JP2002086350A - Polishing fluid for electrophoretic polishing and polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the efficiency and accuracy of a polishing process to be performed using the electrophoretic polishing method whereby it is made practicable to adjust the degree of binding of super-abrasive grains coagulating under the polishing process and allowing the same working machine to perform a series of processes from grinding to final surface finishing. SOLUTION: The working machine is furnished with a polishing fluid tank, electrodes, and wirings for electrophoretic polishing, and the tank is equipped internally with a device to secure a work to be processed, and after subjecting the surface grinding using a grinding wheel, super-abrasive grains are coagulated on the working surface of the grinding wheel by the electrophoretic method so that a semi-fixed abrasive grain layer is formed, whereby surface polishing is made to the work with the same working machine and with the same reference surface held. At the time of electrophoretic polishing, a pH regulating agent is together with salt added to a suspension liquid prepared by suspending super-abrasive grains to a liquid medium, and thereby the degree of binding of the super-abrasive grains coagulating on the working surface of the grinding wheel is regulated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polishing liquid for electrophoretic polishing and a polishing method using an electrophoretic polishing method.

[0002]

2. Description of the Related Art In order to achieve precision finishing of hard and brittle materials such as ceramics, glass, and semiconductors, rough finishing by grinding and the like, and finish polishing by lapping and polishing are often used. Polishing is performed by spraying soft abrasive grains on a polishing pad of a polisher and pressing a workpiece, and more recently, CMP (Chemic) has been used as a high-quality flattening method for semiconductors and the like.
al & Mechanical Polish
A technique called g) is rapidly penetrating.

[0003] As a CMP processing apparatus, there is, for example, an apparatus described in JP-A-7-297195 or JP-A-9-111117. When an LSI device wafer is polished by such a CMP processing apparatus, a polishing pad made of polyurethane having a constant elastic modulus, fiber shape, and shape pattern is used as a polisher, and SiO ₂ is generally used as a soft abrasive. In addition, CaCO ₃ , BaCO _{3 and the} like are also used.

On the other hand, a technique has been proposed in which a free abrasive grain processing method is changed to a fixed abrasive processing method using electrophoresis. For example, Japanese Patent Publication No. Hei 7-16878 discloses that the primary particle diameter is 1 μm.
A method for producing a grindstone is disclosed, in which a suspension in which ultrafine abrasive particles having a particle size of m or less are dispersed is made to aggregate the ultrafine abrasive particles of the suspension by electrophoresis and solidify. The grindstone layer formed by this method is used as a grindstone as it is in a suspension in contact with a workpiece in a suspension. Also, JP-A-10-139412, JP-A-10-139412
JP-A-202509 discloses a method for producing a grindstone and an electrophoretic polishing method in which the composition of a suspension is improved.

[0005]

The use of electrophoresis as described above makes it possible to solidify ultrafine abrasive grains at a high density, and to solve the problems of the free abrasive grain processing method to carry out CMP processing. It is said that high-precision polishing can be performed. However, the grindstone disclosed in Japanese Patent Publication No. Hei 7-16878 has no means for adjusting the degree of bonding of ultrafine abrasive grains in a grindstone layer when polishing with the grindstone is performed in a suspension. There is a problem that the hardness of the abrasive layer cannot be adjusted according to the material and the degree of surface polishing. Further, the method of fixing diamond fine particles described in Japanese Patent Application Laid-Open No. 10-139412 is a method of completely fixing diamond fine particles to a tool, and employs an electrophoretic polishing method utilizing aggregation of ultrafine abrasive particles by electrophoresis. Is different in gist. Further, since the abrasive for electrophoretic polishing described in JP-A-10-202509 is an abrasive only obtained by suspending ultrafine abrasive grains in water, the grinding stone described in JP-B-7-16878 is used. As in the above case, there is no means for adjusting the degree of bonding of the ultrafine abrasive grains.

Further, even if such an electrophoretic polishing method is used as a polishing method, in the conventional polishing method, grinding and polishing are performed on different processing machines, respectively. Since the transfer operation to the machine is necessary, and the transfer reference surface of the workpiece changes, there is a limit to the improvement of the processing efficiency and the processing accuracy.

