JP2007005482A - Manufacturing method of semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To smooth a polished surface of a wafer which has concentric circlular unevenness, by the correction using a usual polishing device. <P>SOLUTION: As for a polishing pad 2, a rotation symmetry axis of a rotation symmetry pattern is set as a rotation axis 1a of a platen 1, it is shaped so that the pattern overlaps only a part of a wafer 3 when the center of the rotation symmetry axis 1a and the center of the wafer 3 may coincide so as to overlap each other, and polish is carried out in such a way that the rotation axis 1a of the platen 1 and the rotation axis 4a of the wafer 3 coincide. The shape of the polishing pad 2, for example, is made into an annular pattern of an inner diameter smaller than the wafer 3 so as to polish the outer edge of the wafer 3. As an annular pattern of an outer diameter smaller than the wafer 3, the wafer 3 is polished annularly. Otherwise, as a circular pattern of a reduced diameter smaller than the wafer, the central part of the wafer 3 is polished. The unevenness of a polished surface is corrected, since only a part is polished in the shape of a concentric circle. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a semiconductor device including a wafer polishing step, and more particularly to a method for manufacturing a semiconductor device using chemical mechanical polishing (CMP) to planarize a thin film formed on a wafer surface.

  Chemical mechanical polishing (CMP) is widely used not only for manufacturing a semiconductor wafer but also for manufacturing a semiconductor element structure by flattening a thin film during the manufacturing process of a semiconductor device. However, in the conventional CMP, precise planarization is difficult as described below.

  FIG. 3 is an explanatory view of a conventional polishing method, and shows a polishing state of a wafer using CMP. 3A and 3B are a plan view and an AB cross-sectional view, respectively. In the conventional polishing, referring to FIG. 3, a polishing pad 2 is attached to the upper surface of a platen 1 that rotates in a horizontal plane around a vertical rotation axis 1 a, and the lower surface of the wafer 3 is pressed onto the polishing pad 2. Grind. The wafer 3 is held on the lower surface of the head 4 pivotally mounted around the rotating shaft 4a, and is pressed onto the polishing pad 2 and polished by the head 4.

  The head 4 is held at a position away from the rotation axis 1 a of the platen 1 or swings on the platen 1. As a result, the average relative speed between the lower surface of the wafer 3 and the polishing pad 2 becomes uniform over the entire surface of the wafer 3, and the wafer 2 is polished flatly. Further, the wafer 3 is concentrically held with the head 4 and rotates together with the head 4, so that it is avoided that the wafer 3 is polished obliquely along the diameter of the wafer 3. However, in order to achieve high flatness, the position and swing of the head 4, the rotation of the wafer, and the slurry and polishing pad must be precisely controlled according to the polishing conditions. It is very difficult to obtain a sufficient flatness by controlling this. (See Patent Document 3 regarding the difficulty of control for flattening.)

  FIG. 4 is a cross-sectional view of a wafer manufactured by a conventional polishing method, and shows the cross-sectional shape of the polished surface of the wafer polished by the polishing method shown in FIG. As described above, since the wafer 3 rotates, it is polished concentrically, and the polished surface 3a tends to be a rotationally symmetric surface. For example, as shown in FIG. 4A, the lower surface of the wafer 3 (polishing surface 3a) becomes a convex surface. Conversely, as shown in FIG. 4B, the lower surface of the wafer 3 is concave. Furthermore, a concave surface may be formed at the central portion of the lower surface of the wafer 3 and a convex surface may be formed at the outer peripheral portion, resulting in an annular convex portion.

  Such irregularities on the polished surface increase the variation in the structure of the semiconductor element and cause a decrease in the manufacturing yield of the semiconductor device. Therefore, a polishing method has been devised that measures the flatness (distribution of unevenness on the surface) of the polished surface of the polished wafer and improves the flatness of the entire polished surface by partially polishing only the recesses.

  For example, Japanese Patent Application Laid-Open No. 11-265860 discloses a method of partially polishing only convex portions. In this method, a wafer is mounted on an XY table, and the convexity is detected by measuring the flatness of the upper surface of the wafer. Thereafter, a small polishing pad that rotates is pressed against the convex portion to selectively polish only the convex portion. Thereby, a convex part is grind | polished and the flatness of a grinding | polishing surface improves. (See Patent Document 1).

