JPS5918360B2 - Method for producing gadolinium garnet - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method 25 for producing a massive, single crystal gadolinium gallium garnet material.

In particular, the present invention relates to a method for producing such materials from an oxide melt contained in an iridium crucible. Single crystal gadolinium gallium garnet material in bulk form consists of 30Gd2 in a molar ratio of 3:5
It is manufactured according to the well-known Czochralski technique by pulling a seed rod from a melt of Ga2O3 and Ga2O3.

The melt is, however, usually held in an inodium crucible. This is because iridium is considered to be a highly desirable metal for this purpose due to its physical and chemical properties. Furthermore, it is known to provide iridium crucibles with iridium cover members or 10-heart lids that act as radiant heat shields.

Gadolinium gallium garnet is produced in the form of elongated bowls (mass grown crystals) of circular cross-section, which are then made into wafers that are used as substrates in the electronics industry, such as for the epitaxial growth of iron garnet films. It is cut down. It is very important that these substrates, and therefore the crystals from which they are formed, are free of impurities, such as iridium inclusions. This is because the presence of such inclusions can propagate into epitaxial layers formed on crystalline substrates with well-known deleterious effects.
It has been found that the above-mentioned iridium inclusions are present with a significant frequency in the lower section of the Czyochralski growth bowl, that is, in the last grown part of the bowl.Therefore, it is an object of the present invention to
The object of the present invention is to provide a method for manufacturing a robust single-crystal gadolinium gallium garnet bowl that is substantially free of such iridium inclusions. The method of the present invention for producing a substantially pure single crystal gadolinium gallium garnet bowl of substantially circular cross section includes the following steps: (
[) Gd2O3 and Ga2O in a molar ratio of 3:5
forming a melt by heating the mixture of No. 3 in an iridium crucible equipped with an iridium lid having a circular opening positioned above the melt that is slightly larger than the cross-section of the bowl to be produced; i;) inserting a seed rod of single crystal gadolinium gallium garnet into the melt through a circular opening in the iridium lid member; providing an ambient atmosphere of nitrogen containing about 0.5-3% oxygen by volume; , a massive single crystal bowl in which gadolinium gallium garnet material solidifies into a seed rod and crystallizes to progressively increase in length and has a substantially circular cross-section slightly smaller than the circular opening in said iridium lid member. A seed rod is pulled out of the melt to form a product, with the bowl passing through a circular opening in the iridium lid as it increases in length to form a seed rod on the walls of the crucible, on the lid and on the periphery of the bowl. substantially covering and closing the surface of the melt within the crucible in the compartment thus defined; introducing a continuous flow of nitrogen containing about 0.5 to 3% oxygen by volume into the compartment; volume%
Introducing a nitrogen atmosphere containing oxygen at a rate sufficient to maintain it.

The improvements of the present invention over conventional crystal growth techniques using iridium crucibles and iridium lids include:
Nitrogen and about 0.5-3%. Preferably, an atmosphere of 2% oxygen is continuously maintained in a region formed by the surface crystal growth interface of the melt in the crucible, the lower surface of the lid, and the inner surface of the crucible above the melt, substantially standing out from the periphery of the crucible. There is a particular thing.

Referring to FIG. 1, a chamber 1 defined by a persuader 3 surrounding a crystal pulling device and its surrounding space is illustrated.

In the crystal pulling apparatus, an iridium crucible 8 contains a melt 9 of Gd2O3 and Ga2O3 in a molar ratio of 3:5. An iridium cover or lid member 16 is placed on top of the crucible 8. The lid member 16 has a central circular opening 17. The lower surface of the lid member 16 acts as a radiant heat shield in a manner well known in the art to reduce heat loss from the melt 9. The central circular opening 17 is shown in FIG.
It is designed to have a cross-section slightly larger than the circular cross-section of the bowl to be manufactured, shown at 5. The crucible 8 is surrounded by a heat insulating material 15 on its side and bottom surfaces. The insulation is preferably made of zirconia and maintains a melt 9;
It serves to reduce thermal gradients along the crucible, as well as temperature fluctuations resulting from line voltage fluctuations, convective cooling effects from the atmosphere, and other disturbances. The hollow space 11 forms a hole in the crucible bottom wall through which the temperature of the crucible bottom can be measured, for example by a radiation pyrometer focused on the center of the crucible bottom. A ceramic washer 4, made for example from alumina, is supported by a tube 5, preferably made of zirconia.

Washer 4 acts as a secondary radiation shield, restricting atmospheric convection from entering the top of the crucible and touching the growing crystal. Washer 4 thus serves to reduce the vertical temperature gradient in the vicinity of the growing crystal and to enhance the action of lid member 16. The sleeve 6, made of silicon dioxide, for example, serves to contain the insulation 15 and thus functions as part of the insulation assembly surrounding the crucible 8.

