TWI825858B - Method for detecting metal impurities in polishing fluids - Google Patents

Abstract

The invention belongs to a method for detecting metal impurities in polishing liquid, which includes the following steps: adding a second volume _V2 of nitric acid aqueous solution to a first container containing a first volume _V1 of polishing liquid, wherein the polishing liquid The liquid contains high molecular polymer and SiO ₂ particles; put the first container into the second container containing ultrapure water, perform ultrasonic treatment and heating treatment, so that the polishing liquid and the nitric acid aqueous solution are fully mixed, so that the polishing liquid The metal ions combined with the polymer through coordination or covalent bonding are released, and a first solution is obtained; the first solution is vacuum filtered to obtain a second solution that does not contain solid SiO ₂ particles; the second solution is Leave to stand and separate to obtain a third solution in which metal ions are dissolved; analyze and test the third solution using ICP/MS analysis to obtain the first concentration n ₁ of metal ions in the third solution; obtain the concentration of metal ions in the polishing liquid according to the following formula The concentration of metal ions n ₂ : n ₂ = n ₁ *V ₂ /V ₁ .

Description

Method for detecting metal impurities in polishing fluids

The present invention belongs to the technical field of metal content detection, and in particular relates to a method for detecting metal impurities in polishing liquid.

In the related silicon wafer manufacturing process technology, chemical mechanical polishing is to cause friction between the wafer (wafer) and the pad (fixed plate) at relative speeds through the upper and lower fixing plates under pressure, resulting in a mechanical reaction. At the same time, during the mechanical reaction, Slurry (mortar, or polishing fluid) is continuously supplied, and a Chemical reaction occurs at the interface between Slurry and Wafer. Under the interaction of these two reactions, fine grinding is achieved, which is the key to obtaining high flatness. , a key step for high-purity silicon wafers. At present, the ingredients of Slurry slurry used in the chemical mechanical polishing process generally include silica, alumina, polymers, complexing agents, dispersants, DIW, etc. If the equipment used in the process or the processing slurry is not pure enough, it contains Metal impurities, these impurities will be adsorbed on the surface of the silicon wafer or penetrate into the body of the silicon wafer under high temperature conditions during the processing. The metal adsorbed on the surface of the silicon wafer can be removed through subsequent cleaning steps, while the bulk metal will be removed during subsequent processing. It is difficult to remove, which will have a greater impact on the back-end process. Therefore, in order to avoid metal contamination during the mechanical polishing process, it is particularly important to ensure the purity of the Slurry slurry used in the mechanical polishing process.

Slurry slurry contains solid silica, alumina particles, polymers, etc. The polymers exist in the form of micelle structures and cannot enter the central area of the plasma in the form of aerosols of aqueous solutions for deionization and vaporization. ionization, dissociation and ionization, making it impossible to detect and analyze it by ICP-MS analysis. Therefore, it is impossible to perform qualitative and quantitative analysis of metal impurities on Slurry used in the chemical mechanical polishing process of silicon wafers.

In order to solve the above technical problems, the present invention provides a method for detecting metal impurities in the polishing liquid to solve the problem of being unable to analyze the metal in the polishing liquid.

In order to achieve the above object, the technical solution adopted in the embodiment of the present invention is: a method for detecting metal impurities in polishing fluid, which includes the following steps: Step 1: Add water to a first container containing polishing fluid with a first capacity V ₁ , add a second volume of nitric acid aqueous solution, wherein the polishing liquid contains polymer micelles and SiO ₂ particles; Step 2: Place the first container into a second container containing ultrapure water, and proceed Ultrasonic treatment and heat treatment to fully mix the polishing liquid and the nitric acid aqueous solution to release the metal ions bound to the polymer through coordination or covalent bonding in the polishing liquid and obtain the first solution; Steps 3: Vacuum filter the first solution to obtain a second solution that does not contain solid SiO ₂ particles; Step 4: Leave the second solution to stand and separate to obtain a third solution in which only metal ions are dissolved. The capacity is V ₂ ,; Step 4: The third solution is analyzed and tested using the ICP/MS analysis method to obtain the first concentration n ₁ of metal ions in the third solution; Step 5: The polishing slurry is obtained according to the following formula The concentration of metal ions in n ₂ : n ₂ =n ₁ *V ₂ /V ₁ .

Optionally, the components of the nitric acid aqueous solution include nitric acid and ultrapure water, wherein the concentration of nitric acid is 1%-10%.

Optionally, the concentration of nitric acid in the nitric acid aqueous solution is 5%.

Optional, in this step 2: The bottom or side wall of the second container is provided with an ultrasonic structure, and the mixed solution is subjected to ultrasonic treatment through the ultrasonic structure; During the ultrasonic treatment, the second container is heated to 50-100 degrees and maintained for a preset time.

