JPH0319372A - Semiconductor device - Google Patents

Abstract

PURPOSE:To obtain a capacitor and a non-volatile memory provided with a high dielectric film operable at a low voltage, high in polarization speed, and stable by a method wherein the electrode end of the capacitor of ferroelectric film is formed of paraelectric film. CONSTITUTION:A lower electrode 8 is kept at a fixed potential of a capacitor. A paraelectric film 11 of SiO2 or the like is formed. The disused part of the paraelectric film 11 is removed through photoetching so as to leave the end of the capacitor electrode unremoved. Then, a ferroelectric film 9 of PbTiO3, for instance, is formed. The ferroelectric film 9 is thermally treated in an atmosphere of N2. The ferroelectric film 9 is formed into a pattern of prescribed shape through a photoetching method so as to leave the inside of the paraelectric film 11 unremoved. Then, Pt is deposited, for instance, as an upper electrode 10, which is formed into a pattern of prescribed shape through photoetching. A second interlaminar insulating film 12 is formed, a connection hole is provided in the upper electrode 10 and a source 5 through photoetching, and an AC film 13 is, for instance, formed, which is subjected to photoetching so as to connect the upper electrode 10 and the source 5 together.

Description

[Detailed Description of the Invention] r Industrial Application Field] The present invention relates to a nonvolatile memory using a ferroelectric material,
In particular, it concerns techniques that are effective when applied to capacitors. [Conventional technology 1] As a semiconductor non-volatile memory, an MIS type transistor uses a phenomenon in which the surface potential of the silicon substrate is modulated by injecting charge from the silicon substrate into a trap or a floating gate in an insulated gate. It is commonly used and has been put into practical use as EPROM (ultraviolet erasable non-volatile memory) and EEPROM (electronically rewritable non-volatile memory). However, these nonvolatile memories have drawbacks such as the high voltage required for rewriting information, usually around 20V. For non-volatile memory that uses ferroelectric material whose polarization can be reversed automatically, the write voltage is the commonly used 5V, and the polarization is maintained even when the power is turned off, making it ideal. It has the potential to become a non-volatile memory. A nonvolatile memory structure using such a ferroelectric material, W. I. KINNEY:・A NON-VOLATI
LE MEMORY(:ELL BASED ON F
ERRQELECTRIC STORAGE CAPA
CITORS'. IEDM, 8 7, PP8 5
0-, a capacitor as typified by FIG. 3 is laminated on top of a transistor with an insulating film interposed therebetween. There is a so-called stacked structure. [Problems to be Solved by the Invention] Figure 4 shows the relationship between the ideal applied voltage and accumulated charge in a capacitor using a ferroelectric material. However, in the case of the capacitor shown in Figure 3, the relationship between the applied voltage and the accumulated charge is as shown in Figure 5. This is because, as shown in Figure 6, the electric field at the electrode end of the capacitor wraps around to the outside under the electrode, and that part needs to be polarized. Therefore, compared to the rational case, a higher voltage is required to generate polarization or reverse polarization. Furthermore, if this is used as a capacitor for non-volatile memory, the write voltage must be set high and the write time will be long. Also, the polarization charge is not constant.
Additionally, since high voltage is required, there is no margin for nonvolatile memory design, and it becomes unstable when operated at low voltages. The present invention is intended to solve these problems, and its purpose is to enable low voltage operation and to increase the polarization speed. Our goal is to provide capacitors and nonvolatile memories using stable high dielectric films. [Means for Solving the Problems 1] The semiconductor device of the present invention includes: (1) an insulating film is formed on a semiconductor substrate, a lower electrode is formed on the insulating layer, and a ferroelectric material is formed on the lower electrode. In a capacitor in which a thin film is formed and an upper electrode is formed on the ferroelectric thin film, the upper M
It is characterized in that a paraelectric material is formed at the end of the part sandwiched between the pole and the lower part. [Embodiment] FIG. 1 is a sectional view of a semiconductor device in an embodiment of the present invention. Moreover, FIGS. 2(a) to 2(C) are main cross-sectional views for each manufacturing process. In all the figures of the embodiment, parts having the same functions are given the same reference numerals, and repeated explanations will be omitted. The explanation will be given below according to Fig. 2(a) to Fig. 2(c). For convenience of explanation, an example using an N-channel transistor will be explained here. First, as shown in Figure 2 (a),
For example, use a P-type Si substrate. Specific resistance is 20ohh
m. About cm would be appropriate. Approximately 6,000 people then form an insulating film 2 for element isolation using, for example, the LOCOS method. Reference numeral 7 denotes a gate film, which is formed by thermal oxidation in an oxidizing atmosphere after the element isolation insulating film 2 is formed. For example 30
Approximately 0 people would be appropriate. 4 is gate 1! Sun and what? , for example, is polycrystalline S1, and is formed with a film thickness of, for example, 4000. 5 and 6 are N-type diffusion layers that become the source and drain of the UOS transistor; for example, the gate electrode 4
After forming, 4X phosphorus is added by ion implantation
Formed by implanting 10 cm-. 3
is the first interlayer insulating film for separating from the MOS transistor formed on the above-mentioned Si substrate.
form. Then, as the lower electrode 8 of the capacitor, for example, 5,000 layers of PT is formed by the Subac method. Then, a predetermined pattern is formed using a photo-etching process. In this embodiment, the lower electrode 8 has a fixed potential of a capacitor.

