Plasma processing method

Abstract

As an etching method for an object to be processed by which fine holes in a porous film and joints, referred to as seams, present in the porous film can be protected without the need to substitute a plurality of gases, provided is a plasma processing method for plasma-etching a low-k film having voids, the plasma processing method involving etching the low-k film containing silicon elements by using plasma generated from a mixed gas of fluorine element-containing gas and carbon element-containing gas.

Description

Plasma treatment method

[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.

[0002] In the field of semiconductors, low-dielectric-constant interlayer insulating film materials (hereinafter referred to as "low-k films") have been developed for next-generation semiconductors. Low-k films are a general term for films with a relative dielectric constant lower than 4.0. An example of a low-k film is a SiOC film.

[0003] To minimize the dielectric constant of a low-k film, it is necessary to create a porous film containing many pores. However, the introduction of pores significantly reduces mechanical strength, such as elastic modulus and hardness, in proportion to the amount of pores, making the film susceptible to damage by plasma etching and prone to problems such as peeling during the process.

[0004] In the manufacture of such electronic devices, fine patterns formed in a photoresist by lithography are etched by plasma etching, as required, using a TiN film, SiO ２ film, or Si ３ N ４ This is followed by a process to transfer the pattern to a hard mask such as a membrane, followed by a process to transfer the pattern to a porous membrane.

[0005] In plasma etching, radicals are generated by exciting the etching gas in the processing chamber of the plasma processing equipment, but these radicals can penetrate into the pores of the porous film and damage the film. For this reason, technologies have been proposed to protect the porous film from radicals.

[0006] For example, Patent Document 1 discloses a method in which 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 film by capillary condensation, and then SiF ４ , N.F. ３ It has been proposed to replace the fluorocarbon gas or hydrocarbon gas with an etching gas such as a gas, and then generate plasma in the etching gas to perform the etching process.

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

[0008] JP 2016-207768 A

[0009] The technology described in Patent Document 1 requires two steps: a step of introducing a gas that liquefies in 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 results in a time-consuming process. Furthermore, in order to liquefy the gas in the pores, the pressure, temperature, etc. in the processing chamber must be more strictly controlled.

[0010] An object of the present invention is to provide an etching method for a workpiece that can protect pores in a porous film and seams present in the porous film during etching without the need for replacement with multiple gas species.

[0011] The present invention has the following configuration to achieve the above object.

[0012] A plasma processing method for plasma etching a low-k film having voids, the plasma processing method comprising etching the low-k film containing silicon element using plasma generated from a mixed gas of a fluorine element-containing gas and a carbon element-containing gas.

[0013] According to the present invention, it is possible to provide an etching method for an object to be treated that can protect pores in a porous film and seams present in the porous film simultaneously with the etching process without the need for substitution with multiple gas species.

[0014] It is a schematic diagram showing the configuration of a plasma processing apparatus according to an embodiment of the present invention. It is a diagram showing a flowchart of an etching method of the present invention. It is a diagram showing a timing chart of an etching method of the present invention. It is a diagram showing a film structure of a wafer used in the present invention and an etching shape when the wafer is etched by the technology of the present invention.

[0015] First, an example of a plasma etching apparatus for carrying out the plasma processing method of the present invention will be described.

[0016] FIG. 1 shows the configuration of a plasma etching apparatus. In this case, a vacuum vessel 101, which constitutes a processing chamber, is a cylindrical vessel made of a conductive material such as aluminum and is electrically grounded. The upper opening of the vacuum vessel 101 is sealed with a top plate 102 made of a material that is electromagnetically transparent, such as quartz. A device for evacuating the interior of the vacuum vessel 101 to a predetermined pressure, such as a turbomolecular pump 103, and an auxiliary pump, such as a dry pump 104, connected to the turbomolecular pump 103, are connected to the bottom center of the vacuum vessel 101. A waveguide 105 covering the top plate 102 is provided above the top plate 102, and a high-frequency power source for generating plasma (hereinafter referred to as "plasma power source 107") is connected to the top plate 102 via a matching box 106.

