Method for forming a titanium nitride film, and apparatus for forming a titanium nitride film.

Abstract

To provide a titanium nitride film with a low specific resistance.SOLUTION: A method of forming a titanium nitride film includes: forming the titanium nitride film by alternately repeating supplying a raw material gas, which contains a titanium compound including chlorine and titanium, to a substrate accommodated in a processing container, and supplying a reaction gas, which contains a nitrogen compound including nitrogen and reactive with the titanium compound to form titanium nitride, to the substrate. The process of forming the titanium nitride film is executed under a condition in which a pressure in the processing container is set within a range of 2.7-12.6 kPa so that a specific resistance of the titanium nitride film becomes 57 μΩ cm or less.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This disclosure relates to a method for forming a titanium nitride film and an apparatus for forming a titanium nitride film. [Background technology]

[0002] Titanium nitride (TiN) films are used in various applications in the manufacturing of semiconductor devices. These TiN films are deposited using, for example, a titanium (Ti)-containing gas, such as titanium tetrachloride (TiCl4) gas, and a nitrogen (N)-containing gas, such as ammonia (NH3) gas, as deposition gases.

[0003] Regarding TiN films, Patent Document 1 describes a technique for forming them using TiCl4 gas and NH3 gas under a pressure set to within 1.3 kPa (10 Torr) by ALD (Atomic Layer Deposition). Furthermore, Patent Document 2 describes a technique using the same gases to form a film at 10 -3 This document describes a technique for depositing films using the CVD (Chemical Vapor Deposition) method under pressures set within the range of Torr to several tens of Torr. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2018-66050 [Patent Document 2] Japanese Patent Application Publication No. 6-188205 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] This disclosure provides a technology for forming titanium nitride films with low resistivity. [Means for solving the problem]

[0006] This disclosure is, A method for forming a titanium nitride film, A method for forming a titanium nitride film, The process includes the steps of alternately and repeatedly supplying a raw material gas containing a titanium compound including chlorine and titanium to a substrate housed in a processing container, and supplying a reaction gas containing nitrogen, which contains nitrogen and reacts with the titanium compound to form titanium nitride to the substrate, thereby forming the titanium nitride film. The process of forming the titanium nitride film is carried out under conditions in which the pressure inside the processing vessel is set to a range of 2.7 to 12.6 kPa such that the resistivity of the titanium nitride film is 57 μΩ·cm or less. 、 In the process of forming the titanium nitride film, during the raw material gas supply period in which the raw material gas is supplied into the processing container, an additive gas containing a silicon compound that reacts with chlorine contained in the titanium compound is supplied. During the raw material gas supply period, the timing of stopping the supply of the additive gas into the processing container is earlier than the timing of stopping the supply of the raw material gas, or at the same time as stopping the supply of the raw material gas. The process of forming the titanium nitride film is carried out while supplying an inert gas into the processing container. At the timing when the supply of the raw material gas and the supply of the reaction gas are switched, only the inert gas from the inert gas and hydrogen gas is supplied into the processing container, and then both the inert gas and the hydrogen gas are supplied. It is characterized by the following: [Effects of the Invention]

[0007] According to this disclosure, a titanium nitride film with low resistivity can be formed. [Brief explanation of the drawing]

[0008] [Figure 1] This is a longitudinal cross-sectional side view showing an example of an apparatus for depositing a titanium nitride film according to the present disclosure. [Figure 2] This figure shows an example of a gas supply sequence for the method of depositing a titanium nitride film according to the present disclosure. [Figure 3] This is a longitudinal cross-sectional side view showing the titanium nitride film formed on one side of the substrate. [Figure 4] This is a characteristic diagram illustrating the pressure conditions for the film deposition method. [Figure 5] This is the first characteristic diagram showing the evaluation results of the titanium nitride film. [Figure 6] This is the second characteristic diagram showing the evaluation results of the titanium nitride film. [Figure 7] This is the third characteristic diagram showing the evaluation results of the titanium nitride film. [Figure 8] It is a fourth characteristic diagram showing the evaluation results of the titanium nitride film. [Figure 9] It is a fifth characteristic diagram showing the evaluation results of the titanium nitride film. [Figure 10] It is a sixth characteristic diagram showing the evaluation results of the titanium nitride film.

Embodiments for Carrying Out the Invention

[0009] <Film Forming Apparatus> An embodiment of an apparatus for forming a titanium nitride film (TiN film) on a substrate (hereinafter referred to as "film forming apparatus") will be described with reference to FIG. 1. The film forming apparatus 1 includes a processing container 10 that houses a semiconductor wafer (hereinafter referred to as "wafer") W as a substrate. An annular exhaust duct 13, for example, is disposed at the upper part of the side wall of the processing container 10. Further, a ceiling wall 14 is provided on the upper surface of the exhaust duct 13 so as to close the upper opening of the processing container 10. The processing container 10 is connected to a vacuum exhaust unit 17 composed of, for example, a vacuum pump through a vacuum exhaust path 16 via an exhaust port 131 of the exhaust duct 13.

[0010] An APC (Auto pressure Controller) valve 18 serving as a pressure adjustment unit is interposed in the vacuum exhaust path 16. The APC valve 18 is composed of, for example, a butterfly valve, is provided in the vacuum exhaust path 16 so as to be openable and closable, and is configured to adjust the pressure in the processing container 10 by increasing or decreasing the conductance of the vacuum exhaust path 16 by adjusting its opening degree.

