KR100913634B1 - Fabrication method of 45 degree tilt mirror - Google Patents

Abstract

The present invention relates to a method of manufacturing a 45 ° reflecting mirror using a semiconductor wafer, by which the smoothness of the 45 ° reflecting surface can be improved and a thin film having a high refractive index and low refractive index can be easily deposited on the reflecting surface. In order to increase the reflectivity of the mirror, a 45 ° inclined surface is formed by etching on a semiconductor wafer and a reflective metal material or a dielectric thin film is deposited on the upper surface of the polished wafer instead of the inclined surface. Instead of using the etched inclined surface as a reflecting surface, a very flat wafer surface (upper surface) obtained by polishing during semiconductor wafer fabrication is used as a reflecting surface, and the etched inclined surface is used to form only the angle of the reflecting mirror. Diffuse reflection is suppressed and reflectance can be improved.

45 °, reflective mirror, semiconductor wafer, polished surface, improved reflectivity, suppressed reflection

Description

Fabrication method of 45 ° reflection mirror {Fabrication method of 45 degree tilt mirror}

1 is a schematic diagram of a method of forming an inclined surface by slicing and etching of a conventional semiconductor wafer;

Figure 2 is a schematic diagram showing a part of the manufacturing process of the 45 ° reflection mirror using a conventional semiconductor wafer,

3 is a process chart of manufacturing a 45 ° reflecting mirror using the semiconductor wafer manufactured by the process of FIG.

4 is a plan view showing a mask alignment state in the manufacturing process of the conventional 45 ° reflection mirror,

5 is a plan view showing the roughness of the reflective surface in the conventional manufacturing method,

6 is a manufacturing process diagram of a 45 ° reflecting mirror according to a conventional manufacturing method,

7a to 7i is a manufacturing process of the 45 ° reflection mirror according to the present invention,

8 is an exemplary view of a shape likely to occur when the mirror is cut out by a conventional method.

* Explanation of symbols for main parts of the drawings

1: semiconductor ingot 2: semiconductor wafer

2a: bottom 3: photoresist

4 coating layer (reflective layer) 5 cut line

7: trench 10: 45 ° reflecting mirror

R: path of light

The present invention relates to a mirror used in a semiconductor light emitting device such as a laser diode, and provides a method of manufacturing a wedge-shaped mirror that changes the direction of light at a 45 ° angle in detail, an etching that can cause surface roughness Instead of using the inclined surface as a reflecting surface, a very flat wafer surface obtained by polishing in the semiconductor wafer manufacturing process is used as the reflecting surface, so that the smoothness of the 45 ° reflecting surface can be improved, and a multilayer film having a high refractive index and a low refractive index is used. By easily depositing on the reflective surface, it is possible to increase the reflectivity of the mirror.

Patent application No. 2007-0026558, filed by the present applicant, describes a method of fabricating a 45 ° reflecting mirror manufactured by a semiconductor technique using a semiconductor wafer, wherein the semiconductor wafer uses a 9.74 ° tilted substrate. After wet etching the substrate to expose a surface having inclined surfaces of 45.00 ° and 64.48 °, Ag or Al is coated on the inclined surface to form a wedge shaped mirror having a 45 ° inclined surface.

1 illustrates a method of manufacturing a mirror using a semiconductor wafer having a precise (100) plane orientation, which is conventionally implemented by a method, which exposes the (111) plane by etching the semiconductor wafer with an anisotropic etching solution. It is a way. Since the (111) plane forms an angle of 54.74 ° with respect to the (100) plane, the inclined plane in FIG. 1 has an angle of 54.74 ° with the etched bottom surface 2a. Therefore, it is impossible to produce a 45 ° reflecting mirror in this way.

However, as briefly introduced above, the applicant cuts the semiconductor wafer 2 so that it is 9.74 ° tilted from the (100) plane when slicing the semiconductor wafer 2 from the semiconductor ingot 1 in FIG. Maintains an angle of 9.74 ° with respect to the cut semiconductor wafer surface. In this case, since the (111) plane forms an angle of 54.74 ° with respect to the (100) plane, the (111) plane forms an angle of exactly 45.00 ° and 64.48 ° with respect to the wafer 2 surface.

The manufacturing process in the case of manufacturing the 45.00 ° reflection mirror in this manner is shown in detail in FIG. 3.

First, as shown in FIG. 3A, a portion of the upper surface of the semiconductor wafer 2 having the upper surface direction of the (100) plane is covered with a photoresist 3.

