JP2001220294A - Method for forming film by atomic layer epitaxial growing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a layer structure in which aluminum oxide and titanium oxide are separated and do not mix each other, in a film forming method in which an insulating membrane is formed by alternately laminating the aluminum oxide and the titanium oxide by using an ALE method. SOLUTION: This method for forming a film is provided by setting a base substrate temperature at which the aluminum oxide and the titanium oxide do not mix with each other based on the aimed film thickness of the aluminum oxide and the titanium oxide by utilizing a phenomenon in that when the film thickness of the titanium oxide becomes smaller, then the base substrate temperature so as not to mix the titanium oxide with the aluminum oxide, becomes higher and a conditional zone R1 for realizing such layer structure having the separated aluminum oxide and titanium oxide, moves to high temperature side, and forming the film at the above set base substrate temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an atomic layer epitaxial growth method (atomic layer epitaxy method,
A method for forming an insulating film in which aluminum oxide and titanium oxide are alternately stacked by the ALE method is used for, for example, an insulating film for a display, an insulating film of a semiconductor, and a passive coating of various materials. Can be

[0002]

2. Description of the Related Art For example, a method described in Japanese Patent Application Laid-Open No. 64-5440 is related to this type of film forming method by the ALE method. This is because the aluminum oxide and the dielectric are made to alternately perform the reaction of producing aluminum oxide by aluminum chloride and water and the reaction of producing titanium oxide by titanium chloride and water in the reaction chamber. This is to form an insulating film (ATO film) having excellent insulating properties, in which certain titanium oxides are alternately laminated.

[0003]

SUMMARY OF THE INVENTION However, when the present inventors prototyped an insulating film based on the above-mentioned conventional gazette, they found that a layer structure in which aluminum oxide and titanium oxide were not properly separated was formed. It was found that the structure was a mixture of aluminum oxide and titanium oxide.

[0004] The present inventors have developed a TEM (transmission electron microscope).
According to observations, both materials are in an amorphous state in a layer structure where aluminum oxide and titanium oxide are properly separated, whereas in a mixed structure portion, they are crystallized (aluminum oxide). And titanium oxide). This is considered to be due to the fact that crystallization progresses over each layer with the titanium oxide crystal as a nucleus.

[0005] In a structure in which aluminum oxide and titanium oxide are not separated layers but mixed, a phenomenon in which current leaks through crystal grain boundaries tends to occur. Further, in some cases, titanium oxide as a resistor penetrates through aluminum oxide as an insulating film and causes current leakage. There is a problem that the performance of the insulating film is deteriorated due to the leak current, and the durability of the insulating film is deteriorated. For this purpose, it is necessary to form a layer structure which is not separated from the other materials and is properly separated.

The present invention has been made based on the above-mentioned problems newly found by the present inventors. The object of the present invention is to alternately laminate aluminum oxide and titanium oxide by the ALE method. In a film formation method for forming an insulating film, an object is to realize a layer structure in which aluminum oxide and titanium oxide are separated without being mixed.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above object, it is found that aluminum oxide and titanium oxide are easily mixed unless the film forming temperature is lowered as the thickness of titanium oxide increases. Was found experimentally (see FIG. 1). The inventions described in claims 1 to 4 have been made based on the results of this study.

That is, in the present invention, a film forming temperature is set based on the film thickness of aluminum oxide and titanium oxide so that aluminum oxide and titanium oxide are not mixed. It is characterized in that the insulating film is formed at the formed film forming temperature. Thereby,
A layer structure in which aluminum oxide and titanium oxide are separated without being mixed can be realized.

Here, the thickness of the aluminum oxide is set to 5 nm.
When the film formation temperature is set to 400 ° C. or less, a separated layer structure can be realized regardless of the thickness of the titanium oxide film. In this case, the film formation temperature is preferably set to less than 450 ° C., and when the thickness of titanium oxide is set to 1.1 nm or more, the film formation temperature is preferably set to less than 500 ° C. (see FIG. 1). ).

Further studies have shown that a mixed structure of aluminum oxide and titanium oxide hardly occurs in a portion close to the base (substrate), and extends from a middle portion of the laminated structure to a portion on the surface side of the insulating film. It was found that it was easy to occur.
Furthermore, it was found that the degree of disorder in the layer structure became more severe from the middle of the laminated structure, which is the starting point of the occurrence of the mixed structure, to the portion on the surface side of the insulating film.

