Etching method and etching apparatus

Abstract

To etch a silicon oxide film at a desired etching rate.SOLUTION: An etching method includes: a first gas supply step of supplying a fluorine-containing gas during a first period into a processing vessel storing a substrate on which a silicon oxide film has been formed; a second gas supply step of supplying a basic gas into the processing vessel during a second period including a common supply period overlapping with the first period; and a first evacuation step of evacuating the processing vessel such that the pressure in the processing vessel during the common supply period becomes a first pressure higher than 50 Torr in order to etch the silicon oxide film using the fluorine-containing gas and the basic gas.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present disclosure relates to an etching method and an etching apparatus. [Background technology]

[0002] In manufacturing a semiconductor device, a silicon oxide film formed on the surface of a semiconductor wafer (hereinafter, referred to as a wafer) serving as a substrate may be etched. Patent Document 1 describes a technique for performing the above etching by supplying HF gas and NH3 gas to the silicon oxide film on the surface of the wafer to generate ammonium fluorosilicate (AFS) as a reaction product, and then heating the wafer to vaporize the AFS. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-180281 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure provides a technique capable of etching a silicon oxide film at a desirable etching rate. [Means for solving the problem]

[0005] The etching method disclosed herein includes a first gas supply step of supplying a fluorine-containing gas into a processing vessel housing a substrate having a silicon oxide film formed thereon for a first period of time; a second gas supplying step of supplying a basic gas into the processing vessel during a second period including a common supply period overlapping with the first period; a first evacuation process of evacuating the processing vessel so that a pressure in the processing vessel during the common supply period becomes a first pressure higher than 50 Torr in order to etch the silicon oxide film with the fluorine-containing gas and the basic gas; Includes. Effect of the Invention

[0006] The present disclosure is capable of etching silicon oxide films at a desirable etch rate. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a vertical cross-sectional side view of an etching apparatus according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 is an explanatory diagram showing a processing operation in the etching apparatus. [Diagram 3] FIG. 2 is an explanatory diagram showing a processing operation in the etching apparatus. [Figure 4] FIG. 2 is an explanatory diagram showing a processing operation in the etching apparatus. [Diagram 5] FIG. 2 is an explanatory diagram showing a processing operation in the etching apparatus. [Figure 6] FIG. 2 is an explanatory diagram showing a processing operation in the etching apparatus. [Figure 7] 5 is a chart showing supply and cut-off of gas to a processing vessel and a pressure change within the processing vessel. FIG. [Figure 8] 1A and 1B are longitudinal sectional side views of a wafer before and after etching. [Figure 9] FIG. 11 is a graph showing the results of an evaluation test. [Figure 10] FIG. 11 is an explanatory diagram showing a processing example in an evaluation test. [Figure 11] FIG. 11 is an explanatory diagram showing a processing example in an evaluation test. [Figure 12] FIG. 11 is an explanatory diagram showing a processing example in an evaluation test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] An embodiment of the etching method of the present disclosure will be described. Fig. 1 is a vertical cross-sectional side view of an etching apparatus 1 for carrying out this etching method. This etching apparatus 1 etches a film formed on the surface of a substrate, a wafer W, in a non-plasma environment of a vacuum atmosphere. The films to be etched are a thermal oxide film 11 and a silicon oxide film 12. The thermal oxide film 11 is a silicon oxide film obtained by heating a silicon film at a temperature of 700°C or higher in an oxygen atmosphere or a water vapor atmosphere, which is a non-plasma environment.

[0009] The silicon oxide film 12 is a silicon oxide film of a different type from the thermal oxide film 11. Specifically, the silicon oxide film 12 includes a silicon oxide film formed by CVD (Chemical Vapor Deposition) or ALD (Atomic Layer Deposition), a silicon oxide film containing an additive element such as a PSG (Phosphorous Silicate Glass) film or a BSG (Borosilicate Glass) film, and a film obtained by oxidizing silicon in a plasma environment. Film formation by CVD or ALD includes both film formation in a plasma environment and film formation in a non-plasma environment. An example of a silicon oxide film formed by CVD or ALD is a silicon oxide film formed by supplying TEOS (tetra ethoxy silane) gas to the wafer W as a film formation gas, and the silicon oxide film may be referred to as a TEOS film from here on. In addition, in order to avoid confusion with the thermal oxide film 11, the silicon oxide film 12 may be referred to as a non-thermal oxide film 12 from here on.

