JPH04263425A - Grinding device for semiconductor substrate and method thereof - Google Patents

Abstract

PURPOSE:To make it possible to conduct grinding of excellent dimensional accuracy. CONSTITUTION:The title grinding device is constituted in such a manner that the disc-shaped grindstone 11, on which a rotating shaft is attached to the center point, or a substrate jig 9, with which a semiconductor substrate 5 is horizontally retained, can be moved in parallel and in vertical direction against the surface of the semiconductor substrate 5, and the upper surface of the above- mentioned substrate retaining jig 9 and the rotating shaft RG of the grindstone are in parallel with each other.

Description

[Detailed description of the invention]

[Object of the invention]

0002

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor substrate processing apparatus, and more particularly to a technique for removing an unbonded portion on the outer periphery of a bonded semiconductor substrate formed by bonding or bonding two semiconductor substrates together.

0003

[Prior Art] In recent years, after performing pretreatment on semiconductor substrates (wafers) such as silicon that have been polished to a mirror surface, the mirror surfaces of two wafers are bonded together and heat treated to form a strong bonded wafer. The technology that forms them is attracting attention. This method not only makes it easy to create a dielectric isolation substrate by bonding wafers with oxidized surfaces, but also uses a silicon substrate on the side where the elements are formed, so it has good crystallinity and is relatively This is an excellent method that has features such as less warping, and has been put into practical use in recent years. Conventionally, P-
N-junction isolation and dielectric isolation are known, but dielectric isolation does not cause latch-up. ■High voltage resistance can be obtained. ■High-speed operation is possible with low parasitic capacitance. Due to these characteristics, applications such as high-speed ICs and high-voltage PW-ICs are expanding. Therefore, the scope of application of bonded wafers is also increasing.

FIG. 8 shows a sectional view of the outer periphery of a bonded wafer. FIG. 4(a) is a diagram before grinding, and FIG. 2(b) is a diagram after grinding by a conventional grinding method. In the figure, 1 is an active layer side substrate, 3 is a stand side substrate, 5 is an adhesive wafer formed by integrating the active layer side substrate 1 and the stand side substrate 3, 7 is an adhesive interface,
21 is the unbonded portion, W1 is the width of the unbonded portion 21, and W2 is the grinding margin in the conventional grinding method.

[0005] Since bonded wafers are made by bonding the mirror surfaces of two semiconductor substrates together, the flatness of the surfaces has a large effect. With the miniaturization of semiconductor devices in recent years, their precision has improved, but since there is surface sagging on the outer periphery of the wafer in the 3 to 5 mm periphery, as shown in Figure 8 (a), this area (A - outside A') are not bonded (a gap remains). For this reason, dust accumulates in this area, causing contamination during the process.
It is a source of dust and must be removed.

As shown in FIG. 8(b), a common method for removing the wafer is to use a grindstone or the like to grind at least the outer peripheral portion of the wafer beyond the line A-A'. However, this method reduces the diameter of the wafer,
There is a problem of large material loss. That is, in general,
Semiconductor substrate is 25mm (1 inch) step (however, 1 inch)
For diameters larger than 50mmφ, the diameter is determined in 50mm (2 inch) steps.
) bonded wafer is made by bonding two wafers of 150mmφ (6 inchφ) together and then cutting the outer periphery to 125mm.
It will be formed into φ. However, with this method, 150m
To make mφ wafers (because 175 mmφ is generally not available), 200 mmφ wafers must be bonded and molded to 150 mmφ, which takes about 4
4% will be removed, resulting in a very large material loss. Furthermore, as mentioned above, the unbonded part that must be removed is about 3 mm from the periphery, so with the above method,
Since the adhesive portion, that is, the area where the element can be formed, is largely cut away, material loss increases. Conversely, it is also possible to make the diameter of the two wafers used for bonding larger than the final processed outer diameter by only the size of the unbonded part (about +6 mm or more), but in this case, in order to produce a 125 mmφ bonded wafer, If a mirror-finished wafer with a diameter of about 131 mm is prepared, material loss will be the least. However, 131m
Wafers with a special shape of mφ are not generally available,
Since it is custom-made, specialized jigs and other equipment must be used, resulting in high wafer costs and long delivery times, so it has not been put into practical use. do not have.

Therefore, as a measure to remove the peripheral unbonded portion 21 without reducing the external shape, as shown in FIG. 9, the outer periphery of the inner board 3 of the two bonded boards is left,
It is conceivable to shave the active layer side substrate 1 to the peripheral unbonded portion. This makes it possible to maximize the area in which the element is actually fabricated while adjusting the outer shape to the diameter of the aforementioned 25 mm step. Incidentally, FIG. 9 shows a cross-sectional view of the outer periphery of the bonded wafer, in which the unbonded portion has been ground without reducing the diameter of the outermost periphery.

Here, as a method for removing the peripheral portion of the active layer side substrate 1, there is the following method.

1) Method of removing by etching 2) Method of removing by grinding First, method 1) will be explained using FIG. 10. 1st
Figure 0 shows a method of removing the unbonded part without reducing the diameter of the outermost periphery using etching. , (c) is a cross-sectional view after etching, (d) is a cross-sectional view after removing the protective film, and (e) is a cross-sectional view after polishing the active layer side substrate 1. show. In the figure, 23 is a protective film on the front surface, 25 is a protective film on the back and side surfaces,
Reference numeral 27 indicates "sag" at the corner portion due to etching removal.

As shown in FIG. 10, in this method, 600
Since etching is performed in the vicinity of μm, all portions (front and back surfaces) that are not desired to be removed must be protected with some kind of film. SiO2 or resist can be considered as the film, but
In any case, the process of applying the film (FIG. 10(b)) and the process of peeling it off after etching (FIG. 10(c)) (FIG. 10(d))
) is required, and the film itself is also required to have resistance to etching solutions. Furthermore, the etching solution is also 600 μm.
Since the etching cost is large, it is necessary to have a high etching speed, and HF-HNO3-based etching solutions are mainly suitable, but since toxic NO2 gas is generated during etching, detoxification equipment is required. . Also, the cross section is also the first
As shown in Figure 0, a large sag 27 occurs, the dimensional accuracy is poor, and it is difficult to control the shape to a constant shape.

Next, using FIGS. 11 to 13, 2
). Fig. 11 is a diagram showing the state of grinding the unbonded part without reducing the diameter of the outermost periphery using a conventional grinding device, and Fig. 11 (a) is a cross-sectional view before grinding;
FIG. 5(b) is a cross-sectional view during grinding, FIG. 2(c) is a top view before grinding, and FIG. 4(d) is a top view during grinding. In the figure, 9 is a wafer chuck, 11 is a grindstone,
29 indicates a portion removed by grinding. Also, the 12th
The figure shows the force acting on a grindstone during grinding with a conventional grinding device, where 31 is a corner and 33 is a grinding surface. Furthermore, the first
FIG. 3 is a diagram showing the force acting on the grindstone during grinding when a tapered grindstone is used in a conventional grinding device.

As shown in FIG. 11, in this method, the cross-sectional shape is determined by the shape of the grindstone, so the dimensional accuracy is better than in the method 1) described above. However, when grinding is performed, the rotation axis of the wafer to be ground and the rotation axis of the grindstone are approximately parallel, so the grindstone enters from the side as shown in FIGS. In this case, as shown in FIG. 12, a force acting on the grindstone that tends to escape upwardly causes the corner portion 31 to be tapered. Furthermore, since the corner portion 31 is a right angle, dust tends to accumulate in this portion 31 during the process. As a countermeasure to this problem, a method is known in which the tip of the grinding wheel 11 is tapered as shown in FIG. Whetstone 11
The load on the rotating bearing also increases. In addition, the part of the grinding wheel 11 that performs grinding is the grinding surface 33 shown in FIGS. 12 and 13, but since the corner parts 31 are worn most severely, the shape of the grinding wheel 11 is not as shown in the figures. It will change like a wavy line, and it is necessary to frequently replace the grindstone 11 in order to maintain dimensional accuracy. This results in an increase in costs. Furthermore, in the worn whetstone 11,
There is also a possibility that the unbonded portion 21 cannot be removed and remains.

[0013]

[Problems to be Solved by the Invention] As mentioned above, in removing the peripheral portion of a semiconductor substrate, (1) the etching method requires a large number of steps and special equipment, resulting in high cost and also causes sagging. Poor dimensional accuracy.

(2) In the method using a conventional grinding device,
The cost is high, as the grindstone needs to be replaced frequently, and the dimensional accuracy is poor.

[0015] There was a drawback.

[0016] The present invention solves the above problems.
The purpose is to provide a semiconductor substrate grinding device and grinding method that is lower in cost and has better dimensional accuracy.

[Configuration of the invention]

[0018]

[Means for Solving the Problems] In order to solve the above problems, the first feature of the present invention, as shown in FIG. A grindstone 11 and a substrate fixing jig 9 that holds the semiconductor substrate 5 horizontally.
In a semiconductor substrate grinding apparatus, the grinding wheel 11 or the substrate fixing jig 9 can move in parallel and perpendicular directions with respect to the surface of the semiconductor substrate 5. The rotation axes RG of the two are parallel to each other.

A second feature of the present invention is that in the semiconductor substrate grinding apparatus according to claim 1, as shown in FIG. The outer periphery of the semiconductor substrate 5 is ground by rotating around the RC, and the grindstone 11 or the substrate fixing jig 9 moves perpendicularly to the rotation axis RG of the grindstone and grinds against the semiconductor substrate 5. It is to move in parallel.

Furthermore, the third feature of the present invention is a semiconductor substrate grinding method for removing the unbonded portion of the wafer outer periphery of a bonded wafer obtained by bonding two semiconductor wafers together and heating them together, as shown in FIG. As shown, while rotating a grindstone 11 having a rotation axis RG parallel to the surface of the bonded wafer 5, the substrate 3 on the lower side of the bonded wafer 5 is at least as thick as the substrate. Insert the bonded wafer 5 or the grindstone 11 into the bonded wafer 5 with the center of the bonded wafer 5 set as the rotation axis RC, leaving one-half or more of the bonded wafer 5 or more inside the unbonded part.
rotation along the outer periphery of the

[0021]

[Operation] In the semiconductor substrate grinding apparatus of the present invention, the grinding wheel 11 has a rotation axis RG that is parallel to the surface of the bonded wafer 5.
While rotating about the rotation axis RG, at least the substrate 3 on the lower side of the bonded wafer 5 is removed by half the thickness of the substrate.
Leaving the above-described portions intact, the wafer is inserted to the inside of the unbonded portion, and then the bonded wafer 5 or the grindstone 11 is rotated along the outer periphery of the bonded wafer 5 with the center of the bonded wafer 5 as the rotation axis RC.

[0022]

Embodiments Hereinafter, embodiments of the present invention will be explained based on the drawings.

FIG. 1 shows a first embodiment of the present invention. This figure shows a schematic view of the outer periphery being ground using the semiconductor substrate grinding apparatus according to the present invention.

In the figure, the semiconductor substrate grinding device is
It is composed of a grindstone 11 and a substrate fixing jig 9, and the grindstone 11 has a rotation axis RG that is parallel to the upper surface of the substrate fixing jig 9.
The substrate fixing jig 9 is a disk-shaped device that is attached around the semiconductor substrate 5 and can move in parallel and perpendicular directions with respect to the semiconductor substrate 5. The substrate fixing jig 9 holds the semiconductor substrate 5 horizontally, and The semiconductor substrate 5 rotates around the center and can move in parallel and perpendicular directions with respect to the semiconductor substrate 5. Incidentally, the semiconductor substrate 5 shown in the figure is a bonded wafer in which the active layer side substrate 1 and the stand side substrate 3 are pasted together and integrated by heating.

