Etching solution, method for processing substrates using the etching solution, and method for manufacturing semiconductor devices.

Abstract

Silicon carbonitride, with its excellent dielectric properties, is sometimes used in the manufacture of semiconductor devices. During manufacturing, silicon carbonitride often needs to be etched instead of silicon oxide. However, an etchant solution that allows for more selective etching of carbon-containing silicon carbonitride compared to silicon nitride for the same purpose is currently unknown. This invention addresses the problem of providing an etchant solution with high selectivity for etching silicon carbonitride (silicon oxide), a method for processing a substrate including a step of contacting the etchant solution, and a method for manufacturing a semiconductor device using the substrate processing method. This problem can be solved by using an etchant solution containing a homogeneous solution of phosphoric acid, water, and cerium ions for etching silicon carbonitride.

Description

Etching solution, method for processing substrates using the etching solution, and method for manufacturing semiconductor devices. This invention relates to an etching solution for etching silicon carbonitride. Furthermore, this invention relates to a method for processing a substrate using this etching solution. Also, this invention relates to a method for manufacturing a semiconductor device using this etching solution. The substrate includes a semiconductor wafer or a silicon substrate, etc. Various materials are used in the manufacturing process of semiconductor devices, among which silicon nitride or silicon carbonitride is known to be useful in various fields such as copper diffusion barrier films, passivation films, etch stop films, surface protection films, and gas barrier films. For example, silicon nitride films (SiN films, silicon nitride films) or silicon carbonitride films (SiCN films, silicon carbonitride films) are formed on substrates such as silicon wafers or such processed bodies. The term silicon carbonitride, for example, as shown in Non-Patent Document 1, also includes compounds that further contain hydrogen or oxygen in a framework of silicon, carbon, and nitrogen. In semiconductor patterning, there are sometimes necessary steps to selectively etch silicon nitride or silicon carbonitride films formed on a substrate, leaving a silicon oxide film (and, unless otherwise specified below, "selective" means more selective than silicon oxide). In the etching of silicon nitride, an aqueous solution of phosphoric acid is generally used. However, silicon carbonitride, unlike silicon nitride, is hardly etched in an aqueous solution of phosphoric acid. Regarding methods for etching silicon carbonitride films, some have proposed methods using a composition containing an oxidant, a fluorine compound, and water (Patent Document 1). However, the etching rate of silicon carbonitride described in the examples is less than 250 Å / 30 min, which is insufficient. Furthermore, such a composition can also etch the silicon oxide film (SiO₂). 2. Film, silicon oxide film). [Prior Art Documents] [Patent Documents] [Patent Document 1] Japanese Patent Application Publication No. 2007-049145 [Non-Patent Document] [Non-patent literature 1] ECS Journal of Solid State Science and Technology, 8 (6) P346-P350 (2019) [The problem solved by the invention] In the manufacture of semiconductor devices, while silicon carbonitride films can impart superior performance, as mentioned above, there is a lack of etchants that allow for highly selective etching of silicon carbonitride compared to silicon oxide, severely limiting its applications. Therefore, the object of this invention is to provide an etchant that offers higher etching selectivity for silicon carbonitride compared to silicon oxide, a substrate processing method including a step of contacting the etchant with the silicon oxide, and a method for manufacturing a semiconductor device including the substrate processing method. [Means for Solving the Problem] In view of the above-mentioned problems, the inventors conducted a detailed review of the composition of selectively etchable silicon carbonitride. As a result, they discovered that by further containing cerium ions in a phosphoric acid aqueous solution used in the selective etching of silicon nitride in the past, the etching rate of silicon carbonitride can be significantly increased without changing the etching rate of silicon oxide, thus completing the present invention. That is, the present invention is as follows. [1] An etching solution for etching silicon carbonitride, comprising a homogeneous solution containing phosphoric acid, water and cerium ions. [2] An etching solution as described in [1], wherein the amount of cerium ions contained in the etching solution is 0.001 mol / L or more and 0.2 mol / L or less. [3] An etching solution as described in [1] or [2] further containing sulfuric acid. [4] An etching solution as described in any one of [1] to [3] for use in the manufacture of semiconductor devices. [5] An etching solution for etching silicon carbonitride, comprising a solution containing phosphoric acid, water and a cerium compound other than cerium dioxide. [6] A substrate processing method comprising the step of contacting a substrate having a silicon oxide film and a silicon carbonitride