JP4797204B2 - Grinding equipment - Google Patents

Description

  The present invention relates to a grinding apparatus, and more particularly, to a grinding apparatus suitable for grinding a surface of hard and brittle material ceramics such as silicon and sapphire with a precision of a unit of submicron or less.

  A semiconductor substrate such as a sapphire wafer used for a white light emitting diode (white LED) using a GaN system is subjected to a required mirror finish through a grinding process, a lapping process, and a polishing process. When using a conventional grinding machine designed to feed the workpiece support at a constant speed, a damaged layer of about several μm is formed on the sapphire wafer at the end of grinding and lapping, and this damaged layer is removed in the final polishing process. At this time, since about 1 hour per 1 μm is required, the polishing process becomes a bottleneck in LED production.

Therefore, in Patent Document 1, as shown in FIG. 8, a rotating grindstone (72) that is held in a predetermined position by a grindstone feeding means and grinds the work (W), and a work support base that supports the work (W) ( 73) and a work support feed means (74) for moving the work support (73) in a direction parallel to the work surface of the work (W). The grindstone feed means (not shown) includes a grinding head. It is a fixed-size feed means that moves up and down by the head feed motor and controls the position of the rotating grindstone to approach the work, and the work support feed means (74) is a hydraulic cylinder that moves the work support (73) 75) The load that the workpiece receives from the rotating grindstone is kept constant by setting the air / air pressure converter (not shown) that converts the air pressure to oil pressure and the air pressure supplied to the air pressure chamber of the oil / air pressure converter. Constant thrust feed means consisting of electropneumatic regulator (not shown) A grinding device (71) has been proposed.
JP 2000-317830 A

  According to the grinding device of the above-mentioned patent document 1, although the damage layer of the work can be reduced by using the work support base feed means as the constant thrust feed means, the constant thrust feed means is pneumatically controlled. There was a problem that it was difficult to control the position of the support base and it was difficult to automate the grinding apparatus.

  An object of the present invention is to provide a grinding apparatus that can reduce the damage layer of a workpiece, can easily control the position of a workpiece support base, and can automate the grinding device.

A grinding apparatus according to the present invention includes a workpiece support table that supports a workpiece to be ground by a rotating grindstone held at a predetermined position, and a workpiece support table feed unit that moves the workpiece support table in a direction parallel to the workpiece surface. In the grinding apparatus having the above, the workpiece support feed means detects the tension of the linear motor, the wire that connects the linear motor and the workpiece support table and transmits the thrust generated by the linear motor to the workpiece support table, and the tension of the wire. Tension detecting means for detecting the speed of the linear motor, feed speed detecting means for detecting the feed speed of the linear motor, and control of the thrust generated by the linear motor based on the tension value obtained from the tension detecting means and the feed speed obtained from the feed speed detecting means. and a motor control means for, workpiece support feeding means, further the biasing means for applying a tension in the opposite direction from the force of the wire to the workpiece support And it is characterized in that it comprises.

  Hard and brittle materials such as sapphire wafers used for white LEDs, crystallized glass used for hard disks, silicon wafers, and alumina sintered bodies are suitable as workpieces to be ground by this grinding apparatus.

  As the rotating grindstone, for example, a metal bond grindstone using diamond, cubic boron nitride or the like as abrasive grains is used.

  The grindstone feeding means is a fixed-size feeding means, for example, configured such that the grinding head is moved up and down by a head feed motor and the position of the rotating grindstone is controlled to approach the workpiece. The rotating grindstone is stopped at a predetermined position according to the grinding thickness by the fixed-size feeding means.

  The workpiece support base holds the workpiece by, for example, a vacuum chuck or wax. Further, the work support base is, for example, an air table (slide table) of an air slide device in order to reduce the frictional resistance.

  The wire is, for example, a steel wire, as long as the distance between the linear motor movable element and the work support base is kept constant and the work support base can be pulled with a tension according to the thrust generated by the linear motor. The material is not particularly limited.

