KR100277939B1 - bottom electrode of capacitor with ferroelectric - Google Patents

Abstract

The present invention relates to a lower electrode of a ferroelectric capacitor and includes a first layer made of any one of Ti, Cr, TiW, and TiN, a second layer formed on the first layer and made of Ir and a second layer made of IrO ₂ 3 layers and a fourth layer formed on the third layer and made of Ir to improve adhesion, prevent oxidation, and improve other electrical characteristics (fatigue phenomenon, leakage current).

Description

A bottom electrode of a capacitor having a ferroelectric capacitor (ferroelectric)

The present invention relates to a capacitor, and more particularly to a lower electrode of a ferroelectric capacitor.

In general, the capacitors of semiconductor devices have gradually reduced the thickness of the dielectric film in order to compensate for the decrease in the capacitor capacity due to the smaller area as the degree of integration of the elements increases.

However, as the thickness of the dielectric layer decreases, the leakage current due to tunneling increases, and the reliability of the dielectric layer decreases due to the leakage current and the reduced thickness of the dielectric layer.

In order to avoid such a problem, a method of increasing the effective area of the capacitor by forming a very complicated surface curvature has been selected and used. However, this method also causes severe steps on the surface to make the photolithograph process difficult, It was difficult to use in the device.

Therefore, much research has been conducted to reduce the surface curvature while dramatically improving the capacitance of the capacitor.

Among them, a method of using a high dielectric constant material as a dielectric film of a capacitor has been proposed.

The capacitors using such a high-dielectric-constant film have many achievements, but the dielectric constant is not high, and the use range of the capacitors is not expected to be wide considering the tendency to be highly integrated in the future.

In recent years, interest in ferroelectrics having a crystal structure called a perovskite type has been increasingly intensified as a dielectric to be used in semiconductor devices.

A ferroelectric substance is a material exhibiting spontaneous polarization at a Curie temperature or lower, and is a material that generates a spontaneous polarization even if no electric field is applied.

Examples of the ferroelectric material include PZT (Pb (Zr, Ti) O ₃ ), PLZT ((Pb, La) (Zr, Ti) O ₃ ), BST (Ba, Sr) TiO ₃ , BaTiO ₃ , SrTiO ₃ , .

However, such a ferroelectric easily reacts with silicon and silicide as substrates, and the surface of the ferroelectric is exposed in a strong oxidizing atmosphere during the thin film formation process, resulting in many problems such as oxidation of the electrode.

In order to solve these problems, researches on the material and the structure of the electrode have been continued.

In making ferroelectric capacitors, the material to be used as an electrode should be a ferroelectric and a material that has poor reactivity.

The reason for this is that the ferroelectric is an oxide and therefore a conductive material which is not easily oxidized should be used as the electrode.

As such electrodes, oxide electrodes have been newly spotlighted.

IrO ₂ , RuO _2, etc. were used as the representative materials of the oxide electrode. These materials increased the possibility of the electrode, but they could not be used alone because of increased leakage current. Ir / IrO ₂ , Ru / A hybrid electrode such as RuO _2, Pt / IrO ₂ , and Pt / RuO ₂ has been used.

However, Ru has a difficulty in research because RuO ₄ is extremely toxic at the time of etching, and Ir has difficulty in proceeding because adhesion is poor.

Therefore, it is necessary to provide an electrode having good electrical characteristics while improving the adhesion.

The following problems have been encountered in the electrodes of general ferroelectric capacitors.

When a capacitor using an oxide electrode is used for a highly integrated device, the leakage current flowing through the capacitor increases and it is difficult to obtain a high dielectric constant. When Ru or Ir is used as the electrode material, RuO _{4, which} is a toxic gas, is produced. The characteristics are degraded.

It is an object of the present invention to provide a lower electrode of a ferroelectric capacitor having a novel electrode structure and having good adhesion to a substrate and capable of improving electrical characteristics.

