WO2011116956A1

WO2011116956A1 - Fluid separating media and use thereof

Info

Publication number: WO2011116956A1
Application number: PCT/EP2011/001453
Authority: WO
Inventors: Beate Bussemer; Christine Fugger; Thomas Schmiady
Original assignee: Schott Solar Ag
Priority date: 2010-03-23
Filing date: 2011-03-23
Publication date: 2011-09-29
Also published as: DE102010015111A1

Abstract

The invention relates to a fluid for sawing of brittle hard material blocks in particular using multi-wire saws. The fluid contains at least one basic glycol of the general formula HO-[ (CH₂-)_x-O]_n-H, where n denotes a whole number from 1-14 and x denotes 1, 2, 3 or 4, as well as optionally further additives. The fluid is characterised by an additional content of at least one glycol etherified with an alkyl group and having the general formula HO-[ (CH₂-)_a-O]_b-R, where a denotes 1, 2, 3 or 4 and b is a whole number from 1-10 and R represents a linear or branched alkyl group having 1-8 carbon atoms and is substantially anhydrous. Such a sawing fluid is suitable in particular for producing wafers, electronic components and photovoltaic cells.

Description

Fluide separation media and their use

The invention relates to improved fluid separation media, such as sawing fluids or slurries, in particular for sawing brittle-hard material blocks, and their use, in particular for the production of wafers, and

Photovoltaic elements.

Wafer, z. As those of silicon, serve as

Support plate for electronic components, in particular for semiconductor components and photovoltaic elements. They form the basis for the production of

Solar cells, which are further processed into ready-to-use solar modules. The wafers are obtained even by sawing multicrystalline block-shaped blocks, columns or bricks or monocrystalline, round or squared ingots, wherein the sawing usually takes place by means of wire saws, in which a plurality of parallel, closely

adjacent wires are moved at a sufficiently high speed along their longitudinal direction over the material to be sawn. Such

Wire saw is described for example in US-A 2006/0249134.

When sawing cutting or cutting tools, ie the saw wires, at least at the respective cutting point (cutting gap) brought into contact with a fluid separation medium, which inter alia to

Cooling the saw surface and the wire is used and therefore also referred to as Coolant. The fluid may optionally contain Abrasions- or abrasive particles and is therefore referred to as slurry. When using saw wires with bonded grain, the fluid usually contains none of these Abrasions- or

Abrasive particles.

In the former case, the abrasive particles contained in the slurry by the with large

Speed moving wire entrained and cause by their movement in the cutting gap

Chipping of brittle material in the cutting gap, which thereby constantly deepens and so to

Cutting the brittle starting body and the separation of the individual wafer slices leads.

In the second case are the hard ones

Abrasion particles, e.g. be made of diamond

can, tied on the surface of the

Sawing wire and chip by the rapid movement of the wire in the kerf brittle material, whereby the cutting gap is constantly deepening and thus leads to the severing of the brittle hard starting body and its severing in individual wafer slices. In both cases of the sawing process known as wafer sawing, different fluids are used

Used separation media whose liquid phase are also referred to only as fluid, coolant, sawing fluid or carrier fluid and z. B. from oil or

different glycols exist, which may additionally rheologically active agents may be added.

The proportion of the production costs of the silicon wafers amounts to approx. 55% of the total costs of the

Solar cell production, again with the largest portion of the costs associated with wafer production being associated with sawing alone. For example, the use of slurries accounts for approximately 10% to 15% of the total sawing process. By a

economical and ecological reprocessing of such spent slurries or coolants, therefore, the costs can be significantly reduced in the production of such wafers, especially when using slurries in the sawing process.

In addition, the use of such slurries or coolants in the production of silicon wafers will gain in importance in the future, because these determine whether the production of silicon wafers with low cutting loss or low

Energy consumption or high yield at high Surface quality of the wafers succeeds. The production of thin silicon wafers or sawing with a low cutting loss (kerf) is also desired in order to minimize the use of material as high as possible afern per Brick mass used

to produce.

The carrier fluids or

Carrier fluids usually differ, inter alia, by their viscosity. Frequently used carrier fluids are oil, and in particular glycols, such as PEG300, PEG400 or PEG200.

