensile stress of the resulting tungsten film is high, at 1700-1900 MPa, at a film thickness of about 50-100 nm. Increasing the chlorine concentration in the film can reduce the tensile stress. Furthermore, by increasing the chlorine concentration to 4 at% or more, the tensile stress can be reduced to 500 MPa or less, and the film stress can even be made compressive.

[0016] The mechanism by which a generally deposited tungsten film has tensile stress can be explained by the model shown in Figure 5. As shown in Figure 5(a), if the size of the crystal lattice 211 of the tungsten crystal is smaller than the size of the crystal lattice 212 of the underlying crystal (e.g., substrate stage), as shown in Figure 5(b), the tungsten crystal lattice 211 is pulled by the underlying crystal lattice 212 and has tensile stress, as shown in Figure 5(c). Therefore, for example, a tungsten film 222 deposited on a substrate stage 221 has tensile stress as a whole, as shown in Figure 5(c). This tendency does not change even if the film contains approximately 2 at% chlorine as an impurity.

[0017] 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, for example, by the model shown in Figure 6. 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 underlying crystal (e.g., the substrate stage). In some cases, as shown in Figure 6(a), the size of the crystal lattice 213 of the tungsten crystal becomes larger than the size of the crystal lattice 212 of the underlying crystal. When the size of the crystal lattice 213 of the tungsten crystal approaches the size of the crystal lattice 212 of the underlying crystal, the tensile stress is alleviated. Furthermore, when the crystal lattice 213 of the tungsten crystal becomes larger as shown in Figure 6(a), the crystal lattice 213 of the high-chlorine-containing tungsten crystal is pulled by the crystal lattice 212 of the underlying crystal, resulting in compressive stress, as shown in Figure 6(b). In this case, as shown in FIG. 6(c), for example, the high chlorine concentration tungsten film 223 formed on the substrate stage 221 as the base comes to have compressive stress as a whole.

[0018] Prior to deposition of a tungsten film on a substrate, chamber interior components, such as the chamber walls, substrate stage, and showerhead, are precoated with a tungsten film. While a chlorine-containing tungsten film with a chlorine concentration adjusted as described above may be deposited from the beginning of the precoating process, a tungsten film with a high chlorine concentration (e.g., 4 at% or higher) may be difficult to deposit on the surface of the chamber interior components using standard CVD or ALD techniques. For this reason, as shown in FIG. 7(a), an initial tungsten film 232 with a low chlorine concentration and tensile stress is deposited under standard conditions on a chamber interior component, such as a substrate stage 231, to allow deposition of a chlorine-containing tungsten film with a high chlorine concentration. Then, as shown in FIG. 7(b), a chlorine-containing tungsten film 233 is deposited on the initial tungsten film 232. The thickness of the initial tungsten film 232 is preferably 0.5 nm or greater, more preferably in the range of 1 to 15 nm.

[0019] By depositing a tungsten film having tensile stress under normal conditions as described above and then depositing a tungsten film containing chlorine, if the tungsten film containing chlorine has compressive stress, the stress of the tungsten film containing tensile stress can be alleviated or offset. Also, even if the tungsten film containing chlorine has low tensile stress, the stress of the entire film can be alleviated.

[0020] Next, an example of a method for reducing stress when forming a tungsten film by CVD or ALD using tungsten chloride gas and a reducing gas, by converting at least a portion of the tungsten film deposited on a chamber interior member into a chlorine-containing tungsten film with a high chlorine concentration, will be described.

[0021] Typical conditions for depositing tungsten films using tungsten chloride gas and reducing gas are a substrate temperature of 400°C or higher and a flow rate of H2 gas (reducing gas) of 1000-10000 sccm (H2 gas partial pressure of 3.73-21.36 Torr (497-2848 Pa)). Tungsten films deposited under these conditions exhibit high tensile stresses of 1700-1900 MPa with thicknesses of approximately 50-100 nm. Furthermore, tungsten films deposited under these conditions have low chlorine concentrations of 2 at% or less. Tungsten films are also deposited on the chamber interior, and similarly, large tensile stresses are also generated in these deposited tungsten films. Furthermore, when the chamber interior is precoated without a substrate being loaded into it, tungsten films with low chlorine concentrations and high tensile stresses are deposited on the chamber interior.

