JP3411367B2 - Composite structure of ferroelectric thin film and substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for forming a ferroelectric thin film on a substrate containing Si (silicon).
The present invention relates to a technique for forming a Pb-based ferroelectric thin film such as PbTiO ₃ (lead titanate) without interposing a conductive thin film such as Pt (platinum) or RuO ₂ (ruthenium dioxide).

[0002]

2. Description of the Related Art Ferroelectrics having spontaneous polarization and interesting physical properties such as piezoelectricity, pyroelectricity, high dielectric constant, and Curie temperature phase transition property have already been utilized in the field of consumer and industrial fields. Various applications are expected. Above all, Pb
So-called Pb-based ferroelectrics such as TiO ₃ , PZT (lead titan zirconate titanate), PLT (lead lanthanum titanate titanate), PLZT (lead lanthanum zirconate titanate), PBZT (barium lead zirconate titanate), etc., apply an alternating electric field. Characteristics, such as excellent spontaneous polarization reversal characteristics, large electromechanical coupling constant, high relative permittivity up to several thousand, and curie temperature in a wide range by doping. In addition to this, because it combines the price appeal of being composed of inexpensive materials, development has proceeded from early on centering on ceramic materials, and various discrete parts have been launched as products. Piezoelectric firing elements, high-capacity capacitors, ultrasonic oscillators, temperature sensitive elements (so-called thermistors), etc. are just a few examples.

In recent years, Pb-based ferroelectrics have been thinned to form Si.
An ambitious attempt to mount on a semiconductor substrate has become active. This is based on the intention to combine ferroelectricity (which cannot be sufficiently achieved with Si materials) and high-speed arithmetic processing of Si semiconductors as described above to realize integrated circuits and smart devices with high added value. . Currently, the most spotlighted example is MI formed of metal (M) -insulating film (I) -semiconductor (S).
It may be an MFS type non-volatile memory in which the I part of the S transistor is composed of a ferroelectric film (F). As can be easily inferred from the above example, the composite structure of the ferroelectric substance and Si is
It is one of the basic structures that are indispensable when incorporating a ferroelectric film into a traditional Si semiconductor substrate together with a composite structure of a ferroelectric and a metal. A number of efforts have been made in the past to achieve this structure. But Si
There have been no reports of forming a good Pb-based ferroelectric on a substrate.

The obstacle to the realization of a good composite structure of Pb-based ferroelectric and Si is that the Si element contained in the substrate diffuses into the Pb-based ferroelectric film in the manufacturing process of the Pb-based ferroelectric. The main cause is The above-mentioned problem caused by Si diffusion is that when a Pb-based ferroelectric film is vapor-deposited on Si by CVD or sputtering, a large amount of Si element diffuses rapidly to the surface of the Pb-based ferroelectric film. The perovskite structure cannot be formed because it is successively taken in as a film component. Even if a perovskite structure is formed, Si is accumulated in the film in other subsequent heat treatment processes and the ferroelectric properties are deteriorated. Since defects will remain in the substrate after Si is removed by diffusion, it is difficult to form an active region (a portion where a channel of a transistor is formed) in the substrate. In addition, the same problem of Si diffusion as above is caused by SiO ₂ , Si.
It has been confirmed that it also occurs in Si substrates such as ₃ N ₄ and silicide (hereinafter, these and Si substrates together are referred to as Si-based substrate). For example, "Journal of Material
Research ”(RARoy and KF Etzold,“ Journal of
Material Research, Vol.7, 1455 1992 ”).

[0005]

As described above, in the prior art, the above-mentioned problems caused mainly by the diffusion of the Si element contained in the substrate into the Pb-based ferroelectric film.
However, there is a problem that it is difficult to realize a composite structure of a Pb-based ferroelectric and a Si-based substrate.

The present invention has been made in order to solve the problems of the prior art as described above, and provides a composite structure of a Pb-based ferroelectric material and a Si-based substrate having good characteristics in which the diffusion of Si is suppressed. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention is constructed as described in the claims. That is, the invention described in claim 1 is
On a substrate containing silicon or a substrate consisting of a thin film,
In a composite structure of a ferroelectric thin film on which a ferroelectric thin film containing lead is mounted and a substrate, lead is insufficient between the ferroelectric thin film and the substrate due to deviation from the stoichiometric composition. is obtained by configured to pinching the lead titanate layer or Ranaru dielectric thin film are. The above stoichiometric lead titanate layer or Ranaru dielectric thin film lead is missing out of the composition, paraelectric a thin film, it does not have itself a ferroelectric thin film. Note that the structure was sandwiched a lead titanate layer lead out from the above stoichiometric composition is insufficient, for example, Ru phase equivalent to the below first and second embodiments.

