JP5494552B2 - Double-head grinding method and double-head grinding apparatus - Google Patents

Description

  The present invention relates to a double-head grinding method and a double-head grinding apparatus for simultaneously grinding both surfaces of a thin plate-like workpiece such as a silicon wafer having a diameter of 300 mm or more.

In general, for example, processing of a workpiece such as a large-diameter silicon wafer represented by a diameter of 300 mm is performed mainly in the following processing steps as shown in FIG. However, the cleaning process and the inspection process between processes are omitted.
First, in a wire saw cutting process, an ingot is cut into a thin plate-like wafer from a block divided into a plurality of pieces. At this time, a free abrasive slurry in which abrasive grains such as silicon carbide are suspended is supplied to a plurality of wire trains reciprocating at high speed, and the block is pressed against the wire train to which the slurry is adhered while being pressed at a predetermined speed to form a thin plate Cut into shapes. Recently, a cutting method using a wire in which a fixed abrasive such as diamond is fixed to the surface of the wire by electrodeposition or the like is also employed.

In the chamfering process, in order to prevent chipping or cracking of the wafer obtained in the wire saw cutting process, the outer periphery of the wafer is rounded using a rotating diamond grindstone or the like having a total groove.
In the lapping process, while supplying a slurry in which abrasive grains such as alumina and zirconia are suspended, a cast iron upper and lower surface plate to which a load is applied is rotated, and the carrier is held between the upper and lower surface plates. A plurality of the chamfered wafers are lapped while being rotated.

In the etching step, the wrapped wafer is immersed in a high temperature sodium hydroxide aqueous solution or potassium hydroxide aqueous solution to remove the work-affected layer (damage layer) introduced into the front and back surfaces and the chamfered portion.
In the edge polishing step, using a slurry with adjusted pH containing colloidal silica or the like, a resin pad such as urethane is pressed against the chamfered portion of the wafer with a predetermined pressure to mirror the chamfered portion.
In the double-sided polishing process, the above-mentioned etching held by a carrier between the upper and lower surface plates is rotated by rotating the upper and lower surface plates to which a resin pad such as urethane is affixed using a slurry with adjusted pH containing colloidal silica or the like. Then, the edge-polished wafer is polished while rotating, and both surfaces are mirrored simultaneously.

Finally, in the final polishing step, using a slurry with adjusted pH containing colloidal silica, etc., pressure is applied from the back of the double-side polished wafer to a surface plate with a resin pad such as urethane applied to the wafer. Only the surface of the surface is contacted, and the fine surface roughness and surface condition are adjusted.
Here, since the occupying area of the wafer with respect to the surface plate is not uniform, the surface of the surface plate is likely to be unevenly worn and the shape of the wafer is likely to deteriorate, so that there is a limit to the production of a highly flat wafer. Further, it is difficult to make the abrasive grains fine, and it is not suitable for reducing the depth of the work-affected layer. In order to solve such a problem, a single wafer type lapping method or a double-head grinding method has been proposed as an alternative method of the lapping process described above.

  For example, Patent Document 1 proposes a single wafer type lapping method for improving deterioration of a wafer shape, which is a problem of lapping processing for simultaneously processing a plurality of conventional sheets. In this method, a pair of ring-shaped surface plates having an outer diameter substantially equal to the radius of the wafer are opposed to each other and pressed from the center to the periphery of the wafer. Wrap both sides of a wafer at the same time. In this method, the surface plate size is smaller than the wafer diameter, so there is no uneven wear on the surface plate compared to conventional laps where the surface plate outer diameter is larger than the wafer diameter, and the flatness of the wafer is less likely to collapse. Since the surface plate area is smaller than the wafer area, the wear amount of the surface plate is large and the platen is frequently replaced. Moreover, since the slurry to be used is the same as the conventional lapping, it is not possible to reduce the work-affected layer introduced on the wafer surface. Furthermore, since the single sheet processing is performed, the equipment productivity is remarkably inferior compared to the case of processing a plurality of sheets.

  In order to solve the problems of the lapping method using such a loose abrasive slurry and a surface plate, a double-head grinding method employing a grindstone containing abrasive grains such as diamond has been proposed (see Patent Document 2). . In this method, a wafer is inserted into a hole of a resin or metal ring-shaped holder that is thinner than the wafer, and is rotated and held by the engagement between the notch portion of the wafer and the protrusion formed on the holder, and the radius of the wafer is increased. The wafers are ground from both sides simultaneously by rotating the grindstones that are almost equal to each other. Because it is a grinding process using fixed abrasive grains, it can be processed at a higher speed than a lapping process using loose abrasive slurry, and a shallower damaged layer can be obtained by reducing the abrasive grain size. Therefore, it is easy to reduce the polishing amount and the polishing time in the double-side polishing process, which is a subsequent process.

