Methods, devices, and systems for measuring concentration of amine-based compounds in etching solutions

Abstract

This invention describes a method, related equipment, and system for measuring the concentration of photosensitive groups in a liquid (e.g., the concentration of amine-based inhibitors in an etching solution).

Description

Technical Field

[0001] This invention relates to a method, equipment, and method for measuring the amount of amine-based compounds in an etching solution. Background Technology

[0002] Silicon nitride is used in the microelectronics manufacturing industry, including as a rigid shielding layer for fabricating high aspect ratio structures included in solid-state 3D NAND memory devices. According to this exemplary application, the silicon nitride layer acts as a sacrificial layer between silicon oxide layers. The silicon nitride layer is removed by etching to leave a space between the two silicon oxide layers.

[0003] Some types of silicon nitride etching processes use liquid etching baths and liquid etching solutions containing hot phosphoric acid. Hot phosphoric acid can be used to efficiently remove silicon nitride at high etching rates and with high selectivity relative to silicon oxide still present on the substrate surface.

[0004] Typical etching solutions are primarily a combination of an aqueous phosphoric acid solution and a small amount of one or more dissolved components that enhance etching performance. Examples of minor components include dissolved silicate compounds, which improve the etching rate and selectivity of silicon nitride. As another example, the etching solution may contain dissolved amine-containing or "amine-based compounds" to further improve the etching rate and selectivity of silicon nitride.

[0005] To achieve consistent and predictable results in silicon nitride wet etching, the amount of a minor dissolved component in the etching solution that affects the etching rate or selectivity is selected to produce the desired etching rate and selectivity for silicon nitride. The amount of one of these dissolved components in the etching solution is a critical operating parameter and is gradually reduced during the use of the etching solution. If the concentration of this component becomes too low, the etching solution will not function as required, and the amount and yield of etched substrate will be affected.

[0006] Therefore, silicon nitride etch solutions can have a usable lifespan based on the gradually decreasing concentration of their dissolved components (e.g., amine-based inhibitors or silica compounds). These components are gradually depleted from the etch solution during use and the etch solution containing one of these components is periodically replaced or replenished. The timing of the replacement or replenishment of the etch solution is designed to maintain a usable concentration of one of these dissolved components. For example, the etch solution can be replaced or replenished after a predetermined amount of use (e.g., after a predetermined amount of time (e.g., days) of using the etch solution or after a predetermined number of wafers have been processed in the etch solution).

[0007] In either case, the method has an inherent inefficiency problem because the etch solution replaced on either basis may still contain a usable amount of dissolved components (e.g., amine-based inhibitors or dissolved silica), and if so, the etch solution must be replaced before it reaches the end of its usable life. Summary of the Invention

[0008] The microelectronics manufacturing industry requires continuously improving methods to control the efficiency and cost of manufacturing microelectronic devices. In silicon nitride etching processes, there is an opportunity to reduce the overall cost of these etching processes by minimizing the inherent inefficiencies in the method of replacing the etching solution at the estimated end-of-life, which is assessed by tracking the amount of etching solution used.

[0009] The following describes an improved method for determining when a silicon nitride etch solution reaches the end of its usable lifetime due to an undesirably low concentration of dissolved amine-based inhibitors. According to an example method, the end of the usable lifetime of the etch solution is assessed by directly measuring the concentration of amine-based inhibitors in a sample of the etch solution used in a wet etching process. If the measured concentration of the amine-based inhibitors in the etch solution is too low (e.g., below a predetermined or required minimum level), the etch solution for the wet etching process can be replaced or replenished.

[0010] According to the example method and system, the method for measuring the amount of amine-based inhibitors in an etching solution can be performed efficiently, accurately, and preferably automatically. An automated method can be performed using a system operably connected to a silicon nitride wet etching apparatus, comprising the steps of: obtaining an etching solution sample from a silicon nitride etching bath, forming a test solution from the etching solution sample, and analyzing the test solution using spectroscopic techniques to determine the concentration of the amine-based inhibitor in the etching solution sample.

[0011] According to the example method, the concentration of amine-based inhibitors in an etching solution can be analyzed and evaluated by first chemically converting the amine group of an amine-based inhibitor molecule into a photosensitive group (“photosensitive cyclic amine complex”). An amine-based inhibitor molecule having a photosensitive group derived from an amine is called a “photosensitive inhibitor complex”. After converting the amine-based inhibitor to form the photosensitive inhibitor complex, the concentration of the photosensitive inhibitor complex in the test solution is measured using spectrometry. The concentration of the photosensitive inhibitor complex in the test solution can be correlated with the concentration of the amine-based inhibitor in the etching solution sample.

[0012] The following description includes specific examples of a method for measuring the concentration of an amine-based inhibitor in a silicon nitride etch solution during a wet etching process, while the etch solution is at a high temperature. Although not specified as an example, the method described below can alternatively be used to measure the concentration of an amine-based inhibitor in a silicon nitride etch solution at different times or at lower temperatures, for example, before the etch solution is used in the wet etching process. Therefore, the concentration of an amine-based inhibitor in the etch solution can be measured before the silicon nitride etch solution is used in the wet etching process, while the etch solution is at room temperature.

[0013] In one aspect, the present invention relates to a method for determining the concentration of an amine-based inhibitor in a silicon nitride etching solution. The method includes: preparing a test solution comprising a silicon nitride etching solution, a complexing agent, and water, the silicon nitride etching solution comprising phosphoric acid and an amine-based inhibitor; reacting the complexing agent with the amine group of the amine-based inhibitor to form a photosensitive inhibitor complex; using spectrometry to determine the concentration of the photosensitive inhibitor complex in the test solution; and determining the concentration of the amine-based inhibitor in the etching solution from the concentration of the photosensitive inhibitor complex in the test solution.

