JPH11168073A - Manufacture of semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deterioration of the film quality of a dielectric film when a conductive film is grown, and reduce the leakage current of the dielectric film, in a manufacturing method of a semiconductor device which contains a process where a metal film is grown on the dielectric film. SOLUTION: After subjecting to the film quality improving treatment of a dielectric film 5, the surface of the dielectric film 5 is exposed to a reduced pressure atmosphere containing an oxidizing gas. By supplying a first reacting gas and a second reacting gas which are used for growing a dielectric film 6 made of a metal or metal nitride in the reduced pressure atmosphere, the conductive film 6 is formed by reaction of the first reactive gas, the second reactive gas and the oxidizing gas. A process where the oxidizing gas is stopped or reduced in the course of the formation is included.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a semiconductor device, and more particularly, to a method for manufacturing a semiconductor device including a step of growing a metal film on a dielectric film.

[0002]

2. Description of the Related Art As a technique for forming a dielectric film, a physical method and a chemical method are roughly classified. Physical methods include vacuum deposition, sputtering, and ion plating. Chemical methods include CVD, sol-gel, liquid phase epitaxy, thermal spray, fine particle sintering, and melt quenching. is there.

There are a physical method and a chemical method as a technique for forming a metal film or a metal nitride to be a wiring on a dielectric film. A typical physical method is a sputtering method. The sputtering method is a method in which an ionized gas in a glow discharge collides with a target made of a constituent material of a thin film to be formed into a film, thereby depositing particles hit from the target on a substrate.

A typical chemical method is a CVD method. In the CVD method, a gas which is a gas among the compounds of the elements constituting the thin film to be formed is introduced into a reaction furnace,
Alternatively, this is a method in which a film is grown on the substrate surface by a chemical reaction using plasma energy or the like, and a better crystal film can be obtained because the film is formed in an equilibrium state on the substrate surface. However, in recent semiconductor devices, high integration and the adoption of three-dimensional capacitors require a film formation method with good coverage, so that the CVD method has become popular in order to form a metal film or a metal nitride film. ing.

[0005]

When an oxide is grown as a dielectric film of a capacitor by a CVD method, a current leak of the dielectric film is caused in order to keep the oxide dielectric film of good quality. It is necessary to prevent oxygen deficiency. On the other hand, there is a method of thermally oxidizing the dielectric film or exposing the dielectric film to oxygen plasma in order to supplement oxygen in the dielectric film.

However, when forming a metal film or a metal nitride film by CVD, the dielectric film is exposed to a reducing atmosphere.
When forming the upper electrode of the capacitor using a reducing gas, the present inventors mix a very small amount of oxygen with the reaction gas, thereby supplying oxygen to the dielectric film, and forming the upper electrode of titanium nitride. To prevent an increase in resistance is proposed in Japanese Patent Application Laid-Open No. 9-213659. The preferable flow rate of the oxygen gas is set to 5 sccm or less or less than 1% of the total gas. The oxygen gas is introduced into the reaction chamber not only during the formation of the upper electrode but also before and after the formation of the upper electrode.

However, with such a flow rate of oxygen gas,
Reduction of leakage current of the oxide dielectric film due to oxygen deficiency when forming the upper electrode using a reducing gas and improvement of the film quality of the dielectric film cannot be sufficiently achieved, and further improvement is required. An object of the present invention is to provide a method of manufacturing a semiconductor device having a process capable of preventing oxygen deficiency of an oxide dielectric film used for a capacitor and reducing the resistance of an upper electrode of the capacitor.

[0008]

Means for Solving the Problems (1) The above-mentioned problems are:
As shown in FIGS. 3, 4, and 20, a step of forming a dielectric film on a semiconductor substrate, a step of introducing an oxidizing gas into the semiconductor substrate, and a step of introducing a metal or metal nitride into the oxidizing gas. Introducing a first reactant gas and a second reactant gas for growing a substance, and then reducing the oxidizing gas, and using the first reactant gas and the second reactant gas to form the dielectric film. Forming a conductive film containing the metal or the metal nitride thereon.

In the method of manufacturing a semiconductor device, after forming the dielectric film and before introducing the oxidizing gas, the dielectric film may be heated in an oxygen-containing heating atmosphere or an oxygen-containing plasma atmosphere. The method further comprises a step of exposing the inside. In the method of manufacturing a semiconductor device, the step of exposing the dielectric film to a heating atmosphere containing oxygen or a plasma atmosphere containing oxygen is performed in a first chamber, and a step of introducing the different oxidizing gas. Is performed in a second chamber different from the first chamber. (2) As shown in FIG. 3, the above-mentioned problems include a step of performing a process for improving the film quality of the dielectric film, a step of exposing the surface of the dielectric film to a reduced-pressure atmosphere containing an oxidizing gas, By supplying a first reaction gas and a second reaction gas for growing a conductive film made of metal nitride to the reduced pressure atmosphere, the first reaction gas and the second reaction gas are formed on the dielectric film. Forming an oxygen-containing metal layer or an oxygen-containing metal nitride layer by reacting a reaction gas with the oxidizing gas;
Reacting the first reaction gas and the second reaction gas to form the conductive film serving as an electrode on the dielectric film with the oxygen-containing metal layer or the oxygen-containing metal nitride layer interposed therebetween; A step of stopping the supply of the oxidizing gas during the formation of the conductive film. (3) As shown in FIG. 4, the above-mentioned problems include a step of performing a process for improving the film quality of the dielectric film, a step of exposing the surface of the dielectric film to a reduced-pressure atmosphere containing an oxidizing gas, By supplying a first reaction gas and a second reaction gas for growing a conductive film made of metal nitride to the reduced pressure atmosphere, the first reaction gas and the second reaction gas are formed on the dielectric film. Forming a conductive film containing oxygen by reacting a reactive gas with the oxidizing gas, and reducing a flow rate of the oxidizing gas during the formation of the conductive film. Solve. In this case, the oxidizing gas may be stopped simultaneously with or after the supply of the first reaction gas and the second reaction gas is stopped. (4) The method of manufacturing a semiconductor device according to (2) or (3) further has the following features.

[0010] The dielectric film is made of an oxide dielectric. Alternatively, the method further includes a step of forming a lower electrode made of a metal, a conductive metal oxide or a metal nitride between the semiconductor substrate and the dielectric film. The lower electrode is made of tungsten, ruthenium, ruthenium oxide, iridium oxide, titanium nitride, tungsten nitride,
It is formed from any of molybdenum, molybdenum nitride, tantalum, and tantalum nitride.

