Etching method using a halogen fluoride, method for manufacturing a semiconductor

Abstract

[Problem] The present invention relates to a method for plasma etching a fine pattern on a silicon substrate having a silicon or silicon oxide film with high precision. An etching method in which a silicon substrate having a silicon or silicon oxide film is plasma-etched using a halogen fluoride containing 1% or less by volume of nitrogen (N2) as the etching gas.

Description

Technical Field

[0001] The present invention relates to a semiconductor manufacturing process using a halogen fluoride with a low N2 content. More specifically, it relates to a method for accurately etching silicon or a silicon oxide film using a halogen fluoride with an N2 content of 1% by volume or less, and a method for manufacturing a semiconductor using the etching method.

Background Art

[0002] Today, in semiconductor manufacturing, extremely fine processing technologies are required, and the dry etching method has become the mainstream instead of the wet method. The dry etching method is a method of generating plasma in a vacuum space and forming a fine pattern on the surface of a substance at the molecular level.

[0003] In the etching of semiconductor materials such as silicon dioxide (SiO2), in order to increase the etching rate of SiO2 with respect to silicon, polysilicon, silicon nitride, etc. used as the base material, perfluorocarbons (PFCs) such as CF4, CHF3, C2F6, C3F8, C4F8, etc. and hydrofluorocarbons (HFCs) have been used as the etching agent.

[0004] However, these PFCs and HFCs are all substances with a long atmospheric lifetime and have a high global warming potential (GWP), so they have become substances subject to emission regulations in the Kyoto Protocol (COP3). In the semiconductor industry, there has been a demand for alternative substances with high economic efficiency and low GWP that enable miniaturization.

[0005] Therefore, the inventors of the present invention focused on using a halogen fluoride as an etching gas in the semiconductor manufacturing process. For example, Patent Document 1 discloses a method of forming a laminated film in which an insulating film and polysilicon are laminated, forming a hole penetrating the laminated film, and introducing one or more gases selected from ClF3, BrF5, IF3, IF7, ClF, BrF3, IF5, and BrF into the hole after diluting with an inert gas to isotropically and selectively etch the polysilicon film. Patent Document 1 describes an etching under conditions where plasma is not generated, and an example using N2 as a dilution gas is described.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In the manufacturing process of semiconductor integrated circuits, in recent years, due to the remarkable miniaturization of the processing patterns, the development of high-precision (high selectivity, high aspect ratio, high speed) dry etching technology has been strongly demanded.

[0008] In ordinary etching, N2 may be included as an inert gas, a deposition agent, or a diluent. However, when using a halogen fluoride as an etching gas, in high-precision dry etching, if N2 is present in the etching gas, when plasma-etching silicon or a silicon oxide film, silicon nitride is generated by the reaction between silicon fluoride generated and N2, and the generated silicon nitride accumulates on the substrate and becomes an obstacle to fine processing, the inventors considered. Also, there is a concern that the etching rate may decrease due to the consumption of the halogen fluoride by the reaction with silicon nitride. Although Patent Document 1 describes an example using N2 as a dilution gas, since it is an etching under conditions where plasma is not generated, no suggestion is given at all about the influence of silicon nitride film formation during plasma generation.

Means for Solving the Problem

[0009] Under such circumstances, as a result of intensive studies to solve the above problems, the inventors of the present invention have found that the influence of the nitride film can be extremely reduced by adjusting the nitrogen content in the halogen fluoride etching gas for etching a semiconductor wafer having silicon or a silicon oxide film to a predetermined amount or less, and have completed the present invention.

[0010] The gist of the present invention is as follows. [1] An etching method for plasma-etching a silicon substrate having silicon or a silicon oxide film using a halogen fluoride having a nitrogen (N2) content of 1% by volume or less as an etching gas. [2] The etching method according to [1], wherein the halogen fluoride is at least one selected from ClF3, BrF5, IF3, IF7, ClF, BrF3, IF5, and BrF. [3] The etching method according to [1] or [2], wherein the etching gas further contains a dilution gas selected from Ar, Ne, Kr, and Xe in an amount of 90% by volume or less. [4] A process of providing a mask on a silicon substrate having silicon or a silicon oxide film, transporting the substrate into a processing chamber, and placing the substrate on a mounting table in the processing chamber; a process of reducing the pressure in the processing chamber; a process of supplying the etching gas into the processing chamber; a process of forming plasma in the processing chamber and performing anisotropic etching by a potential difference between the plasma and the placed substrate, the etching method according to [1] to [3]. [5] A semiconductor manufacturing method using the etching method according to [1] to [4].

