JP7036085B2 - Etching method for silicon wafer - Google Patents

Description

The present invention relates to an etching method for a silicon wafer.

In the silicon wafer manufacturing process, a wafer sliced thinly from a single crystal ingot state is generally flattened through chamfering and grinding. At this time, various large and small scratches and processing strains due to the above processing are introduced on the front and back surfaces of the wafer, and if these are manifested in the subsequent process, it may cause a serious quality problem.

Therefore, usually, an etching process is performed to remove these scratches and processing strains. As an etching method, a batch method in which the front and back surfaces of a plurality of wafers are simultaneously processed and a spin etching method in which the front and back surfaces of the wafer are sequentially processed by a single sheet are known (see Patent Document 1). In addition, there are two means depending on the purpose, one is treatment with an acid etching solution and the other is treatment with an alkaline etching solution. For example, in the case of acid etching, a mixed acid containing fluorine and nitric acid whose concentration is appropriately adjusted. Is generally used.

Japanese Unexamined Patent Publication No. 2007-53178

When acid etching a silicon wafer is performed by a spin etching method, the used etching solution is usually recovered and used again as an etching solution. Therefore, when the silicon wafer is acid-etched, the amount of Si dissolved in the etching solution increases according to the number of processed sheets. Further, since the increase in the amount of Si dissolved means the decrease in the etching chemical species contained in the etching solution, the average etching rate decreases. Therefore, a decrease in the average etching rate is unavoidable during continuous processing.

Further, the wafer etching rate in spin etching has an in-plane distribution of the wafer according to the processing conditions and the fluid characteristics of the etching solution. This distribution fluctuates even if either one of the processing conditions and the fluid characteristics changes. Therefore, when performing spin etching processing accompanied by a change in the amount of Si dissolved as described above, it is necessary to consider not only the average etching rate but also the change in the etching rate distribution in the wafer surface. Conventionally, it is common to replenish fluoroacid during continuous processing, but this method has a problem that it can cope with a decrease in the average etching rate but cannot cope with a change in the etching rate distribution in the wafer surface.

The present invention has been made in view of such circumstances, and even if the amount of Si dissolved in the acid etching solution changes, it is possible to suppress the change in the etching rate distribution in the wafer surface, and the wafer shape after etching can be suppressed. It is an object of the present invention to provide an etching method for a silicon wafer, which can improve the etching method.

In order to solve the above object, in the present invention, the supply range of the acid etching solution is set by rotating the silicon wafer while supplying the acid etching solution to the front surface and / or the back surface of the silicon wafer through a supply nozzle. A silicon wafer etching method including a spin etching step in which acid etching is performed by enlarging the entire surface of the front surface and / or the back surface of the silicon wafer.
Provided is an etching method for a silicon wafer, which comprises performing acid etching by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution in the spin etching step.

In the silicon wafer etching method of the present invention, by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution, the change in the etching rate distribution in the wafer surface due to the increase in the amount of Si dissolved is suppressed. It becomes possible. Further, even if the amount of Si dissolved increases, the shape of the wafer after etching can be improved.

At this time, by repeating the spin etching process, a plurality of silicon wafers are continuously processed.
During the continuous processing, it is preferable to recover the acid etching solution used in the spin etching step, return it to the etching solution tank for storing the acid etching solution, and use it again as the acid etching solution.

With such a method, it is possible to minimize the change in the shape of the silicon wafer even during continuous machining accompanied by a change in the amount of Si dissolved.

Further, as the acid etching solution, it is preferable to use a mixed solution containing fluoroacid and nitric acid, or a mixed solution in which at least one of acetic acid, phosphoric acid and sulfuric acid is added thereto.

Such a mixed liquid can be suitably used for spin etching of a silicon wafer.

According to the silicon wafer etching method of the present invention, it is possible to suppress a change in the etching rate distribution in the wafer surface by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution. Further, even if the amount of Si dissolved increases, the shape of the wafer after etching can be improved.

It is a figure which shows the change of the flatness by the Si dissolution amount when the rotation speed of a silicon wafer is changed. It is a schematic diagram of a general etching apparatus used in a spin etching method.

As described above, in the acid etching by the spin etching method, there is a problem that the etching rate distribution in the wafer surface changes when the amount of Si dissolved in the acid etching solution changes.

When the amount of Si dissolved in the acid etching solution increases, not only the etching reaction chemical species contained in the acid etching solution decrease, but also the kinematic viscosity of the acid etching solution decreases. Therefore, in the spin-type acid etching in which the fluid characteristics of the acid etching solution cannot be ignored, not only the average etching rate decreases but also the distribution state of the etching rate in the plane changes due to the increase in the amount of Si dissolved.

