JP2011119405A - Abrasive for polishing silicon wafer and method of polishing silicon wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an abrasive for polishing a silicon wafer that improves the surface haze of the silicon wafer and especially never deteriorates the productivity of a mirror-finishing process of the silicon wafer, and also to provide a method of polishing the silicon wafer by using the same. <P>SOLUTION: The abrasive for polishing a silicon wafer contains at least alkaline silica, a water-soluble high molecule, and a cyclic organic compound. The cyclic organic compound is water-soluble, has a molecular weight of ≥80 and <500, contains two or more oxygen atoms as atoms that form a cyclic structure. The cyclic organic component is added in a concentration of ≥0.1 wt.% and ≤500 wt.% with respect to the alkaline silica as a solid content. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an abrasive mainly used for mirror polishing of a silicon wafer in a semiconductor manufacturing process, and a silicon wafer polishing method using the same.

In recent years, with the high integration of electronic devices, a silicon wafer as a substrate is subjected to finer processing by optical lithography. At this time, the minimum line width is 32 nm or less, and miniaturization is progressing day by day. For this reason, if there are particles having a diameter of at least about 32 nm on the surface of the silicon wafer, the manufacturing yield of the electronic device is lowered.
Therefore, in order to stabilize the manufacturing yield, it is necessary to inspect particles having a diameter of about 32 nm on the surface of the silicon wafer.

Usually, in order to detect particles, laser light is irradiated onto the mirror-finished silicon wafer surface, and the particles are measured at high speed by detecting scattered light. In order to detect with high accuracy, it is necessary to reduce the roughness of the wafer surface and improve the S / N ratio.
There is a numerical value called “haze” as a parameter directly related to the S / N ratio at the time of particle measurement. This is done by irradiating laser light vertically onto the mirror-finished silicon wafer surface, measuring the amount of light irregularly reflected by the detector placed around the incident optical axis, and calculating it as the ratio to the amount of incident laser light. Is done. Making this haze value smaller is important for accurately detecting particles having a diameter of 32 nm or less.

The haze of the mirror-finished silicon wafer is determined in the final mirror processing step of the surface processing step.
At that time, as shown in FIG. 2, for example, a general polishing apparatus used includes a polishing surface plate 13 to which a finishing polishing cloth 14 is attached, a finishing abrasive supply mechanism 16, a polishing head 12, and the like. Has been.
In such a polishing apparatus 11, the work (silicon wafer) W is held by the polishing head 12, the finishing abrasive 15 is supplied from the finishing abrasive supply mechanism 16 onto the finishing polishing cloth 14, and the polishing surface plate 13 and the polishing plate 13 are polished. Each of the heads 12 is rotated, a pressurized fluid is supplied to the polishing head 12 by a pressure adjusting mechanism (not shown), and the surface of the work W is pressed against and slidably contacted with the finishing polishing cloth 14 to perform polishing.

In this final mirror finishing process, there are a finishing polishing cloth 14 and a finishing abrasive 15 as members that are in direct contact with the silicon wafer, both of which have a great influence on haze.
Conventionally, soft artificial leather or the like has been used for the finishing polishing cloth 14, and polishing powder of pH 8-12 alkaline colloidal silica or silica powder dispersed in water has been used for the finishing abrasive 15. And this polishing liquid and a silicon wafer raise | generate a mechanochemical effect | action, and final polishing advances.

Here, in Patent Document 1, as an abrasive for improving haze, nonionic surfactant having an HLB value of 13 or more and less than 20 is added to alkaline colloidal silica having an average particle size of 7 to 10 nm to 1 wt. % Abrasives are disclosed.
Patent Document 2 discloses a polishing composition containing silicon dioxide, water, a water-soluble polymer compound, a basic compound, and a compound having 1 to 10 alcoholic hydroxyl groups.

JP-A-4-291722 JP 11-116942 A

However, when a polishing composition containing a nonionic surfactant is used, foaming occurs during polishing, a sufficient polishing rate cannot be obtained within a short time, haze becomes unstable, and productivity is lowered. It was.
Moreover, the polishing composition containing a compound containing an alcoholic hydroxyl group could not satisfy the demand for haze on the surface of a silicon wafer for electronic devices that has been miniaturized.

  The present invention has been made in view of the above problems, and improves the haze of the silicon wafer surface, and in particular, an abrasive for polishing a silicon wafer that does not deteriorate the productivity of the mirror finishing process of the silicon wafer, and An object of the present invention is to provide a method for polishing a used silicon wafer.

