Etching Method

Abstract

Provided is a method for etching a silicon nitride film with high accuracy and high selectivity with respect to a silicon oxide film, while preventing deterioration of the shape of a silicon oxide film portion during etching. This etching method serves to dry etch a film structure, which is preliminarily formed on a wafer disposed inside a processing chamber and comprises film layers in which a silicon nitride film is vertically sandwiched between silicon oxide films and an end portion of the film layers forms a side wall of a groove or hole, the dry etching being carried out in a state where processing gas is supplied to the processing chamber without the use of plasma by repeating a first step and a second step multiple times to etch the silicon nitride film in the horizontal direction from the end portion, wherein: in the first step, hydrogen fluoride gas is reacted at 30°C or higher and 55°C or lower to form a reaction layer on a silicon nitride film; in the second step after the first step, heating is carried out at 70°C or higher and 110°C or lower without flowing hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first step.

Description

[Technical field]

[0001] The present disclosure relates to an etching method, and more particularly to an isotropic dry etching process technology used in the process of removing silicon nitride films in semiconductor elements such as 3D memories. [Background technology]

[0002] In semiconductor devices, the demand for lower power consumption and increased memory capacity has led to further miniaturization and three-dimensional device structures. In the manufacture of three-dimensional devices, the structure is three-dimensional and complex, so in addition to the conventional "vertical (anisotropic) etching" that etches vertically to the wafer surface, "isotropic etching" that can etch horizontally is now widely used. Conventionally, isotropic etching has been performed by wet processing using chemicals, but with the progress of miniaturization, problems such as pattern collapse due to the surface tension of the chemicals and etching residue in fine gaps have become apparent. Another problem is the need for large amounts of chemical processing. Therefore, in isotropic etching, it is necessary to replace the conventional wet processing using chemicals with dry processing that does not use chemicals.

[0003] Silicon nitride films are often used in semiconductor devices, and there are known examples of dry etching processes that use hydrogen fluoride (HF) gas but do not use plasma. For example, Patent Document 1 describes a method of supplying hydrogen fluoride gas at a wafer temperature of 60°C to 200°C to etch a silicon nitride film without damaging a thermal oxide film. Patent Document 2 describes a method of supplying hydrogen fluoride gas at a temperature of 10 to 120°C at a pressure in a chamber of 1333 Pa or more to selectively etch a silicon nitride film relative to a silicon oxide film.

[0004] As a known example of adding another component to HF gas, Patent Document 3 describes a method of selectively etching a silicon nitride film by supplying NO gas or / and ozone gas and HF gas, and Patent Document 4 describes a method of etching a silicon nitride film by contacting a mixed gas containing a fluorine-containing carboxylic acid and HF gas at less than 100° C. without plasma.

[0005] As an example of etching with a fluorine-containing gas other than HF gas, Patent Document 5 discloses ClF 3 A method for selectively etching a silicon nitride film with respect to a silicon oxide film using a gas is disclosed. 3 NO, FNO 2 and a method for selectively etching a silicon nitride film using a fluorine-containing etching gas selected from the group consisting of fluorine, iodine, and combinations thereof. Furthermore, Patent Document 7 discloses etching a silicon nitride film using an etching gas containing a halogen fluoride, which is a compound of bromine or iodine and fluorine, under a pressure of 1 Pa to 80 kPa without using plasma.

[0006] As an example of using radicals generated by some kind of plasma, Patent Document 8 describes a method of forming a fluorine-containing gas, an alcohol gas, and O 2 A method is described in which a gas and an inert gas are supplied in a state excited by an external plasma, thereby selectively etching a silicon nitride film relative to a silicon and / or silicon oxide film. Patent Document 9 also shows a method for selectively etching a silicon nitride film, including a step of introducing a gas containing H and F, and a step of selectively introducing radicals of an inert gas into a processing space. Patent Document 10 further describes selectively etching a silicon nitride film in the lateral direction from a structure in which a silicon nitride film and a silicon oxide film are stacked, using a precursor containing oxygen and a precursor containing fluorine generated by plasma at -20°C or lower.

[0007] Furthermore, Patent Documents 6 and 10 describe selectively etching a silicon nitride film laterally from the sidewall of a high aspect ratio opening formed in a structure in which silicon nitride films and silicon oxide films of a 3D-NAND device, which is a 3D memory, are stacked in multiple layers.

[0008] In addition, Patent Document 11 describes the formation of ammonium silicofluoride [(NH 4 ) 2 SiF 6 ], ammonium hydrogen fluoride [NH 4 HF 2 It has been shown that the following can be removed by heating using a lamp or the like. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2008-187105 A [Patent Document 2] JP 2018-207088 A [Patent Document 3] JP 2014-197603 A [Patent Document 4] JP 2019-091890 A [Patent Document 5] JP 2016-58544 A [Patent Document 6] Special Publication No. 2021-509538 [Patent Document 7] International Publication No. 2021 / 079780 [Patent Document 8] JP 2015-228433 A [Patent Document 9] JP 2019-012759 A [Patent Document 10] U.S. Pat. No. 10,319,603 [Patent Document 11] JP 2005-161493 A Summary of the Invention [Problem to be solved by the invention]

[0010] For example, in the processing of stacked films for 3D-NAND flash memory, which is a semiconductor element with a three-dimensional structure, and in the processing around the gate of Fin-type FET, a technology is required to etch silicon nitride films isotropically and highly selectively with respect to polycrystalline silicon films and silicon oxide films, with controllability at the atomic layer level. 2 The structure is made up of multiple alternating layers of silicon nitride (SiN) and silicon nitride (SiN) films, with deep holes and grooves formed in them, and includes a process for selectively isotropically etching a small amount of the silicon nitride film in the lateral direction.

[0011] As described in the Background Art section, conventional wet etching using hydrofluoric acid solution or buffered hydrofluoric acid solution has problems such as etching residues in minute gaps and poor etching controllability. In addition, in the case of dry etching, it is difficult to etch a silicon nitride film with high precision at a high selectivity to a silicon oxide film, and there is a problem of deterioration of the shape of the silicon oxide film portion that is to be left.

[0012] The present disclosure has been made in consideration of the above problems, and provides an etching method capable of highly selectively and accurately etching a silicon nitride film relative to a silicon oxide film without deteriorating the shape of the silicon oxide film that is desired to be left. [Means for solving the problem]

[0013] The etching method of the present disclosure is an etching method for dry etching a film structure, which has been formed in advance on a wafer placed in a processing chamber and in which a film layer in which a silicon nitride film is sandwiched between silicon oxide films and whose ends form side walls of a groove or hole, by supplying a processing gas into the processing chamber without using plasma, in which a first step involves reacting hydrogen fluoride gas at a temperature of 30°C or higher and 55°C or lower to form a reaction layer on the silicon nitride film, and after the first step, in a second step, heating is performed at a temperature of 70°C or higher and 110°C or lower without flowing hydrogen fluoride gas to volatilize and remove the reaction layer formed in the first step, and the first step and the second step are repeated multiple times to etch the silicon nitride film laterally from the ends. Effect of the Invention