Normally, since the silicon wafer being spin-etched rotates at a constant angular velocity, the etching rate when a diffusion-controlled acid etching solution is used increases as the peripheral speed of the wafer increases. Therefore, the etching allowance usually increases toward the outer peripheral portion of the wafer.

Here, since the kinematic viscosity of the acid etching solution decreases as the amount of Si dissolved increases, the average flow velocity of the acid etching solution in the region where the peripheral speed of the wafer is high decreases as compared with the case where the amount of Si dissolved decreases. Therefore, the etching allowance on the outer peripheral portion of the wafer is reduced as compared with the case where the amount of Si dissolved is small.

Further, in spin etching, the center of rotation of the wafer and the position of the nozzle for supplying the acid etching liquid to the wafer usually coincide with each other, but the etching rate is affected by the collision jet formed directly under the nozzle in the vicinity thereof. There is a stagnation point at the center of the collision jet, and at the stagnation point, the flow velocity of the acid etching solution in the direction parallel to the wafer surface is theoretically 0 μm / s.

Normally, the region of the stagnation point is a negligible size, and the flow velocity of the acid etching solution immediately increases due to the peripheral speed of the wafer, so that it does not appear as a decrease in the etching allowance. However, when the amount of Si dissolved increases and the kinematic viscosity of the acid etching solution decreases, the average flow velocity of the acid etching solution does not easily increase depending on the peripheral speed, so the etching rate is slower than when the amount of Si dissolved is small. Therefore, the etching allowance in the area is reduced.

That is, even if an acid etching solution having the same processing conditions and the same composition is used, the etching rates around the outer peripheral portion and the center of the silicon wafer change due to the above-mentioned causes, and the etching rate distribution in the wafer surface changes. Therefore, if the amount of Si dissolved in the acid etching solution is different, the shape of the wafer after the spin etching process will be different.

In the present invention, as a means for dealing with such a change in wafer shape, the wafer rotation speed is controlled according to the amount of Si dissolved. Specifically, in an acid etching solution having a small amount of Si dissolved and a relatively high kinematic viscosity, the wafer rotation speed is set as a low rotation speed, and in an acid etching solution having a large amount of Si dissolved and a relatively small kinematic viscosity, the wafer rotation speed is set. By etching at high rotation speed, the change in wafer shape due to the amount of Si dissolution is minimized.

That is, in the present invention, the silicon wafer is rotated while supplying the acid etching solution to the front surface and / or the back surface of the silicon wafer through the supply nozzle, so that the supply range of the acid etching solution is adjusted to the surface and / or the surface of the silicon wafer. Alternatively, it is an etching method for a silicon wafer including a spin etching step in which acid etching is performed by enlarging the entire surface of the back surface.
In the spin etching step, the silicon wafer etching method is characterized in that acid etching is performed by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution.

Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

FIG. 2 is a schematic diagram of a general etching apparatus used in the spin etching method. Specifically, for example, Spin Etcher MSE-7000EL-MH manufactured by Sanmasu Semiconductor Industry Co., Ltd. can be used.

Generally, the etching apparatus 100 is composed of an etching processing unit 11 and an etching liquid supply unit 12.

The etching processing unit 11 can be provided with a vacuum suction stage 2 and a supply nozzle 3. Further, the etching liquid supply unit 12 can include a liquid feeding pump 13 that feeds the acid etching liquid 8 from the etching liquid tank 6 and the etching liquid tank 6 to the etching processing unit 11.

The silicon wafer 1 is horizontally installed in the center of the vacuum suction stage 2 with the front surface or the back surface facing up, and can be held by vacuum suction on the vacuum suction stage 2 connected to the vacuum source 10.

The vacuum suction stage 2 can be rotated in the θ direction in the figure with the center of the vacuum suction stage 2 as the rotation axis by a rotation unit having a θ-axis motor and a θ spindle (not shown) below the stage.

Next, the etching method of the silicon wafer of the present invention will be described by taking the case of using the etching apparatus 100 shown in FIG. 2 as an example.

In the silicon wafer etching method of the present invention, the silicon wafer is rotated to supply the acid etching solution while supplying the acid etching solution 8 stored in the etching solution tank 6 through the supply nozzle to the front surface and / or the back surface of the silicon wafer. It includes a spin etching step of expanding the range to the entire surface of the silicon wafer 1 and performing acid etching.

In the spin etching step, the acid etching liquid 8 is supplied from the etching liquid tank 6 of the etching liquid supply unit 12 to the supply nozzle 3 above the vacuum suction stage via the liquid feed pump 13, and is held on the vacuum suction stage 2. The acid etching liquid 8 can be supplied onto the rotating silicon wafer 1.

