JP3197383B2 - Manufacturing method of thin film by epitaxial growth - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal film, and more particularly to a method for producing a single crystal film by epitaxial growth.

[0002]

2. Description of the Related Art A method of manufacturing a single crystal film by epitaxial growth includes a method of manufacturing a semiconductor, an optical element, a magnetic body, a magneto-optical element, and the like.
It is widely used in the production of various single crystal films used in various fields. In epitaxial growth, a liquid or a gaseous raw material is brought into contact with a surface of a crystal substrate having a lattice constant close to the lattice constant of a crystal to be grown to grow a predetermined crystal. Thereby, a single crystal film having good crystallinity can be manufactured. For example, a magnetic garnet known as a magneto-optical element such as a Faraday rotator uses a liquid-phase raw material, uses a Ca, Mg, Zr-doped GGG single crystal or the like as a crystal substrate, and has a film of 100 μm or more on its surface. It is manufactured by liquid phase epitaxy (LPE) for growing crystals to a large thickness.

[0003]

However, when such a thick film is required, stress often develops between the substrate and the single crystal film, causing distortion in the single crystal film. Cracks occur. Conventionally, it is believed that this problem can be avoided by making the lattice constant of the crystal substrate and the lattice constant of the single crystal film as close as possible, but in reality the chemical composition, thickness, and thermal expansion coefficient of the substrate and the single crystal film It is not enough to make lattice constants coincide with each other.
In addition, a method has been proposed in which two types of films having the same lattice constant are alternately stacked at different temperatures. However, this method requires many steps and is extremely troublesome.

Accordingly, an object of the present invention is to prevent the generation of stress and avoid the problem of cracking when a single crystal film is formed on a crystal substrate by an epitaxial growth method.

[0005]

According to the present invention, when a single crystal film is formed on a crystal substrate by an epitaxial growth method, the lattice constant of the substrate and the lattice constant of the single crystal film are initially set close to each other. A method for manufacturing a single crystal film, characterized in that a deviation of the lattice constant of the single crystal film is increased to a predetermined lattice constant. In this case, the shift of the lattice constant may be either positive or negative. For example, in a magnetic garnet, it is necessary to increase the magnitude of the lattice constant of the single crystal film as it grows to a predetermined lattice constant. FIG. 1 shows a state where a single crystal film of a magnetic garnet is grown and its lattice constant is increased as described later. As a result, no crack was generated at a film thickness of 700 μm.

[0006] The method of the present invention is different from the conventional common sense.
If the lattice constants of the substrate and the single crystal film are close at the starting point,
It is better to shift the lattice constant as the crystal grows,
It is based on a surprising discovery. If the lattice constant is kept constant during crystal growth as in the prior art, the rate of cracking will be higher than in the method of the present invention. The reason for this result has not yet been elucidated. The cause of the crack is presumed as follows. That is, the difference in thermal expansion coefficient between the substrate and the single crystal film is sufficiently large, the growth temperature is sufficiently high, and the grown single crystal film is sufficiently thick (for example, Bi).
When the condition of (substituted magnetic garnet film is 100 μm or more) is satisfied, cracking occurs. Either one of these lacks does not generate stress that causes cracking, or does not cause cracking even if it occurs. First, when a film having a lattice constant different from the lattice constant of the substrate is deposited in the early stage of growth, a warp is generated by the bimetal model. Further, if the subsequent deposited film grows along the radius of curvature due to the warpage, the radius of curvature becomes constant and stabilized.
Here, the radius of curvature corresponds to a constant change in the lattice constant of the film. On the other hand, when a film whose change is smaller than the change in the lattice constant corresponding to the radius of curvature (for example, when the lattice constant is constant) grows on the surface, a tensile stress is applied to the lattice near the surface (in the case of a curvature convex to the film side, That is, the film receives a compressive stress (when the lattice constant of the film is larger than the substrate in the initial stage of growth) or a compressive stress (when the film has a smaller lattice constant than the substrate).
It is thought that cracks are caused when the film is thick. Here, the shift of the lattice constant at the initial stage of growth is caused by the difference in the thermal expansion coefficient between the substrate and the film. That is, when the lattice constants are matched at room temperature, if the coefficients of thermal expansion are different, the lattice constants of the substrate and the film differ at the growth temperature, and the lattice constant shifts. On the other hand, if the lattice constants are matched at the growth temperature, a difference occurs between the lattice constants of the substrate and the film at room temperature, causing a shift in the lattice constant and breaking during cooling after film growth. As a result of the measurement, the Bi-substituted magnetic garnet has a larger thermal expansion coefficient by about 1 × 10 ⁻⁶ / ° C. than the GGG substrate with Ca, Zr, and Mg added. From this, the deviation of the lattice constant at the growth temperature (for example, 800 ° C.) is obtained,
When the radius of curvature at the initial film thickness (50 μm or less) is obtained using a bimetal model, it is about 1-2 m. From this, the change in the lattice constant along the radius of curvature is found to be 0.5 to 1 ×
It was 10 ^-4 % / μm, which was almost in agreement with the experimental result. How close the lattice constant of the substrate and the single crystal film should be at the starting point is not fully understood, but in addition to perfect agreement, a deviation of about ± 0.2% is acceptable. Yes, the conditions under which cracking does not occur can be easily determined for each crystal material.

