JP2001328065A - Precision machining device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for processing articles such as silicon wafers requiring highly by accurate shape precision and roughness of machined surface. SOLUTION: This precision machining device has a displacing table comprising a fine feeding plate and a position control plate, and a precision shift table. A grinding wheel and its rotation device are placed on either one of the displacing table or the precision shift table, a work and its rotation device are placed on the other one, and a grinding wheel shaft and a work shaft are opposed to each other in a horizontal direction. Positioning of the grinding wheel and the work, and the fine feeding are conducted by shift of the precision shift table and displacement of the displacing table, and correction of a deviation between the grinding wheel shaft and the work shaft is conducted by operating the position control mechanism provided on the displacing table.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention]

The present invention relates to an apparatus for processing an article that requires extremely precise shape accuracy and a finished surface roughness, such as a silicon wafer, a magnetic disk substrate, or a substrate for a crystal oscillator, for example. More specifically, a precision processing apparatus having a table for mounting a device for gripping and rotating a workpiece (workpiece) and a table for mounting a device for rotation by mounting means for processing such as a grindstone is provided. Get involved.

[0002]

2. Description of the Related Art In recent years, there has been a need for downsizing, high performance, high productivity, and low price of so-called electronic devices such as computers, and ICs, Ls, which occupy important parts thereof,
There is an urgent need to increase storage capacity and reliability and reduce production costs for SI and VLSI, and also to urgently demand labor and energy savings as a whole industry. Under these circumstances, silicon wafers, magnetic disk substrates, substrates for crystal oscillators, etc., which are the raw materials for these elements and the components supporting the periphery thereof, have dimensional accuracy and / or surface roughness at the processing stage. The demand for improvement is remarkable. On the other hand, there is also a need to respond to demands such as cost reduction in the processing process and remarkable improvement in productivity.
Therefore, it is necessary to develop a processing method and apparatus based on a completely new idea.

In particular, silicon wafers, which are the raw materials of ICs, LSIs, or VLSIs, are required to have uniform thickness, improved dimensional stability, and improved surface roughness at the processing stage. The requirements for the polishing conditions and the accuracy and stability of the apparatus itself in the polishing process to obtain it have also become much more severe. That is, specifically, n
Accuracy at the level of m (nanometer) is required. Furthermore, yield improvement from wafer to product,
Improvements in the diameter (diameter) of wafers are also actively pursued for the purpose of improving productivity, and production of wafers having a diameter of 30 cm (12 inches) has begun to be conducted on a trial basis.

Electronic parts such as ICs, LSIs and VLSIs are manufactured by mirror-finishing a wafer obtained by slicing a single crystal ingot of silicon or another compound semiconductor, and then writing and dividing a large number of fine electric circuits into small parts. It is manufactured based on flake-shaped semiconductor element chips,
The mirror-finished silicon wafer was generally manufactured through the following series of manufacturing processes. That is, after performing the outer peripheral grinding of the silicon single crystal ingot manufactured by the single crystal pulling method, for example, performing orientation flat processing for positioning in the crystal direction, slicing with an inner peripheral blade saw or a wire saw, and as-cutting. Obtain a wafer. After the as-cut wafer is chamfered at the outer peripheral portion by beveling, the wafer is finished to have uniform thickness, parallelism, flatness, straightness, and a certain surface roughness by double-sided lapping. The obtained wrapped wafer is subjected to an etching process with an acid or an alkali to remove a processing damage layer generated by the lapping, and then a mirror finish by pre-polishing and polishing. The mirror wafer obtained here must have excellent surface roughness and shape accuracy. The surface roughness Ra of the final mirror-finished surface of a 30 cm (12 inch) wafer is desirably 1 nm or less, the flatness is 0.2 μm / 300 mm or less, and the processing amount from the as-cut wafer to the final mirror-finished wafer is about 60 μm on both sides. It is.

