DEVICE AND METHOD FOR PRESSING AN UPPER POLISHING CLOTH AGAINST AN UPPER POLISHING PLATE OF A MACHINE FOR SIMULTANEOUSLY POLISHING THE FRONT AND BACK OF A SEMI-CONDUCTIVE DISC

Description

[0001] The invention relates to a device for pressing an upper polishing cloth against an upper polishing plate of a machine for simultaneously polishing the front and back sides of a semiconductor wafer. The invention also relates to a corresponding method that uses the device. State of the art / Problems

[0002] The polishing of both sides of workpieces such as semiconductor wafers is also called double-sided polishing (DSP). The basic principles of DSP for semiconductor wafers are described, for example, in US 2003 0 054 650 A1 and in DE 100 07 390 A1.

[0003] Typically, both polishing pads of a DSP system are covered with polishing cloths. These should be applied without air bubbles to eliminate any potential source of impairing the desired polishing result. The respective polishing cloth should also adhere evenly to the polishing pad. To achieve the necessary adhesion, the polishing cloths can be pressed together between the polishing pads (cloth pressing). Pressing causes the adhesive to flow and bond more effectively. Methods for creating an adhesive bond between the respective polishing cloth and the corresponding polishing pad are described in US 2007 0 087 671 A1.

[0004] JP 2006 289 523 A, JP 2006 346 808 A and DE 102 39 774 A1 are known.

[0005] Before pressing the cloth, the ring-shaped upper polishing cloth is glued to the upper polishing pad. Such a method is described, for example, in EP 4 000 806 A1. Afterwards, any bubbles in the space between the upper polishing pad and the upper polishing cloth must be removed, as this cannot be achieved sufficiently by pressing the cloth alone. These bubbles can be manually pushed to the outer or inner edge of the upper polishing cloth using a squeegee or roller and then pressed out of the space.

[0006] This work is strenuous and difficult because it requires working overhead. While EP 4 000 806 A1 mentions that the process can also be performed by machine, it does not specify how this can be implemented.

[0007] US 2007 0 087 671 A1 recommends, after applying the polishing cloths, clamping a roller unit with radially arranged rollers between the lower and upper polishing pads and rotating the polishing pads in opposite directions. Because radially arranged rollers primarily move bubbles in the space between the polishing pad and the polishing cloth circumferentially, they are only partially effective at removing bubbles from this space.

[0008] DE 10 2019 213 657 A1, which constitutes the closest prior art for independent claim 1, discloses a device for pressing an upper polishing cloth against an upper polishing plate of a machine for simultaneously polishing a front and a back of a semiconductor disk between the upper polishing plate and a lower polishing plate, wherein a base body has a toothing that engages in the outer and inner pin ring of the machine and a roller with which the pressing of the polishing cloth is effected.

[0009] The object of the present invention is to offer a more efficient solution for removing bubbles from the space between the upper polishing pad and the upper polishing cloth.

[0010] The object of the invention is solved by a device for pressing down an upper polishing cloth according to claim 1.

[0011] The linear rails are preferably mounted on a ring as the base body. The ring rests on the lower

[0012] The polishing cloth has a toothed section that engages with the outer and inner pin rings of the machine. The linear rails can extend beyond the edge of the lower polishing pad. However, it is also possible to shorten them to a length corresponding to the distance between the inner and outer pin rings.

[0013] The actuators preferably operate pneumatically or electrically.

[0014] Furthermore, the problem is solved by a method for pressing down an upper polishing cloth according to claim 4.

[0015] The upper polishing cloth is adhered to the upper polishing pad, bringing it into an intermediate state where bubbles are present in the space between the upper polishing cloth and the upper polishing pad, and the upper polishing cloth is not yet uniformly adhered to the upper polishing pad. This can be achieved, for example, by placing the upper polishing cloth on top of the lower polishing cloth, with the adhesive layer of the upper polishing cloth facing upwards (away from the lower polishing pad), and pressing the polishing pads together. Alternatively, the procedure described in EP 4 000 806 A1 can be followed.

