JP2001118815A - Polishing composition for polishing semiconductor wafer edge, and polishing machining method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polishing composition for effectively and stably polishing and machining the edge of a semiconductor wafer that is made of a silicon wafer, a compound wafer, or the like. SOLUTION: In the polishing composition for polishing a semiconductor wafer edge, an average primary particle diameter being calculated by full sphere conversion from a specific surface area being measured by the BET method ranges from 8 to 50 nm, an average secondary particle diameter B being measured by the laser scattering method using a micro track UPA ranges from 12 to 200 nm, a ratio B/A of the average primary particle diameter A to the average secondary particle diameter B ranges from 1.4 to 12, the concentration of a silicon oxide particle for entire solution is 2-30 wt.% in a colloidal solution, and also a buffering operation is achieved between pH 8-11 containing a buffering solution where a weak acid in that the logarithmic value of the inverse number of an acid dissociation constant at 25 deg.C ranges from 8.0 to 12.5 and a strong base are combined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing composition for polishing the edge of a semiconductor wafer such as a silicon wafer or a compound wafer. Furthermore, the present invention relates to a method for mirror-finishing an edge portion of a semiconductor wafer using the polishing composition for polishing a wafer edge.

[0002]

2. Description of the Related Art Electronic components such as ICs, LSIs, and super LSIs, which are made of a semiconductor material such as a silicon single crystal as a raw material, are formed on a wafer obtained by slicing a silicon or other compound semiconductor single crystal ingot into a thin disk shape. It is manufactured based on a small semiconductor element chip obtained by writing and dividing a fine electric circuit. The wafer sliced from the ingot is processed into a mirror-finished wafer having at least one surface mirror-finished through a process of lapping, etching, and polishing. In the subsequent device process, fine electric circuits are formed on the mirror-finished surface in the subsequent device process, but the wafer kept the original disk shape until it was divided into semiconductor element chips It is processed as it is, and steps such as cleaning, drying, and transporting are inserted between each processing step. During that time, if the shape of the outer peripheral side edge of the wafer is a steep and unprocessed rough surface, it contacts equipment and other objects during each process, causing microdestruction and generating fine particles, Contaminant particles are often entangled in rough surfaces, which are dissipated in subsequent steps and contaminate the precision-machined surfaces, greatly affecting product yield and quality. In order to prevent this, it is a common practice to chamfer (bevel) the edge portion at the initial stage of wafer processing and further mirror-finish the edge portion (edge polishing).

[0003] In the edge polishing described above, generally, a beveling, which is a workpiece, is attached to a polishing machine in which a polishing pad made of synthetic resin foam, synthetic leather, nonwoven fabric, or the like is attached to a rotatable drum surface. The edge portion of the applied silicon wafer or the like is inclinedly pressed while rotating, and the edge portion is polished while supplying a polishing composition solution containing colloidal silica as a main component. The polishing composition used here is the same as that used for polishing the surface of the wafer.

As a polishing composition, a solution in which fine colloidal silicon oxide fine particles are dispersed in a solution containing an alkali component is generally used. This processing is different from the so-called mechanical processing using, for example, a diamond grindstone or using hard alumina-based abrasive grains up to the previous step, and the chemical processing of the alkali as its component is performed. The function, specifically, the erosion of a workpiece such as a silicon wafer is applied. That is, a thin soft erosion layer is formed on the surface of a workpiece such as a wafer due to the corrosiveness of the alkali. Processing proceeds by removing the thin layer by mechanical action of fine colloidal silicon oxide particles.

In such processing, the shape of colloidal silica is an important factor. That is, the surface of the workpiece is corroded by the alkali to form a thin layer, and the removal rate of the thin layer greatly changes depending on the shape of the colloidal silica. If the particle diameter of the colloidal silica is increased, the removal rate is increased, but scratches are easily generated on the polished surface. Therefore, the particles must be of a suitable size and must not be easily broken or aggregated and gelled to a higher degree. That is, the silicon oxide particles effectively remove the erosion layer formed by the alkali by mechanical action. Therefore, it must not affect the new polished surface after the removal.

Conventionally, various polishing compositions have been proposed as polishing agents for wafers and the like. For example, US Pat.
In Japanese Patent No. 170273, silica sol and silica gel are proposed as abrasives. See also US Pat.
No. 8141 discloses that the pH of the suspension is from 10.5 to 1
It is disclosed that the polishing rate is increased by setting the ratio within the range of 2.5. U.S. Pat. No. 4,169,337 discloses adding amines to the polishing composition. JP-A-2-158684 discloses a polishing composition comprising water, colloidal silica, a water-soluble polymer having a molecular weight of 100,000 or more, and water-soluble salts. Further, Japanese Patent Application Laid-Open No. 5-154760 discloses a polishing method using a polishing composition containing 10 to 80% by weight of piperazine, which is a kind of water-soluble amine, based on silica of silica sol or silica gel.

Polishing an edge portion of a semiconductor wafer such as a silicon wafer or a compound wafer;
When comparing the planar polishing conditions of silicon wafers or compound wafers, the former has a shorter polishing pad contact time with the edge part, so the polishing pad has a higher pressure applied to the processing surface, and the line of the polishing pad to the processing surface is shorter than the latter. The speed is also faster. That is,
It can be said that the polishing process of the edge portion is a very severe condition as compared with the planar polishing. Since the edge portion of the semiconductor wafer is supplied in a state of being polished with a # 1000 beveling grindstone, its surface roughness is very rough. Under such processing conditions, a sufficient polishing rate and surface roughness cannot be obtained even with a conventional polishing composition for planar polishing of a semiconductor wafer or the like.

[0008]

SUMMARY OF THE INVENTION In view of the problems of the above-mentioned conventional polishing composition and polishing method, the present inventors,
As the polishing composition solution, a colloid containing fine silicon oxide abrasive grains, that is, an aqueous solution of colloidal silica, having an average primary diameter of 8 to 50 nm and an average secondary particle diameter of 12 to 20
A colloid containing 0 to 30% by weight of silicon oxide particles having a ratio of average primary particle diameter to average secondary particle diameter, average secondary particle diameter / average primary particle diameter of 1.4 to 12; It has been found that the mirror polishing of the edge portion of a semiconductor wafer such as a silicon wafer can be effectively performed by using a polishing composition comprising a solution and having an action of buffering the pH between 8 and 11. The purpose of the present invention is to achieve a high polishing rate, and a wafer edge polishing for performing a mirror polishing of an edge portion of a semiconductor wafer capable of obtaining a good surface roughness. It is to provide a polishing composition. Still another object of the present invention is to provide a method for mirror-polishing an edge portion of a semiconductor wafer using the above-described polishing composition for polishing a wafer edge.

[0009]

An object of the present invention is to provide a microtrack U having an average primary particle diameter A of 8 to 50 nm, calculated as a sphere, from a specific surface area measured by the BET method.
Average secondary particle size B measured by laser scattering method with PA
Is in the range of 12 to 200 nm, and the ratio B / A of the average primary particle diameter A to the average secondary particle diameter B is 1.4 to 12
And the concentration with respect to the whole solution is 2-30.
It is a colloidal solution of silicon oxide particles in weight%, and the logarithm of the reciprocal of the acid dissociation constant at 25 ° C. is 8.0.
By including a buffer solution combining a weak acid and a strong base of 〜12.5, a polishing composition for polishing a semiconductor wafer edge characterized by having a buffering action between pH 8 and 11 is achieved. The semiconductor wafer according to the present invention includes a silicon wafer, a compound wafer, and a so-called bare wafer having no surface coated with a compound wafer, a semiconductor film having an insulating film such as silicon dioxide formed on the surface, or a semiconductor film such as polysilicon. Also refers to those provided with a metal conductor film such as a copper thin film.

Still another object of the present invention is to mount a semiconductor wafer to be processed on an edge polishing machine having a rotatable drum to which a polishing pad made of synthetic resin foam, synthetic leather or non-woven fabric is attached. Press
The present invention is attained by a method for edge polishing a semiconductor wafer, characterized in that while the polishing composition for polishing an edge of a semiconductor wafer is supplied, both or one of the drum and the workpiece is rotated and polished.

[0011]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a polishing agent contained in a polishing composition for polishing a semiconductor wafer edge is prepared by using silicon oxide fine particles having a specific particle size and distribution, and further comprising a mother liquor containing the fine particles. Is a buffer having a buffering action in a specific pH range.
That is, the average primary particle diameter A of the silicon oxide fine particles is set to 8 to 5
0 nm, and the average secondary particle diameter B of the secondary aggregation is 1
An excellent edge mirror surface processing can be performed only by controlling the primary particle diameter A and the secondary particle diameter B in the range of 1.4 to 12 by controlling the primary particle diameter A to the secondary particle diameter B in the range of 1.4 to 12. is there. A solution containing silicon oxide fine particles of such a size forms a colloidal solution.

The fine particles of silicon oxide have an average primary particle diameter of 8n.
If it is smaller than m, the colloid solution is likely to aggregate and the stability as a polishing composition is reduced. In addition, the average primary particle size,
When it is 50 nm or more, the performance as a polishing composition is not affected, but it is difficult to stably produce the secondary aggregated particles. Ratio of average primary particle diameter A to average secondary particle diameter B, B / A
Is 1.4 or less, there is no difference between the polishing rate and the fine particles of silicon oxide that are not secondary aggregated. When B / A is 12 or more,
Fine particles of silicon oxide aggregated in a high order are generated, and scratches are likely to occur. The average secondary particle diameter is desirably 200 nm or less. If the average secondary particle diameter exceeds 200 nm, the sedimentation of the particles increases, which is not preferable. It is desirable that the concentration of silicon oxide be 2 to 30% by weight during actual polishing.

The colloidal silica used in the present invention is:
Those produced by deionization from water glass, those obtained by dispersing fumed silica in water or the like, those produced by hydrolyzing an organosilicon compound, and the like can be used. The average primary particle diameter of the silicon oxide fine particles was calculated from the specific surface area of the dried silicon oxide fine particles in terms of a sphere. The specific surface area was measured by the BET method. The average secondary particle diameter of the fine particles of silicon oxide is determined by Microtrac UPA (HONEW
The measurement was performed using a laser scattering particle size distribution analyzer. The measured volume average particle diameter was defined as the average secondary particle diameter.

In the present invention, it is important to maintain the pH of the whole solution in the range of 8 to 11 in order to maintain stable polishing power. When the pH is 8 or less, the polishing rate is remarkably reduced and is out of a practical range. Further, when the pH is 11 or more, colloidal silica starts to agglomerate, so that the stability of the polishing composition is lowered, which is also out of a practical range.
Also, the pH should not be such that it readily changes due to possible external conditions, such as friction, heat, contact with outside air, or mixing with other components. Therefore, in the present invention, it is necessary that the polishing composition solution itself be a liquid having a so-called strong buffering action, which has a small pH change with respect to a change in external conditions. To form a buffer solution, a combination of a weak acid and a strong base having a logarithmic value (pKa) of the reciprocal of the acid dissociation constant (Ka) at 25 ° C. in the range of 8.0 to 12.5 is used. is necessary. 25 ° C
When the reciprocal logarithm of the acid dissociation constant in is 8.0 or less,
In order to raise the pH, it is necessary to add a large amount of a weak acid and a strong base, which is not preferable. If the logarithm of the reciprocal of the acid dissociation constant at 25 ° C. is larger than 12.5, p
It is impossible to form a buffer solution having a large buffering action for stabilizing H in the range of 8 to 11.

