Methods and apparatus for forming a membrane

Abstract

A technique is provided for forming a film containing strontium, titanium, and oxygen on a titanium nitride film. An amorphous film containing strontium and oxygen is formed on top of a titanium nitride film formed on a substrate, wherein the atomic ratio of titanium to strontium is 0 or more but less than 1.0. Next, the substrate on which the amorphous film is formed is heated to a temperature of 500°C or higher to obtain the strontium-, titanium-, and oxygen-containing crystalline film containing titanium diffused from the titanium nitride film.

Description

Methods and apparatus for forming a membrane This disclosure relates to a method for forming a film and an apparatus for forming a film. In the insulating films that constitute semiconductor devices (such as DRAM; Dynamic Random Access Memory), there has been a growing demand for improved capacitor performance. Therefore, the demand for insulating film materials, such as ultra-high-k films with a relative permittivity of around 80-100, is increasing. As an alternative to ultra-high-k films, a crystalline composite oxide (hereinafter also referred to as "STO") containing strontium (Sr) and titanium (Ti) is known. For example, Patent Document 1 describes a technique in which a first Sr-Ti-O film less than 10 nm formed on a Ru film is annealed to crystallize it, and then a second Sr-Ti-O film is formed and annealed to crystallize it. [Previous Art Documents] [Patent Documents] Patent Document 1: WO 2009 / 104621 This disclosure provides a technique for forming a film containing strontium, titanium and oxygen in a crystalline structure on a titanium nitride film. This disclosure discloses a method for forming a film, which includes the following steps in forming a film containing strontium, titanium, and oxygen on a substrate: forming an amorphous film on top of a titanium nitride film formed on the surface of the substrate, wherein the amorphous film contains strontium and oxygen, and the titanium content is adjusted to a value in which the ratio of titanium to strontium atomic number is 0 or more but less than 1.0; and heating the substrate on which the amorphous film is formed at a temperature of 500°C or higher to obtain the film containing strontium, titanium, and oxygen crystalline structure containing titanium diffused from the titanium nitride film. According to this disclosure, a film containing strontium, titanium and oxygen crystal structure can be formed on a titanium nitride film. <First Embodiment> First, the method for forming a crystalline STO film (hereinafter also referred to as a "crystalline STO film") disclosed herein will be described with reference to FIG1. ​​FIG1(a) and (b) schematically show the layered structure of the film formed on a substrate, i.e., a semiconductor wafer (hereinafter referred to as a "wafer") W, during the formation of, for example, DRAM. Furthermore, the description of structures such as trenches or vias formed on the wafer W is omitted in FIG1, FIG6, and FIG7. As illustrated in Figure 1(a), a wafer W with a crystalline STO film is deposited on the surface of a silicon wafer 81, separated by a silicon oxide film (SiO film) 82 (as a base film), trenches, or mesoscopic pores (not shown), and a titanium nitride film (TiN film) 83 is deposited to obtain contact with the silicon wafer 81. A crystalline STO film 85, which is an ultra-high k film, is formed on the TiN film 83. Here, as a method for obtaining a crystalline STO film 85, there is a known technique in which an amorphous STO film (hereinafter also referred to as "amorphous STO film") is formed on a wafer W of the film-forming object, and the wafer W is converted into a crystalline STO film by heat treatment (annealing). On the other hand, as shown in the experimental results of the embodiments described later, the inventors of this disclosure discovered that, unlike ordinary metals, even after heat treatment following the formation of an amorphous STO film on top of the TiN film 83, a crystalline STO film still could not be formed. In this case, the following method was also considered: further depositing an amorphous STO film on top of the heat-treated amorphous STO film and then performing heat treatment to obtain a crystalline STO film in the area not in contact with the TiN film 83. However, even when a crystalline STO film was obtained by this method, it was found that unevenness, referred to as blistering, still formed on the surface of the crystalline STO film. The reason why a crystalline STO film could not be obtained even after heat treatment is still unclear. In this regard, the inventors of this case predict that if the titanium content near the interface between the TiN film 83 and the amorphous STO film is high, conditions will be created that make it difficult for STO crystals to grow. Therefore, the method for forming a crystalline STO film related to the first embodiment is shown in Figure 1(a). A strontium oxide film (SrO film) 84 is formed on the surface of a TiN film 83 without the addition of titanium (a process for forming an amorphous STO film). Then, the wafer W with the SrO film 84 is heat-treated to allow titanium to diffuse from the TiN film 83 to the SrO film 84 to obtain a crystalline STO film 85 (a process for obtaining a crystalline STO film, Figure 1(b)). In obtaining a crystalline STO film 85 with a thickness in the range of, for example, 1 nm or more and 5 nm or less, it is preferable to form an SrO film 84 with a thickness in the range of 2 nm or more and 10 nm or less. Furthermore, the heat treatment is performed under argon (Ar) or nitrogen (N) gas. 2) In an atmosphere of inactive gases such as gas, the process is carried out at a temperature range of 500~700℃ (e.g., 630℃) for 5 minutes to 1 hour (e.g., 1 hour). The following description refers to Figures 2 to 4, outlining the configuration of the apparatus (film forming apparatus 1) for performing the above-described process to form a crystalline STO film 85. The film forming apparatus 1 is configured as, for example, a multi-chamber system vacuum processing apparatus. As shown in Figure 2, the film forming apparatus 1 includes an atmospheric pressure transport chamber 22, which is maintained at atmospheric pressure by using, for example, Ar gas. A loading port 21 is provided at the front of the atmospheric pressure transport chamber 22 for receiving and transferring the wafer W between itself and a carrier C containing, for example, a wafer W. An opening / closing door 27 is provided on the front wall of the atmospheric pressure transport chamber 22, which opens when the wafer W is moved in or out of the carrier C. Furthermore, a transport arm 25 for transporting the wafer W is provided inside the atmospheric pressure transport chamber 22. Additionally, viewed from the loading port 21 side of the atmospheric pressure transport chamber 22, an alignment chamber 26 is provided on the left side wall for adjusting the orientation or centrifugal position of the wafer W. A loading interlock chamber 23 is connected to the wall opposite the mounting port 21 of the atmospheric pressure transfer chamber 22. The loading interlock chamber 23 has the function of switching the internal atmosphere between an atmospheric pressure atmosphere and a vacuum atmosphere when the wafer W is contained within it. Viewed from the atmospheric pressure transfer chamber 22, there are, for example, two loading interlock chambers 23 arranged side-by-side. Viewed from the atmospheric pressure transfer chamber 22, a vacuum transfer chamber 24 is arranged behind these loading interlock chambers 23. The atmospheric pressure transfer chamber 22 and the vacuum transfer chamber 24 are connected to each loading interlock chamber 23 via gate valves 29. The vacuum transfer chamber 24 is connected to a film formation module (film formation section) 101 and a heat treatment module (heat treatment section) 102. The film formation module (film formation section) 101 forms an SrO film 84 on top of the TiN film 83 formed on the wafer W. The heat treatment module (heat treatment section) 102 heat-treats the wafer W after the SrO film 84 is formed to form a crystalline STO film 85 at the interface between the TiN film 83 and the SrO film 84. In this example, two film formation modules 101 and two heat treatment modules 102 are connected to the vacuum transfer chamber 24. The vacuum transfer chamber 24 is equipped with a transfer arm 28, which is used to receive and transfer the wafer W between the loading interlock chambers 23, the film formation module 101, and the heat treatment module 102. Next, an example of the structure of the film-forming module 101 will be described (Fig. 3). This film-forming module 101 forms an SrO film 84 on the upper side of the TiN film 83 using the ALD (Atomic Layer Deposition) method. Furthermore, for ease of explanation, the film-forming module 101 shown in Fig. 3 is based on the second and third embodiments, and can also form a Sr-rich STO film 86 or an STO upper film 87. The formation of the SrO film 84 differs from the formation of the Sr-rich STO film 86 or the STO upper film 87 in that the Ti feed gas supply section 62 related to the supply of titanium (Ti) feed gas is omitted or not used at all. The following description also includes the Ti feed gas supply section 62 in explaining the structure of the film-forming module 101. The film forming module 101 is equipped with a processing container 30 for receiving wafer W. The side of the processing container 30 is formed with a loading and unloading inlet 31 that can be opened and closed freely by the aforementioned gate valve 29. The upper part of the side wall of the processing container 30 is provided with an annular exhaust duct 32. Furthermore, a top plate 33 is provided on the top of the exhaust duct 32 in a manner that closes the upper opening of the processing container 30. The processing container 30 is connected to a vacuum exhaust section 35, such as a vacuum pump, through a vacuum exhaust passage 34 connected to the exhaust port 331 of the exhaust duct 32. The vacuum exhaust passage 34 is provided with an APC (Auto Pressure Controller) valve 36 for regulating the pressure within the processing container 30. The processing container 30 has a mounting stage 4 inside that horizontally supports the wafer W. The mounting stage 4 is equipped with a heater 41 for heating the wafer W. The mounting stage 4 is connected to a lifting mechanism 44 via a support column 43, allowing for free movement. In Figure 3, the mounting stage 4 after being moved to the receiving position of the wafer W is represented by a two-point chain line. In the same figure, symbol 45 refers to a support pin for receiving the wafer W, which is freely movable via the lifting mechanism 46. Symbol 42 refers to a through hole for the support pin 45, and symbols 47 and 48 refer to telescopic tubes that extend and retract with the lifting movement of the mounting stage 4 and the support pin 45. The film-forming module 101 is equipped with a spray head 5 facing the mounting stage 4 for supplying processing gas into the processing container 30. The spray head 5 has a gas diffusion space 51 inside, and its lower part is configured as a spray plate 52 with multiple gas ejection holes 53. The gas diffusion space 51 is connected to the gas supply system 6 through a gas inlet hole 54. The gas supply system 6 includes an Sr raw material gas supply unit 61 for supplying gas for strontium (Sr) raw material to the processing container 30, a Ti raw material gas supply unit 62 for supplying gas for Ti raw material, and an oxidizing gas supply unit 63 for supplying oxidizing gas that oxidizes the Sr and Ti raw materials. The Sr feedstock supplied from the Sr feedstock gas supply unit 61 is Sr(Me5Cp). 