In the above-mentioned process, a processing machine used for lapping, pre-polishing, polishing, or the like means, for example, a double-side processing machine or a single-side processing machine in which a surface plate is disposed on both upper and lower surfaces or one of upper and lower surfaces.
Processing is performed by rotating the surface plate and applying a load (processing pressure) while supplying a processing liquid containing abrasive grains.
The work is rubbed and rubbed by the load applied to the surface of the work, and the processing proceeds. In this case, the load applied to the workpiece is, for example, the load of the upper platen, or in the case of a single-sided machine, a method of performing only by the weight of the pressure plate holding the workpiece, and the lifting load is adjusted by the reverse pressure of the air cylinder. There is a method of controlling the applied load only by the action of the air cylinder (for example, Japanese Patent Publication No. 29470/1990). The quality of the control depends on the shape accuracy, processing efficiency and surface roughness of the processed surface of the workpiece. It is an important factor that affects the quality. However, since these processes are basically processes of a force control method with a constant load,
For example, unlike the processing of the forced cutting method using a diamond grindstone, it is not necessary to control the feed amount (cutting amount) extremely severely, but in such a method, the extremely high level at the nm level described above is required. It has become very difficult to follow the purpose of obtaining precise dimensional accuracy and shape accuracy.

[0006] The above-mentioned respective major operations such as lapping, pre-polishing and polishing are conventionally performed in such a manner that a plurality of works are simultaneously processed by a large-sized processing machine. However, the tendency for the wafer size to increase in diameter has been promoted, and as a result, the size of the equipment has been increased.However, the increase in the size of the equipment is limited in view of its handleability. At the same time, it is difficult to achieve high precision. Recently, many studies have been made on a so-called single-wafer method for processing one sheet at a time, based on a forced cutting method using a diamond grindstone.

For example, a method using a grinding wheel with a grindstone for processing a silicon wafer or the like can be a method using an elastic grindstone (Japanese Patent Publication No. 6-71708) or a method using a diamond grindstone (eg, Japanese Patent Application Laid-Open No. 62-99072). However, these are all extensions of the conventional lapping method, and the generation of a deformed layer having irregular and locally deep cracks due to abrasive flaws is remarkable. Even if the layer was removed by etching, the potential distortion and crack were not completely removed, and there was still a problem in practical use. However,
In the method using diamond whetstones, the high grinding ability of diamond abrasive grains and the possibility of improving the work efficiency due to them are difficult to dispose of, so use a high-count diamond cup type whetstone and change the processing conditions. However, there has been attempted a method of performing the entire process from rough processing to final mirror finishing. Further, for the purpose of maintaining the processing performance of the diamond grindstone and improving the processing efficiency, research and development of a processing method using an electrolytic in-process dressing method in combination (for example, Japanese Patent Application Laid-Open No. 9-237771) are also active. All of these are intended for integrated processing of silicon wafers by a single wafer method using a high-count diamond wheel.

[0008] Grinding using these diamond grindstones has three main movements: rotation of the grindstone, feed of a spindle supporting the grindstone, and positioning of the work. It is possible to perform precision machining by controlling these with high precision.However, in order to perform consistently from rough machining to machining in the ultra-precision area with one device and machine, one of the major movements described above In addition, it is necessary to control the feed of the spindle in a wide range with extremely high accuracy. Conventionally, for the feed control of this spindle in general cutting or grinding, for example, a method that applies feed by a precision screw, servo motor or piezoelectric actuator is often used, but from the purpose of covering a wide range with high accuracy. Is not sufficient, and it is hard to say that it is sufficient for processing in an ultra-precision processing area in which fine feeding is performed extremely precisely under a large load.

Further, in the case of processing a large-diameter wafer of φ300 mm or more, the required flatness is an extremely high level of 0.2 μm / φ300 mm or less, so that the heat generated by the machine body and the base supporting each part is generated. It has been pointed out that the displacement leads to a delicate misalignment between the axis of the work axis and the axis of the grindstone axis, and adversely affects the flatness accuracy of the wafer. Such a problem is at a level that is almost ignored for a small-diameter wafer. In other words, the influence of the delicate dimensional deformation of the entire device due to the temperature change was not as large a problem as in the past, but in the recent trend of large size and high integration, the influence on the nanometer level has been reduced. A problem arises when discussing accuracy, and it is becoming necessary to correct extremely small deviations and inclinations due to temperature changes, that is, to perform attitude control.