The problem to be solved in the present invention is to make it possible to adjust the degree of cohesion of agglomerating ultrafine abrasive grains in polishing using electrophoretic polishing, and to perform a series of processing from grinding to final surface finishing. An object of the present invention is to make it possible to perform processing under the same processing machine, and to further improve processing efficiency and processing accuracy.

[0008]

SUMMARY OF THE INVENTION The present invention provides a polishing liquid for electrophoretic polishing in which ultrafine abrasive grains are suspended in a medium, wherein a salt is added to the suspension in which the ultrafine abrasive grains are suspended. It is characterized by being added. Further, in order to improve the effect of the addition of the salt, it is desirable to add a pH adjuster together with the salt to the suspension.

In electrophoretic polishing using the electrophoretic phenomenon, ultrafine abrasive particles that aggregate on the working surface (electrode surface) of a grindstone are in a state of being loosely bound. In this state, with a polishing liquid in which ultrafine abrasive grains are merely suspended in a medium such as water, the degree of bonding cannot be positively adjusted,
By adding a salt to the suspension in which the ultrafine abrasive grains are suspended, the degree of bonding can be adjusted. More detailed research is needed to elucidate the mechanism by which salt is added to change the degree of bonding, but the addition of salt changes the surface ξ (zeta) potential of ultrafine abrasive grains dispersed in the polishing solution. It is considered that the aggregation of the ultrafine abrasive grains in the liquid is promoted. Further, it is considered that the degree of aggregation in this case also changes depending on the pH state of the polishing liquid.

[0010] By adjusting the degree of bonding of the ultra-fine abrasive grains to be aggregated, the polishing power during electrophoretic polishing can be greatly increased as compared with the conventional polishing liquid. Salts that can be expected to have such an effect include Na ₂ CO ₃ , NaHCO ₃ , N
aCl and the like. The range of the addition amount at which the polishing force at the time of electrophoretic polishing becomes maximum varies depending on the type of salt, but can be experimentally obtained in advance. Further, by adding the pH adjuster in addition to the addition of the salt, it is possible to maximize the improvement of the polishing power due to the addition of the salt. KOH or HCl can be used as the pH adjuster. The range of pH at which the polishing power is maximized depends on the type and amount of salt added and the pH.
Although it depends on the type of modifier, it can be determined experimentally in advance.

The polishing method according to the present invention is directed to a polishing liquid in which a salt is added to a suspension in which ultrafine abrasive grains are suspended in a medium, or a polishing liquid in which a pH modifier is added to the suspension together with the salt. The method is characterized in that the surface of the workpiece is polished while the ultrafine abrasive grains are agglomerated on the working surface of the grindstone by electrophoresis using the method.

As described above, by adding a salt to the suspension in which the ultrafine abrasive grains are suspended, and further by adding a pH adjusting agent together with the salt, the ultrafine abrasive particles which are aggregated on the working surface of the grinding stone are added. Since the degree of bonding of the abrasive grains can be adjusted and the polishing force during electrophoretic polishing can be increased, the polishing efficiency can be increased.

Further, in the polishing method of the present invention, after the surface of the workpiece is ground by a grindstone, ultrafine abrasive grains are agglomerated on the working surface of the grindstone by an electrophoresis method to form a semi-fixed abrasive. A grain layer is formed, and the surface is polished by the semi-fixed abrasive layer on the workpiece under the same processing machine and holding the same reference plane.

[0014] A semi-fixed abrasive layer is formed on the grindstone by electrophoresis after grinding with a grindstone attached to a processing machine, and finish polishing is performed using the semi-fixed abrasive layer.
A series of processing steps can be performed under the same processing machine. As a result, the workpiece can be processed from the beginning to the end of the process without removing it from the processing machine while maintaining the same reference surface, achieving high efficiency and high precision processing. Can be.

The polishing with the semi-fixed abrasive layer has a higher polishing force than the conventional finish polishing with free abrasive grains, and can improve the efficiency of the finish polishing. Particularly, by using a polishing liquid in which a salt is added to a suspension in which ultrafine abrasive grains are suspended or a polishing liquid in which a pH adjuster is added together with salt as a polishing liquid for electrophoretic polishing, the polishing is performed as described above. Since the power can be increased, the polishing efficiency can be further increased.

