JP2008140878A - Silicon wafer and manufacturing method thereof, bonded SOI wafer and manufacturing method thereof. - Google Patents

Abstract

An SOI wafer with high flatness is obtained without the presence of an oxide film on the back surface.
A silicon wafer is bonded to a bonding silicon wafer on which an oxide film is formed to obtain an SOI wafer. The thin disk-shaped wafer is given a bowl-shaped warp having a recessed central portion by either or both of grinding and polishing. The manufacturing method includes a convex wafer in which one main surface of a silicon wafer is held by suction and the other main surface is ground or polished to increase the thickness from the wafer outer periphery toward the wafer center, or from the wafer outer periphery to the wafer center. After manufacturing a concave wafer with a reduced thickness toward the surface, the other main surface formed in a convex or concave shape is sucked and held, and the center of one main surface side is protruded by elastic deformation, The main surface is ground or polished to flatten the main surface, and the suction holding is released to obtain a wafer having a bowl-shaped warp with a recessed central portion.
[Selection] Figure 1

Description

  The present invention relates to a silicon wafer for a support substrate that can obtain an SOI (Silicon-On-Insulator) wafer having high flatness by bonding, a manufacturing method thereof, and an SOI wafer using such a silicon wafer for support substrate. It relates to a manufacturing method.

  In recent years, highly integrated CMOS (Complementary Metal Oxide Semiconductor), ICs, high-voltage devices, etc. have been manufactured using SOI wafers. An SOI wafer in which a single crystal silicon layer used as a device fabrication region on an insulating layer is formed is used to prevent latch-up (abnormal oscillation due to parasitic circuits) in the case of highly integrated CMOS, and in the case of a high voltage device. Is effective for isolation from the base substrate. As a method for manufacturing this SOI wafer, there is known a method in which silicon wafers are bonded to each other via a silicon dioxide layer, that is, an insulating layer. The SOI wafer manufactured by this bonding method has a crystallinity of the SOI layer. It has been viewed as promising because it is extremely good.

Specifically, this silicon wafer bonding method is performed by bonding two silicon wafers each having a diameter of 200 mm and a thickness of about 720 μm through an insulating layer made of a silicon oxide layer, and in a non-oxygen atmosphere at 1100 ° C. After the time-bonding heat treatment, the surface of one of the two silicon wafers was ground with a grindstone and further polished with a polishing cloth to bring the thickness of the silicon wafer to a range of about 1 to 20 μm. A silicon layer with a thickness of about 1 to 20 μm on the side is used as an SOI layer for device formation.
However, since the insulating layer made of a silicon oxide layer has a smaller thermal expansion coefficient than that of single crystal silicon, when the oxide film is not formed on the back surface of the support substrate, the SOI layer side warps in a convex shape, and the device There were problems such as causing adsorption mistakes in the process.

In order to eliminate this point, after heating both wafers to a predetermined temperature and bonding them together, these wafers are thermally oxidized to form an oxide film on the entire surface, and one wafer, preferably before bonding. An SOI wafer manufacturing method has been proposed in which a bonded wafer is obtained by polishing the surface of a wafer on which an oxide film has been formed and making it thin (see, for example, Patent Document 1).
In such a manufacturing method, when the upper wafer is polished and thinned, the upper and lower surfaces of the other supporting substrate silicon wafer are covered with oxide films. The amount of shrinkage is substantially the same, that is, the residual stress distribution is substantially equal on the upper and lower surfaces, so that bending deformation of the silicon wafer for the support substrate can be prevented, and as a result, an SOI wafer with high flatness without warping can be obtained. It is said.
JP-A-3-250615 (Claims)

However, the SOI wafer obtained by the above-mentioned manufacturing method in which an oxide film is formed on the entire surface after bonding both wafers prevents the warpage by making the oxide film exist on the upper and lower surfaces of the silicon wafer for the supporting substrate. To do. For this reason, the presence of an oxide film on the lower surface of the SOI wafer is a prerequisite for preventing warpage, but the oxide film present on the lower surface of the SOI wafer may be peeled off in subsequent device processes. When the oxide film on the lower surface is peeled off in the device process, the SOI wafer has a non-uniform thermal shrinkage on the upper and lower surfaces of the silicon wafer for the supporting substrate, and the SOI wafer is newly warped in the device process. The problem to be solved still remains.
An object of the present invention is to provide a silicon wafer, a manufacturing method thereof, a bonded SOI wafer, and a manufacturing method thereof that can obtain an SOI wafer with high flatness without an oxide film on the back surface.

