Method for forming metal film, and device for forming metal film

Abstract

To provide a feature for suppressing a decrease in a film forming speed when forming a metal film using a raw material having characteristics of decreased film forming speed over time. This method for forming a metal film comprises: a step for supplying a film-forming gas containing a metal halide serving as a raw material of a metal film to a substrate and reacting the film-forming gas to form the metal film on the surface of the substrate; a step for, when the step for forming the metal film has characteristics of decreased film forming speed over time, vacuum-exhausting the atmosphere in which the substrate is disposed while supplying a cleaning gas that reacts with a by-product generated by the reaction of the film-forming gas, after the supply of the film-forming gas is stopped; and a step for performing again the step for forming the metal film after the step for vacuum-exhausting is carried out.

Description

METHOD FOR FORMING METAL FILM AND APPARATUS FOR FORMING METAL FILM

[0001] The present disclosure relates to a method for forming a metal film and an apparatus for forming a metal film.

[0002] In the manufacturing process of semiconductor devices, a process for forming a metal film, such as a titanium film, may be performed in recesses such as trenches and via holes formed in the surface of a semiconductor wafer (hereinafter referred to as "wafer"), which is a substrate. Patent Document 1 proposes a method for forming a pure titanium film by contacting a monolayer of titanium tetrachloride with atomic low-pressure hydrogen. It describes that the hydrogen atoms react with chlorides in the monolayer of titanium tetrachloride to form hydrogen chloride, which is then exhausted, resulting in the formation of a monolayer of titanium.

[0003] Patent Document 2 proposes a method for forming a titanium nitride film using a halogenated source gas and a reactive gas. It describes that the step coverage of the titanium nitride film is improved by performing a predetermined number of steps in a time-division manner: a step of supplying a halogenated source gas, a step of supplying a reaction inhibitor gas that inhibits the reaction between the halogenated source gas and the reactive gas, and a step of supplying a reactive gas.

[0004] JP 2011-184799 A JP 2017-69407 A

[0005] The present disclosure provides a technique for suppressing a decrease in film formation rate when forming a metal film using a raw material that has the property of decreasing the film formation rate over time.

[0006] The present disclosure provides a method for forming a metal film on a substrate, comprising the steps of: supplying a film-forming gas containing a metal halide that is a raw material for the metal film to the substrate, and reacting the film-forming gas to form the metal film on the surface of the substrate; and, if the metal film-forming step has a characteristic that the film-forming rate decreases over time, after stopping the supply of the film-forming gas, evacuating the atmosphere in which the substrate is placed while supplying a cleaning gas that reacts with by-products generated by the reaction of the film-forming gas, and is characterized in that after the vacuum evacuation step is performed, the metal film-forming step is performed again.

[0007] According to the present disclosure, when forming a metal film using a raw material having a characteristic that the film formation rate decreases over time, it is possible to suppress the decrease in the film formation rate.

[0008] FIG. 1 is a longitudinal sectional side view showing an example of the configuration of a film forming apparatus that is an apparatus for forming a metal film according to the present disclosure; FIG. 2 is a schematic diagram showing the state of forming a titanium film that is a metal film; FIG. 3 is a time chart according to a first embodiment of a method for forming a metal film; FIG. 4 is a first example of a combination of a film forming process and a vacuum exhaust process; FIG. 5 is a second example of a combination of a film forming process and a vacuum exhaust process; FIG. 6 is a time chart according to a second embodiment of a method for forming a metal film; FIG. 7 is a characteristic diagram showing the results of evaluation test 1; FIG. 8 is a first table showing the results of evaluation test 2; and FIG. 9 is a second table showing the results of evaluation test 3.

[0009] The present disclosure provides a method for suppressing a decrease in film formation rate when forming a metal film by a chemical vapor deposition (CVD) method using a film formation gas containing a metal halide. Hereinafter, titanium tetrachloride (TiCl) is used as the film formation gas containing a metal halide. ４ ) gas and hydrogen (H ２ The present inventors will explain the case of forming a titanium (Ti) film, which is a metal film, by using a mixed gas of TiCl ４ It has been found that the deposition rate of a Ti film formed by a CVD method using a gas decreases over time, as will be shown in the evaluation test described later. The decrease in deposition rate over time means that the thickness of the metal film formed and the deposition time do not have a linear function relationship, but the slope of the function decreases over time.

[0010] The reason for this is presumably that as the Ti film formation progresses, by-products containing, for example, chlorine (Cl) generated by the reaction of the film formation gas increase, inhibiting the progress of the Ti film formation reaction. Therefore, in the present disclosure, a process of evacuating the atmosphere in which the wafer is placed while supplying a cleaning gas that reacts with the by-products is performed to suppress a decrease in the Ti film formation rate. Hereinafter, with reference to FIG. 1, a configuration example of a film formation apparatus 1, which is an apparatus for forming a metal film according to the present disclosure, will be described.

[0011] <Film Forming Apparatus> Hereinafter, a configuration example of a film forming apparatus 1 according to the present disclosure will be described with reference to Fig. 1. Fig. 1 is a vertical cross-sectional side view of the film forming apparatus 1 according to the present embodiment. The film forming apparatus 1 applies a film forming gas, TiCl ４ Gas and H ２ The apparatus is configured as an apparatus that continuously supplies a gas and argon (Ar) gas and forms a Ti film 6 by plasma CVD.

[0012] The film forming apparatus 1 includes a grounded, substantially cylindrical metal processing vessel 10 that is corrosion-resistant to chlorine. A cylindrical exhaust chamber 11, for example, that protrudes downward is formed in the center of the bottom of the processing vessel 10, and an exhaust path 12 is connected to the side of the exhaust chamber 11. An exhaust unit 13 including a pressure adjustment valve, for example, a butterfly valve, is connected to the exhaust path 12, and the processing vessel 10 can be evacuated to a predetermined vacuum pressure.

[0013] A loading / unloading port 14 is formed on the side of the processing vessel 10 for loading / unloading the wafer W between the processing vessel 10 and a vacuum transfer chamber (not shown), and the loading / unloading port 14 is configured to be freely opened and closed by a gate valve 15. Furthermore, a heater 16 for adjusting the temperature inside the processing vessel 10 is embedded in the wall portion that constitutes the processing vessel 10.