These carrier liquids also serve as a coolant and have mainly the task of the abrasion or the removal of material particles on the

Cutting edge in the kerf by friction absorb heat generated and transported away. In addition, they also serve to remove the chopped-off in the kerf material particles (Kerf) from this. In addition, they also serve as

Suspending agent and transport vehicle in the

Use of loose, unbound abrasion particles or cutting grains.

Since now such carrier liquids from the

Blocks, columns, bricks or ingots in the

Cutting gaps abraded or abgespanten Material particles (kerf) can only absorb in a limited amount, the used slurries or coolants must be replaced from time to time.

In addition, it has been shown that, in particular when sawing silicon blocks, the viscosity of the sawing liquid increases with increasing loading

abradierten or abgespanten material particles (kerf) increases sharply, resulting in an increase of

Energy consumption during sawing leads. At the same time, the generated heat of friction increases sharply, which in turn leads to an increase in energy consumption in the cooling of the Coolants or the slurry.

In addition, it has been shown that at the

Use of saw wires especially with increased loading of the slurry or the coolants with abradierten or abgespanten particles, the saw wires are deflected laterally, whereby wafers are obtained with non-constant thickness, which have no perfectly flat side surfaces but the sawing depths, also called saw marks , exhibit.

EP 1752521 AI describes an aqueous

Carrier fluid for abrasive particles. This aqueous carrier fluid contains glycols and glycol ethers in a ratio of 1: 1 to 99: 1 and 2-50% by weight of water. However, it has been shown that one of a

slurry produced by such carrier fluid Prolonged use undergoes a sudden increase in viscosity, ie "it tilts." Also, this slurry is then difficult to recycle and is therefore usually discarded.

In JP 2002-080883 A is a water-soluble

Carrier fluid for a wire saw which comprises 90-99,499% by weight of a water-soluble glycol,

water-soluble glycol ether and water-soluble

Glycol esters and up to 5 wt .-% of an organic acid and up to 5 wt .-% of an organic smectite. Such a fluid, which is mixed with water to the finished Sägeslurry, should a

show reduced hydrogen formation.

The invention therefore has for its object to provide a carrier fluid or sawing fluid, which avoids the aforementioned disadvantages and which, when used as a cooling component or wafer component in wafer sawing in addition to an increased wafer yield, has a prolonged service life and which energy needed in the production of wafers,

reduced. The invention also aims to provide a sawing fluid or a sawing slurry, which can be recycled many times and with which also after

can be sawed several times using good wafers. This also means that the Sägeslurry does not tip over prolonged use.

These goals are achieved by those in the claims

achieved defined characteristics.

In fact, it has been found that by adding glycols etherified with an alkyl radical to a carrier fluid containing one or more glycols and using this carrier fluid directly as a sawing fluid or coolant or to produce a slurry, not only the energy used for sawing is reduced can, but that also helps to cool the

Slurry or the Coolants necessary energy is reduced. The fluid is substantially free of water or has the lowest possible water content.

The sawing fluid therefore has a maximum of 5% by volume of water, which corresponds to about 4.24% by weight (about 1.13 g / cm ³ ), but typically contains less than 2% by weight of water. Usually, no water is added, ie the water content is produced only by

unavoidable entrainment with the

Starting materials and by entry on the

Humidity.

In addition, it has been found that with the procedure according to the invention, the load of the sawing fluid with kerf can be significantly higher, which drastically increases the service life of the coolant or the slurry. The fluid is substantially free of water or

has the lowest possible water content.

In particular, the sawing fluid contains less than 1.8% by weight or by weight of water, with water contents of less than 1.3 or less than 1% by weight being particularly preferred. Typical levels of water are less than 0.8 and 0.5 wt .-%, with very particular maximum water contents 0.3 or 0.2 wt .-% are preferred. In the unused state, the mixed sawing fluid from the components is down to a delivery specification-related water content of the components except for a minimum fraction of

typically max. 0.2 wt .-% free of water. This content increases during use due to entry of atmospheric moisture or entrainment in other ways. Especially on days or at locations with increased humidity increases the water content of the

Sawing fluids unintentionally during sawing, whereby the service life of the anhydrous or

low-water separating fluids or coolants or the slurry is reduced. Even in such unfavorable cases will be

Water contents of the sawing fluid or the liquid phase of the slurry of greater than or equal to 2 wt .-% by the addition of new unused fluids or recycled used Sägefluid or Slurrys or by

Influencing the environmental conditions during sawing deliberately excluded. In addition, with the sawing fluid or separating fluids according to the invention, the use of this sawing fluid in a slurry results in stain-free wafers or the like

Staining is greatly reduced. After all

can be sawn wafers even with strong

Rinse off silt easily with water.