[0014] According to the above etching method, it is possible to provide a method for preventing the deterioration of the shape of the silicon oxide film portion during etching and for etching a silicon nitride film with high precision at a high selectivity to a silicon oxide film. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0015] [Figure 1A] 1 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with HF supply in the first step of the first embodiment (stage temperature -30°C, total pressure 300 Pa, 10 cycles). [Figure 1B] 1 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with HF supply in the first step according to the first embodiment (stage temperature -30°C, total pressure 600 Pa, 10 cycles). [Figure 1C] 1 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with HF supply in the first step of the first embodiment (stage temperature -30°C, total pressure 900 Pa, 10 cycles). [Figure 2A] 13 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment (stage temperature -20°C, total pressure 900 Pa, 10 cycles). [Figure 2B] 13 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment (stage temperature 0° C., total pressure 900 Pa, 10 cycles). [Figure 2C] This is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the output of an IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment (stage temperature 20° C., total pressure 900 Pa, 10 cycles). [Figure 2D] 13 is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film versus the irradiation time of an IR lamp in the second step of the second embodiment (stage temperature 0° C., total pressure 900 Pa, 10 cycles). [Figure 2E] 13 is a graph showing the thickness of a reaction layer on a silicon nitride film versus the number of cycles when the output of an IR lamp irradiated simultaneously with HF supply is changed in the first step according to the second embodiment. [Figure 3A] 13 is a graph showing the etching film thickness and the selectivity of a silicon nitride film and a silicon oxide film when the stage temperature in the first step according to the third embodiment is changed. [Figure 3B] 13 is a graph showing the thickness of a reaction layer on a silicon nitride film versus the number of cycles when the stage temperature in the first step according to the third embodiment is changed. [Figure 4] 1 is a cross-sectional view showing an outline of an etching apparatus according to a first embodiment. [Diagram 5] 1 is a flow diagram of a method for etching a silicon nitride film according to an embodiment. [Figure 6] 1 is a flow diagram of a method for etching a silicon nitride film according to an embodiment. [Figure 7] 4 is a time chart showing a schematic flow of operations over time in the etching process according to the first embodiment. [Figure 8] 10 is a time chart showing a schematic flow of operations over time in an etching process according to a second embodiment. [Figure 9] 13 is a time chart showing a schematic flow of operations over time in an etching process according to a third embodiment. [Figure 10A] 4 is a partial cross-sectional view for explaining the progress of an etching process (before etching) of a stacked film of a silicon nitride film and a silicon oxide film in the example. FIG. [Figure 10B] 5 is a partial cross-sectional view for explaining the progress of an etching process (after etching) of a stacked film of a silicon nitride film and a silicon oxide film in the example. FIG. [Figure 11A] FIG. 11 is a partial cross-sectional view for explaining the progress of an etching process of a stacked film of a silicon nitride film and a silicon oxide film when the selectivity is poor in the embodiment, in which the shape of the end of the silicon oxide film after etching is round instead of rectangular. [Figure 11B] 1 is a partial cross-sectional view for explaining the progress of an etching process of a stacked film of a silicon nitride film and a silicon oxide film in an embodiment, in which the corners of the silicon oxide film are rounded off to form triangles. FIG. [Figure 12] FIG. 11 is a partial cross-sectional view for explaining the progress of an etching process of a stacked film of a silicon nitride film and a silicon oxide film in an embodiment, in which the selectivity is relatively high, and the thickness of the silicon oxide film portion is reduced while the corners of the silicon oxide film maintain their rectangular shape. [Figure 13] FIG. 11 is a cross-sectional view showing an outline of an etching apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The present inventors have investigated etching, without using plasma, with hydrogen fluoride gas (HF) for single-layer silicon nitride films and silicon oxide films formed by plasma CVD (chemical vapor deposition).

[0017] Hereinafter, examples of the embodiment will be described in detail with reference to the drawings. EXAMPLES

[0018] [Overall configuration of etching processing apparatus 1] First, an outline of the etching processing apparatus according to Example 1 will be described with reference to Fig. 4, including its overall configuration. Fig. 4 is a cross-sectional view showing an outline of the etching apparatus according to the first embodiment. The etching processing apparatus 100 has a processing chamber 1. The processing chamber 1 is composed of a base chamber 11, in which a wafer stage 3 for placing a wafer 2 thereon is installed. A shower plate 23 is installed in the center of the upper side of the processing chamber 1, and processing gas is supplied to the processing chamber 1 via the shower plate 23.

[0019] The supply flow rate of the processing gas is adjusted by a mass flow controller 50 installed for each type of gas. In addition, a gas distributor 51 is installed downstream of the mass flow controller 50, so that the flow rate and composition of the gas supplied near the center of the processing chamber 1 and the gas supplied near the periphery can be controlled independently, and the spatial distribution of the partial pressure of the processing gas can be controlled in detail. In addition, in FIG. 4, argon (Ar) gas, nitrogen (N 2 ) gas, helium (He) gas, and hydrogen fluoride (HF) gas are shown in the figure, but other process gases can also be supplied.

[0020] The lower part of the processing chamber 1 is connected to exhaust means 15 by vacuum exhaust piping 16 in order to reduce the pressure in the processing chamber 1. The exhaust means 15 is composed of, for example, a turbo molecular pump, a mechanical booster pump, or a dry pump. In addition, in order to adjust the pressure in the processing chamber 1, a pressure adjustment means 14 is installed upstream of the exhaust means 15.

[0021] An IR lamp unit (infrared illumination unit) for heating the wafer 2 is installed on the upper part of the wafer stage 3. The IR lamp unit mainly consists of an IR lamp 60, a reflector 61, and an IR light transmission window 72. A circular (circular) lamp is used as the IR lamp 60. The light emitted from the IR lamp 60 is assumed to emit light (herein referred to as IR light) mainly ranging from visible light to infrared light. In this embodiment, three lamps 60-1, 60-2, and 60-3 are installed, but two or four lamps may be installed. A reflector 61 for reflecting IR light downward (toward the placement of the wafer 2) is installed above the IR lamp 60. The material of the IR transmission window 72 is preferably one that does not contain alkali metal ions, transmits light in the infrared light region, and is heat resistant, and specifically, quartz is preferable.

[0022] An IR lamp power supply 73 is connected to the IR lamp 60, and a high frequency cut filter 74 is installed in between to prevent high frequency power noise from entering the IR lamp power supply 73. The IR lamp power supply 73 also has a function to control the power supplied to the IR lamps 60-1, 60-2, and 60-3 independently, so that the radial distribution of the amount of heat applied to the wafer 2 can be adjusted (some of the wiring is not shown). A space is formed in the center of the IR lamp unit to accommodate a shower plate 23 for introducing process gas.

[0023] The wafer stage 3 has a coolant flow path 39 formed therein for cooling the stage, and the coolant is circulated and supplied by a chiller 38. In this embodiment, the wafer stage 3 uses a chiller that can control the temperature from -50°C to 50°C. The wafer stage 3 uses a proximity cooling system.

[0024] The surface of the wafer stage 3 is provided with protrusions 56, and the wafer 2 is mounted in a manner such that it is supported at points by the protrusions 56. The height of the protrusions 56 is desirably about 0.1 mm to 1.0 mm, for example, and the number of supporting points (i.e., the number of protrusions 56) is desirably three or more. Specifically, six protrusions 56 with a height of 0.25 mm are used here. The wafer stage 3 can be made of a material that is corrosion-resistant metal or metal compound with high thermal conductivity.

[0025] Because there is a gap between the wafer stage 3 and the wafer 2 due to the protrusion 56, He, Ar, N 2 By flowing such an inert gas, the inert gas flows through the gap, causing thermal conduction to cool the wafer 2. Note that, as for the cooling method for the wafer 2, the electrostatic adsorption method shown in the second embodiment can also be used.

[0026] Furthermore, a thermocouple 70 for measuring the temperature of the stage 3 is installed inside the wafer stage 3, and the thermocouple 70 is connected to a thermocouple thermometer 71. The temperature of the stage 3 measured by the thermocouple 70 and the thermocouple thermometer 71 had a difference of within ±1°C with respect to the set temperature of the chiller 38.

[0027] The proximity cooling stage 3 described above has the advantage of being simple in structure and therefore low cost. However, when the chamber 11 is in an idling vacuum state, the wafer 2 is insulated, so it takes a certain amount of time before cooling begins by flowing inert gas. In addition, because the distance between the coolant from the chiller 38 and the wafer 2 is relatively long, it was found that the actual temperature of the wafer 2 tends to be higher than the set temperature of the chiller 38. When the temperature during cooling and processing was measured using a wafer with a thermocouple attached, it was found that the actual temperature of the wafer 2 was about 5°C higher than the set temperature of the chiller 38.

[0028] As a mechanism for cooling the stage 3 used in the etching processing apparatus 100 of this embodiment, a Peltier element, which is a thermoelectric conversion device, or the like can also be used in addition to a mechanism for circulating a coolant.

[0029] The etching processing apparatus 100 used in this embodiment can heat the inside of the chamber 11 other than the wafer stage 3 exposed to hydrogen fluoride gas, such as the processing chamber 1. For example, a temperature of about 40° C. to 120° C. can be used. This makes it possible to prevent hydrogen fluoride gas and the like from being adsorbed inside the chamber 11, and makes it possible to reduce corrosion inside the chamber 11 as much as possible.

[0030] In this embodiment, for example, HF of 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less) is used at a stage temperature of 40°C to -30°C of the stage 3. It is considered that HF ​​may aggregate and liquefy on the silicon nitride film depending on the stage temperature of the stage 3. Therefore, when the electrostatic adsorption method is used, when the back surface of the wafer 2 also solidifies or liquefies, the seal band of the back surface cooling gas of the wafer 2 may break, and a cooling gas such as He may leak, resulting in an electrostatic chuck error. In contrast, the proximity cooling stage 3 shown in FIG. 4 has a gap between the wafer stage 3 and the wafer 2 due to the protrusion 56, so that even when HF solidifies or liquefies, no error occurs in the wafer stage 3 and stable processing is possible.

[0031] Furthermore, with the electrostatic adsorption method, because the gap between the wafer 2 and stage 3 is narrow, the wafer 2 is likely to stick to the stage 3 due to surface tension when HF liquefies. As a result, when dechucking the wafer 2, if the wafer 2 is lifted by the pusher pin, the wafer 2 may break. To address this issue, the new system uses a proximity cooling method with a gap of 0.25 mm between the wafer 2 and stage 3, which reduces the problem of the wafer 2 sticking to the stage 3 when HF liquefies.

