JP3169406B2 - Nonvolatile semiconductor memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EEPROM (Electr
TECHNICAL FIELD The present invention relates to a nonvolatile semiconductor memory device such as an imaginary erasable and programmable ROM, and particularly relates to an MFSFET (Metal Ferroelectric) using a ferroelectric film as a gate insulating film.
Semiconductor FET).

[0002]

2. Description of the Related Art Referring to FIG.
The configuration of the ET element will be described. In the drawing, reference numeral 1 denotes, for example, a P-type silicon substrate, on which a drain diffusion layer 2 and a source diffusion layer 3 which are N ⁺ regions are formed. On the substrate between the drain diffusion layer 2 and the source diffusion layer 3, for example, lead zirconate titanate (PZT)
A ferroelectric film 4 is formed, and a gate electrode 5 is formed thereon. Reference numeral 6 in the drawing denotes an interlayer insulating film, and reference numeral 7 denotes a metal wiring connected to a drain and a source.

The ferroelectric film 4 of the above-mentioned MFSFET device
Has a hysteresis characteristic as shown in FIG. In the figure,
The horizontal axis represents the electric field acting on the ferroelectric film, and the vertical axis represents the amount of polarization charge of the ferroelectric film. Here, an electric field E _sat is applied to the ferroelectric film 4.
A positive voltage so as to provide more than the V _MAX. This voltage V
_{When MAX} is applied to the gate electrode 5, the ferroelectric film 4
Polarized to the state of A in the middle, and a channel is formed between the source and the drain of the device shown in FIG. Thereafter, even if the gate voltage is returned to 0 V, the gate electrode 5 is brought into the state shown in FIG. 4B, polarization (spontaneous polarization) remains, and the channel remains formed.

[0004] Conversely, a negative voltage of -V _MAX gate electrode 5 (or positive voltage of the substrate to the + V _MAX) is applied to the ferroelectric film 4 is polarized to the state of C of FIG. afterwards,
When the voltage is returned to 0 V, the state becomes D and negative polarization (spontaneous polarization) remains. In this process, no channel is formed between the source and the drain.

[0005] By associating the polarity of the spontaneous polarization of the ferroelectric film 4 with data "0" and "1", a memory capable of storing information in a nonvolatile manner is constructed.

[0006]

Although the MFSFET device has the above-mentioned characteristics, no device of a practical use level has been published until now. The reason is,
(1) damaging a substrate when a ferroelectric substance is laminated on a silicon substrate by sputtering;
(2) After the ferroelectric substance is laminated on the silicon substrate, heat treatment is performed. At this time, the ferroelectric substance diffuses into the substrate to deteriorate the FET characteristics. When the dielectric substance is directly laminated, the crystal orientation of the ferroelectric film is deteriorated, and it is difficult to obtain a desired hysteresis characteristic.

Therefore, in order to avoid the disadvantages (1) and (2), an S film is provided between the ferroelectric film and the silicon substrate.
MFSF provided with a buffer layer made of an insulating film such as iO ₂
An ET element has been proposed ("Technical Research Report of the Institute of Electrical Communication, Vol. 78, No. 179, pp. 1-81978").

However, according to the above-described device provided with the buffer layer made of an insulating film, the gate structure becomes a laminated capacitor of the ferroelectric film and the buffer layer, so that most of the voltage applied to the gate electrode 5 is reduced. Joins the buffer layer,
Since the partial pressure applied to the ferroelectric film is reduced, another problem arises in that the operating voltage must be set higher accordingly. Also, it is difficult to improve the crystal orientation of the ferroelectric film even with the above buffer layer.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a non-volatile semiconductor memory device (MFSFET element) capable of operating at a low voltage and having a ferroelectric film with good crystallinity has been developed. It is intended to be realized.

[0010]

The present invention has the following configuration in order to achieve the above object. That is, the present invention comprises a ferroelectric capacitor on a channel region of a field effect transistor, the nonvolatile semiconductor memory device that stores the information by utilizing the spontaneous polarization of the ferroelectric film of the capacitor, on a semiconductor substrate or Form on substrate
On the semiconductor layer that is one in which a conductive film containing a metal atom serving as a gate electrode of the lower electrode and the field effect transistor of the capacitor was formed directly.

