Patent ID: 12230505

DETAILED DESCRIPTION TO EXECUTE THE INVENTION

Hereinafter, various exemplary embodiments will be described in detail with reference to the drawings. In the respective drawings, the same or corresponding parts will be denoted by the same symbols.

FIG.1is a flowchart illustrating an etching method according to an exemplary embodiment. Method MT illustrated inFIG.1is a method for selectively etching a first region made of silicon oxide with respect to a second region made of silicon nitride by a plasma processing on a workpiece.

FIG.2is a cross-sectional view illustrating a workpiece to which the etching method according to the exemplary embodiment is applied. As illustrated inFIG.2, the workpiece (i.e., a “wafer W”) includes a substrate SB, a first region R1, a second region R2, and an organic film OL, which will constitute a mask later. In an example, the wafer W is obtained in manufacturing a fin-type field effect transistor, and includes a raised area RA, a silicon-containing antireflection film AL, and a resist mask RM. In addition to the organic film, the material constituting the mask may be titanium nitride, polysilicon, or the like.

The raised area RA is provided to be raised from the substrate SB. The raised area RA may constitute, for example, a gate area. The second region R2is made of silicon nitride (Si3N4), and provided on the surface of the raised area RA and the surface of the substrate SB. As illustrated inFIG.2, the second region R2extends to define a recess. In an example, the depth of the recess is about 150 nm, and the width of the recess is about 20 nm.

The first region R1is made of silicon oxide SiO2, and provided on the second region R2. Specifically, the first region R1is provided to fill the recess defined by the second region R2, and cover the second region R2.

The organic film OL is provided on the first region R1. The antireflection film AL is provided on the organic film OL. The resist mask RM is provided on the antireflection film AL. The resist mask RM provides, over the recess defined by the second region R2, an opening having a width wider than the width of the recess. The width of the opening of the resist mask RM is, for example, 60 nm. Such a pattern of the resist mask RM is formed by a photolithography technique.

In method MT, the workpiece such as the wafer illustrated inFIG.2is processed in a plasma processing apparatus.FIG.3is a view schematically illustrating an exemplary plasma processing apparatus that may be used for performing the method illustrated inFIG.1. The plasma processing apparatus10illustrated inFIG.3is a capacitively coupled plasma etching apparatus, and includes a substantially cylindrical processing container12. The inner wall surface of the processing container12is made of, for example, anodized aluminum. The processing container12is grounded for safety.

A substantially cylindrical support14is provided above the bottom of the processing container12. The support14is made of, for example, an insulating material. The support14extends vertically from the bottom of the processing container12in the processing container12. Further, a placing table PD is provided in the processing container12. The placing table PD is supported by the support14.

The placing table PD holds the wafer W on the top surface thereof. The placing table PD includes a lower electrode LE and an electrostatic chuck ESC. The lower electrode LE includes a first plate18aand a second plate18b. The first plate18aand the second plate18bare made of a metal such as, for example, aluminum, and have a substantially disc shape. The second plate18bis provided on the first plate18aand electrically connected to the first plate18a.

The electrostatic chuck ESC is provided on the second plate18b. The electrostatic chuck ESC has a structure in which an electrode made of a conductive film is disposed between a pair of insulating layers or insulating sheets. The electrode of the electrostatic chuck ESC is electrically connected with a DC power source22via a switch23. The electrostatic chuck ESC attracts the wafer W through an electrostatic force such as, for example, a Coulomb force generated by a DC voltage from the DC power source22. Therefore, the electrostatic chuck ESC is capable of holding the wafer W.

A focus ring FR is disposed on the periphery of the second plate18bto surround the edge of the wafer W and the electrostatic chuck ESC. The focus ring FR is provided to enhance the uniformity of the etching. The focus ring FR is made of a material appropriately selected from materials of an etching target film, and may be made of, for example, quartz.

A coolant flow path24is provided inside the second plate18b. The coolant flow path24constitutes a temperature adjustment mechanism. The coolant flow path24is supplied with a coolant from a chiller unit provided outside the processing container12, through a pipe26a. The coolant supplied to the coolant flow path24is returned to the chiller unit through a pipe26b. In this manner, the coolant is circulated between the coolant flow path24and the chiller unit. The temperature of the wafer W supported by the electrostatic chuck ESC is controlled by controlling the temperature of the coolant.