The tube 5 carrying the washer 4 likewise serves as part of the insulation system. The crucible 8 and the heat insulating assembly surrounding it are placed on a ceramic base 12 made of, for example, zirconium oxide (ZrO2). The entire assembly is surrounded by a Persian 3 which is sealed to the base plate 13. Base plate 13
is made of a suitable material, such as silicone-bonded fiberglass. The main part of the ambient gas atmosphere intended for the interior of the Persian 3, i.e. the gas atmosphere non-reactive with the melt in the crucible, is nitrogen containing e.g. 0.5-3% by volume of oxygen, preferably 2% by volume. , which is introduced as a continuous stream into the sight tube 14 communicating with the hollow tube 11 (suitable discharge openings are provided). The gas introduced into the Persian 3 is exhausted through holes 18 in the Persian 3. A seed rod 2 is inserted through the hole 18. A rod 2 made of Al2 O3, for example, is provided at its lower end with a seed part z in the form of a single-crystal gadolinium gallium garnet barb and has a longitudinal axis 20 coinciding with the growth axis of the crystal 7. The orientation of the single crystal material of the seed portion 21 is a predetermined orientation depending on the final industrial application. Such seed rods can easily be routinely prepared for the production of bulk single crystal materials. When using the above device, the temperature of the melt is 17
00 to 1800° C. and from which single crystals are pulled, e.g. 6 to 18 inches long and 3
It gives a product in the form of a cylinder with an inch diameter.

This procedure is shown, for example, in US Pat. No. 3,715,194. The forming single crystal bowl material, designated 25 in FIG. 2, has a substantially circular uniform cross section. Third
Referring to figure a, there is shown an iridium crucible 8, an iridium lid 16, a melt 9 and a seed crystal rod 2 before crystal pulling.

At this point, the gas atmosphere above the melt 9 in the crucible 8 {
This is substantially the same as the desired ambient atmosphere introduced via tube 11 of FIG. FIG. 3b shows a similar aspect to FIG. 3a after the crystal pulling has proceeded and the length of the bowl 25 being manufactured has been increased until it passes through the hole 17 in the lid 16. For this condition,
This is the desired bowl length (e.g. 15.2-45.7c)
m) is produced until the underside of the lid 16, the crucible 8
A compartment 35 is formed defined by the inner wall surface 36 of the bowl 25, the peripheral surface of the bowl 25, and the melt surface. This compartment substantially covers the surface of the melt 9, and it is this compartment atmosphere that is exposed to the melt 9, the crystal growth interface 40, and the iridium surface. As part of the present invention, for the situation of FIG. 3b that prevails during most of the crystal pulling process, the atmosphere within compartment 35 becomes increasingly oxygenated compared to the ambient atmosphere within Persian 3 unless it is replenished. It was found that there was a shortage of This is because the communication between this compartment and the desired ambient atmosphere in the persian 3 is only through the narrow gap 17/ between the side of the bowl 25 and the opening 17, which would otherwise reduce the atmosphere in the compartment 35. Does not allow complete replenishment or homogenization. That is, it can be said that the atmosphere inside the compartment 35 is substantially separated from the surrounding atmosphere inside the Persian 3. The gradual loss of oxygen in the compartment 35 (if not replenished) and thus the amount of oxygen in the atmosphere touching the melt surface and crystal interface 40 will lead to a gradual increase in the presence of iridium inclusions in the bowl. As a result, the last growing part of the bowl, indicated at 50 in FIG. Contains numerous iridium inclusions. As is well known in this field, inclusions are defined as having a diameter of 1
Individually scattered metallic platelets or granules of ~20 microns. In the present invention, this undesirable adverse effect is achieved by introducing a continuous flow of nitrogen containing about 0.5-3%, preferably 2% oxygen by volume into the compartment 35. This can be avoided by introducing it directly into the This introduction may take place, for example, via an iridium tube 47, which is shown communicating with the compartment 35 through an iridium closure member 16. The gas flow rate into compartment 35 through tube 4r is such that the same desired gas atmosphere as in Persian 3 is maintained in compartment 35 over the melt surface and at the growth interface 40 throughout the crystal pulling process. be done. As a result of this implementation, the presence of undesired iridium inclusions in bowl 25 is substantially avoided. The make-up gas flow as shown in the figures is such that it substantially continuously enters compartment 35 (
It is preferably introduced through a hole located in the iridium lid member 16 close to the side wall of the crucible to ensure the presence of the desired atmospheric pressure therein. Other configurations for introducing makeup flow into compartment 35 may also be used, for example flow may be introduced through the crucible side wall to achieve a similar pouring effect. Appropriate gas flow rates can be readily determined for the particular equipment involved. for example,
If the volume Vc of the compartment 35 is known, the appropriate gas flow rate is 0.
．． It can be expressed as 2Vc to 15Vc/min. That is, if the compartment volume Vc is 0.028 cd, a suitable gas flow range is 0.0028 to 0.43 ciI/min. As long as the melt surface is not disturbed by the gas flow (
f, many more flow rates could be used. Compartment volume V
Since c naturally increases as the melt decreases in the crucible during crystal growth, it is convenient to consider this as a basis for selecting the gas flow rate. Comparative Example: Approximately 11,5007 Gd2O3 and Ga2O3 in a molar ratio of 3:5 (precisely 3.02:4.98) is 13
．． It was placed in an iridium crucible with 5 cm inner diameter x 0.25 cm wall thickness x 14.6 cm height.