[0014] In another aspect, the present invention relates to an automated fluid monitoring system suitable for monitoring the concentration of an amine-based inhibitor in an etching solution. The system comprises: (a) a sampling system suitable for obtaining an etching solution sample from a silicon nitride wet etching apparatus including a silicon nitride etching bath; (b) a deionized water reservoir; (c) a pH buffer solution reservoir; (d) a complexing agent reservoir; (e) a mixing chamber suitable for preparing a test solution comprising at least a portion of the etching solution sample, deionized water, pH buffer, and a complexing agent, and for reacting the complexing agent with the amine groups of an amine-based inhibitor contained in the etching solution sample to form a photosensitive inhibitor complex; (f) a spectrometer suitable for receiving the test solution from the mixing chamber and measuring the concentration of the photosensitive inhibitor complex in the test solution; and (g) a control system suitable for determining the concentration of the amine-based inhibitor in the etching solution sample based on the concentration of the photosensitive inhibitor complex in the test solution.

[0015] In another aspect, the present invention relates to a method for determining the concentration of an amine-based inhibitor contained in a liquid. The method includes: forming a photosensitive group from an amine group of the amine-based inhibitor in the liquid; and using spectroscopy to measure the concentration of the amine-based inhibitor having the photosensitive group in the liquid.

[0016] In another aspect, the present invention relates to a method for forming a photosensitive compound in a liquid. The method includes: preparing a solution comprising phosphoric acid, an amine-based inhibitor comprising an amino group, a complexing agent, and water; and reacting the complexing agent with the amino group to form a photosensitive inhibitor complex. Attached Figure Description

[0017] Figure 1 The steps of the example process are shown.

[0018] Figure 2 A schematic diagram of an example component and system for measuring the concentration of an amine-based inhibitor in a silicon nitride etching solution. Detailed Implementation

[0019] The following description relates to a method for measuring the amount of amine-based inhibitors present in a silicon nitride wet etching solution (or simply "etch solution"). The method, related systems, and equipment can be used to quantitatively measure the amount of amine-based inhibitors in the etching solution, preferably using an automated system that measures the concentration of the amine-based inhibitors in the etching solution when it is used for a wet etching process.

[0020] The method can be performed using an automated measurement system equipped with gear connected to the etching apparatus during the etching operation (i.e., when the etching solution is used in a wet etching operation). Example steps of a method for measuring the concentration of an amine-based inhibitor in an etching solution may include: obtaining an etching solution sample from a silicon nitride etching bath; combining the etching solution sample with other components, including water, to form a test solution that can be analyzed using spectrometry; and analyzing the test solution using spectrometry to measure the concentration of a solute in the test solution. The measured concentration of the solute in the test solution may be correlated with the concentration of an amine-based inhibitor in the etching solution sample. The spectroscopic steps may be based on absorption spectroscopy, fluorescence spectroscopy, or both.

[0021] Other techniques for maintaining an available concentration of amine-based inhibitors in the etching solution do not measure or monitor the concentration of amine-based inhibitors in the etching solution. Instead, previous methods relied on tracking the amount of etching solution used during its application and replacing or replenishing the etching solution after a predetermined amount of time has elapsed or after a predetermined number of wafers have been processed in the etching solution to prevent the concentration of amine-based inhibitors from becoming undesirably low. Either method results in replacing the etching solution before it is necessary and increases costs due to incomplete use of the etching solution.

[0022] In contrast to previous methods, this method uses quantitative measurements of the concentration of amine-based inhibitors in the etching solution to more accurately determine the end-of-life of the etching solution. Quantitative assessment of the concentration of amine-based inhibitors in the etching solution and the end-of-life of the etching solution improves the efficiency of using expensive etching solutions and reduces waste by avoiding premature replacement.

[0023] The method described herein can be used in conjunction with wet etching operations for processing silicon nitride layers. In exemplary applications, silicon nitride is used as a rigid shielding layer in front-end or back-end processes to fabricate high aspect ratio structures included in solid-state logic devices and memory devices (e.g., 3D NAND memory devices). Multiple silicon nitride layers are formed as sacrificial layers between silicon oxide layers. The silicon nitride layers are removed by a silicon nitride etching step to leave space between two silicon oxide layers.

[0024] The term “microelectronic device” (or “microelectronic device substrate” or simply “substrate”) is used herein in a manner consistent with its general understanding in the fields of electronics, microelectronics, and semiconductor manufacturing, referring to, for example, any of the following many different types: semiconductor substrates; integrated circuits; solid-state memory devices; hard disk drives; read, write, and read-write heads and their mechanical or electronic components; flat panel displays; phase-change memory devices; solar panels and other products including one or more solar cell devices; photovoltaic devices; and microelectromechanical systems (MEMS) manufactured for use in microelectronic, integrated circuit, energy harvesting, or computer chip applications. It should be understood that the term “microelectronic device” can refer to any in-process microelectronic device or microelectronic device substrate containing or fabricated to contain functional electronic (current-carrying) structures, functional semiconductor structures, and insulating structures for the final electronic application in a microelectronic device or microelectronic assembly.

[0025] As used herein, the term "silicon nitride" is given the same meaning as the term used in the microelectronics and semiconductor manufacturing industry. Consistent with this, silicon nitride refers to materials comprising thin films of amorphous silicon nitride (Si3N4) (e.g., deposited via chemical vapor deposition from silane (SiH4) and ammonia (NH3)) with commercially available low amounts of other materials or impurities. Silicon nitride can be present as part of a substrate for a microelectronic device as a functional feature of the device, such as as a barrier layer or insulating layer, or it can be present as a material to facilitate multi-step fabrication methods for preparing microelectronic devices.