Further, a gas supply line28is provided in the plasma processing apparatus10. The gas supply line28supplies a heat transfer gas, for example, He gas from a heat transfer gas supply mechanism to a gap between the top surface of the electrostatic chuck ESC and the rear surface of the wafer W.

Further, the plasma processing apparatus10includes an upper electrode30. The upper electrode30is disposed above the placing table PD to face the placing table PD. The lower electrode LE and the upper electrode30are provided substantially in parallel with each other. A processing space S is provided between the upper electrode30and the lower electrode LE to perform a plasma processing on the wafer W.

The upper electrode30is supported in the upper portion of the processing container12through an insulating shielding member32. In an exemplary embodiment, the upper electrode30may be configured such that its distance in the vertical direction from the top surface of the placing table PD (i.e., the wafer placing surface) is variable. The upper electrode30may include an electrode plate34and an electrode support36. The electrode plate34faces the processing space S, and a plurality of gas ejection holes34aare provided in the electrode plate34. In an exemplary embodiment, the electrode plate34is made of silicon.

The electrode support36is configured to detachably support the top plate34, and may be made of a conductive material such as, for example, aluminum. The electrode support36may have a water-cooled structure. A gas diffusion chamber36ais provided inside the electrode support36. From the gas diffusion chamber36a, a plurality of gas flowing holes36bextend downward to be in communication with the gas ejection holes34a, respectively. Further, the electrode support36includes a gas introduction port36cconfigured to introduce the processing gas to the gas diffusion chamber36a. The gas introduction port36cis connected with a gas supply pipe38.

The gas supply pipe38is connected with a gas source group40via a valve group42and a flow rate controller group44. The gas source group40includes a plurality of gas sources. In an example, the gas source group40includes a source of one or more fluorocarbon gases, a source of a noble gas, a source of nitrogen gas (N2gas), a source of hydrogen gas (H2gas), and a source of an oxygen-containing gas. In an example, the source of one or more fluorocarbon gases may include a source of C4F8gas, a source of CF4gas, and a source of C4F6gas. The source of a noble gas may be a source of any noble gas such as, for example, He gas, Ne gas, Ar gas, Kr gas, or Xe gas, and in an example, a source of Ar gas. Further, the source of the oxygen-containing gas may be, for example, a source of oxygen gas (O2gas). The oxygen-containing gas may be any gas containing oxygen, or a carbon oxide gas such as, for example, CO gas or CO2gas.

The valve group42includes a plurality of valves, and the flow rate controller group44includes a plurality of flow rate controllers such as, for example, mass flow controllers. The plurality of gas sources of the gas source group40are connected to the gas supply pipe38via valves corresponding to the valve group42and the flow rate controllers corresponding to the flow rate controller group44, respectively.

Further, in the plasma processing apparatus10, a deposition shield46is provided detachably along the inner wall of the processing container12. The deposit shield46is provided in the outer periphery of the support14as well. The deposit shield46serves to suppress any etching byproduct (deposit) from being attached to the processing container12, and may be formed by coating an aluminum material with a ceramic (e.g., Y2O3).

An exhaust plate48is provided at the bottom side of the processing container12between the support14and the sidewall of the processing container12. The exhaust plate48may be formed by coating an aluminum material with a ceramic (e.g., Y2O3). An exhaust port12eis formed at the lower side of the exhaust plate48in the processing container12. An exhaust port12eis connected with an exhaust device50via an exhaust pipe52. The exhaust device50includes a vacuum pump such as, for example, a turbo molecular pump, and is capable of decompressing the space in the processing container12to a desired degree of vacuum. A carry-in/out port12gof the wafer W is formed in the side wall of the processing container12. The carry-in/out port12gis configured to be opened/closed by a gate valve54.

Further, the plasma processing apparatus10further includes a first high frequency power source62and a second high frequency power source64. The first high frequency power source62is a power source that generates high frequency power for plasma generation, and, for example, generates high frequency power having a frequency of 27 MHz to 100 MHz. The first high frequency power source62is connected to the upper electrode30via a matcher66. The matcher66is a circuit to match the output impedance of the first high frequency power source62and the input impedance of the load side (the upper electrode30side). The first high frequency power source62may be connected to the lower electrode LE via the matcher66.