2(bis(pentamethylcyclopentadienylstrontium) or Sr(THD)) 2. Strontium-containing compounds such as bis(tetramethylheptanedionate) Furthermore, the Ti feedstock supplied from the Ti feedstock gas supply section 62 is Ti(Me5Cp)(MeO). 3(pentamethylcyclopentadienyltrimethoxytitanium) or Ti(Me5Cp)(NMe 2) 3. Compounds containing titanium, such as methylcyclopentadienyltrimethoxytitanium. Also, in this example, highly reactive ozone (O₂) is used. 3) Using a gas as the oxidizing gas. Alternatively, it can be configured to supply, for example, a distal plasma obtained by ionizing oxygen, as the oxidizing gas. The Sr feedstock gas supply unit 61 includes a gas supply source 64 and a gas supply channel 641 for supplying Sr feedstock gas. The Sr feedstock gas supply source 64 has the function of contacting the aforementioned Sr feedstock with the carrier gas to vaporize or sublimate it and supply it as feedstock gas. For example, the Sr gas supply channel 641 is provided with a flow regulating unit 642, a storage tank 643 and a valve V1 sequentially arranged from the upstream side. The Ti feedstock gas supply unit 62 includes a gas supply source 65 and a gas supply channel 651 for supplying Ti feedstock gas. The Ti feedstock gas supply source 65 has the function of contacting the aforementioned Ti feedstock with the carrier gas to vaporize or sublimate it and supply it as feedstock gas. For example, the titanium gas supply channel 651 is provided with a flow regulating unit 652, a storage tank 653 and a valve V2 sequentially arranged from the upstream side. Furthermore, the oxidizing gas supply unit 63 includes an O2 system for supplying oxidizing gases. 3. Gas supply source 66 and its gas supply channel 661. For example, O The gas supply channel 661 is provided with a flow regulating unit 662, a storage tank 663 and a valve V3 in sequence from the upstream side. These Sr feed gas, Ti feed gas and O The gases 3 will be temporarily stored in storage tanks 643, 653, and 663 respectively, and will be supplied to the film-forming module 101 after being pressurized to a specific pressure. The supply and stop of each gas from storage tanks 643, 653, and 663 to the film-forming module 101 are controlled by opening and closing valves V1, V2, and V3. Furthermore, the gas supply system 6 includes an inactive gas supply unit that supplies inactive gas to the film-forming module 101, using, for example, Ar gas as the inactive gas. In this example, the inactive gas supply unit includes Ar gas supply sources 67, 68, and 69 and Ar gas supply channels 671, 681, and 691. In this example, the Ar gas supplied from the Ar gas supply source 67 of the Sr raw material gas supply unit 61 is a purging gas for the Sr raw material gas. This Ar gas supply source 67 is connected to the downstream side of the valve V1 installed in the aforementioned Sr raw material gas supply channel 641 via the Ar gas supply channel 671. Furthermore, the Ar gas supplied from the Ar gas supply source 68 of the Ti raw material gas supply unit 62 is a purging gas for the Ti raw material gas. This Ar gas supply source 68 is connected to the downstream side of the valve V2 installed in the Ti raw material gas supply channel 651 via the Ar gas supply channel 681. Furthermore, the Ar gas supplied from the Ar gas supply source 69 of the oxidizing gas supply section 63 is a purging gas for the oxidizing gas. The Ar gas supply source 69 is connected to the O gas supply channel 691 via the Ar gas supply channel 691. 3. The downstream side of valve V3 installed in gas supply channel 661. In addition, in Figure 3, symbols 672, 682, and 692 refer to flow regulation units, and symbols V4, V5, and V6 refer to valves. When using the film-forming module 101 shown in Figure 3 to form a SrO film 84 (or a Sr-rich STO film 86 as described later) on top of a TiN film 83, the Sr raw material gas supply section 61 corresponds to the first raw material gas supply section, and the Ti raw material gas supply section 62 corresponds to the second raw material gas supply section. Next, the configuration of the heat treatment module 102 will be described with reference to FIG4. In FIG4, for the constituent elements that have the same functions as the film forming module 101 described in FIG3, some common symbols are used and repeated descriptions are omitted. As shown in Figure 4, the heat treatment module 102 includes a processing container 30, a stage 4a on which a wafer W to be processed is placed, and a spray head 5 disposed on the top side of the processing container 30 facing the stage 4a. In this example, the mounting stage 4a is fixedly mounted on the substrate of the processing container 30. The mounting stage 4a is equipped with a wafer W after an SrO film 84 has been formed by the film deposition module 101. The interior of the mounting stage 4a is provided with a plurality of support pins (not shown in the figure) configured to move freely up and down, so that these support pins move in and out from the top of the mounting stage 4a to receive and receive the wafer W. The interior of the mounting stage 4a is equipped with a heater 41 for heating the wafer W to a temperature range of 500~700°C (e.g., 630°C). The substrate surrounding the mounting stage 4a has openings with a plurality of exhaust ports 331 for venting the wastewater from the processing container 30. The spray head 5 is connected to an inert gas supply unit 60 for supplying Ar gas, an example of an inert gas, to the treatment container 30. The inert gas supply unit 60 includes an Ar inert gas supply source 600 and a gas supply channel 601. For example, the Ar gas supply channel 601 is sequentially provided with a flow regulating unit 602 and a valve V7 from the upstream side. As shown in FIG2, the film deposition apparatus 1 having the above-described configuration includes a control unit 100. The control unit 100 is composed of a computer containing a memory unit