Next, a method of grinding using the semiconductor substrate grinding apparatus of this embodiment will be explained. In FIG. 1, first, the grindstone 11 rotating around the rotation axis RG is moved perpendicularly to the rotation axis RG of the grindstone, so that at least the substrate 3 below the bonded wafer 5 is removed by the thickness of the substrate. Insert the wafer into the bonded wafer 5, leaving more than half of the wafer, and inserting it to the inside of the unbonded part.
The substrate fixing jig 9 is rotated along the outer periphery of the bonded wafer 5 with the center of the rotation axis RC, and the outer periphery of the bonded wafer 5 is ground.

Next, the dimensional accuracy of this embodiment will be explained using actual data compared with the conventional example.

First, the bonded wafer used will be explained. Wafer shape is the same (diameter 150.0 mm, thickness 625 μm, rounded edge with radius 200 μm) ρ = 2 to 3 Ω cm, N type 6
100 inch φ wafers, and ρ = 1 to 10Ω・c
Prepare 100 6-inch φ wafers of m and P types,
After cleaning and drying both wafers, the mirror surfaces were brought into contact with each other in a clean atmosphere and brought into close contact. Next, heat treatment was performed at 1100° C. for 1 hour in an N 2 atmosphere containing a small amount of O 2 to directly bond both wafers. When 100 bonded wafers thus prepared were observed using an infrared transmission method, it was found that the peripheral area 2
~3 mm was not bonded.

Next, 50 of these bonded wafers were
Divided into groups, one group used a conventional grinding device (see FIG. 14) and the other group used a grinding device according to the present invention (see FIG. 1) to perform outer periphery grinding. The diameter of the grinding wheel 11 used was 110 mm, and the average grain size was 11 μm, leaving 5 mm inside the outer periphery of the bonded wafer 5.
It was decided to perform grinding at a thickness of 620 μm.

For comparison, for the ground substrate,
The thickness of the surrounding grinding area was measured. That is, the thickness t1 of the corner portion and the thickness t2 of the outer peripheral portion shown in FIG. 2 were measured,
The results are summarized in the table shown in Figure 3. As a result, in the conventional grinding device, there is a difference of approximately 10 μm between the corner portion and the outer peripheral portion, whereas in the grinding device of the present invention, the difference is approximately 2 μm.

Further, when similar grinding was continued and the life of the grindstone 11 was investigated, it was found that the grinding device according to the present invention had a lifespan nearly 20 times longer than that of the conventional grinding device.

Furthermore, when the corner portion is tapered at 45°, the difference in dimensional accuracy from the conventional grinding device becomes even larger. was 15 μm, but with the grinding device of the present invention, there was no change with a difference of 2 μm.

From the above results, it was demonstrated that by using the grinding apparatus of the present invention, outer periphery grinding with good dimensional accuracy can be performed for a long period of time.

Furthermore, by using a grindstone that combines grindstones with different grain sizes as shown in FIG. 4, multi-step grinding using grindstones with different roughness can be easily achieved by simply moving the position of the grindstone. Here, in the same figure, 13 is a grindstone for finishing grinding;
15 is a rough grinding wheel. In general, coarse grinding wheels have a longer lifespan and are easier to achieve accuracy, but on the other hand, they cause more damage to the object to be ground and create a deeper fracture layer. Therefore, first, as shown in FIG. 5(a), first grinding is performed with a coarse grindstone 15, and then, as shown in FIG. 5(b), the crushed layer created by the first grinding is By grinding with a grindstone 13 that is finer than the grinding process described above, it is possible to not only reduce the remaining crushed layer but also reduce the roughness of the ground surface, thereby reducing the possibility of causing defects in the subsequent process.

Further, as shown in FIG. 6, the present invention is also applicable to a case where the outer circumferential grinding is performed by diagonal grinding.

Furthermore, in the above explanation, an example has been described in which the application is applied to removing the unbonded portion of a bonded wafer, but it can also be applied to a single wafer that is not bonded, a wafer with a film such as an epitaxial wafer, and even other things other than semiconductor wafers. Needless to say, it is applicable. For example, FIG. 7 shows a state in which a crown formed on the outer periphery of an epitaxial wafer 17 is being ground using the grinding apparatus according to the present invention.