From the above, since the flatness is inferior in the middle of the laminated structure as compared with the portion close to the base, crystallization with the titanium oxide crystal as a nucleus occurs. Irregularities occur and the flatness of the layer structure deteriorates,
It is considered that the crystallization of titanium oxide is further promoted by the deterioration of the flatness. Therefore, an experimental study was conducted on the assumption that a means for flattening irregularities due to crystallization of titanium oxide may be formed in the laminated structure.

[0012] The invention of claim 5 is based on the result of this examination, and according to the invention of claim 5,
In order to flatten the stacked structure, at least one or more layers of flattening aluminum oxide having a thickness larger than a predetermined thickness of the alternately stacked aluminum oxide are formed in the middle of the stacked structure. I have.

According to this, by forming at least one layer of thick aluminum oxide for flattening in the middle of the laminated structure, it is possible to absorb the unevenness of the layer plane caused by the crystallization of titanium oxide. Therefore, the disordered layer structure is flattened by the flattening aluminum oxide, so that the progress of crystallization over each layer can be suppressed.

Therefore, according to the present invention, a layer structure in which aluminum oxide and titanium oxide are separated without being mixed can be realized. Here, if the predetermined thickness of the aluminum oxide is 5 nm, and if the thickness of the aluminum oxide for flattening is 20 nm, the effect of the invention of claim 5 can be exhibited well.

The invention according to claim 7 is based on the fact that a means for preventing the progress of crystallization is formed in each titanium oxide layer. During the formation, the film formation of titanium oxide is temporarily stopped during the formation, and after the film formation of aluminum oxide,
By forming titanium oxide again, each titanium oxide layer has a sandwich structure in which aluminum oxide is sandwiched between titanium oxides.

According to the present invention, each titanium oxide layer can have a sandwich structure in which aluminum oxide is sandwiched between titanium oxides. Therefore, the aluminum oxide sandwiched in each titanium oxide layer serves as a barrier. In addition, the progress of crystallization of titanium oxide can be prevented. Therefore, according to the present invention, it is possible to realize a layer structure in which aluminum oxide and titanium oxide are separated without being mixed.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment)
The present invention relates to a method of forming an ATO film as an insulating film by an LE (atomic layer epitaxial growth) method, and this film forming method can be realized by a film forming apparatus used in a normal ALE method.

Although not shown, a general film forming apparatus of this type includes a reaction chamber for accommodating a substrate for film formation, a heater provided near the reaction chamber for heating the substrate by radiation or the like, and a gas used for the reaction. A supply system for supplying the reaction chamber and an exhaust system for exhausting gas in the reaction chamber are provided. Further, as a substrate for film formation, a glass substrate for a display, a silicon substrate for a semiconductor element, or the like can be employed.

In the present embodiment, the reaction of forming aluminum oxide (Al ₂ O ₃ ) with aluminum chloride (AlCl ₃ ) and water (H ₂ O) and titanium chloride (TiC)
l ₄ ) and water to generate titanium oxide (TiO ₂ ) alternately in the reaction chamber, whereby Al ₂ O _{3 as} an insulator and TiO _{2 as a} dielectric were alternately laminated. This is for forming an insulating film (ATO film) having excellent insulating properties.

As a film forming method, first, a substrate placed in a reaction chamber is heated by a heater to a temperature at which a desired reaction occurs. When the substrate temperature (film formation temperature) reaches a temperature at which a film can be formed, aluminum chloride gas (AlCl ₃
Gas) together with a nitrogen gas (N ₂ gas) as a carrier gas is introduced into the reaction chamber, flows near the substrate, and is adsorbed on the substrate. Thereafter, in order to remove excess gas other than the gas adsorbed on the substrate, only N ₂ gas is flown and N ₂ purge is performed.

Further, H ₂ O is introduced into the reaction chamber together with the N ₂ gas, flows near the substrate, and reacts with AlCl ₃ on the substrate to form an Al ₂ O ₃ layer as a target thin film. Thereafter, in order to remove excess gas other than the gas used for the reaction, the N ₂ purge is performed again. Thus, one cycle of Al ₂ O ₃ consists of two reactant pulses, AlCl ₃ + purge + H ₂ O + purge, and two purge pulses.

One cycle of such a gas is repeated.
With the above, Al having a desired film thickness _TwoO_ThreeForming a layer
Can be. TiO_TwoAlso for the layer, TiCl_Four+ Purge
+ H _TwoTo repeat one cycle consisting of O + purge
It can be formed more similarly. And both these layers
The insulating film is formed by alternately forming a film of
be able to.

Each of the film forming materials (AlC
l ₃ , H ₂ O, and TiCl ₄ ) are each stored in a solid or liquid state in a separate container (not shown) provided in the film forming apparatus, and sublimated or evaporated in each container to produce a reaction gas. At a desired temperature (container temperature) such that the temperature rises. By controlling a valve of a supply system, the gas in each container is supplied to the reaction chamber together with a predetermined flow rate of N ₂ gas, or only the N ₂ gas flows.

In the film forming method by the ALE method,
As a result of intensive studies, it is determined whether the layer structure is maintained or disturbed.
It has been found that the film thickness and film forming temperature of l ₂ O ₃ and TiO ₂ are the dominant factors. Al ₂ O ₃ and T with a total film thickness of 250 nm
In the case where an insulating film made of iO _{2 is} formed, an example in which film forming conditions for forming a layer structure without mixing each material will be described.

Here, for example, the process pressure (pressure in the reaction chamber) is, for example, about 200 Pa, and the carrier gas is N.
The flow rate of the _two gases was 3 liters / minute, the container temperature of the AlCl ₃ gas was 151 ° C., the container temperature of the H ₂ O gas was 42 ° C., and T
The container temperature of the iCl ₄ gas was 30 ° C. Further, a normal glass substrate was used as the substrate.

One cycle of Al ₂ O ₃ is AlCl ₃ + purge + H ₂ O + purge as described above, and the time of each pulse is, for example, 0.5 seconds + 1.0 seconds + 0.8.
Seconds + 2.0 seconds. On the other hand, one cycle of TiO ₂ is TiCl ₄ + purge + H ₂ O + purge as described above, and the time of each pulse is, for example, 0.4 seconds + 1.0 seconds + 0.6 seconds + 2.0 seconds. did.

Under such film forming conditions, the thickness of the Al ₂ O ₃ single layer was set to 5 nm, and the substrate temperature (the film forming temperature in the present invention) and the thickness of the TiO ₂ single layer were variously examined. did.
Incidentally, in the above film forming conditions, by repeating 111 times the cycle of the Al ₂ O _3, thickness 5nm of Al ₂ O ₃
Can be formed into a single layer. In addition, one cycle of TiO ₂
By repeating once, TiO ₂ having a film thickness of 1.1 nm is obtained.
Can be formed into a single layer. The film thickness of TiO ₂ can be changed by appropriately changing the number of cycles as a reference.

FIG. 1 is a graph showing the relationship between the substrate temperature (° C.) and the thickness of a single layer of TiO ₂ (thickness of titanium oxide, unit: nm). Here, the substrate temperature is obtained by a thermocouple or the like placed near the substrate, and the state of the layer structure is shown by TEM observation of a cross section in the stacking direction of an insulating film made of Al ₂ O ₃ and TiO ₂ having a total thickness of 250 nm. I asked by doing.

Area below graph curve R0 in FIG.
(Hatched area) R1 is Al _TwoO_ThreeAnd TiO_TwoPostcard
This is a condition area for forming a properly separated layer structure.
The region R2 of the rough curve R0 or more is made of Al_TwoO_ThreeAnd TiO_TwoBut
This is a condition area where a mixed structure appears. From FIG.
The condition region R1 shifts to the higher temperature side as the titanium oxide film thickness is smaller.
Movement, and even if the substrate temperature (film formation temperature) is raised,
It can be seen that a properly separated layer structure is formed.

Further, Al ₂ O ₃ and TiO ₂ are formed by the ALE method.
When forming an insulating film consisting of
Is preferably as high as possible. This is because chlorine (C) remaining in the formed layer (thin film) increases as the temperature increases.
This is because impurities such as l) can be easily removed. From these, the following can be said as film forming conditions for forming a layer structure in which Al ₂ O ₃ and TiO ₂ are properly separated.

When a single layer of Al ₂ O ₃ is laminated under the condition of a thickness of 5 nm, first, when the substrate temperature is 400 ° C. or lower,
Regardless of the thickness of the titanium oxide film, each layer has a separated layer structure. Further, it is preferable to set the substrate temperature to less than 450 ° C. when the titanium oxide film thickness is 2 nm or more, and to set the substrate temperature to less than 500 ° C. when the titanium oxide film thickness is 1.1 nm or more.