Alternatively, before forming the dielectric film, a step of forming a semiconductor layer containing impurities between the semiconductor substrate and the dielectric film is provided. Or
The dielectric film is made of Group 3A, Group 4A or Group 5A of the periodic table of elements.
It is characterized by being formed by growing a Group A oxide or by growing any of lead zirconate titanate, strontium titanium oxygen, barium strontium titanate or strontium bismuth tantalate.

Alternatively, the oxidizing gas is a molecular gas containing at least one oxygen in the molecule. The gases are O ₂ , H ₂ O, H ₂ O ₂ , O ₃ , C
It is characterized by containing at least one of O, CO ₂ , NO ₂ , N ₂ O and NO. Alternatively, the step of exposing the dielectric film to the oxidizing gas in a reduced-pressure atmosphere is performed in the same reaction chamber as forming the dielectric film serving as an upper electrode.

Alternatively, the treatment for improving the film quality of the dielectric film is different from the step of exposing to an oxidizing gas in the atmosphere. Alternatively, the oxidizing gas in the reduced-pressure atmosphere is diluted with at least one of helium, argon, and nitrogen. Alternatively, the step of exposing the dielectric film to the oxidizing gas in a reduced-pressure atmosphere includes:
The method is characterized in that the formation of the dielectric film serving as the upper electrode is performed in the same reaction chamber.

Alternatively, the treatment for improving the film quality of the dielectric film is different from the step of exposing to an oxidizing gas in the atmosphere. Alternatively, the first reaction gas for forming the conductive film includes a reducing element as a constituent element. In this case, the first reaction gas may include an ammonia gas.

Alternatively, a non-reducing element may be used as the second reaction gas for forming the conductive film. In this case, as the second reaction gas, TiCl ₄ , TiI ₄ , TiBr
Any of ₄ may be used. Alternatively, the conductive film is
It may be a titanium nitride film, a titanium oxynitride film, or a two-layer structure film of titanium oxynitride / titanium nitride.

Next, the operation of the present invention will be described. The present invention includes a step of forming a capacitor in which a conductive film made of a metal film or a metal nitride is grown on a dielectric film by a CVD method. This is a method of forming a dielectric film.
CVD using an organic metal such as (OC ₂ H ₅ ) ₅ has been widely studied. According to such a CVD method, carbon, hydrogen and CH _x decomposed from the source will be mixed into the dielectric film as an impurity, such as reduced adhesion to the electrode thereon a dielectric film, the dielectric Affects the membrane. Therefore, it is necessary to remove not only oxygen deficiency but also those impurities to obtain a high quality dielectric film.

On the other hand, the conductive film formed on the dielectric film is also CV
Since it is performed in the D method, and most of the processes are performed in a reducing atmosphere, there is a possibility that oxygen in the underlying oxide dielectric film may be pulled out, which causes a decrease in dielectric constant and an increase in leak current and deterioration of crystals. It also causes. According to the present invention, when forming a conductive film made of a metal or a metal containing oxygen or nitrogen on an oxide dielectric film, first, a large amount of oxygen is supplied onto the oxide dielectric film, and the oxygen is In the remaining state, the first and second reaction gases for forming the conductive film are introduced to reduce the amount of oxygen during the formation of the conductive film or to exclude oxygen from the reaction atmosphere.

Thus, before forming a conductive film made of metal or metal nitride on the dielectric film, oxygen deficiency of the dielectric film is prevented, and impurities such as carbon, hydrogen, and CH are oxidized to form a dielectric film. Evaporate from the film. Thereby, the crystallinity of the dielectric film is improved, and the leakage current can be reduced. In the case where a reducing gas is used as the first reaction gas for forming the conductive film, the oxidizing gas suppresses the reducing action, so that oxygen deficiency in the dielectric film is prevented beforehand.

Furthermore, in the initial stage of formation of the conductive film, the first reactive gas, the second reactive gas, and the oxidizing gas cause the surface of the dielectric film to have a thin layer of an oxygen-containing metal or an oxygen-containing metal nitride on the surface thereof. It is formed in a shape. The metal oxide or metal oxynitride layer prevents oxygen in the dielectric film from diffusing into the conductive film. After the metal oxide or metal oxynitride layer is formed on the dielectric film, the supply of the reducing gas to the dielectric film is interrupted by the oxygen-containing metal material or the oxygen-containing metal nitride layer. Subsequent supply of a large amount of oxidizing gas becomes unnecessary.

Therefore, it is very important to mix the oxidizing gas with the first and second reaction gases at the beginning or halfway of the formation of the conductive film. In addition, if a large amount of oxygen-containing gas is continuously introduced during the formation of the conductive film, the oxygen content of the conductive film increases and the sheet resistance increases, so that the function of the conductive film as an upper electrode may be impaired. . Therefore, it is important to reduce the partial pressure of oxygen during the formation of the conductive film to reduce the resistance of the conductive film. In order to reduce the resistance of the conductive film, the partial pressure of oxygen in the reaction chamber is preferably set to 1.5 mTorr or less at the beginning or during the formation of the conductive film.

The partial pressure of oxygen introduced before the conductive film is formed and before the conductive film is formed is preferably 10 mTorr or more, or the partial pressure of oxygen is 6.6 times or more that of the conductive film. Is preferred. Alternatively, it is preferable that the partial pressure of the oxidizing gas is one or more times the partial pressure of the reducing gas.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. 1 (a) to 1 (d)
The MIS (metal insulator semi) according to the embodiment of the present invention
FIG. 4 is a cross-sectional view showing a step of forming a (conductor) type capacitor. First, as shown in FIG. 1A, a field oxide film 2 surrounding a capacitor formation region is formed on the surface of an n-type silicon substrate 1. This field oxide film 2 is formed by a selective oxidation method using, for example, a silicon nitride mask.

Subsequently, an amorphous silicon film 3 entirely doped with impurities is formed to a thickness of 50 nm by the CVD method. The amorphous silicon film 3 is grown using a silane-based gas, and has the same conductivity type as the silicon substrate 1 as the impurity, that is, phosphorus or arsenic in the present embodiment. The amorphous silicon film 3 is patterned by photolithography as shown in FIG. 1A and is left in the capacitor formation region and its periphery.