[0010] It is desirable to increase the etching rate (amount etched per unit time) of the thermal oxide film 11, and in some cases, it is required to make the etching rate higher than the etching rate of the non-thermal oxide film 12. The etching apparatus 1 is configured to meet this demand. In the etching process in the etching apparatus 1, HF (hydrogen fluoride) gas is used as the fluorine-containing gas, and NH3 (ammonia) gas is used as the basic gas. HF and NH3 react with each other to generate (NH4)F, and this (NH4)F undergoes a decomposition reaction. As shown in the following formulas 1 and 2, two types of reactions can occur in this decomposition reaction. In this way, HF and NH3 are generated by the decomposition of NH4F (i.e., returning to the state before the generation of NH4F), or HF2 - This HF2 - It is known that the etching ability of the thermal oxide film 11 is relatively high, while the etching ability of the non-thermal oxide film 12 is relatively low. 2HF+2NH3→2(NH4)F→2NH3+2HF...Formula 1 2HF+2NH3→2(NH4)F→NH3+HF2 - +NH4 + ...Formula 2

[0011] As shown in the evaluation test described below, HF2 - It was confirmed that the generation of HF2 is promoted. Therefore, in the etching apparatus 1, when HF gas and NH3 gas, which are etching gases, are supplied into the processing vessel 21 that contains the wafer W, the processing vessel 21 is set at such a relatively high pressure, specifically, a pressure higher than 50 Torr (6665 Pa). - is generated, so that the etching rate of the thermal oxide film 11 becomes high.

[0012] In addition, in evaluation tests, it was confirmed that the etching rate of the oxide film 11 can be further increased by shifting the timing of starting the supply of HF gas and NH3 gas to the processing vessel 21, and by supplying an inert gas into the processing vessel 21, which is in a relatively high pressure state after the supply of HF gas and NH3 gas is stopped. The etching apparatus 1 is configured to be able to control the operation of these, and by controlling the operation in this way, the etching rate of the thermal oxide film 11 is made higher than the etching rate of the non-thermal oxide film 12.

[0013] Furthermore, the etching apparatus 1 performs etching at a relatively high pressure as described above, while evacuating the processing vessel 21 at a high speed so that the pressure inside the processing vessel 21 becomes relatively low after etching. This makes it possible to quickly remove the etching gas remaining in the processing vessel 21 and reaction products generated from the etching gas.

[0014] The configuration of the etching apparatus 1 will be described in more detail. As described above, the etching apparatus 1 includes a processing vessel 21. In the drawing, reference numeral 22 denotes a transfer port for the wafer W that opens in the side wall of the processing vessel 21 and is opened and closed by a gate valve 23. A stage 24 for placing the wafer W is provided within the processing vessel 21, and 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.

[0015] A temperature adjustment unit 25 is embedded in the stage 24, and the wafer W placed on the stage 24 is heated to a set temperature of, for example, 100° C. or higher. This temperature adjustment unit 25 may be configured as a part of a circulation path through which a temperature adjustment fluid flows, for example, and the fluid may be circulated in the circulation path by a chiller, and the temperature of the wafer W may be adjusted by heat exchange with the fluid. Alternatively, the temperature adjustment unit 25 may be configured by a heater that performs resistance heating.

[0016] A gas shower head 30 is provided at an upper portion of the processing vessel 21 so as to face 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 a flow rate adjustment unit 35. Each flow rate adjustment unit 35 includes a valve and a mass flow controller, and performs supply and cut-off and flow rate adjustment of gas supplied from the gas supply sources 41 to 44 to the downstream side.

[0017] From the gas supply sources 41, 42, 43, and 44, HF gas, Ar (argon) gas, NH3 gas, and N2 (nitrogen) gas are supplied to the respective connected flow paths. Note that N2 gas and Ar gas are the above-mentioned inert gases. The above-mentioned flow rate adjustment units 35 can switch the gases supplied from these gas supply sources 41 to 44 into the processing chamber 21. The flow rate adjustment unit 35 in the gas supply path 32A and the gas supply source 41 that supplies HF gas correspond to a first gas supply unit, and the flow rate adjustment unit 35 in the gas supply path 32A and the gas supply source 43 that supplies NH3 gas correspond to a second gas supply unit.

[0018] An 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 a turbo molecular pump 52 serving as a second exhaust mechanism are sequentially disposed in the exhaust path 51 toward the downstream side, and the downstream end of the exhaust path 51 is connected to a dry vacuum pump 53 serving as a first exhaust mechanism. Although the dry vacuum pump 53 is illustrated as an example of the first exhaust mechanism, the first exhaust mechanism is not limited to the dry vacuum pump 53 and may be constituted by, for example, a rotary pump. Hereinafter, the turbo molecular pump 52 will be referred to as a TMP 52, and the dry vacuum pump 53 will be referred to as a DP 53.

[0019] In the exhaust path 51 which is the first exhaust path, the upstream end of the exhaust path 54 which is the second exhaust path is connected to the upstream side of the valve V1, and the downstream end of the exhaust path 54 is connected to the downstream side of the TMP 52. A valve V2 is interposed in the exhaust path 54. The valve V1 which is the first valve and the valve V2 which is the second valve are called APC (Auto Pressure Control) valves, and the opening degree can be changed during processing of the wafer W according to a control signal output from a control unit 20 which will be described later, so that the pressure inside the processing container 21 becomes a preset value. The exhaust paths 51, 54, the valves V1, V2, the TMP 52, and the DP 53 are collectively referred to as an exhaust unit 5.