[0026] As used herein, the term "silicon oxide" is given the same meaning as the term used in the microelectronics and semiconductor manufacturing industry. Consistent with this, silicon oxide refers to silicon oxide (SiO₂). x (e.g., SiO2, "thermal oxides" (ThO2)) x Thin films made of (etc.).

[0027] According to certain commercial methods, silicon nitride is removed from the surface of a microelectronic device by a wet etching process that involves exposing the substrate surface to phosphoric acid (H3PO4) in an etching bath at high temperatures, such as in the range of 150 to 180 degrees Celsius.

[0028] Conventional wet etching techniques for the selective removal of silicon nitride relative to silicon oxide use an aqueous phosphoric acid (H3PO4) solution as the etching solution. The etching solution contains an amount of aqueous phosphoric acid (e.g., concentrated phosphoric acid) effective in producing the desired amount of silicon nitride. The term "aqueous phosphoric acid" refers to a component of the etching solution that combines with other components of the etching solution to form the etching solution. The term "phosphoric acid solid" refers to the non-aqueous component of the aqueous phosphoric acid component, or a component of an etching solution prepared from the aqueous phosphoric acid component.

[0029] The amount of solid phosphoric acid contained in the etching solution can be such that, in combination with other components of the etching solution, it will provide the desired etching performance (including the desired silicon nitride etching rate and selectivity, which typically requires a relatively high amount (concentration) of solid phosphoric acid). For example, the etching solution may contain a certain amount of solid phosphoric acid, said amount being at least about 50% by weight based on the total weight of the etching solution, such as at least 70, or at least about 80 or 85% by weight based on the total weight of the etching solution. Example etching solutions may contain at least 60, such as at least 80, or at least 90, 93, 95, or at least 98% by weight of concentrated phosphoric acid based on the total weight of the etching solution.

[0030] The silicon nitride etching process is designed to produce a combination of high etch rates and high selectivity of silicon nitride relative to silicon oxide. In addition to phosphoric acid, other components may be included in the etching solution to produce the desired selectivity and silicon nitride etch rate. One such component is an amine-based compound, sometimes referred to herein as an "amine-based inhibitor."

[0031] Examples of amine-based inhibitors include aminoalkylalkoxysilanes, or simply "aminoalkoxysilanes," as used herein, which refer to silane (-SiO-) based compounds or molecules containing at least one silicon atom and at least one amino group, i.e., an aminoalkyl substituent directly or via oxygen bond, attached to the silicon atom. The silicon atom may be substituted with one or more such aminoalkyl substituents and may additionally be substituted via oxygen with one or more of the following: a hydroxyl (-OH), an organic chemical (e.g., alkyl) group, or another silicon atom to form siloxane bonds, i.e., to form a molecule having multiple (e.g., 2, 3, 4, etc.) -Si-O- bonds. Aminoalkylalkoxysilane compounds may include said substituents, wherein at least one substituent for the silicon atom is an aminoalkyl substituent directly bonded to the silicon atom or bonded to the silicon atom via divalent oxygen (-O-), such as an aminoalkyl or aminoalkoxy substituent. See, for example, U.S. Patent No. 10,651,045; also see U.S. Patent No. 8,940,182 and European Patent Application No. 0,498,458.

[0032] An example of an aminoalkoxysilane compound containing only a single silicon atom can be represented by having the following formula:

[0033] Si(R1)(R2)(R3)(R4)

[0034] Each of R1, R2, R3, and R4 is an alkyl, alkoxy, hydroxyl, alkylamino, or alkoxyamine (aminoalkoxy), and at least one of R1, R2, R3, and R4 is an alkyl, alkoxy, or hydroxyl group, and at least one of R1, R2, R3, and R4 is an alkylamino or alkoxyamino group. The R1, R2, R3, or R4 group, including the alkyl chain, may include a branched chain, but a straight chain is preferred, as well as a chain containing a lower alkyl group (e.g., an alkyl group having 1, 2, 3, 4, or 5 carbon atoms). Examples of R1, R2, R3, and R4 groups are acyclic, saturated, and do not contain ether linkages. The amine-containing group can be any group that results in the desired etching properties of the photoresist solution (including a possible combination of silicon nitride etching rate and silicon nitride selectivity). Some general examples of amino groups in aminoalkoxysilane compounds include alkylamino groups containing primary amines (i.e., terminal amines); alkylamino groups containing secondary or tertiary amines; and poly(ethyleneimine) oligomers and similar groups.

[0035] The amount of aminoalkoxysilane (or its derivatives) contained in the etching solution may be such that, in combination with other materials in the etching solution, it will provide the desired etching performance. For example, the etching solution may contain an amount of an aminoalkoxysilane compound, which may be a single species or a combination of two or more species, in an amount of up to 10 percent of the etching solution, for example, in the range of about 20 to 50,000 parts per million based on the total weight of the etching solution (i.e., 0.0020 to 5.0 wt%), or about 20 to 2,000, 4,000, or 5,000 parts per million based on the total weight of the etching solution (i.e., 0.002 to 0.2, 0.4, or 0.5 wt%).

[0036] Other components may also be used in the etching solution as needed to enhance silicon nitride selectivity or etching rate. These include, for example, organic solvents, hexafluorosilicic acid (HFCA), dissolved silica, phosphonic acids, and carboxylic acid compounds. See, for example, U.S. Patent 10,651,045.