The invention described in claim 2 is the same as claim 1.
The dielectric thin film of is an oxide thin film formed by a chemical vapor deposition method. The chemical vapor deposition method corresponds to, for example, a low pressure CVD method or a digital CVD method described later. According to a third aspect of the present invention, the dielectric thin film and the ferroelectric thin film are both thin films formed by a chemical vapor deposition method. According to a fourth aspect of the present invention, the ferroelectric thin film is a perovskite (00
1) It is an oriented ferroelectric thin film. According to the fifth aspect of the invention, the dielectric thin film and the ferroelectric thin film are continuously formed by the same chemical vapor deposition apparatus. According to a sixth aspect of the present invention, a digital chemical vapor phase in which the dielectric thin film and the ferroelectric thin film are deposited while periodically introducing a raw material and laminating thin films of about several atomic layers It is formed by the growth method. This configuration example corresponds to a later second actual施例.

[0009]

[Action] As described above, in the present invention, between the Pb containing ferroelectric and the Si-based substrate, stoichiometry lead titanate layer or Ranaru dielectric thin film lead is missing off the composition By arranging, it is possible to suppress the diffusion of Si and realize a good Pb-based ferroelectric / Si-based substrate structure. As described above, a dielectric film such as a lead titanate layer (for example, Pb _x TiO _{x + 2} (x <1) described in Examples below) having a lead deficiency deviating from the stoichiometric composition is formed by using a Si-based material. The reason why the Si diffusion is suppressed by sandwiching between the substrate and the Pb-based ferroelectric film is currently under investigation, but it has not been confirmed yet.
Several interesting phenomena have been revealed to solve this. That is, according to an experiment recently performed by the present inventors, PbO (lead oxide) is deposited on the Si-based substrate by the CVD method.
It has been found that when the film is deposited, the Si of the substrate violently penetrates into the PbO film. Further, while controlling the supply amount ratio of the Pb source vapor and the Ti source vapor with x as a variable, Pb _x TiO _{x + 2} films of various x values are formed on the Si substrate by the CVD method, and the diffusion amount of Si in the film is increased. Is evaluated, x is 1
The diffusion of Si rapidly increases from the vicinity of (= stoichiometric composition). Further, when x> 1, it is considered that the (x-1) mol excess PbO film is mixed in the PbTiO ₃ film. From the above two experimental facts, it is understood that the Si element penetrates into the upper film when the PbO component is formed on the Si-based substrate. Considering these findings, the lead indium titanate layer lacking lead deviates from the stoichiometric composition of the present invention and the penetration of Si can be suppressed by Pb contained in this film. It is presumed that all of them are PbTiO ₃ components and no PbO component exists.

The reason why the diffusion of Si occurs at the raw material supply ratio which is supposed to give the stoichiometric composition x = 1 is that the raw material vapor is turbulent at the outermost surface where the film formation is progressing due to turbulence of the air flow in the reactor. Instantaneous fluctuation of supply ratio (time average becomes 0)
Therefore, when the supply of the Pb raw material vapor becomes excessive, a PbO component is transiently formed, and Si is expected to invade toward this. Therefore, if the Ti raw material is supplied in a slightly excessive amount (the Pb raw material is small) in advance in anticipation of excess Pb vapor due to instantaneous fluctuations, the risk of PbO being formed at every moment can be avoided. As a result, such a dielectric film becomes a Pb _x TiO _{x + 2} (x <1) film as shown in the embodiments of the present invention . Further, as described in claims 2 to 6, by forming the dielectric thin film or the ferroelectric thin film by the chemical vapor deposition method, a thin film having good characteristics and an accurate film thickness can be obtained. It can be easily formed.

[0011]

EXAMPLES The present invention will be described in detail below with reference to a plurality of specific examples. Before that, a composite structure of a ferroelectric film and a substrate common to all the examples will be described. A typical cross-sectional structure and a film forming apparatus for a dielectric thin film (or a ferroelectric) will be described. First, FIG. 1 is a sectional view of an essential part of a composite structure of a ferroelectric film and a substrate according to the present invention. In FIG. 1, 1 indicates a Si-based substrate. The Si-based substrate is a Si substrate or a thin film containing a Si element formed on an arbitrary substrate, such as a poly-Si film, a SiO ₂ film, or a Si film.
₃ N ₄ film, PSG (phosphorus glass) film, silicide film and the like. For the sake of convenience, a Si single crystal (100) substrate will be treated as a representative of Si-based substrates in the specific examples described later. At the top of the Si-based substrate 1, the stoichiometric lead titanate layer or the lead is missing out of the composition Ranaru dielectric film 2 is placed. The dielectric film 2 is formed by, for example, a CVD method, is dense and thin, and plays an extremely important role in the present invention. Further, on the dielectric film 2, a desired Pb-based ferroelectric film 3, for example, PbTiO ₃ ,
PZT, PLT, PLZT, PBZT, etc. are formed. For forming such a Pb-based ferroelectric film, any known method such as a vacuum vapor deposition method, a sputtering method, a sol-gel method or a CVD method may be used, but a semiconductor having micron-scale fine irregularities on its surface is used. When forming a film on an ultra-high-integrated circuit board, the CVD method is most suitable because it provides conformal coverage. In the description of specific examples described later, this Pb-based ferroelectric film is subjected to CVD.
This is represented by a PbTiO ₃ film formed by the method.
However, this is for the sake of convenience until the user gets tired of it, and completely the same action and effect can be obtained with other Pb-based ferroelectric films formed by other film forming methods. Thus, the ferroelectric film according to the present invention and the S
The composite structure with the i-based substrate has a simple structure. By the way, in order to make this structure an MFS structure, a conductive film is further formed thereon by a sputtering deposition method or an electron beam evaporation method, and then formed into a predetermined pattern by photolithography or the like to form a gate electrode (not shown). Form). Typical electrode materials are Al, W, Pt and poly-Si.

Next, FIG. 2 is a schematic cross-sectional view of a principal part of a cold wall type low pressure CVD apparatus used for explaining the method of forming the dielectric film 2. The device need not be a cold wall type, but may be a hot wall type. Further, although FIG. 2 is also used for convenience of description of a method of forming a Pb-based ferroelectric film (CVD method) described later, the CVD apparatus used for forming the Pb-based ferroelectric film is not necessarily used for the dielectric film 2. Need not be the same as the CVD equipment used to form In FIG. 2, 10 is a reactor. This reactor 1
0 is a susceptor 12 that mechanically supports the substrate 11 on which the Si-based substrate 1 is formed and holds it at a predetermined temperature, and introduces A source vapor, B source vapor, C source vapor, and D source vapor. It is provided with ports 13, 14, 15, 16 and an exhaust port 17 for discharging the generated gas generated by the deposition reaction and the excess source vapor to the outside of the device. Steam inlets 13, 14, 15,
16 are steam supply valves 18, 19, 20, respectively.
A raw material vapor, B raw material vapor, C raw material vapor, D
The raw material vapor transport pipes 22, 23, 24, 25 are connected. Although not shown in the figure, the other ends of the transport pipes 22, 23, 24, and 25 are connected to steam generators (with a transport amount adjusting function) of A raw material, B raw material, C raw material, and D raw material. Also,
The exhaust port 17 is connected to a vacuum exhaust device (not shown) by an exhaust pipe 26, and an exhaust main valve 27, an exhaust sub valve 28, and an exhaust amount controller 29 are provided in the middle of the exhaust port 17. The exhaust amount controller 29 is for maintaining the pressure in the reactor at a predetermined value when necessary when introducing the raw materials, and any system may be used as long as it serves this purpose. The opening / closing timing of the steam supply valves 18, 19, 20, 21 and the exhaust main valve 27 and the exhaust auxiliary valve 28 and the exhaust amount of the exhaust amount controller 29 are controlled integrally by the opening / closing timing control device 30.

After the above description of the cross-sectional structure of the composite structure of the ferroelectric film and the substrate and the film forming apparatus is completed, a specific embodiment of the method for forming the composite structure shown in FIG. explain. Incidentally, as already mentioned, in the following examples, the Si-based substrate is represented by the Si single crystal substrate and the Pb-based ferroelectric is represented by the PbTiO ₃ film. In the first embodiment, in the composite structure shown in FIG. 1, the dielectric film 2 is made of Pb _x.
In this embodiment, TiO _{x + 2} (x <1) is formed by the low pressure CVD method.

First, the film structure of this embodiment will be described with reference to FIG. 1 is a Si single crystal substrate. 2 is Pb _x TiO
_A paraelectric film having a thickness T _ox2 represented by a chemical formula _{x + 2} (x <1) is formed by a CVD method so that the composition of Pb is insufficient as compared with PbTiO ₃ . Pb _x TiO _{x + 2} ferroelectric thin film 3 of PbTiO ₃ is formed on the film is formed.

The method of forming the film structure will be described below. First,
Si single crystal substrate 11 is subjected to RCA cleaning (traditional Si substrate cleaning method comprising first cleaning with a mixed solution of ammonia water and hydrogen peroxide solution and second cleaning with a mixed solution of hydrochloric acid and hydrogen peroxide solution) and a rare fluorine cleaning. After performing acid etching treatment, rinse with ultrapure water. Next, the Si single crystal substrate 11 is placed on the susceptor 12 of the CVD apparatus having the structure shown in FIG. 2, and the temperature of the susceptor 12 is raised to a predetermined film forming temperature T _sub (details of film forming conditions will be described later). And all steam supply valves 18
21 to 21 are closed, the main exhaust valve 27 is opened, and the inside of the reactor is once evacuated.

The CVD raw materials are tetraisopropotitanium Ti (i-OC ₃ H ₇ ) ₄ (= A vapor) and 4-ethyllead Pb (C ₂ H ₅ ) ₄ (= B vapor) kept at a predetermined source temperature. And 5mo
Oxygen O ₂ + O ₃ (5%) gas (= D vapor) containing 1% ozone. Ti (i-OC ₃ H ₇ ) ₄ and Pb (C ₂ H ₅ ) ₄ were vaporized with a special stainless source bottle and pure nitrogen N ₂ was added.
Is used as a carrier gas to be transported to the reactor 10. By the exhaust, the pressure of the reactor 10 becomes 10 to ⁶ Torr or less, and when the temperature of the susceptor 12 (= film forming temperature T _sub ) becomes stable, the exhaust main valve 27 is closed and the exhaust sub valve 28 is opened to adjust the exhaust amount. And the steam supply valves 18, 19 and 21 are opened and the Ti (i-OC) is activated.
₃ H ₇ ) ₄ and Pb (C ₂ H ₅ ) ₄ and O ₂ + O ₃ (5%) were added to reactor 1
0, and the low pressure CVD method for the Pb _x TiO _{x + 2} film is started.

