JP5830931B2 - Wafer cleaning method - Google Patents

Description

  The present invention relates to a cleaning method that is effective in preventing collapse of a concavo-convex pattern when cleaning a wafer surface on which a concavo-convex pattern is formed.

  In the manufacture of semiconductor chips, first, a fine concavo-convex pattern is formed on the wafer surface through film formation, lithography, etching, and the like, and then cleaning is performed using a cleaning liquid to clean the wafer surface. .

  In recent years, semiconductor elements are in the direction of miniaturization, and the intervals between the concave and convex patterns are becoming increasingly narrow. For this reason, when cleaning is performed using a cleaning liquid and the cleaning liquid is dried from the wafer surface, a problem that the concavo-convex pattern collapses due to a capillary phenomenon tends to occur. This problem has become more prominent particularly in semiconductor chips having a narrower pattern spacing, for example, a recess having a width of 20 nm or 10 nm.

  Patent Document 1 discloses a technique for replacing a cleaning liquid from water to 2-propanol before passing through a gas-liquid interface as a technique for suppressing pattern collapse. However, it is said that there is a limit such that the aspect ratio of the pattern that can be handled is 5 or less.

  Further, Patent Document 2 discloses that a wafer surface having a concavo-convex pattern formed by a film containing silicon is surface-modified by oxidation or the like, and a water-repellent protective film is formed on the surface using a water-soluble surfactant or silane coupling agent. A cleaning method is disclosed that reduces the capillary force and prevents the pattern from collapsing.

JP 2003-45843 A Japanese Patent No. 4403202

  At the time of manufacturing a semiconductor chip, the wafer surface is a surface having an uneven pattern. Reduces the capillary force of the concavo-convex pattern portion of the wafer when cleaning a wafer having a concavo-convex pattern on the surface and at least a part of the concavo-convex pattern containing silicon element (hereinafter, sometimes simply referred to as “wafer”). The water-repellent protective film (hereinafter also simply referred to as “protective film”) is formed by the reaction of a silicon compound such as a silane coupling agent with a hydroxyl group (OH group) or the like introduced on the wafer surface. .

  Thus, in order to form a protective film on a concavo-convex pattern containing a silicon element, a reactive site such as a hydroxyl group is formed on the surface of the concavo-convex pattern, and the compound that forms the protective film reacts with the reactive site. There is a need. In the concavo-convex pattern containing silicon element, the unit varies depending on the ease of formation of hydroxyl groups, etc., depending on the type of material constituting the concavo-convex pattern, and the conditions of surface treatment with water, etc. performed when forming hydroxyl groups, etc. Differences may occur in the amount of hydroxyl groups per area.

  The present invention relates to a method for cleaning a wafer that is effective in preventing collapse of a concavo-convex pattern, as well as a wafer in which hydroxyl groups and the like are easily introduced into the surface of the concavo-convex pattern, and a wafer in which hydroxyl groups and the like are not easily introduced into the surface of the concavo-convex pattern. Even so, it is an object to provide a cleaning method capable of cleaning a wafer economically and efficiently.

  Pattern collapse occurs when the gas-liquid interface passes through the pattern when the wafer is dried. This is said to be caused by a difference in residual liquid height between a portion where the aspect ratio of the pattern is high and a portion where the aspect ratio is low, thereby causing a difference in capillary force acting on the pattern. Note that the expression “falling” is sometimes referred to as “collapse”.

For this reason, if the capillary force is reduced, it can be expected that the difference in capillary force due to the difference in the residual liquid height will be reduced and the pattern collapse will be eliminated. The magnitude of the capillary force is the absolute value of P obtained by the following formula. From this formula, it is expected that the capillary force can be reduced by reducing γ or cos θ.
P = 2 × γ × cos θ / S
(Wherein γ is the surface tension of the liquid held in the recess, θ is the contact angle between the recess surface and the liquid held in the recess, and S is the width of the recess.)

  In the present invention, as a result of repeated studies on an economical and efficient method for cleaning a wafer on which a concavo-convex pattern containing silicon element is formed, the idea of examining a method that easily forms an appropriate amount of hydroxyl groups on the concavo-convex pattern surface. It came to. This is because, if a method capable of easily forming an appropriate amount of hydroxyl group or the like on the concavo-convex pattern surface can be provided, the compound species forming the water-repellent protective film can be easily bonded to the concavo-convex pattern surface, and the water-repellent protective film can be stabilized. This is because it is easy to obtain.

The present invention has been made by intensive studies based on the above idea. That is, the method for cleaning a wafer according to the present invention includes:
A pretreatment step having a concavo-convex pattern on the surface, and modifying the surface of the concavo-convex pattern by supplying a chemical solution for pretreatment to the surface of the wafer in which at least part of the concavo-convex pattern contains silicon element
A wafer cleaning method including at least a protective film forming step of forming a water-repellent protective film on the surface of the concavo-convex pattern by supplying a chemical solution for forming a protective film to the surface of the modified concavo-convex pattern,
In the pretreatment step, an uneven pattern is formed at a temperature of 40 ° C. or higher and lower than the boiling point of the pretreatment chemical solution using a pretreatment chemical solution containing 0.001 to 5 mol / L of acid in molar concentration and pH of 3 or less. It is characterized by modifying the surface.

  In the wafer cleaning method of the present invention, a reactive site such as a hydroxyl group is formed on the surface of the concavo-convex pattern by the acid in the pretreatment chemical that is a liquid containing an acid and a solvent for dissolving the acid. Can do. The chemical solution for forming a protective film used when forming a water-repellent protective film on the surface of the concavo-convex pattern includes a compound for forming the protective film such as a silane coupling agent and a solvent for dissolving the compound. When a large number of reactive sites such as hydroxyl groups are present on the surface of the concavo-convex pattern by the pretreatment, the compound that forms the protective film contained in the protective film forming chemical solution and the reactive sites easily react. As a result, a water-repellent protective film can be stably formed on the surface of the uneven pattern.

  In the wafer cleaning method of the present invention, the molar concentration of acid in the pretreatment chemical solution (hereinafter also referred to as “acid concentration”) is 0.001 to 5 mol / L. When the molar concentration of the acid in the pretreatment chemical solution is less than 0.001 mol / L, the effect of modifying the surface of the uneven pattern, that is, the effect of forming reactive sites such as hydroxyl groups on the surface of the uneven pattern is sufficient. It is not obtained. In addition, when the molar concentration of the acid in the pretreatment chemical solution is more than 5 mol / L, the acid concentration becomes too high. Therefore, before the pretreatment step, the metal impurities and the like are ion-exchanged from the pretreatment chemical solution in advance. This makes it difficult to remove and purify.

  In the wafer cleaning method of the present invention, the pH of the pretreatment chemical is 3 or less. If the pH of the pretreatment chemical solution is more than 3, the acidity of the pretreatment chemical solution is weakened, so that the effect of modifying the surface of the concavo-convex pattern, that is, the formation of reactive sites such as hydroxyl groups on the surface of the concavo-convex pattern The effect is weakened.

  When the temperature of the pretreatment chemical is increased, the surface of the concavo-convex pattern is easily modified in a shorter time. On the other hand, if the surface of the concavo-convex pattern is modified at a temperature equal to or higher than the boiling point of the pretreatment chemical, the pattern collapses because the gas-liquid interface is close to passing through the pattern due to rapid evaporation of the pretreatment chemical. Adverse effects such as As described above, in the wafer cleaning method of the present invention, the surface of the concavo-convex pattern is modified at a temperature of 40 ° C. or higher and lower than the boiling point of the pretreatment chemical. Since excellent water repellency can be imparted to the concave surface, the surface modification of the wafer by the pretreatment chemical is preferably performed at a temperature of 65 ° C. or higher and lower than the boiling point of the pretreatment chemical.

  In the wafer cleaning method of the present invention, it is preferable that the liquid is maintained at least on the concave surface of the concave / convex pattern until a protective film is formed on the surface of the concave / convex pattern.

  In the wafer cleaning method of the present invention, the acid contained in the pretreatment chemical is preferably an organic acid. The organic acid is mainly composed of a carbon element, a hydrogen element, and an oxygen element, and is preferable because it does not contain an element that is hated in a semiconductor manufacturing process. In addition, an organic acid is preferable because it has characteristics such that it is easily dissolved in an organic solvent and hardly reacts with a metal as compared with an inorganic acid.