Next, as shown in FIG. 2(b), a paraelectric film l1 of SiOz, for example, is formed to a thickness of 5,000 yen by the CVD method. Then, remove unnecessary portions of the electrical conductor 1l using a photo-etching process so as to leave the ends of the capacitor electrodes intact. Next, the ferroelectric film 9 is made of, for example, PbT.
Form 5,000 iOs using sputtering method. Then heat treatment was performed at 550°C for 1 hour in a N2 atmosphere. Next, as shown in FIG. 2(c), the ferroelectric material 1)i9 is formed into a predetermined pattern by a photo-etching process so as to leave the internal measurements of the paraelectric material 1i1). Next, as the upper electrode 10, PT, for example, is formed by a 5,000-person sputtering method, and is formed into a predetermined pattern by a photo-etching process. Finally, a second interlayer insulating film l2 is formed by chemical vapor deposition, and connection holes are formed on the upper electrode lO and on the source 5 by a photo-etching process. Formed by removing the grass,
By photo-etching the AC film 13 so as to connect the upper electrode IO and the source 5, this embodiment as shown in FIG. 1 is obtained. In this example, PbTtOs is used as the ferroelectric material, but PZTfPbTiOszPbZrOi).
Other ferroelectric materials such as PLZT may also be used. In this way, by using a paraelectric film instead of a ferroelectric film at the end of the capacitor, the electric field at the electrode end of the capacitor wraps around to the outside of the capacitor, as shown in Figure 6, but that part is not a paraelectric film. Since it is a body film, the amount of polarization of the ferroelectric film is constant. Therefore, the relationship between applied voltage and accumulated charge approaches the ideal relationship as shown in FIG. Therefore, low voltage is required because polarization is generated or reversed in the ferroelectric film. Furthermore, if it is used as a capacitor for non-volatile memory, it is possible to set the write voltage lower and the write time becomes shorter. In addition, since it is possible to operate at low voltages, there is a margin in the design of nonvolatile memory, and it is possible to operate stably even at low voltages. Further, although it is desirable that the paraelectric film 1) be provided on all the ends of the capacitor, it is possible to expect an effect equivalent to 6 on a portion. Furthermore, since the present invention is a special improvement of a capacitor using a ferroelectric film, it goes without saying that structures other than the capacitor may be not only the structure explained in this embodiment but also a CMOS structure, a bibolar structure, etc. do not have. Further, in this embodiment, the lower electrode 8 is grounded and a voltage is applied to the upper electrode 10 to form a cavity, but the present invention can also have the opposite structure. In addition, in this example, when forming a ferroelectric film inside a paraelectric film, a normal photo-etching process was used, but if formation was difficult, a lift-off etch-back method was used. It is better to form it. [Effects of the Invention 1] As described above, according to the semiconductor device of the present invention, by using a paraelectric film as the electrode end of a capacitor using a ferroelectric film, internal measurement can be performed instead of at the end of the capacitor. The ferroelectric film becomes polarized, making it possible to create high dielectric film capacitors that can operate at low voltages and operate stably, making it possible to create nonvolatile memories that can operate at low voltages and have short write times. can.

[Brief explanation of the drawing]

FIG. 1 is a main sectional view showing an embodiment of a semiconductor device and a semiconductor memory device of the present invention. FIGS. 2(a) to 2(c) are main cross-sectional views for explaining an example of a method for manufacturing a semiconductor device and a semiconductor memory device according to the present invention in the order of steps. FIG. 3 is a main cross-sectional view showing a conventional semiconductor device and semiconductor memory device. Figure 4 shows an ideal capacitor using a ferroelectric film.
Diagram of the relationship between applied voltage and polarized charge. FIG. 5 is a diagram showing the relationship between applied voltage and polarized charge of a capacitor using a ferroelectric film with a conventional structure. Figure 6 is a diagram showing how an electric field is applied to a capacitor using a conventional ferroelectric film. 1 ・ ・ 2 ・ ・ 3 4 ・ 5 ・ 31 Substrate element isolation insulating film First interlayer insulating film Gate electrode source 6 ・ 7 ・ 8 ・ 9 ・ 1 0 ・ 1) ・ l 2 ・ l 3 ・ l 4 ・ ・Drain, gate film, lower electrode, ferroelectric film, upper electrode, paraelectric second interlayer insulating film, ALIII, electric field

Claims (4)

[Claims] (1) An insulating film is formed on a semiconductor substrate, a lower electrode is formed on the insulating film, a ferroelectric thin film is formed on the lower electrode, and a ferroelectric thin film is formed on the ferroelectric thin film. 1. A semiconductor device characterized in that, in a capacitor in which an upper electrode is formed, a paraelectric material is formed at an end of a portion sandwiched between the upper electrode and the lower electrode. (2) The main component of the ferroelectric thin film is at least PbTi.
O_3, PZT (PbTiO_3/PbZrO_3),
2. The semiconductor device according to claim 1, wherein the semiconductor device is one of PLZT (La/PbTiO_3/PbZrO_3). (3) The semiconductor device according to claim 1, wherein the second upper electrode is made of a polycrystalline silicon film into which impurities are implanted at a high concentration or a polycide film thereof. (4) The semiconductor device according to claim 1, wherein the capacitor is used as a capacitor of a nonvolatile memory.