Etching solution, silicon device manufacturing method using etching solution, and substrate processing method

Abstract

To provide an etching solution that can selectively etch SiCN and suppress surface roughening of Si.SOLUTION: An SiCN etching solution contains a fluorine-containing compound, an acid, and water, and has a fluoride ion concentration of 0.3 mol / kg or more and 9 mol / kg or less, and an acid concentration of 55 mass% or more and 90 mass% or less.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an etching solution for selectively etching SiCN with respect to Si. The present invention also relates to a method for manufacturing a silicon device using the etching solution. The present invention also relates to a substrate processing method using the etching solution. The substrate includes a semiconductor wafer, a silicon substrate, and the like. [Background technology]

[0002] Among various materials used in the manufacturing process of semiconductor devices, SiN and SiCN are known to be useful in various fields such as copper diffusion barrier film, passivation film, etch stop film, surface protection film, and gas barrier film, and are used by forming a SiN film (silicon nitride film, silicon nitride film) or a SiCN film (silicon carbonitride film, silicon carbonitride film) on a substrate such as a silicon wafer or a processed body thereof. Here, SiCN includes compounds that further contain hydrogen and oxygen in addition to a compound composed of a skeleton of silicon, carbon, and nitrogen, as shown in Non-Patent Document 1, for example.

[0003] In semiconductor pattern formation, a process of selectively etching a SiN film or SiCN film formed on a substrate with respect to Si may be required (hereinafter, unless otherwise specified, "selective" means selective with respect to Si).

[0004] Phosphoric acid aqueous solution is generally used for etching SiN. However, unlike SiN, SiCN is hardly etched with phosphoric acid aqueous solution. This is thought to be due to the difference in polarity between Si-C bonds and Si-N bonds. The difference in electronegativity with Si atoms is smaller for C atoms than for N atoms. Therefore, since the Si-C bond has a smaller polarization than the Si-N bond, it is difficult for electrophilic addition reactions to occur with acid, and it is thought that etching of SiCN hardly progresses.

[0005] Regarding the method of etching SiCN, a method using a composition containing an oxidizing agent, a fluorine compound, and water has been proposed (Patent Document 1), but the etching rate of SiCN described in the examples is less than 250 angstroms / 30 min, which is not a sufficient rate. In addition, regarding Si, although it is described that the insulating film can be removed without damaging the substrate, there is no description regarding the etching rate or surface roughness of Si. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2007-049145 A [Non-patent literature]

[0007] [Non-Patent Document 1] ECS Journal of Solid State Science and Technology, 8 (6) P346-P350 (2019) Summary of the Invention [Problem to be solved by the invention]

[0008] In the manufacture of semiconductor devices, the use of SiCN provides superior performance, but as described above, there is no material that has a sufficient etching rate for SiCN, can be selectively etched with respect to Si, and can suppress the surface roughness of Si, so the situations in which it can be used are extremely limited. Therefore, an object of the present invention is to provide an etching solution that can selectively etch SiCN with respect to Si and suppress surface roughness of Si. [Means for solving the problem]

[0009] In view of the above problems, the present inventors have conducted extensive research into compositions capable of selectively etching SiCN. As a result, they have discovered that by further adding a fluorine compound to an acid, such as an aqueous phosphoric acid solution or sulfuric acid, which has been conventionally used for etching SiN, the etching rate of SiCN can be significantly improved without substantially changing the etching rate of Si, and have completed the present invention.