that stores programs, memory, and a CPU. The program contains instructions (steps) to output control signals from the control unit 100 to various parts of the film deposition apparatus 1 to perform SrO film 84 deposition on the wafer W or subsequent heat treatment. The program is stored in the computer's memory unit, such as a floppy disk, CD, hard disk, MO (magneto-optical disk), non-volatile memory, etc., and is read from that memory unit and installed in the control unit 100. The function of the film deposition apparatus 1 with the above-described configuration will be explained. First, a carrier C containing a plurality of wafers W is transported to the carrier port 21 of the film deposition apparatus 1. The top surface of each wafer W is in the state where a SiO film 82 is formed, as shown in the schematic diagram of FIG. 1(a). The wafers W are removed from the carrier C by the transport arm 25 and transported into the alignment chamber 26 through the atmospheric pressure transport chamber 22. After alignment, they are transported into the vacuum transport chamber 24 through the loading interlock chamber 23. Next, wafer W is transported to film deposition module 101 via transfer arm 28, and SrO film 84 is formed using ALD method. Wafer W, transported into processing container 30, is placed on stage 4, and heating of wafer W is initiated by heating heater 41 to a temperature in the range of 250~400°C. Simultaneously with this heating operation, Ar gas is supplied to processing container 30 from Ar gas supply sources 67, 68, and 69 at preset flow rates. Then, vacuum venting is performed within processing container 30 via vacuum venting unit 35, and the opening / closing degree of valve 36 is adjusted to achieve the target pressure within processing container 30. Next, the SrO film 84 formation process is performed according to the film formation sequence shown in Figure 5. When the SrO film 84 is formed, only cycles 1-4 shown in Figure 5 (Cycle 1) are performed. On the other hand, cycles 5-8 (Cycle 2) are performed zero times. First, valve V1 is opened to supply Sr feed gas, and Ar gas is supplied from Ar gas supply sources 67, 68, and 69 at preset flow rates (Step 1). This process causes the Sr feed gas to be adsorbed onto the entire surface of wafer W. Next, valve V1 is closed to stop the supply of Sr feedstock gas, while the supply of Ar gas from Ar gas supply sources 67, 68, and 69 continues. In this way, Ar gas is used to purge and remove the Sr feedstock gas remaining in the processing container 30 (step 2). Next, while Ar gas is continuously supplied from Ar gas supply sources 67, 68, and 69, valve V3 is opened to supply O2, which is an oxidizing gas. 3. This treatment is used to react the Sr material adsorbed on wafer W with O 3. The reaction proceeds to form a thin film of SrO (step 3). Furthermore, as in the aforementioned example of the Sr raw material, when the Sr raw material is composed of an organometallic compound, the SrO thin film may contain carbon-containing components (e.g., SrCO). In case 3), then close valve V3 to stop O. On the one hand, the supply of Ar gas is continuously provided from Ar gas supply sources 67, 68, and 69, and the Ar gas is used for purging to remove residual O in the processing container 30. 3 (Step 4). In this process of forming the SrO film 84, Sr raw material gas and oxidizing gas are alternately supplied to the processing container 30 while Ar gas (an inactive gas) is being supplied. This process is repeated a set number of times as described in steps 1 to 4 to form the SrO film 84 of the desired thickness. An example of the thickness of the SrO film 84 is a thickness of 10 nm, which is in the range of 2 nm or more and 10 nm or less. After the formation of the SrO film 84 is completed, the following process is performed: the wafer W is removed from the film deposition module 101 and moved into the heat treatment module 102 to obtain a crystalline STO film 85. That is, after the wafer W is placed on the stage 4a of the film deposition module 101, the gate valve 29 is closed to supply Ar gas from the inactive gas supply unit 60 while venting the process container 30, thereby adjusting the pressure inside the process container 30 to a preset level. Furthermore, power is supplied from the power supply unit (not shown) to the heater 41 to heat the wafer W on the stage 4a to a temperature range of 500~700°C (e.g., 630°C). Since an SrO film 84 is formed on the upper side of the TiN film 83, titanium gradually diffuses from the TiN film 83 side towards the SrO film 84 side due to the titanium concentration gradient. Titanium diffusion can be promoted by heating the wafer W. Furthermore, even when titanium moves towards the SrO film 84 due to diffusion, compared to traditional amorphous STO films, the titanium concentration is lower and does not become a high concentration that would hinder the crystallization of regions containing strontium, titanium, and oxygen. Therefore, by heat-treating the wafer W on which the SrO film 84 is formed on the TiN film 83, the region on the SrO film 84 side at the interface between the TiN film 83 and the SrO film 84 can be crystallized. As a result, as shown in Figure 1(b), a crystalline STO film 85 can be obtained. For example, when obtaining a crystalline STO film 85 with a thickness in the range of 1 nm to 5 nm at the aforementioned heating temperature, the heat treatment is performed for a processing time in the range of 5 minutes to 1 hour. In addition, the SrO film 84 remaining on the upper side of the crystalline STO film 85 can also be removed by etching or CMP (Chemical Mechanical Polishing) after the wafer W is removed from the film deposition apparatus 1. After heat treatment of wafer W is performed in heat treatment module 102 for a preset time, wafer W is taken out of heat treatment module 102 and transported through vacuum transport chamber 24, loading interlock