Device and method for double-sided machining of flat workpieces

Abstract

Device for double-sided machining of flat workpieces, comprising an upper working disk (40) and a lower working disk, wherein the working disks (40) form a working gap between their mutually facing working surfaces (46) for machining the workpieces, and wherein at least one of the working disks (40) has a plurality of bores (48) extending through the working surface (46) for supplying a liquid working medium into the working gap, characterized in that the bores (48) are grouped into several groups, wherein each group of bores (48) is connected to a separate pressurized supply line (36) for the working medium, wherein at least one pressure regulating device (35) is provided.with which the working fluid pressure in the supply lines (36) can be controlled separately and the cross-section of the bores (48) or the cross-section of fluid lines (52) guided in the bores (48) is reduced in the area of ​​their end opening into the working surface (46)..

Description

[0001] The invention relates to a device for double-sided machining of flat workpieces, comprising an upper working disc and a lower working disc, wherein the working discs form a working gap between their mutually facing working surfaces for machining the workpieces, and wherein at least one of the working discs has a plurality of bores extending through the working surface for supplying a liquid working medium into the working gap.The invention also relates to a method for operating a device for double-sided machining of flat workpieces, wherein the device has an upper working disc and a lower working disc, wherein the working discs form a working gap between their mutually facing working surfaces for machining the workpieces, and wherein at least one of the working discs has a plurality of bores extending through the working surface for supplying a liquid working medium into the working gap.

[0002] Such devices and methods are used, for example, for double-sided polishing of semiconductor wafers. For polishing, a polishing fluid is introduced into the working gap. For this purpose, a two-disc polishing machine is known, for example, from DE 100 07 390 A1. The polishing disc described therein has a series of axially parallel bores that are aligned with corresponding bores in the carrier disc supporting this polishing disc and are connected by lines through which a polishing compound is supplied to the working surface of the polishing disc. The bores are provided in the upper working disc, with the polishing compound being conveyed downwards into the polishing gap by gravity. One problem is that a uniform supply of polishing compound to the working gap cannot always be guaranteed.In particular, areas of the polishing wheel that are frequently crossed by workpieces during processing become depleted of polishing compound. This can impair the polishing result.

[0003] EP 1 918 069 A1 relates to a method for double-sided polishing of wafers. For this purpose, a wafer is clamped in a holder and positioned between an upper and a lower rotary table, which have polishing jaws. The rotary tables have bores for a polishing medium, with several bores being supplied with polishing medium via a supply line.

[0004] JP 2006-346757 A relates to a lapping machine for polishing thin, plate-like workpieces such as crystal fragments or semiconductor chips. In the machine, workpieces are held by a carrier and positioned between an upper and a lower work surface. Polishing is achieved by rotating the carrier, thereby applying a polishing compound. For this purpose, an abrasive layer on the upper work surface has fine channels that connect to bores passing through the upper work surface.

[0005] DE 603 ​​06 295 T2 relates to a grinding machine and a method for grinding a workpiece. The grinding machine comprises, in addition to an upper and a lower grinding wheel, a slurry feed unit that supplies the slurry. The slurry is guided through slurry paths to slurry holes, and a plurality of valve mechanisms are provided for the slurry paths by which the flow of the slurry can be controlled.

[0006] JP 2004-216 541 A relates to a lapping machine comprising a worktable, a polishing compound detection device, a polishing compound feed device, and a polishing compound removal device. Depending on the polishing compound level detected on the worktable by the detection device, polishing compound is fed by the polishing compound feed device or removed by the polishing compound removal device. Furthermore, a load sensor and a speed sensor are provided.

[0007] Based on the prior art described above, the invention aims to provide a device and a method of the type mentioned at the outset, with which an adequate supply of working materials in the working gap is ensured at all times.

[0008] This problem is solved according to the invention by the subject matter of independent claims 1 and 8. Advantageous embodiments are described in the dependent claims, the description, and the figures.

[0009] For a device of the type mentioned at the outset, the invention solves the problem by grouping the bores for the fluid supply into several groups, each group of bores being connected to a separate pressurized supply line for the working fluid, and by providing at least one pressure regulating device with which the working fluid pressure in the supply lines can be controlled separately. For a method of the type mentioned at the outset, the invention solves the problem by grouping the bores into several groups, each group of bores being supplied with pressurized working fluid, and the working fluid pressure of the working fluid supplied to each group being controlled separately.

