JP2020025070A - Etching method and etching device - Google Patents

Abstract

To provide an etching method and an etching device capable of uniformly etching SiN or Si formed on an inner surface of a fine concave portion.SOLUTION: An etching method includes a step of providing, in a processing vessel, a substrate having a concave portion and an etching target portion made of SiN or Si on the inner surface of the concave portion, a step of performing an oxygen-containing plasma treatment on the substrate in the processing vessel, and preferentially modifying the surface of the etching target portion at the top of the concave portion, and then a step of isotropically dry-etching the etching target portion.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an etching method and an etching apparatus.

  Recently, miniaturization etching has been performed in the process of manufacturing semiconductor devices. For example, a technique for isotropically etching SiN or Si on the inner surface of a groove or hole having a high aspect ratio is required.

As a technique for etching SiN, as described in Patent Literature 1, a technique is known in which a fluorine-containing gas such as NF ₃ gas is turned into plasma, and SiN is etched by fluorine radicals and fluorine ions. Patent Literature 1 discloses that SiN can be etched while suppressing etching of SiO ₂ when the fluorine-containing gas contains an oxygen source such as O ₂ gas.

JP 2014-508424 A

  The present disclosure provides an etching method and an etching apparatus capable of uniformly etching SiN or Si formed on an inner surface of a fine concave portion.

  An etching method according to one embodiment of the present disclosure includes a step of providing a substrate having a concave portion and an etching target portion made of SiN or Si on the inner surface of the concave portion in a processing container; A step of performing a containing plasma treatment to preferentially modify the surface of the etching target portion at the top of the recess, and then a step of isotropically dry-etching the etching target portion.

  According to the present disclosure, SiN or Si formed on the inner surface of the concave portion can be uniformly etched.

9 is a flowchart illustrating an etching method according to a specific embodiment. FIG. 3 is a cross-sectional view illustrating an example of a structure of a substrate on which etching is performed. FIG. 3 is a cross-sectional view showing an ideal state when the substrate of FIG. 2 is etched. It is sectional drawing which shows the other example of the structure of the board | substrate in which etching is performed. FIG. 5 is a cross-sectional view showing an ideal state when the substrate of FIG. 4 is etched. FIG. 3 is a cross-sectional view showing a state when the substrate having the structure of FIG. 2 is isotropically etched as it is. FIG. 4 is a diagram showing a concentration distribution of F radicals when performing isotropic dry etching of SiN. FIG. 3 is a diagram illustrating a concentration distribution of O radicals when an oxygen-containing plasma treatment is performed in one embodiment. FIG. 9 is a diagram for explaining the operation of the oxygen-containing plasma treatment when a damaged layer containing carbon is formed on the surface of the portion to be etched. FIG. 1 is a partial cross-sectional plan view schematically illustrating an example of a processing system used for an etching method according to an embodiment. FIG. 11 is a cross-sectional view schematically showing an example of a process module mounted on the processing system of FIG. 10 and functioning as an etching apparatus for performing the etching method of the present embodiment. FIG. 9 is a diagram for explaining an effect in Experimental Example 2.

  Hereinafter, embodiments will be described with reference to the accompanying drawings.

<History and overview>
First, the history and outline of the etching method according to the embodiment of the present disclosure will be described.
For example, in an ONON laminated structure in which a silicon oxide film (SiO ₂ film) and a silicon nitride film (SiN film) are laminated in a 3D-NAND type nonvolatile semiconductor device, a groove formed in the laminating direction is formed. There is a step of isotropically dry-etching SiN.

  In such an ONON laminated structure, since the groove formed has a thickness of 1 μm or more and has a high aspect ratio, SiN at the top of the groove is preferentially etched by a loading effect. Would. For this reason, it is required to suppress the etching of SiN at the top of the groove and to perform etching with the same amount of etching at the top of the groove and the bottom of the groove.

  In some cases, the SiN formed on the entire inner surface of the groove having such a high aspect ratio is etched. In this case, however, the SiN at the groove top is preferentially etched by the loading effect.

  Furthermore, Si may be present on the inner surface of the groove having a high aspect ratio, and the same problem occurs when the Si is etched. Further, such a problem occurs not only in the groove but also in the hole.

  Therefore, in one embodiment, a substrate having a concave portion and an etching target portion made of SiN or Si on the inner surface of the concave portion is provided in a processing container, and the substrate is subjected to oxygen-containing plasma processing in the processing container. The surface of the etching target portion at the top of the concave portion is preferentially modified, and then the etching target portion is isotropically dry-etched.

  Thereby, the etching target portion is relatively harder to be etched in the recess top portion than in other portions, and the loading effect is reduced, so that the etching target portion on the inner surface of the recess can be uniformly etched.

<Specific embodiment>
Next, a specific embodiment will be described.
FIG. 1 is a flowchart illustrating an etching method according to a specific embodiment.
First, a substrate having a concave portion and having an etching target portion made of SiN or Si on the inner surface of the concave portion is provided in a processing container (step 1). Next, oxygen-containing plasma processing is performed on the substrate in the processing chamber to preferentially modify the surface of the etching target portion at the top of the concave portion (step 2). Next, the portion to be etched is dry-etched isotropically (step 3). Steps 2 and 3 may be repeated.

