JP2880415B2 - Non-mirror silicon wafer and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel non-mirror silicon wafer, a method for treating a silicon wafer surface, and a silicon optical device using the non-mirror silicon wafer.

[0002]

2. Description of the Related Art A variety of surface treatments (etching methods) for silicon wafers have been developed in the fields of semiconductors, optoelectronic devices, and the like, and various techniques are used according to the purposes and applications. As these etching methods, a wet etching method, a dry etching method, a chemical mechanical polishing (CMP), and the like are generally used, and a wet etching method that can perform batch processing for deep etching over a wide surface is used. It is used as the mainstream. Generally, the wet etching method is (I) hydrofluoric acid-
The method is roughly classified into an isotropic etching method using nitric acid as an etchant and (II) an anisotropic etching method using an alkali solution such as potassium hydroxide or sodium hydroxide or hydrazine as an etchant. The former is mainly used for processing strain layers and defects extraction of semiconductor substrates, and the latter is mainly used for surface treatment of silicon optical devices.

[0003]

When this wet etching method is applied to the surface processing of a silicon wafer or various optical devices, not only removal of a work-strained layer and crystal defects inherent in the etching technique, but also etching of the entire wafer. The challenge is to achieve both uniformity, reproducibility in ultra-thin finishing, and mass productivity. Furthermore, for optical devices,
It has been demanded that it can be applied to all types of wafers while satisfying good workability including reproducibility and simplicity of production. 1) Ultra-thin wafer finish with high uniformity and uniformity over the entire area of a large area wafer. 2) Reduction of surface reflection to improve photoelectric conversion efficiency
Special surface finish such as enlargement of the unit light receiving surface. However, the finished surface by the conventional hydrofluoric acid-nitric acid acid isotropic etching has a quasi-mirror shape having a gentle undulation, and particularly in the case of a large etching amount, deep etching tends to cause sagging from the peripheral portion of the wafer, There has been a problem in terms of productivity with regard to finishing a highly uniform ultra-thin wafer on a thick large-diameter wafer.

On the other hand, the anisotropic etching method using an alkali solution or hydrazine, which has been generally used for processing the surface of a wafer for an optoelectronic device, requires processing in a boiling state or at a high temperature around 100 ° C. Therefore, there was a problem in workability associated with equipment and technology. The surface crystal orientation of the silicon wafer that can be further processed is limited to the (100) plane.
The present invention solves the conventional problems and provides a novel silicon wafer that cannot be obtained by the conventional chemical etching, and also provides a surface treatment method and a treatment liquid thereof.

[0005]

SUMMARY OF THE INVENTION The present invention provides a non-mirror silicon wafer having a non-sharp curved top with a mean height of 5 μm or less uniformly over the entire surface of the wafer.
The protrusion of the non-sharp curved top portion means that the cross section along the center line in the height direction of the protrusion is not defined by the intersecting straight line but is defined by a curve. The shape of the projection may be substantially a cone. The vertex angle when the projection is simulated as a substantially cone may be a convex angle (an angle smaller than two right angles). The average height of the protrusions is preferably 3 μm or less, most preferably 2 μm or less. Further, as long as the height is the average height and the effects of the present invention are exerted, a projection larger than the above range may be present. FIGS. 1 and 2 show schematic diagrams of the above silicon wafer, and FIG. 3 shows a micrograph.

[0006] The present invention further provides at least 10 ³ / cm ² or more hemispherical or semispherical mounds having an average height of 100 µm or less over the entire surface of the wafer, and the entire surface including the mound surface further has an average height of 5 µm or less. A non-mirror silicon wafer having a non-pointed curved top projection is also provided. The mound refers to a portion raised from the wafer, and has an average height of 100 μm or less.
The silicon wafer of the present invention further has substantially conical or pyramid-shaped protrusions having a non-pointed curved top protrusion on the entire surface of the wafer having such a mound. This projection is similar to the aforementioned projection. The average height of the projections is preferably 3 μm or less, more preferably 2 μm or less. FIGS. 4 and 5 show schematic diagrams of the above silicon wafer, and FIGS. 6-9 show micrographs.

