JP2012049397A - Method of manufacturing silicon wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicon wafer that sufficiently improves gettering capability, and to provide a method of manufacturing the silicon wafer.SOLUTION: A method of manufacturing the silicon wafer comprises the steps of: irradiating a surface of a silicon wafer with laser to melt a surface layer part in the presence of at least one kind of elements of oxygen, carbon and nitrogen; and solidifying the melted surface layer part to dope with elements into the surface part. The silicon wafer obtained by the manufacturing method has a high concentration of at least one kind of elements of oxygen, carbon and nitrogen.

Description

  The present invention relates to a method for manufacturing a silicon wafer, particularly a silicon wafer having a high gettering capability.

  In recent years, miniaturization of semiconductor devices has been increasingly promoted. For example, paying attention to memory devices, not only the area occupied on the silicon wafer is reduced, but also the memory devices are thinned and stacked to realize miniaturization and large capacity.

  With such miniaturization of semiconductor devices, the performance of semiconductor devices is greatly influenced by metal impurities typified by Cu and Ni contained in the devices. Therefore, in order to realize improvement in device performance and yield, it is important to appropriately suppress the mixing of metal impurities into the semiconductor device layer.

Conventionally, a gettering method for capturing metal impurities is generally used as a method for suppressing the mixing of metal impurities into a semiconductor device layer.
In the gettering method, for example, a method is known in which BMD (Bulk Micro Defect), which is an oxygen precipitate, is formed inside a silicon wafer and used as a gettering site. A gettering method with a higher BMD density is known. Ability is high.

In order to increase the BMD density in the silicon wafer, it is effective to increase the oxygen concentration in the silicon wafer. For this reason, usually, in the process of growing a silicon single crystal ingot by the Czochralski method, a single crystal ingot is manufactured by adjusting the pulling conditions so as to increase the interstitial oxygen concentration taken into the single crystal ingot. By processing, a silicon wafer doped with oxygen at a high concentration is manufactured.
In addition, when growing a single crystal ingot by the Czochralski method, a method of doping carbon that promotes oxygen precipitation or a method of doping nitrogen that forms a thermally stable oxygen precipitation nucleus Is also known.

By the way, for example, Patent Document 1 describes that Cu can be captured by forming a Cu—O—C complex with respect to Cu by simultaneously doping oxygen and carbon.
Further, Patent Document 2 describes that oxygen and nitrogen are combined with vacancies in a wafer to form a complex, and the complex can capture impurities such as Cu.
As described above, it is known that oxygen, carbon, and nitrogen in a wafer improve the gettering ability for metal impurities such as Cu by forming a composite.

JP 2003-209114 A JP 2004-228139 A

However, in the method of simultaneously doping oxygen and carbon during the growth of a silicon single crystal ingot by the Czochralski method described in Patent Document 1, it is limited to a concentration range below the solid solution limit concentration that can be doped by the Czochralski method, For example, when carbon is doped to a solid solution limit concentration such that the concentration of carbon contained in the single crystal ingot exceeds 3 × 10 ¹⁷ atoms / cm ³ , the single crystal structure is disturbed and the single crystal ingot becomes polycrystallized (dislocations). Problem).
For this reason, in the method described in Patent Document 1, only a silicon single crystal ingot having low oxygen and carbon concentrations can be obtained, and a silicon wafer processed and manufactured from this ingot cannot exhibit sufficient gettering ability. Similarly to Patent Document 1, the method described in Patent Document 2 causes dislocation of the single crystal ingot when the concentration of nitrogen contained in the single crystal ingot exceeds 5 × 10 ¹⁵ atoms / cm ^3. The amount of doping is less than the concentration, and the silicon wafer cannot exhibit sufficient gettering ability.
Even when a single-crystal ingot with oxygen, carbon, nitrogen, and other impurity concentrations increased as much as possible is grown by the Czochralski method and a silicon wafer is manufactured by processing this single-crystal ingot, the entire wafer is covered. Thus, a wafer having an increased impurity concentration is manufactured. BMD formed in a silicon wafer functions as a gettering site that captures metal impurities such as Cu and Ni, but BMD is a type of defect and exists in the surface layer of the wafer used as a device fabrication area Then, device characteristics are deteriorated. For this reason, a high temperature heat treatment (outward diffusion heat treatment) for reducing the impurity concentration of the surface layer portion is applied to the silicon wafer in advance so that BMD is not formed on the surface layer portion of the silicon wafer used as the de-high speed fabrication region. There are also problems such as having to keep it.

