JP6922851B2 - How to form a gettering layer - Google Patents

Description

The present invention relates to a silicon wafer having a gettering ability.

As a method of imparting gettering ability to a single crystal silicon wafer, it is common practice to form an oxygen precipitate inside the wafer by heat treatment such as RTA to impart a so-called intrinsic gettering (IG) effect. (For example, Patent Document 1).
Further, for wafers in which it is difficult to form oxygen precipitates, such as FZ wafers, low oxygen CZ wafers, and epitaxial wafers, a CVD oxide film or the like is provided on the back surface of the wafer in order to impart gettering ability. Is formed to impart an extrinsic gettering (EG) effect. (For example, Patent Document 2)
Recently, in order to impart gettering ability to impurities with a relatively slow diffusion rate such as Fe, ion implantation is performed on an epitaxial wafer to form a gettering layer in a region close to the device formation region (). So-called proximity gettering) is also performed (for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 10-326790 Japanese Unexamined Patent Publication No. 5-29323 International Publication No. 2015/034075

However, in the formation of proximity gettering by the ion implantation, it is necessary to form an oxide film on the wafer surface before the ion implantation, remove the oxide film after the ion implantation, and perform a crystalline recovery heat treatment step. .. Such a step has a problem that the number of steps required for forming the gettering layer is increased and the throughput is lowered. In addition, as the number of processes increases, the chances of receiving various types of contamination also increase. Therefore, it has been desired to form a gettering layer by a simple method with a small number of steps.

Therefore, the present invention is a simple method that does not require forming an oxide film on the wafer surface before forming the gettering layer or performing a crystallinity recovery heat treatment step after forming the gettering layer, and moreover. It is an object of the present invention to provide a method for surely forming a gettering layer in a desired region, and a new silicon wafer in which a gettering layer is formed inside a single crystal silicon wafer.

The present invention has been made to achieve the above object, and is a method of forming a gettering layer inside a single crystal silicon wafer by irradiating the single crystal silicon wafer with laser light to form the single crystal. A gettering layer that forms a polycrystalline silicon layer as the gettering layer by converting a predetermined region inside the single crystal silicon wafer into polycrystalline silicon by aligning the condensing point of the laser beam inside the silicon wafer. A method of forming is provided.

According to such a method for forming a gettering layer, a gettering layer can be formed inside a single single crystal silicon wafer by a simple method without using a method such as ion implantation or bonding. Further, it is not necessary to form an oxide film or the like on the wafer surface before the process of forming the gettering layer, and it is not necessary to perform a crystallinity recovery heat treatment step after forming the gettering layer.

At this time, the center wavelength of the laser beam can be set to 900 to 1100 nm.

Thereby, the single crystal silicon can be more effectively converted into the polycrystalline silicon within a predetermined range in the depth direction of the single crystal silicon wafer.

At this time, the peak power density at the condensing point of the laser light can be set ^{to 1 × 10 8} to 1 × 10 ¹² W / cm ^2.

This makes it possible to more effectively convert single crystal silicon to polycrystalline silicon.

At this time, the irradiation conditions of the laser beam can be adjusted so that the thickness of the polycrystalline silicon layer is 1 nm or more and 10 μm or less.

This makes it possible to a gettering layer having a more effective gettering ability.

At this time, in order to adjust the depth of forming the polycrystalline silicon layer, the irradiation conditions can be determined based on the following formula.
Xd = 10 ^-11 exp (0.0287λ)
However, Xd: depth of the polycrystalline layer (μm), λ = center wavelength of laser light (nm)

Thereby, the depth for forming the polycrystalline silicon layer can be easily set.

At this time, as the single crystal silicon wafer, any of an FZ wafer, a CZ wafer having an oxygen concentration of 7 ppma (JEIDA) or less, and an epitaxial wafer can be used.

As a result, effective gettering ability can be imparted even to a wafer in which oxygen precipitates are difficult to form.

Further, the present invention is a silicon wafer on which a gettering layer is formed, and is a multi-layer as a gettering layer in contact with a first single crystal silicon layer and the first single crystal silicon layer from the surface of the silicon wafer. It has a crystalline silicon layer and a second single crystal silicon layer in contact with the polycrystalline silicon layer as the gettering layer, and the thickness of the first single crystal silicon layer is 1 μm or more and 500 μm or less. To provide a silicon wafer.

