Silicon etchant

Abstract

To provide a method capable of a wet etching silicon at a high speed without etching an insulating film such as silicon dioxide when manufacturing a semiconductor device or the like.SOLUTION: A Si surface is selectively etched by preparing a composition containing an organic alkali compound such as quaternary ammonium hydroxide, orthoperiodic acid or a salt thereof, and water as an etching solution, having a pH of 12.5 or more, and containing no fluoride ion and no metal, and bringing the etching composition into contact with a substrate having a silicon surface and at least one surface selected from a silicon dioxide surface and a silicon nitride surface. In the etching composition containing the ortho-periodic acid (salt), silicon dioxide and silicon nitride are not substantially etched, while silicon is etched at a higher speed than in the related arts, so that productivity in manufacturing a semiconductor device or the like is improved.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicon etching process used in the manufacture of various silicon devices. [Background technology]

[0002] Silicon (Si) is used in a variety of fields due to its excellent mechanical and electrical properties. Its mechanical properties are utilized in valves, nozzles, printer heads, and semiconductor sensors for detecting various physical quantities such as flow rate, pressure, and acceleration (e.g., diaphragms in semiconductor pressure sensors and cantilevers in semiconductor acceleration sensors). Its electrical properties are also utilized in various semiconductor devices, such as memory devices and logic devices, as materials for metal wiring and gate electrodes.

[0003] Silicon processing in semiconductor device manufacturing is primarily performed by etching. Etching methods include dry etching, such as RIE (reactive ion etching) and ALE (atomic layer etching), and wet etching using an acidic or alkaline aqueous solution. While wet etching is often inferior to dry etching in terms of the fineness of the processing, it is superior to dry etching in terms of productivity, as it can process a larger area and multiple wafers at the same time. In particular, wet etching using an alkaline aqueous solution is preferably used in processes where productivity is important, such as when removing the entire unwanted silicon layer by etching.

[0004] Several etching solutions have been proposed that are highly productive, i.e., capable of removing silicon at high speed. For example, an etching solution has been proposed in which an alkaline compound, an oxidizing agent, and a hydrofluoric acid compound are contained in water and the pH is adjusted to 10 or higher (see Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-135081 [Patent Document 2] International Publication No. 2016 / 068183 Brochure [Patent Document 3] Patent Publication No. 2021-90040 [Patent Document 4] Patent Publication No. 2021-184454 [Patent Document 5] International Publication No. 2021 / 172397 Brochure Summary of the Invention [Problem to be solved by the invention]

[0006] In various semiconductor devices, in addition to silicon, for example, silicon oxide (SiO2) and silicon nitride (SiN) are used as insulating materials. Therefore, silicon etching in the manufacturing process of semiconductor devices may require a high etching selectivity relative to other constituent materials such as silicon oxide and silicon nitride. The hydrofluoric acid compound contained as an essential component in the etching solution of Patent Document 1 generally increases the etching rate relative to other constituent materials such as silicon oxide and silicon nitride. In other words, the etching solution of Patent Document 1 leaves room for improvement in terms of etching selectivity relative to other constituent materials such as silicon oxide and silicon nitride.

[0007] Therefore, an object of the present invention is to provide an alkaline etching solution that can be brought into contact with a substrate having a Si surface and an SiO2 surface or a SiN surface, and that can selectively and quickly etch the Si surface. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have found that by using an etching solution made of an alkaline aqueous solution containing a relatively small amount of orthoperiodic acid, it is possible to dramatically increase the silicon etching rate while suppressing etching of SiO2 and SiN surfaces, which has led to the completion of the present invention.