[0017] In this case, the plasma power source 107 generates microwaves of 2.45 GHz. The generated microwaves propagate through the waveguide 105 and are introduced into the vacuum vessel 101 via the top plate 102. A solenoid coil 108 for forming a magnetic field within the vacuum vessel 101 is wound around the outside of the vacuum vessel 101. A shower plate 109 is provided above the vacuum vessel 101 below the top plate 102, and a gas supply pipe 110 is connected between the top plate 102 of the vacuum vessel 101 and the shower plate 109. A valve group 120, a flow rate controller group 130, and a gas source group 140 are connected to the gas supply pipe 110. The gas source group 140 includes multiple gas sources. The multiple gas sources include one or more gas sources for supplying a fluorine-based gas and a carbon-based gas, which will be described later. The valve group 120 and the flow rate controller group 130 can simultaneously supply the fluorine-based gas and the carbon-based gas to the gas supply pipe 110 at predetermined flow rates.

[0018] A processing gas is supplied from a gas supply pipe 110 into the space between the top plate 102 and the shower plate 109, and is then supplied via the shower plate 109 into a processing chamber formed in the vacuum vessel 101. A sample stage 111 is provided in the vacuum vessel 101, and a wafer is loaded through a wafer loading port (not shown) and placed and held on the sample stage 111. A bias high frequency power supply 114 is connected to the sample stage 111 via a bias matcher 113. The bias matcher is controlled by a control device 115, which controls the high frequency bias applied to the sample stage 111.

[0019] In the apparatus configured as described above, the process gas supplied into the vacuum vessel 101 is converted into plasma by the interaction (for example, electron cyclotron resonance (ECR)) between the electric field of the microwave introduced through the top plate 102 and the magnetic field generated by the solenoid coil 108, and the plasma is generated in the space between the shower plate 109 and the sample stage 111. The magnetic field strength at which the plasma is generated is near the 875 Gauss plane, which is called the ECR plane.

[0020] Furthermore, in this apparatus, an ion shielding plate 112 made of a material that is permeable to electromagnetic waves, such as quartz, divides the inside of the vacuum vessel 101 into an upper vacuum vessel region 101-1 and a lower vacuum vessel region 101-2. If plasma can be generated in the upper vacuum vessel region 101-1, which is above the ion shielding plate 112, ions are shielded, making it possible to process the sample using only radicals. As described above, the position where the plasma is formed can be controlled by the solenoid coil 108. Furthermore, because the ion shielding plate 112 is made of a material that is permeable to electromagnetic waves, dry etching using ordinary plasma is also possible by controlling the solenoid coil 108 so that an ECR surface is formed in the lower vacuum vessel region 101-2.

[0021] When plasma is generated in the lower region 101-2 of the vacuum vessel to perform dry etching, high-frequency power is applied to the sample stage 111 from a bias high-frequency power supply 114 via a bias matcher 113. The high-frequency power applied to the sample stage 111 is controlled independently of the plasma generation, and generates a bias voltage that causes ions in the plasma to be incident on the wafer. The outputs of the plasma power supply 107 and the bias high-frequency power supply 114 are controlled by a control device 115.

[0022] Next, the processing conditions for the etching method of this embodiment will be described. A flowchart of the etching method of the present invention is shown in FIG. 2. A fluorine-based gas and a carbon-based gas are simultaneously introduced into the processing chamber (step ST1). At the same time, high-frequency power is supplied to the plasma power source to convert the introduced gases into plasma, thereby starting etching (step ST2). Although ST1 and ST2 are shown one above the other in the flowchart of FIG. 2, they are actually performed almost simultaneously (step SQ). It is determined whether etching has ended and a stop condition is met (step STJ). If the stop condition is met (YES), the vacuum chamber 101 is evacuated (step ST4), and the process is terminated. The determination of whether the stop condition is met in step STJ is performed using endpoint detection, a well-known technique.