Furthermore, an improvement in gettering ability is required in a subsequent process in the device process. In other words, with the recent thinning of devices, the wafer back surface layer part generated by grinding after mechanically grinding the wafer back side where the device is not manufactured in the subsequent process in the device process to thin the wafer Processes such as etching and polishing are performed so as to remove distortion. For this reason, even if a wafer with excellent gettering capability in which an IG layer (intrinsic gettering layer) with a high BMD density is formed inside the wafer (for example, near the center of the wafer thickness) is used in the device process, the wafer described above Due to the thinning process, even the IG layer formed inside the wafer is scraped, preventing metal contamination during grinding of the backside of the wafer and during each heat treatment process such as sintering performed after this grinding. I can't.
In addition, thinned wafers may be warped or cracked when subjected to high-temperature heat treatment, and high-temperature heat treatment that normally forms BMD is not performed in the device process that is performed after thinning the wafer. . For this reason, there is a need for a gettering technique that does not depend on the formation of BMD by high-temperature heat treatment after wafer thinning.

  The present invention is intended to solve the above-described problems, and an object of the present invention is to provide a method for manufacturing a silicon wafer with sufficiently improved gettering capability.

Here, the inventor has intensively studied to solve the above problems.
As a result, the surface of the silicon wafer is irradiated with a laser in a state where one or more elements of oxygen, carbon, and nitrogen exist, and the surface layer of the wafer is melted and melted. It has been found that the above elements can be doped to a concentration equal to or higher than the solid solution limit concentration that can be doped by the Czochralski method by solidifying the portion. A silicon wafer having a highly doped layer whose impurity concentration is increased to a concentration that cannot be obtained by this Czochralski method does not cause slip in the wafer even when subjected to a high temperature heat treatment of the device process, and gettering It was found that it functions as a silicon wafer with excellent characteristics.

  Further, according to this method, since the melting depth by the laser can be controlled by the laser irradiation condition, the laser irradiation can be performed even after the back surface of the silicon wafer is ground, and the silicon wafer after being thinned. Furthermore, the present inventors have found that the method of the present invention can be applied.

This invention is based on said knowledge, The summary structure is as follows.
(1) Any of the silicon wafers in which the element is present in a state where one or more elements of oxygen, carbon, and nitrogen are present on the surface of at least one of both surfaces of the silicon wafer After irradiating the surface of one of the surfaces with a laser to melt the surface layer portion of the silicon wafer, the surface layer portion is doped by solidifying the melted surface layer portion. A method for manufacturing a silicon wafer.

  (2) Any of the silicon wafers in which the element is present in a state where one or more elements of oxygen, carbon, and nitrogen are present on the surface of at least one of both surfaces of the silicon wafer. The surface of the silicon wafer is irradiated with a laser to melt the surface layer portion of the silicon wafer, and the melted surface layer portion is solidified to dope the element into the surface layer portion, and then the silicon An epitaxial film is formed on the surface of any one surface of a wafer. A method for producing a silicon wafer.

  (3) The method for producing a silicon wafer according to (2), wherein an epitaxial film is formed on a surface of the silicon wafer on which the laser irradiation has been performed.

  (4) After thinning the silicon wafer by machining the back surface of the silicon wafer that is not used as a device region, a state in which one or more elements of oxygen, carbon, and nitrogen are present on the back surface Then, after irradiating the back surface with a laser to melt the surface layer portion on the back surface of the silicon wafer, the surface layer portion is doped by solidifying the melted surface layer portion. A method for manufacturing a silicon wafer.

