JP6180223B2 - Wafer manufacturing method - Google Patents

Description

  The present invention relates to a wafer manufacturing method for manufacturing a wafer by separating a single crystal ingot.

  A semiconductor wafer made of a single crystal such as silicon, SiC (silicon carbide), or GaN (gallium nitride) is cut from a single crystal ingot using a wire saw or a band saw, and the front and back surfaces are polished. By the way, in the semiconductor wafer manufacturing field, there are cases where a semiconductor wafer having a crystal axis offset (hereinafter referred to as “offset wafer”) is required from the device manufacturing process.

  In such a case, the crystal axis of the ingot is detected using an X-ray diffraction method or the like, the separation plane direction tilted (offset) by a predetermined angle with respect to the crystal axis is set, and the wire is ingot with a wire saw or a band saw. The semiconductor wafer was cut out by slicing in parallel with the separation surface direction, and the front and back surfaces were polished to manufacture the semiconductor wafer.

Japanese Patent Laid-Open No. 10-256203

  However, when cutting with a wire saw or a band saw, there is a problem in that chips corresponding to at least the width of the wire or band are generated, and there is a lot of waste in the machining allowance. Moreover, since it is difficult to cut a wire saw or a band saw as thin as 1 mm or less, a wafer cut out to be thicker than necessary is thinned to a desired thickness by grinding later, resulting in waste as grinding waste. .

  The present invention has been made in view of the above points, and an object of the present invention is to provide a wafer manufacturing method capable of suppressing the amount of removal at the time of cutting out from an ingot.

According to the present invention, there is provided a method for producing a wafer for manufacturing a wafer by separating the single crystal ingot, setting the separation plane direction inclined at a predetermined angle with respect to the crystal axis by detecting a crystallographic axis of the single crystal ingot After performing the crystal axis detection step, the crystal axis detection step, the flattening step for flattening the upper surface of the single crystal ingot in parallel with the separation plane direction, and after performing the flattening step, the laser beam collection by irradiating a laser beam spot from the upper surface of the single crystal ingot is flattened positioned inside of the single crystal ingot, reforming surface of forming the modified surface along the separation plane direction within the single crystal ingot Japanese and forming step, after performing the reforming surface forming step, a peeling step of manufacturing a wafer by separating the upper surface of the single crystal ingot a reforming surface boundary, further comprising a Wafer manufacturing method according to is provided.

Preferably, in the wafer manufacturing method, after performing the crystal axis detecting step and before performing the flattening step, the lower surface which is the back surface of the upper surface of the single crystal ingot is ground to be parallel to the separation surface direction. A reference surface forming step for forming a simple reference surface, and the flattening step and the modified surface forming step are performed in a state where the reference surface side of the single crystal ingot is held by a holding means.

  Preferably, in the wafer manufacturing method, after the peeling step is performed, the modified surface side of the wafer separated and manufactured in the peeling step is ground or polished to remove the modified surface remaining on the wafer. And a removal step.

Further, according to the wafer manufacturing method of the present invention, after performing the peeling step, the planarizing step, the modified surface forming step, and the peeling step with the modified surface side of the single crystal ingot as the upper surface, Repeatedly.

  According to the method of manufacturing a wafer of the present invention, a wafer is manufactured from an ingot because a modified surface is formed by irradiating the ingot with a laser beam, and a part of the ingot is peeled off at the modified surface as a boundary. The amount of removal during the process can be greatly reduced compared to the conventional method. In addition, since a wafer having a desired thickness can be manufactured, it is possible to suppress the waste of thinning the wafer after it is cut out thickly.

  In the conventional wafer manufacturing method, warpage or undulation caused by a wire saw occurs in a wafer cut out from an ingot, and the warpage or nanotopography of the final product may be deteriorated by these warpage or undulation.

  In the present invention, since a wire saw is not used to cut out a wafer, warping of the final product and nanotopography (PV value (Peak-Valley difference) is, for example, a very shallow wave of 0.1 to 0.2 μm or less) Can be improved.

It is a perspective view of the single crystal ingot explaining a crystal axis detection step. It is a side view explaining a reference plane formation step. It is a side view explaining the planarization step. It is a side view explaining a modified surface formation step. It is a side view after implementation of a modified surface formation step. It is a side view explaining a peeling step. It is a side view explaining a removal step. It is a side view explaining repetition of a planarization step, a modified surface formation step, and a peeling step.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Referring to FIG. 1, a perspective view of a single crystal ingot 10 such as a silicon ingot is shown. The ingot 10 of this embodiment is an ingot in which the crystal axis 14 is offset with respect to the central axis 12, and has an upper surface 10 a and a lower surface 10 b that are perpendicular to the central axis 12.

