Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-11-30
2004-05-25
Versteeg, Steven (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C430S005000, C427S523000
Reexamination Certificate
active
06740208
ABSTRACT:
BACKGROUND OF THE INVENTION
i) Field of the Invention
The present invention relates to a photo mask for use in manufacturing a semiconductor integrated circuit, and the like, a photo mask blank as a material of the photo mask, and a method of manufacturing the photo mask blank.
ii) Description of the Related Art
In manufacturing of semiconductors such as a semiconductor element, IC and LSI, a manufacturing process of a photo mask for use in transferring a fine pattern onto a semiconductor wafer usually includes: a film forming step of forming films, such as an opaque film, a semi-transmission film (a translucent film), onto a transparent substrate obtained by precisely polishing synthetic quartz glass by sputtering, and the like; a resist coating step of coating a resist film on the films, such as the opaque film, by a spin coating method; an exposure step (delineating step) of irradiating a resist surface with an electron ray or a laser beam to selectively expose the resist film; a development step of developing the exposed resist film with a predetermined developer to form a resist pattern; an etching step of using the resist pattern as a mask to etch the films such as the opaque film and to obtain a predetermined opaque film pattern, and the like. In this case, the substrate thus obtained by the film forming step is generally called a photo mask blank.
Here, in the forming step of forming the opaque film, usually from a viewpoint of productivity, the film is formed by a usual DC magnetron sputtering method by using a DC magnetron sputtering apparatus and a chromium target. Alternatively, a thin film is formed by a reactive sputtering method executed by introducing at least one of gases such as nitrogen and oxygen.
Chromium or a chromium compound is used as the opaque film in an original sheet of the photo mask, that is, a binary photo mask blank, in which light intensity modulation is used to transfer the pattern. In addition, the sputtering method is mainly utilized as a method for forming the opaque film onto the substrate. However, when the opaque film such as a chromium film is formed by the sputtering method, the opaque film usually has a tensile stress, and the photo mask blank including the transparent substrate as a base therefore warps. Such warps bring about a high possibility of an insufficient focus depth for exposure or a design defect. This results in deterioration of the photo mask blank. Here, for a warp amount of the substrate, the substrate is measured by flatness measuring instrument by an optical interferometer, such as FM200 manufactured by TROPEL Co. In this case, a difference of height (P-V value) between a highest point and a lowest point from a level surface of the substrate is measured before and after the film formation, and the warp amount of the substrate generated by the film formation is defined by the difference of the P-V value before and after the film formation. That is, definition is made by:
(warp amount of substrate after film formation)−(warp amount of substrate before film formation)=(warp amount of substrate generated by film formation).
As a stress reduction method of the opaque film, there is a method of applying a bias on a substrate side during sputtering deposition and implanting an ion present in plasma. However, since the photo mask blank has a relatively large film formation area, and the substrate is a dielectric such as glass, it is difficult to obtain a uniform effect in the surface.
On the other hand, when a chromium compound thin film is formed as the opaque film, or a compound thin film such as MoSiN, MoSiON, SiON, SiN is formed as a semi-transmission film (phase shifter film), the film is usually formed by the reactive sputtering method such as the DC magnetron sputtering. However, during the film formation, the compound is also deposited on the surface of a target, and electric discharge becomes unstable (as a result, particles are generated by abnormal discharge). Therefore, there is a problem that a defect is liable to occur in the photo mask blank. Furthermore, the reactive sputtering method has a lower deposition rate and therefore has a problem of a bad productivity, as compared with the usual non-reactive DC magnetron sputtering method.
When the compound target is used to form the film by an RF magnetron sputtering method instead of the DC magnetron sputtering method, plasma during the film formation is widely spread as compared with the DC magnetron sputtering method. Therefore, the film is undesirably deposited inside a chamber, and acts as a generation source of particles on the mask blank and, as a result, there arises a problem that the defect is liable to occur in the photo mask blank.
Moreover, in consideration of precision of a size recently required for the mask pattern, it has been necessary to thin a resist and opaque film during pattern formation. However, in a thin film forming method that uses the conventional DC magnetron sputtering method, the chromium film is inferior to a bulk film in density and denseness. As a result, a sufficient optical density cannot be obtained, and a demand for thin film formation cannot be satisfied.
SUMMARY OF THE INVENTION
The present invention has been developed to solve the aforementioned problems, and a first object thereof is to reduce a warp of a substrate by a film stress generated in a photo mask blank (relax and control the film stress).
Moreover, a second object of the present invention is to thin a film by enhancement of density and denseness, particularly to thin an opaque film by enhancement of a shielding property, and to enhance resistance to chemicals and resistance to light by enhancement of denseness.
Furthermore, a third object of the present invention is to reduce film defects by reduction of particles by abnormal discharge in a reactive DC sputtering method or by reduction of the particles in a reactive RF sputtering method during formation of a compound opaque film or a compound semi-transmission film by a reactive sputtering method, and to enhance a deposition rate (enhance productivity) by acceleration of reactivity (promotion of reactivity).
Additionally, a fourth object of the present invention is to provide a high-quality photo mask blank and photo mask prepared in consideration of the aforementioned objects.
To achieve the aforementioned objects, the present invention has the following constitutions.
(Constitution 1) A method of manufacturing a photo mask blank for forming an opaque film or a semi-transmission film on a transparent substrate, the method comprising a step of forming the opaque film or the semi-transmission film onto the substrate by irradiating the substrate with an ion generated by an ion generator separately disposed in a film formation chamber during the deposition of the opaque film or the semi-transmission film on the transparent substrate by a sputtering method.
(Constitution 2) The method of manufacturing the photo mask blank according to Constitution 1, wherein the step comprises controlling a film stress of the opaque film formed on the substrate; defining (a warp amount of the substrate after film formation)−(a warp amount of the substrate before the film formation)=(a warp amount of the substrate generated by the film formation); and suppressing the warp amount of the substrate generated by the film formation to ±0.1 &mgr;m or less.
(Constitution 3) The method of manufacturing the photo mask blank according to Constitution 1 or 2, wherein the step comprises directly introducing an inert gas into the ion generator from the outside of the film formation chamber; and ionizing the inert gas by the ion generator and irradiating the substrate with the ion.
(Constitution 4) The method of manufacturing the photo mask blank according to Constitution 1 or 2, wherein the step comprises directly introducing a reactive gas into the ion generator from the outside of the film formation chamber; and ionizing the reactive gas by the ion generator and irradiating the substrate with the ion.
(Constit
Kureishi Mitsuhiro
Nozawa Osamu
Hoya Corporation
Sughrue & Mion, PLLC
Versteeg Steven
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