JP2604488B2 - Bonded wafer and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] Bonded wafer and method for manufacturing the same, particularly high quality silicon on insulator (SO)
I) Regarding the structure of an SOI wafer for obtaining a wafer and its manufacturing method, in the manufacture of a bonded SOI, chipping of the element substrate, generation of dust, and cracking of the element substrate due to generation of an acute step on the end face of the element substrate SOI with a structure that can be prevented
And a method for manufacturing the same, by grinding the surface of an element forming wafer by grinding the surface of a wafer for forming an element among two wafers located on both surfaces of a bonded wafer formed by bonding a plurality of wafers. Flattening and adjusting the thickness of the wafer, and then grinding the end face of the bonded wafer to finish the end face to have a continuous curved surface in the cross-sectional direction,
The method for manufacturing a bonded wafer, characterized by polishing the end face, and, among the two wafers located on both sides of the bonded wafer formed by bonding a plurality of wafers, the thickness of the wafer for element formation is reduced. The thickness is suitable for element formation, and the surface of the element formation wafer is flattened, and the end face of the bonded wafer is mirror-finished so as to have a continuous curved surface in a cross-sectional direction. And a bonding wafer characterized by the following.

[Industrial applications]

The present invention relates to a bonded wafer and a method for producing the same, particularly to obtain a high quality silicon-on-insulator wafer.
The present invention relates to a structure of an SOI wafer and a manufacturing method thereof.

In recent years, the fields of use of semiconductors have expanded, and high performance and high quality devices have been increasingly demanded. In particular, devices with high speed and environmental resistance have been demanded. For this reason, devices using SOI substrates have been provided, but the crystallinity of a normal silicon substrate (wafer) cannot be obtained, and the characteristics and yield of the formed elements are not good. There is a need for a way to improve this.

[Conventional technology]

For conventional SOI wafers, the melt method, SIMOX (Sepa
A ration by Implanted Oxygen) method and a joining method (laminating method) are known.

However, it is said that it is extremely difficult to obtain good-quality crystals in each of the melt method and the SIMOX method due to the principle problem of the manufacturing method. On the other hand, the bonding method has an advantage that a good quality SOI substrate can be obtained because good quality crystals are bonded to each other.

Referring to FIG. 4, a melt method which is advantageous for the multilayer LSI structure will be described. As shown in a schematic perspective view of FIG. 4 (a), a wafer 31 having a SiO ₂ film 32 formed on the surface thereof is formed. A plurality of islands 33 are formed. Although only six islands 33 are shown for simplicity of the drawing, more islands are actually formed over the entire surface of the wafer 31. A device is formed by forming a single crystal silicon region on the island 33.

FIG. 4 (b) is a cross-sectional view of a portion of the island 33. In order to form SOI, a polycrystalline silicon (polysilicon) 34 is deposited on the entire surface and then irradiated with a laser beam to melt the polysilicon. 4 As shown in FIG. 4 (c), the melted polysilicon flows into the island 33, and is then recrystallized into a single crystal silicon layer 36.

In this melt method, a crystal defect 37 indicated by a line in the figure is formed.
Generated from the SiO ₂ film 32, for example, when the island 33 has a size of 1 cm square, there are many crystal defects about 2.5 mm from the periphery,
As a result, there is a problem in yield that a single crystal silicon region cannot be formed in about 3/4 of the size of the island.

In the SIMOX method, referring to FIG. 5, first, as shown in FIG. 5 (a), oxygen ions (O ⁺ ) are implanted into a silicon substrate (wafer) 41 from above, and the depth of the silicon substrate 41 is reduced. The oxygen implantation layer 42 (shown by crossing short lines in the figure) is formed by being implanted substantially at the center.

Next, as shown in FIG. 5B, when annealing is performed at 1200 to 1250 ° C., the oxygen injection layer becomes the SiO ₂ layer 43, and the SOI 44 is formed thereon.

However, in this method, oxygen 45 remains in the SOI 44 as shown by sand, and oxygen in silicon causes crystal defects, so that it is difficult to obtain high-quality SOI by the SIMOX method.

