JP4331622B2 - Polishing method for flat workpiece - Google Patents

Description

  In the present invention, the main surface of the flat plate-like workpiece is pressed against a polishing cloth clothed on a surface plate while pressing the main surface of the flat plate-like workpiece such as a semiconductor wafer fixed on the work carrier. The present invention relates to an improvement of a polishing method for a flat workpiece to be polished.

  Semiconductor wafers (hereinafter referred to as “wafers”) require strict flatness of the wafer surface (ie, the mounting surface), which is a polished surface, due to the high integration of semiconductor devices to be mounted. Therefore, due to the sinking (sinking) of the wafer into the polishing cloth, which occurs in the polishing process, the polishing amount of the peripheral portion on the wafer surface is larger than the polishing amount of the central portion, and the cross-sectional shape of the wafer peripheral portion It is necessary to prevent so-called surface dripping (also referred to as “roll-off”, hereinafter the same).

  2. Description of the Related Art Conventionally, there has been proposed a wafer polishing method for improving the flatness of a wafer so as to reduce the sagging of the wafer. In this method, when the wafer is polished by rotating and sliding the hard plate to which the wafer is bonded on the polishing cloth surface affixed on the surface plate, the thickness of the wafer is made thinner than the finished thickness of the wafer at the periphery of the wafer. Polishing is performed on the wafer with the ring attached (see, for example, Patent Document 1).

  In addition to the above, for the purpose of enabling the maximum effect of the retainer ring and preventing sagging of the periphery of the wafer, the slurry is dropped on a surface plate provided with a polishing cloth, There has also been proposed an improved technique related to a wafer polishing method for polishing a wafer surface by pressing and rotating a plate holding a wafer. In this method, a retainer ring is mounted on a plate so that a clearance is formed around the periphery of the wafer, and the wafer is polished while automatically adjusting the clearance (see, for example, Patent Document 2).

JP-A-5-326468 JP 2001-252863 A

  In the wafer polishing methods according to each of the above proposals, the wafer surface, which is the finished surface (processed surface) of the wafer, is aimed to be as flat as possible by suppressing surface drift on the wafer surface as much as possible.

  However, when one-side processing is actually performed on the wafer (that is, polishing processing is performed on the wafer surface), the truly ideal cross-sectional shape of the wafer is simply that the wafer surface is flat (in other words, The wafer surface needs to be parallel to the wafer back surface (that is, the opposite surface of the wafer surface that is the polishing surface), not to be flat on the wafer surface. That is, it is important that the thickness of the wafer after the polishing process is constant. This is because a single wafer after a series of processing is used, for example, because it has a width of 30 to 40 cm while its surface is about 1 μm, it is cut into several parts. This is because if the thickness of the entire wafer is not constant, a wafer that is not suitable for mounting a highly integrated semiconductor device may be manufactured.

  In general, the back surface of the wafer (that is, the surface opposite to the wafer surface, which is the polishing surface) is also subjected to a separate polishing process, but there is usually a slight surface slack on the back surface of the wafer. Therefore, in the polishing process of the wafer surface, the wafer surface should be polished so that the wafer surface has a slight sag in accordance with the surface of the wafer back surface and is parallel to the wafer back surface. Is required.

  Accordingly, it is an object of the present invention to provide a flat work piece in which the surface sag generated in the polishing process of the flat work piece is reduced and the front surface and the back surface have a parallel shape.

In the polishing method for a flat workpiece according to the present invention, the main surface of the flat workpiece (7) fixed on the work carrier (5) is attached to the polishing cloth (3) that is clothed on the surface plate (1). in pressed against those for polishing the main surface of the plate-like workpiece (7), slightly thicker than the specification increased thickness of the flat workpiece (7), and said plate-shaped workpiece (7) The work carrier (5) provided with a processing auxiliary material (8, 9, 10, 12) having a thickness smaller than the pre-working thickness so as to substantially surround the fixing place of the flat workpiece (7). ), The step of fixing the flat plate-like workpiece (7), and the flat plate-like workpiece (7) fixed to the work carrier (5) are pressed against the polishing cloth (3). The thickness of the workpiece (7) is the finished thickness And the step of performing the above processing includes the step of performing the processing until the processing auxiliary material (8, 9, 10, 12) contacts the polishing cloth (3). The first step to be processed and the flat workpiece (7) are finished, and additional polishing is performed so that the peripheral edge of the flat workpiece is slightly warped from the center. And a second step.