[0036]

[Effects of the Invention] As described above, according to the present invention, (1) it is possible to realize a grinding device with good dimensional accuracy, such as a small difference between the inside and outside of the outer periphery grinding part and good remaining thickness accuracy of the outer periphery grinding part; .

(2) Multi-stage grinding using grindstones with different roughness can be easily realized.

(3) The life of the grindstone is long.

(4) Since no etching step that generates toxic gas is required or the amount of etching is small, the etching time is short and the amount of gas generated can be significantly reduced, which is highly effective in preventing pollution.

(5) A low-cost grinding device can be realized with a relatively small number of steps, no special equipment required, and fewer grindstone replacements.

By applying the semiconductor substrate grinding apparatus and grinding method of the present invention, various industrially beneficial effects can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of outer periphery grinding performed by a semiconductor substrate grinding apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a bonded wafer after grinding.

FIG. 3 is a comparison table of dimensional accuracy between a conventional grinding device and a grinding device according to an embodiment of the present invention.

FIG. 4 is a cross-sectional view of a grindstone that combines grindstones with different grain sizes.

FIG. 5 is a schematic diagram of outer periphery grinding when the grindstone of FIG. 4 is applied to the grinding device according to the embodiment of the present invention.

FIG. 6 is a schematic diagram of the case where outer circumferential grinding is performed by diagonal grinding using the grinding device according to the embodiment of the present invention;

FIG. 7 is a schematic diagram when an epitaxial wafer is ground by the grinding apparatus according to the embodiment of the present invention.

FIG. 8 is a cross-sectional view of the outer periphery of the bonded wafer;

FIG. 9 is a cross-sectional view of the outer periphery of the bonded wafer after grinding;

FIG. 10 is a diagram showing a method of removing an unbonded portion without reducing the diameter of the outermost periphery using etching.

FIG. 11 is a diagram illustrating how an unbonded portion is ground using a conventional grinding device without reducing the diameter of the outermost periphery.

FIG. 12 is a diagram showing the force acting on a grindstone during grinding with a conventional grinding device.

FIG. 13 is a diagram showing the force acting on a tapered grindstone during grinding with a conventional grinding device.

FIG. 14 is a schematic diagram of outer periphery grinding by a conventional grinding device.

[Explanation of symbols]

1 Active layer side substrate 3 Base side board 5 Semiconductor substrate (adhesive wafer) 7 Adhesive interface 9　Substrate fixing jig (wafer chuck) 11　Whetstone RG grindstone rotation axis RC board fixing jig rotation axis

Claims (3)

[Claims] 1. A rotating shaft, a disc-shaped grindstone mounted around the rotating shaft, and a substrate fixing jig for horizontally holding a semiconductor substrate, wherein at least the grindstone or the substrate fixing jig is attached to a semiconductor substrate. What is claimed is: 1. A semiconductor substrate grinding device capable of moving in parallel and perpendicular directions to the surface of the substrate, wherein the top surface of the substrate fixing jig and the rotation axis of the grindstone are approximately parallel to each other. 2. The substrate fixing jig grinds the outer periphery of the semiconductor substrate by rotating around the center of the semiconductor substrate to be fixed, and the grindstone or the substrate fixing jig is arranged such that the grinding wheel or the substrate fixing jig rotates around the center of the semiconductor substrate to be fixed. 2. The semiconductor substrate grinding apparatus according to claim 1, wherein the semiconductor substrate grinding apparatus moves perpendicularly to the semiconductor substrate and parallel to the semiconductor substrate. 3. A semiconductor substrate grinding method for removing an unbonded portion of a wafer outer periphery of a bonded wafer obtained by bonding and heating two semiconductor wafers together, the grinding method having a rotation axis parallel to the surface of the bonded wafer. While rotating the grindstone around the rotating shaft, insert at least the substrate below the bonded wafer, leaving at least half of the thickness of the substrate, and inside the unbonded part, and then A method for grinding a semiconductor substrate, comprising rotating the bonded wafer or the grindstone along the outer periphery of the bonded wafer with the center of the wafer serving as a rotation axis.