JPS5933557B2 - Method of manufacturing GGG single crystal - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a single crystal bowl in which cracks in the crystal bowl and crystal defects are almost zero during growth of a GGG single crystal using the Czochralski method.

GGG single crystals are used, for example, in the form of polished wafers as substrates for the epitaxial growth of iron-garnet films.

These films are required to be free of defects such as strain dislocations, but for this purpose, the GGG wafer itself is first required to be crystallically perfect, since defects in the wafer propagate to the film.

Currently, these epitaxially grown films are mainly used for magnetic bubble memories, but it is important to improve the recording density of magnetic bubble memories and improve the device performance.

As the demand for reliability and cost reduction increases, the specifications for defects in pittaxially grown films, that is, defects in GGG wafers, are becoming more stringent.

In the conventional Czochralski method for growing GGG single crystal bowls, a total of 5 tetravalent elements such as Ge and Si are used.
ppm or less High purity Gd2O3 and Ga2 with a total of 5 ppm or less of divalent elements such as Ca, Mg, Ba, Sr, etc.
It has been common practice to use O3 raw material.

However, when growing GGG single crystal bowls using such raw materials, areas with strong local strain appear within the bowl,
While the crystal bowl was being cooled in the growth furnace after growth, cracks frequently occurred in the bowl.

In addition, single crystal bowls grown under such conditions are prone to cracking during slicing, and the slicing conditions must be carefully and appropriately adjusted. Furthermore, crystal defects such as inclusions and dislocations may occur on the wafer surface. A large number of dislocations (several tens of dislocations/
crA or higher) may occur, significantly reducing the yield of good quality crystal parts.

The present invention improves the drawbacks of the GGG single crystal bowl grown by the above-mentioned conventional technology, and has no locally strong strain in the crystal bowl, and not only does it have no cracks during bowl cooling or slicing, but also has almost no crystal defects. The purpose of the present invention is to provide a technology for producing a complete GGG single crystal.

The GGG single crystal production process using the Czochralski method in the present invention is the same as that using the conventional Czochralski method, except that appropriate amounts of appropriate types of additives are added to the raw materials.

That is, the growth of a GGG single crystal by the Czochralski method involves the following steps.

(1) A step of mixing G d 203 and Ga2O3 in a molar ratio of 3:5 to 305:495, heating to form a melt, and maintaining the temperature at 1700°C to 1800°C.

(2) Inserting a seed crystal rod of single crystal GGG into the melt.

(3) A step of creating a chemically inert atmosphere on the surface of the melt.

(4) The melt (which can also be called GGG melt) solidifies into a seed crystal rod, and the seed crystal rod is gradually pulled up and its length gradually increases so that it is coaxial with the seed crystal axis and has a circular cross section. a step of pulling a GGG single crystal having a

In the present invention, at the step (1) above, by adding at least one of (a), Ge, and Si ions in a weight ratio of 3 ppm to 30 ppm to the raw material powder or tart, the local strong It can reduce strain, eliminate cracks during bowl cooling and during slicing, and reduce crystal defects such as inclusions and dislocations on the wafer surface to 0. , 5 pieces/crA
It was possible to reduce it to below.

(b) 3 to 3 ions consisting of Ge, Si 0 group
In addition to 0 ppm addition, Ca, Mg, Ba, Sr
By adding 5 to 25 ppm of divalent metal ions consisting of the group consisting of the group of The number of crystal defects was also suppressed to 0.1/crA or less.

(Ge, Si) ion group and (Ca, Mg, Ba.

The amount of each Sr) ion group added is 3 to 20 ppm.
and 5 to 25 ppm, and Ge, S
The weight ratio of ions from group i to ions from groups of Ca, Mg, Ba, and Sr is 1:1.2 to 1.4.
The greatest effect was found where

In this case, an almost crystallographically perfect GGG single crystal bowl with nearly zero crystal defects such as dislocations and inclusions observed on the wafer surface was obtained.

Addition of ions consisting of Ge, Si group exceeding 40 ppm or Ca, M exceeding 35 ppm
g.

On the contrary, the addition of ions consisting of Sr and Ba causes a facet to appear in the center of the crystal bowl, resulting in the occurrence of distortion in the facet part and often the generation of dislocations from this part, making it difficult to obtain a high-quality GGG single crystal bowl. I couldn't.

730 ppm or more of ions consisting of the groups Ge and Si and ions consisting of the groups Ca, Mg, Ba, and Sr.
A similar phenomenon occurred when 5 ppm or more was added in combination, and high quality crystals could not be obtained.

These additives are added by post-addition to the raw material powder or raw material melt in the form of oxide carbonates or other ionizable compounds to achieve the desired ion content.

