JPH086182B2 - Method for forming nitride film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a nitride film by a plasma CVD method.

[0002]

2. Description of the Related Art In a film forming method using various low temperature plasmas, for example, a physical vapor deposition method (PVD method) such as an ion plating method, a chemical vapor deposition method (CVD method) is used.
It is possible to form a nitride film such as a titanium nitride film at a lower temperature than the above. However, PVD
The method has a problem that the coating power of the coating film on the three-dimensional base material is low. Particularly, in the case of a large-sized complex three-dimensionally shaped substrate, the throwing power is remarkably deteriorated, so that the
It was difficult to apply the D method.

Therefore, the good throwing power of the CVD method and P
A plasma CVD method having both advantages of forming a film at a low temperature in the VD method is being developed. This plasma CVD method uses the thermal energy required for the chemical reaction of the source gas.
It is possible to form a film at low temperature by substituting a part or all of the above with electric energy by plasma. In such a plasma CVD method, a raw material gas in a vacuum chamber is supplied through a nozzle, and direct current or high frequency is applied to a three-dimensional base material arranged in the chamber to cause glow discharge to generate plasma. At this time, the source gas supplied into the chamber becomes active excited species such as ions, radicals, atoms and molecules when passing through the plasma. It is considered that these excited species are capable of forming a thin film on the three-dimensionally shaped substrate at a low temperature because the reaction proceeds at a low temperature. Therefore, the plasma CVD method can form a thin film having good throwing power on a three-dimensional substrate at a low temperature.

By the way, conventionally, in order to form a nitride film such as a titanium nitride film having a uniform thickness on a substrate by a plasma CVD method, a film forming experiment is performed by changing many film forming parameters. The empirical method of setting the optimum film forming conditions by investigating the characteristics of the film was adopted.

[0005]

However, the above empirical method takes a lot of time to find the optimum film forming conditions,
It requires cost and effort. Furthermore, if the shape of the substrate on which the film is formed changes, an experiment must be performed each time, so
Optimal conditions cannot be easily found. Therefore, this hinders the industrial development of the plasma CVD method.

The present invention has been made in order to solve the above-mentioned conventional problems, and by developing a method for easily finding an optimum power supply to a plasma for a base material of any shape, plasma An object of the present invention is to provide a method capable of forming a nitride film having a uniform thickness on the surface of a substrate by the CVD method.

[0007]

The present invention is a plasma CV.
In the method of forming a nitride film on a base material by the D method, a test base material is previously placed on an electrode, plasma is generated in a raw material gas atmosphere under a constant pressure, and the supply voltage to the plasma and the The relationship with the current value flowing through the test substrate
Measure from low voltage region to high voltage region,
And a straight line drawn by connecting at least three measured values of
Connect the measured values of at least 3 points in the high voltage region
The voltage V _s at the change point obtained from the intersection with the drawn straight line is obtained, and the voltage V supplied to the plasma during film formation is V ≦
A method for forming a nitride film, characterized in that the voltage is set to 1.25 V _s, and other conditions are made substantially the same as when the voltage V _s was obtained. As the test base material, it is desirable to use a base material having the same shape and surface area as the base material used in the actual film formation.

In the method for forming a nitride film according to the present invention, the optimum supply voltage value V to the plasma is V ≦ 1.25.
V _s , preferably 0.9 V _s ≦ V ≦ V _s . Here, the supply voltage value V is 0.9V
_{When it is} less than _s, the supply amount of the active nitrogen source necessary for the reaction is reduced, and the excitation and decomposition of halogen metal gas and hydrogen gas,
Since ionization and the like are also suppressed, it becomes difficult to form a nitride film having excellent characteristics. For example, the nitrogen atomic ratio in the nitride film becomes lower than the stoichiometric composition, the color tone deteriorates, and the adhesion of the film to the substrate and the hardness also decrease. On the other hand, when the supply voltage value V exceeds V _s , the plasma density required for the reaction becomes excessive, the precursor formation state deteriorates sharply, and the formation of fine powder occurs due to the occurrence of a uniform gas phase reaction. As a result, the fine powder adheres to the coating film, and the corrosion resistance of the coating film is significantly deteriorated, which may significantly deteriorate the coating properties, and further, the uniformity of the coating film may be significantly reduced.

