Etching method using halogen fluoride, semiconductor manufacturing method

Abstract

To provide a method for plasma etching a fine pattern on a silicon substrate having silicon or a silicon oxide film with high accuracy.SOLUTION: An etching method includes performing plasma etching on a silicon substrate having silicon or a silicon oxide film by using halogen fluoride having a nitrogen content of 1 vol.% or less as etching gas. The nitrogen content in the etching gas composed of the halogen fluoride is adjusted to a predetermined amount or less, and accordingly the silicon or the silicon oxide film can be etched with high accuracy.SELECTED DRAWING: None

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 technology is 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 base materials, perfluorocarbons (PFCs) such as CF4, CHF3, C2F6, C3F8, C4F8, etc. and hydrofluorocarbons (HFCs) have been used as etching agents.

[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 for isotropically and selectively etching a polysilicon film by forming a laminated film by stacking an insulating film and polysilicon, forming holes through the laminated film, and introducing one or more gases selected from ClF3, BrF5, IF3, IF7, ClF, BrF3, IF5, and BrF, diluted with an inert gas, into the holes. Patent Document 1 describes etching under conditions where no plasma is generated, and an example using N2 as the diluent gas is described. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 6080166 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, the manufacturing process of semiconductor integrated circuits has seen a significant reduction in the size of the processed patterns, creating a strong demand for the development of high-precision (high selectivity, high aspect ratio, and high speed) dry etching technology.

[0008] In conventional etching, N2 is sometimes included as an inert gas, deposition agent, or diluent. However, when halogen fluorides are used as etching gases, the inventors believe that in high-precision dry etching, the presence of N2 in the etching gas can lead to the formation of silicon nitride through a reaction between N2 and fluorinated silicon generated during plasma etching of silicon and silicon oxide films. This silicon nitride accumulates on the substrate and becomes an obstacle to microfabrication. Furthermore, there are concerns that the consumption of halogen fluorides through the reaction between halogen fluorides and silicon nitride may lead to a decrease in the etching rate. Patent Document 1 describes an example in which N2 is used as a diluent gas, but since the etching is performed under conditions without plasma generation, it does not mention at all the influence of nitride film formation during plasma generation. [Means for solving the problem]

[0009] Under these circumstances, the inventors diligently studied to solve the above problems and found that by adjusting the nitrogen content in a halogen fluoride etching gas for etching a semiconductor wafer having silicon or a silicon oxide film to a predetermined amount or less, the influence of the nitride film can be greatly reduced, thus completing the present invention.

[0010] The gist of this 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 with a nitrogen (N2) content of 1 volume% or less as the etching gas. [2] An etching method of [1] in which 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 comprises a diluent gas selected from Ar, Ne, Kr, and Xe in an amount of 90 volume% or less. [4] A process of placing 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 stage in the processing chamber, The process of reducing the pressure inside the processing chamber, The process of supplying the etching gas into the processing chamber, An etching method according to [1] to [3], comprising the step of forming plasma in the processing chamber and performing anisotropic etching by the potential difference between the plasma and the substrate placed on it. A semiconductor manufacturing method using etching methods [5][1]~[4]. [Effects of the Invention]

[0011] According to the present invention, since the N2 content in the etching gas, which consists of halogen fluorides, is adjusted to a predetermined amount or less, a method for accurately etching silicon or silicon oxide films can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of the etching apparatus used in the present invention. [Modes for carrying out the invention]

[0013] The following describes embodiments for carrying out the present invention. In the etching method of the present invention, a halogen fluoride is used to etch the silicon or silicon oxide film on the substrate surface.

[0014] substrate The substrate is not particularly limited as long as it can be processed by plasma etching, and examples include glass substrates, silicon substrates, and gallium-arsenide substrates. Of these, the present invention prefers to use a silicon substrate used as a semiconductor wafer because it can be etched with high precision. For example, a silicon oxide film is formed on the silicon substrate.

[0015] A silicon oxide film is a film formed from silicon compounds containing oxygen atoms, such as SiO2, SiOC, and SiOCH. Furthermore, the substrate may be provided with an organic film or metal film processed into a predetermined pattern as a mask. The organic film is a film mainly composed of carbon, and specifically refers to a film formed from carbon-based materials such as amorphous carbon or a resist composition (hereinafter also referred to as a resist film). The resist composition is not particularly limited, and examples include fluorine-containing resin compositions and fluorine-free (meth)acrylic acid-based resin compositions. Examples of metal films 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 using the reaction due to the chemical reaction and physical collision between these active species and the substrate.

[0017] Halogen fluoride 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, the silicon oxide film can be etched with high selectivity, and the formation 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 the plasma etching apparatus, liquefaction in the piping or 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, fluorinated silicon, formed by the reaction of silicon or silicon oxide with halogen fluorides, reacts with N2 under plasma conditions to form a silicon nitride film. When a silicon nitride film is deposited on a semiconductor substrate, it becomes an obstacle to microfabrication and reduces yield. When a silicon nitride film reacts with halogen fluorides, the halogen fluorides are consumed, which can reduce the etching rate of the silicon or silicon oxide film.

[0022] Furthermore, the amount of N2 can be adjusted by using raw materials that do not contain N2. Also, for example, excess N2 can be reduced by cooling the container to liquefy or solidify the halogen fluoride and removing the gas phase with a diaphragm vacuum pump. Specifically, halogen fluoride is prepared, collected, cooled, and the gas phase is replaced with nitrogen. While still cooled, the gas phase is removed to a predetermined pressure with a diaphragm vacuum pump, and the gas composition at room temperature is adjusted to a predetermined amount of N2.

[0023] In the etching method of the present invention, a halogen fluoride with a low N2 content can be used alone as the plasma etching gas, but it is also possible to include an inert gas as a diluent. Furthermore, an additive gas may be included as needed.

[0024] Other gases As the inert gas, at least one gas selected from the group consisting of Ar, Ne, Kr, and Xe is used. In addition, examples of additive gases include reducing gases, fluorocarbons, hydrofluorocarbons, etc., such as 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 the following may be added as an additive gas.

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

[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 transported into a processing chamber, and the substrate is placed on a mounting stage in the processing chamber. The process of reducing the pressure inside the processing chamber, The process of supplying the etching gas into the processing chamber, The process involves forming plasma in the processing chamber and performing anisotropic etching based on the potential difference between the plasma and the substrate placed on it.

[0027] The etching methods that can be used in the present invention are 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 employed.

[0028] Figure 1 is a schematic diagram showing one embodiment of the reaction apparatus used in the etching method of the present invention. A reaction chamber 3, equipped with an etching gas introduction system 1 and a dilution / addition gas introduction system 2, contains a stage 5, which is a mounting platform for applying high frequency to a substrate. The stage 5 is connected to a high-frequency power supply. The stage 5 may also have a function to heat the substrate. Heaters may also be installed around the chamber to heat the chamber walls. The silicon substrate 4 placed on the stage 5 can be etched by bringing the etching gas into contact with it. A pressure gauge 6 and a vacuum pump 7 are installed inside the chamber 3 to create a reduced-pressure environment. The gas used for etching is discharged via a gas discharge line (not shown in the figure).

[0029] The gas components contained in the etching gas may be introduced into the reaction chamber independently, or they may be prepared as a mixed gas beforehand in the storage container before being introduced into the chamber.

[0030] The total flow rate of etching gas introduced into the chamber is appropriately selected considering the volume of the reaction chamber, the exhaust capacity of the exhaust section, and the pressure conditions. A plasma generation mechanism is provided within Chamber 3. This mechanism may involve applying a high-frequency voltage to parallel plates, passing a high-frequency current through a coil, or applying strong radio waves. When a high frequency is applied to a 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, enabling anisotropic etching.

[0031] The etching pressure is preferably 10 Pa or less, and 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 amount of ionized ions will decrease and a sufficient plasma density cannot be obtained, so it is preferable that it be 0.05 Pa or higher. Furthermore, the substrate temperature during etching is preferably 200°C or less, and particularly desirable to be 100°C or less for anisotropic etching. At high temperatures exceeding 150°C, areas other than the silicon and silicon oxide film, which are the intended etching targets, such as mask areas, may be etched, which can cause shape abnormalities.

[0032] Furthermore, the bias power that constitutes the potential difference between the plasma and the substrate generated during etching can be selected from 0 to 10,000 W depending on the desired etching shape, and 0 to 1,000 W is preferable when selective etching is performed.

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

[0034] The invention according to this embodiment will be described in more detail below with reference to examples, but the invention according to this embodiment is not limited to the following examples.

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

[0036] [Table 1]

[0037] <Example 1> A semiconductor wafer having a silicon oxide film was etched using iodine heptafluoride sample number 1, prepared in Preparation Example 1 described above. A Samco ICP etching system RIE-230iP was used for etching.

[0038] Etching was performed by independently flowing iodine heptafluoride (sample number 1) at a rate of 10 mL / min and argon (Ar) at a rate of 40 mL / min into the reaction chamber and applying a high-frequency voltage of 500 W to create a plasma. The etching conditions were a pressure of 3 Pa, a temperature of 20°C, and a bias power of 100 W. After etching, the semiconductor wafer was removed and elemental analysis of the surface was performed using XPS. The results showed no nitrogen and confirmed that a silicon nitride film had not been formed.

[0039] <Examples 2-6> In Example 2, etching was performed in the same manner as in Example 1, except that iodine heptafluoride sample number 2 was used instead of sample number 1 prepared in Preparation Example 1. Similarly, in Examples 3, 4, 5, and 6, etching was performed in the same manner as in Example 1, except that iodine heptafluoride samples 3, 4, 5, and 6 were used, respectively. After etching, the semiconductor wafers were removed and elemental analysis of the surface was performed by XPS. The results showed that nitrogen was not observed in Examples 2-6, confirming that no silicon nitride film had been 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 samples 7 and 8, prepared in Preparation Example 1, were used, respectively. After etching, the semiconductor wafers were removed and elemental analysis of the surface was performed by XPS. As a result, nitrogen was detected in both Comparative Examples 1 and 2, confirming the formation of a silicon nitride film. [Industrial applicability]

[0041] This invention provides an etching method using halogen fluorides with a low N2 content. [Explanation of Symbols]

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

Claims

1. A silicon substrate having a silicon or silicon oxide film is subjected to nitrogen (N ２ This etching method involves using a halogen fluoride with a content of 1 volume percent or less as the etching gas, and performing anisotropic etching by plasma under reduced pressure. An etching method in which the halogen fluoride is at least one selected from ClF3, BrF5, and IF7.

2. The etching method according to claim 1, characterized in that the etching gas further contains a diluent gas selected from Ar, Ne, Kr, and Xe in an amount of 90% by volume or less.

3. The process involves placing 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 stage in the processing chamber. The process of reducing the pressure inside the processing chamber, The process of supplying the etching gas into the processing chamber, The etching method according to claim 1 or 2, characterized in that it comprises a step of forming plasma in the processing chamber and performing anisotropic etching by the potential difference between the plasma and the substrate placed on it.

4. A method for manufacturing a semiconductor, using the etching method described in any one of claims 1 to 3.

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