[0011] Inside the processing container 10 is a mounting table 2 that horizontally supports the wafer W and has a heater 21 embedded in it for heating the wafer W. This mounting table 2 is configured to be able to move up and down by a lifting mechanism 24. In Figure 1, the mounting table 2 at the transfer position is shown by a dashed line. In the figure, reference numeral 25 indicates a support pin for transferring the wafer W, which is configured to be able to move up and down by a lifting mechanism 26. Reference numeral 22 indicates a through hole for the support pin 25, and reference numerals 27 and 28 indicate bellows that expand and contract in conjunction with the lifting and lowering movements of the mounting table 2 and the support pin 25, respectively.

[0012] The processing container 10 is equipped with a showerhead 3 that supplies processing gas into the processing container 10 in a shower-like manner, facing the mounting base 2. The showerhead 3 has a gas diffusion space 31 inside, and its lower surface is configured as a shower plate 32 with numerous gas discharge holes 33 formed therein. The gas supply system 4 is connected to the gas diffusion space 31 via a gas inlet hole 34.

[0013] The gas supply system 4 includes a raw material gas supply unit 4A for supplying raw material gas to the processing container 10, a reaction gas supply unit 4B for supplying reaction gas, an additive gas supply unit 4C for supplying additive gas to be added to the raw material gas, and a hydrogen gas supply unit 4D for supplying hydrogen gas as a purge gas for purging the raw material gas and reaction gas. The raw material gas is a gas containing a titanium compound that includes chlorine (Cl) and titanium (Ti), and for example, titanium tetrachloride (TiCl4) is used as the titanium compound. The reaction gas is a gas containing a nitrogen compound that contains nitrogen (N) and reacts with the titanium compound to form titanium nitride (TiN), and for example, ammonia (NH3) is used as the nitrogen compound. Furthermore, the additive gas is a gas containing a silicon compound that reacts with the chlorine contained in the titanium compound TiCl4, and for example, silane (SiH4) is used as the silicon compound.

[0014] The raw material gas supply unit 4A includes a TiCl4 gas supply source 41 and a supply channel 411, and for example, a flow rate adjustment unit 412, a storage tank 413, and a valve V1 are interposed in the gas supply channel 411 from the upstream side. The reaction gas supply unit 4B includes an NH3 gas supply source 42 and a supply channel 421, and for example, a flow rate adjustment unit 422, a storage tank 423, and a valve V2 are interposed in the gas supply channel 421 from the upstream side. Furthermore, the additive gas supply unit 4C includes a SiH4 gas supply source 43 and a supply channel 431, and for example, a flow rate adjustment unit 432, a storage tank 433, and a valve V3 are interposed in the gas supply channel 431 from the upstream side. Finally, the hydrogen gas supply unit 4D includes an H2 gas supply source 44 and a supply channel 441, and for example, a flow rate adjustment unit 442 and a valve V4 are interposed in the gas supply channel 441 from the upstream side.

[0015] These TiCl4 gas, NH3 gas, and SiH4 gas are temporarily stored in storage tanks 413, 423, and 433, respectively. After being pressurized to a predetermined pressure in these storage tanks, they are supplied to the processing container 10. The supply and cessation of each gas from storage tanks 413, 423, and 433 to the processing container 10 are controlled by opening and closing valves V1 to V3.

[0016] Furthermore, the gas supply system 4 includes an inert gas supply unit that supplies inert gas to the processing container 10, and nitrogen (N2) gas is used as the inert gas. In this example, the inert gas supply unit includes N2 gas supply sources 45, 46, and 47 and supply passages 451, 461, and 471. In this example, the N2 gas supplied from supply source 45 is a purge gas for TiCl4 gas, and supply source 45 is connected to the downstream side of valve V1 in gas supply passage 411 via gas supply passage 451. The N2 gas supplied from supply source 46 is a purge gas for NH3 gas, and supply source 46 is connected to the downstream side of valve V2 in gas supply passage 421 via gas supply passage 461. Furthermore, the N2 gas supplied from supply source 47 is a purge gas for SiH4 gas, and supply source 47 is connected to the downstream side of valve V3 in gas supply passage 431 via gas supply passage 471. Furthermore, the N2 gas supplied from the supply source 48 is a purge gas supplied to the processing container 10 along with the H2 gas, and the supply source 48 is connected to the downstream side of valve V4 in the gas supply passage 421 via the gas supply passage 481. In Figure 1, reference numerals 452, 462, 472, and 482 refer to flow rate adjustment units, respectively, and reference numerals V5 to V8 refer to valves, respectively.

[0017] As described later, the N2 gas supplied from gas supply lines 451, 461, and 471 is a purge gas that is continuously supplied throughout the TiN film deposition process. On the other hand, the H2 gas supplied from gas supply line 441 and the N2 gas supplied from gas supply line 481 are purge gases supplied at predetermined steps. Therefore, in order to distinguish these purge gases, the operation of supplying the latter H2 and N2 gases is called flash purging, and these purge gases are also called flash purge gases.

[0018] The film deposition apparatus 1 is equipped with a control unit 100, which is, for example, a computer and has a data processing unit including a program, memory, and CPU. The program sends control signals from the control unit 100 to each part of the film deposition apparatus 1 and incorporates commands (each step) to proceed with the process of forming the TiN film described later. The program is stored in a computer storage medium, such as a flexible disk, compact disk, hard disk, or MO (magneto-optical disk), and installed in the control unit 100. Specifically, this program controls operations such as the supply of raw material gas, reaction gas, and inert gas in the film deposition apparatus 1, and pressure adjustment in the processing container 10.

[0019] <Film formation method> Next, an example of a method for depositing a TiN film according to this disclosure will be described with reference to the gas supply sequence in Figure 2. In this example, a TiN film is deposited on one side of a wafer W by the ALD method using the previously described deposition apparatus 1. The gas supply sequence in Figure 2 shows the timing of supplying the TiCl4 gas, SiH4 gas, NH3 gas, H2 gas, and each N2 gas used for deposition to the processing container 10. In Figure 2, the N2 below TiCl4 is N2 gas supplied from supply source 45, the N2 below SiH4 is N2 gas supplied from supply source 47, the N2 below NH3 is N2 gas supplied from supply source 46, and the N2 below H2 is N2 gas supplied from supply source 48.