[0032] In the application of a process using a low temperature as in the present embodiment, condensation may occur on components that are in contact with the atmosphere inside the electrostatic chuck electrode, which is the cooling source, and may cause a short circuit in an electric circuit such as a power supply unit. From this point of view, the structure of the stage 3 with proximity cooling, in which the components inside the electrode are simplified, is advantageous.

[0033] [Etching method: Dry etching process flow] Next, the flow of the dry etching process using hydrogen fluoride gas without using plasma proposed in this embodiment will be described with reference to Figures 4, 5, and 7. Figure 5 is a flow diagram of the etching method for silicon nitride film according to the embodiment. Figure 7 is a time chart that shows a schematic flow of the operation over time in the etching process according to the first example.

[0034] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is placed (mounted) on the protrusion 56 on the wafer stage 3.

[0035] Thereafter, Ar gas for cooling the wafer is supplied to the wafer 2 via the mass flow controller 52, the gas distributor 51, and further the shower plate 23, thereby performing wafer cooling in step S101 of FIG. 5. Since the Ar gas serves both the role of heat transfer to the wafer 2 and the role of dilution gas for diluting the HF gas, steps S101 and S102 of FIG. 5 are performed simultaneously. Note that the flow rate of the Ar gas can be changed (different flow rates can be used) when cooling the wafer 2 and when it is used as a dilution gas. Also, the Ar gas for dilution can be allowed to continue to flow until the etching process is completed, or it can be stopped. Also, N can be used as an inert gas instead of Ar gas. 2 A gas may also be used.

[0036] Next, in step S103 of FIG. 5, a predetermined amount of HF gas was supplied to the processing chamber 1 as a processing gas for a predetermined time, and at the same time, the wafer 2 was heated to form a reaction layer on the wafer 2. Here, heating by an IR (infrared) lamp 60 was used as a heating method. The wafer temperature of the wafer 2 obtained as a result of cooling by the stage 3 and heating by the IR lamp 60 is preferably, for example, 30° C. or more and 55° C. or less, and more preferably 35° C. or more and 50° C. or less. As described in the embodiment with changed conditions described later, the film thickness of the reaction layer can be controlled by the total pressure or HF partial pressure, the heating temperature, here the output of the IR lamp 60, the time, the number of repetitions, and the like. Also, when the wafer temperature of the wafer 2 is, for example, lower than 30° C., etching is difficult to occur because the reaction layer cannot be sufficiently formed. Conversely, when the wafer temperature of the wafer 2 is, for example, higher than 55° C., the reaction layer can be formed in excess, and when the excessively formed reaction layer is decomposed and volatilized, the undesired adjacent silicon oxide film is etched, so the etching selectivity decreases.

[0037] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film, and the lower the temperature required for formation. Even when the pressure is increased, by controlling the output of the IR lamp 60, a reaction layer can be formed on the silicon nitride film without affecting the silicon oxide film.

[0038] After forming the reaction layer for a predetermined time, in step S104 of Fig. 5, the supply of HF gas is stopped, and the exhaust means 15 is used to exhaust the HF gas remaining in the gas phase and the reaction products on the silicon nitride film as the reaction layer. When performing vacuum exhaust, it is preferable to set the pressure to, for example, 5 Pa or less. In step S104, the reaction products can be exhausted more efficiently by supplying Ar gas as a diluent gas during and after the exhaust. When exhausting while flowing Ar, it is preferable to set the pressure to, for example, 40 Pa or less.

[0039] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 5). The heating temperature here is preferably, for example, 70° C. to 110° C. (70° C. or more and 110° C. or less), and more preferably 70° C. to 100° C. (70° C. or more and 100° C. or less). Here, an IR lamp 60 is used as a heating method. The heating method is not limited to this, and may be, for example, a method of heating the wafer stage 3, or a method of separately transporting the wafer 2 to an apparatus that only performs heating and performing a heating process. In addition, Ar gas or nitrogen gas can be introduced into the processing chamber 1 during irradiation with the IR lamp 60. In addition, the heating process can be performed multiple times as necessary. After heating, the wafer is cooled in step S106. Thereafter, the process from step S102 to step S106 is regarded as one cycle, and this is repeated N times (N is a positive integer). After repeating the cycle until the required etching amount is obtained, the etching method in FIG. 4 is completed.

[0040] Fig. 7 shows a time chart according to the flow of the etching method shown in Fig. 5. One cycle includes a step (step S103) of heating with the IR lamp 60 while flowing HF gas, and a step (step S105) of heating with the IR lamp 60 without flowing HF gas, and this is repeated N times to cause etching of the silicon nitride film.

[0041] [Etching result 1] The results of etching with hydrogen fluoride (HF) gas without using plasma in this embodiment are shown below. The temperature of stage 3 was set to -30°C, and the etching rates of the single-layer silicon nitride film (PE-SiN) and silicon oxide film (PE-SiO2) formed by plasma CVD were measured.

[0042] In this example, the base wafer 2 used was a high resistance substrate (31 Ωcm) having a diameter of 300 mm, on which coupon samples of a silicon nitride film and a silicon oxide film each having a size of 2 cm square were attached with silicone vacuum grease.

[0043] After placing the wafer 2 in the processing chamber 1 of the etching processing apparatus 100 shown in FIG. 4, etching was performed according to the process flow of the etching method shown in FIG. 5. First, Ar was flowed at a flow rate of 1.4 L / min and 900 Pa for 60 seconds to cool the wafer. After that, after the pressure was set to a set value, HF was introduced at a flow rate of 0.40 L / min and Ar as a dilution gas at a flow rate of 0.20 L / min, while simultaneously irradiating with the IR lamp 60 at a predetermined output. Here, the time for HF introduction and IR irradiation was set to 60 seconds. As a result, a reaction layer was formed on the silicon nitride film.

[0044] Then, the exhaust valve in the pressure adjusting means 14 was opened 100%, and the exhaust was performed for 120 seconds. This exhaust operation exhausted fluorine gas and a part of the reaction products. Next, the IR lamp 60 was heated at a predetermined lamp intensity for 30 to 50 seconds with Ar flowing at a flow rate of 0.50 L / min while the set temperature of the stage 3 was kept as it was, and the exhaust valve in the pressure adjusting means 14 was opened 100%. This removes the reaction layer. Then, returning to the beginning, the wafer 2 was cooled while Ar was flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds. This series of processes (steps S102 to S106) was performed 10 cycles here according to the flow of FIG. 5.

[0045] The etching thickness of the silicon nitride film (PE-SiN), the etching thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film to the silicon oxide film obtained after 10 cycles when the output of the IR lamp 60 was changed are shown in Figs. 1A, 1B, and 1C. Fig. 1A is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first step according to the first embodiment (stage temperature -30°C, total pressure 300 Pa, 10 cycles). Fig. 1B is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first step according to the first embodiment (stage temperature -30°C, total pressure 600 Pa, 10 cycles). Fig. 1C is a graph showing the etching film thickness and selectivity of a silicon nitride film and a silicon oxide film with respect to the output of an IR lamp irradiated simultaneously with the supply of HF in the first step according to the first embodiment (stage temperature -30°C, total pressure 900 Pa, 10 cycles). Here, Figs. 1A, 1B, and 1C show the experimental results in which HF / Ar was introduced and the pressure during IR irradiation was changed to 300 Pa, 600 Pa, and 900 Pa, respectively. Moreover, the IR lamp irradiation for removing the reaction layer formed in the second step (S103) was performed for 50 s at an output of 70%.

[0046] As shown in Figure 1A, when 300 Pa was used and the IR output was 60% or more, an etching amount of about 15 nm of the silicon nitride film (PE-SiN) was obtained in 10 cycles. However, when the IR output was 65% or more, etching of the silicon oxide film (PE-SiO2) also began to occur, and it was found that the selectivity became worse.

[0047] As shown in Figure 1B, when the pressure was increased to 600 Pa, the amount of etching of the silicon nitride film (PE-SiN) increased in proportion to the IR lamp output. By increasing the pressure, the amount of etching of the silicon nitride film (PE-SiN) increased overall, and the selectivity to the silicon oxide film (PE-SiO2) increased. However, even in this case, etching of the silicon oxide film (PE-SiO2) began to occur at IR output of 65% or more. Furthermore, as shown in Figure 1C, when the pressure was increased to 900 Pa, there was a tendency for the amount of etching of the silicon nitride film (PE-SiN) to increase as the IR output increased, and the amount of etching was found to increase further.

