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.SOLUTION: This method for forming a metal film comprises steps 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; 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 performing again the step for forming the metal film after the step for vacuum-exhausting is carried out.SELECTED DRAWING: Figure 3

Description

Technical Field

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

Background Art

[0002] In the manufacturing process of semiconductor devices, a process of forming a metal film, such as a titanium film, may be performed in recesses such as trenches and via holes formed on the surface of a semiconductor wafer (hereinafter referred to as "wafer") serving as a substrate. Patent Document 1 proposes a technique of bringing atomic low-pressure hydrogen into contact with a monomolecular layer of titanium tetrachloride in order to form a pure titanium film. It is described that since hydrogen atoms react with chlorides in the monomolecular layer of titanium tetrachloride to form hydrogen chloride and be exhausted, a monomolecular layer of titanium is formed.

[0003] Patent Document 2 proposes a technique of forming a titanium nitride film using a halogenated raw material gas and a reaction gas. It is described that the step coverage of the titanium nitride film is improved by performing, a predetermined number of times in a time-division manner, a step of supplying a halogenated raw material gas, a step of supplying a reaction inhibition gas that inhibits the reaction between the halogenated raw material gas and the reaction gas, and a step of supplying a reaction gas.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The present disclosure provides a technique for suppressing a decrease in film formation rate when forming a metal film using a raw material having a characteristic that the film formation rate decreases over time.

Means for Solving the Problem

[0006] The present disclosure is 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; when the step of forming the metal film has a characteristic that the film-forming rate decreases with the passage of time, after stopping the supply of the film-forming gas, while supplying a cleaning gas that reacts with a by-product generated by the reaction of the film-forming gas, evacuating the atmosphere in which the substrate is disposed, and after performing the step of evacuating the atmosphere, performing the step of forming the metal film again.

Effect of the Invention

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

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4A

Figure 4B

Figure 5

Figure 6

Figure 7

Figure 8

[0009] The present disclosure provides a method for suppressing a decrease in the deposition rate when forming a metal film by chemical vapor deposition (CVD) using a deposition gas containing a metal halide. Hereinafter, an example will be described in which a titanium (Ti) film is formed using a mixed gas of titanium tetrachloride (TiCl4) gas and hydrogen (H2) gas as the deposition gas containing a metal halide. The inventors have found that Ti film deposition by CVD using TiCl4 gas has a characteristic in which the deposition rate decreases over time, as will be shown in the evaluation tests described below. The characteristic of the deposition rate decreasing over time means that the thickness of the metal film formed and the deposition time do not have a linear relationship, but the slope of the function decreases over time.

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

[0011] <Film forming equipment> Hereinafter, a configuration example of the film forming apparatus 1 of the present disclosure will be described with reference to FIG. 1. FIG. 1 is a longitudinal side view of the film forming apparatus 1 of this example. This film forming apparatus 1 is configured as an apparatus that continuously supplies TiCl4 gas and H2 gas, which are film forming gases, and argon (Ar) gas to the surface of the wafer W, and forms a Ti film 6 by the plasma CVD method.

[0012] The film forming apparatus 1 includes a substantially cylindrical processing container 10 made of metal that has corrosion resistance to chlorine and is grounded. In the central portion of the bottom surface of the processing container 10, for example, a cylindrical exhaust chamber 11 that protrudes downward is formed, and an exhaust passage 12 is connected to the side surface of the exhaust chamber 11. An exhaust unit 13 including a pressure adjustment valve, for example, a butterfly valve, is connected to the exhaust passage 12, and the inside of the processing container 10 can be evacuated to a preset vacuum pressure.

[0013] An carry-in / out port 14 for carrying the wafer W in and out is formed on the side surface of the processing container 10 between the processing container 10 and a vacuum transfer chamber (not shown), and the carry-in / out port 14 is configured to be openable and closable by a gate valve 15. Further, a heater 16 for adjusting the temperature inside the processing container 10 is embedded in the wall portion constituting the processing container 10.

[0014] A mounting table 2 for holding the wafer W substantially horizontally is provided inside the processing container 10. The mounting table 2 is supported by a support portion 21 extending from the bottom of the exhaust chamber 11, and the mounting table 2 and the support portion 21 are made of a conductive member. A heater 20, which is a heating portion, 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 the range of 350°C to 800°C.

[0015] The mounting stage 2 is connected to a high-frequency power supply 23 that supplies high-frequency power for ion drawing-in via a matcher 22. Further, the mounting stage 2 is provided with lift pins (not shown) for holding and lifting the wafer W on the mounting stage 2. By raising and lowering the lift pins, the wafer W can be transferred between the mounting stage 2 and an external transfer mechanism (not shown). Note that the mounting stage 2 may be configured not to supply high-frequency power for ion drawing-in.

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

[0017] The above-described shower head 3 is connected to a high-frequency power supply 34 that supplies high-frequency power for plasma formation via a matcher 33. This high-frequency power supply 34 forms a plasma formation part. Thus, the film-forming apparatus 1 of the present disclosure constitutes a parallel plate type plasma processing apparatus by the shower head 3 serving as an upper electrode and the mounting stage 2 serving as a lower electrode. The wafer W is placed in the space between the shower head 3 and the mounting stage 2, and by supplying gases such as TiCl4 gas, H2 gas, and 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 frequency of 450 KHz, 2 MHz, 13.56 MHz, 27 MHz, 40 MHz, 60 MHz, 100 MHz, or 2.45 GHz. Further, high-frequency power in the range greater than 0 W and equal to or less than 2000 W is supplied from the high-frequency power supply 34.

