CN1093182C

CN1093182C - Decarbonization colour-removing annealing method for sapphire crystal

Info

Publication number: CN1093182C
Application number: CN00111882A
Authority: CN
Inventors: 徐军; 周国清; 邓佩珍
Original assignee: SHANGHAI ZHONGKE JIAPU OPTOELECTRONIC MATERIALS CO Ltd
Current assignee: Shanghai Zhongke Jiapu Optoelectronic Materials Co., Ltd.
Priority date: 2000-03-03
Filing date: 2000-03-03
Publication date: 2002-10-23
Anticipated expiration: 2020-03-03
Also published as: CN1266112A

Abstract

The present invention relates to a decarbonization and decoloration annealing method for sapphire crystals. The method of the present invention main comprises two steps that the sapphire crystal to be annealed is put in an annealing furnace for high temperature and oxidizing atmosphere annealing to eliminate the absorption of visual light by impurity ions Cr<3+> and Ti<3> with low valence states in the crystal to be annealed, and utilize the oxygen decarbonization adsorption function at high temperatures at first; in the second step, the high temperature and strong reducing atmosphere decarburizing annealing is performed; the temperature in the annealing furnace filled with hydrogen rises to 1600 DEG C to 2200 DEG C and is constant for more than 100 hours; through the adsorption carbon of the hydrogen in the molecular state, the purpose of thorough decarbonization is achieved. Through the annealing, the sapphire crystal is colorless and transparent; the transmissivity is enhanced and the dislocation density is reduced.

Description

Decarburization and decoloration annealing method for sapphire crystal

The present invention relates to a sapphire (Al) containing impurity carbon and having variegated colour suitable for using graphite resistance heating body as heating element to grow₂O₃) A decarburization and decoloration annealing method of crystal.

Sapphire crystal is the substrate material of the most widely used and practical GaN blue light semiconductor diode, is an ideal window material of a high-power laser, and is an optical material on a world-grade gravity wave interferometer.

The prior art is as follows: at present, the growing optical grade high-quality sapphire crystal is mainly based on a resistance furnace pulling method and a temperature gradient method (TGT), and graphite resistance heating elements are used as heating elements in both methods. Due to the volatilization of the graphite material at the growth temperature of 2050 ℃, the actual growth atmosphere is a weak reducing atmosphere, and under the condition, the impurity ions in the raw materials are in a low-valence state, such as Cr³⁺，Ti³⁺In the crystal, Cr³⁺，Ti³⁺When the crystal is absorbed in the visible light range, the obtained crystal has different colors, the general sapphire crystal grown by the Czochralski method is reddish or yellowish, and the sapphire grown by the temperature gradient method (A1)₂O₃) The crystals appear in different colors at different positions, generally the upper part is light red and the lower part is light yellow. This color affects the transmittance.

Inv Shunhu et al, 1993, used an oxygen atmosphere at 1200 deg.C for 48 hours to anneal sapphire crystal grown by Bridgman method using graphite resistor as heating element, to eliminate coloration, but the crystal size was only 25 × 25 × 3mm³(see: Proc. Natl. Acad. Sci. 1993(5), Vol. 22, No. 2), and decarburization was incomplete.

The purpose of the invention is as follows: provides a decarburization and color-supporting annealing method of sapphire crystals. The original colored carbon-containing sapphire crystal is changed into colorless and transparent, the transmittance of the crystal is greatly improved, and the integrity of the internal structure of the crystal is further improved.

The method mainly comprises two steps:

(1) and placing the sapphire crystal to be annealed in an annealing furnace, and firstly carrying out high-temperature oxidation atmosphere annealing. And raising the temperature to 1200-1700 ℃ in the air in an annealing furnace for placing the sapphire crystal to be annealed, keeping the temperature for more than 100 hours, and then slowly lowering the temperature to the room temperature.

(2) And carrying out high-temperature strong reducing atmosphere decarburization annealing. The sapphire crystal annealed by the high-temperature oxidizing atmosphere is subjected to annealingThe body is arranged in a sealed annealing furnace, air in the annealing furnace is firstly exhausted, and when the vacuum degree is higher than that of the annealing furnace5×10^-3When Pa is needed, filling hydrogen, raising the temperature to 1600-2200 ℃ when the pressure of the filled hydrogen is 0.02-0.05 MPa, keeping the temperature for more than 100 hours, and then slowly cooling to room temperature.

According to the steps, high-temperature oxidation atmosphere annealing is carried out, and two purposes are mainly achieved: firstly, low valence impurity ions such as Cr in sapphire crystal raw material³⁺，Ti³⁺Fully oxidized into high valence Cr⁴⁺，Ti⁴⁺Elimination of Cr³⁺，Ti³⁺Absorption of visible light; secondly, the high-temperature adsorption of oxygen to carbon is utilized to enable the internal trace carbon to permeate to the surface of the crystal and to react with oxygen such as With CO₂Or CO is separated out, namely the function of decarburization is realized.