[0020] First, an APC setting process is performed to adjust the opening degree of the APC valve 18. In this process, for example, a wafer W is brought into the processing container 10 and placed on the mounting table 2, heating of the wafer W by the heater 21 is started, and N2 gas is supplied into the processing container 10 from supply sources 45, 46, and 47 at preset flow rates. Then, the processing container 10 is evacuated using the vacuum exhaust unit 17, and the opening degree of the APC valve 18 is adjusted so that the pressure inside the processing container 10 is, for example, 4.0 kPa (30 Torr). Following the APC setting process, a film deposition process is performed to form a TiN film, and in this film deposition process as well, the opening degree of the APC valve 18 is maintained at the opening degree adjusted in the APC setting process. During the APC setting process, the wafer W placed on the mounting table 2 is heated to a temperature of, for example, 600°C, which is within the range of 400°C to 750°C.

[0021] Next, a film deposition process is carried out based on the gas supply sequence shown in Figure 2, which is the process of forming a TiN film. The film deposition process consists of steps S1 to S6, which will be described later. First, valve V1 is opened and TiCl4 gas, which is the raw material gas, is supplied into the processing container 10, and N2 gas is supplied into the processing container 10 from supply sources 45, 46, and 47 at preset flow rates. In the film deposition process, the pressure inside the processing container 10 is adjusted to increase as described below. For this pressure adjustment, one example is to set the flow rate of N2 gas to be higher than that of the APC setting process. In addition, a small amount of hydrogen (H2) gas may be supplied along with the N2 gas. In particular, the supply of N2 gas raises the pressure inside the processing container 10 to, for example, 8.6 kPa (64.8 Torr) to 9.0 kPa (67.4 Torr), and this pressure is maintained during the film deposition process. In this way, with the pressure inside the processing container 10 set, TiCl4 gas is adsorbed onto the entire surface of the wafer W (step S1).

[0022] Next, with valve V1 still open, valve V3 is opened, and SiH4 gas, an additive gas, is supplied to the processing container 10 during the period when TiCl4 gas is being supplied, specifically after the supply of TiCl4 gas has started (step S2). As shown in the experimental results described later, SiH4 gas contributes to improving the deposition rate of the TiN film while suppressing the increase in the resistivity of the TiN film. The estimated mechanism by which these effects are obtained by adding SiH4 gas will be described later in conjunction with the experimental results.

[0023] Next, of the two valves that are open, valve 3 is closed to stop the supply of SiH4 gas (step S3). After a predetermined time has elapsed, the other valve V1 is closed to stop the supply of TiCl4 gas. Meanwhile, the supply of N2 gas from supply sources 45, 46, and 47 is continued, and valves V4 and V8 are opened to supply N2 gas and H2 gas for flash purging. In this way, a flash purge is performed by increasing the supply flow rate of N2 gas to remove the TiCl4 gas remaining in the processing container 10. In addition, by supplying H2 gas along with N2 gas during the flash purge, the remaining chlorine (Cl) reacts with hydrogen and is removed as hydrogen chloride (HCl) (step S4). As will be described later, the removal of Cl by adding H2 gas also contributes to reducing the resistivity of the TiN film.

[0024] Next, while continuing to supply N2 gas from supply sources 45, 46, and 47, valve V4 is closed to stop the supply of H2 gas, while valve V2 is opened to supply NH3 gas, which is the reaction gas, into the processing container 10. As previously described, the pressure inside the processing container 10 is set to the pressure of the film deposition process, so under this pressure, the TiCl4 adsorbed on the wafer W and NH3 react to form a TiN film (step S5).

[0025] Next, valve V2 is closed to stop the supply of NH3 gas, while the supply of N2 gas from supply sources 45, 46, and 47 continues. At the same time, valve V8 is opened to increase the N2 gas flow rate and perform a flash purge to remove any remaining NH3 gas in the processing container 10. Furthermore, during the flash purge, valve V4 is opened to supply H2 gas as well (step S6). In this way, during the film formation process, the raw material gas and reaction gas are supplied alternately to the processing container 10 while an inert gas, N2 gas, is supplied, and H2 gas is supplied at the timing of the flash purge when the raw material gas and reaction gas are switched. These steps S1 to S6 are repeated a set number of times to form a TiN film of the desired thickness.

[0026] The TiN film 5 formed by the method of this disclosure, for example, forms a wiring layer that is a word line in a DRAM, and is embedded in a groove-shaped recess 52 formed in the insulating film 51 on one side of the wafer W, as shown in Figure 3. The TiN film 5 is deposited on the inner surface of the bottom and the inner surface of the side wall of the recess 52, and the embedding into the recess 52 progresses by repeating the steps S1 to S6 described above. The insulating film 51 is made of, for example, a silicon oxide (SiO2) film, and the recess 52 is formed to have a depth D of 80 to 200 nm and an aperture width W of about 10 to 20 nm, with a ratio D / W of depth D to aperture width W of about 5 to 20. In general, since the aspect ratio of the word line recess 52 is smaller than that of the recess that forms via holes, the resistance value is lower by embedding TiN in the recess 52 rather than tungsten. In this way, by embedding the wiring layer in the recess 52 with TiN, the thickness of the formed TiN tends to increase.