While the acid etching solution 8 is being supplied, the supply nozzle 3 reciprocates linearly in the radial direction of the silicon wafer 1 through the center of the silicon wafer 1 as shown by the arrow 4 (movement direction of the supply nozzle) in FIG. It is common to exercise.

The acid etching liquid 8 supplied onto the silicon wafer 1 moves on the silicon wafer 1 in accordance with the rotation of the silicon wafer 1, becomes droplets 5 from the outer peripheral portion of the silicon wafer 1, is shaken off and falls, and is etched. It is discharged from the processed part.

At this time, in the present invention, acid etching is performed by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution.

As described above, even if an acid etching solution having the same processing conditions and the same composition is used, the etching rate around the outer periphery and the center of the silicon wafer changes, and the etching rate distribution in the wafer surface changes. If the amount of Si dissolved in the etching solution is different, the shape of the wafer after the spin etching process will be different. According to the present invention, by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution, it is possible to suppress the change in the etching rate distribution in the wafer surface due to the increase in the amount of Si dissolved. Further, even if the amount of Si dissolved increases, the shape of the wafer after etching can be improved.

That is, when an acid etching solution having a small amount of Si dissolved and a large kinematic viscosity is used, the wafer rotation speed is set to a low rotation speed in order to make the flow velocity of the acid etching solution on the wafer appropriate, and the amount of Si dissolved is large. When an acid etching solution having a low viscosity is used, the wafer rotation speed may be set to a high rotation speed in order to suppress a decrease in the flow velocity of the acid etching solution on the wafer.

The wafer rotation speed may be changed, for example, with a Si dissolution amount of 6 g / L, a rotation speed of less than 1300 rpm when the Si dissolution amount is less than 6 g / L, a rotation speed of 1300 rpm or more when the Si dissolution amount is 6 g / L or more, and the like. can. However, since the appropriate amount of Si dissolved differs depending on the processing conditions and the composition of the acid etching solution, the amount of Si dissolved to change the wafer rotation speed is not limited to 6 g / L. Further, the wafer rotation speed before and after the change can be appropriately determined depending on the processing conditions and the composition of the acid etching solution.

After satisfying the predetermined etching allowance, when the etching process is completed, the supply of the acid etching liquid 8 from the etching liquid tank 6 is stopped, water 9 is supplied from the water supply source 7 to the supply nozzle 3, and the water is placed on the vacuum suction stage 2. Water 9 can be supplied onto the silicon wafer 1 that is held and rotated.

The water 9 supplied onto the silicon wafer 1 moves on the silicon wafer 1 following the rotation of the silicon wafer 1, and replaces the acid etching liquid 8 remaining on the silicon wafer 1 with water 9 of the silicon wafer 1. The droplets 5 are discharged from the outer peripheral portion.

When the replacement of the acid etching solution 8 on the silicon wafer 1 with water is completed, the supply of water 9 from the water supply source 7 is stopped, and the silicon wafer 1 is rotated at high speed to scatter all the water on the silicon wafer 1. , A dried silicon wafer 1 can be obtained.

Further, in the present invention, by repeating the spin etching step, a plurality of silicon wafers are continuously machined, and during the continuous machining, the acid etching solution used in the spin etching step is recovered and returned to the etching solution tank. It is preferable to use it again as an acid etching solution. With such a method, it is possible to minimize the change in the shape of the silicon wafer even during continuous machining accompanied by a change in the amount of Si dissolved.

The acid etching liquid droplets 5 discharged from the outer peripheral portion of the silicon wafer 1 can be recovered in the etching liquid tank 6 by the etching liquid recovery mechanism 14. Then, the acid etching solution after recovery can be used as the acid etching solution 8 again.

In the present invention, for the Si dissolution amount, for example, the cumulative total of the Si dissolution amount during continuous processing can be calculated from the etching allowance per silicon wafer, and the wafer rotation speed is reached when an appropriate Si dissolution amount is reached. By changing the above, in the spin etching processing during continuous processing accompanied by a change in the amount of Si dissolved, continuous processing that minimizes the change in wafer shape after processing becomes possible. Further, the method for calculating the Si dissolution amount is not particularly limited, and it is obtained by a mechanism 15 or the like for measuring the Si dissolution amount provided in the etching solution tank or the like, and the silicon wafer is determined according to the obtained Si dissolution amount. You can also change the number of revolutions. Further, the rotation speed of the silicon wafer may be increased in proportion to the value according to the amount of Si dissolved.

