JP7128635B2 - Grinder - Google Patents

Description

TECHNICAL FIELD The present invention relates to a grinder for grinding the back surface of a wafer, and more particularly to a grinder capable of grinding fragile wafers without damaging them.

2. Description of the Related Art In the field of semiconductor manufacturing, back surface grinding is performed to grind the back surface of a semiconductor wafer such as a silicon wafer (hereinafter referred to as “wafer”) in order to form a thin film.

As a grinding machine for grinding the back surface of a wafer, as shown in Patent Document 1, a spindle feeding mechanism with a grindstone attached to the lower end is suspended from a constant pressure cylinder, and the frictional force acting on the grindstone cut into the wafer is predetermined. It is known that a constant pressure cylinder raises the spindle and the spindle feed mechanism vertically above a value.

In such a grinder, when the frictional force acting on the grindstone becomes excessive, the constant pressure cylinder temporarily raises the spindle and the spindle feed mechanism, so that the wafer is ground without excessive contact between the grindstone and the wafer. is ground in the ductile mode, it can be ground stably without damaging the wafer.

Japanese Patent No. 6030265

In the grinder described in Patent Document 1 as described above, the grindstone is worn by repeating the grinding process, so the feeding amount for cutting the grindstone into the wafer needs to be appropriately adjusted according to the wear amount of the grindstone. However, in ductile mode grinding, since the spindle feed mechanism is pulled up by a constant pressure cylinder, it is not possible to accurately grasp how much the grindstone is cutting into the wafer, and it is impossible to adjust the feed amount according to the amount of wear of the grindstone. there were.

Therefore, there arises a technical problem to be solved, which is to grind the wafer with high accuracy in consideration of the abrasion of the grindstone. An object of the present invention is to solve this problem.

The present invention has been proposed in order to achieve the above object, and the invention according to claim 1 is a grinder for grinding a wafer with a grindstone, comprising a rotatable spindle with the grindstone attached to its lower end, a spindle feed mechanism that feeds the spindle in the vertical direction with respect to the column; and a spindle feed mechanism interposed between the spindle feed mechanism and the column so that the frictional force acting on the grindstone when the grindstone cuts into the wafer is greater than a predetermined value. A constant pressure cylinder that vertically raises the spindle and the spindle feed mechanism when the pressure is high, a grinding amount measuring means that measures the grinding amount of the wafer ground by the grindstone, and a displacement amount that measures the displacement amount of the lowered spindle A measuring means calculates the actual wear amount of the grindstone calculated based on the amount of displacement of the spindle and the amount of grinding of the wafer during grinding, and divides the actual amount of wear by the processing time to obtain the actual wear rate . and a control device for calculating and comparing the actual wear rate of the grindstone with a pre-stored proper wear rate range of the grindstone.

According to this configuration, by measuring the amount of grinding of the grindstone and the amount of displacement of the spindle, the actual wear rate of the grindstone can be calculated during the grinding process, and the actual wear rate of the grindstone can be compared with the proper wear rate range. Therefore, the wafer can be ground to a desired finish thickness with good precision, taking into consideration the abrasion of the grindstone.

Further, in the grinder according to the present invention, it is preferable that the controller adjusts the feed speed of the spindle feed mechanism so that the actual wear speed is within the proper wear speed range.

According to this configuration, when the actual wear rate of the grindstone is out of the proper wear rate range, the feed speed of the spindle feed mechanism is adjusted so that the amount of wear of the grindstone is within the proper range. The wafer can be ground to a desired finish thickness with good precision.

Further, in the grinder according to the present invention, it is preferable that the control device adjusts the drive pressure of the constant pressure cylinder so that the actual wear rate falls within the proper wear rate range.

According to this configuration, when the actual wear rate of the grindstone is out of the proper wear rate range, the wear of the grindstone is reduced by adjusting the driving pressure of the constant pressure cylinder so that the amount of wear of the grindstone falls within the proper range. With this in mind, the wafer can be precisely ground to the desired finished thickness.

Moreover, it is preferable that the grinder according to the present invention further comprises dressing means for dressing the grinding surface of the grindstone when the actual wear rate is out of the proper wear rate range.

According to this configuration, by removing clogging of the grindstone at an early stage, it is possible to suppress damage due to excessive frictional force acting on the wafer due to the clogging of the grindstone.

