Plasma processing method

Abstract

Provided is a plasma processing method for plasma etching a Low-k film having pores, the plasma processing method being a method for etching an object to be processed, the object to be processed being capable of protecting pores in a porous film and seams, referred to as slits, existing in the porous film without replacing a plurality of gases. And etching the Low-k film containing the silicon element by using plasma generated by a mixed gas of a fluorine element-containing gas and a carbon element-containing gas.

Description

Technical Field

[0001] The present invention relates to an etching method for an object to be processed such as a semiconductor element, and more particularly to an etching method suitable for etching a semiconductor element having a porous film. Background Art

[0002] In the semiconductor field, low dielectric constant interlayer insulating film materials (hereinafter referred to as "Low-k films") are being developed for next-generation semiconductors. The so-called Low-k film is a general term for films having a relative dielectric constant of less than 4.0. Examples of Low-k films include SiOC films.

[0003] In order to reduce the relative dielectric constant of the Low-k film as much as possible, it is necessary to form a porous film containing a large number of pores. However, if pores are introduced, the mechanical strength such as elastic modulus and hardness will be significantly reduced in proportion to the amount of pores, so it is easy to be damaged by plasma etching, and it is easy to cause problems such as peeling during the process.

[0004] Incidentally, in the manufacture of such electronic devices, a process is performed in which a fine pattern formed on a photoresist by photolithography is transferred to a TiN film, SiO2 film, or the like as needed by plasma etching. 2 Film or Si 3 N 4 The pattern is then transferred onto a hard mask such as a porous film.

[0005] In plasma etching, etching gas is excited in a processing chamber of a plasma processing device to generate free radicals, but the free radicals penetrate into the pores (micropores) of the porous membrane and damage the porous membrane. Therefore, a technology for protecting the porous membrane from free radicals has been proposed.

[0006] For example, Patent Document 1 proposes that a fluorocarbon gas or a hydrocarbon gas is introduced into a processing chamber under specific conditions, and the gas is liquefied in the pores of a porous membrane by capillary condensation, and then SiF 4 NF 3 After replacing the fluorocarbon gas or the hydrocarbon gas with an etching gas such as a gas, plasma is generated in the etching gas to perform etching processing.

[0007] In this method, since the pores are protected by liquefied fluorocarbon gas, hydrocarbon gas, or the like, it is expected that the etching process can be performed without damaging the pores.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2016-207768 Summary of the invention

[0011] Problems to be solved by the invention

[0012] The technology described in Patent Document 1 has the following problems: the process requires two steps: a step of introducing a gas that is liquefied into the pores to fill the pores with the liquefied component, and a step of replacing the gas with an etching gas and then etching with the etching gas, which takes time in the process. In addition, in order to liquefy the gas in the pores, it is necessary to more strictly manage the pressure and temperature in the processing chamber.

[0013] An object of the present invention is to provide a method for etching an object to be processed, which can protect pores in a porous membrane and seams called seams existing in the porous membrane during etching without replacing a plurality of gas species.

[0014] Means of solving the problem

[0015] The present invention for achieving the above-mentioned object is configured as follows.

[0016] A plasma processing method is a plasma processing method for performing plasma etching on a Low-k film having holes, wherein the Low-k film containing silicon is etched using plasma generated from a mixed gas of a fluorine-containing gas and a carbon-containing gas.

[0017] Effects of the Invention

[0018] According to the present invention, it is possible to provide a method for etching an object to be processed, which can protect pores in a porous film and seams called seams existing in the porous film during etching without replacing a plurality of gas species. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 1 is a schematic diagram showing the structure of a plasma processing apparatus according to an embodiment of the present invention.

[0020] Figure 2 It is a diagram showing the flow of the etching method of the invention.

[0021] Figure 3 It is a diagram showing the timing of the etching method of the present invention.

[0022] Figure 4 The diagram shows the film structure of the wafer used in the present invention and the etching shape when the wafer is etched using the technology of the present invention. DETAILED DESCRIPTION

[0023] First, an example of a plasma etching apparatus for carrying out the plasma processing method of the present invention will be described.

