JP2001328900A - Method for forming thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To relax stress generated in a thin film, and improve adhesion to the thin film, and further raise the film developing rate on a substrate by the Atomic Layer Epitaxy(ALE) method. SOLUTION: In forming Al2O3 film by ALE method using TMA and H2O on a glass substrate, CH3OH evaporated before forming film or during formation of film is introduced and surface treatment for increasing surface hydroxyl group concentration of the ground surface is carried out by exposing the ground surface in gas atmosphere of CH3OH.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a thin film on a substrate by an atomic layer epitaxy (Atomic Layer Epitaxy).

[0002]

2. Description of the Related Art Atomic layer growth (Atomic Layer)
r Epitaxy (hereinafter referred to as the ALE method) is a method in which two or more kinds of raw materials (elements or compounds) are alternately supplied to utilize an adsorption reaction on a substrate surface and a difference in vapor pressure between the raw materials and a target product. This is a method of growing crystals one atomic layer or one molecular layer at a time.

[0003]

SUMMARY OF THE INVENTION In the ALE method,
The adsorption mechanism of the source gas molecules is limited to the case where the self-control type adsorption mechanism such as the Langmuir type is dominant. In the Langmuir-type adsorption mechanism, when the surface coverage of the raw material is θi, the adsorption rate constant is Ka, and the desorption rate constant is Kd under the partial pressure Pi of the raw material, the adsorption rate is Ka.
Pi (1−θi) and the desorption rate are represented by Kdθi. Here, since the adsorption rate and the desorption rate are equal, K = (Ka /
Kd), the surface coverage θi of the raw material is given by
Indicated by

[0004]

## EQU1 ## θi = KaPi / (Kd + KaPi) = KPi
/ (1 + KPi) Here, if KPi is sufficiently larger than 1, that is, if the amount of atoms or molecules present in the gas phase is supersaturated with respect to the adsorption amount, it is possible to form a monoatomic layer or a monolayer. Become.

However, even when KPi is set to a value sufficiently larger than 1, in most cases, the steric hindrance of adsorption and the adsorption sites are nonuniform on the base surface, and a monoatomic layer or a monomolecular layer cannot be formed. For example, when a layer is grown by the ALE method at about 500 ° C. by a reaction between AlCl ₃ and H ₂ O, the film formation rate becomes 0.045 nm / cycle, which is less than one molecular layer.

[0006] This may be due to the fact that KPi is not sufficiently larger than 1 due to a low reaction probability or a gas flow. Is considered to be the main cause. First, in the ALE growth process, the element or compound adsorbed on the base surface reacts with the element or compound adsorbed next.

At this time, depending on the system, the next adsorbed element or compound reacts with a plurality of already adsorbed elements or compounds. In other words, the next element or compound to be adsorbed is
The elements and compounds that have already been adsorbed to multiple adsorption sites react and bind, so the binding force (intermolecular force or Van der Waals force) of the generated target product is reduced to the elements or compounds adsorbed to adjacent adsorption sites. Therefore, microscopic distortion occurs.

[0008] Since the bond adsorbed on the base surface is a strong bond such as a hydrogen bond excluding physical adsorption adsorbed by gravity, electrostatic force, or the like, the above distortion is extremely large. For this reason, if film formation is continued by the ALE method, as a result, it is considered that a so-called tensile stress is generated in the formed thin film so that the film tends to shrink.

Here, when a bonding force is exerted between a plurality of such adsorption sites, even if all the adsorption sites are uniformly adsorbed, microscopic distortion occurs in the thin film for the above-mentioned reason. Occurs slightly. In particular, when the adsorption to the underlying surface is non-uniform, the same reaction still occurs, but in this case,
There are micropores (pores generated by a portion where an element or the like is to be adsorbed and is not adsorbed).

[0010] Since these microvoids are usually larger than the interatomic distance of the target product after the reaction, the bonding force acting on a nearby element or compound becomes larger. Therefore, when the adsorption is not uniform, the above-mentioned microscopic distortion is also increased, which causes a problem. Also, it is clear that the non-uniform adsorption on the underlying surface reduces the adhesion of the thin film.
Further, the non-uniform adsorption causes a portion where the film formation rate is partially low in the film formation region, and as a result, the whole film formation rate becomes slow.

As described above, according to the study of the present inventors, although the ALE method can obtain a thin film having an excellent surface coverage due to its growth mechanism, it is possible to obtain a thin film of the element or the compound. The incomplete adsorption of the thin film essentially generates tensile stress in the thin film, causing problems such as cracking and peeling of the thin film, and also causes problems such as a decrease in adhesion of the thin film and a low film forming rate.