  As the tension detecting means, a strain gauge type or a magnetostrictive type utilizing the inverse magnetostrictive effect, a tension detecting dancer roller, or the like is appropriately used.

  The feed speed detecting means is composed of a linear scale arranged in parallel with the linear motor stator, a linear encoder that moves on the linear scale corresponding to the linear motor movable element, and the like.

  The motor control means controls the generated thrust of the linear motor based on the tension value obtained from the tension detection means and the feed speed obtained from the feed speed detection means. At this time, the thrust applied to the work support base may be constant, but the contact area (contact length × cutting amount) between the rotating grindstone and the work, that is, the contact force changes as the work support base moves. In accordance with this, it is more preferable to change the thrust applied to the work support.

  The workpiece support base feeding means may further include urging means for applying a force opposite to the wire tension to the workpiece support base.

  In this way, when the generated thrust of the linear motor becomes zero due to a power failure or a failure of the linear motor, the workpiece support base receives a force in the direction away from the rotating grindstone from the biasing means, and the workpiece is drawn. This prevents the workpiece from being damaged.

  The biasing means can be obtained, for example, by attaching a weight having an appropriate weight to a position opposite to the feed direction of the workpiece support table. Instead, the front end of the workpiece support table in the traveling direction and the linear motor Are connected by a first wire for transmitting the thrust generated by the linear motor to the work support base, and the biasing means is connected to the rear end of the work support base in the travel direction and the front end of the linear motor in the travel direction. You may make it comprise by connecting with a 2nd wire. In the latter case, grinding can be performed also in the returning direction, whereby the grinding efficiency can be further improved.

  In order to prevent the drawing of the workpiece, instead of using the urging means, grinding may be performed with the center position of the workpiece and the center position of the rotating grindstone being eccentric. In order to perform grinding at an eccentric position, the movement direction of the linear motor and the radial direction of the workpiece do not overlap, that is, the diameter in the predetermined direction of the workpiece and the movement direction of the linear motor are maintained in a parallel state at a certain distance. What should I do?

  The relationship between the center position of the workpiece and the center position of the rotating grindstone is not particularly limited. Typically, the feed direction of the workpiece and the central axis direction of the rotating grindstone are orthogonal to each other, but the center position of the workpiece is such that the direction of the force acting on the workpiece from the rotating grindstone does not become the pull-in direction. It may be offset from the center position of the rotating grindstone. When offsetting the center position of the workpiece and the center position of the rotating whetstone, if there is no offset, the angle between the workpiece feed direction that is at a right angle and the direction of the force acting on the workpiece from the rotating whetstone is an obtuse angle. You can do it. In this way, when the thrust generated by the linear motor becomes zero due to a power failure or failure of the linear motor, the direction of the force of the rotating grindstone acting on the workpiece is opposite to the pulling direction (direction away from the rotating grindstone). Thus, the work is prevented from being pulled in, and thus the work is prevented from being damaged.

  According to the grinding apparatus of the present invention, since the workpiece support base feeding means is a linear motor, in the case of a rotation-linear conversion mechanism that combines a ball screw and a servo motor, thrust control becomes difficult when a high reduction ratio is achieved. While low speed ratio makes it difficult to feed at low speed, the thrust to move the work support can be made very small (for example, 2N or less), and the feed speed can be made extremely low by controlling the drive current of the linear motor. (For example, about several mm / s or 1 mm / s or less), and this significantly increases the damage layer that was about several μm in grinding by an existing apparatus in which the work support base feed means is a constant speed feed means. Can be reduced. Therefore, the lapping process performed after the grinding process can be omitted.

