Substrate treatment method and substrate treatment device

Abstract

In the present invention, to remove a silicon-containing film formed on the surface of a substrate, highly uniform removal treatment is performed in sections on the surface of the substrate. This etching method comprises: a step for storing in a treatment vessel a substrate on the surface of which a silicon-containing film has been formed, supplying a treatment gas containing a halogen-containing gas and a basic gas, and modifying the silicon-containing film to generate a reaction product; a step for supplying an inert gas into the treatment vessel and exhausting the inside of the treatment vessel in a state where the supply of the treatment gas to the treatment vessel has been stopped, in order to remove part of the reaction product; a step for alternately repeating the first step and the second step; and a step for causing the pressure inside the treatment vessel to be higher than 200 Pa in each of the second steps so that the treatment gas is supplied to the substrate on which there is residual reaction product, in the second and subsequent iterations of the first step in the repetition step.

Description

Substrate processing method and substrate processing apparatus

[0001] The present disclosure relates to a substrate processing method and a substrate processing apparatus.

[0002] In manufacturing a semiconductor device, SiO formed on the surface of a semiconductor wafer (hereinafter referred to as wafer) as a substrate is ２ In some cases, etching of silicon-containing films such as silicon oxide films is performed. Patent Document 1 discloses a method for etching silicon-containing films such as silicon dioxide films by sequentially repeating a first step of supplying a basic gas to a substrate and a second step of supplying a fluorine-containing gas to a wafer. ２ It is described that, in etching a film, after the second step is completed and before the first step is started, the inside of the processing vessel in which the substrate is stored is purged.

[0003] In Patent Document 2, a process gas containing a halogen-containing gas and a basic gas is supplied to a wafer to form a SiO ２ After generating a reaction product on the surface of the film, a part of the reaction product becomes SiO ２ The pressure in the processing vessel in which the wafer is stored is reduced to 0 to 200 Pa so that the remaining part remains on the film and the other part is removed. After that, the pressure in the processing vessel is increased and the processing gas is supplied to the wafer again, thereby removing the SiO ２ Removal of the membrane is described.

[0004] Patent Publication No. 2021-180281 Patent Publication No. 2021-118250

[0005] The present disclosure provides a technique for removing a silicon-containing film formed on a surface of a substrate, which is capable of performing a highly uniform removal process in each part of the surface of the substrate.

[0006] The etching method of the present disclosure includes the steps of: storing a substrate having a silicon-containing film formed on its surface in a processing vessel; a first step of supplying a processing gas containing a halogen-containing gas and a basic gas into the processing vessel to modify the silicon-containing film and generate a reaction product; a second step of supplying an inert gas into the processing vessel and evacuating the processing vessel while stopping the supply of the processing gas into the processing vessel in order to remove some of the reaction product; a repeating step of alternately repeating the first step and the second step; and a pressure control step of maintaining a pressure in the processing vessel higher than 200 Pa in each of the second steps so that the processing gas is supplied to the substrate on which the reaction product remains in the second and subsequent first steps in the repeating steps.

[0007] The present disclosure makes it possible to perform a highly uniform removal process in each part of the surface of a substrate when removing a silicon-containing film formed on the surface of the substrate.

[0008] FIG. 1 is a longitudinal sectional side view illustrating the surface structure of a substrate before etching processing of an embodiment; FIG. 2 is an enlarged longitudinal sectional side view illustrating a portion of the surface structure of a substrate before etching processing; FIG. 3 is a view showing surface changes of a silicon oxide film caused by etching processing of a comparative embodiment; FIG. 4 is a view showing surface changes of a silicon oxide film caused by etching processing of a comparative embodiment; FIG. 5 is a view showing surface changes of a silicon oxide film caused by etching processing of an embodiment; FIG. 6 is a view showing surface changes of a silicon oxide film caused by etching processing of an embodiment; FIG. 7 is a view showing surface changes of a silicon oxide film caused by etching processing of an embodiment; FIG. 8 is a view showing surface changes of a silicon oxide film caused by etching processing of an embodiment;

