JPH0716885B2 - Inner Circumferential Metal Bond Cutting Wheel Manufacturing Method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing an inner peripheral metal bond cutting grindstone for cutting a semiconductor single crystal rod or the like into a wafer or the like.

[Prior Art] Processing of hard and brittle materials, particularly precision processing of semiconductor single crystals and ceramics, has recently attracted particular attention. Hard and brittle materials generally have much lower tensile strength than compressive strength. Therefore, when processing a hard and brittle material, a series of minute fractures must be performed starting from the point where the external force exceeds the tensile strength.

Against the background of the development of the semiconductor industry, of course, was the need to advance and develop the technology for supplying the semiconductor materials, but semiconductor single crystal rods were cut approximately perpendicular to the axial direction to form circular flakes (wafers). Then, the inner layer metal used in the series of steps of removing the processing strain of the surface layer and forming a high-precision, high-quality mirror surface on one side, especially the step of cutting a semiconductor single crystal rod that is a hard and brittle material The development of bond cutting wheels had important significance.

As shown in FIG. 3, this inner circumference type metal bond cutting grindstone is made of thin annular stainless steel such as SUS301 or SUS3.
A diamond abrasive grain 12 is fixed to the inner peripheral portion of a base metal 10 made of 04 by an electrodeposition method (also referred to as an electroforming method). The diamond abrasive grains 12 are one to two layers, and if they are dropped, the cutting ability is lost.

The electrodeposition method is performed by covering unnecessary portions with a plastic film or the like, arranging diamond abrasive grains 12 or the like on the inner peripheral edge and the upper and lower surfaces of the base metal, and plating the base metal 10 with nickel.

The inner circumference metal bond cutting grindstone was developed to minimize the cutting allowance in cutting semiconductor single crystal rods.
Not only the base metal but also the grindstone itself is thin. The thickness of this grindstone is usually 200 to 320 μm, and the thickness of the base metal is usually 100 to 200 μm.
m. The diamond abrasive grain layer is limited to at most two layers. The diamond abrasive grains 12 used have a diameter of about 40 to 70 μm, and this diameter is empirically selected from the viewpoints of adhesion of the abrasive grains to the metal bond and cutting force.

The inner circumference type metal bond cutting wheel has the following drawbacks.

(1) Since the semiconductor single crystal ingot is easily pulverized during cutting, and the diamond abrasive grains 12 are often dropped off, clogging is likely to occur, resulting in a significant decrease in cutting ability.

(2) Since the number of diamond abrasive grains 12 is small, if the diamond abrasive grains 12 fall off, the cutting ability tends to be anisotropic, which causes warping of the semiconductor wafer, which is a cause of wafer failure.

(3) Due to this anisotropy, a deep processing strain of several tens of μm may occur in the wafer surface layer in some cases. Such processing strain causes deterioration of the mirror surface crystal quality of the mirror-finished semiconductor wafer which is the final processed product, or causes an uneconomical need to remove the wafer surface unnecessarily.

Conventionally, when cutting a semiconductor single crystal ingot with an inner circumference type metal bond cutting grindstone, a mechanical dressing method has been frequently used in order to prevent the above-mentioned clogging. This method mechanically removes the chips of the semiconductor single crystal adhering to the surface of the grindstone by cutting the hard and brittle material, or mechanically scrapes the metal part of the electrodeposition layer to obtain new diamond abrasive grains. Is the method of exposing. Although there is a temporary effect in this way, the cutting operation is interrupted for dressing, or the whetstone portion of the cutting edge is not symmetrically removed with respect to the base metal 10 during dressing, and the cutting edge is asymmetrical. In the case of slicing, the direction of movement of the cutting edge deviates from the base metal surface during slicing, and warpage occurs in the cut thin piece. As described above, it is difficult to sufficiently prevent the warp of the cut thin pieces even by the dressing, and the productivity is lowered due to the interruption of the cutting work, which causes a cost increase.

In order to solve the problem of such dressing, a nozzle block having a plurality of cutting fluid discharge holes and air jetting small holes arranged in parallel to the rotation surface of the thin inner circumference cutting blade is provided, and the grinding fluid is directed toward the cutting blade. Has been proposed to prevent clogging by simultaneously discharging air and ejecting air (Japanese Patent Laid-Open No. 60-970).
No. 9 bulletin).

However, in this method, the grinding fluid and air are simply ejected to the vicinity of the cutting edge, and the fine powder layer of the hard and brittle material causing the clogging adhered only by the ejection energy is destroyed and released, so that effect Is limited. The cutting blade rotates at a high speed, the cutting edge has a peripheral speed of 1000 to 3500 m / min, and when the inner peripheral diameter is 240 mm, the time required for one rotation is only 0.05 sec even at 1000 m / min. Therefore,
Even if a large amount of cutting fluid is discharged from many positions near the cutting edge,
It is difficult to remove the fine chips adhering to the surface with a normal cutting fluid.

On the other hand, a grindstone using a binder containing iron powder as a main component is less likely to cause clogging, and a method for producing the grindstone has been proposed (Japanese Patent Laid-Open No. Sho 63-187)
63-99177).

[Problems to be Solved by the Invention] However, this grindstone is a wheel-type grinding wheel with a thickness of about 10 mm, and with the thin cutting grindstone with a thickness of about 200 to 320 μm,
It was impossible to manufacture by a sintering method using a binder containing iron powder as a main component. Conventionally, the sintering method is not suitable for making a thin-layered grindstone, and it is said that the lower limit is about 1 mm in thickness.

In view of such a problem, an object of the present invention is to thinly sinter and fix the inner peripheral edge portion of the annular metal thin plate in which a super abrasive grain is mixed with a binder containing iron powder as a main component. (EN) Provided is a method for manufacturing a metal bond cutting whetstone.

[Means for Solving the Problems] In the method for manufacturing an inner peripheral type metal bond cutting grindstone according to the present invention, in order to solve the above problems, for example, FIGS. 1A and 1B are used.
As shown in FIG. 3, the metal thin plate is sandwiched by the mold so that the inner peripheral edge of the metal thin plate is positioned in the groove of the mold, and the binder containing iron powder as a main component is held in the groove. And a superabrasive grain, and the inner peripheral edge of the annular metal thin plate is thinly covered with the mixture, and the surface of the mixture is covered with an elastic seal member (rubber or its equivalent) to open the groove. To make the mixture a hermetically sealed state, and in this state, isostatic pressing the mixture by applying static pressure in a compressed liquid,
It is characterized in that the mixture is sintered in an inert or reducing atmosphere, and the cutting edge is finished to a predetermined size by electrolytic action.

The isostatic press molding is performed in two steps, for example, the step shown in FIG. 1A and the step shown in FIG. 1B.

That is, using the first mold in which one surface of the inner peripheral edge portion of the annular metal thin plate is in contact with the bottom surface of the groove in a state where the annular metal thin plate is sandwiched between the molds, Cover the other surface of the inner peripheral edge with the above mixture thinly and
Static press molding is performed, and then, with the annular metal thin plate sandwiched by a mold, a concave portion into which the mixture formed is fitted on one surface of the inner peripheral edge of the annular metal thin plate. In this fitted state, the second mold is used to thinly cover the other surface of the inner peripheral edge portion of the annular metal thin plate with the mixture to perform the isostatic press molding.

The superabrasive grains are preferably diamond grains or cubic boron nitride grains having a grain size in the range of 5 to 60 μm.

The particle size of the iron powder is preferably about 1 / the particle size of the superabrasive particles.
10 or less.

The binder is preferably iron powder to which silicon powder is added.

[Operation] As the diamond abrasive grains, those having a maximum diameter of 70 to 80 μm can be used, but the diameter is preferably 30 μm or less. However, even when the diamond abrasive grains having a diameter of 70 μm are used, in the case of the present invention, since the diamond abrasive grains exert a chemical bonding force with the binder, the diamond abrasive grains are compared with the conventional nickel electrodeposition method. Then, it is more firmly fixed and supported by the sintered metal layer. Therefore, until the diamond abrasive grains lose their cutting force due to abrasion or damage, the abrasive grains have the cutting force almost permanently and exhibit excellent cutting force for a long time. From this point, it can be said that it is sufficiently improved as compared with the conventional inner circumference type metal bond cutting grindstone. Conventionally, the diamond abrasive grains are only embedded in the electrodeposition layer of nickel, so that the diamond abrasive grains are relatively easily removed.

When a semiconductor single crystal rod, for example, a silicon single crystal rod is cut, since the cutting chips are silicon, it is easy to pulverize,
This causes adhesion and solidification on the surface of the inner peripheral edge to cause clogging, resulting in a decrease in cutting ability.However, since the diamond abrasive grains of the grindstone manufactured according to the present invention retain the cutting force for a long time, this can be performed by a conventional method. By cutting hard and brittle materials such as alumina porcelain, dressing can be easily performed.

In the inner circumference type metal bond cutting grindstone manufactured by the present invention, since diamond abrasive grains are hard to fall off, it is theoretically unnecessary to remove the surface portion by dressing the metal bond layer to expose new diamond abrasive grains. However, since the tips of diamond abrasive grains are somewhat worn away, it is necessary to slightly remove the surface portion of the metal bond layer and increase the exposed tips of the diamond abrasive grains. This is natural from the theory of processing of micro-fracture and scratching of hard and brittle materials.

If the cutting ability of the grindstone deteriorates, the cutting edge will bend when the semiconductor material is cut, and the wafer to be cut will deviate from the flat plate and deform. This deformation has various shapes such as a paddle shape and a dish shape, and these are collectively called a sled. In order to obtain a mirror-polished semiconductor single crystal wafer with high dimensional accuracy, it is necessary to produce the same thin pieces with or without warpage at the cutting stage.

If the diamond abrasive grains are large, an abnormally deep processing strain reaching, for example, 70 to 80 μm partially occurs on the cut semiconductor single crystal substrate surface. In general, there are many processing strains, and the average depth reaches half the grain size of diamond used. The degree of processing strain depends on the arrangement, exposure, tip shape, mechanical vibration of the cutting edge, etc. of the diamond abrasive grains on the cutting edge of the grindstone.

As a result of various experiments, the present inventor has found that diamond abrasive grains are
It has been found that a further improved result can be obtained by setting the thickness to be 50 μm to 50 μm. When the diameter of the diamond abrasive grains becomes small, the cutting force becomes small and it becomes impractical. This is close to the state where the blade edge is clogged, and if the cutting speed in the diameter direction of the semiconductor single crystal ingot is increased in this state, warpage occurs in the cut thin piece. With a grindstone using diamond abrasive grains with a diameter of 5 μm and a base metal with a thickness of 150 μm, it is possible to cut about 10 mm per minute under normal working conditions. No clogging occurs when the diameter of diamond abrasive grains is about 30 μm, and the surface processing strain of the semiconductor substrate after cutting is 10 ~
It becomes 15 μm, and a particularly great improvement is that no abnormal processing strain occurs. The reason for this is that the cutting speed of the semiconductor single crystal rod is 50 mm / min per minute, and the cutting ability is such that there is no warp in the cut piece, and the exposed abrasive grains on the surface of the inner peripheral edge of the diamond grindstone have a unit area. It becomes a big hit, and in the cut part of the semiconductor single crystal rod,
It is considered that abnormal pressing due to the protruding single diamond abrasive grains does not occur.

In the present invention, as a result of experiments, it was found that the most preferable mixing ratio of the diamond abrasive grains and the metal binder is about 0.8 to 2:10 by weight. When the amount of diamond abrasive grains increases, the diamond abrasive grains are more likely to fall off, and conversely, when the amount decreases, the cutting ability decreases. However, within the range of the above ratio, there is no significant difference in cutting ability.

As the binder, iron powder is used in the present invention. As the iron powder, powdered cast iron and reduced iron powder generated by cutting or grinding of cast iron are usually used. As the reduced iron, for example, one obtained by reducing iron oxide or thermally decomposing iron carbonyl obtained by heating in carbon monoxide is used. In the latter case, iron powder having a particle size of 1 μm or less can be easily obtained. The particle size of the iron powder is preferably about 1/10 of the particle size of the diamond abrasive grains. This is because the porosity is close to 50% even with the closest packing in the case of the same particle size, so in order to reduce this porosity, the particle size is 1/10 of the particle size of diamond abrasive grains.
This is because if iron powder of a certain degree is added for filling, 90% or more of the closest packing is possible. From a microscopic point of view, the diamond abrasive grains are densely surrounded by iron powder, and there are no voids at least close to the size of the diamond abrasive grains. The iron powder may have a particle size distribution, and the small size particles will fill the gaps between the large size particles.

A mixture of such a binder and diamond abrasive grains is, for example, pressure-molded in the state shown in FIGS. 1A and 1B, and when further heat-sintered, the iron powders are sintered together, and the diamond abrasive grains are Chemically bonds with the contact of iron. That is, unlike the case of the conventional nickel electrodeposition, in which diamond abrasive grains are simply embedded in the sintered metal layer, in the case of the conventional case, the diamond abrasive grains do not drop in the case of the present invention. In the case of conventional nickel electrodeposition, for example, 2B
In the case of the figure, it does not fall off, but in the case of FIG. 2A, the degree of dropout becomes large. However, in the case of the present invention, since the binder fixes the diamond abrasive grains by a chemical action, the diamond abrasive grains do not fall off even in the case of FIG. 2A. Small particles having a large surface area per unit volume have a high surface free energy, so that sintering is performed at a relatively low temperature. In the present invention, sintering proceeds well at 1,000 ° C or lower.

When silicon powder is added to iron powder, the binding force of the diamond abrasive grains is further increased. This is because the silicon powder forms a metal compound with the iron powder and the diamond abrasive grains. Silicon forms SiC with diamond and forms a Si / Fe compound with iron. Since the melting points of the compounds of Si and Fe are lower than the respective melting points, this is considered to enhance the adhesion of the metal sintered layer and the diamond abrasive grains.

Traditionally, the sintering method is unsuitable for making thin-layer grinding stones,
It was said that the minimum thickness was about 1 mm. However, isostatic press molding is performed using a special mold, and 1 hour at 1,000 ° C in an inert gas or hydrogen stream.
If heated for about an hour, a sintered layer having almost the strength of iron itself can be formed even if it is a thin layer. However, since the grindstone portion cannot be precisely formed by this method, after the sintering is finished, it is further processed into an arbitrary shape by the electrolytic polishing method.

Isostatic press molding is characterized in that the molded product can be pressed uniformly and there is no uneven compression. Molding is performed by transmitting a fluid pressure of about 2,000 kg / cm ² through the rubber film. The rubber film deforms according to the shape of the molded product.

[Examples] Examples of the present invention will be described below.

If you outline, the inner circumference metal bond cutting wheel is 1A, 1B
As shown, stainless steel, such as SUS301 or SUS3
A binder made of diamond abrasive grains 12 and cast iron powder and / or pure iron powder on a limited portion of the upper and lower surfaces of the annular base metal 10 of 04 and the upper and lower surfaces in the vicinity thereof, for example, the inner peripheral portion having a width of 3 to 5 mm. It is manufactured by press-molding a mixture of 16 and 16, sintering the mixture, removing an unnecessary iron powder sintered layer by an appropriate method such as electrolytic polishing, and finishing to a desired dimensional accuracy.

In detail, as shown in FIG. 1A, the base metal 10 is fixed to the mold 18, and the diamond abrasive grains 12 and the binder are provided near the inner peripheral end of the base metal 10.
16 mixed powders are filled, this is covered with a rubber mold 20, and a pressing plate 22 is applied to the peripheral edge portion thereof, and the rubber mold 20 is pressed through the pressing plate 22 with a fastener 24.
Is pressed against the mold 18 and is sealed so that the pressurized liquid does not enter the inside of the rubber mold 20. Then, while applying ultrasonic vibration to the mold 18, the whole is subjected to static pressure in a compressed liquid such as glycerin, lubricating oil, or mobile oil. Since press-molding is performed on each of the inner peripheral side surfaces of the base metal 10, press-molding is performed in two steps. As the mold used in the second step, as shown in FIG. 1B, a mold having a recess for accommodating the already molded part is used. The other points are the same as those in the first step.

When molded in this manner, the molded body can be directly sintered in the sintering furnace without damaging the molded body unless a strong impact is applied. For example, if the firing temperature is 1,000 ° C., the base metal 10 itself is also deformed depending on how it is held, so it is better to place it on a suitable heat-resistant base and sinter it. After sintering, since the shape is irregular, electrolytic polishing is performed next.

Since the binder 16 is iron powder as a base material, the electrolytic solution is, for example, NaCl.
A DC voltage is applied using an aqueous solution with the grindstone portion as an anode. As a result, Fe becomes iron hydroxide and dissolves. If the iron of the metal bond melts, the unnecessary diamond grindstone will also fall off. In electrolytic polishing, the blade edge can be processed into an arbitrary shape by adjusting the shape of the electrode. Base metal 10
In order to prevent the metal from being electrolytically polished at the same time, the exposed portion of the base metal 10 is coated with a non-conductive film such as wax.

In sintering, it is important to perform re-quenching, because annealing will occur if it is taken out of the furnace and then slowly cooled. Since the carbon content in the metal bond affects the mechanical properties of the base metal 10, the carbon concentration should be adjusted close to that of the base metal 10.

When a semiconductor single crystal rod, particularly a silicon single crystal rod, is cut using the grindstone of the present invention, an alkaline aqueous solution such as a 10% solution of caustic soda is used as a cutting liquid. This cutting fluid dissolves and removes the silicon chips adhering to the cutting edge of the inner circumference type metal bond cutting grindstone, and at the same time gradually dissolves the iron powder of the metal bond, exposing the diamond abrasive grains 12 and automatically performing chemical treatment. You can also do various dressings.

When silicon is contained in the metal bond, this silicon is also dissolved by the alkali, which promotes automatic chemical dressing.

Since the tip of the grindstone generates an appropriate amount of heat by cutting the silicon single crystal, this thermal energy promotes the above chemical reaction.

Next, a test example of the present invention will be described.

(1) Test Example 1 Diamond abrasive grains 12 having a particle size of 10 to 15 μm, iron powder having a particle size of 1 μm, and silicon powder having a particle size of about 1 μm were uniformly mixed at a weight ratio of 1: 10: 0.05, This has an outer diameter of 690 mm, an inner diameter of 240 mm,
It is placed on the inner periphery of SUS301 base metal 10 with a thickness of 150 μm, preformed by isostatic press molding at a pressure of 1,800 kg / cm ² and sintered in a hydrogen stream at 1000 ° C for 1 hour, then electrolytically polished. I went.

With such an inner circumference type metal bond cutting grindstone, diameter 100 mm
When the silicon single crystal ingot was cut into thin pieces, the warp of the silicon thin pieces was 5 μm or less even after 1,000 sheets were continuously cut.

In addition, when the processing strain was measured by sampling one out of every 1,000 sheets out of these 1,000 sheets, the maximum processing strain of each thin piece was 5
It was less than μm.

In order to compare this with the prior art, a similar test was conducted using a commercially available inner circumference type nickel bond cutting grindstone with the same specifications, and when the 500 sheets were cut, the sled exceeded 30 μm. In addition, the maximum processing strain was found to be an abnormally deep processed groove reaching 50 μm in a part of the first to fourth thin slices in the 5 samples of every 100 sheets.

(2) Test Example 2 Using the inner circumference type metal bond cutting grindstone of Test Example 1 described above, a silicon single crystal rod was sliced into thin pieces using a weak alkaline aqueous solution containing caustic soda as a cutting fluid and using pure water. It was cut into pieces to compare the occurrence of sleds. The number of continuous cuts with a warp of more than 10 μm was about 1,200 when this weak alkaline aqueous solution was used, while it was about 300 when pure water was used.

(3) Test Example 3 Using the inner circumference type metal bond cutting grindstone of Test Example 1 described above, a weak alkaline aqueous surfactant solution was used as a cutting fluid,
When the silicon single crystal was cut into thin pieces while applying an electric field between the grindstone and the silicon single crystal rod, the resistance at the time of cutting became small.
The number of continuous cuts exceeding 10 μm was about 500. In order to prevent the electric field action from reaching the base metal 10, before cutting, the surface of the base metal 10 from the outer end of the abrasive grain layer 12 to the outer end of the base metal 10 is made of Teflon (registered trademark) as an insulating material. It was coated with resin.

On the other hand, when a test was performed using a commercially available inner peripheral type nickel bond cutting grindstone having the same specifications, the sled exceeded 30 μm at the stage of cutting about 600 sheets.

[Effects of the Invention] As described above, according to the manufacturing method of the present invention, the super-abrasive grains are contained in the binder containing iron powder as the main component in the inner peripheral edge of the annular metal thin plate, which has not been conventionally manufactured. It has the effect of being able to manufacture an inner circumference type metal bond cutting grindstone in which the mixed material is thinly sintered and fixed, and with this grindstone, clogging of the inner circumference edge and deformation wear due to cutting of a semiconductor single crystal rod etc. Of high-precision, high-quality mirror-semiconductor single-crystal substrate that can reduce the abnormal processing strain layer or the average depth of the processing strain layer of the surface layer of the wafer after cutting by the inner peripheral blade. It becomes possible to efficiently produce the etc. at a low cost.

[Brief description of drawings]

1A and 1B are cross-sectional views of an essential part showing a method for manufacturing an inner peripheral metal bond cutting grindstone according to an embodiment of the present invention, FIGS. 2A and 2B are from a binder of diamond abrasive grains according to a shape. FIG. 3 is a sectional view showing the structure of a conventional inner circumferential metal bond cutting grindstone showing the difficulty of detachment. In the figure, 10 is a base metal 12 is a diamond abrasive grain 14, 16 is a binder 18, 18 is a mold, 20 is a rubber mold, 22 is a push plate, and 24 is a fastener.

Claims (5)

[Claims] 1. An annular metal thin plate is sandwiched by the mold so that an inner peripheral edge of the annular metal thin plate is positioned in a groove of the mold.
A mixture of a binder containing iron powder as a main component and superabrasive grains is put in the groove, the inner peripheral edge of the annular metal thin plate is thinly covered with the mixture, and the surface of the mixture is covered with an elastic seal member. The mixture is sealed by covering the opening of the groove by applying a static pressure to the mixture in a compressed liquid.
A method for producing an inner peripheral metal bond cutting grindstone, which comprises performing static press molding, sintering the mixture in an inert or reducing atmosphere, and further finishing an edge by electrolysis to a predetermined size. 2. A first mold in which one surface of an inner peripheral edge portion of the circular metal thin plate is in contact with a bottom surface of the groove while the circular metal thin plate is sandwiched by the molds, and the circular ring is used. The other surface of the inner peripheral edge of the thin metal plate is thinly covered with the mixture to perform the isostatic press molding, and then the inner thin metal plate is sandwiched between molds. A second mold having a concave portion into which the mixture formed on one surface of the peripheral edge portion is fitted is used, and in this fitted state, the other surface of the inner peripheral edge portion of the annular metal thin plate is mixed with the mixture. The method according to claim 1, characterized in that the isostatic press molding is performed by covering it with a thin layer. 3. The method according to claim 1, wherein the superabrasive grains are diamond grains or cubic boron nitride grains having a grain size in the range of 5 to 60 μm. 4. The particle size of the iron powder is about the particle size of the superabrasive particles.
The method according to any one of claims 1 to 3, wherein the method is 1/10 or less. 5. The method according to claim 1, wherein the binder is silicon powder added to the iron powder.