JP4440810B2 - Manufacturing method of bonded wafer - Google Patents

Description

  The present invention relates to a method for manufacturing a bonded wafer, and more particularly, to a technique for grinding an outer peripheral portion including an unbonded portion of a bonded bond wafer.

As a wafer for a high-performance device, a bonded wafer in which a bond wafer and a base wafer are bonded together, and then a wafer on which an element is manufactured (bond wafer) is thinned is used.
As one of such bonded wafers, an SOI wafer is known. This can be manufactured, for example, as follows. That is, two mirror-polished silicon wafers (bond wafer and base wafer) are prepared, and an oxide film is formed on at least one of the wafers. And after bonding these wafers, it heat-processes at the temperature of 200-1200 degreeC, and raises bond strength. Then, the SOI wafer on which the SOI (silicon on insulator) layer is formed can be manufactured by grinding and polishing the element production side wafer (bond wafer) to reduce the film thickness to a desired thickness.

  In addition, in the case of manufacturing a bonded wafer, silicon wafers may be bonded directly without using an oxide film. In some cases, an insulating wafer such as quartz, silicon carbide, or alumina is used as the base wafer.

  When manufacturing an SOI wafer as described above, there are chamfered portions or portions called polishing sagging in which the thickness is slightly reduced on the outer peripheral portion of the two mirror-finished wafers to be bonded, and these portions are not joined. Or, it remains as an unbonded portion having a weak bonding force. If the bond wafer is thinned by grinding or the like with such unbonded portions present, a part of the unbonded portions will be peeled off during the thinning process. Therefore, the thinned bond wafer has a smaller diameter than the base wafer (base wafer), and minute irregularities are continuously formed in the peripheral portion.

When such a bonded wafer is introduced into the device process, the remaining unbonded portion is peeled off in the device process, generating particles and reducing the device yield.
In order to prevent this, it is necessary to previously remove the unbonded portion remaining on the outer peripheral portion of the bond wafer before thinning the bond wafer by grinding or the like. A portion where the unbonded portion is removed and the base wafer is exposed is referred to as a terrace portion.

For this reason, several methods have been proposed in the past for removing the unbonded portion remaining on the outer peripheral portion of the bond wafer in advance. As one of them, in Patent Document 1, grinding is performed such that the grindstone is relatively moved from the outer peripheral direction of the substrate toward the central direction, and then etched, whereby the outer periphery including the unbonded portion of the bond wafer. It is proposed to remove the part.
In this method, the outer peripheral portion of the bond wafer is ground from the side surface direction. Therefore, the damage to the terrace portion of the base wafer is less than that when grinding from the main surface direction, and the outer peripheral portion of the bond wafer can be ground thinly. And since the outer peripheral part of a bond wafer can be thinly ground, it has the advantage that subsequent etching can be performed in a short time.

  However, the conventional method including this method cannot completely prevent scratches and dimples generated in the terrace portion of the base wafer when the outer peripheral portion including the unbonded portion of the bonded bond wafer is removed. There was still room for improvement.

Japanese Patent Laid-Open No. 10-209093

  The present invention has been made in view of such a problem, and it is possible to further reduce damage to the terrace portion of the base wafer when the outer peripheral portion including the unbonded portion of the bonded bond wafer is removed. An object is to provide a method for producing a bonded wafer.

The present invention has been made in order to solve the above-described problems. At least, a bond wafer and a base wafer are bonded together, and an outer peripheral portion including an unbonded portion of the bonded bond wafer is ground to a predetermined width and then etched. In the method for manufacturing a bonded wafer by thinning the bond wafer,
Grinding the outer periphery of the bond wafer,
The first step of grinding the bond wafer so as to remove at least a part of the chamfered portion on the bonding surface side of the predetermined width of the outer peripheral portion to be ground,
A second step of grinding the bond wafer with a thickness that does not damage the base wafer, with respect to the remaining inner peripheral side of the predetermined width of the outer peripheral portion to be ground;
That it provides a method for manufacturing a bonded wafer, characterized in that performing by.