[0009] (Surface Layer Structure of Substrate) FIG. 1 is a longitudinal side view illustrating the surface structure of a substrate before etching in this embodiment. As shown in the figure, in the surface layer of the wafer W, a number of protrusions, for example, made of polysilicon film 11, are formed on an underlying film 10 and aligned horizontally, thereby forming a plurality of recesses. The polysilicon film 11 therefore forms the side walls of the recesses. A silicon oxide film 12 is formed within each recess. In this embodiment, etching is performed so that the bottom end of each silicon oxide film 12 remains. This etching is selective to the polysilicon film 11. Note that the above-mentioned underlying film 10 is not shown in any figures other than FIG. 1.

[0010] When the silicon oxide film 12 is formed in the recess, the silicon oxide film 12 grows from various parts of the sidewall of the polysilicon film 11 and joins together, which may result in the formation of a seam 13 in the horizontal center of the silicon oxide film 12. This seam 13 refers to a junction between the interfaces of the silicon oxide film 12 or a void formed in the silicon oxide film 12. Hereinafter, the direction from the front surface side to the back surface side of the wafer W may also be referred to as the vertical direction or height direction. The size of the seam 13, such as the horizontal length (width) and height length, and its position in the height direction, vary between recesses.

[0011] (Comparative Example) To clarify the effects of the etching method of the present disclosure, an etching process of a comparative example will be described first. FIG. 2 shows a wafer W before processing. For the purpose of the description, two silicon oxide films 12a and 12b are shown as the silicon oxide film 12, with no seam 13 formed in the silicon oxide film 12a and a seam 13 formed in the silicon oxide film 12b. In both the process of this comparative example and the processes of the embodiments described below, the wafer W is stored in a processing vessel and adjusted to a predetermined temperature, and processing is performed by supplying various gases into the processing vessel. During processing of the wafer W, the amount of exhaust gas from the processing vessel is adjusted to create a vacuum atmosphere at a desired pressure.

[0012] 3A and 3B show the surface changes of silicon oxide films 12a and 12b due to etching processing according to a comparative example. First, a processing gas is supplied into a processing chamber. This processing gas is a halogen-containing gas and a basic gas. Specifically, HF (hydrogen fluoride) gas is used as the halogen-containing gas and NH 4 gas is used as the basic gas. ３ Ammonia gas is supplied. The surface portions of the silicon oxide films 12a and 12b react with the processing gas and are transformed into ammonium fluorosilicate (AFS), a reaction product, forming an AFS layer. As this reaction progresses, the thickness of the AFS layer increases.

[0013] When the AFS layer is relatively thin, the processing gas can penetrate the AFS layer and alter the silicon oxide films 12a and 12b. However, as the AFS layer becomes thicker, such penetration becomes more difficult. Therefore, after supplying the processing gas for a predetermined time, the supply of processing gas is stopped to maintain a relatively low pressure in the processing chamber. This causes the AFS to sublimate, removing the AFS layer and exposing the surfaces of the silicon oxide films 12a and 12b. By alternately repeating this process of supplying processing gas and removing the AFS layer to expose the surface of the silicon oxide film 12, downward etching of each of the silicon oxide films 12a and 12b progresses (Figure 3A). Note that the dotted arrows in the figure indicate sublimated AFS.

[0014] However, as etching progresses in this manner, when processing gas is supplied to the portion of silicon oxide film 12b where seam 13 has formed, the processing gas flows downward within seam 13 (specifically, the voids that form seam 13 and the minute gaps between the interfaces of silicon oxide film 12). The portion around seam 13 then transforms into AFS, and then sublimes. In other words, etching progresses downward in silicon oxide film 12b more than in silicon oxide film 12a. That is, etching progresses relatively quickly in the portion where seam 13 has formed.

