JPH08158039A - Formation of thin carbon nitride film - Google Patents

Abstract

PURPOSE: To form a thin CNx film having a high N content at a high rate by subjecting a graphite or carbon target to high-frequency sputtering or DC sputtering at a specified output density with gaseous N2 under a specified partial pressure. CONSTITUTION: When a thin carbon nitride film is formed, a target 3 is made of graphite or carbon and N2 -contg. gas is used as sputtering gas. Sputtered C particles are nitrided by a reaction with plasma excited N ion radicals to form gaseous CNx as an intermediate and this intermediate is fed to the top of a substrate 5. At this time, collision with N particles is made vigorous by redulating the partial pressure of the N2 -contg. gas to 50 to <200mTorr, nitriding is accelerated and most of the C particles are converted into CNx to increase the rate of formation of a thin CNx film. Under this partial pressure, high-frequency sputtering or DC sputtering is carried out at 10-35W/cm<3> output density. The objective thin CNx film (x≈1) having a high N content is formed at a high rate of film formation.

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 carbon nitride (CNx) thin film.

[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.

The object of the present invention is to obtain a high N ratio with an N / C ratio of about 1 by high frequency sputtering or DC sputtering.
It is intended to provide a method capable of forming a CNx thin film having a content rate at an increased film forming rate.

[0009]

That is, the present invention is directed to a graphite or carbon target containing N ₂ gas with a partial pressure of 50 to less than 250 mTorr and an output density of 10 to 3.
It is a method for forming a carbon nitride thin film, which comprises performing high frequency sputtering or DC sputtering at 5 W / cm ² .

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 are excited by plasma.
Nitrate by reacting with the generated N ions and radicals,
The body is CN, C₂N₂Gaseous CNx, etc. are formed.
This intermediate is supplied onto the substrate 5, which is conventionally
Higher than 50 and less than 250 mTorr N₂Partial pressure
As a result, collision with N particles becomes active and nitriding is promoted.
Is promoted, most of the C particles become CNx and the CNx thin film
The film formation speed increases. N ₂When the partial pressure is 250 mTorr or more
May cause unstable plasma formation.

In the present invention, when the N ₂ partial pressure is 50 to less than 250 mTorr and the output density (plasma forming output / target area) is 10 to 35 W / cm ² , the N / C ratio is close to 1. CN with high N content
The x thin film can be formed at an increased film forming rate.

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 small, the N necessary for nitriding the sputtered C particles is sufficient. Since the amount of supplied ions / radicals is insufficient, most of the C particles are not nitrided but reach the substrate as they are and grow into a film, which makes it difficult to take in a large amount of N into the film.

On the contrary, if the power density becomes too high,
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. Therefore, as in the case of the conventional film formation with an N ₂ partial pressure of about 20 mTorr, CNx with a high N content ratio is used. It becomes impossible to form a thin film.

The present inventors have found that mTo of 50 to 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 is performed at 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, so that the C particles to be sputtered are more sufficient. 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 present inventors have found that the N / C ratio of CNx near 11
Confirm that the thin film shifts to about 287 eV
Was.

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

[0024]

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

Examples 1 to 7 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 according to 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 X-ray fluorescence 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.

[0030]

[Table 1]

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

Example 8 The CNx thin film obtained in Example 2 was heated in a vacuum atmosphere at 500 ° 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.

[0033]

According to the present invention, a CNx thin film having a high N content having an N / C ratio of about 1 can be formed at a high film forming rate only by performing high frequency sputtering or DC sputtering.

[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 (1)

[Claims] 1. A graphite or carbon target containing N ₂ gas at a partial pressure of 50 to less than 250 mTorr,
A method for forming a carbon nitride thin film, which comprises performing high frequency sputtering or DC sputtering with an output density of 10 to 35 W / cm ² .