JP2012253105A - Cutting liquid for silicon ingot slice - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide cutting liquid for a silicon ingot slice capable of making surface precision of a wafer excellent by reducing cutting resistance, and capable of suppressing corrosion or hydrogen generation of wire and a device.SOLUTION: Cutting liquid for a silicon ingot slice is used, containing organic reducing agent (A) and water as essential components, and having pH of 4.0 to 8.0 in usage.

Description

The present invention relates to a cutting fluid used when a silicon ingot is cut (sliced) using a fixed abrasive wire saw.
More specifically, the present invention relates to a cutting fluid capable of improving wafer surface accuracy by reducing resistance with a wire during cutting.

Conventionally, a wire saw has been used when cutting a silicon ingot.
Cutting with a wire saw includes a fixed abrasive method using a wire in which abrasive grains are fixed by electrodeposition or the like, and a free abrasive method using a slurry in which abrasive particles are dispersed in a cutting fluid. Fixed-abrasive methods have become widespread due to the advantage of reducing the amount of grains used.
In recent years, in order to reduce costs, it is required to further reduce the thickness of the wafer and reduce the kerf loss. However, in order to reduce the thickness of the wafer and reduce the kerf loss, it is necessary to improve surface accuracy such as suppressing the generation of scratches and improving the flatness.
Accordingly, resistance at the time of cutting using an acid component (for example, Patent Document 1) such as nitric acid and hydrofluoric acid or using an alkali component (for example, Patent Document 2) such as sodium hydroxide using an etching action on silicon. There has been proposed a cutting fluid that improves the surface accuracy of a wafer by reducing.

However, in etching with an acid component, corrosion of a wire or an apparatus has been a problem. On the other hand, in etching with an alkaline component, hydrogen is easily generated due to a reaction between silicon and water, and the risk of ignition has been a problem.

JP-A-2005-12917 JP 2008-103690 A

  Accordingly, the present invention provides a cutting fluid for silicon ingot slicing that can improve the surface accuracy of the wafer by reducing the cutting resistance and can suppress the corrosion of the wire and the device and the generation of hydrogen. With the goal.

The inventors of the present invention have reached the present invention as a result of studies to achieve the above object.
That is, the present invention is a cutting fluid for silicon ingot slice characterized by containing an organic reducing agent (A) and water as essential components and having a pH of 4.0 to 8.0 during use.

The cutting fluid of the present invention can obtain a wafer with higher surface accuracy in the cutting process of silicon ingots than in the past.
Moreover, problems such as corrosion of the apparatus and generation of hydrogen do not occur.

The cutting fluid of the present invention is a cutting fluid characterized by containing an organic reducing agent (A) and water as essential components and having a pH of 4.0 to 8.0 when used.

In the present invention, the organic reducing agent refers to an organic compound that reduces other chemical species in an oxidation-reduction reaction.
Examples of the organic reducing agent (A) include reducing phenol compounds (A1), reducing reductones (A2) and esters or salts thereof, reducing sugars (A3), reducing sugar alcohols (A4). ), Reducing organic acids (A5) and esters or salts thereof, reducing aldehydes (A6), reducing amine (A7) and salts thereof, and the following can be exemplified.

Examples of the reducing phenol compound (A1) include monohydric phenols and polyphenols.
Examples of the monohydric phenol include 3-hydroxyflavone and tocopherol (such as α-, β-, γ-, δ-, ε-, or η-tocopherol).
Examples of polyphenols include gallic acid (3,4,5-trihydroxybenzoic acid), pyrocatechol, resorcinol, hydroquinone, naphthoresorcinol, pyrogallol and phloroglucinol.
Of these, gallic acid is preferred.

Examples of the reducing reductones (A2) include L-ascorbic acid, isoascorbic acid and esters thereof (L-ascorbic acid sulfate, L-ascorbic acid phosphate, L-ascorbic acid 2-glucoside, L- Ascorbic acid palmitic acid ester, tetraisopalmitic acid L-ascorbyl, ascorbic acid isopalmitate, erythorbic acid, erythorbic acid phosphoric acid ester, erythorbic acid palmitic acid ester, tetraisopalmitic acid erythovir) and salts thereof.
Of these, L-ascorbic acid is preferred.

  Examples of the reducing sugar (A3) include glucose, mannose, galactose, maltose, and lactose.

Examples of the reducing sugar alcohol (A4) include arabitol, adonitol, xylitol, sorbitol, mannitol, dulcitol and the like.