Further, Japanese Patent Application No. 10-315259 discloses a precision plane machining machine for feeding a grinding wheel shaft by a combination of a servomotor device and a giant magnetostrictive actuator. In the case of this processing machine, the use of a giant magnetostrictive actuator is excellent in the point of fine feeding in which a large load article is extremely precisely and accurately, but the deformation due to the thermal displacement due to the temperature change and the processing force during the movement described above However, there is no solution to the problem of attitude control for correcting subtle deviations in the X, Y, and Z axes, the θ axis, and the ψ axis.

[0011]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, the present inventors have made intensive studies,
As a result of studying an apparatus capable of processing with an ultra-precision flatness of 0.2 μm / φ300 mm or less, the processing method was changed to a form in which infeed (feeding) cutting was performed using a grindstone, and the grindstone and the work were independent of each other. Place it on the table, arrange the grindstone axis and the work axis so as to oppose each other in the horizontal direction, perform positioning using both a superprecision lap screw and a giant magnetostrictive actuator, and always use the giant magnetostrictive actuator to It has been found that the above-described ultra-precision flatness can be achieved by controlling the attitude with respect to the axis, and the present invention has been completed, and the object thereof is to perform from roughing to ultra-precision mirror finishing. An object of the present invention is to provide a precision processing device that can be performed consistently.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide a displacement table comprising a fine feed plate and an attitude control plate, and a precision moving table, wherein one of the displacement table and the precision moving table is provided. The whetstone and its rotating device are mounted on the other, and the work and its rotating device are mounted on the other one, and the whetstone axis and the work axis are arranged so as to oppose each other in the horizontal direction. The positioning and the fine feed are performed by the movement of the precision moving table and the displacement of the displacement table, and the deviation between the grindstone axis and the work axis is corrected by operating an attitude control mechanism provided in the displacement table. Is achieved by a precision processing device. In the above-described precision processing apparatus, one of the fine feed plate and the attitude control plate may be placed on the precision moving table.

In the precision machining apparatus described above, the attitude control plate has a structure in which two plate members are vertically connected via a joint located at the outermost central portion of one side, and the plate of the plate member located above is formed. The giant magnetostrictive actuator is arranged so that the tip rod of the giant magnetostrictive actuator abuts on one side perpendicular to the side where the junction is located, and further, in the opening on the side opposite to the junction, In this structure, the giant magnetostrictive actuator is arranged such that the rod abuts on the lower portion of the plate located above. It is preferable that the junction is made of an elastically deformable material in order to make the action of the giant magnetostrictive actuator effective. The precision moving table has a structure provided with a static pressure air guide and a precision lap screw.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the precision processing apparatus of the present invention performs infeed (feeding) cutting using a grindstone. Therefore, in processing, positioning and setting of a cutting amount are performed in nm (nanometer). ) Must be performed very precisely and accurately. In the present invention, a high-precision feed mechanism using a precision moving table equipped with a static pressure air guide and a precision lap screw to set a unit of 10 nm, and a fine feed mechanism using a displacement table equipped with a giant magnetostrictive actuator to set a unit of 1 nm are used. They are used together. For example, a high-precision feed mechanism using an NC-controlled precision lap screw is provided on the grindstone shaft side, and a fine feed mechanism using a giant magnetostrictive actuator is provided on the work shaft side, but this may be reversed or both mechanisms are on the same side. May be provided. At the time of machining, a predetermined cutting amount is set using any mechanism, and the grinding wheel spindle and the workpiece spindle are rotated at high speed in opposite directions to make contact with each other. Therefore, in terms of functions, what is required of the grindstone spindle and the work spindle is high rotational accuracy, rigidity and thermal displacement characteristics.

