2 form a plurality of stacked films SL. The plurality of stacked films SL are stacked in order. Each of the plurality of stacked films SL includes the first film F1 and the second film F2. In the stacked film SL, the first film F1 is disposed on the second film F2.

Each of the plurality of first films F1 is formed of a material different from the material of each of the plurality of second films F2. Each of the plurality of first films F1 and each of the plurality of second films F2 may be formed of silicon-containing materials different from each other. Each of the plurality of first films F1 may be formed of silicon oxide, and each of the plurality of second films F2 may be formed of silicon nitride. Each of the plurality of first films F1 may be formed of silicon nitride, and each of the plurality of second films F2 may be formed of silicon oxide.

In an embodiment, the multilayer film ML provides a first region R1 and a second region R2 below an opening of the mask MK, as illustrated in FIG. 4B. The second region R2 is adjacent to the first region R1. As illustrated in FIG. 4A, each of the first region R1 and the second region R2 has a step shape in a cross-section perpendicular to a direction in which the first region R1 and the second region R2 are arranged. As illustrated in FIG. 4B, the depth of a first recess C1 defined by the first region R1 below the opening of the mask MK is deeper than the depth of a second recess C2 defined by the second region R2 below the opening of the mask MK. In the following description, the direction in which the first region R1 and the second region R2 are arranged is referred to as an X-direction. Further, a direction perpendicular to the depth direction of the multilayer film ML and the X-direction is referred to as a Y-direction.

In the following, reference is made to FIGS. 5A, 5B, 6A, 6B, 7A, and 7B, together with FIGS. 3, 4A, and 4B. Each of FIGS. 5A, 5B, 6A, 6B, 7A, and 7B is a cross-sectional view illustrating an example of a substrate to which a corresponding step of the etching method illustrated in FIG. 3 is applied.

As illustrated in FIG. 3, Step STb is performed after Step STa, in the method MT. In Step STb, by generating plasma from a first process gas in a chamber 10, one or more first films F1 among the plurality of first films F1 are etched, as illustrated in FIGS. 5A and 5B. In Step STb, a region on which neither the mask MK nor any other layer of the multilayer film ML is present is etched in the entire region of each of the one or more first films F1. The first process gas may contain a fluorocarbon gas. The first process gas may further contain an oxygen-containing gas (for example, an oxygen gas) and/or a noble gas.

In Step STb, the controller 2 controls a gas supply 20 to supply the first process gas into the chamber 10. In Step STb, the controller 2 controls an exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STb, the controller 2 controls a plasma generator 12 to generate plasma from the first process gas in the chamber 10. In an embodiment, the controller 2 controls a first RF generator 31a to supply source radio frequency power HF (that is, a first RF signal) in order to generate plasma from the first process gas. Further, in Step STb, the controller 2 controls a bias power source to supply an electric bias EB to the substrate support 11 (or a lower electrode) in order to attract ions from the plasma in the chamber 10. The bias power source is a second RF generator 31b or a first DC generator 32a. That is, the electric bias EB may be bias radio frequency power. Alternatively, the electric bias EB may be a pulsed first DC signal, that is, a sequence of voltage pulses.

As illustrated in FIG. 3, Step STc is performed after Step STb, in the method MT. In Step STc, by generating plasma from the second process gas in the chamber 10, one or more second films F2 among the plurality of second films F2 are etched as illustrated in FIGS. 6A and 6B. In Step STc, a region on which neither the mask MK nor any other layer of the multilayer film ML is present is etched in the entire region of each of the one or more second films F2. The second process gas may contain a hydrofluorocarbon gas. The second process gas may further contain an oxygen-containing gas (for example, an oxygen gas) and a noble gas. The second process gas may further contain a fluorocarbon gas.