The invention according to claim 1 is characterized in that a bowl-shaped warp having a recessed central portion is imparted by performing either or both of grinding and polishing on a thin disk-shaped wafer. It is. That is, as shown in FIG. 1, a silicon wafer formed such that the center point of the thin disc-shaped wafer in the center plane in the thickness direction is lower than the center point in the thickness direction of the entire circumference of the wafer. is there.
When an SOI wafer is obtained by the bonding method using the silicon wafer described in claim 1, the SOI wafer is obtained by forced warping by grinding and polishing applied to the silicon wafer for supporting substrate Thus, the warpage newly generated in the SOI wafer is surely canceled, and a flat SOI wafer can be obtained.

In the invention according to claim 2, as shown in FIG. 3, one main surface of the thin disk-shaped silicon wafer 13 is sucked and held, and the other main surface is ground or polished. After the convex wafer 14 having a thickness increased from the outer periphery of the wafer toward the wafer center, the other main surface formed in a convex shape is sucked and held, and the center on the one main surface side is formed by elastic deformation. The main surface is flattened by either one or both of grinding and polishing of the main surface, and the suction-holding is released, so that a bowl-shaped warp with a recessed central portion is formed. A method for producing a silicon wafer, characterized in that a given wafer is obtained.
In addition, although not shown, the invention according to claim 3 is either one of or both of grinding and polishing of the other main surface by sucking and holding one main surface of the thin disc-shaped silicon wafer. After making the wafer with the thickness reduced from the wafer outer periphery toward the wafer center, the other main surface formed in the concave shape is sucked and held, and the peripheral portion on the one main surface side is elastically deformed. The main surface is flattened by performing either one or both of grinding and polishing on the one main surface, and the suction holding is released, so that a bowl-shaped warp having a recessed central portion is formed. A method for producing a silicon wafer, characterized in that a given wafer is obtained.
In the silicon wafer manufacturing method according to the second and third aspects of the present invention, the silicon wafer 12 provided with a desired concave warpage necessary for canceling the wafer warpage generated during the SOI wafer manufacturing is accurately obtained. Can be manufactured.

As shown in FIG. 2, the invention according to claim 4 is an improvement of a bonded SOI wafer formed of at least an SOI layer, an insulating layer, and a support substrate.
The characteristic point is that a silicon wafer with a bowl-shaped warp with a concave in the center by performing either or both of grinding and polishing on a thin disk-shaped wafer is used as a support substrate. The concave surface side of the wafer is the main surface of the bonding surface.
In the bonded SOI wafer described in claim 4, the warpage applied to the silicon wafer cancels out the warpage newly generated in the SOI wafer 21 when the SOI wafer 21 is obtained, and the flat SOI wafer 21. Can be obtained.

In the invention according to claim 5, as shown in FIG. 2, a bowl-shaped warp having a recessed central portion is imparted by performing either or both of grinding and polishing on a thin disc-shaped wafer. A silicon wafer is used as a support substrate, and the concave warpage surface of the support substrate wafer and the silicon wafer surface for the active layer substrate are bonded to each other via an oxide film, and then the silicon wafer surface for the active layer substrate is thinned and activated. A method for producing a bonded SOI wafer, wherein a layer is formed.
The invention according to claim 6 is the invention according to claim 5, wherein the thin disc-shaped wafer is subjected to either or both of grinding and polishing, and a bowl-shaped warp in which the central portion is recessed. Bonding is characterized in that the applied silicon wafer is used as a support substrate, and the concave warped surface of the support substrate wafer and the silicon wafer surface for the active layer substrate are mirror-polished at least through the oxide film. This is a method for manufacturing an SOI wafer.
In the SOI wafer manufacturing method according to the fifth and sixth aspects, an SOI wafer with high flatness can be obtained even though no oxide film is present on the back surface. For this reason, the oxide film does not peel off in the device process, and it is possible to obtain an SOI wafer that does not warp in the device process.

In the silicon wafer of the present invention, a thin disc-shaped wafer is subjected to either or both of grinding and polishing, and thus a wafer having a bowl-shaped warp with a recessed central portion is provided. When an SOI wafer is obtained by the bonding method using the wafer, the warp applied to the silicon wafer cancels out the warp newly generated in the SOI wafer when the SOI wafer is obtained, and a flat SOI wafer is obtained. Can do.
In addition, one main surface of a thin disk-shaped silicon wafer is held by suction, and the other main surface is subjected to either or both of grinding and polishing to increase the thickness from the wafer periphery toward the wafer center. After producing a convex wafer, the other main surface formed in a convex shape is sucked and held, and the center of one main surface is protruded by elastic deformation, and the one main surface is ground or polished. By performing either one or both of these processes, the main surface is flattened, and the suction holding is released, so that a silicon wafer having a bowl-shaped warp with a recessed central part can be obtained with high accuracy.