[0010] That is, the present invention is configured as follows. Item 1. An etching solution for SiCN comprising a fluorine-containing compound, an acid, and water, the concentration of fluoride ions being 0.3 mol / kg or more and 9 mol / kg or less, and the concentration of the acid being 55 mass% or more and 90 mass% or less. Item 2. The etching solution according to Item 1, wherein the acid has a boiling point of 105° C. or higher. Item 3. The etching solution according to item 1 or 2, wherein the acid is one or more acids selected from phosphoric acid and sulfuric acid. Item 4. The etching solution according to any one of Items 1 to 3, wherein at least a part of the fluorine-containing compound is a tetraalkylammonium fluoride having a total carbon number of 8 or less. Item 5: A method for treating a substrate, comprising contacting a substrate having a Si surface and a SiCN surface with the etching solution according to any one of Items 1 to 4, and selectively etching the SiCN surface. Item 6. The method for treating a substrate according to item 5, wherein the etching is carried out at a temperature in the range of 105° C. or more and 180° C. or less. Item 7. The method for treating a substrate according to item 5 or 6, wherein the substrate does not have a SiO2 surface. Item 8. A method for producing a silicon device, comprising the method for treating a substrate according to any one of items 5 to 7 in a process. Effect of the Invention

[0011] According to the present invention, by using a solution containing an acid, a fluorine-containing compound, and water at specific concentrations as an etching solution, it is possible to selectively etch SiCN and suppress surface roughness of Si. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] (etchant) The etching solution of the present invention is a solution containing an acid, a fluorine-containing compound, and water, and is used for etching silicon carbonitride (also described as SiCN). The etching solution of the present invention can selectively etch SiCN relative to Si. In other words, the etching solution of the present invention is an etching solution that selectively etches SiCN relative to Si. The "SiCN etching solution" in the present invention is a solution used for etching objects (e.g., substrates, etc.) that contain SiCN.

[0013] The acid in the etching solution of the present invention is an essential component used to promote the etching reaction of SiCN and suppress the etching of silicon (also described as Si). In order to perform etching of SiCN at a higher temperature, it is preferable to use an acid having a boiling point of 105°C or higher.

[0014] The content of acid in the etching solution is 55% by mass or more and 90% by mass or less. If the amount of acid is too small, the etching rate of SiCN is insufficient, the etching rate of Si increases, the selectivity decreases, and the surface roughness of Si tends to increase. It is advantageous to perform etching at a high temperature because the etching rate is faster, and a higher acid content allows stable use at a higher temperature. On the other hand, the etching solution of the present invention requires a fluorine-containing compound and water, and if the acid content exceeds 90 mass%, the amount of the fluorine-containing compound and water blended decreases, and the etching rate of SiCN decreases. The acid content in the etching solution of the present invention is preferably 57 mass% or more and 85 mass% or less, and more preferably 60 mass% or more and 80 mass% or less. This concentration range is effective in that a sufficient etching rate of SiCN can be obtained, and the etching rate of Si and the surface roughness of Si can be suppressed, allowing selective etching of SiCN.

[0015] The acid preferably has a boiling point of 105° C. or higher (decomposition point of 105° C. or higher in the case of a solid). This is because etching of SiCN is performed at a higher temperature of 105° C. or higher, as described below. Specific examples of such acids include one or more acids selected from the group consisting of phosphoric acid, sulfuric acid, nitric acid, hydrochloric acid, acetic acid, citric acid, boric acid, tetrafluoroboric acid, trifluoromethanesulfonic acid, fluorosulfonic acid, and methanesulfonic acid. One of these acids may be used alone, or different types may be used in combination.

[0016] Among the above acids, phosphoric acid and sulfuric acid have high boiling points, and high-purity products are manufactured and sold for semiconductor manufacturing, so that at least one selected from phosphoric acid and sulfuric acid is preferably used in the etching solution of the present invention. When phosphoric acid is used alone, the concentration is 55% by mass to 90% by mass, preferably 57% by mass to 85% by mass, and more preferably 60% by mass to 80% by mass. On the other hand, sulfuric acid is a stronger acid than phosphoric acid, so there are many dissociated protons, and a sufficient effect can be obtained at a lower concentration than phosphoric acid. When sulfuric acid is used alone, the concentration is 55% by mass to 90% by mass, preferably 55% by mass to 85% by mass, and more preferably 55% by mass to 80% by mass. In this specification, when the amount of each component is described in mass%, the value is the ratio when the entire etching solution is 100% by mass.

