JP7209567B2 - Etching method and etching apparatus - Google Patents

Description

The present disclosure relates to etching methods and etching apparatuses.

Recently, miniaturization etching is performed in the manufacturing process of semiconductor devices. For example, there is a demand for a technique for isotropically etching SiN or Si on the inner surfaces of trenches or holes with a high aspect ratio.

As a technique for etching SiN, as described in Patent Document 1, a technique is known in which fluorine _- containing gas such as NF3 gas is turned into plasma and SiN is etched with fluorine radicals and fluorine ions. Further, Patent Document 1 describes that SiN can be etched while suppressing etching of SiO ₂ by including an oxygen source such as O ₂ gas in the fluorine-containing gas.

Japanese Patent Application Publication No. 2014-508424

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

An etching method according to an aspect of the present disclosure has a recess, an etching target portion made of SiN or Si exists on the inner surface of the recess, and a damage layer containing carbon is formed on the surface of the etching target portion. providing the substrate in a processing container; and performing an oxygen-containing plasma treatment on the substrate in the processing container to remove the carbon from the damaged layer and preferentially etch the surface of the etching target portion in the top portion of the recess. and then isotropically dry-etching the portion to be etched.

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

4 is a flow chart showing an etching method according to a specific embodiment; FIG. 4 is a cross-sectional view showing an example of the structure of a substrate on which etching is performed; 3 is a cross-sectional view showing an ideal state when etching the substrate of FIG. 2; FIG. FIG. 4 is a cross-sectional view showing another example of the structure of a substrate on which etching is performed; 5 is a cross-sectional view showing an ideal state when etching the substrate of FIG. 4; FIG. 3 is a cross-sectional view showing a state in which the substrate having the structure of FIG. 2 is isotropically etched as it is; FIG. FIG. 4 is a diagram showing the concentration distribution of F radicals when performing isotropic dry etching of SiN. FIG. 4 is a diagram showing the concentration distribution of O radicals when oxygen-containing plasma treatment is performed in one embodiment. FIG. 10 is a diagram for explaining the effect of the oxygen-containing plasma treatment when a damage layer containing carbon is formed on the surface of an etching target portion; BRIEF DESCRIPTION OF THE DRAWINGS It is a partial cross-sectional plan view which shows roughly an example of the processing system used for the etching method of this embodiment. 11 is a cross-sectional view schematically showing an example of a process module functioning as an etching apparatus for carrying out the etching method of the present embodiment, mounted on the processing system of FIG. 10; FIG. FIG. 10 is a diagram for explaining the effects in Experimental Example 2;

Embodiments will be described below with reference to the accompanying drawings.

<Background 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 a 3D-NAND type nonvolatile semiconductor device, in an ONON laminated structure in which a silicon oxide film (SiO ₂ film) and a silicon nitride film (SiN film) are laminated in multiple layers, through a groove formed in the lamination direction There is a step of isotropically dry etching SiN.

In such an ONON laminated structure, the thickness is 1 μm or more, and the groove formed has a high aspect ratio, so the SiN at the top of the groove is preferentially etched due to the depth loading effect. end up Therefore, it is required to suppress the etching of SiN at the groove top portion and to etch the groove top portion and the groove bottom portion with approximately the same etching amount.

In some cases, the SiN formed on the entire inner surface of such a high aspect ratio groove is etched, but in this case also, the SiN at the top of the groove is preferentially etched due to the loading effect.

Furthermore, Si may exist on the inner surface of the groove with a high aspect ratio, and the same problem arises when the Si is etched. Furthermore, such a problem occurs not only with grooves but also with holes.

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 oxygen-containing plasma processing is performed on the substrate in the processing container, The surface of the etching target portion of the recess top portion is preferentially modified, and then the etching target portion is isotropically dry-etched.

As a result, the portion to be etched in the top portion of the recess is relatively difficult to etch as compared to other portions, and the loading effect can be reduced to uniformly etch the portion to be etched on the inner surface of the recess.

<Specific embodiment>
Next, specific embodiments will be described.
FIG. 1 is a flow chart showing an etching method according to a specific embodiment.
First, 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 placed in a processing container (step 1). Next, the substrate is subjected to an oxygen-containing plasma treatment in the processing container to preferentially modify the surface of the etching target portion of the recess top portion (step 2). Next, the part to be etched is isotropically dry-etched (step 3). Steps 2 and 3 may be repeated.

