JPH06104411A - Method for forming soi structure - Google Patents

Abstract

PURPOSE:To prevent bubbles in a bonding step surely without using a complicated step, by inserting a wedge-shaped part between a silicon substrate and another board so that the bonding faces are projected to each other when these substrate are bonded. CONSTITUTION:A wedge-shaped clamped part 5 is put between a silicon substrate 1 and the other substrate 4 to be bonded so that a gap is generated along a circumferential part thereof. The lower wafer as the substrate 4 is fixed by a supporting stage 6, such as a flat suction stage. Then, the substrate 1 is supported by four points of the wedge-shaped clamped part 5 and put above the substrate 4. During the bonding, a central part of the silicon substrate 1 is put under pressure so that bonding faces become projected to each other while the boards 1 is pressed to the substrate 4. Consequently, force gradually getting away outward works at the wedge-shaped part 5 so that the bonding proceeds from the central part to the boundary part of the substrate 1, and good bonding without bubbles can be ensured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method of forming an SOI structure. The SOI is used, for example, as a structure of an electronic component such as a semiconductor device, and the present invention can be used as a method of forming various SOI structures.

[0002]

2. Description of the Related Art Conventionally, SOI (Sinlicon on Insula)
The tor) structure is a method in which a silicon portion is present on an insulating portion and various semiconductor elements are formed on the silicon portion, and is mainly used in the field of electronic materials.

As one of the means for forming this SOI structure,
There is known a technique in which a silicon substrate is formed on an insulating portion by laminating another substrate on the surface of the silicon substrate on which the insulating portion is formed and polishing the silicon substrate. This is generally called a bonded SOI or the like.

A conventional method of forming such a bonded SOI structure will be described with reference to FIG.

A silicon substrate 1 as shown in FIG.
By using a photolithography technique or an etching technique to pattern one side of one side of the wafer (generally using a high flatness silicon wafer, which will be referred to as a substrate A), and further forming a SiO ₂ film on this side. The insulating part 2 is formed. As a result, as shown in FIG. 6B, a structure is obtained in which the insulating portion 2 is formed on one side of the silicon substrate 1. The insulating portion 2 is formed as a film having irregularities as shown in the figure according to the surface shape of the patterned silicon substrate 1. The structure of FIG. 2B shows a state in which a polysilicon film 3 is further formed on the insulating portion 2. The polysilicon film 3 will be formed on another substrate (see FIG. 6D) in a later step.
This is for forming a highly smooth mating surface when the substrates 4) shown by are bonded together.

Next, the surface of the polysilicon film 3 is flattened and polished to form a highly smooth surface (FIG. 6 (c)).

Another substrate 4 (referred to as substrate B) is brought into close contact with the polished surface of the polysilicon film 3. Both surfaces are joined by the tight compression bonding, and as a result, a joining structure as shown in FIG. 6D is obtained. Generally, it is said that a firm bond is achieved by hydrogen bonding due to the action of water existing on both sides. This is usually heated to heat bond,
Achieve a very strong fit. The bonding strength is generally 200Kg / cm ² or more, and in some cases 2,000
It can be as ^high as 0 kg / cm ² . As another substrate 4 (substrate B) to be bonded together, a silicon substrate similar to the substrate 1 (substrate A) is usually used. Since a heating step is often performed after laminating, inconvenience may occur unless physical properties such as thermal expansion are not the same. If such a problem does not exist, this is not necessarily a silicon substrate, since the other substrate 4 only serves as a support base in the illustrated technique, for example. However, when an element is formed on another substrate 4 (substrate B) to be bonded together, it is necessary that the semiconductor substrate is an element formable semiconductor substrate.

Next, the side peripheral portion is chamfered, and FIG.
The structure of 6E is upside down from FIG. 6D, but this is because the substrate 1 is turned upside down for the chamfering and the next grinding.

After that, the surface of the substrate 1 is ground, and the surface of FIG.
The structure is (f). This surface grinding is stopped before the insulating part 2 is exposed.

Next, selective polishing is performed. Here, polishing is performed with precision finishing until the insulating portion 2 is just exposed.
As a result, as shown in FIG. 6G, a structure in which the silicon portion 10 is surrounded by the uneven insulating portion 2 and the silicon portion 10 exists on the insulating portion 2 is obtained. In the structure (SOI structure) in which the silicon portion 10 exists on the insulating portion 2 in this manner, various elements are formed on the silicon portion 10. In the structure of FIG. 6G, since each silicon portion 10 is surrounded by the insulating portion 2, the element isolation is performed from the beginning.

FIG. 6 shows one silicon part for clarity of illustration.
Although 10 is illustrated in a large scale, in reality, many such fine silicon portions 10 are aggregated.

[0012]

Problems to be Solved by the Invention In the formation of the bonded SOI structure as described above, there are times when bubbles are formed at the bonded interfaces. Explaining with reference to FIG. 6, FIG.
In the above, when the surface of the silicon film 3 on the substrate 1 and the substrate 4 are bonded together, bubbles may be generated at this interface. Bubbles may be generated in a size of 0.5 mm to 5 mm, for example.