Effect of the Invention

[0011] According to the present invention, since the N2 content in the etching gas composed of halogen fluoride is adjusted to a predetermined amount or less, a method for accurately etching silicon or a silicon oxide film can be provided.

Brief Description of the Drawings

[0012]

Fig. 1

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be described. In the etching method of the present invention, silicon or a silicon oxide film on the substrate surface is etched using a hydrogen halide.

[0014] Substrate The substrate is not particularly limited as long as it can be processed by plasma etching, and examples include a glass substrate, a silicon substrate, and a gallium-arsenic substrate. Among these, when using a silicon substrate used as a semiconductor wafer in the present invention, it is suitable because etching can be performed with high precision. For example, a silicon oxide film or the like is formed on the silicon substrate.

[0015] The silicon oxide film refers to a film formed of a silicon compound containing oxygen atoms such as SiO2, SiOC, and SiOCH. Furthermore, an organic film or a metal film processed into a predetermined pattern may be provided on the substrate as a mask. The organic film is a film mainly composed of carbon, and specifically refers to a carbon-based material such as amorphous carbon or a film formed of a resist composition (hereinafter also referred to as a resist film). The resist composition is not particularly limited, and examples include a fluorine-containing resin composition and a (meth)acrylic acid-based resin composition that does not contain fluorine. Examples of the metal film include Ni and Cr.

[0016] In the present invention, silicon or silicon oxide on the substrate surface is etched to etch an extremely highly integrated fine pattern on the substrate surface. Note that plasma etching is a technique in which a high-frequency electric field is applied to a processing gas to cause plasma generation, the processing gas is separated into chemically active ions, electrons, and neutral species, and etching is performed by utilizing the chemical reaction and physical collision between these active species and the substrate.

[0017] Halide gas In the present invention, a gas of a halogen fluoride whose nitrogen content is adjusted to be below a predetermined range is used as an etching gas. Thereby, a silicon oxide film can be etched with high selectivity, and the generation of silicon nitride can be suppressed.

[0018] As the halogen fluoride, one or more selected from ClF3, BrF5, IF3, IF7, ClF, BrF3, IF5, and BrF are used. Among these, it is preferable to include ClF3, BrF3, BrF5, IF5, and IF7, and more preferably to include IF7, ClF3, and BrF5.

[0019] The boiling point of the halogen fluoride is preferably 50°C or lower, and more preferably 40°C or lower. If the boiling point is within the above range, when introducing the gas of the halogen fluoride into a plasma etching apparatus, liquefaction in pipes and the like can be prevented, and the occurrence of failures due to liquefaction can be avoided, so that the plasma etching process can be made more efficient.

[0020] The N2 content in the halogen fluoride is 1% by volume or less, desirably 0.5% by volume or less, preferably 0.1% by volume or less, more preferably 0.05% by volume or less, still more preferably 0.01% by volume or less, and even more preferably 0.005% by volume or less.

[0021] When the N2 content is high, silicon nitride film is formed by the reaction of silicon or silicon oxide film with silicon fluoride produced by the reaction of silicon or silicon oxide film with halogen fluoride and N2 under plasma conditions. When the silicon nitride film is deposited on the semiconductor substrate, it becomes an inhibiting factor for microfabrication and the yield decreases. When the silicon nitride film reacts with the halogen fluoride, the halogen fluoride may be consumed, and the etching rate of the silicon or silicon oxide film may decrease.

[0022] In addition, the adjustment of the N2 amount may be achieved by using materials that do not contain it. For example, excess N2 can be reduced by cooling the container to liquefy or solidify the halogen fluoride and extracting the gas phase with a diaphragm vacuum pump or the like. Specifically, the halogen fluoride is prepared, collected, cooled, the gas phase is replaced with nitrogen, and the gas phase is extracted with a diaphragm vacuum pump to a predetermined pressure while being cooled, and the N2 content is adjusted to a predetermined amount as the gas composition at room temperature.

