JPH06275625A - Wiring containing high-melting-point metal and its manufacture - Google Patents

Abstract

PURPOSE:To relieve the stress of a metal wiring, obtain a thin photoresist film, and reduce the reflectivity in a photolithography process, in a high-melting- point metal wiring. CONSTITUTION:After a BPSG film 2 is formed on a silicon substrate 1, a titanium nitride film 3 and a tungsten film 4 are formed. A silicon nitride film 5 is deposited on the tungsten film 4, and patterned by a photolithography method. A high-melting-point metal wiring is formed by a dry etching method.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wiring including a refractory metal in a semiconductor integrated circuit and a method for forming the wiring.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of semiconductor integrated circuits, high melting point metal wiring such as tungsten and molybdenum has been
As compared with the conventional Al alloy wiring, it has attracted attention because it has good elect migration characteristics, good step coverage, and low cost.

An example of a conventional method of forming a wiring containing a refractory metal will be described below with reference to the drawings.

FIG. 3 shows a wiring forming method when tungsten is used as a wiring material. As shown in FIG. 3A, a silicon oxide film containing boron and phosphorus (hereinafter abbreviated as BPSG film) is formed on the silicon substrate 1. After forming 2, the titanium nitride film 3 is formed on the BPSG film 2 and the tungsten film 4 is formed. Then, a photoresist 6 is formed on the tungsten film 4. Specifically, a BPSG film is formed on the silicon substrate 1 by the CVD method.
After depositing a thickness of 00 nm, a titanium nitride film 3 having a thickness of 100 nm is formed on the BPSG film 2 by a sputtering method, and then CVD is performed.
The tungsten film 4 having a thickness of 500 nm is formed by the method. After that, after applying a resist film on the tungsten 4,
By performing photolithography on the resist film, a photoresist 6 having a desired pattern shape is formed.

Next, as shown in FIG. 3B, while the silicon substrate 1 is cooled to 0 ° C. or lower using the photoresist 6 as a mask and using a mixed gas of sulfur hexafluoride and oxygen, for example, The tungsten film 4 is etched by the reactive ion etching method.

Further, as shown in FIG. 3 (c), the silicon substrate 1 is kept at a temperature of room temperature or higher, and the titanium nitride 3 is etched by chlorine gas, for example, a mixed gas of chlorine and oxygen, using the photoresist 6 as a mask, Pattern is formed.

[0007]

However, with the above structure, in the photolithography process,
For example, when a tungsten film is used, the reflectance of tungsten is 50% at an excimer laser wavelength of 248 nm.
It was very large, and it was very difficult to form a fine wiring pattern such as a 0.5 μm rule.

Further, as the device is miniaturized, the photoresist is thinned. At this time, in the dry etching process, since the selection ratio of tungsten and photoresist at the time of tungsten etching is low, there is a problem that the resist is lost during etching and a desired pattern cannot be obtained. Further, the stress of the tungsten film causes the semiconductor substrate to be convex downward, which is a very big problem in forming a submicron rule device on the semiconductor substrate.

In the dry etching process, the selection ratio of resist to the etching of tungsten is as low as about 2. Further, the substrate is cooled to a low temperature of 0 ° C. or lower when etching the tungsten film, and the substrate is cooled when etching the titanium nitride film. It is necessary to heat the temperature to room temperature or higher, and two or more reaction chambers are required, resulting in a very expensive process.
In view of the above problems, the present invention reduces the substrate reflectance in the photolithography process, thins the photoresist,
Provided is a wiring containing a refractory metal in which stress on a semiconductor substrate is relieved by a metal wiring, and a method for forming the wiring.

[0010]

In order to solve the above problems, the present invention provides a method of forming a silicon nitride film on a refractory metal and performing a dry etching method on a laminated film of the formed metal film and a silicon nitride film. To form wiring.

[0011]

According to the present invention, the silicon nitride film on the refractory metal relaxes the stress of the refractory metal by the above-mentioned structure,
In the photolithography process, the reflection from the wiring surface is suppressed. In the dry etching process,
By using the silicon nitride film as a mask, it is possible to supplement the low selectivity of the refractory metal to the resist.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A wiring containing a refractory metal, which is an embodiment of the present invention, will be described below with reference to the drawings. FIG. 1 is a process cross-sectional view of a wiring containing a refractory metal and a method for forming the wiring in one embodiment of the present invention. Tungsten will be described as an example of the refractory metal. In FIG. 1, 1 is a silicon substrate, 2 is a BPSG film, 3 is a titanium nitride film, 4
Is a tungsten film, 5 is a silicon nitride film, and 6 is a photoresist.

FIG. 1A shows the wiring when tungsten is used as the wiring material. As shown in FIG. 1A, after forming a BPSG film 2 on a silicon substrate 1, a titanium nitride film 3 is formed on the BPSG film 2 and a tungsten film 4 is formed on the titanium nitride film 3. To do. Then, a photoresist 6 is formed on the tungsten film 4 by 1.0
μm is formed. Specifically, CVD is performed on the silicon substrate 1.
Method to deposit 700nm BPSG film,
A titanium nitride film 3 is formed on the G film 2 by a sputtering method.
of the tungsten film 4 is formed to a thickness of 5 by CVD.
00 nm is formed. At this time, if a tungsten film is formed, the semiconductor substrate will be convex downward due to the stress of the tungsten film. When the silicon nitride film 5 is formed on the tungsten film 4, the stress of the silicon nitride film 5 acts so as to make the semiconductor substrate convex upward, so that the stress of the tungsten film 4 can be relaxed. After that, a silicon nitride film 5 is deposited to a thickness of 50 nm on the tungsten 4 by the CVD method.