Although the substrate is not particularly limited, a semiconductor wafer typified by a silicon wafer is exemplified. The SiN or Si forming the etching target portion is typically a film. The SiN film is formed using, for example, a silane-based gas such as SiH ₄ gas, SiH ₂ Cl ₂ or Si ₂ Cl ₆ as a Si precursor, and a nitrogen-containing gas such as an NH ₃ gas, an N ₂ gas, or a hydrazine-based compound gas. , Thermal CVD, plasma CVD, ALD or the like. The Si film is formed by thermal CVD using a silane-based gas such as a SiH ₄ gas or a Si ₂ H ₆ gas as a Si precursor, for example. The Si film may be doped with B, P, C, As, or the like.

  The recess formed in the substrate may be a groove or a hole. As the width of the groove or the diameter of the hole is smaller and the aspect ratio of the concave portion is larger, the loading effect is larger, so that the effect of the present embodiment is easily exerted. The width of the groove and the diameter of the hole are preferably 300 nm or less, and the aspect ratio of the recess is preferably 25 or more.

  FIG. 2 is a cross-sectional view showing an example of the structure of a substrate on which etching is performed, showing a semiconductor wafer (hereinafter simply referred to as a wafer) on which an ONON laminated structure for a 3D-NAND type nonvolatile semiconductor device is formed. It is.

In this example, the wafer W has a laminated structure 102 of a SiO ₂ film 111 and a SiN film 112 on a silicon substrate 100 via a lower structure 101. The number of stacked layers of the SiO ₂ film 111 and the SiN film 112 is actually about 100 layers. A groove (slit) 103 penetrating in the laminating direction is formed in the laminated structure part 102, and a slit SiN film 113 is formed on the entire inner surface of the groove 103.

  From this state, the entirety of the slit SiN film 113 formed on the entire inner surface of the groove 103 and a part of the SiN film 112 of the laminated structure portion 102 are collectively and isotropically etched. To the state shown in.

FIG. 4 is a cross-sectional view showing another example of the structure of the substrate on which etching is performed, and shows a wafer on which the same ONON laminated structure for a 3D-NAND type nonvolatile semiconductor device is formed. This is a case where the slit SiN film 113 does not exist on the inner surface of the groove 103. That is, the case where the SiO ₂ film 111 and the SiN film 112 constituting the ONON laminated structure exist on the inner surface of the groove 103.

  Also in the case of this example, a part of the SiN film 112 of the laminated structure portion 102 is isotropically etched from the state of FIG. 4, and ideally the state shown in FIG. 5 is obtained.

  However, when SiN is isotropically etched as it is in the wafer W having the structure shown in FIG. 2, actually, as shown in FIG. 6, SiN at the top of the groove 103 is preferentially etched by the loading effect. In addition, the etching of the SiN at the top and bottom of the groove 103 becomes non-uniform. The same applies to the wafer W having the structure shown in FIG.

  This is because when performing isotropic dry etching of SiN, the concentration of F radicals generally used as an etchant is higher at the top portion than at the bottom portion of the groove 103 as shown in FIG. .

  Such a phenomenon is caused not only when the slit SiN or the laminated SiN having the ONON laminated structure described above is etched, but also when only the SiN formed on the entire inner surface of the groove or the hole is etched or the Si is etched. The case also occurs.

  Therefore, in the present embodiment, prior to the etching of SiN or Si as an etching target portion, an oxygen-containing plasma treatment is performed to modify the surface of the etching target portion.

  By performing the oxygen-containing plasma treatment, oxygen radicals (O radicals) in the plasma act on the portion to be etched (SiN or Si), and the surface of the portion to be etched is oxidized to form the modified layer 120. With such a modified layer 120, etching becomes relatively difficult. At this time, as shown in FIG. 8, the concentration of O radicals is higher at the top of the recess (groove) 103 and lower at the bottom thereof. The thickness of the modified layer 120 is greater at the top of the concave portion.

  Therefore, by the oxygen-containing plasma treatment, the amount of etching at the top of the concave portion of the portion to be etched can be relatively suppressed. Thereby, the difference between the etching amount of the concave top portion and the etching amount of the concave bottom portion can be suppressed, and more uniform etching can be realized.

  In some cases, a damaged layer containing carbon is formed on the surface of the portion to be etched, and such a damaged layer hinders etching. In such a case, by performing the oxygen-containing plasma treatment, carbon can be removed as CO from the damaged layer 130 on the surface of the slit SiN film 113, for example, as shown in FIG. The amount of etching can be increased.

  Therefore, when a damaged layer containing carbon is formed on the surface of the etching target portion, the effect of relatively suppressing the etching amount of the concave top portion of the etching target portion by the oxygen-containing plasma treatment and the damage Both effects of removing carbon from the layer and increasing the amount of etching are exhibited. Therefore, by subjecting the etching target portion on which the damaged layer is formed to the oxygen-containing plasma treatment and then performing dry etching, the etching amount of the concave top portion and the etching of the concave bottom portion are increased while increasing the etching amount of the entire etching target portion. The difference with the amount can be suppressed.

