JPS63150162A - Grindstone for polishing semiconductive wafer - Google Patents

Abstract

PURPOSE:To exhibit an effect of fine cutting action by setting an area ratio of abrasive grains to 25% or more of a three-dimensional network structure and the bonding degree by Ogoshi type testing machine under 30kg load to 10X1/100mm or more. CONSTITUTION:A structure provided with a three-dimensional network having continuous fine pores equivalent to about 40%-60% porocity is set up by internally bonding together abrasive grains of silicon carbide or aluminum oxide by aid of synthetic resin. Then, volumetric ratio of the abrasive grains to the total structure is set to 25% or more so as to secure polishing capacity by peeled off and separated abrasive grains and the bonding degree by Ogoshi type bonding degree testing machine under 80kg load is set to 10X1/100mm or more so that sufficient effect of uniform plishing may be secured by means of peeling off and separation of abrasive grains. An effect of fine cutting action can be achieved by sliding/rubbing of solidified abrasive grains and rolling action of peeled off abrasive grains in this way, so that semiconductive wafers such as GaAs can be effectively polished.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a grindstone for polishing semiconductor wafers, and more specifically, the present invention relates to a grindstone for polishing semiconductor wafers, and more specifically, the present invention relates to a grindstone for polishing semiconductor wafers, and more specifically, to
The present invention relates to an abrasive material particularly suitable for rough polishing of semiconductor wafers such as arsenic.

(Prior Art) In recent years, the degree of integration of semiconductor materials such as silicon wafers, such as ICs, LSIs, and VSLIs, has improved, and the requirement for precision in manufacturing has become extremely high. At the same time, as the manufacturing technology for silicon single crystals has improved, the diameter of silicon wafers, which are the raw material, has been increasing, and the difficulty of manufacturing technology has been increasing. The required precision is increasing year by year.

Conventionally, in the manufacturing process of silicon wafers, a cylindrical silicon single-crystal ingot is cut into thin disk shapes, and then rough polished using a double-sided flapping method using free abrasive grains to eliminate thickness unevenness and surface roughness during cutting. A very common method was to remove the irregularities and make the thickness constant, then chemically etched it with a strong acid or alkali, followed by polishing to give it a mirror finish.

In the rough polishing process using the above-mentioned double-sided lapping method using free abrasive grains, polishing is performed under slightly high loads between upper and lower opposed iron surface plates, so the silicon single crystal is destroyed at its surface layer. A fracture layer and a strain layer are formed. This layer impairs the properties of the semiconductor, which is the original purpose, and makes the product unusable. In order to remove this layer, chemical etching is performed using a strong acid or a strong alkali. The thickness of the layer removed by chemical etching reaches approximately 50 microns, which is one of the factors that reduces the yield of mirror-finished wafers relative to ingots.

Although rough polishing using free abrasive grains achieves the original purpose of achieving desirable flatness, it has the problem of destroying the crystal layer and requires a chemical etching process as the next step, as mentioned above. , which significantly reduces the yield of mirror-finished wafers to ingots.

Polishing using free abrasive grains consumes a large amount of expensive abrasive grains, is expensive, and is difficult to treat the highly concentrated waste liquid, as well as contaminating the working environment significantly. As for chemical etching, the strong acid method uses a mixed acid of nitric acid, hydrofluoric acid, and acetic acid, which requires a huge investment in equipment and work environment, and it is also difficult to dispose of waste liquid. The strong alkaline method also uses a concentrated KOII solution, and therefore has similar problems, albeit to a slightly lesser extent.

Incidentally, a silicon wafer, that is, a disc-shaped thin piece of silicon single crystal, is an extremely brittle and hard metal, and lacks the characteristics such as ductility and malleability peculiar to metals. In polishing such special metals, polishing with a general grindstone is difficult because the polishing action due to the plastic deformation peculiar to metals is not performed.

(Problems to be solved by the invention) In view of the above-mentioned problems in existing silicon wafer polishing, the inventors of the invention continued their intensive research, and as a result, they developed a method with a specific amount of abrasive grains and a specific degree of abrasive grain bonding. By applying a grinding wheel, on the polishing surface, a large number of abrasive grains that have fallen off and become liberated control the effective rolling action, and the high extreme stress is absorbed by the moderate buffering property of the grinding wheel. This invention has the characteristic that it does not have any adverse effect on the object to be polished, and the present invention was developed based on the fact that the abrasion by the fixed abrasive grains, the rubbing by the abrasive grains, and the rolling by the falling abrasive grains produce a minute cutting action effect. The completed product is intended for silicon and gallium.

To provide a grindstone suitable for polishing semiconductor wafers such as arsenic.