Here, in order to perform electrophoretic polishing subsequent to grinding under the same processing machine, a polishing liquid tank, electrodes, and wiring for electrophoretic polishing are attached to the processing machine, and the polishing liquid tank is covered in the polishing liquid tank. A device is provided for fixing the workpiece.
The polishing liquid may be injected into the polishing liquid tank before or after the grinding, but after the grinding is completed, the grinding wheel is separated from the workpiece by a predetermined distance, and the ultrafine abrasive grains are applied to the working surface of the grinding wheel by electrophoresis. Aggregation will occur. Due to this aggregation, a viscous fluid containing a high concentration of ultrafine abrasive grains is generated between the working surface of the grindstone and the workpiece. This layer of viscous fluid containing ultrafine abrasive grains is referred to herein as a semi-fixed abrasive layer.

Oxide abrasive grains such as silica, manganese oxide, cerium oxide and zirconia are suitable as ultrafine abrasive grains for electrophoretic polishing. The average particle size of the ultrafine abrasive grains is several n
It is preferably about m to 100 nm, and the mixing amount in the medium is preferably in the range of several% to 50% by weight. These conditions are basically the same as in the conventional electrophoretic polishing method.

As a grindstone used in the polishing process of the present invention utilizing electrophoretic polishing, an electrodeposition grindstone in which diamond abrasive grains are fixed to a base metal or a metal bond grindstone can be used. In this case, a strongly acidic or strongly alkaline polishing solution may be used as the CMP process in the electrophoretic polishing. Therefore, from the viewpoint of corrosion resistance to such a polishing solution, in the case of an electrodeposited whetstone, an electroplating whetstone is applied by a Ni plating solution. A whetstone is suitable. In the case of a metal bond whetstone, a metal bond whetstone using a Ni-based metal bond is suitable.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view schematically showing basic steps of a polishing method according to the present invention, wherein (a) is a grinding step using diamond abrasive grains of a grindstone, and (b) is an electrophoresis method. A semi-fixed abrasive layer forming step, and (c) shows a polishing step using the semi-fixed abrasive layer.

In the grinding step shown in FIG. 1A, the workpiece K is formed by the diamond abrasive grains D of the abrasive grain layer T of the grinding stone.
Grinding surface. The workpiece K is a processing machine (not shown)
The polishing liquid W is fixed in a polishing liquid tank (not shown) mounted thereon, and contains a polishing liquid W used in a semi-fixed abrasive layer forming step and a polishing step, which are subsequent steps.

After the surface grinding of the workpiece K is completed, the grindstone is raised and separated from the workpiece K, and a semi-fixed abrasive layer Ta is formed on the surface of the abrasive grain layer T of the grindstone by electrophoresis. In the semi-fixed abrasive grain layer forming step shown in FIG. 3B, the polishing liquid W is a liquid obtained by adding ultrafine silica abrasive grains S and a pH adjuster (not shown) to pure water, and the grindstone is used as an anode. When an electrode (not shown) immersed in the polishing liquid W is used as a cathode and electricity is supplied to the polishing liquid W, the negatively charged silica abrasive grains S move toward the grindstone serving as the anode, and the surface of the abrasive grain layer T of the grindstone is moved. The viscous fluid is aggregated between the workpieces K to form a semi-fixed abrasive grain layer Ta.

After the formation of the semi-fixed abrasive layer Ta, the grindstone is lowered so that the gap with the workpiece K is 10 to 100 μm.
The surface of the workpiece K is polished with the semi-fixed abrasive layer Ta by rotating the grindstone in this state.
In the polishing step shown in FIG. 5C, the workpiece K is fixed at the same position as that in the first grinding step, and the surface of the workpiece K is polished while the polishing liquid W is energized. Polishing liquid W
By using a medium solution and ultrafine abrasive particles having a composition suitable for CMP processing, the polishing step can be a CMP processing step.

When the surface grinding of one workpiece K is completed and the process proceeds to the surface grinding of another workpiece, the power supply to the polishing liquid W is stopped, and the polishing liquid W shown in FIGS. Repeat the process. The formation of the semi-fixed abrasive layer Ta by electrophoresis is reversible, and depends on whether or not the polishing liquid W is energized.
Since the formation and removal of a can be performed, if the power supply to the polishing liquid W is stopped after the surface polishing of the workpiece K is completed, the semi-fixed abrasive formed between the grindstone and the workpiece K is removed. The silica abrasive grains S in the grain layer Ta are in a state of being dispersed in the polishing liquid W.