[0037] Hexafluorosilicic acid may be present in amounts, for example, in the range of about 5 to 10,000 parts or up to 50,000 parts per million based on the total weight of the etching solution (i.e., 0.0005 to 1 or even 5% by weight), or for example, in the range of about 20 to 2,000 parts per million based on the total weight of the etching solution (i.e., 0.002 to 0.2% by weight).

[0038] Examples of usable carboxylic acid compounds include acetic acid, malonic acid, succinic acid, 2-methylsuccinic acid, glutaric acid, adipic acid, salicylic acid, 1,2,3-propanetricarboxylic acid (also known as tricarboxylic acid), 2-phosphonoacetic acid, 3-phosphonopropionic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA), any of which may be used alone, in combination with each other, or in combination with different carboxylic acid compounds. The etching solution may contain any usable amount of one or more carboxylic acid compounds, for example, in amounts ranging from about 0.01 to about 10% by weight based on the total weight of the etching solution, or from about 0.1 to about 5 or 8% by weight based on the total weight of the etching solution.

[0039] The methods and systems described herein can be used to quantitatively determine the concentration of amine-based inhibitors present in a sample of an etching solution taken during a wet etching operation from a silicon nitride wet etching apparatus (e.g., a wet bath of the silicon nitride wet etching apparatus during a wet etching operation). Example methods relate to a spectroscopic approach, which may be based on absorption spectroscopy, fluorescence spectroscopy, or both, to determine the concentration of amine-based inhibitors in the etching solution. One approach, instead of directly measuring the concentration of the amine-based inhibitor itself in the etching solution, first forms a photosensitive chemical derivative or photosensitive group at the amine group of the amine-based inhibitor (an amine-based inhibitor compound containing a photosensitive group is called a "photosensitive inhibitor complex"). The method then uses spectroscopic detection of the photosensitive group to measure the concentration of the photosensitive inhibitor complex in the etching solution.

[0040] Absorption spectroscopy involves measuring the absorption of electromagnetic radiation as a function of frequency or wavelength (typically ultraviolet and visible light (UV-Vis)) based on the interaction between electromagnetic radiation and a sample liquid. The sample liquid absorbs energy (e.g., photons) from the electromagnetic radiation flux passing through it. The level of radiation absorption changes as a function of frequency and can also be related to the amount (concentration) of a particular radiatively absorbing solute in the sample.

[0041] Fluorescence spectroscopy (also known as fluorescence assay or spectrofluorescence assay) is a spectroscopic method for analyzing the fluorescence emitted from a sample. It involves using a light beam, typically ultraviolet or visible light, to excite electrons in molecules of known compounds in the sample, causing the molecules to emit light, which is usually, but not necessarily, visible light. The intensity of the fluorescence emitted from the sample can be related to the amount (concentration) of a particular solute in the sample.

[0042] According to the example method, the concentration of amine-based inhibitors in the etching solution can be assessed by obtaining a sample of the etching solution (“etching solution sample”) and preparing a test solution from the etching solution sample. Typically, the etching solution sample is at a high temperature, contains a concentrated amount of phosphoric acid solids, and is significantly viscous. The etching solution sample is not suitable for analysis using spectroscopic measurements. Therefore, the test solution is prepared at a lower temperature than the etching solution sample, containing a lower concentration of phosphoric acid solids relative to the etching solution sample, and having reduced viscosity, to allow analysis of the test solution using a spectrometer and spectroscopic methods. The test solution can be prepared, for example, by lowering the temperature of the etching solution sample using a cooler and diluting the etching solution sample with water (e.g., deionized water) at ambient temperature to prepare a test solution with reduced viscosity and reduced phosphoric acid concentration.

[0043] Complexing agents are also included in the test solution. Amine-based inhibitors are not photosensitive using spectroscopic techniques and cannot be directly detected according to the methods described herein. Instead, complexing agents are included in the test solution to chemically convert the amino group of the amine-based inhibitor into a photosensitive group, such as a photosensitive cyclic amine complex. A "photosensitive" group is a chemical compound or group that can be detected by spectroscopic methods, such as a chemical compound or group that absorbs light or absorbs light and emits light of different wavelengths, like a chemical compound or group that emits fluorescence.

[0044] The "complexing agent" used in the method is a chemical molecule that, alone or together with co-reactants, reacts with the amino group of an amine-based inhibitor in the test solution to form a photosensitive group from the amino group. The photosensitive group remains part of the amine-based inhibitor and can be detected by spectrometry to determine the concentration of the amine-based inhibitor containing the photosensitive group ("photosensitive inhibitor complex") in the test solution.

[0045] Various complexing agents known and commercially available for forming photosensitive groups from amine groups are used to react with amine groups of larger molecules (with co-reactants as needed) to form photosensitive groups, which remain part of the larger molecule. Non-limiting examples include o-phthalaldehyde (“OPA”), 9-fluorenylmethoxycarbonyl chloride (“9-fluorenylmethylchloroformate” or “Fmoc-Cl”), and fluorescent amine (3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA)). TM (), ninhydrin, fluorescamin, dansyl chloride, phenyl isothiocyanate (PITC) and 6-aminoquinolinyl-N-hydroxysucciniminocarbamate (AQC), although other available examples are also known.