(Means for solving the problem) The above-mentioned object is a structure having a three-dimensional network structure having continuous fine pores in which abrasive particles are bonded with a synthetic resin,
The volume ratio of abrasive grains to the entire structure is 25% or more,
Semiconductor wafer TiJ [achieved with a polishing grindstone] is characterized by the Ohkoshi type or more under 80 k, p load.

The most important thing in the present invention is that the volume of the abrasive grains mentioned above is set to a specific high volume ratio and that the degree of bonding of the abrasive grains in the grindstone is specified.

Here, the volume of the abrasive grains means the true volume, not the volume of the abrasive grains, and is a value determined by weight/true specific gravity. In addition, the degree of bonding measured with an 80 klI load Shimo-Okoshi type bonding tester is JIS standard 6210-1958 5.
．． Using the Okoshi type bonding tester specified in 1, 80
This is the value indicated by the gauge when measured under a load of 1c, 9 (hereinafter abbreviated as degree of bonding).

The abrasive grains that can be applied to the present invention include, for example, silicon carbide, aluminum oxide, boron nitride, diamond, emery, garnet, cerium oxide, chromium oxide, etc., which are made by grinding either a compound or a single abrasive material that has abrasive power. Examples include those classified by an appropriate method to have a particle size specified in JIS Standard R-6001, and silicon carbide and aluminum oxide are particularly suitable.

In order for these abrasive particles to easily fall off the abrasive surface, the volume ratio of the entire structure of the whetstone needs to be 25% or more.

If the volume ratio of abrasive grains is less than 25%, the abrasive grains are relatively small, and even if they fall off easily and become loose, there is not enough to effectively cover the polished surface of the object to be polished, and effective polishing cannot be performed, resulting in a reduction in the amount of polishing. is insufficient.

Due to insufficient release, slippage and roughness appear on the polished surface.
In addition to not being able to achieve the desired uniform polishing, there may be local polishing spots,
Shiny spots and thickness spots occur.

The grindstone according to the present invention has a three-dimensional network structure with continuous fine pores, and the ratio of pores to the entire structure is approximately 40 to 60.
%, and the remaining part is the reticulated material. The pores are continuous and irregular, and the structure as a whole allows relatively free passage of fluid.

To grind using the above whetstone, use the usual method, for example, set the abrasive surface on the upper or lower flat plate while supplying water or water containing grinding fluid quantitatively, and place a blank between the whetstone surfaces. All you have to do is put it in between and rotate the whetstone.

Polishing debris and the like from polishing are trapped in the pore structure to prevent clogging, and the heat generated during polishing can be effectively released to prevent heat accumulation on the polishing surface.

As the binder resin applied to the present invention, it is preferable to use a polyvinyl acetal resin and a thermosetting resin in combination.

As a thermosetting resin, melamine resin is particularly clever.
Favorable results can also be obtained when a phenolic resin is used in combination.

The above-mentioned grindstone according to the present invention is manufactured, for example, by the following method.

An aqueous solution is prepared by mixing polyvinyl alcohol with an average degree of polymerization of about 800 to 2000 and a degree of saponification of 80 mol% or more, or one or more derivatives or modified products thereof;
Fine powder of abrasive grains, a formaldehyde aqueous solution as a hardening agent for polyvinyl alcohol, acidic acids as a hardening catalyst, and the viscous slurry as a pore generator are poured into a mold and heated at a temperature of 40 to 100°C for at least 5 hours. After reaction solidification in a hot water bath or other bath, excess formaldehyde, acid, and starch are removed by washing with water to obtain an intermediate.

+>-161)' Next, the above-mentioned intermediate is immersed in a liquid of a melamine resin dissolved or emulsified in water or an organic solvent to impregnate it with the resin liquid. The amount of resin impregnated is the already obtained continuous fine 1j+
It should not appear to clog the pores, nor should it cover the part corresponding to the skeleton of the network structure. That is, the skeletal part consisting of a matrix of abrasive grains and resin is inserted, and the mixed branches (an amount sufficient to form a new body are placed in air at a temperature of approximately 100°C to evaporate moisture or organic solvents. After removal and drying, heat treatment (curing) for curing reaction of the thermosetting resin is performed.

The temperature and time required for curing can range from 5 to -10 degrees depending on the amount and type of resin used.
It hardens when cured for 0 hours.

Conditions need to be set carefully, as this may affect the quality and homogeneity of the product.

Furthermore, in order to avoid rapid temperature rise during curing, it is also effective to raise the temperature in stages and to perform the curing in an inert gas atmosphere to suppress local oxidative deterioration.

After the whetstone obtained in this way is molded into the desired shape,
Although the polishing device is used for rough polishing of blanks, it is preferable to use it by attaching it to a precision device called a so-called lapping polisher. A general lapping type polishing machine is one that is equipped with shaded or ring-shaped metal surface plates on both the upper and lower surfaces, and is used to form a surface. The blank is placed on a carrier (holding plate) that moves separately from the upper and lower abrasive surfaces.
It is driven by. Also, during operation, water as a polishing aid or water containing an abrasive should be flowed in an appropriate amount and quantitatively.

