JPH08158040A - Thin carbon nitride film and its formation - Google Patents

Abstract

PURPOSE: To form a thin CNx film having a high ratio of N to C at an increased rate of film formation only by carrying out high-frequency sputtering or DC sputtering. CONSTITUTION: When a graphite or carbon target is subjected to high-frequency sputtering or DC sputtering with gaseous N2 under 100-5,000mTorr partial pressure to form a thin carbon nitride film contg. C and N having chemical CN bonds, the objective thin carbon nitride film having such a high atomic ratio of N to C as >1 is formed by regulating the partial pressure of N2 to 250-5,000 mTorr.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carbon nitride (CNx) thin film and a method for forming the same.

[0002]

2. Description of the Related Art β-C ₃ N ₄ is a material which is theoretically predicted to have higher hardness than diamond, and at the same time is expected to have excellent corrosion resistance under high temperature conditions. On the other hand, diamond-like carbon (DLC) is applied to the surface coating of magnetic tapes and magnetic disks because it can be formed at low temperature and has high hardness and excellent sliding characteristics. Amorphous CNx containing N has been studied for film formation in order to reduce the temperature and stabilize the structure.

Conventionally, as a typical film forming technique of a CNx thin film, there is a method of using a sputtering device for forming plasma by high frequency or DC by parallel plate type electrodes. In this case, a part of the C particles sputtered out of the target is nitrided by the plasma containing N to form a gaseous CNx intermediate, which is formed as a CNx thin film on the substrate. N ₂ partial pressure 20 mTo
rr or less [Reference: MY Chen, J. Vac. Sci. Techn
ol.A, 11 (3) (1993) 521, CJTorng, J.Mater.Res.5 (1
1) (1990) 2490].

As a film forming method other than sputtering, a plasma CVD method or IVD in which vapor deposition and ion implantation are used in combination
There is a law (Ion Vapor Deposition) (reference: F. Fuji
moto, Jpn.J.Appl.Phys.32 (1993) 420).

[0005]

However, it is not possible to obtain a CNx thin film having a high N / C ratio (atomic ratio, the same hereinafter) by the ordinary plasma CVD method, and the film forming rate is low. On the other hand, according to the ECR plasma CVD method capable of forming high density plasma, it is possible to form a CNx thin film having an N / C ratio of more than 1, but the obtained film is thermally unstable and 500 It has been reported that it decomposes and disappears when heated to ℃ (Reference: M.Diani, Diamond
and Rlated Materials, 3 (1994) 264). On the other hand, according to the IVD method, N /
Although a CNx thin film having a C ratio of more than 1 has been obtained, this method requires an ion implantation apparatus, resulting in high cost, and it is difficult to form a film on a substrate having a large area.

Further, in the sputtering method widely used for forming a thin film, since the N ₂ partial pressure is low as described above, the C particles sputtered and sputtered from the target collide with the N particles in the gas phase. Less,
The probability of nitriding also decreases, and it becomes difficult to form gaseous CNx intermediates such as CN and C ₂ N _{2, and} CNx with a high N / C ratio
It was difficult to form a thin film, and the film formation rate was low.

Moreover, active species such as ions and radicals in the plasma collide with the substrate while keeping high energy, so that N in the film growing on the substrate is sputtered by it, and N in the film is sputtered. It helped reduce the content.

An object of the present invention is to provide CNx having a high film formation rate.
A method for forming a thin film is provided. Another object of the present invention is to provide a CNx thin film containing N in a sufficient amount to exhibit a function close to the stoichiometric ratio of β-C ₃ N ₄ by high frequency sputtering or DC sputtering.

[0009]

That is, the present invention comprises C and N having a CN chemical bond formed by high frequency sputtering or DC sputtering,
The N / C ratio is more than 1.0, and N ₂ gas is applied to a carbon nitride (CNx) thin film, graphite or carbon target at a partial pressure of 100 to 5000.
In the method for forming a carbon nitride (CNx) thin film, which is characterized by performing high-frequency sputtering or DC sputtering with mTorr, in this forming method, N ₂ partial pressure is set to 2
N / W characterized by 50 to 5000 mTorr
This is a method of forming a carbon nitride (CNx) thin film having a C ratio of more than 1.0.

The present invention will be described in more detail below with reference to FIG.

FIG. 1 is a schematic explanatory view of a high frequency sputtering apparatus. A sputtering gas is introduced into the vacuum device 10 through the gas inlet 13, and a high frequency is applied to the high frequency electrode 2 by the high frequency power supply 11 to form plasma near the target 3. Target 3 -500 to -2000V
The target is sputtered by producing a bias voltage of

The target 3 is made of graphite or carbon, and the sputtering gas is a gas containing N ₂ . In order to stabilize the plasma and improve the film quality, an inert gas such as Ar or He or H ₂ may be mixed with N ₂ gas, and the ratio thereof is less than 50% by volume in the total gas. preferable. If it is 50% by volume or more, the N ₂ concentration becomes too small and the film forming rate decreases.

The sputtered C particles react with plasma-excited N ion radicals and are nitrided to form gaseous CNx such as CN and C ₂ N ₂ which are intermediates.
This intermediate is supplied onto the substrate 5. At this time, by setting the N ₂ partial pressure of 100 to 5000 mTorr, which is higher than that of the conventional one, the collision with N particles is activated and the nitriding is promoted, so that the C particles Most of it becomes CNx, and the film formation rate of the CNx thin film increases. When the N ₂ partial pressure exceeds 5000 mTorr, stable plasma cannot be formed, and abnormal discharge occurs in the vicinity of the substrate, and N in the film is desorbed due to redesorption of N.
A decrease in content occurs.

In the present invention, by setting 250 to 5000 mTorr in the above N ₂ partial pressure range, it is possible to suppress the high energy particles of N ion / radical from directly colliding with the substrate, and to re-desorb N. Since it is possible to prevent a decrease in the N content in the film due to separation, it is possible to form a CNx thin film having a high N / C ratio.

N ₂ partial pressure in the present invention 100 to 5000
At mTorr, preferably 250 to 5000 mTorr, the film formation rate can be increased regardless of the output density (plasma formation output / target area), and high N /
A CNx thin film having a C ratio can be formed. In the present invention, a power density of about 2.5 to 100 W / cm ² can be used.

On the other hand, N ₂ partial pressure is 50 to less than 250 mT
In the case of orr, the power density is 10 to 35 W / cm
^By setting it to ² , it becomes possible to form a CNx thin film having a high N content with an N / C ratio close to 1, and it is expected that the film formation rate can be increased.

That is, 50 to less than 250 mTorr
In the N ₂ partial pressure range, the collision frequency between the sputtered C particles and the N particles is rather small, so that when the power density of the plasma is low, the N ions necessary for sufficiently nitriding the sputtered C particles are necessary.・ Insufficient supply of radicals. Therefore, most of the C particles reach the substrate as they are without being nitrided and grow as a film, so that it becomes difficult to take in a large amount of N into the film.

On the contrary, if the power density is too high,
Since the self-bias of the target becomes large and the particles sputtered out from the target collide with the substrate with such a large amount of energy, the CNx thin film with a high N content as in the case of the conventional film formation with a N ₂ partial pressure of about 20 mTorr Can no longer be formed.

The present inventors have found that mTo of 50 or more and less than 250 mTo
As a result of various studies on the conditions for forming a CNx thin film having an N / C ratio of about 1 at the N ₂ partial pressure of rr, the conditions for an output density of 10 to 35 W / cm ² were found. Under such conditions of N ₂ partial pressure and power density, the sputtering rate of the target is high, so the film formation rate is also high.

In the present invention, when sputtering with the above N ₂ partial pressure and power density, a magnet 4 is arranged behind the target 3 to form a high density plasma by magnetron discharge, and the C particles to be sputtered are further sufficiently It is preferable to nitride it.

Further, the high frequency electrode 12 of the substrate holder 6
Is connected to a high-frequency power source 7 to form plasma around the substrate, and the substrate surface is cleaned before film formation to improve the adhesion between the substrate and the thin film, or to apply an appropriate substrate bias during film formation. As a result, the densification and crystallinity of the CNx thin film can be improved.

In the present invention, a CNx thin film having a high N content can be similarly formed by using DC plasma instead of plasma formation by high frequency. In this case, DC (direct current power) instead of the high frequency power supply in FIG.
Is connected to the electrode 2 and a voltage is applied to form plasma.
In this case, the plasma formation output for calculating the output density can be obtained by the applied voltage × electrode current.

The CNx thin film formed according to the present invention is
It contains C and N, which have a CN chemical bond, and is amorphous when formed at room temperature, but it is a uniform CNx phase or a mixture of carbon or graphite phase and CNx phase depending on the film formation conditions. It is an organization. By heating the substrate to 400 to 700 ° C. during film formation, a thin film containing crystalline is formed, and amorphous and β-C ₃ N
_The structure is a mixture of crystalline materials that are presumed to contain ₄ .