  In order to solve the above problems, the present invention is a silicon wafer polishing abrasive comprising at least alkaline silica, a water-soluble polymer, and a cyclic organic compound, wherein the cyclic organic compound has a water-soluble molecular weight. 80 or more and less than 500, containing at least two oxygen atoms as atoms forming a ring structure, and being added in an amount of 0.1 wt% or more and 500 wt% or less based on the solid content of the alkaline silica. An abrasive for polishing a silicon wafer is provided.

Thus, alkaline silica, a water-soluble polymer, a water-soluble molecular weight of 80 or more and less than 500, containing at least two oxygen atoms as atoms forming a ring structure, and with respect to the solid content of alkaline silica When the abrasive for polishing a silicon wafer includes at least 0.1 wt% or more and 500 wt% or less of a cyclic organic compound added, the added cyclic organic compound suppresses siloxane bonds between silicas, and secondary particle aggregation occurs. It can be suppressed. That is, the secondary particle diameter of alkaline silica is small, and when used for polishing a silicon wafer, the surface roughness of the surface of the silicon wafer can be made smaller than in the prior art. Therefore, the haze can be improved, and the detection of particles having a diameter of about 32 nm can be performed with high accuracy and without problems.
In addition, since it is a water-soluble cyclic organic compound rather than a compound having a chain-like hydrophilic group, its surface activity is small, and a sufficient polishing rate can be obtained within a short time as in the case of containing a nonionic surfactant. Therefore, the haze becomes unstable and problems such as a decrease in productivity do not occur, and the productivity of the polishing process can be increased.
Moreover, it can suppress that the surface is etched by containing water-soluble polymer, and can prevent the haze deterioration.

And if it is a water-soluble, organic compound having a molecular weight of 80 or more and less than 500, and a cyclic organic compound containing at least two oxygen atoms as a ring structure atom, it is suitable for directly bonding to silicon atoms in silica. Suitable for suppression of secondary aggregation.
Furthermore, by adding 0.1 wt% or more and 500 wt% or less with respect to the solid content of the alkaline silica, it is possible to efficiently suppress the secondary aggregation of the silica. When the addition amount is less than 0.1% by weight, the addition amount is too small and there is almost no suppression of secondary aggregation. On the other hand, when the amount is more than 500% by weight, the effect of suppressing secondary aggregation with respect to the addition amount is small just by adding the cyclic organic compound.

Here, the cyclic organic compound is preferably a crown ether having a molecular weight of 80 or more and less than 500.
Thus, a crown ether having a molecular weight of 80 or more and less than 500 is very suitable for directly bonding to a silicon atom in silica, can further suppress secondary aggregation of silica, and is very effective in improving haze. Is preferred.

Moreover, it is preferable that the said abrasive | polishing agent for silicon wafers contains 0.01 to 20 weight% of alkaline silicas with a primary particle diameter of 5-55 nm and pH 9-12 as said alkaline silica.
As the silica is smaller, the number of aggregated particles associated in the liquid tends to increase. However, if the silica is 5 nm or more, the number of aggregated particles can be reduced. Moreover, if it is 55 nm or less, it can prevent that the haze level of the silicon wafer surface deteriorates resulting from an excessive particle diameter. And generation | occurrence | production of the scratch in the silicon wafer surface and the increase in surface roughness can also be prevented.
And if content is 0.01 weight% or more, it can prevent that a grinding | polishing rate becomes extremely small resulting from content being too small. Further, if the content is 20% by weight or less, it is possible to prevent the viscosity of the polishing composition from excessively increasing due to the excessive content.

And it is preferable that the abrasive | polishing agent for a silicon wafer polish contains 0.01 to 10 weight% of water-soluble polymers with a molecular weight of 500 or more as the water-soluble polymer.
Thus, by setting the molecular weight of the water-soluble polymer to 500 or more, the surface protection effect is sufficiently exhibited, and it is possible to prevent the addition amount from being increased more than necessary, and to increase the addition amount of the polymer. The viscosity increases and the risk of the silica particles gelling can be suppressed.
Moreover, the surface protection effect is exhibited by adding 0.01% by weight or more, and by adding 10% by weight or less, the amount added can be prevented from becoming unnecessarily large.