Similarly, one main surface of a thin disk-shaped silicon wafer is sucked and held, and the other main surface is subjected to either or both of grinding and polishing to reduce the thickness from the wafer periphery toward the wafer center. After manufacturing the concave wafer, the other main surface formed in a concave shape is sucked and held, and the peripheral portion on one main surface side is protruded by elastic deformation, and the one main surface is ground or polished. By performing either one or both of these processes, the main surface is flattened, and the suction holding is released, so that a silicon wafer having a bowl-shaped warp with a recessed central part can be obtained with high accuracy.
Furthermore, a silicon wafer to which a bowl-shaped warp with a recessed central portion is applied by performing either or both of grinding and polishing on a thin disk-shaped wafer is supported via an oxide film. After the concave warpage surface of the substrate wafer and the silicon wafer surface for the active layer substrate are bonded together, the active layer is formed by thinning the surface of the silicon wafer for the active layer substrate to form an oxide film on the back surface. In spite of not existing, an SOI wafer with high flatness can be obtained. In this SOI wafer, the oxide film does not peel off in the device process, and it is possible to effectively prevent a new warp from occurring in the device process.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 2, the present invention relates to a silicon wafer 12 used as a support substrate for forming an SOI wafer 21 together with a bonding silicon wafer 11. Each of the support substrate silicon wafer 12 and the bonding silicon wafer 11 is a silicon wafer produced by a silicon single crystal ingot pulled by the CZ method or the FZ method.

  As shown in detail in FIG. 1, the silicon wafer 12 is subjected to either or both of grinding and polishing so that the center point of the thickness at the wafer center is lower than the center point of the thickness at the outer periphery of the wafer. By performing, a bowl-shaped warp with a recessed central part is given. The amount of warpage is less than 0 μm (minus value) in the case of a so-called bow value. That is, with the concave surface as the front surface (upper side), from the three-point reference surface or the best-fit reference surface on the back surface of the support substrate silicon wafer 12 that is not attracted and fixed, to the center point in the thickness direction at the center portion of the wafer 12 A concave warp is formed such that the amount of displacement (distance A) is less than 0 μm (minus value).

A bowl-shaped warp with a recessed central part is formed by obtaining the SOI wafer 21 by the bonding method using this silicon wafer 12 and then cooling it after heat treatment at the time of bonding one silicon for bonding. The support substrate silicon wafer 12 is warped in advance so as to cancel the warpage generated in the SOI wafer 21 when the surface of the wafer 11 is ground or polished, or when the oxide film on the back surface of the SOI wafer is removed. . The amount of warpage provided on the support substrate silicon wafer 12 is, for example, that the SOI layer thickness is 2 μm in a wafer having a diameter of 150 mm, and the thickness of the BOX layer that is a buried oxide film layer is 1.0 μm, Further, it has been clarified from experience that, in the case of a general SOI wafer 21 in which the thickness of the silicon wafer 12 for supporting substrate is 675 μm, a warp value of about 60 μm occurs. For this reason, it is necessary to warp the support substrate silicon wafer 12 in advance with a bow value of about minus 30 μm. The amount of warpage varies depending on the thicknesses of the SOI layer, the BOX layer, the support substrate silicon wafer 12 and the back surface oxide film of the SOI wafer 21 to be obtained.
The warp is a value represented by the difference between the maximum displacement and the minimum displacement from the three-point reference surface or the best-fit reference surface to the central surface in the wafer thickness direction on the back surface of the wafer that is not attracted and fixed. .

  On the other hand, in order to obtain the SOI wafer 21 with high flatness, the uniformity of the thickness of the silicon wafer 12 for supporting substrate is also important. For this reason, the silicon wafer 12 for a support substrate of the present invention is required to have a uniform thickness, and a specific thickness variation is preferably within a range of 1 μm or less in GBIR evaluation. This is because if the GBIR exceeds 1 μm, the flatness of the obtained SOI wafer 21 cannot be sufficiently increased.