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

The recesses formed in the substrate may be grooves or holes. The smaller the width of the groove or the diameter of the hole and the larger the aspect ratio of the concave portion, the greater the loading effect. 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 wafer) on which an ONON laminated structure for a 3D-NAND nonvolatile semiconductor device is formed. is.

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

From this state, all of the slit SiN film 113 formed on the entire inner surface of the groove 103 and part of the SiN film 112 of the laminated structure portion 102 are collectively and isotropically etched, ideally as shown in FIG. to the state shown in .

Further, 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 ONON laminated structure for the same 3D-NAND type nonvolatile semiconductor device is formed. This is the case where the slit SiN film 113 does not exist on the inner surface of the groove 103 . That is, this is the case where the SiO ₂ film 111 and the SiN film 112 forming the ONON laminated structure are present on the inner surface of the trench 103 .

Also in this example, part of the SiN film 112 of the laminated structure 102 is isotropically etched from the state shown in FIG. 4, ideally to the state shown in FIG.

However, when SiN is isotropically etched as it is on the wafer W having the structure shown in FIG. , the etching of SiN becomes non-uniform at the top and bottom of the groove 103 . The same applies to the wafer W having the structure shown in FIG.

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

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

Therefore, in the present embodiment, oxygen-containing plasma treatment is performed prior to etching SiN or Si, which is an etching target portion, 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 etching target portion (SiN or Si), and the surface of the etching target portion is oxidized to form the modified layer 120 . Such modified layer 120 makes etching relatively difficult. At this time, as shown in FIG. 8, the concentration of O radicals is high at the top portion of the concave portion (groove) 103 and low at the bottom portion. The modified layer 120 is thicker at the top of the concave portion.

Therefore, the oxygen-containing plasma treatment can relatively suppress the amount of etching in the recess top portion of the etching target portion. As a result, the difference between the etching amount of the recess top portion and the etching amount of the recess bottom portion can be suppressed, and more uniform etching can be achieved.

In addition, a damaged layer containing carbon may be formed on the surface of the etching target portion, and such a damaged layer hinders etching. In such a case, by performing oxygen-containing plasma treatment, as shown in FIG. 9, for example, carbon can be removed as CO from the damaged layer 130 on the surface of the slit SiN film 113, and the etching target portion of the entire recess can be removed. Etching amount can be increased.

For this reason, when a damage layer containing carbon is formed on the surface of the etching target portion, the oxygen-containing plasma treatment has the effect of relatively suppressing the etching amount of the concave top portion of the etching target portion and the damage. It has both the effect of removing carbon from the layer and increasing the amount of etching. Therefore, by subjecting the part to be etched where the damage layer is formed to oxygen-containing plasma treatment and then dry etching, the amount of etching of the part to be etched of the entire recess is increased, while the amount of etching of the top part of the recess and the etching of the bottom part of the recess are performed. It is possible to suppress the difference from the amount.

The oxygen-containing plasma treatment in step 2 applies oxygen-containing plasma to the substrate housed in the processing container. In the oxygen-containing plasma treatment at this time, it is preferable that oxygen radicals (O radicals) in the plasma act mainly, and therefore remote plasma is preferably used. Remote plasma generates an oxygen-containing plasma in a plasma generation space separate from the processing space in which the substrate is placed, and transports the plasma to the processing space. At this time, oxygen ions (O ₂ ions) in the oxygen-containing plasma are likely to be deactivated during transport, and mainly O radicals are supplied to the processing space. By performing 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 _H2 gas, the oxidizing ability can be enhanced. Plasma can be stabilized by adding a rare gas. The rare gas is not particularly limited, but Ar gas is preferable. Moreover, the pressure at this time is preferably 1 to 3000 mTorr (0.13 to 400 Pa). By setting the thickness within this range, the effect of suppressing etching at the top portion of the concave portion can be further enhanced.

In step 2, the flow rate of each gas is appropriately set according to the device. Moreover, 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. Also, the plasma generation power is preferably 50 to 950 W, although it depends on the device. Also, the time for step 2 is preferably 10 to 180 sec, and the substrate temperature is preferably 5 to 85.degree. More preferably, it is 15 to 85°C.

