WO1999035675A1

WO1999035675A1 - Method for forming titanium film by cvd

Info

Publication number: WO1999035675A1
Application number: PCT/JP1999/000033
Authority: WO
Inventors: Taroh Ikeda
Original assignee: Tokyo Electron Limited
Priority date: 1998-01-09
Filing date: 1999-01-08
Publication date: 1999-07-15
Also published as: JPH11204457A; TW469300B

Abstract

A CVD method by which a titanium film having stable contact resistance and a satisfactory homology of the interface between the film and a silicon substrate can be formed. The method comprises feeding a film-forming gas containing TiCl4 gas to a contact hole (46) at the bottom of which a silicon substrate (41) having an autoxidized silicon film (50) is present to form a titanium film on the silicon substrate (41) by CVD to thereby form a TiSi2 layer (51) on the silicon substrate (41).

Description

Specification

Method of forming titanium film by CVD

The present invention relates to a method for forming a Ti film by CVD, which is used, for example, as a contact metal or an adhesion layer in a semiconductor device.

Background technology

In the manufacture of semiconductor devices, the circuit configuration has tended to have a multilayer Ifi ^ structure in response to recent demands for higher density and higher integration. For this reason, the lower semiconductor device and the upper wiring layer have been developed. The embedding technology for electrical connection between layers such as contact holes, which are the connection parts between them, and via holes, which are the connection parts between the upper and lower IS ^ layers, has become important.

In order to fill such contact holes and via holes, A 1 (aluminum), W (tungsten), or an alloy mainly composed of these is generally used. If it comes into direct contact with the underlying Si (silicon) substrate or A1 wiring, an alloy of both metals may be formed at these boundaries due to the absorption effect of A1. The alloy formed in this way has a large resistance value, and it is not preferable to form such an alloy because of the recent demands for high power and high speed operation 11 ^ .

In the case of using a W or W alloy as a buried layer of the contact hole will result WF ₆ gas used for forming the buried layer tends to degrade the electrical characteristics in the S i substrate, also not preferable .

Therefore, in order to prevent these inconveniences, before forming a buried layer in the contact hole or via hole, a barrier layer is formed on these inner walls, and the barrier layer is buried from above. The formation of the embedded layer is performed. In this case, a barrier layer having a two-layer structure of a Ti (titanium) film and a TiN (titanium nitride) film is generally used.

Traditionally, such barrier layers have been formed using physical vapor deposition (PVD), but recently the demand for device miniaturization and high integration has become particularly demanding, and the design rules have become particularly severe. Accordingly, as the line width and hole opening diameter become smaller and the aspect ratio becomes higher, the electrical resistance of PVD films increases, making it difficult to meet the demands.

Therefore, the Ti film and the TiN film constituting the barrier layer are being formed by chemical vapor deposition (CVD), which can be expected to form a higher quality film. In this case, first, a Ti film as a contact metal is formed on Si at the bottom of the hole. In this case, in order to reduce the contact resistance, the natural oxide film of silicon formed on the underlying Si in the previous process is usually removed by a cleaning treatment with 1% diluted hydrofluoric acid.

However, if the cleaning process for removing the natural oxide film is performed as described above, the electrical characteristics at the time of forming the contact may vary depending on the cleaning conditions and the time management until the next process after the cleaning. There is a problem that it gets stuck.

In the formation of T i layer, the use of T i C 1 ₄ as a film-forming gas, during film formation is T i S i ₂ reacts S i and T i force underlying are formed, the The morphology of the interface with the underlying Si deteriorates in the course of the reaction, and when used in the process of forming a contact hole, junction leakage is likely to occur, and also adversely affects the case of a via hole.

The present invention has been made in view of the above circumstances, and is based on a CVD method capable of forming a Ti film that stabilizes contact resistance and improves morphology at the interface with the underlying Si. An object of the present invention is to provide a method for forming a Ti film. Disclosure of the invention

According to the present invention, a titanium film is formed on a surface of a silicon layer such as a silicon substrate or a polysilicon wiring by CVD using a film forming gas containing a TiC14 gas. shall apply in the method, a step of allowing the formation of a silicon oxide film on the silicon layer surface, the film gas containing T i C 1 ₄ gas in a state where the oxide film is left to be supplied to the silicon layer surface titanium film And a method for forming a titanium film by CVD comprising the steps of:

In a typical example, the silicon layer has its surface exposed at the bottom of a contact hole formed in an insulating film on a silicon substrate, or has its surface exposed at the bottom of a via hole formed in an insulating film on a polysilicon wiring layer. ing.

