JP2004235478A - Stacked soi substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stacked SOI (silicon on insulator) substrate which is provided with an active layer made from a thick film having high uniformity in the thickness and to provide a method of manufacturing the stacked SOI substrate. <P>SOLUTION: The method comprises steps of polishing the surface of the active layer 10A to determine thickness throughout the entire active layer 10A and then to feed back the thickness data to a partial etching rate of the active layer 10A, and subjecting the active layer 10A to plasma etching. Thus, flatness is enhanced on the surface of the active layer 10A to an extent, for example, that thickness tolerance is rendered to be ±0.3μm or below with the active layer 10A having a thickness of 1μm or more. As a result, there is produced the stacked SOI substrate having the active layer 10A of a thick film with high uniformity in thickness. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a bonded SOI substrate and a method of manufacturing the same, and more particularly, to a bonded SOI substrate having a thick active layer and a method of manufacturing the same.
[0002]
[Prior art]
As demands for higher integration and multifunctional LSIs formed on a silicon substrate become more severe, signal delay in wiring has become an important issue. In the conventional LSI, electric circuit elements are integrated on the surface layer (a part of several tens μm from the surface) of a silicon wafer having a thickness of 500 to 800 μm.
An SOI (Silicon On Insulator) substrate is known to solve the problem of signal delay in such wiring. The SOI substrate has a configuration in which a buried silicon oxide film having a thickness of several tens nm to several μm is interposed between an active layer on which a device is formed and a supporting substrate for supporting the active layer.
In this SOI substrate, each device is completely separated by a buried silicon oxide film. Therefore, high integration of devices including multi-functions with a three-dimensional structure is facilitated, high-speed operation is enabled, soft errors can be reduced, high reliability can be achieved, and power consumption can be suppressed.
[0003]
Usually, an SOI substrate having a thin active layer of about several tens of A (angstrom) to about 1 μm is a thin film SOI substrate, and a substrate having a thick active layer of 1 μm or more is a thick film SOI substrate. In particular, a smart cut method (Patent Literature 1 and Patent Literature 2) is known as one of the methods for manufacturing a thin film SOI substrate. In this method, a light element such as hydrogen is ion-implanted into an active layer wafer, and unnecessary portions of the active layer wafer are separated from the implanted portion and peeled off. More specifically, a part of the silicon oxide film is used as a buried silicon oxide film, and the wafer for the active layer and the wafer for the support substrate are bonded to each other. During the subsequent heat treatment, the active layer is separated from the hydrogen ion implanted portion and peeled off. Thus, an SOI substrate having a thin active layer is manufactured.
[Patent Document 1] U.S. Pat. No. 5,374,564 [Patent Document 2] U.S. Pat. No. 6,020,252 and other known laminating methods suitable for manufacturing a thick-film SOI substrate. This means that the wafer for the active layer and the wafer for the support substrate are bonded together with a buried silicon oxide film between them, and after the subsequent bonding heat treatment, the wafer for the active layer is ground from the surface opposite to the bonded surface, By polishing, a bonded SOI substrate having a thick active layer can be obtained.
[0004]
[Problems to be solved by the invention]
However, such a conventional method for manufacturing an SOI substrate has the following disadvantages.
That is, in the smart cut method, although the flatness of the active layer is as high as about ± 0.1 μm, the maximum thickness of the active layer is about 1.5 μm. Therefore, although the film thickness uniformity was high, a thick film SOI substrate could not be manufactured. On the other hand, according to the bonding method, although an active layer having a thickness of 2 μm or more (for example, 100 μm) can be obtained, the tolerance of the thickness of the active layer is as large as about ± 0.5 μm. For this reason, only a thick film SOI substrate having poor film thickness uniformity was produced, and a thick film SOI substrate having high film thickness uniformity could not be produced.
[0005]
Therefore, as a result of earnest research, the inventor measured the entire thickness of the active layer on the bonded SOI substrate, and plasma-etched the active layer based on the thickness data. Nevertheless, they have found that a bonded SOI substrate having high uniformity in film thickness can be manufactured, and have completed the present invention.
[0006]
[Object of the invention]
An object of the present invention is to provide a bonded SOI substrate capable of obtaining a thick active layer with high film thickness uniformity and a method for manufacturing the same.
[0007]
[Means for Solving the Problems]
According to the first aspect of the present invention, in a bonded SOI substrate in which an active layer and a wafer for a support substrate are bonded via a buried silicon oxide film, the thickness of the entire active layer whose surface is polished is measured. And a bonded SOI substrate obtained by plasma etching the active layer based on the obtained thickness data.
[0008]
As the active layer wafer and the support substrate wafer, for example, a single crystal silicon wafer or the like can be used.
