JP7271993B2 - Cleaning solution for removing cerium compound, cleaning method, and method for manufacturing semiconductor wafer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a cleaning solution for removing cerium compounds, a cleaning method, and a method for manufacturing a semiconductor wafer.

Semiconductor wafers are processed by chemical mechanical polishing, which uses a polishing agent consisting of a water-based slurry containing polishing fine particles after depositing a metal film and an interlayer insulating film as wiring on a silicon substrate. Hereinafter, it may be abbreviated as "CMP".) The surface is planarized by a process, and a new layer is stacked on the planarized surface. Microfabrication of semiconductor wafers requires high-precision flatness in each layer, and the importance of planarization processing by CMP is extremely high.

In the semiconductor device manufacturing process, an element isolation structure based on STI (Shallow Trench Isolation), which is more suitable for miniaturization, is used in place of conventional LOCOS (Local Oxidation of Silicon) in order to electrically isolate elements such as transistors. ing. Also, an ILD (Inter Layer Dielectric) is used between the wiring layers. The STI and ILD are made by forming a silicon dioxide film using TEOS (Tetraethyl Orthosilicate) or the like as a raw material and planarizing the film by a CMP process.

After the CMP process, the surface of the semiconductor wafer contains a large amount of polishing fine particles of the abrasive used in the CMP process and organic residues derived from organic compounds contained in the slurry. The semiconductor wafer after the process is subjected to a cleaning process.

In recent years, in the CMP process for silicon dioxide, cerium-based abrasive fine particles such as cerium oxide are used in order to increase the polishing rate. It forms and is difficult to remove in a cleaning process. Therefore, in the past, strong chemicals such as diluted hydrofluoric acid and sulfuric acid/hydrogen peroxide were used for cleaning. Various cleaning solutions have been proposed as alternative cleaning solutions. For example, Patent Document 1 discloses a cleaning liquid containing a reducing agent.

WO2018/136511

During the CMP process, a bond is formed between the cerium compound and silicon dioxide, and it is believed that trivalent cerium contributes to the bond. Since the cleaning solution disclosed in Patent Document 1 contains a reducing agent, this trivalent cerium bond remains, and the removal of the cerium compound is insufficient.

It is also conceivable to use an alkaline cleaning agent such as dilute aqueous ammonia. By using an alkaline cleaning agent such as diluted ammonia water, both the cerium compound and the semiconductor wafer surface are negatively charged in the aqueous solution, and an electrostatic repulsive force acts between the fine particles containing the cerium compound and the semiconductor wafer surface. Although the reattachment of fine particles containing a cerium compound to the surface of a semiconductor wafer can be suppressed, the ability to break the bond between the cerium compound and silicon dioxide was low, and the removability of the cerium compound was insufficient.

The present invention has been made in view of such problems, and an object of the present invention is to provide a cleaning liquid that is excellent in removing cerium compounds.

Conventionally, cleaning solutions containing various components have been studied, but as a result of extensive studies, the present inventors have found a cleaning solution containing the component (A) described later, and this cleaning solution has excellent removal properties for cerium compounds. I found it to be excellent.

That is, the gist of the present invention is as follows.
[1] A cleaning solution for removing cerium compounds, containing the following component (A).
Component (A): Oxidizing agent [2] The cleaning solution for removing cerium compounds according to [1], wherein component (A) contains at least one selected from the group consisting of hydrogen peroxide, nitric acid and nitrate.
[3] The cleaning solution for removing cerium compounds according to [1] or [2], further comprising the following component (B).
Component (B): pH adjuster [4] For removing cerium compounds according to [3], wherein component (B) contains at least one selected from the group consisting of quaternary ammonium hydroxides and alkanolamine compounds. washing liquid.
[5] The cleaning solution for removing cerium compounds according to any one of [1] to [4], further comprising the following component (C).
Component (C): chelating agent [6] The cleaning solution for removing cerium compounds according to any one of [1] to [5], further comprising the following component (D).
Component (D): water [7] The cleaning solution for removing cerium compounds according to any one of [1] to [6], which has a pH of 2 to 12.
[8] The cleaning solution for removing cerium compounds according to any one of [1] to [7], which is used for cleaning after chemical mechanical polishing.
[9] The cleaning solution for removing cerium compounds according to any one of [1] to [8], which is used for removing cerium compounds.
[10] The cleaning solution for removing cerium compounds according to any one of [1] to [9], which is used for cleaning a surface on which silicon dioxide is exposed.
[11] A cleaning method comprising removing a cerium compound using the cleaning liquid according to any one of [1] to [10].
[12] The cleaning method according to [11], wherein the cerium compound on the semiconductor wafer is removed.
[13] A method for manufacturing a semiconductor wafer, comprising a step of removing a cerium compound using the cleaning liquid according to any one of [1] to [10].
[14] The method for manufacturing a semiconductor wafer according to [13], further comprising the step of performing chemical mechanical polishing using a polishing agent containing a cerium compound.