Thereafter, the surface of the amorphous silicon film 3 is
Nmonia (NH_Three) Exposure to atmosphere, amorphous silicon film
A thin silicon nitride layer 4 is formed on the surface of the substrate 3. continue,
As shown in FIG. 1B, a 10 nm-thick
Tantalum (Ta _TwoO_Five) The film 5 is combined with the amorphous silicon film 3
Grown on the surface of the doped oxide film 2. Ta_TwoO_FiveGrow film 5
The reaction gas used at the time of_TwoH_Five)_Five(Pentae
Toxitantalum).

Next, the Ta ₂ O ₅ film 5 is
Ta ₂ O ₅ film 5 by heating to a temperature of over ℃ for several seconds
Improve the crystallinity of This oxygen heating is performed by RTO (rapid the
rmaloxidizing). At this time, oxidation of the surface of the amorphous silicon film 3 is prevented by the silicon nitride film 4. Note that an oxygen plasma process may be used instead of the RTO process.

Thereafter, in order to form a titanium nitride film on the Ta ₂ O ₅ film 5, the silicon substrate 1 is placed in a reduced pressure reaction chamber 21 shown in FIG. Then, after oxygen gas is supplied onto the Ta ₂ O ₅ film 5, a titanium nitride film 6 is formed to a thickness of 50 nm by CVD as shown in FIG. Since oxygen is supplied to the Ta ₂ O ₅ film 5 at least before the growth of the titanium nitride film 6, such a titanium nitride film 6 is hereinafter also referred to as a titanium nitride film obtained by oxygen preflow processing.

Subsequently, after taking out the silicon substrate 1 from the reduced pressure atmosphere, the titanium nitride film 6 is patterned by photolithography, and is left over the amorphous silicon film 3 and over the field oxide film 2 adjacent thereto. . The reaction gas used for this patterning is Cl ₂ (chlorine), BC
l ₃ (boron trichloride), and these gases facilitate patterning of the titanium nitride film 6. This reaction gas is a gas used for patterning the TiN film described in the section of the prior art.

Thus, a basic structure of a MIS type capacitor using the amorphous silicon film 3 as a lower electrode, the Ta ₂ O ₅ film 5 as a dielectric film, and the titanium nitride film 6 formed by oxygen preflow processing as an upper electrode is completed. I do. Further, an SiO ₂ film 7 covering the titanium nitride film 6 is formed by using a vaporized TEOS (tetraethoxysilane) by a plasma CVD method. Subsequently, as shown in FIG. 1D, the SiO ₂ film 7 is patterned by photolithography to form an opening 8 exposing a part of the titanium nitride film 6 on the field oxide film 2.

After that, the wiring 9 is formed on the SiO ₂ film 7. Part of the wiring 9 penetrates the opening 8 and is connected to the titanium nitride film 6. The wiring 9 is composed of Ti, TiN,
It has a three-layer structure in which AlCu is stacked in this order. Through the steps described above, the step of forming a capacitor on the silicon substrate 1 is completed.

Next, a method of forming the titanium nitride film 6 shown in FIG. 1C will be described. The growth is shown in Figure 2
This is performed by using a CVD apparatus as shown in FIG. 3, for example, under growth conditions as shown in FIG. In a reaction chamber 21 of the CVD apparatus shown in FIG. 2, a lower electrode 22 also serving as a substrate mounting table, and a gas shower 23 facing the lower electrode 22 at an interval are arranged. The gas shower 23 has a first gas diffusion chamber 23a and a second gas diffusion chamber 23b, and has a plurality of gas discharge holes formed on the lower surface of the first gas diffusion chamber 23a and the second gas diffusion chamber 23b. Are separately exposed from the bottom of the gas shower 23, respectively. The gas shower 23 has a function as an upper electrode, and is electrically connected to the high frequency power supply RF. Furthermore, the exhaust port 2 at the bottom of the reaction chamber 21
4 is connected to an on-off valve 25, a drag pump 26, and a dry pump 27 so that the pressure inside the reaction chamber 21 is reduced.

First gas diffusion chamber 23 of gas shower 23
a is the first gas cylinder connected to the first to third gas cylinders 31 to 33;
Is connected to the second gas diffusion chamber 23b.
Is connected to a second gas pipe 29 connected to the fourth and fifth gas cylinders 34 and 35. The first gas cylinder 31 is filled with titanium tetrachloride gas (TiCl ₄ ), and the operations of gas flow adjustment, supply start, and supply stop are controlled by the first mass flow controller 41 via the control circuit 30. The second gas cylinder 32 is filled with oxygen (O ₂ ) gas, and the gas flow adjustment, supply start, and supply stop operations are performed via the control circuit 30 through the second mass flow controller 4.
2 is controlled. The third gas cylinder 33 is filled with helium (He) gas, and the gas mass adjustment, supply start, and supply stop supply operations are controlled by the third mass flow controller 43 via the control circuit 30.

The fourth gas cylinder 34 is filled with MMH (monomethylhydrazine) gas, and its gas flow rate is adjusted.
The operation of starting and stopping the supply is performed by the control circuit 30 through the fourth operation.
Is controlled by the mass flow controller 44. Fifth
The gas cylinder 35 is filled with ammonia (NH ₃ ) gas, and the gas flow adjustment, supply start, and supply stop operations are performed by the fifth mass flow controller 45 via the control circuit 30.
Is controlled by

When the titanium nitride film 6 is formed by using such a CVD apparatus, the control circuit 30 controls
By controlling the fifth mass flow controllers 41 to 45, the respective operations of flow rate adjustment, supply start, and supply stop are performed so as to have a flow as shown in FIG. 3, for example. The operation will be described below. First, after the silicon substrate 1 on which the TaO ₅ film 5 is formed is placed on the lower electrode 22 in the reaction chamber 21 of the CVD apparatus, the on-off valve 25 is opened and the drag pump 2 is opened.
6. The pressure inside the reaction chamber 21 is reduced by the dry pump 27, and the temperature of the silicon substrate 1 is set to 500 ° C. by heating the heater H below the lower electrode 22.

