Methods of forming impurity containing insulating films and flash memory devices including the same

A method of fabricating a flash memory device, the method comprising:

• forming a first insulating film on a substrate;
• forming a first impurity concentration peak in a lower portion of the first insulating film, proximate to the substrate, using a thermal process under a first set of processing conditions;
• forming a second impurity concentration peak in an upper portion of the first insulating film, proximate to an upper surface of the first insulating film, using the thermal process under a second set of processing conditions, different from the first set of processing conditions, so that the lower portion of the first insulating film and the upper portion of the first insulating film have their own maximum impurity concentration values, respectively, wherein the lower portion of the first insulating film comprises regions above and below a first region where the first impurity concentration peak occurs that have impurity concentrations less than the first impurity concentration peak, and wherein the upper portion of the first insulating film comprises regions above and below a second region where the second impurity concentration peak occurs that have impurity concentrations less than the second impurity concentration peak;
• annealing the first insulating film having the impurity concentration peaks therein;
• forming a first conductive material film on the first insulating film;
• forming a second insulating film on the first conductive material film;
• forming a second conductive material film on the second insulating film;
• and
• patterning the first insulating film, the first conductive material film, the second insulating film, and the second conductive material film to form a gate structure.

A method of fabricating a flash memory device, the method comprising:

• forming a first insulating film on a substrate;
• forming a first impurity concentration peak in a lower portion of the first insulating film, proximate the substrate, using a thermal process under a first set of processing conditions;
• forming a second impurity concentration peak in an upper portion of the first insulating film, proximate to an upper surface of the first insulating film, using the thermal process under a second set of processing conditions, different from the first set of processing conditions, so that the lower portion of the first insulating film and the upper portion of the first insulating film have their own maximum impurity concentration values, respectively, wherein the lower portion of the first insulating film comprises regions above and below a first region where the first impurity concentration peak occurs that have impurity concentrations less than the first impurity concentration peak, and wherein the upper portion of the first insulating film comprises regions above and below a second region where the second impurity concentration peak occurs that have impurity concentrations less than the second impurity concentration peak;
• annealing the first insulating film having the impurity concentration peaks therein;
• forming a second insulating film on the first insulating film;
• forming a third insulating film on the second insulating film;
• forming a conductive material film on the third insulating film;
• and
• patterning the first insulating film, the second insulating film, the third insulating film, and the conductive material film to form a gate structure.