The change in the lattice constant of the single crystal film is performed by controlling the composition of the raw material. For example, in the LPE method, the composition is adjusted by changing the blending ratio of the melt composition and the growth temperature over time. On the other hand, in the CVD method of the vapor phase method, the composition ratio of the component gas introduced into the vapor deposition chamber is changed with time. The composition can be adjusted by temporally changing the power applied to the target of multiple simultaneous sputtering.

More specifically, when a Bi-substituted magnetic garnet single crystal film is manufactured by, for example, the LPE method, a Bi _x R _3-x Fe _5-w M _w O ₁₂ (where R is Y, C
a, Pb, La, Ce, Pr, Nd, Sm, Eu, G
at least one element selected from d, Tb, Dy, Ho, Er, Tm, Yb, and Lu; M is Al, Ga, In, S
At least one element selected from c, Ti, Si, and Ge. Further, a material weighed so as to give x = 0 to 2 and w = 0 to 2) is grown by LPE on a nonmagnetic single crystal substrate made of, for example, GGG with Ca, Mg and Zr added. As a result, a Bi-substituted rare earth garnet material having substantially predetermined crystallinity is produced. As the time elapses, the growth temperature is lowered, the amount of the component Bi is adjusted, and the lattice constant increases with the film thickness. Parameters affecting the lattice constant include the total amount of the melt, the substrate area, and the film growth rate. The parameters for determining the film growth rate include melt composition ratios R ₁ , R ₃ , R ₄ , and R ₅ (collectively referred to as R parameters). Here, the composition ratio is defined as follows. R ₁ = (Fe ₂ O ₃ + M ₂ O ₃ ) / ΣR ₂ O ₃ R ₃ = (Bi ₂ O ₃ + PbO) / B ₂ O ₃ R ₄ = (Fe ₂ O ₃ + M ₂ O ₃ + ΣR ₂ O ₃ ) More specifically, R ₅ = Bi ₂ O ₃ / PbO More specifically, R ₁ of the magnetic garnet is 5/3, whereas R ₁ is set to 10 or more in the Bi substitution type. Therefore, as the film grows on the substrate, R ₁
Increase, and the molecules of R ₃ , R ₄ , and R ₅ become smaller due to film growth, and decrease. Most R
_3, the change in R ₅ is small. When growing a film having a thickness exceeding 100 μm, these R parameters, especially R ₁ ,
To ignore the change of R ₄ can not. Empirically, the amount of Bi contained in the film composition decreases due to an increase in R _{1 and a} decrease in R ₄ under isothermal conditions, and the lattice constant of the film decreases. Therefore, when fabricating a film having the same composition over the entirety, that is, a single crystal film having the same lattice constant, the growth temperature must be lowered at a gradient taking these factors into consideration.
On the other hand, when Bi is increased, that is, when the lattice constant is increased, it can be realized by lowering the growth temperature at a gradient larger than the above gradient. As described in the examples, the rate of change of the lattice constant is (0.4 to 9) × 10
It was found that it was better to be in the range of ^-4 % / μm.

In addition, the present invention can be applied to SiC, Si-based semiconductors, other crystals, and the like.