In this state, the second and third mass flow controllers 42 and 43 are operated to supply oxygen (O ₂ ) gas and helium (He) gas into the reaction chamber 21 as shown in FIG. The pressure is supplied at a flow rate of 100 sccm and 50 sccm, respectively, and the pressure in the reduced pressure atmosphere is set to 1.0 Torr. By adding a large amount of oxygen into the reaction chamber 21 as described above, the inside of the reaction chamber 21 is made to have a sufficient oxygen atmosphere, and then Ta ₂ O is introduced when introducing ammonia (NH ₃ ) gas and monomethylhydrazine (MMH) gas. ₅ Reduction of the film 5 is prevented. The reduced-pressure oxygen atmosphere is a Ta ₂ O ₅ film 5.
Carbon and hydrogen contained in the Ta ₂ O ₅ film 5 at the time of growth are combined with oxygen to generate volatile CO _x , H ₂ O, and the like. Thereby, carbon, hydrogen and CH groups are converted to Ta ₂ O ₅
Remove from membrane 5. This has the effect of improving the crystallinity of the Ta ₂ O ₅ film 5 and reducing the leak current. In addition, TiN
There is also an effect of replacing impurities, for example, chlorine contained in the film 6 with oxygen.

In this case, the flow rate of the oxygen gas is set to be sufficiently larger than 5 sccm so that oxygen can diffuse into the Ta ₂ O ₅ film 5. 30 days from start of supply of oxygen and helium
After seconds elapsed open fourth and fifth mass flow controllers 44 and 45, as shown in FIG. 3, NH ₃ gas and M
MH gas was introduced into the chamber 21 at a flow rate of 500 sccm and 2 sccm, respectively, and at the same time, the pressure of the reduced pressure atmosphere was reduced to 0.15
rr. Further, after 35 seconds have elapsed from the start of the oxygen supply, the first mass flow controller 41 is opened, and FIG.
As shown in the figure, TiCl ₄ was supplied to the reaction chamber 2 at a flow rate of 5 sccm.
Introduce into 1.

The introduction of the TiCl ₄ gas into the reaction chamber 21 may be set to 20 sccm from the beginning. TiCl mentioned above
₄ after a lapse of 5 seconds from the start of the introduction of the gas increases the flow rate of TiCl ₄ gas to 10 sccm, further increasing the flow rate of the TiCl ₄ gas starts after 10 seconds of introduction of TiCl ₄ gas to 20 sccm.

At the same time as the flow rate of the TiCl ₄ gas is increased to 20 sccm, that is, 45 seconds after the start of oxygen introduction, the second mass flow controller 42 is adjusted to stop supplying the oxygen gas to the chamber 21. As a result, Ta ₂ O ₅
While preventing the film 5 from being reduced, TiN having a high oxygen concentration is formed at the interface with the TiN film 6. Further, since oxygen is not added to the TiN film 6 formed after the supply of oxygen is stopped, the TiN film 6 has a low resistance.

As described above, when the TiCl ₄ gas is increased to 20 sccm, the growth of the titanium nitride (TiN) film 6 starts. Further, after the growth of the titanium nitride film 6 is started, 55
After a lapse of seconds, the first, third, fourth and fifth mass flow controllers 4 are used to terminate the growth of the titanium nitride film 6.
Close the valve in _{1,43~45, TiCl 4, He, NH} 3, M
The supply of MH gas is stopped. Thereby, the pressure in the reduced pressure atmosphere is reduced.

Nitriding under the above gas control conditions
A titanium film 6 is formed.
A titanium nitride film formed by a reflow process.
Thus, oxygen is contained in the lower layer of the titanium nitride film 6. Yo
Therefore, as shown in FIG. _TwoO_FiveBetween the film 5 and the TiN film 6
The TiOx or TION film 6a is formed only on the interface. Place
And Ta_TwoO_FiveThe conditions for growing titanium nitride on the film 5 are shown in FIG.
The conditions are not limited to those shown in FIG.
Trace amount of oxygen during the growth of titanium nitride film
It may be introduced into the atmosphere. The resulting film grows
Titanium oxynitride (TiO) containing oxygen from lower layer to upper layer
N) It is a membrane.

In FIG. 4, the same gas flow conditions as shown in FIG. 3 are set except for the oxygen gas. That is, as shown in FIG. 5A, the silicon substrate 1 on which the Ta ₂ O ₅ film 5 is formed is placed in the reaction chamber 21 under reduced pressure. Then, from a state where the substrate temperature is set to 500 ° C. in a reduced pressure atmosphere,
O ₂ gas and He gas are flowed into the reduced pressure atmosphere at a flow rate of 100
While supplying at sccm and 50 sccm, the pressure in the reduced pressure atmosphere is set to 1.0 Torr.

After a lapse of 30 seconds from the start of the supply of the O ₂ and He gases, the NH ₃ gas and the MMH gas were each supplied at a flow rate of 500 sc.
cm and 2 sccm into the reduced pressure atmosphere, and at the same time, reduce the pressure of the reduced pressure atmosphere to 0.15 Torr. Further, after a lapse of 35 seconds from the start of the supply of oxygen, the introduction of TiCl ₄ gas into the reduced-pressure atmosphere at a flow rate of 5 sccm is started, and the flow rate of the oxygen gas is reduced to 5 sccm.

The increase after a lapse of 5 seconds from the start of the introduction of the TiCl ₄ gas flow rate of TiCl ₄ gas to 10sccm, further TiCl
₄ increase from the start of the introduction of gas after 10 seconds elapse of TiCl ₄ gas flow rate to 20 sccm. Thus, an oxygen-containing titanium nitride film 16 is formed as shown in FIG. The growth of the oxygen-containing titanium nitride (TiON) film 16 starts when the TiCl ₄ gas is introduced. 55 seconds after the start of the growth of the TiON film 16, the introduction of each gas of O ₂ , TiCl ₄ , MMH, NH ₃ and He is stopped in order to finish the growth of the TION film 16. Thereby, the gas pressure in the reduced-pressure atmosphere decreases. When the flow rate of oxygen is 5 sccm or less, FIG.
As shown by the two-dot chain line in FIG.

Next, when the relationship between the specific resistance of the titanium nitride film, the oxygen-containing titanium nitride film, and the titanium nitride film by the oxygen preflow treatment and the temperature was examined, the results shown in FIGS. 6 and 7 were obtained. 6 and 7, plots of ○ indicate the specific resistance of the titanium nitride film containing almost no oxygen, and plots of △ indicate the specific resistance of the titanium nitride film formed by the oxygen preflow treatment formed under the conditions shown in FIG. , □ plots show the specific resistance of the titanium oxynitride film formed in the reaction chamber 21 into which oxygen was introduced at a flow rate of 2 sccm, and ▽ plots show the specific resistance in the reaction chamber 21 into which oxygen was introduced at a flow rate of 5 sccm. 2 shows the specific resistance of the formed titanium oxynitride film.