  Further, since the thrust generated by the linear motor is transmitted to the work support via the wire, the thrust generated by the linear motor can be obtained from the tension detecting means for detecting the tension of the wire. For example, the thrust compared to a dynamometer or the like. Can be detected at low cost, and by controlling the thrust generated by the linear motor based on the tension value obtained from the tension detection means and the feed speed obtained from the feed speed detection means, the friction and wiring of the drive system The thrust required for grinding can be controlled while eliminating the effects of resistance, minute feed ripple, etc., and in addition to thrust control, feed speed (position) can be easily controlled. Therefore, the grinding machine can be easily automated.

  Further, by using a linear motor and a wire, rapid feed is possible until the workpiece comes into contact with the rotating grindstone. For example, working time can be shortened as compared with a case where the workpiece is fed at a constant speed by air pressure. In addition, when the thrust is constant and the moving speed is slow, it can be determined that the sharpness of the rotating grindstone has been lowered, and a criterion for dressing the rotating grindstone can be used.

  Furthermore, by bringing the workpiece drive system to the outside of the grinding part, there is no adhesion of coolant, oil, abrasive debris, etc. to the drive system (motor, linear scale, etc.), and reliability and maintainability are improved.

  In addition to the non-linear characteristic region (low current) where it is difficult to control the thrust generated by the linear motor, it is easy to control the linear characteristic if it is further equipped with a biasing means that applies a force opposite to the wire tension to the work support. It is possible to control in the region (appropriate current), and it is possible to control with high accuracy. Also, for example, when a power failure or a linear motor failure occurs, the workpiece may be pulled into the rotating grindstone and the workpiece may be damaged. However, when the thrust generated by the linear motor becomes zero due to a power failure or a failure of the linear motor, the work support is moved to the opposite side of the rotating grindstone by the biasing means, so the work is pulled in. This prevents the workpiece from being damaged.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a first embodiment of a grinding apparatus according to the present invention. A grinding apparatus (1) includes a rotating grindstone (2) for grinding a workpiece (W) such as a sapphire wafer, and a rotating grindstone (2). Whetstone feed means (not shown) for moving the shaft (2a) of the workpiece in a direction perpendicular to the work surface of the workpiece (W), a workpiece support (3) for supporting the workpiece (W), and a workpiece support (3 ) Is moved in a direction parallel to the work surface of the workpiece (W).

  The work support (3) is a slide table of the air slide device, and is supported by a pair of guide shafts (5) of the air slide device so as to be movable in the longitudinal direction.

  The work support base feed means (4) includes a linear motor (11) whose direction from the bottom to the top is the direction of travel, the front end of the work support base (3) and the travel direction of the linear motor (11). A steel first wire (12) that connects the rear end to transmit the thrust generated by the linear motor (11) to the work support (3), and a first tension sensor that detects the tension of the first wire (12). (First tension detection means) (13), feed speed detection means (14) for detecting the feed speed of the linear motor (11), the front end of the linear motor (11) in the direction of travel, and the work support (3) A steel second wire (biasing means) (15) for connecting the rear end in the direction and applying a force opposite to the first wire (12) to the work support (3), and the second wire (15) A second tension sensor (second tension detecting means) (16) for detecting the tension of the first wire, a plurality of first wire guide rollers (17) for guiding the first wire (12), and a second wire (15). Based on the plurality of second wire guide rollers (18) to be guided and the tension values obtained from the tension sensors (13) and (16) and the feed speed obtained from the feed speed detection means (14), 11) motor control means (not shown, see FIG. 4) for controlling the thrust generated.

  The linear motor (11) includes a linear motor movable element (11a) composed of a plurality of coil units, and a linear motor stator (11b) composed of a plurality of permanent magnets arranged along the traveling path of the movable element (11a). have. The traveling direction of the linear motor (11) is, for convenience, the direction from the bottom to the top in FIG. 1, but the traveling direction may be the direction from the left to the right or from the right to the left in FIG.

  The feed speed detection means (14) includes a linear scale (20) arranged in parallel with the linear motor stator (11b) and a linear scale moving on the linear scale (20) corresponding to the linear motor movable element (11a). An encoder (19), and can detect the feed speed and position of the linear motor movable element (11a).

