JP2003342730A - Method of depositing pzt thin film by chemical vapor growth method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a raw material system, a feed system and a film deposition method by which a process window wherein a film composition Pb/(Zr+Ti)=1 is opened, and the Zr/Ti ratio can fixedly be held to a prescribed value in CVD (chemical vapor deposition) by a system using a liquid mass flow controller and a carburettor effective for the mass production of a PZT (PbZrO<SB>3</SB>-PbTiO<SB>3</SB>) film, and to deposit the film even at a low temperature of ≤500°C. <P>SOLUTION: A cyclohexane solution of Pb(dpm)<SB>2</SB>in a high concentration is fed from a raw material vessel 1 to a carburettor 1 through a mass flow controller 1. A crude mixed liquid of Zr(OtBu)<SB>4</SB>and Ti(OtBu)<SB>4</SB>is fed from a raw material vessel 2 to a carburettor 2 through a mass flow controller 2. These gases and gaseous O<SB>2</SB>are mixed with a shower head and are introduced into the surface of a Pt/SiO<SB>2</SB>/Si substrate, and CVD is carried out under 1 Torr at 480°C to deposit a satisfactory PZT film. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a PZT or PLZT thin film by a chemical vapor deposition method (hereinafter referred to as a CVD method).

[0002]

2. Description of the Related Art PbZr _1-y Ti _y O ₃ (0 <y <, which is used for a highly integrated nonvolatile memory, a piezoelectric element, or the like.
1, hereinafter referred to as PZT), or (Pb _1-x , La _x ).
(Zr _1-y , Ti _y ) O ₃ (0 <x <1, 0 <y <
1) The CVD method is used as a method for producing a thin film (hereinafter referred to as PLZT) with high mass productivity. As the raw material supply method, there are a method of vaporizing and supplying each compound of Pb, Zr, Ti and La as they are and a method of vaporizing and supplying them as a solution, and the latter is more suitable for mass production.

Pb (dpm) ₂ , Zr (OtBu) ₄ ,
In the former type of CVD in which each compound of Ti (OiPr) ₄ is directly vaporized and supplied, the film composition is Pb / (Zr + T
i) = 1, the process window of Pb supply becomes autonomous and becomes wide. Aratani et al, J
pn. J. Appl. Phys. Vol. 40,412
6 (2001) and the like. Here, the process window is the film composition Pb / (Zr + Ti) = 1.0.
The area of the raw material supply rate and its ratio. For example, it means the range of the supply ratio in which the film composition Pb / (Zr + Ti) = 1.0 is maintained even if the supply ratio of the Pb raw material to the (Zr + Ti) raw material changes. Pb / (Zr + Ti) is 1.
If it deviates from 0, the ferroelectric characteristics deteriorate, so it is difficult to adopt it as a mass production process unless the process window is wide. However, it has been found that the solution vaporization method has problems that the CVD rate is lowered and that there is almost no process window, probably because a large amount of solvent is present during CVD.

Regarding this problem, Ozeki et al., Proc. Of the 49th Japan Society of Applied Physics p511 (2002. 3)
Pb (dpm) ₂ / octane (0.1 mol / l), Z
r (OtBu) ₄ / octane (0.1 mol / l), T
It has been reported that as a result of performing CVD at 500 and 600 ° C. by a solution vaporization method using i (OiPr) ₄ / octane (0.1 mol / l), the deposition amount is reduced and there is no process window. M. Miyake et al, J
pn. J. Appl. Phys. Vol. 41,241
(2002) is Pb (dpm) ₂ /THF(0.05
mol / l), Zr (dibm) _{4 /} THF (0.1 m
ol / l), Ti (OiPr) ₂ (dpm) ₂ / THF
Solution vaporization method using (0.1 mol / l), 20T
Although the CVD was performed at orr and 550 ° C., the existence of the process window is not shown. Otani et al., Proceedings of the 49th Japan Society of Applied Physics p511 (2002.3) is [Pb
(Methd) ₂ + Zr (methd) ₄ + Ti (mp
d) (methd) ₂ ] / ethylcyclohexane (0.
049, 0.03, 0.03 mol / l), a solution vaporization method was used, and as a result of performing CVD at a substrate temperature of 3 Torr and 550 ° C., the Pb composition of the film was sensitively affected by the Pb concentration of the solution and the process window was It has announced that it did not open. Here, methd is [1- (2-methoxy) ethoxy-2,2,6,6-tetramethyl-3,5-heptanedionate] and mpd is [2-methyl-2,4-pentanedioxy]. Represent Y. -S. Park, Int
Egged Ferroelectrics, Vo
l. 39,231 (2001) is Pb (dpm) ₂ /
Heptane (0.05 mol / l), Zr (OiPr) ₂
(Dpm) ₂ / heptane (0.05 mol / l), Ti
(OiPr) ₂ (dpm) ₂ / heptane (0.05mo
It is disclosed that the process window did not open as a result of performing the CVD at 480 to 570 ° C. by the solution vaporization method using 1 / l).