The present invention also provides a method for polishing a silicon wafer, comprising polishing the silicon wafer using the polishing agent for polishing a silicon wafer according to the present invention.
The abrasive for polishing a silicon wafer of the present invention is one in which siloxane bonds between silicas are suppressed and secondary particle aggregation is suppressed. Therefore, by polishing the silicon wafer using such an abrasive, the surface roughness of the silicon wafer surface can be reduced as compared with the conventional case, and the haze can be improved as compared with the conventional case. Therefore, particles having a diameter of about 32 nm can be detected with high accuracy, which is effective in stabilizing the manufacturing yield. In particular, the present invention is very suitable for finish polishing.

  As described above, by adding a cyclic organic compound that can be directly bonded to silicon, siloxane bonds between silicas can be prevented, and secondary particle aggregation of silica can be prevented conventionally, and the secondary particle size can be reduced. An abrasive for polishing a silicon wafer can be provided. When such an abrasive for polishing a silicon wafer is used, the haze value of the surface is improved, and the mirror processing of the silicon wafer can be performed without deteriorating the productivity.

It is the graph which showed the relationship between the addition amount of various additives with respect to silica solid content, and the numerical value which divided 50% particle size after addition by 50% particle size before addition. It is the figure which showed an example of the outline of a grinding | polishing apparatus. It is the figure which showed an example of the outline of a washing | cleaning apparatus.

Hereinafter, the present invention will be described more specifically.
When the conventional abrasive | polishing agent was used, there existed a problem that the request | requirement regarding the haze of the silicon wafer surface for electronic devices which progressed miniaturization could not be satisfied. Moreover, even if the haze can be improved, there is a problem that the productivity of the mirror finishing process is deteriorated.

Here, since silica particles are present as secondary particles in the abrasive, it is important to reduce the particle size of the secondary particles to improve haze.
For this reason, the present inventors have made the following studies on additives that reduce the silica secondary particles, that is, improve the dispersibility of silica in the liquid.

A high-purity colloidal silica produced by a commercially available sol-gel method and having a primary particle diameter of 35 nm, a secondary particle diameter of 70 nm, and an association degree of 2 was used, and diluted with ultrapure water so that the silica solid content was 3% by weight.
To this abrasive, the substances shown in Table 1 described later were added as additives for preventing secondary aggregation of silica, and the addition amount was changed from 0.1 to 500% by weight with respect to the silica solid content.
Note that α cyclodextrin and γ cyclodextrin, which are one of the additives, were added at a maximum of 150% with respect to the solid content of silica due to the problem of solubility in water.

Then, 0.5% by weight of polyvinyl alcohol having a molecular weight of 2000 was added to the abrasive with the additive added, and finally 28% high-purity ammonia water was added so that the pH was 10 in order to increase the polishing rate. In addition, it confirmed beforehand with the particle size distribution measuring device that addition of this water-soluble polymer had no influence on the silica secondary particle size distribution.
After sufficiently stirring, the silica secondary particle diameter at each addition amount was measured by a dynamic light scattering method using “Delsa Nano” manufactured by BECKMANCOULTER.

  The results are shown in FIG. FIG. 1 is a graph showing the relationship between the amount of each additive added to the silica solid content and the value obtained by dividing the 50% particle size after addition by the 50% particle size before addition. The horizontal axis represents the weight percentage of additive added relative to the silica solids. The vertical axis is the 50% particle size ratio (the value obtained by dividing the 50% particle size of the silica secondary particles after addition of the additive by the 50% particle size of the silica secondary particles before adding the additive), and this value is small. It shows that the effect of an additive is so large.

  When a polyoxyalkylene alkyl ether having an HLB value of 14 was added as a nonionic surfactant having an HLB value of 13 or more and less than 20 which is an additive disclosed in the above-mentioned Patent Document 1, as shown in FIG. The amount added per minute was 15% or more, and the 50% particle size ratio was constant around 0.65 to 0.70.

Therefore, 20% by weight of polyoxyalkylene alkyl ether (HLB value 14) is added to the silica solid content, and then 0.5% by weight of polyvinyl alcohol having a molecular weight of 2000 is added so that the pH becomes 10. A polishing agent was prepared by adding 28% high-purity ammonia water.
When this abrasive was used to polish an actual silicon wafer, the haze was improved compared to the additive-free abrasive, but foaming occurred during polishing and sufficient polishing was achieved within a short time. The speed could not be obtained and the haze became unstable, causing a decrease in productivity.
In the case of a nonionic surfactant having a hydrophilic group such as a polyalkylene oxide and a hydrophobic group such as an alkyl group in the molecule, the hydrophilic polyalkylene oxide is wound around the silica particles, and the silica secondary particles Although it is thought that the association is inhibited, since it has surface activity, it seems to be easy to foam. Therefore, it was found that nonionic surfactants are not suitable as additives for abrasives for improving haze.