FIG. 4 is a table showing typical conditions for forming a dielectric film according to the present invention. The film forming conditions of this embodiment are shown in the column labeled as the first embodiment of FIG. There is. In addition,
These film forming conditions are representative ones, and the film forming conditions are not limited to these conditions. In FIG. 4, T _soA , T _soB and T _soC are A raw materials, respectively.
Source bottle temperature of B raw material, C raw material, S _A , S _B , S _C ,
S _D is the flow rate of A vapor, B vapor, C vapor, and D vapor (including carrier gas), T _sub is the film formation temperature (susceptor temperature), and t _{1 to} t ₄ are the first zones of the cycle of the digital CVD method. , P is the film forming pressure of the low pressure CVD method, and P _{1 to} P ₄ are the pressures of the first zone of the cycle of the digital CVD method.

A predetermined film thickness T _{ox2 is obtained} by the above film forming process.
When the temperature reaches, the film formation conditions are changed without stopping the film formation, and the film formation of the ferroelectric thin film PbTiO ₃ is started this time. At this time, the film forming condition changed is substantially only the flow rate of the carrier gas of the Pb (C ₂ H ₅ ) ₄ raw material. That is, the carrier gas flow rate, which was set low so as to be insufficient for Pb in the previous Pb _x TiO _{x + 2} film forming step, is increased and readjusted to an appropriate value. By such a simple operation, the film formation can be switched from the Pb _x TiO _{x + 2} film to the PbTiO ₃ film in a short time.

FIG. 5 is a table showing typical conditions for PbTiO ₃ film formation according to the present invention, and the film formation conditions of this embodiment are shown in the column described as the first embodiment of FIG. . The reference numerals in FIG. 5 are the same as those in FIG. Further, in order to obtain ferroelectric PbTiO ₃ , it is important to adjust the source temperature as a first step to adjust the composition of the film to the stoichiometric composition. The film thickness is controlled by the film formation time. The film formation time is almost equal to the opening time of the steam supply valve for supplying the raw materials. Under the conditions shown in FIG. 5, a deposition rate of 0.35 nm / sec is obtained. Next, when the film thickness of the PbTiO ₃ film reaches a predetermined film thickness _Tox3 , the following film formation stopping operation is performed. That is,
Simultaneously with closing the vapor supply valves 18, 19, 21, the main exhaust valve 27 is opened and the sub auxiliary valve 28 is closed to lower the temperature of the susceptor 12. When the temperature of the susceptor 12 has become sufficiently low, the vacuum of the reactor 10 is broken and the substrate 11 is taken out.

Next, a second embodiment of the present invention will be described. In the second embodiment, the same structure as that of the first embodiment is realized by using the digital CVD method, and the composite structure of the ferroelectric thin film and the base shown in the first embodiment (base and Laminated structure of Pb _x TiO _{x + 2} film and PbTiO ₃ film)
Are formed at once by a digital CVD method. The inventors of the present invention have announced the digital CVD method in the following document. "" Proceedings of Symposium on Dry Process "
(S. Tanimoto et.al, “proceedingsof Symposium on
Dry Process ”Tokyo, IEE of japan, p.163, 1992) The digital CVD method is not a continuous method like the low pressure CVD method, but the material is periodically introduced to form a thin film of several atomic layers. This is a method of advancing deposition, which is generally (1) superior in flatness, (2) capable of finely controlling the film thickness, and (3) extremely fine, as compared with the conventional low pressure CVD method. It has advantages such as remarkably good coverage at various steps, and (4) low temperature film formation.

The methods of introducing the raw materials are roughly classified into a method of sequentially introducing different kinds of raw material vapor so that they are not mixed with each other, and a method of introducing all the vapors simultaneously and intermittently. Now, an example will be described in which the former method in which a relatively good film is obtained in the present film structure is applied. First, Si
The single crystal substrate 11 is subjected to RCA cleaning and diluted hydrofluoric acid etching treatment, and then rinsed with ultrapure water. Next, the above Si
The single crystal substrate 11 is placed on the susceptor 12 of the CVD apparatus having the structure shown in FIG. 2, the temperature of the susceptor 12 is raised to a predetermined film forming temperature T _sub , and all the vapor supply valves 18 to
21 is closed, the main exhaust valve 27 is opened, and the inside of the reactor is once evacuated.

The CVD raw material is the same tetraisopropotitanium Ti (i-OC ₃ H ₇ ) ₄ (= A vapor) used in the film formation of the first embodiment.
And 4 ethyl lead Pb (C ₂ H ₅ ) ₄ (= B vapor) and 5 mol%
Oxygen O ₂ + O ₃ (5%) gas (= D vapor) containing ozone
Is. The pressure of the reactor 10 is 10 to ^{6 due} to the above exhaust.
When the temperature becomes equal to or lower than Torr and the temperature of the susceptor 12 (= film forming temperature T _sub ) is stable, first, a Pb _x TiO _{x + 2} film (film thickness T _ox2 ) is formed, and then a PbTiO ₃ film (film thickness T _{sub is formed} ).
_Ox3 ) is continuously formed by a digital CVD method. According to the digital CVD method in this embodiment, as shown in FIG.
The raw material supply sequence as shown in (b) is used. It is to be noted that FIG. 3 schematically shows what vapor is supplied from the gas phase to the substrate 11 placed on the susceptor 12 with the passage of time.