The present invention has been made in view of the above problems, and has been described in view of the above-described circumstances.
It is an object of the present invention to provide a thin film forming method for forming a thin film by a method, in which stress generated in the thin film is relieved, adhesion of the thin film to a base is improved, and a film forming rate is further improved.

[0013]

According to the present invention, a process for increasing the surface density of gas adsorption sites on a base surface before or during film formation by the ALE method may be performed. It was made based on the idea of heels.

What determines the adsorption site is the hydroxyl group on the base surface. This is because a hydroxyl group generates a large bonding force due to a hydrogen bond, so that an element or a compound approaching the base can be attracted and easily adsorbed. That is, by performing the hydroxylation termination treatment for hydroxylating the base surface, the surface density of the adsorption site can be improved, and the adsorption of the raw material gas on the thin film can be promoted.

For example, when the underlying surface is made of TiO ₂ , the process of exposing the underlying surface to H ₂ O gas to generate surface hydroxyl groups on the underlying surface is considered as shown in FIG.
The H ₂ O adsorbed on the coordinatively unsaturated surface Ti ₄ ⁺ ion forms a hydrogen bond with the adjacent O ₂ ^−, and further, the OH of the adsorbed H ₂ O
Breakage of the bond produces two surface hydroxyl groups. It is considered that surface hydroxyl groups are also generated in other oxides by the chemical adsorption of H ₂ O by a substantially similar mechanism.

The invention described in claims 1 to 6 has been found as a result of an experimental study based on such a concept, and a method for forming a thin film on a substrate by an atomic layer growth method. In this case, the surface treatment for increasing the surface hydroxyl group concentration is performed on the underlying surface at least during or before the formation of the thin film.

According to this, the surface density of the adsorption sites on the base surface can be improved and the adsorption of the thin film source gas can be promoted, so that the adsorption of the elements and compounds on the base surface becomes more uniform. Therefore, the stress generated in the thin film can be reduced, the adhesion of the thin film to the base can be improved, and the film formation rate can be further improved.

Further, the invention of claim 2 is characterized in that the above-mentioned surface treatment is performed using a material different from the raw material of the thin film. This surface treatment is performed at a timing shifted from the introduction timing of the thin film raw material so as not to directly participate in the reaction for forming the thin film. However, as in the present invention, if a material different from the thin film raw material is used, the The surface treatment can be more suitably prevented from participating in the thin film forming reaction.

Here, the above-mentioned surface treatment can be performed by exposing the base surface to a gas atmosphere of molecules having hydroxyl groups (the invention of claim 3). In this case, if the gas of the molecule having a hydroxyl group is in a state where the molecule is turned into plasma (the invention of claim 4), the surface treatment can be performed more efficiently. Also, the surface treatment is
Prior to the formation of the thin film, it can be performed by spraying a liquid of a molecule having a hydroxyl group onto the base surface (the invention of claim 5).

As the molecule having a hydroxyl group used in these surface treatment methods, H ₂ O, H ₂ O ₂ , alcohols, or a combination of two or more of these can be employed.

Note that the reference numerals in parentheses of the above means are examples showing the correspondence with specific means described in the embodiments described later.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Atomic layer deposition (ALE) on a substrate
The method of forming a thin film by the method is performed by placing a substrate in a reaction furnace and introducing a raw material gas for the thin film into the reaction furnace. Here, the surface treatment (hereinafter, simply referred to as surface treatment) for increasing the surface hydroxyl group concentration on the base surface may be performed both during the film formation and before the film formation, or only during the film formation. Or may be performed only before film formation.

As the material used for the surface treatment, a compound consisting of a molecule having a hydroxyl group can be used. Specifically, H ₂ O, H ₂ O ₂ , alcohols, or a combination of two or more of these are used. Things can be adopted.
The following method can be employed as a surface treatment method using these surface treatment materials.

First, there is a method in which a compound comprising a molecule having a hydroxyl group is vaporized in advance, and the underlying surface is exposed to this gas (gas of a molecule having a hydroxyl group) atmosphere. For example,
A raw material bottle containing a compound having a hydroxyl group such as methanol or water may be vaporized by heating or the like, and then introduced into a reactor containing a substrate with a carrier gas such as N ₂ or Ar.
As a result, the lower ground of the thin film on the substrate is exposed to the gaseous atmosphere of molecules having hydroxyl groups, and the above-described surface treatment is performed on the underlying surface.

Here, when the gas of the molecule having a hydroxyl group is in a state where the molecule is converted into a plasma, the surface treatment can be performed more efficiently. That is, in the reaction furnace, a pair of electrodes which are opposed to and separated from each other are provided, a substrate is placed between these electrodes, and a gas having a hydroxyl group is introduced in a state where a high frequency voltage is applied. Then, the molecules are converted into plasma (for example, OH ^- and OH radicals are generated in CH ₃ OH), so that a more active reaction can be performed on the substrate, and efficient surface treatment can be performed.