  In the single-wafer type lapping machine and double-head grinding machine, the reason why a tool having an outer diameter substantially equal to the radius of the workpiece to be processed (the above-mentioned surface plate and grindstone) is used is as follows. That is, when the outer diameter of the tool is larger than the radius of the workpiece, as shown in FIG. 7A, a non-uniform load is applied in the tool surface, so that the surface of the tool 105 is easily inclined with respect to the processing surface of the workpiece 104. This causes the workpiece shape after machining to deteriorate. In order to suppress this, it is necessary to increase the rigidity of the entire apparatus for holding the tool 105, and increasing the tool size leads to an increase in the size of the entire apparatus, which is economically disadvantageous.

On the other hand, when the outer diameter of the tool is smaller than the radius of the workpiece, as shown in FIG. 7B, a non-contact portion between the workpiece 104 and the tool 105 (shaded portion in FIG. 7B) is generated. Not satisfied. Therefore, the outer diameter of the tool should be larger than the radius of the workpiece and as small as possible, and it is best that the outer diameter of the tool is almost equal to the radius of the workpiece.
As described above, in order to produce a high-quality, particularly flat work at a low cost, generally in the processing of a work such as a silicon wafer having a large diameter, from a lapping process using a conventional loose abrasive slurry, The shift to double-head grinding using a fixed abrasive wheel is advantageous.

  In recent years, for example, in the manufacture of advanced devices employing a large-diameter silicon wafer typified by a diameter of 300 mm, the size of the surface waviness component called nanotopography greatly affects the yield of device processes. The nanotopography of the final product wafer after finish polishing shows irregularities with a wavelength component of about 0.2 to 20 mm having a wavelength shorter than that of warp or warp and a wavelength longer than the surface roughness, and its PV value is 2 It is a very shallow swell component of ˜20 nm. This nanotopography affects the flattening and polishing of the film in the STI (Shallow Trench Isolation) process in the device process, and a strict level is required as the design rule becomes finer for the silicon wafer as the device substrate.

  The nanotopography of a silicon wafer that has undergone the final process is generally measured by an optical interference measuring machine. However, since the wafer in the process such as the cutting process or the double-head grinding process is non-specular, it cannot be measured by the reflection interference type measuring machine. Therefore, as proposed in Patent Document 3, nanotopography can be easily measured by performing an arithmetic bandpass filter process on a warped shape obtained from a capacitance type measuring machine. . Incidentally, the PV value of the cross-sectional shape (difference between the maximum displacement value and the minimum displacement value) is adopted as the quantitative value of the simple nanotopography, and this is hereinafter referred to as “pseudo nanotopography value”.

  In the above-mentioned double-headed grinding, a difference between the surface of the grindstone and the grinding surface of the workpiece is considered as a factor that deteriorates nanotopography. When an inclination occurs between the grinding surface of the work held and rotated by the holder and the surfaces of the pair of grindstones, local deformation of the work 104 during grinding occurs as shown in FIG. This local deformation is likely to occur at the center of the workpiece where the workpiece 104 and the grindstone 102 are in contact and at the outer periphery of the workpiece where the workpiece 104 and the holder 103 are in contact with each other. This produces a distorted shape.

  In order to suppress such minute distortion of the workpiece during grinding, various improvements have been studied. For example, in Patent Document 4, it is proposed to perform grinding by controlling the relative position between the center of the thickness of the workpiece and / or the center of the support means for supporting the workpiece and the center of the distance between the grinding wheel surfaces of the pair of grinding wheels. Yes. Further, Patent Document 5 relates to a static pressure support method for front and back surfaces that supports a workpiece in the axial direction. A plurality of pockets each have a fluid supply hole, and a static pressure support member that can adjust the static pressure of the fluid for each pocket. It is shown that the swell component is improved by adopting. Further, in Patent Document 2 described above, a means for defining a gap between the holder and the static pressure support member and a static pressure value and rotating the holder with high accuracy is proposed.

JP-A-11-254297 JP 2009-190125 A Patent No. 4420023 JP 2005-238444 A JP 2007-96015 A

  However, as the design rules of next-generation devices, for example, flash memory 1/2 pitch and MPU gate length shift from 32 nm to 20 nm and further to 16 nm, it becomes difficult to satisfy customer requirements with the above-described conventional improvements. It is coming. The nanotopography level required for the final product is expected to be 10 nm or less at a wavelength of 10 mm, and this value corresponds to a pseudo nanotopography value of 0.15 μm in the intermediate product after double-head grinding, as shown in FIG. Further improvement of nanotopography is an issue.