FIG. 6 shows that the titanium nitride film, the oxygen-containing titanium nitride film, and the titanium nitride film obtained by the oxygen preflow process can obtain substantially constant specific resistance values without being affected by the growth temperature. Further, according to FIG. 7 obtained by rewriting the horizontal axis to the growth condition based on FIG. 6, it is possible to compare the magnitude of the specific resistance value due to the difference in the growth condition. Since the oxygen-containing titanium nitride film formed according to the gas flow of FIG. 4 contains a small amount of oxygen as a whole, the titanium nitride film 6 formed by the oxygen preflow process formed according to the gas flow of FIG.
The resistance is larger than that. However, when the specific resistance is 20
When the flow rate of oxygen is 5 sccm or less, there is no problem since the function as the upper electrode of the capacitor is sufficient if the flow rate is less than 00 μΩcm.

However, if the second mass flow controller 42 is adjusted so that the oxygen flow rate becomes 5 sccm before the formation of the TiON film 16, the oxygen flow rate supplied to the Ta ₂ O ₅ film 5 is too small. This is because the oxygen flow rate is 5 before the formation of the TION film 16.
If sccm only not flowing, it is impossible to form a sufficiently improve the film quality of the Ta ₂ O ₅ film 5, a block layer for anti-reducing the interface of TiON film 16 and the Ta ₂ O ₅ film 5 (oxygen-containing layer) Because. Here, before and during the formation of the TiON film 16, an oxygen gas is supplied at a flow rate of 33 sccm (6.6 times) or more, for example, 100 sccm as shown in FIG. 4, and then as shown by the solid line or the dashed line in FIG. It is necessary to reduce the flow rate stepwise to 5 sccm or less.

As can be seen from FIGS. 6 and 7, when the titanium nitride film formed by the oxygen preflow treatment and the TiON film formed by introducing oxygen at 2 sccm are compared with the conventional technology in which oxygen is not introduced at all, specific resistance is obtained. The value hardly changes. Oxygen flow rate during growth of oxygen-containing titanium nitride film 16 and oxygen-containing nitride film 1
When the relationship with the oxygen content in 6 was examined, it was as shown in FIG. 8, and it was confirmed that the oxygen content in the TiON film 16 could be controlled by adjusting the oxygen flow rate. FIG. 8 shows that the flow rate for reducing the oxygen flow rate during the growth of the oxygen-containing nitride film 16 is 2 sc
m, 5 sccm, 10 sccm, and 0 sccm are shown. Note that the XRD (X-ray diffraction) spectrum shown in FIG. 9 shows that the oxygen-containing titanium nitride deviates from the TiN crystal as the oxygen flow rate is increased.

Next, the leak current of the titanium compound film (upper electrode) grown on the Ta ₂ O ₅ film 5 was compared with the leak current of the titanium compound formed by the conventional method in accordance with the gas flow charts of FIGS. The results are described below. However, in the following description, the conditions shown in FIG.
The conditions shown in FIG. Further, the prior art, except that it does not introduce oxygen 3, in which to grow a TiN film on the Ta ₂ 0 ₅ film to form a capacitor with the same conditions as FIG.

The method of forming the upper electrode by the conventional method is described in R. Tamaru et al., Proceedings of VMIC (1997),
The method described on p.571 was used. FIG. 10 shows the leakage current of the capacitor when a voltage is applied to the capacitor with the amorphous silicon film 3 being on the positive side and the wiring 9 being on the negative side. It can be seen that the capacitor of the present embodiment formed by the process including the gas flow chart A or B has an order of magnitude less leakage current than the capacitor formed by the conventional technique.

FIG. 11 shows the leakage current of the capacitor when a voltage is applied to the capacitor with the amorphous silicon film 3 on the negative side and the wiring 9 on the positive side. It can be seen that the capacitor of the present embodiment formed by the process including the gas flow chart A or B has an order of magnitude less leakage current than the capacitor formed by the conventional technique. In both FIGS. 10 and 11, the thickness of the Ta ₂ O ₅ film 5 is 10 n.
m, the RTO after growth of the Ta ₂ O ₅ film 5 was 850 ° C. The SiO ₂ equivalent film thickness when grown according to the gas flow chart A is 3.2 nm, and when grown according to the gas flow chart B.
The SiO ₂ equivalent film was 3.18 nm, and the conventional capacitor was 3.1 nm. The film thickness was estimated from CV characteristics.

Such a leakage current causes the upper electrode to
Investigation was made on how it changes in an atmosphere containing 3% hydrogen and 3% hydrogen. FIG. 10 shows substantially no change as shown in FIG. 12 and FIG. And did not substantially change. Therefore, TiN film or Ti
It can be seen that the ON film shields the Ta ₂ O ₅ film from the reducing atmosphere.

The silicon substrate 1 was placed in a hydrogen and nitrogen atmosphere.
Was left for 30 minutes, during which time the silicon substrate was heated at 450 ° C. Next, the distribution of oxygen from the titanium nitride film 6 to the Ta ₂ O ₅ film 5 formed under the conditions of the gas flow chart A, and the distribution of oxygen from the TiN film formed by the conventional technique to Ta ₂ O 5
_The result of examining the distribution of oxygen up to _five films will be described.
However, since the Ta ₂ O ₅ film contains oxygen, in order to clarify the presence of oxygen, a silicon substrate is used instead of the Ta ₂ O ₅ film, and a gas flow chart A is formed on the silicon substrate.
Under these conditions, a titanium nitride film 6 was formed.

As a result of the experiment, AES (Auger Electron Spectroscopy) analysis results as shown in FIG. That is, the oxygen distribution peak appearing at the interface between the TiN film formed by the conventional technique and the silicon substrate (FIG. 14).
The peak of the oxygen distribution appearing at the interface between the TiN film 6 and the silicon substrate by the oxygen preflow treatment of this embodiment (FIG. 14)
), The peak of the present embodiment was larger. Therefore, since a large amount of oxygen is supplied to the surface of the silicon substrate, the Ta ₂ O ₅ film 5 (dielectric film) is prevented from being deteriorated due to lack of oxygen, and is protected from a reducing atmosphere by NH ₃ . You can see that. Ta ₂ O actually grown
₅ The composition ratio of the film 5 showed a value along the stoichiometric ratio. The chlorine contained in the TiN film 6 by the oxygen preflow process grown under the conditions of the gas flow chart A is about 1/5.
Metal corrosion due to chlorine is greatly suppressed, and Ti
The adhesion between the N film 6 and the Ta ₂ O ₅ film 5 is improved. It is considered that the chlorine was reduced because chlorine in the TiN film 6 was replaced by oxygen by the oxygen preflow treatment.

When the MMH gas is not supplied as shown in the gas flow chart A, the oxygen content at the interface between the TiN film 6 and the silicon substrate by the oxygen preflow process is slightly smaller than when the MMH gas is supplied. As can be seen from FIG. 14, the MMH gas may be omitted in the gas flow chart A because the oxygen content is larger than that of the TiN film formed by the conventional technique.

FIG. 15 is a diagram in which the vertical axis is enlarged for easy understanding of the result shown in FIG. Also, a titanium nitride film formed by oxygen preflow treatment and a Ti film formed at an oxygen flow rate of 2 sccm or 5 sccm are used.
FIG. 16 shows the respective growth rates of the ON film and the conventional titanium nitride film to which oxygen was not introduced at all. According to FIG. 16, the oxygen introduction time of titanium nitride is long, and the growth rate decreases as the oxygen content increases. Therefore, the oxygen by employing the Ti nitride film by preflow processing, to prevent the reduction of the Ta ₂ O ₅ film 5, the Ta ₂ O ₅ film oxygen omission prevents from 5 to titanium nitride film 6, further titanium nitride alloy It has been found that it is preferable to keep the growth rate of the upper electrode higher.

By the way, in the embodiment shown in FIG. 1, the capacitor having the MIS structure in which the amorphous silicon film 3 is applied as the lower electrode has been described, but the MIM (metal insulator) in which the lower electrode is made of metal is used. The upper electrode may be formed in the manufacturing process of the capacitor having the metal) structure by employing the conditions shown in FIGS. Next, a brief description will be given of a manufacturing process of the capacitor having the MIM structure.

First, an amorphous silicon film 3 doped with impurities is formed on the capacitor region on the surface of the silicon substrate 1 in the same manner as shown in FIG. 1 (a). After that, FIG.
(a) As shown in FIG.
The tungsten film 10 is selectively grown to a thickness of 10 nm on the exposed surface. Thereafter, the surface of the tungsten film 10 is nitrided in an ammonia atmosphere to form tungsten nitride (W).
N) grow the film 11; This nitriding process is formed to prevent oxidation of the surface of the tungsten film 10.

Thereafter, as shown in FIG.
A Ta film is formed on the gustene film 10 and the field oxide film 2._TwoO_Fivefilm
5 and the surface thereof is oxygen plasma or oxygen-containing gas.
Oxidized by plasma. The condition is O_Two20 gas
0 sccm, growth temperature 350 ° C, high frequency power 800
W for 3 minutes. Next, the gas flow chart of FIG.
1 according to the gas flow chart B of FIG.
As shown in Fig. 7 (c), Ta_TwoO_FiveOxygen preflow treatment on membrane 5
The TiN film 6 or the TiON film 16 is grown by the process. This
And the tungsten film 10 is_TwoO _FiveDielectric film 5
Body film, TiN film 6 or TION film 1 by oxygen preflow treatment
Basic Structure of MIM Structure Capacitor with 6 as Top Electrode
Is formed.

[0058] Further, as shown in FIG. 17 (d), the SiO ₂ film an opening 8 for exposing a part of the TiN film 6 or TiON film 16 by oxygen preflow treatment after forming the SiO ₂ film 7 covering the capacitor The wiring 9 connected to the TiN film 6 or the TiON film 16 by the oxygen preflow process through the opening 8 is formed on the SiO ₂ film 7. The thickness of each film shown in FIGS. 17A to 17D other than the tungsten film 10 is as follows.
The same as the films shown in FIGS. 1 (a) to (d).

The leakage current of the MIM type capacitor having the TiON upper electrode formed according to the gas flow chart B shown in FIG. 4 was compared with the leakage current of the MIM type capacitor having the TiN upper electrode formed by the prior art.
8. Experimental results as shown in FIG. 19 were obtained. The prior art is a technique for growing a TiN film under the same conditions as in FIG. 4 except that oxygen is not introduced in the step of growing a TiN film serving as an upper electrode.

FIG. 18 shows the leakage current of the capacitor when a voltage is applied to the capacitor with the amorphous silicon film 3 being on the positive side and the wiring 9 being on the negative side.
The MIM type capacitor of the present embodiment formed through the upper electrode forming step of the gas flow chart B has three orders of magnitude less leakage current than the MIM type capacitor formed by the conventional technique.

FIG. 19 shows the leakage current of the capacitor when a voltage is applied to the capacitor with the amorphous silicon film 3 on the negative side and the wiring 9 on the positive side. The MIM-type capacitor of the present embodiment formed through the upper electrode forming step of the gas flow chart B has two orders of magnitude less leakage current than the MIM-type capacitor formed by the conventional technique.

Also in the steps shown in FIGS. 17A to 17D, the peak of the oxygen content appears at the boundary portion between the TiON film 16 or the TiN film 6 and the Ta ₂ O ₅ film 5. _{The 2} O ₅ film 5 is formed according to the stoichiometric ratio.
6 or TiN film 6 is reduced to about 1/5 the chlorine, metal corrosion by chlorine is largely suppressed,
The improvement in the adhesion of the Ta ₂ O ₅ film is shown in FIGS.
It appears in the same way as the process shown in (d).

In the gas flow charts of FIGS. 3 and 4,
Oxygen gas is supplied before growing the TiON film or the TiN film by the oxygen preflow treatment. However, a gas containing a molecule having a structure containing one or more oxygen atoms, for example, water (H ₂ O), hydrogen peroxide (H ₂ O ₂ ), ozone (O ₃ ), carbon monoxide (C
A gas including O), carbon dioxide (CO ₂ ), or nitrogen oxide (NO, N ₂ O, or NO ₂ ) may be used. The gas is preferably a gas that can be diluted with at least one of helium (He), argon (Ar), and nitrogen (N ₂ ).