The second high frequency power source64is a power source that generates high frequency bias power for drawing ions into the wafer W, and, for example, generates high frequency bias power having a frequency in a range of 400 kHz to 13.56 MHz. The second high frequency power source64is connected to the lower electrode LE via a matcher68. The matcher68is a circuit to match the output impedance of the first high frequency power source64and the input impedance of the load side (the lower electrode LE side).

In addition, the plasma processing apparatus10further includes a power source70. The power source70is connected to the upper electrode30. The power source70applies a voltage to the upper electrode30to draw positive ions present in the processing space S into the electrode plate34. In an example, the power source70is a DC power source that generates a negative DC voltage. In another example, the power source70may be an AC power source that generates an AC voltage of a relatively low frequency. The voltage applied from the power source70to the upper electrode may be a voltage of −150 V or less. That is, the voltage applied to the upper electrode30by the power source70may be a negative voltage of which the absolute value is150or more. When such a voltage is applied from the power source70to the upper electrode30, positive ions present in the processing space S collide with the electrode plate34. Accordingly, second electrons and/or silicon are released from the electrode plate34. The released silicon is bonded to the active species of fluorine present in the processing space S, so that the amount of the active species of fluorine is reduced.

Further, in an exemplary embodiment, the plasma processing apparatus10may further include a controller Cnt. The controller Cnt is a computer including, for example, a processor, a storage unit, an input device, and a display device, and controls respective parts of the plasma processing apparatus10. In the controller Cnt, an operator may execute an input operation of a command using the input device to manage the plasma processing apparatus10, and may visualize and display the operation status of the plasma processing apparatus10. Further, the storage unit of the controller Cnt stores a control program for controlling various processings to be performed in the plasma processing apparatus10by the processor, or a program for performing a processing on respective parts of the plasma processing apparatus10in accordance with a processing condition, that is, a processing recipe.

Referring back toFIG.1, method MT will be described in detail. In the following descriptions,FIGS.2and4to16will be referred as appropriate.FIGS.4to16are cross-sectional views illustrating the workpiece in a stage during the performance of method MT. In the following, descriptions will be made on a case where the wafer W illustrated inFIG.2is processed using a single plasma processing apparatus10illustrated inFIG.3in method MT.

First, in method MT, the wafer W illustrated inFIG.2is carried into the plasma processing apparatus10, and the wafer W is placed on the placing table PD and is held by the placing table PD.

In method MT, step ST1is then performed. In step ST1, the antireflection film AL is etched. Therefore, in step ST1, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. The processing gas contains a fluorocarbon gas. The fluorocarbon gas may include, for example, one or more selected from C4F8gas and CF4gas. The processing gas may further contain a noble gas, for example, Ar gas. Further, in step ST1, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. Further, in step ST1, the high frequency power from the first high frequency power source62and the high frequency bias power from the second high frequency power source64are supplied to the lower electrode LE.

Hereinafter, various conditions in step ST1are exemplified.Pressure in processing container: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)Processing gasC4F8gas: 30 sccmCF4gas: 150 sccm to 300 sccmAr gas: 200 sccm to 500 sccmHigh frequency power for plasma generation: 300 W to 1,000 WHigh frequency bias power: 200 W to 500 W

In step ST1, plasma of the processing gas is generated, and the antireflection film AL is etched in a portion exposed from the opening of the resist mask RM, by the active species of fluorocarbon. As a result, as illustrated inFIG.4, in the entire region of the antireflection film AL, a portion exposed from the resist mask RM is removed. That is, the pattern of the resist mask RM is transferred to the antireflection film AL, so that a pattern providing an opening is formed in the antireflection film AL. The operation of each part of the plasma processing apparatus10in the step ST1may be controlled by the controller Cnt.

In the subsequent step ST2, the organic film OL is etched. Therefore, in step ST2, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. The processing gas may contain hydrogen gas and nitrogen gas. Further, the processing gas used in step ST2may be a processing gas containing other gases, for example, oxygen gas, as long as it can etch the organic film. Further, in step ST2, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. At this time, in step ST2, the high frequency power from the first high frequency power source62and the high frequency bias power from the second high frequency power source64are supplied to the lower electrode LE.

