JPH08288239A - Oxygen-diffusion barrier type electrode and manufacture thereof - Google Patents

Abstract

PURPOSE: To avoid poor contact of a polycrystalline Si or Si barrier layer connected to a lower electrode due to oxidation to form an oxide dielectric film. CONSTITUTION: The crystal grain boundary of a Pt or other precious metal thin film generally exists perpendicularly to the surface of a substrate. A metal serving as a barrier against the diffusion of oxygen is placed on the grain boundary to avoid diffusing oxygen, thereby preventing poor electric contact of a polycrystalline Si or Si barrier layer laid beneath the precious metal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure formed on a semiconductor surface and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, when an oxide dielectric such as a ferroelectric is to be incorporated into a semiconductor integrated circuit as a capacitor, a temperature of 500.degree.
Due to the above high temperature and oxidizing atmosphere, there is a problem that the polycrystalline silicon used as the lower electrode for the capacitor is oxidized and a contact failure occurs. Therefore, in many cases, as shown in FIG. 3, a high melting point noble metal such as Pt having high heat resistance and oxidation resistance is used as the lower electrode. That is, a silicon barrier layer 2 such as TiN is formed under the high melting point noble metal layer 1.
Is used as an electrode that can prevent the refractory noble metal from being silicidized and can withstand the production of an oxide dielectric. Since the conductive oxide electrode is also stable against an oxidizing atmosphere, it is considered to use it by providing a silicon barrier layer thereunder to prevent silicidation.

[0003]

However, the conventional lower electrode structure has the following problems. When a high melting point noble metal such as Pt is used, oxygen can pass through the crystal grain boundaries of the high melting point metal thin film, and TiN is used as a silicon barrier layer under the high melting point noble metal when forming an oxide dielectric. Is oxidized to form insulative titanium oxide, resulting in poor conduction with the silicon substrate side. Further, even when a conductive oxide is used, TiN is oxidized at the time of forming the conductive oxide on TiN of the silicon barrier, and conduction failure still occurs, which cannot solve the problem.

An object of the present invention is to provide an electrode structure which can solve the above problems.

[0005]

According to the present invention, in an electrode which makes electrical contact with a semiconductor surface, oxygen is present in a crystal grain boundary of a polycrystalline refractory noble metal layer laminated on a semiconductor diffusion barrier layer formed on the semiconductor surface. An oxygen diffusion barrier electrode having a diffusion barrier portion. Here, it is preferable that the oxygen diffusion barrier portion is made of an oxide of a metal in which one kind or a combination of plural kinds of Ti, Zr, Ta and Ru is combined. Further, in this method for manufacturing an oxidation diffusion barrier electrode, a semiconductor diffusion barrier layer is formed on a semiconductor surface, and any one kind or a combination of plural kinds of Ti, Zr, Ta and Ru is formed on the semiconductor diffusion barrier layer. After forming a polycrystalline high melting point noble metal layer sandwiching the
It is characterized by having a step of heat treatment at 50 to 650 ° C. Here, a step of further removing the barrier metal deposited on the high melting point metal layer may be included.

[0006]

The electrode structure according to the present invention uses Pt as a refractory metal.
An example using is shown in FIG. When Pt is produced by a sputtering method or the like, it becomes a polycrystalline film unless the special substrate is selected, and the crystal grains have a columnar structure. When an oxide dielectric is formed on Pt, oxygen diffuses through the crystal grain boundaries of the columnar Pt and oxidizes a silicon barrier such as TiN under Pt to cause contact failure. In this way, since the grain boundary is the main path for diffusion of oxygen, oxygen that functions as a trap for oxygen before being oxidized at this grain boundary and oxygen that functions as a barrier for oxygen diffusion after being oxidized. By disposing a metal having a barrier property, for example, Ti, the grain boundary diffusion of oxygen can be suppressed, and as a result, the oxidation of TiN can be suppressed. Also P
Since the grain boundary of t is formed perpendicularly to the substrate surface, an oxide of a metal having an oxygen barrier property exists in this portion, and even if the oxide is insulating, it does not increase the contact resistance. , A metal serving as a conductive oxide such as Ru, and a metal serving as an insulating oxide such as Zr and Ta.
Etc. can be used.

[0007]