[0048] Using a wafer 2 equipped with a thermocouple, the HF gas was replaced with Ar, and the process temperature during lamp irradiation was actually measured. Table 1A shows the IR lamp output (IR output: 50%, 55%, 60%, 65%) when the stage temperature was -30°C, and the temperature of wafer 2 after 60 seconds. The temperature reached is shown here. A high resistance substrate was used, just like the base wafer. The measured temperatures were 30°C to 57°C. Temperature measurements were also performed for the process of removing the reaction layer, and it was found that the temperature reached was 80°C.

[0049] [Table 1A] The structure of the film targeted by this embodiment will be described with reference to FIG. 10A and FIG. 10B. FIG. 10A is a partial cross-sectional view for explaining the progress of etching of a laminated film of a silicon nitride film and a silicon oxide film according to the embodiment (before etching). FIG. 10B is a partial cross-sectional view for explaining the progress of etching of a laminated film of a silicon nitride film and a silicon oxide film according to the embodiment (after etching). The structure of the film targeted by this embodiment is a structure required for 3D-NAND in which a large number of silicon nitride films 103 and silicon oxide films 102 are alternately laminated on a substrate 101 as shown in FIG. 10A, and a deep hole shape or a groove shape is formed as an opening 104 therein. That is, this configuration is a film structure in which the end of the film layer in which the silicon nitride film is sandwiched between the silicon oxide films above and below constitutes the side wall of the groove or hole. The thickness of the silicon nitride film 103 used here is several nm to 100 nm, and the thickness of the silicon oxide film 102 is several nm to 100 nm. The number of these layers is several tens to several hundreds. The total thickness 105 of these stacked layers is several μm to several tens of μm. The width of the opening 104 is several tens of nm to several hundreds of nm. By the process of this embodiment, the silicon nitride film 103 is etched laterally with high selectivity to the silicon nitride film 102, as shown in FIG. 10B. The dimension 106 of this lateral etching is several nm to several tens of nm.

[0050] 11A, 11B, and 12 are diagrams for explaining examples of the shape of the end of the silicon oxide film 102 after etching. FIG. 11A is a partial cross-sectional view for explaining the progress of the etching process of the laminated film of the silicon nitride film and the silicon oxide film when the selectivity is poor according to the embodiment, and the shape of the end of the silicon oxide film after etching is round instead of rectangular. FIG. 11B is a partial cross-sectional view for explaining the progress of the etching process of the laminated film of the silicon nitride film and the silicon oxide film according to the embodiment, and the corners of the silicon oxide film are rounded and triangular. FIG. 12 is a partial cross-sectional view for explaining the progress of the etching process of the laminated film of the silicon nitride film and the silicon oxide film according to the embodiment, and the selectivity is relatively high, and the thickness of the silicon oxide film part is thin while the corners of the silicon oxide film remain rectangular.

[0051] Here, when etching the silicon nitride film 103 in the lateral direction, the selectivity to the silicon oxide film 102 is preferably 10 or more, more preferably 20 or more. If this selectivity is low, etching of the silicon oxide film 102, which should not be etched, occurs at the same time, and the shape of the end of the silicon oxide film 102 after etching becomes round instead of rectangular, as shown by 111 in FIG. 11A, which adversely affects device performance.

[0052] Empirically, a shape closer to a rectangle as shown in Fig. 10B can be obtained when the selection ratio is 10 or more, more preferably 20 or more. On the other hand, when the selection ratio is less than 5, the shape of the edge of the silicon oxide film 102 as shown by 111 in Fig. 11A becomes rounded, which is not desirable.

[0053] Here, the etching characteristics in a fine pattern were evaluated using a sample in which a total of 20 layers of silicon nitride film 103 (film thickness 40 nm) and silicon oxide film 102 (film thickness 40 nm) were alternately formed, and a 200 nm slit-shaped space (opening 104) was formed. The experimental conditions were as shown in Figures 1A, 1B, and 1C, and 10 cycles of etching were performed. The results are shown in Tables 1B, 1C, and 1D. Table 1B shows the etching results at a stage temperature of -30°C and 300 Pa. Table 1C shows the etching results at a stage temperature of -30°C and 600 Pa. Table 1D shows the etching results at a stage temperature of -30°C and 900 Pa. Table 1E shows the symbols and standards for the evaluation results of the slit samples.

[0054] As a result, as shown in FIG. 10B, when etching of the silicon nitride film 103 proceeds with high selectivity and in a shape close to a rectangle, as shown in FIG. 11A, the selectivity is poor and the tip of the silicon oxide film 102 to be left is rounded (indicated by 111). Even when the selectivity is relatively good, the corners of the silicon oxide film 102 are rounded and triangular (indicated by 113) as shown in FIG. 11B, and further, even if the corners of the silicon oxide film 102 are rectangular as shown in FIG. 12, the thickness of the tip of the silicon oxide film 102 is thin (indicated by 112). 112 in FIG. 12 is a diagram showing an example of the end of the silicon oxide film 102 after etching, in which the corners of the silicon oxide film 102 are rectangular while the thickness of the silicon oxide film 102 part is thin. 113 in FIG. 11B is a diagram showing an example of the end of the silicon oxide film 102 after etching, in which the corners of the silicon oxide film 102 are rounded and triangular. The composition formula of silicon oxide film is SiO 2 Or, it may be expressed as SiO2.

[0055] Therefore, Tables 1B, 1C, and 1D show the recess amount (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity ratio from the slit pattern results (the amount of silicon nitride film etched from the initial dimension divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (thickness 108 of the tip of silicon oxide film 102 after etching shown in FIG. 12 divided by thickness 107 of initial silicon oxide film 102). Good etching conditions here are those in which the recess amount is relatively large, the selectivity ratio is large, and the remaining SiO2 thickness is close to 1.

[0056] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also listed in Tables 1B, 1C, and 1D. The criteria are shown in Table 1E.

[0057] [Table 1B]

[0058] [Table 1C]

[0059] [Table 1D]

[0060] [Table 1E] As shown in Tables 1B, 1C, and 1D, in all cases, when the IR lamp output (IR output) is high, the remaining SiO2 thickness becomes small, and it is found that this is not a suitable condition. Therefore, even if the selectivity is relatively high, the remaining SiO2 thickness may be low. From the above, it was found that the temperature that satisfies the recess amount, selectivity, and remaining SiO2 thickness is 30°C or more and 55°C or less.

[0061] In addition, high temperature and high pressure contribute to increasing the amount of etching of the silicon nitride film 103. However, as increasing the temperature reduces the remaining SiO2 thickness, it was found that the characteristics are better when the pressure is increased and the temperature is low. EXAMPLES

[0062] [Etching treatment device 2] Next, an outline of an etching processing apparatus 200 according to Example 2 of this embodiment will be described with reference to FIG. 13, including the overall configuration. FIG. 13 is a cross-sectional view showing an outline of an etching apparatus according to Example 2. The etching processing apparatus 200 has a processing chamber 1. The processing chamber 1 is composed of a base chamber 11, in which a wafer stage 3 for placing a wafer 2 is installed. A plasma source is installed above the processing chamber 1, and an ICP discharge method is used. The ICP plasma source can be used for cleaning the inner wall of the chamber 11 by plasma and for generating reactive gas by plasma. A cylindrical quartz chamber 12 constituting the ICP plasma source is installed above the processing chamber 1, and an ICP coil 20 is installed outside the quartz chamber 12. A high-frequency power source 21 for generating plasma is connected to the ICP coil 20 via a matching device 22. The frequency of the high-frequency power generated by the high-frequency power source 21 is assumed to be in a frequency band of several tens of MHz, such as 13.56 MHz. A top plate 25 is installed on the top of the quartz chamber 12. A gas dispersion plate 24 and a shower plate 23 are installed below the top plate 25 , and the process gas is introduced into the quartz chamber 12 via the gas dispersion plate 24 and the shower plate 23 .

[0063] The supply flow rate of the process gas is adjusted by a mass flow controller 50 installed for each type of gas. In addition, a gas distributor 51 is installed downstream of the mass flow controller 50, and the gas distributor 51 controls the flow rate and composition of the gas supplied to the center of the quartz chamber 12 and the gas supplied to the outer periphery independently, thereby enabling detailed control of the spatial distribution of the partial pressure of the process gas. 2 , H.F., O2 is shown as the process gas, however, other gases may be provided as desired.

[0064] An exhaust means 15 is connected to the bottom of the processing chamber 1 by a vacuum exhaust pipe 16 in order to reduce the pressure in the processing chamber. The exhaust means 15 is composed of, for example, a turbo molecular pump, a mechanical booster pump, or a dry pump. In addition, a pressure adjustment means 14 is installed upstream of the exhaust means 15 in order to adjust the pressure in the processing chamber 1.