[0009] That is, the present invention provides a method for preparing an etching composition having a pH of 12.5 or higher and containing no fluoride ions or metals by mixing an organic alkaline compound, orthoperiodic acid or a salt thereof, and water; A step of contacting the etching composition with a substrate having a Si surface and at least one surface selected from a SiO2 surface and a SiN surface, thereby selectively etching the Si surface. A method for treating a substrate comprising: [Effects of the Invention]

[0010] According to the present invention, etching of Si surfaces (silicon wet etching) can be performed at a high etching rate while suppressing etching of SiO2 and SiN surfaces, compared to conventionally widely used alkaline aqueous solutions. Therefore, even in cases where conventional high-speed etching techniques (etchants) are difficult to apply due to the material of the target to be treated, high-speed etching is possible by using the etching agent of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Method of manufacturing etching composition) In the substrate processing method of the present invention, first, an etching composition for etching silicon (hereinafter referred to as "etching solution") is prepared.

[0012] The etching solution is prepared by mixing an organic alkaline compound and orthoperiodic acid or a salt thereof with water to a predetermined concentration and dissolving the mixture uniformly.

[0013] In the present invention, the etching solution prepared as described above has a pH of 12.5 or higher. Since the silicon etching rate tends to increase with increasing alkali concentration (and therefore alkalinity), a pH of 13.0 or higher is preferred, with a pH of 13.2 or higher being particularly preferred. On the other hand, the stronger the alkalinity, the greater the risk of leakage, etc., and the components added to make the solution alkaline tend to be highly harmful and relatively expensive. From these perspectives, the pH may be 14.0 or lower, or even 13.7 or lower. The pH here refers to a value measured at 24°C using a glass electrode method.

[0014] In the manufacture of various semiconductors including silicon devices, if the etching solution or other processing liquid used contains metal, it often has an adverse effect on the object to be processed (not limited to the silicon surface to be etched).

[0015] Therefore, the etching solution of the present invention does not contain metals. More specifically, it is essential that the etching solution does not contain metals at concentrations exceeding at least the impurity level (no metal compounds are actively added). More preferably, the content of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn is 1 ppmw or less, and particularly preferably, the content of each of the above metals is 1 ppbw or less. Note that the metals listed here are metals that are considered to affect the quality of chemical solutions used in semiconductor manufacturing.

[0016] Furthermore, when etching silicon in the manufacture of silicon devices, etching of silicon dioxide (surface) or silicon nitride (surface) is often undesirable, and the present invention relates to such a manufacturing method. Therefore, the etching solution of the present invention does not contain fluoride ions, which are components that promote etching of silicon dioxide (SiO2) or silicon nitride (SiN) under alkaline conditions.

[0017] The alkali compound used to prepare the etching agent must be a metal-free compound, and therefore an organic alkali compound is used. The organic alkali compound is preferably a primary or tertiary amine or a quaternary ammonium hydroxide, with the quaternary ammonium hydroxide being preferred because it is easy to adjust the pH to 12.5 or higher, particularly 13.0 or higher.

[0018] Specific examples of the quaternary ammonium hydroxide include tetramethylammonium hydroxide (TMAH), ethyltrimethylammonium hydroxide (ETMAH), tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, trimethyl-2-hydroxyethylammonium hydroxide (choline hydroxide), dimethylbis(2-hydroxyethyl)ammonium hydroxide, methyltris(2-hydroxyethyl)ammonium hydroxide, phenyltrimethylammonium hydroxide, and benzyltrimethylammonium hydroxide.

[0019] The smaller the size, the higher the etching rate tends to be. Among the above, quaternary ammonium hydroxides having a total carbon number of 8 or less are preferred, and quaternary ammonium hydroxides having a total carbon number of 6 or less (TMAH, ETMAH, etc.) are particularly preferred.

[0020] In the etching solution, these quaternary ammonium hydroxides are usually dissociated and exist as hydroxide ions and quaternary ammonium ions. In other words, the etching solution of the present invention is a liquid containing hydroxide ions for alkaline properties and their counter ions (quaternary ammonium ions).