An outline of the crystal growth chamber and growth process used in the present invention will be explained.

In FIG. 1, a crystal growth chamber 1 is illustrated.

From the ratio corresponding to the stoichiometric composition Gd3Ga5O12, the harmonic melting composition Gd3. .

5 Ga4. Gd between molar ratios corresponding to g5 o1□
The raw material composition is 2O3 and Ga2O3, and the above-mentioned (
Ions consisting of the group of (Ge, Si) and (Ca, Mg
, Sr, Ba) is contained in an iridium crucible 3.

The crucible 3 is surrounded on its side and bottom surfaces by a heat-insulating refractory 6.7 made of zirconia.

Insulating refractories not only save the power required to maintain the melt (hereinafter referred to as melt), but also reduce power supply voltage fluctuations,
It works to reduce temperature fluctuations in the melt caused by convection cooling of the atmosphere.

An induction heating coil 9 is arranged around the outer periphery of the refractory cylinder 6.

The crucible and refractory 7 are placed on a ceramic pedestal 10 made of, for example, ZrO2.

This is placed in a sealed chamber 11 except for the hole 12 and the gas introduction tube 13.

A desirable atmospheric gas for the melt, such as nitrogen with 2% oxygen by volume, is introduced through a gas inlet tube 13 and discharged through a hole 12 fitted in a chamber through which a crystal pulling shaft 14 is inserted.

A single crystal GGG (seed crystal) having a predetermined crystal orientation in the direction of the pulling axis is attached to the tip of the crystal pulling shaft.

Using the above apparatus, (Ge, Si) and (Ca, Mg
, Sr, Ba) are Gd2
Added to O3Ga2O3 melt.

These ions may be added before the raw material powder melts (or may be added after the raw material has melted down).

The melt is maintained at 1700°C to 1800°C.

The seed crystals are dipped into the tart, allowing the melt to solidify into seed crystals bit by bit.

The crystal bowl 5 automatically controls the power input to the induction heating coil 9 while rotating the pulling shaft so that the crystal bowl 5 has a uniform circular cross section.

A specific example of the present invention will be described.

The crystal growth chamber and process used were as described above, but the growth conditions were kept constant in all cases to facilitate comparison between Examples.

That is, Gd2O3 and Ga20 corresponding to a raw material: molar ratio of 3:5
Both 314Ga2O5l45 and Ga2O3 (Ge, S
i) The impurity of ions consisting of the group is 5 ppm or less,
The impurities of ions consisting of the group (CaSMg, Ba, Sr) were also 5 ppm or less.

Crucible used: A crucible with a constant shape and thickness was used.

Atmosphere: N2 containing 2% by volume Additives: GeO2, Sin, powder and CaCO3, Mg so that a given weight of ions is contained in the tart
CO3, BaCO3, and SrCO3 powders were weighed and added and mixed before melting the above raw materials.

Under the above conditions, the iridium crucible is heated by a high-frequency current flowing through an induction heating coil, and the raw material powder is melted into a
The temperature was maintained at 700°C to 1800°C.

Thereafter, the seed crystal rod was immersed in the melt, and while the pulling shaft was rotated at a predetermined rotation speed, the single crystal bowl was pulled up for 50 hours by automatic diameter control using a load cell weight sensor.

The final bowl is approximately 80mm in diameter x 250mm.
It had a circular cross section with uniform length.

76.2XO per 2oomrIL in the center of this bowl
Sliced into 15t wafers, processed with mirror finish and treated with H2SO4
Mixed acid (No. 3 = 1: 1 (volume)) at 200℃
The wafer was immersed in a heated solution for 2 minutes, and dislocation etch pits and etch bits caused by inclusions appearing on the wafer surface were observed under 100 times magnification using a differential interference microscope to inspect for crystal defects.

Observation of distortion in the bowl and wafer was performed using a photoelastic method (observation using crossed nicols).

One of the embodiments will be explained based on FIG.

Figure 2 shows Si as an ion consisting of the group (Ge, Si).
Ions (Ca, Mg5Ba.

Ca ions are selected as ions consisting of the group Sr),
The correlation between crystal defects and the amount of each ion added when added singly or in combination is shown.

The crystal defects were observed within an area of 76.2φ in the above process, which is the number of crystal defects in an average wafer at a bowl length of 200u+.

The following can be said from this experimental result.

(1) The number of crystal defects without additives is 1/ctA
This value is slightly higher than that of

(If 2Si ions are added alone, the number of crystal defects will be 0.5 / 3 ppm to 30 ppm.
cm or less, and the effect is obvious.

However, when 40 ppm is added, the effect becomes small and becomes almost unnoticeable.