Therefore, the bonding SOI was developed. In this method, the surface of the element substrate was ground after bonding the element substrate (the substrate on which the element is formed) whose surface was oxidized to the supporting substrate. Then, the periphery is etched, and finally a polishing method is performed.

[Problems to be solved by the invention]

The junction SOI will be described in some detail with reference to FIG.
A large number of streaks 52 are formed on the surface of the single crystal silicon CZ crystal 51 pulled by the Z method because the CZ crystal 51 is rotated at the time of pulling (FIG. 6 (a)). Therefore, the surface of the CZ crystal 51 is chamfered by cylindrical processing to make the surface uniform and smooth (FIG. 6 (b)). Next, as shown in FIG. 6C, one side surface of the CZ crystal 51 is removed by orientation flat (orientation flat processing).

Next, a wafer 53 (approximately 0.1 mm thick) shown in FIG. 6D is formed by slicing, and chamfering is performed to round the end surface of the wafer 53 as shown in FIG. 6E. Next, a wafer 53 having a thickness of 500 to 700 μm shown in FIG. 6 (f) is formed by lapping, and the surface of the wafer 53 is turned into a mirror surface by polishing. The reason for chamfering the end face of the wafer is that, in addition to improving the wrapping of the abrasive grains in lapping and preventing the stagnation of the abrasive grains, in the transfer and processing of the completed wafer, the formation of an almost vertical end face if not chamfered This is in order to avoid the generation of dust and cracking of the wafer.

Next, the surface of the chamfered wafer 53 is oxidized to form SiO ₂
A film 54 is formed, and two such wafers 53 are bonded as shown in FIG. 6 (g). In the figure, the upper one is an element substrate 53a, the lower one is a support substrate 53b, and the size of the wafer and the thickness of the oxide film are exaggerated and schematically illustrated for the sake of explanation.
Since the surface of the wafer 53 is a mirror surface (mirror finish), the element substrate 53a and the support substrate 53b are bonded at room temperature. Next, hydrogen is removed from the moisture contained in the air taken into the SiO ₂ film 54 by annealing at 1200 ° C., and the element substrate 53a and the support substrate 53b are firmly joined by bonding of oxygen and silicon.

Then, by polishing the element substrate 53a from above by wrapping, as shown in FIG. 6 (h), 0 including an SiO ₂ film 54.
The element substrate 53a side of about 2 to 10 μm is left. Then, a tape 55 serving as a mask material is attached by the next etching on the surface of the element substrate 53a which has been mirror-finished by the lapping.

Subsequently, the peripheral portion not masked by the tape 55 is etched by wet etching (FIG. 6 (i)).
At this time, the thickness of the SiO ₂ film on the bonding surface is about 0.1 to 5 μm, and this SiO ₂ film is an insulator for SOI.

The element substrate 53a after the peripheral etching shown in FIG.
When observing, the end surface is almost vertical and a sharp step is generated, so if the upper corner portion hits another object due to vibration generated during wafer cleaning or transfer, the corner portion is missing, In some cases, cracking of the element substrate 53a was experienced.

In the lapping of the element substrate 53a shown in FIG. 6 (i), the side surface of the element substrate 53a is at an acute angle with respect to the bonding surface 56 shown by the dotted line in FIG. Since the abrasive grains accumulated and the flow of the abrasive grains was not uniform in general, there was also a problem that the lapping was not performed uniformly and the lapping finished surface did not become a perfect mirror surface.

Therefore, the present invention relates to an SOI having a structure capable of preventing chipping of an element substrate and generation of dust due to generation of an acute step on an end face of the element substrate, and cracking of the element substrate in the production of a bonded SOI and the production thereof. The aim is to provide a method.

[Means for solving the problem]

As shown in FIG. 2, the method for manufacturing a bonded wafer according to claim 1 of the present application includes a plurality of wafers (two shown in FIG. 2 for convenience).
Of the two wafers 11 and 12 located on both sides of the bonded wafer 14 formed by bonding the wafers 11 and 12, the surface of the device forming wafer 11 is ground to flatten the surface and reduce the thickness of the wafer. After the adjustment, the end surface of the bonded wafer 14 is ground so that the end surface has a continuous curved surface in the cross-sectional direction, and the end surface is polished.

The method for manufacturing a bonded wafer according to claim 2 of the present application is
The method according to claim 1, wherein polishing or grinding and polishing are performed when the surface of the wafer for element formation is flattened and the thickness of the wafer is adjusted.

Also, the method for manufacturing a bonded wafer according to claim 3 of the present application is as follows.
The method according to claim 1, wherein after grinding the end surface of the bonded wafer, the surface of the wafer for element formation is polished.

The bonded wafer according to claim 4 of the present application is such that, of the two wafers located on both surfaces of the bonded wafer formed by bonding a plurality of wafers, the thickness of the wafer for element formation is a thickness suitable for element formation. In addition, the surface of the element forming wafer is flattened, and the end surface of the bonded wafer is mirror-finished so as to have a continuous curved surface in a cross-sectional direction.

[Action]

FIG. 2 is a diagram showing the principle of the present invention. First, as shown in FIG. 2 (a), a substrate 11 on which an element is to be formed (hereinafter referred to as an element substrate) and a substrate 11 on which the element substrate 11 is to be supported (hereinafter referred to as A bonding wafer 14 is formed by bonding the supporting wafer 12 and a supporting substrate 12. Then
As shown in FIG. 2B, the element substrate 11 is ground and polished. Subsequently, as shown in FIG.
Chamfer the end face of. Further, although not shown in the drawing, the chamfered end surface of the bonded wafer 14 is polished. In addition,
The surface of the element substrate 11 may be polished after grinding the end surface of the bonded wafer.

That is, according to the present invention, the discontinuous surfaces formed by the end faces of the bonded element substrate 11 and the supporting substrate 12 (bonded wafer 14) are finished to have a continuous curved surface in the cross-sectional direction,
Since there is no angular part anywhere, this bonded SOI is prevented from being chipped or cracked even if the end surface comes in contact with other objects due to vibration during cleaning and transport, and all other than the back surface of the bonded wafer Since the surface is ground or polished, there is almost no generation of foreign matter, so that the surface of the element substrate is held as a highly accurate mirror surface.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to the illustrated embodiments.

In the embodiment of the present invention, as shown in FIGS. 1 (a) to 1 (c), the element substrate 11 (corresponding to the element substrate wafer described in the gist of the invention) of the bonded wafer 14 is ground and polished. After polishing, the polishing may be performed after the next chamfering.) Then, chamfering is performed by an end surface grinding process, and although not shown, the end surface of the bonded wafer 14 is polished. In these drawings, the size of the wafer and the thickness of the oxide film are schematically shown exaggeratedly for the sake of explanation. The end surfaces of the element substrate 11 and the support substrate 12 are chamfered, and an SiO ₂ film 13 having a thickness determined by the type of the element to be formed is formed on each surface. Generally, the total thickness of the two SiO ₂ films 13 is 0.1 to
It is set within the range of 5.0 μm. These substrates are first mechanically bonded at room temperature as in the prior art, and then
Annealing at 1200 ° C. is performed to remove hydrogen from the moisture taken in the SiO ₂ film 13, and the bonded wafer 14 is firmly bonded by bonding of oxygen and silicon. In this state 2
The end face formed by the two substrates is a discontinuous face (FIG. 1A).

Next, as shown in FIG. 1B, grinding and polishing (lapping) of the element substrate 11 are performed. For grinding, for example, a diamond grindstone may be used. Also, for polishing,
For example, an amine-based aqueous solution and colloidal milica may be supplied to a polishing surface as an abrasive and polished with a polishing cloth (a polyester nonwoven fabric or the like).

Next, as shown in FIG. 1 (c), the end surfaces of the bonded wafer 14 of the two substrates are chamfered by an end surface grinding process. As a result, the end face, which was a discontinuous face, is finished into a completely chamfered state having a continuous roundness and a curved surface in which the chamfered shape of the substrate is symmetrical on the front and back surfaces.

