JPH0671708B2 - Semiconductor wafer-Whetstone for polishing - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a grinding stone for polishing a semiconductor wafer, and more particularly to a silicon wafer which is a material of IC, LSI and the like, and a compound semiconductor such as a gallium arsenide compound. The present invention relates to an abrasive particularly suitable for rough polishing of wafers.

(Prior Art) In recent years, materials used as semiconductor materials such as silicon wafers
The degree of integration of ICs, LSIs, VSLIs, etc. is improving, and the demand for precision in manufacturing is extremely increasing. At the same time, since the manufacturing technology of silicon single crystal has been improved, the diameter of the silicon wafer as the raw material tends to be large, and the difficulty of the manufacturing technology becomes higher and higher. The required accuracy is increasing year by year.

Conventionally, in the manufacturing process of silicon wafers, a cylindrical ingot of silicon single crystal is cut into a thin disk shape, and rough polishing is performed by a double-sided lapping method using loose abrasive grains, resulting in thickness unevenness and surface at the time of cutting. It was a very general method to remove the irregularities and make the thickness constant and then to carry out chemical etching with a strong acid or a strong alkali, followed by polishing to give a mirror finish.

In the rough polishing step in the double-sided lapping method using the loose abrasive grains, since polishing is performed under a considerably high load between iron surface plates facing each other, the silicon single crystal is broken at the surface layer and destroyed. Forming a layer and a strained layer. This layer cannot be a product that impairs the original properties of the semiconductor. Then, in order to remove this layer, chemical etching with strong acid or strong alkali is performed. The thickness of the removed layer by chemical etching reaches approximately 50 microns, which is one of the factors that reduce the yield of mirror-polished wafers for ingots.

Although the rough polishing using loose abrasive grains achieves the original purpose of providing a preferable flatness, it has a problem of breaking the crystal layer and requires a step of chemical etching as the next step. As described above, the yield of the mirror-finished wafer with respect to the ingot is significantly reduced.

Polishing with free abrasive grains consumes a large amount of expensive abrasive grains and is expensive, and it is difficult to treat the high-concentration drainage liquid, and the work environment is significantly contaminated. The chemical etching also uses a mixed acid of nitric acid, hydrofluoric acid, and acetic acid in the strong acid method, which requires enormous investment in equipment and working environment, and waste liquid treatment is also difficult. The strong alkaline method also uses the KOH solution, so it has a similar problem although it is slightly lighter.

By the way, a silicon wafer, that is, a disk-shaped thin piece of a silicon single crystal, is a metal that is extremely brittle and has high hardness, and lacks the characteristic such as ductility and malleability peculiar to metal. In polishing such a special metal, polishing with a general grindstone is difficult because the polishing action due to plastic deformation peculiar to the metal is not performed.

(Problems to be Solved by the Invention) In view of the above problems in existing silicon wafer polishing, the present inventors have conducted intensive studies and as a result, have a specific abrasive grain amount and a specific abrasive grain bond degree. By applying a grindstone, a large number of dissociated abrasive particles on the polishing surface control the effective rolling action, and the high extreme pressure stress is absorbed by the appropriate damping property of the grindstone and the material to be ground is polished. Having a property that does not adversely affect the body, rubbing by a fixed abrasive, finding that a minute cutting action effect is expressed by the rolling action by a sliding friction and a falling abrasive, the present invention has been completed,
The object is to provide a grindstone suitable for polishing a silicon wafer or a compound semiconductor wafer such as a gallium arsenide compound.

(Means for Solving Problems) The above-mentioned object is a structure having a three-dimensional network structure having continuous fine pores in which abrasive particles are adhered with a synthetic resin, and the porosity is 40 to 60%. The volume ratio of the abrasive grains itself is 25% or more of the entire structure including the pores, and the degree of bonding measured by the Ogoshi-type bonding degree tester under a load of 30 kgf is 1
It is achieved by a grinding wheel for polishing a semiconductor wafer, which has a size of 5 × 1/100 mm or more, and the synthetic resin is a mixture of a polyvinyl acetal resin and a thermosetting resin.

What is most important in the present invention is that the volume of the abrasive particles is set to a specific high volume ratio as described above, and the degree of bonding of the binder that bonds the abrasive particles in the grindstone is specified.

Here, the volume of the abrasive grains means a true volume, not a volume of the abrasive grains, and is a value obtained by weight / true specific gravity. In addition, the degree of bond measured with the Ogoshi-type bond tester under a load of 30 kg means the gauge when measured under a load of 30 kg using the Okoshi-type bond tester specified in JIS R 6210-1958 5.1. It is a value (hereinafter abbreviated as the degree of coupling).

As the abrasive grains applied to the present invention, for example, either a silicon carbide, aluminum oxide, boron nitride, diamond, emery, garnet, cerium oxide, chromium oxide or the like, a compound having a grinding force or an abrasive material consisting of a simple substance is crushed. Examples thereof include those classified by a suitable method to have a particle size specified in JIS Standard R-6001, and silicon carbide and aluminum oxide are particularly preferable.