In the oxygen-containing plasma treatment in step 2, the oxygen-containing plasma is applied to the substrate housed in the processing container. In the oxygen-containing plasma treatment at this time, it is preferable to cause mainly oxygen radicals (O radicals) in the plasma to act, and for that purpose, it is preferable to use remote plasma. The remote plasma generates oxygen-containing plasma in a plasma generation space separate from the processing space in which the substrate is arranged, and transports the plasma to the processing space. At this time, oxygen ions (O ₂ ions) in the oxygen-containing plasma are easily deactivated during transportation, and mainly O radicals are supplied to the processing space. By performing the treatment mainly using O radicals, damage to the substrate can be reduced. The plasma source at this time is not particularly limited, and inductively coupled plasma, microwave plasma, or the like can be used.

The gas used at this time may be O ₂ gas alone, or at least one of H ₂ gas and rare gas may be added to O ₂ gas. By adding H ₂ gas, the oxidizing ability can be increased. Further, the plasma can be stabilized by adding a rare gas. The rare gas is not particularly limited, but Ar gas is preferable. The pressure at this time is preferably from 1 to 3000 mTorr (0.13 to 400 Pa). By setting the content within this range, the effect of suppressing etching at the top of the concave portion can be further enhanced.

In step 2, the flow rate of each gas is appropriately set according to the device. Further, the ratio H ₂ / O ₂ of the H ₂ gas flow rate to the O ₂ gas flow rate is preferably 1 or less. The plasma generation power also depends on the apparatus, but is preferably 50 to 950 W. The time of Step 2 is preferably 10 to 180 seconds, and the substrate temperature is preferably 5 to 85 ° C. More preferably, it is 15 to 85 ° C.

The step of isotropically dry-etching the portion to be etched in step 3 is preferably capable of selectively etching SiN or Si with respect to another material such as SiO ₂ , and is preferably performed using a fluorine-containing gas. . This dry etching may be plasma treatment or gas etching without plasma, but treatment using plasma is preferred, and treatment mainly using fluorine radicals (F radicals) using remote plasma is more preferred. In remote plasma, fluorine-containing plasma is generated in a plasma generation space separate from a processing space in which a substrate is arranged, and the plasma is transferred to the processing space. At this time, fluorine ions (F ions) in the plasma are easily deactivated during transportation, and mainly fluorine radicals (F radicals) are supplied to the processing space. By performing a process mainly using F radicals, damage to the substrate can be reduced. The plasma source at this time is not particularly limited, and inductively coupled plasma, microwave plasma, or the like can be used.

  In the etching step of Step 3, as described above, since the modified layer is formed thick at the top of the concave portion by the oxygen-containing plasma treatment, the difference in the etching amount between the top of the concave portion and the bottom of the concave portion is suppressed. You. When a damaged layer containing carbon is formed on the surface of the etching target portion, the etching amount of the etching target portion of the entire concave portion is increased by the oxygen-containing plasma treatment, and the etching amount of the concave top portion and the concave bottom portion are increased. Can be suppressed from being different from the etching amount.

The fluorine-containing gases include HF, the NF _3. Of these, NF ₃ gas is preferred. Although NF ₃ gas or the like may be used alone, O ₂ gas may be added to NF ₃ gas or the like. By adding the O ₂ gas, a reforming effect (oxidizing effect) of the top of the concave portion by O radicals can be obtained even during etching. Further, a rare gas may be added to the NF ₃ gas or the like. By adding a rare gas, plasma can be stabilized. The rare gas is not particularly limited, but Ar gas is preferable. An NF ₃ gas or the like, an O ₂ gas, and a rare gas may be used. The pressure is preferably 1 to 3000 mTorr (0.13 to 400 Pa). Within this range, the effect of suppressing the difference between the amount of etching at the top of the recess and the amount of etching at the bottom of the recess can be further enhanced. At this time, the flow rate of each gas is appropriately set according to the device. When adding O ₂ gas, the ratio NF ₃ / O ₂ of the flow rate of NF ₃ gas or the like to the flow rate of O ₂ gas is preferably 0.01 or more. Further, the plasma generation power is preferably in the range of 50 to 950 W. Further, the substrate temperature is preferably in the range of 5 to 85 ° C. More preferably, it is 15 to 85 ° C. The time of step 3 is appropriately set according to the etching amount of the etching target portion.

  The oxygen-containing plasma treatment in step 2 and the isotropic dry etching in step 3 are preferably performed in the same processing vessel. Thereby, a high throughput can be maintained. For example, using the same remote plasma device, both Step 2 and Step 3 can be performed by radical processing.

  As described above, step 2 and step 3 may be repeated. Depending on the amount to be etched of the portion to be etched, there is a case where the reforming effect is not sufficient by one oxygen-containing plasma treatment. In such a case, a sufficient reforming effect can be obtained by appropriately repeating Step 2 and Step 3.

<Example of processing system>
Next, an example of a processing system used for the etching method of the present embodiment will be described. FIG. 10 is a partial cross-sectional plan view schematically showing an example of a processing system used for the etching method of the present embodiment.

