AL alloy member having excellent corrosion resistance

#1. Field of the Invention

#This invention relates to an improvement in gas corrosion resistance, plasma resistance and corrosive solution resistance of vacuum chamber members and anodized Al parts used in the inside thereof, which are employed for the manufacturing process of semiconductor and liquid crystal device by a dry etching apparatus, a CVD apparatus, a PVD apparatus, an ion implantation apparatus, a sputtering apparatus or the like. More particularly, the invention relates to an improvement in corrosive solution resistance of Al alloy members that are exposed to a corrosive solution such as an acidic solution.

#2. Description of Related Art

#In the attached drawings:

#FIG. 1 is a sectional view conceptionally showing the rough structure of an anodic oxide film;

#FIG. 2 is a sectional view conceptionally showing Si precipitates (in a vertical direction) and a space; and

#As stated hereinabove, an anodized Al alloy member is poor in corrosion resistance to a corrosive solution, such as an acidic solution, formed upon maintenance through wiping out with use of water (i.e. corrosive solution resistance), and we have made intensive studies to improve the resistance. As a result, we have found that when it is determined as essential that at least a part of the structure of a barrier layer of an anodic oxide film consists of boehmite and/or pseudo-boehmite (which may be hereinafter referred to as “(pseudo) boehmite) and the degree of alteration of the anodic oxide film into (pseudo) boehmite and the state of the film (as to whether or not crack or film defect exist) are properly controlled, the reaction of a corrosive solution with an Al alloy substrate by infiltration through the anodic oxide film can be restrained where while excellent gas corrosion resistance and plasma resistance are maintained, the corrosive solution resistance can be improved.

#FIG. 1 is a sectional view conceptionally showing the schematic structure of the anodic oxide film formed on the surface of an anodized Al alloy member. In the figure, reference numeral 1 designates an Al substrate, and reference numeral 2 designates an anodic oxide film. Likewise, indicated by 3 is a pore, by 4 is a porous layer (i.e. a portion where the pores 3 are formed), by 5 is a barrier layer (i.e. a pore-free layer intervening between the porous layer 4 and the Al substrate 1) and by 6 is a cell.

#In the practice of the invention, at least a part of the structure of the barrier layer should be altered into (pseudo) boehmite. With the case of an anodic oxide film including the porous layer having a multitude of pore opened at the film surface and the pore-free barrier layer as shown in FIG. 1, at least a part of the structure of the barrier layer 5 should be altered into (pseudo) boehmite wherein the pores may be opened or closed. In the invention, the alteration of the film (including at least a part of the barrier layer) into (pseudo) boehmite ensures excellent corrosion resistances. When the degree of alteration of the film into (pseudo) boehmite is such that the dissolution rate of the anodic oxide film determined by an immersion test in phosphoric acid/chromic acid (JIS H8683-2) is 100 mg/dm2/15 minutes or below, and a corroded area percent after allowing to stand in an atmosphere of 5% Cl2—Ar gas at 400° C. for 4 hours is 10% or below, the film is excellent against corrosion resistances (including gas corrosion resistance, plasma resistance and corrosion resistance to solution). Thus, the reaction of a corrosive solution with the Al alloy substrate after infiltration of the solution through the anodic oxide film can be restrained. That is, the alteration of at least a part of the barrier layer into (pseudo) boehmite ensures the good effect of suppressing the infiltration of a corrosive solution. It will be noted that as the barrier layer is altered into (pseudo) boehmite, the portion near the film surface (i.e. a portion of the porous portion other than the barrier layer) is altered into (pseudo) boehmite, which contributes to the control of infiltration of a corrosive solution through the film. In addition, the Al alloy substrate of the invention is not only excellent in corrosive solution resistance, but also excellent in gas corrosion resistance and plasma resistance. Preferred embodiments of a manufacturing method are set out to describe the invention in more detail, which should not be limited the invention thereto. Many modifications and variations of such embodiments may be possible without departing from the scope of the invention.