[0027] In the DRAM manufacturing process, after depositing the TiN film 5 to be embedded in the recesses 52, an annealing treatment is performed for purposes such as diffusion of impurities. However, small voids called microvoids may form in the deposited TiN film 5. Furthermore, heating, such as in the annealing treatment performed after film deposition, can cause even more microvoids 53 to form within the TiN film. When a large number of microvoids 53 are generated in the TiN film used as a wiring layer, the current flow deteriorates, which can increase the resistivity of the TiN wiring layer and raise concerns about adverse effects on device operation.

[0028] The microvoids 53 formed by heating the wafer W are presumed to occur when tiny gaps are created between adjacent grains as the grains (crystal grains) in the TiN film 5 grow during the annealing process. Furthermore, as described later, it has been observed that when a TiN film is deposited using a source gas containing Cl, such as TiCl4, a large number of microvoids 53 tend to be generated during the annealing process. Therefore, it is presumed that reducing the Cl impurity concentration in the TiN film is effective in suppressing the generation of microvoids 53.

[0029] Against this backdrop, the inventors of this disclosure attempted to discharge unwanted TiCl4 gas and Cl-containing components such as reaction byproducts of the film deposition reaction from the processing container 10 by extending the purging time (flash purging time) with N2 gas and H2 gas in steps S4 and S6 described above. As a result, it was found that extending the purging time by about five times made it possible to deposit a TiN film with a low Cl content, and was also effective in suppressing the generation of microvoids 53 during the annealing process. However, in the process of embedding the TiN film 5 in the recesses 52 described above, the thickness of the TiN film 5 is large, at 15 nm to 20 nm, and the number of cycle repetitions is large. Therefore, extending the purging time increases the total processing time of the film deposition process, and a significant decrease in productivity becomes unavoidable.

[0030] Therefore, the inventors reviewed the processing conditions for the TiN film deposition process in order to deposit a TiN film 5 with low resistivity using methods other than increasing the purging time. Conventionally, when depositing TiN films using the ALD method, it is common practice to perform the deposition under conditions where the pressure inside the processing container 10 is 1.33 kPa (10 Torr) or less, as described in Patent Document 1. The ALD method deposits a TiN film by reacting TiCl4 and NH3 adsorbed on one side of the wafer W. Therefore, it is necessary to purge the raw material gas as quickly as possible to prevent the deposition reaction by the CVD method, which reacts TiCl4 and NH3 in the gas phase. This is because increasing the pressure inside the processing container 10 would increase the purging time, so it was considered common sense to perform the process under low-pressure conditions.

[0031] In response, the inventors performed the TiN film deposition process while varying the pressure inside the processing container 10 over a wide range. They discovered that the optimal pressure range for low resistivity of the TiN film was on the higher pressure side than the conventional pressure conditions. The process of optimizing the pressure conditions is described below.

[0032] First, the pressure inside the processing vessel 10 during the TiN film deposition process will be explained based on Figure 4. In Figure 4, the vertical axis represents the pressure inside the processing vessel 10, and the horizontal axis represents the elapsed time. In the same figure, the pressure of the film deposition process of this disclosure is shown by a solid line, and the conventional pressure conditions of 1.33 kPa (10 Torr) or less are shown by a dotted line.

[0033] The film deposition process of this disclosure will be described in the example shown in Figure 4. As previously described, this film deposition process consists of an APC setting process and a film deposition process. At time t1, N2 gas is supplied from supply sources 45, 46, and 47 at 7.5 slm (liters / minute, standard conditions (1 atmosphere, 0°C)) to start the APC setting process. Then, when the pressure inside the processing container 10 is stable (4.0 kPa (30 Torr)), the opening of the APC valve 18 is fixed, and the APC setting process is ended at time t2.

[0034] Next, at time t2, the aforementioned film deposition process is started. In this film deposition process, as previously described, the pressure inside the processing container 10 rises to 8.6 kPa (64.8 Torr) to 9.0 kPa (67.4 Torr) by increasing the flow rate of N2 gas compared to, for example, the APC setting process, as previously described. During the film deposition process, which is carried out by repeating steps S1 to S6 described above, the pressure drops by about 0.3 to 0.4 kPa when TiCl4 gas is supplied in step S1, and then rises again by about 0.3 to 0.4 kPa in steps S2 to S6. The reason why the pressure drops intermittently when TiCl4 gas is supplied is that the flow rate of N2 gas is reduced only when TiCl4 gas is supplied.

[0035] On the other hand, in the conventional film deposition process under pressure conditions, the film deposition process is carried out as described above, except that the set pressure is different. Therefore, at time t1, N2 gas is supplied at 2.5 slm to start the APC setting process. Then, when the pressure inside the processing container 10 is stable (0.67 kPa (5 Torr)), the opening of the APC valve 18 is fixed, and at time t2, the film deposition process described above is started. In this film deposition process, the TiN film is formed when the pressure inside the processing container 10 rises from 0.96 kPa (7.2 Torr) to 1.09 kPa (8.2 Torr).

[0036] Next, Figure 5 will be explained. This figure is a characteristic diagram (first characteristic diagram) showing the relationship between the pressure inside the processing container 10 and the resistivity of the TiN film. It shows the results of measuring the resistivity of the formed TiN film after performing the aforementioned film deposition process while varying the pressure in the APC setting process. In Figure 5, the vertical axis represents the resistivity of the TiN film, and the horizontal axis represents the pressure in the "APC setting process" inside the processing container 10. In Figure 5, data for a purge gas flow rate of 2.5 slm is plotted as ○, data for 5.0 slm as △, data for 7.5 slm as ◇, and data for 10.0 slm as □.