  As shown in FIG. 10, the processing system 10 includes a loading / unloading unit 11 for storing a plurality of wafers W and loading / unloading the wafers W, a transfer module 12 as a transfer chamber for simultaneously transferring two wafers W, A plurality of process modules 13 are provided for performing a SiN film etching process and a heating process on a wafer W, which is a substrate carried in from the transfer module 12. The inside of each process module 13 and the transfer module 12 is maintained in a vacuum atmosphere.

  In the processing system 10, the wafer W stored in the loading / unloading section 11 is transported by the transport arm 14 built in the transfer module 12, and one wafer is transferred to each of the two stages 15 arranged inside the process module 13. Place W. Next, in the processing system 10, after performing the SiN film etching process or the heating process on each wafer W mounted on the stage 15 by the process module 13, the processed wafer W is unloaded to the loading / unloading unit 11 by the transfer arm 14. I do.

  The loading / unloading unit 11 receives the stored wafers W from the FOUPs 16 mounted on the load ports 17 and the plurality of load ports 17 as a mounting table of the FOUP 16 which is a container for storing the plurality of wafers W, or A loader module 18 for transferring the wafer W on which a predetermined process has been performed by the process module 13 to the FOUP 16, and two loads for temporarily holding the wafer W for transferring the wafer W between the loader module 18 and the transfer module 12 It has a lock module 19 and a cooling storage 20 for cooling the wafer W subjected to the heat treatment.

  The loader module 18 has a rectangular housing with an atmospheric pressure atmosphere inside, and a plurality of load ports 17 are juxtaposed on one side forming a long side of the rectangle. Further, the loader module 18 has a transfer arm (not shown) movable inside the rectangular longitudinal direction inside. The transfer arm loads the wafer W from the FOUP 16 placed on each load port 17 to the load lock module 19 or unloads the wafer W from the load lock module 19 to each FOUP 16.

  Each load lock module 19 temporarily holds the wafer W in order to transfer the wafer W stored in the FOUP 16 placed on each load port 17 in the atmospheric pressure atmosphere to the process module 13 in the vacuum atmosphere. Each load lock module 19 has a buffer plate 21 for holding two wafers W. Each load lock module 19 has a gate valve 22a for ensuring airtightness with respect to the loader module 18 and a gate valve 22b for ensuring airtightness with respect to the transfer module 12. Further, a gas introduction system and a gas exhaust system (not shown) are connected to the load lock module 19 by piping, so that the inside can be switched between an atmospheric pressure atmosphere and a vacuum atmosphere.

  The transfer module 12 loads an unprocessed wafer W from the loading / unloading section 11 to the process module 13, and unloads a processed wafer W from the process module 13 to the loading / unloading section 11. The transfer module 12 has a rectangular housing with a vacuum atmosphere inside, and has two transfer arms 14 that hold and move two wafers W, a turntable 23 that rotatably supports each transfer arm 14, It includes a rotary mounting table 24 on which the table 23 is mounted, and a guide rail 25 for guiding the rotary mounting table 24 movably in the longitudinal direction of the transfer module 12. Further, the transfer module 12 is connected to the load lock module 19 of the loading / unloading section 11 and each of the process modules 13 via gate valves 22a and 22b, and gate valves 26 described later. In the transfer module 12, the transfer arm 14 transfers two wafers W from the load lock module 19 to each process module 13, and transfers the processed two wafers W from each process module 13 to another process module 13. Or to the load lock module 19.

  In the processing system 10, each of the process modules 13 performs etching of SiN or Si, which is an etching target, or heat processing. That is, a predetermined number of the six process modules 13 is used for etching, and the remainder is used for heat treatment for removing residues after etching. The number of the process modules 13 for the etching and the process modules 13 for the heat treatment are appropriately determined according to the respective processing times.

  The processing system 10 has a control unit 27. The control unit 27 includes a main control unit having a CPU for controlling the operation of each component of the processing system 10, an input device (keyboard, mouse, etc.), an output device (printer, etc.), a display device (display, etc.), and a storage device. (Storage medium). The main control unit of the control unit 27 causes the processing system 10 to execute a predetermined operation based on a processing recipe stored in a storage medium built in the storage device or a storage medium set in the storage device, for example.

<Etching equipment>
Next, an example of the process module 13 mounted on the processing system 10 and functioning as an etching apparatus for performing the etching method of the present embodiment will be described. FIG. 11 is a sectional view schematically showing an example of the process module 13 functioning as an etching device in the processing system of FIG.

  As shown in FIG. 11, the process module 13 functioning as an etching device includes a processing container 28 having a closed structure that accommodates the wafer W. The processing container 28 is made of, for example, aluminum or an aluminum alloy, and has an upper end opened, and the upper end of the processing container 28 is closed with a lid 29 serving as a ceiling. A loading / unloading port 30 for the wafer W is provided on the side wall 28a of the processing container 28, and the loading / unloading port 30 can be opened and closed by the gate valve 26 described above.