[0023] In the etching method of the present invention, a halogen fluoride with a low N2 content can be used alone as a plasma etching gas, but usually it may contain an inert gas as a dilution gas. Further, an additive gas may be included as necessary.

[0024] Other gas As the inert gas, at least one gas selected from the group consisting of Ar, Ne, Kr, and Xe is used. Examples of the additive gas include reducing gases, fluorocarbons, hydrofluorocarbons, etc. For example, H2, HF, HI, HBr, HCl, NH3, CF4, CF3H, CF2H2, CFH3, C2F6, C2F4H2, C2F5H, C3F8, C3F7H, C3F6H2, C3F5H3, C3F4H4, C3F3H5, C3F5H, C3F3H, C3ClF3H, C4F8, C4F6, C5F8, and C5F 10 At least one gas selected from the group consisting of them may be added as an additive gas.

[0025] The content of the inert gas may be 90% by volume or less, preferably 50% by volume or less, based on the total amount of the etching gas. Also, the content of the additive gas may be 50% by volume or less, preferably 30% by volume or less, based on the total amount of the etching gas.

[0026] Etching method In the present invention, a mask is provided on a silicon substrate having silicon or a silicon oxide film as described above, the substrate is transferred into the processing chamber, and the substrate is placed on the mounting table in the processing chamber. The process of reducing the pressure in the processing chamber. The process of supplying the etching gas into the processing chamber. The process includes forming plasma in the processing chamber and performing anisotropic etching due to the potential difference between the plasma and the placed substrate.

[0027] The etching method that can be used in the present invention is not limited to various etching methods such as capacitively coupled plasma (CCP) etching, reactive ion etching (RIE), inductively coupled plasma (ICP) etching, electron cyclotron resonance (ECR) plasma etching, and microwave etching, and can be adopted.

[0028] FIG. 1 is a schematic diagram showing one aspect of a reaction apparatus employed in the etching method of the present invention. In a reaction chamber 3 equipped with an etching gas introduction system 1 and a dilution / additive gas introduction system 2, a stage 5 which is a mounting table having a function of applying a high frequency to the substrate is installed. The stage 5 is connected to a high frequency power supply. Also, the stage 5 may have a function of heating the substrate. A heater is also installed around the chamber, and it may be configured to heat the chamber wall. The etching gas can be brought into contact with the silicon substrate 4 placed on the stage 5 to etch the silicon substrate 4. Also, a pressure gauge 6 and a vacuum pump 7 are installed to make the inside of the chamber 3 a reduced pressure environment. Although not shown, the gas used for etching is discharged via a gas discharge line.

[0029] Regarding the gas components contained in the etching gas, they may be independently introduced into the reaction chamber, or they may be adjusted in advance as a mixed gas at the rear stage of the storage container and then introduced into the chamber.

[0030] The total flow rate of the etching gas introduced into the chamber is appropriately selected in consideration of the volume of the reaction chamber, the exhaust capacity of the exhaust section, and the pressure conditions. A plasma generation mechanism is provided in chamber 3, and the generation mechanism may apply a high-frequency voltage to parallel plates, pass a high-frequency current through a coil, or apply a strong radio wave. When a high frequency is applied to the substrate in the plasma, a negative voltage is applied to the substrate, and positive ions are incident on the substrate at high speed and perpendicularly, so that anisotropic etching becomes possible.

[0031] The pressure during etching is preferably 10 Pa or less, particularly preferably 5 Pa or less, in order to obtain a stable plasma. On the other hand, if the pressure in the chamber is too low, the number of ionized ions decreases and a sufficient plasma density cannot be obtained, so it is preferably 0.05 Pa or more. Also, the substrate temperature during etching is preferably 200 °C or less, and particularly preferably 100 °C or less for anisotropic etching. At a high temperature exceeding 150 °C, mask portions other than silicon and silicon oxide films, which are the original etching targets, may be etched, resulting in abnormal shapes.

[0032] Regarding the bias power that constitutes the potential difference between the plasma generated during etching and the substrate, it may be selected from 0 to 10000 W according to the desired etching shape, and about 0 to 1000 W is preferable when selectively etching.