Since the joining surface is not in close contact with the portion where bubbles are generated, sufficient joining is not performed and the portion easily peels off.
For example, after the surface grinding shown in FIG. 6 (f), since the substrate 1 on the substrate 4 has a thin film thickness t ₁ of 4 to 20 μm, usually about 5 to 10 μm, bubbles 5 are present. If it is, it will come off easily. This is a source of pollution and may have an important influence on device formation. For example, polishing may cause scratches on the wafer. In this way, the peeling due to the air bubbles causes contamination and impairs the reliability of the device. In the state of FIG. 6 (g), the silicon portion 10 on the substrate 4 has a thinner film thickness t ₂ of about 3 to 4 μm, and if it is peeled off here, it becomes a pollution source as well. Furthermore, it may become a defective element.

For this reason, it is necessary to prevent bubbles from being generated at the bonded portions of both substrates.

Conventionally, when forming a bonded SOI,
In order to prevent bubbles from being generated between the two substrates to be bonded together, as shown in FIG. 5B, the surface of, for example, a semiconductor wafer used as the substrate 1 is made to have a convex shape and is made to be convex toward another substrate 4. We are doing the gluing. This can be achieved by removing the oxide film (insulating film) on one surface (back surface) of the silicon substrate 1 (see FIG. 5A). This is because there is a difference in expansion coefficient between the front and back surfaces.

In order to make the silicon substrate 1 convex as described above, the insulating films 2 and 2a formed simultaneously on the front and back surfaces by treating the silicon substrate 1 as shown in FIG. 5A.
Of the (oxide film) and the polysilicon films 3 and 3a, the insulating film 2a and the polysilicon film 3a on the back surface may be removed.

For this purpose, however, it is necessary to take measures such as removing the polysilicon film 3a on the back surface by polishing and then removing the insulating film 2a (oxide film) by etching. This is an extremely complicated process and takes time.

Further, in order to confirm whether or not it is surely convex, it is necessary to confirm the curvature with a flatness measuring instrument. This is because if it does not surely become convex and is in a different warped state, it will not be possible to carry out laminating without bubbles. As described above, the conventional technique requires a large number of man-hours.

[0019]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, does not require complicated steps such as polishing and etching for making the bonding surface convex, and the warped shape of the bonded substrates is It is an object of the present invention to provide a method for forming a bonded SOI structure capable of achieving a bonding in which bubbles are not reliably generated in any state.

[0020]

According to the present invention, a silicon substrate having an insulating portion formed on one of the gutters is bonded to another face of the silicon substrate having the insulating portion formed thereon, and the other of the silicon substrates is attached. In a method of forming an SOI structure in which a silicon portion is present on an insulating portion by polishing a gutter surface, a method of forming an SOI structure, wherein the silicon substrate and another substrate are bonded together, an outer peripheral portion between the both substrates is provided. A method for forming an SOI structure, characterized in that at least one of the two substrates is bonded to the bonding surface in a convex state by interposing an object to be sandwiched in the SOI structure. It achieves the purpose.

In the present invention, the object to be sandwiched is an object which is sandwiched between the substrates at the outer peripheral portions of the substrates to be bonded together and interposed therebetween. For example, referring to an example of FIG. 1 showing an embodiment of the present invention which will be described in detail later, the object to be sandwiched 5 is an outer peripheral portion between a silicon substrate 1 and another substrate 4 to be bonded thereto. In FIG. 1, any one can be used as long as it can be sandwiched between the substrates 1 and 4 as illustrated. Preferably, the object to be sandwiched 5 has a tapered surface with respect to at least one of the substrates 1 and 4. This tapered surface preferably has a taper toward at least the substrate desired to be convex. More preferably, the object to be sandwiched 5 having a tapered surface with respect to both substrates, and particularly preferably a wedge-shaped object.

In general, the silicon substrate 1 may be convex with respect to the substrate 4, but it need only be relatively convex, and at least one of the substrates 1 and 4 faces the other. Then, the laminating surface may be convex.

[0023]

According to the present invention, since the bonding surfaces of the substrates to be bonded are convex to each other toward the other, the bonding is performed from the central portion of the bonding surface to the outer peripheral portion. It is done in a combined form. As a result, bonding can be performed without bubbles.

In the present invention, since the convex state is forcibly and reliably achieved by the object to be sandwiched, even if the warp shape of the substrates to be laminated is any, the bubble-free laminating by the above action is achieved. Can be realized.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. However, as a matter of course, the present invention is not limited to the following examples.

Embodiment 1 In this embodiment, the present invention is applied to the manufacture of a silicon semiconductor integrated circuit device having an SOI structure.

In this embodiment, as conceptually shown in FIG. 1 as viewed from the side surface at the time of bonding, the silicon substrate 1 (insulating film 2 and, if necessary, a polysilicon film for forming a smooth surface) is formed. 3 and the like (not shown) and another substrate 4 to be bonded to this, both substrates 1,
A wedge-shaped object to be sandwiched 5 is sandwiched and interposed in the outer peripheral portion of 4.