[0014] A mounting table 2 for holding a wafer W substantially horizontally is provided within the processing vessel 10. The mounting table 2 is supported by a support 21 extending from the bottom of the exhaust chamber 11, and the mounting table 2 and the support 21 are made of a conductive material. A heater 20, which is a heating unit, is embedded in the mounting table 2, and the wafer W can be heated to a set temperature. In this example, the heating temperature of the wafer W is set to, for example, 450°C within a range of 350°C to 800°C.

[0015] A high frequency power supply 23 that supplies high frequency power for attracting ions is connected to the mounting table 2 via a matching box 22. The mounting table 2 is further provided with lift pins (not shown) for holding and lifting the wafer W on the mounting table 2. The wafer W can be transferred between the mounting table 2 and an external transfer mechanism (not shown) by raising and lowering the lift pins. The mounting table 2 may also be configured not to supply high frequency power for attracting ions.

[0016] A flat, disk-shaped showerhead 3 for supplying a processing gas toward the wafer W is attached to the ceiling surface of the processing vessel 10 via an insulating member 17. A diffusion chamber 31 for diffusing the gas is formed inside the showerhead 3, and a number of discharge holes 32 for discharging the gas toward the wafer W are provided in a dispersed manner on the bottom surface of the showerhead 3. Furthermore, a heater 36 is embedded in the upper surface of the showerhead 3, for example.

[0017] A high frequency power supply 34 that supplies high frequency power for plasma generation is connected to the shower head 3 via a matching box 33. This high frequency power supply 34 constitutes a plasma generation unit. As described above, the film forming apparatus 1 of the present disclosure is configured as a parallel plate type plasma processing apparatus by the shower head 3 that constitutes an upper electrode and the mounting table 2 that constitutes a lower electrode. A wafer W is placed in the space between the shower head 3 and the mounting table 2, and TiCl ４ Gas, H ２By supplying gas or Ar gas and applying high-frequency power, these gases are ionized to form plasma. The high-frequency power supply 34 may be configured to supply high-frequency power at any of the following frequencies: 450 KHz, 2 MHz, 13.56 MHz, 27 MHz, 40 MHz, 60 MHz, 100 MHz, or 2.45 GHz. The high-frequency power supplied from the high-frequency power supply 34 is in the range of more than 0 W and not more than 2000 W.

[0018] The downstream end of a gas supply line 40 is connected to the diffusion chamber 31 of the shower head 3. The upstream side of the gas supply line 40 is connected to a TiCl 4 gas, which is a source gas for a film formation gas. ４ gas and reactive gas H ２ Gas supply flow paths 41 and 42, a supply flow path 43 for Ar gas added for plasma generation, and a cleaning gas NH ３ Gas supply flow paths 44 join together.

[0019] TiCl ４ At the upstream end of the gas supply flow path 41, TiCl ４ A gas supply source 410 is connected, and a flow rate regulator M41 and a valve V41 are provided in this order from the upstream side. ２ At the upstream end of the gas supply flow path 42, H ２ A gas supply source 420 is connected to the supply flow path 43, and a flow rate regulator M42 and a valve V42 are disposed in this order from the upstream side. Furthermore, an Ar gas supply source 430 is connected to the upstream end of the supply flow path 43 for Ar gas, and a flow rate regulator M43 and a valve V43 are disposed in this order from the upstream side. ３ At the upstream end of the gas supply flow path 44, NH ３ A gas supply source 440 is connected, and a flow rate regulator M44 and a valve V44 are provided in this order from the upstream side.

[0020] In this example, the deposition gas supply unit is TiCl ４ Gas supply passage 41, TiCl ４ Gas supply source 410, H ２ Gas supply flow path 42, H ２ The gas supply unit 420 is configured to include a gas supply source 420 and a gas supply path 40. The cleaning gas supply unit supplies NH ３Gas supply flow path 44, NH ３ The gas supply source 440 and the gas supply path 40 are included.

[0021] The film forming apparatus 1 having the above-described configuration includes a control unit 100 as shown in FIG. 1. The control unit 100 is configured with a computer including a storage unit, a memory, and a CPU that stores a program. The program contains instructions (steps) for executing a process of forming a Ti film 6 by outputting control signals from the control unit 100 to each unit of the film forming apparatus 1 and controlling the supply and cutoff of each gas and the supply of high-frequency power. The program is stored in a storage unit of the computer, such as a flexible disk, compact disk, hard disk, MO (magneto-optical disk), or nonvolatile memory, and is read from the storage unit and installed in the control unit 100.

[0022] <First Embodiment of Method for Forming Ti Film> A first embodiment of the method for forming a Ti film performed by the film forming apparatus 1 described above will be described using as an example the case of forming a Ti film 6 in a recess 50 formed in the surface of a wafer, as shown in Figure 2. In this example, the recess 50 is formed in a silicon oxide film (SiO film 52) covering a silicon member 51 constituting the wafer W. Therefore, the silicon member 51 is exposed at the bottom surface of the recess 50, and the SiO film 52 is exposed at the sidewall surface. Note that instead of the SiO film, the silicon member 51 may be covered with a silicon nitride film (SiN film), and the sidewall surface of the recess 50 may be formed with the SiN film.

[0023] 3 is an example of a time chart relating to the process of forming the Ti film 6 performed using the above-described film forming apparatus 1. This time chart shows the time when the film forming gas (TiCl ４ Gas, H ２ gas) and NH ３The timing of supply and cut-off of gases and the timing of application of high-frequency power (denoted as "plasma power supply" in FIG. 3) from the high-frequency power supply 34 are shown schematically. The supply and cut-off control of each gas and the timing of application of high-frequency power are controlled by the control unit 100, and the time chart shown in FIG. 3 is executed. That is, the control unit 100 controls the opening and closing of valves V41, V42, V43, and V44 to supply and cut off each gas, and also sets the flow rates of the flow rate adjustment units M41, M42, M43, and M44.