[0037] Furthermore, examples of the supply flow rates for each gas are as follows: TiCl4 gas is 34 sccm, NH3 gas is 600 sccm, and SiH4 gas is 250 sccm. The N2 gas continuously supplied from supply lines 451, 461, and 471 is, for example, a value obtained by dividing the flow rates of each of the above-mentioned purge gases into three equal parts. In addition, the N2 gas for flash purging in steps S4 and S6 is 18000 sccm, and the H2 gas for flash purging is 7000 sccm. The execution time for steps S1 to S3 and S5 is 0.05 seconds, the execution time for purging in steps S4 and S6 is approximately 1 second, and one cycle of steps S1 to S6 is set to 2.5 seconds.

[0038] In the TiN film deposition process, steps S1 to S6 were repeated as described above to deposit a TiN film with a thickness of 15 nm. The time required to perform the series of steps S1 to S6 was 2.5 seconds. The resistivity of the deposited TiN film was determined based on the results of measuring the film thickness of the TiN film using an ellipsometer and the sheet resistance value obtained by the 44-probe method.

[0039] Figure 5 omits the description of the pressure inside the processing container 10 during the film formation process, but an example of the corresponding relationship is as follows: Under conditions where the purge gas flow rate is 2.5 slm and the pressure during the APC setting process is 5.3 kPa, the pressure during the film deposition process is 8.8 kPa. Under conditions where the purge gas flow rate is 5.0 slm and the pressure in the APC setting process is 5.3 kPa, the pressure in the film deposition process is 10.4 kPa. Under conditions where the purge gas flow rate is 7.5 slm and the pressure during the APC setting process is 5.3 kPa, the pressure during the film deposition process is 11.8 kPa.

[0040] Thus, although the pressure in the film deposition process varies depending on the flow rates of TiCl4 gas, NH3 gas, and purge gas (N2 gas), in all cases it is approximately twice the pressure in the APC setting process. Therefore, by doubling the indicated value for the pressure conditions of the APC setting process shown on the horizontal axis of Figure 4, it is possible to understand the correspondence with the pressure in the film deposition process. In other words, the trend of the change in resistivity of the TiN film in response to changes in pressure in the film deposition process is almost similar to the trend of the change in resistivity in response to changes in pressure in the APC setting process shown in Figure 4. This is also true in the cases shown in Figures 6 to 8, which will be discussed later.

[0041] The results in Figure 5 show that the resistivity of the TiN film changes depending on the pressure during the APC setting process, i.e., the pressure during the film deposition process. Focusing on the deposition conditions with a purge gas flow rate of 2.5 slm, the resistivity decreases as the pressure during the APC setting process increases from 0.67 kPa (5 Torr). It is lowest at a pressure of 2.7 kPa (20 Torr), but beyond that pressure, the resistivity increases with increasing pressure.

[0042] Furthermore, under deposition conditions with purge gas flow rates of 5 slm, 7.5 slm, and 10 slm, the resistivity of the TiN film varied depending on the pressure during the APC setting process. Under these conditions, the resistivity was lowest at a pressure of 4.0 kPa (30 Torr), reaching 51.6 μΩcm. Moreover, at the same pressure, there was a tendency for the resistivity to decrease as the purge gas flow rate increased. However, it was also observed that the decrease in resistivity with increasing purge gas flow rate gradually decreased and tended to saturate.

[0043] As described above, it is recognized that there are optimal pressure conditions for the film deposition process in order to reduce the resistivity of the TiN film. Under the conventional pressure conditions shown in Figure 4, the pressure in the APC setting process is 6.65 kPa (5 Torr), so the resistivity of the formed TiN film is approximately 59 μΩcm. However, this disclosure aims to deposit a TiN film with a resistivity lower than this value, for example, 57 μΩcm or less.

[0044] As described above, the inventors formed TiN films by varying the pressure conditions inside the processing container 10. As a result, based on the data shown in Figure 5, it was found that if the pressure during the film formation process is within the range of 2.7 kPa (20 Torr) to 12.6 kPa (95 Torr), the resistivity of the formed TiN film is often 57 μΩcm or less. However, as shown in Figure 5, the resistivity of the TiN film also changes depending on the flow rate of the purge gas. Therefore, this disclosure requires that the formation of the TiN film be carried out under conditions where the pressure is within the range of 2.7 kPa (20 Torr) to 12.6 kPa (95 Torr) and the resistivity of the formed TiN film is 57 μΩcm or less. Such conditions can be determined in advance by conducting preliminary experiments as explained using Figure 5.

[0045] As described above, according to the above embodiment, it is possible to reduce the resistivity of the TiN film formed by the ALD method while suppressing the length of the purging time. Furthermore, as will be explained below, by increasing the pressure during the film deposition process, the secondary effect of increasing the film deposition rate of the TiN film can be obtained.

[0046] Figure 6 is a characteristic diagram (second characteristic diagram) showing the relationship between the pressure inside the processing container 10 and the film deposition rate of the TiN film. It shows the results of measuring the film deposition rate of the formed TiN film by performing the same film deposition process as the TiN film in Figure 5 while changing the pressure in the APC setting process. In Figure 6, the vertical axis represents the film deposition rate of the TiN film, and the horizontal axis represents the pressure inside the processing container 10 in the APC setting process. Also, in Figure 5, data with a purge gas flow rate of 2.5 slm is plotted as ○, data with 5.0 slm as △, data with 7.5 slm as ◇, and data with 10.0 slm as □.

[0047] From the results in Figure 6, it can be seen that the film deposition rate of TiN increases as the pressure in the APC setting process, i.e., the pressure in the film deposition process, increases. However, it can also be seen that the decrease in film deposition rate with respect to the increase in purge gas flow rate gradually decreases and saturates. Furthermore, it can be seen that the film deposition rate with respect to the aforementioned pressure is almost the same under film deposition conditions with purge gas flow rates of 5 slm, 7.5 slm, and 10 slm.