[0023] A timing chart of the etching method is shown in Figure 3. As explained in Figure 2, a fluorine-based gas and a carbon-based gas are introduced into the processing chamber, and simultaneously high-frequency power is supplied to the plasma power source to convert the introduced gases into plasma, thereby starting etching. Whether or not the specified etching has been completed is detected using a well-known etching end point detection method, and when it is determined that the etching has reached the end point (when it is determined that the stopping conditions have been met), the processing chamber is evacuated and the process is terminated.

[0024] In this embodiment, nitrogen trifluoride (NF ３ ) was used and supplied to the processing vessel at a flow rate of 10 ml / min by the flow rate controller group 130, and methane (CH ４ ) was used, and this was also supplied to the processing vessel at a flow rate of 5 ml / min by the flow rate controller group 130. ２) was supplied to the processing chamber at a flow rate of 200 ml / min by the flow rate controller group 130. Thereafter, the microwave power applied from the plasma power source 107 was set to 600 W, and the temperature on the wafer surface was set to 40° C., and etching processing was started.

[0025] The fluorine-based gas used as the etching gas is nitrogen trifluoride (NF ３ ), as well as sulfur hexafluoride (SF ６ ), carbon tetrafluoride (CF ４ ), trifluoromethane (CHF ３ ) or fluoromethane (CH ３ The etching rate varies depending on the type of etching gas. Not only one type of gas but also a mixture of gases may be used. In addition to the methane gas mentioned above, carbon-based gases such as fluorine-based gases with the chemical formula C can be used to fill (deposit) voids and seams in the object to be treated while etching with a fluorine-based gas. Ｘ H Ｙ (X and Y are natural numbers) can be used.

[0026] The deposition amount (speed) per unit time is larger when the number of C is larger at the same gas flow rate. ４ C than ２ H ６ (ethane gas) is larger. During deposition, radical species with a high sticking coefficient, such as C, are deposited in large amounts at the top of the hole. ２ Radical species with a lower sticking coefficient than C, such as fluorine, are deposited not only on the top of the hole but also in the void. On the other hand, if the amount of deposition becomes too large, the etching rate decreases. If the gas flow rate is high, the deposition rate increases, resulting in etch stop. Therefore, it is desirable to experimentally determine the optimal setting values ​​for the workpiece, using the gas type and gas flow rate of the fluorine-based gas used as the etching gas, and the gas type and gas flow rate of the carbon-based gas used as the deposition gas as parameters.

[0027] In this example, the parameters shown in Table 1 were used.

[0028] According to experiments conducted by the present inventors, a good balance between the etching rate and the deposition of the seam portion was achieved when a mixed gas of a fluorine-based gas and a carbon-based gas at a flow rate ratio such that the amount of fluorine atoms contained in the fluorine-based gas was 0.1% or more and 30% or less.

[0029] 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 atoms in the carbon-based gas molecule doubles, it is desirable to reduce the flow rate of the carbon-based gas to 1 / 2 of the flow rate of the fluorine-based gas.

[0030] Next, the film structure of the wafer used in this example will be described with reference to Figures 4(a) to 4(c). The film structure of the wafer in Figure 4(a) uses a silicon nitride (SiN) film 201, which is a hard mask layer, as a mask, and the silicon (Si) film 202 has a fin-like structure. A low-k film, for example, a SiOC film 203, is formed around the silicon (Si) film 202. The SiOC film 203 has a seam 204 within the film. In order to etch the SiOC film 203 flat, it is necessary to process it while minimizing damage to the seam portion.

[0031] 4B is a diagram showing the concept of the etching method of this embodiment. ４ By adding carbon-based components, they are deposited mainly in voids and seams, preventing the voids and seams from being preferentially etched during etching and preventing defects. In addition to methane gas, other gases that deposit in pores and seams include carbon-based components with the chemical formula C Ｘ H Ｙ (X and Y are natural numbers) can be used.

