JP2013505576A - Cutting blocks into wafers using diamond-coated wires - Google Patents

Abstract

  A block of material (by moving a planar array of wires (9) embedded with abrasive particles that move rapidly in a direction substantially parallel to the plane of the wire (9) relative to the block (or vice versa) 16) is a process for cutting a plurality of wafers and applying a solvent to the wire (9) before the wire (9) passes through the block (16). The solvent contains an additive, and the solvent is a wire. Reduce the surface tension of the solvent before it is transferred to the block by (9). The present invention includes an apparatus for processing and a wafer made by the processing.

Description

  The present invention relates to cutting a block into a number of thin wafers. In particular, the present invention relates to cutting silicon blocks into wafers for use in the electronics, semiconductor and solar cell industries and similar applications.

  Techniques using multi-wire arrays of rapidly moving wires to cut blocks of material into thin wafers are known. An example of an apparatus related to cutting with a polishing wire is disclosed in Patent Document 1. The present invention is not limited to use in this apparatus, but can be applied to any process for wire cutting a block of material into a thin wafer.

  For example, wafers made of various materials such as Si, SiC, GaAs and sapphire are cut from the material blocks for use in electronic equipment, semiconductors and solar power. Polycrystalline or single crystal Si wafers are manufactured by cutting large Si blocks for use in photovoltaics. Currently, multi-wire cutting is used to cut large quantities of Si wafers from Si blocks, and it is possible to rapidly produce high quality thin wafers (<200 μm). Diamond particles are attached to the wire of the wire saw, and a solvent such as water is carried to the silicon and used to remove heat from the Si block.

  The solvent is carried to the block by an array of parallel wires that travel perpendicular to the block while traveling longitudinally at high speed (5 m / s to 20 m / s). The objective is to cut with high productivity and minimal solvent loss, resulting in high quality wafers at low cost. The wafer is cut within a process window defined by properties such as viscosity, size and shape of the abrasive particles, solvent properties and saw parameters.

  One of the largest loss categories is local area thickness fluctuations (LATF). These changes occur at the beginning of the cut and result in thickness changes that result in unacceptable thick and thin wafers.

  The reason for this is to pair the wires so that they attract each other.

  One of the main reasons for this is the surface tension of the solvent used to cut. This pulls adjacent wires together and therefore pairs them, resulting in a wafer that is 1/2 the pitch thin. This problem escalates as the wafer thickness and wire thickness decrease.

によって与えられ、このうち、符号γは、溶剤の表面張力、符号Ｌは、ワイヤー間の溶剤膜の長さ、符号ｒは、ワイヤー半径、符号Ｒは、ワイヤー間の溶剤表面の曲率、符号θ＝溶剤及びワイヤー間のぬれ角、符号αは、溶剤及びワイヤー間の接触点によって決定される角度である。 For the force with which the wires are pulled together, see FIG.

Where γ is the surface tension of the solvent, L is the length of the solvent film between the wires, r is the wire radius, R is the curvature of the solvent surface between the wires, and θ = Wetting angle between solvent and wire, symbol α is an angle determined by the contact point between solvent and wire.

  The present invention relies on the recognition that the surface tension of the solvent is the primary parameter controlling the force between the wires and should be reduced to prevent local range thickness variation (LATF).

  Patent Document 2 discloses a method for producing a turbid liquid having higher stability by adding different additives such as a surfactant for dispersing SiC.

  U.S. Pat. Nos. 5,057,049 and 5,037,831 disclose methods for producing stable turbid liquids by increasing viscosity and / or by adding dispersants and polymerization electrolytes. However, these publications do not mention PEG-based turbids and apply only to aqueous turbids.

US Pat. No. 2,414,204 US Pat. No. 6,054,422 US Pat. No. 6,602,834 International Patent Application Publication No. 2003/042340 International Patent Application Publication No. 2008/027374 Pamphlet International Patent Application Publication No. 2009/017672 Pamphlet US Patent Application Publication No. 2009/0126713

  These publications do not disclose any configuration that describes preventing the LATF phenomenon.

  The present invention allows multiple blocks of material to be moved by moving a planar array of wires incorporating abrasive particles that move rapidly in a direction perpendicular to the plane of the wire with respect to the block (or vice versa). Provides a process for cutting the wafer and applying solvent to the wire before the wire passes through the block, in which the solvent reduces the surface tension of the solvent before it is carried by the wire to the block Contains additives.