Force to excite plasma of film forming gas in film forming process <desirable. Further, the silicon oxide film is a film having a thickness of about 10 Å or more.

The present inventors have, T i C 1 ₄ using the deposition gas containing the gas by CVD Upon forming a film of the T i layer, the contact resistance with stabilizing I匕of T i layer and the underlying interface between S i As a result of repeated studies to improve the morphology, it was found that the film should be formed with a constant thickness of, for example, a natural oxide film formed on the underlying Si.

Conventionally, Ti films as contact metals are often formed by PVD, and if a natural oxide film remains on the underlying Si at that time, the contact resistance after Ti film formation increases. Therefore, the natural oxide film was removed. Therefore, the native oxide film was similarly removed when forming the Ti film by CVD.

On the other hand, when the Ti film was formed by CVD, the morphology of the interface between the Ti film and the underlying Si was found to be as bad as possible. that these interdiffusion increases with it the unevenness of the surface increases, and T i C 1 ₄ by the gas of the underlying S i is due to be isotropic etching Was found. The reaction formula at that time is considered as follows.

T i Cl ₄ + H2 + 3 S i- T i S i ₂ + S i C l ₂ + 2H l These are caused by the underlying Si being exposed, and the natural oxidation of silicon It has been found that such inconvenience is eliminated by leaving the film. That is, by oxide film of constant thickness is left, to suppress mutual diffusion between T 1 and S i, also it is to a work as an etch barrier of T i C 1 ₄ gas. The reaction formula in this case is considered as follows.

_{T i C 14 + 4H 2 +} S i 0 2 + S i → T i S i 2 + 2H 2 0 + 4HC 1 In the case of CVD deposition, be left natural oxide film, the process gas The oxide film disappears from the interface between Si and Ti due to the reduction reaction, so that the problem that the contact resistance of the Ti film is high does not occur, and there is no need to remove the oxide film. Resistance stability is also high.

Furthermore, since the washing step in the preceding step can be omitted, the number of steps is reduced, and the production efficiency can be made extremely high.

The present invention has been made against the stereotype that the silicon natural oxide film on Si is to be removed, and furthermore, it has an extremely large effect as described above. The target value is high.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional view showing an example of a film forming apparatus for performing a method of forming a Ti film by CVD according to the present invention.

FIG. 2 is a sectional view showing an Si wafer to which the present invention is applied.

FIG. 3 is a schematic diagram for explaining Ti film formation in the present invention.

FIG. 4 is a schematic diagram for explaining conventional Ti film formation.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view showing an example of a Ti film forming apparatus used for carrying out the present invention. This film-forming apparatus has a substantially cylindrical chamber 11 which is airtightly arranged, and a susceptor 2 for horizontally supporting a Si wafer W as an object to be processed is provided at the center thereof. It is arranged in a state where it is supported by a cylindrical support member 3 that can move up and down. Further, the heater 15 is embedded in the susceptor 1 for 4 hours, and the heater 15 is heated by a power source (not shown) to heat the Si wafer W as a processing target to a predetermined temperature.

A shower head 10 is provided at an upper end portion of the chamber 11 so as to face the semiconductor wafer W supported by the susceptor 2, and a plurality of gas discharge holes are provided on a lower surface facing the wafer W. 10 & mosquitoes are formed. Inside the shower head 10, a space 11 is formed, and a dispersion plate 12 having a large number of holes formed therein is provided horizontally. A gas inlet 13 for introducing a gas into the shower head 10 is formed at an upper portion of the shower head 10, and a gas supply pipe 15 is connected to the gas inlet 13.