[0032] Furthermore, even for a structure that does not include a seam, etching can be performed in the same manner as for a structure that includes a seam.

[0033] 4C shows the etching shape of the wafer when processed by the etching method of this example. The SiOC film 203 is etched, and the surface of the SiOC film 203 has a flat shape.

[0034] Even when irradiating with plasma ions, the plasma processing method of the present invention can etch the SiOC film 203 to a flat shape. However, since the silicon (Si) film 202 is also etched, a method of irradiating with plasma radicals is more desirable. One cause of etching of the silicon (Si) film 202 by plasma ions is the electron shading phenomenon. When the SiOC film 203 is etched, the sidewalls of the silicon (Si) film 202 become charged with ions. As etching progresses, the aspect ratio of the trench hole increases, increasing the bending of the incident ions due to the charged sidewalls, making the silicon (Si) film 202 more likely to be etched.

[0035] Although vertical etch-back is shown for the purpose of explaining the shape, horizontal radical etching is also possible.

[0036] Although the present embodiment has been described above with reference to an example of a FinFET (Fin Field-Effect Transistor), the present invention is also applicable to a GAA (Gate All Around) structure or a CFET (Complementary Field-Effect Transistor).

[0037] 101 vacuum vessel, 102 top plate, 103 turbo molecular pump, 104 dry pump, 105 waveguide, 106 matching box, 107 plasma power supply, 108 solenoid coil, 109 shower plate, 110 gas supply pipe, 111 sample stage, 112 ion shielding plate, 113 bias matching box, 114 bias high frequency power supply, 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 voids, comprising the step of etching the low-k film containing silicon element using plasma generated from a mixed gas of a fluorine-containing gas and a carbon-containing gas.

2. The plasma processing method according to claim 1, wherein the Low-k film is a Low-k film embedded between silicon channels in a FinFET (Fin Field-Effect Transistor), a Low-k film separating transistors in a GAA (Gate All Around) structure, or a Low-k film separating transistors in a CFET (Complementary Field-Effect Transistor).

3. The plasma processing method according to claim 1, wherein the low-k film is etched using radicals generated by the plasma.

4. The plasma processing method according to claim 2, wherein the low-k film is etched using radicals generated by the plasma.

5. In the plasma processing method according to any one of claims 1 to 4, the fluorine-containing gas is nitrogen trifluoride gas (NF ３ ), sulfur hexafluoride gas (SF ６ ), carbon tetrafluoride gas (CF ４ ), trifluoromethane gas (CHF ３ ), or fluoromethane gas (CH ３ F).

6. In the plasma processing method according to any one of claims 1 to 4, the carbon element-containing gas is C Ｘ H Ｙ 2. A plasma processing method comprising: a gas; and wherein X and Y are natural numbers.

7. In the plasma processing method according to claim 6, the carbon-containing gas is methane gas (CH ４ ).

8. In the plasma processing method according to claim 1 or 2, the mixed gas of the fluorine-containing gas and the carbon-containing gas is nitrogen trifluoride gas (NF ３ ) and methane gas (CH ４ ) a mixed gas of said first and second gases.

9. The plasma processing method according to claim 8, wherein the low-k film is a SiOC film.

10. The plasma processing method according to claim 9, further comprising the step of etching back the SiOC film.

11. The plasma processing method according to claim 8, wherein the nitrogen trifluoride gas (NF ３ ) and methane gas (CH ４ 2. A plasma processing method comprising the steps of: adding argon gas (Ar) to a mixed gas of 12. The plasma processing method according to claim 11, wherein the nitrogen trifluoride gas (NF ３ ) gas flow rate, the methane gas (CH ４ ) is 0.1% or more and 30% or less.

13. A plasma processing method according to claim 1 or 2, characterized in that the temperature of a sample stage on which a workpiece 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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