[0065] An IR lamp unit for heating the wafer 2 is installed on the upper part of the wafer stage 3. The IR lamp unit mainly consists of an IR lamp 60, a reflector 61, and an IR light transmission window 72. A circular lamp is used as the IR lamp 60. The light emitted from the IR lamp is assumed to be light that is mainly from visible light to infrared light (herein referred to as IR light). In this embodiment, three lamps 60-1, 60-2, and 60-3 are installed, but two or four lamps may be installed. A reflector 61 for reflecting IR light downward (toward the wafer placement direction) is installed above the IR lamp 60. The material of the IR transmission window 72 is preferably one that does not contain alkali metal ions, transmits light in the infrared light region, and is heat resistant, and specifically, quartz is preferable.

[0066] An IR lamp power supply 73 is connected to the IR lamp 60, and a high frequency cut filter 74 is installed in between to prevent high frequency power noise from flowing into the IR lamp power supply 73. The IR lamp power supply 73 is also provided with a function that allows the power supplied to the IR lamps 60-1, 60-2, and 60-3 to be controlled independently of one another, making it possible to adjust the radial distribution of the amount of heat applied to the wafer 2 (some of the wiring is not shown).

[0067] A flow path 27 is formed in the center of the IR lamp unit. A slit plate 26 with a plurality of holes is installed in this flow path 27 to block ions and electrons generated in the plasma and transmit only neutral gases and neutral radicals to irradiate the wafer 2. The material of the slit plate 26 is preferably one that does not contain alkali metal ions and is heat resistant, and specific examples of the material that can be used include alumina and quartz.

[0068] The wafer stage 3 has a coolant flow path 39 formed therein for cooling the stage, and the coolant is circulated and supplied by a chiller 38. In this embodiment, the chiller 38 is one capable of controlling the temperature of the wafer stage 3 to -50°C to 50°C. In addition, in order to fix the wafer 2 by electrostatic adsorption, plate-shaped electrode plates 30 are embedded in the stage 3, and a DC power supply 31 is connected to each of the electrode plates 30. In addition, in order to efficiently cool the wafer 2, He gas can be supplied between the back surface of the wafer 2 and the wafer stage 3. In addition, in order to prevent the back surface of the wafer 2 from being scratched even if heating and cooling are performed while the wafer 2 is adsorbed, the surface of the wafer stage 3 (the surface on which the wafer 2 is placed) is coated with a resin such as polyimide. In addition, a thermocouple 70 for measuring the temperature of the stage 3 is installed inside the wafer stage 3, and the thermocouple 70 is connected to a thermocouple thermometer 71.

[0069] The temperature of stage 3 measured by thermocouple thermometer 71 using thermocouple 70 had a difference of within ±1°C from the set temperature of chiller 38, and the temperature of wafer 2 measured separately by thermocouple 70 had a difference of within ±3°C (within ±2°C from the temperature of stage 3).

[0070] As a mechanism for cooling the stage 3 used in the etching processing apparatus 200 of this embodiment, a Peltier element, which is a thermoelectric conversion device, or the like can be used in addition to a mechanism for circulating a coolant.

[0071] Furthermore, the etching processing apparatus 200 used in this embodiment can heat the inside of the chamber 11 other than the wafer stage 3 exposed to hydrogen fluoride gas, such as the processing chamber 1. For example, a temperature of about 40° C. to 120° C. can be used. This makes it possible to prevent hydrogen fluoride gas from being adsorbed inside the chamber 11, and to minimize corrosion inside the chamber.

[0072] [Etching method: Dry etching process flow 2] Next, the flow of the etching process using hydrogen fluoride gas without using plasma proposed in this embodiment will be explained with reference to Figures 5, 8, and 13 (apparatus diagram). Figure 5 is a flow diagram of the etching method for silicon nitride film according to the embodiment. Figure 8 is a time chart that shows a schematic flow of operation over time in the etching process according to the second example.

[0073] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is fixed to the wafer stage 3 by a DC power source 31 for electrostatic adsorption, and He gas 55 for wafer cooling is supplied to the back surface of the wafer 2, thereby performing wafer cooling in step S101 of Fig. 5. A valve 54 is provided between the He gas 55 and the vacuum exhaust pipe 16.

[0074] 5, Ar gas for diluting the HF gas is supplied to the processing chamber 1 via the mass flow controller 50, the gas distributor 51, and further the shower plate 23. The Ar gas for dilution can be continued to flow until the etching process is completed, or it can be stopped. In addition, N 2 A gas may also be used.

[0075] 5, a predetermined amount of HF gas was supplied to the processing chamber 1 as a processing gas for a predetermined time, and at the same time, heating was performed to form a reaction layer. Here, heating by an IR (infrared) lamp 60 was used as a heating method. The temperature of the wafer 2 obtained as a result of cooling by the stage 3 and heating by the IR lamp 60 is preferably, for example, 30° C. or more and 55° C. or less, and more preferably 35° C. or more and 50° C. or less. As will be described in an embodiment with different conditions below, it is possible to control the film thickness of the reaction layer by the total pressure or HF partial pressure, heating temperature, here the lamp output of the IR lamp 60, time, number of repetitions, and the like.

[0076] In this embodiment, the pressure used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 100 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film 103, and the lower the temperature required for formation. Even when the pressure is increased, by controlling the output of the IR lamp 60, a reaction layer can be formed on the silicon nitride film 103 without affecting the silicon oxide film 102.

[0077] 5, after the reaction layer is formed for a predetermined time, the supply of HF gas is stopped and the HF gas remaining in the gas phase and the reaction products on the silicon nitride film 103 as the reaction layer are exhausted. In step S104, the reaction products can be more efficiently exhausted by supplying Ar gas as a dilution gas during and after the exhaust.

[0078] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 5). The heating temperature here is preferably, for example, 70° C. to 110° C. (70° C. or more and 110° C. or less), and more preferably 70° C. to 100° C. (70° C. or more and 100° C. or less). Here, an IR lamp 60 is used as a heating method. The heating method is not limited to this, and may be, for example, a method of heating the wafer stage 3, or a method of separately transporting the wafer 2 to a device that only performs heating and performing a heating process. In addition, Ar gas or nitrogen gas can be introduced during irradiation with the IR lamp 60. In addition, the heating process can be performed multiple times as necessary. After heating, the wafer is cooled in step S106. Thereafter, the process from step S102 to step S106 is regarded as one cycle, and this is repeated N times (N is a positive integer). The cycle is repeated until the required etching amount is obtained, and then the etching method is completed.

[0079] Fig. 8 shows a time chart according to the flow shown in Fig. 5. One cycle includes a process of performing IR lamp heating while flowing HF gas (step S103) and a process of performing IR lamp heating without flowing HF gas (step S105), and this process is repeated N times to cause etching of the silicon nitride film.

[0080] [Etching result 2] Etching was performed under different conditions using the etching processing apparatus 200 shown in FIG. 13 and the process flows shown in FIG. 5 and FIG. 8. In Example 1, the flow rate was HF / Ar=0.40 / 0.20 (L / min), the stage temperature was fixed at −30° C., and the total pressure was changed to 300 Pa, 600 Pa, and 900 Pa. In Example 2, the total pressure was fixed at 900 Pa, the flow rates of HF and Ar were kept the same, and the stage temperature of the stage 3 was changed to −20° C., 0° C., and 20° C., and etching was performed using hydrogen fluoride gas without using plasma of this embodiment as in Example 1. During etching, a voltage of, for example, ±1200 V was applied to electrostatically adsorb the wafer 2 to the stage 3. In order to improve the thermal conduction of the stage 3, He was flowed from the rear surface of the wafer 2 at a pressure of, for example, 1.0 kPa.

[0081] After Ar was set at a flow rate of 1.0 L / min and the pressure was set at 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a dilution gas was introduced at a flow rate of 0.20 L / min while simultaneously irradiating with the IR lamp 60 at a specified output. Here, the time for HF introduction and IR irradiation was set to 60 seconds. As a result, a reaction layer was formed on the silicon nitride film 103.

[0082] Then, the exhaust valve in the pressure adjusting means 14 was opened 100%, and the exhaust was performed for 120 seconds. This exhaust operation exhausts fluorine gas and a part of the reaction products. Next, the IR lamp 60 was heated at a predetermined lamp intensity for 30 to 50 seconds with Ar flowing at a flow rate of 0.50 L / min while the set temperature of the stage 3 was kept the same, and the exhaust valve in the pressure adjusting means 14 was opened 100%. This removes the reaction layer. Then, returning to the beginning, the Ar was flowed at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds, and the cooling was performed. This series of processes (steps S102 to S106) was performed in 10 cycles according to the flow of FIG. 5.

[0083] The etching thickness of the silicon nitride film (PE-SiN), the etching thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film to the silicon oxide film obtained after 10 cycles when the output of the IR lamp 60 was changed are shown in Figs. 2A, 2B, and 2C. Fig. 2A is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first process according to the second embodiment (stage temperature -20°C, total pressure 900 Pa, 10 cycles). Fig. 2B is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the IR lamp output irradiated simultaneously with the HF supply in the first process according to the second embodiment (stage temperature 0°C, total pressure 900 Pa, 10 cycles). Fig. 2C is a graph showing the etching film thickness and the selectivity of the silicon nitride film and the silicon oxide film with respect to the output of the IR lamp irradiated simultaneously with the HF supply in the first step according to the second embodiment (stage temperature 20°C, total pressure 900 Pa, 10 cycles). Here, Fig. 2A, Fig. 2B, and Fig. 2C show the experimental results in which the temperature of the stage 3 was changed to -20°C, 0°C, and 20°C, respectively. Also, the IR lamp 60 for removing the reaction layer was irradiated for 40 s at an output of 70%.

[0084] Using a wafer 2 equipped with a thermocouple, HF gas was replaced with Ar, and the process temperature during lamp irradiation was actually measured. Table 2A shows the IR lamp output (IR output) and the temperature after 60 seconds when the stage temperature was different. Table 2B shows the temperature after 40 seconds with an IR lamp output of 70%. As shown in Table 2A, the temperature reached was found to be between 21°C and 81°C. Temperature measurements were also performed for the process of removing the reaction layer, and it was found that the reached temperature was as shown in Table 2B.

[0085] [Table 2A]

[0086] [Table 2B] 2A, 2B, and 2C, it is self-evident that the greater the output (IR output) of the IR lamp 60, the greater the etched thickness of the silicon nitride film (PE-SiN). In addition, the higher the temperature of stage 3, the more the graph of the etching amount of the silicon nitride film (PE-SiN) shifts to the left, and it can be seen that the same etching amount can be obtained with a lower output (IR output) of the IR lamp 60. However, when the temperature of stage 3 is high, there is a tendency for the etching amount of the silicon oxide film (PE-SiO2) to increase when the output of the IR lamp 60 is high, and it can be seen that the selectivity decreases.

[0087] Here, when etching the silicon nitride film 103 in the lateral direction, the selection ratio to the silicon oxide film 102 is preferably 10 or more, more preferably 20 or more. If this selection ratio is low, etching of the silicon oxide film 102, which should not be etched, occurs at the same time, and the shape of the end of the silicon oxide film 102 after etching becomes round instead of rectangular, as shown by 111 in Fig. 11A, which adversely affects device performance.

[0088] Empirically, a shape closer to a rectangle as shown in Fig. 10B can be obtained when the selection ratio is 10 or more, more preferably 20 or more. On the other hand, when the selection ratio is less than 5, the shape of the edge of the silicon oxide film 102 as shown by 111 in Fig. 11A becomes rounded, which is not desirable.

[0089] Here, similarly to Example 1, a sample in which a total of 20 layers of silicon nitride film 103 (film thickness 40 nm) and silicon oxide film 102 (film thickness 40 nm) were alternately formed was used to evaluate the etching characteristics in a fine pattern. The etching of the slit sample was performed for 10 cycles under the experimental conditions used in Figs. 2A, 2B, and 2C. The results are shown in Tables 2C, 2D, and 2E. Table 2C shows the etching results at a stage temperature of -20°C and 900 Pa. Table 2D shows the etching results at a stage temperature of 0°C and 900 Pa. Table 2E shows the etching results at a stage temperature of 20°C and 900 Pa.

[0090] As a result, when etching proceeds with high selectivity and in a shape close to a rectangle, as shown in Fig. 10B, the selectivity is poor and the tip of the silicon oxide film that should be left behind may become rounded, as shown in Fig. 11A. Even when the selectivity is relatively good, the corners of the silicon oxide film may be rounded and become triangular, as shown in Fig. 11B, and even if the corners of the silicon oxide film maintain a rectangular shape, as shown in Fig. 12, the thickness of the silicon oxide film may become thin.

[0091] Therefore, Tables 2C, 2D, and 2E show the recess amount (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity ratio from the slit pattern results (the amount of silicon nitride film etched from the initial dimension divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (the thickness 108 of the tip of the silicon oxide film after etching shown in FIG. 12 divided by the initial thickness 107 of the silicon oxide film). Good etching conditions here are those in which the recess amount is relatively large, the selectivity ratio is large, and the remaining SiO2 thickness is close to 1.

[0092] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also shown in Tables 2C, 2D, and 2E. The criteria are as shown in Table 1E above.

[0093] [Table 2C]

[0094] [Table 2D]

[0095] [Table 2E] As shown in Tables 2C, 2D, and 2E, when the stage temperature is higher, the appropriate output of the IR lamp 60 is smaller. In addition, in all cases, when the output of the IR lamp 60 is high, the remaining SiO2 thickness becomes small, and it was found that this is not suitable as a condition. Therefore, it was found that even when the selectivity is relatively high, the remaining SiO2 thickness may be low. Also, as a matter of course, when the IR output is too low, such as when the stage temperature is -20°C and the IR output is 45%, the selectivity is poor. From the above, it was found that the temperature that satisfies the recess amount, selectivity, and remaining SiO2 thickness is 30°C or more and 55°C or less.

[0096] Furthermore, when comparing the residual SiO2 thicknesses in Tables 2C, 2D, and 2E, it was found that the residual SiO2 thickness was larger when the stage temperature shown in Table 2C was lower (stage temperature -20°C), and smaller when the stage temperature shown in Table 2E was higher (stage temperature 20°C). Therefore, it was found that it is desirable to keep the stage 3 at a low temperature and obtain the necessary reaction temperature by irradiation with the IR lamp 60.

[0097] In this experiment, the temperature during irradiation of the second IR lamp 60 to remove the reaction layer was in the range of 70°C to 95°C as shown in Table 2B, but no significant difference was observed within this temperature range. Furthermore, under the conditions of a stage temperature of -20°C and IR output of 55%, which were relatively good performance conditions, the process of exhausting hydrogen fluoride gas and reaction products (step S104) in Fig. 5 was performed for 120 seconds with Ar flowing at 1.4 L / min and the exhaust valve in the pressure adjustment means 14 open 100%, instead of vacuum exhaust. As a result, it was found that there was an effect of reducing residues on the fine pattern compared to the case of vacuum exhaust.

[0098] Next, using the process conditions (stage temperature -20°C) discussed above in FIG. 2A, the output of the IR lamp 60 in the first step (step S103) for forming a reaction layer was fixed at 55%, and the irradiation time (post IR (70%) time) of the IR lamp 60 (output 70%) in the second step (step 105) for removing the reaction layer was changed to 20 seconds, 30 seconds, 40 seconds, and 50 seconds, and 10 cycles of etching were performed according to the flow of FIG. 5.

[0099] FIG. 2D shows the etching thickness of the silicon nitride film (PE-SiN) obtained after 10 cycles, the etching thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film to the silicon oxide film with respect to the IR lamp irradiation (post IR) time of the reaction layer removal in step 105. FIG. 2D is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film with respect to the irradiation time of the IR lamp irradiated in the second process according to the second embodiment (stage temperature 0° C., total pressure 900 Pa, 10 cycles). As a result of the experiment, when the IR irradiation for the reaction layer removal was 20 s, the reaction layer was not removed well, and the film thickness could not be measured with an optical film thickness measuring device. As can be seen from FIG. 2D, there was no significant difference in the results when the IR irradiation for the reaction layer removal in step 105 was 30 s to 50 s.

[0100] Here, as in the previous study, a sample in which a total of 20 layers of silicon nitride film 103 (film thickness 40 nm) and silicon oxide film 102 (film thickness 40 nm) were alternately formed was used to evaluate the etching characteristics in a fine pattern. The experimental conditions were the same as those in Figure 2D, and 10 cycles of etching of the slit sample were performed. The results are shown in Table 2F. Table 2F shows the etching results when the irradiation time of IR for removing the reaction layer (reaction layer removal IR) was changed.

[0101] [Table 2F] When the IR irradiation time for reaction layer removal (reaction layer removal IR) was 30s, 40s, or 50s, the results were good. In contrast, when the reaction layer removal IR was 20s, as mentioned above, the reaction layer could not be removed and etching did not go well. From this result, it was found that if the temperature for removing the reaction layer is too low, the reaction layer is not removed and etching does not go well.

[0102] As described below, the reaction product is ammonium fluorosilicate [(NH 4 ) 2 SiF 6 ] is considered to be the main component. Therefore, a certain degree of temperature is necessary to decompose and volatilize the reacted layer. However, if the temperature is too high, a side reaction such as etching of the silicon oxide film 102 may occur, so the minimum necessary temperature is desirable. From the above, the second temperature for removing the reaction layer is desirably, for example, 70°C or higher and 110°C or lower, and more desirably, 75°C or higher and 100°C or lower.