  In the wafer manufacturing method of the present embodiment, the crystal axis 14 of the ingot 10 is detected using X-ray diffraction as disclosed in, for example, Japanese Patent Application Laid-Open No. 2009-58531. In FIG. 1, only the vertical crystal axis 14 tilted with respect to the central axis 12 is shown, but actually, the vertical crystal axis direction 14 and the horizontal crystal axis direction are detected.

  Then, a separation plane direction 16 is set based on the detected vertical crystal axis 14 and horizontal crystal axis. For example, a plane inclined by a predetermined angle θ with respect to the vertical crystal axis 14 is set as the separation plane direction 16.

  The predetermined angle θ includes 90 °. In this case, the separation plane direction 16 is perpendicular to the crystal axis 14. As an alternative embodiment, a plane inclined by a predetermined angle with respect to a horizontal crystal axis (not shown) may be set as the separation plane direction 16. In the following description, the separation plane direction 16 is described as being perpendicular to the crystal axis 14.

  After performing the crystal axis detection step, a reference surface forming step is performed in which the lower surface 10b, which is the back surface of the upper surface 10a of the ingot 10, is ground to form a reference surface parallel to the separation surface direction 16.

  In this reference surface forming step, first, as shown in FIG. 2A, the upper surface 10a of the ingot 10 is sucked and held by the holding means (chuck table) 18 of the grinding apparatus to expose the lower surface 10b. Next, as shown in FIG. 2B, the holding means 18 is tilted so that the crystal axis 14 of the ingot 10 is vertical, and the lower surface 10 b of the ingot 10 is ground by the grinding unit 20.

  2B, the grinding unit 20 includes a spindle 22 that is rotationally driven, a wheel mount 24 that is fixed to the tip of the spindle 22, and a grinding wheel 26 that is detachably attached to the wheel mount 24. . The grinding wheel 26 includes an annular base 28 and a plurality of grinding wheels 30 fixed to the outer periphery of the lower surface of the annular base 28.

  In the reference surface forming step, the holding means 18 is rotated in the direction of arrow a at 300 rpm, for example, and the grinding wheel 30 is brought into contact with the lower surface 10b of the ingot 10 while rotating the grinding wheel 26 in the direction of arrow b at 6000 rpm, for example. The lower surface 10b is ground at the grinding feed rate to form the reference surface 10c as shown in FIG. This reference plane 10 c is parallel to the separation plane direction 16.

  After performing the reference surface forming step, a flattening step for flattening the upper surface 10a of the ingot 10 in parallel with the separation surface direction 16 is performed. In this flattening step, as shown in FIG. 3, the reference surface 10 c of the ingot 10 is sucked and held by the holding means 18 to expose the upper surface 10 a of the ingot 10.

  Then, the holding means 18 is rotated in the direction of the arrow a at, for example, 300 rpm, and the grinding wheel 30 is brought into contact with the upper surface 10a of the ingot 10 while the grinding wheel 26 is rotated at, for example, 6000 rpm, and the upper surface 10a is ground at a predetermined grinding feed rate. To do. The upper surface 10a after grinding is parallel to the reference surface 10c, that is, parallel to the separation surface direction 16. The vertical cross section of the ingot 10 after the planarization step is a parallelogram as shown in FIG.

  In the above-described embodiment, the planarization step is performed by grinding. However, the planarization step may be performed by polishing, or may be performed by combining grinding and polishing. In this flattening step, it is preferable to finish the flattened surface to a roughness that allows easy transmission of the laser beam in the modified surface forming step described later.

  After performing the flattening step, as shown in FIG. 4, the condensing point P of the laser beam 35 irradiated from the laser beam irradiation head 34 is positioned inside the ingot 10, and the upper surface 10 a of the flattened ingot 10. A modified surface forming step for forming a modified surface along the separation surface direction 16 inside the ingot 10 is performed by irradiating a laser beam toward the surface.

  In this modified surface forming step, the laser beam irradiation means 34 is moved in the direction parallel to the holding surface of the holding means 32 while rotating the holding means (chuck table) 32 of the laser processing apparatus holding the ingot 10 in the arrow A direction. For example, the modified surface is formed by relative movement in the direction of arrow B.

  Since the modified surface needs to be formed on the entire cross section of the ingot 10, it is preferable to use a multi-spot as disclosed in, for example, Japanese Patent Application Laid-Open No. 2011-79044. Referring to FIG. 5, a side view of the ingot 10 held by the holding means 32 after the modified surface 36 is formed is shown.

  The laser beam 35 irradiated in the modified surface forming step preferably has a wavelength that is transmissive to the ingot 10 (for example, 1064 nm). A laser beam having a wavelength of 1064 nm is a fundamental wave of a YAG laser or a YVO4 laser.

  After performing the modified surface forming step, as shown in FIG. 6, the upper surface 10a side of the ingot 10 is sucked and held by the peeling means 38, and the upper surface side of the ingot 10 is separated from the modified surface 36 as a boundary. A stripping step to manufacture 40 is performed.

  The modified surface 36 is a region where the density, refractive index, mechanical strength, and other physical characteristics are different from the surroundings. For example, it includes a melt re-hardened region, a crack region, a dielectric breakdown region, a refractive index change region, etc., and also includes a region where these regions are mixed, and the strength is considerably weaker than the surroundings, so that the peeling means 38 can be easily peeled off.

  After performing the peeling step, a removing step is performed in which the modified surface 36 side of the wafer 40 separated and manufactured in the peeling step is ground or polished to remove the modified surface 36 remaining on the wafer 40. In this removing step, as shown in FIG. 7, for example, the upper surface 10 a side of the wafer 40 is sucked and held by the holding means (chuck table) 18 of the grinding apparatus to expose the modified surface 36.

  The holding means 18 is rotated in the direction of arrow a at, for example, 300 rpm, the grinding wheel 30 of the grinding wheel 26 is brought into contact with the modified surface 36 of the wafer 40, and the grinding wheel 26 is rotated in the direction of arrow B at, for example, 6000 rpm for grinding. The modified surface 36 is ground and removed from the wafer 40 by grinding and feeding the wheel 26 downward.

  Since the upper surface 10a side of the wafer, which is a surface flattened in parallel with the reference surface 10c in the ingot state, is ground by suction, the upper and lower surfaces of the wafer are parallel to the reference surface 10c of the ingot, that is, the separation surface direction 16. Formed.

  Instead of grinding, the modified surface 36 may be removed by polishing using a polishing pad. Alternatively, the removing step may be performed by any one of grinding, polishing, etching, or a combination thereof.

  After performing the peeling step, as shown in FIG. 8A, a planarization step is performed in which the modified surface 36 is ground and removed by using the modified surface 36 of the ingot 10 as an upper surface, and the upper surface of the ingot 10 is planarized. Then, as shown in FIG. 8B, a modified surface forming step of forming a modified surface inside the ingot 10 by irradiating the laser beam 35 from the upper surface 10a side of the ingot 10 is performed. As shown in FIG. 8C, a peeling step for manufacturing the wafer 40 by separating the upper surface of the ingot 10 with the modified surface 36 as a boundary is performed.

  A plurality of wafers 40 are manufactured from the ingot 10 by repeating the flattening step, the modified surface forming step, and the peeling step shown in FIGS. 8A to 8C one after another.

DESCRIPTION OF SYMBOLS 10 Single crystal ingot 10a Upper surface 10b Lower surface 10c Reference surface 12 Center axis 14 Crystal axis 16 Separation surface direction 26 Grinding wheel 34 Laser beam irradiation head 35 Laser beam 36 Modification surface 38 Stripping means 40 Wafer

Claims (4)

A wafer manufacturing method for manufacturing a wafer by separating a single crystal ingot,
A crystal axis detection step of detecting a crystal axis of a single crystal ingot and setting a separation plane direction inclined by a predetermined angle with respect to the crystal axis;
After performing the crystal axis detection step, flattening step of flattening the upper surface of the single crystal ingot parallel to the separation plane direction;
After performing the flattening step, the laser beam is irradiated from the upper surface of the flattened single crystal ingot with the focal point of the laser beam positioned inside the single crystal ingot, and the modification along the separation surface direction is performed. A modified surface forming step for forming a material surface inside the single crystal ingot;
After performing the modified surface forming step, a separation step of manufacturing a wafer by separating the upper surface side of the single crystal ingot with the modified surface as a boundary;
A method for producing a wafer, comprising: After performing the crystal axis detecting step and before performing the flattening step, a reference surface formation is performed by grinding a lower surface which is the back surface of the upper surface of the single crystal ingot to form a reference surface parallel to the separation surface direction. Further comprising a step,
The method for manufacturing a wafer according to claim 1, wherein the planarizing step and the modified surface forming step are performed in a state where the reference surface side of the single crystal ingot is held by a holding unit.   The method further comprises a removing step of removing the modified surface remaining on the wafer by grinding or polishing the modified surface side of the wafer separated and manufactured in the separating step after performing the stripping step. 3. A method for producing a wafer according to 1 or 2. The said planarization step, the said modified surface formation step, and the said peeling step are repeatedly implemented after implementing the said peeling step by making this modified surface side of a single crystal ingot into an upper surface. The manufacturing method of the wafer in any one.

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