[0033] The etching method of the present invention can be used in a semiconductor manufacturing method. Furthermore, the etching method of the present invention is an etching method capable of plasma etching a workpiece having a silicon oxide film.

Example

[0034] Hereinafter, the invention according to the present embodiment will be described more specifically with reference to examples. However, the invention according to the present embodiment is not limited only to the following examples.

[0035] <Preparation Example 1> Iodine heptafluoride obtained by reacting IF5 and F2 in a gas phase at 250 °C was cooled to -70 °C to solidify iodine heptafluoride, and the gas phase portion was replaced with nitrogen. While keeping it cooled, the gas phase portion was extracted to a predetermined pressure with a diaphragm vacuum pump, and it was prepared so that the N2 content in the gas composition at room temperature was about 5, 2, 1, 0.5, 0.1, 0.05, 0.01, 0.005 volume% (see the following table). Table 1 shows the composition of the prepared iodine heptafluoride.

[0036]

Table 1

[0037] <Example 1> Using the iodine heptafluoride of sample number 1 prepared in Preparation Example 1 above, etching of a semiconductor wafer having a silicon oxide film was performed. For the etching, an ICP etching apparatus RIE-230iP manufactured by Samco was used.

[0038] Iodine heptafluoride of sample number 1 was independently circulated into the reaction chamber at 10 mL / min and Ar at 40 mL / min, and etching was performed by applying a high-frequency voltage of 500 W to form plasma. As the etching conditions, the pressure was 3 Pa, the temperature was 20 °C, and the bias power was 100 W for etching. After the etching, the semiconductor wafer was taken out and surface elemental analysis was performed by XPS. As a result, it was confirmed that nitrogen was not observed and no silicon nitride film was formed.

[0039] <Examples 2 to 6> In Example 2, etching was performed in the same manner as in Example 1, except that iodine heptafluoride with sample number 2 prepared in Preparation Example 1 was used instead of the sample with sample number 1. Similarly, in Examples 3, 4, 5, and 6, etching was performed in the same manner as in Example 1, except that iodine heptafluoride with sample numbers 3, 4, 5, and 6 were used, respectively. After etching, the semiconductor wafer was taken out and elemental analysis of the surface was performed by XPS. As a result, it was confirmed that in Examples 2 to 6 as well, nitrogen was not observed and no silicon nitride film was formed.

[0040] <Comparative Examples 1 and 2> In Comparative Examples 1 and 2, etching was performed in the same manner as in Example 1, except that iodine heptafluoride with sample numbers 7 and 8 prepared in Preparation Example 1 were used, respectively. After etching, the semiconductor wafer was taken out and elemental analysis of the surface was performed by XPS. As a result, it was confirmed that in both Comparative Examples 1 and 2, nitrogen was detected and a silicon nitride film was formed.

Industrial Applicability

[0041] Provided is an etching method using a halogen fluoride with a low N2 content.

Explanation of Symbols

[0042] 1: Halogen fluoride introduction system 2: Dilution / additive gas introduction system 3: Reaction chamber 4: Silicon substrate 5: Stage 6: Pressure gauge 7: Vacuum pump

Claims

1. A silicon substrate having silicon or a silicon oxide film is etched with a halogen fluoride having a nitrogen (N ２ ) content of 1% by volume or less as an etching gas (however, except that the etching gas contains fluorocarbon), further containing a dilution gas, and the etching gas and the dilution gas are each independently circulated into a reaction chamber, and anisotropically etched by plasma under reduced pressure. This is an etching method, The halogen fluoride is at least one selected from ClF₃, BrF₅, and IF₇, and the dilution gas is at least one selected from Ar, Ne, Kr, and Xe. An etching method.

2. A process of providing a mask on a silicon substrate having silicon or a silicon oxide film, transporting the substrate into a processing chamber, and placing the substrate on a mounting table in the processing chamber; a process of reducing the pressure in the processing chamber; a process of supplying the etching gas into the processing chamber; a process of forming plasma in the processing chamber and performing anisotropic etching by the potential difference between the plasma and the mounted substrate. The etching method according to claim 1, characterized by comprising the above steps.

3. A method for manufacturing a semiconductor, using the etching method according to claim 1 or 2.

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