JP4412462B2 - Thin film formation method - Google Patents

Description

  The present invention relates to a method for forming a thin film, and more particularly to a method for heating a substrate when an oxide thin film or the like exhibiting superconductivity, ferroelectric, and ferromagnetic properties is formed by vapor deposition.

  When forming a thin film on a substrate by vapor deposition, the substrate is placed on a substrate holder provided in a vacuum chamber, and the substrate is usually heated through the substrate holder. In general, when the substrate temperature is low, the crystallinity of the thin film is impaired. Therefore, when forming an oxide thin film, it is necessary to maintain the substrate temperature at, for example, 800 ° C. or higher. In this case, since there is a fine unevenness between the substrate back surface and the substrate holder surface, simply fixing the substrate with a clamper or the like creates a vacuum space between the substrate back surface and the substrate holder. It is not possible to achieve a good thermal contact. As a result, defective heating, uneven temperature, etc. occur, and good crystal growth is hindered. In order to avoid this, it has been common in the prior art to improve thermal contact using a silver paste (see, for example, Patent Document 1).

This method is performed as follows. After the silver paste is applied to the back surface of the substrate, the substrate is set on the substrate holder. After heating to a high temperature to evaporate the solvent, a thin film is grown. After completion of the thin film formation, the substrate is peeled off from the substrate holder.
JP 7-133189 A

In the prior art, it is easy to fix a 5 to 10 mm square substrate. However, when the substrate size is increased, the following problems arise. With a large-area substrate, it is difficult to apply the silver paste to a uniform film thickness, and when heated to a high temperature, a temperature difference occurs in the substrate surface due to the thickness distribution of the silver paste, and the characteristics of the thin film to be produced are not uniform. In a large area substrate, a long time is required for uniform evaporation of the solvent and complete evaporation of the solvent. Further, the residual solvent evaporates during the thin film growth, and the film quality is deteriorated. Furthermore, in the conventional method, since the substrate is firmly attached to the substrate holder, the substrate is easily damaged when the substrate is peeled off, and a large number of steps are required for removing the substrate. In addition, since the back surface of the substrate is clamped with a vacuum chuck in a lithography process or the like, it is necessary to ensure flatness of the back surface, and it is necessary to provide a process (silver paste removal) for cleaning the back surface of the substrate and the substrate holder after peeling off the substrate. . In addition, since the number of processes increases in the conventional method, the yield decreases.
The problem to be solved by the present invention is firstly to avoid the problem of fixing the substrate using silver paste, and secondly, to bring the substrate to a temperature of 800 ° C. or higher. It is to enable stable heating with good internal uniformity and reproducibility.

In order to solve the above-described problem, according to the present invention, a thin film is formed by a vapor phase method by fixing a substrate with a first metal foil, a second metal foil, and a third metal foil interposed on a substrate holder. The second metal foil has a melting point of 800 ° C. or higher, a Young's modulus of 150 × 10 ⁹ N / m ² or less, a thermal conductivity of 200 W / mK or more, and a thermal expansion coefficient of the substrate. It is made of a metal material larger than that of the holder, and the first and third metal foils are made of a metal material having a higher melting point than the second metal foil and less reactive at a higher temperature than the second metal foil. A thin film forming method is provided.
Preferably, the thickness of the first metal foil and the third metal foil is 3 μm or more and 15 μm or less.

The present invention does not use a silver paste, but a metal foil having a uniform thickness is interposed between the substrate and the substrate holder, so that the disadvantage of using the silver paste, that is, the application of the silver paste, Necessity of various steps such as evaporation of the solvent, peeling of the substrate, and cleaning, non-uniformity of the thin film due to uneven thickness of the coating film, and damage to the substrate can be avoided.
In the present invention, the second metal foil as the main component of the laminated metal foil is formed of a metal material having a Young's modulus of 150 × 10 ⁹ N / m ² or less and a thermal expansion coefficient larger than that of the substrate holder. When the substrate is heated, it expands more than the substrate and the substrate holder, filling the unevenness of the substrate back surface and the substrate holder surface so that no space is created between the substrate back surface and the substrate holder and the metal foil. The substrate can be transmitted evenly with good reproducibility. Since the second metal foil has a melting point of 800 ° C. or higher and a thermal conductivity of 200 W / mK or higher, it can withstand high temperatures and transfer the heat of the substrate holder to the substrate with low thermal resistance. . Further, since the second metal foil is sandwiched between the first and third metal foils made of a metal having higher heat resistance than the second metal foil and less reactive at a higher temperature than the second metal foil, Even during film formation, the metal foil does not stick to the substrate or the substrate holder, or the metal foils are alloyed and bonded together.
Therefore, according to the present invention, film formation at a high temperature can be performed with in-plane uniformity, reproducibility, and workability.

Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic sectional view of a film forming apparatus for explaining an embodiment of the present invention. Although the scope of the present invention is not particularly specified, film formation is performed using, for example, a laser vapor deposition apparatus shown in FIG. As shown in FIG. 1, a substrate holder 12 incorporating a heater 14 is provided in the vacuum chamber 11, a substrate 13 is placed on the upper surface thereof, and is fixed by a substrate clamper 15. A target 17 held by a target holder 16 is disposed facing the substrate 13. The target 17 can be rotated by a drive source not shown. A light introduction window 18 made of quartz glass is attached to the vacuum chamber 11, and a laser beam emitted from the laser light source 20 is irradiated onto the target 17 through the light collector 19 and the light introduction window 18. The gas in the vacuum chamber 11 is exhausted by the vacuum exhaust system 21. In the vacuum chamber 11, inert gas or oxygen gas is supplied from an inert gas cylinder 23 or an oxygen gas cylinder 22. Alternatively, a mixed gas of inert gas and oxygen gas is supplied. For the laser light source 20, for example, a pulse laser such as an Nd: YAG pulse laser or an excimer laser is used.
A ceramic substrate such as SrTiO ₃ is used for the substrate 13, and a magnetic material such as La _1-x Sr _x MnO ₃ is used for the target.
As will be described later, a metal foil is inserted between the substrate holder 12 and the substrate 13 according to the present invention. Preferably, a metal foil is also inserted between the substrate holder 12 and the substrate clamper 15.

FIG. 2A is a sectional view for explaining the first embodiment of the present invention, and FIG. 2B is an enlarged view of a portion surrounded by a circle A in FIG. is there. In FIG. 2, the same reference numerals are given to the parts common to the parts in FIG. As shown in FIG. 2A, the substrate 13 is fixed on the substrate holder 12 by tightening the screws 24. In the present embodiment, the heater 14 is disposed under the substrate holder 12. Then, as shown in FIG. 2B, the first metal foil 31, the second metal foil 32, and the third metal foil 33 are inserted between the substrate holder 12 and the substrate 13. The second metal foil 32 is a metal foil having a thickness 10 times or more than the thickness of the first metal foil 31 and the third metal foil 33, and is a first to third metal foil. It is the main component of the laminated metal foil.
A fourth metal foil 34 is inserted between the substrate holder 12 and the substrate clamper 15.

The characteristics required for the material of the second metal foil 32 are as follows. First, since it is assumed that the substrate is heated to 800 ° C. or higher in the thin film forming method of the present invention, the melting point thereof needs to be 800 ° C. or higher. And since it is necessary to embed the fine unevenness | corrugation of a board | substrate back surface and a board | substrate holder surface with a metal thin film, it has a thermal expansion coefficient larger than a board | substrate and a board | substrate holder, is rich in flexibility, and can deform | transform easily. Generally, the substrate holder of the high-temperature film forming apparatus is formed of inconel, and its thermal expansion coefficient is 11.5 to 12.5 × 10 ⁻⁶ / ° C., so it must be a material having a larger thermal expansion coefficient than this. . In addition, since it is required to be easily deformable, a material having a Young's modulus of 150 × 10 ⁹ N / m ² or less is used in the present invention. Further, since it is required to transfer the heat of the substrate holder to the substrate with a low thermal resistance, a material having high thermal conductivity is desirable. Therefore, in the present invention, a material having a thermal conductivity of 200 W / mK or more is used. Examples of materials that satisfy these requirements simultaneously include copper group elements (copper, silver, gold) and alloys mainly composed of any of these, but the most preferable material is copper, considering the melting point and price. It is. A preferable film thickness of the second metal foil is not less than 30 μm and not more than 150 μm. If the second metal foil is 30 μm or less, the unevenness of the back surface of the substrate and the surface of the substrate holder may not be sufficiently embedded. If the thickness is more than 150 μm, the thermal resistance between the substrate holder and the substrate increases. It is because thermal efficiency falls.

The functions required of the first and third metal foils are firstly to prevent the second metal foil from reacting with or welding to the substrate holder or the substrate, and secondly, It is not hindering free deformation of the second metal foil. In order to achieve the first function, a material having a melting point higher than that of the second metal foil and lower reactivity at a higher temperature than that of the second metal foil is used. Here, “reactivity is low” specifically means that it is difficult to oxidize and that it is difficult to alloy with the second metal foil. In order to achieve the second function, a certain degree of flexibility is required, and a thin film thickness is required. However, if it is too thin, the first and third metal foils crack due to thermal expansion of the second metal foil, and the second metal foil comes into contact with the substrate and the substrate holder. It is desirable that the film thickness be A preferable film thickness range is 3 μm or more and 15 μm or less, and more preferably 5 μm or more and 10 μm or less.
Preferred materials used for the first and third metal foils are heat-resistant alloys such as NiCr, inconel, incoloy, NiCrA1Y, and stainless steel.