[Explanation of the embodiment]

Use Example _{1 Bi 2 O 3, Tb 4} O 7, Nd 2 O 3, Fe 2 O 3 to PbO as flux, not containing added B ₂ O ₃ at the mixing ratio giving the following magnetic garnet lattice constant 12 .
Diameter 2 consisting of GGG added with 497% Ca, Mg and Zr
LPE at 813 ° C on an inch non-magnetic single crystal substrate
A single crystal film was manufactured by the method. The average composition of the grown film was Bi _0.7 Tb _2.1 Nd _0.2 Fe ₅ O ₁₂ and the lattice constant was 12.494 °. At this time, the film forming conditions were as follows: melt total amount 2 kg, R ₁ = 24, R ₃ = 10, R ₄ = 0.12,
R ₅ = 0.3. Next, after epitaxial growth was started at 813 ° C. by the same operation, the furnace temperature was decreased at a rate of 0.6 ° C./H, and the lattice constant was set to 1.9 × 10 ⁻⁵ Å / μm.
(1.5 × 10 ⁻⁴ % / μm) while growing. The lattice constant is a value obtained by measuring a sample at 25 ° C. (the same applies to other examples). The film did not crack up to a thickness of 700 μm.

Example 2 Using the same raw materials as in Example 1 and using the same non-magnetic single-crystal substrate as in Example 1 at a compounding ratio giving the following magnetic garnet, let it be run at a temperature of 908 ° C. by the LPE method. Maku was made. The average composition of the grown film is Bi _0.8 Tb _2.1
Nd _0.1 Fe ₅ O ₁₂ and a lattice constant of 12.491 °. The film forming conditions at this time were as follows: total melt amount 10 kg, R _{1
= 26, R 3 = 10,} R 4 = 0.18, were R ₅ = 0.6. Next, after epitaxial growth is started at 908 ° C. by the same operation, 0.1 ° C./H is applied until the film thickness reaches 200 μm.
When the film thickness is 200 μm, the lattice constant is lowered at 0.3 ° C./H and the lattice constant is set to 1.0 × 10 ⁻⁵ Å / μm (0.8 × 10 ⁻⁴ % / μm).
The growth was carried out while changing the conditions under m). 700 μm film
No cracks occurred up to the thickness. Comparative Example 1 In Example 2, epitaxial growth was performed as follows. The temperature is lowered at a rate of 0.1 ° C./H, and the lattice constant is set to 0.4 × 10 ⁻⁵ Å / μm (0.3 × 10 ⁻⁴ % / μm).
Cultivation while changing the ratio of The film cracked at a thickness of 350 μm.

Embodiment 3 Bi ₂ O ₃ , Ho ₂ O ₃ , La ₂ O ₃ , Y ₂ O ₃ , Fe
PbO, B ₂ O as flux to ₂ O ₃ , Ga ₂ O _3
The mixture obtained by adding ₃ is used in a compounding ratio giving the following magnetic garnet, and a single crystal film is formed by a LPE method at a temperature of 745 ° C. on a nonmagnetic single crystal substrate made of Nd ₃ Ga ₅ O ₁₂ having a lattice constant of 12.502 °. Produced. The average composition of the grown film is B
i _1.4 Ho _0.10 La _0.2 Y _0.4 Fe _4.5 Ga _0.5 O ₁₂ and a lattice constant of 12.504 °. Next, after starting epitaxial growth at 745 ° C. by the same operation,
The furnace temperature was lowered at a rate of 1.2 ° C./H, and the lattice constant was set to 2.
Growing was carried out while changing at a rate of 9 × 10 ⁻⁵ μ / μm (2.3 × 10 ⁻⁴ % / μm). The film did not crack up to a thickness of 500 μm. Comparative Example 2 In Example 3, epitaxial growth was performed as follows. The growth was performed while the temperature was lowered at a rate of 5.0 ° C./H and the lattice constant was changed at a rate of 12 × 10 ⁻⁵ Å / μm (10 × 10 ⁻⁴ % / μm). The film cracked at a thickness of 150 μm.

Example 4 A mixture of Y ₂ O ₃ , La ₂ O ₃ , Ga ₂ O ₃ , and Fe ₂ O ₃ to which PbO and B ₂ O ₃ were added as fluxes was used in a mixing ratio to give the following magnetic garnet. Lattice constant 12.3
A single crystal film was formed on a nonmagnetic single crystal substrate made of GGG (Gd ₃ Ga ₅ O ₁₂ ) at a temperature of 75 ° by the LPE method at a temperature of 745 ° C. The average composition of the grown film is Y _2.9 La _0.1 F
e _4.5 Ga _0.5 O ₁₂ , and the lattice constant was 12.377 °. Next, after epitaxial growth was started at 745 ° C. by the same operation, the furnace temperature was lowered at a rate of 1.2 ° C./H to set the lattice constant to 1.0 × 10 ⁻⁵ Å / μm (0.8 × 10 5 ^-4 %
/ Μm) while changing the ratio. The membrane is 200
No cracks occurred up to a thickness of μm. Example 5 Bi ₂ O ₃ , Gd ₂ O ₃ , Yb ₂ O ₃ , Fe ₂ O ₃ , T
A mixture obtained by adding PbO and B ₂ O ₃ as a flux to iO ₂ at a compounding ratio giving the following magnetic garnet was used. On a nonmagnetic single crystal substrate made of GGG doped with Ca, Mg, and Zr having a lattice constant of 12.497 °, A single crystal film was formed at a temperature of 745 ° C. by an LPE method. The average composition of the grown film is Bi
_1.0 Gd _1.4 Yb _0.6 Fe _4.95 Ti _0.05 O ₁₂ , and the lattice constant was 12.495 °. Next, after the epitaxial growth was started at 745 ° C. by the same operation, the furnace temperature was lowered at a rate of 1.2 ° C./H to set the lattice constant to 2.3 × 10 ⁻⁵ Å / μ.
m (1.8 × 10 ⁻⁴ % / μm) while growing. The film did not crack up to a thickness of 700 μm.

Comparative Example 3 In Example 5, epitaxial growth was performed as follows. The temperature was kept constant at 750 ° C., and the lattice constant was -4.0 ×
Growing was carried out while changing at a rate of 10 ⁻⁵ Å / μm (3.2 × 10 ⁻⁴ % / μm). The film cracked at a thickness of 50 μm.

From the above examples and comparative examples, the lattice constant of the single crystal film to be grown is made to be close to that of the substrate, and the rate of change thereof is set within a predetermined range (0.4 to 9) × 10 ⁻⁴ % / μ.
It can be seen that by setting m, it is possible to prevent generation of stress and prevent cracking. In this embodiment, although no particular reference is made to impurities in the single crystal film, the LPE
According to the method, Pb, Pt, and the like are mixed in the film as inevitable impurities mixed from the flux, the crucible, and the raw material.

[0015]

As can be seen from the examples, according to the present invention, when a single crystal film is formed on a crystal substrate by an epitaxial growth method, generation of stress can be prevented and cracks can be prevented.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a thickness of a single crystal film and a change in a lattice constant in Examples 1 to 5 relating to crystalline garnet.

Continuation of the front page (72) Inventor Shinya Uchida 1-1-13 Nihonbashi, Chuo-ku, Tokyo TDK Corporation (56) References JP-A-63-270396 (JP, A) (58) Fields investigated ( Int.Cl. ⁷ , DB name) C30B 1/00-35/00 CA (STN) JICST file (JOIS) EPAT (QUESTEL) WPI (DIALOG)

Claims (11)

(57) [Claims] 1. A single crystal film obtained by epitaxial growth, wherein the shift of the lattice constant increases from the substrate side toward the growth direction. 2. The single crystal film according to claim 1, wherein the composition has a gradient from the substrate toward the growth direction. 3. The method according to claim 1, wherein the shift of the lattice constant is a change rate (0.4 to 9).
2. The single crystal film according to claim 1, wherein the thickness is increased by × 10 ⁻⁴ % / μm. 4. The single crystal film according to claim 3, wherein the single crystal film is a magnetic garnet. 5. The single crystal film according to claim 4, wherein the single crystal film is formed by a liquid phase epitaxial method. 6. The single crystal film according to claim 1, wherein the single crystal film has a thickness of 100 μm or more. 7. When epitaxially growing a single-crystal film on a substrate, the lattice constant of the substrate and the lattice constant of the single-crystal film are initially set close to each other, and the deviation of the lattice constant of the single-crystal film is reduced as the growth proceeds. A method for producing a single crystal film, characterized by increasing the rate of change. 8. The rate of change of the lattice constant is (0.4 to 9) × 1.
^{8. The} method for producing a single crystal film according to claim 7, wherein the thickness is in the range of 0 ^-4 % / μm. 9. The method according to claim 8, wherein the single crystal film is a magnetic garnet. 10. The method according to claim 9, wherein the single crystal film is manufactured by a liquid phase epitaxial method. 11. The method for producing a single crystal film according to claim 7, wherein the single crystal film has a thickness of 100 μm or more.