Optionally, in the step "during the ultrasonic treatment, heat the second container to 50-100 degrees and maintain it for a preset time", the ultrasonic frequency is 20-60Hz, and the ultrasonic frequency is 20-60Hz. The power is 200-240w, and the preset time is 5-10 minutes.

Optionally, in step 4, the second solution is allowed to stand and separated through a separatory funnel, and the third solution containing dissolved metal ions sinks and is discharged from the liquid outlet at the bottom of the separatory funnel.

Optionally, the separatory funnel is made of PFA material.

Optionally, the first container and the second container are made of PFA material.

Optionally, perform this step 1 to step 5 in a fume hood to detect the metal impurity content in the polishing liquid. During the process of performing this step 1 to step 5, continue to pass inert gas into the fume hood.

The beneficial effects of the present invention are: extracting metal impurities in the polishing liquid, detecting the liquid containing dissolved metal ions, and obtaining the type and concentration of metals contained in the polishing liquid.

In order to help the review committee understand the technical features, content and advantages of the present invention and the effects it can achieve, the present invention is described in detail below in the form of embodiments with the accompanying drawings and attachments, and the drawings used therein are , its purpose is only for illustration and auxiliary description, and may not represent the actual proportions and precise configurations after implementation of the present invention. Therefore, the proportions and configuration relationships of the attached drawings should not be interpreted or limited to the actual implementation of the present invention. The scope shall be stated first.

In the description of the embodiments of the present invention, it should be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical" ", "level", "top", "bottom", "inside", "outside", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of description and simplification of the embodiments of the present invention. The description does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore is not to be construed as a limitation of the invention.

In addition, the terms “first” and “second” are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of indicated technical features. Thus, features defined as “first” and “second” may explicitly or implicitly include one or more of the described features. In the description of the embodiments of the present invention, "plurality" means two or more than two, unless otherwise explicitly and specifically limited.

In the embodiments of the present invention, unless otherwise expressly stipulated and limited, the terms "installation", "connection", "connection", "fixing" and other terms should be understood in a broad sense. For example, it can be a fixed connection or a removable connection. Disassembly and connection, or integration; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be an internal connection between two elements or an interaction between two elements. For those with ordinary knowledge in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

Inductively coupled plasma mass spectrometry (ICP/MS) is a commonly used analytical instrument in elemental analysis. The sample loading process is to atomize the dilute solution containing the element to be measured through an atomizer to form an aerosol, which is brought into the ICP sample gas path by the carrier gas and reaches the ICP torch to achieve detection. The Slurry (mortar, or polishing fluid) used in the mechanical polishing process has complex ingredients, including silica particles, dispersants, polymers, alkali solutions, complex agents, DIW, etc. Some of the metal ions in the polishing fluid are adsorbed. On the surface of the silica particles, part of it is combined with the polymer through coordination bonds or covalent bonds to form organic metal compounds, and some metal ions cannot be dissolved and cannot enter the ICP-MS in the form of aerosols in aqueous solutions. The plasma center area of the instrument undergoes deionization, vaporization, dissociation and ionization. Therefore, the metal impurity content cannot be directly analyzed by ICP-MS.

As shown in Figures 1 to 5, in response to the above problems, this embodiment provides a method for detecting metal impurities in the polishing liquid. As shown in Figure 6, it includes the following steps: S601: To accommodate the first capacity V ₁ In the first container 10 of the polishing liquid 1, add a second volume of nitric acid aqueous solution 2, wherein the polishing liquid 1 contains high molecular polymer and _SiO2 particles, refer to Figures 1 and 2; S602: Add the first The container 10 is placed into the second container 20 containing ultrapure water, and ultrasonic treatment and heat treatment are performed so that the polishing liquid 1 and the nitric acid aqueous solution 2 are fully mixed, so that the polymer in the polishing liquid 1 can pass through The metal ions bound by coordination or covalent bonding are released, and a first solution is obtained, refer to Figure 3; S603: Vacuum filter the first solution to obtain a second solution that does not contain solid SiO ₂ particles, refer to Figure 4; S604: Let the second solution stand and separate to obtain a third solution in which only metal ions are dissolved. The capacity of the third solution is V ₂ , refer to Figure 5; S605: Analyze the third solution using ICP/MS analysis. Test to obtain the first concentration n ₁ of metal ions in the third solution; S606: Obtain the concentration n ₂ of metal ions in the polishing liquid 1 according to the following formula: n ₂ =n ₁ *V ₂ /V ₁ . Micelle refers to a large number of molecularly ordered aggregates that begin to form after the surfactant concentration reaches a certain value in an aqueous solution. In the micelle, the hydrophobic groups of the surfactant molecules aggregate to form the core of the micelle, the hydrophilic polar groups form the outer layer of the micelle, and the metal ions are hydrophilic ions. The metal ions present in polishing fluid 1 may be as follows: Existence form: 1) Metal ions are dissolved in the hydrophilic layer of the outer layer of the micelle structure; 2) Metal atoms will be covalently bonded to carbon atoms in the polymer to form a metal-organic compound with a C-M+ structure; 3) Part of High molecular polymers contain groups that can coordinate with metal ions, such as terminal O, N and other highly electronegative atoms. These atoms can form coordination bonds with metal ions to form metal complexes. .

