JP3208384B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a single crystal silicon,
The present invention relates to a method for manufacturing a semiconductor element including a step of forming an uneven structure called a so-called texture structure on a surface of a substrate made of a crystalline semiconductor such as single crystal germanium, polycrystalline silicon, or polycrystalline germanium. The present invention relates to a technique for forming a concavo-convex structure having good uniformity.

[0002]

2. Description of the Related Art In a semiconductor device such as a solar cell or an optical sensor, an uneven structure called a texture structure is provided on a light receiving surface side in order to improve its photoelectric conversion characteristics. FIG. 6 is an element structure sectional view showing a structure of a solar cell as an example of such a conventional semiconductor element.

In FIG. 1, reference numeral 21 denotes a substrate made of p-type single crystal silicon having a thickness of about 500 μm.
Is provided with a concavo-convex structure A on the light receiving surface. In a region from the light receiving surface of the substrate 21 to a depth of about 0.5 μm, P (phosphorus)
Is thermally diffused to form an n-type region 22. On the n-type region 22, a comb-shaped collector electrode 23 made of a metal such as Ag or Al and an antireflection film 24 made of ITO, SiN or the like are formed. Is provided. A BSF region 25 is provided on the back surface of the substrate 21, and the BSF region 2
A back electrode 26 made of Al is formed on 5.
Incidentally, the BSF region 25 generally has A
1 is thermally diffused into the substrate 21.

[0004] As described above, the process of forming a concavo-convex structure on the surface of a substrate made of a crystalline semiconductor is called a texturing process, and is usually performed by anisotropic etching using an alkali solution such as hydrazine or an aqueous sodium hydroxide solution. Is used. This texturing process is performed, for example, as follows.

[0005] First, after a substrate made of single crystal silicon is washed, primary etching is performed using an aqueous solution of NaOH having a concentration of about 10% by weight. This process has nothing to do with the texturing process, and is merely a process for removing the surface damage layer. For example, 10% by weight N at a temperature of about 80 ° C.
By immersing the substrate in an aOH aqueous solution for 10 to 20 minutes, a region from the substrate surface to a depth of about 20 μm is removed.

Next, after cleaning the substrate, a texturing process is performed. In this texturing process, the NaOH aqueous solution having a concentration of about 1% by weight is kept almost in a boiling state,
Perform the treatment for about 5 minutes. By this processing, a pyramid-shaped uneven structure can be formed on the surface of the substrate made of single crystal silicon.

[0007]

Incidentally, a wafer-shaped substrate is usually used for a substrate of a semiconductor element. Such a wafer-shaped substrate is cut out from a lump of a crystalline semiconductor called an ingot and provided for use. Is done. For this reason, the surface of the wafer-shaped substrate has an unstable portion in a bonding state such as a processing strain or a crystal defect generated when cutting from the ingot.

Most of such unstable portions in the bonded state are removed by removing the surface portion of the substrate by the primary etching as described above, but the primary etching process removes the surface portion of the substrate. Only 2 depths from
It is a region up to about 0 μm, and it is not possible to completely remove an unstable portion of a bonding state such as a processing strain or a crystal defect formed at a deeper place.

If the above-described texturing process is performed in a state where the unstable portion in the bonded state remains, the unstable portion in the bonded state is more easily etched than the other stable portions. Is unevenly applied, which causes unevenness in the size of the uneven structure. If the size of the concavo-convex structure formed on the light-receiving surface side of the substrate is non-uniform, light cannot be effectively confined, and the photoelectric conversion characteristics deteriorate. .

[0010] It is an object of the present invention to solve the conventional problems and improve the device characteristics of a semiconductor device by improving the uniformity of a concavo-convex structure formed on the surface of a substrate.

[0011]

In order to solve the above-mentioned conventional problems, the present invention provides a method for forming a blocking layer on a surface of a substrate made of a crystalline semiconductor, and forming the blocking layer on the surface of the substrate on which the blocking layer is formed. On the other hand, the method further comprises a step of etching the blocking layer by performing an etching process and forming an uneven structure on the surface of the substrate.

[0012] The present invention is characterized in that the blocking layer is formed by a chemical reaction occurring on the surface of the substrate.

Further, the invention is characterized in that the blocking layer is made of an oxide, and the blocking layer is formed by an oxidation treatment in ozone water.

Alternatively, the blocking layer is made of a nitride.

[0015]

FIG. 1 is a sectional view for explaining the concept of a method of manufacturing a semiconductor device according to an embodiment of the present invention.

In the present invention, as shown in FIG. 1, first, the entire surface of the substrate 1 made of a crystalline semiconductor such as monocrystalline silicon or polycrystalline silicon is applied to the surface of the substrate 1 in a gas phase or a liquid phase. The blocking layer 2 is formed by utilizing a chemical reaction generated between the first and second layers. As described above, when a chemical reaction generated between the substrate 1 and the surface of the substrate 1 is used, a chemical reaction is selectively generated from a portion where the crystal state, such as crystal distortion or crystal defect, existing in the substrate 1 is unstable. For this reason, the blocking layer 2 is selectively formed from the portion 3 where the crystal state is unstable, as indicated by the mark x, and as a result, the blocking layer 2 is formed on the portion 3 where the crystal state is unstable. Is formed so as to be thicker than a portion where other crystalline states are good.

As a formation method utilizing a chemical reaction generated between the substrate 1 and the surface, for example, plasma CVD
There is a method using a chemical vapor deposition method such as a method, a method by heat treatment in an oxidizing atmosphere or a nitrogen atmosphere, or a method of oxidizing in an oxidizing solution. Alternatively, the invention is not limited thereto, and any other method may be used as long as the formation method utilizes a chemical reaction generated between the substrate 1 and the surface.

As described above, the blocking layer 2 may be an oxide film or a nitride film formed by a chemical vapor deposition method such as a plasma CVD method, an oxide film formed by a heat treatment in an oxidizing gas atmosphere, or a nitride film. A nitride film formed by heat treatment in a gas atmosphere, an oxide film formed by oxidation in an oxidizing solution, or the like can be used. Alternatively, any other film may be used as the blocking layer as long as the film is formed by a formation method utilizing a chemical reaction occurring between the substrate 1 and the surface of the substrate 1.

Next, the substrate 1 on which the blocking layer 2 is formed as described above is subjected to a texturing process using an alkaline solution. In this step, the etching proceeds from the blocking layer 2, and when the blocking layer 2 is completely etched and the surface of the substrate 1 is exposed, the etching of the substrate 1 is started.

By the way, as described above, the blocking layer 2 is formed on the portion 3 where the crystalline state is unstable, and the blocking layer 2 is formed thicker than on the portion where the crystalline state is stable. Therefore, even when the blocking layer 2 formed on the portion where the crystal state is stable is completely removed by etching, the blocking layer 2 remains on the portion 3 where the crystal state is unstable. For this reason, the etching of the substrate 1 proceeds from the portion where the crystal state is stable, and the etching of the portion 3 where the crystal state is unstable is started with a delay. The etching time is shorter than the etching time at a stable portion. As described above, since the etching time in the portion 3 where the crystal state that is easily etched is unstable is shorter than that in the other portions, the etching depth becomes substantially equal over the entire main surface of the substrate 1, The uniformity of the concavo-convex structure formed on the one main surface can be improved as compared with the related art.

(Embodiment 1) Next, an embodiment of the present invention will be described. In the present embodiment, (10
0) Specific resistance 1Ωcm sliced along the plane, thickness about 4
A substrate made of 00 μm p-type single crystal silicon was used. Then, this substrate is heated to about 85 ° C. at a temperature of 4% by weight.
By immersing in a NaOH aqueous solution for about 5 minutes and performing primary etching, a region up to about 10 μm on the surface side is removed.

Then, after performing a water washing treatment, a treatment with an aqueous HF solution (4% by weight) for removing alkali components, and a water washing treatment, the ozone aqueous solution (ozone concentration: about 10 ppm) at room temperature in which bubbling is performed. 10 substrates
Then, a blocking layer made of an oxide film having a thickness of about 10 ° is formed on the entire surface of the substrate.

Then, NaOH having a temperature of about 85 ° C. (1.
The substrate is immersed in a mixed solution of 5% by weight) and a surfactant (1% by weight) for about 30 minutes to perform a texturing process. By this step, a pyramid-shaped uneven structure is formed on the surface of the substrate.

The shape of the concavo-convex structure formed on the surface of the substrate as described above was observed using an SEM (scanning electron microscope). FIG. 2 shows a schematic diagram of the shape of the concavo-convex structure obtained as a result.
Shown in The figure also shows, for comparison, a schematic diagram of the concavo-convex structure on the substrate of Comparative Example 1 formed by the same method as that of the present example except that the blocking layer made of an oxide film was not formed. FIG. 7A is a schematic diagram of the concave-convex structure of the present example, and FIG. 6B is a schematic diagram of the concave-convex structure of the comparative example. It is apparent from the figure that the present embodiment can obtain a concavo-convex structure having better uniformity.

FIG. 3 shows the diffuse reflectance of the substrates of Example 1 and Comparative Example 1. As shown in the figure, it can be seen that the reflectance of the substrate of Example 1 is smaller and more light is confined in the substrate. This is considered to be due to the fact that the uneven structure of the substrate of Example 1 has better uniformity.

(Embodiment 2) In this embodiment, a substrate made of single crystal silicon which has been subjected to primary etching, water washing, HF treatment and water washing by the same method as in Embodiment 1 is used for about 85%.
The substrate was allowed to stand in a POCl ₃ gas at 0 ° C. for about 10 minutes to form a blocking layer made of a thermal oxide film having a thickness of about 10 ° on the surface of the substrate.

It should be noted that the oxidizing gas P containing P
The heat treatment in the OCl ₃ gas is usually called a gettering treatment, and P is thermally diffused into the substrate at the same time when a blocking layer made of a thermal oxide film is formed on the substrate surface. Then, heavy metals such as Fe and Cr contained in the substrate segregate in the region where P is diffused, so that the characteristics of the substrate itself are improved.

Then, the substrate on which the blocking layer made of the thermal oxide film was formed on the surface of the substrate was subjected to texturing in the same manner as in Example 1 to form a pyramid-shaped uneven structure on the substrate surface. . In this step, the region where the heavy metal segregates is also removed.

(Embodiment 3) In this embodiment, first, Embodiment 2
A thermal oxide film was formed on the surface of the substrate made of single crystal silicon by thermal oxidation in POCl ₃ gas in the same manner as described above.
By the way, according to the thermal oxidation in the POCl ₃ gas, as described above, the thermal diffusion of P into the substrate occurs simultaneously with the formation of the blocking layer, and the heavy metal in the substrate segregates in a region where the P thermally diffuses. Therefore, in this embodiment, after the region where P was thermally diffused was removed by a treatment in a hydrofluoric-nitric acid solution, the blocking layer was formed and textured again by the same method as in the first embodiment.

Using the methods of Examples 1 to 3 and the method of Comparative Example 1, a plurality of single-crystal silicon substrates having an uneven structure on the surface were manufactured. Then, the diffuse reflectance on the substrate surface was measured. FIG.
5 is a characteristic diagram showing the diffuse reflectance of the substrate formed by the method of Comparative Example 1 and the vertical axis represents the reflectance at a wavelength of 600 nm;
The horizontal axis indicates the number of productions. Since the value of the diffuse reflectance in the entire wavelength region increases and decreases substantially in direct proportion to the reflectance at the wavelength of 600 nm, the magnitude of the diffuse reflectance in the entire wavelength region is compared by comparing the values of the reflectance at the wavelength of 600 nm. Can be compared.

As shown in FIG. 4, the reflectivity of the substrate manufactured by the method of Comparative Example 1 is larger than that of Examples 1 and 3, and it varies every time, and the reproducibility is not good. On the other hand, according to the substrates manufactured by the methods of Examples 1 and 3, the reflectance at a wavelength of 600 nm was constant at approximately 0.12, and a substrate having a low reflectance could be obtained with good reproducibility.

