JP2019155488A - Grinding machine - Google Patents

Abstract

To provide a grinding machine which efficiently grinds a wafer in consideration of wear of a grinding stone.SOLUTION: A grinding machine 1 comprises: a rotatable spindle 23 to a lower end of which a grinding stone 21 is fitted; a spindle feeding mechanism 25 which feeds the spindle 23 in a vertical direction V with respect to a column 22; a constant pressure cylinder 26 which lifts the spindle 23 and the spindle feeding mechanism 25 in the vertical direction V when the grinding stone 21 cuts into the wafer W and a friction force acting on the grinding stone 21 is higher than a prescribed value; an in-process gauge 4 which measures a ground amount Δt which is amount of the wafer W ground by the grinding stone 21; a linear encoder 5 which measures a displacement magnitude Δv which is magnitude of lowering of the spindle 23; and a control unit 6 which controls the spindle feeding mechanism 25 so that the grinding stone 21 approaches the wafer W by wear amount of the grinding stone 21 which is calculated by subtracting ground amount Δt of the wafer W from the displacement magnitude Δv of the spindle with respect to the worked wafer W.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a grinder that grinds the back surface of a wafer, and more particularly, to a grinder capable of grinding without damaging a fragile wafer.

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

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

  In such a grinding machine, 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 not in excessive contact between the grindstone and the wafer. Can be stably ground without damaging the wafer.

Japanese Patent No. 6030265

  In the grinding machine described in Patent Document 1 described above, after the grindstone is placed at a predetermined start position before the grinding, the grinding is started by seating the grindstone on the wafer while gradually feeding the spindle. However, since the grinding wheel wears and thins by repeated grinding, when processing multiple wafers continuously, the distance between the starting position of the grinding wheel and the wafer increases by the amount that the grinding wheel wears and thins. There is a problem that it takes more time to transfer the wafer from the start position to the wafer, and the processing throughput is reduced.

  Therefore, a technical problem to be solved arises in which the wafer is efficiently ground in consideration of wear of the grindstone, and the present invention aims to solve this problem.

  The present invention has been proposed to achieve the above object, and the invention according to claim 1 is a grinding machine for grinding a wafer with a grindstone, wherein the grindstone is attached to a lower end and is rotatable. A spindle feed mechanism that feeds the spindle vertically to the column, and a frictional force that is interposed between the spindle feed mechanism and the column and that acts on the grindstone when the grindstone cuts into the wafer from a predetermined value. A constant pressure cylinder that raises the spindle and the spindle feed mechanism in the vertical direction when it is high, a grinding amount measuring means that measures the grinding amount by which the grindstone grinds the wafer, and a displacement amount that measures the displacement amount by which the spindle is lowered The amount of wear of the grinding wheel calculated by subtracting the grinding amount of the wafer from the displacement amount of the spindle relative to the measuring means and the processed wafer The serial grindstone and a, and a control unit for controlling the spindle feed mechanism to approach the wafer.

  According to this configuration, the spindle feed mechanism is calculated by calculating the amount of wear of the grindstone after the grinding of the first wafer and bringing the grindstone closer to the wafer by the amount of wear of the grindstone during the processing of the second wafer. However, it is possible to shorten the time from the initial position before the grinding process until the grindstone is seated on the wafer.

  Further, the grinding machine according to the present invention is arranged on the outer periphery of the spindle so that the grinding wheel sandwiches a processing point for grinding the wafer, and supports the spindle slidably in the vertical direction with respect to the column. It is preferable that the apparatus further includes at least three linear guides, and the center of gravity of the spindle is disposed in a polygon formed by the linear guides in plan view.

  According to this configuration, the linear guide disposed on the outer periphery of the spindle regulates the attitude of the spindle, so that the spindle is yawing, chipping or rolling with respect to the column, and the surface of the grindstone is horizontally applied to the wafer. Since it is pressed, the wafer can be accurately ground.

  In the present invention, when grinding a wafer continuously, the wear amount of the grindstone is calculated based on the processing result of the processed wafer, and the grindstone is moved closer to the wafer as much as the grindstone is worn during the next wafer processing. By doing so, the spindle feed mechanism shortens the time from the initial position until the grindstone is seated on the wafer, so that grinding can be performed efficiently.

The perspective view which shows the grinding machine which concerns on one Example of this invention. The top view of the main unit shown in FIG. The side view of the main unit shown in FIG. The figure which shows a mode that a wafer thickness and a grindstone position change with grinding. The schematic diagram which shows a mode that a grindstone wears and a mode that each member raises or descends.

  Embodiments of the present invention will be described with reference to the drawings. In the following, when referring to the number, numerical value, quantity, range, etc. of the constituent elements, it is limited to the specific number unless otherwise specified and clearly limited to the specific number in principle. It may be more than a specific number or less.

  In addition, when referring to the shapes and positional relationships of components, etc., those that are substantially similar to or similar to the shapes, etc., unless otherwise specified or otherwise considered in principle to be apparent. Including.