Hereinafter, various conditions in step ST2are exemplified.Pressure in processing container: 50 mTorr (6.65 Pa) to 200 mTorr (26.6 Pa)Processing gasN2gas: 200 sccm to 400 sccmH2gas: 200 sccm to 400 sccmHigh frequency power for plasma generation: 500 W to 2,000 WHigh frequency bias power: 200 W to 500 W

In step ST2, plasma of the processing gas is generated, and the organic film OL is etched in a portion exposed from the opening of the antireflection film AL. Further, the resist mask RM is also etched. As a result, as illustrated inFIG.5, the resist mask RM is removed, and in the entire region of the organic film OL, a portion exposed from the antireflection film AL is removed. That is, the pattern of the antireflection film AL is transferred to the organic film OL, and the pattern providing an opening MO is formed in the organic film OL, and a mask MK is produced from the organic film OL. The operation of each part of the plasma processing apparatus10in the step ST2may be controlled by the controller Cnt.

In an exemplary embodiment, step ST3is performed after the performance of step ST2. In step ST3, the first region R1is etched until just before the second region R2is exposed. That is, the first region R1is etched until the first region R1is slightly left on the second region R2. Therefore, in step ST3, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. The processing gas contains a fluorocarbon gas. The processing gas may further contain a noble gas, for example, Ar gas. Further, the processing gas may further contain oxygen gas. Further, in step ST3, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. Further, in step ST3, the high frequency power from the first high frequency power source62and the high frequency bias power from the second high frequency power source64are supplied to the lower electrode LE.

In step ST3, plasma of the processing is generated, and the first region R1is etched in a portion exposed from the opening of the mask MK, by the active species of fluorocarbon. The processing time of step ST3is set such that the first region R1is left in a predetermined thickness on the second region R2at the time of the end of step ST3. As a result of the performance of step ST3, as illustrated inFIG.6, an upper opening UO is partially formed. The operation of each part of the plasma processing apparatus10in the step ST3may be controlled by the controller Cnt.

Here, in step ST11(to be described later), conditions are selected for a mode in which the formation of the fluorocarbon-containing deposit on the surface of the wafer W including the first region R1is dominant to the etching of the first region R1, that is, a deposition mode. Meanwhile, in step ST3, conditions are selected for a mode in which the etching of the first region R1is dominant to the formation of the deposit, that is, an etching mode. Thus, in an example, the fluorocarbon gas used in step ST3may include, for example, one or more selected from C4F8gas and CF4gas. The fluorocarbon gas of this example is a fluorocarbon gas in which a ratio of the number of fluorine atoms to the number of carbon atoms (i.e., the number of fluorine atoms/the number of carbon atoms) is higher than a ratio of the number of fluorine atoms to the number of carbon atoms (i.e., the number of fluorine atoms/the number of carbon atoms) of the fluorocarbon gas used in step ST11. Further, in an example, in order to enhance a dissociation rate of the fluorocarbon gas, the high frequency power for plasma generation used in step ST3may be set to be greater than the high frequency power for plasma generation used in step ST11. According to the example, it is possible to implement the etching mode. Further, in an example, the high frequency bias power used in step ST3may also be set to be greater than the high frequency bias power of step ST11. According to the example, the energy of ions drawn into the wafer W is increased, so that the first region R1may be etched at a high speed.

Hereinafter, various conditions in step ST3are exemplified.Pressure in processing container: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)Processing gasC4F8gas: 10 sccm to 30 sccmCF4gas: 50 sccm to 150 sccmAr gas: 500 sccm to 1,000 sccmO2gas: 10 sccm to 30 sccmHigh frequency power for plasma generation: 500 W to 2,000 WHigh frequency bias power: 500 W to 2,000 W

In an exemplary embodiment, step ST4is then executed. In step ST4, plasma of the processing gas containing an oxygen-containing gas is generated in the processing container12. Therefore, in step ST4, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. In an example, the processing gas may contain oxygen gas as the oxygen-containing gas. Further, the processing gas may further contain an inert gas such as a noble gas (e.g., Ar gas) or nitrogen gas. Further, in step ST4, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. Further, in step ST4, the high frequency power from the first high frequency power source62is supplied to the lower electrode LE. Further, in step ST4, the high frequency bias power from the second high frequency power source64may not be supplied to the lower electrode LE.

In step ST4, active species of oxygen are generated, and the opening MO of the mask MK is widened in its upper end portion by the active species of oxygen. Specifically, as illustrated inFIG.7, etching is performed such that the upper shoulder of the mask MK defining the upper end portion of the opening is tapered. Thus, even though a deposit produced in subsequent steps is attached to the surface defining the opening MO of the mask MK, the amount of reduction in width of the opening MO may be reduced. The operation of each part of the plasma processing apparatus10in the step ST4may be controlled by the controller Cnt.