According to the substrate manufactured by the method of the second embodiment, a substrate having a low reflectance can be obtained in the first and second times, but the reflectance increases as the number of times increases in the third and fourth times. Become. Therefore, in this embodiment, 4
After successively producing a substrate, a texturing treatment was performed using a new NaOH aqueous solution. This is the fifth time,
This is the sixth and seventh data. As shown here,
According to the fifth, sixth, and seventh substrates prepared using a new NaOH aqueous solution, it is understood that a substrate having a small reflectance can be obtained with good reproducibility. As described above, the reason why the reflectance of the third and fourth substrates formed in this embodiment has increased is considered as follows. In the second embodiment, the blocking layer made of a thermal oxide film is formed by a heat treatment in POCl ₃ gas.
Is also thermally diffused into the substrate, and during the texturing process,
P thermally diffused into the substrate is also eluted into the NaOH aqueous solution. It is considered that the concentration of P in the NaOH aqueous solution increases as the number of times increases, so that the uniformity of the concavo-convex structure formed on the substrate surface gradually deteriorates, and as a result, the reflectance increases. However, also in the embodiment 2 described above, the substrate manufactured immediately after the replacement with a new NaOH aqueous solution can obtain a low reflectance with good reproducibility, and is superior to the method of the conventional example 1.

As described above, according to the present invention, a concavo-convex structure having good uniformity can be formed on the surface of a substrate. Therefore, a solar cell substrate having a low reflectance, that is, an improved light confinement effect can be obtained with good reproducibility.

Next, an embodiment of a semiconductor device manufactured by using the present invention will be described.

Example 4 A semiconductor device having the structure shown in FIG. 6 was formed using the substrate having the uneven structure on the surface prepared in Example 1. First, the substrate manufactured in Example 1 was subjected to a water washing treatment, an HF treatment, and a water washing treatment.
P is thermally diffused in an OCl ₃ gas to diffuse P from the substrate surface to a region having a depth of about 0.5 μm to form an n-type region. In such a state, an uneven structure and an n-type region are formed over the entire surface of the p-type substrate.

Next, the entire surface except the light receiving surface of the substrate is subjected to an etching treatment with a hydrofluoric nitric acid solution to remove the uneven structure and the n-type region formed on the portion other than the light receiving surface of the substrate.
Then, a comb-shaped collector electrode made of Ag is formed on the n-type region formed on the light receiving surface side of the substrate by screen printing, and a back electrode made of Al is formed on the back surface of the substrate by sputtering. did. Further, the Al on the back side is diffused into the substrate by heat treatment at about 650 ° C. to form a BSF layer, and an SiN film as an anti-reflection film is formed on the collector electrode by a plasma CVD method, as shown in FIG. A semiconductor device having a structure was manufactured.

Table 1 shows the photoelectric conversion characteristics of the device of this example. For comparison, the characteristics of the semiconductor element of Comparative Example 2 formed using the substrate of Comparative Example 1 by the same method as that of the present example are also shown.

[0038]

[Table 1]

As is clear from the table, the device of this example has higher photoelectric conversion characteristics. This is considered to be due to the fact that the light confinement effect was improved in the present embodiment because the substrate having the concavo-convex structure having better uniformity was used as described above.

Example 5 In this example, a semiconductor device having the structure shown in the element structure sectional view of FIG. 5 was formed using the substrate prepared in Example 2.

In the figure, reference numeral 11 denotes a substrate made of n-type single crystal silicon, and has a concave-convex structure A on the light receiving surface side. In this embodiment, the uneven structure A is the substrate 11
Is formed on the back side, but the uneven structure A on the back side is not necessarily required. Reference numeral 12 denotes a first i-type layer having a thickness of about 100 ° made of intrinsic amorphous silicon formed on the uneven structure A on the light receiving surface side of the substrate 11, and 13 denotes a p-type layer made of p-type amorphous silicon. Layer. And
A first light-transmitting electrode 14 made of ITO is formed on the p-type layer 13.
And a comb-shaped first collector electrode 15 made of Ag and Ag.

On the back surface of the substrate 11, a second i-type layer 16 made of intrinsic amorphous silicon and having a thickness of 100.degree.
N-type layer 1 of amorphous silicon having a thickness of about 400 °
7, a second translucent electrode 18 made of ITO and a comb-shaped second collector electrode 19 made of Ag are sequentially formed on the n-type layer 17. Such a device of this example was manufactured as follows.