[0022] 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 stress of the deposited tungsten film. Specifically, by setting the substrate temperature to 380°C or below or the H gas flow rate to 800 sccm (H gas partial pressure 3.03 Torr (404 Pa)) or below, the chlorine concentration can be increased compared to tungsten films formed under normal conditions, reducing the tensile stress of the film. When the substrate temperature is 380°C or the H gas flow rate (H gas partial pressure) is 800 sccm or below (H gas partial pressure 3.03 Torr (404 Pa) or below), the chlorine concentration in the film can be 4 at% or above. Furthermore, when the H gas flow rate (H gas partial pressure) is 500 sccm or below (H gas partial pressure 1.95 Torr (259 Pa) or below), the tensile stress of the film can be reduced to 500 MPa or below, or the film stress can be compressive, which is more preferable. In order to increase the chlorine concentration in the tungsten film, both the substrate temperature and the H2 gas flow rate may be reduced.

[0023] To deposit such a chlorine-containing tungsten film with a high chlorine concentration on at least a portion of the chamber interior components, the above conditions may be used for pre-coating only, for actual film formation only, or for both pre-coating and actual film formation. Using the above-described low temperature and low hydrogen partial pressure conditions during actual film formation allows a chlorine-containing tungsten film to be deposited on the substrate as well, thereby reducing the tensile stress of the tungsten film deposited on the substrate. However, during actual film formation, it is difficult to deposit a tungsten film with a high chlorine concentration on a silicon wafer or a TiN film as an underlayer. For this reason, during actual film formation, it is preferable to deposit an initial tungsten film with a low chlorine concentration on a silicon wafer or TiN film under normal conditions before depositing the chlorine-containing tungsten film.

[0024] The aforementioned Patent Document 1 describes that when a tungsten film is formed by CVD using WF and a reducing gas, tensile stress increases when the substrate temperature drops to a low temperature of about 400°C. Therefore, pretreatment is performed using a mixed gas of WF and monosilane in a predetermined ratio to reduce the tensile stress. The method described in Patent Document 1 can also reduce the tensile stress of the tungsten film deposited on the components inside the chamber. However, the method described in Patent Document 1 requires complex processes, and there are concerns that the fluorine contained in WF may adversely affect the device, necessitating a different approach.

[0025] In this embodiment, at least a portion of the tungsten film deposited on the chamber interior member during pre-coating in the chamber and deposition of the tungsten film on the substrate is a chlorine-containing tungsten film in which the film stress is reduced due to the chlorine concentration in the film. This makes it possible to easily reduce the tensile stress of the tungsten film deposited on the chamber interior member. In particular, a tungsten film with a chlorine concentration of 4 at % or more has a tensile stress of 500MPa or less can be Since the stress of the film can be made compressive, this has a significant effect of reducing the stress of the entire tungsten film deposited on the members inside the chamber.

[0026] <Specific embodiment> Next, a specific embodiment for reducing the stress of a tungsten film deposited on a chamber interior member in a film formation apparatus that forms a tungsten film by the ALD method will be described.

[0027] [Example of film deposition equipment] FIG. 8 is a cross-sectional view showing an example of a film formation apparatus used when forming a tungsten film by the ALD method.

[0028] The film forming apparatus 100 includes a chamber 1, a susceptor 2 which is a substrate stage for horizontally supporting a semiconductor wafer (hereinafter simply referred to as a wafer) W which is 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 which exhausts the inside of the chamber 1, a process gas supply mechanism 5 which supplies the process gas to the shower head 3, and a control unit 6.

[0029] 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.

[0030] 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.

[0031] 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 .

[0032] 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. 8 and a transfer position, shown by a dashed line below, where a wafer can be transferred. 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 expands and contracts as the susceptor 2 is raised and lowered.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] [Processing Operation] Next, the processing operation of the film forming apparatus of FIG. 8 will be described.

[0048] First, pre-coating is performed inside the chamber 1 without loading the wafer W as a substrate into the chamber 1. Next, the wafer W as a substrate is loaded into the chamber 1 through the loading / unloading port 11, and a tungsten film is formed on the wafer W.