【Example】

(Embodiment 1) FIG. 2 shows the results of composition analysis in the depth direction at each stage of manufacturing the lower electrode and the capacitor when Pt is used as the refractory metal and Ti is used as the oxygen barrier metal. In FIG. 2A, from the substrate side, polycrystalline silicon, a TiN / Ti laminated silicon barrier layer, a Ti oxygen diffusion barrier layer having a thickness of 20 nm, and a Pt layer having a thickness of 200 nm are shown. When the structure of FIG. 2 (a) was heat-treated in nitrogen at 500 ° C. for 30 minutes, the Ti layer under Pt showed P as shown in FIG. 2 (b).
It diffused in the t layer and on the Pt surface. At this time, when the cross section of the sample was observed with a high resolution electron microscope, it was observed that the diffused Ti was deposited on the surface of Pt and on the crystal grain boundaries. Pt
After the Ti deposited on the surface was removed by etching, lead zirconate titanate (PZT) was prepared as an oxide dielectric by heat treatment at 600 ° C. for 60 minutes by the sol-gel method. The composition analysis result after PZT fabrication is as shown in FIG. 2C, and it was found that Ti existing in the Pt grain boundary was oxidized near the Pt surface, but Ti in the Pt grain boundary on the TiN side was oxidized. It was shown that the TiN layer was not oxidized and the TiN layer was not oxidized. This electrode structure is 10μm x 10μm by ion milling method
When microfabrication was performed and contact resistance was measured,
It was confirmed to be 50Ω and there was no problem in conduction as the lower electrode. The required Pt film thickness depended on the heat treatment time and temperature in an oxidizing atmosphere, but if the heat treatment is 600 ° C. or less and 60 minutes or less, 150 nm or more is desirable, and at 150 nm or less, the contact resistance value tends to increase. .

(Example 2) The case where Ir is used as the high melting point noble metal and Ti is used as the oxygen barrier metal will be described. The manufacturing method is the same as in Example 1, and the polycrystalline silicon is
TiN / Ti laminated silicon barrier layer, 20 nm thick Ti
After depositing an oxygen diffusion barrier layer, which is also an Ir layer of 200 nm, and heat-treating this structure in nitrogen at 650 ° C. for 30 minutes, the Ti layer under Ir diffuses the grain boundaries of Ir and the Ir grain boundaries and the Ir surface. Deposited on. After removing Ti deposited on the Ir surface by etching, lead zirconate titanate (PZT) was prepared as an oxide dielectric by a sol-gel method at 600 ° C.
The part where ZT is removed is 10 μm by the ion milling method.
When the contact resistance was measured by microfabrication to × 10 μm, it was found to be 50 to 100 Ω and there was no problem in conduction as the lower electrode. In case of Ir electrode, Ir surface is 6
Although oxidized in oxygen at 00 ° C., IrO ₂ was a conductive oxide and did not interfere with the conductivity of the electrode. In the case of the Ir electrode, the temperature required for diffusing the oxygen barrier metal at the grain boundaries was about 100 to 150 ° C. higher than that in the case of using the Pt electrode.

Table 1 shows the contact resistance of each combination of Pt or Ir electrodes and various oxygen barrier metals. The contact resistance value of each element of Zr, Ta, and Ru was a value that causes no problem when used as the lower electrode.

[0010]

[Table 1]

[0011]

EFFECTS OF THE INVENTION In a polycrystalline high melting point noble metal which makes electrical contact from the semiconductor surface, an oxygen diffusion barrier portion is provided at the grain boundary of the columnar crystal of the polycrystalline high melting point noble metal, so that the semiconductor can be connected through the grain boundary. A polycrystalline high melting point noble metal electrode with good conductivity is provided on the semiconductor surface by preventing the diffusion of oxygen that diffuses between the surface and the high melting point noble metal electrode and ensuring electrical continuity at crystal parts other than the crystal grain boundaries. realizable.

[Brief description of drawings]

FIG. 1 is a diagram showing a lower electrode structure in which an oxygen barrier metal is arranged at a refractory noble metal grain boundary according to the present invention.

FIG. 2 is a result of composition analysis in the depth direction at each stage of manufacturing a lower electrode and a capacitor when Pt is used as a high melting point noble metal and Ti is used as an oxygen barrier metal.

FIG. 3 is a diagram showing a lower electrode structure when a conventional oxygen-barrier metal is not used.

[Explanation of symbols]

 1 Pt lower electrode (high melting point noble metal layer) 2 TiN / Ti laminated silicon barrier layer 3 Polycrystalline silicon 4 Ti (oxygen barrier metal)

Claims (4)

[Claims] 1. An electrode for making electrical contact with a semiconductor surface, wherein an oxygen diffusion barrier portion is provided at a crystal grain boundary of a polycrystalline refractory noble metal layer laminated on a semiconductor diffusion barrier layer provided on the semiconductor surface. An oxygen diffusion barrier electrode characterized by the above. 2. The oxygen diffusion barrier portion comprises Ti, Zr, Ta and R.
2. The oxygen diffusion barrier electrode according to claim 1, which is made of a metal oxide in which any one or a combination of u is combined. 3. A semiconductor diffusion barrier layer is formed on a semiconductor surface, and Ti, Zr, Ta, Ru is formed on the semiconductor diffusion barrier layer.
An oxygen diffusion barrier comprising a step of forming a polycrystalline refractory noble metal layer with a metal layer formed by sandwiching one or a combination of two or more of the above and then performing heat treatment at 450 to 650 ° C. in a non-oxidizing atmosphere. Of manufacturing a conductive electrode. 4. The oxygen diffusion barrier according to claim 3, further comprising a step of removing the barrier metal deposited on the refractory metal layer after heat treatment at 450 to 650 ° C. in a non-oxidizing atmosphere. Of manufacturing a conductive electrode.