[0010] The machining process according to the invention can be material-removing. The device can, for example, be a device for polishing flat workpieces on both sides. The working fluid can accordingly be a polishing fluid. However, other machining processes are also possible, such as grinding or lapping. The workpieces to be machined according to the invention, for example, in a plane-parallel manner, can be semiconductor wafers. The working discs can, for example, be ring-shaped. Accordingly, the working gap can also be ring-shaped. A vertical drive shaft can be connected to one or both working discs. If the working discs are each supported by a carrier disc, this connection can be made through the carrier disc. At least one of these drive shafts can be driven by a suitable drive, so that the working disc connected to this drive shaft is moved in a rotating manner.The workpieces are machined between the rotating work discs. At least one of the work discs, for example the upper one, has through-holes. Of course, such through-holes can also be provided in both work discs. Suitable pressure lines, such as pressure hoses or pipes, can run through the holes in the work disc(s) to deliver the working fluid to the working gap.

[0011] According to the invention, the multitude of provided bores is divided into several groups, for example, three or more. Each group is assigned a pressurized supply line. In the aforementioned example, a total of three or more pressurized supply lines can therefore be provided. For example, specific working gap zones can each be supplied with working fluid by a group of bores. The working fluid pressure is the pressure prevailing in the bores or pressure lines filled with working fluid. It determines the flow rate of working fluid from the bores into the working gap. The invention enables separate control of the working fluid pressure, and thus the working fluid flow rate into the working gap, for the individual supply lines and thus for the individual bore groups or working gap zones supplied by them.This allows the supply of working materials, such as polishing compound, to be flexibly adapted to the prevailing operational requirements. For example, the working material flow can be regulated according to the operating parameters (recipe-based). The zones or groups can be divided so that the bores within a zone are subjected to largely identical operating conditions during operation. This ensures that the bores within a working gap zone are swept by workpieces with essentially the same frequency. For example, the bores in specific radial areas of the working gap can each be assigned to a group. This results in groups of bores located in annular zones. Through these zones or groups, the following applies:For each group, the optimal supply of working fluid can be ensured by a common pressure control system for that zone, which regulates the pressure and thus the flow rate through the bores. In particular, a constant working fluid pressure can be individually specified for each supply line. This enables a constant supply of polishing fluid throughout the entire working gap, even though the bores in different zones are subject to different operating conditions. Of course, more than one control unit can be provided, for example, one for each supply line or bore group. However, it is also conceivable to provide a single control unit that regulates the working fluid pressure in all supply lines.

[0012] According to the invention, a consistent and sufficient supply of working fluid to the working gap is ensured at all times. In addition to optimizing the work result, this also allows for more effective use of the working fluid, thus reducing overall fluid requirements. Scratches or similar machining defects are more reliably avoided. Relatively smooth polishing cloths can also be used. If desired, workpieces can be rinsed off an upper working disc with perforations, for example, by briefly increasing the working fluid pressure significantly. This reliably prevents unwanted adhesion of the workpieces when the upper working disc is lifted after the process is complete. It is also possible to selectively vary the amount of working fluid supplied to the working gap, such as the amount of polishing compound, in order to cool areas with elevated process temperatures.This further optimizes the work result.

[0013] In a particularly practical configuration, the supply lines can each be connected to a common main pressure supply line and to the boreholes of a group of lines. The main supply line is connected to a working fluid reservoir and can, for example, include a pump that pumps the working fluid through the main supply line to the individual supply lines. Each supply line then contains, for example, a pressure regulating unit that allows the working fluid pressure in the respective supply line to be regulated independently of the other supply lines. It is also possible to provide flow meters in the supply lines, the measurement signals of which are applied to corresponding flow control devices, which regulate the fluid flow based on the measurement signals from the flow meters.The supply lines can be ring mains or ring channels in a manner known per se, connected to a multitude of supply lines, for example, supply hoses, which run through the bores of the working disc. Such pressure-tight ring mains serve in a particularly simple and reliable manner to supply a multitude of lines communicating with them. The common main pressure supply line can furthermore be guided through a vertical drive shaft associated with at least one working disc provided with bores. The vertical drive shaft is driven by a drive, for example, a motor. This rotates the working disc connected to the drive shaft. Thus, a pressure-tight single-channel rotary feed-through through the drive shaft is provided to distribute the working fluid to the various supply lines.Advantageously, only one main pressure supply line needs to be routed from the stationary machine housing to the rotating components. However, in this case, it is necessary to provide an electrical control in the working disc for dividing the main pressure supply line into the individual supply lines. This may be undesirable in certain applications. Therefore, an alternative multi-channel rotary feedthrough is also possible, in which the division into the individual supply lines occurs before the drive shaft, and several lines are routed through the drive shaft accordingly.