(3) The effect of adding Ca ions in combination with Si ions is significant.

The effect was greatest when Si ions were added at 3 ppm to 20 ppm and Ca ions were added at 5 ppm to 15 ppm, and the crystal defects were less than 0.1/C77f.

(4) In this composite addition, the effect tends to become weaker as Ca ions are further increased.

When 25 ppm of Ca ions were added, a fairly large effect was observed in the range of Si ion addition amount of 10 to 25 ppm, but when 35 ppm of Ca ions were added, no combined addition effect with Si ions was observed. .

(5) The effect of combined addition of Si ions and Ca ions is greatest at a weight ratio of approximately 1.2 to 14 Ca ions to 1 Si ion.

(6) Si ion addition amount 5 ppm to 20 ppm
The greatest effect on crystal defects was obtained when 75 ppm to 115 ppm of Ca ions were added in combination, and the crystal defects were cello over 60% to 90% of the 200rratt length for all bowls.

From the above, it is clear that the single effect of Si ions on crystal defects and the effect of combined addition of Si 2 ions and Ca 2 ions within an appropriate amount range are evident.

In addition, we observed and checked the distortion of the bowl for the experimental sample shown in Figure 2 for cracks when the bowl was cut, and the result was 30 ppm.
It was observed that the local strain was clearly smaller when Si ions were added alone and when Si ions were added at a concentration of 30 ppm or less and Ca ions were added at a concentration of 25 ppm or less, compared to the case where no Si ions were added.

Also, the occurrence of cracks and chips during slicing was reduced.

On the other hand, when Si ions were added at 40 ppm and Ca ions were added at 35 ppm, the local strain within the bowl was strong regardless of whether it was added alone or in combination, and strong strain was observed in the center of the bowl, especially due to the so-called facet core. It was done.

Therefore, both Si ions and Ca ions have a certain limit value (S
40ppm for i ions, 35ppm for Ca ions
It has been found that addition of more than m) gives a negative crystallographic effect.

According to the present invention, (Si, Ge) ions alone or (Si, Ge)
It has become clear that the combined addition of Ge) ions and ions of the group consisting of (Ca, Mg, Ba, Sr) reduces crystal defects and eliminates local strain in the crystal, and stabilizes an extremely high-quality, almost defect-free GGG single crystal bowl. Now you can get it.

In particular, the average crystal defects of 1 to 2/cyst when no additives are added are (Si, Ge) ions, (Ca, Mg, Ba,
Crystal defects are reduced by 200mm by compound addition of Sr) ions.
Of the bowl? The fact that 0.1/C:IrL or O/crrt can now be obtained over the entire length is great.
We believe that this will greatly contribute not only to GG but also to improving the yield, improving reliability, and reducing costs of magnetic valve memories.

[Brief explanation of the drawing]

Figure 1 is a structural diagram of GGG single crystal bowl growth chamber V.
Figure 2 shows the average number of crystal defects per 76.2φ wafer and Si
It is a correlation diagram of ions and Ca ion addition amounts.

Claims (1)

[Claims] 1 3:5 to 3.05 of Gd2O3 and Ga2O3
Dissolve raw material powder with a molar ratio of 4:95, and add 17
Maintain the temperature within the range of 00℃ to 1800℃, GG
The seed crystal rod of G is solidified into the seed crystal rod in an atmosphere that is chemically inert to the melt, and the seed crystal rod is pulled up and the length is gradually increased. In GGG single crystal growth using the so-called Czochralski method, which grows a single crystal bowl, GGG is added to the raw material powder or melt.
e, 30pp of tetravalent ions consisting of Si alone or in combination
A method for producing a GGG single crystal, characterized in that less than m is added. 2. In claim 1, in addition to the addition of 30 ppm or less of ions consisting of Ge and Si0 groups, Ca
A method for producing a GGG single crystal, characterized in that 25 ppm or less of divalent metal ions consisting of the group consisting of , Mg, Ba, and Sr are added alone or in combination to a mixed raw material powder or melt. 3 In claim 2, for every 1 weight of ions of the group Ge and Si, Ga, Mg, Ba
, the addition weight of divalent metal ions consisting of the group Sr is 1.
2 to 1.4. A method for producing a GGG single crystal. 4Ge, Si The addition weight of divalent metal ions consisting of the groups Ca, Mg, Ba, and Sr is 1.2 to 1.4 per 1 of the addition weight of ions consisting of the 0 groups of Ge and Si.
, Si) and ions (CaSMg, Ba, Sr) are added in a weight range of 3 to 20 ppm and 5 to 25 ppm, respectively.
A method for producing a GGG single crystal, characterized in that: