JP3553196B2 - Method for manufacturing SOI substrate - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for manufacturing an SOI substrate obtained by bonding a semiconductor wafer serving as an active substrate and a semiconductor wafer serving as a support substrate.
[0002]
[Prior art]
In recent years, as the development technology of integrated circuits has improved, the demand for quality improvement in SOI substrate manufacturing from device processes has been stricter. In particular, in order to increase the operating speed of the integrated circuit, it is necessary to make the active layer as thin as possible.
Conventionally, an SOI substrate obtained by bonding a semiconductor wafer serving as an active substrate and a semiconductor wafer serving as a support substrate has been manufactured by the following steps.
(1) An oxide film is generated on the surface of a semiconductor wafer serving as a support substrate, and a semiconductor wafer serving as an active substrate is bonded on the upper surface thereof. Further, an oxide film is also generated on the surface of the active substrate to obtain a bonded wafer. .
(2) Next, the unbonded portion at the periphery of the bonded wafer is removed by grinding or etching.
(3) The surface of the active substrate is ground to reduce its thickness.
(4) The back surface of the support substrate is attached to the attachment block, and the surface of the active substrate is polished to further reduce the thickness of the active substrate.
However, the active substrate thinned by this polishing has a thickness of about 2 to 3 μm. In an SOI substrate used for manufacturing a high-speed integrated circuit, the thickness of the active substrate is reduced to about 0.1 μm. Is required. PACE processing is used for this thinning. That is, the surface of the active substrate polished by the method described above is uniformly thinned by the PACE processing.
[0003]
[Problems to be solved by the invention]
However, in the method of performing PACE processing after attaching and polishing the active substrate in this way, since the back surface of the support substrate is attached to the attachment block for polishing, there is no foreign matter or foreign matter between the attachment surface of the attachment block and the back surface of the support substrate. If there is a dent, minute irregularities occur on the surface of the active substrate after polishing.
For example, when there is a foreign substance 5 on the attaching surface of the attaching block 4 (FIG. 2A), when the supporting substrate 1a is attached to this attaching surface, a dent 5a due to the foreign substance 5 is generated on the back surface of the supporting substrate 1a, The depression 5a further extends to the oxide film 3a and the active substrate 2a via the upper surface of the support substrate 1a, and the upper surface of the active substrate 2a is polished as it is, so that an extremely thin portion 5b is generated on the active substrate 2a. [FIG. 2 (b)]. After the polishing is completed, the support substrate 1a returns to the original state by removing the wax 4a from the attachment block 4 and removing the wax 4a, whereby the ultrathin portion 5b of the active substrate 2a remains in a concave state [FIG. c)].
Also, when there is a dent 6 on the back surface of the support substrate 1b [FIG. 3 (a)], when this support substrate 1b is attached to the attaching block 4 and polished, it corresponds to the oxide film 3b and the dent 6 of the active substrate 2b. The portion is polished while being depressed by this polishing pressure, and this portion becomes an extremely thick portion 6a (FIG. 3B). After the polishing, the wax 4a is removed by peeling off the attachment block 4, and the support substrate 1b returns to the original state, whereby the extremely thick portion 6a remains in a state of protruding from the surface of the active substrate 2b [FIG. 3 (c)].
However, when the fine irregularities as described above are localized on the surface of the active substrate, there is a problem that even if PACE processing is performed, the surface cannot be flattened, and an active substrate having a uniform thickness cannot be obtained. is there.
The present invention has been made in view of the above problems, and has as its object to provide a method for manufacturing an SOI substrate having an active substrate uniformly thinned.
[0004]
[Means for Solving the Problems]
For this reason, in the present invention, the method for manufacturing an SOI substrate is based on a method in which both surfaces of a semiconductor wafer serving as a support substrate are simultaneously polished by a double-side polishing apparatus, and a semiconductor wafer serving as an active substrate is attached to the upper surface of the support substrate polished on both surfaces. The bonded wafer is obtained, the unbonded portion of the peripheral portion of the bonded wafer is removed, and the surface of the active substrate of the bonded wafer from which the unbonded portion is removed is reduced by surface grinding to reduce the thickness. Is spin-etched, and the spin-etched active substrate is thinned by PACE processing. Also, the method for manufacturing an SOI substrate is such that both surfaces of a semiconductor wafer serving as a support substrate are simultaneously polished by a double-side polishing apparatus. Then, a semiconductor wafer serving as an active substrate is bonded to the upper surface of the support substrate polished on both sides to obtain a bonded wafer, and the peripheral edge of the bonded wafer is not bonded. Then, the surface of the active substrate of the bonded wafer from which the unbonded portion has been removed is reduced by surface grinding to reduce the thickness, and the surface-ground bonded bonded wafers are held one by one by a top ring, and the active substrate is removed. The active substrate, which has been polished and polished, is thinned by PACE processing.
[0005]
【Example】
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a side sectional view showing each step of a method of manufacturing an SOI substrate according to the present invention, and FIGS. 2 and 3 are side sectional views of an SOI substrate manufactured by a conventional manufacturing method.
[0006]
The SOI substrate of this embodiment is manufactured by the following method.
(1) Both surfaces of a semiconductor wafer serving as a support substrate 1 are simultaneously polished by a double-side polishing apparatus to obtain a semiconductor wafer having flat front and back surfaces (FIG. 1A). On the back surface of the support substrate 1 polished on both sides, there is no defect such as a dent which adversely affects the thinning of the active substrate in the final step.
(2) An oxide film 3 is generated on the surface of the support substrate 1 which has been polished on both sides, and a semiconductor wafer to be the active substrate 2 is bonded on the upper surface thereof. [FIG. 1 (b)].
(3) An unbonded portion at the peripheral edge of the bonded wafer is removed, an oxide film other than the oxide film 3 between the active substrate 2 and the support substrate 1 is removed, and the top surface of the active substrate 2 is ground to obtain a thickness. Is reduced [FIG. 1 (c)].
(4) The surface of the active substrate 2 whose surface has been ground is etched by spin etching to further reduce the thickness of the active substrate 2 (FIG. 1D). The removal allowance in this spin etching is about 10.0 to 20.0 μm, and the thickness unevenness is within ± 5.0% of the removal allowance, and is a thickness that can be removed by PACE processing in the next step. is there. In contrast to the conventional polishing rate of 0.8 μm / min, the etching rate by spin etching is as high as 30 μm / min, so that the working efficiency is significantly improved.
(5) The surface of the active substrate 1 that has been spin-etched is thinned by PACE processing (FIG. 1E). The thickness unevenness generated by the spin etching is smooth unlike the small unevenness generated by the pasting polishing of the prior art, so that it can be sufficiently processed with the resolution of the PACE processing, so that the active substrate 1 is uniformly thinned. be able to. The thickness unevenness of the active substrate 1 thinned by the PACE processing is about ± 10.0 nm.
[0007]
In the above embodiment, the active substrate 2 having been subjected to surface grinding is processed to be thin by spin etching. However, the present invention is not limited to this. Instead of spin etching, bonded wafers whose surface has been ground are placed one by one. It may be held by a ring and polished one by one. Also in this method, since the semiconductor wafer polished on both sides is used as a support substrate, the single wafer polishing does not adversely affect the active substrate due to a defect on the back surface.
[0008]
【The invention's effect】
Since the present invention is configured as described above, it is possible to prevent thickness unevenness occurring in a pre-process of PACE processing, and to obtain an excellent effect of obtaining an SOI substrate having a uniform thinned active substrate. .
In addition, since a semiconductor wafer polished on both sides is used as a support substrate, there is no problem such as a dent on the back surface, and there is an excellent effect that it does not adversely affect the thinning of the active substrate.
Furthermore, since the rate of spin etching is higher than that of the conventional bonding polishing, there is an excellent effect that production efficiency is good.
[Brief description of the drawings]
FIG. 1 is a side sectional view showing each step of a method for manufacturing an SOI substrate according to the present invention.
FIG. 2 is a side sectional view of an SOI substrate manufactured by a conventional manufacturing method.
FIG. 3 is a side sectional view of an SOI substrate manufactured by a conventional manufacturing method.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support substrate 1a Support substrate 1b Support substrate 2 Active substrate 2a Active substrate 2b Active substrate 3 Oxide film 3a Oxide film 3b Oxide film 4 Sticking block 4a Wax 5 Foreign matter 5a Depression 5b Ultra-thin portion 6 Depression 6a Extremely thick portion