[0049] In both pre-coating and actual film formation on the wafer W, prior to processing, the susceptor 2 is heated to a predetermined temperature by the heater 21, and gas is supplied into the chamber 1 to increase the pressure and stabilize the temperature of the wafer W on the susceptor 2. After the predetermined pressure is reached in the chamber 1, the on-off valves 102 and 103 are closed and the on-off valves 104, 95a, and 95b are opened to increase the pressure in the film-forming raw material tank 91 and make it possible to supply WCl gas, which is a tungsten raw material.

[0050] In this state, the pre-coating of the tungsten film and the actual deposition of the film on the wafer W are both performed by supplying the film deposition source gas WCl5 gas, the reducing gas H2 gas, and the purge gas N2 gas in the sequential manner shown below.

[0051] First, with the on-off valve 76 and the on-off valve 78 open, N gas is continuously supplied from the first N gas supply source 54 and the second N gas supply source 55 via the first continuous N gas supply line 66 and the second continuous N gas supply line 68. Furthermore, by opening the on-off valve 73, WCl gas is supplied from the WCl gas supply mechanism 51 via the WCl gas supply line 61 to the processing space 37 in the chamber 1. At this time, the WCl gas is temporarily stored in the buffer tank 80 before being supplied into the chamber 1. As a result, the WCl gas is adsorbed onto the surfaces of the components inside the chamber during pre-coating. Furthermore, during actual film formation, the WCl gas is adsorbed onto both the surfaces of the wafer W and the components inside the chamber.

[0052] 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.

[0053] 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. 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 via 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 before being supplied into the chamber 1. As a result, during pre-coating, the WCl gas adsorbed on the surfaces of the chamber internal components is reduced to tungsten. Furthermore, during actual film formation, the WCl gas adsorbed on both the surfaces of the wafer W and the surfaces of the chamber internal components is reduced.

[0054] 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.

[0055] 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 a desired thickness is obtained.

[0056] In the film forming apparatus 100, when pre-coating and actual film formation on the wafer W are performed as described above, the chlorine concentration of the tungsten film deposited on the chamber interior components such as the wall of the chamber 1 and the susceptor (substrate stage) is adjusted to reduce tensile stress.

[0057] In this case, the conditions 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.

[0058] Under these conditions, the tungsten film deposited on the chamber interior member has a large tensile stress as described above.

[0059] On the other hand, when depositing a chlorine-containing tungsten film for stress adjustment, the substrate temperature or H2 gas flow rate is lowered compared to the normal conditions described above to increase the chlorine concentration in the film. Specifically, the substrate temperature is set to 380°C or lower or the H2 gas flow rate is set to 800 sccm or lower (H2 gas partial pressure 3.03 Torr (404 Pa) or lower) to achieve a chlorine concentration of 4 at% or higher in the film.

[0060] 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.

[0061] As described above, a chlorine-containing tungsten film with a high chlorine concentration may be formed from the beginning of the precoating process, but a chlorine-containing tungsten film with a high chlorine concentration may be difficult to deposit on the surface of the chamber interior member during precoating. In this case, as shown in FIG. 7 above, an initial tungsten film 232 with a low chlorine concentration and tensile stress is deposited on the surface of the chamber interior member under normal conditions so that a chlorine-containing tungsten film with a high chlorine concentration can be deposited. Then, a chlorine-containing tungsten film 233 is deposited on the initial tungsten film 232. The thickness of the initial tungsten film 232 is preferably 0.5 nm or more, more preferably in the range of 1 to 15 nm.

[0062] In this way, when the chlorine-containing tungsten film 233 is laminated on the initial tungsten film 232, which has tensile stress and is deposited under normal conditions, the chlorine-containing tungsten film 233 has low tensile stress, which can reduce the stress of the entire tungsten film deposited on the chamber interior members. Also, if the chlorine-containing tungsten film 233 has compressive stress, it can reduce or offset the stress of the initial tungsten film 232, which has tensile stress.

[0063] The stress adjustment by adjusting the chlorine concentration of the tungsten film deposited on the chamber interior components may be performed only during pre-coating, or may be performed both during pre-coating and actual film formation. If the conditions during actual film formation are adjusted to increase the chlorine concentration of the tungsten film, a tungsten film with a high chlorine concentration is also formed on the surface of the substrate wafer W, thereby reducing warpage of the wafer W due to the tensile stress of the tungsten film. Since it is difficult to form a chlorine-containing tungsten film with a high chlorine concentration on the wafer W during actual film formation, it is preferable to first form an initial tungsten film under normal conditions and then form a chlorine-containing tungsten film on top of that.