Further, in the grinding machine according to the present invention, the grindstones are arranged on the outer periphery of the spindle so as to sandwich the processing point for grinding the wafer, and support the spindle so as to be slidable in the vertical direction with respect to the column. At least three linear guides are further provided, and the center of gravity of the spindle is preferably located within the polygon formed by the linear guides in plan view.

According to this configuration, the linear guide arranged on the outer circumference of the spindle regulates the attitude of the spindle, thereby regulating the spindle from yawing, chipping or rolling with respect to the column, so that the surface of the grindstone is level with the wafer. Since it is pressed, the wafer can be ground with high precision.

According to the present invention, the actual wear rate of the grindstone can be calculated during grinding by measuring the grinding amount of the grindstone and the amount of displacement of the spindle. The wafer can be accurately ground to a desired finish thickness in consideration of wear of the grindstone.

BRIEF DESCRIPTION OF THE DRAWINGS The perspective view which shows the grinder which concerns on one Example of this invention. FIG. 2 is a plan view of the main unit shown in FIG. 1; FIG. 2 is a side view of the main unit shown in FIG. 1; The figure which shows a mode that wafer thickness and a grindstone position change by grinding. The schematic diagram which shows a mode that a grindstone wears and a mode that each member rises or falls.

An embodiment of the present invention will be described based on the drawings. In addition, hereinafter, when referring to the number, numerical value, amount, range, etc. of the constituent elements, unless otherwise specified or clearly limited to a specific number in principle, it is limited to the specific number It does not matter if the number is greater than or less than a certain number.

In addition, when referring to the shape or positional relationship of components, etc., unless otherwise specified or in principle clearly considered otherwise, etc., those that are substantially similar or similar to the shape include.

In addition, the drawings may exaggerate characteristic parts by enlarging them in order to make the characteristics easier to understand. In addition, in cross-sectional views, hatching of some components may be omitted in order to facilitate understanding of the cross-sectional structure of the components. In this embodiment, the terms "upper" and "lower" correspond to upward and downward in the vertical direction.

FIG. 1 is a perspective view showing a grinding machine 1. FIG. FIG. 2 is a plan view of the main unit 2 shown in FIG. 1. FIG. FIG. 3 is a side view of the main unit 2. FIG.

The grinder 1 grinds the back surface of the wafer W to form a thin film. The wafer W to be ground using the grinder 1 is preferably a silicon wafer, a silicon carbide wafer, or the like showing high hardness and high brittleness, but is not limited to these. The grinder 1 includes a main unit 2 having a grindstone 21 and a transport unit 3 arranged below the main unit 2 .

The main unit 2 includes an arch-shaped column 22, a spindle 23 to which a grindstone 21 is attached, three linear guides 24 that slidably support the spindle 23 in the vertical direction V, and the spindle 23 that moves up and down in the vertical direction V. and a spindle feed mechanism 25 that allows

The transport unit 3 includes a chuck 31 capable of holding the wafer W by suction, and a slider 32 on which the chuck 31 is placed.

The chuck 31 is connected to a vacuum source (not shown) so that the wafer W can be vacuum-adsorbed to the surface of the chuck 31 . Further, the chuck 31 can be rotated around a vertical axis passing through the center of the chuck 31 by a motor (not shown).

The slider 32 is slidable on the rail 33 by a slider driving mechanism (not shown), so that the chuck 31 and the slider 32 slide integrally in the wafer transfer direction D1.

In this way, the wafer W vacuum-sucked onto the chuck 31 is carried in below the grindstone 21 by the slider 32 before grinding, and carried out from below the grindstone 21 to the rear of the main unit 2 after grinding. be.

Next, a specific configuration of the grinder 1 will be described.

The spindle 23 is accommodated in a groove 22b recessed in the vertical direction V in the front surface 22a of the column 22. As shown in FIG. The spindle 23 includes a saddle 23a having a grindstone 21 attached to its lower end, and a motor (not shown) provided in the saddle 23a for rotating the grindstone 21. As shown in FIG.

The linear guides 24 are guide rails for the saddle 23a that moves up and down along the vertical direction V, and are composed of two front linear guides 24a and one rear linear guide 24b.

The front linear guides 24a are arranged at the edge of the groove 22b in front of the column 22 and are provided parallel to each other along the vertical direction V. As shown in FIG. A saddle 23a is directly attached to the front linear guide 24a.

