Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2000-08-31
2002-08-27
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C438S608000, C438S660000
Reexamination Certificate
active
06440751
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method of manufacturing a crystallized thin film formed by ferroelectric substance, such as Pb (Zr, Ti) O
3
(PZT) by the use of a sol-gel method.
When a ferroelectric thin film is used as a capacitor insulating film of a non-volatile memory, it is indispensable to reduce an area of a memory cell in order to improve the integration of the memory.
To this end, it is necessary to directly form the ferroelectric thin film capacitor on a conductive plug which is recently applied to a DRAM (Dynamic Random Access Memory) having high integration.
In this event, when a thermal treatment is performed during a production of the ferroelectric thin film capacitor, the conductive plug and a diffusion barrier layer attached thereto (for example, TiN/Ti) are oxidized. Consequently, the conductivity is often and inevitably lost.
Therefore, it is required that a temperature during the production of the ferroelectric thin film is reduced to 500° C. or less, more preferably 450° C. or less, to avoid such oxidation.
Meanwhile, it is well known that Pb base ferroelectric substance, in particular, Pb (Zr, Ti) O
3
(hereinafter, abbreviated as PZT) and material added slight of additive such as La and Nb into PZT is suitable as ferroelectric thin film material for the non-volatile memory. This is because the Pb base ferroelectric substance has a large residual polarization, and can be produced at about 600° C.
As the production method of the ferroelectric thin film, the sol-gel method is desirable because it has such advantage that an excellent thin film can be obtained with superior repeatability using a cheaper equipment. In such a sol-gel method, an organic metal material is dissolved into desired solvent, and is applied and baked.
For example, it has been reported that PZT of Zr/Ti=53/47 becomes a single perovskite phase by using a buffer layer of PbTiO
3
(hereinafter, abbreviated as PT) by the sol-gel method at 500° C. written in Journal of material research 1993, Vol. 8. Page 339 (C. K. K wok et al., J. Mater. Res. 8, 339 (1993)).
In this case, the production process of the PZT thin film is illustrated in
FIG. 1
, and the PT layer is crystallized before applying PZT. In this paper, although a sapphire substrate is used, the electrical characteristic such as ferroelectric characteristic is not reported at all.
Further, disclosure has been made about such a fact that PZT is produced using a PT buffer layer by the sol-gel method at 450° C. in Japanese Journal of Appl. Phys, 1996, Vol. 35, page 4896 (H. Suzuki et al., Jpn. J. Appl. Phys. 35, 4896 (1996)).
Although the single perovskite phase is formed 450° C. ,as illustrated in
FIG. 4
in this paper, the paper does not disclose or teach the ferroelectric characteristic.
Moreover, the dielectric constant is 30 or less at about 0.2 &mgr;m, as shown in
FIG. 5
in this paper, and the characteristic is not enough to be practically used.
The process for producing the PZT thin film disclosed in this paper is illustrated in
FIG. 2
, and the PT layer is decomposed by an organic thermal process at 350° C. before applying PZT.
As mentioned above, the Pb base ferroelectric substance, in particular, the PZT based ferroelectric thin film (the film thickness of 300 nm or less) having excellent composition at 500° C. or less, more desirably 450° C. or less has not been realized by the use of the sol-gel method
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a method of manufacturing a thin film and a capacitor using excellent PZT base ferroelectric material at a low temperature by the use of the sol-gel method.
In a method of manufacturing a thin film according to this invention, a buffer layer is formed on a substrate. Thereafter, a ferroelectric thin film material is applied thereto before thermally decomposing the buffer layer.
Subsequently, the buffer layer and the ferroelectric thin film are decomposed together. Finally, a crystallized thermal process is performed.
In this event, the buffer layer is provided so as to proceed the crystallization of the thin film on the buffer layer, and may be referred to as a seed forming layer.
The deposition temperature due to the sol-gel method can be lowered by forming the thin film using such a method.
When this method is applied to the PZT thin film, a buffer layer containing PbTiO
3
as main component is formed on the substrate.
Thereafter, a thin film material containing PZT as main component is applied before decomposing the buffer layer by a thermal organic process.
After the buffer layer and the thin film are decomposed together by the thermal organic process, a crystallized thermal process is performed.
More specifically, after the buffer layer containing PbTiO
3
as main component is formed on the substrate, the buffer layer is baked at a temperature at which organic thermal decomposition does not occur.
Subsequently, a thin film material containing PZT as main component is applied on the buffer layer.
After the PZT thin film is baked at a temperature at which the organic thermal decomposition does not occur, the buffer layer and the thin film are decomposed together by the thermal organic process. Finally, the crystallized thermal process is performed.
In this case, the application step of the thin film containing PZT as main component through the crystallized thermal step may be repeated after the crystallized thermal process such that the PZT thin film has the preselected film thickness.
In this event, the duration of the final crystallized thermal process may be longer than that of the previous crystallization thermal process.
This reason will be explained hereinbelow. Namely, when the crystallization is carried out at such a low temperature, as thermal process duration is longer, the characteristic such as the ferroelectric characteristic is more improved.
If the crystallization thermal process is performed for long duration at every application layers, the final crystallization thermal process is unnecessary.
However, long duration is required to manufacture the thin film when the application number is particularly increased. In consequence, the throughput is degraded.
In the meantime, the layer, which is initially applied, is subjected to the thermal process having the longest duration. Consequently, the crystallized thermal process durations are variable for the respective application layers, and the thin film may be formed such that each application layer has not a uniform characteristic.
To this end, it is preferable that the final crystallization thermal process, which is entirely performed, is carried out for longer duration.
Further, in a method of manufacturing a PZT thin film according to this invention, a buffer layer containing PbTiO
3
as main component is formed on the substrate.
Thereafter, the buffer layer is baked at a temperature at which the organic thermal decomposition does not occur.
Subsequently, the thin film material containing PZT as main component is applied on the buffer layer.
After the PZT thin film is baked at a temperature at which the organic thermal decomposition does not occur, the buffer layer and the thin film are decomposed together by the thermal organic process. Finally, the crystallized thermal process is entirely performed.
In this case, the application step of the thin film containing PZT as main component through the thermal decomposition step may be repeated after the crystallized thermal process such that the PZT thin film has the preselected film thickness.
Further, RTA (Rapid Thermal Annealing) decomposition may be performed after decomposing by the organic thermal process.
Alternatively, the RTA decomposition may be carried out instead of the organic thermal decomposition.
The general organic thermal decomposition is carried out within the temperature range between 300° C. and 400° C. for process duration of about 10 minutes in the oxygen atmosphere (in oxygen gas or in H
2
O/O
2
atmosphere).
However, the RTA decomposition is conducted at a slightly higher tem
Everhart Caridad
Scully Scott Murphy & Presser
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