Next, although not shown, after chamfering in FIG. 1 (c), the end face of the bonded wafer 14 is polished.

As described above, in the present embodiment, the end surface of the bonded wafer 14 is finished so as to have a continuous curved surface in the cross-sectional direction, and there is no angular portion. Even if careless, there is no risk of chipping or cracking. Furthermore, since all surfaces except the back surface of the bonded wafer 14 are ground or polished, there is almost no generation of foreign matter, and the surface accuracy of the element substrate 11 can be maintained. Can be suppressed.

As another modified example, the surface of the element substrate 11 of the bonded wafer may be further polished to a mirror surface after the end surface grinding processing.

In order to chamfer the discontinuous end face of the bonded wafer 14, a known grinder shown in FIG. 3 is used to bring the end face of the bonded wafer 14 held by the chuck 21 into contact with the grind surface 22 of the grinder, and then the arm At 23, the chuck 21 is moved in the direction of the arrow to grind the end face. The arm 23 is connected to a drive source (not shown). The drive source automatically operates the arm 23, and the chamfering operation is mechanically automated.

〔The invention's effect〕

In the present invention, the end surface of the bonded wafer is finished so as to have a continuous curved surface in the cross-sectional direction, and since there is no angular portion anywhere, vibration occurs during cleaning or transport and careless handling is caused. In addition, the unique effect that there is no risk of chipping or cracking is obtained, and further, since all surfaces except the back surface of the bonded wafer are ground or polished, there is almost no generation of foreign matter, and furthermore, element formation Since the surface of the wafer for use can be held with high precision, the unique effect that the occurrence of element defects and pattern defects can be significantly suppressed can be obtained.

[Brief description of the drawings]

1 (a) to 1 (c) are cross-sectional views of an embodiment of the present invention, FIG. 2 is a cross-sectional view for explaining the principle of the present invention, FIG. 3 is a view showing a chamfering step, and FIG. 5A is a perspective view, FIGS. 5B and 5C are cross-sectional views, FIG. 5 is a cross-sectional view showing a SIMOX method, and FIG. 6 is a view showing a junction SOI method. ) Is a front view of the CZ crystal, (b) is a front view after the cylindrical processing of the CZ crystal, (c)
1 is a front view of a CZ crystal after orientation flat processing, (d) to (f) are perspective views of a wafer, and (g) to (i) are cross-sectional views of a bonded wafer. 11 (substrate for device formation) ...... element substrate, 12 ... supporting substrate (substrate should support element substrate), 13 ... SiO ₂ film, 14 ...
Bonded wafer, 15 Adhesive surface, 21 Chuck, 22 Grind surface, 23 Arm, 51 CZ crystal, 52 Streaks
53 …… Wafer, 53a …… Element substrate, 53b …… Support substrate, 54
...... SiO ₂ film, 55 ...... tape, 56 ...... adhesive surface.

Claims (4)

(57) [Claims] 1. A wafer for element formation, of two wafers located on both sides of a bonded wafer formed by bonding a plurality of wafers, is planarized by grinding the surface and adjusting the thickness of the wafer. Then, an end surface of the bonded wafer is ground to finish the end surface to have a continuous curved surface in a cross-sectional direction, and further, the end surface is polished. 2. The method for manufacturing a bonded wafer according to claim 1, wherein polishing or grinding and polishing are performed when the surface of the wafer for element formation is flattened and the thickness of the wafer is adjusted. 3. The method for manufacturing a bonded wafer according to claim 1, wherein after grinding the end surface of the bonded wafer, the surface of the wafer for forming an element is polished. 4. A wafer for element formation among two wafers located on both sides of a bonded wafer formed by bonding a plurality of wafers, the thickness of which is suitable for element formation, and
A bonded wafer characterized in that the surface of the element forming wafer is flattened, and the end surface of the bonded wafer is mirror-finished so as to have a continuous curved surface in a cross-sectional direction.