JP2799755B2 - Method for depositing oxides at the atomic layer level by vapor phase epitaxy - Google Patents

Description

The present invention relates to a method for depositing an oxide or the like on a substrate at the atomic layer level by a vapor phase growth method.

[Problems to be Solved by the Related Art and the Invention] In recent years, with the progress of chemical vapor deposition (MOCVD) using organometallic compounds as a raw material, for example, in the field of compound semiconductors, quantum Widespread application to devices. However, MOCVD has achieved epoch-making success only in the field of compound semiconductors, mainly GaAs. This is GaAs
As is selectively adsorbed on the Ga surface in the crystal, and
It is based on the chemical adsorption characteristic that Ga is selectively adsorbed on the surface, and this selectivity has made it possible to adjust the atomic layer level. At present, attention has been paid to the MOCVD method for objects other than GaAs, focusing on such selectivity. Despite attempts to deposit oxide thin films using the MOCVD method, controlled crystal growth cannot be obtained for each atomic layer as in the case of GaAs, and oxides grow randomly on the substrate. It was not too much.

Accordingly, an object of the present invention is to provide a method for growing an oxide thin film while controlling it at an atomic layer level.

[Means for Solving the Problems] The present inventors have conducted intensive studies to achieve the above object, and as a result, when forming an oxide thin film at an atomic layer level, an OH group generated on a substrate by an organometallic complex was formed. By adsorbing it, and then removing only the ligand by a predetermined operation,
They have found that a metal, which is the central atom of the complex, can be formed on the substrate in a form bonded to the O atom of the OH group.

That is, the present invention provides the following steps: a step of introducing a vapor of a metal complex having a ligand having an affinity for an OH group onto a surface of an oxide substrate having an OH group to thereby chemically adsorb the substrate; _{A step} of exposing the metal of the metal complex to the substrate surface via oxygen by decomposing the ligand of the metal complex by exposure to an atmosphere containing ₂ O to form a monoatomic layer of the metal oxide layer on the substrate surface It provides a method of forming at a level.

According to the method of the present invention, first, an oxide substrate having an OH group is prepared. For the oxide substrate that can be used in the present invention, SiO ₂ , ZnO, TiO ₂ , SrTio ₃ , MgO, etc. can be used,
In the present invention, SiO ₂ is preferable because it is easy to control the amount of surface hydroxyl groups.

Normally, the surface of an untreated oxide substrate is considered to be covered with OH groups.However, for atomic layer deposition, it is necessary that the OH groups are sufficiently covered in a thin film on the substrate surface. is there. Therefore, in the present invention, it is preferable to separately perform an OH group introduction operation. That is, according to the present invention, an OH group is formed on the surface of the oxide substrate. Examples of the formation method include a method in which the substrate is exposed to an oxygen atmosphere and a method in which the substrate is evacuated under a high vacuum (10 ^-5 Torr or less). In the present invention, the carbon-containing compound on the substrate surface is removed by oxidation. Is preferred to be exposed to an oxygen atmosphere. In other words, if the substrate temperature is generally 450-500 ° C, and if there is no spare time, completely burn the organic matter in an oxygen atmosphere at 500-600 ° C, then expose it to pure water vapor distilled and raise the temperature again. By doing so, a surface having almost any surface hydroxyl groups can be formed. Further, the oxide surface is preferably exposed to an oxygen atmosphere at a temperature of 300 to 400 ° C. By heating to such a temperature, organic components on the substrate surface evaporate, and stable OH
Only the groups will remain on the substrate surface. The OH groups on the substrate surface thus generated can be easily observed by an IR spectrum as described later.

In the next step of the method of the present invention, a vapor of a metal complex having a ligand having an affinity for an OH group is introduced to the substrate surface.

The metal complex used in the present invention is a complex having a ligand having an affinity for an OH group. And the like. The central metal atom of these complexes forms a metal species of a metal oxide to be deposited on a substrate according to the present invention, and includes, for example, transition metals such as copper, iron and manganese, alkaline earth metals, and lanthanum series elements. And the like. In particular, copper is preferable because it is extremely useful as a copper oxide for a thin film oxygen sensor, a high-temperature oxide superconductor material containing bismuth-calcium-strontium-copper, and the like. Further, a metal-like element capable of forming the above complex can also be used as the complex central atom. From these facts, as a metal complex, for example, dipivaloyl methanate copper (Cu (DP
M) ₂ ), dipivaloyl methanate calcium (Ca (DP
M) ₂ ) and the like. Various CVD devices can be used to introduce the vapor of the metal complex onto the substrate, and there is no particular limitation. The introduction of the deposit material to the substrate surface in the CVD apparatus can be easily achieved by, for example, dispersing and introducing a metal complex vapor in an argon gas onto the substrate. The metal complex is chemically adsorbed and deposited on the substrate surface by the CVD operation, but the pressure inside the container is preferably reduced to, for example, about 10 ^-6 Torr in order to remove the remaining metal complex without being adsorbed thereafter.