The weak acid used for forming the polishing composition solution having a buffering action of the present invention is carbonic acid (pKa = 6.
35, 10.33), boric acid (pKa = 9.24), phosphoric acid (pKa = 2.15, 7.20, 12.35), water-soluble organic acids and the like, and mixtures thereof. It doesn't matter. Further, as the strong base, an alkali metal hydroxide, quaternary ammonium, ammonium or the like can be used. The buffer solution described in the present invention refers to a solution formed in the above-described combination, in which a weak acid is dissociated as an ion having a different valence in the solution, or a solution in which a dissociated state and an undissociated state coexist. It is characterized by little change in pH even if a small amount of acid or base is mixed.

In the present invention, the polishing rate can be significantly improved by increasing the conductivity of the polishing composition solution. The electrical conductivity is a numerical value indicating the ease of passing electricity in the liquid, and is a reciprocal value of the electric resistance per unit length. In the present invention, the numerical value of the conductivity per unit length (micro-Siemens) is shown as a numerical value converted to 1% by weight of silicon oxide. In the present invention, 25 ° C
Is preferably 20 mS / m / 1% -SiO ₂ or more for improving the polishing rate.
/ M / 1% -SiO ₂ or more is more preferable. There are the following two methods for increasing the conductivity. One is to increase the concentration of the buffer solution, and the other is to add salts. In order to increase the concentration of the buffer solution, only the concentration needs to be increased without changing the molar ratio between the acid and the base.
The salts used in the method of adding salts are composed of a combination of an acid and a base. The acid may be a strong acid or a weak acid, and a mineral acid or an organic acid may be used, and a mixture thereof may be used. The base may be either a strong base or a weak base, and may be an alkali metal hydroxide, a water-soluble quaternary ammonium hydroxide, or a water-soluble amine, and may be a mixture thereof. When adding a combination of a weak acid and a strong base, a strong acid and a weak base, or a combination of a weak acid and a weak base, the pH of the buffer solution may be changed. The above two methods may be used in combination.

In order to improve the physical properties of the polishing composition of the present invention, a surfactant, a dispersant, an antisettling agent and the like can be used in combination. Examples of the surfactant, dispersant, and antisettling agent include water-soluble organic substances and inorganic layered compounds. Although the polishing composition of the present invention is in the form of an aqueous solution, an organic solvent may be added. The polishing composition of the present invention may be prepared by mixing colloidal silica, a base, an additive and water during polishing. In general, a composition having a high concentration of 15 to 65% is prepared as colloidal silica, and is often used after being diluted with water or a mixture of water and an organic solvent.

In the case of edge polishing, a work (workpiece) is generally formed on a polishing machine in which a polishing pad made of synthetic resin foam, synthetic leather or non-woven fabric is adhered to the surface of a rotatable drum. The edge portion of a beveled silicon wafer or the like is inclinedly pressed while rotating, and the edge portion is polished while supplying a polishing composition solution. The processing machine for edge polishing used in the present invention is, for example, as shown in an EP-IV type edge polishing device manufactured by Speed Fam Ipec Co., Ltd., and a rotatable drum having a polishing pad attached to the surface, and a work. A grip portion that is gripped, rotated and tilted at an arbitrary angle, and presses an edge portion of the work attached to the grip portion to the drum, and supplies both the work and the drum while supplying a polishing composition liquid. Then, the workpiece is mirror-polished at the edge of the work. That is, the work is rotated and pressed at a fixed angle to a drum that gradually moves up or down to change the position while rotating, and the polishing is performed while the polishing composition liquid is dropped onto the processed portion. The specific method of polishing a semiconductor wafer edge using the polishing composition of the present invention will be clarified in the examples described below.