In order to accurately measure the type and concentration of metals contained in the polishing liquid 1, it is necessary to release the metal ions bound to the polymer and dissolve the metal ions in the aqueous solution. In this embodiment, nitric acid aqueous solution 2 is used to break the bond between the metal ions and the polymer compound through ultrasonic and high-temperature treatment, fully releasing the metal ions, and the metal adsorbed on the surface of the silicon dioxide particles can also be extracted to in DIW (ultrapure water). And metal ions that cannot be dissolved in ultrapure water can be adsorbed by nitric acid. In this way, by performing ICP/MS detection on the solution containing dissolved metal ions, the type and concentration of the metal contained in the polishing liquid 1 can be obtained.

In some implementations of this embodiment, the components of the nitric acid aqueous solution 2 include nitric acid and ultrapure water, where the concentration of nitric acid is 1%-10%, but is not limited to this.

Preferably in this embodiment, the concentration of nitric acid in the nitric acid aqueous solution 2 is 5%.

In some implementations of this embodiment, in step S602: The bottom or side wall of the second container 20 is provided with an ultrasonic structure, and ultrasonic treatment is performed through the ultrasonic structure; During the ultrasonic treatment, the second container 20 is heated to a temperature of 50-100 degrees and maintained for a preset time.

It uses ultrasonic waves and high temperature to break down the bonds between metal ions and polymers, while accelerating the extraction of metal ions and improving efficiency.

In some implementations of this embodiment, in the step "during the ultrasonic treatment, heat the second container 20 to 50-100 degrees and maintain it for a preset time", the ultrasonic frequency is 20-60Hz, ultrasonic power is 200-240w, the preset time is 5-10 minutes.

In a specific implementation of this embodiment, during the ultrasonic treatment, the second container 20 is heated to 80 degrees and maintained for a preset time, but is not limited to this.

In some implementations of this embodiment, in step S603, the first solution is vacuum filtered to obtain a second solution that does not contain solid SiO ₂ particles. This specifically includes: connecting a vacuum filtration device. The vacuum filtration device is generally It includes a volumetric flask 5 with a filter tip, which is connected to a vacuum pump through a pipeline. The vacuum filtration device also includes a funnel 4 arranged on the volumetric flask 5. A filter paper is provided in the funnel 4, and a nanometer is placed in the funnel 4. Grade filter paper, turn on the vacuum pump, slowly pour the first solution into funnel 4, and start the filtration process under the action of the vacuum pump. The SiO ₂ particles in polishing fluid 1 have a particle size of nanometers and will be isolated by the filter paper. The polishing slurry 1 that does not contain SiO ₂ particles will be pumped into the volumetric flask 5 below the funnel 4 under the action of a vacuum pump, see Figure 4.

In some implementations of this embodiment, in S604, the second solution is left to stand and separated through the separatory funnel 4, and the third solution with dissolved metal ions sinks and is discharged from the liquid outlet at the bottom of the separatory funnel 4. .

After standing for separation, the nitric acid aqueous solution 2 with dissolved metal ions has a high density and sinks, and the remaining part of the polishing liquid 1 from which metal ions are separated has a low density and floats, thereby separating the third solution with dissolved metal ions.

In some implementations of this embodiment, the separatory funnel 4 is made of PFA (polytetrafluoroethylene) material to avoid introducing new metal impurities and improve detection accuracy.

Surfactants are dissolved in water and when their concentration is low, they are dispersed as single molecules or adsorbed on the surface of the solution to reduce surface tension. When the concentration of surfactant increases to the point where the surface of the solution is saturated and can no longer be adsorbed, the molecules of the surfactant begin to transfer into the interior of the solution. Since the hydrophobic part of the surfactant molecule has a small affinity with water, the hydrophilic part between When a certain concentration is reached, the hydrophobic parts of many surfactant molecules (generally 50 to 150) attract each other and associate together to form an association, which is a micelle. The interior of the micelle is a hydrophobic core formed by the aggregation of hydrophobic groups, and the exterior of the micelle is a chain of hydrophilic groups. The hydrophilic group will dissolve some metal ions and will also bond with metal ions to form an organic metal compound. In this embodiment, under the action of ultrasonic waves and high temperature, the bond between the hydrophilic group and the metal ion can be broken, so that the metal ion bound to the polymer through coordination or covalent bonding can be released.