In the next step of the present invention, the substrate on which the complex is adsorbed is treated with H ₂
Exposure to an atmosphere containing O. By performing such an operation, only the ligand of the metal complex is removed, and a structure in which the metal that is the central atom of the complex is bonded to oxygen, for example, a Cu—O— structure is formed on the substrate.

Through the above steps, the atoms constituting the metal oxide are deposited on the substrate in a single atomic layer, and an atomically controlled metal oxide layer is obtained.

Further, the present invention provides a method for vapor-phase growing a metal oxide layer at an atomic layer level by repeating the above steps. That is, the above-described steps are repeated on the substrate obtained by the above method and on which the metal oxide is deposited in a single atomic layer. As a result, the metal oxide can be packed at a monoatomic layer level, and an oxide layer having a desired thickness and controlled by an atomic layer can be obtained.

[Operation] The present inventors have conducted studies on a method of vapor-phase growing an oxide layer other than GaAs on a substrate at an atomic layer level.
Focusing on the fact that hydroxyl groups are easily chemically adsorbed on the top surface of an oxide substrate and that metal complexes having a predetermined ligand can be selectively adsorbed on hydroxyl groups, oxygen and metal species constituting oxides are separately atomized. We have invented a method that can be deposited on a substrate while controlling it.

According to the present invention, a hydroxyl group is introduced on an oxide substrate, and then a complex capable of selectively adsorbing such a hydroxyl group, for example, Cu
When the (DMP) ₂ complex is introduced in a later step, a structure as shown in the adsorption model in FIG. 1 is formed on the substrate. In the figure, it is considered that the carbon atoms C ^* and C ^** of the ligand are chemically adsorbed with the hydrogen of the hydroxyl group adsorbed on the substrate. Furthermore, when exposing the suction structure according to an atmosphere containing water ligand is desorbed with a hydrogen of the OH groups, Cu on a SiO ₂ substrate
It is considered that a bond of -O- is formed.

The Cu-O- layer thus obtained is a layer in which Cu and O are deposited at a monoatomic level. By repeating the steps of the present invention and sequentially stacking such layers, a desired atomic layer controlled oxide layer is obtained. It will be formed on the substrate.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 Example 1 FIG. 2 shows a schematic view of a CVD apparatus used in the present invention. CVD
The apparatus mainly comprises a raw material supply system, a reactor and a discharge system. The raw material supply system is provided with a raw material source container 1 containing a metal complex, a gas line 2 connected to a reactor 4, and a gas line 3 for metal vapor. The gas line 3 is provided with an argon gas supply source 5 for diluting the metal vapor. The susceptor 7 is placed inside the reactor 4 made of quartz.
The substrate 8 held thereon is mounted, and a heater 6 for heating the substrate is provided on an outer peripheral portion of the reactor 4. The discharge system gas line 9 is connected to a rotary pump 11 via a valve 10. After setting the SiO ₂ substrate on the susceptor 7 of the CVD apparatus, oxygen gas is supplied through the gas line 2 into the container. Further, the substrate temperature was raised to 500 ° C. by the heater 6 and maintained for 2 hours. Thereafter, in order to confirm the presence of OH groups on the substrate surface, an IR spectrum was observed using a part of the substrate as a sample. FIG. 3 (a) shows the IR spectrum of the sample. A peak indicating stretching vibration of the OH group appears around 3750 cm ^-1 .

Next, the pressure inside the reactor 4 is reduced to 10 ⁻⁵ Torr while the substrate on which the OH groups are adsorbed is mounted in the CVD apparatus. Then, while supplying argon gas to the gas line 2, Cu
(DPM) Raw material source container 1 containing ₂ is heated to Cu
(DPM) ₂ Generate vapor and use argon gas / Cu (DPM) ₂
The steam mixed gas was flowed into the reactor 4 and the pressure inside the reactor 4 was maintained at about 0.1 Torr.

An IR spectrum was measured using a part of the surface of the substrate obtained at this stage as a sample. FIG. 3 (b) and FIG. 4 (b) show the results. In FIG. 3 (b), FIG.
3750cm ^-1 based on the OH stretching vibration observed in the spectrum of
Near peaks have disappeared. FIG. 4 shows an IR spectrum on a lower wavenumber side than that of FIG. 3, and a peak of CH vibration of CH ₃ group appears strongly at 2969 cm ⁻¹ in the spectrum (b) of FIG. According to the IR spectra of FIGS. 3 (b) and 4 (b), a model as shown in FIG. 1 is formed on the substrate surface, and the carbon atom of Cu (DPM) ₂ is
It is presumed that substantially all OH group hydrogen atoms adsorbed on the substrate were chemically adsorbed.

Furthermore, in order to investigate the quantitative relationship between OH groups and CH ₃ groups present on the substrate surface, the IR was measured every time Cu (DPM) _{2 was} introduced.
Measure the spectral intensity and compare CH ₃
The absorption intensity of the group was plotted. The results are shown in FIG. From the figure, it can be seen that the decrease in the absorbance of the OH group and the increase in the absorbance of the CH group correspond to the adsorption of the CH group to the OH site.