  The present invention has been made in view of the above-described problems, and improves the nanotopography by suppressing local deformation of the wafer during double-head grinding, which causes deterioration of the nanotopography of the wafer, and An object is to provide a double-head grinding method and a double-head grinding apparatus that enable stable continuous grinding.

  In order to achieve the above object, according to the present invention, a pair of ring-shaped grindstones are rotated so as to face the workpiece, and the workpiece is supported and rotated from the outer peripheral side along the radial direction. In the double-head grinding method in which both surfaces of the grinding wheel are simultaneously ground, the difference between the peripheral speed of the outer peripheral portion and the peripheral speed of the inner peripheral portion of the rotating grindstone is not less than 30 m / min and not more than 45 m / min, and The workpiece is ground by adjusting the outer diameter and inner diameter of the grindstone and the rotational speed of the grindstone so that the ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed is 10% or more. A double-head grinding method is provided.

  With such a method, local deformation of the wafer during grinding can be suppressed, and nanotopography can be improved. Moreover, the self-generated blade action of the grindstone can be promoted, and stable continuous grinding becomes possible.

At this time, it is preferable to use a resinoid grindstone or a vitrified grindstone in which diamond abrasive grains having an average particle diameter of 2 μm to 6 μm are mixed with a thermosetting resin binder or a porcelain binder as the grindstone.
If it does in this way, the self-generated blade action of a grindstone can be promoted more effectively, and stable continuous grinding can be performed more certainly.

At this time, a silicon wafer having a diameter of 300 mm or more can be used as the workpiece.
In general, as the thickness / area ratio of the wafer decreases, the deformation of the workpiece during grinding becomes more prominent, so the double-head grinding method of the present invention is particularly effective for double-head grinding of silicon wafers having a diameter of 300 mm or more. .

  In addition, according to the present invention, at least the ring-shaped holder that supports the workpiece from the outer peripheral side along the radial direction, and the workpiece supported by the holder is rotated so as to face the workpiece. A double-head grinding apparatus comprising a pair of ring-shaped grinding wheels that grind both surfaces simultaneously, and the difference between the peripheral speed of the outer peripheral part and the peripheral speed of the inner peripheral part of the rotating grindstone is 30 m / min or more and 45 m / min The outer diameter and inner diameter of the grindstone and the rotational speed of the grindstone are adjusted so that the ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed with respect to the outer peripheral peripheral speed is 10% or more. Thus, a double-head grinding apparatus is provided.

  With such a double-head grinding apparatus, local deformation of the wafer being ground can be suppressed and nanotopography can be improved. Moreover, the self-generated blade action of the grindstone can be promoted, and stable continuous grinding can be achieved.

At this time, the grindstone is preferably a resinoid grindstone or vitrified grindstone obtained by mixing diamond abrasive grains having an average particle diameter of 2 μm to 6 μm with a thermosetting resin binder or a porcelain binder.
If it is such, the self-generated blade action of a grindstone can be accelerated | stimulated more effectively, and the stable continuous grinding can be performed more reliably.

At this time, the workpiece can be a silicon wafer having a diameter of 300 mm or more.
In general, as the thickness / area ratio of the wafer decreases, the deformation of the workpiece during grinding becomes significant, so the double-head grinding apparatus of the present invention is particularly effective for double-head grinding of silicon wafers having a diameter of 300 mm or more. .

  In the present invention, in the double-head grinding apparatus, the difference between the peripheral speed of the outer peripheral portion of the rotating grindstone and the peripheral speed of the inner peripheral portion is 30 m / min or more and 45 m / min or less, and the outer peripheral portion with respect to the outer peripheral portion peripheral speed. The workpiece is ground by adjusting the outer diameter and inner diameter of the grindstone and the rotational speed of the grindstone so that the ratio of the difference between the peripheral speed and the inner circumferential speed is 10% or more. Local deformation can be suppressed and nanotopography can be improved. Moreover, the self-generated blade action of the grindstone can be promoted, and stable continuous grinding becomes possible.

It is the schematic which shows an example of the double-head grinding apparatus of this invention. It is explanatory drawing which shows the relationship between the nanotopography after a last process, and the pseudo | simulation nanotopography after a double-head grinding process. It is explanatory drawing which shows the relationship between the relative peripheral speed of a grindstone, and the amount of grindstone wear. It is the schematic which shows an example of the grindstone of this invention. It is a figure which shows the result of the nanotopography of Example 1 and Comparative Example 1. (A) Results of Comparative Example 1. (B) Results of Example 1. It is a flowchart of a general workpiece machining process. It is explanatory drawing explaining the problem in the conventional single wafer type lapping apparatus and a double-head grinding apparatus. It is explanatory drawing explaining the local deformation | transformation of the workpiece | work in grinding in the conventional double-head grinding.