  As shown in FIG. 3, in order to obtain the silicon wafer 12 having the bowl-shaped warp in which the central portion is recessed, the thin disc-shaped silicon wafer 13 is ground and polished by the grinding device 31. 4 to 7 show a grinding apparatus 31 used for obtaining the silicon wafer 12 for supporting substrate. The grinding apparatus 31 includes a flat holding table 32 that sucks the thin disc-shaped silicon wafer 13 placed on a flat upper surface and holds the lower surface of the silicon wafer 13 in a state of forcibly flattening, A plurality of square pillar-shaped grindstones 33 for grinding the upper surface of the silicon wafer 13 held by the table 32, and a grindstone holder 36 for holding these grindstones 33 so as to be positioned on the same circumference around the rotation shaft 34. And a rotation motor 37 (FIGS. 6 and 7) for rotating the grindstone holder 36 via the rotation shaft 34, and a slide means (not shown) that holds the rotation motor 37 so as to be movable up and down. Here, as the grindstone 33, a combination of abrasive grains having a grain size of about # 300 with a metal bond for primary grinding is used, and a grain size of # 1500 (average grain size 7.5 μm) to # 10000 (for secondary grinding). An abrasive having an average particle size of 0.5 μm bonded with a resin bond or a vitrified bond was used. The grindstone 33 functions as a damage reducing means that suppresses damage on the grinding surface of the thin disc-shaped silicon wafer 13 to 5 μm or less.

  As shown in FIGS. 6 and 7, the holding table 32 is a disc made of porous ceramic, and the holding table 32 is embedded in a support base 38. The support base 38 is supported above the fixed base 39 by a single fixed shaft 41 and two lift shafts 42, 42. As shown in FIG. 7, the support point of the support base 38 is moved up and down by the two lift shafts 42, 42. By moving the support table 38, the support table 38 is tilted so that the horizontal upper surface of the holding table 32 embedded in the support table 38 can be tilted to a desired angle. The support base 38 is provided with a rotating means (not shown) for rotating the holding table 32, and the holding table 32 is configured to be rotatable without changing the angle of the inclined upper surface while the upper surface is inclined. The Here, although the case where the holding table 32 is tilted has been described, the rotating shaft 34 of the grindstone 33 may be tilted.

  FIG. 3 shows a method of manufacturing the silicon wafer 12 by grinding and polishing the thin disk-shaped silicon wafer 13 using the grinding apparatus 31 configured as described above. In FIG. 3, a convex surface is formed by increasing the thickness from the outer periphery of the wafer toward the wafer center by sucking and holding one main surface of the silicon wafer 13 and performing either or both of grinding and polishing on the other main surface. After the wafer 14 is manufactured, the other main surface formed in a convex shape is sucked and held, and the center of one main surface is protruded by elastic deformation, and the one main surface is ground or polished. By performing either or both of the processes, the main surface is flattened, and by releasing the sucking and holding, a wafer having a bowl-shaped warp with a recessed central portion is obtained. These will be specifically described below.

<Back grinding process>
First, a thin disk-shaped silicon wafer 13 is prepared. The silicon wafer 13 can be manufactured by slicing a silicon single crystal rod pulled by the CZ method or the FZ method. As shown by a broken line in FIG. 3A, the surface of the thin disk-shaped silicon wafer 13 is placed on a flat holding table 32, and the silicon wafer 13 is placed with the back surface of the silicon wafer 13 being the upper surface. Adsorbed to the holding table 32. Thereafter, the support base 38 in which the holding table 32 is embedded is tilted together with the holding table 32. In order to tilt the support base 38, the support point of the support base 38 is moved up and down by the two lifting shafts 42 and 42 supporting the support base 38. As shown in FIG. The horizontal upper surface of the embedded holding table is tilted to a desired angle. In this state, the holding table 32 is rotated together with the silicon wafer 13 in the direction of the solid line arrow in FIG. 5, and the grindstone holder 36 is rotated in the direction of the broken line arrow in FIG. Next, the grindstone holder 36 is lowered, the grindstone 33 is brought into contact with the back surface of the silicon wafer 13, and the silicon wafer 13 is ground from the back surface side by the grindstone 33. Since the holding table 32 is inclined, the ground back surface has a mountain shape as shown by the solid line in FIG. 3A, and the center of the back surface of the silicon wafer 13 protrudes so that the center is thick. The intermediate wafer 14 is obtained.