[0017] In addition, a concentrated solution of phosphoric acid is in equilibrium between orthophosphoric acid (H3PO4) and polyphosphoric acid in the liquid, but the above content is the amount when the entire amount exists as orthophosphoric acid. The same applies when it exists as pyrophosphoric acid, etc.

[0018] The etching solution of the present invention contains a fluorine-containing compound as an essential component. The fluorine-containing compound is a compound that at least partially dissociates in the etching solution and releases fluoride ions (F - The presence of fluoride ions in the etching solution promotes the cleavage of the Si-C bonds in SiCN, greatly increasing the etching rate of SiCN.

[0019] In the etching solution of the present invention, the content of fluoride ions is 0.3 mol / kg or more and 9 mol / kg or less. If the content of fluoride ions is less than 0.3 mol / kg, the etching rate of SiCN is not practically sufficient. On the other hand, the higher the content of fluoride ions, the higher the effect of promoting etching of SiCN, but if the content of fluoride ions exceeds 9 mol / kg, it becomes difficult to make the amount of phosphoric acid and water sufficient. The content of fluoride ions in the etching solution of the present invention is preferably 0.35 mol / kg or more and 7 mol / kg or less, more preferably 0.4 mol / kg or more and 5 mol / kg or less.

[0020] The fluoride ion concentration can be measured by ion chromatography or a method using a fluoride ion selective electrode. When a compound having a large dissociation constant and considered to be almost completely dissociated is used as the fluorine-containing compound, the amount of fluoride ions calculated from the blending amount may be regarded as the amount of fluoride ions in the etching solution.

[0021] From the viewpoint of the efficiency of making fluoride ions exist in the etching solution, the following fluorine-containing compounds are used: As described above, it is preferable to use a compound that dissociates almost completely. In addition, as described below, it is preferable that the etching solution of the present invention does not contain metals, so it is preferable to avoid metal fluorides such as sodium fluoride.

[0022] Specific examples of such fluorine-containing compounds include ammonium fluoride, tetramethylammonium fluoride, ethyltrimethylammonium fluoride, diethyldimethylammonium fluoride, propyltrimethylammonium fluoride, butyltrimethylammonium fluoride, tetraethylammonium fluoride, tetrapropylammonium fluoride, and tetrabutylammonium fluoride. These fluorine-containing compounds may be used alone or in combination. When these fluorine-containing compounds are used in combination, the compounds exemplified above may be combined in any desired manner.

[0023] Also, although the reason is unclear, the presence of tetraalkylammonium ions having a total carbon number of 8 or less in the etching solution tends to improve the etching rate of SiCN. Therefore, it is preferable that at least a part of the above-mentioned fluorine-containing compound is a tetraalkylammonium fluoride having a total carbon number of 8 or less. Examples of the fluorine compound include tetramethylammonium fluoride, ethyltrimethylammonium fluoride, diethyldimethylammonium fluoride, propyltrimethylammonium fluoride, butyltrimethylammonium fluoride, and tetraethylammonium fluoride. Among them, compounds having a total carbon number of 6 or less, and further 5 or less, are more preferable.

[0024] The concentration of the tetraalkylammonium ion having a total carbon number of 8 or less is preferably 0.001 mol / kg or more and 5 mol / kg or less, more preferably 0.01 mol / kg or more and 3 mol / kg or less. If the concentration is less than 0.001 mol / kg, it is difficult to obtain the effect of improving the etching rate of SiCN. On the other hand, the compound having the tetraalkylammonium ion is expensive, and if the amount is too large, the amount of other components may be insufficient, so that 5 mol / kg or less is preferable.

