Etching method and etching apparatus

Abstract

To provide an etching method and an etching apparatus capable of enhancing a selective ratio of a silicon nitride film over a silicon oxide film or a polysilicon film.SOLUTION: An etching method is a method for selectively etching a first silicon film S1 of a substrate S including the first silicon film S1 and a second silicon film S2. The etching method includes: supplying a hydrogen fluoride gas to the substrate S while heating the substrate S so as to maintain a temperature of the substrate S at a predetermined temperature included in a range of a first temperature or higher and a second temperature or lower; and supplying an activated radical generated from a gas for radical generation to an etching target while heating the substrate S so as to maintain the temperature of the substrate S after the supply of the hydrogen fluoride gas at the predetermined temperature.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Among wafers in which a silicon nitride film and a silicon oxide film are adjacent to each other, an example of a method for selectively etching a silicon nitride film includes a step of supplying hydrogen fluoride gas to a processing space in which the wafer is accommodated, and a step of supplying radicals of an inert gas to the processing space. In the step of supplying fluorine gas and the step of supplying radicals of an inert gas, the temperature of the wafer is maintained at a low temperature. In the etching method, first, hydrogen fluoride gas is supplied to the wafer to adsorb hydrogen fluoride on the surface of the silicon nitride film. Subsequently, radicals of an inert gas are supplied to the wafer, whereby energy equal to or higher than the activation energy of the etching reaction between hydrogen fluoride and silicon nitride is applied to the wafer. As a result, etching of the silicon nitride film proceeds (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the etching method described above, the wafer temperature is maintained at a low temperature throughout the etching process of the silicon nitride film. As a result, ammonia generated by the etching reaction between hydrogen fluoride and silicon nitride does not easily detach from the wafer surface. Consequently, hydrogen fluoride and ammonia are supplied to the silicon oxide film present on the wafer along with the silicon nitride film, leading to the etching of the silicon oxide film. This problem is common not only when the wafer contains both a silicon nitride film and a silicon oxide film, but also when it contains both a silicon nitride film and a polysilicon film. [Means for solving the problem]

[0005] An etching method for solving the above problems is a method for selectively etching a silicon nitride film among an etching target including a silicon nitride film and a silicon oxide film or a polysilicon film. The etching method includes supplying hydrogen fluoride gas to the etching target while heating the etching target to maintain its temperature at a predetermined temperature between a first temperature and a second temperature, and supplying active radicals generated from a radical generation gas to the etching target while heating the etching target to maintain its temperature at the predetermined temperature after the supply of hydrogen fluoride gas.

[0006] An etching apparatus for solving the above problems comprises a vacuum chamber defining a processing space for containing an etching target including a silicon nitride film and a silicon oxide film or a polysilicon film; a heating unit for heating the etching target; a hydrogen fluoride gas supply unit for supplying hydrogen fluoride gas into the processing space; a radical supply unit for supplying active radicals generated from a gas containing oxygen atoms into the processing space; and a control unit for controlling the driving of the heating unit, the hydrogen fluoride gas supply unit, and the radical supply unit. The control unit heats the etching target to maintain it at a predetermined temperature between a first temperature and a second temperature, supplies hydrogen fluoride gas to the hydrogen fluoride gas supply unit, and then supplies the active radicals to the radical supply unit.

[0007] According to the etching method and etching apparatus described above, hydrogen fluoride gas and active radicals are supplied to the etching target heated to a predetermined temperature, which reduces variations in the depth direction of hydrogen fluoride adsorption on the etching target. Furthermore, since hydrogen fluoride and active radicals react on the etching target heated to a predetermined temperature, ammonia, a byproduct of the etching of the silicon nitride film, is easily detached from the etching target. This suppresses etching of the silicon oxide film or polysilicon film by etchant generated from ammonia and hydrogen fluoride. As a result, it is possible to increase the selectivity ratio of the silicon nitride film to the silicon oxide film or polysilicon film.

[0008] In the etching method described above, the first temperature may be 80°C, and the second temperature may be 400°C. According to the etching method described above, since the first temperature is 80°C, the effect of suppressing variations in the depth direction of hydrogen fluoride adsorption on the etching target is enhanced. Furthermore, since the second temperature is 400°C, the problem of hydrogen fluoride being difficult to adsorb onto the etching target due to an excessively high temperature is suppressed.