The details will be described below. In the sequence shown in FIG. 3B, the Aa zone supplied with A vapor and the B zone
It consists of an Ib zone that receives steam supply and an Id zone that receives D steam supply, and Ia + Id + Ib + Id is 1
It consists of a sequence of sequences that are periodic. The Ia zone is realized by opening only the steam supply valve 18 of the steam supply valves for supplying the raw material, closing the exhaust main valve 27, opening the exhaust sub valve 28, and operating the exhaust amount controller 29. Similarly, in the Ib zone, only the steam supply valve 19 of the steam supply valves for supplying the raw material is opened, and I
The d zone is realized by opening only the steam supply valve 21 of the steam supply valves for supplying the raw material, closing the exhaust main valve 27, opening the exhaust sub valve 28, and operating the exhaust amount controller 29. The opening / closing timing control device 30 issues commands for opening / closing these valves and operating the exhaust amount adjuster.

A typical film forming condition in this case is shown in FIG.
This is shown in the Example section. It should be noted that this film forming condition is a typical example and is not limited to this. In the above sequence, the Pb _x TiO _{x + 2} film of about one atomic layer is formed in layers each time Ia + Id + Ib + Id is completed. A PbTiO ₃ film can be formed by changing the conditions in the same sequence as described above. Pb _x Ti
The difference between the O _{x +2} film formation and the PbTiO ₃ film formation is I
It is only the length of the b zone (B vapor = the length of the supply time of Pb (C ₂ H ₅ ) ₄ vapor). That is, in Pb _x TiO _{x + 2} , the supply time of Pb (C ₂ H ₅ ) ₄ vapor is set to be lower than an appropriate value that gives the stoichiometric composition, in order to build up Pb in a deficient manner. In this case, the opening / closing of the steam supply valve and the operation of the exhaust system valve are integrally performed by the programmable opening / closing timing control device 30.

Under the conditions shown in the second embodiment of FIG. 4,
Pb _x TiO _{x + 2} has a deposition rate of 0.38 nm / cyc, and PbTiO ₃ has a deposition rate of 0.40 nm / cyc. In the above film forming step, first, Pb _x TiO _{x + 2 is formed} , and after the film thickness reaches a predetermined film thickness _Tox2 , P
The bTiO ₃ film is formed, and the film thickness is a predetermined film thickness T.
_{When the temperature} exceeds _ox3 , all raw material supply valves are closed, the exhaust main valve 27 is opened, the exhaust sub valve 28 is closed, and the temperature of the susceptor 12 is lowered. Then, when the temperature of the susceptor 12 becomes sufficiently low, the exhaust main valve 27 is closed, the vacuum of the reactor 10 is broken, and the substrate 11 is taken out.

Next, a third embodiment will be described as a reference example of the present invention. The present embodiment is a case where the dielectric thin film 2 is a zircon dioxide (ZrO ₂ ) film in the ferroelectric thin film / Si-based substrate structure common to the present invention shown in FIG. This Zr
The O ₂ film may be formed by a normal low pressure CVD method or the above-mentioned digital CVD method. Here, as a raw material, Zr
(T-OC ₄ H ₉ ) ₄ = C vapor, O ₂ + O ₃ (5%) =
An example of forming a film by a digital CVD method using D vapor will be described. First, the Si single crystal substrate is subjected to RCA cleaning and a dilute hydrofluoric acid etching treatment, and then rinsed with ultrapure water. That Si
The single crystal substrate 11 is placed on the susceptor 12 of the CVD apparatus having the structure shown in FIG. 2, the temperature of the susceptor 12 is raised to a predetermined film forming temperature, and all the vapor supply valves 18 to
21 is closed, the main exhaust valve 27 is opened to evacuate the inside of the reactor 10 once, and then the digital CVD is started.

In order to form the film structure shown in FIG. 1, the present digital CVD continuously uses two periodic raw material supply sequences as shown in FIG. In FIG.
(A) is for forming ZrO ₂ , and (b) is
Is for forming PbTiO ₃ . The details will be described below. (A) consists of a sequence in which the Ic zone receiving the supply of C vapor and the Id zone receiving the supply of D vapor are alternately repeated, and an ultrathin ZrO ₂ layer of about one atomic layer is formed in layers every time Ic + Id is finished. Will be done. I
The c zone is realized by opening only the steam supply valve 20 among the steam supply valves for supplying the raw material, closing the exhaust main valve 27, opening the exhaust sub valve 28, and operating the exhaust gas amount regulator 29. Further, the Id zone is realized by opening only the steam supply valve 21 of the steam supply valves for supplying the raw material, closing the exhaust main valve 27, opening the exhaust sub valve 28, and operating the exhaust amount controller 29. The opening / closing timing control device 30 issues commands for opening / closing the valves and operating the exhaust amount adjuster.

