JP2019104781A - Method for producing hydrophobized hydroxyethyl cellulose and polishing aid - Google Patents

Abstract

To produce hydrophobized hydroxyethyl cellulose useful as a polishing aid which can improve polishing accuracy in combination with polishing grains.SOLUTION: Hydrophobized hydroxyethyl cellulose is obtained by: reacting hydroxyethyl cellulose and aldehydes in the presence of a solvent to obtain a composition containing hydrophobized hydroxyethyl cellulose and the solvent; and, thereafter, removing the solvent from the obtained composition under at least one condition selected from the following conditions (1) and (2): condition (1) a maximum reached temperature α of the hydrophobized hydroxyethyl cellulose is less than 65°C; and condition (2) a heat quantity parameter β calculated from temperature and heating time of the hydrophobized hydroxyethyl cellulose is 2500°C min or less.SELECTED DRAWING: None

Description

  The present invention relates to a method for producing hydrophobized hydroxyethyl cellulose and a polishing aid which can be effectively used as a polishing aid for polishing a semiconductor substrate such as a silicon wafer in combination with abrasive grains.

  Hydroxyethyl cellulose (HEC), which is a semi-synthetic polymer compound, is water-soluble, and is excellent in properties such as dispersibility and viscosity. Such hydroxyethyl cellulose is used in various applications such as dispersants, thickeners, emulsion polymerization stabilizers, protective colloids, paints, cosmetics, water retention agents, pharmaceutical preparations and the like. In particular, in the polishing step of a semiconductor substrate typified by a silicon wafer etc. as the application in which the above-mentioned characteristics are effective, for the purpose of improving the protection of the surface of the object to be polished and the wettability, In addition, it is used.

  JP-A 2003-12535 (patent document 1) uses a mixed solvent I comprising a poorly water-soluble organic solvent, methanol and water, which is obtained by reacting (A) alkaline cellulose with ethylene oxide. A process for producing hydroxyethyl cellulose is described which comprises a first washing step of washing and a second washing step of washing with (B) a mixed solvent II consisting of the mixed solvent I and an acid. In the examples of this document, the mixed solvent I using methyl isobutyl ketone as the poorly water-soluble organic solvent, the methyl isobutyl ketone as the poorly water-soluble organic solvent, and the mixed solvent II using acetic acid as the acid After washing with mixed solvent I and filtering off, it is described that the obtained residue is dried at 70 ° C. under reduced pressure overnight to obtain a dried product of hydroxyethyl cellulose.

  JP-A 2003-171401 (patent document 2) manufactures a hydroxyalkyl cellulose by reacting an alkali cellulose having an alkaline ratio of 14 to 18% by weight and a moisture ratio of 20 to 55% by weight with an alkylene oxide. It has been described that. In Examples of this document, it is described that after hydroxyethyl cellulose separated by filtration from the slurry liquid was washed with a predetermined mixed solvent, it was dried overnight at 70 ° C. under reduced pressure to obtain hydroxyethyl cellulose.

  JP 11-92 707 (patent document 3) relates to biologically stable water comprising a molecular weight reduced polysaccharide derivative (such as hydroxyethyl cellulose (HEC)) resistant to enzymatic hydrolysis, and an aqueous medium paint component. Media paint is described. This document describes Buckeye HVE cellulose (commercially available from Buckeye Corp., Spartananburg, SC) in a reactor containing a mixture of t-butyl alcohol, water, and sodium hydroxide for the preparation of high molecular weight HEC and enzyme treatment. In addition, the mixture is stirred at room temperature, ethylene oxide is added and reacted, the reaction mixture is cooled, nitric acid and additional ethylene oxide are added and reacted, and then neutralized with nitric acid, and the filtered off residue is 80:20 After washing with an acetone / water mixture and dehydrating the product with acetone, the dewatered product is dried in a fluid bed drier at 50 ° C. for 0.5 h, hydroxyethyl molar substitution (MS) 4.3 It is stated that HEC with a 1% solution viscosity of 3350 cps is obtained.

  However, Patent Documents 1 to 3 do not describe using HEC as a polishing aid. Furthermore, in recent polishing of silicon wafers, high surface quality is required to the polishing surface, and there are many insolubles in water, and these HECs have minute defects on the surface after polishing [eg, LPD (Light point defects) occur.

  JP-A-2011-61089 (Patent Document 4) describes a polishing composition containing an abrasive, hydroxyethyl cellulose prepared by hydrolyzing high molecular weight hydroxyethyl cellulose, and a basic compound. There is. In this document, hydroxyethyl cellulose (HEC, Mw = 1.5 million, average molar substitution 2.4) is formed by hydrolysis with hydrochloric acid in a mixed solvent of isopropanol (IPA) / water = 85/15 (weight ratio) The mixed solvent of the above composition is added to the mixed solution, and the filtered precipitate is washed with a mixed solvent of IPA / water = 95/5 (weight ratio), dried under reduced pressure under an atmosphere of 50.degree. It is described that a weight average molecular weight (Mw) of 107,000 and an average molar substitution degree of 2.4) were obtained by the GPC method.

  However, even with hydrolyzed hydroxyethyl cellulose described in this document, it is difficult to improve the polishing accuracy, and surface defects can not be sufficiently suppressed.

Unexamined-Japanese-Patent No. 2003-12535 (Claims, Example) Unexamined-Japanese-Patent No. 2003-171401 (Claims, Example) JP-A-11-92707 (Claims, Examples) JP, 2011-61089, A (claim, example)

  Therefore, an object of the present invention is to provide a method for producing hydrophobized hydroxyethyl cellulose which is useful as a polishing aid capable of improving polishing accuracy in combination with abrasive grains, and a polishing aid comprising hydrophobized hydroxyethyl cellulose obtained by this production method. It is to do.

  Another object of the present invention is to provide a polishing aid which can suppress generation of defects on the surface of a semiconductor substrate even when the semiconductor substrate such as a silicon wafer is polished in combination with abrasive grains.

  As a result of intensive studies to achieve the above-mentioned problems, the present inventors have made it possible to obtain specific heat from a composition containing hydrophobized hydroxyethyl cellulose obtained by reacting hydroxyethyl cellulose and aldehydes in the presence of a solvent and the solvent. It has been found that when the object to be polished is polished by combining the hydrophobized hydroxyethyl cellulose obtained by drying with a history and the abrasive grains, the polishing accuracy can be improved, and the present invention has been completed.

  That is, the method for producing hydrophobized hydroxyethyl cellulose according to the present invention comprises a hydrophobizing step of reacting hydroxyethyl cellulose and aldehydes in the presence of a solvent to obtain hydrophobized hydroxyethyl cellulose and a composition containing the solvent, the following conditions (1 And (2) removing the solvent from the composition under at least one condition selected from (2) to obtain a hydrophobized hydroxyethyl cellulose.

Condition (1): Maximum reaching temperature α of hydrophobized hydroxyethyl cellulose is less than 65 ° C. Condition (2): Calorific parameter β calculated from temperature and heating time of hydrophobized hydroxyethyl cellulose is 2500 ° C. · min or less .

  The method for producing the hydrophobized HEC may be subjected to a drying step without hydrolyzing the hydrophobized HEC obtained in the hydrophobization step. The proportion of the aldehyde may be 1 part by weight or less with respect to 100 parts by weight of HEC. The aldehydes may be dialdehydes (especially glyoxal). In the method for producing the hydrophobized HEC, as a step prior to the hydrophobization step, a cellulose having an intrinsic viscosity of 2 to 6 dl / g is subjected to alcoholization, the produced alkali cellulose is reacted with ethylene oxide, and a reaction including the obtained HEC It may further include an HEC generation step of neutralizing the mixture.

In the present invention, it is a polishing aid for polishing an object to be polished in combination with abrasive particles, which is hydrophobized with an aldehyde and which contains the aldehyde in a proportion of 0.3% by weight or less Abrasive assistants are also included. The ratio of insoluble matter to water in the hydrophobized HEC may be 1000 ppm by weight or less. The weight average molecular weight of the hydrophobized HEC may be about 3 × 10 ^{4 to} 100 × 10 ⁴ . The average degree of substitution of the hydrophobized HEC may be about 0.5 to 2.5. The water content of the hydrophobized HEC may be 10% by weight or less. The viscosity at 25 ° C. in a 1% by weight aqueous solution of the hydrophobized HEC may be 2000 cps or less.

  In the present specification and claims, “hydrophobicized HEC” means HEC treated (or crosslinked) with aldehydes, and may be loosely or weakly crosslinked with aldehydes.

  In the present invention, a dry hydrophobizing HEC obtained by drying a composition containing hydrophobized HEC obtained by reacting HEC with an aldehyde in the presence of a solvent with a specific heat history is used as abrasive grains and abrasive grains. The polishing accuracy can be improved because the object to be polished is polished in combination. In particular, even when a semiconductor substrate such as a silicon wafer is polished in combination with abrasive grains, generation of defects on the surface of the semiconductor substrate can be suppressed.

[Method for producing hydrophobized hydroxyethyl cellulose]
In the method for producing hydrophobized HEC of the present invention, a hydrophobization step of reacting HEC with aldehydes in the presence of a solvent to obtain a liquid composition containing hydrophobized HEC, drying the liquid composition under specific conditions The drying step may be performed to obtain the hydrophobized HEC, but the HEC generation step may be further included as a step prior to the hydrophobization step.

(HEC generation process)
In the HEC production step, the cellulose may be subjected to aceleration, the produced alkali cellulose and ethylene oxide may be reacted, and the reaction mixture containing the obtained hydroxyethyl cellulose may be neutralized.

  As a cellulose, the material should just be formed with the polysaccharide which has a (beta) -1, 4- glucan structure. The shape of the cellulose may be particulate, fibrous or the like, and is usually fibrous. Examples of fibrous cellulose include cellulose fibers derived from higher plants (for example, wood fibers (such as softwoods and wood pulp such as hardwoods), bamboo fibers, sugar cane fibers, seed hair fibers (for example, cotton linters, bombax cotton, kapok Etc.), ginseng fibers (eg hemp, kozo, mitsumata etc.), natural cellulose fibers (pulp fibers) such as leaf fibers (eg manila hemp, New Zealand hemp etc), cellulose fibers of animal origin (eg Etc.), cellulose fibers derived from bacteria (eg, cellulose contained in nata de coco). These celluloses can be used alone or in combination of two or more.

  The intrinsic viscosity (intrinsic viscosity) of the cellulose is, for example, 2 to 6 dl / g, preferably 2.5 to 5.5 dl / g (eg, 3 to 5 dl / g), and more preferably 3.2 to 4.5 dl / g In particular, it is about 3.3 to 4.3 dl / g). If the intrinsic viscosity is too small, the solubility in water may be too strong, and if it is too large, the solubility in water may be too weak. In the present specification and claims, the intrinsic viscosity can be measured in accordance with JIS P8215: 1998 A.

  In the alsification, alkali cellulose is produced by reacting the above-mentioned cellulose and alkali using various methods such as a conventional slurry method (high liquid power method) or a kneader method (low liquid power method). Examples of the alkali include hydroxides of alkali metals (lithium, potassium, sodium, rubidium, cesium and the like), hydroxides of alkaline earth metals (magnesium, calcium, barium and the like), ammonia and the like. Among these alkalis, alkali metal hydroxides (especially sodium hydroxide) are widely used.

