JPH0387373A - Formation of thin film by plasma cvd - Google Patents

Abstract

PURPOSE:To make it possible to form a thin film having satisfactory adhesion and mechanical properties at a low temp. by impressing a specified negative potential to a substrate in a vacuum chamber. CONSTITUTION:A substrate 11 is set on a lower electrode 3 in a vacuum chamber 1 and this chamber 1 is evacuated by working a vacuum pump 6. Hydrogen is fed from a ring nozzle 7, -2,500 to -5,000V DC voltage is impressed on the electrode 3 from a DC power source 4 to generate plasma in the chamber 1 and the surface of the substrate 11 is cleaned with the plasma. A gaseous mixture of TiCl2, N2, H2, etc., is then fed into the chamber 1 through a pipe 8 at a flow rate regulated with mass flow controllers 10 and a thin film of TiN, etc., is formed on the surface of the substrate 11 by plasma CVD.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for forming plasma CVD thin films.

[Prior Art and Problems] Conventionally, a thermal CVD method has been adopted as a method for forming a thin film. This method is a method in which a chemical reaction is caused in a raw material gas using thermal energy in a vacuum chamber to form a thin film on a substrate placed in the chamber. Such a thermal CVD method has the characteristic that a strong thin film can be formed on a substrate with good adhesion and good adhesion.

By the way, the chemical reaction required to form a thin film is usually at 1000°C.
Since this process is often carried out at higher temperatures, there are restrictions on the materials that can be used to form the base. For example, the thermal CV
It becomes difficult to apply method D.

For these reasons, in recent years, physical vapor deposition (PVD method) such as ion blating has been developed, making it possible to form thin films at low temperatures. However, the PVD method has a problem in that the coverage of the vapor deposited substance to the three-dimensional substrate is low.

Therefore, plasma C
The VD method was developed. This plasma CVD method makes it possible to form thin films at low temperatures by substituting part or most of the thermal energy required for the chemical reaction of raw material gases with electrical energy. In the plasma CVD method, raw material gas is supplied into a vacuum chamber and direct current or high frequency is applied to cause glow discharge to generate plasma, and the substrate is placed in the plasma. At this time,
When the raw material gas supplied into the chamber passes through the plasma, it becomes active excited species such as ions, radicals, atoms, molecules, etc. These excited species undergo reactions at low temperatures, so they form a thin film on the substrate at low temperatures. is thought to be formed. Therefore, in the plasma CVD method, it is possible to form a thin film with good coverage on a substrate at a low temperature.

However, although thin films formed by the conventional plasma CVD method described above can be formed at low temperatures, thermal CVD
The problem is that the adhesion to the substrate is not as good as that of thin films formed by the ion-blating method or the ion-blating method. In addition, when forming a hard ceramic thin film such as TiN or TiC, at the same time as the above-mentioned decrease in adhesion, thin films formed at temperatures below 400°C usually have poor mechanical properties such as hardness, and However, it has been difficult to practically apply the plasma CVD method due to problems such as a large amount of impurities.

The present invention has been made in view of the above circumstances, and is a plasma CVD thin film that can form a thin film with good adhesion at low temperatures and a hard ceramic thin film with good mechanical properties even in a temperature range of 400°C or less. The purpose is to provide a formation method.

[Means and effects for solving the problem] The present invention provides a method for forming a thin film on the surface of a substrate in a vacuum chamber by plasma CVD, in which a negative potential of -2500V to -5000V is applied to the substrate with respect to the vacuum chamber. This is a method of forming a plasma CVD thin film characterized by applying a voltage.

In the present invention, the voltage waveform of the negative potential can have any shape. For example, known waveforms such as continuous waves, rectangular waves, and triangular waves can be used.

In the conventional plasma CVD method described above, either direct current or high frequency is often used as a means for generating plasma. When using direct current, a negative potential in the range of 500V to -1500V is applied to the substrate with respect to the vacuum chamber, and when high frequency is used, a negative potential of 0 to -1500V is applied to the substrate with respect to the vacuum chamber. Apply a range of negative potentials. Even if plasma CVD is performed under such conditions, although there are problems as described above, it is possible to form a thin film on the substrate. The above conventional plasma C
It is difficult to definitively determine the causes of problems in the VD method because there are various possible causes, but excited species in the plasma,
In particular, it was assumed that one of the major causes was a lack of ions.

Therefore, the present inventors analyzed the distribution of excited species in the space when forming a thin film under the conditions of the plasma CVD method described above using an analyzer,
The following findings were obtained by measuring using an emission spectrometer. That is, the source gas supplied into the plasma is rapidly excited and ionized mainly within the cathode sheath near the substrate surface. 20 The magnitude of the voltage gradient within the cathode sheath increases as the potential difference between the substrate and the vacuum chamber increases, and it is thought that it is not affected much by other film-forming parameters. Therefore, even if other film-forming parameters are held constant, excitation and ionization will proceed within the cathode sheath simply by increasing the potential difference between the substrate and the vacuum chamber, making it possible to overcome the above-mentioned problems. It was inferred that there is.

However, when forming a thin film by plasma CVDm,
There are no examples of applying a negative potential of 12,000 V or more to the substrate with respect to the empty chamber A, and there are no reports of this in the literature. The present inventors focused on this point and conducted intensive research on the characteristics of the thin film obtained when plasma CVD is performed by applying a negative potential of 12,000 μm or more to the substrate with respect to the vacuum chamber. As a result, we found the following. discovered a new phenomenon.

That is, when plasma CVD is performed by applying a negative potential of -2,500V to -5,000V to the substrate with respect to a vacuum chamber, it is possible to form a thin film with good adhesion at low temperatures, and furthermore, it is possible to form a thin film with good adhesion at a temperature of 400°C or less. It is also possible to form a hard ceramic thin film with good mechanical properties.