Next, ethanol, which is an additive disclosed in Patent Document 2, was added.
Then, as shown in FIG. 1, the amount added with respect to the silica solid content was 150% or more, and the 50% particle size ratio was 0.75 to 0.80.

  Therefore, ethanol was added in an amount of 150% by weight with respect to the silica solid content, followed by addition of 0.5% of polyvinyl alcohol having a molecular weight of 2000, and 28% high-purity ammonia water was added so that the pH would be 10, followed by polishing. An agent was prepared. Using this abrasive, the actual silicon wafer was polished. The haze was almost the same as that of the abrasive with no ethanol added.

Next, in order to improve the foaming property of the nonionic surfactant, a polyethylene glycol portion having a molecular weight of 600 (PEG 600), which is an ethylene oxide portion excluding the hydrophobic alkyl group, is added to the particle size distribution. It was measured.
As a result, as shown in FIG. 1, the amount added to the silica solid content was 29% to 74%, and the 50% particle size ratio became the smallest and became 0.60.

Therefore, a chain polyethylene glycol having a molecular weight of 600 is added in an amount of 50% by weight based on the silica solid content, and subsequently, polyvinyl alcohol having a molecular weight of 2000 is added in an amount of 0.5% by weight. High purity ammonia water was added to prepare an abrasive.
When this silicon abrasive was used to polish an actual silicon wafer, the haze was slightly improved compared to the abrasive with no additive added, foaming did not occur during polishing, and the haze was stable during normal polishing time. did. However, the amount of improvement in haze was not sufficient. In this wafer, particles of about 32 nm could not be detected.

Therefore, water-soluble alcohols, crown ethers, and saccharides, which are cyclic organic compounds and have low surface activity, were studied as additives, not compounds having a chain-like hydrophilic group.
The organic compounds actually evaluated are: cyclopentanol having a ring structure of 5 atoms, 0 oxygen atoms contained in the ring atoms, and a molecular weight of 86, in the order of the number of atoms forming the ring structure. 12 atoms, 12 oxygen atoms contained in the ring-forming atoms, 12 crown 4 ethers having a molecular weight of 176, 15 ring-forming atoms, 5 oxygen atoms contained in the ring-forming atoms, 15 crowns 5 having a molecular weight of 220 Ether, 18 ring-forming atoms, 6 oxygen atoms contained in ring-forming atoms, 18 crown 6 ether having molecular weight of 264, 30 ring-forming atoms, 12 oxygen atoms contained in ring-forming atoms, molecular weight of 973 Α-cyclodextrin, 40 ring-forming atoms, 16 oxygen atoms contained in the ring-forming atoms, and 6 cyclic organic compounds of γ-cyclodextrin having a molecular weight of 1297 were prepared and added. The cloth was measured.

As a result, the crown ethers were effective, and the most effective was 18 crown 6 ether. The amount added to the silica solid content was 15% or more, and the 50% particle size ratio was 0. It became constant around 55-0.60.
The next most effective was 15 crown 5 ether. The amount added to the silica solid content was 29% to 250%, and the 50% particle size ratio was the smallest, about 0.60. The next effect was 12 crown 4 ether, the amount added to the silica solid content was 150% to 250%, and the 50% particle size ratio was the smallest, 0.60 to 0.65. became.

In contrast, in the case of cyclopentanol, which is a cyclic alcohol, the amount added to the silica solid content is 150% or more, and the 50% particle size ratio is 0.65 to 0.70, which is 0.75 of ethanol. It was more effective than ~ 0.80.
It was more effective than 0.80.
In addition, no effect was observed for α-cyclodextrin and γ-cyclodextrin, which are cyclic saccharides.

The 18 crown 6 ether, which had the greatest improvement effect, was added at 20% by weight based on the silica solid content, followed by addition of 0.5% by weight of polyvinyl alcohol having a molecular weight of 2000, and 28% so that the pH was 10. High purity ammonia water was added to prepare an abrasive.
An actual silicon wafer was polished using this abrasive. The haze was greatly improved as compared with the abrasive with no additive added, foaming did not occur during the polishing, and the haze was stabilized with normal polishing time. In this wafer, particles of about 32 nm could be detected.