  In the wafer cleaning method of the present invention, it is preferable that at least a part of the uneven pattern is formed of silicon nitride and / or silicon. When the concavo-convex pattern is formed from silicon nitride or silicon, if the surface of the concavo-convex pattern is not modified, the surface of the concavo-convex pattern has few reactive sites such as hydroxyl groups. Therefore, even if the protective film forming chemical is supplied to the concavo-convex pattern formed from silicon nitride or silicon, it is difficult to form a water-repellent protective film on the surface of the concavo-convex pattern. However, by modifying the surface of the concavo-convex pattern with a pretreatment chemical containing acid, even if the concavo-convex pattern is formed from silicon nitride or silicon, a protective film having sufficient water repellency is formed. Can be formed on the surface.

  In the wafer cleaning method of the present invention, the protective film formed on the surface of the uneven pattern in the cleaning process can stably exhibit water repellency. Therefore, the wafer can be stably cleaned while preventing the concave / convex pattern from falling.

  In addition, when industrially cleaning a wafer, the wafer type may be different for each production lot. In this case, it is necessary to apply cleaning conditions according to the production lot, that is, conditions for forming an appropriate amount of hydroxyl groups on the surface of the concavo-convex pattern and forming a water-repellent protective film. However, by applying the present invention, it is possible to reduce changes in cleaning conditions for each wafer type.

It is a figure which shows a schematic diagram when the wafer 1 by which the surface was made into the surface which has the uneven | corrugated pattern 2 is seen. FIG. 2 shows a part of the a-a ′ cross section in FIG. 1. The recessed part 4 has shown the schematic diagram of the state holding the chemical | medical solution 8 for protective film formation. It is a figure which shows the schematic diagram of the state by which the liquid was hold | maintained at the recessed part 4 in which the water-repellent protective film was formed.

A preferred method for cleaning a wafer according to an embodiment of the present invention is as follows:
(Step 1) The surface has a concavo-convex pattern, and at least a part of the concavo-convex pattern provides a liquid to the surface of the wafer containing silicon element (hereinafter also referred to as “surface of the concavo-convex pattern”), and at least the concave portion of the concavo-convex pattern Holding the liquid on the surface;
(Step 2) A step of replacing the liquid with a chemical solution for forming a protective film and holding the chemical solution on at least the concave surface of the concavo-convex pattern;
(Step 3) A step of removing liquid from the surface of the concavo-convex pattern, and
(Step 4) Step of removing the protective film,
Have

  As the liquid in (Step 1), at least a pretreatment chemical solution is used. In addition to the pretreatment chemical liquid, at least one of an aqueous cleaning liquid composed of an aqueous solution and a cleaning liquid A different from the pretreatment chemical liquid and the aqueous cleaning liquid may be used. When a plurality of liquids are used, the pretreatment chemical solution may be used in combination with at least one of the aqueous cleaning solution and the cleaning solution A, or a mixed solution containing the pretreatment chemical solution and at least one of the aqueous cleaning solution and the cleaning solution A. May be used. In (Step 1), for example, only the pretreatment chemical solution may be used for cleaning the wafer surface and modifying the uneven pattern surface. Further, after holding the aqueous cleaning liquid on at least the concave surface of the concavo-convex pattern, the aqueous cleaning liquid may be replaced with the cleaning liquid A, and the cleaning liquid A may be further replaced with the pretreatment chemical. When the pretreatment chemical solution can be replaced with an aqueous cleaning solution, the aqueous cleaning solution may be replaced with the preprocessing chemical solution after the aqueous cleaning solution is held on at least the concave surface of the concavo-convex pattern.

  Further, after (Step 2), the protective film forming chemical liquid held on at least the concave surface of the concavo-convex pattern is replaced with a cleaning liquid B different from the protective film forming chemical liquid, and then the process proceeds to (Step 3). Good. In addition, after the replacement with the cleaning liquid B, an aqueous cleaning liquid composed of an aqueous solution is held on at least the concave surface of the concave / convex pattern, and then the process may proceed to (Step 3). In addition, when the protective film forming chemical can be replaced with an aqueous cleaning liquid, the replacement with the cleaning liquid B may be omitted.

  In the present invention, the form of the chemical liquid or cleaning liquid when the chemical liquid (pretreatment chemical liquid or protective film forming chemical liquid) or cleaning liquid is supplied to at least the concave surface of the concavo-convex pattern of the wafer is held on the concave surface. There is no particular limitation as long as it sometimes becomes liquid, and examples thereof include liquid and vapor. As will be described later, in the pretreatment step, the surface of the concavo-convex pattern is modified at a temperature lower than the boiling point using a pretreatment chemical solution. Therefore, in the pretreatment step, the form of the chemical liquid when supplying the chemical liquid for pretreatment to at least the concave surface of the concave / convex pattern of the wafer is a liquid.

  In the present invention, the cleaning method of the wafer is not particularly limited as long as the chemical liquid (pretreatment chemical liquid or protective film forming chemical liquid) or cleaning liquid can be held on at least the concave surface of the concave / convex pattern of the wafer. As a wafer cleaning method, a wafer cleaning method represented by spin cleaning in which a wafer is cleaned one by one by supplying liquid to the vicinity of the rotation center while rotating the wafer while holding the wafer substantially horizontal, or a plurality of cleaning methods in the cleaning tank. One example is a batch system in which a single wafer is immersed and washed.

  When cleaning wafers industrially, the wafer type may be the same for each production lot, or the wafer type may be different for each production lot, but the present invention can be applied to either case. it can.

  The uneven pattern formed on the wafer surface is defined as shown in FIGS. FIG. 1 is a schematic view of a wafer 1 whose surface has a concavo-convex pattern 2 as viewed from the perspective, and FIG. 2 shows a part of the a-a ′ cross section in FIG. 1. As shown in FIG. 2, the width 5 of the concave portion is indicated by the interval between the convex portion 3 and the convex portion 3, and is also referred to as “line width” or “space dimension”. The aspect ratio of the convex portion is expressed by dividing the height 6 of the convex portion by the width 7 of the convex portion. When the water-repellent protective film is not formed on the concave surface of the wafer, the pattern collapse in the cleaning process occurs when the concave width is 70 nm or less, particularly 45 nm or less, and the aspect ratio is 4 or more, particularly 6 or more. It tends to occur.

  An example of a method for forming an uneven pattern on the wafer surface is shown below. First, after applying a resist to the wafer surface, the resist is exposed through a resist mask, and the exposed resist or the resist that has not been exposed is removed by etching to produce a resist having a desired concavo-convex pattern. Moreover, the resist which has an uneven | corrugated pattern can be obtained also by pressing the mold which has a pattern to a resist. Next, the wafer is etched. At this time, the concave portion of the resist pattern is selectively etched. Finally, when the resist is removed, a wafer having a concavo-convex pattern on the surface is obtained.

  As the wafer having a concavo-convex pattern on the surface and at least a part of the concavo-convex pattern containing silicon element, silicon or a film containing a silicon element such as silicon oxide or silicon nitride is formed on the wafer surface, or When the concavo-convex pattern is formed, those in which at least a part of the surface of the concavo-convex pattern contains silicon, or silicon element such as silicon oxide or silicon nitride are included. Silicon includes polysilicon and amorphous silicon. In addition, a wafer composed of a plurality of components containing a silicon element, a silicon carbide wafer, and a wafer in which various films containing a silicon element are formed on the wafer can be used as the wafer. Further, various films containing silicon elements may be formed on a wafer not containing silicon elements such as sapphire wafers, various compound semiconductor wafers, and plastic wafers.

  Further, the wafer having a concavo-convex pattern on the surface and at least a part of the concavo-convex pattern containing silicon element is a wafer composed of a plurality of components including at least one selected from silicon, silicon oxide, and silicon nitride. It may be. As the wafer composed of the plurality of components, at least one selected from silicon, silicon oxide, and silicon nitride is formed on the wafer surface, or when a concavo-convex pattern is formed, at least one of the concavo-convex pattern is formed. A part whose part is at least one selected from silicon, silicon oxide, and silicon nitride is also included.

  Hereinafter, each step will be described. First, a step (Step 1) is performed in which a liquid is provided on the surface of the wafer having the concavo-convex pattern (the surface of the concavo-convex pattern), and the liquid is held at least on the surface of the concave / convex pattern.

  Here, a case where a pretreatment chemical is used as the liquid will be described. In this case, in (Step 1), a step of modifying the surface of the concavo-convex pattern by supplying a pretreatment chemical to the surface of the concavo-convex pattern (hereinafter referred to as “pretreatment step”) is performed. In the pretreatment step, the concavo-convex pattern is formed at a temperature of 40 ° C. or higher and less than the boiling point of the pretreatment chemical solution using a pretreatment chemical solution containing 0.001 to 5 mol / L of acid in molar concentration and pH of 3 or less. Modify the surface.

  When a pretreatment chemical is supplied to the surface of the concavo-convex pattern, a reactive site such as a hydroxyl group is formed on the surface of the concavo-convex pattern by the acid in the pretreatment chemical. If there are many reactive sites such as hydroxyl groups on the surface of the concavo-convex pattern, in the later-described (Step 2), the compound that forms the protective film contained in the protective film-forming chemical solution and the reactive sites easily react. As a result, a water-repellent protective film is easily formed on the surface of the uneven pattern.

  Supplying the pretreatment chemical to the surface of the concavo-convex pattern is particularly suitable when at least a part of the concavo-convex pattern is formed of silicon nitride and / or silicon. When the concavo-convex pattern is formed from silicon nitride or silicon, if the surface of the concavo-convex pattern is not modified by the pretreatment chemical solution, the surface of the concavo-convex pattern has few reactive sites such as hydroxyl groups. Therefore, even if the protective film forming chemical is supplied to the concavo-convex pattern formed from silicon nitride or silicon, it is difficult to form a water-repellent protective film on the surface of the concavo-convex pattern. However, by modifying the surface of the concavo-convex pattern with a pretreatment chemical containing acid, even if the concavo-convex pattern is formed from silicon nitride or silicon, a protective film having sufficient water repellency is formed. Can be formed on the surface.

  The concavo-convex pattern formed from silicon nitride or silicon can be formed, for example, by forming a silicon nitride or silicon film on the wafer surface and then etching the silicon nitride or silicon film. Further, the concavo-convex pattern formed from silicon nitride or silicon can also be formed by forming a concavo-convex pattern on the wafer surface and then forming a silicon nitride or silicon film on the concavo-convex pattern.

  In the pretreatment step, the surface of the concavo-convex pattern is modified at a temperature of 40 ° C. or higher and less than the boiling point of the pretreatment chemical solution. As a method for adjusting the temperature for modifying the surface of the concavo-convex pattern, Examples thereof include a method for heating and a method for heating a wafer.

  Examples of the acid contained in the pretreatment chemical solution include organic acids and inorganic acids. Examples of inorganic acids include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid and the like. Examples of organic acids include aliphatic monocarboxylic acids such as acetic acid and propionic acid, aliphatic polycarboxylic acids such as maleic acid and fumaric acid, aromatic monocarboxylic acids such as benzoic acid, aromatics such as phthalic acid and terephthalic acid. Organic sulfonic acids such as aromatic polycarboxylic acid, methanesulfonic acid and benzenesulfonic acid.

  In order to achieve the effect of modifying the surface of the concavo-convex pattern (the effect of forming a reactive site such as a hydroxyl group on the surface of the concavo-convex pattern), the molar concentration of the acid in the pretreatment chemical solution is 0.001 to 5 mol / L. It is necessary to be 0.005 to 2 mol / L.

  In order to achieve the effect of modifying the surface of the concavo-convex pattern (effect of forming a reactive site such as a hydroxyl group on the surface of the concavo-convex pattern), the pH of the pretreatment chemical solution is 3 or less. The pH of the pretreatment chemical solution is preferably 0.1 or more. If the pH of the pretreatment chemical solution is less than 0.1, it becomes difficult to purify the pretreatment chemical solution in advance by the ion exchange method before performing the pretreatment step, which may increase the purification cost.

The pH of the pretreatment chemical solution is obtained from the following equation using the proton concentration in the pretreatment chemical solution.
pH = −Log ₁₀ [H ⁺ ]
In the formula, Log ₁₀ is a logarithm with 10 as the base, [H ⁺ ] represents the proton concentration in the pretreatment chemical solution at 25 ° C., and the unit of the proton concentration is mol / L. The pretreatment chemical solution is not limited to an aqueous solution, and even when only an organic solvent is used as a solvent for the pretreatment chemical solution or when water and an organic solvent are used in combination, the above formula Is the pH of the pretreatment chemical solution. In particular, in the present specification, when the solvent of the pretreatment chemical solution is only water, or when water and an organic solvent are mixed, the pH of the pretreatment chemical solution is for pretreatment at 25 ° C. The value obtained by measuring the chemical solution with a pH meter is used.

  The pretreatment chemical solution is preferably a liquid containing an acid and a solvent for dissolving the acid. Examples of the solvent include water and organic solvents. The type of organic solvent is not particularly limited, but hydrocarbons, esters, ethers, ketones, halogen-containing solvents, sulfoxide solvents, alcohols, polyhydric alcohols, polyhydric alcohol derivatives, nitrogen-containing compound solvents, etc. Is mentioned. Moreover, solvents, such as water and an organic solvent, may be used independently and may use 2 or more types together. For example, water and an organic solvent may be used in combination, or a plurality of organic solvents may be used in combination.

  Examples of the hydrocarbons include toluene, benzene, xylene, hexane, heptane, and octane. Examples of the esters include ethyl acetate, propyl acetate, butyl acetate, and ethyl acetoacetate, and the ether. Examples of such classes include diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, dioxane and the like, and examples of the ketones include acetone, acetylacetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, cyclohexanone, isophorone, and the like. Examples of the halogen-containing solvent include perfluorocarbons such as perfluorooctane, perfluorononane, perfluorocyclopentane, perfluorocyclohexane, hexafluorobenzene, 1,1,1, , 3-pentafluorobutane, octafluorocyclopentane, 2,3-dihydrodecafluoropentane, hydrofluorocarbons such as Zeolora H (manufactured by Nippon Zeon), methyl perfluoroisobutyl ether, methyl perfluorobutyl ether, ethyl perfluorobutyl ether, Hydrofluoroethers such as ethyl perfluoroisobutyl ether, Asahiklin AE-3000 (manufactured by Asahi Glass), Novec HFE-7100, Novec HFE-7200, Novec 7300, and Novec 7600 (all from 3M), chlorocarbons such as tetrachloromethane, chloroform Hydrochlorocarbons such as chlorofluorocarbons such as dichlorodifluoromethane, 1,1-dichloro-2,2,3,3,3-pe Tafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, 1,2-dichloro-3,3,3- There are hydrochlorofluorocarbons such as trifluoropropene, perfluoroethers, perfluoropolyethers, etc. Examples of the sulfoxide solvents include dimethyl sulfoxide, and examples of alcohols include methanol, ethanol, propanol, butanol. Examples of polyhydric alcohols include ethylene glycol and 1,3-propanediol, and examples of the polyhydric alcohol derivatives include diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol mono Butyl A , Propylene glycol monomethyl ether, propylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl There are ether, diethylene glycol diethyl ether, diethylene glycol diacetate, triethylene glycol dimethyl ether, ethylene glycol diacetate, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, etc. Examples include formamide, N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone, diethylamine, triethylamine, and pyridine.

  Considering the modification effect by the pretreatment chemical, the temperature of the pretreatment step is preferably higher. Therefore, it is preferable that the solvent has a high boiling point. When a mixed solvent of water and an organic solvent is used as the solvent for the pretreatment chemical solution, or when an organic solvent is used, the organic solvent should have a boiling point exceeding 100 ° C. Is preferred. Considering these, it is preferable to use a polyhydric alcohol or a derivative of a polyhydric alcohol as a solvent.

In the pretreatment chemical solution, it is preferable that bubbles do not occur at a temperature lower than the boiling point of the pretreatment chemical solution. When bubbles are generated in the pretreatment chemical solution, there arises a problem that it becomes difficult to handle the pretreatment chemical solution. Considering these, it is preferable that the pretreatment chemical solution does not contain an oxidizing agent such as ozone (O ₃ ) or hydrogen peroxide (H ₂ O ₂ ) as a solvent. This is because, when the pretreatment chemical liquid contains an oxidizing agent, the oxidizing agent is decomposed and oxygen is generated when the temperature of the pretreatment chemical liquid becomes high.

  Considering the above, it is preferable that the solvent of the pretreatment chemical solution does not contain an oxidant and consists of only water, only an organic solvent, or only water and an organic solvent. Moreover, when the solvent of the chemical solution for pretreatment consists only of water and an organic solvent, ratio (water / organic solvent) of water and an organic solvent is a mass ratio, and water / organic solvent = 10 / 90-90 / 10. It is preferable that it is, and it is more preferable that it is 20 / 80-60 / 40.

  In the method for preparing the pretreatment chemical solution, it is preferable to purify at least one of the acid and its solution.

  The purification includes adjustment of moisture concentration by adsorbent such as molecular sieve or distillation, removal of metal impurities of each element of Na, Mg, K, Ca, Mn, Fe and Cu by ion exchange resin or distillation, and This is performed using at least one removing means among removing contaminants such as particles by filter filtration. In consideration of the activity of the pretreatment chemical and the cleanliness of the wafer, it is preferable to adjust the water concentration, remove the metal impurities, and remove the contaminants, and the order of removal is not limited.

  As described above, in (Step 1), the aqueous cleaning liquid is provided on the surface of the concave / convex pattern, the aqueous cleaning liquid is retained on at least the concave surface of the concave / convex pattern, and then the aqueous cleaning liquid is replaced with the cleaning liquid A. You may substitute with the chemical | medical solution for a process. When the pretreatment chemical solution can be replaced with an aqueous cleaning solution, the aqueous cleaning solution may be replaced with the preprocessing chemical solution after the aqueous cleaning solution is held on at least the concave surface of the concavo-convex pattern.

  When replacing the aqueous cleaning liquid or the cleaning liquid A with the pretreatment chemical liquid, it is preferable to replace the cleaning liquid with the preprocessing chemical liquid in a state where the aqueous cleaning liquid or the cleaning liquid A is held on at least the concave surface of the concavo-convex pattern. .

  In addition, after (Step 1) and before (Step 2), a cleaning solution different from the pretreatment chemical solution may be provided on the surface of the concavo-convex pattern. Examples of the cleaning liquid different from the pretreatment chemical liquid include an aqueous cleaning liquid and a cleaning liquid A. In this case, until the protective film is formed on the surface of the concavo-convex pattern, it is preferable that the liquid is maintained in at least the surface of the concavo-convex pattern.

  Examples of the aqueous cleaning liquid include water or water mainly containing water mixed with at least one organic solvent, acid or alkali in water (for example, the water content is 50% by mass or more). It is done. Of these, water is preferred.

  As a preferred example of the cleaning liquid A, a protective film forming chemical solution, water, an organic solvent, or a mixture thereof described later, or at least one of an acid, an alkali, a surfactant, and an oxidizing agent is mixed therein. And the like.

  Examples of the organic solvent which is one of the preferred examples of the cleaning liquid A include hydrocarbons, esters, ethers, ketones, halogen-containing solvents, sulfoxide solvents, alcohols, polyhydric alcohol derivatives, And nitrogen-containing compound solvents.

  Examples of the hydrocarbons include toluene, benzene, xylene, hexane, heptane, and octane. Examples of the esters include ethyl acetate, propyl acetate, butyl acetate, and ethyl acetoacetate, and the ether. Examples of such classes include diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, dioxane and the like, and examples of the ketones include acetone, acetylacetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, cyclohexanone, isophorone, and the like. Examples of the halogen-containing solvent include perfluorocarbons such as perfluorooctane, perfluorononane, perfluorocyclopentane, perfluorocyclohexane, hexafluorobenzene, 1,1,1, , 3-pentafluorobutane, octafluorocyclopentane, 2,3-dihydrodecafluoropentane, hydrofluorocarbons such as Zeolora H (manufactured by Nippon Zeon), methyl perfluoroisobutyl ether, methyl perfluorobutyl ether, ethyl perfluorobutyl ether, Hydrofluoroethers such as ethyl perfluoroisobutyl ether, Asahiklin AE-3000 (manufactured by Asahi Glass), Novec HFE-7100, Novec HFE-7200, Novec 7300, and Novec 7600 (all from 3M), chlorocarbons such as tetrachloromethane, chloroform Hydrochlorocarbons such as chlorofluorocarbons such as dichlorodifluoromethane, 1,1-dichloro-2,2,3,3,3-pe Tafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, 1,2-dichloro-3,3,3- There are hydrochlorofluorocarbons such as trifluoropropene, perfluoroethers, perfluoropolyethers, etc. Examples of the sulfoxide solvents include dimethyl sulfoxide, and examples of alcohols include methanol, ethanol, propanol, butanol. Ethylene glycol, 1,3-propanediol, etc. Examples of the derivative of the polyhydric alcohol include diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether. , Propylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether , Diethylene glycol diacetate, triethylene glycol dimethyl ether, ethylene glycol diacetate, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, etc. Examples of nitrogen-containing compound solvents include formamide, N, N-dimethylformamide And N, N-dimethylacetamide, N-methyl-2-pyrrolidone, diethylamine, triethylamine, pyridine and the like.

  Examples of acids that can be mixed with the cleaning liquid A include inorganic acids and organic acids. Examples of inorganic acids include hydrofluoric acid, buffered hydrofluoric acid, sulfuric acid, nitric acid, hydrochloric acid, phosphoric acid, etc. Examples of organic acids include methanesulfonic acid, benzenesulfonic acid, p-toluenesulfonic acid, trifluoromethanesulfonic acid , Acetic acid, trifluoroacetic acid, pentafluoropropionic acid and the like. Examples of the alkali that may be mixed in the cleaning liquid A include ammonia and choline. Examples of the oxidizing agent that may be mixed with the cleaning liquid A include ozone and hydrogen peroxide.

  In addition, it is preferable that the cleaning liquid A is an organic solvent because the chemical liquid for forming a protective film can be provided to the recess without being brought into contact with water. In addition, it is preferable that the cleaning liquid A contains an acid aqueous solution because a protective film can be formed in a short time in (Step 2) described later.

  A plurality of cleaning liquids may be used as the cleaning liquid A. For example, two types of cleaning liquid containing the acid aqueous solution and the organic solvent cleaning liquid can be used.

  Next, a step of replacing the liquid with a protective film-forming chemical solution and holding the chemical solution on at least the concave surface of the concave-convex pattern (step 2) is performed. Specifically, a process of forming a water-repellent protective film on the surface of the concavo-convex pattern by supplying a chemical solution for forming a protective film onto the surface of the modified concavo-convex pattern (hereinafter referred to as “protective film formation process”) To do).

  In this specification, the protective film refers to a film that is formed on the wafer surface to lower the wettability of the wafer surface, that is, a film that imparts water repellency. Also, water repellency is a property that reduces the surface energy of the protective film and reduces interactions (for example, hydrogen bonds, intermolecular forces) between water and other liquids and the surface of the protective film (interface). Means. The protective film is particularly effective in reducing the interaction with water, but also has an effect of reducing the interaction with a liquid mixture other than water and water or a liquid other than water. By reducing the interaction, the contact angle of the liquid with respect to the surface of the protective film can be increased.

  In the protective film forming step, the protective film is formed by reacting a compound that forms the protective film contained in the chemical liquid for forming the protective film with a reactive site such as a hydroxyl group formed on the surface of the concavo-convex pattern. The compound to be formed is formed by chemically bonding with the Si element of the wafer. In the protective film forming step, since a water-repellent protective film is formed on the concave surface of the wafer, when the liquid is removed from the concave portion of the wafer in (Step 3) described later, that is, when the wafer is dried, The capillary force on the surface of the recess is reduced, and pattern collapse is less likely to occur.

  In the protective film forming step, the liquid held in the concave portion before the step (step 2) is replaced with a protective film forming chemical solution, and the protective film forming chemical solution is held on at least the concave surface of the concave / convex pattern. In the meantime, the protective film is formed on at least the concave surface of the concave / convex pattern. In the protective film forming step, the protective film does not necessarily have to be formed continuously, and does not necessarily have to be formed uniformly, but because it can impart better water repellency, continuously, Further, it is more preferably formed uniformly.

  FIG. 3 is a schematic view showing a state in which the recess 4 holds the protective film forming chemical 8 in the cleaning process. The wafer in the schematic diagram of FIG. 3 shows a part of the a-a ′ cross section of FIG. 1. In the protective film forming step, the protective film forming chemical is supplied to the wafer 1 on which the concave / convex pattern 2 is formed. At this time, as shown in FIG. 3, the chemical solution for forming the protective film is held in the concave portion 4, and the protective film is formed on the surface of the concave portion 4 to make the surface water repellent.

  When the temperature of the protective film-forming chemical is increased, it becomes easier to form a water-repellent protective film in a shorter time. The temperature at which a homogeneous protective film is easily formed is preferably 10 ° C. to less than the boiling point of the protective film forming chemical solution, and is preferably maintained at a temperature that is 15 ° C. to 10 ° C. lower than the boiling point of the protective film forming chemical solution. It is preferable that the temperature of the protective film-forming chemical is maintained at the temperature even when the temperature is held on at least the concave surface of the concave-convex pattern.

  Other cleaning liquids may also be held at a temperature of 10 ° C. or higher and lower than the boiling point of the cleaning liquid. For example, when the cleaning liquid A contains an acid aqueous solution, particularly preferably a solution containing an acid aqueous solution and an organic solvent having a boiling point of 100 ° C. or higher, the protective film can be shortened for a short time if the temperature of the cleaning liquid is raised near the boiling point of the cleaning liquid It is preferable because it is easy to form.

  As long as a water-repellent protective film can be formed on the surface of the concavo-convex pattern, the type of compound (hereinafter also referred to as “compound A”) that forms the protective film included in the protective film-forming chemical solution is particularly It is not limited. Examples of compound A include hexamethyldisilazane (HMDS), trimethylsilyldiethylamine (TMSDEA), tetramethyldisilazane, trimethylsilyldimethylamine, octyldimethylsilyldimethylamine, trimethylsilylimidazole, trimethylchlorosilane, propyldimethylchlorosilane, octyldimethylchlorosilane, Examples include silane coupling agents such as dimethyldichlorosilane, methyltrichlorosilane, trimethylmethoxysilane, and trimethylethoxysilane.

  The protective film forming chemical may contain acid A as a catalyst. The acid A in the protective film forming chemical is effective in promoting the reaction between the compound A and the Si element of the wafer. When the acid A contains water, it leads to an increase in the water contained in the protective film-forming chemical solution, making it difficult to form the protective film. Therefore, the acid A is preferably as the water content is low, and the preferable water content is 35% by mass or less, particularly preferably 10% by mass or less, and more preferably 5% by mass or less. Ideally, it is close to 0% by mass.

  In the chemical solution for forming a protective film, the concentration of acid A is preferably 0.01 to 20% by mass with respect to 100% by mass of the total amount of compound A. If the addition amount is small, the catalytic effect of the acid is lowered, which is not preferable. Even if it is excessively added, the catalytic effect is not improved. On the contrary, there is a concern that the wafer surface may be eroded or remain as impurities on the wafer. For this reason, the concentration of the acid A is particularly preferably 0.05 to 10% by mass with respect to 100% by mass of the total amount of the compound A.

  Examples of the acid A include inorganic acids and organic acids. Examples of inorganic acids with a low water content include hydrogen halides, sulfuric acid, perchloric acid, phosphoric acid, etc., and examples of organic acids include some or all of the hydrogen elements substituted with fluorine elements, etc. There may be alkanesulfonic acid, carboxylic acid, benzenesulfonic acid, p-toluenesulfonic acid, etc.

  As the acid A, a Lewis acid can also be used. The definition of Lewis acid is described in, for example, “Physical and Chemical Dictionary (Fifth Edition)”. Examples of Lewis acids include acid anhydrides, boron compounds, and silicon compounds. Examples of acid anhydrides include alkanesulfonic anhydrides such as trifluoromethanesulfonic anhydride, and carboxylic anhydrides such as acetic anhydride, trifluoroacetic anhydride, and pentafluoropropionic anhydride. In the acid anhydride, some or all of the hydrogen elements may be substituted with fluorine elements or the like. Examples of the boron compound include alkyl borate ester, aryl borate ester, tris (trifluoroacetoxy) boron, trialkoxyboroxine, trifluoroboron and the like. Examples of silicon compounds include chlorosilane, alkylsilylalkylsulfonates in which some or all of the hydrogen elements may be substituted with fluorine elements, etc., and some or all of the hydrogen elements may be substituted with fluorine elements, etc. Examples thereof include alkyl silyl esters. In addition, when the said silicon compound is used, at least one part of the said protective film may be formed with this silicon compound.

  In the protective film forming chemical, the compound A and the acid A may be diluted with a solvent. When the total amount of compound A and acid A added is 0.01 to 100% by mass with respect to 100% by mass of the total amount of the chemical solution for forming the protective film, a protective film is uniformly formed on at least the concave surface of the concave / convex pattern. Since it becomes easy to do, it is preferable. If it is less than 0.01% by mass, the effect of preventing the uneven pattern from falling tends to be insufficient. More preferably, it is 0.05-50 mass%.

  Examples of the solvent that may be used for dilution in the chemical solution for forming a protective film include, for example, hydrocarbons, esters, ethers, ketones, halogen-containing solvents, sulfoxide solvents, alcohols, polyhydric alcohol derivatives, and the like. An organic solvent such as a nitrogen compound solvent is preferably used. Of these, hydrocarbons, esters, ethers, ketones, halogen-containing solvents, sulfoxide solvents, and polyhydric alcohol derivatives that do not have an OH group can be used to shorten the protective film on the surface of the concavo-convex pattern. It is more preferable because it can be formed in time.

  Examples of the hydrocarbons include toluene, benzene, xylene, hexane, heptane, and octane. Examples of the esters include ethyl acetate, propyl acetate, butyl acetate, and ethyl acetoacetate, and the ether. Examples of such classes include diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, dioxane and the like, and examples of the ketones include acetone, acetylacetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, cyclohexanone, isophorone, and the like. Examples of the halogen-containing solvent include perfluorocarbons such as perfluorooctane, perfluorononane, perfluorocyclopentane, perfluorocyclohexane, hexafluorobenzene, 1,1,1, , 3-pentafluorobutane, octafluorocyclopentane, 2,3-dihydrodecafluoropentane, hydrofluorocarbons such as Zeolora H (manufactured by Nippon Zeon), methyl perfluoroisobutyl ether, methyl perfluorobutyl ether, ethyl perfluorobutyl ether, Hydrofluoroethers such as ethyl perfluoroisobutyl ether, Asahiklin AE-3000 (manufactured by Asahi Glass), Novec HFE-7100, Novec HFE-7200, Novec 7300, and Novec 7600 (all from 3M), chlorocarbons such as tetrachloromethane, chloroform Hydrochlorocarbons such as chlorofluorocarbons such as dichlorodifluoromethane, 1,1-dichloro-2,2,3,3,3-pe Tafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, 1,2-dichloro-3,3,3- There are hydrochlorofluorocarbons such as trifluoropropene, perfluoroethers, perfluoropolyethers, etc. Examples of the sulfoxide solvents include dimethyl sulfoxide and the like, examples of derivatives of the polyhydric alcohols that do not have an OH group Diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol Lumpur dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol diacetate, diethylene glycol diacetate, triethylene glycol dimethyl ether, ethylene glycol diacetate, ethylene glycol diethyl ether, and the like ethylene glycol dimethyl ether.

  Further, it is preferable to use a nonflammable organic solvent because the chemical liquid for forming the protective film becomes nonflammable, or the flash point becomes high and the risk of the chemical liquid decreases. Many halogen-containing solvents are nonflammable, and the nonflammable halogen-containing solvent can be suitably used as a nonflammable organic solvent.

  In addition, when the protective film forming chemical solution is supplied to the wafer while rotating the wafer, if the boiling point of the organic solvent is too low, the chemical solution tends to dry before the protective film forming chemical solution wets and spreads over the entire surface of the wafer. Absent. Moreover, when the boiling point is too high, the viscosity of the chemical solution tends to be too high, which is not preferable. For this reason, it is preferable to use the organic solvent having a boiling point of 70 to 220 ° C. As such a solvent, in consideration of cost and solubility with other cleaning liquids (ease of replacement), diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, propylene glycol monomethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol ethyl Methyl ether, ethylene glycol dimethyl ether, diethylene glycol diacetate, ethylene glycol diacetate, cyclohexanone and the like are preferable.

  Moreover, it is preferable that the moisture content in the chemical | medical solution for protective film formation is 5000 mass ppm or less with respect to this chemical | medical solution total amount. When the amount of water exceeds 5000 ppm by mass, the activities of the compound A and the acid A are reduced, and it is difficult to form the protective film in a short time. Therefore, it is preferable that the compound A, the acid A contained in the protective film-forming chemical solution, and the solvent that may be contained in the protective film-forming chemical solution do not contain much water. The water content in the protective film forming chemical may be 10 ppm or more.

  Further, it is preferable that the number of particles larger than 0.5 μm is 100 or less per 1 mL of the chemical solution in the particle measurement by the light scattering type submerged particle detector in the liquid phase in the protective film forming chemical solution. If the number of particles larger than 0.5 μm exceeds 100 per 1 mL of the chemical solution, pattern damage due to the particles may be induced, which causes a decrease in device yield and reliability. Further, it is preferable that the number of particles larger than 0.5 μm is 100 or less per mL of the chemical solution because washing with a solvent or water after forming the protective film can be omitted or reduced. For this reason, it is preferable that the number of particles larger than 0.5 μm in the protective film forming chemical solution per 1 mL of the chemical solution is smaller, but the number of particles larger than 0.5 μm is 1 or more per 1 mL of the chemical solution. Also good. The particle measurement in the liquid phase in the protective film forming chemical solution is performed using a commercially available measuring device in a light scattering liquid particle measurement method using a laser as a light source. Means a light scattering equivalent diameter based on PSL (polystyrene latex) standard particles.

  Moreover, it is preferable that the metal impurity content of each element of Na, Mg, K, Ca, Mn, Fe, and Cu in the chemical solution for forming a protective film is 100 mass ppb or less with respect to the total amount of the chemical solution. The metal impurities of each element described above are all those that exist in the chemical solution in the form of metal fine particles, ions, colloids, complexes, oxides and nitrides, whether dissolved or undissolved. If the metal impurity content is more than 100 mass ppb with respect to the total amount of the chemical solution, the junction leakage current of the device may be increased, which causes a decrease in device yield and reliability. Moreover, it is preferable that the metal impurity content is 100 mass ppb or less with respect to the total amount of the chemical solution because washing with a solvent or water after forming the protective film can be omitted or reduced. In addition, 0.01 mass ppb or more of each said metal impurity content may be sufficient with respect to this chemical | medical solution total amount.

  In the method for preparing a protective film-forming chemical solution containing the compound A and the acid A mixed, it is preferable to purify at least one of the compound A before mixing, the acid A, and the mixed solution after mixing. When the protective film-forming chemical solution contains a solvent, the compound A and the acid A before mixing may be in a solution state containing a solvent. In this case, the purification is performed before the compound is mixed. The target may be at least one of A or a solution thereof, acid A or a solution thereof, and a mixed solution after mixing.

  The purification includes removal of water molecules by adsorbent such as molecular sieve or distillation, removal of metal impurities of each element of Na, Mg, K, Ca, Mn, Fe and Cu by ion exchange resin or distillation, and This is performed using at least one removing means among removing contaminants such as particles by filter filtration. In consideration of the activity of the chemical solution for forming the protective film and the cleanliness of the wafer, it is preferable to remove water molecules, remove metal impurities, and remove contaminants, and the removal order is not limited.

  As described above, after (Step 2), the protective film-forming chemical liquid held on at least the concave surface of the concavo-convex pattern may be replaced with a cleaning liquid B different from the chemical liquid, and then transferred to (Step 3). . Examples of the cleaning liquid B include an aqueous cleaning liquid composed of an aqueous solution, or an organic solvent, or a mixture of the aqueous cleaning liquid and an organic solvent, a mixture of at least one of an acid, an alkali, and a surfactant. Alternatively, the compound A contained in the chemical solution for forming a protective film and the acid A added so that the concentration thereof is lower than that of the chemical solution may be used.

  Examples of the organic solvent which is one of the preferable examples of the cleaning liquid B include hydrocarbons, esters, ethers, ketones, halogen-containing solvents, sulfoxide solvents, alcohols, polyhydric alcohol derivatives, And nitrogen-containing compound solvents.

  Examples of the hydrocarbons include toluene, benzene, xylene, hexane, heptane, and octane. Examples of the esters include ethyl acetate, propyl acetate, butyl acetate, and ethyl acetoacetate, and the ether. Examples of such classes include diethyl ether, dipropyl ether, dibutyl ether, tetrahydrofuran, dioxane and the like, and examples of the ketones include acetone, acetylacetone, methyl ethyl ketone, methyl propyl ketone, methyl butyl ketone, cyclohexanone, isophorone, and the like. Examples of the halogen-containing solvent include perfluorocarbons such as perfluorooctane, perfluorononane, perfluorocyclopentane, perfluorocyclohexane, hexafluorobenzene, 1,1,1, , 3-pentafluorobutane, octafluorocyclopentane, 2,3-dihydrodecafluoropentane, hydrofluorocarbons such as Zeolora H (manufactured by Nippon Zeon), methyl perfluoroisobutyl ether, methyl perfluorobutyl ether, ethyl perfluorobutyl ether, Hydrofluoroethers such as ethyl perfluoroisobutyl ether, Asahiklin AE-3000 (manufactured by Asahi Glass), Novec HFE-7100, Novec HFE-7200, Novec 7300, and Novec 7600 (all from 3M), chlorocarbons such as tetrachloromethane, chloroform Hydrochlorocarbons such as chlorofluorocarbons such as dichlorodifluoromethane, 1,1-dichloro-2,2,3,3,3-pe Tafluoropropane, 1,3-dichloro-1,1,2,2,3-pentafluoropropane, 1-chloro-3,3,3-trifluoropropene, 1,2-dichloro-3,3,3- There are hydrochlorofluorocarbons such as trifluoropropene, perfluoroethers, perfluoropolyethers, etc. Examples of the sulfoxide solvents include dimethyl sulfoxide, and examples of alcohols include methanol, ethanol, propanol, butanol. Ethylene glycol, 1,3-propanediol, etc. Examples of the derivative of the polyhydric alcohol include diethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether. , Propylene glycol monoethyl ether, diethylene glycol monoethyl ether acetate, ethylene glycol monomethyl ether acetate, ethylene glycol monobutyl ether acetate, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol dimethyl ether, diethylene glycol ethyl methyl ether, diethylene glycol diethyl ether , Diethylene glycol diacetate, triethylene glycol dimethyl ether, ethylene glycol diacetate, ethylene glycol diethyl ether, ethylene glycol dimethyl ether, etc. Examples of nitrogen-containing compound solvents include formamide, N, N-dimethylformamide And N, N-dimethylacetamide, N-methyl-2-pyrrolidone, diethylamine, triethylamine, pyridine and the like.

  In addition, after the replacement with the cleaning liquid B, an aqueous cleaning liquid composed of an aqueous solution is held on at least the concave surface of the concave / convex pattern, and then the process may proceed to (Step 3).

  A plurality of cleaning liquids may be used as the cleaning liquid B.

  Examples of the aqueous cleaning liquid include water or water mainly containing water mixed with at least one organic solvent, acid or alkali in water (for example, the water content is 50% by mass or more). It is done. In particular, when water is used as the aqueous cleaning liquid, the contact angle θ with the liquid on at least the concave surface of the concave / convex pattern made water-repellent by the chemical solution for forming a protective film increases, and the capillary force P on the concave surface decreases. Further, it is preferable because dirt is hardly left on the wafer surface after drying.

  FIG. 4 shows a schematic diagram when the liquid is held in the recess 4 in which the water-repellent protective film is formed by the protective film forming chemical solution. The wafer in the schematic diagram of FIG. 4 shows a part of the a-a ′ cross section of FIG. 1. The surface of the concavo-convex pattern is made water repellent by forming a protective film 10 with the protective film forming chemical. The protective film 10 is held on the wafer surface even when the liquid 9 is removed from the uneven pattern surface.

  When the liquid is removed from the surface of the concavo-convex pattern, the liquid held on the surface may be a protective film forming chemical solution, a cleaning solution B, an aqueous cleaning solution, and a mixture thereof. The liquid mixture containing the chemical liquid may be a liquid in the middle of replacing the chemical liquid with the cleaning liquid B, or may be a liquid mixture obtained by previously mixing the chemical liquid with a cleaning liquid different from the chemical liquid. Further, after the liquid is once removed from the uneven pattern surface, the uneven pattern surface is held with at least one selected from the cleaning liquid B, the aqueous cleaning liquid, and a mixture thereof, and then dried. Also good.

When the protective film 10 is formed on at least the concave surface of the concave / convex pattern of the wafer by the chemical solution for forming the protective film, the contact angle when assuming that water is held on the surface is 60 to 120 °. It is preferable because it does not easily fall over. Further, the closer the contact angle is to 90 °, the smaller the capillary force on the surface of the concave portion, and the pattern collapse is less likely to occur. The capillary force is preferably 2.1 MN / m ² or less. It is preferable that the capillary force is 2.1 MN / m ² or less because pattern collapse hardly occurs. Also, when the capillary force is small, the collapse is further difficult to occur pattern, capillary force is particularly preferably 1.6MN / ^{m 2} or less, more preferably 1.1 MN / ^{m 2} or less. Furthermore, it is ideal to adjust the contact angle with the liquid to around 90 ° so that the capillary force is as close as possible to 0.0 MN / m ² .

  In the step of removing the liquid from the concavo-convex pattern surface (step 3), for example, the liquid held on the concavo-convex pattern surface is removed by drying. The drying is preferably performed by a known drying method such as spin drying, IPA (2-propanol) vapor drying, Marangoni drying, heat drying, hot air drying, or vacuum drying.

  Next, a step of removing the protective film (step 4) is performed. When removing the protective film, it is effective to cut the C—C bond and C—F bond in the protective film. The method is not particularly limited as long as it can cut the bond, for example, irradiating the wafer surface with light, heating the wafer, exposing the wafer to ozone, irradiating the wafer surface with plasma, For example, corona discharge on the wafer surface may be mentioned.

  When the protective film is removed by light irradiation, it is effective to break the C—C bond and C—F bond in the protective film. For this purpose, their binding energies are 83 kcal / mol, 116 kcal. It is preferable to irradiate ultraviolet rays including wavelengths shorter than 340 nm and 240 nm, which are energy corresponding to / mol. As this light source, a metal halide lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an excimer lamp, a carbon arc, or the like is used.

  Further, when the protective film is removed by light irradiation, if the constituent components of the protective film are decomposed by ultraviolet rays and ozone is generated at the same time, and the constituent components of the protective film are oxidized and volatilized by the ozone, the processing time is shortened. Therefore, it is particularly preferable. As this light source, a low-pressure mercury lamp or an excimer lamp is used. Further, the wafer may be heated while irradiating light.

  When the wafer is heated, the wafer is heated at 400 to 700 ° C, preferably 500 to 700 ° C. This heating time is preferably 0.5 to 60 minutes, preferably 1 to 30 minutes. In this process, ozone exposure, plasma irradiation, corona discharge, etc. may be used in combination. Further, light irradiation may be performed while heating the wafer.

  When the wafer is exposed to ozone, it is preferable that ozone generated by ultraviolet irradiation with a low-pressure mercury lamp or the like or low-temperature discharge with a high voltage is provided on the wafer surface. The wafer may be irradiated with light while being exposed to ozone, or may be heated.

  In the step of removing the protective film on the wafer surface, the protective film on the wafer surface can be efficiently removed by combining light irradiation treatment, heat treatment, ozone exposure treatment, plasma irradiation treatment, corona discharge treatment, and the like. it can.

Making the surface of the wafer a surface having a concavo-convex pattern and replacing the cleaning liquid held at least on the concave surface of the concavo-convex pattern with other cleaning liquids have already been established through various studies in other literature. Since it is a technique, the present invention has been mainly focused on the evaluation of the chemical solution for forming the protective film. In addition, the equation P = 2 × γ × cos θ / S described in the background art
(Wherein γ is the surface tension of the liquid held in the recess, θ is the contact angle between the recess surface and the liquid held in the recess, and S is the width of the recess.)
As can be seen from the above, the pattern collapse greatly depends on the contact angle of the cleaning liquid to the wafer surface, that is, the contact angle of the droplets and the surface tension of the cleaning liquid. In the case of the cleaning liquid held in the concave portion 4 of the concavo-convex pattern 2, the contact angle of the liquid droplet and the capillary force acting on the concave portion, which can be considered as equivalent to the pattern collapse, are correlated. Capillary force may be derived from the evaluation of the contact angle of ten droplets. In the examples, water, which is a typical aqueous cleaning solution, was used as the cleaning solution. From the above formula, as the contact angle is closer to 90 °, the capillary force acting on the concave portion becomes smaller and pattern collapse hardly occurs. Therefore, the contact angle when assuming that water is held on the surface of the protective film is 60 ˜120 ° is preferable, and 70 to 110 ° is particularly preferable.

  The contact angle of water droplets is evaluated by dropping several μl of water droplets on the sample (base material) surface as in JIS R 3257 “Test method for wettability of substrate glass surface”, and the angle between the water droplet and the substrate surface. It is made by measuring. However, in the case of a wafer having a pattern, the contact angle becomes very large. This is because a Wenzel effect and a Cassie effect occur, and the contact angle is affected by the surface shape (roughness) of the substrate, and the apparent contact angle of water droplets increases. Therefore, in the case of a wafer having a concavo-convex pattern on the surface, the contact angle of the protective film 10 itself formed on the concavo-convex pattern surface cannot be accurately evaluated.

Therefore, in this embodiment, the chemical solution is applied to a wafer having a smooth surface, a protective film is formed on the wafer surface, and the protective film is formed on the surface of the wafer 1 on which the uneven pattern 2 is formed. The film 10 was considered and various evaluations were performed. In this example, a smooth silicon wafer having a thermal oxide film (SiO ₂ film) layer or a silicon nitride film (SiN film) layer on the surface was used as the wafer having a smooth surface. Therefore, in this example, application to the present invention including the following steps was made based on various evaluation results for a wafer having a smooth surface.
A step of supplying a pretreatment chemical to the uneven pattern surface (here, this step is referred to as “pretreatment”).
A process of forming a water-repellent protective film by supplying a protective film-forming chemical to the surface of the uneven pattern

[Wafer evaluation method]
In this example, the following evaluations (1) to (3) were performed as a method for evaluating a wafer subjected to both the steps.

(1) Contact angle evaluation of the protective film formed on the wafer surface About 2 μl of pure water is placed on the surface of the wafer on which the protective film is formed, and the angle (contact angle) formed between the water droplet and the wafer surface is measured by a contact angle meter (Kyowa). It was measured by Interface Science: CA-X type). Here, the protective film having a contact angle in the range of 60 to 120 ° was regarded as acceptable.

(2) Removability of protective film The sample was irradiated with UV light from a low-pressure mercury lamp for 1 minute under the following conditions. A sample having a water droplet contact angle of 10 ° or less after irradiation was regarded as acceptable (indicated as “◯” in Table 1).
・ Lamp: Sen Special Light Source PL2003N-10
Illuminance: 15 mW / cm ² (distance from light source to sample is 10 mm)

ここで、Ｘ_Ｌ、Ｘ_Ｒ、Ｙ_Ｂ、Ｙ_Ｔは、それぞれ、Ｘ座標、Ｙ座標の測定範囲を示す。Ｓ_０は、測定面が理想的にフラットであるとした時の面積であり、（Ｘ_Ｒ−Ｘ_Ｌ）×（Ｙ_Ｂ−Ｙ_Ｔ）の値とした。また、Ｆ（Ｘ，Ｙ）は、測定点（Ｘ，Ｙ）における高さ、Ｚ_０は、測定面内の平均高さを表す。 (3) Evaluation of surface smoothness of wafer after removal of protective film Surface observation was performed with an atomic force electron microscope (Seiko-Electronics: SPI3700, 2.5 μm square scan), and centerline average surface roughness: Ra (nm) was determined. Asked. Ra is a three-dimensional extension of the centerline average roughness defined in JIS B 0601 to the measurement surface. “The absolute value of the deviation from the reference surface to the specified surface is averaged. The value was calculated by the following formula. If the Ra value of the wafer after removing the protective film is 1 nm or less, the wafer surface is not eroded by the cleaning, and the protective film residue is not present on the wafer surface. Notation).

Here, X _L , X _R , Y _B , and Y _T indicate measurement ranges of the X coordinate and the Y coordinate, respectively. S ₀ is an area when the measurement surface is ideally flat, and is a value of (X _R −X _L ) × (Y _B −Y _T ). Moreover, F (X, Y) is, the measurement point (X, Y) in height, _{Z 0} represents the average height within the measurement surface.

[Example 1]
(1) Preparation of chemical solution for forming protective film Hexamethyldisilazane (HMDS) as compound A: 3 g, trifluoroacetic acid (TFA) as acid A: 0.1 g, propylene glycol monomethyl ether acetate (PGMEA) as solvent: 96. 9 g was mixed and stirred for about 5 minutes to obtain a protective film-forming chemical.

(2) Cleaning of wafer A silicon wafer with a smooth SiO ₂ film (a silicon wafer having a thermal oxide film layer having a thickness of 1 μm on the surface, which may be simply referred to as “SiO ₂ film” hereinafter) is obtained with a 1% by mass It was immersed in an acid aqueous solution for 2 minutes, then immersed in pure water for 1 minute and in 2-propanol for 1 minute. Further, a silicon wafer with a smooth SiN film (a silicon wafer having a silicon nitride film with a thickness of 50 nm on the surface, which may be simply referred to as “SiN film” hereinafter) manufactured by LP-CVD is 1 mass% hydrofluoric acid. Immerse in an aqueous solution for 2 minutes, then in pure water for 1 minute, 1 minute in a cleaning solution in which 28% by mass ammonia water: 30% by mass hydrogen peroxide water: water is mixed at a volume ratio of 1: 1: 5, and 1% in pure water. Soaked for a minute.

(3) Pretreatment As a pretreatment chemical solution, a 1 mol / L hydrochloric acid (described as HCl in Table 1) aqueous solution (measured pH is 0.1) previously purified by an ion exchange method and filter filtration. It was used and heated with a hot plate so that the liquid temperature was 60 ° C. Thereafter, the cleaned silicon wafer with a SiO ₂ film and the silicon wafer with a SiN film were each pre-treated by being immersed in a pretreatment chemical solution for 1 minute. Thereafter, each wafer was immersed in pure water for 1 minute. The pH of the pretreatment chemical solution was measured using a pH meter (manufactured by ASONE, Lacomtester pH meter pH1100) after leaving the pretreatment chemical solution in a thermostatic bath at 25 ° C. for 1 hour.