[0103] [Study on thickness and composition of reaction layer] Next, the thickness of the reaction layer was examined. Here, the conditions were equivalent to the etching conditions shown in FIG. 2C and Table 2E (stage temperature 20° C., 900 Pa, HF / Ar=0.40 / 0.20 L / min, 60 seconds), and the IR irradiation conditions for forming the reaction layer (output of the IR lamp 60) were changed from 30% to 50%, and cycle processing was performed without performing only the IR irradiation for removing the reaction layer (IR irradiation time for removing the reaction layer (reaction layer removal IR)). Specifically, in the flow of FIG. 5, after exhausting hydrogen fluoride gas and reaction products (step S104), the next wafer cooling (step S106) was performed without removing the reaction layer by heating (step S105), and then the cycle starting from introducing the dilution gas (S102) was repeated (that is, the sequence of S102->S103->S104->S106 was counted as one cycle, and multiple cycles were repeated). Silicon nitride film samples were prepared by performing the reaction layer removal cycle without IR irradiation 2 times, 5 times, and 10 times, respectively, and the cross section was observed with a scanning electron microscope to measure the film thickness of the reaction layer. The results are shown in Figure 2E. Figure 2E is a graph showing the thickness of the reaction layer on the silicon nitride film versus the number of cycles when the output of the IR lamp irradiated simultaneously with the HF supply in the first step of the second embodiment is changed.

[0104] FIG. 2E shows the thickness of the reaction layer versus the number of cycles at a stage temperature of 20° C. The data shows the results when the output of the IR lamp 60 that forms the reaction layer is changed from 30% to 50% (here, the IR output is set to 30%, 35%, 40%, 45%, and 50%). The stage temperature versus the IR output is summarized in Table 2A. It was found that when the IR output is 30% to 45%, the thickness of the reaction layer tends to saturate versus the number of cycles. On the other hand, when the IR output is 50%, the thickness of the reaction layer tends to increase significantly versus the number of cycles. In terms of temperature, it was found that when the temperature is 40° C. to less than 60° C. (IR lamp output 30% to 45%), the thickness of the reaction layer tends to saturate, and when the temperature is 70° C. (IR lamp output 50%), the reaction layer tends to continue to increase versus the number of cycles.

[0105] As shown in Table 2E, the etching results of the fine pattern were good when the stage temperature was 20° C. and the IR output was 35% and 40%. Considering the thickness of the reaction layer, if the reaction layer is too thick (IR output 50%), the amount of reaction layer will be too large when it is decomposed, volatilized and removed by the second IR irradiation, which may cause the shape of the adjacent silicon oxide film 102 to become thin or deteriorate. Therefore, it is important to control not only the temperature for forming and removing the reaction layer, but also the amount of reaction layer generated. Considering FIG. 2E, the thickness of the reaction layer is preferably 50 nm or less for 10 cycles. Therefore, in step S103, which is the first process, it is preferable to form a reaction layer of 5 nm or less per cycle.

[0106] The composition of the reaction layer was analyzed by X-ray photoelectron spectroscopy (XPS). As a result, the surface composition showed that nitrogen (N1s) showed a peak at 402 eV, not the 395 eV of silicon nitride. It was found that this 402 eV peak was attributed to ammonium salt. As for silicon (Si2P), a peak at 103 eV attributed to silicate was seen at 99 eV of silicon nitride, and hexafluorosilicate SiF 6 2- The elemental ratio is also ammonium silicofluoride [(NH 4 ) 2 SiF 6 ], Si=1, F=6, N=2, but the element ratio of the surface of the reaction layer by XPS was Si=1, F=4.4, N=1.6, which was found to be close to this. From the above, it can be concluded that the component generated as the reaction layer is ammonium silicofluoride [(NH 4 ) 2 SiF 6 ] is the main component, and HF and NH are produced when it decomposes and volatilizes. 3 However, depending on the conditions, it is thought that the adjacent silicon oxide film may be etched. EXAMPLES

[0107] [Etching method: Dry etching process flow 3] Next, the etching process using hydrogen fluoride gas without using plasma proposed in Example 3 of this embodiment, which is partially different from the etching process flow 1 shown in Example 1, will be described with reference to Figures 4, 6, and 9. Figure 6 is a flow diagram of the etching method for silicon nitride film according to the embodiment. Figure 9 is a time chart that shows a schematic flow of the operation over time of the etching process according to the third example.

[0108] First, the wafer 2 is transferred into the processing chamber 1 through a transfer port (not shown) provided in the processing chamber 1, and then the wafer 2 is placed on the protrusion 56 on the wafer stage 3. In this case, the stage temperature is set to a predetermined temperature between 30°C and 55°C.

[0109] Thereafter, Ar gas for thermal conduction to the wafer 2 is supplied via the mass flow controller 52, the gas distributor 51, and further the shower plate 23, thereby performing wafer heating on the stage in step S101 of FIG. 6. Since the Ar gas serves the roles of thermal conduction to the wafer 2 and dilution gas for diluting the HF gas, steps S101 and S102 of FIG. 6 are performed simultaneously. The flow rate of the Ar gas can be changed when conducting heat to the wafer 2 and when it is used as a dilution gas. The Ar gas for dilution can be allowed to continue to flow until the etching process is completed, or it can be stopped. Instead of Ar gas, N can be used as an inert gas. 2 A gas may also be used.

[0110] Next, in step S103 of Fig. 6, a predetermined amount of HF gas was supplied to the processing chamber 1 for a predetermined time to form a reaction layer. Here, heating by an IR (infrared) lamp as shown in the flow of Fig. 5 is not used, and only the temperature of heat transfer by the stage 3 is used. The temperature of the stage 3, that is, the temperature of the wafer 2, is preferably, for example, 30°C to 55°C, and more preferably, 35°C to 50°C. The film thickness of the reaction layer can be controlled by the temperature of the stage 3, the total pressure or HF partial pressure, the time, the number of repetitions, etc.

[0111] In this embodiment, the pressure to be used is preferably, for example, about 10 Pa to 1000 Pa, more preferably 50 Pa to 1000 Pa (50 Pa or more and 1000 Pa or less), and particularly preferably 300 Pa to 1000 Pa. The higher the pressure, the easier it is to form a reaction layer on the silicon nitride film, and the lower the temperature required for the formation.

[0112] After forming the reaction layer for a predetermined time, the supply of HF gas is stopped and the HF gas remaining in the gas phase and the reaction products on the silicon nitride film as the reaction layer are exhausted in step S104 of Fig. 6. In step S104, the reaction products can be exhausted more efficiently by supplying Ar gas as a diluent gas during and after the exhaust.

[0113] Next, heating is performed without flowing HF gas to remove the reaction layer (step S105 in FIG. 6). The heating temperature here is preferably, for example, 70° C. to 110° C. (70° C. or more and 110° C. or less), and more preferably 70° C. to 100° C. (70° C. or more and 100° C. or less). Here, an IR lamp 60 is used as a heating method. The heating method is not limited to this, and may be, for example, a method of heating the wafer stage 3, or a method of separately transporting the wafer to an apparatus that only performs heating and performing a heating process. In addition, Ar gas or nitrogen gas can be introduced during irradiation with the IR lamp 60. In addition, the heating process can be performed multiple times as necessary. After heating, the wafer 2 is cooled (wafer cooling) in step S106. Thereafter, the process from step S102 to step S106 is set as one cycle, and this is repeated N times (N is a positive integer). After repeating the cycle until the required etching amount is obtained, the flow in FIG. 6 ends.

[0114] Fig. 9 shows a time chart for the flow shown in Fig. 6. One cycle includes a process of flowing HF gas and Ar (a process of forming a reaction layer: S103) and a process of performing IR lamp heating without flowing HF gas (a process of decomposing and volatilizing the reaction layer: S105), and this process is repeated N times to cause etching of the silicon nitride film.

[0115] [Etching result 3] Using the etching processing apparatus 100 used in Example 1 and the etching process flow of Fig. 6, a process was studied in which the temperature (stage temperature) of the stage 3 was set to 20°C to 40°C, and IR heating was not performed in step S103 where HF / Ar was flowed. First, Ar was flowed at a flow rate of 1.4 L / min and 900 Pa for 60 seconds to conduct heat to the wafer 2. Then, while controlling the pressure at 900 Pa, HF was introduced at a flow rate of 0.40 L / min and Ar as a dilution gas was introduced at a flow rate of 0.20 L / min for 60 seconds. As a result, a reaction layer was formed on the silicon nitride film 103.

[0116] After that, the exhaust valve in the pressure adjusting means 14 was opened 100%, and the air was exhausted for 120 seconds. This exhaust operation exhausts fluorine gas and a part of the reaction products. Next, the temperature setting of the stage 3 was left unchanged (20°C to 40°C), Ar was flowed at a flow rate of 0.50 L / min, and the IR lamp 60 was heated at an output of 70% for 30 seconds with the exhaust valve in the pressure adjusting means 14 open 100%. This removes the reaction layer. After that, returning to the beginning, the wafer 2 was cooled with Ar flowing at a pressure of 900 Pa and a flow rate of 1.4 L / min for 60 seconds, until the temperature became the same as that of the stage 3. This series of processes was performed in 10 cycles according to the flow of FIG. 6.

[0117] The etching thickness of the silicon nitride film (PE-SiN), the etching thickness of the silicon oxide film (PE-SiO2), and the selectivity of the silicon nitride film (PE-SiN) to the silicon oxide film (PE-SiO2) obtained after 10 cycles when the temperature of stage 3 was changed are shown in Fig. 3A. Fig. 3A is a graph showing the etching thickness and selectivity of the silicon nitride film and the silicon oxide film when the stage temperature of the first process according to the third embodiment was changed.

[0118] As shown in Figure 3A, it was found that etching of silicon nitride film (PE-SiN) occurs due to the stage temperature alone, and the amount of etching of silicon nitride film (PE-SiN) is proportional to the stage temperature. In addition, etching of silicon oxide film (PE-SiO2) hardly occurs, and the selectivity is high for a single layer film.

[0119] Here, similarly to Examples 1 and 2, a sample in which a total of 20 layers of silicon nitride film 103 (film thickness 40 nm) and silicon oxide film 102 (film thickness 40 nm) were alternately formed was used to evaluate the etching characteristics in a fine pattern. The experimental conditions were the same as those in FIG. 3A, and etching of the slit sample was performed for 10 cycles and 20 cycles. The results are shown in Table 3. Table 3 shows the results of etching a fine pattern under the conditions of FIG. 3A.

[0120] [Table 3] Therefore, Table 3 shows the stage temperature and the number of cycles, the recess amount (the amount of silicon nitride film etched minus the amount of silicon oxide film etched), the selectivity ratio from the slit pattern results (the amount of silicon nitride film etched from the initial dimension divided by the amount of silicon oxide film etched), and the remaining SiO2 thickness (the thickness 108 of the tip of the silicon oxide film 102 after etching shown in FIG. 12 divided by the initial thickness 107 of the silicon oxide film 102). Good etching conditions here are those in which the recess amount is relatively large, the selectivity ratio is large, and the remaining SiO2 thickness is close to 1.

[0121] To make the evaluation results easier to understand, symbols such as ◎, 〇, △, and × are also shown in Table 3. The criteria are as shown in Table 1E above.

[0122] As a result, it was found that in both cases, the selectivity ratio decreased when the number of cycles was increased to 20 cycles of etching. In particular, when the number of cycles was large, the corners of the silicon oxide film 102 tended to be rounded off and the tip to be triangular, as shown by the shape 113 in FIG. 11B.

[0123] Although etching of silicon nitride film 103 is possible by reaction with HF at only the temperature of stage 3, it was found that etching by a combination of cooling at a low temperature of stage 3 and IR lamp 60 as previously described in Examples 1 and 2 provides better selectivity and pattern shape. In other words, in the first step (step S103) and the second step (step S105), the stage 3 on which wafer 2 is placed is kept at a low temperature of -50°C or higher and 0°C or lower, and then heated by IR lamp 60, to obtain a temperature of 30°C or higher and 55°C or lower in the first step and a temperature of 70°C or higher and 110°C or lower in the second step.

[0124] [Considerations regarding the thickness of the reaction layer] Next, the thickness of the reaction layer was examined in the same manner as in Example 2. Here, the conditions were the etching conditions shown in FIG. 3A and Table 3 (stage temperature 20° C. to 40° C., 900 Pa, HF / Ar=0.40 / 0.20 L / min, 60 seconds), and cycle processing was performed without forming the reaction layer and without IR irradiation for removing the reaction layer. Specifically, in the flow of FIG. 6, after exhausting hydrogen fluoride gas and reaction products (step S104), the reaction layer was not removed by heating (step S105), and the wafer was cooled (step S106), and then a cycle starting from introducing dilution gas (step S102) was repeated (that is, the sequence of S101->S102->S103->S104->S106 was counted as one cycle, and multiple cycles were repeated). Silicon nitride film samples were prepared by performing the reaction layer removal without IR irradiation cycle 2 times, 5 times, and 10 times, respectively, and the cross section was observed with a scanning electron microscope to measure the film thickness of the reaction layer. The results are shown in Figure 3B. Figure 3B is a graph showing the thickness of the reaction layer on the silicon nitride film versus the number of cycles when the stage temperature in the first step of the third embodiment is changed.

[0125] Figure 3B shows the relationship between the thickness of the reaction layer and the number of cycles when the stage temperatures are 30°C, 35°C, and 40°C. It can be seen that when the stage temperatures are 30°C and 35°C, the thickness of the reaction layer tends to saturate with respect to the number of cycles. When the stage temperature is 40°C, it was found that there is a tendency for the thickness of the reaction layer to increase slightly with respect to the number of cycles.

[0126] As described in the second embodiment, if the thickness of the generated reaction layer is too thick, when it is decomposed and volatilized by the second IR irradiation and removed, the amount is too large, which causes the shape of the adjacent silicon oxide film 102 to become thin or deteriorate. Therefore, it is important to control not only the temperature for forming and removing the reaction layer, but also the amount of the reaction layer generated. Considering FIG. 2E of the second embodiment, the thickness of the reaction layer is preferably 50 nm or less for 10 cycles, for example. Therefore, in the first process, step S103, it is preferable to form a reaction layer of 5 nm or less per cycle. [Explanation of symbols]

[0127] 1: processing chamber, 2: wafer, 3: wafer stage, 11: base chamber, 12: quartz chamber, 13: discharge area, 14: pressure adjustment means, 15: exhaust means, 16: vacuum exhaust piping, 20: ICP coil, 21: high frequency power supply, 22: matching machine, 23: shower plate, 24: high gas dispersion plate, 25: top plate, 26: slit plate, 27: flow path, 30: electrostatic adsorption electrode, 31: electrostatic adsorption DC power supply, 38: chiller, 39: refrigerant flow path, 50: mass flow controller, 51: gas distributor, 54: valve, 55: He gas, 56: protrusion for close-range cooling, 60, 60-1, 60-2, 60-3: IR lamp, 61: reflector, 64: power supply for IR lamp, 70: thermocouple, 71: thermocouple thermometer, 72: IR light transmitting window, 73: power supply for IR lamp, 74: high frequency cut filter, 101: substrate, 102: silicon nitride film, 103: silicon oxide film, 104: opening, 105: laminated film, 106: etching amount of silicon oxide film relative to silicon nitride film, 111: end of silicon oxide film after etching when selectivity is low, 112: diagram showing an example of an end of a silicon oxide film after etching, where the corners of the silicon oxide film remain rectangular while the thickness of the silicon oxide film has become thinner, 113: diagram showing an example of an end of a silicon oxide film after etching, where the corners of the silicon oxide film have been rounded off to form triangles.

Claims

1. 1. An etching method for dry-etching a film structure, which is formed in advance on a wafer placed in a processing chamber, and in which a silicon nitride film is sandwiched between silicon oxide films from above and below, and in which an end of a film layer constitutes a side wall of a groove or hole, by supplying a processing gas into the processing chamber without using plasma, comprising: In a first step, hydrogen fluoride gas is reacted at a temperature of 30° C. or more and 55° C. or less to form a reaction layer on the silicon nitride film; After the first step, in a second step, heating is performed at 70° C. or more and 110° C. or less without flowing the hydrogen fluoride gas, and the reaction layer formed in the first step is volatilized and removed; The first step and the second step are repeated a plurality of times to laterally etch the silicon nitride film from the end portion; The etching method is characterized in that, in the first step and the second step, a stage on which the wafer is placed is set to a low temperature of -50°C or more and 0°C or less, and lamp heating is performed thereon, thereby obtaining a temperature of 30°C or more and 55°C or less in the first step and a temperature of 70°C or more and 110°C or less in the second step.

2. 2. The etching method according to claim 1, 4. An etching method, wherein the pressure in the first step is 50 Pa or more and 1000 Pa or less.

3. 2. The etching method according to claim 1, An etching method comprising the steps of: between said first step and said second step, a step of exhausting the gas while flowing an inert gas.

4. 2. The etching method according to claim 1, 4. An etching method comprising the steps of: forming a reaction layer having a thickness of 5 nm or less in the first step.

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