And the abrasive | polishing agent which used cyclopentanol as an additive was produced similarly to the case of 18 crown 6 ether, the silicon wafer was grind | polished using the abrasive | polishing agent, and the haze was evaluated.
As a result, the haze was hardly improved even when compared with the abrasive without additives.

  In summary, the present inventors have found that a cyclic organic compound is effective as an additive for preventing secondary particle aggregation in an abrasive containing silica, and even if it is a cyclic organic compound, the molecular weight is 500. It has been found that a compound that does not contain at least two oxygen atoms as atoms forming the ring structure as described above has little effect on improving haze, although it can prevent secondary aggregation. That is, it has been found that a compound having a molecular weight of 80 or more and less than 500 and containing at least two oxygen atoms as atoms forming a ring structure can improve haze and detect particles having a diameter of about 32 nm.

  And based on the above knowledge, the present inventors, as an additive for suppressing the association of alkaline silica, are water-soluble, have a molecular weight of 80 to less than 500, and at least an oxygen atom as an atom forming a ring structure By adding a cyclic organic compound containing at least 2 and containing 0.1 wt% or more and 500 wt% or less based on the solid content of the alkaline silica, the secondary particle aggregation of silica can be suppressed. The present invention was completed based on the idea that the haze of the surface of a silicon wafer polished with an abrasive can be made better than before.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.
The polishing agent for polishing a silicon wafer according to the present invention includes at least two or more oxygen atoms as atoms forming at least an alkaline silica, a water-soluble polymer, a water-soluble molecular weight of 80 to 500, and a ring structure. And a cyclic organic compound added by 0.1 wt% or more and 500 wt% or less with respect to the solid content of the alkaline silica.

In the abrasive for polishing a silicon wafer having such a composition, the added cyclic organic compound is directly and efficiently bonded to the silicon in the silica, and the siloxane bond between the silicas is suppressed. In other words, secondary particle aggregation is suppressed, the secondary particle diameter of alkaline silica is small, and when used for polishing a silicon wafer, the surface roughness of the silicon wafer surface can be made smaller than before. is there.
Moreover, it can suppress that the surface is etched by containing water-soluble polymer, and can prevent the haze deterioration.

Further, since a water-soluble cyclic organic compound having a low surface activity, a molecular weight of 80 or more and less than 500 and containing at least two oxygen atoms as atoms forming a ring structure is added, Very suitable for direct bonding, suitable for suppressing secondary agglomeration of silica, and sufficient polishing rate in a short time as in the case of abrasives with nonionic surfactant added Is not obtained, the haze becomes unstable, and problems such as a decrease in productivity do not occur, and the productivity of the polishing process can be sufficiently increased.
Since the cyclic organic compound is added in an amount of 0.1 wt% to 500 wt% with respect to the solid content of the alkaline silica, silicon in the silica and the cyclic organic compound are efficiently bonded to suppress secondary aggregation of the silica. it can. When the addition amount is less than 0.1% by weight, there is almost no suppression of secondary aggregation because the addition amount is small. On the other hand, when the amount is more than 500% by weight, the addition of the cyclic organic compound only increases the cost, and the effect of suppressing secondary aggregation with respect to the added amount is small and is wasted.

Here, the cyclic organic compound can be a crown ether having a molecular weight of 80 or more and less than 500.
As described above, the crown ether having a molecular weight of 80 or more and less than 500 has a high ratio of directly bonding to the silicon atom in the silica, and can more effectively suppress the secondary aggregation of the silica. That is, the haze on the surface of the silicon wafer can be greatly improved, and in such a silicon wafer, particles of about 32 nm existing on the surface can be easily detected. In addition, since there is no foaming during polishing and it is not necessary to extend the polishing time, the productivity of the mirror finishing process is not deteriorated, and it has very desirable characteristics as an abrasive.

Alkaline silica having a primary particle diameter of 5 to 55 nm and pH of 9 to 12 can be used, and can be contained in an amount of 0.01% by weight to 20% by weight with respect to the total amount of the abrasive.
If pH is 9-12, it can prevent that the polishing rate of a silicon wafer falls, and productivity of a polishing process does not deteriorate.
And if content of this alkaline silica is 0.01 weight% or more with respect to the whole quantity of an abrasive | polishing agent, it can prevent that a grinding | polishing rate becomes extremely small resulting from content being too small. . Moreover, if it is 20 weight% or less, it will not be contained excessively and it can prevent that the viscosity of polishing composition increases excessively.