film with an etching solution as described in any one of [1] to [5]. [7] A method for manufacturing a semiconductor device comprising the substrate processing method as described in [6]. [Effects of the Invention] According to the present invention, silicon carbonitride can be selectively etched by using a homogeneous solution containing phosphoric acid, water and cerium ions as an etching solution. In addition, the etching solution of the present invention is almost the same as that of the conventional phosphoric acid aqueous solution, and can also etch silicon nitride in the same way. Therefore, under the same etching solution, it is possible to perform both the selective etching step of silicon carbonitride and the selective etching step of silicon nitride, and can also reduce the time required to manage multiple etching solutions as needed. [Form of Invention] (Etching Solution) The etching solution of one embodiment of the present invention is a homogeneous solution containing phosphoric acid, water and cerium ions, used for etching silicon carbonitride. The phosphoric acid content in the etching solution of this embodiment can also be within the same range as that of conventionally known silicon nitride etching solutions, specifically 50% by mass to 98% by mass, and preferably 70% by mass to 94% by mass. Silicon carbonitride etching is faster and more advantageous at high temperatures, and a higher proportion of phosphoric acid allows for stable use at even higher temperatures. On the other hand, the etching solution of this embodiment must contain water or cerium ions, and in reality, the phosphoric acid content cannot exceed 98% by mass. Furthermore, when the proportions of each component are stated as a percentage by mass in this specification, this value represents the entire etching solution as a percentage of 100% by mass. Furthermore, in the case of a concentrated solution of phosphoric acid in the etching solution of this embodiment, the phosphoric acid is orthophosphoric acid (H+) in the liquid. 3PO 4) The equilibrium state with polyphosphoric acid, but the above content is based on the condition that the total content is orthophosphoric acid. The same applies when it exists as pyrophosphoric acid, etc. Water is an essential component of the etching solution in this embodiment. Without water, the etching reaction of silicon carbonitride cannot occur; however, excessive water can make high-temperature operation difficult. While the water content depends on the type and amount of other components, a water content of 1% to 49% by mass is preferred, and 5% to 29% by mass is even better. Furthermore, this amount of water is the same as in the case where the phosphoric acid exists entirely in the form of orthophosphoric acid. The etching solution in this embodiment uses cerium ions as an essential component. The presence of cerium ions in the etching solution significantly increases the etching rate of silicon carbonitride. Silicon carbonitride hardly etches in a phosphoric acid aqueous solution without cerium ions, which is considered to be due to the polarity difference between Si-C and Si-N bonds. The difference in electronegativity between C and N atoms is smaller than that between C and N atoms. Therefore, the Si-C bond has a smaller polarity than the Si-N bond, and it is inferred that it is difficult to induce an electron-addition reaction via acid, making silicon carbonitride etching almost impossible. On the other hand, if a phosphoric acid aqueous solution containing cerium ions is added to the etching solution, the cerium ions will act on the Si-C bonds, thus etching the silicon carbonitride. In etching solutions, cerium ions can exist as monatomic ions or as constituent atoms of fault ions (polyatomic ions). The valence is not limited, but trivalent or tetravalent valence is preferred. Furthermore, cerium ions with different valences can coexist in a mixture. In the etching solution of this embodiment, the content of cerium ions is 0.001 mol / L to 0.2 mol / L, and preferably 0.002 mol / L to 0.1 mol / L. The higher the content of cerium ions, the greater the promoting effect of silicon carbonitride etching. On the other hand, if the content of cerium ions is too high, there is a tendency for a large amount of residue to accumulate on the surface of the etched substrate, and even if a light rinsing process is performed after etching, as described later, the residue may not be removed. The etching solution of this embodiment may also contain counter ions from the compound that serves as the cerium ion source (as described below). Examples of such counter ions include inorganic ions such as fluoride ions, chloride ions, bromide ions, sulfate ions, nitrate ions, carbonate ions, and hydroxide ions, as well as organic ions such as acetate ions and oxalate ions. Furthermore, if the cerium compound used is a double salt, it may also contain ammonium ions from it. The etching solution of this embodiment preferably contains sulfuric acid (in the case of sulfuric acid ions). The presence of sulfuric acid suppresses the etching rate of silicon oxide without impairing the etching rate of silicon carbonitride, resulting in higher selectivity. The concentration of sulfuric acid is preferably 0.1% by mass to 20% by mass, more preferably 0.2% by mass to 5% by mass, and even more preferably 0.5% by mass to 2.0% by