In a preferred embodiment according to the present invention, the first step detects the processing load, and the processing auxiliary material (8, 9, 10, 12) is detected by detecting the variation of the processing load. Detecting the contact with the polishing cloth (3), and the second step is that the processing aid (8, 9, 10, 12) is in contact with the polishing cloth (3). And detecting an additional polishing for the flat workpiece for a preset time .

  As described above, according to the present invention, it is possible to provide a flat-plate workpiece in which the surface sag generated in the polishing process of the flat-plate workpiece is reduced and the front surface and the back surface have a parallel shape. can do.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram of a polishing apparatus applied to batch polishing of wafers according to an embodiment of the present invention.

  This polishing apparatus is used for batch polishing, that is, when polishing a plurality of wafers at a time. The polishing apparatus includes a lower surface plate 1 and a lower surface plate as shown in FIG. 1, a polishing cloth (cross pad) 3 spread on the upper surface of 1, a polishing plate (carrier) 5 provided above the lower surface plate 1 with the bottom surface facing the upper surface of the lower surface plate 1, and the bottom surface of the carrier 5, respectively. A plurality of wafers 7 to be attached and a template ring 9 are provided.

  The lower surface plate 1 is a base for determining the final polished shape of each wafer 7 when polishing each wafer 5, and the rotational force from a driving source (not shown) such as a motor is applied to the lower surface plate 1. It is rotatably supported by a rotational force transmission / support mechanism (not shown) for transmission.

  The carrier 5 is a hard plate made of a hard material such as hard glass or ceramic, and is configured to be movably held in the vertical direction of FIG. 1 by a carrier holding mechanism (not shown), for example. ing.

  The plurality of wafers 7 are fixedly attached to the bottom surface of the carrier 5 by wax, for example.

  The template ring 9 has a plurality of circular holes having a diameter slightly larger than the diameter of each wafer 7, and is fixed to the bottom surface of the carrier 5 by, for example, wax, or formed on the bottom surface of the carrier 5. The bottom surface of the carrier 5 is slidably attached using the surface tension of the water film. The template ring 9 is made of glass epoxy resin whose thickness is thicker than the finished thickness of each wafer 7. The template ring 9 is made of a material that is harder to be polished than at least the wafer 7 such as FRP (fiber reinforced plastic), polycarbonate, or ceramic, in addition to the glass epoxy resin described above. It is also possible.

  FIG. 2 is an explanatory diagram showing an example of a process in which the template ring 9 used for batch polishing of wafers according to an embodiment of the present invention is attached to the bottom surface of the carrier 5.

  In FIG. 2, a plurality of (four in FIG. 2) wafers 7 are fixedly attached to the bottom surface of the carrier 5 with, for example, wax, as shown in FIG. 2A. Next, as shown in FIG. 2B, the template ring 9 is provided with a clearance between the peripheral edge of a plurality of (four in FIG. 2) circular hole portions and the peripheral edge of each wafer 7, For example, it is affixed to the bottom surface of the carrier 5 using the surface tension of a water film formed on the bottom surface of the carrier 5. As described above, the template ring 9 has a plurality of (four in FIG. 2) circular hole portions 9a each having a diameter slightly larger than the diameter of each wafer 7, and the thickness of each template 7 is the finish of each wafer 7. Thicker than the thickness is adopted.

  Each wafer 7 is subjected to batch polishing by the following process using the polishing apparatus shown in FIG.

  That is, by sticking each wafer 7 together with the template ring 9 to the bottom surface of the carrier 5 in the above-described manner, the carrier 5 is moved downward through the carrier holding mechanism (not shown) as shown in FIG. Each wafer 7 and the template ring 9 are brought into a state of being pressed against the polishing pad 3 (that is, each wafer 7 and the template ring 9 are pressed against the polishing pad 3). In this state, while polishing liquid is applied to the polishing surface of each wafer 7 and the polishing cloth 3, the lower surface plate 1 is rotationally driven through the rotational force transmission / support mechanism (not shown) to polish the polishing surface of each wafer 7. By sliding on the cloth 3, polishing processing is performed on the polishing surface of each wafer 7.

  FIG. 4 is a flowchart showing an example of a processing procedure in batch polishing of the wafer 7 according to an embodiment of the present invention. In the batch polishing process performed by the processing procedure shown in FIG. 4, as described above, the template ring 9 has a thickness that is substantially the same as the final finish thickness of each wafer 7 or the final finish thickness of each wafer 7. A slightly thicker template ring is used.

