JPH05154761A - Polishing method for crystalline thin film - Google Patents

Abstract

PURPOSE:To polish a thin film to uniform thickness even when a crystalline thin film is formed on a base having a grade in thickness by polishing the thin film with an eccentric load weight so that the boundary plane between the polished surface of a dummy body and the crystalline thin film of the base is made parallel. CONSTITUTION:A dummy body 2 thicker than a base 3 formed with a crystalline thin film 11 is used as a polishing jig, and the dummy body 2 and the base 3 formed with the crystalline thin film 11 are stuck to a polished body carrier 1. The crystalline thin film 11 is polished and corrected with an eccentric load weight 5 so that the boundary plane 12 between the polished surface 8 of the dummy body 2 and the crystalline thin film 11 of the base 3 is made parallel, then the crystalline thin film 11 is polished with a uniform load weight 9 as required.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polishing a crystalline thin film, and more particularly to a method for polishing a crystalline thin film which has a small variation in parallel flatness and is suitable for obtaining a highly accurate optical device.

[0002]

2. Description of the Related Art In general, surface polishing of a crystalline substrate or a crystalline thin film used in electronic parts and optical parts is performed by Kasai, Noda, and Ida: Precision processing of lithium tantalate electro-optical element, Research Practical Report, Vol. 20. No. 4 p915 (197
As shown in 1), a substrate 3 to be polished made of glass is used as a polishing jig, a substrate 3 having a crystalline thin film formed on the lower surface of the carrier 1 to be polished, and a dummy plate 2 having a similar height. Are fixedly adhered to the periphery of the substrate 3 on which the crystalline thin film is formed with wax 4, and are then brought into contact with the surface plate 10 while applying a load from above the carrier 1 to be polished to perform polishing (see FIG. 3). ..

[0003]

To explain with reference to FIG. 3, in FIG. 3A, the eccentric load weight 5 is arranged so that the surface to be polished of the dummy bodies 2-1 and 2-2 and the bonding surface 6 of the substrate are parallel to each other. To be used for polishing. After the polished surface 8 of the dummy body and the flat surface 7 of the polished carrier 1 become parallel, the uniform thin weight 9 is used to polish the crystalline thin film 11 formed on the substrate as shown in (b). .. However, since the crystalline thin film formed on the substrate and the dummy body have almost the same height, the crystalline thin film is also polished when the dummy body is parallelized. Therefore, if such polishing is performed, the crystalline thin film is shaved more than necessary, and the substrate is exposed. Further, when a crystalline thin film is formed on a substrate having a gradient in thickness, when the conventional method is used for polishing, the bonding surface 6 of the substrate and the surface to be polished become parallel, so that the thin film as shown in FIG. Thickness becomes uneven. Furthermore, in order to shorten the processing time for parallelizing the dummy body, a large abrasive grain is used. However, in this conventional method, the crystalline thin film is damaged when the dummy body is parallelized. Therefore, it is necessary to make the abrasive grains small, which requires a lot of time. Moreover, since the parallelism of the dummy body is not reproducible, the amount of polishing processing is not reproducible.

When the dummy body is first attached and the dummy body is parallelized and then the substrate on which the crystalline thin film is formed is fixed by wax, the substrate on which the crystalline thin film is formed is fixed by wax. When this is done, there is a drawback that the wax is melted by heating again and the parallelism of the dummy is lowered.

An object of the present invention is to overcome the above-mentioned drawbacks of the prior art, and it is possible to form a crystalline thin film having a uniform film thickness even in the case of a substrate having a thickness gradient, and to polish the crystalline thin film. The purpose of the present invention is to provide a polishing method that can minimize the processing time, shorten the processing time, and obtain a crystalline thin film with good thickness reproducibility.

[0006]

As a result of earnest research to achieve the above object, the present inventors have used a dummy body thicker than a substrate on which a crystalline thin film is formed as a polishing jig, After bonding the dummy body and the substrate on which the crystalline thin film is formed to the carrier to be polished, the dummy body is polished so that the boundary surface between the substrate and the crystalline thin film and the polished surface of the dummy body are parallel to each other. It was found that the parallelism of the dummy body can be obtained without damaging the crystalline thin film by making the parallelism.

That is, in the polishing method of the present invention, a dummy body is adhered to the plane of the carrier to be polished, and the boundary plane between the polished surface of the dummy body and the crystalline thin film of the substrate is made parallel by using an eccentric load weight. It is a method of polishing the crystalline thin film using a uniform load weight as needed, and then correcting the crystalline thin film.