mass. The etching solution of this embodiment can only maintain a uniform solution and may further contain known components found in etching solutions with phosphoric acid as the main component. As such well-known ingredients, examples include additives that inhibit the etching rate of silicon oxide and additives that inhibit the precipitation of silica. As additives to suppress the etching rate of silicon oxide, known additives include soluble silicon compounds or acids other than phosphoric acid. Examples of soluble silicon compounds include silicic acid, silicates, hexafluorosilicic acid, hexafluorosilates, tetraethoxysilanes, tetramethoxysilanes, and other alkoxysilanes, as well as alkylsilanes such as methyltrimethoxysilanes. Examples of acids other than phosphoric acid include sulfuric acid, nitric acid, hydrochloric acid, and oxalic acid. Furthermore, as additives to inhibit the precipitation of silica, there are known organic fourth-order ammonium salts and organic fourth-order phosphonium salts. Additionally, there are methods for adding silica organic bases containing organic bases that inhibit silica precipitation. That is, the etching solution of this embodiment may also contain ions generated in the liquid due to the addition of such compounds. The etching solution in this embodiment is a homogeneous solution. A homogeneous solution is defined as one in which the aqueous and organic phases cannot be separated at 25°C, or where no solids are visually dispersed. Whether a solution is homogeneous can be visually confirmed, typically by irradiating the etching solution with a laser pointer (e.g., a TLP-3200 from Dongxin Machinery, maximum output: less than 1mW, wavelength: 650-660nm). Ideally, the solution should not show a visible light path, indicating it is homogeneous. If a visible light path is observed when irradiating the etching solution with the aforementioned laser pointer, it is considered a non-homogeneous solution. Using a non-homogeneous solution as an etching solution can lead to undissolved components causing contamination of the wafer or device, or may contribute to uneven etching; therefore, it is not suitable as an etching solution. (Impurities in the Etching Solution) While maintaining the state of a homogeneous solution as described above, the etching solution of this embodiment may also contain particles or trace amounts of metal as impurities. From the viewpoint of preventing contamination during etching, particles larger than 200 nm are preferably 100 particles / mL or less, more preferably 50 particles / mL or less, and even more preferably 10 particles / mL or less. Particularly preferred is that when passing through a filter with a 50 nm pore size, no particles fail to pass through the filter, and all particles pass through; ideally, all particles pass through a 10 nm filter. From the viewpoint of preventing contamination of the etched object, it is also preferable to have as few metallic impurities as possible. Metallic impurities refer to metals other than cerium, specifically, any one of Ag, Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Zn, and Pr, preferably with a concentration of 1 ppm or less. (Manufacturing Method) There is no particular limitation on the manufacturing method of the etching solution of this embodiment. For example, the above-mentioned phosphoric acid, water and cerium compound can be mixed to a certain concentration to form a homogeneous solution. As mentioned above, phosphoric acid with the lowest possible levels of metallic or insoluble impurities is preferred. If necessary, purified phosphoric acid obtained through recrystallization, column purification, ion exchange purification, distillation, sublimation, or filtration can be used. Furthermore, high-purity phosphoric acid manufactured and sold for semiconductor production is preferred. Water of high purity with few impurities is preferred. The amount of impurities can be assessed by resistivity; specifically, water with a resistivity of 0.1 MΩ·cm or higher is preferred, water with a resistivity of 15 MΩ·cm or higher is even better, and water with a resistivity of 18 MΩ·cm or higher is exceptional. Such water with few impurities can be easily produced and obtained from ultrapure water used in semiconductor manufacturing. Furthermore, in ultrapure water, even impurities that have some influence on resistivity are extremely rare (and have a negligible impact), making ultrapure water ideal for use. As a cerium ion source, a cerium compound can be used that has the solubility to make the etchant prepared in the desired amount uniform. For example, cerium hydroxide, cerium salt, and one or more complex salts containing cerium and cations other than cerium (e.g., ammonium ions) can be used. Furthermore, considering their good solubility and ease of achieving high purity, cerium nitrate, cerium sulfate, ammonium cerium nitrate, and ammonium cerium sulfate are preferred as cerium compounds. These can also be hydrated. Furthermore, when using cerium compounds such as cerium dioxide, which have extremely low solubility in aqueous solutions containing phosphoric acid, the solid cannot be formed as a homogeneous solution because it fails to dissolve in the solution containing both phosphoric acid and water. This insoluble component in the solution becomes a source of particulate matter, leading to uneven etching