Silicon etchant

Abstract

To provide a new chemical solution capable of wet-etching silicon at high speed when manufacturing a semiconductor device or the like.SOLUTION: A silicon etching agent comprises an alkaline aqueous solution containing peroxodisulfate ions in a range of 0.05 to 65 mmol / L, particularly preferably 0.2 to 10 mmol / L, free of metals such as Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb and Zn (preferably each metal is 1 ppbw or less), and having a pH of 12.5 or more, preferably 13.0 or more and 13.7 or less. Production thereof is made possible by mixing high-purity ammonium peroxodisulfate and high-purity quaternary ammonium hydroxide with ultrapure water and uniformly dissolving them.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a silicon etching solution used in the surface processing and etching process when manufacturing 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] US Patent Application Publication No. 2015 / 0104952 Summary of the Invention [Problem to be solved by the invention]

[0006] Generally, productivity in wet etching processes is improved by increasing the etching rate. However, in the production of semiconductor chips, etc., even when wet etching silicon, the same etching agent cannot always be applied depending on the structure of the semiconductor chip being manufactured, and there is a demand for a wide range of technologies to enable selection according to the situation.

[0007] Therefore, an object of the present invention is to provide a novel alkaline etching solution with a high silicon etching rate based on a new technical configuration. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have found that the silicon etching rate can be dramatically increased by adding peroxodisulfate ions to an alkaline aqueous solution within a specific concentration range, thereby completing the present invention.

[0009] That is, the present invention provides a silicon etching agent characterized by comprising an alkaline aqueous solution containing peroxodisulfate ions in the range of 0.05 to 65 mmol / L, containing no metals, and having a pH of 12.5 or higher. [Effects of the Invention]

[0010] According to the present invention, by incorporating peroxodisulfate ions within a specific concentration range, wet etching of silicon can be performed at a high etching rate. Therefore, even in cases where it is difficult to apply conventional high-speed etching techniques (etchants) due to factors such as the material of the target to be etched, high-speed etching is possible by using the etching agent of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] (etchant) The silicon etching solution of the present invention (hereinafter referred to as "etching solution of the present invention") is used for etching silicon (crystalline silicon, amorphous silicon) in the manufacture of semiconductor chips, etc. Silicon etching can be performed under acidic conditions or alkaline conditions, but the etching solution of the present invention is an alkaline aqueous solution and is intended for etching under alkaline conditions.

[0012] In the manufacture of semiconductor chips, if a processing liquid such as an etching liquid contains metal, it often has an adverse effect on the object to be processed (not limited to the silicon surface to be etched).

[0013] Therefore, the etching solution of the present invention must be free of metals. More specifically, it is essential that they are not contained at concentrations exceeding at least the impurity level. Preferably, the contents of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn are all 1 ppmw or less, and more preferably, the contents of each of the above metals are all 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.

[0014] The greatest feature of the etching solution of the present invention is that it contains peroxodisulfate ions in the range of 0.05 to 65 mmol / L. By containing peroxodisulfate ions, the silicon etching rate, particularly the etching rate for the (100) and (110) planes, is improved compared to when the solution does not contain peroxodisulfate ions. On the other hand, if the content is too high, the etching rate will again decrease. This is presumably because if there is too much peroxodisulfate ions, which are an oxidizing agent, the silicon surface is strongly oxidized, making it difficult to etch under alkaline conditions.

[0015] The peroxodisulfate ion content in the etching solution of the present invention is preferably 0.1 mmol / L or more, particularly 0.2 mmol / L or more, and 40 mmol / L or less, particularly 20 mmol / L or less, more particularly 10 mmol / L or less, inclusive ...

[0016] In silicon etching, the higher the alkali concentration (and therefore the higher the alkalinity), the faster the etching rate. From this perspective, the etching solution of the present invention has a strong alkalinity of 12.5 or higher. A pH of 13.0 or higher is more preferable, and a pH of 13.2 or higher is particularly preferable. 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 toxic and relatively expensive. From this perspective, the pH may be 14.0 or lower, or even 13.7 or lower. Because the etching solution of the present invention contains peroxodisulfate ions, as described below, it has a faster silicon etching rate than conventional etching agents even at the same pH. Note that this pH refers to a value measured at 24°C using a glass electrode method.

[0017] The fact that the etching solution has such a pH means that a large amount of hydroxide ions (an amount that indicates the above pH) is present in the etching solution.

[0018] Naturally, there are counter cations for the hydroxide ions and the peroxodisulfate ions. As described above, the etching solution of the present invention does not contain metals, so the counter cations are Na + YaK + That is, the counter cation that may be present in the etching solution is a non-metallic cation such as an ammonium ion.

