JP2002075972A - Method for fabricating semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for fabricating a semiconductor device by forming a first gate insulation film of SiO2 and a second gate insulation film of high dielectric constant metal oxide on a single crystal silicon substrate in which the second gate insulation film is etched without damaging the substrate. SOLUTION: Etching is performed without damaging a silicon substrate 1 by bringing the surface of a second gate insulation film 5 of metal oxide into contact with a chloride atom imparting gas without forming an ion sheath the surface of the second gate insulation film 5 thereby causing reaction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for etching a metal oxide having a high dielectric constant, a semiconductor device using a high dielectric constant gate insulating film, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Thinning of gate insulating films has been promoted for the purpose of reducing power consumption of integrated circuits. As the thickness of the SiO ₂ gate insulation has been reduced, the increase in leakage current due to the direct tunnel between the gate electrode and the channel layer and the decrease in the dielectric breakdown reliability of the gate insulation film have become problems.

[0003] In order to solve this problem, application studies of a high dielectric constant material as a substitute for the SiO ₂ gate insulating film are being studied. By using a high dielectric constant material for the gate insulating film, the same capacitance as that of SiO ₂ can be obtained even when a physically thick film is used, so that leakage current can be suppressed.

As the material of the high dielectric constant gate insulating film,
Specifically, adoption of a thermodynamically stable oxide such as titanium oxide, zirconium oxide, hafnium oxide, tantalum oxide, or alumina oxide has been proposed.

In order to electrically smooth the interface between Si and these gate insulating films, SiO
It has also been proposed to form a two-layer structure by forming _two films.

[0006]

However, these high dielectric constant materials are thermodynamically stable. For this reason, the selection of an etching method suitable for a metal oxide serving as a high dielectric constant material has been an issue.

As one of the methods for etching such a stable substance, there is a reactive ion etching method in which etching is performed by a synergistic effect between the kinetic energy of accelerated ions and active species generated in plasma.

However, in the above-described etching method using ions or plasma, the kinetic energy of ions is used. Therefore, when the film to be etched becomes thin due to the progress of etching, ions may be implanted into a base or a substrate. For this reason, there is a problem in that the interface of the film to be etched or the base or substrate on which the film is formed is damaged, and the subsequent steps are affected.

In order to avoid this problem, it is necessary to employ an etching method which does not cause damage. A typical method is a wet etching method. However, in this method, a chemical solution for efficiently etching the high dielectric constant material has not been found yet. Further, after the wet etching, a drying step is indispensable, and there is a disadvantage that the number of steps is increased as compared with the dry etching method.

The present invention has been made in view of the above points, and has as its object to provide a method for etching a metal oxide which is a thermodynamically stable high dielectric constant material by a dry process, and a method for etching a substrate using the method. It is an object of the present invention to provide a method of manufacturing a semiconductor device having a high dielectric constant insulating film processed into a predetermined shape without damaging the semiconductor device, and a semiconductor device thereof.

[0011]

According to the present invention, there is provided an etching method comprising the steps of:
The etching is performed by bringing a metal oxide having a high dielectric constant such as zirconium oxide, hafnium oxide, tantalum oxide, or alumina oxide into contact with a gas containing chlorine.

In order to achieve the above object, in a method of manufacturing a semiconductor device according to the present invention, a metal oxide film having a high dielectric constant is processed using the etching method according to the present invention to form an insulating film having a desired shape. It is characterized by doing.

According to another aspect of the present invention, there is provided a semiconductor device having an insulating film formed by processing a high-dielectric-constant metal oxide film formed on a silicon substrate, wherein the insulating film is provided on the silicon substrate side. A first insulating film located;
A second insulating film made of the high-dielectric-constant metal oxide film formed on the first insulating film, wherein the insulating film is formed in a region of the silicon substrate surface adjacent to the insulating film. Is characterized in that the elements used in the etching process have no or very few defects that can be generated by impacting the silicon substrate surface.

[0014]

DETAILED DESCRIPTION OF THE INVENTION In the present invention, a metal oxide of a high dielectric constant material which is thermodynamically stable is processed using chlorine atoms, so that the metal oxide base and the substrate surface are greatly damaged. Without providing, an insulating film of a semiconductor device is formed.

(Reasons for Selecting Chlorine Atoms) In order to remove metal oxides by etching in a dry process, the following two items must be satisfied.

The reaction between the metal oxide and the etching gas proceeds.

The vapor pressure of the etching reaction product is high.