[0046] "Guide to Protein Purification," 2nd Edition, James E. Noble and Marc J. J. Bailey, Methods in Enzymology, 2009, describes amine-labeled "derivatives" as a technique for quantifying amino acid mixtures in amino acid analysis using fluorescent probes. This technique can be used to quantify proteins and peptides containing lysine or a free N-terminus. Three probes identified as suitable for quantifying proteins or amino acids include o-phthalaldehyde (OPA) (Hammer and Nagel, 1986), fluorescein (Lorenzen and Kennedy, 1993), and 3-(4-carboxybenzoyl)quinoline-2-carboxaldehyde (CBQCA). TM (Asermely et al., 1997; Bantan-Polak et al., 2001; You et al., 1997). Fluorescent amines react directly with amine functional groups, while OPA and CBQCA... TM The addition of thiols (2-mercaptoethanol) or cyanides (CBQCA) is required. TM Co-reactants.

[0047] OPA has the following structure:

[0048]

[0049] o-phthalaldehyde (OPA) is a non-fluorescent compound that forms a fluorescent isoindole derivative in the presence of a primary amine and a free thiol moiety (which may be provided by, for example, a 2-mercaptoethanol co-reactant). The fluorescent complex is excited by UV light with a peak excitation wavelength of 340 nm and emits light in the blue region of the visible spectrum, with a maximum at approximately 430 nm.

[0050] 9-fluorenylmethoxycarbonyl chloride has the following structure:

[0051]

[0052] The test solution may include a co-reactant required for the reaction of a complexing agent with an amine group to form a photosensitizing group. When the complexing agent is OPA, the test solution also includes a thiol (e.g., 2-mercaptoethanol) as a co-reactant to form a photosensitizing inhibitor complex. When the complexing agent is CBQCA... TM At that time, the test solution included cyanide as a co-reactant to form a photosensitizing inhibitor complex.

[0053] The test solution may also include a buffer solution to control the pH of the test solution.

[0054] Once the test solution is prepared, it is immediately tested using spectroscopy to determine the concentration of the photosensitizing inhibitor complex in the test solution, which can then be used to calculate the concentration of the amine-based inhibitor in the test solution.

[0055] Determining the concentration of photosensitizing inhibitor complexes present in a test solution using absorption spectroscopy involves passing light through the test solution and measuring the amount of light absorbed by the test solution. The amount of light absorbed in the test solution can be compared with the amount of light absorbed by one or more calibration solutions (e.g., in the form of a previously generated calibration curve) to determine the amount (concentration) of the photosensitizing inhibitor complexes in the test solution. The concentration of the photosensitizing inhibitor complexes in the test solution can be used to determine the amount of amine-based inhibitors in the etching solution sample used to prepare the test solution.

[0056] Determining the concentration of a photosensitizing inhibitor complex in a test solution using fluorescence spectroscopy involves passing light through the test solution and measuring the amount of fluorescence emitted from it. The light beam excites electrons in the photosensitive group of the photosensitizing inhibitor complex molecule, causing the molecule to emit light, which is typically, but not necessarily, visible light. The intensity of the fluorescence emitted from the test solution can be compared with the intensity of the fluorescence emitted from the calibration solution (e.g., in the form of a previously generated calibration curve) to determine the amount (concentration) of the photosensitizing inhibitor complex in the test solution. The concentration of the photosensitizing inhibitor complex in the test solution can be used to determine the amount of amine-based inhibitor in the etching solution sample used to prepare the test solution.

[0057] The process of monitoring the concentration of amine-based inhibitors in the etching solution of a silicon nitride wet etching process can be carried out using any available and effective equipment and any step or sequence of steps that effectively obtains a sample of the etching solution (“etch solution sample”) from the etching bath of the silicon nitride wet etching process during operation, and by measuring the concentration of amine-based inhibitors in the etching solution using the method including spectrometry.

[0058] Figure 1A schematic example of a series of steps is shown. As shown, a silicon nitride wet etching apparatus is used to perform a wet etching step on a microelectronic device substrate including a silicon nitride layer (10). While the etching apparatus is operating to perform the etching step, a sample of the etching solution (“etch solution sample”) (20) is obtained from the wet etching apparatus, for example from a wet etching bath. The etching solution sample may be cooled using a cooling device and then used to prepare a test solution (30) by combining the etching solution sample with other components, including water, a complexing agent, optional co-reactants, and buffer solutions. The complexing agent reacts with the amine group of an amine-based inhibitor and optional co-reactants to generate a photosensitive group on the amine-based inhibitor (the resulting amine-based inhibitor with the photosensitive group is referred to as a “photosensitive inhibitor complex”). The concentration of the photosensitive inhibitor complex in the test solution is measured using spectroscopy (40), and the measured concentration of the photosensitive inhibitor complex is used to determine the concentration of the amine-based inhibitor in the etching solution sample (50).

[0059] The concentration of the amine-based inhibitor in the etching solution sample is compared with a predetermined operating concentration range or a predetermined minimum operating concentration (60) and identified as being above or below the minimum operating concentration (70). If the concentration of the amine-based inhibitor is above the minimum operating concentration, the silicon nitride wet etching process can continue in the silicon nitride wet etching apparatus. If the concentration of the amine-based inhibitor is below the minimum operating concentration, the composition of the etching solution is adjusted to contain a concentration of amine-based inhibitor higher than the minimum operating concentration, for example, by partially or completely replacing the etching solution in the apparatus.

[0060] Specifically, regarding step 30, which involves forming a test solution comprising an etching solution sample and a complexing agent (and optionally co-reactants and buffers) to form a photosensitizer complexing agent, certain steps and precautions may be applicable or desired for preparing a test solution suitable for analysis using spectroscopic methods. For example, the etching solution sample contains a high concentration of phosphate solids and will be at a high temperature (typically at least 100, 130, or 150 degrees Celsius) and has significant viscosity when removed from a wet etching apparatus. According to example methods, the etching solution sample may be diluted with water (e.g., deionized water at a lower temperature) for example at room temperature (e.g., 20 to 23 degrees Celsius).