[0019] The nonmetallic cation may be an unsubstituted ammonium ion, a primary or tertiary ammonium cation, or a quaternary ammonium cation. From the viewpoint of easy availability of high-purity raw materials when preparing the etching solution of the present invention, the counter ion is preferably an unsubstituted ammonium ion (NH + ) and / or quaternary ammonium ions, and quaternary ammonium ions are particularly preferred from the viewpoint of ease of adjusting the pH to a high level. In consideration of these, it is preferred that some or all of the counter cations present in the etching solution are quaternary ammonium ions, and even if other counter cations are present, the counter cations are unsubstituted ammonium ions.

[0020] Specific examples of the quaternary ammonium ion include a tetramethylammonium ion, an ethyltrimethylammonium ion, a tetraethylammonium ion, a tetrapropylammonium ion, a tetrabutylammonium ion, a trimethyl-2-hydroxyethylammonium ion, a dimethylbis(2-hydroxyethyl)ammonium ion, a methyltris(2-hydroxyethyl)ammonium ion, a phenyltrimethylammonium ion, and a benzyltrimethylammonium ion.

[0021] The smaller the size, the higher the etching rate tends to be. Among the above-mentioned quaternary ammonium ions, quaternary ammonium ions having a total carbon number of 8 or less are preferred, and quaternary ammonium ions having a total carbon number of 6 or less (tetramethylammonium ion, ethyltrimethylammonium ion, etc.) are particularly preferred.

[0022] It should be noted that such counter cations are counter ions for both hydroxide ions and peroxodisulfate ions, and even if multiple counter cations are present in the etching solution, it is usually not possible to unequivocally determine which counter cation each is. Furthermore, if the etching solution contains other anions, the counter cations may also be the counter ions of those anions.

[0023] The etching solution of the present invention is an alkaline aqueous solution, and water is an essential component. Etching will not proceed without water. Although it depends on the types and amounts 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. There is no particular upper limit as long as the necessary amounts of other components can be contained, but typically 99.5% by mass or less is sufficient, and 99% by mass is sufficient.

[0024] The silicon etching solution of the present invention may further contain known components contained in silicon etching solutions composed of alkaline aqueous solutions. In this case, even if a component that reduces the silicon etching rate is necessary to be added for some purpose, the etching rate can be improved by adding peroxodisulfate ions as described above. This reduces the effect of the addition of other components on the reduction in etching rate. However, because peroxodisulfate ions have a high oxidizing power, it is preferable that components that are easily oxidized are not included from the perspective of storage stability.

[0025] On the other hand, when etching silicon in the manufacture of semiconductor chips, etching of silicon dioxide (surface) or silicon nitride (surface) is often undesirable. Therefore, it is preferable that the etching solution of the present invention does not contain any component that promotes etching of silicon dioxide (SiO2) or silicon nitride (SiN) under alkaline conditions. A typical example of such a component is fluoride ions.

[0026] (Manufacturing method) The method for producing the etching solution of the present invention is not particularly limited. For example, various alkali compounds as a component for imparting alkalinity and peroxodisulfate as a source of peroxodisulfate ions may be mixed with water to give predetermined concentrations, and then dissolved uniformly.

[0027] As mentioned above, since the etching solution of the present invention does not contain metals, it is not preferable to use metal hydroxides such as NaOH and KOH as the alkaline compound.

[0028] Therefore, the alkaline compound contained in the etching solution of the present invention to make it alkaline is preferably ammonia, various primary or tertiary amines, or quaternary ammonium hydroxides, with quaternary ammonium hydroxides being preferred because they make it easy to adjust the pH to 12.5 or higher, particularly 13.0 or higher.

[0029] 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.

[0030] Generally, all of these quaternary ammonium hydroxides are dissociated in the etching solution and exist as hydroxide ions and quaternary ammonium ions as counter cations. Therefore, the quaternary ammonium hydroxides may be appropriately selected depending on the type of counter ion to be contained in the etching solution to be produced.

[0031] It is preferable to use such quaternary ammonium hydroxide with as little metallic impurities and insoluble impurities as possible, and if necessary, commercially available products can be purified by recrystallization, column purification, ion exchange purification, filtration, etc. When using quaternary ammonium hydroxide as the alkaline compound, some types are manufactured and sold at extremely high purity for semiconductor manufacturing, and it is preferable to use such a compound. High-purity quaternary ammonium hydroxide for semiconductor manufacturing is generally sold as a solution such as an aqueous solution. In producing the silicon etching solution of the present invention, this solution can be simply mixed with the required amount of water and other ingredients.

[0032] 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 amount of other components. The higher the amount, the higher the alkalinity, so a blend 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 blend amount may be 1200 mmol / L or less, or even 1000 mmol / L or less, and in most cases sufficient performance can be obtained even with a blend of 800 mmol / L or less.