First, the vapor pressures of the compounds of Ti, Zr and Hf were investigated. As a result, it was found that the vapor pressure of the halide was high. The temperature dependence of the vapor pressure of the halide of Ti, Zr, and Hf is shown in FIGS. From these figures, it can be seen that the halides having a high vapor pressure are chlorides and bromides. The Ti halide has a vapor pressure of 0.1 Torr or more even at room temperature. The halide of Zr and Hf is 100
Shows a vapor pressure of about 1 mTorr at
C shows a pressure close to 760 Torr. But T
Among the halides of i, Zr and Hf, the fluoride has a significantly lower vapor pressure than the other halides.
It can be seen that etching cannot be performed by the dry etching method using a system gas.

Next, the easiness of the reaction between TiO ₂ or ZrO ₂ and each halogen atom was compared. The ease of progress of the reaction is the value obtained by calculating the Gibbs free energy of each metal oxide, chlorine atom, and reaction product, and subtracting the Gibbs free energy of the system before the reaction from the Gibbs free energy of the system after the reaction. (ΔG) can be used as an index. This ΔG and the reaction equilibrium constant (K) have the following relationship.

K∝exp (-ΔG / RT) where R is a gas constant and T is the temperature of the system during the reaction.
From this equation, it can be seen that the reaction hardly proceeds when ΔG is a value of 0 or +, and conversely, when ΔG is −, the reaction tends to progress as the value increases. FIG. 4 shows the result of calculating the temperature dependence of ΔG in each reaction. ΔG of the reaction for producing bromide is 0 or a positive value, indicating that the reaction does not proceed. On the other hand, any reaction that produces chloride has a negative value of ΔG, indicating that the reaction proceeds. Therefore, the use of chlorine atoms makes it possible to etch each metal oxide.

(Selectivity with SiO ₂ ) On the other hand, ΔG at which a chloride of Si is formed from chlorine atoms and SiO ₂ is also a negative value, and the etching reaction may proceed similarly to the metal oxide. However, the rate of the reaction is determined by the rate-limiting step of the reaction. When the rate-limiting step of the reaction is in the process of breaking the bond between the metal or Si and O, the reaction rate is
And the strength of the bond. As a result of examining the bonding strength, Si—O was 806 kJ / mol, whereas
Ti-O: 659 kJ / mol, Zr-O: 634 kJ
/ Mol. Therefore, TiO ₂ or ZrO _{2 has} a higher reaction rate by chlorine atoms than SiO ₂ .

(Method of not giving damage) There are the following two methods for obtaining chlorine atoms.

(1) A method in which a gas containing chlorine is decomposed by heat.

(2) A method in which a gas containing chlorine is decomposed by plasma.

In the method of (1) for obtaining chlorine atoms by using thermal energy, no ions are generated, so that damage to the base of the object to be etched does not occur. But,
In the method (2) for obtaining chlorine atoms using plasma, an ion sheath is formed between the plasma and the object to be etched. For this reason, a potential difference is generated between the plasma and the object to be etched, and the ion is accelerated by the potential difference, thereby damaging a base of the object to be etched.

Therefore, in order not to damage the base, for example, a plasma is formed in another place away from the etching chamber where the etching process is performed, and only the neutral chlorine atoms which are not turned into plasma are etched. It is necessary to supply to a processing chamber and to make it react with an object to be etched.

That is, in the present invention, a semiconductor device having an insulating film made of an etched high dielectric constant material on a silicon substrate is manufactured by contacting with a gas containing a chlorine atom donating gas. Here, examples of the high dielectric constant material include titanium oxide, zirconium oxide, hafnium oxide, tantalum oxide, alumina oxide, and a mixture thereof. Further, as the chlorine atom donating gas, a gas containing at least one kind of gas selected from chlorine atoms and chlorine fluoride is preferable.

Further, in the present invention, in order to reduce or eliminate damage to the substrate in the etching process,
Means for minimizing the amount of plasma or ions contained in the chlorine atom donating gas, means for preventing an ion sheath from being formed on the surface of the film to be etched, and radical chlorine contained in the chlorine atom donating gas It is preferable to include at least one of the means for increasing the amount of atoms as much as possible.

[0029]

EXAMPLE In this example, a manufacturing process of a MOS FET in which a gate insulating film is formed by using the etching process of the present invention will be described with reference to FIGS.

Groove 2 for element isolation on the surface of Si substrate 1
Is formed, and the SiO ₂ film 3 is buried by a thermal CVD method using O ₃ and TEOS (Si (OC ₂ H ₅ ) ₄ ) as source gases,
Flatten using CMP (FIG. 5).

Next, a first gate isolation is provided on the surface of the Si substrate 1.
About 2 nm thick SiO as an edge film _TwoFilm 4 by heat treatment
And a second gate insulating film of about 20 n
m thick TiO_TwoThe film 5 is formed by a CVD method.
Poly Si6 for forming a gate electrode is formed thereon by CVD.
(FIG. 6).

