JPH0366107B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a wafer polishing method, and is a polishing method that obtains a highly accurate single-sided mirror surface without damaging the wafer and improves polishing efficiency. Regarding.

[Prior art]

Wafers are required to have high dimensional accuracy and large diameter in order to respond to higher integration and lower prices of semiconductor devices.

Conventional wafer polishing equipment attaches the wafer to an adhesive tool, and polishes only one side of the wafer by pressing the adhesive tool with the wafer attached onto a rotating disk while supplying an abrasive material.

However, in the current state of high dimensional accuracy and larger diameters, the accuracy of attaching wafers to adhesive tools can no longer meet the required accuracy, and as an alternative, a double-sided polishing machine that eliminates the attaching process has been developed. has been done.

Since both sides of the wafer polished by this double-sided polishing device are polished, a new technical problem arises in the semiconductor manufacturing process that has traditionally polished only one side. Ta.

One way to solve this problem is to use two wafers.
Wafers are stacked and only one side of the wafers is polished.

First, in giving a detailed explanation, an outline of the double-sided polishing apparatus will be explained using FIG. 1. In the figure,
A wafer 1, which is a workpiece, is mounted in a cavity of a carrier 2. The wafer 1 mounted on the carrier 2 in this manner is sandwiched between elastic nonwoven fabrics 5 attached to each of the upper surface plate 3 and the lower surface plate 4. The carrier 2 is held between the gears of a center gear 6 on the inner periphery and an internal gear 7 on the outer periphery, and is connected to a drive shaft 8.
Accordingly, the upper and lower surface plates 3 and 4 and the carrier 2 are rotated, and both surfaces of the wafer 1 are polished by the polishing agent supplied from the cavity 9.

In this double-sided polishing apparatus, when two wafers 1 are simply stacked and polished as shown in FIG. 1, a liquid layer of abrasive enters between the stacked wafers 1 and the two wafers rotates, and the mating surfaces of the wafers are polished. Furthermore, there is a problem in that foreign matter gets mixed into the mating surfaces of the wafers, causing scratches and other flaws on the mating surfaces.

Also, as shown in FIG. 2, it is conceivable to provide recessed holes on both sides of the wafer mounting portion of the carrier 2, and to polish only one side of the wafer by fitting the wafer into the recessed holes, but in this case, There is a problem in that the rotation of the carrier 2 causes the wafer to fly out of the recessed hole, resulting in damage to the wafer.

In addition, as shown in FIG. 3, when polishing is performed by holding wafers one by one in the cavity of the carrier 2 (in this case, both sides of the wafer are polished), the thickness of the carrier 2 is adjusted to the thickness of the wafer. Since it is necessary to make the carrier 2 thinner than the thickness, the tooth tip of the carrier 2 also becomes thinner and the strength of the tooth tip decreases.

As a result, when trying to increase the polishing efficiency by increasing the polishing pressure, the strength of the tooth tips is limited, making it impossible to increase the polishing pressure. There was also a problem that the polishing efficiency was lowered.

[Purpose of the invention]

The present invention aims to provide a wafer polishing method that solves all of the above technical problems.

[Summary of the invention]

That is, in the present invention, two wafers are bonded together while maintaining highly accurate flatness, and after this is mounted on a carrier of a double-sided polishing machine and polished, the two wafers are separated so that only one side is polished. The wafer is heated while maintaining its flatness, then an adhesive is added to this wafer, and another wafer is placed on top of this wafer and pressure bonded. The two wafers crimped together in this way are cooled while maintaining their flatness to form a two-piece wafer, which is then polished using a double-sided polishing machine and then bonded together in an adhesive melt. The method is characterized in that the two wafers are separated by heating and melting the agent.

[Embodiments of the invention]

An embodiment of the present invention will be described in detail below. The two wafers are bonded together using wax or cross adhesive. That is, in FIG. 5, FIG. 1 shows wafers 15 and 16 bonded together with wax 10 interposed between them, and FIG. 2 shows wafers 15 and 16 bonded together.
In the case shown in FIG. 3, the wafers 15 and 16 are bonded together using the suction force of the cloth 11. In the case shown in FIG.

The above bonding process will be explained using FIG. 6. In this bonding process, a heating plate 12, a weight 13, and a cooling plate 14 each having a high degree of flatness are used.

