JPH0383320A - Bonded semiconductor substrate - Google Patents

Abstract

PURPOSE:To remove a part which is liable to break without decreasing the diameter of a substrate and to increase an element forming area by obliquely cutting the peripheral part of the substrate. CONSTITUTION:A first wafer 21 and a second wafer 22 are cleaned and then dried with a spinner. Both mirror surfaces are brought into contact tightly in a clean atmosphere. Then, heat treatment is performed in an nitrogen atmosphere containing a small amount of oxygen at 1,100 deg.C for one hour. Both wafers are directly bonded in this way. Then, a part shown by hatching in the figure at the outside of a straight line A is removed by grinding. The straight line A connects a point 28 on the peripheral surface of the second wafer 21 and a point 29 on the bonding surfaces of both wafers 21 and 22. Since the part which is liable to break in the second wafer 22 (element forming wafer) is removed in this way, the possible breakdown at this part does not give adverse effects on the succeeding process.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Application Field) The present invention relates to a bonded semiconductor substrate in which two semiconductor substrates are bonded or joined to form an integrated structure, and in particular, the present invention relates to a bonded semiconductor substrate in which two semiconductor substrates are bonded or bonded to form an integrated structure, and in particular, the outer periphery thereof is partially cut out. The present invention relates to an adhesive semiconductor substrate.

(Prior art) In recent years, after performing pretreatment on mirror-polished semiconductor substrates (wafers) such as silicon, the mirror surfaces of the two wafers are brought into contact and heat-treated to form a strong bonded wafer. The technology to do this is attracting attention. This technique is called direct bonding or direct bonding. Since directly bonded semiconductor substrates do not use adhesives, they are thermally and chemically stable, and are used for epitaxial growth, as an alternative to diffusion, and in the production of dielectrically isolated substrates, making them suitable for various semiconductor devices. It's being used.

As an alternative to epitaxial growth or diffusion, for example, a highly doped p-type wafer and a lightly doped n-type wafer are bonded together. In the case of a dielectric isolation substrate, a wafer with an oxidized surface is bonded. In either case, the thickness of the wafer on which the devices are fabricated is generally less than or equal to the LOJm. On the other hand, the wafer used for bonding has a thickness of several hundred micrometers. Therefore, after bonding, it is necessary to reduce the thickness of one of the weno sheets by polishing or the like.

By the way, as shown in the cross section of FIG. 3(a), the edge of the wafer 31 is chamfered, which is called round processing. The rounding process is performed to prevent chips from occurring at the edges of the wafer when processing the wafer into a mirror surface or during the process of manufacturing elements on the wafer. When wafers that have been rounded in this way are bonded together,
As shown in FIG. 3(b), the edge portions 33 of the wafers 31 and 32 are not bonded.

When one wafer 31 of such a bonded semiconductor substrate is polished as shown in FIG. is formed. This thin portion 34 is easily broken during polishing and subsequent device manufacturing steps. If a part of the wafer breaks, the debris becomes foreign matter and not only reduces the yield of devices, but also
It can also cause destruction of the wafer itself or manufacturing equipment. In order to prevent this, conventionally, as shown in FIG. 3(d), the edge portion was cut off to eliminate the unbonded portion 33 before polishing or new round processing was performed.

Generally, the portion 33 that is not bonded is about several i from the edge. On the other hand, the wafer size standards are 100gg, 12
5av, 1501I1m, etc. every 25am. Wafers with a size other than the standard are difficult to handle manually and cannot be handled by process equipment used during the device manufacturing process. Therefore, when cutting the edges after gluing, reduce the diameter by 2
It is necessary to reduce the size by 5m5. Reducing the diameter of the wafer by 25 cm leads to a reduction in the area for forming elements, and
The number of devices that can be manufactured on a single wafer will be reduced.

(Problem to be solved by the invention) Conventionally, reducing the substrate diameter by one size after bonding two semiconductor substrates not only requires processing around the substrates, but also reduces the element formation area. This leads to a decrease in the number of elements that can be manufactured on one substrate.

The present invention has been made in consideration of the above circumstances, and its purpose is to provide a bonded semiconductor substrate in which fragile parts can be removed without reducing the substrate diameter and the area for forming elements can be increased. It's about doing.

[Structure of the Invention (Means for Solving the Problems)] The gist of the present invention is to diagonally form the periphery of a substrate in order to remove a fragile portion (a thin portion at the periphery) without reducing the substrate diameter. It's about cutting.

That is, the present invention provides a bonded semiconductor substrate in which a second semiconductor substrate is bonded and integrated onto a first semiconductor substrate, and the surface side of the second semiconductor substrate is made thin by polishing or the like.
A point that is inside the outermost peripheral part of the first semiconductor substrate and in contact with the peripheral part on the second semiconductor substrate side in a cross section passing through the center of each substrate and perpendicular to each substrate; The adhesive portion is removed by cutting along a line connecting a point inside the outermost periphery of the bonded portion with the first and second semiconductor substrates.

An overview of the present invention will be explained with reference to FIG.

FIG. 1 shows a first semiconductor substrate 11 and a second semiconductor substrate 1.
2 is a cross-sectional view of a joined body in which the two are bonded together. m1 diagram (a
), both substrates 11 and 12 are bonded to points 16 from the center. After bonding, the second semiconductor substrate 12 is polished and thinned to a thickness represented by a broken line 17. A feature of the present invention is a bonded semiconductor substrate in which a first semiconductor substrate 11 and a second semiconductor substrate 12 are bonded and integrated;
At least the portion of the second substrate 12 outside the portion where the first and second substrates 11.12 are bonded has been removed, with the largest diameter portion 15 remaining. That is, it is sufficient if the cross section is as shown in FIG. 1(b).

A more desirable adhesive semiconductor substrate of the present invention will be explained with reference to FIG. 1(c). FIG. 1(c) shows the second semiconductor substrate 12.
shows the cross section after it has been thinned.

In FIG. 1(c), the first point 18, the second point 19 and the third point
Here, the first point 18 is located at the outermost peripheral portion 15 of the first semiconductor substrate 11 or more than this. This is a point close to the adhesive surface. The second point 19 is the outermost portion 16 to which the inner substrate is bonded on the adhesive interface;
Or a point inside this point. The line A is a straight line or is convex toward the second substrate (preferably outwardly convex. The third point 20 is the intersection of the line A and the surface 17 of the second semiconductor substrate 12. It is desirable that the point 20 be located at a position less than 12.5 ms inside the outermost peripheral portion 15 of the first semiconductor substrate 11 .

(Function) According to the present invention, even after bonding and processing the periphery, the outermost periphery of the first semiconductor substrate remains, so the overall substrate diameter does not decrease.

Further, since the thin and easily breakable portion of the second semiconductor substrate has been removed, destruction of this portion will not adversely affect subsequent processes.

When manufacturing a semiconductor element on a second semiconductor substrate that has been bonded and thinned, a resist is applied to the surface of the substrate in a PEP process. At this time, depending on the shape of the peripheral area of the substrate, the resist may break off in this area and peeling may occur. Figure 1(c) shows the cross-sectional shape of the peripheral part of the substrate that has been bonded and thinned.
With the cross-sectional shape represented by , peeling of the resist is unlikely to occur. That is, unless the line A representing the cross-sectional shape of the peripheral portion on the front surface side of the substrate is concave toward the second substrate (concave outward), breakage or peeling of the resist at this portion is unlikely to occur. Furthermore, since the angle formed by the line A and the surface 17 of the adhesive substrate at the point 20 is large, breakage or peeling of the resist at this portion is less likely to occur. Specifically, line A is a straight line.

A combination of a plurality of straight lines, a single curve, or a combination of a curve and a straight line can be considered.

On the other hand, the third point 20 is a cross section between the substrate surface 17 and the line A, and an element is formed on the inner substrate surface. This point is 1 point lower than the outer periphery of the bonded substrate, that is, the outermost periphery of the first substrate.
When the distance is 2.5 ms or more toward the center of the substrate, the effect of the present invention cannot be exhibited compared to the conventional method of reducing the substrate diameter by 25 layers.

(Example) Hereinafter, details of the present invention will be explained with reference to illustrated embodiments.

FIG. 2 is a sectional view showing the manufacturing process of a bonded semiconductor substrate according to an embodiment of the present invention.

First, two types of mirror-polished silicon substrates (wafers) are prepared. The first wafer has a resistivity of 0. O1ΩcI
The second wafer has a resistivity of 80Ωel and is n type.
Both types and wafer shapes are the same, with a diameter of 150 m.
m, thickness 80hi, and the edges are rounded with a radius of 30011cm.