[0015] Therefore, as shown in Fig. 3B, there is a risk that the etching amount will differ relatively greatly between the silicon oxide films 12a and 12b (i.e., the surface heights will differ relatively greatly between the silicon oxide films 12a and 12b) at the end of etching. Furthermore, when the periphery of the seam 13 in the silicon oxide film 12b is etched as described above, the seam 13 is etched so as to expand laterally. Therefore, the central portions on both sides of the recess are etched relatively largely, and there is a risk that the surface heights of the respective portions of the silicon oxide film 12b will vary relatively greatly at the end of etching, as shown in Fig. 3B.

[0016] Assuming that a large number of recesses are formed on the wafer W, as described above, the width, height, and height position of the seam in the silicon oxide film 12 within the recesses may differ among the recesses. Therefore, although Fig. 3 shows that the etching amount varies between the silicon oxide film 12b in which the seam 13 is formed and the silicon oxide film 12a in which the seam 13 is not formed, the above-mentioned etching amount may also vary among the silicon oxide films 12 in which the seam 13 is formed due to the difference in the state of the seam 13.

[0017] This embodiment is implemented to prevent the problems described in the comparative example. As with the comparative example, the case where the wafer W shown in FIG. 2 is processed will be described as an example. Figures 4A to 4D are diagrams showing changes in the surfaces of silicon oxide films 12a and 12b due to the etching process according to this embodiment.

[0018] First, as in the comparative example, HF gas and NH 4 gas were supplied as processing gas to a wafer W stored in a processing vessel that had been evacuated to a vacuum atmosphere. ３ Gas is supplied to modify the surfaces of the silicon oxide films 12a and 12b, forming an AFS layer 14 (FIG. 4A). The processing gas selectively acts on the silicon oxide film 12, of the polysilicon film 11 and silicon oxide film 12 that form the sidewall of the recess, to modify it. The chain arrows in the figure indicate the processing gas.

[0019] Thereafter, the supply of the processing gas to the wafer W is stopped. While the supply of the processing gas is stopped, the processing vessel is evacuated to a relatively high pressure, specifically, a pressure higher than 200 Pa (pressure control process). Meanwhile, a purge gas, which is an inert gas, is supplied to remove the processing gas remaining in the processing vessel.

[0020] The pressure inside the processing vessel is relatively high, preventing the AFS layer 14 from rapidly sublimating. When the wafer W is heated, a small amount of AFS sublimes from the surface of the AFS layer 14 and is released into the gas phase near the surface. The flow of purge gas in the gas phase near the surface reduces the AFS concentration in the gas phase. Therefore, sublimation of AFS from the surface of the AFS layer 14 is promoted so that the AFS concentration in the gas phase remains balanced. Thus, while the purge gas is being supplied, the surface portion of the AFS layer 14 continues to sublimate slowly. In FIG. 4B, the purge gas is indicated by a solid line, and the vaporized AFS is indicated by a dotted line. Hereinafter, the process of supplying the processing gas to form the AFS layer 14 will be referred to as the first process, and the process of removing the surface portion of the AFS layer 14 by increasing the pressure inside the processing vessel to more than 200 Pa and supplying the purge gas will be referred to as the second process.

[0021] Before the AFS layer 14 disappears, the supply of processing gas into the processing chamber is resumed ( FIG. 4C ). That is, the first step is performed again. Because the second step has made the AFS layer 14 thinner than at the end of the first step, the processing gas penetrates the AFS layer 14 and acts on the surface layer of the silicon oxide film 12 underneath, converting the surface layer into AFS. That is, the thickness of the AFS layer 14 increases. The second step is then performed again, removing the surface layer of the AFS layer 14. The first and second steps are then repeated in sequence, etching the silicon oxide film 12 downward. In each first step, processing gas is supplied to the silicon oxide film 12, which remains covered with the AFS layer 14, as in the second first step described above.