Then, as shown in FIG. 3B, the photoresist 3 of the portion where the semiconductor wafer 2 is to be etched is removed by a known photo-lithography method.

Next, as shown in FIG. 3C, the semiconductor wafer 2 is etched using an anisotropic Si etching solution such as KOH. At this time, the exposed surface becomes the (111) plane and has an inclination angle of 54.74 ° with the (100) plane.

Thereafter, after removing the remaining photoresist 3 of the etched semiconductor wafer 2 with a photoresist remover, the upper portion of the semiconductor wafer 2 is made of Al, Ag, or gold (Au) as shown in FIG. The coating layer 4 is formed of a material having high reflectivity such as).

Finally, as shown in (e) of FIG. 3, the semiconductor wafer 2 having the metal thin film coating layer 3 formed thereon is cut to a desired size along a cutting line 5 by scribbing and sawing. As shown in (f), the 45 ° reflecting mirror 10 which converts the light path R is completed.

On the other hand, in order for the (111) plane to appear exactly by anisotropic etching, the boundary line of the open portion of the photoresist 3 pattern should be exactly <110> as shown in FIG. 4. The direction of the open portion of the photoresist 3 is made by the method of mask alignment in the photo lithography process, but it is very difficult to have the <110> direction perfectly in the portion, and the mask Some misalignment is likely to occur in alignment. If the open portion of the photoresist has a direction mismatch with the <110> direction, as shown in FIG. 5, the surface roughness of the wrinkled shape indicated by the dotted line is generated on the etched inclined surface.

When the reflective mirror is manufactured using the inclined surface having such a rough surface, the reflection efficiency decreases due to diffuse reflection. Roughness such as surface wrinkles on the inclined surface may cause the PR boundary to not be perfectly straight in the process of removing the portion of the photoresist to create the open portion, even if the open portion of the photoresist remains exactly <110>. Can also occur.

Therefore, the method of forming the (111) plane by the anisotropic etching and using it as a reflecting mirror causes inconveniences that require a very precise photolithography process.

The manufacturing method of the 45 degree reflecting mirror by the patent application 2007-0026558 which the applicant applied for is shown sequentially in FIG.

First, the processes of FIGS. 6 (a), 6 (b), and 6 (c), which cause the (111) plane to appear, are the same as those of FIGS. 4 (a), (b) and (c). In this case, the semiconductor wafer 2 is sliced from a semiconductor ingot (not shown), and the semiconductor wafer 2 is cut out at a tilting of 9.74 ° from the (100) plane, and a part of the upper surface of the semiconductor wafer 2 is cut into the photoresist 3. Covering with; (See Fig. 6 (a))

Removing the photoresist 3 of the portion to be etched by the photolithography method; (see FIG. 6B).

Etching the photoresist removed portion using an anisotropic etching solution to form an exposed surface as a (111) surface having an inclination angle of 54.74 with the (100) surface; (see Fig. 6 (c)) .

Meanwhile, in the related art, reflective metals such as Au, Ag, and Al are deposited on the upper surface of the semiconductor wafer, including the inclined surface. However, in the present invention, as shown in FIG. The reflective metal is deposited on the lower surface to form the coating layer 4. In the case of a semiconductor wafer, mirror surfaces can be made by polishing both sides of the wafer in the manufacturing step, and the mirror surfaces formed by polishing are very smooth and do not have diffuse reflection. The semiconductor wafer thus manufactured can be cut to a suitable size as shown in FIG. 6 (e) to complete the desired 45 ° reflecting mirror 10 (see FIG. 6 (f)). When the (111) plane shown by etching is turned to the bottom as shown in FIG. 6G, the light path R is perpendicular to the light using the reflective metal coating layer 4 formed on the bottom surface of the polished semiconductor wafer. It can be changed.

In addition, since the deposition of the reflective metal is performed on the surface (lower surface) of the flat semiconductor wafer, a method of causing reflection by depositing a dielectric thin film instead of the deposition of the reflective metal can be easily applied.

In addition, when a plurality of dielectric thin films having a high refractive index and a low refractive index are alternately deposited on the surface (lower surface) of the semiconductor wafer, a very high reflectance may be obtained by optical interference.

In the case of dielectric thin film deposition, the deposition rate of the dielectric layer varies depending on the geometry of the surface on which the dielectric thin film is to be deposited. Higher reflectivity can be easily obtained by increasing the thickness control degree of the thin film.

However, when manufacturing the 45 degree reflective mirror by the method of the above-mentioned patent 2007-0026558, the size of the reflecting mirror is determined by a method such as scribing or sawing as shown in Fig. 6E. Generally, the scribing or sawing method has a precision of several tens of um and the fracture surface is not clean. Therefore, it is very difficult to produce a 45 degree reflective mirror with very precise size by scribing or sawing.

The present invention has been made to solve the above-mentioned conventional problems, an object of the present invention is to adjust the size of the mirror very precisely by allowing the size of the mirror to be determined only by the method of anisotropic etching.

In order to achieve the above object, the present invention provides a portion of a 9.74 ° inclined semiconductor wafer to dig a trench using isotropic wet etching or dry etching instead of anisotropic etching, and then performs anisotropic wet etching using the trench. The etching stops at the point where the exposed (111) planes meet, so that the size of the mirror is determined by the distance between the trenches determined by the photolithography method. After removing the photoresist on the upper surface of the wafer thus fabricated, a reflective metal film or a multilayer dielectric thin film is deposited on the upper surface to form a mirror surface. After scribing or sawing the wafer to the appropriate size, a 45-degree reflective mirror can be fabricated with a very precise height adjustment.

Specifically, slicing a semiconductor wafer from a semiconductor ingot, cutting the semiconductor wafer to be 9.74 ° tilted at the (100) plane, and covering a portion of the upper surface of the semiconductor wafer with photoresist; Removing photoresist on both sides of the region where the mirror surface is to be manufactured by a photolithography method; Forming a trench in which the photoresist has been removed by an isotropic wet etching or anisotropic dry etching method; Injecting an anisotropic etching solution through the formed trench to form a (111) surface of the reverse mesa type; Removing the photoresist on the upper surface of the wafer; Manufacturing a reflective mirror by depositing a reflective metal film or a multilayer or single-layer dielectric thin film on an upper surface of the wafer; And cutting the semiconductor wafer coated with the metal thin film or the dielectric thin film to a 45 ° reflecting mirror.

Hereinafter, with reference to the accompanying drawings, preferred embodiments that do not limit the present invention will be described in detail.

7A to 7I schematically illustrate a manufacturing process of the 45 ° reflecting mirror according to the present invention, the manufacturing process of which slices the semiconductor wafer 2 from the semiconductor ingot (not shown), which is 9.74 ° in the (100) plane. Cutting the semiconductor wafer 2 so as to tilt it, and covering a part of the upper surface of the semiconductor wafer 2 with the photoresist 3; (see FIG. 7A)

Removing the photoresist 3 of the portion to be etched by a photolithography method (see FIG. 7B).

Etching the portion of the photoresist removed using an isotropic wet etching method or anisotropic dry etching method to form the trench 7; (see FIG. 7C).

Injecting an anisotropic wet etching solution such as KOH through the trench 7 to form a (111) plane; (see FIG. 7D);

(111) planes having inclination angles of 45.00 ° and 64.48 ° respectively formed on both sides of the trench 7 meet each other to cause an etch stop; (see FIG. 7E)-At this time, the semiconductor portion in the form of a triangle is suspended in the air. It is formed by the semiconductor in the part where the trench is not formed, supporting the triangular part.

Removing the photoresist 3 of the wafer 2; (see FIG. 7F)

Depositing a metal reflective film or a multilayer or single-layer dielectric thin film on the upper surface of the wafer 2 to form a mirror surface 4 (see FIG. 7G);

Comprising a step of completing the reflective mirror by using a scribing or sawing method of the wafer (2) (see Fig. 7 (h)), a 45 ° reflective mirror made in this way is shown in Figure 7i .