[0048] Based on the data under the condition of a 2.5 slm purge gas in Figures 5 (first characteristic diagram) and 6 (second characteristic diagram) described above, the following can be said: When the pressure in the APC setting process is between 1.3 kPa and 3.6 kPa, that is, when the pressure in the film deposition process is in the range of approximately 2.7 kPa to 7.2 kPa, the resistivity of the TiN film is 57 μΩcm or less. On the other hand, outside this pressure range, there is a tendency for the resistivity to increase rapidly. Furthermore, the film deposition rate increases with increasing pressure, regardless of the pressure range.

[0049] From these observations, it can be inferred that when the deposition pressure is within the range of 2.7 kPa to 7.2 kPa, the formation of TiN films by ALD proceeds more easily, resulting in a larger amount of TiN film formed in a single cycle. Furthermore, it is presumed that a denser TiN film with a lower Cl content (an impurity) is formed. On the other hand, when the pressure in the APC setting process exceeds 3.6 kPa, the resistivity increases with increasing pressure. This is presumed to be because, when the pressure exceeds 3.6 kPa, the proportion of TiN film formed by ALD and TiN film formed by CVD, in which TiCl4 and NH3 react in the gas phase, increases.

[0050] Thus, although the mechanism by which the resistivity of the TiN film is improved by the pressure during the film deposition process is not clear, it has been experimentally confirmed that the Cl content of the TiN film decreases, as shown in Figure 7 below. For this reason, it is presumed that under high pressure and in an atmosphere where H2 gas is present, Cl is more easily detached from the surface of the TiN film.

[0051] Figure 7 is a characteristic diagram (third characteristic diagram) showing the relationship between the pressure inside the processing container 10 and the Cl content of the TiN film. It shows the results of measuring the Cl content of the formed TiN film after performing the same film deposition process as in Figure 5 by changing the pressure in the APC setting process. The Cl content (at%) of the TiN film is shown as a result of measuring the proportion of Cl atoms in the TiN film by SIMS (Secondary Ion Mass Spectrometry). In the figure, the vertical axis represents the Cl content, and the horizontal axis represents the pressure inside the processing vessel 10 during the APC setting process. Data with a purge gas flow rate of 2.5 slm is plotted with ○, and data with a purge gas flow rate of 7.5 slm is plotted with ◇.

[0052] Data from a 2.5 slm purge gas test shows that in the APC setting process, when the pressure is in the range of 0.67 kPa (5 Torr) to 4.0 kPa (30 Torr), the Cl content of the formed TiN film gradually decreases as the pressure increases. Therefore, increasing the pressure in the APC setting process, i.e., the film deposition process, reduces the amount of Cl incorporated into the TiN film during formation. This is presumed to suppress the generation of microvoids and lead to a decrease in resistivity.

[0053] In fact, when we investigated the relationship between the pressure inside the processing vessel 10 and the void fraction of the TiN film, we obtained the results shown in Figure 8 (Fourth Characteristic Figure). This figure shows the results of measuring the void fraction of the formed TiN film after annealing, after performing the same film deposition process as in Figure 5 while changing the pressure in the APC setting process. The annealing conditions were 750°C, 2 hours, and an N2 atmosphere. The void fraction was determined by performing TEM (Transmission Electron Microscope) observation of a sample processed parallel to the trench shape and calculating the percentage of the area where the void portion appears white from the total area using image processing. In the figure, the vertical axis represents the void fraction, and the horizontal axis represents the pressure inside the processing vessel 10 during the APC setting process. Data with a purge gas flow rate of 2.5 slm is plotted with ○, and data with a purge gas flow rate of 7.5 slm is plotted with ◇.

[0054] In the data for a 2.5 slm purge gas, it can be seen that in the APC setting process pressure range of 1.3 kPa (10 Torr) to 4.0 kPa (30 Torr), the void ratio of the formed TiN film decreases as the pressure increases. Thus, a correlation is observed between the Cl content and void ratio of the TiN film, and it can be understood that increasing the pressure in the APC setting process, i.e., the film deposition process, reduces the amount of Cl incorporated into the TiN film during formation, and as a result, the generation of voids is suppressed.

[0055] Furthermore, to confirm the effect of adding SiH4 gas, Figures 9 and 10 show examples of how the supply flow rate of SiH4 gas in step S2 was varied to check its effect on the resistivity and deposition rate of the TiN film. The total flow rate of the purge gas (N2 gas) continuously supplied from supply lines 451, 461, and 471 was 7.5 slm, and the pressure inside the processing container 10 was set to 5.3 kPa (40 Torr).

[0056] In Figures 9 and 10, the plot for a SiH4 gas supply flow rate of 450 sccm was formed under the same processing conditions as the diamond-shaped (◇) plot in Figures 5 and 6 at a pressure of 5.3 kPa (40 Torr). When the SiH4 gas supply flow rate was reduced to 250 sccm and then to 0 sccm, there was a slight tendency for the resistivity to increase (Figure 9). Furthermore, the film deposition rate tended to decrease with decreasing SiH4 gas supply flow rate (Figure 10).

