JP2846994B2 - Semiconductor wafer bonding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for bonding semiconductor wafers such as SOI wafers, which does not cause microscopic defects such as crystalline strain at the bonding interface.

[0002]

2. Description of the Related Art A silicon single crystal is grown on an insulator.
SOI structure is next generation due to its high breakdown voltage, high speed, etc.
Has attracted attention as a substrate for semiconductor devices
However, in recent years, large areas have no crystal defects,
SOI structure that can freely control element concentration etc.
It can be obtained relatively easily by the wafer bonding method.
I came. SOI way produced by this lamination
C) Surface of silicon single crystal substrate
It is driven into a strip at a position several μm from the surface, and then heat-treated
Oxygen atoms rearranged by_TwoS forming a layer
IMOX method (Separation by IM
planted Oxygen) and pre-applied S
iO_TwoThe polycrystalline silicon having a thickness of several μm is vapor-phase grown thereon,
ZMR method that melts by laser and single crystallizes
(Zone Melting Recrystalli
zation), etc.
Good crystallinity, use thermal oxidized interface for device side
Si-SiO _TwoThe interface is stable,
It has the advantage that the equipment for mass production is inexpensive.
You.

However, since the bonding step for obtaining such an SOI wafer is performed immediately after cleaning for imparting hydrophilicity, silanol remaining on the surfaces of the two semiconductor wafers before bonding is obtained. Groups (Si-OH), hydrogen ions, and the like are taken into the bonding interface and react by heat treatment after bonding to form bubbles, resulting in voids (bubbles).
Defects easily occur. Further, in addition to these relatively large defects, microscopic crystal distortion generated at the bonding interface due to uneven adhesion at the time of bonding and the like, especially when the device fabrication side is polished to a submicron level, the device may be damaged. Since the electrical characteristics are remarkably deteriorated, its occurrence must be prevented. For this purpose, various bonding methods for suppressing the occurrence of various defects at the bonding interface have been attempted.

For example, JP-A-61-145839, JP-A-63-19807, and JP-A-64-40
No. 13, JP-A-1-169917, and JP-A-2
In JP-A-56918 and the like, as shown in FIG. 5, one semiconductor wafer 1 is bent in a so-called convex shape in which the central portion of the bonding surface protrudes from the peripheral portion, and There is disclosed a method of performing bonding by bringing the semiconductor wafer 2 into contact with the bonding surface of the other semiconductor wafer 2 as a bonding start point.
Japanese Patent Application Laid-Open No. 1-122142 discloses a method of performing bonding while applying a stress in a direction along a contact surface, and Japanese Patent Application Laid-Open No. 2-135722 discloses that at least one principal surface has a shrinkage stress on a substrate. Japanese Patent Application Laid-Open No. Hei 2-267951 discloses a method in which a film that generates a tensile stress is formed and bonded, and a method in which the same pressure is applied from both sides of two wafers to each other. In
Japanese Patent Application Laid-Open No. 3-94416 discloses a method of decompressing the atmosphere surrounding both wafers after bonding the two wafers, and a method of forming a curved surface by removing an oxide film on a surface opposite to a bonding surface and then performing bonding. Are disclosed.

[0005] Japanese Patent Application Laid-Open No. 62-71215 discloses
JP-A-63-9922, JP-A-1-132112
Various types of bonding apparatuses for implementing these bonding methods have been proposed in Japanese Patent Laid-Open Publication No. Hei.

[0006]

However, by using these bonding methods and bonding apparatuses, it is possible to suppress the occurrence of relatively large defects such as voids on the wafer bonding surface as described above. It is difficult to suppress the occurrence of typical crystalline strain. In particular, since these methods start bonding from the center point of the bonding surface of the wafer that has been accumulated in a convex shape, concentric crystalline strains that spread at equal intervals from the center point to the periphery occur. There was a problem that it was easy to do.

Accordingly, the present invention provides a method of bonding wafers in which concentric crystalline strain does not occur,
That is the purpose.

[0008]

Such a problem is solved by the present invention described below. That is, in the method of bonding a semiconductor wafer in which at least one of the first wafer and the second wafer is curved and deformed into a convex bowl shape and their bonding surfaces are overlapped with each other, the periphery of the first wafer is A part of the part and a point of the peripheral part of the second wafer are matched to be a bonding start point, and the opposite pole point opposite to the bonding start point across the center point of the bonding surface of these wafers is set as a bonding end point. The joining is sequentially advanced from the joining start point to the joining end point.

[0009]

According to the present invention, the starting point of bonding is one point around the wafer. The lamination proceeds sequentially in the radial direction sequentially from the starting point as a starting point. Then, the opposite pole point in the peripheral portion on the opposite side in the diameter direction is set as the end point of the bonding.
According to this method, the gas remaining between the two wafers is discharged toward the end direction of the bonding as the bonding progresses on the same principle as the conventional method. As a result, relatively large defects such as bubbles at the bonding interface can be completely prevented. Since the bonding start point is located at the peripheral edge of the wafer, the bonding mechanism changes and the stress at the interface is reduced, so that concentric microscopic shapes which have conventionally occurred from the bonding start point are used as starting points. Generation of crystalline strain can be completely suppressed.

Hereinafter, a specific configuration of the present invention will be described in detail. For example, an SOI wafer to which the bonding method of the present invention is applied and bonded by bonding two silicon wafers with a thermal oxide film interposed therebetween has good crystallinity in the device fabrication region, and has an interface on the thermally oxidized side. A wide range of applications is expected because of its stability and easy mass production. Normally, the bonding of this SOI wafer is performed by first directly superposing two hydrophilic silicon wafers,
The bonds are formed by hydrogen bonding or van der Waals force. As cleaning for imparting hydrophilicity to the wafer surface, SC-1 cleaning (a method of heating a mixed solution of NH ₄ OH / H ₂ O / H ₂ O ₂ to 80 ° C. for cleaning) is frequently used. . Next, a heat treatment is performed on the superposed wafers at a high temperature of 1000 ° C. or more to complete the bonding. Finally, the surface on the side where the device of the wafer is to be manufactured is processed to a desired thickness by surface grinding, polishing, etching or the like. If the conditions of the laminating step are insufficient, the above-described defect may be generated at the bonding interface.

In the present invention, in order to prevent the occurrence of this defect, at least one of the two wafers is bent. As shown in FIG. 1, the second wafer 2 is deflected with respect to the first wafer 1 in an undeformed state, and the first wafer 1 and the second The bonding with the wafer 2 is performed. There is no particular limitation on the bending angle at this time, and a bending angle that is advantageous for the bonding step may be selected. The joining start point 3 does not need to be at the orientation flat position, and the joining can be started from any point on the peripheral edge. Here, the thickness of the second wafer is preferably 100 μm to 900 μm. Below this range, the strength is insufficient, and above this range, the deflection is insufficient. In another aspect of the present invention, the first
The active layer as the wafer may be bent to join the two bent wafers. In this case, since the two wafers are bonded in a similar state, it can be expected that prevention of the occurrence of microscopic crystalline strain will be more effective.

In the method of the present invention, the bonding step is performed using the following jig. FIG. 2 shows this jig 2
1 is shown. The jigs 21 are, for example, in the form of a disk made of Teflon, as shown in FIGS. Is formed with a hole 22 for vacuum suction. The peripheral portion of the wafer is deformed by placing the wafer on the upper surface and performing vacuum suction through the hole 22. The absence of crystalline strain in the bonded wafer can be confirmed by X-ray topography.
If this method is used in combination with a method for evaluating a defective layer by measuring the thermal wave signal and measuring the lifetime, it is possible to more reliably confirm that there is no defective layer.

The above-described method for bonding a semiconductor wafer according to the present invention is applicable to a case where no air bubbles are trapped between the first and second wafers at the time of bonding and a concentric distortion is generated. Since the bonding start point serving as the starting point exists at the peripheral portion of the wafer, it is possible to effectively prevent the occurrence of microscopic crystalline strain. If the first wafer and the second wafer are bonded under reduced pressure, the effects of the present invention can be further enhanced.

[0014]

Embodiments of the present invention will be described below in detail. P-type whose surface is mirror polished, (100), diameter 5 inches, thickness 620 μm, specific resistance 3 Ω · cm, oxygen concentration [O
i] Prepare two silicon wafers of <1.5 × 10 ¹⁸ cm ⁻³ (old ASTM). These two silicon wafers were overlaid at room temperature and bonded by the method of the present invention. Then, two silicon wafers were integrated by heat treatment at 1100 ° C. for 120 minutes to obtain a bonded wafer A. Separately, as a comparative product, a normal bonding method (a method using the center of the bonding surface as the bonding start point)
To obtain a wafer B. The number of samples was 10 each.

These bonded wafers A and B were evaluated by a usual X-ray topography method. As a result, no concentric distortion was observed in all ten wafers A, whereas microscopic crystal distortion was observed in eight out of ten wafers B. FIG. 3 shows a photograph of the wafer A without distortion, and FIG. 4 shows a photograph of the wafer B with distortion produced by the X-ray topography method. Furthermore, when the presence or absence of crystalline strain was evaluated by a thermal wave signal measurement method and a lifetime measurement method, similar results were obtained. From these results, it is clear that the bonding method of the present invention can reliably prevent defects such as bubbles and crystal distortion.

[0016]

According to the method for bonding semiconductor wafers of the present invention, by setting the starting point of bonding to one point on the peripheral portion of the wafer, it is possible to prevent the generation of any defects which easily occur at the bonded wafer interface.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a method for bonding a semiconductor wafer according to the present invention.

FIG. 2 is a schematic view of a bonding jig used in the method of the present invention.

FIG. 3 is an XRT photograph of a bonded semiconductor wafer obtained by the method of the present invention.

FIG. 4 is an XRT photograph of a bonded semiconductor wafer obtained by a conventional method.

FIG. 5 is a schematic view showing an example of a conventional semiconductor wafer bonding method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st wafer 2 2nd wafer 3 Lamination start point

──────────────────────────────────────────────────の Continuing on the front page (72) Hisashi Furiya 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Central Research Laboratory, Mitsubishi Materials Co., Ltd. (72) Takayuki Shinginai 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Address: Mitsui Materials Co., Ltd. Central Research Laboratory Examiner Makoto Onoda (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/02

Claims (1)

(57) [Claims] 1. A bonding method for a semiconductor wafer in which at least one of a first wafer and a second wafer is curved and deformed so that bonding surfaces thereof are overlapped with each other. And a point on the periphery of the second wafer are matched to define a bonding start point, and the opposite pole point opposite to the bonding start point across the center point of the bonding surfaces of these wafers is defined as a bonding end point. A bonding method of a semiconductor wafer, wherein bonding is sequentially advanced from a start point to a bonding end point.