[0009] In the etching method described above, supplying the hydrogen fluoride gas to the etching target may include ensuring that the pressure in the processing space in which the etching target is housed and the hydrogen fluoride gas is supplied is 500 Pa or higher.

[0010] According to the etching method described above, since the pressure in the processing space is 500 Pa or higher, hydrogen fluoride is more easily adsorbed onto the material to be etched, and as a result, the silicon nitride film is more easily etched.

[0011] In the etching method described above, the radical generation gas may be a gas containing oxygen atoms. According to the etching method described above, it is possible to obtain active radicals that are difficult to inactivate and that function as an oxidation source.

[0012] In the etching method described above, the gas containing oxygen atoms may be at least one selected from the group consisting of oxygen gas, a mixed gas of oxygen gas and hydrogen gas, and nitrogen oxide gas.

[0013] In the etching method described above, the step of supplying the radical-generating gas to the etching target may further include supplying the radical-generating gas to the etching target between supplying the hydrogen fluoride gas to the etching target and supplying the active radicals to the etching target.

[0014] According to the etching method described above, at least a portion of the unwanted hydrogen fluoride located on the etching target can be removed from the etching target by the flow of fluid generated by the radical generation gas.

[0015] In the etching method described above, one cycle includes supplying the hydrogen fluoride gas to the etching target and supplying the active radicals to the etching target, and the etching method includes repeating a plurality of such cycles, and each cycle may include supplying an inert gas to the etching target after supplying the active radicals to the etching target.

[0016] According to the etching method described above, the active radicals supplied to the etching target in the nth cycle are less likely to be present near the etching target at the start of the (n+1)th cycle. Therefore, when hydrogen fluoride gas is supplied in the (n+1)th cycle, etching is suppressed in areas of the etching target other than the silicon nitride film.

[0017] In the etching method described above, the silicon nitride film is a first silicon film, the silicon oxide film or the polysilicon film is a second silicon film, the etching target includes a plurality of the first silicon film and the second silicon film, the first silicon film and the second silicon film are alternately stacked in the etching target, the etching target includes holes extending along the thickness direction, and the holes may penetrate two or more layers of the first silicon film and two or more layers of the second silicon film.

[0018] According to the etching method described above, since the material to be etched is heated, hydrogen fluoride is easily supplied to the inside of the pores, which in turn makes it easier to etch the silicon nitride film that defines the pores. [Brief explanation of the drawing]

[0019] [Figure 1] Figure 1 is a diagram showing the configuration of an etching apparatus. [Figure 2] Figure 2 is a diagram showing the configuration of the etching chamber included in the etching apparatus shown in Figure 1. [Figure 3]FIG. 3 is a timing chart for explaining the driving of each supply unit in the etching apparatus. [Figure 4] FIG. 4 is a process diagram for explaining one step included in the etching method. [Figure 5] FIG. 5 is a process diagram for explaining one step included in the etching method. [Figure 6] FIG. 6 is a process diagram for explaining one step included in the etching method. [Figure 7] FIG. 7 is a process diagram for explaining one step included in the etching method. [Figure 8] FIG. 8 is a graph showing the selectivity of the silicon nitride film with respect to the silicon oxide film in the test example.

BEST MODE FOR CARRYING OUT THE INVENTION

[0020] Referring to FIGS. 1 to 8, one embodiment of the etching method and the etching apparatus will be described.

[0021] [ETCHING APPARATUS] Referring to FIG. 1, the etching apparatus will be described. As shown in FIG. 1, the etching apparatus 10 includes an etching chamber 11, a load lock chamber 12, and a gate valve 13. The etching apparatus 10 includes an oxygen-containing gas supply unit 21, a hydrogen fluoride (HF) gas supply unit 22, a plasma supply unit 23, and an inert gas supply unit 24. The etching apparatus 10 includes a control unit 10C.

[0022] The etching chamber 11 is an example of a vacuum chamber. The etching chamber 11 defines a processing space 11S (see Figure 2) that accommodates a substrate S (see Figure 2), which is an example of an object to be etched. The substrate S contains a silicon nitride film and a silicon oxide film or a polysilicon film. The etching chamber 11 etches the silicon nitride film in the processing space 11S. The load lock chamber 12 loads the substrate S into the etching chamber 11 from outside the etching apparatus 10 before etching. The load lock chamber 12 loads the substrate S out of the etching chamber 11 to outside the etching apparatus 10 after etching.

[0023] The gate valve 13 is positioned between the etching chamber 11 and the load lock chamber 12. When the gate valve 13 opens, the etching chamber 11 communicates with the load lock chamber 12. When the gate valve 13 closes, the etching chamber 11 is isolated from the load lock chamber 12.

[0024] The load lock chamber 12 is connected to the cooling gas supply unit 12A. The cooling gas supply unit 12A supplies cooling gas to the load lock chamber 12. The cooling gas is an inert gas used to cool the substrate S after etching.

[0025] The etching chamber 11 includes a heating section 11A and an exhaust section 11B. The heating section 11A heats the etching chamber 11, thereby heating the substrate S in the processing space 11S. The exhaust section 11B reduces the pressure of the etching chamber 11 to a predetermined pressure.

[0026] The etching chamber 11 is connected to an HF gas supply unit 22 and a plasma supply unit 23. The HF gas supply unit 22 supplies HF gas to the processing space 11S. The HF gas supply unit 22 is configured to supply HF gas to the processing space 11S at a predetermined flow rate. The HF gas supply unit 22 is, for example, a mass flow controller.

[0027] The plasma supply unit 23 supplies plasma to the processing space 11S, thereby supplying active radicals contained in the plasma into the processing space 11S. The oxygen-containing gas supply unit 21 and the plasma supply unit 23 constitute an example of a radical supply unit.

[0028] The plasma supply unit 23 comprises a discharge tube 23A, a waveguide 23B, and a microwave irradiation unit 23C. The microwave irradiation unit 23C irradiates the discharge tube 23A with microwaves through the waveguide 23B. The discharge tube 23A is connected to the oxygen-containing gas supply unit 21. The inner surface of the discharge tube 23A is made of an inorganic oxide. The inorganic oxide constituting the inner surface of the discharge tube 23A may be silicon oxide or aluminum oxide. The discharge tube 23A may be, for example, a quartz tube.

[0029] The oxygen-containing gas supply unit 21 supplies gas containing oxygen atoms to the discharge tube 23A. The oxygen-containing gas supply unit 21 is configured to supply gas containing oxygen atoms to the discharge tube 23A at a predetermined flow rate. The oxygen-containing gas supply unit 21 is, for example, a mass flow controller.

[0030] Gases containing oxygen atoms are examples of gases used for radical generation. Gases containing oxygen atoms include oxygen gas, a mixture of oxygen gas and hydrogen gas, and nitrogen oxides (N x O y The nitrogen oxide gas may be at least one selected from the group consisting of the following gases. For example, the nitrogen oxide gas may be nitric oxide (NO) gas, nitrogen dioxide (NO2) gas, nitrous oxide (N2O) gas, dinitrogen trioxide (N2O3) gas, or dinitrogen pentoxide (N2O5) gas.

[0031] The plasma supply unit 23 generates plasma inside the discharge tube 23A by irradiating an oxygen-containing gas with microwaves. The plasma contains oxygen-containing radicals.

[0032] The inert gas supply unit 24 supplies inert gas to the processing space 11S. The inert gas supply unit 24 is configured to supply inert gas to the processing space 11S at a predetermined flow rate. The inert gas supply unit 24 is, for example, a mass flow controller. The inert gas may be, for example, nitrogen (N2) gas or argon (Ar) gas. The inert gas supply unit 24 may supply the inert gas into the processing space 11S using the same piping as the HF gas supply unit 22, or it may supply the inert gas into the processing space 11S using separate piping.

[0033] The control unit 10C includes a memory unit 10CM. The memory unit 10CM stores process conditions for etching the silicon nitride film. The process conditions include the pressure in the etching chamber 11, the temperature of the substrate S, the flow rates of various gases, and the output of the microwave irradiation unit 23C. The control unit 10C controls the operation of the heating unit 11A, the exhaust unit 11B, the oxygen-containing gas supply unit 21, the HF gas supply unit 22, the plasma supply unit 23, and the inert gas supply unit 24 so that the etching conditions match the process conditions.

[0034] The control unit 10C instructs the heating unit 11A to heat the substrate S to a predetermined temperature between the first and second temperatures, while simultaneously supplying HF gas to the HF gas supply unit 22, and then supplying active radicals to the radical supply unit.

[0035] [Etching Chamber] As shown in Figure 2, the etching chamber 11 houses a support section 10A. The support section 10A is capable of supporting multiple substrates S. The multiple substrates S supported by the support section 10A are stacked with gaps between adjacent substrates S. The substrates S comprise a silicon nitride film and a silicon oxide film or a polysilicon film. An example of a substrate S is a disc shape.

[0036] The etching chamber 11 is equipped with a shower head 11D. The shower head 11D is connected to a discharge tube 23A. There may be one discharge tube 23A connected to the shower head 11D, or two or more. Figure 2 shows an example in which two discharge tubes 23A are connected to the shower head 11D. The shower head 11D is equipped with multiple supply ports. The supply ports of the shower head 11D are aligned along the direction in which the substrates S are stacked. The supply ports of the shower head 11D supply plasma supplied from the discharge tubes 23A toward the substrates S.

[0037] The etching chamber 11 is equipped with a rotating part 11E. The rotating part 11E rotates the support part 10A in the circumferential direction of the substrate S. The rotating part 11E disperses the plasma supplied from the shower head 11D toward the substrate S and the HF gas supplied from the HF gas supply unit 22 toward the substrate S in the circumferential direction of the substrate S.

[0038] The etching chamber 11 is equipped with a temperature measuring unit 11F. The temperature measuring unit 11F measures the temperature inside the etching chamber 11 as the temperature of the substrate S. The temperature measuring unit 11F is connected to the control unit 10C. The temperature measurement result from the temperature measuring unit 11F is input to the control unit 10C. The control unit 10C controls the driving of the heating unit 11A based on the measurement result from the temperature measuring unit 11F.

[0039] Figure 3 shows an example of how the control unit 10C drives the heating unit 11A, the oxygen-containing gas supply unit 21, the HF gas supply unit 22, the microwave irradiation unit 23C, and the inert gas supply unit 24. In Figure 3, the state where heating by the heating unit 11A is stopped is indicated as "OFF," and the state where heating by the heating unit 11A is being performed is indicated as "ON." Similarly, the state where microwave irradiation by the microwave irradiation unit 23C is stopped is indicated as "OFF," and the state where microwave irradiation by the microwave irradiation unit 23C is being performed is indicated as "ON."

[0040] Furthermore, the state in which the gas supply from each gas supply unit 21, 22, and 24 is stopped is indicated as "OFF," and the state in which gas is being supplied from each gas supply unit 21, 22, and 24 is indicated as "ON."

[0041] As shown in Figure 3, when etching the substrate S in the etching chamber 11, first, at timing t1, the control unit 10C starts heating the heating unit 11A. As a result, the temperature T of the substrate S begins to rise, and at timing t2, the temperature T of the substrate S reaches a predetermined temperature that falls within the range of a first temperature or higher and a second temperature or lower.

[0042] Subsequently, at timing t3, the control unit 10C starts supplying HF gas to the HF gas supply unit 22. Then, at timing t4, the control unit 10C stops supplying HF gas to the HF gas supply unit 22 and starts supplying oxygen-containing gas to the oxygen-containing gas supply unit 21. Finally, at timing t5, the control unit 10C starts irradiating the microwave irradiation unit 23C with microwaves.

[0043] Next, at timing t6, the control unit 10C stops supplying oxygen-containing gas to the oxygen-containing gas supply unit 21, stops microwave irradiation to the microwave irradiation unit 23C, and starts supplying inert gas to the inert gas supply unit 24. Then, at timing t7, the control unit stops supplying inert gas to the inert gas supply unit 24.

