JPH0319373A - Formation of ferroelectric thin film - Google Patents

Abstract

PURPOSE:To eliminate the occurrence of cracks in a ferroelectric thin film so as to improve it in ferroelectricity by a method wherein a ferroelectric thin film is etched into a prescribed pattern, which is thermally treated. CONSTITUTION:A ferroelectric thin film 104 is formed through, for instance, a sputtering method. For instance, PZT is used as ferroelectric, and a material composed of, for instance, PbZrO3 and PbTiO3 in the ratio 52%/48% to which 5mol% PbO is added is used as a target. Sputtering is executed, for instance, in an atmosphere of Ar/O2 a power of 200W keeping a substrate at from a normal temperature to a temperature of 300 deg.C. Then, the sputtered PZT is etched into a prescribed pattern with mixed acid of HCl and HF, which is thermally treated. The sputtered PZT is turned into a perovskite structure through the thermal treatment concerned and grows to display ferroelectricity.

Description

[Detailed Description of the Invention] "Industrial Application Field" The present invention relates to a method for manufacturing a ferroelectric memo using a ferroelectric, particularly an electrically rewritable nonvolatile memory, and particularly a method for manufacturing a ferroelectric thin film. 6 regarding the method of forming.

[Aspects of the Invention 1] The present invention provides a method for forming a ferroelectric thin film.
, the process of forming the t-film and the ferroelectric thin model.
By performing an etching process to form a pattern and a heat treatment process after forming a predetermined pattern, we are able to obtain a ferroelectric thin film that has excellent properties and does not cause cracking. ．． [Prior art] Conventional semiconductor non-volatile memory uses transistors in insulated gates or flat gates (this uses a phenomenon in which the surface potential of the silicon substrate is modulated by injecting charge from the silicon substrate). M I S type transistors are commonly used and have been put into practical use as IEPROMs (ultraviolet erasable nonvolatile memories), EIEPROMs (electrically rewritable nonvolatile memories), and the like.

[Problems to be solved by the invention] However, in these non-volatile memories, the voltage for rewriting information is usually as high as about 20 V, and the rewriting time is very long (for example, in the case of EEFROM, it takes several tens of milliseconds). ) and other disadvantages. Also, the number of rewrites of information ÷ ]; is about 10 @ times, which is not '11! However, there are many problems when using it repeatedly). For non-volatile memories that use ferroelectric materials whose polarization can be electrically reversed, the write time and read time are in principle almost the same, and the six polarizations are maintained even when the power is turned off, so it is logical that It has the potential to become a tragic non-volatile memory. Regarding nonvolatile memories using such ferroelectric materials, there are, for example, U.S. Pat. M
Proposals have been made for non-volatile memories in which a ferroelectric film is placed on the gate of I S 'rA[・randisk. The non-volatile memory structure is IEDM87pp.
, 850-851. In Figure 3, 3
01 is a P-type Si substrate, and 302 is an LO for element isolation.
The GOS oxide film 303 is an N-type diffusion layer that becomes a sos.
304 is an N-type expanding layer that becomes Draino. 305 is a gate N1%, and 306 is an interlayer insulating film. 30
8 is a ferroelectric film, which is sandwiched between electrodes 308 and 309 to form a capacitor. 310 is a second interlayer insulating film, and 311 is A1 which becomes a wiring electrode. When PZT is used as a ferroelectric thin film, for example, in order to obtain ferroelectricity, it is necessary to have a crystal structure and a perovskite structure. In order to obtain a perovskite structure, for example, when sputtering is used as a method for forming a ferroelectric film, the wetness of the base tFj must be increased to 500°C or higher, or sputtering at a low temperature and then sputtering at 500"C or higher is required. In this way, after forming a ferroelectric thin film by the spanokling method, for example, if near annealing is performed, due to the difference in thermal expansion coefficient between the ferroelectric thin film and the substrate, for example, a Si substrate, annealing may occur. Therefore, the present invention solves this problem, and its purpose is to create a ferroelectric thin film that does not cause cracks and has excellent ferroelectric properties. The present invention provides a method for forming a ferroelectric thin film. It is characterized by a step of enching to a predetermined pattern, and a step of subsequently performing voice nine processing.