The rear linear guides 24b are provided parallel to each other along the vertical direction V at the bottom of the groove 22b. A saddle 23a is attached to the rear linear guide 24b via a nut 25a, which will be described later.

As shown in FIG. 3, the front linear guide 24a and the rear linear guide 24b are arranged so that the center of gravity G of the spindle 23 is arranged within the triangle T formed by the front linear guide 24a and the rear linear guide 24b in plan view. , are spaced apart from each other.

The spindle feed mechanism 25 includes a nut 25a that connects the saddle 23a and the rear linear guide 24b, a ball screw 25b that moves the nut 25a up and down, and a motor 25c that rotates the ball screw 25b.

When the motor 25c drives and the ball screw 25b rotates, the nut 25a slides in the feeding direction D2 of the ball screw 25b parallel to the vertical direction V, thereby lowering the saddle 23a. The feeding direction D2 is on a straight line parallel to the vertical direction V passing through the processing point P where the grindstone 21 processes the wafer W. As shown in FIG. In other words, the rotation axis O of the ball screw 25b and the processing point P of the grindstone 21 are arranged on the same straight line in the vertical direction V. As shown in FIG.

A constant pressure cylinder 26 is provided in the main unit 2 . One constant pressure cylinder 26 is provided on both sides in the horizontal direction H with the spindle feed mechanism 25 interposed therebetween. The constant pressure cylinder 26 is an air cylinder that employs a known configuration consisting of a cylinder, a piston, a piston rod, a compressor and the like (not shown). The constant pressure cylinder 26 suspends the spindle 23 and the spindle feed mechanism 25 within the groove 22b, and the piston rod of the constant pressure cylinder 26 is connected to the motor 25c.

The driving pressure of the constant pressure cylinder 26 is set to a value equal to or less than the frictional force acting on the grindstone 21 when the grindstone 21 cuts the wafer W to the critical cutting depth (Dc value). The Dc value differs depending on the material of the wafer W, and is 0.09 μm for silicon wafers and 0.15 μm for silicon carbide wafers, for example.

The grinding machine 1 is provided with an in-process gauge 4 for measuring the thickness of the wafer W. As shown in FIG. The in-process gauge 4 includes an inner peripheral gauge 41 that contacts the outer peripheral edge of the wafer surface and an outer peripheral gauge 42 that contacts the surface of the chuck 31 , as will be described later. The thickness of the wafer W can be measured by subtracting the height measured by the outer gauge 42 from the height measured by the inner gauge 41 .

The grinding machine 1 is provided with a linear encoder 5 for measuring the amount of displacement in the vertical direction V of the spindle 23 . The linear encoder 5 has a scale 51 and a measuring head 52 . The scale 51 is attached along the vertical direction V to the side surface of the slider of the front linear guide 24a, and moves up and down integrally with the spindle 23. As shown in FIG. The measuring head 52 is fixed to the front surface 22 a of the column 22 so as to face the scale 51 . As long as the displacement of the spindle 23 can be measured, the linear encoder 5 may be installed at any position.

The operation of grinding machine 1 is controlled by control device 6 . The control device 6 controls each component constituting the grinder 1 . The control device 6 is composed of, for example, a CPU, a memory, and the like. The functions of the control device 6 may be realized by controlling using software, or may be realized by operating using hardware.

The control device 6 stores in advance the transition of the wear amount of the grindstone 21 according to the processing time, in other words, the appropriate wear rate range of the grindstone 21 . The appropriate wear rate range of the grindstone 21 is calculated from the amount of wear when the grindstone 21 is appropriately worn by grinding a sample wafer, for example. The appropriate wear rate range varies depending on the grit of the grindstone 21, the material of the wafer W, and the like.

Next, the operation of the grinder 1 will be described by taking the case of grinding a SiC substrate as an example. FIG. 4 is a diagram showing how the wafer thickness and the grindstone position change as the grinding progresses. It is the measured height (μm) of the spindle 23 . 4 indicates the position of the spindle 23 measured by the linear encoder 5, and the dashed line in FIG. 4 indicates the thickness of the wafer W measured by the in-process gauge 4. As shown in FIG. FIG. 5(a) is a schematic diagram showing the state of the wafer W and the grinding machine 1 before grinding, and FIG. 5(b) is a schematic diagram showing the state of the wafer W and the grinding machine 1 during the grinding process. be.