The step of isotropically dry-etching the part to be etched in step 3 is preferably capable of selectively etching SiN or Si with respect to other materials such as _SiO2 , and is preferably performed using a fluorine-containing gas. . This dry etching may be processing using plasma or gas etching without using plasma, but processing using plasma is preferable, and processing mainly using fluorine radicals (F radicals) using remote plasma is more preferable. In remote plasma, fluorine-containing plasma is generated in a plasma generation space separate from the processing space in which the substrate is arranged, and the plasma is transported to the processing space. At this time, fluorine ions (F ions) in the plasma are likely to be deactivated during transport, and mainly fluorine radicals (F radicals) are supplied to the processing space. Damage to the substrate can be reduced by performing the treatment mainly using F radicals. 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 process of step 3, as described above, the reformed layer is formed thicker in the top portion of the recessed portion by the oxygen-containing plasma treatment, so that the difference in etching amount between the top portion of the recessed portion and the bottom portion of the recessed portion is suppressed. be. In addition, 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 recess is increased by the oxygen-containing plasma treatment, and the etching amount of the recess top portion and the recess bottom portion are increased. can suppress the difference from the etching amount of .

HF and NF3 can be mentioned as the fluorine _- containing gas. Among these _, NF3 gas is preferred. NF ₃ gas or the like may be used alone, but O ₂ gas may be added to NF ₃ gas or the like. By adding O ₂ gas, it is possible to obtain the reforming effect (oxidation effect) of the concave top portion by O radicals even during etching. Also, a rare gas may be added to the NF ₃ gas or the like. Plasma can be stabilized by adding a rare gas. The rare gas is not particularly limited, but Ar gas is preferable. NF3 gas or the like _{, O2} gas, and a rare gas may be used. The pressure is preferably 1-3000 mTorr (0.13-400 Pa). With this range, the effect of suppressing the difference between the etching amount of the recess top portion and the etching amount of the recess bottom portion can be further enhanced. At this time, the flow rate of each gas is appropriately set according to the device. Further, 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. Also, the plasma generation power is preferably in the range of 50 to 950W. Also, the substrate temperature is preferably in the range of 5 to 85.degree. 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 container. Thereby, a high throughput can be maintained. For example, both steps 2 and 3 can be performed by radical treatment using the same remote plasma apparatus.

Steps 2 and 3 may be repeated as described above. Depending on the amount of etching to be performed on the part to be etched, a single oxygen-containing plasma treatment may not provide a sufficient reforming effect. In such a case, a sufficient modification effect can be obtained by repeating steps 2 and 3 as appropriate.

<Example of processing system>
Next, an example of a processing system used for the etching method of this embodiment will be described. FIG. 10 is a partial cross-sectional plan view schematically showing an example of a processing system used in the etching method of this 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 SiN film etching processing and heat processing on the wafer W, which is a substrate loaded from the transfer module 12 . Each process module 13 and transfer module 12 are maintained in a vacuum atmosphere inside.

In the processing system 10, the wafer W stored in the loading/unloading section 11 is transferred by the transfer arm 14 built in the transfer module 12, and each wafer is transferred to two stages 15 arranged inside the process module 13. Place W. Next, in the processing system 10 , each wafer W placed on the stage 15 is subjected to SiN film etching processing and heat processing in the process module 13 , and then the processed wafer W is unloaded to the loading/unloading section 11 by the transport arm 14 . do.

The loading/unloading unit 11 receives a plurality of load ports 17 as a mounting table for FOUPs 16, which are containers for accommodating a plurality of wafers W, and receives stored wafers W from the FOUPs 16 mounted on the respective load ports 17, or A loader module 18 that delivers wafers W that have undergone predetermined processing in the process module 13 to the FOUP 16, and two loads that temporarily hold the wafers W between the loader module 18 and the transfer module 12 to deliver the wafers W. It has a lock module 19 and a cooling storage 20 for cooling the wafer W subjected to heat treatment.

The loader module 18 is made up of a rectangular housing whose inside is atmospheric pressure, and a plurality of load ports 17 are arranged side by side on one long side of the rectangle. Furthermore, the loader module 18 has a transport arm (not shown) movable in the longitudinal direction of its rectangular shape. The transfer arm loads wafers W from the FOUPs 16 mounted on the respective load ports 17 into the load lock modules 19 or unloads the wafers W from the load lock modules 19 into the respective FOUPs 16 .