(B) is an Ia zone for supplying A vapor = Ti (i-OC ₃ H ₇ ) ₄ , an Ib zone for supplying B vapor = Pb (C ₂ H ₅ ) ₄ , and a D vapor = O. ₂ + O ₃ (5%) is supplied to the Id zone, and Ia + Id + Ib + Id is 1
It consists of a sequence of sequences that are periodic. In this case, when the first half of Ia + Id is finished, about 1 atomic layer of TiO 2 is formed.
_{When 2} is formed and the latter half of Ib + Id is completed, PbO of about 1 atomic layer is formed on TiO ₂ formed in the previous step.
Are stacked, and when one cycle is completed, a total of about one molecular layer of Pb
A TiO ₃ film is formed in layers. In the Ia zone, the steam supply valve 18 of the steam supply valves for supplying the raw materials is used.
Open only, close exhaust main valve 27, exhaust auxiliary valve 2
It is realized by opening 8 and operating the displacement controller 29. Similarly, in the Ib zone, only the steam supply valve 19 is opened. The opening / closing timing control device 30 issues commands for opening / closing the valves and operating the exhaust amount adjuster.

[0029] In the present embodiment, by forming a ZrO ₂ film is first in the sequence of FIG. 3 (a), ZrO ₂ the desired thickness T
_{When ox2} is reached, the sequence is switched to that shown in FIG. 3B, and PbTiO ₃ is deposited. When PbTiO ₃ reaches a predetermined film thickness _Tox3 , film formation is stopped and the substrate 11 is taken out of the reactor 10. Z in this embodiment
Typical film forming conditions for rO ₂ are shown in the third embodiment in FIG. The PbTiO ₃ film forming conditions are the same as in the second embodiment. Note that these film forming conditions are typical examples and are not limited to these conditions.

In this embodiment, the case where both the ZrO ₂ film and the PbTiO ₃ film are formed by the digital CVD method is illustrated, but one or both of them is depressurized C.
It may be formed by the VD method. For example, when the PbTiO ₃ film is formed by the low pressure CVD method, the ZrO ₂ film is formed in the sequence of FIG. 3A, and then the PbTiO ₃ ferroelectric material is formed by the low pressure CVD method shown in the first embodiment. A film may be deposited. The film forming conditions in that case are the same as those in the column of the first embodiment of FIG.

Having described the film structures of the first to third embodiments and the manufacturing method thereof, the operation of each embodiment will be described next. First, the structure in which the dielectric thin film 2 and the PbTiO ₃ ferroelectric thin film 3 shown in the first to third embodiments are laminated on the single crystal Si (100) substrate is described in each embodiment. -A sample formed under the film forming conditions was manufactured. Then, in those samples, the crystal structure of the PbTiO ₃ ferroelectric thin film was evaluated by XRD (X-ray diffraction method), and the relative permittivity (excluding the dielectric part) was measured by the high frequency capacitance measurement method (100 kHz, 0.1 V). After the evaluation, the amount of Si deposited on the surface of the PbTiO ₃ film subjected to the nitrogen annealing treatment at 650 ° C. for 60 minutes after the film structure formation was measured by XPS.
(X-ray photoelectron spectroscopy) device was used for quantification. The above evaluation was made for the following reasons. That is, as described in the section of the problem to be solved by the present invention, various problems (-) that exist in the conventional film structure are that Si contained in the substrate diffuses into the inside or the surface of the Pb-based ferroelectric film. Since it is caused by the diffusion, the magnitude of the diffusion amount of Si is an important point.
The above is done to evaluate this point.
In the above case, the amount of Si is Si and the main metal raw material T
Ratio of i and total amount of Pb (number of atoms), that is, Si /
It was arranged by the value of (Ti + Pb).

The detection limit of Si in the device used by the present inventors is Si / (Ti + Pb) = 0.005, and the symbol ND used below means that the amount of Si is less than this value. To do. Unless otherwise specified, the thickness of the dielectric thin film used for the test is 16 nm, and the thickness of the ferroelectric film PbTiO ₃ is 300 nm (crystal structure and dielectric constant evaluation) or 30 nm (Si diffusion evaluation). The thickness of the PbTiO ₃ film used for Si diffusion evaluation was made extremely thin at 30 nm in order to detect the Si amount with high sensitivity.

FIG. 8 is a chart showing the results of the above test. In FIG. 8, the conventional example is a PbTiO ₃ film formed by the CVD method.
It is an evaluation result of a conventional film structure in which a ferroelectric thin film is directly formed on a Si substrate, and the ratio of Pb to Ti is at least 1:
The ferroelectric thin film is manufactured so as to be 1. First, according to the results of the conventional example, the crystal structure is amorphous or pyrochlore structure (Pb ₂ Ti ₂ O ₆ ), and a tetragonal perovskite structure exhibiting ferroelectricity cannot be obtained. This is also confirmed by the fact that the non-dielectric constant shows a very low value of ε = 32. On the other hand, in the examples of the present invention, a tetragonal perovskite structure is formed in all cases,
(101) plane, (111) plane, (001) plane, (10
A polycrystalline film in which 0) planes and the like are mixed is obtained. The dielectric constants of all the dielectric films in the examples exceed ε = 100, which proves that the ferroelectric is formed.

