JPH0363224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a semiconductor device having ohmic contact between metal and silicon.

As the density of integrated circuits has increased in recent years,
Impurity-doped polycrystalline silicon has become widely used as a material for gate electrode wiring, electrodes, etc. in MOS (Metal Oxide Semiconductor) integrated circuits. However, this impurity-doped polycrystalline silicon has a high specific resistance of about 1 mΩ·cm, and as the density of integrated circuits increases, the wiring resistance has become impossible to ignore. In particular, the problem is that high-density response becomes difficult. Therefore, recently, attention has been paid to the idea of using a high-melting point metal such as molybdenum for interconnections such as gate electrodes to lower resistance and obtain stable semiconductor devices. This high melting point metal such as molybdenum has a specific resistance of about 10 μΩ·cm, which is about two orders of magnitude smaller than that of impurity-doped polycrystalline silicon, and therefore the wiring resistance is sufficiently small to be ignored. Furthermore, it has a small crystal grain size and is excellent in microprocessability, and is considered to be a material that should replace polycrystalline silicon as a wiring material for high-density integrated circuits and the like.

In semiconductor devices such as MOS-type static memories that use conventional high-melting point metals such as molybdenum as gate electrodes, part of the gate electrode is used as the source or drain of the MOS transistor in order to miniaturize the memory cell area. There is a so-called direct contact region that makes direct ohmic contact with the diffusion layer region on the silicon (hereinafter referred to as Si). In a circuit like the one shown in Figure 1a,
The MOS transistor 10 is an example. The cross-sectional view of the MOS transistor 10 shown in FIG. 1a is as shown in FIG. After that, impurities are implanted into the region 3 that will become the drain by ion implantation. After that, a high temperature heat treatment process of about 1000° C. is required to activate the drain region. At this time, it is necessary that the contact between the region 1 serving as the source and the gate electrode 2 is stable and good ohmic contact is maintained against high-temperature heat treatment.

In FIG. 1b, the source region is connected to the gate electrode 2, which is covered with an insulating film 23, and the drain region is provided with an electrode 24. Further, under the gate electrode 2, an insulating layer 2
6 is connected to a silicon substrate 25 which becomes a channel region.

By the way, high melting point metals are generally heated at 600℃ with Si.
The heat treatment at a relatively low temperature causes a so-called silicide reaction to form a compound with Si, and a high melting point metal silicide is formed. Also,
At high temperatures of around 1000°C, this reaction is extremely violent, and when a high melting point metal with a film thickness of around 3000 Å is used as the wiring, silicide with a thickness of 6000 Å, which is approximately twice as thick, is formed, causing a significant volume change that causes the contact hole to become damaged. Discontinuities can occur between the electrode and the insulating film, electrodes can peel off due to large stress, and countless defects can be created in the silicon substrate. As a result, the contact resistance becomes extremely large and the circuit becomes open, which is a major obstacle in using high-melting point metals as wiring materials in semiconductor devices having such direct contacts.

An object of the present invention is to provide a semiconductor device having an electrode structure that provides stable and good ohmic contact even after high-temperature heat treatment, particularly at about 1000°C.

According to the present invention, especially 500
A two-layer electrode structure in which a silicide layer with a thickness of about 100 Å is formed and a refractory metal nitride layer formed thereon, or a multilayer electrode structure in which a refractory metal layer is further formed on the structure as necessary. A semiconductor device having the above structure is obtained.

The present invention solves the conventional problems based on the following two findings. One of them is that nitrides of high-melting point metals hardly react with Si even when subjected to high-temperature heat treatment at about 1000°C, and act as a barrier to silicide reactions. Another one is
In order to reduce the resistance of the ohmic contact area, it is desirable to have a silicide layer between the Si and the high-melting point metal nitride layer, but if this silicide layer is thick, the stress after high-temperature heat treatment may cause defects in the substrate. A thickness of about 100 Å to 1000 Å is particularly desirable because of the possibility of formation of cracks or peeling. Here, the reaction of high melting point metals such as molybdenum (hereinafter referred to as Mo) and tungsten (hereinafter referred to as W) is rate-limiting in that the reaction products are proportional to time, and noble metals (gold, silver) The reaction mechanism is essentially different from that of nickel (Ni), where the reaction with Si is rate-limited by diffusion.