[0016] The device according to the invention is used in the next step to remove the bubbles from the space between the upper polishing pad and the upper polishing cloth. For this purpose, the device is positioned above the lower polishing cloth, and the upper polishing pad is pivoted over the lower polishing pad so that there is a small gap between the two polishing pads. At this distance, the roller does not yet touch the upper polishing cloth, provided the actuators have not yet lifted it. However, the gap is also sufficiently small to allow the roller to be pressed against the upper polishing cloth by means of the actuators. The upper polishing pad is then rotated, preferably at a speed of not less than 0.1 rpm and not more than 1 rpm, particularly preferably 0.2 rpm, and the roller is lifted by means of the actuators so that it is pressed against the upper polishing cloth.The contact pressure of the roller is preferably 1.8 x 10 5< Pa - 2.0 x 10 5< Pa (1.8 bar - 2.0 bar) and can be varied.

[0017] Simultaneously with the pressing of the roller against the upper polishing cloth, the roller is moved along the linear rails between the inner and outer pin rings of the polishing machine by means of the carriages. In doing so, the roller expels bubbles primarily in a radial direction from the inner edge to the outer edge of the upper polishing cloth, and thus from the space between the upper polishing cloth and the upper polishing pad. The speed of the roller's movement along the linear rails is preferably 0.5 m / s to 1.5 m / s and can also be varied.

[0018] The roller is pressed against the upper polishing cloth at least temporarily, while the upper polishing plate is rotated and the roller is moved between the inner and outer pin rings of the machine.

[0019] According to one embodiment, the roller is moved back and forth between the inner and outer pin rings of the polishing machine and pressed against the upper polishing cloth while the upper polishing plate is rotated.

[0020] According to another embodiment, the roller is moved back and forth between the inner and outer pin rings of the polishing machine and is pressed against the upper polishing cloth only on the forward or return stroke, while the upper polishing plate is rotated.

[0021] The invention will be further described with reference to the drawings. Brief description of the characters

[0022] Fig. 1 shows features of a DSP polishing machine when viewed from above, looking at the lower polishing pad. Fig. 2 shows a preferred embodiment of the invention. List of reference symbols used

[0023] 1 lower polishing plate 2 lower polishing cloth 3 inner edge 4 outer edge 5inner ring of pins 6 outer ring of pins 7 upper polishing cloth 8 upper polishing plate 9 Linear rails 10 Sleds 11 actuator 12 roller 13 steering 14 ring 15 Afford 16 External gearing Detailed description of embodiments according to the invention

[0024] Fig. 1 Figure 1 shows features of a DSP polishing machine in a top view of the lower polishing pad 1, on which an annular lower polishing cloth 2 is glued. Parallel to the inner edge 3 and the outer edge 4 of the lower polishing cloth 2 and the lower polishing pad 1, an inner ring of pins 5 and an outer ring of pins 6 are arranged, by means of which the polishing pads 1, 8 can be rotated.

[0025] As in Fig. 2As shown, the lower polishing pad 1 is used to support the device for pressing the upper polishing cloth 7 against the upper polishing pad 8. The device comprises two parallel linear rails 9, which are arranged a short distance above the lower polishing pad 1, parallel to an intermediate radius of the lower polishing pad 1. Each of the linear rails 9 guides a carriage 10, with each carriage 10 carrying an actuator 11 and a roller 12 attached to the actuators, such that the roller is positioned between the linear rails 9. The actuators can raise and lower the roller 12, and the carriages 10 move it along a path between the outer pin ring 6 and the inner pin ring 5. The carriages 10 and the actuators 11 move synchronously, which is ensured by a controller 13.

[0026] According to the illustrated embodiment, the linear rails 9 rest on a ring 14 and strips 15 lying in the ring 14, the ring 14 having an external toothing 16 which engages in the outer pin ring 6 and in the inner pin ring 5 of the machine.