Next, as shown in FIG. 1B, a resist film 650 nm is applied on the silicon nitride film 5, and then photolithography is performed on the resist film to form a photoresist 6 having a desired pattern shape. To do. The silicon nitride film has much lower reflectance than the tungsten film, and can improve the resolution of fine patterns.

Next, as shown in FIG. 1C, the silicon substrate 1 is placed at -20.degree. C. using the photoresist 6 as a mask.
Then, the silicon nitride film 5 and the tungsten film 4 are etched by reactive ion etching using a fluorine-based gas such as SF ₆ gas. At this time, the etching rate of the tungsten film is about 200 nm / min, the selection ratio to the resist is about 2, and if the tungsten film of 500 nm is over-etched by 40%, the photoresist of 350 nm is lost in the calculation.

Next, as shown in FIG. 1D, while the silicon substrate 1 is cooled to -20 ° C., a chlorine-based gas such as C is used.
The titanium nitride 3 is etched with l ₂ gas. At this time, the etching rate of the TiN film is about 200 nm / min, and the selection ratio with respect to the resist is as low as 0.5. Therefore, the photoresist is 30% with an overetch rate of 50%.
It disappears by 0 nm. That is 650n by dry etching
m photoresist is lost and all the deposited photoresist is lost. However, the etching rate of the silicon nitride film 5 by Cl ₂ gas is very small, and the selection ratio of the titanium nitride 3 and the silicon nitride film, that is, (etching rate of titanium nitride film / etching rate of silicon nitride film) is 10. . Even if the photoresist disappears during the dry etching of the titanium nitride film 5, since the selection ratio with the silicon nitride film 5 is large, the silicon nitride film 5 serves as a mask and the tungsten film 4 is not side-etched. .

As described above, the refractory metal wiring containing tungsten is formed. In addition, since the low selection ratio with respect to the resist can be compensated, the photoresist can be thinned. 2 (a) is a schematic view of the cross-sectional shape of the wiring when the photoresist disappears during etching and the wiring shape deteriorates without using the silicon nitride film, FIG. 2 (b).
FIG. 6 is a schematic view of a cross-sectional shape of a wiring when a silicon nitride film is used for and a photoresist disappears during etching. In FIG. 2B, the photoresist disappeared in the dry etching, but the silicon nitride film served as a mask, and a good wiring shape could be maintained. Furthermore, it is possible to dry the laminated film made of the tungsten film and the titanium nitride film by dry etching while keeping the semiconductor substrate temperature at −20 ° C., and to make the laminated film made of the tungsten film and the titanium nitride film in one reaction chamber. The film can be etched, which greatly contributes to the cost reduction of the etching apparatus.

Although tungsten has been described as an example of the refractory metal in this embodiment, the refractory metal may be molybdenum, titanium, tantalum, an alloy containing molybdenum, an alloy containing titanium, or an alloy containing tantalum. Can also obtain the same effect.

[0019]

As described above, according to the present invention, by depositing a silicon nitride film on a refractory metal, the warpage of a semiconductor substrate is reduced, the reflectance in photolithography is reduced,
In the dry etching process, a good wiring etching shape can be obtained.

[Brief description of drawings]

FIG. 1 is a process cross-sectional view of a method for forming a wiring containing a refractory metal according to an embodiment of the present invention.

[FIG. 2] (a) is a schematic diagram of the cross-sectional shape of the wiring when the photoresist has disappeared during etching and the wiring shape has deteriorated without using the silicon nitride film. (B) uses the silicon nitride film. Then, a schematic diagram of the cross-sectional shape of the wiring when the photoresist disappears during etching

FIG. 3 is a process sectional view showing a conventional wiring forming method.

[Explanation of Codes] 1 Silicon substrate 2 BPSG film 3 Titanium nitride film 4 Tungsten film 5 Silicon nitride film 6 Photoresist

Claims (7)

[Claims] 1. A wiring containing a refractory metal, comprising depositing a refractory metal film on a semiconductor substrate and depositing a silicon nitride film on the refractory metal film. 2. The refractory metal film according to claim 1, which is a laminated film in which a titanium nitride film is deposited on a semiconductor substrate and a tungsten film is deposited on the titanium nitride film. Wiring including. 3. A high melting point metal film is deposited on a semiconductor substrate, a silicon nitride film is deposited on the high melting point metal film, a resist pattern is formed by photolithography, and dry etching is performed. A method for forming a wiring containing a refractory metal. 4. A wiring containing a refractory metal, wherein the refractory metal film according to claim 3 is a laminated film in which a titanium nitride film is deposited on a semiconductor substrate and tungsten is deposited thereon. Forming method. 5. The silicon nitride film and the tungsten film according to claim 4, after being dry-etched with a fluorine-based gas,
A method for forming a wiring containing a refractory metal, which comprises dry-etching a titanium nitride film with a chlorine-based gas. 6. The fluorine-based gas according to claim 5 is SF ₆ ,
A method for forming a wiring containing a refractory metal, which is at least one kind of NF ₃ , CF ₄ , CHF ₃ , and ClF ₃ . 7. The chlorine-based gas according to claim 5 is Cl ₂ , B
A method of forming a wiring containing a refractory metal, which is at least one kind of Cl ₃ , SiCl ₄ , CHCl ₃ , and HCl.