[0018] Further, the downstream end of the gas supply passage 40 is connected to the diffusion chamber 31 of the shower head 3. Upstream of this gas supply passage 40, the supply flow paths 41 and 42 for TiCl4 gas, which is the source gas for the film-forming gas, and H2 gas, which is the reaction gas, the supply flow path 43 for Ar gas added for plasma generation, and the supply flow path 44 for NH3 gas, which is the cleaning gas, merge.

[0019] A TiCl4 gas supply source 410 is connected to the upstream end of the supply flow path 41 for TiCl4 gas, and a flow rate adjustment section M41 and a valve V41 are interposed in order from the upstream side. Further, an H2 gas supply source 420 is connected to the upstream end of the supply flow path 42 for H2 gas, and a flow rate adjustment section M42 and a valve V42 are interposed in 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 adjustment section M43 and a valve V43 are interposed in order from the upstream side. Still further, an NH3 gas supply source 440 is connected to the upstream end of the supply flow path 44 for NH3 gas, and a flow rate adjustment section M44 and a valve V44 are interposed in order from the upstream side.

[0020] The film-forming gas supply section in this example is configured to include the supply flow path 41 for TiCl4 gas, the TiCl4 gas supply source 410, the supply flow path 42 for H2 gas, the H2 gas supply source 420, and the gas supply passage 40. Further, the cleaning gas supply section is configured to include the supply flow path 44 for NH3 gas, the NH3 gas supply source 440, and the gas supply passage 40.

[0021] As shown in FIG. 1, the film-forming apparatus 1 having the above-described configuration includes a control section 100. The control section 100 is configured by a computer including a storage section that stores a program, a memory, and a CPU. The program is composed of instructions (steps) to execute a process of forming the Ti film 6 by outputting control signals from the control section 100 to each part of the film-forming apparatus 1 and performing on / off control of each gas and supply control of high-frequency power. The program is stored in a storage section of a computer, such as a flexible disk, a compact disk, a hard disk, an MO (magneto-optical disk), a non-volatile memory, etc., and is read from this storage section and installed in the control section 100.

[0022] <The first embodiment of the method for forming a Ti film> Regarding the first embodiment of the method for forming a Ti film implemented in the film forming apparatus 1 described above, as shown in FIG. 2, taking the case of forming a Ti film 6 in the recess 50 formed on the surface of the wafer as an example, it will be described. In this example, the recess 50 is formed in the silicon oxide film (SiO film 52) covering the silicon member 51 constituting the wafer W. Therefore, the silicon member 51 is exposed on the bottom surface of the recess 50, and the SiO film 52 is exposed on the side wall surface thereof. Note that, instead of the SiO film, the silicon member 51 may be covered with a silicon nitride film (SiN film), and the side wall surface of the recess 50 may be formed by the SiN film.

[0023] Further, FIG. 3 is an example of a time chart related to the formation process of the Ti film 6 implemented using the above-described film forming apparatus 1. This time chart schematically shows the supply and cutoff timings of the film forming gases (TiCl4 gas, H2 gas) and NH3 gas to the processing chamber 10, and the application timing of the high-frequency power from the high-frequency power supply 34 (described as "plasma power supply" in FIG. 3). The supply and cutoff control of each gas and the application timing control of the 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 performs the opening and closing control of the valves V41, V42, V43, and V44, executes the supply and cutoff of each gas, and performs the flow rate setting of each flow rate adjustment unit M41, M42, M43, and M44.

[0024] The formation process of the Ti film 6 will be described with reference to the time chart in FIG. 3 as well. In this process, first, the gate valve 15 is opened, and the wafer W is carried into the processing container 10 through the carry-in / outlet 14 by a transfer mechanism provided in a vacuum transfer chamber (not shown). The carried-in wafer W is delivered 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, after the transfer mechanism is retracted from the processing container 10 and the gate valve 15 is closed, the exhaust unit 13 evacuates the inside of the processing container 10 to adjust the pressure inside the processing container 10 to a preset pressure. Also, the wafer W is heated to 450°C as described above by the heater 20.

[0025] After that, at time T0 shown in FIG. 3, the supply of the film-forming gas is started, and high-frequency power is applied to the shower head 3 and the mounting table 2 from the high-frequency power supplies 34 and 23, respectively. Thus, the supply of the film-forming gas and the application of high-frequency power are performed for a preset time (for example, 360 seconds) until time T1 shown in FIG. 3. The period from time T0 to time T1 is a process of forming a metal film (Ti film) (hereinafter referred to as "film-forming process").

[0026] In this film-forming process, the film-forming gas (TiCl4 gas and H2 gas) and Ar gas are supplied to the shower head 3 through the respective supply channels 41, 42, 43 and the gas supply channel 40. The mixed gas of these film-forming gases and Ar gas flows into the diffusion chamber 31 of the shower head 3 through the gas supply channel 40 and is discharged into the processing container 10 through the discharge holes 32. Then, by supplying high-frequency power to the shower head 3 and the mounting table 2 from the high-frequency power supplies 34 and 23, respectively, these gases are turned into plasma.