[0033] The peroxodisulfuric acid salt used is also a nonmetallic salt. Specifically, various ammonium salts are more preferred. More specific examples include ammonium salt ((NH4)2S2O8), tetramethylammonium salt (TMA2S2O8), ethyltrimethylammonium salt (ETMA2S2O8), tetraethylammonium salt (TEA2S2O8), tetrapropylammonium salt (TPA2S2O8), tetrabutylammonium salt (TBA2S2O8), trimethyl-2-hydroxyethylammonium salt, phenyltrimethylammonium salt, and benzyltrimethylammonium salt. Ammonium peroxodisulfate ((NH4)2S2O8) is particularly preferred due to its availability in high purity.

[0034] Although free peroxodisulfuric acid (HSO) can also be used, it is not preferred because it tends to undergo a neutralization reaction with the alkaline compound, making it difficult to adjust the pH. In other words, it is preferable to first react free peroxodisulfuric acid with an alkaline compound outside the system to form a salt before use.

[0035] The blending ratio of the ammonium peroxodisulfate salt determines the concentration of peroxodisulfate ions in the etching solution. Therefore, the blending amount is 0.05 to 65 mmol per 1 L of the etching solution to be prepared. The blending amount is preferably 0.1 mmol / L or more, particularly 0.2 mmol / L or more, and is preferably 40 mmol / L or less, particularly 20 mmol / L or less, and more particularly 10 mmol / L or less.

[0036] It is also preferable to use water of high purity with few impurities. The amount of impurities can be evaluated by electrical resistivity; specifically, an electrical resistivity of 0.1 MΩ·cm or higher is preferable, 15 MΩ·cm or higher is more preferable, and 18 MΩ·cm or higher is particularly preferable. Water with such few impurities can be easily produced and obtained as ultrapure water for semiconductor manufacturing. Furthermore, ultrapure water has extremely few impurities that do not affect (have little contribution to) electrical resistivity, making it highly suitable.

[0037] As described above, various compounds known to be components of chemical solutions for semiconductor manufacturing may be blended as needed. However, since peroxodisulfate ions have a high oxidizing power, it is advisable to avoid blending components that are easily oxidized from the viewpoint of storage stability.

[0038] The etching solution of the present invention may also contain quaternary ammonium halogen salts such as tetramethylammonium chloride, ethyltrimethylammonium iodide, dodecyltrimethylammonium bromide, and decyltrimethylammonium bromide. When such ionic compounds are added, the content of counter cations may be further increased by the amount derived from these compounds, and anions other than hydroxide ions and peroxodisulfate ions may also be contained.

[0039] As mentioned above, the etching solution of the present invention preferably does not contain fluoride ions, and therefore it is preferable not to blend fluorides such as ammonium fluoride and tetramethylammonium fluoride, even if they are compounds known to be components of chemical solutions used in semiconductor manufacturing. The same applies to PF6 salts, BF4 salts, etc.

[0040] In producing the etching solution of the present invention, 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.

[0041] 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.

[0042] 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.

[0043] (Use and method of use) The silicon etching solution of the present invention can be used for etching substrates at various stages in the manufacture of silicon wafers or various silicon composite semiconductor devices (silicon devices) including silicon single crystal films, polysilicon films, and amorphous silicon films. Note that silicon single crystal films include those produced by epitaxial growth.

[0044] That is, by contacting a substrate having a silicon (Si) surface with the silicon etching solution of the present invention, the Si surface can be etched. On the other hand, depending on the optional components, the etching solution of the present invention does not etch silicon dioxide (SiO2) or silicon nitride (SiN). Therefore, objects to be treated using the etching agent of the present invention include substrates having a silicon nitride surface and / or a silicon dioxide surface and a silicon surface (including single crystal silicon, polysilicon, and amorphous silicon) on the treatment surface. Various metal films may also be included. Examples include structures in which silicon and silicon dioxide are alternately stacked, and structures in which patterns are formed using polysilicon, silicon nitride, or silicon dioxide on single crystal silicon.

[0045] A substrate processing method using the silicon etching liquid of the present invention includes a substrate holding step of holding a substrate in a horizontal position, and a processing liquid supply step of supplying the etching liquid of the present invention to a main surface of the substrate while rotating the substrate about a vertical rotation axis passing through a center of the substrate.

[0046] Another substrate processing method using the silicon etching solution of the present invention includes a substrate holding step of holding a plurality of substrates in an upright position, and a step of immersing the substrates in an upright position in the etching solution of the present invention stored in a processing tank.

[0047] In a preferred embodiment of the present invention, the silicon etching solution is used in the manufacture of silicon devices, including a step of supplying the etching solution to selectively etch a silicon film when etching a silicon wafer, particularly various silicon composite semiconductor devices containing silicon nitride and / or silicon dioxide.

[0048] The temperature of the silicon etching solution of the present invention during etching may be appropriately determined within a range of 20 to 95°C in consideration of the desired etching rate, the shape and surface state of silicon after etching, productivity, etc., and is preferably within a range of 35 to 90°C.