In order to improve the haze, it is necessary to reduce the surface roughness of the silicon wafer. Naturally, it is better that the particle diameter of silica as an abrasive is also small, and it is not desirable that it is too large. And, since the number of associated particles in the liquid tends to increase as the primary particle size is smaller, 5-55 nm of silica is preferable as the primary particle size.
When the particle diameter of primary particles of silica is 5 nm or more, the number of agglomerated particles can be reduced, and an abrasive suitable for improving haze can be obtained. Moreover, if it is 55 nm or less, the haze deterioration resulting from an excessive particle diameter can be prevented, and the generation | occurrence | production of a surface scratch and the increase in surface roughness can also be prevented.

As silica to be used, it is desirable to use high-purity colloidal silica produced by a sol-gel method with relatively few metal impurities, or fumed silica produced by a gas phase method.
Colloidal silica is usually present in the liquid as secondary particles in which several primary particles are associated. On the other hand, fumed silica is usually present in the liquid as secondary particles in which several primary particles are associated.
High-purity colloidal silica is produced by hydrolyzing an organosilicon compound in a wet manner, and has a feature that it has very few metal impurities and is relatively stable even in a neutral region.
Fumed silica is produced by burning silicon tetrachloride and oxyhydrogen. This forms secondary particles having a chain structure in which several to several tens of primary particles are gathered, and the content of metal impurities is relatively small.

  When actually polishing a silicon wafer, the surface of the wafer is etched by an alkali component added to the polishing agent after the polishing is finished and until the silicon wafer is cleaned, which may deteriorate haze. is there. For this reason, a silicon surface protecting agent is required in the abrasive. As this surface protective agent, a low-foaming non-etching water-soluble polymer is used without affecting the distribution of the silica secondary particle size.

The water-soluble polymer can have a molecular weight of 500 or more, and can be contained in an amount of 0.01% by weight to 10% by weight with respect to the total amount of the abrasive.
If the molecular weight of the water-soluble polymer is 500 or more, the effect of protecting the surface of the silicon wafer is sufficiently exhibited, and it is not necessary to increase the addition amount more than necessary. Therefore, without increasing the addition amount of the polymer more than necessary, the risk that the viscosity increases and the silica particles are gelled can be minimized.
Moreover, if the addition amount with respect to the whole quantity of an abrasive | polishing agent is 0.01 weight% or more, the surface protection effect will fully be exhibited. And if it is 10 weight% or less, it is not necessary to make addition amount larger than necessary.

  The abrasive for polishing a silicon wafer of the present invention may be prepared by diluting the stock solution with ultrapure water. If the dilution rate is 20 times or less, the amount of the stock solution used can be suppressed, and for example, it can be used with sufficient performance to withstand final polishing.

  Although an example of the polishing method of the silicon wafer of the present invention using the polishing agent for polishing a silicon wafer of the present invention as described above is shown below, the present invention is of course not limited thereto.

First, a silicon wafer to be polished is prepared.
In the polishing apparatus 11 as shown in FIG. 2, the silicon wafer W is held by the polishing head 12, and the polishing slurry for silicon wafer polishing of the present invention is supplied onto the finishing polishing cloth 14 from the finishing polishing agent supply mechanism 16. The polishing surface plate 13 and the polishing head 12 are respectively rotated, and a pressurized fluid is supplied to the polishing head 12 by a pressure adjusting mechanism (not shown), and the surface of the work W is pressed against and slidably contacted with the finishing polishing cloth 14. It can be done by.

  In the abrasive for polishing a silicon wafer of the present invention, siloxane bonds between silicas are suppressed, and secondary particle aggregation is suppressed as compared with conventional abrasives. Therefore, when a silicon wafer is polished using such an abrasive, the surface roughness of the silicon wafer surface can be reduced as compared with the conventional case, and the haze can be improved as compared with the conventional case. Therefore, particles having a diameter of about 32 nm can be detected with high accuracy, the manufacturing yield can be stabilized, and the productivity of the polishing process can be increased.