[0024] The process for forming the Ti film 6 will be described with reference to the time chart of FIG. 3 . In this process, first, the gate valve 15 is opened, and a transfer mechanism (not shown) installed in a vacuum transfer chamber loads the wafer W into the processing chamber 10 through the load / unload port 14. The loaded wafer W is then transferred from the transfer mechanism to the mounting table 2 via lift pins (not shown) and placed on the upper surface of the mounting table 2. Next, the transfer mechanism is retracted from the processing chamber 10, and the gate valve 15 is closed. The processing chamber 10 is then evacuated to a vacuum by the exhaust unit 13, and the pressure inside the processing chamber 10 is adjusted to a preset pressure. The wafer W is then heated to the aforementioned 450° C. by the heater 20.

[0025] 3, the supply of the film formation gas is started, and the high-frequency power supplies 34 and 23 start applying high-frequency power to the shower head 3 and the mounting table 2, respectively. In this manner, the supply of the film formation gas and the application of high-frequency power are continued for a preset time (e.g., 360 seconds) until time T1 shown in Fig. 3. The period from time T0 to time T1 is the process of forming a metal film (Ti film) (hereinafter referred to as the "film formation process").

[0026] In this film formation process, a film formation gas (TiCl ４ Gas and H ２ The mixed gas of the film forming gas and Ar gas is supplied to the shower head 3 via the supply passages 41, 42, and 43 and the gas supply passage 40. The mixed gas of the film forming gas and Ar gas flows into the diffusion chamber 31 of the shower head 3 via the gas supply passage 40 and is discharged into the processing vessel 10 through the discharge holes 32. Then, the mixed gas of the film forming gas and Ar gas is converted into plasma by supplying high frequency power from the high frequency power supplies 34 and 23 to the shower head 3 and the mounting table 2, respectively.

[0027] TiCl, which is a deposition gas ４ Gas and H ２ The gas is supplied into the processing chamber 10 at a preset flow rate from time T0 to time T1. For example, Ar gas is supplied continuously from time T0 to the end of the processing sequence. The Ar gas functions as an auxiliary gas that assists in the formation of plasma of the film-forming gas while the high-frequency power for plasma generation is being applied, and functions as a purge gas while the application of the high-frequency power is stopped.

[0028] An example of the film forming process conditions at this time is as follows: wafer W temperature: 450° C., process chamber internal pressure: 1.2 kPa (9 Torr), TiCl ４ Gas flow rate: 25 sccm, H ２ Gas flow rate: 1000 sccm, Ar gas flow rate: 2400 sccm, high frequency power from high frequency power supply 34: 10 kHz, 100 W, high frequency power from high frequency power supply 23: 10 Hz, 100 W.

[0029] In the above-mentioned film forming process, the reactive gas is plasma-formed H ２ The source gas TiCl ４ is reduced to highly reactive TiCl ２ A large amount of ions or radicals are formed. ２ Ions or radicals are adsorbed on the bottom surface of the recess 50, forming a Ti film 6. By applying high-frequency power, plasma is generated between the parallel plates (shower head 3 - mounting table 2) including the inside of the recess 50, and high-frequency power for attracting ions is supplied to the mounting table 2. By this action, TiCl ２ It can be said that ions are supplied and a Ti film 6 can be formed in the region.

[0030] By the way, TiCl ４The gas also has the effect of etching titanium. Furthermore, the SiO film 52 and SiN film have stronger bonds between silicon and oxygen or nitrogen than the silicon member 51, and the bonds with the Ti film 6 formed on the surface thereof are relatively weak. Therefore, compared to the bottom surface of the recess 50 where the silicon member 51 is exposed, the sidewall surface of the recess 50 where the SiO film (SiN film) 52 is exposed is more susceptible to TiCl ４ Therefore, although a Ti film is actually formed on the sidewall surface of the recess 50, the Ti film on the sidewall surface is thinner than the Ti film on the bottom surface. For this reason, the Ti film 6 on the sidewall surface of the recess 50 is not shown in FIG. 2, and only the Ti film 6 formed on the bottom surface is depicted.

[0031] Thus, in the film formation process, TiCl ４ is TiCl ２ The film formation of the Ti film proceeds smoothly at the start of this process. ２ Radicals are generated and a Ti film is rapidly formed. ４ By decomposition of TiCl ２ Along with the radicals, by-products containing Cl are also produced. ４ In this case, among the atoms constituting the by-product, it is Cl that affects the decrease in the reaction rate, which will be described later, and therefore the by-product will be referred to as "Cl" in the following description. This Cl is not consumed in the formation of the Ti film, so the Cl concentration in the processing vessel 10 gradually increases. Here, consider a case in which the film formation gas is continuously supplied for, for example, 360 seconds in the above-mentioned CVD film formation process. When film formation is performed for such a long period of time, even if the processing vessel 10 is evacuated in parallel, the amount of Cl present in the processing vessel 10 is greater than in a film formation process by ALD (atomic layer deposition), in which the film formation gas is supplied for a short period of time and then purged.

[0032] As will be shown in Evaluation Test 1, which will be described later, in the Ti film formation process, the Ti film formation rate gradually decreases over time, and eventually reaches a saturated state where the film thickness does not increase even if the film formation time is increased (Reference Example 1 in FIG. 6, which will be described later). The reason for this is presumed to be as follows: When the Cl concentration in the processing vessel 10 increases, TiCl ２ The reaction between radicals and Cl proceeds more easily, resulting in TiCl ２ The ion or radical is TiCl ３ It changes into radicals or TiCl ４ Here, TiCl ３ Radicals also act as film-forming species, but TiCl ２ Compared to radicals, they have a higher vapor pressure and a lower adsorption rate to the wafer W. In other words, even if they collide with the wafer W, they are less likely to be adsorbed and are more likely to volatilize and be discharged from the processing vessel 10. ２ It is considered that the contribution to film formation is smaller than that of radicals. ４ TiCl by decomposition of ２ Even if radicals are generated, unintended reactions occur afterwards, resulting in the formation of TiCl ２ It is presumed that the amount of radicals decreases, and as a result, the Ti film reaches a saturated state where it is difficult to increase its thickness, and it takes a long time to reach the target film thickness.