[0020] The TMP52 is a main pump for evacuating the processing vessel 21 to a relatively high degree of vacuum. The DP53 is an auxiliary pump for evacuating the processing vessel 21 to a pressure at which the TMP52 can operate in order to achieve such a high degree of vacuum, and for evacuating the processing vessel 21 to a back pressure at which the TMP52 can operate. In other words, both the TMP52 and DP53, which are vacuum pumps, are used to achieve a relatively high degree of vacuum in the processing vessel 21. On the other hand, of the TMP52 and DP53, only the DP53 is used to achieve a relatively low degree of vacuum in the processing vessel 21, such as when supplying an etching gas.

[0021] As is well known, the TMP 52 is configured to use rotating rotor blades to knock out molecules entering through the intake port toward the exhaust port, allowing for high-speed exhaust. However, if the pressure inside the processing vessel 21 facing the intake port is relatively high, there is a risk that the rotor blades will be damaged. On the other hand, as mentioned above, when supplying the etching gas, HF2 - It is necessary to create a relatively low degree of vacuum in the processing vessel 21 in order to generate the etching gas, and it is preferable to create a relatively high degree of vacuum in the processing vessel 21 in order to remove the residue after the supply of the etching gas is stopped. Therefore, the vacuum pump to be used is switched so that the degree of vacuum in the processing vessel 21 can be changed while protecting the TMP 52.

[0022] The operation of the exhaust unit 5 will be described in more detail. To make the degree of vacuum in the processing vessel 21 relatively high, the valve V1 is opened and its aperture is adjusted, while the valve V2 is closed, and an operation (referred to as a first operation) is performed in which the processing vessel 21 is exhausted by the action of the TMP 52 and the DP 53. Therefore, in this first operation, the processing vessel 21 is exhausted without passing through the exhaust path 54 and the valve V2. To make the degree of vacuum in the processing vessel 21 relatively low, the valve V2 is opened and its aperture is adjusted, while the valve V1 is closed, and an operation (referred to as a second operation) is performed in which the processing vessel 21 is exhausted by the action of only the DP 53 of the TMP 52 and the DP 53.

[0023] As described above, the etching apparatus 1 includes the control unit 20, which is a computer, and the control unit 20 includes a program, a memory, and a CPU. The program includes commands (each step) for performing the above-mentioned processing of the wafer W and transport of the wafer W. The program is stored in a storage medium, such as a compact disk, a hard disk, a magneto-optical disk, or a DVD, and is installed in the control unit 20. The control unit 20 outputs a control signal to each part of the etching apparatus 1 according to the program, and controls the operation of each part. The operations controlled in this way include, for example, adjustment of the temperature of the stage 24 (i.e., the temperature of the wafer W), operation of the exhaust unit 5, supply and cut-off of each gas from the gas supply sources 41 to 44 to the inside of the processing vessel 21 by the flow rate adjustment unit 35, adjustment of the flow rate, and the like. The control of the operation of the exhaust unit 5 specifically includes adjustment of the operation of the TMP 52 and the DP 53, and adjustment of the opening of the valves V1 and V2, thereby adjusting the pressure inside the processing vessel 21.

[0024] Next, the processing operation in the etching apparatus 1 and the phenomena that are considered to occur during the processing of the wafer W will be described with reference to the explanatory diagrams of Figs. 2 to 6 which show the etching apparatus 1 in outline, the time chart of Fig. 7, and the schematic diagram of the vertical cross section of the wafer W in Fig. 8. In Figs. 2 to 6, the flow paths in which the exhaust flow is formed in the exhaust unit 5 are shown thicker than the flow paths in which the exhaust flow is not formed, and the open and closed states of the valves V1 and V2 in the exhaust unit 5 are shown by distinguishing between the angles of the valve bodies. The time chart shows the pressure change in the processing vessel 21 and the timing of supply and cut-off of each gas into the processing vessel 21. The supply and cut-off timing of each gas can also be said to be the timing of opening and closing the valves constituting the flow rate adjustment unit 35.

[0025] First, the wafer W is loaded into the processing vessel 21 by a transfer mechanism (not shown). As shown in the upper part of FIG. 8, a thermal oxide film 11 and a non-thermal oxide film 12 are formed on the upper side of the lower layer film 13, and these thermal oxide film 11 and non-thermal oxide film 12 form the surface of the wafer W. Then, the wafer W is placed on the stage 24, the gate valve 23 of the processing vessel 21 is closed, and an inert gas (Ar gas, N2 gas) is supplied from each of the gas supply paths 31 and 32 of the gas supply mechanism 3. The exhaust unit 5 is set to a first operation state using the TMP 52, and the pressure inside the processing vessel 21 is set to a relatively low pressure P0, for example, 10 Torr (1333 Pa).

