JPS63185900A - Heat-treating method of single crystal of composite oxide ferroelectrics - Google Patents

Abstract

PURPOSE:To readily remove a thermal strain in a crystal which is main cause of unevenness of optical characteristics, by heat-treating a wafer of single crystal of composite oxide ferroelectrics while controlling temperature and time. CONSTITUTION:A single crystal wafer of composite oxide ferroelectrics selected from Bi12SiO20, LiTaO3, LiNbO3, Y3AlO12 and BaTiO3 is maintained at 885-895 deg.C for 1hr to heat-treat the wafer. The thermal strain in the crystal can be removed and the single crystal wafer of composite oxide ferroelectrics having wholly uniform optical characteristics can be produced thereby. Therefore, production of bismuth silicon oxide single crystal wafer having big size and high quality which has been difficult hitherto is made possible and the resultant single crystal wafer is preferably used as a photoconductor, etc., for photoimage processing.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to complex oxide ferroelectric materials, particularly bismuth silicon oxide (13i, 2Si(b), which is an optical functional material having electro-optical effects, photoconductive effects, etc.). , hereinafter abbreviated as BS○)) relates to a heat treatment method for single crystal wafers.

Conventional technology BS○, or LiTaO3, LiNbQ, Y3A
Many single crystals of complex oxide ferroelectrics such as +5[+12 and BaT+Oz are grown by a crystal growth technique called a pulling method (Czochralski method). In principle, this is a method in which a small seed crystal is brought into contact with the surface of a crystal raw material heated and melted in a crucible, and the crystal is grown around the seed crystal by slowly pulling it up while rotating it.

Composite oxide ferroelectric materials, especially BSO, are optical functional materials that have electro-optic effects, photoconductive effects, etc., and are used as photoconductors used in optical image processing devices and liquid crystal original images (image processing devices, etc.) When BSO is used as a photoconductor as described above, the amount of information is proportional to the element surface area, so it is particularly desirable to increase the size of the wafer.However, until now, wafers obtained from BSO single crystals have the following There was a problem like this.

The problem to be solved by the invention is that thermal strain occurs in the B, SO single crystal grown by the pulling method during growth, and this strain remains in the crystal.

Wafers made by slicing BSO single crystals with such residual strain have uneven optical properties, which makes it difficult to use them as optical functional materials. Generally, evaluation is performed by using a Rade light source, passing a polarized wave having a polarization plane tilted by π/4 to the optical axis into a crystal, and determining the extinction ratio. Such unevenness in optical properties is influenced by the composition of the melt of the crystal material during single crystal growth, but is often due to thermal distortion that occurs during crystal cooling after crystal growth.

Therefore, an object of the present invention is to remove the residual strain in the crystal and create a composite oxide ferroelectric with uniform optical properties as a whole.
In particular, it provides a heat treatment method that makes it possible to obtain BSO single crystal wafers.

Means for Solving the Problems The present inventors have completed the present invention as a result of various experiments and studies in an attempt to solve the above-mentioned problems of the prior art.

According to the present invention, a method for heat treatment of a single crystal wafer of a composite oxide ferroelectric is characterized by holding the single crystal wafer of a composite oxide ferroelectric at a concentration in the range of 885°C to 895°C for 1 hour or more. is provided.

As a composite oxide ferroelectric material, B11°SlO20, L
iTaO5, L+NbQ3, YzAlsO+2 or B
aTin3, preferably the method of the invention is Bi,2
It is applied to the processing of SiO20 single crystal wafers.

Further, according to a preferred embodiment of the present invention, the single crystal wafer of the composite oxide ferroelectric is formed by forming a single crystal ingot grown by the Czochralski method to a thickness Q of 5 mm or more.
It is sliced into pieces of 0 mm or less.

As described above, according to the present invention, by heat-treating a single crystal wafer of composite oxide ferroelectric, residual strain in the crystal, which has hitherto been a major obstacle to its use as a photoconductor, can be removed. Can be done.

The heat treatment concentration ranges from 885°C to 895°C.

This is because the melting point of SO is 900°C, so heating to a concentration higher than 895°C may cause the single crystal wafer to melt; This is because the time will be longer and the effect of distortion removal will be reduced.