  As described above, two stages 15 (only one is shown) on which one wafer W is mounted in a horizontal state are arranged at the bottom inside the processing container 28. The stage 15 has a substantially columnar shape, and includes a mounting plate 34 on which the wafer W is directly mounted, and a base block 35 that supports the mounting plate 34. A temperature adjustment mechanism 36 for adjusting the temperature of the wafer W is provided inside the mounting plate 34. The temperature control mechanism 36 has, for example, a pipe (not shown) through which a temperature control medium (for example, water or Galden) circulates, and performs heat exchange between the wafer W and the temperature control medium flowing in the pipe. Thus, the temperature of the wafer W is adjusted. The stage 15 is provided with a plurality of elevating pins (not shown) used to carry the wafer W into and out of the processing container 28 so as to be able to protrude and retract from the upper surface of the mounting plate 34.

The interior of the processing vessel 28 is partitioned by a partition plate 37 into an upper plasma generation space P and a lower processing space S. The partition plate 37 functions as a so-called ion trap that suppresses transmission of ions in the plasma from the plasma generation space P to the processing space S when inductively coupled plasma is generated in the plasma generation space P. The plasma generation space P is a space where plasma is generated, and the processing space S is a space where the wafer W is etched by radical processing. Outside the processing container 28, a first gas supply unit 61 that supplies a processing gas used for etching to the plasma generation space P, and a non-plasmaized gas such as a pressure control gas, a purge gas, or a dilution gas, for example, N ₂ gas or A second gas supply unit 62 that supplies an inert gas such as an Ar gas to the processing space S is provided. An exhaust mechanism 39 is connected to the bottom of the processing container 28. The exhaust mechanism 39 has a vacuum pump and exhausts the inside of the processing space S.

  A heat shield plate 48 is provided below the partition plate 37 so as to face the wafer W. The heat shield plate 48 is for suppressing heat from affecting the radical distribution in the processing space S because heat is accumulated in the partition plate 37 by repeatedly generating plasma in the plasma generation space P. is there. The heat shield plate 48 is formed larger than the plate member 44 of the partition plate 37, and a flange portion 48 a forming a peripheral portion is buried in the side wall portion 28 a of the processing container 28. The cooling mechanism 50, for example, a coolant channel, a chiller or a Peltier element is embedded in the flange portion 48a.

The first gas supply unit 61 supplies O ₂ gas, H ₂ gas, NF ₃ gas, and a rare gas, for example, Ar gas, to the plasma generation space P. These gases are turned into plasma in the plasma generation space P. The rare gas functions as a plasma generating gas, but also functions as a pressure adjusting gas, a purge gas, and the like.

  The process module 13 is configured as an inductively coupled plasma etching apparatus using an RF antenna. The lid 29 serving as the ceiling of the processing container 28 is formed of, for example, a circular quartz plate and is configured as a dielectric window. An annular RF antenna 40 for generating inductively coupled plasma in the plasma generation space P of the processing container 28 is formed on the lid 29, and the RF antenna 40 is connected to a high frequency power supply 42 via a matching unit 41. ing. The high frequency power supply 42 outputs a high frequency power of a predetermined frequency (for example, 13.56 MHz or more) suitable for generating plasma by inductively coupled high frequency discharge at a predetermined output value. The matching device 41 has a variable reactance matching circuit (not shown) for matching the impedance on the high frequency power supply 42 side with the impedance on the load (RF antenna 40 or plasma) side.

  Although not shown in detail in the process module 13 that functions as a heat treatment device for performing a heat treatment, two stages 15 are arranged in a treatment container as in the etching device shown in FIG. However, unlike an etching apparatus, it does not have a plasma generation mechanism, and supplies a wafer W placed on the stage 15 by a heater provided in the stage 15 while supplying an inert gas into the processing container. It is configured to heat to a predetermined temperature, and by heating the etched wafer W, an etching residue or a reaction product on the wafer W is removed.

  When the etching method according to the embodiment is performed by the processing system 10, first, the transfer arm of the loader module 18 takes out the wafer W having the structure shown in FIG. It is carried into the module 19. After the load lock module 19 is evacuated, the wafer W in the load lock module 19 is carried into the process module 13 functioning as an etching device by the transfer arm 14 of the transfer module 12 (Step 1).

Next, from the second gas supply unit 62, for example, N ₂ gas is introduced into the processing container 28 as a pressure regulating gas, and the pressure in the processing container 28 is adjusted to, for example, 1000 to 4000 mTorr (133 to 533 Pa) while the temperature is adjusted. The wafer W is held for a predetermined time, for example, 30 seconds, on the stage 15 whose temperature is controlled to 5 to 85 ° C. by the mechanism 36, and the wafer temperature is stabilized at the predetermined temperature.

Next, after purging the inside of the processing container 28, the pressure in the processing container 28 is preferably set to 1 to 3000 mTorr (0.13 to 400 Pa), for example, 500 mTorr (66.5 Pa), and the oxygen-containing plasma treatment in step 2 is performed. Do. In the oxygen-containing plasma processing, the O ₂ gas is supplied from the first gas supply unit 61 to the plasma generation space P, and high-frequency power is supplied to the RF antenna 40 to generate O ₂ plasma which is inductively coupled plasma. At this time, in addition to the O ₂ gas, at least one of a rare gas such as an H ₂ gas and an Ar gas may be supplied.