[0026] Thereafter, the supply of HF gas from the gas supply line 31 into the processing vessel 21 is started, so that both HF gas and Ar gas are supplied from the gas supply line 31, and the aperture of the valve V1 is changed, so that the pressure in the processing vessel 21 starts to rise (time t1 in the chart). Thereafter, the valve V1 is closed, while the valve V2 is opened, so that the exhaust unit 5 switches to the second operation state, and the aperture of the valve V2 is adjusted, so that the pressure in the processing vessel 21 further rises (FIG. 2). In parallel with this pressure rise, the temperature of the wafer W is set to the set temperature described above.

[0027] The inside of the processing vessel 21 is then pressurized to a first pressure P1 higher than 50 Torr, for example, 90 Torr (1.2×104 When the pressure inside the processing vessel 21 reaches P1 Pa (time t2), the pressure increase inside the processing vessel 21 stops, and the pressure is maintained at P1. When the pressure is maintained in this manner, the supply of Ar gas and N2 gas into the processing vessel 21 from the gas supply lines 31 and 32 respectively stops, and the supply of NH3 gas into the processing vessel 21 from the gas supply line 32 starts ( FIG. 3 , time t2).

[0028] The etching gases (HF gas and NH3 gas) supplied into the processing vessel 21 react with each other as shown in the above-mentioned formula 2 to produce HF2 - The HF2 - is supplied to the wafer W. This HF2 - By this action, the thermal oxide film 11 is etched relatively largely, while the etching of the non-thermal oxide film 12 is suppressed. For example, the flow rates of the HF gas and the NH3 gas supplied to the processing vessel 21 are equal, and the partial pressures of the HF gas and the NH3 gas in the processing vessel 21 are 90 Torr / 2=45 Torr.

[0029] Thereafter, the supply of HF gas and NH3 gas into the processing vessel 21 is stopped, and the supply of the inert gas (Ar gas and N2 gas) into the processing vessel 21 is resumed (FIG. 4, time t3). The pressure inside the processing vessel 21 is maintained at a relatively high pressure P1. Therefore, exhaust from the processing vessel 21 is suppressed, and a relatively large amount of etching gas (HF gas, NH3 gas) remains in the processing vessel 21. The supply of the inert gas promotes the flow of the HF gas and NH3 gas inside the processing vessel 21, causing agitation, and promoting the mixing and reaction of the gases with each other. Therefore, the HF gas and NH3 gas continue to flow in the processing vessel 21, and the gases are stirred. - This HF2 - The gas is swept away by the inert gas toward the wafer W, and the etching of the thermal oxide film 11 proceeds further.

[0030] Thereafter, as the opening of the valve V2 increases, the pressure inside the processing vessel 21 decreases and reaches a predetermined pressure (FIG. 5, time t4), and the valve V2 is closed while the valve V1 is opened, and the operation of the exhaust unit 5 is switched from the second operation to the first operation. The exhaust inside the processing vessel 21 progresses rapidly by the action of the TMP 52 (FIG. 6, time t5), and the pressure inside the processing vessel 21 becomes a pressure P2 that is 50 Torr or less and is lower than, for example, the pressure P0 (10 Torr) at the beginning of the process. The pressure P2 corresponds to the second pressure. Then, the etching gas remaining in the processing vessel 21 and various reaction products generated by the action of the etching gas are quickly exhausted, and the etching is completed.

[0031] 8 shows the wafer W at the end of etching. As described above, due to the progress of the etching, the amount of etching of the thermal oxide film 11 is greater than the amount of etching of the non-thermal oxide film 12. After etching is completed, the opening of the valve V1 is adjusted to increase the pressure in the processing vessel 21 (time t6). When the pressure in the processing vessel 21 becomes approximately the same as the ambient pressure, the wafer W is transferred out of the processing vessel 21 by the transfer mechanism.

[0032] As described above, the etching apparatus 1 can etch the thermal oxide film 11 at a relatively high etching rate, and the etching rate of the thermal oxide film 11 can be made higher than the etching rate of the non-thermal oxide film 12. Hereinafter, for convenience of explanation, the step of adjusting the temperature of the wafer W and increasing the pressure in the processing vessel 21 at times t1 to t2 is called a pressure adjustment step, and the step of supplying both HF gas and NH3 gas into the processing vessel 21 at times t2 to t3 is called a main etching step. Then, the step of supplying only an inert gas into the processing vessel 21 without supplying an etching gas while the pressure in the processing vessel 21 is relatively high at times t3 to t4 is called a purge step. Also, the step of removing residues in the processing vessel 21 by creating a relatively high degree of vacuum in the processing vessel 21 at times t4 to t6 is called a vacuum step.