In the case where another metal such as ruthenium, iridium, or tungsten is formed on the dielectric film instead of a metal nitride film such as TiON or TiN, an oxygen-containing gas is introduced into a reduced-pressure atmosphere. May be. As the dielectric film, lead zirconate titanate (PZ) is used instead of Ta ₂ O ₅
T), strontium titanium oxygen (SrTO), barium strontium titanate (BST) or strontium bismuth tantalate (SBT or Y1), or an oxide of Group 3A, 4A or 5A of the Periodic Table of the Elements. May be used.

When a metal film or a metal nitride film formed on a dielectric film is formed by a CVD method, it is preferable that a reaction excitation method includes at least one of heat, light and plasma. The MIS-type or MIM-type capacitor is not limited to the above-described structure. For example, a capacitor having a T-shaped cross section of a lower electrode, a fin-type capacitor, or a capacitor having another structure may be used.
As a constituent material of the lower electrode, tungsten nitride (WN
x) as well as ruthenium (Ru), ruthenium oxide (RuO
_x ), iridium oxide (IrO _x ), titanium nitride (TiN
), Molybdenum (Mo), molybdenum nitride (MoN), tantalum (Ta), tantalum nitride (TaN), and other metals, conductive acid metal oxides, and metal nitrides.

Further, titanium iodide (TiI ₄ ), titanium bromide (TiBrl ₄ ), or titanium fluoride (TiF ₄ ) may be used instead of the above-mentioned titanium tetrachloride. Also ammonia,
Instead of MMH, N ₂ H ₄ , an alkyl compound of hydrazine, or an amine-based substance may be used. By the way, T. Tamur
In the literature of a et al., Proceedings of VMIC (1997), p. 571, Ta ₂ O was introduced by first introducing TiCl ₄ into the reaction chamber.
₅ avoids being exposed to a reducing atmosphere. However, when the method of introducing oxygen first is used as in the present invention, the order of introduction of the ammonia gas, the monomethylhydrazine gas and the titanium tetrachloride gas may be any order. Further, a film with good step coverage is formed by lowering the film forming pressure.

For example, as shown in FIG. 20, TiCl ₄ gas may be introduced before NH ₃ gas and MMH gas. In the above description, the technique of using the titanium nitride film and the oxygen-containing titanium nitride film by the oxygen preflow process as the upper electrode of the capacitor has been described.
It may be used for a gate electrode of a transistor.

[0068]

As described above, according to the present invention, an oxidizing gas is supplied to the surface of a dielectric film before forming an electrode made of metal or metal nitride on the dielectric film. Therefore, impurities taken into the dielectric film when the dielectric film is formed can be removed to improve the crystallinity of the dielectric film and reduce the leak current.

By flowing the oxidizing gas to at least the initial state of the introduction of the reducing gas used for forming the metal film or the metal nitride film, the reducing gas prevents oxygen defects in the oxidized dielectric film. Is done. When the oxidizing gas is introduced to the end of the formation of the metal film or the metal nitride film,
By reducing the flow rate of the oxidizing gas, an increase in the resistivity of the metal film or the metal nitride film can be prevented.

The oxygen-containing metal and the oxygen-containing metal nitride formed in the metal film, the metal nitride film and the dielectric film can prevent oxygen in the dielectric from diffusing into the metal film and the metal nitride film.

[Brief description of the drawings]

FIGS. 1 (a) to 1 (d) show M according to an embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a step of forming an IS-type capacitor.

FIG. 2 is a configuration diagram of a CVD apparatus for forming an upper electrode of a capacitor according to the embodiment of the present invention.

FIG. 3 is a diagram showing a first gas flow chart A of gas and pressure when growing a metal film to be an upper electrode shown in FIG. 1 (c).

FIG. 4 is a view showing a second gas flow chart B of gas and pressure when growing the metal film to be the upper electrode shown in FIG. 1 (c).

5 (a) and 5 (b) are cross-sectional views showing steps of forming an upper electrode of a capacitor according to the second gas flow chart shown in FIG.

FIG. 6 is a graph showing the relationship between the growth temperature and the specific resistance of a titanium nitride film formed by an oxygen preflow process used in the present invention, a titanium nitride oxide film used in the present invention, and a conventional titanium nitride film.

FIG. 7 is a diagram showing differences in specific resistance between a titanium nitride film formed by an oxygen preflow process used in the present invention, a titanium nitride oxide film used in the present invention, and a titanium nitride film formed by a conventional technique.

FIG. 8 is a diagram showing the difference between the oxygen content of a titanium nitride oxide film used in the present invention and the oxygen content of a conventional titanium nitride film.

FIG. 9 is an XRD spectrum diagram showing the difference between the oxygen content of the titanium nitride oxide film used in the present invention and the crystal structure of the conventional titanium nitride film.

FIG. 10 is a first characteristic diagram showing leakage currents of the MIS capacitor having the structure shown in FIG. 1D and a MIS capacitor formed by a conventional method.

FIG. 11 is a second characteristic diagram showing the leakage current of the MIS capacitor having the structure shown in FIG. 1D and the MIS capacitor formed by a conventional method.

FIG. 12 is a first characteristic diagram illustrating a leakage current when the MIS capacitor is formed under the conditions of FIG. 3 and then placed in an atmosphere of hydrogen and nitrogen at 450 ° C. for 3 minutes. It is.

FIG. 13 is a second characteristic diagram showing a leakage current when the MIS capacitor is formed in a hydrogen and nitrogen atmosphere at 450 ° C. for 3 minutes after the MIS capacitor is formed under the conditions of FIG. 3; It is.

FIG. 14 is a view showing an oxygen distribution of a titanium nitride film formed by an oxygen preflow process formed according to the chart shown in FIG. 3 and a silicon substrate thereunder.

FIG. 15 is a diagram in which the scale of the vertical axis in FIG. 14 is changed.

FIG. 16 is a diagram showing the difference between the oxygen content of a titanium nitride oxide film used in the present invention and the growth rate of a conventional titanium nitride film.

FIGS. 17A to 17D are cross-sectional views showing steps of forming an MIM capacitor according to the embodiment of the present invention.

FIG. 18 is a first characteristic diagram showing leakage currents of the MIM type capacitor having the structure shown in FIG. 17D and an MIM type capacitor formed by a conventional method.