Hereinafter, although an embodiment is described about the present invention, the present invention is not limited to this.
As described above, the slight distortion of the workpiece that occurs during double-head grinding, which causes deterioration of the nanotopography of the final product wafer, is caused by the grinding surface of the workpiece that is held and rotated by the holder and the pair of grinding wheels. This is due to the deviation from the surface, and is particularly likely to occur at the work center where the work and the grindstone come in contact and at the work outer periphery where the work and the holder come into contact. This is thought to be due to the contact area between the grindstone that sandwiches the workpiece from both sides during grinding and the workpiece.

Conventionally, for example, when grinding a workpiece having a diameter of 300 mm, a grindstone having an outer diameter of 160 mm and a segment width of 3 mm is generally used. However, the contact area between the grindstone and the workpiece with respect to the workpiece area is only about 2%. The workpiece sandwiched between the whetstones can be easily deformed.
Therefore, the present inventor has intensively studied to solve such problems. And this inventor thought that it was possible to suppress the deformation | transformation of a workpiece | work during grinding and to suppress the distortion of a workpiece | work by expanding a segment width, without changing the outer diameter of a grindstone. .

  For example, when grinding a workpiece having a diameter of 300 mm, if a grindstone having an outer diameter of 160 mm and a segment width of 10 mm is used, the contact area between the grindstone and the workpiece relative to the workpiece area can be increased to about 7%. Therefore, it has been conceived that the larger the segment width of the grindstone, that is, the difference between the outer diameter and the inner diameter of the grindstone, the more the deformation of the wafer is suppressed and finally the nanotopography can be improved.

  On the other hand, when the segment width of the grindstone is expanded, the difference in the relative peripheral speed between the outer peripheral portion and the inner peripheral portion of the rotating grindstone increases, the difference in wear amount between the outer peripheral portion and the inner peripheral portion of the grindstone increases, and the grinding itself The problem that it is not performed stably occurs. This is due to the wear mechanism by the self-generated blade of the grindstone as follows. That is, as shown in FIG. 3, the grindstone is less likely to be worn at the outer peripheral portion of the grindstone having a higher relative peripheral speed, and conversely, it is more likely to be worn at the inner peripheral portion of the grindstone having a lower relative peripheral speed. For this reason, in order to realize stable continuous grinding, it is necessary to adjust the grindstone feed speed, grindstone rotation speed, and grindstone segment width within a predetermined wear amount range.

For example, when the grinding wheel wear amount is too larger than the optimum region (region I in FIG. 3), the grinding of the workpiece is difficult to proceed because the abrasive grains frequently fall off. On the other hand, if the grinding wheel wear is too small than the optimum region (region II in FIG. 3), it can be said that the abrasive grains are not frequently dropped and are easily clogged. Therefore, in grinding with a grindstone with a self-generated blade due to wear, the abrasive grains are appropriately dropped, and stable continuous grinding is performed in a state where the self-generated blade action in which the next abrasive cutting edge appears is continuously performed. Is preferred.
That is, it is necessary to keep the relative peripheral speed of the outer peripheral part and the relative peripheral speed of the inner peripheral part of the rotating grindstone in the peripheral speed region that promotes the optimum self-generated blade action.

  The present inventor repeated further experiments and studies on the outer diameter and inner diameter of the grindstone and the rotational speed, and the difference between the peripheral speed of the outer periphery and the inner speed of the rotating grindstone is 30 m / min or more. The outer diameter and inner diameter of the grindstone and the rotation speed of the grindstone are adjusted so that the ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed with respect to the outer peripheral peripheral speed is 10% or more. By doing so, it has been found that the nanotopography can be suppressed by suppressing local deformation of the wafer during double-head grinding, and that the self-sharpening action of the grindstone can be promoted and stable continuous grinding becomes possible. Was completed.

FIG. 1 is a schematic view showing an example of the double-head grinding apparatus of the present invention.
As shown in FIG. 1, the double-head grinding apparatus 1 mainly includes a ring-shaped holder 3 that supports the workpiece 4 and a pair of grindstones 2 that simultaneously grind both surfaces of the workpiece 4.

As shown in FIG. 1, the holder 3 supports the work 4 from the outer peripheral side along the radial direction, and can rotate. Further, a drive gear (not shown) connected to a motor (not shown) is provided, and the holder 3 can be rotated through the drive gear.
A protrusion projecting inward is formed on the inner peripheral portion of the holder 3, and engages with a notch formed in the workpiece 4. By engaging the notch of the workpiece 4 with the projection formed on the holder 3, the workpiece 4 can be held in rotation.
Here, the material of the holder 3 is not particularly limited, and may be alumina ceramics, for example. If the material is made of alumina ceramic as described above, the workability is good and it is difficult to thermally expand even during processing, so that it can be processed with high accuracy.

