JPH0727902B2 - Method for manufacturing semiconductor device - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a highly integrated device such as a semiconductor memory, and more particularly to a method for forming an electric conduction part.

<Prior Art> Conventionally, polysilicon has been generally used as a wiring material of a semiconductor element. However, with the high integration of semiconductor elements, the wiring within the element has a line width in the submicron unit, and conventional polysilicon has a high resistance and a long delay time. It has been introduced. As a result, nowadays, silicides such as tungsten silicide are generally used as useful materials having a resistance value lower than that of polysilicon by an order of magnitude. However, in the state-of-the-art miniaturized devices such as 166M-DRAM, a material having a resistance an order of magnitude lower than that is required.

In addition, the wiring in the highly integrated device tends to be multi-layered, and the wiring material is required to have chemical and physical stability that does not deteriorate in the subsequent high temperature process.

Tungsten, molybdenum, etc. are considered to be promising to meet these requirements.
Since the thin film can be easily formed by the method, research and development are being actively conducted at present.

On the other hand, as a result of the miniaturization of elements, the diameter of contact holes has also become smaller, and the ratio of the depth to the diameter of the contact hole (aspect ratio) has become larger and larger. It is difficult to make it conductive.

The use of tungsten has been attempted to solve this problem. When tungsten is formed by the CVD method, it has a characteristic of so-called selective growth in that it does not grow on the insulating film but grows only on Si or metal by appropriately selecting the conditions. Utilizing this property, tungsten is grown from the bottom to the top in the contact hole, stopping the growth up to the opening of the contact hole, and reaching the upper surface of the contact hole while maintaining a complete conduction state with the base. Tungsten is embedded. In this way, after burying tungsten in the contact hole, conventionally, a metal thin film of Al or the like is formed by a sputtering method or the like, and further fine processing is performed for wiring. When Al is used for the wiring as described above, tungsten acts as a Si diffusion barrier that prevents Si precipitation, Al spike, and the like due to solid-phase diffusion between Al and Si.

As described above, the tungsten generation technology by the CVD method is indispensable for highly integrated devices.

<Problems to be Solved by the Invention> However, tungsten formed by the CVD method has a large crystal grain size, and depending on the forming conditions, it has a 3000 Å film thickness and a grain size of 1000 to 2000 Å. There was such a problem.

During dry etching when forming a wiring shape after forming the tungsten thin film, the etching rate at the crystal grain boundaries is high, and the processing shape becomes rough, which makes microfabrication difficult and causes a short circuit or disconnection of the wiring.

The shape of the tungsten crystal grains may be transferred to the underlying substrate after etching, in which case the subsequent processes are affected.

When tungsten is used as a barrier metal in the contact portion, Si is easily diffused through large grain boundaries in the subsequent heat treatment step, and the effect as a diffusion barrier is insufficient.

Therefore, it is an object of the present invention to provide a method of manufacturing a semiconductor system having a fine crystalline tungsten thin film which has fine workability and effectively functions as a barrier metal for preventing Si diffusion.

<Means for Solving the Problems> In order to achieve the above object, a method for manufacturing a semiconductor device according to the present invention is a method for manufacturing a semiconductor device, including a step of forming wiring on a conductor layer with an insulating film interposed therebetween. After forming a contact hole in the insulating film and forming a tungsten thin film on the bottom surface and the side surface of the contact hole by a CVD method, the tungsten thin film is formed so that the crystal grains of the tungsten thin film are in a mixed state of fine crystals and amorphous. It is characterized in that ion implantation is carried out, followed by annealing, and then wiring is formed.

In order to bring the crystal grains of the tungsten thin film into a mixed state of fine crystals and amorphous, the ion implantation needs to be performed at an acceleration voltage at which ions stop in the tungsten thin film.

<Operation> When ions are implanted into the tungsten thin film, the crystal grains of tungsten are destroyed and a mixed state of fine crystals and amorphous is generated. As a result, fine processing of the wiring becomes possible, and Si diffusion due to grain boundaries becomes difficult and the barrier property is improved.

<Examples> Hereinafter, the present invention will be described in detail with reference to illustrated examples.

FIG. 1 is a cross-sectional view of an N-channel transistor which is being manufactured using a normal MOS process. A contact hole 7 communicates with an N ⁺ diffusion layer 3 of a source portion formed on a base Si substrate 1 through an interlayer insulating film 5. It shows the state. In the figure, 8 is an element isolation oxide film, and 10 is a gate polysilicon. The present invention relates to the subsequent steps.