[Example 1] Figure 1 shows an example of the semiconductor device {1t} of the present invention.
、． This is the main process diagram. Hereinafter, a method for forming a ferroelectric thin film according to the present invention will be explained with reference to FIG.

(FIG. 1(a)) 1 0 1 is a substrate (if it is arranged in a row, it is a Si substrate). +02 is an insulating film that separates the substrate and the ferroelectric thin film; for example, an oxide film is
If31il2. A lower electrode 103 is formed under the ferroelectric thin film, and is made of, for example, Pt IOOOA.

(Figure 1(b)) Next, ferroelectric material, Cori ni 1o 4
{t) About 5 0 0 0 A by 1λ Subback method
Form. For example, PZT is used as the strong electrical conductor, and for example, P b Z r O 3 /
A cugette prepared by adding 5 mol % of PbO to P b T i O 3 =52%/48% is used. The sputtering conditions are, for example, 200 W in an Ar/02 atmosphere, and the substrate temperature is, for example, between 300° C. (Fig. 1 (C)). Next, a mixed acid of HCL and HF is used. It is etched into a predetermined pattern 105. Then, in this state, heat treatment is performed at 550° C. for 1 hour in, for example, 02 atmosphere. Through this heat treatment, the spattered PZT becomes a perovskite structure and exhibits ferroelectricity. .and,
Because annealing is performed after forming a predetermined pattern,
No cracks occur.

When we investigated the occurrence of cracks and the size of the pattern, we found that when forming a ferroelectric thin film on the lower electrodes 201 to 203 as shown in Fig. 2, It was found that if the body thin films 204 to 206 were formed independently, no cracks would occur. Furthermore, Figure 2 (b
), it was found that no cracks were generated by connecting one piece of the ferroelectric thin film to the lower electrode. We also found that if we made the length of one piece 208 less than 10 um, the other pieces would be connected and 6 would be better. In the above description, only the ferroelectric thin film portion has been described, so the substrate may be not only SiMm but also other substrates. Furthermore, at the same time as the ferroelectric thin film, as an active element, for example, Mos+-
It goes without saying that it is good to integrate transistors.

[Effects of the Invention] As described above, according to the present invention, in the method of forming a ferroelectric thin film, a step of forming a ferroelectric film, a step of etching into a predetermined pattern, and a heat treatment are performed. This process has the effect of making it possible to form a ferroelectric thin film that has excellent ferroelectricity and is free from cracks.

[Brief explanation of the drawing]

FIGS. 1(a) to (C) are main process diagrams of the method for forming a ferroelectric thin film of the present invention, and FIGS. 2(a) and (b) show predetermined patterns of the ferroelectric thin film of the present invention. It is a diagram. FIG. 3 is a cross-sectional view of a conventional ferroelectric memory. 101.301...Si substrate 102 , 302 ・ 104 ・ ・ ・ ・ 1 0 5 ・ ・ ・ ・ 103, 201. 2 0 4...Element portion iii II@...Ferroelectric thin film...Predetermined pattern 202.203...Lower electrodes 205, 206, 207...Predetermined pattern/length of ferroelectric thin film...・N-type spreading layer・Gate electrode・Ferroelectric film・AI electrode・Single-layer insulating film・Bottom electrode・Higher than upper electrode h 1 (α) 2 0 8 303, 304 ・305 ・ ・ ・ ・ 308 ・ ・ ・ 311 ・ ・ ・ ・ 306. 310 307 ・ ・ ・ 309 ・ ・ ・ ・ so5

Claims (5)

[Claims] (1) A method for forming a ferroelectric thin film, comprising the steps of forming a ferroelectric film, etching the ferroelectric thin film into a predetermined pattern, and performing heat treatment. (2) The method for forming a ferroelectric thin film according to claim 1, wherein the step of forming the ferroelectric film is sputtering. (3) The method for forming a ferroelectric thin film according to claim 1, wherein the heat treatment step is performed in an atmosphere containing at least oxygen and at a temperature of 500° C. or higher. (4) The method for forming a ferroelectric thin film according to claim 1, wherein the size of at least one piece of the predetermined pattern is 10 um or less. (5) The step of forming the ferroelectric film is sputtering, and the heat treatment step is performed in an atmosphere containing at least oxygen and at a temperature of 500° C. or higher, and Size is 10um
The method of forming a ferroelectric thin film according to claim 1, characterized in that: