JPH07211951A - Formation of thin film - Google Patents

Abstract

PURPOSE:To reduce the breakdown of one crystalline film when the other crystalline film is formed and, at the same time, to reduce the number of thin film forming processes of a thin film forming technique for forming a plurality of crystalline films having different physical properties. CONSTITUTION:A thin film forming method includes a process in which a seed layer 2 which becomes a core for growing a crystal having different physical properties than a crystal grown by using a substrate 1 as a core on the partial surface of the substrate l which becomes the growing core of the crystal and another process in which the layer 2 is divided into a plurality of phases and a first crystalline film 3 grown from a crystal using the substrate 1 as a core is formed on the surface of the substrate 1 by depositing such a substance that its crystals are segregated on the surface of the substrate 1 or seed layer 2 and the substance follows the stoichiometry on the surface of the substrate 1 over the entire area, and then, second crystalline films 4 grown from crystals using the seed layer 2 as cores are formed on the layer 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film forming technique.
In particular, the present invention relates to a thin film forming technique for forming thin films having different physical properties on the surface of a substrate.

[0002]

2. Description of the Related Art The development of Josephson effect devices has attracted attention as an ultra-high speed device. In this Josephson effect element, a structure having a Josephson junction (SIS Josephson junction) formed by sequentially stacking a superconducting thin film, an insulating thin film, and a superconducting thin film on a substrate is a basic structure. In superconductors such as high-temperature oxide superconductors, the coherence length is extremely short, so it is necessary to form a high-quality ultra-thin film with a steep junction interface that reliably suppresses mutual diffusion near the junction interface. .

A crystal growth technique typified by a semiconductor manufacturing technique is used for forming a superconducting thin film and an insulating thin film which are components of such a junction structure. Crystal growth generally requires a high temperature of about 700 ° C. or higher, and a superconducting thin film and an insulating thin film are formed under independent process conditions such as crystal growth temperature and crystal growth pressure.

In the current crystal growth technology, it is difficult to surely suppress mutual diffusion in the vicinity of the bonded interface, a steep bonded interface cannot be formed, and a high quality ultrathin film cannot be formed. Therefore, a good Josephson junction cannot be obtained, and as a result, the Josephson effect element has not been realized.

[0005]

The following points have not been taken into consideration in the above-mentioned thin film forming technique.

(1) When forming the Josephson effect element, the superconducting thin film and the insulating thin film are formed in different steps and under mutually different process conditions. For example Y ₂ after the formation of the BaCuO _x based insulating film, Y ₁ This crystal growth by changing the process conditions on the insulating thin film is made
A Ba ₂ Cu ₃ O _y based superconducting thin film is formed. Therefore, damage due to the process conditions of the superconducting thin film occurs in the lower insulating thin film. Specifically, Y _{1 on} the surface of the insulating thin film
Ba ₂ Cu ₃ O _y based amorphous particles and polycrystalline particles are scattered and generated. Therefore, the crystallinity of a good insulating thin film, a good crystal interface between the insulating thin film and the superconducting thin film cannot be obtained,
The characteristics of the Josephson effect element deteriorate.

(2) To prevent damage to the insulating thin film, it is effective to form a buffer layer for preventing damage on the surface of the insulating thin film before forming the superconducting thin film. However, the formation of this buffer layer increases the number of steps in the thin film forming process.

(3) In a general Josephson effect element, a thin film deposition process and this deposited thin film patterning process are alternately repeated. That is, after the superconducting thin film is deposited and patterned, the insulating thin film is deposited and patterned, and further the superconducting thin film is deposited and patterned. Therefore, when patterning the upper layer thin film, mask alignment with the lower layer thin film is required, and a mask alignment margin is secured, so that fine processing cannot be realized.

The present invention has been made to solve the above problems, and the objects of the present invention are as follows.

(1) In a thin film forming technique for forming a plurality of crystal films having different physical properties, damage to the other crystal film when forming one crystal film is reduced.

(2) In the thin film forming technique, the step of forming the buffer layer is eliminated and the number of steps of the thin film forming process is reduced.

(3) In the thin film forming technique, the mask alignment margin is eliminated and fine processing is performed.

(4) In the thin film forming technique, the above objects (1) to (3) are achieved and the yield in the thin film forming process is improved.

(5) In the device formed by the thin film forming technique, the above objects (1) to (3) are achieved and the characteristics are improved.

[0015]

According to the invention described in claim 1, in a partial region on the surface of a substrate which becomes a nucleus of crystal growth,
Forming a seed layer that serves as a nucleus for growing a crystal having different physical properties with respect to a crystal that grows with the substrate as a nucleus; and performing phase separation into a plurality of crystals, and crystallizing either on the substrate surface or on the seed layer. Is deposited on the entire surface of the substrate to form a first crystal film on which crystals having the substrate as a nucleus are grown, and the seed layer is formed. And a step of forming a second crystal film on which crystals having the seed layer as a nucleus are grown.

According to a second aspect of the present invention, in the thin film forming method according to the first aspect, the substrate is Ga.
A compound semiconductor substrate or compound semiconductor film such as As is used, a semi-metal thin film such as Sb is used for the seed layer, a semiconductor thin film such as InSb is formed as the first crystal film, and the second crystal film is used. Is characterized in that a semimetal thin film such as Sb is formed.

According to a third aspect of the present invention, there is provided the thin film forming method according to the first aspect, wherein the substrate is made of Mg.
A compound substrate or compound film of O, SrTiO ₃ , NdGaO ₃ or the like is used, an insulator such as Y ₂ BaCuO _x is used for the seed layer, and Y ₁ Ba ₂ Cu is used for the first crystal film.
_{A 3} O _y based superconducting thin film is formed, and a Y ₂ BaCuO _x based insulating thin film is formed as the second crystal film.

[0018]

According to the invention described in claim 1, the following effects can be obtained in the thin film forming method.

(1) Since the seed layer is formed in advance in a partial area on the surface of the substrate, a plurality of types of first crystal film and second crystal having different physical properties are formed in one thin film forming step after the seed layer is formed. A film can be formed. Therefore, since the process conditions such as the growth temperature and the growth pressure of the first crystal film and the second crystal film can be the same in both crystal films, it is possible to damage the other crystal film when forming one crystal film. Disappear.

(2) With the above action and effect (1), when one crystal film is formed, the other crystal film is not damaged. Therefore, the purpose is to prevent damage formed between both crystal films. The buffer layer used can be abolished. Therefore, the number of steps of the thin film forming process can be reduced by an amount corresponding to the step of forming the buffer layer.

(3) Since the thin film is formed of one material layer according to the stoichiometry in which the first crystal film and the second crystal film are phase-separated and the crystals are segregated, both crystal films are formed. The mask alignment margin in the thin film formation process can be eliminated. Therefore, since this mask alignment margin can be eliminated, the first crystal film and the second crystal film can be formed in a fine planar shape.

(4) The function and effect (2) reduces the number of steps in the thin film forming process, and the function and effect (3) eliminates the mask alignment margin in the thin film forming process. The yield can be improved.

(5) Since the first crystal film and the second crystal film are formed by phase separation, there is a steep gap between the first crystal film and the second crystal film so that the crystals of both crystal films do not coexist with each other. It can be formed at a different crystal interface (clear crystal interface). Therefore,
Since the physical characteristics at the crystal interface of both crystal films can be improved, the characteristics of the device utilizing the crystal interface can be improved.

According to the invention described in claim 2, in addition to the effect of the invention described in claim 1, a semiconductor thin film such as InSb and a semi-metal thin film such as Sb having mutually different physical properties are the same. A single thin film can be formed simultaneously in the same process.

According to the invention described in claim 3, in addition to the action and effect of the invention described in claim 1, Y ₁ Ba ₂ Cu ₃ O _y based superconducting thin film and Y _{2 which} have mutually different physical properties.
The BaCuO _x based insulating thin film can be simultaneously formed as a thin film of the same layer in the same process.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

Example 1 Example 1 is a first example of the present invention in which a compound semiconductor thin film and a metalloid thin film having different physical properties are formed in the same step.

FIG. 1 and FIG. 2 show device cross sections for each step for explaining a thin film forming method which is Embodiment 1 of the present invention.

First, the substrate 1 serving as a nucleus for crystal growth of the compound semiconductor thin film is prepared. Since an InSb thin film is formed as the compound semiconductor thin film in this embodiment, a GaAs substrate is used as the substrate 1. The InSb thin film is grown on the (100) crystal plane of the GaAs substrate.

Next, as shown in FIG. 1, a seed layer 2 is formed on a part of the surface of the substrate 1. The seed layer 2 is a crystal that serves as a nucleus for crystal growth, and the seed layer 2 is formed as a nucleus for growing a crystal having different physical properties from the crystal grown with the substrate 1 as a nucleus. Since the Sb thin film is formed as the semi-metal thin film in this embodiment, the Sb thin film is used for the seed layer 2. The Sb thin film as the seed layer 2 is formed by a vapor deposition method using a metal mask. The vapor deposition rate is set to, for example, 5 nm / min, and the temperature of the substrate 1 at this time is set to room temperature. Seed layer 2 is, for example, 50n
It is formed in a film thickness of m. Further, the Sb thin film may be patterned by a photolithography technique instead of the metal mask.

Next, a substance according to the stoichiometry in which a plurality of phases are separated and crystals (Sb) are segregated on the seed layer 2 is deposited on the entire surface of the substrate 1. As the substance according to the stoichiometry, for example, InSb which is set to Sb-rich condition having Sb about 1.2 times that of In is used.
This InSb is deposited by the molecular beam epitaxial (MBE) method, and the deposition rate is set to 12 nm / min, for example. The InSb is formed to have a film thickness of 700 to 750 nm, for example. In the deposition of InSb, the temperature of the substrate 1 is set to about 240 ° C.

Under these conditions, as shown in FIG. 2, two types of crystal films having different physical properties are formed. That is, on the surface of the substrate 1, this substrate 1, that is, G
I grown according to the (100) crystal plane of the aAs substrate I
A compound semiconductor thin film 3 made of nSb is formed. Further, on the surface of the seed layer 2, a semi-metal thin film 4 made of Sb crystal-grown in accordance with the seed layer 2, that is, the crystal of Sb is formed. Therefore, the compound semiconductor thin film 3 and the semi-metal thin film 4 are simultaneously formed as thin films of the same layer in one thin film forming step, and the process conditions can be the same in forming both thin films. Further, InSb has the property of causing phase separation represented by a peritectic system and segregation of crystals,
The crystal interface between the compound semiconductor thin film 3 and the semi-metal thin film 4 is formed as a sharp crystal interface (clear crystal interface) in which crystals of both crystal films do not coexist.

The results of experiments conducted by the present inventor will be described. 3 to 5 show cross-sectional structures of samples that have been subjected to X-ray diffraction. The sample shown in FIG. 3 is obtained by directly growing an InSb thin film (compound semiconductor thin film 3) on a GaAs substrate (substrate 1), and FIG. 6 shows the X-ray diffraction result in the region indicated by reference numeral F6. The sample shown in FIG. 4 is an InSb thin film (compound semiconductor thin film 3) grown on a GaAs substrate (substrate 1) with an amorphous Sb thin film (seed layer 2) intervening over the entire surface. The X-ray diffraction result is shown in FIG. The sample shown in FIG. 5 has the same structure as that described in the above-described thin film forming method and has the same GaA
The InSb thin film (compound semiconductor thin film 3) is grown on the s substrate (substrate 1) with the Sb thin film as the seed layer 2 interposed. FIG. 8 shows the X-ray diffraction result in the region F8 (on the surface of the substrate 1) of FIG. 5, and FIG. 9 shows the X-ray diffraction result in the region F9 (on the seed layer 2).

