JP2868021B2 - Wiring formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method of forming a wiring having a diffusion preventing (barrier) layer between a silicon substrate and a wiring layer of aluminum or an alloy thereof, more particularly to a wiring of a semiconductor device such as an IC or an LSI. An object of the present invention is to provide a method for forming a wiring with a higher barrier effect by adding oxygen at the time of forming a TiN barrier layer so that the characteristics do not deteriorate due to the addition of oxygen by the method already proposed. A contact layer and a barrier layer that is a nitride, boride or carbide of any one of titanium, zirconium, hafnium and tungsten,
In a wiring forming method of sequentially forming a wiring layer of aluminum or an alloy thereof, during the formation of the barrier layer,
The oxygen gas is added to the atmospheric gas in a pulsed manner or added only for one time.

[Industrial applications]

The present invention relates to a method for forming a wiring of a semiconductor device such as an IC or an LSI, and more particularly, to a method of forming a wiring having a diffusion prevention (barrier) layer between a silicon substrate and a wiring layer of aluminum or an alloy thereof (hereinafter, referred to as an aluminum alloy). About.

[Prior Art] With the increase in the degree of integration and the density of a semiconductor device, a wiring serving as a metal electrode has been miniaturized and a contact portion with a silicon substrate has been reduced. Al-1 to 2% Si alloys to which silicon has been added have been widely used to prevent aluminum spikes (jackson leaks) into shallow junctions and to prevent silicon in the substrate from diffusing into the aluminum wiring layer. However, silicon which has exceeded the solid solution limit in the aluminum wiring layer may be deposited at the contact portion between the substrate silicon and the aluminum wiring layer due to heat treatment during the formation of the aluminum wiring layer and subsequent processes. Since the deposited silicon has a high resistance, the effective contact area between the substrate and the wiring layer decreases, and the contact resistance increases. Therefore, in a wiring structure that has recently been miniaturized, Al is not added with silicon, but Al-2% Cu added with copper to prevent migration disconnection failure.
Alloys are used. Further, in order to prevent interdiffusion between the substrate silicon and aluminum, a barrier layer (for example, TiN,
TiW, thin layer such as MoSi _x) is provided. As such a barrier layer, a thin film of a nitride, carbide or boride of a high melting point metal has been attracting attention. In particular, TiN has attracted attention because of its good electrical conductivity and excellent heat resistance, and because of its high contact resistance of TiN / Si, a contact layer having a low contact resistance between the silicon substrate and the TiN barrier layer (for example, (Ti layer).

The present applicant has also proposed a method of forming a wiring having a Ti / TiN / Al structure on a silicon substrate in Japanese Patent Application No. 63-185005 (July 25, 1988).
Application date).

[Problems to be solved by the invention]

The barrier effect of a TiN film formed under conventional ordinary conditions (sputtering a titanium target in an atmosphere of argon gas and nitrogen gas) was insufficient with recent high aspect contact or shallow diffusion layer structures. Therefore, in the method proposed in Japanese Patent Application No. 63-185005, TiN
In order to improve the barrier effect of the film, oxygen is added to an atmosphere of argon and nitrogen to form a TiN film, and an aluminum wiring layer is formed thereon without breaking vacuum.
However, the proposed method has the following problems.

First, as shown in FIG. 5, the specific resistance of the TiN film to be formed increases as the amount of added oxygen increases. Temperature in Fig.5 (200,400 and 600 ℃)
Is the set temperature of the substrate heater during sputtering. On the other hand, in the wiring structure shown in FIG. 6, the relationship between the amount of oxygen added when forming the TiN film and the junction leak current (bias current: -5 V) after heat treatment at 450 ° C. × 30 minutes + 500 ° C. × 60 minutes Then, it is preferable that the amount of added oxygen is large in order to suppress the leak current. In order to obtain the wiring structure shown in FIG.
SiO ₂ film (thickness: 1.0μ) on the silicon substrate 1 by thermal oxidation
m) 2 is formed, and a contact hole (diameter: 1.2 μm) is formed in the SiO ₂ film 2 by photoetching. Arsenic (As ⁺ ) was ion-implanted at an accelerating voltage of 70 keV to 4 × 10
^An n ⁺ region 3 (depth: 0.34 μm) is implanted into the silicon substrate 1 at a dose of ¹⁵ cm ^{−2 and} subjected to activation annealing. Next, the Ti contact layer 4 (thickness: 2) was placed on a heater heated to 600 ° C. in an argon gas atmosphere using a Ti target in an argon gas atmosphere.
0 nm) is formed on the entire surface including the contact holes, sputtering is continued, and a nitrogen gas is flowed to form a TiN layer 5 (thickness:
100 nm). At the time of this TiN layer formation, a set amount of oxygen gas (4 sccm (5 flow%), 7 sccm (9 flow%)) is also flown.
Next, an aluminum wiring layer 6 (thickness: 1.0 μm) is formed by sputtering with an argon gas using a pure aluminum target without breaking vacuum. Then, the substrate having the obtained wiring structure was subjected to the above-described heat treatment, the junction leak current was measured, and the obtained results were shown in a frequency distribution in FIGS. 7A, 7B, and FIG.
FIG. 7C is a diagram. From these drawings, it is necessary to set the oxygen addition amount to 9 flow% or more to suppress the leak current. With such a large amount of added oxygen, the specific resistance becomes considerably large as estimated from the 600 ° C. line in FIG. 6, and it is difficult to use it in an actual semiconductor device.