[0044] Thus, among the processes that the control unit 10C has the etching chamber 11 perform, the process of heating the substrate S is started at timing t1, and the heating of the substrate S continues until the etching of the substrate S is completed. Furthermore, among the processes that the control unit 10C has the etching chamber 11 perform, the process from timing t3 to timing t4 is the process of supplying HF gas, and the process from timing t4 to timing t5 is the process of supplying oxygen-containing gas. Furthermore, among the processes that the control unit 10C has the etching chamber 11 perform, the process from timing t5 to timing t6 is the process of supplying active radicals, and the process from timing t6 to timing t7 is the process of supplying inert gas.

[0045] In other words, the processing from timing t3 to timing t7 constitutes one cycle. The control unit 10C causes the etching chamber 11 to execute multiple cycles until the amount of silicon nitride film etched on the substrate S reaches a predetermined amount. The number of cycles that the control unit 10C causes the etching chamber 11 to execute may be set in advance.

[0046] [Etching method] The etching method will be explained with reference to Figures 4 to 7. The etching method of this disclosure is a method for selectively etching a silicon nitride film among an etching target including a silicon nitride film and a silicon oxide film or a polysilicon film. The etching method includes supplying HF gas and, after supplying HF gas, supplying active radicals. Supplying HF gas involves supplying hydrogen fluoride gas to the etching target while heating the etching target to maintain its temperature at a predetermined temperature between a first temperature and a second temperature. Supplying active radicals involves supplying active radicals generated from a radical generation gas to the etching target while heating the etching target to maintain its temperature at a predetermined temperature after the supply of HF gas.

[0047] According to the etching method of this disclosure, since HF gas and active radicals are supplied to the etching target heated to a predetermined temperature, variations in the depth direction of HF adsorption in the etching target are less likely to occur. Furthermore, since HF and active radicals react in the etching target heated to the predetermined temperature, ammonia (NH3), a byproduct of the etching of silicon nitride films, is easily desorbed from the etching target. As a result, etching of silicon oxide films or polysilicon films by etchants generated from HF and NH3 is suppressed. Consequently, it is possible to increase the selectivity ratio of the silicon nitride film to the silicon oxide film or polysilicon film. The etching method will be described in more detail below with reference to Figures 4 to 7.

[0048] As shown in Figure 4, an example of a substrate S may have a multilayer film. The first silicon film S1 is a silicon nitride film. The second silicon film S2 is a silicon oxide film or a polysilicon film. The substrate S, which is an example of an etching target, contains multiple first silicon films S1 and multiple second silicon films S2. In the substrate S, the first silicon films S1 and the second silicon films S2 are alternately stacked. The substrate S is provided with a support substrate S3. The multilayer film containing the first silicon film S1 and the second silicon film S2 is formed on the support substrate S3.

[0049] The substrate S contains pores SA extending along the thickness direction. The pores SA penetrate two or more first silicon films S1 and two or more second silicon films S2. Although only one pore SA is shown in Figures 4 to 7 for illustrative purposes, the substrate S has multiple pores SA. The substrate S may be, for example, a substrate for 3D NAND.

[0050] In the etching method, first, HF gas is supplied to a substrate S that has been heated to a first temperature. As a result, the HF gas supplied to the substrate S is also supplied to the pores SA. In the etching method of this disclosure, since the substrate S is heated when HF31 is supplied, HF31 is easily supplied to the inside of the pores SA. As a result, the first silicon film S1, which is a silicon nitride film that defines the pores SA, is also easily etched.

[0051] HF31 has high adsorption properties to the substrate S. Therefore, the amount of HF31 adsorbed near the opening of the pores SA tends to be greater than the amount of HF31 adsorbed at the bottom of the pores SA. In this regard, when the substrate S is heated to a temperature above the first temperature, the HF31 supplied to the substrate S is less likely to be consumed near the opening of the pores SA, and as a result, HF31 is more easily introduced to the bottom of the pores SA.

[0052] The first temperature may be 80°C, and the second temperature may be 400°C. Since the first temperature is 80°C, the effect of suppressing variations in the depth direction of HF31 adsorption on the substrate S is enhanced. That is, energy is supplied to the HF31 adsorbed on the surface of the substrate S, thus preventing an excess of HF31 adsorbed on the substrate S near the opening of the pore SA. Furthermore, since the second temperature is 400°C, excessively high temperatures of the substrate S are suppressed, thereby preventing HF31 from adsorbing poorly on the substrate S. In addition, from the viewpoint of further suppressing variations in HF31 adsorption on the substrate S, the first temperature may be 100°C, 120°C, or 140°C.