FIG. 19 is a second characteristic diagram showing leakage currents of the MIM capacitor having the structure shown in FIG. 17D and an MIM capacitor formed by a conventional method.

FIG. 20 is a diagram showing a third gas flow chart of the gas and pressure when growing the metal film to be the upper electrode shown in FIG. 1 (c).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Silicon substrate (semiconductor substrate), 2 ... Field oxide film, 3 ... Amorphous silicon film, 4 ... Silicon nitride film, 5 ...
Ta ₂ O ₅ film (dielectric film), 6 ... by oxygen preflow treatment
TiN film (metal nitride film), 7: SiO ₂ film, 8: opening, 9:
Wiring, 10: tungsten film, 11: tungsten nitride film, 16: TiON film, 21: reaction chamber, 22: lower electrode, 23: gas shower, 23a: first gas diffusion chamber,
23b: second gas diffusion chamber, 24: exhaust port, 25: open / close valve, 26: drag pump, 27: dry pump, 2
8 First gas pipe, 29 Second gas pipe, 30 Control circuit, 31 to 35 Gas cylinder, 41 to 45 Mass flow controller.

Claims (21)

[Claims] A step of forming a dielectric film on a semiconductor substrate; a step of introducing an oxidizing gas into the semiconductor substrate; and a step of growing a metal or metal nitride in the oxidizing gas.
Introducing a reaction gas and a second reaction gas, and then reducing the oxidizing gas, and using the first reaction gas and the second reaction gas to deposit the metal or the metal on the dielectric film. Forming a conductive film containing metal nitride. 2. A step of exposing the dielectric film to a heating atmosphere containing oxygen or a plasma atmosphere containing oxygen before forming the dielectric film and before introducing the oxidizing gas. The method for manufacturing a semiconductor device according to claim 1, further comprising: 3. The step of exposing the dielectric film to a heating atmosphere containing oxygen or a plasma atmosphere containing oxygen is performed in a first chamber. 3. The method according to claim 2, wherein the method is performed in a second chamber different from the first chamber. A step of performing a treatment for improving the film quality of the dielectric film; a step of exposing the surface of the dielectric film to a reduced-pressure atmosphere containing an oxidizing gas; and a step of growing a conductive film made of metal or metal nitride. By supplying the first reaction gas and the second reaction gas to the reduced-pressure atmosphere, the reaction of the first reaction gas, the second reaction gas, and the oxidizing gas on the dielectric film is performed. Forming an oxygen-containing metal layer or an oxygen-containing metal nitride layer; and reacting the first reaction gas and the second reaction gas to form the oxygen-containing metal layer or the oxygen-containing metal on the dielectric film. A method for manufacturing a semiconductor device, comprising: a step of forming the conductive film serving as an electrode with a nitride layer interposed; and a step of stopping supply of the oxidizing gas during the formation of the conductive film. 5. A step of performing a process for improving the film quality of the dielectric film; a step of exposing the surface of the dielectric film to a reduced-pressure atmosphere containing an oxidizing gas; By supplying the first reaction gas and the second reaction gas to the reduced-pressure atmosphere, the reaction of the first reaction gas, the second reaction gas, and the oxidizing gas on the dielectric film is performed. A method for manufacturing a semiconductor device, comprising: a step of forming a conductive film containing oxygen; and a step of reducing a flow rate of the oxidizing gas during the formation of the conductive film. 6. The method for manufacturing a semiconductor device according to claim 5, wherein the oxidizing gas is stopped simultaneously with or after the supply of the first reactant gas and the second reactant gas is stopped. . 7. The method according to claim 4, wherein said dielectric film is made of an oxide dielectric. 8. The method according to claim 4, further comprising the step of forming a lower electrode made of a metal, a conductive metal oxide or a metal nitride between said semiconductor substrate and said dielectric film. Of manufacturing a semiconductor device. 9. The device according to claim 8, wherein the lower electrode is formed of any one of tungsten, ruthenium, ruthenium oxide, iridium oxide, titanium nitride, tungsten nitride, molybdenum, molybdenum nitride, tantalum, and tantalum nitride. The manufacturing method of the semiconductor device described in the above. 10. The method according to claim 4, further comprising the step of forming a semiconductor layer containing impurities between the semiconductor substrate and the dielectric film before forming the dielectric film. Of manufacturing a semiconductor device. 11. The dielectric film according to claim 1, wherein said dielectric film is 3A of the periodic table.
5. The method according to claim 4, wherein the oxide is formed by growing an oxide of a group 4, 4A or 5A group, or by growing any of lead zirconate titanate, strontium titanium oxygen, barium strontium titanate or strontium bismuth tantalate. 6. A method for manufacturing a semiconductor device according to claim 5. 12. The method according to claim 4, wherein the oxidizing gas is a molecular gas containing at least one oxygen in the molecule. 13. The gas according to claim 1, wherein said gas is O ₂ , H ₂ O, H ₂ O ₂ ,
13. The method for manufacturing a semiconductor device according to claim 12, wherein O ₃ , CO, CO ₂ , NO ₂ , N ₂ O, and NO are used. 14. The oxidizing gas in the reduced-pressure atmosphere,
The method according to claim 4, wherein the semiconductor device is diluted with at least one of helium, argon, and nitrogen. 15. The method according to claim 4, wherein the step of exposing the dielectric film to the oxidizing gas in a reduced-pressure atmosphere is performed in the same reaction chamber as forming the dielectric film serving as an upper electrode. 6. The method for manufacturing a semiconductor device according to item 5. 16. The method for manufacturing a semiconductor device according to claim 4, wherein the treatment for improving the film quality of said dielectric film is different from the step of exposing to an oxidizing gas in said atmosphere. . 17. The method according to claim 4, wherein the first reaction gas for forming the conductive film contains a reducing element. 18. The method according to claim 17, wherein the first reaction gas contains an ammonia gas. 19. The method according to claim 4, wherein the second reaction gas for forming the conductive film is made of a non-reducing element. 20. The second reaction gas comprises TiCl ₄ , TiI ₄ ,
A method according to claim 19, wherein a is any one of TiBr _4. 21. The method of manufacturing a semiconductor device according to claim 4, wherein said conductive film is a titanium nitride film, a titanium oxynitride film, or a two-layer film of titanium oxynitride / titanium nitride. Method.