[0022] As etching progresses by repeating the cycle consisting of the first and second steps, etching of the silicon oxide film 12b progresses downward, and the surface of the AFS layer 14 approaches the portion where the seam 13 is formed, resulting in a state in which the process gas is supplied into the seam 13. Even in this state, the AFS layer 14 suppresses permeation, preventing a large amount of process gas from flowing deep into the seam 13. Furthermore, it is assumed that the formed AFS flows on the wafer W, and the lower portion of the AFS layer 14 can penetrate into the seam 13. Figures 4A to 4C show the AFS layer 14 in such a state. In this case, the thickness of the AFS layer 14 is large in the portion where the seam 13 is formed, so that permeation of the process gas is more reliably prevented, and the process gas is more reliably prevented from flowing into the seam 13.

[0023] As a result, during the execution of the above cycle in this embodiment, the portion where seam 13 is formed is prevented from being etched at a relatively high rate, as shown in the comparative example, and etching that would laterally expand seam 13 is prevented. As a result, etching proceeds with high uniformity between silicon oxide films 12 a and 12 b, and also proceeds with high uniformity in each portion within the recess where silicon oxide film 12 b is formed.

[0024] After the cycle of the first and second steps is repeated a predetermined number of times, the pressure inside the processing chamber is increased to a predetermined level and a purge gas is supplied into the processing chamber, thereby removing the AFS layer 14 from the wafer W and completing the etching process. Figure 4D shows the wafer W after etching has been completed.

[0025] 4A to 4D show that variation in the amount of etching is suppressed between silicon oxide film 12b in which seam 13 is formed and silicon oxide film 12a in which seam 13 is not formed. As described above, the high-speed etching of the portion in which seam 13 is formed is suppressed, thereby suppressing variation in the amount of etching even between silicon oxide films 12 in which seam 13 is formed.

[0026] 5 is a longitudinal side view showing a substrate processing apparatus according to this embodiment. As described above, the substrate processing apparatus 1 includes a processing chamber 21 containing a processing space for processing a wafer W. In the figure, reference numeral 22 denotes a transfer port for the wafer W that opens into the sidewall of the processing chamber 21 and is opened and closed by a gate valve 23. A stage 24 on which the wafer W is placed is provided within the processing chamber 21. The stage 24 is provided with lift pins (not shown), the upper ends of which protrude and retract into the upper surface of the stage 24. The wafer W is transferred between the stage 24 and a substrate transfer mechanism (not shown) via the lift pins.

[0027] A temperature adjustment unit 25, which is, for example, a heater that performs resistance heating, is embedded in the stage 24, and heats the wafer W placed on the stage 24 to a set temperature of, for example, 80°C or higher. A gas shower head 30 is provided at an upper portion of the processing vessel 21, facing the stage 24. The downstream sides of gas supply paths 31 and 32 are connected to the gas shower head 30. The upstream side of the gas supply path 31 branches to form gas supply paths 31A and 31B, and the upstream side of the gas supply path 32 branches to form gas supply paths 32A and 32B. The upstream sides of the gas supply paths 31A, 31B, 32A, and 32B are connected to gas supply sources 41, 42, 43, and 44, respectively, via flow rate adjustment units 35. Each flow rate adjustment unit 35 includes a valve and a mass flow controller, and controls the supply and cutoff of gases supplied from the gas supply sources 41 to 44 to the downstream side and adjusts the flow rate.

[0028] Gas supply sources 41, 42, 43, and 44 supply HF gas, Ar (argon) gas, NH ３ Gas, N ２ Nitrogen gas is supplied to the respective connected flow paths. ２ The HF gas and Ar gas constitute the purge gas. The flow rate regulators 35 can switch the gases supplied from the gas supply sources 41 to 44 into the processing chamber 21. The gas supply source 41 and flow rate regulators 35 supplying HF gas in the gas supply line 31A, and the NH gas in the gas supply line 32A ３The gas supply source 43 and the flow rate adjusting unit 35 that supply gas correspond to a process gas supply mechanism. The gas supply source 42 and the flow rate adjusting unit 35 that supply Ar gas in the gas supply line 31B, and the N gas in the gas supply line 32B correspond to a process gas supply mechanism. ２ The gas supply source 44 that supplies gas and the flow rate adjusting unit 35 correspond to an inert gas supply mechanism.