  Moreover, as shown in FIG. 1, a pair of grindstone 2 is arrange | positioned facing the workpiece | work. FIG. 4 shows a schematic diagram of an example of the grindstone 2. As shown in FIGS. 1 and 4, the grindstone 2 is mainly composed of a segment 2 a and a grindstone body 2 b that are in contact with the grinding surface of the work 4 and grind the work 4. The segment 2 a has a predetermined segment width (see FIG. 1). 4 w). Each grindstone 2 is connected to a spindle motor (not shown), and can be rotated around the axis at a predetermined rotational speed by driving the spindle motor. Further, the outer diameter of the grindstone 2 can be set to be approximately equal to the radius of the workpiece to be ground.

Here, the direction of rotation can be controlled so that the pair of grindstones 2 rotate in directions opposite to each other so that the work and the holder are not damaged by applying a force in one direction to the work being ground. ing. In addition, grinding water required for workpiece grinding can be supplied at a predetermined flow rate from a hollow shaft provided at the center of the grindstone.
And while rotating a pair of grindstone 2 facing the workpiece | work 4 and supporting the workpiece | work 4 from an outer peripheral side along a radial direction, both surfaces of a workpiece | work can be ground simultaneously.

Here, the rotational speed of the grindstone during grinding of the workpiece by the double-head grinding apparatus of the present invention and the relationship between the outer circumference and the inner circumference of the grindstone will be described in detail below.
When the outer radius of the grindstone (outer diameter of outer circumference / 2) is A, the inner radius of the grindstone (outer diameter of inner circumference / 2) is B, and the rotational speed of the grindstone is n, the outer circumference and inner circumference of the grindstone The peripheral speed of the part is expressed by Formula 1 and Formula 2, respectively.
2 × π × n × A (Formula 1)
2 × π × n × B (Formula 2)

The peripheral speed difference between the outer peripheral portion and the inner peripheral portion of the grindstone is the difference between Formula 1 and Formula 2, and is expressed by Formula 3.
2 × π × n × (AB) (Formula 3)
First, in order to perform stable continuous grinding, it is necessary to perform grinding in a peripheral speed region that promotes optimum self-generated blade action. Therefore, a smaller value of Equation 3 is better. Here, it can be seen from Equation 3 that the value of Equation 3 decreases as the difference between the outer peripheral radius A and the inner peripheral radius B decreases and as the rotational speed n of the grindstone decreases.

However, as described above, in order to suppress the deformation of the workpiece during grinding, it is better that the segment width of the grindstone, that is, the difference (AB) between the outer radius A and the inner radius B of the grindstone is larger. The optimum value is required for the peripheral speed difference (Equation 3) between the outer peripheral portion and the inner peripheral portion of the grindstone.
This is given by the product of the optimum grindstone segment width (AB) and the optimum grindstone rotational speed n.
Further, the ratio of the difference between the outer circumferential speed (Formula 1) and the inner circumferential speed (Formula 2) with respect to the outer circumferential speed (Formula 1) is expressed by Formula 4.
1- (B ÷ A) (Formula 4)

  Further, from the viewpoint of stable grinding, the value of the ratio (B ÷ A) between the outer peripheral radius and the inner peripheral radius of the grindstone is closer to 1 (100% in percentage display), that is, the smaller the value of Equation 4 is, the better. . On the other hand, from the viewpoint of suppressing the deformation of the workpiece, it is better that the ratio of the outer peripheral radius to the inner peripheral radius (B ÷ A) of the grindstone is small, and Equation 4 is close to 1 (100% in percentage display). Better. Therefore, there is an allowable minimum value in Equation 4.

The present inventor has found that the optimum value of Equation 3 should be in the range of 30 m / min or more and 45 m / min or less, and the allowable minimum value of Equation 4 should be 10% or more.
That is, in the double-head grinding apparatus of the present invention, during grinding of a workpiece, the difference between the peripheral speed of the outer peripheral portion of the rotating grindstone and the peripheral speed of the inner peripheral portion is 30 m / min or more and 45 m / min or less and The outer diameter and inner diameter of the grindstone and the rotational speed of the grindstone are adjusted so that the ratio of the difference between the outer peripheral speed and the inner peripheral speed with respect to the speed is 10% or more.