A specific example of the precision processing apparatus of the present invention will be described with reference to the drawings. FIG. 1 is a side view showing the appearance of the precision processing device body of the present invention. Precision moving table B on bed A
And a displacement table C, a grinding wheel and its rotating device are placed on the precision moving table B, and a work and its rotating device are placed on the displacement table C. The grindstone spindle D and the workpiece spindle E are aligned on the Z-axis such that their surfaces oppose each other. The precision moving table B can perform high precision feeding in the Z-axis direction along the static pressure air guide 2 by the action of the precision lap screw 1. Feeding is performed by NC control, and feeding at a minimum setting unit of 10 nm can be performed. The displacement table C is composed of a fine feed plate 3 having a fine feed mechanism and an attitude control plate 4 having an attitude control mechanism. It can be moved and positioned in a setting unit of 10 nm. In the drawing, the attitude control plate 4 is mounted on the fine feed plate 3, but the present invention is not limited to this, and may be reversed. In the example shown in the drawing, the fine feed plate 3
And the attitude control plate 4 form the displacement table C as if it were an integral structure.
In addition to the ability to feed the minimum setting unit of 1 nm in the axial direction, it is also possible to constantly correct a minute shift in the Z-axis direction of the work axis with respect to the grinding wheel axis due to a temperature change. Further, in the present invention, the fine feed plate and the attitude control plate do not necessarily have to be mounted on the same displacement table, and one of them may be mounted on the precision moving table.

FIG. 2 shows the structure and operation of the displacement table C.
This will be specifically described with reference to FIG. FIG. 2 is an explanatory view showing one embodiment of the fine feed plate, and FIG. 3 is an explanatory view showing one embodiment of the attitude control plate. In the present invention, the material forming the fine feed plate 3 is required to be a material that can be elastically deformed. The fine feed plate 3 shown in FIG. 2 is obtained by processing a parallelogram thick plate, engraving a through groove 5 on each of the four sides, leaving a bridge-like fulcrum 6 at each of the four corners, and passing through the center through the fulcrum 6. A gantry 7 is suspended from the inner surface of a frame 8 surrounding the gantry. A notch 9 is provided at one end of the gantry 7, and a giant magnetostrictive actuator 10 is arranged at that position. The giant magnetostrictive actuator 10 is fixed to the inner surface of the frame 8, and is arranged such that the tip of the rod 11 abuts on the end face of the notch of the gantry 7. The gantry 7 can be minutely displaced in the Z-axis direction by the linear motion of the rod 11 of the giant magnetostrictive actuator 10 in the Z-axis direction.
At the same time as the displacement, the action of the bridge-like fulcrum 6 exerts spring elasticity. That is, it is displaced by applying a preload with a giant magnetostrictive actuator, and returns to the original position if the preload is removed, and in actual use, the position displaced by applying a certain preload is regarded as a fixed position. In other words, the gantry 7 can be freely displaced in either the positive or negative Z-axis direction by adjusting the preload. In order to exhibit such spring elasticity, it is required that the material is a material that can be elastically deformed. A work and its rotating device or a grindstone and its rotating device such as a grindstone and its rotating device, which are several hundred kgf in weight, are mounted on the fine feed plate, and are supported by the fulcrum 6 described above. Therefore, the material is required to have high rigidity at the same time. As a material with such performance,
Specifically, it is preferable to use a steel sheet or the like having a certain thickness, and specifically, a method of processing an integrated steel sheet into a shape as shown in FIG. 2 using a means such as electric discharge machining is exemplified. it can.

Next, an embodiment of the attitude control plate of FIG. 3 will be described. In the drawing, the attitude control plate 4
The junction 1 is located at the outer center of one side of the parallelogram
2, two upper and lower plate members 13 through the joint 12;
14 is arranged, and a slit 17 (opening) is provided at the center. The giant magnetostrictive actuator 10a is arranged on one side of the plate 13 above the side perpendicular to the side where the joining point 12 is located, such that the tip rod 11a abuts. Further, a notch 1 is formed in the opening opposite to the joint.
5 and 16 in which the giant magnetostrictive actuator 10
b and 10c are arranged. The tip rods 11b and 11c of each giant magnetostrictive actuator are configured to abut on the lower portion of the upper plate 13. In addition, the joining point 12 is required to be made of a material that can be elastically deformed.