The cause of these facts is not clear at this time. However, from -2500V to the vacuum chamber on the substrate -
When a negative potential of 5000 V was applied, excited species in the plasma, especially in the cathode sheath, were measured using a mass spectrometer and an emission spectrometer, and it was found that excitation and ionization occurred in the cathode sheath near the substrate surface. It was confirmed that the progress was much greater than before. For these reasons, the implantation effect is increased due to a marked increase in the amount of ions, which improves the adhesion when forming a thin film at a low temperature. At the same time, it is presumed that because the conversion from thermal energy to electrical energy is progressing, it is possible to form a sandy ceramic thin film with good mechanical properties even in a temperature range of 400° C. or lower.

In the present invention, when the applied negative potential is less than 12,500 V, the above-mentioned effects are not fully exhibited, and therefore there are problems similar to the conventional wide one. Furthermore, if the applied negative potential exceeds 15,000 V, the discharge tends to shift to an active discharge, making it difficult to obtain a stable discharge, resulting in a new practical problem.

Examples of the present invention will be described below along with comparative examples.

[Example 1] First, a parallel plate type plasma CVD apparatus according to the present invention will be described with reference to FIG.

1 in the figure is a vacuum chamber, which is at ground potential.

This vacuum chamber has a flat upper electrode 2. Lower electrodes 3 are arranged parallel to each other and facing each other. A DC voltage IJ7.4 is connected to the lower electrode 3. An exhaust pipe 5 is provided near the bottom of the vacuum chamber 1. A vacuum pump 6 is connected to the other end of the exhaust pipe 5.

Further, above the lower electrode 3, a ring nozzle 7 having a large number of gas ejection ports (not shown) formed on the inner circumferential surface is arranged. A gas introduction pipe 8 is connected to this ring nozzle 7 . This introduction pipe 8 is branched into three pipes outside the vacuum chamber 1, each with a valve 9. A mass flow controller IO is interposed.

Next, a thin film forming method using the plasma CVD apparatus described above will be explained.

First, ten substrates 11 made of 5KH51 and having dimensions of 20×20×2 mm were placed on the lower electrode 3. Next, the vacuum pump 6 is operated to exhaust the gas in the vacuum chamber 1 through the exhaust pipe 5, and while hydrogen is supplied into the vacuum chamber 1 from the ring nozzle 7, DC is applied to the lower electrode 3.
Apply 13000V DC from power supply 4 to chamber 1.
The surface of the substrate 11 was cleaned by generating plasma inside. Next, a mixed substrate of T i CN 4 , N2, and N2 (T i
CD4; 50sec, N2; 150sc
N2; 4000 scca+) was supplied into the vacuum chamber 1 from the ring nozzle 7 through the introduction tube 8, and plasma CVD was performed at a temperature of 500° C. to form a 3 μm thick TiN thin film on the surface of the substrate 11.

The adhesion of the obtained TiN thin film was measured using a scratch tester. When Al1 was determined for 10 substrates, the average critical load was 35N.

[Example 2] A layer of 3 μm of Ti was applied to the surface of the cutting board U by the same method as in Example 1.
A N thin film was formed. However, the vacuum chamber 1 was at ground potential, and a negative potential of -3000V was applied to the substrate. or,
The thin film forming temperature was 350°C.

The obtained TiN thin film exhibited a golden color. When the height of the TiN thin film was measured by the log load using a micro-Vickers hardness of 1, the average value was 2200. Also, Ti
When the Cga degree in the N thin film was measured by EPMA, the average value was 4 wt%.

[Comparative Example 1] A 3 μm thick T layer was applied to the surface of the substrate 11 by the same method as in Example 1.
An iN thin film was formed. However, the vacuum chamber was at ground potential, and a negative potential of -1[100V was applied to the substrate.

Further, the thin film forming temperature was 500°C.

The adhesion of the obtained TiN thin film was measured using a scratch tester. When 1+11 was determined for 10 substrates, the average value of the critical load was 2ON.

[Comparative Example 2] A 3 μm thick T layer was applied to the surface of the substrate 11 by the same method as in Example 1.
An iN thin film was formed. However, the vacuum chamber was at ground potential, and a negative potential of -tooov was applied to the substrate. Further, the thin film forming temperature was 350°C.

The TiN thin film that was exposed became a brown thin film with dull luster.

Although the existence of a TiN phase was confirmed by XRD,
As measured by EPMA, the average C9 concentration in the thin film was 3.
It was 0wL%. Furthermore, when the hardness of the thin film was measured using a micro-Vickers hardness meter, the average value was 100.
It was 0.

In the above embodiment, an example in which the present invention was applied to the formation of a TiN thin film was described, but similar effects could be obtained when applied to the formation of thin films of other metals, metal nitrides, metal carbides, and the like.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to form a thin film with good adhesion at low temperatures, and furthermore, it is possible to form a hard ceramic thin film with good mechanical properties even in a temperature range of 400°C or less. It is possible to provide a method for forming a plasma CVD thin film that is possible. ,

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory diagram of a plasma CVD apparatus used in an embodiment of the present invention. 1... Vacuum chamber 2... Upper electrode, 3...
Lower electrode, 4... DC power supply, 5... Exhaust pipe, 6...
・Vacuum pump, 7...Ring nozzle, 8...Gas introduction pipe, 9...Valve, 10...Mass flow controller 11゛°・Board.

Claims (1)

[Claims] A method for forming a thin film on the surface of a substrate in a vacuum chamber by plasma CVD, the method comprising applying a negative potential of -2500V to -5000V to the substrate with respect to the vacuum chamber.