According to the present invention, at least one of oxygen, carbon, and nitrogen can be doped at a high concentration, and more than two of these elements can be simultaneously doped. A silicon wafer having sufficiently high gettering capability can be realized.
Furthermore, a high-strength silicon wafer can also be realized by doping the above elements.

It is a figure showing one embodiment of the present invention typically. It is a figure showing one embodiment of the present invention typically. It is a figure showing one embodiment of the present invention typically.

Hereinafter, the present invention will be described in detail with reference to the drawings.
1 (a) and 1 (b) are diagrams schematically showing a first embodiment of the present invention.
In the method of the present embodiment, first, at least one element of oxygen, carbon, and nitrogen exists on the surface of at least one of both surfaces of the silicon wafer 1.
Next, laser irradiation is performed on the surface of the wafer 1 on which one or more of the above elements are present. In the example shown in FIGS. 1 (a) and 1 (b), when the above elements are present on both surfaces of the wafer 1, laser irradiation is performed on one of the surfaces.

The surface layer portion of the surface irradiated with the laser is melted, and the melted surface layer portion is solidified (recrystallized).
The thickness and impurity concentration of the surface layer portion to be melted can be controlled by adjusting the laser irradiation conditions. For example, by adjusting the energy density, pulse width, etc. according to the wavelength of the laser to be used, the thickness of the surface layer portion to be melted can be controlled in the range of 0.1 μm to 5 μm.
Here, “the element is present on the surface” means that the element is attached to the wafer and the element is taken into the molten silicon by the laser melting. Placed in an atmosphere containing at least one element of oxygen, carbon, and nitrogen, such as in an air atmosphere, an oxygen atmosphere, and a nitrogen atmosphere, and the wafer surface is exposed to the atmosphere, A case where a film containing one or more elements of oxygen, carbon, and nitrogen is added to the surface of one surface.

By the laser irradiation, the elements present on the wafer surface are taken into the molten silicon and solidified, whereby the silicon wafer 1 can be doped with the elements at a high concentration.
The impurity concentration (doping amount) in the wafer by laser irradiation can be controlled by the concentration of the element present on the wafer surface, that is, the concentration of the element in the atmosphere or the concentration of the element contained in the film. Also, by adjusting the number of pulses of laser irradiation, the impurity diffusion amount into the molten silicon layer melted by laser irradiation can be adjusted, and the impurity concentration can be controlled.
This makes it possible to manufacture a silicon wafer in which the concentrations of oxygen, carbon, and nitrogen are increased to a concentration that cannot be achieved by silicon single crystal growth by the Czochralski method. Specifically, in the measurement by secondary ion mass spectrometry (SIMS), the oxygen concentration in the silicon wafer is 1.0 × 10 ^{18 to} 2.0 × 10 ¹⁹ atoms / cm ³ , and the carbon concentration is 1.0 × 10 ^{17 to} 1.0 × 10 ¹⁸ atoms / cm. ^3. Doping can be performed in a nitrogen concentration range of 1.0 × 10 ^{15 to} 1.0 × 10 ¹⁷ atoms / cm ³ .