[0025] At least a portion of the fluorine-containing compounds preferably contains a tetraalkylammonium fluoride having a total carbon number of 8 or less. Here, "at least a portion" means that the tetraalkylammonium fluoride having a total carbon number of 8 or less may be 1 mol % or more and 1000 mol % or less, 5 mol % or more and 500 mol % or less, or 10 mol % or more and 100 mol % or less, based on the total amount of the fluorine-containing compounds. Considering that the higher the content of fluoride ions, the higher the effect of promoting the etching of SiCN, and that the presence of tetraalkylammonium ions having a total carbon number of 8 or less tends to improve the etching rate of SiCN, it is preferable to use, as the fluorine-containing compound, ammonium fluoride having a small molecular weight and a tetraalkylammonium fluoride having a total carbon number of 8 or less in combination. When ammonium fluoride and a tetraalkylammonium fluoride having a total carbon number of 8 or less are used in combination, the molar ratio thereof can be, for example, 9000:1 to 1:4000, may be 90:1 to 1:40, or may be 10:1 to 1:10.

[0026] The etching solution of the present invention contains water as the remaining essential component. If water is not present, the etching reaction of SiCN will not proceed. Depending on the type and amount of other components, the water content is 5% by mass or more and 43.8% by mass or less, preferably 10% by mass or more and 41.8% by mass or less, and more preferably 15% by mass or more and 38.5% by mass or less. In this case, the amount of water is the amount when the etching solution contains phosphoric acid, and the phosphoric acid is all present as orthophosphoric acid.

[0027] Furthermore, the etching solution of the present invention may contain a cerium compound. For example, one or more of cerium hydroxide, cerium salt, and double salts containing cerium and a cation other than cerium (e.g., ammonium ion) may be used. Preferred cerium compounds include cerium nitrate, cerium sulfate, ammonium cerium nitrate, and ammonium cerium sulfate. These may also be hydrates. Furthermore, the etching solution of the present invention may contain a nitric acid compound. For example, one or more selected from the group consisting of nitrates and nitrites can be used. The nitric acid compound is preferably one or more selected from the group consisting of ammonium nitrate and quaternary alkyl ammonium nitrate. The number of carbon atoms of the alkyl of the quaternary alkyl ammonium nitrate may be independently 1 to 5. Specific examples of the nitric acid compound include one or more selected from the group consisting of ammonium nitrate, tetramethyl ammonium nitrate, tetraethyl ammonium nitrate, tetrapropyl ammonium nitrate, and tetrabutyl ammonium nitrate. When the etching solution contains a nitric acid compound, the etching rate of SiCN can be improved.

[0028] The etching solution of the present invention may be composed of only the above-mentioned acid, the fluorine-containing compound, and water, and sufficient etching rate and selectivity can be obtained with these three components. However, as long as the object of the present invention is not impaired, components such as a surfactant may be further contained. As the surfactant, any of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants may be used as long as they do not decompose in the etching solution. Such surfactants improve the wettability of the silicon substrate surface and make the contact between the SiCN surface and the etching solution more uniform, thereby contributing to uniform etching of the SiCN surface.

[0029] The etching solution of the present invention is a homogeneous acidic 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 more is preferably 100 pieces / mL or less, and more preferably 50 pieces / mL or less.

[0030] From the viewpoint of preventing contamination of the etching target, it is preferable that the amount of metal impurities is as small as possible. Specifically, it is preferable that the amount of Ag, Al, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, and Zn is each 1 ppm or less, and more preferably 1 ppb or less.

[0031] The etching solution of the present invention may contain complex salts, decomposition products, impurities, etc. derived from the components blended. For example, when four components, phosphoric acid, ammonium fluoride, tetramethylammonium fluoride, and water, are blended, the etching solution may contain ammonium phosphate, tetramethylammonium phosphate, trimethylamine, hydrofluoric acid, etc.

[0032] (Manufacturing method) The method for producing the etching solution of the present invention is not particularly limited. For example, the above-mentioned acid, fluorine-containing compound and water may be mixed to a predetermined concentration and dissolved uniformly.