Claims (2)

A method for manufacturing an SOI substrate, comprising the following steps.
(1) A double-side polishing step of simultaneously polishing both surfaces of a semiconductor wafer as a support substrate by a double-side polishing apparatus.
(2) A bonding step in which a semiconductor wafer serving as an active substrate is bonded to the upper surface of the support substrate polished on both sides to obtain a bonded wafer.
(3) An unbonded portion removing step of removing an unbonded portion at a peripheral portion of the bonded wafer.
(4) A surface grinding step of reducing the thickness by surface grinding the surface of the active substrate of the bonded wafer from which the unbonded portion has been removed.
(5) A spin etching step of etching the surface of the active substrate that has been ground by spin etching.
(6) A PACE processing step of thinning the spin-etched active substrate by PACE processing. A method for manufacturing an SOI substrate, comprising the following steps.
(1) A double-side polishing step of simultaneously polishing both surfaces of a semiconductor wafer as a support substrate by a double-side polishing apparatus.
(2) A bonding step in which a semiconductor wafer serving as an active substrate is bonded to the upper surface of the support substrate polished on both sides to obtain a bonded wafer.
(3) An unbonded portion removing step of removing an unbonded portion at a peripheral portion of the bonded wafer.
(4) A surface grinding step of reducing the thickness by surface grinding the surface of the active substrate of the bonded wafer from which the unbonded portion has been removed.
(5) A single wafer polishing step of holding the surface-ground bonded wafers one by one by a top ring and polishing the active substrate.
(6) A PACE processing step of thinning the active substrate polished by a single wafer by PACE processing.

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