  Reducing organic acids (A5) and salts thereof include ketoglutaric acid, gluconic acid, ketogulonic acid, formic acid, succinic acid, lactic acid, malic acid, butyric acid, maleic acid, 2-oxopropanoic acid, malonic acid and these Salt.

Examples of reducing aldehydes (A6) include formaldehyde, acetaldehyde, propionaldehyde and vinyl aldehyde, benzaldehyde and cinnamaldehyde.

Examples of the reducing amine (A7) include alkylamines, alkanolamines, alkylenediamines, cyclic amines, aromatic amines, amidine compounds, poly (n = 2 to 5) alkylene (carbon number 2 to 6) poly (n = 3). -6) amines and the like.

  Among these organic reducing agents (A), from the viewpoint of wafer surface accuracy, reducing phenolic compounds (A1), reducing reductones (A2), reducing sugars (A3), reducing sugar alcohols. (A4) and a reducing organic acid (A5) are preferable, and a reducing phenol compound (A1) and reducing reductones (A2) are more preferable.

Specifically, gallic acid, ascorbic acid, glucose, arabitol, formic acid, citric acid, and salts thereof are preferable, and gallic acid and ascorbic acid are particularly preferable.
In addition, (A) may be used independently and may use 2 or more types together.

  The content of the organic reducing agent (A) in use in the cutting fluid of the present invention is 0.0001 to 10% by weight, and preferably 0.001 to 1% by weight from the viewpoint of flatness.

  Examples of water that is another essential component of the cutting fluid of the present invention include ultrapure water, ion exchange water, RO water, distilled water, and tap water, but are not particularly limited.

The cutting fluid of the present invention may further contain a lubricant and a viscosity modifier.
Examples of the lubricant include caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid and the like.
The content of the lubricant is usually 0.01 to 10% by weight, preferably 0.01 to 1% by weight, more preferably 0.01 to 0.5% by weight, out of 100% by weight of the cutting fluid. . If it is less than 0.01% by weight, the lubricity is insufficient, and if it exceeds 10% by weight, the antifoaming property is insufficient.

  Examples of the viscosity modifier include polyethylene glycol, ethylene glycol, diethylene glycol, propylene glycol, glycerin and the like.

  The cutting fluid of the present invention is suitably used when slicing a silicon ingot with a wire saw, and a wafer with high surface accuracy can be obtained after slicing.

Examples of a method for slicing a silicon ingot include a method using free abrasive grains and fixed abrasive wires. The cutting fluid of the present invention can be used by either method, but is particularly suitable for sizing processing of a silicon ingot using a fixed abrasive wire.

  Examples of electronic materials manufactured using a silicon wafer manufactured by slicing a silicon ingot using the cutting fluid of the present invention include a memory element, an oscillation element, an amplifying element, a transistor, a diode, a CCD, a solar cell, and an IC. LSI and the like.

  Hereinafter, although an example and a comparative example explain the present invention further, the present invention is not limited to these. Hereinafter, unless otherwise specified, “%” represents “% by weight” and “parts” represents “parts by weight”.

  The cutting fluids of Examples 1 and 2 and Comparative Examples 1 to 3 were prepared by blending in the number of parts described in Table 1.

About the obtained cutting fluid, the measurement of pH, the surface roughness of a wafer, scratch suppression, a friction coefficient, corrosion resistance, and reaction suppression evaluation by the amount of hydrogen generation were evaluated. The results are shown in Table 1.
The pH at 25 ° C. was measured with a pH meter.

<Evaluation of wafer surface roughness>
A commercially available 25 mm square single crystal silicon ingot is used as the material to be cut, using a fixed abrasive wire, single wire saw type cutting machine “850” (manufactured by SOUTH BAY TECHNOLOGY), cutting fluid flow rate is 50 ml / min, SPEED CONTROL The cutting test was performed under the cutting conditions of No. 3.
The wafer surface roughness (Ra) after cutting was measured by using an atomic force microscope “E-Sweep” (manufactured by SII Nanotechnology Inc.).