  As described above, in the present invention, the outer peripheral grinding process is divided into two times, and in the first process, the chamfered portion on the bonding surface side of the bond wafer that is chipped during grinding and causes a scratch on the terrace portion in advance is provided. Then, in the second step, the bond wafer is ground to a thickness that does not damage the base wafer as in the conventional case. For this reason, it is difficult for “chips” to occur on the outer periphery of the bond wafer during grinding, and there is little risk of damaging the terrace portion of the base wafer.

Further, in the method for manufacturing the bonded wafer of the present invention, in the first step, he has preferred to grind the bond wafer at an angle.

  Thus, if the bond wafer is ground obliquely in the first step, it is possible to prevent the grindstone used for grinding from directly hitting the base wafer. In addition, if grinding is performed obliquely, even if a “chip” occurs, it can be prevented from growing inward. This eliminates the possibility of damaging the base wafer.

The method for manufacturing the bonded wafer of the present invention, the grinding of the outer peripheral portion of the bond wafer, not the preferred performed so as to relatively move toward the center of the grinding wheel from the outer circumferential direction of the bond wafer.

  If grinding of the outer peripheral portion of the bond wafer is performed by relatively moving the grindstone from the outer peripheral direction of the bond wafer toward the central direction in this way, damage in the thickness direction of the wafer can be suppressed, and the base The bond wafer can be ground thinly while suppressing damage to the wafer.

At this time, in the second step, Ru can be ground to the bond wafer is 20~150μm thickness.

  Since the bond wafer can be thinly ground without damaging the base wafer in this way, the time required for the subsequent etching process can be shortened, and a high-quality bonded wafer can be produced with high productivity and low cost. Obtainable.

In the bonded wafer manufacturing method of the present invention, in the first step, the bond wafer is ground with a predetermined maximum allowance, and in the second step, the maximum allowance is smaller than the maximum allowance in the first step. it has preferred to grind the bond wafer.

Here, the “maximum machining allowance” when grinding a bond wafer is the maximum of the depth from the principal surface of the bond wafer before grinding (the principal surface opposite to the bonded surface side) to the ground surface after grinding. Refers to things.
In the present invention, the maximum machining allowance in the first step is increased as described above, and most of the chamfered portion on the bonding surface side of the bond wafer causing the chipping is removed. However, if the inner part is ground with the maximum machining allowance in the first process, the terrace portion of the base wafer may be damaged. Therefore, in the second step of grinding the inner peripheral side, the bond wafer is ground with a maximum machining allowance that is smaller than the maximum machining allowance of the first process so as not to damage the terrace portion of the base wafer.

The bonded wafer manufacturing method of the present invention, the bonding of the bond wafer and the base wafer, not the preferred conducted through the oxide film.

  When chipping occurs when grinding the outer peripheral portion of the bond wafer, there arises a problem that the broken piece damages the oxide film and the base wafer is etched in the subsequent etching. However, in the present invention, as described above, since the portion where the bond wafer is likely to be chipped is removed in advance and then etched, there is no possibility of such a problem.

In the manufacturing method of a bonded wafer of the present invention, the bond wafer and the base wafer, Ru can be a silicon single crystal wafer.

  In recent years, bonded wafers obtained by bonding silicon single crystal wafers such as SOI wafers have attracted attention, and quality requirements have become increasingly severe. According to the method for manufacturing a bonded wafer of the present invention, it is possible to manufacture a high-quality bonded wafer that can satisfy the strict quality requirements.

  As described above, according to the present invention, grinding of the outer peripheral portion of the bond wafer is performed in two steps, a first step and a second step. Then, in the first step, at least part of the chamfered portion on the bonding surface side of the outer peripheral portion of the bond wafer, that is, most of the portion where chipping is likely to occur, is removed, and then in the second step, the outer peripheral portion Grind the remaining part. For this reason, there is no fear of chipping during grinding of the outer peripheral portion of the bond wafer, and damage to the terrace portion of the base wafer can be further reduced.

The inventor has repeatedly studied factors that cause damage to the terrace portion of the base wafer when grinding the outer peripheral portion including the unbonded portion of the bond wafer. Among them, the present inventor has focused on “chips” that may occur on the outer peripheral portion of the wafer when the outer peripheral portion of the bond wafer is ground.
That is, as shown in FIG. 4, there are usually chamfered portions on the outer peripheral portions of the bond wafer 2 and the base wafer 3. For this reason, even if the bond wafer 2 and the base wafer 3 are bonded together, the chamfered portion of the bond wafer 2 becomes a “floating portion” from the base wafer 3. For example, in the conventional grinding method as shown in FIG. 4, the “floating portion” is not considered, and the “floating portion” is once measured by the grindstone 10c in the same manner as the other portions. (Fig. 4 (a)). For this reason, after grinding, as shown in FIG. 4B, the “floating part” (the part surrounded by a circle in FIG. 4B) becomes extremely thin compared to the other parts, and is being ground. The “floating part” had a “chip”. Due to the chipping, a part of the oxide film underneath is peeled off, or fragments due to the chipping damage the oxide films 4 and 5 on the terrace portion of the base wafer. As a result, the etching of the base wafer 3 is performed by the subsequent etching. This caused damage such as generating dimples on the terrace.

  Therefore, the present inventor performs grinding of the outer periphery of the bond wafer in two steps, a first step and a second step, and in the first step, the “floating portion” in which the bond wafer is easily chipped in advance. If the bond wafer is ground to a thickness that does not damage the base wafer in the second step, it will be difficult for chipping to occur on the outer periphery of the bond wafer during grinding. The present invention has been completed by conceiving that there is no risk of damaging the terrace portion of the base wafer.

  That is, the method for manufacturing a bonded wafer according to the present invention includes at least bonding a bond wafer and a base wafer, grinding an outer peripheral portion including an unbonded portion of the bonded bond wafer to a predetermined width, and then etching to remove. Then, in the method of manufacturing a bonded wafer by thinning the bond wafer, grinding the outer peripheral portion of the bond wafer is performed on the bonded surface side with respect to the outer peripheral side of the predetermined width of the outer peripheral portion to be ground. The first step of grinding the bond wafer so as to remove at least a part of the chamfered portion of the wafer, and the remaining inner peripheral side of the predetermined width of the outer peripheral portion to be ground with a thickness that does not damage the base wafer And a second step of grinding the bond wafer.

The method for producing the bonded wafer according to the present invention will be described more specifically with reference to the drawings.
FIG. 1 is an explanatory view showing a case where the outer peripheral portion of a bond wafer is ground by the method of the present invention. The bonded wafer 1 used here is a wafer in which the base wafer 3 and the bond wafer 2 covered with the oxide film 4 are heat-treated in an oxidizing atmosphere and bonded together. The entire surface of the bonded wafer 1 is It is covered with an oxide film 5 generated by heat treatment in an oxidizing atmosphere.

First, as shown in FIG. 1A, in the first step, at least a part of the chamfered portion on the bonding surface side of the bond wafer 2 by the grindstone 10a on the outer peripheral side of the predetermined width of the outer peripheral portion to be ground. The bond wafer 2 is ground so as to remove.
Here, most of the “floating portion” of the bond wafer 2 is removed in advance. For example, when the predetermined width (terrace width) of the outer peripheral portion to be ground is 3 mm and the chamfered portion before grinding is about 0.3 to 0.4 mm, the chamfered portion on the bonding surface side of the bond wafer 2 is 0. Grind so that only about 05-0.1 mm remains.

  Moreover, the grindstone 10a used here can grind the chamfered part of the bonded wafer 2 on the bonding surface side obliquely. If such a grindstone 10a is used to grind obliquely, there is little possibility that the grindstone 10a directly hits the base wafer 3. In addition, if grinding is performed obliquely, even if a “chip” occurs, it can be prevented from growing inward. For this reason, there is no fear of damaging the terrace portion of the base wafer 3.

Next, as shown in FIG. 1B, in the second step, the position of the grindstone 10a is relatively shifted upward, away from the bonding surface, and the remaining thickness is increased so that the base wafer 3 becomes thicker. The bond wafer 2 is ground with a thickness t that does not cause damage.
However, since most of the “floating portion” of the bond wafer 2 is previously removed in the first step, there is no possibility of “chip” in the second step.

  At this time, in FIG. 1, in order to grind and remove the outer peripheral portion of the bond wafer 2 to a predetermined thickness t, the grindstone 10a is ground by moving relatively from the outer peripheral direction of the bond wafer 2 toward the central direction. Like to do.

  In this case, for example, the height and distance of the bonded wafer 1 and the grindstone 10a are kept at predetermined positions, rotated in opposite directions by a rotation mechanism (not shown), and horizontally moved by the movement mechanism (not shown). Then, the outer periphery of the bond wafer 2 is ground toward the center of the wafer. Conversely, the position of the grindstone 10a may be fixed, the bonded wafer may be moved horizontally by a moving mechanism (not shown), and the outer periphery of the bond wafer 2 may be pressed against the grindstone 10a.

  The predetermined thickness t after the outer periphery grinding of the bond wafer 2 can be controlled by adjusting the positional relationship in the height direction between the grindstone 10a and the bond wafer 2. In the present invention, the predetermined thickness t can be set to 20 to 150 μm by adjusting the relative height position of the grindstone 10 a and the bond wafer 2.

  If grinding of the outer peripheral portion of the bond wafer 2 is performed by relatively moving the grindstone 10 from the outer peripheral direction of the bond wafer 2 toward the center direction in this way, damage in the thickness direction of the wafer can be suppressed. The bond wafer can be thinly ground without damaging the base wafer. Furthermore, since it can be thinly ground, the time for the subsequent etching process can be shortened, and a high-quality bonded wafer can be obtained with high productivity and low cost.

FIG. 1C shows the bonded wafer 1 after the outer peripheral portion has been ground in two steps.
As can be seen from the figure, in the first step, the bond wafer 2 is ground with a predetermined maximum allowance (d ₁ ), and in the second step, the maximum allowance (d ₂ ) is less than the maximum allowance in the first step. The bond wafer 2 is ground. By doing so, it is possible to reliably reduce the “floating portion” and suppress the occurrence of chipping as compared with the case where the outer peripheral portion is ground at a time.
As shown in FIG. 1 (c), the “maximum machining allowance” when the bond wafer 2 is ground is the maximum depth from the main surface of the bond wafer before grinding to the ground surface after grinding. Point to.

On the other hand, FIG. 2 is explanatory drawing which showed another example in the case of grinding the outer peripheral part of a bond wafer by the method of this invention.
Here, as in the example shown in FIG. 1, first, as shown in FIG. 2 (a), in the first step, a part of the chamfered portion on the bonding surface side of the bond wafer 2 is formed by the grindstone 10b. The bond wafer 2 on the outer peripheral side of the predetermined width is ground so as to be removed. Then, as shown in FIG. 2 (b), in the second step, the position of the grindstone 10b is relatively shifted upward so that the remaining thickness is increased on the remaining inner peripheral side to damage the base wafer 3. The bond wafer 2 is ground at a thickness t that does not give the thickness. FIG. 2C shows a bonded wafer after the outer peripheral portion is ground.

  The difference from the example of FIG. 1 is the shape of the grindstone 10b and the shape of the bond wafer 2 after grinding. That is, in the example of FIG. 2, the bond wafer is not ground obliquely in the first step. However, even in this case, since most of the “floating part” of the bond wafer 2 is previously removed in the first step, the “chip” that occurs during grinding is significantly larger than when grinding at one time. Can be reduced.

  In the above two examples, grinding is performed such that the grindstone is relatively moved from the outer peripheral direction of the bond wafer 2 toward the central direction. However, in addition to this, in the present invention, grinding can be performed by relatively moving the grindstone from the main surface direction (upper side) of the bond wafer toward the lower side.

Below, the outline of the whole manufacturing method of a bonded wafer is demonstrated with reference to FIG.
First, a bond wafer 2 and a base wafer which are raw material wafers (silicon single crystal wafer: for example, 8 inches (200 mm) in diameter, oriented <100> manufactured by the Czochralski method) for manufacturing an SOI wafer by bonding 3 is prepared (FIG. 3A). Then, among the prepared silicon single crystal wafers, the bond wafer 2 is subjected to heat treatment to form an oxide film 4 on the bond wafer surface (FIG. 3B).
Of course, an oxide film may be formed on the base wafer 3 instead of the bond wafer 2.

  Next, the bond wafer 2 and the base wafer 3 on which this oxide film is formed are bonded together in a clean atmosphere (FIG. 3C). This is subjected to a heat treatment in an oxidizing atmosphere to bond the bond wafer 2 and the base wafer 3 firmly to obtain a bonded wafer 1. As the heat treatment condition, for example, the heat treatment may be performed at a temperature of 200 ° C. to 1200 ° C. in an atmosphere containing oxygen or water vapor (FIG. 3D). At this time, the bond wafer 2 and the base wafer 3 are firmly bonded to each other, and an oxide film 5 serving as an etching film in a subsequent process is formed on the entire outer surface of the bonded wafer 1.

  An unbonded portion of the bond wafer 2 and the base wafer 3 exists in the outer peripheral portion 1 to 3 mm of the bonded wafer 1 thus bonded. Such an unbonded portion cannot be used as an SOI layer for manufacturing a device, and is peeled off in a later process to cause various problems, and thus needs to be removed.

  In order to remove the unbonded portion, as shown in FIG. 3E, first, the outer peripheral portion of the bond wafer 2 where the unbonded portion exists is ground and removed to a predetermined thickness. This is because grinding can be removed at high speed and the processing accuracy is good.

  The present invention is applied to an outer peripheral grinding step for removing the unbonded portion, and the outer peripheral portion of the bond wafer is ground in two steps. A detailed description of these steps has been described above.

  Next, as shown in FIG. 3F, the outer peripheral portion including the unbonded portion of the bond wafer 2 is completely removed by etching, and the terrace portion 7 is formed. This can be easily performed by immersing the bonded wafer 1 in an etching solution in which the etching rate of the silicon single crystal is significantly higher than that of the oxide film. That is, the outer peripheral portion of the bond wafer 2 is etched by the etching solution because silicon is exposed by grinding, but the other portion of the bonded wafer 1 is etched because it is covered with the oxide film 5. Not. Examples of such etching include so-called alkaline etching with KOH, NaOH, or the like.

  Finally, as shown in FIG. 3G, if the surface of the bond wafer 2 is thinned to a desired thickness by grinding and polishing according to a normal method, an SOI wafer having the SOI layer 6 can be manufactured. .

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Examples and comparative examples)
First, 20 CZ substrates with a diameter of 150 mm (6 inches), a thickness of 625 microns, a conductive p-type, and a resistivity of 4 to 6 Ω · cm are prepared, 10 for a bond wafer and 10 for a base. Classified for wafers. Then, these wafers were combined in accordance with the steps (a) to (d) of FIG. 3, and 10 bonded substrates as shown in FIG. 3 (d) were produced.

  Of these, five sheets were ground in two steps as shown in FIG. 1 (Example), and the remaining five sheets were ground in one step as shown in FIG. 4 (comparative example). ).

That is, as a grinding condition of the example (FIG. 1), a # 800 diamond grindstone was used, and they were reversely rotated at a circumferential speed of 1600 m / min of the grindstone and a peripheral speed of 300 mm / min of the wafer. The grinding speed was 0.6 mm / min. In the first step (FIG. 1 (a)), the outer peripheral side of the outer periphery of the bond wafer is ground so that only 0.1 mm of the chamfered portion of 0.3 mm before grinding remains (maximum machining allowance). The remaining thickness at the part is 15 μm). Next, in the second step, the remaining inner peripheral side of the outer periphery of 3 mm was ground so that the position of the grindstone 10a was relatively shifted upward to a thickness of 80 μm.
On the other hand, in the comparative example (FIG. 4), the outer periphery of the bond wafer was ground in about 3 mm with a grinding wheel 10c until the thickness reached 80 μm under the same grinding conditions as in the “second step” of the above example. .

  In this way, the condition is such that about 130 microns of silicon single crystal are etched so that the unbonded portion of the ground outer periphery of the 10 bonded substrates on which the outer periphery of the bond wafer has been ground is completely removed. The substrate was immersed in a 50% NaOH solution for about 3.5 hours to completely remove the unbonded portion on the outer periphery of the wafer.

Thereafter, usual grinding and polishing were performed, and a bonded substrate having an SOI layer having a thickness of 2 microns as shown in FIG.
The number of scratches present on the terrace portion 7 on the surface of the base wafer 3 of the 10 SOI substrates thus formed was counted with an optical microscope.
As a result, 20 to 50 scratches / sheet were observed in the ground by the method of the comparative example, which is a conventional method, but in the ground ground by the method of the present invention, scratches caused by grinding were observed. Was not detected.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

  For example, in the above embodiment, the description has focused on the case where two semiconductor substrates, in particular, a silicon wafer are bonded to produce a bonded substrate, but the present invention is directed to a semiconductor substrate and quartz, silicon carbide, silicon nitride, alumina, Even when an insulating substrate such as sapphire or another ceramic material is bonded to produce a bonded substrate, a peripheral unbonded portion is generated, which is effective in removing this.

It is explanatory drawing which showed the case where the outer peripheral part of a bond wafer was ground by the method of this invention. It is explanatory drawing which showed another example in the case of grinding the outer peripheral part of a bond wafer with the method of this invention. It is explanatory drawing which showed the outline of the manufacturing method of a bonded wafer. It is explanatory drawing which showed the case where the outer peripheral part of a bond wafer was ground by the conventional method.

Explanation of symbols

1 ... Bonded wafer, 2 ... Bond wafer, 3 ... Base wafer,
4, 5 ... oxide film, 6 ... SOI layer, 7 ... terrace part,
10a, 10b, 10c ... Whetstone.

Claims (7)

At least by bonding the bond wafer and the base wafer, grinding the outer peripheral portion including the unbonded portion of the bonded bond wafer to a predetermined width, and then removing by etching, and then thinning the bond wafer In a method for manufacturing a bonded wafer,
Grinding the outer periphery of the bond wafer,
A first step of grinding the bond wafer so as to remove at least a part of the chamfered portion on the bonding surface side of the width of the unbonded portion of the outer peripheral portion to be ground;
A second step of grinding the bond wafer with a thickness that does not damage the base wafer, with respect to the remaining inner peripheral side of the width of the unbonded portion of the outer peripheral portion to be ground;
The manufacturing method of the bonding wafer characterized by performing by these.   The method for producing a bonded wafer according to claim 1, wherein in the first step, the bond wafer is ground obliquely.   The bonded wafer according to claim 1 or 2, wherein grinding of the outer peripheral portion of the bond wafer is performed by relatively moving the grindstone from the outer peripheral direction of the bond wafer toward the center direction. Manufacturing method.   4. The method for manufacturing a bonded wafer according to claim 1, wherein in the second step, grinding is performed until the bond wafer has a thickness of 20 to 150 μm. 5.   In the first step, the bond wafer is ground with a predetermined maximum allowance, and in the second step, the bond wafer is ground with a maximum allowance smaller than the maximum allowance in the first step. The manufacturing method of the bonding wafer as described in any one of Claims 1 thru | or 4.   6. The method for producing a bonded wafer according to claim 1, wherein the bonding of the bond wafer and the base wafer is performed through an oxide film.   The method for manufacturing a bonded wafer according to any one of claims 1 to 6, wherein the bond wafer and the base wafer are silicon single crystal wafers.

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