As described above, solution vaporization type CVD
There is no report that a process window has been opened in the method of manufacturing a PZT film by.

Zr raw materials used in the solution vaporization system are Zr (dpm) ₄ and Zr (OiPr) ₂ (dpm).
₂ , Zr (OiPr) (dpm) ₃ , Zr (dibm)
₄ , Zr (methd) _4, etc., but it has been found that there is a problem that the incorporation of Zr into the film by CVD is unstable. The Zr / Ti ratio of the PZT film is PZ
Since the crystal type of the T film is determined and the ferroelectric property is determined, it is necessary to control it to a predetermined value. If the Zr uptake is unstable, the Zr / Ti ratio may fluctuate, which is a problem.

If a non-volatile memory of PZT is manufactured at a temperature lower than the Al wiring can withstand, a highly integrated semiconductor device having a multi-layer metal structure can be obtained. The manufacturing method is disclosed in Japanese Patent Laid-Open No. 2000-58526. However, this embodiment is not a solution vaporization system but a system that does not use a solvent at all.

Zr (OtBu) ₄ and Ti (OiPr) ₄
It is preferable to mass-produce the liquid raw material by vaporizing and supplying it with a liquid mass flow controller and a vaporizer rather than bubbling it, because a large amount of gas can be sent. A method of vaporizing and supplying raw liquid alkoxide with a liquid mass flow controller and a vaporizer has been industrialized with Si (OEt) ₄ and Ta (OEt) ₅ . However, Zr (OtBu) ₄ and Ti (Oi
In order to maintain the ratio of Pr) _{4 at} a predetermined value with high accuracy, it is necessary to control the supply amounts thereof with high accuracy by the respective liquid mass flow controllers, but this is not easy. Instead of using two liquid mass flow controllers, Zr (OtBu) ₄ and T
It may be mixed with i (OiPr) ₄ in a predetermined ratio, but when mixed with a liquid, the alkoxyl group is exchanged instantly and a precipitate is formed, so this method cannot be used.

[0009]

The object of the present invention is to provide a PZ
Since a method using a liquid mass flow controller and a vaporizer is preferable for mass production of T film, it is an object to provide a raw material system and a supply system capable of facilitating the method. Further, in that method, the amount of solvent is reduced as much as possible so that the process window can be easily opened, and the Zr / Ti ratio can be maintained at a predetermined value.
It is to provide a method capable of forming a film even at a low temperature of 00 ° C. or less.

[0010]

The present inventor has found that Pb (dp
m) Only ₂ is used as a solution, and the other Zr and Ti raw materials are raw volatile alkoxides.
If Ti (OtBu) ₄ that does not react with r (OtBu) ₄ is used, a mixed solution having a predetermined Zr / Ti ratio can be formed in one raw material container, and a Pb (dpm) ₂ solution is vaporized by a vaporizer 1 to produce Zr. The inventors have found that if a mixture of (OtBu) ₄ and Ti (OtBu) ₄ is vaporized in a vaporizer 2 and then combined with a gas, CVD can be carried out without causing an inconvenient reaction and a process window can be opened, thereby completing the present invention. Came to.

