Coating processes – Direct application of electrical – magnetic – wave – or... – Plasma
Reexamination Certificate
2000-08-10
2003-12-09
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Plasma
C427S569000, C427S575000, C427S576000, C427S577000, C427S578000, C427S249700, C427S249150, C427S255380, C427S255391, C427S255392, C427S255394, C118S7230MP, C118S7230MW, C118S7230MR, C118S7230MA
Reexamination Certificate
active
06660342
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for forming a film.
2. Description of the Prior Art
Films have been heretofore deposited by various processes such as CVD (chemical vapor deposition), sputtering, MBE (molecular beam epitaxy), and the like. In plasma enhanced CVD (referred to simply hereinafter as plasma CVD), the use of high frequency excitation, microwave excitation, hybrid resonance and the like has been developed. Particularly in the plasma CVD process which utilizes a resonance with a magnetic field (referred to as “plasma CVD in magnetic field”, hereinafter), the development thereof has actively taken place and, because of its high film deposition efficiency which results from the use of a high density plasma, its diversification in application has been expected. In the practical film deposition in the presence of a magnetic field, however, a difficulty has been encountered to deposit uniform films on an irregular surface without being influenced by such surface irregularity. This difficulty has hindered practical progress of the microwave CVD in magnetic field in the industries. The fact that a plasma CVD in magnetic field consumes an enormous amount of energy at its operation also is a bar to its gaining popularity in the industrial field. A diamond-like carbon (DLC) film can be uniformly deposited on a substrate as large as 10 cm or more in diameter by the use of microwave plasma CVD in magnetic field. In the deposition of such DLC films by this process, the diamond nuclei formed in the vapor phase are trapped on the substrate upon their contact with the substrate. Thus, the DLC film grows spread in a tapered form from each nucleus, and results in a film having poor adhesion with the substrate. Furthermore, since the diamond crystals grow in a tapered form from a diamond nucleus center trapped on the substrate, a compression stress accumulates around the grain boundaries within the DLC film. The poor adhesion of the film with the substrate and the compression stress within the film have constituted a hindrance to the practical use of DLC films.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process of depositing uniform films.
Another object of the present invention is to provide a process of depositing films with small power consumption.
Still another object of the present invention is to provide a process of depositing films which have excellent adhesion with substrates.
The foregoing objects and other objects have been achieved by depositing films by a plasma CVD process which takes advantage of the interaction between a magnetic field and an electric field, e.g. a high frequency electric field, induced by supplying an electric energy intermittently, or of that between a magnetic field and an electric field, e.g. a high frequency electric field, induced by supplying thereto an electric energy intermittently and a stationary electromagnetic energy continuously which are superposed upon each other. The magnetic field may be generated by supplying an electric energy intermittently. Alternatively, the magnetic field may be obtained by supplying either a DC current or a pulsed current to a Helmholtz coil. Furthermore, rise and decay of the pulsed current for generating the magnetic field intermittently and those of the electric power for generating the electric field intermittently may be synchronized with each other. In a typical embodiment, a microwave electric energy is supplied to generate the high frequency electric field.
In FIGS.
3
(A),
3
(B), and
3
(C) are given examples of time versus power (effective value of power). FIG.
3
(A) shows a shape having two different peak values. Such a power is particularly effective in increasing production of substances over a certain threshold value while suppressing the production of substances having an energy of production lower than the threshold value. FIG.
3
(B) shows time versus power (effective value of power) of a wave obtained by superposing a high frequency electric wave supplied intermittently upon a low power electromagnetic stationary wave supplied continuously, wherein the initial waves have the same frequency. FIG.
3
(C) also shows time versus power (effective value of power)of a wave obtained by superposing a high frequency electric wave supplied intermittently upon a low power electromagnetic stationary wave supplied continuously, however, the frequency of the initial waves are differed. The plasma CVD of the present invention is referred also to as a pulsed plasma CVD hereinafter since the power has a pulse shape as shown in FIGS.
3
(A) to
3
(C). The use of waves obtained by the superposition enables rapid deposition of the films, and is useful when a stable plasma cannot be obtained only by an intermittently supplied wave due to the structural allowance of the apparatus or to the conditions restricting the film deposition process. Thus, from the characteristic of a pulsed plasma CVD which enables a uniform formation of nuclei for film growth on the surface of substrates, the process enables deposition of a highly homogeneous film on an article having an irregular surface on one hand; on the other hand, from the fact that a high electric power can be concentrated at a pulse peak as compared with a stationary continuous power, the film deposition can be carried out at an increased efficiency.
To obtain a film of uniform thickness extended over a large area on a substrate, the film deposition is conducted in an apparatus the inner pressure of which is elevated to a range of from 0.03 to 30 Torr, preferably, from 0.3 to 3 Torr, using a high density plasma taking advantage of hybridized resonance. Since the pressure is maintained high, the mean free path of the reactive gas is shortened to a range of from 0.05 mm to several millimeters, particularly to 1 mm or less. This facilitates dispersion of the reactive gas to various directions, which is advantageous for depositing films on the sides of the articles having irregular surfaces. Thus, the rate of film growth is accelerated.
The article to be coated with a film is placed either in a hybridized resonance environment or in an activated environment remote from the hybridized resonance environment, to thereby coat the surface thereof with the reaction product. To achieve efficient coating, the article is located in the region at which a maximum electric field intensity of the microwave power can be obtained, or in the vicinity thereof. Furthermore, to generate and maintain a high density plasma at a pressure as high as in the range of from 0.03 to 30 Torr, an ECR (electron cyclotron resonance) should be generated in a columnar space under a low vacuum of 1×10
−4
to 1×10
−5
Torr and a gas, a liquid, or a solid is then introduced into the columnar space to produce a plasma, which is then maintained under a high pressure in the range of from 0.03 to 30 Torr, preferably from 0.3 to 30 Torr, so as to obtain a space having a highly concentrated product gas, said concentration per volume being about 10
2
to 10
4
times as large as the gas concentration normally used in a conventional ECR CVD process. By thus realizing the particular environment, the film deposition of a material which undergoes decomposition or reaction only at such a high pressure becomes possible. The particular films which can be obtained include carbon films, diamond films, i-carbon (carbon films containing diamonds or microcrystal grains), DLC (diamond-like carbon films), and insulating ceramics, and metallic films, in particular films of metal having high melting point.
In summary, the process according to the present invention utilizes plasma glow discharge and comprises a known microwave plasma CVS process to which a magnetic field is added to utilize the interaction of the magnetic field with the high frequency (micro wave) electric field. However, the ECR conditions are omitted from the process. The process according to the present invention conducts the film deposition
Inoue Tohru
Miyanaga Akiharu
Yamazaki Shunpei
Beck Shrive P.
Costellia Jeffrey L.
Markham Wesley
Nixon & Peabody LLP
Semiconductor Energy Laboratory Co,. Ltd.
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