Each load lock module 19 temporarily holds the wafer W in order to deliver the wafer W accommodated in the FOUP 16 mounted on each load port 17 in the atmospheric pressure atmosphere to the process module 13 in which the inside is in the vacuum atmosphere. Each load lock module 19 has a buffer plate 21 that holds two wafers W; Each load lock module 19 also has a gate valve 22 a 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 . Furthermore, a gas introduction system and a gas exhaust system (not shown) are connected to the load lock module 19 by pipes so that the internal atmosphere can be switched between atmospheric pressure atmosphere and vacuum atmosphere.

The transfer module 12 loads an unprocessed wafer W from the loading/unloading unit 11 into the process module 13 and unloads the processed wafer W from the process module 13 to the loading/unloading unit 11 . The transfer module 12 consists of a rectangular housing whose interior is in a vacuum atmosphere, and includes two transfer arms 14 that hold and move two wafers W, a turntable 23 that rotatably supports each transfer arm 14, and a rotary table. It includes a rotary mounting table 24 on which a table 23 is mounted, and guide rails 25 that guide the rotary mounting table 24 movably in the longitudinal direction of the transfer module 12 . Also, the transfer module 12 is connected to the load lock module 19 of the loading/unloading section 11 and each process module 13 via the gate valve 22b and each gate valve 26 to be 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 two processed wafers W from each process module 13 to the other process module 13. or the load lock module 19 .

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

The processing system 10 has a controller 27 . The control unit 27 includes a main control unit having a CPU that controls 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 perform a predetermined operation based on a processing recipe stored in, for example, a storage medium built in a storage device or a storage medium set in the storage device.

<Etching equipment>
Next, an example of the process module 13 that functions as an etching apparatus that carries out the etching method of the present embodiment and that is mounted in the processing system 10 will be described. FIG. 11 is a cross-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 apparatus includes a processing container 28 having a sealed structure in which wafers W are accommodated. The processing container 28 is made of, for example, aluminum or an aluminum alloy, has an open upper end, and is closed with a lid 29 serving as a ceiling. A loading/unloading port 30 for the wafer W is provided in the side wall portion 28a of the processing container 28, and the loading/unloading port 30 can be opened and closed by the gate valve 26 described above.

In addition, as described above, two stages 15 (only one of which is shown) on which the wafers W are horizontally mounted are arranged at the bottom of the processing container 28 . The stage 15 has a substantially cylindrical shape, and has 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 control mechanism 36 for controlling 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) in which a temperature control medium (eg, water or Galden) circulates, and heat exchange between the temperature control medium flowing in the pipe and the wafer W is performed. The temperature of the wafer W is adjusted by doing so. Further, the stage 15 is provided with a plurality of elevating pins (not shown) which are used for loading and unloading the wafer W into and out of the processing container 28 so as to protrude from the upper surface of the mounting plate 34 .

The inside of the processing container 28 is partitioned into an upper plasma generation space P and a lower processing space S by a partition plate 37 . 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 generating space P is a space in which plasma is generated, and the processing space S is a space in which the wafer W is etched by radical processing. Outside the processing chamber 28, there is a first gas supply unit 61 for supplying a processing gas used for etching to the plasma generation space P, and a non-plasma gas such as a pressure regulation gas, a purge gas or a diluent gas, such as _N2 gas or A second gas supply unit 62 for supplying an inert gas such as Ar gas to the processing space S is provided. An exhaust mechanism 39 is connected to the bottom of the processing container 28 . The evacuation mechanism 39 has a vacuum pump and evacuates the inside of the processing space S.

A heat shield plate 48 is provided under the partition plate 37 so as to face the wafer W. As shown in FIG. The heat shield plate 48 is for suppressing the influence of the heat on the distribution of radicals in the processing space S because heat is accumulated in the partition plate 37 by repeating plasma generation in the plasma generation space P. be. The heat shield plate 48 is formed larger than the partition plate 37 , and the flange portion 48 a constituting the peripheral portion is embedded in the side wall portion 28 a of the processing container 28 . A cooling mechanism 50 such as a coolant channel, a chiller, or a Peltier element is embedded in the flange portion 48a.

The first gas supply unit 61 supplies the plasma generation space P with O ₂ gas, H ₂ gas, NF ₃ gas, rare gas such as Ar gas. These gases are turned into plasma in the plasma generation space P. As shown in FIG. The rare gas functions as a plasma generation gas, but also functions as a pressure control gas, a purge gas, and the like.