[0014] According to the invention, the cross-section of the bores or the cross-section of fluid lines guided in the bores is reduced in the region of their end opening into the working surface. The cross-section can be reduced, for example, by more than 50%. Such cross-sectional reductions in the region of the opening into the working gap create a back pressure when the working fluid flows out, which ensures the maintenance of a minimum pressure in the supply line even with free outflow. In particular, a collapse of the working fluid pressure does not occur if one or more outlet openings are exposed. Unlike in the prior art, the polishing fluid does not only exit through bores free of workpieces, but can also exit from bores that are covered by workpieces.In particular, fluid will leak if the pressure in the supply line is equal to or greater than the specific working pressure in the working gap. Maintaining a certain pressure level in the supply lines ensures that flow occurs at all outlet openings.

[0015] Since the friction between the working surface of the work discs and the workpieces depends on the amount of fluid, a measuring device can be provided to measure the torque applied by a rotary drive to at least one vertical drive shaft connected to at least one of the work discs. The control device compares the torque measured by the measuring device with a target torque or a target torque range and, if the measured torque deviates from the target torque or the target torque range, adjusts the working fluid pressure in at least some supply lines so that the measured torque again reaches the target torque or is within the target torque range. The control device can also be provided to compare the measured torque with a predetermined limit torque.If the measured torque falls below the limit torque, the control device reduces the working fluid pressure in at least some supply lines so that the measured torque again reaches a value above the limit torque. This design is based on the understanding that an oversupply of working fluid to the working gap causes the torque required by the drive to achieve a predetermined speed to drop abruptly, similar to aquaplaning. This leads to an undesirable impairment of workpiece machining. Therefore, in such a case, the working fluid supply is reduced by lowering the pressure in the supply lines until the torque is back within the predetermined range. In particular, the pressure can, of course, be changed, especially reduced, in all supply lines.

[0016] The bores can be grouped according to how frequently they are obscured by the workpieces during operation of the device. Based on this, the working fluid pressure in the supply lines of each group can be set higher the more frequently the bores of a particular group are obscured by the workpieces during operation. Thus, different target pressure values ​​are specified for the respective supply line of the different groups, with the target pressure values ​​being selected depending on the frequency of obscuration of the bores by the workpieces expected during operation. According to the invention, rotor discs with at least one, and in particular a plurality, receptacles can be provided in a manner known per se, in which the workpieces to be machined are held in a floating manner.The rotor discs are driven by rotation within the working gap, with the workpieces held within them moving along cycloidal paths within the gap. During workpiece machining, this results in varying probabilities of workpiece presence in the radial direction of the working gap. For example, the probability of workpieces being located in the peripheral areas of the working gap, and especially at the inner edge, can be higher than in the center. The aforementioned design takes this into account. Bores in specific annular zones of the working gap can be grouped together, with each annular zone assigned a specific probability of workpiece presence. The higher this probability of workpiece presence for a particular annular zone or group, the greater the target working pressure for the supply line assigned to that group.

[0017] The regulation can be implemented in such a way as to result in the most homogeneous distribution possible of the working material in the entire working gap.

[0018] The method according to the invention can be carried out in particular with the device according to the invention. Accordingly, the device is suitable for carrying out the method according to the invention.

[0019] An embodiment of the invention is explained in more detail below with reference to the figures. They schematically show: Fig. 1 a part of a device according to the invention in a vertical sectional view, Fig. 2 an enlarged representation of a section of a view according to Fig. 1 according to a further embodiment, Fig. 3 an enlarged view of section B from Fig. 2, and Fig. 4 a circuit diagram to illustrate the control according to the invention.

