Method of determining defective die containing non-volatile memory cells

A method of testing non-volatile memory cells formed on a die, comprising:

• erasing the non-volatile memory cells;
• performing a first read operation on the non-volatile memory cells after the erasing of the non-volatile memory cells to determine a highest threshold voltage TV1 for the non-volatile memory cells during the first read operation and a first number N1 of the non-volatile memory cells having the highest threshold voltage TV1 during the first read operation;
• performing a second read operation on the non-volatile memory cells to determine a second number N2 of the non-volatile memory cells having a threshold voltage during the second read operation not below a target threshold voltage TV2, wherein the target threshold voltage TV2 is equal to the highest threshold voltage TV1 minus a predetermined voltage value;
• determining whether the second number N2 exceeds the first number N1 plus a predetermined number;
• and
• determining the die is acceptable if the second number N2 is determined to exceed the first number N1 plus the predetermined number, or determining the die is defective if the second number N2 is determined not to exceed the first number N1 plus the predetermined number.

A method of testing non-volatile memory cells formed on a die, comprising:

• programming the non-volatile memory cells;
• performing a first read operation on the non-volatile memory cells after the programming of the non-volatile memory cells to determine a lowest threshold voltage TV3 for the non-volatile memory cells during the first read operation and a first number N1 of the non-volatile memory cells having the lowest threshold voltage TV3 during the first read operation;
• performing a second read operation on the non-volatile memory cells to determine a second number N2 of the non-volatile memory cells having a threshold voltage during the second read operation not exceeding a target threshold voltage TV4, wherein the target threshold voltage TV4 is equal to the lowest threshold voltage TV3 plus a predetermined voltage value;
• determining whether the second number N2 exceeds the first number N1 plus a predetermined number;
• and
• determining the die is acceptable if the second number N2 is determined to exceed the first number N1 plus the predetermined number, or determining the die is defective if the second number N2 is determined not to exceed the first number N1 plus the predetermined number.