The present invention will be explained in detail below with reference to the drawings.

In FIG.
A thermal oxide film 12 with a thickness of about 400 Å is formed, then a hole is partially formed in a portion to become a diffusion region, and a thermal oxide film 13 with a thickness of about 400 Å is formed thereon. Thereafter, arsenic ions (AS ⁺ ) of 100 Kev5×10 ¹⁵ cm ^-2 were injected into the Si substrate 11 through this 400 Å thick oxide film 13 by ion implantation, and heat treated at 1000°C for 20 minutes in nitrogen.
Arsenic ions are activated to form an n ⁺ diffusion layer 14.

Thereafter, as shown in FIG. 2b, a contact hole 15 is opened, a first molybdenum film 16 of about 300 Å is formed by sputtering, and a titanium nitride (TiN) film 17 of about 1000 Å is formed by reactive sputtering.
A second molybdenum film 18 is formed at a thickness of 1,500 Å.
Å form. This third layer of molybdenum film 18 is formed to lower wiring resistance, and here
A TiN film of 2500 Å may be formed. The electrode on the n ⁺ diffusion layer 14 formed in this way is made of Mo
(1500Å)/TiN (1000Å)/Mo (300Å). The first layer of Mo with a thickness of 300 Å undergoes high-temperature heat treatment at about 1000°C during the subsequent transistor manufacturing process, and finally becomes Mo (1500 Å thick).
)/TiN (1000Å)/MoSi ₂ (600Å).
This _is shown in ^FIG .
It becomes 9.

FIG. 3 is a characteristic diagram showing the dependence of the specific contact resistance on the heat treatment temperature when a device having a cross section as shown in FIG. 2b is subjected to heat treatment for 20 minutes in a nitrogen atmosphere.
The characteristic curve 21 is the case based on the present example of the present invention, and the characteristic curve 22 is the case of the electrode made only of molybdenum. For molybdenum-only electrodes,
In contrast to heat treatment at 700° C. or higher, which causes a very large increase in contact resistance, this example shows only a slight increase in contact resistance, indicating excellent ohmic properties.

As described above, according to the present invention, even after high-temperature heat treatment of approximately 1000°C, the property is extremely stable and good.
Semiconductor devices with ohmic contact with Si metal can be made.

In addition, in the embodiment of the present invention, MoSi ₂ on the n ⁺ diffusion layer
Although the layer was formed by heat treatment, MoSi ₂ may be directly formed in advance by a sputtering method or the like.

In addition, in the embodiment of the present invention, MoSi ₂ is used as the refractory metal silicide, TiN is used as the refractory metal nitride, and Mo is used as the refractory metal of the refractory metal layer.
However, the present invention is not limited thereto, and the refractory metal forming the silicide or nitride or the refractory metal of the refractory metal layer may be W, tantalium (Ta), or other refractory metal. It is also valid when

[Brief explanation of drawings]

FIG. 1a is a circuit diagram in a memory cell with direct contact, FIG. 1b is a cross-sectional view of the MOS transistor with direct contact of FIG. 1a, and FIGS. 2a to 2c are Third sectional view for explaining ohmic contact in the embodiment
This figure is a characteristic diagram showing the heat treatment temperature dependence of the specific contact resistance obtained from the element having the structure shown in FIG. In the figure, 1...A region that becomes a source, 2...A gate electrode, 3...A region that becomes a drain, 10...
MOS transistor, 11... P-type Si substrate, 12,
13...thermal oxide film, 14...n ⁺ diffusion layer, 16,
18...Molybdenum film, 17...Titanium nitride film,
19...Molybdenum silicide film, 21...Characteristic curve when titanium nitride film, etc. are provided, 22...
Characteristic curve when the electrode is formed only of molybdenum, 23...Insulating film, 24... Electrode, 26... Insulating layer, 25... Silicon substrate.

Claims (1)

[Claims] 1. In a semiconductor device having ohmic contact between a metal and silicon, a high melting point metal silicide layer is provided in a portion where ohmic contact is to be made with the silicon, and a high melting point metal nitride layer is further formed on the high melting point metal silicide layer. A semiconductor device characterized by having a physical layer.