The cleaning liquid of the present invention is excellent in removing cerium compounds.
Moreover, the cleaning method of the present invention is excellent in removability of cerium compounds.
Furthermore, since the method for manufacturing a semiconductor wafer of the present invention includes a cleaning step that is excellent in removability of cerium compounds, malfunction of semiconductor devices can be suppressed.

Although the present invention will be described in detail below, the present invention is not limited to the following embodiments, and can be implemented with various modifications within the scope of the gist thereof. In addition, when the expression "~" is used in this specification, it is used as an expression including numerical values or physical property values before and after it.

(washing liquid)
The cleaning liquid of the present invention contains the following component (A).
Component (A): Oxidizing agent

(Component (A))
Component (A) is an oxidizing agent.
By containing the component (A), the cleaning solution of the present invention can selectively act on cerium ions, cut the bond between the cerium compound and silicon dioxide without damaging the silicon dioxide, and remove the cerium compound. It is excellent in durability and low damage property of silicon dioxide.

Examples of component (A) include hydrogen peroxide, ozone, nitric acid, nitrous acid, persulfuric acid, dichromic acid, permanganic acid, chloric acid, bromic acid, iodic acid and salts thereof. These components (A) may be used individually by 1 type, and may use 2 or more types together. Among these components (A), hydrogen peroxide, nitric acid, nitrates, and persulfuric acid are preferable, and hydrogen peroxide, nitric acid, and nitrates are more preferable because of their excellent oxidizing power.

(Component (B))
Since the cleaning liquid of the present invention can adjust the pH of the cleaning liquid, it is preferable that the following component (B) is included in addition to the component (A).
Component (B): pH adjuster

Examples of component (B) include acids and alkalis. Among the component (B), alkali is preferable because it can adjust the zeta potential and sufficiently exhibit the effect of the component (A), and the component (B) itself remains on the semiconductor wafer after cleaning. Quaternary ammonium hydroxides and alkanolamine compounds are more preferable because they can be suppressed.

Examples of acids include inorganic acids and organic acids. These acids may be used individually by 1 type, and may use 2 or more types together. Among these acids, inorganic acids and organic acids are preferred, and organic acids are more preferred, since they contain less metal impurities.

Examples of inorganic acids include sulfuric acid, hydrochloric acid, nitric acid and phosphoric acid. These inorganic acids may be used singly or in combination of two or more. Among these inorganic acids, sulfuric acid and phosphoric acid are preferred, and sulfuric acid is more preferred, because of their low volatility.

Examples of organic acids include organic compounds having amino groups, carboxyl groups, sulfonic acid groups, and phosphonic acid groups. These organic acids may be used singly or in combination of two or more. Among these organic acids, an amino group-containing organic compound and a carboxyl group-containing organic compound are preferable, and a carboxyl group-containing organic compound is more preferable, because of their excellent chelating power.

Examples of alkalis include inorganic alkalis and organic alkalis. These alkalis may be used individually by 1 type, and may use 2 or more types together. Among these alkalis, inorganic alkalis and organic alkalis are preferable because the alkali itself can be easily produced, and ammonia, quaternary ammonium hydroxides, and alkanolamine compounds are more preferable because they do not contain metal components. Quaternary ammonium hydroxides and alkanolamine compounds are more preferred, and tetramethylammonium hydroxide, tetraethylammonium hydroxide, ethanolamine, propanolamine and isopropanolamine are particularly preferred.