The process module 13 is configured as an inductively coupled plasma etching apparatus using an RF antenna. A lid 29 serving as the ceiling of the processing container 28 is formed of, for example, a circular quartz plate and configured as a dielectric window. An annular RF antenna 40 for generating inductively coupled plasma in the plasma generating 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 box 41. ing. The high-frequency power supply 42 outputs high-frequency power of a predetermined frequency (for example, 13.56 MHz or higher) suitable for plasma generation by inductively coupled high-frequency discharge at a predetermined output value. The matching unit 41 has a reactance variable 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.

Of the process modules 13, the one that functions as a heat treatment apparatus that performs heat treatment is not shown in detail, but two stages 15 are arranged in the processing container like the etching apparatus shown in FIG. However, unlike the etching apparatus, it does not have a plasma generation mechanism, and the wafer W mounted on the stage 15 is heated 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 wafer W after etching, etching residues or reaction products on the wafer W are removed.

When the etching method according to the above embodiment is carried out by the processing system 10, first, the wafer W having the structure shown in FIG. Load into module 19 . After the load-lock module 19 is evacuated, the wafer W in the load-lock module 19 is transferred by the transfer arm 14 of the transfer module 12 to the process module 13 functioning as an etching device (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 adjusting gas, and the pressure inside the processing container 28 is adjusted to 1000 to 4000 mTorr (133 to 533 Pa), for example, while the temperature is adjusted. The wafer W is held for a predetermined time, eg, 30 seconds, on the stage 15 whose temperature is controlled to 5 to 85° C. by the mechanism 36 to stabilize the wafer temperature at a predetermined temperature.

Next, after purging the inside of the processing container 28, the pressure inside the processing container 28 is preferably 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. conduct. In the oxygen-containing plasma treatment, 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 O ₂ gas, at least one of H ₂ gas and rare gas such as 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 by the partition plate 37 , and mainly O radicals in the O ₂ plasma are selectively introduced into the processing space S. A portion of the wafer W to be etched is modified (oxidized) by the O radicals. At this time, since the concentration of O radicals is higher in the top portion of the concave portion, the top portion of the concave portion on the surface of the etching target portion is preferentially modified, and the thickness of the modified layer which is relatively difficult to etch is greater in the top portion of the concave portion. thicken. Therefore, in subsequent etching, the amount of etching of the recess top portion of the etching target portion can be relatively suppressed compared to other portions. As a result, the difference between the etching amount of the recess top portion and the etching amount of the recess bottom portion can be suppressed, and more uniform etching can be achieved. Further, since the treatment is mainly based on O radicals, ion damage to the wafer W is small.

Further, when a damage layer containing carbon is formed on the surface of the etching target portion, carbon can be removed as CO from the damage layer on the etching target surface by performing the oxygen-containing plasma treatment. Therefore, in the next etching step, it is possible to increase the etching amount of the etching target portion of the entire concave portion.

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

At this time, the gas flow rate is preferably O ₂ gas flow rate: 1 to 1000 sccm, H ₂ gas flow rate: 1 to 500 sccm, rare gas (Ar gas) flow rate: 1 to 1500 sccm. Also, the plasma generation power is preferably 50 to 950W. Moreover, the processing time is preferably 10 to 180 sec.

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

Next, isotropic dry etching in step 3 is performed by setting the pressure in the processing container 28 to preferably 1 to 3000 mTorr (0.13 to 400 Pa), for example, 225 mTorr (30 Pa). In the isotropic dry etching, NF3 gas, which is a fluorine-containing 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 fluorine-containing gas, which is an inductively coupled plasma. Generate plasma. At this time, in addition to the NF3 gas, at _least one of _O2 gas and a rare gas such as Ar gas may be supplied.

Fluorine-containing plasma generated in the plasma generation space P is transferred to the processing space S. At this time, F ions are deactivated by the partition plate 37, and mainly F radicals in the plasma are selectively introduced into the processing space S. The F radicals isotropically etch the SiN film or Si film, which is the part to be etched. At this time, as described above, the oxygen-containing plasma treatment forms a thicker modified layer in the etching target portion of the recess top portion where the concentration of O radicals is high. is suppressed. In addition, 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 recess is increased by the oxygen-containing plasma treatment, and the etching amount of the recess top portion and the recess bottom portion are increased. can suppress the difference from the etching amount of .

Further, by adding O ₂ gas to the NF ₃ gas during etching, the reforming effect (oxidation effect) of the concave top portion by O radicals can be obtained during etching as well. In order 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. As for gas flow rates, NF ₃ gas flow rate: 1 to 1000 sccm, O ₂ gas flow rate: 1 to 1000 sccm, rare gas (Ar gas) flow rate: 1 to 1500 sccm are preferable. Also, the plasma generation power is preferably in the range of 50 to 950W. Also, the processing time is appropriately set according to the etching amount.

Depending on the amount to be etched of the part to be etched, a single oxygen-containing plasma treatment may not provide a sufficient reforming effect. In this case, steps 2 and 3 are repeated a predetermined number of times.

After the etching is finished, the inside of the processing chamber 28 is purged, and the processed wafer W is unloaded from the processing chamber 28 by the transfer arm 14 incorporated in the transfer module 12 . If heat treatment is required to remove residues after etching, the wafer W after etching is transferred by the transfer arm 14 to the process module 13 functioning as a heating device, and heat treatment is performed. After the etching process or heat treatment is completed, the wafer W is transferred to the load lock module 19 by the transfer arm 14, and after the load lock module 19 is brought to the atmosphere, the transfer arm of the loader module 18 moves the wafer W into the load lock module 19. wafer W is returned to the FOUP 16 .

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

<Experimental example>

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

In Case A, no oxygen-containing plasma treatment was performed, and only isotropic etching treatment was performed using NF3 gas _, Ar gas, and _O2 gas. The conditions at this time were as follows.
Pressure: 150-300mTorr (20-40Pa)
Gas flow rate: NF ₃ = 1 to 100 sccm
_O2 : 1-400 sccm
Ar gas = 1 to 200 sccm
Stage (mounting plate) temperature: 5 to 60°C
Time: 480sec
High frequency power: 400-800W

In case B, oxygen _- containing plasma treatment was performed using _O2 gas, H2 gas, and Ar gas, followed by isotropic etching treatment using NF3 gas _, Ar gas, and _O2 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
H2 ₌ 1-100 sccm
Ar = 1 to 100 sccm
Stage (mounting plate) temperature: 5 to 60°C
Time: 60sec
High frequency power: 400-800W
・Etching Same as case A

In Case C, as in Case B, isotropic etching is performed after oxidizing plasma treatment, the _O2 gas flow rate during oxygen-containing plasma treatment is increased more than in Case B, and the total gas for the isotropic etching treatment is 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 to 700 sccm
H2 ₌ 1-100 sccm
Ar = 1 to 100 sccm
Stage (mounting plate) temperature: 5 to 60°C
Time: 60sec
High frequency power: 400-800W
・Etching process pressure: 150 to 300 mTorr (20 to 40 Pa)
Gas flow rate: NF ₃ = 1 to 100 sccm
_O2 : 100-400 sccm
Ar gas = 50 to 250 sccm
Stage (mounting plate) temperature: 5 to 60°C
Time: 480sec
High frequency power: 400-800W

After etching in Cases A to C, the etched amount of the laminated SiN and the difference in the etched amount between the top and bottom (ΔEA) for four points in the depth direction of the groove (slit) (top, middle 1, middle 2, bottom). asked for 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: 21.2 nm
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, comparing case A in which no oxygen-containing plasma treatment is performed and case B in which oxygen-containing plasma treatment is performed, it can be seen that the difference in etching amount between the groove top portion and the groove bottom portion due to the oxygen-containing plasma treatment. can be reduced. In addition, when comparing case B and case C, in which oxygen-containing plasma processing was performed in both cases, case C, in which the amount of O ₂ gas was greater during etching, reduced the difference in etching amount between the groove top and groove bottom portions. confirmed to be possible.

Similar results were obtained when the laminated SiN film was etched in cases A to C on the wafer having the structure shown in FIG.

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

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

The results are shown in FIG. As shown in this figure, when a damaged layer is formed on the surface of the slit SiN film, the oxygen-containing plasma treatment has the effect of removing carbon as CO from the damaged layer on the surface of the etching target and improving the top of the groove. It was confirmed that the etching amount can be increased as a whole and the difference (ΔEA) between the top and bottom etching amounts can be reduced by the effect of relatively increasing the quality.

<Other applications>
Although the embodiments have been described above, the embodiments disclosed this time should be considered as examples and not restrictive in all respects. The above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

For example, in the above embodiments, the case where the slit SiN film and a part of the laminated SiN film are etched, and the case where the laminated SiN film is etched without the slit SiN film present are shown. It is also applicable to SiN and Si existing on the inner surface of the recess formed in the structural portion.

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

13 Process module (etching device)
15 Stage 28 Processing Container 37 Partition Plate 39 Exhaust Mechanism 40 RF Antenna 42 High-Frequency Power Source 61 First Gas Supply Section 62 Second Gas Supply Section 100 Silicon Substrate 102 Laminated Structure Section 103 Groove (Recess)
111 SiO ₂ film 112 SiN film 113 slit SiN film 120 modification layer 130 damage layer P plasma generation space S processing space W wafer (substrate)

Claims (19)

A step of providing in a processing container a substrate having a recess, a portion to be etched made of SiN or Si on the inner surface of the recess, and a damaged layer containing carbon in the surface of the portion to be etched.
a step of subjecting the substrate to oxygen-containing plasma treatment in a processing container to remove the carbon from the damaged layer and preferentially modify the surface of the etching target portion in the top portion of the recess;
Then, a step of isotropically dry-etching the etching target portion;
An etching method. 2. The etching method according to claim 1, wherein said recess is a groove or a hole. 3. The etching method according to claim 2, wherein the recess has a diameter or width of 300 nm or less and an aspect ratio of 25 or more. The substrate has a layered structure of SiO ₂ and SiN, the recess is formed in the layered structure, the SiO ₂ and the SiN of the layered structure are present on the inner surface of the recess, and the layered structure has the The etching method according to any one of claims 1 to 3, wherein part of said SiN is said etching target portion . The substrate has a layered structure of SiO ₂ and SiN, the layered structure has another SiN on the inner surface of the recess, and the part to be etched is all of the other SiN and the layered structure. 4. The etching method according to any one of claims 1 to 3, wherein said SiN part is part of SiN, and said step of dry etching etches part of said other SiN and part of said SiN of said laminated structure. The etching according to any one of claims 1 to 5 , wherein the oxygen-containing plasma treatment is performed using _O2 gas alone or _O2 gas and at _least one of H2 gas and a noble gas. Method. 7. The etching method according to claim 1 , wherein the oxygen-containing plasma treatment is performed by remote plasma, and the substrate is treated mainly by oxygen radicals in the oxygen-containing plasma. The etching method according to any one of claims 1 to 7 , wherein the oxygen-containing plasma treatment is performed at a pressure in the range of 0.13-400Pa. The etching method according to any one of claims 1 to 8 , wherein the dry etching step is performed with a fluorine-containing gas. 10. The etching method of claim ₉ , wherein the fluorine containing gas comprises NF3 gas. 11. The etching method according to claim 9 , wherein the dry etching step is performed using the fluorine - containing gas and _O2 gas. 12. The etching method according to claim 11 , wherein the dry etching step is performed so that the ratio of the flow rate of the fluorine-containing gas to the flow rate of the _O2 gas is 0.01 or more. 13. The etching method according to any one of claims 1 to 12 , wherein the step of dry etching is performed by plasma treatment mainly containing radicals. 14. The etching method according to any one of claims 1 to 13 , wherein the dry etching step is performed at a pressure in the range of 0.13 to 400Pa. 15. The etching method according to any one of claims 1 to 14 , wherein said modifying step and said dry etching step are performed in the same processing container. 16. The etching method according to any one of claims 1 to 15 , wherein said modifying step and said dry etching step are repeated multiple times. A processing container for accommodating a substrate having a recess, an etching target portion made of SiN or Si on the inner surface of the recess, and a damage layer containing carbon in the surface of the etching target portion .
a partition that partitions the processing container into an upper plasma generation space and a lower processing space;
a gas supply unit that supplies an oxygen gas and a 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 provided in the processing space on which the substrate is mounted;
an exhaust mechanism for evacuating the inside of the processing container;
a control unit;
has
The control unit
placing the substrate in a processing vessel;
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. removing carbon and preferentially modifying the surface of the etching target portion in the top portion of the recess;
Fluorine-containing plasma is generated in the plasma generation space, and mainly fluorine radicals in the fluorine-containing plasma are transported from the plasma generation space to the processing space to the processing space, and the portion to be etched is etched by the fluorine radicals. an etching apparatus for controlling to perform an etching step; 18. The etching apparatus according to claim 17 , wherein said controller performs control such that said modifying step and said etching step are repeated multiple times. 19. The etching apparatus of claim 17 , wherein the controller controls to add oxygen gas during the etching process.

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