[0024] Figure 1 The structure of the plasma etching device is shown in . In this case, the vacuum container 101 constituting the processing chamber is, for example, a cylindrical container made of a conductive material such as aluminum, and is electrically grounded (earthed). The upper opening of the vacuum container 101 is sealed by a top plate 102 made of a material that can penetrate electromagnetic waves, such as quartz. In the lower center of the vacuum container 101, there is connected a device for decompressing and exhausting the interior to a specified pressure, such as a turbomolecular pump 103 and an auxiliary pump connected thereto, such as a dry pump 104. A waveguide 105 covering the top plate 102 is provided on the upper part of the top plate 102, and a high-frequency power supply for plasma generation (hereinafter referred to as "plasma power supply 107") is connected via a matcher 106.

[0025] In this case, the plasma power supply 107 oscillates microwaves of 2.45 GHz. The oscillated microwaves are transmitted through the waveguide 105 and introduced into the vacuum container 101 via the top plate 102. An electromagnetic valve coil 108 for forming a magnetic field in the vacuum container 101 is wound on the outside of the vacuum container 101. A shower plate 109 is provided on the upper part of the vacuum container 101 below the top plate 102, and a gas supply pipe 110 is connected between the top plate 102 of the vacuum container 101 and the shower plate 109. A valve group 120, a flow controller group 130, and a gas source group 140 are connected to the gas supply pipe 110. The gas source group 140 includes a plurality of gas sources. The plurality of gas sources include one or more gas sources for supplying the fluorine-based gas and the carbon-based gas described later. The valve group 120 and the flow controller group 130 can simultaneously supply the fluorine-based gas and the carbon-based gas to the gas supply pipe 110 at a specified flow rate.

[0026] Processing gas is supplied from a gas supply pipe 110 to a space between the top plate 102 and the shower plate 109, and the processing gas is supplied to a processing chamber formed in the vacuum container 101 through the shower plate 109. A sample stage 111 is provided in the vacuum container 101, and a wafer is carried in from a wafer carrying port (not shown) and arranged and held on the sample stage 111. A bias high-frequency power supply 114 is connected to the sample stage 111 through a bias matching device 113. The bias matching device is controlled by a control device 115 to control the high-frequency bias applied to the sample stage 111.

[0027] In the apparatus constructed as described above, the processing gas supplied into the vacuum container 101 is plasmatized by the electric field of the microwave introduced through the top plate 102 and the magnetic field formed by the electromagnetic valve coil 108 (for example, Electron Cyclotron Resonance (ECR)), and plasma is formed in the space between the shower plate 109 and the sample stage 111. In addition, the surface near which the magnetic field strength of plasma is 875 Gauss is called the ECR surface.

[0028] In addition, in this device, the vacuum container 101 is divided into the upper region 101-1 and the lower region 101-2 of the vacuum container by an ion shielding plate 112 made of a material that can transmit electromagnetic waves, such as quartz. If plasma can be generated above the ion shielding plate 112, that is, in the upper region 101-1 of the vacuum container, ions are shielded, and the sample can be processed only by free radicals. As described above, the position where plasma is formed can be controlled by the electromagnetic valve coil 108. In addition, since the ion shielding plate 112 is made of a material that can transmit electromagnetic waves, by controlling the electromagnetic valve coil 108 in such a way that an ECR surface is formed in the lower region 101-2 of the vacuum container, conventional dry etching using plasma can also be performed.

[0029] When plasma is formed in the lower region 101-2 of the vacuum container for dry etching, high-frequency electric power is applied to the sample stage 111 from the high-frequency bias power supply 114 via the bias matching device 113. The high-frequency electric power applied to the sample stage 111 is controlled independently of the generation of plasma, and a bias voltage is generated to cause ions in the plasma to enter the wafer.

[0030] The plasma power supply 107 and the bias high frequency power supply 114 are controlled by a control device 115 to control the output of each power supply.

[0031] Next, the processing conditions of the etching method of this embodiment are described.

[0032] Figure 2 The process of the etching method of the present invention is shown in FIG. Fluorine-based gas and carbon-based gas are introduced into the processing container at the same time (step ST1). At the same time, high-frequency electric power is supplied to the plasma power supply to plasmatize the introduced gas and start etching (step ST2). Figure 2 The process of FIG. 1 shows that ST1 and ST2 are arranged in a row, but in fact, they are basically implemented at the same time (step SQ). It is determined whether the etching is completed and the stop condition is met (step STJ). When the stop condition is met (in the case of YES), the vacuum container 101 is evacuated (step ST4) as completion. In addition, it is determined whether the stop condition of step STJ is met by endpoint detection, which is a well-known technology.