  In addition, the drawings may be exaggerated by enlarging characteristic portions in order to make the features easy to understand, and the dimensional ratios and the like of the constituent elements are not always the same. In the cross-sectional view, hatching of some components may be omitted in order to facilitate understanding of the cross-sectional structure of the components. In the present embodiment, the terms “upper” and “lower” correspond to upper and lower in the vertical direction.

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

  The grinding machine 1 forms a thin film by grinding the back surface of the wafer W. The wafer W to be ground using the grinder 1 is preferably a silicon wafer, silicon carbide wafer, or the like that exhibits high hardness and high brittleness, but is not limited thereto. The grinding machine 1 includes a main unit 2 including a grindstone 21 and a transport unit 3 disposed below the main unit 2.

  The main unit 2 includes an arched column 22, a spindle 23 to which a grindstone 21 is attached, three linear guides 24 that support the spindle 23 so as to be slidable in the vertical direction V, and the spindle 23 is moved up and down in the vertical direction V. A spindle feed mechanism 25 to be moved.

  The transfer unit 3 includes a chuck 31 that can hold 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) and can vacuum-suck the wafer W onto 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 can slide on the rail 33 by a slider drive mechanism (not shown), whereby the chuck 31 and the slider 32 slide together in the wafer transfer direction D1.

  Thus, the wafer W vacuum-sucked on the chuck 31 is carried to the lower part of the grindstone 21 by the slider 32 before the grinding process, and is carried out from the lower part of the grindstone 21 to the rear of the main unit 2 after the grinding process. The

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

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

  The linear guide 24 is a guide rail of the saddle 23a that moves up and down along the vertical direction V, and includes two front linear guides 24a and one rear linear guide 24b.

  The front linear guide 24 a is disposed at the edge of the groove 22 b in front of the column 22, and is provided in parallel with each other along the vertical direction V. A saddle 23a is directly attached to the front linear guide 24a.

  The rear linear guide 24b is provided in 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 described later.

  As shown in FIG. 3, the front linear guide 24a and the rear linear guide 24b are arranged such that the center of gravity G of the spindle 23 is arranged in a 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 is driven to rotate the ball screw 25b, the nut 25a slides in the feeding direction D2 of the ball screw 25b parallel to the vertical direction V, so that the saddle 23a is lowered. The feeding direction D2 is on a straight line parallel to the vertical direction V through the processing point P where the grindstone 21 processes the wafer W. 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.

  The main unit 2 is provided with a constant pressure cylinder 26. One constant pressure cylinder 26 is provided on each side of the horizontal direction H across the spindle feed mechanism 25. The constant pressure cylinder 26 is an air cylinder that employs a known configuration including a cylinder, a piston, a piston rod, a compressor, and the like (not shown). The constant pressure cylinder 26 has a spindle 23 and a spindle feed mechanism 25 suspended in a groove 22b, and a piston rod of the constant pressure cylinder 26 is connected to a motor 25c.

  The driving pressure of the constant pressure cylinder 26 is set to a value corresponding to the frictional force acting on the grindstone 21 when the grindstone 21 is cut by the critical cutting depth (Dc value) of the wafer W. The Dc value varies depending on the material of the wafer W, and is 0.09 μm for a silicon wafer and 0.15 μm for a silicon carbide wafer, for example.

  The grinding machine 1 is provided with an in-process gauge 4 that measures the thickness of the wafer W. As will be described later, 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. The thickness of the wafer W can be measured by subtracting the height measured by the outer peripheral side gauge 42 from the height measured by the inner peripheral side gauge 41.

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

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

  In the control device 6, an appropriate wear amount of the grindstone 21 accompanying grinding of one wafer W is stored in advance. The appropriate wear amount of the grindstone 21 is calculated from the wear amount when the grindstone 21 is properly worn by grinding the sample wafer, for example. The appropriate wear speed range varies depending on the count of the grindstone 21, the material of the wafer W, and the like.

  Next, the operation of the grinding machine 1 will be described by taking as an example the case of grinding a SiC substrate. FIG. 4 is a diagram showing how the wafer thickness and the grindstone position change as the grinding process proceeds. The horizontal axis represents time, the left vertical axis represents the thickness (μm) of the wafer W, and the right vertical axis represents the in-process gauge 4. The measured height of the spindle 23 (μm). A solid line in FIG. 4 indicates the position of the spindle 23 measured by the linear encoder 5, and a broken line in FIG. 4 indicates the thickness of the wafer W measured by the in-process gauge 4. FIG. 5A is a schematic diagram showing the state of the wafer W and the grinding machine 1 before grinding, and FIG. 5B is a schematic diagram showing the state of the wafer W and the grinding machine 1 during grinding. is there.

[Preparation for processing]
First, the wafer W is attracted and held on the chuck 31. 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 (reference A in FIG. 4). Next, the grindstone 21 and the chuck 31 are rotated. For example, the rotation speed of the spindle 23 is set to 2000 rpm, and the rotation speed of the chuck 31 is set to 300 rpm. The count of the grindstone 21 is, for example, # 8000.