  According to the second wire (biasing means) (15) that connects the front end of the linear motor (11) in the direction of travel and the rear end of the work support (3) in the direction of travel, for example, when a power failure occurs or the linear motor fails For example, the workpiece (W) may be pulled into the rotating grindstone (2) and the workpiece (W) may be damaged, but the generated thrust of the linear motor (11) becomes zero due to a power failure or failure of the linear motor. When this happens, the work support (3) receives a force in the direction away from the rotating grindstone (2) from the second wire (15), and the work (W) is prevented from being pulled in. ) Is prevented.

  FIG. 2 shows the principle of the mechanism of the grinding device (1), where each alphabetic symbol is x: the position of the workpiece in the feed direction, p: the position of the mover of the linear motor, Ua: the tension of the first wire, Ub: tension of the second wire, fn: feed resistance force by grinding, f: linear motor generated thrust, r: friction resistance of the linear motor.

In the model shown in the figure, M is the mass of the work table, αw is the acceleration of the work (work table) (= d ² x / dt ² ), η is the resistance coefficient (val), and l (x) is the contact between the grindstone and the work. Arc length (hereinafter referred to as “contact length”), v: work (work table) moving speed (= dx / dt), m: mass of linear motor mover, q: movement of linear motor mover Speed (= dp / dt), αm: linear motor mover acceleration (= d ² p / dt ² ), Kt: motor thrust constant, I: motor control current, K: wire spring constant, workpiece feed With the direction as the positive direction in the x direction, the following equation holds.

M · αw = Ua−fn−Ub (1)
fn = η · l (x) · v (2)
m · αm = fr−Ua (3)
r = μ · q (4)
f = Kt · I (5)
Ua = K (p−x) (6)
For low speed feed (v ≦ several mm / s or less), αw and αm are approximately zero, and Ub is a constant term. Therefore, it can be seen from Equation (3) that the tension Ua is measured as a value obtained by subtracting the frictional resistance r from the motor generated thrust f. Since l (x) is known as will be described later, if driving is performed with v = dx / dt = constant, the tension Ua (= fn + Ub = η · l (x) · v + Ub) is l (x). Appear with the same profile. That is, in order to keep Ua constant, v draws a 1 / l (x) profile, and in order to keep the surface pressure of the grinding surface constant, Ua may be controlled in accordance with l (x). If Ua is determined, the linear motor generated thrust f is obtained from the equation (3), and the control current I of the linear motor (11) is controlled based on the equation (5). Such constant surface pressure control makes it possible to suppress the pressure applied to the grinding surface below the pressure at which damage occurs, and to eliminate grinding damage.

  In order to perform appropriate grinding on a hard and brittle material, it is necessary to have a feed thrust of several hundred gf or less and a grinding speed of several μm to several mm / s as low thrust / low speed. If this is performed with a rotary motor, it is necessary to achieve a large reduction ratio, and it is difficult to achieve both low thrust and high thrust. According to the linear motor (11), thrust can be directly generated by current control, and both low thrust and low speed can be easily achieved. In addition, when the low thrust is applied, the second wire tension Ub acts, so that the operation of the linear motor can be used in the linear region instead of the low current nonlinear region.

  FIG. 3 shows a model of the grinding load used in the control system of the grinding apparatus of the present invention. As can be seen from FIG. 3A, l (x) included in the above equation (2): contact length Is changed by z (slowly increases after gradually increasing) when the distance from the front end of the wafer (work) to the center of the contact position between the rotating grindstone and the wafer is x = z. Therefore, if the thrust generated by the linear motor is kept constant, the load applied per unit length of the workpiece will fluctuate, and thrust control in consideration of changes in l (z) is desired. l (z) and xp: The shortest distances from the front end of the wafer (workpiece) to the contact position between the rotating grindstone and the wafer can be obtained by the equations shown in FIG. FIG. 4B compares the contact length l (z) obtained from this model with the contact length obtained from the circular approximation model.

