JPH08222775A - Manufacture of oxide element - Google Patents

Abstract

PURPOSE: To provide a manufacturing method of an oxide element which contains a process for adjusting the conductivity of the surface layer of an oxide layer, regarding the manufacturing method of an oxide element wherein an oxide layer of perovskite structure is made to serve as a carrier transit region. CONSTITUTION: A process for superposing and forming a second oxide layer 12 of perovskite structure on a first oxide layer 11 of perovskite structure which is turned into a base is performed. By heat treatment, at least one out of the following is performed; mutual difusion of bivalent or trivalent elements constituting the first oxide layer and bivalent or trivalent elements constituting the second oxide layer 12, and mutual diffusion of 3d transition metal elements constituting the first oxide layer 11 and 3d transition metal elements constituting the second oxide layer 12. Thereby a process for forming a third oxide layer 13 on the surface layer or the surface of the first oxide layer 11 is contained. The conductivity of the third oxide layer 13 is different from that of the first oxide layer 11 and that of the second oxide film 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an oxide element, and more particularly, to a method for manufacturing an oxide element having an oxide layer having a perovskite structure as a carrier transit region.

[0002]

2. Description of the Related Art Research and development of memory applications of ferroelectric and high-dielectric oxides have become popular. For example, LaSrCoO 2 and CaRuO 2 are attracting attention as electrode applications, and some oxides having a perovskite structure have characteristics that semiconductors do not have, such as superconductivity, ferromagnetism, and metal-insulator transition.

Utilizing such various characteristics, including non-volatile memory and transparent transistor display elements,
There is a possibility of realizing various new functional elements that semiconductors do not have. In addition, there is a possibility of building a field called oxide electronics beyond the auxiliary position of silicon electronics. Integration technology using oxides will be
It is expected to advance with the development of oxide devices.

As one example of oxide devices, a dielectric base transistor using a SrTiO ₃ substrate has been proposed. In this dielectric base transistor, as shown in FIG. 5, tunnel barrier layers 2 and 3 made of silicon are formed at two locations on a top surface of a dielectric base layer 1 made of a SrTiO ₃ substrate having a high dielectric constant. The emitter layer 4 and the collector layer 5 are formed on the tunnel barrier layers 2 and 3. Further, a metal base electrode 6 is formed on the lower surface of the high dielectric constant base layer 2, and the potential of the dielectric base layer 1 is controlled by the potential applied to the base electrode 6.

When electrons are supplied to the emitter layer 4 at a low temperature, the electrons pass through the tunnel barrier layer 2 therebelow by the tunnel effect and travel on the surface layer of the dielectric base layer 1 while the other tunnel barrier layer 3 is formed. To reach the collector layer 5 over the barrier. In this case, when the voltage applied from the base electrode 6 to the dielectric base layer 1 is changed, the amount of carriers injected from the emitter layer 4 into the dielectric base layer is changed, which controls the current of the transistor. Become.

By the way, changing the conductivity of the surface layer of an oxide substrate such as SrTiO ₃ used as the dielectric base layer 1 is useful for adjusting the characteristics of the device. The method is Nb or La by vapor deposition or sputtering.
A method of depositing a metal such as the above on the surface of the oxide substrate and then diffusing the metal on the surface of the oxide substrate by heat treatment is conceivable.

[0007]

However, metals such as Nb and La do not diffuse into the SrTiO ₃ substrate even by the heat treatment at about 1000 ° C., the crystal structure of the SrTiO ₃ substrate does not change, and Ti sites are not formed. It is difficult to replace Nb or Sr site with La. The present invention has been made in view of such a problem, and an object thereof is to provide a method for manufacturing an oxide element including a step of adjusting the conductivity of the surface layer of the oxide layer.

[0008]

[Means for Solving the Problems]
As illustrated in FIG. 2, a step of forming second oxide layers 12 and 15 having a perovskite structure on the first oxide layers 11 and 14 having a perovskite structure, which are underlying layers,
By the heat treatment, the divalent or trivalent element constituting the first oxide layers 11 and 14 and the second oxide layers 12 and 1 are formed.
Interdiffusion of divalent or trivalent elements forming 5 and 3d transition metal element forming the first oxide layers 11 and 14 and 3d transition metal forming the second oxide layers 12 and 15 By performing at least one of mutual diffusion of elements, the first oxide layers 11 and 14 and the second oxide layer 12 are formed on the surface or surface of the first oxide layers 11 and 14. Third oxide layer 1 having a conductivity different from 15
The method for manufacturing an oxide element is characterized by including the steps of forming 3, 16.