Second, as described above, TiN in an oxygen gas added atmosphere is used.
When a layer is formed and an aluminum wiring layer is formed thereon, the mean time to failure MTF becomes shorter as the amount of added oxygen increases, as shown in FIG. The wiring structure in this case is the same as that shown in FIG. 6, but Al-2% Cu is used for the aluminum wiring layer. As can be seen from FIG.
Assuming that the MTF when oxygen is not added is 1, the MTF when 9% oxygen is added is less than half.

An object of the present invention is to provide a method for forming a wiring with a higher barrier effect than the conventional method by adding oxygen at the time of forming a TiN barrier layer so as not to cause deterioration in characteristics due to oxygen addition by the above proposed method. It is.

[Means for solving the problem]

The above-described object is to sequentially form a contact layer, a barrier layer of a nitride, boride or carbide of any one of titanium, zirconium, hafnium and tungsten on a silicon substrate, and a wiring layer of aluminum or an alloy thereof on a silicon substrate. In the method of forming a wiring to be formed, a method of forming a wiring is characterized in that oxygen gas is added to an atmospheric gas in a pulsed manner or only for one time during the formation of the barrier layer.

[Action]

According to the present invention, instead of flowing (adding) oxygen gas in synchronization with nitrogen gas during the formation of the barrier (TiN) layer as in the case proposed in Japanese Patent Application No. Oxygen barrier (TiN) by pulsed repetition or once-only flow (addition) at one time
It is localized in a part of the layer. As a result, the barrier effect can be improved, and the increase in specific resistance and the shortening of the wiring MTF due to the addition of oxygen during the entire period can be significantly reduced.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 4 shows a MOSF to which the wiring forming method according to the present invention is applied.
FIG. 7 is a schematic sectional view of the ET, and its wiring structure is basically the same as FIG. 6 referred to in the description of the prior art. This MOSF
The structures of the ET and its wiring are known, and the production thereof can be performed based on a known method only in the way of adding the oxygen gas when forming the barrier layer (TiN layer).

As shown in FIG. 4, a p-type silicon substrate 11 is prepared,
Field SiO ₂ by selective oxidation (LOCOS process)
An oxide film 12 is formed. After forming a gate (SiO ₂ ) oxide film 13, a polysilicon gate electrode 14 is formed. Using the gate electrode 14 and the field oxide film 13 as a mask, arsenic (As ⁺ ) is doped into the silicon substrate 11 by ion implantation to form a source region 15 and a drain region 16 of an N ⁺ region, and a predetermined annealing heat treatment is performed. Rub A PSG film serving as an interlayer insulating film 17 is formed on the entire surface by a CVD method, and a contact hole (diameter: 0.6 μm, depth: 0.6 μm) in which the source / drain regions 15 and 16 are exposed is formed by a photoetching method.

Next, a contact (Ti) layer 18, a barrier layer (TiN layer) 19 and an aluminum wiring layer 20 are sequentially formed using the same sputtering apparatus as used in Japanese Patent Application No. 63-185005.

The Ti contact layer 18 is formed under the following sputtering conditions.

Target: Titanium metal of 99.99% purity Introduced gas: Argon (20 sccm) Internal pressure: 2 mTorr Substrate heater temperature: 600 ° C Sputter DC power: 5 kW Ti layer thickness: 20 nm Next, using the same target, nitrogen gas ( The TiN layer 19 (thickness: 100 nm) was formed on the Ti layer 18 under the above-mentioned sputtering conditions except that the introduction of 80 sccm) and the addition (introduction) of oxygen gas as shown in FIG. 1 or FIG. Formed.