or potentially causing defects in subsequent steps. Therefore, cerium ion sources other than cerium dioxide are preferable when using them as the cerium ion source in the manufacture of the etching solution of this embodiment. Also, cerium compounds such as cerium acetate, cerium phosphate, and cerium carbonate also have low solubility in aqueous solutions containing phosphoric acid. Therefore, it is preferable to use cerium compounds other than cerium acetate, cerium phosphate, cerium carbonate, and cerium dioxide as the cerium ion source. Cerium compounds should be used with the highest possible purity. If necessary, purified commercial products can be used through recrystallization, column purification, ion exchange purification, filtration, etc. In the manufacture of the etching solution of this embodiment, it is preferable to remove particles by passing the solution through a filter with a diameter of several nm to tens of nm after mixing and dissolving the various components. Multiple filtration processes may also be performed if necessary. Furthermore, various treatments known in semiconductor manufacturing methods may also be applied. (Applications and Usage) The etching solution of this embodiment can be used for etching substrates containing silicon carbonitride during the manufacture of semiconductor devices. Furthermore, there is no limitation on the method of forming the silicon carbonitride film on the substrate; silicon carbonitride films formed by known methods such as CVD and PVD can be used for etching. Also, the silicon carbonitride film used in the manufacture of semiconductor devices may contain hydrogen at a maximum amount of 133 atomic percent relative to silicon due to the manufacturing method; the presence of such hydrogen is equivalent to the silicon carbonitride to be etched by the etching solution of this embodiment. Furthermore, the silicon carbonitride to be etched may also contain various impurity elements (e.g., oxygen) within a normal range. The etching solution of this embodiment can be further used for processing substrates having silicon oxide and silicon carbonitride films. Using the etching solution of this embodiment, silicon oxide etching can be suppressed while silicon carbonitride is selectively etched. Such selective etching was practically impossible with conventional etching solutions. The following provides a more detailed explanation of the treatment methods for silicon carbonitride films. The substrate processing method using the etching solution of this embodiment includes a step of contacting a substrate having a silicon oxide film and a silicon carbonitride film with the etching solution of this embodiment. Preferably, it includes a step of holding the substrate in a horizontal position, rotating the substrate around a vertical axis of rotation at the center of the substrate, and supplying the processing solution of the etching solution of this embodiment to the main surface of the substrate. In other preferred embodiments, the substrate processing method using the etching solution of this embodiment includes a step of holding a plurality of substrates in an upright position and immersing the substrates in the etching solution of this embodiment stored in a processing tank in an upright position. In a preferred embodiment of the present invention, the etching solution is used in the manufacture of a semiconductor device incorporating the above-described processing method. When using the etching solution of this embodiment for etching, the etching solution temperature can be selected within a suitable range of 100 to 200°C, taking into account the desired etching rate, post-etching surface condition, and productivity, with a range of 130 to 180°C being preferred. Temperatures exceeding 200°C can damage semiconductor materials other than silicon carbonitride, and if the temperature is below 100°C, it is difficult to etch silicon carbonitride at an industrially satisfactory speed. When etching with the etching solution of this embodiment, ultrasound or the like can also be used to promote etching. After processing the substrate using the etching solution of this embodiment, if impurities remain on the substrate surface, various known treatments can be applied to remove these impurities. For example, there is a method of lightly cleaning the substrate using a cleaning solution. Known cleaning solutions include acidic aqueous solutions such as hydrochloric acid, hydrofluoric acid, and sulfuric acid; alkaline aqueous solutions such as ammonia; a mixture of hydrofluoric acid and hydrogen peroxide solution (FPM); a mixture of sulfuric acid and hydrogen peroxide solution (SPM); a mixture of ammonia and hydrogen peroxide solution (APM); and a mixture of hydrochloric acid and hydrogen peroxide solution (HPM). These solutions can be used individually or in combination. When using the etching solution of this embodiment for substrate processing, the etching solution after wafer processing can be recovered and regenerated through processes such as filtration or concentration adjustment of the etching solution components, and then reused for processing other wafers. For concentration adjustment, a mechanism can be included to add fresh phosphoric acid or water while monitoring the concentration of phosphoric acid or water. Furthermore, water or a low-concentration phosphoric acid