The thickness of the active layer is, for example, 1 to 100 μm. In particular, the present invention exerts a great effect on a bonded SOI substrate having a thick active layer having a thickness of 1 μm or more. The thickness of the buried silicon oxide film is, for example, several tens nm to several μm.
The active layer after plasma etching may be a thin film of less than 2 μm or a thick film of more than 2 μm.
[0009]
According to a second aspect of the present invention, there is provided the bonded SOI substrate according to the first aspect, wherein an etching amount by the plasma etching is 0.01 to 2 μm. At this time, the thickness of the active layer after the plasma etching is 1 μm or more or less than 1 μm, and the thickness tolerance is ± 0.3 μm or less.
[0010]
According to a third aspect of the present invention, in the method for manufacturing a bonded SOI substrate in which an active layer and a wafer for a support substrate are bonded via a buried silicon oxide film, a polishing step of polishing a surface of the active layer; A method for manufacturing a bonded SOI substrate, comprising: a wafer thickness measuring step of measuring the thickness of the entire active layer; and a plasma etching step of plasma etching the active layer based on the obtained thickness data. .
The bonding of the wafer for the active layer and the wafer for the support substrate is performed, for example, by bonding both wafers at room temperature to produce a bonded wafer, and then performing the bonding heat treatment by inserting the bonded wafer into a thermal oxidation furnace. Increase the bonding strength. The heating temperature of the bonding heat treatment is 800 ° C. or higher, for example, 1100 ° C. The bonding heat treatment time is, for example, 2 hours. Oxygen or the like is used as an atmosphere gas in the thermal oxidation furnace.
[0011]
After the bonding heat treatment, the thickness of the active layer wafer is reduced. For example, grinding and polishing are sequentially performed on the active layer wafer side of the bonded wafer to reduce the thickness of the active layer wafer to a predetermined thickness. For grinding, for example, a grinding wheel is used. Known grinding conditions may be used. For example, grinding is performed using a resinoid grinding wheel of # 360 to # 2000 until the remaining active layer thickness reaches the target active layer thickness ± 5 μm or more.
In the polishing step, the surface of the active layer reduced in thickness by grinding is polished. The polishing device is not limited. It may be a single wafer type or a batch type. Further, a single-side polishing apparatus for polishing only one surface of the semiconductor wafer or a double-side polishing apparatus for simultaneously polishing both front and back surfaces of the semiconductor wafer may be used.
Further, there is provided a polishing surface plate and a polishing head arranged opposite thereto, and a waxless type single-side polishing device for filling a semiconductor wafer with water via a back pad on a surface of the polishing head facing the polishing surface plate. May be.
As the polishing cloth, for example, a porous non-woven cloth polishing cloth in which polyester felt is impregnated with polyurethane, or a foamable urethane type obtained by slicing a foamed urethane block can be used.
As the abrasive, for example, a slurry containing free abrasive grains such as colloidal silica (silica sol) or fumed silica can be employed. Further, a ceria-based slurry using cerium oxide can also be employed.
[0012]
The measurement of the thickness of the active layer is performed, for example, for each wafer. As a device for measuring the thickness of the active layer, for example, a spectroscopic ellipsometer that measures the thickness of the active layer by irradiating polarized light on the surface of the active layer and measuring a change in the polarization state of the reflected light may be used. Can be. In addition, a Fourier transform infrared spectroscopy using Fourier Transform Infrared (FTIR) method using infrared rays as a light source can be employed.
The etching rate of the plasma etching is about 0.01 to 1.0 μm / min. The active layer tolerance of the semiconductor wafer after the plasma etching has a high flatness of ± 0.3 μm or less.
When the semiconductor wafer is a silicon wafer, a gas containing halogen is used as the etching gas. For example, in addition to a mixed gas of CF ₄ and O ₂ , SF ₆ , SiF ₄ , SiCl ₄ , SiBr ₄ or the like can be used.
[0013]
The plasma etching apparatus is not limited. For example, while flowing an etching gas into an etching reaction furnace, a high-frequency voltage is continuously supplied from a high-frequency power supply between a plasma generating electrode disposed in the reaction furnace and a chuck / electrode also serving as a vacuum chuck for a semiconductor wafer. To generate plasma in the plasma generating electrode. Next, the plasma generating electrode is moved while controlling the magnitude or moving speed of the high frequency based on the thickness data of the entire area of the active layer obtained in advance by the active layer thickness measuring device, and is excited by the plasma. It is possible to employ a plasma etching apparatus or the like that sequentially supplies the radical species from the supply pipe to a predetermined position of the wafer and performs etching. That is, this plasma etching apparatus is an apparatus for feeding back wafer shape information before etching to a partial etching amount. Specifically, a plasma etching apparatus manufactured by Speed Fam Co., Ltd., trade name “DCP-200X”, or the like can be used.
