This invention relates to introducing substances into a vacuum, for example, for alteration of a precisely localized site on a substrate such as a transparent defect site in a photolithographic mask.
Photolithographic masks are used to pass light (usually ultraviolet light) to a workpiece in a specified pattern. Such masks often consist of a clear substrate such as glass or quartz onto which a pattern of an opaque material such as chrome has been deposited. For various reasons, a mask may develop or be manufactured with small defects or imperfections, for example pinholes in the chrome layer, that allow exposure of the workpiece in undesired locations. Also, it may be desirable to alter the pattern on the mask, by rendering a previously transparent site opaque. Mask alteration should be rapid, automated, effective and durable without complex processing steps that can introduce contaminants or cause further defects.
One way to repair mask imperfections involves a lift-off procedure using a positive photoresist. The resist is applied to the affected area, exposed, and developed, after which any resist that was applied to a transparent imperfection is removed. An opaque layer, e.g., of aluminum, is deposited over the area, and any of the deposited layer that overlies photoresist is lifted off using a solvent that dissolves the resist.
Laser beams are also used to repair photolithographic mask defects, particularly opaque defects, by removing the undesired opaque material.
Three publications [Gamo et al. (1984) Intern. Conf. on Solid State Devices and Materials (Kobe 9/1/84); Gamo et al. (1984) Japanese J. Appl. Physics 23(5): L293-L295; and Takahura et al. "Maskless Deposition Using Focused Ion Beam" 15th Symposium On Ion Implantation and Sub-micron Fabrication, February 1984] disclose the use of a focused or broad argon or gold ion beam in an atmosphere of trimethyl aluminum. The resulting deposited film contains oxygen, carbon, and aluminum in varying ratios. The technique is reported to be promising for mask repair or mask fabrication for optical, ion, or X-ray lithography. It is further reported that inclusion of C and O in the film may be decreased by using other metallo-compounds (tungsten hexafluoride is suggested) and reducing the background pressure. Finally, the rate of film deposition reportedly is increased if the molecules resulting from the bombardment are not volatile.
Osias et al. (1984) Kodak Microelectronics Seminar, San Diego, October 29-30, Abstract, discloses mask repair using an ion flood beam to convert a previously applied layer of photoresist into a vitreous carbon film. "The resultant material is an excellent hard mask fabrication or repair material having scratch resistance and UV optical density comparable to that of chrome and having chemical resistance and substrate adhesion superior to that of chrome." The disclosed method involves wet processing of a negative photoresist to create a layer of resist at the site of transparent imperfections.
Kellogg, Ph.D. thesis, University of Pennsylvania, November 1965, discloses a method of making a self-supporting carbon target for helium bombardment by heating a nickel foil substrate in an atmosphere of methyl iodide to deposit a carbon film on the nickel. Hydrogen is released as a gas, and iodine is deposited as an amorphous layer on the walls of the chamber. The nickel is dissolved later to leave a carbon target.
Moller et al. (1981) Nuclear Instruments and Methods Vol. 182/183, pp. 297-203 discloses ion-induced carbon buildup on a nickel surface in various hydrocarbon atmospheres at pressures in the 10.sup.-6 millibar (7.5.times.10.sup.-7 torr) range; for example, unwanted buildup from vacuum pump oil occurs when performing ion implantation, ion beam analysis, or experimental nuclear physics. Methane, benzene, roughing pump oil, and squalene were bombarded with ion beams of hydrogen, helium, and lithium ions at between 100 and 400 keV. The gases were provided as controlled atmospheres (10.sup.-7 to 10.sup.-5 mbar) by means of a needle valve or by means of a small liquid container installed in a vacuum chamber; the container temperature could be varied between -30.degree. C. and 40.degree. C., depending on the gas. The residual gas consists mainly of water, nitrogen, carbon dioxide, and argon. The amount of deposited material increases with increasing molecular weight of the gas and with dose rate (between 1.5.times.10.sup.13 and 1.times.10.sup. 15 cm.sup.-2 seconds.sup.-1). The authors conclude that deposition is controlled by ion-induced polymerization in an adsorbed layer.
Venkatesan et al., (1983) J. Applied Phys. Letters 54: 3150-3153 disclose irradiating polymer films (e.g., positive photoresists) with high electron or ion beam doses causing the resist layer to become conductive and to behave as a negative resist as a result of carbonization--i.e., creation of a highly cross-linked carbon structure. The Raman spectra of such films resemble, but are consistently different from, the spectra of amorphous carbon films.
Calcagno et al., (1984) J. Applied Phys. Letters 44: 761-763 disclose ion bombardment of frozen benzene to produce a stable polymeric film. The resulting film has a carbon-to-hydrogen ratio of between 1:2 and 1:3 as compared to 1:1 for benzene.
Lincoln et al. (1983) J. Vac. Sci. Techn. B1(No. 4): 1043-1046; and Geis et al. (1981) J. Vac. Sci. Techn. 19(4): 1390-1393 disclose etching a substrate with a reactive gas such as chlorine, using an Ar.sup.+ flood beam to assist the etching. Etching takes place in a vacuum chamber and Cl.sub.2 gas is introduced through a gas inlet shown in FIG. 1 of each article, positioned approximately 3.5 cm from the substrate.
Aisenberg U.S. Pat. No. 3,961,103 discloses thin film deposition apparatus having an ion source (10 in FIG. 1) to generate ionized plasma (Ar, H, He, N, or O). A constrictor electrode 26 and an extraction electrode 24 have small apertures to permit differential pumping to maintain a good vacuum in deposition chamber 20, while a somewhat higher pressure is maintained in plasma ion source 10 (4: 4-9). The use of a hydrocarbon gas in chamber 10 permits the deposition of carbon films since ions exiting from the ion source will consist of carbon ions and hydrogen ions (5: 61-65).
Holland U.S. Pat. No. 4,382,100 discloses applying a layer of carbonaceous material to a surface by exposing the surface to a plasma generated in a hydrocarbon gas. Conditions may be controlled to select a polymeric layer, an amorphous layer, or a graphite layer.
Wolfe, U.S. Pat. No. 4,085,330 discloses a liquid metal ion source and a gaseous ion source for removal of areas of a mask. The liquid metal ion source is said to be advantageous because there is no need for a pressure differential between the source and the deposition chamber (4: 21-36).
Japan 53-135276 discloses repairing a photomask by irradiating vacuum pump oil with an electron beam.
Japan 58-6133 discloses repairing a mask pattern by electron beam irradiation of a carbon-containing gas to bake carbon molecules to the mask surface.
Japan 57-32630 discloses repairing a photo-mask by applying powdered carbon dissolved in albumin and sintering with a laser beam.
Japan 57-102019 discloses ion-beam irradiation to remove undesired material from an X-ray adsorbing mask pattern and ion injection to correct pin holes in the pattern.
Miyauchi U.S. Pat. No. 4,463,073 discloses an optical system for viewing repair of a mask defect.