In one embodiment of the present invention, first, a tungsten thin film 9 is grown as an electrically conductive portion on the Si substrate 1 by using the conventional selective CVD method. FIG. 2 shows a state in which the tungsten thus grows only on Si and the contact hole 7 is completely filled with tungsten.

Then, an inert gas such as Ar is injected into the substrate on which the tungsten thin film 9 is formed by the ion injection method. At this time, typical conditions for ion implantation are an acceleration voltage of 550 keV and an implantation amount, that is, the number of ions is 1 × 10 ¹⁶ / cm ² .

As a result of this ion implantation, the tungsten crystal grains are destroyed by the ions, and a mixed state of fine crystals and amorphous is realized. The tungsten crystal grains are destroyed by the ions because the implanted ions remain in the tungsten thin film and thus have a large destructive force.

After that, a metal thin film (not shown) such as Al is formed by a sputtering method or the like, and further fine processing is performed to complete the wiring.

According to this embodiment, by refining the crystal grains of tungsten, diffusion of Si into Al through grain boundaries is prevented, and the barrier property is improved. Therefore, it is possible to prevent the precipitation of Si and the spike of Al due to the solid phase diffusion between Al and Si.

In the above embodiment, the contact portion and the wiring portion of the electric conduction portion were separately formed. Next, a method of simultaneously forming the contact portion and the wiring portion with tungsten will be described.

First, in the state shown in FIG. 1, a metal thin film 11 of titanium or titanium-tungsten alloy is formed in the contact hole 7 and on the interlayer insulating film 5 by a sputtering method or the like,
Then, a tungsten thin film 13 is formed on the metal thin film 11 by a non-selective CVD method. The reason for forming the metal thin film 11 in advance is as follows. If the film is grown as it is immediately after the contact hole 7 shown in FIG. 1 is formed, the selective growth by the base substrate 1 occurs and the adhesion of the tungsten film 13 formed on the insulating film 5 is poor. The film 13 is peeled off so that it cannot be practically used. Therefore, the metal thin film 11 is formed for the purpose of eliminating the selectivity and improving the adhesion. By doing so, the tungsten thin film 13 can be non-selectively grown with sufficient adhesion on the entire surface of the wafer.

Next, as in the above-described embodiment, an inert gas such as Ar is injected into the substrate on which the tungsten thin film 13 is formed by the ion injection method. Typical conditions for ion implantation at this time are 3000 Å tungsten thin film, Ar ion, accelerating voltage of 550 keV, and implantation amount of 1 × 10 ¹⁶ / cm ² . The ions implanted by the accelerating voltage of 550 keV remain in the tungsten thin film 13. After ion implantation, the tungsten thin film 13 on the insulating film 5 is subjected to fine processing to form wiring.

According to the present embodiment, the large crystal grains of tungsten are broken by the ion implantation and a fine crystal and an amorphous state are mixed, so that fine wiring can be easily and surely performed. Therefore, the occurrence of short circuit and disconnection is prevented, and the reliability is improved.

It should be noted that the damage caused in the electrically conductive portion due to the variation in the Ar ion implantation depth is recovered by performing heat treatment (annealing) such as sintering in a nitrogen atmosphere at 440 ° C.

<Effect> As is clear from the above, according to the present invention, since the crystal grains of the tungsten thin film are in a mixed state of fine crystals and amorphous, the effect as the diffusion barrier of the tungsten thin film is improved, and the precipitation of Si and Al spikes can be effectively prevented. Further, since fine workability is extremely improved by refining the crystal grains of tungsten, it is possible to prevent a short circuit or a break in the wiring.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an N-channel transistor in the process of fabrication according to this example, FIG. 2 is a cross-sectional view of the transistor after the selective CVD tungsten is buried in the contact hole of FIG. 1, and FIG. FIG. 6 is a cross-sectional view of the transistor after forming a non-selective CVD tungsten thin film after opening the contact hole in the figure. 1 ... Si substrate, 3 ... N ⁺ diffusion layer, 5 ... Interlayer insulating film, 7 ... Contact hole, 9 ... Selective CVD tungsten film, 11 ... Metal thin film, 13 ... Nonselective CVD tungsten Thin film.

Claims (1)

[Claims] 1. A method of manufacturing a semiconductor device, comprising a step of forming wiring on a conductor layer via an insulating film, wherein a contact hole is formed in the insulating film, and tungsten is formed on a bottom surface and a side surface of the contact hole by a CVD method. After forming the thin film, the tungsten thin film is ion-implanted so that the crystal grains of the tungsten thin film are in a mixed state of fine crystals and amorphous, followed by annealing, and then forming the wiring. A method for manufacturing a characteristic semiconductor device.