The O ₂ plasma generated in the plasma generation space P is transferred to the processing space S. At this time, O ₂ ions are deactivated in the partition plate 37, and mainly O radicals in the O ₂ plasma are selectively introduced into the processing space S. Due to the O radicals, a modification process (oxidation process) is performed on a portion to be etched of the wafer W. At this time, since the concentration of O radicals is higher in the concave top portion, the concave top portion on the surface to be etched is preferentially modified, and the thickness of the modified layer that is relatively difficult to etch is larger in the concave top portion. It gets thicker. For this reason, in the subsequent etching, the etching amount of the concave top portion of the etching target portion can be relatively suppressed as compared with other portions. Thereby, the difference between the etching amount of the concave top portion and the etching amount of the concave bottom portion can be suppressed, and more uniform etching can be realized. In addition, since the processing is mainly for O radicals, ion damage to the wafer W is small.

  When a damaged layer containing carbon is formed on the surface of the portion to be etched, carbon can be removed as CO from the damaged layer on the surface of the portion to be etched by performing the oxygen-containing plasma treatment. For this reason, in the next etching step, the etching amount of the etching target portion in the entire concave portion can be increased.

  Due to the synergistic effect of this effect and the effect of relatively suppressing the etching amount of the concave top portion of the etching target portion by forming the modified layer, after etching, while increasing the etching amount of the entire etching target portion of the concave portion, The difference between the etching amount of the concave top portion and the etching amount of the concave bottom portion can be suppressed.

At this time, the gas flow rates are preferably O ₂ gas flow rate: 1 to 1000 sccm, H ₂ gas flow rate: 1 to 500 sccm, and rare gas (Ar gas) flow rate: 1 to 1500 sccm. Further, the plasma generation power is preferably 50 to 950 W. The processing time is preferably from 10 to 180 seconds.

  After the oxygen-containing plasma processing as described above, the purging of the processing container 28 is performed, and the etching gas is discharged from the processing space S.

Next, the pressure in the processing container 28 is preferably set to 1 to 3000 mTorr (0.13 to 400 Pa), for example, 225 mTorr (30 Pa), and the isotropic dry etching of Step 3 is performed. In the isotropic dry etching, the NF ₃ gas, which is a fluorine-containing gas, is supplied from the first gas supply unit 61 to the plasma generation space P, and the RF antenna 40 is supplied with high-frequency power to supply the RF antenna 40 with the fluorine-containing inductively coupled plasma. Generates plasma. At this time, in addition to the NF ₃ gas, at least one of rare gases such as O ₂ gas and Ar gas may be supplied.

  The fluorine-containing plasma generated in the plasma generation space P is transported to the processing space S. At this time, F ions are deactivated in the partition plate 37, and mainly F radicals in the plasma are selectively introduced into the processing space S. With the F radical, the SiN film or the Si film, which is the etching target portion, is isotropically etched. At this time, as described above, since the oxygen-containing plasma treatment forms a thicker modified layer in the portion to be etched at the top of the recess where the O radical concentration is high, the difference in etching amount between the top of the recess and the bottom of the recess is increased. Is suppressed. Further, when a damage layer containing carbon is formed on the surface of the etching target portion, the etching amount of the etching target portion of the entire concave portion is increased by the oxygen-containing plasma treatment, and the etching amount of the concave top portion and the concave bottom portion are increased. Can be suppressed from being different from the etching amount.

In addition, by adding O ₂ gas to NF ₃ gas at the time of etching, a reforming effect (oxidation effect) of the top of the concave portion by O radicals can be obtained at the time of etching. To obtain this effect, the ratio NF ₃ / O ₂ of the NF ₃ gas flow rate to the O ₂ gas flow rate is preferably 0.01 or more. The gas flow rate is preferably NF ₃ gas flow rate: 1 to 1000 sccm, O ₂ gas flow rate: 1 to 1000 sccm, and rare gas (Ar gas) flow rate: 1 to 1500 sccm. Further, the plasma generation power is preferably in the range of 50 to 950 W. Further, the processing time is appropriately set according to the etching amount.

  Depending on the amount of the portion to be etched to be etched, there is a case where the reforming effect is not sufficient by one oxygen-containing plasma treatment. In such a case, the above steps 2 and 3 are repeated a predetermined number of times.

  After the etching, the inside of the processing container 28 is purged, and the processed wafer W is unloaded from the processing container 28 by the transfer arm 14 built in the transfer module 12. When heat treatment for removing residues after etching is necessary, the wafer W after etching is transferred to the process module 13 functioning as a heating device by the transfer arm 14, and heat treatment is performed. After the etching process or the heating process is completed, the wafer W is transferred to the load lock module 19 by the transfer arm 14 and the load lock module 19 is set to the atmosphere, and then the transfer arm of the loader module 18 is used. Is returned to the FOUP 16.

  With the processing system 10 as described above, the oxygen-containing plasma processing of the portion to be etched and the isotropic dry etching processing can be continuously performed in the same processing vessel, so that the processing can be performed with high throughput. it can.