[0021] The amount of quaternary ammonium hydroxide required to raise the pH of the etching solution to 12.5 or higher is generally 35 mmol / L or more, depending on the type and content of other components. The higher the content, the higher the alkalinity; a content of 50 mmol / L or more is preferred, 100 mmol / L or more is more preferred, and 150 mmol / L or more is particularly preferred. The content may be 1200 mmol / L or less, or even 1000 mmol / L or less, and sufficient performance can often be obtained even with a content of 800 mmol / L or less.

[0022] If you want to check the content of organic alkaline compounds in the etching solution, you can calculate it from the pH if the concentration is low, but if the concentration is high, the error will be large. Therefore, it is more accurate to measure the content of counter cations such as quaternary ammonium ions using ion chromatography and then calculate from that.

[0023] The etching solution of the present invention contains orthoperiodic acid or a salt thereof. By including orthoperiodic acid or a salt thereof, the etching rate of silicon is significantly improved compared to when the orthoperiodic acid or a salt thereof is not included. When an orthoperiodic acid salt is included, a salt other than a metal salt is naturally used.

[0024] The orthoperiodate is preferably an ammonium salt, and specific examples thereof that can be used include unsubstituted ammonium salts and quaternary ammonium salts such as tetramethylammonium salts, ethyltrimethylammonium salts, tetraethylammonium salts, tetrapropylammonium salts, tetrabutylammonium salts, phenyltrimethylammonium salts, and benzyltrimethylammonium salts.

[0025] Even if an orthoperiodate is not commercially available, it can be easily obtained by reacting free orthoperiodic acid (HIO) with an alkali compound. Specifically, for example, an aqueous solution of unsubstituted ammonium orthoperiodic acid or an aqueous solution of quaternary ammonium orthoperiodic acid can be produced by adding orthoperiodic acid to an aqueous solution of ammonia or a quaternary ammonium hydroxide.

[0026] The content of orthoperiodic acid or a salt thereof to be added when preparing the etching solution of the present invention is not particularly limited as long as it can be dissolved to form a homogeneous solution, but the lower limit is preferably 0.05 mmol / L or more, more preferably 0.1 mmol / L or more. The upper limit is preferably 500 mmol / L or less, more preferably 300 mmol / L or less, even more preferably 100 mmol / L or less, and particularly preferably 50 mmol / L or less. Even if it is 10 mmol / L or less, sufficient effects can be obtained.

[0027] The etching solution of the present invention may further contain known components contained in silicon etching solutions consisting of alkaline aqueous solutions. In this case, even if a component that reduces the silicon etching rate is required for some purpose, the etching rate can be improved by adding orthoperiodic acid or a salt thereof as described above. Therefore, the effect of reducing the etching rate due to the addition of the other component can be reduced.

[0028] For example, the etching solution of the present invention may contain a halogen salt of quaternary ammonium (excluding fluoride salts), such as tetramethylammonium chloride, ethyltrimethylammonium iodide, dodecyltrimethylammonium bromide, or decyltrimethylammonium bromide.

[0029] On the other hand, as mentioned above, the etching solution of the present invention does not contain fluoride ions. Therefore, even if the etching solution is a compound known to be a component of a chemical solution used in semiconductor manufacturing, fluorides that can release fluoride ions, such as ammonium fluoride and tetramethylammonium fluoride, should not be blended. The same applies to PF6 salts, BF4 salts, etc.

[0030] It is preferable to use organic alkali compounds, orthoperiodic acid or its salts, and other compounds to be blended that contain as few metal impurities and insoluble impurities as possible, and if necessary, commercially available products can be purified by recrystallization, column purification, ion exchange purification, distillation, sublimation, filtration, etc. When using quaternary ammonium hydroxide as the organic alkali compound, some types are manufactured and sold as extremely high-purity compounds for semiconductor manufacturing, and it is preferable to use such compounds.