[0033] The time period t1 to t3 during which HF gas is supplied is a first period, and the supply process of HF gas from the time period t1 to t3 is a first gas supply process. The time period t2 to t3 during which NH3 gas is supplied is a second period, and is a common supply period that overlaps with the first period. The supply process of NH3 gas from the time period t1 to t3 is a second gas supply process. The exhaust process of the processing vessel 21 performed by the exhaust unit 5 from the time period t2 to t3 during which both HF gas and NH3 gas are supplied is a first exhaust process.

[0034] The exhaust process performed by the exhaust unit 5 from time t4 to t6 when the vacuum step is performed is the second exhaust process, of which the exhaust process performed by the exhaust unit 5 in the second operation from time t4 to t5 is the pre-exhaust process, and the exhaust process performed by the exhaust unit 5 in the first operation from time t5 to t6 is the post-exhaust process. The purge step corresponds to a continuous etching process for continuing etching even after the supply of HF gas and NH3 gas is stopped.

[0035] When the required etching amount of the thermal oxide film 11 is relatively large, the pressure adjustment step, the main etching step, the purge step, and the vacuum step are treated as one cycle, and this cycle may be repeated. That is, after the vacuum step is completed at time t6, the operation of the apparatus at times t1 to t6 may be performed again before the wafer W is unloaded from the processing vessel 21. The number of times the cycle is repeated may be set arbitrarily according to the desired etching amount. As described above, the pressure adjustment step includes the pressure adjustment in the processing vessel 21 as well as the temperature adjustment of the wafer W. However, since the temperature adjustment of the wafer W is completed in the first pressure adjustment step, only the pressure adjustment in the processing vessel 21 is performed in the second and subsequent pressure adjustment steps.

[0036] Incidentally, the timings of starting and stopping the supply of HF gas and NH3 gas into the processing vessel 21 may be synchronized. That is, in the process shown in the above chart, HF gas may not be supplied into the processing vessel 21 from time t1 to t2, but may be supplied into the processing vessel 21 starting from time t2, so that the supply times of HF gas and NH3 gas are the same.

[0037] However, as shown in the evaluation test, it is preferable to set the HF gas supply start time before the NH3 gas supply start time and the HF gas supply time longer than the NH3 gas supply time as in the processing example described with reference to Figures 2 to 7, because this makes it possible to increase the etching rate of the thermal oxide film 11 relative to the etching rate of the non-thermal oxide film 12. This is because HF gas is already present in the processing vessel 21 when the supply of NH3 gas begins in the processing vessel 21, and the mixability and reactivity of these gases is increased, resulting in the HF2 - This may be due to an increase in the amount of generated NH3 gas. Note that NH3 gas may be supplied instead of HF gas during the time when HF gas is being supplied in the chart of Fig. 7, and HF gas may be supplied instead of NH3 gas during the time when NH3 gas is being supplied. In other words, the supply start time of NH3 gas may be set to precede the supply start time of HF gas, so that the supply time of NH3 gas is longer than the supply time of HF gas.

[0038] Although the above processing example shows that the supply of HF gas and the supply of NH3 gas are stopped simultaneously, if there is a period during which HF gas and NH3 gas are simultaneously supplied to the processing vessel 21 at a relatively high pressure, the HF2 - Since the gas supply can be generated, the supply of these gases may be stopped at different times. That is, even after the gas supplied into the processing vessel 21 for one of the gas supply paths 31 and 32 is switched from the etching gas to the inert gas, the etching gas continues to be supplied from the other of the gas supply paths 31 and 32. Thereafter, the gas supplied into the processing vessel 21 for the other of the gas supply paths 31 and 32 may also be switched from the etching gas to the inert gas.

[0039] In addition, the pressure in the processing vessel 21 in the main etching step and the pressure in the processing vessel 21 in the purge step are the same pressure P1 in the above processing example, but the pressures may be different between these steps. However, the purge step is also HF2 - Since this is a step in which a gas is generated and processed, it is preferable to use a pressure of more than 50 Torr, similar to the main etching step.

[0040] The purge step may not be performed, and a vacuum step may be performed after the main etching step, but it is preferable to perform the vacuum step because it is possible to increase the etching rate of the thermal oxide film 11 relative to the etching rate of the non-thermal oxide film 12 as shown in the evaluation test.

[0041] After the main etching step is performed, the etching gas and reaction products remaining in the processing vessel 21 may be removed by, for example, evacuating the processing vessel 21 so that the pressure inside the processing vessel 21 is maintained at the same pressure as during the main etching step. That is, the vacuum step for lowering the pressure inside the processing vessel 21 does not have to be performed, but it is preferable to perform the vacuum step in order to quickly remove the above-mentioned residues.