[0057] Thus, the mechanism by which supplying SiH4 gas as an additive gas reduces the resistivity of the TiN film and improves the film deposition rate is unclear. One hypothesis is that when TiCl4 gas is supplied in steps S1-S3, TiCl4 is adsorbed onto the Ti-NH2 layer formed in the previous cycle, and Ti-N-Ti-Cl forms on the film surface. X This Ti-N-Ti-Cl is formed. XIt is thought that it may limit the formation of the adsorption sites of TiCl4 to be supplied in the next cycle. At this time, when SiH4 gas, which is a silicon compound that reacts with Cl contained in Ti-N-Ti-Cl, is added to the TiCl4 gas, Ti-N-Ti-H X is formed on the film surface, and Cl becomes a compound of SiH X Cl Y Cl (4-Y) and is extracted from the film. Since Ti-N-Ti-H X is considered to have a smaller effect of inhibiting the formation of adsorption sites compared to Ti-N-Ti-Cl X , it is possible to suppress the inhibition of the adsorption of new TiCl4. For example, based on the above reaction mechanism, it is estimated that while suppressing the remaining Cl in the TiN film, many adsorption sites are formed on the surface of the film, and the film formation rate of the TiN film may be improved.

[0058] However, if Si of SiH4 is incorporated into the TiN film, SiN, which is an insulating material, is formed, which also becomes a factor increasing the specific resistance of the TiN film. Therefore, as shown in FIG. 2, regarding the timing of starting the supply of SiH4 gas, it is set after starting the supply of TiCl4 gas (steps S1, S2). Thereby, after sufficiently adsorbing TiCl4 on the surface of the film, it becomes possible to proceed with the reaction with SiH4, and the incorporation of Si into the TiN film can be suppressed. Also, regarding the timing of stopping the SiH4 gas, by setting it before stopping the supply of the TiCl4 gas, the remaining amount of SiH4 in the processing container 10 can be reduced, and the effect of suppressing the incorporation of Si into the TiN film can also be obtained.

[0059] However, starting the supply of SiH4 gas after starting the supply of TiCl4 gas and stopping the supply of SiH4 gas before stopping the supply of TiCl4 gas are not essential requirements. For example, as long as the specific resistance of the TiN film is 57 μΩcm or less as described above, the TiCl4 gas and the SiH4 gas may be stopped simultaneously, or the timing of starting the supply may be set simultaneously.

[0060] Furthermore, in the example shown in Figure 9, the resistivity of the TiN film is around 60 μΩcm, which is greater than the target value of 57 μΩcm. However, as previously mentioned, the resistivity of the TiN film also changes depending on other processing conditions, such as the flow rate of the purge gas. The results shown in Figure 9 show that even when the flow rate of the added SiH4 gas is changed, the resistivity does not change as significantly as the deposition rate shown in Figure 10. Therefore, if conditions are met to deposit a TiN film with a resistivity of 57 μΩcm or less, the SiH4 gas supply flow rate may be set to a lower flow rate than 450 sccm, as long as the required deposition rate is obtained (including the case where the SiH4 gas supply flow rate is 0 sccm). Conversely, to achieve a higher deposition rate, the SiH4 gas supply flow rate may be increased beyond 450 sccm, as long as the effect of Si incorporation into the TiN film does not increase.

[0061] As described above, according to this disclosure, by optimizing the pressure conditions in the film deposition process, it is possible to form a TiN film with low resistivity. Furthermore, the film deposition rate of the TiN film can be increased. Consequently, the length of steps S4 and S6, in which raw material gases and reaction gases are purged, can be reduced. In addition, by increasing the film deposition rate, the number of cycles (steps S1 to S6) of the film deposition process required to reach the target film thickness can be reduced compared to conventional methods. This contributes to shortening the total processing time of the film deposition process and improves productivity. Thus, by optimizing the pressure conditions in the film deposition process, it is possible to reduce the resistivity of the TiN film and increase the film deposition rate, making it possible to significantly improve productivity using existing equipment.

[0062] In addition to titanium tetrachloride (TiCl4), titanium trichloride (TiCl3), titanium dichloride (TiCl2), titanium tetrabromide (TiBr4), and titanium tetraiodide (TiI4) can be used as the titanium compounds in the raw material gas. In addition to ammonia, other nitrogen compounds that can be used as reaction gases include hydrazine (N2H4), monomethylhydrazine (CH3NH-NH2), or nitrogen radicals. Furthermore, in the additive gas, disilane (Si2H6) may be used as the silicon compound that reacts with the chlorine contained in the titanium compound, in addition to silane (SiH4). However, if an increase in resistivity is a concern, it is preferable to avoid silicon compounds containing chlorine, such as SiH2Cl2. In addition to nitrogen gas, argon (Ar) gas or helium (He) gas may be used as the inert gas.

[0063] In the above-described embodiment, the setting pressure for the APC setting process is lower than that for the film deposition process, and the opening degree of the APC valve 18 is set accordingly. However, this is not limited to this example; in the APC setting process, the supply amount of inert gas may be set to approximately the same level as during the film deposition process, and the opening degree of the APC valve 18 may be set to adjust the pressure inside the processing container 10 to a pressure within the range of 2.7 to 12.6 kPa, which is the pressure during the film deposition process.

[0064] Furthermore, pressure control during the film formation process may be performed not only by controlling the flow rates of the raw material gas, reaction gas, and inert gas, but also in combination with adjusting the opening degree of the APC valve 18. For example, in the above example, an inert gas was supplied during the process of forming the TiN film, but when supplying the raw material gas or reaction gas, the supply of the inert gas may be stopped, while the opening degree of the APC valve 18 is changed to adjust the pressure inside the processing vessel 10 as described above. In addition, performing a flash purge by simultaneously supplying N2 gas and H2 gas is not a mandatory requirement. Within the range in which a TiN film with a resistivity of 57 μΩcm or less can be obtained, a flash purge may be performed using only N2 gas, for example. Alternatively, a flash purge may be omitted, and only a purge using the continuously supplied N2 gas may be performed.

[0065] Furthermore, the apparatus for depositing the TiN film is not limited to the configuration shown in Figure 1. For example, a batch-type deposition apparatus that deposits films on multiple wafers W simultaneously may be used. In this case as well, when depositing the TiN film by the ALD method, the deposition process can be carried out under pressure conditions within the range of 2.7 to 12.6 kPa, such that the resistivity of the TiN film is 57 μΩ·cm or less.