  The proportion of the alkali (sodium hydroxide or the like) is, for example, about 10 to 100 parts by weight, preferably about 15 to 70 parts by weight, and more preferably about 20 to 50 parts by weight with respect to 100 parts by weight of cellulose.

  Alcification may be performed in the presence of a solvent. As the solvent, an aqueous solvent is preferable. For example, water, alcohols (ethanol, isopropanol, butyl alcohol, isobutyl alcohol, t-butyl alcohol etc.), ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone etc.), cyclic ethers ( Tetrahydrofuran, dioxane and the like), cellosolves (methyl cellosolve, ethyl cellosolve and the like) and the like can be exemplified. These solvents can be used alone or in combination of two or more. Among these solvents, water and alcohols are generally used, and alcohols such as t-butyl alcohol are preferably contained as main solvents.

  The cellulose concentration is, for example, about 1 to 20% by weight, preferably about 2 to 15% by weight, and more preferably about 3 to 10% by weight.

  Alcification may be reacted, for example, at a temperature of about 10 to 50 ° C. (particularly 15 to 40 ° C.) with stirring. The reaction time is about 5 minutes to 2 hours (particularly, 1 hour to 2 hours).

  The ratio of ethylene oxide (ethylene oxide) is, for example, 10 to 300 parts by weight, preferably 30 to 200 parts by weight, and more preferably 50 to 150 parts by weight, with respect to 100 parts by weight of cellulose which is a raw material of the produced alkali cellulose. In particular, it is about 50 to 100 parts by weight.

  The mixing temperature of the alkali cellulose and ethylene oxide is about 5 to 30 ° C. (especially 10 to 25 ° C.) from the point that the reaction can proceed uniformly, and the mixing time is 5 minutes to 2 hours (especially 5 minutes to 1 hour). Time) degree.

  The reaction temperature of the alkali cellulose and ethylene oxide is, for example, 35 to 90 ° C., preferably 40 to 90 ° C., and more preferably 50 to 85 ° C. (particularly 50 to 80 ° C.). The reaction time is, for example, about 1 to 15 hours, preferably about 1.5 to 10 hours, and more preferably about 2 to 5 hours.

  As an acid for neutralizing the reaction mixture (usually, liquid composition) containing the obtained hydroxyethyl cellulose, protonic acids, for example, inorganic acids (for example, hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid etc.), organic acids (for example, For example, carboxylic acid, sulfonic acid and the like can be mentioned. Among these acids, inorganic acids such as nitric acid are widely used. The proportion of the acid is such that the pH of the mixture can be adjusted to, for example, 3.5 to 6.5, preferably 4 to 6, more preferably 4.3 to 5.5 (particularly 4.5 to 5). If it is

(Hydrophobization process)
In the hydrophobization step (crosslinking step), HEC is reacted with an aldehyde in the presence of a solvent to obtain hydrophobized HEC. In the hydrophobization step, HEC can be hydrophobized and crosslinked by reacting the hydrophilic group (usually hydroxyl group) of HEC with aldehydes, and the solubility of HEC in aqueous solvent (especially water) It can be reduced. Therefore, even when hydrophobized HEC is used as a polishing aid or the like, aggregation of hydrophobized HEC in an aqueous solution to form lumps (mammako) can be suppressed. On the other hand, in the case of HEC which is not hydrophobized, when it is added to water in powder form, its solubility in water is too high, so the contact surface with water immediately dissolves to form a gel-like layer and Thus, the handling is likely to be reduced.

  As aldehydes, for example, monoaldehyde (formaldehyde, acetaldehyde, butyraldehyde, isobutyraldehyde, glyceraldehyde etc.), polyaldehyde [glyoxal (oxalic acid aldehyde or ethanedial), malonaldehyde (propanedial), succinaldehyde (butanedial) And dialdehydes such as glutaraldehyde, adipinaldehyde, octanedialdehyde and phthalaldehyde; and trialdehydes such as triformylmethane and triformylethane]. These aldehydes can be used alone or in combination of two or more. Of these aldehydes, dialdehydes are preferred, and glyoxal is particularly preferred.

  The proportion of aldehydes (in particular, dialdehydes such as glyoxal) may be, for example, 5 parts by weight or less (particularly, 1 part by weight or less) with respect to 100 parts by weight of HEC, for example, 0.05 to 1 part by weight, preferably The amount is about 0.1 to 0.8 parts by weight, and more preferably about 0.3 to 0.8 parts by weight (particularly 0.5 to 0.7 parts by weight). If the proportion of aldehydes is too small, there is a possibility that the hydrophilicity is too high, and if too large, crosslinking proceeds too much, which may make it difficult to use in aqueous systems.

  As a solvent, a solvent exemplified as a solvent for the acetalization step of the HEC generation step can be used, and preferred embodiments are also the same. The solvent may be the solvent used in the HEC generation step, or may be a solvent newly added. The HEC concentration is, for example, about 1 to 20% by weight, preferably about 2 to 15% by weight, and more preferably about 3 to 10% by weight.

  The hydrophobization reaction may be reacted, for example, at a temperature of about 10 to 50 ° C. (particularly 15 to 40 ° C.) with stirring. The reaction time is about 10 minutes to 3 hours (particularly, 30 minutes to 2 hours).