To function as a CNx thin film, a high N content
And the N is simply adsorbed or solid-solved.
However, it is important to form a CN bond chemically.
And. In the present invention, the CNx thin film is identified by FT
2200 cm by IR analysis ^-1-CN-3 double binding in
The presence of combined peaks and C in ESCA analysis_1SPeak
Shifting to high energy side, that is, C-C bond
Value of 284.6 eV binds to N with high electronegativity
High energy indicating that the N / C ratio has increased
Check the existence of a shift to the
You can The inventor has found that the N / C ratio exceeds 1 CNx
In thin film, C_1SThe peak is around 288 eV, and the ratio is
The CNx thin film near 1 shifts to about 287 eV
I was sure that.

The CNx thin film of the present invention contains C and N having a CN chemical bond, but may contain 10 atom% or less of O or H mixed from the atmosphere during film formation.

[0026]

EXAMPLES The present invention will be described more specifically with reference to Examples and Comparative Examples.

Examples 1 to 6 Comparative Examples 1 to 3 Using the film forming apparatus shown in FIG. 1, the film forming test of the CNx thin film was conducted by changing the N ₂ partial pressure and the power density variously by the following procedure. The film speed, the N / C ratio of the film, and the CN binding state were measured. The results are shown in Table 1.

That is, a graphite target having a diameter of 30 mm and a purity of 99.999 was attached to the high frequency electrode 2 of the sputtering apparatus, and a matching unit of a high frequency power source of 13.56 MHz was connected so that the distance between the substrates was 5 cm.
A ground shield 1 having a ground potential was attached around the high frequency electrode 2 to prevent abnormal discharge.

The Si substrate 5 of (100) orientation is set on the substrate holder 6, and the inside of the vacuum chamber is set to 2 × 10 ^-6 by the exhaust device 9 equipped with the composite turbo molecular pump prior to film formation.
Exhausted to Torr. After that, 50 ccm of N ₂ gas was introduced into the vacuum device 10 by the mass flow controller, and the pressure in the vacuum device was adjusted to a predetermined value using the pressure adjuster 8. The pressure was measured using a Baratron pressure gauge.

A high frequency power source 7 is used to induce plasma,
After the surface of the substrate was sputter cleaned, a high frequency was applied to the high frequency electrode 2 so as to have a predetermined output density, and plasma was formed. The substrate was deposited at room temperature without heating.

The film thickness of the obtained CNx thin film was measured by a contact type step meter to calculate the film forming rate. The N / C ratio was measured by ESCA and fluorescent X-ray analysis, and the state of CN chemical bond was analyzed by measuring the C _1s binding peak position by ESCA. In addition, ESCA is PE
RKINELMER "5500MC" is used to prevent C contamination in the analyzer from 10 ^-9 to 10 ^-10 T
Approximately 30 by irradiating Ar ions for 1 minute at a vacuum degree of orr
Å Sputtering was performed to remove the adsorbed substances on the surface before measurement. In fluorescent X-ray analysis, a calibration curve was prepared in advance using a substance containing C and N, such as a phthalocyanine thin film, and the measurement was performed. This method is in good agreement with the theoretical calculation by the fundamental parameter method, and highly accurate quantification It was confirmed that analysis was possible.

[0032]

[Table 1] (Note: In Comparative Example 3, the plasma became unstable and film formation could not be performed.)

As is clear from Table 1, according to the present invention, a CNx thin film having a CN chemical bond and having a high N / C ratio can be formed at a high film forming rate.

Example 7 The CNx thin film obtained in Example 2 was heated in a vacuum atmosphere at 600 ° C. for 3 hours to examine the thermal stability. As a result, no change was observed in the N / C ratio, C _1S peak position / shape, and FTIR spectrum before and after heating, and it was found that the film was a CNx thin film having high thermal stability.

[0035]

According to the present invention, it is possible to increase the film formation rate and
x Thin films can be formed. In addition, by appropriately adjusting the N ₂ partial pressure, high frequency sputtering or DC
High N with an N / C ratio of more than 1 only by performing sputtering
A CNx thin film having a / C ratio can be formed.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a sputtering apparatus used in an example of the present invention.

[Explanation of symbols]

 1 ground shield 2 high frequency electrode 3 target 4 magnetite 5 base plate 6 substrate holder 7 high frequency power supply 8 pressure regulator 9 exhaust device 10 vacuum device 11 high frequency power supply 12 high frequency electrode 13 gas inlet

Claims (3)

[Claims] 1. A carbon nitride containing C and N having a CN chemical bond formed by high frequency sputtering or DC sputtering, and having an N / C atomic ratio of more than 1.0. Thin film. 2. A method for forming a carbon nitride thin film, which comprises subjecting a graphite or carbon target to N ₂ gas at a partial pressure of 100 to 5000 mTorr and performing high frequency sputtering or DC sputtering. 3. The N ₂ partial pressure according to claim 2,
The method for forming a carbon nitride thin film according to claim 1, wherein the thickness is 5000 mTorr.