Further, a liquid of a compound comprising a molecule having a hydroxyl group may be sprayed on the base surface. For example, it is possible to use an injector or the like to spray into a reactor in which the substrate is arranged. However, in this case, compared with the method of exposing the base surface to a gaseous atmosphere of molecules having a hydroxyl group, the number of compounds physically adsorbed is much larger, which hinders the layer growth by the ALE method.

For this reason, the substrate is slightly heated or N ₂ or A
It is desirable to remove this physically adsorbed component by using an atmosphere such as r gas. Furthermore, if a suitable amount of a liquid of a compound having a hydroxyl group is sprayed into a evacuated reactor, the compound is vaporized by rapid adiabatic expansion, so that surface treatment by spraying can be performed more efficiently.

Next, the present embodiment will be further described with reference to specific examples. Surface treatment by gas exposure of methanol (CH ₃ OH) while performing ALE growth of an Al ₂ O ₃ film as a thin film with TMA (tetramethyl aluminum, AlCl ₃ ) and H ₂ O on a glass substrate No case (Comparative Example) is shown.

First, in a thin film forming method for forming an Al ₂ O ₃ film on a glass substrate by an ALE method using TMA and H ₂ O, the CH ₂ film is formed before and during the formation of the Al ₂ O ₃ film. _Three
A case where a surface treatment with OH is performed (a specific example of the present embodiment) is shown. The flow is shown in FIG.

A glass substrate having a size of 40 mm × 40 mm and a thickness of 1.1 mm was placed in a reaction furnace. 40 Pa of the reactor
The substrate was heated under a vacuum of about 400 ° C. while flowing N ₂ gas at about 400 sccm to stabilize the substrate temperature at 100 ° C. C
H ₃ OH is vaporized in the raw material bottle at 30 ° C., and N ₂ gas 4
It was introduced into the reactor at 00 sccm for 30 seconds. This CH ₃ O
By introducing H, surface treatment before film formation was performed.

Thereafter, TMA, H ₂ O, and CH ₃ OH were introduced into the reaction furnace in the order of 400 sccm of N ₂ gas as a carrier gas. TMA and H ₂ O are vaporized in the raw material bottle at room temperature, and N ₂ gas 400 scc as a carrier gas
m into the reactor.

The gas to be supplied to the reaction furnace is prepared by first evaporating TMA to 0.1.
After the introduction for 6 seconds, N ₂ gas was introduced for 2.4 seconds as a purge. Thereafter, similarly, a film was formed with a gas introduction time of vaporized H ₂ O of 1.0 second and N ₂ purge of 1.0 second. Thereafter, in order to perform surface treatment during film formation, vaporized CH ₃ OH is changed to N ₂ gas 4.
Introduced to the reaction furnace at 00 sccm for 3 seconds, and CH ₃ O
N ₂ purge was performed at 3 sccm to exhaust H.

This TMA introduction → purge → H ₂ O introduction → purge → CH ₃ OH introduction → purge cycle was repeated 5000 times to form a film. During this time, the reactor pressure was 150
The substrate temperature was kept at 100 ° C. by a heater in the reaction furnace. After completion of the film formation, the substrate was left standing and cooled while introducing N ₂ gas at 400 sccm, and when the substrate temperature reached 70 ° C., the reactor was brought to atmospheric pressure and the substrate was taken out.

By this method, an Al film having a thickness of about 480 nm
_{A 2} O ₃ film was obtained. The deposition rate at this time is 0.096 n
m / cycle. The stress of the Al ₂ O ₃ film measured from the amount of warpage of the glass substrate before and after film formation is a tensile stress,
It was 220 MPa.

Next, as a comparative example, TM was placed on a glass substrate.
A case is shown in which an Al ₂ O ₃ film is grown by ALE using A and H ₂ O, and no surface treatment is performed. The flow is shown in FIG. A glass substrate of the same size as above is placed in a reaction furnace, and the reaction furnace is evacuated to about 40 Pa and heated to a substrate temperature of 100 ° C. while flowing N ₂ gas at about 400 sccm, similarly to the above specific example. Stabilized.

Thereafter, TMA and H ₂ O were introduced into the reaction furnace in the order of 400 sccm of N ₂ gas as a carrier gas.
First, vaporized TMA was introduced into the reaction furnace for 0.6 seconds, and then N ₂ gas was purged for 2.4 seconds as a purge for removing excess TMA existing in the gas phase other than molecules adsorbed on the substrate surface. Introduced. Thereafter, similarly, vaporized H ₂ O was added for 1.0 hour.
The N ₂ purge was formed for 4.0 seconds with a gas introduction time of 4.0 seconds.

