JPH08176798A - Production of functional thin film - Google Patents

Abstract

PURPOSE: To relieve internal stress produced in a functional thin film at the action temp. of the film even when the material of the film on a substrate is different from the material of the substrate in the coefft. of thermal expansion. CONSTITUTION: When a film of the material 2 of a functional thin film is formed on a substrate 1 at a film formation temp. different from the action temp. of the film to produce a functional thin film, the substrate 1 is elastically deformed and a film of the material 2 is formed on the deformed substrate 1. After thin film formation, the substrate 1 is straightened.

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 functional thin film in which a functional thin film material is formed on a substrate.

[0002]

2. Description of the Related Art Conventionally, functional thin film materials such as superconductors, semiconductors, ELs, and magnetic materials (functional thin film materials have functional characteristics in addition to the mechanical characteristics of the materials themselves) are placed on a substrate. When forming a film on the substrate, a vapor deposition method, a sputtering method, a CVD method or the like is used. In any of the methods, the film forming temperature as a film forming condition is important for obtaining sufficient characteristics of the functional thin film, and a functional thin film of good quality cannot be obtained unless the temperature is a predetermined temperature.

[0003]

By the way, the film forming temperature of the functional thin film is generally different from the operating temperature. Therefore, internal stress does not occur in the functional thin film during film formation, but if the substrate material and the functional thin film material have different thermal expansion coefficients, internal stress occurs in the functional thin film during operation.
This internal stress deteriorates the characteristics of the functional thin film (199
Proceedings of 55th Annual Meeting of the Japan Society of Applied Physics, Autumn 4th year, No. 122a-ZT-8). Therefore, it is desirable to suppress internal stress at operating temperatures.

In order to reduce the internal stress at the operating temperature, a material having a coefficient of thermal expansion equal to that of the functional thin film may be used for the substrate. However, for example, when a functional thin film is epitaxially grown on a substrate, the substrate material is limited to a material having a crystal lattice constant close to that of the functional thin film. In this case, therefore, only a material having a thermal expansion coefficient and a lattice constant close to each other is used. It is also conceivable that no such substrate exists in some cases.

The present invention has been made in view of the above problems, and an object thereof is to reduce internal stress during operation and to increase the degree of freedom in selecting a substrate material.

[0006]

The inventor of the present application states that the functional thin film is formed without stress at the time of film formation, so that if the internal stress can be suppressed at the subsequent operating temperature, the degree of freedom in selecting the substrate material can be increased. Focused on the point. The present invention made based on this point of view has the features described in each of the claims. That is, in the invention according to claim 1, in the method for producing a functional thin film, wherein the functional thin film material (2) having a different film forming temperature and an operating temperature is formed on the substrate (1), the substrate (1) is elastic. After the deformation, the functional thin film material (2) is formed into a film on the substrate (1), and after this film formation, the elastic deformation of the substrate (1) is released.

According to a second aspect of the invention, in the invention of the first aspect, the degree of expansion and contraction (L3-L2) of the film-forming side surface of the substrate (1) is equal to the thermal expansion coefficient of the functional thin film material. The difference in expansion and contraction amount (ΔT) between the substrate and the functional thin film, which is determined by the difference (Δρ) in the coefficient of thermal expansion of the material of the substrate and the difference (ΔT) in the film forming temperature and the operating temperature of the functional thin film.
The substrate (1) is elastically deformed so as to correspond to L).

According to a third aspect of the present invention, in the first or second aspect of the invention, the bending stress generated in the substrate (1) during the elastic deformation is less than the bending strength of the substrate (1). It is characterized by that. In the invention according to claim 4, in the method for producing a functional thin film, wherein a functional thin film material (2) having a different film forming temperature and an operating temperature is formed on a substrate (1), the temperature of the film forming temperature and the operating temperature is Due to the difference
In order to cancel the difference in expansion / contraction amount between the functional thin film and the substrate, the substrate (1) is elastically deformed before the film formation, and the deformation is maintained during the film formation.

In a fifth aspect of the invention, the functional thin film material (2) having a film forming temperature higher than the operating temperature is provided on the substrate (1).
In the method for producing a functional thin film formed on the substrate, the substrate is formed so that the film-forming side of the substrate (1) is uneven depending on the size relationship between the functional thin film material and the substrate material. Elastically deformed, and the functional thin film material (2) is deposited on the elastically and elastically deformed substrate (1),
After this film formation, the elastic deformation of the substrate (1) is released.