In the case of FIG. 1, oxygen gas (20
ccm) is pulsed three times at 5 second intervals for 5 seconds, and in the case of FIG. 2, only 15 seconds during the film formation. At the final stage of TiN layer formation, no oxygen gas is added. Since there is no oxygen at a depth of 10 to 25 nm from the surface of the TiN layer, there is no effect on the upper aluminum wiring layer. In FIG. 1 and FIG. 2, argon gas (total 20 sccm) is introduced by another system (different introduction pipe), and Ar (1) flows from the back surface of the substrate mounted on the substrate heating table. Ar (2) is supplied by flowing directly into the sputtering chamber.

For comparison, according to the method proposed in Japanese Patent Application No. 63-185005, a gas (nitrogen gas, oxygen gas and argon gas) is introduced into a sputtering apparatus to form a TiN layer as shown in FIG. That is, the oxygen gas is added together with the nitrogen gas during the formation of the TiN layer.

A TiN layer (thickness: 500 nm) was formed directly on the SiO ₂ film by sputtering under the above conditions, and the specific resistance was measured. The results shown in Table 1 below were obtained.

Thus, the specific resistance of the TiN layer in the formation method according to the present invention is much smaller than that of the proposed method by about one tenth.

After the formation of the TiN layer 19, the aluminum layer 20 is formed under the following sputtering conditions using the same sputtering apparatus.

Target: pure Al Introduced gas: argon (50 sccm) Internal pressure: 5 mTorr Substrate heating temperature: 180 ° C Sputter DC power: 10 kW Al layer thickness: 1.0 μm In the MOSFET having the wiring thus formed, the MTF is It is almost the same as the case of no oxygen addition shown in FIG. 8, and the MTF does not decrease irrespective of the oxygen addition during the formation of the TiN layer, which is an improvement over the proposed conventional method.

Polysilicon can be used for the contact layer 18 in addition to the above-mentioned Ti. In this case, the contact layer 18 is formed by a CVD method. Further, titanium silicide, tungsten, and tungsten silicide can also be used as the material of the contact layer 18.

For the barrier layer 19, besides titanium nitride (TiN), nitride, carbide or boride of titanium, zirconium, hafnium and tungsten as shown in Table 2 can be used.

Table 2 Metal Nitride Carbide Boride Ti (TiN) TiC TiB Ta TaN TaC TaB Zr ZrN ZrC ZrB Hf HfN HfC HfB W WN WC WB In order to form carbides and borides, carbon compounds are used instead of nitrogen gas. A gas (for example, methane CH ₄ ) or a boron compound gas (for example, diborane B ₂ H ₆ ) may be used. Alternatively, target Ti, Ta, Zr, Hf,
W carbides and borides may be used.

〔The invention's effect〕

As described above, according to the present invention, when the barrier layer of the aluminum wiring is formed, the addition method of the oxygen gas is changed to a pulse type or one-time addition different from the conventional method, so that the oxygen gas is localized in a part of the barrier film. Let it. In this way, the barrier effect can be improved, and the increase in the specific resistance of the barrier layer and the decrease in the MTF as the wiring due to the conventional oxygen addition can be largely prevented. Therefore, the performance and reliability of the semiconductor device can be improved.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a gas flow rate and a formation time in a pulse oxygen addition method during sputtering for forming a barrier (TiN) layer according to the method according to the present invention, and FIG. FIG. 3 is a graph showing a relationship between a gas flow rate and a formation time in a one-time oxygen addition method at the time of forming a barrier (TiN) layer by sputtering according to the method according to FIG. FIG. 4 is a graph showing the relationship between the time and the formation time, and FIG. 4 shows a MOSF having a wiring formed by the method of the present invention.
FIG. 5 is a partial cross-sectional view of the ET, FIG. 5 is a graph showing the relationship between the specific resistance ratio, the oxygen flow rate and the substrate heating temperature when oxygen is added by the conventional method at the time of forming the TiN layer, and FIG. FIG. 7A, FIG. 7B and FIG. 7C are partial cross-sectional views of a semiconductor device showing a wiring structure having a layer. FIG. 7A, FIG. 7B, and FIG. 7C are graphs showing a frequency distribution of junction leak current in a semiconductor device having a wiring having a TiN barrier layer. FIG. 8 is a graph showing the relationship between the MTF and the amount of oxygen added during the formation of the TiN layer in a semiconductor device having a wiring with a TiN barrier layer. 11: silicon substrate, 15: source region, 16: drain region, 17: interlayer insulating film, 18: contact (Ti) film, 19: barrier (TiN) layer, 20: aluminum wiring layer.

Claims (1)

(57) [Claims] A contact layer, a barrier layer of a nitride, boride or carbide of any one of titanium, zirconium, hafnium and tungsten, and a wiring layer of aluminum or an alloy thereof are sequentially formed on a silicon substrate. In a method for forming a wiring to be formed, an oxygen gas is added to an atmospheric gas in a pulsed manner or only for one time during the formation of the barrier layer.