[0033] From the above, in the present disclosure, after the supply of the film forming gas is stopped, the cleaning gas NH ３ While supplying the gas, a process of evacuating the processing chamber 10 (hereinafter referred to as the "evacuation process") is carried out. ３ The gas is supplied for, for example, 3 seconds. In this evacuation step, no high frequency power is applied, and NH ３ Ar gas and H ２ Gas is also supplied at the same time (Fig. 3 shows the cleaning gas NH ３ Only the gas supply is shown. ２The reason why the gas is also supplied is to react with the Cl remaining in the processing vessel 10 to generate hydrogen chloride (HCl), which is then exhausted from the processing vessel 10. It is presumed that by changing the Cl present in an unstable state in the processing vessel 10 to a stable state (HCl), the remaining Cl is more easily purged. Note that, during the period from time T1 to time T2, the supply of Ar gas and the evacuation of the processing vessel 10 are continuously performed, and the inside of the processing vessel 10 is purged (purge process). However, during the period when the application of high frequency power for plasma generation is stopped or the evacuation process is being performed, the supply of Ar gas is stopped, and nitrogen gas (N) is used as the purge gas instead of Ar gas. ２ Gas) may be supplied.

[0034] NH ３ When the gas is supplied, Cl present in the processing vessel 10 is converted into NH ３ It reacts with HCl and NH ４ Cl is generated, and these reaction products are discharged to the outside as the processing vessel 10 is evacuated. It is believed that Cl is present in the atmosphere inside the processing vessel 10, and that Cl is also attached to members exposed inside the processing vessel 10, such as the sidewall surface of the processing vessel 10 and the surface of the mounting table 2. As such, it may be difficult to remove Cl attached inside the processing vessel 10 by simply evacuating the vessel while supplying an inert gas such as Ar gas as a purge gas. Therefore, NH ３ This supplies Cl and NH ３ It is estimated that the Cl concentration in the processing vessel 10 can be reduced because the reaction products with TiCl are discharged to the outside of the processing vessel 10. As a result, the TiCl ２ The decrease in the amount of radicals is suppressed, and NH ３ The decrease in the film formation rate can be suppressed compared to when the vacuum evacuation step is not performed while supplying gas.

[0035] An example of the processing conditions for the above vacuum exhaust step is as follows: wafer temperature: 450° C., pressure inside the processing chamber: 0.4 kPa (3 Torr), NH ３ Gas flow rate: 9000 sccm, H ２The gas flow rate was 4500 sccm, and the Ar gas flow rate was 2000 sccm. ３ The gas supply is stopped, and the second film formation process is started at time T4. However, during the period from time T3 to time T4, similar to the period from time T1 to time T2, Ar gas is supplied and the processing vessel 10 is evacuated to a vacuum, and a purge process is performed. As a result, NH ３ HCl, NH ４ Cl and other substances are discharged to the outside.

[0036] Next, from time T4 to time T5, a second film formation process is performed by supplying film formation gas and applying high-frequency power, and a Ti film is formed in the same manner as in the first film formation process described above. Subsequently, a purge process is performed from time T5 to time T6, a second evacuation process is performed from time T6 to time T7, and a purge process is performed from time T7 to time T8, each performed by the same methods as described above. After this, a third film formation process is started at time T8.

[0037] 3 shows the process up to time T8, but in reality, a process cycle is formed by performing a vacuum evacuation process after a film formation process and then performing the film formation process again, and this process cycle is repeated one or more times as predetermined to form a Ti film. The number of times the process cycle is repeated is set appropriately depending on the target film thickness of the Ti film, the process conditions for the film formation process, and the process conditions for the vacuum evacuation process.

[0038] In this case, for example, the respective execution times of the film formation process and the evacuation process can be set so as to minimize the total execution time of the film formation process and the evacuation process until the thickness of the Ti film reaches a preset target thickness. As mentioned above, if the film formation process is continued as is, a saturation state will occur in which the thickness of the Ti film is difficult to increase, and the time until the target thickness is reached will be longer. On the other hand, if the evacuation process is performed, the saturation state will be improved, but film formation will not be possible during the period when evacuation is being performed.

[0039] Therefore, for example, in a preliminary experiment, a Ti film is formed by changing the film formation time required for the film formation process and the cleaning evacuation time required for the evacuation process. Ｔ 4A shows a schematic diagram of the change in the thickness of the Ti film over time during the film formation period when one cycle of a vacuum exhaust process and a second film formation process is carried out after the first film formation process. In the example shown in FIG. 4A, in the first film formation process, film formation is carried out for a period (time T0-T1) until the increase in film thickness reaches a saturated state. Thereafter, a vacuum exhaust process is carried out while supplying cleaning gas (time T2-T3), and then the thickness of the Ti film is again increased to the target film thickness D Ｔ In this example, the film formation process was performed for a period (time T4-T5) until the temperature reached 100°C. If the first film formation process is performed for a long time, the amount of Cl remaining in the processing vessel 10 also increases, and in the film formation process after the evacuation process, the film formation rate may not recover to the same level as in the first process. However, in this example, there is only one evacuation process period during which no film formation is performed.

[0040] In comparison with the above example, FIG. 4B shows a case where the target film thickness D is achieved by performing two cycles of a vacuum exhaust process and a second film formation process after the first film formation process. Ｔ 4B shows a schematic diagram of the change in the thickness of a Ti film over time when film formation is performed up to the time T0-T1, T4-T5, and T8-T9. In the example shown in FIG. 4B, in each film formation process (time T0-T1, time T4-T5, and time T8-T9), film formation is completed in a short time before the increase in film thickness reaches saturation. Therefore, the amount of Cl remaining in the processing vessel 10 is relatively small, and the film formation rate recovers significantly in the next film formation process after the evacuation process (time T2-T3, time T6-T7). However, in this example, there are two evacuation processes during which no film formation is performed.

[0041] Comparing FIG. 4A and FIG. 4B, if we focus only on the film formation process, it is clear that FIG. 4B is able to achieve the target film thickness D in a shorter time. ＴIt appears that film formation up to this point can be performed. However, as described above, the vacuum evacuation process in which no film formation is performed occurs once in the example of FIG. 4A and twice in the example of FIG. 4B. Therefore, when evaluating the preliminary experiment, the overall time including the vacuum evacuation process in which no film formation is performed (times T0-T5 in the case of FIG. 4A and T0-T9 in the case of FIG. 4B) is compared. Then, the implementation time of each process and the number of cycles are determined so that the total implementation time of the film formation process and vacuum evacuation process is minimized.