The present invention provides a method for producing a PZT thin film by a chemical vapor deposition method, which comprises bis (β-diketonate).
A method for producing a PZT thin film is characterized in that a lead solution, Zr (OtBu) ₄ , Ti (OtBu) _4, and an oxidizing agent are used as raw materials.

The present invention relates to a method for producing a PZT thin film by a chemical vapor deposition method, wherein a Pb (dpm) ₂ solution and Z are used.
This is a method for producing a PZT thin film, which uses r (OtBu) ₄ , Ti (OtBu) _4, and an oxidant as raw materials.

In the present invention, a bis (β-diketonate) lead solution is vaporized by a vaporizer 1 to obtain Zr (OtBu) ₄ and Ti.
This is a method for producing a PZT thin film, characterized in that a mixed liquid with (OtBu) ₄ is vaporized by a vaporizer 2 and the gas from these two vaporizers and an oxidant are mixed and introduced into a CVD chamber.

In the present invention, a bis (β-diketonate) lead solution is vaporized in a vaporizer 1 and a mixed liquid of Zr (OtBu) ₄ and Ti (OtBu) ₄ supplied from one raw material container at a predetermined ratio is prepared. This is a method for producing a PZT thin film, which is characterized in that the vaporizer 2 vaporizes, the gas from these two vaporizers and the oxidant are mixed and introduced into a CVD chamber.

The present invention is the method for producing a PZT thin film described above, characterized in that the substrate temperature is 400 to 500 ° C.

The present invention is characterized in that the solvent of the bis (β-diketonate) lead solution is one selected from the group consisting of THF, toluene, butyl acetate, cyclohexane, methylcyclohexane and ethylcyclohexane. This is a method for manufacturing a PZT thin film.

The present invention is a method for producing the PLZT thin film described above, wherein Pb of the PZT thin film is partially replaced with La.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION As bis (β-diketonato) lead used in the present invention, Pb (dpm) ₂ , [bis (2,2,6,6-tetramethyl-3,5-octanedionate)] Lead], bis (2,2,6-trimethyl-3,
5-heptanedionato) lead, bis (6-ethyl-2,
2-Dimethyl-3,5-octanedionate) Lead, Pb
(Methd) ₂ and the like. Pb (dpm) ₂ which is easily available and has the highest thermal stability is preferable.

In order to reduce the amount of the solvent entering the CVD chamber as much as possible, the solvent of the bis (β-diketonate) lead solution used in the present invention has a high dissolving ability and Zr.
It is necessary that it is difficult to react with (OtBu) ₄ or Ti (OtBu) ₄ . Those which meet these requirements include THF, toluene, butyl acetate, cyclohexane, methylcyclohexane and ethylcyclohexane. Pb (dp dissolved in 1 L of various solvents at room temperature
Table 1 shows the mass of m) ₂ (unit: g).

[0020]

[Table 1]

In order to reduce the amount of solvent as much as possible, Pb (d
It is desirable to use a solvent with a high solubility of pm) ₂ and to keep the vaporizer pressure as low as possible and the vaporizer temperature as high as possible. However, considering the low vapor pressure and thermal stability of Pb (dpm) ₂ , it is in the range of about 200 to 250 ° C.

The saturated vapor pressure of Pb (dpm) ₂ is expressed by the following Clausius-Clapeyron equation as a result of the measurement by the present inventor at 130 to 170 ° C. by the gas saturation method. Log ₁₀ P = −4480 / T + 9.94 (P:
Torr, T: K) Also, the boiling point of Pb (dpm) ₂ at 1 atmosphere of Ar is TG-D.
When examined by TA, it was 350 to 359 ° C. This is in good agreement with the value 361 ° C. obtained from the extrapolation of the vapor pressure formula, so the extrapolation of the formula is reliable. Then Pb (dpm) ₂
When the saturated vapor pressure of is calculated from the above equation, it is 3.0 Torr /
It becomes 200 degrees Celsius and 24 Torr / 250 degrees Celsius.

If the gas temperature in the vaporizer is completely equal to the vaporizer temperature, and if the vaporizer pressure at 200 ° C. is 10 Torr, (10-3.0 =) 7.0 Torr of solvent is available. In principle, the whole amount can be gas. That is, the minimum required amount of solvent is (7.0 / 3.0) of Pb (dpm) _2.
=) 2.4 times the molar amount. The molecular weight of the solvents in Table 1 is T
Since it is between 72 of HF and 116 of butyl acetate, it is represented by a molecular weight of 100 and a density of 0.8 g / cm ³ for simplicity. The volume of the mixture of 1 mol of Pb (dpm) ₂ and 2.4 mol of the solvent is about Pb (dpm) ₂ min + solvent = (574 / 1.52) +
(240 / 0.8) = 378 + 300 = 678 ml. That is, the Pb (dpm) ₂ concentration is 1 / 0.67
8 = 1.47 mol / l. This is the equilibrium case and is not achieved in practice, thus requiring more solvent and higher vaporizer temperature.

From the above, Pb (dpm) ₂ 1mo
The l / l solution has a vaporizer pressure of 10 Torr and a vaporizer temperature of 2
It is considered that vaporization is possible at about 50 ° C. He, Ar, N
If an inert gas such as ₂ coexists, it can be vaporized at a lower vaporizer temperature. If the vaporizer pressure is as low as 5 Torr, vaporization can be performed at a lower vaporizer temperature. Of course, it is necessary to devise the structure and usage of the vaporizer so as not to cause clogging and skipping of the solvent. THF, toluene, acetic acid n in Table 1
-Butyl, cyclohexane, and methylcyclohexane are convenient because a solution of about 0.5 mol / l Pb (dpm) ₂ can be formed.

Ti (OtBu) ₄ is a compound which is liquid at room temperature and has a melting point of 4 ° C., and its physical properties are very similar to those of Zr (OtBu) ₄ . The physical properties of each are shown in Table 2.

[0026]

[Table 2]

Both are monomers, and when they are mixed, they only mix with each other and do not associate with each other. Since the physical properties are similar, a completely uniform mixture can be obtained. There is no problem at all even if mixed in the pipe just before the vaporizer or mixed in the raw material container. If there is no water or oxygen, the vaporizer temperature is 150 ° C.
But it does not pyrolyze.

Zr (OtBu) ₄ and Ti (OtBu) ₄
It is preferable to use a mixture of the materials in one raw material container at a predetermined ratio. Then, there is an advantage that the mixing uniformity of Zr and Ti is good, the mass flow controller is one, and the accuracy of the flow control may be slightly low. The mixing ratio of Zr (OtBu) ₄ and Ti (OtBu) ₄ is influenced by the film composition, the film forming temperature, the coexistence of Pb (dpm) ₂ , and the like, and may be determined in advance by experiments.

When PZT is formed after forming an underlayer of PbTiO ₃ , Zr (OtBu) ₄ and Ti (O
raw material container A containing a mixture with tBu) ₄ and Ti (O
It is better to set and use the raw material container B containing tBu) ₄ . In this case, the mass flow controller is 1
The base may be used, and the accuracy may be a little low when using B or when using A. However, Zr (Ot
When the raw material container C containing Bu) ₄ and the raw material container B containing Ti (OtBu) ₄ are set, the two mass flow controllers are required to have high accuracy during PZT film formation. This should be avoided industrially.

In the present invention, the substrate temperature for PZT film formation is set to 40.
It can be 0 to 500 ° C. Since the Pb, Zr, and Ti sources are all compounds that can be deposited at a low temperature, a film exhibiting good ferroelectricity even at such a low temperature can be obtained.

The pressure in the CVD chamber is 0.001-10To.
rr. It is preferably 0.01 to 3 Torr. If the pressure is higher than 3 Torr, the vaporizer pressure will be 10T.
Inevitably it will be as high as orr. As a result, Pb
Since (dpm) ₂ is less likely to be vaporized, the concentration must be lowered to use a large amount of solvent, a large amount of carrier gas, and a higher temperature. The presence of high concentrations of solvent narrows the process window for Pb / (Zr + Ti) = 1. In order to eliminate these drawbacks, a low pressure is preferable as much as possible, but if the pressure is too low, the film formation rate will decrease.

As the oxidizing gas, O ₂ , O ₃ , N ₂ O,
NO ₂ etc. can be used. For lowering the temperature, selection of these types and assist methods such as plasma may be used.

In the case of PLZT, the above applies as it is. As the La raw material, La (dpm) ₃ , La
(Dibm) ₃ [tris (diisobutyryl methanate)
Lantern] can be used. The latter is preferable for lowering the temperature. In addition, the latter is more soluble in various solvents, so that supply and vaporization can be performed with a small amount of solvent. These La compounds and Pb
If (dpm) ₂ is mixed at a predetermined ratio and supplied from one raw material container, the composition has good accuracy and uniformity, and there are industrial advantages such that one mass flow controller can send two raw materials.

[0034]

[Example] Production of PZT thin film A cyclohexane solution of Pb (dpm) ₂ (concentration: 0.5 mol / l) was fed from a raw material container 1 through a mass flow controller 1 to a vaporizer 1 at 240 ° C. together with 300 sccm of preheated Ar gas. It was evaporated and sent to the gas mixing section. From the raw material container 2 Zr (OtBu) ₄ and Ti (OtB)
u) 0.1 of a raw mixture of _{4 with} a molar ratio of 0.35 / 0.65
Pass 0 ml / min through the mass flow controller 2,
Preheated Ar gas 70sc sent to 140 ° C vaporizer 2.
It was evaporated together with cm and sent to the gas mixing section. The pressure of the two vaporizers was nominally 5-7 Torr. Pb, Zr, and Ti compound gas from the mixing section and preheated O
₂ gas 400sccm introduced into the shower head CVD chamber, led to Pt / _SiO 2 / Si substrate. The CVD chamber pressure was 1.0 Torr, and the substrate temperature was 480 ° C. The film was formed for 20 minutes to obtain a film having a thickness of 200 to 250 nm.
According to XRD analysis, the film was tetragonal perovskite. A part of the film was dissolved and the composition was analyzed by ICP emission spectroscopy. Table 3 shows the relationship with the supply rate of the Pb (dpm) ₂ solution.
Shown in.

[0035]

[Table 3]

From this result, the film composition Pb / Pb / (dpm) _{2 was} supplied at a rate of 0.50 to 0.60 ml / min.
It can be seen that (Zr + Ti) = 1.00 to 1.01 was achieved and the process window was opened. Also Zr / Ti
It can be seen that the value of 0.38 to 0.39 was also constant.

[0037]

EFFECT OF THE INVENTION When a PZT film is formed by a raw material supply method using a liquid mass flow controller and a vaporizer, a process window with a film composition Pb / (Zr + Ti) = 1 can be opened and Zr / Ti can be kept constant. . PZT or PLZT
Effective for mass production of membranes.

Claims (7)

[Claims] 1. A method for producing a PZT thin film by a chemical vapor deposition method, comprising a bis (β-diketonate) lead solution and Z.
A method for producing a PZT thin film, which comprises using r (OtBu) ₄ , Ti (OtBu) _4, and an oxidant as raw materials. 2. Bis (β-diketonate) lead is Pb (dp
m) _2. The method for producing a PZT thin film according to claim 1, wherein 3. A bis (β-diketonate) lead solution is vaporized by a vaporizer 1 to obtain Zr (OtBu) ₄ and Ti (OtBu).
_4. The method for producing a PZT thin film according to claim 1 or 2, wherein the mixed liquid with ₄ is vaporized in the vaporizer 2, and the gas from these two vaporizers and the oxidant are mixed and introduced into the CVD chamber. . 4. The method for producing a PZT thin film according to claim 3, wherein a mixed liquid of Zr (OtBu) ₄ and Ti (OtBu) ₄ at a predetermined ratio is supplied to the vaporizer 2 from one raw material container. 5. The method for producing a PZT thin film according to claim 3 or 4, wherein the substrate temperature is 400 to 500 ° C. 6. The solvent for the bis (β-diketonate) lead solution is one selected from the group consisting of THF, toluene, butyl acetate, cyclohexane, methylcyclohexane and ethylcyclohexane. P described
Manufacturing method of ZT thin film. 7. The method for producing a PLZT thin film according to claim 1, wherein Pb of the PZT thin film is partially replaced with La.