1 is a structural cross-sectional view showing a lower electrode of a ferroelectric capacitor according to the present invention;

DESCRIPTION OF THE REFERENCE NUMERALS

11: substrate 12: first layer

13: second layer 14: third layer

15: fourth floor

Features of the ferroelectric capacitor, the lower electrode according to the invention with Ti, Cr, TiW, TiN first layer consisting of any one of the, first formed on the first layer and the second layer consisting of Ir, are formed on the second layer IrO ₂ And a fourth layer formed on the third layer and made of Ir.

The lower electrode of the ferroelectric capacitor according to the present invention having the above-described characteristics will now be described in more detail with reference to the accompanying drawings.

First, in the present invention, a composite electrode made of Ir / IrO ₂ is used because both Ir and IrO ₂ are metals having a high electrical conductivity, and in particular, IrO ₂ can be formed in Ir / poly-Si (polysilicon) This is because it acts to block the iridium silicide and at the same time to escape from the ferroelectric thin film and to prevent the oxygen supplied from the atmosphere during the process.

However, Ir / IrO ₂ composite electrode having the above advantages is not the adhesive force (adhesion) between the polysilicon plugs (plug) at the bottom good there is a problem that SiO ₂ is generated at the interface between the polysilicon and IrO _2.

Therefore, in order to solve the above problem, in the present invention, a Ti metal material is placed under a composite electrode made of Ir / IrO ₂ .

Here, instead of Ti, any one of Cr, TiW and TiN can be selectively used.

The reason why the above-described metal materials are used for adhesion to the lower electrode and the plugs thereunder is that they have been used in conventional semiconductor integrated circuits, and Ti and Cr can be relatively easily deposited. TiW, TiN, And the step coverage is excellent.

However, Ti, Cr, TiW, because the material, such as TiN also becomes very vulnerable to oxygen must configure the electrode does not come in direct contact with the IrO ₂ solves the above problem by forming a layer between the Ir IrO ₂ and Ti.

FIG. 1 is a cross-sectional view illustrating a lower electrode of a ferroelectric capacitor according to the present invention. As shown in FIG. 1, a ferroelectric capacitor is formed on a Si or poly-Si substrate 11 by using any one of Ti, Cr, TiW, and TiN A first layer 12, a second layer 13 made of Ir, a third layer 14 made of IrO ₂ , and a fourth layer 15 made of Ir are sequentially stacked to form a lower electrode.

Here, the thickness of the first layer of the lower electrode is 50 to 500 angstroms, if possible.

The thickness of the second layer is 300 to 1000 angstroms.

The thickness of the third layer is in the range of 100 to 500 ANGSTROM. If the thickness is too thin, the oxygen is not blocked. If the thickness is too thick, the thin film becomes rough.

Finally, the thickness of the fourth layer is between 300 and 1000 angstroms, which is too thin to oxidize and affect the roughness of the third layer.

As described above, in the present invention, the lower electrode is formed of Ir / IrO ₂ / Ir / Ti (or any one of Cr, TiW, and TiN), thereby improving the adhesive force with the plug and improving the electrical characteristics.

The lower electrode of the ferroelectric capacitor according to the present invention has the following effects.

The lower electrode is formed of Ir / IrO ₂ / Ir / Ti (or any one of Cr, TiW, and TiN) to improve adhesion, prevent oxidation, and improve other electrical characteristics (fatigue phenomenon, leakage current).

Claims (2)

In a capacitor formed on a substrate and having a ferroelectric between the upper electrode and the lower electrode, A first layer made of any one of Ti, Cr, TiW, and TiN; A second layer formed on the first layer and made of Ir; A third layer formed on the second layer and made of IrO2; And a fourth layer formed on the third layer and made of Ir. The lower electrode of the capacitor having the ferroelectric layer. The method of claim 1, wherein the thickness of the first layer of the lower electrode is 50 to 500 ANGSTROM, the thickness of the second layer is 300 ANGSTROM to 1000 ANGSTROM, the thickness of the third layer is 100 ANGSTROM to 500 ANGSTROM, Wherein the lower electrode of the capacitor has a ferroelectric layer.

Images