In this way, by performing a series of processing steps from surface grinding to polishing of the workpiece K under the same processing machine, the workpiece K can be removed from the processing machine from the beginning to the end of the processing. In addition, the machining can be continued under the condition of maintaining the same reference plane, so that high-efficiency and high-accuracy machining can be achieved.

Next, the present invention will be described in more detail based on experimental examples. FIG. 2 is a view showing a configuration of a main part of the processing apparatus used in the experiment, and a right half of the figure is shown in a sectional view for convenience of explanation. In FIG. 2, reference numeral 1 denotes a main shaft of a vertical machining center, which is a processing machine; 2, an insulating jig for insulating between the main shaft 1 and the grinding wheel 3;
A grinding wheel attached to the pedestal 4, a workpiece 4 attached to the pedestal 5,
6 is an electrode, 7 is an O-ring, 8 is a bottom plate of a polishing liquid tank, 9
Indicates silica abrasive grains in the polishing liquid. The gap between the abrasive layer 3a of the grindstone 3 and the workpiece 4 and the silica abrasive 9 are shown in an enlarged manner.

The grindstone 3 is provided with an abrasive layer 3a composed of fine diamond abrasive grains and a nickel-based bond.
It is a whetstone. The workpiece 4 is obtained by preforming amorphous glass for a magnetic disk into a size of 30 mm × 16 mm.
The polishing liquid is obtained by mixing 40% by weight of silica abrasive grains 9 having an average particle diameter of 17 nm with pure water of pH 7, and adding a salt and a pH adjuster for adjusting the aggregation state of the silica abrasive grains 9.

EXPERIMENTAL EXAMPLE 1 The pH of the polishing solution and the type of salt to be added to the polishing solution were changed, and the silica abrasive particles 9 aggregated between the abrasive layer 3a of the grinding wheel 3 and the workpiece 4 by electrophoresis. The effect on the degree of bonding was investigated. The experimental conditions were spindle 1
Has a rotation speed of 500 min ^-1 and a feed speed of 400 mm /
min, the applied voltage to the electrode is 10 V, the abrasive layer 3 of the grindstone 3
The gap between a and the workpiece 4 is 10 μm.

FIG. 3 shows the relationship between the pH and the polishing power for each type of salt charged into the polishing liquid. Na ₂ CO ₃ , NaH
CO ₃ and NaCl are used, and KOH is used as a pH adjuster.
And HCl were used. As the polishing force, the tangential resistance of the grindstone 3 when the grindstone 3 is rotated and polished is expressed as a tangential polishing force. It is determined that the greater the tangential polishing force, the greater the polishing force of the semi-fixed abrasive layer.

As can be seen from FIG. 3, in any of the salts, the tangential polishing force sharply increases when the pH of the polishing liquid is in a specific range, and the ultrafine particles of the semi-fixed abrasive layer are formed by adding the salt and adjusting the pH. It was confirmed that the degree of bonding of the abrasive grains could be improved and the polishing power could be increased. In addition, the pH at which the tangential polishing force is maximized
Since the range is neither the strongly acidic side nor the strongly alkaline side, the problem of waste liquid treatment and the problem of corrosion of machine tools during conventional CMP processing are reduced.

[Experimental Example 2] FIG. 4 shows the relationship between the presence or absence of the addition of salt to the polishing liquid and the polishing power. The pH was set to 9 using NaCl as a salt and HCl as a pH adjuster, the voltage applied to the electrode was 10 V, and the gap between the abrasive layer 3 a of the grindstone 3 and the workpiece 4 was 100 μm.

As can be seen from FIG. 4, the tangential polishing force changes at about 10 N when NaCl is not introduced.
When the pH was adjusted by adding Cl, the polishing power of 30 N or more continued, and it was confirmed that the degree of bonding of the semi-fixed abrasive layer was improved by the pH adjustment.

Experimental Example 3 FIG. 5 shows the effect of improving the processing accuracy when polishing is performed for a long time according to the method of the present invention. The abrasive grains of # 400 (SD400) and # 1500 (SD1500) are used as the diamond abrasive grains of the grindstone, the pH of the suspension is 9.7, and the abrasive layer 3a of the grindstone 3 and the workpiece 4 Under the conditions that the gap was set to 100 μm and the tangential polishing force was set to 40 N, the same workpiece was continuously polished using each grindstone.