First, the substrate 11 prepared in Example 2 is subjected to a water washing treatment, a 4% by weight HF treatment and a water washing treatment, and then an amorphous silicon film is formed. In forming the amorphous silicon film, first, the second i-type layer 16 and the n-type layer 16 are sequentially formed on the back surface side of the substrate 11 by using the plasma CVD method, and then the first i-type layer 16 is formed on the light-receiving surface side of the substrate. Layer 12 and p
The mold layer 13 is formed sequentially.

Further, the p-type layer 1 is formed by sputtering.
The first light-transmitting electrode 14 and the second light-transmitting electrode 18 are formed on the n-type layer 3 and the n-type layer 17.
First and second collector electrodes 15 and 19 made of Ag are formed on the fourth and fourth electrodes 18 by screen printing. Through the above steps, a semiconductor device having the structure shown in FIG. 5 is manufactured.

Example 6 As Example 6, a semiconductor device having the structure shown in FIG. 5 was manufactured using the substrate prepared in Example 3. Except for using the substrate prepared in the third embodiment, the same steps as those in the fifth embodiment were used, and the description is omitted here.

Table 2 shows the photoelectric conversion characteristics of the semiconductor devices of Examples 5 and 6. Also, for comparison, POC
l ₃ After heavy metals by gettering process using the heat treatment in a gas deletes a segregated region and the oxide film, the element of Comparative Example 3 except performing the texturing treatment formed in the same manner as in Example 5 Are also shown.

[0047]

[Table 2]

From the table, it can be seen that, in these examples, the device of the example has higher photoelectric conversion characteristics.

As described above, in the substrate fabricated in Example 2, the reflectance increases as the number of fabrications increases.
The effect of light confinement is reduced. However, this problem can be solved by replacing the aqueous solution of NaOH used for the texturing with a new one. in addition,
As described above, the gettering process for improving the characteristics of the substrate itself and the formation of the blocking layer can be performed simultaneously, and further, the removal of the region where the heavy metal generated by the gettering process is segregated, and the texturing process Can be performed simultaneously. For this reason, the steps of the manufacturing process can be greatly simplified, and the manufacturing cost can be reduced.

Although the case where the blocking layer is formed from an oxide film has been described above, the blocking layer may be formed from a nitride film.

The present invention is not limited to a solar cell, but can be applied to any semiconductor element using a substrate made of a crystalline semiconductor and having an uneven structure on the surface.

[0052]

As described above, according to the present invention, the uniformity of the concavo-convex structure formed on the surface of the substrate can be improved, and the device characteristics of the semiconductor device can be improved. For example, when the present invention is applied to the manufacture of a solar cell, the light confinement effect of the substrate can be increased, and the photoelectric conversion characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining the concept of the manufacturing method of the present invention.

FIG. 2 is a schematic diagram showing a shape of a concavo-convex structure obtained in Example 1.

FIG. 3 is a characteristic diagram showing the reflectance of the substrate of Example 1.

FIG. 4 is a characteristic diagram showing the reflectance of the substrates manufactured according to Examples 1 to 3.

FIG. 5 is an element structure sectional view of a semiconductor element according to Examples 5 and 6.

FIG. 6 is a sectional view of an element structure of a conventional semiconductor element.

[Explanation of symbols]

1, 11, 21 ... substrate, 2 ... blocking layer, 3 ... part where crystal state is unstable, A ... uneven structure

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-136444 (JP, A) JP-A-3-206669 (JP, A) JP-A-11-214722 (JP, A) 504785 (JP, A) US Patent 4,131,488 (US, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 31/04-31/078

Claims (5)

(57) [Claims] 1. A blocking layer is formed on a surface of a substrate made of a crystalline semiconductor, and an etching process is performed on the surface of the substrate on which the blocking layer is formed.
A method for manufacturing a semiconductor device, comprising a step of etching the blocking layer and forming an uneven structure on a surface of the substrate. 2. The method according to claim 1, wherein the blocking layer is formed by a chemical reaction occurring on a surface of the substrate. 3. The method according to claim 1, wherein said blocking layer is made of an oxide. The method according to claim 4, wherein the blocking layer, a method of manufacturing a semiconductor device according to any one of claims 1 to 3, characterized in that formed by oxidation treatment with ozone water. 5. The method according to claim 1, wherein the blocking layer is made of a nitride.