[0031] The etching solution of the present invention requires water as an essential component. Etching will not proceed without water. While this depends on the type and amount of other components, the water content is generally preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 60% by mass or more, and particularly preferably 75% by mass or more. While there is no upper limit as long as the necessary amounts of other components are contained, typically 99.5% by mass or less is sufficient, with 99% by mass being sufficient. It is also preferable to use water of high purity with few impurities. The amount of impurities can be evaluated by electrical resistivity. Specifically, electrical resistivity of 0.1 MΩ·cm or more is preferred, 15 MΩ·cm or more is more preferred, and 18 MΩ·cm or more is particularly preferred. Water with such low impurities can be easily produced and obtained as ultrapure water for semiconductor manufacturing. Furthermore, ultrapure water has significantly fewer impurities that do not affect (have little contribution to) electrical resistivity, making it highly suitable.

[0032] In the present invention, the above-mentioned components are mixed to prepare an etching solution having the above-mentioned properties. The preparation method is not particularly limited, and any known method may be appropriately selected and carried out.

[0033] For example, the method is not limited to a method in which a predetermined amount of pure product of each component to be blended is weighed out, mixed with water, and stirred until uniform. Alternatively, a method in which some or all of the blended components are prepared as concentrated aqueous solutions and then mixed with water in a predetermined ratio to obtain a uniform solution, or a method in which a concentrated aqueous solution containing all of the blended components is first prepared and then this is diluted with water can be employed.

[0034] The high-purity quaternary ammonium hydroxide for semiconductor manufacturing described above is commercially available in relatively high concentrations as a solution such as an aqueous solution. Therefore, when producing the etching solution of the present invention, it is preferable to adopt a preparation method that allows the solution to be used as is, i.e., the latter two methods among those mentioned above. Specifically, a high-purity quaternary ammonium hydroxide aqueous solution may be mixed with pure water and orthoperiodic acid or a salt thereof. The order of mixing is also not particularly limited.

[0035] The etching solution of the present invention should be a homogeneous solution in which all of the components are dissolved. Furthermore, in order to prevent contamination during etching, the number of particles of 200 nm or larger is preferably 100 particles / mL or less, more preferably 50 particles / mL or less, and particularly preferably 10 particles / mL or less.

[0036] From this viewpoint, in preparing the etching solution, it is also preferable to mix and dissolve the components, and then pass the mixture through a filter of several nm to several tens of nm to remove particles. If necessary, the filter passing process may be carried out multiple times.

[0037] Furthermore, various known treatments that are performed to obtain necessary physical properties in the production of chemicals for semiconductor manufacturing, such as reducing dissolved oxygen by bubbling with an inert gas such as high-purity nitrogen gas, can be performed.

[0038] For mixing and dissolving (and storage), it is preferable to use a container or device formed of or coated with a material known for the inner walls of chemicals used in semiconductor manufacturing, specifically a material that does not easily leach contaminants into the etching solution, such as polyfluoroethylene or high-purity polypropylene. It is also preferable to clean these containers and devices in advance.

[0039] (etching process) In the substrate processing method of the present invention, the etching solution prepared as described above is brought into contact with a substrate having a Si surface and at least one surface selected from a SiO2 surface and a SiN surface to etch silicon (Si). Note that the "surface" is not limited to a flat surface and may have a three-dimensional shape. (Hereinafter, contacting the etching solution with the substrate may be referred to as "etching process.") The substrates in question include substrates at various stages in the manufacture of various silicon composite semiconductor devices (silicon devices), such as substrates having a silicon (Si) surface, such as silicon single crystal films (including those produced by epitaxial growth), polysilicon films, and amorphous silicon films.

[0040] In the substrate processing method of the present invention, the substrate to be contacted during etching has at least one of an SiO2 (silicon dioxide) surface and an SiN (silicon nitride) surface in addition to the Si surface. The etching solution of the present invention does not substantially etch these surfaces, and is therefore useful in etching substrates having contact surfaces made of such materials. The substrate may also include various metal films, ferroelectric films, and the like.