Here, step ST11(to be described later) is a step of reducing a trace amount of the deposit formed in each sequence, and it is necessary to suppress excessive reduction of the deposit. Meanwhile, step ST4is performed to widen the width of the upper end portion of the opening MO of the mask MK, and a short processing time is required.

Hereinafter, various conditions in step ST4are exemplified.Pressure in processing container: 30 mTorr (3.99 Pa) to 200 mTorr (26.6 Pa)Processing gasO2gas: 15 sccm to 500 sccmAr gas: 200 sccm to 1,500 sccmHigh frequency power for plasma generation: 100 W to 500 WHigh frequency bias power: 0 W to 200 W

Subsequently, in method MT, one or more sequences SQ1are executed, and then, one or more sequences SQ2are executed. Further, in an exemplary embodiment, one or more sequences SQ3may be executed as necessary after the execution of one or more sequences SQ2. The sequence SQ1, sequence SQ2, and sequence SQ3are executed to etch the first region R1. Each of the sequence SQ1, the sequence SQ2, and the sequence SQ3includes step ST11and step ST12. Hereinafter, details of step ST1and step ST2common to all of the sequence SQ1, the sequence SQ2, and the sequence SQ3will be described, and the difference between the sequence SQ1, the sequence SQ2, and the sequence SQ3will be described below.

In each sequence, step ST11is first executed. In step ST11, plasma of a processing gas containing a fluorocarbon gas and plasma of a processing gas containing an oxygen-containing gas and an inert gas are generated in the processing container12in which the wafer W is accommodated. Therefore, in step ST11, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. The processing gas contains a fluorocarbon gas, an oxygen-containing gas, and an inert gas. In step ST11, conditions for setting the deposition mode are selected as described above. Thus, in an example, C4F6gas is used as the fluorocarbon gas. The oxygen-containing gas includes, for example, oxygen gas, and the inert gas includes a noble gas such as Ar gas. The inert gas may be nitrogen gas. Further, in step ST11, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. Further, in step ST11, the high frequency power from the first high frequency power source62is supplied to the lower electrode LE.

In step ST11, plasma of the processing gas containing the fluorocarbon gas or the processing gas containing the fluorocarbon gas and the inert gas is generated, so that dissociated fluorocarbon is deposited on the surface of the wafer W to form a deposit DP (seeFIGS.8,11, and14). The operation of each part of the plasma processing apparatus10in the step ST11may be controlled by the controller Cnt.

In step ST11, active species of oxygen is generated over a period in which the deposit DP is formed by the fluorocarbon, and the amount of the deposit DP on the wafer W is moderately reduced by the active species of the oxygen (seeFIGS.9,12, and15). These states illustrated inFIGS.8and9occur simultaneously in step ST11. As a result, blockage of the opening MO and the upper opening UO by excessive deposit DP is suppressed. Further, in the processing gas used in step ST11, since the oxygen gas is diluted by the inert gas, the deposit DP is suppressed from being excessively removed. The operation of each part of the plasma processing apparatus10in the step ST11may be controlled by the controller Cnt.

Hereinafter, various conditions in step ST11are exemplified.Pressure in processing container: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)Processing gasC4F6gas flow rate: 1 sccm to 20 sccmAr gas flow rate: 200 sccm to 1,500 sccmO2gas flow rate: 1 sccm to 20 sccmHigh frequency power of first high frequency power source62: 40 MHz, 50 W to 500 WHigh frequency bias power of second high frequency power source64: 13 MHz, 0 W to 50 W.DC voltage of power source70: 0 V to −500 V