(4) Surface treatment with a chemical solution for forming a protective film on the wafer surface Each pretreated silicon wafer with SiO ₂ film and silicon wafer with SiN film was immersed in 2-propanol for 1 minute, and then the “(1) The film was immersed for 1 minute at 20 ° C. in the protective film forming chemical prepared in “Preparation of protective film forming chemical”. Thereafter, each wafer was immersed in 2-propanol for 1 minute, and then immersed in pure water for 1 minute. Finally, each wafer was taken out from the pure water and air was blown to remove the pure water on the surface.

Each of the obtained wafers was evaluated in the manner described in “Wafer Evaluation Method” above. Hereinafter, when referring to a silicon wafer with a SiO ₂ film, it is simply referred to as “SiO ₂ film”, and when referring to a silicon wafer with a SiN film, it is simply referred to as “SiN film”. As shown in Table 1, the evaluation results showed that the SiO ₂ film had an initial contact angle before the surface treatment of less than 10 °, but the contact angle after the surface treatment was 88 °, indicating the effect of imparting water repellency. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

  Further, in the SiN film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 69 °, which showed the effect of imparting water repellency. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

As described above, when pretreatment is performed with a 1 mol / L hydrochloric acid aqueous solution heated to 60 ° C., either a silicon wafer with a SiO ₂ film having a large hydroxyl group on the wafer surface or a silicon wafer with a SiN film having a few hydroxyl groups on the wafer surface. As a result, it was confirmed that a good water repellency imparting effect was obtained and cleaning could be performed efficiently.

[Examples 2 to 18]
The surface treatment of the wafer is carried out by appropriately changing the conditions such as the acid, acid concentration, solvent, pH, temperature of the pretreatment chemical solution used in Example 1 and the temperature and time of the surface treatment of the chemical solution for forming the protective film. Further evaluation was performed. The results are shown in Table 1.

In Table 1, HNO ₃ means nitric acid, CH ₃ COOH means acetic acid, HOOCCHCHCOOH means maleic acid, and water / EG = 60/40 is a solvent in which water / ethylene glycol is mixed at a mass ratio of 60/40. Water / EG = 20/80 means a solvent in which water / ethylene glycol is mixed at a mass ratio of 20/80, and HMDS / TFA / PGMEA forms a protective film having the same composition ratio as in Example 1. Means medical solution.

[Comparative Example 1]
All were the same as Example 1 except that no pretreatment was performed. The evaluation results are shown in Table 1. In the case of the SiO ₂ film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 91 °, indicating a water repellency imparting effect. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

  On the other hand, in the SiN film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 47 °, and the water repellency imparting effect was not sufficient.

  From the evaluation result of Comparative Example 1, when no pretreatment is performed, the amount of reactive sites such as hydroxyl groups existing on the surface hardly changes. It is considered that the protective film is not sufficiently formed.

[Comparative Example 2]
All were the same as Example 1 except that 0.0005 mol / L hydrochloric acid aqueous solution (measured pH was 3.5) was used as the pretreatment chemical solution. The evaluation results are shown in Table 1. In the case of the SiO ₂ film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 88 °, indicating a water repellency imparting effect. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

  On the other hand, in the SiN film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 59 °, and the water repellency imparting effect was not sufficient.

[Comparative Example 3]
All were the same as in Example 1 except that 0.01 mol / L acetic acid aqueous solution (measured pH was 3.6) was used as the pretreatment chemical solution. The evaluation results are shown in Table 1. In the case of the SiO ₂ film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 89 °, indicating a water repellency imparting effect. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

  On the other hand, in the SiN film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 58 °, and the water repellency imparting effect was not sufficient.

  From the evaluation results of Comparative Examples 2 and 3, if the acid concentration in the pretreatment chemical solution is too low, or if the pH value of the pretreatment chemical solution is too large, the effect of modifying the wafer surface is weakened. Originally, it is considered that a water-repellent protective film is not sufficiently formed in a silicon wafer with a SiN film having few hydroxyl groups on the wafer surface.

[Comparative Example 4]
A 7 mol / L hydrochloric acid aqueous solution (measured pH is 0.0) was used as a pretreatment chemical solution. However, since the acid concentration of the pretreatment chemical solution is too high, the pretreatment chemical solution could not be purified by the ion exchange method.

[Comparative Example 5]
1 mol / L hydrochloric acid aqueous solution; 90 g, 30% hydrogen peroxide (hereinafter referred to as H ₂ O ₂ ) aqueous solution; 10 g were mixed and stirred for 5 minutes to prepare a pretreatment chemical solution (measured pH was 0.0). did. The concentration of hydrochloric acid in the pretreatment chemical solution is 0.9 mol / L, and the composition of the solvent is water / H ₂ O ₂ = 97/3 (mass ratio). When the pretreatment chemical was heated with a hot plate so that the liquid temperature became 90 ° C., bubbles were generated. This is considered that hydrogen peroxide decomposed and oxygen was generated. The pretreatment could not be performed due to the generation of the bubbles.

[Comparative Example 6]
All the pretreatment chemicals were the same as in Example 1 except that they were used at 30 ° C. The evaluation results are shown in Table 1. In the case of the SiO ₂ film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 87 °, indicating a water repellency imparting effect. Moreover, the contact angle after UV irradiation was less than 10 °, and the protective film could be removed. Furthermore, the Ra value of the wafer after UV irradiation was less than 0.5 nm, and it was confirmed that the wafer was not eroded during cleaning, and that no protective film residue remained after UV irradiation.

  On the other hand, in the SiN film, the initial contact angle before the surface treatment was less than 10 °, but the contact angle after the surface treatment was 51 °, and the water repellency imparting effect was not sufficient.

  From the evaluation result of Comparative Example 2, if the temperature of the pretreatment chemical solution is too low, the effect of modifying the wafer surface is weakened. Therefore, in a silicon wafer with a SiN film having a small hydroxyl group on the wafer surface, water repellency protection It is considered that the film is not sufficiently formed.

  In this example, a silicon wafer with a SiN film was used as a wafer with few hydroxyl groups on the wafer surface. However, even when a silicon wafer with a silicon film such as polysilicon is used, it is assumed that the same result as that when a silicon wafer with a SiN film is used is obtained.

DESCRIPTION OF SYMBOLS 1 Wafer 2 Convex / concave pattern on wafer surface 3 Convex part 4 Pattern concave part 5 Concave width 6 Convex height 7 Convex width 8 Protective film forming chemical solution 9 held in concave part 4 Contained in concave part 4 Liquid 10 Protective film (water-repellent protective film)

Claims (5)

The surface has a concavo-convex pattern, and at least a part of the concavo-convex pattern is modified to generate a hydroxyl group on the surface of the concavo-convex pattern by supplying a pretreatment chemical to the surface of the wafer containing silicon element. Processing steps, and
A protective film forming step of forming a water-repellent protective film on the surface of the concavo-convex pattern by supplying a chemical solution for forming a protective film containing a silane coupling agent that reacts with a hydroxyl group to the surface of the modified concavo-convex pattern; A method for cleaning at least a wafer comprising:
In the pretreatment step, an uneven pattern is formed at a temperature of 40 ° C. or higher and lower than the boiling point of the pretreatment chemical solution using a pretreatment chemical solution containing 0.001 to 5 mol / L of acid in molar concentration and pH of 3 or less. A method for cleaning a wafer, comprising modifying the surface of the wafer. 2. The wafer cleaning method according to claim 1, wherein the acid contained in the pretreatment chemical is an organic acid. The method for cleaning a wafer according to claim 1, wherein at least a part of the uneven pattern is formed of silicon nitride and / or silicon. The silane coupling agent is hexamethyldisilazane, trimethylsilyldiethylamine, tetramethyldisilazane, trimethylsilyldimethylamine, octyldimethylsilyldimethylamine, trimethylsilylimidazole, trimethylchlorosilane, propyldimethylchlorosilane, octyldimethylchlorosilane, dimethyldichlorosilane, methyltrimethyl. The method for cleaning a wafer according to any one of claims 1 to 3, wherein the cleaning method is at least one selected from the group consisting of chlorosilane, trimethylmethoxysilane, and trimethylethoxysilane. 5. The wafer cleaning method according to claim 1, wherein the protective film forming chemical further contains an acid.

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