Japanese Laid-Open Patent Publication No. 9-260316 discloses a polishing method that improves the flatness by increasing the polishing rate of the recesses by providing an in-plane distribution in the wafer pressing (rear pressure). In this method, a minute pressure applying element (for example, an actuator that generates pressure using a piezo element) is disposed on the entire rear surface of the wafer, and the wafer is pressed with an arbitrary pressure distribution. Then, the entire polishing surface can be accurately flattened by increasing the pressure of the recesses and polishing.
Japanese Patent Laid-Open No. 11-205860 JP-A-9-260316 Japanese Patent Laid-Open No. 11-58219

  As described above, it is very difficult to obtain a precise flat surface by controlling the polishing conditions in the conventional polishing method because the polishing conditions change with time.

  In the conventional method devised to solve this problem, the flatness of the polished wafer surface is measured, and then a small polishing pad is pressed against the convex part to partially polish only the convex part. To improve the flatness by modifying the polished surface. However, this method requires a mechanism for moving a small polishing pad to an arbitrary position within the polishing surface of the wafer, and there is a problem that the apparatus becomes complicated.

  In addition, the conventional method of obtaining a precise flat surface by polishing with the wafer back pressure raised at the convex part and lowered at the concave part requires a mechanism for arbitrarily generating the wafer back pressure distribution, and is an extremely precise device. There is a problem that requires.

  The present invention corrects irregularities of a polished surface using a normal polishing apparatus that presses and polishes a wafer held rotatably on a polishing pad fixed to a rotating platen, and makes the polished surface of the wafer flat easily. It is an object of the present invention to provide a method for manufacturing a semiconductor device using a wafer polishing method that can be used.

  In order to solve the above problems, according to the present invention, when the planar pattern shape of the polishing pad is overlapped with the rotation axis of the platen as the rotational symmetry axis and the rotational symmetry axis and the center of the wafer coincided, the pattern is one of the wafers. A pattern is formed so as to overlap only the portion, and further, polishing is performed with the rotation axis of the platen and the rotation axis of the wafer aligned.

  The planar shape of the polishing pad according to the present invention is a rotationally symmetric pattern having the rotational axis of the platen as the rotational symmetry axis. Then, when the wafer and the polishing pad are overlapped with each other so that the center of the wafer coincides with the rotational symmetry axis of the polishing pad, the planar shape of the polishing pad is such that the polishing pad overlaps only a part of the wafer. That is, when the wafer and the polishing pad are overlapped, the polishing pad does not exist on the entire surface of the wafer, and a region where the polishing pad is missing occurs in a part of the wafer surface, in other words, there is a portion where the wafer and the polishing pad do not overlap. The planar shape is formed in the wafer plane. Note that the polishing pad may extend outside the wafer.

  Examples of the planar shape of such a polishing pad include a pattern having a hole having a diameter smaller than the diameter of the wafer at the center, a pattern having a diameter smaller than the diameter of the wafer, and an annular pattern having an outer diameter smaller than the diameter of the wafer. . The pattern is not limited to a continuous pattern, and may be a pattern in which a large number of small polishing pads are arranged along a circle having a diameter smaller than the diameter of the wafer.

  In the present invention, the rotational symmetry axis of the polishing pad having such a shape (corresponding to the rotational symmetry axis of the platen) and the center of the wafer (passing through the rotation axis of the wafer pass) are made to coincide with each other. Rotate around the same rotation axis for polishing.

  In such a configuration, the length of the polishing pad contacting the wafer and the relative speed between the polishing pad and the wafer are determined by the distance from the center of the wafer. As a result, the distribution of the polishing rate becomes a concentric distribution from the center of the wafer. This concentric polishing speed distribution can be easily controlled by controlling the planar shape of the polishing pad or the rotation speed and rotation direction of the wafer. Therefore, the concentric irregularities on the wafer surface can be selectively polished by forming the planar shape of the polishing pad so that the polishing rate is increased at the concentric convex parts. As a result, the wafer surface having concentric concavities and convexities can be corrected to a precise flat surface.

  According to the present invention, a concentric polishing rate distribution can be obtained, and the distribution can be easily adjusted by changing the planar shape of the polishing pad, so that the surface of the wafer having concentric unevenness is corrected. It is easy to make a precise flat surface.

  FIG. 1 is an explanatory diagram of an embodiment of the present invention, and shows a polishing state of a wafer using CMP. 1A and 1B are a plan view and a CD sectional view, respectively. FIG. 2 is a plan view of a polishing pad according to an embodiment of the present invention, and shows a planar shape of a polishing pad fixed on a platen in comparison with a wafer.

  Referring to FIG. 1, the polishing apparatus used in the present embodiment holds a platen 1 rotating in a horizontal plane around a vertical rotation axis 1a and a wafer 3 on the lower surface, and is rotatable around a vertical rotation axis 4a. And a pivoted head 4. A polishing pad 2 is adhered and fixed to the upper surface of the platen 1. The polishing is chemical mechanical polishing (CMP) performed while supplying the slurry onto the polishing pad 2. This is the same as the polishing apparatus used in the conventional polishing method described above.

  In this embodiment, the rotating shaft 1a of the platen 1 and the rotating shaft 4a of the head 4 are aligned and polished. The platen 1 is rotationally driven in one direction by a rotational driving device (not shown). On the other hand, the head 4 presses the wafer 3 against the polishing pad 2, and is rotated or decelerated by another rotational drive device or rotational speed reducer (not shown) to rotate at a rotational speed different from that of the platen 1. In this rotation, the rotation and rotation speed in the same direction as or opposite to those of the platen 1 and the rotation speed are appropriately selected depending on the state of correction of the polished surface shape by polishing. The wafer 3 is held concentrically with the head 4, and the wafer 3 is fixed to the head 4 and rotates around the rotation shaft 4 a as the head 4 rotates.

  The wafer 3 used for polishing in this embodiment is a wafer 3 polished by the above-described conventional polishing method using CMP in which the rotating shaft 4a (spinning shaft) of the rotating head 4 is swung on the platen 1. is there. As shown in FIG. 4B, the first wafer 3 used in this embodiment has a polished surface 3a formed as a concave surface.

  A polishing pad 2 for correcting and polishing the first wafer 3 has an annular shape having an outer periphery 2a having a diameter larger than that of the wafer 3 and an inner periphery 2b having a smaller diameter, as shown in FIGS. 2 (a) and 1 (a). 1 is fixed on the platen 1 so as to be concentric with the rotating shaft 1a of the platen 1. As shown in FIG. A central portion from the inner periphery 2b is a hollow portion 2c where the polishing pad 2 does not exist.

  When polishing is performed using the planar polishing pad 2, the peripheral portion of the wafer 3 outside the inner periphery of the polishing pad 2 is polished, while the central portion (the portion corresponding to the hollow portion 2 c) from the inner periphery of the polishing pad 2. Is not polished, the concave surface of the polishing surface 3a is corrected to a flat surface.

  In this embodiment, a flexible pad 6, for example, a soft pad that has been buffed, can be attached to the upper surface of the platen 1 exposed in the hollow portion 2 c that occupies the central portion of the polishing pad 2. Thereby, it can avoid that the wafer 3 contacts the platen 1 and is damaged. The flexible pad 6 may be any pad that can prevent the wafer 3 from being damaged, and need not substantially contribute to polishing.

  In the present embodiment for correcting the concave wafer 3 described above, the inner periphery of the polishing pad 2 can be meandered as shown in FIG. Thereby, the level | step difference resulting from the sharp difference of the grinding | polishing speed of a center part and an outer side along the inner periphery of the annular | circular shaped polishing pad 2 can be eased, and it can be set as the smooth polishing surface 3a without a level | step difference.

  As shown in FIG. 4A, the second wafer 3 subjected to the polishing of the present embodiment has a polished surface 3a formed as a convex surface.

  A polishing pad 2 for correcting and polishing the second wafer 3 has a circular (disc-like) planar shape (see FIG. 2B) having an outer periphery 2a having a smaller diameter than the wafer 3 with reference to FIG. ) And is fixed on the platen 1 so as to be concentric with the rotating shaft 1 a of the platen 1. There is no polishing pad 2 outside the outer periphery 2a.

  In the polishing using the polishing pad 2, the inner side of the outer periphery 2a of the polishing pad 2 is polished and the outer side is not polished. Therefore, the polished surface 3a, which was a convex surface, is corrected to a flat surface.

  In addition, damage to the wafer 3 can be avoided by attaching a flexible pad to the outside of the outer periphery 2 a of the polishing pad 2. Further, as shown in FIG. 2 (e), by causing the outer periphery to meander, a step generated along the outer periphery 2a can be avoided and the polishing surface 3a can be made smooth.

  As shown in FIG. 4C, the third wafer 3 subjected to the polishing of this embodiment was polished concavely at the central portion of the polishing surface 3a and convexly at the peripheral portion. That is, an annular portion concentric with the wafer 3 is convex.

  A polishing pad 2 for correcting and polishing the third wafer 3 has an annular planar shape (see FIG. 2) having an outer periphery 2a having a smaller diameter than the wafer 3 and an inner periphery 2b having a smaller diameter. (C) a shape indicated by hatching), and is fixed on the platen 1 so as to be concentric with the rotating shaft 1a of the platen 1.

  In the polishing using the polishing pad 2, the portion of the annular polishing pad 2, that is, the portion between the inner periphery 2b and the outer periphery 2a is polished in an annular shape. Therefore, by matching the inner periphery 2b and the outer periphery 2a with the annular convex portion of the wafer 3, the annular convex portion is selectively polished. For this reason, the polished surface 3a of the wafer 3 is corrected and flattened.

  In addition, damage to the wafer 3 can be avoided by attaching a flexible pad to the outside of the outer periphery 2 a of the polishing pad 2. Further, as shown in FIG. 1 (e), by causing the outer periphery to meander, a step generated along the outer periphery 2a can be avoided and the polishing surface 3a can be made smooth.

The present invention described above discloses the invention described in the following supplementary notes.
(Appendix 1) Manufacture of a semiconductor device including a wafer polishing step for polishing by pressing a wafer held rotatably around a rotation axis passing through the center of the wafer on the upper surface of a polishing pad fixed to the upper surface of the rotating platen In the method
The polishing pad is a pattern having a rotational axis of the platen as a rotational symmetry axis, and the pattern overlaps only a part of the wafer when the rotational symmetry axis and the center of the wafer are overlapped with each other. A step of forming the pattern,
A method of manufacturing a semiconductor device, comprising: a step of polishing the wafer by aligning the rotation axis of the platen with the rotation axis of the wafer.
(Supplementary note 2) The method of manufacturing a semiconductor device according to supplementary note 1, wherein the pattern is an annular pattern having an outer diameter larger than the wafer and an inner diameter smaller than the wafer.
(Supplementary note 3) The method for manufacturing a semiconductor device according to supplementary note 1, wherein the pattern is an annular pattern having an outer diameter smaller than that of the wafer.
(Additional remark 4) The manufacturing method of the semiconductor device of Additional remark 2 or 3 characterized by providing the flexible pad which protects the surface of a wafer inside the internal diameter of this pattern.
(Supplementary note 5) The method for manufacturing a semiconductor device according to supplementary note 1, wherein the pattern is a circular pattern having an outer diameter smaller than that of the wafer.
(Additional remark 6) The manufacturing method of the semiconductor device of Additional remarks 1, 2, 3, 4, and 5 characterized by the outline bent in this pattern.

  By applying the present invention to the CMP process of a semiconductor device, a very flat insulating film or wiring layer can be formed, so that a precise semiconductor device can be easily manufactured.

Explanatory drawing of embodiment of this invention Embodiment polishing pad top view of the present invention Explanatory drawing of conventional polishing method Wafer cross section manufactured by conventional polishing method

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Platen 1a, 2a Rotating shaft 2 Polishing pad 2a Outer periphery 2b Inner periphery 2c Hollow part 3 Wafer 3a Polishing surface 4 Head 4a Rotating shaft 6 Flexible pad

Claims (5)

In a method for manufacturing a semiconductor device, including a wafer polishing step for pressing and polishing a wafer held rotatably around a rotation axis passing through the center of a wafer on an upper surface of a polishing pad fixed to an upper surface of a rotating platen.
The polishing pad is a pattern having a rotational axis of the platen as a rotational symmetry axis, and the pattern overlaps only a part of the wafer when the rotational symmetry axis and the center of the wafer are overlapped with each other. A step of forming the pattern,
A method of manufacturing a semiconductor device, comprising: a step of polishing the wafer by aligning the rotation axis of the platen with the rotation axis of the wafer.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the pattern is an annular pattern having an outer diameter larger than the wafer and an inner diameter smaller than the wafer.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the pattern is an annular pattern having an outer diameter smaller than that of the wafer.   2. The method of manufacturing a semiconductor device according to claim 1, wherein the pattern is a circular pattern having an outer diameter smaller than that of the wafer.   5. The method of manufacturing a semiconductor device according to claim 1, wherein the pattern has a bent contour.

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