[0007] The silicon wafer according to the present invention in the above-described embodiment is particularly applicable to a crystalline silicon solar cell.
The texture structure as surface reflection reduction for high conversion efficiency acts as a composite (double) texture structure,
Further, the light receiving area per unit plane is greatly increased, for example, about 45-85%. The silicon wafer according to the present invention can be manufactured by anisotropic etching using a mixture of sulfuric acid, nitric acid and hydrofluoric acid as an etchant. The mixing ratios of sulfuric acid, nitric acid and hydrofluoric acid are 95% sulfuric acid, 70% nitric acid and 49% hydrofluoric acid, respectively. Particularly favorable results are obtained when the acid is 4-40% and the volume ratio of sulfuric acid, nitric acid and hydrofluoric acid is 12: 2: 1, 10: 4: 1 or 8: 8: 1.

In the surface treatment method according to the present invention, the etching is preferably performed at a temperature of 60 ° C. or less. In the surface treatment method and the surface treatment solution according to the present invention, in order to simultaneously achieve a practical etching rate, etching anisotropy and uniformity, the ratio of the sulfuric acid to the entire mixed solution is determined by volume ratio. 33-90%, hydrofluoric acid is 5-
Preferably, 40% and nitric acid are 5-50%. Considering the practical etching rate, the uniformity of the entire surface during thin processing, and the cleanliness of the anisotropic etched surface (specifically, the denseness of the silicon surface), most preferably, sulfuric acid: nitric acid: hydrofluoric acid Is 12: 2: 1 or 8:
8: 1. The above volume ratio is 49% hydrofluoric acid,
70% nitric acid and 95% sulfuric acid. By performing etching with the above-mentioned processing solution, it is possible to easily obtain ultra-thin silicon wafers having a large area and high uniformity up to a thickness of about 10 μm or wafers having a composite texture surface at a low temperature with good reproducibility. it can. In order to obtain a large-diameter ultra-thin wafer, it is necessary to perform etching without causing sagging of the peripheral portion. According to the present invention, the wafer has a diameter of 2 inches and a diameter of 1 inch.
An epoch-making large-diameter ultra-thin silicon wafer having a thickness of about 0 μm can be obtained. Hereinafter, the present invention will be described in more detail with reference to Examples, but these Examples do not limit the scope of the present invention in any way.

Example 1 Hydrofluoric acid (49% concentration, the same applies hereinafter) and nitric acid (70% concentration,
In the case where sulfuric acid (95% concentration, hereinafter the same) is mixed at various ratios with respect to the same, the composition of the mixed solution, the etching surface state, that is, the etching speed, the uniformity (in thin processing), the anisotropy ( The non-reflective surface) and the finished surface (substitution and stain) were observed and evaluated on four scales of ×, Δ, ○ and ◎. The temperature was set to 40-45 ° C. Table 1 shows the results
Shown in This table shows the isotropic to anisotropic conversion conditions depending on the amount of sulfuric acid added in the treatment method of the present invention. Sulfuric acid is added to hydrofluoric acid and nitric acid at a volume ratio of 33 to the entire mixture.
% (Sample No. 3), the anisotropic etching property (non-mirror) starts to be added, and when the volume ratio becomes 45% or more (sample No. 6), the anisotropy (non-mirror) occurs within a practical processing time. (State) It can be seen that the etching characteristics are dominant.

[0010]

[Table 1]

Example 2 3 inch wafer (7.6 cm diameter), thickness 380 ± 5
Wafers (111) and (100) having different surface crystal orientations in μm and P-TYPE were subjected to sulfuric acid: nitric acid: hydrofluoric acid = 12:
FIG. 10 shows the result of confirming the etching amount depending on the wafer plane orientation at a temperature of 30 ± 3 ° C. at a ratio of 2: 1. In addition,
The specific resistance of the (111) plane was 2-24 Ωcm, and the specific resistance of the (100) plane was 0.01-0.1 Ωcm. Compared with the conventional anisotropic etching using an alkaline solution or the like, (1.
Although there is no significant difference in the amount of etching on each of the surfaces (11) and (100), the present invention provides that the anisotropic etching proceeds with this small difference.
This is considered to be a factor for obtaining a non-mirror wafer having fine projections of several μm or less with high uniformity over the entire area of any wafer.