[0027] The TiCl4 gas and H2 gas, which are film-forming gases, are supplied into the processing container 10 at preset flow rates during the period from time T0 to time T1. Also, for example, Ar gas is continuously supplied constantly from time T0 until the end of a series of processes. Ar gas functions as an auxiliary gas to assist in the formation of the plasma of the film-forming gas during the period when high-frequency power for plasma formation is applied, and functions as a purge gas during the period when the application of the high-frequency power is stopped.

[0028] As an example of the film formation treatment conditions at this time, the wafer W temperature is 450°C, the pressure inside the processing chamber is 1.2 kPa (9 Torr), the flow rate of TiCl4 gas is 25 sccm, the flow rate of H2 gas is 1000 sccm, the flow rate of Ar gas is 2400 sccm, the high-frequency power from the high-frequency power supply 34 is 10 kHz, 100 W, and the high-frequency power from the high-frequency power supply 23 is 10 Hz, 100 W.

[0029] In the above film formation process, TiCl4, which is the source gas, is reduced by the plasmaized H2, which is the reaction gas, and highly reactive TiCl2 ions or radicals are abundantly formed. Then, these TiCl2 ions or radicals are adsorbed on the bottom surface of the concave portion 50 to form the Ti film 6. By applying high-frequency power, plasma is formed between the parallel plates (shower head 3 - mounting stage 2) including the inside of the concave portion 50, and high-frequency power for ion drawing is supplied to the mounting stage 2. Due to this action, it can be said that TiCl2 ions are supplied to the bottom surface at a deep position inside the concave portion 50, and the Ti film 6 can be formed in this region.

[0030] Incidentally, TiCl4 gas also has the effect of etching titanium. Also, compared with the silicon member 51, the SiO film 52 and the SiN film have stronger bonds between silicon and oxygen or nitrogen, and their bonds with the Ti film 6 formed on their surfaces are relatively weak. For this reason, etching by TiCl4 gas progresses more easily on the side wall surface of the concave portion 50 where the SiO film (SiN film) 52 is exposed than on the bottom surface of the concave portion 50 where the silicon member 51 is exposed. Therefore, although a Ti film is actually formed on the side wall surface of the concave portion 50, the Ti film on the side wall surface has a smaller film thickness than the Ti film on the bottom surface. For this reason, in FIG. 2, the Ti film 6 on the side wall surface of the concave portion 50 is not shown, and only the Ti film 6 formed on the bottom surface is depicted.

[0031] Thus, in the film formation process, TiCl4 is decomposed into TiCl2 radicals, and the formation of the Ti film progresses. At the start of this process, TiCl2 radicals are generated smoothly, and the Ti film is rapidly formed. On the one hand, the decomposition of TiCl4 generates, together with TiCl2 radicals, by-products containing Cl. When the metal halide is TiCl4, among the atoms constituting the by-products, Cl affects the subsequent decrease in the reaction rate, so here the by-product is described as "Cl". Since this Cl is not consumed in the formation of the Ti film, the Cl concentration in the processing chamber 10 gradually increases. Here, consider the case where the film-forming gas is continuously supplied for, for example, 360 seconds in the film-forming process by the above-mentioned CVD method. When film formation is carried out for such a long time, even if the inside of the processing chamber 10 is evacuated in parallel, compared with the film-forming process by the ALD (atomic layer deposition) method in which the film-forming gas is supplied for a short time and purged, the amount of Cl present in the processing chamber 10 increases.

[0032] And as also shown in Evaluation Test 1 described later, in the film-forming process of the Ti film, the film-forming rate of the Ti film gradually decreases with the passage of time, and eventually reaches a saturation state where it becomes difficult to increase the film thickness even if the film-forming time is increased (Reference Example 1 in FIG. 6 described later). The reason for this is speculated as follows. When the Cl concentration in the processing chamber 10 increases, the reaction between TiCl2 radicals and Cl proceeds easily, and TiCl2 ions or radicals change to TiCl3 radicals or return to TiCl4. Here, although TiCl3 radicals also act as film-forming species, they have a higher vapor pressure and a lower adsorption rate to the wafer W compared to TiCl2 radicals. That is, even if they collide with the wafer W once, they are difficult to adsorb and are easily volatilized and discharged from the processing chamber 10, so it is considered that their contribution to film formation is smaller than that of TiCl2 radicals. Thus, when the Cl concentration in the processing chamber 10 increases, even if TiCl2 radicals are generated by the decomposition of TiCl4, subsequent unintended reactions occur, and as a result, it is speculated that the amount of TiCl2 radicals contributing to film formation decreases. As a result, it is considered that a saturation state is reached where the film thickness of the Ti film is difficult to increase, and the time required to reach the target film thickness becomes long.