As shown in FIGS. 1 (a) and 1 (b), the impurity doped layer 2 is formed by doping the silicon wafer 1 with one or more elements of oxygen, carbon, and nitrogen as described above. This becomes the gettering layer. The impurity-doped layer 2 that functions as a gettering layer is a region where BMD, which is a defect, is formed at a high density, and cannot be used as a device region, so the side opposite to the surface 1b on which the impurity-doped layer 2 is formed The surface 1a side is a device layer.
Thereby, as described above, the gettering ability is achieved by the BMD formed by the heat treatment in the pre-process of the formation of the complex or the device process by any one or more of oxygen, carbon, and nitrogen of the impurity doped layer 2. A sufficiently high silicon wafer can be manufactured.
Moreover, oxygen and nitrogen are effective in increasing the wafer strength by being doped into the wafer, and carbon is effective in increasing the wafer strength by being doped in the presence of oxygen in the wafer. Usually, a silicon wafer has an interstitial oxygen concentration of about 1.0 to 1.5 × 10 ¹⁸ atoms / cm ^{3 when} it is manufactured by the Czochralski method or the like.
Therefore, according to the present invention, the wafer strength can be increased by doping one or more of oxygen, carbon, and nitrogen.
Also, the wafer strength is increased by forming the BMD by the heat treatment in the previous process of the device process.
In addition, since the elements to be doped by the method of the present invention are oxygen, carbon, and nitrogen, the electrical resistivity of the wafer is not affected, and in the present invention, the wafer surface layer portion used as a device layer is not affected. Is not doped with oxygen, carbon, or nitrogen, and does not degrade device characteristics.
In addition, the conductivity type and resistivity of the silicon wafer 1 to be used can be arbitrary, but in the case of a p-type wafer, a p + wafer doped with boron at a high concentration can be used as a Cu-O-B. A composite can be formed to give the wafer a high gettering ability for Cu.
When performing laser irradiation on the silicon wafer surface, it is necessary to hold the surface 1a on the side not subjected to laser irradiation with a vacuum suction member, etc., so that there is particle adhesion or contact damage on the surface of the surface 1a not subjected to laser irradiation. May occur. For this reason, the surface of the surface side 1a not subjected to laser irradiation is polished after laser irradiation, or the surface of the surface side 1a not subjected to laser irradiation is covered with a protective film such as an oxide film, and then laser irradiation is performed. Next, it is preferable to remove the protective film.

  Furthermore, as shown in FIG. 2 (a), by forming the epitaxial layer 3 on the surface of the surface 1a that has not been irradiated with the laser, it has a defect-free and high-quality device layer, and has a getter. A silicon wafer having a sufficiently high ring ability and improved wafer strength can be manufactured.

Here, the silicon wafer 1 shown in FIG. 2 (a) may be subjected to the laser irradiation described above on the back surface of the silicon wafer 1 prior to forming the epitaxial layer 3, and after forming the epitaxial layer 3, The above laser irradiation may be performed on the back surface of the silicon wafer 1.
If laser irradiation is performed on the back surface of the wafer after the epitaxial layer 3 is formed, there is a risk of particle adhesion or scratching on the surface of the epitaxial layer 3 during laser irradiation. Is desirable. When laser irradiation is performed on the back surface of the wafer after the epitaxial layer 3 is formed, the surface of the epitaxial layer 3 is polished after the laser irradiation, or the epitaxial layer 3 is covered with a protective film such as an oxide film and then laser irradiation is performed. Preferably, the protective film is then removed.
Here, the “back surface of the wafer” means the surface opposite to the surface on which the device layer is formed (the surface side on which the epitaxial growth process is not performed).

The epitaxial layer can be formed by a usual method.
For example, in an epitaxial apparatus, a wafer is mounted on a susceptor, hydrogen gas is introduced, the temperature is raised to 1100 ° C. to 1200 ° C. in a hydrogen gas atmosphere, and baking is performed.
Next, a trichlorosilane gas as a source gas, a hydrogen gas as a carrier gas, and a diborane gas as a dopant gas can be introduced into an epitaxial furnace to form an epitaxial layer on the wafer surface.
In this way, an epitaxial layer having a thickness of 1 μm to 100 μm can be formed.
In the following embodiments, the epitaxial film can be formed using a normal epitaxial growth method.