chamber 23 and atmospheric pressure transport chamber 22 in the opposite path to when it was transported in. Then the treated wafer W is stored in the original carrier C. According to the film-forming apparatus 1 disclosed herein, a titanium-free SrO film 84 is formed on top of a TiN film 83, followed by heat treatment of the wafer W. As a result, excessive increase in titanium content at the interface between the TiN film 83 and the SrO film 84 can be suppressed, thereby forming a crystalline STO film 85 on the TiN film 83, which was previously difficult to crystallize from amorphous STO films. Here, the film formed on top of the TiN film 83 to obtain a crystalline STO film 85 using the method illustrated in Figures 1(a) and (b) is not limited to a titanium-free SrO film 84. For example, a strontium-rich (Sr) STO film with a relatively low titanium-to-strontium content ratio (atomic number basis) can also be used. The composition of the Sr-rich STO film is illustrated in the second embodiment described below. <Second Embodiment> Figure 6 schematically illustrates a method for forming a crystalline STO film 85 according to the second embodiment. In the second embodiment, an SrO film 84a (or a Sr-rich STO film 86) with a thickness in the range of 5 nm to 10 nm (approximately the thickness of the crystalline STO film 85 formed on the upper side of the TiN film 83) is formed. Then, the SrO film 84a (or the Sr-rich STO film 86) is completely converted into a crystalline STO film 85 by heat treatment, which differs from the first embodiment in that the interface region between the SrO film 84 and the TiN film 83 is crystallized. Compared to the SrO film 84 shown in FIG1(a) (for example, a thickness of 2 nm or more and 10 nm or less), the film formation method of the SrO film 84a shown in FIG6(a-1) is the same as that of the first embodiment, except that its thickness is within the range of 5 nm or more and 10 nm or less. Furthermore, if the heat treatment time for converting the SrO film 84a into a crystalline STO film 85 can be ensured, the heat treatment method can also be made the same as that of the first embodiment. If the titanium diffused from the TiN film 83 has a thickness that extends throughout the thickness direction of the SrO film 84a, then the SrO film 84a can be converted into a crystalline STO film 85 by means of the same mechanism as described in the first embodiment. Furthermore, the films that can be converted into crystalline STO films 85 by heat treatment are not limited to titanium-free SrO films 84. Figure 6(a-2) shows an example of a Sr-rich STO film 86 formed on the upper side of a TiN film 83, where the titanium-to-strontium content ratio is relatively low. The Sr-rich STO film 86, in atomic number terms, is formed when the titanium-to-strontium atomic number ratio is greater than 0 and less than 1.0, preferably greater than 0 and less than 0.7. The thickness range of the Sr-rich STO film 86 is the same as that of the aforementioned SrO film 84a. The Sr-rich STO film 86 can be formed by using the film-forming module 101 illustrated in FIG3 (which also has a Ti raw material gas supply unit 62) to perform steps 1 to 8 of the film-forming sequence shown in FIG5. That is, when forming the Sr-rich STO film 86, the aforementioned steps 1 to 4 are repeated to form the SrO film. Next, the following steps are performed: supplying Ti raw material gas, adsorbing Ti raw material onto wafer W (step 5), stopping the supply of Ti raw material gas, purging the processing container 30 (step 6), and applying oxidation gas (O2). The TiO film is formed by cycling through steps 3) of supplying Ti raw material gas (step 7), stopping the supply of Ti raw material gas, and purging the processing container 30 (step 8). Then, the cycles of steps 1 to 4 (first cycle) and steps 5 to 8 (second cycle) are repeated multiple times. In this way, an Sr-rich STO film 86 of the desired thickness can be formed. In Figure 5, the number of times the first cycle and the second cycle are repeated is recorded as "Z". Here, the titanium-to-strontium content ratio in the Sr-rich STO film 86 is adjusted by changing the ratio of the number of times the first cycle is performed (referred to as "X" in Figure 5) to the number of times the second cycle is performed (referred to as "Y" in Figure 5). Specifically, compositional analysis of amorphous STO films obtained by changing the cycle ratio "X:Y" is conducted through preliminary experiments (e.g., secondary ion mass analysis). Then, the number of cycles X and Y corresponding to the desired titanium-to-strontium content ratio (atomic number basis) within the range of greater than 0 and less than 1.0 are used as the actual film formation conditions for the Sr-rich STO film 86. The Sr-rich STO film 86 formed by the above method can also be converted into a crystalline STO film 85 by heat treatment using the heat treatment module 102, similar to the case of the SrO film 84a shown in FIG6(a-1). <Third Embodiment> If a crystalline STO film 85 can be formed on the TiN film 83 by the method described in the first or second embodiment, then the crystalline STO film 85 can be used as a separator relative to the TiN film 83 to further form a thick crystalline STO film. The third embodiment shown in Figures 7(a) to (d) illustrates an example of forming a crystalline STO film by this method. Figures 7(a) and (b) are re-illustrations of Figures 6(a-1) and (b), respectively, showing an example of obtaining a crystalline STO film 85 by heat treatment after forming an SrO film 84a on top of a TiN film 83. Next, an amorphous STO upper layer film 87 (Figure 7(c)) is formed on top of this crystalline STO film 85. The STO upper film 87 can be formed using a film-forming module 101 equipped with a Ti feed gas supply unit 62 as illustrated in FIG. 3. The film-forming module 101 for forming the STO upper film 87 corresponds to the upper film