(Component (C))
Since the cleaning liquid of the present invention can break the bond between the cerium compound and silicon dioxide and is excellent in removing the cerium compound, it preferably contains the following component (C) in addition to the component (A).
Component (C): chelating agent

The component (C) may be a compound capable of coordinating with a metal ion. A chelating agent having an atom is preferable, a chelating agent having an amino group, a chelating agent having a carboxyl group, and a chelating agent having a phosphonic acid group are more preferable, and a chelating agent having an amino group and a chelating agent having a carboxyl group are more preferable. Chelating agents having both amino and carboxyl groups are particularly preferred.

Examples of chelating agents having both an amino group and a carboxyl group include amino acids such as glycine, serine, aspartic acid and histidine and their derivatives; aminopolycarboxylic acids such as diethylenetriaminepentaacetic acid and triethylenetetraaminehexaacetic acid; Derivatives thereof and the like are included. These chelating agents having both an amino group and a carboxyl group may be used singly or in combination of two or more. Among these chelating agents having both an amino group and a carboxyl group, diethylenetriaminepentaacetic acid and triethylenetetraaminehexaacetic acid are preferable, and diethylenetriaminepentaacetic acid is more preferable, because of their excellent coordinating power to cerium.

Chelating agents having an amino group include, for example, diamines such as ethylenediamine, diaminopropane and diaminobutane and derivatives thereof; polyfunctional amines and derivatives thereof. These amino group-containing chelating agents may be used alone or in combination of two or more.

Chelating agents having a carboxyl group include, for example, monocarboxylic acids such as acetic acid and derivatives thereof; dicarboxylic acids such as oxalic acid, tartaric acid and malic acid and derivatives thereof; tricarboxylic acids such as citric acid and derivatives thereof. mentioned. These chelating agents having a carboxyl group may be used singly or in combination of two or more.

Chelating agents having a phosphonic acid group include, for example, etidronic acid, nitrilotris (methylene phosphonic acid) and derivatives thereof. These chelating agents having a phosphonic acid group may be used singly or in combination of two or more. Among these chelating agents having a phosphosphonic acid group, nitrilotris (methylene phosphonic acid) and derivatives of nitrilotris (methylene phosphonic acid) are preferable because of their excellent coordinating power to cerium. Nitrilotris (methylene phosphonic acid) is more preferred.

The chelating agent having a sulfur atom includes, for example, thiols such as cysteine, methanethiol, ethanethiol, thiophenol and glutathione and their derivatives; thioethers such as methionine and dimethylsulfide and their derivatives and the like. These sulfur atom-containing chelating agents may be used singly or in combination of two or more.

(Component (D))
Since the cleaning liquid of the present invention is excellent in removing fine particles, it preferably contains the following component (D) in addition to the component (A).
Component (D): water

The cleaning solution of the present invention may contain components other than components (A) to (D) within the range that does not impair the effects of the present invention.

Other components include, for example, surfactants and etching inhibitors.

(Physical properties of washing solution)
The pH of the cleaning solution is preferably 1-13, more preferably 2-12. When the pH is 1 or more, the handling of the cleaning liquid is excellent. Moreover, the damage of a semiconductor wafer can be suppressed as pH is 13 or less.

The oxidation-reduction potential of the cleaning liquid is preferably 0 mV to 400 mV, more preferably 50 mV to 400 mV, because it can oxidize trivalent cerium to tetravalent cerium.

(Mass ratio of components)
When the cleaning solution of the present invention contains component (B), the mass ratio of component (A) to component (B) (mass of component (A)/mass of component (B)) is preferably 0.1 to 60. 0.2 to 10 is more preferred. When the mass ratio of component (A) to component (B) is 0.1 or more, the cerium compound is excellent in removability. Moreover, when the mass ratio of the component (A) to the component (B) is 60 or less, the pH of the cleaning liquid can be easily adjusted.

When the cleaning solution of the present invention contains component (C), the mass ratio of component (A) to component (C) (mass of component (A)/mass of component (C)) is preferably from 1 to 200, and from 5 to 150 is more preferred. When the mass ratio of the component (A) to the component (C) is 1 or more, the removability of the cerium compound is excellent. Moreover, when the mass ratio of the component (A) to the component (C) is 200 or less, the removal of the cerium compound is excellent.

When the cleaning liquid of the present invention contains component (B) and component (C), the mass ratio of component (C) to component (B) (mass of component (C)/mass of component (B)) is 0.01. ~5 is preferred, and 0.05 to 1 is more preferred. When the mass ratio of the component (C) to the component (B) is 0.01 or more, the removability of the cerium compound is excellent. Moreover, when the mass ratio of the component (C) to the component (B) is 5 or less, the pH of the cleaning liquid can be easily adjusted.

(Content in cleaning solution)
The content of component (A) is preferably 0.001% by mass to 10% by mass, more preferably 0.005% by mass to 7% by mass, and 0.01% by mass to 5% by mass in 100% by mass of the cleaning liquid. More preferred. When the content of component (A) is 0.001% by mass or more, the removability of the cerium compound is excellent. Further, when the content of component (A) is 10% by mass or less, the stability of the cleaning liquid is excellent, and the manufacturing cost of the cleaning liquid can be suppressed.

When the cleaning solution of the present invention contains component (B), the content of component (B) is preferably 0.001% by mass to 30% by mass, and 0.005% by mass to 20% by mass, based on 100% by mass of the cleaning solution. More preferably, 0.01% by mass to 15% by mass is even more preferable. When the content of component (B) is 0.001% by mass or more, the pH of the cleaning liquid can be easily adjusted. Moreover, pH can be adjusted, without impairing the effect of this invention as the content rate of a component (B) is 10 mass % or less.

When the cleaning solution of the present invention contains component (C), the content of component (C) is preferably 0.0005% by mass to 30% by mass, and 0.001% by mass to 20% by mass, based on 100% by mass of the cleaning solution. More preferably, 0.002% by mass to 15% by mass is even more preferable. When the content of component (C) is 0.0005% by mass or more, the removability of the cerium compound is excellent. Further, when the content of component (C) is 30% by mass or less, component (C) can be dissolved in component (D), and the manufacturing cost of the cleaning liquid can be suppressed.

When the cleaning solution of the present invention contains other components, the content of the other components is preferably 20% by mass or less, more preferably 0% to 10% by mass, and 0% to 5% by mass in 100% by mass of the cleaning solution. % is more preferred. When the content of other components is 20% by mass or less, the effects of the other components can be imparted without impairing the effects of the present invention.

When the cleaning solution of the present invention contains component (D), the content of component (D) can be the balance of components other than component (D) (components (A) to component (C) and other components). preferable.

(Method for producing cleaning solution)
The method for producing the cleaning liquid of the present invention is not particularly limited, and it can be produced by mixing component (A) and, if necessary, components (B) to (D) and other components.
The order of mixing is not particularly limited, and all components may be mixed at once, or some components may be premixed and then the remaining components mixed.

In the method for producing the cleaning solution of the present invention, each component may be blended so that the content is suitable for cleaning. After preparing a cleaning solution containing a high content of each component, the cleaning solution may be prepared by diluting with component (D) before cleaning.
The dilution ratio can be appropriately set according to the object to be washed, but is preferably 30-fold to 150-fold, more preferably 40-fold to 120-fold.

(Washing target)
Objects to be cleaned with the cleaning liquid of the present invention include, for example, semiconductor wafers, glass, metals, ceramics, resins, magnetic substances, superconductors, and the like. Among these objects to be cleaned, those having surfaces with exposed silicon dioxide are preferable, and semiconductor wafers having surfaces with exposed silicon dioxide are more preferable, because the effects of the present invention are remarkably excellent.

Silicon nitride and metal may coexist in addition to silicon dioxide on the surface of the semiconductor wafer having the surface where silicon dioxide is exposed.

(Washing process type)
Since the cleaning liquid of the present invention is excellent in removability of cerium compounds, it can be suitably used for cleaning after chemical mechanical polishing.

A chemical mechanical polishing (CMP) process refers to a process for mechanically processing and planarizing the surface of a semiconductor wafer. Usually, in the CMP process, a special device is used, the back surface of the semiconductor wafer is adsorbed to a jig called a platen, the front surface of the semiconductor wafer is pressed against a polishing pad, and an abrasive containing abrasive particles is dripped onto the polishing pad to remove the semiconductor. Polish the surface of the wafer.

(CMP)
CMP is performed by rubbing an object to be polished against a polishing pad using an abrasive.
The abrasive is not particularly limited as long as it does not require water and can polish the object to be polished. However, fine abrasive particles of a cerium compound are preferred because the effects of the cleaning liquid of the present invention can be fully exhibited.
The abrasive fine particles may coexist with colloidal silica (SiO ₂ ), fumed silica (SiO ₂ ), or alumina (Al ₂ O ₃ ) in addition to the cerium compound abrasive fine particles.

Examples of cerium compounds include cerium oxide and cerium hydroxide. These cerium compounds may be used singly or in combination of two or more. Among these cerium compounds, cerium oxide and cerium hydroxide are preferable, and cerium oxide is more preferable, because they are excellent in polishing rate and scratch resistance.

The abrasive may contain additives such as an oxidizing agent and a dispersing agent in addition to the fine abrasive particles. In particular, in CMP of a semiconductor wafer having a surface where metal is exposed, anticorrosion agents are often included because metal is easily corroded.

When the cleaning solution of the present invention is applied to a semiconductor wafer having a surface on which silicon dioxide is exposed after being polished with an abrasive containing such cerium compound polishing fine particles, the contamination of the semiconductor wafer derived from the cerium compound is greatly reduced. can be effectively removed.

(Washing conditions)
The object to be washed is preferably washed by a method of directly contacting the object to be washed with the cleaning liquid of the present invention.
As a method of bringing the cleaning solution of the present invention into direct contact with an object to be cleaned, for example, a dip method in which a cleaning tank is filled with the cleaning solution of the present invention and the object to be cleaned is immersed; A spin type in which an object is rotated at high speed; and a spray type in which the cleaning liquid of the present invention is sprayed onto an object to be cleaned. Among these methods, the spin method and the spray method are preferable because they can remove contamination more efficiently in a short time.

Devices for performing such cleaning include, for example, a batch-type cleaning device that simultaneously cleans a plurality of cleaning targets contained in a cassette, and a single-wafer cleaning device that cleans a single cleaning target by attaching it to a holder. equipment and the like. Among these apparatuses, the single-wafer cleaning apparatus is preferable because it can shorten the cleaning time and reduce the use of the cleaning liquid of the present invention.

As for the method for cleaning the object to be cleaned, it is preferable to use physical force for cleaning, because it further improves the ability to remove contamination caused by fine particles adhering to the object and shortens the cleaning time. Scrub cleaning using a cleaning brush, frequency 0.5. Ultrasonic cleaning of megahertz or higher is more preferable, and scrub cleaning using a resin brush is even more preferable because it is more suitable for cleaning after CMP.
The material of the resin brush is not particularly limited, but polyvinyl alcohol and polyvinyl formal are preferable because the resin brush itself can be easily manufactured.

The cleaning temperature may be room temperature, or may be increased to 30 to 70° C. within a range that does not impair the performance of the semiconductor wafer.

(Washing method)
The cleaning method of the present invention is a method of cleaning a semiconductor wafer using the cleaning liquid of the present invention, and is as described above.

(Method for manufacturing semiconductor wafer)
The semiconductor wafer manufacturing method of the present invention is a method including the step of cleaning the semiconductor wafer using the cleaning solution of the present invention, as described above.

The present invention will be described in more detail below using examples, but the present invention is not limited to the description of the following examples unless it departs from the gist thereof.