[0042] In addition, after the wafer W is loaded into the processing vessel 21, a pre-processing may be performed by supplying a desired gas into the processing vessel 21 with the pressure in the processing vessel 21 set to P0. The type of pre-processing is arbitrary, but as an example, a film other than the thermal oxide film 11 and the non-thermal oxide film 12 is formed on the surface of the wafer W. In order to etch this film together with the thermal oxide film 11 and the non-thermal oxide film 12, an oxidation process may be performed as a pre-processing by supplying an oxidation gas such as oxygen or a gas containing O (oxygen) radicals into the processing vessel 21. When performing a pre-processing by supplying a gas for the oxidation process in this way, a gas supply source and a flow rate adjustment unit for the gas are provided in the etching apparatus 1 so that such a process can be performed. The pressure adjustment step described above can be performed as a step of adjusting the pressure in the processing vessel 21 after the pre-processing has been performed in this way. When pre-processing is not performed, the pressure in the processing vessel 21 between time t1 and time t2, which is described in FIG. 7 as the pressure adjustment step, does not need to be set to P0. The operation of the exhaust unit 5 may be controlled so that the pressure in the processing vessel 21 between time t1 and time t2 becomes P1, which is the same as the pressure during the main etching step.

[0043] Incidentally, although an example has been shown in which a wafer W on which both a thermal oxide film 11 and a non-thermal oxide film 12 are formed is processed, a wafer W on which only the thermal oxide film 11 is formed among these films may also be processed using the present technology. Also, a wafer W on which no thermal oxide film 11 is formed and only the non-thermal oxide film 12 is formed may also be processed using the present technology to etch the non-thermal oxide film 12. However, since a high etching rate can be obtained, it is particularly preferable to apply the present technology to etching the thermal oxide film 11.

[0044] The same reaction was also observed with various amines, which are compounds with a structure similar to NH3. - Therefore, amine gas may be used instead of NH3 gas as the basic gas. Also, by using ClF3 (chlorine trifluoride) gas or F2 (fluorine) gas instead of HF gas as the fluorine-containing gas, HF2 can be produced. -Although the etching apparatus 1 has been described as a so-called single-wafer processing apparatus in which one wafer W is accommodated in the processing vessel 21 and processed, the etching apparatus 1 may be configured to accommodate a plurality of wafers W in the processing vessel 21 and process them collectively.

[0045] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The above-described embodiments may be omitted, substituted, modified, or combined in various forms without departing from the scope and spirit of the appended claims.

[0046] [Evaluation test] Evaluation tests carried out in relation to the technology of the present disclosure will be described.

[0047] Evaluation test 1 As explained in Equations 1 and 2, (NH4)F produced from HF and NH3 decomposes to form HF or HF2 - By performing a simulation, the ratio of the number of HF molecules produced to the number of HF2 molecules produced can be calculated. - The correspondence between the ratio of the number of molecules and the pressure in the space where decomposition occurs was investigated. The simulation was performed by changing the pressure in the space from 10 Torr or more to less than 100 Torr. The temperature of the space was also changed in 10°C increments in the range of 70°C to 130°C, and the above correspondence at each temperature was investigated.

[0048] FIG. 9 is a graph showing the results of the simulation. The horizontal axis shows the pressure in the space (unit: Torr), and the vertical axis shows the amount of HF2 - The ratio of HF2 molecules to the number of HF molecules produced × 100 (unit: %) is shown. Note that the results for temperatures between 110°C and 130°C were almost the same, so only the result for 110°C is shown. As shown in the graph, regardless of the temperature setting, the ratio of HF2 molecules to the number of HF molecules increased as the pressure increased within the pressure range in which the measurements were performed. - Therefore, from this evaluation test 1, the ratio of the number of HF2 molecules is large. -It has been confirmed that in order to produce a large amount of , it is preferable to set the pressure inside the treatment vessel 21 to a relatively high pressure.

[0049] Evaluation test 2 Using the etching apparatus 1, processing was performed in a different procedure for each wafer W. Then, the etching amount of each of the oxide film 11 and the non-thermal oxide film 12 formed on each wafer W was measured, and the difference in the etching amount of the oxide film 11 relative to the etching amount of the non-thermal oxide film 12 (etching amount of the oxide film 11 - etching amount of the non-thermal oxide film 12) was calculated. The oxide film 11 and the non-thermal oxide film 12 were formed on the surface of the flat underlayer film 13 without a concave-convex pattern. Therefore, the oxide film 11 and the non-thermal oxide film 12 also have flat surfaces as shown in FIG. 8. The non-thermal oxide film 12 in this evaluation test 2 was a TEOS film.

[0050] As the processing procedure, any one of the first procedure to the fourth procedure was selected and performed. The fourth procedure was the processing procedure described in the embodiment with reference to Figs. 2 to 7, and the time from time t1 to t2, which is the pressure adjustment step, was 5 seconds, the time from time t2 to t3, which is the main etching step, was 5 seconds, the time from time t3 to t4, which is the purge step, was 60 seconds, and the time from time t4 to t6, which is the vacuum step, was 30 seconds. The temperature of the wafer W during processing was set to 100°C or higher, as in the embodiment.