The upper plate 13 is moved by the linear motion of the tip rod 11a of the giant magnetostrictive actuator 10a in the X-axis direction.
Enables a minute rotational displacement at a minute angle (Δθ) in seconds around the Y axis centered on the junction point 12. As described above, since the material forming the joint point 12 is a material that undergoes elastic deformation, it is displaced when a preload is applied by a giant magnetostrictive actuator, and returns to its original position when the preload is removed. is there. Further, the giant magnetostrictive actuators 10b, 10
Due to the linear movement of the tip rods 11b and 11c in the Y-axis direction, the upper plate 13 rotates around the X-axis centering on the joining point 12 and the minute inclination displacement at the minute angle (Δψ) in the Y-axis direction in the unit of second. It becomes possible. That is, the giant magnetostrictive actuator 10
Due to the action of b, 10c, the upper plate 13 is
Can be displaced so that the slit 17 can be opened and closed up and down with the side having the axis as the axis (X axis). That is, by controlling the displacement at the minute angle in both directions, it is possible to correct a slight deviation (deviation) between the grinding wheel axis and the work axis aligned along the Z axis. As a specific means of correction, a small dimensional displacement of each constituent material due to temperature change is predicted and calculated in advance and stored in a computer, and the small displacement due to the actually measured actual temperature change is automatically corrected. A computer instructs the giant magnetostrictive actuators with necessary displacement values of Δθ and Δψ, and operates the giant magnetostrictive actuators to control the attitude of the apparatus. As a material constituting the attitude control plate having such performance, specifically, it is preferable to use a steel plate or the like having a certain thickness, and specifically,
For example, there can be exemplified a method in which a slit 17 is formed in a central portion of an integrated steel plate by using a means such as electric discharge machining and a part thereof is left as the joint portion 12.

The material of the displacement table and the precision movement table of the present invention is not particularly limited, but as described above, it is structurally tough, has high rigidity, has preferable elastic deformation, In addition to being required to exhibit elasticity, it is required that the deformation due to heat is small, so specifically, a steel material, as a more realistic specific preferable example, a material that minimizes deformation due to heat, For example, austenitic steel and the like can be mentioned.

The giant magnetostrictive actuator referred to in the present invention is:
A giant magnetostrictive material, which is a polycrystalline or single crystal alloy with a specific rare earth element and an iron group element consisting of nickel, cobalt, and iron, and undergoes a strong dimensional change when a magnetic field is applied, has been applied as an actuator. Things. Usually, a rod made of a giant magnetostrictive material is placed at the center and its periphery is surrounded by a driving coil.However, those with permanent magnets arranged above and below do not need to apply a magnetic bias by offset current, so that Only Joule heat can be suppressed. The giant magnetostrictive actuator of the present invention displaces the distance of ± several μm with the accuracy of nanometer when the displacement table and the precision moving table are placed with a large load, so that the displacement amount due to Joule heat is irregular. Is required to be as small as possible, and therefore, it is preferable to use one having the aforementioned permanent magnet built-in.

The grinding wheel used in the precision machining apparatus of the present invention is not particularly limited. However, as described above, the diamond is excellent in rigidity and grinding power because of the in-feed cutting. It is preferable to use a grindstone. The shape is preferably a cup shape. The diamond cup type grindstone here is
It refers to diamond fine powder as abrasive grains, which are made of a hard resin such as phenol, special alloy, ceramics, etc. as a binder, or fixed using electrodeposition or other means. The side surface is used. Size of diamond abrasive used (count)
Is not particularly limited, but for the purpose of precision machining, it is at least smaller than 3000 in the standard of JIS-R6001 (grain size of abrasive), that is, dv
It is preferable to use one having a −50 value of 4.0 ± 0.5 μm or less.