[0029] The upstream end of an exhaust path 51 is connected to the bottom of the processing vessel 21 and opens into the processing vessel 21. A valve V1 and an exhaust mechanism 52 are sequentially provided on the exhaust path 51 toward the downstream side, and the exhaust mechanism 52 is configured by a vacuum pump or the like. The valve V1 is, for example, an APC (Auto Pressure Control) valve, and its opening degree can be changed during processing of the wafer W in accordance with a control signal output from a control unit 20 (described later) so that the pressure inside the processing vessel 21 becomes a preset value.

[0030] The substrate processing apparatus 1 includes a control unit 20, which is a computer, and the control unit 20 includes a program, a memory, and a CPU. The program includes instructions (steps) for processing the wafer W and transporting the wafer W as described above. The program is stored on a storage medium, such as a compact disc, a hard disk, a magneto-optical disc, or a DVD, and is installed in the control unit 20. The control unit 20 outputs control signals to each component of the substrate processing apparatus 1 based on the program, thereby controlling the operation of each component. The operations controlled in this manner include, for example, adjustment of the temperature of the stage 24 (i.e., the temperature of the wafer W), operation of the exhaust mechanism 52, adjustment of the opening of the valve V1 (i.e., adjustment of the pressure inside the processing chamber 21), supply and cutoff of each gas from the gas supply sources 41 to 44 into the processing chamber 21 by the flow rate adjustment unit 35, and adjustment of the flow rate.

[0031] 4A to 4D, the processing operation of the substrate processing apparatus 1 for performing the processes described with reference to FIGS. 6A to 6D will be described using the time chart of FIG. 6, which shows two cycles of operation. The time chart of FIG. 6 shows the timing of supply and cutoff of the processing gas into the processing vessel 21 and the timing of changes in the supply amount of the purge gas. The timing of the supply and cutoff of the processing gas corresponds to the timing of opening and closing the valve of the flow rate adjuster 35, and the timing of changes in the supply amount of the purge gas corresponds to the timing of flow rate adjustment by the mass flow controller of the flow rate adjuster 35.

[0032] 4A to 4D, the process is performed by alternately repeating a first process in which a processing gas is supplied to the wafer W and a second process in which a purge gas is supplied in a relatively high-pressure, reduced-pressure atmosphere to remove AFS. In each of the first and second processes illustrated here, the interior of the processing vessel 21 is adjusted to the same pressure P0. The times t1 to t2 and t3 to t4 shown in the chart are periods during which the first process is performed, and the times t2 to t3 and t4 to t5 are periods during which the second process is performed. Hereinafter, the time during which the first process is performed in one cycle (i.e., the respective lengths between times t1 and t2 and between times t3 and t4) may be referred to as the processing gas supply time, and the time during which the second process is performed in one cycle (i.e., the respective lengths between times t2 and t3 and between times t4 and t5) may be referred to as the purge time. As described above, the second step is performed so as to prevent the silicon oxide film 12 from being exposed, and therefore the purge time is set to be relatively short. Therefore, the processing gas supply time is, for example, longer than the purge time.

[0033] 2 is loaded into the processing chamber 21, placed on the stage 24, and heated to the above-mentioned temperature. Then, HF gas and NH ３ gas, and Ar gas and N ２ The gases are supplied, and the opening of the valve V1 is adjusted to bring the pressure inside the processing chamber 21 to P0 (FIG. 4A, time t1 in FIG. 5). The pressure P0 is, for example, 800 Pa (6 Torr) or higher, more specifically, for example, 1000 Pa (7.5 Torr) to 4000 Pa (30 Torr), which is higher than the vapor pressure of the AFS.