According to such a silicon wafer, it becomes a novel silicon wafer which has an effective gettering layer by a polycrystalline silicon layer in a single single crystal silicon wafer.

As described above, according to the gettering layer forming method of the present invention, a gettering layer is formed inside a single single crystal silicon wafer by a simple method without using a method such as ion implantation or bonding. It becomes possible to form. Further, according to the silicon wafer of the present invention, it is a novel silicon wafer having an effective gettering layer composed of a polycrystalline silicon layer in a single single crystal silicon wafer.

It is a conceptual diagram of the formation method of the gettering layer of this invention. It is a figure which showed an example of the processing flow including the method of forming a gettering layer by this invention together with the schematic diagram of a wafer. The relationship between the center wavelength of the laser and the depth at which the polycrystalline silicon layer is formed is shown. It is a cross-sectional SEM image of the silicon wafer in which the polycrystalline silicon layer was formed in the Example. This is the result of verifying the gettering ability of the silicon wafer of the present invention.

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

As described above, it is not necessary to form an oxide film on the wafer surface before forming the gettering layer, or to perform a crystallinity recovery heat treatment step after forming the gettering layer, which is a simple method and is desired. There has been a demand for a method for reliably forming a gettering layer in the above region and a new silicon wafer in which a gettering layer is formed inside a single crystal silicon wafer.

As a result of diligent studies on the above problems, the present inventors have formed a gettering layer inside a single crystal silicon wafer by irradiating the single crystal silicon wafer with laser light to form the single crystal silicon. By aligning the condensing point of the laser beam inside the wafer, a predetermined region inside the single crystal silicon wafer is made into polycrystalline silicon, and the gettering layer forming the polycrystalline silicon layer as the gettering layer is formed. We have found that a gettering layer composed of a polycrystalline silicon layer can be formed inside a single single crystal silicon wafer by a simple method without using a method such as ion injection or bonding, and the present invention has been made. completed.

Further, as a result of diligent studies on the above problems, the present inventors have formed a silicon wafer in which a gettering layer is formed, and from the surface of the silicon wafer, a first single crystal silicon layer and the first single crystal layer. It has a polycrystalline silicon layer as a gettering layer in contact with a crystalline silicon layer, a second single crystal silicon layer in contact with a polycrystalline silicon layer as the gettering layer, and a thickness of the first single crystal silicon layer. We have found that a silicon wafer having a thickness of 1 μm or more and 500 μm or less becomes a novel silicon wafer having an effective gettering layer in a single single crystal silicon wafer, and completed the present invention.

Hereinafter, description will be made with reference to the drawings.

By irradiating a silicon wafer with laser light, the present inventors melt the silicon in the irradiation region, and when the melted silicon recrystallizes, a polycrystalline silicon layer is formed, which functions as a gettering layer. I found out to do.

FIG. 1 shows a conceptual diagram of a method for forming a gettering layer of the present invention. Laser light 3 is irradiated from the surface 2 side of the single crystal silicon wafer 1, the light is focused inside the single crystal silicon wafer 1, and the single crystal silicon is melted and recrystallized at the condensing part to be converted into polycrystalline silicon. Quality and form the polycrystalline silicon layer 4.
FIG. 2 shows a process flow for forming the polycrystalline silicon layer 4 inside the single crystal silicon wafer 1 according to the present invention.
First, the single crystal silicon wafer 1 is prepared. As the wafer to be prepared, an FZ wafer, a CZ wafer having an oxygen concentration of 7 ppma (JEIDA) or less, an epitaxial wafer, or the like can be used. By applying the method for forming a gettering layer of the present invention to a wafer in which such oxygen precipitates are difficult to form, an effective gettering ability can be imparted.

Next, the oxide film 5 for surface protection may be formed on the single crystal silicon wafer 1. In the formation of the polycrystalline silicon layer 4 as the gettering layer of the present invention, the laser beam only passes through the single crystal silicon wafer 1 as described later, and in principle there is no concern about contamination. Therefore, the ion implantation process is performed. It is not necessary to form the oxide film 5 for surface protection as in the above. However, it goes without saying that the formation of the oxide film 5 for surface protection is not excluded, and the oxide film 5 for surface protection may be formed in order to lower the level of contamination. FIG. 2 shows a process flow in the case of forming the oxide film 5 for surface protection.