(Effect of the invention) The grindstone according to the present invention can be replaced with the conventional AI! 209 When the polishing was replaced with lapping using a free abrasive slurry, the following effects were obtained.

(1) Since fixed abrasive grains were used instead of free abrasive grains, expensive slurry was not consumed, and the polishing cost was reduced to about 172.

(2) Since free abrasive grains are not used, the environment around the polishing machine is extremely clean and there is little contamination of workers.

(3) There are very few crystal-destroyed layers and strained layers due to polishing, and the chemical etching process, which takes 2 to 8 steps to remove them, can be reduced to approximately one step.

(4) By omitting the chemical etching step, the wafer removal allowance was reduced, and the yield from silicon ingots to needle-faced wafers could be increased by about 10%.

The present invention will be specifically described below with reference to Examples.

The Okoshi type bonding tester and its measurement method in the examples are as follows.

The Okoshi type coupling degree measuring device is JIS R62105-1
, is a test machine described in the bond strength test, and when a bit with a certain wedge angle, blade length, and blade thickness is pressed against a test whetstone and rotated by a specified angle while applying a specified load, the whetstone The degree of bonding is measured by using a dial gauge to indicate the depth of biting caused by the bit. In the JIS method, the load is 50 k.9, but in the present invention, the load is 80 k! The measurement was carried out as i.

Example Polyvinyl alcohol with a degree of polymerization of 1700 and complete saponification 1
．． Dissolve 0kJ in water to make an approximately 15wt% aqueous solution at 50%
% sulfuric acid 0.6J 165% phenolic resin aqueous solution 1.77
2000 abrasive grain 7, li+, silicon carbide fine powder
．． 64kj/, cornstarch 0.6, F, 87% formalin 1. (1) was added in this order, and finally water was added to make the whole company to and oz, and then stirred uniformly with a stirrer to make a homogeneous slurry-like offshore liquid.This mixed liquid was placed in the specified mold. It was poured and immersed in a 60°C water bath for a solidification reaction for 20 hours to obtain an intermediate. After 20 hours, the solidified intermediate was removed from the mold and poured with sulfuric acid, After removing formalin and corn starch by washing with water, it was cut into pieces approximately 60 mm thick.

The cut pieces were placed in a ventilation dryer to remove moisture and dry.

As a water-soluble melamine resin, 5M-70 manufactured by Showa Kobunshi ■
Prepare 2.29 J of a 35% aqueous solution of 0, impregnate the entire amount into the dried product of the intermediate, air dry it, and then put it in a heat treatment machine for 14 hours.
Heat treatment was performed at a temperature of 0° C. for 10 hours (Sample-1). This was molded and placed on a Speed Fam Model 8FD-5B-5 double-sided polisher.

Attached to the bottom plate. After setting a 3-inch silicon wafer to be polished into the polishing machine using a carrier plate,
Polishing was performed under predetermined conditions. Water was used as the polishing liquid, and after polishing for a predetermined time, the surface condition of the silicon wafer as the object to be polished was measured (Experiment No. 1). Try 2-5 in the same way
A similar test was conducted using the following grindstones (Experiment No. 2~
5). As is clear from Table 1, the abrasive grain size ratio is 25.
% or less, the amount of polishing was small and the thickness was uneven due to polishing, making it impossible to apply it as a polishing material for silicon wafers.

The grinding wheel according to the present invention had an excellent grinding amount and good flattening of dust, and also had an extremely small amount of broken crystal layers.

Claims (6)

[Claims] (1) A structure with a three-dimensional network structure having continuous fine pores in which abrasive grain particles are bonded with a synthetic resin, and the volume ratio of the abrasive grains to the entire structure is 25% or more, and 3
The degree of bonding measured with the Okoshi type bonding tester under a 0 kg load is 1.
A grindstone for polishing semiconductor wafers having a diameter of 0x1/100 mm or more. (2) The grindstone for polishing semiconductor wafers according to claim (1), wherein the abrasive grains are mixed in a volume ratio of 30% or more with respect to the entire structure. (3) The grindstone for polishing semiconductor wafers according to claim (1) or (2), which has a degree of bonding of 15 x 1/100 mm or more. (4) Degree of bonding is 20 x 1/100mm to 80 x 1/10
The grindstone for polishing semiconductor wafers according to claim 1 or claim 2, which has a diameter of 0 mm. (5) The grindstone for polishing semiconductor wafers according to any one of claims (1) to (4), wherein the synthetic resin is a mixture of a polyvinyl alcohol resin and a thermosetting resin. (6) The grindstone for polishing semiconductor wafers according to any one of claims (1) to (5), wherein the thermosetting resin is a melamine resin or a phenol resin.