(material)
Component (A-1): hydrogen peroxide (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
Component (B-1): Tetraethylammonium hydroxide (manufactured by Tokyo Chemical Industry Co., Ltd.)
Component (C-1): Diethylenetriaminepentaacetic acid (manufactured by Tokyo Chemical Industry Co., Ltd.)
Component (D-1): water

(pH measurement, oxidation-reduction potential measurement)
While stirring the cleaning solutions obtained in Examples 1 and 2 and Comparative Example 1 using a magnetic stirrer, pH and oxidation-reduction potential were measured using a pH meter (model name “D-74”, manufactured by Horiba, Ltd.). It was measured.

(Cerium oxide residual amount measurement)
A silicon substrate having a silicon dioxide film formed thereon by plasma CVD using tetraethoxysilane (TEOS) was cut into a size of 30 mm×30 mm. Next, using a polishing agent containing cerium oxide (an aqueous dispersion of cerium oxide fine particles having a particle diameter of 200 nm or less) and a polishing pad (trade name “IC1000” manufactured by Nitta Haas Co., Ltd.), the silicon substrate was polished for 1 minute. Chemical mechanical polishing (CMP). Next, the silicon substrate was placed in the cleaning solutions obtained in Examples 1 and 2 and Comparative Example 1 and ultrasonically cleaned for 10 minutes. Next, it was rinsed with water and dried, and the amount (μg/cm ² ) of cerium oxide remaining on the surface of the silicon substrate was measured using a fluorescent X-ray spectrometer (model name “ZSX100e”, manufactured by Rigaku Corporation). .

[Example 1]
Each component is mixed so that the component (A-1) is 0.10% by mass, the component (B-1) is 0.18% by mass, and the component (D-1) is the balance in 100% by mass of the cleaning liquid, A washing solution was obtained.
Table 1 shows the evaluation results of the obtained cleaning solution.

[Example 2, Comparative Example 1]
A washing liquid was obtained in the same manner as in Example 1, except that the types and contents of the raw materials shown in Table 1 were used.
Table 1 shows the evaluation results of the obtained cleaning solution.

As can be seen from Table 1, the cleaning solutions obtained in Examples containing component (A) were able to suppress the amount of residual cerium oxide.
On the other hand, since the cleaning liquid obtained in Comparative Example 1 did not contain the component (A), the residual amount of cerium oxide could not be suppressed.

Since the cleaning liquid of the present invention is excellent in removability of cerium compounds, it can be suitably used for cleaning after chemical mechanical polishing.

Claims (12)

A cleaning solution for removing cerium compounds for cleaning surfaces where silicon dioxide is exposed, containing the following component (A).
Component (A): Oxidizing agent 2. The cleaning solution for removing cerium compounds according to claim 1, wherein component (A) contains at least one selected from the group consisting of hydrogen peroxide, nitric acid and nitrates. The cleaning solution for removing cerium compounds according to claim 1 or 2, further comprising the following component (B).
Component (B): pH adjuster 4. The cleaning solution for removing cerium compounds according to claim 3, wherein component (B) contains at least one selected from the group consisting of quaternary ammonium hydroxides and alkanolamine compounds. The cleaning solution for removing cerium compounds according to any one of claims 1 to 4, further comprising the following component (C).
Component (C): chelating agent The cleaning solution for removing cerium compounds according to any one of claims 1 to 5, further comprising the following component (D).
Component (D): water The cleaning solution for removing cerium compounds according to any one of claims 1 to 6, which has a pH of 2 to 12. The cleaning solution for removing cerium compounds according to any one of claims 1 to 7, which is used for cleaning after chemical mechanical polishing. A cleaning method comprising removing a cerium compound using the cleaning liquid according to any one of claims 1 to 8 . 10. The cleaning method according to claim 9 , which removes cerium compounds on semiconductor wafers. A method for manufacturing a semiconductor wafer, comprising a step of removing a cerium compound using the cleaning liquid according to any one of claims 1 to 8 . 12. The method of manufacturing a semiconductor wafer according to claim 11 , further comprising the step of performing chemical mechanical polishing using a polishing agent containing a cerium compound.