[0061] Diluting etching solution samples with deionized water enables several functionalities. One function is to prepare test solutions with viscosity and phosphoric acid concentration suitable for spectroscopic analysis of the test solution. Another function is to dilute the concentration of amine-based inhibitors to a range lower than the concentration of amine-based inhibitors in the etching solution sample. Spectroscopy, used to measure the concentration of solutes (e.g., photosensitizing inhibitor complexes) in solutions (e.g., test solutions), is suitable for determining concentration levels within a specific concentration range. Etching solution samples can be diluted with water to form test solutions containing amine-based inhibitors (converted to photosensitizing inhibitor complexes) within a range that can be effectively measured by spectroscopy.

[0062] In the example step (30) of preparing the test solution, a known volume of the etching solution sample is combined (diluted) with a known volume of deionized water to form a test solution with a temperature approximately equal to ambient temperature and a concentration of the amine-based inhibitor. The amine-based inhibitor, after being converted into a photosensitizing inhibitor complex, allows for accurate measurement of the concentration of the photosensitizing inhibitor complex in the test solution. The test solution also has a viscosity and phosphate solids concentration suitable for analysis of the sample using spectroscopic techniques and equipment.

[0063] The volume of the etching solution sample can be determined as needed, with an example volume of up to 20 ml, for example, in the range of 0.001 to 10 ml. The volume of deionized water that can be combined with the etching solution sample can be the volume that can be used to produce the usable test solution, for example, the volume of deionized water is at least 100 times the volume of the etching solution sample, for example, the volume of deionized water is in the range of 100 to 500 times the volume of the etching solution sample.

[0064] The amount of complexing agent included in the test solution can be any available amount, such as an amount of complexing agent in excess of the amine stoichiometry relative to an amine-based inhibitor. The complexing agent can be added alone or in combination with a certain amount of water and, if necessary, with a buffer solution.

[0065] Other components (e.g., co-reactants) that can be used to react the complexing agent with the amine group of the amine-based inhibitor may also be included in the test solution. For example, a test solution containing OPA as a complexing agent may include a thiol (e.g., 2-mercaptoethanol) as a co-reactant to form a photosensitizing inhibitor complex. (The text also mentions CBQCA, but this seems unrelated to the test solution description.) TM The test solution, acting as a complexing agent, may include cyanide as a co-reactant to form a photosensitizing inhibitor complex. Any desired co-reactant may be provided in an amount that is stoichiometrically excess of the amine group relative to the amine-based inhibitor and included in the test solution.

[0066] pH buffers may be included in the test solution to control the pH and produce the desired pH for the test solution. The desired pH range may vary depending on the type of amine-based inhibitor or complexing agent, with examples of OPA or FMOC complexing agents having a pH range of 9 to 11. Importantly, while the pH range can be used to measure the concentration of the amine-based inhibitor in the test solution, the pH of different test solutions and associated calibration solutions should be the same to allow for usable comparisons.

[0067] Figure 2 This illustrates an example of an automated fluid monitoring system for monitoring the concentration of amine-based inhibitors in an etching solution. System 100 is an automated system for monitoring the concentration of amine-based inhibitors in an etching solution and is operatively connectable to a wet etching apparatus 150. The wet etching apparatus 150 includes a wet etching bath 152 containing an etching solution 154, which is a phosphoric acid etching solution and also contains amine-based inhibitors and other optional components as described herein. A semiconductor wafer (substrate) 156 can be placed in the etching solution 154 in the bath 152 for an etching step to remove silicon nitride (e.g., selectively removing silicon oxide from the surface of a semiconductor wafer containing both silicon nitride and silicon oxide).

[0068] The wet etching apparatus 150 can be operatively connected to the system 100, including via a sampling connection 102. The sampling connection 102 includes a closed fluid connection that allows a sample of the etching solution 154 (“etching solution sample”) to be removed from the bath 152 and pass through the connection 102 to the system 100, for example, using one or more pumps, valves, and control devices to obtain and transfer a specific volume of the etching solution sample.

[0069] Example system 100 includes a control module 104 and a test solution module 110. These are described as two independent (separate) modules, wherein the test solution module 110 is physically separated (or "distancing") from the control module 104. Alternatively, the two modules may be integrated. As shown, the test solution module 110 is separated from the control module 104. The test solution module 110 may be designed and structured as a temperature grading module, physically adapted to receive and process an etching solution sample received from bath 152 at a relatively high temperature and with a high concentration of phosphoric acid. Separating the test module 110 from the control module 104 prevents other components of the control module 110 from being exposed to the high temperature and concentrated phosphoric acid of the etching solution sample.

[0070] The control module 104 includes multiple fluid reservoirs, as shown in the figure. These reservoirs may include: a deionized water reservoir 114, a complexing agent reservoir 116, a co-reactant module 118, and a buffer solution module 120. Each of the reservoirs 114, 116, 118, and 120 is adapted to supply the required amounts of different liquids (deionized water, complexing agent, co-reactant, and buffer solution) to the test solution module. Control and sensor devices are adapted to control the volume and rate of each fluid flow.

[0071] The control module 104 also includes a control system 130 and a spectrometer or fluorometer 142 for measuring the concentration of the solute (photosensitive inhibitor complex) in the test solution using spectroscopy and the control system 130.

[0072] The control module 104 also includes a reservoir 122 for holding one or more calibration solutions. In use, the control module 104 and the reservoir 122 are adapted to supply a certain amount of one or more calibration solutions to the test solution module for the step of calibrating the spectrometer 142.

