JP5040564B2 - Silicon wafer manufacturing method - Google Patents

Description

  The present invention relates to an etching solution and a method for manufacturing a silicon wafer, and more particularly to an etching solution that can improve the surface roughness of a silicon wafer after etching and a method for manufacturing a silicon wafer using the etching solution.

Conventionally, in a silicon wafer manufacturing process, etching of a silicon wafer with an alkaline aqueous solution has been performed in order to remove processing damage during lapping, chamfering, and grinding (see, for example, “Non-patent Document 1”).
Supervised by Tadahiro Omi and Yuhisa Nitta, "Science of Silicon" UCS Semiconductor Fundamental Technology Study Group, June 28, 1996, P286-288

However, in the conventional etching of a silicon wafer with an aqueous alkali solution, the processed strain layer can be processed, but the surface roughness of the silicon wafer after etching is rough, so it is required to further improve the surface roughness. It was.
This invention is made | formed in view of said situation, and provides the manufacturing method of the silicon wafer using the etching liquid which can improve the surface roughness of the silicon wafer after etching, and the etching liquid Objective.

In order to solve the above-mentioned problems, the method for producing a silicon wafer of the present invention includes at least Ni ions and Co ions , which are metal ions, the concentration of the metal ions is in the range of 100 ppb to 100 ppm, and the alkali concentration is 30 to Etching a silicon wafer using an alkaline etchant in the range of 70% by weight, and changing the texture size according to the Ni concentration and the Co concentration as a texture reducing agent on the surface of the silicon wafer. .
The etching solution of the present invention is an alkaline etching solution used in the production process of a silicon wafer, and may contain metal ions as a texture reducing agent on the surface of the silicon wafer.
In the etching solution of the present invention, the metal ion may be at least one ion selected from Fe, Cu, Ni, Co, and Mg.
In the etching solution of the present invention, the metal ion concentration may be in the range of 10 ppb to 200 ppm.
Moreover, in the etching liquid of this invention, the alkali concentration of the said alkali etching liquid shall be the range of 30 to 70 weight%.
The method for producing a silicon wafer according to the present invention is characterized in that the silicon wafer is etched using any of the etching solutions described above.
Moreover, in the manufacturing method of the silicon wafer of this invention, it can be set as the method of wash | cleaning the silicon wafer after performing the said etching.
The method for producing a silicon wafer according to the present invention is characterized in that the silicon wafer is cleaned using any of the etching solutions described above.
Furthermore, the silicon wafer of the present invention is manufactured by the above-described silicon wafer manufacturing method.

The present inventor has found the present invention by paying attention to the texture on the surface of the silicon wafer in order to improve the surface roughness of the silicon wafer after etching.
FIG. 6 is a photograph of the texture on the surface of the silicon wafer. The larger the texture size shown in FIG. 6, the rougher the surface roughness of the silicon wafer. Since the etching solution of the present invention is an alkali etching solution containing metal ions as a texture reducing agent on the surface of the silicon wafer, the size of the texture on the surface of the silicon wafer after etching is determined by alkali etching not containing metal ions. Compared with the case where a liquid is used, the surface roughness can be improved.

In addition, the present inventors have found that metal ions suitable as a texture reducing agent form anions and water in an alkaline etching solution to suppress local reactions on the surface of the silicon wafer being etched. I found out.
For example, Fe ions form Fe (OH) ₃ that is a hydroxide in the alkaline etching solution, and also form HFeO ₂ (−) and H ₂ O.
Moreover, Cu ion forms Cu (OH) ₂ which is a hydroxide in an alkaline etching solution, and also forms HCuO ₂ (−) and H ₂ O.
Further, Ni ions form Ni (OH) ₂ that is a hydroxide in the alkaline etching solution, and also form HNiO ₂ (−) and H ₂ O.
The Co ions form Co (OH) ₂ which is a hydroxide in the alkaline etching solution, and also forms HCoO ₂ (−) and H ₂ O.
The Mg ions form Mg (OH) ₂ that is a hydroxide in the alkaline etching solution, and also form HMgO ₂ (−) and H ₂ O.
Here, H ₂ O formed by metal ions is a reaction between the etchant and the silicon wafer during etching. Si + 2NaOH + H ₂ O → Na ₂ SiO ₄
It is thought that it contributes to the direction that promotes and suppresses local reactions.

  In the etching solution of the present invention, the metal ion is at least one ion selected from Fe, Cu, Ni, Co, and Mg, thereby suppressing local reaction between the etching solution and the silicon wafer during etching. In addition, the surface roughness of the surface of the silicon wafer after etching can be further reduced.

In the etching solution of the present invention, the concentration of metal ions can be in the range of 10 ppb to 200 ppm. If the concentration of metal ions is less than 10 ppb, the effect of reducing the texture size on the surface of the silicon wafer after etching cannot be sufficiently obtained, which is not preferable. On the other hand, if the concentration of metal ions exceeds 200 ppm, the alkali concentration relatively decreases, which is not preferable because the roughness of the silicon wafer after etching increases.
Furthermore, by setting the metal ion concentration in the range of 100 ppb to 100 ppm, the effect of reducing the texture size on the surface of the silicon wafer after etching can be obtained more effectively.

  The alkaline etching solution of the present invention is an alkaline solution containing alkali metal ions. As the alkali metal, lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), francium (Fr) or a compound thereof belonging to Group 1A of the periodic table may be employed. In addition, sodium and potassium are preferable because they can be used at low cost. Furthermore, in the case of the same weight concentration, sodium is more preferable because sodium has a higher mol concentration and can be formed with a smaller texture size during etching.

  In the etching solution of the present invention, the alkali concentration of the alkali etching solution can be in the range of 30 to 70% by weight. An alkali concentration of less than 30% by weight is not preferable because the roughness of the silicon wafer after etching is increased. Further, the alkali is saturated at a concentration of about 70% by weight.

  According to the present invention, the surface roughness of the silicon wafer after etching can be improved by reducing the texture size when the etching conditions such as the etching allowance thickness and processing time are set to the same level. An etching solution and the etching solution can be provided.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a first embodiment of the invention will be described with reference to the drawings.
FIG. 1 is a flowchart for explaining a method of manufacturing a silicon wafer according to this embodiment. In order to manufacture a silicon wafer, for example, as shown by reference numeral S1 in FIG. 1, an ingot made of a silicon single crystal is manufactured, and the obtained ingot is sliced to form a wafer. Etching to remove chamfering step S3 for chamfering (beveling) the periphery, lapping step S4 for smoothing irregularities on the plane generated by slicing step S2, and processing distortion layer generated by slicing step S2 and wrapping step S4 Step S5, mirror polishing step S6 for polishing the surface of the silicon wafer like a mirror, and cleaning step S7 for removing heavy metal impurities and particulate foreign matters to obtain a clean surface are sequentially performed.
At this time, in this embodiment, the alkali etching liquid containing the metal ion of the present invention is used as the etching liquid used when performing the etching step S5. Therefore, the surface roughness of the silicon wafer after performing the etching step S5 can be improved.
Here, in the present invention, as in the present embodiment, the process can be performed not only after the lapping step S4 but also after the slicing step S2 and before the mirror polishing step S6 at an arbitrary silicon wafer manufacturing stage. Furthermore, only double-sided etching and single-sided etching can be performed.

FIG. 2 is a flowchart for explaining a silicon wafer manufacturing method according to the second embodiment of the present invention. The second embodiment shown in FIG. 2 is the same as the first embodiment shown in FIG. 1 in steps S1 to S6 for producing an ingot, and therefore only the steps after the mirror polishing step S6 will be described. . In the second embodiment shown in FIG. 2, after performing the mirror polishing step S6, a one-side etching step S8 for etching only one surface of the silicon wafer is performed to obtain a silicon wafer having only one surface as a mirror-polished surface. A cleaning step S7 for obtaining a clean surface is performed in the same manner as in the first embodiment.
Also in this embodiment, the alkaline etching solution containing the metal ion of the present invention is used as the etching solution used when performing the etching step S5. Therefore, the surface roughness of the silicon wafer after performing the etching step S5 can be improved.

  In addition, this invention is not limited to embodiment mentioned above, The alkali etching liquid containing the metal ion of this invention is not only when performing etching process S5, but process S1-washing process S7 of manufacturing an ingot. It can be suitably used as an etching solution or a cleaning solution used when any one or more steps are performed.