(Drying process)
In the drying step, the solvent is removed from the obtained composition (usually a liquid composition) containing the hydrophobized HEC and the solvent with a specific heat history (heat load), whereby the crosslinked structure with aldehydes is obtained in the drying step. It is possible to suppress the change. When the cross-linked structure by the aldehydes is changed, the solubility in water of the hydrophobized HEC is too low, and when it is used as a polishing aid, defects are easily generated on the surface of the workpiece. Although the details of the mechanism by which hydrophobized HEC expresses appropriate water solubility by removing the solvent with a specific heat history is unclear, hydrophobized HEC in which aldehydes are cross-linked by acetal bond etc. in the hydrophobization process. In the beginning, when mixed with water, it shows appropriate hydrophobicity, suppresses aggregation of hydrophobized HEC, and improves solubility, whereas when the heat load is too large, the cross-linked structure changes, It can be estimated that it is because it becomes insoluble matter.

  In the present invention, the hydrophobized HEC obtained in the hydrophobization step is subjected to a drying step without hydrolysis.

  In the drying step, from the viewpoint of productivity, the solvent is usually removed from the composition by heating. Furthermore, when the composition is a liquid composition, from the viewpoint of productivity, a part of the solvent is usually removed from the liquid composition prior to the heat treatment to contain the hydrophobized HEC and the remaining solvent. After preparing the composition (solid or gel composition), the composition obtained is subjected to a heat treatment.

  In the liquid removal treatment, part of the solvent may be removed from the liquid composition by a conventional method such as filtration. Furthermore, the drainage process may be combined with a washing process for purifying hydrophobized HEC. For example, a solid composition subjected to a liquid removal treatment is added to an aqueous solvent and stirred, and then the liquid composition after stirring is subjected to a washing treatment for further removing a part of the solvent by a conventional method such as filtration. You may use it. Furthermore, the washing process may be repeated multiple times.

  As an aqueous solvent used in the washing treatment, a solvent exemplified as a solvent for the alcification step of the HEC forming step can be used. Among the above solvents, water, ketones and the like are widely used, and solvents containing ketones such as acetone as a main solvent are preferable.

  The proportion of water (water content) in the composition subjected to liquid removal treatment (and washing treatment) is, for example, about 20 to 80% by weight, preferably about 30 to 70% by weight, and more preferably about 40 to 60% by weight. In the present specification and claims, the water content in the drained composition can be measured using a halogen moisture meter or the like.

  As a method of heat treatment, a conventional method using a drier can be used. As the drier, for example, a material static drier (for example, a batch box drier etc.), a material transfer drier (tunnel drier, ventilated bath drier, nozzle jet drier, vented air drier etc) ), Material stirring type driers (eg, cylindrical and groove type stirring driers, kneading driers, disc driers, disc driers, rotary driers, rotary driers with steam tubes, fluidized bed driers such as through-flow rotary driers, cones) Type dryer, vibratory transport dryer, etc.), mid-air transfer type dryer (eg, spray dryer, flash dryer, etc.), cylindrical dryer (eg, drum dryer, multiple cylindrical dryer, etc.), infrared dryer , Lyophilizer, high frequency dryer and the like. It is preferable to use a material transfer type drier with less adhesion of products in the drier.

  The heating temperature is not particularly limited as long as it satisfies the heat history (maximum attainable temperature α and thermal energy parameter β) described later, and may be 35 ° C. or more (eg 35 to 150 ° C.), for example 40 to 120 ° C. Preferably it is 45-100 degreeC, More preferably, it is about 50-90 degreeC. The heating time can be appropriately selected from the range of about 1 minute to 10 hours depending on the heating temperature, for example, about 2 minutes to 8 hours, preferably about 3 minutes to 5 hours, and both the adjustment of crosslinking and productivity can be achieved. It may be about 10 minutes to 4 hours (particularly, 1 to 3 hours) from the point of being able to.

  The heat treatment may be carried out under pressure, normal pressure or reduced pressure, but it is preferable to perform treatment under normal pressure or reduced pressure from the viewpoint of being able to remove the solvent while reducing the heat load.

  In the present invention, in the drying step, the solvent is removed from the liquid composition under at least one condition selected from the following conditions (1) and (2). That is, in the present invention, appropriate crosslinking by aldehydes can be realized by adjusting the maximum reaching temperature α and the heat quantity parameter β to the following ranges as the heat history of the hydrophobized HEC.

Condition (1): Maximum reached temperature α of hydrophobized HEC is less than 65 ° C. Condition (2): Calorific parameter β calculated from the temperature of hydrophobized HEC and heating time is 2500 ° C. · min or less.

  Under the condition (1), the maximum reaching temperature α of the hydrophobized HEC may be less than 65 ° C., but it is easy to adjust the degree of crosslinking and excellent in productivity, for example, 20 ° C. or more and less than 65 ° C. Is about 25 to 63 ° C. (eg, 35 to 60 ° C.), and more preferably about 40 to 55 ° C. (particularly 45 to 50 ° C.).

  In the present specification and claims, the maximum temperature α means a temperature at which the surface temperature of the hydrophobized HEC (hereinafter referred to as “material temperature”) becomes the highest in the drying step. The product temperature of the hydrophobized HEC can be determined, for example, by measuring the temperature inside the hydrophobized HEC assembly using a temperature sensor such as a thermometer or a thermocouple.

  In the condition (2), the heat quantity parameter β of the hydrophobized HEC may be 2500 ° C. · min or less, but from the viewpoint of easy adjustment of the degree of crosslinking and excellent productivity, for example, 30 to 2500 ° C. · min, The thermal energy parameter β may be preferably 50 to 2000 ° C. · min, more preferably 75 to 1500 ° C. · min (especially 300 to 1000 ° C. · min), and further, if the maximum reaching temperature α is a lower value. The degree of crosslinking and the productivity can be highly compatible, and may be, for example, about 1500 to 2500 ° C. · min (in particular, about 2000 to 2500 ° C. · min).