[0041] Examples of such substrates include those in which silicon and silicon dioxide are alternately stacked, structures in which patterns are formed using polysilicon, silicon nitride, or silicon dioxide on single crystal silicon, etc. More specifically, in a semiconductor manufacturing flow using a gate-last process, when etching a device structure in which a polysilicon dummy gate is surrounded by insulating films of silicon nitride and silicon dioxide, this method is suitable because it allows selective removal of only the silicon.

[0042] In the substrate processing method of the present invention, the method and conditions for bringing the etching solution into contact with the substrate are not particularly limited and can be set appropriately depending on the structure of the substrate, etc. Commonly used means include a substrate holding step of holding the substrate in a horizontal position and a means (single-wafer type) of supplying the etching solution to the main surface of the substrate while rotating the substrate about a vertical axis of rotation passing through the center of the substrate to bring the substrate into contact with the etching solution, and a substrate holding step of holding multiple substrates in an upright position and a means (batch type) of immersing the substrates in an upright position in the etching solution stored in a processing tank to bring the substrates into contact with the etching solution, and any of these means can be suitably used in the substrate processing method of the present invention.

[0043] In the substrate processing method of the present invention, the temperature during the etching process may be appropriately determined within the range of 20 to 95°C taking into consideration the desired etching rate, the shape and surface condition of the silicon after etching, productivity, etc., but is preferably within the range of 35 to 90°C.

[0044] In the substrate processing method of the present invention, the etching process can be performed while degassing under vacuum or reduced pressure or bubbling with an inert gas, which can prevent or reduce the increase in dissolved oxygen during the etching process.

[0045] In the substrate processing method of the present invention, after the etching treatment as described above, further post-treatments such as alkaline silicon etching, i.e., rinsing and drying, can be carried out as necessary. These can be carried out in the usual manner.

[0046] The substrate processing method of the present invention can be incorporated as an intermediate step in the manufacture of silicon devices, and various other processes known as methods for manufacturing silicon devices can be performed before or after the substrate processing method of the present invention. Furthermore, the substrate processing method of the present invention can be applied multiple times in the manufacture of one type of silicon device. [Example]

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0048] The experimental methods / evaluation methods used in the examples and comparative examples are as follows.

[0049] (Abbreviation) The abbreviations for the compounds used are as follows:

[0050] TMAH: tetramethylammonium hydroxide TMAClO4: Tetramethylammonium perchlorate NH4NO3: Ammonium nitrate mCPBA: m-chloroperbenzoic acid H2O2: Hydrogen peroxide (Method for preparing etching solution) A commercially available TMAH aqueous solution (2730 mmol / L) for semiconductor manufacturing was diluted with ultrapure water and mixed to make a uniform solution, and then various additives were added to prepare the etching solutions according to the examples and comparative examples shown in Table 1. The forms of the additives used in the preparations are as follows:

[0051] <Forms of each additive used in the preparation> Orthoperiodic acid: single powder TMAClO4: Single powder NH4NO3: single powder mCPBA: Single powder H2O2 aqueous solution: 10300mmol / L aqueous solution

[0052] In both the examples and comparative examples, the alkaline compound tetramethylammonium hydroxide was blended in an amount such that the final concentration was 260 mmol / L (2.38% by mass).

[0053] (Method for measuring the pH of etching solution) Measurements were made at a temperature of 24°C using a Horiba Ltd. tabletop pH meter F-73 and a Horiba Ltd. pH electrode for strong alkaline samples 9632-10D.

[0054] (Evaluation method for etching rate (unit: nm / min)) First, the following three types of Si substrates were prepared to determine the etching rates for the Si(100), Si(110), and Si(111) crystal planes.

[0055] Substrate A: A 2 cm square single crystal silicon substrate (manufactured by SUMTEC Service) with mirror-finished Si(100) surfaces on both sides. Substrate B: A 2 cm square single crystal silicon substrate (manufactured by SUMTEC Service) with mirror-finished Si(110) surfaces on both sides. Substrate C: A 2 cm square single-crystal silicon substrate (manufactured by Enatech) with mirror-finished Si(111) surfaces on both sides.