The method for forming a nitride film according to the present invention comprises:
The current density is controlled in the voltage range (V ≦ 1.25 V _s ) obtained from the above relationship, and film formation is allowed under the other conditions substantially the same as when the above relationship was obtained.

[0010]

The present inventors have invented a method capable of forming a nitride film having good characteristics with a uniform thickness distribution from a flat base material to a large three-dimensional base material based on the knowledge described below.

That is, the inventors of the present invention, as a result of the research on the nitride film formation mechanism and the research on the dependence of various film formation characteristics on various parameters, decompose the source gas in the plasma space, particularly in the sheath portion near the surface of the substrate, and ionize it. It has been clarified that the current density flowing in the substrate plays an important role in the reaction in the reaction process of forming a film-forming seed through the reaction. This will be described by taking the TiN film forming reaction as an example.

FIG. 1 shows H ₂ —N ₂ system, H ₂ —N ₂ —Ti
₅ shows VI characteristics of plasma using a Cl ₄ mixed gas. A predetermined flow rate of H ₂ gas and N ₂ gas, or H ₂ gas, N ₂ gas and TiCl ₄ gas was supplied to the plasma CVD reaction tank to make the pressure constant, and then the power applied to the plasma was gradually increased. The applied voltage dependency of the current value flowing through the material is measured. At this time, the substrate surface area and shape,
Other conditions such as the pressure in the reaction layer are the same as in the actual film formation. When the measurement is performed, in the H ₂ —N ₂ system gas, the value of the current flowing through the substrate linearly increases as the voltage applied to the plasma increases. On the other hand, in the H ₂ —N ₂ —TiCl ₄ system gas, when the voltage applied to the plasma is increased, the current value flowing through the substrate gradually increases almost linearly, and when the voltage exceeds a certain value, the rate of increase in the current value increases. Increase sharply. Therefore, a change point lacking continuity appears in the current characteristics, and the voltage V _{s at the} change point becomes the optimum supply power value under the film forming condition for the reason described below.

When the source gas is supplied into the plasma,
Especially in the plasma sheath, it is easily decomposed
Active plasma species such as hydrogen, radicals, atoms and molecules.
Turn into. H₂-N₂In case of system gas, N in plasma
₂Molecules are ionized and N₂ ⁺ Become an ion, H₂molecule
Are either excited or dissociated to H atoms, part of both
Synthesizes NH radical by ion-radical reaction
It is known. These plasma species supply
It continuously increases as the applied voltage increases.

On the other hand, in the case of H ₂ —N ₂ —TiCl ₄ type gas, as a result of research by plasma diagnostics using emission spectroscopy, Ti ⁺ in the TiN film forming process. It was presumed that ions and NH radicals are plasma species with important roles. Further, it has been found that the plasma species react directly or indirectly to form a TiN precursor, which reacts on the substrate surface to form a TiN coating.
At an applied voltage equal to or lower than the voltage V _{s at the} change point, NH radicals are consumed by the formation of the precursor, and the equilibrium of the ion-radical reaction shifts to the NH radical synthesis reaction side. This allows N ₂ ⁺ Ions are reduced, and as a result, the ion density of the plasma is reduced, and the rate of increase in current value is suppressed. On the contrary, when the applied voltage is equal to or higher than the voltage V _{s at the} change point, more NH radicals than necessary for the precursor synthesis are formed, and the reaction returns to the equilibrium. Therefore, the ion density increases and the current value rapidly increases.

This is the result shown in the VI characteristic of the plasma of FIG. 1 described above, and it is optimum to obtain a plasma state for forming an optimum precursor so that the optimum TiN film can be formed. Was estimated. The optimum precursor formation state means that Ti ⁺ existing in the plasma space near the surface of the substrate is The amount of ions and the amount of plasma species respectively existing, that is, the ion density is optimized, and the optimum value is the voltage at the V _s point obtained by the present invention, and the current value (base material Current density).

