Etching processing method and etching processing apparatus

Abstract

Provided are an etching processing method and an etching processing apparatus, comprising: a step for forming an oxide layer (5) on the surface of a SiCO film (1) by supplying oxygen radicals or ozone to a wafer (8) placed on a wafer stage (9) in a processing chamber (7) inside a vacuum container (11); a step for modifying the oxide layer (5) into a surface-modified layer (6) by generating a reactive radical from a gas containing CF4 and NH3 by generating plasma; and a step in which the oxide layer (5) is formed, a step in which the surface modification layer (6) is removed, and the SiCO film (1) formed on the wafer (8) is etched by repeating the step in which the oxide layer (5) is formed, the step in which the surface modification layer (6) is formed, and the step in which the surface modification layer (6) is removed.

Description

Technical Field

[0001] The present invention relates to an etching treatment method and an etching treatment device for a SiCO (low-k) film. Background Art

[0002] In the field of semiconductor devices, due to the demand for low power consumption and increased storage capacity, both logic circuits and storage devices are promoting further miniaturization and three-dimensional device structures. For example, in logic devices, since Fin-type FETs (FinFET: fin field effect transistors) are approaching the limit of miniaturization, device manufacturers are developing Gate-All-Around (GAA: full-surround gate) devices. In addition, regarding storage devices, 3D NAND flash memory has become mainstream, and the development of 3D DRAM is also being vigorously carried out.

[0003] Compared with two-dimensional devices, three-dimensional devices have more complex structures. In their manufacturing, in addition to vertical (anisotropic) etching that etches in a direction perpendicular to the wafer surface, isotropic etching that can also etch in the lateral direction relative to the wafer surface is also widely used.

[0004] Isotropic etching has been performed by wet processing using chemical liquids, but as miniaturization progresses, problems such as pattern collapse and etching residues in fine gaps due to the surface tension of the chemical liquids have become apparent. Therefore, in isotropic etching, there is a growing trend to replace the conventional wet processing using chemical liquids with dry processing that does not use chemical liquids.

[0005] Patent Document 1 discloses, as an example of isotropic dry etching of a silicon oxide film, a method using HF gas and NH 3 The silicon oxide film is removed by modifying the silicon oxide surface with a gas, and then heating the substrate to separate and remove the modified layer.

[0006] In addition, Non-Patent Document 1 discloses that as an isotropic dry etching method for silicon oxide film, CF 4 / NH 3 A treatment method in which the surface is modified by plasma and then the modified layer is removed, thereby removing the silicon oxide film.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2020-4837

[0010] Non-patent literature

[0011] Non-patent literature 1: Journal of Vacuum Science and Technology A, 38 022604 (2020). Summary of the invention

[0012] Problems to be solved by the invention

[0013] For example, in the processing around the gate of FinFET and Gate-All-Around (GAA) devices, it is expected that technology will be required to isotropically and uniformly etch the SiCO film, which is one of the low-k materials, with controllable etching at the atomic layer level within the substrate surface and in the depth direction.

[0014] Figure 1 In the figure, as an example, the isotropic processing of the SiCO film 1 of the next generation GAA device is shown. The SiCO film 1 is formed in a manner covering the Si nanosheet 2, the SiGe sacrificial layer 3, and the CMOS gate 4. Under this gate structure is a silicon oxide film layer or a silicon substrate. In this etching process, it is required to etch the SiCO film 1 isotropically and control the etching amount with high precision and uniformity in all directions (in the substrate surface and in the depth direction) of the three-dimensional structure.

[0015] In the existing wet processing, it is difficult to control the etching amount with high precision, and the pattern collapse and etching residue in fine gaps caused by the surface tension of the chemical solution have become problems. In addition, in the spontaneous etching caused by reactive free radicals, the etching rate of the SiCO film is different between the upper and lower parts of the pattern due to the supply rate of free radicals, making it difficult to process the SiCO film uniformly on the pattern.

[0016] Furthermore, in the method shown in Patent Document 1, Figure 2 As shown in FIG. 1 , it is confirmed that as the number of etching cycles increases, the silicon dioxide film (SiO 2 ) is etched, whereas the SiCO film is not etched. In addition, in the isotropic atomic layer etching method for silicon oxide film shown in Non-Patent Document 1, there is also a problem that the etching rate of the SiCO film is extremely low.

[0017] The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide an isotropic etching method and an etching apparatus capable of achieving high-precision control of the etching amount.

