JPH02249278A - Manufacture of ferroelectric film - Google Patents

Abstract

PURPOSE:To achieve a manufacturing method for improving stability of a ferroelectric body film, especially stoichiometry of the ferroelectric body film by performing annealing within a high-pressure oxygen after forming the ferroelectric body film, sputtering the ferroelectric body target. CONSTITUTION:After forming a ferroelectric body thin film 104 by sputtering a ferroelectric body target. annealing is made within a high-pressure oxygen 105. For example, an insulating film 102 is clad on an Si substrate 101, tungsten is clad as a lower-part electrode 103 by the sputtering method, and then patterning is made by using the photolithography method. Then, after cladding PZT (PbZr0.65Ti0.35O3) as the ferroelectric body thin film by the sputtering method, annealing is made at 8 atmospheric pressure, 800 deg.% within a high- pressure oxygen 105 for 30 minutes. After that, Al is formed by the sputtering method as an upper electrode 106 and then Al and the ferroelectric body thin film PZT are subjected to patterning simultaneously by photolithography Further more, by cladding an insulating film 107 for opening a contact hole and forming Al as a wiring metal 108, and then patterning is made.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric film and a method of manufacturing a nonvolatile memory using the same.

[Summary of the invention]

The present invention is a method for manufacturing a ferroelectric film, in which a ferroelectric film is formed by sputtering and then annealed in high pressure oxygen to form a dense film with a close to stoichiometric composition. When applied to a nonvolatile memory, the present invention provides a highly reliable nonvolatile memory that can be electrically rewritten many times.

[Conventional technology]

Conventional semiconductor non-volatile memories generally use MIS transistors, which utilize a phenomenon in which the surface potential of a silicon substrate is modulated by injecting charge from the silicon substrate into a trap or floating gate in an insulated gate. It has been put into practical use as EFROM (ultraviolet erasable nonvolatile memory) and EEPROM (electrically rewritable nonvolatile memory).

[Problem to be solved by the invention]

However, these nonvolatile memories have drawbacks such as a high voltage for rewriting information, usually around 20 V, and a very long rewriting time (for example, several tens of m5ec in the case of EEPROM). In addition, the number of times information is rewritten is very small, approximately 105 times.

There are many problems when using it repeatedly.

Non-volatile memory using ferroelectric materials whose polarization can be electrically reversed is ideal because the write time and read time are basically the same, and the polarization is maintained even when the power is turned off. It has the potential to become non-volatile memory. Regarding non-volatile memories using such ferroelectric materials, for example, as in US Pat. No. 4,149,302, there is a structure in which a ferroelectric capacitor is integrated on a silicon substrate, and as in US Pat. Proposals have been made for non-volatile memories in which a ferroelectric film is placed in some areas. However, in reality, it has not yet been put into practical use because ferroelectric films lack stability and are not suitable for integration. Further, although a sputtering method is usually used to form a ferroelectric film, the ferroelectric film formed by this method is often deficient in oxygen.

SUMMARY OF THE INVENTION The present invention is intended to solve these problems, and its purpose is to provide a manufacturing method that improves the stability of a ferroelectric film, particularly the stoichiometry of a ferroelectric film.

[Means for Solving the Problems] In the method for manufacturing a ferroelectric film of the present invention, in the step of forming a ferroelectric film, after forming a ferroelectric thin film by sputtering a ferroelectric target, sputtering is performed in a high pressure oxygen atmosphere. It is characterized by annealing.

〔Example〕

FIG. 1 is a manufacturing process diagram showing an embodiment of the present invention. First, an insulating film 102 is deposited on an 81 substrate 101. Next, a lower electrode 103, such as tungsten (W), is deposited by sputtering and patterned by photolithography. (FIG. 1(a)) Furthermore, the ferroelectric thin film 104
, for example PzT (PbZro, 6s'Tio, qO
g) is deposited by sputtering. In this state, annealing is performed in high pressure oxygen 105 at, for example, 8 atm and 800° C. for 30 minutes.

(FIG. 1(b)) As a result, oxygen is incorporated into PZT, forming stoichiometric PZT. In addition, the ferroelectric thin film 104 immediately after sputtering has insufficient crystallinity and poor orientation, but by annealing at high pressure oxygen 105 and high temperature, the orientation becomes better and the density increases. , the properties as a ferroelectric crystal are improved.

Thereafter, an upper electrode 106, for example AI, is formed by sputtering, and the AI and the ferroelectric thin film PZT are simultaneously patterned by photolithography. (Figure 1 (C)
) Further, an insulating film 107 is deposited, a contact hole is opened, and a wiring metal 108, for example /'47, is formed and then patterned (Fig. 1(d)). However, this method depleted oxygen in PZT and deteriorated the polarization characteristics of the ferroelectric material, making it difficult to apply it to nonvolatile semiconductor memories. There is also a method of annealing in atmospheric pressure oxygen after sputtering, but according to this method,
For example, when Ag is used for the lower electrode, the temperature cannot be raised, resulting in insufficient annealing effects. According to the present invention, since high-pressure oxygen is used, the annealing effect can be achieved even at low temperatures, and it is sufficient if the temperature is 500° C. or higher. Therefore, the lower electrode is A
Even 11 has a sufficient annealing effect, and the characteristics of the ferroelectric film are improved. If a high melting point metal such as W is used for the lower electrode as in this embodiment, the annealing temperature can be raised to nearly 900° C., which further improves the annealing effect.

Furthermore, although PZT was used as the ferroelectric film in this embodiment, it goes without saying that other perovskite-type oxide ferroelectrics such as B a T L O 3 and PLZT can also be used to provide similar effects.

The ferroelectric thin film according to the present invention can be applied to non-volatile memories, and can be used to manufacture highly reliable non-volatile memories that can be electrically rewritten many times. It can also be applied when integrating capacitors.

[Effects of the Invention] According to the present invention, there is an effect of improving the stability of a ferroelectric film, particularly the stoichiometry of the ferroelectric film. For example, when applied to nonvolatile memory, it becomes possible to manufacture highly reliable nonvolatile memory that can be electrically rewritten many times.

[Brief explanation of drawings]

FIGS. 1(a, 1d) to 1(d) are manufacturing process diagrams showing one embodiment of the present invention. 1, 01 ・ 102 ・ 103 ・ ] 04 φ 105 ・ 106 ・ 107 ・ 108 company

Claims (1)

[Claims] A method for producing a ferroelectric film, which comprises forming a ferroelectric thin film by sputtering a ferroelectric target, and then annealing the film in high-pressure oxygen.