In a sixth aspect of the present invention, the functional thin film material (2) whose film forming temperature is lower than the operating temperature is formed on the substrate (1).
In the method of manufacturing a functional thin film formed on the substrate, the substrate is formed so that the film-forming side of the substrate (1) becomes uneven depending on the size relationship between the functional thin film material and the substrate material. Elastically deformed, and the functional thin film material (2) is deposited on the elastically and elastically deformed substrate (1),
After this film formation, the elastic deformation of the substrate (1) is released.

According to a seventh aspect of the present invention, in the invention according to any one of the first to sixth aspects, a predetermined load is applied to the central portion of the substrate with the end portion of the substrate (1) as a fulcrum. By doing so, the substrate is elastically deformed (example of FIG. 3). In the invention according to claim 8, in the invention according to any one of claims 1 to 6, the pressure on the back surface side of the substrate (1) and the substrate (1)
The substrate (1) is elastically deformed by the difference in pressure on the surface side of the substrate (1) (example of FIG. 4).

According to a ninth aspect of the invention, in the invention according to any one of the first to sixth aspects, the substrate (1) is provided along the curved shape of the substrate holder (51) having a predetermined curved shape. ) By fixing the substrate (1)
Is elastically deformed (example of FIG. 5).
According to a tenth aspect of the invention, in the invention according to any one of the first to sixth aspects, the substrate (1) is provided with a substrate deforming member (61), and the substrate (1) is provided at the film forming temperature. The substrate (1) is elastically deformed by the difference in thermal expansion coefficient between the substrate deformation member (61) and the substrate deformation member (61) (example of FIG. 6).

The reference numerals in parentheses for the above means are as follows:
It shows a correspondence relationship with a specific means described in the embodiments described later.

[0014]

According to the invention described in each claim,
After the substrate is elastically deformed, the functional thin film material is deposited, and then the elastic deformation of the substrate is released. Therefore, even if there is a difference in the coefficient of thermal expansion between the substrate material and the functional thin film material, the internal stress generated in the film at the operating temperature of the functional thin film can be reduced by deforming the substrate during film formation of the functional thin film. You can

Further, since the stress can be reduced even if the difference in the coefficient of thermal expansion between the substrate material and the functional thin film material is small, the degree of freedom in selecting the substrate material can be increased.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a process schematic sectional view showing an embodiment of a method for producing a functional thin film to which the present invention is applied. As an example, a high temperature superconductor (High Temperature
The case of a Superconductors: HTS) thin film will be described. Further, it is assumed that the thermal expansion coefficient of the HTS material is larger than the thermal expansion coefficient of the substrate material.

First, the material to be the substrate 1 is set in the film forming apparatus (FIG. 1 (a)). At this time, the temperature of the substrate is room temperature. Next, the substrate temperature is raised to the film formation temperature and the substrate 1 is elastically deformed by a predetermined amount (FIG. 1B).
Here, since it is assumed that the thermal expansion coefficient of the HTS material is larger than the thermal expansion coefficient of the substrate material, it is elastically deformed so that the film formation side surface becomes convex. The HTS material 2 is deposited on the substrate 1 while maintaining the state of the substrate 1 (see FIG. 1).
(C)). This film formation is performed by epitaxially growing an HTS material by a laser ablation vapor deposition method, a sputtering method, a CVD method or the like. At this time, the substrate 1
Is stressed due to deformation, but the HTS film 2 is stress-free.

After the film formation is completed, the substrate 1 and the HTS film 2 are cooled to room temperature and the deformation of the substrate 1 is released (FIG. 1).
(D)). In this case, since the HTS material has a larger coefficient of thermal expansion than the substrate material, the HTS film 2 shrinks more than the substrate 1 during cooling. Therefore, when the film is formed without deforming the substrate 1, tensile stress is generated in the HTS film 2, but if the substrate is deformed in advance as shown in FIG. Since the substrate 1 contracts by that amount, it is possible to cancel the generation of internal stress due to the difference in thermal expansion coefficient.