[0033] exist Figure 3 The timing of the etching method is shown in FIG. Figure 2 As described above, fluorine-based gas and carbon-based gas are introduced into the processing container, and high-frequency electric power is supplied to the plasma power supply to plasmatize the introduced gas to start etching. Whether the prescribed etching is completed is detected by a known etching endpoint detection method, and when it is determined that the endpoint has been reached (when it is determined that the stop condition is satisfied), the processing container is evacuated to complete the process.

[0034] In this embodiment, nitrogen trifluoride (NF 3 ) as the fluorine-based gas, which is supplied to the processing container at a flow rate of 10 ml / min through the flow controller group 130, and methane (CH 4 ) as a carbon-based gas, which is also supplied to the processing container at a flow rate of 5 ml / min through the flow controller group 130. In addition, nitrogen (N 2 ) is supplied into the processing container. Thereafter, the microwave power output from the plasma power supply 107 is set to 600 W, the temperature on the wafer surface is set to 40° C., and the etching process is started.

[0035] Fluorine-based gases used as etching gases include nitrogen trifluoride (NF 3 ) can also be used. 6 ), carbon tetrafluoride (CF 4 ), trifluoromethane (CHF 3 ) or fluoromethane (CH 3 F), etc. Depending on the type of these etching gases, the etching speed varies. Not only one gas but also a mixed gas can be used. While etching with the fluorine-based gas, as a carbon-based gas that fills (deposits) the pores (holes) and seams (joints) in the processed object with a precipitate (precipitate), in addition to the above-mentioned methane gas, a carbon-based gas represented by the chemical formula C X H Y (X, Y are natural numbers) represents the type of gas.

[0036] Regarding the precipitation amount (rate) per unit time, if the gas flow rate is the same, the larger the number of C, the greater the precipitation amount (rate). 2 H 6 (Ethane gas) is greater than CH 4 During precipitation, free radical species with high adhesion coefficients such as C precipitate in large quantities on the upper part of the hole. 2Radical species with an adhesion coefficient lower than C are not only deposited on the upper part of the cavity, but also in the hole part. On the other hand, if the deposition amount is too much, the etching speed is reduced. If the gas flow rate is large, the deposition speed becomes large and etching stops. Therefore, it is desired to experimentally find the optimal setting value based on the object to be processed by using the gas type and gas flow rate of the fluorine-based gas as the etching gas and the gas type and gas flow rate of the carbon-based gas as the deposition gas as parameters.

[0037] In this embodiment, the parameters shown in Table 1 are used.

[0038] [Table 1]

[0039] Fluorine gas Carbon-based gases Dilution gas <![CDATA[NF 3 :10ml / min]]> <![CDATA[CH 4 :5ml / min]]> Ar: 200ml / min <![CDATA[sF 6 :15ml / min]]> <![CDATA[C 2 H 6 :5ml / min]]> Ar: 200ml / min

[0040] According to the experiments of the present inventors, when a mixed gas of a fluorine-based gas and a carbon-based gas having a flow ratio of 0.1% to 30% relative to the amount of fluorine atoms contained in the fluorine-based gas is used, the balance between the etching speed and the deposition of the seam is good.

[0041] The ratio of the amount of fluorine atoms contained in the fluorine-based gas to the amount of carbon atoms contained in the carbon-based gas is preferably 10% or more and 20% or less. In this case, if the number of C in the carbon-based gas molecule is 2 times, it is desirable to make the flow rate of the carbon-based gas 1 / 2 relative to the flow rate of the fluorine-based gas.

[0042] Next, use Figure 4 (a)~ Figure 4 (c) illustrates the film structure of the wafer used in this embodiment. Figure 4 The film structure of the wafer of (a) is a silicon nitride (SiN) film 201 as a hard mask layer as a mask, and a silicon (Si) film 202 has a fin structure. A low-k film, such as a SiOC film 203, is formed around the silicon (Si) film 202. The SiOC film 203 has a seam 204 in the film. In order to smoothly etch the SiOC film 203, it is necessary to perform processing while suppressing damage to the seam portion.

