Coating processes – Direct application of electrical – magnetic – wave – or... – Electrostatic charge – field – or force utilized
Reexamination Certificate
2000-12-21
2002-10-15
Parker, Fred J. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Electrostatic charge, field, or force utilized
C427S460000, C427S461000
Reexamination Certificate
active
06465049
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for the preparation of a diamond film or, more particularly, to a method for the preparation of a diamond film for lithography.
By utilizing the unique characteristics possessed by diamond, laminated bodies with a diamond film formed on a substrate are widely employed as a material of a photomask for patterning light-exposure in the lithographic technology used in the manufacture of semiconductor devices or as a grinding and polishing tool.
Attempts are made for the formation of a diamond film on a substrate by the method of vapor-phase synthesis. In order to form and grow a vapor-phase synthesized diamond film on a substrate, it is desirable that the substrate is provided in advance with particulate bodies to serve as the nuclei for the growth of the diamond film or with scratches to serve as the sites for the incipient nucleus formation.
As an efficient method for the advance formation of nuclei or scratches for the growth of a diamond film on the substrate, one of the inventors previously proposed a method of so-called fluidized-bed pretreatment in which a pretreatment of the substrate is conducted by holding the substrate within a bed of diamond particles under fluidization by means of an ascending gas flow at a velocity not lower than the fluidization-initiating velocity of the particles (see Japanese Patent Kokai 9-260251).
This method is characterized in that a semiconductor silicon wafer, which is advantageous with regard to semiconductor processes, is employed as the substrate so as to be adaptable to the preparation of a lithographic mask membrane and that the velocity of gas flow for fluidization of the diamond particles is at least five times of the fluidization-initiating velocity.
In this fluidized-bed pretreatment method, however, diamond particles as an insulating material having a volume resistivity of 10
12
ohm·cm or higher are brought into fluidization by using a fluidizing gas, which is dry nitrogen gas in many cases, so that the diamond particles are readily charged electrostatically. When the substrate to be subjected to the fluidized-bed treatment is made of a material of low electric conductivity, a sufficient effect of the pretreatment cannot be obtained because the surface of the substrate per se is electrostatically charged by the deposition of the charged diamond particles which inhibit impingement of further diamond particles at the substrate surface. This phenomenon results in a disadvantage of local decrease in the effect of the pretreatment to give a non-uniform film due to local inhibition of growth of the diamond film in the course of formation and growth of the diamond film.
In view of the above described problems, the present invention has an object to provide a method for the fluidized-bed pretreatment capable of effectively preventing a decrease in the effect of pretreatment due to the phenomenon of electrostatic charging when a substrate material of low electric conductivity is subjected to a pretreatment by holding within a fluidized bed of diamond particles for the formation of a diamond film on the surface thereof.
SUMMARY OF THE INVENTION
In order to accomplish the above mentioned object, the method of the present invention for the preparation of a diamond film is characterized in that, when the pretreatment of a substrate is conducted within a fluidized bed of diamond particles for the formation of a film consisting of vapor-phase synthesized diamond, the potential of the substrate due to electrostatic charging is kept in a range from −1.5 to +1.5 kV. It is desirable in order to keep the electrostatic potential of the substrate in the above mentioned range that the relative humidity of the fluidizing gas for the diamond particles is controlled at 40% or higher. It is more desirable that the electrostatic charges are neutralized by undertaking ion bombardment at the substrate surface. Further, it is preferable in order to control the relative humidity of the fluidizing gas for the diamond particles that a dry fluidizing gas is humidified by bubbling into water or by spraying of water.
REFERENCES:
patent: 4084018 (1978-04-01), Karr
patent: 4689241 (1987-08-01), Richart et al.
patent: 5567468 (1996-10-01), Lucas
Kubota Yoshihiro
Noguchi Hitoshi
Parker Fred J.
Shin-Etsu Chemical Co. , Ltd.
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