In the sample shown in FIG. 3, InSb and Sb peaks are present in the InSb thin film (compound semiconductor thin film 3) between the diffraction angles of 20 to 30 degrees as shown in FIG. Since the seed layer 2 serving as the nucleus of Sb is not previously formed on the GaAs substrate (substrate 1), as shown in FIG.
It is presumed that Sb crystal grains 41 are phase-separated and scattered in the Sb thin film.

In the sample shown in FIG. 4, as shown in FIG. 7, only the InSb peak exists in the InSb thin film (compound semiconductor thin film 3) at the same diffraction angle portion.
It is estimated that Sb in the InSb thin film is almost absorbed by the underlying amorphous Sb thin film. In other words, InS
It is presumed that Sb in the b thin film will perform crystal growth with this seed layer 2 as a nucleus if the seed layer 2 that serves as a nucleus for crystal growth is formed.

In the sample shown in FIG. 5, there is only an InSb peak in the InSb thin film (compound semiconductor thin film 3) in the portion having the same diffraction angle as shown in FIG. Almost no Sb exists. Ideally, it is desirable that there is no Sb.
It is presumed that Sb in the InSb thin film is segregated on the surface of the Sb thin film as the seed layer 2. In addition, FIG.
As shown in (1), there is almost no InSb peak in the portion having the same diffraction angle, and if it exists, it is presumed that it is only amorphous Sb. That is, from the results shown in FIG. 9, it is estimated that Sb in the InSb thin film is segregated on the surface of the Sb thin film as the seed layer 2.

As is clear from the results of experiments conducted by the present inventor, according to the present invention, the following effects can be obtained in the thin film forming method.

(1) Since the seed layer 2 is formed in advance in a partial region on the surface of the substrate 1, a plurality of types of compound semiconductor thin films 3 having different physical properties are formed in one thin film forming step after the seed layer 2 is formed. The semi-metal thin film 4 can be formed. Therefore, the growth temperature, the growth pressure, etc. of the compound semiconductor thin film 3 and the semi-metal thin film 4
Since the process conditions can be matched for both crystal films,
When forming one crystal film, the other crystal film is not damaged.

(2) Since the above effect (1) does not damage the other crystal film when forming one crystal film, the purpose is to prevent damage between the two crystal films. The buffer layer used can be abolished. Therefore, the number of steps of the thin film forming process can be reduced by an amount corresponding to the step of forming the buffer layer.

(3) Since the compound semiconductor thin film 3 and the semi-metal thin film 4 are phase-separated into a plurality of layers and are formed of one material layer according to the stoichiometry in which crystals are segregated, both crystal films are formed. The mask alignment margin in the thin film formation process can be eliminated. Therefore, the mask alignment margin can be eliminated,
The compound semiconductor thin film 3 and the semimetal thin film 4 can be formed in a fine planar shape.

(4) The operational effect (2) reduces the number of steps in the thin film forming process, and the operational effect (3) eliminates the mask alignment margin in the thin film forming process. The yield can be improved.

(5) Since the compound semiconductor thin film 3 and the metalloid thin film 4 are formed by phase separation, the compound semiconductor thin film 3 and the metalloid thin film 4 are steep so that the crystals of both crystal films do not coexist with each other. Can be formed at various crystal interfaces. Therefore,
Since the physical characteristics at the crystal interface of both crystal films can be improved, the characteristics of the device utilizing the crystal interface can be improved.

In the sectional structure shown in FIG. 2, the surface position of the compound semiconductor thin film 3 and the surface position of the semi-metal thin film 4 do not coincide with each other, and there is a step, but this step is the film of the seed layer 2. In deposited by thick and molecular beam epitaxy
It can be reduced by controlling the In content of Sb. That is,
The surface position of the compound semiconductor thin film 3 and the surface position of the semi-metal thin film 4 can be matched, and the surface can be flattened.