[0033] It is preferable to use an acid that contains as few metal impurities and insoluble impurities as possible, as described above, and a commercially available product can be used after purification, as necessary, by recrystallization, column purification, ion exchange purification, distillation, sublimation, filtration, etc. It is also preferable to use high-purity phosphoric acid and sulfuric acid that are manufactured and sold for semiconductor manufacturing.

[0034] It is preferable to use a fluorine-containing compound with as high a purity as possible. If necessary, a commercially available product may be used after purification by recrystallization, column purification, ion exchange purification, filtration, etc. It is preferable to use high-purity ammonium fluoride that is manufactured and sold for semiconductor manufacturing. For example, tetramethylammonium fluoride can be obtained by neutralizing an aqueous solution of tetramethylammonium hydroxide (TMAH) manufactured and sold for semiconductor manufacturing with hydrofluoric acid, and it is preferable to use such a high-purity product.

[0035] The remainder of the etching solution is water. It is preferable to use water of high purity with few impurities. The amount of impurities can be evaluated by electrical resistivity, and specifically, electrical resistivity of 0.1 MΩ·cm or more is preferable, 15 MΩ·cm or more is more preferable, and 18 MΩ·cm or more is particularly preferable. Water with such few impurities can be easily manufactured 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.

[0036] In the production of the etching solution of the present invention, it is also preferable to remove particles by passing the mixture through a filter of several nm to several tens of nm after mixing and dissolving each component. If necessary, the filter passing process may be performed multiple times. In addition, various other processes known as a method for producing a chemical solution for semiconductor manufacturing can be performed.

[0037] (Application and method of use) The etching solution of the present invention can be used for etching a substrate containing a SiCN surface during the manufacture of a semiconductor device. A substrate having a SiCN surface is usually obtained by forming a SiCN film on the substrate by a method such as a chemical vapor deposition (CVD) method, a physical vapor deposition (PVD) method, or a sublimation recrystallization method. The etching solution of the present invention can etch any SiCN surface formed by the above-mentioned known method. In addition, the SiCN film used during the manufacture of a semiconductor device may contain hydrogen in an amount of up to 133 atomic % relative to silicon depending on the manufacturing method, and such hydrogen-containing SiCN also falls under the SiCN to be etched in the present invention. Furthermore, the SiCN to be etched in the present invention may contain various impurity elements (e.g., oxygen) within the range normally contained. The etching solution of the present invention can also etch a SiC film and a SiC single crystal substrate, and may be used for these.

[0038] Furthermore, the etching solution of the present invention can be used to treat a substrate having a Si surface and a SiCN surface. By using the etching solution of the present invention, the SiCN surface can be selectively etched while suppressing etching of the Si surface.

[0039] In addition, since the etching solution of the present invention contains fluoride ions, it also etches SiO2 at high speed. Although it depends on the targeted etching amount (depth), it is generally difficult to simultaneously etch SiCN, so it is preferable that the substrate having the Si surface and the SiCN surface does not have a SiO2 surface.

[0040] The etching solution of the present invention is particularly effective when used in a process for selectively etching the SiCN surface portion of a substrate having a Si surface and a SiCN surface, which was substantially impossible with conventional etching solutions.

[0041] A substrate processing method using the etching liquid of the present invention includes a substrate holding step of holding the 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 axis of rotation passing through the center of the substrate.

[0042] Another substrate processing method using the etching solution of the present invention includes a substrate holding step of holding a plurality of substrates in an upright position, and immersing the substrates in an upright position in the etching solution of the present invention stored in a processing tank. In a preferred embodiment of the present invention, the etching solution is used in the manufacture of a semiconductor device, which includes a step of selectively etching a SiCN surface portion by supplying the etching solution when etching a substrate having a SiCN surface, particularly a Si surface and a SiCN surface.