With such a double-head grinding apparatus, the deformation of the wafer during grinding can be suppressed and nanotopography can be improved. In addition, the self-generated blade action of the grindstone can be promoted, and stable and continuous grinding can be achieved.
In addition, since the rotational speed of the workpiece is very slow at 20 to 50 rpm with respect to the peripheral speed of the outer peripheral part and the inner peripheral part of the grindstone, the relative peripheral speed with the grindstone is hardly affected, and the above-mentioned stable continuous grinding is performed. There is no need to consider it as a parameter to do.

At this time, the grindstone 2 is preferably a resinoid grindstone or vitrified grindstone in which diamond abrasive grains having an average particle diameter of 2 μm to 6 μm are mixed with a thermosetting resin binder or a porcelain binder.
If it is such, the self-generated blade action of a grindstone can be accelerated | stimulated more effectively, and the stable continuous grinding can be performed more reliably.

At this time, the workpiece can be a silicon wafer having a diameter of 300 mm or more.
In general, as the thickness / area ratio of the wafer becomes smaller, the deformation of the workpiece during grinding becomes more prominent. Therefore, the double-head grinding apparatus of the present invention is a silicon wafer having a diameter of 300 mm or more such as a diameter of 300 mm and a diameter of 450 mm. This is particularly effective for double-head grinding.

  In addition, a pair of static pressure support members (not shown) that support the holder 3 in a non-contact manner by the static pressure of the fluid can be provided. The static pressure support member includes a holder static pressure portion that supports the holder 3 in a non-contact manner on the outer peripheral side, and a wafer static pressure portion that supports the wafer in a non-contact manner on the inner peripheral side. Moreover, the hole for inserting the drive gear used for rotating the holder 3 and the hole for inserting the grindstone 2 are formed in the static pressure support member.

  Such a static pressure support member is arranged on both sides of the holder, and the holder is supported in a non-contact manner while supplying fluid between the static pressure support member and the holder during double-head grinding, thereby stabilizing the position of the holder that supports the workpiece. And deterioration of the nanotopography can be suppressed. However, the double-head grinding apparatus of the present invention is not particularly limited to the presence or absence of a static pressure support member.

Next, the double-head grinding method of the present invention will be described.
Here, the case where the double-head grinding apparatus 1 of the present invention as shown in FIG. 1 is used will be described.

First, the holder 3 is used to support from the outer peripheral side along the radial direction of the workpiece 4. At this time, the protrusion of the holder 3 and the notch of the workpiece can be engaged and supported.
Here, when the double-head grinding apparatus 1 includes the above-described static pressure support member, the holder for supporting the workpiece has a gap between the static pressure support member and the holder between the pair of static pressure support members. In this way, a fluid such as water is supplied from the static pressure support member to support the holder in a non-contact manner.

  In this way, by supporting the holder in a non-contact manner while supplying fluid between the static pressure support member and the holder, the position of the holder that supports the workpiece can be stabilized during double-head grinding, and the nanotopography is deteriorated. However, the wafer manufacturing method of the present invention is not limited to the presence or absence of this support mechanism.

Then, the work 4 is rotated by rotating the holder 3 while the work is supported by the holder 3, and a pair of ring-shaped grindstones 2 are opposed to the work 4 and are brought into contact with both surfaces of the work 4. Then, both surfaces of the workpiece 4 are ground simultaneously by feeding the grinding stones facing each other while supplying the grinding water at a predetermined flow rate and gradually reducing the interval.
At this time, as described in the double-head grinding apparatus described above, the difference between the peripheral speed of the outer peripheral portion of the rotating grindstone 2 and the peripheral speed of the inner peripheral portion is 30 m / min or more and 45 m / min or less, and the outer peripheral portion The workpiece is ground by adjusting the outer diameter and inner diameter of the grindstone 2 and the rotational speed of the grindstone 2 so that the ratio of the difference between the outer peripheral speed and the inner peripheral speed with respect to the peripheral speed is 10% or more.

With such a method, deformation of the wafer during grinding can be suppressed and nanotopography can be improved. Moreover, the self-generated blade action of the grindstone can be promoted, and stable continuous grinding becomes possible.
Grinding proceeds in this way, and when it is recognized by a sizing device (not shown) that the workpiece has reached a predetermined thickness, the feeding of the pair of grindstones is stopped, and grinding is performed by opening the grindstones to the left and right. Complete.
At this time, it is preferable to use a resinoid grindstone or a vitrified grindstone in which diamond abrasive grains having an average particle diameter of 2 μm to 6 μm are mixed in a thermosetting resin binder or a porcelain binder.
If it does in this way, the self-generated blade action of a grindstone can be promoted more effectively, and stable continuous grinding can be performed more certainly.