[0018] Means of solving the problem

[0019] An etching method as one embodiment of the present invention is an etching method for etching a SiCO film formed on a wafer, wherein the following steps are repeated: a step of supplying oxygen radicals or ozone to a wafer placed on a wafer stage in a processing chamber inside a vacuum container to oxidize the surface of the SiCO film; a step of supplying reactive radicals to the wafer using plasma to form a modified layer from the oxide layer on the surface of the SiCO film; and a step of detaching and removing the modified layer.

[0020] In addition, as another embodiment of the present invention, an etching processing device comprises: a vacuum container, which is equipped with a processing chamber and a plasma source disposed above the processing chamber; a wafer stage, which is disposed in the processing chamber and carries a wafer formed with a SiCO film; a first mass flow controller, which supplies a processing gas for plasma processing to the plasma source; a heating device, which heats the wafer; a control unit, which controls the etching processing of the SiCO film, and the control unit repeatedly performs the following steps: introducing a gas containing oxygen whose supply flow rate is adjusted by the first mass flow controller into the plasma source, generating plasma in the plasma source, thereby supplying the generated oxygen radicals or ozone to the wafer, thereby oxidizing the surface of the SiCO film; introducing a gas containing CF whose supply flow rate is adjusted by the first mass flow controller into the plasma source, generating plasma in the plasma source, and ... 4 and NH 3 The process includes introducing a gas into a plasma source, generating plasma in the plasma source, supplying the generated reactive radicals to the wafer, and forming a modified layer on the surface of the SiCO film; and heating the wafer by a heating device to remove the modified layer.

[0021] Effects of the Invention

[0022] In isotropic dry etching of SiCO films, high-precision control of the etching amount and uniform processing in the wafer surface and in the depth direction can be achieved. Other problems, structures and effects than those described above are disclosed by the following description of the embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the isotropic etching step of the SiCO film in the manufacturing process of the GAA device.

[0024] Figure 2 This is a method for etching SiO using the method shown in Patent Document 1. 2 A graph showing the experimental results of the relationship between the etching amount and the number of cycles after forming a SiCO film and a SiC film.

[0025] Figure 3 This is a schematic diagram of the etching process procedure of this embodiment.

[0026] Figure 4This is a diagram showing the dependency of the etching amount on the number of cycles in the etching method of this embodiment.

[0027] Figure 5 This is a graph showing the dependency of the etching rate on the surface oxidation time in the etching method of this embodiment.

[0028] Figure 6 This is a graph showing the dependency of the etching rate on the surface modification time in the etching method of this embodiment.

[0029] Figure 7 This is a schematic diagram of an etching processing apparatus.

[0030] Figure 8 This is the timing of the etching method of this embodiment.

[0031] Explanation of symbols

[0032] 1: SiCO film, 2: Si nanosheet, 3: SiGe sacrificial layer, 4: CMOS gate, 5: oxide layer, 6: surface modification layer, 7: processing chamber, 8: wafer, 9: wafer stage, 11: base chamber chamber), 12: discharge tube, 13: discharge area, 14: voltage regulating mechanism, 15: exhaust mechanism, 16: vacuum exhaust pipeline, 20: ICP coil, 21: high-frequency power supply, 22: matching machine, 23: shower electrode plate, 24: gas dispersion plate, 25: top plate, 26: slit plate, 27: flow channel, 30: electrode plate, 31: DC power supply, 38: cooler, 39: flow channel, 50: mass flow controller, 51: gas distributor, 55: mass flow controller, 60: IR lamp, 61: reflection plate, 70: thermocouple, 71: thermocouple thermometer, 72: IR light transmission window, 73: power supply for IR lamp, 74: high-frequency cutoff filter, 80: control unit, 81: control line. DETAILED DESCRIPTION

[0033] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0034] The etching process of this embodiment is schematically shown in Figure 3 As a first step, a gas containing oxygen is introduced into the vacuum container, and a plasma device is used to generate plasma inside the vacuum container to generate oxygen radicals or ozone, thereby forming an oxide layer 5 on the surface of the SiCO film 1. As a second step, the gas containing oxygen remaining in the gas phase is evacuated. As a third step, a gas containing CF is introduced into the vacuum container. 4 and NH 3The gas is used to generate plasma inside the vacuum device by a plasma device, thereby generating reactive free radicals, and modifying the oxide layer 5 into a layer (surface modification layer) 6 containing compounds of nitrogen, hydrogen, silicon, fluorine, carbon and oxygen. As a fourth step, the gas remaining in the gas phase is evacuated by vacuum. As a fifth step, the surface modification layer 6 is thermally decomposed into volatile molecules by applying thermal energy to the wafer, thereby etching the SiCO film 1. Thereafter, as a sixth step, the wafer is cooled to the temperature at which the surface is oxidized. By repeating the first to sixth steps, the etching amount is finally controlled to the desired value. The dependence of the etching amount of the SiCO film 1 after repeating the first to sixth steps on the number of cycles is shown in Figure 4 The results with and without the surface oxidation step are shown. It can be seen that the etching amount of the SiCO film increases with the increase in the number of cycles. In addition, it can be seen that by adding the surface oxidation step, the etching amount increases by about 8 times. Next, the dependence of the etching rate (etching amount per cycle) on the surface oxidation time is shown in Figure 5 In this case, the surface modification time is fixed at 150s. It can be seen that as the oxidation time increases, the increase in etching rate saturates, and its saturation time is 10s. In addition, the dependence of etching rate on surface modification time is shown in Figure 6 At this time, the surface oxidation time is fixed at 30s. It can be seen that with the increase of surface modification time, the increase of etching rate is saturated, and the saturation time is about from 30s to 60s.