The surface roughness was evaluated according to the following criteria.
○: Ra is less than 0.5 μm Δ: Ra is 0.5 μm to 0.8 μm
×: Ra is 0.8 μm or more

<Evaluation of scratch>
Using a laser microscope “VK-8700” (manufactured by Keyence Co., Ltd.), the scratches generated in the range of 270 × 202 μm were observed at a magnification of 50 times for the three wafers using a laser microscope “VK-8700” (made by Keyence Corporation) . The total number of scratches at the three locations was evaluated according to the following criteria.
○: 0 to 3 △: 4 to 7 ×: 8 or more

<Evaluation of corrosion resistance>
(1) Preparation of object to be plated An iron test piece (trade name: “SPCC-SD test piece”, manufactured by Partec Co., Ltd., thickness: 0.6 mm) was cut into a length of 2.0 cm and a width of 0.8 cm to obtain a metal. The surface was polished with a sandpaper (trade name: Wetdry Tri-M-ite Paper # 1000, manufactured by 3M), and then subjected to immersion cleaning with a 200 kHz ultrasonic cleaner (ion-exchanged water, 25 ° C., 5 minutes). Then, it was made to dry with nitrogen stream and the to-be-plated object was created.

(2) Preparation of test pieces for metal plating Prepared with a blending number of 18 parts by weight of nickel sulfate hexahydrate, 3.5 parts by weight of nickel chloride hexahydrate, 2 parts by weight of boric acid and 76.5 parts by weight of ion-exchanged water. A metal plating test piece was prepared by weighing 50 g of the metal plating solution in a 50 ml beaker, immersing the object to be plated, and conducting electroplating by applying electricity at a cathode current density of 0.44 mA / cm ³ for 10 minutes. .

(3) Evaluation of corrosion resistance after plating A metal plating product was immersed in 50 g of each cutting fluid, and this was left to stand for 48 hours in a thermostat set at 50 ° C.
Then, the surface of the taken-out test piece was observed visually, and corrosion resistance was evaluated by the following criteria.

○: Plating is not peeled Δ: Plating is peeled off by 1-30% ×: Plating is peeled off by 30% or more

<Evaluation of reaction inhibition by hydrogen generation amount>
10 g of silicon powder (purity 99%, average particle size 1 μm) is added to 100 g of each cutting fluid, and stirred for 15 minutes at 5000 rpm using a homomixer (TK-ROBOMICS manufactured by Tokushu Kika Kogyo Co., Ltd.). To obtain a slurry.
Transfer the resulting slurry to a glass sample bottle, place a rubber stopper through a glass tube and leave it in a constant temperature bath at 60 ° C. for 72 hours, and collect the hydrogen generated during this period in a graduated cylinder by the water displacement method. The amount of hydrogen generation was measured.

Evaluation of reaction inhibition was performed according to the following criteria.
○: Hydrogen gas generation amount is less than 30 ml Δ: Hydrogen gas generation amount is 30-60 ml
×: Hydrogen gas generation amount is 60 ml or more

The cutting fluids of Examples 1 and 2 of the present invention all had excellent flatness, a small friction coefficient, excellent corrosion resistance, and almost no hydrogen gas was generated.
On the other hand, Comparative Example 1 using an inorganic reducing agent instead of an organic reducing agent has insufficient surface roughness and scratch suppression.
Further, Comparative Example 2, which uses acid etching while lowering the pH, has not only low corrosion resistance but also insufficient surface roughness and scratch suppression.
On the other hand, Comparative Example 3 using an alkali etching with a raised pH not only has a low hydrogen generation reaction suppression property, but also has a poor surface roughness and scratch suppression property.

The cutting fluid of the present invention is useful as a cutting fluid used when cutting a silicon ingot because the surface accuracy of a wafer obtained by slicing is excellent.
The cutting fluid of the present invention is also useful for cutting glass or the like that may corrode or dissolve depending on pH.
Examples of electronic materials manufactured using a silicon wafer manufactured by slicing a silicon ingot using the cutting fluid of the present invention include a memory element, an oscillation element, an amplifying element, a transistor, a diode, a CCD, a solar cell, and an IC. LSI, and the like can be used for, for example, displays, personal computers, mobile phones, digital cameras, portable music players, and the like.

Claims (6)

A cutting fluid for silicon ingot slice, which contains an organic reducing agent (A) and water as essential components, and has a pH of 4.0 to 8.0 when used. The cutting fluid for silicon ingot slice according to claim 1, wherein the organic reducing agent (A) is at least one selected from the group consisting of a phenol compound (A1) and a reductone (A2). The cutting fluid for silicon ingot slice according to claim 1, wherein the organic reducing agent (A) is at least one selected from the group consisting of gallic acid, ascorbic acid, glucose, arabitol, formic acid and citric acid. The manufacturing method of a silicon wafer including the process of cut | disconnecting a silicon ingot by a fixed abrasive using the cutting fluid for silicon ingot slices in any one of Claims 1-3. A silicon wafer produced by slicing a silicon ingot using the silicon ingot slicing cutting fluid according to claim 1. An electronic material manufactured using the silicon wafer according to claim 5.