[0053] In the step of supplying HF gas to the substrate S, the pressure in the processing space 11S in which the substrate S is housed and to which the HF gas is supplied may be 500 Pa or higher. When the pressure in the processing space 11S is 500 Pa or higher, HF31 is more easily adsorbed onto the substrate S, and as a result, the first silicon film S1 is more easily etched.

[0054] As shown in Figure 5, after HF gas is supplied to the substrate S, the HF gas is switched to a radical generation gas. As mentioned above, the radical generation gas may be a gas containing oxygen atoms. This makes it possible to obtain active radicals that are difficult to deactivate and that function as an oxidation source. As mentioned above, gases containing oxygen atoms include O2 gas, a mixture of O2 gas and H2 gas, and N x O y It may be at least one selected from the group consisting of gases.

[0055] The gas containing oxygen atoms may be, for example, O2 gas. When O2 gas is supplied to the substrate S, the affinity of O232 to the second silicon film S2 is higher than the affinity of HF31, so the HF31 adsorbed on the second silicon film S2 that defines the pore SA is replaced by O232. However, since O232 has low adsorption capacity, it is difficult for O232 to remain on the second silicon film S2.

[0056] Furthermore, if a radical-generating gas is supplied to the substrate S between supplying HF gas to the substrate S and supplying active radicals to the substrate S, it is possible to remove at least a portion of the unwanted HF31 located on the substrate S from the substrate S by the fluid flow generated by the radical-generating gas.

[0057] As shown in Figure 6, active radicals 33 generated from a radical generation gas are supplied to the substrate S. This generates etchant 34 that etches the first silicon film S1 from HF31 adsorbed on the first silicon film S1 defining the pores SA and the active radicals 33. In this way, the first silicon film S1 is etched by the surface reaction between HF31 and active radicals 33 on the substrate S. The etching of the first silicon film S1 proceeds in a direction perpendicular to the depth direction of the pores SA.

[0058] When the gas used for radical generation is O2 gas, the active radicals 33 are particularly difficult to inactivate, making it easier for them to be supplied to the interior of the pores SA. This makes it possible to proceed with etching of the first silicon film S1 even inside the pores SA. Furthermore, when the second silicon film S2 is a silicon oxide film and the active radicals 33 are generated from a gas containing oxygen atoms, the surface of the second silicon film S2 can be repaired by the active radicals 33. This further increases the selectivity ratio of the first silicon film S1 to the second silicon film S2.

[0059] As shown in Figure 7, after supplying the active radical 33 to the substrate S, the active radical 33 is switched to an inert gas. The inert gas can be, for example, N2 gas, as described above. As described above, in the etching method, one cycle includes supplying HF gas to the substrate S and supplying active radicals 33 to the substrate S. The etching method may also include repeating multiple cycles. Each cycle includes supplying an inert gas to the substrate S after supplying active radicals 33 to the substrate S.

[0060] As a result, the active radicals supplied to the etching target in the nth cycle are less likely to be present near the substrate S at the start of the (n+1)th cycle. Therefore, when HF gas is supplied in the (n+1)th cycle, etching is suppressed in areas of the substrate S other than the first silicon film S1.

[0061] When nitrogen gas is supplied to the substrate S, nitrogen 35 is supplied into the pores SA, thereby replacing the HF 31, active radicals 33, and etchant 34 remaining in the pores SA with nitrogen 35.

[0062] Furthermore, if etching of the substrate S is repeated multiple times, the temperature of the substrate S is maintained at a predetermined value between the first temperature and the second temperature from the first cycle until the end of the final cycle.

[0063] [Example Test] Refer to Figure 8 to explain the test example. [Test Example 1] A first silicon substrate with a silicon nitride film formed on it and a second silicon substrate with a silicon oxide film formed on it were prepared. Then, the HF gas supply process, oxygen gas supply process, oxygen radical supply process, and nitrogen gas supply process were carried out under the following conditions. The first and second silicon substrates were etched by repeating the cycle including the four processes 400 times. During this process, the temperature of each substrate was set to 120°C.