In the present specification and claims, the calorific parameter β is a parameter calculated as the product of temperature and time, and the time is the time after the material temperature of the hydrophobized HEC reaches 40 ° C. or more. The temperature is a temperature obtained by subtracting 40 ° C. from the substance temperature of the hydrophobized HEC. Typically, the thermal parameter β is:
β = ∫ a _̃b {f (t) −40} dt
It can be calculated by In the above equation, f (t) is the product temperature T (° C.) of the hydrophobized HEC in the drying step as the ordinate and the time t (min) as the abscissa, the product temperature T of the hydrophobized HEC Is a function that indicates the transition of Reference symbols a to b denote integration intervals, which are intervals when the product temperature T of the hydrophobized HEC is 40 ° C. or higher. That is, in the section a ≦ t ≦ b when the product temperature T of the hydrophobized HEC is 40 ° C. or higher, the area of the portion surrounded by the functions T = f (t) and T = 40 is the heat quantity parameter β Calculated as

  In the present invention, when either of the conditions (1) and (2) is satisfied, and the condition (1) is satisfied, the heat quantity parameter β is, for example, over 2500 ° C. · min and 6000 ° C. ··· The temperature may be about min, preferably about 2800 to 5000 ° C. · min, more preferably about 3000 to 4500 ° C. · min, and conversely, when the condition (2) is satisfied, the maximum reach temperature α is, for example, 65 to 150 C., preferably 70 to 120.degree. C., and more preferably 80 to 120.degree. C., but both conditions (1) and (2) should be satisfied in terms of highly compatible control of crosslinking and productivity. It is particularly preferred to satisfy.

  In the drying step, the proportion of water in the heat-treated hydrophobized HEC (water content) is less than 20% by weight (eg, 10% by weight or less, preferably 5% by weight or less, more preferably 1% by weight or less) You can adjust it to In addition, the hydrophobized HEC may be subjected to processing such as classification, pulverization and the like, as necessary. In the present specification and claims, the water content in the hydrophobized HEC can be measured using the loss on drying method.

[Hydrophobicized hydroxyethyl cellulose or grinding aid]
In the hydrophobized HEC obtained by the above method, the proportion of water in the hydrophobized HEC (water content) is less than 20% by weight (for example, 10% by weight or less, preferably 5% by weight or less, more preferably 1% by weight or less) For example, it is about 0.01 to 18% by weight, preferably 0.1 to 15% by weight, and more preferably 0.3 to 10% by weight (particularly 0.5 to 5% by weight).

  The hydrophobized HEC is hydrophobized with aldehydes, and the proportion of aldehydes (particularly dialdehyde such as glyoxal) in the hydrophobized HEC may be 0.3% by weight or less, for example, 0.03 to It is about 0.25 wt%, preferably about 0.05 to 0.2 wt%, and more preferably about 0.08 to 0.15 wt% (particularly about 0.1 to 0.13 wt%). If the proportion of aldehydes is too small, the degree of crosslinking may be too small to cause lumps in water. On the contrary, if the proportion is too large, the degree of crosslinking may be too large to lower the solubility in water. . In the present specification and claims, the proportion of aldehydes can be evaluated by measuring the absorbance of a compound derivatized with hydrazine with a spectrophotometer.

  The hydrophobized HEC can be selected from the range of an average molar substitution (MS) of ethylene oxide of about 1.5 to 7, for example, 1.55 to 6, preferably 1.6 to 5, and more preferably 1.7. It is about -3 (especially 1.8-2.5). If the MS is too small, the solubility in water may be reduced, and on the contrary, if the MS is too large, the solubility in water may be too large to result in lumps in water. In the present specification and claims, MS can be measured using a nuclear magnetic resonance apparatus (NMR).

  The average molar degree of substitution (DS) of the hydrophobized HEC is, for example, about 0.5 to 2.5, preferably about 1 to 2, more preferably about 1.1 to 1.6 (particularly about 1.2 to 1.4). It is. If the DS is too small, the solubility in water may be too large to cause lumps in water. On the other hand, if it is too large, the solubility in water may be reduced. In the present specification and claims, DS can be measured using a nuclear magnetic resonance apparatus (NMR).

The weight average molecular weight (Mw) of the hydrophobized HEC is, for example, 3 × 10 ⁴ to 200 × 10 ⁴ , preferably 5 × 10 ⁴ to 70 × 10 ⁴ , and more preferably 10 × 10 ⁴ to 50 × 10 ⁴ It is about 20 × 10 ⁴ to 30 × 10 ⁴ ). By decreasing the upper limit of the Mw of the hydrophobized HEC, the dispersibility in the polishing composition is improved. By increasing the lower limit value of Mw, the hydrophilicity is enhanced, and the wettability of the polished surface can be improved. In the present specification and claims, Mw can be measured in terms of polyethylene oxide (water system) in gel permeation chromatography (GPC).

  The viscosity (25 ° C.) of the hydrophobized HEC in a 1% by weight aqueous solution is, for example, 2000 cps or less, for example, 1 to 1000 cps, preferably 3 to 500 cps (eg 5 to 300 cps), more preferably 10 to 100 cps (especially 20 to 20 cps) 60 cps). If the viscosity is too high, the solubility in water may be reduced. In the present specification and claims, the viscosity can be measured using a B-type viscometer.

[Abrasive assistant and polishing method]
The hydrophobized HEC is appropriately crosslinked and dissolves in water without being damaged, and may be used as a polishing aid for polishing an object in combination with abrasive grains in water.

  As the abrasive grains, conventional abrasive grains can be used, which may be organic particles or inorganic particles, but inorganic particles are generally used. As the inorganic particles, silica particles, alumina particles, cerium oxide particles, chromium oxide particles, titanium dioxide particles, zirconium oxide particles, magnesium oxide particles, manganese dioxide particles, zinc oxide particles, oxide particles such as bengara particles; silicon nitride particles And nitride particles such as boron nitride particles; carbide particles such as silicon carbide particles and boron carbide particles; diamond particles; and carbonates such as calcium carbonate and barium carbonate. Among these, silica particles are generally used in semiconductor substrates such as silicon wafers. The average particle size of the abrasive may be 5 nm or more, and is, for example, about 5 to 100 nm, preferably about 10 to 80 nm, and more preferably about 20 to 50 nm.

  In the polishing using the abrasive grains and the abrasive grain assistant, the body to be polished is usually polished using a polishing composition containing the abrasive grains, the abrasive grain adjuvant and water as a polishing liquid. The proportion of abrasive grains is about 0.01 to 10% by weight (particularly 0.1 to 1% by weight) in the composition. The proportion of the abrasive grain assistant is about 0.0001 to 1% by weight (especially 0.01 to 0.1% by weight) in the composition.

  The polishing composition contains, in addition to the abrasive grains, abrasive grain assistant and water, conventional grinding assistants or additives, such as basic compounds, water-soluble polymers, surfactants, chelating agents, organic acids, organic acids, etc. Acid salts, inorganic acids, inorganic acid salts, preservatives, fungicides and the like may be included.

  The polishing composition can be used to polish an object to be polished having various materials and shapes. The material of the polishing body is, for example, a metal or semimetal such as silicon, aluminum, nickel, tungsten, copper, tantalum, titanium, stainless steel, etc. or an alloy thereof; glassy such as quartz glass, aluminosilicate glass, glassy carbon, etc. Substances: Ceramic materials such as alumina, silica, sapphire, silicon nitride, tantalum nitride and titanium carbide; Compound semiconductor substrate materials such as silicon carbide, gallium nitride and gallium arsenide; Resin materials such as polyimide resin and the like. Among these, silicon is generally used.

  The polishing method may be a conventional method, and for example, polishing may be performed using a polishing pad of a foamed polyurethane type, non-woven type, suede type or the like in the presence of a polishing liquid.

  The present invention will be described in more detail based on examples given below, but the present invention is not limited by these examples.

Synthesis example of undried hydrophobized HEC To a heating and cooling jacketed 5L separable flask equipped with a dropping funnel, a cooling condenser, and a stirrer, add 3.3 L of tertiary butyl alcohol, 0.02 L of water, and 67 g of sodium hydroxide. The mixed solution was mixed with 244 g of wood pulp with an intrinsic viscosity of 370 ml / g (3.7 dl / g), and subjected to an alcification reaction under stirring at 20 ° C. for 60 minutes. In addition, in order to maintain the liquid temperature in a flask in a predetermined | prescribed range during this reaction, cold water or warm water was suitably supplied to the jacket (following the same).

  In addition, the intrinsic viscosity of the said pulp was measured based on JISP8215: 1998 A method.

  After the alcification reaction, 0.23 L of ethylene oxide is added dropwise from the dropping funnel over 15 minutes while keeping the solution temperature in the flask at 20 to 25 ° C. under stirring, and the temperature is raised after the dropping is completed, Heating and stirring were continued at 75 ° C. for 3 hours. Thereafter, the temperature in the flask was cooled to 25 ° C. with stirring, and the reaction slurry was neutralized to pH 4.7 with 67.5% nitric acid.

  After neutralization, 2.5 mL of glyoxal was added to the reaction mixture and stirred for 50 minutes while maintaining the temperature in the flask at 20 to 25 ° C. The reaction slurry was wrapped with a filter cloth and drained.

  Put the drained hydrophobized HEC into a 5 L polypropylene hand-made beaker (size ID 19 cm × 27 cm), add water / acetone mixed solution (concentration: about 90% solution of acetone, liquid volume: about 3.0 L) and add polytetrafluoroethylene The mixture was stirred for 20 minutes at a rotational speed of 350 rpm with a stirring rod (diameter 8 mm × length 400 mm) coated with (PTFE), and the solution was drained in the same manner as described above. This washing and draining operation was repeated twice in total to obtain undried HEC. The volatile content of the wet hydrophobized HEC was about 50% by weight, as measured with a halogen moisture meter ("HG53" manufactured by METTLER TOLEDO).

Example 1 (Production of dry hydrophobized HEC)
The undried hydrophobized HEC obtained in the synthesis example was dried as follows. The drying time was adjusted so that the moisture content of HEC after drying was 5% by weight or less (the same applies hereinafter).

  Put 100 g of undried, hydrophobized HEC in a stainless steel vat (30 cm wide x 23 cm wide x 5.5 cm high) and heat it under normal pressure at a drying temperature (dry) in a shelf-type drier (product number: SPH-301S manufactured by Espec) The in-machine temperature was kept at 50 ° C. and heated for 170 minutes. Thereafter, the heating of the tray dryer was stopped, and left as it was, and cooled to normal temperature. Next, the dried HEC was crushed by a small grinder (“Force Mill FM-1” manufactured by Osaka Chemical Co., Ltd.) to obtain a dry hydrophobized HEC having a water content of 3.0% by weight.

  The weight average molecular weight (Mw), the average molar substitution degree (MS) of ethylene oxide, the average molar substitution degree (DS), the glyoxal content, and the viscosity of a 1% by weight aqueous solution of the obtained dry hydrophobized HEC were measured as follows: did.

(Weight average molecular weight)
As a result of measuring Mw of hydrophobized HEC by GPC method under the following measurement conditions, it was 27.5 × 10 ⁴ .

Analyzer: "20A" manufactured by Shimadzu Corporation
Column: "TSKgel GMPWxl × 2" manufactured by Tosoh Corporation
Column temperature: 35 ° C
Eluent: 0.1 M NaCl aq.
Flow rate: 0.6 mL / min
Detection: "RID-20A (35 ° C) Porrarity (+)" manufactured by Shimadzu Corporation
Injection volume: 50 μL
Sample concentration: 0.1% by weight (dissolved in 3 mg / 3 ml ultrapure water overnight, filtered with 0.2 μm filter after addition of 17 mg NaCl, n = 2 prepared, n = 1 measured)
Standard sample: Easi Vial PEG.

(Average molar substitution degree and average molar substitution degree of ethylene oxide)
As a result of measuring MS and DS of hydrophobized HEC by NMR under the following measurement conditions, MS was 2.25 and DS was 1.32.

Device: AVANCE 600
Probe: 10mm BBO
Pulse program: zgig 45 (45 ° pulse, no NOE)
Temperature: Room temperature Integration number: 2500 times Wait time: 20s
_Solvent: D 2 O.

(Glyoxal content)
As a result of measuring the glyoxal content of hydrophobized HEC by the following method, it was 0.11% by weight.

1) Dissolution of hydrophobized HEC 0.2 g of hydrophobized HEC was placed in a 100 mL measuring flask, and 0.1 N hydrochloric acid was added to make up to 100 mL.

2) Determination of Glyoxal The solution obtained in 1) was reacted with 2,4-dinitrophenylhydrazine to be derivatized and quantified by measuring absorbance with a spectrophotometer. Specifically, it was performed according to the following reference. However, an aqueous solution of dimethylsulfoxide and an alkaline solution (an aqueous solution of potassium hydroxide in ethanol) of a solvent of 2,4-dinitrophenylhydrazine were replaced with a pyridine solution of diethanolamine.

(References)
Susumu Honda, Kazuaki Kakehi, Hidetaka Yuki, Kiyoshi Takiura, Analytica Chimica Acta Volume 74, Issue 1, January 1975, Pages 67-73
Periodate oxidation analysis of carbohydrates: Part I. Spectrophotometric determination of glyoxal in dialyzed fragments formed from glycosides with 2,4-dinitrophenylhydrazine.

(1 wt% aqueous solution viscosity)
The viscosity of a 1% by weight aqueous solution of hydrophobized HEC was measured at 30 revolutions at 25 ° C. using a Brookfield viscometer, and was 40 cps.

  The maximum temperature α and the heat quantity parameter β were measured by the following method.

(How to measure the maximum achievable temperature α)
Place 350 g of undried, hydrophobized HEC in a stainless steel vat (30 cm wide × 23 cm wide × 5.5 cm high) to form a layer of about 3-5 cm. Into a tray drier (product number: SPH-301S manufactured by Espec, Inc.), the Stensless bat containing the undried, hydrophobized HEC is placed to start drying. The temperature of the HEC component during drying was measured by inserting a thermocouple into the HEC layer so that it could be measured at all times. It dried until the moisture of HEC became 5% or less, and made the maximum temperature of the material temperature in the meantime the maximum attainment temperature alpha.

(Method of measuring heat quantity parameter β)
Create a graph with the product temperature T (° C) of the hydrophobized HEC at the time of drying the above-mentioned undried hydrophobized HEC as the ordinate and the time t (min) as the abscissa, and the product temperature T of the hydrophobized HEC is 40 ° C The area of the above section was calculated, and the area (° C. · min) was used as the heat quantity parameter β.

Examples 2 to 6 and Comparative Examples 1 to 2
A dry hydrophobized HEC was obtained in the same manner as in Example 1 except that the heating temperature and time were changed to the heating temperature and time shown in Table 1.

  The silicon wafer was polished by the following method using the dry and hydrophobized HEC obtained in Examples and Comparative Examples as a polishing aid, and the defects on the surface of the silicon wafer were measured. The results are shown in Table 1.

<Preliminary polishing process>
A preliminary polishing composition was prepared containing 0.95% by weight of abrasive grains and 0.065% by weight of a basic compound, with the balance being water. As the abrasive grains, colloidal silica having an average primary particle diameter of 35 nm was used. Potassium hydroxide was used as a basic compound.

  Using this preliminary polishing composition as it was as a polishing solution (working slurry), a silicon wafer as a polishing target was polished under the following preliminary polishing conditions. As a silicon wafer, a commercially available silicon single crystal wafer 300 mm in diameter (conductive type: P type, crystal orientation: <100>, resistivity: 1 Ω · cm or more and less than 100 Ω · cm, COP free) having a diameter of 300 mm after lapping and etching is used did.

(Preliminary polishing conditions)
Polishing device: Sheet-fed polishing machine manufactured by Okamoto Machine Tool Mfg. Co., Ltd., model "PNX-332B"
Polishing load: 12kPa
Plate rotation speed: 50 rpm
Carrier rotation speed: 50 rpm
Polishing pad: manufactured by Fujibo Ehime, product name "FP55"
Polishing fluid supply rate: 1 liter / min Polishing fluid temperature: 20 ° C.
Plate surface cooling water temperature: 20 ° C
Polishing time: 6 minutes.