[0042] In this manner, the process cycle is performed a preset number of times to form a Ti film having a target thickness. Next, the application of high-frequency power from the high-frequency power sources 34 and 23 is terminated, and the supply of the film-forming gas and Ar gas and the heating of the wafer W are stopped. Thereafter, the wafer W is unloaded from the process vessel 10 in the reverse order of the loading procedure, and the process vessel 10 waits for the loading of the next wafer W. Here, in the Ti film 6 formed along the exposed surface (bottom surface) of the silicon member 51, silicon atoms diffuse from the silicon member 51 side over time, and the Ti film 6 eventually becomes a titanium silicide (TiSi) film.

[0043] As described above, the technology according to the present disclosure is a method for producing a SiO2 film by using a source gas (TiCl ４ gas) and a reactive gas (H ２ This technology aims to improve the film formation rate by recognizing the characteristic that the film formation rate decreases as the CVD processing time increases in CVD, in which a source gas and a reactant gas are simultaneously supplied and reacted. Unlike ALD, which alternately supplies and exhausts a source gas and a reactant gas, CVD supplies the source gas and the reactant gas continuously. Therefore, even if the processing vessel 10 is evacuated, the amount of by-products generated by the reaction between the source gas and the reactant gas increases as the processing time increases. However, the influence of the by-products remaining in the processing vessel 10 has not been given much attention in the past. Furthermore, the above-mentioned prior art documents 1 and 2 do not mention that materials remaining in the processing vessel affect the growth of the Ti film.

[0044] The present disclosure has found that by-products remaining in the processing vessel 10 inhibit the growth of the Ti film, and has improved the saturation state of the increase in the thickness of the Ti film by reducing the by-products. As a specific method for this improvement, after the film formation process, a cleaning gas (NH ３ The process chamber 10 is evacuated to a vacuum while the cleaning gas is being supplied, and the by-products containing Cl remaining in the process chamber 10 are reacted with the cleaning gas and removed. This reduces the amount of Cl in the process chamber 10 and removes the highly reactive TiCl. ２ It is believed that the reaction between radicals and Cl can be suppressed. ２ It is presumed that the radicals can be utilized to form the Ti film, and the decrease in the film formation rate over time can be suppressed.

[0045] Second Embodiment of the Method for Forming a Ti Film Next, a second embodiment of the method for forming a Ti film will be described with reference to the time chart of Fig. 5. In this embodiment, NH 4 is used as a cleaning gas in the vacuum evacuation process. ３ Plasma H instead of gas ２ 5, the first film formation process is performed from time T10 to time T11, and the second film formation process is performed from time T14 to time T15, similar to the first embodiment.

[0046] Then, a first evacuation process is carried out from time T12 to time T13, and a second evacuation process is carried out from time T16 to time T17. ２ The gas and Ar gas are supplied to the shower head 3, and high frequency power is supplied to the shower head 3 from the high frequency power supply 34, thereby converting these gases into plasma.

[0047] Plasma H ２The gas reacts with Cl present in the processing vessel 10 to generate HCl, and this HCl is discharged to the outside as the processing vessel 10 is evacuated. Thus, in this embodiment, the Cl concentration in the processing vessel 10 decreases as a result of the evacuation process. Examples of processing conditions for the evacuation process in this embodiment are: wafer W temperature: 450° C., processing vessel internal pressure: 0.133 kPa (1 Torr), processing time: 30 seconds, H ２ Gas flow rate: 4500 sccm, Ar gas flow rate: 1000 sccm, high frequency power from high frequency power supply 34: 10 kHz, 500 W.

[0048] In this embodiment, purge steps are also performed in the periods T11-T12, T13-T14, T15-T16, and T17-T18 between the film formation step and the evacuation step, as in the first embodiment. As a result, the inside of the processing vessel 10 is purged with Ar gas, and the H 2 gas present in the processing vessel 10 is purged. ２ In this embodiment, the cleaning gas is also plasma-converted H ２ Since the processing vessel 10 is evacuated to a vacuum while the gas is being supplied, Cl in the processing vessel 10 is reduced, and TiCl ２ This can suppress the reaction between the radicals and Cl, thereby preventing a decrease in the film formation rate in the processing chamber 10.

[0049] As described above, the present disclosure has a process cycle in which a vacuum exhaust process is performed after a film formation process, and then a film formation process is performed again. However, the process conditions for the film formation process performed before the vacuum exhaust process and the film formation process performed after the vacuum exhaust process do not necessarily have to be set to the same conditions, and for example, the film formation time may be changed.

[0050] The metal halide is TiCl ４ Examples of gases include, but are not limited to, metal halides such as tungsten pentachloride (WCl ５ ) and tungsten hexachloride (WCl ６The present invention can also be applied to a method for forming a tungsten (W) film using a deposition gas containing a metal halide. ４ gas) and a reactive gas (e.g., H ２ The source gas may be used alone as a film-forming gas and applied to a process for forming a metal film by thermal decomposition CVD.

[0051] Furthermore, NH ３ Gas or plasma H ２ Supplying a gas is not an essential requirement. ２ Gas, silane (SiH ４ ) gas, disilane (Si ２ H ６ ) gas, nitrogen trifluoride (NF ３ In the first embodiment, at least one gas selected from the cleaning gas group consisting of NH 3 ３ The gas is plasma NH ３ If a gas is used, nitrides may be formed on the surface of the wafer W, so it is considered that plasma generation is not preferable.

[0052] Furthermore, the target on which the Ti film 6 is formed using the technique of the present disclosure is not limited to the recess 50 shown in FIG. 2 . For example, a vertical groove may be formed on the surface of the wafer W, and multiple horizontal grooves may be further formed on the sidewall surface of the vertical groove so as to be aligned in the thickness direction of the wafer W. These horizontal grooves may be used as recesses, and the Ti film 6 may be formed within the recesses. Furthermore, the member on which the Ti film 6 is formed is not limited to the silicon member 51, and may be other metals or metal compounds.