forming unit in this example. As the upper film forming unit, a film-forming module 101 common to those forming the SrO film 84 related to the first embodiment, the SrO film 84a related to the second embodiment, or the Sr-rich STO film 86 can also be used. Furthermore, film-forming modules 101 different from those forming the films 84, 84a, and 86 can be connected to the vacuum transfer chamber 24. The STO top film 87 is formed to a thickness of 3 nm or more but less than 30 nm, which is thicker than the crystalline STO film 85. Furthermore, the atomic ratio of titanium to strontium in the STO top film 87 can be 1.0 or more. Since the STO top film 87 is not directly in contact with the TiN film 83, it is not limited to a range of 0 or more but less than 1.0, allowing for more flexible adjustment of the strontium to titanium ratio. For example, when conditions are included where a crystalline STO film with higher relative capacitance can be obtained in a range close to or greater than 1.0, the limitation of forming a crystalline STO film 85 on top of the TiN film 83 is not imposed, and a high-quality STO top film 87 can be formed. As a preferred ratio in this case, an example is the STO top film 87 with a titanium to strontium atomic ratio in the range of 0.8 or more but less than 1.2. The STO upper film 87 formed by the above method can also be converted into a crystalline STO film 88 by heat treatment using the heat treatment module 102. As the upper film heat treatment unit that performs heat treatment of the STO upper film 87, the heat treatment module 102 common to those performing heat treatment of the SrO film 84 related to the first embodiment, the SrO film 84a related to the second embodiment, or the Sr-rich STO film 86 can also be used. Furthermore, other heat treatment modules 102 different from those used to form the films 84, 84a, and 86 can be connected to the vacuum transfer chamber 24. The first to third embodiments described above are configured such that the film-forming module 101, which is a monolithic module, and the heat treatment module 102 are connected in a common vacuum transfer chamber 24. On the other hand, the process of forming amorphous films (SrO films 84, 84a, Sr-rich STO films 86), or the process of converting these films 84, 84a, 86 into crystalline STO films 85 by heat treatment, is not limited to being carried out in the common film-forming apparatus 1. For example, a batch processing apparatus that holds a multiple wafers W in a heating furnace for processing can also be used to separately form amorphous films and perform heat treatment. Regarding heat treatment, a rapid thermal annealing (RTA) device, such as an infrared lamp, can be used to heat the wafers W in a shorter processing time than the aforementioned 5 minutes. Furthermore, amorphous films can also be formed using a semi-batch film formation apparatus, which arranges multiple wafers W on a rotating stage and makes the wafers W revolve around a rotation axis to pass through multiple processing spaces that are separated from each other, so as to repeatedly perform the adsorption of raw material gases and the formation of SiO or TiO thin films caused by oxidizing gases. On the other hand, other modules, such as the module that forms the TiN film 83, can be connected to the vacuum transfer chamber 24 of the film forming apparatus 1 shown in FIG2, for example. In this case, a multilayer structure of various films formed on the wafer W can be formed using a common film forming apparatus 1. The embodiments disclosed in this specification should be considered illustrative in all respects and not intended to limit the scope of the invention. The aforementioned embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the claims. [Example] (Experiment 1) Corresponding to the first embodiment, an SrO film 84 was formed on the upper side of the TiN film 83 illustrated in FIG. 1 to confirm the difference in film structure caused by heat treatment. A. Experimental conditions (Example 1) A TiN film 83 with a thickness of 10 nm was formed on wafer W. Further, an SrO film 84 with a thickness of 10 nm was formed on its upper side by means of ALD method according to steps 1 to 4 in FIG. 5. The Sr raw material used was a cyclopentadiene-based strontium compound, and the heating temperature of wafer W was set to 350 °C. Then, wafer W was heated to 600 °C under an argon-supplied atmosphere (pressure 400 Pa (3 Torr)) and heat-treated for 1 hour. The crystal structure of the heat-treated wafer W was analyzed by XRD (X-ray Diffraction), and cross-sectional observation was performed by TEM (Transmission Electron Microscope). (Comparative Example 1) After the SrO film 84 was formed, the same analysis as in Example 1 was performed on the wafer W that had not undergone heat treatment. B. Experimental Results The results of XRD analysis related to Example 1 and Comparative Example 1 are shown in Figure 8. The horizontal axis of Figure 8 represents the diffraction angle of X-rays, and the vertical axis represents the detected X-ray intensity. Figure 9 shows the results of stacking the TiN film 83, SrO film 84, and crystalline STO film 85 based on TEM observations in a bar chart of the thickness of each layer. Based on the XRD analysis results shown in Figure 8, in Example 1 where heat treatment was performed after the formation of the SrO film 84, X-ray diffraction peaks were confirmed at the diffraction angle corresponding to the crystallization plane of the crystalline STO. This suggests that a crystalline STO film 85 can be formed by heat treating the wafer W on which the SrO film 84 is formed on top of the TiN film 83. On the other hand, in Comparative Example 1, no diffraction peaks corresponding to the crystalline STO were confirmed. Based on the TEM observation results shown in Figure 9, it was confirmed that a layer with a thickness of approximately 6 nm was formed between the