As another embodiment of the present invention, as shown in FIG. 2 (b), an epitaxial layer 3 can be formed on the surface 1a subjected to the laser irradiation described above.
As a result, an impurity-doped layer 2 in which one or more elements of oxygen, carbon, and nitrogen are doped at a high concentration exists immediately below the epitaxial layer 3 that is a defect-free and high-quality device layer. Therefore, the silicon wafer 1 having higher gettering capability can be realized. In addition, the presence of the impurity-doped layer 2 immediately below the epitaxial layer 3 reduces the gettering ability because the impurity-doped layer remains even when the back surface of the silicon wafer 1 is thinned by grinding in the device post-process. Never do.
Further, as in the case of the embodiment shown in FIGS. 1 (a) and 1 (b), there is an effect of increasing the wafer strength by doping with high concentrations of oxygen, carbon, and nitrogen.
In order to improve the flatness of the surface of the epitaxial layer 3, it is preferable to planarize the surface of the surface irradiated with the laser before the epitaxial layer 3 is formed.
Note that the back surface grinding in the device post-process is usually performed in a range in which a thickness of 20 to 100 μm remains from the surface on which the device is formed.

Further, as shown in FIG. 2 (c), after laser irradiation is performed on both sides of the silicon wafer to form the impurity doped layers 2a and 2b, either side of the wafer, in the illustrated example, the impurity doped layer The epitaxial layer 3 can be formed on the surface on the 2a side.
Thereby, the silicon wafer 1 shown in FIG. 2 (c) has both the gettering effect by the impurity doped layer 2b and the proximity gettering effect by the impurity doped layer 2a before grinding the back surface of the wafer.
In addition, even when the impurity-doped layer 2b is removed during grinding of the wafer back surface, it has a proximity gettering effect by the impurity-doped layer 2a against Cu contamination during back-surface grinding and after grinding.
Further, as in the case of the embodiment shown in FIGS. 1 (a) and 1 (b), there is an effect of increasing the wafer strength.
Here, laser irradiation on both surfaces of the wafer may be performed on both surfaces simultaneously or sequentially. However, at the time of laser irradiation, the above elements must be present on the surface of the laser irradiation surface. There is.
The silicon wafer 1 shown in FIG. 2 (c) is formed by first irradiating a laser on one side to form a gettering layer 2a, and then forming an epitaxial layer 3 on the surface of the gettering layer 2a. It is also possible to obtain the gettering layer 2b by irradiating with laser. In this case, as described above, the surface of the epitaxial layer 3 is polished after the laser irradiation so as not to deteriorate the quality of the epitaxial film, or the epitaxial layer 3 is covered with a protective film such as an oxide film and then irradiated with the laser. Preferably, the protective film is then removed.

Further, the laser irradiation described above can be performed even after the back surface 1b of the silicon wafer 1 is ground and the wafer 1 is thinned as shown in FIG.
That is, after the back surface of the wafer 1 is ground and thinned, the back surface 1b is irradiated with laser in a state where one or more elements of oxygen, carbon, and nitrogen are present on the surface of the back surface 1b. The element 1 can be doped into the wafer 1 by melting and solidifying the surface layer portion of the back surface 1b.
As a result, the thinned wafer 1 has the impurity doped layer 2 on the back surface 1b surface layer portion located immediately below the wafer surface layer portion on which the device is formed. Sufficient gettering capability is provided for Cu contamination during back surface grinding or after grinding in a later process.
Further, as in the case of the embodiment of FIGS. 1 (a) and 1 (b), there is an effect of increasing the strength of the wafer.
Furthermore, in the post-process of the normal device process, a processing strain is generated on the wafer back surface 1b by the back surface grinding performed to reduce the thickness of the wafer 1. Therefore, a process of removing the processing strain by polishing or etching is required. By applying laser irradiation instead of these polishing and etching processes, processing strain is removed by melting and solidifying the surface layer portion.
For this reason, there is an advantage that the wafer strength is increased by removing the processing strain and the above polishing or etching process is not required.

Experiment 1
In order to confirm the effect of the present invention, the following experiment was conducted.
First, prepare a plurality of p-silicon wafers with a diameter of 300 mm and a thickness of 780 μm (boron concentration 1.0 × 10 ¹⁵ atoms / cm ³ , interstitial oxygen concentration 1.2 × 10 ¹⁸ atoms / cm ³ ). Was irradiated with laser (Invention Example 1), and the other half of the wafers were not irradiated with laser (Comparative Example 1).
The laser irradiation conditions were irradiation in the air atmosphere, the wavelength was a double wave (532 nm) of the YAG laser, the energy density was 10 J / cm ² , the pulse width was 300 ns, and the number of pulses was 10 times.
The surface layer portion on one side of the wafer irradiated with the laser was melted to a depth of about 2 μm, and the melted surface layer portion was solidified.
As a result of observing the surface layer portion melted and solidified by laser irradiation with an electron microscope (TEM), no defects were observed. This indicates that the surface layer portion was solidified without any defects.