[0053] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive, and the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0054] (Evaluation Experiment 1) A Ti film 6 was formed in accordance with the first and second embodiments, and the state of formation of the Ti film 6 in the recess 50 was confirmed. An example of the recess 50 has a width (diameter) W of 40 nm and a depth H of 160 nm. A. Experimental Conditions A Ti film 6 was formed on a wafer W having the recess 50 formed therein using the film forming apparatus 1 described with reference to FIG. 1 in Reference Example 1, in which only the film forming process was performed; Comparative Example 1, in which the film forming process was performed twice with a purge process in which no cleaning gas was supplied therebetween; Example 1-1, which was performed based on the time chart of FIG. 3; and Example 1-2, which was performed based on the time chart of FIG. 5. The respective processing conditions were set as follows:

[0055] (Processing conditions for Reference Example 1) Wafer temperature: 450° C., TiCl ４ Gas supply flow rate: 25 sccm, H ２ The film formation process of the Ti film 6 was carried out under the following conditions: gas supply flow rate: 1000 sccm, Ar gas supply flow rate: 2400 sccm, pressure inside the processing vessel 10: 1.2 kPa (9 Torr), high frequency power supply 34: 10 kHz, 100 W, high frequency power supply 23: no application. Under these conditions, the film formation process was carried out for 10 seconds, 30 seconds, 60 seconds, 120 seconds, 360 seconds, and 540 seconds from the start of the process, and the thickness of the Ti film formed in each case was measured.

[0056] (Processing Conditions for Comparative Example 1) After the film formation process was performed for 360 seconds from the start of the process under the same conditions as in Reference Example 1, the supply of film formation gas and the application of high-frequency power from the high-frequency power supply 34 were stopped. Next, a purging process was performed for 45 seconds to evacuate the processing vessel 10 while supplying Ar gas into the processing vessel 10 at a flow rate of 2400 sccm. After this, the film formation process was performed again under the same conditions as in Reference Example 1, and the thickness of the resulting Ti film was measured when the total processing time reached 540 seconds. Thus, Comparative Example 1 is an example in which a purging process was performed after the first film formation process, and then a second film formation process was performed, and the total processing time is the time required from the start of the first film formation process to the end of the second film formation process.

[0057] (Processing Conditions for Example 1-1) A film forming process was carried out for 360 seconds from the start of the process under the same conditions as in Reference Example 1, and then a purging process was carried out under the same conditions as in Comparative Example 1. After that, the NH ３ After a vacuum evacuation process using NH gas was carried out for 3 seconds, a second film formation process was carried out under the same conditions as in Reference Example 1, and the thickness of the Ti film obtained was measured when the total processing time reached 540 seconds. ３ The processing conditions for the vacuum evacuation process using gas were: wafer temperature: 450°C, NH ３ Gas supply flow rate: 9000 sccm, H ２ The gas supply flow rate was set to 4500 sccm, the Ar gas supply flow rate was set to 24000 sccm, and the pressure inside the processing chamber 10 was set to 400 Pa (3 Torr).

[0058] (Processing Conditions for Example 1-2) A film forming process was carried out for 360 seconds from the start of the process under the same conditions as in Reference Example 1, and then a purging process was carried out under the same conditions as in Comparative Example 1. After that, the plasma H 2 described in the second embodiment was purged. ２ After a vacuum evacuation process using gas was carried out for 30 seconds, a second film formation process was carried out under the same conditions as in Reference Example 1, and the thickness of the Ti film obtained was measured when the total processing time reached 540 seconds. ２ The processing conditions for the vacuum evacuation process using gas were: wafer temperature: 450° C., H ２ The gas supply flow rate was set to 4500 sccm, the Ar gas supply flow rate was set to 2400 sccm, the pressure inside the processing chamber 10 was set to 133 Pa (1 Torr), and the high frequency power source 34 was set to 450 kHz and 500 W.

[0059] B. Experimental Results For each of the wafers W subjected to Reference Example 1, Comparative Example 1, Example 1-1, and Example 1-2, the film thickness of the Ti film 6 formed on the bottom surface of the recess 50 was measured by fluorescent X-ray analysis. The measurement results are shown in FIG. 6. In FIG. 6, the vertical axis represents the film thickness of the Ti film, and the horizontal axis represents the film formation time. The measurement results are plotted as "◯" for Reference Example 1, "△" for Comparative Example 1, "●" for Example 1-1, and "▪" for Example 1-2. Note that for the measurement results of Comparative Example 1, Example 1-1, and Example 1-2, the total processing time is regarded as the film formation time, and is plotted at 540 seconds.

[0060] 6, it was confirmed that the Ti film was smoothly formed at a high film formation rate of about 0.5 Å / s for about 30 seconds after the start of the film formation process, but that the film formation rate gradually decreased and eventually reached a saturation state where the film thickness did not increase easily. Specifically, the film formation rate from 120 to 360 seconds was 0.033 Å / s, and from 360 to 540 seconds was 0.022 Å / s. It was confirmed that the amount of film increase decreased and reached a saturation state after 120 seconds.

[0061] Furthermore, when the film thickness of the Ti film formed at a film formation time of 540 seconds was compared, it was 58 angstroms in Reference Example 1, 59 angstroms in Comparative Example 1, 65 angstroms in Example 1-1, and 63 angstroms in Example 1-2. As described above, there was almost no difference in the film thickness between Reference Example 1 and Comparative Example 1, and it was found that even if the purging process was performed when the film formation time reached 360 seconds, it would not be very effective in reducing Cl inside the processing vessel 10.

[0062] On the other hand, it was observed that the Ti films formed by the methods of Examples 1-1 and 1-2 had a thickness increase of 5 to 7 angstroms compared to Reference Example 1. The film formation rate from 360 seconds to 540 seconds in Example 1-1 was 0.056 angstroms / second in Example 1-1 and 0.044 angstroms / second in Example 1-2, and it can be said that the saturation state of the increase in film thickness was improved and the decrease in the film formation rate was suppressed compared to Reference Example 1. From the results of Examples 1-1 and 1-2, it can be evaluated that the technology according to the present disclosure is a suitable method for forming Ti film 6 while suppressing a decrease in the film formation rate.