  Preferably, the abrasive particles are made of diamond.

  Advantageously, the solvent consists of polyethylene glycol (PEG) or consists of 5% to 100% based on the weight of water.

  Preferably, the additive is a surfactant that is easily soluble in a solvent.

  In this last mentioned form, the surfactant has no metal ions.

  Surfactants may be able to withstand the temperatures encountered when the wire begins to cut into a block, but may not be able to withstand the temperatures encountered during the cutting process within the block. Preferably, the temperature encountered during the cutting process within the block is more preferably sufficient to destroy the additive.

  Advantageously, a thickener is introduced to adjust the viscosity of the solvent. Advantageously, antifoaming agents are used to reduce solvent bubble formation.

  In one form, the surfactant is preferably nonionic, such as a block copolymer of ethylene and propylene oxide or octylphenol ethoxylate.

  In another form, the surfactant is preferably ionic.

  The present invention includes an apparatus for performing the above-described processing.

  The present invention includes a wafer produced by the process described above or in an apparatus related to the process.

FIG. 6 shows pulling two adjacent wires. FIG. 6 shows a special embodiment of the invention.

  A special embodiment of the invention will now be described by way of example with reference to the accompanying drawing (FIG. 2), which schematically shows a wire cutting device, in which the solvent blocks or It is given when engaging the ingot. This diagram is merely a schematic and does not represent any particular machine.

  As shown in FIG. 2, a machine for cutting a block into a plurality of thin wafers has four parallel rollers configured such that their axes form a rectangle. The wire 9 incorporating diamond is supplied to the first roller 11 beyond the guide 10. Thereafter, the wire 9 passes through the roller 12 horizontally as a whole and from there to the roller 14 vertically upward. The roller 14 is a driven drive unit, and after passing through the roller 14, the wire 9 then passes horizontally through the cut zone 15, and a block or ingot 16 is inserted into this cut zone. After passing through the cut zone 15, the wire 9 passes through the roller 17 which is the main driving unit, and then turns downward from the first roller 11 to make a second turn. In this method, an array of parallel wires passing through the cut zone 15 is formed. At the far end of the roller, the wire 9 is drawn over the second guide 18. The wire 9 is propelled at a high speed (5 m / s to 20 m / s), and the ingot 16 is slowly moved up through the cutting zone where it is cut into a thin wafer by the wire.

  The solvent is guided by a nozzle 19 to a wire between the roller 14 and the ingot 16. The present invention relates to the composition of a solvent.

Examples Examples are given below for common solvents used for wire cutting. The amount of surfactant increases with decreasing wafer and wire thickness. The same surfactant is used in all examples.

Example 1
A solvent for cutting with a wire embedded with diamond is prepared by dissolving 5 wt% of a nonionic surfactant consisting of an ethylene oxide / propylene oxide block copolymer (viscosity 280 cST at 35 ° C.) in water. This solvent is used to cut a 160 μm thick silicon wafer with a 120 μm wire embedded with diamond.

Example 2
A solvent for cutting with a wire embedded with diamond is prepared by dissolving 10 wt% ethylene oxide / propylene oxide block copolymer (viscosity 280 cST at 35 ° C.) in water. This solvent is used to cut a 140 μm thick silicon wafer with a 100 μm wire embedded with diamond.

Example 3
The solvent for cutting with a diamond-embedded wire is prepared by dissolving 5 wt% octphenol ethoxylate nonionic surfactant (1.5 mol ethylene oxide) in water. 1 wt% ethylene glycol-polypropylene glycol block copolymer (20% molecular weight 2750 polypropylene) is added as an antifoaming agent. This solvent is used to cut a 160 μm thick silicon wafer with a 120 μm wire incorporating diamond.

Example 4
The solvent for cutting with diamond embedded wire is prepared by dissolving 5 wt% ethylene glycol-polypropylene glycol block copolymer (20% polypropylene with a molecular weight of 2750) in water. This solvent is used to cut a 160 μm thick silicon wafer with a 120 μm wire embedded with diamond.

Example 5
The solvent for cutting with diamond embedded wire is prepared by dissolving 8 wt% ethylene glycol-polypropylene glycol copolymer (20% polypropylene with a molecular weight of 2750) in water. This solvent is used to cut a 140 μm thick silicon wafer with a 100 μm wire embedded with diamond.