[0020] Unless otherwise stated, identical reference symbols in the figures denote identical objects. Fig. Figure 1 shows a section of a device 10 according to the invention for double-sided processing of flat workpieces. In this example, it is a double-sided polishing machine for planar-parallel polishing of semiconductor wafers. In the example shown, the device has three supply lines 36 coming from a polishing fluid reservoir, each of which is guided through a vertical drive shaft 20 of the device via a connector 22 and a multi-channel rotary insertion 18. By means of a Fig. Polishing fluid can be pumped from the fluid reservoir through supply line 36 by a pump (not shown in detail). In the example shown, the supply lines 36 each form a ring main 36 with branches to the respective group of bores. The supply lines 36 can be formed by supply hoses. Furthermore, pressure regulating devices (not shown in detail) are provided, each designed to regulate the working fluid pressure in one of the supply lines 36, as will be explained in more detail below.

[0021] The device 10 further comprises, in a manner known per se, an upper and lower annular support disk and an annular upper and lower working disk respectively connected to the upper and lower support disks. Fig. Figure 1 shows only the upper support disc 38 and the upper working disc 40 connected to it. The upper support disc 38 is ring-shaped. The device 10 has a lower support disc and working disc (not shown) that is largely symmetrical to the upper support and working discs 38 and 40. Between their mutually facing ring-shaped working surfaces, of which in Fig. As shown in Figure 1, the working surface of the upper working disc 40 is depicted at reference numeral 46. The working discs define an annular working gap. The basic design of such a double-sided polishing machine with upper and lower working discs is known per se and is described, for example, in DE 100 07 390 A1.

[0022] In Fig. Figure 1 further shows that the upper working disc 40 has a plurality of axial bores 48, each of which aligns with corresponding bores 50 in the upper support disc 38. Pressure tubes 52 extend through each of these bores. Fig. 1 can further be seen that the ring-shaped supply lines 36 are each connected to the upper openings of the pressure pipes 52.

[0023] The design of bores 48, 50 and pressure pipes 52 is shown in the enlarged illustrations in the Fig. 2 and Fig. 3 will be explained in more detail. In contrast to the embodiment according to Fig. 1 is in the embodiment according to the Fig. 2 and Fig. 3 a larger number of supply lines 36, boreholes 48, 50 and pressure pipes 52 are provided. Apart from this, the embodiments do not differ. In the Fig. 2 and Fig. Figure 3 shows that the pressure pipes 52 are each connected to the ring lines 36 at their upper end via a connection 54. The pressure pipes 52 are made of, for example, a plastic material. A metallic sleeve 58 is inserted into the bores 50 and 48 in the upper support disc 38 and the upper working disc 40, respectively. In the area of ​​its end opening into the working surface 46, a ring seal 60 seals the pressure pipes 52 against the sleeve 58. Furthermore, in Fig. Figure 3 shows that the pressure pipes 52 have a significant cross-sectional reduction 62 of more than 50% at their lower end. The outlet opening 64 of the pressure pipes 52 therefore has a considerably smaller diameter than the main section 66 of the pressure pipes 52.

[0024] As especially in the Fig. 1 and Fig. As can be seen in Figure 2, bores 48 and 50 are arranged at different radial distances from the working and support discs. The upper working disc, and thus also the upper support disc that carries it, has several circular rows of axial bores arranged at different radial distances from the central axis of rotation of the working disc 40 and support disc 38, which runs through the vertical drive shaft 20. The bores at each radial distance are grouped together and supplied with polishing compound by a ring line 36.

[0025] The function of the device according to the invention is to be explained with reference to the schematic circuit diagram in Fig.4 will be explained in more detail below. A pump 68 pumps polishing compound from a polishing compound reservoir (not shown), which is connected to the pump 68 via a check valve 70, into the supply lines 36. From there, the polishing compound is pumped to the pressure regulating devices 35. Each supply line 36 also contains a two-way valve 72 for switching the supply circuits supplied by the respective supply lines 36 on and off. The pressure regulating devices 35 allow the polishing compound pressure in each of the ring lines 36 to be regulated separately to a specific value. Each supply line 36 also contains a flow meter 74. Such regulation or flow control is known to those skilled in the art and will therefore not be explained in detail.The workpieces to be machined can, for example, be held in rotating disks in a manner known per se, so that they move along cycloidal paths in the working gap. This results in different probabilities of the workpieces being in the working gap during machining. In particular, the different radial groups of bores in the upper working disk 40 are obscured by workpieces with varying frequency during operation. According to the invention, this can be taken into account by supplying the radial areas of bores that are expected to be obscured more frequently with a higher working fluid pressure via the respective ring line 36 and the corresponding pressure regulating device 35.

