Capacitor method for improved oxide dielectric

Claim 1

A method for fabricating a capacitor having an aluminum oxide electrical insulation layer of dielectric breakdown capability exceeding the oxide formation voltage, on a silicon substrate supported sputtered metallic aluminum film comprising the steps of: forming on said silicon substrate supported sputtered metallic aluminum film a first electrolyte anodization layer of porous soft aluminum oxide, said forming step including soft anodizing in a sulfuric acid electrolyte maintained at a temperature of six degrees Celsius and also a constant anodizing current density per square centimeter of aluminum film surface; hard anodize transforming at least a portion of said porous soft aluminum oxide to a harder layer by anodizing in an ethylene glycol diluted aqueous boric acid electrolyte solution which has been adjusted to a pH of five to five and four tenths by the addition of ammonium hydroxide using a constant anodizing voltage or stepwise incremented successively larger magnitudes of constant anodizing voltage and terminating the hard anodizing when the anodizing current rate of change attains a non-zero value of 0.025 milliamperes per square centimeter per minute or less; and forming over said layers of aluminum oxide a second layer of aluminum which is electrically insulated from said sputtered metallic aluminum film by said oxide layers.

Claim 2

A method for fabricating a capacitor having an aluminum oxide electrical insulation layer of dielectric breakdown capability exceeding the oxide formation voltage, on a silicon substrate supported sputtered metallic aluminum film comprising the steps of: forming on said silicon substrate supported sputtered metallic aluminum film a first electrolyte anodization layer of porous soft aluminum oxide, said forming step including soft anodizing in a sulfuric acid electrolyte maintained at a temperature of six degrees Celsius and also a constant anodizing current density per square centimeter of aluminum film surface; hard anodize transforming at least a portion of said porous soft aluminum oxide to a harder layer by anodizing in an ethylene glycol diluted aqueous boric acid electrolyte solution which has been adjusted to a pH of five to five and four tenths by the addition of ammonium hydroxide using a constant anodizing voltage or stepwise incremented successively larger magnitudes of constant anodizing voltage and terminating the hard anodizing when the anodizing current rate of change attains a non-zero value of 0.025 milliamperes per square centimeter per minute or less; and forming over said layers of aluminum oxide a second layer of aluminum which is electrically insulated from said sputtered metallic aluminum film by said oxide layers.