"Experimental Example 1-Experimental Example 3"
Metal ions were added at a concentration shown in Table 1 to a 48 wt% aqueous sodium hydroxide solution to produce alkaline etching solutions of Experimental Examples 1 to 3. And the silicon wafer was immersed in the obtained etching liquid of Experimental Examples 1 to 3, and the surface was etched. The etching conditions at this time were 70 ° C., 15 minutes, and a surface removal allowance (etching thickness) of about 20 μm. Thereafter, the texture size and surface roughness Ra on the surface of the silicon wafer after etching were examined as shown below. The results are shown in Table 1.

The texture size was obtained by observing the etched wafer surface with a microscope. As shown in FIG. 6, the texture size was a substantially rectangular one of the observable textures and the length measured along the diagonal line. For textures other than rectangles, the diagonal length that is the longest in the texture, or the length corresponding to it, is taken as the texture size.
Specifically, for example, arrows are shown vertically and horizontally in FIG. 6, but the length obtained by drawing a straight line on the opposite side of the arrow as a rectangle (two adjacent sides of the rectangle) is calculated from the magnification of this image. Then, the length dimension is calculated.
For the surface roughness Ra, the surface roughness of the wafer was measured using Surfcom (trade name: manufactured by Tokyo Seimitsu Co., Ltd.) which is a stylus type surface roughness measuring device.

  From Table 1, compared to Experimental Example 1 in which the total concentration of metal ions is less than 10 ppb, in Experimental Example 2 and Experimental Example 3 in which the total concentration of metal ions is in the range of 100 ppb to 100 ppm, the texture size and It was confirmed that the surface roughness Ra was reduced.

"Experimental example 4"
An alkaline etching solution was prepared by adding Fe ions at a concentration of 0, 10 ppb, 100 ppb, 1 ppm, 10 ppm, and 100 ppm to a 48 wt% sodium hydroxide aqueous solution. And the silicon wafer was immersed in each obtained etching liquid, and the surface was etched. The etching conditions at this time were 70 ° C., 15 minutes, and a surface removal allowance (etching thickness) of about 20 μm. Thereafter, the surface roughness Ra of each etched silicon wafer was examined in the same manner as in Experimental Example 1. Further, the maximum texture size Rmax of each etched silicon wafer was examined as shown below. The result is shown in FIG.

  For the maximum texture size Rmax, the largest texture size of the texture sizes measured as described above was used as the maximum texture size.

FIG. 3 is a graph showing the relationship between the Fe ion concentration added to the etching solution, the surface roughness Ra, and the maximum texture size Rmax. As shown in FIG. 3, it was confirmed that the surface roughness Ra and the maximum texture size Rmax were smaller when the Fe ion concentration was 10 ppb to 100 ppm than when the Fe ion was not added.
Moreover, as shown in FIG. 3, it has confirmed that the effect of making surface roughness Ra small was acquired more effectively by making the density | concentration of Fe ion into the range of 100ppb-100ppm.

“Experimental Example 5”
An alkaline etching solution was prepared by adding Fe ions, Al ions, Mn ions, Cr ions, Cu ions, Ni ions, Co ions, and Mg ions to a 48 wt% aqueous sodium hydroxide solution at a concentration of 1 ppm. And in each obtained etching liquid, the silicon wafer was immersed for 15 minutes at 70 degreeC, and the surface was removed about 20 micrometers. Thereafter, the surface roughness Ra and the maximum texture size Rmax of each etched silicon wafer were examined in the same manner as in Experimental Example 4. The result is shown in FIG. Further, the texture size of each etched silicon wafer was examined in the same manner as in Experimental Example 1. The result is shown in FIG.

  FIG. 4 is a graph showing the relationship between the type of metal ions added to the etching solution, the surface roughness Ra, and the maximum texture size Rmax. As shown in FIG. 4, when the metal ions are Fe ions, Cu ions, Ni ions, Co ions, and Mg ions, the surface roughness Ra and the maximum texture size Rmax are compared with the case where the metal ions are not added. It was confirmed that becomes smaller. Moreover, as shown in FIG. 4, when a metal ion is Al ion, Mn ion, Cr ion, and Ti ion, it turned out that the effect which makes surface roughness Ra and maximum texture size Rmax small is not acquired.