  For the wafers according to Invention Example 1 and Comparative Example 1, the depth profiles of oxygen, carbon, and nitrogen were evaluated by secondary ion mass spectrometry (SIMS). The evaluation results are shown in Table 1 below.

Next, for the wafer according to Invention Example 1, since the surface roughness of the laser-irradiated surface was large, the surface was polished by about 1 μm to a mirror surface, and the gettering layer remained about 1 μm. The surface that was not irradiated with the laser was also polished into a mirror surface.
Thereafter, the wafer according to Invention Example 1 and Comparative Example 1 was subjected to a high-temperature heat treatment (slip evaluation heat treatment) for 1 hour at a temperature of 1200 ° C. in an inert gas atmosphere, and then at a temperature of 800 ° C. in an oxidizing atmosphere. Following the heat treatment for a period of time, a two-step heat treatment (BMD density evaluation heat treatment) was performed in which heat treatment was performed at 1000 ° C. for 16 hours in an oxidizing atmosphere.

The wafer according to Invention Example 1 and Comparative Example 1 subjected to the heat treatment was subjected to a test for evaluating the occurrence of slip using X-ray topography.
Further, the BMD density of the wafer surface layer portion according to Invention Example 1 and Comparative Example 1 was evaluated by infrared light scattering tomography.
Furthermore, in order to confirm the gettering effect of the wafer according to Invention Example 1 and Comparative Example 1, the Cu concentration and Ni concentration in the range of 1 μm of the wafer surface layer portion were evaluated by chemical analysis.
These evaluation results are also shown in Table 1 below.

Experiment 2
Next, a similar experiment was performed on a p + silicon wafer (boron concentration: 1.0 × 10 ¹⁹ atoms / cm ³ , interstitial oxygen concentration: 1.2 × 10 ¹⁸ atoms / cm ³ ) having a diameter of 300 mm and a thickness of 780 μm.
The laser irradiation conditions are the same as those in Experiment 1 except that the irradiation is performed in the air, the wavelength is 308 nm, the energy density is 5 J / cm ² , the pulse width is ²⁰⁰ ns, and the number of pulses is one.
The evaluation results are shown in Table 1.
In Table 1, Invention Example 2 and Comparative Example 2 mean the wafer that was subjected to the laser irradiation and the wafer that was not performed in Experiment 2, respectively.