[0034] Next, the supply of the process gas is stopped, and the supply rate of the purge gas is increased (time t2). This purges the process gas in the process vessel 21, stopping the generation of new AFS, and also removing the surface of the AFS layer 14. The removed AFS is then discharged together with the purge gas (FIG. 4B). At time t3, a preset time after time t2, the supply of the process gas into the process vessel 21 is resumed, and the supply rate of the purge gas is reduced. At this time, the removal of the AFS layer 14 is stopped, the second step is completed, and a second run of the first step is initiated. From time t3 to t4, the same operations as from time t1 to t2 are performed, and from time t4 to t5, the same operations as from time t2 to t3 are performed.

[0035] As an example of the volumetric flow rate per unit time of each gas (hereinafter simply referred to as flow rate) in the etching process of this embodiment, the flow rate of the processing gas in the first step is set in the range of 10 sccm to 1000 sccm, for example, NH ３ The flow rate of the purge gas in the first step is set to be in the range of 0 sccm to 10,000 sccm, for example, N ２ The flow rate of the purge gas in the second step is set to about twice the flow rate of the Ar gas. ２ The flow rate of the gas is set to about twice the flow rate of the Ar gas, and the flow rate of the purge gas in the second step is preferably set to about or more than twice the flow rates of the process gas and purge gas in the first step.

[0036] (Modification) In this embodiment, the purge gas is Ar gas and N ２ The processing gas is not necessarily a HF gas, and only one of the gases may be used, or another inert gas may be used. ３ The gas is not limited to a fluorine-containing gas, and any halogen-containing gas and basic gas may be used. The halogen-containing gas is not limited to a fluorine-containing gas, and any halogen-containing gas containing other halogen molecules such as Cl (chlorine) or Br (bromine) may be used. The same applies to the basic gas.

[0037] Regarding the pressures in the first step and the second step of the present disclosure, it is not essential that they be the same as the pressure P0, but they may be different and may be set appropriately for each step. Also, in the processing example shown in Figure 6, the supply amount of purge gas is different between the first step and the second step, but it may be the same.

[0038] The surface shape of the wafer W is not limited to the shapes shown in FIGS. 1 and 2 . For example, the polysilicon film 11 may not be provided on the surface, and a silicon oxide film 12 may be uniformly provided. In other words, the present technology is not limited to etching the silicon oxide film 12 formed in the recesses. However, as described above, the silicon oxide film 12 formed in the recesses is prone to forming seams 13 due to film growth. Therefore, the present technology is particularly effective for etching the silicon oxide film 12 formed in the recesses. Furthermore, the recesses having the silicon oxide film 12 formed therein are not limited to opening upward (i.e., in the thickness direction of the wafer W) but may also open sideways (i.e., in the direction along the main surface of the wafer W).

[0039] Furthermore, the silicon-containing film to be etched is not limited to the silicon oxide film 12, but may be, for example, a SiON film (silicon oxynitride film). Even when etching a SiON film, the use of the processing gas described above allows AFS to be generated from the SiON film as a reaction product, thereby achieving the same effect as when etching the silicon oxide film 12. Furthermore, the silicon-containing film may be a SiN film (silicon nitride film). When etching this SiN film, NF is used as the processing gas. ３ Gas, NH ３ Gas, O ２ By supplying the gas, AFS is generated from the SiN film, which allows etching to be performed with high uniformity within the surface of the wafer W, similar to the case of etching the silicon oxide film 12 described above.

[0040] The above-described embodiments of the present disclosure should be considered to be illustrative in all respects and not restrictive, and various omissions, substitutions, modifications, and combinations may be made in the above-described embodiments without departing from the scope and spirit of the appended claims.