[0011]

The operation of the present invention is as follows. That is,
According to the present invention, almost all of the voltage applied to the ferroelectric capacitor acts on the ferroelectric film between the upper electrode and the lower electrode (conductor film). The device can be operated at a low voltage. In addition, since the conductor film containing metal atoms has good matching with the ferroelectric film, the crystal orientation of the ferroelectric film is improved.

[0012]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a configuration of a nonvolatile semiconductor memory device according to one embodiment of the present invention.

In FIG. 1, reference numeral 11 denotes a P-type GaAs substrate as a semiconductor substrate. The substrate material is a silicon substrate or GaAs grown on a silicon substrate.
s or the like. In the GaAs substrate 11, a drain diffusion layer 12 and a source diffusion layer 13, which are N ⁺ regions, are formed. In the channel region between the two diffusion layers 12 and 13, an N ^- diffusion layer 14 for controlling the threshold value of the transistor is formed.

On the N ^- diffusion layer 14, a conductive film 15 containing metal electrons also serving as a gate electrode of the field effect transistor Tr and a lower electrode of the ferroelectric capacitor FC;
The ferroelectric film 16 and the upper electrode 17 are stacked in that order. Here, platinum (Pt) is used as the conductive film 15.
And PZT (PbZr _x Ti) as the ferroelectric film 16
_1-X O ₃ ) is used. The reason is that when PZT is formed on Pt, a ferroelectric film having good crystal orientation can be obtained.

The conductor film 15 may be made of Au or the like in addition to Pt. The ferroelectric film is not limited to PZT, but has a perovskite structure of the same type of ABO ₃ type (A and B are metal elements) (for example, PLZT).
ZT, PbTiO ₃ , BaTiO _3, etc.). In addition, BaMgF ₄ , N
halogen compounds such as aCaF ₃ and K ₂ ZnCl ₄ ;
Chalcogen compounds such as n ₁ -x Cd _x Te, GeTe, and Sn ₂ P ₂ S ₆ can also be used.

Further, in order to prevent metal atoms of the conductor film 15 from spiking into the substrate, it is preferable that the conductor film 15 has a laminated structure. For example, on a silicon substrate,
As the conductor film 15, Pt / PtSi, Au / AuS
It is preferred to use i.

As the upper electrode 17, a polysilicon film doped with phosphorus or the like may be used in addition to a metal such as Pt.
Reference numeral 18 in FIG. 1 denotes SiO ₂ (P
SG), an interlayer insulating film made of boron-doped PSG or the like, and 19 is a drain diffusion layer 12 and a source diffusion layer 13.
Are individually connected to metal wiring.

FIG. 2 is an equivalent circuit diagram of the above-mentioned nonvolatile semiconductor memory device (MFSFET element). In the figure, Tr
Is a field effect transistor including a drain diffusion layer 12, a source diffusion layer 13, an N ⁻ diffusion layer 14, and a conductor film 15. FC is a conductor film 15, a ferroelectric film 16,
And a ferroelectric capacitor including the upper electrode 17.

A method for manufacturing the above-mentioned MFSFET device will be briefly described. First, an N ^- diffusion layer 14 is formed in a GaAs substrate 11. Subsequently, the conductor film 15, the ferroelectric film 1
6. The upper electrode 17 is laminated in that order. Ferroelectric film 16
The ferroelectric substance such as PZT for forming the sol is formed by a sol-gel method using spin coating or MOD (Metal Organic Decomp.).
osition) method, sputtering method, MOCVD (M
(etal Organic Chemical Vapor Deposition) method, laser ablation method. Each of the laminated films is
Ion milling, reactive ion etching (RIE)
Process continuously by anisotropic etching such as Using the ferroelectric capacitor FC formed as described above as a mask, an N-type impurity is ion-implanted to form the drain diffusion layer 12.
And a source diffusion layer 13 is formed. Next, an interlayer insulating film 18 is deposited by a CVD (Chemical Vapor Deposition) method, a contact hole is formed in a region of the drain / source diffusion layers 12 and 13, and a metal film is deposited and patterned. The metal wiring 19 is formed.