As can be seen from FIG. 5, in any of the whetstones, the surface roughness of the workpiece decreases as the polishing time elapses, and in the case of SD400, the surface roughness Ry after 30 minutes.
In the case of 100 nm and SD1500, a good processed grade with a surface roughness Ry of 20 nm was obtained after 20 minutes.

[0034]

According to the present invention, the following effects can be obtained.

(1) In electrophoretic polishing using the electrophoretic phenomenon, by adding a salt to a suspension in which ultrafine abrasive grains are suspended, the bonding degree of the aggregated ultrafine abrasive grains is adjusted. The polishing force during electrophoretic polishing can be greatly increased as compared with the conventional polishing liquid. Further, by adding the pH adjuster in addition to the addition of the salt, it is possible to maximize the polishing power by the addition of the salt. By performing electrophoretic polishing using this polishing liquid, polishing efficiency can be improved.

(2) After subjecting the workpiece to surface grinding with a grindstone, ultrafine abrasive grains are agglomerated by electrophoresis on the working surface of the grindstone to form a semi-fixed abrasive layer, and the same machining is performed. By performing surface polishing on a workpiece with a semi-fixed abrasive layer while maintaining the same reference plane with a machine, a series of processing steps can be performed under the same processing machine. As a result, the workpiece can be processed from the beginning to the end of the process without removing it from the processing machine while maintaining the same reference surface, achieving high efficiency and high precision processing. Can be. Particularly, by using a polishing liquid in which a salt is added to a suspension in which ultrafine abrasive grains are suspended or a polishing liquid in which a pH adjuster is added together with salt as a polishing liquid for electrophoretic polishing, the polishing is performed as described above. Since the power can be increased, the polishing efficiency can be further increased.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing basic steps of a polishing method of the present invention, wherein (a) is a grinding step using diamond abrasive grains of a grindstone, and (b) is a semi-fixed abrasive layer formation by an electrophoresis method. Step (c) shows a polishing step using a semi-fixed abrasive layer.

FIG. 2 is a diagram showing a configuration of a main part of a processing apparatus used in an experiment.

FIG. 3 is a graph showing experimental results.

FIG. 4 is a graph showing experimental results.

FIG. 5 is a graph showing experimental results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft of processing machine 2 Insulating jig 3 Whetstone 3a Abrasive layer 4 Workpiece 5 Pedestal 6 Electrode 7 O ring 8 Bottom plate of polishing liquid tank 9 Silica abrasive grain T Abrasive layer D Diamond abrasive grain K Workpiece W Polishing liquid S silica abrasive grain Ta semi-fixed abrasive layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Keizo Takeuchi 1 Noritake Daiza Co., Ltd. Nagoya Plant, No. 16 at Ninowari, Tsushima City, Aichi Prefecture F term (reference) 3C058 AA07 AC04 CA05 CB01 CB03 DA12

Claims (7)

[Claims] 1. An electrophoretic polishing polishing liquid in which ultrafine abrasive grains are suspended in a medium, wherein a salt is added to a suspension in which the ultrafine abrasive grains are suspended. Polishing solution for electrophoretic polishing. 2. The polishing liquid for electrophoretic polishing according to claim 1, wherein a pH adjuster is added to the suspension together with a salt. 3. An object to be processed while agglomerating the ultrafine abrasive particles on the working surface of the grindstone by electrophoresis using a polishing liquid in which a salt is added to a suspension in which ultrafine abrasive particles are suspended in a medium solution. A polishing method characterized by performing a surface polishing process. 4. The polishing method according to claim 3, wherein a polishing liquid in which a pH adjuster is added to the suspension together with a salt is used. 5. After a surface grinding process is performed on a workpiece with a grindstone, ultrafine abrasive grains are agglomerated by electrophoresis on the working surface of the grindstone to form a semi-fixed abrasive layer, and the same processing is performed. A polishing method comprising: performing a surface polishing process on a workpiece with the semi-fixed abrasive layer while maintaining the same reference plane with a machine. 6. The polishing method according to claim 5, wherein a polishing liquid obtained by adding a salt to a suspension in which ultrafine abrasive grains are suspended is used as a polishing liquid when performing surface polishing with the semi-fixed abrasive layer. Processing method. 7. The polishing method according to claim 6, wherein a polishing liquid in which a pH adjuster is added to the suspension together with a salt is used.