[0033] From the above, in the present disclosure, after the supply of the film-forming gas is stopped, a step of evacuating the inside of the processing vessel 10 while supplying NH3 gas, which is a cleaning gas, into the processing vessel 10 from time T2 to time T3 shown in FIG. 3 (hereinafter referred to as the "vacuum evacuation step") is carried out. The period during which NH3 gas is supplied is, for example, 3 seconds. In this vacuum evacuation step, high-frequency power is not applied, and Ar gas and H2 gas are also supplied simultaneously with NH3 gas (only the supply of NH3 gas, which is a cleaning gas, is shown in FIG. 3). The reason for supplying H2 gas in this way is to react with Cl remaining in the processing vessel 10 to generate hydrogen chloride (HCl) and exhaust it from the processing vessel 10. It is presumed that by changing Cl, which exists in an unstable state in the processing vessel 10, to a stable state (HCl), the remaining Cl can be more easily purged. During the period from time T1 to time T2, the supply of Ar gas and the evacuation of the inside of the processing vessel 10 are continuously carried out, and the inside of the processing vessel 10 is purged (purging step). However, during the period when the application of high-frequency power for plasma formation is stopped or when the vacuum evacuation step is carried out, the supply of Ar gas may be stopped, and nitrogen gas (N2 gas) may be supplied as a purge gas instead of Ar gas.

[0034] When NH3 gas is supplied into the processing container 10, Cl present in the processing container 10 reacts with NH3 to generate HCl and NH4Cl, and these reaction products are discharged to the outside along with the exhaust in the processing container 10. It is considered that Cl exists in the atmosphere in the processing container 10 and Cl adheres to the members exposed in the processing container 10, such as the side wall surface of the processing container 10 and the surface of the mounting table 2. Thus, regarding the Cl adhering to the inside of the processing container 10, it may be difficult to remove it only by performing vacuum exhaust while supplying an inert gas such as Ar gas as a purge gas. Therefore, NH3 gas is supplied as a cleaning gas that reacts with Cl. As a result, it is estimated that the reaction products of Cl and NH3 are discharged to the outside of the processing container 10, so that the Cl concentration in the processing container 10 can be reduced. As a result, a decrease in the amount of TiCl2 radicals contributing to film formation is suppressed, and a decrease in the film formation rate can be suppressed as compared with the case where the vacuum exhaust process while supplying NH3 gas is not performed.

[0035] As an example of the processing conditions of the above vacuum exhaust process, the wafer temperature is 450 °C, the pressure inside the processing container is 0.4 kPa (3 Torr), the flow rate of NH3 gas is 9000 sccm, the flow rate of H2 gas is 4500 sccm, and the flow rate of Ar gas is 2000 sccm. Thus, the supply of NH3 gas is stopped at time T3, 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, the supply of Ar gas and the vacuum exhaust inside the processing container 10 are performed, and the purge process is carried out. As a result, NH3, HCl, NH4Cl, etc. present in the processing container 10 are discharged to the outside.

[0036] Next, during the period from time T4 to time T5, as the second film formation process, the supply of the film formation gas and the application of high-frequency power are performed, and a Ti film is formed in the same manner as the first film formation process described above. Subsequently, a purge process is performed from time T5 to time T6, a second vacuum exhaust process is performed during the period from time T6 to time T7, and a purge process is performed during the period from time T7 to time T8, each implemented by the method described above. After this, the third film formation process is started at time T8.

[0037] The time chart shown in FIG. 3 depicts up to time T8. In reality, after the film formation process, a vacuum evacuation process is performed, and further, a process of performing the film formation process again is defined as a series of processing cycles. By repeating this processing cycle a preset number of times or more, the film formation process of the Ti film is carried out. The number of repetitions of the processing cycle is appropriately set according to the target film thickness of the Ti film, the processing conditions of the film formation process, and the processing conditions of the vacuum evacuation process.

[0038] At this time, for example, the implementation time of each of the film formation process and the vacuum evacuation process can be set so that the total implementation time of the film formation process and the vacuum evacuation process until the film thickness of the Ti film reaches a preset target film thickness is the shortest. As described above, if the film formation process is continued as it is, the film thickness of the Ti film becomes saturated and difficult to increase, and the time required to reach the target film thickness becomes long. On the other hand, when the vacuum evacuation process is performed, the saturation state is improved, but film formation cannot be performed during the period of evacuation.

[0039] Therefore, for example, through preliminary experiments, the film formation time required for the film formation process and the cleaning evacuation time required for the vacuum evacuation process are varied to form the Ti film. For example, FIG. 4A schematically shows the change over time in the film thickness of the Ti film during the film formation period when, in forming the Ti film up to the target film thickness D T , after the first film formation process, one cycle of the vacuum evacuation process and the film formation process again is carried out. In the example shown in FIG. 4A, in the first film formation process, film formation is carried out during the period (time T0 - T1) until the increase in film thickness reaches a saturated state. Thereafter, the vacuum evacuation process is carried out while supplying the cleaning gas (time T2 - T3), and then, again, the film formation process is carried out during the period (time T4 - T5) until the film thickness of the Ti film reaches the target film thickness D T . If the first film formation process is carried out for a long time, the amount of Cl remaining in the processing container 10 also increases, and in the film formation process after the vacuum evacuation process, the film formation rate may not recover to the same extent as the first time. However, in this example, the period of the vacuum evacuation process during which no film formation is carried out is only once.