[0041] [Evaluation Tests] Evaluation tests performed on the etching process of the present disclosure are described below. <Evaluation Test 1> In Evaluation Test 1, the first process was performed on multiple test substrates each having a flat silicon oxide film on its surface, so that the AFS layer had a predetermined thickness. The combination of the pressure in the processing chamber and the flow rate of the purge gas supplied into the processing chamber was then changed for each substrate, and the time required for the AFS layer to be completely removed (referred to as the purge-out time) was measured for each substrate. The pressure in the processing chamber was set to 1000 Pa (7.5 Torr), 2000 Pa (15 Torr), or 4000 Pa (30 Torr). The tests performed with the pressure set to 1000 Pa, 2000 Pa, and 4000 Pa are designated Evaluation Tests 1-1, 1-2, and 1-3, respectively. As a comparative test, the purge-out time was examined for one of the substrates on which the AFS layer was formed as described above, with the valve V1 fully opened to set the pressure in the processing chamber to approximately 0 Torr and the flow rate of the purge gas to 0 sccm.

[0042] FIG. 7 is a graph showing the results of Evaluation Tests 1-1 to 1-3 and the Comparative Test, with the horizontal axis representing the purge gas flow rate and the vertical axis representing the purge-out time. As shown in the graph, the results of Evaluation Tests 1-1 to 1-3 reveal that the higher the pressure inside the processing vessel, the longer the purge-out time, and the lower the purge gas flow rate, the longer the purge-out time. If the purge-out time is too short, it is difficult to leave an appropriate amount of AFS on the silicon oxide film at the end of the second process, as described in the embodiment. In the Comparative Test, the purge-out time was as short as 10 seconds, making such a residue difficult. However, Evaluation Tests 1-1 to 1-3 demonstrated that it is possible to leave AFS for a relatively long time by appropriately setting the purge gas flow rate. Since the pressure inside the processing vessel was set to 7.5 Torr or higher in Evaluation Tests 1-1 to 1-3, Evaluation Test 1 demonstrated that it is preferable to set the pressure inside the processing vessel to 7.5 Torr or higher. It is believed that even at a pressure slightly lower than 7.5 Torr, AFS can be allowed to remain on the substrate for a sufficient period of time depending on the setting of the purge gas flow rate, so it is believed that the pressure inside the processing vessel during the second step should be, for example, 800 Pa (6 Torr) or higher.

[0043] <Evaluation Test 2> In Evaluation Test 2, the etching process of this embodiment was performed on multiple substrates having the surface layer structure described in FIGS. 1 and 2 . In this etching, a cycle consisting of the first and second steps was performed 55 times, with the purge time varied for each substrate. The purge time was set to 2 seconds, 2.4 seconds, 2.6 seconds, 2.7 seconds, 2.8 seconds, or 3.0 seconds. The substrates after the etching process were evaluated by acquiring SEM images of the surface shape, etching amount, and variation in the surface height of the silicon oxide film 12. The etching amount was measured at multiple positions within a single recess, the average value of the measured values ​​was obtained, and the average value was then used to obtain an average value across multiple recesses. The variation in the surface height of the silicon oxide film 12 was calculated as a 3σ value obtained by averaging the heights of multiple positions on the surface of the silicon oxide film 12 within a single recess and then averaging the average values ​​across the recesses. This value indicates the variation in the etching amount across the recesses.

[0044] Other processing conditions are a pressure in the processing chamber of 4000 Pa (30 Torr), a wafer temperature of 130° C., and a processing gas supply time of 4 seconds. ２ The gas was 14,800 sccm and the Ar gas was 6,000 sccm.

[0045] 8 is a graph showing the results of Evaluation Test 2, with the horizontal axis representing purge time (sec), the vertical axis on the left representing the etching amount (nm), and the vertical axis on the right representing the variation in surface height (nm) of the silicon oxide film 12. As shown in the figure, it was confirmed that the etching amount increased as the purge time increased. This is thought to be because the longer the purge time, the smaller the amount of AFS remaining on the silicon oxide film 12 at the end of the second step (the smaller the thickness of the AFS layer 14), and therefore the thickness of the silicon oxide film 12 that is transformed into the AFS layer 14 in the subsequent first step increases.