[0064] [HF gas supply process] • HF gas flow rate: 5000 sccm • Pressure in the processing space: 3500 Pa ·Supply time 30 seconds

[0065] [Oxygen gas supply process] • Oxygen gas flow rate: 5500 sccm • Pressure in the processing space: 500 Pa ·Supply time 6 seconds

[0066] [Activated radical supply process] • Oxygen gas flow rate: 5500 sccm • Pressure in the processing space: 500 Pa ·Supply time 1 second • Microwave irradiation intensity: 2800W

[0067] [Inert gas supply process] • Nitrogen gas flow rate: 60,000 sccm • Pressure in the processing space: 60 Pa ·Supply time 6 seconds

[0068] [Test Example 2] In Test Example 1, each substrate was etched using the same method as in Test Example 1, except that the temperature of each substrate was set to 140°C.

[0069] [Test Example 3] In Test Example 1, each substrate was etched using the same method as in Test Example 1, except that the temperature of each substrate was set to 150°C.

[0070] [Test Example 4] In Test Example 1, each substrate was etched using the same method as in Test Example 1, except that the temperature of each substrate was set to 160°C.

[0071] [Test Example 5] In Test Example 1, each substrate was etched using the same method as in Test Example 1, except that the temperature of each substrate was set to 170°C.

[0072] [Evaluation Method] In each test example, the thickness of the silicon nitride film on the first substrate before etching and the thickness of the silicon oxide film on the second substrate were measured using an ellipsometer (RE-3500, manufactured by SCREEN Holdings Co., Ltd.). Furthermore, the thickness of the silicon nitride film on the first substrate after etching and the thickness of the silicon oxide film on the second substrate were measured using the same ellipsometer.

[0073] The amount of etching in the silicon nitride film was calculated by subtracting the thickness of the silicon nitride film after etching from the thickness of the silicon nitride film before etching. Similarly, the amount of etching in the silicon oxide film was calculated by subtracting the thickness of the silicon oxide film after etching from the thickness of the silicon oxide film before etching.

[0074] For each test example, the selectivity ratio of the silicon nitride film to the silicon oxide film was calculated by dividing the etching amount of the silicon nitride film by the etching amount of the silicon oxide film.

[0075] [Evaluation Results] As shown in Figure 8, the selectivity ratio for Test Example 1 was 0, for Test Example 2 it was 18, for Test Example 3 it was 25, for Test Example 4 it was 42, and for Test Example 5 it was 63. Thus, it was found that the selectivity ratio of the silicon nitride film to the silicon oxide film can be significantly increased by raising the substrate temperature to 140°C or higher.

[0076] As described above, according to one embodiment of the etching method and etching apparatus, the following effects can be obtained. (1) Since HF gas and active radicals are supplied to the substrate S heated to a predetermined temperature, variations in the adsorption of HF31 on the substrate S are less likely to occur. Also, since HF31 and active radicals 33 react on the substrate S heated to a predetermined temperature, NH3, a byproduct of etching the first silicon film S1, is more easily detached from the substrate S. As a result, etching of the second silicon film S2 by the etchant generated from HF31 and NH3 is suppressed. Consequently, it is possible to increase the selectivity ratio of the first silicon film S1 to the second silicon film S2.

[0077] (2) When the first temperature is 80°C, the reliability of suppressing variations in HF adsorption on the substrate S is increased. Also, when the second temperature is 400°C, the temperature of the substrate S is prevented from becoming excessively high, thereby preventing HF31 from adsorbing poorly on the substrate S.

[0078] (3) When the pressure in the processing space 11S is 500 Pa or higher, HF31 is more likely to be adsorbed onto the substrate S, and as a result the first silicon film S1 is more likely to be etched. (4) When the gas used to generate radicals contains oxygen, it is possible to obtain active radicals 33 that are difficult to inactivate and that function as an oxidation source.

[0079] (5) If the etching method includes a radical generation gas supply step, at least a portion of the unwanted HF located on the substrate S can be removed from the substrate S by the fluid flow generated by the radical generation gas.

[0080] (6) When the etching method includes an inert gas supply step, the active radicals 33 supplied to the substrate S in the nth cycle are less likely to be present near the substrate S at the start of the (n+1)th cycle. Therefore, when HF gas is supplied in the (n+1)th cycle, etching is suppressed in areas of the substrate S other than the first silicon film S1.