TiN film 83 and the SrO film 84 in Example 1. This layer can be understood as corresponding to the crystalline STO film 85, which shows diffraction peaks corresponding to the crystalline plane of crystalline STO in XRD analysis. On the other hand, the TEM observation results of Comparative Example 1 also showed a thin layer of approximately 3.5 nm formed between the TiN film 83 and the SrO film 84. However, considering that diffraction peaks corresponding to the crystalline plane of crystalline STO could not be identified in the XRD analysis, it can be understood as a mixed amorphous layer of SrO and SiN formed during the formation of the SrO film 84. (Experiment 2) Corresponding to the second embodiment, the type of film formed on the upper side of the TiN film 83 illustrated in FIG. 6 was changed to confirm the difference in film structure after heat treatment. A. Experimental conditions (Example 2-1) Except for the thickness being 5 nm, the SrO film 84a was formed under the same conditions as in Example 1. Then, the wafer W was heated to 630°C and heat-treated for 1 hour under an argon-supplied atmosphere (pressure 400 Pa (3 Torr)). The wafer W after heat treatment was analyzed by XRD for crystal structure and observed by SEM (Scanning Electron Microscope). (Example 2-2) Instead of the SrO film 84a, according to cycles 1 to 8 in FIG. 5, a Sr-rich STO film 86 with a titanium to strontium content ratio of 9.4 (first cycle X: second cycle Y = 10:1) was formed by ALD. The wafer W was analyzed in the same way as in Example 2-1. (Comparative Example 2-1) An amorphous STO film with a titanium to strontium content ratio of 1.0 (first cycle X: second cycle Y = 2:3) was formed using the same method as in Example 2-1. The wafer W was subjected to the same heat treatment and analysis as in Example 2-1. B. Experimental Results The XRD analysis results of Examples 2-1, 2-2, and Comparative Example 2-1 are shown in Figure 10. The horizontal and vertical axes of Figure 10 are the same as those of Figure 8. In addition, SEM images of the W surface of each wafer are shown in Figures 11(a) to (c). Based on the XRD analysis results shown in Figure 10, diffraction peaks corresponding to crystalline STO were confirmed in Example 2-1, which formed a 5 nm thick SrO film 84a, and in Example 2-2, which formed a 5 nm thick Sr-rich STO film 86. Therefore, the XRD analysis results indicate that these films 84a and 86 have been converted into crystalline STO films 85. On the other hand, in Comparative Example 2-1, which has a relatively high titanium content, no diffraction peaks corresponding to crystalline STO were confirmed. Furthermore, according to the SEM images shown in Figures 11(a) and (b), the crystalline STO films 85 related to Examples 2-1 and 2-2 obtained by heat-treating the SrO film 84a and the Sr-rich STO film 86 both have flat surfaces. On the other hand, according to Figure 11(c), the surface of the wafer W related to Comparative Example 2-2, obtained by heat-treating the amorphous STO with a titanium to strontium content ratio of 1.0, has multiple protrusions formed on its surface, which are called bubbles. These bubbles are formed due to the peeling off of a portion of the amorphous STO film, and they can cause film property degradation such as film peeling or a decrease in relative permittivity, which is undesirable. (Experiment 3) Corresponding to the third embodiment, the type of film formed on the underside of the STO upper film 87 illustrated in Figure 7 was changed to confirm the difference in film structure after heat treatment. A. Experimental conditions (Example 3-1) An STO upper film 87 with a thickness of 20 nm and a titanium to strontium content ratio of 1.0 was formed on the top of the crystalline STO film 85 formed by the method described in Example 2-2. The method for forming the STO upper film 87 was the same as in Comparative Example 2-1. For the wafer W with the STO upper film 87 formed, the wafer W was heated to 630°C under an argon atmosphere (pressure 400 Pa (3 Torr)) and heat-treated for 1 hour. The surface of the heat-treated wafer W was observed using SEM. (Comparative Example 3-1) After heat treatment of the amorphous STO film with a titanium to strontium content ratio of 1.0 formed in the method described in Comparative Example 2-1, the formation and heat treatment of the STO upper film 87 were carried out under the same conditions as in Example 3-1, except that an STO upper film 87 was formed on it, and the surface was observed by SEM. B. Experimental Results SEM images of Example 3-1 and Comparative Example 3-1 are shown in Figures 12(a) and (b), respectively. Furthermore, XRD analysis confirmed that in both experiments, a crystalline STO film 88 was formed after heat treatment of the STO upper film 87. Based on the results shown in Figure 12(a), it can be confirmed that when the STO upper film 87 is formed on the surface of the flat crystalline STO film 85 shown in Figure 11(b), the surface of the crystalline STO film 88 after heat treatment is also flat. On the other hand, based on the results shown in Figure 12(b), it can be seen that when the STO upper film 87 is formed on the surface of the film with the blister shown in Figure 11(c), a blister is also formed on the surface of the crystalline STO film 88 after heat treatment. W: Wafer 1: Film deposition apparatus 101: Film deposition module 102: Heat treatment module 83: TiN film 84: SrO film 85: Crystallized STO film Figure 1 is a schematic diagram showing a method for forming an STO film with a crystal structure related to the first embodiment. Figure 2 is a top view of a film-forming apparatus for forming the STO film. Figure 3 is a longitudinal sectional side view of the film-forming section. Figure 4 is a longitudinal sectional side view of the heat treatment section. Figure 5 is a diagram showing an example of the film-forming sequence. Figure 6 is a schematic diagram