At this time, a silicon wafer having a diameter of 300 mm or more can be used as the workpiece.
In general, as the thickness / area ratio of the wafer becomes smaller, the deformation of the workpiece during grinding becomes more prominent. Therefore, the double-head grinding method of the present invention is a silicon wafer having a diameter of 300 mm or more such as a diameter of 300 mm and a diameter of 450 mm. This is particularly effective for double-head grinding.
In addition, the pair of grindstones 2 can be rotated in opposite directions so that the work and the holder are not damaged by applying a force in one direction to the work being ground.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples of the present invention, but the present invention is not limited to these.

(Example 1-3)
A double-sided grinding apparatus of the present invention as shown in FIG. 1 was used to double-sided a silicon wafer having a diameter of 300 mm, and the nanotopography of the ground wafer and grinding stability were evaluated. Here, the evaluated nanotopography was a pseudo nanotopography value. Moreover, the double-head grinding apparatus used was provided with a static pressure support part. The silicon wafer was cut with a wire saw using GC # 2000 slurry, and the grinding amount was 50 μm. Moreover, the feed rate of the grindstone was 20 μm per minute per side.

  Here, the load current value of the spindle motor that rotationally drives the grindstone was used as means for judging stability during grinding. When this load current value exceeded 20 amperes, or when the difference between the load current values of a pair of grindstones exceeded 5 amperes, it was determined that grinding was abnormal, and in that case, the apparatus was automatically stopped.

Moreover, as shown in FIG. 4, the grindstone main body 2b which took the adhesion area | region 5 of the segment large was used so that the segment width | variety of a grindstone could be changed. Moreover, it was set as the shape which escapes the part of the bolt hole 6 for grindstone fixation from the segment adhesion | attachment area | region 5 of a grindstone. Thus, the segment width can be changed by bonding the segments having different widths to the same grindstone body.
The grindstone segments were composed of vitrified binder and diamond (SD2000) abrasive grains, and were bonded and arranged in a ring shape at regular intervals as shown in FIG. Grinding was performed by changing the width w of this segment to 10 mm (Example 1), 15 mm (Example 2), and 20 mm (Example 3).

In order to prevent the segment from interfering with the bolt hole 6 for attaching the grindstone, as shown in FIG. 4, a segment having a short width was disposed only in the vicinity of the bolt hole. Moreover, in order to accelerate | stimulate discharge | emission of grinding water and cuttings, the space | interval of the circumferential direction of the segment was 1-4 mm, and the thickness of the segment was 3 mm.
And as shown in Table 1, the outer diameter and inner diameter of the grindstone used in each example and the rotational speed of the grindstone were adjusted, and the difference between the peripheral speed of the outer peripheral portion of the grindstone and the peripheral speed of the inner peripheral portion was 30 m / min. As described above, a plurality of workpieces were continuously ground so that the ratio was 45 m / min or less and the ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed with respect to the outer peripheral peripheral speed was 10% or more.

As a result, in Example 1-3, the load current value of the spindle motor that rotationally drives the grindstone was 15 amperes or less, and the difference in the load current values of the spindle motor of the pair of grindstones was 2 amperes or less.
Further, as shown in Table 1, as the inner peripheral radius B decreases, that is, as the segment width of the grindstone increases, the rotational speed region of the grindstone necessary for stable grinding decreases, and the stable rotational speed region (upper limit value) It can be seen that the difference between the upper limit and the lower limit tends to decrease. This result agrees with an empirical result that a smaller grinding wheel segment width tends to obtain a stable grinding state, and it can be said that the conventional grinding wheel segment width of 3 mm is generally adopted.

Thus, it turns out that the stable continuous grinding is attained by the difference of the peripheral speed of the outer peripheral part of a rotating grindstone, and the peripheral speed of an inner peripheral part being 30 m / min or more and 45 m / min or less.
Moreover, the pseudo-nanotopography value of the wafer after grinding was measured using a capacitance type measuring machine (SBW-330 Bow / warp, manufactured by Kobelco Kaken Co., Ltd.). This pseudo nanotopography value is obtained by cutting off the wavelength band of the short wavelength period component of 1 mm or less and the long wavelength component of 50 mm or more from the cross-sectional shape data obtained by measurement and performing bandpass filtering. Here, the maximum value as a result of the bandpass filtering processing to the cross-sectional warp shape every 45 ° was set as a pseudo nanotopography value.

  Table 1 shows the results of the measured pseudo nanotopography. As shown in Table 1, in Example 1-3 where the inner peripheral radius B of the grindstone is smaller than the outer peripheral radius (A = 80 mm) of the grindstone as compared with Comparative Example 1-3 described later, The graphic value is improved, that is, the deformation of the wafer during grinding due to the increase in the grindstone (segment) area tends to be suppressed, and the ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed with respect to the outer peripheral peripheral speed is It can be seen that good pseudo-nanotopography can be obtained when the ratio is 10% or more.

Further, the double-headed wafer in Example 1 was etched by 20 μm with a 55% aqueous solution of caustic soda and subjected to double-side polishing treatment of about 10 μm, and nanotopography was measured using Nanomapper (manufactured by KLA-Tencor).
The result is shown in FIG. As shown in FIG. 5B, there is no particularly characteristic shape in the wafer surface and it is very smooth. Thus, it can be seen that the result of this nanotopography after the double-side polishing process, which is a subsequent process, is in good agreement with the result of the pseudo-nanotopography value immediately after grinding.

(Comparative Example 1-3)
The ratio of the difference between the outer peripheral peripheral speed and the inner peripheral peripheral speed with respect to the outer peripheral peripheral speed is 3.8% (Comparative Example 1), 6.3% (Comparative Example 2), and 8.8% (Comparative Example 3). The silicon wafer is cut with a wire saw using a GC # 2000 slurry under the same conditions as in Example 1-3, except that the outer diameter and inner diameter of the grindstone are set to be less than 10%, and the rotation speed of the grindstone is further set. Then, the grinding amount was 50 μm, the grinding stone feed rate was 20 μm per minute per side, and evaluation was performed in the same manner as in Example 1-3.
The results are shown in Table 1. As shown in Table 1, it can be seen that the results of any pseudo nanotopography are worse than the results of Example 1-3.
Furthermore, the result of having measured the nanotopography about the thing of the comparative example 1 similarly to Example 1 is shown to FIG. 5 (A). As shown in FIG. 5A, a strong convex shape is generated at the center, and it can be seen that the nanotopography after the double-side polishing process, which is a subsequent process, is deteriorated.

(Comparative Example 4)
A silicon wafer under the same conditions as in the example except that the grinding wheel was rotated at a rotational speed that did not fall within the range of 30 m / min or more and 45 m / min or less between the peripheral speed of the outer peripheral portion and the inner peripheral portion of the grindstone. Was ground.
As a result, the load current value of the spindle motor exceeded 20 amperes, or the difference between the load current values of the pair of grinding wheels exceeded 5 amperes. Therefore, the grinding was interrupted and the grinding could not be completed.

  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 1 ... Double-head grinding apparatus, 2 ... Grinding stone, 2a ... Segment, 2b ... Grinding stone main body,
3 ... Holder, 4 ... Workpiece, 5 ... Segment adhesion region, 6 ... Bolt hole.

Claims (6)

In the double-head grinding method of rotating a pair of ring-shaped grindstones facing the workpiece and simultaneously grinding the both surfaces of the workpiece by supporting and rotating the workpiece from the outer peripheral side along the radial direction,
The difference between the peripheral speed of the outer peripheral part and the peripheral speed of the inner peripheral part of the rotating grindstone is 30 m / min or more and 45 m / min or less, and the outer peripheral part peripheral speed and the inner peripheral part peripheral speed with respect to the outer peripheral part peripheral speed. A double-head grinding method, wherein the workpiece is ground by adjusting an outer diameter and an inner diameter of the grindstone and a rotation speed of the grindstone so that a difference ratio of 10% or more is achieved.   The double-headed grinding according to claim 1, wherein a resinoid grindstone or a vitrified grindstone in which diamond abrasive grains having an average particle diameter of 2 to 6 µm are mixed in a thermosetting resin binder or a porcelain binder is used as the grindstone. Method.   The double-head grinding method according to claim 1 or 2, wherein a silicon wafer having a diameter of 300 mm or more is used as the workpiece. At least a ring-shaped holder that supports the workpiece from the outer peripheral side along the radial direction, and a ring-shaped workpiece that simultaneously grinds both surfaces of the workpiece by rotating opposite to the workpiece supported by the holder. A double-head grinding device comprising a pair of grinding wheels,
The difference between the peripheral speed of the outer peripheral part and the peripheral speed of the inner peripheral part of the rotating grindstone is 30 m / min or more and 45 m / min or less, and the outer peripheral part peripheral speed and the inner peripheral part peripheral speed with respect to the outer peripheral part peripheral speed. The double-head grinding apparatus is characterized in that the outer diameter and inner diameter of the grindstone and the rotational speed of the grindstone are adjusted so that the ratio of the difference is 10% or more.   5. The double-headed grinding according to claim 4, wherein the grindstone is a resinoid grindstone or vitrified grindstone in which diamond abrasive grains having an average particle diameter of 2 μm to 6 μm are mixed with a thermosetting resin binder or a porcelain binder. apparatus. The double-head grinding apparatus according to claim 4 or 5, wherein the workpiece is a silicon wafer having a diameter of 300 mm or more.

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