First, the wafer 15 is heated on the heating plate 12 while maintaining high flatness. A small amount of wax 10 is dropped onto the wafer 15 heated in this manner. Next, another wafer 16 is placed on top of this and pressed against it by the weight 13. By pressing the wafers 15 and 16 in this manner, the wax 10 has a uniform thickness, and the wax 10 is formed between the wafers 15 and 16.
form a layer. Next, this is sandwiched between cooling plates 14 and wafers 15 and 16 are simultaneously cooled, thereby forming two wafers each having high flatness and having wax 10 as an intermediate layer.

After polishing these two integrated wafers with a double-sided polishing machine, they are heated in a solution such as trichloride,
Separate the wafers to obtain single-sided polished wafers.

The operation of this embodiment configured as above will be explained next. First, a wafer 15 is heated on a heating plate 12 having a high degree of flatness, a small amount of wax 10 is dropped onto the wafer 15, and another wafer 16 is placed on top of this and pressed by a weight 13 having a high degree of flatness. As a result, the wax 10 is spread as a uniform layer between the two wafers 15 and 16 while being melted by the heat of the wafer 15. In this state, next, the wafers 15 and 16 are placed on a cooling plate 14 having a high degree of flatness.
By simultaneously cooling the wafer 1 by
5, 16 and the wax 10 are cooled and solidified without causing thermal distortion. When solidified in this manner, a wafer with high flatness is formed with the wax 10 as an intermediate layer. In other words, two wafers 15 and 16
The total thickness of the wax layer 10 becomes one wafer.

As shown in FIG. 4, these wafers 15 and 16 are
Attach it to the hole in carrier 2.

In this case, since the wafer to be mounted is thick, the carrier 2 can have a sufficiently thick structure, and the tooth tip strength of the carrier 2 can also be made sufficiently strong.

Therefore, a large number of holes are provided in the carrier 2, a large number of wafers are mounted in the holes, and the upper and lower surface plates 3, 4 are mounted.
Polish by increasing the clamping force (polishing pressure). In addition, the abrasive containing free abrasive grains supplied from the cavity 9 is
The two wafers 15 and 16 are integrated with the wax layer 10 in between, so that no penetration occurs. Further, even if it penetrates, it is protected by the wax layer 10 and polishing does not occur on the mating surfaces of the wafers 15 and 16.

After polishing in this manner, the wafer is taken out and heated in a solution such as trichloride to separate the two wafers 15 and 16.

Although the above explanation has been made using wax as an example of the adhesive, the same effect can be obtained by using a cross adhesive liquid.

〔Effect of the invention〕

As detailed above, according to the wafer polishing method of the present invention, the wafer is heated while maintaining its flatness,
By adding an adhesive onto this wafer, placing another wafer on top of it, and pressing it together while maintaining flatness, the adhesive is melted by the heat of the wafer and stretched evenly, resulting in two wafers. A uniform intermediate layer can be formed between the wafers. By simultaneously cooling the two integrated wafers with intermediate layers while maintaining their flatness, thermal distortion between them can be prevented and an integrated composite wafer with high flatness can be created. Obtainable.

When polishing composite wafers made in this way using a double-sided polishing machine, the thickness of the carrier can be increased to sufficiently increase its strength, so a large number of wafers can be mounted at once, and Polishing can be performed with increased polishing pressure, and polishing efficiency can be greatly improved.

Furthermore, since an intermediate layer of adhesive is formed on the mating surfaces of the two wafers, this intermediate layer protects the mating surfaces and prevents them from being polished and from being scratched even if foreign matter intervenes. It has excellent effects such as being able to obtain high-quality wafers that are polished on only one side.

[Brief explanation of drawings]

1 to 3 are cross-sectional views of a conventional polishing method using a double-sided polishing device, FIG. 4 is a diagram showing the polishing method of this embodiment using a double-sided polishing device, and FIG. The figure shows the state in which two wafers are stacked in this example, and FIG. 6 is a diagram showing the process of stacking and fixing the two wafers using wax as an adhesive. . 2...Carrier, 3...Upper surface plate, 4...Lower surface plate, 5...Nonwoven fabric, 6...Center gear, 7...
Internal Gear, 10... Wax, 11...
Cross, 12... Heating plate, 13... Weight, 14...
...cooling plate, 15, 16...wafer.

Claims (1)

[Claims] 1. Heat the wafer while maintaining its flatness, then add an adhesive onto this wafer, then stack another wafer on top of this wafer and press-bond it, and the two wafers bonded in this way The two wafers are simultaneously cooled while maintaining their flatness to form two integrated wafers, and this wafer is polished using a double-sided polishing machine, and then heated and melted in an adhesive melt to form the two wafers. A method for polishing a wafer, characterized by separating the wafer.