Performing high-temperature strong reducing atmosphere decarburization annealing on the crystal subjected to the high-temperature oxidizing atmosphere annealing, and performing hydrogen (H) annealing at a temperature higher than 900 DEG C₂) Mainly adsorbs carbon in molecular state, and has a mass loss rate of 0.133g/cm at 2000 deg.C²S, four times as high as 1800 ℃. The high-temperature strong reducing atmosphere annealing plays a role of complete decarburization, but does not cause high-valence Cr⁴⁺，Ti⁴⁺Ion orientation low valence Cr³⁺，Ti³⁺Due to Cr in a high valence state⁴⁺，Ti⁴⁺Ion in Al₂O₃Very stable in crystal structure.

The method has the advantages that: using Al₂O₃High valence Cr in crystal structure⁴⁺，Ti⁴⁺Ion stability ratio of Cr³⁺，Ti³⁺The high stability of ion, the annealing process of oxidizing atmosphere first, reducing atmosphere later, to the graphite resistance heating element for the carbon-containing and variegated sapphire crystal that heating element grows realizes the effect of decoloration, decarbonization many times for the crystal becomes colorless transparent, has improved the transmissivity, and the crystal structure more approaches the integrality, and dislocation density reduces nearly two orders of magnitude.

Description of the drawings:

FIG. 1 shows a sapphire crystal (phi 110X 80 mm) grown by a temperature gradient method and containing impurity carbon and having a variegated color³) And (5) blank.

FIG. 2 shows a sapphire crystal annealed in a high-temperature oxidizing atmosphere and having carbon oxide attached to the surface thereof.

FIG. 3 is a colorless transparent crystal annealed in an oxidizing atmosphere and then in a strongly reducing atmosphere.

Example 1

And placing the sapphire crystal to be annealed in an annealing furnace, and sequentially carrying out annealing of high-temperature oxidation, high-temperature strong reduction, decoloration and decarburization according to the steps.

Al grown by temperature gradient method₂O₃The crystal size is phi 110 multiplied by 80mm³The crystal is complete but has various colors, the part near the seed crystal (upper part) is light red, and the lower part is slightly green, as shown in figure 1. Mixing Al₂O₃Placing the crystal blank in an annealing furnace of a KSY-12D-18 silicon-molybdenum rod heating body resistance furnace, heating at the rate of 60 ℃/hr, gradually heating to 1600 ℃, keeping the temperature for 120 hours, and performing high-temperature oxidation atmosphere (air) decoloring and decoloringAnd (5) annealing carbon. Keeping the temperature for 120 hours, slowly cooling to room temperature at the rate of 40 ℃/hr, taking out after the crystal is completely cooled, wherein Al is obtained at the moment₂O₃The crystal blank is black as shown in fig. 2. Annealing the Al in an oxidizing atmosphere₂O₃The crystal is then placed in an annealing furnace of a bell-jar vacuum resistance furnace. After the bell-type resistance furnace is sealed, the furnace is vacuumized to 10 degrees of vacuum at room temperature^-3After Pa, the temperature is raised to 1200 ℃ at the rate of 80 ℃/hr, and the temperature is kept for 1 hour, so that moisture and highly volatile impurities adsorbed in the hearth can be removed as far as possible. Then, high-purity H having a strong carbon adsorbing ability is charged₂High-purity hydrogen is adopted as protective gas to play a role in decarburization for many times, the pressure in the furnace is 0.03MPa, after the temperature in the furnace is balanced, the temperature is raised to 1900 ℃ at the speed of 60 ℃/hr, the temperature is kept for 120 hours, and high-temperature reduction decarburization annealing is carried out. Keeping the temperature for 120 hours, then slowly cooling to room temperature at the rate of 20 ℃/hr until Al is obtained₂O₃After the crystal is completely cooled, the crystal is taken out, and Al is generated at the moment₂O₃The crystals were colorless and transparent as shown in FIG. 3. The dislocation density of the crystal before annealing was tested to be 10⁵/cm²Of the order of 10 dislocation density of the annealed crystal³-10⁴/cm²Magnitude; the optical transmittance of the crystal before annealing was 85%, and the optical transmittance of the crystal after annealing was 88%. It can be seen that after the above two anneals, Al₂O₃The internal structural integrity and optical transmittance of the crystal are significantly improved.

Claims

A method for decarburization and decoloration annealing of sapphire crystals, which is to anneal the sapphire crystals to be annealed in an annealing furnace, is characterized by mainly comprising two steps:

<1>high temperature oxidizing atmosphere annealing is first performed: heating the sapphire crystal to be annealed to 1200-1700 ℃ at the speed of 60 ℃/hr in the air in an annealing furnace, keeping the temperature for more than 100 hours, and then slowly cooling to room temperature at the speed of 40 ℃/hr;

<2>and (3) carrying out high-temperature strong reducing atmosphere decarburization annealing: placing the sapphire crystal annealed in the high-temperature oxidizing atmosphere in a sealed annealing furnace, firstly removing the air in the annealing furnace, and when the vacuum degree is higher than 5 multiplied by 10^-3When Pa, filling hydrogen, when the pressure of hydrogen is 0.02MPa to 0.05MPa, heating to 1600 deg.C to 2200 deg.C at 60 deg.C/hr, holding for more than 100 hr, and slowly cooling to room temperature at 20 deg.C/hr.