  In FIG. 4, a series of batch polishing processes for each wafer 7 is started from the state in which each wafer 7 and template ring 9 are attached to the bottom surface of the carrier 5 in the above-described manner.

  That is, by moving the carrier 5 downward through the carrier holding mechanism (not shown), each wafer 7 is pressed against the polishing pad 3, and from this state, the rotational force transmitting / supporting mechanism (not shown). The wafer 7 is polished by rotating the lower surface plate 1 through (not) (step S21).

  Next, it is appropriately checked whether or not the polishing load has increased. In this check, for example, a controller (not shown) that controls driving of each part of the polishing apparatus shown in FIG. 1 rotates the lower surface plate 1 through the rotational force transmission / support mechanism (not shown) (not shown). Input) a current detection signal from a current detection means (not shown) provided to detect the drive current (hereinafter referred to as “motor current”) to check whether the motor current has increased. Is done by. If the polishing load is not increased, that is, if the motor current is not increased, it indicates that the polishing is not performed until the thickness of each wafer 7 reaches the thickness of the template ring 9.

  On the contrary, if the polishing load is increased, that is, if the motor current is increased, it indicates that polishing is performed until the thickness of each wafer 7 substantially matches the thickness of the template ring 9. Yes. If the thickness of each wafer 7 is substantially equal to the thickness of the template ring 9, in addition to the pressure contact state between the polishing surface of each wafer 7 and the polishing cloth 3, also between the template ring 9 and the polishing cloth 3. Since the pressure contact state occurs, the motor current increases compared to before the template ring 9 and the polishing pad 3 are in pressure contact (step S22).

  When the controller (not shown) determines that the motor current has not increased based on the current detection signal from the current detection means (not shown) (No in step S22), the process returns to step S21. The polishing process of each wafer 7 is continued as it is.

  On the other hand, if the controller (not shown) determines that the motor current is increasing based on the current detection signal (YES in step S22), for each wafer 7 for a preset time, Further polishing (follow-up polishing) is performed (up to the finished thickness of each wafer 7). Here, the preset time is the amount of additional polishing (that is, the difference between the thickness of the template ring 9 and the final finished thickness of each wafer 7, for example, 2 μm), and the polishing rate (that is, per unit time). It can be obtained by dividing by (polishing amount) (step S23).

  The additional polishing shown in step S23 is performed on each wafer 7 (the polished surface thereof), so that the cross-sectional shape of each wafer 7 corresponds to the surface of the opposite surface of each polished surface, and the peripheral edge is from the center. Can be formed in a slightly warped state.

  FIG. 5 is an explanatory diagram showing changes in the positional relationship among the wafer 7, the template ring 9, and the polishing pad 3 during batch polishing of the wafer 7 according to an embodiment of the present invention.

  In FIG. 5, when batch polishing is started for each wafer 7, as shown in FIG. 5A, each wafer 7 in a state of being stuck to the bottom surface of the carrier 5, and the template ring 9. Then, the thickness of each wafer 7 is thicker than the thickness of the template ring 9, so that each wafer 7 protrudes downward from the template ring 9. At this time, not only the template ring 9 but also the polishing surface of each wafer 7 is not in contact with the polishing cloth 3 laid on the upper surface of the lower surface plate 1, and each wafer 7 and template 9 are It is located above the polishing cloth 3. This state corresponds to the process of step S21 in the flowchart described in FIG.

  Next, the lower surface plate 1 is rotated in a state where the carrier 5 moves downward and the respective wafers 7 (the polishing surface thereof) are pressed against the polishing cloth 3, and the polishing liquid is applied to the polishing surface of each wafer 7 and the polishing cloth 3. , The polishing surface of each wafer 7 is polished. That is, the polishing surface of each wafer 7 is gradually polished, and eventually the thickness of each wafer 7 becomes substantially equal to the thickness of the template ring 9 as shown in FIG. As a result, not only each wafer 7 but also the template ring 9 sinks (submerges) into the polishing cloth 3, so that the polishing load, that is, the motor current for rotationally driving the lower surface plate 1 as described above. Will increase. This state corresponds to the process of step S22 in the flowchart described in FIG.

  Next, for each wafer 7 whose polishing surface has been polished to a thickness substantially equal to the thickness of the template ring 9, the thickness of each wafer 7 has a predetermined finish thickness (that is, the above-described final finish thickness). Until then, the lower surface plate 1 is driven to rotate so-called polishing. This corresponds to the process of step S23 in the flowchart described in FIG. Thereby, as shown in FIGS. 5C and 5D, the cross-sectional shape of each wafer 7 is slightly warped from the center, corresponding to the surface of the opposite surface of each polishing surface. It will be formed in the up state.