In an exemplary embodiment, step ST11of each sequence, that is, one step ST11is executed for 2 seconds or more, for example, 2.5 seconds to 3 seconds. The deposition time in step ST11may be set to 3 seconds in the first sequence SQ1and a shorter time in the second sequence SQ2, for example, 2.5 seconds. Therefore, it is possible to appropriately control the increase in the film thickness of the protective film on the silicon nitride, thereby obtaining the effect of improving the releasability. When the etching rate of the deposit DP is too high during such a period of time, the deposit for protecting the second region R2may be excessively removed. Thus, in step ST11, the deposit DP is etched at a rate of 1 nm/sec or less. Accordingly, it is possible to appropriately adjust the amount of the deposit DP formed on the wafer W. The rate of 1 nm/sec or less for the etching of the deposit DP in step ST11may be achieved by selecting the pressure in the processing container, a degree of dilution of the oxygen in the processing gas with the noble gas, that is, the oxygen concentration, and the high frequency power for plasma generation within the conditions described above. In the case where the fluorocarbon gas, the inert gas, and the oxygen gas are supplied within the overlapping period (the same period) in the step ST11, it is unnecessary to take into consideration the stabilization time accompanying the switching of the gas and the discharge stabilization time, compared with the case where the fluorocarbon gas and the oxygen gas are supplied in different periods. That is, it is not necessary to consider the stabilization time accompanying the switching of the processing gas and the discharge stabilization time. Further, the molar ratio of the fluorocarbon gas to the oxygen gas in the deposition step may be about 1:0.5 to about 1:1.5. In this case, it is possible to obtain effects such as improvement of microloading and improvement of releasability. Further, in the case of forming the opening shape using the deposit, the planar shape may be circular, rectangular, slit, or long-hole shape. Further, it has been confirmed that the formed opening may be patterned as designed without greatly distorting it.

In each sequence, step ST12is then executed. In step ST12, the first region R1is etched. Therefore, in step ST12, the processing gas is supplied into the processing container12from a gas source selected among the plurality of gas sources of the gas source group40. The processing gas contains an inert gas. In an example, the inert gas may be a noble gas such as Ar gas. Alternatively, the inert gas may be nitrogen gas. The etching of step ST12is performed with a substantially oxygen-free processing gas. By “substantially oxygen-free” is meant that oxygen is not intentionally introduced into the processing gas. Further, in step ST12, the exhaust device50is operated, so that the pressure in the processing container12is set to a predetermined pressure. Furthermore, in step ST12, the high frequency power from the first high frequency power source62is supplied to the lower electrode LE. Further, in step ST12, the high frequency bias power from the first high frequency power source64is supplied to the lower electrode LE.

Hereinafter, various conditions in step ST12are exemplified.Pressure in processing container: 10 mTorr (1.33 Pa) to 50 mTorr (6.65 Pa)Processing gasAr gas: 200 sccm to 1,500 sccmHigh frequency power of first high frequency power source62: 40 MHz, 50 W to 500 WHigh frequency bias power of second high frequency power source64: 13 MHz, 0 W to 50 WDC voltage of power source70: 0 V to −500 V

In step ST12, plasma of the inert gas is generated, and ions are drawn to the wafer W. Then, the first region R1is etched by radicals of the fluorocarbon contained in the deposit DP (seeFIGS.10,13, and16). The operation of each part of the plasma processing apparatus10in the step ST12may be controlled by the controller Cnt.

In method MT, the sequence SQ1is executed in a period including the time when the second region R2is exposed. In step ST11of the sequence SQ1, a deposit DP is formed on the wafer W as illustrated inFIG.8.FIG.8illustrates a state where etching of the first region R1proceeds, the second region R2is exposed, and the deposit DP is formed on the second region R2. The deposit DP protects the second region R2. Then, in step ST11of the sequence SQ1, as illustrated inFIG.9, the amount of the deposit DP formed in the same step ST11is reduced. Then, in step ST12of the sequence SQ1, the first region R1is etched by radicals of the fluorocarbon contained in the deposit DR With this sequence SQ1, the second region R2is exposed, and the first region R1in the recess provided by the second region R2is etched while the second region R2is protected by the deposit DP. As a result, as illustrated inFIG.10, a lower opening LO is gradually formed.

The sequence SQ1is repeated once or more. In an example, the sequence SQ1is repeated30times. Therefore, as illustrated inFIG.1, after execution of step ST12, it is determined whether s stop condition is satisfied in step STa. The stop condition is determined to be satisfied when the sequence SQ1is executed a predetermined number of times. In step STa, when it is determined that the stop condition is not satisfied, the sequence SQ1is executed from step ST11. Meanwhile, when it is determined that the stop condition is satisfied in step STa, a sequence SQ2is subsequently executed. Further, the high frequency bias power of the second high frequency power source64is lowered to 50 W in the first sequence SQ1, and to 20 W in the second sequence. The etching time in the first sequence SQ1is set to 5 seconds, and the etching time in the second sequence SQ2set to a longer time, for example, 10 seconds. Therefore, the effect of suppressing wear of silicon nitride may be obtained in a state where the releasability is maintained.