An H ₂ (hydrogen) gas source 16, an Ar (argon) gas source 17, and a TiC 14 (tetrashidani titanium) gas source 18 are connected to the gas supply pipe 15. Each gas is supplied from these gas sources into the chamber 1 through the gas supply pipe 15 and the shower head 10, and a Ti film is formed on the Si wafer W. In addition, the piping connected to each gas source is provided with a valve 19 and a mass opening controller 20 times. A high-frequency power supply 23 is connected to the shower head 10 via a matching circuit 22 so that high-frequency power can be applied to the shower head 10 from the high-frequency power supply 23. With this high frequency power, a plasma force of the film forming gas is formed in the chamber 11. The shower head 10 and the chamber 1 are electrically insulated by an insulating member 14, and the chamber 11 is grounded.

An exhaust port 8 is provided on the bottom wall of the chamber 1. Is connected to an exhaust system 9 for exhausting the inside of the chamber 11. Further, a loading / unloading port 24 for the wafer W is provided below the side wall of the chamber 1, and the loading / unloading port 24 can be opened and closed by a gate valve 25. The loading and unloading of wafer W is performed with susceptor 2 lowered.

In order to form a Ti film by such a film forming apparatus, the gate valve 25 is opened, the Si wafer W is loaded into the chamber 1, and is placed on the susceptor 2. and evacuated to a high vacuum state by S i wafer W while heating the vacuum pump of the exhaust system 9 by one coater 4, subsequently, T i C 1 ₄ gas, H ₂ gas, is introduced to a r gas, high frequency Plasma is generated by applying high frequency power from the power supply 23.

Here, the target for forming the T i layer, as shown in FIG. 2 A, S i board 4 1 S i 0 ₂ film 4 2 as an insulating film on are formed, there contactor Tohoru 4 3 forms As shown in FIG. 2B, and as shown in FIG. 2B, the Si 0 ₂ film 4 5 is formed as an interlayer insulating film on the polysilicon film 44 directly or via an insulating film. A via hole 46 is formed there.

In the present embodiment, the Ti film is formed as described above without previously removing the natural oxide film formed on the base Si. In this case, specifically, as shown in FIG. 3A, with the silicon natural oxide film 50 remaining on the Si substrate 41 at the bottom of the hole 43, the TiCl + gas, H ₂ gas and Ar gas are introduced, and a high frequency power is applied from a high frequency power source 23 to generate plasma to form a Ti film. In this case, the interdiffusion between T i and S i is suppressed by the presence of a natural oxide film 5 0, and the etching of S i by T i C 1 ₄ gas is suppressed. Therefore, as shown in FIG. 3B, the morphology of the interface between the Ti Si ₂ film 51 and the underlying Si substrate 41 caused by the diffusion of Ti and Si is improved.

On the other hand, if the native oxide film is removed as before, as shown in Fig. 4A, With T i C 1 ₄ is directly etched S i substrate 41 underlying, since there is no intervening layers between S i and T i, these interdiffusion intensified, as a result, as shown in FIG. 4 B Furthermore, the morphology at the interface between the TiSi ₂ film 51 and the underlying Si substrate 41 deteriorates. In this case, since the etching of T i C 1 ₄ is isotropic, also etched in the transverse direction as well as S i substrate depth direction only, the junction leakage is likely to occur.

As described above, when a Ti film is formed on Si by CVD, the conventional oxide film is formed with the natural oxide film remaining without passing through the step of removing the natural oxide film. The morphology does not deteriorate as in the case of removing the natural oxide film, and it is difficult to cause a junction leak or the like. In addition, there is a great advantage in the process that the number of steps is reduced because the washing step is not required, and it is not necessary to consider variations in electrical characteristics due to the washing step. In addition, natural oxide film of silicon

(S i 0 ₂ film) is the surface of the silicon is formed instantaneously when exposed to the atmosphere. The thickness of the silicon oxide film formed instantaneously is about 10 angstroms. Oxide thickness increases gradually with continued exposure to silicon-based surface air and typically saturates at thicknesses of 30-40 Angstroms.

If 〇 ¥ 0? Unlike the case of 0, even if the native oxide film is not removed, oxygen does not ultimately remain at the interface but is removed by a chemical reaction.