A resist is applied thereon, leaving the resist only in the gate electrode forming portion 6a, removing the resist in the other areas by exposure and development, and using this resist as a mask, poly-Si is anisotropically treated with an F-based gas. Etching is performed (FIG. 7). Here, the reason for using the F-based gas is to remove the poly-Si film by etching without etching the TiO ₂ film 5 as described above.

[0033] After the resist is removed, a SiO ₂ film is deposited by a thermal CVD method using TEOS as a source gas to the entire surface, the resist leaving only the gate electrode portion as a mask, anisotropic SiO ₂ of the other region Etchback is removed by dry etching, and SiO
_{A second} spacer layer 7 is formed (FIG. 8).

Thereafter, the TiO ₂ layer 5 in the source / drain region is removed by etching using chlorine atoms of the present invention without etching the gate electrode using the SiO ₂ spacer layer 7 as a protective film (FIG. 9).

After that, the source / drain regions of thin Si
The O ₂ film 4 is removed by wet etching, silicon is selectively epitaxially grown only in the source / drain regions, implantation is performed on the source / drain regions where the silicon epitaxial film 8 is formed, and dopant implanted by annealing is removed. Activation was performed to form the source / drain 9, and the SiO ₂ spacer layer 7 on the gate electrode 6a was removed to form an FET (FIG. 1).
0).

Next, the etching process of the TiO ₂ film 5 will be described in detail.

FIG. 11 shows an example of the structure of an etching apparatus. In the etching apparatus of the present embodiment, the etching chamber 21 includes an exhaust pump 22 for keeping the pressure in the etching chamber constant, a pressure regulating valve 23, a susceptor 24 for heating the substrate to be etched, and a chlorine atom for supplying a chlorine atom. A supply unit 25, a pipe 26 for guiding chlorine atoms to the etching chamber 21, and a shower plate 27 for uniformly supplying the chlorine atoms to the substrate surface on the susceptor 24.
It is composed of

FIG. 12 shows an example of the structure of the chlorine atom supplier 25. The chlorine atom supply device 25 of this example includes an alumina tube 31 for generating chlorine atoms, a chlorine gas supply device 32 for supplying chlorine gas and, for example, argon gas as a carrier gas, and an argon gas supply device 33, 2.4.
It comprises a 5 GHz microwave generation source 34 and a waveguide 35 for guiding the microwave from the generation source to the alumina tube 31.

In the chlorine atom supply device 25 of this embodiment, a microwave is irradiated from a microwave generation source 34 through a waveguide 35 in a state where chlorine gas and argon gas are flown into the alumina tube 31, and the inside of the alumina tube 31 is To generate chlorine atoms by generating plasma. The generated chlorine atoms are supplied to the etching chamber 21 through the pipe 26 together with the flow of the gas.

The chlorine atom supplier 25 of this embodiment employs a well-known remote radical generation method. By introducing a gas through the pipe 26 into the etching chamber 21 at a predetermined distance from the alumina tube 31, Many chlorine atoms introduced into the etching chamber 21 are not in a charged state, and some are in a radical state.

In this embodiment, the method of generating a chlorine atom is a remote radical generation method, but the method of generating a chlorine atom in the present invention is not limited to this. While introducing non-ionized chlorine atoms into the etching chamber 21, it prevents plasma or ionized gas from entering the etching chamber 21, or forms an ion sheath on the surface of the substrate to be etched. As long as it can be prevented, chlorine atoms may be generated by another method and introduced into the etching chamber 21.

For example, a configuration may be adopted in which an electromagnetic field is applied to the middle of the pipe 26 to deflect or trap ionized atomic molecules, or to supply electrons for neutralizing ions.

In this embodiment, etching using chlorine atoms is performed, for example, in the following procedure.

First, the pressure in the etching processing chamber 21 is set to 0.001 Torr or less by the exhaust pump 22. The substrate to be processed is transferred from the transfer chamber (not shown) to the etching chamber 21.
To the susceptor 24 in the inside. Set the substrate temperature to 100
Heat to ° C.

Next, a chlorine gas and a carrier gas are flowed from the chlorine atom supplier 25 while the microwave generation source 34 is not operated, and the pressure in the etching chamber 21 is adjusted to 0.05 Torr by the pressure adjusting valve 23. afterwards,
The microwave generation source 34 is operated, and a gas containing neutral chlorine atoms in a partially radical state is etched.
And the TiO ₂ film 5 formed on the surface of the substrate to be processed disposed on the susceptor 24 was removed by etching.

In this embodiment, the substrate to be processed is Si
Although a substrate is assumed, the present invention can be similarly applied to the manufacture of a TFT using a glass substrate or a quartz substrate.

FIG. 1 shows the result of measuring the junction leakage current of the source or drain of the FET thus prepared.
3 is shown. According to the etching method of this embodiment, T
As compared with the case where the iO ₂ film was etched by the conventional ion-assisted etching method, the junction leakage current when a negative voltage was applied could be suppressed to a value as shown in FIG. This is considered that no defect level was formed because no etching damage occurred at the interface between the silicon substrate and the silicon epitaxial layer.