[0081] (7) Even when the substrate S has holes SA, the substrate S is heated, so HF is easily supplied to the inside of the holes SA, and as a result the first silicon film S1 defining the holes SA is also easily etched.

[0082] The above-described embodiment can be implemented with the following modifications. [Etching method] A single cycle of the etching method does not necessarily have to include at least one of the radical generation gas supply step and the inert gas supply step. That is, a single cycle only needs to include at least the HF gas supply step and the active radical supply step. Even in this case, it is possible to obtain the same effects as described in (1) above.

[0083] [Gas for radical generation] • The gas used for radical generation does not need to contain oxygen atoms. The gas used for radical generation may be, for example, an inert gas. The inert gas may be, for example, Ar gas.

[0084] [substrate] The substrate S may include a first silicon film S1 and a second silicon film S2 on the same plane. Even in this case, the effects similar to those described in (1) above can be obtained. [Explanation of Symbols]

[0085] 10…Etching equipment 10C…Control Unit 11…Etching Chamber 11S… Processing space 11A…Heating part 21…Oxygen-containing gas supply unit 22…Hydrogen Fluoride Gas Supply Department 23…Plasma supply unit 24...Inert gas supply unit 31…Hydrogen fluoride 32…Oxygen 33…Reactive radicals 34... Etchanto 35… Nitrogen S... Circuit board S1…First silicon membrane S2...Second silicon membrane

Claims

1. A method for selectively etching a silicon nitride film among an etching target including a silicon nitride film and a silicon oxide film or a polysilicon film, The process involves heating the etching target to maintain its temperature within a predetermined range of a first temperature and a second temperature, while simultaneously supplying hydrogen fluoride gas to the etching target. This includes supplying active radicals generated from a radical generating gas to the etching target while heating the etching target to maintain its temperature at the predetermined temperature after the supply of the hydrogen fluoride gas, The first temperature is 80°C. The second temperature is 400°C. The radical generation gas is a gas containing oxygen atoms. Etching method.

2. Supplying the hydrogen fluoride gas to the etching target means The process includes a pressure of 500 Pa or more within the processing space in which the etching target is housed and the hydrogen fluoride gas is supplied. The etching method according to claim 1.

3. The gas containing the oxygen atom is at least one selected from the group consisting of oxygen gas, a mixture of the oxygen gas and hydrogen gas, and nitrogen oxide gas. The etching method according to claim 1.

4. The process of supplying the hydrogen fluoride gas to the etching target and supplying the active radicals to the etching target further includes supplying the radical generation gas to the etching target. The etching method according to claim 1 or 2.

5. One cycle includes supplying the hydrogen fluoride gas to the etching target and supplying the active radicals to the etching target, The etching method includes repeating a plurality of the cycles, The cycle includes supplying the active radicals to the etching target, followed by supplying an inert gas to the etching target. The etching method according to claim 1 or 2.

6. The silicon nitride film is the first silicon film, The silicon oxide film or the polysilicon film is a second silicon film, The etching target includes multiple first silicon films and multiple second silicon films, In the etching target, the first silicon film and the second silicon film are alternately stacked. The etching target includes a hole extending along the thickness direction, The holes penetrate the two or more layers of the first silicon film and the two or more layers of the second silicon film. The etching method according to claim 1 or 2.

7. A vacuum chamber defining a processing space for containing an etching target including a silicon nitride film and a silicon oxide film or a polysilicon film, A heating unit for heating the object to be etched, A hydrogen fluoride gas supply unit that supplies hydrogen fluoride gas into the processing space, A radical supply unit that supplies active radicals generated from a gas containing oxygen atoms into the processing space, The system comprises the heating unit, the hydrogen fluoride gas supply unit, and a control unit that controls the operation of the radical supply unit, The control unit, while heating the etching target to the heating unit to maintain it at a predetermined temperature between the first and second temperatures, supplies the hydrogen fluoride gas to the hydrogen fluoride gas supply unit, and then supplies the active radical to the radical supply unit. The first temperature is 80°C. The second temperature is 400°C. Etching equipment.

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