[0063] (Evaluation Experiment 2) In accordance with the first embodiment, Ti film 6 was formed under conditions different from those in Evaluation Test 1, and the state of formation of Ti film 6 in recess 50 was confirmed. A. Experimental Conditions As in Evaluation Test 1, Ti film 6 was formed in each of Reference Example 2, in which only the film formation process was performed, Comparative Example 2, in which the film formation process was performed twice with a purge process in which no cleaning gas was supplied sandwiched between them, and Example 2-1, which was performed based on the time chart of Figure 3. The shape of recess 50 formed in wafer W was the same as in Evaluation Test 1, and the respective processing conditions were set as follows.

[0064] (Processing conditions for Reference Example 2) Wafer temperature: 450° C., TiCl ４ Gas supply flow rate: 25 sccm, H ２ The film formation process for the Ti film 6 was carried out under the following conditions: gas supply flow rate: 1000 sccm, Ar gas supply flow rate: 2400 sccm, pressure inside the process vessel 10: 1.2 kPa (9 Torr), high frequency power supply 34: 100 kHz, 100 W, high frequency power supply 23: no application. The film formation process was carried out under these conditions for 360 seconds, and the thickness of the formed Ti film was measured.

[0065] (Processing Conditions for Comparative Example 2) A first film formation process was carried out for 360 seconds from the start of processing under the same conditions as in Reference Example 2, and then a purge process of evacuating the processing vessel 10 was carried out for 45 seconds while supplying Ar gas at a flow rate of 2400 sccm into the processing vessel 10. Thereafter, a second film formation process was carried out under the same conditions as in Reference Example 2, and the thickness of the obtained Ti film was measured when the total processing time reached 540 seconds.

[0066] (Processing Conditions for Example 2-1) A film forming process was carried out for 360 seconds from the start of the process under the same conditions as in Reference Example 2, and then a purging process was carried out under the same conditions as in Comparative Example 2. ３ After a vacuum exhaust process using a gas was carried out for 3 seconds, a second film formation process was carried out again under the same conditions as in Reference Example 2, and the thickness of the Ti film obtained was measured when the total processing time reached 540 seconds. The processing conditions for the vacuum exhaust process were: wafer temperature: 450°C, NH ３ Gas supply flow rate: 9000 sccm, H ２The gas supply flow rate was set to 4500 sccm, the Ar gas supply flow rate was set to 2000 sccm, and the pressure inside the processing chamber 10 was set to 0.4 kPa (3 Torr).

[0067] B. Experimental Results For wafers W of Reference Example 2, Comparative Example 2, and Example 2-1, the formation area of ​​the recess 50 was enlarged and photographed using a TEM (Transmission Electron Microscope), and the film thickness of the Ti film formed on the bottom surface of the recess 50 was measured. The results are shown in Table 1 of FIG. 7. As shown in FIG. 7, even for Ti films formed under film formation conditions different from those in Evaluation Test 1, the thickness of the Ti film formed under the NH ３ In Example 2-1, in which a vacuum evacuation process using gas was carried out, the thickness of the Ti film was larger than that of Comparative Example 2, in which only a purging process was carried out, and it was confirmed that a decrease in the film formation rate of the Ti film could be suppressed.

[0068] (Evaluation Experiment 3) In accordance with the second embodiment, the Ti film 6 was formed under conditions different from those in Evaluation Test 1, and the formation state of the Ti film 6 in the recess 50 was confirmed. A. Experimental Conditions As in Evaluation Test 1, the Ti film 6 was formed based on the time chart of Fig. 5. The shape of the recess 50 formed in the wafer W was the same as in Evaluation Test 1, and the processing conditions were set as follows.

[0069] (Processing Conditions for Example 3-1) After the film formation process was carried out for 120 seconds from the start of the process under the same conditions as Reference Example 1 of Evaluation Test 1, the supply of film formation gas and the application of high frequency power from the high frequency power sources 34 and 23 were stopped. Next, a purge process was carried out for 45 seconds to evacuate the processing vessel 10 while supplying Ar gas at a flow rate of 2400 sccm. After this, the evacuation process of the second embodiment was carried out for 30 seconds, and then a second film formation process was carried out for 120 seconds under the same conditions as Reference Example 1, and the thickness of the obtained Ti film was measured. In Example 3-1, the film formation process was repeated twice. The processing conditions for the evacuation process were: wafer temperature: 450°C, H ２ The gas supply flow rate was set to 4500 sccm, the Ar gas supply flow rate to 1000 sccm, the pressure inside the processing vessel 10 to 0.13 kPa (1 Torr), the processing time to 30 seconds, and the high frequency power supply 34 to 450 kHz and 500 W.

[0070] (Processing conditions for Example 3-2) As in Example 3-1, the film formation process → purging process → vacuum exhaust process → film formation process was performed, and this process cycle was repeated four times to measure the thickness of the resulting Ti film. The Ti film was formed under the same conditions as in Example 3-1, except that the processing time for each film formation process was set to 60 seconds.

[0071] (Processing conditions of Example 3-3) As in Example 3-1, the film formation process → purging process → vacuum exhaust process → film formation process was performed, and this process cycle was repeated 8 times to measure the thickness of the resulting Ti film. The Ti film was formed under the same conditions as in Example 3-1, except that the processing time for each film formation process was set to 30 seconds.

[0072] (Processing Conditions for Example 3-4) The film formation process was repeated eight times in the same manner as in Example 3-3, and the thickness of the resulting Ti film was measured. The processing conditions were set as follows: Wafer temperature: 450° C., H ２ The gas supply flow rate was set to 4500 sccm, the Ar gas supply flow rate was set to 2000 sccm, the pressure inside the processing vessel 10 was set to 0.13 kPa (1 Torr), the processing time was set to 30 seconds, and the high frequency power source 34 was set to 450 kHz and 500 W.