[0040] Compared with the above example, in FIG. 4B, after the first film formation step, a vacuum evacuation step and a second film formation step are performed for two cycles to form a film up to the target film thickness D T The change with time in the film thickness of the Ti film is schematically shown when forming a film up to. In the example shown in FIG. 4B, in each film formation step (time T0 - T1, time T4 - T5, time T8 - T9), the film formation is completed in a short time before the increase in film thickness reaches the saturation state. Therefore, the amount of Cl remaining in the processing vessel 10 is also relatively small, and the recovery of the film formation rate in the second film formation step after performing the vacuum evacuation step (time T2 - T3, time T6 - T7) is large. However, in this example, the period of the vacuum evacuation step during which no film formation is performed is two times.

[0041] Comparing FIG. 4A and FIG. 4B, if only the film formation step is considered, it seems that in FIG. 4B, the film can be formed up to the target film thickness D T in a shorter time. However, as described above, in the example of FIG. 4A, the period of the vacuum evacuation step during which no film formation is performed is one time, and in the example of FIG. 4B, it is two times. Therefore, in the evaluation of the preliminary experiment, the total time including the period of the vacuum evacuation step during which no film formation is performed (in the case of FIG. 4A, time T0 - T5, and in the case of FIG. 4B, time T0 - T9) is compared. Then, the execution time and the number of cycles of each step are determined so that the total execution time of the film formation step and the vacuum evacuation step is the shortest.

[0042] In this way, the preset number of times and processing cycles are executed to form a Ti film with the target film thickness. Next, the application of high-frequency power from the high-frequency power supplies 34 and 23 is terminated, and the supply of the film formation gas and the Ar gas and the heating of the wafer W are stopped. Then, the wafer W is unloaded from the processing vessel 10 in the reverse procedure from when it was loaded, and waits for the next wafer W to be loaded. 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 eventually become a titanium silicide (TiSi) film.

[0043] As described above, the technology according to the present disclosure grasps the characteristic that the film formation rate decreases as the processing time of CVD increases in CVD in which a raw material gas (TiCl4 gas) and a reaction gas (H2 gas) are simultaneously supplied and reacted, and aims to improve the film formation rate. Different from ALD in which the supply and exhaust of the raw material gas and the supply and exhaust of the reaction gas are alternately repeated, in CVD, the raw material gas and the reaction gas are continuously supplied. For this reason, even when the inside of the processing container 10 is evacuated, as the processing time becomes longer, the amount of by-products due to the reaction between the raw material gas and the reaction gas increases, but the influence of the by-products remaining in the processing container 10 has not been conventionally noticed. Also, in the above-mentioned prior art documents 1 and 2, there is no description about the influence of the substances remaining in the processing container on the growth of the Ti film.

[0044] The present disclosure has found that the by-products remaining in the processing container 10 inhibit the growth of the Ti film, and by reducing these by-products, the saturation state of the increase in the film thickness of the Ti film has been improved. As a specific method for this improvement, after the film formation step, a step of evacuating the inside of the processing container 10 while supplying a cleaning gas (NH3 gas) is carried out, and the by-products containing Cl remaining in the processing container 10 are reacted with the cleaning gas and removed. By this, it is considered that the Cl in the processing container 10 can be reduced and the reaction between highly reactive TiCl2 radicals and Cl can be suppressed. For this reason, it is estimated that in the processing container 10, TiCl2 radicals can be utilized for the formation of 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> Subsequently, 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, in the evacuation step, as the cleaning gas, plasma-converted H2 gas is supplied instead of NH3 gas. The period from time T10 to time T11 shown in FIG. 5 is the first film formation step, and the period from time T14 to time T15 is the second film formation step, each of which is carried out in the same manner as the first embodiment.

[0046] And during the period from time T12 to time T13, the first vacuum evacuation process is carried out, and during the period from time T16 to time T17, the second vacuum evacuation process is carried out respectively. In these vacuum evacuation processes, while H2 gas and Ar gas are supplied to the shower head 3, high-frequency power is supplied from the high-frequency power supply 34 to the shower head 3 to plasmaize these gases.

[0047] The plasmaized H2 gas reacts with Cl present in the processing chamber 10 to generate HCl, and this HCl is discharged to the outside as the processing chamber 10 is evacuated. Thus, also in this embodiment, the Cl concentration in the processing chamber 10 decreases due to the implementation of the vacuum evacuation process. Taking an example of the processing conditions of the vacuum evacuation process of this embodiment, the wafer W temperature is 450 °C, the pressure inside the processing chamber is 0.133 kPa (1 Torr), the processing time is 30 seconds, the H2 gas flow rate is 4500 sccm, the Ar gas flow rate is 1000 sccm, and the high-frequency power from the high-frequency power supply 34 is 10 kHz, 500 W.

[0048] Note that also in this embodiment, purge processes are carried out during the periods T11 - T12, T13 - T14, T15 - T16, and T17 between the film formation process and the vacuum evacuation process, in the same manner as in the first embodiment. Thereby, the inside of the processing chamber 10 is purged with Ar gas, and H2, HCl, etc. present in the processing chamber 10 are discharged to the outside. Also according to this embodiment, since the inside of the processing chamber 10 is evacuated while supplying plasmaized H2 gas as the cleaning gas, Cl in the processing chamber 10 is reduced, and the reaction between TiCl2 radicals and Cl can be suppressed. For this reason, a decrease in the film formation rate can be suppressed inside the processing chamber 10.

[0049] As described above, in the present disclosure, a process of performing a vacuum evacuation step after a film formation step and then performing the film formation step again is defined as a series of processing cycles. However, in the film formation step performed before the vacuum evacuation step and the film formation step performed after the vacuum evacuation step, the respective processing conditions do not necessarily have to be set to the same conditions. For example, the film formation time may be changed.

[0050] Further, the metal halide is not limited to the example of TiCl4 gas, and the method can also be applied to a method of forming a tungsten (W) film using a film formation gas containing tungsten pentachloride (WCl5) or tungsten hexachloride (WCl6) as the metal halide. Furthermore, the film formation gas containing a metal halide is not limited to a mixed gas of a raw material gas (e.g., TiCl4 gas) and a reaction gas (e.g., H2 gas). The raw material gas may be used alone as the film formation gas and applied to a process of forming a metal film by thermal decomposition CVD.

[0051] Furthermore, it is not an essential requirement to supply NH3 gas or plasma-treated H2 gas as the cleaning gas. As the cleaning gas, at least one gas selected from the group of cleaning gases consisting of NH3 gas, H2 gas, silane (SiH4) gas, disilane (Si2H6) gas, and nitrogen trifluoride (NF3) gas can be used. In the first embodiment, regarding the NH3 gas used as the cleaning gas, plasma treatment of the NH3 gas is not preferred because there is a risk of forming nitrides on the surface of the wafer W.

[0052] Furthermore, the object on which the Ti film 6 is formed using the method of the present disclosure is not limited to the recess 50 shown in FIG. 2. For example, vertical grooves may be formed on the surface of the wafer W, and a plurality of horizontal grooves may be formed so as to be arranged in the thickness direction of the wafer W with respect to the side wall surfaces of the vertical grooves. The Ti film 6 may be formed in these horizontal grooves as recesses. Also, the member on which the Ti film 6 is formed is not limited to the silicon member 51, and other metals or metal compounds may be used.

[0053] The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The above embodiments may be omitted, substituted, or changed in various forms without departing from the scope and gist of the appended claims.

Example

[0054] (Evaluation Experiment 1) The Ti film 6 was formed corresponding to the first embodiment and the second embodiment, and the formation state of the Ti film 6 in the concave portion 50 was confirmed. As an example of the concave portion 50, the width dimension (diameter) W is 40 nm and the depth dimension H is 160 nm. A. Experimental Conditions For the wafer W on which the concave portion 50 was formed, using the film forming apparatus 1 described with reference to FIG. 1, only the film forming process was carried out in Reference Example 1, Comparative Example 1 in which the film forming process was carried out twice with a purge process without supplying a cleaning gas interposed therebetween, Example 1-1 carried out based on the time chart of FIG. 3, and Example 1-2 carried out based on the time chart of FIG. 5, the Ti film 6 was formed in each case. The respective processing conditions were set as follows.

[0055] (Processing Conditions of Reference Example 1) Wafer temperature: 450 °C, supply flow rate of TiCl4 gas: 25 sccm, supply flow rate of H2 gas: 1000 sccm, supply flow rate of Ar gas: 2400 sccm, pressure in the processing container 10: 1.2 kPa (9 Torr), high frequency power supply 34: 10 kHz, 100 W, high frequency power supply 23: not applied, under these conditions, the film forming process of the Ti film 6 was carried out. From the start of processing under these conditions, film forming processing was carried out for 10 seconds, 30 seconds, 60 seconds, 120 seconds, 360 seconds, and 540 seconds respectively, and the film thickness of the formed Ti film was measured in each case.

[0056] (Processing Conditions of Comparative Example 1) After performing the film formation process for 360 seconds from the start of the process under the same conditions as in Reference Example 1, the supply of the film formation gas and the application of the high-frequency power from the high-frequency power supply 34 were stopped. Next, while supplying Ar gas into the processing chamber 10 at a flow rate of 2400 sccm, a purge process for evacuating the inside of the processing chamber 10 was carried out for 45 seconds. After that, the film formation process was performed again under the same conditions as in Reference Example 1, and the film thickness of the Ti film obtained at the timing when the total processing time became 540 seconds was measured. Thus, Comparative Example 1 is an example in which after the first film formation process, a purge process was performed, and then the second film formation process was carried out, 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 of Example 1-1) After performing the film formation process for 360 seconds from the start of the process under the same conditions as in Reference Example 1, a purge process was carried out under the same conditions as in Comparative Example 1. After that, after performing the evacuation process using NH3 gas described in the first embodiment for 3 seconds, the second film formation process was carried out again under the same conditions as in Reference Example 1, and the film thickness of the Ti film obtained at the timing when the total processing time became 540 seconds was measured. The processing conditions of the evacuation process using NH3 gas were set as follows: wafer temperature: 450 °C, supply flow rate of NH3 gas: 9000 sccm, supply flow rate of H2 gas: 4500 sccm, supply flow rate of Ar gas: 24000 sccm, pressure inside the processing chamber 10: 400 Pa (3 Torr).