showing a method for forming an STO film with a crystal structure related to the second embodiment. Figure 7 is a schematic diagram showing a method for forming an STO film with a crystal structure related to the third embodiment. Figure 8 is a first diffraction spectrum showing the XRD analysis results of the STO films related to the examples and comparative examples. Figure 9 is a graph showing the layered structure of the STO film. Figure 10 is a second diffraction spectrum showing the XRD analysis results of the STO films related to the examples and comparative examples. Figure 11 is a first electron microscope image of the surface of the STO film related to the examples and comparative examples. Figure 12 is a second electron microscope image of the surface of the STO film related to the examples and comparative examples. W: Wafer 81: Silicon wafer 82: SiO film 83: TiN film 84:SrO membrane 85: Crystalline STO film

Claims

1. A method for forming a film, comprising the steps of forming a film containing strontium, titanium, and oxygen in a substrate: forming an amorphous film on top of a titanium nitride film formed on the surface of the substrate, the amorphous film containing strontium and oxygen, and the titanium content being adjusted to a value in which the ratio of titanium to strontium atomic number is 0 or more but less than 1.0; heating the substrate on which the amorphous film is formed at a temperature of 500°C or higher to obtain the crystalline film containing strontium, titanium, and oxygen; in the step of forming the amorphous film, the amorphous film is formed with a thickness in the range of 5 nm or more and 10 nm or less; in the step of obtaining the crystalline film, the amorphous film has been converted into the crystalline film; the method for forming the film further comprises the following steps: After obtaining the crystalline film, a process is performed to form an upper layer film containing strontium, titanium and oxygen on the surface of the crystalline film; and then, the substrate on which the upper layer film is formed is heated at a temperature of 500°C or higher to convert the upper layer film into the crystalline film containing strontium, titanium and oxygen.

2. The method for forming a film as described in claim 1, wherein the upper film system of the amorphous structure is formed to have a thickness of 3 nm or more.

3. The method of forming a film as described in claim 1 or 2, wherein the content ratio of titanium to strontium in the upper layer of the amorphous structure is in the range of 0.8 or more and 1.2 or less.

4. An apparatus for forming a film, comprising: a film forming section for forming an amorphous film on a substrate containing a crystalline structure of strontium, titanium, and oxygen, wherein the amorphous film contains strontium and oxygen, and the titanium content is adjusted to a value in which the ratio of titanium to strontium atomic number is 0 or more but less than 1.0; a heat treatment section for heat treatment, wherein the substrate on which the amorphous film is formed is heated at a temperature of 500°C or higher to obtain the crystalline film containing strontium, titanium, and oxygen containing titanium diffused from the titanium nitride film; wherein the heat treatment section forms the amorphous film with a thickness in the range of 5 nm or more and 10 nm or less; wherein the heat treatment section converts the amorphous film into the crystalline film by means of the heat treatment; the apparatus for forming the film further comprises: The upper film forming section forms an amorphous upper film containing strontium, titanium, and oxygen on the surface of the crystalline film after heat treatment in the heat treatment section; and the upper film heat treatment section that performs heat treatment heats the substrate on which the upper film is formed at a temperature of 500°C or higher to convert the upper film into the crystalline film containing strontium, titanium, and oxygen.

5. The film-forming apparatus according to claim 4, wherein the film-forming section comprises: a processing container for housing the substrate on which the titanium nitride film is formed; a first raw material gas supply unit for supplying a gas containing strontium to the processing container; a second raw material gas supply unit for supplying a gas containing titanium to the processing container; and an oxidation gas supply unit for supplying an oxidation gas for oxidizing the strontium and titanium raw materials to the processing container; further, the film-forming apparatus comprises a control unit; the control unit is configured to output control signals for repeatedly performing a first cycle and a second cycle respectively: the first cycle includes the step of supplying the gas containing the strontium raw material to the substrate in the processing container from the first gas supply unit to adsorb the strontium raw material onto the substrate; and then, the step of supplying an oxidation gas to the substrate from the oxidation gas supply unit to oxidize the strontium raw material; The second cycle includes the step of supplying gas to the titanium raw material from the second gas supply unit to adsorb the titanium raw material onto the substrate; and then, the step of supplying oxidizing gas to the substrate from the oxidizing gas supply unit to oxidize the titanium raw material; the content ratio in the amorphous film is adjusted by the ratio of the number of times each of the first and second cycles is performed.

6. The apparatus for forming a film as described in claim 4, wherein the upper film forming section has an upper film with a thickness of 3 nm or more.

7. The apparatus for forming a film as described in claim 4 or 6, wherein the content ratio of titanium to strontium in the upper layer of the amorphous structure is in the range of 0.8 or more and 1.2 or less.

Images