[0043] The temperature of the etching solution used in the etching of the present invention may be appropriately determined from the range of 105°C to 180°C in consideration of the desired etching rate, surface state after etching, productivity, etc., but is preferably set to the range of 105°C to 170°C (but below the boiling point of the etching solution used). In etching SiN, phosphoric acid aqueous solution has been used at high temperatures of 140°C to 180°C in the past, but the etching solution of the present invention can etch SiCN even at relatively low temperatures. At temperatures exceeding 180°C, damage may occur to semiconductor materials other than SiCN, and at temperatures below 105°C, it is difficult to etch SiCN at an industrially satisfactory rate. Within this temperature range, etching is also possible at the boiling point of the etching solution, which is one of the preferred modes of use in controlling the etching temperature to a constant temperature.

[0044] During etching using the etching solution of the present invention, ultrasonic waves or the like may be used to accelerate the etching.

[0045] After the substrate treatment using the etching solution of the present invention, if there are impurities remaining on the surface of the substrate, various known treatments may be performed to remove the impurities. For example, there is a method of performing a rinse treatment on the substrate using a rinse solution. Known rinse solutions can be used, including acidic aqueous solutions such as hydrochloric acid, hydrofluoric acid, and sulfuric acid, alkaline aqueous solutions such as ammonia water, a mixture of hydrofluoric acid and hydrogen peroxide (FPM), a mixture of sulfuric acid and hydrogen peroxide (SPM), a mixture of ammonia water and hydrogen peroxide (APM), a mixture of hydrochloric acid and hydrogen peroxide (HPM), and the like. These may be used alone, or multiple rinse solutions may be used in combination.

[0046] In the substrate processing method using the etching solution of the present invention, the etching solution after processing the wafer may be collected and used for processing another wafer after regeneration such as filtering or adjusting the concentration of the etching solution components. A mechanism for adding fresh acid, water, and a fluorine-containing compound while monitoring the concentrations of acid, moisture, and fluoride ions may be provided to adjust the concentration of the components. Water or a low-concentration acid diluted with water may be used to adjust the moisture.

[0047] (Silicon device manufacturing method) The method for manufacturing a silicon device of the present invention includes the above-mentioned substrate processing method as an etching step, and the above-described conditions can be applied to the etching step as they are. The method for manufacturing a silicon device may include known steps used in the manufacture of silicon devices, such as one or more steps selected from a wafer fabrication step, an oxide film formation step, a transistor formation step, a wiring formation step, and a chemical mechanical polishing (CMP) step. EXAMPLES

[0048] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0049] The experimental methods / evaluation methods in the examples and comparative examples are as follows.

[0050] (Method of preparing etching solution) Predetermined amounts of acid, water, and a fluorine-containing compound were placed in a fluororesin flask, and the flask was immersed in an oil bath whose temperature was set to be the same as the boiling point of the etching solution (predetermined temperature in Example 12), and heated for 30 minutes while stirring the solution at 600 rpm.

[0051] (Method of Etching Rate Evaluation) A silicon wafer (SiCN film) of 2×1 cm size on which SiCN was formed was prepared, and the initial film thickness was measured using a spectroscopic ellipsometer. The SiCN film was immersed in 300 g of etching solution heated to the same temperature as the boiling point (predetermined temperature in Example 12). After washing and drying the wafer by rinsing, the film thickness was measured using a spectroscopic ellipsometer. The etching rate was calculated by calculating the amount of SiCN etched from the difference between the initial and post-treatment film thicknesses, and dividing the amount by the etching time.

[0052] A silicon wafer (Si film) having a size of 2×1 cm on which a Si film was formed was also immersed in the solution in the same manner as in the case of the SiCN film, and the etching rate was calculated.

[0053] From these measurement results, the etching rate ratio of the SiCN film to the Si film (SiCN / Si selectivity) was obtained.

[0054] The immersion time in the etching solution was 30 seconds for the SiCN film and 10 minutes for the Si film in Example 11, and 1 minute for the SiCN film and 10 minutes for the Si film in the other examples. In the comparative example, the immersion time was 10 minutes for both the SiCN film and the Si film.

[0055] (Abbreviation) The fluorine-containing compounds used are abbreviated in the tables as follows:

[0056] NH4F: Ammonium fluoride TMAF: Tetramethylammonium fluoride ETMAF: Ethyltrimethylammonium fluoride TEAF: Tetraethylammonium fluoride

[0057] Example 1 In Example 1, an etching solution was prepared by blending ammonium fluoride as a fluorine-containing compound in addition to phosphoric acid and water. The specific composition is shown in Table 1.

[0058] The etching temperature was evaluated at 131° C., which is the boiling point of this composition. In this case, the etching rate of SiCN was high, and an excellent selectivity ratio (SiCN / Si, etching rate ratio) was shown in Table 1.

[0059] Example 2 In Example 2, evaluation was carried out in the same manner as in Example 1, except that tetramethylammonium fluoride was used as the fluorine-containing compound instead of ammonium fluoride. The specific composition is shown in Table 1, and the amount of the fluorine-containing compound was adjusted so that the amount of fluoride ions was the same.

[0060] The results are shown in Table 1, and the etching rate of SiCN was improved further than in Example 1. Therefore, the selectivity (SiCN / Si, etching rate ratio) was also good.

[0061] (Examples 3 to 5) In Examples 3 to 5, etching solutions were prepared using tetramethylammonium fluoride, ethyltrimethylammonium fluoride, and tetraethylammonium fluoride as fluorine-containing compounds. The specific compositions are shown in Table 1, and the amounts of fluorine-containing compounds were adjusted so that the amounts of fluoride ions were the same.

[0062] The results are shown in Table 1. Although the etching temperature was lower than that of Comparative Examples 1 to 3, Therefore, the etching rate was much higher than that of the conventional etchant, and the selectivity (SiCN / Si, etching rate ratio) was also good.

[0063] Comparative Example 1 In Comparative Example 1, an etching solution containing no fluorine-containing compound and consisting of phosphoric acid and water, which has been conventionally used for etching silicon nitride (also referred to as SiN) films, was prepared. The specific composition is shown in Table 1.

[0064] The etching temperature was evaluated at 131° C., which is the boiling point of this composition, and the results are shown in Table 1. With this composition, SiCN was hardly etched.

[0065] (Comparative Examples 2 and 3) In Comparative Example 2 and Comparative Example 3, an etching solution was prepared by further mixing acetic acid or citric acid in addition to phosphoric acid and water. The etching solution did not contain a fluorine-containing compound. Acetic acid and citric acid are silica precipitation inhibitors that have been mixed into SiN etching solutions mainly composed of phosphoric acid and water. The specific compositions are shown in Table 1.

[0066] The results of evaluation performed in the same manner as in Comparative Example 1 are shown in Table 1. However, even when such an additive (citric acid or acetic acid) was added, the etching rate of SiCN did not improve when a fluorine-containing compound was not included.

[0067] Comparative Example 4 In Comparative Example 4, an etching solution was prepared by mixing hydrofluoric acid (also referred to as hydrofluoric acid) in addition to phosphoric acid and water. The specific composition is shown in Table 1.

[0068] The etching temperature was set to 50° C., and the evaluation results are shown in Table 1. With this composition, SiCN was hardly etched.

[0069] (Comparative Examples 5 and 6) In Comparative Examples 5 and 6, etching solutions were prepared with different tetramethylammonium fluoride contents and reduced fluoride ion concentrations. The specific compositions are shown in Table 1. Etching was performed at the etching temperatures shown in Table 1. With these compositions, the etching rate of SiCN was lower than that of the Examples.

[0070] [Table 1]

[0071] Example 6 In Example 6, except that the blending amount of ammonium fluoride was increased, evaluation was carried out in the same manner as in Example 1. The specific composition is shown in Table 2.

[0072] The results are shown in Table 2. As the amount of fluoride ions increased, the etching rate of SiCN was further improved.