Embodiment 2 This embodiment 2 is a second embodiment of the present invention in which a superconducting thin film and an insulating thin film having different physical properties are formed in the same step. Since the thin film forming method of the present embodiment is similar to the thin film forming method of the first embodiment described above, the thin film forming method of the present embodiment will be described with reference to FIGS.

First, the substrate 1 serving as a nucleus for crystal growth of the superconducting thin film is prepared. In this embodiment, since a Y ₁ Ba ₂ Cu ₃ O _y based superconducting thin film is formed as the superconducting thin film, a compound substrate of MgO, SrTiO ₃ , NdGaO ₃ or the like is used as the substrate 1.

Next, as shown in FIG. 1, a seed layer 2 is formed on a part of the surface of the substrate 1. As the seed layer 2, a Y ₂ BaCuO _x type insulating thin film is used in this embodiment.
The insulating thin film as the seed layer 2 is deposited by a radio frequency (RF) magnetron sputtering method. The target used is, for example, Y ₂ Ba _1.5 Cu _4.0 O _x . The temperature of the substrate 1 is set to 650 ° C., the RF output is set to 100 W, the sputtering gas pressure is set to 6 mtorr for Ar and 20 mtorr for O ₂ . The seed layer 2 is patterned by a metal mask or photolithography technique.

Next, a substance according to a stoichiometry in which a crystal of a superconducting thin film is segregated on the surface of the substrate 1 and an insulating thin film is segregated on the seed layer 2 on the surface of the substrate 1 is separated into a plurality of phases. Deposit on all areas of. As the substance according to the above stoichiometry, Y ₂ BaCuO _x (21
The compound in the region where the crystals of 1) and Y ₁ Ba ₂ Cu ₃ O _y (123) are mixed is used. Specifically, for example as the target _{Y 1 Ba 1. 2 Cu 2.0 O} x (Y 2 BaCuO
_x : Y ₁ Ba ₂ Cu ₃ O _y = 1: 1) is used and deposited by radio frequency magnetron sputtering. The temperature of the substrate 1 is set to 650 ° C., the RF output is set to 100 W, the sputtering gas pressure is set to 6 mtorr for Ar and 20 mtorr for O ₂ .

After depositing the substance according to the above stoichiometry, annealing is performed to activate the deposited thin film. The annealing is performed, for example, in an O ₂ gas atmosphere at 800 ° C. for 1 hour.

Under such a condition, as shown in FIG.
As shown in, two types of crystal films having different physical properties are formed. That is, on the surface of the substrate 1, Y ₁ Ba ₂ Cu ₃ O _y crystal-grown according to the crystal plane of the substrate 1, that is, the compound substrate of MgO, SrTiO ₃ , NdGaO _3, or the like.
The superconducting thin film 3 is formed. Further, on the surface of the seed layer 2, a Y ₂ BaCuO _x type insulating thin film 4 which is crystal-grown according to the crystal of the seed layer 2, that is, the Y ₂ BaCuO _x type insulating thin film is formed. Therefore, the superconducting thin film 3 and the insulating thin film 4 are simultaneously formed as thin films of the same layer in one thin film forming step, and the process conditions can be the same in forming both thin films.

The superconducting thin film 3 and the insulating thin film 4 are shown in FIG.
As shown in 0, since it has a property of phase separation and segregation of crystals, the crystal interface between the superconducting thin film 3 and the insulating thin film 4 is formed as a steep crystal interface in which the crystals of both crystal films do not coexist. To be done. Therefore, the physical characteristics at the crystal interface can be improved, and the characteristics of the Josephson effect element can be improved.

As described above, according to the present invention, in the thin film forming method, the same effects as those of the above-described first embodiment can be obtained.

The present invention is not limited to the above-mentioned embodiment, but various modifications can be made without departing from the scope of the invention.