[0008]

As shown in FIG. 1, the polishing jig of the present invention includes a carrier 1 to be polished having flat surfaces on both sides thereof, a substrate around which a crystalline thin film is formed, and a flat surface of the carrier to be polished. A dummy body 2, which is preferably 50 to 100 μm thicker than the substrate on which the crystalline thin film is formed, an eccentric load arranged on a plane opposite to the plane of the carrier to be polished on which the dummy body is arranged. It is composed of the weight 5. The dummy body 2 surrounding the substrate 3 on which the crystalline thin film is formed has a ring shape and is preferably thicker than the substrate on which the crystalline thin film is formed by about 50 to 100 μm. This is because if it is larger than 100 μm, it takes time to polish the dummy body, and if it is smaller than 50 μm, parallel alignment cannot be completed while polishing the dummy body. Advantageously, the thickness of the dummy body is about 50 to 100 μm thicker than the thickness of the substrate on which the crystalline thin film is formed.

The polishing method will be specifically described with reference to FIG. The substrate 3 on which the crystalline thin film 11 is formed and the dummy body 2 are bonded to the carrier 1 to be polished by the wax 4.
At this time, only one of the three dummy bodies is bonded to the substrate 3 on which the crystalline thin film is formed. (A in FIG. 1). At this time, it is desirable to smooth the adhesive surface 6 of the substrate 3 on which the crystalline thin film 11 is formed by polishing or the like, if necessary. After that, the substrate is attached to the carrier to be polished using wax. Then, the thickness of the substrate and the crystalline thin film is measured with a height gauge, and the thickness of the crystalline thin film is measured with an optical interference type film thickness meter.

After that, the eccentric load weight 5 is used to polish the surface 8 to be polished of the dummy body 2 and the boundary plane 12 between the crystalline thin film of the substrate and the parallel plane 12 (b in FIG. 1). That is, FIG.
In (b), the surface 8 to be polished of the dummy body is made parallel to the boundary plane between the substrate and the crystalline thin film. For example, when it is desired to polish the point a more than the point b, the X portion of the eccentric load weight in FIG. 2 corresponds to the point A in FIG. 1B while measuring the heights of the points a and b. Polish in the same way. After the surface 8 to be polished of the dummy body becomes parallel to the boundary plane 12 with the crystalline thin film of the substrate, the dummy body 2 and the crystalline thin film 11 are polished with the uniform load weight 9 if necessary. (FIG. 1c). By this polishing method, the parallelism can be corrected by polishing the dummy body 2 without damaging the crystalline thin film 11. Also, the surface to be polished 8
Since the interface 12 between the substrate and the crystalline thin film of the substrate can be made parallel, a crystalline thin film having a uniform film thickness can be formed even in the case of a substrate having a gradient in thickness. Furthermore, since it is possible to change the abrasive grains when polishing the dummy body and the crystalline thin film, use large abrasive grains for polishing the dummy body and small abrasive grains for polishing the crystalline thin film. You can Therefore, the polishing time can be shortened. Furthermore, a crystalline thin film having a uniform thickness can be produced with good reproducibility.

As the carrier to be polished, a fixing jig made of alumina having a diameter of 138 mm and a parallel flatness of 0.3 μm or less is suitable.

The dummy body 2 may have the same hardness as the crystalline thin film 11, such as alumina, silicon carbide, silicon oxide,
Zirconia, silicon nitride, glass, etc. may be used. LiN
When polishing a bO ₃ thin film or the like, a glass having a Mohs hardness of 6 to 7 is desirable in terms of characteristics and economy.

The abrasive-platen used in the polishing method of the present invention is preferably as follows. When polishing the dummy body, a diamond slurry having a particle diameter of 2 μm and a copper kemet disk are used. And for polishing a crystalline thin film, the grain size is 1/4
Polish using a diamond slurry of μm, tin-lead kemet board. The reason for changing the abrasive grains and the kemet disk is as follows. When polishing the dummy body, it is possible to shorten the processing time by increasing the polishing rate, and when polishing the crystalline thin film, scratches due to polishing can be minimized. Abrasive grains-change of surface plate is made of crystalline thin film 11
And when the difference in height between the dummy body 2 and the carrier to be polished is about several μm. This is a crystalline thin film 1
This is because no large lap mark is generated in No. 1.

A height gauge is used to measure the thickness of the crystalline thin film and the substrate. An optical interference type film thickness meter is used to measure the thickness of the crystalline thin film.