The cycle of TMA introduction → purge → H ₂ O introduction → purge was repeated 5000 times to form a film. During this time, the pressure in the reactor was 150 to 300 Pa, and the substrate temperature was kept at 100 ° C. by a heater in the reactor.
After completion of the film formation, the substrate was left standing and cooled while introducing N ₂ gas at 400 sccm, and when the substrate temperature reached 70 ° C., the reactor was brought to atmospheric pressure and the substrate was taken out.

By this method, an Al film having a thickness of about 400 nm
_{A 2} O ₃ film was obtained. The deposition rate at this time is 0.08 nm
/ Cycle. The stress of the Al ₂ O ₃ film measured from the amount of warpage of the glass substrate before and after film formation is a tensile stress,
It was 430 MPa.

FIG. 3 is a diagram specifically showing the effect of stress relaxation of the present invention based on the results of the specific example of this embodiment and the comparative example. It can be seen that the stress was reduced when the surface treatment was performed. FIG. 4 is a diagram specifically showing the effect of improving the film forming rate of the present invention based on the results of the specific example of the present embodiment and the comparative example. When the surface treatment was performed, the film formation rate was about 1.2 times faster than when the surface treatment was not performed, and the film formation rate was also improved. In addition, it can be said that since the film formation rate has been improved, the adsorption has become uniform, and the adhesion of the thin film has also been improved.

As described above, in the ALE method, the surface treatment for increasing the surface hydroxyl concentration on the base surface is performed at least during or before the formation of the thin film, so that the adsorption sites on the base surface can be reduced. Surface density can be improved,
Since the adsorption of the thin-film source gas can be promoted, the adsorption of the elements and compounds on the base surface becomes more uniform. Therefore, the stress generated in the thin film can be reduced, the adhesion of the thin film to the base can be improved, and the film formation rate can be further improved.

Here, the surface treatment is performed by using a material (CH ₃ OH in the above example) different from the raw material of the thin film (TMA or H ₂ O in the above example).
It is possible to suitably realize that the reaction for forming a thin film is not directly involved. The surface treatment may be performed using the same material as the thin film material. For example, in the case of the above example,
The surface treatment may be performed with H ₂ O. In this case, it is sufficient to perform the cycle of H ₂ O introduced → purge as H ₂ O introduced → purge → surface treatment material as TMA introduction → purge → thin material.

Examples of the surface treatment material include molecules having an ether bond, a carboxyl group, and a carbonyl group, such as ether compounds, ketone compounds, and carboxylic compounds, in addition to molecules having a hydroxyl group. It may be selected as appropriate.

The present invention provides, for example, a protective film for covering and protecting this structure in an organic EL device having a structure in which an organic light emitting layer is interposed between a pair of electrodes on a substrate. Can be applied.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a method for forming a thin film according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a method for forming a thin film as a comparative example.

FIG. 3 is a view specifically showing the effect of stress relaxation of the thin film of the present invention.

FIG. 4 is a diagram specifically showing an effect of improving a film forming rate according to the present invention.

FIG. 5 is a view showing a presumed mechanism of a process in which a surface hydroxyl group is generated by exposure to H ₂ O when a base surface is TiO ₂ .

Continued on the front page (72) Inventor Harumi Suzuki 1-1-1, Showa-cho, Kariya-shi, Aichi F-term in DENSO Corporation (reference) 4G077 AA03 BB01 DB08 DB13 EE01

Claims (6)

[Claims] 1. A method for forming a thin film on a substrate by an atomic layer growth method, comprising: increasing a surface hydroxyl group concentration with respect to an underlayer surface at least during or before forming the thin film. A method for forming a thin film, comprising performing a treatment. 2. The method according to claim 1, wherein the surface treatment is performed using a material different from a material of the thin film. 3. The method according to claim 1, wherein the surface treatment is performed by exposing the base surface to a gas atmosphere of molecules having hydroxyl groups. 4. The method for forming a thin film according to claim 3, wherein the gas of the molecule having a hydroxyl group is in a state where the molecule is converted into a plasma. 5. The method according to claim 1, wherein the surface treatment is performed before forming the thin film.
The method according to claim 1, wherein the method is performed by spraying a liquid of a molecule having a hydroxyl group onto the base surface. 6. The compound having a hydroxyl group as H ₂ O, H ₂ O
_2, an alcohol or forming a thin film according to any one of claims 3 to 5, characterized in that a combination of two or more thereof.