Next, the single crystal silicon wafer 1 is irradiated with a laser, and a part of the region inside the wafer is melted and recrystallized to form polycrystalline silicon to form the polycrystalline silicon layer 4.
At this time, for example, a near-infrared region semiconductor laser having a laser center wavelength of 900 to 1100 nm can be used. With such a central wavelength of laser light, by absorbing sufficient photons into the wafer, single crystal silicon can be melted more effectively, and the depth and thickness of the melted silicon layer can be controlled. Can be higher.

Next, when the oxide film 5 for surface protection is formed, the oxide film 5 is removed.
In this way, from the surface of the silicon wafer, the first single crystal silicon layer 6, the polycrystalline silicon layer 4 as the gettering layer in contact with the first single crystal silicon layer 6, and the multi-layer as the gettering layer. A silicon wafer 8 having a second single crystal silicon layer 7 in contact with the crystalline silicon layer 4 can be obtained.

Here, the control of the depth at which the polycrystalline silicon layer is formed will be described.
The central wavelength of the laser beam is a parameter for controlling the penetration depth of the laser beam. A near-infrared region semiconductor laser beam was used as the laser beam, and the central wavelength of the laser beam was changed to investigate the relationship with the depth (distance from the wafer surface) of the formed polycrystalline silicon layer. The result is shown in FIG. Of the graph of FIG. 3 (A), an enlarged low wavelength region of the central wavelength of the laser beam is shown in FIG. 3 (B).
The irradiation conditions of the other laser light, a peak power density of the laser beam ^{1 × 10 8 (W / cm} 2), the irradiation morphism time was 30 nsec.

By obtaining the regression equation from the results of FIG. 3, it was found that the relationship between the center wavelength of the laser and the depth at which the polycrystalline silicon layer was formed (distance from the wafer surface) is expressed by the following equation.
Xd = 10 ^-11 exp (0.0287λ)
Here, Xd is the depth of the polycrystalline layer (distance from the wafer surface; μm), and λ is the center wavelength (nm) of the laser beam.
From the above formula, it can be seen that when the central wavelength of the laser beam is 900 to 1100 nm, the depth from the surface on which the polycrystalline silicon layer is formed can be controlled in the range of 1 μm to 500 μm. In other words, it is possible to obtain a silicon wafer in which the thickness of the first single crystal silicon layer 6 is 1 μm or more and 500 μm or less.

Further, the thickness (width in the depth direction) of the polycrystalline silicon layer can be controlled by adjusting the intensity of the laser beam and the irradiation time.
The thickness of the polycrystalline silicon layer is preferably 1 nm or more and 10 μm or less. With such a range, a gettering layer having a more effective gettering ability can be obtained.
The intensity of the laser light is determined by the peak power density (W / cm ^{2) at the focusing point of the laser light.} The peak power density at the condensing point is preferably ^{1 × 10 8} to 1 × 10 ¹² W / cm ^2. With such a peak power density, it is possible to more effectively melt the single crystal silicon by converting the energy absorbed by the irradiation part into thermal energy, and the depth and thickness of the single crystal silicon layer to be melted. The controllability of the energy can be improved.

The laser light irradiation may be performed at room temperature of the single crystal silicon wafer, or may be performed, for example, in a state of being heated to about 400 ° C. The upper limit of the temperature at the time of laser light irradiation is not particularly limited, but it is preferably 800 ° C. or lower in consideration of melting only the inside of the single crystal silicon wafer and productivity.

Further, the irradiation of the laser light is preferably a low-power laser, for example, an ultrashort pulse laser such as a femtosecond laser. This is because the low-power laser can transfer heat energy only to a predetermined depth position with better controllability as compared with a high-power laser such as a YAG laser.

Hereinafter, the present invention will be described in detail with reference to examples, but this does not limit the present invention.

(Example)
First, a single crystal silicon wafer having a resistivity of 10 Ωcm, a diameter of 200 mm, and a crystal plane orientation (100) was prepared.
Next, an oxide film as a pollution-preventing oxide layer was formed on the surface of the single crystal silicon wafer. The oxidizing conditions were 900 ° C. for 2 hours and an oxidizing atmosphere.