The flatness is measured by using an optical flat (λ = 0.54 μm) with an accuracy of λ / 20. If the interference fringes are parallel, the flatness of the crystalline thin film 11 is 0.54 / 2.
0 = 0.027 μm or less. If the interference fringes are the same when the crystalline thin film 11 is adhered to the carrier 1 by the wax 4 and when the substrate 3 on which the crystalline thin film is formed is removed, there is no adhesive distortion and the flatness is 0.027 μm.
It is below. The present invention relates to LiNbO ₃ , LiTaO ₃ ,
ZnO ₂ , PbTiO ₃ , Al ₂ O ₃ , TiO ₂ , ZrO
It is preferably used for polishing crystalline thin films such as ₂ .

[0016]

EXAMPLES The specific method of the present invention will be described below, but the present invention is not limited to these examples.

Example 1 LiNbO having a film thickness of 9 μm formed on a LiTaO ₃ substrate
₃ Thin film was polished. LiTaO ₃ substrate 3 (diameter 20
mm, thickness 1 mm), a substrate having a parallelism of 1 μm / 138 mm or less and a flatness of 0.027 μm or less was used. The dummy body 2 has an outer diameter of 46 mm, an inner diameter of 23 mm, and a thickness of 1.1.
A ring-shaped glass plate of mm was used. A LiTaO ₃ substrate 3 having a LiNbO ₃ thin film formed thereon and a dummy body 2 were bonded to a carrier 1 to be polished (diameter 138 mm, parallel flatness 0.3 μm or less) by a wax 4. Then L
The thicknesses of the iNbO ₃ thin film and the LiTaO ₃ substrate were measured with a height gauge and an optical interference type film thickness meter, and the inclination of the boundary plane between the LiTaO ₃ substrate and the LiNbO ₃ thin film was obtained. Then, while the dummy body 2 is being polished, the eccentric load weight 5 shown in Table 1 is used to polish the surface to be polished 8 and Li of the dummy body 2.
The parallelism was corrected so that the boundary plane 12 between the TaO ₃ substrate and the LiNbO ₃ thin film was parallel. After that, a uniform load weight 9 (made by casting, mass 3.1 kg) was applied and polished. A diamond slurry having a particle size of 2 μm and a copper kemet disk are used for polishing the dummy body, and if the difference in thickness between the dummy body 2 and the LiNbO ₃ thin film 11 becomes several μm, the diamond slurry having a particle size of 1/4 μm. Polished using a tin-lead kemet board. After the entire surface of the LiNbO ₃ thin film 11 is polished, the parallelism is measured by an optical flat (λ = 0.54 μm) with an accuracy of λ / 20.
The interference fringes were parallel. Then, the LiTaO ₃ substrate 3 on which the LiNbO ₃ thin film 11 is formed is used as the carrier 1 to be polished.
The interference fringes were the same when they were removed and the flatness was measured again. In this way, the film thickness is 2 μm, the parallel flatness is ± 0.
A LiNbO ₃ thin film having a portion of 1 μm / 5 mm □ (this indicates that the parallel flatness of a square portion having a side length of 5 mm is ± 0.1 μm) was obtained. The time required for processing was 14 hours. L three times in the same way
As a result of polishing the iNbO ₃ substrate, the film thickness is 2 ± 0.1 μm
Then, a thin film having a portion with a parallel flatness of ± 0.1 μm / 5 mm □ was obtained.

Example 2 A LiNbO ₃ thin film (film thickness 10 μm) formed on a LiTaO ₃ substrate 3 (diameter 20 mm, thickness 1 mm) having a parallelism of 4 μm / 20 mm and a flatness of 0.027 μm was also used in Example 1. Polishing was performed in the same manner as in. As the dummy body 2, a ring-shaped glass body having a thickness of 1.07 mm was used. L having a LiNbO ₃ thin film formed on carrier 1 to be polished (diameter 138 mm, parallel flatness 0.3 μm or less)
The iTaO ₃ substrate 3 and the dummy body 2 were adhered with a wax 4. After that, LiNbO ₃ thin film and LiTaO
₃ height gauge the thickness of the substrate was measured by an optical interference type film thickness meter to determine the inclination of the boundary plane between the LiNbO ₃ thin film of LiTaO ₃ substrate. Then, while the dummy body 2 is being polished, the surface 8 to be polished of the dummy body 2 and the boundary plane 12 between the LiNbO ₃ thin film of the LiTaO ₃ substrate are parallel to each other by using the eccentric load weight 5 shown in Table 1. The parallelism was corrected as follows. After that, a uniform load weight 9 (made by true casting, mass 3.1)
(kg) and polished. LiNbO ₃ thin film 11
After polishing the entire surface of, the flatness was measured by an optical flat (λ = 0.54 μm) with an accuracy of λ / 20, and the interference fringes were parallel. And LiNbO ₃ thin film 1
When the LiTaO ₃ substrate on which No. 1 was formed was removed from the carrier 1 to be polished and the flatness was measured again, the interference fringes were the same. In this way, the film thickness is 2 μm and the parallel flatness ±
A LiNbO ₃ thin film having a portion of 0.1 μm / 5 mm □ was obtained. The time required for processing was 16 hours. Also, the parallelism is 2 to 5 μm / 20 mm, and the flatness is 0.027 μ.
As a result of polishing the LiNbO ₃ thin film formed on the LiTaO ₃ substrate with a thickness of 2 ± 0.1 μm, the parallel flatness ±
A thin film having a portion of 0.1 μm / 5 mm □ was obtained.

Comparative Example LiTaO ₃ substrate 3 (diameter 20 mm, thickness 0.991 m, parallelism 4 μm / 20 mm, flatness 0.027 μm)
m) LiNbO ₃ thin film formed on the substrate (film thickness 9μ
m) was polished. Outer diameter 46 as dummy body 2
A donut-shaped glass plate having a diameter of 23 mm, an inner diameter of 23 mm, and a thickness of 1 mm was used. Carrier to be polished 1 (diameter 138 mm,
A LiTaO ₃ substrate 3 on which a LiNbO ₃ thin film was formed and a dummy body 2 were adhered to each other by a wax 4 in a parallel flatness of 0.3 μm or less). Then, using the eccentric load weight 5, the LiNbO ₃ thin film was corrected so as to have a uniform film thickness while polishing. For polishing, a diamond slurry having a particle diameter of 1/4 μm and a tin-lead kemet disk were used. Li
After polishing the entire surface of the NbO ₃ thin film 11, the accuracy is λ / 20.
When the flatness was measured with an optical flat (λ = 0.54 μm), the interference fringes were parallel. And Li
Even if the LiTaO ₃ substrate on which the NbO ₃ thin film 11 is formed is removed from the carrier 1 to be polished and the flatness is measured again,
The interference fringes were the same. LiN created in this way
The bO ₃ thin film has a thickness of 1.5 μm and a parallel flatness of ± 0.6 μ.
It was m / 5 mm □. The time required for processing was 24 hours. Further, L formed on a LiTaO ₃ substrate having a parallelism of 2 to 5 μm / 20 mm and a flatness of 0.027 μm.
As a result of polishing the iNbO ₃ thin film by the same method, the parallel flatness was ± 0.6 μm / 5 mm □. Further, while polishing the thin film, the film thickness could not be corrected to be uniform, and the thin film was scraped too much to expose the substrate.

[0020]

[Table 1]

[0021]

As described above, according to the present invention, even when a crystalline thin film is formed on a substrate having a thickness gradient, the thin film can be polished to a uniform film thickness and the processing time can be shortened. can do. Furthermore, since the thin film can be polished to the same film thickness with good reproducibility, it is effective for obtaining a highly accurate optical device.

[Brief description of drawings]

FIG. 1 is a process drawing showing a state of a polishing method of the present invention.

FIG. 2 is a diagram showing an eccentric load weight and a uniform load weight according to the present invention.

FIG. 3 is an explanatory diagram showing a conventional polishing method.

[Explanation of symbols]

 1 Carrier to be Polished 2 Dummy Body 3 Substrate 4 Wax 5 Eccentric Load Weight 6 Adhesive Surface of Substrate 7 Plane of Carrier to be Polished 8 Polished Surface of Dummy Body 9 Uniform Load Weight 10 Surface Plate 11 Crystalline Thin Film 12 Crystal of Substrate Boundary plane with thin film

Claims (2)

[Claims] 1. When bonding a substrate on which a crystalline thin film is formed and a dummy body to a carrier to be polished, a dummy body adjusted so that the surface of the crystalline thin film to be polished does not come into contact with a surface plate is provided. A step of arranging around a crystalline thin film and bonding with an adhesive. (B) A step of polishing with an eccentric load weight so that the boundary plane between the surface to be polished of the dummy body and the crystalline thin film of the substrate becomes parallel. (C) A step of polishing the crystalline thin film to a desired thickness. A method for polishing a crystalline thin film constituted by the above steps (a) to (c). 2. In the step (a), the polished surface of the dummy body is 50 to 100 μm thicker than the polished surface of the crystalline thin film.
The method for polishing a crystalline thin film according to claim 1, wherein the surface to be polished of the crystalline thin film does not come into contact with the surface plate by increasing the height by m.