In particular, the silicon wafer polishing method of the present invention is very effective for the final mirror finishing process.
In the mirror polishing process, multiple stages of polishing are usually performed. Of these, the polishing agent has a great influence on haze in the final final polishing, so the silicon wafer polishing abrasive of the present invention improves this final polishing process. It plays a big role.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Examples 1 and 2, Comparative Example 1-4)
As a silicon wafer to be polished, a P-type, <100> pulled up by the Czochralski method, a single crystal silicon ingot having a resistivity of 8-12 Ωcm and a diameter of 300 mm was sliced to obtain a thin disc-shaped silicon wafer.
Then, in order to prevent the silicon wafer from being cracked or chipped, the outer edge portion was chamfered and then lapped for planarization.
Next, an etching process was performed to remove the processing strain remaining on the surface of the wafer after lapping. Furthermore, both sides of the front and back surfaces of the silicon wafer were polished, and the chamfered portion was also polished. Mirror polishing is further performed on one side of the silicon wafer. In this polishing step, a polishing machine as shown in FIG. 2 was used to perform rough polishing and final polishing of the silicon wafer. The polishing conditions were as follows.

<Rough polishing>
A polyester nonwoven fabric impregnated urethane resin impregnated product (Asker C hardness 76 °) was used as the polishing cloth, and an alkaline solution having a pH of 10.5 containing colloidal silica was used as the polishing slurry. The polishing head and the polishing platen were each rotated at 30 rpm, and the polishing pressure of the silicon wafer was set to 15 kPa for rough polishing.
In advance, a 10% concentration of citric acid is dropped into the storage tank so that the pH of the storage water is maintained at 3 to 7, and a surfactant (polyoxyethylene alkyl ether) is added at a concentration of 0.01%. It was dripped so that it might be kept above.
The wafer after rough polishing was stored in storage water as described above, and then final polishing was performed within 10 minutes.

<Finishing polishing>
Using a suede type polishing cloth (“Ciegal 7355” Asker C hardness 73 ° manufactured by Toray Coating Co., Ltd.), the final abrasive was diluted 15 times with ultrapure water by the method described later. The polishing head and the polishing platen were each rotated at 20 rpm, the polishing pressure of the wafer was set to 10 kPa, and final polishing was performed for 3 minutes.

The final abrasive was produced by the following procedure.
A high-purity colloidal silica produced by a commercially available sol-gel method, a primary particle diameter of 35 nm, a secondary particle diameter of 70 nm, and an association degree of 2 were prepared, and diluted with ultrapure water so that the silica solid content was 3% by weight. The silica particle diameter was measured by a dynamic light scattering method using “Delsa Nano” manufactured by BECKMANCOULTER.

  As an additive for preventing silica secondary particle aggregation, commercially available 18 crown 6 ether is 20% by weight based on the silica solid content (Example 1), and commercially available 15 crown 5 ether is based on the silica solid content. 40 wt% (Example 2), commercially available polyoxyalkylene alkyl ether having an HLB value of 14 with respect to silica solid content (Comparative Example 1), and commercially available ethanol with 150 wt% based on silica solid content (Comparative Example 2), a commercially available chain polyethylene glycol having a molecular weight of 600 is 50% by weight (Comparative Example 3) based on the silica solid content, and a commercially available α-cyclodextrin is 40% by weight (Comparative Example). 4) is added, and subsequently, 0.5% by weight of polyvinyl alcohol having a molecular weight of 2000 is added, and 28% high-purity ammonia water is added so that the pH becomes 10. , To prepare a polishing agent for final polishing.

<Cleaning after polishing>
Using a cleaning apparatus as shown in FIG. 3, ozone cleaning and two-fluid cleaning were performed as cleaning after finish polishing.
In ozone cleaning, pure water 26 containing 20 ppm ozone was sprayed from the ozone water nozzle 23 toward the silicon wafer W rotating at 60 rpm at a flow rate of 12 L / min. At this time, the temperature of the ozone water 26 was normal temperature, the distance between the nozzle 23 and the silicon wafer W was 30 mm, and the angle of the nozzle 23 was 75 °. The nozzle 23 was scanned so that one reciprocation was 30 seconds in the radial direction of the silicon wafer W.
Thereafter, two-fluid cleaning was performed. The ultrapure water 25 to which carbon dioxide (CO ₂ ) has been added is 0.2 L / min · 0.5 MPa, and the nitrogen (N ₂ ) gas 24 is 235 L / mim · 0.4 MPa to the two-fluid cleaning nozzle 22. The mixed fluid 25 was jetted toward the silicon wafer W rotating at 1800 rpm. At this time, the distance between the nozzle 22 and the silicon wafer W was 20 mm, and the angle of the nozzle 22 was 90 °. The nozzle 22 was scanned so that one reciprocation in the radial direction of the silicon wafer W was 30 seconds.
Thereafter, chemical cleaning using a mixed aqueous solution of ammonia water, hydrogen peroxide water and water was performed. In this chemical cleaning, a water purification tank was filled with a cleaning solution having a composition ratio of ammonia: hydrogen peroxide: water of 1: 1: 100, and a silicon wafer was immersed therein. At this time, the etching allowance was adjusted to be 0.2 nm.