In order for the abrasive grains to easily fall off the polishing surface, the volume ratio of the grindstone to the entire structure must be 25% or more.

If the volume ratio of the abrasive grains is less than 25%, the amount of the abrasive grains is relatively small, and even if they are easily detached and liberated, there is not enough amount to effectively cover the polishing surface of the object to be polished and effective polishing cannot be performed. Insufficient amount.

In addition, the degree of coupling If less than, slipping off of the abrasive grains is insufficient and slippage on the polishing surface,
Scratches and the like appear, the desired uniform polishing cannot be performed, and partial polishing unevenness, gloss unevenness, and thickness unevenness occur.

The grindstone according to the present invention has a three-dimensional network structure having continuous fine pores, the ratio of pores in the entire structure is 40 to 60%, and the remaining portion is an abrasive material having a network structure. The pores are continuous in an irregular state, and the structure as a whole allows relatively free passage of fluid.

In order to polish using the above grindstone, a usual method, for example, while quantitatively supplying water or water containing a grinding liquid, attach a grinding surface to an upper or lower flat plate and insert a blank between the grinding wheel surfaces. Just rotate the Mikomi whetstone.

Polishing debris and the like due to polishing are trapped in the pore structure to prevent the clogging phenomenon, and also effectively dissipate heat generated during polishing and prevent heat accumulation on the polishing surface.

As the binder resin applied to the present invention, a polyvinyl acetal resin and a thermosetting resin are used in combination.

As the thermosetting resin, a melamine resin is particularly preferable, but a phenol resin in combination with a melamine resin is particularly preferable.

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

Polyvinyl alcohol with an average degree of polymerization of about 300-2000 and a degree of saponification of 80 mol% or more, or one or more of its derivatives or modified products is mixed to form an aqueous solution, fine powder of abrasive grains, and crosslinking of polyvinyl alcohol. An aqueous formaldehyde solution as an agent, acids as a crosslinking catalyst, starches as a pore-forming agent, and a thermosetting resin such as a phenolic resin are added and stirred to prepare a uniform viscous slurry.

After pouring the viscous slurry into a mold and performing reaction solidification in a water bath or another bath at a temperature of 40 to 100 ° C for at least 5 hours, it is washed with water to remove excess formaldehyde, acid and starch. And an intermediate is obtained.

Here, the polyvinyl alcohol concentration in the uniform viscous slurry is preferably 3 to 6 wt / vol%, more preferably 4 to 5 wt / vol%. Further, the phenolic resin is preferably 15 to 220 with respect to 100 parts by weight of polyvinyl alcohol.
Parts by weight, more preferably 50 to 150 parts by weight. On the other hand, the intermediate obtained here has a porosity of usually 50.
~ 65%.

Next, the above-mentioned intermediate is immersed in a liquid of melamine resin dissolved or emulsified and dispersed in water or an organic solvent to impregnate the resin liquid. The resin impregnation amount should not be so large as to fill the already obtained continuous fine pores, and may be kept within the range of maintaining the porosity of 40 to 60%. The total amount of the resin may be about 10 to 25% of the total volume including the pores. That is, an aqueous solution, an emulsion or a solution of 10 to 40% is preferable in such an amount that it enters the skeleton portion composed of the abrasive grains and the resin matrix to form the mixed resin body. The above intermediate or an intermediate obtained by impregnating the intermediate with a resin liquid is placed in an atmosphere of about 100 ° C. to evaporate and remove water or an organic solvent, and then dried, followed by a heat treatment (curing) for curing reaction of the thermosetting resin. )I do. The temperature and time required for curing are important factors that ultimately determine the degree of bonding of the grindstone as a product, and therefore must be carefully selected according to the amount and type of resin used. In the case of a melanmine resin or a phenol resin, it is usually 5 to 100 at a temperature of 120 ° C to 180 ° C.
If curing is performed for a period of time, curing is performed within the range of the required degree of bonding.

If the curing is insufficient, the bond strength of the resin as a binder is too high (the value of the degree of bonding is small), the detachment and liberation of abrasive grains is insufficient, and if the curing conditions are severe, thermal decomposition occurs. Etc. are caused to affect the properties and homogeneity of the product.

Further, in order to avoid a rapid temperature rise during curing, it is also effective to raise the temperature stepwise or to suppress local oxidative deterioration by carrying out in an inert gas atmosphere.

The grindstone thus obtained is used for rough polishing of as-cut wafers after being molded into a desired shape, but the polishing device is mounted on a precise device called a so-called lapping type polishing machine. It is preferable to use. A general lapping type polishing machine is a type in which a circular or ring-shaped metal plate is provided on both upper and lower surfaces, and the object to be polished is sandwiched between them to rotate the surface of the object to be polished. An apparatus for polishing by sliding and rubbing, and when the grindstone according to the present invention is applied, the grindstone is mounted instead of the metal surface plate, and the grindstone is used so as to form a uniform working surface. It is suitable. The as-cut wafer is driven by a carrier (holding plate) so as to move differently from the upper and lower polishing surfaces. Also, when in operation, an appropriate amount of water that is a polishing aid or water that contains an abrasive,
It is preferable to use it so as to flow quantitatively.