[0064] <Experimental Example> Next, an experimental example will be described. To simulate the stress reduction of tungsten films deposited on chamber components, a bare silicon substrate with a 1-nm-thick TiN film was prepared as shown in Figure 9. Then, using the deposition system shown in Figure 8, 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 10(a) for tensile stress and in Figure 10(b) for compressive stress. The initial tungsten film was deposited using the conditions for the initial tungsten film described above. Then, the substrate temperature was varied between 350 and 440°C, and the H gas flow rate was varied between 500 and 5000 sccm, and tungsten films with thicknesses of 10 to 130 nm were deposited. An H2 gas flow rate of 500 to 5000 sccm is equivalent to an H2 gas partial pressure of 1.95 to 14.00 Torr (259 to 1867 Pa).

[0065] Figure 11 shows the relationship between film thickness and film stress when the substrate temperature is changed. As shown in Figure 11, when the substrate temperature is 440°C, the film stress is a large tensile stress of 1700 to 1900 MPa when the film thickness is 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 when the film thickness is 10 to 130 nm, and it is confirmed that the tensile stress changes to compressive stress as the film thickness increases.

[0066] Figure 12 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 12, 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.

[0067] 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 13 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 13, similar to the results in Figures 11 and 12, Ref results in a large tensile stress of 1700 to 1900 MPa, while Low Temp and Low H2 results in a tensile stress of 500 MPa or less, or a slight compressive stress in the thick film region.

[0068] The chlorine (Cl) concentrations of the tungsten films at Low Temp, Low H2, and Ref were measured using X-ray photoelectron spectroscopy (XPS). Figure 14(a) shows the XPS spectra, and Figure 14(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.

[0069] 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 15(a). Figure 15(b) shows the angles of the diffraction peaks for these (110) planes, and Figure 15(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 5 and 6.

[0070] <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.

[0071] For example, in the above embodiment, the case where a tungsten film is formed using tungsten chloride and a reducing gas is described, but the present invention is not limited to this.

[0072] 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]

[0073] 1; Chamber 2: Susceptor (substrate stage) 3. Shower head 4. Exhaust section 5. Gas supply mechanism 6; Control unit 32; shower plate 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 222;Tungsten film 211;Crystal lattice of tungsten crystal 212; Substrate crystal lattice 213;Crystal lattice of tungsten crystals with high chlorine content 221, 231; Substrate stage 223;High chlorine concentration tungsten film 232; Initial tungsten film 233; Chlorine-containing tungsten film W: semiconductor wafer

Claims

1. preparing a film formation apparatus that supplies a tungsten source gas and a reducing gas into a chamber to form a tungsten film on a substrate in the chamber; a step of reducing stress in the deposited tungsten film by converting at least a portion of the tungsten film deposited on a chamber internal member present in the chamber into a chlorine-containing tungsten film having a chlorine concentration of 4 at % or more when pre-coating inside the chamber and / or forming a tungsten film on the substrate using the tungsten source gas and the reducing gas; and When performing the pre-coating and film formation on the substrate, an initial tungsten film having a lower chlorine concentration than the chlorine-containing tungsten film is deposited on the surface of the chamber interior member, and the chlorine-containing tungsten film is then deposited thereon.

2. 2. The stress reduction method of claim 1, wherein the chlorine-containing tungsten film has a tensile stress or compressive stress of 500 MPa or less.

3. When the precoating and the film formation on the substrate are performed, tungsten chloride is used as the tungsten source gas, and H is used as the reducing gas. ２ 3. The method for reducing stress according to claim 1 or claim 2, wherein a gas is used.

4. When depositing the chlorine-containing tungsten film, H ２ 4. The method for reducing stress according to claim 3, wherein the partial pressure of the gas is set to 404 Pa or less.

5. When forming the chlorine-containing tungsten film, H ２ 5. The stress reducing method according to claim 4, 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.

6. 6. The stress reducing method according to claim 1, wherein the chamber internal components include a substrate stage for placing a substrate thereon, a shower head for supplying gas into the chamber, and a wall portion of the chamber.

Images