<Surface grinding process>
Next, the silicon wafer 13 is ground from the surface side. Therefore, first, the intermediate wafer 14 ground so that the center of the back surface protrudes is separated from the holding table 32. Then, as shown by the solid line in FIG. 3B, the back surface protruding from the center is placed on the holding table 32, and the back surface is sucked as shown by the broken line arrow to hold the intermediate wafer 14 on the flat upper surface of the holding table 32. Let Then, as indicated by a broken line in FIG. 3B, the upper surface of the holding table 32 is flat, so that the back surface of the intermediate wafer 14 is elastically deformed and flattened while being attracted to the holding table. The center of the surface will protrude upward. Then, before or after the rear surface of the intermediate wafer 14 is sucked and held on the holding table 32, the support point of the support table 38 is moved up and down by the two lifting shafts 42 and 42 supporting the support table 38 in FIG. As shown, the support base 38 is returned to the horizontal position, and the upper surface of the holding table 32 embedded in the support base 38 is returned to the horizontal position.

  Next, the holding table 32 is rotated together with the intermediate wafer 14, and at the same time, the grindstone holder 36 is rotated by the rotation motor 37. Next, the grindstone holder 36 is lowered in the direction of the solid line arrow in FIG. 3C, the grindstone 33 is brought into contact with the surface of the intermediate wafer 14, and the intermediate wafer 14 is ground from the surface side by the grindstone 33. Since the holding table 32 is returned to the horizontal position, the ground surface is parallel to the holding table 32, and the intermediate wafer 14 has a uniform thickness as shown by a broken line. When the intermediate wafer 14 having such a uniform thickness is separated from the holding table 32, the wafer 14 is restored by elasticity as shown by an arrow as shown in FIG. Thus, the silicon wafer 12 for supporting substrate having a uniform thickness can be obtained.

Here, the bowl-shaped support substrate silicon wafer 12 having a concave central portion is ground so that the entire concave surface has a gentle curved surface, and is slightly wavy in the circumferential direction. It includes a concave shape, a substantially conical shape, and the like.
In such a manufacturing method of the silicon wafer 12, it is possible to obtain the silicon wafer 12 provided with the concave warpage in which the central point of the thickness at the wafer central portion is lower than the central point of the thickness at the outer peripheral portion of the wafer.

  As an embodiment of the present invention, in the surface grinding step and the back surface grinding step, surface grinding in the case of producing a convex intermediate wafer 14 with the center of the back surface protruding so that the center of the silicon wafer 13 is thick. The process and the back grinding process when this convex wafer is used have been explained. First, a concave intermediate wafer 14 having a recessed center at the back is prepared so that the center of the silicon wafer 13 is thin. Even when a convex silicon wafer 12 having a uniform thickness is manufactured, it can be used as a similar concave silicon wafer 12 if the wafer is inverted. On the contrary, if a concave wafer is produced and reversed, it can be used as a convex wafer. In short, a wafer provided with a warp in a direction opposite to the direction in which the SOI wafer warps during manufacture of the SOI wafer may be used as the supporting substrate.

  Further, in each grinding step, the case where the wafer is processed using the grinding device 31 has been described. However, even when a known mirror polishing device is used instead of the grinding device 31, a similar bowl-shaped warp in which the central portion is recessed is used. A silicon wafer can be obtained, and a grinding apparatus and a mirror polishing apparatus can be used in combination. In this case, the mirror polishing process before the SOI wafer fabrication can be omitted.

Next, a manufacturing method of the SOI wafer 21 using the silicon wafer 12 provided with the bowl-shaped warp with the recessed central part as described above as a support substrate will be described in detail with reference to FIG.
As shown in FIG. 2 (a), a silicon wafer 12 having a bowl-shaped warp with a recessed central portion is obtained by first performing either or both of grinding and polishing on a thin disk-shaped wafer. Prepare as a support substrate. Separately, a silicon wafer 11 for bonding is prepared. The silicon wafer 11 for bonding is produced by slicing a silicon single crystal ingot pulled by the CZ method or the FZ method. In FIG. 2, for easy understanding, the support substrate silicon wafer 12 is drawn with a larger curvature than the actual warpage.

Next, as shown in FIG. 2B, an insulating layer 11 a is formed on the entire surface of the bonding silicon wafer 11. The thickness of the insulating layer 11a is in the range of about 0.5 to about 2.0 μm, preferably in the range of about 0.5 to about 1.0 μm, although it depends on the use of the SOI to be produced. The insulating layer 11a is a silicon oxide layer (SiO ₂ layer), and is formed by thermally oxidizing the silicon wafer 11 or by a CVD method. In this embodiment, since the case of thermal oxidation is described, the insulating layer 11a is formed on the entire surface of the bonding silicon wafer 11. However, according to the CVD method, the side surface of the bonding silicon wafer 11 is formed. The insulating layer 11a may be formed only on both surfaces or only one surface.

Next, as shown in FIG. 2C, the bonding silicon wafer 11 is recessed at the center of the support substrate silicon wafer 12 with the insulating layer 11a formed directly on the bonding silicon wafer 11 as a bonding surface. Bonded to the surface. Here, in order to activate the surface of the silicon wafer 12 for supporting substrate, the center is recessed with an SC1 (Standard Cleaning 1) cleaning solution which is a mixed solution of NH ₄ OH and H ₂ O ₂ .H ₂ O. It is preferable to wash. Then, as shown in FIG. 2D, the support substrate silicon wafer 12 and the bonding silicon wafer 11 are bonded to each other at a temperature of 1100 ° C. or higher in a dry oxygen (dryO ₂ ) atmosphere or a nitrogen (N ₂ ) atmosphere. Below, heat treatment is performed for 1 to 3 hours, preferably about 2 hours.

  Further, as shown in FIG. 2 (e), after the two integrated silicon wafers 11 and 12 are allowed to cool to room temperature, the silicon wafer 11 for bonding to be an SOI layer is ground with a grindstone, and then polished. It is polished with a polishing cloth while flowing the agent, and processed into a thin film having a thickness of about 1 to 20 μm. Thereby, the SOI wafer 21 in which the SOI layer 11b for device formation having a thickness of about 1 to 20 μm is formed on the insulating layer 11a is obtained.

The SOI wafer 21 obtained in this way has no oxide film on the back surface, or has a thin back oxide film thickness with respect to the Box layer thickness. The warp applied to the support substrate silicon wafer 12 cancels out the warp that occurs when the silicon wafer for bonding 11 serving as the SOI layer is ground with a grindstone, and a flat SOI wafer 21 can be obtained. For this reason, in this SOI wafer 21, the oxide film does not peel off in the device process, and it is possible to effectively prevent a new warp from occurring in the device process.
In addition, when a silicon wafer having a bowl-shaped warp with a recessed central portion is used as a support substrate, the concave warp surface of the support substrate wafer bonded through at least the oxide film and the silicon wafer surface for the active layer substrate Each is preferably mirror-polished.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
<Example 1>
First, a silicon single crystal ingot pulled by the CZ method was cut with a wire saw to obtain 25 thin disc-shaped silicon wafers 13 having a diameter of 200 mm (8 inches). All of these were used as the support substrate silicon wafer 12 having a bowl-shaped warp with a recessed central portion according to the procedure shown in FIG. That is, an intermediate wafer in which the surface of the thin disc-shaped silicon wafer 13 is held by suction on the flat upper surface of the holding table 32 and ground so that the center is thick from the back side, and the center of the back surface protrudes by about 30 μm. 14, the intermediate wafer 14 is separated from the holding table 32, and the back surface protruding from the center is sucked and held on the flat upper surface of the holding table 32 so that the center of the surface of the intermediate wafer 14 protrudes upward by elastic deformation. Then, the intermediate wafer 14 was ground from the surface side so that the thickness variation in the wafer surface became a uniform thickness of 1 μm or less. Thereafter, the intermediate wafer 14 having a uniform thickness is separated from the holding table 32 and is elastically restored, so that 25 silicon wafers 12 for supporting substrate having a uniform bowl thickness and a uniform thickness are formed in the center of the surface. Obtained.

  The warpage of the 25 support substrate silicon wafers 12 was measured with a flatness measuring instrument manufactured by ADE, and the distribution is shown in FIG. The warp distribution in FIG. 8A shows a warp distribution at a so-called bow value, and this bow value has a concave surface as the surface side (upper side) and is not fixed by suction. This is a value expressed as the maximum amount of displacement from the three-point reference surface or the best-fit reference surface on the back surface of the substrate silicon wafer 12 to the center point in the thickness direction at the center portion of the wafer 12.

Next, the silicon single crystal ingot pulled up by the CZ method was cut with a wire saw to prepare 25 silicon wafers 11 for bonding. The bonded silicon wafer 11 has a diameter of 200 mm (8 inches) and a thickness of about 725 μm. Then, the silicon wafer 11 for bonding is heat-treated at 1000 ° C. for 3 hours in a wet oxygen (wetO ₂ , O ₂ : H ₂ = 2.0 liter / min: 1.0 liter / min) atmosphere. An insulating layer 11a made of a silicon oxide layer (SiO ₂ ) having a thickness of 0.5 μm was formed on the entire surface of the substrate 11.