[0035] thus Figure 5 and 6 The results shown confirm that the etching process of this embodiment is a self-limiting atomic layer etching (ALE) process. By adopting this etching process, in the isotropic dry etching of SiCO film, high-precision control of etching amount and uniform processing in the wafer surface and depth direction can be achieved.

[0036] use Figure 7 The overall structure of the etching processing device is briefly described. The processing chamber 7 is composed of a base chamber (vacuum container) 11, in which a wafer stage 9 for mounting a wafer 8 is provided. A plasma source (ICP plasma source) using an ICP (Inductively Coupled Plasma) discharge method is provided above the processing chamber 7. The ICP plasma source is used to clean the inner wall of the chamber by plasma and to generate reactive gas by plasma.

[0037] The cylindrical discharge tube 12 constituting the ICP plasma source is arranged above the processing chamber 7, and an ICP coil 20 is arranged outside the discharge tube 12. A high-frequency power supply 21 for plasma generation is connected to the ICP coil 20 via a matching machine 22. The frequency of the high-frequency power of the high-frequency power supply 21 adopts a frequency band of several tens of MHz such as 13.56MHz. A top plate 25 is arranged above the discharge tube 12. A gas dispersion plate 24 and a shower plate 23 are arranged below the top plate 25, and the processing gas is introduced into the discharge tube 12 via the gas dispersion plate 24 and the shower plate 23. The plasma source is constituted by the discharge tube 12 and the high-frequency power supply 21.

[0038] The supply flow rate of the processing gas is adjusted by a mass flow controller 50 provided for each gas. In addition, a gas distributor 51 is provided on the downstream side of the mass flow controller 50 to independently control and supply the flow rate and composition of the gas supplied to the center of the discharge tube 12 and the gas supplied to the periphery. In this way, the spatial distribution of the partial pressure of the processing gas can be controlled in detail. Figure 7 In the figure, Ar, N 2 , CHF 3 CF 4 , SF 6 , O 2 NF 3 , HF, Cl 2 , BCl 3 NH 3 , H 2 , CH 2 F 2 , CH 3 F, CH 3 OH is used as an example of the processing gas, but other gases may also be used.

[0039] In order to reduce the pressure of the processing chamber 7, an exhaust mechanism 15 is connected to the lower part of the processing chamber 7 via a vacuum exhaust pipe 16. The exhaust mechanism 15 is composed of, for example, a turbomolecular pump, a mechanical booster pump, or a dry pump, but is not limited thereto. In addition, in order to adjust the pressure of the processing chamber 7, a pressure regulating mechanism 14 is provided on the vacuum exhaust pipe 16 connected to the exhaust mechanism 15.

[0040] An IR lamp unit for heating the wafer 8 is provided on the wafer stage 9. The IR lamp unit includes an IR lamp 60, a reflector 61 for reflecting IR light, and an IR light transmission window 72. Here, the IR lamps 60 are encircling (circular) IR lamps 60-1, 60-2, and 60-3.

[0041] The IR lamp 60 emits light mainly in the visible to infrared range (herein referred to as IR light). In this example, three circles of IR lamps 60-1, 60-2, and 60-3 are arranged in concentric circles, but it can also be 2 circles or 4 circles or more. A reflector 61 is arranged above the IR lamp 60 to reflect the IR light downward (in the wafer setting direction).

[0042] The IR lamp 60 is connected to an IR lamp power supply 73, and a high-frequency cutoff filter 74 is provided in the middle to prevent the noise of the high-frequency power from flowing into the IR lamp power supply 73. In addition, the IR lamp power supply 73 has a function of independently controlling the power supplied to the IR lamps 60-1 to 3, and can adjust the radial distribution of the heating amount of the wafer 8 (the wiring part is omitted in the figure).