  FIG. 5 is a graph showing the relationship between the type of metal ions added to the etching solution and the texture size. As shown in FIG. 5, when the metal ions are Fe ions, Cu ions, Ni ions, Co ions, and Mg ions, it can be confirmed that the texture size is smaller than when no metal ions are added. It was. Moreover, as shown in FIG. 5, when a metal ion is Al ion, Mn ion, and Cr ion, it turned out that the effect which makes a texture size small is not acquired.

  7 to 11 show images obtained by photographing actual textures.

In the images shown in FIGS. 7 and 8, (a) is after etching with a NaOH solution having the composition shown in T1 in Table 2, (b) is a NaOH solution having an Fe concentration of 1 ppm, (c) is NaOH shown in T2 in Table 2. It is a texture after etching by a solution. Here, the etching conditions were the same as in the above experimental example. FIG. 7 and FIG. 8 differ only in the photographed magnification. FIG. 7 is 500 times and FIG. 8 is 1250 times.
7 and 8, it can be seen that the texture is reduced in T2 shown in (c) with more metal ions than in T1 shown in (a). This shows that metal ions are effective as a texture reducing agent in alkaline etching.

FIGS. 9 and 10 are texture images similar to the above experimental example and FIGS. 7 and 8 and in the case where only the Fe concentration in the NaOH etching solution is varied.
9 and 10, the Fe concentrations of the respective etching solutions are as follows: (a) Fe-free addition, (b) Fe concentration 10 ppb, (c) Fe concentration 100 ppb, (d) Fe concentration 1 ppm, (e ) Is an Fe concentration of 10 ppm, and (f) is an Fe concentration of 100 ppm. 9 and 10 differ only in the photographed magnification.
From FIG. 9 and FIG. 10, it can be clearly seen that the texture size changes depending on the Fe concentration.

FIG. 11 is a texture image similar to the above experimental example and FIGS. 7 and 8, and in which only the Ni concentration in the NaOH etching solution is varied.
In FIG. 11, the Ni concentration of each etching solution is that Ni is not added in (a) and (c), and the Ni concentration is 1 ppm in (b) and (d). In FIG. 11, (a), (c), and (b) (d) differ only in the photographed magnification.
From FIG. 11, it can be clearly read that the texture size changes depending on the Ni concentration.

FIG. 1 is a flowchart for explaining a silicon wafer manufacturing method according to the first embodiment of the present invention. FIG. 2 is a flowchart for explaining a silicon wafer manufacturing method according to the second embodiment of the present invention. FIG. 3 is a graph showing the relationship between the Fe ion concentration added to the etching solution, the surface roughness Ra, and the maximum texture size Rmax. FIG. 4 is a graph showing the relationship between the type of metal ions added to the etching solution, the surface roughness Ra, and the maximum texture size Rmax. FIG. 5 is a graph showing the relationship between the type of metal ions added to the etching solution and the texture size. FIG. 6 is a photograph of the texture on the surface of the silicon wafer. FIG. 7 is a photograph of the texture on the surface of the silicon wafer. FIG. 8 is a photograph of the texture on the surface of the silicon wafer. FIG. 9 is a photograph of the texture on the surface of the silicon wafer. FIG. 10 is a photograph of the texture on the surface of the silicon wafer. FIG. 11 is a photograph of the texture on the surface of the silicon wafer.

Explanation of symbols

  S2: Slicing step, S3: Chamfering step, S4: Lapping step, S5: Etching step, S6: Mirror polishing step, S7: Cleaning step

Claims (3)

Etching a silicon wafer using an alkaline etchant containing at least Ni ions and Co ions , which are metal ions, the metal ion concentration is in the range of 100 ppb to 100 ppm, and the alkali concentration is in the range of 30 to 70% by weight. A method for producing a silicon wafer, characterized in that the texture size is changed by the Ni concentration and the Co concentration as a texture reducing agent on the surface of the silicon wafer.   The silicon wafer manufacturing method according to claim 1, wherein the silicon wafer after the etching is cleaned. Cleaning of a silicon wafer using an alkaline etching solution containing at least Ni ions and Co ions, which are metal ions, a concentration of the metal ions in a range of 100 ppb to 100 ppm, and an alkali concentration in a range of 30 to 70% by weight. The method for producing a silicon wafer according to claim 1, wherein the method is performed.

Images