[0056] Before etching, the weight of each sample was measured in grams to five decimal places using an electronic balance AUW220D manufactured by Shimadzu Corporation.

[0057] Each Si substrate was immersed in 100 ml of etching solution heated to 70°C for 10 minutes for etching treatment, then washed with ultrapure water and dried.

[0058] The weight of each substrate after the etching process was measured in the same manner as before the etching process. The weight change before and after etching and the density of typical single crystal silicon, 2.329 g / cm 3 The etching rate per substrate surface was calculated using the following formula (1): In the formula below, the unit of "etching rate" is "nm / min" and the unit of "area of ​​the front and back surfaces of the substrate" is "cm 2 " and the unit of "2.329", which indicates the density of single crystal silicon, is "g / cm 3 ", the unit of "weight change before and after etching" is "g", and the unit of "etching time" is "min".

[0059] Etching rate = area of ​​front and back surfaces of substrate x 10 / 2.329 / weight change before and after etching / etching time (evaluation) The following evaluation was given based on how many times the silicon etching rate was increased compared to the reference example (TMAH aqueous solution).

[0060] ◎:1.50 times or more 〇: 1.30 times or more, less than 1.50 times △: 0.80 times or more, less than 1.30 times ×: Less than 0.80 times

[0061] The overall evaluation was then given as "excellent" if both (100) and (110) were ◎, "excellent" if either was ◎, "good" if either was 〇, "average" (no particular effect) if both were △, and "poor" otherwise.

[0062] For reference, the etching rate multiplication factor for the (111) plane is also rated as ⊚ to × in the same manner as above.

[0063] Reference example The etching rate of silicon was evaluated using a 260 mmol / L TMAH aqueous solution, and the results are shown in Table 1.

[0064] Example 1 The silicon etching rate was evaluated using an aqueous solution with a TMAH concentration of 260 mmol / L and an orthoperiodic acid concentration of 4.4 mmol / L. The results are shown in Table 1. In this experiment, both the (100) and (110) surfaces were rated as excellent, and the overall rating was "excellent."

[0065] Examples 2 and 3 Etching solutions were prepared and evaluated by varying the concentration of orthoperiodic acid as shown in Table 1. The results are also shown in Table 1.

[0066] Comparative Examples 1-2 An etching solution containing hydrogen peroxide instead of orthoperiodic acid was prepared and evaluated. The composition and evaluation results are shown in Table 1.

[0067] Comparative Example 2 An etching solution containing mCPBA instead of orthoperiodic acid was prepared and evaluated. The composition and evaluation results are shown in Table 1.

[0068] Comparative Examples 4-5 An etching solution containing TMAClO4 instead of orthoperiodic acid was prepared and evaluated. The composition and evaluation results are shown in Table 1.

[0069] Comparative Example 6 An etching solution containing NH4NO3 instead of orthoperiodic acid was prepared and evaluated. The composition and evaluation results are shown in Table 1.

[0070] [Table 1]

Claims

1. a step of mixing an organic alkali compound, orthoperiodic acid or a salt thereof, and water to prepare an etching composition having a pH of 12.5 or more and containing no fluoride ions or metals; The etching composition is applied to the Si surface and the SiO ２ a step of selectively etching the Si surface by contacting the silicon nitride film with a substrate having at least one surface selected from a SiN surface and a SiN surface; A method for treating a substrate comprising:

2. 2. The method for treating a substrate according to claim 1, wherein the organic alkaline compound is a quaternary ammonium hydroxide.

3. 3. A method for manufacturing a silicon device, comprising the substrate processing method according to claim 1 or 2 in the course of its processing.

4. Si surface and SiO ２ A composition for selectively etching a substrate having at least one surface selected from a SiN surface and a SiN surface, the composition comprising: The composition comprises an organic alkaline compound, orthoperiodic acid or a salt thereof, and water, The pH is 12.5 or higher, and An etching composition characterized by being free of fluoride ions and metals.

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