[0073] B. Experimental Results For the wafers W of Examples 3-1, 3-2, 3-3, and 3-4, the formation area of ​​the recess 50 was enlarged and photographed using a TEM, and the film thickness of the Ti film formed on the bottom of the recess 50 was measured. The results are shown in the second table of FIG. 8. The number of cycles is the number of film formation steps. As shown in these results, even for Ti films formed under film formation conditions different from those of Evaluation Test 1, the thickness of the Ti film formed on the bottom of the recess 50 was measured using plasma H ２ It was confirmed that the Ti film was increased in thickness by performing the vacuum evacuation process using gas, and the amount of film increase increased as the number of film formation processes increased.

[0074] Furthermore, when Examples 3-3 and 3-4 are compared, it is found that the thickness of the Ti film increases further by increasing the supply flow rate of Ar gas even when the number of cycles (number of film formation steps) is the same. Therefore, it is understood that by optimizing the processing conditions of the evacuation step, it is possible to suppress a decrease in the film formation rate of the Ti film and further increase the thickness of the Ti film 6.

[0075] In Example 1-2 of Evaluation Test 1, the total film formation time was set to 540 seconds, and the thickness of the Ti film was 63 angstroms. On the other hand, in Evaluation Test 3, the total film formation time was set to 240 seconds, and it was confirmed that the thickness of the Ti film was 73 angstroms or more when the number of cycles was four or more.

[0076] Evaluation Test 1 and Evaluation Test 3 cannot be simply compared because the processing conditions for the film formation process and the evacuation process are different. However, from the trend of the film formation rate of the Ti film shown in Figure 6, it is recognized that the film formation rate is high up to 60 seconds after the start of the film formation process. Therefore, by stopping the film formation process at a relatively early timing, for example, up to 60 seconds after the film formation process, and performing the evacuation process, and increasing the number of film formation processes, the thickness of the Ti film can be increased even if the total processing time is the same, and it can be said that this is a suitable technique for forming a Ti film.

[0077] From another perspective, this result means that the total processing time required for the Ti film to reach the target thickness can be minimized by setting the processing conditions for the film formation process. Therefore, for example, the film formation process time and cleaning exhaust time are specified so as to maximize the film formation rate per unit time when forming the target film thickness. This makes it possible to set the total processing time, including the film formation time and cleaning exhaust time, to be as short as possible, thereby improving throughput.

[0078] However, the appropriate processing conditions for each of the film formation process, evacuation process, and purging process vary depending on the type of metal film and film formation gas, the shape of the recess 50 formed in the wafer W, the material of the film on the bottom and sidewall surfaces of the recess 50, the target film thickness, etc. Therefore, it is preferable to appropriately set the duration of the film formation process and evacuation process and the number of repetitions according to each case.

[0079] W wafer 1 film forming apparatus 10 processing vessel 13 exhaust unit 2 mounting table 410 TiCl ４ Gas supply source 440 NH ３ Gas supply source 6 Ti film 100 Control section

Claims

1. In a method of forming a metal film on a substrate, a step of supplying a film-forming gas containing a metal halide as a raw material of the metal film to the substrate and reacting the film-forming gas to form the metal film on the surface of the substrate; and when the step of forming the metal film has a characteristic that the film-forming rate decreases over time, a step of evacuating the atmosphere in which the substrate is disposed while supplying a cleaning gas that reacts with a by-product generated by the reaction of the film-forming gas after the supply of the film-forming gas is stopped. After performing the step of evacuating the vacuum, the method of performing the step of forming the metal film again.

2. The method according to claim 1, wherein a cycle of the step of evacuating the vacuum and the subsequent step of forming the metal film is repeated a plurality of times.

3. The metal halide is TiCl ４ and the deposition gas is TiCl ４ Gas and H ２ 2. The method according to claim 1, wherein the metal film is formed by converting the deposition gas into plasma in the step of forming the metal film.

4. The by-product contains Cl, and the cleaning gas is selected from at least one of a cleaning gas group consisting of NH ３ gas, plasma-treated H ２ gas, H ２ gas, SiH ４ gas, Si ２ H ６ gas, NF ３ gas, and the method according to claim 3, which is selected from at least one of the cleaning gas groups.

5. Each execution time of the step of forming the metal film and the step of evacuating the vacuum is set so that the total execution time of the step of forming the metal film and the step of evacuating the vacuum until the film thickness of the metal film reaches a preset target film thickness is the shortest. The method according to claim 1.

6. An apparatus for forming a metal film on a substrate, comprising: a processing container provided with a mounting table on which the substrate is mounted; a film-forming gas supply unit for supplying a film-forming gas containing a metal halide as a raw material of the metal film to the processing container; a cleaning gas supply unit for supplying a cleaning gas that reacts with a by-product generated by the reaction of the film-forming gas to the processing container; an exhaust unit for evacuating the inside of the processing container; and a control unit. The control unit supplies the film-forming gas to the processing container and reacts the film-forming gas to form the metal film on the surface of the substrate mounted on the mounting table. When the step of forming the metal film has a characteristic that the film-forming rate decreases over time, after the supply of the film-forming gas is stopped, a step of evacuating the inside of the processing container while supplying the cleaning gas to the processing container. After performing the step of evacuating, the apparatus is configured to output a control signal for performing the step of forming the metal film again.

7. The apparatus according to claim 6, wherein the control unit is configured to output a control signal for repeating a cycle of the step of evacuating the vacuum and the subsequent step of forming the metal film a plurality of times.

8. It includes a plasma forming part for plasmaizing the film-forming gas, and the metal halide is TiCl ４ and the film-forming gas is a mixed gas of TiCl ４ gas and H ２ gas. In the step of forming the metal film, the film-forming gas is plasmaized to form the metal film. The apparatus according to claim 6.

9. The by-product contains Cl, and the cleaning gas is selected from at least one of a cleaning gas group consisting of NH ３ gas or plasmaized H ２ gas, H ２ gas, SiH ４ gas, Si ２ H ６ gas, NF ３ gas, and the apparatus according to claim 8, which is selected from at least one of the cleaning gas group 10. The implementation time of each of the step of forming the metal film and the step of evacuating the vacuum is set such that the total implementation time of the step of forming the metal film and the step of evacuating the vacuum until the film thickness of the metal film reaches a preset target film thickness is the shortest. The apparatus according to claim 6.

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