Both the first capacity and the second capacity can be set according to actual needs. In one implementation of this embodiment, the first capacity is 10 ml and the second capacity is 100 ml. However, this is not a limitation as long as the nitric acid is ensured. The amount of aqueous solution can completely dissolve the metal ions in the polishing liquid 1. .

In some implementations of this embodiment, the first container 10 and the second container 20 are made of PFA (polytetrafluoroethylene) material to avoid introducing new metal impurities and improve detection accuracy.

In some implementations of this embodiment, steps S601 to S606 are performed in a fume hood to detect the metal impurity content in the polishing liquid 1. During the execution of steps S601 to S606, the fume hood is continuously Pour in inert gas.

The inert gas may be nitrogen, but is not limited to this.

By adopting the above solution, the entire process of detecting metal in the polishing liquid in this embodiment can be performed in an inert gas environment, thereby avoiding the introduction of metal impurities in the environment.

The above are only preferred embodiments of the present invention and are not intended to limit the implementation scope of the present invention. If the present invention is modified or equivalently substituted without departing from the spirit and scope of the present invention, the protection shall be covered by the patent scope of the present invention. within the range.

1: Polishing fluid 2: Nitric acid aqueous solution 4: Funnel 5: Volumetric flask 10:First container 20:Second container S601-S606: Steps

Figure 1 shows a schematic diagram of a first container containing polishing fluid in an embodiment of the present invention; Figure 2 shows a schematic diagram of adding nitric acid aqueous solution to the first container in an embodiment of the present invention; Figure 3 shows a schematic diagram of the state of step S602 in the embodiment of the present invention; Figure 4 shows a schematic diagram of the state of the second solution obtained after performing step S603 in the embodiment of the present invention; Figure 5 shows a schematic diagram of the state of static separation in the embodiment of the present invention; Figure 6 shows a schematic flow chart of detecting metal in the polishing liquid in an embodiment of the present invention.

S601-S606: Steps

Claims (7)

A method for detecting metal impurities in polishing liquid, including the following steps: Step 1: Add a second volume of nitric acid aqueous solution to a first container containing a polishing liquid of first volume V ₁ , wherein the polishing liquid Contains high molecular polymer and SiO ₂ particles; Step 2: Place the first container into a second container containing ultrapure water, and perform ultrasonic treatment and heating treatment to fully mix the polishing slurry and the nitric acid aqueous solution , to release the metal ions bound to the polymer through coordination or covalent bonding in the polishing slurry, and obtain the first solution; Step 3: Vacuum filter the first solution to obtain solid-free SiO ₂ The second solution of particles; Step 4: Let the second solution stand and separate to obtain a third solution in which only metal ions are dissolved. The capacity of the third solution is V ₂ ; Step 5: Use ICP/MS to Analyze and test using the analytical method to obtain the first concentration n ₁ of the metal ions in the third solution; Step 6: Obtain the concentration n ₂ of the metal ions in the polishing liquid according to the following formula: n ₂ =n ₁ *V ₂ / V ₁ ; In this step 2: the bottom or side wall of the second container is provided with an ultrasonic structure, and ultrasonic treatment is performed through the ultrasonic structure; during the ultrasonic treatment, the second container is heated and the temperature is raised to 50-100 degrees and maintain the preset time; among which, the ultrasonic frequency is 20-60Hz, the ultrasonic power is 200-240w, and the preset time is 5-10 minutes. The method for detecting metal impurities in polishing fluid as described in claim 1, wherein the components of the nitric acid aqueous solution include nitric acid and ultrapure water, wherein the concentration of nitric acid is 1%-10%. The method for detecting metal impurities in polishing liquid as described in claim 2, wherein the concentration of nitric acid in the nitric acid aqueous solution is 5%. The method for detecting metal impurities in polishing liquid as described in claim 1, wherein in step 4, the second solution is left to stand and separated through a separatory funnel, and the third solution with dissolved metal ions sinks, And discharge from the liquid outlet at the bottom of the separatory funnel. The method for detecting metal impurities in polishing fluid as described in claim 4, wherein the separatory funnel is made of PFA material. The method for detecting metal impurities in polishing fluid as described in claim 1, wherein the first container and the second container are made of PFA material. The method for detecting metal impurities in the polishing liquid as described in claim 1, wherein steps 1 to 5 are performed in a fume hood to detect the metal impurity content in the polishing liquid. During step 5, continue to pass inert gas into the fume hood.