[0073] The control system 130 can be operatively (e.g., electronically) connected to each of the following: wet etching equipment 150 and its various components, test solution module 110 and its various components, spectrometer 142, and tanks 114, 116, 118, 120 and 122, including associated control devices (e.g. valves and pumps), sensors, and flow control devices associated with each (not specifically shown) to monitor and control the status of each component and the flow rate (volume, velocity) of fluids between the components.

[0074] Figure 2 The steps involving various sensors and control devices (e.g., valves, flow meters, sensors, etc.) included as part of etching apparatus 150, test module 110, system 100, and control system 130, and their associated components, for measuring the concentration of amine-based inhibitors in the etching solution sample obtained from bath 152 are not specifically shown. The sensors and control devices may be adapted to cooperate with at least a computerized hardware processor and memory device of control system 130 to measure, monitor, or control one or more of the temperature and flow rate (volume, rate) of fluids (including fluids in tanks 114, 116, 118, 120, and 122) of etching apparatus 150 and system 100. The memory device may store instructions that will be executed at the processor in response to electronic signals indicating measurements, statuses, or inputs received from components of etching apparatus 150, system 100, or one of these. According to various examples, control system 130 may include a computer processor, any form of microprocessor, such as a process logic controller (PLC controller) embodied in an application-specific integrated circuit (ASIC).

[0075] The test solution module 110 includes a mixing chamber 112 connected to a bath 152 and adapted to receive an etching solution sample of etching solution 154 from the bath 152 via a sampling connection 102. A cooling device 108 receives the sample of etching solution 154 (which is at a high temperature) and lowers the temperature of the sample to form a test solution in the mixing chamber 112. The test solution module 110 also includes a fluid reservoir connected to a control module 104 to receive the fluids required to form a test solution in the mixing chamber 112 by combining the etching solution sample with one or more fluids (e.g., deionized water, complexing agents, buffers, and optional co-reactants) from the fluid reservoir.

[0076] although Figure 1 and 2 The methods and procedures described are particularly suitable for measuring the concentration of amine-based absorbents in etching solutions during wet etching processes and at high temperatures. However, comparable procedures can be used to measure the concentration of amine-based inhibitors in etching solutions at different times or at lower temperatures. For example, the methods and systems can be used to measure the concentration of amine-based inhibitors in etching solutions before use in the etching process, while the etching solution is at room temperature. These methods do not require a step of cooling the etching solution before or during the formation of the test solution.

[0077] The spectroscopic methods described using absorber spectroscopy or fluorescence spectroscopy may require calibration of the spectrometer using one or more calibration solutions (contained in reservoir 122) each containing known concentrations of amine-based inhibitors.

[0078] The calibration solution may be a solution containing a known concentration of phosphoric acid and an amine-based inhibitor, compared to the etching solution 154. One or more calibration solutions may be used to perform the calibration step of the spectrometer 142 by: delivering a known volume of calibration solution (containing a known concentration of amine-based inhibitor) to the mixing chamber 112; combining the volume of calibration solution with the components (e.g., deionized water, complexing agent and optional co-reactants, and buffer) to form a test solution; measuring the absorbance or fluorescence of the test solution using the spectrometer 142; and correlating the absorbance or fluorescence of the test solution with the known concentration of the amine-based inhibitor in the calibration solution.

[0079] By measuring the absorbance of fluorescence in various calibration solutions with different known concentrations of amine-based inhibitors, system 100 (e.g., using software of control system 130) can generate calibration curves that correlate the measured absorbance or fluorescence value with the concentration of the amine-based inhibitor in the calibration solution. The measured absorbance or fluorescence value of a test solution prepared from a sample etching solution obtained from an etching bath in a self-operated wet etching operation (150) can be compared with the calibration curves to determine the concentration of the amine-based inhibitor in the sample etching solution.

Claims

1. A method for determining the concentration of an amine-based inhibitor in a silicon nitride etching solution, the method comprising: A test solution comprising a silicon nitride etching solution, a complexing agent, and water was prepared, wherein the silicon nitride etching solution contained phosphoric acid and an amine-based inhibitor. The complexing agent is reacted with the amino group of the amine-based inhibitor to form a photosensitizing inhibitor complex. The concentration of the photosensitizing inhibitor complex in the test solution was determined using spectroscopic methods, and The concentration of the amine-based inhibitor in the etching solution is determined from the concentration of the photosensitizing inhibitor complex in the test solution.

2. The method according to claim 1, comprising: When the test solution is exposed to radiation, the absorbance value of the test solution is determined, and The absorbance value of the test solution is used to determine the concentration of the photosensitizing inhibitor complex in the test solution, and The concentration of the amine-based inhibitor in the etching solution is determined from the concentration of the photosensitizing inhibitor complex in the test solution.

3. The method according to claim 2, further comprising comparing the absorbance value with the absorbance value of the correction solution.

4. The method according to claim 1, comprising: When the test solution is exposed to radiation, the fluorescence intensity of the test solution is determined, and The fluorescence intensity of the test solution is used to determine the concentration of the photosensitizing inhibitor complex in the test solution, and The concentration of the amine-based inhibitor in the etching solution is determined from the concentration of the photosensitizing inhibitor complex in the test solution.

5. The method of claim 4, further comprising comparing the fluorescence intensity of the test solution with the absorbance value of the calibration solution.

6. The method of claim 1, wherein the amine-based inhibitor comprises an aminoalkylsilane compound or an aminoalkoxysilane compound.

7. The method according to claim 1, wherein the complexing agent comprises phthalaldehyde, 9-fluorenylmethoxycarbonyl chloride, or fluorescent amine (3-(4-carboxybenzoyl)quinoline-2-carboxylaldehyde).