As described above, according to the present embodiment,
By using chlorine atoms as etching gas, TiO ₂
The film can be removed by etching.

Further, according to the present embodiment, since the etching reaction does not cause damage such as ion bombardment, the junction leakage current at the source / drain can be suppressed.

Further, in this embodiment, an example has been described in which a case of etching using chlorine atoms in the manufacture of a MOS type FET using titanium oxide for the gate insulating film has been described. The types of the object, the semiconductor device, and the insulating film are not limited to those in this embodiment, and other metal oxides, semiconductor devices, and insulating films can be etched in the same manner as in this embodiment.

[0051]

As described in detail above, according to the present invention,
By using chlorine atoms as an etching gas, a metal oxide which is a high dielectric constant material can be removed by etching, and a semiconductor device using the metal oxide as an insulating film can be manufactured.

Further, according to the present invention, since damage such as ion bombardment does not occur during the etching process, the junction leakage current at the source / drain can be suppressed, and the reliability and the production yield of the semiconductor device can be improved. Was completed.

[Brief description of the drawings]

FIG. 1 is a graph showing a vapor pressure curve of a halide of Ti.

FIG. 2 is a graph showing a vapor pressure curve of a halide of Zr.

FIG. 3 is a graph showing a vapor pressure curve of a halide of Hf.

FIG. 4 is a graph showing the temperature dependence of ΔG in the reaction between each metal oxide and a halogen atom.

FIG. 5 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 6 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 7 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 8 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 9 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 10 is an essential part cross sectional view showing one step of a method of manufacturing an FET according to an embodiment of the present invention;

FIG. 11 is a block diagram showing a configuration example of an etching apparatus according to another embodiment of the present invention.

FIG. 12 is a block diagram showing a configuration example of a chlorine atom supply device according to another embodiment of the present invention.

FIG. 13 is a graph comparing the junction currents of semiconductor devices manufactured using the conventional ion assisted etching method and the etching method of the present invention.

[Explanation of symbols]

1 ... Si substrate 2 ... grooves 3 ... SiO ₂ film 4 ... SiO ₂ gate insulating film 5 ... TiO ₂ gate insulating film 6 ... gate electrode 7 ... SiO ₂ spacer layer 8 ... silicon epitaxial film 9 ... activation region 21 ... etching Chamber 22 ... Exhaust pump 23 ... Pressure regulating valve 24 ... Susceptor 25 ... Chlorine atom supply 26 ... Piping 27 ... Shower plate 31 ... Alumina tube 32 ... Chlorine gas supply 33 ... Argon gas supply 34 ... Microwave generation source 35 ... Waveguide.

Continued on the front page F-term (reference) HK09 HK13 HK32 HK39 HM02 NN62 NN65 QQ04 QQ11 QQ19

Claims (8)

[Claims] 1. A method for manufacturing a semiconductor device comprising an insulating film formed by processing a metal oxide film having a high dielectric constant formed on a substrate, comprising: contacting a gas containing chlorine with the metal oxide film;
A method for manufacturing a semiconductor device, comprising etching the metal oxide film. 2. The metal oxide film according to claim 1, wherein the metal oxide film is any one of titanium oxide, zirconium oxide, hafnium oxide, alumina oxide, and tantalum oxide, or a plurality of these oxides. A method for manufacturing a semiconductor device, characterized by comprising a mixture of: 3. The insulating film according to claim 1, wherein the insulating film is formed on the substrate, and is formed so as to overlap the first insulating film located on the substrate side and the first insulating film. And a second insulating film made of the metal oxide film. 4. A method for manufacturing a semiconductor device according to claim 1, wherein said gas containing chlorine includes a gas capable of donating chlorine atoms. 5. A method for manufacturing a semiconductor device according to claim 1, wherein said gas containing chlorine does not contain ionized atoms and molecules. 6. A method of manufacturing a semiconductor device according to claim 1, wherein an ion sheath is not formed on a surface of said metal oxide film during said etching process. 7. A method for etching a metal oxide having a high dielectric constant, comprising: bringing a gas containing chlorine into contact with the metal oxide;
An etching method comprising etching the metal oxide. 8. A semiconductor device comprising an insulating film formed by processing a metal oxide film having a high dielectric constant formed on a silicon substrate, wherein the insulating film includes a first insulating film located on the silicon substrate side; A second insulating film made of the high-dielectric-constant metal oxide film formed on the first insulating film; and a defect in the film in a region of the silicon substrate surface adjacent to the insulating film. A semiconductor device having a density lower than that obtained by using an ion-assisted etching process.