Next, as described above, based on the relationship between the central wavelength of the laser beam derived based on FIG. 3 and the depth at which the polycrystalline silicon layer is formed, the polycrystalline silicon is located at a depth of about 20 μm from the surface. In order to form a layer, laser light irradiation was performed with the central wavelength of the near-infrared region semiconductor laser light set to 987 nm. As another condition, 2 mm beam diameter at the focal point, the peak of the laser beam power density ^{1 × 10 8 (W / cm} 2), the irradiation morphism time was 30 nsec.

The silicon wafer provided with the polycrystalline silicon layer thus obtained was cleaved and etched, and the internal structure of the wafer was observed with a high-magnification microscope.
The observation results are shown in FIG. As shown in the upper figure of FIG. 4, the single crystal silicon is modified to a thickness of about 10 μm in the depth direction from a place having a depth of about 20 μm from the surface, and is shown in the lower figure (enlarged image) of FIG. As a result, it was found that only the modified portion was a polycrystalline silicon layer.

Next, in order to confirm the gettering ability of the polycrystalline silicon layer, the silicon wafer having the produced polycrystalline silicon layer was intentionally contaminated and evaluated.
First, Ni was applied to the wafer surface at ^{a contamination amount of 1 × 10 11} atoms / cm ^2. Then, it was subjected to diffusion heat treatment at 800 ° C. for 20 minutes and cooled to room temperature. This silicon wafer is selectively etched (1 to 5 μm / Step) from the surface using a mixed acid chemical solution (HF / HNO ₃ / H ₂ O = 1: 7.5: 5), and Ni is used by ICP-MS. The distribution in the depth direction was measured. The result is shown in FIG.

As can be seen from FIG. 5, a Ni peak was confirmed in the region where the polycrystalline silicon layer having a depth of about 20 μm was formed from the surface. It was confirmed that the formed polycrystalline silicon layer functions as a gettering layer.

According to the method for forming a gettering layer of the present invention, a polycrystalline silicon layer that functions as a gettering layer can be easily formed inside a single single crystal silicon wafer. Further, when the method for forming the gettering layer of the present invention is applied to a substrate such as an FZ wafer, a CZ wafer having an oxygen concentration of 7 ppma (JEIDA) or less, and an epitaxial wafer, even a wafer in which oxygen precipitates are difficult to form can be formed. , Can impart effective gettering ability.

The present invention is not limited to the above embodiment. The above-described embodiment is an example, and any object having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect and effect is the present invention. Is included in the technical scope of.

1 ... Single crystal silicon wafer, 2 ... Surface, 3 ... Laser light,
4 ... Polycrystalline silicon layer (gettering layer), 5 ... Oxide film,
6 ... 1st single crystal silicon layer, 7 ... 2nd single crystal silicon layer,
8 ... Silicon wafer.

Claims (5)

A method of forming a gettering layer inside a single crystal silicon wafer.
By irradiating the single crystal silicon wafer with laser light and aligning the focusing point of the laser light with the inside of the single crystal silicon wafer, a predetermined region inside the single crystal silicon wafer is made into polycrystalline silicon, and the above. Forming a polycrystalline silicon layer as a gettering layer ,
A method for forming a gettering layer, which comprises determining irradiation conditions based on the following formula in order to adjust the depth at which the polycrystalline silicon layer is formed.
Xd = 10 ^-11 exp (0.0287λ)
However, Xd: depth of polycrystalline silicon layer (μm), λ = center wavelength of laser light (nm) The method for forming a gettering layer according to claim 1, wherein the central wavelength of the laser beam is 900 to 1100 nm. The method for forming a gettering layer according to claim 1 or 2, wherein the peak power density at the condensing point of the laser light is 1 × 10 ⁸ to 1 × 10 ¹² W / cm ^2. The gettering according to any one of claims 1 to 3, wherein the irradiation conditions of the laser beam are adjusted so that the thickness of the polycrystalline silicon layer is 1 nm or more and 10 μm or less. How to form a layer. The getter according to any one of claims 1 to 4 , wherein an FZ wafer, a CZ wafer having an oxygen concentration of 7 ppma (JEIDA) or less, or an epitaxial wafer is used as the single crystal silicon wafer. How to form a ring layer.

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