The bonding silicon wafer 11 and the supporting substrate silicon wafer 12 on which the insulating layer 11a is formed are respectively combined with an aqueous NH ₄ OH solution with a specific gravity of 0.9, an aqueous H ₂ O ₂ solution with a specific gravity of 1.1 and H ₂ O with NH. ₄ OH: H ₂ O ₂ : H ₂ O = 1: 2: 7 mixed and prepared with SC1 (Standard Cleaning 1) cleaning liquid maintained at about 80 ° C. 2), the silicon wafer 11 for bonding was superposed on the surface where the center of the silicon wafer 12 for supporting substrate was recessed with the insulating layer 11a of the wafer 11 as the bonding surface, and both were bonded together.

  As shown in FIG. 2D, the wafers 11 and 12 bonded together as described above are inserted into a heat treatment furnace set at room temperature to 800 ° C. at a rate of 10 to 15 cm / min, and a nitrogen atmosphere is obtained. The temperature was increased from 800 ° C. at a rate of 10 ° C./min, maintained for 2 hours when it reached 1100 ° C., then cooled at a rate of 4 ° C./min, cooled to 800 ° C., and then 10-15 cm / min Was removed from the furnace at room temperature to room temperature. Thereafter, as shown in FIG. 2 (e), the surface of the silicon wafer 11 for bonding is ground with a grindstone, and then polished with a soft polishing cloth while flowing an abrasive, and the insulating layer 11a has a thickness of 1 to 20 μm. The SOI wafer 21 was obtained by forming the SOI layer 11b. This SOI wafer 21 was referred to as Example 1.

<Comparative Example 1>
Although not shown, a silicon single crystal ingot pulled up by the CZ method was cut with a wire saw, and 25 thin silicon wafers for a support substrate were prepared. The thin disc-shaped silicon wafer for a support substrate has a diameter of 200 mm (8 inches) and a thickness of about 725 μm. The warpage of the 25 thin-plate-shaped silicon wafers for the support substrate was measured by a flatness measuring instrument manufactured by ADE, and the distribution is shown in FIG. The warp distribution in FIG. 9A shows the warp distribution in the bow value, as in FIG. 8A.

On the other hand, 25 silicon wafers for bonding same as those in Example 1 were prepared, and a silicon oxide layer (SiO ₂ ) having a thickness of 0.5 μm was formed on the entire surface of the silicon wafer for bonding under the same conditions as in Example 1. An insulating layer was formed. Thereafter, the silicon wafer for bonding on which the insulating layer was formed and the silicon wafer for supporting substrate having a thin disk shape were superposed under the same conditions as in Example 1 and bonded together. Then, both bonded wafers were heat-treated under the same conditions as in Example 1, and then taken out from the furnace to room temperature. Thereafter, the surface of the silicon wafer for bonding on which the insulating layer is formed is ground with a grindstone, and then polished with a soft polishing cloth while flowing an abrasive, thereby forming an SOI layer having a thickness of 0.1 to 10 μm on the insulating layer. As a result, an SOI wafer was obtained. This SOI wafer was designated as Comparative Example 1.

<Comparison test and evaluation>
The warpages of the 25 SOI wafers 21 in Example 1 and the 25 SOI wafers in Comparative Example 1 were measured by a flatness measuring instrument manufactured by ADE, respectively, and the distributions thereof were shown in FIGS. 8B and 9B. Shown in The warp distributions in FIGS. 8B and 9B show the warp distribution in the so-called warp value, and this warp value is the three-point reference surface or the best fit reference on the back surface of the wafer that is not attracted and fixed. This value is represented by the difference between the maximum displacement and the minimum displacement from the surface to the center surface in the wafer thickness direction.

  Here, the warp distribution in FIGS. 8A and 9A is represented by a bow value so that the height level of the unevenness can be understood, and the warp distribution in FIGS. 8B and 9B. Is expressed by a warp value because a warp value that reflects the warp distribution of the entire wafer is generally used as a wafer warp specification. As is clear from FIGS. 8A and 9A, the warpage (Bow value) of the silicon wafer serving as the support substrate is in the range of minus 5 μm to plus 5 μm in Comparative Example 1, and the average value is minus. In contrast to 2.3 μm, in Example 1, it is concentrated in the range of −20 μm to −30 μm, and the average value is −28.1 μm, so that a relatively stable amount of warpage can be obtained on the negative side.