[0051] 10, 11, and 12 show the first, second, and third procedures, respectively. Differences between the first to third procedures and the fourth procedure will be described. As shown in FIG. 10, in the first procedure, HF gas is not supplied in the pressure adjustment step, and the supply of HF gas starts at time t2 in the chart of FIG. 7. Therefore, the main etching step starts when both HF gas and NH3 gas start to be supplied. In the first procedure, a purge step is not performed, and a vacuum step is performed following the main etching step. Therefore, the supply of HF gas and NH3 gas into the processing vessel 21 is stopped, and the pressure inside the processing vessel 21 starts to decrease.

[0052] As shown in Fig. 11, in the second procedure, HF gas is supplied at the start of the pressure adjustment step, as in the fourth procedure, but the purge step is not performed as in the first procedure. As shown in Fig. 12, in the third procedure, HF gas is not supplied in the pressure adjustment step, as in the first procedure, and the main etching step is started by starting the supply of HF gas and NH3 gas. In the third procedure, a purge step is performed as in the fourth procedure.

[0053] The difference between the etching amount measured after carrying out the first to fourth steps and the calculated etching amount was normalized by dividing the difference by a predetermined positive value, and the normalized value is shown in the following Table 1. Note that the larger the normalized value, the larger the actual value (value before normalization).

[0054] [Table 1]

[0055] From the results of the above first to fourth procedures, it is found that the etching rate of the thermal oxide film 11 can be increased by supplying HF gas before NH3 gas into the processing vessel 21 or by performing a purge step. In addition, in the fourth procedure in which both the advance supply of HF gas and the purge step are performed, it was confirmed that the etching rate of the oxide film 11 can be made higher than the etching rate of the non-thermal oxide film 12, which is a TEOS film, as described in the embodiment.

[0056] As described above, the non-thermal oxide film 12, which is a silicon oxide film, in this film formation test 2 is a TEOS film. In the film formation process of the TEOS film, elements other than silicon and oxygen, such as carbon and hydrogen, which constitute the film formation gas, are mixed into the film. In other words, the TEOS film can be seen as a silicon oxide film mixed with impurities, and the atomic arrangement of silicon (Si) and oxygen (O) is not dense, and it is less strong than the thermal oxide film 11. Similarly, films other than the TEOS film, such as BSG, which is exemplified as the non-thermal oxide film 12, can be seen as a structure in which elements other than Si and O are mixed into silicon oxide, and it is less strong than the thermal oxide film 11. In addition, a silicon oxide film formed by oxidizing a Si film in a plasma environment is also damaged by plasma during formation, and therefore the arrangement of Si and O is not dense and it is less strong than the thermal oxide film 11. In this way, considering the structure and properties of each film, even if the non-thermal oxide film 12 is a film other than the TEOS film, which has already been exemplified, it is expected to have the same results as in this evaluation test 2 using a TEOS film.

[0057] The pressure in the process vessel 21 during the main etching step and the purge step of this evaluation test 2 is 90 Torr, the same as in the embodiment. As shown in the above-mentioned evaluation test 1, the higher the pressure, the lower the HF2 - In addition, at a relatively high temperature, the amount of HF produced does not vary significantly even if the pressure changes. Considering the results of the evaluation tests 1 and 2, the pressure in the process vessel 21 during the main etching step and the purge step is set to, for example, 70 Torr (9.33×10 3 Pa) to 100 Torr (1.33 × 10 4 It is considered preferable to set the temperature to 1 Pa.

[0058] Furthermore, by comparing the results of Evaluation Tests 1 and 2 with those of Evaluation Tests 3 and 4, it is found that performing a purge step is effective in increasing the etching rate of thermal oxide film 11. However, even in Evaluation Tests 1 and 2 in which a purge step is not performed, the pressure in processing vessel 21 is relatively high immediately after the start of the vacuum step, and an inert gas is being supplied into processing vessel 21. That is, a state similar to that during the execution of the purge step is formed. In other words, if the time during which the process of supplying an inert gas at a relatively high pressure is performed is short, a sufficient continuous etching effect cannot be obtained.

[0059] Therefore, it is preferable to set the purge step to be sufficiently long. For example, as in the third and fourth procedures of this evaluation test 2, it is preferable to set the purge step to be performed for a time longer than the time (between time t1 and t3) during which any of the etching gases is supplied into the processing vessel 21. As described above, the timing of stopping the supply of the etching gas is not limited to the same timing between HF gas and NH3 gas as in the example shown in the chart of FIG. 7, but the start of the purge step is the time when the supply of the etching gas to the processing vessel 21 is stopped and the supply of the inert gas is started from each gas supply path 31, 32. The end of the purge step is the time when the pressure in the processing vessel 21 starts to decrease toward a pressure of 50 Torr or less, as shown as time t4 in FIG. 7, and is the start of the period during which the pressure in the processing vessel 21 continues to decrease until the pressure becomes 50 Torr or less.