  FIG. 4 shows a schematic configuration of the motor control means for controlling the thrust generated by the linear motor (11). The motor control means applies a control current to the linear motor (11) via the current amplifier (22). Motion controller (21), which is obtained by the feed amount and feed speed obtained from the linear encoder (19) constituting the feed speed detection means (14) and the two tension sensors (13) (16). The wire tension value is fed back to the controller (21), and based on this, the control current of the linear motor (11) is controlled.

  FIG. 5 shows a second embodiment of the grinding apparatus of the present invention. This embodiment is different from the first embodiment in the configuration of the work support base feed means (34) of the grinding apparatus (31). In the following description, the same configuration as that of the first embodiment is used. Are given the same reference numerals and their description is omitted.

  The workpiece support table feed means (34) of this embodiment includes a linear motor (11), a linear motor (11), and a linear motor (11) connected to the front end of the workpiece support table (3) and the rear end of the linear motor (11). 11) a steel first wire (12) for transmitting the generated thrust to the work support (3), a plurality of first wire guide rollers (17) for guiding the first wire (12), and the first wire Dancer roller (first tension detecting means) (41) for detecting the tension of (12), feed speed detecting means (14) for detecting the feed speed of the linear motor (11), and the direction of movement of the work support (3) Weight (biasing means) (42) suspended by a steel second wire (43) and pulley (44) provided at the rear end, and tension value and feed speed detection means obtained from the dancer roller (41) Motor control means (not shown) for controlling the thrust generated by the linear motor (11) based on the feed speed obtained from (14) That.

  According to the weight (biasing means) (42), there is a possibility that the workpiece (W) may be damaged by pulling the workpiece (W) into the rotating grindstone (2), for example, in the event of a power failure or failure of the linear motor. However, when the thrust generated by the linear motor (11) becomes zero due to a power failure or failure of the linear motor, the work support (3) corresponds to the weight of the weight (42) from the second wire (43). The workpiece (W) is prevented from being drawn by receiving a force in a direction away from the size of the rotating grindstone (2), thereby preventing the workpiece (W) from being damaged.

  In addition, (45) of FIG. 5 has shown the grinding part cover. In the grinding apparatus according to the first and second embodiments, the linear motor (11), which is a drive system for the workpiece (W), can be taken out of the grinding part. It prevents adhesion of coolant, oil, abrasive debris, etc. to the encoder etc., and is excellent in reliability and maintainability. In addition, when the wiring of the linear motor (11) is attached to the work support base (3), the resistance that increases due to the wiring hinders securing low thrust, but the work support base (3) has a wire (12 ) (43) is simply attached, so low thrust can be easily secured.

  FIG. 6 shows an example of a timing chart for controlling the grinding apparatus of the present invention, which is created based on the grinding load model shown in FIG. As described above with reference to FIG. 3, after the start of grinding, the contact length l (z) gradually increases due to the movement of the workpiece (W), and accordingly, the grinding resistance increases. Then, after finishing approximately half of the grinding, the contact length gradually decreases due to the movement of the workpiece (W), and accordingly, the grinding resistance also decreases. Therefore, in thrust control considering the change of l (z), as shown in FIG. 6, the workpiece support (3), that is, the linear motor movable element (11a) is fed at a high speed up to the grinding position. In the grinding stage, the thrust is preferably increased or decreased according to the increase or decrease of the contact length, and after the grinding is completed, it is preferably moved again to the standby position at a high speed (rapid retreat). The feed rate during grinding varies depending on the state of the workpiece (W) and the grindstone (2), but as a result of thrust control, distortion occurs corresponding to l (z). Basically, as shown in the figure It becomes a gentle arc shape.