  <Example of experiment>

Hereinafter, experimental examples will be described.
[Experimental example 1]
Here, using a process module 13 functioning as an etching apparatus of the processing system 10 shown in FIGS. 10 to 11 above, a wafer having the structure of FIG. Etching was performed.

In case A, only isotropic etching was performed using NF ₃ gas, Ar gas, and O ₂ gas without performing oxygen-containing plasma processing. The conditions at this time were as follows.
Pressure: 150 to 300 mTorr (20 to 40 Pa)
Gas flow rate: NF ₃ = 1 to 100 sccm
O ₂ : 1 to 400 sccm
Ar gas = 1-200 sccm
Stage (mounting plate) temperature: 5 to 60 ° C
Time: 480 sec
High frequency power: 400-800W

In case B, oxygen-containing plasma processing was performed using O ₂ gas, H ₂ gas, and Ar gas, and then isotropic etching processing was performed using NF ₃ gas, Ar gas, and O ₂ gas. The conditions at this time were as follows.
-Oxygen-containing plasma treatment Pressure: 400 to 600 mTorr (53.2 to 79.8 Pa)
Gas flow rate: O ₂ = 200 to 400 sccm
H ₂ = 1 to 100 sccm
Ar = 1-100 sccm
Stage (mounting plate) temperature: 5 to 60 ° C
Time: 60 sec
High frequency power: 400-800W
・ Etching treatment Same as Case A

In case C, as in case B, an isotropic etching process is performed after the oxidizing plasma process, and the O ₂ gas flow rate during the oxygen-containing plasma process is increased as compared with the case B, so that the total gas in the isotropic etching process is increased. The flow rate was increased over Case B. The conditions at this time were as follows.

-Oxygen-containing plasma treatment Pressure: 400 to 600 mTorr (53.2 to 79.8 Pa)
Gas flow rate: O ₂ = 500-700 sccm
H ₂ = 1 to 100 sccm
Ar = 1-100 sccm
Stage (mounting plate) temperature: 5 to 60 ° C
Time: 60 sec
High frequency power: 400-800W
-Etching pressure: 150-300 mTorr (20-40 Pa)
Gas flow rate: NF ₃ = 1 to 100 sccm
O ₂ : 100 to 400 sccm
Ar gas = 50-250 sccm
Stage (mounting plate) temperature: 5 to 60 ° C
Time: 480 sec
High frequency power: 400-800W

At four points (top, middle 1, middle 2, bottom) in the groove (slit) depth direction after etching in cases A to C, the etching amount of the laminated SiN and the difference between the etching amounts of the top and bottom (ΔEA) I asked. The results are shown below.
・ Case A
Top: 21.8 nm
Middle 1: 19.8 nm
Middle 2: 17.2 nm
Bottom: 11.2 nm
ΔEA: 10.6 nm
・ Case B
Top: 25.1 nm
Middle 1: 25.1 nm
Middle 2: 21.2 nm
Bottom: 21.2nm
ΔEA: 3.9 nm
・ Case C
Top: 20.5 nm
Middle 1: 20.5 nm
Middle 2: 20.6 nm
Bottom: 19.8 nm
ΔEA: 0.7 nm

From the above results, a comparison between Case A in which the oxygen-containing plasma treatment was not performed and Case B in which the oxygen-containing plasma treatment was performed showed that the difference in the etching amount between the groove top portion and the groove bottom portion by performing the oxygen-containing plasma treatment. Was confirmed to be able to be reduced. In addition, comparing Case B and Case C, each of which was subjected to the oxygen-containing plasma treatment, Case C, in which the amount of O ₂ gas was large during the etching treatment, reduced the difference in the etching amount between the groove top and the groove bottom. It was confirmed that it was possible.

  When the laminated SiN film was similarly etched on the wafer having the structure shown in FIG. 4 using Cases A to C, similar results were obtained.

[Experimental example 2]
Here, the slit SiN film and the wafer with the damaged layer formed on the surface of the slit SiN film are etched after performing the oxygen-containing plasma treatment, and the wafer is etched without performing the oxygen-containing plasma treatment. Etching of the laminated SiN film was performed. Specifically, the process module 13 of the processing system 10 was used as an apparatus, and a wafer having the structure shown in FIG. 2 and having a damage layer formed on the surface of a slit SiN film was used as a wafer. With respect to these, the etching amount of the laminated SiN at three points (top, middle, and bottom) in the depth direction of the groove (slit) and the difference (ΔEA) between the etching amounts of the top and bottom were determined.

  The conditions for the oxygen-containing plasma treatment were the same as those in Case B of Experimental Example 1, and the conditions for the etching were the same as those in Case A of Experimental Example 1, except that the time was 441 sec.

  FIG. 12 shows the result. As shown in this figure, when a damage layer is formed on the surface of the slit SiN film, the effect of removing carbon as CO from the damage layer on the surface to be etched by the oxygen-containing plasma treatment and the improvement of the groove top portion It was confirmed that the effect of increasing the quality relatively can increase the etching amount as a whole and reduce the difference (ΔEA) between the etching amount at the top and the bottom.

<Other applications>
Although the embodiments have been described above, the embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The above embodiments may be omitted, replaced, or changed in various forms without departing from the scope of the appended claims and the spirit thereof.