  The metal foil inserted between the substrate holder 12 and the substrate clamper 15 may be a single metal foil as shown in the figure, but, like the substrate holder 12 and the substrate 13, three metal foils may be used. May be laminated. When a single metal foil is used as the fourth metal foil 34, the same material as the first and third metal foils is used. That is, a heat resistant alloy foil is used. When the substrate clamper 15 is heated and the substrate 13 is also heated from the side surface of the substrate clamper 15, it is desirable to use a laminated metal foil in which a material having high thermal conductivity such as copper is sandwiched between heat-resistant metal foils. . However, when the substrate is accommodated in the concave portion of the substrate holder, which will be described later, in order to suppress the heat dissipated from the substrate holder through the substrate clamper as much as possible, only a metal foil made of a material having poor thermal conductivity is used. It is desirable.

  FIG. 3A is a cross-sectional view for explaining a second embodiment of the present invention, and FIG. 3B is an enlarged view of a portion surrounded by a circle A in FIG. is there. In FIG. 3, the same reference numerals are given to the portions common to the portions in FIG. 2 is different from the previous embodiment shown in FIG. 2 in that the heater 14 is built in the substrate holder and a recess is provided on the upper surface of the substrate holder 12, and the substrate 13 is placed in the recess. It is a point that was contained. According to this configuration, since the substrate is also heated from the side surface of the substrate holder recess, the substrate temperature can be made more uniform.

A 15 mm square SrTiO ₃ substrate was fixed with a clamp to the Inconel substrate holder 12 shown in FIG. Here, both the clamp and the screw are made of Inconel. A backing plate consisting of a NiCr foil with a thickness of 8 μm as the first metal foil, a Cu foil with a thickness of 100 μm as the second metal foil, and a NiCr foil with a thickness of 8 μm as the third metal foil between the substrate and the substrate holder Inserted. In order to obtain the reproducibility of tightening and to tighten the screws uniformly, the tightening torque was adjusted using a torque driver. Thereafter, the substrate holder was placed in the film formation chamber, and the temperature on the back surface of the substrate holder was measured with a thermocouple, and the temperature was controlled to be 960 ° C. When the temperature was measured with a pyrometer at any five points on the substrate, it showed good soaking characteristics of about 880 ° C. ± 10 ° C.

1 is a schematic sectional view showing an example of a film forming apparatus used in the present invention. Sectional drawing which shows the 1st Embodiment of this invention. Sectional drawing which shows the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Vacuum chamber 12 Substrate holder 13 Substrate 14 Heater 15 Substrate clamper 16 Target holder 17 Target 18 Light introduction window 19 Condenser 20 Laser light source 21 Vacuum exhaust system 22 Oxygen gas cylinder 23 Inert gas cylinder 24 Screw 31 First metal foil 32 First Second metal foil 33 Third metal foil 34 Fourth metal foil

Claims (10)

A thin film forming method for growing a thin film by a vapor phase method by fixing a substrate with a first metal foil, a second metal foil, and a third metal foil interposed on a substrate holder, wherein the second metal The foil has a melting point of 800 ° C or higher, Young's modulus of 150 × 10 ⁹ N / m ² or lower, thermal conductivity of 200 W / mK or higher, and a coefficient of thermal expansion greater than that of the substrate holder. A thin film forming method, wherein the third metal foil is made of a metal material having a higher melting point than the second metal foil and a low reactivity at a higher temperature than the second metal foil. 2. The thin film forming method according to claim 1, wherein the thickness of the second metal foil is 30 μm or more and 150 μm or less. The thin film forming method according to claim 1 or 2, wherein the thickness of the first metal foil and the third metal foil is 3 µm or more and 15 µm or less.

4. The thin film forming method according to claim 1, wherein a recess is formed on a surface of the substrate holder, and the substrate is accommodated in the recess. 5. The thin film forming method according to claim 1, wherein one or a plurality of metal foils are interposed between the substrate holder and a substrate clamper that holds the substrate. 6. The metal foil interposed between the substrate holder and the substrate clamper has a configuration equivalent to that of the metal foil interposed between the substrate holder and the substrate. Thin film forming method. The metal foil interposed between the substrate holder and the substrate clamper is constituted only by a metal foil made of a metal material having a higher melting point than the second metal foil and a low reactivity at a higher temperature than the second metal foil. The thin film forming method according to claim 5, wherein: 8. The thin film forming method according to claim 1, wherein the first and third metal foils are formed of an alloy material containing Ni and Cr. 9. The thin film forming method according to claim 8, wherein the first and third metal foils are formed of any one of NiCr, inconel, incoloy, NiCrA1Y, and stainless steel. The thin film forming method according to claim 1, wherein the second metal foil is formed of copper or an alloy containing copper as a main component.

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