After the etching, the surface of the active layer may be finish-polished. As the final polishing, chemical mechanical polishing (CMP) utilizing both a chemical action and a mechanical action can be employed. The polishing apparatus for CMP is not limited.
[0014]
The invention according to claim 4 is the method for manufacturing a bonded SOI substrate according to claim 3, wherein an etching amount by the plasma etching is 0.01 to 2 μm. The active layer after the plasma etching has a thickness of 1 μm or more or less than 1 μm, and a thickness tolerance of ± 0.3 μm or less.
[0015]
[Action]
According to the bonded SOI substrate and the method of manufacturing the same of the present invention, after polishing the surface of the active layer, the thickness of the entire area of the active layer is measured, and the obtained thickness data is used as the partial etching amount of the active layer. And the active layer is plasma-etched. That is, the etching amount by plasma etching is partially changed in accordance with the surface shape of the semiconductor wafer, and the wafer surface is processed. The processing amount is, for example, 0.01 to 2 μm. As a result, the flatness of the surface of the active layer is increased. For example, even if the active layer has a thickness of 20 μm or more, the thickness tolerance becomes ± 0.3 μm or less. As a result, a bonded SOI substrate having a thick active layer with high film thickness uniformity can be obtained.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for manufacturing a bonded SOI substrate according to an embodiment of the present invention will be described. As shown in the flow sheet of FIG. 1, first, a single crystal silicon ingot is pulled up by a CZ method or the like, and then, the obtained single crystal silicon ingot is subjected to block cutting, slicing, chamfering, mirror polishing, etc., to achieve a mirror finish. Of the active layer wafer 10 is prepared. On the other hand, a mirror-finished support substrate wafer 20 having the same diameter is prepared by the same manufacturing method as that of the active layer wafer 10 (FIG. 1A). Of these, the active layer wafer 10 or the support substrate wafer 20 is inserted into a thermal oxidation furnace and subjected to thermal oxidation treatment, and the entire exposed surface is covered with an insulating silicon oxide film 10a (FIG. 1B). ).
[0017]
Next, after cleaning both wafers 10 and 20, mirror surfaces are superimposed on each other at room temperature in a clean room (FIG. 1 (c)). Thereby, a bonded wafer 30 is formed. By this bonding, a portion of the silicon oxide film 10a interposed between the active layer wafer 10 and the support substrate wafer 20 becomes a buried silicon oxide film 10b.
Thereafter, the bonded wafer 30 is inserted into a thermal oxidation furnace for bonding and subjected to a bonding heat treatment in an oxidizing atmosphere. As a result, the entire exposed surface of the bonded wafer 30 is covered with the silicon oxide film 30a. Therefore, the oxide film thickness of the active layer wafer 10 increases. At this time, the bonding temperature is about 1100 ° C., and the heat treatment time is about 2 hours (also FIG. 1C).
[0018]
Next, a void inspection by ultrasonic irradiation is performed. Then, with respect to the non-defective bonded wafer 30, the surface of the active layer wafer 10 is ground by 500 to 650 μm from the device forming surface side by using # 360 to # 1500 resinoid grinding wheels (FIG. 1D). After the processing, the remaining thickness of the active layer wafer 10 is about several μm to several hundred μm. After the surface grinding, the ground surface of the active layer wafer 10 is mirror-polished to produce an active layer 10A (also FIG. 1 (d)).
[0019]
Specifically, the bonded wafer 30 whose surface has been ground is mounted on a carrier plate mounted on a single-wafer or batch-type polishing apparatus (not shown), and while supplying a slurry containing colloidal silica, The ground surface of the wafer 10 is pressed against a foaming urethane polishing cloth stuck on a polishing platen to perform mirror polishing.
Next, the thickness is measured over the entire area of the active layer (FIG. 1E). Specifically, a spectroscopic thin film measuring apparatus is used. This involves irradiating the entire surface of the wafer with light that has passed through several types of filters, analyzing the reflected light, and measuring the thickness of the active layer.
[0020]
Thereafter, based on the obtained thickness data of the active layer, the vicinity of the surface of the active layer (surface layer portion) is subjected to plasma etching (FIG. 1F). Specifically, plasma-assisted chemical etching is performed using a plasma etching apparatus 50 manufactured by Speed Fam Co., Ltd., trade name "DCP-200X" shown in the schematic diagram of FIG.