By the way, when the substrate temperature is 450 ° C., if the thickness of the titanium oxide is thinner than 2 nm, the structure becomes a separated layer structure. If the thickness is 2 nm or more, the layers are mixed.
When the substrate temperature was 500 ° C., the thickness of the titanium oxide film was 1.
If the thickness is smaller than 5 nm, a separated layer structure is obtained, and 1.5
When the thickness is not less than nm, each layer becomes a mixed film.

As described above, according to the present embodiment, as the thickness of titanium oxide is reduced, the substrate temperature (film formation temperature) at which aluminum oxide and titanium oxide are not mixed increases. The present invention utilizes a phenomenon uniquely found by a person or the like, and is characterized by setting a substrate temperature (film formation temperature) based on a target film thickness of aluminum oxide and titanium oxide. Then, according to the present film forming method, a layer structure in which aluminum oxide and titanium oxide are separated without being mixed can be realized.

(Second Embodiment) In a second embodiment, an insulating film (ATO film) in which aluminum oxide and titanium oxide are alternately laminated in a predetermined film thickness by an atomic layer epitaxial growth method is formed. In the film formation method, at least one layer of planarizing aluminum oxide having a thickness larger than a predetermined thickness of aluminum oxide is formed in the middle of the layered structure to planarize the layered structure. Things. Hereinafter, the points different from the first embodiment will be mainly described.

FIG. 2 shows a sectional structure of the insulating film according to this embodiment.
FIG. FIG. 2B is a diagram showing a schematic cross-sectional structure of a conventional insulating film as a comparative example.
In FIG. 2, 1 is an aluminum oxide layer (Al ₂ O ₃ layer), 2 is a titanium oxide layer (TiO ₂ layer), and 3 is an aluminum oxide layer for flattening (hereinafter, referred to as a flattening layer).

By forming at least one flattening layer 3 thicker than the Al ₂ O ₃ layer 1 having a predetermined thickness in the middle of the laminated structure, the flattening layer 3 is generated as the TiO ₂ layer 2 is crystallized. The unevenness on the layer plane can be absorbed. Therefore, the disordered layer structure is flattened by the flattening layer 3, so that the progress of crystallization over each layer can be suppressed.

In the laminated structure shown in FIG.
An example of film forming conditions for forming a layer structure without mixing each material when forming an insulating film composed of an Al ₂ O ₃ layer 1 and a TiO ₂ layer 2 of 0 nm will be described. The thickness of each of the single layers of the Al ₂ O ₃ layer 1 and the TiO ₂ layer 2 is 5 nm, and the thickness of the flattening layer 3 is 20.
nm. Each of the layers 1 to 3 can be formed to have a desired film thickness by appropriately changing the number of cycles based on the example of the film forming conditions described in the first embodiment. No. ₃ can be formed by increasing the number of cycles of the Al ₂ O ₃ layer 1 (about four times in this example).

As described above, when the single layers of the layers 1 and 2 are laminated under the condition that the thickness of each layer is 5 nm, according to TEM observation, the first few layers have a layer structure in which each material is separated. However, the layer structure of each material is disturbed as the layers are stacked.
This is because, as mentioned in the “Solution” section, TiO ₂
Is considered to affect the Al ₂ O ₃ layer.

However, in the insulating film of the present embodiment shown in FIG.
By stacking about m layers, the upper surface of the planarizing layer 3 becomes a flat surface, so that it is possible to prevent the layer structure from being significantly disturbed before the layer structure is disturbed. Therefore, according to the present embodiment, it is possible to realize a layer structure in which the respective materials of Al ₂ O ₃ and TiO ₂ are separated without being mixed by the planarization layer 3.

The flattening layer 3 of this embodiment is made of ATO.
Since the film is formed of Al ₂ O ₃ which is a constituent material of the film, the film can be formed using a normal ALE film forming apparatus. However, needless to say, the thickness of the flattening layer 3 is of course limited to such a level that the performance of the insulating film can be maintained. Note that the planarization layer 3 may be interposed at two or more portions in the middle of the laminated structure.

(Third Embodiment) FIG. 3 schematically shows a cross-sectional structure of an insulating film according to a third embodiment, and mainly different points from the first embodiment will be described. This embodiment, the individual TiO ₂ layer 2, which has been made in view of forming means for preventing the progress of crystallization, individual TiO ₂ layer 2, a first TiO ₂ layer 2a And the second T
It is characterized by having a sandwich-like three-layer structure in which an Al ₂ O ₃ barrier layer 2c is sandwiched between iO ₂ layers 2b.