Alternatively, as illustrated in FIG. 2, the first oxide layer 11 is made of titanium oxide containing the element A,
The second oxide layer 12 is made of titanium oxide containing the element a, and the third oxide layer 13 is made of titanium oxide containing the element A and the element a (where A and a are divalent). Or a trivalent element) to solve the problem.

Alternatively, as illustrated in FIG. 3, a first oxide layer 17 having a perovskite structure doped with an electron doping element and a second oxide layer having a perovskite structure doped with a hole doping element. A layer of at least the vicinity of the interface between the first oxide layer 17 and the second oxide layer 18 by interdiffusing the electron-doping element and the hole-doping element by a process of stacking 18 and heat treatment. The problem is solved by a method for manufacturing an oxide element, which is characterized by changing the carriers of

Alternatively, as illustrated in FIG. 4, a first oxide layer 20 having a perovskite structure having a deficiency in constituent element sites and a perovskite structure having a higher conductivity than the first oxide layer 20. The second oxide layer 21 and the second oxide layer 21 are overlapped with each other, and the defects are propagated to the second oxide layer 21 by a heat treatment,
And a step of reducing the electrical conductivity of No. 1).

[0012]

[Operation] According to the present invention, the oxide having a perovskite structure has substantially the same lattice constants at the cut surface of the metal-oxygen surface, and another oxide layer having a perovskite structure is formed on the oxide layer having a perovskite structure. Taking advantage of the nature of the oxide of the perovskite structure that epitaxial growth is often possible, A ′ is formed on the ABO ₃ underlying oxide layer.
After growing the B'O ₃ thin film, a quaternary A
By forming the A'BB 'solid solution layer or the binary solid solution layer of AA' or BB ', the underlying oxide layer and the thin film oxide layer form a solid solution having different conductivity. However, A and A'are divalent or trivalent metal ions, B and B'are 3d transition group metals, and O is oxygen.

According to the present invention, the second oxide having the perovskite structure is deposited on the first oxide layer having the perovskite structure, and then the first oxide layer and the second oxide are heat-treated. The divalent or trivalent elements forming each layer are mutually diffused and at least one of the 3d transition metal elements forming each of the first oxide layer and the second oxide layer is mutually diffused. A third oxide layer having a conductivity different from that of the first oxide layer and the second oxide layer is formed on the surface layer or the surface of the one oxide layer.

The third oxide is formed by replacing elements having different valences contained in the first oxide layer and the second oxide layer, and carriers are introduced by the replaced elements. It has a wide range of conductivity from insulator to metal. In addition, after forming a second oxide layer of a perovskite structure in which a hole-doping element is introduced on a first oxide layer of a perovskite structure in which an element for electron-doping is introduced, a second oxide layer for electron-doping is formed by heat treatment. Since the element and the hole doping element are interdiffused to change the carriers on the surfaces of the second oxide layer and the first oxide layer, the conductivity of the region is adjusted.

Furthermore, after forming a second oxide layer having a conductive perovskite structure on the first oxide layer having a perovskite structure having a deficiency of constituent elements, the first oxide layer is heat-treated. The defects inside are propagated to the second oxide layer. As a result, the conductivity of the second oxide layer changes so as to decrease.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a sectional view showing a step of controlling the conductivity of the surface of an oxide layer according to the first embodiment of the present invention.

First, as shown in FIG. 1 (a), the resistivity is 1
Resistivity of 1 × on LaMnO ₃ substrate (underlayer) 11 of 0Ωcm
A 10 ⁻³ Ωcm LaMn _1-x1 Ni _x1 O ₃ layer 12 is formed by laser ablation to a thickness of 100 nm. Note that x1 is Ni
Shows the composition ratio of. Next, in a gas atmosphere in which hydrogen (H 2) is mixed at 5% and helium (He) is mixed at 95%.
LaMnO ₃ substrate 11 and LaMn _1-x1 Ni _x1 O ₃ layer 12 are placed and 1
Heat them for 2 hours at a temperature of 000 ° C. As a result, Mn in the LaMnO ₃ substrate 11 and LaMn _1-x1 Ni _x1 O ₃ layer 12
Since Ni diffuses into each other, the surface layer of LaMnO ₃ substrate 11 and LaMnO _3
A metal-insulator transition occurs in the _1-x1 Ni _x1 O ₃ layer 12, and the transition region is La with a resistivity of 10 Ωcm or less as shown in Fig. 1 (b).
It becomes Mn _1-x1-y Ni _{x1 + y} O ₃ solid solution 13. Note that y represents the composition ratio of Ni.

LaMn_1-x1-yNi_{x1 + y}O₃The solid solution 13 is a metal
Therefore, the resistivity can be changed by changing the composition ratio x, y or heating.
1 × 10 by changing the temperature^-3Ωcm to 10Ωcm range
Change to the desired value in the box. In this example, LaMnO₃As a substrate
But the general formula ABO₃Of the perovskite structure displayed by
An oxide may be used as the base. Further, in this example, the oxide
LaMn on the substrate _1-x1Ni_x1O₃Layer 12 was formed with the general formula
abO₃Uses perovskite structure oxide
May be. Here, A and a are divalent or trivalent metal ions.
B, b are 3d transition metals, and O is oxygen. Element A,
B, a, and b may each be two elements.

In this case, the A _{1 -Z} a _Z B _{1 -Y} b _Y O ₃ solid solution is formed on the surface layer of the substrate made of ABO ₃ . In addition, Z and Y have shown the composition ratio, respectively. (Second Embodiment) FIG. 2 is a sectional view showing a step of controlling the conductivity of the surface of an oxide layer according to the second embodiment of the present invention.

First, as shown in FIG. 2 (a), the resistivity is 1
A LaTiO ₃ layer 15 having a resistivity of several Ωcm is formed by laser ablation to a thickness of 10 nm on a SrTiO ₃ substrate 14 having a size larger than × 10 ⁵ Ωcm. Ti in SrTiO ₃ is tetravalent,
Ti in LaTiO ₃ is trivalent. Next, H is 5% and He is 95
%, The SrTiO ₃ substrate 14 and the LaTiO ₃ layer 15 are placed in an atmosphere of gas mixed at a ratio of 10%, and they are mixed at a temperature of 1010 ° C.
Heat for hours.

As a result, Sr and LaTi in the SrTiO ₃ substrate 14 are
La in the O ₃ layer 15 interdiffuses with the surface layer of the SrTiO ₃ substrate 14.
A metal-insulator transition occurs in the LaTiO ₃ layer 15, and the transition region has a resistivity of 10 ⁻³ to 10 ⁻⁵ Ωcm as shown in FIG. 2 (b).
It becomes La _1-x2 Sr _x2 TiO ₃ solid solution 16. This La _1-x2 Sr _x2 TiO ₃
The solid solution 16 is in a state in which holes are doped with Sr. It should be noted that x ₂ represents the composition ratio of Sr, and the metal-insulator transition occurs when the composition ratio x 2 is about 0.05 or more.

Since the atmosphere is slightly reduced due to the presence of hydrogen, oxygen deficiency is slightly generated in the SrTiO ₃ substrate 14. The deficiency is eliminated by forming a La _{1 -x2} Sr _x2 TiO ₃ solid solution 16 and then performing a heat treatment in an oxygen atmosphere at 600 ° C. for 2 hours. The conductivity of La _1-x2 Sr _x2 TiO ₃ solid solution 16 changes depending on the heating temperature. For example, when the heating temperature is 980 ° C., the carrier areal density of the solid solution is about 1 × 10 ¹³ / cm ² , the mobility is 200 cm ² / Vs, and when the heating temperature is 1000 ° C., the carrier areal density is about 1 × 10 ¹⁵ / cm ² , and the mobility is 35.
It changes to 00 cm ² / Vs.

In this embodiment, SrTiO ₃ is used as the substrate, but an oxide having a perovskite structure represented by the general formula ABO ₃ may be used as a base. Although the LaTiO ₃ layer is formed on the substrate in this embodiment, an oxide having a perovskite structure represented by the general formula abO ₃ may be used. here,
A and a are divalent or trivalent metal ions, B and b are 3d transition metals, and O is oxygen.

In this case, an A _{1-z az} B _1-Y b _Y O ₃ solid solution is formed on the surface layer of the underlayer made of ABO ₃ . (Third Embodiment) FIG. 3 is a sectional view showing a step of controlling the conductivity of the surface of an oxide layer according to a third embodiment of the present invention.

First, as shown in FIG. 3 (a), a resistivity of 10
^-3 on to 10 ^-4 [Omega] cm of SrTi _1-y3 Nb _y3 O ₃ substrate 17, to form a SrTi _1-x3 Al _x3 O ₃ layer 18 of resistivity to 10 ² [Omega] cm to a thickness of 10nm by laser ablation. In this case, pentavalent Nb replaces tetravalent Ti and becomes an electron supply dopant, and trivalent Al replaces tetravalent Ti and becomes a hole supply dopant. In addition, x3 shows the composition ratio of Al and y3 shows the composition ratio of Nb.

Next, the _{H 5%, SrTi 1-y3} Nb y3 O 3 substrate 17 and SrTi in an atmosphere of a gas in a mixing ratio of 95% of He
Place _1-x3 Al _x3 O ₃ layer 18 and heat them at a temperature of 1200 ° C. for 2 hours. As a result, the SrTi _1-y3 Nb _y3 O ₃ substrate 17
Nb and Al in the SrTi _1-x3 Al _x3 O ₃ layer 18 interdiffuse to form Sr
The surface layer of the Ti _1-y3 Nb _y3 O ₃ substrate 17 and the SrTi _1-x3 Al _x3 O ₃ layer 18 are composed of the SrTi _1-x3-Z2 Nb _Z1 Al _Z2 O ₃ solid solution 19 as shown in FIG. 3 (b).
Becomes In the SrTi _{1-x3-Z 2} Nb _Z1 Al _Z2 O ₃ solid solution 19, the hole carriers and the electron carriers compensate each other and the conductivity decreases or becomes zero. In addition, z1 is the composition ratio of Nb, and z2 is
The composition ratio of Al is shown.

[0027] Since the atmosphere in which the heat treatment is a slight reduction _{atmosphere, SrTi 1-y2 Nb y2 O} 3 in order to eliminate the crystals generated in the substrate 17, in an oxygen atmosphere at 600 ° C. After forming the solid solution 19 2 Perform heat treatment for an hour. In this embodiment, Nb-doped SrTiO ₃ is used as the substrate, but an oxide having a perovskite structure represented by the general formula ABO ₃ containing an electron supply dopant or a donor may be used as a base. Also, in this example, an Al-doped SrTiO ₃ layer was formed on the substrate, but an oxide of the perovskite structure represented by the general formula abO ₃ containing a hole-supplying dopant or acceptor was used. May be. Here, A and a are divalent or trivalent metal ions, B and b are 3d transition metals, and O is oxygen. (Fourth Embodiment) FIG. 4 is a sectional view showing a step of controlling the conductivity of the surface of an oxide layer according to a fourth embodiment of the present invention.

First, as shown in FIG. 4 (a), La having a resistivity of 1 × 10 ⁻⁴ Ωcm was formed on a Sr _0.95 TiO ₃ substrate 20 having Sr deficiency.
_{The 0.5} Sr _0.5 TiO ₃ layer 21 was laser ablated to 10
It is formed to a thickness of nm. Next, the Sr _0.95 TiO ₃ substrate 20 and
The La _0.5 Sr _0.5 TiO ₃ layer 21 is placed and they are heated at a temperature of 1010 ° C. for 2 hours. Thereby, the Sr _0.95 TiO ₃ substrate 20
The internal defects propagate to the La _0.5 Sr _0.5 TiO ₃ layer 21 and are shown in Fig. 4 (b).
As shown in Fig. ₃ , the La _0.5 Sr _0.5 TiO ₃ layer 21 is formed of La _0.5 Sr _0.5-d Ti.
It becomes the O ₃ layer 22. In addition, d shows the composition ratio of Sr smaller than 0.5.

The resistivity of the La _0.5 Sr _0.5-d TiO ₃ layer 22 is 10 times that of the La _0.5 Sr _0.5 TiO ₃ layer 21 depending on the value of the composition ratio d.
The size can be changed to about 1000 times. In this example
Although Sr _0.95 TiO ₃ deficient in Sr was used as the substrate, an oxide having a perovskite structure represented by the general formula ABO ₃ having deficiency may be used as a base. In addition, although the La _0.5 Sr _0.5 TiO ₃ layer was formed on the substrate in this example, an oxide having a perovskite structure represented by the general formula abcO ₃ containing a dopant supplying electrons or holes was used. Good. Here, A and a are divalent or trivalent metal ions, and B and b are 3
d transition metal, c is hole or electron donating dopant, O is oxygen. (Other Examples) The thickness of the oxide layer on the substrate is 200.
When the thickness is less than or equal to nm, all of the oxide layer becomes a solid solution as described above due to heat, but when it is thicker than 200 nm, the upper layer portion of the oxide layer does not change to a solid solution, and The layer becomes a solid solution.