Next, preferable conditions in the present invention will be described. From the viewpoint of obtaining good electrical contact while maintaining good interface morphology, the thickness of the native oxide film is preferably in the range of about 10 to 40 Å. More preferably, it is in the range of about 20 to 30 angstroms. The amount of T i C 1 ₄ gas, H ₂ gas, A r gas is deposition gas, respectively, 3~30 SCCM, 0. 5~3 SLM, 0. 5~3 in the range of SLM Is preferred. Substrate temperature: 400 to 700 ° C, input power to high-frequency power supply: 100 to 1000 W, pressure in chamber: 0.5 ~ 3. It is preferable to set within the range of OTorr.

As an example, chamber internal pressure: 1.5 Torr, input power to high frequency power supply (13.56 MHz): 30 OW, H2 gas ¾ifi: 0.5 SLM, Ar gas flow rate: 1.0 SLM, T i C 1 ₄ gas flow rate: 7 SC CM, at a substrate temperature of 600 ° C conditions, without removing the natural oxide film, a film was formed of T i membrane contactor Tohoru formed S i 0 ₂ film . For comparison, the same Ti film was formed on the wafer from which the natural oxide film was removed in the previous step.

As a result, when subjected to T i deposition immediately after removing the native oxide film, as shown in FIG. 4 described above, poor interfacial morphology of the T i S i ₂ and the base S i board hole portion and the interface is, by S i is etched by T i C 1 _4, it was confirmed that the spread in the lateral direction. On the other hand, in the example of the present invention in which a native oxide film having a thickness of about 10 angstroms or more was left, as shown in FIG. Power was confirmed. The present invention can be variously modified without being limited to the above embodiment. For example, in the above embodiment, T i C 1 ₄ gas as the film forming gas, H ₂ gas, was used Ar gas, may contain other gases. Further, the manufacturing conditions are not limited to the above conditions, and may be appropriately set so that a desired Ti film is formed. In the above description, an example in which the silicon oxide film on the silicon surface is a natural oxide film has been described. Since the natural oxide film is formed only by exposing the silicon surface to the atmosphere, it is not necessary to provide a new process for forming the oxide film. However, the silicon oxide film remaining on the silicon surface is not limited to the natural oxide film. For example, after the silicon surface is exposed in a previous process such as etching, a silicon oxide film with a thickness of about 10 to 40 angstroms is formed in the same chamber or another chamber in a reduced-pressure oxidizing atmosphere. good.

That is, a certain range of thickness is deposited on the silicon surface during CVD-Ti film formation. It is important that the silicon oxide film remains, regardless of how the silicon oxide film was formed. The oxide film may be formed with a thickness of about 10 to 40 angstroms, or may be left as it is, or once formed to be thicker than 40 angstroms, and then to a thickness of 10 to 40 angstroms. Etching may be done until it is.

As described above, according to the present invention, when forming a Ti film by CVD in a hole of an insulating film formed on the Si substrate or on the Si film thereon, the underlying natural oxide film is Since the film is formed without being removed, the contact resistance is stabilized, and the morphology of the interface with the underlying Si can be improved.

Claims

The scope of the claims

1. A method of depositing a titanium film on a silicon layer by CVD using a deposition gas containing a TiC gas,

Allowing formation of a silicon native oxide film on the silicon layer surface;

A step of forming the titanium film by supplying a deposition gas containing T i C 1 ₄ gas into the silicon layer in a state of being left to the natural oxide film,

A method for forming a titanium film by CVD.

2. The method for forming a titanium film by CVD according to claim 1, wherein the natural silicon oxide film has a thickness of not less than about 10 angstroms.

3. The method according to claim 1, wherein the silicon native oxide film has a thickness of about 20 to 40 angstroms.

4. A method of forming a titanium film by CVD on a substrate surface having an exposed surface of silicon, comprising the following steps:

Forming a silicon oxide film at least about 10 angstroms thick on the exposed silicon surface of the substrate surface;

While leaving the silicon oxide film with a thickness of about 10 to 40 Angstroms, T i C 1 ₄ performs the supply of the gas containing the step of deposition of the titanium film on the substrate surface by CVD.