(Effect of the Invention) The following effects were obtained when the grindstone according to the present invention was replaced with conventional lapping polishing using Al ₂ O ₃ free abrasive slurry.

(1) Since fixed abrasive grains were used instead of loose abrasive grains, consumption of expensive slurry was reduced and polishing cost could be reduced to about 1/2.

(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) The crystal etching layer and the strained layer due to polishing are extremely few, and the chemical etching process for removing them can be shortened to approximately one process.

(4) By omitting the above-mentioned chemical etching process, the wafer removal margin is reduced, and the yield from the silicon ingot to the mirror-finished wafer can be increased by about 10%.

Hereinafter, the present invention will be specifically described with reference to examples.

The Ogoshi type bondability tester and its measuring method in the examples are as follows.

The Ogoshi-type bonding degree measuring device is a tester described in JIS R 62105-1, bonding degree test, and a bit having a certain wedge angle, blade length and blade thickness is pressed against a test grindstone to give a predetermined value. The degree of bite generated in the grindstone when rotated by a predetermined angle while applying a load is indicated by a dial gauge to measure the degree of coupling. JI
In the S method, the load when measuring the bond degree of the resinoid grindstone is 80 kgf, but in the present invention, the load is 30 kg because the grindstone is extremely fragile as a grindstone.
The measurement was performed as f.

Examples and Comparative Examples Polymerization degree 1700, completely saponified polyvinyl alcohol 1.0 kg
Is dissolved in water to form an aqueous solution of about 15 wt% and 50% sulfuric acid 0.5
, 65% phenol resin aqueous solution 1.77 kg, 2000 abrasive grains consisting of silicon carbide fine powder 7.64 kg, corn starch 0.6 kg, 37
% Formalin 1.0 was added in this order, and finally water was added to bring the total amount to 10.0, and then the mixture was uniformly stirred with a stirrer to obtain a homogeneous slurry-like mixed liquid. This mixed solution was poured into a predetermined mold, immersed in a water bath at 60 ° C. and solidified for 20 hours to obtain an intermediate. After 20 hours, the solidified intermediate was taken out of the mold, and after removing excess sulfuric acid, formalin, and corn starch with water while flowing water in a shower shape, about 60
It was cut to a thickness of mm. The cut pieces were placed in a ventilation dryer to remove water and dry.

As water-soluble melamine resin, Showa High Polymer Co., Ltd. SM-70
A 35% aqueous solution 2.29 of 0 was prepared, and the dried product of the intermediate was completely impregnated, air-dried and then placed in a heat treatment machine, and heat-treated at a temperature of 140 ° C. for 10 hours (Sample-1). This was molded and attached to the upper and lower plates of SFD-5B-5 double-sided polishing machine manufactured by Speed Fam Co., Ltd. A 3-inch silicon wafer to be polished was set on the polishing machine using a carrier plate and then polished under predetermined conditions. Water was used as the polishing liquid, and after polishing for a predetermined time, the surface condition of the silicon wafer that was the object to be polished was measured (Experiment No. 1). Try 2 in the same way
The grindstones of Nos. 5 to 5 were prepared and the same test was conducted (Experiment No. 2 to 5). Experiment numbers 2 to 4 are examples, and experiment number 1
5 is a comparative example. The test results were as shown in Table 1.

In the test results, the surface roughness Ra and the flatness Wcm represent the flatness of the surface, and smaller values are preferable because the surface is more flat. Surface roughness Ra
Is the center line average roughness (μ) in the roughness curve measured by a surface roughness meter, and the flatness Wcm is a value indicating the difference between the maximum peak height and the maximum bath depth in the filtered waviness curve.

Scratch was judged by whether or not fine scratches were observed when the surface condition after polishing was visually observed. Further, the polishing spots were marked with a circle when the surface condition after polishing was visually observed, and were marked with a triangle when a part of the surface was not mirror-finished.

As is apparent from Table 1, those having a volume ratio of abrasive grains of 25% or less had a small amount of polishing and had a large amount of thickness unevenness due to polishing, and could not be applied as an abrasive for silicon wafers.

The grindstone according to the present invention has an excellent polishing amount, a good flatness, and an extremely small crystal fracture layer.

Claims (4)

[Claims] 1. A structure having a three-dimensional network structure having continuous fine pores, wherein abrasive grains are adhered by a synthetic resin.
The porosity is 40 to 60%, the volume ratio of the abrasive grains themselves is 25% or more with respect to the entire structure including the pores, and 30
Coupling degree measured by Ogoshi type coupling tester under kgf load is 15 x 1
A grindstone for polishing a semiconductor wafer, wherein the synthetic resin is made of a mixture of a polyvinyl acetal resin and a thermosetting resin. 2. A grinding wheel for polishing a semiconductor wafer 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. A grinding wheel for polishing a semiconductor wafer according to claim 1, wherein the degree of bonding is 20 × 1/100 mm to 80 × 1/100 mm. 4. The grindstone for polishing a semiconductor wafer according to claim 1, wherein the thermosetting resin is a melamine resin or a phenol resin.