Further, in the optimum precursor formation state, when the film forming parameters are changed, the ion density of plasma species is changed, and as a result, the film forming characteristics are largely changed. Therefore, as described above, the V-I characteristic is previously investigated, and the V _s
By determining the point, the optimum power supply value to the plasma can be easily set under any film forming condition, and thus the controllability and reproducibility of the nitride film formation can be improved, and the applicability is large. Can be expanded.

[0017]

Embodiments of the present invention will now be described in detail with reference to FIG.

FIG. 2 is a schematic view showing the DC plasma CVD apparatus used in this embodiment. Reference numeral 1 in the drawing is a vacuum chamber. A DC electrode 2 having a rotating mechanism is installed in the lower part of the vacuum chamber 1. A DC power supply 3 is connected to the DC electrode 2. An exhaust pipe 4 is provided near the lower portion of the vacuum chamber 1. A pressure control valve 5 and a vacuum pump 6 are sequentially connected to the exhaust pipe 4 from the vacuum chamber 1 side.

On the outer wall of the vacuum chamber 1, there is provided a heater 7 for uniformly heating the large three-dimensional base material placed on the DC electrode 2. For example, four gas supply nozzles 8 are provided on the side wall of the vacuum chamber 1, and the raw material gas supplied from the gas supply nozzles 8 is sprayed on the entire large three-dimensional base material installed on the DC electrode 2. It is designed to be used. The other end of each gas supply nozzle 8 extends through the side wall of the vacuum chamber 1 to the outside and is connected to a gas introduction pipe 9. Four gas branch pipes 10 are connected to the gas introduction pipe 9. A mass flow controller 11 is provided in each of the gas branch pipes. A supply line of hydrogen (H ₂ ) gas, titanium tetrachloride (TiCl ₄ ) gas, nitrogen (N ₂ ) gas, and ammonia (NH ₃ ) is connected to each mass flow controller 11.
A window 12 made of quartz glass is provided on the side wall of the vacuum chamber 1.
Is arranged. Example A thin film forming method will be described using the above-described DC plasma CVD apparatus.

First, a total surface area of 11200 cm ² was formed on the DC electrode 2 in the vacuum chamber 1. 400 × 400 × 6 with
A large-sized three-dimensional base material 13 of 00 mm was installed. Subsequently, the vacuum pump 6 was operated to exhaust the gas in the vacuum chamber 1 through the exhaust pipe 4. Continuing, 2000sccm whose flow rate was adjusted by the mass flow controller 11.
Of the H ₂ gas from the gas supply nozzle 8 into the chamber 1 by the external heater 7
The temperature was raised to 0 ° C. After the temperature is raised, a DC voltage is gradually applied to the DC electrode 2 from the DC power supply 3 to -300V to -3000V to generate plasma in the chamber 1 to clean the inner surface of the chamber 1 and the surface of the electrode 2 for 30 minutes. did.

Next, the applied voltage is lowered to -300 V, and the flow rate is adjusted to 50 by the mass flow controller 11.
A mixed gas consisting of 0 sccm N ₂ gas and 800 sccm H ₂ gas was supplied into the chamber 1 through each gas supply nozzle 8, and the pressure in the chamber 1 was set to 0.43 Torr by a pressure control valve 5. Hold for 30 minutes. Subsequently, 150 sccm of TiCl ₄ gas whose flow rate was adjusted by the mass flow controller 11 was supplied into the chamber 1 through the gas supply nozzle 8, and -3
The applied voltage was increased within the range of 00 to -50V.

From the results of the above preliminary experiments, V- shown in FIG.
I characteristic was obtained. Of the H ₂ —N ₂ —TiCl ₄ system shown in FIG.
In the VI characteristics of plasma using mixed gas,
Plotted by connecting at least three measurement values in the pressure area
Measure the measured values of the straight line and at least three points in the high voltage range.
When the voltage V _s at the change point obtained from the intersection with the straight line drawn by connecting is calculated, the DC voltage is −1500 V (1.6
It was A). Then, the power supply to the plasma is controlled so that a DC voltage of −1500 V is supplied from the DC power supply 3 to the electrode 2, and 150 sccm of TiCl ₄ gas whose flow rate is adjusted by the mass flow controller 11 is passed through the gas supply nozzle 8. The TiN coating film was formed on the surface of the SKH51 base material by supplying the same into the chamber 1 and other conditions in the same manner as in the preliminary experiment.