Example 3 3 inch wafer (7.6 cm diameter), thickness 380 ± 5
μm, P-TYPE, (111) wafer (resistivity
(2-24 Ωcm), the change in the amount of etching at various temperatures was examined. As an etchant, a mixed solution of hydrofluoric acid (49%): nitric acid (70%): sulfuric acid (95%) = 1: 2: 12 was used. The results are shown in FIG. The measured value is the value at the center of the wafer, and the etching amount is the reduction value of the wafer thickness, that is, the total value of the etching depth on both sides. 20
1 μm / min at ± 3 ° C., 3 μm / min at 30 ± 3 ° C., 4
6 μm / min at 0 ± 3 ° C., 10 μm / min at 50 ± 3 ° C.
Min, 16 μm / min at 60 ± 3 ° C. An ultra-thin finish requiring a relatively low etching rate is desired to be at around room temperature, specifically, 50 ° C. or less, preferably 40 ° C.
The following temperatures are preferred:

Example 4 Hydrofluoric acid (49%): nitric acid (70) was used as an etchant on an N-TYPE silicon wafer (111) surface (# 2000 finish) having a thickness of 275 ± 3 μm and a diameter of 40 mm.
%): Dip etching is performed at 50 to 55 ° C. using a mixture of sulfuric acid (95%) = 1: 2: 12,
A non-mirror wafer having a finished thickness of 30 μm was obtained in 15 minutes. FIG. 12 shows the wafer thickness with respect to the integrated etching time. The numerical value is the thickness at the center of the wafer.
The four consecutive numerical values in the above are thicknesses of 1 to 2 mm from the upper, lower, left, and right peripheral edges, respectively. As is clear from the results, there is no thickness unevenness due to sagging at the peripheral portion of the wafer, and extremely uniform anisotropic (non-mirror) etching is performed on the entire surface. That is, it was confirmed that the anisotropy due to the etchant composition was sufficiently developed.

[0014]

The non-mirror wafer obtained by the present invention is a very thin wafer having a very large area and a very high uniformity over the entire surface. In addition, when a wafer having a composite (double) texture structure is applied to an optical device, prevention of light surface reflection and a large increase in a light receiving surface on a unit wafer surface are achieved, thereby improving photoelectric conversion efficiency. Further, according to the etching method of the present invention, the non-mirror wafer according to the present invention can be processed in a simple manner without complicated steps or facilities, and regardless of the crystal orientation of the wafer surface (1).
11) and (100) enable effective anisotropic etching at room temperature.

[Brief description of the drawings]

FIG. 1 is a schematic view of the surface of a silicon wafer according to the present invention.

FIG. 2 is an enlarged view of a portion surrounded by a square in FIG.

FIG. 3 is a micrograph of a crystal structure of a silicon wafer surface according to the present invention.

FIG. 4 is a schematic view of the surface of a silicon wafer according to the present invention.

FIG. 5 is an enlarged view of a portion surrounded by a square in FIG. 4;

FIG. 6 is a micrograph of a crystal structure of a silicon wafer surface according to the present invention.

FIG. 7 is a micrograph of a crystal structure of a silicon wafer surface according to the present invention.

FIG. 8 is a micrograph of a crystal structure of a silicon wafer surface according to the present invention.

FIG. 9 is a micrograph of a crystal structure of a silicon wafer surface according to the present invention.

FIG. 10 is a diagram showing the results of Example 2.

FIG. 11 is a diagram showing the results of Example 3.

FIG. 12 shows the results of Example 4.

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/306-21/3063 H01L 21/308 H01L 31/04 H01L 21/00-21/02 H01L 21 / 04-21/06 C23F 1/00-3/06

Claims (5)

(57) [Claims] 1. A substantially hemispherical or semispherical mound having an average height of 100 μm or less is provided on at least 10 ^{3 over the} entire surface of a wafer.
A non-mirror silicon wafer having a number of pieces / cm ² or more, and further having a projection with a non-sharp curved top having an average height of 5 μm or less on the entire surface including the mound surface. 2. A silicon optoelectronic device manufactured using the silicon wafer according to claim 1. 3. An anisotropic etching method for a silicon wafer using a mixture of sulfuric acid, nitric acid and hydrofluoric acid as an etchant. 4. Sulfuric acid, nitric acid and hydrofluoric acid are each 95%
% Sulfuric acid, 70% nitric acid, 49% hydrofluoric acid, sulfuric acid, nitric acid,
And sulfuric acid in a volume ratio of 33-90%, nitric acid 5-50
%, And 4 to 40% of hydrofluoric acid. 5. Sulfuric acid, nitric acid and hydrofluoric acid are each 95%
% Sulfuric acid, 70% nitric acid, 49% hydrofluoric acid, sulfuric acid, nitric acid,
And the volume ratio of hydrofluoric acid is 12: 2: 1, 10: 4: 1,
4. The etching method according to claim 3, wherein the ratio is 8: 8: 1.