Claims

[1] Device for double-sided machining of flat workpieces, comprising an upper working disk (40) and a lower working disk, wherein the working disks (40) form a working gap between their mutually facing working surfaces (46) for machining the workpieces, and wherein at least one of the working disks (40) has a plurality of bores (48) extending through the working surface (46) for supplying a liquid working medium into the working gap, characterized by, that the bores (48) are grouped into several groups, each group of bores (48) being connected to a separate pressurized supply line (36) for the working medium, wherein at least one pressure regulating device (35) is provided with which the working medium pressure in the supply lines (36) can be controlled separately and the cross-section of the bores (48) or the cross-section of fluid lines (52) guided in the bores (48) decreases in the region of their end opening into the working surface (46). [2] Device according to claim 1, characterized by , that the supply lines (36) are each connected on the one hand to a common main pressure supply line and on the other hand to the boreholes (48) of a group. [3] Device according to claim 2, characterized by, that the common main pressure supply line is guided through one of the vertical drive shafts (20) associated with at least one working disk (40) provided with bores (48). [4] Device according to claim 2, characterized by , that the supply lines (36) are guided through one of the vertical drive shafts (20) associated with at least one working disk (40) provided with bores (48). [5] Device according to one of the preceding claims, furthermore characterized bya measuring device for measuring the torque applied by a rotary drive to at least one vertical drive shaft (20) connected to at least one of the working discs, wherein the control device (35) compares the torque measured by the measuring device with a target torque or a target torque range and, in the event of a deviation of the measured torque from the target torque or the target torque range, changes the working medium pressure in at least some supply lines (36) so that the measured torque again assumes the target torque or is within the target torque range. [6] Device according to claim 5, characterized by, that the control device (35) compares the measured torque with a predetermined limit torque and that, if the measured torque falls below the limit torque, the control device (35) reduces the working medium pressure in at least some supply lines (36) so that the measured torque again assumes a value above the limit torque. [7] Device according to any one of the preceding claims, characterized by , that the control device (35) adjusts the working fluid pressure in the supply lines (36) of the groups depending on how frequently the bores (48) of a respective group are covered by the workpieces to be machined during operation of the device (10), [8] Method for operating a device for double-sided machining of flat workpieces, wherein the device has an upper working disk (40) and a lower working disk, wherein the working disks (40) form a working gap between their mutually facing working surfaces (46) for machining the workpieces, and wherein at least one of the working disks (40) has a plurality of bores (48) extending through the working surface (46) for supplying a liquid working medium into the working gap, characterized by, that the bores (48) are grouped into several groups, wherein each group of bores (48) is supplied with pressurized working fluid, wherein the working fluid pressure of the working fluid supplied to each of the groups (48) is controlled separately and the cross-section of the bores (48) or the cross-section of fluid lines (52) guided in the bores (48) is reduced in the area of ​​their end opening into the working surface (46). [9] Method according to claim 8, characterized by, that the torque applied by a rotary drive to at least one vertical drive shaft (20) connected to at least one of the working discs is measured, and that the torque measured by the measuring device is compared with a target torque or a target torque range, and if the measured torque deviates from the target torque or the target torque range, the working medium pressure of the working medium supplied to at least some groups is changed so that the measured torque again assumes the target torque or is within the target torque range. [10] Method according to claim 9, characterized by, that the measured torque is compared with a predetermined limit torque and that if the measured torque falls below the limit torque, the working fluid pressure of the working fluid supplied to at least some groups is reduced so that the measured torque again assumes a value above the limit torque. [11] Method according to any one of claims 8 to 10, characterized by , that the bores (48) are grouped together depending on how often the bores (48) are covered by the workpieces to be machined during operation of the device. [12] Method according to claim 11, characterized by , that the working medium pressure of the working medium supplied to the groups is adjusted depending on how frequently the bores (48) of a respective group are covered by the workpieces to be machined during operation of the device.

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