First, both wafers were cleaned. Both wafers were cleaned using a mixture of sulfuric acid and hydrogen peroxide, a mixture of hydrochloric acid and hydrogen peroxide, dilute hydrofluoric acid, and water washing. After cleaning, both wafers were dried using a spinner, and the mirror surfaces were brought into contact with each other in a clean atmosphere to make them adhere closely. Then, heat treatment was performed at 1100°C for 1
The bonding process was carried out in a nitrogen atmosphere containing a small amount of oxygen for a period of time, and both wafers were directly bonded. A cross section of the edge of the bonded wafer is shown in FIG. 2(a). The round processing has a radius of 300t■, but in reality, due to the surface sagging that occurs during mirror polishing, both wafers 21 and 22 are 2 to
31111% The area up to point 26 in the figure was not bonded.

Next, peripheral processing as shown in FIG. 2(b) was performed, and mainly the edge portion of the second wafer 22 was obliquely removed. That is, a point 28 on the peripheral surface of the first wafer 21 and both wafers 2
The portion outside the straight line A connecting the two points on the adhesive surfaces of Nos. 1 and 22, indicated by hatching in the figure, was removed by grinding.

Here, the point 28 is 450 μm from the bottom of the first wafer 21.
(above the outermost periphery 25, that is, on the inside), the point 29 is located at a position 511 inward from the wafer outermost periphery 25 on the adhesive surface of the first wafer 21 and the second wafer 22. It was set to

Further, although not shown in the drawings, the portion at point 28 was chamfered to have a corner.

After peripheral processing, the second wafer 22 is removed as shown in FIG. 3(e).
was polished to a thickness of 50 μm to form a thin film. The edge 30 of the substrate surface 27 after polishing had surface sag due to polishing, and was approximately 8 cm inward from the outermost peripheral portion 25 of the wafer. When semiconductor devices were manufactured on this substrate, sea urchins were removed during the manufacturing process.
No breakage, breakage, or peeling of the resist occurred.

Thus, according to this embodiment, the periphery of the bonded semiconductor substrate in which two wafers 21 and 22 are bonded and integrated is cut diagonally to remove the fragile portion (thickness) of the second wafer 22 (device forming wafer). Since the thin part of the wafer is removed, destruction of this part will not adversely affect subsequent processes.

In this case, since the outermost portion of the first wafer 21 remains, the diameter of the substrate does not decrease and can be used as a standard semiconductor substrate. Further, unlike the conventional method in which the substrate diameter is reduced by 25 mm, the diameter of the second wafer 22 is only slightly reduced, so the area for forming elements can be increased compared to the conventional method. This leads to effective use of the substrate, and as a result, it is possible to reduce product costs. Further, as can be seen from FIG. 2(b), diagonal cutting around the substrate periphery can be easily performed by a normal polishing process.

Note that the present invention is not limited to the embodiments described above. In the embodiments, substrates bonded by a method called direct adhesion or direct bonding have been described, but the present invention is also applicable to bonding two substrates by other methods such as electrostatic adhesion, bonding with adhesives, resins, metals, etc. The same can be applied to other substrates. Furthermore, the invention can also be applied to two substrates that are integrated by interposing an oxide film or other film between them. Further, since the first substrate is not used for forming elements but is used as a support, it is not necessarily limited to a semiconductor, and an insulating plate or a metal plate can also be used. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the periphery of the substrate is cut diagonally in order to remove the fragile portion (thin peripheral portion) of the substrate. A bonded semiconductor substrate can be realized in which fragile parts can be removed without reducing the diameter, and the area for forming elements can be increased.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view for explaining the present invention in detail, Fig. 2 is a cross-sectional view showing the manufacturing process of a bonded semiconductor substrate according to an embodiment of the present invention, and Fig. 3 is a cross-sectional view for explaining conventional problems. FIG. 11.21...First semiconductor substrate, 12.22...Second semiconductor substrate, 15.25...Outermost periphery, 16.26...Outermost periphery of adhesive part, 17.27... - Polished surface, 18.28...1st point (point inside the outermost periphery), one. 29...Second point (point inside the outermost periphery of the adhesive part) 20°0...Third point (intersection of line A and substrate surface)

Claims (1)

[Scope of Claims] A bonded semiconductor substrate in which a second semiconductor substrate is bonded and integrated on a first semiconductor substrate, and the thickness of the second semiconductor substrate is reduced from the front side to make it a thin film, comprising: The peripheral portion of the second semiconductor substrate is a point that is inside the outermost peripheral portion of the first semiconductor substrate and touches the peripheral portion on the second semiconductor substrate side in a cross section passing through the center of each substrate and perpendicular to each substrate. and a point inside the outermost periphery of the bonded portion of the first and second semiconductor substrates.