  For example, in the above embodiment, the case where the slit SiN film and a part of the laminated SiN film are etched, and the case where the slit SiN film does not exist and the laminated SiN film is etched are described. The present invention is also applicable to SiN and Si existing on the inner surface of the concave portion formed in the structure.

  Further, the devices of the above embodiments are merely examples, and devices having various configurations can be used. Although the case where a semiconductor wafer is used as the substrate to be processed has been described, the present invention is not limited to the semiconductor wafer, and other substrates such as an FPD (flat panel display) substrate typified by an LCD (liquid crystal display) substrate and a ceramic substrate It may be.

13 Process module (etching equipment)
Reference Signs List 15 Stage 28 Processing container 37 Partition plate 39 Exhaust mechanism 40 RF antenna 42 High frequency power supply 61 First gas supply unit 62 Second gas supply unit 100 Silicon base 102 Laminated structure unit 103 Groove (recess)
111 SiO ₂ film 112 SiN film 113 Slit SiN film 120 Modified layer 130 Damage layer P Plasma generation space S Processing space W Wafer (substrate)

Claims (20)

A step of providing a substrate having a concave portion and an etching target portion made of SiN or Si on the inner surface of the concave portion in a processing container;
Performing an oxygen-containing plasma treatment on the substrate in the treatment container, and preferentially modifying the surface of the etching target portion at the top of the recess,
Next, a step of isotropically dry-etching the etching target portion,
An etching method comprising:   The etching method according to claim 1, wherein the recess is a groove or a hole.   The etching method according to claim 2, wherein the concave portion has a diameter or a width of 300 nm or less and an aspect ratio of 25 or more. The substrate has a laminated structure of SiO ₂ and SiN, the recess is formed in the laminated structure, wherein the SiO ₂ and the SiN is present in the laminated structure on the inner surface of the recess, of the multilayer structure The etching method according to any one of claims 1 to 3, wherein a part of the SiN is the object to be etched. The substrate has a laminated structure of SiO ₂ and SiN, the laminated structure has another SiN on the inner surface of the concave portion, and the etching target is all of the other SiN, and the SiN of the laminated structure is 4. The etching method according to claim 1, wherein the step of performing the dry etching includes etching the other SiN and a part of the SiN of the stacked structure. 5.   The etching method according to claim 1, wherein a damage layer containing carbon is formed on a surface of the etching target portion. It said oxygen-containing plasma treatment, O ₂ gas alone or with O ₂ gas, is carried out using at least one of H ₂ gas and a rare gas, etching as claimed in any one of claims 6 Method.   The etching method according to any one of claims 1 to 7, wherein the oxygen-containing plasma treatment is performed by remote plasma, and the substrate is subjected to a treatment mainly using oxygen radicals in the oxygen-containing plasma.   The etching method according to any one of claims 1 to 8, wherein the oxygen-containing plasma treatment is performed at a pressure in a range of 0.13 to 400 Pa.   The etching method according to claim 1, wherein the dry etching is performed using a fluorine-containing gas. The etching method according to claim 10, wherein the fluorine-containing gas includes an NF ₃ gas. The etching method according to claim 10, wherein the dry etching is performed using the fluorine-containing gas and an O ₂ gas. The etching method according to claim 12, wherein the dry etching is performed such that a ratio of a flow rate of the fluorine-containing gas to a flow rate of the O ₂ gas becomes 0.01 or more.   The etching method according to any one of claims 1 to 13, wherein the dry etching is performed by plasma processing mainly using radicals.   The etching method according to any one of claims 1 to 14, wherein the dry etching is performed at a pressure in a range of 0.13 to 400 Pa.   The etching method according to any one of claims 1 to 15, wherein the oxygen-containing plasma treatment and the dry etching are performed in the same processing container.   17. The etching method according to claim 1, wherein the oxygen-containing plasma treatment and the dry etching are repeated a plurality of times. A processing container that has a recess and accommodates a substrate having an etching target portion made of SiN or Si on an inner surface of the recess;
A partitioning section that partitions the processing vessel into an upper plasma generation space and a lower processing space,
A gas supply unit for supplying oxygen gas and fluorine-containing gas to the plasma generation space,
A plasma generation mechanism for generating plasma of oxygen gas and / or fluorine-containing gas in the plasma generation space;
A mounting table for mounting the substrate provided in the processing space,
An exhaust mechanism for evacuating the inside of the processing container,
A control unit;
Has,
The control unit includes:
Providing the substrate in a processing vessel;
An oxygen-containing plasma is generated in the plasma generation space, and mainly oxygen radicals in the oxygen-containing plasma are transported from the plasma generation space to the processing space to the processing space. A step of preferentially modifying the surface of the portion to be etched in
A fluorine-containing plasma is generated in the plasma generation space, and mainly fluorine radicals in the fluorine-containing plasma are transferred from the plasma generation space to the processing space to the processing space. An etching apparatus for controlling to perform an etching step.   19. The etching apparatus according to claim 18, wherein the control unit controls the reforming step and the etching step to be repeated a plurality of times.   20. The etching apparatus according to claim 18, wherein the control unit performs control so that oxygen gas is added during the etching step.

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