  The inner peripheral gauge 41 is landed on the surface of the wafer W, and the outer peripheral gauge 42 is landed on the surface of the chuck 31. The control device 6 stores the difference between the inner peripheral side gauge 41 and the outer peripheral side gauge 42 before starting grinding, that is, the initial thickness (for example, 775 μm) of the wafer W.

  The linear encoder 5 is activated, and the initial height (for example, 795 μm) of the spindle 23 in the vertical direction V before starting grinding is stored in the control device 6. Therefore, in this embodiment, the distance (dimension stop distance) between the spindle 23 and the wafer W before the start of processing is 20 μm. Hereinafter, the position of the spindle 23 at the initial height is referred to as an initial position.

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

  The grinding process is performed by performing 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 the grinding process (reference numeral D in FIG. 4).

  Specifically, grinding is performed while the spindle 23 presses the grindstone 21 against the wafer W with 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. The piston is raised so as to push back the compressed air. Therefore, when the grindstone 21 tries to cut deeper than a 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. Thereby, it is suppressed that the grindstone 21 cuts more than Dc value.

  Further, 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 grindstone 21, the spindle feed is performed so as to suppress the reaction force when the grindstone 21 contacts the wafer W. Since the mechanism 25 feeds the spindle 23, ductile mode grinding with the spindle 23 floating can be stably performed.

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

  When the measured value of the in-process gauge 4 reaches the finished thickness (for example, 80 μm) of the wafer W, the ball screw 25b is rotated in the reverse direction to raise the nut 25a and the saddle 23a, thereby separating the grindstone 21 from the wafer W. Thus, the grinding process is completed (reference E in FIG. 4).

[Post-processing]
As shown in FIG. 5B, as the grinding process proceeds, the thickness of the wafer W and the thickness of the grindstone 21 are gradually reduced. Further, the spindle 23 moves up and down due to the lowering by the spindle feed mechanism 25 and the raising by the constant pressure cylinder 26.

  Therefore, the control device 6 calculates the wear amount of the grindstone 21 after the completion of grinding. Specifically, the wear amount of the grindstone 21 is calculated by subtracting the grinding amount Δt by which the grindstone 21 grinds the wafer W from the displacement amount Δv of the spindle 23.

  Then, the control device 6 adjusts the initial position of the spindle 23 when processing the wafer W to be processed next by the wear amount of the grindstone 21.

  For example, as shown in FIG. 4, when the wear amount is 1.5 μm, the wear amount is subtracted from the dimension stop distance (20 μm) when processing the next wafer W, in other words, the grindstone 21 is worn. Is brought closer to the wafer W by this amount. In this embodiment, the initial height of the spindle 23 is corrected to 793.5 μm. As a result, the time required for lowering the spindle 23 and seating the grindstone 21 on the wafer W can be shortened by the amount that the initial position has been lowered according to the wear of the grindstone 21.

  In this way, when the grinding machine 1 described above continuously grinds the wafer W, it calculates the wear amount of the grindstone 21 based on the processing result of the processed wafer W, and processes the next wafer W. At this time, by bringing the grindstone 21 closer to the wafer W by the amount of wear, the spindle feed mechanism 25 shortens the time until the grindstone 21 is seated on the wafer W from the initial position before the grinding process. Processing can be performed.

  The present invention can be variously modified without departing from the spirit of the present invention, and the present invention naturally extends to the modified ones.

DESCRIPTION OF SYMBOLS 1 ... Grinding machine 2 ... Main unit 21 ... Grinding wheel 22 ... Column 22a ... Front 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 ・ ・ ・ Conveyance unit 31 ・ ・ ・Chuck 32 ... Slider 33 ... Rail 4 ... In-process gauge (grinding amount measuring means)
41 ... Inner peripheral side gauge 42 ... Outer peripheral side gauge 5 ... Linear encoder (displacement measuring means)
DESCRIPTION OF SYMBOLS 51 ... Scale 52 ... Measuring head 6 ... Control apparatus D1 ... Wafer conveyance direction D2 ... Feeding direction H ... Horizontal direction V ... Vertical direction W ... Wafer

Claims (2)

A grinding machine for grinding a wafer with a grindstone,
A spindle that can be rotated by attaching the grindstone to the lower end;
A spindle feed mechanism for feeding the spindle vertically to the column;
A constant pressure that is interposed between the spindle feed mechanism and the column, and raises the spindle and the spindle feed mechanism in the vertical direction when the grinding stone cuts into the wafer and the frictional force acting on the grinding stone is higher than a predetermined value. A cylinder,
A grinding amount measuring means for measuring a grinding amount by which the grindstone grinds the wafer;
A displacement measuring means for measuring the amount of displacement of the spindle lowered;
A control device for controlling the spindle feed mechanism so that the grindstone approaches the wafer by the amount of wear of the grindstone calculated by subtracting the grinding amount of the wafer from the displacement of the spindle with respect to the processed wafer;
A grinding machine comprising: The grindstone further includes at least three linear guides arranged on the outer periphery of the spindle so as to sandwich a processing point for grinding the wafer, and supporting the spindle slidably in the vertical direction with respect to the column;
5. The grinding machine according to claim 1, wherein a center of gravity of the spindle is arranged in a polygon formed by the linear guide in a plan view.