When the elastic deformation of the substrate 1 is to be released after the film formation, it is not necessary to lower the temperature to the operating temperature at once and then to release it. It is sufficient to be able to cancel the generation of the internal stress when it is reduced to here,
In the above embodiment, it is necessary to prevent the substrate from being destroyed when elastically deforming the substrate. Therefore, the deformation amount and the internal stress (bending stress) of the substrate are specifically obtained, and this point will be considered by comparison with the bending strength of the substrate material.

FIG. 2 shows dimensional parameters before and after the deformation of the substrate. A disk having a diameter L2 and a plate thickness t is assumed as the substrate (FIG. 2A). It is assumed that this disk is deformed into a spherical shell shape as shown in FIG. Here, the center of the spherical shell does not change at the diameter L2 before deformation, the inner side of the spherical shell shrinks to L1, and the outer side of the spherical shell extends to L3. The radii of curvature are R2, R1 and R3, respectively. Here, assuming that the solid angle of the spherical shell at this time is θ, the numbers 1 to 3 are between L, R, and θ.
Have the relationship shown in.

[0021]

## EQU1 ## L1 = R1 × θ = (2πR1 × (θ / 2π))

[0022]

(2) L2 = R2 × θ

[0023]

[Equation 3] L3 = R3 × θ Therefore, the amount of elongation of the film formation side surface due to deformation (L3−L2)
Is given by the equation (4).

[0024]

## EQU00004 ## L3-L2 = (R3-R2) *. Theta. = (R2 + t
/ 2-R2) × θ = t × θ / 2 where Δ is the difference in thermal expansion coefficient between the substrate material and the HTS material.
If ρ, the film formation temperature and the temperature difference at the time of cooling are ΔT, it is sufficient that the deviation ΔL of the shrinkage due to the temperature difference can be canceled by (L3−L2), and therefore the relationship of Equation 5 holds.

[0025]

ΔL = L2 × Δρ × ΔT = L3-L2 = t × θ / 2 Therefore, θ = 2 × L2 × Δρ × ΔT / t. Also,
When the plate having the diameter L2 is curved by the solid angle θ, the amount of deflection Δ
R is represented by Formula 6.

[0026]

## EQU6 ## ΔR = R2-R2 × cos (θ / 2) = R2 × (1-cos (L2 × Δρ × ΔT / t) Further, the deflection amount ΔR when a uniform load p is applied to the entire surface of the substrate. The bending stress σ is given by the equations (7) and (8).

[0027]

ΔR = p × a ⁴ × (5 + ν) / 64D / (1 + ν)

[0028]

Equation 8] σ = 3 × (3 + ν ) × p × a 2/8 / t 2 ^{where, D = E × t 3/} 12 / (1-ν 2), a = L2
/ 2 and E and ν are the Young's modulus and Poisson's ratio of the substrate material, respectively. Based on the above assumptions, YB ₂ Cu ₃ O ₇ was actually used as the HTS material, and LaA was used as the substrate material.
The load p and bending stress when using 10 ₃ are obtained. The linear thermal expansion coefficient of YB ₂ Cu ₃ O ₇ and LaAlO ₃ is described in the paper “Supercond. Sci. Technol. 7 (1994) 609-622.
Is given in Table 1.

[0029]

[Table 1] If the temperature during film formation is 973 K and the temperature during cooling is 77 K, the difference ΔT is 896 deg. Since the mechanical properties of LaAlO ₃ have not been sufficiently investigated, Al ₂
I decided to substitute the value of O ₃ . Young's modulus is 380GN
/ M (3,877,511 kg / cm ² ), Poisson's ratio is 0.25, and bending strength is from the document “Keras's Book Fine Ceramics Eresera Publishing Committee, page 140”.
784 MN / m ² (8,000 kg / cm ² ).
The results calculated by these are shown in Table 2.

[0030]

[Table 2] From Table 2, LaAl with a diameter of 2.5 cm and a plate thickness of 500 μm
O ₃ case of a substrate, the amount of deflection is 280 .mu.m, bending stress at this time is smaller than the bending strength 8,000 kg / cm ² for a 5,734kg / cm ^2, no destruction due to deformation.

As a matter of course, the bending strength of the substrate material is not sufficiently large, and it may be broken when it is deformed into a predetermined shape. In this case, the deformation is performed within the allowable range of the bending strength of the substrate. Although this cannot completely reduce the internal stress, it is certain that the internal stress can be reduced as compared with the conventional one, and the characteristics of the functional thin film are improved.

Next, a specific method of deforming the substrate will be described. FIG. 3 shows a first method for applying a deformation to the substrate. The substrate 1 is held by the substrate holder 31, and the substrate 1 is deformed by pressing the pressure pin 32 against the substrate 1. Therefore, a predetermined load is applied to the central portion of the substrate 1 with the end portion of the substrate 1 as a fulcrum, and the substrate 1 elastically deforms.
In addition, 33 is a spring and 34 is a pressure gauge.

The substrate 1 is pressed by the pressure pin 32 at a predetermined pressure to form a film, and after the film formation is completed, the pressure of the pressure pin 32 is released as the temperature of the substrate is lowered.
Cancel the transformation of. FIG. 4 shows a second method for deforming the substrate. In this method, the substrate 1 is held by the substrate holder 41, and a pressure medium is used instead of the pressure pins 32 shown in FIG. 3 to apply a uniform load to the entire back surface of the substrate 1.

Here, a pressure introducing case 42 and a seal member (O ring) 43 are installed on the back surface of the substrate 1, and pressure is applied in a sealed state as shown in the figure. When the pressure of the pressurizing medium at the time of pressurization is p1 and the pressure on the substrate surface side is p2, the substrate 1 is deformed by the pressure corresponding to the pressure difference of (p1-p2). Film formation is performed in this state, and after the film formation is completed, the substrate temperature is lowered and the pressure of the pressurizing medium is reduced to release the deformation of the substrate 1.

FIG. 5 shows a third method of deforming the substrate. In this method, a predetermined curved surface is formed on the substrate holder 51, and the substrate 1 is placed on the substrate holder 51.
The substrate 1 is deformed by fixing the substrate 1. Specifically, the substrate 1 is fixed by the substrate fixing jig 52 to the substrate holder 51.
Fixed to (fixed at multiple locations or the entire circumference)
Then, the substrate 1 is forcibly deformed (FIG. 5A). After that, the heater wire 53 is heated to a predetermined temperature, and the HTS
The film 2 is formed (FIG. 5B). After completion of film formation, when the substrate 1 is cooled and taken out, the deformation of the substrate 1 is released (FIG. 5).
(C)).

FIG. 6 shows a fourth method for deforming the substrate. In this method, a substrate-deforming film 61 is formed on the back surface of the substrate 1, and thereby the substrate 1 is deformed. First, the substrate deformation film 61 is formed on the back surface of the substrate 1 (FIG. 6).
(A)). The substrate deforming film 61 deforms the substrate 1 by a predetermined amount at the temperature at which the HTS film 2 is formed, and a material having a smaller thermal expansion coefficient than the substrate 1 is selected. The substrate 1 having the substrate deforming film 61 formed on the back surface is deformed so that the side (front surface side) on which the HTS film 2 is formed is convex due to the difference in the coefficient of thermal expansion during heating (FIG. 6).
(B)).

After that, the HTS film 2 is formed (see FIG. 6).
(C)), when this is cooled, the deformation of the substrate 1 is released,
It becomes a flat plate (FIG. 6 (d)). Then, the substrate deformation film 61
Is removed. In the above example, when the film forming temperature of the functional thin film is higher than the operating temperature and the coefficient of thermal expansion of the functional thin film material is larger than the coefficient of thermal expansion of the material of the substrate, the film forming side of the substrate becomes convex. Although the substrate is elastically deformed as described above, the method of deforming the substrate can be as follows.

That is, when the film forming temperature of the functional thin film is higher than the operating temperature and the coefficient of thermal expansion of the functional thin film material is smaller than the coefficient of thermal expansion of the material of the substrate, the film forming side of the substrate becomes concave. The substrate is elastically deformed. In addition, when the film-forming temperature of the functional thin film is lower than the operating temperature, the film-forming side of the substrate is concave when the coefficient of thermal expansion of the functional thin-film material is larger than the coefficient of thermal expansion of the substrate material. Elastically deform.

As described above, when there is a difference in the coefficient of thermal expansion between the substrate material and the functional thin film, the internal stress generated in the film at the operating temperature of the functional thin film can be reduced by deforming the substrate when the functional thin film is formed. Since it can be reduced or eased, it is possible to maintain high quality without deteriorating the characteristics of the functional thin film. Although the HTS film is taken as the functional thin film in the above-mentioned embodiments, the thermal expansion coefficient of the substrate material and the functional thin film material are different even in other functional materials (semiconductor thin film, EL film, magnetic thin film, etc.) The present invention can be applied when the film temperature and the operating temperature are different.

[Brief description of drawings]

FIG. 1 is a process schematic cross-sectional view showing an example of a method for producing a functional thin film to which the present invention is applied.

FIG. 2 is an explanatory diagram for explaining dimensional parameters before and after deformation of a substrate.

FIG. 3 is a diagram showing a first method for applying deformation to a substrate.

FIG. 4 is a diagram showing a second method for applying deformation to a substrate.

FIG. 5 is a diagram showing a third method of applying deformation to a substrate.

FIG. 6 is a diagram showing a fourth method of applying deformation to a substrate.

[Explanation of symbols]

1 ... Substrate, 2 ... HTS film, 31, 41, 51 ... Substrate holder, 32 ... Pressurizing pin, 42 ... Pressure introducing case, 52 ...
Substrate fixing jig, 61 ... Substrate deforming film.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication H01L 21/205 // C23C 14/28 ZAA 14/34 ZAA

Claims (10)

[Claims] 1. A method of manufacturing a functional thin film, wherein a functional thin film material having different film forming temperatures and operating temperatures is formed on a substrate, wherein the functional thin film material is formed on the substrate after elastically deforming the substrate. Then, the method for producing a functional thin film, wherein the elastic deformation of the substrate is released after the film formation. 2. The degree of expansion and contraction of the film formation side surface of the substrate is
Equivalent to the difference between the expansion and contraction amounts of the substrate and the functional thin film, which is determined by the difference between the coefficient of thermal expansion of the functional thin film material and the coefficient of thermal expansion of the material of the substrate and the difference between the film forming temperature and the operating temperature of the functional thin film. The method for producing a functional thin film according to claim 1, wherein the substrate is elastically deformed so as to do so. 3. The method for producing a functional thin film according to claim 1, wherein the bending stress generated in the substrate during the elastic deformation is not more than the bending strength of the substrate. 4. A method for manufacturing a functional thin film, wherein functional thin film materials having different film forming temperatures and operating temperatures are formed on a substrate, wherein expansion and contraction of the functional thin film and the substrate due to a temperature difference between the film forming temperature and the operating temperature. A method for producing a functional thin film, comprising elastically deforming the substrate before the film formation so as to cancel the difference in the amount, and maintaining the deformation during the film formation. 5. A method of manufacturing a functional thin film, wherein a functional thin film material having a film forming temperature higher than an operating temperature is formed on a substrate, the thermal expansion coefficient of the functional thin film material and the substrate material being set to correspond to the magnitude relationship. The substrate is elastically deformed so that the film forming sides of the substrate are uneven, and the functional thin film material is formed on the elastically deformed substrate, and after this film formation, the elastic deformation of the substrate is released. A method for producing a functional thin film, comprising: 6. A method of manufacturing a functional thin film, wherein a functional thin film material having a film forming temperature lower than an operating temperature is formed on a substrate, the thermal expansion coefficient of the functional thin film material and the substrate material is used to correspond to the magnitude relationship. The substrate is elastically deformed so that the film formation side of the substrate becomes uneven, and the functional thin film material is formed on the elastically elastically deformed substrate, and after this film formation, the elastic deformation of the substrate is released. A method for producing a functional thin film, comprising: 7. The substrate according to claim 1, wherein the substrate is elastically deformed by applying a predetermined load to a central portion of the substrate with the end portion of the substrate as a fulcrum. Of the functional thin film of. 8. The functional thin film according to claim 1, wherein the substrate is elastically deformed by the difference between the pressure on the back side of the substrate and the pressure on the front side of the substrate. Production method. 9. The substrate according to claim 1, wherein the substrate is elastically deformed by fixing the substrate along the curved shape of the substrate holder having a predetermined curved shape. Of the functional thin film of. 10. The substrate deforming member is provided on the substrate, and the substrate is elastically deformed by a difference in thermal expansion coefficient between the substrate and the substrate deforming member at the film forming temperature. The method for producing a functional thin film according to any one of claims.