In the present example, as shown in the conceptual view seen in a plane in FIG. 2, wedges are put at four points to make the object to be pinched 5, thereby forming a gap in the outer peripheral portion.

As shown in FIG. 1, the lower wafer which is the substrate 4 is fixed to the flat suction stage which is the support stage 6. A substrate 1 (wafer) supported by four points of the sandwiched object 5 (wedge) is brought on top of it. Object 5
The contact portion between the (wedge) and the silicon substrate 1 is enlarged and shown in FIG. Here, the protrusion length T ₁ of the sandwiched object 5 (wedge) is set to 1 to 1.5 mm. Since the length T ₂ of the chamfered portion of the wafer which is the silicon substrate 1 is about 1 mm, it is the same as or slightly longer.

At the time of bonding, as shown in FIG. 4, the central portion of the silicon substrate 1 (upper wafer) is pressed, the bonding surface is bent so as to be convex, and pressed against the substrate 4 (lower wafer). To do. At that time, the sandwiched object 5 forming the wedge is gradually released outward. When the object to be clamped 5 is formed in a wedge shape as in this example, it has a tapered surface and both surfaces are tapered surfaces, so that the operation of releasing the object to be clamped 5 to the outside in accordance with the bonding is smooth at this time. Proceeding to step 3, good bonding can be achieved.

In FIG. 4, 7 is a pressing means for pressing the substrate 1 for bonding, 72 is a convex pressing portion in contact with the substrate 1, 71 is a space between the pressing portion 72 and the body of the pressing means 7. Is a biasing means (spring). Reference numeral 51 denotes an arm that integrally supports the object to be clamped 5, and forms a sliding portion 52 at the base of the arm, which is a truncated cone part of the slider 8 that moves the object to be clamped 5 (wedge) outward. It is slidably in contact with 81 as shown. In this structure, the pitch (A) or the pressing force of the urging means 71 is detected, and the movement (B) of the slider 8 is fed back so that the slider 8 is interlocked with the wedge-shaped object 5 to be clamped gradually. It can be pulled out smoothly between the substrates 1 and 4.

As shown in FIG. 4, when the central portion of the substrate 1 is pressed, the bonding force between the substrates 1 and 4 also acts on the peripheral portion to spread the bond. After this pressure-bonding, strong bonding will be performed by heating.

The object to be sandwiched 5 is preferably made of a material that does not cause metal contamination, and is preferably made of quartz or a ceramic material that does not cause metal contamination. In this example, the wedge-shaped object to be sandwiched 5 is made of quartz.

In the present example, the sandwiched object 5 (wedge) is set at four points, but it may be better to set it at about eight points so that the substrates to be laminated can be made to be convex to the edges. Also,
The wedge may be longer around the substrate (wafer) periphery.

In this embodiment, the substrate 1 (wafer)
The outer peripheral portion of the substrate is held by the wedge-shaped object to be sandwiched 5 to form a gap, and the forcibly deflecting the bonding surface side so as to form a convex shape. Since it is made to proceed, good bonding without bubbles can be achieved. Further, this can be realized without requiring the steps of polishing the wafer to remove the polysilicon film and etching to remove the oxide film. In addition, it can be generally used for wafers having any shape (warp).

[0036]

As described above, the bonded SOI of the present invention
The structure forming method does not require complicated steps such as polishing and etching to make the bonding surface convex, and no bubbles are surely generated regardless of the warped shape of the bonded substrate. It has an effect that the bonding can be achieved.

[Brief description of drawings]

FIG. 1 shows Example 1 and is a side view conceptual diagram at the time of laminating.

FIG. 2 shows Example 1 and is a conceptual plan view at the time of laminating.

FIG. 3 shows the first embodiment and is an enlarged side sectional view of a contact portion between the substrate and the object to be sandwiched.

FIG. 4 illustrates the first embodiment and is an operation explanatory diagram at the time of bonding.

FIG. 5 is a diagram showing a conventional technique.

FIG. 6 is a sectional view showing, in order, general steps for forming a bonded SOI structure.

[Explanation of symbols]

 1 Silicon Substrate 2 Insulating Part 3 Polysilicon Film 4 Another Substrate 5 Object to be sandwiched (wedge)

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[Procedure amendment]

[Submission date] September 16, 1993

[Procedure Amendment 2]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 6

[Correction method] Change

[Correction content]

[Figure 6]

Claims (1)

[Claims] Claim: What is claimed is: 1. A silicon substrate having an insulating portion formed on one of the gutters is attached to another surface of the silicon substrate having the insulating portion formed thereon, and the other gutter surface of the silicon substrate is polished. SOI in which a silicon part exists on the insulating part due to
In a method for forming an SOI structure for obtaining a structure, at least one of the two substrates is bonded by interposing an object to be sandwiched in an outer peripheral portion between the two substrates when the silicon substrate and another substrate are bonded to each other. A method for forming an SOI structure, characterized in that bonding is performed in a state of being convex with respect to a mating surface.