Next, regarding the amount of Si diffusion, Si / (Ti + Pb) = 0.13 was shown in the conventional example, and Si was deposited on the surface in an amount comparable to Ti and Pb which are the main materials of the ferroelectric. ing. However, it can be seen that in the embodiment, the amount of Si diffusion is below the detection limit (ND) or a value close to this. As described above, when the embodiment according to the present invention is adopted, Si invasion from the substrate into the Pb-based ferroelectric film, which occurs during the film formation and the subsequent thermal process, is significantly suppressed, and as a result, S
It can be seen that a ferroelectric film showing good characteristics can be formed on the i substrate.

Next, it is obvious, without mentioning the reason, that the dielectric film sandwiched between the Pb-based ferroelectric film and the Si-based substrate plays an important role in the film structure of the present invention. Is. In order to apply such a film structure to various devices, one of the essential information is how thin the dielectric film can be. FIG. 6 shows the Si diffusion amount Si / (Ti + Pb) on the surface of a PbTiO ₃ film (thickness 30 nm) having a film structure produced by the first and third embodiments and subjected to heat treatment at 650 ° C. for 60 minutes. It is a figure which shows the result of having tested the thickness _{Tox2 of a} body membrane as a variable.
In FIG. 6 , ● indicates the characteristics of the first embodiment and □ indicates the characteristics of the third embodiment. Further, as described above, the dielectric film of the first embodiment is the Pb _x TiO _{x + 2} film and the dielectric film of the third embodiment is the ZrO ₂ film. The test method is
The method is the same as that described in FIG. 8 except for the value of _Tox2 .

As is apparent from FIG. 6, the dielectric film thickness T
_It can be seen that the Si diffusion amount sharply decreases with the increase of _ox2 . The second embodiment, which is not shown in FIG. 6, has a similar tendency. Although there is a slight difference in the rate of decrease in each example, the diffusion amount of Si decreases to 0.01 or less in all cases when T _ox2 = 6 nm or more is exceeded. According to a large number of experiments and experiences that the inventors have conducted so far with respect to the first to third embodiments, when the Si diffusion amount is 0.01 or less, the perovskite structure is all except a few exceptions. It has been proved that a Pb-based ferroelectric film having is obtained. Therefore, _{Tox 2} ≧ 6 nm is a measure of the film thickness of the dielectric to fully exert the effect of the present invention.

Next, another problem caused by diffusion of Si in the substrate into the Pb-based ferroelectric film is Si in the substrate.
A defect due to the removal is left, which makes it difficult to form an active region there. The present invention also provides a solution to this problem. Hereinafter, description will be given with reference to FIG. 7. FIG. 7 shows a PbTiO ₃ ferroelectric film / Pb _{x obtained} by applying the first embodiment of the present invention to an n-type single crystal Si (100) substrate.
After forming a TiO _{x + 2} (x <1) dielectric film / Si structure, a high frequency (100 kHz) in a simple MOS structure in which a platinum Pt gate electrode is placed on a PbTiO ₃ ferroelectric film.
z) A diagram showing a capacitance-DC bias voltage (CV) characteristic. In FIG. 7, C / C _{ox on} the vertical axis means the normalized capacity. This characteristic is close to the so-called ideal CV characteristic, which has a low capacitance inversion region on the low voltage side and a high capacitance storage region on the high voltage side across a steep transition region. This is P
It clearly shows that a good semiconductor active region is formed under the bTiO ₃ ferroelectric film. In other examples, almost the same high frequency CV characteristics were obtained.

Further, according to the characteristic of FIG. 7, the position of the transition region moves to the high frequency CV characteristic when the DC bias is swept from the low voltage side to the high voltage side and vice versa. It can be seen that there is a "hysteresis around" phenomenon. Such a phenomenon is a phenomenon that occurs when extremely strong spontaneous polarization along the C axis of the PbTiO ₃ ferroelectric film is inverted depending on the direction and magnitude of the DC bias. As described above, the MFS type nonvolatile semiconductor memory is
Since the device positively applies the spontaneous polarization reversal phenomenon of the ferroelectric film, it is possible to realize an effective MFS type memory by having such a hysteresis characteristic.

[0039]

As described above, according to the present invention, in the Pb type ferroelectric film / Si type base structure, the P
between the b-based ferroelectric and said Si-based substrate, by which is configured to place the lead titanate layer or Ranaru dielectric thin film lead is missing out of the stoichiometric composition, the structure It was possible to substantially solve the problem that the Si element of the substrate diffused into the ferroelectric film, which had been a problem for many years. As a result, a good-quality Pb-based ferroelectric thin film having a perovskite structure can be stably formed even on a Si-based substrate, and Si intrusion does not occur, so that the ferroelectric thin film is not deteriorated even by heat treatment. The excellent effect that a good Si semiconductor active layer (and therefore a semiconductor element) can be formed under the ferroelectric thin film is obtained.

The invention according to claims 2 to 6 is characterized in that the dielectric thin film is formed by a CVD method using a part of a constituent metal of the Pb-based ferroelectric thin film as a main raw material. Therefore, when the Pb-based ferroelectric thin film is produced by the CVD method, the Pb-based ferroelectric thin-film CVD apparatus can be used as the above-mentioned dielectric thin-film deposition apparatus without making a large-scale modification. There is a remarkable advantage that it can be done. This is an effect that cannot be obtained when the dielectric thin film is formed by another material or a film forming method. Further, according to claim 6 (corresponding to Example 2)
In the above, since the dielectric thin film and the Pb-based ferroelectric thin film are both formed by the digital CVD method, even if the substrate structure has an extremely fine unevenness of several μm, it is smooth and has a large thickness.
The effect that a ferroelectric / substrate structure having a uniform film quality can be achieved is obtained. Such features are extremely preferable features when applied to Si semiconductor ultra-high integrated circuits and the like.

[Brief description of drawings]

FIG. 1 is a sectional view of an essential part of an embodiment of a ferroelectric film / base structure according to the present invention.

FIG. 2 is a cross-sectional view of an essential part of an embodiment of a chemical vapor deposition apparatus used in the present invention.

FIG. 3 is a diagram showing an example of a raw material supply sequence of digital CVD.

FIG. 4 is a chart showing conditions for forming a dielectric film.

FIG. 5 is a chart showing film forming conditions for a PbTiO ₃ ferroelectric film.

FIG. 6 is a characteristic diagram showing the relationship between the dielectric film thickness _Tox2 and the amount of Si diffusion on the surface of the PbTiO ₃ film.

FIG. 7 is a characteristic diagram showing high-frequency capacitance-DC bias voltage characteristics of the MFS structure manufactured in the first example.

FIG. 8 is a chart showing characteristics of a PbTiO ₃ ferroelectric film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Si type | system | group base | substrate 2 ... Dielectric thin film 3 ... Pb type | system | group ferroelectric film 10 ... which consists of a lead titanate layer which is deviated from the stoichiometric composition, or an oxide layer whose main metal element is zircon ... Reactor 11 ... Substrate (base) 22-25 ... Transport pipe 12 ... Susceptor 26 ... Exhaust pipe 13 ... Raw material vapor introduction port 27 ... Exhaust main valve 14-16 ... Steam introduction port 28 ... Exhaust auxiliary valve 17 ... Exhaust port 29 ... Displacement regulators 18 to 21 ... Steam supply valve 30 ... Opening / closing timing control device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI H01L 27/04 29/788 29/792 (72) Inventor Masahiko Hirai 2-1 Samejima, Fuji City, Shizuoka Prefecture Asahi Kasei Kogyo Co., Ltd. 72) Inventor Satoshi Tanimoto 2 Takara-cho, Kanagawa-ku, Yokohama City, Kanagawa Prefecture Nissan Motor Co., Ltd. (56) Reference JP 5-243562 (JP, A) JP 4-279069 (JP, A) JP JP-A-49-118371 (JP, A) JP-A-4-111316 (JP, A) JP-A-5-259386 (JP, A) JP-A-4-11730 (JP, A) JP-A-7-161838 (JP , A) JP 2-200782 (JP, A) JP 6-29549 (JP, A) JP 5-121760 (JP, A) JP 7-90587 (JP, A) JP 7-172996 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 27/105 H01L 21/316 H01L 21/822 H01L 21/8247 H01L 27/04 H01L 29/788 H01L 29/792 JISC file (JOIS)

Claims (6)

(57) [Claims] 1. A composite structure of a ferroelectric thin film and a substrate, wherein a ferroelectric thin film containing lead is placed on a substrate or a substrate made of a thin film containing silicon. between the base, the composite structure of the ferroelectric thin film and the substrate, wherein the lead was sandwiched lead titanate layer or Ranaru dielectric thin film missing out of the stoichiometric composition. 2. The composite structure of a ferroelectric thin film and a substrate according to claim 1, wherein the dielectric thin film is an oxide thin film formed by a chemical vapor deposition method. 3. The ferroelectric thin film according to claim 1, wherein both the dielectric thin film and the lead-containing ferroelectric thin film are thin films formed by a chemical vapor deposition method. And a composite structure of a substrate. 4. The ferroelectric thin film is a perovskite (0
01) An oriented ferroelectric thin film, wherein the composite structure of the ferroelectric thin film and the substrate according to claim 1 or 3. 5. The dielectric thin film and the ferroelectric thin film,
The composite structure of a ferroelectric thin film and a substrate according to any one of claims 1 to 4, wherein the composite structure is continuously formed by the same chemical vapor deposition apparatus. 6. The dielectric thin film and the ferroelectric thin film,
6. The method according to claim 1, wherein the material is formed by a digital chemical vapor deposition method in which a raw material is periodically introduced to deposit thin films of several atomic layers while being stacked.
7. A composite structure comprising the ferroelectric thin film according to any one of 1 to 4 and a substrate.