[0043] Figure 4 (b) is a diagram showing the concept of the etching method of this embodiment. By adding methane (CH 4 ), the carbon-based components are mainly precipitated in the holes and seams, which inhibits the holes and seams from being etched preferentially during etching and prevents defects.

[0044] As the gas species precipitated (deposited) in the pores and seams, in addition to methane gas, a gas having the chemical formula C X H Y (X, Y are natural numbers) represents the type of gas.

[0045] In addition, even for a structure that does not include a seam, etching similar to that in the case of including a seam can be performed.

[0046] Figure 4 (c) is a diagram showing an etching shape when the wafer is processed by the etching method of this embodiment. The SiOC film 203 is etched, and the surface of the SiOC film 203 is flat.

[0047] In the case of irradiation with plasma ions, the shape of the SiOC film 203 can also be etched flat by the plasma processing method of the present invention. However, since the silicon (Si) film 202 will be etched, a method of irradiating plasma free radicals is more desirable. As the reason why the silicon (Si) film 202 is etched by plasma ions, the electron masking phenomenon can be cited. If the SiOC film 203 is etched, the side walls of the silicon (Si) film 202 are charged due to the ions. As the etching proceeds, the aspect ratio of the slot increases, the incident bending of the ions caused by the charged side walls increases, and the etching of the silicon (Si) film 202 is likely to occur.

[0048] For shape illustration, vertical etching is shown, but horizontal radical etching is also possible.

[0049] In the above, the present embodiment describes the example of FinFET (Fin Field-Effect Transistor), but the present invention can also be applied to GAA (Gate All Around) structure or CFET (Complete Field-Effect Transistor).

[0050] Explanation of symbols

[0051] 101 vacuum container, 102 top plate, 103 turbomolecular pump, 104 dry pump, 105 waveguide, 106 matching device, 107 plasma power supply, 108 solenoid valve coil, 109 shower electrode, 110 gas supply pipeline, 111 sample table, 112 ion shielding plate, 113 bias matching device, 114 high-frequency power supply for bias, 115 control device, 201 SiN film, 202 Si film, 203 SiOC film, 204 seam in film.

Claims

1. A plasma processing method for plasma etching a Low-k film having holes, characterized in that: The Low-k film containing silicon element is etched using plasma generated from a mixed gas of a fluorine element gas and a carbon element gas.

2. The plasma treatment method according to claim 1, characterized in that: The Low-k film is a Low-k film buried between silicon channels in FinFET, or a Low-k film separating transistors in GAA, or a Low-k film separating transistors in CFET, or a Low-k film separating transistors in complementary field effect transistor.

3. The plasma treatment method according to claim 1, characterized in that: The Low-k film is etched using radicals generated by the plasma.

4. The plasma treatment method according to claim 2, characterized in that: The Low-k film is etched using radicals generated by the plasma.

5. The plasma processing method according to any one of claims 1 to 4, characterized in that: The fluorine-containing gas includes any gas selected from nitrogen trifluoride gas NF3, sulfur hexafluoride gas SF6, carbon tetrafluoride gas CF4, trifluoromethane gas CHF3 or fluoromethane gas CH3F.

6. The plasma processing method according to any one of claims 1 to 4, characterized in that: The carbon-containing gas includes C X H Y gas, the X and the Y are natural numbers.

7. The plasma processing method according to claim 6, characterized in that: The carbon-containing gas contains methane gas CH4.

8. The plasma treatment method according to claim 1 or claim 2, characterized in that: The mixed gas of the fluorine-containing gas and the carbon-containing gas is a mixed gas of nitrogen trifluoride gas NF3 and methane gas CH4.

9. The plasma processing method according to claim 8, characterized in that: The Low-k film is a SiOC film.

10. The plasma processing method according to claim 9, characterized in that: The SiOC film is etched back.

11. The plasma processing method according to claim 8, characterized in that: Argon gas Ar is added to the mixed gas of the nitrogen trifluoride gas NF3 and the methane gas CH4.

12. The plasma processing method according to claim 11, characterized in that: The gas flow rate ratio of the methane gas CH4 to the gas flow rate of the nitrogen trifluoride gas NF3 is greater than or equal to 0.1% and less than or equal to 30%.

13. The plasma treatment method according to claim 1 or claim 2, characterized in that: The temperature of the sample stage on which the object to be processed on which the low-k film is formed is placed is equal to or higher than the liquefaction temperature of the gas.

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