That is, the plasma etching apparatus 50 uses the microwave generator 51 to flow a mixed gas of the etching gas CF ₄ and O ₃ into the discharge chamber at a rate of 10 to 500 cc / min. A 1000 Watt microwave is applied continuously. As a result, a plasma is generated, and the plasma is irradiated onto the surface of the active layer 10A to partially etch the active layer 10A.
[0021]
Thereafter, the plasma generating electrode 52 is moved along the surface of the active layer 10A while changing the moving speed in accordance with the thickness of the undulation on the surface of the active layer 10A. Accordingly, radical species 55 excited by the plasma 54 are sequentially supplied from the supply pipe 56 to a predetermined position of the active layer 10A. As a result, the silicon under the plasma region is etched at an etching rate of 0.01 nm to 2 μm / min and an etching amount of 0.01 to 2 μm according to the thickness of the undulating portion (for example, 0.1 μm). Thus, immediately after polishing, the active layer 10A (FIG. 3A) having a thickness of 30 μm or less and a thickness tolerance of ± 0.5 μm increases the flatness of the surface of the active layer 10A after plasma etching, and the thickness tolerance is reduced. It is reduced to ± 0.3 μm or less (FIG. 3B). As a result, a bonded SOI substrate having an active layer 10A having a high uniformity in film thickness can be manufactured despite its large thickness.
[0022]
Next, finish polishing is performed on the surface of the active layer 10A (FIG. 1 (g)). The polishing cloth to be used is a suede type in which a urethane resin is foamed on a base cloth of a nonwoven fabric for finish polishing. The polishing amount is 0.5 μm or less.
After that, finish cleaning of the bonded wafer 30 is performed (FIG. 1H). This cleaning is RCA cleaning based on two kinds of cleaning liquids, SC-1 and SC-2.
In this way, a bonded SOI substrate having the thick active layer 10A with high film thickness uniformity is manufactured.
[0023]
Here, with reference to FIG. 4, the results of a comparative study of the relationship between the thickness tolerance of the active layer and the yield thereof for the bonded SOI substrate of the present invention and the conventional bonded SOI substrate will be reported.
As shown in FIG. 4A, in the bonded SOI substrate of the present invention, the thickness of the active layer was measured at nine points on ten bonded SOI substrates, and the difference between the maximum value and the minimum value was investigated. . The difference was 0.3 μm or less (corresponding to a thickness tolerance of ± 0.15 μm or less), and a good result was obtained with a yield of 100%.
On the other hand, in the conventional bonded SOI substrate shown in FIG. 4B, when the difference is 0.6 μm or less (corresponding to a thickness tolerance of ± 0.3 μm or less), the yield is reduced to 80%. This is a result of measurement on ten bonded SOI substrates in the same manner.
[0024]
【The invention's effect】
According to the present invention, after polishing the surface of the active layer, the thickness of the entire active layer is measured, and the active layer is plasma-etched by partially changing the amount of plasma etching based on the obtained thickness data. Since etching is performed, a bonded SOI substrate having a thick active layer with high film thickness uniformity can be manufactured.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method for manufacturing a bonded SOI substrate according to one embodiment of the present invention.
FIG. 2 is a schematic view of a plasma etching apparatus used in a method for manufacturing a bonded SOI substrate according to one embodiment of the present invention.
FIG. 3A is an enlarged cross-sectional view of a bonded SOI substrate immediately after polishing.
(B) is an enlarged sectional view of the bonded SOI substrate immediately after plasma etching.
FIG. 4A is a graph showing a relationship between a thickness tolerance of an active layer of a bonded SOI substrate according to the present invention and a yield thereof.
(B) is a graph showing the relationship between the thickness tolerance of the active layer of the bonded SOI substrate according to the conventional means and the yield thereof.
[Explanation of symbols]
10A active layer,
10b buried silicon oxide film,
20 Support substrate wafer.

Claims (4)

In a bonded SOI substrate in which an active layer and a wafer for a support substrate are bonded via a buried silicon oxide film,
A bonded SOI substrate in which the thickness of the entire active layer whose surface is polished is measured, and the active layer is plasma-etched based on the obtained thickness data. The bonded SOI substrate according to claim 1, wherein an etching amount by the plasma etching is 0.01 to 2 m. In a method for manufacturing a bonded SOI substrate in which an active layer and a wafer for a support substrate are bonded via a buried silicon oxide film,
A polishing step of polishing the surface of the active layer,
Wafer thickness measurement step of measuring the thickness of the entire active layer,
A method for producing a bonded SOI substrate, comprising: a plasma etching step of plasma-etching the active layer based on the obtained thickness data. 4. The method for manufacturing a bonded SOI substrate according to claim 3, wherein an etching amount by the plasma etching is 0.01 to 2 [mu] m.

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