For example, according to the present invention, even in the combination of a compound semiconductor other than InSb and a semimetal, a thin film is formed in the same layer as long as it is a substance that complies with the stoichiometry in which phase separation occurs and crystals are deflected. Can be realized. However, since As is out-diffused in the As-based compound semiconductor among the compound semiconductors, the deposition substance cannot be set to the As-rich condition, and the thin film formation according to the present invention cannot be realized.

The present invention is not limited to the case where the thin film is directly crystal-grown on the substrate surface, but a buffer layer may be formed on the substrate surface and the thin film may be crystal-grown on the buffer layer surface. In this case, as the buffer layer, the compound semiconductor thin film such as the GsAs film is used in the first embodiment, and the compound thin film such as the MgO film is used in the second embodiment. In the present invention, the substrate and the buffer layer are collectively referred to as a base.

[0055]

As described above, according to the present invention,
The following effects can be obtained.

(1) In the thin film forming technique for forming a plurality of crystal films having mutually different physical properties, damage to the other crystal film when forming one crystal film can be reduced.

(2) In the thin film forming technique, the step of forming the buffer layer can be eliminated and the number of steps of the thin film forming process can be reduced.

(3) In the thin film forming technique, the mask alignment margin can be eliminated and fine processing can be achieved.

(4) In the thin film forming technique, the effects (1) to (3) can be obtained, and the yield in the thin film forming process can be improved.

(5) In the device formed by the thin film forming technique, the above effects (1) to (3) can be obtained and the characteristics can be improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view in a first step of a device illustrating a thin film forming method that is Embodiment 1 of the present invention.

FIG. 2 is a sectional view of the device in a second step.

FIG. 3 is a cross-sectional view of a first sample for performing the X-ray diffraction.

FIG. 4 is a cross-sectional view of a second sample that performs the X-ray diffraction.

FIG. 5 is a cross-sectional view of a third sample for performing the X-ray diffraction.

FIG. 6 is a diagram showing an X-ray diffraction intensity result.

FIG. 7 is a diagram showing an X-ray diffraction intensity result.

FIG. 8 is a diagram showing an X-ray diffraction intensity result.

FIG. 9 is a diagram showing an X-ray diffraction intensity result.

FIG. 10 is a binary system phase diagram of a YBaCuO-based material.

[Explanation of symbols]

 1 substrate 2 type layer 3 semiconductor thin film or superconducting thin film 4 semimetal thin film or insulating thin film

Claims (3)

[Claims] 1. A step of forming a seed layer, which serves as a nucleus for growing a crystal having different physical properties from a crystal grown with the substrate as a nucleus, in a partial region on the surface of the substrate as a nucleus for crystal growth. A substance according to a stoichiometry in which a plurality of phases are separated and crystals are segregated either on the surface of the substrate or on the seed layer is deposited on the entire region of the surface of the substrate, and the substrate is formed on the surface of the substrate. Forming a first crystal film on which a crystal having nuclei as a core is grown and growing a crystal having a seed layer as a nuclei on the seed layer;
A method of forming a thin film, comprising: a step of forming a crystal film. 2. The thin film forming method according to claim 1, wherein the base is a compound semiconductor substrate or compound semiconductor film such as GaAs, and the seed layer is a semi-metal thin film such as Sb. A semiconductor thin film such as InSb is formed as the first crystal film, and a semi-metal thin film such as Sb is formed as the second crystal film. 3. The thin film forming method according to claim 1, wherein a compound substrate or compound film of MgO, SrTiO ₃ , NdGaO ₃ or the like is used for the base, and an insulating material of Y ₂ BaCuO _x or the like is used for the seed layer. A thin film is used, a Y ₁ Ba ₂ Cu ₃ O _y based superconducting thin film is formed as the first crystal film, and a Y ₂ B ₂ B film is formed as the second crystal film.
An aCuO _x -based insulating thin film is formed.