Next, the operation of the above-mentioned MFSFET device will be described. Pt is deposited on a semiconductor substrate such as a GaAs substrate 11.
When the conductor film 15 made of a metal such as PtSi or a conductive metal compound such as PtSi is directly formed, a Schottky barrier is formed, and the drain diffusion layer 12 and the source diffusion layer 13 are formed on both sides of the conductor film 15. Thereby, an FET element is configured. The FET element can be switched between a conductive state and a non-conductive state by generating a voltage on the conductive film 15 serving as a gate electrode.

Therefore, a ferroelectric capacitor FC having the conductive film 15 as a lower electrode is formed on the channel region of the FET element, and a voltage is applied to the upper electrode 17 of the ferroelectric capacitor FC (the embodiment of FIG. 1). Applying a negative voltage)
A voltage (positive voltage in the embodiment) is generated in the conductor film 15, whereby a channel is formed and the FET becomes conductive. Thereafter, even when the voltage of the upper electrode 17 is set to 0 V, the spontaneous polarization of the ferroelectric film 16 causes the conductive film 15 and the substrate 11
The voltage between them is held, and the FET is kept conductive.

On the other hand, when a positive voltage is applied to the upper electrode 17 of the ferroelectric capacitor FC or a negative voltage is applied to the terminal T ′ derived from the conductor film 15 as shown in FIG. The polarity of the spontaneous polarization of the film 16 is reversed, and F
ET becomes non-conductive and is maintained as it is.

As described above, the conduction of the MFSFET element
By associating non-conduction with data “0” and “1”, a nonvolatile memory that maintains a written state without applying a power supply voltage is realized.

[0024]

As is apparent from the above description, according to the present invention , a strong effect is formed on the channel region of the field effect transistor.
A ferroelectric film comprising a dielectric capacitor
Nonvolatile semiconductor memory that stores information using spontaneous polarization
Memory device, formed on a semiconductor substrate or on a substrate
Since the conductor film containing metal atoms also serving as the lower electrode of the capacitor and the gate electrode of the field-effect transistor is directly formed on the semiconductor layer , almost all of the voltage applied to the ferroelectric capacitor is reduced. Acts on ferroelectric films. Therefore, the memory device can be operated at a lower voltage than a conventional memory device in which a buffer layer made of an insulating film is provided between a ferroelectric film and a semiconductor substrate.

In addition, since a ferroelectric film having good crystal orientation can be formed on a conductive film containing metal atoms, spontaneous polarization of the ferroelectric film increases, and the reading margin increases accordingly. Thus, a highly practical nonvolatile semiconductor memory device can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an element structure of a nonvolatile semiconductor memory device according to one embodiment of the present invention.

FIG. 2 is an equivalent circuit diagram of the device shown in FIG.

FIG. 3 is a cross-sectional view showing a structure of a conventional MFSFET device.

FIG. 4 is a diagram showing a hysteresis characteristic of a ferroelectric film.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 11 ... GaAs substrate 12 ... Drain diffusion layer 13 ... Source diffusion layer 14 ... N ^- diffusion layer 15 ... Conductor film 16 ... Ferroelectric film 17 ... Upper electrode 18 ... Interlayer insulating film 19 ... Metal wiring Tr ... Field effect transistor FC ... Ferroelectric capacitors

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G11C 11/22 G11C 16/04 H01L 21/8247 H01L 29/788 H01L 29/792

Claims (1)

(57) [Claims] [Claim 1 further comprising a ferroelectric capacitor on a channel region of a field effect transistor, the nonvolatile semiconductor memory device that stores the information by utilizing the spontaneous polarization of the ferroelectric film of the capacitor, the semiconductor substrate or substrate On the semiconductor layer formed above ,
A conductor film containing metal atoms also serving as a lower electrode of the capacitor and a gate electrode of the field effect transistor
A non-volatile semiconductor memory device formed directly .