As shown in Table 1, 1.0 × 10 ¹⁹ atoms / cm ³ of oxygen, 1.0 × 10 ¹⁸ atoms / cm ³ of carbon, 1.0 in a region of about 2 μm from the laser-irradiated surface of the wafer according to Invention Example 1. × 10 ¹⁶ atoms / cm ³ of nitrogen was detected, and it was confirmed that an impurity doped layer was formed in this region. Further, in the wafer according to Invention Example 2, 1.0 × 10 ¹⁹ atoms / cm ³ of oxygen, 1.0 × 10 ¹⁸ atoms / cm ³ of carbon, 1.0 × 10 ^{16 in} a region of about 0.2 μm from the surface of the wafer irradiated with laser. Atom / cm ³ nitrogen was detected, and it was confirmed that an impurity-doped layer was formed in this region.
On the other hand, since the wafers according to Comparative Examples 1 and 2 were not subjected to laser treatment, carbon and nitrogen were not detected, and the oxygen concentration in the surface layer of the wafer caused a decrease in oxygen concentration due to oxygen outward diffusion by high-temperature heat treatment. It was.
In addition, the occurrence of a large number of slips was confirmed in the wafer according to Comparative Example 1, and the occurrence of a small number of slips was confirmed in the wafer according to Comparative Example 2, but the slip was observed in the wafers according to Invention Examples 1 and 2. There wasn't.
Further, high-density BMD was detected in the wafers according to Invention Examples 1 and 2, but BMD was not detected in the wafer according to Comparative Example 1, and the BMD density of the wafer according to Comparative Example 2 was low.
Regarding the occurrence of BMD density and slip, there is a difference between Comparative Examples 1 and 2 because the boron concentration in Comparative Example 2 is higher, which improves the strength of the wafer and promotes the precipitation of oxygen. It is thought that.
Further, about 1.0 × 10 ¹⁴ atoms / cm ³ of Cu and about 1.0 × 10 ¹⁵ atoms / cm ³ of Ni were detected in the wafer according to Comparative Example 1, and about 5.0 × 10 ¹³ in the wafer according to Comparative Example 2. Although atoms / cm ³ in Cu and about 5.0 × 10 ¹⁴ atoms / cm ³ of Ni were detected, Cu and Ni in a wafer according to the invention examples 1 and 2 were not detected.
From these results, it can be seen that the wafers according to Invention Examples 1 and 2 have sufficient gettering capability and improved wafer strength as a result of laser irradiation.

Experiment 3
Prepare multiple p-silicon wafers with a diameter of 300 mm and a thickness of 780 μm (boron concentration 1.0 × 10 ¹⁵ atoms / cm ³ , interstitial oxygen concentration 1.2 × 10 ¹⁸ atoms / cm ³ ), and test one side of half of the wafers Laser irradiation was performed under the same conditions as in Example 1 (Invention Example 3), and the other half of the wafers were not irradiated with laser (Comparative Example 3).
Here, the depth profiles of oxygen, carbon, and nitrogen were evaluated by SIMS, and the evaluation results were the same as those in Experiment 1.
Next, the surface of the wafer subjected to laser irradiation according to Invention Example 3 is polished by 1 μm to be a mirror surface, and after leaving the gettering layer by 1 μm, an epitaxial layer of about 3 μm is formed on the gettering layer. Formed. In Comparative Example 3, an epitaxial layer of about 3 μm was formed on one side of the wafer.
Thereafter, the wafer according to Invention Example 3 and Comparative Example 3 was subjected to the same batch heat treatment as in Experiment 1, and then the back surface of the wafer was ground to simulate the post-process of the device process, and the wafer thickness was reduced. The thickness was 100 μm.
In order to confirm the gettering effect against Cu and Ni contamination by grinding simulating this post-process, the same gettering effect as in Experiment 1 was evaluated.

Experiment 4
Next, an experiment similar to Experiment 3 was performed on a p + silicon wafer having a thickness of 780 μm (boron concentration: 1.0 × 10 ¹⁹ atoms / cm ³ and interstitial oxygen concentration: 1.2 × 10 ¹⁸ atoms / cm ³ ).
The laser irradiation conditions were the same as in Experiment 2, and the wafer thickness was 20 μm in the grinding of the back surface of the wafer simulating the post-process of the device process.
The evaluation results of Experiments 3 and 4 are shown in Table 2.
Here, Invention Example 4 and Comparative Example 4 in Table 2 mean the wafer that was subjected to the laser irradiation and the wafer that was not performed in Experiment 4, respectively.

From Table 2, 1.0 × 10 ¹⁵ atoms / cm ³ of Cu and 1.0 × 10 ¹⁵ atoms / cm ³ of Ni were detected in the wafer according to Comparative Example 3, and 1.0 × 10 ¹⁴ atoms in the wafer according to Comparative Example 4. / cm ³ Cu and 5.0 × 10 ¹⁴ atoms / cm ³ Ni were detected, but Cu and Ni were not detected in the wafers according to Invention Examples 3 and 4.
From this, it can be seen that the wafers according to Invention Examples 3 and 4 subjected to the laser irradiation described above have sufficient gettering ability against Cu and Ni contamination due to grinding simulating the post-process.

Experiment 5
Prepare multiple p-silicon wafers with a thickness of 780 μm (boron concentration 1.0 × 10 ¹⁵ atoms / cm ³ , interstitial oxygen concentration 1.2 × 10 ¹⁸ atoms / cm ³ ), grind the back surface of the wafer, After the thickness was reduced to 100 μm, one side of half of the wafers were irradiated with laser under the same conditions as in Experiment 1 (Invention Example 5), and the other half of the wafers were not irradiated with laser (Comparative Example 5).
As a result of observing the surface layer portion melted and solidified by laser irradiation with an electron microscope (TEM), no defects were observed. This indicates that the surface layer portion was solidified without any defects.

  Thereafter, for the wafers according to Invention Example 5 and Comparative Example 5, evaluation of the depth profile of oxygen, carbon, and nitrogen was performed in the same manner as in Experiment 1, and the gettering effect against Cu contamination by grinding simulating the post-process Was evaluated in the same manner as in Experiment 3.

Experiment 6
Next, an experiment similar to Experiment 5 was performed on a p + silicon wafer having a thickness of 780 μm (boron concentration: 1.0 × 10 ¹⁹ atoms / cm ³ and interstitial oxygen concentration: 1.2 × 10 ¹⁸ atoms / cm ³ ).
The laser irradiation conditions were the same as those in Experiment 2, and the wafer backside grinding was performed by grinding the wafer thickness to 20 μm.
The evaluation results of Experiments 5 and 6 are shown in Table 3.
Here, in Table 3, Invention Example 6 and Comparative Example 6 mean the wafer that was subjected to the laser irradiation and the wafer that was not performed in Experiment 6, respectively.

  From Table 3, it is possible to dope oxygen, carbon, and nitrogen at a high concentration by adjusting the laser irradiation conditions even for thinned wafers that simulate grinding in the subsequent process. It can be seen that a wafer having sufficient gettering ability can be realized against Cu contamination caused by grinding.

Similarly, as a result of performing the above experiment on an n− wafer and an n + wafer, the wafer subjected to the laser irradiation described above had sufficient gettering ability and improved wafer strength.
In addition, when laser irradiation is performed in an oxygen atmosphere or nitrogen atmosphere, or the result of laser irradiation with an oxide film, nitride film, carbide film, etc. added to the surface of the laser irradiation surface, sufficient gettering is also achieved. The wafer strength was improved.

1 Silicon wafer
1a, 1b One side of silicon wafer
2, 2a, 2b Impurity doped layer (gettering layer)
3 Epitaxial layer

Claims (4)

  In the state where one or more of oxygen, carbon, and nitrogen are present on the surface of at least one of both surfaces of the silicon wafer, the element is present, and one of the silicon wafers is present. The surface of the silicon wafer is irradiated with a laser to melt the surface layer portion of the silicon wafer, and then the molten surface layer portion is solidified to dope the element into the surface layer portion. Wafer manufacturing method.   In the state where one or more of oxygen, carbon, and nitrogen are present on the surface of at least one of both surfaces of the silicon wafer, the element is present, and one of the silicon wafers is present. The surface of the silicon wafer is irradiated with a laser to melt the surface layer portion of the silicon wafer, and then the molten surface layer portion is solidified to dope the element into the surface layer portion, and then to any of the silicon wafers A method for producing a silicon wafer, comprising forming an epitaxial film on the surface of one of the surfaces.   3. The method for producing a silicon wafer according to claim 2, wherein an epitaxial film is formed on a surface of the silicon wafer on which the laser irradiation has been performed.   By thinning the silicon wafer by machining the back surface of the silicon wafer that is not used as a device region, in the state where one or more elements of oxygen, carbon, nitrogen are present on the back surface, The back surface of the silicon wafer is irradiated with a laser to melt the surface layer portion of the silicon wafer, and then the molten surface layer portion is solidified to dope the element into the surface layer portion. Wafer manufacturing method.

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