[0073] Example 7 In Example 7, both ammonium fluoride and tetramethylammonium fluoride were used as fluorine-containing compounds. The amount of fluoride ions was adjusted to be the same as in Example 6. The specific composition is shown in Table 2.

[0074] The results are shown in Table 2. Although the amount of fluoride ions was the same, the etching rate of SiCN was improved compared to Example 6 by using tetramethylammonium fluoride in combination.

[0075] [Table 2]

[0076] Example 8 In Example 8, except that the amount of ammonium fluoride was increased, evaluation was performed in the same manner as in Example 7. The specific composition is shown in Table 3.

[0077] The results are shown in Table 3. As the amount of fluoride ions increased, the etching rate of SiCN was further improved.

[0078] (Examples 9 and 10) In Examples 9 and 10, etching solutions were prepared similarly to those in Example 8, except that the amount of phosphoric acid was reduced and the proportion of water was increased. The specific compositions are shown in Table 3. Note that the boiling point (=etching temperature) of the etching solution was lowered by the amount of phosphoric acid reduced.

[0079] The results are shown in Table 3. Although the etching rate tends to decrease as the processing temperature decreases, the etching rate was still far superior to that of the comparative example.

[0080] If the composition has a low amount of phosphoric acid, the etching time will be longer, but on the other hand, the amount of phosphoric acid, which is relatively expensive, can be reduced, and the heating cost can also be reduced. Therefore, the composition of the etching solution can be adjusted depending on which is prioritized.

[0081] Example 11 In Example 11, sulfuric acid was used as the acid, and both ammonium fluoride and tetramethylammonium fluoride were used as the fluorine-containing compound. The specific composition is shown in Table 3.

[0082] The results are shown in Table 3. By using sulfuric acid, the boiling point was increased, and the etching rate of SiCN was improved accordingly.

[0083] Example 12 In Example 12, evaluation was performed in the same manner as in Example 11, except that the etching temperature was set to 123° C., which is lower than the boiling point. The results are shown in Table 3. Although the etching rate tends to decrease as the processing temperature decreases, the etching rate was still far superior to that of the comparative example.

[0084] [Table 3]

[0085] (Example 13) An etching solution was prepared with the same composition as in Example 7 using 85% phosphoric acid, 40% ammonium fluoride, 25% tetramethylammonium hydroxide, and 50% hydrofluoric acid, which are high-purity products for semiconductor manufacturing. The preparation method was to first put a certain amount of water and tetramethylammonium hydroxide into a fluororesin flask, add hydrofluoric acid to neutralize it, and obtain an aqueous solution of tetramethylammonium fluoride. After adding ammonium fluoride and phosphoric acid, the solution was heated and evaluated in the same manner as in the other examples. As a result, the etching rate of SiCN was 5.8 nm / min, and the etching rate of Si was <0.1 nm / min, which was equivalent to that of Example 7.

Claims

1. It comprises a fluorine-containing compound, an acid, and water. The concentration of fluoride ions is between 0.3 mol / kg and 9 mol / kg. The acid concentration is 55% by mass or more and 90% by mass or less. Etching solution for SiCN.

2. The etching solution according to claim 1, wherein the boiling point of the acid is 105°C or higher.

3. The etching solution according to claim 1, wherein the acid is one or more acids selected from phosphoric acid and sulfuric acid.

4. The etching solution according to claim 1, wherein at least a portion of the fluorine-containing compound is a tetraalkylammonium fluoride with a total carbon number of 8 or less.

5. A method for processing a substrate having a Si surface and a SiCN surface, wherein the etching solution described in any one of claims 1 to 4 is brought into contact with the substrate, and the SiCN surface is selectively etched.

6. The substrate processing method according to claim 5, wherein the etching is performed in a range of 105°C to 180°C.

7. The substrate is SiO ２ A method for processing a substrate according to claim 5, wherein the substrate does not have a surface.

8. A method for manufacturing a silicon device, comprising the substrate processing method described in claim 5 as part of the process.