[0049] When etching is performed using the silicon etching solution of the present invention, the etching can be performed while degassing under vacuum or reduced pressure or bubbling with an inert gas. By such operations, the increase in dissolved oxygen during etching can be suppressed or reduced.

[0050] When etching is performed using the silicon etching solution of the present invention, the object to be etched may be simply brought into contact with the etching solution by, for example, immersing it in the etching solution, but an electrochemical etching method in which a constant potential is applied to the object to be etched may also be employed.

[0051] The etching solution of the present invention can selectively remove only silicon from a device structure in which a polysilicon dummy gate is surrounded by insulating films of silicon nitride and silicon dioxide in a semiconductor manufacturing flow using a gate-last process, for example, and thus contributes to the formation of a gate structure. Therefore, the silicon etching solution of the present invention can be suitably used as an etching solution in the manufacture of semiconductor devices (silicon devices) such as silicon devices, which include steps of etching silicon wafers, silicon single crystal films, polysilicon films, and amorphous silicon films. [Example]

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] The experimental methods / evaluation methods used in the examples and comparative examples are as follows.

[0054] (Abbreviation) The abbreviations for the compounds used are as follows:

[0055] TMAH: Tetramethylammonium hydroxide (NH4)2S2O8: Ammonium peroxodisulfate H2O2: Hydrogen peroxide TMAClO4: Tetramethylammonium perchlorate NH4NO3: Ammonium nitrate

[0056] (Method of adjusting 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, after which various additives (oxidizing agents) 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:

[0057] <Forms of each additive used in the preparation> (NH4)2S2O8: Single powder H2O2 aqueous solution: 10300mmol / L aqueous solution TMAClO4: Single powder NH4NO3: single powder

[0058] 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).

[0059] (Method for measuring pH of etching chemicals) 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.

[0060] (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.

[0061] 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.

[0062] Before etching, the weight of each sample was measured in grams to five decimal places using an electronic balance AUW220D manufactured by Shimadzu Corporation.

[0063] 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.

[0064] 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 3The etching rate per substrate surface was calculated using the following formula (1): In the following formula (1), 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".

[0065] Etching rate = area of ​​the front and back surfaces of the substrate × 10 / 2.329 / weight change before and after etching / etching time (1)

[0066] (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).

[0067] ◎: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 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.

[0068] For reference, the etching rate multiplication factor for the (111) plane is also rated as ⊚ to × in the same manner as above.

[0069] 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.

[0070] Example 1 The etching rate of silicon was evaluated using an aqueous solution with a TMAH concentration of 260 mmol / L and a peroxodisulfate ion concentration of 0.4 mmol / L. The results are shown in Table 1. In this experiment, both the (100) and (110) planes were rated as excellent, and the overall rating was "excellent." Furthermore, with this composition, the etching rate for the (111) plane was also improved by approximately 1.3 times (equivalent to a good rating), demonstrating excellent overall performance.

[0071] Although the pH of the prepared etching solution was not measured, it is clear from the data of Reference Example and Example 2 that it was approximately 13.4 to 13.5.

[0072] Example 2 An etching solution was prepared with a peroxodisulfate ion concentration of 4.4 mmol / L and evaluated. The results are shown in Table 1. Compared to Example 1, the etching rates for both the (100) and (110) planes increased as the peroxodisulfate ion concentration increased.

[0073] Comparative Example 1 An etching solution was prepared with a peroxodisulfate ion concentration of 70 mmol / L and evaluated. The results are shown in Table 1. If the peroxodisulfate ion concentration is too high, the etching rate tends to decrease. With this composition, the etching rate on each surface decreased to less than 0.4 times (equivalent to ×).

[0074] Comparative Example 2 An etching solution containing hydrogen peroxide instead of peroxodisulfate ions was prepared and evaluated. The concentrations and evaluation results are shown in Table 1.

[0075] Comparative Examples 3 and 4 An etching solution containing perchlorate ions instead of peroxodisulfate ions was prepared and evaluated. The concentrations and evaluation results are shown in Table 1.

[0076] Comparative Example 5 An etching solution containing nitrate ions instead of peroxodisulfate ions was prepared and evaluated. The concentrations and evaluation results are shown in Table 1.

[0077]

Table 1

Claims

1. Contains peroxodisulfate ions in the range of 0.05 to 65 mmol / L, Contains no metal and A silicon etching agent comprising an alkaline aqueous solution having a pH of 12.5 or higher.

2. 10. The silicon etchant of claim 1, comprising a quaternary ammonium ion.

3. 3. A method for treating a substrate having a Si surface, comprising contacting the substrate with the silicon etching solution according to claim 1 or 2 to etch the Si surface.

4. A method for manufacturing a silicon device, comprising the substrate processing method according to claim 3 in a process.

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