In Step STc, the controller 2 controls the gas supply 20 to supply the second process gas into the chamber 10. In Step STc, the controller 2 controls the exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STc, the controller 2 controls a plasma generator 12 to generate plasma from the second process gas in the chamber 10. In an embodiment, the controller 2 controls the first RF generator 31a to supply the source radio frequency power HF in order to generate plasma from the second process gas. Further, in Step STc, the controller 2 controls the bias power source to supply the electric bias EB to the substrate support 11 (or a lower electrode) in order to attract ions from the plasma in the chamber 10.

In an embodiment, Step STb and Step STc may be alternately repeated. In this case, whether or not a stop condition is satisfied is determined, in Step STJ. The stop condition is satisfied when the number of times of alternate repetitions of Step STb and Step STc reaches a predetermined number of times. When it is determined, in Step STJ, that the stop condition is not satisfied, Step STb and Step STc are repeated in order. By alternately repeating Step STb and Step STc, the multilayer film ML is etched as illustrated in FIGS. 7A and 7B. On the other hand, when it is determined, in Step STJ, that the stop condition is satisfied, the method MT is ended.

In each of Step STb and Step STc of the method MT, a pulse HFP of the source radio frequency power HF and a pulse EBP of the electric bias EB may be supplied intermittently or periodically.

FIGS. 8 and 9 are referred to below. Each of FIGS. 8 and 9 is a timing chart of an example of the source radio frequency power and the electric bias. In each of FIGS. 8 and 9, “ON” of the source radio frequency power HF indicates that the pulse HFP is supplied, and “OFF” of the source radio frequency power HF indicates that the pulse HFP is not supplied. In each of FIGS. 8 and 9, “ON” of the electric bias EB indicates that the pulse EBP is supplied, and “OFF” of the electric bias EB indicates that the pulse EBP is not supplied.

In an embodiment, as illustrated in FIG. 8, the pulse HFP and the pulse EBP may be synchronized with each other. That is, a supply start timing of the pulse HFP may be the same as a supply start timing of the pulse EBP, and an end timing of the pulse HFP may be the same as an end timing of the pulse EBP. In this case, the duty ratio of each of the pulse HFP and the pulse EBP may be 40% or more and 80% or less. The duty ratio is a ratio (%) of the time length of a period in which each of the pulse HFP and the pulse EBP is supplied to the time length of a pulse cycle PC.

In another embodiment, as illustrated in FIG. 9, the pulse cycle PC in Step STb may include a first period P1 and a second period P2. In addition, the pulse cycle PC in Step STc may include a third period P3 and a fourth period P4. The pulse HFP may be supplied in the first period P1 and the third period P3, and the pulse EBP may be supplied in the second period P2 and the fourth period P4.

The power level of the source radio frequency power HF in the second period P2 may be lower than the power level of the source radio frequency power HF in the first period P1. Further, the power level of the source radio frequency power HF in the fourth period P4 may be lower than the power level of the source radio frequency power HF in the third period P3.

The electric bias EB may have a level in the first period P1, which is lower than the level of the electric bias EB in the second period P2, or may be stopped in the first period P1. Further, the electric bias EB may have a level in the third period P3, which is lower than the level of the electric bias EB in the fourth period P4, or may be stopped in the third period P3. When the electric bias EB is the bias radio frequency power, the level of the electric bias EB is a power level thereof. When the electric bias EB includes a voltage pulse, the level of the electric bias EB increases as the voltage level of the voltage pulse has a larger difference from the reference voltage (for example, 0 V) in a negative direction, and increases as the absolute value of the negative level becomes larger.

Each of the ratio of the time length of the first period P1 in the pulse cycle PC and the ratio of the time length of the third period P3 in the pulse cycle PC, that is, the duty ratio may be 50% or more. This duty ratio may be 65% or more or 70% or more.

According to such a method MT, even when the depth of the recess of the substrate W is increased by etching the multilayer film ML, the expansion of the width of the recess is suppressed. For example, expansion of a width W1 in the X-direction (see FIG. 7B) and a width W3 in the Y-direction at the deepest portion of the first recess C1 is suppressed. In addition, expansion of a width W2 in the X-direction (see FIG. 7B) and a width in the Y-direction at the deepest portion of the second recess C2 is suppressed.

In the following, reference is made to FIGS. 10, 11A, 11B, 12A, 12B, 13, 14A, 14B, 15A, and 15B. FIG. 10 is a flowchart illustrating an example of Step STb of the etching method illustrated in FIG. 3. FIG. 13 is a flowchart illustrating an example of Step STc of the etching method illustrated in FIG. 3. Each of FIGS. 11A, 11B, 12A, 12B, 14A, 14B, 15A, and 15B is a cross-sectional view illustrating an example of a substrate to which a corresponding step of the etching method illustrated in FIG. 3 is applied.

In an embodiment, Step STb may include repeating a first cycle CY1 as illustrated in FIG. 10. The first cycle CY1 includes Step STb1 and Step STb2.

Step STb1 is performed in the first period. In Step STb1, as illustrated in FIGS. 11A and 11B, a deposit D1 (first deposit) is formed on one or more first films F1 among the plurality of first films F1. The deposit D1 is formed on a region in the entire region of each of the one or more first films F1 on which neither the mask MK nor any other film of the multilayer film ML is present. The deposit D1 may be formed on the entire surface of the substrate W. The deposit D1 is supplied to the substrate W from the plasma generated from the first process gas described above in the chamber 10. A period in which Step STb1 is performed may be the first period P1 described above. That is, the pulse HFP may be supplied in Step STb1. In Step STb1, the electric bias EB may not be supplied, or the level of the electric bias EB may be set to a level lower than the level of the electric bias EB in Step STb2.

In Step STb1, the controller 2 controls a gas supply 20 to supply the first process gas into the chamber 10. In Step STb1, the controller 2 controls an exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STb1, the controller 2 controls a plasma generator 12 to generate plasma from the first process gas in the chamber 10. In an embodiment, the controller 2 controls a first RF generator 31a to supply source radio frequency power HF (or the pulse HFP thereof) in order to generate plasma from the first process gas.

Step STb2 is performed in the second period after the first period. In Step STb2, one or more first films F1 are etched by using plasma generated from the first process gas described above in the chamber 10, as illustrated in FIGS. 12A and 12B. In Step STb2, a region in the entire region of each of the one or more first films F1 on which neither the mask MK nor any other film of the multilayer film ML is present is etched. Further, in Step STb2, a reaction product generated by the etching is deposited on the substrate W as a deposit D3 (third deposit). A portion of the deposit D3 is formed on the side wall surface defining the recess formed in the substrate W, specifically, the side wall surface including the cross-section of the second film F2. A period in which Step STb2 is performed may be the second period P2 described above. That is, the electric bias EB is supplied in Step STb2. In Step STb2, the source radio frequency power HF may be supplied. In Step STb2, the power level of the source radio frequency power HF may be set to a level lower than the power level of the source radio frequency power HF in Step STb1.

In Step STb2, the controller 2 controls a gas supply 20 to supply the first process gas into the chamber 10. In Step STb2, the controller 2 controls an exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STb2, the controller 2 controls a plasma generator 12 to generate plasma from the first process gas in the chamber 10. In an embodiment, the controller 2 controls the first RF generator 31a to supply the source radio frequency power HF in order to generate plasma from the first process gas. In addition, the controller 2 controls the bias power source to supply the electric bias EB (or the pulse EBP thereof) to the substrate support 11 (or the lower electrode).

Step STb may further include Step STbJ. In Step STbJ, it is determined whether or not the stop condition is satisfied. The stop condition is satisfied when the number of times of performing the first cycle CY1 has reached a predetermined number of times. When it is determined, in Step STbJ, that the stop condition is not satisfied, the first cycle CY1 is performed again. On the other hand, when it is determined, in Step STbJ, that the stop condition is satisfied, Step STb is ended, and the process proceeds to Step STc.

In an embodiment, Step STc may include repeating a second cycle CY2 as illustrated in FIG. 13. The second cycle CY2 includes Step STc1 and Step STc2.

Step STc1 is performed in the third period. In Step STc1, as illustrated in FIGS. 14A and 14B, a deposit D2 (second deposit) is formed on one or more second films F2 among the plurality of second films F2. The deposit D2 is formed on a region in the entire region of each of the one or more second films F2 on which neither the mask MK nor any other film of the multilayer film ML is present. The deposit D2 may be formed on the entire surface of the substrate W. The deposit D2 is supplied to the substrate W from the plasma generated from the second process gas described above in the chamber 10. A period in which Step STc1 is performed may be the third period P3 described above. That is, the pulse HFP may be supplied in Step STc1. In Step STc1, the electric bias EB may not be supplied, or the level of the electric bias EB may be set to a level lower than the level of the electric bias EB in Step STc2.

In Step STc1, the controller 2 controls the gas supply 20 to supply the second process gas into the chamber 10. In Step STc1, the controller 2 controls the exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STc1, the controller 2 controls a plasma generator 12 to generate plasma from the second process gas in the chamber 10. In an embodiment, the controller 2 controls the first RF generator 31a to supply source radio frequency power HF (or the pulse HFP thereof) in order to generate plasma from the second process gas.

Step STc2 is performed in the fourth period after the third period. In Step STc2, one or more second films F2 are etched by using plasma generated from the second process gas described above in the chamber 10, as illustrated in FIGS. 15A and 15B. In Step STc2, a region in the entire region of each of the one or more second films F2 on which neither the mask MK nor any other film of the multilayer film ML is present is etched. In Step STc2, the deposit D3 is etched together with the one or more second films F2.

A period in which Step STc2 is performed may be the fourth period P4 described above. That is, the electric bias EB is supplied in Step STc2. In Step STc2, the source radio frequency power HF may be supplied. In Step STc2, the power level of the source radio frequency power HF may be set to a level lower than the power level of the source radio frequency power HF in Step STc1.

In Step STc2, the controller 2 controls the gas supply 20 to supply the second process gas into the chamber 10. In Step STc2, the controller 2 controls the exhaust system 40 to set the pressure in the chamber 10 to designated pressure. In Step STc2, the controller 2 controls a plasma generator 12 to generate plasma from the second process gas in the chamber 10. In an embodiment, the controller 2 controls the first RF generator 31a to supply the source radio frequency power HF in order to generate plasma from the second process gas. In addition, the controller 2 controls the bias power source to supply the electric bias EB (or the pulse EBP thereof) to the substrate support 11 (or the lower electrode).

Step STc may further include Step STcJ. In Step STcJ, it is determined whether or not the stop condition is satisfied. The stop condition is satisfied when the number of times of performing the second cycle CY2 has reached a predetermined number of times. When it is determined, in Step STcJ, that the stop condition is not satisfied, the second cycle CY2 is performed again. On the other hand, when it is determined, in Step STcJ, that the stop condition is satisfied, Step STc is ended.

While various exemplary embodiments have been described above, various additions, omissions, substitutions and changes may be made without being limited to the exemplary embodiments described above. Elements of the different embodiments may be combined to form another embodiment.

For example, the multilayer film ML of the substrate W to which the method MT is applied may not have a step shape. Further, the multilayer film ML of the substrate W before the method MT is applied may not have the recess.

In addition, each of the first process gas and the second process gas described above may further contain a halogen element and phosphorus. The halogen element contained in each of the first process gas and the second process gas may be fluorine. Each of the first process gas and the second process gas may contain at least one halogen-containing molecule. Each of the first process gas and the second process gas may contain at least one of fluorocarbon or hydrofluorocarbon as at least the one halogen-containing molecule. The fluorocarbon is, for example, at least one of CF₄, C₃F₈, CF₆, or CAF₈. The hydrofluorocarbon is, for example, at least one of CH₂F₂, CHF₃, or CH₃F. The hydrofluorocarbon may contain two or more carbons. The hydrofluorocarbon may contain, for example, three carbons or four carbons.

Each of the first process gas and the second process gas may contain at least one phosphorus-containing molecule as phosphorus described above. The phosphorus-containing molecules may be oxides such as tetraphosphorus decaoxide (P₄O₁₀), tetraphosphorus octoxide (P₄O₈), and tetraphosphorus hexaoxide (P₄O₆). The tetraphosphorus decaoxide is sometimes called diphosphorus pentoxide (P₂O₆). The phosphorus-containing molecules may be halides such as phosphorus trifluoride (PF₃), phosphorus pentafluoride (PF₅), phosphorus trichloride (PCl₃), phosphorus pentachloride (PCl₅), phosphorus tribromide (PBr₃), phosphorus pentabromide (PBr₅), and phosphorus iodide (PI₃). That is, the molecule containing phosphorus may contain fluorine as the halogen element. Alternatively, the molecule containing phosphorus may contain a halogen element other than fluorine as the halogen element. The phosphorus-containing molecules may be halogenated phosphoryl such as phosphoryl fluoride (POF₃), phosphoryl chloride (POCl₃), and phosphoryl bromide (POBr₃). The phosphorus-containing molecules may be phosphine (PH₃), calcium phosphide (Ca₃P₂or the like), phosphoric acid (H₃PO₄), sodium phosphate (Na₃PO₄), a hexafluorophosphoric acid (HPF₆), and the like. The phosphorus-containing molecule may be fluorophosphine (H_xPF_y). Here, the sum of x and y is 3 or 5. As the fluorophosphine, HPF₂and H₂PF₃are exemplified. Each of the first process gas and the second process gas may contain one or more phosphorus-containing molecules among the phosphorus-containing molecules described above, as the at least one phosphorus-containing molecule. For example, each of the first process gas and the second process gas may contain at least one of PF₃, PCl₃, PF₅, PCl₅, POCl₃, PH₃, PBr₃, and PBr₅, as the at least one phosphorus-containing molecule. When each phosphorus-containing molecule contained in each of the first process gas and the second process gas is a liquid or a solid, each phosphorus-containing molecule may be vaporized by heating or the like and be supplied into the chamber 10.

Each of the first process gas and the second process gas may further contain carbon and hydrogen. Each of the first process gas and the second process gas may contain at least one of H₂, hydrogen fluoride (HF), hydrocarbon (C_xH_y), hydrofluorocarbon (CH_xF_y), and NH₃, as a molecule containing hydrogen. The hydrocarbon is, for example, CH₄or C₃H₆. Here, each of x and y is a natural number. Each of the first process gas and the second process gas may contain fluorocarbon or hydrocarbon (for example, CH₄) as the molecules containing carbon. Each of the first process gas and the second process gas may further contain oxygen. The process gases may contain, for example, O₂. Alternatively, the process gases may not contain oxygen.

In an embodiment, each of the first process gas and the second process gas may contain a phosphorus-containing gas, a fluorine-containing gas, and a hydrogen-containing gas. The hydrogen-containing gas contains at least one selected from the group consisting of hydrogen fluoride (HF), H₂, ammonia (NH₃), and hydrocarbon. The phosphorus-containing gas contains at least one of the phosphorus-containing molecules described above. The fluorine-containing gas contains at least one gas selected from the group consisting of a fluorocarbon gas and a carbon-free fluorine-containing gas. The fluorocarbon gas is a gas containing fluorocarbon described above. The carbon-free fluorine-containing gas is, for example, a nitrogen trifluoride gas (NF₃gas) or a sulfur hexafluoride gas (SF₆gas). In addition, each of the first process gas and the second process gas may further contain a hydrofluorocarbon gas. The hydrofluorocarbon gas is a gas of hydrofluorocarbon described above. Further, each of the first process gas and the second process gas may further contain a halogen-containing gas containing a halogen element other than fluorine. The halogen-containing gas is, for example, a Cl₂gas and/or an HBr gas.

In an example, each of the first process gas and the second process gas may contain the phosphorus-containing gas, the fluorocarbon gas, the hydrogen-containing gas, and the oxygen-containing gas (for example, an O₂gas), or may substantially be formed by these gases. In another example, each of the first process gas and the second process gas may contain the phosphorus-containing gas, the carbon-free fluorine-containing gas, the fluorocarbon gas, the hydrogen-containing gas, the hydrofluorocarbon gas, and the halogen-containing gas containing a halogen element other than fluorine, or may be substantially formed by these gases.

In another embodiment, each of the first process gas and the second process gas may contain the phosphorus-containing gas described above, the fluorine-containing gas described above, the hydrofluorocarbon gas described above, and the halogen-containing gas containing a halogen element other than fluorine described above, or may be substantially formed by these gases.

In an embodiment, each of the first process gas and the second process gas may contain a first gas and a second gas. The first gas is a phosphorus-free gas. That is, the first gas is all gases other than the phosphorus-containing gas contained in the process gas. The first gas may contain a halogen element. The first gas may contain the gas of at least one halogen-containing molecule described above. The first gas may further contain carbon and hydrogen. The first gas may further contain the gas of a molecule containing hydrogen and/or a gas of a molecule containing carbon, as described above. The first gas may further contain oxygen. The first gas may contain an O₂gas. Alternatively, the first gas may not contain oxygen. The second gas is a gas containing phosphorus. That is, the second gas is the phosphorus-containing gas described above. The second gas may contain a gas of at least one phosphorus-containing molecule described above.

In each of the first process gas and the second process gas, a flow rate ratio which is the ratio of the flow rate of the second gas to the flow rate of the first gas may be set to be more than 0 and 0.5 or less. The flow rate ratio may be set to 0.075 or more and 0.3 or less. The flow rate ratio may be set to 0.1 or more and 0.25 or less.

In the following, various experiments performed for evaluating the method MT are described. It should be noted that the method MT is not limited by various experiments described below.

First to Third Experiments

In each of first to third experiments, a sample substrate having the same structure as the substrate W illustrated in FIG. 4A and FIG. 4B was prepared. In the sample substrate, each of a plurality of first films F1 was a silicon oxide film, and each of a plurality of second films F2 was a silicon nitride film. In each of the first to third experiments, the multilayer film ML of the sample substrate was etched by using the plasma processing apparatus 1 until the underlying region UR was exposed. In each of the first to third experiments, a gas mixture containing a fluorocarbon gas, an oxygen gas, and an argon gas was used as the first process gas. Further, in each of the first to third experiments, a gas mixture containing a hydrofluorocarbon gas, a fluorocarbon gas, an oxygen gas, and an argon gas was used as the second process gas. In the first experiment, the source radio frequency power HF and the electric bias were continuously supplied in each of Step STb and Step STc. In the second experiment, in each of Step STb and Step STc of the method MT, the pulse HFP and the pulse EBP that were synchronized with each other were supplied as illustrated in FIG. 8. In the second experiment, the pulse frequency, which is the reciprocal of the time length of the pulse cycle PC, was 5 kHz, and the duty ratio was 80%. In the third experiment, the pulse HFP and the pulse EBP were supplied as illustrated in FIG. 9 in each of Step STb and Step STc of the method MT. In the third experiment, the pulse frequency, which is the reciprocal of the time length of the pulse cycle PC, was 2 kHz. Further, in the third experiment, each of the ratio of the time length of the first period P1 in the pulse cycle PC and the ratio of the time length of the third period P3 in the pulse cycle PC, that is, the duty ratio was 70%.