In each TiO ₂ layer 2, the Al ₂ O ₃ barrier layer 2c sandwiched between the two TiO ₂ layers 2a and 2b is made of TiO ₂
Is a means for preventing the progress of crystallization. This Al ₂ O ₃
The thickness of the barrier layer 2c is Al ₂ O ₃
It is thinner than layer 1. For example, when forming an insulating film having a total film thickness of 250 nm including an Al ₂ O ₃ layer 1 and a TiO ₂ layer 2 each having a single layer thickness of 5 nm,
A single layer of the O ₂ layer 2 includes an Al ₂ O ₃ barrier layer 2 c having a thickness of about 1 nm and two TiO ₂ layers 2 a and 2 each having a thickness of 2 nm.
b to form a three-layer structure.

In forming the insulating film of this embodiment,
In forming the individual TiO ₂ layer 2 once stops the formation of TiO ₂ in the course of its formation, after forming the Al ₂ O _3, by re-forming the TiO _2, each of the TiO ₂
Layer 2 can have the above sandwich structure. At this time, a film can be formed with a desired film thickness by appropriately changing the number of cycles based on the example of the film forming conditions described in the first embodiment.

According to the present embodiment, each Ti
Since the Al ₂ O ₃ barrier layer 2 c sandwiched between the O ₂ layers 2 serves as a barrier to prevent the progress of crystallization of TiO _2, a layer in which Al ₂ O ₃ and TiO ₂ are separated without being mixed. The structure can be realized. Of course, A
The thickness of the l ₂ O ₃ barrier layer 2c may be any thickness as long as it functions as a means for preventing the progress of crystallization.

According to each of the above embodiments, a layer structure in which aluminum oxide and titanium oxide are separated without being mixed can be realized, so that a leak current is hardly generated, insulation is excellent, and durability is excellent. Insulating film (ATO film) can be provided. The present embodiment is effective for realizing an EL (electroluminescence), a liquid crystal display, or a semiconductor device having such an excellent insulating film.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a substrate temperature and a titanium oxide film thickness.

FIG. 2A is a schematic cross-sectional view of an insulating film according to a second embodiment of the present invention, and FIG. 2B is a schematic cross-sectional view of a conventional insulating film.

FIG. 3 is a schematic sectional view of an insulating film according to a third embodiment of the present invention.

[Explanation of symbols]

1, 2c: aluminum oxide layer, 2: titanium oxide layer, 2
a: a first titanium oxide layer, 2b: a second titanium oxide layer,
2c: aluminum oxide barrier layer, 3: flattening layer.

Claims (7)

[Claims] 1. A film forming method for forming an insulating film in which aluminum oxide and titanium oxide are alternately laminated by an atomic layer epitaxial growth method, wherein the aluminum oxide and the titanium oxide are based on the film thickness of the aluminum oxide and the titanium oxide. A film forming temperature that does not cause mixing of the insulating film, and forming the insulating film at the set film forming temperature. 2. The film forming method according to claim 1, wherein the film forming temperature is set to 400 ° C. or less when the film thickness of the aluminum oxide is 5 nm. 3. The method according to claim 1, wherein the film forming temperature is set to less than 450 ° C. when the film thickness of the aluminum oxide is 5 nm and the film thickness of the titanium oxide is 2 nm or more. Film formation method. 4. The method according to claim 1, wherein when the thickness of the aluminum oxide is 5 nm and the thickness of the titanium oxide is 1.1 nm or more, the film forming temperature is set to less than 500 ° C. The film forming method according to the above. 5. A film forming method for forming an insulating film in which aluminum oxide and titanium oxide are respectively alternately laminated with a predetermined film thickness by an atomic layer epitaxial growth method. A film formation method, comprising forming at least one layer of aluminum oxide for planarization having a thickness larger than a predetermined thickness of aluminum oxide in the middle of the laminated structure. 6. A predetermined film thickness of said aluminum oxide is 5 n
m, and the thickness of the flattening aluminum oxide is 20
The film forming method according to claim 5, wherein the thickness is set to nm. 7. A film forming method for forming an insulating film in which aluminum oxide and titanium oxide are alternately stacked by atomic layer epitaxial growth, wherein when forming each of said titanium oxide layers, By temporarily stopping the formation of titanium oxide, forming aluminum oxide, and then forming titanium oxide again, the individual titanium oxide layers have a sandwich structure in which aluminum oxide is sandwiched between titanium oxides. A film forming method characterized by the above-mentioned.