The sawing fluid or separating fluid according to the invention usually contains at least one base glycol.

Typical basic glycols have the formula

HO- [(CH ₂ ) _x -O] _n -H. Where n is an integer. Usual maximum values for n are 14 or in particular 10, where

Maximum values of 7 or 5 are particularly preferred.

In particular, a preferred lower value for n is 2, although a lower value of 3 has proven to be suitable. x is 1, 2, 3 or 4.

Also suitable glycols have as repetition units such glycols which consist of ethylene, Propylene and butylene units are constructed. The units may be constructed both linearly and from branched or isomeric units. They can also be composed of mixed units.

Typical basic glycols are PEG200, as well as PEG300 and PEG400. However, preferred are ethylene glycols and propylene glycols and mixtures thereof. Especially

ethylene glycol, diethylene glycol and triethylene glycol or dipropylene glycol are preferred.

The etherified glycol added according to the invention is in particular a polyethylene glycol which has been etherified with an alkyl radical. It preferably has the formula

HO- [(CH ₂ -) _a -O] _b -R.

In this case, b is an integer of at least 1 or 2, in particular 1-8 and a is 1, 2, 3 or 4. R is a linear or branched alkyl radical having 1-10 or 1-8 C atoms.

Is the base glycol PEG300 or PEG400 can

According to the invention, the addition of an ethylene glycol of general formula HO [CH ₂ -0] _m -H with m = 1 or 2. In this particular case, it is possible to dispense with the addition of a glycol ether etherified with an alkyl radical.

In a preferred embodiment, a = 2.

R is an alkyl radical having 1-10 C atoms

preferably 2-8 C-atoms. Particularly preferred are etherified alkyl radicals having a maximum proportion of C atoms of 6, in particular of 4.

Typically, the proportion of one with

Alkyl group of etherified glycol on the total amount of the sawing fluid (i.e., without possibly contained

Cutting grains, as well as other additives) at least 1% by weight, with a minimum amount of 3, in particular 5% by weight are preferred. Particularly preferred

Minimum quantities of 10% by weight. A usual maximum proportion of the etherified with an alkyl glycol content of the total fluid is at most 50% by weight, with a maximum of 40% by weight is preferred. Particularly preferred

Maximum values of 35 or 30% by weight.

It has been found that the fluid according to the invention also with high sludge, ie a high Content of abgespanten material particles, is usable.

In a particularly preferred embodiment, used from time to time consumed sawing slurry or Coolant and partially replaced by new.

It has proven particularly expedient to have a content of cut-off material particles (Kerf) of 2-8% by weight, preferably 2-6% by weight.

adjust.

In a preferred embodiment, z. B. the slurry up to 5 vol .-% water, but preferably the liquid phase of the slurry, the sawing fluid only less than 2 wt .-% water.

In a further embodiment of the invention, the water has a slightly acidic pH of 3-6, wherein a pH of 3 to 5, in particular a pH of

4 +/- 0.5 is particularly preferred. The content of acid in this water is between 0.1 and 3 mol / l, with a value between 0.5 and 2 mol / l

is particularly preferred. A typical concentration is 1 +/- 0.5 mol / 1. According to the invention, all acids can be used here, as long as they do not contain saw wire or the material to be cut in use attack. However, it has been shown here that

Citric acid is particularly suitable.

Typical materials to be diced are all brittle-hard, especially crystalline materials, with mono- or polycrystalline silicon being particularly preferred.

The sawing fluid according to the invention is particularly suitable for use with wire saws, especially so-called.