Example 6
0.5 wt% and 1 wt% nonionic surfactant (viscosity 280 cST at 35 ° C) consisting of an ethylene oxide / propylene oxide block copolymer was dissolved in water and tested for its wetting properties on steel. The results show that 1 wt% is required to provide effective wetting and that 0.5 wt% is insufficient to obtain a dominant effect.

Example 7
A solvent for cutting with a wire embedded with diamond is prepared by dissolving 1 wt% of a nonionic surfactant (viscosity 280 cST at 35 ° C.) made of an ethylene oxide / propylene oxide block copolymer in water. This solvent is used to cut a 160 μm thick silicon wafer with a 120 μm wire embedded with diamond.

Example 8
A solvent for cutting with a wire embedded with diamond is prepared by dissolving 3 wt% of a nonionic surfactant (viscosity 280 cST at 35 ° C.) made of an ethylene oxide / propylene oxide block copolymer in water. This solvent is used to cut a 160 μm thick silicon wafer with a 120 μm wire embedded with diamond.

  1 wt% to 10 wt% surfactant is recommended.

  A special selection of materials used in the process of the present invention follows.

  The surfactants used are, for example, ethylene oxide, propylene oxide copolymers (Pluronic series provided by BASF and Tergitol L series provided by DOW), and nonylphenol / alcohol ethoxylate (provided by DOW). Block copolymers of alkylene oxides such as Tergitol series), octylphenol ethoxylate (triton X series provided by DOW), iso and oxo alcohols (Lutensol TO and AO series provided by BASF), etc. There may be.

  Nonionic surfactants are used because they are easy to use (no need for neutralization reaction) and to attach silicon blocks to glass plates attached to saws Preferred due to its compatibility with existing adhesives. In addition, the system is compatible with the cleaning chemistry used in the manufacturing industry.

  The thickeners used may be synthetic substances based on materials such as carboxymethylcellulose and ethylcellulose or natural clays, gelatin, xanthan gum, polyvinyl alcohol and cellulose.

  By using the present invention, the LATF problem is reduced. The surface tension of the solvent is reduced, leading to better wetting of the wire and some cleaning of the wafer after cutting. A reduction in surface tension also means that the force between the two wafers (after cutting) will be smaller, leading to a smaller force required to separate the wafers. Better wetting of the wire ensures that the solvent is transferred to the block during cutting. Using the present invention makes it possible to produce thinner wafers with thinner wires. Better SiC may be used as well to cut, resulting in a more favorable surface finish for the wafer.

9 wires, 16 blocks (ingot)

Claims (16)

Move the block of material to multiple wafers by moving a planar array of wires embedded with abrasive particles that move rapidly in parallel to the plane of the wire in a direction perpendicular to the plane of the wire (or vice versa). Cutting and applying a solvent to the wire before the wire passes through the block,
The process wherein the solvent includes an additive to reduce the surface tension of the solvent before the solvent is carried to the block by the wire.   The process according to claim 1, wherein the abrasive particles are made of diamond.   The treatment according to claim 1, wherein the solvent is polyethylene glycol (PEG).   The treatment according to claim 1 or 2, wherein the solvent is 5% to 100% based on the weight of water.   The treatment according to any one of claims 1 to 4, wherein the additive is a surfactant that is easily soluble in the solvent.   The treatment according to claim 5, wherein the surfactant does not have a metal ion.   The surfactant can withstand the temperatures encountered when the wire begins to cut into the block, but can withstand the temperatures encountered during the cutting process within the block The processing according to claim 5 or 6, wherein the processing is not.   The process of claim 7, wherein the temperature encountered during the cutting process in the block is sufficient to destroy the additive.   The treatment according to any one of claims 5 to 8, wherein a thickener is introduced to adjust the viscosity of the solvent.   The treatment according to any one of claims 5 to 9, wherein an antifoaming agent is used to reduce bubble formation of the solvent.   The treatment according to claim 5, wherein the surfactant is nonionic.   The treatment according to claim 11, wherein the nonionic surfactant is a block copolymer of ethylene and propylene oxide.   The treatment according to claim 11, wherein the nonionic surfactant is one of ethylene oxide, propylene oxide copolymer, octylphenol ethoxylate, nonylphenol / alcohol ethoxylate, isoalcohol or oxoalcohol.   The treatment according to claim 5, wherein the surfactant is ionic.   The apparatus which performs the process as described in any one of Claim 1 to 14.   A wafer produced by the process according to any one of claims 1 to 14 or with the apparatus according to claim 15.

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