[0066] <Other applications> It should be noted that the embodiments disclosed herein are illustrative and not restrictive in all respects. The above embodiments may be omitted, substituted, modified or combined in various ways without departing from the scope and spirit of the appended claims. [Explanation of Symbols]

[0067] W Semiconductor wafer 1 Film deposition equipment 10 Processing containers 4A Raw Gas Supply Section 4B Reaction gas supply unit 4C Additive Gas Supply Unit 4D Hydrogen Gas Supply Unit

Claims

1. A method for forming a titanium nitride film, The process includes the steps of alternately and repeatedly supplying a raw material gas containing a titanium compound including chlorine and titanium to a substrate housed in a processing container, and supplying a reaction gas containing nitrogen, which contains nitrogen and reacts with the titanium compound to form titanium nitride to the substrate, thereby forming the titanium nitride film. The process of forming the titanium nitride film is carried out under conditions in which the pressure inside the processing vessel is set to be within the range of 2.7 to 12.6 kPa, such that the resistivity of the titanium nitride film is 57 μΩ·cm or less. In the process of forming the titanium nitride film, during the raw material gas supply period in which the raw material gas is supplied into the processing container, an additive gas containing a silicon compound that reacts with chlorine contained in the titanium compound is supplied. During the raw material gas supply period, the timing of stopping the supply of the additive gas into the processing container is earlier than the timing of stopping the supply of the raw material gas, or at the same time as stopping the supply of the raw material gas. The process of forming the titanium nitride film is carried out while supplying an inert gas into the processing container. A method comprising supplying only the inert gas from the inert gas and hydrogen gas into the processing vessel at the timing when the supply of the raw material gas and the supply of the reaction gas are switched, and then supplying both the inert gas and the hydrogen gas.

2. The method according to claim 1, wherein the titanium compound is titanium tetrachloride.

3. The method according to claim 1 or 2, wherein the nitrogen compound is ammonia.

4. The method according to any one of claims 1 to 3, wherein the timing for starting the supply of the additive gas is after the start of the supply of the raw material gas.

5. The method according to any one of claims 1 to 4, wherein the silicon compound is silane.

6. The method according to any one of claims 1 to 5, wherein the step of forming the titanium nitride film is carried out under conditions in which the substrate is heated to a temperature in the range of 400 to 750°C.

7. The processing container has an exhaust passage for exhausting the inside of the processing container, A valve is provided that changes the pressure inside the processing container by changing the conductance of the exhaust passage, During the process of forming the titanium nitride film, the opening degree of the valve is fixed. The method according to any one of claims 1 to 6, wherein the pressure inside the processing vessel during the process of forming the titanium nitride film is maintained at a pressure higher than the pressure inside the processing vessel at the time when the opening of the valve switches from unfixed to fixed in order to perform the process of forming the titanium nitride film.

8. An apparatus for depositing a titanium nitride film on a substrate, A processing container configured to house the aforementioned substrate, The processing container is provided with a raw material gas supply unit that supplies a raw material gas containing a titanium compound including chlorine and titanium, The processing container is provided with a reaction gas supply unit that supplies a reaction gas containing nitrogen and a nitrogen compound that reacts with the titanium compound to form titanium nitride, The processing container is provided with an additive gas supply unit that supplies an additive gas containing a silicon compound that reacts with the chlorine contained in the titanium compound, The processing container is provided with a hydrogen gas supply unit that supplies hydrogen gas, The processing container is equipped with an inert gas supply unit for supplying inert gas, It has a control unit and The control unit repeatedly alternately performs the operation of supplying raw material gas from the raw material gas supply unit and the operation of supplying reaction gas from the reaction gas supply unit into the processing container, and performs the step of forming the titanium nitride film under conditions in which the pressure inside the processing container is set to be within the range of 2.7 to 12.6 kPa and the resistivity of the titanium nitride film is 57 μΩ·cm or less. During the raw material gas supply period in which the raw material gas is supplied into the processing container, the step of supplying the additive gas into the processing container is performed. During the raw material gas supply period, the timing of stopping the supply of the additive gas into the processing container is earlier than the timing of stopping the supply of the raw material gas, or at the same time as stopping the supply of the raw material gas. The step of forming the titanium nitride film is carried out while supplying inert gas from the inert gas supply unit into the processing container. An apparatus that, at the timing when the supply of the raw material gas and the supply of the reaction gas are switched, first supplies only the inert gas from the inert gas and the hydrogen gas into the processing container, and then supplies the inert gas and the hydrogen gas.

9. The apparatus according to claim 8, wherein the titanium compound is titanium tetrachloride.

10. The apparatus according to claim 8 or 9, wherein the nitrogen compound is ammonia.

11. The apparatus according to any one of claims 8 to 10, wherein the control unit controls the raw material gas supply unit and the additive gas supply unit so that the timing for starting the supply of the additive gas is after the start of the supply of the raw material gas.

12. The apparatus according to any one of claims 8 to 11, wherein the silicon compound is silane.

13. The processing container has an exhaust passage for exhausting the inside of the processing container, A valve is provided that changes the pressure inside the processing container by changing the conductance of the exhaust passage, From before the step of forming the titanium nitride film is performed until the end of the process, the opening degree of the valve is fixed. The apparatus according to any one of claims 8 to 12, wherein the pressure inside the processing vessel during the step of forming the titanium nitride film is maintained at a pressure higher than the pressure inside the processing vessel at the time when the opening of the valve switches from unfixed to fixed in order to perform the step of forming the titanium nitride film.

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