Although the precision machining apparatus of the present invention is used for many purposes, its features are utilized particularly in the field of ultra-precision machining. That is, it is used for mirror finishing of silicon wafers, mirror finishing of crystallized glass, and other precision machining of hard-to-cut materials. For this purpose, for example, lapping, etching, pre-polishing, polishing, etc. , And efficient processing can be performed.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

[0024]

EXAMPLE A silicon wafer having a size of 300 mm was processed using the apparatus shown in FIG. The as-cut wafer sliced from the ingot was set to a certain degree of parallel by rough lapping, and a workpiece close to the finished dimensions and having a degree of parallelism was used as a workpiece. As a grindstone, a cup-shaped metal bond grindstone using diamond fine powder was used. Using water as a processing liquid, processing was performed for about 10 minutes. As a result, a surface having a surface roughness of 0.8 nmRa could be obtained. The allowance during that time is about 2 μm,
The flatness could achieve 0.20 μm or less for a diameter of φ300 mm. That is, if it is carried out by a usual method, several steps of lapping, etching, pre-polishing, and polishing are required, and a total of about 30 minutes can be performed in only one step, and in about 10 minutes. Was.

[0025]

As described above, by using the precision processing apparatus according to the present invention, it is possible to carry out finishing processing of a silicon wafer, which has conventionally been performed in several steps, in one step, and to achieve a large diameter of φ300 mm. And a flatness of 0.20 μm or less with respect to the silicon wafer. This not only made it possible to deal with large-diameter wafers, which was a major problem in the past, but also made it possible to drastically shorten the process itself and significantly improve accuracy.
The processing object is not limited to silicon wafers,
For example, it is possible to process difficult-to-cut materials such as ceramics or composite materials, and the effect on the industry is extremely large.

[Brief description of the drawings]

FIG. 1 is a side view showing an external appearance of a main body of an embodiment of a precision processing apparatus according to the present invention.

FIG. 2 is an explanatory view showing one embodiment of a fine feed plate.

FIG. 3 is an explanatory view showing an embodiment of a posture control plate.

[Explanation of symbols]

1, 1 ': super-precision lap screw, 2, 2': static pressure air guide, 3: fine feed plate, 4: attitude control plate,
5: through groove, 6: fulcrum, 7: gantry, 8: frame, 9: notch, 10, 10a, 10b, 10c: giant magnetostrictive actuator, 11, 11a, 11b, 11c: rod, 12:
Joining point, 13: upper plate, 14: lower plate, 15: notch, 16: notch, 17: slit, 18: whetstone, 1
9: Work A: Bed B: Precision moving table C: Displacement table D: Whetstone spindle E: Work spindle

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hirominori Nakano 6-9-9 Ayukawacho, Hitachi City, Ibaraki Prefecture B-403 (72) Inventor Takuji Tajima 2100 Kamimaizumi, Ebina City, Kanagawa Prefecture Inside Hitachi Via Mechanics (72) Inventor Kazu Watanabe 2100 Kamimaizumi, Ebina-shi, Kanagawa F-term in Hitachi Via Mechanics Co., Ltd.

Claims (4)

[Claims] A displacement table comprising a fine feed plate and an attitude control plate; and a precision movement table.
A grindstone and its rotating device are mounted on one of the displacement table and the precision moving table, and a work and its rotating device are mounted on the other one. Is arranged to oppose
The positioning and fine feed between the grindstone and the work are performed by the movement of the precision moving table and the displacement of the displacement table, and the deviation between the grindstone axis and the work axis is corrected by operating the attitude control mechanism provided in the displacement table. Precision processing equipment characterized by performing 2. The precision processing apparatus according to claim 1, wherein one of the fine feed plate and the attitude control plate is mounted on a precision moving table. 3. The attitude control plate has a structure in which two plate members are vertically connected via a joint located at the outermost central portion of one side, and the material forming the joint undergoes elastic deformation. A giant magnetostrictive actuator is arranged such that the tip rod of the giant magnetostrictive actuator abuts on one side orthogonal to the side where the joining point of the plate material located above is located,
Further, the giant magnetostrictive actuator is arranged in the opening on the side opposite to the joining point such that the tip rod of the giant magnetostrictive actuator contacts the lower part of the plate material located above the above. The precision processing device according to claim 1 or 2. 4. A precision lap screw is actuated to move a precision movement table to perform a feed in units of 10 nm, and a giant magnetostrictive actuator is driven to displace either a displacement table or a precision movement table, thereby causing a feed in units of 1 nm. 4. The precision processing apparatus according to claim 1, wherein the feeding is performed.