After this cleaning, a haze and particles on the surface of the silicon wafer were measured using a particle counter (“Surfscan SP-2” manufactured by KLA Tencor).
Specifically, particles of about 32 nm were detected by performing measurement under a high resolution condition of a particle counter (“Surfscan SP-2” manufactured by KLA Tencor).
Moreover, about haze, it measured simultaneously at the time of particle | grain measurement, and used the haze value in a dark field wide diagonal incidence channel (DWO). Here, DWO represents a path for carrying scattered light focused by an elliptical mirror from oblique irradiation light. The results are shown in Table 2.

As shown in Table 2, the surface of the silicon wafer polished using the silicon wafer polishing abrasive of Example 1 has an average haze value of 0.05 ppm, and 0.09 ppm of the additive-free abrasive. Compared to a significant improvement. Further, foaming did not occur during polishing, and the haze was stable after 3 minutes of polishing. In the silicon wafer of Example 1, particles of about 32 nm could be detected.
Further, the average haze value of the silicon wafer of Example 2 was 0.06 ppm, which was greatly improved. Further, as in Example 1, foaming did not occur during the polishing, and the haze was stabilized with a normal polishing time of 3 minutes. Even in this silicon wafer, particles of about 32 nm could be detected as in Example 1.

In the silicon wafer of Comparative Example 1, the haze in the wafer surface varied in 3 minutes of the normal polishing time, and an area where particles of about 32 nm could not be detected partially occurred. In addition, foaming during finish polishing was severe, and the finish polishing rate was slower than that of the additive-free finish polishing agent.
Moreover, the average haze value of the silicon wafer of Comparative Example 2 was 0.09 ppm, 0.07 ppm for the silicon wafer of Comparative Example 3, and 0.09 ppm for the silicon wafer of Comparative Example 4, which was 0. Compared to 09 ppm, there was no change or almost no improvement. Further, none of the silicon wafers could detect particles of about 32 nm.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.

DESCRIPTION OF SYMBOLS 11 ... Polishing apparatus, 12 ... Polishing head, 13 ... Polishing surface plate, 14 ... Finish polishing cloth, 15 ... Finish polishing agent, 16 ... Finish polishing agent supply mechanism,
22 ... two-fluid cleaning nozzle, 23 ... ozone water nozzle, 24 ... nitrogen gas, 25 ... CO ₂ containing ultrapure water, 26 ... ozone water,
W: Silicon wafer.

Claims (5)

A polishing agent for polishing a silicon wafer containing at least alkaline silica, a water-soluble polymer, and a cyclic organic compound,
The cyclic organic compound is water-soluble, has a molecular weight of 80 or more and less than 500, contains at least two oxygen atoms as atoms forming a ring structure, and is 0.1% by weight or more based on the solid content of the alkaline silica A polishing agent for polishing silicon wafers, wherein 500 wt% or less is added.   The abrasive for polishing a silicon wafer according to claim 1, wherein the cyclic organic compound is a crown ether having a molecular weight of 80 or more and less than 500.   The abrasive for polishing a silicon wafer contains 0.01 wt% or more and 20 wt% or less of alkaline silica having a primary particle diameter of 5 to 55 nm and a pH of 9 to 12 as the alkaline silica. The polishing agent for polishing a silicon wafer according to claim 2.   The abrasive for polishing a silicon wafer contains 0.01 to 10% by weight of a water-soluble polymer having a molecular weight of 500 or more as the water-soluble polymer. The abrasive | polishing agent for silicon wafers of any one of Claims 1.   A method for polishing a silicon wafer, comprising polishing the silicon wafer using the polishing agent for polishing a silicon wafer according to any one of claims 1 to 4.

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