The heat treatment is performed by holding the single crystal wafer at a concentration in the range of 885° C. to 395° C. for one hour or more. This is because residual strain may not be removed sufficiently if the holding time is less than one hour. Furthermore, it is necessary to heat and cool the single crystal wafer gradually so as not to cause thermal distortion, and it is particularly important to gradually cool the single crystal wafer in a heating furnace.

Furthermore, the thickness of the wafer to be processed is 0.5 mm to 3 mm,
A range of 0 mm is preferred. 3. Wafers thicker than 0 mm are difficult to uniformly heat, and furthermore, residual strains once formed in such thick wafers are difficult to remove. Furthermore, it takes a very long time to cool the entire crystal in a uniformly heated state without causing thermal distortion again. If cooling is performed with uneven heat distribution, new thermal distortion will occur during cooling, which is fatal.

On the other hand, if heat treatment is applied to a thin wafer with a thickness of less than Q, 5 mm, residual strain can be easily alleviated, but at the same time, there is a risk that the crystal will deform and cracks will occur.

Therefore, under the above conditions, complex oxide ferroelectrics, especially BSO
By applying heat treatment to a single crystal wafer, residual strain in the crystal is removed, and a large wafer with uniform optical properties can be obtained.
It becomes possible to use it as a high-quality photoconductor.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but what is shown below is merely an example of the present invention, and does not limit the technical scope of the present invention in any way.

First, a BSO single crystal grown by the Czochralski method was sliced into wafers. The size of the obtained wafer was 45 x 45 xl, 5 mm3.

Before heat-treating the wafer, both sides of the wafer were mirror-polished, and the distribution of residual strain was evaluated using a photoelastic method. As a result, it was found that the extinction ratio within the wafer plane varied widely, ranging from 25 dB to 40 dB, and that strong residual distortion existed.

According to the present invention, this wafer was placed in a horizontal furnace called a gold furnace to uniformly heat the wafer. The heated cloud atmosphere was the atmosphere, and the temperature was raised from room temperature to 890° C. over 2 hours, and maintained at this concentration for 4 hours. Thereafter, it was cooled to room temperature over 4 hours.

Since the surface of the wafer that had been heat-treated as described above had unevenness due to heat, mirror polishing was performed again. When the polished wafer was evaluated using the same photoelastic method as that used before heat treatment, the extinction ratio in the wafer plane was 35 dB.
It was confirmed that the variation was extremely small at ~40 dB, and that the uniformity of optical characteristics across the entire wafer subjected to the heat treatment method according to the present invention was improved.

As described in detail, according to the present invention, residual strain in the crystal, which is the main cause of uneven optical properties, is removed by heat-treating a single crystal wafer of a composite oxide ferroelectric material, particularly BSO. removed. Therefore, the optical properties of the wafer processed by the method of the present invention are made uniform throughout, and the quality as an optical functional material is further improved. Therefore, large, high quality BSO single crystal wafers, which have been difficult to achieve up to now, have been realized and are particularly advantageous when used as photoconductors for optical imaging.

Claims (4)

[Claims] (1) A single crystal wafer of composite oxide ferroelectric material was heated to 885°C.
1. A method for heat treatment of a single crystal wafer of a composite oxide ferroelectric, characterized by holding the concentration at a temperature in the range of 895° C. to 895° C. for 1 hour or more to remove thermal strain in the crystal. (2) The above composite oxide ferroelectric material is Bi_1_2SiO
_2_0, LiTaO_3, LiNbO_3, Y_3A
The method for heat treatment of a single crystal wafer of a composite oxide ferroelectric according to claim 1, characterized in that the single crystal wafer is one selected from the group consisting of l_3O_1_2 and BaTiO_3. (3) The above composite oxide ferroelectric material is Bi_1_2SiO
_2_0. The heat treatment method for a single crystal wafer of a composite oxide ferroelectric material according to claim 2, wherein the wafer is _2_0. (4) The single crystal wafer of the above-mentioned composite oxide ferroelectric material is a single crystal grown by the Czochralski method to a thickness of 0.5 cm.
The method for heat treatment of a single crystal wafer of a composite oxide ferroelectric according to any one of claims 1 to 3, wherein the wafer is sliced into wafers of 3.0 mm or more and 3.0 mm or more.