8. The method of claim 1, wherein preparing the test solution comprises combining a volume of etching solution with at least 100 volumes of deionized water.

9. The method according to claim 1, comprising: An etching solution sample was obtained from a silicon nitride wet etching apparatus including a silicon nitride etching bath, the etching solution sample having a volume in the range of 0.001 to 20 ml, and the etching solution sample having a temperature of at least 150 degrees Celsius. Combine one volume of etching solution sample with at least 100 volumes of deionized water.

10. The method of claim 1, further comprising: An etching solution sample was obtained from a silicon nitride wet etching apparatus including a silicon nitride etching bath, the etching solution sample having a volume in the range of 0.001 to 20 ml, and the etching solution having a temperature of at least 150 degrees Celsius. A test solution is formed, the test solution comprising: The etching solution, Each volume of etching solution contains at least 100 volumes of deionized water. pH buffer solution, and Complexing agents; The complexing agent is reacted with the amino group of the amine-based inhibitor to form a photosensitizing inhibitor complex. The test solution was placed in the spectrometer. Electromagnetic radiation is allowed to pass through the test solution. Analyze the intensity of light leaving the analysis unit, and The concentration of the amine-based inhibitor in the etching solution is determined from the intensity of the light leaving the analysis unit.

11. The method of claim 1, wherein it is performed using an automated fluid monitoring system operably connected to a silicon nitride wet etching apparatus, the automated fluid monitoring system comprising: (a) A sampling system suitable for extracting etching solution samples from a silicon nitride wet etching apparatus that includes a silicon nitride etching bath. (b) Deionized water storage tank (c) pH buffer solution storage tank (d) Complexing agent storage tank (e) A mixed chamber suitable for preparing a test solution comprising at least a portion of the etching solution sample, deionized water, pH buffer, and a complexing agent, wherein the complexing agent reacts with the amine group of an amine-based inhibitor contained in the etching solution sample to form a photosensitizing inhibitor complex. (f) A spectrometer suitable for receiving the test solution from the mixing chamber and measuring the concentration of the photosensitizing inhibitor complex in the test solution, and (g) A control system suitable for determining the concentration of amine-based inhibitors in the etching solution sample based on the measured concentration of the photosensitizing inhibitor complex in the test solution.

12. An automated fluid monitoring system suitable for monitoring the concentration of an amine-based inhibitor in an etching solution, the system comprising: (a) A sampling system suitable for obtaining etching solution samples from silicon nitride wet etching equipment including a silicon nitride etching bath. (b) Deionized water storage tank (c) pH buffer solution storage tank (d) Complexing agent storage tank (e) A mixed chamber suitable for preparing a test solution comprising at least a portion of the etching solution sample, deionized water, pH buffer, and a complexing agent, wherein the complexing agent reacts with the amine group of an amine-based inhibitor contained in the etching solution sample to form a photosensitizing inhibitor complex. (f) A spectrometer suitable for receiving the test solution from the mixing chamber and measuring the concentration of the photosensitizing inhibitor complex in the test solution, and (g) A control system suitable for determining the concentration of amine-based inhibitors in the etching solution sample based on the concentration of the photosensitizing inhibitor complex in the test solution.

13. The system of claim 12, wherein the control system compares the concentration of the amine-based inhibitor in the etching solution with a predetermined minimum concentration.

14. The system of claim 12, wherein the sampling system includes a fluid connection that allows the etching solution sample to be delivered from the silicon nitride wet etching apparatus to the mixing chamber.

15. The system of claim 12, wherein the amine-based inhibitor comprises an aminoalkylsilane compound or an aminoalkoxysilane compound.

16. The system of claim 12, wherein the complexing agent comprises phthalaldehyde, 9-fluorenylmethoxycarbonyl chloride, or fluorescent amine (3-(4-carboxybenzoyl)quinoline-2-carboxylaldehyde).

17. The system according to claim 12, comprising a control module and a remote test solution module, wherein: The control module includes: the deionized water storage tank, the pH buffer solution storage tank, the complexing agent storage tank, the spectrometer, and the control system. The remote test solution module includes a mixing chamber with fluid connections to each of the following: the silicon nitride etching bath, the deionized water reservoir, the pH buffer solution reservoir, the complexing agent reservoir, and the spectrometer.

18. A method for determining the concentration of an amine-based inhibitor contained in a liquid, the method comprising: From the amine groups of amine-based inhibitors in liquids, photosensitive groups are formed, and The concentration of the amine-based inhibitor having the photosensitive group in the liquid was measured using a spectroscopic method.

19. The method of claim 18, wherein the liquid comprises a silicon nitride etching solution containing phosphoric acid and the amine-based inhibitor.

20. The method of claim 19, wherein the liquid is a test solution comprising the silicon nitride etching solution and deionized water.

21. The method according to claim 18, wherein the photosensitive group is a cyclic amine group.

22. A method for forming a photosensitive compound in a liquid, the method comprising: Prepare a solution, the solution comprising: Phosphoric acid, Amine-based inhibitors containing an amino group. Complexing agents, and water, The complexing agent is reacted with the amine group to form a photosensitizing inhibitor complex.

23. The method of claim 22, wherein the amine-based inhibitor comprises an aminoalkylsilane compound or an aminoalkoxysilane compound.

24. The method of claim 22, wherein the complexing agent comprises phthalaldehyde, 9-fluorenylmethoxycarbonyl chloride, or fluorescent amine (3-(4-carboxybenzoyl)quinoline-2-carboxylaldehyde).

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