[0058] (Processing conditions of Example 1-2) After performing the film formation process for 360 seconds from the start of the process under the same conditions as in Reference Example 1, a purge process was carried out under the same conditions as in Comparative Example 1. After that, after performing the evacuation process using the plasmaized H2 gas described in the second embodiment for 30 seconds, the second film formation process was carried out again under the same conditions as in Reference Example 1, and the film thickness of the Ti film obtained at the timing when the total processing time became 540 seconds was measured. The processing conditions of the evacuation process using the plasmaized H2 gas were set as follows: wafer temperature: 450°C, supply flow rate of H2 gas: 4500 sccm, supply flow rate of Ar gas: 2400 sccm, pressure inside the processing vessel 10: 133 Pa (1 Torr), high-frequency power supply 34: 450 kHz, 500 W.

[0059] B. Experimental Results For each of the wafers W on which Reference Example 1, Comparative Example 1, Example 1-1, and Example 1-2 were performed, the film thickness of the Ti film 6 formed on the bottom surface of the concave portion 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 of Reference Example 1 are plotted with "○", Comparative Example 1 with "△", Example 1-1 with "●", and Example 1-2 with "■". Note that the measurement results of Comparative Example 1, Example 1-1, and Example 1-2 are plotted at the position of 540 seconds, considering the total processing time as the film formation time.

[0060] Reference Example 1 is a case where a conventional film formation process was performed. From the results shown in FIG. 6, it was confirmed that until about 30 seconds after the start of the film formation process, the Ti film was smoothly formed at a relatively large film formation rate of about 0.5 angstroms / second. However, the film formation rate gradually decreased, and eventually, a saturated state was reached where the film thickness hardly increased. Specifically, the film formation rate from 120 seconds to 360 seconds was 0.033 angstroms / second, and the film formation rate from 360 seconds to 540 seconds was 0.022 angstroms / second. It was recognized that when the film formation time exceeded 120 seconds, the film thickness increase amount became small and a saturated state was reached.

[0061] Also, when comparing the film thickness of the Ti film with a film formation time of 540 seconds, the film thickness of Reference Example 1 was 58 angstroms, that of Comparative Example 1 was 59 angstroms, that of Example 1-1 was 65 angstroms, and that of Example 1-2 was 63 angstroms. Thus, it was found that the film thicknesses of Reference Example 1 and Comparative Example 1 hardly changed, and even when the purge process was performed at the time when the film formation time reached 360 seconds, little effect was observed in reducing Cl inside the processing vessel 10.

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

[0063] (Evaluation Experiment 2) Corresponding to the first embodiment, the Ti film 6 was formed under conditions different from those of Evaluation Test 1, and the formation state of the Ti film 6 in the recess 50 was confirmed. A. Experimental Conditions Similar to Evaluation Test 1, in Reference Example 2 where only the film formation process was carried out, Comparative Example 2 where the film formation process was carried out twice with a purge process without supplying a cleaning gas in between, and Example 2-1 carried out based on the time chart of FIG. 3, the Ti film 6 was formed respectively. The shape of the recess 50 formed in the wafer W was the same as that in Evaluation Test 1, and the respective processing conditions were set as follows.

[0064] (Processing Conditions of Reference Example 2) Wafer temperature: 450 °C, supply flow rate of TiCl4 gas: 25 sccm, supply flow rate of H2 gas: 1000 sccm, supply flow rate of Ar gas: 2400 sccm, pressure in the processing container 10: 1.2 kPa (9 Torr), high-frequency power supply 34: 100 kHz, 100 W, high-frequency power supply 23: not applied. Under these conditions, the film formation process of the Ti film 6 was carried out for 360 seconds, and the film thickness of the formed Ti film was measured.

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

[0066] (Processing conditions of Example 2-1) After performing the film formation process for 360 seconds from the start of the process under the same conditions as in Reference Example 2, a purge process was carried out under the same conditions as in Comparative Example 2. After this, a vacuum exhaust process using NH3 gas was carried out for 3 seconds, and then the second film formation process was carried out again under the same conditions as in Reference Example 2, and the film thickness of the Ti film obtained at the timing when the total processing time became 540 seconds was measured. The processing conditions of the vacuum exhaust process were set as follows: wafer temperature: 450 °C, supply flow rate of NH3 gas: 9000 sccm, supply flow rate of H2 gas: 4500 sccm, supply flow rate of Ar gas: 2000 sccm, pressure inside the processing vessel 10: 0.4 kPa (3 Torr).

[0067] B. Experimental results Regarding the wafers W of Reference Example 2, Comparative Example 2, and Example 2-1, the formation region of the recess 50 was magnified 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 FIG. 7 as the first table. As shown in FIG. 7, also for the Ti film formed under film formation conditions different from those in Evaluation Test 1, in Example 2-1 where a vacuum exhaust process using NH3 gas was carried out, the film thickness of the Ti film was larger compared to Comparative Example 2 where only the purge 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) Corresponding to 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 Similar to 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 that in Evaluation Test 1, and the processing conditions were set as follows.