On the other hand, in the prior art of Patent Application No. 2007-0026558, anisotropic wet etching occurs directly to the open opening of the photoresist, thereby causing mesa etching. Therefore, the angle formed by the 45 ° etched slope and the upper surface of the wafer is 135 °, and the angle formed by the etched slope and the lower surface of the wafer is 45 °. Therefore, Au is formed on the lower surface of the wafer to complete the 45 ° reflective mirror. A 45 ° reflective mirror is completed by depositing a reflective metal or dielectric thin film such as Ag, Al, or the like. In the reflective mirror manufacturing method manufactured in such a form, in order to cut the reflective mirror, the reflective mirror is cut out of the wafer by scribing or sawing. Scribing is a method of breaking a wafer at a desired point by hitting the wafer with a very thin blade, and sawing is a method of cutting a wafer by slicing the wafer with a very thin tooth. These methods work effectively only when they are perpendicular to the wafer, and when scribing or sawing on an inclined surface, the blade slips, making it difficult to cut the wafer into a desired shape or size. Therefore, in case of scribing or sawing, scribing or sawing should be done at the top and bottom horizontal plane points of the wafer, not at the inclined plane. Therefore, in the case of using the conventional technology, the protruding portion of the lower part as shown in FIG. 8 is easily formed. Since the protruding portion of the lower part of FIG. 8 forms the lower surface of the mirror, it is a factor that prevents the reflective coating surface 4 of the mirror from achieving 45 °. In order to prevent such protrusions, scribing or sawing must be closely attached to the bent portion of the inclined surface and the lower surface of the wafer, which requires very precise scribing or sawing and increases the possibility of failure.

In addition, in the prior art, the size of the mirror is made by scribing or sawing, and scribing or sawing is a method of mechanical processing, in which a position accuracy of generally +/- 20um or more is generally taken. In particular, in the case of sawing, it is a less precise processing method, for example, an unsuitable method for making a very small mirror having a length of several tens of um or less, and the size of the bottom surface of the mirror depends on the thickness of the semiconductor wafer. It is difficult to manufacture a variety of mirrors of various sizes in one process.

According to the present invention, a deep trench is formed by anisotropic dry etching such as reactive ion etching (RIE) as shown in FIG. 7C, and anisotropic wet etching is performed so that the (111) plane appears as shown in FIG. 7C. Unlike the mesa-shaped (111) plane in the description, the inverse mesa-shaped (111) plane appears. In the prior art, when the first etching is started, the etching occurs only in the downward direction, and since the etching does not occur in the transverse direction, the (111) plane of the mesa type appears. On the other hand, when the anisotropic wet etching is performed after the trench is formed as in the present invention, etching occurs in the lateral direction of the trench, and the etching occurs until the (111) plane of the reverse mesa type appears. Also in this case, the (111) plane of the mesa shape appears in the lower portion of the trench. When the trench is formed and wet etching is performed by anisotropic etching as in the present invention, an inverted mesa shape (111) plane appears on the upper portion of the trench. In this case, if the wet etching is continued, the etching is finally stopped in the shape of FIG. 7E by the wet etching in which the semiconductor layers between the trenches proceed from both sides. When two (111) planes formed in both trenches meet, the (111) plane is an etch stop layer so that no further etching occurs and shape and size are maintained. The semiconductor layer thus produced is supported by the semiconductor layer in a direction not shown in the drawings and manufactured in the form of floating in the air. At this time, the size of the mirror is determined only by the distance between the trenches, and the distance between the trenches is very easily and very precisely adjusted by the photolithography method, so that the size of the mirror can be adjusted very precisely and also a very small mirror can be manufactured. It becomes possible. In addition, since the distance between the wrenches can be varied in one photolithography method, it is possible to manufacture mirrors of various sizes in a single mirror manufacturing process.

On the other hand, in the semiconductor wafer, instead of conventional silicon, semiconductor substrates such as InP or GaAs can all be used for fabricating the reflective mirror of the present invention.

As described above, the present invention determines the size of the height of the reflective mirror and the like by a photolithography method and a wet etching method capable of very precise size adjustment, which is very precise and has a useful effect of manufacturing a small mirror.

Claims (4)

delete Slicing the semiconductor wafer 2 from the semiconductor ingot, cutting the semiconductor wafer 2 so that it is 9.74 ° tilted at the (100) plane, and covering a portion of the upper surface of the semiconductor wafer 2 with the photoresist 3; Removing the photoresist 3 of the portion to be etched by a photolithography method; Forming a trench using the method of isotropic wet etching or anisotropic dry etching the portion where the photoresist has been removed; Injecting the anisotropic etching solution into the formed trench to etch the semiconductor wafer 2 to form an exposed surface as a (111) surface having an inclination angle of 45.0 ° and 64.48 ° with the upper surface of the semiconductor wafer 2, respectively; Removing the photoresist 3 on the upper surface of the semiconductor wafer 2; Depositing a reflective metal or a single layer or a multilayer dielectric thin film on the upper surface of the semiconductor wafer 2 to form a reflective coating layer 4; And cutting the semiconductor wafer (2) coated with the metal thin film or the dielectric thin film to a 45 ° reflecting mirror. delete delete

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