[0019]

EXAMPLES Next, the composition for polishing a semiconductor wafer edge and the polishing method using the same according to the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not particularly limited thereto. . The semiconductor wafer edge polishing apparatus used in the present invention and polishing conditions by the apparatus are as follows. Polishing equipment: Speed Fam IPEC Co., Ltd., E
P-200-V type Drum rotation speed: 1800 RPM Drum vertical speed: 0.8 mm / sec Abrasive cloth: SUBA400 (manufactured by Rodel Nitta) Polishing composition flow rate: 600 ml / min Processing time: 90 seconds on one side for a total of 3 minutes Polishing composition The pH of the product was measured using a pH meter. In the measurement, the pH electrode was calibrated in advance with pH standard solutions of pH 6.86 and 9.18, and then measured.
The conductivity was measured with a conductivity meter. In the evaluation of the polished surface, haze and pit states were visually observed under a condensing lamp. The polishing rate was determined from the difference in weight between the silicon wafer before and after polishing. For the evaluation of the polished surface, the surface roughness of the edge surface was measured using Surfcom Profiler M2000 (manufactured by Chapman Instruments). The remaining thread generated due to incomplete edge polishing was examined by using an optical microscope at 800 times magnification over the entire circumference of the processed workpiece.

The polishing compositions used in Examples and Comparative Examples had an average primary particle diameter of 17 nm and an average secondary particle diameter of 28 nm.
Silicon oxide fine particles of the prototype of the above, and an average primary particle diameter of 18
fumed silica having an average secondary particle diameter of 180 nm. This was used as an experimental polishing agent, and a required amount was collected as silica, and while stirring, a predetermined amount of the type and amount of the additives shown in Tables 1 to 5 was added, and pure water was added to adjust the concentration. This was a polishing composition of the present invention. Among the additives, tetramethylammonium carbonate, tetramethylammonium bicarbonate, calcium carbonate, calcium bicarbonate, sodium carbonate and sodium bicarbonate are salts which form a combination of carbonic acid (pKa = 10.33) as a weak acid and a strong base. And the buffer solution of the present invention. Calcium sulfate and diethanolamine are additives for increasing electric conductivity. Each of the semiconductor wafers was polished by the above-described method. In Example 1, 2 μm
An 8-inch silicon wafer to which a polysilicon film was applied was used.

Examples 1 to 10 and Comparative Examples 1 to 5 An 8-inch silicon wafer having a surface coated with a 2 μm polysilicon film was used as a work, and the edge portions were formed using the polishing compositions shown in Tables 1 to 3. A mirror polishing test was performed. The results are shown in Tables 1 to 3. The abbreviations used in the table indicate the following. TMA ₂ CO ₃ : tetramethylammonium carbonate TMAHCO ₃ : tetramethylammonium hydrogen carbonate DEA: diethanolamine The units in the table are as follows. * 1 (additive concentration): M / Kg-SiO ₂ * 2 (conductivity): mS / m / 1% -SiO ₂

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

As is clear from the results shown in the examples of Tables 1 and 2, B / A is in the range of 1.4 to 12, the concentration of silicon oxide is 2 to 30% by weight, and 25 ° C. Logarithm of the reciprocal of the acid dissociation constant in pH 8.0 to 12.5 including a buffer solution in which a weak acid and a strong base are combined.
In an experiment in which an edge portion of an 8-inch silicon wafer provided with a 2 μm polysilicon film on a surface thereof was processed with a polishing composition having a buffering effect between 11 and 11, a polishing rate and a surface roughness were measured. In both cases, satisfactory results were obtained, and the surface quality was good without any serious defects. On the other hand, as shown in the comparative example of Table 3, B /
A deviates from the scope of the present invention, or when using a polishing composition having no buffering action, the polishing rate is low,
In particular, it is clear that the surface roughness is not improved due to insufficient polishing, and the original rough surface remains and is not polished. Defects also appear significantly.