  In each of the above embodiments, the relationship between the center position of the workpiece (W) and the center position of the rotating grindstone (2) is not particularly limited.For example, the feed direction of the workpiece (W) and the rotating grindstone ( As shown in FIG. 7A, the center position (GO) of the rotating grindstone (2) is the center position of the workpiece (W) (see FIG. 7A). It may be on the movement line (TL) of WO). More preferably, the center position (WO) of the workpiece (W) is as shown in FIG. 7 (b) so that the direction of the force acting on the workpiece (W) from the rotating grindstone (2) does not become the retraction direction. Offset from the center position (GO) of the rotating wheel (2). When offset in this way, the direction of the force acting on the workpiece (W) from the rotating grindstone (2) is the upper right direction of the figure (work feed direction = the movement line (TL) of the center position (WO) of the workpiece (W) and rotation) When the angle between the grinding wheel (2) and the direction of the force acting on the workpiece (W) is an obtuse angle), the thrust generated by the linear motor (11) becomes zero due to a power failure or a failure of the linear motor. The direction of the force of the rotating grindstone (2) acting on the workpiece (W) is opposite to the pulling direction (the direction away from the rotating grindstone (2)), preventing the workpiece (W) from being pulled in, Work (W) scratches are prevented.

FIG. 1 is a side view schematically showing a first embodiment of a grinding apparatus of the present invention. FIG. 2 is a view showing the principle of the mechanism of the first embodiment of the grinding apparatus of the present invention. FIG. 3 is a diagram for explaining a grinding load model used in the control system of the grinding apparatus of the present invention. (A) is a diagram showing the modeling and calculation formula, and (b) is obtained by this model. It is the figure which compared the contact length and circular approximation which are obtained. FIG. 4 is a block diagram showing the configuration of the control system of the first embodiment of the grinding apparatus of the present invention. FIG. 5 is a side view schematically showing a second embodiment of the grinding apparatus of the present invention. FIG. 6 is a diagram showing an example of a timing chart of the grinding apparatus of the present invention. FIGS. 7A and 7B are diagrams for explaining the planar arrangement of the first and second embodiments. FIG. 7A shows a first example, and FIG. 7B shows one means for canceling the pulling force of the rotating grindstone. A second example is shown. FIG. 8 is a side view showing a conventional grinding apparatus.

Explanation of symbols

(1) Grinding equipment
(2) Rotary grinding wheel
(3) Work support base
(4) Work support table feed means
(11) Linear motor
(12) First wire
(13) First tension detection means
(14) Feed rate detection means
(15) Second wire
(16) Second tension detection means
(W) Workpiece
(WO) Work center position
(GO) Center position of rotating wheel

Claims (4)

In a grinding apparatus provided with a workpiece support table for supporting a workpiece to be ground by a rotating grindstone held at a predetermined position, and a workpiece support table feed means for moving the workpiece support table in a direction parallel to the work surface of the workpiece. The work support base feed means includes a linear motor, a wire that connects the linear motor and the work support base to transmit the generated thrust of the linear motor to the work support base, a tension detection means that detects the tension of the wire, and a linear Feed speed detection means for detecting the feed speed of the motor, and motor control means for controlling the thrust generated by the linear motor based on the tension value obtained from the tension detection means and the feed speed obtained from the feed speed detection means. and which, in workpiece support feeding means, to characterized in that it further comprises a biasing means for applying a tension in the opposite direction from the force of the wire to the workpiece support Grinding apparatus. 2. The grinding apparatus according to claim 1, wherein the urging means is constituted by a weight attached at a position opposite to the feed direction of the workpiece support base . The front end of the workpiece support in the direction of travel and the rear end of the linear motor in the direction of travel are connected by a first wire for transmitting the thrust generated by the linear motor to the workpiece support, and the biasing means is the direction of travel of the workpiece support. The grinding apparatus according to claim 1 , wherein the rear end and the front end in the traveling direction of the linear motor are connected by a second wire.   The grinding apparatus according to claim 1, wherein the center position of the workpiece is offset from the center position of the rotating grindstone so that the direction of the force acting on the workpiece from the rotating grindstone does not become the pulling direction.

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