[0060] It is possible to etch the thermal oxide film 11 by performing the main etching step for a relatively long time without performing the purge step. However, it has been confirmed that in this case, the etching rate of the thermal oxide film 11 cannot be made sufficiently large relative to the etching rate of the non-thermal oxide film 12, which indicates the effectiveness of performing the purge step. The reason why the etching rate of the thermal oxide film 11 is not made sufficiently large is that the reaction of formula 1 proceeds more rapidly than the reaction of formula 2, and while the etching that produces AFS, as described in the Background Art, proceeds relatively, the HF2 - It is presumed that this is because etching due to the action of the above-mentioned factors did not proceed easily. In Evaluation Test 2, etching was performed on the oxide film 11 and non-thermal oxide film 12 formed on the underlayer film 13 on which no uneven pattern was formed, but it is considered that the reactivity of each film does not change depending on the presence or absence of an uneven pattern. In other words, etching may be performed on the oxide film 11 and non-thermal oxide film 12 formed on the uneven pattern, and even in this case, it is considered that etching selectivity with the same tendency as that shown in Evaluation Test 2 can be obtained for the oxide film 11 and non-thermal oxide film 12. [Explanation of symbols]

[0061] W wafer 11 Thermal oxide film 21 Processing vessel

Claims

1. a first gas supply step of supplying a fluorine-containing gas into a processing vessel storing a substrate on which a silicon oxide film is formed, during a first period of time; a second gas supplying step of supplying a basic gas into the processing vessel during a second period including a common supply period overlapping with the first period; a first evacuation step of evacuating the processing vessel so that a pressure in the processing vessel during the common supply period becomes a first pressure higher than 50 Torr in order to etch the silicon oxide film with the fluorine-containing gas and the basic gas; An etching method comprising:

2. 2. The etching method according to claim 1, wherein the fluorine-containing gas is hydrogen fluoride gas, and the basic gas is ammonia gas.

3. 3. The etching method according to claim 2, further comprising a second evacuation step of evacuating the inside of the processing vessel to a second pressure of 50 Torr or less, which is lower than the first pressure, after the first evacuation step.

4. The processing vessel is connected to an upstream end of a first exhaust passage having a downstream end connected to a first exhaust mechanism and a first valve and a second exhaust mechanism disposed in this order toward a downstream side; an upstream end and a downstream end of a second exhaust path, in which a second valve is interposed, are connected to an upstream side of the first valve in the first exhaust path and a downstream side of the second exhaust mechanism in the first exhaust path, respectively; The second exhaust step includes: a pre-exhaust step in which the first valve is closed and the inside of the processing vessel is exhausted by the first exhaust mechanism; a post-exhaust process in which the second valve is subsequently closed and the inside of the processing chamber is exhausted by the first exhaust mechanism and the second exhaust mechanism; The etching method of claim 3, comprising:

5. After the first exhaust step, and before continuing to reduce the pressure in the processing vessel to the second pressure, 4. The etching method according to claim 3, further comprising a continuous etching step of supplying an inert gas into the processing vessel to continue the etching while the supply of the fluorine-containing gas and the basic gas into the processing vessel is stopped.

6. 6. The etching method according to claim 5, wherein a period during which the continuous etching step is performed is longer than a period during which either the fluorine-containing gas or the basic gas is supplied into the processing vessel.

7. 4. The etching method according to claim 3, wherein one of the first period and the second period precedes the other of the first period and the second period and is longer than the other of the first period and the second period.

8. 8. The etching method according to claim 7, wherein one of the first period and the second period is the first period.

9. 2. The etching method according to claim 1, wherein the first pressure is between 70 Torr and 100 Torr.

10. 2. The etching method according to claim 1, further comprising the step of: setting the temperature of the substrate to 100[deg.] C. or higher during the common supply period.

11. 11. The etching method according to claim 1, wherein the silicon oxide film includes a thermal oxide film.

12. 12. The etching method according to claim 11, wherein the silicon oxide film includes the thermal oxide film and a silicon oxide film of a different type from the thermal oxide film.

13. a processing vessel for storing a substrate on which a silicon oxide film is formed; a first gas supply unit that supplies a fluorine-containing gas into the processing vessel during a first period; a second gas supply unit that supplies a basic gas into the processing vessel during a second period including a common supply period that overlaps with the first period; an exhaust unit that exhausts the inside of the processing vessel so that a pressure in the processing vessel during the common supply period becomes a first pressure higher than 50 Torr in order to etch the silicon oxide film with the fluorine-containing gas and the basic gas; An etching apparatus comprising:

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