[0069] (Processing conditions of Example 3-1) Under the same conditions as in Reference Example 1 of Evaluation Test 1, after performing the film formation process for 120 seconds from the start of the process, the supply of the film formation gas and the application of the high-frequency power from the high-frequency power supplies 34 and 23 were stopped. Next, while supplying Ar gas into the processing container 10 at a flow rate of 2400 sccm, a purge process of performing vacuum exhaust was carried out for 45 seconds. After that, after performing the vacuum exhaust process of the second embodiment for 30 seconds, the second film formation process was carried out for 120 seconds again under the same conditions as in Reference Example 1, and the film thickness of the obtained Ti film was measured. In Example 3-1, the film formation process was repeated twice. The processing conditions of the vacuum exhaust process were set as follows: wafer temperature: 450 °C, supply flow rate of H2 gas: 4500 sccm, supply flow rate of Ar gas: 1000 sccm, pressure inside the processing container 10: 0.13 kPa (1 Torr), processing time: 30 seconds, high-frequency power supply 34: 450 kHz, 500 W.

[0070] (Processing conditions of Example 3-2) Similar to Example 3-1, the film formation process → purge process → vacuum exhaust process → film formation process were carried out, and in this processing cycle, the film formation process was repeated 4 times, and the film thickness of the obtained Ti film was measured. The film formation of the Ti film was carried out under the same conditions as in Example 3-1 except that the processing time of each film formation process was set to 60 seconds.

[0071] (Processing conditions of Example 3-3) Similar to Example 3-1, the film formation process → purge process → vacuum exhaust process → film formation process were carried out, and in this processing cycle, the film formation process was repeated 8 times, and the film thickness of the obtained Ti film was measured. The film formation of the Ti film was carried out under the same conditions as in Example 3-1 except that the processing time of each film formation process was set to 30 seconds.

[0072] (Processing conditions of Example 3-4) The film formation process was repeated 8 times in the same manner as in Example 3-3, and the film thickness of the obtained Ti film was measured. The processing conditions at this time were set as follows. Wafer temperature: 450 °C, supply flow rate of H2 gas: 4500 sccm, supply flow rate of Ar gas: 2000 sccm, pressure inside the processing vessel 10: 0.13 kPa (1 Torr), processing time: 30 seconds, high-frequency power supply 34: 450 kHz, 500 W were set.

[0073] B. Experimental Results For the wafers W of Examples 3-1, 3-2, 3-3, and 3-4, the formation region of the recess 50 was magnified and photographed using TEM, and the film thickness of the Ti film formed at the bottom of the recess �0 was measured. The results are shown in FIG. 8 as the second table. The number of cycles is the number of times of the film formation process. As shown in this result, for the Ti film formed under film formation conditions different from those in Evaluation Test 1, the Ti film increased in thickness by performing a vacuum evacuation process with plasmaized H2 gas, and it was confirmed that the amount of film increase became larger as the number of film formation processes increased.

[0074] Also, when comparing Examples 3-3 and 3-4, it was observed that even when the number of cycles (the number of film formation processes) was the same, the film thickness of the Ti film further increased by increasing the supply flow rate of Ar gas. Therefore, it is understood that by optimizing the processing conditions of the vacuum evacuation process, a decrease in the film formation rate of the Ti film can be suppressed, and the Ti film 6 can be further increased in thickness.

[0075] In Example 1-2 of Evaluation Test 1, the total film formation time was set to 540 seconds, and the film 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 film thickness of the Ti film was 73 angstroms or more when the number of cycles was 4 or more.

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

[0077] Looking at this result from a different perspective, it means that by setting the processing conditions of the film formation process, the total processing time for the Ti film thickness to reach the target film thickness can be minimized. Therefore, for example, when forming the target film thickness, the implementation time of the film formation process is specified so that the film formation rate per unit time is maximized, and the cleaning evacuation time is specified. From this, it can be understood that the total processing time of these film formation time and cleaning evacuation time can be set to be the shortest, and the throughput can be improved.

[0078] However, depending on the metal film, the type of film formation gas, the shape of the concave portion 50 formed on the wafer W, the material of the film on the bottom surface and side wall surface of the concave portion 50, the target film thickness, etc., the appropriate processing conditions for each of the film formation process, the vacuum evacuation process, and the purge process are different. Therefore, it is preferable that the implementation time and the number of repetitions of the film formation process and the vacuum evacuation process are appropriately set according to each case.

Explanation of Signs

[0079] W Wafer 1 Film formation apparatus 10 Processing container 13 Exhaust part 2 Mounting table 410 TiCl4 gas supply source 440 NH3 gas supply source 6 Ti film 100 Control unit

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; 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; and a method of performing the step of forming the metal film again after performing the step of evacuating the vacuum.

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 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 converted into plasma to form the metal film. The method according to claim 1.

4. The by-product contains Cl, and the cleaning gas is selected from at least one of a group of cleaning gases consisting of NH ３ gas, plasmaized 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 group.

5. The method according to claim 1, wherein 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.

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, wherein 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, and when the step of forming the metal film has a characteristic that the film-forming rate decreases over time, after stopping the supply of the film-forming gas, the control unit evacuates the inside of the processing container while supplying the cleaning gas to the processing container, and after performing the step of evacuating the vacuum, the control unit 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. comprising a plasma forming unit that forms the film-forming gas into plasma, 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 made into plasma to form the metal film. The apparatus according to claim 6.

9. The by-product contains Cl, and the cleaning gas is NH ３ gas or plasmaized H ２ gas, SiH ４ gas, Si ２ H ６ gas, NF ３ gas, and is at least one selected from a group of cleaning gases, the apparatus according to claim 8.

10. For the apparatus according to claim 6, 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 minimized.

Images