  On the other hand, as is apparent from the results of FIGS. 8B and 9B, the warp in the so-called warp value of the SOI wafer 21 in Example 1 is concentrated at 20 μm, and the average value is 18.5 μm. On the other hand, the warp in the so-called warp value of the SOI wafer in Comparative Example 1 is concentrated at 50 μm, which is larger than Example 1, and the average value is 48.9 μm. That is, it can be seen that the SOI wafer 21 in Example 1 is flat compared to the SOI wafer in Comparative Example 1 and has a smaller warp value. This is considered to be caused by the fact that the concave warpage formed in the silicon wafer 12 for support substrate in Example 1 cancels out the warpage generated when the SOI wafer 21 was obtained, and the effect of the present invention was confirmed. .

It is a figure which shows the means to represent the curvature of the silicon wafer for support substrates of this embodiment by what is called a bow value. It is a fragmentary sectional view which shows the manufacturing method of the SOI wafer using the silicon wafer for the support substrate. It is a fragmentary sectional view which shows the manufacturing method of the silicon wafer for the support substrate. It is a principal part perspective view of the grinding device used in order to manufacture the silicon wafer for the support substrate. It is a top view which shows the relationship between the grindstone of the grinding device and a wafer. It is a block diagram of the grinding device which has a horizontal holding table. It is a block diagram corresponding to FIG. 6 which shows the state which inclined the holding table of the grinding device. (A) It is a figure which shows the distribution state of the curvature represented by the so-called bow value of the silicon wafer for support substrates of Example 1. FIG. (B) It is a figure which shows the distribution state of the curvature represented by what is called a warp value of the SOI wafer obtained using the silicon wafer for the support substrate. (A) It is a figure which shows the distribution state of the curvature represented by the so-called bow value of the disk-shaped silicon wafer for support substrates of the comparative example 1. FIG. (B) It is a figure which shows the distribution state of the curvature represented by what is called the warp value of the SOI wafer obtained using the silicon wafer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Silicon wafer for bonding 11a Oxide film 12 Silicon wafer 13 Disk-shaped silicon wafer 14 Intermediate wafer 21 SOI wafer 32 Holding table

Claims (6)

  A silicon wafer having a bowl-shaped warp in which a central portion is recessed by performing either or both of grinding and polishing on a thin disk-shaped wafer.   Convex convexly increased in thickness from the outer periphery of the wafer toward the wafer center by sucking and holding one main surface of a thin disc-shaped silicon wafer and performing either or both of grinding and polishing on the other main surface. After manufacturing the wafer, the other main surface formed in a convex shape is sucked and held, and the center of the one main surface is protruded by elastic deformation, and the one main surface is ground or polished. A method for producing a silicon wafer, characterized in that a main surface is flattened by performing either one or both of the processes, and a wafer having a bowl-shaped warp with a recessed central portion is obtained by releasing the suction and holding. .   A concave shape in which one main surface of a thin disc-shaped silicon wafer is held by suction and the other main surface is subjected to either or both of grinding and polishing to reduce the thickness from the wafer periphery toward the wafer center. After manufacturing the wafer, the other main surface formed in a concave shape is sucked and held, and the peripheral portion on the one main surface side is projected by elastic deformation, and the one main surface is either ground or polished. A method for producing a silicon wafer, characterized in that a main surface is flattened by performing either or both of the processes, and a wafer having a bowl-like warp with a recessed central portion is obtained by releasing the suction and holding.   A bonded SOI wafer formed of at least an SOI layer, an insulating layer, and a support substrate, and the center portion of the thin disk-shaped wafer is recessed by performing either or both of grinding and polishing. A bonded SOI wafer, wherein a silicon wafer to which a warp is applied is used as a support substrate, and the concave surface side of the silicon wafer is used as a main surface of the bonded surface.   A silicon wafer to which a bowl-shaped warp having a recessed central portion is provided by performing either or both of grinding and polishing on a thin disk-shaped wafer, and the support substrate is interposed through an oxide film. A bonded SOI wafer comprising: an active layer is formed by thinning the surface of the active layer substrate silicon wafer after the concave warped surface of the wafer for use and the silicon wafer surface for the active layer substrate are bonded together Manufacturing method.   A silicon wafer with a bowl-shaped warp with a concave in the center by applying either or both of grinding and polishing to a thin disk-shaped wafer is used as a support substrate, and is bonded via at least an oxide film. 6. The method for producing a bonded SOI wafer according to claim 5, wherein the concave warped surface of the supporting substrate wafer and the surface of the active layer substrate silicon wafer are mirror-polished.

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