After the introduction of Cu (DPM) ₂ vapor, 10 ^-6 To
The pressure was reduced to rr, and the substrate temperature was heated to 400 ° C. afterwards,
D ₂ O vapor is introduced into the reactor 4 through the gas line 1 to maintain the pressure in the reactor 4 at 30 Torr. Thereafter, IR spectrum measurement was performed using a part of the obtained substrate as a sample. The obtained results are shown in FIGS. 3 (d) and 4 (d). For comparison, after the Cu (DPM) ₂ vapor introduction operation was completed, the substrate
The IR spectrum is shown in the spectrum (c) in those figures.

The spectra (c) and (d) in FIGS. 3 and 4 indicate that the ligand DPM of the complex adsorbed on the OH group on the substrate was removed by introducing D ₂ O vapor.

Further, in order to confirm the presence of copper atoms remaining on the substrate, a part of the substrate sample was subjected to X-ray photoelectron spectroscopy (XP
S). FIG. 6 shows the results. In the figure, the spectrum (a) is the XPS spectrum of Cu (DPM) ₂ alone, and (b)
Shows the spectrum after Cu (DPM) ₂ vapor was introduced onto the substrate, and (c) shows the spectrum after further introducing D ₂ O vapor. From this figure, a peak derived from electrons from the 2p orbit of Cu atoms appears at 932.951 eV, and it can be seen that Cu atoms remain on the substrate even after the introduction of D ₂ O. Furthermore, since the spectrum (c) does not show a satellite peak peculiar to the Cu ²⁺ spectrum and that copper is not considered to remain without being oxidized under this processing condition, Cu is in a state close to Cu ^1+. It is thought that it exists in.

The step of introducing oxygen, the step of introducing Cu (DPM) ₂ vapor, and the step of introducing H ₂ O while the substrate on which Cu—O is deposited at the atomic layer level as described above is further installed in the reactor 4.
Is repeated to obtain a copper oxide / oxide substrate laminate in which a copper oxide layer is laminated on a substrate at an atomic layer level.

[Effects of the Invention] By using the method of the present invention, it is possible to obtain an atomically controlled oxide crystal on an oxide substrate such as SiO ₂ by stacking an oxide layer at an atomic layer level. became. Therefore, the present invention is extremely useful for manufacturing various devices such as oxide superconductors, and the industrial value of the present invention in the semiconductor industry and the like is extremely high.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a state where Cu (DPM) ₂ is adsorbed on a SiO ₂ substrate on which OH groups are adsorbed. FIG. 2 is a layout diagram of a CVD apparatus used in the present invention. FIG. 3 is an IR spectrum observing the presence of OH groups on the substrate. FIG. 4 is an IR spectrum observing the presence of a CH ₃ group on the substrate. FIG. 5 is a graph in which the IR absorption intensity of the CH ₃ group due to CH vibration is plotted against the IR absorption intensity due to OH vibration on the IR spectrum. FIG. 6 is an XPS spectrum for observing the presence of Cu (DPM) ₂ or Cu present on the substrate.

Claims (10)

(57) [Claims] 1. The following steps: and a step of introducing a vapor of a metal complex having a ligand having an affinity for an OH group onto a surface of an oxide substrate having an OH group to cause chemical adsorption. _{A step} of exposing the metal of the metal complex to the substrate surface via oxygen by decomposing the ligand of the metal complex by exposure to an atmosphere containing ₂ O to form a monoatomic layer of the metal oxide layer on the substrate surface How to form at the level. 2. The following steps: a step of forming an OH group on the oxide substrate, a step of introducing a vapor of a metal complex having a ligand having an affinity for the OH group onto the surface of the substrate, and chemically adsorbing the vapor. Exposing the substrate to an atmosphere containing H ₂ O to decompose a ligand of the metal complex, thereby chemically adsorbing the metal of the metal complex onto the substrate surface via oxygen, thereby forming a metal oxide layer on the substrate surface. Is formed at the monoatomic layer level. 3. The method according to claim 1, wherein the metal complex is Cu (DPM) ₂ . 4. oxide substrate is SiO ₂ according to claim 1 or 2
The method described in. 5. The method according to claim 2, wherein the oxide substrate is exposed to an atmosphere containing oxygen to form OH groups on the oxide substrate. 6. A method in which a metal oxide layer is vapor-phase grown on a substrate surface at an atomic layer level by repeating the steps from 2). 7. The process according to claim 2, wherein the metal oxide is deposited on the substrate at a monoatomic layer level by the method of claim 1.
By vapor-phase growing a metal oxide layer on the substrate surface at the atomic layer level by repeating the above steps. 8. The method according to claim 6, wherein the metal complex is Cu (DPM) ₂ . 9. The oxide substrate according to claim 6, wherein the oxide substrate is SiO _2.
The method described in. 10. The method according to claim 6, wherein the oxide substrate is exposed to an atmosphere containing oxygen to form OH groups on the oxide substrate.