In step ST11of the sequence SQ2, a deposit DP is formed on the wafer W as illustrated inFIG.11. Then, in step ST11of the sequence SQ1, as illustrated inFIG.12, the amount of the deposit DP formed in the same step ST11is further reduced. Then, in step ST12of the sequence SQ2, the first region R1is etched by radicals of the fluorocarbon contained in the deposit DP. With this sequence SQ1, the first region R1in the recess provided by the second region R2is further etched while the second region R2is protected by the deposit DP. As a result, as illustrated inFIG.13, the depth of the lower opening LO is increased.

In an exemplary embodiment, since the method includes the second step of selectively etching the first region made of silicon oxide by radicals of fluorocarbon, the first region is etched, and the second region made of silicon nitride is suppressed from being worn. Further, in step ST11, the deposit DP is formed by the processing gas containing the fluorocarbon gas, or the plasma of the processing gas containing the fluorocarbon gas and the inert gas. Along with this, in the same step, the amount of the deposit DP on the wafer W is appropriately reduced by the active species of oxygen. Formation of the deposit DP and moderate reduction of the amount of the deposit DP are carried out in the first step, and it is not necessary to switch the processing gas. Thus, it is not necessary to consider the discharge stabilization time accompanying the switching of the processing gas.

Further, in an exemplary embodiment of the method, the etching of the second step is performed with a substantially oxygen-free processing gas. In this method, the selective etching of the first region with respect to the second region is efficiently performed.

The sequence SQ1is repeated once or more. In an example, the sequence SQ1is repeated40times. Therefore, as illustrated inFIG.1, after execution of step ST12, it is determined whether s stop condition is satisfied in step STb. The stop condition is determined when the sequence SQ2is performed a predetermined number of times. In step STb, when it is determined that the stop condition is not satisfied, the sequence SQ2is performed from step ST11. Meanwhile, when it is determined that the stop condition is satisfied in step STb, the execution of the sequence SQ2is subsequently terminated.

In method MT, the processing condition of the sequence SQ1is set such that the amount by which the first region R1is etched in each sequence SQ1is smaller than the amount by which the first region R1is etched in each sequence SQ2. In an example, the execution time length of each sequence SQ1is set to be shorter than the execution time length of each sequence SQ2. In this example, the ratio of the execution time length of step ST11and the execution time length of step ST12in the sequence SQ1may be set similarly to the ratio of the execution time length of step ST11and the execution time length of step ST13in the sequence SQ2. For example, in the sequence SQ1, the execution time length of step ST11is selected in a range of 2 seconds to 5 seconds, and the execution time length of step ST12is selected in a range of 5 seconds to 10 seconds. Further, in the sequence SQ2, the execution time length of step ST11is selected in a range of 2 seconds to 10 seconds, and the execution time length of step ST12is selected in a range of 5 seconds to 20 seconds.

The active species of the fluorocarbon produced in step ST11is deposited on the second region R2and protects the second region R2. However, when the first region R1is etched so that the second region R2is exposed, the active species may etch the second region R2. Therefore, in method MT, the sequence SQ1is executed once or more during the period in which the second region R2is exposed. Accordingly, the deposit DP is formed on the wafer W while the etching amount is suppressed, and the second region R2is protected by the deposit DP. Thereafter, the sequence SQ2having a large etching amount is executed once or more. Thus, according to method MT, it is possible to etch the first region R1while suppressing wear of the second region R2.

Further, since the deposit DP has already been formed on the second region R2in the sequence SQ1, the wear of the second region R2may be suppressed even when the etching amount in each sequence SQ2is increased. As described above, by increasing the etching amount of each sequence SQ2more than the etching amount of each sequence SQ1, the etching rate of the first region R1in method MT may be improved.

In method MT of an exemplary embodiment, after the execution of sequence SQ2, a sequence SQ3may be further executed as necessary. In step ST11of the sequence SQ3, a deposit DP is formed on the wafer W as illustrated inFIG.14. Then, in step ST11of the sequence SQ3, as illustrated inFIG.15, the amount of the deposit DP formed in the same step ST11is reduced. Then, in step ST12of the sequence SQ3, the first region R1is etched by radicals of the fluorocarbon contained in the deposit DP. With this sequence SQ3, the first region R1in the recess provided by the second region R2is further etched while the second region R2is protected by the deposit DR As a result, as illustrated inFIG.16, the depth of the lower opening LO is further increased, and finally, as illustrated inFIG.16, the first region R1is etched until the second region R2present on the bottom of the recess is exposed.