Multiwire saws. The sawing fluid is suitable for both loose and bonded grain sawing. When sawing with loose grain is a slurry, which consists of a suspension of abrasive grains, usually SiC, diamond or corundum, and the sawing fluid, on a formed on one of many wires

Wire field applied. Each of the individual wires routed parallel to each other undergoes wetting by the material before it penetrates into the brittle-hard material

Slurry. The slurry is entrained by each of the rapidly moving wires and penetrates into the cutting gap along with the wire. In the narrow

Cutting gap, the Abrasionskörner unfold their abrading effect by temporarily touching both the wire and the brittle-hard material so or jamming in this space that material from the contact point or contact surface chipped or removed. The wires intersect so deeper into the brittle-hard material, forming cutting gap and ultimately lead to a

complete cutting of the to be sawn

Material e.g. a block, a column, one

Bricks.

When sawing with bonded grain, a sawing wire is used, at the surface of which the correspondingly hard abrasion particles are firmly connected to this sawing wire. In contrast to the above-described sawing with loose grain grind on the wire

adhering Abrasionspartikel over the surface of the cutting gap and thereby chip something brittle hard material. The sawing fluid according to the invention is used in this method for cooling and recording on abgespanntem brittle material. Also here

the wires intersect deeper and deeper into it

Brittle-hard material, forming cutting gap and ultimately lead to a complete

Cutting the material to be sawn e.g. a block, a column, a brick or a

squared or round ingots leads.

The invention also relates to the use of such a fluid in the manufacture of

electronic components, such as in particular

Computer chips and in particular photovoltaic cells, and such installations. The invention will be explained in more detail by the following examples: It was a SägefFuid diethylene glycol and

Diethylene glycol monobutyl ether in the ratio 4: 1 prepared. This sawing fluid was in a

Ratio of 52% by weight of sawing fluid to 48%

Silicon carbide mixed into a slurry. With this slurry, a 6-inch-long silicon ingot was sawn to a thickness of 200 μm. The wire speed was 14 m / s and the feed rate 400 pm / min. A wire of 130 μm in diameter was used, the pitch (the distance between 2 wires) being 360 μm.

The same experiment was carried out with a commercially available slurry using PEG200 as the sawing fluid. When comparing the slurry according to the invention to a commercially available slurry, it was found that in the case of the PEG200-based slurry according to the prior art, the starting viscosity was already substantially higher and continuously increased during the loading with chipped silicon material particles (Kerf). In contrast, the initial viscosity was

Slurry invention already significantly lower and even decreased slightly during the loading with silicon particles (Kerf). The course is shown in FIG.

Claims

claims

1. Fluid for sawing brittle-hard blocks of material

especially with multiwire saws containing at least one base glycol of the general formula

HO - [(CH ₂ -) x -O] "- H in which n is an integer from 1-14 and x is 1, 2, 3 or 4, and optionally contains further additives, thereby

in that it additionally has at least one glycol etherified with an alkyl radical of the general formula

HO- [(CH ₂ -) _a -O] _b -R, where a is 1, 2, 3 or 4 and b is an integer from 1 to 10 and R is a linear or

branched alkyl radical with 1-8

C atoms, characterized in that the proportion of water is less than 2 wt .-%.

2. Fluid according to claim 1, characterized in that the glycol is an ethylene glycol.

3. Fluid according to one of the preceding claims, characterized in that the base glycol comprises PEG200, PEG300, PEG400 or a mixture thereof. Fluid according to one of the preceding claims, characterized in that the proportion of etherified glycol in the total fluid is 1-50 wt .-%.

Fluid according to one of the preceding claims, characterized in that the etherified glycol

Diethylene glycol monobutyl ether,

Fluid according to one of the preceding claims, characterized in that the base glycol a

Diethylene glycol is.

Fluid according to one of the preceding claims, characterized in that it contains at most 1% by weight of water

contains.

Fluid according to one of the preceding claims, characterized in that the water 0.1-3 mol / 1 at

Contains citric acid.

Method for producing wafers, electronic components and photovoltaic cells by dicing ingots into wafers, in particular with multiwire saws by means of a separating fluid according to one of claims 1-8.

Use of a fluid according to any one of claims 1-8 for the production of wafers, electronic components and photovoltaic cells.