The substrate on which the above solid solution is formed becomes an oxide element such as a transistor by forming the tunnel layer and electrodes as shown in FIG. The electrical characteristics of the above oxides and solid solutions are shown by resistivity, but may be shown by conductivity.

[0031]

As described above, according to the present invention, the second oxide having the perovskite structure is deposited on the first oxide layer having the perovskite structure, and then the first oxide is heat-treated. At least one of divalent or trivalent elements forming each of the layer and the second oxide layer and at least one of 3d transition metal elements forming each of the first oxide layer and the second oxide layer Interdiffusion causes the formation of a third oxide layer having a conductivity different from that of the first oxide layer and the second oxide layer on the surface or surface of the first oxide layer. , A third oxide formed by replacing elements having different valences contained in the first oxide layer and the second oxide layer is an insulator by introducing carriers by the replaced element. Can obtain a wide range of conductivity from metal to metal .

Further, after the second oxide layer of the perovskite structure in which the element for hole doping is introduced is formed on the first oxide layer of the perovskite structure in which the element for electron doping is introduced, a heat treatment is performed. Since the electron-doping element and the hole-doping element are interdiffused to change the carriers on the surfaces of the second oxide layer and the first oxide layer, the conductivity of the region can be adjusted.

Further, after forming a second oxide layer having a conductive perovskite structure on the first oxide layer having a perovskite structure having a deficiency of a constituent element, heat treatment is performed in the first oxide layer. Since the deficiency of 1 was propagated to the second oxide layer, the conductivity of the second oxide layer can be changed to be small.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a process of a first embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the process of the second embodiment of the present invention.

FIG. 3 is a sectional view showing a process of the third embodiment of the present invention.

FIG. 4 is a sectional view showing a process of the fourth embodiment of the present invention.

FIG. 5 is a cross-sectional view showing an example of an oxide device using an oxide substrate formed by a conventional method.

[Explanation of symbols]

11 LaMnO ₃ substrate 12 LaMn _1-x1 Ni _x1 O ₃ layer 13 LaMn _1-x1-y Ni _{x1 + y} O ₃ solid solution 14 SrTiO ₃ substrate 15 LaTiO ₃ layer 16 La _1-x2 Sr _x2 TiO ₃ solid solution 17 SrTi _{1- y2} Nb _y2 O ₃ substrate 18 SrTi _1-x2 Al _x2 O ₃ layer 19 SrTi _1-x2-Z2 Nb _Z1 Al _Z2 O ₃ solid solution 20 Sr _0.95 TiO ₃ substrate 21 La _0.5 Sr _0.5-d TiO ₃ layer 22 La _0.5 Sr _0.5-d TiO ₃ layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H01B 1/08 H01B 1/08 13/00 501 13/00 501Z H01L 39/02 ZAA H01L 39/02 ZAAB

Claims (4)

[Claims] 1. A step of forming a second oxide layer having a perovskite structure on a first oxide layer having a perovskite structure, which is an underlayer, and a divalent metal forming the first oxide layer by heat treatment. Alternatively, interdiffusion of a trivalent element and a divalent or trivalent element forming the second oxide layer, and forming a 3d transition metal element forming the first oxide and the second oxide At least one of the interdiffusion of the 3d transition metal element with the conductivity of the first oxide layer and the second oxide layer on the surface layer or surface of the first oxide layer. And a step of forming third oxide layers different from each other. 2. The first oxide layer is made of titanium oxide containing an element A, the second oxide layer is made of titanium oxide containing an element a, and the third oxide layer is made of an element. The method for producing an oxide element according to claim 1, wherein the oxide is a titanium oxide containing A and element a (wherein A and a are divalent or trivalent elements). 3. A step of forming a first oxide layer having a perovskite structure doped with an element for electron doping and a second oxide layer having a perovskite structure doped with an element for hole doping in an overlapping manner, and a heat treatment. An oxide characterized in that the electron-doping element and the hole-doping element are interdiffused to change carriers in at least a layer near the interface between the first oxide layer and the second oxide layer. Device manufacturing method. 4. A first oxide layer having a perovskite structure having a deficiency in a constituent element site and a second oxide layer having a perovskite structure having higher conductivity than the first oxide layer are overlapped with each other. And a step of causing the defects to propagate to the second oxide layer by heat treatment to reduce the conductivity of the second oxide layer. .