The sequence SQ3is repeated once or more. Therefore, as illustrated inFIG.1, after execution of step ST12, it is determined whether s stop condition is satisfied in step STc. The stop condition is determined to be satisfied when the sequence SQ3is executed a predetermined number of times. In step STc, when it is determined that the stop condition is not satisfied, the sequence SQ3is executed from step ST11. Meanwhile, in step STc, when it is determined that the stop condition is satisfied, the performance of method MT is ended.

In step ST12of the sequence SQ3, the high-frequency bias power is set to be greater than the high-frequency bias power used in step ST12of the sequence SQ1and the sequence SQ2. For example, in step ST12of the sequence SQ1and the sequence SQ2, the high frequency bias power is set to 20 W to 100 W, and in step ST12of the sequence SQ3, the high frequency bias power is set to 100 W to 300 W. Further, in the sequence SQ2in an example, the execution time length of step ST11is selected in a range of 3 seconds to 10 seconds, and the execution time length of step ST12is selected in a range of 5 seconds to 15 seconds.

As illustrated inFIG.14, after execution of the sequence SQ1and the sequence SQ2, the amount of the deposit DP on the wafer W considerably increases. When the amount of the deposit DP increases, the width of the opening MO, the width of the upper opening UO, and the width of the lower opening LO are narrowed by the deposit DP. As a result, there is a possibility that the flux of ions reaching the deep portion of the lower opening LO becomes insufficient. However, since the high frequency bias used in step ST13of the sequence SQ3is relatively high, the energy of ions drawn into the wafer W is increased. As a result, even though the lower opening LO is deep, it is possible to supply ions to the deep portion of the lower opening LO.

FIGS.17A to17Care cross-sectional views illustrating a first region and a second region of a workpiece according to an exemplary embodiment, andFIGS.17A to17Cillustrate a technique of selectively etching the first region with respect to the second region.FIG.17Aillustrates a wafer W1on which a first region R1and a second region R2are formed on a substrate SB.FIG.17Billustrates a cross-sectional view of the wafer W1after step ST11is executed, andFIG.17Cillustrates a cross-sectional view of the wafer W1after step ST12is executed. The first region R1is made of silicon oxide (SiO2), and the second region R2is made of silicon nitride (Si3N4). Various conditions such as pressures inside the processing container in step ST11and step ST12may be the same as the conditions described above.

As illustrated inFIG.17B, when the step ST11is executed on the wafer W1, a deposit DP is formed on the first region R1and the second region R2by plasma of a processing gas containing a fluorocarbon gas and oxygen gas. In an example, C4F6gas is used as the fluorocarbon gas. A noble gas such as Ar gas may be contained in the processing gas of step ST11. In step ST11, since active species of oxygen are additionally contained in the processing gas, the amount of the deposit DP on the wafer W is appropriately reduced by the active species of the oxygen.

As illustrated inFIG.17C, when step ST12is executed on the wafer W1, the wafer W after the processing of step ST11is exposed to plasma of the noble gas, The noble gas includes, for example, Ar. After the processing of step ST12, the first region R1is etched by radicals of the fluorocarbon contained in the deposit DP.

In step ST12, active species of the noble gas atoms, for example, ions of Ar gas atoms collide with the deposit DP. Therefore, as illustrated inFIG.17C, the fluorocarbon radicals in the deposit DP advance the etching of the first region R1and reduce the thickness of the first region R1. Further, in the first region R1, the film thickness of the deposit DP decreases. Meanwhile, in the second region R2, the film thickness of the deposit DP decreases, but the etching of the second region R2is suppressed. Thus, the amount of decrease in the thickness of the second region R2is significantly smaller than the amount of decrease in the thickness of the first region R1.

DESCRIPTION OF SYMBOLS

10: plasma processing apparatus,12: processing container,30: upper electrode, PD: placing table, LE: lower electrode, ESC: electrostatic chuck,40: gas source group,42: valve group,44: flow rate controller group,50: exhaust device,62: first high frequency power source,64: second high frequency power source, Cnt: controller, W: wafer, W1: wafer, R1: first region, R2: second region, OL: organic film, AL: silicon-containing antireflection film, MK: mask, DP: deposit