diluted with water can be used for water adjustment. [Example] The present invention will be described in more detail below with reference to the embodiments, but the present invention is not limited to these embodiments. Example 1 (Preparation method of etching solution) Phosphoric acid, water and cerium ammonium nitrate as a cerium compound were placed in a flask in the proportions recorded in Table 1, and immersed in an oil bath at a set temperature and heated at 600 rpm while stirring for 30 minutes. (Evaluation Method for the Uniformity of Etching Solution) After heating and stirring the etching solution at 25°C for 30 minutes, no solid matter was observed. Furthermore, when the etching solution was irradiated at 25°C with a laser pointer (TLP-3200, maximum output: less than 1mw, wavelength: 650-660nm), the absence of a visible light path indicated that it had become a completely dissolved and homogeneous solution. The results are shown in Table 2. In the table, those that have become homogeneous solutions are indicated by 0. (Etching Rate Evaluation Method) A silicon wafer with a silicon carbonitride film size of 2×1 cm was prepared, and the initial film thickness was measured using a spectrophotometer. The silicon carbonitride film was immersed in 200g of etching solution heated to 166°C for 5 minutes. After cleaning the wafer with a light wash and drying, the film thickness was measured again using a spectrophotometer. The etching rate (RSiCN) was calculated by dividing the difference between the initial and post-treatment film thicknesses, which yielded the amount of silicon carbonitride etched, by the etching time. The results are shown in Table 2. For silicon wafers with a silicon nitride film size of 2×1cm and silicon oxide film size of 2×1cm, the etching rates (RSiN, RSiO) are calculated similarly to those for silicon carbonitride films: silicon nitride films are immersed for 2 minutes and silicon oxide films are immersed for 10 minutes. 2). The results are shown in Table 2. From these measurement results, the etching selectivity ratio (RSiCN / RSiO) between silicon carbonitride films and silicon oxide films can be determined. 2) Etching selectivity ratio of silicon nitride film to silicon oxide film (RSiN / RSiO) 2). The results are shown in Table 2. Examples 2-13 and Comparative Example 1: Using the etching solution with the composition shown in Table 1, the absolute amount of etching was varied to the same extent as in Example 1, and the immersion time was changed at the temperature recorded in Table 1. The etching was performed, and the evaluation was conducted in the same manner as in Example 1. The results are shown in Table 2. Examples 1-10, which use cerium compounds dissolved in a solution containing phosphoric acid and water, significantly improved the etching rate of silicon carbonitride compared to an etching solution without cerium ions (Comparative Example 1). On the other hand, the etching rate of silicon oxide remained almost unchanged, while the etching rate of silicon nitride was also good. Therefore, it can be seen that the etching solution of one embodiment of the present invention exhibits excellent etching rate for silicon carbonitride, and compared to silicon oxide, silicon carbonitride shows higher selectivity. Furthermore, in Examples 11 to 13, which used an etching solution containing added sulfuric acid, compared with Example 2, which had the same composition as other components besides sulfuric acid, the etching rate of silicon oxide was suppressed, resulting in improved selectivity. Comparative Examples 2 and 3 used cerium dioxide (IV) as a cerium compound, with a concentration of 2 mmol / L (Comparative Example 2; 0.03 wt% as cerium dioxide) or 18 mmol / L (Comparative Example 3; 0.3 wt% as cerium dioxide). When mixed with phosphoric acid to form a water content of 15 wt%, it was confirmed that the liquid contained a solid particulate source, and a light path was visible when irradiated with a laser pointer, indicating that a homogeneous solution could not be obtained. Therefore, the solutions of Comparative Examples 2 and 3 are not suitable for use as etching solutions.

Claims

1. An etching solution for etching silicon carbonitride, comprising a homogeneous solution containing phosphoric acid, water and cerium ions, wherein the phosphoric acid content in the etching solution is 50% by mass or more and 98% by mass or less, and the cerium ion content in the etching solution is 0.001 mol / L or more and 0.2 mol / L or less.

2. The etching solution of claim 1, further comprising sulfuric acid.

3. The etching solution as described in claim 1 or 2 is used in the manufacture of semiconductor devices.

4. An etching solution for etching silicon carbonitride, comprising a solution containing phosphoric acid, water and cerium compounds other than cerium dioxide, wherein the phosphoric acid content in the etching solution is 50% by mass or more and 98% by mass or less, and the cerium ion content in the etching solution is 0.001 mol / L or more and 0.2 mol / L or less.

5. A method for processing a substrate, comprising the step of contacting a substrate having a silicon oxide film and a silicon carbonitride film with an etching solution as claimed in claim 1 or 4.

6. A method for manufacturing a semiconductor device, comprising a method for processing a substrate as described in claim 5.