  FIG. 6 is an explanatory view showing a modified example of the template ring (9) or the carrier (5) used for batch polishing of the wafer 7 according to an embodiment of the present invention, and another ring different from the template ring. It is.

  As the template ring, instead of the template ring 9 having the shape as described above (shown in FIG. 2), for example, one piece having an inner diameter slightly larger than the outer diameter of the wafer 7 as shown in FIG. It is also possible to use as many rings 8 as the number of wafers 7 for each wafer 7. Alternatively, in place of the template ring 9 described above, as shown in FIG. 6B, an outer ring 10a having an outer diameter that is substantially the same as the outer diameter of the carrier 5, and an inner peripheral side of the outer ring 10a. It is also possible to use a template ring 10 having a plurality of inner rings 10b which are arranged at a predetermined interval and formed integrally with the outer ring 10a and whose inner diameter is slightly larger than the outer diameter of each wafer 7.

  Furthermore, without using the ring 8 or the template ring 10 at all, instead of the carrier 5 having a substantially flat bottom surface as described above, the inner diameter is arranged at a predetermined interval and the outer diameter of each wafer 7 is set. By using a carrier 12 having a plurality of circular recesses 12a that are slightly larger than those, polishing is performed on each wafer 7 in the same manner as in the case of using the ring 8, the template ring 10, or the like. be able to.

  The preferred embodiment of the present invention has been described above, but this is an example for explaining the present invention, and the scope of the present invention is not limited to this embodiment. The present invention can be implemented in various other forms. In the embodiment described above, wafer batch polishing has been described as an example. However, the present invention is not limited to batch polishing, but can be applied to so-called single wafer polishing in which wafers are polished one by one.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing of the grinding | polishing apparatus applied to the batch grinding | polishing of the wafer which concerns on one Embodiment of this invention. Explanatory drawing which shows one Example of the process in which the template ring used for the batch grinding | polishing process of the wafer which concerns on one Embodiment of this invention is affixed on the bottom face of a carrier. Explanatory drawing which shows operation | movement of the grinding | polishing apparatus at the time of performing a batch grinding | polishing process to a wafer using the wafer grinding | polishing apparatus of FIG. The flowchart which shows an example of the process sequence in the batch grinding | polishing process of the wafer which concerns on one Embodiment of this invention. Explanatory drawing which shows the transition of the positional relationship between a wafer, the template ring, and polishing cloth at the time of the batch grinding | polishing process of the wafer which concerns on one Embodiment of this invention. Explanatory drawing which shows the template ring used for the batch grinding | polishing process of the wafer which concerns on one Embodiment of this invention, or the modified example of a carrier, and another ring different from a template ring.

Explanation of symbols

1 Lower surface plate 3 Polishing cloth 5, 12 Polishing plate (carrier)
7 Wafer 8 Ring (different from template ring) 9, 10 Template ring

Claims (2)

In the state where the main surface of the flat workpiece (7) fixed on the work carrier (5) is pressed against the polishing cloth (3) spread on the surface plate (1), the flat workpiece (7 In the polishing method of a flat workpiece for polishing the main surface of
Said tabular workpieces (7) Specification raised slightly thicker than the thickness of, and, processing aids material having a pre-working thinner than the thickness of said tabular workpieces (7) (8, 9, 10, 12) Fixing the flat workpiece (7) to the work carrier (5) provided so as to substantially surround a fixing place of the flat workpiece (7);
The flat plate workpiece (7) fixed to the work carrier (5) is pressed against the polishing cloth (3), and processing is performed until the thickness of the flat plate workpiece (7) reaches a finished thickness. Steps,
With
The step of performing the processing comprises:
A first step of processing the flat workpiece (7) until the processing aid (8, 9, 10, 12) contacts the polishing cloth (3);
A second step of performing additional polishing so that the flat workpiece (7) has a finished thickness and the peripheral edge of the flat workpiece is slightly warped from the center ;
A method for polishing a flat workpiece having a surface. In the polishing method of the flat workpiece according to claim 1,
The first step comprises:
Detecting a machining load;
Detecting that the processing auxiliary material (8, 9, 10, 12) is in contact with the polishing pad (3) by detecting a variation in processing load ,
The second step comprises:
A step of performing additional polishing on the flat workpiece for a preset time when it is detected that the processing aid (8, 9, 10, 12) has contacted the polishing cloth (3). the polishing method of a flat workpiece with.

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