[Processing preparation]
First, the wafer W is held by the chuck 31 by suction. Further, the ball screw 25b is rotated forward, the nut 25a and the saddle 23a are slid in the feeding direction D2, and the grindstone 21 is lowered to the vicinity of the wafer W (symbol A in FIG. 4). Next, the grindstone 21 and the chuck 31 are each rotated. For example, the rotational speed of the spindle 23 is set at 2000 rpm, and the rotational speed of the chuck 31 is set at 300 rpm. The number of the grindstone 21 is, for example, #8000.

The inner circumference side gauge 41 is brought into contact with the surface of the wafer W, and the outer circumference side gauge 42 is brought into contact with the surface of the chuck 31 . The controller 6 stores the difference between the inner circumference side gauge 41 and the outer circumference side gauge 42 before starting the grinding process, that is, the initial thickness of the wafer W (for example, 775 μm).

The linear encoder 5 is activated, and the initial height (for example, 795 μm) of the spindle 23 in the vertical direction V before the start of grinding is stored in the controller 6 .

[Grinding]
The spindle feed mechanism 25 brings the spindle 23 closer to the wafer W (symbol B in FIG. 4), and the grindstone 21 is seated on the wafer W (symbol C in FIG. 4) to start grinding. For example, the feed speed of the spindle feed mechanism 25 is set to 0.4 μm/s.

Grinding is performed by ductile mode grinding of the wafer W in a so-called floating state, in which the abrasive grains of the grindstone 21 do not excessively contact the wafer W during grinding (symbol D in FIG. 4).

Specifically, grinding is performed while the spindle 23 presses the grindstone 21 against the wafer W by its own weight (for example, 20 kg), and when the frictional force acting on the grindstone 21 is transmitted to the piston rod, the cylinder of the constant pressure cylinder 26 is filled with the constant pressure cylinder 26 . The piston is raised to push back the compressed air. Therefore, when the grindstone 21 tries to cut deeper than the desired grinding amount (for example, Dc value) and the frictional force acting on the grindstone 21 becomes excessive, the spindle 23 and the spindle feed mechanism 25 are temporarily raised. This suppresses the grindstone 21 from cutting beyond the Dc value.

In addition, since the feeding direction D2 is parallel to the vertical direction V and arranged on a straight line passing through the processing point P of the grinding wheel 21, the spindle feeding is performed so as to suppress the reaction force when the grinding wheel 21 contacts the wafer W. Since the mechanism 25 sends out the spindle 23, the ductile mode grinding can be stably performed while the spindle 23 is floating.

Further, since the constant pressure cylinders 26 are provided on both sides in the horizontal direction H with the spindle feed mechanism 25 interposed therebetween, the spindle feed mechanism 25 is prevented from tilting in the horizontal direction H when the spindle feed mechanism 25 is raised.

Then, when the measured value of the in-process gauge 4 reaches the finished thickness of the wafer W (for example, 80 μm), the ball screw 25b is reversely rotated to raise the nut 25a and the saddle 23a, thereby separating the grindstone 21 from the wafer W. to complete the grinding process (symbol E in FIG. 4).

[Control according to wear of grindstone]
As shown in FIG. 5B, as the grinding progresses, the thickness of the wafer W and the thickness of the grindstone 21 gradually decrease. Further, the spindle 23 moves up and down as it is lowered by the spindle feed mechanism 25 and raised by the constant pressure cylinder 26 .

Therefore, the control device 6 appropriately calculates the actual wear amount and the actual wear rate of the grindstone 21 during the grinding process. Specifically, the actual wear amount of the grindstone 21 is calculated by subtracting the grinding amount Δt of the wafer W ground by the grindstone 21 from the displacement amount Δv of the spindle 23 . By dividing the actual wear amount of the grindstone 21 by the processing time, the actual wear rate of the grindstone 21 can be obtained.

Then, the control device 6 compares the actual wear rate of the grindstone 21 with a pre-stored appropriate wear rate range, and if the actual wear rate of the grindstone 21 is out of the appropriate wear rate range, the actual wear rate is within the appropriate wear rate range. Such control includes at least one or more of feedback control of the feed speed of the grindstone 21 , feedback control of the pressing force of the grindstone 21 , and dressing of the grindstone 21 .