A 14.0 cm diameter x 0.25 cm thick iridium lid with an 8.9 cm diameter central circular opening was placed over the crucible.

The crucible was placed within an 8-turn induction heating coil with an inner diameter of 19.1 cm. A crucible was placed on a pedestal filled with zirconia grains, and the gap between the coil and the crucible was also filled with zirconia grains. The entire apparatus was housed in an aluminum persier (0.80 m3) with a hole in the top. Approximately 2
A nitrogen atmosphere containing % by volume was supplied into the Persian via an inlet located below the crucible and away from the crucible. The gas flow rate was 1.10 d/hour. An iridium tube (0.64 cm 1.D.) positioned 254 cm from the crucible side wall was communicated through the lid to the interior of the crucible. However, in this example no gas flow was introduced through this tube. The induction heating coil is a well-known R. F. The induction heating device was energized and the power was increased until the induced current in the crucible made the crucible white hot. A melt was formed within the crucible due to heat transfer from the crucible. At this point, the height of the crucible wall above the melt is approximately 1
．． It was 3cm long. A 0.95 cm diameter single crystal gadolinium gallium garnet seed crystal (111> orientation) was lowered through an opening in the lid until it contacted the melt surface.

The seed crystal was then pulled at a rate of about 0.76 cm/hour for 30 hours. The height of the crucible wall above the melt at the end of growth was 11.4 cm. 228 with 8.2cm circular cross section
A c'' long bowl was obtained which contained a large number of iridium inclusions (at least 100/c!i) in the bottom, ie, in the last formed third of the bowl.

Example 1 A test was conducted using the same procedure as in the comparative example except that nitrogen gas containing 2% oxygen by volume was continuously flowed into the crucible through the iridium tube at a rate of 0.28 d/hour.

A bowl of 8.2 cm diameter by approximately 20.3 cm long was produced which was virtually free of iridium inclusions (less than 5/Cd) throughout its length.

Example 2 A test was carried out in the same manner as in the comparative example except that nitrogen gas containing vol% oxygen was continuously flowed into the crucible through the iridium tube at a rate of 0.057 d/hour. .

An 8.1 cm diameter by approximately 20.3 cm long bowl was produced that was virtually free of iridium inclusions (less than 5/Cd) throughout its length.

[Brief explanation of drawings]

FIG. 1 shows a suitable apparatus for carrying out the invention, and FIG.
The Figures illustrate a single crystal bowl of substantially circular cross section produced by the practice of the present invention, with Figure 3a showing the crucible of Figure 1 before crystal growth initiation and Figure 3b during crystal growth. Figure 3c shows the aspect of the crucible, and Figure 3c is similar to Figure 3c-3 of Figure 3b.
FIG. 3 is a top view taken from the direction of line 3c. 3: Belgear, 18: Hole, 2: Seed rod, 8: Crucible, 16: Lid member, 17: Center opening, 9: Melt, 6: Sleeve, 5: Cylinder, 4: Washer, 15: Heat insulator , 12:
Pedestal, 47: Tube, 40: Interface, 7: Growth crystal, 25: Bowl, 35: Compartment chamber.

Claims (1)

[Claims] 1 A method for producing a substantially pure single crystal gadolinium gallium garnet bowl of substantially circular cross section, comprising: (i) Gd_2O_3 and G in a molar ratio of 3:5;
A melt is formed by heating a mixture of a_2O_3 in an iridium crucible covered with an iridium lid having a circular opening positioned above the melt that is slightly larger than the cross-section of the bowl to be produced; ii) inserting a seed rod of monocrystalline gadolinium gallium garnet into the melt through a circular opening in the iridium lid; (iii) inserting the crucible with the lid consisting of nitrogen containing about 0.5-3% oxygen by volume; (iv) gadolinium gallium garnet material solidifies and crystallizes onto the seed rod, gradually increasing in length and having a substantially circular cross section that is only slightly smaller than the circular aperture in said iridium lid member; The seed rod is pulled out of the melt to form a lumpy monocrystalline bowl product having passing through a circular opening in an iridium lid member to substantially cover and close a melt surface within the crucible in a compartment defined by the crucible wall, the lid member, the circular circumferential surface of the bowl, and the melt surface; and about 0.5% oxygen to the compartment at a rate sufficient to maintain about 0.5% to 3% oxygen by volume within the compartment.
The method characterized in that a continuous flow of nitrogen containing ~3% by volume oxygen is introduced and discharged through the gap between the peripheral surface of the bowl and the iridium lid member.