FIG. 3 shows the dependency of the TiN film formation rate and the film thickness distribution on the applied voltage under the above conditions. The solid line shows the film thickness speed and the dotted line shows the film thickness distribution. The film thickness distribution index (Di) in FIG. 3 was obtained from the following formula. Di = [absolute value of (maximum displacement value from average film thickness−average film thickness value)] / average film thickness × 100 (%) Further, symbols WG, G, and RG in FIG. 3 are as follows. WG: Platinum TiN coating G: TiN specific golden TiN coating RG: Reddish brown TiN coating

The TiN film formed by the power supplied to the plasma under the above conditions (DC voltage; -1500V) is
It was found that it had a golden color (G) peculiar to the TiN coating and had a uniform film thickness distribution. It was also found that the TiN coating had a micro Vickers hardness of 2000 Hv or more, and the coating had an N / Ti atomic ratio close to 1 and had excellent properties. Comparative example

The above-mentioned graph showing the applied voltage dependence of the TiN film formation rate and the film thickness distribution when the DC voltage is varied in the unit of -250V from -750V to -2750V centering on the optimum voltage of -1500V. 3 shows.

As is apparent from FIG. 3, the optimum voltage (-15
00V) or less, the coating formed under the condition of platinum color (W
G) is exhibited, the film thickness distribution is deteriorated and the film formation rate is reduced. Further, it was detected by X-ray diffraction that the hardness was low and that Ti ₂ N crystal was contained in addition to the TiN crystal.

On the other hand, the coating film formed under the condition of the optimum voltage (-1500 V) or more exhibits a light reddish brown color (RG), and although the film formation rate is high, the film thickness distribution becomes remarkably large. That is, as the applied voltage increases, the film formation condition region becomes WG → G
→ Become RG. The deposition rate increases linearly,
The maximum value is shown in the area. The Di value is the smallest in the G region.

[0028] From the results of the above Examples and Comparative Examples, to form a TiN coating having good properties such as hardness with uniform thickness in the voltage V _s of the resultant change points from V-I characteristics of Figure 1 You can Conventionally, the optimum value of the power supplied to the plasma has been obtained by conducting detailed experiments from a low applied voltage to a high applied voltage and measuring the film characteristics under each of these conditions. Therefore, much time and effort was required to determine the optimum supply voltage.

[0029]

As described in detail above, according to the present invention, when the metal nitride film is formed by the plasma CVD method, it is possible to easily find the optimum power supply value to the plasma for forming the film, and to obtain the uniform thickness. In that case, a remarkable effect such as a nitride film having excellent characteristics such as hardness and color tone can be formed with good reproducibility.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a current value flowing through a base material and an applied voltage measured in an example of the present invention.

FIG. 2 is a DC plasma CVD used in an example of the present invention.
Schematic which shows an apparatus.

FIG. 3 is a characteristic diagram showing the DC voltage dependence of the film formation rate and the film thickness distribution index (Di).

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vacuum chamber, 2 ... DC electrode, 4 ... Exhaust pipe, 8 ... Gas supply nozzle, 13 ... Substrate.

Claims (2)

[Claims] 1. A method for forming a nitride film on a base material by a plasma CVD method, wherein a test base material is previously set on an electrode, and plasma is generated in a source gas atmosphere under a constant pressure to obtain the plasma. The relationship between the voltage supplied to the test substrate and the value of the current flowing through the test base material was changed from the low voltage region to the high voltage region.
At least 3 points in the low voltage region
At least the straight line drawn by connecting the values and the high voltage region
The voltage V _s at the change point obtained from the intersection with the straight line drawn by connecting the measured values of 3 or more points is obtained, and the supply voltage V to the plasma during film formation is set to V ≦ 1.25 V _s, and other conditions are set. A method for forming a nitride film, which is substantially the same as when the voltage V _s was obtained. 2. The voltage range (V ≦
2. The method for forming a nitride film according to claim 1, wherein the film formation is performed by controlling the current density at 1.25 V _s ) and making other conditions substantially the same as when the relation was obtained.