Further, the acid etching solution used in the present invention may be a mixed solution containing fluoroacid and nitric acid, but acetic acid, sulfuric acid or phosphoric acid may be appropriately combined and mixed with the mixed solution. Such a mixed liquid can be suitably used for spin etching of a silicon wafer. The mixing ratio may be an acid etching solution in which, for example, 1 to 80% of phosphoric acid and 10 to 80% of nitric acid are mixed in mass ratio, but acetic acid is, for example, 10 to 30%, and sulfuric acid is, for example, 10 to 80% by mass ratio. 25% and, for example, 10 to 50% of phosphoric acid may be mixed in an arbitrary ratio.

In the above description, the case where one side of the silicon wafer is spin-etched has been described as an example, but the present invention is not limited to this, and the acid etching solution is supplied not only from the upper surface but also from the lower surface to simultaneously etch the front and back surfaces. You can also do it.

Hereinafter, the present invention will be described in more detail with reference to experimental examples.

[Experimental example]
The silicon wafer was etched using the etching apparatus shown in FIG. 2. At this time, using acid etching solutions having different Si dissolution amounts, the silicon wafer has a low rotation speed, specifically, a rotation speed of 300 rpm and a rotation speed of 800 rpm, and a high rotation speed, specifically, a rotation speed of 1800 rpm. It was processed at 2500 rpm. FIG. 1 shows a change in flatness depending on the amount of Si dissolved when the rotation speed of the silicon wafer is changed. The flatness referred to here indicates a allowance PV (Peek-Valley) in the surface of a silicon wafer. At this time, a mixed solution of phosphoric acid and nitric acid was used as the acid etching solution (by mass%, 4% of fluorousic acid and 47% of nitric acid, and the balance of less than 100% was water), and the amount of etching solution was 2. It was processed at 5 L / m and an acid etching solution temperature of 24 ° C.

As shown in FIG. 1, when the wafer is processed by fixing it at a low rotation speed, for example, 300 rpm or 800 rpm, the wafer flatness deteriorates to around 1.0 μm in this example when the Si dissolution amount increases. When the wafer is processed at a high rotation speed, for example, 1800 rpm or 2500 rpm, the wafer flatness deteriorates to around 1.0 μm in this example when the Si dissolution amount is small, contrary to the case of the low rotation speed. do.

Therefore, according to the example shown in FIG. 1, when the Si dissolution amount of the acid etching solution is less than 6 g / L, the rotation speed is as low as 300 rpm or 800 rpm, and when the Si dissolution amount is 6 g / L or more, the rotation speed is 1800 rpm or more. It can be seen that the wafer flatness can be reduced to 0.7 μm or less regardless of the amount of Si dissolved by changing to a high rotation speed such as 2500 rpm and performing etching.

From the above, in the method of the present invention, by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution, the change in the etching rate distribution in the wafer surface due to the increase in the amount of Si dissolved is suppressed. It was shown that the wafer flatness can be improved even if the amount of Si dissolved in the acid etching solution changes.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and the present invention can be anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same function and effect. Is included in the technical scope of.

100 ... Etching device,
1 ... Silicon wafer, 2 ... Vacuum suction stage,
3 ... Supply nozzle, 4 ... Supply nozzle movement direction, 5 ... Droplet,
6 ... Etching liquid tank, 7 ... Water supply source, 8 ... Acid etching liquid,
9 ... water, 10 ... vacuum source, 11 ... etching processing part,
12 ... Etching liquid supply unit, 13 ... Liquid feeding pump,
14 ... Etching liquid recovery mechanism, 15 ... Mechanism for measuring the amount of Si dissolved.

Claims (3)

By rotating the silicon wafer while supplying the acid etching solution to the front surface and / or the back surface of the silicon wafer through a supply nozzle, the supply range of the acid etching solution is expanded to the entire surface of the front surface and / or the back surface of the silicon wafer. This is a silicon wafer etching method that includes a spin etching process that performs acid etching.
A method for etching a silicon wafer, which comprises performing acid etching by changing the rotation speed of the silicon wafer according to the amount of Si dissolved in the acid etching solution in the spin etching step. By repeating the spin etching process, a plurality of silicon wafers can be continuously processed.
The first aspect of the present invention is characterized in that, during the continuous processing, the acid etching solution used in the spin etching step is recovered, returned to the etching solution tank for storing the acid etching solution, and used again as the acid etching solution. The method for etching a silicon wafer according to the description. Claim 1 or claim 2 is characterized in that, as the acid etching solution, a mixed solution containing fluoroacid and nitric acid, or a mixed solution in which at least one of acetic acid, phosphoric acid, and sulfuric acid is added is used. The method for etching a silicon wafer according to the above.

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