Examples 11 to 15 and Comparative Examples 6 to 10 A low-temperature thermally oxidized silicon oxide film having a thickness of 0.3 μm was formed on the surface of an 8-inch silicon wafer whose edges were machined with a # 1000 beveling grindstone. Using the applied composition as a workpiece, a mirror polishing test of the edge portion was performed using the polishing compositions shown in Tables 4 and 5 under the conditions described above. The results are shown in Tables 4 and 5.

[0027]

[Table 4]

[0028]

[Table 5]

As is clear from the results of the examples shown in Table 4, when the polishing composition within the scope of the present invention was used, good results were obtained in edge polishing of a silicon wafer having an oxide film. As shown in the comparative example of Table 5, B /
When A deviates from the scope of the present invention or uses a polishing composition that does not satisfy the other conditions, the polishing power for a highly hard oxide film is low, and the surface roughness is particularly low due to insufficient polishing. It is apparent that the polishing has not progressed and the original rough surface remains and polishing has hardly progressed. Defects also appear significantly. In particular, as shown in Comparative Example 10, even if silicon oxide which was sufficiently aggregated was used, a sufficient polishing rate could not be obtained only by adding the amine, and a thread residue of the oxide film was observed.

[0030]

As described above, it is clear that the use of the polishing composition according to the present invention provides an excellent effect in edge polishing of silicon wafers and the like, and particularly, difficult-to-cut materials provided with an oxide film or the like. Good results can be obtained even for a silicon wafer having a good quality. According to the present invention, a polishing composition having excellent polishing power and its durability in mirror polishing of the edge portion of a wafer, which has been relatively inadequate in the past, has been obtained. The effect is extremely large.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C09K 3/14 550 C09K 3/14 550Z (72) Inventor Yoshihisa Ogawa 2647 Hayakawa Hayakawa, Ayase City, Kanagawa Prefecture Inside IPEC Corporation (72) Inventor Yusuke Inoue 2647 Hayakawa, Ayase-shi, Kanagawa Prefecture F-term in Ipec Corporation (Reference) 3C049 AA07 AA09 CA05 CB01 3C058 AA06 AA07 AA09 AC04 CB10 DA02 DA12 DA17

Claims (4)

[Claims] 1. An average primary particle diameter A calculated from a specific surface area measured by a BET method in terms of a sphere is 8 to 50 nm, and an average secondary particle diameter B measured by a laser scattering method using Microtrac UPA is 12 to 50 nm. It is in the range of 200 nm, the ratio B / A of the average primary particle diameter A to the average secondary particle diameter B is in the range of 1.4 to 12, and the concentration in the whole solution is 2 to 30% by weight. A buffer solution containing a combination of a weak acid and a strong base, which is a colloid solution of silicon oxide particles and has a logarithm of the reciprocal of the acid dissociation constant at 25 ° C. of 8.0 to 12.5, has a pH of 8 to 1
1. A polishing composition for polishing a semiconductor wafer edge, wherein the polishing composition has a buffering action between 1 and 2. 2. The method according to claim 1, wherein the conductivity at 25.degree.
2. The polishing composition for polishing a semiconductor wafer edge according to claim 1, wherein the polishing composition is at least 20 ms / m per part by weight. 3. An anion constituting a weak acid is a carbonate ion or a bicarbonate ion, and a cation constituting a strong base is at least one of an alkali metal ion, a choline ion, a tetramethylammonium ion and an ammonium ion. 3. The polishing composition for polishing a semiconductor wafer edge according to claim 1, wherein the polishing composition is provided. 4. A semiconductor wafer as a workpiece is placed and pressed on an edge polishing machine having a rotatable drum to which a polishing pad made of synthetic resin foam, synthetic leather or non-woven fabric is attached. A semiconductor, wherein the polishing composition for polishing a semiconductor wafer edge according to any one of claims 1 to 3 is supplied, and the drum and / or the workpiece is rotated and polished. Edge polishing method for wafers.