The feedback control of the feed speed of the grindstone 21 means that when the actual wear speed exceeds the upper limit of the appropriate wear speed range, the rotational speed of the motor 25c is reduced to slow down the descent speed of the spindle 23. If the wear rate is lower than the lower limit of the appropriate wear rate range, the rotation speed of the motor 25c is increased to speed up the descent speed of the spindle 23.

Further, the feedback control of the pressing force of the grinding wheel 21 means that when the actual wear rate exceeds the upper limit of the appropriate wear rate range, the pressure of the grinding wheel 21 pressing against the wafer W is reduced. The compressor 26 is controlled to lower the drive pressure of the constant pressure cylinder 26, and when the actual wear rate is below the lower limit of the appropriate wear rate range, the pressure with which the grindstone 21 presses the wafer W increases. The driving pressure of the constant pressure cylinder 26 is increased by controlling the compressor of the constant pressure cylinder 26 .

Further, the dressing of the grindstone 21 is to remove the clogging of the grindstone 21 by dressing the surface of the grindstone 21 with a dressing unit (not shown) when the actual wear rate is out of the proper wear rate range. . The dressing of the grindstone 21 may be performed by interrupting the machining once or by continuing the machining.

In this manner, the above-described grinder 1 calculates the actual wear rate of the grindstone 21 during grinding based on the grinding amount Δt of the grindstone 21 and the displacement amount Δv of the spindle 23, and adjusts the actual wear rate of the grindstone 21 to an appropriate value. By comparing with the wear rate range, the wafer W can be accurately ground to a desired finish thickness in consideration of the wear of the grindstone 21 .

It should be noted that the present invention can be modified in various ways without departing from the spirit of the present invention, and it is a matter of course that the present invention extends to the modified ones.

Reference Signs List 1 Grinding machine 2 Main unit 21 Whetstone 22 Column 22a Front face 22b Groove 23 Spindle 23a Saddle 24 Linear guide 24a ... Front linear guide 24b ... Rear linear guide 25 ... Spindle feed mechanism 25a ... Nut 25b ... Ball screw 25c ... Motor 26 ... Constant pressure cylinder 3 ... Transfer unit 31 ... Chuck 32 Slider 33 Rail 4 In-process gauge (grinding amount measuring means)
41: Inner circumference gauge 42: Outer circumference gauge 5: Linear encoder (displacement measuring means)
51 ... Scale 52 ... Measuring head 6 ... Control device D1 ... Wafer transfer direction D2 ... Sending direction H ... Horizontal direction V ... Vertical direction W ... Wafer

Claims (5)

A grinder for grinding a wafer with a grindstone,
a rotatable spindle with the grindstone attached to its lower end;
a spindle feed mechanism that feeds the spindle in a vertical direction with respect to the column;
A constant pressure interposed between the spindle feed mechanism and the column for vertically raising the spindle and the spindle feed mechanism when the grindstone cuts into the wafer and the frictional force acting on the grindstone is higher than a predetermined value. a cylinder;
a grinding amount measuring means for measuring a grinding amount of the wafer ground by the grindstone;
a displacement amount measuring means for measuring a displacement amount by which the spindle descends;
calculating the actual wear amount of the grindstone calculated based on the amount of displacement of the spindle and the amount of grinding of the wafer during grinding, dividing the actual amount of wear by the processing time to calculate the actual wear rate; a control device that compares the actual wear rate of the grindstone with a pre-stored appropriate wear rate range of the grindstone;
A grinding machine comprising: 2. The grinder according to claim 1, wherein said controller adjusts the feed speed of said spindle feed mechanism so that said actual wear speed falls within said appropriate wear speed range. 3. The grinder according to claim 1, wherein the controller adjusts the drive pressure of the constant pressure cylinder so that the actual wear rate falls within the proper wear rate range. 4. The grinding according to any one of claims 1 to 3, further comprising dressing means for dressing the grinding surface of the grindstone when the actual wear rate is out of the proper wear rate range. board. further comprising at least three linear guides arranged on the outer periphery of the spindle so as to sandwich the processing point where the grindstone grinds the wafer, and supporting the spindle so as to be slidable in the vertical direction with respect to the column;
5. The grinding machine according to claim 1, wherein the center of gravity of said spindle is arranged within a polygon formed by said linear guide in plan view.

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