<Preparation of Polishing Composition and Finishing Polishing>
The dry hydrophobized HEC obtained in Examples and Comparative Examples, abrasive grains, a basic compound, and water were mixed to prepare a polishing composition. As abrasive grains, silica particles having an average primary particle diameter of 35 nm were used. Ammonia was used as the basic compound. The content of abrasive grains in the polishing composition was 9% by weight, the content of dry hydrophobized HEC was 0.86% by weight, and the content of ammonia was 0.09% by weight. In the polishing composition of each example, the drying temperature (the set temperature of the drying furnace), the maximum reaching temperature α, the drying time, the calorific parameter β and the water content of the dry hydrophobized HEC used are shown in Table 1. The material temperature of the dry and hydrophobized HEC and the maximum reaching temperature α are measured by the above-mentioned method using a thermometer. The heat quantity parameter β is obtained from the temperature and time of the hydrophobized cellulose derivative in the drying step according to the above-mentioned method. Also, the water content is a value measured using a loss on drying method. Specifically, 1.0 g of hydrophobic cellulose was dried at 105 ° C. for 1 hour, and calculated from the weight loss after drying.

  Using the polishing composition diluted 20 times with water as a polishing solution, the silicon wafer after the preliminary polishing step was polished under the following finish polishing conditions.

(Finish polishing conditions)
Polishing device: Sheet-fed polishing machine manufactured by Okamoto Machine Tool Mfg. Co., Ltd., model "PNX-332B"
Polishing load: 15kPa
Plate rotation speed: 50 rpm
Carrier rotation speed: 50 rpm
Polishing pad: Fujibo Ehime Co., Ltd. polishing pad, trade name "POLYPAS 27NX"
Polishing fluid supply rate: 2 liters / minute Polishing fluid temperature: 20 ° C.
Plate surface cooling water temperature: 20 ° C
Polishing time: 8 minutes.

The silicon wafer after polishing is removed from the polishing apparatus and washed with a cleaning solution of NH ₄ OH (29%): H ₂ O ₂ (31%): deionized water (DIW) = 1: 3: 30 (volume ratio) (SC-1 wash). More specifically, two cleaning baths provided with an ultrasonic oscillator with a frequency of 950 kHz are prepared, the cleaning bath is stored in each of the first and second cleaning baths, and kept at 60 ° C. Immerse the silicon wafer in the first cleaning tank for 6 minutes, then pass through the rinse tank with ultrapure water and ultrasonic waves, and immerse it in the second cleaning tank for 6 minutes with the ultrasonic oscillator activated, isopropyl alcohol (IPA) It pulled up to atmosphere and was made to dry.

<Evaluation>
The following evaluation was performed about the silicon wafer obtained by said each example.

(Defect count measurement)
The number of defects present on the surface (polished surface) of the silicon wafer was measured for defects of 37 nm or more using a wafer inspection apparatus (manufactured by KLA Tencor Corporation, trade name “Surfscan SP2XP”). The number of defects measured is shown in Table 1.

  As shown in Table 1, the silicon wafers polished with hydrophobized HEC obtained in Examples 1 to 6 have surface defects more than the silicon wafers polished with hydrophobized HEC obtained in Comparative Examples 1 and 2 There were few.

  The hydrophobized hydroxyethyl cellulose obtained by the method of the present invention can be used for various applications such as, for example, dispersants, thickeners, emulsion polymerization stabilizers, protective colloids, paints, cosmetics, water retention agents, pharmaceutical preparations and the like. In particular, since the content of insoluble matter in the form of an aqueous composition is small, it is useful as a polishing aid for applications requiring fine processing, for example, a semiconductor substrate (for example, a substrate formed of silicon wafer, silicon carbide, etc.) is there.

Claims (12)

A step of reacting hydroxyethyl cellulose with aldehydes in the presence of a solvent to obtain hydrophobized hydroxyethyl cellulose and a composition comprising the solvent, at least one of conditions selected from the following conditions (1) and (2): A method for producing hydrophobized hydroxyethyl cellulose, comprising a drying step of removing the solvent from the composition to obtain hydrophobized hydroxyethyl cellulose.
Condition (1): Maximum reaching temperature α of hydrophobized hydroxyethyl cellulose is less than 65 ° C. Condition (2): Calorific parameter β calculated from temperature and heating time of hydrophobized hydroxyethyl cellulose is 2500 ° C. · min or less   The method according to claim 1, wherein the hydrophobized hydroxyethyl cellulose obtained in the hydrophobization step is subjected to a drying step without hydrolysis.   The method according to claim 1 or 2, wherein the proportion of aldehydes is 1 part by weight or less with respect to 100 parts by weight of hydroxyethyl cellulose.   The method according to any one of claims 1 to 3, wherein the aldehyde is a dialdehyde.   The process according to claim 4, wherein the aldehyde is glyoxal.   As a step prior to the hydrophobization step, cellulose having an intrinsic viscosity of 2 to 6 dl / g is subjected to acelation, the produced alkali cellulose is reacted with ethylene oxide, and the resulting reaction mixture containing hydroxyethyl cellulose is neutralized to form hydroxyethyl cellulose. The method according to any one of claims 1 to 5, further comprising a step.   A polishing aid for polishing an object to be polished in combination with abrasive particles, comprising: hydrophobized hydroxyethyl cellulose hydrophobized with aldehydes and containing said aldehydes in a proportion of 0.3% by weight or less Agent.   The polishing aid according to claim 7, wherein the ratio of insolubles to water in the hydrophobized hydroxyethyl cellulose is 1000 ppm by weight or less. The polishing aid according to claim 7 or 8, wherein the weight average molecular weight of the hydrophobized hydroxyethyl cellulose is 3 × 10 ^{4 to} 100 × 10 ⁴ .   The grinding aid according to any one of claims 7 to 9, wherein the average degree of substitution of the hydrophobized hydroxyethyl cellulose is 0.5 to 2.5.   The polishing aid according to any one of claims 7 to 10, wherein the water content of the hydrophobized hydroxyethyl cellulose is 10% by weight or less.   The polishing assistant according to any one of claims 7 to 11, wherein the viscosity at 25 ° C in a 1% by weight aqueous solution of hydrophobized hydroxyethyl cellulose is 2000 cps or less.