[0043] A flow channel 27 is formed in the center of the IR lamp unit. A slit plate 26 having a plurality of holes is provided on the flow channel 27 to shield ions and electrons generated in the plasma and to allow only neutral gas and neutral radicals to pass through and be irradiated onto the wafer 8.

[0044] In the wafer stage 9, a flow channel 39 for a refrigerant for cooling the stage is formed inside, and the refrigerant is circulated and supplied by the cooler 38 via the flow channel 39. In addition, in order to fix the wafer 8 by electrostatic adsorption, a plate-shaped electrode plate 30 is buried in the stage and connected to a DC power supply 31. In addition, in order to efficiently cool the wafer 8, helium (He) gas whose flow rate is regulated by a mass flow controller 55 can be supplied between the back side of the wafer 8 and the wafer stage 9. In addition, in order to heat and cool the wafer 8 while adsorbing it and to prevent scratches on the back side of the wafer, the surface of the wafer stage 9 (the surface on which the wafer 8 is placed) is coated with a resin such as polyimide. In addition, a thermocouple 70 for measuring the temperature of the stage is provided inside the wafer stage 9, and the thermocouple is connected to a thermocouple thermometer 71.

[0045] use Figure 8 The etching process of this embodiment is described. Figure 8 The order is controlled by the control unit 80 of the etching processing device. The control unit 80 is connected to the power supply, mechanism, and controller of the etching processing device via the control line 81, and controls them in a manner of executing the prescribed order. First, after the wafer 8 is transported to the processing chamber 7 through the transport port (omitted in the figure) provided in the processing chamber 7, the wafer 8 is fixed on the wafer stage 9 by electrostatic adsorption through the power supply of the DC power supply 31, and He gas for wafer cooling is supplied to the back of the wafer 8. The pressure of the He gas is, for example, 1 kPa or 2 kPa.

[0046] Next, Ar gas for diluting the etching gas is supplied to the processing chamber 7 via the mass flow controller 50, the gas distributor 51, and the shower plate 23. The flow rate of the Ar gas is, for example, 0.5 L, 1 L, or 2 L. Thereafter, the Ar gas for dilution continues to flow until the etching is completed.

[0047] In the first step, a gas containing oxygen molecules is introduced into the processing chamber 7, and the high-frequency power supply 21 is turned on to form a plasma in the discharge area 13, generating oxygen free radicals or ozone. For example, the gas flow rate when using oxygen is 0.5L, 1L or 2L. In addition, the power supplied to the high-frequency power supply 21 is, for example, 1000W, 1500W or 2000W. In addition, the total pressure of the Ar gas and oxygen used for dilution is, for example, 50Pa, 100Pa, 200Pa or 300Pa. These reaction species generated in the plasma are supplied to the processing chamber 7 via the flow channel 27 and the slit plate 26, and adsorbed on the surface of the wafer 8. These reaction species react with the surface of the SiCO film 1 to form an oxide layer 5 containing silicon, carbon, oxygen and hydrogen on the surface of the SiCO film 1. Thereafter, the high-frequency power supply 21 is turned off to stop the plasma generation and terminate the supply of the reaction species.

[0048] In the second step, the gas containing oxygen molecules remaining in the gas phase is evacuated by vacuum to prepare for the gas supply in the subsequent third step.

[0049] In the third step, the CF 4 Molecules and NH 3 The high frequency power source 21 is turned on to form plasma in the discharge region 13, thereby generating reactive radicals. 4 The flow rate of the gas is, for example, 0.05 L, 0.1 L, 0.2 L or 0.3 L. 3 The flow rate of the gas is, for example, 0.1 L, 0.2 L, 0.3 L, 0.4 L or 0.5 L. The dilution gas, CF 4 Gas and NH 3 The total pressure of the gas is, for example, 50Pa, 100Pa, 200Pa or 300Pa. The reactive radicals generated in the plasma are supplied to the processing chamber 7 via the flow channel 27 and the slit plate 26, and adsorbed on the surface of the oxide layer 5. The reactive radicals react with the oxide layer 5 to form a layer (surface modification layer) 6 containing compounds of nitrogen, hydrogen, silicon, fluorine, carbon and oxygen in the oxide layer. In order to suppress the spontaneous formation and separation of the surface modification layer 6, the surface temperature during the radical irradiation needs to be maintained below 80°C. Thereafter, the high frequency power supply 21 is turned OFF to stop the plasma generation and terminate the supply of reactive radicals.

[0050] In the fourth step, the residual CF in the gas phase is discharged under vacuum. 4 Molecules and NH 3Molecular gas, ready for the next step 5.

[0051] In the fifth step, the wafer is heated by an IR lamp 60 to thermally decompose and detach the surface modification layer 6 formed on the film surface, thereby etching (removing) the SiCO film 1. The wafer temperature at this time is also preferably above 100°C. In order to improve the heating efficiency of the IR lamp 60, the supply of He gas to the back of the wafer 8 is stopped before this treatment. In addition, in order to suppress the damage to the semiconductor device caused by the heat load, the maximum temperature reached by the wafer is preferably below 350°C.

[0052] In the sixth step, He gas for cooling the wafer is supplied to the back side of the wafer 8 to cool the wafer, and the wafer temperature is returned to the temperature of the wafer stage 9 .

[0053] By repeating the first to sixth steps, the etching amount is finally controlled to a desired value.

[0054] like Figure 5 and Figure 6 As described in the figure, in the etching process of this embodiment, since the etching rate is saturated with respect to the surface oxidation time and the surface modification time, uniform etching can be performed within the wafer surface and in the depth direction.

[0055] In addition, the present embodiment shows an example of heating the wafer using the IR lamp 60, but the heating method is not limited thereto, and for example, a method of heating the wafer stage or a method of transferring the wafer to a device that only performs heating and performing heat treatment may also be used.

[0056] In addition, the present invention is not limited to the above-mentioned embodiments, and includes various modified examples. For example, the above-mentioned embodiments are described in detail in order to explain the present invention in an easy-to-understand manner, but are not necessarily limited to having all the structures described. In addition, a part of the structure in a certain embodiment can be replaced with the structure of other embodiments, and in addition, the structure of other embodiments can be added to the structure of a certain embodiment. In addition, other structures can be added, deleted, or replaced for a part of the structure of each embodiment.

Claims

1. An etching method for etching a SiCO film formed on a wafer, wherein: The process is as follows: A first step of supplying oxygen radicals or ozone to the wafer placed on a wafer stage in a processing chamber inside a vacuum container to oxidize the surface of the SiCO film; A second step of supplying reactive radicals to the wafer using plasma to form a modified layer from the oxide layer on the surface of the SiCO film; a third step of heating the wafer to remove the modified layer; Repeat the first to third steps.

2. The etching method according to claim 1, wherein: Helium gas is supplied between the wafer and the wafer stage, and the modified layer is formed on the surface of the SiCO film.

3. The etching method according to claim 1, wherein: The modified layer is a layer containing a compound of nitrogen, hydrogen, silicon, fluorine, oxygen, and carbon.

4. The etching method according to claim 1, wherein: The reactive radicals are generated by introducing a gas containing CF 4 and NH 3 into the vacuum container and generating plasma in the vacuum container.

5. The etching method according to claim 1, wherein: The wafer is irradiated with light mainly in the visible light to infrared light range from above the wafer, thereby heating the wafer.

6. An etching processing device, comprising: A vacuum container, wherein the vacuum container has a processing chamber inside and a plasma source disposed above the processing chamber; A wafer stage, which is disposed in the processing chamber and carries a wafer having a SiCO film formed thereon; a first mass flow controller that supplies a process gas to the plasma source; A heating device, wherein the heating device heats the wafer; a control unit that controls etching of the SiCO film, The control unit repeatedly performs the following steps: A step of introducing a gas containing oxygen whose supply flow rate is adjusted by the first mass flow controller into the plasma source, generating plasma in the plasma source, thereby supplying oxygen radicals or ozone to the wafer to oxidize the surface of the SiCO film; A step of introducing a gas containing CF4 and NH3, the supply flow of which is adjusted by the first mass flow controller, into the plasma source, generating plasma in the plasma source, thereby supplying the generated reactive radicals to the wafer, and forming a modified layer on the surface of the SiCO film; The step of heating the wafer by the heating device to remove the modified layer.

7. The etching processing apparatus according to claim 6, wherein: having a second mass flow controller for supplying helium gas between the wafer and the wafer stage, In the step of forming the modified layer on the surface of the SiCO film, the control unit introduces the helium gas whose supply flow rate is adjusted by the second mass flow controller into between the wafer and the wafer stage.

8. The etching processing apparatus according to claim 6, wherein: The modified layer is a layer containing a compound of nitrogen, hydrogen, silicon, fluorine, oxygen, and carbon.

9. The etching processing apparatus according to claim 6, wherein: The heating device includes a lamp that irradiates the wafer with light mainly in the visible light to infrared light range from above the wafer.

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