[0027] To carry out the method according to the invention, the upper polishing cloth 7 is brought into an intermediate state in which bubbles are present in the space between the upper polishing cloth 7 and the upper polishing plate 8 and the upper polishing cloth 7 does not yet adhere uniformly to the upper polishing plate 8.

[0028] The device for pressing the upper polishing cloth 7 against the upper polishing plate 8 is then positioned over the lower polishing cloth 2, and the upper polishing plate 8 is slid over the lower polishing plate 1. The two polishing plates 8, 1 are spaced apart to allow the roller 12 of the device to be pressed against the upper polishing cloth 7.

[0029] Fig. 2 It shows the situation before the upper polishing plate 8 was positioned over the lower polishing plate 1.

[0030] The upper polishing plate 8 is then slowly rotated and the roller 12 is moved back and forth between the outer pin ring 6 and the inner pin ring 5 by means of the slides 10, while the actuators 11 press the roller 12 at least temporarily against the upper polishing cloth 7.

[0031] It was demonstrated that the advantage of the method lies not only in avoiding strenuous manual labor, but also in its beneficial effect on the polishing result. The geometry, i.e., the flatness and planar parallelism of polished semiconductor wafers made of single-crystal silicon, was measured, including the local geometry at the edge, and combined into a single measurement that integrates the results of GBIR (global flatness back ideal range) and ESFQR (edge ​​site front least squares range). This measurement was on average almost 17.8% lower when the upper polishing cloth was pressed against the upper polishing pad according to the invention, rather than manually, before polishing.

Claims

1. Device for pressing an upper polishing cloth (7) against an upper polishing plate (8) of a machine for simultaneously polishing a front side and a rear side of a semiconductor wafer between the upper polishing plate (8) and a lower polishing plate (1), comprising two parallel linear rails (9) which, during use in the machine, are arranged at a small distance above the lower polishing plate (1) parallel to a radius, lying in between, of the lower polishing plate (1); a base body (14) to which the linear rails (9) are fastened, wherein the base body (14) has teeth which, during use of the device in the machine, engage into an outer (6) and into an inner (5) pin crown of the machine; two driven carriages (10) which are movable along the linear rails (9); actuators (11), carried by the carriages (10), for raising and lowering a roller (12) which is fastened to the actuators (11) and arranged between the linear rails (9); and a controller (13) for synchronously moving the carriages (10) to and fro between the inner (5) and the outer (6) pin crown of the machine and for synchronously moving the actuators (11).

2. Device according to Claim 1, characterized by a ring (14) as the base body (14) and bars (15), located in the ring (14), on which the linear rails (9) are supported, wherein the ring (14) has the teeth which engage into the outer (6) and into the inner (5) pin crown of the machine.

3. Device according to Claim 1 or Claim 2, characterized in that the actuators (11) work pneumatically or electrically.

4. Method for pressing an upper polishing cloth (7) against an upper polishing plate (8) of a machine for simultaneously polishing a front side and a rear side of a semiconductor wafer, comprising adhesively bonding the upper polishing cloth (7) to the upper polishing plate (8); and arranging the device according to one of Claims 1 to 3 above the lower polishing cloth (2); arranging the upper polishing plate (8) over the lower polishing plate (1) at a distance from one another which allows the roller (12) of the device to press against the upper polishing cloth (7); and pressing the roller (12) at least intermittently against the upper polishing cloth (7) while at the same time rotating the upper polishing plate (8) and moving the roller (12) to and fro between the inner (5) and the outer (6) pin crown of the machine.

5. Method according to Claim 4, characterized in that the roller (12) is moved to and fro between the outer (6) and the inner (5) pin crown of the polishing machine and at the same time is pressed against the upper polishing cloth (7).

6. Method according to Claim 4, characterized in that the roller (12) is moved to and fro between the outer (6) and the inner (5) pin crown of the polishing machine and is pressed against the upper polishing cloth (7) only on the outward or return travel.