[0046] The variation in the surface height of the silicon oxide film 12 decreased as the purge time decreased within the range of 2.6 seconds or more, but increased when the purge time was shorter than 2.6 seconds. In other words, the variation in the etching amount between the recesses was minimized with a purge time of 2.6 seconds. Furthermore, SEM images confirmed that the surface flatness of the silicon oxide film 12 within the recesses was also highest with a purge time of 2.6 seconds. When the purge time is longer within the range of 2.6 seconds or more, the amount of AFS remaining on the silicon oxide film 12 during the first step is small (the thickness of the AFS layer 14 is small), which increases the etching rate in the area where the seam 13 is formed, as described in the comparative example. This is presumably why the variation in the surface height of the silicon oxide film 12 increases. When the purge time is shorter than 2.6 seconds, it is believed that the amount of AFS remaining on the silicon oxide film 12 during the first step (the AFS layer 14 is too thick) significantly hinders the permeation of the processing gas in some recesses, resulting in variations. As described above, Evaluation Test 2 confirmed that there is an appropriate range for the purge time. The preferable purge time can be affected by factors such as the surface shape, the volume of the processing space, the wafer temperature, and the processing gas supply conditions, but since the relatively short time of 2.6 seconds was achieved in this evaluation test, it is believed to be 30 seconds or less, and at most 1 minute or less.

[0047] W wafer 12 silicon oxide film 14 AFS layer 21 processing vessel

Claims

1. A substrate processing method comprising: a step of storing a substrate having a silicon-containing film formed on its surface in a processing vessel; a first step of supplying a processing gas containing a halogen-containing gas and a basic gas into the processing vessel to modify the silicon-containing film and generate reaction products; a second step of supplying an inert gas into the processing vessel and evacuating the processing vessel while stopping the supply of the processing gas into the processing vessel in order to remove some of the reaction products; a repeating step of alternately repeating the first step and the second step; and a pressure control step of maintaining a pressure in the processing vessel higher than 200 Pa in each of the second steps so that the processing gas is supplied to the substrate on which the reaction products remain in the first step from the second time onwards in the repeating step.

2. A substrate processing method according to claim 1, wherein the pressure control step is a step of controlling the pressure inside the processing vessel to 800 Pa or higher.

3. The substrate processing method according to claim 2, wherein the silicon-containing film is a silicon oxide film.

4. A substrate processing method according to claim 3, wherein the halogen-containing gas is hydrogen fluoride gas, and the basic gas is ammonia gas.

5. A substrate processing method according to claim 4, wherein the silicon-containing film is formed in a recess formed in the substrate, and the first step is a step of selectively altering the silicon-containing film so that the silicon-containing film is selectively removed from the sidewall of the recess and the silicon-containing film in the second step.

6. The substrate processing method according to claim 5, wherein the silicon-containing film contains voids or junctions between interfaces of the silicon-containing film before the processing gas is supplied.

7. A substrate processing apparatus comprising: a processing vessel for storing substrates having a silicon-containing film formed on their surfaces; a processing gas supply mechanism for supplying a processing gas containing a halogen-containing gas and a basic gas into the processing vessel; an inert gas supply mechanism for supplying an inert gas into the processing vessel; an exhaust mechanism for evacuating the processing vessel; and a control unit that outputs control signals to execute a first step of supplying the processing gas into the processing vessel to modify the silicon-containing film and generate reaction products; a second step of supplying the inert gas into the processing vessel and evacuating the processing vessel while stopping the supply of the processing gas into the processing vessel in order to remove some of the reaction products; a repeating step of alternately repeating the first step and the second step; and a pressure control step of maintaining a pressure in the processing vessel higher than 200 Pa in each second step so that the processing gas is supplied to the substrates having remaining reaction products in the first step from the second time onwards in the repeating step.

8. The substrate processing apparatus according to claim 7, wherein the pressure control step maintains the pressure inside the processing vessel at 800 Pa or higher in each of the second steps.

Images